Transfer-type sheet-like bonding material

Abstract

Provided is a transfer-type sheet-like bonding material with which (I) cracks can be sufficiently suppressed, (II) excellent transfer properties can be obtained even under slow transfer conditions in which copper particles are not sintered, and (III) sufficient bonding strength can be ensured even when bonded at low temperatures of 250 DEG C or less. The transfer-type sheet-like bonding material is characterized in that the transfer-type sheet-like bonding material is obtained by applying and drying a paste on a resin substrate, the paste containing copper particles, a reducing agent, an organic material, and a solvent, the organic material containing a resin and any plasticizer, and the transfer-type sheet-like bonding material has a glass transition point of-35 DEG C or more and 25 DEG C or less.

Description

Technical Field

[0001] The present invention relates to a transfer-type sheet joining material. Background Art

[0002] Conventionally, as a joining material for electronic components, a solder material has been widely used. However, the solder material has a problem of poor heat resistance. Therefore, for example, in a power device using a SiC element expected to be used at a temperature of 150°C or higher, it is difficult to use the solder material as a joining material.

[0003] Therefore, as a sintered joining material, a joining material using silver particles has been proposed. In addition, from the viewpoints of cost and ion migration, copper particles are highly expected, and the industry is developing a transfer-type sheet joining material using copper particles.

[0004] The transfer-type sheet joining material is formed by coating a paste containing at least copper particles, a reducing agent, a resin, and a solvent on a resin substrate such as a release PET film and drying it. The joining of two components (a first component and a second component) using the transfer-type sheet joining material is performed as follows. First, the sheet joining material is transferred to the first component under specified transfer conditions, and then the resin substrate is peeled off. Next, the sheet joining material transferred to the first component is brought into contact with the second component, and the first component and the second component are joined via the sheet joining material under specified joining conditions.

[0005] In Patent Document 1, there is described a sheet joining material obtained by coating a paste on a PET film and drying it, wherein the paste contains: copper particles (D10; 100 nm or more, D90; 2000 nm or less) whose surfaces are coated with triethanolamine as a covering agent, a dicarboxylic acid as an activator, a dispersant, epoxy methacrylate urethane as an adhesive, and terpineol as an organic solvent. In Patent Document 1, it is described that the sheet joining material can be transferred to a gold-plated silicon mold under transfer conditions of a transfer temperature of 200°C to 225°C, a pressing force of 5 MPa, and a transfer time of 1 second to 10 seconds.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-529258 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] However, according to the research of the present inventors and others, it was found that although there is no resin called epoxy methacrylate urethane described in Patent Document 1, in any case, in existing sheet joining materials, since the sheet joining material (paste dry film) contains a resin component, cracks are generated in the dry film.

[0011] In addition, in Patent Document 1, since the transfer temperature is 200°C or higher, copper is sintered during transfer, and the surface activity of the copper particles is impaired. Therefore, sometimes the sintering of copper during subsequent joining and the diffusion of atoms into the material to be joined are impaired, and there is a problem that the sinterability and atomic diffusion (joinability) tend to become unstable. If transfer is performed under slow transfer conditions without sintering the copper particles, there is a problem that the sheet joining material cannot be transferred onto the entire surface of the material to be transferred, or residues of the paste dry film (transfer-type sheet joining material) remain on the resin substrate.

[0012] In addition, in the sheet joining material of Patent Document 1, although low-temperature joining can be performed at a joining temperature of 250°C or lower, there is also a problem that it is difficult to ensure sufficient joining strength.

[0013] In view of the above problems, an object of the present invention is to provide a transfer-type sheet joining material that can (I) sufficiently suppress cracks, (II) obtain excellent transferability even under slow transfer conditions without sintering copper particles, and (III) ensure sufficient joining strength even for low-temperature joining at 250°C or lower.

[0014] Means for Solving the Problems

[0015] In order to solve the above problems, the present inventors conducted in-depth research and found that in a transfer-type sheet joining material obtained by coating a paste containing copper particles, a reducing agent, a solvent, and an organic material containing a resin and optionally a plasticizer on a resin substrate and drying it, by optimizing the glass transition point of the transfer-type sheet joining material, the above problems (I) to (III) can be solved.

[0016] The main configuration of the present invention completed based on the above findings is as follows.

