Conductive adhesive

Abstract

Provided is an electrically conductive adhesive that, when formed into an electrically conductive adhesive, can be appropriately sintered at low temperature without pressure during sintering of the electrically conductive adhesive, and forms a sintered body having high density and mechanical strength (shear strength). An electrically conductive adhesive comprising: silver particles A having an average particle diameter of less than 40 nm; silver particles B having an average particle diameter in the range of 40 nm or more and less than 500 nm; silver particles C having an average particle diameter in the range of 0.5 or more and less than 5.5 μm; and a solvent, wherein the mass ratio of silver particles A: silver particles B: silver particles C is 1 to 20: 30 to 60: 40 to 70.

Description

Technical Field

[0001] The present invention relates to conductive adhesives, sintered bodies of the conductive adhesives and methods for manufacturing the same, and electronic components having the sintered bodies between components and methods for manufacturing the same. Background Technology

[0002] Conductive adhesives, such as chip bonding agents, are bonding materials used in electronic components such as semiconductors, LEDs, and power semiconductors. Common bonding methods include bonding using pressure and heat, and bonding to a substrate via sintering using pressureless heating. In recent years, from the viewpoint of simplifying and improving manufacturing processes, the development of pressureless bonding materials has been ongoing.

[0003] One example of a pressureless bonding material is a conductive adhesive containing epoxy resin. This bonding material is used by curing the epoxy resin at low temperature, which can suppress the generation of vacancies and improve the bonding strength with the substrate (Patent Document 1). However, because the epoxy resin itself becomes a resistive material, the resulting electrical conductivity and thermal conductivity will be lower.

[0004] On the other hand, the development of silver particles as a bonding material free of thermosetting resins such as epoxy resin has been promoted in recent years. Silver particles are characterized by their ease of sintering through short-time heat treatment at low temperatures. For example, Patent Document 2 discloses a metal paste in which a solid component containing silver particles is mixed with a solvent. The solid component consists of silver particles containing at least 30% silver particles with a particle size of 100-200 nm, based on the particle number. Furthermore, the silver particles constituting the solid component are bonded as a protective agent to an amine compound with a total carbon atom number of 4-8. According to this metal paste, silver particles can be sintered in a low-temperature region, and a sintered body with low electrical resistance and excellent thermal conductivity can be formed. Existing technical documents Patent documents

[0005] Patent Document 1: International Publication No. 2010 / 18712 Patent Document 2: Japanese Patent Application Publication No. 2015-159096 Summary of the Invention The problem that the invention aims to solve

[0006] In the field of conductive adhesives, to reduce the porosity (increase density) of the sintered body obtained by coating and sintering conductive adhesives onto components (such as substrates and semiconductor chips used in electronic components), pressure is generally applied during sintering (the pressure is, for example, around 10 to 30 MPa). Sintering the conductive adhesive under pressure simultaneously reduces the porosity of the sintered body. It should be noted that a high porosity in the sintered body can lead to insufficient mechanical strength (shear strength) or the formation of cracks and defects, resulting in reliability issues. On the other hand, the pressure applied during sintering can damage the component coated with the conductive adhesive, and special equipment is required for applying the pressure. Furthermore, when forming the sintered body on semiconductor chips or similar components with complex structures, there is a problem that the conductive adhesive cannot be pressurized.

[0007] In recent years, with the increasing size of semiconductor chips, the demand for durability has grown. To mitigate the stress exerted on the bonding area between the semiconductor chip and the substrate, and on the semiconductor chip itself, measures have been taken to increase the film thickness when applying conductive adhesives to the substrate and the film thickness of the bonding body itself. Furthermore, it is known that the Young's modulus (longitudinal elastic modulus) and other physical properties of the semiconductor chip, substrate, and other components differ, resulting in different deformation amplitudes during sintering. Therefore, stress is applied to each material, but by thickening the film of the bonding body, the bonding body can bear this stress. For example, in conductive adhesives using solder, a thick film is usually formed to mitigate stress. However, in sintered bodies using silver, when a thick film (50 μm or more) is formed through the sintering shrinkage of silver, problems arise such as voids caused by difficulty in venting exhaust generated during sintering, cracking, defects, and internal cracks in the sintered body due to shrinkage. Especially when ensuring high density, it is necessary to use metal particles with high sinterability and high shrinkage, making it difficult to balance density and film thickness. Therefore, using particles smaller than 30nm as bonding materials is not suitable for use alone.

[0008] Therefore, in recent years, there has been a need to develop conductive adhesives that can form sintered bodies with high density and mechanical strength (shear strength) even without pressure during the sintering of conductive adhesives.

[0009] In addition, conductive adhesives are generally sintered at a sintering temperature of around 300°C, but they can be sintered at lower temperatures (e.g., sintering temperature below 250°C). Furthermore, when producing thick films (e.g., above 50 μm), conductive adhesives that do not produce defects such as voids, cracks, or internal cracks are also required.

[0010] Even without pressure, conductive adhesives can be properly sintered at low temperatures during sintering to form sintered bodies with high density and mechanical strength (shear strength). In particular, the above problems can be solved if novel conductive adhesives with excellent density and mechanical strength are provided for thick films.

[0011] Under these circumstances, the main objective of the present invention is to provide a conductive adhesive that can be appropriately sintered at low temperatures even without pressure during sintering, forming a sintered body with high density and mechanical strength (shear strength). Furthermore, the present invention aims to provide a conductive adhesive that is not prone to cracking, defects, vacancies, or fissures even when formed into a thick film (50 μm or more). Moreover, the present invention also aims to provide a sintered body of the conductive adhesive and an electronic component incorporating the sintered body between components. Solution for solving the problem

[0012] The inventors of this invention conducted in-depth research to solve the aforementioned problems. As a result, they discovered that when a conductive adhesive is made by combining relatively small silver particles with an average particle size within a specified range, relatively medium-sized silver particles with an average particle size within a specified range, and relatively large silver particles with an average particle size within a specified range, and combining the average particle sizes of large, medium, and small silver particles in a specific ratio, appropriate sintering at low temperatures is achieved even without pressure during the sintering of the conductive adhesive, thereby forming a sintered body with high density and mechanical strength (shear strength). Furthermore, it was found that even when a thick film is formed, it is difficult to produce cracks, defects, vacancies, or internal cracks, thus forming a sintered body. This invention was completed based on further repeated research based on these insights.

[0013] That is, the present invention provides an invention in the manner disclosed below. Item 1. A conductive adhesive comprising: silver particles A with an average particle size of less than 40 nm; silver particles B with an average particle size of 40 nm or more and less than 500 nm; silver particles C with an average particle size of 0.5 μm or more and less than 5.5 μm; and a solvent, wherein the mass ratio of the silver particles A: the silver particles B: the silver particles C is 1–20: 30–60: 40–70. Item 2. The conductive adhesive according to Item 1, wherein an amine compound is attached to the surface of the silver particles A and / or the silver particles B. Item 3. A sintered body, which is a sintered body of the conductive adhesive described in Item 1 or 2. Item 4. An electronic component formed by bonding components together via the sintered body described in Item 3. Item 5. A method for manufacturing a sintered body, comprising a step of sintering the conductive adhesive described in Item 1 or 2 at a temperature above 200°C and below 250°C. Item 6. A method for manufacturing an electronic component, comprising bonding components together in a sintered body to form the electronic component, wherein the method includes a step of distributing the conductive adhesive described in item 1 or 2 between the components and a step of sintering the conductive adhesive at a temperature of 200°C or higher and 250°C or lower. Invention Effects

[0014] According to the present invention, a novel conductive adhesive can be provided, which, when manufactured as a conductive adhesive, can be appropriately sintered at low temperatures even without pressure during sintering, forming a sintered body with high density and mechanical strength (shear strength). Furthermore, according to the present invention, by using particles with different sintering temperatures, the conductive adhesive is not sintered all at once, but rather a dense sintered body is gradually formed starting with particles at lower sintering temperatures, resulting in a sintered body with high density and high shear strength. Moreover, it is a preferred composition for suppressing sintering shrinkage during sintering, and even when forming a thick film, it can form a good sintered body that is less prone to defect layers (cracks, defects, vacancies, internal cracks). Furthermore, according to the present invention, a conductive adhesive containing the silver particles, a sintered body of the conductive adhesive, and an electronic component having the sintered body between components can also be provided. Attached Figure Description

