Composite particles and method for producing composite particles

Abstract

The present invention provides composite particles which can be sintered at a low temperature when used for sintering bonding, and are still capable of forming a sintered body that has excellent heat resistance. Composite particles according to the present disclosure are characterized by comprising base material particles and Ag and / or Cu that is supported by the base material particles. The composite particles are also characterized in that: the linear expansion coefficient of the base material particles is 8 ppm / K or less; and the average value of the numbers of particle aggregates A in images captured at any given five locations in a cross-section with use of an SEM at a magnification of 1,000 times is two or less. Particle aggregate A: A plurality of base material particles and Ag and / or Cu are contained therein, the area ratio of the supported Ag and / or Cu is 70 area% or more with respect to the base material particles, and the diameter of the longest part of the aggregate is 5 μm or more.

Description

Composite particles and method for producing composite particles

[0001] This disclosure relates to composite particles and a method for producing composite particles. This application claims priority to Japanese Patent Application No. 2024-34445 filed in Japan on March 6, 2024, and Japanese Patent Application No. 2024-157032 filed in Japan on September 10, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, when die-bonding (die-attaching) semiconductor elements that operate at high temperatures, such as SiC chips, sinter bonding has been considered, in which a metal paste containing nano-sized or micro-sized particles of silver or copper is used as a bonding material, and the bonding material is interposed between objects to be bonded and heated for a predetermined time to sinter the metal, such as silver, in the bonding material, thereby bonding the objects to be bonded together by a metal bonding layer (see, for example, Patent Document 1). This metal bonding technology is expected to be applied to various electronic elements, such as power semiconductor elements and LED elements.

[0003] However, metals such as silver are too hard as die-attach materials, and the difference in thermal expansion coefficient between a semiconductor element such as Si or SiC and a metal layer such as silver is very large, so that in thermal fatigue tests exceeding 200° C., cracks develop in the sintered portion, and insulating substrates such as the semiconductor element or DBC (Direct Bonded Copper) break, resulting in insufficient heat resistance. Furthermore, when metal is used as the bonding material, the only way to improve bonding strength and heat resistance is to control the density of the sintering, which poses the problem of not being able to essentially change the mechanical properties of the bonded body.

[0004] To solve the above problems, a material having specific metal nanoparticles supported on a carrier is known as a material that combines low-temperature processability and heat resistance (for example, Patent Document 2).

[0005] International Publication No. 2018 / 037992 Japanese Patent Application Laid-Open No. 2010-65265

[0006] However, there are limitations to the combinations of conventionally known metal nanoparticles with simple substances, and the functions that can be exhibited are also limited. Therefore, there has been a demand for materials with better low-temperature sintering properties and heat resistance.

[0007] Therefore, an object of the present disclosure is to provide composite particles that, when used in sinter bonding, can be sintered at low temperatures and can form a sintered body that has excellent heat resistance.

[0008] As a result of intensive research to solve the above problems, the inventors of the present disclosure have found that composite particles containing base particles and Ag and / or Cu supported on the base particles, where the base particles exhibit specific physical properties, can be sintered at low temperatures to form a sintered body with excellent heat resistance. The present invention has been completed based on these findings.

[0009] That is, the present disclosure provides composite particles comprising base particles and Ag and / or Cu supported on the base particles, wherein the base particles have a linear expansion coefficient of 8 ppm / K or less, and wherein an average number of the following particle agglomerates A is 2 or less in an image taken at 1000x magnification using an SEM at any five points in a cross section: Particle agglomerate A: Comprising a plurality of base particles and Ag and / or Cu, wherein the area ratio of the supported Ag and / or Cu to the base particles is 70 area % or more, and the diameter of the longest point in the agglomerates is 5 μm or more.

[0010] The composite particle contains the base particle and the Ag and / or Cu, and the average number of particle agglomerates A in an image taken at 1000x magnification using an SEM at any five locations in the cross section is 2 or less, which allows sintering at a low temperature while providing an appropriate amount of Ag and / or Cu, resulting in excellent heat resistance.

[0011] The base particles are Si, W, SiO ２ , Cr, and Mo.

[0012] The average particle size of the base particles is preferably 0.05 to 50 μm.

[0013] In the composite particles, the volume ratio of the Ag and / or Cu to the base particles [base particles:Ag and / or Cu] is preferably 99.9:0.1 to 50:50.

[0014] The present disclosure also provides a method for producing composite particles in which a metal is supported on a base particle, the method comprising the step of irradiating with ultrasonic waves a composition containing the base particle, a metal compound serving as a raw material for the metal, and a solvent, to obtain composite particles in which the average number of the following particle agglomerates A in images taken at 1000x magnification using an SEM at any five locations on a cross section is 2 or less: Particle agglomerate A: Comprising a plurality of base particles and Ag and / or Cu, the area ratio of the supported Ag and / or Cu to the base particle is 70 area % or more, and the diameter of the longest part of the agglomerates is 5 μm or more.

