Dispersion medium for metal particle sintering and conductive paste

Abstract

Provided are a dispersion medium for metal particle sintering that provides an electroconductive paste whereby metal particles are satisfactorily sintered at low temperature even when not in a reducing atmosphere, and an electroconductive paste in which the dispersion medium is used.　This dispersion medium for metal particle sintering contains formic acid and a basic compound, the basic compound being a nitrogen-containing compound represented by formula (1), and the mole ratio (basic group / formic acid) of basic groups included in the basic compound and formic acid being 0.50-1.20. [Chemical Formula 1] In formula (1): Ra-Rc are the same or different and represent a hydrogen atom or a hydrocarbon group that may have a substituent; the double line including a dashed line represents a single bond or a double bond, with Rc being absent in the case of a double bond; and any two of Ra-Rc may bond with each other to form a ring with the adjacent nitrogen atom.

Description

[Technical Field]

[0001] The present disclosure relates to a dispersion medium for sintering metal particles and a conductive paste. This application claims priority from Japanese Patent Application No. 2020-025765, filed on February 19, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conductive pastes are used as materials for semiconductor bonding, wire bonding, clip bonding, wiring formation, bump formation, etc. in the manufacture of electronic devices such as printed wiring boards, capacitors, inductors, varistors, thermistors, transistors, speakers, actuators, antennas, solid oxide fuel cells, and hybrid ICs.

[0003] Metal particles, such as copper particles, used in conductive pastes are prone to forming oxide coatings on their surfaces that inhibit sintering. Therefore, conductive pastes using metal particles coated with an organic substance to prevent the formation of oxide coatings have been investigated. Examples include a copper bonding paste containing copper particles coated with an organic protective agent and a dispersion medium (Patent Document 1), and a conductor-forming composition containing copper-containing particles coated with an organic substance containing an alkylamine having a hydrocarbon group with seven or fewer carbon atoms, an organic acid, and a dispersion medium (Patent Document 2). However, these conductive pastes have problems with the organic coating, such as the complexity of the coating process and increased costs, as well as the need for high-temperature firing to remove the coating film and the introduction of a reducing gas such as formic acid to promote sintering. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-156736 [Patent Document 2] Japanese Patent Application Publication No. 2018-170228 Summary of the Invention [Problem to be solved by the invention]

[0005] To solve the above problems, the inventors focused on an azeotropic composition containing formic acid (formic acid / triethylamine molar ratio: 5 / 2) and attempted to use it as a dispersion medium capable of supplying reducing gas (formic acid) during firing. However, pastes using the above azeotropic composition had problems in that good sintered bodies could not be obtained due to corrosion of the metal particles, and the metal particles aggregated, significantly reducing storage stability.

[0006] Therefore, an object of the present disclosure is to provide a dispersion medium for sintering metal particles that solves the above problems, produces a sintered body that exhibits good conductivity and bonding strength even without a reducing atmosphere, and provides a conductive paste with excellent storage stability. Another object of the present disclosure is to provide a dispersion medium for sintering metal particles in which formic acid volatilizes in a high-temperature range of 100°C or higher, produces a sintered body that exhibits good conductivity and bonding strength even without a reducing atmosphere, and provides a conductive paste with excellent storage stability. Another object of the present disclosure is to provide a conductive paste using the above dispersion medium. [Means for solving the problem]

[0007] As a result of intensive research to solve the above problems, the present inventors have found that when a mixture of formic acid and a basic compound in a specific molar ratio is used as a dispersion medium in a conductive paste, corrosion of metal particles by formic acid is suppressed, a good sintered body can be obtained even without a reducing atmosphere, and aggregation of metal particles can be suppressed. The present invention has been completed based on these findings.

[0008] That is, the present disclosure provides a dispersion medium for sintering metal particles, which contains formic acid and a basic compound, wherein the basic compound is a nitrogen-containing compound represented by the following formula (1), and the molar ratio of a basic group contained in the basic compound to formic acid (basic group / formic acid) is 0.50 to 1.20. [ka] (In formula (1), R a ~R c are the same or different and represent a hydrogen atom or a hydrocarbon group which may have a substituent. The substituent may be the same or different and represent at least one group selected from an amino group, an N-substituted amino group, an N,N-substituted amino group, an imino group, an N-substituted imino group, and a hydroxyl group. However, R a ~R c are not hydrogen atoms at the same time. A double line including a dashed line represents a single bond or a double bond. If it is a double bond, R c does not exist. R a ~R c Any two of may be bonded to each other to form a ring together with the adjacent nitrogen atom.

[0009] The present disclosure also provides a conductive paste containing metal particles and the above-described dispersion medium.

[0010] The conductive paste was measured for viscosity (25°C, shear rate 10 s) of the conductive paste measured by a rheometer immediately after mixing the metal particles and the dispersion medium. -1 ) and the viscosity of the conductive paste measured by a rheometer after storing it at 25°C or below for 7 days (25°C, shear rate 10 s -1 ) (viscosity after storage / viscosity immediately after mixing) is preferably 10.0 or less.

[0011] The conductive paste preferably has a maximum peak temperature of 100 to 220°C when measured by differential thermogravimetric analysis (DTG) at a temperature rise rate of 10°C / min in a nitrogen atmosphere.

[0012] The metal particles are preferably at least one selected from copper particles, silver particles, and particles of oxides thereof.

[0013] The volume average particle size of the metal particles is preferably 1 nm or more and 100 μm or less. [Effects of the Invention]

[0014] The dispersion medium of the present disclosure, by incorporating formic acid, reduces metal particles and promotes sintering even in an inert atmosphere, not just a reducing atmosphere. Furthermore, a sufficient amount of basic groups neutralizes and stabilizes the formic acid, preventing corrosion of the metal particles and ensuring the storage stability of the conductive paste. In the conductive paste of the present disclosure, the formic acid and the basic compound form an azeotropic composition, preventing drying. Furthermore, the volatilization of formic acid occurs at high temperatures of 100°C or higher, promoting sintering of the metal particles. Furthermore, after the volatilization of formic acid and the basic compound, very little organic residue remains, allowing for the production of sintered bodies that exhibit good conductivity even at temperatures as low as 200°C. Furthermore, the conductive paste of the present disclosure can achieve high bonding strength even at temperatures as low as 200°C and with a slight pressure of 1 MPa or less. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Dispersion medium] The dispersion medium for sintering metal particles according to the present disclosure contains formic acid and a basic compound such that the molar ratio of the basic group contained in the basic compound to formic acid (basic group / formic acid) is 0.50 to 1.20.

[0016] <Formic acid> In the present disclosure, formic acid is compatible with the basic compound described below and serves as a dispersion medium for metal particles. It also reduces the oxide film on the surface of the metal particles, promoting sintering of the metal particles.

[0017] To incorporate formic acid into the dispersion medium of the present disclosure so that the molar ratio (basic group / formic acid) is 0.50 to 1.20, formic acid or a mixture containing formic acid can be used. Among these, a mixture containing 50% by weight or more of formic acid is preferred from the viewpoint of ease of handling, and a formic acid-triethylamine azeotropic composition (for example, formic acid:triethylamine=5:2 (molar ratio)), 98% formic acid, or an aqueous solution of 88% formic acid is more preferred.

