Composite microparticles

Abstract

This invention relates to composite microparticles that can suppress oxidation even after storage for a certain period of time, have low viscosity when used as a dispersion, and have high bonding strength after coating, as well as a composite microparticle dispersion using said composite microparticles. [Solution] [1] Composite fine particles in which at least a portion of the surface of copper fine particles is coated with a sulfur-containing organic compound, wherein the sulfur atom content in the sulfur-containing organic compound coating the composite fine particles is 1.0% by mass or more and 7.0% by mass or less; [2] A composite fine particle dispersion using the composite fine particles described in [1].

Description

Technical Field

[0001] The present invention relates to composite fine particles in which a part of the surface of copper fine particles is coated with a sulfur-containing organic compound, a composite fine particle dispersion containing the composite fine particles, and the like.

Background Art

[0002] Copper is excellent in electrical conductivity and thermal conductivity, and is therefore widely used, for example, as a conductor wiring material, a heat transfer material, a heat exchange material, a heat dissipation material, etc., or as a bonding material for joining a bonded object. When used as a conductor wiring material, a copper fine particle dispersion in which copper fine particles are dispersed is applied to an object in an arbitrary shape by various coating means and fired to form a conductor wiring pattern. When used as a bonding material, various techniques have been proposed in which a copper fine particle dispersion in which copper fine particles are dispersed is used, applied to an object by various coating means, and fired to bond the bonded object.

[0003] For example, Patent Document 1 aims to provide copper powder that can exhibit stable properties without significant changes in properties such as viscosity and dry film density over time when producing a copper paste. The amount of Fe contained in the copper powder is 0.001% by mass or less, the amount of S is 0.001% by mass or less, the amount of N is 0.05% by mass or less, and the powder pH of the copper powder is 7.0 or less. Copper powder is disclosed. Further, Patent Document 2 aims to provide a copper powder having high resistance to oxidation. It is a copper powder containing copper and a sulfur-containing compound, and the particle size D when the cumulative frequency in the volume-based particle size histogram obtained using the laser diffraction scattering method is 50%. 50 is 0.1 μm or more and 0.5 μm or less, the content of cuprous oxide and cupric oxide obtained by X-ray diffraction is less than 4% by mass, the average circularity is 0.97 or more, and the average circularity is the average of the circularities of the copper particles contained in the copper powder. Copper powder is disclosed.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-204837 [Patent Document 2] Japanese Patent Publication No. 2022-167683 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the copper powder described in Patent Document 1 and the copper powder material described in Patent Document 2 had the problem of being prone to oxidation when stored for a certain period of time. As a result, when the copper powder or copper powder material was used as a dispersion of copper fine particles, the viscosity was high, reducing the coating properties, and the bonding strength after coating was sometimes low. The present invention relates to composite microparticles that can suppress oxidation even after storage for a certain period of time, have low viscosity when used as a dispersion, and have high bonding strength after coating, and to a composite microparticle dispersion using said composite microparticles. [Means for solving the problem]

[0006] The present inventors have found that the above problem can be solved by using composite microparticles in which a portion of the surface of copper microparticles is coated with a sulfur-containing organic compound, and by keeping the content of sulfur atoms in the sulfur-containing compound coating the copper microparticles within a predetermined range. The present invention relates to the following [1] to [6]. [1] A composite fine particle in which a portion of the surface of copper fine particles is coated with a sulfur-containing organic compound, wherein the sulfur atom content in the sulfur-containing organic compound coating the copper fine particles is 1.0% by mass or more and 7.0% by mass or less. [2] A method for producing composite fine particles as described in [1] above, To prepare a mixed solution containing a copper raw material compound, a reducing agent, a sulfur-containing organic compound, and a dispersion medium; to reduce the copper raw material compound in the mixed solution with the reducing agent to obtain a dispersion of composite fine particles containing copper fine particles and a sulfur-containing organic compound that coats a portion of the surface thereof; A method for producing composite fine particles, comprising separating the composite fine particles from a dispersion of the composite fine particles. [3] A composite particle dispersion containing the composite particle described in [1] above. [4] A method for manufacturing a bonded body, comprising coating a metal substrate with the composite fine particle dispersion described in [3] above, and placing the members to be bonded on the composite fine particle dispersion coated on the metal substrate, and then pressurizing and firing them. [5] A method for manufacturing an electronic device, comprising using the composite fine particle dispersion described in [3] above for forming a conductive member of the electronic device. [6] Use of the composite fine particle dispersion described in [3] above as a bonding material for joining members to be joined together. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide composite microparticles that can suppress oxidation even after storage for a certain period of time, have low viscosity when used as a composite microparticle dispersion, and have high bonding strength after coating, as well as a composite microparticle dispersion using said composite microparticles. [Modes for carrying out the invention]

[0008] [Composite fine particles] The composite fine particles of the present invention are particles comprising copper fine particles and a sulfur-containing organic compound coating at least a portion of the surface of the copper fine particles, wherein the sulfur atom content in the sulfur-containing organic compound coating the copper fine particles is 1.0% by mass or more and 7.0% by mass or less. In this invention, "composite fine particles in which at least a portion of the surface of copper fine particles is coated with a sulfur-containing organic compound" is synonymous with "composite fine particles comprising copper fine particles and a sulfur-containing organic compound that coats at least a portion of the surface of copper fine particles." "Copper nanoparticles" are granular copper components derived from the copper raw material compound used in the manufacturing method of composite nanoparticles, which will be described in detail later. They are produced by the reduction of the copper raw material compound. The copper component preferably consists only of copper, but may contain some of the aforementioned unavoidable impurities. The copper content in the copper component is preferably 95% by mass or more, more preferably 98% by mass or more, even more preferably 99% by mass or more, and even more preferably substantially 100% by mass. "Substantially 100% by mass" means that it may contain components that are unintentionally included (unavoidable impurities).

[0009] The composite microparticles of the present invention exhibit suppressed oxidation even after storage for a certain period, have low viscosity when used as a composite microparticle dispersion, and possess high bonding strength after coating. The reason for this is not entirely clear, but it is thought to be as follows. Typically, when a composite microparticle dispersion is obtained by adding a solvent to composite microparticles, a high sulfur content inhibits the adsorption of the dispersant to the composite microparticles, resulting in reduced dispersibility and poor coating properties. Furthermore, the sintered body obtained by sintering the composite microparticle dispersion after coating also suffers from poor coating quality, leading to reduced bonding strength. Therefore, from the viewpoint of viscosity and bonding strength of the composite microparticle dispersion, a low sulfur content is generally preferable. On the other hand, since sulfur atoms have antioxidant properties that suppress the oxidation of metals, it is preferable to include a certain amount of sulfur atoms in the composite fine particles from the viewpoint of suppressing the oxidation of copper fine particles. In relation to the above, the composite fine particles of the present invention are characterized in that at least a portion of the surface of the copper fine particles is coated with a sulfur-containing organic compound, and the sulfur atom content in the sulfur-containing organic compound coating the copper fine particles is 1.0% by mass or more and 7.0% by mass or less. By ensuring that the sulfur atom content in the sulfur-containing organic compound coating the copper nanoparticles is 1.0% by mass or more, a sufficient amount of sulfur atoms can be present in the composite nanoparticles, thereby suppressing the oxidation of the copper nanoparticles. Furthermore, by limiting the sulfur atom content in the sulfur-containing organic compound coating the copper nanoparticles to 7.0% by mass or less, excessive adsorption of the sulfur-containing organic compound onto the copper nanoparticles by sulfur atoms can be suppressed while still allowing a sufficient amount of the sulfur-containing organic compound to be present on the copper nanoparticle surface. This improves the dispersibility of the composite nanoparticles due to steric repulsion of the sulfur-containing organic compound, enhances the coating properties of the resulting composite nanoparticle dispersion, and consequently improves the bonding strength. Moreover, since the sulfur-containing organic compound is adsorbed onto the copper nanoparticles, it is believed that the sulfur atoms are also present near the copper surface. Therefore, even with a small sulfur atom content of 7.0% by mass or less in the sulfur-containing organic compound coating the copper nanoparticles, it is considered that oxidation of the copper nanoparticles can be efficiently suppressed.

[0010] In the present invention, the sulfur atom content in the sulfur-containing organic compound coated on copper fine particles is preferably 1.2% by mass or more, more preferably 1.5% by mass or more, even more preferably 2.0% by mass or more, and even more preferably 2.5% by mass or more, from the viewpoint of suppressing oxidation after storage, the rate of change in viscosity of the composite fine particle dispersion before and after storage, and the rate of change in bonding strength before and after storage. Furthermore, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving bonding strength after coating, it is preferably 6.5% by mass or less, more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less. The sulfur atom content in the sulfur-containing organic compound coated on copper nanoparticles can be determined by the method described in the examples.