[0015] In the method for producing composite particles, the temperature of the composition is preferably 20 to 100°C in the step of irradiating with ultrasonic waves.

[0016] In the step of irradiating with ultrasonic waves, the ultrasonic irradiation conditions are preferably a frequency of 5 to 1000 kHz and an output of 10 to 1000 W.

[0017] The solvent preferably contains water or an alcohol.

[0018] The composition preferably further comprises a reducing agent.

[0019] Preferably, the composition further comprises a carboxylic acid.

[0020] The base particles are Si, W, SiO ２ , Cr, and Mo.

[0021] The metal compound is preferably a metal oxide and / or a metal carboxylate.

[0022] When the composite particles of the present disclosure are used for sinter bonding, they can be sintered at low temperatures and still form a sintered body that has excellent heat resistance.

[0023] 1A and 1B are SEM images of an example of a composite particle according to an embodiment of the present disclosure, in which Ag particles are supported on the surface of a base particle, and Cu particles are supported on the surface of a base particle.

[0024] [Composite Particles] The composite particles of the present disclosure comprise a substrate particle and Ag and / or Cu supported on the substrate particle, wherein the substrate particle has a linear expansion coefficient of 8 ppm / K or less, and the average number of particle aggregates A described below in images taken at 1000x magnification using an SEM at any five locations on a cross section is 2 or less. When used for sinter bonding, this allows for low-temperature sintering while maintaining an appropriate amount of Ag and / or Cu, resulting in the formation of a sintered body with excellent heat resistance. The composite particles may also be referred to as "composite particles of the present disclosure." Particle aggregate A: comprises multiple substrate particles and Ag and / or Cu, wherein the area ratio of the supported Ag and / or Cu to the substrate particle is 70 area% or more, and the longest diameter of the aggregate is 5 μm or more.

[0025] Fig. 1 is an SEM image of one embodiment of a composite particle according to the present disclosure. It can be seen that white Ag particles 2 are supported on black base particles 1. Fig. 2 is an SEM image of another embodiment of a composite particle according to the present disclosure. It can be seen that spherical Cu particles 3 are supported on base particles 1.

[0026] The number of base particles contained in the particle agglomerate A is preferably 30% or less, more preferably 15% or less, even more preferably 5% or less, and particularly preferably 3% or less, of the total number of base particles, and most preferably there is no particle agglomerate A. By having the total number of base particles contained in the particle agglomerate A be 30% or less, the amount of Ag and / or Cu in the composite particles can be made appropriate, making it easier to exhibit heat resistance.

[0027] Furthermore, the number of particle agglomerates A in an image taken at 1000x magnification using an SEM is 2 or less, preferably 1 or less, and more preferably there is no particle agglomerate A. Having the number of particle agglomerates A be 2 or less not only facilitates the exertion of heat resistance but also means that Ag or Cu is not unevenly distributed in the composite particle, and Ag and / or Cu is uniformly supported on the base particle, resulting in excellent sinterability.

[0028] The number of particle agglomerates A, the number of base particles contained in the particle agglomerates A, and the number of base particles can be counted by embedding the composite particle of the present disclosure in an epoxy resin, curing the resin, and then observing the cross section with an SEM. The number of base particles also includes the number of base particles contained in the particle agglomerates A. The evaluation of the number of particle agglomerates A and the number of base particles represents the average value measured at any five locations in the sample.

[0029] The composite particle of the present disclosure preferably contains a small amount of particle agglomerates B described below. The number of base particles contained in the particle agglomerates B is preferably 30% or less, more preferably 15% or less, even more preferably 5% or less, and particularly preferably 3% or less, relative to the number of base particles, and most preferably no particle agglomerates B are present. By containing 30% or less of the number of base particles in the particle agglomerates B, the amount of Ag and / or Cu in the composite particle can be made appropriate, making it easier to exhibit heat resistance. Particle agglomerates B: contain a plurality of base particles and Ag and / or Cu, the area ratio of the supported Ag and / or Cu to the base particles is 70 area% or more, the voids in the particle agglomerates are 30 area% or less, and the diameter of the longest part in the agglomerates is 5 μm or more.

[0030] In addition, the number of particle agglomerates B in an image photographed at 1000x magnification using an SEM is preferably 2 or less, more preferably 1 or less, and even more preferably there is no particle agglomerate B. Having the number of particle agglomerates B be 2 or less not only facilitates the exertion of heat resistance but also means that Ag or Cu is not unevenly distributed in the composite particle, and Ag and / or Cu is uniformly supported on the base particle, resulting in excellent sinterability.