[0018] <Basic compounds> The basic compound in the present disclosure increases the temperature at which formic acid volatilizes in the conductive paste, makes the compatible substance a good dispersion medium, and inhibits corrosion of the metal particle surfaces by formic acid.

[0019] The basic compound used in the present disclosure is a nitrogen-containing compound represented by the following formula (1). [ka] (In formula (1), R a ~R c are the same or different and represent a hydrogen atom or a hydrocarbon group which may have a substituent. The substituent may be the same or different and represent at least one group selected from an amino group, an N-substituted amino group, an N,N-substituted amino group, an imino group, an N-substituted imino group, and a hydroxyl group. However, R a ~R c are not hydrogen atoms at the same time. A double line including a dashed line represents a single bond or a double bond. If it is a double bond, R c does not exist. R a ~R c Any two of may be bonded to each other to form a ring together with the adjacent nitrogen atom.

[0020] R a ~R c Examples of the hydrocarbon group include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. Of these, an aliphatic hydrocarbon group and an alicyclic hydrocarbon group are preferred, and an aliphatic hydrocarbon group is more preferred.

[0021] Examples of the aliphatic hydrocarbon group include a linear or branched alkyl group, a linear or branched alkenyl group, a linear or branched alkynyl group, and a linear or branched alkylidene group, and among these, a linear or branched alkyl group is preferred.

[0022] The linear or branched alkyl group is preferably a linear alkyl group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkyl group having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a decyl group, a dodecyl group, a tetradecyl group, an octadecyl group, an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, and a 2-ethylhexyl group.

[0023] The linear or branched alkenyl group is preferably a linear alkenyl group having 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkenyl group having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a 1-pentenyl group, a 2-pentenyl group, a 3-pentenyl group, a 4-pentenyl group, a 1-hexenyl group, a 3-hexenyl group, a 5-hexenyl group, a 1-heptenyl group, a 1-octenyl group, a 1-nonenyl group, a 1-decenyl group, an isopropenyl group, a 2-methyl-1-propenyl group, a methallyl group, a 3-methyl-2-butenyl group, and a 4-methyl-3-pentenyl group.

[0024] The linear or branched alkynyl group is preferably a linear alkynyl group having 2 to 12 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkynyl group having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples of the linear or branched alkynyl group include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a 1-butynyl group, a 2-butynyl group, a 3-butynyl group, a 1-pentynyl group, a 2-pentynyl group, a 3-pentynyl group, a 4-pentynyl group, a 1-hexynyl group, a 2-hexynyl group, a 3-hexynyl group, a 4-hexynyl group, a 5-hexynyl group, a 1-heptynyl group, a 1-octynyl group, a 1-nonynyl group, a 1-decynyl group, a trimethylsilylethynyl group, and a triethylsilylethynyl group.

[0025] The linear or branched alkylidene group is preferably a linear alkylidene group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms, or a branched alkylidene group having 3 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms. Examples include a methylidene group, a propylidene group, an isopropylidene group, a butylidene group, an isobutylidene group, a sec-butylidene group, a pentylidene group, an isopentylidene group, an octylidene group, and an isooctylidene group.

[0026] Examples of the alicyclic hydrocarbon group include a cycloalkyl group and a cycloalkenyl group.

[0027] The cycloalkyl group is preferably a cycloalkyl group having 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and even more preferably 5 to 8 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group.

[0028] The cycloalkenyl group is preferably a cycloalkenyl group having 3 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and even more preferably 5 to 8 carbon atoms, and examples thereof include a cyclopentenyl group and a cyclohexenyl group.

[0029] The aromatic hydrocarbon group is preferably an aryl group having 6 to 18 carbon atoms, more preferably 6 to 18 carbon atoms, and even more preferably 6 to 10 carbon atoms, and examples thereof include a phenyl group and a naphthyl group.

[0030] In formula (1), the double line including the dashed line represents a single bond or a double bond. When the double line including the dashed line is a double bond, R c does not exist, and R in formula (1) a and R b The nitrogen atom to which is bonded represents an imino group or an N-substituted imino group.

[0031] Ra ~R c The total number of amino groups, N-substituted amino groups and N,N-substituted amino groups that may be contained in the alkyl group is preferably 0 to 6, more preferably 1 to 4, and even more preferably 1 or 2.

[0032] R a ~R c The total number of imino groups and N-substituted imino groups that may be contained in the alkyl group is preferably 0 to 4, more preferably 1 to 3, and even more preferably 1 or 2.

[0033] R a ~R c The total number of hydroxyl groups that may be possessed by is preferably 0 to 6, more preferably 1 to 4, and even more preferably 1 or 2.

[0034] The substituents of the N-substituted amino group, N,N-substituted amino group, and N-substituted imino group are the same as those of the R a ~R c The hydrocarbon groups are the same as those described above.

[0035] R a ~R c Any two of these may be bonded to each other to form a ring together with the adjacent nitrogen atom. Examples of the ring formed include a pyrrolidine ring, a pyrroline ring, a piperidine ring, a pyrrole ring, an imidazolidine ring, an imidazole ring, a piperazine ring, an imidazolidine ring, a pyridine ring, a diazine ring, and a triazine ring.

[0036] R a ~R cThe hydrocarbon group in the above formula (1) may have a substituent other than an amino group, an N-substituted amino group, an N,N-substituted amino group, an imino group, an N-substituted imino group, or a hydroxyl group. Examples of such a substituent include a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an oxo group, a substituted oxy group (an alkoxy group having 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, an aralkyloxy group having 7 to 16 carbon atoms, an acyloxy group having 1 to 4 carbon atoms, etc.), a carboxyl group, a substituted oxycarbonyl group (an alkoxycarbonyl group having 1 to 4 carbon atoms, an aryloxycarbonyl group having 6 to 10 carbon atoms, an aralkyloxycarbonyl group having 7 to 16 carbon atoms, etc.), a cyano group, a nitro group, a sulfo group, a mercapto group, and a heterocyclic group.

[0037] Specific examples of the basic compound represented by formula (1) include, for example, R a ~R c an alkylamine in which at least one of R is a linear or branched alkyl group; a , R b is a hydrogen atom, and R c is a linear or branched alkyl group having one hydroxyl group; a is a hydrogen atom, and R b and R c are the same or different and are linear or branched alkyl groups each having one hydroxyl group; R in formula (1) a ~R c are the same or different and are linear or branched alkyl groups having one hydroxyl group; R in formula (1) a , R b are the same or different and are a hydrogen atom or a linear or branched alkyl group, and R c is a linear or branched alkyl group having two hydroxyl groups; a ~R c a diamine having a total of one amino group; R in formula (1) a ~R c a triamine having a total of two amino groups; R in formula (1) a~R c is a diaminoalkanol having a total of one amino group and a total of one hydroxyl group; R in formula (1) a ~R c an imidazole compound containing one imino group in total, and a ring formed by incorporating the nitrogen atoms of the imino groups; a , R b is bonded to an imino group, and a ring is formed containing the imino group (such as a pyridine-based compound, a diazine-based compound, or a triazine-based compound).