[0011] In the present invention, the sulfur atom content in the composite fine particles is preferably 50 ppm by mass or more, more preferably 80 ppm by mass or more, even more preferably 110 ppm or more, even more preferably 150 ppm by mass or more, and even more preferably 200 ppm by mass or more, from the viewpoint of suppressing oxidation after storage, reducing the rate of change in viscosity of the composite fine particle dispersion before and after storage, and reducing the rate of change in bonding strength before and after storage. Furthermore, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving bonding strength after coating, the content is preferably 400 ppm by mass or less, more preferably 350 ppm by mass or less, even more preferably 300 ppm by mass or less, and even more preferably 280 ppm by mass or less. The sulfur atom content in the composite fine particles can be determined by the method described in the examples.

[0012] In the present invention, the content of the sulfur-containing organic compound in the composite fine particles is preferably 0.5% by mass or more, more preferably 0.55% by mass or more, still more preferably 0.58% by mass or more, even more preferably 0.6% by mass or more, from the viewpoints of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving the bonding strength after coating. And it is preferably 2.5% by mass or less, more preferably 1.5% by mass or less, still more preferably 1.2% by mass or less, even more preferably 1.0% by mass or less, even more preferably 0.9% by mass or less. The content of the sulfur-containing organic compound in the composite fine particles is determined by the method described in the Examples.

[0013] In the present invention, the particle size (D50) when the cumulative number frequency of the composite fine particles is 50% is preferably 80 nm or more, more preferably 100 nm or more, still more preferably 120 nm or more, even more preferably 130 nm or more, from the viewpoint of suppressing oxidation after storage. And from the viewpoints of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, it is preferably 500 nm or less, more preferably 350 nm or less, still more preferably 250 nm or less, even more preferably 220 nm or less, even more preferably 200 nm or less.

[0014] In the present invention, the particle size (D90) when the cumulative number frequency of the composite fine particles is 90% is preferably 150 nm or more, more preferably 160 nm or more, still more preferably 165 nm or more, even more preferably 170 nm or more, from the viewpoint of suppressing oxidation after storage. And from the viewpoints of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, it is preferably 500 nm or less, more preferably 400 nm or less, still more preferably 350 nm or less, even more preferably 320 nm or less, even more preferably 300 nm or less.

[0015] In the present invention, the particle size (D10) when the cumulative number frequency of the composite fine particles is 10% is preferably 30 nm or more, more preferably 40 nm or more, still more preferably 45 nm or more, and even more preferably 50 nm or more from the viewpoint of suppressing oxidation after storage. And from the viewpoints of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, it is preferably 200 nm or less, more preferably 150 nm or less, still more preferably 100 nm or less, even more preferably 90 nm or less, and even more preferably 80 nm or less. In the present invention, D10, D50, and D90 of the composite fine particles are determined by the method described in the examples.

[0016] <Sulfur-containing organic compound> In the present invention, the sulfur-containing organic compound refers to an organic compound containing a sulfur atom in its molecular structure.

[0017] (Sulfur-containing polymer P) In the present invention, the sulfur-containing organic compound preferably contains a sulfur-containing polymer P, and the number average molecular weight of the sulfur-containing polymer P is preferably 1,000 or more and 10,000 or less. When the sulfur-containing organic compound contains the sulfur-containing polymer P, sufficient sulfur atoms are present in the composite fine particles, and the oxidation of the copper fine particles can be further suppressed. Further, due to the steric repulsion of the sulfur-containing polymer P, the dispersibility of the composite fine particles can be further improved, and the viscosity of the composite fine particle dispersion can be further reduced. Also, the bonding property after coating can be further improved. Also, the change rate of the viscosity of the composite fine particle dispersion before and after storage and the change rate of the bonding strength before and after storage can be reduced.

[0018] In the present invention, the number-average molecular weight of the sulfur-containing polymer P is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 2,500 or more, and even more preferably 3,000 or more, from the viewpoint of further improving the dispersibility of the composite fine particles, reducing the viscosity of the composite fine particle dispersion, and improving the bonding strength after coating. Furthermore, from the viewpoint of ensuring sufficient sulfur atoms are present in the composite fine particles to further suppress the oxidation of copper fine particles, reducing the rate of change in the viscosity of the composite fine particle dispersion before and after storage, and reducing the rate of change in bonding strength before and after storage, the number-average molecular weight is preferably 10,000 or less, more preferably 7,000 or less, even more preferably 5,000 or less, even more preferably 4,500 or less, and even more preferably 4,000 or less. The number-average molecular weight of the sulfur-containing polymer P is determined by the method described in the examples.

[0019] In the present invention, the sulfur atom content in the sulfur-containing polymer P used for preparing composite fine particles, i.e., used for coating copper fine particles, is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.6% by mass or more, even more preferably 0.7% by mass or more, and even more preferably 1.2% by mass or more, from the viewpoint of suppressing oxidation after storage, reducing the rate of change in viscosity of the composite fine particle dispersion before and after storage, and reducing the rate of change in bonding strength before and after storage. Furthermore, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving bonding strength after coating, it is preferably 3.5% by mass or less, more preferably 3.0% by mass or less, even more preferably 2.5% by mass or less, even more preferably 2.2% by mass or less, and even more preferably 1.8% by mass or less. The sulfur atom content in the sulfur-containing polymer P can be adjusted by appropriately adding a compound containing sulfur atoms to the raw materials of the sulfur-containing polymer P. The sulfur atom content in the sulfur-containing polymer P can be determined by the method described in the examples.

[0020] In the present invention, the sulfur-containing polymer P is preferably a vinyl polymer. Vinyl polymers refer to polymers obtained by addition polymerization of monomers having vinyl groups. Examples of sulfur-containing polymers P in this invention include vinyl polymers such as acrylic resins, styrene resins, styrene-acrylic resins, and acrylic silicone resins.

[0021] In the present invention, when the sulfur-containing polymer P is a vinyl polymer, the sulfur atom content in the sulfur-containing polymer P can be adjusted, for example, by the amount of a chain transfer agent containing sulfur atoms added. The chain transfer agent containing a sulfur atom is preferably at least one selected from 1-butanethiol, 1-decanethiol, 2,4-diphenyl-4-methyl-1-pentene, 1-dodecanethiol, 2-ethylhexyl mercaptoacetate, ethyl mercaptoacetate, 1-hexadecanethiol, 2-mercaptoethanol, 3-mercapto-1,2-propanediol, mercaptoacetic acid, sodium 2-mercaptoethasulfonate, 3-mercaptopropionic acid, methyl mercaptoacetate, mercaptosuccinic acid, 1-octanthiol, 1-octadecanethiol, tridecyl 3-mercaptopropionate, and thiophenol, and more preferably at least one selected from 3-mercaptopropionic acid and 2-mercapto-1,2-propanediol.

[0022] In the present invention, when the sulfur-containing polymer P is a vinyl polymer, the sulfur-containing polymer P preferably comprises at least one selected from a monomer having a carboxyl group (p-1), a monomer having a polyalkylene glycol segment (p-2), and a hydrophobic monomer (p-3), from the viewpoint of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving bonding strength after coating. More preferably, it comprises at least two selected from a monomer having a carboxyl group (p-1), a monomer having a polyalkylene glycol segment (p-2), and a hydrophobic monomer (p-3). Even more preferably, it comprises a monomer having a carboxyl group (p-1), a monomer having a polyalkylene glycol segment (p-2), and a hydrophobic monomer (p-3).

[0023] (Carboxylated monomer (p-1)) Examples of monomers (p-1) having a carboxyl group (hereinafter also referred to as "monomer (p-1)") include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, and 2-methacryloyloxymethylsuccinic acid; and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and citraconic acid. The aforementioned unsaturated dicarboxylic acids may also be anhydrides. The monomer (p-1) may be used alone or in combination of two or more types. From the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, monomer (p-1) is preferably at least one selected from (meth)acrylic acid and maleic acid, more preferably (meth)acrylic acid, and even more preferably methacrylic acid. In this specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acrylic acid" below.

[0024] (Monomer having a polyalkylene glycol segment (p-2)) Examples of monomers (p-2) having a polyalkylene glycol segment (hereinafter also referred to as "monomer (p-2)") include polyalkylene glycol (meth)acrylate, alkoxy polyalkylene glycol (meth)acrylate, and phenoxy polyalkylene glycol (meth)acrylate. Monomers (p-2) may be used individually or in combination of two or more. In this specification, "(meth)acrylate" means at least one selected from acrylates and methacrylates. The same applies to "(meth)acrylate" below.

[0025] From the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, the monomer (p-2) is preferably at least one selected from polyalkylene glycol (meth)acrylate and alkoxy polyalkylene glycol (meth)acrylate, more preferably alkoxy polyalkylene glycol (meth)acrylate, and even more preferably alkoxy polyalkylene glycol methacrylate.

