Copper microparticle dispersion

Abstract

This invention relates to a copper fine particle dispersion, etc., which has excellent coating properties, suppresses cracking during firing, and exhibits excellent bonding strength. [Solution] In one embodiment, the present invention relates to a copper microparticle dispersion. The copper microparticle dispersion is a copper microparticle dispersion containing copper microparticles A and a dispersion medium C. The content of the dispersion medium C is 3% by mass or more and 40% by mass or less, and the dispersion medium C includes a dispersion medium C1 having a boiling point of 200°C or more and 270°C or less, and a dispersion medium C2 having a boiling point greater than 270°C. The mass ratio of the dispersion medium C1 to the dispersion medium C2, C1 / C2, is greater than 1. The content of the dispersion medium C2 in the dispersion medium C is 10% by mass or more and 48% by mass or less.

Description

Technical Field

[0001] The present invention relates to a copper fine particle dispersion and a method for manufacturing a bonded body using the copper fine particle dispersion.

Background Art

[0002] Since copper has excellent electrical conductivity and thermal conductivity, it is widely used as, for example, a conductor wiring material, a heat transfer material, a heat exchange material, a heat dissipation material, and the like. Since copper has excellent thermal conductivity, it may also be used as an alternative material to solder for joining an object to be joined.

[0003] In recent years, semiconductor devices called power devices have been increasingly used as power conversion and control devices such as inverters. Unlike integrated circuits such as memories and microprocessors, power devices are for controlling high currents and generate a large amount of heat during operation. Therefore, the solder used for mounting power devices is required to have heat resistance in addition to bonding strength. However, the lead-free solder widely used recently has a drawback of low heat resistance. Therefore, various techniques have been proposed in which a copper fine particle dispersion is used instead of solder, and this is applied to an object by various coating means and fired to join the object to be joined. Since copper has a stable oxidation state at room temperature (25°C), it contains copper atoms in an oxidized state. Therefore, in order to join an object to be joined with a copper fine particle dispersion, it is necessary to reduce the copper atoms in the oxidized state and fire them to form a continuous body of copper.

[0004] For example, Patent Document 1 discloses a copper nanoparticle dispersion containing copper nanoparticles A dispersed in polymer B and a dispersion medium C, wherein polymer B includes constituent units derived from monomer (b-1) having a carboxyl group and constituent units derived from monomer (b-2) having a polyalkylene glycol segment, the content of polyalkylene glycol segments in polymer B is 55% by mass or more and 97% by mass or less, the acid value of polymer B is 20 mg KOH / g or more and 250 mg KOH / g or less, and the dispersion medium C contains at least one selected from the group consisting of (poly)alkylene glycol, (poly)alkylene glycol derivatives, terpene alcohols, glycerin and glycerin derivatives. Furthermore, Patent Document 2 discloses a copper paste for forming sintered copper pillars that join members together, comprising metal particles and an organic dispersion medium, wherein the metal particles include copper particles, and the organic dispersion medium contains 50 to 99% by mass of a high-boiling-point solvent with a boiling point of 280°C or higher, based on the total mass of the organic dispersion medium. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2023 / 013034 [Patent Document 2] International Publication No. 2021 / 060204 [Overview of the project] [Problems that the invention aims to solve]

[0006] Copper nanoparticle dispersions, which have been proposed as solder alternative bonding materials, have higher heat resistance than solder, but uneven coating can occur during application, and there is still room for improvement in terms of coating properties. In addition, conventional copper nanoparticle dispersions sometimes develop defects such as cracking during firing depending on the drying state after coating. The copper fine particle dispersion disclosed in Patent Document 1 has storage stability, but it has problems with coating properties when forming bonded bodies. In addition, the copper paste disclosed in Patent Document 2 has insufficient coating properties when forming bonded bodies, and cracks and other defects sometimes occur during firing. The present invention relates to a copper microparticle dispersion that exhibits excellent coating properties, suppresses cracking during firing, and has excellent bonding strength, and to a method for manufacturing a bonded body using the copper microparticle dispersion. [Means for solving the problem]

[0007] The present inventors have found that the above problem can be solved by including in a copper nanoparticle dispersion containing copper nanoparticles A and a dispersion medium C, in a specific ratio, dispersion mediums C1 and C2 containing a specific boiling point in the dispersion medium C. The present invention relates to the following [1] to [3]. [1] A copper nanoparticle dispersion comprising copper nanoparticles A and a dispersion medium C, wherein the content of the dispersion medium C is 3% by mass or more and 40% by mass or less, and the dispersion medium C comprises a dispersion medium C1 having a boiling point of 200°C or more and 270°C or less, and a dispersion medium C2 having a boiling point greater than 270°C, the mass ratio of the dispersion medium C1 to the dispersion medium C2 C1 / C2 is greater than 1, and the content of the dispersion medium C2 in the dispersion medium C is 10% by mass or more and 48% by mass or less. [2] A method for manufacturing a joint, comprising the following steps 1 to 3 in this order. Step 1: A step of coating a metal substrate with the copper fine particle dispersion described in [1] above. Step 2: A step in which the metal substrate obtained in Step 1 is pre-baked at a temperature of 100°C to 150°C. Step 3: The workpiece to be bonded is placed on the copper fine particle dispersion of the metal substrate pre-baked in Step 2, and then pressure-fired under conditions of a temperature of 150°C to 300°C and a pressure of 5 MPa to 50 MPa. [3] Use of the copper fine particle dispersion described in [1] above as a bonding material for joining objects to be joined together. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a copper fine particle dispersion that has excellent coating properties, suppresses cracking during firing, and has excellent bonding strength, as well as a method for manufacturing a bonded body using the copper fine particle dispersion. [Modes for carrying out the invention]

[0009] [Copper fine particle dispersion] The copper fine particle dispersion of the present invention is a copper fine particle dispersion comprising copper fine particles A and a dispersion medium C, wherein the content of the dispersion medium C is 3% by mass or more and 40% by mass or less, and the dispersion medium C comprises a dispersion medium C1 having a boiling point of 200°C or more and 270°C or less, and a dispersion medium C2 having a boiling point greater than 270°C, the mass ratio of the dispersion medium C1 to the dispersion medium C2 C1 / C2 is greater than 1, and the content of the dispersion medium C2 in the dispersion medium C is 10% by mass or more and 48% by mass or less.

