JP7434786B2 - Copper/copper oxide fine particle paste - Google Patents

Description

The present invention relates to a bonding material for bonding a plurality of metal members to each other, the bonding material having copper/copper oxide fine particles as a main ingredient for bonding.

In recent years, it has become clear that nanometer-level metal particles exhibit thermal and magnetic properties that are different from those of ordinary bulk metals, and new reactions and material development that utilize these properties has been actively conducted. ing.
Nanometer-level metal fine particles differ from general millimeter-order metal powders in that they have the property of mutually melting at a temperature significantly lower than the melting point of a single element. Therefore, from the point of view of lowering the temperature during sintering, the use of metal particles with a small particle size is being considered.

Bonding using fine metal particles can be expected to have high reliability under high-temperature conditions. Metal fine particles can be suitably used for bonding power semiconductors and bonding for circuit mounting used in high-temperature environments such as the engine room of an automobile. Furthermore, when metal particles are fused together to form a bulk, they do not re-melt to the melting point of the bulk material, so the property that the bonding is stable when performing secondary mounting is also of practical value.
Fine metal particles can be made into ink or paint by dispersing them in a solvent or/and resin, and can be easily handled using various printing machines, dispensers, and the like.

Various metal fine particle materials such as gold, silver, copper, and nickel are known as types of metal fine particles. Among them, copper is excellent in safety during production, raw material cost, anti-migration characteristics, and dispersion stability of dispersion, and is attracting particular attention from these points.
Although the melting point of copper exceeds 1000°C, copper fine particles having a particle size of 100 nm or less have the advantage that fusion progresses at a temperature of 350°C or less and can be made into bulk.

However, copper is more easily oxidized than metals such as gold and silver, and oxidation of finely divided copper is particularly accelerated due to its large specific surface area. Among them, copper fine particles having a particle size of 100 nm or less have a very large specific surface area and are easily oxidized in the atmosphere.

When the copper fine particles are oxidized, a layer of highly crystalline cuprite (cuprous oxide, copper (I) oxide) is formed on the outermost surface of the copper fine particles. This cuprite layer inhibits fusion between copper fine particles. Therefore, copper fine particles having a cuprite layer cannot be fused and bonded to each other at a temperature of 350° C. or lower.

In order to fuse and join these copper fine particles together,
(1) Using a hydrogen mixed gas or formic acid vapor to sinter the copper fine particles, the cuprite layer on the surface of the copper fine particles is reduced to copper (Patent Document 1, Patent Document 2),
(2) Handling the copper particles is carried out under an inert gas atmosphere to prevent the formation of a cuprite layer;
(3) Reducing the metal complex to copper using thermal decomposition (Patent Document 3),
(4) A method of preventing the formation of a cuprite layer on the surface of copper fine particles by coating the copper fine particles with a noble metal (Patent Document 4)
It has been known.

Patent No. 6544840 JP2015-214722A JP2017-124986A Japanese Patent Application Publication No. 2007-227156

Conventional copper fine particles with oxidation resistance are only defined by the type of protective agent, average particle size, crystallite size, etc. of the metal fine particles, and the degree of oxidation of the copper fine particles and the relationship between oxidation of the copper fine particles and bonding strength are limited. Nothing was known about the relationship, that is, the degree of oxidation of copper fine particles and the relationship between oxidation of copper fine particles and bonding strength.

Furthermore, the peak intensity ratio [Cu ₂ O (111)/Cu (111)] between the surface index Cu ₂ O (111) and Cu (111) determined by X-ray diffraction, or/and the surface index CuO (111) determined by X-ray diffraction. It is not known that the peak intensity ratio [CuO(111)/Cu(111)] in Cu(111) and Cu(111) affects the bonding strength when copper fine particles are used in bonding members, and these are not specified. Copper fine particles that exhibit good bonding strength by doing so have also not been known.
Further, when the particle size is 100 nm or more, it is difficult to fuse or join at 350° C. or lower due to a decrease in the surface energy of the particles.

The problem to be solved by the present invention is to provide copper/copper oxide fine particles that can be fused and joined by low-temperature sintering.

The present invention relates to copper fine particles or a copper fine particle dispersion used for bonding with metal.
The present invention will be specifically described below.

(1) Copper fine particles having an average primary particle diameter (D _TEM ) of less than 100 nm,
The value obtained by dividing the peak intensity value of the plane index (111) plane of Cu ₂ O by the peak intensity value of the plane index (111) plane of Cu obtained in X-ray diffraction using the Kα ray of Cu as a radiation source is Copper/copper oxide fine particles having a particle size of 0.008 or more and 0.3 or less.

(2) Copper fine particles having an average primary particle diameter (D _TEM ) of less than 100 nm,
The value obtained by dividing the peak intensity value of the plane index (111) plane of CuO by the peak intensity value of the plane index (111) plane of Cu obtained by X-ray diffraction using the Kα ray of Cu as a radiation source is 0. Copper/copper oxide fine particles having a particle size of 0.005 or more and 0.03 or less.

(3) The crystallite diameter (D _{x (111)} ) at the plane index (111) of Cu obtained by X-ray diffraction using the Kα ray of Cu as a radiation source is 50 nm or less (1) or (2) Copper/copper oxide fine particles according to any of the above.

(4) Copper/copper oxide fine particles according to any one of (1) to (3);
A compound having at least one functional group selected from among an amino group, a carbonyl group, a thiol group, a thioether group, and a phosphoric acid group and having a molecular weight of 1000 or more;
A conductive material or a conductive pillar using a copper/copper oxide fine particle dispersion characterized by comprising:

(5) A conductive material or conductive pillar obtained by sintering the copper/copper oxide fine particles described in any one of (1) to (4).

