Silver particles

Abstract

The present invention provides novel silver particles which enable the achievement of excellent adhesion of a sintered body to a copper member in cases where the silver particles are used as a conductive adhesive and the sintered body is obtained by sintering the conductive adhesive in a nitrogen atmosphere, and which enable the sintered body adhered to the copper member to exhibit high mechanical strength (shear strength) in cases where a shear force is applied thereto.　Provided are silver particles in each of which a compound represented by general formula (1) below adheres to the surface of a silver particle. (In general formula (1), R1 represents an alkyl group having 2 to 8 carbon atoms, R2 represents an alkyl group having 1 to 4 carbon atoms, and R3 represents a hydrogen atom, or an alkyl group having 1 to 4 carbon atoms.)

Description

Silver particles

[0001] The present invention relates to silver particles, a conductive adhesive, a sintered body of the conductive adhesive, and an electronic component having the sintered body between members.

[0002] Conductive adhesives, including die bonding agents, are bonding materials used in electronic components such as semiconductors, LEDs, and power semiconductors. Generally, bonding is performed by applying pressure and heat, or by sintering using heat without applying pressure. In recent years, pressureless bonding materials have been developed to simplify and streamline the manufacturing process.

[0003] In recent years, the development of conductive adhesives containing silver particles has progressed. Silver particles have the characteristic of being easily sintered by short-term heat treatment at low temperatures. For example, Patent Document 1 discloses a metal paste prepared by kneading a solid content of silver particles with a solvent, in which the solid content is composed of silver particles containing 30% or more, by particle number, of silver particles with a particle size of 100 to 200 nm, and further, the silver particles constituting the solid content are bonded to an amine compound having a total carbon number of 4 to 8 as a protective agent. This metal paste allows silver particles to be sintered at low temperatures, and is capable of forming a sintered body with low resistance and excellent thermal conductivity.

[0004] JP 2015-159096 A

[0005] Conductive adhesives containing silver particles have silver particles dispersed in a solvent, and can be applied to the surfaces of components (e.g., substrates used in electronic components, semiconductor chips, etc.) and sintered to bond the components together.

[0006] For example, when a conductive adhesive containing silver particles is used in the manufacturing process of components such as substrates and semiconductor chips used in electronic components, the manufacturing process must be carried out in a nitrogen atmosphere to prevent deterioration of the components (for example, deterioration due to heating in the atmosphere). Furthermore, manufacturing in a nitrogen atmosphere has the advantage of allowing the manufacturing process to be carried out in a constant environment.

[0007] Furthermore, when a conductive adhesive containing silver particles is applied to a copper member such as a copper substrate, it is necessary to sinter it in a nitrogen atmosphere, not in an air atmosphere.

[0008] However, when a conventional conductive adhesive containing silver particles is applied to a copper member and sintered in a nitrogen atmosphere to obtain a laminate, the adhesion of the sintered body to the copper member may be insufficient (specifically, when a shear force is applied to the sintered body that has adhered to the copper member, the mechanical strength (shear strength) of the laminate is low, and the sintered body and the copper member may easily peel off).

[0009] Under these circumstances, the present invention has as its main object the provision of novel silver particles that, when used in a conductive adhesive, provide excellent adhesion to a laminate between the copper member and the resulting sintered body obtained by sintering the conductive adhesive on the surface of the copper member in a nitrogen atmosphere, and that exhibit high mechanical strength (shear strength) when a shear force is applied to the sintered body of the laminate. Another object of the present invention is to provide a conductive adhesive containing the silver particles, a sintered body of the conductive adhesive, and an electronic component having the sintered body between members.

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have made the novel discovery that, by using novel silver particles, in which a specific acidic compound is attached to the surface of silver particles, in a conductive adhesive, excellent adhesion can be achieved between a sintered body obtained by sintering the conductive adhesive in a nitrogen atmosphere and a copper member. The present invention was completed based on this discovery and through further research.

[0011] That is, the present invention provides the following aspects: Item 1. Silver particles having a compound represented by the following general formula (1) attached to the surface of the silver particles: [In general formula (1), R 1 is an alkyl group having 2 to 8 carbon atoms, and R 2 is an alkyl group having 1 to 4 carbon atoms, and R 3is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Item 2. Silver particles according to Item 1, wherein the average particle size of the silver particles is 60 to 600 nm. Item 3. Silver particles according to Item 1 or 2, wherein the silver particles are dispersed in a solvent. Item 4. Silver particles according to Item 3, wherein the SPAN value measured by a light transmission centrifugal sedimentation method under the following conditions when the concentration of the silver particles in the solvent is 50% by mass is 0.1 or more and 5.0 or less: SPAN: (X90 - X10) / X50 Formula (1) When particle sizes are expressed as a cumulative distribution, X10 is the particle size at 10% of the cumulative particle size distribution. X90 is the particle size at 90% of the cumulative particle size distribution. X50 (median particle size) is the particle size at 50% of the cumulative particle size distribution. (Conditions for SPAN Measurement) A measurement sample is prepared in which the concentration of the silver particles in the solvent is 50% by mass. The solvent used in the measurement sample has an octanol / water partition coefficient (Log Pow) of -2 or more and 4 or less. 0.2 ml of the measurement sample is filled into a glass cell (a glass cell with an optical path length of 2 mm), and the cell is rotated at a low speed of 130 G centrifugal acceleration at 25°C to acquire data for 500 points at intervals of 5 seconds. Then, the cell is rotated at a high speed of 1160 G centrifugal acceleration to acquire data for 500 points at intervals of 5 seconds. Three points are arbitrarily selected between the gas-liquid interface (the liquid surface of the measurement sample) and the solid-liquid interface (the interface between the settled silver particles and the solvent) of the measurement sample. Each of the three points is analyzed with a node width of 1 mm. The settling velocity is calculated from the distance traveled by the particles and the time required for that movement. This is converted to a particle size using the viscosity and refractive index of the solvent used, and particle sizes X90, X10, and X50 are determined, and SPAN is calculated using formula (1). Item 6. A conductive adhesive comprising the silver particles according to any one of items 1 to 4. Item 7. A conductive adhesive comprising the silver particles according to any one of items 1 to 4 and a resin. Item 8. A sintered body of the conductive adhesive according to item 5. Item 9. An electronic component in which members are joined by the sintered body according to item 7.

[0012] According to the present invention, novel silver particles can be provided that, when used in a conductive adhesive, the resulting sintered body obtained by sintering the conductive adhesive on the surface of a copper member in a nitrogen atmosphere exhibits excellent adhesion to a laminate between the copper member and the sintered body, and exhibits high mechanical strength (shear strength) when a shear force is applied to the sintered body of the laminate.Furthermore, according to the present invention, it is also possible to provide a conductive adhesive containing the silver particles, a sintered body of the conductive adhesive, and an electronic component having the sintered body between members.

[0013] In the silver particles of the present invention, a compound represented by the following general formula (1) is adhered to the surface of the silver particles composed of silver. Because the silver particles of the present invention have this specific acidic compound adhered to the surface of the silver particles, when used as a conductive adhesive, the sintered body obtained by sintering the conductive adhesive in a nitrogen atmosphere has excellent adhesion to copper members, and when a shear force is applied to the sintered body adhered to the copper member, high mechanical strength (shear strength) is exhibited. The silver particles of the present invention, the conductive adhesive, the sintered body of the conductive adhesive, and the electronic component having the sintered body between members are described in detail below.

