EP4613403A1

EP4613403A1 - Solvent composition and method for producing sintered object

Info

Publication number: EP4613403A1
Application number: EP23885461.6A
Authority: EP
Inventors: Takanori KOBATAKE; Motoharu Haga
Original assignee: Daicel Corp
Current assignee: Daicel Corp
Priority date: 2022-10-31
Filing date: 2023-10-06
Publication date: 2025-09-10
Also published as: TW202432278A; CN120129581A; WO2024095698A1; KR20250103672A; JPWO2024095698A1

Abstract

There is provided a solvent composition which does not need to be removed after application and allows a sintered object having excellent electroconductivity and bondability to be easily produced. The solvent composition of the present disclosure is a solvent composition for sintering aids, the solvent composition containing a reducing organic substance and a basic compound. The solvent composition of the present disclosure is also a solvent composition including a reducing organic substance, a basic compound, and a coordinating organic compound other than compounds included as the basic compound, and the coordinating organic compound has a higher boiling point than the reducing organic substance.

Description

Technical Field

An invention according to the present disclosure relates to a solvent composition and a method for producing a sintered object. Priority is claimed on Japanese Patent Application No. 2022-174348, filed October 31, 2022 , the content of which is incorporated herein by reference.

Background Art

In recent years, in rotating electrical machines mounted in electric vehicles, hybrid cars and the like, a localized temperature rise due to a higher output may more likely cause malfunctions in control power modules and the like, and in order to prevent this, heat sinks have been attached to metal housings of the rotating electrical machines to promote heat dissipation. For example, lead solder is used to attach a heat sink, but a problem may arise in bonding that uses lead solder, as can be exemplified by a base part being easily distorted due to heating.
As an alternative to bonding using lead solder, for example, PTL 1 discloses a bonding method which uses a copper sintered object and in which copper nanoparticles are formed into sheets and sintered, laminated with an object to be bonded, and then bonded by applying pressure and heat to prepare a laminate.
In addition, for example, PTL 2 discloses an electroconductive paste which is used for forming a metal sintered object, and which contains, as a dispersion medium, a mixture of formic acid and a basic compound combined at a specific molar ratio, whereby formic acid gas is generated, favorable sintering can be implemented even without a reducing atmosphere, and corrosion of metal particles due to formic acid can be suppressed.

Citation List

Patent Literature

PTL 1: Japanese Patent Application Publication No. 2022-029194
PTL 2: Japanese Patent Application Publication No. 2020-025765

Summary of Invention

Technical Problem

However, the bonding method using the copper sintered object in PTL 1 has problems of the operation being complicated: for example, a copper sintered object, obtained by sintering a sintering precursor (copper nanoparticle aggregate) in a reducing atmosphere, needs to be sintered immediately after removal in order to prevent re-oxidation before bonding to an object to be bonded; and when a surface oxide film is removed using a reducing agent (formic acid) or an etching solution (sulfuric acid aqueous solution) after sintering, it is necessary to make laborious efforts to remove these before bonding in order to prevent corrosion. In addition, when the electroconductive paste in PTL 2 is used, a sintering precursor (metal particle aggregate) can be sintered without removing the dispersion medium containing formic acid and even without a reducing atmosphere, but when metal particle aggregates are molded, the generation of voids due to a formic acid decomposition gas is not sufficiently suppressed, and when voids are generated, the bondability may decrease.
Therefore, an object of the present disclosure is to provide a solvent composition which does not need to be removed after being applied and allows a sintered object having excellent electroconductivity and bondability to be easily produced.

Solution to Problem

The inventors conducted extensive studies in order to address the above problems, and as a result, found that, when a solvent composition containing a reducing organic substance and a basic compound is applied to a metal member, a metal oxide film on the surface of the metal member can be dissolved, and a sintered object having excellent electroconductivity can be easily obtained from the thus-obtained solvent-treated metal member without removing the solvent after the treatment. In addition, the inventors found that, when a solvent composition containing a reducing organic substance, a basic compound, and a coordinating organic substance is applied to a metal member, a metal oxide film on the surface of the metal member can be dissolved, metal microparticles can be precipitated on the surface of the metal member, and a sintered object having excellent electroconductivity and bondability can be easily obtained from such a solvent-treated metal member without removing the solvent after the treatment. The invention according to the present disclosure has been completed based on these findings.
Specifically, the present disclosure provides a solvent composition for sintering aids, the solvent composition containing a reducing organic substance and a basic compound.
The present disclosure also provides a solvent composition containing a reducing organic substance, a basic compound, and a coordinating organic compound other than compounds included as the basic compound, and the coordinating organic compound has a higher boiling point than the reducing organic substance.
The reducing organic substance is preferably formic acid.
Preferably, the solvent composition further contains a reducing organic substance other than formic acid.
Preferably, the basic compound is a nitrogen-containing compound represented by Formula (1) below: (in Formula (1), R^a to R^c are the same as or different from each other and each represent a hydrogen atom or a hydrocarbon group which may have a substituent; the substituents are the same as or different from each other, and are at least one group selected from among 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; provided that R^a to R^c are never hydrogen atoms simultaneously; a double line including a dashed line represents a single bond or a double bond, and when the double line represents a double bond, there is no R^c; and any two of R^a to R^c may be bonded to each other to form a ring together with an adjacent nitrogen atom).
Preferably, the basic compound has, in a molecular structure thereof, an ethylenediamine structure or an ethanolamine structure, and an amino group in the structure is a tertiary amino group.
Preferably, the ratio (basic groups/acidic groups) of a total number of moles of basic groups contained in the basic compound to a total number of moles of acidic groups contained in the reducing organic substance is 0.40 to 2.50.
Preferably, the coordinating organic compound is a compound having a carboxyl group.
Preferably, the solvent composition further contains a solvent.
The present disclosure also provides a method for producing a solvent-treated metal member, the method including applying the solvent composition to a metal member.
Preferably, in the production method, the metal member before application is an aggregate of metal particles having a number average particle size of 600 nm or more.
The present disclosure also provides a method for producing a solvent-treated metal member, the method including dissolving a metal compound in the solvent composition and then applying the solvent composition to a metal member.
Preferably, the metal member contains copper.
Preferably, the metal compound is at least one selected from among copper(I) oxide, copper(II) oxide and copper(II) hydroxide.
The present disclosure also provides a method for producing a sintered object, the method including heating the solvent-treated metal member obtained by the production method to obtain a sintered object.
The present disclosure also provides a method for producing a bonded object, the method including bringing the solvent-treated metal member obtained by the production method into contact with an object to be bonded and heating the same to obtain a bonded object.
The present disclosure also provides a method for producing a bonded object, the method including applying the solvent composition to a metal particle aggregate layer formed on the surface of a substrate to form a treated aggregate layer, then bringing an object to be bonded into contact with the treated aggregate layer, and heating the same to bond the substrate and the object to be bonded.
The present disclosure also provides a method for producing a metal member having, on a surface thereof, metal nanoparticles, the method including applying a solvent composition to a metal member, dissolving at least a part of the surface of the metal member to form a metal complex, and thermally decomposing and/or reductively decomposing the formed metal complex to precipitate metal nanoparticles on the surface of the metal member.

Advantageous Effects of Invention

When the solvent composition of the present disclosure is applied to a metal member (a metal particle aggregate, etc.) and used to aid in sintering, it is not necessary to remove the solvent composition after application, and it is possible to produce a sintered object having excellent electroconductivity and bondability.