[0010] According to the present invention, a copper fine particle dispersion can be obtained that exhibits excellent coating properties, suppresses cracking during firing, and has excellent bonding strength. The reason for this is not entirely clear, but it is thought to be as follows. Typically, bonded semiconductor devices are manufactured by coating a substrate with a bonding material such as a dispersion of copper nanoparticles, going through a pre-baking process, placing components such as electronic chips on the pre-baked bonding material, and then pressurizing and firing it. In coating with copper nanoparticle dispersions, the dispersion must contain an appropriate amount of dispersion medium to achieve a suitable viscosity for coating. However, if the dispersion medium content is too high, it cannot be sufficiently removed during pre-baking, resulting in insufficient sintering of the copper nanoparticles during pressure firing. On the other hand, if the dispersion medium content is too low, the amount of dispersion medium in the copper nanoparticle dispersion after pre-baking is reduced, preventing atomic diffusion of copper nanoparticles through the dispersion medium during pressure firing, thus slowing down the sintering of the copper nanoparticles. As a result, it has been difficult to achieve both coating properties and crack suppression and bonding strength during sintering with conventional copper nanoparticle dispersions.

[0011] The copper fine particle dispersion of the present invention maintains a viscosity suitable for coating because the dispersion medium C content is 3% by mass or more and 40% by mass or less, thereby improving coating properties. Furthermore, since the copper nanoparticle dispersion of the present invention contains 20% to 48% by mass of dispersion medium C2, which has a boiling point above 270°C, it can retain a sufficient amount of dispersion medium to promote the sintering of copper nanoparticles during pressurized firing, thereby suppressing cracking after firing and improving bonding strength. Furthermore, the copper fine particle dispersion of the present invention contains a dispersion medium C1 having a boiling point of 200°C to 270°C, and the mass ratio of dispersion medium C1 to dispersion medium C2, C1 / C2, is greater than 1, so the viscosity of the copper fine particle dispersion can be maintained within an appropriate range for coating. Moreover, because the content of dispersion medium C1 is within the above range, the dispersion medium C1 with a low boiling point is removed from the coated copper fine particle dispersion from the pre-bake process to the initial stage of pressurized firing, thus increasing the sintering rate, suppressing cracking after firing, and improving bonding strength.

[0012] <Copper fine particles A> In the present invention, copper nanoparticles A are preferably at least one selected from copper nanoparticles A1 and copper microparticles A2, and more preferably consist of copper nanoparticles A1 and copper microparticles A2.

[0013] The copper content in copper fine particles A 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, from the viewpoint of improving conductivity, suppressing cracking, and improving bonding strength. Here, "effectively 100% by mass" means that it may include components that are present unintentionally. Examples of unintentionally present components include unavoidable impurities.

[0014] In the present invention, from the viewpoints of improving coatability, suppressing cracking, and improving bonding strength, the content of copper fine particles A in the copper fine particle dispersion is preferably 60% by mass or more, more preferably 68% by mass or more, still more preferably 75% by mass or more, even more preferably 85% by mass or more, and even more preferably 90% by mass or more, and is preferably 97% by mass or less, more preferably 96% by mass or less, still more preferably 95% by mass or less, even more preferably 94% by mass or less, and even more preferably 93% by mass or less.

[0015] (Copper nanoparticle A1) In the present invention, from the viewpoints of improving coatability, suppressing cracking, and improving bonding strength, the copper nanoparticle A1 is preferably copper nanoparticle A1 dispersed with a dispersant B.

[0016] From the viewpoints of improving coatability, suppressing cracking, and improving bonding strength, the average particle diameter of the copper nanoparticle A1 is preferably 105 nm or more, more preferably 110 nm or more, still more preferably 115 nm or more, and even more preferably 120 nm or more, and is preferably 270 nm or less, more preferably 250 nm or less, still more preferably 240 nm or less, and even more preferably 230 nm or less. The average particle diameter of the copper nanoparticle A1 is measured by the method described in the examples. The average particle diameter of the copper nanoparticle A1 can be adjusted by the production conditions of copper fine particles such as the reduction metal ratio, the type and amount of the reducing agent, the type and amount of the dispersant B, and the reduction temperature and reduction time.

[0017] In the present invention, the content of the copper nanoparticles A1 in the copper microparticle dispersion is preferably 40% by mass or more, more preferably 45% by mass or more, still more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 65% by mass or more, from the viewpoints of improving coating properties, suppressing cracking, and improving bonding strength, and is preferably 97% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0018] 〔Dispersant B〕 In the present invention, when the copper nanoparticles A1 are dispersed by the dispersant B, the dispersibility of the copper nanoparticles A1 is improved, the coating properties of the copper microparticle dispersion are further improved, cracking is further suppressed, and the bonding strength is further improved.

[0019] From the viewpoints of improving coating properties, suppressing cracking, and improving bonding strength, the dispersant B is preferably a vinyl polymer P containing a structural unit derived from a monomer (p-1) having a carboxy group and a structural unit derived from a monomer (p-2) having a polyalkylene glycol segment. The vinyl polymer refers to a polymer obtained by addition polymerization of a monomer having a vinyl group. Examples of the vinyl polymer P in the present invention include vinyl polymers such as acrylic resins, styrene resins, styrene-acrylic resins, and acrylic silicone resins.

[0020] ≪Monomer (p-1) having a carboxy group≫ Examples of the monomer (p-1) having a carboxy group (hereinafter also referred to as "monomer (p-1)") include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, and 2-methacryloyloxymethyl succinic acid; and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and citraconic acid. The unsaturated dicarboxylic acid may be an anhydride. The monomer (p-1) may be used alone or in combination of two or more.

[0021] From the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, 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.

[0022] <<Monomers (p-2) having polyalkylene glycol segments>> 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.

[0023] From the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, 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.

