JP7613286B2 - Bonding paste, bonded body using same, and method for manufacturing bonded body - Google Patents

Description

The present invention relates to a metal particle-containing composition, a bonding paste, and a bonded body.

Conventionally, solder has been used as a joining material for joining metal members together, between a metal member and a semiconductor element, or between a metal member and an LED element, etc. In recent years, in the field of next-generation power electronics, there has been a demand for alternatives to solder as a joining material for devices such as SiC that can operate at high temperatures, from the viewpoint of high-temperature operation reliability. For example, the use of joining pastes using metal particles has been proposed, as shown in Patent Documents 1 and 2.

Patent Document 1 discloses a bonding agent that contains metal particles, a polyamide that is a polymer of a polybasic acid monomer and a polyamine monomer and has phenolic hydroxyl groups on its side chains, and a trifunctional or higher compound that can react with the phenolic hydroxyl groups.

Patent Document 2 discloses a bonding material that contains metal submicron particles with an average primary particle size of 0.5 to 3.0 μm and metal nanoparticles with an average primary particle size of 1 to 200 nm that are coated with an organic compound with 6 to 8 carbon atoms.

JP 2017-137375 A JP 2011-80147 A

However, the bonding agent described in Patent Document 1 has problems in applicability due to insufficient dispersibility of metal particles, and therefore the coating film after application has poor smoothness and leveling properties, and the film is not dense enough, resulting in poor bonding strength, and the bonding strength decreases with thermal cycling.
Furthermore, the bonding material described in Patent Document 2 has a problem in that the bonding strength at the bonded portion is poor, and the bonding strength decreases with thermal cycles.
Furthermore, the bonding materials described in Patent Documents 1 and 2 have a problem that when an adherend is a material (e.g., silicon carbide (hereinafter, referred to as SiC)) that has a smaller linear expansion coefficient and is more rigid than the metal that is the main component of the bonding material, stress is concentrated on the bonding coating film during a thermal cycle test, and the bonding coating film cannot withstand the resulting stress, causing cracks.
In other words, the problem to be solved by the present invention is to provide a bonding paste that has excellent bonding strength and can maintain its bonding strength even after thermal cycling when an adherend having a small linear expansion coefficient and a rigidity is used, and a bonded body using the bonding paste that has excellent bonding strength and resistance to thermal cycling.

The present invention relates to a bonding paste containing a polyamide (A), which is a polymer of a polybasic acid monomer and a polyamine monomer and has a phenolic hydroxyl group in a side chain, metal particles (B), and a dispersion medium (C), in which the polyamide (A) satisfies the following (i) and/or (ii), and the metal particles (B) are particles having a particle size (d50) corresponding to 50% of an accumulated particle size distribution of 100 to 350 nm.
(i) The polyamide (A) is a polyamide (A-1) in which the phenolic hydroxyl group and the hydrocarbon group having 20 to 60 carbon atoms (but excluding the aromatic ring to which the phenolic hydroxyl group is bonded) are contained within the same polymer.
(ii) The polyamide (A) is a polyamide (A-3) which is a mixture of a polyamide (a-1) having a phenolic hydroxyl group in a side chain and a polyamide (a-2) having a hydrocarbon group having 20 to 60 carbon atoms.

The present invention also relates to the above-mentioned bonding agent, in which the content of the polyamide (A) is in the range of 0.01 to 1.70 mass % based on the mass of the metal particles (B).

The present invention also relates to the above-mentioned joining paste, in which the metal particles (B) have a particle diameter (d1) corresponding to 1% of the cumulative particle diameter distribution of 30 to 200 nm, and a particle diameter (d99) corresponding to 99% of the cumulative particle diameter distribution of 300 to 900 nm.

The present invention also relates to the above-mentioned joining paste, in which the metal particles (B) are particles with a mass reduction rate of 0.5 to 7.0 mass%.

The present invention also relates to a bonded body in which a first object to be bonded and a second object to be bonded are bonded using the bonding paste.

The present invention further relates to a method for manufacturing a joined body, in which the above-mentioned joining paste is applied to a first joined body and a second joined body is placed on the applied surface.

The present invention makes it possible to provide a metal particle-containing composition and a bonding paste that have high bonding strength at the joint and that do not decrease with thermal cycles. It also makes it possible to provide a bonded body that does not deteriorate with thermal cycles.

FIG. 1 is a schematic diagram showing the DTA curve and TG curve of the metal particles of the present invention during heating, measured using a simultaneous differential thermal-thermogravimetric measurement apparatus (TG-DTA).