Brief Description of Drawings

[Fig. 1]
Fig. 1 shows an electron microscope image of the surface of a solvent-treated copper foil of Example 6.
[Fig. 2]
Fig. 2 shows an electron microscope image of the surface of a solvent-treated copper foil of Example 11.
[Fig. 3]
Fig. 3 shows an electron microscope image of the surface of a solvent-treated copper foil of Comparative Example 3.
[Fig. 4]
Fig. 4 shows an SAT image of a bonded object of Example 24.
[Fig. 5]
Fig. 5 shows an electron microscope image of an arrangement pattern of a Si chip with copper bumps used in Example 25.
[Fig. 6]
Fig. 6 shows an electron microscope image of the surface of a copper bump part of a Si chip with copper bumps used in Example 25.
[Fig. 7]
Fig. 7 shows an electron microscope image of the surface of a copper bump part of a solvent-treated Si chip in Example 25. Description of Embodiments

[Solvent Composition]

A solvent composition according to a first aspect of the present disclosure is a solvent composition for sintering aids, the solvent composition containing a reducing organic substance and a basic compound. Since the solvent composition contains a reducing organic substance, by applying the solvent composition to the surface of a metal member, oxidation of the surface of the metal member can be suppressed even without a reducing atmosphere during sintering. In addition, since the solvent composition contains a basic compound, the surface of the metal member can be dissolved and a metal oxide film can be removed, and even if the solvent composition is not removed after being applied to the surface of the metal member, it is possible to suppress corrosion of the surface of the metal member caused by the reducing organic substance. For this reason, the solvent composition is suitable as a solvent composition for sintering aids for sintering a metal member.
A solvent composition according to a second aspect of the present disclosure contains a reducing organic substance, a basic compound, and a coordinating organic compound other than compounds included as the basic compound, and the coordinating organic compound has a higher boiling point than the reducing organic substance.
When the solvent composition contains a coordinating organic compound, since a metal complex is easily formed when the surface of the metal member is dissolved, and the formed metal complex is additionally thermally decomposed or reductively decomposed, and is precipitated on the surface of the metal member, it is likely to become metal nanoparticles. Furthermore, when metal nanoparticles are present on the surface of the metal member, since the influence of surface diffusion becomes stronger, the metal member is easily sintered even at a lower temperature.

Examples of reducing organic substances contained in the solvent compositions according to the first and second aspects of the present disclosure include alcohols (lower alcohols such as ethanol, higher alcohols such as palmitol, and aminoalkanols such as ethanol amines), amino acids, organic acids (carboxylic acids, etc.), and aromatic compounds (polyphenols, phenolic acid compounds, etc.). Among these, organic acids (carboxylic acids, etc.) and aromatic compounds are preferable because they exhibit acidity, and carboxylic acids are more preferable because they are liquids at room temperature, easy to handle, and not highly toxic. These may be used alone or two or more thereof may be used in combination.
Examples of carboxylic acids include formic acid, acetic acid, lactic acid, propionic acid, acrylic acid, malic acid, n-hexanoic acid, succinic acid, n-octanoic acid, tartaric acid, and oxalic acid, and among these, formic acid and oxalic acid are preferable because a sintered object having excellent reducibility and excellent electroconductivity can be easily obtained.
In addition, the reducing organic substance used in the solvent composition according to the second aspect of the present disclosure is preferably formic acid because it has a low boiling point, and can be easily used in combination with a coordinating organic substance having a higher boiling point than the reducing organic substance.
When two or more types including formic acid are used in combination as the reducing organic substance, the content of the reducing organic substance other than formic acid with respect to 1 part by mole of formic acid is preferably 1 part by mole or less.