[0038] Examples of the alkylamine include methylamine, ethylamine, propylamine, butylamine, pentylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, piperidine, trimethylamine, triethylamine, 4-dimethylaminopyridine, 2-aminopyrazine, 2-aminopyrimidine, 3-aminopyridazine, 2-aminotriazine, diazabicyclononene, and diazabicycloundecene.

[0039] Examples of the monoalkanolamine include 2-aminoethanol, 3-aminopropanol, 1-amino-2-propanol, 1-amino-2-methyl-2-propanol, 2-amino-2-methyl-1-propanol, 4-amino-1-butanol, 6-amino-1-hexanol, 10-amino-1-decanol, 12-amino-1-dodecanol, N-methyl-2-aminoethanol, N-ethyl-2-aminoethanol, N-propyl-2-aminoethanol, 2-dimethylaminoethanol, 6-diethylaminohexanol, 1-(2-hydroxyethyl)pyrrolidine, 2-(hydroxymethyl)pyrrolidine, 2-(2-hydroxyethyl)-1-methylpyrrolidine, 1-piperidineethanol, and 1-ethanol-4-propanolpiperidine.

[0040] Examples of the dialkanolamine include diethanolamine, di-n-propanolamine, diisopropanolamine, di-n-butanolamine, and diisobutanolamine.

[0041] Examples of the trialkanolamine include triethanolamine, tri-n-propanolamine, triisopropanolamine, tri-n-butanolamine, and triisobutanolamine.

[0042] Examples of the aminoalkanediol include 1-amino-2,3-propanediol, 4-amino-1,2-butanediol, 4-amino-1,3-butanediol, 2-amino-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 1-methylamino-2,3-propanediol, 1-ethylamino-2,3-propanediol, 1-propylamino-2,3-propanediol, 1-butylamino-2,3-propanediol, 3-dimethylamino-1,2-propanediol, and 2-diethylamino-1,3-propanediol.

[0043] Examples of the diamine include 1,3-propanediamine, 2,2-dimethyl-1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,5-diamino-2-methylpentane, N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethyl-1,3-propanediamine, N,N'-diethyl-1,3-propanediamine, N,N'-dimethyl-1,4-butanediamine, N,N'-diethyl-1,4-butanediamine, and N,N'-di Examples of the alkyl esters include methyl-1,6-hexanediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine (=diethylaminopropylamine), N,N-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, 1,2-cyclohexanediamine, 1,4-cyclohexanediamine, piperazine, N-methylpiperazine, N-ethylpiperazine, N,N'-dimethylpiperazine, and homopiperazine.

[0044] Examples of the triamine include diethylenetriamine, N,N,N',N",N"-pentamethyldiethylenetriamine (=pentamethyldiethylenetriamine), N,N,N',N",N"-pentakis(2-hydroxypropyl)diethylenetriamine, 3,3'-diaminodipropylamine, N-(3-aminopropyl)-N-methyl-1,3-propanediamine, N'-[3-(dimethylamino)propyl]-N,N-dimethyl-1,3-propanediamine, 2,6,10-trimethyl-2,6,10-triazaundecane, N-(2-aminoethyl)piperazine, 1,4,7-triazacyclononane, N,N,N',N",N"-pentakis(2-hydroxypropyl)diethylenetriamine, 1-(2-aminoethyl)-4-methylpiperazine, and 1-(2-dimethylaminoethyl)-4-methylpiperazine.

[0045] Examples of the diaminoalkanol include 1,3-diaminopropan-2-ol, 2-(2-aminoethylamino)ethanol, 2-(2-aminopropylamino)ethanol, 2-(2-aminoethylmethylamino)ethanol, 1-(2-hydroxyethyl)piperazine, 4-methylpiperazine-1-ethanol, and 1,4-bis(2-hydroxyethyl)piperazine.

[0046] Examples of the imidazole compound include imidazole, 2-methylimidazole, 2-propylimidazole, N-methylimidazole (=1-methylimidazole), N-propylimidazole, N-butylimidazole, 1-(2-hydroxyethyl)imidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-acetylimidazole, and 2-hydroxybenzimidazole.

[0047] Examples of the nitrogen-containing aromatic compound include pyridine, α-picoline, β-picoline, γ-picoline, 2,6-lutidine, 2,3-lutidine, pyrazine, 2-hydroxypyrazine, pyrimidine, 2-hydroxypyrimidine, 4-hydroxypyrimidine, pyridazine, 3-hydroxypyridazine, 4-hydroxypyridazine, triazine, and 2-hydroxytriazine.

[0048] These may be used alone or in combination of two or more.

[0049] The basic compound may be liquid or solid at room temperature and pressure. The dispersion medium of the present disclosure is a mixture containing formic acid and the above-described basic compound, and is a liquid or solid at room temperature and normal pressure. However, it is preferable that the dispersion medium is an organic substance that becomes liquid when mixed with metal particles and can disperse the metal particles into a paste.

[0050] In the dispersion medium of the present disclosure, the molar ratio of the number of moles of basic groups in the basic compound to the number of moles of formic acid (basic groups / formic acid) is preferably 0.50 to 1.20, more preferably 0.55 to 1.15, and even more preferably 0.60 to 1.10. If the molar ratio is below 0.50, the storage stability of the conductive paste tends to deteriorate, while if it exceeds 1.20, it tends to be difficult to obtain a sintered body exhibiting good conductivity. The number of moles of basic groups in the basic compound is calculated by multiplying the number of moles of the basic compound by the number of basic groups contained in the basic compound, and the basic group in the imidazole compound is attached to the nitrogen atom at position 1.

[0051] In order to adjust the fluidity (viscosity) and operability, the dispersion medium of the present disclosure may contain organic solvents other than water or a mixture of formic acid and the above-mentioned basic compound (for example, organic acids other than formic acid (acetic acid, propionic acid, n-octanoic acid, etc.); ester-based solvents such as acetates (ethyl acetate, butyl acetate, etc.); ether-based solvents such as dioxane and tetrahydrofuran; ketone-based solvents such as acetone; aromatic solvents such as toluene and xylene; halogen-based solvents such as dichloromethane and chloroform; alcohol-based solvents such as methanol, ethanol, isopropanol, and butanol; nitrile-based solvents such as acetonitrile and benzonitrile), resin components (for example, polymer compounds having a number average molecular weight of 10,000 or more, such as ethyl cellulose resin, alkyl cellulose resin, polyvinyl acetal resin, and acrylic resin), basic compounds other than the above-mentioned basic compounds (inorganic bases (sodium hydroxide, potassium hydroxide, ammonia, etc.)), additives (surface conditioners (leveling agents), antifoaming agents, dispersants, thixotropy-imparting agents, etc.), etc.

[0052] The dispersion medium of the present disclosure can be produced through a process of mixing the above-mentioned formic acid and basic compound with other components to cause them to be compatible with each other.

[0053] The temperature during mixing preferably does not exceed 100°C.

[0054] The mixture may be cooled to room temperature (for example, 25° C.) or below after mixing, and may be gradually cooled to room temperature or rapidly cooled by ice or the like.

[0055] [Conductive paste] The conductive paste of the present disclosure contains metal particles and a dispersion medium containing formic acid and a basic compound, and can be suitably used as a material for semiconductor bonding, wire bonding, clip bonding, wiring formation, bump formation, etc. in the manufacture of electronic devices (printed wiring boards, capacitors, inductors, varistors, thermistors, transistors, speakers, actuators, antennas, solid oxide fuel cells, hybrid ICs, etc.).

