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

Composite copper particles, their manufacturing method, and uses

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

[0002] When manufacturing a power semiconductor product substrate by joining a semiconductor element to a base material such as a lead frame, a joining material with high thermal conductivity is used. Among various joining materials, copper is preferably used for joining semiconductor elements because it is cheaper than silver and is less susceptible to ion migration.

[0003] In addition to the above-mentioned bonding applications, copper has high electrical conductivity and is therefore also suitable for use as a conductive material in inks for printed electronics.

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

[0005] Patent Document 2 describes a copper nanoparticle dispersion having a volume average particle size of 500 nm or less, which is obtained by combining copper nanoparticles with a carboxylic acid, an alkylamine, and a polymer dispersant having a specific amine value or acid value.

[0006] JP 2009-74171 A JP 2015-210973 A

[0007] The present inventors have confirmed that in a bonding member using conventional copper particles, the bonding performance of the copper particles deteriorates when the copper particles are exposed to the atmosphere, making the bonding member unusable. Furthermore, phenomena observed when copper particles are exposed to the atmosphere include heat generation from the copper particles and elution of copper ions during dispersion production, and there is concern that the copper of conventional copper particles may be oxidized when exposed to the atmosphere.

[0008] When copper particles are used as bonding members, conductive materials, etc., they are processed into a form suitable for the intended use, such as a paste or dispersion. There is concern that exposure of the copper particles to the atmosphere may result in a deterioration in the performance of the copper particles, such as bonding properties and conductive properties. On the other hand, it is difficult to completely avoid oxidation of the copper particles in the processes from production to processing. For these reasons, there is a need for the development of copper particles that can be used for various applications even after exposure to the atmosphere.

[0009] Patent Document 1 discloses metal colloid particles containing metal nanoparticles at a high concentration, and evaluates storage stability by determining whether or not sedimentation or aggregation occurs after leaving a paste prepared by adding ethylene glycol to silver colloid particles in which silver nanoparticles are protected by a protective colloid at room temperature for six months. However, the examples only disclose silver nanoparticles, and do not recognize the issues associated with metals that are easily oxidized in the atmosphere, such as copper particles.

[0010] Patent Document 2 discloses a copper nanoparticle dispersion with excellent oxidation resistance, in which the copper nanoparticles are immediately dispersed and an alkylamine is attached to the surface of the copper particles, thereby achieving the oxidation resistance of the copper nanoparticle dispersion. However, in the examples, only copper particles with an average primary particle size of less than 100 nm are disclosed, and it is commonly understood that copper particles of this particle size are easily oxidized in the atmosphere and generate significant heat, making them difficult to apply to various applications after exposure to the atmosphere.

[0011] Although the above-mentioned prior art documents have examined the stability and oxidation resistance of copper particles in the form of pastes or dispersions, they have not examined whether the copper particles themselves can be used for various purposes after exposure to the atmosphere. Furthermore, there is no description or suggestion as to whether the metal colloid particles, pastes containing the same, and copper nanoparticle dispersions disclosed in the above-mentioned prior art documents can be used for bonding purposes.

[0012] The present invention has been made in view of the above problems, and aims to provide copper particles that can be used for various purposes even after the copper particles themselves are exposed to the atmosphere.

[0013] Therefore, the inventors conducted extensive research and discovered that by subjecting a certain amount of an organic component containing a carboxylic acid or its salt and a specific polymer dispersant to a specific treatment together with copper particles of a specific particle size, composite copper particles can be obtained that can be used for various purposes even after the copper particles are exposed to the atmosphere, and thus completed the present invention.

[0014] That is, the present invention provides: (1) composite copper particles comprising copper particles and an organic component, wherein the composite copper particles have an average particle diameter of 100 nm or more and 600 nm or less as measured with a scanning electron microscope, the organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, and the content of the organic component is 0.3 mass % or more and 6.0 mass % or less based on the total composite copper particle, and the polymer dispersant has an acid value of 60 mg KOH / g or more, and exhibits a mass loss rate of 70% or more in air when heated from 30°C to 250°C at a heating rate of 10°C / min using a thermogravimetric differential thermal analyzer; (2) the composite copper particles according to (1), wherein the polymer dispersant has an exothermic peak temperature of 300°C or less as measured with a thermogravimetric differential thermal analyzer; (3) the composite copper particles according to (1) or (2), wherein the carboxylic acid or the salt thereof has a carbon number of 2 or more and 20 or less; (4) (5) Composite copper particles according to any one of (1) to (3), in which the organic component has a mass ratio of the carboxylic acid or salt thereof to the polymer dispersant of 1.0 or more and 12.0 or less; (6) Composite copper particles according to any one of (1) to (4), in which the surfaces of the copper particles are coated with the carboxylic acid or salt thereof; (7) A bonding member comprising composite copper particles or a copper paste, in which 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, in which 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) (10) A sintered body containing the joining member according to (7) as a raw material; (11) A conductor containing the conductive material according to (8); (12) 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) A method for producing composite copper particles according to (11), which includes a step of mixing carboxylic acid-coated copper particles with a treatment liquid containing a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent; (13) A method for producing composite copper particles according to (11) or (12), which includes a step of mixing carboxylic acid-coated copper particles with a treatment liquid containing a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent, and drying the mixture; and

[0015] The composite copper particles of the present invention have high bonding strength not only before exposure to the atmosphere but also after exposure to the atmosphere, and exhibit practical conductivity, so they can be suitably used for bonding applications (e.g., bonding members) or conductive applications (e.g., conductive materials).

[0016] Fig. 1 is a diagram showing X-ray diffraction (sometimes referred to herein as "XRD") patterns of the composite copper particles of Example 1 before and after exposure to the atmosphere. Fig. 2 is a diagram showing a transmission electron microscope (sometimes referred to herein as "TEM") photograph of the composite copper particles of Example 1 before exposure to the atmosphere. Fig. 3 is a diagram showing a transmission electron microscope (TEM) photograph of the composite copper particles of Example 1 after exposure to the atmosphere. Fig. 4 is a diagram showing a scanning electron microscope (sometimes referred to herein as "SEM") photograph of the composite copper particles of Example 1 before exposure to the atmosphere.

[0017] The composite copper particles of the present invention are composite copper particles containing copper particles and an organic component, wherein the composite copper particles have an average particle diameter of 100 nm or more and 600 nm or less as 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 being 0.3 mass % or more and 6.0 mass % or less with respect to the entire composite copper particle, the polymer dispersant having an acid value of 60 mg KOH / g or more, and exhibiting a mass loss rate of 70% or more when heated from 30°C to 250°C at a heating rate of 10°C / min using a thermogravimetric differential thermal analyzer.

[0018] <Copper Particles> The composite copper particles of the present invention contain copper particles.

[0019] 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.

[0020] The copper particles may contain components or compounds other than the copper component, such as raw materials or reactants used in the manufacturing process, to the extent that it does not cause any problems depending on the application.

[0021] The shape of the copper particles used in the composite copper particles of the present invention is not particularly limited, and may be any shape, such as irregular, spherical, polyhedral, spindle-shaped, or plate-shaped.

[0022] The average particle size of the copper particles is not particularly limited as long as composite copper particles having a desired average particle size can be obtained. For example, it is preferably 100 nm or more and 600 nm or less, more preferably 150 nm or more and 500 nm or less, and even more preferably 200 nm or more and 400 nm or less.

[0023] The average particle size of the copper particles is measured by photographing the copper particles using a scanning electron microscope (SEM), measuring the maximum Feret diameter (hereinafter simply referred to as Feret diameter) of each of 50 primary particle diameters in the SEM field of view, and taking the arithmetic mean thereof as the average particle size.

[0024] The copper particles may exist as primary particles or as secondary particles formed by aggregation of primary particles.

[0025] <Organic Component> The composite copper particle of the present invention contains, as organic components, a carboxylic acid or a salt thereof and a polymer dispersant, and the content of the organic component is 0.3 mass % or more and 6.0 mass % or less based on the total mass of the composite copper particle.

[0026] The content of organic components 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 the total mass of the composite copper particles.

[0027] When the content of the organic component is within the above range, the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention are not deteriorated even when the composite copper particles of the present invention are exposed to the atmosphere, and therefore the composite copper particles of the present invention can be suitably used for bonding applications (e.g., bonding members) or conductive applications (e.g., conductive materials). In this application, "even when exposed to the atmosphere" means "even immediately after exposure to the atmosphere," but also includes the time of exposure to the atmosphere.

[0028] The amount of organic components contained in the composite copper particles of the present invention is measured using a thermogravimetric differential thermal analyzer (sometimes referred to as "TG-DTA" in this application). Specifically, the composite copper particles are heated from 30°C to 500°C at a heating rate of 10°C / min in a nitrogen atmosphere. Based on the mass of the composite copper particles at the start of the measurement, the mass loss rate in the temperature range from 30°C to 350°C in the obtained profile is taken as the amount of organic components contained in the composite copper particles.

[0029] In the composite copper particles of the present invention, the state of the organic component is not particularly limited. For example, the organic component may be present on the surface of the copper particles, or may be chemically bonded to the surface of the copper particles. Examples of the chemical bond include ionic bonds, coordinate bonds, and intermolecular forces (e.g., van der Waals forces and hydrogen bonds). Furthermore, for example, the organic component may be adsorbed onto the surface of the copper particles. In this application, "chemical bond" and "adsorption" are sometimes referred to as "interaction."

[0030] The state of adsorption of the organic component on the surface of the copper particles is not particularly limited, and may be, for example, a state in which the organic component is physically adsorbed and / or chemically adsorbed on the surface of the copper particles, or a state in which the organic component is present on the surface of the copper particles due to an electrical interaction (e.g., Coulomb force).

[0031] When the organic component is present on the surface of the copper particles, the organic component may coat the surface of the copper particles. Specifically, the organic component may coat the entire surface of the copper particles, or the organic component may coat only a portion of the surface of the copper particles. Furthermore, when the organic component coats the entire surface of the copper particles, the coating may be uniform or non-uniform.

[0032] <Carboxylic Acid or Salt Thereof> The organic component contained in the composite copper particles of the present invention includes a carboxylic acid or a salt thereof.

[0033] In the composite copper particles of the present invention, the carboxylic acid or salt thereof used is not particularly limited. The carboxylic acid or salt thereof may be of one type or of two or more types.

