Electroconductive adhesive

Abstract

Provided is a novel electroconductive adhesive that, when used as an electroconductive adhesive, provides an excellent adherence between a copper member and a sintered body yielded by sintering the electroconductive adhesive in a nitrogen atmosphere, wherein a high mechanical strength (shear strength) is exhibited when the sintered body adhered to the copper member is subjected to shear.　The electroconductive adhesive comprises: silver particles A in which at least one C8-10 straight-chain fatty acid is attached to the surface thereof and that have an average particle diameter in the range of 60 nm to less than 500 nm; silver particles B having an average particle diameter in the range of 0.5 μm to 20 μm; and a solvent. The silver particle A : silver particle B mass ratio (silver particle A : silver particle B) is in the range of 25 : 75 to 95 : 5.

Description

conductive adhesive

[0001] The present invention relates to 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 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). In particular, as the average particle size of the silver particles increases to 100 nm or more, further 150 nm or more, and even 200 nm or more, the adhesion of the sintered body to the copper member tends to decrease.

[0009] Sintering begins when the organic components attached to the surface of silver particles are released and decomposed, exposing the particle surface, but the smaller the particle size, the greater the amount of organic components attached to the surface. Therefore, when using a conductive adhesive consisting solely of nano-sized silver particles, sintering takes time and it is difficult to achieve high densification.

[0010] Therefore, a combination of nano-sized particles or submicron-sized particles with larger particles (e.g., micro-sized particles) is considered. It has been suggested that a highly reliable bonded body can be formed by suitably combining nano-sized particles or submicron-sized particles with micro-sized particles. For example, International Publication No. 2021 / 044817 has shown that a highly dense sintered body can be formed by sintering in air using a suitable combination range.

[0011] In order to form a highly reliable sintered body, it is preferable to design it so that it is closest packed and determine the composition of the particles. However, when ultrafine silver particles of less than 60 nm are used, the amount of organic components attached to the particle surface is large, and if the design is intended for closest packing, the organic matter on the particle surface is difficult to desorb during firing due to the lack of a gas passage. As a result, sintering may take a long time, unsintered parts may remain due to poor desorption, or problems such as the occurrence of voids and cracks may occur. Therefore, the use of ultrafine silver particles with a large amount of attached organic components is disadvantageous for forming a highly dense sintered body.

[0012] Furthermore, even fine silver particles generally having particle sizes in the nano to submicron range, e.g., 60 nm or greater, tend to aggregate and often have a secondary particle distribution. When combining silver particles with secondary particle morphology and micro-sized silver particles, fine silver particles with a broad secondary particle distribution make it difficult to properly design a packing structure, which is disadvantageous for forming a dense sintered body or a sintered structure that facilitates the desorption of protective groups. In addition, if the aggregation state is not controlled, variations in the contact potential of the particles and the desorbed organic components with the copper substrate occur. As a result, the reduction and bonding effects on the copper substrate are not uniform, making it difficult to achieve uniform bonding across the entire copper substrate, and it is difficult to achieve high bonding strength when sintering to the copper substrate under nitrogen.

[0013] Under these circumstances, the main object of the present invention is to provide a novel conductive adhesive that, when silver particles are used in the conductive adhesive, exhibits 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 exhibits high mechanical strength (shear strength) when a shear force is applied to the sintered body of the laminate.Furthermore, the present invention also aims to provide a sintered body containing the conductive adhesive, and an electronic component that has the sintered body between members.

[0014] The present inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered a novel finding: a conductive adhesive containing a predetermined range of large and small particles, in which a linear fatty acid having a carbon number within a predetermined range is attached to the surface of silver particles composed of silver, is used to form a sintered body obtained by sintering under a nitrogen atmosphere, and the resulting sintered body has excellent adhesion to copper components and high density and mechanical strength (shear strength). To achieve a dense sintered structure and a packed structure in which protective groups are easily released, it is necessary to use fine silver particles that have a fairly uniform secondary particle distribution, exhibit high sinterability even under nitrogen, and have good dispersion stability while the protective groups are released at high temperatures. By combining this with a suitable range of micro-sized silver particles and designing a packed structure, a more reliable sintered structure can be produced. The present invention was completed based on this finding and further research.

[0015] That is, the present invention provides the following aspects of the invention: Item 1. A conductive adhesive comprising: silver particles A having at least one straight-chain fatty acid having 8 to 10 carbon atoms attached to the surface thereof and having an average particle size in the range of 60 nm or more and less than 500 nm; silver particles B having an average particle size in the range of 0.5 μm or more and 20 μm or less; and a solvent, wherein the mass ratio of silver particles A:silver particles B (silver particles A:silver particles B) is in the range of 25:75 to 95:5. Item 2. The conductive adhesive according to Item 1, wherein the silver particles A have a SPAN value of 0.1 or more and 5.0 or less, measured by a light transmission centrifugal sedimentation method under the following conditions, when the concentration of silver particles A in the solvent is 50% by mass: 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). (SPAN Measurement Conditions) A measurement sample is prepared in which the concentration of the silver particles A in the solvent is 50% by mass. The solvent for 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 (glass cell with an optical path length of 2 mm), and rotated at a low speed of 130 G centrifugal acceleration at 25°C, acquiring data for 500 points at 5-second intervals. Then, the cell is rotated at a high speed of 1160 G centrifugal acceleration, acquiring data for 500 points at 5-second intervals. Three points are 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 the three points is analyzed with a node width of 1 mm. The settling velocity is calculated from the particle movement distance and the time required for movement. This is converted to particle diameter using the viscosity and refractive index of the solvent used to determine particle diameters X90, X10, and X50, and SPAN is calculated using formula (1). Item 3. A sintered body of the conductive adhesive according to Item 1 or 2. Item 4. The sintered body according to Item 3, wherein the shear strength of the sintered body is 60 MPa or more. Item 5. Item 6. The sintered body according to item 3 or 4, wherein the density of the sintered body is 80% or more. Item 7. An electronic component in which members are joined together by the sintered body according to any one of items 3 to 5.Item 7. A method for producing a sintered body, comprising a step of sintering the conductive adhesive according to Item 1 or 2 at a temperature of 150° C. or higher and 275° C. or lower. Item 8. A method for producing an electronic component in which members are joined together by a sintered body, comprising a step of placing the conductive adhesive according to Item 1 or 2 between the members, and a step of sintering the conductive adhesive at a temperature of 150° C. or higher and 275° C. or lower.