[0017] [1] A transfer-type sheet joining material, characterized in that it is obtained by coating a paste containing copper particles, a reducing agent, an organic material, and a solvent on a resin substrate and drying it, the organic material contains a resin and optionally contains a plasticizer,

[0018] The transfer-type sheet joining material has a glass transition point of -35°C or higher and 25°C or lower.

[0019] [2] The transfer-type sheet joining material according to the above [1], wherein the resin contains an acrylic resin.

[0020] [3] The transfer-type sheet bonding material according to [1] or [2] above, wherein the content of the resin is 1.0 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the copper particles.

[0021] [4] The transfer-type sheet bonding material according to any one of [1] - [3] above, wherein the plasticizer is composed of one or more selected from butylphthalylbutyl glycollate, dimethyl phthalate, dioctyl phthalate, and diisodecyl phthalate.

[0022] [5] The transfer-type sheet bonding material according to any one of [1] - [4] above, wherein the content of the plasticizer is 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the resin.

[0023] [6] The transfer-type sheet bonding material according to any one of [1] - [5] above, wherein the reducing agent consists of triethanolamine.

[0024] [7] The transfer-type sheet bonding material according to any one of [1] - [6] above, wherein the content of the reducing agent is 3 parts by mass or more and 9 parts by mass or less with respect to 100 parts by mass of the copper particles.

[0025] [8] The transfer-type sheet bonding material according to any one of [1] - [7] above, wherein the average particle diameter of the copper particles is 70 nm or more and 300 nm or less.

[0026] Effects of the Invention

[0027] The transfer-type sheet bonding material of the present invention can (I) sufficiently suppress cracks, (II) obtain excellent transferability even under slow transfer conditions without sintering of the copper particles, and (III) ensure sufficient bonding strength even for low-temperature bonding at 250 °C or lower. Detailed Description of the Invention

[0028] [Transfer-Type Sheet Bonding Material]

[0029] The transfer-type sheet bonding material according to one embodiment of the present invention is characterized in that it is obtained by coating a paste containing copper particles, a reducing agent, a solvent, and an organic material containing a resin and optionally a plasticizer on a resin substrate and drying it, and has a glass transition point of -35 °C or higher and 25 °C or lower.

[0030] (Copper Particles)

[0031] The copper particles mainly consist of copper. With respect to 100% by mass of the copper particles, the content of copper element in the copper particles is preferably 95% by mass or more and 100% by mass or less, more preferably 97% by mass or more. When the copper element content is 95% by mass or more, the heat resistance of the bonding material is excellent and the bonding strength is better.

[0032] The average particle size of the copper particles is preferably 300 nm or less. By making the average particle size of the copper particles 300 nm or less, sufficient high bonding strength can be ensured even for low-temperature bonding below 250°C. The average particle size of the copper particles is more preferably 150 nm or less. In addition, the average particle size of the copper particles is preferably 5 nm or more. If the average particle size of the copper particles is 5 nm or more, it is easy to obtain copper fine particles. The average particle size of the copper particles is more preferably 70 nm or more. By making the average particle size of the copper particles 70 nm or more, sufficient high bonding strength can be ensured even for low-temperature bonding below 250°C.

[0033] The shape (morphology) of the copper particles is not particularly limited. Examples of the shape of the copper particles include spherical (sphere), elliptical (ellipsoid), plate-like, etc. Among them, spherical or elliptical is preferred, and spherical is more preferred.

[0034] The average particle size of the copper particles can be determined by the following operation: Observe 10 fields of view at a magnification of 10,000 times using a scanning electron microscope (SEM). For all the copper particles selected according to the following selection criteria (1) to (5) in the 10 fields of view, measure the particle size of each copper particle, and calculate its D50, thereby the average particle size of the copper particles can be determined. In addition, for non-circular particles such as ellipses, the major axis is used as the particle size. In addition, the particle size distribution of the copper particles is also determined based on the particle sizes of all the copper particles to be measured as described above. Here, when determining the average particle size and particle size distribution of the copper particles in the sheet-like bonding material, observe the outermost surface of the sheet. In the powder state before sheet production, place the powder on a carbon tape with a spatula, remove the excess powder with an air dust collector, and observe the surface of the tape.

[0035] (1) Do not measure the particles whose part exceeds the image field of view.

[0036] (2) Measure the particles with clear contours and isolated existence.

