WO2024106298A1 - Bonding paste, bonded body, and method for producing bonded body - Google Patents

Abstract

The present invention addresses the problem of providing: a bonding paste which uses silver particles and enables pressureless bonding, while achieving excellent bonding strength and being suppressed in decrease of the bonding strength associated with temperature cycles; a bonded body which uses this bonding paste; and a method for producing a bonded body. The problem is solved by: a bonding paste which contains (A) silver particles that have an average particle diameter of 100 nm to 500 nm, (B) a compound which comprises at least one kind of nitrogen atom selected from the group consisting of a secondary nitrogen atom and a tertiary nitrogen atom, and four or more hydroxyl groups, and (C) a dispersion medium; and a bonded body and a method for producing a bonded body, each of which uses this bonding paste.

Description

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

This disclosure relates to a bonding paste, a bonded body, and a method for manufacturing the bonded body.

　Conventionally, solder has been used as a bonding material for bonding metal members together, between metal members and semiconductor elements, between metal members and light-emitting diode (LED) elements, etc. In recent years, in the field of next-generation power electronics technology, there has been a demand for devices such as SiC that can operate at high temperatures. As a bonding material for manufacturing such devices, there is a demand for alternative materials to solder from the viewpoint of high-temperature operating reliability. For example, as shown in Patent Documents 1 to 3, bonding materials such as bonding pastes using sinterable metal particles have been proposed.

Patent Document 1 discloses a bonding material containing metal nanoparticles coated with an amine and an amine that is a linear alkylamine or alkanolamine. Patent Document 2 discloses the use of a conductive adhesive containing silver particles with an average particle size of 20 to 500 nm, alkanolamines, and a solvent as a bonding material. Patent Document 3 discloses a bonding composition that contains copper powder, a liquid medium, and a reducing agent, the reducing agent having at least one amino group and multiple hydroxyl groups.

JP 2014-214357 A JP 2022-117824 A International Publication No. 2020-032161

There are two types of bonding processes using such bonding materials: 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 suppresses cracks originating from voids, and therefore has the advantage of excellent bonding strength and thermal cycle properties. However, pressure bonding requires dedicated equipment, and furthermore, the objects to be bonded must be able to withstand a pressurized environment, which limits the objects to be bonded and their applications. Therefore, there is a demand for reducing voids in pressureless bonding and improving bonding strength and thermal cycle properties.
On the other hand, in recent years, the area of semiconductor elements has been increased, but 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 voids tend to occur. In addition, the difference between the linear expansion coefficient of Si or SiC elements and the linear expansion coefficient of copper used as silver particles and base material is very large, and during thermal cycles, distortion occurs between the copper base material/bonding layer containing silver particles/Si element layers, which tends to cause cracks and reduce thermal cycle characteristics. Furthermore, although the linear expansion coefficient of SiC elements is about the same as that of Si elements, the hardness is higher than that of Si elements, so that the distortion during thermal cycles is larger than that of Si elements, and cracks tend to occur in the bonding layer. That is, the level of requirements for improving the bonding strength and thermal cycle characteristics of SiC semiconductor elements has been increasing in recent years.
However, the invention described in Patent Document 1 uses a bonding material containing silver particles and an alkanolamine such as triethanolamine to pressure-bond a small copper element, and cannot solve the problems of pressureless bonding and bonding strength and thermal cycle characteristics in large-area SiC elements. In addition, the invention described in Patent Document 2 uses a bonding material containing silver particles and an alkanolamine such as diglycolamine to pressurelessly bond a small Si element, and cannot solve the problems of bonding strength and thermal cycle characteristics in large-area SiC elements. Furthermore, the invention described in Patent Document 3 uses a bonding material containing copper particles and an alkanolamine to pressure-bond a small copper element, but copper particles are more easily oxidized than silver particles, and when oxidized, the function of copper particles cannot be expressed, so there is a problem in handling. In particular, in bonding applications where heating is performed to about 200°C or higher, if a small amount of oxygen is present during the heating process, oxidation progresses, making it difficult to suppress oxidation, and the problems of pressureless bonding and bonding strength and thermal cycle characteristics in large-area SiC elements cannot be solved. It should be noted that Patent Document 3 does not mention the use of silver particles.

The problem that this disclosure aims to solve is therefore to provide a joining paste that uses silver particles, has excellent joining strength, is suppressed from decreasing in joining strength due to thermal cycling, and allows joining without the application of pressure, and a joined body that uses this joining paste.

The present inventors have conducted extensive research to solve the above problems, and as a result have arrived at the present disclosure.
A bonding paste according to one embodiment of the present disclosure is characterized by containing silver particles (A) having an average particle size of 100 nm to 500 nm, a compound (B) having at least one type of nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms and having four or more hydroxyl groups, and a dispersion medium (C).

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

The joining paste according to one embodiment of the present disclosure is characterized in that T2 is 200 to 300°C.

The joining paste according to one embodiment of the present disclosure is characterized in that the compound (B) has a tertiary nitrogen atom.

The joining paste according to one embodiment of the present disclosure is characterized in that the number of tertiary nitrogen atoms in the compound (B) is 1 to 3.

The joining paste according to one embodiment of the present disclosure is characterized in that the number of hydroxyl groups in the compound (B) is 4 to 6.

The joining paste according to one embodiment of the present disclosure is characterized in that the compound (B) is liquid at 25°C.

The joining paste according to one embodiment of the present disclosure is characterized in that the content of the compound (B) is 0.05 to 1.0 mass % based on the mass of the silver particles (A).

The joining paste according to one embodiment of the present disclosure is characterized in that the silver particles (A) have an average particle size of 150 nm to 400 nm.

The joining paste according to one embodiment of the present disclosure is characterized in that the dispersion medium (C) has a boiling point of 250°C or higher.

The joining paste according to one embodiment of the present disclosure is further characterized by containing a compound (D) having 20 to 80 carbon atoms and having two or more functional groups of at least one type selected from the group consisting of hydroxyl groups, carboxy groups, and amino groups.

The joining paste according to one embodiment of the present disclosure is further characterized by containing a compound (E) having one carboxy group and 14 to 20 carbon atoms.

The bonding paste according to one embodiment of the present disclosure is characterized in that the content of the silver particles (A) is 80 to 95 mass % based on the mass of the bonding paste.

The bonded body according to one aspect of the present disclosure is characterized in that a first bonded portion and a second bonded portion are bonded by the bonding paste.

The joined body according to one embodiment of the present disclosure is characterized in that the first joined portion is a non-plated substrate.

The bonded body according to one embodiment of the present disclosure is characterized in that the second bonded portion is made of SiC.

A method for producing a joined body according to one embodiment of the present disclosure is a method for producing a joined body in which a first joined portion and a second joined portion are joined by the above-mentioned joining paste, and is characterized in that it includes the following steps.
(1) A step of applying a bonding paste to a first object to be bonded.
(2) A step of placing a second part to be joined on the application portion of the first part to be joined that has been applied with the joining paste.
(2a) A step of pre-drying the placed laminate by heating.
(3) A step of sintering the placed laminate in a pressureless environment.

