Transfer-type sheet-like bonding material

Abstract

To provide a transfer type sheet-like joint material which (I) can obtain excellent transferability even under a moderate transfer condition that does not progress sintering of copper particles, and (II) can stably 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, a resin and a solvent onto a resin substrate, and has a solvent-containing ratio of 0.5 mass% or more and 2.0 mass% or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

[0003] Therefore, as a sintered bonding material, a bonding material using silver particles has been proposed. Also, copper particles are expected from the viewpoints of cost and ion migration, and the development of a transfer-type sheet-like bonding material using copper particles has been underway.

[0004] A 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) by the transfer-type sheet-like bonding material is performed as follows. First, after transferring the sheet-like bonding material to the first member under predetermined transfer conditions, 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 through the sheet-like bonding material under predetermined bonding conditions.

[0005] Patent Document 1 describes a sheet-like bonding material obtained by applying a paste containing copper particles (D10; 100 nm or more, D90; 2000 nm or less) whose surface is coated with triethanolamine as a capping agent, a dicarboxylic acid as an activator, a dispersant, an epoxy methacrylate urethane as a binder, and terpineol as an organic solvent onto a PET film and drying it. In Patent Document 1, it is described that this sheet-like bonding material can be transferred to an Au-plated silicon die under transfer conditions of a transfer temperature of 200 to 225°C, a pressure of 5 MPa, and a transfer time of 1 to 10 seconds. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2021-529258 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in Patent Document 1, since the transfer temperature is 200°C or higher, the copper sintersects during transfer, impairing the surface activity of the copper particles. This can impair the subsequent sintering of copper and atomic diffusion into the material to be bonded, leading to problems such as unstable sinterability and atomic diffusion (bonding properties). If the transfer is performed under slow transfer conditions where the sintering of copper particles 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 transferred, or the remaining residue of the paste-dried film (transfer-type sheet-like bonding material) on the resin substrate.

[0008] Furthermore, the sheet-like bonding material described in Patent Document 1 has the problem of difficulty in stably ensuring sufficient bonding strength when bonding at low temperatures of 250°C or below. In other words, it has been found that the sheet-like bonding material described in Patent Document 1 may result in variations in the shear strength of the bonded sample after bonding. Variations in shear strength can lead to variations in power module performance, which poses a practical problem.

[0009] In view of the above problems, the present invention aims to provide a transfer-type sheet-like bonding material that (I) can obtain excellent transferability even under slow transfer conditions in which sintering of copper particles does not proceed, and (II) can stably ensure sufficient bonding strength even when bonding at low temperatures of 250°C or below. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors diligently conducted research and found that, in a transfer-type sheet-like bonding material which is a paste-dried film obtained by applying and drying a paste containing copper particles, a reducing agent, a resin, and a solvent onto a resin substrate, the above problems (I) and (II) can be solved by optimizing the solvent content of the transfer-type sheet-like bonding material.

[0011] 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, a resin, and a solvent onto a resin substrate and drying it. A transfer-type sheet-like bonding material characterized by having a solvent content of 0.5% by mass or more and 2.0% by mass or less.

[0012] [2] The transfer-type sheet-like bonding material according to [1] above, wherein the reducing agent is triethanolamine.

[0013] [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.

[0014] [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.

[0015] [5] A transfer-type sheet-like bonding material according to any one of the above [1] to [4], wherein the resin is made of acrylic resin.

[0016] [6] The transfer-type sheet-like bonding material according to any one of the above [1] to [5], wherein the resin content is 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of copper particles.

[0017] [7] The copper particles are a coating in which at least a portion of the surface layer contains cuprous oxide and copper carbonate, the carbon concentration is 0.03% by mass or more and 0.30% by mass or less, and the oxygen concentration is 0.5% by mass or more and 3.0% by mass or less, as described in any one of the above [1] to [6]. [Effects of the Invention]

[0018] The transfer-type sheet-like bonding material of the present invention (I) provides excellent transferability even under slow transfer conditions in which copper particle sintering does not progress, and (II) can stably ensure sufficient bonding strength even when bonding at low temperatures of 250°C or below. [Modes for carrying out the invention]

[0019] [Transfer-type sheet-like bonding material] A transfer-type sheet-like bonding material according to one embodiment of the present invention is a paste-dried film obtained by applying and drying a paste containing copper particles, a reducing agent, a resin, and a solvent onto a resin substrate, characterized in that it has a solvent content of 0.5% by mass or more and 2.0% by mass or less.

[0020] (Copper particles) Copper particles are mainly composed of copper. Preferably, the copper particles contain 95% to 100% by mass of copper element per 100% by mass of copper particles, and more preferably 97% or more by mass. Containing 95% or more by mass of copper element results in superior heat resistance and even better bonding strength of the bonding material.

[0021] 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.