[0014] [In general formula (1), R 1 is an alkyl group having 2 to 8 carbon atoms, and R 2 is an alkyl group having 1 to 4 carbon atoms, and R 3 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0015] In this specification, a numerical value connected with "~" means a numerical range that includes the numerical values ​​before and after "~" as the lower limit and upper limit. When multiple lower limit values ​​and multiple upper limit values ​​are listed separately, any lower limit value and upper limit value can be selected and connected with "~".

[0016] 1. Silver Particles The silver particles of the present invention are particles containing silver. A compound represented by the general formula (1) (hereinafter, sometimes referred to as compound (1)) is attached to the surface of the silver particles. That is, the silver particles of the present invention have a structure in which compound (1) is attached to the surface of a particle composed of silver.

[0017] In the present invention, particles composed of silver (particles composed essentially of silver) without compound (1) attached to their surfaces are referred to as "silver particles," and particles composed of silver with compound (1) attached to their surfaces are also referred to as "silver particles" for convenience. The term "silver particles of the present invention" refers to particles composed of silver with compound (1) attached to their surfaces.

[0018] In the silver particles of the present invention, compound (1) attached to the surface of the silver particles can be expressed as forming a protective layer (or surface layer, etc.). Specifically, the silver particles have a protective layer on the surface of the particles composed of silver. The protective layer also contains a compound represented by general formula (1). The conductive adhesive of the present invention contains silver particles having such a protective layer, and therefore has excellent adhesion to a laminate between a sintered body obtained by sintering the conductive adhesive in a nitrogen atmosphere and a copper member, and when a shear force is applied to the sintered body in contact with the copper member in the laminate, the laminate exhibits high mechanical strength (shear strength).

[0019] As described above, in general formula (1), R 1 is an alkyl group having 2 to 8 carbon atoms, and from the viewpoint of more suitably exerting the effects of the present invention, is preferably an alkyl group having 3 to 7 carbon atoms, and more preferably an alkyl group having 3 to 6 carbon atoms.

[0020] In addition, in the general formula (1), R 2 is an alkyl group having 1 to 4 carbon atoms, and from the viewpoint of more suitably exerting the effects of the present invention, is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably an alkyl group having 1 or 2 carbon atoms.

[0021] In addition, in the general formula (1), R 3 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and from the viewpoint of more suitably exerting the effects of the present invention, is preferably a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and more preferably a hydrogen atom.

[0022] From the viewpoint of more suitably exhibiting the effects of the present invention, among the compounds represented by general formula (1), 2-methylbutanoic acid, 2-ethylbutanoic acid, 2,2-dimethylbutanoic acid, 2-methylpentanoic acid, 2,2-dimethylpentanoic acid, 2-ethylpentanoic acid, 2-propylpentanoic acid, 2-methylhexanoic acid, 2,2-dimethylhexanoic acid, 2-ethylhexanoic acid, 2,2-diethylhexanoic acid, 2-propylhexanoic acid, 2-butylhexanoic acid, 2-methylheptanoic acid, 2-ethylheptanoic acid, 2-propylheptanoic acid, 2-methyloctanoic acid, 2-ethyloctanoic acid, 2-propyloctanoic acid, 2-methylnonanoic acid, 2-ethylnonanoic acid, 2-methyldecanoic acid, 2-ethyldecanoic acid, and the like are particularly preferred, with 2-ethylhexanoic acid being particularly preferred. The compound represented by general formula (1) contained in the protective layer may be one type or two or more types.

[0023] The amount of compound (1) attached to the silver particles of the present invention is not particularly limited, but is preferably 1.5% by mass or less, more preferably 1.3% by mass or less, and the lower limit is preferably 0.05% by mass or more, based on 100% by mass of the silver particles. The content of compound (1) attached to the silver particles can be measured by thermogravimetric differential thermal analysis.

[0024] The protective layer may contain a compound different from the compound represented by general formula (1). Examples of the different compound include amine compounds, fatty acids, and hydroxy fatty acids. When the protective layer contains a compound different from the compound represented by general formula (1), the different compound contained in the protective layer may be one type or two or more types.

[0025] The amine compound is not particularly limited, but is preferably an alkylamine having an alkyl group with 3 to 18 carbon atoms, more preferably an alkylamine having an alkyl group with 4 to 12 carbon atoms.

[0026] Preferred specific examples of alkylamines include ethylamine, n-propylamine, isopropylamine, 1,2-dimethylpropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, isoamylamine, tert-amylamine, 3-pentylamine, n-amylamine, n-hexylamine, n-heptylamine, n-octylamine, 2-octylamine, 2-ethylhexylamine, n-nonylamine, n-aminodecane, n-aminoundecane, n-dodecylamine, and n-tridecylamine. , 2-tridecylamine, n-tetradecylamine, n-pentadecylamine, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, n-oleylamine, N-ethyl-1,3-diaminopropane, N,N-diisopropylethylamine, N,N-dimethylaminopropane, N,N-dibutylaminopropane, N,N-dimethyl-1,3-diaminopropane, N,N-diethyl-1,3-diaminopropane, N,N-diisobutyl-1,3-diaminopropane, N-lauryldiaminopropane, etc. Further examples include dibutylamine, which is a secondary amine, and cyclopropylamine, cyclobutylamine, cyclopropylamine, cyclohexylamine, cycloheptylamine, cyclooctylamine, 2-(2-aminoethylamino)ethanol, etc. Among these, from the viewpoint of more suitably exhibiting the effects of the present invention, n-propylamine, isopropylamine, cyclopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclobutylamine, n-amylamine, n-hexylamine, cyclohexylamine, n-octylamine, 2-ethylhexylamine, n-dodecylamine, n-oleylamine, N,N-dimethyl-1,3-diaminopropane, and N,N-diethyl-1,3-diaminopropane are preferred, n-butylamine, n-hexylamine, cyclohexylamine, n-octylamine, n-dodecylamine, N,N-dimethyl-1,3-diaminopropane, and N,N-diethyl-1,3-diaminopropane are more preferred, and n-hexylamine is particularly preferred.The compound (1) may be used alone or in combination of two or more.

[0027] In the silver particles of the present invention, the amount of the amine compound attached is also adjusted appropriately, as in the case of compound (1). The specific amount of the amine compound attached is not particularly limited, but is preferably 1.5% by mass or less, and more preferably 1.3% by mass or less, with the mass of the silver particles taken as 100% by mass. The lower limit is 0.00% by mass, 0.01% by mass or more, and the like. The content of the amine compound attached to the silver particles can be measured by differential thermal analysis.