[0016] According to the present invention, it is possible to provide a novel conductive adhesive that, when used as a conductive adhesive, can be sintered on the surface of a copper member in a nitrogen atmosphere to form a laminate between the resulting sintered body and the copper member, with excellent adhesion and high density and mechanical strength (shear strength).Furthermore, according to the present invention, it is also possible to provide a sintered body of the conductive adhesive and an electronic component having the sintered body between members.

[0017] The conductive adhesive of the present invention comprises silver particles A and silver particles B, wherein the silver particles A are silver particles having at least one straight-chain fatty acid having 8 to 10 carbon atoms attached to the surface thereof, and have an average particle size in the range of 60 nm or more and less than 500 nm, and the silver particles B have an average particle size in the range of 0.5 μm or more and 20 μm or less, and the mass ratio of the silver particles A to the silver particles B (silver particles A:silver particles B) is in the range of 25:75 to 95:5. By virtue of having such a configuration, when used as a conductive adhesive, the conductive adhesive provides a sintered body obtained by sintering the conductive adhesive in a nitrogen atmosphere, which has excellent adhesion to a copper member, and when a shear force is applied to the sintered body adhered to the copper member, the sintered body exhibits high mechanical strength (shear strength), resulting in the formation of a highly dense sintered body.

[0018] The conductive adhesive of the present invention, a sintered body of the conductive adhesive, and an electronic component having the sintered body between members are described in detail below. In this specification, numerical values ​​connected with "to" mean a numerical range that includes the numerical values ​​before and after "to" as the lower and upper limits. 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 "to."

[0019] The conductive adhesive of the present invention comprises silver particles A each having an average particle size of 60 nm or more and less than 500 nm, silver particles B each having an average particle size of 0.5 μm or more and 20 μm or less, and silver particles A having at least one straight-chain fatty acid having 8 to 10 carbon atoms attached to the surface of the silver particles, the mass ratio of the silver particles A to the silver particles B (silver particles A:silver particles B) being in the range of 25:75 to 95:5.

[0020] Silver Particles A The silver particles A contained in the conductive adhesive of the present invention have a structure in which at least one straight-chain fatty acid having 8 to 10 carbon atoms is attached to the surface of the silver particles A, and have an average particle size in the range of 60 nm or more and less than 500 nm.

[0021] In silver particles A of the present invention, the straight-chain fatty acid having 8 to 10 carbon atoms attached to the surface of the silver particles can be described as forming a protective layer (or surface layer, etc.). Specifically, silver particles A are provided with a protective layer on the surface of particles composed of silver. Furthermore, the protective layer contains a straight-chain fatty acid having 8 to 10 carbon atoms. That is, silver particles A of the present invention are surface-treated with a treatment solution containing a straight-chain fatty acid having 8 to 10 carbon atoms (surface-treated silver particles). The conductive adhesive of the present invention contains silver particles A having such a protective layer, and thereby the conductive adhesive 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 the laminate exhibits high mechanical strength (shear strength) when a shear force is applied to the sintered body adhered to the copper member.

[0022] The straight-chain fatty acid having 8 to 10 carbon atoms may be either a saturated fatty acid or an unsaturated fatty acid, but is preferably a saturated fatty acid. Specific examples of straight-chain fatty acids having 8 to 10 carbon atoms include octanoic acid, nonanoic acid, and decanoic acid. The straight-chain fatty acids having 8 to 10 carbon atoms attached to the surface of silver particles A may be of one type, or two or more types.

[0023] The amount of the straight-chain fatty acid having 8 to 10 carbon atoms attached to silver particles A of the present invention is not particularly limited, but is preferably 1.5% by mass or less, and 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 mass of silver particles A. The content of the straight-chain fatty acid having 8 to 10 carbon atoms attached to silver particles A can be measured by thermogravimetric differential thermal analysis.

[0024] The protective layer may also contain a compound other than the straight-chain fatty acid having 8 to 10 carbon atoms. Examples of the different compound include amine compounds, fatty acids, hydroxy fatty acids, and polymer dispersants. When the protective layer contains a compound other than the straight-chain fatty acid having 8 to 10 carbon atoms, 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 straight chain fatty acids having 8 to 10 carbon atoms may be used alone or in combination of two or more.

[0027] In silver particles A of the present invention, the amount of the amine compound attached is also adjusted appropriately, as in the case of the straight-chain fatty acid having 8 to 10 carbon atoms. 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, relative to 100% by mass of the silver particles, with the lower limit being 0.00% by mass or 0.01% by mass or more. The content of the amine compound attached to silver particles A can be measured by differential thermal analysis.

[0028] Furthermore, fatty acids (excluding straight-chain fatty acids having 8 to 10 carbon atoms), hydroxy fatty acids, etc. may be attached to the surfaces of the silver particles A. 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, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, α-linolenic acid, and 2-ethylhexanoic acid. Specific examples of fatty acids also include cyclic alkyl carboxylic acids such as cyclohexanecarboxylic acid. The 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 silver particles A of the present invention, the amount of fatty acid or hydroxy fatty acid attached is also adjusted appropriately, as in the case of the straight-chain fatty acid having 8 to 10 carbon atoms. 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 silver particles A, and the lower limit is, for example, 0.01% by mass or 0.01% by mass or more. The content of fatty acid or hydroxy fatty acid attached to silver particles A can be measured by differential thermal analysis.