[0026] The number of carbon atoms in the alkoxy group of the alkoxy polyalkylene glycol (meth)acrylate is preferably 1 to 18, more preferably 1 to 12, even more preferably 1 to 6, and even more preferably 1 to 3, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. Examples of alkoxypolyalkylene glycol (meth)acrylates include methoxypolyalkylene glycol (meth)acrylate, ethoxypolyalkylene glycol (meth)acrylate, propoxypolyalkylene glycol (meth)acrylate, butoxypolyalkylene glycol (meth)acrylate, octoxypolyalkylene glycol (meth)acrylate, and lauroxypolyalkylene glycol (meth)acrylate. Among these, methoxypolyalkylene glycol (meth)acrylate is preferred, and methoxypolyalkylene glycol methacrylate is more preferred.

[0027] The monomer (p-2) polyalkylene glycol segment preferably contains units derived from an alkylene oxide having 2 to 4 carbon atoms, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. Examples of alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide, and preferably at least one selected from ethylene oxide and propylene oxide, and more preferably ethylene oxide. The number of alkylene oxide-derived units in the polyalkylene glycol segment is preferably 2 or more, more preferably 4 or more, even more preferably 10 or more, and even more preferably 15 or more, and preferably 100 or less, more preferably 70 or less, even more preferably 50 or less, even more preferably 40 or less, even more preferably 35 or less, and even more preferably 23 or less, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. The polyalkylene glycol segment may be a copolymer containing ethylene oxide-derived units and propylene oxide-derived units, from the viewpoint of improving the dispersibility of composite fine particles, reducing the viscosity of the composite fine particle dispersion, and improving the bonding strength after coating. The copolymer containing units derived from ethylene oxide and units derived from propylene oxide may be a block copolymer, a random copolymer, or an alternating copolymer.

[0028] Specific examples of commercially available monomers (p-2) include NK ester AM-90G, AM-130G, AM-230G, AMP-20GY, M-20G, M-40G, M-90G, M-230G, etc., manufactured by Shin Nakamura Chemical Industry Co., Ltd.; and Bremmer PE-90, PE-200, PE-350, PME-100, P, etc., manufactured by NOF Corporation. Examples include ME-200, PME-400, PME-1000, PME-4000, PP-500, PP-500D, PP-800, PP-1000, PP-2000D, AP-150, AP-400, AP-550, 50PEP-300, 50POEP-800B, 43PAPE-600B, and PLE-1300.

[0029] (Hydrophobic monomer (p-3)) In this specification, "hydrophobic monomer" means a monomer in which the amount dissolved when dissolved in 100 g of deionized water at 25°C until saturated is less than 10 g. The amount of monomer (p-3) dissolved is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. The monomer (p-3) is preferably at least one selected from aromatic group-containing monomers and (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols.

[0030] The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have substituents including heteroatoms, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. More preferably, it is at least one selected from styrene monomers and aromatic group-containing (meth)acrylates. The molecular weight of the aromatic group-containing monomer is preferably less than 500. Examples of styrene monomers include styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), and divinylbenzene. Examples of aromatic group-containing (meth)acrylates include phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

[0031] (Meth)acrylates having hydrocarbon groups derived from aliphatic alcohols are preferably those having hydrocarbon groups derived from aliphatic alcohols with 1 to 22 carbon atoms, more preferably those having hydrocarbon groups derived from aliphatic alcohols with 1 to 12 carbon atoms, even more preferably those having hydrocarbon groups derived from aliphatic alcohols with 1 to 8 carbon atoms, and even more preferably those having hydrocarbon groups derived from aliphatic alcohols with 1 to 4 carbon atoms, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. Examples of (meth)acrylates having hydrocarbon groups derived from aliphatic alcohols include (meth)acrylates having linear alkyl groups, (meth)acrylates having branched alkyl groups, and (meth)acrylates having alicyclic alkyl groups. Examples of (meth)acrylates having a linear alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate. Examples of (meth)acrylates having branched alkyl groups include isopropyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isopentyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isostearyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of (meth)acrylates having an alicyclic alkyl group include cyclohexyl (meth)acrylate. The monomer (p-3) may be used alone or in combination of two or more types.

[0032] From the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, the monomer (p-3) is preferably at least one selected from aromatic group-containing monomers and (meth)acrylates having a linear alkyl group, more preferably at least one selected from styrene monomers and (meth)acrylates having a linear alkyl group with 1 to 4 carbon atoms, even more preferably at least one selected from styrene, α-methylstyrene, 2-methylstyrene, 4-vinyltoluene (4-methylstyrene), methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate, even more preferably at least one selected from styrene and methyl (meth)acrylate, even more preferably at least one selected from methyl (meth)acrylate, and even more preferably methyl methacrylate.

[0033] When the sulfur-containing polymer P contains constituent units derived from monomer (p-1), the content of monomer (p-1) in the raw material monomer during the production of the sulfur-containing polymer P, or the content of constituent units derived from monomer (p-1) in the sulfur-containing polymer P, is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, even more preferably 12% by mass or more, and preferably 25% by mass or less, more preferably 23% by mass or less, even more preferably 20% by mass or less, and even more preferably 18% by mass or less.

[0034] When the sulfur-containing polymer P contains constituent units derived from monomer (p-2), the amount of monomer (p-2) in the raw material monomer during the production of the sulfur-containing polymer P, or the amount of constituent units derived from monomer (p-2) in the sulfur-containing polymer P, is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 73% by mass or less, and even more preferably 70% by mass or less.

[0035] When the sulfur-containing polymer P contains constituent units derived from monomer (p-3), the amount of monomer (p-3) in the raw material monomer during the production of the sulfur-containing polymer P, or the amount of constituent units derived from monomer (p-3) in the sulfur-containing polymer P, is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, even more preferably 12% by mass or more, and preferably 25% by mass or less, more preferably 23% by mass or less, even more preferably 20% by mass or less, and even more preferably 18% by mass or less.

[0036] In the present invention, the amount of a chain transfer agent containing sulfur atoms blended with 100 parts by mass of raw material monomer in the raw materials when producing the sulfur-containing polymer P is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 1.5 parts by mass or more, even more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, from the viewpoint of suppressing oxidation after storage, reducing the rate of change in viscosity of the composite fine particle dispersion before and after storage, and reducing the rate of change in bonding strength before and after storage. Furthermore, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving bonding strength after coating, it is preferably 10.0 parts by mass or less, more preferably 9.0 parts by mass or less, even more preferably 8.5 parts by mass or less, even more preferably 8.0 parts by mass or less, and even more preferably 6.0 parts by mass or less.

[0037] The acid value of the sulfur-containing polymer P is preferably 50 mg KOH / g or more, more preferably 70 mg KOH / g or more, even more preferably 90 mg KOH / g or more, even more preferably 100 mg KOH / g or more, even more preferably 105 mg KOH / g or more, and preferably 250 mg KOH / g or less, more preferably 200 mg KOH / g or less, even more preferably 170 mg KOH / g or less, even more preferably 160 mg KOH / g or less, and even more preferably 145 mg KOH / g or less, from the viewpoint of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving bonding strength after coating. The acid value of the sulfur-containing polymer P is measured by the method described in the examples.

[0038] (Low molecular weight sulfur-containing organic compound Q) In the present invention, the sulfur-containing organic compound may further contain a low molecular weight sulfur-containing organic compound Q. By using the low molecular weight sulfur-containing organic compound Q, it becomes easy to adjust the sulfur atom content in the composite fine particles to a desired range.

[0039] In the present invention, the molecular weight of the low molecular weight sulfur-containing organic compound Q is preferably 1,000 or less, more preferably 500 or less, even more preferably 300 or less, even more preferably 150 or less, and even more preferably 120 or less, and also preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, and even more preferably 100 or more, from the viewpoint of reducing the viscosity of the composite fine particle dispersion.

[0040] In the present invention, the sulfur atom content in the low molecular weight sulfur-containing organic compound Q is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of suppressing oxidation after storage, and from the viewpoint of reducing the viscosity of the composite fine particle dispersion, it is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less. Furthermore, the sulfur atom content in the low molecular weight sulfur-containing organic compound Q can be calculated using the following formula. The amount of sulfur atoms in a low molecular weight sulfur-containing organic compound Q = Number of sulfur atoms in the low molecular weight sulfur-containing organic compound Q × Atomic weight of sulfur atoms / Molecular weight of the low molecular weight sulfur-containing organic compound Q

[0041] In the present invention, as the low molecular weight sulfur-containing organic compound Q, compounds similar to those of the above-mentioned sulfur atom-containing chain transfer agents can be suitably used, and as the sulfur atom-containing chain transfer agent, from the viewpoint of suppressing oxidation after storage, preferably 1-butanethiol, 1-decanethiol, 2,4-diphenyl-4-methyl-1-pentene, 1-dodecanethiol, 2-ethylhexyl mercaptoacetate, ethyl mercaptoacetate, 1-hexadecanethiol, 2-mercaptoethanol, 3-mercapto-1, At least one selected from 2-propanediol, mercaptoacetic acid, sodium 2-mercaptoethasulfonate, 3-mercaptopropionic acid, methyl mercaptoacetate, mercaptosuccinic acid, 1-octanthiol, 1-octadecanethiol, tridecyl 3-mercaptopropionic acid, and thiophenol, more preferably 3-mercaptopropionic acid and at least one selected from 3-mercapto-1,2-propanediol, and even more preferably 3-mercaptopropionic acid.