The present invention provides a bonding paste that uses silver particles, has high bonding strength at the bonded points, and is suppressed from decreasing in bonding strength due to thermal cycles, and can bond without pressure, as well as a bonded body using the bonding paste. As a result, even when large-area SiC elements are bonded without pressure, excellent bonding strength and thermal cycle characteristics can be achieved.

In this specification, "silver particles (A) having an average particle size of 100 nm to 500 nm" may 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 four or more hydroxyl groups" may be abbreviated as "compound (B)."

The bonding paste of the present disclosure is characterized by containing silver particles (A) having an average particle size of 100 nm to 500 nm, a compound (B) having at least one type of nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms and having four or more hydroxyl groups, and a dispersion medium (C).
The bonding paste of the present disclosure combines silver particles (A) with a compound (B) having a predetermined structure, and due to the high non-volatility of compound (B), the wettability of silver particles (A) having a predetermined particle size to the substrate is improved at the sintering stage, and the generation of voids in the coating film is suppressed, resulting in the formation of a dense coating film even in pressureless bonding.
Furthermore, when the bonded portion is a substrate (plating-free substrate) that has not been plated, such as plated copper, the surface of the plating-free substrate is oxidized to form an oxide by heating during sintering, and the bonding between the silver particles and the plating-free substrate covered with the oxide tends to be insufficient, resulting in a decrease in bonding strength and a deterioration in thermal cycle characteristics. However, by including the compound (B), the oxidation of the surface of the plating-free substrate is suppressed and/or the oxide is reduced by the reducing function of the compound (B), and strong bonding between the silver particles (A) and the plating-free substrate is possible. Therefore, not only can the bonding strength be improved and good thermal cycle characteristics be obtained, but also the steps of plating the substrate or cleaning the substrate in advance can be omitted.
As a result, even in pressureless bonding, and in bonding of parts that are difficult to bond stably, such as plating-free substrates and large-area SiC semiconductor elements, the generation of voids is suppressed, and excellent bonding strength and bonding strength after thermal cycles can be exhibited.

<Silver Particles (A)>
The silver particles (A) exert the electrical conductivity and thermal conductivity of the bonded body and play a role in bonding the bonded bodies during the sintering process, and include silver-coated particles in which a core body is an alloy containing silver, silver oxide, or a metal (except silver) and the surface of the core body is coated with silver. By using the silver particles (A), a bonded body having excellent strength can be obtained. In addition, the silver particles (A) can be used at a wide range of firing temperatures and can be used in various firing environments such as atmospheric pressure, nitrogen atmosphere, vacuum, or reducing atmosphere.

The silver particles (A) have an average particle size in the range of 100 nm to 500 nm, and therefore have the ability to melt or bond together (hereinafter also referred to as sintering) in the temperature range of 200°C to 350°C at which the bonding paste is heated and sintered, making it possible for the particles to change into bulk metal. As a result, the objects to be bonded are bonded together. Hereinafter, the area formed by sintering the silver particles (A) between the objects to be bonded is referred to as the bonding layer.

In this disclosure, it is important to use silver particles (A) having a specific average particle size. In this specification, "average particle size" means the 50% cumulative particle size distribution particle size (d50) on a volume basis determined by the measurement method described in the Examples. The d50 of silver particles (A) is 100 to 500 nm, preferably 150 nm or more, more preferably 180 nm or more, and even more preferably 200 nm or more. In addition, the d50 of silver particles (A) is preferably 450 nm or less, more preferably 400 nm or less, even more preferably 350 nm or less, and particularly preferably 300 nm or less.

The silver particles (A) are preferably surface-coated with an organic component (a). That is, the silver particles (A) are preferably particles whose surfaces are coated with an organic component (a), and the coated organic component (a) is also called a protective agent. When coated with the organic component (a), it is expected that the storage stability of the joining paste will increase. Examples of the organic component (a) include fatty acids, aliphatic amines, and aliphatic alcohols, and saturated or unsaturated fatty acids are preferred, saturated or unsaturated fatty acids having 3 to 18 carbon atoms are more preferred, and saturated or unsaturated fatty acids having 6 to 18 carbon atoms are even more preferred. The organic component (a) may contain one or more types.

Silver particles (A) may be used alone or in combination. If necessary, metal particles other than silver particles (A) may be used in combination. When metal particles other than silver particles (A) are used in combination, metal particles having an average particle diameter of more than 500 nm may be combined, or metal particles having an average particle diameter of more than 1000 nm may be combined.

<Compound (B)>
The bonding paste of the present disclosure contains a compound (B) having at least one type of nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms, and having four or more hydroxyl groups.
The compound (B) has the function of uniformly dispersing the silver particles (A), suppressing the aggregation of the silver particles (A) over time, and enabling better viscosity characteristics and coatability. In particular, the secondary nitrogen atom and the tertiary nitrogen atom have an excellent function of reducing the silver particles (A) and the bonded portion. In addition, the secondary nitrogen atom and the tertiary nitrogen atom have excellent bonding properties with the silver particles (A), improving dispersibility. In particular, the tertiary nitrogen atom has a branched structure, and therefore has excellent dispersibility due to the steric hindrance effect.
In addition, since secondary nitrogen atoms and tertiary nitrogen atoms have an excellent function of reducing the silver particles (A) and the bonded portion, the inclusion of the compound (B) reduces the silver particles (A) and strengthens the silver layer after sintering. In addition, oxidation of the substrate surface, which is the bonded portion, is suppressed, and the bonding strength of the interface is strengthened.
Furthermore, the compound (B) imparts fluidity to the silver particles (A) during firing and serves to densify the silver layer after sintering.
From the viewpoints of bonding strength and thermal cycle properties, compound (B) preferably has a tertiary nitrogen atom, and the number of tertiary nitrogen atoms is preferably 1 to 3, more preferably 2 to 3. When the number of tertiary nitrogen atoms is 2 or more, the bondability with silver particles (A) is enhanced and dispersibility is significantly improved. In addition, the tertiary nitrogen atom has a function of reducing silver particles (A) and the bonded portion, and when the number of tertiary nitrogen atoms is 2 or more, the reducing function is enhanced.
From the viewpoints of dispersibility and reducing function, the number of hydroxyl groups in compound (B) is preferably 4 to 6. In particular, hydroxyl groups have excellent bonding properties with silver particles (A) and therefore tend to improve dispersibility, and a hydroxyl group number of 4 or more enhances bonding properties with silver particles (A) and significantly improves dispersibility. Hydroxyl groups also have the function of reducing silver particles (A) and the bonded portions, and a hydroxyl group number of 4 or more significantly improves the reducing function.

The compound (B) is preferably a compound that is liquid at 25° C. In this specification, liquid means that the compound is not solid but has fluidity, and has a viscosity of 1000 Pa s or less as measured using an E-type viscometer at 25° C. and 2.5 rpm.
Being liquid at 25°C increases the wettability at the bonding interface with the bonded parts during the process from solvent drying to sintering, and the contact area increases. As a result, it is possible to manufacture a bonded body having a strong bonding interface. In addition, even if voids are formed in the bonding layer during the process from solvent drying to sintering, the fluidity of the bonding paste increases, so that the liquid compound (B) flows into defective parts such as voids, making it possible to obtain a bonding layer and bonded body with fewer defects.

