Paste for bonding, and bonded body

Abstract

The present invention provides: a paste for bonding, which exhibits high thermal conductivity by suppressing voids in a coating film after sintering under a non-pressurized condition and / or under a pressurized condition, and which has excellent bonding strength and is capable of suppressing a decrease in the bonding strength due to a thermal cycle; and a bonded body which is obtained by using the paste for bonding.　The above problem is solved by a paste for bonding, which contains metal particles (A) and a dispersion medium (B), wherein if the paste for bonding is heated from 30°C at a heating rate of 3°C / min and the weight loss M650 as measured by a thermogravimetric-differential thermal analysis device is taken as 100, the weight loss M200 is 88.0 to 98.0 inclusive, and at least one of (1) the average particle diameter of the metal particles (A) is within a specific range, and (2) the weight loss M100, M150, and M250 are each within a specific range, is satisfied.

Description

Bonding paste and bonded body

[0001] The present disclosure relates to a bonding paste and a bonded body. In particular, the present disclosure relates to a bonding paste that has excellent thermal conductivity and bonding strength under at least one of a non-pressurized condition and a pressurized condition and that can suppress a decrease in bonding strength due to thermal cycling, and a bonded body using the bonding paste.

[0002] Conventionally, solder has been used as a bonding material for bonding metal members together, between a metal member and a semiconductor element, between a metal member and a light-emitting diode (LED) element, or the like. In recent years, in the technical field of next-generation power electronics, devices such as SiC that can operate at high temperatures are in demand. As a bonding material for manufacturing such devices, an alternative material to solder is required from the viewpoint of high-temperature operation reliability. As such an alternative material, bonding materials such as bonding pastes using sinterable metal particles have been proposed, for example, as shown in Patent Documents 1 and 2.

[0003] Patent Document 1 discloses a bonding material containing metal nanoparticles and a solvent, in which the values ​​of heat loss at 100°C, 150°C, and 200°C are specified, where the heat loss L700 when the material is heated from 40°C to 700°C at a heating rate of 3°C / min in a nitrogen atmosphere is set to 100%. Patent Document 2 discloses a bonding composition containing inorganic particles and a specific organic substance attached to at least a portion of the surface of the inorganic particles, in which the values ​​of weight loss rate when heated from room temperature to 200°C and when heated from 200°C to 300°C are specified by thermal analysis.

[0004] JP 2020-164895 A International Publication No. 2013-061527

[0005] Bonding processes using such bonding materials include methods performed without pressure (hereinafter referred to as pressureless bonding) and methods performed under pressure (hereinafter referred to as pressure bonding). Pressure bonding is effective in reducing voids, improving thermal conductivity, and promoting sintering of metal particles, thereby enabling strong bonding and offering excellent bonding strength and thermal cycle characteristics. However, pressure bonding requires dedicated equipment, and the objects to be bonded must be able to withstand a pressurized environment, limiting the objects and applications to be bonded. Therefore, there is a need to reduce voids and achieve high thermal conductivity not only in pressure bonding but also in pressureless bonding, while achieving strong bonding and improving bonding strength and thermal cycle characteristics. Meanwhile, while the area of ​​semiconductor elements has been increasing in recent years, it is known that the larger the area of ​​the element, the more difficult it is for internal gases and other substances to escape, making voids more likely to occur. Furthermore, there tends to be a significant difference between the linear expansion coefficients of Si and SiC elements and the linear expansion coefficients of the silver particles and copper used as the substrate. Therefore, during thermal cycling tests, strain is likely to occur between the copper substrate / the bonding layer containing silver particles / the Si or SiC element, which tends to cause cracks and reduce thermal cycling performance. Furthermore, although the SiC element has a linear expansion coefficient similar to that of the Si element, it has a higher hardness than the Si element, so it is subject to greater strain during thermal cycling than the Si element, which tends to cause cracks in the bonding layer. In other words, the level of demand for improving the bonding strength and thermal cycling performance of SiC semiconductor elements has been increasing in recent years.

[0006] However, the inventions described in Patent Documents 1 and 2 do not satisfy the constituent elements of the present disclosure, and may not be able to solve the problems of bonding strength and thermal cycle characteristics when large-area SiC elements are bonded by pressureless bonding or pressure bonding.

[0007] Therefore, the problem to be solved by the present disclosure is to provide a joining paste that suppresses voids in a coating film after sintering under at least one of pressure-free conditions and pressure conditions, thereby exhibiting high thermal conductivity, excellent bonding strength, and capable of suppressing a decrease in bonding strength due to thermal cycling, and a joined body using the joining paste.

[0008] The present inventors have conducted extensive research and found that the above-mentioned problems can be solved. [1]: A bonding paste containing metal particles (A) and a dispersion medium (B), wherein the bonding paste is heated from 30°C at a heating rate of 3°C / min, and the weight loss at 200°C, M200, measured with a thermogravimetric differential thermal analyzer, is 88.0 or more and 98.0 or less, where M650 at 650°C is set to 100, and the bonding paste satisfies at least one of the following conditions (1) and (2): (1) the metal particles (A) contain metal particles (a) having an average particle diameter of 100 nm or more and 10 μm or less in an amount of 50 mass% or more based on the total mass of the metal particles (A); (2) When the bonding paste is heated from 30°C at a heating rate of 3°C / min, the weight loss at 650°C, M650, measured with a thermogravimetric differential thermal analyzer is 100. When the weight loss at 650°C, M100, is 10.0 or more and 70.0 or less, the weight loss at 150°C, M150, is 85.0 or more and 96.0 or less, and the weight loss at 250°C, M250, is 93.0 or more and 99.5 or less. [2]: The bonding paste according to [1], which satisfies the condition (1) and in which the metal particles (a) have an average particle size of 100 nm or more and 500 nm or less. [3]: The bonding paste according to [1], which satisfies the condition (1) and in which the metal particles (a) have an average particle size of more than 500 nm and 10 μm or less. [4]: The joining paste according to [3], wherein the dispersion medium (B) contains a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower, and the content of the dispersion medium (b1) is 55% by mass or higher based on the total mass of the dispersion medium (B). [5]: The joining paste according to any of [1] to [4], wherein the ratio (M150 / M200) of the weight loss M150 to the weight loss M200, where M650 is taken as 100, is 0.975 or higher. [6]: The joining paste according to any of [1], [2], and [5], wherein the dispersion medium (B) contains a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower, and the content of the dispersion medium (b1) is 50% by mass or higher based on the total mass of the dispersion medium (B).[7]: The bonding paste according to [4] or [6], wherein the dispersion medium (b1) contains at least one selected from the group consisting of terpenes and glycol ethers. [8]: The bonding paste according to any one of [1] to [7], wherein the dispersion medium (B) contains a dispersion medium (b2) having a boiling point exceeding 300°C in a content of 20 mass% or less, based on the total mass of the dispersion medium (B). [9]: The bonding paste according to [8], wherein the content of the dispersion medium (b2) is 10 mass% or less, based on the total mass of the dispersion medium (B).

[10] : The bonding paste according to any one of [1] to [9], wherein the dispersion medium (B) contains a dispersion medium having a hydroxyl group, and the content of the dispersion medium having a hydroxyl group is 90 mass% or more, based on the total mass of the dispersion medium (B).

[11] : The bonding paste according to any one of [1] to

[10] , wherein the metal particles (A) contain at least one metal selected from the group consisting of silver, copper, a silver-containing alloy, silver oxide, and copper oxide.

[12] : A bonded body in which a first part to be bonded and a second part to be bonded are bonded with the bonding paste according to any one of [1] to

[11] .

[13] : The bonded body according to

[12] , wherein the first part to be bonded is an untreated substrate.

[14] : The bonded body according to

[12] or

[13] , wherein the second part to be bonded is SiC.

[0009] The present disclosure makes it possible to provide a joining paste that suppresses voids in a coating film after sintering under at least one of pressure-free conditions and pressure-applied conditions, thereby exhibiting high thermal conductivity, excellent bonding strength, and capable of suppressing a decrease in bonding strength due to thermal cycling, as well as a joined body using the joining paste.

[0010] The bonding paste and bonded body according to the present disclosure will be described below in order. In this specification, the term "to" indicating a numerical range includes the upper and lower limits unless otherwise specified. In the numerical ranges described in stages in this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the examples.

[0011] <<Bonding Paste>> The bonding paste according to the present disclosure (hereinafter also referred to as the present bonding paste) is a bonding paste containing metal particles (A) and a dispersion medium (B). Furthermore, in this bonding paste, when the temperature of the bonding paste is increased from 30°C at a heating rate of 3°C / min, the weight loss at 200°C, M200, measured using a thermogravimetric differential thermal analyzer, is 88.0 or more and 98.0 or less, where M650 at 650°C is set to 100. Furthermore, this bonding paste satisfies at least one of the following conditions (1) and (2): (1) The metal particles (A) contain 50 mass% or more of metal particles (a) having an average particle diameter of 100 nm or more and 10 μm or less, based on the total mass of the metal particles (A). (2) When the temperature of the bonding paste is increased from 30°C at a heating rate of 3°C / min, the weight loss at 100°C, M100, is 10.0 or more and 70.0 or less, the weight loss at 150°C, M150, is 85.0 or more and 96.0 or less, and the weight loss at 250°C, M250, is 93.0 or more and 99.5 or less, where M650 at 650°C is 100, as measured by a thermogravimetric differential thermal analyzer.