[0037] (3) Even in the case of particles with a shape deviating from the average, measure the independent particles that can be measured as individual particles.

[0038] (4) For the particles with overlapping with each other, but the boundary between the two is clear and the overall shape of the particles can be judged, measure each particle as an individual particle.

[0039] (5) For overlapping particles, particles with unclear boundaries and whose entire shape cannot be determined are not measured as particles whose shape cannot be determined.

[0040] As the copper particles, copper particles that do not require a protective agent, a dispersant, etc. are preferably used. As such copper particles, for example, the metal ultrafine powder obtained by the production method described in Japanese Patent No. 4304221. However, the copper particles are not limited to this example.

[0041] The copper particles preferably have a coating film containing copper carbonate on the surface. By making the copper particles have a coating film containing copper carbonate on the surface, the sintering temperature of the copper particles can be suppressed to be lower compared with the prior art, and at the same time, the bonding strength can be improved. The coating film containing copper carbonate may also contain cuprous oxide.

[0042] The copper particles preferably use particles not coated with an organic protective film. When the copper particles are coated with an organic protective film, if the organic protective film is not decomposed, the sintering of the copper particles will not occur. Therefore, a bonding temperature above the decomposition temperature of the organic protective film is required, and sometimes a low-temperature bonding below 250°C cannot be performed. In addition, the decomposition gas of the organic protective film forms voids in the bonding layer or cracks in the bonding layer, and there is a risk of reduced reliability.

[0043] From the viewpoints of reducing the reactivity with oxygen in the air and reducing the influence of re-oxidation, the ratio of the mass oxygen concentration of the copper particles to the specific surface area is preferably 0.1 mass%·g / m 2 or more, and more preferably 0.2 mass%·g / m 2 or more. On the other hand, from the viewpoints of easily removing the oxide film during bonding and further improving the bonding strength, the ratio of the mass oxygen concentration of the copper particles to the specific surface area is preferably 1.2 mass%·g / m 2 or less, and more preferably 0.5 mass%·g / m 2 or less.

[0044] From the viewpoints of suppressing the generation of voids and cracks and further improving the bonding strength, the ratio of the mass carbon concentration of the copper particles to the specific surface area is preferably 0.3 mass%·g / m 2 or less, and more preferably 0.1 mass%·g / m 2 or less, and further preferably 0.05 mass%·g / m 2 or less. The ratio of the mass carbon concentration of the copper particles to the specific surface area is preferably 0.008 mass%·g / m 2 or more.

[0045] The ratio of the mass oxygen concentration of the copper particles to the specific surface area can be calculated from the measured specific surface area and mass oxygen concentration, respectively. The specific surface area can be measured using a BET adsorption apparatus for nitrogen (e.g., "MACSORB HM-1201" manufactured by Mountech Co., Ltd., Japan). The mass oxygen concentration can be measured using an oxygen-nitrogen analyzer (e.g., "TC600" manufactured by LECO Corporation).

[0046] The ratio of the mass carbon concentration of the copper particles to the specific surface area can be calculated from the measured specific surface area and mass carbon concentration, respectively. The specific surface area can be measured using a BET adsorption apparatus for nitrogen (e.g., "MACSORB HM-1201" manufactured by Mountech Co., Ltd., Japan). The mass carbon concentration can be measured using a carbon-sulfur analyzer (e.g., "EMIA-920V" manufactured by Horiba, Ltd., Japan).

[0047] The "content of copper particles" in the sheet-like bonding material is the same as the content of copper particles in the paste. For example, the sheet can be heated to about 1000 °C in a nitrogen atmosphere, and the content can be determined based on the weight after heating.

[0048] (Reducing agent)

[0049] The reducing agent is a compound that reduces the oxide film inevitably present on the surface of the copper particles during bonding. During bonding, by removing the oxide film using the reducing agent, the copper particles (pure copper) come into contact with each other and are sintered, thereby performing diffusion bonding.

[0050] In the present embodiment, the reducing agent preferably consists of triethanolamine. Triethanolamine has a high effect of removing the oxide film, and is also a high-boiling point and low-volatility substance, so it is not easily detached during transfer, and has high stability over time. Therefore, the storage stability before bonding is excellent.

