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

Abstract

The present invention provides: composite copper particles which are suitable as a starting material for a paste that can be sintered even in an inert atmosphere and can be applied to a pressureless bonding method and for a bonding member that contains the paste; and a method for producing the composite copper particles.　The present invention provides composite copper particles which contain copper particles, a monocarboxylic acid or a salt thereof, and a compound represented by general formula 1: R1(OCH2CH2)nOR2. (In the formula, R1 represents an alkyl group, an aryl group or a hydrogen atom; R2 represents an alkyl group, an aryl group, a hydrogen atom or an acetyl group; and n represents an integer of 1 to 4. However, the cases where both R1 and R2 are hydrogen atoms are excluded.) The composite copper particles have an average particle diameter of 170 nm to 600 nm inclusive as measured by a scanning electron microscope.

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, as well as a copper paste containing the composite copper particles and a joining member containing the paste.

[0002] When manufacturing semiconductor devices, high-melting-point lead solder is used to join semiconductor elements to lead frames, etc. In recent years, in joining power semiconductors and large-scale integrations (LSIs) that operate at high temperatures of 150°C or higher, the operating temperature of semiconductors has risen to near the melting point of high-melting-point lead solder due to the increasing capacity and space-saving nature of semiconductor elements. In addition, with the strengthening of RoHS (Restriction of Hazardous Substances) regulations, there is a demand for lead-free joining materials.

[0003] Examples of such joining members include pastes containing metal particles such as copper and silver. However, silver is a precious metal and has disadvantages such as high cost and limited application due to migration (specifically, silver migration). Therefore, copper has been considered as a suitable metal particle for use in such pastes.

[0004] For example, Patent Document 1 discloses a method for producing a copper core particle and a 1 nm thick film on the surface of the copper core particle. ２The publication discloses composite particles containing a plurality of aliphatic carboxylic acid molecules adsorbed at a density of 2.5 to 5.2 molecules per particle, and a plurality of polar organic low molecules having hydrophilic and hydrophobic groups and interacting with the aliphatic carboxylic acid molecules. Example 1 describes a copper paste prepared by blending and dispersing the coated copper particles obtained in Production Example 2 having an average primary particle size of 90.4 nm, a first copper powder having an average particle size of 2.0 μm, a second copper powder having an average particle size of 0.8 μm, a polymer dispersant, a polymer thickener, lauric acid 3-propanolamide as a polar organic low molecule, which is an acid amide compound, and a medium. Patent Document 1 discusses the copper paste, which produces composite particles in which a plurality of acid amide compound molecules interacting with the aliphatic carboxylic acid molecules are arranged around coated copper particles, each of which has a copper core particle surface coated with a plurality of aliphatic carboxylic acid molecules.

[0005] Patent Document 2 discloses copper powder having an average primary particle size of 0.1 to 0.6 μm, the particle surfaces of which are treated with an organic surface treatment agent, and the proportion of the organic surface treatment agent in the particles in the coated state is 0.25 to 5.50 mass% in terms of carbon atoms. The examples also describe organically surface-treated copper powder having an average primary particle size of 150 to 165 nm and treated with a specific fatty acid or aliphatic amine.

[0006] Furthermore, Patent Document 3 discloses a method for producing copper particles for bonding, which includes a step of mixing a copper compound, an amine compound, and a reducing compound in an organic solvent to obtain a copper particle dispersion, and a cleaning step of washing the copper particle dispersion obtained in this step with a solvent to perform solid-liquid separation of the copper particles from the copper particle dispersion, wherein the cleaning step is performed in a closed system. Furthermore, Synthesis Example 1 discloses a method for producing copper particles, which includes adding hydrazine monohydrate dropwise to a copper precursor solution obtained by mixing copper (II) acetate hydrate and hexylamine nonanoate in an organic solvent, and then performing solvent substitution with diethylene glycol in a closed system, and a concentrate containing copper particles with an average particle size of 50 nm produced by this method.

[0007] JP 2020-090725 A JP 2015-168878 A JP 2020-035978 A

[0008] Semiconductor bonding can be performed using two methods: a pressure bonding method in which a laminate of a substrate and a material to be bonded is heated while a load is applied to the laminate, and the metal particles contained in the bonding material are sintered to bond the substrate; and a pressureless bonding method in which the metal particles contained in the bonding material are sintered to bond the substrate by heating only without applying a load.

[0009] Of these, the pressureless bonding method is expected to improve production efficiency because it does not require pressure to be applied to the materials to be bonded during bonding. Furthermore, damage to the materials to be bonded (such as semiconductors) can be minimized during bonding. However, the pressureless bonding method has the problem of not being able to obtain sufficient bonding strength. Therefore, there is a demand for bonding components that can be used to produce sintered bodies with sufficient bonding strength using the pressureless bonding method.

[0010] In addition, copper particles are metal particles that easily form an oxide film on their surface, making it difficult to obtain sufficient bonding strength. Therefore, when sintering joining members using copper particles, sintering in a reducing atmosphere has been required to remove the oxide film on the surface of the copper particles. However, sintering in a reducing atmosphere incurs additional costs, such as the introduction of dedicated equipment, and therefore there is a demand for joining members that can be sintered in an inert atmosphere and that can obtain sufficient bonding strength.

[0011] In Patent Document 1, the copper paste composition obtained by blending two copper powders with different average particle sizes, a polymer dispersant, a polymer thickener, a polar organic low molecular weight compound, and a medium with the coated copper particles produced is pressure-sintered at 350°C and 30 MPa, and SEM cross-sectional images of the resulting laminate show that a dense and highly uniform copper bonding layer is obtained. However, this requires the use of pressure sintering (pressure bonding), which has the aforementioned problems. Furthermore, the bonding strength between materials has not been investigated. Furthermore, the suitability of the method for pressureless bonding has not been investigated.

[0012] Although Patent Document 2 discloses low-temperature sinterable copper particles, it only measures the sintering initiation temperature of the copper particles in a hydrogen-containing atmosphere using a thermal analyzer, and does not examine the bonding strength of the copper particles when used as a bonding member. Furthermore, it does not examine whether the copper particles can be suitably used for sintering in an inert atmosphere or for pressureless bonding. In this regard, given that the examples show that the produced copper powder is pressure-molded at 1.0 MPa to produce pellets, and then sintering (firing) of the pellets is initiated, it is generally understood that even if the produced copper powder is used as a bonding member, a method in which the copper powder metal particles are pressurized (loaded) to produce pellets and then the substrate and the workpiece are sintered under pressure via the pellets (pressure bonding method) is applied. Furthermore, the examples disclose copper particles with an average primary particle size of 150 nm to 165 nm, and it is generally understood that such copper particles do not achieve sufficient bonding strength.

[0013] Patent Document 3 discloses that the bonding paste obtained by kneading the produced copper particles with an organic solvent has a bonding strength of 35 to 40 MPa when cured under pressure in a nitrogen-3% hydrogen atmosphere at 200°C for 60 minutes. However, the bonding paste described in Patent Document 3 is sintered in a reducing atmosphere containing hydrogen, which increases the cost of the equipment.

[0014] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a paste that exhibits sufficient bonding strength even when pressure-free bonding is performed in an inert atmosphere, and composite copper particles that are suitable as a raw material for bonding members containing the paste.

[0015] The present inventors have conducted extensive research and found that a significant effect can be achieved by adjusting the average particle size of copper particles to a specific range and treating the surfaces of the copper particles with a specific organic species. As a result, they have discovered composite copper particles that can be suitably used as a paste for joining a substrate and a workpiece to be joined with a desired joining strength in an inert atmosphere without pressure, a joining member containing the paste, a simple method for producing the same, a paste containing the composite copper particles, and a joining member containing the paste, and have completed the present invention.