[0034] The chemical structure of the molecule of the carboxylic acid or salt thereof is not particularly limited, as long as it has a hydrocarbon group portion and a carboxyl group portion in its structure.

[0035] The hydrocarbon group portion is not particularly limited as long as it can provide the composite copper particles of the present invention. For example, it may be composed of only single bonds, or may have multiple bonds in the middle or at the end. Furthermore, it may contain a heteroatom at any position in the hydrocarbon group.

[0036] The carboxyl group portion is not particularly limited as long as the composite copper particles according to the present invention can be obtained. For example, the carboxylic acid or salt thereof may have one carboxyl group in its molecule, or two or more carboxyl groups in its molecule. In particular, it is preferable that the carboxylic acid or salt thereof has one carboxyl group in its molecule.

[0037] The carboxylic acid or salt thereof preferably has one carboxyl group, as this improves low-temperature sintering performance. The state of the carboxylic acid or salt thereof is described below, but it is understood that the carboxylic acid or salt thereof is present in the composite copper particles of the present invention with the carboxyl group as a contact point. For example, when a carboxylic acid or salt thereof is present on the surface of a copper particle, the carboxylic acid or salt thereof is present on the surface of the copper particle with the carboxyl group as a contact point. Carboxylic acids or salts thereof with fewer contact points are thermally decomposed at low temperatures, which is understood to more effectively improve low-temperature sintering performance. Furthermore, carboxylic acids or salts thereof with one carboxyl group are preferred because they are less likely to remain as residue during sintering, thereby more effectively avoiding degradation of low-temperature sintering performance due to residual components. In this specification, the phrase "the carboxylic acid or salt thereof is thermally decomposed at low temperatures" refers to the carboxylic acid or salt thereof being thermally decomposed, dissociated, and / or volatilized by heat, in addition to being thermally decomposed.

[0038] The term "low-temperature sintering performance" as used herein means the performance of the composite copper particles and copper paste of the present invention to be sufficiently sintered at a temperature of 300°C or less.

[0039] The number of carbon atoms in the molecule of the carboxylic acid or salt thereof is not particularly limited as long as the composite copper particles of the present invention can be obtained, but for example, it is preferably 2 or more and 20 or less, more preferably 4 or more and 18 or less, and even more preferably 6 or more and 16 or less.

[0040] The number of carbon atoms in the molecule of the carboxylic acid or salt thereof is defined as the number of carbon atoms in the entire carboxylic acid molecule, i.e., the number of carbon atoms in the molecule of the carboxylic acid or salt thereof is the sum 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 if the carbon number is 2 or more, oxidation of copper in the composite copper particles of the present invention due to exposure to the atmosphere can be more effectively avoided. Therefore, deterioration of the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention due to exposure to the atmosphere can be more effectively avoided, which is preferable. Furthermore, if the carbon number is 20 or less, the carboxylic acid or salt thereof in the composite copper particles of the present invention is easily thermally decomposed even at low temperatures, which more effectively improves low-temperature sintering performance, which is also preferable. Furthermore, carboxylic acids or salts thereof having a carbon number of 20 or less are less likely to remain as residues during sintering, which more effectively prevents deterioration of low-temperature sintering performance due to residual components, which is also preferable.

[0042] Examples of the carboxylic acid include 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 carboxylic acids include alkali metal salts such as sodium salts and potassium salts of the above-mentioned carboxylic acids, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0044] Among carboxylic acids or salts thereof, acetic acid, caproic acid, caprylic acid, or capric acid or salts thereof are preferred. This is because such carboxylic acids or salts thereof are easily thermally decomposed even at low temperatures, and are understood to improve low-temperature sintering performance. Furthermore, the above-mentioned carboxylic acids or salts thereof are preferred because they are less likely to remain as residues during sintering, and therefore, deterioration of low-temperature sintering performance due to residual components can be more effectively avoided.

[0045] The content of the carboxylic acid or its salt is not particularly limited as long as the total amount of the organic component together with the polymer dispersant is in the range of 0.3% by mass to 6% by mass. When the total amount of the organic component together with the polymer dispersant is in the range of 0.3% by mass to 6.0% by mass, the content of the carboxylic acid or its salt is, for example, preferably 0.15% by mass to 5.0% by mass, more preferably 0.15% by mass to 4.5% by mass, even more preferably 0.20% by mass to 4.0% by mass, and particularly preferably 0.25% by mass to 3.5% by mass, based on the total amount of the composite copper particles.

[0046] The content of the carboxylic acid or salt thereof can be measured using TG-DTA in the same manner as in the measurement of the content of the organic component described above.

[0047] In the composite copper particles of the present invention, it is understood that if the content of carboxylic acid or its salt is 0.15% by mass or more, oxidation of copper in the composite copper particles of the present invention due to exposure to the atmosphere can be more effectively avoided. Therefore, deterioration of the properties of the composite copper particles of the present invention (specifically, bonding strength and conductivity) due to exposure to the atmosphere can be more effectively avoided, which is preferable. If the content of carboxylic acid or its salt is 5.0% by mass or less, deterioration of low-temperature sintering performance due to excess carboxylic acid or its salt remaining as a residual component in the composite copper particles of the present invention can be more effectively avoided, which is preferable. Furthermore, if the content of carboxylic acid or its salt is 5.0% by mass or less, the carboxylic acid or its salt undergoes thermal decomposition at low temperatures, which more effectively improves low-temperature sintering performance, which is preferable.

[0048] <Polymer Dispersant> The organic component contained in the composite copper particles of the present invention includes a polymer dispersant, and the polymer dispersant has an acid value of 60 mg KOH / g or more and exhibits a mass loss rate of 70% or more in the air when heated from 30°C to 250°C at a heating rate of 10°C / min using a thermogravimetric differential thermal analyzer.

[0049] By using a polymer dispersant having the above-described properties in the composite copper particles of the present invention, the composite copper particles of the present invention can be suitably used for bonding applications (e.g., bonding members) or conductive applications (e.g., conductive materials) even when the composite copper particles are exposed to the atmosphere.

[0050] In the composite copper particles of the present invention, the polymer dispersant used has an acid value of 60 mgKOH / g or more. More preferably, it is 70 mgKOH / g or more, and even more preferably, it is 86 mgKOH / g or more. An acid value of 70 mgKOH / g or more is preferable because the composite copper particles of the present invention exhibit high bonding strength before and after exposure to the atmosphere and can further suppress a decrease in conductivity (specifically, an increase in volume resistivity) after exposure to the atmosphere. There is no particular upper limit to the acid value of the polymer dispersant, but an acid value of 200 mgKOH / g or less is preferable because the composite copper particles of the present invention can further suppress a decrease in bonding strength and conductivity after exposure to the atmosphere. The acid value of the polymer dispersant is more preferably 70 mgKOH / g or more and 200 mgKOH / g or less, and even more preferably 86 mgKOH / g or more and 200 mgKOH / g or less.

[0051] For the acid value of a polymer dispersant, if it is a commercially available product, refer to the catalog value. If the polymer dispersant is homemade, the acid value can be measured using the following method. An automatic titrator (GT-310BRT (manufactured by Nitto Analytech Co., Ltd.)) is used to measure the acid value of the polymer dispersant by non-aqueous neutralization titration. The titration solution is a 0.1 mol / L potassium hydroxide ethanol solution (manufactured by Nacalai Tesque Inc.), and the titration sample is prepared by dissolving 0.5 g of the polymer dispersant in 100 mL of ethanol.

[0052] The polymer dispersant used in the present invention has a mass loss rate of 70% or more, more preferably 80% or more, and even more preferably 90% or more, in air when heated from 30°C to 250°C at a heating rate of 10°C / min using a thermogravimetric differential thermal analyzer.

[0053] When the mass loss rate of the polymer dispersant is equal to or greater than the above value, the composite copper particles after exposure to the atmosphere can be suitably used for bonding applications (e.g., bonding members) or conductive applications (e.g., conductive materials). Furthermore, the polymer dispersant is easily thermally decomposed even at low temperatures, and the decomposition products obtained by the thermal decomposition are easily detached or dissociated from the composite copper particles at low temperatures, which is preferable because the polymer dispersant is less likely to remain during sintering, and the degradation of low-temperature sintering performance due to residual components can be more effectively avoided.

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

[0055] The amine value of the polymer dispersant is not particularly limited. For example, the amine value of the polymer dispersant is preferably 45 mg KOH / g or less, more preferably 20 mg KOH / g or less, and even more preferably 5 mg KOH / g or less. Most preferably, a polymer dispersant without an amine value is used.

[0056] When the amine value of the polymer dispersant is the above value or less, the reaction between the carboxylic acid or salt thereof treated on the surface of the copper particles and the component derived from the amine value can be more effectively avoided.

[0057] The exothermic peak temperature due to thermal decomposition of the 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 less, more preferably 280° C. or less, and even more preferably 250° C. or less. When multiple exothermic peaks are observed, the temperature of the highest exothermic peak observed among the peaks is used.

[0058] If the exothermic peak temperature due to thermal decomposition of the polymer dispersant is equal to or lower than the above-mentioned value, the polymer dispersant is easily thermally decomposed even at low temperatures, and the decomposition products obtained by the thermal decomposition are easily detached or dissociated from the composite copper particles at low temperatures, which is preferable because the low-temperature sintering performance is more effectively improved.Furthermore, it is preferable because the polymer dispersant is less likely to remain during sintering, which makes it possible to more effectively avoid deterioration of the low-temperature sintering performance due to residual components.

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

[0060] The weight-average molecular weight of the 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 even more preferably 700 or more and 8,000 or less.

[0061] A weight-average molecular weight of 600 or more is preferred because, as described in the preferred embodiment below, the carboxylic acid or its salt can be retained on the surface of the copper particles, and aggregation of the composite copper particles of the present invention can be effectively avoided. This is preferred because it more effectively prevents deterioration of the properties (specifically, bonding strength and conductivity) of the composite copper particles of the present invention when exposed to the atmosphere. A weight-average molecular weight of 10,000 or less is preferred because the polymer dispersant is easily thermally decomposed even at low temperatures, and the decomposition products obtained by the thermal decomposition are easily detached or dissociated from the composite copper particles at low temperatures, thereby more effectively improving low-temperature sintering performance. Furthermore, it is preferred because the polymer dispersant is less likely to remain during sintering, and deterioration of low-temperature sintering performance due to residual components can be more effectively avoided.

