Silver-coated resin particle and filler-containing paste

Abstract

Silver-coated resin particles (10) each comprise: a resin particle (11) formed from a resin composition; and a silver coating layer (12) formed on the surface of the resin particle (11). The silver-coated resin particles are characterized by containing silicon oxide in a range of 0.04-3.00 mass%, and containing tin in an amount of 0.20 mass% or less. The silver-coated resin particles preferably have a 5%-compressive elastic modulus (5%-K value) of 2.5 GPa or less. The resin composition is preferably one or more selected from acrylic resins, styrene resins, phenol resins, urethane resins, and polyimide resins.　

Description

Silver-coated resin particles and filler-containing paste

[0001] The present invention relates to silver-coated resin particles and a filler-containing paste. This application claims priority to Japanese Patent Application No. 2024-034043, filed on March 6, 2024, the contents of which are incorporated herein by reference.

[0002] For example, conductive adhesives such as conductive pastes and conductive films made by mixing silver-coated resin particles, which are resin particles coated with silver, with resin are known as conductive materials that can replace lead solder or lead-free solder. Conductive adhesives are used, for example, as materials for forming electrodes and electrical wiring that constitute electronic devices such as solar cell panels, liquid crystal displays, and touch panels. Furthermore, pastes and films made by mixing the above-mentioned silver-coated resin particles with resin are also used as TIM (Thermal Interface Material) materials because of their excellent thermal conductivity.

[0003] As the above-mentioned silver-coated resin particles, for example, Patent Document 1 discloses silver-coated resin particles in which resin particles are subjected to a pretreatment to be catalyzed with tin, and then the pretreated resin particles are subjected to electroless plating of silver, thereby improving adhesion between the resin particles and the silver coating layer.

[0004] Japanese Patent Application Publication No. 2015-199970 (A)

[0005] Recently, power electronics semiconductor elements for controlling large amounts of power, such as those used to control wind power generation, electric vehicles, and hybrid vehicles, generate a large amount of heat during operation and have a large area. Therefore, when bonding these elements, it is necessary to ensure high bonding reliability even under thermal cycle loads. Therefore, in filler-containing pastes containing the above-mentioned silver-coated resin particles as a filler, silver-coated resin particles that have particularly excellent adhesion between the resin particles and the silver-coating layer are required to improve the thermal cycle reliability of the bonding layer.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide silver-coated resin particles that have excellent adhesion between the resin particles and the silver coating layer and excellent heat cycle resistance, and a filler-containing paste that includes these silver-coated resin particles as a filler.

[0007] In order to solve the above problems, the present inventors have conducted extensive research and found that if a large amount of tin is used as a pretreatment (catalysis treatment) for plating, the silver coating layer is likely to peel off under thermal cycle loading, and therefore it is necessary to reduce the tin content. Furthermore, they have found that by disposing silicon oxide on the surfaces of resin particles, it is possible to effectively plate silver on the surfaces of resin particles.

[0008] The present invention has been made based on the above-mentioned findings, and the silver-coated resin particles of aspect 1 of the present invention are silver-coated resin particles comprising resin particles made of a resin composition and a silver coating layer formed on the surface of the resin particles, and are characterized in that they contain silicon oxide in a range of 0.04 mass% to 3.00 mass%, and have a tin content of 0.20 mass% or less.

[0009] According to the silver-coated resin particles of the present invention, the silicon oxide content is in the range of 0.04% by mass to 3.00% by mass, which allows for good silver plating on the surface of the resin particles and reduces the amount of tin used in the catalysis treatment. Furthermore, the tin content is limited to 0.20% by mass or less, which prevents the silver coating layer from peeling off during thermal cycling. Therefore, silver-coated resin particles with excellent adhesion between the resin particles and the silver coating layer and excellent thermal cycle resistance can be provided.

