Composite copper particles, method for producing same, and use of same

Abstract

The present invention provides copper particles which can be used for various applications even after the copper particles themselves are exposed to the atmosphere. Provided are composite copper particles which include copper particles and an organic component, wherein: the composite copper particles have a value of of 100 nm or more and 600 nm or less as an average particle diameter that is measured with a scanning electron microscope; the organic component contains at least a carboxylic acid or a salt thereof, and a polymer dispersant; the content of the organic component is 0.3% by mass or more to 6.0% by mass or less with respect to the copper particles; and the polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass reduction rate in the atmosphere of 70% or more under the condition that the temperature thereof is raised from 30°C to 250°C at a heating rate of 10°C / min by means of a thermogravimetric-differential thermal analyzer.

Description

TECHNICAL FIELD

[0001] The present invention relates to composite copper particles, a method for producing the same, a copper paste comprising the composite copper particles, a bonding material or conductive material comprising the composite copper particles or the copper paste, a sintered body comprising the bonding material as a raw material, and a conductor comprising the conductive material.BACKGROUND ART

[0002] A bonding material having a high thermal conductivity is used when a substrate of a power semiconductor product is produced by bonding a material to be bonded, which is a semiconductor element, and a base material such as a lead frame. Among various bonding materials, copper is preferably used for bonding of a semiconductor element because it is less expensive than silver and hardly causes ion migration.

[0003] In addition to the above-mentioned bonding uses, copper has high conductivity, and thus is preferably used as a conductive material such as an ink for printed electronics.

[0004] Patent Literature 1 describes that metal colloid particles in which the generation of coarse particles is suppressed can be obtained by constituting a protective colloid (or a dispersant), which coats or protects metal nanoparticles, with an organic compound having a carboxyl group and a polymer dispersant (in particular, a polymer dispersant having a carboxyl group).

[0005] Patent Literature 2 describes a copper nanoparticle dispersion having a volume average particle diameter of 500 nm or less obtained by combining copper nanoparticles with a carboxylic acid, an alkylamine, and a polymer dispersant having a specific amine value or acid value.CITATION LIST PATENT LITERATURE

[0006] PATENT LITERATURE 1: JP 2009-74171 A PATENT LITERATURE 2: JP 2015-210973 A SUMMARY OF INVENTION TECHNICAL PROBLEM

[0007] The present inventors have confirmed that in a bonding material using conventional copper particles, the bonding performance is reduced due to exposure of the copper particles to the atmosphere, thereby resulting in the bonding material becoming unusable. Also, as a phenomenon observed when copper particles were exposed to the atmosphere, heat generation of the copper particles and elution of copper ions during the production of the dispersion have been confirmed, and there is a concern that in conventional copper particles, copper may be oxidized due to atmospheric exposure.

[0008] When copper particles are used for a bonding material, a conductive material, or the like, the copper particles are processed into a form suitable for their use, such as a paste or a dispersion. There is a concern that the performance of the copper particles such as bonding properties and conductive properties may be reduced due to exposure of the copper particles to the atmosphere at that time. On the other hand, it is difficult to completely avoid oxidation of copper particles in the process from production to processing of the copper particles. For these reasons, there has been a demand for the development of copper particles that can be used for various uses even after atmospheric exposure. Patent Literature 1 discloses metal colloid particles comprising metal nanoparticles at a high concentration, and evaluates storage stability using, as an index, the presence or absence of sedimentation or agglomeration after a paste produced by adding ethylene glycol to silver colloid particles in which silver nanoparticles are protected by a protective colloid is left to stand at room temperature for 6 months. However, the metal nanoparticles disclosed in the Examples are only silver nanoparticles, and a problem caused by metals that are easily oxidized in the atmosphere, such as copper particles, is not recognized. Patent Literature 2 discloses a copper nanoparticle dispersion having excellent oxidation resistance, and achieves oxidation resistance of the copper nanoparticle dispersion by immediately dispersing copper nanoparticles and attaching an alkylamine to the surfaces of the copper particles. However, in examples, only copper particles having an average primary particle diameter of less than 100 nm are disclosed, and it is commonly understood that copper particles having such a particle diameter are easily oxidized in the atmosphere and generate significant heat, thereby making it difficult to apply them to various uses after atmospheric exposure.

[0009] In the above-mentioned patent literatures, although stability and oxidation resistance in the state of a paste or a dispersion have been studied, there has been no study on whether copper particles after atmospheric exposure can be used for various uses when the copper particles themselves are exposed to the atmosphere. Furthermore, there is no description or suggestion as to whether the metal colloid particles and the paste comprising the same, as well as the copper nanoparticle dispersion disclosed in the above-mentioned patent literatures can be used for bonding uses.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide copper particles that can be used for various uses even after exposure of the copper particles themselves to the atmosphere.SOLUTION TO PROBLEM

[0011] Accordingly, the present inventors have conducted intensive studies and found that composite copper particles that can be used for various uses even after exposing copper particles to the atmosphere can be obtained by performing a specific treatment with copper particles having a specific particle diameter together with a certain amount of an organic component comprising a carboxylic acid or a salt thereof and a specific polymer dispersant, thereby completing the present invention.

[0012] That is, the present invention provides the following: (1) Composite copper particles comprising copper particles and an organic component, wherein the composite copper particles have a value of 100 nm or more and 600 nm or less as an average particle diameter measured by means of a scanning electron microscope, the organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, wherein a content of the organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the composite copper particles, and the polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in an atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer; (2) The composite copper particles according to (1), wherein the polymer dispersant has a temperature of 300°C or lower as a temperature of an exothermic peak of the polymer dispersant measured by means of a thermogravimetric differential thermal analyzer; (3) The composite copper particles according to (1) or (2), wherein the carboxylic acid or the salt thereof has 2 or more and 20 or less carbon atoms; (4) The composite copper particles according to any one of (1) to (3), wherein the organic component has a value of 1.0 or more and 12.0 or less as a mass ratio of the carboxylic acid or the salt thereof to the polymer dispersant; (5) The composite copper particles according to any one of (1) to (4), wherein surfaces of the copper particles are coated with the carboxylic acid or the salt thereof; (6) A copper paste comprising the composite copper particles according to any one of (1) to (5) and a paste solvent; (7) A bonding material comprising composite copper particles or a copper paste, wherein the composite copper particles are the composite copper particles according to any one of (1) to (5), and the copper paste comprises the composite copper particles according to any one of (1) to (5) and a paste solvent; (8) A conductive material comprising composite copper particles or a copper paste, wherein the composite copper particles are the composite copper particles according to any one of (1) to (5), and the copper paste comprises the composite copper particles according to any one of (1) to (5) and a paste solvent; (9) A sintered body comprising the bonding material according to (7) as a raw material; (10) A conductor comprising the conductive material according to (8); (11) A method for producing composite copper particles, the method comprising a step of mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent; (12) The method according to (11) comprising a step of mixing the carboxylic acid-coated copper particles with a treatment solution comprising the carboxylic acid or the salt thereof, the polymer dispersant, and the solvent; (13) The method according to (11) or (12) comprising a step of mixing the carboxylic acid-coated copper particles with the treatment solution comprising the carboxylic acid or the salt thereof, the polymer dispersant, and the solvent, followed by drying; and the like.ADVANTAGEOUS EFFECTS OF INVENTION

[0013] The composite copper particles of the present invention have a high bonding strength not only before atmospheric exposure but also after atmospheric exposure and exhibit practically usable conductivity, and therefore are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material).BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 is a view showing X-ray diffraction (which is often referred to as "XRD" in the present application) patterns of composite copper particles of Example 1 before and after atmospheric exposure. FIG. 2 is a view showing a transmission electron microscope (which is often referred to as "TEM" in the present application) photograph of composite copper particles of Example 1 before atmospheric exposure. FIG. 3 is a view showing a transmission electron microscope (TEM) photograph of composite copper particles of Example 1 after atmospheric exposure. FIG. 4 is a view showing a scanning electron microscope (which is often referred to as "SEM" in the present application) photograph of composite copper particles of Example 1 before atmospheric exposure. DESCRIPTION OF EMBODIMENTS

[0015] The composite copper particles of the present invention are composite copper particles comprising copper particles and an organic component, wherein the above-mentioned composite copper particles have a value of 100 nm or more and 600 nm or less as an average particle diameter measured by means of a scanning electron microscope, the above-mentioned organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, wherein a content of the above-mentioned organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the above-mentioned composite copper particles, and the above-mentioned polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in an atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer.<Copper particles>

[0016] The composite copper particles of the present invention comprise copper particles.

[0017] The copper particles used in the composite copper particles of the present invention are not particularly limited. For example, commercially available copper particles may be purchased, or copper particles produced by a known method may be used.

[0018] The above-mentioned copper particles may comprise a component or a compound other than the copper component, such as a raw material or a reactant used in the production process, to such an extent that no problem is caused according to their uses.

[0019] The shape of the copper particles used in the composite copper particles of the present invention is not particularly limited. For example, any shape such as an irregular shape, a spherical shape, a polyhedron, a spindle shape, or a plate shape may be used.

[0020] The average particle diameter of the above-mentioned copper particles is not particularly limited as long as composite copper particles having a desired average particle diameter can be obtained. For example, the average particle diameter of the above-mentioned copper particles is preferably 100 nm or more and 600 nm or less, more preferably 150 nm or more and 500 nm or less, and still more preferably 200 nm or more and 400 nm or less.

[0021] In the measurement of the average particle diameter of the copper particles, the above-mentioned copper particles are photographed using a scanning electron microscope (SEM), the maximum Feret diameter (which is simply referred to as Feret diameter, hereinafter) of each of 50 primary particle diameters in the SEM visual field is measured, and the arithmetic average thereof is taken as the average particle diameter.

[0022] The above-mentioned copper particles may exist as primary particles, or may exist as secondary particles in which primary particles are agglomerated.<Organic component>

[0023] The composite copper particles of the present invention comprise a carboxylic acid or a salt thereof and a polymer dispersant as an organic component, and the content of the above-mentioned organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the composite copper particles.

[0024] The content of the organic component in the composite copper particles of the present invention is 0.3 mass% or more and 6.0 mass% or less, preferably 0.5 mass% or more and 4.5 mass% or less, and more preferably 0.7 mass% or more and 3.0 mass% or less based on a total mass of the composite copper particles.

[0025] When the content of the organic component is within the above-mentioned range, the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention are not reduced even when the composite copper particles of the present invention are exposed to the atmosphere, and therefore they are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material). In the present application, such expressions as "even when exposed to the atmosphere" are intended to mean "even immediately after exposure to the atmosphere" and also comprise the time point of atmospheric exposure.

[0026] The amount of the organic component that the composite copper particles of the present invention comprise is measured by means of a thermogravimetric differential thermal analyzer (which is often referred to as "TG-DTA" in the present application). Specifically, the composite copper particles are heated from 30°C to 500°C under conditions of a heating rate of 10°C / min in a nitrogen atmosphere. Based on the mass of the composite copper particles at the start of measurement, the mass loss rate in the temperature range from 30°C to 350°C in the obtained profile is used as the amount of the organic component that the composite copper particles comprise.

[0027] In the composite copper particles of the present invention, the state in which the organic component is present is not particularly limited. For example, the organic component may be present on the surfaces of the copper particles, and may be chemically bonded to the surfaces of the copper particles. Examples of the above-mentioned chemical bonds comprise an ionic bond, a coordinate bond, and an intermolecular force (for example, a van der Waals force or a hydrogen bond). In addition, for example, the organic component may be adsorbed on the surfaces of the copper particles. In the present application, "chemical bonding" or "adsorption" is often referred to as "interaction".

[0028] The adsorption state when the above-mentioned organic component is adsorbed on the surfaces of the copper particles is not particularly limited. For example, the organic component may be in a state of being physically adsorbed and / or chemically adsorbed on the surfaces of the copper particles, and examples of the adsorption states comprise a state in which the organic component is present due to an electrical action (for example, Coulomb force) with the surfaces of the copper particles.

[0029] When the above-mentioned organic component is present on the surfaces of the copper particles, the above-mentioned organic component may coat the surfaces of the above-mentioned copper particles. Specifically, the organic component may coat the entire surface of the copper particles, or the organic component may coat only a part of the surfaces of the copper particles. In addition, when the organic component coats the entire surface of the copper particles, the coating may be uniform or non-uniform.<Carboxylic acid or salt thereof>

[0030] The organic component, which the composite copper particles of the present invention comprises, comprises a carboxylic acid or a salt thereof.

[0031] In the composite copper particles of the present invention, the carboxylic acid or a salt thereof to be used is not particularly limited. The above-mentioned carboxylic acid or a salt thereof may be only one species or may be two or more species.

[0032] The chemical structure of the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as it has a hydrocarbon group moiety and a carboxyl group moiety in its structure.

[0033] The above-mentioned hydrocarbon group moiety is not particularly limited as long as the composite copper particles of the present invention are obtained. For example, it may consist only of a single bond or may have a multiple bond in the middle or at the end. In addition, the hydrocarbon group may comprise a heteroatom at any position.

[0034] The above-mentioned carboxyl group moiety is not particularly limited as long as the composite copper particles according to the present invention are obtained. For example, the carboxylic acid or a salt thereof may have one carboxyl group in the molecule, or may have two or more carboxyl groups in the molecule. Among them, the number of carboxyl groups in the molecule of the carboxylic acid or a salt thereof is preferably one.

[0035] It is preferable that the number of carboxyl groups in the above-mentioned carboxylic acid or a salt thereof is one because the low-temperature sintering performance increases. The state in which the above-mentioned carboxylic acid or a salt thereof is present is mentioned later, but it is understood that the above-mentioned carboxylic acid or a salt thereof is present in the composite copper particles of the present invention via a carboxyl group as a contact point. For example, when a carboxylic acid or a salt thereof is present on the surfaces of the copper particles, the above-mentioned carboxylic acid or a salt thereof is present on the surfaces of the copper particles via a carboxyl group as a contact point. It is understood that in a case where a carboxylic acid or a salt thereof has a small number of the above-mentioned contact points, the carboxylic acid or the salt thereof is thermally decomposed or the like at a low temperature, and thus the low-temperature sintering performance is more effectively improved.

[0036] In addition, a carboxylic acid or a salt thereof having one carboxyl group is preferred because it is less likely to remain as a residue during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0037] Such expressions as "the carboxylic acid or the salt thereof is thermally decomposed or the like at a low temperature" mentioned above in the present specification are intended to comprise desorption by heat, and / or dissociation by heat, and / or volatilization by heat, in addition to decomposition of the carboxylic acid or the salt thereof by heat.

[0038] The "low-temperature sintering performance" as used in the present application is intended to mean performance that the composite copper particles and the copper paste of the present invention are sufficiently sintered at a temperature of 300°C or lower.

[0039] The number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as the composite copper particles according to the present invention are obtained, but is preferably, for example, 2 or more and 20 or less, more preferably 4 or more and 18 or less, and still more preferably 6 or more and 16 or less.

[0040] The number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is defined as the number of carbon atoms in the entire carboxylic acid molecule. That is, the number of carbon atoms in the molecule of the carboxylic acid or a salt thereof is the total of the number of carbon atoms in the hydrocarbon group and the number of carbon atoms in the carboxyl group.

[0041] It is understood that when the above-mentioned number of carbon atoms is 2 or more, oxidation of copper in the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. Therefore, this is preferred because reduction in the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. Further, it is preferable that the above-mentioned number of carbon atoms is 20 or less because the carboxylic acid or a salt thereof in the composite copper particles of the present invention is easily thermally decomposed or the like even at a low temperature, and the low-temperature sintering performance is more effectively improved. In addition, a carboxylic acid or a salt thereof when the above-mentioned number of carbon atoms is 20 or less is preferred because it is less likely to remain as a residue during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0042] Examples of the above-mentioned carboxylic acids comprise formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, lauric acid, oleic acid, and stearic acid.

[0043] Examples of the salts of the above-mentioned carboxylic acids comprise: alkali metal salts such as a sodium salt and a potassium salt; alkaline earth metal salts such as a magnesium salt and a calcium salt; an ammonium salt; and an amine salt.

[0044] Among the carboxylic acids or salts thereof, acetic acid, caproic acid, caprylic acid, capric acid, or a salt thereof is preferred. This is because such a carboxylic acid or a salt thereof is easily thermally decomposed or the like even at a low temperature, and it is understood that the low-temperature sintering performance is improved. In addition, the above-mentioned carboxylic acid or a salt thereof is preferable because it is less likely to remain as a residue during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0045] The content of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as the total content of the organic component comprising the polymer dispersant is in the range of 0.3 mass% or more and 6 mass% or less. When the total content of the organic component comprising the polymer dispersant is in the range of 0.3 mass% or more and 6.0 mass% or less, the content of the carboxylic acid or a salt thereof is preferably, for example, 0.15 mass% or more and 5.0 mass% or less, more preferably 0.15 mass% or more and 4.5 mass% or less, still more preferably 0.20 mass% or more and 4.0 mass% or less, and particularly preferably 0.25 mass% or more and 3.5 mass% or less based on a total mass of the composite copper particles.

[0046] The measurement of the content of the carboxylic acid or a salt thereof can be performed by means of TG-DTA in the same manner as the measurement of the content of the above-mentioned organic component.

[0047] It is understood that in the composite copper particles of the present invention, when the content of the carboxylic acid or a salt thereof is 0.15 mass% or more, oxidation of copper in the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. Therefore, this is preferred because reduction in the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. It is preferable that the content of the carboxylic acid or a salt thereof is 5.0 mass% or less because reduction in the low-temperature sintering performance due to the excessive carboxylic acid or salt thereof in the composite copper particles of the present invention remaining as a residual component can be more effectively avoided. In addition, it is preferable that the content of the carboxylic acid or a salt thereof is 5.0 mass% or less because the carboxylic acid or a salt thereof is thermally decomposed or the like at a low temperature, and the low-temperature sintering performance is more effectively improved.<Polymer dispersant>

[0048] The organic component, which the composite copper particles of the present invention comprises, comprises a polymer dispersant, and the polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in the atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer.

[0049] When the polymer dispersant having the above-mentioned properties is used in the composite copper particles of the present invention, the composite copper particles of the present invention are preferably used for bonding uses (for example, a bonding material) or conductive use (for example, a conductive material) even when the composite copper particles are exposed to the atmosphere.

[0050] In the composite copper particles of the present invention, the polymer dispersant to be used has an acid value of 60 mgKOH / g or more. The acid value is more preferably 70 mgKOH / g or more, still more preferably 86 mgKOH / g or more. An acid value of 70 mgKOH / g or more is preferred because the composite copper particles of the present invention exhibit a high bonding strength before and after atmospheric exposure, and can further suppress reduction in the conductivity (specifically, an increase in volume resistivity) after atmospheric exposure. The upper limit of the acid value of the polymer dispersant is not particularly limited, but an acid value of 200 mgKOH / g or less is preferred because reduction in the bonding strength and conductivity of the composite copper particles of the present invention after atmospheric exposure can be further suppressed. The acid value of the above-mentioned polymer dispersant is more preferably 70 mgKOH / g or more and 200 mgKOH / g or less, and still more preferably 86 mgKOH / g or more and 200 mgKOH / g or less.

[0051] As the acid value of the polymer dispersant, if it is a commercially available product, a catalog value is referred to. When the polymer dispersant is prepared in-house, the acid value can be measured by the following method. The acid value of the polymer dispersant is measured by non-aqueous neutralization titration by means of an automatic titrator (GT-310BRT (manufactured by Nittoh Analytech Co., Ltd.)). A 0.1 mol / L potassium hydroxide / ethanol solution (manufactured by NACALAI TESQUE, INC.) is used as a titration solution, and the titration sample is prepared by dissolving 0.5 g of the polymer dispersant in 100 mL of ethanol.

[0052] In the above-mentioned polymer dispersant, the mass loss rate in the atmosphere of the polymer dispersant used is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer. The above-mentioned mass loss rate is more preferably 80% or more, still more preferably 90% or more.

[0053] It is preferable that the mass loss rate of the polymer dispersant is equal to or more than the above-mentioned value. The reasons are as follows: the composite copper particles after atmospheric exposure are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material); the polymer dispersant is easily thermally decomposed even at a low temperature; and the decomposition products obtained by the above-mentioned thermal decomposition can be easily desorbed or dissociated from the composite copper particles at a low temperature, thereby more effectively improving the low-temperature sintering performance. Furthermore, this is preferred because the polymer dispersant is less likely to remain during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0054] The mass loss rate of the polymer dispersant is measured by means of TG-DTA. Specifically, the polymer dispersant is heated from 25°C to 1000°C under conditions of a heating rate of 10°C / min in the atmosphere. Based on the mass of the polymer dispersant at the start of measurement, the mass loss rate of the polymer dispersant in the atmosphere is calculated from the mass loss amount when the temperature is raised from 30°C to 250°C.

[0055] The amine value of the above-mentioned polymer dispersant is not particularly limited. For example, the amine value of the polymer dispersant is preferably 45 mgKOH / g or less, more preferably 20 mgKOH / g or less, and still more preferably 5 mgKOH / g or less. It is most preferable to use a polymer dispersant having no amine value.

[0056] When the amine value of the polymer dispersant is equal to or less than the above-mentioned value, the reaction between the carboxylic acid or a salt thereof with which the surfaces of the copper particles is treated and the component derived from the amine value can be more effectively avoided.

[0057] The exothermic peak temperature due to thermal decomposition of the above-mentioned polymer dispersant is not particularly limited. For example, the exothermic peak temperature due to thermal decomposition of the polymer dispersant is preferably 300°C or lower, more preferably 280°C, and still more preferably 250°C or lower. When a plurality of exothermic peaks can be confirmed, the temperature of the exothermic peak observed at the highest temperature among the observed peaks is adopted.

[0058] It is preferable that the exothermic peak temperature due to thermal decomposition of the polymer dispersant is equal to or lower than the above-mentioned value because the polymer dispersant is easily thermally decomposed even at a low temperature, and the decomposition product obtained by the above-mentioned thermal decomposition is easily desorbed or dissociated from the composite copper particles at a low temperature, and the low-temperature sintering performance is more effectively improved. Further, this is preferred because the polymer dispersant is less likely to remain during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0059] The temperature of the exothermic peak due to thermal decomposition of the polymer dispersant can be measured by means of TG-DTA in the same manner as the measurement of the mass loss rate of the above-mentioned polymer dispersant.

[0060] The weight average molecular weight of the above-mentioned polymer dispersant is not particularly limited. For example, the weight average molecular weight is preferably 600 or more and 10,000 or less, more preferably 650 or more and 9,000 or less, and still more preferably 700 or more and 8,000 or less.

[0061] It is preferable that the weight average molecular weight of the polymer dispersant is 600 or more. This is because the carboxylic acid or a salt thereof can be held on the surfaces of the copper particles as in the preferred embodiment mentioned later, and agglomeration of the composite copper particles of the present invention can be effectively avoided. As a result, reduction in the properties (specifically, bonding strength and conductivity) when the composite copper particles of the present invention are exposed to the atmosphere can be more effectively avoided. Accordingly, the weight average molecular weight of 600 or more is preferred. It is preferable that the weight average molecular weight is 10,000 or less. This is because the polymer dispersant is easily thermally decomposed even at a low temperature, and the decomposition products obtained by the above-mentioned thermal decomposition can be easily desorbed or dissociated from the composite copper particles at a low temperature, and the low-temperature sintering performance is more effectively improved. Further, the polymer dispersant is less likely to remain during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided. Accordingly, the weight average molecular weight of 10,000 or less is preferred.

[0062] The weight average molecular weight of the polymer dispersant can be measured by means of gel permeation chromatography (which is often referred to as "GPC" in the present application). Specifically, the polymer dispersant is dissolved in tetrahydrofuran (which is often referred to as "THF" in the present application), and the solution is filtered through a membrane filter to prepare a sample solution, and GPC analysis is performed.

[0063] When the average value of the weight average molecular weights measured three times by means of the above-mentioned GPC is defined as a reference value, the error range of the weight average molecular weight of the above-mentioned polymer dispersant is within the range of 500 or less and 500 or more of the above-mentioned reference value (for example, when the average of three measurements of the weight average molecular weight is 1000, the range of 500 or more and 1500 or less is the error range.).

[0064] The content of the above-mentioned polymer dispersant is not particularly limited as long as the total content of the organic component comprising the carboxylic acid or a salt thereof is in the range of 0.3 mass% or more and 6.0 mass% or less. When the total content of the organic component comprising the carboxylic acid or a salt thereof is in the range of 0.3 mass% or more and 6.0 mass% or less, the content of the polymer dispersant is preferably, for example, 0.15 mass% or more and 1.5 mass% or less, more preferably 0.16 mass% or more and 1.25 mass% or less, and still more preferably 0.17 mass% or more and 1.0 mass% or less based on a total mass of the composite copper particles.

[0065] In the composite copper particles of the present invention, it is preferable that the content of the polymer dispersant is 0.15 mass% or more because desorption of the carboxylic acid or a salt thereof from the surfaces of the copper particles can be more effectively avoided when the composite copper particles of the present invention are exposed to the atmosphere. It is preferable that the content of the polymer dispersant is 1.5 mass% or less because the polymer dispersant is easily thermally decomposed even at a low temperature, and the decomposition products obtained by the above-mentioned thermal decomposition can be easily desorbed or dissociated from the composite copper particles at a low temperature, and the low-temperature sintering performance is more effectively improved. Further, this is preferred because reduction in the low-temperature sintering performance of the composite copper particles of the present invention, which is caused by the polymer dispersant that the composite copper particles comprise remaining during sintering, can be more effectively avoided.