The bonding paste of the present invention contains a polyamide (A) which is a polymer of a polybasic acid monomer and a polyamine monomer and has a phenolic hydroxyl group on a side chain, metal particles (B), and a dispersion medium (C), and is characterized in that the polyamide (A) satisfies the following (i) and/or (ii), and the metal particles (B) are particles having a particle size (d50) corresponding to 50% of the cumulative particle size distribution of 100 to 350 nm.
(i) The polyamide (A) is a polyamide (A-1) in which the phenolic hydroxyl group and the hydrocarbon group having 20 to 60 carbon atoms (but excluding the aromatic ring to which the phenolic hydroxyl group is bonded) are contained within the same polymer.
(ii) The polyamide (A) is a polyamide (A-3) which is a mixture of a polyamide (a-1) having a phenolic hydroxyl group in a side chain and a polyamide (a-2) having a hydrocarbon group having 20 to 60 carbon atoms.
By using a combination of a specific polyamide (A) and metal particles (B) having a particle size (d50) corresponding to 50% of the cumulative particle size distribution of 100 to 350 nm, not only is excellent coating property achieved, but the occurrence of voids in the bonded coating film is suppressed, enabling the formation of a dense coating film, and as a result, excellent bonding strength and cycle characteristics are exhibited.
The present invention will be described in detail below. In the following description, the parentheses for a hydrocarbon group having 20 to 60 carbon atoms (not including the aromatic ring to which the phenolic hydroxyl group is bonded) may be omitted, but when a "hydrocarbon group having 20 to 60 carbon atoms" is written, it is assumed that the condition in the parentheses is satisfied. Furthermore, a "hydrocarbon group having 20 to 60 carbon atoms" may be written as a "C20 to 60 hydrocarbon group".

<Metal Particles (B)>
The bonding paste of the present invention contains metal particles (B) having a particle diameter (d50) corresponding to 50% of the cumulative particle diameter distribution of 100 to 350 nm.
Examples of the metal in the metal particles (B) include gold, silver, copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, platinum, and alloys thereof. In addition, fine particles coated with a core and a material different from the core material, specifically, for example, silver-coated copper powder in which copper is used as the core and its surface is coated with silver, can be mentioned. In addition, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, ITO (tin-doped indium oxide), AZO (aluminum-doped zinc oxide), and GZO (gallium-doped zinc oxide), as well as powders surface-coated with these metal oxides, can be mentioned. The type of metal used may be one type, or two or more types may be used in combination.

In the present invention, it is important to use metal particles (B) having a particle diameter (d50) corresponding to 50% of the cumulative particle diameter distribution of 100 to 350 nm.
From the viewpoint of suppressing the generation of voids (hereinafter also referred to as voids) to exhibit high bonding strength, and from the viewpoint of sufficiently progressing melting and integration (hereinafter also referred to as sintering) between the metal particles to suppress a decrease in bonding strength after thermal cycles, the d50 of the metal particles (B) is preferably 120 to 300 nm, more preferably 180 to 300 nm.

In addition, the metal particles (B) preferably have a size (particle diameter) distribution, and are preferably particles with a particle diameter (d1) corresponding to 1% of the cumulative particle diameter distribution and a particle diameter (d99) corresponding to 99% of the cumulative particle diameter distribution controlled. By having the metal particles (B) have a particle diameter distribution, it is possible to effectively fill the gaps between the metal particles, and the occurrence of voids in the bonding coating film is further suppressed, which is preferable.
The d1 of the metal particles (B) is preferably 30 to 200 nm, more preferably 40 to 180 nm, and further preferably 50 to 150 nm.
The d99 of the metal particles (B) is preferably 300 to 900 nm, more preferably 300 to 750 nm, and even more preferably 350 to 600 nm.

The 1% cumulative particle size distribution particle diameter (d1), 50% cumulative particle size distribution particle diameter (d50), and 99% cumulative particle size distribution particle diameter (d99) of the metal particles (B) were determined for a dispersion obtained by dispersing the metal particles (B) in an organic solvent (IPA: isopropyl alcohol) to a concentration of 0.5 mass% using an ultrasonic disperser.
For example, Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.) can be used for the measurement. In this specification, the 1% cumulative particle size distribution particle size (d1), 50% cumulative particle size distribution particle size (d50), and 99% cumulative particle size distribution particle size (d99) refer to particle sizes (volume basis) corresponding to 1%, 50%, and 99%, respectively, of the cumulative particle size distribution.

The surfaces of the metal particles (B) are preferably coated with an organic component (b).
Examples of the organic component (b) include fatty acids, aliphatic amines, and aliphatic alcohols. Preferably, it is a saturated or unsaturated fatty acid, more preferably, it is a saturated or unsaturated fatty acid having 3 to 22 carbon atoms, and even more preferably, it is a saturated or unsaturated fatty acid having 6 to 18 carbon atoms. The organic component (b) may contain one type or two or more types.

