Transfer-type sheet-like bonding 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] Traditionally, solder materials have been widely used as bonding materials for electronic components. However, solder materials have the problem of poor heat resistance. Therefore, for example, it was difficult to use solder materials as bonding materials in power devices using SiC elements that are expected to be used at high temperatures of 150°C or higher.

[0003] Therefore, a sintered bonding material using silver particles has been proposed. Furthermore, copper particles are promising from the perspective of cost and ion migration, and development of transfer-type sheet bonding materials 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 it. The 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 together via the sheet-like bonding material under predetermined bonding conditions.

[0005] Patent Document 1 describes d of about 0.001 to about 10 μm 50 The invention describes a sheet-like bonding material obtained by forming a paste containing a range of metal powders, a rosin binder, and a solvent on a substrate, and then removing and drying all of the solvent. Patent Document 1 describes transferring the sheet-like bonding material to the material to be bonded by placing the material to be bonded on this 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. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-62715 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in the sheet-like bonding material described in Patent Document 1, since all solvents are removed, there is a risk of cracking occurring in the sheet-like bonding material, which is a paste-dried film.

[0008] Patent Document 1 states that in order to reduce the risk of cracking and impart transferability, it is necessary to add a flexible resin (rosin) that softens when heated to the sheet-like bonding material, and a heating process of 50°C or higher is essential for transfer to the material to be bonded. Heating during transfer leads to increased costs for the transfer equipment. In addition, depending on the transfer temperature, metal nanoparticles may sinter during transfer, impairing the surface activity of the metal nanoparticles, which may impair the sintering of metal nanoparticles and atomic diffusion into the material to be bonded during subsequent bonding, resulting in unstable sinterability and atomic diffusion (bonding ability). If transfer is performed under slow transfer conditions where sintering of metal nanoparticles does not progress, problems arise such as the inability to transfer the sheet-like bonding material to the entire surface of the material to be bonded, or the remaining residue of the paste-dried film (transfer-type sheet-like bonding material) on the resin substrate. Furthermore, when the metal nanoparticles are copper, transfer in a heated environment carries the risk of copper oxidation depending on the atmosphere (for example, 150°C in air), and in the case of copper, it was sometimes necessary to use an inert atmosphere, such as an N2 atmosphere, during transfer.

[0009] Furthermore, the sheet-like bonding material described in Patent Document 1 has the problem of being difficult to ensure sufficient bonding strength when bonding at low temperatures of 250°C or below.

[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 in which sintering of copper particles does not progress, and (III) ensures sufficient bonding strength even when bonding at low temperatures of 250°C or below. [Means for solving the problem]

[0011] In order to solve the above problems, the inventors of the present invention conducted diligent research and found that, in a transfer-type sheet-like bonding material which is a paste-dried film obtained 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, the above problems (I) to (III) can be solved by optimizing the solvent content of the transfer-type sheet-like bonding material.

[0012] Based on the above findings, the gist of the present invention is as follows. [1] A paste-dried film obtained by coating a paste containing copper particles, a reducing agent, and a solvent onto a resin substrate and drying it. A transfer-type sheet-like bonding material characterized by 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-type sheet-like bonding material according to [1] or [2] above, 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] A transfer-type sheet-like bonding material according to any one of the above [1] to [3], wherein the average particle diameter of the copper particles is 70 nm or more and 300 nm or less.

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

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

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

[0019] The transfer-type sheet-like bonding material of the present invention has (I) sufficiently suppressed cracking, (II) excellent transferability even under normal-temperature transfer conditions where sintering of copper particles does not progress, and (III) sufficient bonding strength can be ensured even in low-temperature bonding at 250°C or lower. [Embodiments for Carrying Out the Invention]

[0020] [Transfer-Type Sheet-Like Bonding Material] The transfer-type sheet-like bonding material according to one embodiment of the present invention is a paste dry film obtained by applying and drying a paste containing copper particles, a reducing agent, and a solvent, and optionally further containing a resin, on a resin substrate, and having a solvent content rate of 5.0% by mass or more and 15.0% by mass or less.

[0021] (Copper Particles) The copper particles are mainly composed of copper. It is preferable that the copper particles contain 95% by mass or more and 100% by mass or less of copper element with respect to 100% by mass of the copper particles, and more preferably 97% by mass or more. When the copper element is contained at 95% by mass or more, the heat resistance of the bonding material is excellent and the bonding strength is further excellent.

[0022] The average particle diameter of the copper particles is preferably 300 nm or less. A minimum average particle diameter of 300 nm ensures sufficiently high bonding strength even at low temperatures below 250°C. A minimum average particle diameter of 150 nm is more preferable. Furthermore, a minimum average particle diameter of 5 nm is preferable. A minimum average particle diameter of 5 nm makes it easier to obtain copper nanoparticles. A minimum average particle diameter of 70 nm is more preferable. A minimum average particle diameter of 70 nm ensures sufficiently high bonding strength even at low temperatures below 250°C.

