Transfer type sheet-like joint material

Abstract

To provide a transfer type sheet-like joint material which (I) sufficiently suppresses cracking, (II) can obtain excellent transferability even under a transfer condition at a normal temperature that does not progress sintering of copper particles, and (III) can secure sufficient joint strength even in low temperature joint at 250°C or lower.SOLUTION: A transfer type sheet-like joint material is a paste dry film obtained by coating and drying a paste containing copper particles, a reducer and a solvent onto a resin substrate, and has a solvent-containing ratio of 5.0 mass% or more and 15.0 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a transfer type sheet-like bonding material. [Background technology]

[0002] Solder has traditionally been widely used as a bonding material for electronic components. However, solder has a problem of poor heat resistance. For example, it has been difficult to use solder as a bonding material for power devices using SiC elements, which are expected to be used at high temperatures of 150°C or higher.

[0003] Therefore, a bonding material using silver particles has been proposed as a sintered bonding material. In addition, copper particles are expected to be a promising option from the viewpoints of cost and ion migration, and the development of a transfer-type sheet-type bonding material using copper particles is underway.

[0004] The transfer-type sheet-like bonding material is formed by applying a paste containing at least copper particles, a reducing agent, a resin, and a solvent onto a resin substrate such as a release PET film and drying the paste. Bonding of two members (a first member and a second member) using the transfer-type sheet-like bonding material is performed as follows: First, the sheet-like bonding material is transferred to the first member under predetermined transfer conditions, and then the resin substrate is peeled off. Next, the sheet-like bonding material transferred onto the first member is brought into contact with the second member, and the first member and the second member are bonded via the sheet-like bonding material under predetermined bonding conditions.

[0005] Patent Document 1 describes a d of about 0.001 to about 10 μm. 50 Patent Document 1 describes a sheet-like bonding material obtained by forming a film on a substrate from a paste containing a metal powder having a specific surface area, a rosin binder, and a solvent, and then removing all of the solvent and drying the film. Patent Document 1 also describes a method of placing materials to be bonded on the sheet-like bonding material, applying heat in the range of 50 to 200°C, and applying pressure in the range of 0.05 to 10 MPa, thereby transferring the sheet-like bonding material to the materials to be bonded. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-62715 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the sheet-like bonding material described in Patent Document 1, since the solvent has been completely removed, there is a risk that cracks will occur in the sheet-like bonding material, which is a dried paste film.

[0008] In Patent Document 1, to reduce the risk of cracking and improve transferability, a flexible resin (rosin) that softens when heated must be added to the sheet-shaped bonding material. Transferring the material to the bonded material requires a heating process of 50°C or higher. Heating during transfer increases the cost of the transfer device. Furthermore, depending on the transfer temperature, metal nanoparticles may sinter during transfer, impairing their surface activity. This can impair the sintering of the metal nanoparticles and their atomic diffusion into the bonded material during subsequent bonding, resulting in unstable sinterability and atomic diffusion (bondability). Transferring under gentle transfer conditions that do not promote sintering of the metal nanoparticles can result in issues such as failure to transfer the sheet-shaped bonding material to the entire surface of the bonded material or leaving residue of the dried paste film (transfer-type sheet-shaped bonding material) on the resin substrate. Furthermore, when the metal nanoparticles are copper, transferring in a heated environment can pose a risk of copper oxidation depending on the atmosphere (e.g., 150°C in air). In the case of copper, the transfer atmosphere may require an inert atmosphere, such as N2.

[0009] Furthermore, the sheet-shaped bonding material of Patent Document 1 has the problem that it is difficult to ensure sufficient bonding strength during low-temperature bonding at a bonding temperature of 250° C. or less.

[0010] In view of the above problems, the present invention aims to provide a transfer-type sheet-like bonding material that (I) sufficiently suppresses cracking, (II) provides excellent transferability even under room temperature transfer conditions where sintering of copper particles does not progress, and (III) ensures sufficient bonding strength even at low-temperature bonding of 250°C or less. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors have conducted extensive research and have found that the above problems (I) to (III) can be solved by optimizing the solvent content of a transfer-type sheet-like bonding material, which is a paste-dried film formed by applying a paste containing copper particles, a reducing agent, and a solvent, and optionally further containing a resin, onto a resin substrate and drying the paste.

