Bonding paste, bonded body, and method for producing bonded body

Abstract

Provided are: a bonding paste which uses silver particles, has excellent bonding strength, suppresses a decrease in bonding strength accompanying thermal and cold cycles, and enables non-pressure bonding; a bonded body which uses the bonding paste; and a method for producing the bonded body. The problem is solved by a bonding paste containing: (A) silver particles having an average particle diameter of 100 nm to 500 nm; a compound (B) having at least one nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms, and having 4 or more hydroxyl groups; and a dispersion medium (C), a bonded body using the bonding paste, and a method for producing the bonded body.

Description

Technical Field

[0001] The present disclosure relates to a bonding paste, a bonded body, and a method for manufacturing a bonded body. Background Art

[0002] Conventionally, solder has been used as a bonding material for bonding metal members to each other, a metal member to a semiconductor element, a metal member to a light emitting diode (LED) element, and the like. In recent years, in the technical field of next-generation power electronics, devices such as SiC that can operate at high temperatures have been demanded. As a bonding material for manufacturing such devices, from the viewpoint of high-temperature driving reliability, a substitute material for solder is required. For example, as shown in Patent Documents 1 to 3, a bonding paste and other bonding materials using sinterable metal particles have been proposed.

[0003] Patent Document 1 discloses a bonding material including amine-coated metal nanoparticles and an amine that is a linear alkylamine or alkanolamine. Patent Document 2 discloses a technique of using a conductive adhesive including silver particles having an average particle size of 20 nm to 500 nm, alkanolamines, and a solvent as a bonding material. Patent Document 3 discloses a bonding composition including copper powder, a liquid medium, and a reducing agent, and the reducing agent has at least one amino group and a plurality of hydroxyl groups.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-214357

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2022-117824

[0008] Patent Document 3: International Publication No. 2020-032161 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] As bonding processes using such bonding materials, there are a method performed without pressure (hereinafter referred to as pressureless bonding) and a method performed under pressure (hereinafter referred to as pressure bonding). Pressure bonding is effective in reducing voids and suppressing cracks starting from voids, and thus has the advantages of excellent bonding strength and thermal cycle characteristics. However, pressure bonding requires dedicated equipment, and furthermore, the object to be bonded must be able to withstand the pressurized environment, and the bonding object or application is limited. Therefore, it is required to reduce voids, improve the bonding strength, and improve the thermal cycle characteristics in pressureless bonding.

[0011] On the other hand, in recent years, the large-areaization of semiconductor elements has been continuously developing. However, it is known that the larger the area of the element, the more difficult it is for gases and the like inside to escape, and there is a tendency to easily generate voids. In addition, the difference in the coefficient of linear expansion between Si or SiC elements and that of silver particles and copper used as a base material is very large. During thermal cycling, strain is generated between the copper base material / silver particle-containing bonding layer / Si element layers, and there is a tendency for cracks to occur and the thermal cycling characteristics to easily deteriorate. Furthermore, although the SiC element has a coefficient of linear expansion similar to that of the Si element, due to its higher hardness compared to the Si element, the strain during thermal cycling is larger than that of the Si element, and there is a tendency for cracks to easily occur in the bonding layer. That is, in recent years, the requirements for improving the bonding strength and thermal cycling characteristics of SiC semiconductor elements have been increasing.

[0012] However, the invention described in Patent Document 1 uses a bonding material containing silver particles and alkanolamines such as triethanolamine to perform pressure bonding on a small-area copper element, and thus cannot solve the problems of the bonding strength and thermal cycling characteristics of a large-area SiC element without pressure bonding. In addition, the invention described in Patent Document 2 uses a bonding material containing silver particles and alkanolamines such as diethanolamine to perform non-pressure bonding on a small-area Si element, and thus cannot solve the problems of the bonding strength and thermal cycling characteristics of a large-area SiC element. Furthermore, the invention described in Patent Document 3 uses a bonding material containing copper particles and alkanolamine to perform pressure bonding on a small-area copper element. However, compared with silver particles, copper particles are easily oxidized, and if oxidized, the functions of copper particles cannot be exhibited, so there are problems in processing. In particular, in bonding applications where heating is performed to about 200 °C or higher, if there is a trace amount of oxygen during the heating process, oxidation will occur, so it is difficult to suppress oxidation, and the problems of the bonding strength and thermal cycling characteristics of a large-area SiC element without pressure bonding cannot be solved. In addition, the use of silver particles is not described in Patent Document 3.

[0013] Therefore, the problem to be solved by the present disclosure is to provide a bonding paste and a bonded body using the bonding paste, the bonding paste uses silver particles, has excellent bonding strength, suppresses the decrease in bonding strength accompanying thermal cycling, and can perform bonding even without pressure.

[0014] Technical means for solving the problem

[0015] The inventors of the present invention have repeatedly conducted in-depth research to solve the above problems, and as a result, the present disclosure has been completed.

[0016] One embodiment of the bonding paste of the present disclosure is characterized by containing: silver particles (A) with an average particle size of 100 nm to 500 nm; a compound (B) having at least one nitrogen atom selected from the group consisting of a secondary nitrogen atom and a tertiary nitrogen atom, and having 4 or more hydroxyl groups; and a dispersion medium (C).

[0017] One embodiment of the bonding paste of the present disclosure is characterized in that when the sintering temperature of the silver particles (A) is set to T1 °C, the 50% weight loss temperature of the compound (B) is set to T2 °C, and the 50% weight loss temperature of the dispersion medium (C) is set to T3 °C, T3 < T1 < (T2 + 10) is satisfied.

[0018] One embodiment of the bonding paste of the present disclosure is characterized in that T2 is 200 °C to 300 °C.

[0019] One embodiment of the bonding paste of the present disclosure is characterized in that the compound (B) has a tertiary nitrogen atom.

[0020] One embodiment of the bonding paste of the present disclosure is characterized in that the number of tertiary nitrogen atoms in the compound (B) is 1 to 3.

[0021] One embodiment of the bonding paste of the present disclosure is characterized in that the number of hydroxyl groups in the compound (B) is 4 to 6.

[0022] One embodiment of the bonding paste of the present disclosure is characterized in that the compound (B) is liquid at 25 °C.

[0023] One embodiment of the bonding paste of the present disclosure is characterized in that based on the mass of the silver particles (A), the content of the compound (B) is 0.05% by mass to 1.0% by mass.

[0024] One embodiment of the bonding paste of the present disclosure is characterized in that the average particle size of the silver particles (A) is 150 nm to 400 nm.

[0025] One embodiment of the bonding paste of the present disclosure is characterized in that the boiling point of the dispersion medium (C) is 250 °C or higher.

[0026] One embodiment of the bonding paste of the present disclosure is characterized by further containing a compound (D) having 20 to 80 carbon atoms and having two or more functional groups selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group.

[0027] One embodiment of the bonding paste of the present disclosure is characterized by further containing a compound (E) having 14 to 20 carbon atoms and having one carboxyl group.

[0028] One aspect of the bonding paste of the present disclosure is characterized in that, based on the mass of the bonding paste, the content of the silver particles (A) is 80% by mass to 95% by mass.

[0029] One aspect of the bonded body of the present disclosure is characterized in that the first bonded portion and the second bonded portion are bonded by the bonding paste.

[0030] One aspect of the bonded body of the present disclosure is characterized in that the first bonded portion is an unplated substrate.

[0031] One aspect of the bonded body of the present disclosure is characterized in that the second bonded portion is SiC.

[0032] A method for manufacturing a bonded body according to one aspect of the present disclosure is a method for manufacturing a bonded body in which a first bonded portion and a second bonded portion are bonded by the bonding paste, and is characterized by including the following steps.

[0033] (1) A step of applying the bonding paste to the first bonded body.

[0034] (2) A step of placing the second bonded portion on the coated portion of the first bonded portion coated with the bonding paste.

[0035] (2a) A step of heating the stacked body after placement for pre-drying.

[0036] (3) A step of sintering the stacked body after placement in a non-pressurized environment.

[0037] Effects of the Invention

[0038] According to the present invention, there can be provided a bonding paste and a bonded body using the bonding paste. The bonding paste uses silver particles, and the bonding strength of the bonded portion is high, the decrease in bonding strength accompanying thermal cycling is suppressed, and bonding can be performed even without pressure. Thus, even in the case of bonding a large SiC element without pressure, excellent bonding strength and thermal cycling characteristics can be exhibited. Detailed Embodiments

[0039] In the present specification, "silver particles (A) having an average particle size of 100 nm to 500 nm" may sometimes be abbreviated as "silver particles (A)", and "compound (B) having at least one nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms and having 4 or more hydroxyl groups" may be abbreviated as "compound (B)".