[0012] The present bonding paste, which satisfies at least one of the above conditions (1) and (2), has the excellent effects described above under either or both of non-pressurized and pressurized conditions, and can solve the above-mentioned problems.

[0013] Hereinafter, among the present bonding pastes that satisfy the above condition (1), a bonding paste according to a first embodiment (also referred to as a first bonding paste) contains a specific amount of metal particles (a) (hereinafter also referred to as metal particles (a1)) having an average particle diameter of 100 nm or more and 500 nm or less. This first bonding paste has particularly excellent effects under pressure-free conditions and can solve the above-mentioned problems.

[0014] Furthermore, hereinafter, among the present bonding pastes that satisfy the above condition (1), a bonding paste according to a second embodiment (also referred to as a second bonding paste) contains a specific amount of metal particles (a) (hereinafter also referred to as metal particles (a2)) having an average particle diameter of more than 500 nm and not more than 10 μm. This second bonding paste has particularly excellent effects under pressurized conditions and can solve the above-mentioned problems.

[0015] Furthermore, hereinafter, the present bonding paste that satisfies the above condition (2) will be referred to as a bonding paste according to a third embodiment (also referred to as a third bonding paste). The third bonding paste has particularly excellent effects under both non-pressurized and pressurized conditions, and can solve the above-mentioned problems.

[0016] The bonding paste according to each embodiment will be described in detail below. The bonding paste may satisfy either the above conditions (1) or (2), or may satisfy both the above conditions (1) and (2). The bonding paste may also satisfy one, two, or all three of the first to third embodiments described above. That is, these embodiments may overlap.

[0017] <First Bonding Paste> As described above, the bonding paste according to the first embodiment includes metal particles (A) and a dispersion medium (B). The first bonding paste may also include the compound (C), compound (D), and other additives described below. The first bonding paste includes 50 mass% or more of metal particles (a1) having an average particle diameter of 100 nm or more and 500 nm or less in the metal particles (A). Furthermore, the first bonding paste has a weight loss (M200) of 88.0 or more and 98.0 or less at 200°C, where M650 is defined as 100, measured using a thermogravimetric differential thermal analyzer when the bonding paste is heated from 30°C at a heating rate of 3°C / min. Here, the first bonding paste contains a specific amount of metal particles (a1) having a specific average particle size, allowing the particles to fuse or bond (hereinafter also referred to as sintering) with each other at temperatures ranging from 200°C to 350°C when the bonding paste is heated and sintered, thereby converting the paste into a bulk metal. Furthermore, by setting the weight loss M200 at 200°C within a predetermined range, based on the weight loss M650 at 650°C, the first bonding paste can exhibit excellent bonding strength and bonding strength after thermal cycling, even under strict pressure-free bonding conditions and when the bonded members are untreated substrates such as plateless substrates or SiC semiconductor elements, for which stable bonding is difficult. As described above, the first bonding paste having the above configuration can provide a bonding paste capable of pressureless bonding, which has high thermal conductivity, high bonding strength at the bonded points, and suppresses loss of bonding strength due to thermal cycling, and a bonded body using the bonding paste. Furthermore, by using the first bonding paste, even when a large-area SiC element is bonded under pressure-free conditions, high thermal conductivity, excellent bonding strength, and thermal cycling characteristics can be exhibited.

[0018] [Metal Particles (A)] The metal particles (A) impart electrical conductivity and thermal conductivity to the bonded body and serve to bond the bodies to be bonded during the sintering process. The metal particles (A) preferably contain at least one metal selected from the group consisting of silver, copper, silver alloys, silver oxide, copper oxide, and other metals (excluding silver and copper). More specifically, the metal particles (A) preferably contain coated particles having a core made of one of these metals and a surface coated with a metal such as silver. The first bonding paste uses the metal particles (A) to obtain a bonded body with excellent strength. The first bonding paste uses the metal particles (A) to enable a wide range of firing temperatures and to support various firing environments, such as atmospheric pressure, a nitrogen atmosphere, a vacuum, or a reducing atmosphere.

[0019] As described above, the first bonding paste contains 50 mass% or more of metal particles (a1) having an average particle diameter of 100 nm or more and 500 nm or less among the metal particles (A). This allows the particles to sinter together at temperatures ranging from 200°C to 350°C when the first bonding paste is heated and sintered, converting them into bulk metal and easily bonding the bonded bodies. Hereinafter, the portion formed by sintering the metal particles (A) between the bonded bodies is referred to as the bonding layer. Note that the first bonding paste may or may not contain the metal particles (a2) having an average particle diameter of more than 500 nm and 10 μm or less, as long as the effects of the present disclosure are obtained. However, a low content of the metal particles (a2) is preferred, and it is more preferable that the metal particles (a2) are not contained. The metal particles (A) (e.g., metal particles (a1)) contained in the first bonding paste are preferably particles containing silver or copper from the viewpoint of electrical conductivity and thermal conductivity, and more preferably particles containing silver (silver particles) from the viewpoint of oxidation resistance.

[0020] Thus, in the first bonding paste, it is important that the metal particles (A) contain 50 mass% or more of metal particles (a1) having a specific average particle size. Here, the term "average particle size" as used herein refers to the volume-based 50% cumulative particle size distribution particle size (d50) determined by the measurement method described in the Examples. The d50 of the metal particles (a1) is 100 nm or more, and from the viewpoints of bonding strength and thermal conductivity, it is preferably 150 nm or more, more preferably 200 nm or more. Furthermore, the d50 of the metal particles (a1) is 500 nm or less, and from the viewpoints of bonding strength and thermal cycle properties, it is preferably 400 nm or less, more preferably 300 nm or less.

[0021] The metal particles (A) (e.g., metal particles (a1)) may have their surfaces coated with an organic component. That is, the metal particles (A) may be, for example, silver particles whose surfaces are coated with an organic component. Hereinafter, the organic component will also be referred to as a protective agent. When the metal particles (A) are coated with an organic component, the storage stability of the bonding paste is further improved. Examples of the organic component include fatty acids, aliphatic amines, and aliphatic alcohols. Among these, the organic component is preferably a saturated or unsaturated fatty acid, more preferably a saturated or unsaturated fatty acid having 3 to 18 carbon atoms, and even more preferably a saturated or unsaturated fatty acid having 6 to 18 carbon atoms. The metal particles (A) may contain one or more organic components.

[0022] The content of metal particles (a1) having a specific average particle size in the metal particles (A) is 50% by mass or more, and from the viewpoint of bonding strength and thermal cycle properties, it is preferably 70% by mass or more, more preferably 85% by mass or more. The content of metal particles (a1) in the metal particles (A) may be 100% by mass, or the metal particles (A) may be composed of metal particles (a1). The metal particles (A) and the metal particles (a1) may each independently be used alone or in combination. As described above, the metal particles (A) may contain metal particles other than the metal particles (a1) as long as the effects of the present disclosure are not impaired. The metal particles (A) may contain metal particles with an average particle diameter of more than 500 nm, or may be combined with metal particles with an average particle diameter of more than 1000 nm, or different metal species may be used.

[0023] [Dispersion medium (B)] The first bonding paste contains a dispersion medium (B). The dispersion medium (B) has the function of dispersing the metal particles (A) and the role of imparting fluidity to the coating film in the sintering step of the metal (e.g., silver). Examples of the dispersion medium (B) include terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersolve TOE100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol), Tersolve MTPH (isobornylcyclohexanol) (trade name, manufactured by Nippon Terpene Co., Ltd.), Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate), carbitol, carbitol acetate, butyl carbitol, isophorone, γ-butyl lactone, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol methyl-n-propyl ether, 3-methoxy-3-methylbutyl acetate, ethylene glycol Examples of the dispersing medium include ethylene glycol, propylene glycol diacetate, dipropylene glycol methyl ether acetate, 1,3-butylene glycol, 1,3 butanediol, 1,4 butanediol, 2-ethyl-1,3 hexanediol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, polyethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and isoparaffin-based dispersing mediums contained in hydrocarbon-based dispersing mediums. These dispersing mediums may be used alone or in combination of two or more.

[0024] The dispersion medium (B) preferably contains 50 mass% or more of a dispersion medium (b1) (hereinafter referred to as dispersion medium (b1)) having a boiling point of 250°C or higher and 300°C or lower, based on the total mass of the dispersion medium (B). By including 50 mass% or more of the dispersion medium (b1), the dispersion medium is more likely to remain during the metal sintering process, making it easier to maintain the weight loss M200 value at 200°C within a predetermined range (88.0 or higher and 98.0 or lower). From the viewpoints of thermal cycle characteristics and thermal conductivity, the content of the dispersion medium (b1) is more preferably 55 mass% or more, even more preferably 60 mass% or higher, and particularly preferably 70 mass% or higher, based on the total mass of the dispersion medium (B). The content of the dispersion medium (b1) in the dispersion medium (B) may be 100 mass%, or the dispersion medium (B) may be composed entirely of the dispersion medium (b1). The boiling point of the dispersion medium (b1) is preferably 260°C or higher.

[0025] Examples of the dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower include terpenes such as Tersolve TOE-100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol) (manufactured by Nippon Terpene Chemical Co., Ltd.); glycol ethers such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether; Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate); and 1,6-diacetoxyhexane. Among these, at least one solvent selected from the group consisting of terpenes and glycol ethers is preferably used as the dispersion medium (b1).