[0056] <Metal particles> The metal particles used in the present disclosure may be any metal particles that have electrical conductivity after sintering, and examples thereof include particles of gold, silver, copper, nickel, palladium, tin, aluminum, or alloys thereof, or oxides thereof (copper oxide (CuO, CuO)), silver oxide, etc.) Among these, at least one selected from copper particles, silver particles, and particles of oxides thereof is preferred, as this allows for the production of a sintered body with high electrical conductivity, with copper particles and / or silver particles being more preferred, and copper particles being even more preferred. These may be used alone or in combination of two or more.

[0057] The metal particles may be in various shapes such as spherical, ellipsoidal flake (flat), fibrous, or irregular, but are preferably spherical or flake in shape from the viewpoint of the coating properties and storage stability of the conductive paste. These may be used alone or in combination of two or more.

[0058] The volume average particle diameter (median diameter, D 50 ) is preferably 1 nm to 100 μm, more preferably 10 nm to 50 μm, even more preferably 30 nm to 35 μm, particularly preferably 50 nm to 10 μm, and most preferably 70 nm to 1 μm.

[0059] The metal particles may be a mixture of two or more types of metal particles having different volume average particle diameters, such as nanoparticles having a volume average particle diameter of preferably 1 nm or more but less than 300 nm, more preferably 1 to 200 nm, and even more preferably 1 to 150 nm; subnanoparticles having a volume average particle diameter of preferably 0.30 μm or more but less than 1.00 μm, more preferably 0.40 to 0.95 μm, and even more preferably 0.50 to 0.90 μm; or microparticles having a volume average particle diameter of preferably 1.0 to 100 μm, more preferably 1.5 to 50 μm, even more preferably 2.0 to 35 μm, particularly preferably 2.5 to 10 μm, and most preferably 3.0 to 10 μm. The volume average particle diameter of the metal particles can be measured, for example, using a commercially available laser particle size distribution analyzer (e.g., the SALD-7000 manufactured by Shimadzu Corporation).

[0060] When metal particles having different volume average particle sizes are used in combination, the weight ratio of the nano-sized particles to the total metal particles (nano-sized particles / total metal particles) is preferably 0.10 to 0.90, more preferably 0.15 to 0.85, and even more preferably 0.20 to 0.80.

[0061] When metal particles of two or more types of metals are used in combination, the weight ratio of copper particles to all metal particles (copper particles / all metal particles) is preferably 0.35 to 0.90, more preferably 0.40 to 0.87, and even more preferably 0.45 to 0.84.

[0062] The content of the above metal particles in the conductive paste of the present disclosure (the total content when two or more types of metals and / or metal particles of two or more particle sizes are contained) is preferably 70 to 99 wt %, more preferably 72 to 95 wt %, even more preferably 74 to 93 wt %, particularly preferably 76 to 95 wt %, and most preferably 78 to 93 wt %.

[0063] In the conductive paste of the present disclosure, the content of formic acid, the content of the basic compound, and the weight ratio (basic compound / formic acid) preferably simultaneously satisfy the following ranges, since this facilitates the production of a sintered body exhibiting good conductivity: The content of formic acid is preferably 4.0 to 8.9 wt %, more preferably 4.3 to 8.0 wt %, and even more preferably 4.5 to 7.5 wt %, the content of the basic compound (total content when two or more types are used in combination) is preferably 6.5 to 12.0 wt %, more preferably 6.6 to 11.8 wt %, and even more preferably 6.7 to 11.5 wt %, and the weight ratio of the basic compound to formic acid (basic compound / formic acid) is preferably 0.70 to 3.50, more preferably 0.72 to 3.40, and even more preferably 0.74 to 3.30.

[0064] The viscosity of the conductive paste of the present disclosure measured by a rheometer immediately after mixing the dispersion medium and the metal particles (at 25°C and a shear rate of 10 s -1 ) is preferably 10 to 1000 Pa·s, more preferably 50 to 900 Pa·s, and even more preferably 100 to 800 Pa·s, from the viewpoints of suppressing sagging or flow of the applied conductive paste, improving application accuracy, and stably maintaining a uniform dispersion state of the metal particles.

[0065] The conductive paste of the present disclosure exhibits excellent storage stability, for example, at temperatures between -50°C and 30°C. The viscosity of the conductive paste measured by a rheometer after storage at 25°C or lower (e.g., 25°C, 5°C) for 7 days or more, usually 35 days or less, is -1 ) is preferably 4 to 10,000 Pa·s, more preferably 20 to 4,500 Pa·s, and even more preferably 50 to 2,400 Pa·s. The viscosity can be measured by the method described in the examples.

[0066] The conductive paste of the present disclosure was measured for viscosity (25°C, shear rate 10 s) measured by a rheometer immediately after mixing the dispersion medium and the metal particles. -1) and the viscosity of the conductive paste measured by a rheometer after storing it at 25°C or below (for example, 25°C, 5°C) for 7 days (25°C, shear rate 10 s -1 The viscosity ratio (viscosity after storage / viscosity immediately after mixing) to the total viscosity of the mixture is preferably 10.0 or less, more preferably 0.4 to 5.0, and even more preferably 0.5 to 3.0.

[0067] The reason why the incorporation of the above basic compound provides excellent storage stability is unclear, but it is presumed that this is because the basic compound stabilizes formic acid and prevents the formic acid from reacting with the metal particles to generate aggregates.

[0068] The conductive paste of the present disclosure has a maximum peak temperature in differential thermogravimetry (DTG), which is the temperature at which the weight loss slope is greatest in thermogravimetry analysis TG (heating rate 10°C / min, in a nitrogen atmosphere), of preferably 100 to 220°C, more preferably 110 to 210°C, and even more preferably 120 to 200°C. If the peak temperature is below 100°C, the formic acid tends to volatilize too quickly, resulting in insufficient reduction of the metal particles, while if it exceeds 220°C, the entire dispersion medium tends to remain, which can easily inhibit low-temperature firing.

[0069] The conductive paste of the present disclosure can be produced by mixing metal particles with the dispersion medium, or by mixing metal particles with the formic acid, basic compound, and other components.

[0070] The temperature during mixing preferably does not exceed 100°C.

[0071] The mixture may be cooled to room temperature (for example, 25° C.) or below after mixing, and may be gradually cooled to room temperature or rapidly cooled by ice or the like.

[0072] The total content of water, organic solvents other than the mixture of formic acid and the basic compound, basic compounds other than the basic compounds, additives, etc. in the conductive paste of the present disclosure is preferably 10 wt % or less.

[0073] Since the conductive paste of the present disclosure has a suitable viscosity as described above, it is not necessary to add a resin component. Even if a resin component is added, the content of the resin component in the conductive paste is preferably 10% by weight or less, more preferably 5% by weight or less. If the amount of resin component added exceeds the above range, ash derived from the resin component generated by firing will cause a deterioration in electrical properties, which is not preferable.