[0024] The number of carbon atoms in the alkoxy group of alkoxy polyalkylene glycol (meth)acrylate is preferably 1 to 18, more preferably 1 to 14, even more preferably 1 to 12, even more preferably 1 to 4, even more preferably 1 to 3, and even more preferably 1 to 2, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0025] Examples of alkoxy polyalkylene glycol (meth)acrylates include methoxy polyalkylene glycol (meth)acrylate, ethoxy polyalkylene glycol (meth)acrylate, propoxy polyalkylene glycol (meth)acrylate, butoxy polyalkylene glycol (meth)acrylate, octoxy polyalkylene glycol (meth)acrylate, and lauroxy polyalkylene glycol (meth)acrylate. Among these, from the viewpoint of availability, methoxy polyalkylene glycol (meth)acrylate is preferred, and methoxy polyalkylene glycol methacrylate is more preferred.

[0026] 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 improving coating properties, suppressing cracking, and improving bonding strength. 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 3 or more, even more preferably 4 or more, and preferably 100 or less, more preferably 70 or less, even more preferably 50 or less, even more preferably 40 or less, and even more preferably 35 or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. The polyalkylene glycol segment may be a copolymer containing ethylene oxide-derived units and propylene oxide-derived units, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. 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.

[0027] 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.

[0028] Hydrophobic monomer (p-3) From the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, it is preferable that the vinyl polymer P further contains constituent units derived from hydrophobic monomer (p-3) (hereinafter also referred to as "monomer (p-3)"). In this specification, "hydrophobic monomer" means a monomer whose dissolution amount is less than 10 g when dissolved in 100 g of deionized water at 25°C until saturated. The amount of dissolution of monomer (p-3) is preferably 5 g or less, more preferably 1 g or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. 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.

[0029] From the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, 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, and more preferably 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.

[0030] (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. Examples 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.

[0031] From the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, 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.

[0032] The total content of monomer (p-1) and monomer (p-2) in the raw material monomer used in the production of vinyl polymer P, or the total content of constituent units derived from monomer (p-1) and constituent units derived from monomer (p-2) in all constituent units of vinyl polymer P, is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 78% by mass or more, even more preferably 80% by mass or more, and preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0033] The content of monomer (p-1) in the raw material monomer used in the production of vinyl polymer P, or the content of monomer (p-1)-derived constituent units in all constituent units of vinyl polymer P, is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 12% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 18% by mass or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0034] The content of monomer (p-2) in the raw material monomer used in the production of vinyl polymer P, or the content of monomer (p-2)-derived constituent units in all constituent units of vinyl 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 97% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0035] If the vinyl polymer P further contains constituent units derived from monomer (p-3), the amount of monomer (p-3) in the raw material monomer used to produce the vinyl polymer P, or the amount of constituent units derived from monomer (p-3) in the total constituent units of the vinyl polymer P, is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 22% by mass or less, and even more preferably 20% by mass or less.

[0036] The content of polyalkylene glycol segments in the vinyl polymer P is preferably 55% by mass or more, more preferably 56% by mass or more, even more preferably 58% by mass or more, even more preferably 60% by mass or more, and preferably 97% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0037] The number-average molecular weight Mn of the vinyl polymer P is preferably 4,000 or more, more preferably 6,000 or more, even more preferably 7,000 or more, and preferably 50,000 or less, more preferably 30,000 or less, and even more preferably 10,000 or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. The number-average molecular weight Mn of the vinyl polymer P is measured by the method described in the examples.

[0038] The acid value of the vinyl polymer P is preferably 20 mg KOH / g or more, more preferably 40 mg KOH / g or more, even more preferably 60 mg KOH / g or more, and even more preferably 80 mg KOH / g or more, and preferably 250 mg KOH / g or less, more preferably 200 mg KOH / g or less, even more preferably 150 mg KOH / g or less, and even more preferably 120 mg KOH / g or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. The acid value of the vinyl polymer P is measured by the method described in the examples.

[0039] In the present invention, the content of dispersant B in the copper fine particle dispersion is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, even more preferably 0.9% by mass or more, and preferably 10% by mass or less, more preferably 8.0% by mass or less, even more preferably 5.0% by mass or less, even more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, and even more preferably 1.2% by mass or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0040] In the present invention, the mass ratio of the content of dispersant B to the total content of copper nanoparticles A1 and dispersant B in the copper nanoparticle dispersion [dispersant B / (copper nanoparticles A1 + dispersant B)] (hereinafter also referred to as the "dispersant B mass ratio") is preferably 0.005 or more, more preferably 0.008 or more, even more preferably 0.010 or more, and preferably 0.025 or less, more preferably 0.022 or less, even more preferably 0.020 or less, and even more preferably 0.018 or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. The mass ratio of dispersant B is calculated from the content of copper nanoparticles A1 and dispersant B in the copper nanoparticle dispersion, which are measured using a differential thermogravimetric analyzer (TG / DTA) by the method described in the examples.

[0041] [Manufacturing of copper nanoparticles A1] Copper nanoparticles A1 can be obtained by mixing a copper raw material compound, a reducing agent, and a dispersant B. In this mixture, the copper raw material compound is reduced by the reducing agent, resulting in a dispersion of copper nanoparticles A1 containing the dispersion medium B. This dispersion is then dried. In the production of copper nanoparticles A1, a solvent, complexing agent, etc., for dispersing the copper raw material compound and reducing agent may be mixed as needed. In the production of copper nanoparticles A1, the reducing agent may be added simultaneously with the other raw materials, or it may be added dropwise to the mixture of other raw materials afterwards.

[0042] There are no particular restrictions on the copper raw material compound, as long as it contains copper. Examples of copper raw material compounds include copper sulfate, copper nitrate, cupric oxide, cuprous oxide, copper formate, copper acetate, and copper oxalate. Among these, copper sulfate is preferred as the copper raw material compound from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. The copper raw material compound may be used individually or as a mixture of two or more types.