[0042] In the present invention, the amount of sulfur-containing polymer P in the sulfur-containing organic compound is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass, from the viewpoint of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving bonding strength after coating.

[0043] Furthermore, in the present invention, the amount of low molecular weight sulfur-containing organic compound Q in the sulfur-containing organic compound is preferably not included from the viewpoint of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving bonding strength after coating. If it is included, it is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0044] In the present invention, the content of sulfur-containing polymer P in the composite fine particles is preferably 0.5% by mass or more, more preferably 0.55% by mass or more, even more preferably 0.58% by mass or more, even more preferably 0.6% by mass or more, and preferably 2.5% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.2% by mass or less, even more preferably 1.0% by mass or less, and even more preferably 0.9% by mass or less, from the viewpoint of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving bonding strength after coating. The content of sulfur-containing polymer P in the composite fine particles can be determined by the method described in the examples.

[0045] Furthermore, in the present invention, the content of the low molecular weight sulfur-containing organic compound Q in the composite fine particles is preferably not present from the viewpoint of suppressing oxidation after storage, reducing the viscosity of the composite fine particle dispersion, and improving bonding strength after coating. If it is present, it is preferably 0.3% by mass or less, more preferably 0.2% by mass or less, even more preferably 0.15% by mass or less, and even more preferably 0.1% by mass or less. The content of the low molecular weight sulfur-containing organic compound Q in the composite fine particles is determined by the method described in the examples.

[0046] Furthermore, in the present invention, when the composite fine particles contain a sulfur-containing polymer P and a low molecular weight sulfur-containing organic compound Q as sulfur-containing organic compounds, the ratio of the content of the low molecular weight sulfur-containing organic compound Q to the content of the sulfur-containing polymer P in the composite fine particles (low molecular weight sulfur-containing organic compound Q / sulfur-containing polymer P) is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and preferably 0.20 or less, more preferably 0.18 or less, and even more preferably 0.16 or less.

[0047] The composite fine particles of the present invention may contain a small amount of solvent (hereinafter also referred to as the dispersion medium) used to disperse the sulfur-containing organic compound and the copper raw material compound. From the viewpoint of obtaining stable performance of composite fine particle dispersion, the content of the dispersion medium in the composite fine particles of the present invention is preferably 1% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.01% by mass or less.

[0048] <Manufacturing of composite microparticles> Composite fine particles can be obtained by preparing a mixture containing a copper raw material compound, a sulfur-containing organic compound, and a dispersion medium; reducing the copper raw material compound with a reducing agent in this mixture to obtain copper fine particles; obtaining a dispersion of composite fine particles containing the copper fine particles and a sulfur-containing organic compound that coats at least a portion of their surface; and separating the composite particles from this dispersion. In the method for producing composite fine particles, a solvent for dispersing the copper raw material compound and reducing agent, a complexing agent, etc., may be further added to the mixture as needed. In a preferred embodiment, the method for producing composite fine particles of the present invention is a method for producing composite fine particles in which at least a portion of the surface of copper fine particles is coated with a sulfur-containing organic compound, and comprises the following steps (1) to (3). Step (1): A step of preparing a mixture containing a copper raw material compound, a reducing agent, a sulfur-containing organic compound, and a dispersion medium. Step (2): A step of reducing the copper raw material compound in the mixed liquid with a reducing agent to obtain a dispersion of composite fine particles containing copper fine particles and a sulfur-containing organic compound that coats at least a portion of the surface thereof. Step (3): Step of separating the composite fine particles from the dispersion of the composite fine particles.

[0049] (Process (1)) In step (1), for example, copper oxide, a sulfur-containing organic compound, and a dispersion medium are added to the reaction vessel and stirred to prepare a mixture containing copper oxide, a sulfur-containing organic compound, and a dispersion medium. The copper oxide is preferably copper oxide from the viewpoint of obtaining composite fine particles with excellent low-temperature sintering speed. The copper oxide is preferably cupric oxide and / or cuprous oxide, more preferably cupric oxide, from the viewpoint of obtaining composite fine particles with excellent low-temperature sintering speed. Examples of dispersion media include water, methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol. Among these, ethanol is preferred as the solvent.

[0050] In step (1), the amount of copper oxide added is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 9% by mass or more, relative to the mixed liquid obtained in step (1), from the viewpoint of improving the dispersibility of the composite fine particles, improving sinterability at low temperatures, and improving the sintering rate. Similarly, from the same viewpoint, it is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 20% by mass or less.

[0051] In step (1) described above, the mass ratio of the amount of sulfur-containing organic compound added to the amount of copper oxide added (sulfur-containing organic compound / copper oxide) is preferably 0.001 or more, more preferably 0.002 or more, even more preferably 0.005 or more, from the viewpoint of improving the dispersibility of composite fine particles, improving sinterability at low temperatures, and improving the sintering rate, and from the same viewpoint, preferably 0.03 or less, more preferably less than 0.016, and even more preferably 0.01 or less.

[0052] In step (1) above, the mass ratio of the amount of dispersion medium added to the amount of copper oxide added (dispersion medium / copper oxide) is preferably 1 or more, more preferably 1.5 or more, and even more preferably 2.5 or more, from the viewpoint of improving the dispersibility of composite fine particles, improving sinterability at low temperatures, and improving the sintering rate, and from the same viewpoint, preferably 100 or less, more preferably 20 or less, and even more preferably 10 or less.

[0053] (Process (2)) The reducing agent can be added in step (1) or step (2). From the viewpoint of efficiently obtaining composite fine particles, it is preferable to add the reducing agent in step (2) while raising the temperature of the mixture. Examples of the reducing agent include hydrazine compounds, boron compounds, inorganic salts, etc. Examples of hydrazine compounds include hydrazine, hydrazine hydrochloride, hydrazine sulfate, and hydrazine monohydrate. Examples of boron compounds include sodium borohydride. Examples of inorganic acid salts include sodium sulfite, sodium bisulfite, sodium thiosulfate, sodium nitrite, sodium hyponitrite, phosphorous acid, sodium phosphite, hypophosphorous acid, and sodium hypophosphite. Among these, the reducing agent is preferably one or more selected from the group consisting of hydrazine compounds, more preferably hydrazine and hydrated hydrazine, and even more preferably hydrated hydrazine (hydrazine monohydrate), from the viewpoint of obtaining composite fine particles with excellent low-temperature sintering speed. The reducing agent may be used individually or in combination of two or more types.

[0054] In step (2), the reduction of copper oxide with a reducing agent is preferably carried out by raising the temperature of the mixture obtained in step (1), from the viewpoint of obtaining composite fine particles with excellent low-temperature sintering rate. In step (2), the temperature of the mixture after raising the temperature is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher, from the viewpoint of reducing and making the particle size of the composite fine particles uniform, and preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 80°C or lower, from the viewpoint of obtaining composite fine particles stably. From the viewpoint of obtaining composite fine particles with excellent low-temperature sintering rate, the temperature of the mixed liquid in step (2) after heating is preferably maintained for 1 hour or more, more preferably 1.5 hours or more, even more preferably 2 hours or more, and from the same viewpoint, preferably 24 hours or less, more preferably 5 hours or less, and even more preferably 3 hours or less. The above step (2) may be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen gas.

[0055] In step (2) above, the molar ratio of the amount of reducing agent added to the amount of copper oxide added (reducing agent / copper oxide) is preferably 1.0 or higher, more preferably 1.2 or higher, and even more preferably 1.5 or higher, from the viewpoint of improving the dispersibility of composite fine particles, improving sinterability at low temperatures, and improving the sintering rate, and from the same viewpoint, preferably 5.0 or lower, more preferably 4.0 or lower, and even more preferably 3.0 or lower.