The basic compound contained in the solvent compositions according to the first and second aspects of the present disclosure is not particularly limited as long as it functions as a base and the effects of the present disclosure are realized, and specific examples thereof include hydroxides such as alkali metals and alkaline earth metals, nitrogen-containing compounds such as ammonia and amine compounds, and phosphorus-containing compounds such as phosphines and phosphite esters. Among these, the nitrogen-containing compound represented by Formula (1) below is preferable because a sintered object having excellent electroconductivity can be easily obtained. (In Formula (1), R^a to R^c are the same as or different from each other and each represent a hydrogen atom or a hydrocarbon group which may have a substituent; the substituents are the same as or different from each other, and are at least one group selected from among 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; provided that R^a to R^c are never hydrogen atoms simultaneously; a double line including a dashed line represents a single bond or a double bond, and when the double line represents a double bond, there is no R^c; and any two of R^a to R^c may be bonded to each other to form a ring together with an adjacent nitrogen atom.)
Examples of hydrocarbon groups for R^a to R^c include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group, and among these, an aliphatic hydrocarbon group and an alicyclic hydrocarbon group are preferable, and an aliphatic hydrocarbon group is more preferable.
Examples of aliphatic hydrocarbon groups 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 preferable.
The linear or branched alkyl group is preferably a linear alkyl group having 1 to 20 carbon atoms and more preferably a linear alkyl group having 1 to 15 carbon atoms or preferably a branched alkyl group having 3 to 12 carbon atoms, more preferably a branched alkyl group having 3 to 8 carbon atoms, and still more preferably a branched alkyl group having 3 to 6 carbon atoms, and examples thereof include a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, decyl group, dodecyl group, tetradecyl group, octadecyl group, isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, and 2-ethylhexyl group.
The linear or branched alkenyl group is preferably a linear alkenyl group having 2 to 12 carbon atoms, more preferably a linear alkenyl group having 2 to 8 carbon atoms, and still more preferably a linear alkenyl group having 2 to 4 carbon atoms or preferably a branched alkenyl group having 3 to 12 carbon atoms, more preferably a branched alkenyl group having 3 to 8 carbon atoms, and still more preferably a branched alkenyl group having 3 to 6 carbon atoms, and examples thereof include a vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1-pentenyl group, 2-pentenyl group, 3-pentenyl group, 4-pentenyl group, 1-hexenyl group, 3-hexenyl group, 5-hexenyl group, 1-heptenyl group, 1-octenyl group, 1-nonenyl group, 1-decenyl group, isopropenyl group, 2-methyl-1-propenyl group, methallyl group, 3-methyl-2-butenyl group, and 4-methyl-3-pentenyl group.
The linear or branched alkynyl group is preferably a linear alkynyl group having 2 to 12 carbon atoms, more preferably a linear alkynyl group having 2 to 8 carbon atoms, and still more preferably a linear alkynyl group having 2 to 4 carbon atoms or preferably a branched alkynyl group having 3 to 12 carbon atoms, more preferably a branched alkynyl group having 3 to 8 carbon atoms, and still more preferably a branched alkynyl group having 3 to 6 carbon atoms, and examples thereof include an ethynyl group, 1-propynyl group, 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl group, 4-pentynyl group, 1-hexynyl group, 2-hexynyl group, 3-hexynyl group, 4-hexynyl group, 5-hexynyl group, 1-heptynyl group, 1-octynyl group, 1-nonynyl group, 1-decenyl group, trimethylsilylethynyl group, and triethylsilylethynyl group.
The linear or branched alkylidene group is preferably a linear alkylidene group having 1 to 12 carbon atoms, more preferably a linear alkylidene group having 1 to 8 carbon atoms, and still more preferably a linear alkylidene group having 2 to 4 carbon atoms or preferably a branched alkylidene group having 3 to 12 carbon atoms, more preferably a branched alkylidene group having 3 to 8 carbon atoms, and still more preferably a branched alkylidene group having 3 to 6 carbon atoms, and examples thereof include a methylidene group, propylidene group, isopropylidene group, butylidene group, isobutylidene group, sec-butylidene group, pentylidene group, isopentylidene group, octylidene group, and isooctylidene group.
Examples of alicyclic hydrocarbon groups include a cycloalkyl group and cycloalkenyl group.
The cycloalkyl group is preferably a cycloalkyl group having 3 to 12 carbon atoms, more preferably a cycloalkyl group having 4 to 10 carbon atoms, and still more preferably a cycloalkyl group having 5 to 8 carbon atoms, and examples thereof include a cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, and cyclodecyl group.
The cycloalkenyl group is preferably a cycloalkenyl group having 3 to 12 carbon atoms, more preferably a cycloalkenyl group having 4 to 10 carbon atoms, and still more preferably a cycloalkenyl group having 5 to 8 carbon atoms, and examples thereof include a cyclopentenyl group and cyclohexenyl group.
The aromatic hydrocarbon group is preferably an aryl group having 6 to 18 carbon atoms, more preferably an aryl group having 6 to 18 carbon atoms, and still more preferably an aryl group having 6 to 10 carbon atoms, and examples thereof include a phenyl group and naphthyl group.
In Formula (1), the double line including a dashed line represents a single bond or a double bond. When the double line including a dashed line represents a double bond, there is no R^c, and in Formula (1), a nitrogen atom to which R^a and R^b are bonded represents an imino group or an N-substituted imino group.
The total number of amino groups, N-substituted amino groups, and N,N-substituted amino groups which R^a to R^c may have is preferably 0 to 6, more preferably 1 to 4, and still more preferably 1 to 2.
The total number of imino groups and N-substituted imino groups which R^a to R^c may have is preferably 0 to 4, more preferably 1 to 3, and still more preferably 1 to 2.
The total number of hydroxyl groups which R^a to R^c may have is preferably 0 to 6, more preferably 1 to 4, and still more preferably 1 to 2.
The substituents which the N-substituted amino group, N,N-substituted amino group, and N-substituted imino group have are the same as those of the hydrocarbon groups for R^a to R^c.
Any two of R^a to R^c may be bonded to each other to form a ring together with an adjacent nitrogen atom. Examples of rings formed include a pyrrolidine ring, pyrroline ring, piperidine ring, pyrrole ring, imidazolidine ring, imidazole ring, piperazine ring, imidazolidine ring, pyridine ring, diazine ring, and triazine ring.
The hydrocarbon group for R^a to R^c 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 substituents include a halogen atom (fluorine atom, chlorine atom, bromine atom, 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, 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.
Specific examples of basic compounds represented by Formula (1) include alkylamines in which, in Formula (1), at least one of R^a to R^c is a linear or branched alkyl group; monoalkanolamines in which, in Formula (1), R^a and R^b are a hydrogen atom, and R^c is a linear or branched alkyl group having one hydroxyl group; dialkanolamines in which, in Formula (1), R^a is a hydrogen atom, and R^b and R^c are the same as or different from each other and each represent a linear or branched alkyl group having one hydroxyl group; trialkanolamines in which, in Formula (1), R^a to R^c are the same as or different from each other and each represent a linear or branched alkyl group having one hydroxyl group; aminoalkanediols in which, in Formula (1), R^a and R^b are the same as or different from each other and each represent a hydrogen atom or a linear or branched alkyl group, and R^c represents a linear or branched alkyl group having two hydroxyl groups; diamines in which, in Formula (1), R^a to R^c have a total of one amino group; triamines in which, in Formula (1), R^a to R^c have a total of two amino groups; diaminoalkanols in which, in Formula (1), R^a to R^c have a total of one amino group and a total of one hydroxyl group; imidazole compounds in which, in Formula (1), R^a to R^c each have a total of one imino group, and a ring is formed by incorporating nitrogen atoms of the imino groups; and nitrogen-containing aromatic compounds (a pyridine-based compound, a diazine-based compound, a triazine-based compound, etc.) in which, in Formula (1), a nitrogen atom to which R^a and R^b are bonded is an imino group, and a ring is formed by incorporating the imino group.
Examples of alkylamines include methylamine, ethylamine, propylamine, butylamine, pentylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, piperidine, trimethylamine, triethylamine, dimethyldodecylamine, 4-dimethylaminopyridine, 2-aminopyrazine, 2-aminopyrimidine, 3-aminopyridazine, 2-aminotriazine, diazabicyclononene, and diazabicycloundecene.
Examples of monoalkanolamines 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, 1-dimethylamino-2-propanol, N-propyl-2-aminoethanol, 2-dimethylaminoethanol, 6-diethylaminohexanol, 1-(2-hydroxyethyl) pyrrolidine, 2-(hydroxymethyl) pyrrolidine, 2-(2-hydroxyethyl)-1-methyl pyrrolidine, 1-piperidine ethanol, and 1-ethanol-4-propanolpiperidine.
Examples of dialkanolamines include diethanolamine, di-n-propanolamine, diisopropanolamine, di-n-butanolamine, diisobutanolamine, N-methyl-diethanolamine, and N-ethyldiethanolamine.
Examples of trialkanolamines include triethanolamine, tri-n-propanolamine, triisopropanolamine, tri-n-butanolamine, and triisobutanolamine.
Examples of aminoalkanediols 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.
Examples of diamines 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, N,N'-dimethyl-1,6-hexanediamine, 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, N,N-dimethyl-1,6-hexanediamine, 1,2-cyclohexanediamine, 1,4-cyclohexanediamine, piperazine, N-methylpiperazine, N-ethylpiperazine, N,N'-dimethylpiperazine, and homopiperazine.
Examples of triamines include diethylenetriamine, N,N,N',N",N"-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.
Examples of diaminoalkanols 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.
Examples of imidazole compounds include imidazole, 2-methylimidazole, 2-propylimidazole, N-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.
Examples of nitrogen-containing aromatic compounds 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.
The basic compound contained in the solvent compositions according to the first and second aspects of the present disclosure is preferably a chelate coordinating basic compound having an ethylenediamine structure or ethanolamine structure in its molecular structure because metal ions formed when metal oxides on the surface of the metal member are dissolved are easily stabilized by chelate coordination. The amino group in the structure may be any of primary, secondary and tertiary amino groups, but is preferably a tertiary amino group because it is less likely to cause a side reaction such as amidation between the reducing organic substance and the basic compound.
The content of the basic compound with respect to 1 part by weight of the reducing organic substance is preferably 0.25 to 10.0 parts by weight, more preferably 0.50 to 5.0 parts by weight, and still more preferably 0.75 to 3.0 parts by weight because it is easier to adjust the molar ratio (basic groups/acidic groups) to be described below.
The basic compound preferably contains an alkylamine having at least one linear alkyl group having 1 to 20 carbon atoms (preferably 1 to 15 carbon atoms) together with the chelate coordinating basic compound because it has a relatively low polarity and thus the viscosity and wettability of the solvent composition are easily adjusted. The content of the alkylamine with respect to 1 part by weight of the reducing organic substance is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.75 parts by weight, and still more preferably 0.1 to 0.5 parts by weight.
The basic compounds may be used alone or two or more thereof may be used in combination.
In the solution composition of the present disclosure, the ratio (basic groups/acidic groups) of a total number of moles of basic groups contained in the basic compound to a total number of moles of acidic groups contained in the reducing organic substance is preferably 0.40 to 2.50, more preferably 0.45 to 2.40, and still more preferably 0.50 to 2.30. When the molar ratio is 0.40 or more, the reducing agent is thermally stabilized, the reduction easily proceeds during a heating process, and metal ions eluted from the surface of the metal member are easily stabilized. In addition, when the molar ratio is 2.50 or less, the influence of organic residues remaining after solvent drying on sintering is reduced. Here, the total number of moles of acidic groups contained in the reducing organic substance is obtained by multiplying the number of moles of the reducing organic substance by the number of acidic groups contained in the reducing organic substance, and the total number of moles of basic groups contained in the basic compound is obtained by multiplying the number of moles of the basic compound by the number of basic groups contained in the basic compound.