[0040] The bonding paste of the present disclosure is characterized by containing: silver particles (A) with an average particle size of 100 nm to 500 nm; a compound (B) having at least one nitrogen atom selected from the group consisting of a secondary nitrogen atom and a tertiary nitrogen atom and having 4 or more hydroxyl groups; and a dispersion medium (C).

[0041] By combining the silver particles (A) with the compound (B) having a specified structure, the bonding paste of the present disclosure utilizes the high non-volatility of the compound (B) to improve the wettability to the substrate at the sintering stage of the silver particles (A) having a specified particle size, and suppress the generation of voids and holes in the coating film, and form a dense coating film even without pressure bonding.

[0042] Furthermore, in the case where the joined part is a substrate that has not been subjected to a plating treatment such as unplated copper (unplated substrate), due to the heating during sintering, the surface of the unplated substrate is oxidized to form an oxide. Therefore, the bonding between the silver particles and the unplated substrate covered with the oxide becomes insufficient, and there is a tendency for the bonding strength to decrease or the thermal cycle characteristics to deteriorate. However, by including the compound (B), the reduction function of the compound (B) is utilized to suppress the oxidation of the surface of the unplated substrate and / or the reduction of the oxide, and a firm bond can be achieved between the silver particles (A) and the unplated substrate. Therefore, not only an improvement in bonding strength or good thermal cycle characteristics can be obtained, but also operations such as subjecting the substrate to a plating treatment or pre-cleaning the substrate can be omitted.

[0043] As described above, even in the case of pressureless bonding and in the bonding of joined parts that are difficult to stably bond such as unplated substrates and large-area SiC semiconductor elements, the generation of holes can be suppressed, and excellent bonding strength and bonding strength after thermal cycling can be exhibited.

[0044] <Silver particles (A)>

[0045] The silver particles (A) exhibit the conductivity and thermal conductivity of the joined body, and play a role in joining the joined body during the sintering process, and also include alloys containing silver, silver oxide, and silver-coated particles having a metal (excluding silver) as a core and silver coating its surface. By using the silver particles (A), a joined body with excellent strength can be obtained. In addition, a wide range of calcination temperatures can be accommodated, and various calcination environments such as under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere can also be accommodated.

[0046] The silver particles (A) have the following function due to the average particle size being in the range of 100 nm to 500 nm, that is, the function of melting or bonding (hereinafter also referred to as sintering) with each other within the temperature range of 200 °C to 350 °C for heating and sintering the bonding paste, so that they can be transformed into a massive metal. As a result, the bonding of the objects to be bonded is completed. Hereinafter, the portion existing between the objects to be bonded and formed by sintering of the silver particles (A) is referred to as the bonding layer.

[0047] In the present disclosure, it is important to use silver particles (A) having a specific average particle size. The so-called "average particle size" in this specification refers to the volume-based 50% cumulative particle size distribution diameter (d50) obtained by the measurement method described in the examples. The d50 of the silver particles (A) is 100 nm to 500 nm, preferably 150 nm or more, more preferably 180 nm or more, and still more preferably 200 nm or more. In addition, the d50 of the silver particles (A) is preferably 450 nm or less, more preferably 400 nm or less, still more preferably 350 nm or less, and particularly preferably 300 nm or less.

[0048] The silver particles (A) are preferably coated on the surface with the organic component (a). That is, the silver particles (A) are preferably particles in which the surface of the silver particles is coated with the organic component (a), and the coated organic component (a) is also referred to as a protective agent. If coated with the organic component (a), an increase in the storage stability of the bonding paste can be expected. Examples of the organic component (a) include fatty acids, aliphatic amines, aliphatic alcohols, etc., preferably saturated or unsaturated fatty acids, more preferably saturated or unsaturated fatty acids having 3 to 18 carbon atoms, and still more preferably saturated or unsaturated fatty acids having 6 to 18 carbon atoms. The organic component (a) may contain one or more than two kinds.

[0049] The silver particles (A) can be used alone or in combination of multiple kinds. In addition, if necessary, metal particles other than the silver particles (A) can also be used in combination. When using metal particles other than the silver particles (A) in combination, metal particles having a particle size with an average particle size exceeding 500 nm can be combined, or metal particles having a particle size with an average particle size exceeding 1000 nm can be combined.

[0050] <Compound (B)>

[0051] The bonding paste of the present disclosure contains a compound (B) having at least one nitrogen atom selected from the group consisting of a secondary nitrogen atom and a tertiary nitrogen atom and having 4 or more hydroxyl groups.

[0052] Compound (B) functions to uniformly disperse silver particles (A), inhibits the aggregation of silver particles (A) over time, and can thus achieve good viscosity characteristics and coatability. Specifically, the function of reducing silver particles (A) or the joint portion of secondary nitrogen atoms and tertiary nitrogen atoms is excellent. In addition, since the binding property of secondary nitrogen atoms and tertiary nitrogen atoms with silver particles (A) is excellent, the dispersibility is improved. In particular, since the tertiary nitrogen atom has a branched structure, the dispersibility is excellent due to the steric effect.

[0053] In addition, since the function of reducing silver particles (A) or the joint portion of secondary nitrogen atoms and tertiary nitrogen atoms is excellent, by including compound (B), silver particles (A) are reduced, and the sintered silver layer becomes firm. In addition, the oxidation of the substrate surface as the joint portion is inhibited, and the interfacial bonding force is strengthened.

[0054] Furthermore, compound (B) imparts fluidity to silver particles (A) during calcination and functions to densify the sintered silver layer.

[0055] From the viewpoints of bonding strength and thermal cycle characteristics, compound (B) preferably has a tertiary nitrogen atom, preferably the number of tertiary nitrogen atoms is 1 to 3, more preferably 2 to 3. When the number of tertiary nitrogen atoms is 2 or more, the binding property with silver particles (A) becomes higher, and the dispersibility is significantly improved. In addition, the tertiary nitrogen atom has the function of reducing silver particles (A) or the joint portion, and when the number of tertiary nitrogen atoms is 2 or more, the reduction function is improved.

[0056] In addition, from the viewpoints of dispersibility and reduction function, the number of hydroxyl groups of compound (B) is preferably 4 to 6. In particular, since the binding property of the hydroxyl group with silver particles (A) is excellent, there is a tendency to improve the dispersibility. When the number of hydroxyl groups is 4 or more, the binding property with silver particles (A) becomes higher, and the dispersibility is significantly improved. In addition, the hydroxyl group has the function of reducing silver particles (A) or the joint portion, and when the number of hydroxyl groups is 4 or more, the reduction function is greatly improved.

[0057] Compound (B) is preferably a compound that is liquid at 25°C. In this specification, the term "liquid" means having fluidity rather than being in a solid state, and the viscosity measured using an E-type viscometer under the conditions of 25°C and 2.5 rpm is 1000 Pa·s or less.

[0058] By being liquid at 25°C, the wettability of the bonding interface with the joint portion increases during the process from solvent drying to sintering, and the contact area increases. As a result, a bonded body having a firm bonding interface can be manufactured. In addition, during the process from solvent drying to sintering, even when holes are formed in the bonding layer, the fluidity of the bonding paste increases, so the liquid compound (B) flows into defect portions such as holes, and a bonding layer and a bonded body with few defects can be obtained.

[0059] Generally, since the silver particles (A) are in powder form, in the case where the compound (B) is not included, as the following dispersion medium (C) volatilizes from the bonding paste, it is difficult to form an interface with the portion to be bonded. However, by including the compound (B) of the present disclosure, even after a part or all of the dispersion medium (C) has volatilized, it can exist in the form of a liquid composition, and thus a good bonding interface integrated with the portion to be bonded can be formed.

[0060] In addition, as one of the main causes of defects (holes) in the bonding layer, it can be cited that in the case where the volatilization of the dispersion medium (C) is insufficient, the dispersion medium (C) volatilizes sharply in the calcination temperature range. However, by including the compound (B), even after the dispersion medium (C) is dried and removed, the coating film will flow and a bonding interface can be formed. Thus, a pre-drying step for pre-drying the dispersion medium (C) can be provided, and a bonding layer with fewer defects can be formed.