In the present invention, the metal particles (B) have a d50 of 100 to 350 nm, so that an excessive amount of the organic component (b) is not required, and the organic component is prevented from remaining in the bonding material, thereby preventing the generation of voids and providing high bonding strength.
Furthermore, the metal particles (B) in the present invention have a d50 of 100 to 350 nm, so that the melting point is not too high. This allows the sintering of the metal particles to proceed sufficiently without excessively high temperatures, forming a dense bonding coating film, and suppressing a decrease in bonding strength after thermal cycling.

The metal particles (B) preferably have a mass reduction rate of 0.5 to 7.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 2.0 to 4.0% by mass.
When the mass reduction rate of the metal particles (B) is 0.5% by mass or more, the viscosity of the bonding paste can be suppressed, good coating performance can be exhibited, a dense bonding coating film can be formed, and good bonding strength can be exhibited, which is preferable. On the other hand, when the mass reduction rate of the metal particles (B) is 7.0% by mass or less, the organic component (b) can be suppressed from remaining after sintering, the generation of voids in the bonding coating film can be suppressed, and good bonding strength can be exhibited, which is preferable.

The method for calculating the mass reduction rate will be described below.
As shown in Fig. 1, the start temperature Ts of the lowest exothermic peak shown in the DTA curve represents the extrapolated start temperature, and is the temperature at the intersection of a straight line extending the low-temperature baseline to the high-temperature side in the heating measurement with a tangent drawn at the point where the gradient is maximum on the low-temperature side curve of the lowest exothermic peak. Similarly, the end temperature Te of the highest exothermic peak shown in the DTA curve represents the extrapolated end temperature, and is the temperature at the intersection of a straight line extending the high-temperature baseline to the low-temperature side in the heating measurement with a tangent drawn at the point where the gradient is maximum on the curve of the highest peak.
It is believed that the decomposition of the organic component (b) begins at the extrapolated onset temperature Ts of the lowest exothermic peak, the mass of the metal particles begins to decrease, and the decomposition of the organic component (b) ends at the extrapolated end temperature Te. Therefore, Ts is also referred to as the decomposition onset temperature, and Te is also referred to as the decomposition end temperature.
That is, the mass reduction rate is expressed by the following formula.
Mass reduction rate=[(mass of metal particles (B) at Ts−mass of metal particles (B) at Te)/mass of metal particles (B) at Ts]×100
In the above formula, "the mass of the metal particles (B) at Ts - the mass of the metal particles (B) at Te" is understood to be the amount of the organic component (b).
Although some mass loss of the metal particles may be observed in the region lower than Ts or higher than Te, if no clear exothermic peak is observed, it is understood that this is not due to decomposition.

The metal particles (B) may be used alone or in combination of two or more kinds.
In addition, the bonding paste of the present invention may contain metal particles other than the metal particles (B) as long as the effects of the present invention are not impaired.

<Dispersion medium (C)>
The bonding paste of the present invention contains a dispersion medium (C). The dispersion medium (C) disperses the metal particles (B), ensures the smoothness/leveling of the bonding film after application, and promotes densification of the bonding coating film.

Specific examples of the dispersion medium (C) include terpineol, dihydroterpineol, carbitol, carbitol acetate, butyl carbitol, isophorone, γ-butyl lactone, dipropylene glycol monomethyl ether, dipropylene glycol methyl-n-propyl ether, 3-methoxy-3-methylbutyl acetate, ethylene glycol, hexanoic acid, propylene glycol diacetate, dipropylene glycol methyl ether acetate, 1,3-butylene glycol, and isoparaffin-based solvents contained in hydrocarbon-based solvents.
Among these, at least one selected from the group consisting of terpineol, dihydroterpineol, carbitol, carbitol acetate, butyl carbitol, isophorone, γ-butyrolactone, and dipropylene glycol monomethyl ether is preferred.
These dispersion media (C) may be used alone or in combination of two or more.

<Polyamide (A)>
The bonding paste of the present invention is a polymer of a polybasic acid monomer and a polyamine monomer, and contains a polyamide (A) having a phenolic hydroxyl group in its side chain (hereinafter referred to as "phenolic hydroxyl group-containing polyamide (A)").
Moreover, the polyamide (A) satisfies the following (i) and/or (ii):
(i) The polyamide (A) is a polyamide (A-1) in which the phenolic hydroxyl group and the hydrocarbon group having 20 to 60 carbon atoms (but excluding the aromatic ring to which the phenolic hydroxyl group is bonded) are contained within the same polymer.
(ii) The polyamide (A) is a polyamide (A-3) which is a mixture of a polyamide (a-1) having a phenolic hydroxyl group in a side chain and a polyamide (a-2) having a hydrocarbon group having 20 to 60 carbon atoms.
By combining the specific polyamide of the present application having such a phenolic hydroxyl group and a hydrocarbon group having 20 to 60 carbon atoms with the above-mentioned metal particles (B), the resulting bonding paste exhibits excellent coating properties. In addition, the generation of voids in the bonding coating film is suppressed, and a dense coating film is formed. As a result, it is possible to achieve both excellent bonding strength and cycle characteristics.