Generally, since the silver particles (A) are powder, when the compound (B) is not included, as the dispersion medium (C) described later volatilizes from the bonding paste, it becomes difficult to form an interface with the bonded parts. However, by including the compound (B) of the present disclosure, the bonding paste can exist as a liquid composition even after a part or all of the dispersion medium (C) has volatilized, so that a good bonding interface that is integrated with the bonded parts can be formed.
In addition, one of the causes of defects (voids) in the bonding layer is the sudden evaporation of the dispersion medium (C) at the firing temperature range when the dispersion medium (C) is insufficiently evaporated, but by including the compound (B), the coating film can flow and form a bonding interface even after the dispersion medium (C) has dried and been removed. This makes it possible to provide a pre-drying step for drying the dispersion medium (C) in advance, and to form a bonding layer with fewer defects.
In addition, when the compound (B) has a property of being liquid in the sintering temperature range of the silver particles (A), the wettability at the bonding interface with the bonded parts is improved and the contact area is increased, so that a bonded body having a stronger bonding interface can be obtained. Furthermore, even if voids are generated in the bonding layer during sintering, the bonding paste has fluidity, so that the liquid compound (B) flows into the voids, thereby reducing the voids.

Specific examples of the compound (B) include bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane (1 tertiary nitrogen atom, 5 hydroxyl groups), N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (2 tertiary nitrogen atoms, 4 hydroxyl groups), N,N,N',N'',N''-pentakis(2-hydroxyethyl)diethylenetriamine (3 tertiary nitrogen atoms, 5 hydroxyl groups), N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (3 tertiary nitrogen atoms, 5 hydroxyl groups), number of tertiary nitrogen atoms: 1, number of hydroxyl groups: 5), 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), and N,N,N',N'',N''-pentakis(2-hydroxypropyl)diethylenetriamine (number of tertiary nitrogen atoms: 3, number of hydroxyl groups: 5.
In particular, bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane, N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, and N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine are preferably used. These compounds (B) may be used alone or in combination.

The content of the compound (B) is preferably 0.02% by mass or more based on the mass of the silver particles (A). If it is 0.02% by mass or more, the dispersibility of the silver particles (A) is improved, and sintering proceeds with the compound (B) remaining in the coating film, and the coating film has fluidity, so that adhesion to the substrate and 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 even more preferably 0.10% by mass or more.
The content of the compound (B) is preferably 2.00% by mass or less based on the mass of the silver particles (A). By making it 2.00% by mass or less, the amount remaining in the coating film after sintering can be reduced, and the bonding strength and thermal cycle properties are excellent. From the viewpoint of reducing the amount remaining, it is more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less.

<Dispersion medium (C)>
The bonding paste of the present disclosure contains a dispersion medium (C) (excluding compound (B) and compound (D) described below). The dispersion medium (C) serves to disperse silver particles (A) and compound (B). The dispersion medium (C) also serves to impart fluidity to the coating film in the silver sintering process. The number of carbon atoms in the dispersion medium (C) is preferably less than 20.

The dispersion medium (C) may be any medium capable of uniformly dispersing the silver particles (A) and the compound (B). Specific examples include, for example, terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersolve TOE-100, Tersolve MTPH (manufactured by Nippon 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 monomethyl ether, dipropylene glycol methyl-n-propyl ether, 3-methoxy-3-methylbutyl acetate, ethylene glycol, propylene glycol. Examples of such solvents include, but are not limited to, isoparaffin-based solvents contained in hydrocarbon solvents, such as 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 solvents contained in hydrocarbon solvents.

The dispersion medium (C) preferably contains a dispersion medium with a boiling point of 200°C or higher. If it contains a dispersion medium with a boiling point of 200°C or higher, the dispersion medium in the coating dries and reduces relatively slowly during the silver sintering process, so the coating can be sintered while maintaining high fluidity. This makes it possible to improve adhesion to the parts to be joined and to obtain a stronger bonded body with fewer defects. The proportion of the dispersion medium with a boiling point of 200°C or higher in the mass of the dispersion medium (C) is preferably 70 mass% or more.

The boiling point of the dispersion medium with a boiling point of 200°C or higher is preferably 240°C or higher, and more preferably 250°C or higher. If it is 250°C or higher, the coating film can be sintered for a longer period of time while maintaining high fluidity. This is preferable because it forms a stronger bond with fewer defects and has excellent thermal cycle properties. In addition, the boiling point is preferably 350°C or lower from the viewpoint of suppressing residual dispersion medium. When multiple types of dispersion medium with a boiling point of 200°C or higher are included, the boiling points of the dispersion mediums with a boiling point of 200°C or higher can be calculated from the boiling points of each type and their mass ratios.

Examples of dispersion media with a boiling point of 200°C or higher include, but are not limited to, terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersolve TOE-100, Tersolve MTPH (manufactured by Nippon 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 with a boiling point of 200°C or higher. These dispersion media with a boiling point of 200°C or higher can be used alone or in combination.

Among the dispersion media having a boiling point of 200° C. or higher, diol-based dispersion media such as 1,3-butanediol, 1,4-butanediol, and 2-ethyl-1,3-hexanediol, 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 are preferably used. Glycol ether-based dispersion media are more preferred.
As glycol ether-based dispersion media having a boiling point of 250° C. or higher, diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether are particularly preferably used.

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 mediums, the boiling point of the dispersion medium (C) can be calculated from the boiling points of the respective dispersion mediums and their mass ratios.
If the boiling point of the dispersion medium (C) as a whole is 250° C. or higher, the dispersion medium in the coating film dries and decreases relatively slowly in the silver sintering process, so that the coating film can be sintered while maintaining high fluidity. This is preferable because it improves the adhesion with the bonded parts and makes it possible to obtain a stronger bonded body with fewer defects.

<Sintering temperature, 50% weight loss temperature>
In the bonding paste of the present disclosure, when the sintering temperature of the silver particles (A) is T1 ° C., the 50% weight loss temperature of the compound (B) is T2 ° C., and the 50% weight loss temperature of the dispersion medium (C) is T3 ° C., it is preferable that T3 < T1 < (T2 + 10) is satisfied. In this case, it is preferable to satisfy T3 < T2. In this way, by making the 50% weight loss temperature T3 of the dispersion medium (C) lower than the 50% weight loss temperature T1 of the silver particles (A) and the 50% weight loss temperature T2 of the compound (B), and making the 50% weight loss temperature T2 of the compound (B) a temperature zone exceeding a temperature about 10 ° C. lower than the 50% weight loss temperature T1 (sintering temperature) of the silver particles (A), it is presumed that the dispersion medium (C) is first volatilized and removed, and the compound (B) is present during and after the sintering of the silver particles (A). This reduces defects in the bonding layer, enabling the formation of a strong bonding interface and dense bonding, which is believed to result in excellent bonding strength and thermal cycle properties.