[0061] In addition, in the case where the compound (B) has the property of being liquid in the sintering temperature range of the silver particles (A), the wettability of the bonding interface with the portion to be bonded is improved and the contact area is increased. Therefore, a bonded body with a more firm bonding interface can be obtained. Furthermore, even if holes are generated in the bonding layer during sintering, since the bonding paste has fluidity, the liquid compound (B) also flows into the hole portion, and the holes can be reduced.

[0062] As a specific example of the compound (B), for example, bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane (number of tertiary nitrogen atoms 1, number of hydroxyl groups 5), N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (number of tertiary nitrogen atoms 2, number of hydroxyl groups 4), N,N,N',N'',N''-pentakis(2-hydroxyethyl)diethylenetriamine (number of tertiary nitrogen atoms 3, number of hydroxyl groups 5), N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (number of tertiary nitrogen atoms 2, number of hydroxyl groups 4), 1,3-bis[tris(hydroxymethyl)methylamino]propane (number of secondary nitrogen atoms 2, number of hydroxyl groups 6), N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide (number of tertiary nitrogen atoms 2, number of hydroxyl groups 4), bis(2-hydroxypropyl)aminotris(hydroxymethyl)methane (number of tertiary nitrogen atoms 1, number of hydroxyl groups 5), N,N,N',N'',N''-pentakis(2-hydroxypropyl)diethylenetriamine (number of tertiary nitrogen atoms 3, number of hydroxyl groups 5) can be cited.

[0063] Particularly preferably, bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane, N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, and N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine are used. These compounds (B) can be used alone or in combination of multiple ones.

[0064] Based on the mass of silver particles (A), the content rate of compound (B) is preferably 0.02% by mass or more. If it is 0.02% by mass or more, the dispersibility of silver particles (A) is improved. In addition, sintering is performed in a state where compound (B) remains on the coating film, so that sintering is performed in a state where the coating film has fluidity. Therefore, the adhesion to the substrate and the defects in the bonding layer are reduced. From the viewpoints of dispersibility, adhesion to the substrate, and reduction of defects in the bonding layer, it is more preferably 0.05% by mass or more, and further preferably 0.10% by mass or more.

[0065] In addition, based on the mass of silver particles (A), the content rate of compound (B) is preferably 2.00% by mass or less. By being 2.00% by mass or less, the remaining amount on the coating film after sintering can be reduced, and the bonding strength and thermal cycle characteristics are excellent. From the viewpoint of reducing the remaining amount, it is more preferably 1.0% by mass or less, and further preferably 0.5% by mass or less.

[0066] <Dispersion medium (C)>

[0067] The bonding paste of the present disclosure contains a dispersion medium (C) (excluding compound (B) and compound (D) described later). The dispersion medium (C) functions to disperse silver particles (A) and compound (B). In addition, the dispersion medium (C) functions to impart fluidity to the coating film in the silver sintering process. The number of carbon atoms of the dispersion medium (C) is preferably less than 20.

[0068] The dispersion medium (C) only needs to uniformly disperse silver particles (A) and compound (B). As specific examples, for example, terpineol, dihydroterpineol, dihydroterpineol acetate, Terusolve TOE-100, Terusolve MTPH (manufactured by Japan Terpene Chemical Co., Ltd.), Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate), carbitol, carbitol acetate, butyl carbitol, isophorone, γ-butyrolactone, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol methyl n-propyl ether, 3-methoxy-3-methylbutyl acetate, 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 isoparaffinic solvents contained in hydrocarbon solvents are exemplified, but are not limited to these.

[0069] The dispersion medium (C) is preferably a dispersion medium having a boiling point of 200 °C or higher. If a dispersion medium having a boiling point of 200 °C or higher is included, in the silver sintering process, the dispersion medium in the coating film dries and decreases relatively slowly, so that the coating film can be sintered while maintaining a high fluidity state. Thereby, the close contact with the joint portion can be improved, or a joint body with fewer defects and higher strength can be obtained. The proportion of the dispersion medium having a boiling point of 200 °C or higher in the mass of the dispersion medium (C) is preferably 70% by mass or more.

[0070] The boiling point of the dispersion medium having a boiling point of 200 °C or higher is preferably 240 °C or higher, more preferably 250 °C or higher. If it is 250 °C or higher, the coating film can be sintered while maintaining a high fluidity state for a longer time. Therefore, a joint body with fewer defects and higher strength is formed, and the thermal cycle resistance is excellent, so it is preferred. In addition, from the viewpoint of suppressing the residue of the dispersion medium, the boiling point is preferably 350 °C or lower. In the case of including a plurality of dispersion media having a boiling point of 200 °C or higher, the boiling point of the dispersion medium having a boiling point of 200 °C or higher can be calculated based on their respective boiling points and mass ratios.

[0071] Examples of the dispersion medium having a boiling point of 200 °C or higher include: terpineol, dihydroterpineol, dihydroterpinyl acetate, Terusolve TOE-100, Terusolve MTPH (manufactured by Japan Terpene Chemical Co., Ltd.), Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate), isophorone, γ-butyrolactone, dipropylene, 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, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, polyethylene glycol monobutyl ether, and hydrocarbon solvents having a boiling point of 200 °C or higher, but are not limited thereto. These dispersion media having a boiling point of 200 °C or higher can be used alone or in combination of a plurality of them.

[0072] Among the dispersion media having a boiling point of 200 °C or higher, it is preferable to use glycols such as 1,3-butanediol, 1,4-butanediol, and 2-ethyl-1,3-hexanediol; and glycol ethers such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether. More preferably, it is a glycol ether.

[0073] As the dispersion medium of the glycol ether type having a boiling point of 250 °C or higher, it is particularly preferable to use diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether.

[0074] Particularly preferably, the boiling point of the dispersion medium (C) is 250°C or higher. When the dispersion medium (C) contains a plurality of dispersion media, it can be calculated as the boiling point of the dispersion medium (C) based on the boiling points and mass ratios of the respective dispersion media.

[0075] If the boiling point of the dispersion medium (C) as a whole is 250°C or higher, then in the silver sintering process, the dispersion medium in the coating film dries and decreases relatively slowly, so that the coating film can be sintered while maintaining a high fluidity state. Thereby, the close contact with the joint portion can be improved, and a strong joint body with fewer defects can be obtained, which is therefore preferable.

[0076] <Sintering temperature, 50% weight reduction temperature>

[0077] The joint paste of the present disclosure preferably satisfies T3 < T1 < (T2 + 10) when the sintering temperature of the silver particles (A) is set to T1 °C, the 50% weight reduction temperature of the compound (B) is set to T2 °C, and the 50% weight reduction temperature of the dispersion medium (C) is set to T3 °C. At this time, it is preferably satisfied that T3 < T2. In this way, a temperature range is formed, that is, the 50% weight reduction temperature T3 of the dispersion medium (C) is lower than the 50% weight reduction temperature T1 of the silver particles (A) and the 50% weight reduction temperature T2 of the compound (B), and the 50% weight reduction temperature T2 of the compound (B) exceeds a temperature about 10 °C lower than the 50% weight reduction temperature T1 (sintering temperature) of the silver particles (A). From this, it is speculated that the dispersion medium (C) is first volatilized and removed, and the compound (B) exists during and after the sintering of the silver particles (A). Therefore, it is considered that the defects in the joint layer are reduced, a strong joint interface can be formed, and a dense joint can be performed, exhibiting excellent joint strength and thermal cycle characteristics.

[0078] The 50% weight reduction temperature T2 of the compound (B) and the 50% weight reduction temperature T3 of the dispersion medium (C) can be measured using thermogravimetric-differential thermal analysis (hereinafter also referred to as TG-DTA analysis). As the measurement method, for example, the following methods can be cited.

[0079] Using a thermogravimetric-differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)), heating is performed at a heating rate of 1 °C / minute in a nitrogen atmosphere, and the temperatures at which the weight is reduced by 50% are respectively set as the 50% weight reduction temperature T2 and the 50% weight reduction temperature T3. When the compound (B) or the dispersion medium (C) is a mixture of two or more, the results of the measurement using the mixture are used.

[0080] The 50% weight loss temperature T2 of the compound (B) is preferably 200°C to 300°C, more preferably 210°C to 270°C, and still more preferably 210°C to 255°C. If it is 200°C or higher, the compound (B) can remain sufficiently in the coating film even in the sintering temperature range, the fluidity of the coating film during sintering is improved, the adhesion to the substrate is improved, and the bonding strength is excellent. If it is 300°C or lower, the residue in the coating film after sintering can be reduced, and the bonding strength and thermal cycle characteristics are excellent.