The method for synthesizing the polyamide (A) is not limited, but it is usually synthesized using a polybasic acid compound selected from dibasic or higher polybasic acids, and their acid anhydrides or lower alkyl esters, and a dibasic or higher polyamine compound.
The phenolic hydroxyl group-containing polyamide (A) used in the present invention may have a terminal carboxy group or an amino group, or may not have a functional group at the terminal.

In the present invention, the hydrocarbon group having 20 to 60 carbon atoms refers to a hydrocarbon group having 20 to 60 carbon atoms contained in all or part of a residue other than a functional group that contributes to the polymerization of a monomer, and the number of carbon atoms is the number of carbon atoms in a continuous structure that does not contain elements other than carbon and hydrogen.
As the hydrocarbon group having 20 to 60 carbon atoms, preferably, all of the residues other than the functional groups that contribute to the polymerization of the monomer are hydrocarbon groups having 20 to 60 carbon atoms.
That is, the carbon number refers to the total number of carbon atoms in the continuous hydrocarbon groups, including the main chain and the side chains directly connected to the main chain of the polyamide, and includes aliphatic hydrocarbon groups (having alicyclic hydrocarbon groups) as well as aromatic hydrocarbon groups. However, aromatic rings to which phenolic hydroxyl groups are bonded are not included in the carbon number. On the other hand, carbon atoms in the hydrocarbon groups bonded via aromatic rings to which phenolic hydroxyl groups are bonded are each counted as a separate hydrocarbon group.

Moreover, it is more preferable that the polyamide (A) satisfies the following (iii) to (v).
(iii) The monomers constituting the polyamide (A-1) include a monomer having a phenolic hydroxyl group and a monomer having a hydrocarbon group having 20 to 60 carbon atoms.
(iv) The polybasic acid monomer and/or the polyamine monomer constituting the polyamide (a-1) contain a monomer having a phenolic hydroxyl group, and the polybasic acid monomer and the polyamine monomer do not contain a monomer having a hydrocarbon group having 20 to 60 carbon atoms.
(v) The polybasic acid monomer and/or the polyamine monomer constituting the polyamide (a-2) contain a monomer having a hydrocarbon group having 20 to 60 carbon atoms, and the polybasic acid monomer and the polyamine monomer do not contain a monomer having a phenolic hydroxyl group.

More preferably, the polyamide (A) further satisfies the following (vi):
(vi) At least a part of the monomers having a hydrocarbon group having 20 to 60 carbon atoms includes a compound having a cyclic structure having 5 to 10 carbon atoms.

In (iii), it goes without saying that a monomer having a phenolic hydroxyl group and a hydrocarbon group having 20 to 60 carbon atoms may be used within the same monomer.
In addition, in (vi), "including a compound having a cyclic structure having 5 to 10 carbon atoms" means that at least a part of the monomer having a hydrocarbon group having 20 to 60 carbon atoms contains a monomer having a cyclic structure having 5 to 10 carbon atoms.

From the viewpoint of effectively bringing out solubility and flexibility, the carbon number of the monomer having a hydrocarbon group with 20 to 60 carbon atoms is preferably 24 to 56 carbon atoms, more preferably 28 to 48 carbon atoms, and even more preferably 36 to 44 carbon atoms.

From the viewpoints of solubility in general-purpose solvents, productivity, and initial bonding strength, it is preferable that polyamide (A) is polyamide (A-1).

<Polyamide (A-1)>
A preferred embodiment of the polyamide (A-1) is one obtained by polymerizing a polybasic acid monomer (m1) and a polyamine monomer (m2), has a phenolic hydroxyl group in a side chain, and has a phenolic hydroxyl group and a C20 to C60 hydrocarbon group in the same polymer. The polyamide (A-1) only needs to satisfy the above conditions, and polybasic acid monomers and polyamine monomers having other structures can be appropriately used within the scope of the present invention.
That is, the polybasic acid monomer (m1) is selected from at least one selected from the group consisting of polybasic acid compounds having a phenolic hydroxyl group, polybasic acid compounds having a C20-60 hydrocarbon group, and other polybasic acid compounds, and the polyamine monomer (m2) is selected from at least one selected from the group consisting of polyamine compounds having a phenolic hydroxyl group, polyamine compounds having a C20-60 hydrocarbon group, and other polyamine compounds, so that the polymer contains a phenolic hydroxyl group and a C20-60 hydrocarbon group.
The compound having a C20-60 hydrocarbon group and the compound having a phenolic hydroxyl group can be polymerized by selecting a polybasic acid monomer (m1) and the polyamine monomer (m2) so that they are contained in the same monomer or in different monomers, to obtain a phenolic hydroxyl group-containing polyamide (A-1).