The 50% weight loss temperatures T2 and T3 of the compound (B) and the dispersion medium (C) can be measured by thermogravimetric differential thermal analysis (hereinafter, also referred to as TG-DTA analysis). Examples of the measurement method include the following method.
Using a thermogravimetric differential thermal analyzer (TG/DTA8122 (manufactured by RIGAKU Corporation)), the samples were heated in a nitrogen atmosphere at a heating rate of 1° C./min, and the temperatures at which the samples lost 50% weight were defined as 50% weight loss temperatures T2 and T3, respectively. When the compound (B) or the dispersion medium (C) is a mixture of two or more kinds, the results of the above measurement using the mixture are used.

The 50% weight loss temperature T2 of compound (B) is preferably 200 to 300°C, more preferably 210 to 270°C, and even more preferably 210 to 255°C. If it is 200°C or higher, compound (B) can remain sufficiently in the coating even in the sintering temperature range, improving the fluidity of the coating during sintering, improving adhesion to the substrate, and providing excellent bonding strength. If it is 300°C or lower, it is possible to reduce the amount of compound (B) remaining in the coating after sintering, and providing excellent bonding strength and thermal cycle properties.

The sintering temperature T1 of the silver particles (A) can be measured using thermogravimetric differential thermal analysis (hereinafter, also referred to as TG-DTA analysis). Examples of the measurement method include the following method.
The sintering temperature T1 of silver particles (A) is defined as the temperature at which the protective agent is decomposed by heating to 400° C. in a nitrogen atmosphere at a temperature increase rate of 1° C./min, and the weight loss is defined as 100, and the temperature at which the weight is reduced by 50% is defined as T1.

<Compound (D)>
The bonding paste of the present disclosure may contain a compound (D) having 20 to 80 carbon atoms and having two or more functional groups (hereinafter referred to as functional group (d)) selected from the group consisting of hydroxyl groups, carboxy groups, and amino groups. By including such a compound (D), the composition can exist as a liquid composition even after a part or all of the dispersion medium (C) has volatilized, so that a good bonding interface integrated with the parts to be bonded can be formed. In addition, each functional group has high binding ability with silver particles (A) and exhibits excellent dispersibility.

The number of carbon atoms in compound (D) includes the number of carbon atoms in functional group (d). Therefore, if the functional group (d) in compound (D) is a carboxy group, the number of carbon atoms in compound (D) includes the number of carbon atoms in the carboxy group.

In compound (D), the skeleton (partial structure) excluding functional group (d) is an organic residue, but is preferably a hydrocarbon group or a group in which multiple hydrocarbon groups are bonded 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 (D) does not have any functional groups other than functional group (d).

The properties of compound (D) are not particularly limited, but it is preferable that the compound (D) is liquid at 200°C to 350°C, which is the temperature range in which the joining paste of the present disclosure is fired. Compound (D) may be solid or liquid at room temperature (25°C), but it is more preferable that the compound (D) is liquid at room temperature from the viewpoint of being uniformly dispersed in the joining paste and acting effectively.

If compound (D) has the property of being liquid in the above temperature range, it is expected that the wettability at the bonding interface with the parts to be bonded will increase, and the contact area will increase. As a result, it will be possible to manufacture a bonded body with a strong bonding interface. Furthermore, even if voids are formed in the bonding layer during sintering, the fluidity of the bonding paste will increase, so that liquid compound (D) will flow into defective parts such as voids, making it possible to obtain a bonding layer and bonded body with fewer defects.

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

Compound (D) may have a linear structure or a branched and/or cyclic structure, but preferably has a branched and/or cyclic structure. When it has a branched and/or cyclic structure, it is preferable in that it has low crystallinity and is likely to become a liquid with good fluidity.

When the number of functional groups (d) in compound (D) is n, compound (D) preferably has an n-valent hydrocarbon group. In compound (D), the skeleton excluding functional group (d) is more preferably composed only of n-valent hydrocarbon groups, in that a strong bond can be obtained.

For the above reasons, it is preferable that compound (D) does not evaporate immediately when sintering begins. However, it does not necessarily have to remain in the formed bonding layer when sintering is completed. When the carbon number of the n-valent hydrocarbon group is 30 to 60, the amount of compound (D) remaining in the bonding layer after sintering can be further reduced, which is preferable because it makes it easier to obtain a denser bonding layer. As a result, the initial bonding strength is excellent, and it can be expected that the decrease in bonding strength due to thermal cycles will be further suppressed.

Examples of compounds (D) having a straight-chain structure include, but are not limited to, eicosane diacid, heneicosane diacid, docosane diacid, tetracosane diacid, triacontanedioic acid, dotriacontanedioic acid, tetracontanedioic acid, pentacontanedioic acid, hexacontanedioic acid, and batyl alcohol.

Examples of compounds (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 tetraol, dimer diamine, trimer triamine, tetramer tetramine, and phytantriol.

Of these, for the reasons mentioned above, it is more preferable that compound (D) is a compound selected from the group consisting of dimer acid, trimer acid, dimer diol, trimer triol, dimer diamine, and trimer triamine.

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 between oleic acid (carbon number 18) and linoleic acid (carbon number 18) or by radical reaction. 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 used as the raw material, it is possible to produce a compound (D) having a carbon number other than the above. In this specification, the dimer, trimer, and tetramer of unsaturated fatty acids having 12 or more carbon atoms are referred to as dimer acid, trimer acid, and tetramer acid, respectively.

Dimer diol has a structure in which the carboxy group of dimer acid has been reduced to a hydroxyl group, trimer triol has a structure in which the carboxy group of trimer acid has been reduced to a hydroxyl group, and tetramer tetraol has a structure in which the carboxy group of tetramer acid has been reduced to a hydroxyl group. It is preferable that the carbon number of dimer diol is 36, the carbon number of trimer triol is 54, and the carbon number of tetramer tetraol is 72.

Dimer diamine has a structure in which the carboxy group of dimer acid, trimer triamine has a structure in which the carboxy group of trimer acid, and tetramer tetramine has a structure in which the carboxy group of tetramer acid are converted to an amino group as a functional group. It is preferable that the carbon number of dimer diamine is 36, the carbon number of trimer triamine is 54, and the carbon number of tetramer tetramine is 72.

Due to the manufacturing process, compound (D) may be a mixture of compounds with different degrees of polymerization, but it may be used as a mixture of different polymerizations, or a specific single compound may be used.

In the bonding paste of the present disclosure, the content of compound (D) is preferably 0.05 to 2.0 parts by mass, and more preferably 0.1 to 1.0 parts by mass, per 100 parts by mass of silver particles (A). Within this range, it is possible to obtain a bonded body that is particularly excellent in initial bonding strength and in which the decrease in bonding strength due to thermal cycles is suppressed.

[Compound (Dx)]
The bonding paste of the present disclosure preferably contains, as the compound (D), a compound (Dx) having 20 to 80 carbon atoms and three carboxy groups. The compound (Dx) may have a linear structure or a branched and/or cyclic structure, but preferably has a branched and/or cyclic structure. When the compound (Dx) has a branched and/or cyclic structure, it is preferable that the compound (Dx) has a branched and/or cyclic structure, since the compound (Dx) is likely to be liquid with low crystallinity and good fluidity. The compound (Dx) preferably has a trivalent hydrocarbon group. In the compound (Dx), the skeleton excluding the carboxy group is more preferably composed of only a trivalent hydrocarbon group, since a strong bonded body can be obtained. A specific example of the compound (Dx) having a branched and/or cyclic structure is trimer acid, which is preferably used.