[0016] That is, the present invention provides: (1) a composition comprising copper particles, a monocarboxylic acid or a salt thereof, and a compound represented by general formula 1: R １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ and (2) a compound represented by the formula (I) and (II) above, wherein the compound is a compound represented by the formula (I) and (II) above, and ... ２(3) Composite copper particles according to (1) or (2), in which the number of carbon atoms in the monocarboxylic acid or its salt is 2 or more and 12 or less; (4) Composite copper particles according to any one of (1) to (3), in which the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (5) Composite copper particles according to any one of (1) to (4), in which the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid and capric acid; (6) Composite copper particles according to any one of (1) to (5), in which the molecular weight of the compound represented by General Formula 1 is 100 or more and 400 or less; (7) Composite copper particles according to any one of (1) to (6), in which the compound represented by General Formula 1 is diethylene glycol monohexyl ether or diethylene glycol monobutyl ether; (8) (9) Composite copper particles according to any one of (1) to (8), in which the content of the compound represented by the general formula 1 is 0.1% by mass or more and 2.0% by mass or less based on the total composite copper particle; (10) Composite copper particles according to any one of (1) to (8), in which the total amount of the monocarboxylic acid or its salt and the compound represented by the general formula 1 is 0.3% by mass or more and 3.5% by mass or less based on the total composite copper particle; (11) Composite copper particles according to any one of (1) to (8), in which the total amount of the monocarboxylic acid or its salt and the compound represented by the general formula 1 is 0.3% by mass or more and 3.5% by mass or less based on the total composite copper particle; １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２and (12) the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (13) the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid and capric acid; (14) the compound represented by the general formula 1 has a molecular weight of at least 100 and at most 400; (15) the compound represented by the general formula 1 has a molecular weight of at least 100 and at most 400; (16) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (17) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (18) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (19) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (20) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (21) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (22) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid; (23) the compound represented by the general formula 1 is at least one carboxylic acid or its salt selected from the group consisting (16) A method for producing composite copper particles according to any one of (10) to (15), wherein the monocarboxylic acid or its salt is mixed in an amount of 1% by mass or more and 30% by mass or less relative to the solvent; (17) A method for producing composite copper particles according to any one of (10) to (16), wherein the monocarboxylic acid or its salt is contained in the solvent in an amount of 1% by mass or more and 30% by mass or less relative to the solvent; (18) A method for producing composite copper particles according to any one of (10) to (17), wherein the compound represented by general formula 1 is mixed in an amount of 1% by mass or more and 30% by mass or less relative to the solvent; (19) A method for producing composite copper particles according to any one of (10) to (18), wherein the compound represented by general formula 1 is mixed in an amount of 1% by mass or more and 30% by mass or less relative to the solvent; (20) The method for producing composite copper particles according to any one of (10) to (19), wherein the monocarboxylic acid or the salt thereof and the compound represented by General Formula 1 are mixed in a total amount of 2% by mass or more and 35% by mass or less relative to the solvent;(21) A method for producing composite copper particles according to any one of (10) to (20), in which the total amount of the monocarboxylic acid or its salt and the compound represented by General Formula 1 is contained in the solvent in an amount of 2% by mass or more and 35% by mass or less, based on the solvent; (22) A copper paste comprising the composite copper particles according to any one of (1) to (9) and a paste solvent; (23) A joining member comprising the copper paste according to (22), and the like.

[0017] According to the composite copper particles of the present invention, a copper paste containing the composite copper particles can be sintered even in an inert atmosphere and can be suitably used as a joining member for a pressureless joining method. Therefore, the paste containing the composite copper particles of the present invention and the joining member containing the paste can join a substrate and a joined material by a pressureless joining method even in an inert atmosphere, and the sintered body produced thereby has excellent joining strength.

[0018] 1 is a scanning electron microscope photograph of Sample 1. FIG. 2 is a scanning electron microscope photograph of Sample 6. FIG. 3 is a scanning electron microscope photograph of Sample 7.

[0019] <Composite Copper Particles> The composite copper particles of the present invention comprise copper particles, a monocarboxylic acid or a salt thereof, and a compound represented by the general formula 1: R １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ and (excluding cases where both are hydrogen atoms).

[0020] The composite copper particles of the present invention have an average particle size of 170 nm or more and 600 nm or less, preferably 180 nm or more and 500 nm or less, and more preferably 200 nm or more and 400 nm or less. By setting the average particle size of the composite copper particles within this range, the formation of an oxide film (copper oxide) can be suppressed. Furthermore, by setting the average particle size of the composite copper particles within this range, the dispersibility of the composite copper particles in a paste when the composite copper particles are used in a joining member can be improved. Furthermore, the joining strength of a paste containing the composite copper particles and a joining member containing the paste can be improved.

[0021] The average particle size of the composite copper particles is measured as follows: The composite copper particles of the present invention are photographed using a scanning electron microscope (S4800, manufactured by Hitachi High-Technologies Corporation, hereinafter also referred to as "SEM"), the maximum Feret diameters (hereinafter simply referred to as Feret diameters) of 50 primary particles in the SEM field of view are measured, and the arithmetic mean value thereof is taken as the average particle size.

[0022] <Copper Particles> The composite copper particles of the present invention contain copper particles. The average particle size of the copper particles is preferably 170 nm or more and 600 nm or less, more preferably 180 nm or more and 500 nm or less, and even more preferably 200 nm or more and 400 nm or less. By adjusting the average particle size within these ranges, the composite copper particles of the present invention can have a desired average particle size. The copper particles may be commercially available copper particles, or may be produced by a known method, or may be produced by the production method described below.

[0023] The average particle size of the copper particles can be measured in the same manner as the average particle size of the composite copper particles described above.

[0024] In addition, since the increase in average particle size of the composite copper particles due to the inclusion of a monocarboxylic acid or its salt, and a compound represented by the general formula 1 is very small, in the present application, it can be considered that the average particle size of the copper particles does not change due to the monocarboxylic acid and the compound represented by the general formula 1.

[0025] The shape of the copper particles is not particularly limited, and any shape such as irregular, spherical, polyhedral, spindle-like, or plate-like may be used.

[0026] The copper particles may contain substances other than metallic copper, such as raw materials and reactants used in the manufacturing process, to the extent that it does not cause any problems depending on the application.

[0027] <Monocarboxylic acid or salt thereof> The composite copper particles of the present invention contain a monocarboxylic acid or a salt thereof. The type of the monocarboxylic acid is not particularly limited. The hydrocarbon group in the monocarboxylic acid molecule may be composed of only single bonds, or may contain one or more multiple bonds along the chain. Furthermore, the hydrocarbon group portion in the monocarboxylic acid molecule may be linear, may contain a branch along the chain, or may contain a cyclic structure along the chain or at the end. Furthermore, the monocarboxylic acid molecule may contain a heteroatom at any position.

[0028] Examples of monocarboxylic acids 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, stearic acid, isostearic acid, 2-ethylcaproic acid, isopalmitic acid, etc. Examples of monocarboxylic acid salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0029] The composite copper particles may contain only one type of monocarboxylic acid or salt thereof, or two or more types. In particular, it is preferable to contain a monocarboxylic acid or salt thereof having from 2 to 12 carbon atoms in one molecule, including the carboxyl group, and more preferably caprylic acid, capric acid, or 2-ethylcaproic acid. The composite copper particles preferably contain the monocarboxylic acid or salt thereof, because this improves the bonding strength of the paste containing the composite copper particles of the present invention and the bonding member containing the paste.