[0015] Figure 1 This is a SEM image of silver particles A1. Figure 2 This is a SEM image of silver particles B1. Figure 3 This is a SEM image of silver particles B2. Figure 4 This is a SEM image of silver particles C1. Figure 5 This is a SEM image of silver particles C2. Figure 6 This is a SEM image of the cross-section of the sintered body of Example 2, magnified 2000 times. Figure 7 This is a 100x SEM image of the cross-section of the sintered body of Example 2. Figure 8 This is a SEM image of the cross-section of the sintered body of Comparative Example 2 at a magnification of 2000. Figure 9 This is a SEM image of the cross-section of the sintered body of Comparative Example 2 at a magnification of 200x. Figure 10This is a SEM image of the cross-section of the sintered body of Example 5 at a magnification of 2000. Figure 11 This is a SEM image of the cross-section of the sintered body of Comparative Example 4 at a magnification of 1000. Detailed Implementation

[0016] The conductive adhesive of the present invention comprises silver particles A with an average particle size of less than 40 nm, silver particles B with an average particle size of 40 nm or more and less than 500 nm, silver particles C with an average particle size of 0.5 μm or more and less than 5.5 μm, and a solvent. The characteristic feature is that the mass ratio of silver particles A: silver particles B: silver particles C is 1–20:30–60:40–70. By possessing this feature, the conductive adhesive of the present invention can provide a novel conductive adhesive that can be appropriately sintered at low temperatures to form a sintered body with high density and mechanical strength (shear strength), even without pressure during sintering.

[0017] The conductive adhesive of the present invention, the sintered body of the conductive adhesive, the manufacturing method thereof, and the electronic component having the sintered body between components, and the manufacturing method thereof, will be described in detail below. It should be noted that in this specification, numerical values ​​connected by “~” refer to the range of values ​​before and after the “~” as lower and upper limits. When multiple lower and upper limits are described separately, any lower and upper limits can be connected by “~”.

[0018] 1. Conductive adhesive The conductive adhesive of the present invention is characterized by comprising silver particles A, silver particles B, silver particles C, and a solvent. By including the solvent, fluidity is improved, and the conductive adhesive of the present invention can be easily formulated into the desired location. Details regarding the silver particles contained in the conductive adhesive of the present invention are described below.

[0019] Silver Particle A The average particle size of the silver particles A in this invention is less than 40 nm. While the average particle size of the silver particles A only needs to be less than 40 nm, from the viewpoint of further enhancing the effects of this invention, regarding the lower limit, preferably 10 nm or more, more preferably 15 nm or more, and regarding the upper limit, preferably 35 nm or less, and as preferred ranges, 1 to 40 nm, more preferably 10 to 35 nm, and even more preferably 15 to 35 nm, etc.

[0020] In this invention, the average particle size of silver particle A is the volume-based average particle size measured from 200 randomly selected particles in a SEM image using image analysis software (e.g., Macview, manufactured by Mountech). It should be noted that during SEM observation, SED mode (secondary electron detector) is used, with an accelerating voltage of 20 kV and an observation magnification of 5000–60000 times, observing a width of 1–20 μm. It should be noted that the vertical axis of the SEM image is defined as the width of at least 200 (typically around 200–300) silver particles within a width of 1–20 μm. Furthermore, the volume-based average particle size is a value measured assuming the particles observed in the SEM image are spherical with their diameter. The specific measurement method is as described in the examples.

[0021] Furthermore, the weight loss rate of the dried powder of silver particles A of the present invention when heated from 30°C to 500°C by thermogravimetric differential thermal analysis is preferably 2.0% by weight or less, more preferably 0.05% to 1.5% by weight. The method of thermogravimetric differential thermal analysis is as follows.

[0022] <Thermogravimetric Differential Thermal Analysis (TG-DTA)> First, prepare air-dried silver particles A. For example, in the case of analyzing silver particles obtained from a conductive binder, add 2g of methanol to 1g of each conductive binder and disperse thoroughly. Filter and air-dry the silver particles A to obtain a dry silver powder, which is used as the analyte. Measure the TG-DTA of the dry silver powder A using a thermogravimetric differential thermal analysis (TG-DTA) apparatus (e.g., HITACHI G300A ST-2). The measurement conditions are set as follows: atmosphere: air; measurement temperature: 30–500°C; heating rate: 10°C / min. From the obtained TG-DTA graph, obtain the pyrothermal peak caused by the binding of silver particles in the TG-DTA analysis and the weight loss rate when heated from 30°C to 500°C by thermal analysis.

[0023] From the viewpoint of further suitably achieving the effects of the present invention, it is preferable to perform surface treatment on the silver particles A. That is, the silver particles A of the present invention are preferably surface-treated silver particles.

[0024] More specifically, an amine compound is preferably attached to the surface of the silver particles A of the present invention. The amine compound can adhere to the surface of the silver particles A to form a protective layer. Preferably, the amine compound is attached to the silver particles A of the present invention in such a way that the average particle size is set to the aforementioned specific range.

[0025] As amine compounds, there are no particular limitations. From the viewpoint of further suitably achieving the effects of the present invention, examples can be given of primary amines, secondary amines, tertiary amines, and diamine compounds having two amino groups in one compound.

[0026] Examples of primary amines include monoethanolamine, ethylamine, n-propylamine, isopropylamine, 1,2-dimethylpropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, isopentylamine, n-octylamine, 2-octylamine, tert-octylamine, 2-ethylhexylamine, n-nonylamine, n-decylamine, n-undecylamine, n-dodecylamine, n-tridecylamine, 2-tridecylamine, n-tetradecylamine, n-pentadecanylamine, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, and n- Amines with straight-chain or branched hydrocarbon groups include oleylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, 3-butoxypropylamine, N-ethyl-1,3-diaminopropane, N,N-diisopropylethylamine, N,N-dimethyl-1,3-diaminopropane, N,N-dibutyl-1,3-aminopropane, N,N-diisobutyl-1,3-diaminopropane, and N-lauryldiaminopropane.

[0027] Examples of other examples include cyclopropylamine, cyclobutylamine, cyclopropylamine, cyclohexylamine, cycloheptylamine, cyclooctylamine, and aniline, which are alicyclic amines. Other examples include ether amines such as 3-isopropoxypropylamine and isobutoxypropylamine.

[0028] Examples of secondary amines include dialkyl monoamines such as N,N-dipropylamine, N,N-dibutylamine, N,N-dipentylamine, N,N-dihexylamine, N,N-diheptylamine, N,N-dioctylamine, N,N-dinonylamine, N,N-didecylamine, N,N-di(undecyl)amine, N,N-di(dodecyl)amine, N,N-distearatelamine, N-methyl-N-propylamine, N-ethyl-N-propylamine, and N-propyl-N-butylamine, as well as cyclic amines such as piperidine.

[0029] Examples of tertiary amines include: triethylamine, tributylamine, trihexylamine, dimethyloctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilauryl monomethylamine, etc.

[0030] Furthermore, as an amine, a diamine compound having two amino groups in one compound can also be used. Examples of diamine compounds include ethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, N,N'-diethylethylenediamine, 1,3-propanediamine, 2,2-dimethyl-1,3-propanediamine, N,N-dimethyl-1,3-propanediamine, N,N'-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine, N,N'-diethyl-1,3-propanediamine, 1, 4-Butanediamine, N,N-dimethyl-1,4-butanediamine, N,N'-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N'-diethyl-1,4-butanediamine, 1,5-pentanediamine, 1,5-diamino-2-methylpentane, 1,6-hexanediamine, N,N-dimethyl-1,6-hexanediamine, N,N'-dimethyl-1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, etc.

[0031] The preferred amine compounds on the surface of the silver particles A of the present invention are n-propylamine, isopropylamine, cyclopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclobutylamine, n-pentylamine, n-hexylamine, cyclohexylamine, n-octylamine, 2-ethylhexylamine, n-dodecylamine, n-oleylamine, 3-methoxypropylamine, 3-ethoxypropylamine, N,N-dimethyl-1,3-diaminopropane, N,N-diethyl-1,3-diaminopropane, and more preferably n-butylamine, n-hexylamine, n-octylamine, 3-methoxypropylamine, n-dodecylamine, N,N-dimethyl-1,3-diaminopropane, N,N-diethyl-1,3-diaminopropane, and cyclohexylamine.