[0026] Furthermore, the proportion of the dispersion medium (b2) (hereinafter referred to as dispersion medium (b2)) having a boiling point exceeding 300°C, based on the total mass of the dispersion medium (B), is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less. By having the proportion of dispersion medium (b2) be 20% by mass or less, excessive dispersion medium does not remain during the silver sintering process, making it easy to keep the weight loss M200 value at 200°C within a predetermined range. Dispersion medium (b2) does not necessarily need to be included in dispersion medium (B). By keeping the weight loss M200 value at 200°C within a predetermined range, the dispersion medium is more likely to remain during the sintering stage, the fluidity of the coating film is increased, the generation of voids in the coating film after sintering is further suppressed, and high thermal conductivity can be easily achieved. Furthermore, the wettability to the bonded parts is further improved, increasing the contact area, thereby forming a strong bond. This allows excellent bonding strength and thermal cycle resistance to be easily achieved.

[0027] Examples of the dispersion medium (b2) having a boiling point exceeding 300° C. include Tersolve MTPH (isobornylcyclohexanol) (trade name, manufactured by Nippon Terpene Chemical Co., Ltd.) and tetraethylene glycol monobutyl ether.

[0028] The dispersion medium (B) preferably contains a dispersion medium containing hydroxyl groups. The dispersion medium containing hydroxyl groups may be the dispersion medium (b1) or (b2) described above. When the dispersion medium (B) contains hydroxyl groups, it adsorbs to the metal particles (A) and further improves dispersibility. Furthermore, the evaporation of the dispersion medium is slowed, which tends to moderate film shrinkage that occurs during sintering. This further increases the fluidity of the coating film, suppresses the generation of voids in the coating film after sintering, and easily achieves high thermal conductivity. Furthermore, the wettability of the bonded parts is further improved, increasing the contact area, making it easy to form a strong bond. This easily achieves excellent bonding strength and thermal cycle resistance. From the above perspectives, the content of the dispersion medium containing hydroxyl groups is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total mass of the dispersion medium (B).

[0029] Examples of dispersion media containing a hydroxyl group include terpineol-based dispersion media such as terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersolve TOE-100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol), and Tersolve MTPH (isobornylcyclohexanol); and glycol ether-based dispersion media such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether.

[0030] [Weight Loss] As described above, it is important that the first bonding paste has a weight loss M200 of 88.0 or more and 98.0 or less when heated from 30°C (to 650°C) at a heating rate of 3°C / min, as measured by a thermogravimetric differential thermal analyzer. When the weight loss M650 at 650°C is taken as 100, the weight loss M200 at 200°C is 100. When the weight loss M200 is within the above range, the dispersion medium remains during the sintering stage, enhancing the fluidity of the coating film, suppressing the generation of voids in the coating film after sintering and providing high thermal conductivity. Furthermore, improved wettability with respect to the bonded parts increases the contact area, resulting in the formation of a strong bond. This allows for excellent bonding strength and thermal cycle resistance. From the same perspective, the weight loss M200, when the weight loss M650 is taken as 100, is preferably 89.0 or more and 97.0 or less, more preferably 90.0 or more and 96.0 or less. Furthermore, in this specification, when the temperature is raised from 30°C (to 650°C) at a heating rate of 3°C / min, the weight loss at 650°C measured with a thermogravimetric differential thermal analyzer, M650, is set to 100, and the weight losses at 100°C, 150°C, 200°C, 250°C, and 300°C are also simply referred to as M100 / M150 / M200 / M250 / M300, respectively. The weight loss can be measured using a thermogravimetric differential thermal analysis method (hereinafter also referred to as TG-DTA analysis method). For example, the weight loss can be determined using a thermogravimetric differential thermal analyzer (trade name: TG / DTA8122 (manufactured by RIGAKU Corporation)) by heating 10 mg of a sample in a nitrogen atmosphere at a heating rate of 3°C / min, starting at a temperature of 30°C.

[0031] From the viewpoints of the thermal conductivity, bonding strength, and thermal cycle characteristics described above, the first bonding paste preferably has an M100 of 10.0 or more and 70.0 or less, an M150 of 85.0 or more and 96.0 or less, an M250 of 93.0 or more and 99.5 or less, and an M300 of 96.0 or more and 99.0 or less. Thus, the first bonding paste preferably satisfies the above-mentioned condition (2) that defines all of the parameters other than M300. From the same viewpoint, it is more preferable that the M100 be 10.0 or more and 50.0 or less, the M150 be 87.0 or more and 95.0 or less, the M250 be 93.0 or more and 98.5 or less, and the M300 be 97.0 or more and 98.0 or less. While it is preferable that the first bonding paste satisfy all of these preferred ranges for M100, M150, M250, and M300, it is also preferable that it satisfy one or more of these preferred ranges.

[0032] Furthermore, the ratio of M150 to M200 (M150 / M200) of the first bonding paste is preferably 0.975 or greater. Having an M150 / M200 value of 0.975 or greater further suppresses the rapid volatilization of dispersion media and other organic substances during the sintering process between 150°C and 200°C, thereby mitigating the shrinkage of the coating film that occurs during sintering. This increases the fluidity of the coating film, easily suppressing the generation of voids in the coating film after sintering and easily achieving high thermal conductivity. Furthermore, the wettability of the bonded parts is further improved, increasing the contact area, making it easy to form a strong bond. This facilitates the development of excellent bonding strength and thermal cycle resistance. From the same perspective, the M150 / M200 value is more preferably 0.980 or greater, and even more preferably 0.985 or greater.

[0033] In the first bonding paste, from the viewpoints of the thermal conductivity, bonding strength, and thermal cycle characteristics described above, the ratio of M200 to M250 (M200 / M250) is preferably 0.950 or more, more preferably 0.955 or more, even more preferably 0.960 or more, and particularly preferably 0.965 or more. From the same viewpoint, the ratio of M150 to M250 (M150 / M250) is preferably 0.930 or more, more preferably 0.940 or more, and even more preferably 0.950 or more.

[0034] [Compound (C)] The first bonding paste may contain a compound (C) (hereinafter referred to as compound (C)) having 20 to 80 carbon atoms and two or more functional groups (c) selected from the group consisting of hydroxyl groups, carboxy groups, and amino groups. The inclusion of such a compound (C) facilitates the formation of a liquid composition even after partial or complete evaporation of the dispersion medium (B), thereby facilitating the formation of a favorable bonding interface integrated with the bonded parts. Furthermore, each functional group (c) has high bonding affinity with metal particles and can easily exhibit excellent dispersibility. The carbon number of compound (C) represents a value that includes the carbon atoms in the functional group (c). Therefore, if the functional group (c) in compound (C) is a carboxy group, the carbon number of compound (C) is deemed to include the carbon atoms in the carboxy group.

[0035] In compound (C), the skeleton (partial structure) excluding functional group (c) is an organic residue, but is preferably a hydrocarbon group or a group in which multiple hydrocarbon groups are linked via a linking group containing a heteroatom. Examples of such linking groups containing a heteroatom include an -O- group (ether group), a -C(=O)- group (carbonyl group), a -C(=O)-O- group (ester group or oxycarbonyl group), and a -C(=O)-NH- group (amide group or iminocarbonyl group). It is preferable that compound (C) does not have any functional groups other than functional group (c).

[0036] When the number of functional groups (c) in compound (C) is n, compound (C) preferably has an n-valent hydrocarbon group. In compound (C), the skeleton excluding functional groups (c) is more preferably composed only of n-valent hydrocarbon groups, in order to obtain a strong bonded body.

[0037] The number of functional groups (c) in compound (C) is preferably 2 or 3. Compound (C) may have a linear structure or a branched and / or cyclic structure, but preferably has a branched and / or cyclic structure. When compound (C) has a branched and / or cyclic structure, it is preferred in that it has low crystallinity and is likely to become a liquid with good fluidity.

[0038] Examples of the compound (C) having a linear structure include eicosane diacid, heneicosane diacid, docosane diacid, tetracosane diacid, triacontanedioic acid, dotriacontanedioic acid, tetracontanedioic acid, pentacontanedioic acid, hexacontanedioic acid, and batyl alcohol. Examples of the compound (C) having a branched and / or cyclic structure include dimer acid, trimer acid, tetramer acid, dimer diol, trimer triol, tetramer tetraol, dimer diamine, trimer triamine, tetramer tetramine, and phytantriol. Among these, it is more preferable that the compound (C) is a compound selected from the group consisting of dimer acid, trimer acid, dimer diol, trimer triol, dimer diamine, and trimer triamine.

[0039] In the first bonding paste, the content of the compound (C) is preferably 0.05 to 2.0 mass%, more preferably 0.10 to 1.0 mass%, based on the mass of the metal particles (A), from the viewpoints of initial bonding strength and thermal cycle characteristics.