[0030] The monocarboxylic acid or its salt is added to copper particles having a surface area of ​​1 nm ２ It is preferable that the amount of the cations contained in the composite copper particles is 5.3 molecules or more.

[0031] In one embodiment of the composite copper particle of the present invention, the monocarboxylic acid or salt thereof is a copper particle having a surface area of ​​1 nm ２ The monocarboxylic acid or its salt may be present on the surface of the copper particle so that the number of molecules is 5.3 or more relative to the number of molecules of the monocarboxylic acid or its salt. A specific embodiment of this invention is understood to be an embodiment in which the monocarboxylic acid or its salt forms a built-up film (like a stack of monomolecular films) on the surface of the copper particle.

[0032] The molecular density of the monocarboxylic acid or its salt in the liquid condensed film region is ２ In this case, it is understood that the monocarboxylic acid or its salt forms a monomolecular film on the surface of the copper particle.

[0033] In contrast, in the above-described embodiment of the composite copper particles of the present invention, the monocarboxylic acid or the salt thereof is a copper particle having a surface area of ​​1 nm ２ Since the ratio of the monocarboxylic acid to the salt thereof is 5.3 or more, as described above, a monomolecular film of the monocarboxylic acid on the surface of the copper particle is further bonded to a monocarboxylic acid or a salt thereof to form a built-up film, which can preferably suppress the formation of an oxide film (copper oxide) on the composite copper particle. Furthermore, when the composite copper particle is used as a paste or a bonding member containing the paste, the bonding strength of the bonding member is preferably improved.

[0034] Copper particle surface area 1 nm ２ The molecular density of the monocarboxylic acid or its salt is ２ By setting the molecular density in this range, it is possible to suppress the formation of an oxide film (copper oxide), and the bonding strength of a paste containing the composite copper particles of the present invention and a bonding member containing the paste is preferably improved. In addition, the upper limit of the molecular density is set to a value less than 1 nm2 of the surface area of ​​the copper particles, from the viewpoint that the effect of suppressing the formation of an oxide film (copper oxide) cannot be expected to be improved. ２ It is sufficient that the number of molecules is 50.0 or less.

[0035] Hereinafter, the surface area of ​​copper particles is 1 nm ２The number of molecules of monocarboxylic acid or its salt relative to the total amount is referred to as molecular density, and is calculated as follows:

[0036] In the composite copper particles, the identity and content of the monocarboxylic acid or its salt component (hereinafter also referred to as the monocarboxylic acid component) are measured using gas chromatography as follows. When multiple monocarboxylic acids or salts thereof are used in combination, the total amount is defined as the content of the monocarboxylic acid component. From the viewpoint of measurement accuracy, if the content of the monocarboxylic acid component is 0.03 mass% or less based on the total mass of the composite copper particles, it is considered that the monocarboxylic acid component is not contained in the composite copper particles.

[0037] For gas chromatography, a gas chromatograph mass spectrometer equipped with a pyrolysis device is used. The pyrolysis device may be, for example, a Multi-Shot Pyrolyzer Model EGA / PY-3030D (manufactured by Frontier Labs), and the gas chromatograph mass spectrometer may be, for example, a Nexis GC-2030 (manufactured by Shimadzu Corporation).

[0038] The number of molecules of the monocarboxylic acid component contained in 1 g of the composite copper particles is expressed by the following formula (a): [Number of molecules of the monocarboxylic acid component] = M ａｃｉｄ / (M ｗ / N Ａ ) ...(a) where M ａｃｉｄ is the content (g) of monocarboxylic acid or its salt contained in 1 g of composite copper particles, and M ｗ is the molecular weight of the monocarboxylic acid component (g / mol), and N Ａ is Avogadro's constant (i.e., 6.02 × 10 ２３ mol －１ )

[0039] Composite copper particle surface area: 1 nm ２ Molecular density of monocarboxylic acid component (molecules / nm ２ The molecular density is calculated by the following formula (b): [Molecular density] = number of molecules of monocarboxylic acid component / specific surface area of ​​copper particles (b).

[0040] The specific surface area of ​​the copper particles may be measured using a known specific surface area measuring device, such as Macsorb (registered trademark) HM Model-1201 (manufactured by Mountec Co., Ltd.) For measuring the specific surface area, copper particles prepared by the following procedure are used.

[0041] 5 g of the composite copper particles of the present invention are mixed with 50 ml of 2-propanol, and the mixture is subjected to solid-liquid separation using a centrifuge at a centrifugal force of 400 G for 5 minutes, and this operation is repeated twice to obtain a solid content of copper particles from which the monocarboxylic acid or its salt and the compound represented by General Formula 1 have been released. After recovering the solid content of copper particles, the recovered solid content of copper particles is pre-dried under vacuum to remove the solvent, and then dried under a nitrogen atmosphere to remove adsorbed moisture, thereby obtaining copper particles.

[0042] The content of the monocarboxylic acid or its salt is preferably in the range of 0.2% by mass to 2.0% by mass, more preferably in the range of 0.3% by mass to 1.5% by mass, based on the total mass of the composite copper particles, and by this range, the bonding strength of the paste containing the composite copper particles of the present invention and the bonding member containing the paste is preferably improved.

[0043] <Compound Represented by General Formula 1> The composite copper particles of the present invention are compounds represented by General Formula 1: R １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ and (excluding cases where both are hydrogen atoms).

[0044] The compound represented by the general formula 1 is R １ The number of carbon atoms in R is preferably 1 or more and 10 or less, １ It is more preferable that the number of carbon atoms in R is 1 or more and 6 or less. ２ The number of carbon atoms in R is preferably 0 to 10. ２It is more preferable that the number of carbon atoms is from 0 to 6. By setting the number of carbon atoms in this range, the bonding strength of a paste containing the composite copper particles of the present invention and a bonding member containing the paste is preferably improved.

[0045] Examples of the compound represented by General Formula 1 include glycol ethers. Examples of the glycol ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, diethylene glycol monopropyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol dipropyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, and diethylene glycol methyl ethyl ether.

[0046] The molecular weight of the compound represented by General Formula 1 is preferably 100 or more and 400 or less, more preferably 100 or more and 300 or less, and even more preferably 100 or more and 200 or less. Diethylene glycol monobutyl ether (hereinafter also referred to as DGMBE) or diethylene glycol monohexyl ether (hereinafter also referred to as DGMHE) is more preferred. By setting the molecular weight of the compound represented by General Formula 1 within the above range, or by using DGMBE or DGMHE as the compound represented by General Formula 1, the bonding strength of the paste containing the composite copper particles of the present invention and the bonding member containing the paste is preferably improved.

[0047] In the composite copper particles, the identity and content of the compound represented by General Formula 1 can be determined by gas chromatography in the same manner as in the determination of the monocarboxylic acid or salt thereof described above.

[0048] The content of the compound represented by General Formula 1 in the composite copper particles is preferably 0.1% by mass or more and 2.0% by mass or less, and more preferably 0.1% by mass or more and 1.5% by mass or less, based on the total mass of the composite copper particles. By setting the content within such a range, the bonding strength of a paste containing the composite copper particles of the present invention and a bonding member containing the paste is preferably improved.

[0049] In the composite copper particles of the present invention, the bonding mode between the monocarboxylic acid or its salt and the compound represented by the general formula 1 when they form a built-up film on the surface of the copper particle is not particularly limited, and may be, for example, an intermolecular force such as van der Waals force, polar attraction, or hydrogen bonding, or may be physically or chemically adsorbed.