[0030] A polymer dispersant may be attached to the surface of the silver particles A. Commercially available polymer dispersants can be used as the polymer dispersant. Examples of commercially available polymer dispersants include Solsperse 11200, Solsperse 13940, Solsperse 16000, Solsperse 17000, Solsperse 18000, Solsperse 20000, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000, Solsperse 36000, Solsperse 41000, Solsperse 45000, Solsperse 79000, Solsperse 85000, and Solsperse M387 (manufactured by The Lubrizol Company, Ltd.); DISPERBYK-102, 110, 111, 170, 190, 194N, 2015, 2090, and 2096 (manufactured by Bic Chemie Japan Co., Ltd.); EFKA-46, EFKA-47, EFKA-48, EFKA-49 (manufactured by EFKA Chemical Co., Ltd.); Polymer 100, Polymer 120, Polymer 150, Polymer 400, Polymer 401, Polymer 402, Polymer 403, Polymer 450, Polymer 451, Polymer 452, Polymer 453 (manufactured by EFKA Chemical Co., Ltd.); Ajisper PB711, Ajisper PA111, Ajisper PB811, Ajisper PW911 (manufactured by Ajinomoto Co., Inc.); S-Leam SP-0201, S-Leam MP-071K, S-Leam C-2091I, S-Leam C-2093I, S-Leam C-2095I (manufactured by NOF Corporation, "S-Leam" is a registered trademark), and the like.

[0031] The amount of polymer dispersant attached is preferably 0.01 to 15% by mass. If the amount of polymer dispersant attached is 0.1% or more, the dispersion stability of the resulting bonding composition is improved, but if the amount attached is too high, the dispersion stability will decrease, and the bonding to the substrate may also decrease. From this perspective, the amount of polymer dispersant attached is more preferably 0.03 to 3% by mass, and even more preferably 0.05 to 2% by mass.

[0032] In the silver particles A of the present invention, the straight-chain fatty acid having 8 to 10 carbon atoms may be used in combination with at least one of an amine compound, a fatty acid, and a hydroxy fatty acid, as long as the straight-chain fatty acid having 8 to 10 carbon atoms is attached to the surface and the effects of the present invention can be exhibited. Alternatively, a compound different from these may also be attached to the surface of the silver particles A.

[0033] From the viewpoint of more suitably exhibiting the effects of the present invention, in silver particles A of the present invention, the content of straight-chain fatty acids having 8 to 10 carbon atoms among the compounds attached to the surface of silver particles A is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass.

[0034] From the viewpoint of more suitably exhibiting the effects of the present invention, the silver particles A of the present invention are preferably used as a silver particle dispersion in a conductive adhesive. As a solvent for dispersing the silver particles A, the solvents described below can be suitably used.

[0035] The concentration of silver particles A in the silver particle dispersion 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 silver particles A of the present invention, the concentration is adjusted to 50% by mass.

[0036] The silver particles A 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 described below. The SPAN:(X90-X10) / X50 value measured by the light transmission centrifugal sedimentation method correlates with the particle size distribution of the secondary particles of silver particles A, and it can be said that the smaller the SPAN:(X90-X10) / X50 value, the narrower the particle size distribution of the secondary particles of silver particles A. In the present invention, when the SPAN:(X90-X10) / X50 value of silver particles A to which straight-chain fatty acids having 8 to 10 carbon atoms are attached falls within the specific range of 0.1 to 5.0, it can be evaluated that the particle size distribution of the secondary particles of silver particles A falls within an appropriate range, and further aggregation of the secondary particles is suppressed and they are appropriately dispersed in the solvent. Conventionally, 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 particles of silver particles A, and by controlling the value of SPAN: (X90-X10) / X50 measured by centrifugal sedimentation with light transmission within a specific range, silver particles A dispersed in a solvent can be made to have both good fluidity and excellent sinterability. As a result, the effects of the present invention can be more suitably exhibited. Specific measurement conditions for centrifugal sedimentation with light transmission are described in the Examples.

[0037] From the viewpoint of optimally exerting the effects of the present invention, the value of SPAN:(X90-X10) / X50 for silver particles A 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.

[0038] In the present invention, there are no particular limitations on the method for setting the SPAN: (X90-X10) / X50 value of silver particles A within the specific range of 0.1 to 5.0. However, as described below, the value can be adjusted by, for example, the refining solvent (washing solvent) used in the production of silver particles and the washing method used therewith, the solvent used to replace the amine compound on the surface of the silver particles with an acid (protecting group) (i.e., a straight-chain fatty acid having 8 to 10 carbon atoms), the selection of a dispersion solvent and the method of dispersion in that dispersion solvent, and, if concentration is required, the centrifugation conditions during the production of silver particles. In particular, the refining solvent must be selected based on the particle size and protecting groups. If an appropriate solvent is not used, the particle size distribution of 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, since too weak centrifugation conditions tend to broaden the distribution of secondary particles, it is necessary to determine appropriate centrifugation conditions depending on the particle size and the type of solvent used during centrifugation.

[0039] The average particle size of silver particles A may be in the range of 60 nm or more and less than 500 nm. The upper limit of the average particle size is preferably 480 nm or less, more preferably 460 nm or less, and even more preferably 450 nm or less, and may be 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, or 200 nm or less, for example. The lower limit is preferably 65 nm or more, and also preferably 80 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, or 300 nm or more. Preferred ranges for the average particle size of silver particles A of the present invention include 60 to 490 nm, 60 to 480 nm, 60 to 460 nm, 60 to 450 nm, 60 to 400 nm, 60 to 350 nm, 60 to 300 nm, 60 to 250 nm, 60 to 200 nm, 65 to 490 nm, 65 to 480 nm, 65 to 460 nm, 65 to 450 nm, 65 to 400 nm, 65 to 350 nm, 65 to 300 nm, 65 to 250 nm, 65 to 200 nm, 80 to 490 nm, 80 to 480 nm, 80 to 460 nm, 80 to 450 nm, 80 to 400 nm, 80 to 350 nm, 80 to 300 nm, and 80 to 250 nm. 0 to 250 nm, 80 to 200 nm, 100 to 490 nm, 100 to 480 nm, 100 to 460 nm, 100 to 450 nm, 100 to 400 nm, 100 to 350 nm, 100 to 300 nm, 100 to 250 nm, 100 to 200 nm, 200 to 490 nm, 200 to 480 nm, 200 to 460 nm, 200 to 450 nm, 200 to 400 nm, 200 to 350 nm, 200 to 300 nm, 200 to 250 nm, 300 to 490 nm, 300 to 480 nm, 300 to 460 nm, 300 to 450 nm, 300 to 400 nm, and 300 to 350 nm are listed.

