JP7550252B2 - Transferable sheet adhesive material - Google Patents

Description

The present invention relates to a transferable sheet-like bonding material.

Conventionally, solder materials have been widely used as a bonding material for electronic components. However, solder materials have a problem in that they have poor heat resistance. For example, it has been difficult to use solder materials as a bonding material in power devices using SiC elements that are expected to be used at high temperatures of 150°C or more.

As a result, a bonding material using silver particles has been proposed as a sintered bonding material. In addition, copper particles are promising from the standpoint of cost and ion migration, and development of a transferable sheet-type bonding material using copper particles is underway.

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 then drying the paste. 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 specified 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 specified bonding conditions.

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 surfaces are coated with triethanolamine as a capping agent, dicarboxylic acid as an activator, a dispersant, epoxy methacrylate urethane as a binder, and terpineol as an organic solvent onto a PET film and drying the paste. Patent Document 1 describes 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.

Special Publication No. 2021-529258

However, according to the inventors' investigations, although the epoxy methacrylate urethane resin described in Patent Document 1 does not exist, it was found that in any case, in existing sheet-like bonding materials, cracks occur in the dried film due to the resin components contained in the sheet-like bonding material (paste dried film).

In addition, in Patent Document 1, the transfer temperature is 200°C or higher, so copper sinters during transfer and the surface activity of the copper particles is impaired, which may impair the sintering of copper and atomic diffusion into the joined material during subsequent joining, resulting in a problem that sinterability and atomic diffusion (joinability) tend to become unstable. If transfer is performed under gentle transfer conditions that do not allow sintering of copper particles, there are problems such as the sheet-shaped joining material not being able to be transferred to the entire surface of the transferred material, or residues of the paste dried film (transfer-type sheet-shaped joining material) remaining on the resin substrate.

In addition, although the sheet-shaped bonding material in Patent Document 1 allows for low-temperature bonding at a bonding temperature of 250°C or less, there is also the issue that it is difficult to ensure sufficient bonding strength.

In view of the above problems, the present invention aims to provide a transferable sheet-like bonding material that (I) sufficiently suppresses cracking, (II) provides excellent transferability even under gentle 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.

In order to solve the above problems, the inventors conducted extensive research and discovered that the above problems (I) to (III) can be solved by optimizing the glass transition point of a transfer type sheet-like bonding material obtained by applying a paste containing copper particles, a reducing agent, an organic material containing a resin and optionally a plasticizer, and a solvent onto a resin substrate and drying the paste.

The present invention, which has been completed based on the above findings, has the following essential features.
[1] A paste containing copper particles, a reducing agent, an organic material containing a resin and optionally a plasticizer, and a solvent is applied onto a resin substrate and dried;
A transferable sheet-like bonding material having a glass transition temperature of -35°C or higher and 25°C or lower.

[2] The transferable sheet-like bonding material described in [1] above, in which the resin is an acrylic resin.

[3] The transferable sheet-like bonding material according to [1] or [2] above, in which the resin content is 1.0 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of copper particles.

[4] The transfer type sheet-like bonding material according to any one of [1] to [3] above, wherein the plasticizer is one or more selected from the group consisting of butyl phthalyl butyl glycolate, dimethyl phthalate, dioctyl phthalate, and diisodecyl phthalate.

[5] The transferable sheet-like bonding material according to any one of [1] to [4] above, in which the content of the plasticizer is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the resin.

[6] The transferable sheet-like bonding material according to any one of [1] to [5] above, wherein the reducing agent is triethanolamine.

[7] The transferable sheet-like bonding material according to any one of [1] to [6] above, in which 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.

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

The transferable sheet-like bonding material of the present invention (I) sufficiently suppresses cracking, (II) provides excellent transferability even under gentle transfer conditions where sintering of copper particles does not progress, and (III) ensures sufficient bonding strength even at low temperatures of 250°C or less.

[Transfer-type sheet-like bonding material]
The transferable sheet-like bonding material according to one embodiment of the present invention is obtained by applying a paste containing copper particles, a reducing agent, an organic material containing a resin and optionally a plasticizer, and a solvent onto a resin substrate and drying the paste, and is characterized by having a glass transition point of -35°C or higher and 25°C or lower.