[0010] The silver-coated resin particles of Aspect 2 of the present invention are the silver-coated resin particles of Aspect 1 of the present invention, characterized in that they have a 5% compressive modulus (5% K value) of 2.5 GPa or less. The silver-coated resin particles of Aspect 2 of the present invention have a 5% compressive modulus (5% K value) of 2.5 GPa or less, and are sufficiently soft and easily deformable, making it possible to suppress the occurrence of cracks in a cured paste containing the silver-coated resin particles as a filler, for example.

[0011] The silver-coated resin particles of Aspect 3 of the present invention are the silver-coated resin particles of Aspect 1 or Aspect 2 of the present invention, characterized in that the resin composition is one or more resins selected from acrylic resins, styrene resins, phenolic resins, urethane resins, and polyimide resins. According to the silver-coated resin particles of Aspect 3 of the present invention, the resin composition is one or more resins selected from acrylic resins, styrene resins, phenolic resins, urethane resins, and polyimide resins, so that the resin particles have excellent flexibility and are particularly suitable as fillers.

[0012] The silver-coated resin particles of Aspect 4 of the present invention are the silver-coated resin particles of any one of Aspects 1 to 3 of the present invention, characterized in that the particle diameter is in the range of 2 μm to 50 μm. Since the silver-coated resin particles of Aspect 4 of the present invention have a particle diameter in the range of 2 μm to 50 μm, the amount of expensive silver used can be reduced, thereby achieving cost reduction, and the particles can be used as a filler in pastes and the like for forming fine patterns.

[0013] A filler-containing paste according to Aspect 5 of the present invention is characterized by containing a binder resin and, as a filler, the silver-coated resin particles according to any one of Aspects 1 to 4 of the present invention. According to the filler-containing paste according to Aspect 5 of the present invention, since the filler contains the silver-coated resin particles according to any one of Aspects 1 to 4 of the present invention, the thermal cycle reliability of a cured product of this filler-containing paste can be improved, and the paste can be stably used as a conductive adhesive or heat transfer material even in applications where it is subjected to severe thermal cycles.

[0014] According to the present invention, it is possible to provide silver-coated resin particles that have excellent adhesion between the resin particles and the silver coating layer and excellent heat cycle resistance, and a filler-containing paste that includes these silver-coated resin particles as a filler.

[0015] FIG. 1 is a cross-sectional view of a silver-coated resin particle according to one embodiment of the present invention. FIG. 2 is a flow diagram showing a method for producing a silver-coated resin particle according to one embodiment of the present invention. FIG. 3 is an explanatory diagram of a semiconductor device using a cured paste according to one embodiment of the present invention. FIG. 4 is a photograph showing the results of SEM observation of silver-coated resin particles of Inventive Example 1 in the Examples. FIG. 5 is a photograph showing the results of SEM observation of silver-coated resin particles of Inventive Example 1 in the Examples. FIG. 6 is a photograph showing the results of SEM observation of silver-coated resin particles of Inventive Example 6 in the Examples. FIG. 7 is a photograph showing the results of SEM observation of silver-coated resin particles of Comparative Example 5 in the Examples. FIG. 8 is a photograph showing the results of SEM observation of silver-coated resin particles of Comparative Example 5 in the Examples. FIG. 9 is a photograph showing the results of SEM observation of silver-coated resin particles of Comparative Example 6 in the Examples.

[0016] Silver-coated resin particles and filler-containing pastes according to embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the present invention.

[0017] Figure 1 shows a silver-coated resin particle 10 according to one embodiment of the present invention. As shown in Figure 1, the silver-coated resin particle 10 according to this embodiment includes a resin particle 11 made of a resin composition and a silver coating layer 12 formed on the surface of the resin particle 11. The silver-coated resin particle 10 contains silicon oxide in a range of 0.04% by mass to 3.00% by mass, and has a tin content of 0.20% by mass or less.