The coordinating organic compound contained in the solution composition according to the second aspect of the present disclosure is a coordinating organic compound other than compounds included as the basic compound. Since the coordinating organic compound has a higher boiling point than the reducing organic substance, it is more likely to remain than the reducing organic substance during sintering, and it is easier to restrict contact between the reducing organic substance and the surface of an active metal, and thus it is easier to restrict decomposition of the reducing organic substance.
Examples of coordinating organic compounds include a compound having a carboxyl group (carboxylic acid, etc.), a compound having a ketone group (for example, diketones such as acetylacetone and β-ketoesters), and a compound having a hydroxyl group, a sulfo group and a thiol group. Among these, a compound having a carboxyl group (carboxylic acid, etc.) is preferable because it allows dissolved metal oxides to be easily precipitated as metal nanoparticles.
The compound having a carboxyl group is preferably a monovalent or divalent carboxylic acid, and is more preferably a monovalent carboxylic acid because the precipitated metal nanoparticles are easily sintered.
Examples of carboxylic acids include acetic acid (a boiling point of 118°C), lactic acid (a boiling point of 122°C), propionic acid (a boiling point of 141°C), acrylic acid (a boiling point of 141°C), malic acid (a boiling point of 167°C), n-hexanoic acid (a boiling point of 205°C), succinic acid (a boiling point of 235°C), n-octanoic acid (a boiling point of 237°C), tartaric acid (a boiling point of 275°C), and oxalic acid (a boiling point of 365°C). Since carboxylic acids may function as reducing organic substances or coordinating organic compounds, when carboxylic acids are used as reducing organic substances, other carboxylic acids having a higher boiling point than the carboxylic acids can be used in combination as coordinating organic compounds.
The boiling point of the carboxylic acid at normal pressure is preferably higher than 110°C, more preferably 150°C or higher, and still more preferably 200°C or higher because the carboxylic acid is less likely to be volatile than formic acid (a boiling point of 101°C).
The content of the coordinating organic compound in the solution composition according to the second aspect of the present disclosure with respect to 1 part by weight of the reducing organic substance is preferably 0.05 to 1.00 part by weight, more preferably 0.10 to 0.75 parts by weight, and still more preferably 0.15 to 0.50 parts by weight. When the content is 0.05 parts by weight or more, metal nanoparticles are easily precipitated, and when the content is 1.00 part by weight or less, the solution composition is unlikely to remain during sintering.
In the solution composition according to the second aspect of the present disclosure, the molar ratio of the coordinating organic compound to the basic compound (coordinating organic compound/basic compound) is preferably 0.01 to 1.00, more preferably 0.05 to 0.50, and still more preferably 0.10 to 0.40. When the molar ratio is 0.01 or more, metal nanoparticles are likely to precipitate, and when the molar ratio is 1.00 or less, the solution composition is unlikely to remain during sintering.

The solvent compositions according to the first and second aspects of the present disclosure may contain a solvent such as water or an organic solvent in addition to the above reducing organic substance, basic compound, and coordinating organic compound in order to adjust the fluidity (viscosity) and operability. Examples of organic solvents include ester-based solvents such as acetates (ethyl acetate, butyl acetate, etc.), and ester oils (butyl stearate, hexyl laurate, triethyl citrate, etc.); ether-based solvents such as dioxane and tetrahydrofuran; ketone-based solvents such as acetone; aromatic-based solvents such as toluene and xylene; halogen-based solvents such as dichloromethane and chloroform; alcohol-based solvents such as methanol, ethanol, isopropanol, and butanol; and nitrile-based solvents such as acetonitrile and benzonitrile. These may be used alone or two or more thereof may be used in combination.
The content of the solvent with respect to 1 part by weight of the reducing organic substance is preferably 0 to 200 parts by weight, more preferably 0.10 to 100 parts by weight, still more preferably 0.20 to 40 parts by weight, particularly preferably 0.50 to 10 parts by weight, and most preferably 1 to 5 parts by weight.
The solvent compositions according to the first and second aspects of the present disclosure may contain other components, for example, a resin component (for example, a polymer compound having a number average molecular weight of 10,000 or more, such as an ethyl cellulose resin, an alkyl cellulose resin, a polyvinyl acetal resin, and an acrylic resin), additives (a surface adjusting agent, a leveling agent, a defoaming agent, a dispersant, a thixotropy imparting agent, etc.), as long as the effects of the present disclosure are not impaired. The content of the other components in the solvent composition is, for example, 1 wt% or less (preferably 0.5 wt% or less).
The solvent compositions according to the first and second aspects of the present disclosure can be produced according to a process of mixing the reducing organic substance, basic compound, and coordinating organic compound with the solvent and other components.
Preferably, the temperature during mixing does not exceed 100°C.
For cooling after mixing, the mixture may be cooled to room temperature (for example, 25°C) or lower, may be gradually cooled to room temperature, or may be rapidly cooled by ice cooling or the like.

[Method for Producing Solvent-treated Metal Member]