[0040] [Compound (D)] The first bonding paste may contain a compound (D) (hereinafter referred to as compound (D)) having at least one nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms and having four or more hydroxyl groups. From the viewpoints of bonding strength and thermal cycle characteristics, compound (D) preferably has a tertiary nitrogen atom. The number of tertiary nitrogen atoms is preferably 1 to 3, more preferably 2 to 3. Having one or more tertiary nitrogen atoms (preferably two or more) enhances bonding with the metal particles (A) and significantly improves dispersibility. Furthermore, tertiary nitrogen atoms have the function of reducing the metal particles (A) and the bonded portions, and having one or more tertiary nitrogen atoms (preferably two or more) further enhances the reduction function. Furthermore, from the viewpoints of dispersibility and reduction function, the number of hydroxyl groups in compound (D) is preferably 4 to 6. In particular, hydroxyl groups have excellent bonding properties with metal particles (A), and therefore tend to improve dispersibility, and when the number of hydroxyl groups is 4 or more, the bonding properties with metal particles (A) are further enhanced, and dispersibility is significantly improved. Furthermore, hydroxyl groups have the function of reducing metal particles (A) and the bonded portions, and when the number of hydroxyl groups is 4 or more, the reducing function is significantly improved.

[0041] The content of compound (D) is preferably 0.02% by mass or more, based on the mass of metal particles (A). When the content of compound (D) is 0.02% by mass or more, the dispersibility of metal particles (A) is further improved, and sintering proceeds with compound (D) remaining in the coating film, and sintering proceeds easily while the coating film has fluidity, thereby further reducing adhesion to the bonded parts and defects in the bonding layer. From the viewpoints of dispersibility, adhesion to the bonded parts, and reducing defects in the bonding layer, the content of compound (D) is more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more. Furthermore, the content of compound (D) is preferably 2.00% by mass or less, based on the mass of metal particles (A). When the content of compound (D) is 2.00% by mass or less, the amount remaining in the coating film after sintering can be further reduced, resulting in better bonding strength and thermal cycle properties. From the viewpoint of reducing the residual amount, the content of compound (D) is more preferably 1.00% by mass or less, and even more preferably 0.50% by mass or less.

[0042] [Other Additives] Examples of other additives that can be contained in the first bonding paste include a sintering accelerator, a binder resin, a resin-type dispersant, a reducing agent, etc. These additives can be conventionally known additives, and the blending amounts of these additives can be set within a range that can obtain the effects of the present disclosure, and are not particularly limited.

[0043] <Second Bonding Paste> The bonding paste according to the second embodiment differs from the first bonding paste in that the metal particles (A) contain 50 mass% or more of metal particles (a2) having an average particle diameter of more than 500 nm and not more than 10 μm, instead of the above-mentioned metal particles (a1). Note that the second bonding paste may or may not contain the above-mentioned metal particles (a1) as long as the effects of the present disclosure can be obtained. However, it is preferable that the content of the metal particles (a1) is small, and it is more preferable that the metal particles (a1) are not contained.

[0044] The second bonding paste contains a specific amount of the above-mentioned metal particles (a2), and when the above-mentioned M650 is used as a reference, the M200 is within a predetermined range (88.0 or more and 98.0 or less), thereby achieving the following excellent effects: That is, by having this configuration, the second bonding paste can exhibit excellent bonding strength and bonding strength after thermal cycling under pressurized conditions, even when the members to be bonded are untreated substrates such as plating-less substrates or SiC semiconductor elements, for which stable bonding is difficult.

[0045] In addition, in the second bonding paste, from the viewpoint of further exerting these excellent effects, it is preferable that the content of the dispersion medium (b1) having a boiling point of 250°C or more and 300°C or less in the dispersion medium (B) is particularly 55 mass% or more, based on the total mass of the dispersion medium (B).

[0046] The second bonding paste has high thermal conductivity, high bonding strength at the bonded portion, and suppresses a decrease in bonding strength due to thermal cycling. It is possible to provide a bonding paste capable of pressure bonding, and a bonded body using the bonding paste. Furthermore, the second bonding paste can exhibit high thermal conductivity, excellent bonding strength, and thermal cycling characteristics even when bonding large-area SiC elements. As described above, the second bonding paste differs from the first bonding paste in the composition of the metal particles (A). The following description will focus on this difference. Therefore, descriptions that overlap with the first bonding paste will be omitted. Note that preferred aspects of the second bonding paste other than those described below are the same as those of the first bonding paste, and therefore descriptions of these aspects will also be omitted.

[0047] [Metal Particles (A)] The metal particles (A) contained in the second bonding paste contain 50 mass% or more of metal particles (a2) having an average particle diameter of more than 500 nm and less than 10 μm. This allows the particles to fuse or bond (sinter) with each other at temperatures ranging from 200°C to 350°C, where the second bonding paste is heated and sintered under pressure, and to transform into bulk metal. As a result, the bonded objects can be easily bonded. Thus, it is important that the metal particles (A) contained in the second bonding paste contain 50 mass% or more of the metal particles (a2). The d50 of the metal particles (a2) is greater than 500 nm, and from the viewpoints of bonding strength, thermal cycle characteristics, and thermal conductivity, it is preferably 600 nm or more, more preferably 700 nm or more. Furthermore, the d50 of the metal particles (a) is 10 μm or less, and from the viewpoints of bonding strength, thermal cycle characteristics, and thermal conductivity, it is preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0048] The metal particles (a2) may have their surfaces coated with an organic component, as in the case of the metal particles (a1). For details of the organic component, see the description of the metal particles (a1).

[0049] The content of the metal particles (a2) in the metal particles (A) is 50% by mass or more, and from the viewpoints of bonding strength, thermal cycle characteristics, and thermal conductivity, it is preferably 70% by mass or more, more preferably 85% by mass or more. The content of the metal particles (a2) in the metal particles (A) may be 100% by mass, or the metal particles (A) may be composed of the metal particles (a2). The metal particles (A) and the metal particles (a2) may each independently be used alone or in combination. The metal particles (A) may contain metal particles other than the metal particles (a2) as long as the effects of the present disclosure are not impaired. The metal particles (A) may contain metal particles having an average particle diameter of 500 nm or less, or may be combined with metal particles having an average particle diameter of more than 10 μm, and the metal species may be different.

[0050] [Dispersion medium (B)] The dispersion medium (B) contained in the second bonding paste preferably contains 55 mass% or more of a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower, based on the total mass of the dispersion medium (B). By containing 55 mass% or more of the dispersion medium (b1), the dispersion medium is more likely to remain during the metal sintering process, making it easier to keep the weight loss M200 value within a predetermined range. From the same viewpoint, the content of the dispersion medium (b1) is preferably 60 mass% or more, more preferably 70 mass% or more, based on the total mass of the dispersion medium (B). The content of the dispersion medium (b1) in the dispersion medium (B) may be 100 mass%, or the dispersion medium (B) may be composed of the dispersion medium (b1). The boiling point of the dispersion medium (b1) is preferably 260°C or higher. Similarly to the first bonding paste, the second bonding paste may contain the above-mentioned dispersion medium (b2) (for example, 10 mass % or less) as the dispersion medium (B). Specific examples and preferred content ratios of the dispersion media (b1) and (b2) other than those described above are as described for the first bonding paste.

[0051] [Weight Loss] The weight loss of the second bonding paste is the same as that of the first bonding paste, and therefore will not be described here. In addition, the second bonding paste may contain, in addition to the metal particles (A) and the dispersion medium (B), the compound (C), the compound (D), and other additives. However, since these are the same as those in the first bonding paste, their description will not be repeated here.

[0052] <Third Bonding Paste> As described above, the bonding paste according to the third embodiment satisfies condition (2). Therefore, the following description will focus on condition (2). The third bonding paste may also satisfy condition (1) described above. The third bonding paste satisfies the following (1) to (4) when the weight loss at 100°C, 150°C, 200°C, and 250°C, respectively, is expressed as M100 / M150 / M200 / M250, when the weight loss at 650°C, M650, is defined as 100, as measured with a thermogravimetric differential thermal analyzer when the bonding paste is heated from 30°C at a heating rate of 3°C / min. (1) M100 is 10.0 or more and 70.0 or less. (2) M150 is 85.0 or more and 96.0 or less. (3) M200 is 88.0 or more and 98.0 or less. (4) M250 is 93.0 or more and 99.5 or less. The third bonding paste, having the above-described configuration, can exhibit excellent bonding strength and bonding strength after thermal cycling, regardless of whether pressure is applied or not, even when the bonded members are untreated substrates such as those without plating, or SiC semiconductor elements, for which stable bonding is difficult. Specifically, the above-described configuration allows the third bonding paste to provide a bonding paste with high thermal conductivity, high bonding strength at the bonded points, and suppressed reduction in bonding strength due to thermal cycling, as well as a bonded body using the bonding paste. Furthermore, the third bonding paste can exhibit high thermal conductivity, excellent bonding strength, and thermal cycling characteristics, even when bonding large-area SiC elements. From the viewpoints of bonding strength, thermal cycling characteristics, and thermal conductivity, it is particularly preferable that the content of the dispersion medium (b2) having a boiling point exceeding 300°C in the dispersion medium (B) be 20 mass% or less based on the total mass of the dispersion medium.

[0053] [Metal Particles (A)] The metal particles (A) contained in the third bonding paste can be the same as those described in the first bonding paste and the second bonding paste. In the third bonding paste, the average particle size of the metal particles (A) can be appropriately selected depending on the application and bonding conditions. Typically, particles having an average particle size of 100 nm or more and 10 μm (satisfying the above condition (1)) are preferably used. That is, in the third bonding paste, the d50 of the metal particles (A) is preferably 100 nm or more, more preferably 150 nm or more, and even more preferably 200 nm or more from the viewpoints of bonding strength, thermal cycle characteristics, and thermal conductivity. In addition, the d50 of the metal particles (A) is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 5 μm or less from the viewpoints of bonding strength, thermal cycle characteristics, and thermal conductivity.