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

[0063] The error range of the weight-average molecular weight of the polymer dispersant is a range of 500 or less and 500 or more, based on the average value of the weight-average molecular weight measured three times by GPC (for example, if the average of three weight-average molecular weight measurements is 1000, the error range is 500 or more and 1500 or less).

[0064] The content of the polymer dispersant is not particularly limited as long as the total amount of the organic component together with the carboxylic acid or its salt is in the range of 0.3% by mass to 6.0% by mass. When the total amount of the organic component together with the carboxylic acid or its salt is in the range of 0.3% by mass to 6.0% by mass, the content of the polymer dispersant is, for example, preferably 0.15% by mass to 1.5% by mass, more preferably 0.16% by mass to 1.25% by mass, and even more preferably 0.17% by mass to 1.0% by mass, based on the total amount of the composite copper particles.

[0065] In the composite copper particles of the present invention, a polymer dispersant content of 0.15% by mass or more is preferred because it more effectively prevents detachment of carboxylic acid or its salt from the surface of the copper particles when the composite copper particles of the present invention are exposed to the atmosphere.A polymer dispersant content of 1.5% by mass or less is preferred because the polymer dispersant is easily thermally decomposed even at low temperatures, and the decomposition products obtained by the thermal decomposition are easily detached or dissociated from the composite copper particles at low temperatures, more effectively improving the low-temperature sintering performance.Furthermore, it is preferred because it more effectively prevents a decrease in the low-temperature sintering performance of the composite copper particles of the present invention due to the polymer dispersant remaining in the composite copper particles during sintering.

[0066] The content of the polymer dispersant can be measured using TG-DTA in the same manner as in the measurement of the content of the organic component described above.

[0067] <Composite Copper Particles> The composite copper particles of the present invention have an average particle size 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 range, the composite copper particles of the present invention can be suitably used for bonding applications (e.g., bonding members) or conductive applications (e.g., conductive materials) even when exposed to the atmosphere.

[0069] The average particle size of the composite copper particles can be measured using an SEM in the same manner as in the measurement of the average particle size of the copper particles described above.

[0070] Furthermore, in the composite copper particles of the present invention, the change in particle size of the copper particles due to the presence of organic components is very small, so the average particle size of the composite copper particles of the present invention can be considered to be the same as the average particle size of the copper particles.

[0071] When evaluating the presence or absence of copper oxide formation in the composite copper particles of the present invention using an X-ray diffraction (XRD) device, the composite copper particles of the present invention exposed to the atmosphere are measured using an XRD device, and the X-ray diffraction pattern obtained is evaluated. For example, if the X-ray diffraction pattern shows peaks at 2θ = 43.3 ° (Cu (111) plane) and 2θ = 50.4 ° (Cu (200) plane), which are peaks attributable to metallic copper, it can be evaluated that only metallic copper is present (in other words, copper oxide is not formed). In addition to the two peaks, if a peak at 2θ = 74.08 ° (Cu (220) plane), which is a peak attributable to metallic copper, is observed, it can be evaluated that only metallic copper is present (in other words, copper oxide is not formed). In addition, as the XRD device, for example, SmartLab SE (Rigaku Corporation) can be used. In addition, dedicated software may be used to control the device, collect data, perform calculations, and generate reports. For example, SmartLab Studio II (Rigaku Corporation) may be used as such software.

[0072] When evaluating the presence or absence of copper oxide formation in the composite copper particles of the present invention using a transmission electron microscope (TEM), the composite copper particles of the present invention exposed to the atmosphere are observed using a TEM, and evaluation is made based on the lattice spacing of the atomic arrangement in the crystal (i.e., lattice fringes). For example, when the lattice spacing of the observed lattice fringes is only 2.1 Å (0.21 nm), which is the lattice spacing of the metallic copper (111) plane, it can be evaluated that only metallic copper is present (no copper oxide is formed). Note that, for example, an H-9000 (Hitachi High-Technologies Corporation) can be used as the TEM.

[0073] In the organic component contained in the composite copper particles of the present invention, the mass ratio of the carboxylic acid or its salt to the polymer dispersant is not particularly limited as long as it is at least a gram equivalent. For example, the mass ratio expressed as "(mass of the carboxylic acid or its salt) / (mass of the 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 even more preferably 1.5 or more and 10.0 or less.

[0074] A mass ratio of 1.0 or more is preferred because it is likely that the carboxylic acid or its salt is present on the surface of the copper particles, as described below as a preferred embodiment. This improves the low-temperature sintering performance of the composite copper particles of the present invention. A mass ratio of 12.0 or less is preferred because it more effectively avoids the increase in production costs caused by using a large amount of carboxylic acid or its salt.

[0075] The mass ratio of the carboxylic acid or its salt to the polymeric dispersant ("(mass of the carboxylic acid or its salt) / (mass of the polymeric dispersant)") can be measured using TG-DTA in the same manner as in the measurement of the content of the organic component described above. In the obtained profile, the mass loss rate in the temperature range from 30°C to 200°C is the mass of the carboxylic acid or its salt, and the mass loss rate in the temperature range from 200°C to 350°C is the mass of the polymeric dispersant. The mass loss rate in the temperature range from 200°C to 350°C is calculated by subtracting the mass loss rate of the carboxylic acid or its salt from the overall mass loss rate (30°C to 350°C).

[0076] In the composite copper particles of the present invention, the state in which the carboxylic acid or its salt is present is not particularly limited. For example, the carboxylic acid or its salt may be contained in the composite copper particles, and / or the carboxylic acid or its salt may be present on the surface of the copper particles. When the carboxylic acid or its salt is present on the surface of the copper particles, for example, the carboxylic acid or its salt may be present chemically bonded to the copper particle surface and / or the carboxylic acid or its salt may be present chemically bonded to a polymer dispersant. Furthermore, the carboxylic acid or its salt may be present by adsorption to the copper particle surface and / or the polymer dispersant.

[0077] Regarding chemical bonding and adsorption, the explanation regarding chemical bonding and adsorption in "<Organic Component>" above applies.

[0078] When the carboxylic acid or its salt is present on the surface of copper particles, the carboxylic acid or its salt may coat the surface of the copper particles. Specifically, the carboxylic acid or its salt may coat the entire surface of the copper particles, or the carboxylic acid or its salt may coat only a portion of the surface of the copper particles. Furthermore, when the carboxylic acid or its salt coats the entire surface of the copper particles, the coating may be uniform or non-uniform.

[0079] Furthermore, when the carboxylic acid or its salt coats the surface of copper particles, the carboxylic acid or its salt may coat the copper particle surface as a monomolecular film, or may coat the copper particle surface as a multilayer film. Furthermore, the carboxylic acid or its salt constituting the monomolecular film and the multilayer film may consist of only the same type of carboxylic acid or its salt, or may consist of two or more different types. The term "multilayer film" as used herein refers to a film composed of a monomolecular film of a carboxylic acid or its salt that is in direct contact with the copper particle surface and a carboxylic acid or its salt that is chemically bonded or adsorbed to the monomolecular film.

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

[0081] Examples of interactions with the carboxylic acid or its salt present on the surface of the copper particles include a state in which the polymer dispersant interacts with the carboxylic acid or its salt through physical adsorption and / or chemical adsorption, and / or a state in which the polymer dispersant interacts electrically with the carboxylic acid or its salt (e.g., Coulomb force), and / or a state in which the polymer dispersant is chemically bonded to the carboxylic acid or its salt.

[0082] When the polymer dispersant interacts with a carboxylic acid or a salt thereof present on the surface of copper particles, the polymer dispersant may coat a film (specifically, a monomolecular film or a multilayer film) composed of the carboxylic acid or the salt thereof. Specifically, the polymer dispersant may coat the entire surface of the film, or may coat only a portion of the 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 containing a carboxylic acid or a salt thereof, and the molecular film of the carboxylic acid or a salt thereof is coated with a polymer dispersant. When the composite copper particles of the present invention are in this embodiment, aggregation of the composite copper particles can be more preferably suppressed. It is understood that the ability to more preferably suppress aggregation of the composite copper particles can more preferably maintain low-temperature sintering performance even after the composite copper particles of the present invention are exposed to the atmosphere.

[0084] In the case where the composite copper particles are one of the above-described more preferred embodiments, the decomposition temperature of the carboxylic acid or its salt is preferably lower than that of the polymeric dispersant. When the composite copper particles of the present invention are sintered, the carboxylic acid or its salt, which is relatively easily thermally decomposed, is more preferably released, and at the same time, the polymeric dispersant is also more preferably released. Therefore, it is understood that the composite copper particles of the present invention have excellent low-temperature sintering performance.

[0085] In a more preferred embodiment, the molecular film of the carboxylic acid or its salt is composed of a monomolecular film or a multilayer film, and the polymer dispersant may coat the monomolecular film or multilayer film.

[0086] When a monomolecular film of a carboxylic acid or a salt thereof is formed on the surface of the copper particles, the composite copper particles of the present invention are understood to not only be suitable for use in bonding applications (e.g., bonding components) or conductive applications (e.g., conductive materials) after exposure to the atmosphere, but also to contribute more favorably to the expression of low-temperature sintering performance.

[0087] When a built-up film of a carboxylic acid or its salt is formed on the monomolecular film, it is understood that the composite copper particles of the present invention can not only be suitably used for bonding applications (e.g., bonding components) or conductive applications (e.g., conductive materials) after exposure to the atmosphere, but also contribute more favorably to the suppression of oxidation of the copper contained in the composite copper particles.

[0088] It is also understood that the monomolecular film or multilayer film of carboxylic acid or its salt coated on the surface of the copper particles functions more preferably as a scaffold for coating with the polymer dispersant.

[0089] Since the carboxylic acid or salt thereof coated on the surface of the copper particle is adsorbed and desorbed, if the composite copper particle of the present invention is in the above-mentioned more preferred embodiment, even if a part of the carboxylic acid or salt thereof is desorbed when the composite copper particle of the present invention is exposed to the atmosphere, the exposure of the copper is more preferably reduced because the polymer dispersant is coated, and therefore it is understood that the composite copper particle of the present invention has a high oxidation suppression effect.