(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 contain 97% by mass or more. When the copper particle contains 95% by mass or more of copper element, the bonding material has excellent heat resistance and further excellent bonding strength.

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

The shape (form) of the copper particles is not particularly limited. Examples of the shape of the copper particles include spherical (sphere), ellipsoid (ellipsoid), plate-like, etc., and among these, spherical and ellipsoidal shapes are preferred, with spherical shapes being more preferred.

The average particle size of the copper particles can be determined by observing 10 fields of view at a magnification of 10,000 times using a scanning electron microscope (SEM), measuring the particle size of each copper particle for all copper particles selected according to the following selection criteria (1) to (5) in the 10 fields of view, and determining the D50. For particles that are not perfectly round, such as ellipses, the major axis is taken as the particle size. The particle size distribution of the copper particles is also determined by the particle sizes of all the copper particles that are the subject of the above measurement. Here, when determining the average particle size 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 the sheet is produced, 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 with any part lying outside the field of view of the image will not be measured.
(2) Particles that have clear contours and exist in isolation are measured.
(3) Even if a particle shape deviates from the average particle shape, 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.

It is preferable to use copper particles that do not require protective agents, dispersants, etc. An example of such copper particles is ultrafine metal powder obtained by the manufacturing method described in Japanese Patent No. 4304221. However, the copper particles are not limited to this example.

It is preferable that the copper particles have a coating containing copper carbonate on the surface. By having the copper particles have a coating containing copper carbonate on the surface, the sintering temperature of the copper particles can be kept lower than before while increasing the bonding strength. The coating containing copper carbonate may further contain cuprous oxide.

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, so a bonding temperature above the decomposition temperature of the organic protective film is required, and low-temperature bonding at 250°C or below 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, posing a risk of reducing reliability.

The ratio of the mass oxygen concentration to the specific surface area of the copper particles is preferably 0.1 mass% g/m 2 or more, more preferably 0.2 mass% g/m ² or more, from the viewpoint of reducing the reactivity with oxygen in the air and reducing the effect of reoxidation. On the other hand, the ratio of the mass oxygen concentration to the specific surface area of the copper particles is preferably 1.2 mass% g/m ² or less, more preferably 0.5 mass% g/m ² or ^less , from the viewpoint of making it easier to remove the oxide film during bonding and further increasing the bonding strength.

From the viewpoint of suppressing the occurrence of voids and cracks and further increasing the bonding strength, the ratio of the mass carbon concentration to the specific surface area of the copper particles is preferably 0.3 mass% g/ ^m2 or less, more preferably 0.1 mass% g/ ^m2 or less, and even more preferably 0.05 mass% g/ ^m2 or less. The ratio of the mass carbon concentration to the specific surface area of the copper particles is preferably 0.008 mass% g/ ^m2 or more.

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).

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 mass carbon 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 carbon concentration can be measured using a carbon-sulfur analyzer (e.g., EMIA-920V manufactured by Horiba, Ltd.).

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 determining its weight after heating.

(Reducing Agent)
The reducing agent is a compound that reduces the oxide film that inevitably exists on the surface of the copper particles during bonding. During bonding, the oxide film is removed by the reducing agent, causing the copper particles (pure copper) to come into contact with each other, and sintering progresses, leading to diffusion bonding.

In this embodiment, the reducing agent is preferably triethanolamine. Triethanolamine is highly effective at removing oxide films, and because it has a high boiling point and low volatility, it is less likely to come off during transfer, and because it has high stability over time, it has excellent storage stability before bonding.

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 copper particles are sufficiently sintered, and a 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, and transfer and bonding in the same shape as the materials to be bonded can be achieved. Furthermore, there is no increase in decomposition gas components, and voids and cracks are less likely to occur in the bonding layer.

The reducing agent content in the sheet-like bonding material is the same as the reducing agent content in the paste.

(Organic Materials)
In this embodiment, the organic material includes a resin and optionally a plasticizer.

<Resin>
The resin functions as an adhesive when the transfer-type bonding sheet is transferred to the first member, and preferably also functions as a dispersant for dispersing the copper particles.