[0056] (Step (3)) Step (3) preferably includes, from the viewpoint of separating the composite fine particles from unreacted reducing agents, excess sulfur-containing organic compounds and other impurities and dispersion medium in the mixture obtained in step (2), a step of membrane treatment such as dialysis, vacuum filtration, pressure filtration, or ultrafiltration on the mixture obtained in step (2) and / or a step of centrifugal treatment on the mixture obtained in step (2). Furthermore, from the viewpoint of obtaining composite fine particles with a low dispersion medium content, step (3) preferably further comprises a vacuum drying step, and more preferably a freeze-drying step.

[0057] <Applications of composite microparticles> The composite microparticles of the present invention exhibit suppressed oxidation even after storage for a certain period, have low viscosity when used as a composite microparticle dispersion, and possess high bonding strength after coating. Therefore, the composite microparticles of the present invention can be used to form conductive members for various electronic and electrical devices. Examples of such conductive members include those conventionally formed using conductive bonding agents such as solder. Furthermore, the composite microparticles of the present invention are preferably used to form conductive members constituting antennas such as RFID (radio frequency identifier) ​​tags; capacitors such as MLCCs (multilayer ceramic capacitors); electronic paper; image display devices such as liquid crystal displays and organic EL displays; organic EL elements; organic transistors; wiring boards such as printed circuit boards and flexible circuit boards; organic solar cells; and sensors such as flexible sensors.

[0058] [Composite fine particle dispersion] The composite microparticle dispersion of the present invention is prepared using the composite microparticles of the present invention as described above. That is, the composite microparticle dispersion of the present invention contains the composite microparticles of the present invention as described above. Because the composite microparticle dispersion of the present invention contains the above-mentioned composite microparticles, it exhibits excellent sinterability at low temperatures and a high low-temperature sintering rate.

[0059] The composite microparticle dispersion of the present invention preferably contains a dispersion medium C, which is a solvent for dispersing the composite microparticles. That is, the composite microparticle dispersant of the present invention preferably contains the composite microparticles of the present invention described above and the dispersion medium C. The dispersion medium C preferably includes at least one selected from aliphatic monohydric alcohols, (poly)alkylene glycols, (poly)alkylene glycol derivatives, glycerin, and glycerin derivatives, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating.

[0060] Examples of aliphatic monohydric alcohols include allyl alcohol, n-heptanol, n-octanol, 2-ethylhexanol, n-nonanol, and terpene alcohols. Examples of terpene alcohols include monoterpene alcohols such as α-terpineol, linalool, geraniol, and citronellol.

[0061] In this specification, "(poly)alkylene glycol" means at least one selected from alkylene glycols and polyalkylene glycols. Examples of alkylene glycols include ethylene glycol, propylene glycol, and butylene glycol (1,3-butanediol). Examples of polyalkylene glycols include diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, and polytetramethylene glycol. The number-average molecular weight of polyethylene glycol is preferably 70 to 1000, more preferably 80 to 500, and even more preferably 90 to 200, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. The number-average molecular weight of polypropylene glycol is preferably 100 to 1000, more preferably 110 to 600, and even more preferably 120 to 500, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating. Among these, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating, at least one selected from tetraethylene glycol and dipropylene glycol is preferred.

[0062] Examples of (poly)alkylene glycol derivatives include compounds in which the terminal hydroxyl groups of the (poly)alkylene glycol are etherified or esterified.

[0063] In this specification, "(poly)alkylene glycol alkyl ether" means at least one selected from alkylene glycol alkyl ethers and polyalkylene glycol alkyl ethers. Examples of alkylene glycol alkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monobutyl ether. Examples of polyalkylene glycol alkyl ethers include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.

[0064] In this specification, "(poly)alkylene glycol monoalkyl ether acetate" means at least one selected from alkylene glycol monoalkyl ether acetate and polyalkylene glycol monoalkyl ether acetate. Examples of alkylene glycol monoalkyl ether acetates include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate. Examples of polyalkylene glycol monoalkyl ether acetates include diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate.

[0065] There are no particular restrictions on glycerin derivatives as long as they are solvents containing a structure derived from glycerin. Examples include glycerin ether derivatives, glycerin ester derivatives, polyglycerins, and glycerin alkylene oxide adducts (e.g., ethylene oxide adducts and propylene oxide adducts). Preferred polyglycerins include, for example, diglycerin and triglycerin. Commercially available polyglycerins include, for example, polyglycerin #310, polyglycerin #500, and polyglycerin #750 manufactured by Sakamoto Pharmaceutical Co., Ltd. A preferred ether derivative of glycerin is, for example, 3-(2-ethylhexyloxy)-1,2-propanediol. As an ester derivative of glycerin, glyceryl tributyrate (tributyline) is a preferred example.

[0066] The dispersion medium C preferably contains (poly)alkylene glycol, and more preferably contains at least one selected from tetraethylene glycol and dipropylene glycol, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating.

[0067] In the composite fine particle dispersion of the present invention, the content of the dispersion medium C is preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and even more preferably 6% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less, from the viewpoint of reducing the viscosity of the composite fine particle dispersion and improving the bonding strength after coating.

[0068] In the composite microparticle dispersion of the present invention, the content of composite microparticles is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and preferably 97% by mass or less, more preferably 96% by mass or less, even more preferably 95% by mass or less, and even more preferably 94% by mass or less, from the viewpoint of reducing the viscosity of the composite microparticle dispersion and improving the bonding strength after coating.

[0069] <Manufacturing of composite microparticle dispersions> The composite microparticle dispersion of the present invention is obtained by mixing the composite microparticles of the present invention described above with the dispersion medium C. The present invention provides a method for producing a composite microparticle dispersion, which can be obtained by adding and mixing pre-prepared composite microparticles, a dispersion medium C, and various additives as needed. As for the mixing method, known methods can be used, and from the viewpoint of better dispersing the composite fine particles in the dispersion medium C, it is preferable to pre-mix the composite fine particles and the dispersion medium C using an agate mortar or the like, and then further mix the resulting mixture using a stirring device such as a rotational stirring device.

[0070] <Applications of composite particulate dispersions> The composite microparticle dispersion of the present invention has low viscosity and high bonding strength after coating. Therefore, the composite microparticle dispersion of the present invention can be used as a bonding material to join members to be joined together, and can be used, for example, to form conductive members that join members to be joined together in various electronic and electrical devices. Examples of such conductive members include conductive members that were conventionally formed using conductive bonding agents such as solder. Furthermore, the composite microparticle dispersion of the present invention is preferably used to form conductive members that constitute antennas such as RFID (radio frequency identifier) ​​tags; capacitors such as MLCCs (multilayer ceramic capacitors); electronic paper; image display devices such as liquid crystal displays and organic EL displays; organic EL elements; organic transistors; wiring boards such as printed circuit boards and flexible circuit boards; organic solar cells; and sensors such as flexible sensors.

[0071] In the present invention, the member to be joined is, for example, a metal member, and examples of metal members include metal substrates or metal substrates such as gold substrates, gold-plated substrates, silver substrates, silver-plated metal substrates, copper substrates, palladium substrates, palladium-plated metal substrates, platinum substrates, platinum-plated metal substrates, aluminum substrates, nickel substrates, nickel-plated metal substrates, tin substrates, and tin-plated metal substrates; and metal parts such as electrodes of an electrically insulating substrate. The multiple metal members used in the present invention may be of the same type or different types of metal members. Among these, the metal component preferably includes one or more selected from the group consisting of gold substrates, gold-plated substrates, silver substrates, silver-plated metal substrates, copper substrates, palladium substrates, palladium-plated metal substrates, platinum substrates, platinum-plated metal substrates, aluminum substrates, nickel substrates, nickel-plated metal substrates, tin substrates, tin-plated metal substrates, and the metal portion of an electrically insulating substrate. The joining of members to be joined (metal members) in this invention can be used for joining chip components such as capacitors and resistors to a circuit board; joining semiconductor chips such as memory, diodes, transistors, ICs, and CPUs to a lead frame or circuit board; and joining high-heat-generating semiconductor chips to a cooling plate.

[0072] [Method for manufacturing a jointed body] In one embodiment, the present invention relates to a method for manufacturing a joined body, and in one embodiment, the method for manufacturing a joined body of the present invention includes the following steps 1 to 2 in this order. Step 1: A step of coating a metal substrate with the composite fine particle dispersion of the present invention described above. Step 2: A step in which the members to be joined are placed on a composite fine particle dispersion coated onto a metal substrate and then fired under pressure.

[0073] (Process 1) Step 1 is a step of coating one main surface of a metal substrate, which is one of the members to be bonded, with the composite fine particle dispersion of the present invention. Examples of metal substrates include gold substrates, gold-plated substrates, silver substrates, silver-plated metal substrates, copper substrates, palladium substrates, palladium-plated metal substrates, platinum substrates, platinum-plated metal substrates, aluminum substrates, nickel substrates, nickel-plated metal substrates, tin substrates, and tin-plated metal substrates.