[0040] Furthermore, from the viewpoint of optimally exhibiting the effects of the present invention, in thermogravimetric differential thermal analysis, silver particles A of the present invention preferably exhibit at least one exothermic peak in the range of 120 to 300° C., more preferably at least one in the range of 140 to 200° C., and even more preferably at least one in the range of 180 to 300° C. It should be noted that at least one of these exothermic peaks is usually observed within 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] Method for Producing Silver Particles A First, a composition (silver particle preparation composition) for producing silver particles A of the present invention (particles composed of silver) is prepared. Specifically, a silver compound that serves as the raw material for the silver particles, a straight-chain fatty acid having 8 to 10 carbon atoms to be attached to the surfaces of the silver particles, and solvents to be used in each step (such as a solvent used in synthesizing the silver particles, a solvent for purifying the silver particles, and a solvent used in substituting the straight-chain fatty acid having 8 to 10 carbon atoms) are prepared.

[0044] Silver particles A of the present invention are synthesized through 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., a straight-chain fatty acid having 8 to 10 carbon atoms) as described below, and other steps, and separation of the silver particles may be included during or between each step.

[0045] 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.

[0046] The solvent used in synthesizing silver particles A from a silver compound is not particularly limited as long as it synthesizes 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.

[0047] 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.

[0048] In the step of synthesizing silver particles A from a silver compound, a silver compound, a straight-chain fatty acid having 8 to 10 carbon atoms, 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 the straight-chain fatty acid having 8 to 10 carbon atoms 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.

[0049] It is possible to first synthesize silver particles to which an amine compound is attached, and then substitute the amine compound with a linear fatty acid having 8 to 10 carbon atoms by the method described below.

[0050] 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.

[0051] Next, the composition for preparing silver particles is subjected to a reaction, usually a reaction by heating, in a reaction vessel, which causes a thermal decomposition reaction of the silver compound to produce silver particles A. In the reaction, the composition may be introduced into a reaction vessel that has been heated in advance, or the composition may be introduced into the reaction vessel and then heated.

[0052] 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.

[0053] Since silver particles A 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 an organic solvent. Solid-liquid separation methods include 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.

[0054] The average particle size of the resulting silver particles A 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, isopropyl alcohol, 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.

[0055] Method for Substituting and Adjusting Amine Compounds, etc. on the Silver Particle Surface: Silver particles synthesized by the above method (with amine compounds 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 the C8-C10 linear fatty acids on the silver particle surface affects the SPAN (X90-X10) / X50 value of the silver particles of the present invention. Next, another C8-C10 linear fatty acid is added in an amount of 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. This allows the amine compounds attached to the silver particle surface to be substituted with C8-C10 linear fatty acids. Silver particles A with the surface amine compounds substituted with C8-C10 linear fatty acids can be recovered by the above-mentioned solid-liquid separation method, etc. The solvent used for this solid-liquid separation is preferably ethanol, n-propanol, isopropyl alcohol, 1-butanol, etc. The choice of solvent also affects the SPAN: (X90-X10) / X50 value of the silver particles of the present invention.

[0056] Silver Particles B The silver particles B contained in the conductive adhesive of the present invention have an average particle size in the range of 0.5 μm or more and 20 μm or less. If the average particle size of silver particles B is less than 0.5 μm, the particle size distribution of the silver particles contained in the conductive adhesive becomes narrow, making it difficult for the solvent and the protective layer of silver particles A attached to the surface to volatilize during firing, and making sintering at low temperatures difficult. On the other hand, if the average particle size of silver particles B exceeds 20 μm, the difference in average particle size between silver particles B and silver particles A is too large, making it impossible to obtain a dense and high-strength bonded body during sintering.

[0057] The average particle size of silver particles B may be in the range of 0.5 μm or more and 20 μm or less. From the viewpoint of more suitably exhibiting the effects of the present invention, the lower limit is preferably 0.6 μm or more, and the upper limit is preferably 20 μm or less, more preferably 15 μm or less, more preferably 10 μm or less, even more preferably 7.5 μm or less, still more preferably 5.5 μm or less, even more preferably 5.0 μm or less, still more preferably 4.9 μm or less, even more preferably 3.0 μm or less, still more preferably 2.5 μm or less, and still more preferably 2.0 μm or less. μm or less, and preferred ranges include 0.5 to 20 μm, 0.5 to 15 μm, 0.5 to 10 μm, 0.5 to 7.5 μm, 0.6 to 20 μm, 0.6 to 15 μm, 0.5 to 5.5 μm, 0.5 to 5.0 μm, 0.5 to 4.9 μm, 0.5 to 3.0 μm, 0.5 to 2.5 μm, 0.5 to 2.0 μm, 0.6 to 20 μm, 0.6 to 15 μm, 0.6 to 10 μm, 0.6 to 7.5 μm, 0.6 to 5.5 μm, 0.6 to 5.0 μm, 0.6 to 4.9 μm, 0.6 to 3.0 μm, 0.6 to 2.5 μm, and 0.6 to 2.0 μm. The average particle size of silver particles B can be measured using a dynamic light scattering method or image analysis software described below.

[0058] In the present invention, the average particle diameter of silver particles A and silver particles B is the volume-based average particle diameter measured for 200 randomly selected particles using image analysis software (for example, Macview (manufactured by Mountech Co., Ltd.)) on an SEM image. 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 (typically, approximately 200 to 300 particles) within a range of 1 to 20 μm in width. The volume-based average particle diameter is a value measured assuming that the particles observed in the SEM image are spherical with the diameter. Specific measurement methods are as described in the Examples.

[0059] Silver particles B preferably have a protective layer on the surface of silver particles. The protective layer can be formed, for example, by a fatty acid having 6 to 22 carbon atoms attached to the surface of the silver particles. That is, silver particles B of the present invention are preferably surface-treated with a treatment solution containing a fatty acid having 6 to 22 carbon atoms (surface-treated silver particles).