[0054] [Dispersion medium (B)] The dispersion medium (B) contained in the third bonding paste can be the same as that described for the first bonding paste and the second bonding paste, so explanation will be omitted. In order to satisfy the four weight reduction conditions described above, the content of the dispersion medium (b1) in the dispersion medium (B) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. In addition, in order to satisfy the four weight reduction conditions described above, the content of the dispersion medium (b2) in the dispersion medium (B) is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

[0055] [Weight Loss] As described above, it is important that the third bonding paste satisfy the following (1) to (4). (1) M100 is 10.0 or more and 70.0 or less. (2) M150 is 85.0 or more and 96.0 or less. (3) M200 is 88.0 or more and 98.0 or less. (4) M250 is 93.0 or more and 99.5 or less. By satisfying these conditions, the drying behavior of the dispersion medium during the sintering process can be controlled. Specifically, since an appropriate amount of dispersion medium remains during the sintering stage, the fluidity of the coating film is increased, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity can be achieved. Furthermore, improved wettability with respect to the bonded parts and an increased contact area enable the formation of a strong bond. This allows for excellent bonding strength and thermal cycle resistance.

[0056] In addition, from the viewpoints of the thermal conductivity, bonding strength, and thermal cycle characteristics described above, the third bonding paste preferably has an M100 value of 10.0 or more and 50.0 or less, an M150 value of 87.0 or more and 95.0 or less, an M200 value of 90.0 or more and 96.0 or less, and an M250 value of 93.0 or more and 98.5 or less. Furthermore, when M650 is taken as 100, the weight loss M300 value at 300°C is preferably 96.0 or more and 99.0 or less, and more preferably 97.0 or more and 98.0 or less.

[0057] In the third bonding paste, as in the first and second bonding pastes, the ratio of M150 to M200 (M150 / M200) is preferably 0.975 or more, more preferably 0.980 or more, and even more preferably 0.985 or more. The ratios of M200 / M250 and M150 / M250 in the third bonding paste are also the same as those in the first and second bonding pastes.

[0058] In addition, the third bonding paste may contain, in addition to the metal particles (A) and the dispersion medium (B), the compound (C), the compound (D), and other additives, but these are the same as in the first and second bonding pastes, so their explanation will be omitted.

[0059] <<Method for Producing the Present Bonding Paste>> The bonding paste according to the present disclosure (e.g., the first to third bonding pastes) only needs to contain at least the metal particles (A) and the dispersion medium (B), and may contain the above-mentioned compounds (C) and (D) and other additives as necessary. The method for producing the present bonding paste is not particularly limited, and known methods can be used. Examples of devices for preparing the bonding paste from materials such as the metal particles (A) and the dispersion medium (B) include a disper, a three-roll mill, a bead mill, an ultrasonic disperser, and a planetary stirrer.

[0060] The content of the metal particles (A) in the bonding paste is preferably 80% by mass to 95% by mass, more preferably 85% by mass to 94% by mass. By including the metal particles (A) in this range, the bonding paste can easily exhibit good printability, easily suppress the residue of the dispersion medium (B) in the bonded body, easily suppress the generation of voids due to the dispersion medium (B), and easily exhibit good bonding strength.

[0061] <<Bonded Body and Method for Manufacturing the Bonded Body>> The present bonding paste can be used to bond a first bonded part and a second bonded part to obtain a bonded body. The bonded body can be manufactured, for example, by the following manufacturing method (I) using pressureless bonding or manufacturing method (II) using pressure bonding. The present bonding pastes both have controlled weight loss during sintering, and can suppress voids in the coating film after sintering and exhibit high thermal conductivity even under pressureless or pressured conditions. Furthermore, the present bonding pastes have excellent bonding strength and can suppress the decrease in bonding strength due to thermal cycling.

[0062] [Manufacturing Method (I)] Manufacturing method (I) is a pressureless joining method, and preferably includes, for example, the following steps (1) to (3): (1) applying the present bonding paste to a first part to be joined; (2) placing a second part to be joined on the first part to be joined that has been applied with the present bonding paste; and (3) sintering the placed laminate in a pressureless environment.

[0063] (1) Application Step The method for applying the present bonding paste to the bonded parts (bonded bodies) is not particularly limited as long as it can be applied uniformly to the members. Examples of the application method include various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, and gravure offset printing, and a discharge method using a dispenser. Because the present bonding paste has excellent fluidity even when it contains a high concentration of metal particles, it is particularly preferable to use it in combination with metal mask printing.

[0064] (2) Placement Step Next, the second part to be joined is placed on the first part to be joined that has been coated with this bonding paste. When this bonding paste is used, the parts can be placed without pressure. In pressure-free joining, this placement step is preferably also performed without pressure, but it is also possible to place the parts while applying pressure. When pressure is applied, the pressure is appropriately set depending on the viscosity of the bonding paste and the drying state of the paste, but is preferably 0.001 to 40 MPa, more preferably 0.003 to 30 MPa.

[0065] (3) Sintering Process The sintering conditions for pressurelessly bonding a laminate in which a second bonded portion is placed on a first bonded portion can be varied as needed, but examples include conditions such as atmospheric pressure, a nitrogen atmosphere, a vacuum, or a reducing atmosphere at 200 to 350°C. Examples of sintering devices include hot air ovens, sintering furnaces, electric furnaces, infrared ovens, reflow ovens, microwave ovens, hot plates, and optical sintering devices. These devices can be used alone or in combination as appropriate. Pressureless sintering conditions are preferably such that the temperature is raised to a set temperature at a rate of 2°C to 30°C / min, and then maintained at a temperature equal to or higher than the set temperature for approximately 10 minutes to 2 hours. The set temperature is preferably 200 to 350°C, more preferably 230 to 300°C, and even more preferably 250 to 280°C.

[0066] (2a) Pre-drying Step In the manufacturing method (I) using pressureless bonding, a pre-drying step (2a) is preferably performed between steps (2) and (3) to remove organic components from the bonding coating film. This pre-drying step is preferable because it can suppress the residual dispersion medium (B), which is one of the causes of defects (voids) in the bonding layer, and improves the density of the bonding layer. Pre-drying can be performed, for example, using a device similar to a baking device at a temperature range of 60 to 220°C for 1 to 300 minutes. Pre-drying is preferably performed at a temperature range of 70 to 100°C for 30 to 120 minutes.

[0067] That is, a particularly preferred manufacturing method (I) includes the following steps: (1) a step of applying a bonding paste to a first part to be joined, (2) a step of placing a second part to be joined on the first part to be joined to which the bonding paste has been applied, (2a) a step of heating the placed laminate to pre-dry it, and (3) a step of sintering the placed laminate in a pressureless environment.

[0068] [Manufacturing Method (II)] Manufacturing method (II) is a method using pressure bonding, and preferably includes, for example, the following steps (10) to (30): (10) A step of applying a bonding paste to a first part to be bonded; (10a) A step of heating and pre-drying the applied laminate; (20) A step of placing a second part to be bonded on the first part to be bonded that has been applied with the bonding paste and pre-dried; and (30) A step of sintering the placed laminate in a pressurized environment.

[0069] (10) Application Step The method for applying the bonding paste to the parts to be bonded can be the same as the method described in the above manufacturing method (I).

[0070] (10a) Pre-drying Step In the manufacturing method (II) using pressure bonding, a pre-drying step (10a) can be performed between steps (10) and (20) to remove organic components from the bonding coating film. By performing the pre-drying step, the residual dispersion medium (B), which is one of the causes of defects (voids) in the bonding layer, can be suppressed, resulting in excellent density in the bonding layer, which is preferable. Pre-drying can be performed, for example, using a device similar to a baking device at a temperature of 60 to 220 ° C for 1 to 300 minutes.

[0071] (20) Placement Step: Next, the second part to be joined is placed on the first part to be joined, which has been coated with and pre-dried with the bonding paste. In the case of pressurized bonding, the placement step may also be performed under pressure. The pressure is appropriately set depending on the viscosity of the bonding paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, more preferably 0.3 to 30 MPa.

[0072] (30) Sintering Step The sintering conditions for pressure-bonding a laminate in which a second bonded portion is placed on a first bonded portion may be changed as appropriate, but examples thereof include conditions such as atmospheric pressure, a nitrogen atmosphere, a vacuum, or a reducing atmosphere at 200 to 350° C. The pressure is set as appropriate depending on the viscosity of the bonding paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, and more preferably 1 to 30 MPa.

[0073] In either manufacturing method, there is no limitation on the thickness of the bonding layer formed when the bonding parts are bonded with the bonding paste, and the thickness of the bonding layer is preferably 3 μm to 500 μm, more preferably 10 μm to 200 μm, and even more preferably 20 μm to 100 μm.

[0074] [Joined Part] The type of each joined part is not particularly limited, and examples thereof include metal materials, semiconductor materials, plastic materials, ceramic materials, and electronic elements. Examples of metals include copper, gold, and aluminum. Examples of semiconductor materials include silicon, germanium, gallium arsenide, gallium phosphide, cadmium sulfide, silicon nitride, graphite, yttrium oxide, magnesium oxide, silicon carbide, and gallium nitride. Examples of plastic materials include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate. Examples of ceramic materials include glass and silicon. Examples of electronic elements include semiconductor elements, LED elements, and power device elements.