[0090] By coating the monomolecular film or multilayer film of the carboxylic acid or its salt with a polymer dispersant, the composite copper particles of the present invention can be suitably used for bonding applications (e.g., bonding members) or conductive applications (e.g., conductive materials) after exposure to the atmosphere.

[0091] That is, when a monomolecular film or multilayer film of a carboxylic acid or its salt is formed by a relatively weak force (e.g., an intermolecular force), the polymer dispersant coats the surface of the monomolecular film or multilayer film, making it difficult for the carboxylic acid or its salt to be released. This allows the polymer dispersant to play a supporting role in achieving the effects of the monomolecular film or multilayer film of a carboxylic acid or its salt (specifically, the ability to suppress deterioration of properties even after exposure to the atmosphere). Furthermore, one of the general effects of a polymer dispersant is that it can more favorably contribute to the suppression of aggregation of composite copper particles.

[0092] <Production of Composite Copper Particles> A method for producing the composite copper particles of the present invention will be described.

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

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

[0095] Furthermore, the composite copper particles of the present invention can also be produced by a method including the steps of mixing carboxylic acid-coated copper particles with a treatment liquid containing a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent, and drying the mixture.

[0096] (Preparation process of carboxylic acid coated copper particles) In the composite copper particles of the present invention, the copper particles 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 copper particles produced by a known method, copper particles treated with carboxylic acid will be described later.

[0097] The copper particles may contain components or compounds other than the copper component, such as raw materials or reactants used in the manufacturing process, to the extent that it does not cause any problems depending on the application.

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

[0099] The average particle size of the copper particles is not particularly limited, and is, for example, 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] If the average particle size of the copper particles is within the above range, composite copper particles having the desired average particle size can be obtained, which is preferable.

[0101] The solvent is not particularly limited as long as it does not react with the carboxylic acid or its salt or the polymer dispersant. Examples of such a solvent include methanol, ethanol, 1-propanol, 2-propanol, acetone, and methyl ethyl ketone.

[0102] The raw materials used in the production method can be selected from those explained above and used appropriately according to the production method.

[0103] (Surface Treatment Step) In the composite copper particles of the present invention, carboxylic acid-coated copper particles, a carboxylic acid or a salt thereof, a polymer dispersant, and a solvent are mixed as raw materials, and the carboxylic acid-coated copper particles are surface-treated with the carboxylic acid or a salt thereof and the polymer dispersant.

[0104] The mixing order of the raw materials is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. Alternatively, a liquid containing a solvent and at least one raw material may be prepared, and the liquid may be mixed in any order. Specifically, a treatment liquid containing a solvent, a polymer dispersant, and a carboxylic acid or a salt thereof may be prepared, and the treatment liquid may be mixed with carboxylic acid-coated copper particles. A dispersion containing carboxylic acid-coated copper particles prepared by mixing a solvent and carboxylic acid-coated copper particles may be mixed with a treatment liquid containing a solvent, a polymer dispersant, and a carboxylic acid or a salt thereof.

[0105] The step of mixing the raw materials can use a known agitator. Examples include a planetary mixer, an ultrasonic disperser, a blade agitator, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also includes contact or coexistence of the materials with each other.

[0106] The stirring time and stirring speed are not particularly limited as long as the raw materials can be sufficiently mixed. For example, the stirring time may be 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. A stirring time of 5 minutes or more and a stirring speed of 100 rpm or more are preferred because the 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 including a step of mixing carboxylic acid-coated copper particles with a treatment liquid containing a polymer dispersant, a carboxylic acid or a salt thereof, and a solvent. This production method is preferred because it allows the carboxylic acid or a salt thereof and the polymer dispersant contained in the treatment liquid to be more efficiently present on the surfaces of the copper particles.

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

[0109] In the process for preparing the treatment liquid, the order in which the raw materials are added is not particularly limited. For example, all the raw materials may be mixed at once, or the solvent and the other raw materials may be mixed one by one in any order.

[0110] In the process of preparing the treatment liquid, the treatment liquid may be mixed using a known stirrer, such as a planetary centrifugal mixer, an ultrasonic disperser, a blade stirrer, a disperser mixer, or a homomixer.

[0111] In the stirring step, stirring conditions such as stirring time and stirring speed are not particularly limited as long as the raw materials can be sufficiently mixed. For example, the stirring time may be 1 minute or more, and more preferably 5 minutes or more. Furthermore, for example, the stirring speed may be 50 rpm or more, and more preferably 100 rpm or more. A stirring time of 5 minutes or more and a stirring speed of 100 rpm or more are preferred because they allow the raw materials to be mixed uniformly.

[0112] The total amount of the carboxylic acid or its salt and the polymer dispersant in the treatment liquid is not particularly limited as long as a predetermined amount of organic component can be treated on the copper particles. For example, the total amount of the carboxylic acid or its salt and the polymer dispersant in the treatment liquid 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 even more preferably 2.0 mass % or more and 20 mass % or less, based on the total amount of the treatment liquid.

[0113] The content of the carboxylic acid or its salt in the treatment liquid is not particularly limited, and is preferably 0.7% by mass or more and 25% by mass or less, more preferably 1.5% by mass or more and 18% by mass or less, and even more preferably 2.0% by mass or more and 16% by mass or less, based on the total mass of the treatment liquid.

[0114] The content of the polymer dispersant in the treatment liquid is not particularly limited, and for example, the content of the polymer dispersant in the treatment liquid is preferably 0.3% by mass or more and 5.0% by mass or less, more preferably 0.4% by mass or more and 4.5% by mass or less, and even more preferably 0.5% by mass or more and 4.0% by mass or less, based on the total mass of the treatment liquid.

[0115] It is preferable that the composition of the treatment solution is within the above range, since the copper particles can be treated more effectively with a predetermined amount of organic component so as to obtain the composite copper particles of the present invention.

[0116] The step of mixing the carboxylic acid-coated copper particles with the treatment liquid can be carried out using a known agitator. Examples include a planetary mixer, an ultrasonic disperser, a blade agitator, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also includes contact or coexistence of the materials with each other. Examples include a method of immersing copper particles in the treatment liquid and a method of permeating the copper particles with the treatment liquid.

[0117] The stirring time and stirring speed are not particularly limited as long as the raw materials can be sufficiently mixed. For example, the stirring time is preferably 1 minute or more, more preferably 5 minutes or more. Furthermore, for example, the stirring speed is preferably 50 rpm or more, more preferably 100 rpm or more. A stirring time of 5 minutes or more and a stirring speed of 100 rpm or more are preferred because the carboxylic acid-coated copper particles can be uniformly treated with the organic component. Furthermore, when immersing or permeating, the immersion or permeation time may be 10 minutes or more.

[0118] After the surface treatment step, solid-liquid separation may be performed as needed. A known filtration method can be used for 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, or a centrifuge can be used. Decantation may be performed as appropriate.

[0119] After the surface treatment step, the recovered solid matter may be washed as needed. A known washing method can be used to wash the solid matter. The solvent used for washing is not particularly limited.

[0120] (Drying Step) The composite copper particles of the present invention can be produced by a method including a step of drying the mixture of the carboxylic acid-coated copper particles and the treatment liquid, if necessary.

[0121] The conditions in the drying step, such as the drying temperature, drying time, and drying atmosphere, can be set appropriately. 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 higher and 10 hours or lower, and the drying atmosphere is preferably under vacuum or an inert gas such as nitrogen or argon.

[0122] In the drying step, a known dryer may be used for drying. For example, a heating device such as a dryer, oven, or electric furnace, or a desiccator, vacuum dryer, or reduced-pressure dryer controlled to a predetermined temperature may be used.

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

[0124] A vacuum pump may be used to create a vacuum atmosphere inside the desiccator, such as the G-20DA manufactured by ULVAC, Inc.

[0125] After the drying step, the composite copper particles may be crushed or disintegrated to adjust the particle size, if necessary. For crushing or disintegration, a known crusher, classifier, or the like can be used.

[0126] (Production Example of Carboxylic Acid Coated Copper Particles) An example of a production method (steps A and B) of carboxylic acid coated copper particles will be described below.

[0127] (Step A) In this step, a copper compound, a carboxylic acid or a salt thereof, an amine compound, and a solvent are mixed to obtain a mixed solution containing the copper compound.

[0128] The copper compound is not particularly limited as long as it contains a copper atom. The copper compound used in step A may be one type or two or more types.

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

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

[0131] The amount of the copper compound to be added is not particularly limited, but is preferably 1 part by mass or more and 100 parts by mass or less relative to the solvent.

[0132] It is preferable that the amount of the copper compound is 1 part by mass or more relative to the solvent, since this effectively avoids a decrease in the amount of copper particles obtained in step B. It is preferable that the amount of the copper compound is 100 parts by mass or less relative to the solvent, since this effectively avoids a non-uniform reaction due to an increase in viscosity when the solvent and the copper compound are mixed in this step.

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

[0134] The hydrocarbon group portion is not particularly limited as long as it can produce carboxylic acid-coated copper particles used in the production of composite copper particles according to the present invention. For example, it may be composed of only single bonds, or may have multiple bonds in the middle or at the end. Furthermore, it may contain a heteroatom at any position in the hydrocarbon group.

[0135] The carboxyl group moiety is not particularly limited as long as it can provide carboxylic acid-coated copper particles for use in the production of composite copper particles according to the present invention. For example, the carboxylic acid or salt thereof may have one carboxyl group in its molecule, or two or more carboxyl groups in its molecule. In particular, it is preferable that the carboxylic acid or salt thereof has one carboxyl group in its molecule.

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

[0137] Examples of the carboxylic acid include 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 carboxylic acids include alkali metal salts such as sodium salts and potassium salts of the above-mentioned carboxylic acids, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0139] Among the carboxylic acids or salts thereof, acetic acid, caproic acid, caprylic acid, or capric acid is more preferred, since the copper particles obtained in the step B described below can be more efficiently adjusted to a desired average particle size by using such carboxylic acids or salts thereof.

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

[0141] If the amount of the carboxylic acid or salt thereof added is within the above range, copper particles having the desired average particle size can be obtained in step B, which is preferable.

[0142] The 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 amine compound is preferably an amino alcohol. By using an amino alcohol, foaming of the mixed solution containing the copper compound in step A can be preferably suppressed.