[0018] In this embodiment, the content of silicon oxide in the silver-coated resin particles 10 is determined by collecting a measurement sample from the silver-coated resin particles 10, performing elemental analysis, and calculating the silicon oxide (SiO ２ The tin content in the silver-coated resin particles 10 is determined by taking a measurement sample from the silver-coated resin particles 10 and performing elemental analysis on the sample, thereby determining the amount of tin measured.

[0019] In addition, in the silver-coated resin particles 10 of this embodiment, the 5% compressive modulus (5% K value) is preferably 2.5 GPa or less. Furthermore, in the silver-coated resin particles 10 of this embodiment, the particle diameter is preferably in the range of 2 μm or more and 50 μm or less. In the silver-coated resin particles 10 of this embodiment, the resin composition constituting the resin particles 11 is preferably one or more selected from acrylic resin, styrene resin, phenolic resin, urethane resin, and polyimide resin. In the silver-coated resin particles 10 of this embodiment, flexibility is imparted to increase the interference effect against expansion and contraction, so it is more preferable to use urethane resin or acrylic resin, which are particularly excellent in flexibility.

[0020] The reasons for the above-described definition of the silver-coated resin particles 10 of this embodiment will be explained below.

[0021] (Silicon Oxide) In the silver-coated resin particles 10 of this embodiment, the inclusion of silicon oxide (e.g., a compound composed of silicon and oxygen, expressed as SiO2, SiO2, etc.) makes it possible to satisfactorily plate silver on the surfaces of the resin particles 11, thereby improving the adhesion between the resin particles 11 and the silver coating layer 12. Here, if the silicon oxide content in the silver-coated resin particles 10 is less than 0.04% by mass, the adhesion between the resin particles 11 and the silver coating layer 12 may not be sufficiently improved. On the other hand, if the silicon oxide content exceeds 3.00% by mass, the flexibility of the silver-coated resin particles 10 may be reduced. For this reason, the silicon oxide content in the silver-coated resin particles 10 of this embodiment is set to be in the range of 0.04% by mass or more and 3.00% by mass or less.

[0022] In order to further improve the adhesion between the resin particles 11 and the silver coating layer 12, the silicon oxide content in the silver-coated resin particles 10 is preferably 0.10% by mass or more, and more preferably 0.20% by mass or more. In order to further ensure the flexibility of the silver-coated resin particles 10, the silicon oxide content in the silver-coated resin particles 10 is preferably 3.00% by mass or less, and more preferably 2.00% by mass or less.

[0023] (Tin Content) In the silver-coated resin particles 10 of this embodiment, if a catalysis treatment using tin is performed as a pretreatment for plating the surfaces of the resin particles 11, the silver-coated resin particles 10 will contain tin. If the tin content exceeds 0.20% by mass, the silver-coating layer 12 may be prone to peeling during thermal cycling. For this reason, the tin content in the silver-coated resin particles 10 of this embodiment is limited to 0.20% by mass or less.

[0024] In order to more reliably prevent peeling of the silver coating layer 12 during thermal cycling, the tin content in the silver-coated resin particles 10 is preferably 0.20% by mass or less, and more preferably 0.10% by mass or less. There is no lower limit for the tin content in the silver-coated resin particles 10, and the tin content may be 0.00% by mass without performing a tin-based catalytic treatment as a pretreatment for plating the surfaces of the resin particles 11.

[0025] (5% Compressive Elastic Modulus (5% K Value)) In the silver-coated resin particles 10 of this embodiment, when the 5% compressive elastic modulus (5% K value) is 2.5 GPa or less, the flexibility of the silver-coated resin particles 10 is sufficiently ensured, and therefore, the occurrence of cracks in the cured paste of a paste containing these silver-coated resin particles 10 as a filler can be suppressed.