[0066] The measurement of the content of the polymer dispersant can be performed by means of TG-DTA in the same manner as the measurement of the content of the above-mentioned organic component.<Composite copper particles>

[0067] The composite copper particles of the present invention have an average particle diameter of 100 nm or more and 600 nm or less, preferably 150 nm or more and 500 nm or less, and more preferably 200 nm or more and 400 nm or less.

[0068] When the average particle diameter of the composite copper particles is within the above-mentioned range, the composite copper particles of the present invention are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) even when the composite copper particles of the present invention are exposed to the atmosphere.

[0069] The average particle diameter of the composite copper particles can be measured by means of SEM in the same manner as the measurement of the average particle diameter of the above-mentioned copper particles.

[0070] In the composite copper particles of the present invention, since the change in the particle diameter of the copper particles due to the presence of the organic component is very small, the average particle diameter of the composite copper particles of the present invention can be regarded as being the same as the average particle diameter of the copper particles.

[0071] When the presence or absence of copper oxide formation in the composite copper particles of the present invention is evaluated by means of an X-ray diffraction (XRD) apparatus, the composite copper particles of the present invention exposed to the atmosphere are measured by means of an XRD apparatus and evaluated based on the obtained X-ray diffraction pattern. For example, when peaks are observed only at around 2θ = 43.3° (Cu(111) plane) and around 2θ = 50.4° (Cu(200) plane), which are peaks attributed to metallic copper, from the above-mentioned X-ray diffraction pattern, it can be evaluated that only metallic copper is present (in other words, copper oxide is not formed). Further, when a peak is observed at around 2θ = 74.08° (Cu(220) plane), which is a peak attributed to metallic copper, in addition to the above-mentioned two peaks, it can be evaluated that only metallic copper is present (in other words, copper oxide is not formed). As the XRD apparatus, for example, SmartLab SE (Rigaku Corporation) can be used. Further, control of the apparatus, data collection, calculation, and report generation may be performed by means of a dedicated software, and for example, SmartLab Studio II (Rigaku Corporation) can be used as such a software.

[0072] When the presence or absence of copper oxide formation in the composite copper particles of the present invention is evaluated by means of a transmission electron microscope (TEM), the composite copper particles of the present invention exposed to the atmosphere are observed by means of TEM and evaluated based on the lattice spacing in the atomic arrangement (that is, lattice fringes) in the crystal. For example, when only 2.1 Å (0.21 nm) which is the lattice spacing of the metallic copper (111) plane is observed as the lattice spacing of the observed lattice fringes, it can be evaluated that only metallic copper is present (i.e., copper oxide is not formed). As the TEM, for example, H-9000 (Hitachi High-Tech Corporation) can be used.

[0073] In the organic component that the composite copper particles of the present invention comprise, the mass ratio of the carboxylic acid or a salt thereof to the polymer dispersant is not particularly limited as long as it is a gram equivalent or more. For example, the value of the mass ratio represented by "(mass of carboxylic acid or salt thereof) / (mass of polymer dispersant)" is preferably 1.0 or more and 12.0 or less, more preferably 1.2 or more and 11.0 or less, and still more preferably 1.5 or more and 10.0 or less.

[0074] It is preferable that the above-mentioned mass ratio is 1.0 or more because a form in which the carboxylic acid or a salt thereof is present on the surfaces of the copper particles can be easily provided, as in a preferred embodiment mentioned later. This improves the low-temperature sintering performance of the composite copper particles of the present invention. It is preferable that the above-mentioned mass ratio is 12.0 or less from the viewpoint that an increase in production cost due to the use of a large amount of the carboxylic acid or a salt thereof can be more effectively avoided.

[0075] The measurement of the mass ratio of the carboxylic acid or a salt thereof to the polymer dispersant ("(mass of carboxylic acid or salt thereof) / (mass of polymer dispersant)") can be performed by means of TG-DTA in the same manner as the measurement of the content of the above-mentioned organic component. Here, in the obtained profile, the mass loss rate in the temperature range from 30°C to 200°C is defined as the mass of the carboxylic acid or a salt thereof, and the mass loss rate in the temperature range from 200°C to 350°C is defined as the mass of the polymer dispersant. The mass loss rate in the temperature range from 200°C to 350°C is obtained by subtracting the mass loss rate of the carboxylic acid or a salt thereof from the total mass loss rate (in the temperature range from 30°C to 350°C).

[0076] In the composite copper particles of the present invention, the state in which the carboxylic acid or a salt thereof is present is not particularly limited. For example, the composite copper particles may comprise the carboxylic acid or a salt thereof, and / or the carboxylic acid or a salt thereof may be present on the surfaces of the copper particles. When the carboxylic acid or a salt thereof is present on the surfaces of the copper particles, for example, the carboxylic acid or a salt thereof may be present by being chemically bonded to the surfaces of the above-mentioned copper particles, and / or the carboxylic acid or a salt thereof may be present by being chemically bonded to the polymer dispersant. In addition, the carboxylic acid or a salt thereof may be present by being adsorbed on the surfaces of the copper particles and / or the polymer dispersant.

[0077] The descriptions regarding the chemical bonding and the adsorption in the above-mentioned "<Organic component>" are applied to the chemical bonding and the adsorption.

[0078] When the above-mentioned carboxylic acid or a salt thereof is present on the surfaces of the copper particles, the above-mentioned carboxylic acid or a salt thereof may coat the surfaces of the copper particles. Specifically, the carboxylic acid or a salt thereof may entirely coat the surfaces of the copper particles, or the carboxylic acid or a salt thereof may only partially coat the surfaces of the copper particles. In addition, when the carboxylic acid or a salt thereof entirely coats the surfaces of the copper particles, the coating may be uniform or non-uniform.

[0079] In addition, when the above-mentioned carboxylic acid or a salt thereof coats the surfaces of the copper particles, the above-mentioned carboxylic acid or a salt thereof may coat the surfaces of the copper particles as a monomolecular film, or may coat the surfaces of the copper particles as a cumulative film. Further, the carboxylic acid or a salt thereof constituting the above-mentioned monomolecular film and the above-mentioned cumulative film may be formed only of the same species or two or more different species. The "cumulative film" as used herein is intended to mean a monomolecular film constituted by the carboxylic acid or a salt thereof, which is in direct contact with the surfaces of the copper particles, and a film constituted by the carboxylic acid or a salt thereof, which is chemically bonded to, adsorbed on the monomolecular film, or the like.

[0080] In the composite copper particles of the present invention, the state in which the polymer dispersant is present is not particularly limited. For example, the composite copper particles may comprise the polymer dispersant and / or the polymer dispersant may be present on the surfaces of the copper particles. When the polymer dispersant is present on the surfaces of the copper particles, for example, the polymer dispersant may interact with the surfaces of the copper particles and / or may interact with the carboxylic acid or a salt thereof present on the surfaces of the copper particles.

[0081] Examples of the interactions with the carboxylic acid or a salt thereof present on the surfaces of the above-mentioned copper particles comprise a state in which the polymer dispersant interacts with the carboxylic acid or a salt thereof by physical adsorption, chemical adsorption, or the like, a state in which the polymer dispersant electrically interacts with the carboxylic acid or a salt thereof (for example, Coulomb force), and / or a state in which the polymer dispersant is chemically bonded to the carboxylic acid or a salt thereof.

[0082] When the above-mentioned polymer dispersant interacts with the carboxylic acid or a salt thereof present on the surfaces of the copper particles, the above-mentioned polymer dispersant may coat a film (specifically, a monomolecular film or a cumulative film) constituted by the above-mentioned carboxylic acid or a salt thereof. Specifically, the polymer dispersant may entirely coat the surface of the above-mentioned film, or the polymer dispersant may only partially coat the above-mentioned film.

[0083] In a more preferred embodiment of the composite copper particles of the present invention, the surfaces of the copper particles are coated with a molecular film comprising the carboxylic acid or a salt thereof, and the molecular film of the carboxylic acid or a salt thereof is coated with the polymer dispersant. When the composite copper particles of the present invention are in such an embodiment, agglomeration of the composite copper particles is more preferably suppressed. It is understood that since the agglomeration of the composite copper particles can be more preferably suppressed, the low-temperature sintering performance is more preferably maintained even after the composite copper particles of the present invention are exposed to the atmosphere.

[0084] In one embodiment, when the composite copper particles are in the above-mentioned more preferred embodiment, the decomposition temperature of the carboxylic acid or a salt thereof is preferably lower than that of the polymer dispersant. When the composite copper particles of the present invention are sintered, the carboxylic acid or a salt thereof which is relatively easily thermally decomposed is more preferably desorbed, and at the same time, the polymer dispersant can also be more preferably desorbed. Therefore, it is understood that the composite copper particles of the present invention have excellent low-temperature sintering performance.

[0085] In a still more preferred embodiment, the molecular film of the above-mentioned carboxylic acid or a salt thereof may be constituted by a monomolecular film or a cumulative film, and the polymer dispersant may coat the above-mentioned monomolecular film or cumulative film.

[0086] When a monomolecular film of the carboxylic acid or a salt thereof is formed on the surfaces of the above-mentioned copper particles, it is understood that the composite copper particles of the present invention not only are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) after atmospheric exposure, but also more preferably contribute to the exhibition of low-temperature sintering performance.

[0087] When a cumulative film of the carboxylic acid or a salt thereof is formed on the above-mentioned monomolecular film, it is understood that the composite copper particles of the present invention not only can be preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) after atmospheric exposure, but also more preferably contribute to the suppression in oxidation of copper that the composite copper particles comprise.

[0088] In addition, it is understood that the monomolecular film or the cumulative film of the carboxylic acid or a salt thereof coated on the surfaces of the copper particles also functions more preferably as a scaffold upon coating with the polymer dispersant.

[0089] Since the carboxylic acid or a salt thereof coated on the surfaces of the copper particles is adsorbed and desorbed, when the composite copper particles of the present invention are in the still more preferred embodiment as mentioned above, even if the carboxylic acid or a salt thereof is partially desorbed when the composite copper particles of the present invention are exposed to the atmosphere, the polymer dispersant coats the surfaces. As a result, the exposure of copper is more preferably reduced. Accordingly, it is understood that the composite copper particles of the present invention have a high effect of suppressing oxidation.

[0090] By coating the monomolecular film or the cumulative film of the above-mentioned carboxylic acid or a salt thereof with the polymer dispersant, the composite copper particles of the present invention are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) after atmospheric exposure.

[0091] That is, when the monomolecular film or the cumulative film of the carboxylic acid or a salt thereof is formed through relatively weak forces (for example, intermolecular force or the like), the surface of the above-mentioned monomolecular film or cumulative film is coated with the polymer dispersant, so that the carboxylic acid or a salt thereof is less likely to be desorbed. As a result, the polymer dispersant plays an auxiliary role for exhibiting the effect (specifically, deterioration of properties can be suppressed even after atmospheric exposure) of the monomolecular film or cumulative film of the above-mentioned carboxylic acid or a salt thereof. In addition, as one of the general effects of the polymer dispersant, the polymer dispersant can more preferably contribute to suppression in agglomeration of the composite copper particles.<Production of composite copper particles>

[0092] A method for producing composite copper particles of the present invention will be described.

[0093] The composite copper particles of the present invention are produced by a method comprising a step of mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0094] The composite copper particles of the present invention can also be produced by a method comprising a step of mixing carboxylic acid-coated copper particles with a treatment solution comprising a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0095] The composite copper particles of the present invention can also be produced by a method comprising a step of mixing carboxylic acid-coated copper particles with a treatment solution comprising a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent, followed by drying.(Step of preparing carboxylic acid-coated copper particles)

[0096] In the composite copper particles of the present invention, the copper particles to be used are not particularly limited. For example, commercially available copper particles may be purchased, or copper particles produced by a known method may be used. As the copper particles produced by a known method, copper particles treated with a carboxylic acid will be mentioned later.

[0097] The above-mentioned copper particles may comprise a component or a compound other than the copper component, such as a raw material or a reactant used in the production process, to such an extent that no problem is caused according to their use.

[0098] The shape of the above-mentioned copper particles used in the composite copper particles of the present invention is not particularly limited. For example, any shape such as an irregular shape, a spherical shape, a polyhedron, a spindle shape, or a plate shape may be used.

[0099] The average particle diameter of the above-mentioned copper particles is not particularly limited. For example, it is 100 nm or more and 600 nm or less, preferably 150 nm or more and 500 nm or less, and more preferably 200 nm or more and 400 nm or less.

[0100] It is preferable that the average particle diameter of the copper particles is within the above-mentioned range because composite copper particles having a desired average particle diameter can be obtained.<Solvent>

[0101] The above-mentioned solvent is not particularly limited as long as it does not react with the above-mentioned carboxylic acid or a salt thereof or the polymer dispersant. As such a solvent, for example, methanol, ethanol, 1-propanol, 2-propanol, acetone, methyl ethyl ketone, or the like can be used.

[0102] The individual raw materials used in the above-mentioned production method can be appropriately used from among those mentioned above in accordance with the production method.(Surface treatment step)

[0103] In the composite copper particles of the present invention, by mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent as raw materials, the carboxylic acid-coated copper particles are subjected to a surface treatment with the carboxylic acid or a salt thereof and the polymer dispersant.

[0104] The mixing order of the above-mentioned individual raw materials is not particularly limited. For example, all the raw materials may be mixed together at once, or the solvent and other raw materials may be mixed individually in any order. In addition, a solution obtained by mixing a solvent and at least one raw material may be prepared, and then the solution may be mixed with the remaining raw materials in any order. Specifically, a treatment solution in which a solvent, a polymer dispersant, and a carboxylic acid or a salt thereof are mixed is prepared in advance, and the above-mentioned treatment solution and the carboxylic acid-coated copper particles may be mixed. A dispersion solution comprising carboxylic acid-coated copper particles obtained by mixing a solvent and carboxylic acid-coated copper particles may be mixed with a treatment solution in which a solvent, a polymer dispersant, and a carboxylic acid or a salt thereof are mixed.

[0105] In the step of mixing the above-mentioned individual raw materials, a known stirrer can be used. Examples thereof comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials.

[0106] The stirring time and the stirring speed are not particularly limited as long as the above-mentioned individual raw materials can be sufficiently mixed. For example, the stirring time may be 1 minute or more, and is more preferably 5 minutes or more. For example, the stirring speed is preferably 50 rpm or more, and more preferably 100 rpm or more. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the above-mentioned carboxylic acid-coated copper particles can be uniformly treated with the organic component.

[0107] The composite copper particles of the present invention can be produced by a method comprising a step of mixing carboxylic acid-coated copper particles with a treatment solution comprising a polymer dispersant, a carboxylic acid or a salt thereof, and a solvent. This production method is preferred because the carboxylic acid or a salt thereof and the polymer dispersant that the treatment solution comprises can be more efficiently made present on the surfaces of the copper particles.(Step of preparing treatment solution)

[0108] In the method for producing composite copper particles of the present invention, the treatment solution is prepared by a method comprising a step of mixing a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0109] In the step of preparing the above-mentioned treatment solution, the addition order of the raw materials is not particularly limited. For example, all the raw materials may be mixed together at once, or the solvent and other raw materials may be mixed individually in any order.

[0110] In the step of preparing the above-mentioned treatment solution, in a case of mixing the above-mentioned treatment solution, stirring may be performed by means of a known stirrer. Examples of such stirrers comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser mixer, and a homomixer.

[0111] In the above-mentioned step of stirring, stirring conditions such as a stirring time and a stirring speed are not particularly limited as long as the above-mentioned individual raw materials can be sufficiently mixed. For example, the stirring time may be 1 minute or more, and is more preferably 5 minutes or more. For example, the stirring speed may be 50 rpm or more, and is more preferably 100 rpm or more. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the above-mentioned individual raw materials can be uniformly mixed.

[0112] The total amount of the carboxylic acid or a salt thereof and the polymer dispersant in the above-mentioned treatment solution is not particularly limited as long as the copper particles can be treated with a predetermined amount of the organic component. For example, the total amount of the carboxylic acid or a salt thereof and the polymer dispersant in the treatment solution is preferably 1.0 mass% or more and 30 mass% or less, more preferably 1.5 mass% or more and 25 mass% or less, and still more preferably 2.0 mass% or more and 20 mass% or less based on a total mass of the treatment solution.

[0113] The content of the carboxylic acid or a salt thereof in the above-mentioned treatment solution is not particularly limited. For example, the content of the carboxylic acid or a salt thereof in the treatment solution is preferably 0.7 mass% or more and 25 mass% or less, more preferably 1.5 mass% or more and 18 mass% or less, and still more preferably 2.0 mass% or more and 16 mass% or less based on a total mass of the treatment solution.

[0114] The content of the polymer dispersant in the above-mentioned treatment solution is not particularly limited. For example, the content of the polymer dispersant in the treatment solution is preferably 0.3 mass% or more and 5.0 mass% or less, more preferably 0.4 mass% or more and 4.5 mass% or less, and still more preferably 0.5 mass% or more and 4.0 mass% or less based on a total mass of the treatment solution.

[0115] It is preferable that the composition of the treatment solution is within the above-mentioned range because the copper particles can be more effectively treated with a predetermined amount of the organic component so that the composite copper particles of the present invention can be obtained.

[0116] In the step of mixing the above-mentioned carboxylic acid-coated copper particles and the above-mentioned treatment solution, a known stirrer can be used. Examples thereof comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser, and a homomixer. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials. Examples thereof comprise a method of immersing the copper particles in the treatment solution and a method of allowing the treatment solution to permeate into the copper particles.

[0117] The stirring time and the stirring speed are not particularly limited as long as the above-mentioned individual raw materials can be sufficiently mixed. For example, the stirring time is preferably 1 minute or more, and more preferably 5 minutes or more. For example, the stirring speed is preferably 50 rpm or more, and more preferably 100 rpm or more. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the above-mentioned carboxylic acid-coated copper particles can be uniformly treated with the organic component. In addition, in the case of immersion or permeation, the immersion or permeation time may be 10 minutes or more.

[0118] After the above-mentioned surface treatment step, solid-liquid separation may be performed as necessary. A known filtration method can be used in solid-liquid separation. For example, a pressure filtration device such as a rotary press or a filter press, a vacuum filtration device such as a Nutsche filter or a Moore filter, a centrifuge, or the like can be used. Decantation operation may be performed as appropriate.

[0119] After the above-mentioned surface treatment step, the collected solid content may be washed as necessary. A known washing method can be used for washing the solid content. The solvent used for washing is not particularly limited.(Drying step)

[0120] The composite copper particles of the present invention can be produced by a method comprising a step of drying the mixture of the carboxylic acid-coated copper particles and the treatment solution as necessary.

[0121] Conditions such as drying temperature, drying time, and drying atmosphere in the drying step can be appropriately set. For example, the drying temperature is preferably 20°C or higher and 120°C or lower, the drying time is preferably 0.5 hours or more and 10 hours or less, and the drying atmosphere is preferably under vacuum or under an inert gas such as nitrogen or argon.

[0122] In the drying step, drying may be performed by means of a known dryer. For example, a heating device such as a dryer, an oven, or an electric furnace, a desiccator controlled to a predetermined temperature, a vacuum dryer, a decompression dryer, or the like can be used.

[0123] When a desiccator is used in the drying step, the mixture of the copper particles and the treatment solution can be dried by controlling the inside of the desiccator to a predetermined temperature and creating a vacuum atmosphere.

[0124] When the inside of the desiccator is brought into a vacuum atmosphere, a vacuum pump may be used. As the vacuum pump, for example, G-20DA manufactured by ULVAC, Inc. or the like can be used.

[0125] After the above-mentioned drying step, the composite copper particles may be ground or crushed as necessary to adjust the particle size. A known grinding machine, classifier, or the like can be used for grinding or crushing.(Production Example of carboxylic acid-coated copper particles)

[0126] Hereinafter, an example of a method for producing carboxylic acid-coated copper particles (steps A and B) will be described.(Step A)

[0127] This step is a step of mixing a copper compound, a carboxylic acid or a salt thereof, an amine compound, and a solvent. In this step, a mixed solution comprising a copper compound can be obtained.

[0128] The above-mentioned copper compound is not particularly limited as long as it comprises a copper atom. The copper compound used in step A may be only one species or may be two or more species.

[0129] Examples thereof comprise: copper carboxylates such as copper(I) formate, copper(I) acetate, copper(I) propionate, copper(I) butyrate, copper(I) valerate, copper(I) caproate, copper(I) caprylate, copper(I) caprate, copper(II) formate, copper(II) acetate, copper(II) propionate, copper(II) butyrate, copper(II) valerate, copper(II) caproate, copper(II) caprylate, copper(II) caprate, and copper(II) citrate; copper oxides such as copper(II) oxide and copper(I) oxide; copper hydroxides such as copper(II) hydroxide and copper(I) hydroxide; and copper nitride.

[0130] Among the above-mentioned copper compounds, copper(II) oxide is preferred from the viewpoint of reducing the production cost.

[0131] The added amount of the above-mentioned copper compound is not particularly limited. For example, the added amount of the above-mentioned copper compound is preferably 1 part by mass or more and 100 parts by mass or less with respect to the solvent.

[0132] It is preferable that the amount of the copper compound is 1 part by mass or more with respect to the solvent because the decrease in the amount of copper particles produced in step B can be effectively avoided. It is preferable that the amount of the copper compound is 100 parts by mass or less with respect to the solvent because an uneven reaction due to thickening when the solvent and the above-mentioned copper compound are mixed in this step can be effectively avoided.

[0133] The chemical structure of the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as it has a hydrocarbon group moiety and a carboxyl group moiety in its structure.

[0134] The above-mentioned hydrocarbon group moiety is not particularly limited as long as the carboxylic acid-coated copper particles used for producing the composite copper particles according to the present invention can be obtained. For example, it may be formed only of a single bond or may have a multiple bond in the middle or at the end. In addition, the hydrocarbon group may comprise a heteroatom at any position.

[0135] The above-mentioned carboxyl group moiety is not particularly limited as long as the carboxylic acid-coated copper particles used for producing the composite copper particles according to the present invention can be obtained. For example, the carboxylic acid or a salt thereof may have one carboxyl group in the molecule, or may have two or more carboxyl groups in the molecule. Among them, the number of carboxyl groups in the molecule of the carboxylic acid or a salt thereof is preferably one.

[0136] The number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as the carboxylic acid-coated copper particles used for producing the composite copper particles according to the present invention can be obtained. For example, the number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is preferably 2 or more and 20 or less, more preferably 2 or more and 18 or less, and still more preferably 2 or more and 16 or less.

[0137] Examples of the above-mentioned carboxylic acids comprise formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, lauric acid, oleic acid, and stearic acid.

[0138] Examples of the salts of the above-mentioned carboxylic acids comprise: alkali metal salts such as a sodium salt and a potassium salt; alkaline earth metal salts such as a magnesium salt and a calcium salt; an ammonium salt; and an amine salt.

[0139] Among the above-mentioned carboxylic acids or salts thereof, it is more preferable to comprise acetic acid, caproic acid, caprylic acid, or capric acid. Use of such a carboxylic acid or a salt thereof is preferred because copper particles obtained in step B mentioned later more efficiently achieve a desired average particle diameter.

[0140] The added amount of the above-mentioned carboxylic acid or a salt thereof is not particularly limited, and may be 0.01 mol or more and 2 mol or less per 1 mol of the copper compound.

[0141] It is preferable that the added amount of the carboxylic acid or a salt thereof is within the above-mentioned range because copper particles having a desired average particle diameter can be obtained in step B.

[0142] The above-mentioned amine compound used in step A is not particularly limited as long as it has an amino group and a hydroxy group in its structure.

[0143] Specifically, the above-mentioned amine compound is preferably an amino alcohol. Use of the amino alcohol preferably suppresses foaming of the mixed solution comprising the copper compound in step A.

[0144] Examples of the above-mentioned amino alcohols comprise methanolamine, monoethanolamine (which is also referred to as "2-aminoethanol"), diethanolamine, triethanolamine, 3-amino-1-propanol, 1-dimethylamino-2-propanol, 3-(dimethylamino)-1-propanol, 4-ethylamino-1-butanol, N-methylethanolamine, 2-diethylethanolamine, 2-aminodibutanol, heptaminol, isoetharine, sphingosine, 3-dimethylamino-1,2-propanediol, 3-diethylamino-1,2-propanediol, 3-methylamino-1,2-propanediol, 3-(dimethylamino)-1,2-propanediol, 2-amino-2-methyl-1,3-propanediol, 3-(diethylamino)-1,2-propanediol, 2-amino-2-ethyl-1,3-propanediol, 3-amino-1,2-propanediol, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, and 2-amino-1,3-propanediol.

[0145] Among the above-mentioned amine compounds, it is more preferable to comprise monoethanolamine. Monoethanolamine is preferred because even if monoethanolamine remains in the synthesized copper particles, monoethanolamine is thermally decomposed or the like at a low temperature, so that deterioration of the low-temperature sintering performance can be more effectively avoided.

[0146] The added amount of the above-mentioned amine compound is not particularly limited, and is preferably 0.25 mol or more and 2 mol or less per 1 mol of the above-mentioned carboxylic acid.

[0147] It is preferable that the added amount of the amine compound is within the above-mentioned range because thickening of the mixed solution comprising the copper compound can be effectively avoided.