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

In this embodiment, the resin content is preferably 1.0 part by mass or more and 5.0 parts by mass or less per 100 parts by mass of copper particles. If the resin content is less than 1.0 part by mass, cracks are likely to occur in the paste dried film, and excellent transferability is difficult to obtain under gentle transfer conditions in which sintering of the copper particles does not progress. Furthermore, if the resin content exceeds 5.0 parts by mass, decomposable components and undecomposed substances in the binder form voids in the bonding layer, impairing adhesion with the bonded materials, and sufficient bonding strength cannot be ensured at low temperatures of 250°C or less.

The resin content in the sheet-shaped bonding material is the same as the resin content in the paste.

<Plasticizer>
The plasticizer lowers the glass transition point of the sheet-like bonding material, imparts flexibility to the sheet, and also plays a role in suppressing drying shrinkage of the coating film containing copper particles.

The plasticizer may be one or more selected from the group consisting of dimethyl phthalate, diethyl phthalate, diallyl phthalate, dibutyl phthalate, diisobutyl phthalate, di-n-hexyl phthalate, bis(2-ethylhexyl) phthalate, di-octyl phthalate, di-isononyl phthalate, di-isodecyl phthalate, di-nonyl phthalate, bis-butyl benzyl phthalate, and butyl phthalyl butyl glycolate. In particular, the plasticizer is preferably one or more selected from the group consisting of butyl phthalyl butyl glycolate, dimethyl phthalate, di-octyl phthalate, and di-isodecyl phthalate.

In this embodiment, the content of the plasticizer is preferably 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the resin. If the content of the plasticizer is less than 10 parts by mass, the plasticizing effect is not easily exerted, so that the paste dried film is likely to crack, and excellent transferability is difficult to obtain under gentle transfer conditions in which sintering of the copper particles does not proceed. In addition, since the copper particles may sinter during transfer, sufficient bonding strength cannot be ensured at low temperatures of 250°C or less. In addition, if the content of the plasticizer exceeds 50 parts by mass, poor dispersion of the copper particles, binder, and reducing agent in the paste is likely to occur, so that excellent transferability is difficult to obtain under gentle transfer conditions in which sintering of the copper particles does not proceed, and sufficient bonding strength cannot be ensured at low temperatures of 250°C or less.

The plasticizer content in the sheet-like bonding material is the same as the plasticizer content in the paste.

<Glass transition temperature of transfer type sheet-like bonding material>
It is important that the transfer type sheet-like bonding material of this embodiment has a glass transition point of -35 ° C or more and 25 ° C or less. By setting the glass transition point of the transfer type sheet-like bonding material to 25 ° C or less, a flexible transfer type sheet-like bonding material can be obtained, (I) cracking is sufficiently suppressed, (II) excellent transferability can be obtained even under gentle transfer conditions where sintering of copper particles does not progress, and (III) sufficient bonding strength can be ensured even at low temperature bonding of 250 ° C or less. From this viewpoint, the glass transition point of the transfer type sheet-like bonding material is preferably 10 ° C or less. On the other hand, if the glass transition point of the transfer type sheet-like bonding material is too low, the sheet-like bonding material may not be able to be transferred from the resin substrate. Therefore, the glass transition point of the transfer type sheet-like bonding material is -35 ° C or more, preferably -20 ° C or more.

The glass transition point of the transferable sheet-like adhesive material can be controlled mainly by the type of resin and the type and content of plasticizer.

The glass transition point of the transfer-type sheet-like bonding material can be determined by peeling off the paste-dried film (transfer-type sheet-like bonding material) from the resin substrate and subjecting the resulting powder to differential scanning calorimetry. For example, a Shimadzu Corporation differential scanning calorimeter (DSC60) is used, and 20 mg of the paste-dried powder (dried for 60 minutes at 70°C) is placed in the device, and measurements are taken under conditions of a measurement range of -50°C to 150°C (heating rate: 10°C/min) in a nitrogen atmosphere (flow rate 50 mL/min). In the DSC thermograph obtained, the glass transition point can be calculated as the midpoint of the displacement from the original baseline when the baseline shifts downward due to the glass transition.

(solvent)
The solvent should have a boiling point of about 200°C and low volatility. If the solvent evaporates during paste application and the metal concentration changes, the thickness of the coating film will become uneven. The solvent must also be capable of dissolving the resin used. From these perspectives, for example, a terpene-based solvent such as terpineol can be used.