[0060] The fatty acid having 6 to 22 carbon atoms may be either a saturated fatty acid or an unsaturated fatty acid. Specific examples of fatty acids having 6 to 20 carbon atoms include hexanoic acid, sorbic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pendadecylic acid, palmitic acid, margaric acid, stearic acid, oleic acid, and behenic acid. The fatty acids having 6 to 22 carbon atoms attached to the surfaces of silver particles B may be of one type, or two or more types.

[0061] The amount of fatty acid having 6 to 22 carbon atoms attached to silver particles B of the present invention is not particularly limited, but is preferably 1.5% by mass or less, and more preferably 1.3% by mass or less, and the lower limit is preferably 0.05% by mass or more, relative to 100% by mass of the mass of silver particles B. The content of fatty acid having 6 to 22 carbon atoms attached to silver particles B can be measured by thermogravimetric differential thermal analysis.

[0062] Furthermore, in silver particles B, the protective layer may contain a compound different from the fatty acids having 6 to 22 carbon atoms. Examples of such a compound include amine compounds, fatty acids (excluding fatty acids having 6 to 22 carbon atoms), hydroxy fatty acids, and polymer dispersants. Specific examples of these compounds and the amounts of adhesion are the same as those exemplified for silver particles A. When a compound different from the fatty acids having 6 to 22 carbon atoms is contained in the protective layer, the different compound contained in the protective layer may be one type, or two or more types.

[0063] When a fatty acid having 6 to 22 carbon atoms is attached to silver particles B of the present invention, the fatty acid having 6 to 22 carbon atoms may be used in combination with at least one of an amine compound, a fatty acid, and a hydroxy fatty acid, as long as the fatty acid having 6 to 22 carbon atoms is attached to the surface and the effects of the present invention can be exhibited. Alternatively, a compound different from these may also be attached to the surface of silver particles B.

[0064] From the viewpoint of more suitably exhibiting the effects of the present invention, in silver particles B of the present invention, the content of fatty acids having 6 to 22 carbon atoms among the compounds attached to the surface of silver particles B is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass.

[0065] The solvent contained in the conductive adhesive of the present invention is not particularly limited as long as it can disperse silver particles, but it is preferable to contain 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.

[0066] 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.

[0067] When both a polar organic solvent and a non-polar organic solvent are contained, the ratio of the polar organic solvent to the total amount of solvent is preferably 5% by volume or more, more preferably 10% by volume or more, and even more preferably 15% by volume or more. It can also be 60% by volume or less, 55% by volume or less, or even 50% by volume or less. The solvent can also consist solely of a polar organic solvent. The conductive adhesive of the present invention has good dispersibility of silver particles even when it contains a large amount of polar organic solvent.

[0068] In the conductive adhesive of the present invention, the proportion of the solvent is not particularly limited, but is preferably 20% by mass or less, and more preferably about 5% to 15% by mass.

[0069] The total content of silver particles A and silver particles B contained in the conductive adhesive of the present invention is preferably 80% by mass or more, and more preferably 85% by mass or more.

[0070] The conductive adhesive of the present invention can be produced by a method comprising a step of mixing the silver particles of the present invention with a solvent.

[0071] Furthermore, in the method for producing a conductive adhesive of the present invention, the silver particles of the present invention produced in a solvent in the method for producing silver particles of the present invention described above may be used together with the solvent to form the conductive adhesive of the present invention.

[0072] In the conductive adhesive of the present invention, the mass ratio of silver particles A to silver particles B (silver particles A:silver particles B) is preferably in the range of 25:75 to 95:5, more preferably in the range of 30:70 to 90:10, and even more preferably in the range of 40:60 to 80:20. The conductive adhesive of the present invention predominantly contains silver particles A and silver particles B, and the total content thereof is preferably 80% by mass or more, more preferably 83% by mass to less than 85% by mass, even more preferably 85% by mass or more but less than 87% by mass, and particularly preferably 87% by mass or more but less than 92% by mass.

[0073] More specifically, for example, when the average particle size of silver particles A is from 60 nm to 100 nm and the average particle size of silver particles B is from 0.6 μm to 5.0 μm, the mass ratio of silver particles A to silver particles B (silver particles A:silver particles B) is preferably in the range of 90:10 to 70:30, more preferably 70:30 to 50:50, and even more preferably 50:50 to 25:75. Furthermore, when the average particle size of silver particles A is from 100 nm to 300 nm and the average particle size of silver particles B is from 0.6 μm to 5.0 μm, the mass ratio of silver particles A to silver particles B (silver particles A:silver particles B) is preferably in the range of 25:75 to 30:70, more preferably 30:70 to 40:60, and even more preferably 40:60 to 80:20.

[0074] The conductive adhesive of the present invention may contain silver particles having a particle diameter of less than 60 nm. However, from the viewpoint of more suitably achieving the effects of the present invention, the proportion of silver particles having a particle diameter of less than 60 nm is, for example, 30% or less, preferably 20% or less, and more preferably 10% or less, based on the number of silver particles. Similarly, the silver particles of the present invention may contain silver particles having a particle diameter of greater than 5.5 μm. However, from the viewpoint of more suitably achieving the effects of the present invention, the proportion of silver particles having a particle diameter of greater than 5.5 μm is, for example, 30% or less, preferably 20% or less, and more preferably 10% or less, based on the number of silver particles. Note that the particle diameter referred to here refers to the volume-based particle diameter, calculated using the particle diameter measurement method described above. The number proportion of such particles is measured from 200 silver particles using image analysis software (Macview).

[0075] 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 "Conductive Adhesive." In the sintered body of the conductive adhesive of the present invention, most of the components (such as straight-chain fatty acids having 8 to 10 carbon atoms) 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.