[0026] To further ensure flexibility, the 5% compressive elastic modulus (5% K value) of the silver-coated resin particles 10 is preferably 1.5 GPa or less, and more preferably 0.5 GPa or less. There is no particular lower limit for the 5% compressive elastic modulus (5% K value) of the silver-coated resin particles 10, but from the viewpoint of the shape stability of the cured paste, it is preferably 0.2 GPa or more, and more preferably 0.3 GPa or more.

[0027] (Particle diameter) In the silver-coated resin particles 10 of this embodiment, when the particle diameter is 2 μm or more, the specific surface area does not become larger than necessary, and the amount of silver used to constitute the silver-coating layer 12 can be reduced, making it possible to keep production costs low. On the other hand, in the silver-coated resin particles 10 of this embodiment, when the particle diameter is 50 μm or less, a paste containing these silver-coated resin particles 10 as a filler can be applied in a fine pattern, making it possible to apply the silver-coated resin particles 10 to highly integrated or highly precise semiconductor devices, etc.

[0028] In order to further reduce the amount of silver used in the silver coating layer 12, the particle diameter of the silver-coated resin particles 10 is preferably 4 μm or more, and more preferably 6 μm or more. In order to accommodate even finer patterns, the particle diameter of the silver-coated resin particles 10 is preferably 15 μm or less, and even more preferably 10 μm or less.

[0029] (Resin composition) In this embodiment, when the resin composition constituting the resin particles 11 is one or more selected from acrylic resin, styrene resin, phenolic resin, urethane resin, and polyimide resin, the resin particles 11 have excellent flexibility and can stably form the silver coating layer 12.

[0030] Next, an example of a method for producing the silver-coated resin particles 10 according to this embodiment will be described with reference to the flow chart of FIG.

[0031] (Silicon oxide disposing step S01) First, silicon oxide is disposed on the surfaces of the resin particles 11. Examples of methods for disposing silicon oxide include a method of forming a silicate film or a silica film on the surfaces of the resin particles 11 (manufacturing method 1) and a method of physically attaching silica particles to the surfaces of the resin particles 11 (manufacturing method 2).

[0032] In manufacturing method 1, for example, resin particles 11 are dispersed in a mixed solvent of water and ethanol, and a predetermined amount of methyl silicate and a small amount of nitric acid or the like are added as a catalyst to form a silicate film on the surface of the resin particles 11. The raw material for forming the silica film is not limited to methyl silicate, and organic silicates such as ethyl silicate and propyl silicate, and inorganic silicon salts such as sodium silicate can also be used.

[0033] In manufacturing method 2, for example, predetermined amounts of resin particles 11 and silica particles are mixed and then processed in a planetary ball mill or the like, thereby adhering the silica particles to the surfaces of the resin particles 11. The silica particles that can be used range in size from minute particles of several nanometers to several micrometers, and can be spherical, needle-like, or bead-like in shape.

[0034] (Catalyzing Treatment Step S02) Next, tin (divalent tin ions) serving as a catalyst is adsorbed onto the resin particles 11 having silicon oxide disposed on their surfaces. The resin particles 11 are added to an aqueous solution of a tin compound and stirred. Here, examples of the tin compound that can be used include stannous chloride, stannous fluoride, stannous bromide, and stannous iodide.

[0035] (Silver Coating Step S03) Next, silver is electrolessly plated on the surfaces of the resin particles 11 to form a silver coating layer 12. Methods for forming the silver coating layer 12 by electroless plating include: (1) a method in which the resin particles 11 are introduced into an aqueous solution containing a complexing agent, a reducing agent, etc. to prepare a slurry, and a silver salt aqueous solution is added dropwise to the slurry; (2) a method in which the resin particles 11 are introduced into an aqueous silver salt solution containing a complexing agent to prepare a slurry, and a reducing agent aqueous solution is added dropwise to the slurry; and (3) a method in which the resin particles 11 are introduced into an aqueous silver salt solution containing a complexing agent and a reducing agent to prepare a slurry, and a caustic alkali aqueous solution is added dropwise to the slurry.