[0050] When forming a built-up film on the surface of the copper particles, the compound that bonds with the copper particle surface to form a monomolecular film on the copper particle surface is not particularly limited. Specifically, a monocarboxylic acid or a salt thereof may bond with the copper particle surface to form a monomolecular film, or a compound represented by General Formula 1 may bond with the copper particle surface to form a monomolecular film, or both (a monocarboxylic acid or a salt thereof and a compound represented by General Formula 1) may bond with the copper particle surface to form a monomolecular film. The built-up film is understood to be formed by bonding a monocarboxylic acid or a salt thereof (not bonded to the copper particle surface) with the compound represented by General Formula 1 on the monomolecular film formed as described above. Among these, it is preferable that a monocarboxylic acid or a salt thereof bonds with the copper particle surface to form a monomolecular film. This preferably improves the bonding strength of the paste containing the composite copper particles of the present invention and the bonding member containing the paste.

[0051] In the composite copper particles of the present invention, the total content (total amount) of the monocarboxylic acid or its salt and the compound represented by General Formula 1 is preferably 0.3 mass% or more and 3.5 mass% or less, based on the total composite copper particle. By setting the content within this range, the bonding strength of a paste containing the composite copper particles of the present invention and a bonding member containing the paste is preferably improved.

[0052] <Production of Composite Copper Particles> A method for producing the composite copper particles of the present invention will be described. The composite copper particles of the present invention are produced by mixing copper particles, a monocarboxylic acid or a salt thereof, and a compound represented by the general formula 1: R １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ and R 1 and R 2 are hydrogen atoms, and the like.

[0053] In the method for producing composite copper particles of the present invention, the monocarboxylic acid or its salt is not particularly limited. The hydrocarbon group in the monocarboxylic acid molecule may be composed of only single bonds, or may contain one or more multiple bonds along the chain. The hydrocarbon group portion in the monocarboxylic acid molecule may be linear, may contain a branch along the chain, or may contain a cyclic structure along the chain or at the end. The monocarboxylic acid molecule may also contain a heteroatom at any position.

[0054] Examples of monocarboxylic acids 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, stearic acid, isostearic acid, 2-ethylcaproic acid, isopalmitic acid, etc. Examples of monocarboxylic acid salts include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0055] The monocarboxylic acid or salt thereof may be used alone or in combination with two or more kinds. It is particularly preferred to use a monocarboxylic acid or salt thereof having from 2 to 12 carbon atoms in one molecule, including the carboxyl group, and more preferably caprylic acid, capric acid, or 2-ethylcaproic acid. The use of the monocarboxylic acid or salt thereof favorably improves the bonding strength of a paste containing composite copper particles and a bonding member containing the paste.

[0056] In the method for producing composite copper particles of the present invention, the monocarboxylic acid or its salt is mixed with the solvent in an amount of preferably 1% by mass to 30% by mass, more preferably 2% by mass to 20% by mass, inclusive, because this range efficiently ensures that the content of the monocarboxylic acid or its salt relative to the total composite copper particle falls within the desired range.

[0057] In the method for producing composite copper particles of the present invention, the monocarboxylic acid or its salt is preferably contained in the solvent in an amount of 1% by mass or more and 30% by mass or less relative to the solvent. Furthermore, it is more preferable that the monocarboxylic acid or its salt is contained in the solvent in an amount of 2% by mass or more and 20% by mass or less. This range is preferable because the content of the monocarboxylic acid or its salt relative to the entire composite copper particle efficiently falls within the desired range. Furthermore, the inclusion of the monocarboxylic acid or its salt in the solvent is preferable because the monocarboxylic acid or its salt efficiently bonds to the copper particle surface (or the monomolecular film formed on the copper particle surface) to efficiently form a built-up film.

[0058] In the method for producing composite copper particles of the present invention, １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ The compounds represented by R １ The number of carbon atoms in R is preferably 1 or more and 10 or less, １ It is more preferable that the number of carbon atoms in R is 1 or more and 6 or less. ２ The number of carbon atoms in R is preferably 0 to 10. ２ It is more preferable that the number of carbon atoms is from 0 to 6. By doing so, the bonding strength of a paste containing the composite copper particles of the present invention and a bonding member containing the paste is preferably improved.

[0059] Examples of the glycol ether include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, diethylene glycol monopropyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol dipropyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, and diethylene glycol methyl ethyl ether.

[0060] The molecular weight of the compound represented by General Formula 1 is preferably 100 or more and 400 or less, more preferably 100 or more and 300 or less, and even more preferably 100 or more and 200 or less. Diethylene glycol monobutyl ether (DGMBE) or diethylene glycol monohexyl ether (DGMHE) is even more preferred. By setting the molecular weight of the compound represented by General Formula 1 within the above range, or by using DGMBE or DGMHE as the compound represented by General Formula 1, the bonding strength of a paste containing the composite copper particles of the present invention and a bonding member containing the paste is preferably improved.

[0061] In the method for producing composite copper particles of the present invention, the compound represented by General Formula 1 is mixed with the solvent in an amount of preferably 1% by mass to 30% by mass, more preferably 2% by mass to 20% by mass, inclusive, inclusive. By adjusting the amount to such a range, the content of the compound represented by General Formula 1 relative to the total composite copper particles is efficiently adjusted to the desired range, which is preferable.

[0062] In the method for producing composite copper particles of the present invention, the compound represented by General Formula 1 is preferably contained in the solvent in an amount of 1% by mass or more and 30% by mass or less relative to the solvent. Furthermore, the compound represented by General Formula 1 is more preferably contained in the solvent in an amount of 2% by mass or more and 20% by mass or less. This range is preferable because the content of the compound represented by General Formula 1 relative to the entire composite copper particle falls within a desired range. Furthermore, the compound represented by General Formula 1 is preferably contained in the solvent because the compound represented by General Formula 1 efficiently bonds to the copper particle surface (or a monomolecular film formed on the copper particle surface) to efficiently form a built-up film.

[0063] In the method for producing composite copper particles of the present invention, the total amount of the monocarboxylic acid or salt thereof and the compound represented by General Formula 1 is preferably 2% by mass or more and 35% by mass or less relative to the solvent. By setting the total amount within this range, the burden on the drying step is preferably reduced because the solvent does not contain an excessive amount of organic components.

[0064] In the method for producing composite copper particles of the present invention, the total amount of the monocarboxylic acid or its salt and the compound represented by General Formula 1 contained in the solvent is preferably 2% by mass or more and 35% by mass or less relative to the solvent. By setting the total amount within this range, the burden on the drying step due to the inclusion of an excessive amount of organic components can be reduced. Furthermore, the inclusion of the carboxylic acid or its salt and the compound represented by General Formula 1 in the solvent is preferred because they efficiently bond with the copper particle surface (or the monomolecular film formed on the copper particle surface) to efficiently form a built-up film.

[0065] In the method for producing composite copper particles of the present invention, the solvent is not particularly limited as long as it does not interact with the monocarboxylic acid or its salt or the compound represented by General Formula 1. Examples of such solvents that can be used include methanol, ethanol, 1-propanol, 2-propanol, acetone, and methyl ethyl ketone.

[0066] 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 solution containing a solvent and at least one raw material may be prepared, and the resulting solution may be mixed in any order. Specifically, it is preferable to prepare a treatment solution containing a solvent, a monocarboxylic acid or its salt, and a compound represented by General Formula 1, and then mix the treatment solution with copper particles. It is more preferable to mix a dispersion containing copper particles containing a solvent and copper particles with a treatment solution containing a solvent, a monocarboxylic acid or its salt, and a compound represented by General Formula 1. This is preferable because the monocarboxylic acid or its salt and the compound represented by General Formula 1 efficiently bond to the copper particle surface (or the monomolecular film formed on the copper particle surface) to efficiently form a built-up film.