[0023] The shape (morphology) of the copper particles is not particularly limited. Examples of copper particle shapes include spherical, elliptical, and plate-like shapes, with spherical and elliptical shapes being preferred, and spherical shapes being more preferred.

[0024] The average particle size of copper particles can be determined by observing 10 fields of view at a magnification of 10,000x using a scanning electron microscope (SEM), measuring the particle size of each copper particle selected according to the following selection criteria (1) to (5) in each of the 10 fields of view, and determining its 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 the 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. In the powder state before sheet fabrication, the powder is placed on a carbon tape with a spatula, excess powder is removed with an air duster, and the tape surface is observed. (1) Particles whose portion extends outside the field of view of the image will not be measured. (2) Particles with clear outlines that exist in isolation should be measured. (3) Even if a particle deviates from the average particle shape, if it is independent and can be measured as a single particle, it will be measured. (4) If there is overlap between particles, but the boundary between them is clear and the overall shape of the particles can be determined, each particle will be measured as a single particle. (5) Particles that overlap and whose boundaries are unclear, and whose overall shape cannot be determined, will not be measured as their shape cannot be determined.

[0025] It is preferable to use copper particles that do not require protective agents, dispersants, 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, the copper particles have a coating containing copper carbonate on at least a portion of their surface. Having a copper carbonate coating on the surface of the copper particles allows for increased bonding strength while keeping the sintering temperature of the copper particles lower than in conventional methods. The copper carbonate coating 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, the sintering of the copper particles will not proceed unless the organic protective film is decomposed, requiring a bonding temperature higher than the decomposition temperature of the organic protective film, which may prevent low-temperature bonding below 250°C. In addition, the decomposition gases of the organic protective film may form voids in the bonding layer or cause cracks in the bonding layer, posing a risk of reduced reliability.

[0028] The ratio of mass oxygen concentration to specific surface area of ​​copper particles is set to 0.1 mass%·g / m², from the viewpoint of reducing reactivity with oxygen in the air and minimizing the effects of re-oxidation. 2 Preferably, it is 0.2% by mass·g / m³ 2 The above is more preferable. On the other hand, the ratio of mass oxygen concentration to the specific surface area of ​​copper particles should be 1.2 mass%·g / m² from the viewpoint of making it easier to remove the oxide film during bonding and further increasing the bonding strength. 2 Preferably, it is 0.5% by mass·g / m³ 2 The following is more preferable:

[0029] The ratio of the mass carbon concentration to the specific surface area of the copper particles is preferably 0.3 mass%·g / m 2 or less from the viewpoint of suppressing the generation of voids and cracks and further increasing the bonding strength, more preferably 0.1 mass%·g / m 2 or less, and even more preferably 0.05 mass%·g / m 2 or less. The ratio of the mass carbon concentration to the specific surface area of the copper particles is preferably 0.008 mass%·g / m 2 or more.

[0030] The ratio of the mass oxygen concentration to the specific surface area of the copper particles can be calculated from the measured specific surface area and the mass oxygen concentration. The specific surface area can be measured using a BET adsorption apparatus for nitrogen gas (for example, "MACSORB HM-1201" manufactured by Mountech Co., Ltd.). The mass oxygen concentration can be measured using an oxygen-nitrogen analyzer (for example, "TC600" manufactured by LECO).

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

[0032] The "content of copper particles" in the sheet-like bonding material is equivalent to the content of copper particles in the paste, and can be grasped from the weight after heating, for example, by heating the sheet to about 1000°C in a nitrogen atmosphere.

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

[0034] In this embodiment, the reducing agent is preferably triethanolamine. Triethanolamine has a high oxide film removal effect, a high boiling point and low volatility, so it does not easily escape during transfer and has high stability over time, resulting in excellent storage stability before bonding.

[0035] In this embodiment, the reducing agent content 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 reducing agent content is 3 parts by mass or more, the amount of reducing agent is sufficient, and even at low-temperature bonding of 250°C or below, sufficient sintering of copper particles can be achieved, ensuring sufficiently high bonding strength. Furthermore, if the reducing agent content is 9 parts by mass or less, leakage of the reducing agent is less likely to occur during transfer and bonding, enabling transfer and bonding with the same shape as the material to be bonded. In addition, the decomposition gas components do not increase, and voids and cracks are less likely to occur in the bonded layer.

[0036] Furthermore, the reducing agent content in the sheet-type bonding material is equivalent to the reducing agent content in the paste.

[0037] (resin) In this embodiment, it is not essential for the paste to contain resin, but it is preferable that the paste contains 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 functions as a dispersant for dispersing copper particles.