[0036] Examples of silver salts that can be used include silver nitrate and silver dissolved in nitric acid. Examples of complexing agents that can be used include ammonia, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetate, nitrotriacetic acid, triethylenetetraamminehexaacetic acid, sodium thiosulfate, succinate, succinimide, citrate, and iodide salts. Examples of reducing agents that can be used include formalin, glucose, imidazole, Rochelle salt (potassium sodium tartrate), hydrazine and its derivatives, hydroquinone, L-ascorbic acid, and formic acid. Examples of reducing agents that can be used include formaldehyde, a mixture of two or more reducing agents containing at least formaldehyde is more preferred, and a mixture of reducing agents containing formaldehyde and glucose is most preferred.

[0037] If divalent tin ions are adsorbed on the surface of the resin particles 11 by the catalysis treatment step S02, the divalent tin ions dissolve as tetravalent ions, releasing divalent electrons. Then, silver ions receive the divalent electrons and precipitate as metallic silver. This results in efficient formation of the silver coating layer 12. However, if the tin content increases as a result of the catalysis treatment step S02, there is a risk of peeling between the resin particles 11 and the silver coating layer 12 during thermal cycling. Therefore, it is necessary to consider the implementation status of the catalysis treatment step S02, taking the tin content into account. In this embodiment, since silicon oxide is disposed on the surface of the resin particles 11, it is possible to successfully plate silver on the surface of the resin particles 11 even if the catalysis treatment step S02 is omitted. While the reason why the formation of silicon oxide on the surface improves the adhesion of silver is unclear, it is thought that this is due to its excellent affinity with the silver precipitate particles and the improved adsorption effect of tin.

[0038] Through the steps described above, the silver-coated resin particles 10 of this embodiment are produced.

[0039] The filler-containing paste of this embodiment contains a binder resin and the above-described silver-coated resin particles 10 as a filler. It may contain a solvent or additive as needed. The binder resin is not particularly limited, and examples thereof include thermoplastic resins and compositions that harden with heat or light, such as curable resin compositions. Examples of thermoplastic resins include styrene-butadiene block copolymers, acrylic resins, ethylene-vinyl acetate resins, and phenoxy resins. Examples of thermosetting resin compositions include resin compositions containing, as a main component, a resin such as a silicone resin or an epoxy resin, or a mixture thereof. A resin that is compatible with the silver-coated resin particles is suitable to achieve compatibility in terms of adhesion, hardness, electrical properties, electrothermal properties, and the like.

[0040] To improve affinity (compatibility) with the binder resin, the surfaces of the silver-coated resin particles can be subjected to a surface treatment with an organic acid, etc. Examples of surface treatments include fatty acids such as stearic acid, isostearic acid, palmitic acid, and oleic acid, dicarboxylic acids such as maleic acid and succinic acid, carboxylic acid polymers such as polyacrylic acid, amine compounds such as dodecylamine and octadecylamine, amine polymers such as polyetheramine, sulfide compounds such as octadecyl disulfide, thiol compounds such as dodecanethiol, and silane coupling agents.

[0041] Furthermore, to obtain higher electrical and thermal conductivity, a conductive filler other than the silver-coated resin particles 10 (hereinafter referred to as "other conductive filler") may be added. Examples of other conductive fillers include metal particles such as silver powder, copper powder, and nickel powder, organic particles such as carbon, and conductive ceramic particles. However, silver powder, which has excellent electrical and thermal conductivity properties, is preferred. Furthermore, the particle shape is preferably not only spherical but also flake (flat) particles. The ratio of the added silver-coated resin particles 10:other conductive filler = 5 to 95% by mass:95 to 5% by mass depending on the desired electrical and thermal conductivity. The filler-containing paste of this embodiment is produced by weighing out predetermined amounts of a binder resin (e.g., epoxy resin) and the above-described silver-coated resin particles 10 and kneading them using a planetary mixer, a three-roll mill, or the like.