[0075] The first and second bonded parts may be the same or different types of components. The surfaces of these bonded parts may be subjected to corona treatment, plating, or other treatments to increase the bond strength of the bonded parts. Because this bonding paste can reduce voids and achieve strong bonding, it can achieve high thermal conductivity, excellent bonding strength, and thermal cycle performance even with substrates that have not been treated with corona treatment, plating, or other treatments (also known as untreated substrates or plateless substrates). For example, this bonding paste is suitable when the first bonded part is an untreated substrate (e.g., an untreated copper substrate). Furthermore, because this bonding paste can reduce voids and achieve strong bonding, it can achieve high thermal conductivity, excellent bonding strength, and thermal cycle performance even with a configuration such as a copper substrate / a bonding layer containing silver particles / a SiC element, which is prone to distortion during thermal cycle testing. For example, this bonding paste is suitable when the second bonded part is SiC.

[0076] The present disclosure will be described in detail below using examples, but the technical scope of the present disclosure is not limited to these examples. Examples X1 to X35 correspond to examples of the bonding paste (first bonding paste) according to the first embodiment, and Examples X36 to X41 correspond to comparative examples of the first bonding paste. Examples Y1 to Y21, Y23, and Y24 correspond to examples of the bonding paste (second bonding paste) according to the second embodiment, and Examples Y22 and 25 to 26 correspond to comparative examples of the second bonding paste. Examples Z1 to Z32 correspond to examples of the bonding paste (third bonding paste) according to the third embodiment, and Examples Z33 to Z40 correspond to comparative examples of the third bonding paste. In the examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively. Numerical values ​​in the tables represent "parts" unless otherwise specified.

[0077] [Weight loss] The weight loss of this bonding paste was measured using a thermogravimetric differential thermal analyzer (TG / DTA8122 (manufactured by RIGAKU Corporation)) by heating 10 mg of a sample in a nitrogen atmosphere from a starting temperature of 30 ° C. to 650 ° C. at a heating rate of 3 ° C. / min. The weight loss at each temperature was determined. When the weight loss at 650 ° C. (M650) was set to 100, the weight loss at 100 ° C. was set to M100, the weight loss at 150 ° C. was set to M150, the weight loss at 200 ° C. was set to M200, the weight loss at 250 ° C. was set to M250, and the weight loss at 300 ° C. was set to M300.

[0078] <<First Bonding Paste>> <Production of Metal Particles> (Production Example X1) Metal Particles A1 200 parts of toluene and 22.3 parts of silver hexanoate were mixed under a nitrogen atmosphere at 25°C while stirring to obtain a 0.5M solution, and then 1.6 parts of diethylaminoethanol and 0.28 parts of oleic acid were added as a dispersant and dissolved. Subsequently, 73.1 parts of a 20% aqueous solution of succinic acid dihydrazide (hereinafter referred to as SUDH) was added dropwise as a reducing agent, causing the liquid color to change from pale yellow to dark brown. To further promote the reaction, the temperature was raised to 40°C, and the reaction was allowed to proceed. After allowing to stand and separating, the aqueous phase was removed to remove excess reducing agent and impurities. Distilled water was added to the toluene layer several times, followed by repeated washing and separation. This process of adding toluene, centrifuging, and removing the supernatant was repeated twice. The precipitate was dried to obtain metal particles A1, corresponding to metal particles (a1), in which silver particles were coated with hexanoic acid and oleic acid. The average particle size of the metal particles A1 was determined by the method described below, and d50 was found to be 210 nm.

[0079] (Production Example X2) Metal Particles A2 Metal particles A2 corresponding to metal particles (a1) were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 1.8 parts and the amount of oleic acid was 0.31 parts. The d50 was 185 nm.

[0080] (Production Example X3) Metal Particles A3 Metal particles A3 corresponding to metal particles (a1) were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 1.2 parts and the amount of oleic acid was 0.18 parts. The d50 was 290 nm.

[0081] (Production Example X4) Metal Particles A4 Metal particles A4 corresponding to metal particles (a1) were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 1.0 part and the amount of oleic acid was 0.14 part. d50 was 390 nm.

[0082] (Production Example X5) Metal Particles A5 Metal particles A5 corresponding to metal particles (a1) were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 2.4 parts and the amount of oleic acid was 0.42 parts. The d50 was 120 nm.

[0083] (Production Example X6) Metal Particles A6 Metal particles A6 corresponding to metal particles (a1) were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 0.7 parts and the amount of oleic acid was 0.12 parts. The d50 was 450 nm.

[0084] (Production Example X7) Metal Particles A7 Metal particles A7, which are copper particles corresponding to metal particles (a1), were obtained in the same manner as in Production Example X1, except that the silver hexanoate was changed to 17.0 parts of copper pentanoate, the amount of diethylaminoethanol was 1.8 parts, and the amount of oleic acid was 0.45 parts. The d50 was 150 nm.

[0085] (Production Example X8) Metal Particles A10 Metal particles A10 were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 2.1 parts and the amount of oleic acid was 0.71 parts. d50 was 85 nm.

[0086] (Production Example X9) Metal Particles A11 Metal particles A11 were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 1.4 parts and the amount of oleic acid was 0.09 parts. d50 was 600 nm.

[0087] (Production Example X10) Metal Particles A12 Metal particles A12 were obtained in the same manner as in Production Example X1, except that the amount of diethylaminoethanol was 0.6 parts and the amount of oleic acid was 0.07 parts. The d50 was 1100 nm.

[0088] [Method for measuring the average particle size of metal particles] Isopropyl alcohol was added to each metal particle and dispersed using an ultrasonic disperser to obtain a 0.5% by mass dispersion. The particle size of the metal particles in the obtained dispersion was measured using Nanotrac UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.) to determine the average particle size (d50). Of the metal particles produced by the above method, metal particles A1-A7 correspond to the metal particles (a1) of the present disclosure, and metal particles A10-A12 correspond to metal particles other than the metal particles (a1).

[0089] <Dispersion medium (B)> The following materials were used as dispersion medium (B). The manufacturer's name, supplementary information, and boiling point are listed in parentheses. Dispersion medium B1: triethylene glycol monobutyl ether (glycol ether type, containing hydroxyl groups, boiling point 278°C) Dispersion medium B2: Tersolve TOE-100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol) (trade name, manufactured by Nippon Terpene Chemical Co., Ltd., terpene type, containing hydroxyl groups, boiling point 268°C) Dispersion medium B3: 1,6-diacetoxyhexane (manufactured by Tokyo Chemical Industry Co., Ltd., no hydroxyl groups, boiling point 260°C) Dispersion medium B4: dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd., terpene type, containing hydroxyl groups, boiling point 210°C) Dispersion medium B5: diethylene glycol monomethyl ether (glycol ether type, containing hydroxyl groups, boiling point 193°C) Dispersion medium B6: Tersolve MTPH (isobornylcyclohexanol) (trade name, manufactured by Nippon Terpene Chemical Co., Ltd., terpene type, containing hydroxyl groups, boiling point 308°C) Dispersion medium B7: Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate) (manufactured by Tokyo Chemical Industry Co., Ltd., containing hydroxyl groups, boiling point 255°C) Dispersion medium B8: Dipropylene glycol methyl ether acetate (manufactured by Sigma-Aldrich, glycol ether type, no hydroxyl groups, boiling point 209°C) Dispersion medium B9: 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd., containing hydroxyl groups, boiling point 244°C)

[0090] <Compound (C)> The following materials were used as compound (C). Compound C1: Pripol 2033 (trade name, manufactured by Croda Japan Co., Ltd.; a dimer diol having 36 carbon atoms, consisting of two hydroxyl groups and a divalent hydrocarbon group having a branched and cyclic structure; liquid form) Compound C2: Priamine 1071 (trade name, manufactured by Croda Japan Co., Ltd.; a mixture of a dimer diamine having 36 carbon atoms (consisting of two amino groups and a divalent hydrocarbon group having a branched and cyclic structure; liquid form) and a trimer triamine having 54 carbon atoms (consisting of three amino groups and a trivalent hydrocarbon group having a branched and cyclic structure; liquid form)) Compound C3: Pripol 1009 (trade name, manufactured by Croda Japan Co., Ltd.; a hydrogenated dimer acid having 36 carbon atoms, consisting of two carboxy groups and a divalent hydrocarbon group having a branched and cyclic structure; liquid form at 25°C) Compound C4: Pripol 1040 (trade name, manufactured by Croda Japan Co., Ltd., a trimer acid having 54 carbon atoms, consisting of three carboxy groups and a trivalent hydrocarbon group having a branched and cyclic structure, liquid at 25°C)

[0091] <Compound (D)> Compound D1: Alkanolamine (number of hydroxyl groups: 4, number of tertiary nitrogen atoms: 2)

[0092] <Production of First Bonding Paste> [Example X1] Metal particles A1 (88 parts) and triethylene glycol monobutyl ether (12 parts) were mixed using a planetary stirrer to prepare a bonding paste.