[0022] The shape (form) of the copper particles is not particularly limited. Examples of the shape of the copper particles include spherical (spheres), elliptical (ellipsoids), plate-like, etc. Among these, spherical and elliptical shapes are preferred, and a spherical shape is more preferred.

[0023] The average particle diameter of the copper particles can be determined by observing 10 fields at a magnification of 10,000 times using a scanning electron microscope (SEM), measuring the particle diameter of all the copper particles selected according to the following selection criteria (1) to (5) in the 10 fields, and obtaining the D50 thereof. For particles that are not perfect circles such as ellipses, the major axis is taken as the particle diameter. The particle size distribution of the copper particles is also specified by the particle diameters of all the copper particles measured above. Here, when determining the average particle diameter and particle size distribution of the copper particles in the sheet-like bonding material, the outermost surface of the sheet is observed. In the powder state before sheet production, 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 with a part protruding outside the field of view of the image are not measured. (2) Particles with a clear contour and existing independently are measured. (3) Even if it deviates from the average particle shape, particles that are independent and can be measured as single particles are measured. (4) Particles that overlap each other but have a clear boundary between the two and whose overall shape can be judged are measured as single particles respectively. (5) Overlapping particles with an unclear boundary and an undetermined overall shape of the particles are not measured as those whose particle shape cannot be judged.

[0024] As the copper particles, it is preferable to use those that do not require a protective agent, a dispersant, etc. Examples of such copper particles include metal ultrafine powders obtained by the production method described in Japanese Patent No. 4304221 and copper fine particles obtained by the production method described in Japanese Patent No. 6130616. However, the copper particles are not limited to this exemplification.

[0025] 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.

[0026] 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.

[0027] The carbon concentration of the copper particles is preferably 0.03% by mass or more and 0.30% by mass or less. If the carbon concentration of the copper particles is 0.03% by mass or more, the dispersibility of the copper particles in organic solvents is ensured, and aggregates of the copper particles are less likely to form, so sufficient bonding strength can be stably ensured even at low temperatures of 250°C or below. If the carbon concentration of the copper particles is 0.30% by mass or less, the sintering of the copper particles is not inhibited by the carbon contained in the surface layer of the copper particles, so sufficient bonding strength can be stably ensured even at low temperatures of 250°C or below. The carbon concentration of the copper particles can be measured using a carbon-sulfur analyzer (for example, "EMIA-920V" manufactured by Horiba, Ltd.).

[0028] The oxygen concentration of the copper particles is preferably 0.5% by mass or more and 3.0% by mass or less. If the oxygen concentration of the copper particles is 0.5% by mass or more, the reactivity with oxygen in the air is suppressed, so sufficient bonding strength can be stably ensured even at low temperatures of 250°C or below. If the oxygen concentration of the copper particles is 3.0% by mass or less, the oxide film is easier to remove during bonding and sintering is less likely to be inhibited, so sufficient bonding strength can be stably ensured even at low temperatures of 250°C or below. The oxygen concentration of the copper particles can be measured using an oxygen-nitrogen analyzer (for example, LECO's "TC600").

[0029] The "copper particle content" in sheet-like bonding materials is equivalent to the copper particle content in pastes, and can be determined, for example, by heating the sheet to about 1000°C under a nitrogen atmosphere and measuring its weight after heating.

[0030] (Reducing agent) A reducing agent is a compound that reduces the oxide film that inevitably exists on the surface of copper particles during bonding. During bonding, the removal of the oxide film by the reducing agent causes the copper particles (pure copper) to come into contact with each other, promoting sintering and diffusion bonding.

[0031] 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.

[0032] 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, and sufficiently high bonding strength can be stably secured. 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, 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 and cracks are less likely to occur in the bonded layer.

[0033] Furthermore, the reducing agent content in the sheet-type bonding material is equivalent to the reducing agent content in the paste.

[0034] (resin) The resin functions as an adhesive when transferring the transfer-type sheet-like bonding material to the first component. It would also be beneficial if it also functioned as a dispersant to disperse copper particles.

[0035] 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.

[0036] 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, and more preferably 1.5 parts by mass or more. 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 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 bonding layer, and adhesion to the materials to be bonded is not impaired, so sufficient bonding strength can be stably ensured even at low temperatures of 250°C or below.

[0037] Furthermore, the resin content in the sheet-like bonding material is equivalent to the resin content in the paste.

[0038] (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.

[0039] 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.

[0040] (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 0.5% by mass or more and 2.0% by mass or less. By setting the solvent content within an appropriate range, (I) excellent transferability can be obtained even under slow transfer conditions in which copper particle sintering does not progress, and (II) sufficient bonding strength can be stably ensured even at low temperatures of 250°C or below. If the solvent content is too low, cracks will occur in the paste-dried film, and excellent transferability cannot be obtained under slow transfer conditions in which copper particle sintering does not progress. Therefore, the solvent content should be 0.5% by mass or more. On the other hand, if the solvent content is too high, transfer can be performed well, but the solvent remaining in the sheet-like bonding material will cause voids and cracks in the bonding layer, making it impossible to stably ensure sufficient bonding strength at low temperatures of 250°C or below. Therefore, the solvent content should be 2.0% by mass or less, preferably 1.7% by mass or less, and more preferably 1.5% by mass or less.