[0074] The mixture of formic acid and the basic compound contained in the conductive paste of the present disclosure quickly volatilizes during firing, and furthermore, the formic acid reduces the surface oxidation of the metal particles, making it possible to fire the conductive paste at low temperatures (preferably 120 to 320°C, more preferably 150 to 290°C, and even more preferably 180 to 260°C) without using a reducing atmosphere.

[0075] Because the conductive paste of the present disclosure combines the above-mentioned properties, it can be effectively discharged onto the surface of a substrate (e.g., a ceramic substrate, a green sheet, etc.) by, for example, screen printing, and can improve printing accuracy by making the edges of the printed portion sharper. Furthermore, it can be discharged and printed while stably maintaining a uniformly highly dispersed state by preventing the sedimentation and local aggregation of metal particles, and by drying and firing the discharged conductive paste, it is possible to accurately form wiring and the like with excellent conductivity.

[0076] Furthermore, the conductive paste of the present disclosure can be selectively ejected onto desired positions on the surface of a substrate on which electrodes, circuits, etc. have been provided by, for example, screen printing, and then the electronic components, etc. are attached and fired, thereby electrically connecting the substrate and the electronic components, etc. Furthermore, since it can be fired at a low temperature, mounting can be performed at a lower temperature than mounting using solder, and it can be used to mount electronic components, etc. that have poor heat resistance.

[0077] Therefore, the conductive paste of the present disclosure is particularly useful for producing, for example, printed wiring boards such as multilayer printed wiring boards, capacitors such as multilayer ceramic capacitors, inductors, varistors, thermistors, transistors, speakers, actuators, antennas, solid oxide fuel cells (SOFCs), hybrid ICs, and the like, in particular, multilayer ceramic capacitors.

[0078] The configurations and combinations thereof in the above-described embodiments are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope of the gist of the present disclosure. The present disclosure is not limited to the embodiments, but is limited only by the scope of the claims. [Example]

[0079] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples in any way.

[0080] In the following, the volume average particle diameter (median diameter, D 50 ) are values ​​measured by laser diffraction / scattering method unless otherwise specified. The metal particles (copper particles, silver particles, copper oxide), solvents (formic acid, basic compounds, organic solvents, organic acids other than formic acid), and additives used are as follows.

[0081] <Copper particles> TNCu: Volume average particle size 110 nm (calculated by SEM observation), manufactured by Taiyo Nippon Sanso Corporation 1200YP: Volume average particle size 3.1 μm, manufactured by Mitsui Mining & Smelting Co., Ltd. CT-0500: Volume average particle size 0.74 μm, manufactured by Mitsui Mining & Smelting Co., Ltd. 1050Y, volume average particle size 0.81 μm, manufactured by Mitsui Mining & Smelting Co., Ltd.

[0082] <Silver particles> S211A-10: Volume average particle size 0.54 μm, manufactured by Daiken Chemical Co., Ltd.

[0083] <Copper oxide> Cu2O: Copper(I) oxide 99.5%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. CuO: Copper(II) oxide powder, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0084] <Formic acid> Formic acid 88% aqueous solution: Fujifilm Wako Pure Chemical Industries, Ltd. Formic acid / triethylamine (5:2 molar ratio azeotropic composition): manufactured by Tokyo Chemical Industry Co., Ltd.

[0085] <Basic compounds> Triethanolamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. 1-Methylimidazole: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Pentamethyldiethylenetriamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. N-Ethyldiethanolamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Diethanolamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. Diethylaminopropylamine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. N,N'-Dimethylpiperazine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd. 1-(2-Dimethylaminoethyl)-4-methylpiperazine: Reagent manufactured by Tokyo Chemical Industry Co., Ltd.

[0086] <Organic solvents> Triethylene glycol: Reagent manufactured by Tokyo Chemical Industry Co., Ltd.

[0087] <Organic acids other than formic acid> Acetic acid: Reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. n-Octanoic acid: Reagent manufactured by Tokyo Chemical Industry Co., Ltd.

[0088] <Additives> BYK-067A: Silicone defoamer, manufactured by BYK Additives & Instruments

[0089] [Peak temperature at which the weight loss slope is greatest (maximum DTG peak temperature)] A thermogravimetric analyzer (TG-DSC STA200, Hitachi High-Tech Science Corporation) was used to measure the temperature under a nitrogen atmosphere (flow rate 200 ml / min) at a heating rate of 10°C / min. The differential thermogravimetric (DTG) curve was obtained by differentiating the TG curve. The peak with the largest negative value was determined as the maximum DTG peak.

[0090] [Storage stability evaluation] The storage stability of the conductive paste was evaluated by storing samples for storage stability evaluation in the atmosphere at room temperature (25°C) or 5°C for one or two weeks. The samples were measured using a rheometer (MCR302, manufactured by Anton Paar) with a PP12 measuring jig, a gap of 0.05 mm, and a shear rate of 0.01 to 1000 s in logarithmic increments at 25°C. -1 The viscosity curve was obtained by changing the shear rate from 10 s -1 The viscosity was measured by measuring the initial viscosity (B0) immediately after blending, the viscosity after one week of storage at 25°C (B1), the viscosity after two weeks of storage at 25°C (B2), the viscosity after one week of storage at 5°C (B3), and the viscosity after two weeks of storage at 5°C (B4), and comparing these values.

[0091] Example 1 A paste was prepared by blending a formic acid / triethylamine mixed solvent (a 5:2 molar ratio azeotropic composition), triethanolamine, and TNCu in the amounts shown in Table 1 and stirring for 5 minutes using a planetary centrifugal mixer (Thinky Corporation's Awatori Rentaro). The molar ratio of formic acid to basic groups (basic groups / formic acid) was 0.96. The DTG maximum peak temperature was 130°C. The viscosity ratios B1 / B0, B2 / B0, B3 / B0, and B4 / B0 of the pastes of Example 1 after storage were all less than 1, indicating good storage stability.

[0092] (Comparative Example 1) Pastes were prepared in the same manner as in Example 1 using the blending ratios shown in Table 1, excluding triethanolamine. The paste of Comparative Example 1 exhibited poor storage stability, with aggregates forming inside the paste during storage, making viscosity measurement difficult. The DTG maximum peak temperature was 123°C.

[0093] Example 2 An 88% aqueous solution of formic acid, 1-methylimidazole, and TNCu were mixed to the contents shown in Table 1, and a paste was prepared in the same manner as in Example 1. The molar ratio of formic acid to basic groups was 0.61. The DTG maximum peak temperature was 135°C. Regarding the viscosities B1 to B4 of the paste of Example 2 after storage, the viscosity ratios B1 / B0, B2 / B0, and B4 / B0 were less than 1, and B3 / B0 was 1.09, indicating good storage stability.

[0094] (Comparative Example 2) A paste was prepared in the same manner as in Example 1, except that the blending ratio of 1-methylimidazole was reduced compared to Example 2, as shown in Table 1. The molar ratio of formic acid to basic groups was 0.40. The paste of Comparative Example 2, like the paste of Comparative Example 1, exhibited poor storage stability, as aggregates formed within the paste during storage, making viscosity measurement difficult. The DTG maximum peak temperature was 117°C.