A solvent-treated metal member can be produced by applying the solvent compositions according to the first and second aspects of the present disclosure to a metal member. In the solvent-treated metal member, the metal oxide film on the surface is dissolved and removed using the solvent composition. Furthermore, when the solvent-treated metal member is used, it is possible to produce a sintered object and a bonded object having excellent electroconductivity even without a reducing atmosphere according to the solvent composition remaining on the surface during sintering.
In addition, when the solvent composition according to the second aspect of the present disclosure is applied to a metal member, the metal oxide film on the surface is dissolved and removed, and it is possible to produce a solvent-treated metal member having a metal member surface on which metal nanoparticles having a number average particle size of less than 600 nm (1 nm or more and less than 600 nm, 5 nm or more and less than 100 nm, or 10 nm or more and less than 60 nm) are precipitated. That is, when the second solvent composition of the present disclosure is used, a metal member having metal nanoparticles on its surface can be produced by applying the solvent composition to a metal member, dissolving at least a part of the surface of the metal member to form a metal complex, and thermally decomposing and/or reductively decomposing the formed metal complex to precipitate metal nanoparticles on the surface of the metal member. The thermal decomposition and/or reductive decomposition is realized by performing heating in the presence of the reducing organic substance. Since the metal member has nano metal particles on its surface, it can be sintered at a lower temperature. For example, the number average particle size of the metal nanoparticles can be calculated based on the number observed under an electron microscope.
The metal member may be any member that is used to form a conductive film, a conductive circuit, or conductive bonding, and is a target to which the solvent composition is applied, and is of various forms and shapes, and examples thereof include a metal particle aggregate and a semi-sintered object thereof, a woven metal fiber fabric, a non-woven metal fiber fabric, and a metal member having a dense internal structure having a surface to be bonded to an object to be bonded.
Examples of metals forming the metal member include gold, silver, copper, nickel, palladium, tin, aluminum and alloys thereof. Among these, since copper and silver are likely to form a metal oxide film on the surface, when the solvent composition is used, an improvement effect of obtaining a sintered object and a bonded object having excellent electroconductivity is significant.
The shape of metal particles contained in the aggregate, which is the metal member, may be various shapes such as a spherical shape, an ellipsoidal flake shape (flat shape), and a short fiber shape, or may be an irregular shape. These may be used alone or two or more thereof may be used in combination.
The volume average particle size (median size, D₅₀) of the metal particles used to form the aggregate, which is the metal member, may be, for example, 1 nm to 100 µm, and when the second solvent composition is applied, since the metal nanoparticles are precipitated, the volume average particle size may be 600 nm or more (600 nm to 100 µm or 1 to 10 µm). The average particle size of the metal particles can be measured, for example, by a laser diffraction/scattering method.
When the solvent-treated metal member is produced, the amount of metal nanoparticles precipitated can be adjusted by separately dissolving a metal compound in the solvent compositions according to the first and second aspects of the present disclosure and then applying the solvent compositions.
As the metal compound to be dissolved, a metal compound containing copper is preferable because copper nanoparticles that are easily sintered are precipitated, and copper(II) oxide, copper(I) oxide, or copper(II) hydroxide is more preferable because it does not require much time or effort for storage. These may be used alone or two or more thereof may be used in combination.
A sintered object can be obtained by heating the solvent-treated metal member obtained by the production method, and a bonded object can be obtained by bringing the solvent-treated metal member into contact with an object to be bonded and performing heating.
The bonded object may be one in which the solvent composition according to the first or second aspect of the present disclosure is applied to the metal particle aggregate layer formed on the surface of the substrate to form a treated aggregate layer, and an object to be bonded and the treated aggregate layer are then brought into contact with each other and heated to bond the substrate and the object to be bonded.
The substrate is not particularly limited as long as it can be bonded by the treated aggregate layer, and examples thereof include substrates formed of metals (including alloys), ceramics (metal oxides, metal nitrides, silicon, silicon nitride, aluminum nitride, etc.), glass, polymer materials and the like, substrates formed of the above materials that have been surface-treated by metal plating, and multi-layer boards obtained by combining the above materials.
The object to be bonded is not particularly limited as long as it can be bonded by the solvent-treated metal member or the treated aggregate layer, and examples thereof include semiconductor chips (capacitors, transistors, diodes, MOS FET, discrete semiconductors such as IGBT, and integrated circuits such as IC and LSI), compound semiconductor chips (GaN, SiC, etc.), electric and electronic components such as a heat sink, bus bars for in-vehicle components, connectors, and harnesses.
The heating can be performed, for example, in a temperature range of 100 to 400°C (120 to 300°C or 150 to 250°C). The heating time may be, for example, 1 to 120 minutes (or 5 to 60 minutes). In addition, for example, the bonded object (laminate) may be pressed against the bonding surface at a pressure of 10 MPa or less.
The solvent-treated metal member and the treated aggregate layer can be used for semiconductor bonding, wire bonding, clip bonding, forming wirings on wiring boards, forming multi-layer printed wiring boards, forming bumps, bonding between bumps, and the like, and can be suitably used in the production of electronic devices (printed wiring boards, capacitors, inductors, varistors, thermistors, transistors, speakers, actuators, antennas, solid oxide fuel cells, hybrid ICs, etc.), rotating electrical machines and the like.
The configurations and combinations thereof in the above embodiments are only examples, and additions, omissions, substitutions, and other modifications of the configurations can be made as appropriate without departing from the spirit and scope of the present disclosure. The present disclosure is not limited to the embodiments but is limited only by the scope of the claims.

Examples

Hereinafter, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to these examples.
The reducing organic substances, basic compounds, coordinating organic compounds, solvents, and metal particles (copper particles) used are as follows.

·Formic acid: reagent (commercially available from FUJIFILM Wako Pure Chemical Corporation)
·Oxalic acid: reagent (commercially available from FUJIFILM Wako Pure Chemical Corporation)

·MDETA: N-methyldiethanolamine, reagent (commercially available from FUJIFILM Wako Pure Chemical Corporation)
·PMDTA: pentamethyldiethylenetriamine, reagent (commercially available from Tokyo Chemical Industry Co., Ltd.)
·DMAMPZ: 1-(2-dimethylaminoethyl)-4-methylpiperazine, reagent (commercially available from Tokyo Chemical Industry Co., Ltd.)
·DMDA: N,N-dimethyldodecylamine, reagent (commercially available from Tokyo Chemical Industry Co., Ltd.)

·Acetic acid: reagent (commercially available from FUJIFILM Wako Pure Chemical Corporation)
·nHxA: n-hexanoic acid, reagent (commercially available from Tokyo Chemical Industry Co., Ltd.)
·nOcA: n-octanoic acid, reagent (commercially available from Tokyo Chemical Industry Co., Ltd.)

·TEC: triethyl citrate, reagent (commercially available from Tokyo Chemical Industry Co., Ltd.)
·EtOH: ethanol, reagent (commercially available from FUJIFILM Wako Pure Chemical Corporation)

·CH-0200L1: product name "CH-0200L1," a volume average particle size of 200 nm, commercially available from Mitsui Mining & Smelting Co., Ltd.
·CT-0500: product name "CT-0500," a volume average particle size of 800 nm, commercially available from Mitsui Mining & Smelting Co., Ltd.

(Preparation of Solvent Sample)

The reducing organic substances, basic compounds, coordinating organic compounds, and solvents were weighed out and mixed in a screw tube so that the contents shown in Tables 1 and 2 were obtained and then stirred using a rotation/revolution mixer (product name "Thinky Mixer," commercially available from Thinky Corporation) at 2,000 rpm for 1 minute to prepare solvent samples 1 to 22 used in evaluation of oxide film removal performance, metal nanoparticle precipitation, electroconductivity, and bondability.

[Table 1]

Table 1

(Parts by weight)		Solvent sample
(Parts by weight)		1	2	3	4	5	6	7	8	9	10	11	12
Reducing organic substance	Formic acid	1	1	1	1	1	1	1	1	1	1	1	1
Basic compound	MDETA	1.5		1.5
	PMDTA		0.75		0.75		1.3		0.62
	DMAMPZ					0.75		1.3	0.62	1.3	1.3
	DMDA			0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Coordinating organic compound	nOcA				0.4	0.4	0.4	0.4	0.4				0.4
	nHxA									0.4
	Acetic acid										0.4
Molar ratio (basic groupy/acidic group)		0.60	0.60	0.64	0.64	0.64	1.04	1.04	1.04	1.04	1.04	-	-
Molar ratio (coordinating/basic)		-	-	-	0.21	0.21	0.13	0.13	0.13	0.16	0.31	-	-
Solvent	TEC						2.9	2.9	2.84	2.9	2.7

[Table 2]

Table 2

(Parts by weight)		Solvent sample
(Parts by weight)		13	14	15	16	17	18	19	20	21	22
Reducing organic substance	Formic acid	1	1	1	1	1	1	1	1		1
Reducing organic substance	Oxalic acid							0.2
Basic compound	MDETA	1.3	2.6	1.5		1	1.3	1.3	2	1
	PMDTA				0.75
	DMDA					0.2
Molar ratio (basic group/acidic group)		0.50	1.00	0.60	0.60	0.44	0.60	0.50	2.00	-	-
Solvent	EtOH	0	0	0	0	0	2.3	2.5	0	0	0

The above solvent samples were used to evaluate "performance of removing the oxide film from the surface of the copper foil."