(6) An electronic device comprising the conductive material or conductive pillar described in (5).

(7) The method described in (1), which comprises the step of continuously or intermittently exposing copper fine particles produced in an atmosphere with an oxygen concentration of less than 1% to an atmosphere with an oxygen concentration of 200 ppm or more for a period of 1 minute to 12 hours. Method for producing copper/copper oxide fine particles.

According to the present invention, copper fine particles having an average primary particle diameter (D _TEM ) of less than 100 nm have a surface index (111) of Cu ₂ O obtained by X-ray diffraction using Cu Kα rays as a radiation source. Copper/copper oxide fine particles, which are characterized in that the value obtained by dividing the peak strength value of the plane by the peak strength value of the plane with a plane index (111) of Cu, is 0.008 or more and 0.3 or less as the main bonding agent. When used as a bonding material, copper/copper oxide can bond multiple metal members to each other under no-pressure conditions and at low temperatures below 250°C, and can also be fused and bonded by low-temperature sintering. Microparticles can be provided.

TEM image of copper/copper oxide fine particles synthesized according to Example 1 TEM image of copper/copper oxide fine particles synthesized according to Example 1 Powder X-ray diffraction image of copper/copper oxide fine particles

The present invention will be explained in detail below. Here, the unit "%" is "mass % concentration" unless otherwise specified.

<Copper/copper oxide fine particles>
The copper/copper oxide fine particles according to the present invention will be explained in detail below.

The metal species of the metal fine particles according to the present invention is copper. Copper has excellent safety during production, raw material cost, anti-migration properties, and dispersion stability of dispersions.

<Average primary particle diameter ( _DTEM )>
Copper/copper oxide fine particles having an average primary particle diameter (D _TEM ) of 100 nm or less are suitable as a bonding material because fusion progresses at a temperature of 350° C. or less and they can be bulk-formed. The copper/copper oxide fine particles according to the present invention may contain gold, silver, nickel, or an alloy thereof in addition to copper and copper oxide, as long as the object of the invention is not impaired.

The average primary particle diameter can be calculated by transmission electron microscopy (TEM) observation. That is, in this specification, the average primary particle diameter of metal fine particles is calculated by taking a photograph of a sample using a transmission electron microscope (TEM) and analyzing the image.

The prepared copper/copper oxide fine particles are diluted with a good solvent to an arbitrary concentration, and the diluted solution is cast onto a carbon film-coated grid and dried to provide a specimen for observation with a transmission electron microscope (TEM).
The average primary particle diameter is a value calculated by randomly extracting 200 fine particles from the obtained TEM image, determining the area of each particle, and using the particle diameter when converted to a perfect sphere as the number standard. Particles in which two particles overlap are excluded from the randomly sampled particles. When a large number of particles are aggregated, either in contact or by secondary aggregation, the particles constituting the aggregate are treated as independent particles. For example, when five primary particles contact or secondary aggregate to form one set, each of the five particles forming the set becomes a target for calculating the average primary particle diameter of the metal fine particles.
Moreover, the value before sintering is adopted as the average primary particle diameter. That is, the value before fusion occurs due to sintering is adopted.

<X-ray diffraction>
The composition of the particle structure of the copper/copper oxide fine particles according to the present invention is determined by the intensity value of the peak attributed to the Cu ₂ O (111) plane and the intensity value of the peak attributed to the Cu (111) plane in X-ray diffraction. The ratio, that is, the value obtained by dividing the peak intensity value of the plane index (111) plane of Cu ₂ O by the peak intensity value of the plane index (111) plane of Cu, can be used as an index, and the index is 0.3. It is preferably at most 0.18, more preferably at most 0.18.

When the metal species is copper, it originates from the (111) plane around 2θ = 43.3°, and when the metal species is copper (I) oxide, it originates from the (111) plane around 2θ = 36.4°. peaks can be observed.
It is known that the (111) plane has a higher atomic density than other planes and exhibits high reactivity. Copper fine particles with many (111) planes (higher abundance ratio than other planes) are easily fused at relatively low temperatures and exhibit good bonding strength with other metals when used as a bonding material. can do.

Furthermore, the composition of the particle structure of the copper/copper oxide fine particles according to the present invention is determined by the intensity value of the peak attributed to the copper (II) (111) plane in X-ray diffraction and the peak attributed to the copper (111) plane. The ratio to the intensity value of the plane index (111) plane of copper (II) oxide, that is, the value obtained by dividing the peak intensity value of the plane index (111) plane of copper, can be used as an index, The index is preferably 0.03 or less, more preferably 0.007 or less.

<Crystallite diameter ( _DX )>
The size of the copper crystallites in the copper/copper oxide fine particles is determined by the Scherrer equation. Similar to the average primary particle diameter, the smaller the crystallite diameter _DX in each lattice plane, the more likely fusion will occur at low temperatures.

Specifically, among the diffraction lines obtained by X-ray diffraction measurement, the diffraction line with the highest intensity (Cu (111), 2θ = 43.3°) and the diffraction line with the second highest intensity (Cu (200)) , 2θ=50.4°) and the third highest intensity diffraction line (Cu(220), 2θ=74.1°), the crystallite diameter D _X can be determined, respectively. Among the three crystallite diameters, it is preferable that the crystallite diameter D _{X (111)} at Miller index (111) is 50 nm or less. In particular, it is preferable that each crystallite diameter is 50 nm or less. Further, more preferably, D _{X (111)} is 20 nm or less.