[0038] The resin is preferably a highly biodegradable binder such as acrylic resin or aliphatic polycarbonate. In particular, it is preferable that the resin be acrylic resin. This is because acrylic resin has adhesive properties and therefore excellent transferability. Specifically, one or more selected from polyalkyl methacrylate, polyalkyl methacrylate, and methacrylic 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. If the resin content is 1 part by mass or more, full-surface transfer is possible without unevenness in density under gentle transfer conditions where the sintering of the copper particles does not progress. Furthermore, if the resin content is 5 parts by mass or less, degradable components and undegraded substances in the binder do not form voids in the bonded layer, and adhesion to the materials to be bonded is not impaired, so sufficient bonding strength can be ensured even at low temperatures of 250°C or below.

[0040] Furthermore, the resin content in the sheet-like bonding material is equivalent to the resin content in the paste.

[0041] (solvent) The solvent should preferably have a boiling point of around 200°C and low volatility. This is because if the solvent evaporates during paste application and the metal concentration changes, uneven thickness of the coated film will occur. Furthermore, if the paste contains a resin, the solvent must be able to dissolve the resin used. From these viewpoints, 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 (initial 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 is less likely to run after paste application, making it easy to adjust the coating film.

[0043] (Solvent content of transfer-type sheet-like bonding material) In this embodiment, it is important that the transfer-type sheet-like bonding material 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, which (I) sufficiently suppresses cracking, (II) provides excellent transferability even under room temperature transfer conditions where copper particle sintering does not progress, and (III) ensures sufficient bonding strength even at low temperatures of 250°C or below. If the solvent content is too low, cracking will occur in the paste-dried film, and excellent transferability cannot be obtained under room temperature transfer conditions where copper particle sintering does not progress. Therefore, the solvent content should be 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 cannot be sufficiently peeled from the resin substrate during transfer, and excellent transferability cannot be obtained. Therefore, the solvent content should be 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 applied to the resin substrate, specifically the drying temperature and drying time.

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

[0046] (Storage of transfer-type sheet-like bonding materials) To suppress the evaporation of 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 (paste-dried film) formed on the resin substrate is stored with another resin substrate placed on top. When using a release PET film as the resin substrate, the side coated with the release agent should be in contact with the sheet-like bonding material. The storage temperature should preferably be 10°C or higher. Furthermore, it is even better to store it together with an oxygen absorber to suppress copper oxidation.

[0047] (Sheet form) The bonding material in this embodiment is in the form of a sheet. 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.

[0048] Furthermore, the shape of the joining material (the shape when viewed from a plan perspective in the thickness direction) is not particularly limited and can be appropriately selected according to the shape of the joining surface of the members to be joined, for example, rectangular or circular shapes.

[0049] [Method for manufacturing transfer-type sheet-like bonding material] The transfer-type sheet-like bonding material of this embodiment can be manufactured 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 each component using methods such as a rotary mixer, mortar and pestle, mill stirring, or stirrer stirring. The method for applying and drying the paste on the resin substrate is also not particularly limited; for example, a paste-dried film (transfer-type sheet-like bonding material) can be obtained by applying the paste to the resin substrate using an applicator and drying the paste-coated film in a hot air oven. The drying conditions should be adjusted as appropriate so that the solvent liquid content is between 5.0% by mass and 15.0% by mass. For example, the drying temperature (ambient temperature) can be selected from a range of 50°C to 90°C, and the drying time can be selected from a range of 5 minutes to 300 minutes. Furthermore, the solvent liquid content does not depend only on the above drying temperature and drying time, but also on the drying rate, etc. That is, when adjusting the solvent liquid content, it is desirable to allow drying to proceed slowly. Specifically, if the drying rate is between 0.1% / min and 0.5% / min, with the weight before drying as 100, it is easier to adjust the solvent liquid content. For example, drying can be done slowly by using a semi-sealed system (such as placing the coating sample on a tray and covering it) to prevent drying steam from escaping.

[0051] The resin substrate is not particularly limited and can be, for example, release PET film, silicon film, fluororesin film, etc. The thickness of the resin substrate can be about 50 to 200 μm, taking into consideration release properties.

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

[0053] (Transcription) 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 in which sintering of copper particles does not progress, 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 set to 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 it may be 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 and second members are joined 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 with low-temperature bonding below 250°C. The bonding conditions can be set as follows: bonding temperature (ambient temperature) between 200°C and 250°C, applied pressure between 1 MPa and 40 MPa, and transfer time between 1 minute and 60 minutes. It is preferable to use an inert atmosphere such as nitrogen (N2) during bonding. [Examples]

[0055] [Manufacturing of transfer-type sheet-like bonding materials] (Test Example No. 1) A paste was obtained by mixing 40g of copper particles manufactured by Taiyo Nippon Sanso (particle size 110nm; D10; 39nm, D50; 112nm, D90; 310nm), 3.2g of triethanolamine as a reducing agent, and 13.9g of terpineol as a solvent using a self-rotating mixer. The surface layer of the copper particles was a coating containing cuprous oxide, and the ratio of mass oxygen concentration to the specific surface area of ​​the copper particles was 0.25 mass%·g / m². 2 The ratio of mass carbon concentration to the specific surface area of ​​copper particles is 0.03 mass%·g / m². 2 The solvent concentration (initial solvent concentration) C0 in the paste was set to 24.4% by mass.