[0041] 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.

[0042] 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.

[0043] (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.

[0044] Furthermore, the shape of the joining material (the shape when viewed from a planar 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.

[0045] [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, a resin, and a solvent onto a resin substrate and drying it.

[0046] The method for preparing the paste is not particularly limited; it can be prepared by mixing each component using methods such as a self-rotating 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 content is between 0.5% by mass and 2.0% 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 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 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 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.

[0047] 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 the release properties.

[0048] 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.

[0049] (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 where the sintering of copper particles does not progress, such as a transfer temperature (ambient temperature) of 150°C or less, a pressure of 10 MPa or less, and a transfer time of 1 minute or less. The transfer conditions can be within the range of a transfer temperature of 50°C to 150°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.

[0050] (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 stably 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]

[0051] [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, 0.8g of acrylic binder (Oricox KC-1700, manufactured by Kyoeisha Chemical Co., Ltd.), and 13.14g of terpineol as a solvent in a self-rotating mixer. The surface layer of the copper particles was a coating containing cuprous oxide and copper carbonate, the carbon concentration of the copper particles was 0.17 mass%, and the oxygen concentration of the copper particles was 1.6 mass%. The solvent concentration (initial solvent concentration) C0 in the paste was 23.0 mass%.

[0052] 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 80°C for 240 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.

[0053] (Example Tests No. 2-29) The copper particle content was kept fixed at 40g, and the specifications of the copper particles (particle size, carbon concentration, and oxygen concentration), the reducing agent content, the type and content of the resin, and the type of solvent were changed to those shown in Table 1. 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.

[0054] [Evaluation of transcriptional properties] In each test example, a SiC (5 mm square, 350 μm 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 of 150°C, pressure of 10 MPa, transfer time of 30 seconds, and in an atmospheric environment. The transfer performance was rated as "Excellent" if the sheet-like bonding material was transferred uniformly and without unevenness across the entire surface of the SiC, "Acceptable" if the entire surface was transferred to the SiC but there were some areas of unevenness in density, and "Poor" if the entire surface could not be transferred to the SiC. These ratings are shown in the "Transferability" column of Table 2. In cases where the transferability was "Poor," there was a significant variation in the shear strength of the bonded sample after bonding, so no further bonding tests were conducted.

[0055] [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. Five bonded products were manufactured for each test example, and the results of the shear strength measurements are shown in Table 2.

[0056] Table 2 shows the average shear strength of the five jointed products in each test example. An average of 70 MPa or higher is classified as "Excellent," 50 MPa or higher but less than 70 MPa as "Acceptable," and less than 50 MPa as "Poor," as indicated in the "Shear Strength Judgment" column of Table 2.

[0057] For each test example, the average value of {(maximum shear strength - minimum shear strength) × 100} / shear strength was calculated as the shear strength variability index (%) and is shown in Table 2. If the variability index is less than 15%, it is classified as "Excellent"; if it is between 15% and 25%, it is classified as "Good"; and if it is 25% or more, it is classified as "Poor," as shown in the "Shear Strength Variability Judgment" column of Table 2.

[0058] [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 2.

[0059] [Table 1]

[0060] *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)

[0061] [Table 2]

[0062] As is clear from Tables 1 and 2, in Comparative Example No. 1, where the solvent content of the transfer-type sheet-like bonding material was less than 0.5% by mass, excellent transferability could not be obtained. In Comparative Example No. 5, where the solvent content of the transfer-type sheet-like bonding material exceeded 2.0% by mass, sufficient bonding strength could not be stably secured. In contrast, in the inventive example, where the solvent content of the transfer-type sheet-like bonding material was in the range of 0.5% by mass or more and 2.0% by mass or less, excellent transferability was obtained even under slow transfer conditions where the sintering of copper particles did not progress, and sufficient bonding strength could be stably secured even with low-temperature bonding at 250°C. [Industrial applicability]

[0063] 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, a resin, and a solvent onto a resin substrate and drying it. A transfer-type sheet-like bonding material characterized by having a solvent content of 0.5% by mass or more and 2.0% 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 resin is made of acrylic resin.

6. The transfer-type sheet-like bonding material according to claim 1 or 2, 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.

7. The transfer-type sheet-like bonding material according to claim 1 or 2, wherein the copper particles have a coating on which at least a portion of the surface layer contains cuprous oxide and copper carbonate, the carbon concentration is 0.03% by mass or more and 0.30% by mass or less, and the oxygen concentration is 0.5% by mass or more and 3.0% by mass or less.

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