[0081] The sintering temperature T1 of the silver particles (A) can be measured by thermogravimetric differential thermal analysis (hereinafter also referred to as TG-DTA analysis). As a measurement method, for example, the following methods can be cited.

[0082] Regarding the sintering temperature T1 of the silver particles (A), in a nitrogen atmosphere, it is heated to 400°C at a heating rate of 1°C / minute to decompose the protective agent. When the reduction amount is set to 100, the temperature at which the weight is reduced by 50% is set as T1.

[0083] <Compound (D)>

[0084] The bonding paste of the present disclosure may also contain a compound (D) having 20 to 80 carbon atoms having at least one functional group (hereinafter referred to as functional group (d)) selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group. By including such a compound (D), even after a part or all of the dispersion medium (C) volatilizes, it can exist in the form of a liquid composition, and thus a good bonding interface integrated with the bonded portion can be formed. In addition, each functional group has a high binding property with the silver particles (A) and exhibits excellent dispersibility.

[0085] The carbon number representation of the compound (D) also includes the carbon in the functional group (d). Therefore, when the functional group (d) in the compound (D) is a carboxyl group, the carbon number including the carbon in the carboxyl group is regarded as the carbon number of the compound (D).

[0086] In the compound (D), the skeleton (partial structure) after removing the functional group (d) is an organic residue, but it is preferably a hydrocarbon group or a group formed by bonding a plurality of hydrocarbon groups with a linking group containing a heteroatom. As such a linking group containing a heteroatom, for example, an -O- group (ether group), a -C(=O)- group (carbonyl group), a -C(=O)-O- group (ester group or oxycarbonyl group), a -C(=O)-NH- group (amide group or iminocarbonyl group) can be cited. The compound (D) preferably does not have a functional group other than the functional group (d).

[0087] The properties of compound (D) are not particularly limited, but it is preferably liquid in the temperature range of 200°C to 350°C, which is the temperature range for calcining the bonding paste of the present disclosure. Compound (D) can be solid or liquid at normal temperature (25°C), but from the perspective of being uniformly dispersed in the bonding paste and effectively playing its role, it is more preferably liquid at normal temperature.

[0088] When compound (D) has the property of being liquid in the above temperature range, an improvement in wettability at the bonding interface with the bonded part can be expected, and the contact area increases. As a result, a bonded body with a strong bonding interface can be manufactured. In addition, it is considered that even when holes are formed in the bonding layer during sintering, due to the increased fluidity of the bonding paste, the liquid compound (D) flows into defect parts such as holes, and a bonding layer and a bonded body with fewer defects can be obtained.

[0089] The number of functional groups (d) in compound (D) is preferably 2 or 3.

[0090] Compound (D) can have a linear structure, or can have a branched and / or cyclic structure, and preferably has a branched and / or cyclic structure. In terms of having low crystallinity and being easily in a liquid state with good fluidity, the case of having a branched and / or cyclic structure is preferred.

[0091] When the number of functional groups (d) of compound (D) is set to n, compound (D) preferably has an n-valent hydrocarbon group. In compound (D), in terms of obtaining a strong bonded body, the skeleton after removing the functional group (d) is more preferably composed only of an n-valent hydrocarbon group.

[0092] For the above reasons, compound (D) is preferably not evaporated immediately at the start of sintering. However, at the end of sintering, it does not have to remain in the formed bonding layer. When the carbon number of the n-valent hydrocarbon group is 30 to 60, the amount of compound (D) remaining in the sintered bonding layer can be further reduced, and a denser bonding layer is easily obtained, so it is preferred. As a result, the initial bonding strength is excellent, and a reduction in bonding strength accompanied by thermal cycling can be further expected to be suppressed.

[0093] Examples of compound (D) having a linear structure include, but are not limited to, eicosanedioic acid, heneicosanedioic acid, docosanedioic acid, tetracosanedioic acid, triacontanedioic acid, dotriacontanedioic acid, tetracontanedioic acid, pentacontanedioic acid, hexacontanedioic acid, and squalene alcohol.

[0094] Examples of compound (D) having a branched and / or cyclic structure include, but are not limited to, dimer acid, trimer acid, tetramer acid, dimer diol, trimer triol, tetramer tetrol, dimer diamine, trimer triamine, tetramer tetramine, and phytanetriol.

[0095] Among them, as the compound (D), for the reasons described above, it is more preferably a compound selected from the group consisting of dimer acid, trimer acid, dimer diol, trimer triol, dimer diamine, and trimer triamine.

[0096] Dimer acid, trimer acid, and tetramer acid can be produced by the polymerization reaction of unsaturated fatty acids. For example, they can be produced by the Diels - Alder reaction or free radical reaction of oleic acid (carbon number 18) and linoleic acid (carbon number 18). The carbon number of dimer acid is preferably 36 or 44, the carbon number of trimer acid is preferably 54, and the carbon number of tetramer acid is preferably 72. In addition, by appropriately changing the carbon number of the unsaturated fatty acid as a raw material, a compound (D) having a carbon number other than the above can be produced. In addition, in this specification, dimers, trimers, and tetramers of unsaturated fatty acids having 12 or more carbon atoms are respectively referred to as dimer acid, trimer acid, and tetramer acid.

[0097] Dimer diol has a structure in which the carboxyl group of dimer acid is reduced to a hydroxyl group, trimer triol has a structure in which the carboxyl group of trimer acid is reduced to a hydroxyl group, and tetramer tetrol has a structure in which the carboxyl group of tetramer acid is reduced to a hydroxyl group. The carbon number of dimer diol is preferably 36, the carbon number of trimer triol is preferably 54, and the carbon number of tetramer tetrol is preferably 72.

[0098] Dimer diamine has a structure in which the carboxyl group of dimer acid is subjected to functional group conversion to be converted into an amino group, trimer triamine has a structure in which the carboxyl group of trimer acid is subjected to functional group conversion to be converted into an amino group, and tetramer tetramine has a structure in which the carboxyl group of tetramer acid is subjected to functional group conversion to be converted into an amino group. The carbon number of dimer diamine is preferably 36, the carbon number of trimer triamine is preferably 54, and the carbon number of tetramer tetramine is preferably 72.

[0099] The compound (D) may sometimes be a mixture of compounds with different degrees of polymerization in the manufacturing method, and can be used as a mixture of different polymers or a specific single compound can be used.

[0100] In the bonding paste of the present disclosure, relative to 100 parts by mass of silver particles (A), the content of the compound (D) is preferably 0.05 parts by mass to 2.0 parts by mass, more preferably 0.1 parts by mass to 1.0 parts by mass. If it is within the above range, a bonded body having particularly excellent initial bonding strength and suppressing the reduction of bonding strength accompanying thermal cycling can be obtained.

[0101] [Compound (Dx)]

[0102] The bonding paste of the present disclosure preferably contains a compound (Dx) having three carboxyl groups and 20 to 80 carbon atoms as the compound (D). The compound (Dx) may have a linear structure, or may have a branched and / or cyclic structure, and preferably has a branched and / or cyclic structure. In terms of low crystallinity and being easily in a liquid state with good fluidity, the case of having a branched and / or cyclic structure is preferred. The compound (Dx) preferably has a trivalent hydrocarbon group. In the compound (Dx), in terms of obtaining a strong bonded body, the skeleton after removing the carboxyl group is more preferably composed of only a trivalent hydrocarbon group. As a specific example of the compound (Dx) having a branched and / or cyclic structure, trimer acid can be cited and can be preferably used.

[0103] The bonding paste of the present disclosure preferably contains 0.03 to 2.0 parts by mass of the compound (Dx) relative to 100 parts by mass of the silver particles (A). By being in the above range, excellent bonding strength and thermal cycle characteristics can be exhibited even under more severe conditions such as when using an unplated base material to be bonded.

[0104] [Compound (Dy)]

[0105] The bonding paste of the present disclosure preferably further contains a compound (Dy) having two carboxyl groups and 20 to 80 carbon atoms as the compound (D). The volatilization or decomposition temperatures of the compound (Dx) and the compound (Dy) with a different number of carboxyl groups are different, and the volatilization or decomposition temperature of the compound (Dy) is lower than that of the compound (Dx). Therefore, if these are used in combination, volatilization or decomposition together at a specific temperature can be suppressed during the silver sintering process. Thus, the coating film can be sintered while maintaining a highly fluid state for a longer time. As a result, the adhesion to the bonded portion is further improved, and a stronger bonded body with fewer defects can be obtained.