[0032] The amount of amine compound adhering to the silver particles A of the present invention is not particularly limited. Using the mass of the silver particles as 100% by mass, it is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and preferably 0.05% by mass or more regarding the lower limit. The content of amine compound adhering to the silver particles can be determined by thermogravimetric differential thermal analysis.

[0033] Furthermore, fatty acids, hydroxy fatty acids, etc., may be attached to the surface of silver particles A. There are no particular limitations on the fatty acid, but fatty acids with 3 or more but less than 18 carbon atoms in the alkyl group are preferred, and fatty acids with 4 or more but less than 18 carbon atoms in the alkyl group are more preferred. Specific examples of preferred fatty acids include acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, octanoic acid, 2-ethylhexanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and α-linolenic acid. Additionally, cyclic alkyl carboxylic acids such as cyclohexanecarboxylic acid may also be used as specific examples of fatty acids. Furthermore, compounds with 3 to 24 carbon atoms and having one or more (e.g., one) hydroxyl groups can be used as hydroxy fatty acids. In addition, 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-hydroxydocosahexadecanoic acid, 2-hydroxytricosahexadecanoic acid, 2-hydroxytetracosanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, 3-hydroxyheptadecanoic acid, 3-hydroxyheptadecanoic acid, 3-hydroxyoctadecanoic acid, ω-hydroxy-2-decenoic acid, ω-hydroxypentadecanoic acid, ω-hydroxyheptadecanoic acid, ω-hydroxyeicosanoic acid, ω-hydroxydocosahexadecanoic acid, ω-hydroxyeicosanoic acid, 6-hydroxyoctadecanoic acid, ricinoleic acid, 12-hydroxyoctadecanoic acid, [R-(E)]-12-hydroxy-9-octadecenoic acid, etc. Preferably, hydroxy fatty acids have 4 to 18 carbon atoms and a hydroxyl group other than the ω-position (especially the 12-position), with ricinoleic acid, 12-hydroxystearic acid, and oleic acid being more preferred. One type of fatty acid and one type of hydroxy fatty acid may be used alone, or two or more may be used in combination.

[0034] In the silver particles A of the present invention, the amount of fatty acids and hydroxy fatty acids attached is adjusted appropriately, similar to that of amine compounds. There are no particular limitations on the specific amount of fatty acids or hydroxy fatty acids attached; using the mass of silver particles A as 100% by mass, it is preferably 1.5% by mass or less, more preferably 1.3% by mass or less, and most preferably 0.01% by mass or more. The content of fatty acids and hydroxy fatty acids attached to silver particles A can be determined by differential thermal analysis.

[0035] It should be noted that, limited to the aforementioned average particle size, amine compounds, fatty acids, and hydroxy fatty acids can also be used in combination, and other compounds different from these can also be attached to the surface of the silver particles. Amine compounds are particularly preferably attached to the surface of the silver particles A of the present invention.

[0036] Silver Particle B The silver particles B of the present invention are in the range of 40 nm to 500 nm. While the average particle size of silver particles B only needs to be in the range of 40 nm to 500 nm, from the viewpoint of further suitably achieving the effects of the present invention, regarding the lower limit, preferably 50 nm or more, more preferably 60 nm or more, and regarding the upper limit, preferably 300 nm or less, more preferably 250 nm or less, and even more preferably 200 nm or less. Preferred ranges include 40–300 nm, 40–250 nm, 40–200 nm, 50–300 nm, 50–250 nm, 50–200 nm, 60–300 nm, 60–250 nm, and 60–200 nm.

[0037] In this invention, the average particle size of silver particles B is the volume-based average particle size measured from 200 randomly selected particles in a SEM image using image analysis software (e.g., Macview, manufactured by Mountech). It should be noted that during SEM observation, SED mode (secondary electron detector) is used, with an accelerating voltage of 20 kV and an observation magnification of 5000 to 30000 times, observing a width of 1 to 20 μm. It should be noted that the vertical dimension of the SEM image is set to the width of at least 200 (typically around 200 to 300) silver particles within a width of 1 to 20 μm. Furthermore, the volume-based average particle size is a value measured assuming the particles observed in the SEM image are spherical with their diameter. The specific measurement method is as described in the examples.

[0038] Furthermore, the weight reduction rate of the dried powder of silver particles B of the present invention when heated from 30°C to 500°C by thermogravimetric differential thermal analysis is preferably 1.5% by weight or less, more preferably 0.05% to 1.3% by weight. The thermogravimetric differential thermal analysis method is as follows.

[0039] <Thermogravimetric Differential Thermal Analysis (TG-DTA)> First, prepare air-dried silver particles B. For example, in the case of analyzing silver particles B obtained from a conductive binder, add 2g of methanol to 1g of each conductive binder and disperse thoroughly. Filter and air-dry the silver particles B to obtain a dry silver powder, which is used as the analyte. Measure the TG-DTA of the dry silver powder using a thermogravimetric differential thermal analysis (TG-DTA) apparatus (e.g., HITACHI G300 AST-2). The measurement conditions are set as follows: atmosphere: air; measurement temperature: 30–500°C; heating rate: 10°C / min. From the obtained TG-DTA graph, obtain the pyrothermal peak caused by the binding of silver particles B in the TG-DTA analysis and the weight loss rate when heated from 30°C to 500°C by thermal analysis.

[0040] From the viewpoint of further suitably achieving the effects of the present invention, it is preferable to perform surface treatment on the silver particles B. That is, the silver particles B of the present invention are preferably surface-treated silver particles.

[0041] More specifically, the surface of the silver particles B of the present invention is preferably coated with an amine compound. The amine compound can adhere to the surface of the silver particles B to form a protective layer. Preferably, in the silver particles B of the present invention, the amine compound is adhered in such a way that the average particle size is set to the aforementioned specific range.

[0042] There are no particular limitations on the amine compounds. From the viewpoint of further suitably achieving the effects of the present invention, examples include primary amines, secondary amines, tertiary amines, and diamine compounds having two amino groups in one compound.

[0043] Examples of primary amines include: ethylamine, n-propylamine, isopropylamine, 1,2-dimethylpropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, isopentylamine, n-octylamine, 2-octylamine, tert-octylamine, 2-ethylhexylamine, n-nonylamine, n-decylamine, n-undecylamine, n-dodecylamine, n-tridecylamine, 2-tridecylamine, n-tetradecylamine, n-pentadecanylamine, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, and n-oleylamine. Amines with straight-chain or branched hydrocarbon groups, such as 3-methoxypropylamine, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, 3-butoxypropylamine, N-ethyl-1,3-diaminopropane, N,N-diisopropylethylamine, N,N-dimethyl-1,3-diaminopropane, N,N-dibutyl-1,3-aminopropane, N,N-diisobutyl-1,3-diaminopropane, and N-lauryldiaminopropane.

[0044] Examples of other examples include cyclopropylamine, cyclobutylamine, cyclopropylamine, cyclohexylamine, cycloheptylamine, cyclooctylamine, and aniline, which are alicyclic amines. Other examples include ether amines such as 3-isopropoxypropylamine and isobutoxypropylamine.

[0045] Examples of secondary amines include dialkyl monoamines such as N,N-dipropylamine, N,N-dibutylamine, N,N-dipentylamine, N,N-dihexylamine, N,N-diheptylamine, N,N-dioctylamine, N,N-dinonylamine, N,N-didecylamine, N,N-di(undecyl)amine, N,N-di(dodecyl)amine, N,N-distearatelamine, N-methyl-N-propylamine, N-ethyl-N-propylamine, and N-propyl-N-butylamine, as well as cyclic amines such as piperidine.

[0046] Examples of tertiary amines include: triethylamine, tributylamine, trihexylamine, dimethyloctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilauryl monomethylamine, etc.

[0047] Furthermore, as an amine, a diamine compound having two amino groups in one compound can also be used. Examples of diamine compounds include ethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N-diethylethylenediamine, N,N'-diethylethylenediamine, 1,3-propanediamine, 2,2-dimethyl-1,3-propanediamine, N,N-dimethyl-1,3-propanediamine, N,N'-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine, N,N'-diethyl-1,3-propanediamine, 1, 4-Butanediamine, N,N-dimethyl-1,4-butanediamine, N,N'-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine, N,N'-diethyl-1,4-butanediamine, 1,5-pentanediamine, 1,5-diamino-2-methylpentane, 1,6-hexanediamine, N,N-dimethyl-1,6-hexanediamine, N,N'-dimethyl-1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, etc.