[0042] 3, the filler-containing paste of this embodiment forms a bonding layer 4 that bonds a circuit layer 2 of an insulating circuit board to a semiconductor element 3 in a semiconductor device 1. That is, by applying the filler-containing paste of this embodiment to the mounting surface of the circuit layer 2, laminating the semiconductor element 3, and performing a heat treatment, a bonding layer 4 made of a cured product of the filler-containing paste of this embodiment is formed, and the circuit layer 2 and the semiconductor element 3 are bonded together.

[0043] Here, the filler-containing paste of this embodiment contains the above-mentioned silver-coated resin particles 10 as a filler, and therefore has excellent electrical conductivity and thermal conductivity, and can electrically connect the semiconductor element 3 and the circuit layer 2, and can efficiently dissipate heat generated in the semiconductor element 3 to the insulating circuit board side. Furthermore, since the bonding layer 4 has excellent thermal cycle reliability, it is possible to suppress peeling between the semiconductor element 3 and the circuit layer 2 even when a thermal cycle is applied.

[0044] The silver-coated resin particles 10 of this embodiment, configured as described above, contain silicon oxide in the range of 0.04% by mass to 3.00% by mass, which enables silver to be well plated on the surfaces of the resin particles 11 and reduces the amount of tin used in the catalysis treatment step S02. Furthermore, because the tin content is limited to 0.20% by mass or less, peeling of the silver-coating layer 12 during thermal cycling can be suppressed.

[0045] In this embodiment, when the 5% compressive elastic modulus (5% K value) of the silver-coated resin particles 10 is 2.5 GPa or less, the particles are sufficiently soft and easily deformed, and therefore, for example, cracks can be suppressed in the cured paste of a filler-containing paste that contains the silver-coated resin particles 10 as a filler.

[0046] In this embodiment, when the resin composition constituting the resin particles 11 is one or more selected from acrylic resin, styrene resin, phenolic resin, urethane resin, and polyimide resin, the resin particles 11 have excellent flexibility and are particularly suitable as a filler.

[0047] In this embodiment, when the particle diameter of the silver-coated resin particles 10 is within the range of 2 μm or more and 50 μm or less, the amount of expensive silver used can be reduced, thereby reducing costs, and the particles can be used as a filler in pastes, etc., for forming fine patterns.

[0048] The filler-containing paste of this embodiment contains the silver-coated resin particles 10 of this embodiment as a filler, and therefore has excellent heat cycle resistance, and can be used stably as a conductive adhesive or heat transfer material even in applications where severe heat cycles are applied.

[0049] Although one embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate within the scope of the technical concept of the invention. In this embodiment, the present invention has been described as being applied to a filler-containing paste used in forming a bonding layer that bonds a circuit layer and a semiconductor element of a semiconductor device, but the present invention is not limited thereto and may be used for other purposes.

[0050] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0051] (Invention Examples 1-5, Comparative Examples 2 and 3: Wet Process) Resin particles having the materials and average particle sizes shown in Table 1 were dispersed in a solvent of water:ethanol = 1:1 to obtain a slurry with a solids concentration of 5 mass %. Methyl silicate (product name MS-51, manufactured by Mitsubishi Chemical) was added to this slurry so that the silica concentration became the value shown in Table 1, and a very small amount of nitric acid was added dropwise to prepare silica-coated resin particles.

[0052] After filtering, washing, and drying at 120°C for 5 hours, the mixture was dispersed in water, and stannous chloride was added so that the tin concentration was the value shown in Table 1. The mixture was stirred at 40°C for 1 hour and filtered again. The resulting cake was dispersed in water to obtain resin particles with divalent tin ions adsorbed on their surfaces (catalyzed resin particles). A silver coating layer was then formed on the surface of the resin particles by electroless plating so that the silver concentration was the value shown in Table 1.