[0093] [Examples X2 to X41] Bonding pastes were obtained in the same manner as in Example X1, except that the types and amounts (parts) of materials were changed according to the compositions shown in Tables 1 to 3. In the tables, blank spaces indicate that no material was blended.

[0094] <Evaluation of Bonding Paste> Bonded bodies were produced using the obtained bonding pastes by the production methods described in Tables 1 to 3. Note that Examples X1 to X27, X30 to X33, and X36 to X41 used the following Production Method 1, Example X28 used the following Production Method 2, and Examples X29, X34, and X35 used the following Production Method 3. Details of the production methods and printing conditions for the bonding pastes are as follows. [Printing Conditions (Metal Mask Printing)] Metal mask: opening 7.5 mm square, plate thickness 100 μm (manufactured by Ceria Corporation) Metal squeegee: 40 mm x 250 mm, thickness 1 mm (manufactured by Ceria Corporation)

[0095] [Manufacturing Method 1] After printing the bonding paste once on a first bonded portion (copper substrate (plating-free): 20 mm × 20 mm × 3 mm) under the above printing conditions, a second bonded portion (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed with the plated surface facing the bonding paste surface, and pressureless bonding was performed under the following sintering condition 1 to obtain a bonded body. [Sintering Condition 1] The laminate placed in a sintering furnace with a nitrogen atmosphere was placed, and the temperature was increased from 25°C to 80°C at a rate of 5°C / min, and pre-dried at 80°C for 90 minutes. Thereafter, the temperature was increased to 300°C at a rate of 8°C / min, and after reaching 300°C, it was held at 300°C for 2 hours.

[0096] [Manufacturing method 2] After printing the bonding paste once on a first bonded part (copper substrate (plating-free): 20 mm × 20 mm × 3 mm) under the above printing conditions, a second bonded part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed with the plated surface facing the bonding paste surface, and pressureless bonding was performed under the following sintering conditions to obtain a bonded body. [Sintering condition 2] The laminated body placed in a sintering furnace in a nitrogen atmosphere was placed, and the temperature was raised from 25°C to 300°C at a rate of 8°C / min. After reaching 300°C, it was held at 300°C for 2 hours.

[0097] [Manufacturing Method 3] The bonding paste was printed once on a first bonded part (copper substrate (plating-free): 20 mm × 20 mm × 3 mm) under the above printing conditions, and then placed in a hot air oven and pre-dried at 180°C for 10 minutes. Next, the second bonded part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed with the plated surface facing the pre-dried bonding paste surface, and pressure-bonded under the following sintering condition 3 to obtain a bonded body. [Sintering Condition 3] In a nitrogen atmosphere, the second bonded part was pressurized at a pressure of 30 MPa from above, while the temperature was raised from room temperature to 300°C at a rate of 20°C / min. After reaching 300°C, the temperature was maintained at that temperature for 5 minutes.

[0098] The resulting bonded bodies were evaluated for bonding strength and thermal cycle properties. Furthermore, thermal conductivity was evaluated under the conditions described below. The results are shown in Tables 1 to 3.

[0099] [Bonding strength] The bonded body was fixed at the location of the first bonded portion, and pushed from the interface between the first bonded portion and the bonding layer toward the second bonded portion at a height of 100 μm at a speed of 500 μm / s, and the bonding strength (die shear strength) at which the bond was broken was determined and evaluated based on the following evaluation criteria. The higher the die shear strength value, the better, and 5 MPa or more is within the practical range. The measurement conditions are as follows. [Measurement conditions] Measurement device: Universal bond tester (4000 series, manufactured by Daisi Japan Co., Ltd.) Measurement height: 100 μm Measurement speed: 500 μm / s

[0100] (Evaluation criteria) S: Die shear strength is 35 MPa or more A: Die shear strength is 25 MPa or more and less than 35 MPa B: Die shear strength is 15 MPa or more and less than 25 MPa C: Die shear strength is 10 MPa or more and less than 15 MPa D: Die shear strength is 5 MPa or more and less than 10 MPa E: Die shear strength is less than 5 MPa

[0101] [Cold-heat cycle characteristics] The bonded body was subjected to the following cycle test, and the bond strength (die shear strength) of the bonded body after the cycle test was determined and evaluated in the same manner as in the above-mentioned [Bonding strength]. A practical range is 5 MPa or more. [Cycle test] The bonded body was stored for 500 cycles, with one cycle consisting of holding it at -40°C for 30 minutes and then at 150°C for 30 minutes.

[0102] [Thermal Conductivity] The thermal conductivity was calculated from the thermal diffusivity, specific heat, and density according to the following formula: Thermal conductivity (W / m·K) = Density (g / cm ３ ) x specific heat (J / kg K) x thermal diffusivity (mm ２ / s) The thermal diffusivity was determined as follows. The bonding paste was printed once on a first bonded portion (copper substrate (plating-free): 20 mm × 20 mm × 3 mm) using a metal mask (opening 20 mm square, plate thickness 200 μm) and a metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by Ceria Corporation). Then, a second bonded portion (copper substrate (plating-free): 20 mm × 20 mm × 3 mm) was placed on top. The laminate was then placed in a firing furnace with a nitrogen atmosphere, heated from 25 ° C to 300 ° C at a rate of 8 ° C / min, and maintained at 300 ° C for 2 hours to obtain a bonded body. The resulting bonded body was coated with carbon using a carbon spray. The thermal diffusivity was then measured using a xenon flash analyzer LFA447 Nano Flash (trade name, manufactured by NETZSCH). The larger the thermal conductivity value, the better, and a value of 60 W / (m·K) or more is within the practical range.

[0103] (Evaluation criteria) S: 250W / (m.K) or more A: 200W / (m.K) or more but less than 250W / (m.K) B: 150W / (m.K) or more but less than 200W / (m.K) C: 80W / (m.K) or more but less than 150W / (m.K) D: 60W / (m.K) or more but less than 80W / (m.K) E: Less than 60W / (m.K)

[0104]

[0105]

[0106]

[0107] According to the results in Tables 1 to 3, when the first bonding paste was used, the thermal conductivity and bonding strength were very high, even in a configuration in which stable bonding is extremely difficult, such as a pressureless, non-plated substrate and a large-area SiC element, and a decrease in bonding strength was suppressed even after a thermal cycle test was performed. In particular, a bonding paste having an M150 / M200 value of 0.975 or more, a bonding paste having a dispersion medium (b1) with a boiling point of 250 to 300 ° C. inclusive of 50% by mass or more, a bonding paste in which the dispersion medium (b1) contains at least one selected from the group consisting of terpenes and glycol ethers, a bonding paste having a content of dispersion medium (b2) with a boiling point exceeding 300 ° C. of 10% by mass or less, and a bonding paste having a dispersion medium (B) with a content of 90% by mass or more based on the total mass of the dispersion medium (B). Even under pressure-free conditions, voids in the coating film after sintering are suppressed, high thermal conductivity is exhibited, excellent bonding strength, and a decrease in bonding strength due to thermal cycling is suppressed (for example, see Examples X1 and X7, X7 and X17, X2 and X6, X1 and X13, and X2 and X6). On the other hand, when the bonding pastes of Examples X36 to X41 were used, the thermal conductivity and bonding strength were significantly low, and the bonding strength after the thermal cycle test also decreased significantly.

[0108] <<Second Bonding Paste>> <Production of Metal Particles> (Production Example Y1) Metal Particles A21 200 parts of toluene and 22.3 parts of silver hexanoate were mixed under a nitrogen atmosphere at 25°C while stirring to obtain a 0.5M solution, and then 1.4 parts of diethylaminoethanol and 0.09 parts of oleic acid were added as a dispersant and dissolved. Then, 73.1 parts of a 20% aqueous solution of succinic acid dihydrazide (hereinafter referred to as SUDH) was added dropwise as a reducing agent, causing the liquid color to change from pale yellow to dark brown. To further promote the reaction, the temperature was raised to 40°C, and the reaction was allowed to proceed. After allowing to stand and separating, the aqueous phase was removed to remove excess reducing agent and impurities. Distilled water was added to the toluene layer several times, followed by repeated washing and separation. This process of adding toluene, centrifuging, and removing the supernatant was repeated twice. The precipitate was dried to obtain metal particles A21, corresponding to metal particles (a2), in which silver particles were coated with hexanoic acid and oleic acid. The particle size of the metal particles A21 was determined by the method described below, and d50 was 600 nm.

[0109] (Production Example Y2) Metal Particles A22 Metal particles A22 were obtained in the same manner as in Production Example Y1, except that the amount of diethylaminoethanol was 0.6 parts and the amount of oleic acid was 0.070 parts. The d50 was 1.1 μm.

[0110] (Production Example Y3) Metal Particles A26 Metal particles A26 were obtained in the same manner as in Production Example Y1, except that the silver hexanoate was replaced with 17.0 parts of copper pentanoate, the amount of diethylaminoethanol was 1.0 part, and the amount of oleic acid was 0.12 part. The d50 was 650 nm.

[0111] (Production Example Y4) Metal Particles A30 Metal particles A30 were obtained in the same manner as in Production Example Y1, except that the amount of diethylaminoethanol was 1.6 parts and the amount of oleic acid was 0.29 parts. The d50 was 210 nm.

[0112] (Production Example Y5) Metal Particles A31 Metal particles A31 were obtained in the same manner as in Production Example Y1, except that the amount of diethylaminoethanol was 1.0 part and the amount of oleic acid was 0.14 part. The d50 was 390 nm.