[0095] [Table 1]

[0096] [Conductivity evaluation] The conductivity of the conductive paste was evaluated by applying the conductive paste with a squeegee to a glass slide masked on all four sides with masking tape (polyester film adhesive tape 631U #12, manufactured by Teraoka Seisakusho Co., Ltd.) to form a 25 μm-thick film of the conductive paste, and sintering the film in a nitrogen atmosphere using a sintering furnace (RSS-450-210-FA, manufactured by UNITEMP) at the sintering temperature and for the sintering time listed in Table 2 to obtain a sample for conductivity evaluation. The volume resistivity of the sample was measured using a resistivity meter (Loresta GP MCP-T610, manufactured by Mitsubishi Chemical Analytech Corporation).

[0097] (Examples 1 and 2) The pastes of Examples 1 and 2 both exhibited good electrical conductivity with a volume resistivity of 100 μΩ·cm or less. The paste of Example 2 also exhibited good electrical conductivity even when sintered at a low temperature of 200°C.

[0098] (Examples 3 and 4) An 88% aqueous solution of formic acid, triethanolamine, and TNCu were mixed to the contents shown in Table 2, and pastes were prepared in the same manner as in Example 1. The molar ratios of formic acid to basic groups were 1.00 and 0.60, respectively. The DTG maximum peak temperatures were 192°C and 132°C, respectively. The pastes of Examples 3 and 4 both exhibited good conductivity.

[0099] Examples 5 to 7 A paste obtained in the same manner as in Example 1 by blending an 88% aqueous solution of formic acid, pentadiethylenetriamine (a polyfunctional amine), and TNCu in amounts shown in Table 2 also exhibited good conductivity.

[0100] Example 8 A paste obtained in the same manner as in Example 1 by mixing an 88% aqueous solution of formic acid, diethanolamine, and TNCu in the amounts shown in Table 2 also showed good conductivity. The maximum DTG peak temperature was 133°C.

[0101] Example 9 A paste obtained in the same manner as in Example 1 by mixing an 88% aqueous solution of formic acid, diethylaminopropylamine, and TNCu in the amounts shown in Table 2 also showed good conductivity. The maximum DTG peak temperature was 129°C.

[0102] (Examples 10 to 13) A paste obtained in the same manner as in Example 1 by blending an 88% aqueous solution of formic acid, a combination of two basic compounds, 1-methylimidazole and N-ethyldiethanolamine, and TNCu, in the ratios shown in Table 2 also showed good conductivity. The maximum DTG peak temperature for Example 10 was 131°C.

[0103] (Comparative Example 3) A paste was prepared in the same manner as in Example 1, using an 88% aqueous solution of formic acid, a combination of two basic compounds (1-methylimidazole and N-ethyldiethanolamine), and TNCu, in the proportions shown in Table 2, so that the molar ratio of formic acid to basicity was 1.31. The volume resistivity of the paste of Comparative Example 3 was 377 μΩ·cm, indicating poor conductivity. The DTG maximum peak temperature was 136°C.

[0104] [Table 2] In Table 2, "-" for the DTG maximum peak temperature indicates that it was not measured.

[0105] Example 14 Formic acid, n-octanoic acid, pentamethyldiethylenetriamine, and TNCu were mixed to the contents shown in Table 3, and a paste was prepared in the same manner as in Example 1. The volume resistivity of the paste of Example 14 was 11 μΩ cm, indicating good conductivity.

[0106] Example 15 Pastes obtained in the same manner as in Example 1 by blending formic acid, pentamethyldiethylenetriamine, triethylene glycol as another organic solvent, and TNCu in the amounts shown in Table 3 also showed good conductivity.

[0107] Comparative Example 4 A paste was prepared in the same manner as in Example 1, without adding formic acid, by adding 1-methylimidazole, diethanolethylamine, and TNCu in the amounts shown in Table 3. The volume resistivity of the paste of Comparative Example 4 was very high at 6020 μΩ cm, and, unlike Example 13 (Table 2), it showed very poor conductivity.

[0108] (Comparative Examples 5 and 6) Acetic acid or n-octanoic acid, which is an organic acid other than formic acid, pentamethyldiethylenetriamine, and TNCu were mixed to the contents shown in Table 3, and pastes were prepared in the same manner as in Example 1. The paste samples of Comparative Examples 5 and 6 did not exhibit conductivity.

[0109] [Table 3]

[0110] Example 16 A paste was prepared in the same manner as in Example 2 (using TNCu: copper nanoparticles, average particle diameter 110 nm) except that 1200YP (copper flake particles, average particle diameter 3.1 μm) was used as the metal particles. The volume resistivity of the paste of Example 16 was 46 μΩ cm, and similar to the paste of Example 2, it showed good conductivity.

[0111] (Examples 17 and 18) Pastes were prepared in the same manner as in Example 2, except that CT-0500 (copper submicroparticles, average particle diameter 0.74 μm) or 1050Y (copper submicroparticles, average particle diameter 0.81 μm) were used as the metal particles. The volume resistivities of the pastes of Examples 17 and 18 were 84 μΩ cm and 64 μΩ cm, respectively, and, like the paste of Example 2, they exhibited good conductivity.

[0112] (Examples 19 to 35) The pastes obtained in the same manner as in Example 2, except that mixtures of TNCu and 1200YP, TNCu and CT-0500, and TNCu and 1050Y were used as metal particles in the amounts shown in Table 4, all showed good conductivity.

[0113] Example 36 The paste obtained in the same manner as in Example 7, except that a mixture of TNCu and S211A-10 (silver submicroparticles, average particle diameter 0.54 μm) was used as the metal particles in the amounts shown in Table 4, exhibited good conductivity.

[0114] (Examples 37 and 38) A paste obtained in the same manner as in Example 2, except that a mixture of TNCu and the metal compounds cuprous oxide (CuO) or copper oxide (CuO) in the amounts shown in Table 4 was used as the metal particles, exhibited good conductivity.

[0115] [Table 4]

[0116] [Bonding performance evaluation] The bonding performance evaluation was carried out on pastes of Examples 1, 5, 13, 15, and Example 39, which had the same composition as Example 5 but further contained BYK-067A as an additive.

[0117] The bonding performance of the conductive paste was evaluated by applying the conductive paste to a copper substrate (oxygen-free copper plate, 14 mm x 9 mm x 1 mm, manufactured by Asahi Seisakusho Co., Ltd.) using a metal mask printing method (metal mask: 4 mm x 4 mm, mesh thickness: 100 μm, manufactured by Towa Tech Co., Ltd.) to form a coating film (coating film thickness: approximately 100 μm). A copper dummy chip (oxygen-free copper plate, 14 mm x 9 mm x 1 mm, manufactured by Asahi Seisakusho Co., Ltd.) was placed on the coating film and then heated in a nitrogen atmosphere using the same method as in International Publication WO2018 / 029983. The temperature was raised from room temperature of 25°C to 300°C, 250°C, 200°C or 180°C at a heating rate of 20°C / min under pressure, and then heated for a further 30 minutes to obtain a bonding performance evaluation sample (copper substrate / sintered conductive paste / copper dummy chip).The bonding strength of these samples was measured at room temperature, at a test speed of 50μm / s, and at a test height of 50μm using a die shear tester (SERIES4000, manufactured by DAGE).