[0051] In the present embodiment, the content of the reducing agent is preferably 3 parts by mass or more and 9 parts by mass or less with respect to 100 parts by mass of the copper particles. If the content of the reducing agent is 3 parts by mass or more, the amount of the reducing agent is sufficient, and even for low-temperature bonding at 250 °C or lower, the sintering of the copper particles is sufficient, and a sufficiently high bonding strength can be ensured. In addition, if the content of the reducing agent is 9 parts by mass or less, exudation of the reducing agent is not likely to occur during transfer and bonding, and transfer and bonding with the same shape as the material to be bonded can be achieved. In addition, the decomposition gas components do not increase, and voids or cracks are not likely to appear in the bonding layer.

[0052] In addition, the content of the reducing agent in the sheet-like bonding material is the same as the content of the reducing agent in the paste.

[0053] (Organic material)

[0054] In the present embodiment, the organic material includes a resin and optionally contains a plasticizer.

[0055] <Resin>

[0056] The resin functions as an adhesive material when transferring the transfer-type bonding sheet to the first component. Additionally, it is better if it also has the function of a dispersant for dispersing copper particles.

[0057] The resin is preferably a resin such as an acrylic resin or an aliphatic polycarbonate, which is a highly decomposable adhesive. In particular, the resin is preferably composed of an acrylic resin. The reason is that the acrylic resin has an adhesive function, so the transferability is excellent. Specifically, one or more selected from polyalkyl methacrylate, polyalkylmethacrylate, and methacrylate copolymers can be used.

[0058] In the present embodiment, with respect to 100 parts by mass of copper particles, the content of the resin is preferably 1.0 part by mass or more and 5.0 parts by mass or less. When the resin content is less than 1.0 part by mass, cracks are likely to occur in the dried film of the paste, and it is difficult to obtain excellent transferability under slow transfer conditions without sintering the copper particles. Additionally, when the resin content exceeds 5.0 parts by mass, voids are formed in the bonding layer by the decomposable components and undissolved substances in the adhesive, damaging the adhesion to the material to be bonded, so sufficient bonding strength cannot be ensured in low-temperature bonding at 250 °C or below.

[0059] In addition, the resin content in the sheet-like bonding material is the same as the resin content in the paste.

[0060] <Plasticizer>

[0061] The plasticizer reduces the glass transition point of the sheet-like bonding material and imparts flexibility to the sheet, while also suppressing the drying shrinkage of the coating film containing copper particles.

[0062] As the plasticizer, one or more selected from dimethyl phthalate, diethyl phthalate, diallyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, di-n-hexyl phthalate, bis(2-ethylhexyl) phthalate, dioctyl phthalate, di-n-octyl phthalate, diisononyl phthalate, diisodecyl phthalate, dinonyl phthalate, bis(butylbenzyl) phthalate, and butyl phthalyl butyl glycolate can be used. In particular, the plasticizer is preferably composed of one or more selected from butyl phthalyl butyl glycolate, dimethyl phthalate, dioctyl phthalate, and diisodecyl phthalate.

[0063] In the present embodiment, relative to 100 parts by mass of the resin, the content of the plasticizer is preferably 10 parts by mass or more and 50 parts by mass or less. When the content of the plasticizer is less than 10 parts by mass, since it is difficult to exhibit the plasticizing effect, cracks are likely to occur in the dried film of the paste, and excellent transfer performance is difficult to obtain under slow transfer conditions without sintering of the copper particles. In addition, since the copper particles may sinter during transfer, sufficient bonding strength cannot be ensured in low-temperature bonding at 250°C or lower. Further, if the content of the plasticizer exceeds 50 parts by mass, poor dispersion of the copper particles, binder, and reducing agent in the paste is likely to occur, so that excellent transferability is difficult to obtain under slow transfer conditions without sintering of the copper particles, and sufficient bonding strength cannot be ensured in low-temperature bonding at 250°C or lower.

[0064] In addition, the content of the plasticizer in the sheet-like bonding material is the same as the content of the plasticizer in the paste.