[0106] The compound (Dy) may have a linear structure, or may have a branched and / or cyclic structure, and preferably has a branched and / or cyclic structure. In terms of low crystallinity and being easily in a liquid state with good fluidity, the case of having a branched and / or cyclic structure is preferred. The compound (Dy) preferably has a divalent hydrocarbon group. In the compound (Dy), in terms of obtaining a strong bonded body, the skeleton after removing the carboxyl group is more preferably composed of only a divalent hydrocarbon group.

[0107] As the compound (Dy) having a linear structure, for example, eicosanedioic acid, heneicosanedioic acid, docosanedioic acid, tetracosanedioic acid, triacontanedioic acid, dotriacontanedioic acid, tetracontanedioic acid, pentacontanedioic acid, hexacontanedioic acid can be cited, but are not limited to these. As the compound (Dy) having a branched and / or cyclic structure, for example, dimer acid can be cited and can be preferably used.

[0108] The paste for bonding of the present invention preferably contains 0.03 to 2.0 parts by mass of compound (Dy) relative to 100 parts by mass of silver particles (A). By being in the above-mentioned range, excellent bonding strength and thermal cycle characteristics can be exhibited even under more severe conditions such as when using a base material to be bonded that has not been plated.

[0109] The paste for bonding of the present disclosure preferably contains 0.05 to 2.0 parts by mass in total of compound (Dx) and compound (Dy) relative to 100 parts by mass of silver particles (A). If the total of compound (Dx) and compound (Dy) is in the above-mentioned range, a bonded body with particularly excellent initial bonding strength and suppression of the decrease in bonding strength accompanying thermal cycling can be obtained.

[0110] <Compound (E)>

[0111] The paste for bonding of the present disclosure may also contain a compound (E) having 14 to 20 carbon atoms and one carboxyl group. The carbon number of compound (E) is the carbon number including the carbon of the carboxyl group.

[0112] Compound (E) is a fatty acid. By including such compound (E), even after part or all of the dispersion medium (C) volatilizes, it can exist in the form of a liquid composition, and thus a good bonding interface integrated with the part to be bonded can be formed. In addition, the binding property of each functional group to the silver particles (A) is high, and excellent dispersibility is exhibited.

[0113] Examples of compound (E) include linear saturated fatty acids, linear unsaturated fatty acids, or branched fatty acids. Examples of linear saturated fatty acids include: myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachidic acid. Examples of linear unsaturated fatty acids include: palmitoleic acid, oleic acid, erucic acid. Examples of branched fatty acids include 2-hexyldecanoic acid.

[0114] Compound (E) is preferably a linear unsaturated fatty acid. By the paste for bonding of the present disclosure containing a linear unsaturated fatty acid, the lipophilicity becomes higher and the stability in a non-aqueous solvent is improved. In addition, the decomposition temperature of the linear unsaturated fatty acid is low and the low-temperature sinterability is excellent, so it is preferred. Compound (E) can be used alone or in combination of multiple kinds.

[0115] Relative to 100 parts by mass of silver particles (A), the paste for bonding of the present disclosure preferably contains 0.1 to 2.0 parts by mass of compound (E), and more preferably contains 0.2 to 1.0 parts by mass of compound (E). If it is in the above-mentioned range, excellent bonding strength and thermal cycle characteristics can be exhibited even when the part to be bonded is a base material that has not been plated.

[0116] <Manufacture of paste for bonding>

[0117] The paste for bonding of the present disclosure only needs to contain at least silver particles (A), a compound (B), and a dispersion medium (C), and its manufacturing method is not particularly limited and can be adjusted using known methods. As a device for preparing the paste for bonding from silver particles (A), a compound (B), and a dispersion medium (C), examples include: a disperser, a three-roll mill, a bead mill, an ultrasonic disperser, a rotation-revolution type stirrer, etc.

[0118] The proportion of the mass of silver particles (A) based on the mass of the paste for bonding is preferably 80% by mass to 95% by mass, more preferably 85% by mass to 94% by mass. By including silver particles (A) within the above range, good printing adaptability is exhibited as the paste for bonding, and the residue of the dispersion medium (C) in the bonded body can be suppressed, and the generation of holes derived from the dispersion medium (C) can be suppressed, thereby exhibiting good bonding strength.

[0119] The paste for bonding of the present disclosure may contain additives, for example, a sintering accelerator, an adhesive resin, or a resin type dispersant may be contained.

[0120] <Bonded body and manufacturing method of bonded body>

[0121] With the paste for bonding of the present disclosure, a first bonded portion and a second bonded portion can be bonded to obtain a bonded body. The bonded body can be manufactured, for example, by the following manufacturing method (I) or manufacturing method (II).

[0122] [Manufacturing method (I)]

[0123] Manufacturing method (I) is a method based on non-pressure bonding, and preferably includes the following steps (1) to (3), for example.

[0124] (1) Step of applying the paste for bonding to the first bonded body.

[0125] (2) Step of placing the second bonded portion on the first bonded portion coated with the paste for bonding.

[0126] (3) Step of sintering the stacked body after placement in a non-pressure environment.

[0127] (1) Coating step

[0128] As a method of applying the paste for bonding to the bonded body, as long as it is a method that can be uniformly applied to the member, there is no particular limitation. For example, various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, and intaglio offset printing can be cited; a spraying method using a dispenser, etc. The paste for bonding of the present disclosure has excellent fluidity even when containing metal particles at a high concentration, and therefore is particularly preferably used in combination with metal mask printing.

[0129] (2) Mounting process

[0130] Next, mount the second joint part on the first joint part coated with the joint paste of the present disclosure. When using the joint paste of the present disclosure, it can be mounted without pressure. In the case of non-pressure bonding, it is preferable that this mounting process is also carried out without pressure, but it is also possible to mount while applying pressure. When pressure is applied, the pressure is appropriately set according to the viscosity of the joint paste or the drying state of the paste, preferably 0.1 MPa to 40 MPa, more preferably 0.3 MPa to 30 MPa.

[0131] (3) Sintering process

[0132] The sintering conditions for non-pressure bonding of the laminate with the second joint part mounted on the first joint part can be appropriately changed. For example, conditions such as under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere and at 200°C to 350°C can be cited. As the calcining device, the following can be cited: hot air oven, calcining furnace, electric furnace, infrared oven, reflux oven, microwave oven, heating plate, light calcining device, etc. These devices can be appropriately used alone or in combination.

[0133] As the non-pressure sintering conditions, it is preferable to measure the temperature rise at a rate of 2°C / minute to 30°C / minute until the set temperature is reached, and then maintain the temperature at the set temperature or higher for about 10 minutes to 2 hours. As the set temperature, it is preferably 200°C to 350°C, more preferably 250°C to 330°C, and further preferably 280°C to 320°C.

[0134] (2a) Pre-drying process

[0135] In the manufacturing method (I) using non-pressure bonding, it is preferable to provide a pre-drying process (2a) between process (2) and process (3) to remove the organic components in the joint coating film. Since the joint paste of the present disclosure contains compound (B), even after pre-drying and removing the dispersion medium (C), the coating film can flow to form a joint interface, so a pre-drying process can be provided. By providing the pre-drying process, the residual of the dispersion medium (C), which is one of the causes of defects (holes) in the joint layer, can be suppressed, and the denseness of the joint layer is excellent, so it is preferable.

[0136] Pre-drying can be carried out, for example, using the same device as the calcining device, under the conditions of 1 minute to 300 minutes in the range of 60°C to 220°C. It is preferably 30 minutes to 120 minutes in the range of 70°C to 100°C.

[0137] That is, as the manufacturing method (I), it is particularly preferable to include the following processes.

[0138] (1) Step of applying the bonding paste to the first adherend.

[0139] (2) Step of placing the second adherend on the coated portion of the first adherend where the bonding paste has been applied.

[0140] (2a) Step of heating the placed laminate for pre-drying.

[0141] (3) Step of sintering the placed laminate in a non-pressurized environment.

[0142] [Manufacturing Method (II)]

[0143] Manufacturing Method (II) is a method based on pressure bonding, and preferably includes the following steps (10) to (30), for example.

[0144] (10) Step of applying the bonding paste to the first adherend.

[0145] (10a) Step of heating the applied laminate for pre-drying.

[0146] (20) Step of placing the second adherend on the first adherend where the bonding paste has been applied and pre-dried.