[0028] In addition, fatty acids, hydroxy fatty acids, and the like may be attached to the surface of the silver particles. The fatty acids are not particularly limited, but are preferably fatty acids having an alkyl group with 3 to 18 carbon atoms, and more preferably fatty acids having an alkyl group with 4 to 18 carbon atoms. Specific preferred fatty acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and α-linolenic acid. Specific examples of fatty acids also include cyclic alkyl carboxylic acids such as cyclohexanecarboxylic acid. Hydroxy fatty acids that can be used include compounds having 3 to 24 carbon atoms and one or more (for example, one) hydroxyl groups. Further, examples of hydroxy fatty acids include 2-hydroxydecanoic acid, 2-hydroxydodecanoic acid, 2-hydroxytetradecanoic acid, 2-hydroxyhexadecanoic acid, 2-hydroxyoctadecanoic acid, 2-hydroxyeicosanoic acid, 2-hydroxydocosanoic acid, 2-hydroxytricosanoic acid, 2-hydroxytetracosanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, and 3-hydroxydodeca Examples of such fatty acids include hydroxy fatty acids having 4 to 18 carbon atoms and one hydroxy group at a position other than the ω-position (particularly the 12-position), such as ricinoleic acid, 12-hydroxystearic acid, and [R-(E)]-12-hydroxy-9-octadecenoic acid. These fatty acids and hydroxy fatty acids may be used singly or in combination of two or more.

[0029] In the silver particles of the present invention, the amount of fatty acid or hydroxy fatty acid attached is also adjusted appropriately, as in the case of compound (1). The specific amount of fatty acid or hydroxy fatty acid attached is not particularly limited, but is preferably 1.5% by mass or less, and more preferably 1.3% by mass or less, based on 100% by mass of the silver particles. The lower limit is 0.01% by mass, 0.01% by mass or more, etc. The content of fatty acid or hydroxy fatty acid attached to the silver particles can be measured by differential thermal analysis.

[0030] In the silver particles of the present invention, compound (1), an amine compound, a fatty acid, or a hydroxy fatty acid may be used in combination, or a compound other than these may be adhered to the surface of the silver particles, as long as compound (1) is adhered to the surface and the effects of the present invention can be exhibited.

[0031] The silver particles of the present invention can be prepared in a state of being dispersed in a solvent. In this case, the silver particles of the present invention are present in a state of being dispersed in the solvent. The solvent is not particularly limited as long as it allows the silver particles of the present invention to be dispersed, but a solvent with an octanol / water partition coefficient (Log Pow) of -2 or more and 4 or less is preferred.

[0032] From the viewpoint of suitably exerting the effects of the present invention, preferred examples of the solvent include diethylene glycol monohexyl ether (Log Pow: 1.7), Texanol (Log Pow: 3.2), isopropyl alcohol (Log Pow: 0.05), α-terpineol (Log Pow: 2.98), diethylene glycol (Log Pow: −1.98), ethylene glycol (Log Pow: −1.36), 2-ethyl-1,3-hexanediol (Log Pow: 1.60), diethylene glycol mono-2-ethylhexyl ether (Log Pow: 2.23), butyl carbitol (Log Pow: 0.56), butyl carbitol acetate (Log Pow: 2.9), and butanediol (Log Pow: −0.34). The solvent may be one kind or two or more kinds, but preferably one kind.

[0033] From the viewpoint of more suitably exerting the effects of the present invention, the concentration of the silver particles of the present invention in the solvent is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 88% by mass or more, and is preferably 95% by mass or less, more preferably 93% by mass or less, even more preferably 92% by mass or less; preferred ranges include 80 to 95% by mass, 85 to 93% by mass, and 88 to 92% by mass. When measuring the SPAN: (X90-X10) / X50 value described below for the silver particles of the present invention, the concentration is adjusted to 50% by mass.

[0034] The silver particles of the present invention preferably have a SPAN:(X90-X10) / X50 value of 0.1 or more and 5.0 or less, as measured by the light transmission centrifugal sedimentation method under the above conditions. The SPAN:(X90-X10) / X50 value, as measured by the light transmission centrifugal sedimentation method, correlates with the particle size distribution of the secondary particles of the silver particles; the smaller the SPAN:(X90-X10) / X50 value, the narrower the particle size distribution of the secondary particles of the silver particles. In the present invention, when the SPAN:(X90-X10) / X50 value of the silver particles having compound (1) attached thereto is within the specific range of 0.1 to 5.0, it can be evaluated that the particle size distribution of the secondary particles of the silver particles is within an appropriate range, and further aggregation of the secondary particles is suppressed and the secondary particles are appropriately dispersed in the solvent. Previously, attempts have been made to adjust the properties of conductive adhesives containing silver particles by controlling the primary particle size of the silver particles. However, in the present invention, attention is focused on the dispersibility of secondary silver particles, and by controlling the SPAN: (X90-X10) / X50 value measured by centrifugal sedimentation with light transmission within a specific range, the silver particles dispersed in a solvent are able to achieve both good fluidity and excellent sinterability. As a result, the effects of the present invention can be more effectively achieved. Specific measurement conditions for the centrifugal sedimentation with light transmission are described in the Examples.

[0035] From the viewpoint of optimally exerting the effects of the present invention, the value of SPAN: (X90-X10) / X50 of the silver particles of the present invention is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and particularly preferably 0.4 or more. It is also preferably 5.0 or less, more preferably 4.9 or less, even more preferably 4.8 or less, and particularly preferably 4.7 or less. Preferred ranges include 0.1 to 5.0, 0.2 to 4.9, 0.3 to 4.8, and 0.4 to 4.7.

[0036] In the present invention, the method for setting the SPAN: (X90-X10) / X50 value of the silver particles within the specific range of 0.1 to 5.0 is not particularly limited. However, as described below, the SPAN can be adjusted by, for example, the refining solvent (washing solvent) used in the production of the silver particles and the washing method used therein, the solvent used to replace the amine compound on the surface of the silver particles with an acid (protecting group) (i.e., compound (1)), the selection of the dispersion solvent and the method of dispersion in the dispersion solvent, and, if concentration is required, the centrifugation conditions during the production of the silver particles. In particular, the refining solvent must be selected based on the particle size and the protective group. If an appropriate solvent is not used, the particle size distribution of the secondary particles may broaden when a highly concentrated dispersion is obtained, or extremely large secondary particles may be generated. Furthermore, the centrifugation conditions also have a similar effect on the secondary particles if an excessively strong load G is applied. In addition, too weak centrifugation conditions tend to broaden the distribution of secondary particles, and therefore appropriate centrifugation conditions must be determined depending on the particle size and the type of solvent used during centrifugation.

[0037] Furthermore, from the viewpoint of suitably exhibiting the effects of the present invention, the average particle diameter (primary particle diameter) of the silver particles is, for example, 600 nm or less, preferably 580 nm or less, more preferably 560 nm or less, and even more preferably 550 nm or less, and is preferably 50 nm or more, more preferably 60 nm or more, and even more preferably 65 nm or more. Preferred ranges include 50 to 600 nm, 50 to 580 nm, 50 to 560 nm, 50 to 550 nm, 60 to 600 nm, 60 to 580 nm, 60 to 560 nm, 60 to 550 nm, 65 to 600 nm, 65 to 580 nm, 65 to 560 nm, and 65 to 550 nm.