[0144] Examples of the amino alcohol include methanolamine, monoethanolamine (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, isoethanoline, sphingosine, 3-dimethylamino-1,2-propanediol, 3-methyl ... -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 amine compounds, it is more preferable to include monoethanolamine, because even if monoethanolamine remains in the copper particles after synthesis, it undergoes thermal decomposition at low temperatures, and therefore, deterioration of low-temperature sintering performance can be more effectively avoided.

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

[0147] If the amount of the amine compound added is within the above range, it is possible to effectively avoid an increase in viscosity of the mixed liquid containing the copper compound, which is preferable.

[0148] The time for adding the amine compound is not particularly limited, but is preferably from 10 seconds to 30 minutes, which preferably suppresses the rapid heat generation of the mixed solution containing the copper compound in step A.

[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. Only one type of solvent may be used, or two or more types may be used.

[0150] Alcohols can be suitably used as the solvent. Examples of the alcohol include 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 salt thereof and the amine compound.

[0151] The order of mixing the raw materials is not particularly limited. For example, all raw materials may be mixed at once, or the solvent and other raw materials may be mixed one by one in any order. In particular, it is preferable to mix the solvent, copper compound, and carboxylic acid or a salt thereof, and then mix them with the amine compound.

[0152] In the mixing step, a known agitator can be used. Examples include a planetary mixer, an ultrasonic disperser, a blade agitator, a disperser mixer, and a homomixer. The materials may be mixed without using a mixer. Mixing also includes contact or coexistence of materials with each other.

[0153] The mixing conditions in the mixing step can be set appropriately. For example, the stirring time may be 1 minute or more, and more preferably 5 minutes or more. The stirring speed may be 50 rpm or more, and more preferably 100 rpm or more. The above mixing conditions allow the raw materials to be thoroughly mixed. Furthermore, a stirring time of 5 minutes or more and a stirring speed of 100 rpm or more are preferred, as these allow the raw materials to be more thoroughly mixed and the reaction to proceed uniformly.

[0154] (Step B) This step is a step of intermittently or continuously adding a reducing agent to the mixed liquid containing the copper compound obtained in Step A, and the liquid temperature of the mixed liquid during the addition of the reducing agent is 40° C. or higher and 95° C. or lower. By this step, a dispersion liquid containing copper particles can be obtained.

[0155] The reducing agent may be any agent capable of reducing the copper compound, and specifically, it preferably has a boiling point of 70° C. or higher, and more preferably has a boiling point equal to or higher than the heating temperature in the heating step. Use of such a reducing agent is preferred because it allows the copper compound to be reduced more efficiently even when the temperature of the mixed solution is 40° C. or higher and 95° C. or lower. Furthermore, only one type of reducing agent may be used, or two or more types may be used.

[0156] Examples of the reducing agent include hydrazine derivatives, such as 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, and n-octylhydrazine. Examples of the hydrazine include 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, dodecanediohydrazide, isophthalic acid dihydrazide, and salicylic acid hydrazide.

[0157] The reducing agent is added intermittently or continuously to the mixed solution containing the copper compound obtained in step A, rather than being added all at once in a short period of time. The time period for adding the reducing agent is preferably 50 minutes to 6 hours, more preferably 60 minutes to 6 hours.

[0158] In the present application, the term "intermittently or continuously added" means that the reducing agent is added in small amounts over time. Alternatively, the reducing agent may be added in multiple portions.

[0159] In the present application, the "addition time" refers to the time required from the time when the reducing agent is added to the mixed solution containing the copper compound until the entire amount of the reducing agent is added to the mixed solution (hereinafter, this may also be referred to as "the time required to add the entire amount of the reducing agent").

[0160] By adding the reducing agent intermittently or continuously, the heat generated during the reduction reaction is suppressed, and the average particle size of the copper particles obtained by this step can be adjusted to a desired range.

[0161] The amount of the reducing agent added is preferably 1.0 mol or more and 4.0 mol or less relative to 1.0 mol of the copper compound. Amounts of 1.0 mol or more are preferred because the copper compound can be sufficiently reduced. Furthermore, amounts of 4.0 mol or less are preferred because the load during washing of solids containing copper particles can be further reduced.

[0162] The temperature of the mixed solution containing the copper compound when the reducing agent is added 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 liquid temperature of the mixed liquid containing the copper compound is within the above range, copper particles having a desired average particle size can be obtained.

[0164] The temperature of the mixed solution containing 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 containing the copper compound is adjusted to the above range before the addition of the reducing agent.

[0165] In this step, a known mixer such as a stirrer, mixer, homogenizer, or agitator can be used as needed. The stirring speed is not limited, but may be 50 rpm or higher. 100 rpm or higher is more preferred. Setting the stirring speed to 100 rpm or higher is preferred because the copper compound is uniformly reduced, resulting in more uniform copper particles.

[0166] The dispersion containing copper particles obtained in this step may be aged as needed.

[0167] The aging conditions can be set appropriately. 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, even 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 higher and 2.0 hours or lower, more preferably 5 minutes or higher and 2.0 hours or lower. Furthermore, during aging, stirring may be performed using the known mixer described above. The stirring speed is not limited, but may be 50 rpm or higher. The stirring speed is preferably 100 rpm or higher.

[0168] The dispersion containing copper particles obtained in this step may be subjected to solid-liquid separation, if necessary.

[0169] For solid-liquid separation, known methods can be used. For example, pressure filtration devices typically used industrially, such as rotary presses and filter presses, vacuum filtration devices such as Nutsche filters and Moore filters, and centrifugation can be used. Decantation may also be performed as appropriate.

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

[0171] The solid content obtained by the solid-liquid separation may be dried by a known method, for example, using a heating device such as a dryer, oven, or electric furnace, or a desiccator, vacuum dryer, or reduced-pressure dryer controlled to a predetermined temperature.

[0172] When a desiccator is used in the drying step, the inside of the desiccator can be controlled to a predetermined temperature and a vacuum atmosphere can be created to dry the solid content. A vacuum pump can be used to create a vacuum atmosphere inside the desiccator. For example, a G-20DA manufactured by ULVAC, Inc. can be used as the vacuum pump.

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

[0174] The production method including the above-mentioned steps A and B can produce carboxylic acid-coated copper particles having an average particle diameter of 100 nm or more and 600 nm or less, and the carboxylic acid-coated copper particles obtained here can be used as a raw material for producing the composite copper particles of the present invention.

[0175] <Copper Paste> The copper paste of the present invention contains the composite copper particles of the present invention and a paste solvent.

[0176] The solvent for the paste 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 a plurality of solvents can be used in combination as appropriate.

[0177] In the present invention, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, and ester-based solvents are preferably used because they have high affinity with polymer dispersants having an acid value and carboxylic acids.

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

[0179] Examples of glycol solvents that can be used include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,2-propanediol, 1,3-propanediol, and butanediol.

[0180] Glycol ether solvents include ethylene glycol ethers and propylene glycol ethers.

[0181] Examples of ethylene glycol ethers include 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 propylene glycol ethers include 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 solvent include methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, and n-propyl acetate.

[0184] In the copper paste of the present invention, only one paste solvent may be used, or two or more paste solvents may be used. The type and blending ratio may be set arbitrarily, taking into consideration the properties required for the copper paste, the properties required for the bonding member, the properties required for the conductive material, and compatibility with other blended components. An example of a combination of multiple paste solvents is a combination of dipropylene glycol and hexyl carbitol.

[0185] The copper paste of the present invention may contain various additives as needed, such as various commonly used reducing agents, dispersants, emulsifiers, antifreeze agents, pH adjusters, thickeners, antifoaming agents, and film-forming aids.

[0186] When the copper paste of the present invention contains the above-mentioned reducing agent, examples of the reducing agent that can be used include monoethanolamine, diethanolamine, triethanolamine, dimethylaminoethanol, N-methyldiethanolamine, hydrazine, and formic acid.

[0187] The copper paste of the present invention may also contain copper particles other than the composite copper particles of the present invention. Specifically, it may contain microcopper particles having an average particle diameter of 1 μm to 50 μm or nanocopper particles having an average particle diameter of 100 nm or less. The shape of the microcopper particles or nanocopper particles is not particularly limited, and examples thereof include spherical, blocky, acicular, flake-like, approximately spherical, irregular, polyhedral, spindle-like, and flattened shapes, as well as aggregates of these shapes. The average particle diameter of the microcopper particles or nanocopper particles can be measured in the same manner as the average particle diameter of the composite copper particles described above.

[0188] The content of the composite copper particles in the copper paste of the present invention may be adjusted appropriately depending on the intended use. The content of the copper particles in the copper paste can be confirmed, for example, by thermogravimetric analysis.

[0189] The copper paste of the present invention is prepared by mixing the raw materials. A known mixer can be used in this mixing step. Examples include a twin-shaft mixer, a three-roll mill, a sand mill, a planetary mixer, and the like that are commonly used industrially. Furthermore, for laboratory scale mixing, a stirrer, a hybrid mixer, a homogenizer, a paint shaker, and the like can be used. The materials may be mixed without using a mixer. Mixing also includes contact or coexistence of materials with each other.

[0190] The mixer may use grinding media as needed, such as those containing glass, alumina, zirconia, zirconium silicate, etc.

[0191] During or after the mixing step, degassing may be carried out as necessary.

[0192] The atmosphere in the mixing step may be any of air, an inert gas, and a vacuum, and is preferably an inert gas or a vacuum from the viewpoint of more effectively suppressing performance degradation due to oxidation of the copper particles.

[0193] <Bonding Member> The composite copper particles of the present invention, or a copper paste containing the composite copper particles of the present invention, can be used as a bonding member and can satisfactorily bond a substrate and a material to be bonded. They can also be used for bonding three-dimensional integrated circuits (3D-ICs). The composite copper particles of the present invention may be used as a bonding member as is, or the composite copper particles may be made into a copper paste and then used as a bonding member.

[0194] When the copper paste is used for the joining member, the copper paste preferably contains the composite copper particles in an amount of 80% by mass or more and 98% by mass or less, and more preferably 85% by mass or more and 96% by mass or less, based on the total amount of the copper paste. When the copper paste contains the composite copper particles in an amount of 80% by mass or more, the generation of voids during heating can be more effectively suppressed, and the joining strength can be further improved, which is preferable. Furthermore, when the copper paste contains the composite copper particles in an amount of 98% by mass or less, aggregation of the composite copper particles in the paste can be more efficiently prevented, and the coatability of the paste can be preferably improved.