[0147] (30) Step of sintering the placed laminate in a pressurized environment.

[0148] (10) Coating Step

[0149] As a method of applying the bonding paste to the adherend, as long as it can be evenly applied to the member, there is no particular limitation. For example, various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, and intaglio offset printing can be cited; a spraying method using a dispenser, etc. The bonding paste of the present disclosure has excellent fluidity even when containing metal particles at a high concentration, so it is particularly preferably used in combination with metal mask printing.

[0150] (10a) Pre-drying Step

[0151] In Manufacturing Method (II) using pressure bonding, a pre-drying step (10a) can be provided between step (10) and step (20) to remove the organic components in the bonding coating film. Due to the provision of the pre-drying step, pre-drying can be carried out, for example, using the same apparatus as the calcination apparatus, under the conditions of 1 minute to 300 minutes in the range of 60°C to 220°C.

[0152] (20) Placement Step

[0153] Next, place the second joint part on the first joint part coated with the joint paste of the present disclosure and pre-dried. In the case of pressure bonding, the placement process can also be carried out under pressure. The pressure is appropriately set according to the viscosity of the joint paste or the drying state of the paste, preferably 0.1 MPa to 40 MPa, more preferably 0.3 MPa to 30 MPa.

[0154] (30) Sintering process

[0155] The sintering conditions for pressure bonding the laminate with the second joint part placed on the first joint part can be appropriately changed. For example, conditions such as under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere and at 200°C to 350°C can be cited. As the calcining device, the following can be cited: hot air oven, calcining furnace, electric furnace, infrared oven, reflux oven, microwave oven, heating plate, light calcining device, etc. These devices can be appropriately used alone or in combination.

[0156] As the pressure, it is appropriately set according to the viscosity of the joint paste or the drying state of the paste, preferably 0.1 MPa to 40 MPa, and further preferably 0.3 MPa to 30 MPa.

[0157] Even in any of the manufacturing methods, the thickness of the joint layer formed when joining the joint parts using the joint paste is not limited. The thickness of the joint layer is preferably 3 μm to 500 μm, more preferably 10 μm to 200 μm, and further preferably 20 μm to 100 μm.

[0158] [Joint part]

[0159] The type of the joint part is not particularly limited. For example, in addition to metal materials, semiconductor materials, plastic materials, and ceramic materials, electronic components can also be cited. As metals, for example, copper, gold, and aluminum can be cited. As semiconductor materials, for example, silicon, germanium, gallium arsenide, gallium phosphide, cadmium sulfide, silicon nitride, graphite, yttrium oxide, magnesium oxide, silicon carbide, and gallium nitride can be cited. As plastic materials, for example, polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate can be cited. As ceramic materials, for example, glass and silicon can be cited. As electronic components, for example, semiconductor components, LED components, and power device components can be cited.

[0160] The first joint part and the second joint part can be not only the same type of component but also different types of components. Regarding the joint part, in order to increase the joint strength of the joint part, the surface of the joint part can also be subjected to corona treatment, plating treatment, etc.

[0161] The bonding paste of the present disclosure has excellent bonding strength to a non-plated substrate and a SiC element, and is suitable for a bonded body in which the first bonded portion is a non-plated substrate. In addition, the second bonded portion is suitable for a bonded body made of SiC.

[0162] Among them, by containing the compound (B), oxidation of the substrate surface and / or reduction of the oxide are inhibited, and a firm bond can be achieved between the silver particles (A) and the substrate. Since the above effects are particularly effective for easily oxidizable substrates, the bonding paste of the present invention is very effective as a bonding material for easily oxidizable copper substrates, particularly non-plated copper substrates.

[0163] Examples

[0164] Hereinafter, the present disclosure will be described in detail using examples and comparative examples, but the technical scope of the present disclosure is not limited thereto. In addition, in the examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively. Unless otherwise specified, the values in the tables represent "parts".

[0165] [Sintering temperature T1 of silver particles (A)]

[0166] Regarding the sintering temperature T1 of the silver particles (A), using a thermogravimetric differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)), in a nitrogen atmosphere, it was heated at a heating rate of 1 °C / minute to 400 °C to decompose the protective agent, and the temperature at which the weight decreased by 50% when the reduction amount was 100 was used.

[0167] [50% weight reduction temperature T2 and 50% weight reduction temperature T3 of compound (B) and dispersion medium (C)]

[0168] Regarding the 50% weight reduction temperature T2 and 50% weight reduction temperature T3 of the compound (B) and the dispersion medium (C), using a thermogravimetric differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)), in a nitrogen atmosphere, it was heated at a heating rate of 1 °C / minute, and the temperatures at which the weight decreased by 50% were set as the 50% weight reduction temperature T2 and the 50% weight reduction temperature T3, respectively. In the case where the compound (B) or the dispersion medium (C) is a mixture of two or more, the results of the measurement using the mixture were used.

[0169] <Manufacture of metal particles>

[0170] (Production Example 1) Metal particles A1

[0171] Under a nitrogen atmosphere, 200 parts of toluene and 22.3 parts of silver hexanoate were mixed with stirring at 25 °C to prepare a 0.5 M solution. Then, 1.6 parts of diethylaminoethanol and 0.28 parts of oleic acid as dispersants were added and dissolved. Subsequently, 73.1 parts of an aqueous solution of 20% succinic dihydrazide (hereinafter referred to as SUDH) as a reducing agent was added dropwise, and the color of the liquid changed from light yellow to dark brown. To further promote the reaction, the temperature was raised to 40 °C and the reaction was carried out. After standing and separating, the aqueous phase was taken out to remove excess reducing agent or impurities. Furthermore, distilled water was added several times to the toluene layer, and after repeated washing and separation, toluene was added, followed by centrifugation to remove the supernatant. The above process was repeated twice. The precipitate was dried to obtain metal particles A1 in which silver particles were coated with hexanoic acid and oleic acid. The average particle size (d50) of metal particles A1 was determined by the method described below, and the result was d50 = 210 nm.

[0172] (Production Example 2) Metal Particles A2

[0173] Using 2.4 parts of diethylaminoethanol and 0.42 parts of oleic acid, metal particles A2 were obtained in the same manner as in Production Example 1. d50 = 120 nm.

[0174] (Production Example 3) Metal Particles A3

[0175] Using 2.0 parts of diethylaminoethanol and 0.34 parts of oleic acid, metal particles A3 were obtained in the same manner as in Production Example 1. d50 = 155 nm.

[0176] (Production Example 4) Metal Particles A4

[0177] Using 1.8 parts of diethylaminoethanol and 0.31 parts of oleic acid, metal particles A4 were obtained in the same manner as in Production Example 1. d50 = 185 nm.

[0178] (Production Example 5) Metal Particles A5

[0179] Using 1.2 parts of diethylaminoethanol and 0.18 parts of oleic acid, metal particles A5 were obtained in the same manner as in Production Example 1. d50 = 290 nm.

[0180] (Production Example 6) Metal Particles A6

[0181] Using 1.0 parts of diethylaminoethanol and 0.14 parts of oleic acid, metal particles A6 were obtained in the same manner as in Production Example 1. d50 = 390 nm.

[0182] (Production Example 10) Comparative Example Metal Particles A10

[0183] Set diethylaminoethanol to 1.4 parts and the amount of oleic acid to 0.09 part. Otherwise, obtain metal particles A10 in the same manner as in Production Example 1. The d50 is 600 nm.

[0184] (Production Example 11) Comparative example metal particles A11

[0185] Set diethylaminoethanol to 0.6 part and the amount of oleic acid to 0.070 part. Otherwise, obtain metal particles A11 in the same manner as in Production Example 1. The d50 is 1100 nm.

[0186] (Production Example 12) Comparative example metal particles A12

[0187] Set diethylaminoethanol to 2.3 parts and the amount of oleic acid to 2.8 parts. Otherwise, obtain metal particles A12 in the same manner as in Production Example 1. The d50 is 20 nm.

[0188] (Production Example 13) Comparative example metal particles A13

[0189] Set diethylaminoethanol to 2.1 parts and the amount of oleic acid to 0.71 part. Otherwise, obtain metal particles A13 in the same manner as in Production Example 1. The d50 is 85 nm.