[0148] The addition time of the above-mentioned amine compound is not particularly limited, and is preferably 10 seconds or more and 30 minutes or less. In this way, rapid heat generation of the mixed solution comprising the copper compound in step A is preferably suppressed.

[0149] The solvent used in step A is not particularly limited as long as it does not react with other raw materials to inhibit the production of copper particles. The above-mentioned solvent used may be only one species or may be two or more species.

[0150] As the above-mentioned solvent, an alcohol is preferably used. Examples of the above-mentioned alcohols comprise 1-propanol, 2-propanol, butanol, pentanol, hexanol, heptanol, octanol, and ethyl carbitol. These alcohols are preferred because they exhibit high compatibility with the carboxylic acid or a salt thereof and the above-mentioned amine compound.

[0151] The mixing order of the above-mentioned individual raw materials is not particularly limited. For example, all the raw materials may be mixed together at once, or the solvent and other raw materials may be mixed individually in any order. In particular, it is preferable to mix a solvent, a copper compound, and a carboxylic acid or a salt thereof, followed by further mixing with an amine compound.

[0152] In the above-mentioned mixing step, a known stirrer can be used. Examples thereof comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials.

[0153] The above-mentioned mixing conditions in the mixing step can be appropriately set. For example, the stirring time may be 1 minute or more. The stirring time is more preferably 5 minutes or more. The stirring speed may be 50 rpm or more. The stirring speed is more preferably 100 rpm or more. With the above-mentioned mixing conditions, the raw materials can be sufficiently mixed. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the raw materials are more sufficiently mixed and the reaction proceeds uniformly.(Step B)

[0154] This step is a step of intermittently or continuously adding a reducing agent to the mixed solution comprising the copper compound obtained in step A, and the solution temperature of the above-mentioned mixed solution during addition of the above-mentioned reducing agent is 40°C or higher and 95°C or lower. By this step, a dispersion solution comprising copper particles can be obtained.

[0155] The above-mentioned reducing agent may be any reducing agent as long as it reduces the copper compound, and specifically, the boiling point thereof is preferably 70°C or higher, and the boiling point of the above-mentioned reducing agent is more preferably equal to or higher than the heating temperature in the heating step. Use of such a reducing agent is preferred because the copper compound is more efficiently reduced even when the temperature of the mixed solution is 40°C or higher and 95°C or lower. The above-mentioned reducing agent used may be only one species or may be two or more species.

[0156] Examples of the above-mentioned reducing agents comprise hydrazine derivatives. Examples of the hydrazine derivatives comprise hydrazine monohydrate, hydrazine hydrate, methylhydrazine, ethylhydrazine, n-propylhydrazine, i-propylhydrazine, n-butylhydrazine, i-butylhydrazine, sec-butylhydrazine, t-butylhydrazine, n-pentylhydrazine, i-pentylhydrazine, neo-pentylhydrazine, t-pentylhydrazine, n-hexylhydrazine, i-hexylhydrazine, n-heptylhydrazine, n-octylhydrazine, n-nonylhydrazine, n-decylhydrazine, n-undecylhydrazine, n-dodecylhydrazine, cyclohexylhydrazine, phenylhydrazine, 4-methylphenylhydrazine, benzylhydrazine, 2-phenylethylhydrazine, 2-hydrazinoethanol, acetohydrazine, adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, isophthalic acid dihydrazide, and salicylic acid hydrazide.

[0157] When the above-mentioned reducing agent is added to the mixed solution comprising the copper compound obtained in step A, the reducing agent is not added thereto at once in a short time but is added thereto intermittently or continuously. The addition time of the reducing agent is preferably 50 minutes or more and 6 hours or less, and more preferably 60 minutes or more and 6 hours or less.

[0158] In the present application, such expressions as "adding intermittently or continuously" are intended to mean adding gradually in small amounts over time. In addition, the reducing agent may be added in two or more portions.

[0159] In the present application, the "addition time" is defined as the time required from the start point when the reducing agent is added to the mixed solution comprising the copper compound until a total amount of the above-mentioned reducing agent is added to the above-mentioned mixed solution (which may also be referred to as "time required to add a total amount of the reducing agent" hereinafter).

[0160] By adding the reducing agent intermittently or continuously, heat generation occurring during the reduction reaction is suppressed, thereby allowing the average particle diameter of the copper particles obtained in this step to fall within the desired range.

[0161] The added amount of the above-mentioned reducing agent is preferably 1.0 mol or more and 4.0 mol or less per 1.0 mol of the above-mentioned copper compound. An added amount of 1.0 mol or more is preferred because the copper compound can be sufficiently reduced. Further, an added amount of 4.0 mol or less is preferred because the load during the washing of the solid content comprising the copper particles can be further reduced.

[0162] The temperature of the mixed solution comprising the copper compound at the time of addition of the above-mentioned reducing agent is preferably 40°C or higher and 95°C or lower, and more preferably 45°C or higher and 90°C or lower.

[0163] When the temperature of the mixed solution comprising the copper compound is within the above-mentioned range, copper particles having a desired average particle diameter can be obtained.

[0164] The temperature of the mixed solution comprising the copper compound may be adjusted before the addition of the reducing agent or during the addition of the reducing agent. Preferably, the temperature of the mixed solution comprising the copper compound is adjusted to the above-mentioned range before the addition of the reducing agent.

[0165] In this step, a known mixing machine such as a stirrer, a mixer, a homogenizer, or an agitator can be used as necessary. The stirring speed is not limited, but may be 50 rpm or more. The stirring speed is more preferably 100 rpm or more. A stirring speed of 100 rpm or more is preferred because the copper compound is uniformly reduced, and more uniform copper particles can be obtained.

[0166] The dispersion solution comprising the copper particles obtained in this step may be aged as necessary.

[0167] The aging conditions can be appropriately set. For example, the aging temperature is preferably 40°C or higher and 120°C or lower, more preferably 40°C or higher and 100°C or lower, still more preferably 60°C or higher and 100°C or lower, and particularly preferably 60°C or higher and 95°C or lower. The aging time is preferably 1 minute or more and 2.0 hours or less, and more preferably 5 minutes or more and 2.0 hours or less. Furthermore, during aging, stirring may be performed by means of the above-mentioned known mixing machine. The stirring speed is not limited, but may be 50 rpm or more. The above-mentioned stirring speed is preferably 100 rpm or more.

[0168] The dispersion solution comprising the copper particles obtained in this step may be subjected to solid-liquid separation as necessary.

[0169] A known method can be used in solid-liquid separation. For example, a pressure filtration device such as a rotary press or a filter press commonly used industrially, a vacuum filtration device such as a Nutsche filter or a Moore filter, a centrifuge, or the like can be used. Decantation operation may be performed as appropriate.

[0170] The solid content obtained by the above-mentioned solid-liquid separation may be washed by a known method.

[0171] The solid content obtained by the above-mentioned solid-liquid separation may be dried by a known method. For example, a heating device such as a dryer, an oven, or an electric furnace, a desiccator controlled to a predetermined temperature, a vacuum dryer, a decompression dryer, or the like can be used.

[0172] When a desiccator is used in the drying step, the above-mentioned solid content can be dried by controlling the inside of the desiccator to a predetermined temperature and creating a vacuum atmosphere. When the inside of the desiccator is brought into a vacuum atmosphere, a vacuum pump may be used. As the vacuum pump, for example, G-20DA manufactured by ULVAC, Inc. or the like can be used.

[0173] The drying conditions can be appropriately set. For example, the drying temperature is preferably 20°C or higher and 120°C or lower, the drying time is preferably 0.5 hours or more and 10 hours or less. From the viewpoint of more effectively suppressing the oxidation of the copper particles, the drying atmosphere is preferably maintained under a flow of an inert gas such as nitrogen or argon or under a vacuum atmosphere.

[0174] Carboxylic acid-coated copper particles having an average particle diameter of 100 nm or more and 600 nm or less can be obtained by the production method comprising the above above-mentioned step A and step B, and the carboxylic acid-coated copper particles obtained here can be used as a raw material when the composite copper particles of the present invention are produced.<Copper paste>

[0175] The copper paste of the present invention comprises the composite copper particles of the present invention and a paste solvent.

[0176] The paste solvent is not particularly limited, and any organic solvent can be used. For example, a protic polar solvent or an aprotic solvent can be used, and two or more of solvent species can be appropriately combined and used.

[0177] In the present invention, an alcohol-based solvent, a glycol-based solvent, a glycol ether-based solvent, and an ester-based solvent have high affinity for a polymer dispersant having an acid value or a carboxylic acid, and can be preferably used.

[0178] Examples of the alcohol-based solvents comprise methanol, ethanol, propyl alcohol, butyl alcohol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, modified alcohol, and aromatic alcohols such as benzyl alcohol, menthol, and terpineol (α, β, γ, δ).

[0179] As the glycol-based solvent, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, or the like can be used.

[0180] Examples of the glycol ether-based solvents comprise an ethylene-based glycol ether and a propylene-based glycol ether.

[0181] Examples of the ethylene-based glycol ethers comprise ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether (ethyl carbitol), diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether (hexyl carbitol), triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monohexyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, ethylene glycol diacetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, and ethylene glycol phenyl ether.

[0182] Examples of the propylene-based glycol ethers comprise propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monohexyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monohexyl ether, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol diacetate, propylene glycol monobutyl ether acetate, dipropylene glycol monobutyl ether acetate, and propylene glycol phenyl ether.

[0183] Examples of the ester-based solvents comprise methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, and normal propyl acetate.

[0184] In the copper paste of the present invention, the paste solvent used may be only one species or may be two or more species. The species and the blending ratio may be appropriately set in consideration of properties required for the copper paste, properties required for the bonding material, properties required for the conductive material, compatibility with other blended components, and the like. Examples of the combinations of two or more species of paste solvents comprise a combination of dipropylene glycol and hexyl carbitol.

[0185] The copper paste of the present invention can comprise various additives as necessary. Examples of the additives comprise various commonly used reducing agents, dispersants, emulsifiers, antifreeze agents, pH adjusters, thickeners, defoamers, and film-forming agents.

[0186] In a case where the copper paste of the present invention comprises the above-mentioned reducing agent, examples of the usable reducing agents comprise monoethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol, N-methyldiethanolamine, hydrazine, and formic acid.

[0187] The copper paste of the present invention may comprise copper particles other than the composite copper particles of the present invention. Specifically, the copper paste of the present invention may comprise micro-copper particles having an average particle diameter of 1 µm to 50 µm or nano-copper particles having an average particle diameter of 100 nm or less. The shapes of the above-mentioned micro-copper particles and the nano-copper particles are not particularly limited, and examples thereof comprise any shape such as a spherical shape, a massive shape, a needle shape, a flake shape, a substantially spherical shape, an irregular shape, a polyhedral shape, a spindle shape, and a flat shape, as well as agglomeration of these shapes. The average particle diameter of the micro-copper particles and the nano-copper particles can be measured in the same manner as the average particle diameter of the above-mentioned composite copper particles.

[0188] The content of the above-mentioned composite copper particles in the copper paste of the present invention may be appropriately adjusted in accordance with the uses. The content of the copper particles in the copper paste can be confirmed by, for example, thermogravimetric analysis.

[0189] The copper paste of the present invention is produced by mixing the above-mentioned raw materials. In this mixing step, a known mixer can be used. Examples thereof comprise a biaxial mixer, a triple roll, a sand mill, and a planetary mixer which are commonly used industrially. In addition, in the case of a laboratory scale, a stirrer, a hybrid mixer, a homogenizer, a paint shaker, or the like can be used. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials.

[0190] In the mixer, grinding media may be used as necessary. Examples thereof comprise those comprising glass, alumina, zirconia, zirconium silicate, or the like as a component.

[0191] Defoaming may be performed as necessary during the above-mentioned mixing step or after the mixing step.

[0192] The atmosphere in the mixing step may be any of air, inert gas, and vacuum. From the viewpoint of more effectively suppressing reduction in the performance due to oxidation of the copper particles, an inert gas or vacuum is preferred.<Bonding material>

[0193] The composite copper particles of the present invention or the copper paste comprising the composite copper particles of the present invention can be used as a bonding material, and can preferably bond a base material and a material to be bonded. It can also be used for bonding three-dimensional stacked integrated circuits (3D-ICs). The composite copper particles of the present invention may be used as a bonding material as they are, or may be used as a bonding material after the composite copper particles are formed into a copper paste.

[0194] When the above-mentioned copper paste is used for the above-mentioned bonding material, the above-mentioned copper paste preferably comprises the composite copper particles in an amount of 80 mass% or more and 98 mass% or less, and more preferably 85 mass% or more and 96 mass% or less based on a total amount of the copper paste.

[0195] The incorporation of 80 mass% or more of the above-mentioned composite copper particles in the above-mentioned copper paste is preferred because generation of voids during heating can be effectively suppressed, and the bonding strength is further improved. The incorporation thereof in an amount of 98 mass% or less can more efficiently avoid agglomeration of the composite copper particles in the paste, and preferably improves the coatability of the paste.

[0196] The above-mentioned bonding material may appropriately comprise additives in accordance with its uses. Examples of the additives comprise the above-mentioned various additives.

[0197] The above-mentioned base material and the above-mentioned material to be bonded may be the same material or different materials. The above-mentioned material to be bonded is not particularly limited. Examples thereof comprise various metal materials, semiconductor materials (for example, chips), ceramic materials, and resin materials.

[0198] The surfaces of the above-mentioned base material and the above-mentioned material to be bonded may be polished as necessary.

[0199] In the case of the metal materials, grindstone polishing, lapping polishing, buffing polishing, barrel polishing, electrolytic polishing, and the like can be used. As polishing agents and abrasive grains used for polishing, known materials can be appropriately used. Examples of abrasive grains comprise diamond, alumina, silicon carbide, and cubic boron nitride.

[0200] In the case of the semiconductor material, chemical mechanical polishing (CMP) and the like can be used. Examples of abrasive grains comprise inorganic metal oxides such as cerium oxide and silicon oxide.

[0201] In the case of a ceramic material or a resin material, mechanochemical polishing can be used.

[0202] The surfaces of the above-mentioned base material and the above-mentioned material to be bonded may be subjected to a plating treatment as necessary.

[0203] The plating metal species can be appropriately selected in accordance with the uses. Examples thereof comprise gold plating, silver plating, copper plating, nickel plating, chromium plating, and alloy plating of various metals. When alloy plating is performed, the composition of plating can also be appropriately adjusted in accordance with the uses.

[0204] As a plating method, a known method can be used. Examples thereof comprise dry plating such as physical vapor deposition plating and chemical vapor deposition plating, and wet plating such as displacement plating, electroplating, and electroless plating.

[0205] Specific examples of the above-mentioned base materials comprise: a semiconductor substrate such as a silicon substrate; a metal substrate such as a copper substrate; a lead frame; a ceramic substrate attached with a metal plate (for example, Direct Bonded Copper: DBC); a substrate for mounting a semiconductor element such as an LED (Light-Emitting Diode) package; a power supply component such as a copper ribbon, a metal block, and a terminal; a heat dissipation plate; and a water cooling plate.

[0206] The bonding method using the bonding material of the present invention is a method in which a bonding material is provided on a base material, a material to be bonded is placed on a side of the bonding material opposite to the base material to obtain a laminate, and the laminate is heated to bond the base material and the material to be bonded. However, the bonding method using the bonding material of the present invention is not limited to the above-mentioned bonding method as long as the object of the present invention can be achieved.

[0207] Examples of methods for applying the bonding material to the base material comprise screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, jet printing, a dispenser, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0208] The base material applied by the bonding material may be dried as necessary. The drying conditions can be appropriately set. By drying the above-mentioned base material before sintering, suppression in the flow of the bonding material and generation of voids during sintering can be more preferably achieved.

[0209] As the above-mentioned drying conditions, for example, the drying atmosphere may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere. The pressure during drying may be atmospheric pressure or reduced pressure. The drying temperature is not particularly limited as long as the composite copper particles that the bonding material comprises are not sintered.

[0210] The copper paste and the bonding material of the present invention can be preferably used in a pressureless bonding method because a sintered body that achieves a high bonding strength by only sintering through heating can be obtained. Of course, the copper paste and the bonding material of the present invention can also be preferably used in a pressure bonding method.

[0211] In the present application, the "pressureless bonding method" refers to a method in which a laminate obtained by disposing a bonding material between a base material and a material to be bonded is prepared, and the above-mentioned laminate is heated in a state where the bonding material and the material to be bonded are disposed in a direction where the weight of the base material acts or in a state where a load of 0.01 MPa or less is applied.

[0212] In the present application, the "pressure bonding method" refers to a method in which a laminate obtained by disposing a bonding material between a base material and a material to be bonded is prepared, and the above-mentioned laminate is heated in a state where a load of more than 0.01 MPa is applied.

[0213] The heating atmosphere for the laminate in the above-mentioned pressureless bonding method or the above-mentioned pressure bonding method may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but is more preferably an inert atmosphere from the viewpoint that an increase in size of the production equipment for the sintered body can be more effectively avoided.

[0214] The laminate in the above-mentioned pressureless bonding method may be preheated before being completely sintered. The preheating temperature is preferably 150°C or lower, more preferably 140°C or lower. The preheating temperature is more preferably 130°C or lower from the viewpoint of the volatilization speed of the solvent. In addition, by setting the heating rate applied to the laminate to 10°C / min or less, the need for preheating can also be eliminated. The copper particles may be sintered during the preheating, but may not be sintered. The preheating conditions may be appropriately set in accordance with the desired bonding properties.

[0215] The heating temperature of the laminate in the above-mentioned pressureless bonding method or the above-mentioned pressure bonding method is preferably 100°C or higher and 400°C or lower, and more preferably 150°C or higher and 300°C or lower. When the sintering temperature is 300°C or lower, it can be said that the bonding material of the present invention can be sintered at a sufficiently low temperature.

[0216] The heating time of the laminate in the above-mentioned pressureless bonding method is preferably 1 minute or more and 120 minutes or less from the viewpoint of sufficiently volatilizing the solvent that the bonding material comprises and sufficiently promoting the sintering of the composite copper particles that the bonding material comprises. The heating time of the laminate in the above-mentioned pressure bonding method is preferably 1 minute or more and 60 minutes or less.

[0217] The bonding strength of the sintered body obtained by the pressureless bonding method or the pressure bonding method is measured in accordance with the method described in the Examples mentioned later.

[0218] The bonding strength of the sintered body obtained by the pressureless bonding method is preferably 20 MPa or more, more preferably 25 MPa or more, and still more preferably 27 MPa or more. A sintered body having such a bonding strength can be determined to be sufficiently bonded, and it can be confirmed that the bonding material of the present invention can be preferably used for a pressureless bonding paste. As mentioned above, the atmosphere during pressureless bonding is preferably an inert atmosphere, but a sintered body obtained by pressureless bonding in another atmosphere (for example, a reducing atmosphere) can be determined to be sufficiently bonded if the bonding strength of the sintered body is also within the above-mentioned range.

[0219] Also, the bonding strength of the sintered body obtained by the pressure bonding method is preferably 20 MPa or more, more preferably 25 MPa or more, and still more preferably 27 MPa or more. A sintered body having such a bonding strength can be determined to be sufficiently bonded, and it can also be determined that the bonding material of the present invention can be preferably used for a pressure bonding paste.<Conductive material>

[0220] The composite copper particles of the present invention or the copper paste comprising the composite copper particles of the present invention can be used as a conductive material. For example, the composite copper particles of the present invention may be used as a conductive material as they are, or may be used as a conductive material after the composite copper particles are formed into a copper paste. Specifically, the above-mentioned copper paste can be used as a material of a conductor such as a conductive film, an electrode, or a wiring line.

[0221] When the copper paste of the present invention is used as a material for a conductive film, an electrode, or a wiring line, the copper paste can be used by being applied on a base material. Examples of methods for applying the above-mentioned paste comprise screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, inkjet printing, soft lithography, a dispenser, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0222] When the above-mentioned copper paste is used as the above-mentioned conductive material, the concentration of the above-mentioned composite copper particles that the above-mentioned copper paste comprises may be appropriately adjusted in accordance with the above-mentioned applying methods.

[0223] The thickness of the above-mentioned applied layer is not particularly limited, and is preferably 0.1 µm or more and 100 µm or less. The application pattern at this time can be applied on the entire surface of the base material, as well as can be applied in the form of a pattern or a design. The above-mentioned applied layer may appropriately comprise an additive in accordance with the applying methods, intended purposes, and uses. Examples of the additives comprise the above-mentioned various additives.

[0224] Specific examples of the above-mentioned base materials comprise a semiconductor substrate such as a silicon substrate, a metal substrate such as a copper substrate, a lead frame, a ceramic substrate attached with a metal plate (for example, Direct Bonded Copper: DBC), a substrate for mounting a semiconductor element such as an LED (Light-Emitting Diode) package, a power supply component such as a copper ribbon, a metal block, and a terminal, a heat dissipation plate, a water cooling plate, and glass. In addition, an organic material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene, polycarbonate, an acrylic resin such as polymethyl methacrylate, a vinyl chloride-based resin such as polyvinyl chloride or a vinyl chloride copolymer, an epoxy resin, polyarylate, polysulfone, polyether sulfone, polyimide, a fluororesin, a phenoxy resin, a polyolefin resin, nylon, a styrene-based resin, or an ABS resin may be used. Depending on the uses, appropriate selection from these materials can be made to form a film-like flexible base material or rigid base material. The size of the base material is not limited, and the shape may be any shape such as a disk shape, a card shape, or a sheet shape, and the surface of the base material does not need to be flat and may have a shape having irregularities or a curved surface.<Conductor>

[0225] The conductor of the present invention comprises the above-mentioned conductive material. In addition, the conductor may be obtained by heating the above-mentioned conductive material. The above-mentioned conductor preferably has a low volume resistivity (which is also referred to as "electrical resistivity" in the present application). For example, the volume resistivity (electrical resistivity) is 100 µΩ·cm or less, and preferably 50 µΩ·cm or less. Within such a range, the conductor of the present invention can be used for practical use (for example, a conductive film, an electrode, and a wiring line). The volume resistivity of the above-mentioned conductor is measured by the method described in the Examples mentioned later.

[0226] The above-mentioned heating method is not particularly limited. Examples of the above-mentioned heating methods comprise resistance heating, electron beam heating, laser light heating, flash light heating, plasma heating, dielectric heating, induction heating, and heating by means of a heat source such as a burner.

[0227] The above-mentioned heating temperature may be appropriately adjusted in accordance with the above-mentioned base material. For example, when a semiconductor substrate such as a silicon substrate, a metal substrate such as a copper substrate, polyimide, or glass is used as a substrate, the heating temperature can be set to 300°C or lower. When PET or PEN is used as a substrate, the heating temperature can be set to 150°C or lower.

[0228] The above-mentioned heating atmosphere may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but an inert atmosphere is more preferable from the viewpoint that an increase in size of the production equipment can be more effectively avoided.

[0229] It is sufficient that the above-mentioned heating time is 1 minute or more and 60 minutes or less.EXAMPLES

[0230] The present invention will be described in detail with reference to the Examples and the Comparative Examples, but the present invention is not limited thereto.(Measurement of average particle diameter of copper particles)

[0231] Copper particles produced in a production example were photographed by means of a scanning electron microscope (S4800 manufactured by Hitachi High-Technologies Corporation) set at a magnification of 50,000 times, and a scanning electron micrograph was taken. With respect to 50 primary particle diameters in the above-mentioned scanning electron micrograph, the Feret diameters were measured, and the arithmetic average value thereof was calculated as the average particle diameter.(Thermal decomposition properties of polymer dispersant)

[0232] The thermal decomposition properties of the polymer dispersants used in examples and comparative examples of the present application were measured by means of a thermogravimetric differential thermal analyzer (TG-DTA 8122 manufactured by Rigaku Corporation) under the following conditions. The mass loss rate was calculated from the mass difference between 30°C and 250°C.∘ Measurement conditions

[0233] Measurement atmosphere: in the atmosphere Atmospheric flow rate: 100 mL / min Measurement temperature range: 25°C to 1000°C heating rate: 10°C / min (Measurement of weight average molecular weight of polymer dispersant)

[0234] The weight average molecular weights of the polymer dispersants used in the Examples and the Comparative Examples of the present application were measured by means of gel permeation chromatography (HLC-8420GPC manufactured by Tosoh Corporation) under the following conditions. EcoSEC Elite, which is a dedicated software, was used for control of the apparatus, data collection, calculation, and report generation.∘ Measurement conditions

[0235] Sample concentration: 1 mg / mL (a solution obtained by dissolving 5 mg of the polymer dispersant in 5 mL of tetrahydrofuran, followed by filtration through a membrane filter was adjusted to the concentration of 1 mg / mL) Sample injection amount: 10 µL Column: TSKgel Super HZM-M (manufactured by Tosoh Corporation, base material: styrene divinylbenzene, particle diameter: 3 µm and 5 µm, column size: inner diameter 4.6 mm × 15 cm × 2 columns) Column temperature: 40°C Detector: differential refractometer (RI detector) Solvent: tetrahydrofuran (THF) Flow rate: 0.35 mL / min

[0236] The analysis results of the above-mentioned polymer dispersants are shown in Table 1. In addition, the acid values and the amine values of the polymer dispersants are also shown together. The active ingredient content of each polymer dispersant was 100%. [Table 1]DispersantAcid value / Amine value (mgKOH / g)Mass loss rate (%)Peak temperature (°C)Weight average molecular weight (Mw)BYK-LP C 2212485 / -53.4294.2553BYK-LP C 22146- / 4812.4294.33078BYK-LP C 22435- / -44.1343.611502BYK-LP C 2436589 / -95.3223.9918*In the table, "-" indicates zero. (Production Example 1)

[0237] A 10 L four-neck glass flask was placed in an oil bath, 2 L of 1-propanol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, 637.6 g of copper(II) oxide (N-300 manufactured by Nisshin Chemco Ltd.), 96.0 g of acetic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 82.7 g of capric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added thereto, followed by stirring at room temperature under conditions of a rotation speed of 250 rpm. In the subsequent steps as well, stirring was performed at a constant rotation speed.