[0043] There are no particular restrictions on the reducing agent, as long as it is a compound that can reduce copper raw material compounds. Examples of reducing agents include hydrazine compounds, boron compounds, and inorganic salts. 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, from the viewpoint of productivity, the reducing agent is preferably a hydrazine compound, more preferably at least one selected from the group consisting of hydrazine and hydrated hydrazine, and even more preferably hydrated hydrazine (hydrazine monohydrate). The reducing agent may be used individually or in combination of two or more types.

[0044] Examples of solvents for dispersing the copper raw material compound and reducing agent include water, methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol. Among these, water is preferred as the solvent from the viewpoint of availability and cost-effectiveness. The solvent may be used individually or in combination of two or more types.

[0045] The temperature of the reduction reaction is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 20°C or higher, and even more preferably 30°C or higher, from the viewpoint of reducing and homogenizing the particle size of copper nanoparticles A1. Furthermore, from the viewpoint of stably producing copper nanoparticles A1, it is preferable to carry out the reaction in the range of preferably 100°C or lower, more preferably 80°C or lower, even more preferably 60°C or lower, and even more preferably 50°C or lower. The reduction reaction may be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen gas.

[0046] In the production of copper nanoparticle dispersions, the dispersion of copper nanoparticles A1 may be purified before drying to remove impurities such as unreacted reducing agents and excess dispersant B that does not contribute to the dispersion of copper nanoparticles A1. There are no particular limitations on the method for purifying the dispersion of copper nanoparticles A1, and examples include membrane treatment such as dialysis and ultrafiltration; and centrifugation. Among these, membrane treatment is preferred from the viewpoint of efficiently removing impurities, and dialysis is more preferred. As the material of the dialysis membrane used for dialysis, regenerated cellulose is preferred. From the viewpoint of efficiently removing impurities, the molecular weight cutoff of the dialysis membrane is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, and more preferably 70,000 or less.

[0047] (Copper microparticles A2) In the present invention, copper fine particles A preferably include copper microparticles A2 from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0048] The average particle size of copper microparticles A2 is preferably greater than 0.27 μm, more preferably 1 μm or more, even more preferably 1.5 μm or more, even more preferably 2 μm or more, even more preferably 2.5 μm or more, and preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, and even more preferably 4 μm or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. The average particle size of copper microparticles A2 is measured by the method described in the examples.

[0049] In the present invention, the content of copper microparticles A2 in the copper fine particle dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, even more preferably 15% by mass or more, even more preferably 18% by mass or more, even more preferably 20% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0050] In the present invention, the mass ratio of the content of copper nanoparticles A1 to the total content of copper nanoparticles A1 and copper microparticles A2 in the copper nanoparticle dispersion [copper nanoparticles A1 / (copper nanoparticles A1 + copper microparticles A2)] is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, even more preferably 0.6 or more, and preferably 1.0 or less, more preferably 0.9 or less, even more preferably 0.85 or less, and even more preferably 0.8 or less.

[0051] In the present invention, the total content of copper nanoparticles A1 and copper microparticles A2 in the copper fine particle dispersion is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even 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 95% by mass or less, more preferably 94% by mass or less, even more preferably 93% by mass or less, and even more preferably 92% by mass or less.

[0052] <Dispersion medium C> The copper fine particle dispersion of the present invention has a dispersion medium C content of 3% by mass or more and 40% by mass or less, and the dispersion medium C comprises a dispersion medium C1 having a boiling point of 200°C or more and 270°C or less, and a dispersion medium C2 having a boiling point greater than 270°C, the mass ratio of dispersion medium C1 to dispersion medium C2 C1 / C2 is greater than 1, and the content of the dispersion medium C2 in the dispersion medium C is 20% by mass or more and 48% by mass or less. In this specification, the boiling points of dispersion media C1 and C2 refer to the boiling points under normal pressure (1 atmosphere).

[0053] In the present invention, the content of the dispersion medium C in the copper fine particle dispersion is 3% by mass or more, preferably 4% by mass or more, more preferably 4.5% by mass or more, even more preferably 5% by mass or more, even more preferably 5.5% by mass or more, and 40% by mass or less, preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0054] In the present invention, the content of the dispersion medium C1 in the dispersion medium C is preferably 52% by mass or more, more preferably 54% by mass or more, even more preferably 55% by mass or more, even more preferably 56% by mass or more, even more preferably 57% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 65% ​​by mass or less, even more preferably 62% by mass or less, and even more preferably 60% by mass or less.

[0055] In the present invention, the content of the dispersion medium C2 in the dispersion medium C is 10% by mass or more, preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 35% by mass or more, even more preferably 38% by mass or more, even more preferably 40% by mass or more, and 48% by mass or less, preferably 46% by mass or less, more preferably 45% by mass or less, even more preferably 44% by mass or less, and even more preferably 43% by mass or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. In the present invention, the mass ratio C1 / C2 of the dispersion medium C1 to the dispersion medium C2 in the copper fine particle dispersion is greater than 1, preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and preferably 10.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0056] (Dispersion medium C1) In the present invention, the dispersion medium C1 is preferably at least one selected from (poly)alkylene glycol, (poly)alkylene glycol derivatives, and terpene alcohols, having a boiling point of 200°C or higher and 270°C or lower, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0057] In this specification, "(poly)alkylene glycol" means at least one selected from alkylene glycols and polyalkylene glycols. Examples of (poly)alkylene glycols with a boiling point between 200°C and 270°C include diethylene glycol (boiling point: 244°C), dipropylene glycol (boiling point: 232°C), and 2-ethyl-1,3-hexanediol (boiling point: 244°C).

[0058] In this specification, "(poly)alkylene glycol derivative" means at least one selected from alkylene glycol derivatives and polyalkylene glycol derivatives. Examples of (poly)alkylene glycol derivatives having a boiling point of 200°C or higher and 270°C or lower include compounds in which the terminal hydroxyl groups of the (poly)alkylene glycol are etherified or esterified. Examples of compounds in which the hydroxyl groups at both ends of the (poly)alkylene glycol are etherified or esterified include diethylene glycol dibutyl ether (boiling point: 254°C), triethylene glycol dimethyl ether (boiling point: 216°C), diethylene glycol monoethyl ether acetate (boiling point: 217°C), and diethylene glycol monobutyl ether acetate (boiling point: 247°C). Examples of compounds in which the hydroxyl group at one end of the polyalkylene glycol is etherified or esterified include diethylene glycol monoethyl ether (boiling point: 202°C) and diethylene glycol monobutyl ether (boiling point: 231°C).