[0031] The number of particle aggregates B, the number of base particles contained in the particle aggregates B, and the number of base particles can also be measured in the same manner as in the particle aggregates A.

[0032] In the composite particles of the present disclosure, the Ag and / or Cu are preferably supported on the base particle in the form of uniform particles, as Ag particles and / or Cu particles, or may be supported on the base particle in the form of a film as the amount of adhesion increases. When supported in the form of a film, it may be a film of Ag or Cu alone, or may be a film containing both Ag and Cu.

[0033] When the Ag is supported as particles, the Ag content in 100% by mass of the Ag particles is preferably 95% by mass or more, more preferably 99% by mass or more, and may be 99.9% by mass or more, or even 100% by mass. That is, it may be Ag particles alone. Furthermore, other components besides Ag may include silver oxide as a raw material, silver carboxylate as a reaction intermediate, additives such as a protective agent, etc., but from the viewpoint of exhibiting sinterability, it is preferable that no other components than the Ag are included. Incidentally, when Ag is supported in the form of a single film, it is preferable that the same range as above is satisfied.

[0034] Similarly, when the Cu is supported as particles, the Cu content in 100% by mass of the Cu particles is preferably 95% by mass or more, more preferably 99% by mass or more, and may be 99.9% by mass or more, or even 100% by mass. That is, it may be simple Cu particles. Furthermore, other components besides Cu may include copper oxide as a raw material, copper carboxylate as a reaction intermediate, additives such as a protective agent, etc., but from the viewpoint of exhibiting sinterability, it is preferable that no other components besides the Cu are included. Incidentally, when Cu is supported in the form of a simple film, it is preferable that the same range as above is satisfied.

[0035] The average particle size (median size) of the Ag particles and Cu particles is preferably 10,000 nm or less, more preferably 1,000 nm or less, even more preferably 500 nm or less, particularly preferably 200 nm or less, particularly preferably 100 nm or less, and particularly preferably 50 nm or less. The lower limit is not particularly limited, but from the viewpoint of production, it is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The average particle size (median size) is calculated based on the volume of the particles and can be measured by a laser diffraction / scattering method.

[0036] When the Ag and / or Cu is supported on the base particle in the form of a film, the thickness thereof is preferably 10 nm to 10 μm, more preferably 50 nm to 5 μm, and even more preferably 100 nm to 3 μm. A thickness of 10 nm or more facilitates bonding during sintering. Furthermore, a thickness of 10 μm or less facilitates low-temperature sintering.

[0037] In order to reduce the coefficient of linear thermal expansion of the composite particles and to enhance heat resistance, when Ag is supported on the composite particles, Si and / or SiO are used as the base particles. ２ When Cu is supported, the base particles are preferably particles of a raw material selected from the group consisting of W, Cr, and Mo. However, when Si is used as the base particles and Ag is supported, from the viewpoint of reducing the particle agglomerates A, it is preferable that the base particles are not composite particles produced by physical treatment such as a ball mill. Only one type of base particle may be used, or two or more types may be used.

[0038] The base particles may contain components other than those exemplified above. However, in order to facilitate the loading of Ag and Cu, the base particles should contain Si, SiO, etc., in the total amount (100% by mass) of the base particles. ２、 The total content of W, Cr, and Mo is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, particularly preferably 99.9% by mass or more, and may be 100% by mass.２、 When any of W, Cr, and Mo is not contained, it is preferable that the total content ratio of the contained elements satisfies the above range.

[0039] The average particle size (median diameter) of the base particles is preferably 0.05 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.5 to 10 μm. When the average particle size is 0.05 μm or more, the surface area of ​​the simple substance is appropriate, and metal particles are easily supported on the surface. Furthermore, when the average particle size is 50 μm or less, heat resistance is easily exhibited when sintered. The average particle size (median diameter) is calculated based on the volume of the particles and can be measured by a laser diffraction / scattering method.

[0040] The shape of the base particles is not particularly limited, but examples thereof include spherical, flake (flat) and polyhedral shapes.

[0041] In the composite particles of the present disclosure, the volume ratio of the Ag and / or Cu to the base particle [base particle:Ag and / or Cu] is preferably 99.9:0.1 to 50:50, more preferably 99.5:0.5 to 80:20, and even more preferably 99:1 to 90:10.