The bonding paste of the present disclosure preferably contains 0.03 to 2.0 parts by mass of compound (Dx) per 100 parts by mass of silver particles (A). By containing the compound (Dx) in the above range, it is possible to exhibit excellent bonding strength and thermal cycle properties even under more severe conditions, such as when a non-plated substrate is used for bonding.

[Compound (Dy)]
The bonding paste of the present disclosure preferably further contains a compound (Dy) having two carboxy groups and a carbon number of 20 to 80. The above-mentioned compound (Dx) and the compound (Dy) having a different number of carboxy groups have different volatilization or decomposition temperatures, and the compound (Dy) has a lower volatilization or decomposition temperature than the compound (Dx). Therefore, when these are used in combination, it is possible to suppress simultaneous volatilization or decomposition at a specific temperature in the sintering process of silver. Therefore, the coating film can be sintered for a longer time while maintaining high fluidity. This further improves the adhesion to the joined parts, making it possible to obtain a stronger bonded body with fewer defects.

The compound (Dy) may have a linear structure or a branched and/or cyclic structure, but preferably has a branched and/or cyclic structure. When the compound has a branched and/or cyclic structure, it is preferable that the compound has a branched and/or cyclic structure, since it tends to be a liquid with low crystallinity and good fluidity. The compound (Dy) preferably has a divalent hydrocarbon group. In the compound (Dy), it is more preferable that the skeleton excluding the carboxyl group is composed only of a divalent hydrocarbon group, since a strong bonded body can be obtained.

Examples of the compound (Dy) having a linear structure include, but are not limited to, eicosane diacid, heneicosane diacid, docosane diacid, tetracosane diacid, triacontanedioic acid, dotriacontanedioic acid, tetracontanedioic acid, pentacontanedioic acid, and hexacontanedioic acid. Examples of the compound (Dy) having a branched and/or cyclic structure include dimer acid, which is preferably used.

The bonding paste of the present disclosure preferably contains 0.03 to 2.0 parts by mass of the compound (Dy) per 100 parts by mass of the silver particles (A). By containing the compound (Dy) in the above range, it is possible to exhibit excellent bonding strength and thermal cycle properties even under more severe conditions, such as when a non-plated substrate is used for bonding.

The bonding paste of the present disclosure preferably contains 0.05 to 2.0 parts by mass of compound (Dx) and compound (Dy) in total relative to 100 parts by mass of silver particles (A). When the total of compound (Dx) and compound (Dy) is within the above range, a bonded body can be obtained that is particularly excellent in initial bonding strength and in which the decrease in bonding strength due to thermal cycles is suppressed.

<Compound (E)>
The bonding paste of the present disclosure may contain a compound (E) having one carboxy group and having 14 to 20 carbon atoms. The number of carbon atoms in the compound (E) includes the carbon atom in the carboxy group.
The compound (E) is a fatty acid, and by including such a compound (E), the composition can exist as a liquid composition even after a part or all of the dispersion medium (C) has evaporated, so that a good bonding interface can be formed that is integrated with the bonded parts. In addition, each functional group has high binding affinity with the silver particles (A) and exhibits excellent dispersibility.

Examples of the compound (E) include linear saturated fatty acids, linear unsaturated fatty acids, and branched fatty acids. Examples of linear saturated fatty acids include myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, and arachic acid. Examples of linear unsaturated fatty acids include palmitoleic acid, oleic acid, and erucic acid. Examples of branched fatty acids include 2-hexyldecanoic acid.
The compound (E) is preferably a linear unsaturated fatty acid. The joining paste of the present disclosure contains a linear unsaturated fatty acid, which enhances lipophilicity and improves stability in non-aqueous solvents. In addition, linear unsaturated fatty acids are preferred because they have a low decomposition temperature and excellent low-temperature sintering properties. The compound (E) may be used alone or in combination of multiple types.

The bonding paste of the present disclosure preferably contains 0.1 to 2.0 parts by mass, and more preferably 0.2 to 1.0 parts by mass, of compound (E) per 100 parts by mass of silver particles (A). When the content is within the above range, excellent bonding strength and thermal cycle properties can be exhibited even if the substrate to be bonded is not plated.

<Production of bonding paste>
The bonding paste of the present disclosure may contain at least silver particles (A), a compound (B), and a dispersion medium (C), and the manufacturing method thereof is not particularly limited and may be prepared using a known method. Examples of devices for preparing the bonding paste from silver particles (A), a compound (B), and a dispersion medium (C) include a disperser, a three-roll mill, a bead mill, an ultrasonic disperser, and a self-revolving mixer.

The mass ratio of silver particles (A) based on the mass of the bonding paste is preferably 80% by mass to 95% by mass, and more preferably 85% by mass to 94% by mass. By including silver particles (A) in the above range, the bonding paste exhibits good printability, while suppressing the residue of dispersion medium (C) in the bonded body and suppressing the occurrence of voids originating from the dispersion medium (C), thereby exhibiting good bonding strength.

The joining paste of the present disclosure may contain additives, such as a sintering accelerator, a binder resin, or a resin-type dispersant.

<Jointed body and method for producing the joined body>
The bonding paste of the present disclosure can be used to bond a first bonded part and a second bonded part to obtain a bonded body. The bonded body can be produced, for example, by the following production method (I) or production method (II).

[Production method (I)]
The manufacturing method (I) is a pressure-free joining method, and preferably includes, for example, the following steps (1) to (3).
(1) A step of applying a bonding paste to a first object to be bonded.
(2) A step of placing a second part to be joined on the first part to be joined that has been applied with the joining paste.
(3) A step of sintering the placed laminate in a pressureless environment.

(1) Coating process The method of coating the bonding paste on the bonded body is not particularly limited as long as it can be uniformly coated on the member, and examples thereof include various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, gravure offset printing, and the like, and a discharge method using a dispenser, etc. The bonding paste of the present disclosure has excellent fluidity even when it contains metal particles at a high concentration, and is therefore preferably used in combination with metal mask printing.

(2) Placing Step Next, the second part to be joined is placed on the first part to be joined to which the joining paste of the present disclosure has been applied. When the joining paste of the present disclosure is used, the second part to be joined can be placed without applying pressure. In the pressure-free joining, the placing step is preferably also performed without applying pressure, but it is also possible to place the second part while applying pressure. When applying pressure, the pressure is appropriately set depending on the viscosity of the joining paste and the drying state of the paste, and is preferably 0.1 to 40 MPa, more preferably 0.3 to 30 MPa.

(3) Sintering process Sintering conditions for pressurelessly bonding a laminate in which a second bonded portion is placed on a first bonded portion may be appropriately changed, and may include, for example, conditions of 200 to 350°C under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere. 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 may be used alone or in combination as appropriate.
The 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 the temperature is maintained at or above the set temperature for about 10 minutes to 2 hours. The set temperature is preferably 200 to 350°C, more preferably 250 to 330°C, and even more preferably 280 to 320°C.