[0059] Examples of terpene alcohols with a boiling point between 200°C and 270°C include α-terpineol (boiling point: 219°C), geraniol (boiling point: 229°C), and citronellol (boiling point: 225°C).

[0060] Among these, the dispersion medium C1 is more preferably a (poly)alkylene glycol having a boiling point of 200°C or higher and 270°C or lower, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, even more preferably at least one selected from diethylene glycol and dipropylene glycol, and even more preferably diethylene glycol and dipropylene glycol.

[0061] (Dispersion medium C2) In the present invention, the dispersion medium C2 is preferably at least one selected from (poly)alkylene glycol, glycerin (boiling point: 290°C), and glycerin derivatives, with a boiling point greater than 270°C, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength.

[0062] Examples of (poly)alkylene glycols with a boiling point above 270°C include triethylene glycol (boiling point: 287°C), tetraethylene glycol (boiling point: 327°C), tripropylene glycol (boiling point: 273°C), tetrapropylene glycol (boiling point: 300°C or higher), polyethylene glycol (number average molecular weight preferably 100 to 1000, more preferably 150 to 600, and even more preferably 180 to 500), and polypropylene glycol (number average molecular weight preferably 150 to 1000, more preferably 180 to 600, and even more preferably 200 to 500).

[0063] Glycerin derivatives with a temperature exceeding 270°C are not particularly limited as long as they contain a solvent with 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). Examples of polyglycerins include diglycerin and triglycerin. Examples of commercially available polyglycerins include polyglycerin #310, polyglycerin #500, and polyglycerin #750 manufactured by Sakamoto Pharmaceutical Co., Ltd. Examples of ether derivatives of glycerin include 3-(2-ethylhexyloxy)-1,2-propanediol (boiling point: 325°C). Examples of glycerol ester derivatives include glyceryl tributyrate (boiling point: 305°C).

[0064] Among these, the dispersion medium C2 is more preferably (poly)alkylene glycol with a temperature of over 270°C, from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength, and more preferably at least one selected from tetraethylene glycol and polyethylene glycol (number average molecular weight preferably 100 to 1000, more preferably 150 to 600, and even more preferably 180 to 500), and even more preferably at least one selected from tetraethylene glycol and polyethylene glycol (number average molecular weight 180 to 500).

[0065] The copper nanoparticle dispersion of the present invention may contain various additives as components other than the aforementioned components, to the extent that they do not impair the effects of the present invention. Examples of such additives include metal particles other than copper nanoparticles A, dispersion aids, sintering accelerators such as glass frit, antioxidants, viscosity modifiers, pH adjusters, buffers, defoamers, leveling agents, volatilization inhibitors, and the like. Examples of metal particles other than copper nanoparticles A include zinc, nickel, silver, gold, palladium, and platinum. Examples of dispersing aids include, for example, 2,4,7,9-tetramethyl-5-decine-4,7-diol, ethylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4,7-diol, etc., from the viewpoint of improving the dispersibility of copper fine particles and reducing the surface tension of the dispersion medium C to suppress cracking. The content of the additive in the copper fine particle dispersion according to the present invention is preferably 1% by mass or less.

[0066] In the present invention, the mass ratio (C / A) of the content of dispersion medium C to the content of copper fine particles A in the copper particle dispersion is preferably 0.03 or more, more preferably 0.04 or more, even more preferably 0.05 or more, even more preferably 0.06 or more, and preferably 0.70 or less, more preferably 0.67 or less, even more preferably 0.55 or less, even more preferably 0.50 or less, even more preferably 0.30 or less, even more preferably 0.20 or less, even more preferably 0.15 or less, and even more preferably 0.10 or less.

[0067] <Method for producing copper particle dispersions> The copper fine particle dispersion of the present invention is obtained by mixing the copper fine particles A and dispersion medium C described above. The present invention provides a method for producing a copper particle dispersion, which can be obtained by adding and mixing pre-prepared copper fine particles A, a dispersion medium C, and various additives as needed; or by mixing a copper raw material compound, a reducing agent, and a dispersant B, and optionally a solvent for dispersing the copper raw material compound and the reducing agent, reducing the copper raw material compound to obtain a dispersion of copper nanoparticles A1, and then adding and mixing the dispersion medium C, and optionally copper microparticles A2 and various additives. Among these, the method of adding and mixing pre-prepared copper fine particles A and a dispersion medium C, and various additives as needed is preferred from the viewpoint of improving coating properties, suppressing cracking, and improving bonding strength. As for the mixing method, known methods can be used, and from the viewpoint of further dispersing the copper fine particles A in the dispersion medium C, it is preferable to pre-mix the copper fine particles A and the dispersion medium C using an agate mortar or the like, and then further mix them using an agitator such as a rotating agitator.

[0068] <Application> The copper nanoparticle dispersion of the present invention has excellent coating properties, suppresses cracking during firing, and has excellent bonding strength, making it suitable for use in forming conductive components of various electronic and electrical devices. The copper nanoparticle dispersion of the present invention can be used as a substitute for bonding agents such as solder in the formation of conductive components. Furthermore, the copper nanoparticle dispersion of the present invention can be used in forming conductive components 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.

[0069] [Method for manufacturing a jointed body] The method for manufacturing the joint of the present invention comprises the following steps 1 to 3 in this order. Step 1: A step of coating a metal substrate with the copper fine particle dispersion of the present invention described above. Step 2: A step in which the metal substrate obtained in Step 1 is pre-baked at a temperature of 100°C to 150°C. Step 3: The workpiece to be bonded is placed on the copper nanoparticle dispersion on the metal substrate pre-baked in Step 2, and then pressure-fired under conditions of a temperature of 150°C to 300°C and a pressure of 5 MPa to 50 MPa.