[0195] The joining member may contain an additive as appropriate depending on the intended use, examples of which include the various additives mentioned above.

[0196] The substrate and the workpiece may be made of the same material or different materials. The workpiece may be made of any suitable material, including, but not limited to, various metal materials, semiconductor materials (e.g., chips), ceramic materials, and resin materials.

[0197] The surfaces of the substrate and the materials to be joined may be polished as needed.

[0198] For metal materials, methods include grinding stone polishing, lapping polishing, buffing, barrel polishing, and electrolytic polishing. Known materials can be used as appropriate for the polishing agent and abrasive grains used. Examples of abrasive grains include diamond, alumina, silicon carbide, and cubic boron nitride.

[0199] For semiconductor materials, chemical mechanical polishing (CMP) is used, etc. Examples of abrasive grains include inorganic metal oxides such as cerium oxide and silicon oxide.

[0200] For ceramic materials and resin materials, mechanochemical polishing is an example.

[0201] The surfaces of the substrate and the materials to be joined may be plated as required.

[0202] The type of metal to be plated can be selected appropriately depending on the application. Examples include gold plating, silver plating, copper plating, nickel plating, chromium plating, and alloy plating of various metals. When alloy plating is used, the composition of the plating can also be adjusted appropriately depending on the application.

[0203] The plating method may be any known method, including dry plating such as physical vapor deposition plating or chemical vapor deposition plating, and wet plating such as displacement plating, electroplating, or electroless plating.

[0204] Specific examples of the substrate include semiconductor substrates such as silicon substrates, metal substrates such as copper substrates, lead frames, metal plate-attached ceramic substrates (for example, Direct Bonded Copper: DBC), substrates for mounting semiconductor elements such as LED (Light-Emitting Diode) packages, power supply members such as copper ribbons, metal blocks, and terminals, heat sinks, and water-cooled plates.

[0205] The joining method using the joining member of the present invention is a method of joining the substrate and the workpiece by providing the joining member on a substrate, placing the workpiece on the side of the joining member opposite the substrate to obtain a laminate, and heating the laminate. However, the joining method using the joining member of the present invention is not limited to the above joining method as long as the object of the present invention can be achieved.

[0206] Examples of methods for applying the bonding member to the substrate include screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, jet printing, dispenser, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0207] The substrate coated with the bonding material may be dried as needed. Drying conditions can be set appropriately. By drying the substrate before sintering, it is possible to more effectively prevent the bonding material from flowing or voids from occurring during sintering.

[0208] As for the drying conditions, for example, the drying atmosphere may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere. The drying pressure may be atmospheric pressure or reduced pressure. The drying temperature is not particularly limited as long as the composite copper particles contained in the joining member are not sintered.

[0209] The copper paste and bonding member of the present invention can be suitably used in pressureless bonding methods because a sintered body that achieves high bonding strength can be obtained by simply sintering through heating. Of course, the copper paste and bonding member of the present invention can also be suitably used in pressure bonding methods.

[0210] In this application, the term "pressureless joining method" refers to a method of preparing a laminate in which a joining member is placed between a base material and a material to be joined, and heating the laminate in a state in which the joining member and the material to be joined are placed in a direction in which the weight of the base material acts, or in a state in which a load of 0.01 MPa or less is applied.

[0211] In this application, the term "pressure bonding method" refers to a method in which a laminate is prepared in which a bonding member is placed between a base material and a material to be bonded, and the laminate is heated while a load exceeding 0.01 MPa is applied.

[0212] The heating atmosphere for the laminate in the pressureless bonding method or pressure bonding method may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but an inert atmosphere is more preferable from the viewpoint of more effectively avoiding an increase in the size of the manufacturing equipment for the sintered body.

[0213] Preheating may be performed before the laminate in the pressureless bonding method is completely sintered. The preheating temperature is preferably 150°C or less, more preferably 140°C or less. From the viewpoint of the evaporation rate of the solvent, it is even more preferably 130°C or less. Preheating can also be avoided by setting the temperature rise rate applied to the laminate to 10°C / min or less. Copper particles may be sintered during preheating, but sintering is not necessary. Preheating conditions may be set appropriately depending on the desired bonding characteristics.

[0214] The heating temperature of the laminate in the pressureless bonding method or 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. If the sintering temperature is 300° C. or lower, it can be said that the bonding member of the present invention can be sintered at a sufficiently low temperature.

[0215] The heating time of the laminate in the pressureless bonding method is preferably 1 minute to 120 minutes in order to sufficiently volatilize the solvent contained in the bonding member and to sufficiently promote sintering of the composite copper particles contained in the bonding member. Also, the heating time of the laminate in the pressure bonding method is preferably 1 minute to 60 minutes in order to sufficiently volatilize the solvent contained in the bonding member and to sufficiently promote sintering of the composite copper particles contained in the bonding member.

[0216] The bonding strength of the sintered body obtained by the pressureless bonding method or the pressure bonding method is measured by the method described in the Examples.

[0217] 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 even more preferably 27 MPa or more. A sintered body having such a bonding strength can be judged to be sufficiently bonded, and it can be confirmed that the bonding member of the present invention can be suitably used with a pressureless bonding paste. As mentioned above, an inert atmosphere is preferable for pressureless bonding, but if the bonding strength of a sintered body obtained by pressureless bonding in other atmospheres (e.g., a reducing atmosphere) is within the above range, it can be judged to be sufficiently bonded.

[0218] Furthermore, 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 even more preferably 27 MPa or more. If the sintered body has such a bonding strength, it can be determined that the bonding is sufficient, and it can also be determined that the bonding member of the present invention can be suitably used for pressure bonding paste.

[0219] <Conductive Material> The composite copper particles of the present invention or a copper paste containing the composite copper particles of the present invention can be used as a conductive material. The composite copper particles of the present invention may be used as a conductive material as is, for example, or the composite copper particles may be made into a copper paste and then used as a conductive material. Specifically, the copper paste can be used as a material for conductive bodies such as conductive films, electrodes, and wiring.

[0220] When the copper paste of the present invention is used as a material for a conductive film, an electrode, or a wiring, it can be applied to a substrate by coating it. Methods for applying the paste include screen printing, transfer printing, offset printing, letterpress printing, intaglio printing, gravure printing, stencil printing, inkjet printing, soft lithography, dispenser, comma coating, slit coating, die coating, gravure coating, bar coating, spray coating, spin coating, and electrodeposition coating.

[0221] When the copper paste is used as the conductive material, the concentration of the composite copper particles contained in the copper paste may be adjusted appropriately depending on the above-mentioned application method.

[0222] The thickness of the coating layer is not particularly limited, and is preferably 0.1 μm or more and 100 μm or less. The coating pattern at this time can be coating the entire surface of the substrate, or coating in a pattern or design. Depending on the coating method, purpose of use, and application, additives may be appropriately contained. Examples of additives include the various additives mentioned above.

[0223] Specific examples of the substrate include semiconductor substrates such as silicon substrates, metal substrates such as copper substrates, lead frames, metal-plate-attached ceramic substrates (e.g., Direct Bonded Copper (DBC)), substrates for mounting semiconductor elements such as LED (Light-Emitting Diode) packages, copper ribbons, metal blocks, power supply members such as terminals, heat sinks, water-cooled plates, and glass. Organic materials such as acrylic resins such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polypropylene, polycarbonate, and polymethyl methacrylate, vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers, epoxy resins, polyarylates, polysulfones, polyethersulfones, polyimides, fluororesins, phenoxy resins, polyolefin resins, nylons, styrene-based resins, and ABS resins may also be used. Depending on the application, a film-like flexible substrate or a rigid substrate can be formed by appropriately selecting from these materials. There is no limitation on the size of the substrate, and the shape may be any shape such as a disk, a card, or a sheet. The surface of the substrate does not need to be flat, and may have an uneven or curved surface.

[0224] <Conductor> The conductor of the present invention includes the conductive material. Alternatively, the conductor may be obtained by heating the conductive material. The conductor preferably has a low volume resistivity (sometimes referred to as "specific resistivity" in the present application). For example, the volume resistivity (specific resistivity) is 100 μΩ·cm or less, and preferably 50 μΩ·cm or less. Within this range, the conductor of the present invention can be used for practical applications (e.g., conductive films, electrodes, wiring). The volume resistivity of the conductor is measured by the method described in the examples.

[0225] The heating method is not particularly limited, and examples of the heating method include resistance heating, electron beam heating, laser light heating, flash light heating, plasma heating, dielectric heating, induction heating, and heating with a heat source such as a burner.

[0226] The heating temperature may be adjusted appropriately depending on the substrate. 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 the substrate, the heating temperature may be 300° C. or less. When a PET or PEN substrate is used as the substrate, the heating temperature may be 150° C. or less.

[0227] The 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 of more effectively avoiding an increase in the size of the production equipment.

[0228] The heating time is sufficient if it is 1 minute or more and 60 minutes or less.

[0229] The present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these.

[0230] (Measurement of average particle size of copper particles) The copper particles produced in the production examples were photographed using a scanning electron microscope (S4800 manufactured by Hitachi High-Technologies Corporation) set at a magnification of 50,000 times to obtain a scanning electron micrograph. The Feret diameters of 50 primary particles in the scanning electron micrograph were measured, and the arithmetic mean value thereof was calculated as the average particle size.

[0231] (Thermal decomposition characteristics of polymer dispersants) The thermal decomposition characteristics of the polymer dispersants used in the examples and comparative examples of this application were measured using a thermogravimetric differential thermal analyzer (TG-DTA8122, manufactured by Rigaku Corporation) under the conditions shown below. The mass loss rate was calculated from the difference in mass between 30°C and 250°C.

[0232] Measurement conditions: Measurement atmosphere: air; Atmospheric flow rate: 100 mL / min; Measurement temperature range: 25°C to 1000°C; Temperature rise rate: 10°C / min

[0233] (Measurement of Weight-Average Molecular Weight of Polymer Dispersant) The weight-average molecular weight of the polymer dispersant used in the Examples and Comparative Examples of this application was measured using gel permeation chromatography (HLC-8420GPC, manufactured by Tosoh Corporation) under the conditions shown below. Dedicated software, EcoSEC Elite, was used for controlling the device, collecting data, performing calculations, and creating reports.