<Protective agent>
The protective agent protects the surface of the copper/copper oxide fine particles, prevents agglomeration of the copper/copper oxide fine particles, and stably disperses the copper/copper oxide fine particles in the dispersion medium. The protective agent is not particularly limited as long as it is a compound that has a functional group and/or molecular structure that has affinity with the copper/copper oxide fine particles and the dispersion medium. For example, a compound having the functional group and molecular structure shown below is used. be able to.
The protective agent used can be used regardless of its molecular weight, and high conductivity and dispersion stability can be imparted to the copper/copper oxide fine particles by designing the protective agent according to the desired physical properties and characteristics. is possible.

By selecting a protective agent according to various purposes, the characteristics of the copper/copper oxide fine particles can be freely changed. When using a high molecular weight protective agent, various properties can be expressed by changing the number and type of functional groups in the compound. When using a low molecular weight protective agent, various properties can be expressed by using two or more kinds of compounds together.

Specific examples of the functional group contained in the protective agent include a thiol group, a thioether group, a carboxy group, an amino group, a hydroxy group, a phosphoric acid group, a phosphoric ester group, a sulfonic acid group, and an aromatic group. By using a protective agent having these functional groups, dispersion stability can be added to the fine particles.
Among them, it is preferable to use a protective agent having a thioether group, a phosphate ester group, an amino group, or a hydroxyl group, which can add high conductivity that exhibits a lower volume resistivity when sintered at a low temperature.

When a high molecular weight protective agent is used as the protective agent, any molecular structure that has affinity with the dispersion medium can be adopted as the selectable molecular structure. For example, when the dispersion medium is a polar solvent such as alcohol or water, an organic compound containing a polyethylene oxide structure having 8 to 200 carbon atoms can be suitably used; Organic compounds containing the above can be used more preferably.
Since the polyethylene oxide moiety of the protective agent has excellent affinity with alcoholic solvents having a boiling point of 250° C. or lower, aggregation of metal fine particles can be strongly suppressed and metal fine particles can be highly dispersed. This results in a state in which metal fine particles are packed at a high density, and voids caused by decomposition and removal of the protective agent and solvent by heat treatment do not occur, making it possible to fill the metal particles at a high density.

Examples of metal fine particles (composite of an organic compound and metal fine particles) containing an organic compound containing a polyethylene oxide structure having a carbon number of 8 to 200 as a protective agent include Japanese Patent No. 4784847, Japanese Patent Application Laid-open No. 2013-60637, or a patent. Examples include metal fine particles described in Japanese Patent No. 5077728, and can be synthesized by the methods described therein. These are characterized by the fact that the thioether type (R-S-R') compound has an appropriate affinity adsorption effect on the surface of copper/copper oxide fine particles and rapid desorption properties upon heating. It can also be used as a protective agent that imparts low-temperature fusion properties to copper oxide fine particles.

As another example, among the polymer compounds having a thioether group described in JP-A No. 2010-209421, metal fine particles composited with a polymer compound having a polyethylene oxide moiety having 8 to 200 carbon atoms, and furthermore, Among the polymer compounds having a thioether group and a phosphoric acid ester group described in Japanese Patent No. 4,697,356, fine metal particles composited with a polymer compound having a polyethylene oxide moiety having 8 to 200 carbon atoms can be mentioned. These polymer compounds containing a polyethylene oxide structure can be produced according to the methods described in these publications.
These phosphate ester type organic compounds containing a polyethylene oxide structure have a thioether group and a phosphate ester group, and by having these groups, they have an appropriate affinity adsorption effect on the surface of copper/copper oxide fine particles. , it is possible to add rapid desorption properties by heating.

When using a low molecular weight compound having a carboxyl group as a protective agent, the following substances can be used as specific examples.
For example, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, behenic acid, oleic acid, Palmitoleic acid, eicosenoic acid, erucic acid, nervonic acid, ricinoleic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, diglycolic acid, maleic acid , itaconic acid, benzoic acid, N-oleylsarcosine, N-carbobenzoxy-4-aminobutyric acid, p-coumaric acid, 3-(4-hydroxyphenyl)propionic acid, 3-hydroxymyristic acid, 2-hydroxypalmitic acid , 2-hydroxyicosanoic acid, 2-hydroxydocosanoic acid, 2-hydroxytricosanoic acid, 2-hydroxytetracosanoic acid, 3-hydroxycaproic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxy Decanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, 3-hydroxyheptadecanoic acid, 3-hydroxyoctadecanoic acid, 15-hydroxy Pentadecanoic acid, 17-hydroxyheptadecanoic acid, 15-hydroxypentadecanoic acid, 17-hydroxyheptadecanoic acid, lauroylsarcosine, 6-aminohexanoic acid, 2-benzoylbenzoic acid, 12-hydroxystearic acid, 12-hydroxypentadecanoic acid, 2-hydroxypalmitic acid, 3-hydroxydecanoic acid, 15-hydroxypentadecanoic acid, lauroylsarcosine, 6-aminohexanoic acid, N-(tert-butoxycarbonyl)-6-aminohexanoic acid, [2-(2-methoxyethoxy) ) ethoxy]acetic acid, N-carbobenzoxy-β-alanine, and the like. Further, as long as the compound forms a multimer, these multimers from dimers and trimers to hexamers may be used. Furthermore, one or more carboxylic acids may be used in combination in any proportion.

When using a low molecular weight compound having an amino group as a protecting agent, the following substances can be used as specific examples.
For example, 2-methoxyethylamine, 2-ethoxyethylamine, 2-isopropoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 3-isopropoxypropylamine, 3-(2-ethylhexyloxy)propylamine, N- Methylethylenediamine, N-ethylethylenediamine, N-isopropylethylenediamine, N-methyl-1,3-propanediamine, 3-isopropylaminopropylamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dimethyl -1,3-propanediamine, N,N-diethyl-1,3-propanediamine, N-(3-aminopropyl)morpholine, N-(tert-butoxycarbonyl)-1,4-diaminobutane, N-( tert-butoxycarbonyl)-1,5-diaminopentane, N-(tert-butoxycarbonyl)-1,6-diaminohexane, 2-(aminoethylamino)ethanol, 2-(aminoethoxy)ethanol, 3-(2 Examples include -hydroxyethylamino)propylamine, N-(2-hydroxypropyl)ethylenediamine, and N-(3-aminopropyl)diethanolamine. In addition, secondary amine compounds or tertiary amine compounds can also be used as amines.