[0070] (Process 1) Step 1 is the process of coating a metal substrate with the copper particle dispersion of the present invention.

[0071] 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.

[0072] As a method for coating the copper 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. Among these methods, stencil printing is preferred from the viewpoint of improving coating properties. The amount of copper fine particle dispersion applied to the metal component can be appropriately adjusted according to the size and type of the metal substrate.

[0073] (Process 2) This step involves pre-baking the metal substrate obtained in step 1 at a temperature of 100°C to 150°C. Step 2 allows for the pre-baking process, which removes a portion of the dispersion medium C (especially dispersion medium C1) from the coated copper nanoparticle dispersion. At the same time, the pressure firing in Step 3 allows for the retention of the dispersion medium C (especially dispersion medium C2) necessary to promote the sintering of the copper nanoparticles. This suppresses cracking at the joints of the resulting bonded structure and improves the joint strength.

[0074] The pre-bake temperature in step 2 is 100°C or higher, preferably 105°C or higher, more preferably 110°C or higher, even more preferably 115°C or higher, and 150°C or lower, preferably 140°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower, from the viewpoint of suppressing cracking and improving joint strength.

[0075] The pre-bake processing time in step 2 is preferably 1 minute or more, more preferably 3 minutes or more, even more preferably 5 minutes or more, and preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less, from the viewpoint of suppressing cracking and improving joint strength.

[0076] The atmosphere in step 2 may be an air atmosphere (atmospheric atmosphere), an inert gas atmosphere such as nitrogen gas, or a reducing gas atmosphere such as hydrogen gas, but from the viewpoint of productivity, it is an air atmosphere.

[0077] (Step 3) Step 3 involves placing the object to be bonded onto the copper fine particle dispersion on the metal substrate pre-baked in Step 2, and then pressurizing and firing it under conditions of a temperature of 150°C to 300°C and a pressure of 5 MPa to 50 MPa.

[0078] Examples of objects to be bonded include metal substrates, electrically insulating substrates, chip components, and semiconductor chips. Examples of metal substrates include those similar to the metal substrate used in step 1 above. Examples of chip components include capacitors and resistors. Examples of semiconductor chips include silicon chips, memory, diodes, transistors, ICs, and CPUs.

[0079] The temperature of the pressurized firing process in step 3 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 components.

[0080] The pressure for the pressurized firing process in step 3 is 5 MPa or more, preferably 10 MPa or more, more preferably 12 MPa or more, and even more preferably 15 MPa or more, from the viewpoint of suppressing cracking and improving joint strength, and from the viewpoint of preventing damage to surrounding members, it is 50 MPa or less, preferably 40 MPa or less, more preferably 30 MPa or less, and even more preferably 25 MPa or less.

[0081] The processing time for the pressurized firing treatment in step 3 is preferably 30 seconds or more, more preferably 60 seconds or more, and even more preferably 120 seconds or more, from the viewpoint of suppressing cracking and improving joint strength, and from the viewpoint of productivity, preferably 300 seconds or less, more preferably 240 seconds or less, and even more preferably 180 seconds or less.

[0082] The atmosphere during the heating process 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]

[0083] 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. Furthermore, in the following manufacturing examples, embodiments, and comparative examples, "parts" and "%" refer to "parts by mass" and "% by mass" respectively, unless otherwise specified. Various physical properties were measured or calculated using the following methods.

[0084] <Number-average molecular weight Mn of vinyl polymer P> The results were obtained by gel permeation chromatography under the following measurement conditions. The sample was prepared by mixing 0.1 g of polymer with 10 mL of eluent in a glass vial, stirring with a magnetic stirrer at 25°C for 10 hours, and filtering 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)"

[0085] <Acid value of vinyl polymer P> The acid value of polymer B was measured according to JIS K0070-1992 (potentiometric titration method). However, the measurement solvent was changed from the ethanol and ether mixture specified in JIS K 0070 to an acetone and toluene mixture (acetone:toluene = 4:6 (volume ratio)).

[0086] <Calculation of the content of polyalkylene glycol segments in vinyl polymer P> The polyalkylene glycol segment content of vinyl polymer P was determined by multiplying the composition (parts by mass) of each monomer in vinyl polymer P by the ratio of polyalkylene glycol segments in each monomer.

[0087] <Average particle size of copper nanoparticles A1 and copper microparticles A2> Scanning electron microscope (SEM) images of copper nanoparticles A1 and copper microparticles A2 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, 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 100 particles per sample. The arithmetic mean of these values ​​was taken as the average particle size of copper nanoparticles A1 and copper microparticles A2.

[0088] <Dispersant B mass ratio [Dispersant B / (Copper nanoparticles A1 + Dispersant B)]> Using a differential thermogravimetric / thermogravimetric analysis system (TG / DTA) (manufactured by Hitachi High-Tech Science Corporation, product name: STA7200RV), 10 mg of the sample (dried powder of copper nanoparticles A1 containing dispersant B) 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 polymer B, and the remaining mass at 550°C was taken as the mass of copper nanoparticles A1. The mass ratio of dispersant B [dispersant B / (copper nanoparticles A1 + dispersant B)] was calculated using the following formula. Mass ratio of dispersant B = (mass loss from 35°C to 550°C) / (mass loss from 35°C to 550°C + remaining mass at 550°C)

[0089] [Manufacturing of vinyl polymer P] Manufacturing Example 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 flask was then heated to 80°C in an oil bath, and nitrogen bubbling was performed for 10 minutes. Next, 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 (EO 23 mol) methacrylate (manufactured by NOF Corporation, "PME-1000", polyalkylene glycol segment ratio: 93.8%), 1.0g of 3-mercaptopropionic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), and 28.7g of ethanol were mixed and dissolved in a poly beaker and placed in a dropping funnel (1). Separately, 1.3g of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., "V-65", polymerization initiator) was dissolved in 51.3g of ethanol 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 to the flask over 90 minutes each. After that, the internal temperature of the flask was raised to 90°C, and stirring was continued for another hour to complete the reaction. The resin solution 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) under drying conditions (-25°C for 1 hour freezing, -10°C for 9 hours under reduced pressure, 25°C for 5 hours under reduced pressure. Reduced pressure degree: 5 Pa) to obtain an oven-dried vinyl polymer P-1 (methacrylic acid / methyl methacrylate / methoxypolyethylene glycol (EO 23 mol) methacrylate polymer, acid value: 100 mg KOH / g, Mn: 8,000). The physical properties of the obtained vinyl polymer P-1 are shown in Table 1.