[0234] Measurement conditions Sample concentration: 1 mg / mL (5 mg of polymer dispersant was dissolved in 5 mL of tetrahydrofuran, filtered through a membrane filter, and adjusted to the concentration shown on the left.) Sample injection volume: 10 μL Column: TSKgel Super HZM-M (manufactured by Tosoh Corporation, base material: styrene divinylbenzene, particle size: 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

[0235] The analysis results of the polymer dispersants are shown in Table 1. The acid value and amine value of the polymer dispersants are also shown. The active ingredient of each polymer dispersant was 100%.

[0236]

[0237] (Production Example 1) A 10 L four-necked glass flask was placed in an oil bath, and 2 L of 1-propanol (Kishida Chemical Co., Ltd.) as a solvent, 637.6 g of cupric oxide (N-300, Nisshin Chemco Corporation), 96.0 g of acetic acid (Fujifilm Wako Pure Chemical Industries, Ltd.), and 82.7 g of capric acid (Fujifilm Wako Pure Chemical Industries, Ltd.) were added thereto, followed by stirring at room temperature at a rotation speed of 250 rpm. Stirring was also carried out at a constant rotation speed in subsequent steps. Furthermore, 127.0 g of 2-aminoethanol (Tokyo Chemical Industry Co., Ltd.) was added over 10 minutes, and stirring was continued to produce a mixed solution containing a copper compound. The mixed solution containing the copper compound was heated in an oil bath until the liquid temperature reached 50°C, and 80 g of 60% hydrazine hydrate (Mitsubishi Gas Chemical Company, Inc.) as a reducing agent was added dropwise over 3 minutes and 45 seconds, followed by stirring for 40 minutes. Next, the "step of adding 80 g of 60% hydrazine hydrate dropwise over 3 minutes and 45 seconds and stirring for 15 minutes" was repeated three times (i.e., a total of 240 g of 60% hydrazine hydrate was added in this step). 680 g of 60% hydrazine hydrate was then added dropwise over 30 minutes. In this step, the total amount of reducing agent added was 1,000 g, and the time required for addition was 130 minutes. The oil bath temperature during the addition of the reducing agent was set to 50°C. After the entire amount of reducing agent was added, the mixture was heated to 90°C and stirred for 2 hours to obtain a dispersion containing copper particles. The dispersion containing copper particles was naturally cooled with stirring until it reached 50°C or below, allowed to stand for 30 minutes, and then 30 g of solids were weighed out and recovered by solid-liquid separation. In the washing step, the solid content and 75 mL of 2-propanol (manufactured by Nacalai Tesque, Inc.) were stirred at 2000 rpm for 10 minutes using a mixer (Thinky Mixer AR-250). Then, solid content was obtained by solid-liquid separation using a centrifuge (Beckman Coulter, Allegra X-30R) at a centrifugal force of 400 G for 5 minutes. The above-mentioned washing step was repeated to obtain carboxylic acid-coated copper particles of Production Example 1. The average particle diameter of the carboxylic acid-coated copper particles of Production Example 1 was 297 nm.

[0238] Example 1 Caprylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 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, the caprylic acid content in the treatment solution was 6 mass %, and the BYK-LP C 24365 content was 2 mass %. The carboxylic acid-coated copper particles obtained in Production Example 1 were mixed with the treatment solution and stirred at 2000 rpm for 10 minutes using a mixer (Awatori Rentaro AR-250, manufactured by Thinky Corporation). Thereafter, solid-liquid separation was performed for 5 minutes at a centrifugal force of 400 G using a centrifuge, and the solid content was recovered. The recovered solid content was placed in a desiccator, and the pressure inside the desiccator was reduced using a vacuum pump (G-20DA, manufactured by ULVAC, Inc.). The pressure inside the desiccator was adjusted to 1.3 Pa and 25° C., and the mixture was vacuum dried for 300 minutes to obtain composite copper particles of Example 1.

[0239] Example 2 Composite copper particles of Example 2 were obtained in the same manner as in Example 1, except that the amount of caprylic acid was changed from 6% by mass to 12% by mass and the amount of BYK-LP C 24365 was changed from 2% by mass to 4% by mass.

[0240] Example 3 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 in Example 1 was changed from 2% by mass to 0.5% by mass.

[0241] Example 4 Composite copper particles of Example 4 were obtained in the same manner as in Example 1, except that caprylic acid (having 8 carbon atoms) in Example 1 was changed to capric acid (having 10 carbon atoms).

[0242] Comparative Example 1 Copper particles of Comparative Example 1 were obtained in the same manner as in Example 1, except that BYK-LP C 24365 was not included.

[0243] Comparative Example 2 Copper particles of Comparative Example 2 were obtained in the same manner as in Example 1, except that caprylic acid was not contained.

[0244] Comparative Example 3 Copper particles of Comparative Example 3 were obtained in the same manner as in Example 1, except that BYK-LP C 24365 in Example 1 was changed to BYK-LP C 22124.

[0245] Comparative Example 4 Copper particles of Comparative Example 4 were obtained in the same manner as in Example 1, except that BYK-LP C 24365 in Example 1 was changed to BYK-LP C 22146.

[0246] Comparative Example 5 Copper particles of Comparative Example 5 were obtained in the same manner as in Example 1, except that BYK-LP C 24365 in Example 1 was changed to BYK-LP C 22435.

[0247] (Comparative Example 6) Copper particles of Comparative Example 6 were obtained in the same manner as in Example 1, except that the amount of caprylic acid was changed from 6% by mass to 30% by mass and the amount of BYK-LP C 24365 was changed from 2% by mass to 10% by mass.

[0248] (Comparative Example 7) Copper particles of Comparative Example 7 were obtained in the same manner as in Example 1, except that the amount of caprylic acid was changed from 6% by mass to 0.6% by mass and the amount of BYK-LP C 24365 was changed from 2% by mass to 0.2% by mass.

[0249] (Production Example 2) A 10 L glass four-neck flask was placed in an oil bath, and 1 L of ethyl carbitol (Kishida Chemical Co., Ltd.) as a solvent, 159.1 g of cupric oxide (Nisshin Chemco Co., Ltd.), and 13.9 g of hexanoic acid (Tokyo Chemical Industry Co., Ltd.) were added thereto. The mixture was stirred at room temperature at a rotation speed of 200 rpm to prepare a mixed solution containing a copper compound. The mixed solution containing the copper compound was heated to 90 ° C., and when the temperature reached 90 ° C., 200 g of hydrazine monohydrate (Nacalai Tesque) was added as a reducing agent to the mixed solution within 30 seconds. After adding the reducing agent, the mixed solution was stirred at 90 ° C. for 20 minutes to obtain a dispersion containing copper particles. The dispersion containing copper particles was naturally cooled to below 50 ° C., allowed to stand for 30 minutes, and then 30 g of solids were weighed and collected by solid-liquid separation. In the washing step, the solid content and 75 mL of 2-propanol (manufactured by Nacalai Tesque, Inc.) were stirred at 2000 rpm for 10 minutes using a mixer (Thinky Mixer AR-250). Then, solid content was obtained by solid-liquid separation using a centrifuge (Beckman Coulter, Allegra X-30R) at a centrifugal force of 400 G for 5 minutes. The above-mentioned washing step was repeated to obtain carboxylic acid-coated copper particles of Production Example 2. The average particle diameter of the carboxylic acid-coated copper particles of Production Example 2 was 80 nm.

[0250] Comparative Example 8 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.

[0251] (Measurement of the crystalline state of composite copper particles and copper particles before and after air exposure) Using an X-ray diffraction (XRD) device (Rigaku Corporation: SmartLab SE), the 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 air exposure were measured under the following conditions. From the obtained diffraction patterns, the oxidation state before and after air exposure was confirmed. Dedicated software, SmartLab Studio II, was used for device control, data collection, calculation, and report creation. Figure 1 shows the X-ray diffraction patterns of the composite copper particles of Example 1 before and after air exposure. As shown in Figure 1, only peaks attributable to metallic copper were observed both before and after air exposure. Here, the Cu (111) plane is observed near 2θ = 43.3 °, and the Cu (200) plane is observed near 2θ = 50.4 °.

[0252] Measurement conditions: Tube: CuKα, Tube voltage: 40 kV, Tube current: 40 mA, Measurement range: 30° to 70°, Step: 0.01°, Speed: 5° / min

[0253] (Observation of Composite Copper Particles and Lattice Fringes of Copper Particles Before and After Air Exposure) The composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 were observed before and after air exposure using a transmission electron microscope (TEM (Hitachi High-Technologies Corporation: H-9000)), and the oxidation state of copper was confirmed from the atomic arrangement (lattice fringes) in the crystal. Here, the lattice spacing of the metallic copper (111) plane was 2.1 Å (0.21 nm). Figure 2 shows a TEM photograph of the composite copper particles of Example 1 before air exposure, and Figure 3 shows a TEM photograph of the composite copper particles of Example 1 after air exposure. In the TEM photographs before and after air exposure, only the lattice spacing of 0.21 nm derived from the metallic copper (111) plane was observed on the copper particle surface, and no copper oxidation was observed. For reference, Figure 4 also shows an SEM photograph of the composite copper particles of Example 1 before air exposure.

[0254] (Measurement of Amount of Organic Component) Using a thermogravimetric differential thermal analyzer (TG-DTA8122, manufactured by Rigaku Corporation), the mass loss of the composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 to 8 was measured under the following conditions. In the obtained profiles, the mass loss rate in the temperature range from 30°C to 200°C was taken as the mass of the carboxylic acid, the mass loss rate in the temperature range from 200°C to 350°C was taken as the mass of the polymer dispersant, and the mass loss rate in the temperature range from 30°C to 350°C was taken as the mass of the organic component treated on the copper particles. From these results, the masses of the carboxylic acid (caprylic acid or capric acid) contained in the composite copper particles and copper particles, and the ratio of carboxylic acid to polymer dispersant are shown in Table 2.