[0053] (Invention Examples 6-8, Comparative Examples 4-6: Dry Process) Resin particles having the materials and average particle diameters shown in Table 1 and silica nanoparticles having an average particle diameter of 50 nm were mixed so that the content of silica nanoparticles was the value shown in Table 1, and the mixture was put through a planetary ball mill to adhere the silica nanoparticles to the surfaces of the resin particles. The resin particles with the silica nanoparticles adhered to their surfaces were subjected to a catalyzation treatment and electroless plating in the same manner as in Invention Examples 1-5, to form a silver coating layer.

[0054] Comparative Example 1: Urethane particles (resin particles) with an average particle size of 15 μm were dispersed in water, and stannous chloride was added so that the tin concentration was 0.1% by mass. The mixture was stirred at 40° C. for 1 hour and filtered. The resulting cake was dispersed in water to obtain resin particles (catalyzed resin particles) with divalent tin ions adsorbed on the surface. A silver coating layer was formed on the surface of these resin particles by electroless plating so that the silver concentration was 45% by mass.

[0055] The 5% compressive elastic modulus (5% K value) of the silver-coated resin particles of Inventive Examples 1-8 and Comparative Examples 1-6 obtained as described above was calculated as follows. The evaluation results are shown in Table 1.

[0056] First, a compression test was performed on one silver-coated resin particle using a flat indenter (Fisher Instruments, model number: HM500) at a load change rate of 0.3 mN / s and 20°C, and the displacement and load were measured when the silver-coated resin particle was compressed 5% relative to its major axis. The starting point (zero point) for displacement measurement was not the point at which the microcompression tester recognized contact with the silver-coated resin particle, but the point at which the microcompression tester changed the load applied to the silver-coated resin particle. The measured displacement and load were then substituted into the following equation (1) to calculate the 5% compression modulus (5% K value).

[0057] Equation (1): 5% compressive elastic modulus (5% K value) [GPa] = 3F / (2S ３ R) １ / ２ F: Load [N] when silver-coated resin particle is compressed by 5% S: Displacement [mm] when silver-coated resin particle is compressed by 5% R: Radius [mm] of silver-coated resin particle before compression

[0058] Furthermore, the silver-coated resin particles of Invention Examples 1-8 and Comparative Examples 1-6 were subjected to a thermal cycle test of -20°C and then 80°C, and their cross sections were observed under an SEM to check for the presence or absence of peeling. The evaluation results are shown in Table 1. Furthermore, Figures 4A and 4B show the SEM observation results of Invention Example 1 after the thermal cycle test, Figure 5 shows the SEM observation results of Invention Example 6 after the thermal cycle test, Figures 6A and 6B show the SEM observation results of Comparative Example 5 after the thermal cycle test, and Figure 7 shows the SEM observation results of Comparative Example 6 after the thermal cycle test.

[0059] Furthermore, the silver-coated resin particles of Invention Examples 1-8 and Comparative Examples 1-6 were subjected to a thermal cycle test of -20°C ←→ 80°C, and then an epoxy resin-based filler-containing paste with a filler ratio of 60 vol% was prepared using a planetary mixer. A coating film with a thickness of 50 μm was formed using this filler-containing paste. The volume resistivity of this coating film was measured using the four-probe method according to JIS-K-7194. The evaluation results are shown in Table 1.

[0060]

[0061] In Comparative Example 1, peeling of the silver coating layer was confirmed after the thermal cycle test. This is presumably because silicon oxide was not provided on the surface of the resin particles, and the adhesion between the resin particles and the silver coating layer was insufficient. The 5% compressive elastic modulus (5% K value) was 0.5 GPa. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Comparative Example 1 was 5.0 × 10 －３ The value was Ω·cm.