[0067] The mixing may be performed using a known agitator, such as a blade agitator, a disperser mixer, or a homomixer. The mixing time is not particularly limited, but should be 5 minutes or more. This mixing time allows the raw materials to be sufficiently mixed. The rotation speed is also not particularly limited, but should be 100 rpm or more, and this rotation speed allows the raw materials to be sufficiently mixed.

[0068] The composite copper particles obtained in this step may be subjected to solid-liquid separation as necessary. For solid-liquid separation, a known filtration method can be used, for example, a pressure filtration device such as a rotary press or a filter press, or a vacuum filtration device such as a Nutsche filter or a Moore filter, which are commonly used in industry. Centrifugal separation can also be used.

[0069] During the solid-liquid separation, the solid content may be washed by a known method.

[0070] The method may further include a step of drying the solid content obtained by solid-liquid separation. When the drying step is included, the drying temperature, drying time, and drying atmosphere can be appropriately set. For example, the drying temperature is preferably 20°C or higher and 120°C or lower, the drying time is preferably 0.5 hours or higher and 10 hours or lower, and the drying atmosphere is preferably a vacuum atmosphere.

[0071] In the drying step, 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 can be used.

[0072] 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.

[0073] The composite copper particles produced by the above method may be subjected to appropriate particle size adjustment using a known pulverizer, classifier, or the like.

[0074] In the method for producing composite copper particles of the present invention, the average particle size of the copper particles is preferably 170 nm or more and 600 nm or less, more preferably 180 nm or more and 500 nm or less, and even more preferably 200 nm or more and 400 nm or less. Setting the average particle size within such a range is preferable because it allows the composite copper particles of the present invention to efficiently achieve the desired average particle size. The copper particles may be commercially available copper particles, or may be produced by a known method. The copper particles may also be synthesized, for example, by a method including the following steps A and B.

[0075] (Step A) In this step, a copper compound, a monocarboxylic acid or a salt thereof, an amine compound, and a solvent are mixed to obtain a mixed solution containing the copper compound.

[0076] The copper compound is not particularly limited as long as it contains a copper atom. Examples of copper compounds include 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) as copper carboxylates; 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. Among these, copper oxide (II) is preferred from the viewpoint of cost. These compounds may be used alone or in combination of two or more.

[0077] The amount of the copper compound added is preferably 1 part by mass or more and 100 parts by mass or less relative to the solvent. The amount of the copper compound added is preferably 1 part by mass or more relative to the solvent, in that it is possible to more effectively avoid a decrease in the amount of copper particles produced by step B. On the other hand, the amount of the copper compound added is preferably 100 parts by mass or less relative to the solvent, in that it is possible to effectively avoid a non-uniform reaction due to an increase in viscosity when the solvent and the copper compound are mixed in this step.

[0078] The monocarboxylic acid or salt thereof used in step A is not particularly limited. The hydrocarbon group in the monocarboxylic acid molecule may be composed of only single bonds, or may contain one or more multiple bonds along the chain. The hydrocarbon group portion in the monocarboxylic acid molecule may be linear, may contain a branch along the chain, or may contain a cyclic structure along the chain or at the end. The monocarboxylic acid molecule may contain a heteroatom at any position.

[0079] Examples of the monocarboxylic 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, stearic acid, isostearic acid, etc. Examples of the carboxylate salt include alkali metal salts such as sodium salts and potassium salts, alkaline earth metal salts such as magnesium salts and calcium salts, ammonium salts, and amine salts.

[0080] The monocarboxylic acid or its salt may be used alone or in combination of two or more. It is particularly preferred to use a monocarboxylic acid or its salt having from 2 to 12 carbon atoms in one molecule, including the carboxyl group, and among these, acetic acid, caprylic acid, capric acid, or a salt thereof is preferred. The use of such a carboxylic acid or its salt is preferred because it allows the copper particles obtained in step B described below to have a desired average particle size efficiently.

[0081] The amount of the monocarboxylic acid or its salt added is preferably 0.01 mol to 2 mol per mol of the copper compound, since this range allows the copper particles obtained in step B to have a desired average particle size efficiently.

[0082] The amine compound used in step A is not particularly limited. Among them, amino alcohols are preferably used. By using amino alcohols, foaming of the mixed solution containing the copper compound in step A can be preferably suppressed.

[0083] There are no limitations on the structure of the amino alcohol, and examples thereof include alkanol monoamines having one amino group.

[0084] Specific examples include monoethanolamine, heptaminol, isoethanol, propanolamine, sphingosine, 1-amino-2-propanol, 2-aminodibutanol, 2-diethylaminoethanol, 3-diethylamino-1,2-propanediol, 3-dimethylamino-1,2-propanediol, 3-methylamino-1,2-propanediol, and 3-amino-1,2-propanediol.

[0085] The amount of the amine compound added is preferably 0.25 mol or more and 2 mol or less per mol of the monocarboxylic acid, which is preferable in that thickening of the mixed solution containing the copper compound can be avoided.

[0086] The addition time of the amine compound is preferably 10 seconds to 30 minutes, which preferably suppresses the sudden heat generation of the mixed solution containing the copper compound in step A.

[0087] The solvent used in step A is not particularly limited, but alcohol is preferably used.

[0088] Examples of the alcohol include 1-propanol, 2-propanol, butanol, pentanol, hexanol, heptanol, and octanol. These may be used alone or in combination of two or more. These alcohols are preferred because they exhibit high compatibility with the reducing agent described below.

[0089] 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 monocarboxylic acid or its salt, and then further mix with the amine compound.

[0090] The mixing may be performed using a known agitator, such as a blade agitator, a disperser mixer, or a homomixer. The mixing time is not particularly limited, but may be 5 minutes or more. This mixing time allows the raw materials to be sufficiently mixed. The rotation speed is also not particularly limited, but may be 100 rpm or more, and this rotation speed allows the raw materials to be sufficiently mixed.

[0091] (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.

[0092] The reducing agent is not particularly limited as long as it reduces the copper compound. Furthermore, the reducing agent preferably has a boiling point of 70°C or higher, more preferably 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 efficiently reduced even when the liquid temperature of the mixed solution is 40°C or higher and 95°C or lower.

[0093] 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-hexylhydrazine. n-octylhydrazine, n-nonylhydrazine, n-decylhydrazine, n-undecylhydrazine, n-dodecylhydrazine, cyclohexylhydrazine, phenylhydrazine, 4-methylphenylhydrazine, benzylhydrazine, 2-phenylethylhydrazine, 2-hydrazinoethanol, acetohydrazine, adipic acid dihydrazide, sebacic acid dihydrazide, dodecanediohydrazide, isophthalic acid dihydrazide, salicylic acid hydrazide, etc. These may be used alone or in combination of two or more.

[0094] 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. In the present application, "intermittently or continuously added" means adding the reducing agent in small amounts over a long period of time.

[0095] The addition time of the reducing agent is preferably 50 minutes to 6 hours, more preferably 60 minutes to 6 hours. In this 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"). Furthermore, within this addition time range, the reducing agent may be added in multiple portions.

[0096] By adding the reducing agent intermittently or continuously, the heat generated during reduction is suppressed and the average particle size of the copper particles obtained by this process can be adjusted to the desired range. Therefore, it is preferable to add the reducing agent intermittently or continuously over a period of 50 minutes to 6 hours.

[0097] The amount of the reducing agent added is preferably 1.0 mol or more and 4.0 mol or less per 1.0 mol of the copper compound.