The concentration of the protective agent in the copper/copper oxide fine particle paste is not particularly limited, but the concentration of the protective agent in the copper/copper oxide fine particle paste is determined from the viewpoint of ease of fusion of the copper/copper oxide fine particles during sintering, and improvement of conductivity and bonding strength. The content is preferably 15% or less, more preferably 10% or less of the total amount.

<Dispersion medium>
Water or a solvent can be added to the copper/copper oxide fine particles according to the present invention as a dispersion medium within a range that does not impair the effects of the invention. The dispersion medium can be added for the purpose of imparting wettability to the base material and adjusting the concentration of copper/copper oxide fine particles in the paste. As the dispersion medium that can be used in the present invention, it is desirable that the dispersion medium does not remain inside the pillar after sintering, and it is preferable to use a compound or mixture with a boiling point of 250° C. or lower.

The dispersion medium is not particularly limited as long as it is a compound having a boiling point of 250° C. or lower, and water and/or an organic solvent can be used as the dispersion medium. It is preferable to use a good dispersion medium that does not cause the copper/copper oxide fine particles to aggregate as the dispersion medium in order to produce a paste having a uniform particle size.

Examples of solvents that can be suitably used are listed below.

For example, as a solvent having a hydroxyl group, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, isobutanol, sec-butanol, tert-butanol, amyl alcohol, tert-amyl alcohol, 1-hexanol, cyclohexanol, benzyl Alcohol, 2-ethyl-1-butanol, 1-heptanol, 1-octanol, 4-methyl-2-pentanol, neopentyl glycol, propionitrile, ethylene glycol, propylene glycol, 1,3-butanediol, 1, 4-butanediol, 2,3-butanediol, isobutylene glycol, 2,2-dimethyl-1,3-butanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, Diethylene glycol, triethylene glycol, tetraethylene glycol, 1,5-pentanediol, 2,4-pentanediol, dipropylene glycol, 2,5-hexanediol, glycerin, diethylene glycol monobutyl ether, ethylene glycol monobenzyl ether, ethylene glycol mono Examples include ethyl ether, ethylene glycol monomethyl ether, ethylene glycol monophenyl ether, propylene glycol dimethyl ether, polyethylene glycol, polypropylene glycol, and ethyl lactate. Among them, 1-butanol, ethanol, 1-propanol, ethylene glycol, and glycerin can be preferably used.

Other organic solvents that do not contain hydroxyl groups include acetone, cyclopentanone, cyclohexanone, acetophenone, acrylonitrile, propionitrile, n-butyronitrile, isobutyronitrile, γ-butyrolactone, ε-caprolactone, propiolactone, carbonic acid-2 , 3-butylene, ethylene carbonate, 1,2-ethylene carbonate, dimethyl carbonate, ethylene carbonate, dimethyl malonate, methyl benzoate, methyl salicylate, ethylene glycol diacetate, ε-caprolactam, dimethyl sulfoxide, N,N-dimethylformamide , N,N-dimethylacetamide, N-methylformamide, N-methylacetamide, N-ethylacetamide, N,N-diethylformamide, formamide, pyrrolidine, 1-methyl-2-pyrrolidinone, hexamethylphosphate triamide, naphthalene, Kerosene or the like can be used.

(Method for measuring boiling point of mixture)
When a mixed solvent consisting of multiple solvents is used as a dispersion medium, the boiling point of the mixed solvent shall be determined according to the "Equilibrium reflux boiling point test method" specified in JIS K2233-1989 "Non-mineral oil-based brake fluid for automobiles" 7.1. can be measured.

<Method for producing copper/copper oxide fine particles>
As a method for producing copper/copper oxide fine particles, any conventionally known method can be employed. For example, wet methods such as chemical reduction, thermal decomposition, and electrochemical methods, and dry methods such as evaporation in gas and sputtering can be used.
Copper/copper oxide fine particles according to the present invention were produced by reducing copper ions with a reducing agent in a polar solvent. Furthermore, by allowing a protective agent to coexist during synthesis, the outermost surface of the reduced copper fine particles can be covered with the protective agent. The protective agent that covers the surface of the copper fine particles suppresses the growth and aggregation of the fine particles, making it possible to produce fine particles having a uniform particle size.

According to the method of producing copper/copper oxide fine particles by reducing copper ions with a reducing agent in a polar solvent and in the presence of a protective agent in a reaction vessel filled with an inert gas, X-ray diffraction The ratio of the intensity value of the peak attributed to the Cu ₂ O (111) plane to the intensity value of the peak attributed to the Cu (111) plane, that is, the peak intensity value of the plane index (111) plane of Cu ₂ O , the value divided by the peak intensity value of the plane index (111) plane of Cu is 0.3 or less, or/and the peak intensity value of the plane index (111) plane of copper (II) oxide is divided by the plane index (111) plane of copper. Copper/copper oxide fine particles having a value divided by the surface peak intensity value of 0.03 or less can be obtained.