[0048] The preferred amine compounds on the surface of the silver particles B of the present invention are n-propylamine, isopropylamine, cyclopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclobutylamine, n-pentylamine, n-hexylamine, cyclohexylamine, n-octylamine, 2-ethylhexylamine, n-dodecylamine, n-oleylamine, 3-methoxypropylamine, 3-ethoxypropylamine, N,N-dimethyl-1,3-diaminopropane, and N,N-diethyl-1,3-diaminopropane. More preferred are n-butylamine, n-hexylamine, n-octylamine, 3-methoxypropylamine, n-dodecylamine, N,N-dimethyl-1,3-diaminopropane, and N,N-diethyl-1,3-diaminopropane.

[0049] The amount of amine compound adhering to the silver particles B of the present invention is not particularly limited. Using the mass of the silver particles as 100% by mass, it is preferably 1.5% by mass or less, more preferably 1.3% by mass or less, and preferably 0.05% by mass or more regarding the lower limit. The content of amine compound adhering to the silver particles can be determined by thermogravimetric differential thermal analysis.

[0050] Furthermore, fatty acids, hydroxy fatty acids, etc., may be attached to the surface of silver particles B. There are no particular limitations on the fatty acid, but fatty acids with 3 or more and 18 or fewer carbon atoms in the alkyl group are preferred, and fatty acids with 4 or more and 18 or fewer carbon atoms in the alkyl group are more preferred. Specific examples of preferred fatty acids include acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, octanoic acid, 2-ethylhexanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and α-linolenic acid. Additionally, cyclic alkyl carboxylic acids such as cyclohexanecarboxylic acid may also be used as specific examples of fatty acids. Furthermore, compounds with 3 to 24 carbon atoms and having one or more (e.g., one) hydroxyl groups can be used as hydroxy fatty acids. In addition, 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-hydroxydocosahexadecanoic acid, 2-hydroxytricosahexadecanoic acid, 2-hydroxytetracosanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, 3-hydroxyheptadecanoic acid, 3-hydroxyheptadecanoic acid, 3-hydroxyoctadecanoic acid, ω-hydroxy-2-decenoic acid, ω-hydroxypentadecanoic acid, ω-hydroxyheptadecanoic acid, ω-hydroxyeicosanoic acid, ω-hydroxydocosahexadecanoic acid, ω-hydroxyeicosanoic acid, ω-hydroxydocosahexadecanoic acid, 6-hydroxyoctadecanoic acid, ricinoleic acid, 12-hydroxystearic acid, [R-(E)]-12-hydroxy-9-octadecenoic acid, etc. Preferably, hydroxy fatty acids have 4 to 18 carbon atoms and one hydroxyl group except for the ω position (especially the 12 position), and more preferably ricinoleic acid and 12-hydroxystearic acid. One type of fatty acid and one type of hydroxy fatty acid may be used alone, or two or more types may be used in combination.

[0051] In the silver particles B of the present invention, the amount of fatty acids and hydroxy fatty acids attached is adjusted appropriately, similar to that of amine compounds. There are no particular limitations on the specific amount of fatty acids or hydroxy fatty acids attached; using the mass of silver particles B as 100% by mass, it is preferably 1.5% by mass or less, more preferably 1.3% by mass or less, and most preferably 0.01% by mass or more. The content of fatty acids and hydroxy fatty acids attached to the silver particles B can be determined by differential thermal analysis.

[0052] It should be noted that, limited to the aforementioned average particle size, amine compounds, fatty acids, and hydroxy fatty acids can also be used in combination, and other compounds different from these can also be attached to the surface of the silver particles. Amine compounds are particularly preferably attached to the surface of the silver particles B of the present invention.

[0053] Silver Particle C The average particle size of the silver particles C in this invention only needs to be in the range of 0.5 to 5.5 μm. However, from the viewpoint of further suitably achieving the effects of this invention, it is preferable that the lower limit is 0.6 μm or more, and the upper limit is preferably 3.0 μm or less, more preferably 2.5 μm or less, and even more preferably 2.0 μm or less. As preferred ranges, 0.5 to 3.0 μm, 0.5 to 2.5 μm, 0.5 to 2.0 μm, 0.6 to 3.0 μm, 0.6 to 2.5 μm, and 0.6 to 2.0 μm are also mentioned.

[0054] In this invention, the average particle size of silver particles C can be determined by a particle size distribution measuring device using laser diffraction and scattering, or it can be measured by an electron microscope image, and then calculated from the electron microscope image using an image processing device.

[0055] In this invention, the silver particles C can be commercially available products or substances synthesized by known synthetic methods.

[0056] From the viewpoint of effectively improving the mechanical strength of the sintered body, in the conductive adhesive of the present invention, the mass ratio (A:B:C) of silver particles A, silver particles B, and silver particles C is only about 1 to 20:30 to 60:40 to 70, and preferably about 1 to 15:30 to 50:40 to 60.

[0057] solvent As a solvent, there are no particular limitations as long as it can disperse silver particles, but polar organic solvents are preferred. 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; and ethers such as 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-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 1, Diols such as 2-octanediol, 1,8-octanediol, and 2-ethyl-1,3-hexanediol; glycerol; straight-chain or branched alcohols with 1 to 5 carbon atoms, cyclohexanol, 3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, etc.; fatty acid esters such as ethyl acetate, butyl acetate, ethyl butyrate, ethyl formate, and Texanol; polyethylene glycol, triethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, etc. Ethers, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 3-methoxybutyl acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monoethyl 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 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, propylene 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, tripropylene glycol monobutyl ether, etc., are ethylene glycol or ethylene glycol ethers; N,N-dimethylformamide; dimethyl sulfoxide; terpenoids such as terpineol; acetonitrile; γ-butyrolactone; 2-pyrrolidone; N-methylpyrrolidone; dimethyl sulfoxide N-(2-aminoethyl)piperazine, etc. From the viewpoint of further suitably achieving the effects of the present invention, the preferred choices are straight-chain or branched alcohols having 3 to 5 carbon atoms, such as 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.

[0058] Regarding solvents, in addition to polar organic solvents, nonpolar or hydrophobic solvents may be further included. Examples of nonpolar organic solvents include straight-chain, branched, or cyclic saturated hydrocarbons such as hexane, heptane, octane, nonane, decane, 2-ethylhexane, and cyclohexane; alcohols such as straight-chain or branched alcohols with 6 or more carbon atoms; aromatic compounds such as benzene, toluene, and benzonitrile; halogenated hydrocarbons such as dichloromethane, chloroform, and dichloroethane; methyl pentyl ketone; methyl ethyl ketone oxime; and triacetin. Among these, saturated hydrocarbons and straight-chain or branched alcohols with 6 or more carbon atoms are preferred, and hexane, octane, decane, octanol, decanol, and dodecanol are more preferred. One solvent may be used alone, or two or more solvents may be used in combination.

[0059] When both polar and non-polar organic solvents are included, the ratio of 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. Furthermore, it can be set to 60% by volume or less, 55% by volume or less, or 50% by volume or less. The solvent may also consist solely of polar organic solvents. Even when the conductive adhesive of the present invention contains a large amount of polar organic solvent, the silver particles exhibit good dispersibility.

[0060] In the conductive adhesive of the present invention, the ratio of solvent is not particularly limited, but is preferably 20% by mass or less, and more preferably about 5% to 15% by mass.

[0061] The content of silver particles (the sum of silver particles A, silver particles B, and silver particles C) in the conductive adhesive of the present invention is preferably 80% by mass or more, and more preferably 85% by mass or more.

[0062] The conductive adhesive of the present invention can be manufactured by a method comprising a step of mixing each silver particle with a solvent.

[0063] Furthermore, in the method for manufacturing the conductive adhesive of the present invention, the silver particles of the present invention generated in the solvent in the method for manufacturing the silver particles of the present invention described later may also be used together with the solvent as the conductive adhesive of the present invention.

[0064] The shear strength of the sintered body obtained by heating the conductive adhesive of the present invention at 200°C is preferably 73 MPa or more, more preferably 77 MPa or more, and even more preferably 80 MPa or more. It should be noted that the upper limit of this shear strength is, for example, 200 MPa or less. Furthermore, the shear strength of the sintered body obtained by heating the conductive adhesive of the present invention at 250°C is preferably 70 MPa or more, more preferably 72 MPa or more, and even more preferably 75 MPa or more. It should be noted that the upper limit of this shear strength is, for example, 200 MPa or less. The method for measuring the shear strength of the sintered body is as described below; specifically, it can be measured using the method described in the examples.