[0042] The linear expansion coefficient of the base particle is 8 ppm / K or less, preferably 7 ppm / K or less, and more preferably 6 ppm / K or less. When the linear expansion coefficient is 8 ppm / K or less, heat resistance is easily exhibited. The lower limit is not particularly limited, but may be 1 ppm / K or more. The thermal expansion coefficient can be measured, for example, using a thermomechanical analyzer (apparatus name "TMA-60", manufactured by Shimadzu Corporation).

[0043] [Method for producing composite particles] One embodiment of the present disclosure is a method for producing composite particles in which a metal is supported on a base particle, the method comprising: irradiating with ultrasonic waves a composition containing the base particle, a metal compound serving as a raw material for the metal, and a solvent; and obtaining composite particles in which the average number of particle agglomerates A described below is 2 or less in images taken at 1000x magnification using an SEM at any five locations on a cross section. Hereinafter, this method for producing composite particles may be referred to as the "method for producing composite particles of the present disclosure." Furthermore, the composite particle of the present disclosure can be produced by the method for producing composite particles of the present disclosure. Particle agglomerate A: Contains multiple base particles and Ag and / or Cu, in which the area ratio of the supported Ag and / or Cu to the base particle is 70 area% or more, and the diameter of the longest part of the agglomerate is 5 μm or more.

[0044] The metal may be supported in the form of particles on the base particles, or the amount of metal attached may increase and the metal may be supported in the form of a film on the base particles.

[0045] The metal is preferably Ag and / or Cu, and the base particles are preferably Si, W, SiO ２ Preferably, the base particle is one or more materials selected from the group consisting of Ag, Cr, and Mo. When the metal is Ag, the base particle is Si and / or SiO ２ When the metal is Cu, the base particles are preferably particles made of a raw material selected from the group consisting of W, Cr, and Mo. The Ag, Cu, and base particles are preferably the same as those described in the section on composite particles.

[0046] The temperature of the composition during the ultrasonic irradiation is preferably 20 to 100°C, more preferably 25 to 90°C, and even more preferably 30 to 80°C. The temperature of the composition can be appropriately changed within the above range depending on the specific process. Furthermore, ultrasonic treatment instantaneously generates tiny bubbles called cavitation, which undergo repeated quasi-adiabatic expansion and compression, eventually collapsing. During this process, the cavitation itself reaches extremely high temperatures and pressures, and shock waves and jet streams are also generated during collapse. Therefore, in the method for producing composite particles of the present disclosure, the reduction reaction of the metal compound can occur even when the temperature of the composition is kept relatively low within the above range.

[0047] The irradiation conditions for the ultrasonic irradiation are preferably a frequency in the range of 5 to 1000 kHz, more preferably 20 to 200 kHz. Although the output and irradiation time are affected by the capacity and temperature, the output is preferably 10 to 1000 W, more preferably 20 to 300 W. Furthermore, the irradiation time is preferably in the range of 0.5 to 50 hours.

[0048] Furthermore, the method for producing composite particles according to the present disclosure may include a heat irradiation step in addition to the ultrasonic irradiation step. Examples of heat irradiation methods include those using lasers or microwaves. Specifically, the laser can be generated using an excimer laser device or a YAG laser device, and the microwaves can be generated using a microwave generator with a frequency of 2.45 GHz and an output of approximately 50 to 1500 W. While the heat irradiation step may be performed before the ultrasonic treatment step, it is preferable that the heat irradiation step be performed after the ultrasonic treatment step from the viewpoint of efficiently forming composite particles.

[0049] Examples of the solvent include water and organic solvents. Examples of the organic solvent include reducing organic solvents and non-reducing organic solvents. Specific examples of the reducing organic solvent include alcohols such as ethanol, methanol, 2-propanol, and 2-ethylhexyl alcohol, aldehydes such as acetaldehyde, and polyols such as glycol. Examples of the non-reducing organic solvent include toluene, hexane, cyclohexane, xylene, and benzene. Of these, water and alcohols are preferred, and water, ethanol, methanol, and 2-propanol are more preferred. Note that only one type of the solvent may be used, or two or more types may be used.

[0050] The viscosity of the solvent is preferably 10 mPa·s or less in order to fully exert the effect of the ultrasonic treatment, and although there is no particular lower limit, it may be 0.1 mPa·s or more.

[0051] The metal compound is a component that serves as a raw material for Ag and Cu in the composite particles of the present disclosure. The metal compound is not particularly limited as long as it contains Ag or Cu, but specific examples include metal oxides such as silver oxide and copper oxide, and metal carboxylates such as silver acetate and copper acetate. Note that only one type of the metal compound may be used, or two or more types may be used.

[0052] The metal compounds may include compounds that are directly added as raw materials as well as compounds that are produced as reaction intermediates.