[0090] [Table 1]

[0091] Details of each monomer in Table 1 are as follows: (Monomer (p-1)) • MAA: Methacrylic acid (Monomer (p-2)) PEG(23)MA: Methoxypolyethylene glycol (EO23 mol) methacrylate (polyalkylene glycol segment ratio: 93.8%) (Monomer (p-3)) • MMA: Methyl methacrylate

[0092] [Synthesis of dried copper nanoparticle A1] Synthesis Example 1 In a 2L beaker, 88.4g of copper sulfate pentahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) as the copper raw material compound, 0.7g of vinyl polymer P-1 obtained in Production Example 1 in a completely dry state as dispersant B, and 1000g of deionized water were added. The mixture was stirred at 40°C using a magnetic stirrer until it became visually clear to obtain the mixed solution. Next, 17.8 g of hydrazine monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent), placed in a 50 mL dropping funnel, was added dropwise to the mixture over 60 minutes at 25°C. The reaction solution was then stirred for 5 hours in an oil bath while controlling the temperature to 40°C, and then air-cooled to obtain a reddish-brown dispersion containing dispersed copper nanoparticles. The entire volume of the obtained dispersion was placed into a dialysis tube (REPLIGEN, product name: Spectra / Pore 6, dialysis membrane: regenerated cellulose, molecular weight cutoff (MWCO) = 50K), and the top and bottom of the tube were sealed with a closeer. This tube was immersed in 5L of deionized water in a 5L glass beaker, and stirred for 1 hour while maintaining the water temperature at 20-25°C. Subsequently, the process of completely replacing the deionized water was repeated every hour. Sampling was performed before replacing the deionized water, and dialysis was terminated when the conductivity of the copper nanoparticle dispersion fell to 7 mS / m or less, to obtain the copper nanoparticle dispersion. Conductivity was measured after diluting with deionized water to adjust the copper concentration to 1%. A dispersion of purified copper nanoparticles was freeze-dried using a freeze-dryer (FDU-2110, manufactured by Tokyo Rikakikai Co., Ltd.) equipped with a dry chamber (DRC-1000, manufactured by Tokyo Rikakikai Co., Ltd.) to obtain 21.3 g of dried powder containing vinyl polymer P-1 and copper nanoparticles A1-1 as dispersant B. Freeze-drying was performed by freezing at -25°C for 1 hour, then drying under reduced pressure at 5 Pa at -10°C for 9 hours, and finally drying under reduced pressure at 5 Pa at 25°C for 5 hours. The obtained copper nanoparticles A1-1 had an average particle size of 160 nm and a mass ratio of dispersant B of 0.014. The physical properties of the obtained dried powder are shown in Table 2.

[0093] [Table 2]

[0094] Example 1 <Manufacturing of copper particle dispersions> 3.7 parts by mass of dipropylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent) as dispersion medium C1, 2.8 parts by mass of polyethylene glycol 200 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent, number average molecular weight: 200) as dispersion medium C2, 70 parts by mass of dried powder containing vinyl polymer P-1 obtained in Synthesis Example 1 and copper nanoparticles A1-1 as copper nanoparticles A1 and dispersant B, 23 parts by mass of MA-C03K (Mitsui Mining & Smelting Co., Ltd., particle size 3.4 μm) as copper microparticles A2, and 0.5 parts by mass of 2,4,7,9-tetramethyl-5-decine-4,7-diol (manufactured by Tokyo Chemical Industry Co., Ltd., DL-,meso- mixture) as other additives were added to an agate mortar and kneaded until the dried powder was no longer visible, and the resulting mixture was transferred to a plastic bottle. A tightly sealed plastic bottle was subjected to a rotation-and-revolving stirring device (Sinky Co., Ltd., Planetary Vacuum Mixer ARV-310) for 2000 mins. -1 The mixture was stirred at 2000 revolutions per minute for 5 minutes to obtain a dispersion of copper fine particles.

[0095] <Manufacturing of jointed parts> Using the obtained copper nanoparticle dispersion, a bonded body was manufactured according to the following method. (Process 1) First, 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 plate (total thickness: 1 mm), and a dispersion of copper fine particles was applied to the copper plate using stencil printing with a metal squeegee. (Process 2) Subsequently, the product was pre-baked at 120°C for 10 minutes on a Shamal hot plate (HHP-441, manufactured by AS ONE Corporation) under open air. (Step 3) Subsequently, silicon chips measuring 5 mm x 5 mm (thickness: 400 μm) were prepared by sputtering titanium, nickel, and gold in that order. These silicon chips were then placed on a coated copper microparticle dispersion so that the gold was in contact with the copper microparticle dispersion. This resulted in a laminate in which a copper plate, copper microparticle dispersion, and silicon chips were stacked in that order. The resulting laminate was fired using the following method to obtain a bonded body. First, the 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.

[0096] Examples 2-6, Comparative Examples 1-4 Except for changing the composition of the copper nanoparticle dispersion to the composition shown in Table 3, the procedure was carried out in the same manner as in Example 1 to obtain the copper nanoparticle dispersions and composites of Examples 2 to 6 and Comparative Examples 1 to 4, respectively.