[0012] The gist and configuration of the present invention, which has been completed based on the above findings, is as follows. [1] A paste-dried film formed by applying a paste containing copper particles, a reducing agent, and a solvent onto a resin substrate and drying the paste. A transfer-type sheet-like bonding material having a solvent content of 5.0% by mass or more and 15.0% by mass or less.

[0013] [2] The transfer-type sheet-like bonding material according to [1] above, wherein the reducing agent is triethanolamine.

[0014] [3] The transfer sheet-like bonding material according to the above [1] or [2], wherein the content of the reducing agent is 3 parts by mass or more and 9 parts by mass or less per 100 parts by mass of copper particles.

[0015] [4] The transfer sheet-like bonding material according to any one of the above [1] to [3], wherein the copper particles have an average particle size of 70 nm or more and 300 nm or less.

[0016] [5] The transfer sheet-like bonding material according to any one of the above [1] to [4], wherein the paste further contains a resin.

[0017] [6] The transfer type sheet-like bonding material according to the above [5], wherein the resin is an acrylic resin.

[0018] [7] The transfer sheet-like bonding material according to the above [5] or [6], wherein the content of the resin is 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of copper particles. [Effects of the Invention]

[0019] The transfer-type sheet-like bonding material of the present invention (I) sufficiently suppresses cracking, (II) provides excellent transferability even under room temperature transfer conditions where sintering of copper particles does not progress, and (III) ensures sufficient bonding strength even at low-temperature bonding of 250°C or less. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Transfer-type sheet adhesive material] A transferable sheet-like bonding material according to one embodiment of the present invention is a paste-dried film formed by applying a paste containing copper particles, a reducing agent, and a solvent, and optionally further containing a resin, onto a resin substrate and drying it, and is characterized by having a solvent liquid content of 5.0 mass % or more and 15.0 mass % or less.

[0021] (copper particles) The copper particles are mainly composed of copper. The copper particles preferably contain 95% by mass or more and 100% by mass or less of copper element relative to 100% by mass of the copper particles, and more preferably 97% by mass or more. When the copper element is contained in an amount of 95% by mass or more, the bonding material has excellent heat resistance and further excellent bonding strength.

[0022] The average particle diameter of the copper particles is preferably 300 nm or less. By having an average particle diameter of 300 nm or less, a sufficiently high bonding strength can be ensured even at low-temperature bonding at 250°C or less. The average particle diameter of the copper particles is more preferably 150 nm or less. Furthermore, the average particle diameter of the copper particles is preferably 5 nm or more. When the average particle diameter of the copper particles is 5 nm or more, copper microparticles are easily available. The average particle diameter of the copper particles is more preferably 70 nm or more. When the average particle diameter of the copper particles is 70 nm or more, a sufficiently high bonding strength can be ensured even at low-temperature bonding at 250°C or less.

[0023] The shape (form) of the copper particles is not particularly limited. Examples of the shape of the copper particles include spherical (sphere), ellipsoid (ellipsoid), and plate-like shapes. Among these, spherical and ellipsoid shapes are preferred, and spherical shapes are more preferred.

[0024] The average particle size of copper particles can be determined by observing 10 fields of view at 10,000x magnification using a scanning electron microscope (SEM), measuring the particle size of each copper particle in the 10 fields of view for all copper particles selected according to the following selection criteria (1) to (5), and calculating the D50. For particles that are not perfectly round, such as ellipses, the major axis is used as the particle size. The particle size distribution of copper particles is also determined by the particle sizes of all copper particles measured as described above. When determining the average particle size and particle size distribution of copper particles in a sheet-like bonding material, the outermost surface of the sheet is observed. Before producing a sheet, the powder is placed on carbon tape with a spatula, excess powder is removed with an air duster, and the tape surface is observed. (1) Particles that are partly outside the field of view of the image will not be measured. (2) Particles that have clear outlines and exist in isolation are measured. (3) Even if a particle shape deviates from the average, it is measured if it is independent and can be measured as a single particle. (4) When particles overlap each other but the boundaries between them are clear and the overall shape of the particle can be determined, each particle is measured as a single particle. (5) Particles that overlap each other, have unclear boundaries, and whose overall shape cannot be determined are not measured as their shape cannot be determined.