[0238] Furthermore, 127.0 g of 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added thereto over 10 minutes, and stirring was continued to produce a mixed solution comprising a copper compound.

[0239] The mixed solution comprising the above-mentioned copper compound was heated in an oil bath to a solution temperature of 50°C, and 80 g of 60% hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Company, Inc.) as a reducing agent was added dropwise thereto over 3 minutes and 45 seconds, followed by stirring for 40 minutes. Next, a "step of adding 80 g of 60% hydrazine hydrate dropwise over 3 minutes and 45 seconds, and performing stirring for 15 minutes" was repeated three times (that is, in this step, 240 g of 60% hydrazine hydrate was added in total). Thereto, 680 g of 60% hydrazine hydrate was added dropwise over 30 minutes. In this step, the total amount of the reducing agent added was 1000 g, and the time required for addition was 130 minutes. Also, the set temperature of the oil bath while the reducing agent was added was 50°C.

[0240] After the total amount of the reducing agent was added, the above-mentioned mixed solution was heated to 90°C and stirred for 2 hours to obtain a dispersion solution comprising copper particles.

[0241] The above-mentioned dispersion solution comprising copper particles was naturally cooled to 50°C or lower while being stirred, and allowed to stand for 30 minutes, and then 30 g of a solid content was weighed out by a solid-liquid separation operation and collected.

[0242] As a washing step, the above-mentioned solid content and 75 mL of 2-propanol (manufactured by NACALAI TESQUE, INC.) were stirred at 2000 rpm for 10 minutes by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation). Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge (Allegra X-30R manufactured by Beckman Coulter, Inc.) to obtain a solid content.

[0243] The above-mentioned washing step was performed again to obtain carboxylic acid-coated copper particles of Production Example 1. The carboxylic acid-coated copper particles of Production Example 1 had an average particle diameter of 297 nm.(Example 1)

[0244] Caprylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymer dispersant (BYK-LP C 24365), and 2-propanol (manufactured by NACALAI TESQUE, INC.) were mixed to prepare 75 mL of a treatment solution. Here, in the above-mentioned treatment solution, the amount of caprylic acid was 6 mass%, and the amount of BYK-LP C 24365 was 2 mass%.

[0245] The carboxylic acid-coated copper particles obtained in Production Example 1 and the above-mentioned treatment solution were mixed, followed by stirring by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation) under conditions of 2000 rpm for 10 minutes.

[0246] Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge, and a solid content was collected.

[0247] The collected solid content was allowed to stand in a desiccator, and the inside of the desiccator was depressurized by means of a vacuum pump (G-20DA manufactured by ULVAC, Inc.). The inside of the desiccator was adjusted to 1.3 Pa and 25°C, and vacuum drying was performed for 300 minutes to obtain composite copper particles of Example 1.(Example 2)

[0248] Composite copper particles of Example 2 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 12 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 4 mass%.(Example 3)

[0249] Composite copper particles of Example 3 were obtained in the same manner as in Example 1 except that the amount of BYK-LP C 24365 used in Example 1was changed from 2 mass% to 0.5 mass%.(Example 4)

[0250] Composite copper particles of Example 4 were obtained in the same manner as in Example 1 except that caprylic acid (in which the number of the carbon atoms is 8) used in Example 1 was changed to capric acid (in which the number of the carbon atoms is 10).(Comparative Example 1)

[0251] Copper particles of Comparative Example 1 were obtained in the same manner as in Example 1 except for the absence of BYK-LP C 24365 used in Example 1.(Comparative Example 2)

[0252] Copper particles of Comparative Example 2 were obtained in the same manner as in Example 1 except for the absence of caprylic acid used in Example 1.(Comparative Example 3)

[0253] Copper particles of Comparative Example 3 were obtained in the same manner as in Example 1 except that BYK-LP C 24365 used in Example 1was changed to BYK-LP C 22124.(Comparative Example 4)

[0254] Copper particles of Comparative Example 4 were obtained in the same manner as in Example 1 except that BYK-LP C 24365 used in Example 1 was changed to BYK-LP C 22146.(Comparative Example 5)

[0255] Copper particles of Comparative Example 5 were obtained in the same manner as in Example 1 except that BYK-LP C 24365 used in Example 1 was changed to BYK-LP C 22435.(Comparative Example 6)

[0256] Copper particles of Comparative Example 6 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 30 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 10 mass%.(Comparative Example 7)

[0257] Copper particles of Comparative Example 7 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 0.6 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 0.2 mass%.(Production Example 2)

[0258] A 10 L four-neck glass flask was placed in an oil bath, 1 L of ethyl carbitol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, 159.1 g of copper(II) oxide (manufactured by Nisshin Chemco Ltd.), and 13.9 g of hexanoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) were added thereto, followed by stirring at room temperature under conditions of a rotation speed of 200 rpm to produce a mixed solution comprising a copper compound.

[0259] The above-mentioned mixed solution comprising a copper compound was heated up to a solution temperature of 90°C, and when the solution temperature reached 90°C, 200 g of hydrazine monohydrate (manufactured by NACALAI TESQUE, INC.) as a reducing agent was added to the mixed solution within 30 seconds.

[0260] After the reducing agent was added, the above-mentioned mixed solution was stirred at 90°C for 20 minutes to obtain a dispersion solution comprising copper particles.

[0261] The above-mentioned dispersion solution comprising copper particles was naturally cooled up to 50°C or lower, and allowed to stand for 30 minutes, and then 30 g of a solid content was weighed out by a solid-liquid separation operation and collected.

[0262] As a washing step, the above-mentioned solid content and 75 mL of 2-propanol (manufactured by NACALAI TESQUE, INC.) were stirred at 2000 rpm for 10 minutes by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation). Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge (Allegra X-30R manufactured by Beckman Coulter, Inc.) to obtain a solid content.

[0263] The above-mentioned washing step was performed again to obtain carboxylic acid-coated copper particles of Production Example 2. The carboxylic acid-coated copper particles of Production Example 2 had an average particle diameter of 80 nm.(Comparative Example 8)

[0264] Copper particles of Comparative Example 8 were obtained in the same manner as in Example 1 except that the carboxylic acid-coated copper particles obtained in Production Example 2 were used instead of the carboxylic acid-coated copper particles used in Example 1.(Measurement of crystalline states of composite copper particles and copper particles before and after atmospheric exposure)

[0265] X-ray diffraction patterns of the composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 before and after atmospheric exposure were measured by means of an X-ray diffraction (XRD) apparatus (SmartLab SE manufactured by Rigaku Corporation) under the following conditions. From the obtained diffraction patterns, the oxidation state before and after atmospheric exposure was confirmed. SmartLab Studio II, which is a dedicated software, was used for control of the apparatus, data collection, calculation, and report generation.

[0266] FIG. 1 shows X-ray diffraction patterns of the composite copper particles of Example 1 before and after atmospheric exposure. From FIG. 1, only peaks derived from metallic copper were observed both before and after atmospheric exposure. Here, the Cu(111) plane is observed at around 2θ = 43.3°, and the Cu(200) plane is observed at around 2θ = 50.4°.∘ Measurement conditions

[0267] Tube: CuKα Tube voltage: 40 kV Tube current: 40 mA Measurement range: 30° to 70° Step: 0.01° Speed: 5° / min (Observation of lattice fringes of composite copper particles and copper particles before and after atmospheric exposure)

[0268] The composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 before and after atmospheric exposure were observed by means of a transmission electron microscope (TEM (H-9000 manufactured by Hitachi High-Tech Corporation)), and the oxidation state of copper was confirmed from the atomic arrangement (lattice fringes) in the crystal. Here, the lattice spacing of the metal copper (111) plane is 2.1Å (0.21 nm).

[0269] A TEM photograph of the composite copper particles of Example 1 before atmospheric exposure is shown in FIG. 2, and a TEM photograph of the composite copper particles of Example 1 after atmospheric exposure is shown in FIG. 3. Also in the TEM photographs before and after atmospheric exposure, only a lattice spacing of 0.21 nm derived from the metal copper (111) plane was observed on the surfaces of the copper particles, and oxidation of copper was not observed. For reference, an SEM photograph of the composite copper particles of Example 1 before atmospheric exposure is also shown in FIG. 4.(Measurement of amount of organic component)

[0270] The individual mass losses of the composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 were measured by means of a thermogravimetric differential thermal analyzer (TG-DTA 8122 manufactured by Rigaku Corporation) under the following conditions. In the obtained profile, the mass loss rate in the temperature range from 30°C to 200°C was defined as the mass of the carboxylic acid, the mass loss rate in the temperature range from 200°C to 350°C was defined as the mass of the polymer dispersant, and the mass loss rate in the temperature range from 30°C to 350°C was defined as the mass of the organic component treated on the copper particles.

[0271] From this result, the mass of the carboxylic acid (caprylic acid or capric acid) that the composite copper particles and the copper particles comprise, and the ratio of the carboxylic acid to the polymer dispersant are shown in Table 2.∘ Measurement conditions

[0272] Measurement atmosphere: nitrogen (purity: 99.995%) Atmospheric flow rate: 500 mL / min Measurement temperature range: 30°C to 500°C heating rate: 10°C / min [Table 2] Composition of treatment solutionMass of carboxylic acid (mass%)Mass of polymer dispersant (mass%)Mass of organic component (mass%)Carboxylic acid / Polymer dispersantExample 1Caprylic acid: 6 mass%0.730.281.012.61BYK-LP C 24365: 2 mass%Example 2Caprylic acid: 12 mass%1.140.381.523.00BYK-LP C 24365: 4 mass%Example 3Caprylic acid: 6 mass%0.960.191.155.05BYK-LP C 24365: 0.5 mass%Example 4Capric acid: 6 mass%1.000.371.372.70BYK-LP C 24365: 2 mass% [Table 3] Composition of treatment solutionMass of carboxylic acid (mass%)Mass of polymer dispersant (mass%)Mass of organic component (mass%)Carboxylic acid / Polymer dispersantComparative Example 1Caprylic acid: 6 mass%0.49-0.50-No polymer dispersantComparative Example 2No carboxylic acid-0.380.38-BYK-LP C 24365: 2 mass%Comparative Example 3Caprylic acid: 6 mass%0.720.210.933.30BYK-LP C 22124: 2 mass%Comparative Example 4Caprylic acid: 6 mass%0.500.240.742.08BYK-LP C 22146: 2 mass%Comparative Example 5Caprylic acid: 6 mass%0.550.220.772.50BYK-LP C 22435: 2 mass%Comparative Example 6Caprylic acid: 30 mass%5.621.547.163.65BYK-LP C 24365: 10 mass%Comparative Example 7Caprylic acid: 0.6 mass%0.110.110.221.00BYK-LP C 24365: 0.2 mass%Comparative Example 8Caprylic acid: 6 mass%0.730.891.620.82BYK-LP C 24365: 2 mass% (Production of copper paste)

[0273] As the proportion of the entire copper paste, 92.5 mass% of any of the following: the composite copper particles of Examples 1 to 4, the copper particles of Comparative Example 1 and Comparative Examples 3 to 7; 3.6 mass% of dipropylene glycol; 3.6 mass% of hexyl carbitol; and 0.3 mass% of triethanolamine were blended and then kneaded at 2000 rpm for 4 minutes by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation).

[0274] Thereafter, defoaming was performed at 2200 rpm for 2 minutes to obtain copper pastes of Samples 1 to 4 and 6 to 9 and Samples 12 to 13.

[0275] The paste comprising the copper particles of Comparative Example 8 prepared by the above-mentioned method did not have an applicable viscosity and could not be evaluated (not shown in the table).

[0276] A copper paste of Sample 5 was obtained in the same manner as in the above-mentioned production of copper paste except that the paste was formulated such that 92.5 mass% of the copper particles of Example 1, 3.75 mass% of dipropylene glycol, and 3.75 mass% of hexyl carbitol were blended.

[0277] A copper paste of Sample 10 was obtained in the same manner as in the above-mentioned production of copper paste except that the paste was formulated such that 92.5 mass% of the copper particles of Comparative Example 1, 3.5 mass% of dipropylene glycol, 3.5 mass% of hexyl carbitol, 0.3 mass% of triethanolamine, and 0.2 mass% of BYK-LP C 24365 were blended.

[0278] A copper paste of Sample 11 was obtained in the same manner as in the above-mentioned production of copper paste except that the paste was formulated such that 92.5 mass% of the copper particles of Comparative Example 2, 3.35 mass% of dipropylene glycol, 3.35 mass% of hexyl carbitol, 0.3 mass% of triethanolamine, and 0.5 mass% of caprylic acid were blended.

[0279] In addition, a copper paste was produced in the same manner as in the above-mentioned production of copper paste except that the composite copper particles or the copper particles were exposed in the atmosphere (temperature: 28°C, humidity: 60%) for 1 hour, and changes in bonding strength and electrical resistivity due to atmospheric exposure were confirmed.

[0280] When the copper particles of Comparative Example 8 were exposed in the atmosphere (temperature: 28°C, humidity: 60%) for 1 hour, heat generation due to oxidation and smoke generation occurred, and therefore a paste could not be produced (not shown in the table). [Table 4]Copper paste composition (wt%)(Composite) copper particlesDPG 1HC 2TEA 324365 4CA 5Sample 1Example 192.53.63.60.300Sample 2Example 292.53.63.60.300Sample 3Example 392.53.63.60.300Sample 4Example 492.53.63.60.300Sample 5Example 192.53.753.75000Sample 6Comparative Example 192.53.63.60.300Sample 7Comparative Example 392.53.63.60.300Sample 8Comparative Example 492.53.63.60.300Sample 9Comparative Example 592.53.63.60.300Sample 10Comparative Example 192.53.53.50.30.20Sample 11Comparative Example 292.53.353.350.300.5Sample 12Comparative Example 692.53.63.60.300Sample 13Comparative Example 792.53.63.60.3001: DPG ··· dipropylene glycol 2: HC ··· hexyl carbitol 3: TEA ··· triethanolamine 4: 24365 ··· BYK-LP C 24365 5: CA ··· caprylic acid (Production of sintered body)

[0281] On a base material having a diameter (which is referred to as Φ hereinafter) of 10 mm, a thickness of 5 mm, and a surface roughness (Ra: arithmetic average roughness) of 0.1 to 0.2 µm, a metal mask having an opening Φ of 5 mm and a thickness of 0.1 mm was placed, and a copper paste obtained by the above-mentioned procedure was applied as a bonding material to the opening.

[0282] The metal mask was removed, and a copper piece (tough pitch copper, alloy number C1100) having a diameter of 5 mm, a thickness of 5 mm, and a surface roughness (Ra: arithmetic average roughness) of 0.1 µm to 0.2 µm was allowed to stand at the portion to which the bonding material was applied to obtain a laminate. The above-mentioned surface roughness was determined as the average value of Ra measured with a laser microscope for 3 test pieces randomly taken out among 100 test pieces.

[0283] The above-mentioned laminate was set in a jig having a space of 10.5 mm on 3 sides, nitrogen (purity 99.995%) was allowed to flow at 100 mL / min, and the above-mentioned laminate was allowed to stand on a hot plate heated to 200°C and held for 30 minutes. Thereafter, the resultant was naturally cooled to 50°C to obtain a sintered body.(Measurement of bonding strength)

[0284] The above-mentioned sintered body was set in a strength tester (JSL-1KN manufactured by Japan Instrumentation System Co., Ltd.), a shearing force was applied in a direction parallel to the bonding surface under conditions of 1 mm / sec from the base material side, and the bonding strength was calculated from the load applied at the time when the base material and the copper piece were peeled off.(Production of conductive film)

[0285] The copper paste obtained by the above-mentioned procedure was coated with an applicator on a polyimide film having a thickness of 100 µm as a base material.

[0286] The base material coated with the copper paste was placed in a tubular furnace (JTEKT Thermo Systems Co., Ltd., KTF-035N1).

[0287] Nitrogen (purity: 99.995%) was allowed to flow in the tubular furnace at 100 mL / min, and the temperature was raised from 25°C to 150°C at a heating rate of 5°C / min, and held for 60 minutes. Thereafter, the resultant was naturally cooled to 50°C to obtain a conductive film.(Measurement of conductivity)

[0288] The surface resistivity of the above-mentioned conductive film was measured by means of a low resistivity meter (Loresta-GX MCP-T700 manufactured by Nitto Seiko Analytech Co., Ltd.).

[0289] Thereafter, the film thickness of the conductive film was measured by means of a film thickness meter (Mitutoyo Corporation, ID-C112X), and the volume resistivity (electrical resistivity) was calculated by multiplying the surface resistivity by the film thickness.

[0290] The bonding strength of the sintered body and the volume resistivity of the conductive film measured by the above-mentioned methods are shown in Table 5. [Table 5]Paste(Composite) copper particlesBonding strength (MPa)Volume resistivity (electrical resistivity) (µΩ·cm)Without atmospheric exposureWith atmospheric exposureWithout atmospheric exposureWith atmospheric exposureSample 1Example 145.651.010.417.0Sample 2Example 250.226.919.028.4Sample 3Example 344.551.010.114.0Sample 4Example 443.351.011.114.1Sample 5Example 128.324.29.910.6Sample 6Comparative Example 145.110.217.222.7Sample 7Comparative Example 37.70.026.074.7Sample 8Comparative Example 434.07.447.427.4Sample 9Comparative Example 526.710.829.740.6Sample 10Comparative Example 125.610.713.616.3Sample 11Comparative Example 27.85.131.434.1Sample 12Comparative Example 632.418.652.8×10 7< 14.5×10 7< Sample 13Comparative Example 749.82.112.617.6

[0291] Samples 1 to 5 comprising the composite copper particles of the present invention had a sufficient bonding strength (20 MPa or more) before and after atmospheric exposure. Also, Samples 1 to 5 have an electrical resistivity on the order of micro-ohms both before and after atmospheric exposure, which is below 100 µΩ·cm, and therefore can be used for conductive uses; furthermore, since the value is further below 50 µΩ·cm, they can be more preferably used for conductive uses.

[0292] In Sample 6 in which the copper particles of Comparative Example 1 (copper particles produced by means of the treatment solution not comprising a polymer dispersant) were used, the bonding strength after atmospheric exposure was 10.2 MPa, and a desired bonding strength was not obtained.

[0293] In Sample 10 in which the copper particles of Comparative Example 1 were similarly used and a polymer dispersant was added during production of the paste, the bonding strength after atmospheric exposure was 10.7 MPa, and a desired bonding strength was not obtained.

[0294] This indicates that for preferred uses in bonding uses even after atmospheric exposure, it is necessary for the composite copper particles to comprise a polymer dispersant, and moreover, it is understood that the polymer dispersant needs to be treated on the copper particles in the copper particle production process rather than during paste production.

[0295] In Sample 11 in which a carboxylic acid (caprylic acid) was added during production of the paste using the copper particles of Comparative Example 2 (copper particles produced using the treatment solution not comprising a carboxylic acid), a sufficient bonding strength was not obtained either before or after atmospheric exposure.

[0296] It is understood that the copper particles of Comparative Example 2 were treated with the polymer dispersant, but the treatment solution did not comprise a carboxylic acid, and therefore the sinterability was reduced. In addition, it has been found that a sufficient bonding strength cannot be obtained only by treating copper particles with a polymer dispersant, and therefore the copper particles cannot be used for bonding uses after atmospheric exposure.

[0297] In Sample 7 in which the copper particles of Comparative Example 3 (copper particles treated with the polymer dispersant having an acid value of 60 mgKOH / g or more and a mass loss rate of less than 70%) were used, the bonding strength was reduced from 7.7 MPa to 0 MPa by atmospheric exposure.

[0298] It is understood that since the polymer dispersant treated on the copper particles of Comparative Example 3 had a small mass loss rate at 250°C (specifically, mass loss rate = 53.4%), Sample 7 had a low bonding strength before atmospheric exposure.

[0299] In addition, it is understood that since the polymer dispersant treated on the copper particles of Comparative Example 3 had a small weight average molecular weight (weight average molecular weight = 553) and a bonding strength of 0 MPa after atmospheric exposure, the organic component treated on the copper particles was desorbed by atmospheric exposure, and oxidation of copper occurs.

[0300] In Sample 8 in which the copper particles of Comparative Example 4 (copper particles treated with the polymer dispersant having an amine value, no acid value, and a mass loss rate of less than 70%) were used, the bonding strength significantly decreased from 34.0 MPa to 7.4 MPa (decreased by about 78%) by atmospheric exposure. Therefore, it has been found that the influence on performance deterioration due to atmospheric exposure is very large.

[0301] In Sample 9 in which the copper particles of Comparative Example 5 (copper particles having no acid value or amine value and having a mass loss rate of the polymer dispersant of less than 70%) were used, the bonding strength after atmospheric exposure was 10.8 MPa, and a desired bonding strength was not obtained.

[0302] In Sample 12 in which the copper particles of Comparative Example 6 (copper particles having an excessive content of the organic component) were used, the amount of the organic component treated on the copper particles was 7.16 mass%, the bonding strength after atmospheric exposure was 18.6 MPa, and a desired bonding strength was not obtained.

[0303] In Sample 13 in which the copper particles of Comparative Example 7 (copper particles having an insufficient content of the organic component) were used, the amount of the organic component treated on the copper particles was 0.22 mass%, and the bonding strength after atmospheric exposure significantly decreased to 2.1 MPa.INDUSTRIAL APPLICABILITY

[0304] The composite copper particles of the present invention can be preferably used for bonding uses (for example, a bonding material) not only before atmospheric exposure but also after atmospheric exposure. Furthermore, since the electrical resistivity is small, the composite copper particles can also be used for conductive uses (for example, a conductive material). In addition, the bonding material comprising the composite copper particles of the present invention can provide a sintered body having a sufficient bonding strength even under conditions of the pressureless bonding method. In producing the composite copper particles of the present invention, the composite copper particles can be easily produced without any limitation on the production process.

Examples

production example 1

(Production Example 1)

[0237]A 10 L four-neck glass flask was placed in an oil bath, 2 L of 1-propanol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, 637.6 g of copper(II) oxide (N-300 manufactured by Nisshin Chemco Ltd.), 96.0 g of acetic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 82.7 g of capric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added thereto, followed by stirring at room temperature under conditions of a rotation speed of 250 rpm. In the subsequent steps as well, stirring was performed at a constant rotation speed.

[0238]Furthermore, 127.0 g of 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added thereto over 10 minutes, and stirring was continued to produce a mixed solution comprising a copper compound.

[0239]The mixed solution comprising the above-mentioned copper compound was heated in an oil bath to a solution temperature of 50°C, and 80 g of 60% hydrazine hydrate (manufactured by Mit...

example 1

(Example 1)

[0244]Caprylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymer dispersant (BYK-LP C 24365), and 2-propanol (manufactured by NACALAI TESQUE, INC.) were mixed to prepare 75 mL of a treatment solution. Here, in the above-mentioned treatment solution, the amount of caprylic acid was 6 mass%, and the amount of BYK-LP C 24365 was 2 mass%.

[0245]The carboxylic acid-coated copper particles obtained in Production Example 1 and the above-mentioned treatment solution were mixed, followed by stirring by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation) under conditions of 2000 rpm for 10 minutes.

[0246]Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge, and a solid content was collected.

[0247]The collected solid content was allowed to stand in a desiccator, and the inside of the desiccator was depressurized by means of a vacuum pump (G-20DA manufactured by ULVAC, In...

example 2

(Example 2)

[0248]Composite copper particles of Example 2 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 12 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 4 mass%.

TECHNICAL FIELD

[0001] The present invention relates to composite copper particles, a method for producing the same, a copper paste comprising the composite copper particles, a bonding material or conductive material comprising the composite copper particles or the copper paste, a sintered body comprising the bonding material as a raw material, and a conductor comprising the conductive material.BACKGROUND ART

[0002] A bonding material having a high thermal conductivity is used when a substrate of a power semiconductor product is produced by bonding a material to be bonded, which is a semiconductor element, and a base material such as a lead frame. Among various bonding materials, copper is preferably used for bonding of a semiconductor element because it is less expensive than silver and hardly causes ion migration.

[0003] In addition to the above-mentioned bonding uses, copper has high conductivity, and thus is preferably used as a conductive material such as an ink for printed electronics.

[0004] Patent Literature 1 describes that metal colloid particles in which the generation of coarse particles is suppressed can be obtained by constituting a protective colloid (or a dispersant), which coats or protects metal nanoparticles, with an organic compound having a carboxyl group and a polymer dispersant (in particular, a polymer dispersant having a carboxyl group).