[0065] <Shear Strength> First, a substrate with a 0.5 μm non-electrolytic silver plating is prepared on a copper plate. A conductive binder (a dispersion of silver particles comprising 90% by mass of silver particles and 10% by mass of solvent (e.g., Texanol)) is uniformly coated onto the substrate (the silver-plated surface) to a thickness of 50–100 μm (adjusted to the thickness of the bond after sintering). Next, a silicon wafer (2 mm × 2 mm) with a gold-plated back side (the side in contact with the conductive binder) is stacked on top of the coating to obtain a laminate. Then, using a dryer (circulating type), the resulting laminate is heated at a specific sintering temperature (200°C or 250°C) for 60 minutes to sinter the conductive binders between the substrate and the silicon wafer, creating nine laminates formed by bonding the substrate and silicon wafer via sintering. The thickness of the bond is 30–90 μm, ensuring that the thickness of the conductive binders to be compared is consistent. For the obtained laminates, a shear test was performed on each laminate at room temperature using a bonding tester (e.g., Nishishin Shoji SS30-WD) at a speed of 0.120 mm / s, and the maximum load at fracture was measured. The maximum load obtained was divided by the bonding area to obtain the shear strength value. It should be noted that the measurement result is the average of nine gold-plated silicon wafers whose shear strength was measured. It should also be noted that the sintering time at the specific sintering temperature can be more than 60 minutes, or a pre-sintering of less than 2 hours at 50–100°C can be performed before the formal sintering at the specific sintering temperature.

[0066] Furthermore, the density of the sintered body obtained by heating the conductive adhesive of the present invention at 200°C is preferably 80% or more, more preferably 85% or more. It should be noted that the upper limit of this density is, for example, 95% or less. Additionally, the density of the sintered body obtained by heating the conductive adhesive of the present invention at 250°C is preferably 83% or more, more preferably 85% or more. It should be noted that the upper limit of this density is, for example, 97% or less. The method for measuring the density of the sintered body is as follows; specifically, it can be measured using the method described in the examples.

[0067] <Density> Similar to the method described in the <Shear Strength> section, a laminate in which the substrate and silicon wafer are bonded via a sintering body is obtained. Next, the sintering body is resin-embedded with the laminate and epoxy resin (e.g., manufactured by Buehler), and left to stand for 24 hours to allow the resin to cure. Then, the resin-embedded laminate is cut using a precision low-speed cutting machine (e.g., the TechCut4 manufactured by ALLIED), and the cross-section is ground using an ion milling machine (e.g., the IM4000PLUS manufactured by Hitachi High-Tech). It should be noted that the cross-section grinding is performed with a discharge voltage of 1.5 kV, an accelerating voltage of 6 kV, and an argon flow rate of 0.07 cm³. 3 The ion beam was irradiated at a rate of ±30° per minute. The cross-section of the sintered body obtained through cross-sectional grinding was observed using a scanning electron microscope (SEM) to obtain SEM images. In the SEM observation, SED mode (secondary electron detector) was used, with an accelerating voltage of 20 kV and a field of view of 2000x, observing a width of 60 μm. It should be noted that the longitudinal direction of the SEM image was set to a width of 30 μm or more but less than 200 μm for the sintered silver layer. This is because if the sintered silver layer is less than 10 μm, its mechanical strength as a bonding agent may be compromised; furthermore, if it exceeds 200 μm, the volume of the laminate increases, making it difficult for venting during sintering to occur uniformly, which is disadvantageous from a reliability standpoint. This observation range is not limited to 2 mm × 2 mm chips; even chips of 5 mm × 5 mm or larger are observed within the same range. It should be noted that when the sintered body structure has high inhomogeneity, multiple observations were conducted over a range with a width of 60 μm and a length of 30 μm or more, and the average value was taken as the density. The density was calculated by converting the intensity of the obtained SEM image into two gray levels of white and black using binarization software (Imagej), and then obtaining the density using the following formula. Density (%) = Sintered silver area (number of white pixels) ÷ Total sintered body area {Sintered silver area (number of white pixels) + Void area (number of black pixels)} × 100

[0068] <Specific resistivity> A conductive binder (a silver particle dispersion comprising 90% by mass of silver particles and 10% by mass of solvent (e.g., Texanol)) was uniformly coated onto a polyimide film at a thickness of 50 μm, with a diameter of 2 mm × 60 mm. The film was then sintered at a specific temperature (200°C or 250°C) for 60 minutes to obtain a sintered body. Next, the resistance of the sintered body was measured at room temperature using a ohmmeter (e.g., HIOKIRM3548). The specific resistivity (volume resistivity) was calculated based on the value obtained by measuring the actual film thickness using a micrometer. It should be noted that this specific resistivity value is the average of values ​​obtained from measurements at four locations on the sintered body.

[0069] Furthermore, the resistivity of the sintered body obtained by heating the conductive adhesive of the present invention at 200°C is preferably 3.5 μΩ·cm or less, more preferably 3.3 μΩ·cm or less, and even more preferably 3.0 μΩ·cm or less. It should be noted that the lower limit of this resistivity value is, for example, 2.0 μΩ·cm or more. Additionally, the resistivity of the sintered body obtained by heating the conductive adhesive of the present invention at 250°C is preferably 3.2 μΩ·cm or less, more preferably 3.0 μΩ·cm or less. It should be noted that the lower limit of this resistivity value is, for example, 1.8 μΩ·cm or more. The method for measuring the resistivity of the sintered body is as described in the aforementioned <Resistivity Value> section; specifically, it can be measured using the method described in the examples.

[0070] <Gap> Similar to the density measurement described above, SEM images of the sintered body were obtained. For the SEM images binarized using Imagej, image processing was performed using Macview image analysis software (manufactured by Mounttech). (Through automatic color difference reading, the void portions of the binarized image were analyzed as particles). The voids in the sintered body were assumed to be spherical, and the average size of the number of voids was calculated. The specific surface area of ​​the sintered body was then calculated from the surface area per unit volume of the aforementioned sphere. It should be noted that void portions refer to fine pores generated by degassing and particle growth, distinct from vacancies and cracks. Fine pores are defined as materials with a diameter of 50 nm or more but less than 10 μm. Holes exceeding 10 μm in diameter formed by continuous voids are called vacancies or cracks, and are excluded from the void portion calculation. This value is obtained by calculating the voids that appear when the cross-sectional SEM image is binarized as described above.

[0071] Furthermore, the sintered body obtained by heating the conductive adhesive of the present invention at 200°C has the following characteristics in terms of its voids. It should be noted that the sintered body is a material formed by the method described in the aforementioned <Shear Strength> section. The average size of the voids is, for example, 0.3 to 1.1 μm. The specific surface area of ​​the voids is, for example, 0.15 to 1.0 μm². 2 The average size of the number of elements was calculated using the image processing methods described above in Macview.

[0072] 2. Method for manufacturing silver particles The following illustrates an example of a method for manufacturing silver particles contained in the conductive adhesive of the present invention.

[0073] First, a composition for manufacturing silver particles (composition for preparing silver particles) is prepared. Specifically, a silver compound as a raw material for silver particles, an amine compound to be attached to the surface of the silver particles as needed, and a solvent are prepared. From the viewpoint of further suitably achieving the effects of the present invention, preferred silver compounds include silver nitrate, silver oxalate, etc., with silver oxalate being particularly preferred. It should be noted that the same substance as that exemplified as the solvent used in conjunction with the conductive binder described later can be used as an example of a solvent. Next, these components are mixed to obtain the composition for preparing silver particles. The proportions of the components in this composition are appropriately adjusted. For example, the content of silver oxalate in the composition is preferably about 20 to 70% by mass relative to the total amount of the composition. Furthermore, if an amine compound is attached to the surface of the silver particles, the content of the amine compound is preferably about 5% to 55% by mass relative to the total amount of the composition. Furthermore, if a fatty acid is attached to the surface of the silver particles, the content of the fatty acid is preferably about 0.1% to 20% by mass relative to the total amount of the composition. If the hydroxy fatty acids are attached to the surface of the silver particles, the content of the hydroxy fatty acids, relative to the total amount of the composition, is preferably set to about 0.1% to 15% by mass.