[0098] In this step, the liquid temperature of the mixed liquid containing the copper compound when the reducing agent is added is preferably 40°C or higher and 95°C or lower, more preferably 45°C or higher and 90°C or lower. By adjusting the liquid temperature of the mixed liquid containing the copper compound to the above temperature range when the reducing agent is added, copper particles having a desired average particle size can be obtained. The liquid temperature of the mixed liquid containing the copper compound may be adjusted before the reducing agent is added or during the addition of the reducing agent. Preferably, the liquid temperature of the mixed liquid containing the copper compound is adjusted to the above range before the reducing agent is added.

[0099] In this step, a known mixer such as a stirrer, a mixer, a homogenizer, an agitator, etc. may be used as needed. The rotation speed is not limited, but may be 100 rpm or higher.

[0100] The dispersion containing copper particles obtained by this step may be aged for several tens of minutes to several hours. The aging temperature is preferably 40°C or higher and 100°C or lower, more preferably 60°C or higher and 95°C or lower. The aging time is preferably 5 minutes or higher and 2.0 hours or lower. Furthermore, during aging, the dispersion may be stirred using the known mixer described above. The rotation speed is not limited, but may be 100 rpm or higher.

[0101] The dispersion containing copper particles obtained in this step may be used as is in the step of producing composite copper particles, or may be subjected to solid-liquid separation as necessary. For solid-liquid separation, a known filtration method may be used, for example, a pressure filtration device such as a rotary press or a filter press, or a vacuum filtration device such as a Nutsche filter or a Moore filter, which are commonly used in industry. Centrifugal separation may also be used.

[0102] During the solid-liquid separation, the solid content may be washed by a known method.

[0103] Furthermore, the solid fraction obtained by the solid-liquid separation may be subjected to a drying step. When a drying step is included, the drying temperature, drying time, and drying atmosphere can be appropriately set. For example, the drying temperature is preferably 20°C or higher and 120°C or lower, the drying time is preferably 0.5 hours or higher and 10 hours or lower, and the drying atmosphere is preferably an inert gas stream such as nitrogen or argon, or a vacuum atmosphere.

[0104] In the drying step, 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 can be used.

[0105] 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.

[0106] By the manufacturing method including the above-mentioned steps A and B, copper particles having an average particle diameter of 170 nm or more and 600 nm or less can be obtained, and the copper particles obtained here can be used as a raw material when manufacturing the composite copper particles of the present invention.

[0107] <Copper Paste> The copper paste of the present invention contains the above-described composite copper particles and a paste solvent.

[0108] Examples of the solvent for the paste that can be used include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, 1,2-propanediol, 1,3-propanediol, α-terpineol, etc. The solvent for the paste may be used alone or in combination of two or more.

[0109] 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.

[0110] 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 flat 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.

[0111] 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.

[0112] The copper paste of the present invention preferably contains the composite copper particles in an amount of 80% by mass or more and 98% by mass or less, more preferably 85% by mass or more and 96% by mass or less, based on the total amount of the paste. By containing 80% by mass or more of the composite copper particles, the generation of voids during heating can be suppressed, which is preferable, and the bonding strength can be further improved. Furthermore, by containing 98% by mass or less, aggregation of the composite copper particles in the paste can be efficiently prevented, and the coatability of the paste can be preferably improved.

[0113] A known mixer can be used in the mixing step when preparing the copper paste of the present invention. Furthermore, during the mixing, degassing may be performed as necessary.

[0114] Examples of mixers include those commonly used industrially, such as a twin-shaft mixer, a three-roll mill, a sand mill, and a planetary mixer. Furthermore, for laboratory scale mixers, a stirrer, a hybrid mixer, a homogenizer, a paint shaker, and the like can be used. In this case, grinding media containing glass, alumina, zirconia, zirconium silicate, and the like may be used as needed.

[0115] <Bonding member> The copper paste of the present invention can be used as a bonding member. The bonding member may contain an appropriate additive depending on the application. This bonding member can satisfactorily bond a substrate and a workpiece.

[0116] The substrate and the material to be joined may be made of the same material or different materials. The material to be joined is not particularly limited, and examples thereof include various metal materials, semiconductor materials (e.g., chips), ceramic materials, and resin materials.

[0117] 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.

[0118] In the bonding method using the bonding member of the present invention, a substrate is provided with the bonding member, and a workpiece is placed on the opposite side of the bonding member to the substrate to obtain a laminate. The substrate and the workpiece are bonded by heating the laminate.

[0119] As a method for applying a copper paste as a bonding member to a substrate, various coating methods can be used, such as 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.

[0120] The bonding members provided on the substrate may be dried as appropriate. This can prevent the bonding members from flowing or voids from occurring during heating. The atmosphere during drying may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere. The pressure during drying may be atmospheric pressure or reduced pressure. Drying under reduced pressure can promote the drying of the bonding members provided on the substrate. The temperature during drying may be room temperature, or may be heated as long as the metal particles contained in the bonding members do not fuse together.

[0121] In particular, a bonding member containing the copper paste of the present invention can achieve high bondability simply by sintering by heating, and is therefore suitable for use as a pressureless bonding paste.

[0122] 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.

[0123] 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.

[0124] When the joining member is sintered by heating, the fusion of metal particles contained in the joining member progresses, and the base material and the materials to be joined are joined to form a sintered body.

[0125] The heating atmosphere for the laminate in the pressureless bonding method or pressure bonding may be an oxygen-free atmosphere, an inert atmosphere, or a reducing atmosphere, but an inert atmosphere is more preferable in terms of avoiding the need for large-scale production equipment for the sintered body.

[0126] The heating temperature of the laminate in the pressureless bonding method or pressure bonding 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.

[0127] The heating time of the laminate in the pressureless bonding method or pressure bonding method is preferably 1 minute or more and 60 minutes or less in order to sufficiently volatilize the solvent contained in the bonding material and to sufficiently promote sintering of the metal particles contained in the bonding material.

[0128] The bonding strength of the sintered body obtained by the pressureless bonding method or pressure bonding method is measured by the method described in the examples.

[0129] 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.

[0130] 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. A sintered body having such a bonding strength can be determined to be sufficiently bonded, and it can also be confirmed that the bonding member of the present invention can be suitably used for pressure bonding paste.

[0131] The present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to these.

[0132] (Measurement of average particle size) A sample was observed using a scanning electron microscope (Hitachi High-Technologies Corporation: S4800) to obtain a scanning electron micrograph at a magnification of 50,000. 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.

[0133] (Measurement of Specific Surface Area) 5 g of sample was mixed with 2-propanol (50 ml), and the solid-liquid separation was performed twice using a centrifuge (Allegra X-30R, manufactured by Beckman Coulter) at a centrifugal force of 400 G for 5 minutes to recover the solid content of copper particles. The recovered solid content of copper particles was pre-dried under vacuum at 1.3 Pa, 25°C, and 300 minutes to remove the solvent, and then dried under a nitrogen atmosphere to remove adsorbed moisture, thereby obtaining a measurement sample. The specific surface area of ​​the measurement sample was measured under the following conditions using a specific surface area measurement device (Macsorb HM Model-1201, manufactured by Mountec Co., Ltd.). Drying conditions Drying atmosphere: nitrogen gas (purity 99.99999%) Gas flow rate: 50 mL / min Drying temperature: 80°C Drying time: 15 minutes Measurement conditions Drying atmosphere: mixed gas of 70% helium and 30% nitrogen Gas flow rate: 25 mL / min Degassing temperature: 80°C Adsorption temperature: -196°C