[0005] Patent Literature 2 describes a copper nanoparticle dispersion having a volume average particle diameter of 500 nm or less obtained by combining copper nanoparticles with a carboxylic acid, an alkylamine, and a polymer dispersant having a specific amine value or acid value.CITATION LIST PATENT LITERATURE

[0006] PATENT LITERATURE 1: JP 2009-74171 A PATENT LITERATURE 2: JP 2015-210973 A SUMMARY OF INVENTION TECHNICAL PROBLEM

[0007] The present inventors have confirmed that in a bonding material using conventional copper particles, the bonding performance is reduced due to exposure of the copper particles to the atmosphere, thereby resulting in the bonding material becoming unusable. Also, as a phenomenon observed when copper particles were exposed to the atmosphere, heat generation of the copper particles and elution of copper ions during the production of the dispersion have been confirmed, and there is a concern that in conventional copper particles, copper may be oxidized due to atmospheric exposure.

[0008] When copper particles are used for a bonding material, a conductive material, or the like, the copper particles are processed into a form suitable for their use, such as a paste or a dispersion. There is a concern that the performance of the copper particles such as bonding properties and conductive properties may be reduced due to exposure of the copper particles to the atmosphere at that time. On the other hand, it is difficult to completely avoid oxidation of copper particles in the process from production to processing of the copper particles. For these reasons, there has been a demand for the development of copper particles that can be used for various uses even after atmospheric exposure. Patent Literature 1 discloses metal colloid particles comprising metal nanoparticles at a high concentration, and evaluates storage stability using, as an index, the presence or absence of sedimentation or agglomeration after a paste produced by adding ethylene glycol to silver colloid particles in which silver nanoparticles are protected by a protective colloid is left to stand at room temperature for 6 months. However, the metal nanoparticles disclosed in the Examples are only silver nanoparticles, and a problem caused by metals that are easily oxidized in the atmosphere, such as copper particles, is not recognized. Patent Literature 2 discloses a copper nanoparticle dispersion having excellent oxidation resistance, and achieves oxidation resistance of the copper nanoparticle dispersion by immediately dispersing copper nanoparticles and attaching an alkylamine to the surfaces of the copper particles. However, in examples, only copper particles having an average primary particle diameter of less than 100 nm are disclosed, and it is commonly understood that copper particles having such a particle diameter are easily oxidized in the atmosphere and generate significant heat, thereby making it difficult to apply them to various uses after atmospheric exposure.

[0009] In the above-mentioned patent literatures, although stability and oxidation resistance in the state of a paste or a dispersion have been studied, there has been no study on whether copper particles after atmospheric exposure can be used for various uses when the copper particles themselves are exposed to the atmosphere. Furthermore, there is no description or suggestion as to whether the metal colloid particles and the paste comprising the same, as well as the copper nanoparticle dispersion disclosed in the above-mentioned patent literatures can be used for bonding uses.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide copper particles that can be used for various uses even after exposure of the copper particles themselves to the atmosphere.SOLUTION TO PROBLEM

[0011] Accordingly, the present inventors have conducted intensive studies and found that composite copper particles that can be used for various uses even after exposing copper particles to the atmosphere can be obtained by performing a specific treatment with copper particles having a specific particle diameter together with a certain amount of an organic component comprising a carboxylic acid or a salt thereof and a specific polymer dispersant, thereby completing the present invention.

[0012] That is, the present invention provides the following: (1) Composite copper particles comprising copper particles and an organic component, wherein the composite copper particles have a value of 100 nm or more and 600 nm or less as an average particle diameter measured by means of a scanning electron microscope, the organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, wherein a content of the organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the composite copper particles, and the polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in an atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer; (2) The composite copper particles according to (1), wherein the polymer dispersant has a temperature of 300°C or lower as a temperature of an exothermic peak of the polymer dispersant measured by means of a thermogravimetric differential thermal analyzer; (3) The composite copper particles according to (1) or (2), wherein the carboxylic acid or the salt thereof has 2 or more and 20 or less carbon atoms; (4) The composite copper particles according to any one of (1) to (3), wherein the organic component has a value of 1.0 or more and 12.0 or less as a mass ratio of the carboxylic acid or the salt thereof to the polymer dispersant; (5) The composite copper particles according to any one of (1) to (4), wherein surfaces of the copper particles are coated with the carboxylic acid or the salt thereof; (6) A copper paste comprising the composite copper particles according to any one of (1) to (5) and a paste solvent; (7) A bonding material comprising composite copper particles or a copper paste, wherein the composite copper particles are the composite copper particles according to any one of (1) to (5), and the copper paste comprises the composite copper particles according to any one of (1) to (5) and a paste solvent; (8) A conductive material comprising composite copper particles or a copper paste, wherein the composite copper particles are the composite copper particles according to any one of (1) to (5), and the copper paste comprises the composite copper particles according to any one of (1) to (5) and a paste solvent; (9) A sintered body comprising the bonding material according to (7) as a raw material; (10) A conductor comprising the conductive material according to (8); (11) A method for producing composite copper particles, the method comprising a step of mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent; (12) The method according to (11) comprising a step of mixing the carboxylic acid-coated copper particles with a treatment solution comprising the carboxylic acid or the salt thereof, the polymer dispersant, and the solvent; (13) The method according to (11) or (12) comprising a step of mixing the carboxylic acid-coated copper particles with the treatment solution comprising the carboxylic acid or the salt thereof, the polymer dispersant, and the solvent, followed by drying; and the like.ADVANTAGEOUS EFFECTS OF INVENTION

[0013] The composite copper particles of the present invention have a high bonding strength not only before atmospheric exposure but also after atmospheric exposure and exhibit practically usable conductivity, and therefore are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material).BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 is a view showing X-ray diffraction (which is often referred to as "XRD" in the present application) patterns of composite copper particles of Example 1 before and after atmospheric exposure. FIG. 2 is a view showing a transmission electron microscope (which is often referred to as "TEM" in the present application) photograph of composite copper particles of Example 1 before atmospheric exposure. FIG. 3 is a view showing a transmission electron microscope (TEM) photograph of composite copper particles of Example 1 after atmospheric exposure. FIG. 4 is a view showing a scanning electron microscope (which is often referred to as "SEM" in the present application) photograph of composite copper particles of Example 1 before atmospheric exposure. DESCRIPTION OF EMBODIMENTS

[0015] The composite copper particles of the present invention are composite copper particles comprising copper particles and an organic component, wherein the above-mentioned composite copper particles have a value of 100 nm or more and 600 nm or less as an average particle diameter measured by means of a scanning electron microscope, the above-mentioned organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, wherein a content of the above-mentioned organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the above-mentioned composite copper particles, and the above-mentioned polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in an atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer.<Copper particles>

[0016] The composite copper particles of the present invention comprise copper particles.

[0017] The copper particles used in the composite copper particles of the present invention are not particularly limited. For example, commercially available copper particles may be purchased, or copper particles produced by a known method may be used.

[0018] The above-mentioned copper particles may comprise a component or a compound other than the copper component, such as a raw material or a reactant used in the production process, to such an extent that no problem is caused according to their uses.

[0019] The shape of the copper particles used in the composite copper particles of the present invention is not particularly limited. For example, any shape such as an irregular shape, a spherical shape, a polyhedron, a spindle shape, or a plate shape may be used.

[0020] The average particle diameter of the above-mentioned copper particles is not particularly limited as long as composite copper particles having a desired average particle diameter can be obtained. For example, the average particle diameter of the above-mentioned copper particles is preferably 100 nm or more and 600 nm or less, more preferably 150 nm or more and 500 nm or less, and still more preferably 200 nm or more and 400 nm or less.

[0021] In the measurement of the average particle diameter of the copper particles, the above-mentioned copper particles are photographed using a scanning electron microscope (SEM), the maximum Feret diameter (which is simply referred to as Feret diameter, hereinafter) of each of 50 primary particle diameters in the SEM visual field is measured, and the arithmetic average thereof is taken as the average particle diameter.

[0022] The above-mentioned copper particles may exist as primary particles, or may exist as secondary particles in which primary particles are agglomerated.<Organic component>

[0023] The composite copper particles of the present invention comprise a carboxylic acid or a salt thereof and a polymer dispersant as an organic component, and the content of the above-mentioned organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the composite copper particles.

[0024] The content of the organic component in the composite copper particles of the present invention is 0.3 mass% or more and 6.0 mass% or less, preferably 0.5 mass% or more and 4.5 mass% or less, and more preferably 0.7 mass% or more and 3.0 mass% or less based on a total mass of the composite copper particles.

[0025] When the content of the organic component is within the above-mentioned range, the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention are not reduced even when the composite copper particles of the present invention are exposed to the atmosphere, and therefore they are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material). In the present application, such expressions as "even when exposed to the atmosphere" are intended to mean "even immediately after exposure to the atmosphere" and also comprise the time point of atmospheric exposure.

[0026] The amount of the organic component that the composite copper particles of the present invention comprise is measured by means of a thermogravimetric differential thermal analyzer (which is often referred to as "TG-DTA" in the present application). Specifically, the composite copper particles are heated from 30°C to 500°C under conditions of a heating rate of 10°C / min in a nitrogen atmosphere. Based on the mass of the composite copper particles at the start of measurement, the mass loss rate in the temperature range from 30°C to 350°C in the obtained profile is used as the amount of the organic component that the composite copper particles comprise.

[0027] In the composite copper particles of the present invention, the state in which the organic component is present is not particularly limited. For example, the organic component may be present on the surfaces of the copper particles, and may be chemically bonded to the surfaces of the copper particles. Examples of the above-mentioned chemical bonds comprise an ionic bond, a coordinate bond, and an intermolecular force (for example, a van der Waals force or a hydrogen bond). In addition, for example, the organic component may be adsorbed on the surfaces of the copper particles. In the present application, "chemical bonding" or "adsorption" is often referred to as "interaction".

[0028] The adsorption state when the above-mentioned organic component is adsorbed on the surfaces of the copper particles is not particularly limited. For example, the organic component may be in a state of being physically adsorbed and / or chemically adsorbed on the surfaces of the copper particles, and examples of the adsorption states comprise a state in which the organic component is present due to an electrical action (for example, Coulomb force) with the surfaces of the copper particles.

[0029] When the above-mentioned organic component is present on the surfaces of the copper particles, the above-mentioned organic component may coat the surfaces of the above-mentioned copper particles. Specifically, the organic component may coat the entire surface of the copper particles, or the organic component may coat only a part of the surfaces of the copper particles. In addition, when the organic component coats the entire surface of the copper particles, the coating may be uniform or non-uniform.<Carboxylic acid or salt thereof>

[0030] The organic component, which the composite copper particles of the present invention comprises, comprises a carboxylic acid or a salt thereof.

[0031] In the composite copper particles of the present invention, the carboxylic acid or a salt thereof to be used is not particularly limited. The above-mentioned carboxylic acid or a salt thereof may be only one species or may be two or more species.

[0032] The chemical structure of the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as it has a hydrocarbon group moiety and a carboxyl group moiety in its structure.

[0033] The above-mentioned hydrocarbon group moiety is not particularly limited as long as the composite copper particles of the present invention are obtained. For example, it may consist only of a single bond or may have a multiple bond in the middle or at the end. In addition, the hydrocarbon group may comprise a heteroatom at any position.

[0034] The above-mentioned carboxyl group moiety is not particularly limited as long as the composite copper particles according to the present invention are obtained. For example, the carboxylic acid or a salt thereof may have one carboxyl group in the molecule, or may have two or more carboxyl groups in the molecule. Among them, the number of carboxyl groups in the molecule of the carboxylic acid or a salt thereof is preferably one.

[0035] It is preferable that the number of carboxyl groups in the above-mentioned carboxylic acid or a salt thereof is one because the low-temperature sintering performance increases. The state in which the above-mentioned carboxylic acid or a salt thereof is present is mentioned later, but it is understood that the above-mentioned carboxylic acid or a salt thereof is present in the composite copper particles of the present invention via a carboxyl group as a contact point. For example, when a carboxylic acid or a salt thereof is present on the surfaces of the copper particles, the above-mentioned carboxylic acid or a salt thereof is present on the surfaces of the copper particles via a carboxyl group as a contact point. It is understood that in a case where a carboxylic acid or a salt thereof has a small number of the above-mentioned contact points, the carboxylic acid or the salt thereof is thermally decomposed or the like at a low temperature, and thus the low-temperature sintering performance is more effectively improved.

[0036] In addition, a carboxylic acid or a salt thereof having one carboxyl group is preferred because it is less likely to remain as a residue during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0037] Such expressions as "the carboxylic acid or the salt thereof is thermally decomposed or the like at a low temperature" mentioned above in the present specification are intended to comprise desorption by heat, and / or dissociation by heat, and / or volatilization by heat, in addition to decomposition of the carboxylic acid or the salt thereof by heat.

[0038] The "low-temperature sintering performance" as used in the present application is intended to mean performance that the composite copper particles and the copper paste of the present invention are sufficiently sintered at a temperature of 300°C or lower.

[0039] The number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as the composite copper particles according to the present invention are obtained, but is preferably, for example, 2 or more and 20 or less, more preferably 4 or more and 18 or less, and still more preferably 6 or more and 16 or less.

[0040] The number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is defined as the number of carbon atoms in the entire carboxylic acid molecule. That is, the number of carbon atoms in the molecule of the carboxylic acid or a salt thereof is the total of the number of carbon atoms in the hydrocarbon group and the number of carbon atoms in the carboxyl group.

[0041] It is understood that when the above-mentioned number of carbon atoms is 2 or more, oxidation of copper in the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. Therefore, this is preferred because reduction in the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. Further, it is preferable that the above-mentioned number of carbon atoms is 20 or less because the carboxylic acid or a salt thereof in the composite copper particles of the present invention is easily thermally decomposed or the like even at a low temperature, and the low-temperature sintering performance is more effectively improved. In addition, a carboxylic acid or a salt thereof when the above-mentioned number of carbon atoms is 20 or less is preferred because it is less likely to remain as a residue during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0042] Examples of the above-mentioned carboxylic acids comprise formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, lauric acid, oleic acid, and stearic acid.

[0043] Examples of the salts of the above-mentioned carboxylic acids comprise: alkali metal salts such as a sodium salt and a potassium salt; alkaline earth metal salts such as a magnesium salt and a calcium salt; an ammonium salt; and an amine salt.

[0044] Among the carboxylic acids or salts thereof, acetic acid, caproic acid, caprylic acid, capric acid, or a salt thereof is preferred. This is because such a carboxylic acid or a salt thereof is easily thermally decomposed or the like even at a low temperature, and it is understood that the low-temperature sintering performance is improved. In addition, the above-mentioned carboxylic acid or a salt thereof is preferable because it is less likely to remain as a residue during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0045] The content of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as the total content of the organic component comprising the polymer dispersant is in the range of 0.3 mass% or more and 6 mass% or less. When the total content of the organic component comprising the polymer dispersant is in the range of 0.3 mass% or more and 6.0 mass% or less, the content of the carboxylic acid or a salt thereof is preferably, for example, 0.15 mass% or more and 5.0 mass% or less, more preferably 0.15 mass% or more and 4.5 mass% or less, still more preferably 0.20 mass% or more and 4.0 mass% or less, and particularly preferably 0.25 mass% or more and 3.5 mass% or less based on a total mass of the composite copper particles.

[0046] The measurement of the content of the carboxylic acid or a salt thereof can be performed by means of TG-DTA in the same manner as the measurement of the content of the above-mentioned organic component.

[0047] It is understood that in the composite copper particles of the present invention, when the content of the carboxylic acid or a salt thereof is 0.15 mass% or more, oxidation of copper in the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. Therefore, this is preferred because reduction in the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention due to atmospheric exposure can be more effectively avoided. It is preferable that the content of the carboxylic acid or a salt thereof is 5.0 mass% or less because reduction in the low-temperature sintering performance due to the excessive carboxylic acid or salt thereof in the composite copper particles of the present invention remaining as a residual component can be more effectively avoided. In addition, it is preferable that the content of the carboxylic acid or a salt thereof is 5.0 mass% or less because the carboxylic acid or a salt thereof is thermally decomposed or the like at a low temperature, and the low-temperature sintering performance is more effectively improved.<Polymer dispersant>

[0048] The organic component, which the composite copper particles of the present invention comprises, comprises a polymer dispersant, and the polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in the atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer.

[0049] When the polymer dispersant having the above-mentioned properties is used in the composite copper particles of the present invention, the composite copper particles of the present invention are preferably used for bonding uses (for example, a bonding material) or conductive use (for example, a conductive material) even when the composite copper particles are exposed to the atmosphere.

[0050] In the composite copper particles of the present invention, the polymer dispersant to be used has an acid value of 60 mgKOH / g or more. The acid value is more preferably 70 mgKOH / g or more, still more preferably 86 mgKOH / g or more. An acid value of 70 mgKOH / g or more is preferred because the composite copper particles of the present invention exhibit a high bonding strength before and after atmospheric exposure, and can further suppress reduction in the conductivity (specifically, an increase in volume resistivity) after atmospheric exposure. The upper limit of the acid value of the polymer dispersant is not particularly limited, but an acid value of 200 mgKOH / g or less is preferred because reduction in the bonding strength and conductivity of the composite copper particles of the present invention after atmospheric exposure can be further suppressed. The acid value of the above-mentioned polymer dispersant is more preferably 70 mgKOH / g or more and 200 mgKOH / g or less, and still more preferably 86 mgKOH / g or more and 200 mgKOH / g or less.

[0051] As the acid value of the polymer dispersant, if it is a commercially available product, a catalog value is referred to. When the polymer dispersant is prepared in-house, the acid value can be measured by the following method. The acid value of the polymer dispersant is measured by non-aqueous neutralization titration by means of an automatic titrator (GT-310BRT (manufactured by Nittoh Analytech Co., Ltd.)). A 0.1 mol / L potassium hydroxide / ethanol solution (manufactured by NACALAI TESQUE, INC.) is used as a titration solution, and the titration sample is prepared by dissolving 0.5 g of the polymer dispersant in 100 mL of ethanol.

[0052] In the above-mentioned polymer dispersant, the mass loss rate in the atmosphere of the polymer dispersant used is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer. The above-mentioned mass loss rate is more preferably 80% or more, still more preferably 90% or more.

[0053] It is preferable that the mass loss rate of the polymer dispersant is equal to or more than the above-mentioned value. The reasons are as follows: the composite copper particles after atmospheric exposure are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material); the polymer dispersant is easily thermally decomposed even at a low temperature; and the decomposition products obtained by the above-mentioned thermal decomposition can be easily desorbed or dissociated from the composite copper particles at a low temperature, thereby more effectively improving the low-temperature sintering performance. Furthermore, this is preferred because the polymer dispersant is less likely to remain during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0054] The mass loss rate of the polymer dispersant is measured by means of TG-DTA. Specifically, the polymer dispersant is heated from 25°C to 1000°C under conditions of a heating rate of 10°C / min in the atmosphere. Based on the mass of the polymer dispersant at the start of measurement, the mass loss rate of the polymer dispersant in the atmosphere is calculated from the mass loss amount when the temperature is raised from 30°C to 250°C.

[0055] The amine value of the above-mentioned polymer dispersant is not particularly limited. For example, the amine value of the polymer dispersant is preferably 45 mgKOH / g or less, more preferably 20 mgKOH / g or less, and still more preferably 5 mgKOH / g or less. It is most preferable to use a polymer dispersant having no amine value.

[0056] When the amine value of the polymer dispersant is equal to or less than the above-mentioned value, the reaction between the carboxylic acid or a salt thereof with which the surfaces of the copper particles is treated and the component derived from the amine value can be more effectively avoided.

[0057] The exothermic peak temperature due to thermal decomposition of the above-mentioned polymer dispersant is not particularly limited. For example, the exothermic peak temperature due to thermal decomposition of the polymer dispersant is preferably 300°C or lower, more preferably 280°C, and still more preferably 250°C or lower. When a plurality of exothermic peaks can be confirmed, the temperature of the exothermic peak observed at the highest temperature among the observed peaks is adopted.

[0058] It is preferable that the exothermic peak temperature due to thermal decomposition of the polymer dispersant is equal to or lower than the above-mentioned value because the polymer dispersant is easily thermally decomposed even at a low temperature, and the decomposition product obtained by the above-mentioned thermal decomposition is easily desorbed or dissociated from the composite copper particles at a low temperature, and the low-temperature sintering performance is more effectively improved. Further, this is preferred because the polymer dispersant is less likely to remain during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided.

[0059] The temperature of the exothermic peak due to thermal decomposition of the polymer dispersant can be measured by means of TG-DTA in the same manner as the measurement of the mass loss rate of the above-mentioned polymer dispersant.

[0060] The weight average molecular weight of the above-mentioned polymer dispersant is not particularly limited. For example, the weight average molecular weight is preferably 600 or more and 10,000 or less, more preferably 650 or more and 9,000 or less, and still more preferably 700 or more and 8,000 or less.

[0061] It is preferable that the weight average molecular weight of the polymer dispersant is 600 or more. This is because the carboxylic acid or a salt thereof can be held on the surfaces of the copper particles as in the preferred embodiment mentioned later, and agglomeration of the composite copper particles of the present invention can be effectively avoided. As a result, reduction in the properties (specifically, bonding strength and conductivity) when the composite copper particles of the present invention are exposed to the atmosphere can be more effectively avoided. Accordingly, the weight average molecular weight of 600 or more is preferred. It is preferable that the weight average molecular weight is 10,000 or less. This is because the polymer dispersant is easily thermally decomposed even at a low temperature, and the decomposition products obtained by the above-mentioned thermal decomposition can be easily desorbed or dissociated from the composite copper particles at a low temperature, and the low-temperature sintering performance is more effectively improved. Further, the polymer dispersant is less likely to remain during sintering, and reduction in the low-temperature sintering performance due to a residual component can be more effectively avoided. Accordingly, the weight average molecular weight of 10,000 or less is preferred.

[0062] The weight average molecular weight of the polymer dispersant can be measured by means of gel permeation chromatography (which is often referred to as "GPC" in the present application). Specifically, the polymer dispersant is dissolved in tetrahydrofuran (which is often referred to as "THF" in the present application), and the solution is filtered through a membrane filter to prepare a sample solution, and GPC analysis is performed.

[0063] When the average value of the weight average molecular weights measured three times by means of the above-mentioned GPC is defined as a reference value, the error range of the weight average molecular weight of the above-mentioned polymer dispersant is within the range of 500 or less and 500 or more of the above-mentioned reference value (for example, when the average of three measurements of the weight average molecular weight is 1000, the range of 500 or more and 1500 or less is the error range.).

[0064] The content of the above-mentioned polymer dispersant is not particularly limited as long as the total content of the organic component comprising the carboxylic acid or a salt thereof is in the range of 0.3 mass% or more and 6.0 mass% or less. When the total content of the organic component comprising the carboxylic acid or a salt thereof is in the range of 0.3 mass% or more and 6.0 mass% or less, the content of the polymer dispersant is preferably, for example, 0.15 mass% or more and 1.5 mass% or less, more preferably 0.16 mass% or more and 1.25 mass% or less, and still more preferably 0.17 mass% or more and 1.0 mass% or less based on a total mass of the composite copper particles.

[0065] In the composite copper particles of the present invention, it is preferable that the content of the polymer dispersant is 0.15 mass% or more because desorption of the carboxylic acid or a salt thereof from the surfaces of the copper particles can be more effectively avoided when the composite copper particles of the present invention are exposed to the atmosphere. It is preferable that the content of the polymer dispersant is 1.5 mass% or less because the polymer dispersant is easily thermally decomposed even at a low temperature, and the decomposition products obtained by the above-mentioned thermal decomposition can be easily desorbed or dissociated from the composite copper particles at a low temperature, and the low-temperature sintering performance is more effectively improved. Further, this is preferred because reduction in the low-temperature sintering performance of the composite copper particles of the present invention, which is caused by the polymer dispersant that the composite copper particles comprise remaining during sintering, can be more effectively avoided.

[0066] The measurement of the content of the polymer dispersant can be performed by means of TG-DTA in the same manner as the measurement of the content of the above-mentioned organic component.<Composite copper particles>

[0067] The composite copper particles of the present invention have an average particle diameter of 100 nm or more and 600 nm or less, preferably 150 nm or more and 500 nm or less, and more preferably 200 nm or more and 400 nm or less.

[0068] When the average particle diameter of the composite copper particles is within the above-mentioned range, the composite copper particles of the present invention are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) even when the composite copper particles of the present invention are exposed to the atmosphere.

[0069] The average particle diameter of the composite copper particles can be measured by means of SEM in the same manner as the measurement of the average particle diameter of the above-mentioned copper particles.

[0070] In the composite copper particles of the present invention, since the change in the particle diameter of the copper particles due to the presence of the organic component is very small, the average particle diameter of the composite copper particles of the present invention can be regarded as being the same as the average particle diameter of the copper particles.

[0071] When the presence or absence of copper oxide formation in the composite copper particles of the present invention is evaluated by means of an X-ray diffraction (XRD) apparatus, the composite copper particles of the present invention exposed to the atmosphere are measured by means of an XRD apparatus and evaluated based on the obtained X-ray diffraction pattern. For example, when peaks are observed only at around 2θ = 43.3° (Cu(111) plane) and around 2θ = 50.4° (Cu(200) plane), which are peaks attributed to metallic copper, from the above-mentioned X-ray diffraction pattern, it can be evaluated that only metallic copper is present (in other words, copper oxide is not formed). Further, when a peak is observed at around 2θ = 74.08° (Cu(220) plane), which is a peak attributed to metallic copper, in addition to the above-mentioned two peaks, it can be evaluated that only metallic copper is present (in other words, copper oxide is not formed). As the XRD apparatus, for example, SmartLab SE (Rigaku Corporation) can be used. Further, control of the apparatus, data collection, calculation, and report generation may be performed by means of a dedicated software, and for example, SmartLab Studio II (Rigaku Corporation) can be used as such a software.