[0118] In all cases of Examples 1, 5, 13, 15, and 39, the bonding strength exceeded 20 MPa, demonstrating good bonding performance. This indicates that conductive pastes containing formic acid and a base can be used for bonding. Furthermore, in Examples 5 and 39, the bonding strength exceeded 20 MPa even at extremely low sintering temperatures such as 200°C and 180°C, demonstrating good bonding performance. Furthermore, in Example 39, by incorporating an additive such as BYK-067A, the bonding strength exceeded 20 MPa, demonstrating good bonding performance, even when sintered without pressure or at an extremely low applied pressure of 0.05 MPa.

[0119] [Table 5]

[0120] As a summary of the above, the configuration of the present disclosure and its variations are described below. [1] A dispersion medium for sintering metal particles, comprising formic acid and a basic compound, wherein the basic compound is a nitrogen-containing compound represented by formula (1), and the molar ratio of a basic group contained in the basic compound to formic acid (basic group / formic acid) is 0.50 to 1.20. [2] R in the formula (1) a ~R c The dispersion medium for sintering metal particles according to [1], wherein [3] The dispersion medium for sintering metal particles according to [2], wherein the aliphatic hydrocarbon group is a linear or branched alkyl group. [4] The dispersion medium for sintering metal particles according to [2], wherein the aliphatic hydrocarbon group is a linear alkyl group having 2 to 12 carbon atoms (preferably 2 to 8, more preferably 2 to 4), or a branched alkyl group having 3 to 12 carbon atoms (preferably 3 to 8, more preferably 3 to 6). [5] R in the formula (1) a ~R c The dispersion medium for sintering metal particles according to any one of [1] to [4], wherein the total number of amino groups, N-substituted amino groups, or N,N-substituted amino groups that may be present is 0 to 6 (preferably 1 to 4, more preferably 1 to 2). [6] R in the formula (1) a ~R c The dispersion medium for sintering metal particles according to any one of [1] to [5], wherein the total number of imino groups or N-substituted imino groups that may be contained in the dispersion medium is 0 to 4 (preferably 1 to 3, more preferably 1 to 2). [7] R in the formula (1) a ~R c The dispersion medium for sintering metal particles according to any one of [1] to [6], wherein the total number of hydroxyl groups that the dispersion medium may have is 0 to 6 (preferably 1 to 4, more preferably 1 to 2). [8] R in the formula (1) a ~R c The dispersion medium for sintering metal particles according to [2], wherein the ring that any two of the above may bond to each other to form together with the adjacent nitrogen atom is at least one selected from a pyrrolidine ring, a pyrroline ring, a piperidine ring, a pyrrole ring, an imidazolidine ring, an imidazole ring, a piperazine ring, an imidazolidine ring, a pyridine ring, a diazine ring, and a triazine ring. [9] The dispersion medium for sintering metal particles according to [8], wherein the ring is an imidazole ring.

[10] The dispersion medium for sintering metal particles according to [1], wherein the basic compound is at least one compound selected from alkylamines, dialkanolamines, trialkanolamines, aminoalkanediols, diamines, triamines, diaminoalkanols, imidazole compounds, pyridine-based compounds, diazine-based compounds, and triazine-based compounds.

[11] The dispersion medium for sintering metal particles according to [1], wherein the basic compound is at least one compound selected from alkylamines, dialkanolamines, trialkanolamines, diamines, triamines, diaminoalkanols, and imidazole compounds.

[12] The dispersion medium for sintering metal particles according to [1], wherein the basic compound is at least one compound selected from the group consisting of triethylamine, diethanolamine, N,N-diethyl-1,3-propanediamine, N,N,N',N",N"-pentamethyldiethylenetriamine, N,N'-dimethylpiperazine, 1-(2-aminoethyl)-4-methylpiperazine, and N-methylimidazole.

[13] The dispersion medium for sintering metal particles according to any one of [1] to

[12] , wherein the molar ratio (basic group / formic acid) is 0.55 to 1.15 (preferably 0.60 to 1.10).

[14] A method for producing a dispersion medium for sintering metal particles according to any one of [1] to

[13] , comprising a step of mixing the formic acid and the basic compound to dissolve them together.

[15] A conductive paste containing metal particles and the dispersion medium according to any one of [1] to

[13] .

[16] The viscosity measured by a rheometer immediately after mixing the dispersion medium and the metal particles (25°C, shear rate 10 s -1 ) is 10 to 1000 Pa·s (preferably 50 to 900 Pa·s, more preferably 100 to 800 Pa·s).

[17] Viscosity measured by a rheometer after storage at 25°C for 7 days (25°C, shear rate 10 s-1 The conductive paste according to

[15] or

[16] , wherein the viscosity is 4 to 10,000 Pa·s (preferably 20 to 4,500 Pa·s, more preferably 50 to 2,400 Pa·s).

[18] Viscosity measured by a rheometer after storage at 5°C for 7 days (25°C, shear rate 10 s -1 The conductive paste according to any one of

[15] to

[17] , wherein the viscosity is 4 to 10,000 Pa·s (preferably 20 to 4,500 Pa·s, more preferably 50 to 2,400 Pa·s).

[19] Viscosity measured by a rheometer after storage at 25°C for 14 days (25°C, shear rate 10 s -1 The conductive paste according to any one of

[15] to

[18] , wherein the viscosity is 4 to 10,000 Pa·s (preferably 20 to 4,500 Pa·s, more preferably 50 to 2,400 Pa·s).

[20] Viscosity measured by a rheometer after storage at 5°C for 14 days (25°C, shear rate 10 s -1 The conductive paste according to any one of

[15] to

[19] , wherein the viscosity is 4 to 10,000 Pa·s (preferably 20 to 4,500 Pa·s, more preferably 50 to 2,400 Pa·s).

[21] The viscosity of the conductive paste measured by a rheometer immediately after mixing the dispersion medium and the metal particles (25°C, shear rate 10 s -1 ) and the viscosity of the conductive paste measured by a rheometer after storing it at 25°C or below for 7 days (25°C, shear rate 10 s -1 20. The conductive paste according to any one of

[15] to

[20] , wherein the viscosity ratio (viscosity after storage / viscosity immediately after mixing) to the conductive paste (viscosity after storage / viscosity immediately after mixing) is 10.0 or less.

[22] The viscosity of the conductive paste measured by a rheometer immediately after mixing the dispersion medium and the metal particles (25°C, shear rate 10 s -1 ) and the viscosity of the conductive paste measured by a rheometer after storing it at 25°C for 7 days (25°C, shear rate 10 s -1 The conductive paste according to any one of

[15] to

[20] , wherein the viscosity ratio (viscosity after storage / viscosity immediately after mixing) to the conductive paste (storage viscosity / viscosity immediately after mixing) is 10.0 or less (preferably 0.4 to 5.0, more preferably 0.5 to 3.0).

[23] The conductive paste according to any one of

[15] to

[22] , wherein the maximum peak temperature in differential thermogravimetric analysis (DTG) at a heating rate of 10°C / min under a nitrogen atmosphere is 100 to 220°C (preferably 110 to 210°C, more preferably 120 to 200°C).

[24] The conductive paste according to any one of

[15] to

[23] , wherein the metal particles are at least one kind selected from copper particles, silver particles, and particles of oxides thereof.