(2a) Pre-drying step In the manufacturing method (I) using pressureless bonding, it is preferable to provide a pre-drying step (2a) between steps (2) and (3) for the purpose of removing organic components in the bonding coating film. Since the bonding paste of the present disclosure contains the compound (B), the coating film can flow and form a bonding interface even after the dispersion medium (C) has been dried and removed in advance, so a pre-drying step can be provided. By providing a pre-drying step, the residual dispersion medium (C), which is one of the causes of defects (voids) in the bonding layer, can be suppressed, and the bonding layer has excellent density, which is preferable.
The preliminary drying can be carried out, for example, using an apparatus similar to the calcination apparatus at a temperature in the range of 60 to 220° C. for 1 to 300 minutes, preferably at a temperature in the range of 70 to 100° C. for 30 to 120 minutes.

That is, the production method (I) is particularly preferably one comprising the following steps:
(1) A step of applying a bonding paste to a first object to be bonded.
(2) A step of placing a second part to be joined on the application portion of the first part to be joined that has been applied with the joining paste.
(2a) A step of pre-drying the placed laminate by heating.
(3) A step of sintering the placed laminate in a pressureless environment.

[Production method (II)]
The manufacturing method (II) is a pressure bonding method, and preferably includes, for example, the following steps (10) to (30).
(10) A step of applying a bonding paste to a first object to be bonded.
(10a) A step of pre-drying the coated laminate by heating.
(20) A step of placing a second part to be joined on a first part to be joined that has been coated with a joining paste and pre-dried.
(30) A step of sintering the placed laminate in a pressurized environment.

(10) Coating Step The method of applying the bonding paste to the bonded body is not particularly limited as long as it can be uniformly applied to the member, and examples thereof include various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, gravure offset printing, and the like, and a discharge method using a dispenser, etc. The bonding paste of the present disclosure has excellent fluidity even when it contains metal particles at a high concentration, and is therefore preferably used in combination with metal mask printing.

(10a) Pre-drying step In the manufacturing method (II) using pressure bonding, a pre-drying step (10a) can be provided between steps (10) and (20) for the purpose of removing organic components in the bonding coating film. By providing the pre-drying step, the pre-drying can be carried out, for example, using a device similar to a baking device at a temperature in the range of 60 to 220° C. for 1 to 300 minutes.

(20) Placing step Next, the second part to be joined is placed on the first part to be joined, which has been applied with the bonding paste of the present disclosure and pre-dried. In the case of pressurized bonding, the placing 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.

(30) Sintering process Sintering conditions for pressure bonding a laminate in which a second bonded portion is placed on a first bonded portion may be appropriately changed, and may include, for example, conditions of atmospheric pressure, a nitrogen atmosphere, a vacuum, or a reducing atmosphere at 200 to 350°C. Examples of the sintering device include a hot air oven, a sintering furnace, an electric furnace, an infrared oven, a reflow oven, a microwave oven, a hot plate, a light sintering device, etc. These devices may be used alone or in combination as appropriate.
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, and more preferably 0.3 to 30 MPa.

In either manufacturing method, there is no restriction on the thickness of the bonding layer formed when the parts to be bonded 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.

[Part to be joined]
The type of the 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.

The first and second joined parts may be of the same type or different types. The surfaces of the joined parts may be subjected to a corona treatment, a plating treatment, or the like in order to increase the joining strength of the joined parts.
The bonding paste of the present disclosure has excellent bonding strength to a plating-less substrate and a SiC element, and is preferably used for a bonded body in which a first bonded part is a plating-less substrate, and a second bonded part is SiC.
In particular, by containing the compound (B), oxidation of the substrate surface is suppressed and/or the oxide is reduced, enabling strong bonding between the silver particles (A) and the substrate. The above effect is particularly effective for substrates that are easily oxidized, so the bonding paste of the present invention is extremely effective as a bonding material for copper substrates that are easily oxidized, particularly non-plated copper substrates.

Below, the present disclosure will be explained in detail using examples and comparative examples, but the technical scope of the present disclosure is not limited thereto. In the examples, "parts" and "%" represent "parts by mass" and "% by mass", respectively, unless otherwise specified. Numerical values in tables represent "parts" unless otherwise specified.

[Sintering temperature T1 of silver particles (A)]
The sintering temperature T1 of silver particles (A) was measured by heating the particles to 400° C. at a temperature increase rate of 1° C./min in a nitrogen atmosphere using a thermogravimetric differential thermal analyzer (TG/DTA8122, manufactured by RIGAKU Corporation) to decompose the protective agent. The sintering temperature T1 was determined as the temperature at which the weight was reduced by 50%, assuming that the weight loss was 100.

[50% Weight Loss Temperatures T2 and T3 of Compound (B) and Dispersion Medium (C)]
The 50% weight loss temperatures T2 and T3 of the compound (B) and the dispersion medium (C) were determined by heating at a heating rate of 1° C./min under a nitrogen atmosphere using a thermogravimetric differential thermal analyzer (TG/DTA8122 (manufactured by RIGAKU Corporation)) and determining the temperatures at which the weight of the compound (B) and the dispersion medium (C) was reduced by 50%, respectively. When the compound (B) or the dispersion medium (C) was a mixture of two or more kinds, the results of the above measurement using the mixture were used.

<Production of Metal Particles>
(Production Example 1) Metal Particles A1
Under a nitrogen atmosphere, 200 parts of toluene and 22.3 parts of silver hexanoate were mixed while stirring at 25 ° C. to obtain a 0.5 M solution, and then 1.6 parts of diethylaminoethanol and 0.28 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, SUDH) was dropped as a reducing agent, and the liquid color changed from light yellow to dark brown. In order to further promote the reaction, the temperature was raised to 40 ° C., and the reaction was allowed to proceed. After standing and separating, the aqueous phase was removed to remove excess reducing agent and impurities, and distilled water was added to the toluene layer several times, washing and separation were repeated, and then the process of adding toluene, centrifuging, and removing the supernatant 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 d50 was 210 nm.

(Production Example 2) Metal Particles A2
Metal particles A2 were obtained in the same manner as in Production Example 1, 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.
(Production Example 3) Metal Particles A3
Metal particles A3 were obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was 2.0 parts and the amount of oleic acid was 0.34 parts. The d50 was 155 nm.
(Production Example 4) Metal Particles A4
Metal particles A4 were obtained in the same manner as in Production Example 1, 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.
(Production Example 5) Metal Particles A5
Metal particles A5 were obtained in the same manner as in Production Example 1, 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.
(Production Example 6) Metal Particles A6
Metal particles A6 were obtained in the same manner as in Production Example 1, 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.

(Production Example 10) Comparative metal particles A10
Metal particles A10 were obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was 1.4 parts and the amount of oleic acid was 0.09 parts. The d50 was 600 nm.
(Production Example 11) Comparative metal particles A11
Metal particles A11 were obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was 0.6 parts and the amount of oleic acid was 0.070 parts. The d50 was 1100 nm.
(Production Example 12) Comparative metal particles A12
Metal particles A12 were obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was 2.3 parts and the amount of oleic acid was 2.8 parts. The d50 was 20 nm.
(Production Example 13) Comparative metal particles A13
Metal particles A13 were obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was 2.1 parts and the amount of oleic acid was 0.71 parts. The d50 was 85 nm.