[0074] As a method for coating the composite fine particle dispersion, known coating methods can be used, such as various coating methods including slot die coating, dip coating, spray coating, spin coating, doctor bladeding, knife edge coating, and bar coating; and various patterning printing methods such as stencil printing, screen printing, flexographic printing, gravure printing, offset printing, dispenser printing, and inkjet printing. The amount of composite fine particle dispersion applied to the metal substrate can be adjusted as appropriate depending on the size and type of the metal substrate.

[0075] (Process 2) In step 2, the composite fine particle dispersion coated on one main surface of the metal substrate may be dried in the atmosphere, and then the other member to be joined may be placed on the dried composite fine particle dispersion. The drying temperature is preferably 60°C or higher, more preferably 70°C or higher, from the viewpoint of bonding strength, and preferably 150°C or lower, more preferably 130°C or lower, from the viewpoint of leaving the dispersion medium necessary to promote the sintering of the composite fine particles. The drying time is preferably 3 minutes or more, more preferably 5 minutes or more, from the viewpoint of leaving the dispersion medium necessary to promote the sintering of the fine particles, and preferably 20 minutes or less, more preferably 15 minutes or less, from the viewpoint of leaving the dispersion medium necessary to promote the sintering of the composite fine particles.

[0076] Examples of the other member to be joined include metal substrates, electrically insulating substrates, chip components, and semiconductor chips. Examples of metal substrates include those similar to the metal substrate in step 1 described above. Examples of chip components include capacitors and resistors. Examples of semiconductor chips include silicon chips, memory chips, diodes, transistors, ICs, and CPUs.

[0077] The temperature of the pressurized firing treatment in step 2 is 150°C or higher, preferably 160°C or higher, more preferably 170°C or higher, and even more preferably 180°C or higher, from the viewpoint of improving bonding strength, and preferably 300°C or lower from the viewpoint of preventing damage to surrounding members.

[0078] The pressure for the pressurized firing process in step 2 is 5 MPa or higher, preferably 10 MPa or higher, more preferably 12 MPa or higher, and even more preferably 15 MPa or higher, from the viewpoint of improving bonding strength, and 50 MPa or lower, preferably 40 MPa or lower, more preferably 30 MPa or lower, and even more preferably 25 MPa or lower, from the viewpoint of preventing damage to surrounding components.

[0079] The processing time for the pressurized firing treatment in step 2 is preferably 30 seconds or more, more preferably 60 seconds or more, and even more preferably 120 seconds or more, from the viewpoint of improving bonding strength, and preferably 300 seconds or less, more preferably 240 seconds or less, and even more preferably 180 seconds or less, from the viewpoint of productivity.

[0080] The atmosphere in which the pressurized firing treatment is performed may be an air atmosphere (atmosphere), an inert gas atmosphere such as nitrogen gas, or a reducing gas atmosphere such as hydrogen gas. However, from the viewpoint of suppressing copper oxidation and ensuring safety, an inert gas atmosphere is preferred, and a nitrogen gas atmosphere is more preferred. [Examples]

[0081] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In the following manufacturing examples, examples, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. Various physical properties were measured or calculated using the following methods.

[0082] <Number-average molecular weight (Mn) of sulfur-containing polymer P> The number-average molecular weight (Mn) of the sulfur-containing polymer P was determined by gel permeation chromatography under the following conditions. The sample prepared for measurement consisted of 0.1 g of polymer mixed with 10 mL of eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter (DISMIC-13HP PTFE 0.2 μm, manufactured by Advantec Toyo Co., Ltd.). (Measurement conditions) GPC device: Tosoh Corporation "HLC-8320GPC" Columns: Tosoh Corporation products "TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H" Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kit manufactured by Tosoh Corporation: "PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)"

[0083] <Acid value of sulfur-containing polymer P> The acid value of sulfur-containing polymer P was measured in accordance with JIS K0070-1992 (potentiometric titration method). However, the measurement solvent was changed from the ethanol and ether mixture specified in JIS K0070 to an acetone and toluene mixture (acetone:toluene = 4:6 (volume ratio)).

[0084] <Sulfur atom content in sulfur-containing polymer P> The sulfur atom content in the sulfur-containing polymer P used in the preparation of composite microparticles was determined from the raw material composition listed in Table 1 using the following formula. Sulfur atom content (mass%) in sulfur-containing polymer P = {Chain transfer agent content (parts by mass) × (Atomic weight of sulfur atom (32.07) / Molecular weight of chain transfer agent)} / Total mass parts of raw material composition × 100

[0085] <Particle size of composite microparticles> Scanning electron microscope (SEM) images of composite microparticles were taken using a scanning electron microscope (Hitachi High-Tech Corporation, electrolytic emission scanning electron microscope: S-4800). The magnification was determined according to the particle size of the composite microparticles, and images were taken in the range of 5,000x to 150,000x. The SEM images were analyzed using the image analysis software ImageJ (National Institutes of Health, USA), and the particle size was determined for more than 200 particles per sample. When the determined particle sizes were arranged in ascending order, the particle size at which the smallest particle accounted for 10% of the total number of particles was defined as the particle size at which the cumulative number frequency was 10% (D10), similarly the particle size at which the smallest particle accounted for 50% was defined as the particle size at which the cumulative number frequency was 50% (D50), and similarly the particle size at which the smallest particle accounted for 90% was defined as the particle size at which the cumulative number frequency was 90% (D90), as follows.

[0086] <Content of sulfur-containing organic compounds in composite microparticles> Using a differential thermogravimetric / thermogravimetric analysis system (TG / DTA) (manufactured by Hitachi High-Tech Science Corporation, product name: STA7200RV), 10 mg of the sample (composite microparticles) was weighed into an aluminum pancell and heated from 35°C to 550°C at a heating rate of 10°C / min under a nitrogen flow of 50 mL / min, and the mass loss was measured. The mass loss from 35°C to 550°C was taken as the mass of the sulfur-containing organic compound, and the remaining mass at 550°C was taken as the mass of the copper content in the composite microparticles. The content of the sulfur-containing organic compound in the composite microparticles was calculated using the following formula. Content of sulfur-containing organic compounds in composite microparticles (mass %) = (mass loss from 35°C to 550°C) / (mass loss from 35°C to 550°C + remaining mass at 550°C) × 100

[0087] <Sulfur atom content in sulfur-containing organic compounds coated on copper nanoparticles> The sulfur atom content (mass ppm) in the composite microparticles was quantified using a C / S analyzer (Horiba, Ltd., "EMIA-Expert") by melt-infrared absorption spectroscopy. The sulfur atom content (mass ppm) in the composite microparticles and the sulfur-containing organic compound content (mass%) in the composite microparticles were then used to determine the sulfur atom content (mass%) in the sulfur-containing organic compound coating the copper microparticles using the following formula. Sulfur atom content (mass%) in sulfur-containing organic compound coated on copper nanoparticles = (Sulfur atom content (mass ppm) in composite nanoparticles) / 10 6 ) / (Content of sulfur-containing organic compounds in composite fine particles (mass%) / 10 2 ) × 10 2

[0088] <Content of sulfur-containing polymer P and low molecular weight sulfur-containing organic compound Q in composite microparticles> 1.0 g of composite microparticles and 99.0 g of 25% aqueous ammonia were added to a 100 mL heat-resistant bottle, and the mixture was stirred at 40°C for 24 hours with the lid closed to obtain a blue solution. The obtained solution was measured by gas chromatography under the following measurement conditions to quantify the low molecular weight sulfur-containing organic compound Q. From the measurement results, the content of the low molecular weight sulfur-containing organic compound Q and the content of the sulfur-containing polymer P in the composite microparticles was determined using the following calculation formula. Content (mass%) of low molecular weight sulfur-containing organic compound Q in composite microparticles = Content (mass%) of low molecular weight sulfur-containing organic compound Q in solution × 100 / 1.0 Content of sulfur-containing polymer P in composite microparticles (mass%) = Content of sulfur-containing organic compound in composite microparticles (mass%) - Content of low molecular weight sulfur-containing organic compound Q in composite microparticles (mass%) (Measurement conditions) • Equipment: Brevis GC-2050 (manufactured by Shimadzu Corporation) • Column: USR28024316H Column oven temperature conditions: Hold at 40°C for 3 minutes, increase temperature to 230°C at a rate of 10°C / minute, hold at 230°C for 3 minutes.