[25] The conductive paste according to any one of

[15] to

[23] , wherein the metal particles are copper particles and / or silver particles.

[26] The conductive paste according to

[24] or

[25] , wherein the weight ratio of the copper particles to the total metal particles (copper particles / total metal particles) is 0.35 to 0.90 (preferably 0.40 to 0.87, more preferably 0.45 to 0.84).

[27] The conductive paste according to any one of

[15] to

[26] , wherein the volume average particle diameter of the metal particles is 1 nm or more and 100 μm or less (preferably 10 nm to 50 μm, more preferably 30 nm to 35 μm, even more preferably 50 nm to 10 μm, and particularly preferably 70 nm to 1 μm).

[28] The conductive paste according to any one of

[15] to

[26] , wherein the metal particles are a combination of metal particles having two or more different volume average particle sizes selected from nano-sized particles (having a volume average particle size of 1 nm or more and less than 300 nm, preferably 1 to 200 nm, and more preferably 1 to 150 nm), sub-nano-sized particles (having a volume average particle size of 0.30 μm or more and less than 1.00 μm, preferably 0.40 to 0.95 μm, and more preferably 0.50 to 0.90 μm), and micro-sized particles (having a volume average particle size of 1.0 to 100 μm, preferably 1.5 to 50 μm, more preferably 2.0 to 35 μm, even more preferably 2.5 to 10 μm, and particularly preferably 3.0 to 10 μm).

[29] The conductive paste according to

[28] , wherein the weight ratio of the nano-sized particles to the total metal particles (nano-sized particles / total metal particles) is 0.10 to 0.90 (preferably 0.15 to 0.85, more preferably 0.20 to 0.80).

[30] The conductive paste according to any one of

[15] to

[29] , wherein the content of the metal particles is 70 to 99% by weight (preferably 72 to 95% by weight, more preferably 74 to 93% by weight, even more preferably 76 to 95% by weight, and particularly preferably 78 to 93% by weight).

[31] The conductive paste according to any one of

[15] to

[30] , wherein the content of the formic acid is 4.0 to 8.9 wt % (preferably 4.3 to 8.0 wt %, more preferably 4.5 to 7.5 wt %), and the content of the basic compound is 6.5 to 12.0 wt % (preferably 6.6 to 11.8 wt %, more preferably 6.7 to 11.5 wt %).

[32] The conductive paste according to any one of

[15] to

[31] , wherein the content of the formic acid is 4.0 to 8.9 wt % (preferably 4.3 to 8.0 wt %, more preferably 4.5 to 7.5 wt %), and the weight ratio of the basic compound to the formic acid (basic compound / formic acid) is 0.70 to 3.50 (preferably 0.72 to 3.40, more preferably 0.74 to 3.30).

[33] The conductive paste according to any one of

[15] to

[32] , wherein the content of the basic compound is 6.5 to 12.0 wt % (preferably 6.6 to 11.8 wt %, more preferably 6.7 to 11.5 wt %), and the weight ratio of the basic compound to the formic acid (basic compound / formic acid) is 0.70 to 3.50 (preferably 0.72 to 3.40, more preferably 0.74 to 3.30).

[34] A method for producing a conductive paste according to any one of

[15] to

[33] , comprising the step of mixing the metal particles with the dispersion medium.

[35] Use of a dispersion medium containing formic acid and the following basic compound as a dispersion medium for sintering metal particles. Basic compound: a nitrogen-containing compound represented by formula (1)

[36] Use of a composition containing metal particles and the following dispersion medium as a conductive paste. Dispersion medium: containing formic acid and a basic compound, the basic compound being a nitrogen-containing compound represented by formula (1), and the molar ratio of the basic group contained in the basic compound to formic acid (basic group / formic acid) being 0.50 to 1.20. [Industrial Applicability]

[0121] The metal particle sintering dispersion medium of the present disclosure can reduce metal particles and promote sintering even without a reducing atmosphere, ensuring the storage stability of the conductive paste and preventing the conductive paste from drying out. Furthermore, the conductive paste of the present disclosure can be sintered even at low temperatures of around 200°C because it contains very little organic residue, and achieves high bonding strength even with a slight pressure of 1 MPa or less. Therefore, the present disclosure has industrial applicability.

Claims

1. Contains formic acid and a basic compound, The basic compound is represented by the following formula (1): 【Chemistry 1】 (In formula (1), R ａ ~R ｃ are the same or different and represent a hydrogen atom or a hydrocarbon group which may have a substituent. The hydrocarbon group is a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, a linear alkenyl group having 2 to 12 carbon atoms, or a branched alkenyl group having 3 to 12 carbon atoms. The substituent is the same or different and is at least one group selected from an amino group, an N-substituted amino group, an N,N-substituted amino group, an imino group, an N-substituted imino group, and a hydroxyl group. However, R ａ ~R ｃ does not become a hydrogen atom at the same time. A double line including a dashed line represents a single bond or a double bond, and in the case of a double bond, R ｃ does not exist. ａ ~R ｃ any two of may be bonded to each other to form an imidazole ring or a piperazine ring together with the adjacent nitrogen atom) wherein the molar ratio of the basic group contained in the basic compound to formic acid (basic group / formic acid) is 0.50 to 1.20; A dispersion medium for sintering metal particles, which is used for sintering at least one type of metal particles selected from copper particles, silver particles, particles of an alloy thereof, and particles of an oxide thereof.

2. A conductive paste containing metal particles and the dispersion medium according to claim 1.

3. The viscosity of the conductive paste measured by a rheometer immediately after mixing the dispersion medium and the metal particles (at 25°C and a shear rate of 10 s －１ ) and the viscosity of the conductive paste measured by a rheometer after storing it at 25°C or less for 7 days (25°C, shear rate 10 s －１ 3. The conductive paste according to claim 2, wherein the viscosity ratio (viscosity after storage / viscosity immediately after mixing) to the viscosity of the conductive paste is 10.0 or less.

4. 4. The conductive paste according to claim 2, wherein the maximum peak temperature in differential thermogravimetric analysis (DTG) at a temperature rise rate of 10° C. / min in a nitrogen atmosphere is 100 to 220° C.

5. The conductive paste according to any one of claims 2 to 4, wherein the metal particles are at least one selected from copper particles, silver particles, and particles of oxides thereof.

6. The conductive paste according to any one of claims 2 to 5, wherein the volume average particle diameter of the metal particles is 1 nm or more and 100 µm or less.

7. The conductive paste according to claim 5 or 6, wherein the weight ratio of the copper particles to the total metal particles (copper particles / total metal particles) is 0.35 to 0.

90.

8. The conductive paste according to any one of claims 2 to 7, wherein the content of the formic acid is 4.0 to 8.9% by weight, and the content of the basic compound is 6.5 to 12.0% by weight.

9. 9. The conductive paste according to claim 2, wherein the content of the basic compound is 6.5 to 12.0 wt %, and the weight ratio of the basic compound to the formic acid (basic compound / formic acid) is 0.70 to 3.

50.

10. A sintered body of the conductive paste according to any one of claims 2 to 9.

11. An electronic device comprising a substrate and a sintered body of the conductive paste according to any one of claims 2 to 9.

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