[Method for measuring the average particle size of silver particles]
Isopropyl alcohol was added to each silver particle and dispersed in an ultrasonic disperser to obtain a 0.5% by mass dispersion. The particle diameter of the metal particles in the obtained dispersion was measured using a Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.) to determine the average particle diameter (d50). Of 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 other than silver particles (A).

<Compound (B)>
As the compound (B), the following material was used.
B1: Bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane (1 tertiary nitrogen atom, 5 hydroxyl groups, solid at 25°C)
B2: N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (2 tertiary nitrogen atoms, 4 hydroxyl groups, liquid at 25°C)
B3: N,N,N',N'',N''-pentakis(2-hydroxypropyl)diethylenetriamine (3 tertiary nitrogen atoms, 5 hydroxyl groups, liquid at 25°C)
B4: N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (2 tertiary nitrogen atoms, 4 hydroxyl groups, liquid at 25°C)
B5: 1,3-bis[tris(hydroxymethyl)methylamino]propane (2 secondary nitrogen atoms, 6 hydroxyl groups, solid at 25°C)
B6: N,N,N',N'-tetrakis(2-hydroxyethyl)adipamide (2 tertiary nitrogen atoms, 4 hydroxyl groups, solid at 25°C)
B11: Triethanolamine (1 tertiary nitrogen atom, 3 hydroxyl groups, liquid at 25°C)
B12: 2-amino-2-hydroxymethyl-1,3-propanediol (3 hydroxyl groups, solid at 25°C)
B13: 2-(2-aminoethoxy)ethanol (1 hydroxyl group, liquid at 25°C)
B14: Xylitol (5 hydroxyl groups, solid at 25°C)
B15: Imidazole (solid at 25°C)

<Dispersion medium (C)>
The following materials were used as the dispersion medium (C). The manufacturer's name, supplementary information, and boiling point are given in parentheses.
Dispersion medium C1: Diethylene glycol monohexyl ether (glycol ether type, boiling point 255°C)
Dispersion medium C2: Triethylene glycol monobutyl ether (glycol ether type, boiling point 278°C)
Dispersion medium C3: Triethylene glycol monomethyl ether (glycol ether type, boiling point 248°C)
Dispersion medium C4: 2-ethyl-1,3-hexanediol (diol type, boiling point 244°C)
Dispersion medium C5: Diethylene glycol monomethyl ether (glycol ether type, boiling point 193°C)
Dispersion medium C6: 1-decanol (boiling point 233°C)
Dispersion medium C7: "Tersolv TOE-100" (boiling point 260°C) manufactured by Nippon Terpene Chemical Co., Ltd.

<Compound (D)>
The following material was used as compound (D): Compounds D1 to D4 are all manufactured by Croda Japan Co., Ltd. The carbon number, material name, and properties at 25° C. are given in parentheses.
Compound D1: Pripol 1009 (a hydrogenated dimer acid having 36 carbon atoms. It consists of two carboxyl groups and a divalent hydrocarbon group having a branched and cyclic structure. Liquid)
Compound D2: Pripol 1040 (a trimer acid having 54 carbon atoms. It consists of three carboxyl groups and a trivalent hydrocarbon group having a branched and cyclic structure. Liquid)
Compound D3: Pripol 2033 (a dimer diol having 36 carbon atoms. It consists of two hydroxyl groups and a divalent hydrocarbon group having a branched and cyclic structure. Liquid)
Compound D4: Priamine 1075 (a dimer diamine having 36 carbon atoms. It consists of two amino groups and a divalent hydrocarbon group having a branched and cyclic structure. Liquid)

<Compound (E)>
As the compound (E), the following material was used.
Compound E1: Oleic acid

<Production of bonding paste>
[Example 1]
Metal particles A1 (90 parts), diethylene glycol monohexyl ether (10 parts), compound B1 (0.2 parts), other component D1 (0.1 parts), and other component D2 (0.1 parts) were mixed using a planetary stirrer to prepare a joining paste.

[Examples 2 to 43, Comparative Examples 1 to 9]
A joining paste was obtained in the same manner as in Example 1, except that the types of materials and the amounts (parts) of the materials were changed according to the compositions shown in Tables 1A to 2B. In the tables, blank spaces indicate that no materials were added.

<Evaluation of bonding paste>
The resulting bonding paste was used to fabricate a bonded body by any one of manufacturing methods 1 to 5 described below. The resulting bonded body was evaluated for bonding strength and thermal cycle characteristics. The results are shown in Tables 1A to 2B.

[Production method 1]
Using the bonding pastes obtained in Examples 1 to 39 and Comparative Examples 1 to 9, bonded bodies were manufactured in the following manner.
The bonding paste obtained in each of Examples 1 to 36 and Comparative Examples 1 to 9 was printed once on the bonded part 1 (copper base material (plating-free): 20 mm × 20 mm × 3 mm) under the printing conditions described below, and then 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 bonded without pressure under the sintering conditions described below to obtain each bonded body.
[Sintering conditions]
The laminate was placed in a firing furnace in a nitrogen atmosphere, 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., the laminate was maintained at 300° C. for 2 hours.

[Production method 2]
Using the bonding paste obtained in Example 40, a bonded body was produced in the following manner.
The bonding paste obtained in Example 37 was printed once on the bonded part 1 (copper base material (plating-free): 20 mm × 20 mm × 3 mm) under the printing conditions described below, and then 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 bonded without pressure under the sintering conditions described below to obtain a bonded body.
[Sintering conditions]
The laminate was placed in a firing furnace in a nitrogen atmosphere, 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 2° C./min, and after reaching 300° C., the laminate was maintained at 300° C. for 2 hours.

[Production method 3]
Using the bonding paste obtained in Example 41, a bonded body was produced in the following manner.
The bonding paste obtained in Example 38 was printed once on the bonded part 1 (copper base material (plating-free): 20 mm × 20 mm × 3 mm) under the printing conditions described below, and then 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 bonded without pressure under the sintering conditions described below to obtain a bonded body.
[Sintering conditions]
The laminate was placed in a firing furnace in a nitrogen atmosphere, and the temperature was raised from 25° C. to 300° C. at a rate of 8° C./min. After reaching 300° C., the laminate was held at 300° C. for 2 hours.

[Production Method 4]
Using the bonding paste obtained in Example 42, a bonded body was produced in the following manner.
The bonding paste obtained in Example 39 was printed once on the bonded part 1 (copper base material (plating-free): 20 mm × 20 mm × 3 mm) under the printing conditions described below, and then 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 bonded without pressure under the sintering conditions described below to obtain a bonded body.
[Sintering conditions]
The laminate was placed in a firing furnace in a nitrogen atmosphere, and the temperature was raised from 25° C. to 300° C. at 2° C./min. After reaching 300° C., it was held at 300° C. for 2 hours.