[0097] The details of the raw materials (each raw material in Table 3) used in the production of the copper nanoparticle dispersions in the examples and comparative examples are as follows. (Copper microparticles A2) • MA-C03K (Mitsui Mining & Smelting Co., Ltd., particle size 3.4 μm) (Dispersion medium C1) • DPG: Dipropylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent, boiling point: 232°C) • DEG: Diethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., primary reagent grade, boiling point: 244°C) (Dispersion medium C2) • TEG: Tetraethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent, 327°C) • PEG200: Polyethylene glycol 200 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., first-grade reagent, number-average molecular weight: 200, boiling point: 270°C or higher) (Other additives) • TMDD: 2,4,7,9-tetramethyl-5-decine-4,7-diol (manufactured by Tokyo Chemical Industry Co., Ltd., DL-,meso- mixture)

[0098] [Evaluation of copper nanoparticle dispersions] <Coating properties> 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 plate (total thickness: 1 mm), and a dispersion of copper fine particles was applied to the copper plate by stencil printing using a metal squeegee. The state of the copper fine particle dispersion after coating was visually inspected and evaluated according to the following evaluation criteria. (Evaluation Criteria) A: The copper particle dispersion, coated in three rows, was uniformly applied without contact with each other. B: The copper fine particle dispersions coated in three rows were in contact with each other or were not uniformly coated.

[0099] <Cracks> The cracking at the joint interface of the joints in the examples and comparative examples was evaluated according to the following procedure. An ultrasonic flaw detection system (Hitachi Power Solutions Co., Ltd., model: FS100III) equipped with a 50MHz frequency probe was used to observe the bonding interface from the copper plate side of the bonded body. The probe was adjusted to the condition where the reflected wave from the bonding interface was strongest (highest peak), and measurements were taken under the following conditions. The obtained images were visually inspected and evaluated according to the following evaluation criteria. (Measurement conditions) ·Material sound velocity=Cu:4700mm / s Gain = 28dB (Evaluation Criteria) A: No cracks were found. B: A crack was found.

[0100] <Joining strength> The bonding strength of the joints of the examples and comparative examples was measured according to the following procedure. 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 tip of the bonded structure horizontally at a test speed of 5 mm / min and a shear height of 50 μm. Three tests were performed on each bonded structure, and the average value obtained from the measurements of the three bonded structures was taken as the bond strength of the bonded structure.

[0101] [Table 3]

[0102] Table 3 shows that the copper nanoparticle dispersions of Examples 1-6 exhibited superior coating properties, suppressed cracking during firing, and demonstrated superior bonding strength compared to the copper nanoparticle dispersions of Comparative Examples 1-4. [Industrial applicability]

[0103] According to the present invention, it is possible to provide a copper fine particle dispersion that has excellent coating properties, suppresses cracking during firing, and has excellent bonding strength, as well as a method for manufacturing a bonded body using the copper fine particle dispersion.

Claims

1. A copper nanoparticle dispersion containing copper nanoparticles A and a dispersion medium C, The content of the dispersion medium C is 3% by mass or more and 40% by mass or less. The dispersion medium C comprises a dispersion medium C1 having a boiling point of 200°C or higher and 270°C or lower, and a dispersion medium C2 having a boiling point greater than 270°C. The mass ratio C1 / C2 of the dispersion medium to the dispersion medium C2 is greater than 1. A copper fine particle dispersion wherein the content of the dispersion medium C2 in the dispersion medium C is 10% by mass or more and 48% by mass or less.

2. The copper nanoparticle dispersion according to claim 1, wherein the copper nanoparticle A is at least one selected from copper nanoparticles A1 and copper microparticles A2.

3. The copper nanoparticle dispersion according to claim 2, wherein copper nanoparticles A1 are dispersed in a dispersant B.

4. The copper nanoparticle dispersion according to claim 2, wherein the average particle size of copper nanoparticles A1 is 105 nm or more and 270 nm or less.

5. The copper nanoparticle dispersion according to claim 2, wherein the content of copper nanoparticles A1 in the copper nanoparticle dispersion is 40% by mass or more and 97% by mass or less.

6. The copper fine particle dispersion according to claim 3, wherein the dispersant B is a vinyl polymer P comprising a constituent unit derived from a monomer having a carboxyl group (p-1) and a constituent unit derived from a monomer having a polyalkylene glycol segment (p-2).

7. The copper fine particle dispersion according to claim 6, wherein the number average molecular weight Mn of the vinyl polymer P is 4,000 or more and 50,000 or less.

8. The copper nanoparticle dispersion according to claim 6, wherein the acid value of the vinyl polymer P is 20 mg KOH / g or more and 250 mg KOH / g or less.

9. The copper nanoparticle dispersion according to claim 3, wherein the mass ratio of the content of dispersant B to the total content of copper nanoparticles A1 and dispersant B in the copper nanoparticle dispersion [dispersant B / (copper nanoparticles A1 + dispersant B)] is 0.005 or more and 0.025 or less.

10. The copper microparticle dispersion according to claim 2, wherein the average particle size of copper microparticles A2 is greater than 0.27 μm and less than or equal to 10 μm.

11. The copper fine particle dispersion according to claim 1, wherein the dispersion medium C1 is at least one selected from (poly)alkylene glycol, (poly)alkylene glycol derivatives, and terpene alcohols, having a boiling point of 200°C or higher and 270°C or lower.

12. The copper fine particle dispersion according to claim 1, wherein the dispersion medium C2 is at least one selected from (poly)alkylene glycol, glycerin, and glycerin derivatives, having a boiling point greater than 270°C.

13. The copper fine particle dispersion according to claim 1, wherein the mass ratio of the content of the dispersion medium C to the content of the copper fine particles A (C / A) is 0.03 or more and 0.70 or less.

14. A method for manufacturing a joined body, comprising the following steps 1 to 3 in this order. Step 1: A step of coating a copper fine particle dispersion according to any one of claims 1 to 13 onto a metal substrate. Step 2: A step in which the metal substrate obtained in Step 1 is pre-baked at a temperature of 100°C to 150°C. Step 3: The workpiece to be bonded is placed on the copper fine particle dispersion of the metal substrate pre-baked in Step 2, and then pressure-fired under conditions of a temperature of 150°C to 300°C and a pressure of 5 MPa to 50 MPa.

15. Use of the copper fine particle dispersion according to any one of claims 1 to 13 as a bonding material for joining objects to be joined together.

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