[0056] Next, the prepared paste was applied to a 100 μm thick release PET film using an applicator to create a 200 μm thick coating. The coating was then dried in a hot air oven at a drying temperature of 70°C for 15 minutes to remove some of the terpineol, thereby obtaining a paste-dried film (transfer-type sheet-like bonding material). Table 1 shows 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.

[0057] (Example Tests No. 2-19) The copper particle content was kept fixed at 40g, and the type of copper particles and the content of the reducing agent were changed to those shown in Table 1. Acrylic binder (manufactured by Kyoeisha Chemical Co., Ltd., Oricox KC-1700 or Oricox KC-500) was added to the paste in the amounts shown in Table 1, and a paste was obtained in the same manner as in Test Example No. 1. The solvent concentration (starting solvent concentration) C0 in the paste was set to the value shown in Table 1. Next, a paste-dried 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, 21) The copper particle content was kept fixed at 40g, 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 (starting solvent concentration) C0 in the paste was set to the value shown in Table 1. Next, the prepared paste was applied to a 100μm thick release PET film using an applicator to create a 200μm thick coating film. The coating film sample was placed on a tray to prevent drying vapors from escaping, and the lid was closed to dry the coating film in a semi-sealed hot air oven under the drying conditions shown in Table 1, thereby removing some of the terpineol and 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 content of the transfer-type sheet-like bonding material measured by the method described above are shown in Table 1.

[0059] [Evaluation of cracking in paste-dried films] In each test example, the paste-dried film (transfer-type sheet-like bonding material) was observed under a microscope at 20x magnification for 10 fields of view. A score of "Excellent" was given if no cracks were observed in any of the 10 fields of view, while a score of "Poor" was given if cracks were observed in even one field of view. These scores are shown in the "Paste-Dried Film Cracking Resistance" column of Table 1. Note that if cracks occurred in the paste-dried film, the shear strength of the bonded sample after bonding would vary, and therefore, subsequent transfer and bonding tests were not performed.

[0060] [Evaluation of transcriptional properties] In each test example, a SiC (5mm square, 350μm thick) with Au plating was mounted on a transfer-type sheet-like bonding material. The transfer-type sheet-like bonding material was transferred to the Au-plated surface of the SiC under the following conditions: transfer temperature at room temperature (25°C), pressure of 5MPa, transfer time of 30 seconds, and in an atmospheric environment. "Excellent" was rated when the sheet-like bonding material was transferred uniformly and without unevenness across the entire surface of the SiC; "Acceptable" was rated when the entire surface of the SiC was transferred but with some unevenness in density; and "Poor" was rated when the entire surface of the SiC could not be transferred. These ratings are shown in the "Transferability" column of Table 1. In cases where the transferability was "Poor," variations in the shear strength of the bonded sample after bonding occurred, so no further bonding tests were performed.

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

[0062] [Evaluation of seepage in the bonded 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 (HOZAN Corporation, L-KIT504) to check for the presence or absence of liquid seepage around the outer periphery of the SiC, as 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 in the acrylic binder per 100 parts by mass of copper particles (parts by mass)

[0065] As is clear from Table 1, in Comparative Example No. 2, where the solvent content of the transfer-type sheet-like bonding material was less than 5.0% by mass, cracks were observed in the paste-dried film, and excellent transferability could not be obtained under room temperature transfer conditions. Similarly, in Comparative Example No. 7, where the solvent content of the transfer-type sheet-like bonding material exceeded 15.0% by mass, excellent transferability could not be obtained under room temperature transfer conditions. In contrast, in the inventive examples where the solvent content of the transfer-type sheet-like bonding material was within the range of 5.0% by mass to 15.0% by mass, no cracks occurred in the paste-dried film, excellent transferability was obtained even under room temperature transfer conditions, and sufficient bonding strength was secured even with low-temperature bonding at 250°C. In particular, in some inventive examples where the acrylic binder content, reducing agent content, and average particle size of 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 is industrially applicable for bonding electronic components. Specifically, examples of its use include bonding components such as substrates and elements in high-temperature environments where the use of bonding materials such as solder is difficult, such as within electronic devices called power devices.

Claims

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

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

3. The transfer-type 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 copper particles.

4. The transfer-type sheet-like bonding material according to claim 1 or 2, wherein the average particle diameter of the copper particles is 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 comprises a resin.

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

7. The transfer-type 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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