[0074] It should be noted that a composition for preparing silver particles may also be used, in which the content of amine compounds, etc., is adjusted to be outside the aforementioned range, to temporarily synthesize silver particles, and the type and amount of amine compounds, etc., can be adjusted by the method described later to achieve the aforementioned physical properties (displacement of amine compounds).

[0075] Furthermore, there are no particular restrictions on the mixing method of the components; common equipment such as mechanical stirrers, magnetic stirrers, vortex mixers, planetary mills, ball mills, three-roll mills, pipeline mixers, planetary mixers, and dissolvers can be used for mixing. To avoid the temperature rise of the composition and the initiation of thermal decomposition of the silver particles due to the heat of solution, frictional heat, etc., during mixing, it is preferable to mix while keeping the temperature of the composition below, for example, 60°C, and especially below 40°C.

[0076] Next, by reacting the silver particle preparation composition in a reaction vessel, typically using heating, a thermal decomposition reaction of the silver compound occurs, and silver particles are generated. In the reaction, the composition can be introduced into a preheated reaction vessel, or it can be introduced into the reaction vessel and then heated.

[0077] The reaction temperature can be any temperature at which the thermal decomposition reaction takes place and silver particles are formed, for example, around 50 to 250°C. Furthermore, the reaction time can be appropriately selected based on the desired average particle size and the corresponding composition of the mixture. Examples of reaction times include 1 minute to 100 hours.

[0078] Since the silver particles generated by the thermal decomposition reaction are obtained as a mixture containing unreacted raw materials, it is preferable to refine the silver particles. Refining methods include solid-liquid separation methods and precipitation methods utilizing the density difference between the silver particles and unreacted raw materials such as organic solvents. Solid-liquid separation methods include filtration, centrifugation, cyclone separation, or decantering. To facilitate the refining process, the mixture containing silver particles can be diluted with low-boiling-point solvents such as acetone or methanol to adjust its viscosity.

[0079] The average particle size of the resulting silver particles can be adjusted by changing the composition of the silver particle manufacturing composition and the reaction conditions.

[0080] Methods for replacing and adjusting amine compounds on the surface of silver particles Using the aforementioned method, temporarily synthesized silver particles (with amine compounds attached to their surface) are prepared and dispersed in a solvent. Examples of solvents include substances similar to those used in conjunction with the conductive binder described later. Next, other amine compounds are added in an amount ranging from 0.1 to 5 times the mass of the silver particles, and a stirring process is performed at room temperature to 80°C for 1 minute to 24 hours. This allows for the replacement of the type of amine compound attached to the surface of the silver particles or adjustment of the amount attached. The silver particles with replaced amine compounds can be recovered using methods such as the aforementioned solid-liquid separation.

[0081] 3. Sintered bodies of conductive adhesives The sintered body of the conductive adhesive of the present invention is obtained by sintering the conductive adhesive of the present invention as detailed in "1. Conductive Adhesive". In the sintered body of the conductive adhesive of the present invention, most of the components (amine compounds, etc.) and solvents adhering to the surface of the silver particles are removed by the high heat during sintering, and the sintered body is substantially composed of silver.

[0082] There are no particular limitations on the sintering temperature, but from the viewpoint of improving the shear strength and density of the resulting sintered body while appropriately sintering at a low temperature, examples include temperatures below 250°C, preferably around 150°C to 250°C, and more preferably around 200°C to 250°C. Similarly, from the same viewpoint, the sintering time is preferably around 0.4 hours to 2.0 hours, and more preferably around 0.5 hours to 1.5 hours. It should be noted that the sintering time refers to the time for formal sintering (maintaining the specified temperature after reaching it). In addition, pre-sintering (a process of gently heating at a low temperature below 100°C before reaching the specified temperature) may also be performed. In this invention, the conductive adhesive contains silver particles A with an average particle size of less than 40 nm, silver particles B with an average particle size in the range of 40 to 500 nm, and silver particles C with an average particle size in the range of 0.5 to 5.5 μm. By satisfying a specific ratio range for silver particles A, B, and C, the conductive adhesive can be suitably sintered at low temperatures below 250°C even without pressure during sintering, forming a sintered body with high density and mechanical strength (shear strength). Therefore, pressure is not necessary during the sintering of the conductive adhesive of this invention. That is, the conductive adhesive of this invention can be suitably used for applications where pressure is not applied during sintering. It should be noted that pressure can also be applied during the sintering of the conductive adhesive of this invention, for example, at a pressure of about 10 to 30 MPa. Sintering can be carried out in an atmosphere such as air or an inert gas (nitrogen, argon). There are no particular restrictions on sintering methods; examples include ovens, hot air drying furnaces, infrared drying furnaces, laser irradiation, flash lamp irradiation, and microwaves.

[0083] The sintered body of the conductive adhesive of the present invention can be obtained by sintering a substance uniformly coated on a substrate at a specific temperature. However, the film thickness when coated on the substrate can be appropriately adjusted according to the purpose, for example, a thickness of about 10 to 100 μm is sufficient. Furthermore, when using large semiconductor chips (e.g., about 10 mm × 10 mm), a thicker film is preferred. Therefore, a film thickness of 30 μm or more when coated on the substrate is preferred, preferably 40 μm or more, and more preferably 50 μm or more. It should be noted that the upper limit of the film thickness in this case is 200 μm or less, preferably 100 μm or less. By setting the film thickness as described above, even when using large semiconductor chips, sufficient shear strength can be obtained, resulting in a sintered body that is not prone to cracking, defects, vacancies, or fissures.

[0084] The sintered body of the present invention preferably satisfies at least one of the shear strength, density, and resistivity values ​​shown in the "1. Conductive binder" column. The methods for measuring these properties are as described in the aforementioned <Shear Strength>, <Density>, and <Resistivity> columns.

[0085] 4. Electronic components The electronic component of the present invention includes a portion in which components are bonded together using a sintered body of the present invention. That is, the electronic component of the present invention is an adhesive that bonds the components together by disposing the conductive adhesive of the present invention, which is described in detail in "2. Conductive Adhesive", between the components of the electronic component (e.g., between components included in a circuit) and sintering the conductive adhesive.

[0086] As mentioned above, the sintered body of the present invention has high density and shear strength, thus resulting in high inter-component shear strength in electronic components incorporating it. Furthermore, the resistivity of the electronic components of the present invention can be set to a lower value. Example

[0087] The invention will be described in more detail in the following embodiments, but the invention is not limited to these embodiments.

[0088] Details of the components 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-Dimethyl-1,3-diaminopropane (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • N,N-Diethyl-1,3-Diaminopropane (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • Hexylamine (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • Octylamine (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • Dodecylamine (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) Cyclohexylamine (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • n-Butylamine (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • Ricinol (manufactured by Tokyo Chemical Industry Co., Ltd.) Oleic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) ·1-Butanol (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) Methanol (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) • Texanol (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.)

[0089] <Synthesis Example 1> Synthesis of silver particles A1 (average particle size 33 nm) Oleic acid (0.06 g), n-octylamine (1.40 g), N,N-dimethyl-1,3-diaminopropane (0.43 g), n-dodecylamine (0.16 g), cyclohexylamine (0.12 g), and n-butylamine (0.64 g) were added to a 50 mL glass centrifuge tube equipped with a magnetic stirrer. After stirring for about 1 minute, silver oxalate (3.2 g) was added, and the mixture was stirred for about 10 minutes to obtain a composition for preparing silver particles. These glass centrifuge tubes were then placed upright on a heated stirrer equipped with an aluminum block (HHE-19G-U manufactured by Koike Precision Machinery Co., Ltd.), and stirred in a 40°C hot water bath for 30 minutes, followed by stirring in a 90°C oil bath for 30 minutes. After cooling, remove the magnetic stir bar, add 15g of methanol to each composition, stir with a vortex mixer, and then centrifuge (Hitachi Kogyo CF7D2) at 3000rpm (approximately 1600×G) for 1 minute, tilting the centrifuge tube to remove the supernatant. Repeat the process of adding 15g of methanol, stirring, centrifuging, and removing the supernatant twice to recover the manufactured silver particles A1 (average particle size 33nm).