[0076] The sintering temperature is not particularly limited, but from the viewpoint of achieving favorable sintering at low temperatures while increasing the shear strength and density of the resulting sintered body, examples include 275°C or lower, preferably about 150°C to 250°C, and more preferably about 200°C to 250°C. From the same viewpoint, the sintering time is preferably about 0.4 hours to 2.0 hours, and more preferably about 0.5 hours to 1.2 hours. In the present invention, the silver particles contained in the conductive adhesive include silver particles A having at least one straight-chain fatty acid having 8 to 10 carbon atoms attached to the surface of the silver particles A and having an average particle size in the range of 60 nm to less than 500 nm, and silver particles B having an average particle size in the range of 0.5 μm to 20 μm, and the mass ratio of silver particles A to silver particles B (silver particles A:silver particles B) is in the range of 25:75 to 90:10. This allows the conductive adhesive to be favorably sintered at low temperatures of 250°C or lower without the need for pressure during sintering, resulting in the formation of a sintered body with high density and mechanical strength (shear strength). Therefore, there is no need to apply pressure when sintering the conductive adhesive of the present invention. In other words, the conductive adhesive of the present invention can be suitably used in applications where no pressure is applied during sintering. Note that pressure may be applied when sintering the conductive adhesive of the present invention, and if pressure is applied, the pressure is, 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 oven, an infrared drying oven, laser irradiation, flash lamp irradiation, and microwaves.

[0077] The sintered body of the present invention preferably satisfies at least one of the shear strength and density. The methods for measuring these are described below.

[0078] When the silver particles of the present invention are used to form a conductive adhesive, the shear strength of a sintered body obtained by heating the conductive adhesive at 200°C is preferably 60 MPa or more, more preferably 70 MPa or more, and even more preferably 80 MPa or more. The upper limit of the shear strength is, for example, 200 MPa or less. When the silver particles of the present invention are used to form a conductive adhesive, the shear strength of a sintered body obtained by heating the conductive adhesive at 250°C is preferably 70 MPa or more, more preferably 75 MPa or more, and even more preferably 80 MPa or more. The upper limit of the shear strength is, for example, 200 MPa or less. The shear strength of the sintered body is measured by the following method, specifically, by the method described in the Examples.

[0079] <Shear Strength> First, a substrate is prepared by electrolessly plating a copper plate with a thickness of 0.5 μm. A conductive adhesive (a silver particle dispersion containing 90% by weight of silver particles and 10% by weight of ethylene glycol mono-2-ethylhexyl ether) is uniformly applied to the substrate (the surface on which the silver plating is formed) to a thickness of 50 μm. A silicon wafer (2 mm x 2 mm) with a gold-plated back surface (the surface that comes into contact with the conductive adhesive) is then laminated on top of the coating to obtain a laminate. Next, the resulting laminate is heated in a circulating dryer at a predetermined sintering temperature (200°C or 250°C) for 60 minutes to sinter the conductive adhesive between the substrate and silicon wafer, producing nine laminates in which the substrate and silicon wafer are bonded via the sintered body. For each of the resulting laminates, a die shear test was performed using a bond tester (e.g., SS30-WD manufactured by Seishin Shoji) at room temperature, applying a load of 0.120 mm / s to the sintered body, and measuring the maximum load at break. The shear strength value was obtained by dividing the maximum load thus obtained by the bond area. The measurement result is the average value of the nine gold-plated silicon wafers for which shear strength was measured.

[0080] Furthermore, when the silver particles of the present invention are used to form a conductive adhesive, the density of the sintered body obtained by heating the conductive adhesive at 200°C is preferably 80% or more, more preferably 83% or more, and even more preferably 85% or more. The upper limit of the density is, for example, 95% or less. When the silver particles of the present invention are used to form a conductive adhesive, the density of the sintered body obtained by heating the conductive adhesive at 250°C is preferably 80% or more, more preferably 83% or more, and even more preferably 85% or more. The upper limit of the density is, for example, 97% or less. The density of the sintered body can be measured by the following method, specifically, by the method described in the Examples.

[0081] <Density> A laminate in which a substrate and a silicon wafer are bonded via a sintered body is obtained in the same manner as described in the <Shear strength> section. Next, the sintered body and the laminate are embedded in epoxy resin (e.g., manufactured by Buehler) and left to stand for 24 hours to harden the resin. Next, the resin-embedded laminate is cut using a precision low-speed cutting machine (e.g., TechCut4 manufactured by ALLIED), and cross-section milling is performed using an ion milling machine (e.g., IM4000PLUS manufactured by Hitachi High-Technologies Corporation) (e.g., manufactured by Hitachi High-Technologies Corporation). Note that cross-section milling is performed at a discharge voltage of 1.5 kV, an acceleration voltage of 6 kV, and an argon gas flow rate of 0.07 cm. 3The ion beam is irradiated at a speed of 1 / min with a swing of ±30°. The cross section of the sintered body obtained by cross-section milling is observed with a scanning electron microscope to obtain an SEM image. For observation, a 25 μm wide area is observed using SED mode (secondary electron detector) at an acceleration voltage of 20 kV and a field of view of 5000x magnification. The vertical direction of the SEM image is set to a range of 10 μm to 200 μm. This is because a silver sintered layer less than 10 μm thick may impair the mechanical strength of the bonded body. Furthermore, a thickness greater than 200 μm increases the bulk of the laminate, making it difficult for outgassing to occur uniformly during sintering, which is unfavorable from a reliability standpoint. The density is calculated by converting the resulting SEM image into a two-tone image of black and white using binarization software (Imagej) and calculating using the following equation: Density (%) = sintered silver area (number of white pixels) ÷ total area of ​​sintered body {sintered silver area (number of white pixels) + void area (number of black pixels)} × 100

[0082] The electronic component of the present invention has a portion where components are bonded together by the sintered body of the present invention. That is, the electronic component of the present invention is formed by placing the conductive adhesive of the present invention, described in detail above in the "Conductive Adhesive" section, between components of the electronic component (for example, between components included in a circuit) and sintering the conductive adhesive to bond the components together.

[0083] As described above, the sintered body of the present invention has high density and shear strength, and therefore, electronic components including the sintered body also have high shear strength between components. Furthermore, the electronic components of the present invention can have low resistivity.