[0190] [Method for measuring average particle diameter of silver particles]

[0191] Isopropanol was added to each silver particle and dispersed using an ultrasonic disperser to obtain a 0.5 mass% dispersion. For the obtained dispersion, the particle diameter of the metal particles in the dispersion was measured using Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.), and the average particle diameter (d50) was determined. Among the metal particles produced by the above method, metal particles A1 - A6 correspond to the silver particles (A) of the present disclosure, and metal particles A10 - A13 correspond to metal particles that are not silver particles (A).

[0192] <Compound (B)>

[0193] The following materials were used as compound (B).

[0194] B1: Bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane (number of tertiary nitrogen atoms 1, number of hydroxyl groups 5, solid at 25°C)

[0195] B2: N,N,N',N'-Tetra(2-hydroxyethyl)ethylenediamine (number of tertiary nitrogen atoms 2, number of hydroxyl groups 4, liquid at 25°C)

[0196] B3: N,N,N',N'',N''-Pentakis(2-hydroxypropyl)diethylenetriamine (number of tertiary nitrogen atoms: 3, number of hydroxyl groups: 5, liquid at 25°C)

[0197] B4: N,N,N',N'-Tetrakis(2-hydroxypropyl)ethylenediamine (number of tertiary nitrogen atoms: 2, number of hydroxyl groups: 4, liquid at 25°C)

[0198] B5: 1,3-Bis[tris(hydroxymethyl)methylamino]propane (number of secondary nitrogen atoms: 2, number of hydroxyl groups: 6, solid at 25°C)

[0199] B6: N,N,N',N'-Tetrakis(2-hydroxyethyl)adipamide (number of tertiary nitrogen atoms: 2, number of hydroxyl groups: 4, solid at 25°C)

[0200] B11: Triethanolamine (number of tertiary nitrogen atoms: 1, number of hydroxyl groups: 3, liquid at 25°C)

[0201] B12: 2-Amino-2-hydroxymethyl-1,3-propanediol (number of hydroxyl groups: 3, solid at 25°C)

[0202] B13: 2-(2-Aminoethoxy)ethanol (number of hydroxyl groups: 1, liquid at 25°C)

[0203] B14: Xylitol (number of hydroxyl groups: 5, solid at 25°C)

[0204] B15: Imidazole (solid at 25°C)

[0205] <Dispersion medium (C)>

[0206] The following materials are used as the dispersion medium (C). The manufacturer name, supplementary information, and boiling point obtained are indicated in parentheses.

[0207] Dispersion medium C1: Diethylene glycol monohexyl ether (glycol ether type, boiling point 255°C)

[0208] Dispersion medium C2: Triethylene glycol monobutyl ether (glycol ether type, boiling point 278°C)

[0209] Dispersion medium C3: Triethylene glycol monomethyl ether (glycol ether type, boiling point 248°C)

[0210] Dispersion medium C4: 2-Ethyl-1,3-hexanediol (glycol type, boiling point 244°C)

[0211] Dispersion medium C5: Diethylene glycol monomethyl ether (glycol ether type, boiling point 193°C)

[0212] Dispersion medium C6: 1-Decanol (boiling point 233°C)

[0213] Dispersion medium C7: "Terusolve TOE-100" (boiling point 260 °C) manufactured by Japan Terpene Chemical Co., Ltd.

[0214] <Compound (D)>

[0215] The following materials are used as Compound (D). Compounds D1 to D4 are all manufactured by Croda Japan Co., Ltd., and the number of carbon atoms, material name, and properties at 25 °C are described in parentheses.

[0216] Compound D1: PRIPOL 1009 (hydrogenated dimer acid with 36 carbon atoms; containing two carboxyl groups and a divalent hydrocarbon group with branched and cyclic structures; liquid)

[0217] Compound D2: PRIPOL 1040 (trimer acid with 54 carbon atoms; containing three carboxyl groups and a trivalent hydrocarbon group with branched and cyclic structures; liquid)

[0218] Compound D3: PRIPOL 2033 (dimer diol with 36 carbon atoms; containing two hydroxyl groups and a divalent hydrocarbon group with branched and cyclic structures; liquid)

[0219] Compound D4: Priamine 1075 (dimer diamine with 36 carbon atoms; containing two amino groups and a divalent hydrocarbon group with branched and cyclic structures; liquid)

[0220] <Compound (E)>

[0221] The following materials are used as Compound (E).

[0222] Compound E1: Oleic acid

[0223] <Manufacture of bonding paste>

[0224] [Example 1]

[0225] Using a rotation-revolution type stirrer, metal particles A1 (90 parts), diethylene glycol monohexyl ether (10 parts), Compound B1 (0.2 parts), other component D1 (0.1 part), and other component D2 (0.1 part) are mixed to prepare a bonding paste.

[0226] [Examples 2 to 43, Comparative Examples 1 to 9]

[0227] According to the compositions described in Tables 1A to 2B, the types and blending amounts (parts) of the materials are changed, and except for this, a bonding paste is obtained in the same manner as in Example 1. In the tables, blanks indicate non-blending.

[0228] <Evaluation of bonding paste>

[0229] Using the obtained bonding paste, a bonded body is produced by any one of the following production methods 1 to 5. The bonding strength and thermal cycle characteristics of the obtained bonded body are evaluated. The results are shown in Tables 1A to 2B.

[0230] [Production method 1]

[0231] Using the bonding paste obtained in Examples 1 to 39 and Comparative Examples 1 to 9, a bonded body is produced in the following order.

[0232] On the bonded part 1 (copper substrate (unplated): 20 mm × 20 mm × 3 mm), after printing the bonding paste obtained in Examples 1 to 36 and Comparative Examples 1 to 9 once under the following printing conditions, the plated surface of the bonded part 2 (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) is placed facing the bonding paste surface, and non-pressure bonding is performed under the following sintering conditions to obtain a bonded body respectively.

[0233] [Sintering conditions]

[0234] The stacked body on which the placement has been performed is placed in a calcination furnace in a nitrogen atmosphere, heated from 25°C to 80°C at a rate of 5°C / minute, and pre-dried at 80°C for 90 minutes. Then, it is heated to 300°C at a rate of 8°C / minute, and after reaching 300°C, it is held at 300°C for 2 hours.

[0235] [Production method 2]

[0236] Using the bonding paste obtained in Example 40, a bonded body is produced in the following order.

[0237] On the bonded part 1 (copper substrate (unplated): 20 mm × 20 mm × 3 mm), after printing the bonding paste obtained in Example 37 once under the following printing conditions, the plated surface of the bonded part 2 (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) is placed facing the bonding paste surface, and non-pressure bonding is performed under the following sintering conditions to obtain a bonded body.

[0238] [Sintering conditions]

[0239] The stacked body on which the placement has been performed is placed in a calcination furnace in a nitrogen atmosphere, heated from 25°C to 80°C at a rate of 5°C / minute, and pre-dried at 80°C for 90 minutes. Then, it is heated to 300°C at a rate of 2°C / minute, and after reaching 300°C, it is held at 300°C for 2 hours.

[0240] [Production method 3]

[0241] Using the bonding paste obtained in Example 41, a bonded body was manufactured in the following order.

[0242] On the bonded part 1 (copper substrate (unplated): 20 mm × 20 mm × 3 mm), after printing the bonding paste obtained in Example 38 once under the following printing conditions, the plated surface of the bonded part 2 (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the bonding paste surface, and it was bonded without pressure under the following sintering conditions to obtain a bonded body.

[0243] 〔Sintering conditions〕

[0244] The stacked body on which the placement was performed was placed in a calcining furnace in a nitrogen atmosphere, heated from 25°C to 300°C at a rate of 8°C / minute, and after reaching 300°C, it was held at 300°C for 2 hours.

[0245] [Manufacturing method 4]

[0246] Using the bonding paste obtained in Example 42, a bonded body was manufactured in the following order.

[0247] On the bonded part 1 (copper substrate (unplated): 20 mm × 20 mm × 3 mm), after printing the bonding paste obtained in Example 39 once under the following printing conditions, the plated surface of the bonded part 2 (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the bonding paste surface, and it was bonded without pressure under the following sintering conditions to obtain a bonded body.

[0248] 〔Sintering conditions〕

[0249] The stacked body on which the placement was performed was placed in a calcining furnace in a nitrogen atmosphere, heated from 25°C to 300°C at a rate of 2°C / minute, and after reaching 300°C, it was held at 300°C for 2 hours.

[0250] [Manufacturing method 5]

[0251] Using the bonding paste obtained in Example 43, a bonded body was manufactured in the following order.