As the inert gas species used during the production of copper/copper oxide fine particles, for example, nitrogen, argon, etc. can be used, and it is preferable that the oxygen concentration in the reaction vessel is less than 1%, particularly preferably 0. Less than .1%.
If the proportion of cuprous oxide or copper oxide increases, the fusion between copper particles will be inhibited, so that not only sufficient bonding strength will not be exhibited, but also high electrical conductivity will not be exhibited. Furthermore, since the surface of the copper fine particles cannot be uniformly covered with the protective agent, aggregation and poor dispersion occur.

In order to explain the effects of the present invention, a method for producing a paste will be described when an organic compound containing a polyethylene oxide structure having 8 to 200 carbon atoms is used as a protective agent.
A copper fine particle dispersion in which an organic compound containing a polyethylene oxide structure having a carbon number of 8 to 200 is composite is produced by a process of mixing a divalent copper ion compound with a solvent in the presence of a thioether type organic compound, and reducing the copper ion. It can be easily manufactured by combining the steps.

As the divalent copper ion compound, commonly available copper compounds can be used, and sulfates, nitrates, carboxylates, carbonates, chlorides, acetylacetonate complexes, etc. can be used. When obtaining a composite with zero-valent copper fine particles, it may be manufactured from a divalent compound or a monovalent compound, and may contain water or crystal water.
Specifically, divalent copper ion compounds include CuSO ₄ , Cu(NO ₃ ) ₂ , Cu(OAc) ₂ , Cu(CH ₃ CH ₂ COO) ₂ , Cu(HCOO) ₂ , CuCO ₃ , CuCl ₂ , _{Cu2O , C5H7CuO2} , hydrates thereof, _and the like can be used. In addition, basic salts obtained by heating the above salts or exposing them to a basic atmosphere, such as Cu(OAc) _2.CuO , Cu(OAc) _2.2CuO , Cu ₂ Cl(OH) ₃ , etc., are preferably used. Can be used.
These basic salts may be prepared within the reaction system, or those prepared separately outside the reaction system may be used. Further, a general method of adding ammonia or an amine compound to form a complex, ensuring solubility, and then performing reduction can also be applied.

These copper ion compounds are dissolved or mixed in a solvent in which a thioether type organic compound has been dissolved or dispersed in advance. Suitable solvents that can be used at this time include alcohols such as ethanol, ethylene glycol, diethylene glycol, and glycerin, polar solvents such as water, acetone, and mixtures thereof, depending on the structure of the organic compound used. Can be used. Among these, a water-ethylene glycol mixture is particularly preferred.

The concentration of the thioether type organic compound in various solvents is preferably adjusted to a range of 0.3 to 10% from the viewpoint of easy control of the subsequent reduction reaction.

The copper ion compound is added all at once or in portions to the solvent prepared above and mixed. When using a poorly soluble solvent, it may be dissolved in a small amount of a good solvent in advance and added to the solvent.

The mixing ratio of the thioether type organic compound and the copper ion compound to be mixed can be appropriately selected depending on the protective ability of the thioether type organic compound in the reaction solvent. The thioether type organic compound is prepared in a range of 1 mmol to 30 mmol per mol of the copper ion compound, and preferably used in a range of 15 to 30 mmol. Here, the same procedure can be carried out using a phosphate ester type organic compound containing a polyethylene oxide structure, and the amount of the organic compound used per 1 mol of the copper ion compound is also the same as above.

Subsequently, a reduction reaction of copper ions is carried out using various reducing agents. Reducing agents include hydrazine compounds, hydroxylamine and its derivatives, metal hydrides, phosphinates, aldehydes, enediols, hydroxyketones, etc., which allow the reduction reaction of copper to proceed at temperatures ranging from ice-cold temperatures to 80°C or less. Therefore, it can be suitably used.

Reducing agents such as hydrazine hydrate, asymmetric dimethylhydrazine, hydroxylamine aqueous solution, and sodium borohydride are suitable for reducing copper ions. These reducing agents can reduce a copper compound to zero valence, and are suitable for producing a composite of an organic compound and copper fine particles by converting divalent and monovalent copper compounds into reduced copper.

The conditions for the reduction reaction can be appropriately set depending on the copper compound used as a raw material, the type of reducing agent, the presence or absence of complexing, the solvent, and the type of thioether type organic compound. For example, when copper (II) acetate is reduced with sodium borohydride in an aqueous solvent, zero-valent copper fine particles can be prepared even at a temperature comparable to ice cooling. On the other hand, when hydrazine is used, the reaction is slow at room temperature, and a smooth reduction reaction occurs only after heating to about 60°C. Further, when reducing copper acetate with an ethylene glycol/water system, a reaction time of about 2 hours is required at 60°C. As a result of these reduction reactions, a reaction mixture containing a complex of an organic compound and copper fine particles is obtained.

Due to the effect of the protective agent, the copper fine particles prepared in this way can be dispersed as highly as before drying even when the water is completely removed to form a dry powder and then dispersed in a solvent again. be.

After the reduction reaction, a so-called purification step for removing metal compound residues, reducing reagent residues, excess organic compounds containing a polyethylene oxide structure, etc. can be provided as necessary. The process of purifying the copper fine particles can be carried out by known methods such as reprecipitation, centrifugal sedimentation, and ultrafiltration. Furthermore, when using a method such as reprecipitation or centrifugal sedimentation, the above-mentioned impurities present in excess can be washed away by washing the reaction mixture containing copper fine particles with water, ethanol, acetone, etc.

If excessive reducing reagent residues, excess organic compounds containing polyethylene oxide structures, etc. are removed during the dispersion purification process, the amount of reducing agent and antioxidant present in the copper particles decreases, causing the copper particles to become oxidized. It becomes easier. Therefore, the refined copper particles are preferably handled in an environment with an oxygen concentration of less than 0.1%, and more preferably in an environment with an oxygen concentration of less than 200 ppm.