[0038] For example, a conductive adhesive containing silver particles with an average particle size of approximately 100 nm (approximately 50 to 150 nm) has excellent sinterability and is therefore suitable for use in thin-film power device junctions and solar cell applications. Furthermore, a conductive adhesive containing silver particles with an average particle size of approximately 200 nm (approximately 150 to 300 nm) has low shrinkage while maintaining sinterability and is therefore suitable for use in power device and power amplifier junctions. Furthermore, a conductive adhesive containing silver particles with an average particle size of approximately 500 nm (approximately 300 to 600 nm) has low shrinkage and is therefore suitable for use in thick-film power device junctions. The properties required for a conductive adhesive vary depending on the application, but by adjusting the average particle size of the silver particles of the present invention, the conductive adhesive of the present invention can be made suitable for each application.

[0039] The average particle size (primary particle size) of the silver particles of the present invention is the volume-based average particle size measured for 200 randomly selected particles using image analysis software (e.g., Macview (manufactured by Mountech Co., Ltd.)) on an SEM image. The observation is performed using an SED mode (secondary electron detector) at an accelerating voltage of 20 kV and a magnification of 5,000 to 30,000 times, over a range of 1 to 20 μm in width. The vertical direction of the SEM image is defined as a width that includes 200 or more silver particles (usually about 200 to 300 particles) within a range of 1 to 20 μm in width. The volume-based average particle size is a value measured assuming that the particles observed in the SEM image are spherical with the diameter of the particles. Specific measurement methods are as described in the Examples.

[0040] Furthermore, from the viewpoint of optimally exerting the effects of the present invention, the silver particles of the present invention preferably exhibit at least one exothermic peak in thermogravimetric differential thermal analysis in the range of 120 to 300° C., more preferably at least one in the range of 120 to 160° C., and even more preferably at least one in the range of 160 to 300° C. These exothermic peaks are usually observed in these ranges.

[0041] Furthermore, the dry powder of silver particles of the present invention preferably exhibits a weight loss rate of 1.5% by weight or less, and more preferably 0.05 to 1.3% by weight, when heated from 30° C. to 500° C. by thermogravimetric differential thermal analysis. The thermogravimetric differential thermal analysis method is as follows.

[0042] <Thermogravimetric Differential Thermal Analysis (TG-DTA)> TG-DTA of silver particles dispersed in a solvent is measured using a thermogravimetric differential thermal analyzer (e.g., a Hitachi G300 AST-2). The measurement conditions are as follows: atmosphere: air (when measuring the silver content in the dispersion) or nitrogen (when measuring the exothermic peak or weight loss), measurement temperature: 30 to 500°C, and heating rate: 10°C / min. From the obtained TG-DTA chart, the exothermic peak due to bonding of silver particles in TG-DTA analysis and the weight loss rate when heated from 30°C to 500°C by thermal analysis are obtained.

[0043] The silver content in the silver particles of the present invention is preferably 95% by mass or more, and more preferably 98% by mass or more.

[0044] Compound (1) is adhered to the surface of the silver particles of the present invention. That is, the silver particles of the present invention are surface-treated with a treatment solution containing compound (1) (surface-treated silver particles). Compound (1) is adhered to the surface of the silver particles to form a protective layer.

[0045] 2. Method for Producing Silver Particles An example of a method for producing silver particles of the present invention is shown below.

[0046] First, a composition (silver particle preparation composition) for producing the silver particles (particles composed of silver) of the present invention is prepared. Specifically, a silver compound that serves as the raw material for the silver particles, compound (1) to be attached to the surfaces of the silver particles, and solvents to be used in each step (such as solvents used in synthesizing the silver particles, solvents for purifying the silver particles, and solvents used in substituting compound (1)) are prepared.

[0047] The silver particles of the present invention are synthesized through a process including a step of synthesizing silver particles (particles composed of silver) from a silver compound, a step of substituting an amine compound on the surface of the silver particles with an acid (protecting group) (i.e., compound (1)) as described below, and the separation of the silver particles may be included during or between each step.

[0048] From the viewpoint of more suitably achieving the effects of the present invention, preferred silver compounds include silver nitrate and silver oxalate, with silver oxalate being particularly preferred.

[0049] The solvent used in synthesizing silver particles from a silver compound is not particularly limited as long as it can synthesize silver particles composed of silver, but it preferably contains a polar organic solvent. Examples of polar organic solvents include ketones such as acetone, acetylacetone, and methyl ethyl ketone; ethers such as diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, and 1,4-dioxane; 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-pentanediol, 1,5-pentanediol, 2- Diols such as methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 1,2-octanediol, 1,8-octanediol, and 2-ethyl-1,3-hexanediol; glycerol; alcohols such as linear or branched alcohols having 1 to 5 carbon atoms, cyclohexanol, 3-methoxy-3-methyl-1-butanol, and 3-methoxy-1-butanol; fatty acid esters such as ethyl acetate, butyl acetate, ethyl butyrate, ethyl formate, and texanol;Polyethylene glycol, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 3-methoxybutyl acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monohexyl ether, ethylene glycol monooctyl ether, ethylene glycol mono-2-ethylhexyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl Glycols or glycol ethers such as ether, diethylene glycol monobutyl ether acetate, diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, polypropylene glycol, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, and tripropylene glycol monobutyl ether; N,N-dimethylformamide; dimethyl sulfoxide; terpenes such as terpineol; acetonitrile; γ-butyrolactone; 2-pyrrolidone; N-methylpyrrolidone;Among these, from the viewpoint of more suitably exhibiting the effects of the present invention, linear or branched alcohols having 3 to 5 carbon atoms, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monohexyl ether, diethylene glycol mono-2-ethylhexyl ether, terpineol, and texanol are preferred.

[0050] The solvent may further contain a nonpolar or hydrophobic solvent in addition to the polar organic solvent. Examples of nonpolar organic solvents include linear, branched, or cyclic saturated hydrocarbons such as hexane, heptane, octane, nonane, decane, 2-ethylhexane, and cyclohexane; alcohols such as linear or branched alcohols having 6 or more carbon atoms; aromatic compounds such as benzene, toluene, and benzonitrile; halogenated hydrocarbons such as dichloromethane, chloroform, and dichloroethane; methyl-n-amyl ketone; methyl ethyl ketone oxime; and triacetin. Among these, saturated hydrocarbons and linear or branched alcohols having 6 or more carbon atoms are preferred, and hexane, octane, decane, octanol, decanol, and dodecanol are more preferred. The solvents can be used alone or in combination of two or more.

[0051] In the process of synthesizing silver particles from a silver compound, a silver compound, compound (1), and a solvent are mixed to obtain a composition for preparing silver particles. The proportions of each component in the composition are adjusted as appropriate. For example, the content of silver oxalate in the composition is preferably about 20 to 70% by mass, based on the total amount of the composition. Furthermore, the content of compound (1) is preferably about 5 to 55% by mass, based on the total amount of the composition. Furthermore, when a fatty acid is attached to the surface of silver particles, the content of the fatty acid is preferably about 0.1 to 20% by mass, based on the total amount of the composition. When a hydroxy fatty acid is attached to the surface of silver particles, the content of the hydroxy fatty acid is preferably about 0.1 to 15% by mass, based on the total amount of the composition.

[0052] It is possible to first synthesize silver particles to which an amine compound is attached, and then replace the amine compound with compound (1) by the method described below.