[0065] <Glass transition point of transfer-type sheet-like bonding material>

[0066] For the transfer-type sheet-like bonding material of the present embodiment, it is important to have a glass transition point of -35°C or higher and 25°C or lower. By setting the glass transition point of the transfer-type sheet-like bonding material to 25°C or lower, a flexible transfer-type sheet-like bonding material can be obtained, and (I) cracks can be sufficiently suppressed, (II) excellent transferability can be obtained even under slow transfer conditions without sintering of the copper particles, and (III) sufficient bonding strength can be ensured even in low-temperature bonding at 250°C or lower. From this viewpoint, the glass transition point of the transfer-type sheet-like bonding material is preferably 10°C or lower. On the other hand, if the glass transition point of the transfer-type sheet-like bonding material is too low, it may sometimes be impossible to transfer the sheet-like bonding material from the resin substrate. Therefore, the glass transition point of the transfer-type sheet-like bonding material is set to -35°C or higher, preferably -20°C or higher.

[0067] The glass transition point of the transfer-type sheet-like bonding material can be mainly controlled according to the type of resin, the type and content of the plasticizer.

[0068] The glass transition point of the transfer-type sheet bonding material can be determined by peeling off the paste dry film (transfer-type sheet bonding material) from the resin substrate and subjecting the resulting powder to differential scanning calorimetry. For example, using a differential scanning calorimeter (DSC60) manufactured by Shimadzu Corporation, Japan, 20 mg of the paste dry powder (a sample dried at 70 °C for 60 minutes) is placed in the apparatus, and in the DSC thermogram (Differential Scanning Calorimetry Thermogram) obtained under the conditions of a measurement range of -50 °C to 150 °C (heating rate: 10 °C / minute) and a nitrogen atmosphere (flow rate 50 mL / minute), the midpoint of the displacement between the original baseline and the baseline when the baseline moves downward due to the glass transition can be calculated as the glass transition point.

[0069] (Solvent)

[0070] It is desirable that the solvent have a boiling point of about 200 °C and low volatility. This is because if the solvent evaporates during paste coating and the metal concentration changes, thickness unevenness of the coating film will occur. In addition, the solvent needs to be able to dissolve the resin used. From these viewpoints, for example, terpene solvents such as terpineol can be used.

[0071] (Sheet)

[0072] The bonding material of this embodiment is in sheet form. Here, the thickness of the bonding material is not particularly limited and can be, for example, 10 μm or more and less than 1 mm.

[0073] In addition, the shape of the bonding material (the shape when viewed from above in the thickness direction) is not particularly limited and can be appropriately selected according to the shape of the bonding surface of the component to be bonded, etc. For example, a rectangle or a circle can be cited.

[0074] [Manufacturing method of transfer-type sheet bonding material]

[0075] The transfer-type sheet bonding material of this embodiment can be produced by coating a paste containing copper particles, a reducing agent, a solvent, and an organic material containing a resin and optionally containing (containing or not containing) a plasticizer on a resin substrate and drying it.

[0076] The method for producing the paste is not particularly limited, and the components can be mixed by methods such as using a self-revolving stirrer, a mortar, a grinder for stirring, or a mixer for stirring. The method for coating the paste on the resin substrate and drying it is also not particularly limited. For example, a coater (Applicator) can be used to coat the paste on the resin substrate, and the coating film can be dried in a hot air oven to obtain a paste dry film. The drying conditions can be 50 °C to 110 °C (atmospheric temperature) and a drying time of 10 minutes to 90 minutes.

[0077] The resin substrate is not particularly limited, and examples thereof include a release PET film, a silicon film, a fluororesin film, etc. Considering the releasability, the thickness of the resin substrate can be about 50 μm to 200 μm.

[0078] The joining of two components (a first component and a second component) by a transfer-type sheet joining material is carried out through the following two processes of transfer and joining.

[0079] (Transfer)

[0080] First, after the sheet joining material is joined to the first component, the resin substrate is peeled off. That is, the sheet joining material is transferred onto the first component. The conditions for transferring the transfer-type sheet joining material formed on the resin substrate onto the first component are not particularly limited, but in the present embodiment, excellent transferability can be obtained even under slow transfer conditions where the transfer temperature is 150°C or lower, the applied pressure is 10 MPa or lower, and the transfer time is 1 minute or shorter without copper particle sintering. As the transfer conditions, the transfer temperature can be set to 50°C to 150°C, the applied pressure can be set to 1 MPa to 10 MPa, and the transfer time can be set within the range of 10 seconds to 1 minute. The atmosphere during transfer is preferably an inert atmosphere such as nitrogen (N2).