The above phrase "so as to be included in the same type of monomer" means that a polybasic acid compound having a phenolic hydroxyl group and a polybasic acid compound having a C20-60 hydrocarbon group may be used as the polybasic acid monomer (m1), or a polyamine compound having a phenolic hydroxyl group and a polyamine compound having a C20-60 hydrocarbon group may be used as the polyamine monomer (m2). Also, the phrase "so as to be included in another monomer" means that a polybasic acid compound having a phenolic hydroxyl group may be included as the polybasic acid monomer (m1) and a polyamine compound having a C20-60 hydrocarbon group may be included as the polyamine monomer (m2), or a polybasic acid compound having a C20-60 hydrocarbon group may be included as the polyamine monomer (m1) and a polyamine compound having a phenolic hydroxyl group may be included as the polyamine monomer (m2). In either case, other polybasic acid compounds and other polyamine compounds may be used as appropriate.

When a dibasic acid monomer and a diamine monomer are used as the monomers, the resulting polyamide (A) has a structural unit represented by the following general formula (1).

In general formula (1), R ₁ is a divalent linking group which is a polybasic acid compound residue which may have an independent structure for each structural unit, R ₂ is a divalent linking group which is a polyamine compound residue which may have an independent structure for each structural unit, at least one of R ₁ and R ₂ contains a linking group having a phenolic hydroxyl group, and at least one of R ₁ and R ₂ has a linking group having a C20-60 hydrocarbon group. Polyamide (A-1) is a compound in which the structural unit represented by -CO-R ₁ -CO-NH-R ₂ -NH- is repeated at least twice.
Within the scope of the present invention, a compound having one structural unit of general formula (1) and having a blocked end may be contained in the thermosetting resin composition.

The monomer having a phenolic hydroxyl group and the monomer having a C20-60 hydrocarbon group may be contained in at least one of the dibasic acid compound and the diamine compound, and these groups may be contained in both the dibasic acid compound and the diamine compound.

<Polybasic acid monomer (m1)>
[Polybasic acid compound having a phenolic hydroxyl group]
The polybasic acid compound having a phenolic hydroxyl group is not particularly limited, and examples thereof include hydroxyisophthalic acids such as 2-hydroxyisophthalic acid, 4-hydroxyisophthalic acid, and 5-hydroxyisophthalic acid, dihydroxyisophthalic acids such as 2,5-dihydroxyisophthalic acid, 2,4-dihydroxyisophthalic acid, and 4,6-dihydroxyisophthalic acid, dihydroxyterephthalic acids such as 2-hydroxyterephthalic acid, 2,3-dihydroxyterephthalic acid, and 2,6-dihydroxyterephthalic acid, hydroxyphthalic acids such as 4-hydroxyphthalic acid and 3-hydroxyphthalic acid, and dihydroxyphthalic acids such as 3,4-dihydroxyphthalic acid, 3,5-dihydroxyphthalic acid, 4,5-dihydroxyphthalic acid, and 3,6-dihydroxyphthalic acid. In addition, acid anhydrides of these acids and ester derivatives such as polybasic acid methyl esters may also be used. The only difference is that in the case of free polybasic acids and acid anhydrides, a dehydration reaction occurs, while in the case of ester derivatives, a corresponding dealcoholization reaction occurs.
Among these, 5-hydroxyisophthalic acid is preferred from the viewpoints of copolymerizability, ease of availability, etc. When 5-hydroxyisophthalic acid is used, R ₁ in general formula (1), i.e., the divalent linking group which is a polybasic acid compound residue, is the moiety obtained by removing two carboxy groups from the 5-hydroxyisophthalic acid.

[Polybasic acid compound having C20-60 hydrocarbon group]
Suitable examples of polybasic acid compounds having a C20-60 hydrocarbon group include polybasic acid compounds having a cyclic structure and 5-10 carbon atoms, which are obtained by reacting a monobasic unsaturated fatty acid having 10-24 carbon atoms and one or more double bonds or triple bonds.
As such polybasic acid compounds, for example, polybasic acid compounds containing dimerized fatty acids (dimer acids) obtained by subjecting natural fatty acids such as soybean oil fatty acids, tall oil fatty acids, rapeseed oil fatty acids, and the like, which are refined from these fatty acids, such as oleic acid, linoleic acid, linolenic acid, and erucic acid, to a Diels-Alder reaction are preferably used.