(Surface Treatment of Copper Foil)

A copper foil with a thickness of 100 µm (product name "C1020P") was cut into a square (5 cm×5 cm) and heated at 200°C for 10 minutes in the atmosphere using a hot plate to prepare a test piece of an oxidation-treated copper foil having an oxide film on its surface.
Two drops (about 40 mg) of the solvent sample were added dropwise to the center of the oxidation-treated copper foil using a dropper, the oxidation-treated copper foil test piece was placed on a hot plate in a glove box in a nitrogen atmosphere (an oxygen concentration of 100 ppm or less), the temperature was raised from room temperature (25°C) to 150°C at a heating rate of 10°C/min and then held for 5 minutes, the temperature was additionally raised to 200°C at a heating rate of 10°C/min and then held for 10 minutes, the sample was then naturally cooled to room temperature (25°C), and after cooling, the sample was washed with methanol to prepare a solvent-treated copper foil.

(Measurement of Thickness of Oxide Film on Surface of Copper Foil)

Using an oxide film/metal film thickness measuring machine (product name "QC-100," commercially available from ECI TECHNOLOGY), the thickness of the oxide film formed of an oxide or the like on the surface of the treated copper foil was measured by a continuous electrochemical method. The measurement conditions were as follows. The value of the total thickness of copper(I) oxide and copper(II) oxide, and copper sulfide obtained from the measurement results was defined as the thickness of the oxide film. The measurement was performed on the part where droplets remained to the end when the solvent was evaporated. If the measurement was not possible within the 10-minute measurement time, the thickness was 100Å or more. Table 3 shows the solvent samples used and the evaluation results. Here, the thickness of the copper oxide on the copper foil before the oxidation treatment was 35Å.

·Measurement range (gasket size): φ3.2 mm
·Current value: 30 µA/cm²
·Measurement time: a maximum of 10 minutes

(Evaluation Criteria for Oxide Film Removal Performance)

The performance of removing the oxide film from the surface of the copper foil was evaluated according to the following criteria.

∘ (good): 30Å or less
Δ (fair): more than 30Å and less than 100Å
× (poor): 100Å or more

[Table 3]

Table 3

	Example Comparative				Example
	1	2	3	4	1	2
Solvent sample	1	2	3	4	11	12
Oxide film thickness (a)	13	20	5	50	>100	>100
Evaluation	○	○	○	△	×	×

Examples 1 to 4 were evaluated as o or Δ, which indicate that the oxide film was successfully removed by the treatment using the solvent composition of the present disclosure. On the other hand, Comparative Examples 1 and 2 in which no basic compound was contained were evaluated as ×, which indicates that the oxide film removing performance was poor.

"Precipitation of metal nanoparticles on the surface of the copper foil" was evaluated. For the evaluation, solvent-treated copper foils prepared in the same manner as in the evaluation of "performance of removing the oxide film from the surface of the copper foil" were used.

(Surface of Copper Foil)

It was determined whether metal nanoparticles were precipitated according to observation under an electron microscope, and when precipitation of metal nanoparticles was observed, the particle sizes of 100 metal nanoparticles were measured, and the average value was calculated to obtain the number average particle size. Table 4 shows the solvent samples used and the evaluation results. In addition, Figs. 1 to 3 show electron microscope images of Example 6, Example 11, and Comparative Example 3 (the bottom right bar in Fig. 1: 1 µm, the bottom right bar in Fig. 2: 100 nm, the bottom right bar in Fig. 3: 1 µm).

[Table 4]

Table 4

	Example										Comparative Example
	5	6	7	8	9	10	11	12	13	14	3
Solvent sample	1	2	3	4	5	6	7	8	9	10	12
Number average particle size(nm)	>1000	>1000	>1000	20	50	25	50	36	63	500	-

The "-" in the particle size column indicates that no particulate deformation was observed on the surface.
It was shown that copper nanoparticles were precipitated in Examples 8 to 14, and it was shown that copper particles larger than 1,000 nm were precipitated in Examples 5 to 7 in which no coordinating organic compound was added. On the other hand, it was shown that copper particles were not precipitated in Comparative Example 3 in which no basic compound was contained.

The above solvent samples were used to evaluate "electroconductivity" of sintered objects of copper particle aggregates.

(Preparation of Copper Particle Aggregate)

10.5 g of formic acid, 10.5 g of nOcA, 2.6 g of PMDTA, 10.9 g of MDEtA, and 13.5 g of DMDA were mixed and 0.5 g of a polyvinyl butyral resin (product name "S-LEC B BL-1," commercially available from Sekisui Chemical Co., Ltd.) was then additionally added as a binder resin, and the mixture was uniformly mixed to obtain a copper paste dispersion solvent.
10 g of copper particles CH-0200L1, 10 g of copper particles CT-0500, and 2.4 g of the copper paste dispersion solvent were stirred and mixed using a rotation/revolution mixer (product name "ARE-310," commercially available from Thinky Corporation) at 2,000 rpm for 3 minutes to obtain a copper paste.
The copper paste was molded and heated in a nitrogen atmosphere at 200°C for 5 minutes to prepare a copper particle aggregate (rectangle shape, length 50 mm, width 10 mm, thickness 20 µm). The copper particle aggregate was not sintered, and did not exhibit electroconductivity.
The solvent sample was applied to the prepared copper particle aggregate, which was sintered in a nitrogen atmosphere at 200°C for 30 minutes to obtain a sintered object, and the volume resistivity of the sintered object was measured using a resistivity meter (product name "Loresta GP MCP-T610," commercially available from Mitsubishi Chemical Analytech Co., Ltd.). A smaller volume resistivity value indicates better "electroconductivity." Table 5 shows the solvent samples used and the evaluation results.

(Evaluation Criteria for Electroconductivity)

The electroconductivity was evaluated according to the following criteria.

∘ (good): volume resistivity of less than 20 µΩ·cm
Δ (fair): volume resistivity of 20 µΩ·cm or more and less than 100 µΩ·cm
× (poor): volume resistivity of 100 µΩ·cm or more

[Table 5]

Table 5

	Example								Comparative Example
	15	16	17	18	19	20	21	22	4	5
Solvent sample	13	14	15	16	17	18	19	20	21	22
Volume resistivity (µΩ·cm)	12	15	13	9	10	11	8	25	130	-
Electroconductivity evaluation	○	○	○	○	○	○	○	△	×	×

The "-" in the particle size column indicates that no current flowed and no measurement value was obtained.
Examples 15 to 22 were evaluated as ∘ or Δ, which indicate that the volume resistivity was low and good electroconductivity was obtained. On the other hand, Comparative Examples 4 and 5 in which no reducing organic substance or basic compound was contained showed that the volume resistivity was high and the electroconductivity was poor.

The above solvent samples were used to evaluate the "bondability." For bonding evaluation, the above copper paste used for evaluating the electroconductivity was used.