[Production Method 5]
Using the bonding paste obtained in Example 43, a bonded body was produced in the following manner.
The bonding paste obtained in Example 40 was printed once on the bonded part 1 (copper base material (plating-free): 20 mm x 20 mm x 3 mm) under the printing conditions described below, and then the bonded part was placed in a hot air oven and pre-dried for 10 minutes at 180°C. Next, the plated surface of the bonded part 2 (gold-plated SiC element: 8 mm x 8 mm x 0.3 mm) was placed facing the pre-dried bonding paste surface, and pressure-bonded under the sintering conditions described below to obtain a bonded body.
[Sintering conditions]
In a nitrogen atmosphere, the joint portion 2 was heated from room temperature to 300° C. at a rate of 20° C./min while being pressurized at a pressure of 30 MPa from above, and after reaching 300° C., was maintained at that temperature for 5 minutes.

[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 Seria Corporation)

[Bonding strength]
The obtained bonded body was fixed at the site of the bonded part 1, and pushed toward the bonded part 2 at a height of 100 μm from the interface between the bonded part 1 and the bonding layer at a speed of 500 μm/s to determine the bond strength (die shear strength) at which the bond was broken, and evaluated based on the following evaluation criteria. The larger the adhesive strength value, the better, and 10 MPa or more is within the practical range. The measurement conditions are shown below.
〔Measurement condition〕
Measurement device: Universal bond tester (4000 series, manufactured by Daisy Japan Co., Ltd.)
Measurement height: 100 μm
Measurement speed: 500 μm/s

(Evaluation criteria)
S: 35 MPa or more A+: 30 MPa or more and less than 35 MPa A: 25 MPa or more and less than 30 MPa A-: 20 MPa or more and less than 25 MPa B: 15 MPa or more and less than 20 MPa C: 10 MPa or more and less than 15 MPa D: Less than 10 MPa

[Heat cycle characteristics]
The bonded bodies thus obtained were subjected to the following cycle test, and the bond strength (die shear strength) of the bonded bodies after the cycle test was determined and evaluated in the same manner as in the above-mentioned [Bonding strength].
[Cycle test]
The bonded body was held at -40°C for 30 minutes and then held at 150°C for 30 minutes, which constituted one cycle, and 500 cycles were carried out.

As shown in the results of Tables 1A to 2B, when the bonding paste of the present disclosure, which combines a specified silver particle (A) and a specified compound (B), was used, it was confirmed that the bonding strength was extremely high and that a decrease in the bonding strength was suppressed even after the thermal cycle test was performed.
In particular, the bonding paste satisfying T3<T1<(T2+10) had extremely high bonding strength even in configurations where stable bonding is extremely difficult, such as plating-free substrates and large-area SiC elements, and the decrease in bonding strength was suppressed even after performing thermal cycle tests (Examples 26 and 27, and Examples 28 and 29).
In addition, the bonding paste containing a compound having 2 to 3 tertiary nitrogen atoms had very high bonding strength even in configurations where stable bonding is extremely difficult, such as plating-free substrates and large-area SiC elements, and the decrease in bonding strength was suppressed even after performing a thermal cycle test (Examples 1 and 2).
In addition, the bonding paste containing a dispersion medium having a boiling point of 250°C or higher had a very high bonding strength even in configurations where stable bonding is extremely difficult, such as a plating-less substrate and a large-area SiC element, and the decrease in bonding strength was suppressed even after a thermal cycle test (Examples 4, 30, and 35 and Examples 31 to 34).
In addition, the bonding paste containing the compound (D) having 20 to 80 carbon atoms and having two or more functional groups selected from the group consisting of hydroxyl groups, carboxy groups, and amino groups had extremely high bonding strength even in configurations where stable bonding is extremely difficult, such as plating-less substrates and large-area SiC elements, and the decrease in bonding strength was suppressed even after a thermal cycle test (Examples 2 and 15, and Examples 4 and 16).
In addition, the bonding paste containing the compound (E) having one carboxy group and 14 to 20 carbon atoms had a very high bonding strength even in the case of a configuration in which stable bonding is extremely difficult, such as a plating-less substrate and a large-area SiC element, and the decrease in bonding strength was suppressed even after a thermal cycle test (Examples 15 and 21, and Examples 16 and 22).
In addition, the bonded bodies bonded using the pressureless bonding method including the above-mentioned preliminary drying step (2a) had extremely high bonding strength even in the case of configurations for which stable bonding is extremely difficult, such as plating-less substrates and large-area SiC elements, and even after carrying out thermal cycle tests, the decrease in bonding strength was suppressed (Examples 4 and 41, and Examples 40 and 42).
On the other hand, when the bonding paste of the comparative example was used, the bonding strength was significantly low, and the bonding strength after the thermal cycle test was also significantly low.

This application claims priority based on Japanese Patent Application No. 2022-183808, filed on November 17, 2022, the entire disclosure of which is incorporated herein by reference.

Claims (17)

1. Silver particles (A) having 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 bonding paste containing a dispersion medium (C).
2. The joining paste according to claim 1, in which T3 < T1 < (T2 + 10) is satisfied, where T1°C is the sintering temperature of the silver particles (A), T2°C is the 50% weight loss temperature of the compound (B), and T3°C is the 50% weight loss temperature of the dispersion medium (C).
3. The joining paste according to claim 2, wherein T2 is 200 to 300°C.
4. The joining paste according to any one of claims 1 to 3, wherein the compound (B) has a tertiary nitrogen atom.
5. The joining paste according to claim 4, wherein the number of tertiary nitrogen atoms in the compound (B) is 2 to 3.
6. The joining paste 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 joining paste according to any one of claims 1 to 3, wherein the compound (B) is liquid at 25°C.
8. The joining paste according to any one of claims 1 to 3, wherein the content of the compound (B) is 0.05 to 1.0 mass% based on the mass of the silver particles (A).
9. The bonding paste according to any one of claims 1 to 3, wherein the silver particles (A) have an average particle diameter of 150 nm to 400 nm.
10. The joining paste according to any one of claims 1 to 3, wherein the dispersion medium (C) has a boiling point of 250°C or higher.
11. The joining paste according to any one of claims 1 to 3 further contains a compound (D) having 20 to 80 carbon atoms and two or more functional groups selected from the group consisting of hydroxyl groups, carboxy groups, and amino groups.
12. The joining paste according to any one of claims 1 to 3 further contains a compound (E) having one carboxy group and 14 to 20 carbon atoms.
13. The joining paste according to any one of claims 1 to 3, wherein the content of the silver particles (A) is 80 to 95 mass% based on the mass of the joining paste.
14. A bonded body in which a first bonded part and a second bonded part are bonded using the bonding paste according to any one of claims 1 to 3.
15. The bonded body according to claim 14, wherein the first bonded portion is a non-plated substrate.
16. The bonded body according to claim 14, wherein the second bonded portion is SiC.
17. A method for producing a joined body in which a first joined part and a second joined part are joined by the joining paste according to any one of claims 1 to 3, comprising the following steps:
    (1) A step of applying a bonding paste to a first object to be bonded.
    (2) A step of placing a second part to be joined on the application portion of the first part to be joined that has been applied with the joining paste.
    (2a) A step of pre-drying the placed laminate by heating.
    (3) A step of sintering the placed laminate in a pressureless environment.