[0053] The means for mixing the components is not particularly limited, and they can be mixed using general-purpose devices such as a mechanical stirrer, magnetic stirrer, vortex mixer, planetary mill, ball mill, three-roll mill, line mixer, planetary mixer, dissolver, etc. To avoid the temperature of the composition increasing due to the heat of dissolution, frictional heat, etc. during mixing, which could lead to the initiation of a thermal decomposition reaction of the silver particles, it is preferable to mix the components while maintaining the temperature of the composition at, for example, 60°C or below, particularly 40°C or below.

[0054] Next, the composition for preparing silver particles is subjected to a reaction, usually by heating, in a reaction vessel, whereby a thermal decomposition reaction of the silver compound occurs and silver particles are produced. In the reaction, the composition may be introduced into a preheated reaction vessel, or the composition may be introduced into the reaction vessel and then heated.

[0055] The reaction temperature may be any temperature at which the thermal decomposition reaction proceeds and silver particles are produced, and may be, for example, about 50 to 250°C. The reaction time may be appropriately selected depending on the desired average particle size and the composition of the composition corresponding to that size. The reaction time may be, for example, 1 minute to 100 hours.

[0056] Since the silver particles produced by the thermal decomposition reaction are obtained as a mixture containing unreacted raw materials, it is preferable to purify the silver particles. Purification methods include solid-liquid separation methods and precipitation methods that utilize the difference in specific gravity between the silver particles and unreacted raw materials such as organic solvents. Solid-liquid separation methods include filter filtration, centrifugal separation, cyclone separation, and decanting. To facilitate handling during purification, the mixture containing the silver particles may be diluted with a low-boiling point solvent such as acetone or methanol to adjust its viscosity.

[0057] The average particle size (primary particle size) of the resulting silver particles can be adjusted by adjusting the composition of the silver particle production composition and the reaction conditions. Furthermore, in the present invention, from the viewpoint of setting the SPAN:(X90-X10) / X50 value within the specific range, it is preferable to use n-propanol, 1-butanol, or the like as the refining solvent. The selection of the refining solvent affects the SPAN:(X90-X10) / X50 value of the silver particles of the present invention.

[0058] Method for Substituting and Adjusting Amine Compounds, etc. on the Silver Particle Surface: Silver particles synthesized by the above method (with an amine compound attached to the surface) are prepared and dispersed in a solvent. Examples of the solvent include the same solvents as those used in the silver particle synthesis process, but ethanol, n-propanol, isopropyl alcohol, 1-butanol, etc. are preferred. The choice of solvent used to substitute and adjust compound (1) on the silver particle surface affects the SPAN (X90-X10) / X50 value of the silver particles of the present invention. Next, another compound (1) is added in an amount ranging from 0.1 to 5 times the mass of the silver particles, and the mixture is stirred at room temperature to 80°C for 1 minute to 24 hours, thereby substituting compound (1) for the amine compound attached to the silver particle surface. Silver particles with the amine compound on their surface substituted with compound (1) can be recovered by the solid-liquid separation method described above. Ethanol, n-propanol, isopropyl alcohol, 1-butanol, etc. are preferred solvents used in this solid-liquid separation. The selection of the solvent also affects the SPAN: (X90-X10) / X50 value of the silver particles of the present invention.

[0059] 3. Conductive Adhesive The conductive adhesive of the present invention is characterized by containing the silver particles of the present invention. That is, the conductive adhesive of the present invention contains the silver particles of the present invention and a solvent. Details of the silver particles and solvent of the present invention are as described above.

[0060] The conductive adhesive of the present invention may further contain a resin in addition to the silver particles and solvent of the present invention. The resin is not particularly limited, and resins used in known conductive adhesives containing silver particles can also be used in the present invention, including thermoplastic resins and thermosetting resins. Examples of thermoplastic resins include urethane resins, acrylic resins, methacrylic resins, polyvinyl alcohol resins, vinyl acetate resins, polycarbonate resins, polyorganosiloxane resins, and polyamide resins, and mixtures thereof are also acceptable. Examples of thermosetting resins include epoxy resins, acrylic resins, silicone resins, urethane resins, vinyl ester resins, phenolic resins, urea resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins, and polyimide resins. In the present invention, specific examples of preferable solvents include diethylene glycol monohexyl ether (Log Pow: 1.7), Texanol (Log Pow: 3.2), isopropyl alcohol (Log Pow: 0.05), α-terpineol (Log Pow: 2.98), diethylene glycol (Log Pow: -1.98), ethylene glycol (Log Pow: -1.36), 2-ethyl-1,3-hexanediol (Log Pow: 1.60), diethylene glycol mono-2-ethylhexyl ether (Log Pow: 2.23), butyl carbitol (Log Pow: 0.56), butyl carbitol acetate (Log Pow: 2.9), and butanediol (Log Pow: -0.34). Particularly preferred solvents are diethylene glycol monohexyl ether (Log Pow: 1.7), 2-ethyl-1,3-hexanediol (Log Pow: 1.60), diethylene glycol mono-2-ethylhexyl ether (Log Pow: 2.23), and Texanol (Log Pow: 3.2). When the conductive adhesive of the present invention further contains a solvent, the conductive adhesive may contain one type of solvent, or two or more types of solvents.

[0061] The content of silver particles in the conductive adhesive of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 88% by mass or more, and preferably 95% by mass or less, more preferably 93% by mass or less, even more preferably 92% by mass or less, with preferred ranges including 80 to 95% by mass, 85 to 93% by mass, and 88 to 92% by mass. Furthermore, when the conductive adhesive of the present invention contains a resin, the content of the resin in the conductive adhesive of the present invention is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, and preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 3% by mass or less, with preferred ranges including 0.001 to 10% by mass, 0.005 to 7% by mass, and 0.01 to 3% by mass.

[0062] 4. Sintered Body of Conductive Adhesive The sintered body of the conductive adhesive of the present invention can be obtained by sintering the conductive adhesive of the present invention described in detail above in "2. Conductive Adhesive." In the sintered body of the conductive adhesive of the present invention, most of the components (compound (1), etc.) and solvent attached to the surfaces of the silver particles are removed by the high heat during sintering, and the sintered body is essentially composed of silver.

[0063] The sintering temperature is not particularly limited, but may be, for example, 300°C or lower, preferably about 150°C to 250°C, and more preferably about 200°C to 250°C. The sintering time is preferably about 0.4 hours to 2.0 hours, and more preferably about 0.5 hours to 1.2 hours. The conductive adhesive of the present invention may or may not be pressurized during sintering. If pressurized, the pressure may be, for example, about 10 to 30 MPa. Sintering can be carried out in an atmosphere such as air or an inert gas (nitrogen gas, argon gas). In the present invention, a nitrogen gas atmosphere is particularly preferred. The sintering method is not particularly limited, and examples include an oven, a hot air drying furnace, an infrared drying furnace, laser irradiation, flash lamp irradiation, and microwaves.

[0064] 5. Electronic Components The electronic components of the present invention include portions in which components are bonded together using the sintered body of the present invention. That is, the electronic components of the present invention are formed by placing the conductive adhesive of the present invention, as described in detail above in "2. Conductive Adhesive," between components of the electronic component (e.g., between components included in a circuit) and sintering the conductive adhesive to bond the components together. In the present invention, copper, silver, gold, nickel, aluminum, etc. can be selected as the components to be bonded, and more preferably copper, silver, or gold, and particularly copper components, are preferably used as the bonding targets (e.g., between copper components, between copper components and gold components, or between copper components and silver components).