[0084] The present invention will be described in more detail in the following examples, but the present invention is not limited to these examples.

[0085] 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.) Octanoic acid (Fujifilm Wako Pure Chemical Industries, Ltd.) Decanoic acid (Fujifilm Wako Pure Chemical Industries, Ltd.) Ricinoleic acid (Tokyo Chemical Industry Co., Ltd.) 1-Butanol (Fujifilm Wako Pure Chemical Industries, Ltd.) Isopropyl alcohol (Fujifilm Wako Pure Chemical Industries, Ltd.) Diethylene glycol mono-2-ethylhexyl ether (Fujifilm Wako Pure Chemical Industries, Ltd.) Texanol (KH Neochem Co., Ltd.) Silver powder B1) (DOWA Electronics Co., Ltd.: 3-8FDI) B2) Product name 2-1C, particle size 0.7 μm: DOWA Electronics Co., Ltd. B3) Product name Ag-HWQ 5 μm, particle size 4.9 μm: Fukuda Metal Foil & Powder Co., Ltd.

[0086] 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.

[0087] <Synthesis of Silver Particles A> (1) Silver Particles A1 (Average Particle Diameter: 171 nm) Silver particles A1 dispersed in a solvent were produced by the following procedure. Ricinoleic acid (0.05 g), N,N-diethyl-1,3-diaminopropane (3.3 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 A. 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 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 octanoic acid, equivalent to the mass of the silver particles, 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 A1 (average particle size: 171 nm).

[0088] (2) Silver Particles A2 (Average Particle Diameter: 171 nm) Silver particles A2 dispersed in a solvent were prepared by the following procedure. Ricinoleic acid (0.05 g), N,N-diethyl-1,3-diaminopropane (3.3 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, yielding a composition for preparing silver particles A2. 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 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 process of adding 15 g of isopropyl alcohol, stirring, centrifugation, and removing the supernatant was repeated twice to recover the silver particles. Next, 15 g of decanoic acid, equivalent to the mass of the silver particles, 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 Texanol, stirring, centrifuging, and removing the supernatant were repeated twice to recover silver particles A2 (average particle size 171 nm).

[0089] (3) Silver Particles A3 (Average Particle Diameter: 81 nm) Silver particles A3 dispersed in a solvent were prepared by the following procedure. Ricinoleic acid (0.04 g), N,N-diethyl-1,3-diaminopropane (4.6 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, yielding a composition for preparing silver particles A3. 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 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 isopropanol 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 isopropanol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of octanoic 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 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 A3 (average particle size: 81 nm).

[0090] (4) Silver Particles A4 (Average Particle Diameter: 68 nm) Silver particles A4 dispersed in a solvent were prepared 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, yielding a composition for preparing silver particles A4. 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 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 isopropanol 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 isopropanol, stirring, centrifugation, and removing the supernatant were repeated twice to recover the silver particles. Next, 15 g of octanoic 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 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 A4 (average particle size 68 nm).

[0091] <Silver Particles B> Silver particles B1 were manufactured by Dowa Electronics Co., Ltd. under the trade name 3-8FDI (average particle size 1.9 μm). B2 were manufactured by Dowa Electronics Co., Ltd. under the trade name 2-1C (particle size 0.7 μm). B3 were manufactured by Fukuda Foil Powder Co., Ltd. under the trade name Ag-HWQ (5 μm, particle size 4.9 μm).

[0092] For silver particles A and B used in the examples and comparative examples, observation with a scanning electron microscope (acquisition of SEM images), measurement of average particle diameter (volume-based average particle diameter), and measurement of particle size distribution were carried out under the following conditions.

[0093] <Observation with an Electron Microscope> SEM images of silver particles A and B used in the examples and comparative examples were obtained using a scanning electron microscope (SEM (JSM-IT500HR manufactured by JEOL Ltd.)).

[0094] <Measurement of Average Particle Diameter (Volume-Based Average Particle Diameter)> For the SEM images (width 1 to 50 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 (Mountech Co., Ltd.)). The vertical direction of the SEM image was observed within a width range of 1 to 50 μm. Note that the vertical direction of the SEM image was defined as a width that included 200 or more silver particles (typically, approximately 200 to 300 particles) within a width range of 1 to 50 μm. The volume-based average particle diameter (primary particle diameter) was a value measured assuming that the particles observed in the SEM image were spherical with the diameter. The volume-based average particle diameters (primary particle diameters) of Silver Particles A and B are shown in Table 1.

[0095] <Light Transmission Centrifugal Sedimentation Method> The following SPAN value was determined for each of the silver particles A used in the Examples and Comparative Examples by light transmission centrifugal sedimentation method. SPAN: (X90 - X10) / X50 Equation (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.

[0096] (SPAN Measurement Conditions) A measurement sample was prepared in which the concentration of silver particles A in the solvent was 50% by mass. The solvent used for the measurement sample had an octanol / water partition coefficient (Log Pow) of -2 or more and 4 or less. Each silver particle (A1 to A4) was dispensed into a 50 ml vial, and silver particles A1, A3, and A4 were diluted with diethylene glycol mono-2-ethylhexyl ether, while silver particles A2 were diluted with Texanol to a total of 100% (50% by mass silver and 50% solvent). A vortex mixer was used for kneading, and the mixture was dispersed at 2000 rpm for 2 minutes. If the mixture is not visibly dispersed (solids remain) at this point, it may be dispersed further by rough kneading using a spatula or using a planetary mixer. 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.

[0097]

[0098] In Table 1, OA means octanoic acid, DA means decanoic acid, EHDG means diethylene glycol mono-2-ethylhexyl ether, and TEX means Texanol.