[0025] It is preferable to use copper particles that do not require a protective agent, a dispersant, etc. Examples of such copper particles include ultrafine metal powder obtained by the manufacturing method described in Japanese Patent No. 4304221 and copper fine particles obtained by the manufacturing method described in Japanese Patent No. 6130616. However, the copper particles are not limited to these examples.

[0026] Preferably, at least a portion of the surface layer of the copper particles is a coating containing copper carbonate. By forming the surface layer of the copper particles with a coating containing copper carbonate, the sintering temperature of the copper particles can be kept lower than conventionally while increasing the bonding strength. The coating containing copper carbonate may further contain cuprous oxide.

[0027] It is preferable to use copper particles that are not coated with an organic protective film. If the copper particles are coated with an organic protective film, sintering of the copper particles will not proceed unless the organic protective film is decomposed. This requires a bonding temperature higher than the decomposition temperature of the organic protective film, and low-temperature bonding below 250°C may not be possible. In addition, the decomposition gas of the organic protective film may form voids in the bonding layer or cause cracks in the bonding layer, which may reduce reliability.

[0028] The ratio of mass oxygen concentration to the specific surface area of ​​copper particles was set to 0.1 mass% g / m to reduce reactivity with oxygen in the air and reduce the effects of reoxidation. 2 It is preferable that the content is 0.2 mass% g / m or more. 2 On the other hand, the ratio of the mass oxygen concentration to the specific surface area of ​​the copper particles is 1.2 mass% g / m from the viewpoint of making it easier to remove the oxide film during bonding and further increasing the bonding strength. 2 It is preferable that the concentration is 0.5 mass% g / m or less. 2 More preferably, it is:

[0029] The ratio of the mass carbon concentration to the specific surface area of ​​the copper particles was set to 0.3 mass% g / m to suppress the occurrence of voids and cracks and further increase the bonding strength. 2 It is preferable that the concentration is 0.1 mass% g / m or less. 2 More preferably, it is 0.05 mass% g / m or less. 2 The ratio of the mass carbon concentration to the specific surface area of ​​the copper particles is more preferably 0.008 mass% g / m or less. 2 It is preferable that this is equal to or greater than this.

[0030] The ratio of mass oxygen concentration to the specific surface area of ​​copper particles can be calculated from the measured specific surface area and mass oxygen concentration. The specific surface area can be measured using a nitrogen gas BET adsorption device (e.g., MACSORB HM-1201 manufactured by Mountec Co., Ltd.). The mass oxygen concentration can be measured using an oxygen / nitrogen analyzer (e.g., TC600 manufactured by LECO Corporation).

[0031] The ratio of mass carbon concentration to the specific surface area of ​​copper particles can be calculated from the measured specific surface area and mass carbon concentration. The specific surface area can be measured using a nitrogen gas BET adsorption device (e.g., MACSORB HM-1201 manufactured by Mountech Co., Ltd.). The mass carbon concentration can be measured using a carbon-sulfur analyzer (e.g., EMIA-920V manufactured by Horiba, Ltd.).

[0032] The "copper particle content" in the sheet-shaped bonding material is equivalent to the copper particle content in the paste, and can be determined, for example, by heating the sheet to about 1000°C in a nitrogen atmosphere and measuring the weight after heating.

[0033] (reducing agent) The reducing agent is a compound that reduces the oxide film that inevitably exists on the surface of copper particles during bonding. During bonding, the oxide film is removed by the reducing agent, allowing the copper particles (pure copper) to come into contact with each other, sintering to proceed, and diffusion bonding to proceed.

[0034] In this embodiment, the reducing agent is preferably triethanolamine, which is highly effective in removing oxide films, has a high boiling point, and is low volatile, so it is not easily removed during transfer, and has high stability over time, so it has excellent storage stability before bonding.