[0134] (Identification and Measurement of Monocarboxylic Acid and Compound Represented by General Formula 1) Using a gas chromatograph mass spectrometer (Shimadzu Corporation, Nexis GC-203) equipped with a multi-shot pyrolyzer (Frontier Labs, Model EGA / PY-3030D), the monocarboxylic acid or its salt component contained in the sample, and the compound represented by General Formula 1:R were measured under the following conditions. １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ The components of the compound represented by the formula (I) were identified and their contents were measured. - Multi-shot pyrolyzer Furnace temperature: 300°C Sample amount: 5 mg - Gas chromatograph mass spectrometer Column temperature: After holding at 60°C for 3 minutes, the temperature was increased and held at 220°C for 5 minutes Heating rate: 25°C / min Separation column: Ultra ALLOY-1 (Frontier Labs, product number: UA-15W-5.0F) Column flow rate: Nitrogen (99.999% UP) 6mL / min - Detector (Flame ionization detector: FID) Detector temperature: 320°C Hydrogen flow rate: 30mL / min Air flow rate: 300mL / min

[0135] (Calculation of molecular density) Surface area of ​​sample: 1 nm ２ Molecular density of monocarboxylic acid component (molecules / nm ２ The molecular density was calculated by the following formula: [Molecular density] = number of molecules of monocarboxylic acid component / specific surface area of ​​copper particles. Here, the number of molecules of monocarboxylic acid component is expressed as follows: [Number of molecules of monocarboxylic acid component] = M ａｃｉｄ / (M ｗ / N Ａ ) (M ａｃｉｄ is the content (g) of monocarboxylic acid or its salt contained in 1 g of sample, and M ｗ is the molecular weight of the monocarboxylic acid component (g / mol), and N Ａis Avogadro's constant (i.e., 6.02 × 10 ２３ mol －１ )

[0136] (Preparation of bonding members) The samples and the paste solvent were mixed in the ratios shown in Tables 1 to 3 below, and the mixture was kneaded for 4 minutes using a mixer (Awatori Rentaro AR-250, manufactured by Thinky Corporation). This process was repeated twice to obtain bonding members.

[0137] (Bonding Strength Measurement) A metal mask with an opening of 5 mm and a thickness of 0.1 mm was placed on a substrate with a diameter (hereinafter referred to as φ) of 10 mm and a thickness of 5 mm, and the above-mentioned bonding member was applied to the opening. A copper piece with a diameter of 5 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 applied portion of the bonding member to obtain a laminate. The surface roughness was the average value of Ra measured with a laser microscope for three test pieces randomly selected from 100 test pieces. The laminate was placed on a hot plate heated to 200 ° C and maintained for 30 minutes while nitrogen (purity 99.995%) was circulated at 100 mL / min. The laminate was then naturally cooled to 50 ° C to obtain a sintered body. The sintered body was set in a strength tester (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 peeled off.

[0138] (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, manufactured by Nisshin Chemco Co., Ltd.), 96 g of acetic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 82.7 g of capric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added thereto, followed by stirring at room temperature at a rotation speed of 250 rpm. Furthermore, 127.0 g of 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added over 10 minutes, and stirring was continued to prepare a mixed solution containing a copper compound. The rotation speed was also kept at 250 rpm for subsequent stirring. The mixed solution containing the copper compound was heated to 50°C, and 160 g of 60% hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Co., Inc.) as a reducing agent was added dropwise over 7 minutes and 30 seconds, followed by stirring for 40 minutes. To this mixture, 160 g of 60% hydrazine hydrate was added dropwise over 7 minutes and 30 seconds, followed by stirring for 15 minutes. 680 g of 60% hydrazine hydrate was then added dropwise over 30 minutes, after which the temperature was raised to 90°C and stirring continued for 2 hours to obtain a dispersion containing copper particles. The time required to add the entire amount of reducing agent was 100 minutes, and the oil bath temperature during the addition of the reducing agent was set to 50°C. The dispersion containing copper particles was naturally cooled to 50°C or below, then allowed to stand for 30 minutes for solid-liquid separation, and 30 g of solids were weighed and recovered. The solids were mixed with 75 mL of 2-propanol (manufactured by Nacalai Tesque) and stirred for 10 minutes. Solid-liquid separation was then performed for 5 minutes using a centrifuge (manufactured by Beckman Coulter, Allegra X-30R) at a centrifugal force of 400 G to obtain the solid content of copper particles of Production Example 1.

[0139] (Production Example 2) A solid content of copper particles in Production Example 2 was obtained in the same manner as in Production Example 1, except that the conditions for dropping the reducing agent in Example 1 were changed to the following conditions. The mixed liquid was heated to 50°C, and 80 g of 60% hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Company, Inc.) as a reducing agent was added dropwise over 3 minutes 45 seconds, followed by stirring for 60 minutes. 80 g of 60% hydrazine hydrate was added dropwise over 3 minutes 45 seconds, followed by stirring for 40 minutes. 80 g of 60% hydrazine hydrate was added dropwise over 3 minutes 45 seconds, followed by stirring for 40 minutes. 680 g of 60% hydrazine hydrate was added dropwise over 30 minutes, followed by heating to 90°C and stirring for 2 hours, to obtain a dispersion containing copper particles. The time required to add the entire amount of the reducing agent was 225 minutes, and the temperature of the oil bath was set to 50° C. during the addition of the reducing agent.

[0140] (Production Example 3) A 10 L glass four-neck 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, manufactured by Nisshin Chemco Co., Ltd.), 96 g of acetic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 82.7 g of capric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added thereto, followed by stirring at room temperature at a rotation speed of 250 rpm. Furthermore, 127.0 g of 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added over 10 minutes, and stirring was continued to produce a mixed solution containing a copper compound. The rotation speed for subsequent stirring was also 250 rpm. The mixed solution containing the copper compound was heated to 90°C, and 996 g of 60% hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Company, Inc.) was added dropwise over 300 minutes. The mixture was then stirred for 10 minutes while maintaining the temperature at 90°C to obtain a dispersion of copper particles. The dispersion containing copper particles was naturally cooled to 50°C or below, and then allowed to stand for 30 minutes for solid-liquid separation. 30 g of solids were weighed and collected. The solids were mixed with 75 mL of 2-propanol (manufactured by Nacalai Tesque, Inc.) and stirred for 10 minutes. The solids were then subjected to solid-liquid separation for 5 minutes using a centrifuge (manufactured by Beckman Coulter, Allegra X-30R) at a centrifugal force of 400 G to obtain the solid content of copper particles of Production Example 3.

[0141] (Manufacturing Example 4) The solid content of copper particles for Manufacturing Example 4 was obtained in the same manner as Manufacturing Example 1, except that the weight of each raw material in Manufacturing Example 1 was halved and the conditions for dripping the reducing agent were changed to dripping over 45 minutes.

[0142] Example 1 Caprylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), diethylene glycol monohexyl ether (DGMHE (manufactured by Tokyo Chemical Industry Co., Ltd.)), and 2-propanol were stirred so that the caprylic acid and DGMHE concentrations were 6% by mass relative to the 2-propanol, and 75 mL of a treatment solution was prepared. The solid content of the copper particles of Production Example 1 was mixed with the treatment solution and then stirred for 10 minutes, thereby subjecting the copper particles of Production Example 1 to a surface treatment. Thereafter, solid-liquid separation was performed for 5 minutes at a centrifugal force of 400 G using a centrifuge (Allegra X-30R, manufactured by Beckman Coulter, Inc.). This operation was repeated twice, and the solid content was recovered. The obtained solid content was placed in a desiccator, the pressure in the desiccator was reduced using a vacuum pump (G-20DA, manufactured by ULVAC), and the solid content was vacuum dried at 1.3 Pa and 25° C. for 300 minutes to obtain Sample 1.

[0143] Example 2 Sample 2 was obtained in the same manner as in Example 1, except that DGMHE was changed to diethylene glycol monobutyl ether (DGMBE (manufactured by Tokyo Chemical Industry Co., Ltd.)).