[0053] The content of the metal compound is preferably 0.05 to 10 mass %, and more preferably 0.1 to 5 mass %, relative to the total amount (100 mass %) of the composition. When the amount of the metal compound added is within the above range, it becomes easier to form a metal on the surface of the base particle.

[0054] The composition may contain other components in addition to the base particles, the metal compound, and the solvent, such as additives such as a protective agent and a reducing agent.

[0055] The protective agent may be a component that coats the Ag and Cu surfaces. A compound having a functional group with an unshared electron pair and capable of coordinately adsorbing to Ag and Cu can be used as the protective agent. Compounds having a functional group containing a nitrogen atom are particularly preferred because they can coordinately adsorb to the metal surface. Examples of the functional group containing a nitrogen atom include an amine group and an imide group. Only one type of protective agent may be used, or two or more types may be used.

[0056] Specific examples of the protective agent include primary amine compounds such as ethylamine and dodecylamine, secondary amine compounds such as dimethylamine and diethylamine, tertiary amine compounds such as triethylamine, and polymers having a functional group containing a nitrogen atom, such as ethylpolyvinylpyrrolidone.

[0057] The content of the protective agent is preferably 1 to 10 mass %, and more preferably 2 to 5 mass %, relative to the total amount (100 mass %) of the composition. By keeping the amount of the protective agent added within the above range, the amount added relative to Ag and Cu can be sufficient.

[0058] The reducing agent is a component added to reduce the metal compound by ultrasonic treatment and facilitate the formation of Ag and Cu on the base particle. Only one type of reducing agent may be used, or two or more types may be used.

[0059] Specific examples of the reducing agent include lithium aluminum hydroxide, sodium thiosulfate, hydrogen peroxide, hydrogen sulfide, borane, diborane, hydrazine, potassium iodide, and carboxylic acids such as citric acid, oxalic acid, and ascorbic acid. Of these, it is preferable to use carboxylic acids and hydrazine.

[0060] The content of the reducing agent is preferably 1 to 10 mass %, and more preferably 2 to 7 mass %, relative to 100 mass % of the total amount of the composition. When the amount of the protective agent added is within the above range, Ag and Cu can be easily produced from the metal compound.

[0061] After synthesizing the composite particles using the above method, they can be separated and purified by known or conventional methods to produce composite particles. The composite particles produced in this manner include the composite particles of the present disclosure. Furthermore, since only relatively low-toxicity raw materials are used and production can be performed at low temperatures, the composite particles can be produced safely and at low cost. Furthermore, ultrasonic treatment can create a localized high-energy environment, which causes decomposition and reduction reactions in the metal compound while simultaneously precipitating Ag and / or Cu on the surface of the base particle, thereby producing composite particles in which Ag and / or Cu are present at a high density on the surface of the base particle.

[0062] Furthermore, when an attempt is made to physically support Ag and / or Cu on the surface of the base particle using a ball mill or the like, an excessive amount of Ag and / or Cu is supported, and the above-mentioned particle aggregates are likely to be formed, resulting in poor heat resistance. On the other hand, in the composite particle manufacturing method of the present disclosure, Ag and / or Cu are precipitated on the surface of the base particle, so that an appropriate amount of Ag and / or Cu can be supported, making it easier to exhibit heat resistance.

[0063] (Sintered body) A sintered body can be produced by sintering the composite particles. The temperature of the heat treatment during sintering is preferably 150 to 400°C, more preferably 180 to 350°C, and even more preferably 200 to 300°C. By setting the heat treatment temperature to 400°C or less, the influence of the heat treatment on the substrate and non-bonded materials described below can be suppressed. The sintering time is preferably, for example, 10 seconds to 2 hours, more preferably 3 minutes to 1 hour. Furthermore, the sintered body may be sintered without pressure, or may be sintered with pressure. When pressure is applied, the pressure during pressing is, for example, 0.3 to 40 MPa.

[0064] In the sintered body, the base particle and the Ag and / or Cu in the composite particle are preferably in close contact with each other. In the present disclosure, "close contact" means that no gaps are observed between the base particle and the Ag and / or Cu when a cross section of the sintered body is observed with an SEM.

[0065] The sintered body produced as described above can be used, for example, as a bonded body for bonding a substrate and an object to be bonded.

[0066] (Jointed Body) The joined body can be produced by dispersing the composite particles of the present disclosure in a solvent or the like, applying the dispersion to a substrate by a printing method (specifically, dispenser printing, mask printing, screen printing, inkjet printing, or the like), mounting an object to be joined on the coating layer, and then sintering the resulting mixture. The sintering conditions can be the same as those for producing the sintered body.