[0035] In this embodiment, the content of the reducing agent is preferably 3 parts by mass or more and 9 parts by mass or less per 100 parts by mass of copper particles. If the content of the reducing agent is 3 parts by mass or more, the amount of reducing agent is sufficient, and even at low-temperature bonding at 250°C or less, the amount of reducing agent is sufficient, and sufficiently high bonding strength can be ensured. Furthermore, if the content of the reducing agent is 9 parts by mass or less, the reducing agent is less likely to seep out during transfer and bonding, making it possible to achieve transfer and bonding in the same shape as the materials to be bonded. Furthermore, there is no increase in decomposition gas components, and voids and cracks are less likely to occur in the bonding layer.

[0036] 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.

[0037] (resin) In this embodiment, it is not essential that the paste contains a resin, but it is preferable that the paste contains a resin. The resin functions as an adhesive when transferring the transfer-type sheet-like bonding material to the first member. It is also preferable that the resin also functions as a dispersant for dispersing copper particles.

[0038] The resin is preferably a resin such as an acrylic resin or an aliphatic polycarbonate, which is a highly degradable binder. In particular, the resin is preferably an acrylic resin. This is because acrylic resin has an adhesive function and therefore has excellent transferability. Specifically, one or more selected from poly(alkyl methacrylate), poly(alkyl methacrylate), and methacrylic acid ester copolymers can be used.

[0039] In this embodiment, the resin content is preferably 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of copper particles. When the resin content is 1 part by mass or more, full-surface transfer is possible without uneven shading under gentle transfer conditions that do not cause sintering of the copper particles. Furthermore, when the resin content is 5 parts by mass or less, decomposable components and undecomposed substances in the binder do not form voids in the bonding layer, and adhesion to the bonded materials is not impaired, ensuring sufficient bonding strength at low temperatures of 250°C or less.

[0040] The resin content in the sheet-like bonding material is the same as the resin content in the paste.

[0041] (solvent) The solvent should preferably have a boiling point of about 200°C and low volatility. This is because if the solvent evaporates during paste application and the metal concentration changes, uneven thickness of the coating film will occur. Furthermore, if a resin is contained in the paste, the solvent must be able to dissolve the resin used. From these perspectives, for example, one or more solvents selected from the group consisting of terpene solvents such as terpineol, dihydroterpineol, dihydroterpinyl acetate, and dihydroterpinyl methyl ether; alcohols such as 1-propanol, 2-propanol, butanol, pentanol, hexanol, heptanol, and octanol; ketones such as acetone and methyl ethyl ketone; and aromatic solvents such as toluene can be used.

[0042] The solvent concentration (charged solvent concentration) C0 in the paste is preferably 5% by mass or more and 40% by mass or more. If the solvent concentration in the paste is 5% by mass or more, proper coating can be performed, and if the solvent concentration in the paste is 40% by mass or less, the coating film does not easily flow after the paste is applied, and the coating film can be easily adjusted.

[0043] (Solvent content of transfer type sheet bonding material) It is important that the transfer-type sheet-like bonding material of this embodiment has a solvent content of 5.0% by mass or more and 15.0% by mass or less. By setting the solvent content within an appropriate range, a flexible transfer-type sheet-like bonding material can be obtained, (I) cracking is sufficiently suppressed, (II) excellent transferability is obtained even under room-temperature transfer conditions where sintering of copper particles does not proceed, and (III) sufficient bonding strength can be ensured even at low temperatures of 250°C or less. If the solvent content is too low, cracks will occur in the paste dried film, and excellent transferability will not be obtained under room-temperature transfer conditions where sintering of copper particles does not proceed. Therefore, the solvent content is set to 5.0% by mass or more, preferably 7.5% by mass or more. On the other hand, if the solvent content is too high, the paste dried film will not be sufficiently peeled from the resin substrate during transfer, and excellent transferability will not be obtained. Therefore, the solvent content is set to 15.0% by mass or less, preferably 12.5% ​​by mass or less.

[0044] The solvent content of the transfer type sheet-like bonding material can be adjusted by controlling the drying conditions of the paste coating film applied to the resin substrate, specifically, the drying temperature and drying time.