[0065] The present invention will be described in more detail in the following examples, but the present invention is not limited to these examples.

[0066] Details of each component used in the examples and comparative examples are as follows: Silver oxalate ((COOAg)2) was synthesized by the method described in Japanese Patent No. 5574761. N,N-Diethyl-1,3-diaminopropane (Fujifilm Wako Pure Chemical Industries, Ltd.) 2-Ethylhexanoic acid (Tokyo Chemical Industry Co., Ltd.) 2-Hydroxyisobutyric acid (Tokyo Chemical Industry Co., Ltd.) n-Hexylamine (C6, Fujifilm Wako Pure Chemical Industries, Ltd.) 2-(2-Aminoethylamino)ethanol (Tokyo Chemical Industry Co., Ltd.) Ricinoleic acid (Tokyo Chemical Industry Co., Ltd.) Ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.) 1-Butanol (Fujifilm Wako Pure Chemical Industries, Ltd.) Isopropyl alcohol (Fujifilm Wako Pure Chemical Industries, Ltd.) 2-Ethyl-1,3-hexanediol (Fujifilm Wako Pure Chemical Industries, Ltd.) Diethylene glycol mono-2-ethylhexyl ether (Fujifilm Wako Pure Chemical Industries, Ltd.)

[0067] Silver particles were produced using the following procedure. When a larger quantity was required for evaluation, the required sample amount was prepared by increasing the number of trials in the same manner.

[0068] Synthesis Example 1 Synthesis of Silver Particles 1 Silver particles 1 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.05 g), N,N-diethyl-1,3-diaminopropane (4.1 g), and 1-butanol (7.5 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. After that, silver oxalate (5 g) was added and stirred for approximately 10 minutes, thereby obtaining a composition for preparing silver particles 1. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of isopropanol was added to each composition. The mixture was stirred using a vortex mixer, then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) using a centrifuge (Hitachi Koki CF7D2). The supernatant was removed by tilting the centrifuge tube. The steps of adding 15 g of isopropanol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of 2-ethylhexanoic acid (the mass of the silver particles) was added to the resulting silver particle dispersion (isopropanol solution), and the mixture was stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, 15 g of isopropanol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged at 3,000 rpm (centrifugal acceleration: approximately 1,600 × G) for 1 minute using a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. Next, the steps of adding 15 g of 2-ethyl-1,3-hexanediol, stirring, centrifugation, and removing the supernatant were repeated twice to recover Silver Particles 1.

[0069] Synthesis Example 2: Synthesis of Silver Particles 2 Silver particles 2 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.13 g), N,N-diethyl-1,3-diaminopropane (4.1 g), 1-butanol (3.8 g), and ethylene glycol (3.8 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. After that, silver oxalate (5 g) was added and stirred for approximately 10 minutes, thereby obtaining a composition for preparing silver particles 2. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of 2-ethylhexanoic acid was added to the resulting silver particle dispersion (isopropyl alcohol solution) and stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. Next, the steps of adding 15 g of 2-ethyl-1,3-hexanediol, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 2.

[0070] Synthesis Example 3: Synthesis of Silver Particles 3 Silver particles 3 dispersed in a solvent were produced by the following procedure. 2-(2-aminoethylamino)ethanol (1.74 g) and 1-butanol (7.5 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. After that, silver oxalate (5 g) was added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 3. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of 2-ethylhexanoic acid was added to the resulting silver particle dispersion (isopropyl alcohol solution) and stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. Next, the steps of adding 15 g of 2-ethyl-1,3-hexanediol, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 3.

[0071] Synthesis Example 4 Synthesis of Silver Particles 4 Silver particles 4 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.05 g), N,N-diethyl-1,3-diaminopropane (4.1 g), and 1-butanol (7.5 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. Silver oxalate (5 g) was then added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 4. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of 2-hydroxyisobutyric acid was added to the resulting silver particle dispersion (isopropyl alcohol solution) and stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. Next, the steps of adding 15 g of 2-ethyl-1,3-hexanediol, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 4.

[0072] Synthesis Example 5 Synthesis of Silver Particles 5 Silver particles 5 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.13 g), N,N-diethyl-1,3-diaminopropane (4.1 g), 1-butanol (3.8 g), and ethylene glycol (3.8 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. Silver oxalate (5 g) was then added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 5. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of 2-hydroxyisobutyric acid was added to the resulting silver particle dispersion (isopropyl alcohol solution) and stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. Next, the steps of adding 15 g of 2-ethyl-1,3-hexanediol, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 5.

[0073] Synthesis Example 6: Synthesis of Silver Particles 6 Silver particles 6 dispersed in a solvent were produced by the following procedure. 2-(2-aminoethylamino)ethanol (1.74 g) and 1-butanol (7.5 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute, after which silver oxalate (5 g) was added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 6. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of 2-hydroxyisobutyric acid was added to the resulting silver particle dispersion (isopropyl alcohol solution) and stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, and 15 g of isopropyl alcohol was added to each composition. The mixture was then stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2). The supernatant was then removed by tilting the centrifuge tube. Next, the steps of adding 15 g of 2-ethyl-1,3-hexanediol, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 6.

[0074] Synthesis Example 7 Synthesis of Silver Particles 7 Silver particles 7 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.05 g), N,N-diethyl-1,3-diaminopropane (4.1 g), and 1-butanol (7.5 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. Silver oxalate (5 g) was then added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 7. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, 15 g of isopropyl alcohol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of n-hexylamine was added to the resulting silver particle dispersion (isopropyl alcohol solution), and the mixture was stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, 15 g of isopropyl alcohol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. Next, the steps of adding 15 g of diethylene glycol mono-2-ethylhexyl ether, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 7.

[0075] Synthesis Example 8: Synthesis of Silver Particles 8 Silver particles 8 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.13 g), N,N-diethyl-1,3-diaminopropane (4.1 g), 1-butanol (3.8 g), and ethylene glycol (3.8 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. Silver oxalate (5 g) was then added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 8. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Co., Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, 15 g of isopropyl alcohol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of n-hexylamine was added to the resulting silver particle dispersion (isopropyl alcohol solution), and the mixture was stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, 15 g of isopropyl alcohol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 3,000 rpm (centrifugal acceleration of approximately 1,600 x G) in a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. Next, the steps of adding 15 g of diethylene glycol mono-2-ethylhexyl ether, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 8.