[0113] In addition, the following metal particles were used: A23: Silver powder Silcoat AgC-A (average particle size 3.5 μm), manufactured by Fukuda Metal Foil & Powder Industrial Co., Ltd. A24: Silver powder Silcoat AgC-74T (average particle size 6.2 μm), manufactured by Fukuda Metal Foil & Powder Industrial Co., Ltd. A25: Silver Silcoat AgC-224 (average particle size 9.0 μm), manufactured by Fukuda Metal Foil & Powder Industrial Co., Ltd.

[0114] [Method for measuring the average particle size of metal particles] Isopropyl alcohol was added to each metal particle and dispersed using an ultrasonic disperser to obtain a 0.5% by mass dispersion. The particle size of the metal particles in the obtained dispersion was measured using Nanotrac UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.) to determine the average particle size (d50). Of the metal particles produced by the above method, metal particles A21-A26 correspond to the metal particles (a2) of the present disclosure, and metal particles A30 and A31 correspond to metal particles other than the metal particles (a2).

[0115] <Dispersion Medium (B)> The material described in the first bonding paste was used as the dispersion medium (B).

[0116] <Compound (C)> As the compound (C), the material described in the first bonding paste was used.

[0117] <Compound (D)> As the compound (D), the material described in the first bonding paste was used.

[0118] <Production of Bonding Paste> [Example Y1] Metal particles A21 (90 parts) and triethylene glycol monobutyl ether (10 parts) were mixed using a planetary stirrer to prepare a bonding paste.

[0119] [Examples Y2 to Y26] Bonding pastes were obtained in the same manner as in Example Y1, except that the types and amounts (parts) of materials were changed according to the compositions shown in Tables 4 to 6. In the tables, blank spaces indicate that no material was added.

[0120] <Evaluation of Bonding Paste> A bonded body was produced using the obtained bonding paste by the following manufacturing method. Details of the manufacturing method and printing conditions for the bonding paste are as follows. [Printing Conditions (Metal Mask Printing)] Metal mask: opening 7.5 mm square, plate thickness 100 μm (manufactured by Ceria Corporation) Metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by Ceria Corporation)

[0121] [Manufacturing Method] The bonding paste was printed once on a first bonded part (copper substrate (plating-free): 20 mm × 20 mm × 3 mm) under the above printing conditions, and then placed in a hot air oven and pre-dried at 150°C for 2 minutes. Next, the second bonded part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed with the plated surface facing the pre-dried bonding paste surface, and pressure-bonded under the following sintering conditions to obtain a bonded body. [Sintering Conditions] In a nitrogen atmosphere, the second bonded part was pressurized at a pressure of 30 MPa from above, while the temperature was raised from room temperature to 300°C at a rate of 20°C / min. After reaching 300°C, the temperature was maintained at that temperature for 5 minutes.

[0122] The resulting bonded bodies were evaluated for bonding strength, thermal cycle characteristics, and thermal conductivity using the same evaluation methods as those used for the first bonding paste. The results are shown in Tables 4 to 6.

[0123]

[0124]

[0125]

[0126] According to the results in Tables 4 to 6, when the second bonding paste is used, even in configurations where stable bonding is extremely difficult, such as between a non-plated substrate and a large-area SiC element, under pressurized conditions, the thermal conductivity and bonding strength are very high, and the decrease in bonding strength is suppressed even after performing a thermal cycling test. In particular, bonding pastes having an M150 / M200 value of 0.975 or more, bonding pastes containing at least one dispersion medium (b1) selected from the group consisting of terpenes and glycol ethers, bonding pastes containing 10% or less by mass of a dispersion medium (b2) having a boiling point exceeding 300 ° C, and bonding pastes containing 90% or more by mass of a dispersion medium having a hydroxyl group, based on the total mass of the dispersion medium (B), suppress voids in the coating film after sintering, exhibit high thermal conductivity, excellent bonding strength, and suppress the decrease in bonding strength due to thermal cycling (see, for example, Examples Y6 and Y12, Examples Y5 and Y7, and Examples Y1 and Y11).

[0127] <<Third Bonding Paste>> <Production of Metal Particles> Metal particles A1 to A7 and A10 to A12 were produced according to the method described for the first bonding paste.

[0128] <Dispersion Medium (B)> As the dispersion media B1 to B6, the same ones used in the first bonding paste were used.

[0129] <Compound (C)> Compounds C1 to C4 were the same as those used in the first bonding paste.

[0130] <Compound (D)> As the compound D1, the same compound as used in the first bonding paste was used.

[0131] <Production of Bonding Paste> [Example Z1] Metal particles A1 (88 parts) and triethylene glycol monobutyl ether (12 parts) were mixed using a planetary stirrer to prepare a bonding paste.

[0132] [Examples Z2 to Z40] Joining pastes were obtained in the same manner as in Example Z1, except that the types and amounts (parts) of materials were changed according to the compositions shown in Tables 7 to 9. In the tables, blank spaces indicate that no material was added.

[0133] <Evaluation of Bonding Paste> Using the obtained bonding paste, bonded bodies were produced by the production methods described in Tables 7 to 9. Note that for Examples Z1 to Z30 and Examples Z33 to Z40, the first bonding paste was used according to Production Method 1 described above, for Example Z31 according to Production Method 2 described above, and for Example Z32 according to Production Method 3 described above.

[0134]

[0135]

[0136]

[0137] According to the results in Tables 7 to 9, when the third bonding paste was used, the thermal conductivity and bonding strength were very high, even in a configuration in which stable bonding is extremely difficult, such as a non-plated substrate and a large-area SiC element, both under no pressure and under pressure, and a decrease in bonding strength was suppressed even after a thermal cycling test was performed.

[0138] This application claims priority based on Japanese Patent Application Nos. 2023-221137, filed December 27, 2023, 2023-221138, filed December 27, 2023, and 2023-221139, filed December 27, 2023, the disclosures of which are incorporated herein in their entireties.

Claims

1. A paste for bonding containing metal particles (A) and a dispersion medium (B), when the temperature of the paste for bonding is raised from 30°C at a heating rate of 3°C / min, and when the weight loss M650 at 650°C measured by a thermogravimetric differential thermal analyzer is taken as 100, the weight loss M200 at 200°C is 88.0 or more and 98.0 or less, and the paste for bonding satisfying at least one of the following conditions (1) and (2): (1) The metal particles (A) contain metal particles (a) having an average particle diameter of 100 nm or more and 10 µm or less, in an amount of 50% by mass or more based on the total mass of the metal particles (A). (2) When the temperature of the paste for bonding is raised from 30°C at a heating rate of 3°C / min, and when the weight loss M650 at 650°C measured by a thermogravimetric differential thermal analyzer is taken as 100, the weight loss M100 at 100°C is 10.0 or more and 70.0 or less, the weight loss M150 at 150°C is 85.0 or more and 96.0 or less, and the weight loss M250 at 250°C is 93.0 or more and 99.5 or less.

2. The paste for bonding according to claim 1, satisfying the condition of (1) and having an average particle diameter of the metal particles (a) of 100 nm or more and 500 nm or less.

3. The paste for bonding according to claim 1, satisfying the condition of (1) and having an average particle diameter of the metal particles (a) of more than 500 nm and 10 µm or less.

4. The paste for bonding according to claim 3, wherein the dispersion medium (B) contains a dispersion medium (b1) having a boiling point of 250°C or more and 300°C or less, and the content of the dispersion medium (b1) is 55% by mass or more based on the total mass of the dispersion medium (B).

5. The paste for bonding according to any one of claims 1 to 4, wherein the ratio (M150 / M200) of the weight loss M150 to the weight loss M200 when the weight loss M650 is taken as 100 is 0.975 or more.

6. The paste for bonding according to any one of claims 1, 2, and 5, wherein the dispersion medium (B) contains a dispersion medium (b1) having a boiling point of 250°C or more and 300°C or less, and the content of the dispersion medium (b1) is 50% by mass or more based on the total mass of the dispersion medium (B).

7. The paste for bonding according to claim 4 or 6, wherein the dispersion medium (b1) contains at least one selected from the group consisting of terpene-based and glycol ether-based.

8. The paste for bonding according to any one of claims 1 to 7, wherein the content of the dispersion medium (b2) having a boiling point exceeding 300°C in the dispersion medium (B) is 20% by mass or less based on the total mass of the dispersion medium (B).

9. The paste for bonding according to claim 8, wherein the content of the dispersion medium (b2) is 10% by mass or less based on the total mass of the dispersion medium (B).

10. The paste for bonding according to any one of claims 1 to 9, wherein the dispersion medium (B) contains a dispersion medium having a hydroxyl group, and the content of the dispersion medium having a hydroxyl group is 90% by mass or more based on the total mass of the dispersion medium (B).

11. The paste for bonding according to any one of claims 1 to 10, wherein the metal particles (A) contain at least one metal selected from the group consisting of silver, copper, an alloy containing silver, silver oxide, and copper oxide.

12. A bonded body in which a first bonded portion and a second bonded portion are bonded by the paste for bonding according to any one of claims 1 to 11.

13. The bonded body according to claim 12, wherein the first bonded portion is an untreated base material.

14. The bonded body according to claim 12 or 13, wherein the second bonded portion is SiC.

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