The number of cyclic structures may be one or two, and in the case of two, the two rings may be independent or continuous. Examples of the cyclic structure include a saturated alicyclic structure, an unsaturated alicyclic structure, and an aromatic ring. The carboxy group may be directly bonded to the cyclic structure, but from the viewpoint of improving solubility and flexibility, it is preferable that the carboxy group is bonded to the cyclic structure via an aliphatic chain. The number of carbon atoms between the carboxy group and the cyclic structure is preferably 2 to 25.
In addition, from the viewpoints of improving solubility, improving flexibility, and decreasing the dielectric constant and dielectric tangent, it is preferable that the polybasic acid compound having a C20-60 hydrocarbon group has a chain-like alkyl group having high freedom and hydrophobicity as a portion other than the cyclic structure. It is preferable that there are two or more alkyl groups per cyclic structure. The number of carbon atoms in the alkyl group is preferably 2 to 25.

Polybasic acid compounds having a C20-60 hydrocarbon group are generally obtained as a composition containing, as a main component, a monomer containing a dimer derived from a dimer acid as a residue, and also containing fatty acids as raw materials and fatty acids of trimerization or higher. In particular, it is preferable that, in 100% by mass of polybasic acid compounds having a C20-60 hydrocarbon group, the monomer containing a dimer derived from a dimer acid as a residue is contained in an amount of preferably 70% by mass or more, more preferably 95% by mass or more.
Also, dimers with a lower degree of unsaturation obtained by hydrogenation (hydrogenation reaction) are preferably used from the viewpoints of oxidation resistance (particularly coloration at high temperatures) and suppression of gelation during synthesis. As the polybasic acid compound having a C20-60 hydrocarbon group, it is preferable to use a polybasic acid compound containing a dimer derived from a monobasic unsaturated fatty acid having 10-24 carbon atoms as a residue. Furthermore, it is preferable to use a monomer containing a trimer, which is a tricarboxylic acid, as a residue, derived from a monobasic unsaturated fatty acid having 10-24 carbon atoms as part of the polybasic acid compound having a C20-60 hydrocarbon group.

Examples of commercially available polybasic acid compounds having a C20-60 hydrocarbon group include "Pripol 1004", "Pripol 1006", "Pripol 1009", "Pripol 1013", "Pripol 1015", "Pripol 1017", "Pripol 1022", "Pripol 1025", and "Pripol 1040" manufactured by Croda Japan Ltd.; and "EMPOL 1008", "EMPOL 1012", "EMPOL 1016", "EMPOL 1026", "EMPOL 1028", "EMPOL 1043", "EMPOL 1061", and "EMPOL 1062" manufactured by BASF Japan Ltd.
These polybasic acid compounds can be used alone or in combination.

[Other polybasic acid compounds]
The polybasic acid compounds other than the polybasic acid compound having a phenolic hydroxyl group and the polybasic acid compound having a C20-60 hydrocarbon group are not particularly limited within the scope of the present invention. Examples of such other polybasic acid compounds include dibasic acid compounds and polybasic acid compounds having three or more functional groups.
Examples of the dibasic acid compound include aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, and 4,4'-biphenyldicarboxylic acid; aliphatic dibasic acids such as oxalic acid, malonic acid, methylmalonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, malic acid, tartaric acid, thiomalic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexadecanedioic acid, and diglycolic acid; and alicyclic dibasic acids such as 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 1,3-cyclopentanedicarboxylic acid.
Examples of trifunctional or higher polybasic acid compounds include trimellitic acid, hydrogenated trimellitic acid, pyromellitic acid, hydrogenated pyromellitic acid, and 1,4,5,8-naphthalenetetracarboxylic acid.

The other polybasic acid compounds mentioned above may be used alone or in combination. Among them, isophthalic acid and 1,4-cyclohexanedicarboxylic acid are preferably used because they can produce a stronger polyamide with better heat resistance. In addition, by using a compound having three or more functional groups, a branched structure can be introduced into the polyamide, which can increase the molecular weight and increase the cohesive strength of the resulting polyamide. As a result, the heat resistance can be improved without adversely affecting the adhesiveness.

Furthermore, in the present invention, a monofunctional monobasic acid compound can be used in combination. By using a monofunctional compound, it is possible to reduce the number of carboxyl groups and amino groups that can become terminal functional groups of the polyamide, and it is possible to control the molecular weight of the resulting polyamide. As a result, it is possible to improve the stability over time of the polyamide resin in particular. Examples of monobasic acid compounds include benzoic acid, 4-hydroxybenzoic acid, and 2-ethylhexanoic acid.

<Polyamine monomer (m2)>
The polyamine compound having a phenolic hydroxyl group is not particularly limited, and examples thereof include polyamines represented by the following general formula (2).

In the formula, R ₃ represents a direct bond or a group consisting of carbon, hydrogen, oxygen, nitrogen, sulfur, or halogen, and examples thereof include a divalent hydrocarbon group having 1 to 30 carbon atoms, a divalent hydrocarbon group having 1 to 30 carbon atoms in which some or all of the hydrogen atoms have been substituted by halogen atoms, -(C═O)-, -SO ₂ -, -O-, -S-, -NH-(C═O)-, -(C═O)-O-, a group represented by the following general formula (3), and a group represented by the following general formula (4): In the formula, r and s each independently represent an integer of 1 to 20, and R ₄ represents a hydrogen atom or a methyl group.