[0144] Example 3 Sample 3 was obtained in the same manner as in Example 1, except that the caprylic acid content was changed from 6% by mass to 15% by mass, and the DGMHE content was changed from 6% by mass to 15% by mass.

[0145] Example 4 Sample 4 was obtained in the same manner as in Example 1, except that the caprylic acid content was changed from 6% by mass to 3% by mass and the DGMHE content was changed from 6% by mass to 3% by mass.

[0146] Example 5 Sample 5 was obtained in the same manner as in Example 1, except that caprylic acid in Example 4 was changed to capric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0147] Example 6 Sample 6 was obtained in the same manner as in Example 1, except that the copper particles were produced in Production Example 2.

[0148] Example 7 Sample 7 was obtained in the same manner as in Example 1, except that the copper particles in Example 1 were produced in Production Example 3.

[0149] (Example 8) Sample 8 was obtained in the same manner as in Example 1, except that the copper particles were produced in Production Example 2 and the caprylic acid in the treatment solution was changed to 2-ethylcaproic acid (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0150] Comparative Example 1 Sample 9 was obtained in the same manner as in Example 1, except that DGMHE was not contained in the treatment liquid as the compound represented by the general formula 1 above.

[0151] Comparative Example 2 Sample 10 was obtained in the same manner as in Example 1, except that the treatment liquid did not contain caprylic acid as the carboxylic acid or its salt.

[0152] Comparative Example 3 Sample 11 was obtained in the same manner as in Example 4, except that the copper particles in Example 4 were produced in Production Example 4.

[0153] For Samples 1 to 11, the average particle size, the type and content of the monocarboxylic acid component, and the carboxylic acid component of the general formula 1: R １ (OCH ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 or more and 4 or less. １ and R ２ The content of the compound represented by the formula (I) and the bonding strength of the sintered body were evaluated. The results are shown in Tables 1 to 3 (in the tables, the compound represented by the formula 1 is simply referred to as "compound of formula 1"). Scanning electron microscope photographs of Samples 1, 6, and 7 are shown in Figures 1 to 3.

[0154]

[0155]

[0156]

[0157] The composite copper particles of Samples 1 to 8 contain a monocarboxylic acid and a compound represented by General Formula 1, and have an average particle size of 170 nm or more. Sintered bodies using these samples as joining members were found to have sufficient joining strength (20 MPa or more). This indicates that the composite copper particles of the present invention can be sintered even in an inert atmosphere and are suitable for use as joining members for pressureless joining methods.

[0158] On the other hand, Samples 9 and 10 had an average particle size of 170 nm or more, but did not contain a monocarboxylic acid or a compound represented by General Formula 1. Sample 11 contained a monocarboxylic acid and a compound represented by General Formula 1, but had an average particle size of less than 170 nm. It was found that sintered bodies using such samples as joining members had insufficient joining strength (less than 20 MPa).

[0159] The composite copper particles of the present invention can be easily produced without any limitations during production. Furthermore, a copper paste containing the obtained composite copper particles can also be produced. A joining member containing the copper paste exhibits excellent joining properties even under pressureless joining conditions, and by using the copper paste of the present invention for a joining member, a sintered body with sufficient joining strength can be obtained.

Claims

1. Copper particles, a monocarboxylic acid or a salt thereof, and a compound represented by the general formula 1: R １ (O.C.H. ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 to 4. １ and R ２ and a compound represented by the formula:

2. The monocarboxylic acid or its salt is a copper particle having a surface area of ​​1 nm ２ The composite copper particle according to claim 1, wherein the amount of the copper particles is 5.3 molecules or more and 50.0 molecules or less.

3. The composite copper particles according to claim 1 or 2, wherein the carbon number of the monocarboxylic acid or its salt is 2 or more and 12 or less.

4. The composite copper particles according to claim 1 or 2, wherein the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid, capric acid and 2-ethylcaproic acid.

5. The composite copper particles according to claim 1 or 2, wherein the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid and capric acid.

6. Composite copper particles according to claim 1 or 2, wherein the molecular weight of the compound represented by general formula 1 is 100 or more and 400 or less.

7. Composite copper particles according to claim 1 or 2, wherein the compound represented by general formula 1 is diethylene glycol monohexyl ether or diethylene glycol monobutyl ether.

8. Composite copper particles according to claim 1 or 2, wherein the content of the compound represented by general formula 1 is 0.1 mass% or more and 2.0 mass% or less based on the total composite copper particles.

9. Composite copper particles according to claim 1 or 2, wherein the total amount of the monocarboxylic acid or its salt and the compound represented by general formula 1 is 0.3 mass% or more and 3.5 mass% or less based on the entire composite copper particle.

10. A method for producing a compound comprising the steps of: copper particles; a monocarboxylic acid or a salt thereof; and a compound represented by the general formula 1: R １ (O.C.H. ２ CH ２ ) ｎ OR ２ (In the formula, R １ represents an alkyl group, an aryl group, or a hydrogen atom; R ２ represents an alkyl group, an aryl group, a hydrogen atom, or an acetyl group, and n is an integer of 1 to 4. １ and R ２ and R 1 and R 2 are hydrogen atoms, respectively, and a solvent is mixed with the compound represented by the formula (I) and R 1 and R 2 , and the average particle size measured by a scanning electron microscope is 170 nm or more and 600 nm or less.

11. The method for producing composite copper particles according to claim 10, wherein the number of carbon atoms in the monocarboxylic acid or its salt is 2 or more and 12 or less.

12. The method for producing composite copper particles according to claim 10 or 11, wherein the monocarboxylic acid or salt thereof is at least one carboxylic acid or salt thereof selected from the group consisting of caprylic acid, capric acid, and 2-ethylcaproic acid.

13. A method for producing composite copper particles as described in claim 10 or 11, wherein the monocarboxylic acid or its salt is at least one carboxylic acid or its salt selected from the group consisting of caprylic acid and capric acid.

14. A method for producing composite copper particles as described in claim 10 or 11, wherein the molecular weight of the compound represented by general formula 1 is 100 or more and 400 or less.

15. A method for producing composite copper particles as described in claim 10 or 11, wherein the compound represented by general formula 1 is diethylene glycol monohexyl ether or diethylene glycol monobutyl ether.

16. A method for producing composite copper particles as described in claim 10 or 11, wherein the monocarboxylic acid or its salt is mixed in an amount of 1 mass % or more and 30 mass % or less relative to the solvent.

17. A method for producing composite copper particles as described in claim 10 or 11, wherein the monocarboxylic acid or its salt is contained in the solvent in an amount of 1% by mass or more and 30% by mass or less relative to the solvent.

18. A method for producing composite copper particles as described in claim 10 or 11, in which the compound represented by general formula 1 is mixed in an amount of 1 mass % or more and 30 mass % or less relative to the solvent.

19. A method for producing composite copper particles as described in claim 10 or 11, wherein the compound represented by general formula 1 is contained in the solvent in an amount of 1 mass % or more and 30 mass % or less relative to the solvent.

20. A method for producing composite copper particles as described in claim 10 or 11, wherein the total amount of the monocarboxylic acid or its salt and the compound represented by general formula 1 is mixed in an amount of 2 mass% or more and 35 mass% or less relative to the solvent.

21. A method for producing composite copper particles as described in claim 10 or 11, wherein the total amount of the monocarboxylic acid or its salt and the compound represented by general formula 1 is contained in the solvent in an amount of 2 mass% or more and 35 mass% or less relative to the solvent.

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

23. A joining member comprising the copper paste according to claim 22.

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