[0045] The solvent content V of the transfer type sheet-like bonding material can be calculated by the following formulas (1) and (2). V = {W0 - (WB - WA)} / WA × 100 Equation (1) W0=WB×C0 / 100...Formula (2) where: W0: Theoretical weight of solvent present in the paste coating film WB: Weight of the paste coating film immediately after applying the paste to the resin substrate WA: Weight of dry paste film C0: Solvent concentration in the paste WB can be calculated by measuring the weight of the substrate including the paste coating film after coating and subtracting the weight of the substrate measured before coating from this weight. WA can be calculated by subtracting the weight of the substrate with the dried paste film removed from the weight of the substrate including the dried paste film.

[0046] (Storage of transfer-type sheet-type bonding material) To prevent the evaporation of the solvent remaining in the transfer-type sheet-like bonding material, it is preferable to store the sheet-like bonding material sandwiched between two resin substrates. That is, the sheet-like bonding material (dried paste film) formed on the resin substrate is stored with another resin substrate placed on top of it. When a release PET film is used as the resin substrate, the surface coated with the release agent should be in contact with the sheet-like bonding material. The storage temperature is preferably 10°C or higher. Furthermore, to prevent the oxidation of copper, it is even better to store the material together with an oxygen scavenger.

[0047] (sheet type) The bonding material of this embodiment is in the form of a sheet. The thickness of the bonding material is not particularly limited, and can be, for example, 10 μm or more and less than 1 mm.

[0048] Furthermore, the shape of the joining material (the shape when viewed in a plane from the thickness direction) is not particularly limited and can be appropriately selected depending on the shape of the joining surfaces of the joined members, etc., and examples include rectangular and circular shapes.

[0049] [Method of manufacturing transfer-type sheet-shaped bonding material] The transfer type sheet-like bonding material of this embodiment can be produced by applying a paste containing copper particles, a reducing agent, and a solvent, and optionally further containing a resin, onto a resin substrate and drying it.

[0050] The method for preparing the paste is not particularly limited. It can be prepared by mixing the components using a planetary mixer, a mortar, a mill, a stirrer, or other methods. The method for applying and drying the paste to a resin substrate is also not particularly limited. For example, the paste can be applied to a resin substrate using an applicator and the resulting paste-coated film can be dried in a hot air oven to obtain a dried paste film (transfer-type sheet-like bonding material). Drying conditions are appropriately adjusted so that the solvent content is 5.0% to 15.0% by mass. For example, the drying temperature (ambient temperature) can be selected from the range of 50°C to 90°C, and the drying time can be selected from the range of 5 minutes to 300 minutes. The solvent content depends not only on the drying temperature and drying time, but also on the drying rate. In other words, slow drying is desirable for adjusting the solvent content. Specifically, a drying rate of 0.1% / min to 0.5% / min, based on the weight before drying (100), facilitates adjustment of the solvent content. For example, slow drying can be achieved by drying in a semi-closed system (such as placing the coating film sample on a tray and covering it with a lid) so that the drying vapor does not easily escape.

[0051] The resin substrate is not particularly limited, and examples thereof include a release PET film, a silicone film, a fluororesin film, etc. The thickness of the resin substrate can be set to about 50 to 200 μm in consideration of release properties.

[0052] The joining of two members (a first member and a second member) using a transfer-type sheet-like joining material is carried out through the following two steps of transfer and joining.

[0053] (Transcript) First, the sheet-like bonding material is bonded to the first member, and then the resin substrate is peeled off. That is, the sheet-like bonding material is transferred to the first member. The conditions for transferring the transfer-type sheet-like bonding material formed on the resin substrate to the first member are not particularly limited, but in this embodiment, excellent transferability can be obtained even under gentle transfer conditions that do not promote sintering of the copper particles, such as a transfer temperature (ambient temperature) of room temperature (5°C to 35°C), a pressure of 10 MPa or less, and a transfer time of 1 minute or less. The transfer conditions can be a transfer temperature of room temperature (5°C to 35°C), a pressure of 1 MPa to 10 MPa, and a transfer time of 10 seconds to 1 minute. The atmosphere during transfer may be an inert atmosphere such as nitrogen (N2), or air.