[0090] <Synthesis Example 2> Synthesis of silver particles B1 (average particle size 68 nm) Castor oil acid (2.34 g), N,N-diethyl-1,3-diaminopropane (203 g), and 1-butanol (375 g) were added to 50 mL glass centrifuge tubes equipped with a magnetic stir bar. After stirring for about 1 minute, silver oxalate (250 g) was added, and the mixture was stirred for about 10 minutes to obtain a composition for preparing silver particles B1. These glass centrifuge tubes were then placed upright on a heated 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 another 30 minutes. After cooling, the magnetic stir bar was removed, and 15 g of methanol was added to each composition. After stirring with a vortex mixer, the mixture was centrifuged at 3000 rpm (approximately 1600 × G) for 1 minute using a centrifuge (Hitachi Kogyo CF7D2), with the centrifuge tubes tilted to remove the supernatant. The process of adding 15g of methanol, stirring, centrifuging, and removing the supernatant was repeated twice to recover the silver particles.

[0091] Next, using the resulting silver particle dispersion (methanol solution), hexylamine was added at three times the mass of the silver particles, and the mixture was stirred at room temperature for 4 hours. After stirring, the magnetic stir bar was removed, and 15g of methanol was added to each composition. After stirring with a vortex mixer, the mixture was centrifuged at 3000 rpm (approximately 1600 × G) for 1 minute using a centrifuge (Hitachi Kogyo CF7D2), with the centrifuge tube tilted to remove the supernatant. The process of adding 15g of methanol, stirring, centrifuging, and removing the supernatant was repeated twice to recover silver particles B1 (average particle size 68nm) that had replaced the protective layer on the surface of the silver particles with hexylamine.

[0092] <Synthesis Example 3> Synthesis of silver particles B2 (average particle size 181 nm) Castor oil acid (6.25 g), N,N-diethyl-1,3-diaminopropane (203 g), and 1-butanol (187.5 g) were added to 50 mL glass centrifuge tubes equipped with a magnetic stir bar. After stirring for about 1 minute, silver oxalate (250 g) was added, and the mixture was stirred for about 10 minutes to obtain a composition for preparing silver particles B2. These glass centrifuge tubes were then placed upright on a heated 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 another 30 minutes. After cooling, the magnetic stir bar was removed, and 15 g of methanol was added to each composition. After stirring with a vortex mixer, the mixture was centrifuged at 3000 rpm (approximately 1600 × G) for 1 minute using a centrifuge (Hitachi Kogyo CF7D2), with the centrifuge tubes tilted to remove the supernatant. The process of adding 15g of methanol, stirring, centrifuging, and removing the supernatant was repeated twice to recover the silver particles.

[0093] Next, using the resulting silver particle dispersion (methanol solution), hexylamine was added at three times the mass of the silver particles, and the mixture was stirred at room temperature for 4 hours. After stirring, the magnetic stir bar was removed, and 15g of methanol was added to each composition. After stirring with a vortex mixer, the mixture was centrifuged at 3000 rpm (approximately 1600 × G) for 1 minute using a centrifuge (Hitachi Kogyo CF7D2), with the centrifuge tube tilted to remove the supernatant. The process of adding 15g of methanol, stirring, centrifuging, and removing the supernatant was repeated twice to recover silver particles B2 (average particle size 181nm) with the protective layer replaced by hexylamine.

[0094] <Silver Particle C> • As silver particles C1 (average particle size 0.65μm), the product name AG2-1C manufactured by Dowa Electronics Corporation is used. • As silver particles C2 (average particle size 1.88μm), it uses the product name AG3-1F manufactured by Dowa Electronics Corporation.

[0095] Silver particles A1, B1, B2, C1, and C2 were observed using a scanning electron microscope (SEM image acquisition) and their average particle size (volume-based average particle size) was measured under the following conditions. The results are shown in Table 1.

[0096] <Observations using an electron microscope> For silver particles A1, B1, B2, C1, and C2, SEM images were obtained using a scanning electron microscope (SEM, JSM-IT500HR, Nippon Electron). [Images were then extracted from the images.] Figure 1 The image shows a SEM image of silver particle A1. Figure 2 The image shows a SEM image of silver particle B1. Figure 3 The image shows a SEM image of silver particles B2. Figure 4 The image shows a SEM image of silver particles C1. Figure 5 The image shown is an SEM image of silver particles C2.

[0097] <Thermogravimetric Differential Thermal Analysis (TG-DTA Determination)> Silver particles A1, B1, and B2 were analyzed using TG-DTA. Specifically, firstly, similar to the process described later in <Preparation of Conductive Adhesive>, silver particles A1, B1, and B2 were each mixed with a solvent (Texanol) to prepare a 90% by mass dispersion of each silver particle. Next, 1g of each silver particle dispersion was added to 2g of methanol, and after thorough dispersion, the silver particles were filtered, air-dried, and the resulting dry powder was obtained. The TG-DTA of the obtained dry silver particle powder was measured using a HITACHI G300 AST-2 thermometer. The measurement conditions were set as follows: atmosphere: air; measurement temperature: 30–500°C; heating rate: 10°C / min. From the obtained TG-DTA graph, the weight loss rate when heated from 30°C to 500°C was obtained through thermal analysis. The results are shown in Table 1.

[0098] [Table 1]

[0099] <Manufacturing of Conductive Adhesives> Conductive adhesives were prepared by mixing silver particles A1, B1, B2, C1, and C2 with a solvent (Texanol) in the manner shown in Tables 2, 3, and 4. Specifically, firstly, 10% by mass of Texanol was added to silver particles A1, B1, B2, C1, and C2 respectively to prepare silver particle dispersions with a concentration of 90% by mass (silver particle dispersions A1, B1, B2, C1, and C2, respectively). During mixing, MAZERUSTAR manufactured by Kurabo Co., Ltd. was used, and mixing was performed in a double-stirring priority mode. Next, each silver particle dispersion and Texanol were mixed in the manner shown in Table 4 to obtain conductive adhesives having the compositions of Examples 1-6 and Comparative Examples 1-8.

[0100] [Table 2] The values ​​for silver particles A, B, C and solvent in Table 2 are in parts by mass.

[0101] [Table 3] The values ​​for silver particles A, B, C and solvent in Table 3 are in parts by mass.

[0102] [Table 4] The values ​​for silver particles A, B, C and solvent in Table 4 are in parts by mass.

[0103] Manufacturing of sintered bodies (sintering temperature 200℃) First, a substrate with a 0.5 μm non-electrolytic silver plating was prepared on a copper plate. A conductive binder (a dispersion of 90% by mass silver particles and 10% by mass Texanol silver particles) was uniformly coated onto the substrate (the silver-plated surface) to a thickness of 50-100 μm. Next, a silicon wafer (2 mm × 2 mm) with a gold-plated back side (the side in contact with the conductive binder) was stacked on top of the coating to obtain a laminate. Then, using a dryer (circulating type), the resulting laminate was heated under specific sintering conditions (200 °C) for 60 minutes to sinter the conductive binders between the substrate and the silicon wafer, creating nine laminates in which the substrate and silicon wafer are bonded via sintering. It should be noted that the thickness of the sintered laminate was made to be 30 μm to 90 μm.

[0104] Various physical properties of each sintered body obtained from the conductive adhesives of Examples 1-6 and Comparative Examples 1-8 were measured under the following test conditions.

[0105] <Mechanical strength (shear strength) of sintered body> For the obtained laminates, a shear test was performed on the sintered body at room temperature using a bonding tester (Nishishin Shoji SS30-WD) at a speed of 0.120 mm / s, and the maximum load at fracture was measured. The maximum load obtained was divided by the bonding area to obtain the shear strength value. It should be noted that the measurement result is the average of the shear strength of nine gold-plated silicon wafers for which shear strength was measured. The shear strength measurement results are shown in Tables 5, 6, and 7.