[0255] Measurement conditions: Measurement atmosphere: nitrogen (purity: 99.995%), atmosphere flow rate: 500 mL / min, measurement temperature range: 30°C to 500°C, temperature rise rate: 10°C / min

[0256]

[0257]

[0258] (Preparation of Copper Paste) The composite copper particles of Examples 1 to 4 and the copper particles of Comparative Examples 1 and 3 to 7 were blended in a total proportion of 92.5% by mass, 3.6% by mass of dipropylene glycol, 3.6% by mass of hexyl carbitol, and 0.3% by mass of triethanolamine, and the mixture was kneaded at 2000 rpm for 4 minutes using a mixer (Thinky Mixer AR-250). The mixture was then degassed at 2200 rpm for 2 minutes to obtain copper pastes of Samples 1 to 4, 6 to 9, and 12 to 13. The paste containing the copper particles of Comparative Example 8 prepared by the above method did not have a viscosity suitable for application and could not be evaluated (not shown in the table).

[0259] A copper paste of Sample 5 was obtained in the same manner as in the copper paste manufacturing method described above, except that the paste was formulated so that the copper particles of Example 1 were 92.5% by mass, dipropylene glycol was 3.75% by mass, and hexyl carbitol was 3.75% by mass.

[0260] In the copper paste manufacturing method described above, the copper particles of Comparative Example 1 were mixed in an amount of 92.5% by mass, dipropylene glycol in an amount of 3.5% by mass, hexyl carbitol in an amount of 3.5% by mass, triethanolamine in an amount of 0.3% by mass, and BYK-LP C 24365 in an amount of 0.2% by mass. A copper paste of Sample 10 was obtained in the same manner as described above.

[0261] A copper paste of Sample 11 was obtained in the same manner as in the copper paste manufacturing method described above, except that the paste was formulated to contain 92.5% by mass of the copper particles of Comparative Example 2, 3.35% by mass of dipropylene glycol, 3.35% by mass of hexyl carbitol, 0.3% by mass of triethanolamine, and 0.5% by mass of caprylic acid.

[0262] In addition, copper pastes were prepared in the same manner as in the copper paste preparation method, except that the composite copper particles or copper particles were exposed to the atmosphere (temperature 28°C, humidity 60%) for 1 hour, and the changes in bonding strength and resistivity due to exposure to the atmosphere were confirmed. Note that when the copper particles of Comparative Example 8 were exposed to the atmosphere (temperature 28°C, humidity 60%) for 1 hour, heat generation and smoke due to oxidation occurred, and therefore paste preparation was not possible (not shown in the table).

[0263]

[0264] (Preparation of Sintered Body) A metal mask with an opening of φ5 mm and a thickness of 0.1 mm was placed on a substrate having a diameter (hereinafter, φ) of 10 mm, a thickness of 5 mm, and a surface roughness (Ra: arithmetic mean roughness) of 0.1 to 0.2 μm. The opening was coated with the copper paste obtained by the above-described procedure as a bonding member. The metal mask was removed, and a copper piece (tough pitch copper, alloy number C1100) with a diameter of φ5 mm, a thickness of 5 mm, and a surface roughness (Ra: arithmetic mean roughness) of 0.1 to 0.2 μm was placed on the area where the bonding member was applied, to obtain a laminate. The surface roughness was the average value of Ra measured by a laser microscope for three test pieces randomly selected from 100 test pieces. The laminate was set in a jig having a space of 10.5 mm on three sides, and nitrogen (purity 99.995%) was circulated at 100 mL / min. The laminate was placed on a hot plate heated to 200° C. and held there for 30 minutes. Thereafter, the laminate was allowed to cool naturally to 50° C. to obtain a sintered body.

[0265] (Measurement of Bonding Strength) The sintered body was set in a strength testing machine (manufactured by Japan Measurement Systems Co., Ltd., JSL-1KN), and a shear force was applied from the substrate side in a direction parallel to the bonding surface at a rate of 1 mm / sec. The bonding strength was calculated from the load applied when the substrate and the copper piece were peeled off.

[0266] (Preparation of Conductive Film) The copper paste obtained by the above-described procedure was applied to a 100 μm thick polyimide film substrate using an applicator. The substrate coated with the copper paste was placed in a tubular furnace (JTEKT Thermosystems, KTF-035N1). Nitrogen (purity 99.995%) was circulated through the tubular furnace at 100 mL / min, and the temperature was increased from 25°C to 150°C at a rate of 5°C / min and maintained at this temperature for 60 minutes. The resulting mixture was then naturally cooled to 50°C to obtain a conductive film.

[0267] (Measurement of Conductivity) The surface resistivity of the conductive film was measured using a low resistivity meter (Loresta-GX MCP-T700, manufactured by Nitto Seiko Analytech Co., Ltd.). Thereafter, the thickness of the conductive film was measured using a film thickness meter (ID-C112X, manufactured by Mitutoyo Corporation), and the volume resistivity (specific resistivity) was calculated by multiplying the thickness by the surface resistivity.

[0268] The bonding strength of the sintered body and the volume resistivity of the conductive film measured by the above-mentioned method are shown in Table 5.

[0269]

[0270] Samples 1 to 5 containing the composite copper particles of the present invention had sufficient bonding strength (20 MPa or more) before and after exposure to the atmosphere. Furthermore, the resistivity of Samples 1 to 5 was on the order of microns, less than 100 μΩ cm, before and after exposure to the atmosphere, making them suitable for use in conductive applications. Furthermore, the resistivity was also less than 50 μΩ cm, making them more suitable for use in conductive applications.

[0271] In sample 6, which used the copper particles of Comparative Example 1 (copper particles produced using a treatment solution containing no polymer dispersant), the bond strength after exposure to the atmosphere was 10.2 MPa, which was not the desired bond strength. Similarly, in sample 10, which used the copper particles of Comparative Example 1 but added a polymer dispersant during paste preparation, the bond strength after exposure to the atmosphere was 10.7 MPa, which was not the desired bond strength. From this, it can be understood that in order to be suitable for bonding applications even after exposure to the atmosphere, it is necessary for the composite copper particles to contain a polymer dispersant, and further, the polymer dispersant needs to be applied to the copper particles during the copper particle production process, not during paste preparation.

[0272] In Sample 11, which used the copper particles of Comparative Example 2 (copper particles produced using a treatment solution containing no carboxylic acid) and added a carboxylic acid (caprylic acid) during paste preparation, sufficient bonding strength was not obtained either before or after exposure to the atmosphere. The copper particles of Comparative Example 2 were treated with a polymer dispersant, but the treatment solution did not contain a carboxylic acid, which is understood to have reduced sinterability. Furthermore, it was found that simply treating the copper particles with a polymer dispersant did not provide sufficient bonding strength, making them unusable for bonding applications after exposure to the atmosphere.

[0273] In Sample 7, which used the copper particles of Comparative Example 3 (copper particles treated with a polymeric dispersant having an acid value of 60 mg KOH / g or more and a mass loss rate of less than 70%), the bond strength decreased from 7.7 MPa to 0 MPa due to exposure to the atmosphere. The polymeric dispersant used to treat the copper particles of Comparative Example 3 had a small mass loss rate at 250 °C (specifically, a mass loss rate of 53.4%), so it is understood that Sample 7 had a low bond strength before exposure to the atmosphere. Furthermore, the polymeric dispersant used to treat the copper particles of Comparative Example 3 had a small weight average molecular weight (weight average molecular weight = 553) and a bond strength of 0 MPa after exposure to the atmosphere. Therefore, it is understood that the organic components treated on the copper particles were desorbed due to exposure to the atmosphere, resulting in oxidation of the copper.

[0274] In sample 8, which used copper particles of comparative example 4 (copper particles treated with a polymer dispersant having an amine value, no acid value, and a mass reduction rate of less than 70%), the bonding strength decreased significantly from 34.0 MPa to 7.4 MPa (a decrease of about 78%) due to exposure to the atmosphere, indicating that the impact of performance degradation due to exposure to the atmosphere is very large.

[0275] In sample 9, which used copper particles of comparative example 5 (copper particles having no acid value or amine value and in which the mass reduction rate of the polymer dispersant was less than 70%), the bonding strength after exposure to the atmosphere was 10.8 MPa, and the desired bonding strength was not obtained.

[0276] In sample 12, which used copper particles of comparative example 6 (copper particles with an excessive content of organic components), the amount of organic components treated on the copper particles was 7.16 mass%, and the bonding strength after exposure to the atmosphere was 18.6 MPa, which was not the desired bonding strength.

[0277] In sample 13, which used copper particles of comparative example 7 (copper particles with an insufficient content of organic components), the amount of organic components treated on the copper particles was 0.22 mass%, and the bonding strength after exposure to the atmosphere was significantly reduced to 2.1 MPa.

[0278] The composite copper particles of the present invention can be suitably used for bonding applications (e.g., bonding members) not only before exposure to the atmosphere but also after exposure to the atmosphere. Furthermore, because of their low resistivity, they can also be used for conductive applications (e.g., conductive materials). Furthermore, bonding members containing the composite copper particles of the present invention can be sintered to have sufficient bonding strength even under pressureless bonding conditions. The composite copper particles of the present invention can be produced easily without any restrictions on the production process.

Claims

1. Composite copper particles comprising copper particles and an organic component, wherein the composite copper particles have an average particle diameter measured with a scanning electron microscope of 100 nm or more and 600 nm or less, the organic component comprises at least a carboxylic acid or a salt thereof and a polymer dispersant, and the content of the organic component is 0.3 mass% or more and 6.0 mass% or less with respect to the entire composite copper particles, and the polymer dispersant has an acid value of 60 mg KOH / g or more, and exhibits a mass loss rate of 70% or more in the air when heated from 30°C to 250°C at a heating rate of 10°C / min using a thermogravimetric differential thermal analyzer.

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

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

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

5. Composite copper particles according to claim 1 or 2, wherein the carboxylic acid or its salt is coated on the surface of the copper particles.

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

7. A joining member 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 joining member according to claim 7 as a raw material.

10. A conductor comprising the conductive material of claim 8.

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

12. A method for producing composite copper particles according to claim 11, comprising a step of mixing carboxylic acid-coated copper particles with a treatment liquid containing a carboxylic acid or a salt thereof, a polymeric dispersant, and a solvent.

13. A method for producing composite copper particles according to claim 11 or 12, comprising a step of mixing carboxylic acid-coated copper particles with a treatment liquid containing a carboxylic acid or a salt thereof, a polymeric dispersant and a solvent, and drying the mixture.