[0054] (Joining) Next, the sheet-like bonding material transferred onto the first member is brought into contact with the second member, and the first member and the second member are bonded via the sheet-like bonding material under predetermined bonding conditions. The bonding conditions are not particularly limited, but in this embodiment, sufficient bonding strength can be ensured even at low temperatures of 250°C or less. The bonding conditions can be a bonding temperature (ambient temperature) of 200°C to 250°C, a pressure of 1 MPa to 40 MPa, and a transfer time of 1 minute to 60 minutes. The bonding atmosphere is preferably an inert atmosphere such as nitrogen (N2). [Example]

[0055] [Manufacturing transfer-type sheet-type bonding material] (Test Example No. 1) 40 g of Taiyo Nippon Sanso copper particles (particle diameter 110 nm; D10: 39 nm, D50: 112 nm, D90: 310 nm), 3.2 g of triethanolamine as a reducing agent, and 13.9 g of terpineol as a solvent were mixed in a planetary mixer to obtain a paste. The surface layer of the copper particles was a coating containing cuprous oxide, and the ratio of the mass oxygen concentration to the specific surface area of ​​the copper particles was 0.25 mass% g / m 2 The ratio of the mass carbon concentration to the specific surface area of ​​the copper particles is 0.03 mass% g / m 2 The solvent concentration in the paste (charged solvent concentration) C0 was set to 24.4 mass %.

[0056] Next, the prepared paste was applied to a 100 μm thick release PET film using an applicator to form a coating film with a thickness of 200 μm, and the coating film was dried in a hot air oven at a drying temperature of 70 °C for 15 minutes to remove part of the terpineol, thereby obtaining a paste dried film (transfer-type sheet-like bonding material). The composition of the obtained transfer-type sheet-like bonding material and the solvent liquid content of the transfer-type sheet-like bonding material measured by the above-mentioned method are shown in Table 1.

[0057] (Test Examples No. 2 to 19) The copper particle content was fixed at 40 g, but the type of copper particles and the content of the reducing agent were changed as shown in Table 1. An acrylic binder (Orikox KC-1700 or Orikox KC-500, manufactured by Kyoeisha Chemical Co., Ltd.) was added to the paste in the amount shown in Table 1, and a paste was obtained in the same manner as in Test Example No. 1. The solvent concentration (charged solvent concentration) C0 in the paste was set to the value shown in Table 1. Next, a dried paste film (transfer-type sheet-like bonding material) was obtained in the same manner as in Test Example No. 1 under the drying conditions shown in Table 1. The composition of the obtained transfer-type sheet-like bonding material and the solvent content of the transfer-type sheet-like bonding material measured by the method described above are shown in Table 1.

[0058] (Test Examples No. 20 and 21) The copper particle content was fixed at 40 g, and a paste was obtained in the same manner as in Test Example No. 1 with the composition shown in Table 1. The solvent concentration in the paste (charged solvent concentration) C0 was set to the value shown in Table 1. Next, the prepared paste was applied to a 100 μm-thick release PET film using an applicator to form a coating film with a thickness of 200 μm. The coating film sample was placed on a tray and covered to prevent the drying steam from escaping. The coating film was dried in a semi-closed hot air oven under the drying conditions shown in Table 1 to remove a portion of the terpineol, and a dried paste film (transfer-type sheet-like bonding material) was obtained. The composition of the obtained transfer-type sheet-like bonding material and the solvent content of the transfer-type sheet-like bonding material measured by the method described above are shown in Table 1.

[0059] [Evaluation of cracks in dried paste film] In each test example, the paste dried film (transfer-type sheet-like bonding material) was observed under a microscope at a magnification of 20x in 10 fields of view. The results are shown in the "Cracking resistance of paste dried film" column in Table 1, with the absence of cracks in all 10 fields of view being rated "excellent" and the presence of cracks in even one field of view being rated "poor." If cracks were found in the paste dried film, the shear strength of the bonded sample would vary after bonding, so subsequent transfer and bonding tests were not conducted.