[0067] The thickness of the bonded body is preferably 5 to 500 μm, more preferably 20 to 300 μm, and even more preferably 40 to 150 μm.

[0068] Examples of the substrate include metal substrates such as copper substrates, ceramic substrates, metal-laminated ceramic substrates, SiC substrates, gallium nitride substrates, glass epoxy substrates, BT resin substrates, glass substrates, and resin substrates.

[0069] Examples of the bonded object include electronic components, heat dissipation substrates, etc. Examples of electronic components include electronic elements (chips, dies) such as semiconductor elements and LED elements, and a specific example of the semiconductor element is a power semiconductor element. Examples of the material of the bonded object include Si (silicon), SiC (silicon carbide), GaN, diamond, etc.

[0070] The bonded body thus produced can be sintered at low temperatures and has excellent heat resistance because the substrate and the non-bonded object are bonded via the composite particles of the present disclosure, which have excellent heat resistance. Furthermore, since the bonded body can be produced by heat treatment at a relatively low temperature, it can be used to bond even common materials.

[0071] Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Furthermore, each configuration and their combination in each embodiment is merely an example, and additions, omissions, and other modifications of configurations are possible as appropriate within the scope of the gist of this disclosure. The present disclosure is not limited by the embodiments, but is limited only by the scope of the claims.

[0072] Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

[0073] Example 1 Ag ２ 2.2 parts by mass of O powder, 1 part by mass of Si as base particles, and 100 ml of ethanol as a solvent were used. The above raw materials were mixed in a 300 ml Erlenmeyer flask, and ultrasonic irradiation was performed for 24 hours using an ultrasonic generator (trade name "Sonoreactor", manufactured by Honda Electronics Co., Ltd.) at a temperature of 40°C, a frequency of 50 kHz, and an output of 100 W, to produce composite particles of Example 1. The average particle diameter D50 of the supported Ag in Example 1 was 50 nm.

[0074] Examples 2 to 7 Composite particles of Examples 2 to 7 were produced in the same manner as in Example 1, except that the raw materials and compounding ratios were changed to those shown in Table 1. The average particle diameter D50 of the supported Ag in Example 2 was 100 nm.

[0075] Example 8: 0.14 parts by mass of CuO powder, 1 part by mass of W as base particles, 100 ml of ethanol as a solvent, 1.14 ml of acetic acid as an additive, and 4.84 ml of hydrazine were used. The raw materials were mixed in a 300 ml Erlenmeyer flask, and ultrasonic irradiation was performed for 1 hour at a temperature of 40°C, a frequency of 45 kHz, and an output of 100 W using an ultrasonic generator (trade name "Sonoreactor", manufactured by Honda Electronics Co., Ltd.). Subsequently, microwave heating was performed at a water temperature of 80°C, a frequency of 2.45 GHz, and an output of 100 W using a microwave generator (trade name "μReactor", manufactured by Shikoku Keisoku Kogyo Co., Ltd.) to produce composite particles of Example 8.

[0076] Examples 9 to 13 Composite particles of Examples 9 to 13 were prepared in the same manner as in Example 8, except that the raw materials and compounding ratios were changed to those shown in Table 1.

[0077] Comparative Example 1: One part by mass of Cu powder and one part by mass of W powder were mixed and then pressed at a pressure of 400 MPa to produce a green compact. The green compact was sintered at 400°C for one hour under vacuum conditions to produce particles of Comparative Example 1.

[0078] Comparative Example 2 75 parts by mass (40% by volume) of silver flakes (product name "AgC-239", manufactured by Fukuda Metal Foil & Powder Co., Ltd., average particle size: 5 μm) and 25 parts by mass (60% by volume) of silicon particles (Si purity >98.9%, average particle size: 32.8 μm) were mixed and pulverized using the high-speed three-dimensional motion (strong frictional force motion) of a three-dimensional ball mill (product name "3D Ball Mill", manufactured by Nagao System Co., Ltd.) to obtain particles of Comparative Example 2.

[0079] [Evaluation] The particles of the examples and comparative examples prepared above were evaluated as follows, and the results are shown in Table 1.

[0080] (1) Supporting The particles of the Examples and Comparative Examples were observed under an SEM, and were evaluated as follows: ⊚ when a sufficient amount of Ag and / or Cu was observed on the surface of the base particle; ◯ when even a small amount of Ag and / or Cu was observed; and × when no Ag and / or Cu was observed at all.

[0081] (2) Number of Particle Aggregates A Samples were prepared by embedding the particles of the Examples and Comparative Examples in epoxy resin and curing the resin. The number of particle aggregates A described below was counted from an image of the cross section of each sample taken at 1000x magnification using an SEM. The evaluation of the number of particle aggregates A described above represents the average value measured at any five points on the cross section of the sample. Particle aggregate A: Contains multiple base particles and Ag and / or Cu, the area ratio of the supported Ag and / or Cu to the base particles is 70 area % or more, and the diameter of the longest part of the aggregate is 5 μm or more.