(Example 23, Cu-Cu Bonding (Length 10 mm, Width 10 mm))

Using a metal mask with an opening size of 10 mm×10 mm and a thickness of 100 µm, the copper paste was printed on a copper plate with a size of 30 mm×30 mm and a thickness of 1 mm. The copper paste was heated at 200°C for 5 minutes in a nitrogen atmosphere to obtain a copper particle aggregate. Solvent sample 19 was added dropwise to the copper particle aggregate so that the solvent permeated the entire aggregate, and a copper plate with a size of 10 mm×10 mm and a thickness of 1 mm was arranged on the copper particle aggregate to which the solvent was applied. Then, the sample was pressurized at 10 MPa from above and heated at 200°C for 30 minutes in a nitrogen atmosphere to obtain a bonded object in which the copper plate and the copper plate were bonded.
The bonded object was divided into four parts, and the bond strength was measured using a universal bond tester (product name "Die Shear Tester SERIES4000," commercially available from Nordson DAGE). The bond strength was 40 MPa or more, which indicates that the bondability was sufficiently excellent.
In addition, when the void fraction of the bonded object was measured using an ultrasound imaging device (SAT, Scanning Acoustic Tomograph) (product name "FineSAT FS300II," commercially available from Hitachi High-Tech Corporation), the void fraction was 1% or less, indicating excellent bondability.

(Example 24, Cu-Cu Bonding (Length 20 mm, Width 20 mm))

Using a metal mask with an opening size of 20 mm×20 mm and a thickness of 150 µm, the copper paste was printed on a copper plate with a size of 30 mm×30 mm and a thickness of 1 mm and a bonded object was obtained in the same manner as in Example 23. The void fraction of the bonded object was also 1% or less. Fig. 4 shows an SAT image of the bonded object (in the drawing, white parts indicate voids).

(Example 25, Bonding Between Fine Electrodes)

A Si chip with copper bumps (product name "WALTS-TEG CC40," 10 mm×10 mm, commercially available from Walts Co., Ltd.) with a pattern in which 28,224 (168×168) copper bumps (with a height of 15 µm, 22 µmφ) were arranged at 40 µm intervals within the 10 mm×10 mm range, and a Si interposer (product name "WALTS-TEG IP40," commercially available from Walts Co., Ltd.) with copper pads corresponding to the pattern were used. Fig. 5 shows an electron microscope image of an arrangement pattern of the copper bumps, and Fig. 6 shows an electron microscope image of the surface of the copper bump part (the bottom right bar in Fig. 5: 10 µm, the bottom right bar in Fig. 6: 100 nm).
The Si chip with copper bumps was heated in the atmosphere at 200°C for 5 minutes using a hot plate, and the surfaces of the copper bumps were oxidized.
5 µL of the solvent sample 7 was applied to the oxidized Si chip with copper bumps using a micropipette, and the sample was then placed on a hot plate in a glove box in a nitrogen atmosphere (an oxygen concentration of 100 ppm or less), the temperature was raised from room temperature (25°C) to 150°C at a heating rate of 10°C/min and then held for 5 minutes, the temperature was additionally raised to 200°C at a heating rate of 10°C/min and then held for 10 minutes, and the sample was then naturally cooled to room temperature (25°C). After cooling, the sample was washed with methanol to obtain a solvent-treated Si chip. Fig. 7 shows an electron microscope image of the surface of the copper bump part of the solvent-treated Si chip (the bottom right bar in Fig. 7: 100 nm). Copper nanoparticles were precipitated on the surfaces of the copper bumps.
Using a micropipette, 5 µL of the solvent sample 19 was applied onto the Si interposer to obtain a solvent-coated Si interposer. The solvent-coated Si interposer and the solvent-treated Si chip were laminated so that the copper pads were positioned to correspond to the copper bumps, and bonded using a flip chip bonder (product name "T-3000-PRO-HF," commercially available from Dr. TRESKY) by heating in a nitrogen atmosphere under a load of 5 kgf at 200°C for 10 minutes.
The bond strength of the bonded object was measured using a universal bond tester (product name "Die Shear Tester SERIES4000," commercially available from Nordson DAGE). The bond strength was 25 MPa, indicating that the strength was sufficient, and the bondability was excellent.
Hereinafter, variations of the invention according to the present disclosure will be described.