The copper/copper oxide fine particles according to the present invention may optionally contain a binder component such as a resin, an anti-drying agent, an antifoaming agent, an adhesion agent to the base material, as long as the effects of the present invention are not impaired. Antioxidants, various catalysts for promoting film formation, various surfactants such as silicone surfactants and fluorine surfactants, leveling agents, mold release promoters, etc. can be added as auxiliaries.

A flux component can be added to the copper/copper oxide fine particles according to the present invention within a range that does not impair the effects of the present invention. By adding a flux component, it can be used with further reducing power. As the flux, it is possible to use a commonly used flux, and there is no particular restriction on the flux. This flux may contain commonly used rosin, activator, thixotropic agent, etc.

The copper/copper oxide fine particles according to the present invention can be given suitability as a copper/copper oxide fine particle paste by adding a solvent that is easy to use as a filling paste to the prepared metal fine particles or by exchanging the medium. .

<Metal fine particle content and its calculation>
The metal fine particle content in the copper/copper oxide fine particle paste can be calculated by thermogravimetric analysis (TG/DTA). The copper/copper oxide fine particle paste was precisely weighed in an aluminum pan for thermogravimetric analysis, placed on a differential thermogravimetric analyzer, and heated at a rate of 10°C per minute from room temperature to 600°C under an inert gas atmosphere. The metal fine particle content was calculated based on the weight reduction rate.
There is no need to set any particular restrictions on the content of metal fine particles, and any concentration can be determined within a range that does not impair the dispersion stability of the fine particles. Further, the metal fine particle content of the copper/copper oxide fine particle paste can be adjusted to any concentration depending on the intended use and purpose.

The copper/copper oxide fine particle paste can be used for conductive wiring materials and bonding materials. In addition, it can also be used for mounting various electronic components and devices.

<Sintering of copper/copper oxide fine particles>
When the copper/copper oxide fine particles according to the present invention are heated to a temperature at which the metal fine particles are fused, fusion occurs between the particles, and conductivity is developed. The temperature at which the metal fine particles are fused differs depending on the type of metal, protective agent, and solvent used. The temperature at which fine metal particles fuse can be estimated using thermogravimetric analysis (TG-DTA) or differential scanning calorimetry (DSC).

The firing temperature and firing time are not particularly limited as long as sufficient values can be obtained for the conductivity and bonding strength of the pillars, but preferably the firing temperature is 150 to 350°C and the firing time is 1 to 350°C. The duration is 60 minutes. More preferably, the firing temperature is in the range of 200 to 250° C. or less and the firing time is in the range of 5 to 15 minutes. If the paste according to the present invention is used, sufficient performance can be exhibited even when firing is performed for a short time.
Further, if necessary, firing can be performed using a temperature profile, such as performing preliminary firing at a low temperature to volatilize the solvent, followed by main firing at a temperature in the range of 150 to 350°C.
The firing method for sintering the metal fine particles is not particularly limited as long as the metal fine particles are fused together, and baking methods using heat such as a hot plate or hot air oven, visible light, infrared light, or laser light can be used. Plasma treatments including irradiation, flash lamps, and hydrogen gas may also be used.

There are no particular restrictions on the type of gas used during sintering. Sintering is possible not only in an inert gas environment such as nitrogen gas or argon gas, but also in the presence of oxygen.

By using the copper fine particles of this embodiment, conductive structures such as wiring and electrodes can be formed with sufficiently low resistivity. Therefore, the metal fine particles of this embodiment can be used for thin film transistors, integrated circuits including thin film transistors, touch panels, RFID, flexible displays, organic EL, circuit boards, sensor devices, conductive pillars, conductive materials for flip-chip mounting, power semiconductors, etc. It can be suitably used for manufacturing various electronic components such as bonding materials.

Hereinafter, the present invention will be specifically explained with reference to Examples. Here, "%" is "mass percent concentration" unless otherwise specified.

(Synthesis example 1)
<Preparation of copper fine particle dispersion>
(Synthesis of dispersion)
Copper (II) acetate monohydrate (3.00 g, 15.0 mmol) (manufactured by Tokyo Kasei Kogyo Co., Ltd.), ethyl 3-(3-(methoxy(polyethoxy)ethoxy)-2-hydroxypropylsulfanyl)propionate [polyethylene glycol In a mixture consisting of methyl glycidyl ether (addition compound of ethyl 3-mercaptopropionate to polyethylene glycol chain molecular weight 2000 (carbon number 91)) (0.451 g) and ethylene glycol (10 mL) (manufactured by Kanto Kagaku Co., Ltd.) The mixture was heated while blowing nitrogen at a flow rate of 50 mL/min, and degassed by stirring at 125° C. for 2 hours. This mixture was returned to room temperature, and a solution of hydrazine hydrate (1.50 g, 30.0 mmol) (manufactured by Tokyo Chemical Industry Co., Ltd.) diluted with 7 mL of water was added dropwise using a syringe pump. Approximately 1/4 of the amount was added dropwise over 2 hours, the addition was stopped once, and after stirring for 2 hours to confirm that the foaming had subsided, the remaining amount was further added dropwise over 1 hour. The resulting brown solution was heated to 60° C. and further stirred for 2 hours to terminate the reduction reaction. The synthesis of the dispersion was carried out in a nitrogen gas atmosphere, and the oxygen concentration was less than 0.1%.