[0072] When the presence or absence of copper oxide formation in the composite copper particles of the present invention is evaluated by means of a transmission electron microscope (TEM), the composite copper particles of the present invention exposed to the atmosphere are observed by means of TEM and evaluated based on the lattice spacing in the atomic arrangement (that is, lattice fringes) in the crystal. For example, when only 2.1 Å (0.21 nm) which is the lattice spacing of the metallic copper (111) plane is observed as the lattice spacing of the observed lattice fringes, it can be evaluated that only metallic copper is present (i.e., copper oxide is not formed). As the TEM, for example, H-9000 (Hitachi High-Tech Corporation) can be used.

[0073] In the organic component that the composite copper particles of the present invention comprise, the mass ratio of the carboxylic acid or a salt thereof to the polymer dispersant is not particularly limited as long as it is a gram equivalent or more. For example, the value of the mass ratio represented by "(mass of carboxylic acid or salt thereof) / (mass of polymer dispersant)" is preferably 1.0 or more and 12.0 or less, more preferably 1.2 or more and 11.0 or less, and still more preferably 1.5 or more and 10.0 or less.

[0074] It is preferable that the above-mentioned mass ratio is 1.0 or more because a form in which the carboxylic acid or a salt thereof is present on the surfaces of the copper particles can be easily provided, as in a preferred embodiment mentioned later. This improves the low-temperature sintering performance of the composite copper particles of the present invention. It is preferable that the above-mentioned mass ratio is 12.0 or less from the viewpoint that an increase in production cost due to the use of a large amount of the carboxylic acid or a salt thereof can be more effectively avoided.

[0075] The measurement of the mass ratio of the carboxylic acid or a salt thereof to the polymer dispersant ("(mass of carboxylic acid or salt thereof) / (mass of polymer dispersant)") can be performed by means of TG-DTA in the same manner as the measurement of the content of the above-mentioned organic component. Here, in the obtained profile, the mass loss rate in the temperature range from 30°C to 200°C is defined as the mass of the carboxylic acid or a salt thereof, and the mass loss rate in the temperature range from 200°C to 350°C is defined as the mass of the polymer dispersant. The mass loss rate in the temperature range from 200°C to 350°C is obtained by subtracting the mass loss rate of the carboxylic acid or a salt thereof from the total mass loss rate (in the temperature range from 30°C to 350°C).

[0076] In the composite copper particles of the present invention, the state in which the carboxylic acid or a salt thereof is present is not particularly limited. For example, the composite copper particles may comprise the carboxylic acid or a salt thereof, and / or the carboxylic acid or a salt thereof may be present on the surfaces of the copper particles. When the carboxylic acid or a salt thereof is present on the surfaces of the copper particles, for example, the carboxylic acid or a salt thereof may be present by being chemically bonded to the surfaces of the above-mentioned copper particles, and / or the carboxylic acid or a salt thereof may be present by being chemically bonded to the polymer dispersant. In addition, the carboxylic acid or a salt thereof may be present by being adsorbed on the surfaces of the copper particles and / or the polymer dispersant.

[0077] The descriptions regarding the chemical bonding and the adsorption in the above-mentioned "<Organic component>" are applied to the chemical bonding and the adsorption.

[0078] When the above-mentioned carboxylic acid or a salt thereof is present on the surfaces of the copper particles, the above-mentioned carboxylic acid or a salt thereof may coat the surfaces of the copper particles. Specifically, the carboxylic acid or a salt thereof may entirely coat the surfaces of the copper particles, or the carboxylic acid or a salt thereof may only partially coat the surfaces of the copper particles. In addition, when the carboxylic acid or a salt thereof entirely coats the surfaces of the copper particles, the coating may be uniform or non-uniform.

[0079] In addition, when the above-mentioned carboxylic acid or a salt thereof coats the surfaces of the copper particles, the above-mentioned carboxylic acid or a salt thereof may coat the surfaces of the copper particles as a monomolecular film, or may coat the surfaces of the copper particles as a cumulative film. Further, the carboxylic acid or a salt thereof constituting the above-mentioned monomolecular film and the above-mentioned cumulative film may be formed only of the same species or two or more different species. The "cumulative film" as used herein is intended to mean a monomolecular film constituted by the carboxylic acid or a salt thereof, which is in direct contact with the surfaces of the copper particles, and a film constituted by the carboxylic acid or a salt thereof, which is chemically bonded to, adsorbed on the monomolecular film, or the like.

[0080] In the composite copper particles of the present invention, the state in which the polymer dispersant is present is not particularly limited. For example, the composite copper particles may comprise the polymer dispersant and / or the polymer dispersant may be present on the surfaces of the copper particles. When the polymer dispersant is present on the surfaces of the copper particles, for example, the polymer dispersant may interact with the surfaces of the copper particles and / or may interact with the carboxylic acid or a salt thereof present on the surfaces of the copper particles.

[0081] Examples of the interactions with the carboxylic acid or a salt thereof present on the surfaces of the above-mentioned copper particles comprise a state in which the polymer dispersant interacts with the carboxylic acid or a salt thereof by physical adsorption, chemical adsorption, or the like, a state in which the polymer dispersant electrically interacts with the carboxylic acid or a salt thereof (for example, Coulomb force), and / or a state in which the polymer dispersant is chemically bonded to the carboxylic acid or a salt thereof.

[0082] When the above-mentioned polymer dispersant interacts with the carboxylic acid or a salt thereof present on the surfaces of the copper particles, the above-mentioned polymer dispersant may coat a film (specifically, a monomolecular film or a cumulative film) constituted by the above-mentioned carboxylic acid or a salt thereof. Specifically, the polymer dispersant may entirely coat the surface of the above-mentioned film, or the polymer dispersant may only partially coat the above-mentioned film.

[0083] In a more preferred embodiment of the composite copper particles of the present invention, the surfaces of the copper particles are coated with a molecular film comprising the carboxylic acid or a salt thereof, and the molecular film of the carboxylic acid or a salt thereof is coated with the polymer dispersant. When the composite copper particles of the present invention are in such an embodiment, agglomeration of the composite copper particles is more preferably suppressed. It is understood that since the agglomeration of the composite copper particles can be more preferably suppressed, the low-temperature sintering performance is more preferably maintained even after the composite copper particles of the present invention are exposed to the atmosphere.

[0084] In one embodiment, when the composite copper particles are in the above-mentioned more preferred embodiment, the decomposition temperature of the carboxylic acid or a salt thereof is preferably lower than that of the polymer dispersant. When the composite copper particles of the present invention are sintered, the carboxylic acid or a salt thereof which is relatively easily thermally decomposed is more preferably desorbed, and at the same time, the polymer dispersant can also be more preferably desorbed. Therefore, it is understood that the composite copper particles of the present invention have excellent low-temperature sintering performance.

[0085] In a still more preferred embodiment, the molecular film of the above-mentioned carboxylic acid or a salt thereof may be constituted by a monomolecular film or a cumulative film, and the polymer dispersant may coat the above-mentioned monomolecular film or cumulative film.

[0086] When a monomolecular film of the carboxylic acid or a salt thereof is formed on the surfaces of the above-mentioned copper particles, it is understood that the composite copper particles of the present invention not only are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) after atmospheric exposure, but also more preferably contribute to the exhibition of low-temperature sintering performance.

[0087] When a cumulative film of the carboxylic acid or a salt thereof is formed on the above-mentioned monomolecular film, it is understood that the composite copper particles of the present invention not only can be preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) after atmospheric exposure, but also more preferably contribute to the suppression in oxidation of copper that the composite copper particles comprise.

[0088] In addition, it is understood that the monomolecular film or the cumulative film of the carboxylic acid or a salt thereof coated on the surfaces of the copper particles also functions more preferably as a scaffold upon coating with the polymer dispersant.

[0089] Since the carboxylic acid or a salt thereof coated on the surfaces of the copper particles is adsorbed and desorbed, when the composite copper particles of the present invention are in the still more preferred embodiment as mentioned above, even if the carboxylic acid or a salt thereof is partially desorbed when the composite copper particles of the present invention are exposed to the atmosphere, the polymer dispersant coats the surfaces. As a result, the exposure of copper is more preferably reduced. Accordingly, it is understood that the composite copper particles of the present invention have a high effect of suppressing oxidation.

[0090] By coating the monomolecular film or the cumulative film of the above-mentioned carboxylic acid or a salt thereof with the polymer dispersant, the composite copper particles of the present invention are preferably used for bonding uses (for example, a bonding material) or conductive uses (for example, a conductive material) after atmospheric exposure.

[0091] That is, when the monomolecular film or the cumulative film of the carboxylic acid or a salt thereof is formed through relatively weak forces (for example, intermolecular force or the like), the surface of the above-mentioned monomolecular film or cumulative film is coated with the polymer dispersant, so that the carboxylic acid or a salt thereof is less likely to be desorbed. As a result, the polymer dispersant plays an auxiliary role for exhibiting the effect (specifically, deterioration of properties can be suppressed even after atmospheric exposure) of the monomolecular film or cumulative film of the above-mentioned carboxylic acid or a salt thereof. In addition, as one of the general effects of the polymer dispersant, the polymer dispersant can more preferably contribute to suppression in agglomeration of the composite copper particles.<Production of composite copper particles>

[0092] A method for producing composite copper particles of the present invention will be described.

[0093] The composite copper particles of the present invention are produced by a method comprising a step of mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0094] The composite copper particles of the present invention can also be produced by a method comprising a step of mixing carboxylic acid-coated copper particles with a treatment solution comprising a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0095] The composite copper particles of the present invention can also be produced by a method comprising a step of mixing carboxylic acid-coated copper particles with a treatment solution comprising a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent, followed by drying.(Step of preparing carboxylic acid-coated copper particles)

[0096] In the composite copper particles of the present invention, the copper particles to be used are not particularly limited. For example, commercially available copper particles may be purchased, or copper particles produced by a known method may be used. As the copper particles produced by a known method, copper particles treated with a carboxylic acid will be mentioned later.

[0097] The above-mentioned copper particles may comprise a component or a compound other than the copper component, such as a raw material or a reactant used in the production process, to such an extent that no problem is caused according to their use.

[0098] The shape of the above-mentioned copper particles used in the composite copper particles of the present invention is not particularly limited. For example, any shape such as an irregular shape, a spherical shape, a polyhedron, a spindle shape, or a plate shape may be used.

[0099] The average particle diameter of the above-mentioned copper particles is not particularly limited. For example, it is 100 nm or more and 600 nm or less, preferably 150 nm or more and 500 nm or less, and more preferably 200 nm or more and 400 nm or less.

[0100] It is preferable that the average particle diameter of the copper particles is within the above-mentioned range because composite copper particles having a desired average particle diameter can be obtained.<Solvent>

[0101] The above-mentioned solvent is not particularly limited as long as it does not react with the above-mentioned carboxylic acid or a salt thereof or the polymer dispersant. As such a solvent, for example, methanol, ethanol, 1-propanol, 2-propanol, acetone, methyl ethyl ketone, or the like can be used.

[0102] The individual raw materials used in the above-mentioned production method can be appropriately used from among those mentioned above in accordance with the production method.(Surface treatment step)

[0103] In the composite copper particles of the present invention, by mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent as raw materials, the carboxylic acid-coated copper particles are subjected to a surface treatment with the carboxylic acid or a salt thereof and the polymer dispersant.

[0104] The mixing order of the above-mentioned individual raw materials is not particularly limited. For example, all the raw materials may be mixed together at once, or the solvent and other raw materials may be mixed individually in any order. In addition, a solution obtained by mixing a solvent and at least one raw material may be prepared, and then the solution may be mixed with the remaining raw materials in any order. Specifically, a treatment solution in which a solvent, a polymer dispersant, and a carboxylic acid or a salt thereof are mixed is prepared in advance, and the above-mentioned treatment solution and the carboxylic acid-coated copper particles may be mixed. A dispersion solution comprising carboxylic acid-coated copper particles obtained by mixing a solvent and carboxylic acid-coated copper particles may be mixed with a treatment solution in which a solvent, a polymer dispersant, and a carboxylic acid or a salt thereof are mixed.

[0105] In the step of mixing the above-mentioned individual raw materials, a known stirrer can be used. Examples thereof comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials.

[0106] The stirring time and the stirring speed are not particularly limited as long as the above-mentioned individual raw materials can be sufficiently mixed. For example, the stirring time may be 1 minute or more, and is more preferably 5 minutes or more. For example, the stirring speed is preferably 50 rpm or more, and more preferably 100 rpm or more. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the above-mentioned carboxylic acid-coated copper particles can be uniformly treated with the organic component.

[0107] The composite copper particles of the present invention can be produced by a method comprising a step of mixing carboxylic acid-coated copper particles with a treatment solution comprising a polymer dispersant, a carboxylic acid or a salt thereof, and a solvent. This production method is preferred because the carboxylic acid or a salt thereof and the polymer dispersant that the treatment solution comprises can be more efficiently made present on the surfaces of the copper particles.(Step of preparing treatment solution)

[0108] In the method for producing composite copper particles of the present invention, the treatment solution is prepared by a method comprising a step of mixing a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

[0109] In the step of preparing the above-mentioned treatment solution, the addition order of the raw materials is not particularly limited. For example, all the raw materials may be mixed together at once, or the solvent and other raw materials may be mixed individually in any order.

[0110] In the step of preparing the above-mentioned treatment solution, in a case of mixing the above-mentioned treatment solution, stirring may be performed by means of a known stirrer. Examples of such stirrers comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser mixer, and a homomixer.

[0111] In the above-mentioned step of stirring, stirring conditions such as a stirring time and a stirring speed are not particularly limited as long as the above-mentioned individual raw materials can be sufficiently mixed. For example, the stirring time may be 1 minute or more, and is more preferably 5 minutes or more. For example, the stirring speed may be 50 rpm or more, and is more preferably 100 rpm or more. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the above-mentioned individual raw materials can be uniformly mixed.

[0112] The total amount of the carboxylic acid or a salt thereof and the polymer dispersant in the above-mentioned treatment solution is not particularly limited as long as the copper particles can be treated with a predetermined amount of the organic component. For example, the total amount of the carboxylic acid or a salt thereof and the polymer dispersant in the treatment solution is preferably 1.0 mass% or more and 30 mass% or less, more preferably 1.5 mass% or more and 25 mass% or less, and still more preferably 2.0 mass% or more and 20 mass% or less based on a total mass of the treatment solution.

[0113] The content of the carboxylic acid or a salt thereof in the above-mentioned treatment solution is not particularly limited. For example, the content of the carboxylic acid or a salt thereof in the treatment solution is preferably 0.7 mass% or more and 25 mass% or less, more preferably 1.5 mass% or more and 18 mass% or less, and still more preferably 2.0 mass% or more and 16 mass% or less based on a total mass of the treatment solution.

[0114] The content of the polymer dispersant in the above-mentioned treatment solution is not particularly limited. For example, the content of the polymer dispersant in the treatment solution is preferably 0.3 mass% or more and 5.0 mass% or less, more preferably 0.4 mass% or more and 4.5 mass% or less, and still more preferably 0.5 mass% or more and 4.0 mass% or less based on a total mass of the treatment solution.

[0115] It is preferable that the composition of the treatment solution is within the above-mentioned range because the copper particles can be more effectively treated with a predetermined amount of the organic component so that the composite copper particles of the present invention can be obtained.

[0116] In the step of mixing the above-mentioned carboxylic acid-coated copper particles and the above-mentioned treatment solution, a known stirrer can be used. Examples thereof comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser, and a homomixer. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials. Examples thereof comprise a method of immersing the copper particles in the treatment solution and a method of allowing the treatment solution to permeate into the copper particles.

[0117] The stirring time and the stirring speed are not particularly limited as long as the above-mentioned individual raw materials can be sufficiently mixed. For example, the stirring time is preferably 1 minute or more, and more preferably 5 minutes or more. For example, the stirring speed is preferably 50 rpm or more, and more preferably 100 rpm or more. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the above-mentioned carboxylic acid-coated copper particles can be uniformly treated with the organic component. In addition, in the case of immersion or permeation, the immersion or permeation time may be 10 minutes or more.

[0118] After the above-mentioned surface treatment step, solid-liquid separation may be performed as necessary. A known filtration method can be used in solid-liquid separation. For example, a pressure filtration device such as a rotary press or a filter press, a vacuum filtration device such as a Nutsche filter or a Moore filter, a centrifuge, or the like can be used. Decantation operation may be performed as appropriate.

[0119] After the above-mentioned surface treatment step, the collected solid content may be washed as necessary. A known washing method can be used for washing the solid content. The solvent used for washing is not particularly limited.(Drying step)

[0120] The composite copper particles of the present invention can be produced by a method comprising a step of drying the mixture of the carboxylic acid-coated copper particles and the treatment solution as necessary.

[0121] Conditions such as drying temperature, drying time, and drying atmosphere in the drying step can be appropriately set. For example, the drying temperature is preferably 20°C or higher and 120°C or lower, the drying time is preferably 0.5 hours or more and 10 hours or less, and the drying atmosphere is preferably under vacuum or under an inert gas such as nitrogen or argon.

[0122] In the drying step, drying may be performed by means of a known dryer. For example, a heating device such as a dryer, an oven, or an electric furnace, a desiccator controlled to a predetermined temperature, a vacuum dryer, a decompression dryer, or the like can be used.

[0123] When a desiccator is used in the drying step, the mixture of the copper particles and the treatment solution can be dried by controlling the inside of the desiccator to a predetermined temperature and creating a vacuum atmosphere.

[0124] When the inside of the desiccator is brought into a vacuum atmosphere, a vacuum pump may be used. As the vacuum pump, for example, G-20DA manufactured by ULVAC, Inc. or the like can be used.

[0125] After the above-mentioned drying step, the composite copper particles may be ground or crushed as necessary to adjust the particle size. A known grinding machine, classifier, or the like can be used for grinding or crushing.(Production Example of carboxylic acid-coated copper particles)

[0126] Hereinafter, an example of a method for producing carboxylic acid-coated copper particles (steps A and B) will be described.(Step A)

[0127] This step is a step of mixing a copper compound, a carboxylic acid or a salt thereof, an amine compound, and a solvent. In this step, a mixed solution comprising a copper compound can be obtained.

[0128] The above-mentioned copper compound is not particularly limited as long as it comprises a copper atom. The copper compound used in step A may be only one species or may be two or more species.

[0129] Examples thereof comprise: copper carboxylates such as copper(I) formate, copper(I) acetate, copper(I) propionate, copper(I) butyrate, copper(I) valerate, copper(I) caproate, copper(I) caprylate, copper(I) caprate, copper(II) formate, copper(II) acetate, copper(II) propionate, copper(II) butyrate, copper(II) valerate, copper(II) caproate, copper(II) caprylate, copper(II) caprate, and copper(II) citrate; copper oxides such as copper(II) oxide and copper(I) oxide; copper hydroxides such as copper(II) hydroxide and copper(I) hydroxide; and copper nitride.

[0130] Among the above-mentioned copper compounds, copper(II) oxide is preferred from the viewpoint of reducing the production cost.

[0131] The added amount of the above-mentioned copper compound is not particularly limited. For example, the added amount of the above-mentioned copper compound is preferably 1 part by mass or more and 100 parts by mass or less with respect to the solvent.

[0132] It is preferable that the amount of the copper compound is 1 part by mass or more with respect to the solvent because the decrease in the amount of copper particles produced in step B can be effectively avoided. It is preferable that the amount of the copper compound is 100 parts by mass or less with respect to the solvent because an uneven reaction due to thickening when the solvent and the above-mentioned copper compound are mixed in this step can be effectively avoided.

[0133] The chemical structure of the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as it has a hydrocarbon group moiety and a carboxyl group moiety in its structure.

[0134] The above-mentioned hydrocarbon group moiety is not particularly limited as long as the carboxylic acid-coated copper particles used for producing the composite copper particles according to the present invention can be obtained. For example, it may be formed only of a single bond or may have a multiple bond in the middle or at the end. In addition, the hydrocarbon group may comprise a heteroatom at any position.

[0135] The above-mentioned carboxyl group moiety is not particularly limited as long as the carboxylic acid-coated copper particles used for producing the composite copper particles according to the present invention can be obtained. For example, the carboxylic acid or a salt thereof may have one carboxyl group in the molecule, or may have two or more carboxyl groups in the molecule. Among them, the number of carboxyl groups in the molecule of the carboxylic acid or a salt thereof is preferably one.

[0136] The number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is not particularly limited as long as the carboxylic acid-coated copper particles used for producing the composite copper particles according to the present invention can be obtained. For example, the number of carbon atoms in the molecule of the above-mentioned carboxylic acid or a salt thereof is preferably 2 or more and 20 or less, more preferably 2 or more and 18 or less, and still more preferably 2 or more and 16 or less.

[0137] Examples of the above-mentioned carboxylic acids comprise formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, enanthic acid, pelargonic acid, capric acid, lauric acid, oleic acid, and stearic acid.

[0138] Examples of the salts of the above-mentioned carboxylic acids comprise: alkali metal salts such as a sodium salt and a potassium salt; alkaline earth metal salts such as a magnesium salt and a calcium salt; an ammonium salt; and an amine salt.

[0139] Among the above-mentioned carboxylic acids or salts thereof, it is more preferable to comprise acetic acid, caproic acid, caprylic acid, or capric acid. Use of such a carboxylic acid or a salt thereof is preferred because copper particles obtained in step B mentioned later more efficiently achieve a desired average particle diameter.

[0140] The added amount of the above-mentioned carboxylic acid or a salt thereof is not particularly limited, and may be 0.01 mol or more and 2 mol or less per 1 mol of the copper compound.

[0141] It is preferable that the added amount of the carboxylic acid or a salt thereof is within the above-mentioned range because copper particles having a desired average particle diameter can be obtained in step B.

[0142] The above-mentioned amine compound used in step A is not particularly limited as long as it has an amino group and a hydroxy group in its structure.

[0143] Specifically, the above-mentioned amine compound is preferably an amino alcohol. Use of the amino alcohol preferably suppresses foaming of the mixed solution comprising the copper compound in step A.

[0144] Examples of the above-mentioned amino alcohols comprise methanolamine, monoethanolamine (which is also referred to as "2-aminoethanol"), diethanolamine, triethanolamine, 3-amino-1-propanol, 1-dimethylamino-2-propanol, 3-(dimethylamino)-1-propanol, 4-ethylamino-1-butanol, N-methylethanolamine, 2-diethylethanolamine, 2-aminodibutanol, heptaminol, isoetharine, sphingosine, 3-dimethylamino-1,2-propanediol, 3-diethylamino-1,2-propanediol, 3-methylamino-1,2-propanediol, 3-(dimethylamino)-1,2-propanediol, 2-amino-2-methyl-1,3-propanediol, 3-(diethylamino)-1,2-propanediol, 2-amino-2-ethyl-1,3-propanediol, 3-amino-1,2-propanediol, 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, and 2-amino-1,3-propanediol.

[0145] Among the above-mentioned amine compounds, it is more preferable to comprise monoethanolamine. Monoethanolamine is preferred because even if monoethanolamine remains in the synthesized copper particles, monoethanolamine is thermally decomposed or the like at a low temperature, so that deterioration of the low-temperature sintering performance can be more effectively avoided.

[0146] The added amount of the above-mentioned amine compound is not particularly limited, and is preferably 0.25 mol or more and 2 mol or less per 1 mol of the above-mentioned carboxylic acid.

[0147] It is preferable that the added amount of the amine compound is within the above-mentioned range because thickening of the mixed solution comprising the copper compound can be effectively avoided.

[0148] The addition time of the above-mentioned amine compound is not particularly limited, and is preferably 10 seconds or more and 30 minutes or less. In this way, rapid heat generation of the mixed solution comprising the copper compound in step A is preferably suppressed.

[0149] The solvent used in step A is not particularly limited as long as it does not react with other raw materials to inhibit the production of copper particles. The above-mentioned solvent used may be only one species or may be two or more species.

[0150] As the above-mentioned solvent, an alcohol is preferably used. Examples of the above-mentioned alcohols comprise 1-propanol, 2-propanol, butanol, pentanol, hexanol, heptanol, octanol, and ethyl carbitol. These alcohols are preferred because they exhibit high compatibility with the carboxylic acid or a salt thereof and the above-mentioned amine compound.

[0151] The mixing order of the above-mentioned individual raw materials is not particularly limited. For example, all the raw materials may be mixed together at once, or the solvent and other raw materials may be mixed individually in any order. In particular, it is preferable to mix a solvent, a copper compound, and a carboxylic acid or a salt thereof, followed by further mixing with an amine compound.

[0152] In the above-mentioned mixing step, a known stirrer can be used. Examples thereof comprise a planetary centrifugal mixer, an ultrasonic disperser, a blade-type stirrer, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials.

[0153] The above-mentioned mixing conditions in the mixing step can be appropriately set. For example, the stirring time may be 1 minute or more. The stirring time is more preferably 5 minutes or more. The stirring speed may be 50 rpm or more. The stirring speed is more preferably 100 rpm or more. With the above-mentioned mixing conditions, the raw materials can be sufficiently mixed. It is preferable that the stirring time is 5 minutes or more and the stirring speed is 100 rpm or more because the raw materials are more sufficiently mixed and the reaction proceeds uniformly.(Step B)

[0154] This step is a step of intermittently or continuously adding a reducing agent to the mixed solution comprising the copper compound obtained in step A, and the solution temperature of the above-mentioned mixed solution during addition of the above-mentioned reducing agent is 40°C or higher and 95°C or lower. By this step, a dispersion solution comprising copper particles can be obtained.