The above R ₃ is preferably a direct bond.

In addition, when a compound of general formula (2) is used, _R2 in general formula (1), i.e., a divalent linking group which is a polyamine compound residue, is the portion obtained by removing two amino groups from the compound of general formula (2).

[Polyamine compound having C20-60 hydrocarbon group]
Examples of polyamine compounds having a C20-60 hydrocarbon group include compounds obtained by converting the carboxy group of the polybasic acid compound having a C20-60 hydrocarbon group into an amino group. Commercially available products of such polyamine compounds include "Priamine 1071", "Priamine 1073", "Priamine 1074", and "Priamine 1075" manufactured by Croda Japan Ltd. and "Versamine 551" manufactured by BASF Japan Ltd.
These polyamine compounds can be used alone or in combination. Among them, "Priamine 1071" containing about 20 to 25% by mass of a trimer triamine component is preferred because it improves the cohesive force of the polyamide and improves heat resistance. From the viewpoint of the production stability of the polyamide, the total amount of the trimer triamine and the trimer tricarboxylic acid is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, of the total monomers 100% by mass used to form the polyamide.

[Other polyamine compounds]
The polyamine compounds other than the polyamine compounds having a phenolic hydroxyl group and the polyamine compounds having a C20-60 hydrocarbon group are not particularly limited within the scope of the present invention. Examples of such other polyamine compounds include trifunctional or higher polyamine compounds such as diamine compounds and triamine compounds.
Examples of the diamine compound include 1,4-diaminobenzene, 1,3-diaminobenzene, 1,2-diaminobenzene, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, 2,3-diaminonaphthalene, 2,6-diaminotoluene, 2,4-diaminotoluene, 3,4-diaminotoluene, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylether, 4,4'-diaminodiphenylether, 4,4'-diamino-1,2-diphenylethane, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, 4,4'-diamino aromatic diamines such as 3,3'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, and 3,3'-diaminodiphenylsulfone; aliphatic diamines such as ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,9-nonanediamine, 1,12-dodecamethylenediamine, and metaxylenediamine; and alicyclic diamines such as isophoronediamine, norbornanediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 4,4'-diaminodicyclohexylmethane, and piperazine.
Examples of trifunctional or higher polyamine compounds include 1,2,4-triaminobenzene and 3,4,4'-triaminodiphenyl ether. In addition, even if an aromatic ring is included, if the amino group is not directly bonded, it is classified as an aliphatic compound.

The other polyamine compounds may be used alone or in combination. Among them, isophorone diamine and norbornane diamine are preferably used because they can provide a polyamide having excellent heat resistance and toughness.
In addition, by using a trifunctional or higher functional group, a branched structure can be introduced into the polyamide, which can increase the molecular weight and the cohesive strength of the resulting polyamide, thereby improving the adhesiveness, heat resistance, etc.

Furthermore, in the present invention, a monofunctional amine compound can be used in combination. By using a monofunctional compound, it is possible to reduce the number of carboxyl groups and amino groups that can become terminal functional groups of the polyamide, and it is possible to control the molecular weight of the resulting polyamide. As a result, it is possible to improve the stability over time of the polyamide resin in particular. Examples of monofunctional amine compounds include aniline, 4-aminophenol, and 2-ethylhexylamine.

The phenolic hydroxyl group-containing polyamide (A-1) of the present invention can be obtained by appropriately selecting the polybasic monomer (m1) and polyamine monomer (m2) according to the properties that need to be improved, such as adhesion and heat resistance.

The polyamide (A-1) obtained by polymerization may be a random polymer or a block polymer of a component having a phenolic hydroxyl group and a component having a C20-60 hydrocarbon group. That is, it may be a polymer of a mixture of multiple polybasic acid monomer compounds and one polyamine compound, a polymer of a mixture of multiple polybasic acid compounds and a mixture of multiple polyamine compounds, a polymer of one polybasic acid compound and a mixture of multiple polyamine compounds, or a polymer of one polybasic acid compound and one polyamine compound. The polymer may further be polymerized with other polybasic acid compounds or other polyamine compounds depending on the functional groups remaining at the terminals.

The polyamide (A-1) of the present invention preferably contains 10 to 95 mol %, more preferably 14 to 92 mol %, and even more preferably 18 to 88 mol % of a compound having a C20-60 hydrocarbon group out of a total of 100 mol of all monomers used in the synthesis of the polyamide, i.e., polybasic acid monomer (m1), polyamine monomer (m2), and monobasic acid or monofunctional amine compound used as needed.