[0062] In Comparative Example 2, peeling of the silver coating layer was confirmed after the thermal cycle test. This is presumably because the tin content was as high as 0.35% by mass, resulting in insufficient adhesion between the resin particles and the silver coating layer. The 5% compressive modulus (5% K value) was 2.6 GPa. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Comparative Example 2 was 1.0 × 10 －１ The value was Ω·cm.

[0063] In Comparative Example 3, peeling of the silver coating layer was confirmed after the thermal cycle test. This is presumably because the silicon oxide content was as low as 0.02 mass%, resulting in insufficient adhesion between the resin particles and the silver coating layer. The 5% compressive modulus (5% K value) was 3.9 GPa. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Comparative Example 3 was 3.0 × 10 －２ The value was Ω·cm.

[0064] In Comparative Example 4, peeling of the silver coating layer was confirmed after the thermal cycle test. This is presumably because the silicon oxide content was as high as 3.1 mass %, reducing the flexibility of the resin particles. The 5% compressive modulus (5% K value) was 2.0 GPa. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Comparative Example 4 was 4.0 × 10 －３ The value was Ω·cm.

[0065] In Comparative Example 5, peeling of the silver coating layer was confirmed after the thermal cycle test. This is presumably because the tin content was as high as 0.35% by mass, resulting in insufficient adhesion between the resin particles and the silver coating layer. The 5% compressive modulus (5% K value) was 2.8 GPa. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Comparative Example 5 was 1.0 × 10 －１ The value was Ω·cm.

[0066] In Comparative Example 6, peeling of the silver coating layer was confirmed after the thermal cycle test. This is presumably because the tin content was as high as 0.4 mass%, resulting in insufficient adhesion between the resin particles and the silver coating layer, and because the silicon oxide content was as high as 7.2 mass%, resulting in reduced flexibility of the resin particles. The 5% compressive elastic modulus (5% K value) was 5.0 GPa. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Comparative Example 6 was 1.0 × 10 －２ The value was Ω·cm.

[0067] In contrast, in Inventive Example 1-8, the silicon oxide content was in the range of 0.04 mass% to 3.00 mass%, and the tin content was 0.20 mass% or less, and no peeling of the silver coating layer was observed after the thermal cycle test. This is presumably because the low tin content and the appropriate amount of silicon oxide sufficiently improved the adhesion between the resin particles and the silver coating layer. Furthermore, the volume resistivity of the coating film formed using the filler-containing paste containing the silver-coated resin particles of Inventive Example 1-8 was sufficiently low, confirming that it was possible to form a coating film with excellent electrical conductivity.

[0068] As described above, it has been confirmed that the present invention can provide silver-coated resin particles that have excellent adhesion between the resin particles and the silver coating layer and excellent heat cycle resistance, as well as a filler-containing paste that includes these silver-coated resin particles as a filler.

[0069] The silver-coated resin particles and filler-containing paste of the present invention can be used as anisotropic conductive film formers (ACF, ACP) used in liquid crystal displays, touch panels, etc., conductive pastes used in touch panels, etc., conductive pastes and films for die bonding, and TIM materials.

[0070] 10 Silver-coated resin particle 11 Resin particle 12 Silver-coated layer

Claims

1. Silver-coated resin particles comprising resin particles made of a resin composition and a silver coating layer formed on the surface of the resin particles, characterized in that the silver-coated resin particles contain silicon oxide in the range of 0.04% by mass to 3.00% by mass, and the tin content is 0.20% by mass or less.

2. Silver-coated resin particles according to claim 1, characterized in that the 5% compressive modulus (5% K value) is 2.5 GPa or less.

3. The silver-coated resin particles according to claim 1, wherein the resin composition is one or more resins selected from the group consisting of acrylic resin, styrene resin, phenolic resin, urethane resin, and polyimide resin.

4. Silver-coated resin particles according to claim 1, characterized in that the particle diameter is in the range of 2 μm to 50 μm.

5. A filler-containing paste comprising a binder resin and the silver-coated resin particles according to any one of claims 1 to 4 as a filler.

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