[0076] Synthesis Example 9: Synthesis of Silver Particles 9 Silver particles 9 dispersed in a solvent were produced by the following procedure. 2-(2-aminoethylamino)ethanol (1.74 g) and 1-butanol (7.5 g) were added to a 50 mL glass centrifuge tube containing a magnetic stirrer and stirred for approximately 1 minute. After that, silver oxalate (5 g) was added and stirred for approximately 10 minutes to obtain a composition for preparing silver particles 9. The glass centrifuge tube was then placed upright on a hot stirrer (HHE-19G-U, manufactured by Koike Precision Machinery Works, Ltd.) equipped with an aluminum block, and the mixture was stirred at 40°C for 30 minutes, followed by stirring at 90°C for an additional 30 minutes. After cooling, the magnetic stirrer was removed, 15 g of isopropyl alcohol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. The steps of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of n-hexylamine was added to the resulting silver particle dispersion (isopropyl alcohol solution), and the mixture was stirred at room temperature for 4 hours. After stirring, the magnetic stirrer was removed, 15 g of isopropyl alcohol was added to each composition, and the mixture was stirred using a vortex mixer. The mixture was then centrifuged for 1 minute at 2500 rpm (centrifugal acceleration of approximately 1110 x G) in a centrifuge (Hitachi Koki CF7D2), and the supernatant was removed by tilting the centrifuge tube. Next, the steps of adding 15 g of diethylene glycol mono-2-ethylhexyl ether, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles 9.

[0077] For each of the obtained Silver Particles 1 to 9, observation with a scanning electron microscope (acquisition of SEM images), measurement of the average particle diameter (volume-based average particle diameter), measurement of the particle size distribution, and measurement of TG-DTA were performed under the following conditions.

[0078] <Observation by Electron Microscope> For each of the silver particles obtained in the Examples and Comparative Examples, a scanning electron microscope (SEM (JSM-IT500HR manufactured by JEOL Ltd.)) was used to obtain an SEM image.

[0079] <Measurement of Average Particle Diameter (Volume-Based Average Particle Diameter)> For each SEM image (width 1 to 20 μm) obtained in the above <Observation with an Electron Microscope>, the volume-based average particle diameter (primary particle diameter) of 200 randomly selected particles was measured using image analysis software (MacView (manufactured by Mountech Co., Ltd.)). The vertical direction of the SEM image was observed within a range of width 1 to 20 μm. Note that the vertical direction of the SEM image was determined to be a width that included 200 or more silver particles (usually about 200 to 300 particles) within a range of width 1 to 20 μm. Note that the volume-based average particle diameter is a value measured assuming that the particles observed in the SEM image were spherical with that diameter. The results are shown in Table 1.

[0080] <Light Transmission Centrifugal Sedimentation Method> For each of the obtained Silver Particles 1 to 9, the following SPAN value was determined by light transmission centrifugal sedimentation method. SPAN: (X90 - X10) / X50 Formula (1) When particle sizes are expressed as a cumulative distribution, X10 is the particle size at 10% of the cumulative particle size distribution. X90 is the particle size at 90% of the cumulative particle size distribution. X50 (median particle size) is the particle size at 50% of the cumulative particle size distribution.

[0081] (SPAN Measurement Conditions) A measurement sample was prepared in which the concentration of silver particles in the solvent was 50% by mass. The solvent used for the measurement sample was a solvent with an octanol / water partition coefficient (Log Pow) of -2 or greater and 4 or less. Each silver particle (1 to 9) was dispensed into a 50 ml vial, and silver particles 1 to 6 were diluted with 2-ethyl-1,3-hexanediol, and silver particles 7 to 9 were diluted with diethylene glycol mono-2-ethylhexyl ether to a total of 100% (50% by mass silver and 50% by mass solvent). A vortex mixer was used for mixing, and the mixture was dispersed at 2000 rpm for 2 minutes. If the particles are not visibly dispersed (solids remain), they may be roughly mixed using a spatula or a planetary mixer to disperse them. When using a planetary mixer, ensure that the rotation and revolution are balanced to prevent the particles from settling. Furthermore, when preparing a measurement sample using a silver particle dispersion in which silver particles are dispersed, the solvent in which the silver particles are dispersed should be used as a diluent to prepare the measurement sample. If the dispersion contains multiple solvents, multiple solvents may be used, and they should be diluted in an equal volume ratio to the dispersion. SPAN ((X90-X10) / X50) was measured using a LUM Japan LS-610 dispersibility evaluation / particle size distribution analyzer. Specifically, 0.2 ml of the measurement sample was filled into a glass cell (glass cell with an optical path length of 2 mm), rotated at a low speed of 130 G centrifugal acceleration at 25°C, and data for 500 points was acquired at 5-second intervals. Then, the cell was rotated at a high speed of 1160 G centrifugal acceleration, and data for 500 points was acquired at 5-second intervals. Three points were arbitrarily selected between the gas-liquid interface (liquid surface of the measurement sample) and the solid-liquid interface (interface between the settled silver particles and the solvent) of the measurement sample. Each of these three points was analyzed with a node width of 1 mm. The settling velocity was calculated from the particle movement distance and the time required for that movement. This was converted to particle diameter using the viscosity and refractive index of the solvent used to determine particle diameters X90, X10, and X50, and the SPAN was calculated using equation (1). The light factor during measurement was set to 6. If a glass cell is not used during measurement, the silver particles will adhere and become blocked from light, making it impossible to measure accurate luminosity (absorbance). Furthermore, if the LightFactor is not set to 6, the light intensity will be insufficient due to the nature of the measurement object, which is a highly concentrated metal particle dispersion liquid.Therefore, to measure the secondary particle state of a high-concentration particle dispersion, it is necessary to set it to 6. When measuring the morphology of secondary particles using a similar principle, attention must be paid to the light source of the measurement device. Furthermore, if nodes (analysis widths) overlap, an appropriate number of measurement profiles (number of measurement points) cannot be obtained, so analysis must be performed so that the nodes do not overlap. The measurement results are shown in Table 1.

[0082] <Production of Conductive Adhesive> Using each of the silver particles obtained in the Examples and Comparative Examples, a conductive adhesive was produced according to the following procedure.

[0083] Conductive adhesives were prepared by mixing silver particles 1 to 9 obtained in the synthesis examples with a solvent (2-ethyl-1,3-hexanediol for silver particles 1 to 6, and diethylene glycol mono-2-ethylhexyl ether for silver particles 7 to 9). Specifically, for each of silver particles 1 to 9, diethylene glycol mono-2-ethylhexyl ether was added so that the silver content in the conductive adhesive was 90% by mass, to prepare a silver particle dispersion with a concentration of 90% by mass. Mixing was performed using a Mazelstar manufactured by Kurabo Industries, Ltd. in double stirring priority mode. This resulted in the preparation of each conductive adhesive to be used in producing the sintered body.

[0084] <Production of Sintered Body (in Air)> The silver particle dispersions (conductive adhesives) obtained in the Examples and Comparative Examples were each sintered in air to produce sintered bodies. First, an Ag member (a Cu member with a 3 μm-thick silver plating on its surface) was prepared. A conductive adhesive (a silver particle dispersion containing 90% by mass of silver particles, 2-ethyl-1,3-hexanediol for Silver Particles 1 to 6, and 10% by mass of diethylene glycol mono-2-ethylhexyl ether for Silver Particles 7 to 9) was uniformly applied to the substrate (the surface on which the silver plating was formed) to a coating thickness of 50 μm. A silicon wafer (2 mm × 2 mm) with a gold plating (1 μm thick) on its back surface (the surface in contact with the conductive adhesive) was then laminated on top of the coating to obtain a laminate. Next, the obtained laminate was heated using a dryer (circulation type) under sintering conditions of a predetermined sintering temperature (heating rate of 3°C / min up to 200°C or 225°C, and 60 minutes at (200°C or 225°C)), and each conductive adhesive between the substrate and the silicon wafer was sintered, and nine laminates in which the substrate and the silicon wafer were bonded via the sintered body were obtained.