[0106] <Density of sintered body> Each sintered body was resin-embedded with the aforementioned laminate and epoxy resin (manufactured by Buehler), and allowed to stand for 24 hours to allow the resin to cure. Next, the resin-embedded sintered bodies were cut using a TechCut4 precision low-speed cutter (manufactured by Allied), and the cross-sections were ground for 3 hours using an ion milling machine (IM4000PLUS, manufactured by Hitachi High-Tech). It should be noted that the cross-section grinding was performed with a discharge voltage of 1.5kV, an accelerating voltage of 6kV, and an argon flow rate of 0.07cm³. 3The ion beam was irradiated at a rate of ±30° per minute. The cross-section of the sintered body obtained through cross-sectional grinding was observed using a JSM-IT500HR scanning electron microscope (JEOL Ltd.), and SEM images were obtained. It should be noted that the observation was performed using SED mode (secondary electron detector), with an accelerating voltage of 20 kV and a field of view of 2000x, observing a width of 60 μm. Density was calculated by converting the density of the obtained SEM images to two gray levels (white and black) using binarization software (Imagej), and then using the following formula. The density measurement results are shown in Tables 5 and 6. Density (%) = Sintered silver area (number of white pixels) ÷ Total sintered body area {Sintered silver area (number of white pixels) + Void area (number of black pixels)} × 100

[0107] <Specific resistivity of sintered body> A conductive binder (a dispersion of 90% by mass silver particles and 10% by mass Texanol silver particles) was uniformly coated onto a polyimide film at a thickness of 2 mm × 60 mm × 50 μm. The film was then sintered at a specific temperature (200°C or 250°C) for 60 minutes to obtain a sintered body. Next, at room temperature, the resistance of the sintered body was measured using a two-terminal method with a ohmmeter (HIOKI RM3548). The specific resistivity (volume resistivity) was calculated based on the value obtained by measuring the actual film thickness with a micrometer. It should be noted that this specific resistivity value is the average of the values ​​obtained from measuring four locations on the sintered body. The results of the specific resistivity measurements are shown in Tables 5, 6, and 7.

[0108] <Membrane defects> Each sintered body was observed using SEM in the same manner as 0106, and then image processing was performed to obtain a binarized image of the silver sintered body. In the binarized image, sintered bodies with a diameter exceeding 10 μm and forming voids (black pixels), even if only one void exists, were marked with ×, and sintered bodies without a diameter exceeding 10 μm (black pixels) were marked with ○. It should be noted that, in order not to miss defective areas, observations were performed at least three locations with SEM magnifications that ensured a field of view of approximately 300 μm in width for the rectangular bonding layer. In addition, in the cross-sectional SEM image, sintered bodies with obvious large voids of tens of μm in diameter, even without binarization, chip interfaces, and silver sintered bodies exceeding 10 μm in diameter without a contact point on the lead frame interface, which were judged as unfused, were also marked with ×. It should be noted that the wide range of the cross-sectional SEM image when judging film defects refers to a range with a width of 1 mm to 5 mm. The results regarding the presence or absence of membrane defects are shown in Tables 5, 6, and 7. Furthermore, for the obtained sintered body, in Figure 6 and Figure 7The image shows a cross-sectional SEM photograph of the sintered body of Example 2. Figure 8 and Figure 9 The image shows a cross-sectional SEM photograph of the sintered body of Comparative Example 2. Figure 10 The image shows a cross-sectional SEM photograph of the sintered body of Example 5. Figure 11 The image shows a cross-sectional SEM photograph of the sintered body of the comparative example.

[0109] [Table 5]

[0110] As shown in Table 5, Comparative Example 1, which does not contain silver particles A, exhibits good basic density and shear strength, but its initial filling structure is not dense. This results in an attempt to fill the loose volume portion through silver sintering, leading to defects such as stress cracking. Such poor shrinkage is detrimental to reliability tests and heat resistance tests. On the other hand, Examples 1, 2, and 3 all show higher density than Comparative Example 1, forming a very dense structure. Furthermore, shear strength and resistivity also show good values, with Example 2, containing 10% by weight of silver particles A, showing particularly excellent values. Figure 6 The image shown is a 2000x SEM image of Example 2. It is speculated that they do not produce defects when fabricating films with a thickness greater than 50 μm, which is advantageous in terms of reliability. (As shown in...) Figure 7 As can be confirmed by the wide observation range shown, it is evident that a uniform, dense film can be formed in the composition of the present invention, regardless of the thickness of the film. On the other hand, in Figure 8 The image shown is a 2000x SEM image of Comparative Example 2 with excessive silver particles A. Although some parts are very dense, defects and cracks caused by shrinkage stress are present near the interface. Figure 9 The results show a wider range of observations, but multiple defects are present across the entire surface. Furthermore, despite having the same coating thickness as other samples, this suggests that the sintered body thickness is around 35 μm, indicating significant shrinkage. The presence of numerous very small and highly sinterable particles, such as silver particle A, reveals defects caused by high sintering activity, demonstrating an optimal value when multiple silver particles are combined, as in the case of silver particles A, B, and C.

[0111] [Table 6]

[0112] As shown in Table 6, it can be seen that Comparative Example 3, which does not contain silver particles A, has good basic density and strength, but the initial filling structure is not dense, thus creating an effect that requires sintering silver to fill the loose volume portion. On the other hand, it can be seen that Examples 4, 5, and 6 can form good films without defects caused by shrinkage and with a density exceeding 91%. Generally, when particles known as microsilver are used alone, shrinkage is small due to low sinterability, making it difficult to produce film defects. However, no increase in density is observed, and it is considered to have poor heat resistance. It is demonstrated that the silver particles in the present invention do not produce film defects, maintain a high strength of over 70 MPa, and have a density exceeding 91%. Furthermore, a 2000x SEM image of Example 5 is shown. Figure 10 It can be seen that the density reaches 93% as shown in Example 5, indicating that a more preferred composition exists. In the composition shown in Comparative Example 4, due to the excessive amount of silver particles A, it is presumed that this originates from the generation of vacancies due to shrinkage and degassing. A 1000x SEM image of the defective portion including Comparative Example 4 is shown. Figure 11 It can be inferred that although the density of the parts without vacancies is as high as 94%, when it becomes a thick film, the release site of gas from the microparticles disappears, making it easy to generate vacancies.

[0113] [Table 7]

[0114] As shown in Table 7, Comparative Examples 5, 6, 7, and 8 demonstrate that even combinations of highly sinterable microparticles like silver particle A with other particles can easily lead to defects if not optimally combined. For example, it is evident that compositions combining relatively small, highly sinterable particles, as in Comparative Example 5, resulted in shrinkage-induced defects. Furthermore, as in Comparative Example 8, the combination of highly sinterable particles with coarse particles exhibited a low shear strength of 40 MPa and a high resistivity of 4.8 μΩ·cm. This indicates that even with a large number of microparticles, the composition is not sufficient to adequately fill the gaps between particles and cannot prevent shrinkage caused by film defects. As these results suggest, it is difficult to form a dense, thick film composite using only highly sinterable particles under pressureless conditions, highlighting the importance of combining multiple silver particles with a suitable composition.

[0115] <Porosity of sintered body (sintering temperature 200℃)> Similar to the observation via electron microscopy described above, SEM images of each sintered body obtained in the manufacturing process of the sintered body (sintering temperature 200°C) were acquired. For each SEM image, image processing was performed using Macview image analysis software (manufactured by Mounttech Co., Ltd.). (By automatically reading color difference, the void portions of the binarized image were analyzed as particles.) The average number of voids and the specific surface area of ​​the sintered body were calculated. The results are shown in Table 8. It should be noted that the average number of voids mentioned here is a value obtained by assuming the voids are spheres and analyzing them using the image analysis software (Macview). The specific surface area value is obtained by calculating the surface area per unit volume of the aforementioned spheres. The average number of voids and the specific surface area of ​​Examples 1 to 6 are shown in Table 8.

[0116] [Table 8]

Claims

1. A conductive adhesive comprising: silver particles A with an average particle size of less than 40 nm; silver particles B with an average particle size of 40 nm or more and less than 500 nm; silver particles C with an average particle size of 0.5 μm or more and less than 5.5 μm; and a solvent, wherein the mass ratio of silver particles A:silver particles B:silver particles C is 1–20:30–60:40–70. In the conductive adhesive, the solvent accounts for 5% to 15% by mass. An amine compound is attached to the surface of the silver particles A and B.

2. The conductive adhesive according to claim 1, wherein, The amine compound is selected from primary amines, secondary amines, tertiary amines, and diamine compounds having two amino groups in one compound.

3. A sintered body, which is a sintered body of the conductive adhesive according to claim 1 or 2.

4. An electronic component formed by joining components together using the sintered body as described in claim 3.

5. A method for manufacturing a sintered body, comprising a step of sintering the conductive adhesive according to claim 1 or 2 at a temperature above 200°C and below 250°C.

6. A method for manufacturing an electronic component, comprising joining components together by sintering to form the electronic component. It includes the following processes: The step of distributing the conductive adhesive according to claim 1 or 2 between the components; and The process of sintering the conductive adhesive at a temperature above 200°C and below 250°C.

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