[0155] The above-mentioned reducing agent may be any reducing agent as long as it reduces the copper compound, and specifically, the boiling point thereof is preferably 70°C or higher, and the boiling point of the above-mentioned reducing agent is more preferably equal to or higher than the heating temperature in the heating step. Use of such a reducing agent is preferred because the copper compound is more efficiently reduced even when the temperature of the mixed solution is 40°C or higher and 95°C or lower. The above-mentioned reducing agent used may be only one species or may be two or more species.

[0156] Examples of the above-mentioned reducing agents comprise hydrazine derivatives. Examples of the hydrazine derivatives comprise hydrazine monohydrate, hydrazine hydrate, methylhydrazine, ethylhydrazine, n-propylhydrazine, i-propylhydrazine, n-butylhydrazine, i-butylhydrazine, sec-butylhydrazine, t-butylhydrazine, n-pentylhydrazine, i-pentylhydrazine, neo-pentylhydrazine, t-pentylhydrazine, n-hexylhydrazine, i-hexylhydrazine, n-heptylhydrazine, n-octylhydrazine, n-nonylhydrazine, n-decylhydrazine, n-undecylhydrazine, n-dodecylhydrazine, cyclohexylhydrazine, phenylhydrazine, 4-methylphenylhydrazine, benzylhydrazine, 2-phenylethylhydrazine, 2-hydrazinoethanol, acetohydrazine, adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, isophthalic acid dihydrazide, and salicylic acid hydrazide.

[0157] When the above-mentioned reducing agent is added to the mixed solution comprising the copper compound obtained in step A, the reducing agent is not added thereto at once in a short time but is added thereto intermittently or continuously. The addition time of the reducing agent is preferably 50 minutes or more and 6 hours or less, and more preferably 60 minutes or more and 6 hours or less.

[0158] In the present application, such expressions as "adding intermittently or continuously" are intended to mean adding gradually in small amounts over time. In addition, the reducing agent may be added in two or more portions.

[0159] In the present application, the "addition time" is defined as the time required from the start point when the reducing agent is added to the mixed solution comprising the copper compound until a total amount of the above-mentioned reducing agent is added to the above-mentioned mixed solution (which may also be referred to as "time required to add a total amount of the reducing agent" hereinafter).

[0160] By adding the reducing agent intermittently or continuously, heat generation occurring during the reduction reaction is suppressed, thereby allowing the average particle diameter of the copper particles obtained in this step to fall within the desired range.

[0161] The added amount of the above-mentioned reducing agent is preferably 1.0 mol or more and 4.0 mol or less per 1.0 mol of the above-mentioned copper compound. An added amount of 1.0 mol or more is preferred because the copper compound can be sufficiently reduced. Further, an added amount of 4.0 mol or less is preferred because the load during the washing of the solid content comprising the copper particles can be further reduced.

[0162] The temperature of the mixed solution comprising the copper compound at the time of addition of the above-mentioned reducing agent is preferably 40°C or higher and 95°C or lower, and more preferably 45°C or higher and 90°C or lower.

[0163] When the temperature of the mixed solution comprising the copper compound is within the above-mentioned range, copper particles having a desired average particle diameter can be obtained.

[0164] The temperature of the mixed solution comprising the copper compound may be adjusted before the addition of the reducing agent or during the addition of the reducing agent. Preferably, the temperature of the mixed solution comprising the copper compound is adjusted to the above-mentioned range before the addition of the reducing agent.

[0165] In this step, a known mixing machine such as a stirrer, a mixer, a homogenizer, or an agitator can be used as necessary. The stirring speed is not limited, but may be 50 rpm or more. The stirring speed is more preferably 100 rpm or more. A stirring speed of 100 rpm or more is preferred because the copper compound is uniformly reduced, and more uniform copper particles can be obtained.

[0166] The dispersion solution comprising the copper particles obtained in this step may be aged as necessary.

[0167] The aging conditions can be appropriately set. For example, the aging temperature is preferably 40°C or higher and 120°C or lower, more preferably 40°C or higher and 100°C or lower, still more preferably 60°C or higher and 100°C or lower, and particularly preferably 60°C or higher and 95°C or lower. The aging time is preferably 1 minute or more and 2.0 hours or less, and more preferably 5 minutes or more and 2.0 hours or less. Furthermore, during aging, stirring may be performed by means of the above-mentioned known mixing machine. The stirring speed is not limited, but may be 50 rpm or more. The above-mentioned stirring speed is preferably 100 rpm or more.

[0168] The dispersion solution comprising the copper particles obtained in this step may be subjected to solid-liquid separation as necessary.

[0169] A known method can be used in solid-liquid separation. For example, a pressure filtration device such as a rotary press or a filter press commonly used industrially, a vacuum filtration device such as a Nutsche filter or a Moore filter, a centrifuge, or the like can be used. Decantation operation may be performed as appropriate.

[0170] The solid content obtained by the above-mentioned solid-liquid separation may be washed by a known method.

[0171] The solid content obtained by the above-mentioned solid-liquid separation may be dried by a known method. For example, a heating device such as a dryer, an oven, or an electric furnace, a desiccator controlled to a predetermined temperature, a vacuum dryer, a decompression dryer, or the like can be used.

[0172] When a desiccator is used in the drying step, the above-mentioned solid content can be dried by controlling the inside of the desiccator to a predetermined temperature and creating a vacuum atmosphere. When the inside of the desiccator is brought into a vacuum atmosphere, a vacuum pump may be used. As the vacuum pump, for example, G-20DA manufactured by ULVAC, Inc. or the like can be used.

[0173] The drying conditions can be appropriately set. For example, the drying temperature is preferably 20°C or higher and 120°C or lower, the drying time is preferably 0.5 hours or more and 10 hours or less. From the viewpoint of more effectively suppressing the oxidation of the copper particles, the drying atmosphere is preferably maintained under a flow of an inert gas such as nitrogen or argon or under a vacuum atmosphere.

[0174] Carboxylic acid-coated copper particles having an average particle diameter of 100 nm or more and 600 nm or less can be obtained by the production method comprising the above above-mentioned step A and step B, and the carboxylic acid-coated copper particles obtained here can be used as a raw material when the composite copper particles of the present invention are produced.<Copper paste>

[0175] The copper paste of the present invention comprises the composite copper particles of the present invention and a paste solvent.

[0176] The paste solvent is not particularly limited, and any organic solvent can be used. For example, a protic polar solvent or an aprotic solvent can be used, and two or more of solvent species can be appropriately combined and used.

[0177] In the present invention, an alcohol-based solvent, a glycol-based solvent, a glycol ether-based solvent, and an ester-based solvent have high affinity for a polymer dispersant having an acid value or a carboxylic acid, and can be preferably used.

[0178] Examples of the alcohol-based solvents comprise methanol, ethanol, propyl alcohol, butyl alcohol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, modified alcohol, and aromatic alcohols such as benzyl alcohol, menthol, and terpineol (α, β, γ, δ).

[0179] As the glycol-based solvent, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, or the like can be used.

[0180] Examples of the glycol ether-based solvents comprise an ethylene-based glycol ether and a propylene-based glycol ether.

[0181] Examples of the ethylene-based glycol ethers comprise ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether (ethyl carbitol), diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether (hexyl carbitol), triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, triethylene glycol monohexyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, ethylene glycol diacetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, and ethylene glycol phenyl ether.

[0182] Examples of the propylene-based glycol ethers comprise propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monohexyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monohexyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, tripropylene glycol monohexyl ether, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, propylene glycol diacetate, propylene glycol monobutyl ether acetate, dipropylene glycol monobutyl ether acetate, and propylene glycol phenyl ether.

[0183] Examples of the ester-based solvents comprise methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, and normal propyl acetate.

[0184] In the copper paste of the present invention, the paste solvent used may be only one species or may be two or more species. The species and the blending ratio may be appropriately set in consideration of properties required for the copper paste, properties required for the bonding material, properties required for the conductive material, compatibility with other blended components, and the like. Examples of the combinations of two or more species of paste solvents comprise a combination of dipropylene glycol and hexyl carbitol.

[0185] The copper paste of the present invention can comprise various additives as necessary. Examples of the additives comprise various commonly used reducing agents, dispersants, emulsifiers, antifreeze agents, pH adjusters, thickeners, defoamers, and film-forming agents.

[0186] In a case where the copper paste of the present invention comprises the above-mentioned reducing agent, examples of the usable reducing agents comprise monoethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol, N-methyldiethanolamine, hydrazine, and formic acid.

[0187] The copper paste of the present invention may comprise copper particles other than the composite copper particles of the present invention. Specifically, the copper paste of the present invention may comprise micro-copper particles having an average particle diameter of 1 µm to 50 µm or nano-copper particles having an average particle diameter of 100 nm or less. The shapes of the above-mentioned micro-copper particles and the nano-copper particles are not particularly limited, and examples thereof comprise any shape such as a spherical shape, a massive shape, a needle shape, a flake shape, a substantially spherical shape, an irregular shape, a polyhedral shape, a spindle shape, and a flat shape, as well as agglomeration of these shapes. The average particle diameter of the micro-copper particles and the nano-copper particles can be measured in the same manner as the average particle diameter of the above-mentioned composite copper particles.

[0188] The content of the above-mentioned composite copper particles in the copper paste of the present invention may be appropriately adjusted in accordance with the uses. The content of the copper particles in the copper paste can be confirmed by, for example, thermogravimetric analysis.

[0189] The copper paste of the present invention is produced by mixing the above-mentioned raw materials. In this mixing step, a known mixer can be used. Examples thereof comprise a biaxial mixer, a triple roll, a sand mill, and a planetary mixer which are commonly used industrially. In addition, in the case of a laboratory scale, a stirrer, a hybrid mixer, a homogenizer, a paint shaker, or the like can be used. The materials may be mixed without using a mixer. Mixing also comprises contact and coexistence of materials.

[0190] In the mixer, grinding media may be used as necessary. Examples thereof comprise those comprising glass, alumina, zirconia, zirconium silicate, or the like as a component.

[0191] Defoaming may be performed as necessary during the above-mentioned mixing step or after the mixing step.

[0192] The atmosphere in the mixing step may be any of air, inert gas, and vacuum. From the viewpoint of more effectively suppressing reduction in the performance due to oxidation of the copper particles, an inert gas or vacuum is preferred.<Bonding material>

[0193] The composite copper particles of the present invention or the copper paste comprising the composite copper particles of the present invention can be used as a bonding material, and can preferably bond a base material and a material to be bonded. It can also be used for bonding three-dimensional stacked integrated circuits (3D-ICs). The composite copper particles of the present invention may be used as a bonding material as they are, or may be used as a bonding material after the composite copper particles are formed into a copper paste.

[0194] When the above-mentioned copper paste is used for the above-mentioned bonding material, the above-mentioned copper paste preferably comprises the composite copper particles in an amount of 80 mass% or more and 98 mass% or less, and more preferably 85 mass% or more and 96 mass% or less based on a total amount of the copper paste.

[0195] The incorporation of 80 mass% or more of the above-mentioned composite copper particles in the above-mentioned copper paste is preferred because generation of voids during heating can be effectively suppressed, and the bonding strength is further improved. The incorporation thereof in an amount of 98 mass% or less can more efficiently avoid agglomeration of the composite copper particles in the paste, and preferably improves the coatability of the paste.

[0196] The above-mentioned bonding material may appropriately comprise additives in accordance with its uses. Examples of the additives comprise the above-mentioned various additives.

[0197] The above-mentioned base material and the above-mentioned material to be bonded may be the same material or different materials. The above-mentioned material to be bonded is not particularly limited. Examples thereof comprise various metal materials, semiconductor materials (for example, chips), ceramic materials, and resin materials.

[0198] The surfaces of the above-mentioned base material and the above-mentioned material to be bonded may be polished as necessary.

[0199] In the case of the metal materials, grindstone polishing, lapping polishing, buffing polishing, barrel polishing, electrolytic polishing, and the like can be used. As polishing agents and abrasive grains used for polishing, known materials can be appropriately used. Examples of abrasive grains comprise diamond, alumina, silicon carbide, and cubic boron nitride.

[0200] In the case of the semiconductor material, chemical mechanical polishing (CMP) and the like can be used. Examples of abrasive grains comprise inorganic metal oxides such as cerium oxide and silicon oxide.

[0201] In the case of a ceramic material or a resin material, mechanochemical polishing can be used.

[0202] The surfaces of the above-mentioned base material and the above-mentioned material to be bonded may be subjected to a plating treatment as necessary.

[0203] The plating metal species can be appropriately selected in accordance with the uses. Examples thereof comprise gold plating, silver plating, copper plating, nickel plating, chromium plating, and alloy plating of various metals. When alloy plating is performed, the composition of plating can also be appropriately adjusted in accordance with the uses.

[0204] As a plating method, a known method can be used. Examples thereof comprise dry plating such as physical vapor deposition plating and chemical vapor deposition plating, and wet plating such as displacement plating, electroplating, and electroless plating.

[0205] Specific examples of the above-mentioned base materials comprise: a semiconductor substrate such as a silicon substrate; a metal substrate such as a copper substrate; a lead frame; a ceramic substrate attached with a metal plate (for example, Direct Bonded Copper: DBC); a substrate for mounting a semiconductor element such as an LED (Light-Emitting Diode) package; a power supply component such as a copper ribbon, a metal block, and a terminal; a heat dissipation plate; and a water cooling plate.

[0206] The bonding method using the bonding material of the present invention is a method in which a bonding material is provided on a base material, a material to be bonded is placed on a side of the bonding material opposite to the base material to obtain a laminate, and the laminate is heated to bond the base material and the material to be bonded. However, the bonding method using the bonding material of the present invention is not limited to the above-mentioned bonding method as long as the object of the present invention can be achieved.

[0207] Examples of methods for applying the bonding material to the base material comprise screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, jet printing, a dispenser, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0208] The base material applied by the bonding material may be dried as necessary. The drying conditions can be appropriately set. By drying the above-mentioned base material before sintering, suppression in the flow of the bonding material and generation of voids during sintering can be more preferably achieved.

[0209] As the above-mentioned drying conditions, for example, the drying atmosphere may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere. The pressure during drying may be atmospheric pressure or reduced pressure. The drying temperature is not particularly limited as long as the composite copper particles that the bonding material comprises are not sintered.

[0210] The copper paste and the bonding material of the present invention can be preferably used in a pressureless bonding method because a sintered body that achieves a high bonding strength by only sintering through heating can be obtained. Of course, the copper paste and the bonding material of the present invention can also be preferably used in a pressure bonding method.

[0211] In the present application, the "pressureless bonding method" refers to a method in which a laminate obtained by disposing a bonding material between a base material and a material to be bonded is prepared, and the above-mentioned laminate is heated in a state where the bonding material and the material to be bonded are disposed in a direction where the weight of the base material acts or in a state where a load of 0.01 MPa or less is applied.

[0212] In the present application, the "pressure bonding method" refers to a method in which a laminate obtained by disposing a bonding material between a base material and a material to be bonded is prepared, and the above-mentioned laminate is heated in a state where a load of more than 0.01 MPa is applied.

[0213] The heating atmosphere for the laminate in the above-mentioned pressureless bonding method or the above-mentioned pressure bonding method may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but is more preferably an inert atmosphere from the viewpoint that an increase in size of the production equipment for the sintered body can be more effectively avoided.

[0214] The laminate in the above-mentioned pressureless bonding method may be preheated before being completely sintered. The preheating temperature is preferably 150°C or lower, more preferably 140°C or lower. The preheating temperature is more preferably 130°C or lower from the viewpoint of the volatilization speed of the solvent. In addition, by setting the heating rate applied to the laminate to 10°C / min or less, the need for preheating can also be eliminated. The copper particles may be sintered during the preheating, but may not be sintered. The preheating conditions may be appropriately set in accordance with the desired bonding properties.

[0215] The heating temperature of the laminate in the above-mentioned pressureless bonding method or the above-mentioned pressure bonding method is preferably 100°C or higher and 400°C or lower, and more preferably 150°C or higher and 300°C or lower. When the sintering temperature is 300°C or lower, it can be said that the bonding material of the present invention can be sintered at a sufficiently low temperature.

[0216] The heating time of the laminate in the above-mentioned pressureless bonding method is preferably 1 minute or more and 120 minutes or less from the viewpoint of sufficiently volatilizing the solvent that the bonding material comprises and sufficiently promoting the sintering of the composite copper particles that the bonding material comprises. The heating time of the laminate in the above-mentioned pressure bonding method is preferably 1 minute or more and 60 minutes or less.

[0217] The bonding strength of the sintered body obtained by the pressureless bonding method or the pressure bonding method is measured in accordance with the method described in the Examples mentioned later.

[0218] The bonding strength of the sintered body obtained by the pressureless bonding method is preferably 20 MPa or more, more preferably 25 MPa or more, and still more preferably 27 MPa or more. A sintered body having such a bonding strength can be determined to be sufficiently bonded, and it can be confirmed that the bonding material of the present invention can be preferably used for a pressureless bonding paste. As mentioned above, the atmosphere during pressureless bonding is preferably an inert atmosphere, but a sintered body obtained by pressureless bonding in another atmosphere (for example, a reducing atmosphere) can be determined to be sufficiently bonded if the bonding strength of the sintered body is also within the above-mentioned range.

[0219] Also, the bonding strength of the sintered body obtained by the pressure bonding method is preferably 20 MPa or more, more preferably 25 MPa or more, and still more preferably 27 MPa or more. A sintered body having such a bonding strength can be determined to be sufficiently bonded, and it can also be determined that the bonding material of the present invention can be preferably used for a pressure bonding paste.<Conductive material>

[0220] The composite copper particles of the present invention or the copper paste comprising the composite copper particles of the present invention can be used as a conductive material. For example, the composite copper particles of the present invention may be used as a conductive material as they are, or may be used as a conductive material after the composite copper particles are formed into a copper paste. Specifically, the above-mentioned copper paste can be used as a material of a conductor such as a conductive film, an electrode, or a wiring line.

[0221] When the copper paste of the present invention is used as a material for a conductive film, an electrode, or a wiring line, the copper paste can be used by being applied on a base material. Examples of methods for applying the above-mentioned paste comprise screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, inkjet printing, soft lithography, a dispenser, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0222] When the above-mentioned copper paste is used as the above-mentioned conductive material, the concentration of the above-mentioned composite copper particles that the above-mentioned copper paste comprises may be appropriately adjusted in accordance with the above-mentioned applying methods.

[0223] The thickness of the above-mentioned applied layer is not particularly limited, and is preferably 0.1 µm or more and 100 µm or less. The application pattern at this time can be applied on the entire surface of the base material, as well as can be applied in the form of a pattern or a design. The above-mentioned applied layer may appropriately comprise an additive in accordance with the applying methods, intended purposes, and uses. Examples of the additives comprise the above-mentioned various additives.

[0224] Specific examples of the above-mentioned base materials comprise a semiconductor substrate such as a silicon substrate, a metal substrate such as a copper substrate, a lead frame, a ceramic substrate attached with a metal plate (for example, Direct Bonded Copper: DBC), a substrate for mounting a semiconductor element such as an LED (Light-Emitting Diode) package, a power supply component such as a copper ribbon, a metal block, and a terminal, a heat dissipation plate, a water cooling plate, and glass. In addition, an organic material such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polypropylene, polycarbonate, an acrylic resin such as polymethyl methacrylate, a vinyl chloride-based resin such as polyvinyl chloride or a vinyl chloride copolymer, an epoxy resin, polyarylate, polysulfone, polyether sulfone, polyimide, a fluororesin, a phenoxy resin, a polyolefin resin, nylon, a styrene-based resin, or an ABS resin may be used. Depending on the uses, appropriate selection from these materials can be made to form a film-like flexible base material or rigid base material. The size of the base material is not limited, and the shape may be any shape such as a disk shape, a card shape, or a sheet shape, and the surface of the base material does not need to be flat and may have a shape having irregularities or a curved surface.<Conductor>

[0225] The conductor of the present invention comprises the above-mentioned conductive material. In addition, the conductor may be obtained by heating the above-mentioned conductive material. The above-mentioned conductor preferably has a low volume resistivity (which is also referred to as "electrical resistivity" in the present application). For example, the volume resistivity (electrical resistivity) is 100 µΩ·cm or less, and preferably 50 µΩ·cm or less. Within such a range, the conductor of the present invention can be used for practical use (for example, a conductive film, an electrode, and a wiring line). The volume resistivity of the above-mentioned conductor is measured by the method described in the Examples mentioned later.

[0226] The above-mentioned heating method is not particularly limited. Examples of the above-mentioned heating methods comprise resistance heating, electron beam heating, laser light heating, flash light heating, plasma heating, dielectric heating, induction heating, and heating by means of a heat source such as a burner.

[0227] The above-mentioned heating temperature may be appropriately adjusted in accordance with the above-mentioned base material. For example, when a semiconductor substrate such as a silicon substrate, a metal substrate such as a copper substrate, polyimide, or glass is used as a substrate, the heating temperature can be set to 300°C or lower. When PET or PEN is used as a substrate, the heating temperature can be set to 150°C or lower.

[0228] The above-mentioned heating atmosphere may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but an inert atmosphere is more preferable from the viewpoint that an increase in size of the production equipment can be more effectively avoided.

[0229] It is sufficient that the above-mentioned heating time is 1 minute or more and 60 minutes or less.EXAMPLES

[0230] The present invention will be described in detail with reference to the Examples and the Comparative Examples, but the present invention is not limited thereto.(Measurement of average particle diameter of copper particles)

[0231] Copper particles produced in a production example were photographed by means of a scanning electron microscope (S4800 manufactured by Hitachi High-Technologies Corporation) set at a magnification of 50,000 times, and a scanning electron micrograph was taken. With respect to 50 primary particle diameters in the above-mentioned scanning electron micrograph, the Feret diameters were measured, and the arithmetic average value thereof was calculated as the average particle diameter.(Thermal decomposition properties of polymer dispersant)

[0232] The thermal decomposition properties of the polymer dispersants used in examples and comparative examples of the present application were measured by means of a thermogravimetric differential thermal analyzer (TG-DTA 8122 manufactured by Rigaku Corporation) under the following conditions. The mass loss rate was calculated from the mass difference between 30°C and 250°C.∘ Measurement conditions

[0233] Measurement atmosphere: in the atmosphere Atmospheric flow rate: 100 mL / min Measurement temperature range: 25°C to 1000°C heating rate: 10°C / min (Measurement of weight average molecular weight of polymer dispersant)

[0234] The weight average molecular weights of the polymer dispersants used in the Examples and the Comparative Examples of the present application were measured by means of gel permeation chromatography (HLC-8420GPC manufactured by Tosoh Corporation) under the following conditions. EcoSEC Elite, which is a dedicated software, was used for control of the apparatus, data collection, calculation, and report generation.∘ Measurement conditions

[0235] Sample concentration: 1 mg / mL (a solution obtained by dissolving 5 mg of the polymer dispersant in 5 mL of tetrahydrofuran, followed by filtration through a membrane filter was adjusted to the concentration of 1 mg / mL) Sample injection amount: 10 µL Column: TSKgel Super HZM-M (manufactured by Tosoh Corporation, base material: styrene divinylbenzene, particle diameter: 3 µm and 5 µm, column size: inner diameter 4.6 mm × 15 cm × 2 columns) Column temperature: 40°C Detector: differential refractometer (RI detector) Solvent: tetrahydrofuran (THF) Flow rate: 0.35 mL / min

[0236] The analysis results of the above-mentioned polymer dispersants are shown in Table 1. In addition, the acid values and the amine values of the polymer dispersants are also shown together. The active ingredient content of each polymer dispersant was 100%. [Table 1]DispersantAcid value / Amine value (mgKOH / g)Mass loss rate (%)Peak temperature (°C)Weight average molecular weight (Mw)BYK-LP C 2212485 / -53.4294.2553BYK-LP C 22146- / 4812.4294.33078BYK-LP C 22435- / -44.1343.611502BYK-LP C 2436589 / -95.3223.9918*In the table, "-" indicates zero. (Production Example 1)

[0237] A 10 L four-neck glass flask was placed in an oil bath, 2 L of 1-propanol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, 637.6 g of copper(II) oxide (N-300 manufactured by Nisshin Chemco Ltd.), 96.0 g of acetic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 82.7 g of capric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added thereto, followed by stirring at room temperature under conditions of a rotation speed of 250 rpm. In the subsequent steps as well, stirring was performed at a constant rotation speed.

[0238] Furthermore, 127.0 g of 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added thereto over 10 minutes, and stirring was continued to produce a mixed solution comprising a copper compound.

[0239] The mixed solution comprising the above-mentioned copper compound was heated in an oil bath to a solution temperature of 50°C, and 80 g of 60% hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Company, Inc.) as a reducing agent was added dropwise thereto over 3 minutes and 45 seconds, followed by stirring for 40 minutes. Next, a "step of adding 80 g of 60% hydrazine hydrate dropwise over 3 minutes and 45 seconds, and performing stirring for 15 minutes" was repeated three times (that is, in this step, 240 g of 60% hydrazine hydrate was added in total). Thereto, 680 g of 60% hydrazine hydrate was added dropwise over 30 minutes. In this step, the total amount of the reducing agent added was 1000 g, and the time required for addition was 130 minutes. Also, the set temperature of the oil bath while the reducing agent was added was 50°C.