(Sheet form)
The bonding material of the present embodiment is in a sheet form. The thickness of the bonding material is not particularly limited, and may be, for example, 10 μm or more and less than 1 mm.

The shape of the joining material (when viewed in a planar view from the thickness direction) is not particularly limited and can be appropriately selected depending on the shape of the joining surfaces of the members to be joined, and examples include rectangular and circular shapes.

[Method of manufacturing transfer type sheet-like 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, an organic material containing a resin and optionally a plasticizer, and a solvent onto a resin substrate and drying it.

The method for producing the paste is not particularly limited, and the paste can be produced by mixing the components using a planetary mixer, a mortar, mill stirring, stirrer stirring, etc. The method for applying and drying the paste onto a resin substrate is also not particularly limited, and for example, a paste dried film can be obtained by applying the paste onto a resin substrate using an applicator and drying the applied film in a hot air oven. Drying conditions can be 50 to 110°C (ambient temperature) and a drying time of 10 to 90 minutes.

The resin substrate is not particularly limited, and examples include a release PET film, a silicone film, and a fluororesin film. The thickness of the resin substrate can be about 50 to 200 μm, taking into account releasability.

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.

(Transcription)
First, the sheet-shaped bonding material is bonded to the first member, and then the resin substrate is peeled off. That is, the sheet-shaped bonding material is transferred to the first member. The conditions for transferring the transfer-type sheet-shaped 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 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 in the range of a transfer temperature of 50 to 150° C., a pressure of 1 to 10 MPa, and a transfer time of 10 seconds to 1 minute. The atmosphere during transfer is preferably an inert atmosphere such as nitrogen (N ₂ ).

(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 in the range of a bonding temperature of 200 to 250°C, a pressure of 1 to 40 MPa, and a transfer time of 1 to 60 minutes. The bonding atmosphere is preferably an inert atmosphere such as nitrogen (N ₂ ).

[Production of transfer type sheet-like bonding material]
(Test Example No. 1)
A paste was obtained by mixing 40 g of Taiyo Nippon Sanso copper particles (particle size 110 nm; D10; 39 nm, D50; 112 nm, D90; 310 nm), 3.2 g of triethanolamine as a reducing agent, 1.78 g of acrylic binder (Oricox KC-500, manufactured by Kyoeisha Chemical Co., Ltd.), and 12.2 g of terpineol as a solvent in a planetary mixer. The surface layer of the copper particles was coated with cuprous oxide, and the ratio of the mass oxygen concentration to the specific surface area of the copper particles was 0.25 mass% g/ ^m2 , and the mass carbon concentration was 0.03 mass% g/ ^m2 .

The paste thus prepared was then applied to a 100 μm-thick release PET film using an applicator to form a coating film of 200 μm thickness, and the coating film was dried in a hot air oven at 70°C for 60 minutes to remove the terpineol, yielding a paste-dried film (transfer-type sheet-like bonding material). The composition of the resulting transfer-type sheet-like bonding material and the glass transition point of the transfer-type sheet-like bonding material measured by the method described above are shown in Table 1.

(Test Examples No. 2 to 26)
The content of copper particles was fixed at 40 g, and the type of copper particles, the type and content of reducing agent, the type and content of acrylic binder, and the type and content of plasticizer were changed to those shown in Table 1, and a paste was obtained in the same manner as in Test Example No. 1. The content of terpineol was set so that the concentration of copper particles in the paste was 70 mass%. Next, a paste dried film (transfer type sheet-like bonding material) was obtained in the same manner as in Test Example No. 1. The composition of the obtained transfer type sheet-like bonding material and the glass transition point of the organic material measured by the above-mentioned method are shown in Table 1.

[Evaluation of cracks in dried paste film]
In each test example, the paste dried film (transfer type sheet-like bonding material) was observed in 10 fields of view at a magnification of 20 times using a microscope. The cases where there were no cracks in all 10 fields of view were rated as "excellent," and the cases where there were cracks in even one field of view were rated as "poor," and these were shown in the "Crack Resistance of Paste Dried Film" column in Table 1. In the case of "poor" where the dried film had cracks, the crack pattern and degree could not be controlled, and therefore the shear strength of the bonded sample after bonding varied, so the subsequent transfer and bonding tests were not performed.