[0089] [Manufacturing of sulfur-containing polymer P] Manufacturing Example 1 (Manufacturing of sulfur-containing polymer P-1) A 1000 mL four-necked round-bottom flask equipped with a thermometer, two 100 mL dropping funnels with nitrogen bypasses, and a reflux apparatus was filled with 20.0 g of ethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent). The internal temperature of the four-necked round-bottom flask was then raised to 80°C using an oil bath, followed by nitrogen bubbling for 10 minutes. Separately, 15.3g of methacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), 17.2g of methyl methacrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), 67.5g of methoxypolyethylene glycol (EO23 mol) monomethacrylate (manufactured by NOF Corporation, "PME-1000"), 2.0g of 3-mercaptopropionic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), and 28.7g of ethanol were dissolved in a poly beaker and placed in a dropping funnel (1). In addition, 51.3 g of ethanol and 1.3 g of 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., polymerization initiator) were dissolved separately in a poly beaker and placed in a dropping funnel (2). Next, the mixtures in dropping funnel (1) and dropping funnel (2) were simultaneously added dropwise into the four-necked round-bottom flask over a period of 90 minutes each. After that, the internal temperature of the four-necked round-bottom flask was raised to 90°C, and stirring was continued for another hour to complete the reaction. After the reaction was complete, the resulting solution was freeze-dried using a freeze-dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd., model: FDU-2110) equipped with a dry chamber (DRC-1000, manufactured by Tokyo Rikakikai Co., Ltd.) under drying conditions (freezing at -25°C for 1 hour, reduced pressure at -10°C for 9 hours, reduced pressure at 25°C for 5 hours; pressure of 5 Pa) to obtain an oven-dried sulfur-containing polymer P-1 (methacrylic acid / methyl methacrylate / methoxypolyethylene glycol (EO 23 mol) methacrylate polymer, acid value: 126 mg KOH / g, Mn: 5,900). The physical properties of sulfur-containing polymer P-1 are shown in Table 1.

[0090] Manufacturing Examples 2-7 (Manufacturing of sulfur-containing polymers P-2-P-7) Sulfur-containing polymers P-2 to P-7 were obtained in the same manner as in Production Example 1, except that the type and amount of chain transfer agent were changed as shown in Table 1. The physical properties of sulfur-containing polymers P-2 to P-7 are shown in Table 1.

[0091] [Table 1]

[0092] Details of each ingredient in Table 1 are as follows: [Monomer (p-1)] • MAA: Methacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) [Monomer (p-2)] • PEG(23)MA: Methoxypolyethylene glycol (EO23 mol) monomethacrylate (manufactured by NOF Corporation, "PME-1000") [Monomer (p-3)] • MMA: Methyl methacrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) [Chain transfer agent] • MPA: 3-mercaptopropionic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) • MPD: 3-mercapto-1,2-propanediol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent)

[0093] [Manufacturing of composite microparticles] Example 1 (Production of composite microparticles 1) In a 2L beaker, 50.0g of copper oxide (N-120 (cupric oxide) manufactured by Nisshin Chemco Co., Ltd.), 1.20g of sulfur-containing polymer P-1, and 500g of ethanol (first-grade reagent, ethanol (95) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added and the mixture was stirred for 15 minutes. During stirring, an oil bath was used to control the temperature of the reaction solution to 70°C. Next, 63.0 g of hydrazine monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), placed in a 100 mL dropping funnel, was added dropwise to the reaction solution over 20 minutes. The reaction solution was then stirred for 1 hour while controlling the temperature to 70°C in an oil bath, and then air-cooled to obtain a reddish-brown dispersion containing composite fine particles. The entire amount of the obtained dispersion was placed in a Hitachi Koki Co., Ltd. refrigerated centrifuge "himacCR22G" and rotor (R12A, radius 15.1 cm) into a Hitachi Koki Co., Ltd. 500PA centrifugal sedimentation tube bottle and centrifuged at 3000 rpm and a centrifugal acceleration of 675 G for 30 minutes. 300 g of ethanol was added to the precipitate separated by centrifugation, and the mixture was stirred for 15 minutes to redisperse it. The entire redispersed liquid was then centrifuged under the same conditions as above, and the precipitate was separated. This procedure was repeated a total of three times. The precipitate of the purified composite microparticles was freeze-dried using a freeze-dryer (Tokyo Rikakikai Co., Ltd., model: FDU-2110) equipped with a dry chamber (Tokyo Rikakikai Co., Ltd., model: DRC-1000) to obtain composite microparticle 1. Freeze-drying was performed by freezing at -25°C for 1 hour, drying under reduced pressure at -10°C for 9 hours at 5 Pa, and then drying under reduced pressure at 25°C for 5 hours at 5 Pa. The physical properties of composite microparticle 1 are shown in Table 2.

[0094] Furthermore, the impurity elements of composite microparticle 1 were quantified using various measurement methods. The results are shown below. (Quantitative results of impurity elements in composite microparticle 1) Bi: 0.24 ppm by mass (measured by ICP-MS) Fe: 9.4 ppm by mass (measured by ICP-MS) Na: 1.9 ppm by mass (measured by ICP-MS) Ni: 1.4 ppm by mass (measured by ICP-MS) P: Less than 100 ppm by mass (measured by ICP-AES) Si: Less than 200 ppm by mass (measured by ICP-AES)

[0095] Examples 2-5, Comparative Examples 1-2 (Production of composite microparticles 2-5 and C1-C2) Composite fine particles 2-5 and C1-C2 were obtained in the same manner as in Example 1, except that the composition of the sulfur-containing organic compound was changed to the composition shown in Table 2. The physical properties of composite fine particles 2-5 and C1-C2 are shown in Table 2.

[0096] Example 6 (Production of composite microparticles 6) In a 2L beaker, 50.0g of copper oxide (N-120 (cupric oxide) manufactured by Nisshin Chemco Co., Ltd.) as the copper raw material compound, 0.90g of sulfur-containing polymer P-6, 0.30g of 3-mercaptopropionic acid as the low molecular weight sulfur-containing organic compound Q, and 500g of ethanol were added and stirred for 15 minutes. During stirring, an oil bath was used to control the temperature of the reaction solution to 70°C. Next, 63.0 g of hydrazine monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), placed in a 100 mL dropping funnel, was added dropwise to the reaction solution over 20 minutes. The reaction solution was then stirred for 1 hour while controlling the temperature to 70°C in an oil bath, and then air-cooled to obtain a reddish-brown dispersion containing composite fine particles. The entire volume of the obtained dispersion was placed in a Hitachi Koki Co., Ltd. refrigerated centrifuge "himacCR22G" and rotor (R12A, radius 15.1 cm) into a Hitachi Koki Co., Ltd. 500PA centrifugal sedimentation tube bottle and subjected to centrifugal separation for 30 minutes at 3000 revolutions per minute and a centrifugal acceleration of 675 G. To the precipitate separated by centrifugation, 300 g of ethanol was added, and the mixture was stirred for 15 minutes to redisperse it. The entire redispersed liquid was then centrifuged under the same conditions as before, and the precipitate was separated. This procedure was repeated a total of three times. The precipitate of the purified composite microparticles was freeze-dried using a freeze-dryer (Tokyo Rikakikai Co., Ltd., model: FDU-2110) equipped with a dry chamber (Tokyo Rikakikai Co., Ltd., model: DRC-1000) to obtain composite microparticles 6. Freeze-drying was performed by freezing at -25°C for 1 hour, drying under reduced pressure at -10°C for 9 hours at 5 Pa, and then drying under reduced pressure at 25°C for 5 hours at 5 Pa. The physical properties of composite microparticle 6 are shown in Table 2.

[0097] Example 7, Comparative Example 3 (Production of composite microparticles 7 and C3) Composite fine particles 7 and C3 were obtained in the same manner as in Example 6, except that the composition of the sulfur-containing organic compound was changed to the composition shown in Table 2. The physical properties of composite fine particles 7 and C3 are shown in Table 2.

[0098] [evaluation] <Preservation Test> 20.0 g of the composite microparticles obtained in the examples and comparative examples were placed in a No. 5 screw vial, and stored for 1 hour in an environment of 15°C and 15% RH with the lid open to conduct a storage test. The composite microparticles were evaluated as follows, using the composite microparticles before and after the storage test.