[Appendix 1] A solvent composition for sintering aids, the solvent composition containing a reducing organic substance and a basic compound.
[Appendix 2] A solvent composition including a reducing organic substance, a basic compound, and a coordinating organic compound other than compounds included as the basic compound, wherein the coordinating organic compound has a higher boiling point than the reducing organic substance.
[Appendix 3] The solvent composition according to Appendix 1 or 2, wherein the reducing organic substance is formic acid.
[Appendix 4] The solvent composition according to Appendix 3, further including a reducing organic substance other than formic acid.
[Appendix 5] The solvent composition according to Appendix 4, wherein the reducing organic substance other than the formic acid is oxalic acid.
[Appendix 6] The solvent composition according to Appendix 4 or 5, wherein a content of the reducing organic substance other than formic acid is 1 part by mole or less with respect to 1 mole of formic acid.
[Appendix 7] The solvent composition according to any one of Appendices 1 to 6, wherein the basic compound is a nitrogen-containing compound represented by Formula (1) below: (in Formula (1), R^a to R^c are the same as or different from each other and each represent a hydrogen atom or a hydrocarbon group which may have a substituent; the substituents are the same as or different from each other, and are at least one group selected from among 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; provided that R^a to R^c are never hydrogen atoms simultaneously; a double line including a dashed line represents a single bond or a double bond, and when the double line is a double bond, there is no R^c; and any two of R^a to R^c may be bonded to each other to form a ring together with an adjacent nitrogen atom).
[Appendix 8] The solvent composition according to any one of Appendices 1 to 7, wherein the basic compound has, in a molecular structure thereof, an ethylenediamine structure or ethanolamine structure, and an amino group in the structure is a tertiary amino group.
[Appendix 9] The solvent composition according to any one of Appendices 1 to 8, wherein the basic compound is at least one selected from among dialkanolamines and triamines.
[Appendix 10] The solvent composition according to Appendix 9, wherein the basic compound is at least one selected from among N-methyldiethanolamine, pentamethyldiethylenetriamine and 1-(2-dimethylaminoethyl)-4-methylpiperazine.
[Appendix 11] The solvent composition according to any one of Appendices 1 to 10, wherein the basic compound includes an alkylamine having at least one linear alkyl group having 1 to 20 carbon atoms (preferably 1 to 15 carbon atoms) together with a chelate coordinating basic compound.
[Appendix 12] The solvent composition according to Appendix 11, wherein the alkylamine is N,N-dimethyldodecylamine.
[Appendix 13] The solvent composition according to Appendix 11 or 12, wherein a content of the alkylamine with respect to 1 part by weight of the reducing organic substance is 0.01 to 1 part by weight (preferably 0.05 to 0.75 parts by weight, and more preferably 0.1 to 0.5 parts by weight).
[Appendix 14] The solvent composition according to any one of Appendices 1 to 13, wherein the content of the basic compound with respect to 1 part by weight of the reducing organic
substance is 0.25 to 10.0 parts by weight (preferably 0.50 to 5.0 parts by weight, and more preferably 0.75 to 3.0 parts by weight).
[Appendix 15] The solvent composition according to any one of Appendices 1 to 14, wherein the ratio (basic groups/acidic groups) of a total number of moles of basic groups contained in the basic compound to a total number of moles of acidic groups contained in the reducing organic substance is 0.40 to 2.50 (preferably 0.45 to 2.40, and more preferably 0.50 to 2.30).
[Appendix 16] The solvent composition according to any one of Appendices 2 to 15, wherein the coordinating organic compound is a compound having a carboxyl group.
[Appendix 17] The solvent composition according to Appendix 16, wherein the compound having a carboxyl group is a monovalent or divalent (preferably monovalent) carboxylic acid.
[Appendix 18] The solvent composition according to Appendix 17, wherein a boiling point of the carboxylic acid at normal pressure is higher than 110°C (preferably 150°C or higher, and more preferably 200°C or higher).
[Appendix 19] The solvent composition according to any one of Appendices 2 to 18, wherein a content of the coordinating organic compound with respect to 1 part by weight of the reducing organic substance is 0.05 to 1.00 part by weight (preferably 0.10 to 0.75 parts by weight, and more preferably 0.15 to 0.50 parts by weight).
[Appendix 20] The solvent composition according to any one of Appendices 2 to 19, wherein a molar ratio of the coordinating organic compound to the basic compound (coordinating organic compound/basic compound) is 0.01 to 1.00 (preferably 0.05 to 0.50, and more preferably 0.10 to 0.40).
[Appendix 21] The solvent composition according to any one of Appendices 1 to 20, further including a solvent.
[Appendix 22] The solvent composition according to Appendix 21, wherein the solvent is at least one selected from among an ester-based solvent and an alcohol-based solvent.
[Appendix 23] The solvent composition according to Appendix 21, wherein the solvent is at least one selected from among triethyl citrate and ethanol.
[Appendix 24] The solvent composition according to any one of Appendices 1 to 23, wherein a content of the solvent with respect to 1 part by weight of the reducing organic substance is 0 to 200 parts by weight (preferably 0.10 to 100 parts by weight, more preferably 0.20 to 40 parts by weight, still more preferably 0.50 to 10 parts by weight, and particularly preferably 1 to 5 parts by weight).
[Appendix 25] A method for producing a solvent-treated metal member, the method including applying the solvent composition according to any one of Appendices 1 to 24 to a metal member.
[Appendix 26] The method for producing a solvent-treated metal member according to Appendix 25, wherein the metal member before application is an aggregate of metal particles having a volume average particle size of 1 nm to 100 µm.
[Appendix 27] A method for producing a solvent-treated metal member, the method including applying the solvent composition according to any one of Appendices 2, and 16 to 24 to a metal member, wherein the solvent-treated metal member has a metal member surface on which metal nanoparticles having a number average particle size of less than 600 nm (1 nm or more and less than 600 nm, 5 nm or more and less than 100 nm, or 10 nm or more and less than 60 nm) are precipitated.
[Appendix 28] The method for producing a solvent-treated metal member according to Appendix 27, wherein the metal member before application is an aggregate of metal particles having a volume average particle size of 600 nm or more (600 nm to 100 µm, or 1 to 10 µm).
[Appendix 29] The method for producing a solvent-treated metal member according to any one of Appendices 25 to 28, wherein a metal compound is dissolved in the solvent composition according to any one of Appendices 1 to 24 and then the solvent composition is applied to a metal member.
[Appendix 30] The method for producing a solvent-treated metal member according to any one of Appendices 25 to 29, wherein the metal member contains copper.
[Appendix 31] The method for producing a solvent-treated metal member according to Appendix 29 or 30, wherein the metal compound is at least one selected from among copper(I) oxide, copper(II) oxide and copper(II) hydroxide.
[Appendix 32] A method for producing a sintered object, the method including heating the solvent-treated metal member obtained by the production method according to any one of Appendices 25 to 31 to obtain a sintered object.
[Appendix 33] A method for producing a bonded object, the method including bringing the solvent-treated metal member obtained by the production method according to any one of Appendices 25 to 31 into contact with an object to be bonded and heating the same to obtain a bonded object.
[Appendix 34] A method for producing a bonded object, the method including applying the solvent composition according to any one of Appendices 1 to 24 to a metal particle aggregate layer formed on the surface of a substrate to form a treated aggregate layer, then bringing an object to be bonded into contact with the treated aggregate layer, and heating the same to bond the substrate and the object to be bonded.
[Appendix 35] A method for producing a metal member having, on a surface thereof, metal nanoparticles, the method including applying a solvent composition to a metal member, dissolving at least a part of the surface of the metal member to form a metal complex, and thermally decomposing and/or reductively decomposing the formed metal complex to precipitate metal nanoparticles on the surface of the metal member.

Claims

A solvent composition for sintering aids, the solvent composition comprising a reducing organic substance and a basic compound.
A solvent composition comprising a reducing organic substance, a basic compound, and a coordinating organic compound other than compounds included as the basic compound,
wherein the coordinating organic compound has a higher boiling point than the reducing organic substance.
The solvent composition according to claim 1 or 2,
wherein the reducing organic substance is formic acid.
The solvent composition according to claim 3, further comprising a reducing organic substance other than formic acid.
The solvent composition according to claim 1 or 2,
wherein the basic compound is a nitrogen-containing compound represented by Formula (1) below: (in Formula (1), R^a to R^c are the same as or different from each other and each represent a hydrogen atom or a hydrocarbon group which may have a substituent; the substituents are the same as or different from each other, and are at least one group selected from among 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; provided that R^a to R^c are never hydrogen atoms simultaneously; a double line including a dashed line represents a single bond or a double bond, and when the double line represents a double bond, there is no R^c; and any two of R^a to R^c may be bonded to each other to form a ring together with an adjacent nitrogen atom).
The solvent composition according to claim 1 or 2,
wherein the basic compound has, in a molecular structure thereof, an ethylenediamine structure or ethanolamine structure, and an amino group in the structure is a tertiary amino group.
The solvent composition according to claim 1 or 2,
wherein the ratio (basic groups/acidic groups) of a total number of moles of basic groups contained in the basic compound to a total number of moles of acidic groups contained in the reducing organic substance is 0.40 to 2.50.
The solvent composition according to claim 2,
wherein the coordinating organic compound is a compound having a carboxyl group.
The solvent composition according to claim 1 or 2, further comprising a solvent.
A method for producing a solvent-treated metal member, the method comprising
applying the solvent composition according to claim 1 or 2 to a metal member.
The method for producing a solvent-treated metal member according to claim 10,
wherein the metal member before application is an aggregate of metal particles having a volume average particle size of 600 nm or more.
A method for producing a solvent-treated metal member, the method comprising
dissolving a metal compound in the solvent composition according to claim 1 or 2 and then applying the solvent composition to a metal member.
The method for producing a solvent-treated metal member according to claim 10,
wherein the metal member contains copper.
The method for producing a solvent-treated metal member according to claim 12,
wherein the metal compound is at least one selected from among copper(I) oxide, copper(II) oxide and copper(II) hydroxide.
A method for producing a sintered object, the method comprising
heating the solvent-treated metal member obtained by the production method according to claim 10 to obtain a sintered object.
A method for producing a bonded object, the method comprising
bringing the solvent-treated metal member obtained by the production method according to claim 10 into contact with an object to be bonded and heating the same to obtain a bonded object.
A method for producing a bonded object, the method comprising
applying the solvent composition according to claim 1 or 2 to a metal particle aggregate layer formed on the surface of a substrate to form a treated aggregate layer, then bringing an object to be bonded into contact with the treated aggregate layer, and heating the same to bond the substrate and the object to be bonded.
A method for producing a metal member having, on a surface thereof, metal nanoparticles, the method comprising
applying a solvent composition to a metal member, dissolving at least a part of the surface of the metal member to form a metal complex, and thermally decomposing and/or reductively decomposing the formed metal complex to precipitate metal nanoparticles on the surface of the metal member.