[0252] On the bonded part 1 (copper substrate (unplated): 20 mm × 20 mm × 3 mm), after printing the bonding paste obtained in Example 40 once under the following printing conditions, it was placed in a hot air oven and pre-dried at 180°C for 10 minutes. Next, the plated surface of the bonded part 2 (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the pre-dried bonding paste surface, and it was bonded under pressure under the following sintering conditions to obtain a bonded body.

[0253] 〔Sintering conditions〕

[0254] In a nitrogen atmosphere, while applying a pressure of 30 MPa to the joint part 2, the temperature is raised from room temperature to 300 °C at a rate of 20 °C per minute. After reaching 300 °C, it is maintained at that temperature for 5 minutes.

[0255] 〔Printing conditions (metal mask printing)〕

[0256] Metal mask: The opening is 7.5 mm square and the plate thickness is 100 μm (manufactured by SERIA CORPORATION).

[0257] Metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by SERIA CORPORATION).

[0258] [Bonding strength]

[0259] For the obtained bonded body, the bonded body is fixed at the joint part 1, and pressed at a speed of 500 μm / s from the interface between the joint part 1 and the bonding layer to a position 100 μm in height toward the joint part 2, and the bonding strength (die shear strength) at which the bond is broken is obtained and evaluated based on the following evaluation criteria. The larger the value of the bonding strength, the better, and 10 MPa or more is within the practical range. The following shows the measurement conditions.

[0260] 〔Measurement conditions〕

[0261] Measuring device: Universal bonding strength tester (bond tester) (manufactured by Dage Japan Co., Ltd., 4000 series)

[0262] Measuring height: 100 μm

[0263] Measuring speed: 500 μm / s

[0264] (Evaluation criteria)

[0265] S: 35 MPa or more

[0266] A+: 30 MPa or more and less than 35 MPa

[0267] A: 25 MPa or more and less than 30 MPa

[0268] A-: 20 MPa or more and less than 25 MPa

[0269] B: 15 MPa or more and less than 20 MPa

[0270] C: 10 MPa or more and less than 15 MPa

[0271] D: Less than 10 MPa

[0272] [Thermal cycling characteristics]

[0273] Perform the following cycle test using the obtained bonded body. Using the bonded body after the cycle test, find the bonding strength (grain shear strength) and evaluate it in the same manner as the [bonding strength].

[0274] [Cycle test]

[0275] After holding the bonded body at -40°C for 30 minutes, take the process of holding at 150°C for 30 minutes as one cycle and perform 500 cycles.

[0276] [Table 1A]

[0277] Table 1A.

[0278]

[0279] ※1: Sintering temperature or decomposition temperature (°C)

[0280] [Table 1B]

[0281] Table 1B.

[0282]

[0283] ※1: Sintering temperature or decomposition temperature (°C)

[0284] [Table 2A]

[0285] Table 2A.

[0286]

[0287] ※1: Sintering temperature or decomposition temperature (°C)

[0288] [Table 2B]

[0289] Table 2B.

[0290]

[0291] ※1: Sintering temperature or decomposition temperature (°C)

[0292] As shown in the results of Tables 1A to 2B, it was confirmed that when using the bonding paste of the present disclosure in which a specified silver particle (A) and a specified compound (B) are combined, the bonding strength is very high, and even after performing the thermal cycling test, the decrease in the bonding strength is suppressed.

[0293] In particular, the bonding paste that satisfies T3 < T1 < (T2 + 10) has a very high bonding strength even in cases where the structure is extremely difficult to stably bond, such as a non-plated substrate and a large-area SiC element. Even after performing a thermal cycle test, the decrease in bonding strength is suppressed (Examples 26 and 27, and Examples 28 and 29).

[0294] In addition, the bonding paste containing a compound having 2 to 3 tertiary nitrogen atoms has a very high bonding strength even in cases where the structure is extremely difficult to stably bond, such as a non-plated substrate and a large-area SiC element. Even after performing a thermal cycle test, the decrease in bonding strength is suppressed (Examples 1 and 2).

[0295] In addition, the bonding paste containing a dispersion medium having a boiling point of 250°C or higher has a very high bonding strength even in cases where the structure is extremely difficult to stably bond, such as a non-plated substrate and a large-area SiC element. Even after performing a thermal cycle test, the decrease in bonding strength is suppressed (Examples 4, 30, 35, and Examples 31 to 34).

[0296] In addition, the bonding paste containing a compound (D) having 20 to 80 carbon atoms and having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group has a very high bonding strength even in cases where the structure is extremely difficult to stably bond, such as a non-plated substrate and a large-area SiC element. Even after performing a thermal cycle test, the decrease in bonding strength is suppressed (Examples 2 and 15, and Examples 4 and 16).

[0297] In addition, the bonding paste containing a compound (E) having 14 to 20 carbon atoms and having one carboxyl group has a very high bonding strength even in cases where the structure is extremely difficult to stably bond, such as a non-plated substrate and a large-area SiC element. Even after performing a thermal cycle test, the decrease in bonding strength is suppressed (Examples 15 and 21, and Examples 16 and 22).

[0298] In addition, the bonded body bonded using the non-pressure bonding method including the pre-drying step (2a) has a very high bonding strength even in a structure that is extremely difficult to stably bond, such as a non-plated substrate and a large-area SiC element. Even after performing a thermal cycle test, the decrease in bonding strength is suppressed (Examples 4 and 41, and Examples 40 and 42).

[0299] On the other hand, in the case of using the bonding paste of the comparative example, the bonding strength is significantly low, and the bonding strength after performing the thermal cycle test is also significantly low.

[0300] This application claims priority based on Japanese Patent Application No. 2022-183808 filed on November 17, 2022, and incorporates the entire contents disclosed therein into this application.

Claims

1. A paste for bonding, comprising: Silver particles (A) having an average particle diameter of 100 nm to 500 nm; A compound (B) having at least one nitrogen atom selected from the group consisting of a secondary nitrogen atom and a tertiary nitrogen atom, and having 4 or more hydroxyl groups; and A dispersion medium (C).

2. The paste for bonding according to claim 1, wherein when the sintering temperature of the silver particles (A) is set to T1 °C, the 50% weight reduction temperature of the compound (B) is set to T2 °C, and the 50% weight reduction temperature of the dispersion medium (C) is set to T3 °C, T3 < T1 < (T2 + 10) is satisfied.

3. The paste for bonding according to claim 2, wherein T2 is 200 °C to 300 °C.

4. The paste for bonding according to any one of claims 1 to 3, wherein the compound (B) has a tertiary nitrogen atom.

5. The paste for bonding according to claim 4, wherein the number of tertiary nitrogen atoms in the compound (B) is 2 to 3.

6. The paste for bonding according to any one of claims 1 to 3, wherein the number of hydroxyl groups in the compound (B) is 4 to 6.

7. The paste for bonding according to any one of claims 1 to 3, wherein the compound (B) is liquid at 25 °C.

8. The paste for bonding according to any one of claims 1 to 3, wherein the content of the compound (B) is 0.05% by mass to 1.0% by mass based on the mass of the silver particles (A).

9. The paste for bonding according to any one of claims 1 to 3, wherein the average particle diameter of the silver particles (A) is 150 nm to 400 nm.

10. The paste for bonding according to any one of claims 1 to 3, wherein the boiling point of the dispersion medium (C) is 250 °C or higher.

11. The paste for bonding according to any one of claims 1 to 3, further comprising a compound (D) having 20 to 80 carbon atoms and having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group.

12. The paste for bonding according to any one of claims 1 to 3, further comprising a compound (E) having 14 to 20 carbon atoms and having one carboxyl group.

13. The paste for bonding according to any one of claims 1 to 3, wherein the content of the silver particles (A) is 80% by mass to 95% by mass based on the mass of the paste for bonding.

14. A bonded body formed by bonding a first bonded portion and a second bonded portion with the paste for bonding according to any one of claims 1 to 3.

15. The bonded body according to claim 14, wherein the first bonded portion is an unplated substrate.

16. The bonded body according to claim 14, wherein the second bonded portion is SiC.

17. A method for manufacturing a bonded body, which is a method for manufacturing a bonded body by bonding a first bonded portion and a second bonded portion with the bonding paste according to any one of claims 1 to 3, characterized in that Including the following steps: (1) A step of applying the paste for bonding to the first bonded body; (2) A step of placing the second bonded portion on the coated portion of the first bonded portion coated with the paste for bonding; (2a) A step of heating the stacked body on which placement has been performed for pre-drying; and (3) A step of sintering the stacked body on which placement has been performed in a non-pressurized environment.

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