[0240] After the total amount of the reducing agent was added, the above-mentioned mixed solution was heated to 90°C and stirred for 2 hours to obtain a dispersion solution comprising copper particles.

[0241] The above-mentioned dispersion solution comprising copper particles was naturally cooled to 50°C or lower while being stirred, and allowed to stand for 30 minutes, and then 30 g of a solid content was weighed out by a solid-liquid separation operation and collected.

[0242] As a washing step, the above-mentioned solid content and 75 mL of 2-propanol (manufactured by NACALAI TESQUE, INC.) were stirred at 2000 rpm for 10 minutes by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation). Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge (Allegra X-30R manufactured by Beckman Coulter, Inc.) to obtain a solid content.

[0243] The above-mentioned washing step was performed again to obtain carboxylic acid-coated copper particles of Production Example 1. The carboxylic acid-coated copper particles of Production Example 1 had an average particle diameter of 297 nm.(Example 1)

[0244] Caprylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymer dispersant (BYK-LP C 24365), and 2-propanol (manufactured by NACALAI TESQUE, INC.) were mixed to prepare 75 mL of a treatment solution. Here, in the above-mentioned treatment solution, the amount of caprylic acid was 6 mass%, and the amount of BYK-LP C 24365 was 2 mass%.

[0245] The carboxylic acid-coated copper particles obtained in Production Example 1 and the above-mentioned treatment solution were mixed, followed by stirring by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation) under conditions of 2000 rpm for 10 minutes.

[0246] Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge, and a solid content was collected.

[0247] The collected solid content was allowed to stand in a desiccator, and the inside of the desiccator was depressurized by means of a vacuum pump (G-20DA manufactured by ULVAC, Inc.). The inside of the desiccator was adjusted to 1.3 Pa and 25°C, and vacuum drying was performed for 300 minutes to obtain composite copper particles of Example 1.(Example 2)

[0248] Composite copper particles of Example 2 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 12 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 4 mass%.(Example 3)

[0249] Composite copper particles of Example 3 were obtained in the same manner as in Example 1 except that the amount of BYK-LP C 24365 used in Example 1was changed from 2 mass% to 0.5 mass%.(Example 4)

[0250] Composite copper particles of Example 4 were obtained in the same manner as in Example 1 except that caprylic acid (in which the number of the carbon atoms is 8) used in Example 1 was changed to capric acid (in which the number of the carbon atoms is 10).(Comparative Example 1)

[0251] Copper particles of Comparative Example 1 were obtained in the same manner as in Example 1 except for the absence of BYK-LP C 24365 used in Example 1.(Comparative Example 2)

[0252] Copper particles of Comparative Example 2 were obtained in the same manner as in Example 1 except for the absence of caprylic acid used in Example 1.(Comparative Example 3)

[0253] Copper particles of Comparative Example 3 were obtained in the same manner as in Example 1 except that BYK-LP C 24365 used in Example 1was changed to BYK-LP C 22124.(Comparative Example 4)

[0254] Copper particles of Comparative Example 4 were obtained in the same manner as in Example 1 except that BYK-LP C 24365 used in Example 1 was changed to BYK-LP C 22146.(Comparative Example 5)

[0255] Copper particles of Comparative Example 5 were obtained in the same manner as in Example 1 except that BYK-LP C 24365 used in Example 1 was changed to BYK-LP C 22435.(Comparative Example 6)

[0256] Copper particles of Comparative Example 6 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 30 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 10 mass%.(Comparative Example 7)

[0257] Copper particles of Comparative Example 7 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 0.6 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 0.2 mass%.(Production Example 2)

[0258] A 10 L four-neck glass flask was placed in an oil bath, 1 L of ethyl carbitol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, 159.1 g of copper(II) oxide (manufactured by Nisshin Chemco Ltd.), and 13.9 g of hexanoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) were added thereto, followed by stirring at room temperature under conditions of a rotation speed of 200 rpm to produce a mixed solution comprising a copper compound.

[0259] The above-mentioned mixed solution comprising a copper compound was heated up to a solution temperature of 90°C, and when the solution temperature reached 90°C, 200 g of hydrazine monohydrate (manufactured by NACALAI TESQUE, INC.) as a reducing agent was added to the mixed solution within 30 seconds.

[0260] After the reducing agent was added, the above-mentioned mixed solution was stirred at 90°C for 20 minutes to obtain a dispersion solution comprising copper particles.

[0261] The above-mentioned dispersion solution comprising copper particles was naturally cooled up to 50°C or lower, and allowed to stand for 30 minutes, and then 30 g of a solid content was weighed out by a solid-liquid separation operation and collected.

[0262] As a washing step, the above-mentioned solid content and 75 mL of 2-propanol (manufactured by NACALAI TESQUE, INC.) were stirred at 2000 rpm for 10 minutes by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation). Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge (Allegra X-30R manufactured by Beckman Coulter, Inc.) to obtain a solid content.

[0263] The above-mentioned washing step was performed again to obtain carboxylic acid-coated copper particles of Production Example 2. The carboxylic acid-coated copper particles of Production Example 2 had an average particle diameter of 80 nm.(Comparative Example 8)

[0264] Copper particles of Comparative Example 8 were obtained in the same manner as in Example 1 except that the carboxylic acid-coated copper particles obtained in Production Example 2 were used instead of the carboxylic acid-coated copper particles used in Example 1.(Measurement of crystalline states of composite copper particles and copper particles before and after atmospheric exposure)

[0265] X-ray diffraction patterns of the composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 before and after atmospheric exposure were measured by means of an X-ray diffraction (XRD) apparatus (SmartLab SE manufactured by Rigaku Corporation) under the following conditions. From the obtained diffraction patterns, the oxidation state before and after atmospheric exposure was confirmed. SmartLab Studio II, which is a dedicated software, was used for control of the apparatus, data collection, calculation, and report generation.

[0266] FIG. 1 shows X-ray diffraction patterns of the composite copper particles of Example 1 before and after atmospheric exposure. From FIG. 1, only peaks derived from metallic copper were observed both before and after atmospheric exposure. Here, the Cu(111) plane is observed at around 2θ = 43.3°, and the Cu(200) plane is observed at around 2θ = 50.4°.∘ Measurement conditions

[0267] Tube: CuKα Tube voltage: 40 kV Tube current: 40 mA Measurement range: 30° to 70° Step: 0.01° Speed: 5° / min (Observation of lattice fringes of composite copper particles and copper particles before and after atmospheric exposure)

[0268] The composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 before and after atmospheric exposure were observed by means of a transmission electron microscope (TEM (H-9000 manufactured by Hitachi High-Tech Corporation)), and the oxidation state of copper was confirmed from the atomic arrangement (lattice fringes) in the crystal. Here, the lattice spacing of the metal copper (111) plane is 2.1Å (0.21 nm).

[0269] A TEM photograph of the composite copper particles of Example 1 before atmospheric exposure is shown in FIG. 2, and a TEM photograph of the composite copper particles of Example 1 after atmospheric exposure is shown in FIG. 3. Also in the TEM photographs before and after atmospheric exposure, only a lattice spacing of 0.21 nm derived from the metal copper (111) plane was observed on the surfaces of the copper particles, and oxidation of copper was not observed. For reference, an SEM photograph of the composite copper particles of Example 1 before atmospheric exposure is also shown in FIG. 4.(Measurement of amount of organic component)

[0270] The individual mass losses of the composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 were measured by means of a thermogravimetric differential thermal analyzer (TG-DTA 8122 manufactured by Rigaku Corporation) under the following conditions. In the obtained profile, the mass loss rate in the temperature range from 30°C to 200°C was defined as the mass of the carboxylic acid, the mass loss rate in the temperature range from 200°C to 350°C was defined as the mass of the polymer dispersant, and the mass loss rate in the temperature range from 30°C to 350°C was defined as the mass of the organic component treated on the copper particles.

[0271] From this result, the mass of the carboxylic acid (caprylic acid or capric acid) that the composite copper particles and the copper particles comprise, and the ratio of the carboxylic acid to the polymer dispersant are shown in Table 2.∘ Measurement conditions

[0272] Measurement atmosphere: nitrogen (purity: 99.995%) Atmospheric flow rate: 500 mL / min Measurement temperature range: 30°C to 500°C heating rate: 10°C / min [Table 2] Composition of treatment solutionMass of carboxylic acid (mass%)Mass of polymer dispersant (mass%)Mass of organic component (mass%)Carboxylic acid / Polymer dispersantExample 1Caprylic acid: 6 mass%0.730.281.012.61BYK-LP C 24365: 2 mass%Example 2Caprylic acid: 12 mass%1.140.381.523.00BYK-LP C 24365: 4 mass%Example 3Caprylic acid: 6 mass%0.960.191.155.05BYK-LP C 24365: 0.5 mass%Example 4Capric acid: 6 mass%1.000.371.372.70BYK-LP C 24365: 2 mass% [Table 3] Composition of treatment solutionMass of carboxylic acid (mass%)Mass of polymer dispersant (mass%)Mass of organic component (mass%)Carboxylic acid / Polymer dispersantComparative Example 1Caprylic acid: 6 mass%0.49-0.50-No polymer dispersantComparative Example 2No carboxylic acid-0.380.38-BYK-LP C 24365: 2 mass%Comparative Example 3Caprylic acid: 6 mass%0.720.210.933.30BYK-LP C 22124: 2 mass%Comparative Example 4Caprylic acid: 6 mass%0.500.240.742.08BYK-LP C 22146: 2 mass%Comparative Example 5Caprylic acid: 6 mass%0.550.220.772.50BYK-LP C 22435: 2 mass%Comparative Example 6Caprylic acid: 30 mass%5.621.547.163.65BYK-LP C 24365: 10 mass%Comparative Example 7Caprylic acid: 0.6 mass%0.110.110.221.00BYK-LP C 24365: 0.2 mass%Comparative Example 8Caprylic acid: 6 mass%0.730.891.620.82BYK-LP C 24365: 2 mass% (Production of copper paste)

[0273] As the proportion of the entire copper paste, 92.5 mass% of any of the following: the composite copper particles of Examples 1 to 4, the copper particles of Comparative Example 1 and Comparative Examples 3 to 7; 3.6 mass% of dipropylene glycol; 3.6 mass% of hexyl carbitol; and 0.3 mass% of triethanolamine were blended and then kneaded at 2000 rpm for 4 minutes by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation).

[0274] Thereafter, defoaming was performed at 2200 rpm for 2 minutes to obtain copper pastes of Samples 1 to 4 and 6 to 9 and Samples 12 to 13.

[0275] The paste comprising the copper particles of Comparative Example 8 prepared by the above-mentioned method did not have an applicable viscosity and could not be evaluated (not shown in the table).

[0276] A copper paste of Sample 5 was obtained in the same manner as in the above-mentioned production of copper paste except that the paste was formulated such that 92.5 mass% of the copper particles of Example 1, 3.75 mass% of dipropylene glycol, and 3.75 mass% of hexyl carbitol were blended.

[0277] A copper paste of Sample 10 was obtained in the same manner as in the above-mentioned production of copper paste except that the paste was formulated such that 92.5 mass% of the copper particles of Comparative Example 1, 3.5 mass% of dipropylene glycol, 3.5 mass% of hexyl carbitol, 0.3 mass% of triethanolamine, and 0.2 mass% of BYK-LP C 24365 were blended.

[0278] A copper paste of Sample 11 was obtained in the same manner as in the above-mentioned production of copper paste except that the paste was formulated such that 92.5 mass% of the copper particles of Comparative Example 2, 3.35 mass% of dipropylene glycol, 3.35 mass% of hexyl carbitol, 0.3 mass% of triethanolamine, and 0.5 mass% of caprylic acid were blended.

[0279] In addition, a copper paste was produced in the same manner as in the above-mentioned production of copper paste except that the composite copper particles or the copper particles were exposed in the atmosphere (temperature: 28°C, humidity: 60%) for 1 hour, and changes in bonding strength and electrical resistivity due to atmospheric exposure were confirmed.

[0280] When the copper particles of Comparative Example 8 were exposed in the atmosphere (temperature: 28°C, humidity: 60%) for 1 hour, heat generation due to oxidation and smoke generation occurred, and therefore a paste could not be produced (not shown in the table). [Table 4]Copper paste composition (wt%)(Composite) copper particlesDPG 1HC 2TEA 324365 4CA 5Sample 1Example 192.53.63.60.300Sample 2Example 292.53.63.60.300Sample 3Example 392.53.63.60.300Sample 4Example 492.53.63.60.300Sample 5Example 192.53.753.75000Sample 6Comparative Example 192.53.63.60.300Sample 7Comparative Example 392.53.63.60.300Sample 8Comparative Example 492.53.63.60.300Sample 9Comparative Example 592.53.63.60.300Sample 10Comparative Example 192.53.53.50.30.20Sample 11Comparative Example 292.53.353.350.300.5Sample 12Comparative Example 692.53.63.60.300Sample 13Comparative Example 792.53.63.60.3001: DPG ··· dipropylene glycol 2: HC ··· hexyl carbitol 3: TEA ··· triethanolamine 4: 24365 ··· BYK-LP C 24365 5: CA ··· caprylic acid (Production of sintered body)

[0281] On a base material having a diameter (which is referred to as Φ hereinafter) of 10 mm, a thickness of 5 mm, and a surface roughness (Ra: arithmetic average roughness) of 0.1 to 0.2 µm, a metal mask having an opening Φ of 5 mm and a thickness of 0.1 mm was placed, and a copper paste obtained by the above-mentioned procedure was applied as a bonding material to the opening.

[0282] The metal mask was removed, and a copper piece (tough pitch copper, alloy number C1100) having a diameter of 5 mm, a thickness of 5 mm, and a surface roughness (Ra: arithmetic average roughness) of 0.1 µm to 0.2 µm was allowed to stand at the portion to which the bonding material was applied to obtain a laminate. The above-mentioned surface roughness was determined as the average value of Ra measured with a laser microscope for 3 test pieces randomly taken out among 100 test pieces.

[0283] The above-mentioned laminate was set in a jig having a space of 10.5 mm on 3 sides, nitrogen (purity 99.995%) was allowed to flow at 100 mL / min, and the above-mentioned laminate was allowed to stand on a hot plate heated to 200°C and held for 30 minutes. Thereafter, the resultant was naturally cooled to 50°C to obtain a sintered body.(Measurement of bonding strength)

[0284] The above-mentioned sintered body was set in a strength tester (JSL-1KN manufactured by Japan Instrumentation System Co., Ltd.), a shearing force was applied in a direction parallel to the bonding surface under conditions of 1 mm / sec from the base material side, and the bonding strength was calculated from the load applied at the time when the base material and the copper piece were peeled off.(Production of conductive film)

[0285] The copper paste obtained by the above-mentioned procedure was coated with an applicator on a polyimide film having a thickness of 100 µm as a base material.

[0286] The base material coated with the copper paste was placed in a tubular furnace (JTEKT Thermo Systems Co., Ltd., KTF-035N1).

[0287] Nitrogen (purity: 99.995%) was allowed to flow in the tubular furnace at 100 mL / min, and the temperature was raised from 25°C to 150°C at a heating rate of 5°C / min, and held for 60 minutes. Thereafter, the resultant was naturally cooled to 50°C to obtain a conductive film.(Measurement of conductivity)

[0288] The surface resistivity of the above-mentioned conductive film was measured by means of a low resistivity meter (Loresta-GX MCP-T700 manufactured by Nitto Seiko Analytech Co., Ltd.).

[0289] Thereafter, the film thickness of the conductive film was measured by means of a film thickness meter (Mitutoyo Corporation, ID-C112X), and the volume resistivity (electrical resistivity) was calculated by multiplying the surface resistivity by the film thickness.

[0290] The bonding strength of the sintered body and the volume resistivity of the conductive film measured by the above-mentioned methods are shown in Table 5. [Table 5]Paste(Composite) copper particlesBonding strength (MPa)Volume resistivity (electrical resistivity) (µΩ·cm)Without atmospheric exposureWith atmospheric exposureWithout atmospheric exposureWith atmospheric exposureSample 1Example 145.651.010.417.0Sample 2Example 250.226.919.028.4Sample 3Example 344.551.010.114.0Sample 4Example 443.351.011.114.1Sample 5Example 128.324.29.910.6Sample 6Comparative Example 145.110.217.222.7Sample 7Comparative Example 37.70.026.074.7Sample 8Comparative Example 434.07.447.427.4Sample 9Comparative Example 526.710.829.740.6Sample 10Comparative Example 125.610.713.616.3Sample 11Comparative Example 27.85.131.434.1Sample 12Comparative Example 632.418.652.8×10 7< 14.5×10 7< Sample 13Comparative Example 749.82.112.617.6

[0291] Samples 1 to 5 comprising the composite copper particles of the present invention had a sufficient bonding strength (20 MPa or more) before and after atmospheric exposure. Also, Samples 1 to 5 have an electrical resistivity on the order of micro-ohms both before and after atmospheric exposure, which is below 100 µΩ·cm, and therefore can be used for conductive uses; furthermore, since the value is further below 50 µΩ·cm, they can be more preferably used for conductive uses.

[0292] In Sample 6 in which the copper particles of Comparative Example 1 (copper particles produced by means of the treatment solution not comprising a polymer dispersant) were used, the bonding strength after atmospheric exposure was 10.2 MPa, and a desired bonding strength was not obtained.

[0293] In Sample 10 in which the copper particles of Comparative Example 1 were similarly used and a polymer dispersant was added during production of the paste, the bonding strength after atmospheric exposure was 10.7 MPa, and a desired bonding strength was not obtained.

[0294] This indicates that for preferred uses in bonding uses even after atmospheric exposure, it is necessary for the composite copper particles to comprise a polymer dispersant, and moreover, it is understood that the polymer dispersant needs to be treated on the copper particles in the copper particle production process rather than during paste production.

[0295] In Sample 11 in which a carboxylic acid (caprylic acid) was added during production of the paste using the copper particles of Comparative Example 2 (copper particles produced using the treatment solution not comprising a carboxylic acid), a sufficient bonding strength was not obtained either before or after atmospheric exposure.

[0296] It is understood that the copper particles of Comparative Example 2 were treated with the polymer dispersant, but the treatment solution did not comprise a carboxylic acid, and therefore the sinterability was reduced. In addition, it has been found that a sufficient bonding strength cannot be obtained only by treating copper particles with a polymer dispersant, and therefore the copper particles cannot be used for bonding uses after atmospheric exposure.

[0297] In Sample 7 in which the copper particles of Comparative Example 3 (copper particles treated with the polymer dispersant having an acid value of 60 mgKOH / g or more and a mass loss rate of less than 70%) were used, the bonding strength was reduced from 7.7 MPa to 0 MPa by atmospheric exposure.

[0298] It is understood that since the polymer dispersant treated on the copper particles of Comparative Example 3 had a small mass loss rate at 250°C (specifically, mass loss rate = 53.4%), Sample 7 had a low bonding strength before atmospheric exposure.

[0299] In addition, it is understood that since the polymer dispersant treated on the copper particles of Comparative Example 3 had a small weight average molecular weight (weight average molecular weight = 553) and a bonding strength of 0 MPa after atmospheric exposure, the organic component treated on the copper particles was desorbed by atmospheric exposure, and oxidation of copper occurs.

[0300] In Sample 8 in which the copper particles of Comparative Example 4 (copper particles treated with the polymer dispersant having an amine value, no acid value, and a mass loss rate of less than 70%) were used, the bonding strength significantly decreased from 34.0 MPa to 7.4 MPa (decreased by about 78%) by atmospheric exposure. Therefore, it has been found that the influence on performance deterioration due to atmospheric exposure is very large.

[0301] In Sample 9 in which the copper particles of Comparative Example 5 (copper particles having no acid value or amine value and having a mass loss rate of the polymer dispersant of less than 70%) were used, the bonding strength after atmospheric exposure was 10.8 MPa, and a desired bonding strength was not obtained.

[0302] In Sample 12 in which the copper particles of Comparative Example 6 (copper particles having an excessive content of the organic component) were used, the amount of the organic component treated on the copper particles was 7.16 mass%, the bonding strength after atmospheric exposure was 18.6 MPa, and a desired bonding strength was not obtained.

[0303] In Sample 13 in which the copper particles of Comparative Example 7 (copper particles having an insufficient content of the organic component) were used, the amount of the organic component treated on the copper particles was 0.22 mass%, and the bonding strength after atmospheric exposure significantly decreased to 2.1 MPa.INDUSTRIAL APPLICABILITY

[0304] The composite copper particles of the present invention can be preferably used for bonding uses (for example, a bonding material) not only before atmospheric exposure but also after atmospheric exposure. Furthermore, since the electrical resistivity is small, the composite copper particles can also be used for conductive uses (for example, a conductive material). In addition, the bonding material comprising the composite copper particles of the present invention can provide a sintered body having a sufficient bonding strength even under conditions of the pressureless bonding method. In producing the composite copper particles of the present invention, the composite copper particles can be easily produced without any limitation on the production process.

Examples

production example 1

(Production Example 1)

[0237]A 10 L four-neck glass flask was placed in an oil bath, 2 L of 1-propanol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, 637.6 g of copper(II) oxide (N-300 manufactured by Nisshin Chemco Ltd.), 96.0 g of acetic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 82.7 g of capric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added thereto, followed by stirring at room temperature under conditions of a rotation speed of 250 rpm. In the subsequent steps as well, stirring was performed at a constant rotation speed.

[0238]Furthermore, 127.0 g of 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added thereto over 10 minutes, and stirring was continued to produce a mixed solution comprising a copper compound.

[0239]The mixed solution comprising the above-mentioned copper compound was heated in an oil bath to a solution temperature of 50°C, and 80 g of 60% hydrazine hydrate (manufactured by Mit...

example 1

(Example 1)

[0244]Caprylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymer dispersant (BYK-LP C 24365), and 2-propanol (manufactured by NACALAI TESQUE, INC.) were mixed to prepare 75 mL of a treatment solution. Here, in the above-mentioned treatment solution, the amount of caprylic acid was 6 mass%, and the amount of BYK-LP C 24365 was 2 mass%.

[0245]The carboxylic acid-coated copper particles obtained in Production Example 1 and the above-mentioned treatment solution were mixed, followed by stirring by means of a mixer (Awatori Rentaro AR-250 manufactured by Thinky Corporation) under conditions of 2000 rpm for 10 minutes.

[0246]Thereafter, solid-liquid separation was performed at a centrifugal force of 400G for 5 minutes by means of a centrifuge, and a solid content was collected.

[0247]The collected solid content was allowed to stand in a desiccator, and the inside of the desiccator was depressurized by means of a vacuum pump (G-20DA manufactured by ULVAC, In...

example 2

(Example 2)

[0248]Composite copper particles of Example 2 were obtained in the same manner as in Example 1 except that the amount of caprylic acid used in Example 1 was changed from 6 mass% to 12 mass% and the amount of BYK-LP C 24365 used in Example 1 was changed from 2 mass% to 4 mass%.

Claims

1. Composite copper particles comprising copper particles and an organic component, wherein the composite copper particles have a value of 100 nm or more and 600 nm or less as an average particle diameter measured by means of a scanning electron microscope, the organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, wherein a content of the organic component is 0.3 mass% or more and 6.0 mass% or less based on a total mass of the composite copper particles, and the polymer dispersant has an acid value of 60 mgKOH / g or more, and a mass loss rate in an atmosphere is 70% or more when the temperature is raised from 30°C to 250°C under conditions of a heating rate of 10°C / min by means of a thermogravimetric differential thermal analyzer.

2. The composite copper particles according to claim 1, wherein the polymer dispersant has a temperature of 300°C or lower as a temperature of an exothermic peak of the polymer dispersant measured by means of a thermogravimetric differential thermal analyzer.

3. The composite copper particles according to claim 1 or 2, wherein the carboxylic acid or the salt thereof has 2 or more and 20 or less carbon atoms.

4. The composite copper particles according to claim 1 or 2, wherein the organic component has a value of 1.0 or more and 12.0 or less as a mass ratio of the carboxylic acid or the salt thereof to the polymer dispersant.

5. The composite copper particles according to claim 1 or 2, wherein surfaces of the copper particles are coated with the carboxylic acid or the salt thereof.

6. A copper paste comprising the composite copper particles according to claim 1 and a paste solvent.

7. A bonding material comprising composite copper particles or a copper paste, wherein the composite copper particles are the composite copper particles according to claim 1, and the copper paste comprises the composite copper particles according to claim 1 and a paste solvent.

8. A conductive material comprising composite copper particles or a copper paste, wherein the composite copper particles are the composite copper particles according to claim 1, and the copper paste comprises the composite copper particles according to claim 1 and a paste solvent.

9. A sintered body comprising the bonding material according to claim 7 as a raw material.

10. A conductor comprising the conductive material according to claim 8.

11. A method for producing composite copper particles, the method comprising a step of mixing carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent.

12. The method according to claim 11 comprising a step of mixing the carboxylic acid-coated copper particles with a treatment solution comprising the carboxylic acid or the salt thereof, the polymer dispersant, and the solvent.

13. The method according to claim 11 or 12 comprising a step of mixing the carboxylic acid-coated copper particles with the treatment solution comprising the carboxylic acid or the salt thereof, the polymer dispersant, and the solvent, followed by drying.

Images