[0082] (3) Adhesion after sintering Pellets with a diameter of 6 mm and a thickness of 3 mm were prepared using the particles of the examples and comparative examples. The prepared pellets were heated to 400°C at a heating rate of 10°C / min under nitrogen flow using a tubular furnace, held for 60 minutes, and then allowed to cool to obtain sintered bodies. The sintered bodies were crushed in half and the sintered surfaces were observed with an SEM. Adhesion was evaluated as ◯ when the base particles and Ag and / or Cu were still in close contact after sintering, and x when gaps were observed between the base particles and Ag and / or Cu.

[0083]

[0084] The composite particles of the examples have Ag and / or Cu supported on the base particles, and the Ag and / or Cu remain in close contact with the base particles even after sintering, making them sinterable at relatively low temperatures. Images of five randomly selected locations on a cross section taken at 1000x magnification using an SEM show that the composite particles contain multiple base particles and Ag and / or Cu, the area ratio of the supported Ag and / or Cu to the base particles is 70 area% or more, and the average number of particle agglomerates A with a longest diameter of 5 μm or more is 2 or less. Since the composite particles contain base particles with a low thermal expansion coefficient, it is presumed that the composite particles have excellent heat resistance. On the other hand, when Ag and Cu are not supported on the surface of the base particles, adhesion is not achieved even after sintering (Comparative Example 1). When merely physically mixed, more than two particle agglomerates A were observed, suggesting poor heat resistance, and furthermore, adhesion is not achieved after sintering (Comparative Example 2).

[0085] Variations of the present disclosure are described below. [Appendix 1] Composite particles comprising base particles and Ag and / or Cu supported on the base particles, wherein the base particles have a linear expansion coefficient of 8 ppm / K or less, and wherein the average number of particle agglomerates A described below in images taken at 1000x magnification using an SEM at any five points in a cross section is 2 or less. Particle agglomerate A: Comprises a plurality of base particles and Ag and / or Cu, wherein the area ratio of the supported Ag and / or Cu to the base particles is 70 area% or more, and the diameter of the longest part in the agglomerates is 5 μm or more. [Appendix 2] Composite particles according to Appendix 1, wherein the number of base particles contained in particle agglomerates A is 30% or less of the total number of base particles. [Appendix 3] Composite particles according to Appendix 1 or 2, wherein the number of base particles contained in particle agglomerates B described below is 30% or less of the number of base particles. Particle agglomerate B: Comprising a plurality of base particles and Ag and / or Cu, wherein the area ratio of the supported Ag and / or Cu is 70 area % or more relative to the base particles, the voids in the particle agglomerate are 30 area % or less, and the diameter of the longest part in the agglomerate is 5 μm or more. [Appendix 4] Composite particles according to Appendix 3, wherein the average number of particle agglomerates B in images taken at 1000x magnification using an SEM at any five points in a cross section is 2 or less. [Appendix 5] Composite particles according to any one of Appendixes 1 to 4, wherein the Ag and / or Cu are supported on the base particles as Ag particles and / or Cu particles in a uniform particulate form. [Appendix 6] Composite particles according to any one of Appendixes 1 to 4, wherein the Ag and / or Cu are supported on the base particles in the form of a film. [Appendix 7] The composite particles according to Appendix 5, wherein the content of Ag in 100% by mass of the Ag particles is 95% by mass or more. [Appendix 8] The composite particles according to Appendix 5, wherein the content of Cu in 100% by mass of the Cu particles is 95% by mass or more. [Appendix 9] The composite particles according to any one of Appendices 5 and 7 to 8, wherein the average particle diameter (median diameter) of the Ag particles and the Cu particles is 1 nm or more and 10,000 nm or less.[Appendix 10] The composite particles according to any one of Appendices 5, 7 to 8, wherein the Ag particles and the Cu particles have an average particle size (median size) of 5 nm or more and 1000 nm or less. [Appendix 11] The composite particles according to any one of Appendices 5, 7 to 8, wherein the Ag particles and the Cu particles have an average particle size (median size) of 10 nm or more and 500 nm or less. [Appendix 12] The composite particles according to Appendices 6, wherein the Ag and / or the Cu are supported on the base particle in the form of a film, the film having a thickness of 10 nm to 10 μm. [Appendix 13] The base particle is Si, W, or SiO. ２, Cr, and Mo. [Appendix 14] Composite particles according to any one of Appendices 1 to 13, wherein the average particle size of the base particles is 0.05 to 50 μm. [Appendix 15] Composite particles according to any one of Appendices 1 to 14, wherein a volume ratio of the Ag and / or Cu to the base particles [base particles:Ag and / or Cu] is 99.9:0.1 to 50:50. [Appendix 16] A method for producing composite particles in which a metal is supported on a base particle, the method comprising: irradiating with ultrasonic waves a composition containing the base particle, a metal compound serving as a raw material for the metal, and a solvent, to obtain composite particles in which the average number of particle aggregates A described below is 2 or less in images taken at 1000x magnification using an SEM at any five points in a cross section. Particle agglomerate A: Comprising a plurality of base particles and Ag and / or Cu, wherein the area ratio of the supported Ag and / or Cu to the base particles is 70 area % or more, and the longest diameter of the agglomerate is 5 μm or more. [Appendix 17] The method for producing composite particles according to Appendices 16, wherein the temperature of the composition is 20 to 100° C. in the step of applying ultrasonic waves. [Appendix 18] The method for producing composite particles according to Appendices 16 or 17, wherein the ultrasonic irradiation conditions in the step of applying ultrasonic waves are a frequency of 5 to 1000 kHz and an output of 10 to 1000 W. [Appendix 19] The method for producing composite particles according to any one of Appendices 16 to 18, wherein the solvent comprises water or an alcohol. [Appendix 20] The method for producing composite particles according to any one of Appendices 16 to 19, wherein the composition further comprises a reducing agent. [Appendix 21] The method for producing composite particles according to any one of Appendices 16 to 20, wherein the composition further comprises a carboxylic acid. [Appendix 22] The base particle is Si, W, SiO ２ The method for producing composite particles according to any one of Appendices 16 to 21, wherein the metal compound is a raw material particle selected from the group consisting of Mo, Cr, and Mo. [Appendix 23] The method for producing composite particles according to any one of Appendices 16 to 22, wherein the metal compound is a metal oxide and / or a metal carboxylate.