[0081] (Joining)

[0082] Next, the sheet joining material transferred onto the first component is brought into contact with the second component, and the first component and the second component are joined via the sheet joining material under specified joining conditions. The joining conditions are not particularly limited, but in the present embodiment, sufficient joining strength can be ensured even for low-temperature joining at 250°C or lower. As the joining conditions, the joining temperature can be set to 200°C to 250°C, the applied pressure can be set to 1 MPa to 40 MPa, and the transfer time can be set within the range of 1 minute to 60 minutes. The atmosphere during joining is preferably an inert atmosphere such as nitrogen (N2).

[0083] Examples

[0084] [Manufacture of Transfer-Type Sheet Joining Material]

[0085] (Test Example No. 1)

[0086] 40 g of copper particles (sample with a particle size of 110 nm; D10: 39 nm, D50: 112 nm, D90: 310 nm) produced from solar acid, 3.2 g of triethanolamine as a reducing agent, 1.78 g of an acrylic binder (manufactured by Kyoeisha Chemical Co., Ltd., Olycox KC-500), and 12.2 g of terpineol as a solvent were mixed in a self-revolving stirrer to obtain a paste. In addition, the surface layer of the copper particles was coated with cuprous oxide, and the ratio of the mass oxygen concentration of the copper particles to the specific surface area was 0.25 mass%·g / m 2 , and the ratio of the mass carbon concentration to the specific surface area was 0.03 mass%·g / m 2 .

[0087] Then, the obtained paste was coated on a release PET film with a thickness of 100 μm to a film thickness of 200 μm using an applicator, and the film was dried in a hot air oven at 70 °C for 60 minutes to remove terpineol, obtaining a dried paste film (transfer-type sheet-like bonding material). The mixing ratio of the obtained transfer-type sheet-like bonding material and the glass transition point of the transfer-type sheet-like bonding material measured by the above-described method are shown in Table 1.

[0088] (Test Examples No. 2 to 26)

[0089] The content of the copper particles was still 40 g, and the type of the copper particles, the type and content of the reducing agent, the type and content of the acrylic binder, and the type and content of the plasticizer were changed to the types and contents shown in Table 1, and a paste was obtained in the same manner as in Test Example No. 1. In addition, the content of terpineol was set so that the concentration of the copper particles in the paste was 70 mass%. Then, the same operation as in Test Example No. 1 was performed to obtain a dried paste film (transfer-type sheet-like bonding material). The mixing ratio of the obtained transfer-type sheet-like bonding material and the glass transition point of the organic material measured by the above-described method are shown in Table 1.

[0090] [Evaluation of cracks in the dried paste film]

[0091] In each test example, the dried paste film (transfer-type sheet-like bonding material) was observed with a microscope at a magnification of 20 times in 10 fields of view. The case where all 10 fields of view had no cracks was recorded as "excellent", and the case where there was even one field of view with a crack was determined as "poor", and the results were recorded in the column of "crack resistance of the dried paste film" in Table 1. In addition, in the case of "poor" where the dried film had cracks, since the crack pattern and its degree could not be controlled, the shear strength of the bonded sample after bonding would deviate, so the subsequent transfer and bonding tests were not carried out.

[0092] [Evaluation of transferability]

[0093] In each test example, a gold-plated SiC (4 mm square, 350 μm thick) was mounted on a transfer-type sheet joining material, and the transfer-type sheet joining material was transferred onto the gold-plated surface of the SiC under the transfer conditions of a transfer temperature (atmosphere temperature) of 150°C, a pressing force of 10 MPa, a transfer time of 30 s, and an N2 atmosphere. The case where the sheet joining material could be transferred onto the entire surface of the SiC and there was no residue of the paste dry film (transfer-type sheet joining material) on the release PET film was regarded as "excellent", and the case where the sheet joining material could not be transferred onto the entire surface of the SiC or there was residue of the paste dry film (transfer-type sheet joining material) on the release PET film was regarded as "poor", which is shown in the "Transferability" column of Table 1. In addition, in the case where the transferability was "poor", since there would be a deviation in the shear strength of the joined sample after joining, the subsequent joining tests were not carried out.