(Purification of dispersion)
Subsequently, this reaction mixture was circulated through a hollow fiber ultrafiltration membrane module manufactured by Daisen Membrane Systems (HIT-1-FUS1582, 145 cm ² , molecular weight cut off 150,000), and the amount of filtrate exuded was the same as that of the filtrate. While adding 0.1% aqueous hydrazine hydrate solution, the filtrate from the ultrafiltration module was circulated until the volume was about 500 mL for purification. When the supply of the 0.1% hydrazine hydrate aqueous solution was stopped and the solution was concentrated by ultrafiltration, an aqueous dispersion of a complex of an organic compound containing 2.85 g of thioether and copper/copper oxide fine particles was obtained. . The nonvolatile content in the aqueous dispersion was 16%.

(Preparation of dispersion)
5 mL of the above aqueous dispersion was sealed in each 50 mL three-necked flask, and while heating to 40°C using a water bath, water was completely removed by flowing nitrogen at a flow rate of 5 mL/min under reduced pressure. , 1.0 g of dry powder of copper/copper oxide fine particles was obtained.
The dispersion preparation process was performed in an environment with an oxygen concentration of less than 200 ppm.

<Measurement of weight loss rate by thermogravimetric analysis (TG-DTA)>
Approximately 25 mg of the synthesized dry powder of copper/copper oxide particles was precisely weighed on an aluminum pan for thermogravimetric analysis, placed on an EXSTAR TG/DTA6300 differential thermogravimetric analyzer (manufactured by SII Nanotechnology Co., Ltd.), and placed in a nitrogen gas atmosphere. Below, the temperature was raised from room temperature to 600°C at a rate of 10°C per minute, and the weight loss rate from 100°C to 600°C was measured. The organic matter content was calculated from the weight loss rate.

From the weight loss determined by TG-DTA measurement, it was confirmed that the obtained copper/copper oxide fine particle powder contained 3% of an organic substance containing a polyethylene oxide structure.

(Example 1)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 3 minutes while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was estimated by transmission electron microscopy (TEM) observation. The prepared metal fine particles were diluted 100 times with a good solvent (water, terpineol, 1-butanol, or ethylene glycol), and the diluted solution was cast onto a carbon membrane-coated grid, dried, and placed under a transmission electron microscope (equipment). : TEMJEM-1400 (manufactured by JEOL), acceleration voltage: 120 kV).
The average primary particle diameter was calculated by randomly extracting 200 fine particles from the obtained TEM image, determining the area of each particle, and using the particle diameter when converted to a perfect sphere as the number standard.

When the obtained copper/copper oxide fine particles were observed using a transmission electron microscope (TEM), the average primary particle diameter of the obtained copper/copper oxide fine particles was 46 nm. The obtained electron micrographs are shown in FIGS. 1 and 2.

<X-ray diffraction analysis>
A powder X-ray diffractometer (SmartLab, manufactured by Rigaku) was used. The measurement conditions were 2θ/θ method 2θ=30 to 70deg. step=0.02deg. speed=2.0deg/min. And so. Kα rays generated in a Cu tube at 40 kV and 30 mA were used.

1.5 g of the copper/copper oxide fine particle paste prepared in Synthesis Example 1 was vacuum dried. The powder of copper/copper oxide fine particles obtained by drying was subjected to powder X-ray diffraction analysis under the above conditions. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The value obtained by dividing the peak intensity value derived from the Cu ₂ O (111) plane by the peak intensity value derived from the Cu (111) plane obtained by powder X-ray diffraction is defined as the peak intensity ratio (Cu ₂ O / Cu). I calculated it. Further, a value obtained by dividing the peak intensity value originating from the CuO(111) plane by the peak intensity value originating from the Cu(111) plane was calculated as the peak intensity ratio (CuO/Cu).
The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern of the metal powder using the Scherrer equation below was 14 nm.
D=Kλ/(βcosθ) (1)
In the above formula, D represents the crystallite size (Å), K represents the Scherrer constant (0.9 is used), and λ represents the wavelength of the X-ray source (1.540562 Å for CuKα1). , β represents the full width at half maximum (FWHM) of the diffraction peak in the XRD pattern, and θ represents the diffraction angle (degree).

<Measurement of bonding strength>
The measurement of bonding strength was carried out under the conditions described below. Regarding conditions not described below, measurements were performed in accordance with the method described in JIS Z-03918-5:2003 "Lead-free solder test method". In this measurement, shear force is applied to the joint test piece to measure the joint strength. This measurement is also referred to as a shear strength test.

The method for preparing the test piece used for joint strength measurement will be explained. The test piece is produced by joining a cylindrical test material to a copper test material (base material).
A copper plate (C1020) with a thickness of 1 mm and a side of 20 mm was used as the test material (base material).
Copper (C1020) having a cylindrical shape (diameter 3 mm, height 2 mm) was used as the test material to be bonded to the base material.
In a nitrogen gas atmosphere, the copper/copper oxide fine particle paste obtained by the method described in Example 1 was applied onto the base material to a thickness of 30 μm, and then the base material and the cylindrical test material were joined. I let it happen.
The obtained joined body was fired at 250° C. for 10 minutes in a nitrogen gas atmosphere to prepare a test piece.
The bonding strength of the prepared test piece was measured by a die shear test. The bonding strength by die shear test was measured using a die shear tester (manufactured by Nordson) at a shear speed of 200 μm/s.

For the bonding strength measurement, five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
The bonding strength was evaluated. The evaluation criteria were as follows.
◎: The highest value of shear strength of the produced conductive pillar was 10 MPa or more, indicating that the bonding strength was very good.
○: The highest value of the shear strength of the produced conductive pillar was 5 MPa or more, indicating that the bonding strength was good.
Δ: The highest value of the shear strength of the produced conductive pillar was less than 5 MPa, indicating that it was possible to join.
×: Indicates that the maximum value of the shear strength of the produced conductive pillar is 0 MPa or that it is not bonded.
The obtained evaluation results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
The volume resistivity was measured using a low resistivity meter Lorester EP (manufactured by Mitsubishi Chemical Corporation) using a four-terminal measurement method.
A coating film was prepared by spin coating a copper/copper oxide fine particle paste on a 0.7 mm thick alkali-free glass substrate (40 mm x 50 mm).
A sintered film was obtained by baking the obtained coating film at 250° C. for 10 minutes in a nitrogen gas atmosphere. The rotation speed during spin coating was adjusted so that the thickness of the sintered film was 1 μm.
Table 1 shows the volume resistivity of the resulting coating film.