[0086] 1: Base material particles 2: Ag particles 3: Cu particles

Claims

1. Composite particles comprising a base particle and Ag and / or Cu supported on the base particle, wherein the base particle has a linear expansion coefficient of 8 ppm / K or less, and wherein the average number of particle agglomerates A described below in an image taken at 1000x magnification using an SEM at any five points in a cross section is 2 or less: Particle agglomerate A: Comprises a plurality of base particles and Ag and / or Cu, wherein the area ratio of the supported Ag and / or Cu to the base particle is 70 area% or more, and the diameter of the longest point in the agglomerate is 5 μm or more.

2. The base particles are Si, W, SiO ２ 2. The composite particle according to claim 1, which is made of one or more raw materials selected from the group consisting of Fe, Cr, and Mo.

3. The composite particles according to claim 1 or 2, wherein the average particle size of the base particles is 0.05 to 50 μm.

4. Composite particles according to claim 1 or 2, wherein the volume ratio of the Ag and / or Cu to the base particle [base particle:Ag and / or Cu] is 99.9:0.1 to 50:

50.

5. A method for producing composite particles in which a metal is supported on a base particle, the method comprising: irradiating with ultrasonic waves a composition containing the base particle, a metal compound serving as a raw material for the metal, and a solvent, to obtain composite particles in which the average number of particle agglomerates A below is 2 or less in images taken at 1000x magnification using an SEM at any five points on a cross section: Particle agglomerate A: Comprising a plurality of base particles and Ag and / or Cu, the area ratio of the supported Ag and / or Cu to the base particle is 70 area% or more, and the diameter of the longest part of the agglomerate is 5 μm or more.

6. The method for producing composite particles according to claim 5, wherein the temperature of the composition is 20 to 100°C in the step of irradiating with ultrasonic waves.

7. The method for producing composite particles according to claim 5 or 6, wherein in the step of irradiating with ultrasonic waves, the ultrasonic irradiation conditions are a frequency of 5 to 1000 kHz and an output of 10 to 1000 W.

8. The method for producing composite particles according to claim 5 or 6, wherein the solvent comprises water or an alcohol.

9. The method for producing composite particles according to claim 5 or 6, wherein the composition further comprises a reducing agent.

10. The method for producing composite particles according to claim 5 or 6, wherein the composition further comprises a carboxylic acid.

11. The base particles are Si, W, SiO ２ 7. The method for producing composite particles according to claim 5 or 6, wherein the composite particles are particles of a raw material selected from the group consisting of Fe, Cr, and Mo.

12. The method for producing composite particles according to claim 5 or 6, wherein the metal compound is a metal oxide and / or a metal carboxylate.

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