[0099] (oxygen content) The oxygen content of the composite microparticles before and after the storage test was measured using the inert gas fusion-infrared absorption method. The rate of change in oxygen content was calculated from the measured values ​​using the following formula. A smaller rate of change in oxygen content indicates that oxidation of the composite microparticles after storage is suppressed. [Calculation of the rate of change in oxygen content] (Percentage change in oxygen content [%]) = {(Oxygen content in composite microparticles after storage test [mass %]) / (Oxygen content in composite microparticles before storage test [mass %]) - 1} × 100 [Measurement conditions] Measuring device: LECO ON736) Standard sample: Nickel capsule (P / N 502-822) Crucible: Standard crucible (P / N 776-247) Carrier gas: Argon Analysis mode: Automatic Reactor control mode: Power Outgassing: 5000W, 15 seconds x 2 Analysis delay: 50 seconds Integration delay: 0 seconds Integration time: 40 seconds Comparator usage: None End line: Yes, 2 seconds

[0100] (Viscosity of composite microparticle dispersion) Composite microparticle dispersions were prepared using the composite microparticles obtained in the examples and comparative examples, both before and after the storage test described above. The viscosity of each prepared composite microparticle dispersion was then measured. From the measured viscosities, the rate of change in viscosity was calculated using the following formula. Lower viscosity indicates better fluidity, and superior dispersion stability and coating properties of the composite microparticle dispersion. Furthermore, a smaller rate of change in viscosity indicates that the increase in viscosity of the composite microparticle dispersion containing the composite microparticles after storage is suppressed. [Calculation of the rate of change in viscosity of a composite fine particle dispersion] (Percentage change in viscosity of composite microparticle dispersion [%]) = {(Viscosity of composite microparticle dispersion containing composite microparticles after storage test [Pa·s]) / (Viscosity of composite microparticle dispersion containing composite microparticles before storage test [Pa·s]) - 1} × 100 [Preparation of composite microparticle dispersion] 9.0 g of composite microparticles, 0.5 g of dipropylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent), and 0.5 g of tetraethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent) were added to an agate mortar and kneaded until the composite microparticles were no longer visible to the naked eye, to obtain a mixed solution. The resulting mixture was transferred to a plastic bottle and sealed tightly. The sealed plastic bottle was then stirred for 2000 minutes using a rotation-and-revolution type stirring device (Sinky Co., Ltd., Planetary Vacuum Mixer ARV-310). -1 The mixture was stirred at 2000 revolutions per minute for 5 minutes to obtain a composite fine particle dispersion. [Measurement of viscosity of composite fine particle dispersions] The viscosity of the obtained composite fine particle dispersion was measured using a CR301 rheometer (manufactured by Anton Paar, using a CP50-1 cone plate) at a temperature of 25°C and a shear rate of 1000 (1 / s).

[0101] [Joining strength] For the composite microparticles obtained in the examples and comparative examples, bonded bodies were fabricated using the composite microparticles before and after the above storage test, as described below, and the bonding strength of each was measured. From the measured bonding strengths, the rate of change in bonding strength was calculated using the following formula. A larger rate of change in bonding strength (closer to 0) indicates that the decrease in bonding strength after storage of the composite microparticles is suppressed. [Calculation of the rate of change in joint strength] (Percentage change in bonding strength [%]) = {(Bonding strength of the bond containing the sintered composite microparticles after the storage test [MPa]) / (Bonding strength of the bond containing the sintered composite microparticles before the storage test [MPa]) - 1} × 100 [Fabrication of the joint] Using the composite microparticle dispersion obtained by the same method as described above for the preparation of the composite microparticle dispersion, a composite composite was prepared as follows. A stainless steel metal mask (thickness: 150 μm) with three rows of 6 mm x 6 mm square openings was placed on a 30 mm x 30 mm copper substrate (total thickness: 1 mm), and a composite fine particle dispersion was applied to three locations on the copper substrate by stencil printing using a metal squeegee. Subsequently, the copper substrate coated with the composite fine particle dispersion was dried on a Shamal hot plate (HHP-441, manufactured by AS ONE Corporation) at 120°C for 10 minutes under air. Next, three 5mm x 5mm silicon chips (thickness: 400μm, with titanium, nickel, and gold sputtered onto the silicon chip in that order) were prepared. The copper substrate and the three silicon chips were then stacked so that the gold-side surface of each silicon chip was in contact with the coated composite fine particle dispersion. This resulted in a laminate in which the copper substrate, composite fine particle dispersion, and silicon chips were stacked in that order. Next, the resulting laminate was placed in a pressurized firing machine (HTM-1000, manufactured by Meisho Kiko Co., Ltd.), and nitrogen was flowed into the furnace at a rate of 500 mL / min to replace the air inside the furnace with nitrogen. Then, the laminate was pressurized at 20 MPa using the upper and lower heating heads, and the temperature of the heating heads was raised to 200°C over 10 minutes. After raising the temperature, the laminate was held at 200°C for 150 seconds to perform sintering and obtain a bonded body. After sintering, the heating heads were water-cooled at -60°C / min, and the bonded body was removed into the air at a temperature below 100°C. [Measurement of bonding strength] A universal bond tester (Prospector, manufactured by Nordson Advanced Technologies, Inc.) was used to measure the die shear strength of the bonded structure by pressing the silicon chip of the bonded structure horizontally at a test speed of 5 mm / min with the shear tool height set to 50 μm. The die shear strength was measured for three silicon chips in the bonded structure, and the average value obtained from the measurements was taken as the bond strength of the bonded structure.

[0102] [Table 2]

[0103] As shown in Table 2, the composite microparticles of Examples 1 to 7, in which at least a portion of the surface of copper microparticles is coated with a sulfur-containing organic compound, and the sulfur atom content in the sulfur-containing organic compound coating the copper microparticles is 1.2% by mass or more and 7.0% by mass or less, show suppressed oxidation even after storage for a certain period of time. Furthermore, when used as a composite microparticle dispersion, the dispersion exhibits low viscosity and high bonding strength after coating. On the other hand, in Comparative Example 1, the sulfur atom content in the sulfur-containing organic compound coating the copper nanoparticles was less than 1.0% by mass, resulting in a significantly higher rate of change in oxygen content and viscosity of the composite nanoparticle dispersion. Furthermore, in Comparative Examples 2 and 3, the composite microparticles had a significantly high viscosity of the composite microparticle dispersion, regardless of whether it was before or after storage, because the sulfur atom content in the sulfur-containing organic compound coating the copper microparticles exceeded 7.0% by mass. As a result, the bonding strength was low.

Claims

1. Composite microparticles in which at least a portion of the surface of copper microparticles is coated with a sulfur-containing organic compound, Composite fine particles wherein the sulfur content in the sulfur-containing organic compound coated on the copper fine particles is 1.0% by mass or more and 7.0% by mass or less.

2. The composite fine particles according to claim 1, wherein the sulfur atom content in the composite fine particles is 50 ppm by mass or more and 400 ppm by mass or less.

3. The composite fine particles according to claim 1, wherein the content of the sulfur-containing organic compound in the composite fine particles is 0.5% by mass or more and 2.5% by mass or less.

4. The composite fine particles according to claim 1, wherein the particle size (D50) at which the cumulative number frequency is 50% is 80 nm or more and 500 nm or less.

5. The composite fine particles according to claim 1, wherein the particle size (D90) at which the cumulative count frequency is 90% is 150 nm or more and 500 nm or less.

6. The composite fine particles according to claim 1, wherein the particle size (D10) at a cumulative frequency of 10% is 30 nm or more and 200 nm or less.

7. The sulfur-containing organic compound comprises a sulfur-containing polymer P. The composite fine particles according to claim 1, wherein the number-average molecular weight of the sulfur-containing polymer P is 1,000 or more and 10,000 or less.

8. The composite fine particles according to claim 7, wherein the sulfur atom content in the sulfur-containing polymer P used to coat the copper fine particles is 0.4% by mass or more and 3.5% by mass or less.

9. The composite fine particles according to claim 7, wherein the sulfur-containing polymer P is a vinyl polymer.

10. The composite fine particles according to claim 7, wherein the amount of sulfur-containing polymer P in the sulfur-containing organic compound is 40% by mass or more.

11. The composite fine particles according to claim 7, wherein the content of the sulfur-containing polymer P in the composite fine particles is 0.5% by mass or more and 2.5% by mass or less.

12. This is a method for manufacturing composite microparticles. To prepare a mixture containing a copper raw material compound, a reducing agent, a sulfur-containing organic compound, and a dispersion medium; to reduce the copper raw material compound in the mixture with the reducing agent to obtain a dispersion of composite fine particles containing copper fine particles and a sulfur-containing organic compound that coats at least a portion of their surface; A method for producing composite fine particles, comprising separating the composite fine particles from a dispersion of the composite fine particles.

13. The sulfur-containing organic compound comprises a sulfur-containing polymer P. The method for producing the composite fine particles further includes preparing the sulfur-containing polymer P, The method for producing composite fine particles according to claim 12, wherein in the preparation of the sulfur-containing polymer P, a chain transfer agent containing sulfur atoms is used as a raw material for the sulfur-containing polymer P.

14. A composite particle dispersion comprising composite particles according to any one of claims 1 to 11.

15. A method for manufacturing a bonded body, comprising: coating a metal substrate with the composite fine particle dispersion described in claim 14; placing a member to be bonded on the composite fine particle dispersion coated on the metal substrate; and pressurizing and firing the members.

16. A method for manufacturing an electronic or electrical device, comprising using the composite fine particle dispersion described in claim 14 for forming a conductive member of the electronic or electrical device.

17. The composite fine particle dispersion described in claim 14 is used as a bonding material for joining members to be joined together.

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