<Evaluation of coating film conductivity>
The conductivity of the sintered film produced by the above method was evaluated. The evaluation criteria were as follows.
◎: The volume resistivity of the prepared coating film was 10 μΩ·cm or less, indicating that it had a very good volume resistivity.
○: The volume resistivity of the prepared coating film was 50 μΩ·cm or less, indicating that it had a good volume resistivity.
Δ: The volume resistivity of the produced coating film was less than 500 μΩ·cm, indicating that it had a good volume resistivity.
×: The volume resistivity of the produced coating film was 500 μΩ·cm or more, indicating that the volume resistivity was low.
The obtained evaluation results are shown in Table 1.

(Example 2)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 60 minutes while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 46 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern using the same method as described in Example 1 was 15 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 180 minutes while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 47 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern using the same method as described in Example 1 was 15 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 4)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 6 hours while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 48 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern using the same method as described in Example 1 was 14 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 9 hours while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 47 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern using the same method as described in Example 1 was 14 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 6)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 12 hours while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 49 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern using the same method as described in Example 1 was 14 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 1)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 24 hours while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 51 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern in the same manner as in Example 1 was 13 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 2)
<Preparation of copper/copper oxide fine particle paste>
Ethylene glycol bubbled with nitrogen was added to the dry powder of copper/copper oxide fine particles obtained by the method described in Synthesis Example 1 so that the metal fine particle content was 70%. After the addition, the mixture was exposed to air for 72 hours while being kneaded in the atmosphere to produce a copper/copper oxide fine particle paste.
The physical properties of the produced copper/copper oxide fine particle paste were evaluated by the method described below.

<Measurement of average primary particle diameter>
The average primary particle diameter was measured using an electron microscope in the same manner as in Example 1. The average primary particle diameter of the obtained copper/copper oxide fine particles was 51 nm.

<X-ray diffraction analysis>
Powder X-ray diffraction analysis was performed on the metal powder obtained by drying the copper/copper oxide fine particle paste in the same manner as in Example 1. The X-ray diffraction image obtained by this analysis is shown in FIG.

<Calculation of peak intensity ratio>
The peak intensity ratio (Cu ₂ O/Cu) and the peak intensity ratio (CuO/Cu) were calculated in the same manner as in the method described in Example 1. The obtained values are shown in Table 1.

<Calculation of crystallite diameter _DX >
The crystallite diameter estimated from the full width at half maximum of the Cu(111) diffraction peak in the powder X-ray diffraction (XRD) pattern using the same method as described in Example 1 was 14 nm.

<Measurement of bonding strength>
The bonding strength was measured using the same method as described in Example 1, in which five test pieces were prepared and the measurement was performed five times. The results are shown in Table 1, with the median value of the obtained values taken as the bonding strength.

<Evaluation of joint strength>
Bonding strength was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Measurement of electrical conductivity of paint film>
Table 1 shows the volume resistivity of the coating film obtained in the same manner as in Example 1.

<Evaluation of conductivity>
The conductivity of the sintered film was evaluated in the same manner as in Example 1. The results are shown in Table 1.

FIG. 3 is a powder XRD image of copper/copper oxide fine particles obtained in each example and comparative example. By exposing the produced copper/copper oxide fine particle paste to the atmosphere, the diffraction peak attributed to the Cu (111) plane of the copper/copper oxide fine particles in the paste decreases, and the diffraction peak attributed to the Cu ₂ O (111) plane decreases. It was found that the diffraction peaks were increasing. Diffraction intensity ratios were calculated for the diffraction peaks obtained by this XRD measurement.

Table 1 shows the measurement results and evaluation results obtained in each example and comparative example. When the Cu ₂ O/Cu peak intensity ratio was 0.3 or less and the CuO/Cu peak intensity ratio was 0.03 or less, a bonding strength of about 1 MPa or more was obtained.
The above results revealed that the copper/copper oxide fine particles having the above-mentioned ratio function as a good intermetallic bonding material in low-temperature sintering at 250°C. Furthermore, it has been revealed that the copper/copper oxide fine particles having the above ratio exhibit good electrical conductivity.

Claims (3)

Copper fine particles having an average primary particle diameter (DTEM) of less than 100 nm,
The value obtained by dividing the peak intensity value of the plane index (111) plane of CuO by the peak intensity value of the plane index (111) plane of Cu obtained by X-ray diffraction using the Kα ray of Cu as a radiation source is 0. Copper/copper oxide fine particles having a particle size of 0.005 or more and 0.03 or less;
A compound having a thiol group or a thioether group and a molecular weight of 1000 or more,
A copper/copper oxide fine particle paste characterized by containing. The copper/oxide particles according to claim 1 , wherein the crystallite diameter (Dx (111)) at the planar index (111) of Cu obtained by X-ray diffraction using the Kα ray of Cu as a radiation source is 50 nm or less;
A compound having a thiol group or a thioether group and a molecular weight of 1000 or more,
A copper/copper oxide fine particle paste characterized by containing. A method for producing a conductive material or a conductive pillar, which comprises heating the copper/copper oxide fine particle paste according to claim 1 or 2 at a temperature in the range of 150°C to 350°C.

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