[Evaluation of transferability]
In each test example, SiC (4 mm square, 350 μm thick) plated with Au was mounted on the transfer type sheet-shaped bonding material, and the transfer type sheet-shaped bonding material was transferred to the Au-plated surface of SiC under the following transfer conditions: transfer temperature (atmosphere temperature) 150 ° C., pressure 10 MPa, transfer time 30 seconds, and _N2 atmosphere. The case where the sheet-shaped bonding material can be transferred to the entire surface of SiC and there is no residue of the paste dry film (transfer type sheet-shaped bonding material) on the release PET film is rated as "excellent", and the case where the sheet-shaped bonding material cannot be transferred to the entire surface of SiC or there is a residue of the paste dry film (transfer type sheet-shaped bonding material) on the release PET film is rated as "poor", and is shown in the "transferability" column of Table 1. In addition, when the transferability is "poor", the shear strength of the bonded sample after bonding varies, so subsequent bonding tests were not performed.

[Evaluation of shear strength of bonded products]
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 the oxygen-free copper plate were bonded to each other via the sheet-like bonding material in a pressure bonding device under the following bonding conditions: bonding temperature (atmospheric temperature) 250 ° C, pressure 10 MPa, bonding time 5 minutes, and _N2 atmosphere. The bonded product was manufactured. The shear strength of the bonded product was measured using a bond tester (manufactured by Daige, 4000Plus) at a tool height of 100 μm and a tool speed of 200 μm/s, and is shown in Table 1. A shear strength of 50 MPa or more is good.

[Evaluation of bleeding of 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 Corporation) to check for the presence or absence of liquid seepage around the outer periphery of the SiC. The results are shown in Table 1.

*1
110nm product (D10; 39nm, D50; 112nm, D90; 310nm)
300 nm products (D10; 52 nm, D50; 298 nm, D90; 652 nm)
70nm product (D10; 24nm, D50; 72nm, D90; 284nm)
100nm product (D10; 34nm, D50; 101nm, D90; 308nm)
400nm product (D10; 66nm, D50; 403nm, D90; 811nm)
50nm product (D10; 15nm, D50; 51nm, D90; 194nm)
*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
*4: Plasticizer content (parts by mass) per 100 parts by mass of acrylic resin

As is clear from Table 1, in the comparative examples in which the glass transition point of the transfer-type sheet-like bonding material was outside the range of -35°C or more and 25°C or less, cracks were observed in the dried film, whereas in the invention examples in which the glass transition point of the transfer-type sheet-like bonding material was within the range of -35°C or more and 25°C or less, no cracks occurred in the dried film, excellent transferability was obtained even under gentle transfer conditions in which sintering of the copper particles did not progress, and sufficient bonding strength was ensured even at a low temperature of 250°C. In particular, in some of the invention examples in which the acrylic binder content, reducing agent content, and average particle size of the copper particles were optimized, a high shear strength of 50 MPa or more was obtained.

The transferable sheet-like bonding material of the present invention can be used industrially for bonding electronic components. Specifically, it can be used to bond components such as circuit boards 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 (8)

A paste including copper particles, a reducing agent for reducing an oxide film inevitably present on the surface of the copper particles , an organic material including a resin and optionally a plasticizer, and a solvent is applied onto a resin substrate, and then dried;
A transferable sheet-like bonding material having a glass transition temperature of -35°C or higher and 25°C or lower. The transferable sheet-like bonding material according to claim 1, wherein the resin is an acrylic resin. The transferable sheet-like bonding material according to claim 1 or 2, wherein the content of the resin is 1.0 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of copper particles. The transferable sheet-like bonding material according to claim 1 or 2, wherein the plasticizer is one or more selected from the group consisting of butylphthalyl butyl glycolate, dimethyl phthalate, dioctyl phthalate, and diisodecyl phthalate. The transferable sheet-like bonding material according to claim 1 or 2, wherein the content of the plasticizer is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the resin. The transferable sheet-like bonding material according to claim 1 or 2, wherein the reducing agent is triethanolamine. The transferable 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. The transferable 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.