[0094] [Evaluation of Shear Strength of Joined Sample]

[0095] In each test example, the transfer-type sheet joining material transferred onto the SiC was brought into contact with an oxygen-free copper plate C1020 (20 mm square, 2 mm thick), and in a pressure joining device, the SiC and the oxygen-free copper plate were joined via the sheet joining material under the joining conditions of a joining temperature (atmosphere temperature) of 250°C, a pressing force of 10 MPa, a joining time of 5 minutes, and an N2 atmosphere, and a joined sample was manufactured. The shear strength of the joined sample was measured using a bond tester (manufactured by Dage Co., Ltd., 4000Plus) at a tool height of 100 μm and a tool speed of 200 μm / s, as shown in Table 1. A shear strength of 50 MPa or more was considered good.

[0096] [Evaluation of Exudation of Joined Layer after Joining]

[0097] In each test example, the outer peripheral part of the SiC of the joined sample was observed with a microscope (manufactured by Hozan Co., Ltd., L-KIT504) at a magnification of 20 times to confirm whether there was liquid exudation around the outer peripheral part of the SiC, as shown in Table 1.

[0098] Table 1

[0099]

[0100] ※1

[0101] 110 nm sample (D10: 39 nm, D50: 112 nm, D90: 310 nm)

[0102] 300 nm sample (D10: 52 nm, D50: 298 nm, D90: 652 nm)

[0103] 70 nm sample (D10: 24 nm, D50: 72 nm, D90: 284 nm)

[0104] 100 nm sample (D10: 34 nm, D50: 101 nm, D90: 308 nm)

[0105] 400 nm sample (D10: 66 nm, D50: 403 nm, D90: 811 nm)

[0106] 50 nm sample (D10: 15 nm, D50: 51 nm, D90: 194 nm)

[0107] ※2: Content (parts by mass) of reducing agent relative to 100 parts by mass of copper particles

[0108] ※3: Content (parts by mass) of acrylic resin in the acrylic binder relative to 100 parts by mass of copper particles

[0109] ※4: Content (parts by mass) of plasticizer relative to 100 parts by mass of acrylic resin

[0110] As can be seen from Table 1, in comparative examples where the glass transition point of the transfer-type sheet joining material is outside the range of -35°C or higher and 25°C or lower, cracks were observed in the dry film. In contrast, in inventive examples where the glass transition point of the transfer-type sheet joining material is in the range of -35°C or higher and 25°C or lower, no cracks were generated in the dry film, and excellent transferability could be obtained even under slow transfer conditions without sintering the copper particles. Moreover, even for low-temperature joining at 250°C, sufficient joining strength could be ensured. In particular, in some inventive examples where the content of the acrylic binder, the content of the reducing agent, and the average particle diameter of the copper particles were optimized, a relatively high shear strength of 50 MPa or more was obtained.

[0111] Industrial Applicability

[0112] The transfer-type sheet joining material of the present invention can be industrially used for joining electronic components. Specifically, joining applications of components such as substrates and elements in high-temperature environments where it is difficult to use joining materials such as solder, for example, inside electronic devices called power devices, are listed.

Claims

1. A transfer-type sheet bonding material, characterized in that: The transfer-type sheet bonding material is formed by coating a paste on a resin substrate and drying it. The paste contains copper particles, a reducing agent, an organic material, and a solvent. The organic material contains a resin and selectively contains a plasticizer. The transfer-type sheet bonding material has a glass transition point of -35°C or higher and 25°C or lower.

2. The transfer-type sheet joining material according to claim 1, wherein, The resin contains an acrylic resin.

3. The transfer-type sheet bonding material according to claim 1 or 2, wherein, The content of the resin is 1.0 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the copper particles.

4. The transfer-type sheet joining material according to claim 1 or 2, wherein, The plasticizer is composed of one or more selected from butyl phthalyl butyl glycolate, dimethyl phthalate, dioctyl phthalate, and diisodecyl phthalate.

5. The transfer-type sheet joining material according to claim 1 or 2, wherein, The content of the plasticizer is 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the resin.

6. The transfer-type sheet joining material according to claim 1 or 2, wherein The reducing agent is composed of triethanolamine.

7. The transfer-type sheet joining material according to claim 1 or 2, wherein, The content of the reducing agent is 3 parts by mass or more and 9 parts by mass or less with respect to 100 parts by mass of the copper particles.

8. The transfer-type sheet joining material according to claim 1 or 2, wherein The average particle size of the copper particles is 70 nm or more and 300 nm or less.

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