[0060] [Evaluation of transferability] In each test example, an Au-plated SiC (5 mm square, 350 μm thick) was mounted on a transfer-type sheet bonding material, and the transfer-type sheet bonding material was transferred to the Au-plated surface of the SiC under the following transfer conditions: room temperature (25°C), pressure of 5 MPa, transfer time of 30 seconds, and transfer in an atmospheric atmosphere. The results are shown in the "Transferability" column in Table 1: "Excellent" indicates that the sheet bonding material was transferred evenly to the SiC without any unevenness across the entire surface; "Fair" indicates that the sheet bonding material was transferred to the SiC entirely but with some unevenness in shading; and "Poor" indicates that the sheet bonding material could not be transferred to the SiC entirely. Note that if the transferability was "Poor," subsequent bonding tests were not performed because the shear strength of the bonded sample varied after bonding.

[0061] [Evaluation of shear strength of joints] In each test example, the transfer-type sheet-like bonding material transferred onto the SiC was brought into contact with an oxygen-free copper plate C1020 (20 mm square, 2 mm thick), and the SiC and oxygen-free copper plate were bonded together using a pressure bonding device under the following conditions: bonding temperature: 250°C, pressure: 10 MPa, bonding time: 5 minutes, in a N2 atmosphere. The shear strength of the bonded parts was measured using a bond tester (Dage, 4000Plus) at a tool height of 100 μm and a tool speed of 200 μm / s, and the results are shown in Table 1. A shear strength of 50 MPa or more is considered good.

[0062] [Evaluation of bleeding from the bonding layer after bonding] In each test example, the outer periphery of the SiC in the bonded product was observed at 20x magnification using a microscope (L-KIT504, manufactured by Hozan Co., Ltd.) to check for the presence or absence of liquid seepage around the outer periphery of the SiC. The results are shown in Table 1.

[0063] [Table 1]

[0064] *1 110nm products (D10; 39nm, D50; 112nm, D90; 310nm) 50nm products (D10; 15nm, D50; 51nm, D90; 194nm) 70nm products (D10; 24nm, D50; 72nm, D90; 284nm) 300nm products (D10; 52nm, D50; 298nm, D90; 652nm) 400nm products (D10; 66nm, D50; 403nm, D90; 811nm) *2: Reducing agent content (parts by mass) per 100 parts by mass of copper particles *3: Acrylic resin content (parts by mass) in the acrylic binder per 100 parts by mass of copper particles

[0065] As is clear from Table 1, in Comparative Example No. 2, in which the solvent content of the transfer-type sheet-like bonding material was less than 5.0 mass%, cracks were observed in the dried paste film, and excellent transferability was not obtained under room temperature transfer conditions. In Comparative Example No. 7, in which the solvent content of the transfer-type sheet-like bonding material was more than 15.0 mass%, excellent transferability was not obtained under room temperature transfer conditions. In contrast, in the inventive examples in which the solvent content of the transfer-type sheet-like bonding material was in the range of 5.0 mass% to 15.0 mass%, no cracks occurred in the dried paste film, excellent transferability was obtained even under room temperature transfer conditions, and sufficient bonding strength was ensured even at a low temperature of 250 ° C. In particular, in some of the inventive examples in which the acrylic binder content, reducing agent content, and average particle size of the copper particles were optimized, high shear strength of 50 MPa or more was obtained. [Industrial Applicability]

[0066] The transfer type sheet-like bonding material of the present invention can be industrially used for bonding electronic components. Specifically, it can be used to bond components such as substrates and elements in high-temperature environments where it is difficult to use bonding materials such as solder, such as in electronic devices called power devices.

Claims

1. A paste dried film formed by applying a paste containing copper particles, a reducing agent, and a solvent onto a resin substrate and drying the paste. A transfer-type sheet-like bonding material having a solvent content of 5.0% by mass or more and 15.0% by mass or less.

2. 2. The transfer-type sheet-like bonding material according to claim 1, wherein the reducing agent comprises triethanolamine.

3. The transfer sheet-like bonding 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 per 100 parts by mass of the copper particles.

4. The transfer type sheet-like bonding material according to claim 1 or 2, wherein the copper particles have an average particle diameter of 70 nm or more and 300 nm or less.

5. The transfer type sheet-like bonding material according to claim 1 or 2, wherein the paste further contains a resin.

6. The transfer type sheet-like bonding material according to claim 5 , wherein the resin is an acrylic resin.

7. The transfer sheet-like bonding material according to claim 5 , wherein the content of the resin is 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of copper particles.

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