[0085] <Production of Sintered Body (in Nitrogen)> The silver particle dispersions (conductive adhesives) obtained in the Examples and Comparative Examples were sintered in a nitrogen gas atmosphere to produce sintered bodies. First, an Ag member, an Au member (with a 50 nm gold plating on the surface of the Cu member), and a Cu member (C1020) were prepared. Next, a conductive adhesive (a silver particle dispersion containing 90% by mass of silver particles, 2-ethyl-1,3-hexanediol for Silver Particles 1 to 6, and 10% by mass of diethylene glycol mono-2-ethylhexyl ether for Silver Particles 7 to 9) was uniformly applied to the surface of each member to a coating thickness of 50 μm. A silicon wafer (2 mm x 2 mm) with a gold plating on the back surface (the surface in contact with the conductive adhesive) was then laminated on top of the coating to obtain a laminate. Next, the obtained laminate was heated in a nitrogen furnace under sintering conditions of a predetermined sintering temperature (heating rate of 3°C / min to 200°C or 225°C, and 60 minutes at (200°C or 225°C)), whereby each conductive adhesive between the substrate and the silicon wafer was sintered, and nine laminates were obtained in which the substrate and the silicon wafer were bonded via the sintered body.

[0086] <Mechanical strength (shear strength) of sintered body> For the laminates obtained by the production of the sintered body described above, a load of 0.120 mm / s was applied to the sintered body at room temperature using a bond tester (SS30-WD manufactured by Seishin Shoji), and a die shear test was performed on each laminate to measure the maximum load at break. The shear strength value was obtained by dividing the maximum load thus obtained by the bond area. The measurement results are the average value of the nine gold-plated silicon wafers for which shear strength was measured. The shear strength measurement results are shown in Table 1-3.

[0087]

[0088] *1: 2EHA (2-ethylhexanoic acid) *2: HBA (2-hydroxyisobutyric acid) *3: HA (hexylamine) *4: EHD (2-ethyl-1,3-hexanediol) *5: EHDG (diethylene glycol mono-2-ethylhexyl ether)

[0089] As is clear from the results shown in Table 1, the conductive adhesive using silver particles with an average particle size of approximately 100 nm and the silver particles of Example 1, which used 2-ethylhexanoic acid for the protective layer, produced sintered bodies (particularly those formed on the surface of copper members) with significantly higher mechanical strength under a nitrogen gas atmosphere than conventional silver particles (Comparative Examples 1 and 2) that used 2-hydroxyisobutyric acid or n-hexylamine for the protective layer. Conductive adhesives using silver particles with an average particle size of approximately 100 nm are particularly suitable for use in applications requiring sintering under a nitrogen gas atmosphere, such as thin-film power device junctions and solar cell applications.

[0090]

[0091] *1: 2EHA (2-ethylhexanoic acid) *2: HBA (2-hydroxyisobutyric acid) *3: HA (hexylamine) *4: EHD (2-ethyl-1,3-hexanediol) *5: EHDG (diethylene glycol mono-2-ethylhexyl ether)

[0092] As is clear from the results shown in Table 2, the conductive adhesive using silver particles with an average particle size of approximately 200 nm, in which 2-ethylhexanoic acid was used for the protective layer, produced sintered bodies (particularly those formed on the surface of copper members) with significantly higher mechanical strength under a nitrogen gas atmosphere than conventional silver particles (Comparative Examples 3 and 4) that used 2-hydroxyisobutyric acid or n-hexylamine for the protective layer. Conductive adhesives using silver particles with an average particle size of approximately 200 nm are particularly suitable for use in applications such as the joints of power devices and power amplifiers, which require sintering under a nitrogen gas atmosphere.

[0093]

[0094] *1: 2EHA (2-ethylhexanoic acid) *2: HBA (2-hydroxyisobutyric acid) *3: HA (hexylamine) *4: EHD (2-ethyl-1,3-hexanediol) *5: EHDG (diethylene glycol mono-2-ethylhexyl ether)

[0095] As is clear from the results shown in Table 3, the conductive adhesive using silver particles with an average particle size of approximately 500 nm and the silver particles of Example 3, which used 2-ethylhexanoic acid for the protective layer, produced sintered bodies (particularly those formed on the surface of copper members) with significantly higher mechanical strength under a nitrogen gas atmosphere than conventional silver particles (Comparative Examples 5 and 6) that used 2-hydroxyisobutyric acid or n-hexylamine for the protective layer. Conductive adhesives using silver particles with an average particle size of approximately 500 nm are particularly suitable for use in applications such as thick-film power device joints, which require sintering under a nitrogen gas atmosphere.

Claims

1. Silver particles having a compound represented by the following general formula (1) attached to the surface of the silver particles: [In general formula (1), R 1 is an alkyl group having 2 to 8 carbon atoms; R 2 is an alkyl group having 1 to 4 carbon atoms, R 3 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

2. The silver particles according to claim 1, wherein the average particle size of the silver particles is 60 to 600 nm.

3. The silver particles according to claim 1, wherein the silver particles are dispersed in a solvent.

4. Silver particles according to claim 3, wherein the SPAN value measured by a light transmission centrifugal sedimentation method under the following conditions when the concentration of the silver particles in the solvent is 50% by mass is 0.1 or more and 5.0 or less. SPAN: (X90-X10) / X50...Equation (1) When particle sizes are expressed as a cumulative distribution, the particle size at 10% of the cumulative particle size distribution is X10. The particle size at 90% of the cumulative particle size distribution is X90. The particle size at 50% of the cumulative particle size distribution is X50 (median particle size). (Conditions for measuring SPAN) A measurement sample is prepared in which the concentration of the silver particles in the solvent is 50% by mass. The solvent used for the measurement sample has an octanol / water partition coefficient (Log Pow) of -2 or more and 4 or less. A glass cell (glass cell having an optical path length of 2 mm) was filled with 0.2 ml of the measurement sample, and rotated at a low speed of 130 G centrifugal acceleration under a condition of 25° C. to obtain data for 500 points at intervals of 5 seconds. Then, the cell was rotated at a high speed of 1,160 G centrifugal acceleration to obtain data for 500 points at intervals of 5 seconds. Three points were arbitrarily selected between the gas-liquid interface (liquid surface of the measurement sample) and the solid-liquid interface (interface between the settled silver particles and the solvent) of the measurement sample, and each of the three points was analyzed with a node width of 1 mm. The settling velocity was calculated from the moving distance of the particles and the time required for the movement. The particle diameters X90, X10, and X50 were converted into particle diameters using the viscosity and refractive index of the solvent used, and SPAN was calculated using formula (1).

5. A conductive adhesive comprising the silver particles according to claim 1 or 2.

6. A conductive adhesive comprising the silver particles according to claim 1 or 2 and a resin.

7. A sintered body of the conductive adhesive according to claim 5.

8. An electronic component having members bonded together by the sintered body according to claim 7.

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