[0099] <Production of conductive adhesive> Silver particles A, silver particles B, and diethylene glycol mono-2-ethylhexyl ether or Texanol solvent were added to obtain the compositions shown in Table 2, and the conductive adhesive was prepared so that the silver content was 90%. Specifically, diethylene glycol mono-2-ethylhexyl ether was added to Examples 1 to 5, 8 to 13, and Comparative Examples 1 to 4, and Texanol was added to Examples 6 and 7, so that the silver content was 90%. Silver particles A and silver particles B were blended in a mass ratio of 0:100 (Comparative Example 1), 20:80 (Comparative Examples 2 and 4), 30:70 (Examples 1, 6, 8, and 10), 40:60 (Example 2), 50:50 (Examples 3 and 12), 70:30 (Example 4), 80:20 (Example 5), 90:10 (Examples 7, 9, 11, and 13), or 100:0 (Comparative Example 3), and these were used to prepare conductive adhesives. The mixing was carried out using a Mazerustar manufactured by Kurabo Industries Ltd. in a double stirring priority mode, thereby obtaining each conductive adhesive to be used in the production of the sintered body.

[0100] <Production of Sintered Body (Nitrogen Atmosphere)> The conductive adhesives (silver particle dispersions) obtained in the Examples and Comparative Examples were each sintered under a nitrogen gas atmosphere to produce sintered bodies. First, Cu members (C1020) were prepared. Next, the conductive adhesive was uniformly applied to the surface of each member to a coating thickness of 50 μm. A silicon wafer (2 mm × 2 mm) with a gold-plated back surface (the surface in contact with the conductive adhesive) was then laminated on top of the coating to obtain a laminate. Next, the resulting laminate was fired in a nitrogen furnace at 250°C (heated to 250°C at a heating rate of 3°C / min and held for 60 minutes) to sinter the conductive adhesives between the substrate and the silicon wafer, yielding nine laminates in which the substrate and the silicon wafer were bonded via the sintered body.

[0101] <Mechanical strength (shear strength) of sintered body> For the laminates obtained by the production of the sintered body described above, a die shear test was performed on each laminate at room temperature using a bond tester (SS30-WD manufactured by Seishin Shoji) at a load of 0.120 mm / s 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 2.

[0102] <Density of sintered body> Each sintered body was embedded in epoxy resin (manufactured by Bühler) together with the laminate, and left to stand for 24 hours to harden the resin. Next, the resin-embedded sintered body was cut with a diamond wire saw CS-203 (manufactured by ALLIED), and cross-section milling was carried out for 3 hours using an ion milling machine (IM4000PLUS) (manufactured by Hitachi High-Technologies Corporation). The cross-section milling was carried out at a discharge voltage of 1.5 kV, an acceleration voltage of 6 kV, and an argon gas flow rate of 0.07 cm 3The ion beam was irradiated at a speed of 1 / min with a swing of ±30°. The cross section of the sintered body obtained by cross-section milling was observed using a JEOL JSM-IT500HR scanning electron microscope to obtain SEM images. The observations were performed using SED mode (secondary electron detector) at an acceleration voltage of 20 kV and a field of view of 5000x magnification, over a 25 μm wide area. The vertical direction of the SEM image was limited to a vertical width of 10 μm or more and 200 μm or less for the silver sintered layer. The density was calculated by converting the obtained SEM image into a two-tone image of black and white using the binarization software "Image J," and using the following formula: The density measurement results are shown in Table 2. Density (%) = sintered silver area (number of white pixels) ÷ total area of ​​sintered body {sintered silver area (number of white pixels) + void area (number of black pixels)} × 100

[0103] High density not only contributes to improved thermal conductivity, electrical conductivity, and mechanical properties such as shear strength, but also affects long-term reliability. Low-density sintered bodies with a density of less than 80% are likely to experience void coalescence and crack development as the sintering of silver particles progresses in environments where high temperatures are applied for long periods of time or where temperature changes are severe, which is likely to impair reliability. Therefore, we rated compacts with a density of 80% or more as ○ and those with a density of less than 80% as ×.

[0104]

[0105] As is clear from the results shown in Table 2, the conductive adhesives of Examples 1 to 13, in which the mass ratio of silver particles A:silver particles B was in the range of 30:70 to 90:10, were good in both shear strength and density when formed into a sintered body, compared to the conductive adhesive containing silver particles B alone (Comparative Example 1), the conductive adhesive containing silver particles A alone (Comparative Example 3), the conductive adhesive in which the mass ratio of silver particles A:silver particles B was 20:80 (Comparative Example 2), and the conductive adhesive in which the mass ratio of silver particles A:silver particles B was 18:72 (Comparative Example 4).

Claims

1. A conductive adhesive comprising: silver particles A having at least one straight-chain fatty acid having 8 to 10 carbon atoms attached to the surface and having an average particle size in the range of 60 nm or more and less than 500 nm; silver particles B having an average particle size in the range of 0.5 μm or more and 20 μm or less; and a solvent, wherein the mass ratio of silver particles A:silver particles B (silver particles A:silver particles B) is in the range of 25:75 to 95:

5.

2. The conductive adhesive according to claim 1, wherein the silver particles A have a SPAN value of 0.1 or more and 5.0 or less, when the concentration of silver particles A in the solvent is 50% by mass, as measured by a light transmission centrifugal sedimentation method under the following conditions: SPAN: (X90 - X10) / X50 Formula (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). (SPAN Measurement Conditions) A measurement sample is prepared in which the concentration of silver particles A 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. The cell is then 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, and each of the three points is analyzed at 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. The sedimentation velocity is converted to a particle size using the viscosity and refractive index of the solvent used, particle sizes X90, X10, and X50 are determined, and SPAN is calculated using formula (1).

3. A sintered body of the conductive adhesive according to claim 1 or 2.

4. The sintered body according to claim 3, wherein the shear strength of the sintered body is 60 MPa or more.

5. The sintered body according to claim 3, wherein the density of said sintered body is 80% or more.

6. An electronic component in which members are joined together by the sintered body according to claim 3.

7. A method for producing a sintered body, comprising the step of sintering the conductive adhesive according to claim 1 or 2 at a temperature of 150°C or higher and 275°C or lower.

8. A method for manufacturing an electronic component in which members are joined together by a sintered body, comprising the steps of: placing the conductive adhesive according to claim 1 or 2 between the members; and sintering the conductive adhesive at a temperature of 150°C or higher and 275°C or lower.

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