The method for calculating the number of moles of a monomer having a C20-60 hydrocarbon group will now be described.
First, the molecular weight (M) of a monomer having a C20-60 hydrocarbon group is calculated according to the following formula.
M=(56.11×F×1000)/E
F: Number of functional groups of monomers having C20-60 hydrocarbon groups E: Acid value of monomers having C20-60 hydrocarbon groups (mgKOH/g)
Next, the mass of the compound having a C20-60 hydrocarbon group that was subjected to polymerization is divided by the molecular weight (M) to determine the number of moles of the compound having a C20-60 hydrocarbon group that was subjected to polymerization. In the same manner, the number of moles of each monomer that was subjected to polymerization is determined, and these are summed to determine the number of moles of all monomers that were subjected to polymerization. Then, the proportion (mol %) of the compound having a C20-60 hydrocarbon group can be determined by dividing the number of moles of the compound having a C20-60 hydrocarbon group by the number of moles of all monomers.

<Polyamide (A-3)>
The polyamide (A-3) is a polyamide obtained by mixing a polyamide (a-1) having a phenolic hydroxyl group in the side chain and a polyamide (a-2) having a hydrocarbon group having 20 to 60 carbon atoms.
One of the preferred aspects of the polyamide (a-1) is a polyamide obtained by polymerizing a polybasic acid monomer (m3) and a polyamine monomer (m4), has a phenolic hydroxyl group in the side chain, and does not have a C20-60 hydrocarbon group. The polyamide (a-1) may be any other polybasic acid monomer or polyamine monomer that satisfies the above conditions. That is, the polybasic acid monomer (m3) is at least one selected from the group consisting of a polybasic acid compound having a phenolic hydroxyl group and other polybasic acid compounds (excluding polybasic acid compounds having a C20-60 hydrocarbon group), the polyamine monomer (m4) is at least one selected from the group consisting of a polyamine compound having a phenolic hydroxyl group and other polyamine compounds (excluding polyamine compounds having a C20-60 hydrocarbon group), and at least one of the polybasic acid monomer (m3) and the polyamine monomer (m4) has a phenolic hydroxyl group.
The polyamide (a-1) may be prepared by combining a divalent monomer with a trivalent or higher monomer to introduce a branched structure and adjust the molecular weight appropriately. It is also possible to maintain the molecular weight appropriately by using a monovalent monomer.

One of the preferred embodiments of the polyamide (a-2) is obtained by polymerizing a polybasic acid monomer (m5) and a polyamine monomer (m6), and has a C20-60 hydrocarbon group but does not have a phenolic hydroxyl group in the side chain.
The polybasic acid monomer (m5) is at least one selected from the group consisting of polybasic acid compounds having a C20 to 60 hydrocarbon group and other polybasic acid compounds (excluding polybasic acid compounds having a phenolic hydroxyl group), and the polyamine monomer (m6) is at least one selected from the group consisting of polyamine compounds having a C20 to 60 hydrocarbon group and other polyamine compounds (excluding polyamine compounds having a phenolic hydroxyl group), and at least one of the polybasic acid monomer (m5) and the polyamine monomer (m6) has a C20 to 60 hydrocarbon group.

In other words, polyamide (A-3) is a mixture of polyamide (a-1) having a phenolic hydroxyl group in the side chain but no C20-60 hydrocarbon group, and polyamide (a-2) having a C20-60 hydrocarbon group but no phenolic hydroxyl group in the side chain.
The mixing ratio of polyamide (a-1) to polyamide (a-2) can be appropriately adjusted depending on the phenolic hydroxyl value and molecular weight of (a-1). However, polyamide (a-1):polyamide (a-2) is preferably 5:95 to 80:20 (mass ratio), and more preferably 10:90 to 50:50.

The polybasic acid monomer (m3) may be any of the above-mentioned polybasic acid monomers (m1) other than the polybasic acid compounds having a C20 to C60 hydrocarbon group. A monobasic compound may also be used in combination.
The polyamine monomer (m4) may be any of the above-mentioned polyamine monomers (m2) other than the polyamine compounds having a C20 to C60 hydrocarbon group. A monofunctional amine compound may also be used in combination.

The polybasic acid monomer (m5) may be any of the above-mentioned polybasic acid monomers (m1) other than the polybasic acid compounds having a phenolic hydroxyl group. A monobasic compound may also be used in combination.
The polyamine monomer (m6) may be any of the above-mentioned polyamine monomers (m2) other than the polyamine compound having a phenolic hydroxyl group. A monofunctional amine compound may also be used in combination.

The polyamide (A-3) of the present invention preferably contains 10 to 95 mol %, more preferably 14 to 92 mol %, and even more preferably 18 to 88 mol % of a compound having a C20 to 60 hydrocarbon group out of a total of 100 mol of all monomers (m3) to (m6) used in the formation and monobasic acid and monofunctional amine compounds used as necessary.

[Phenol hydroxyl value]
The amount of phenolic hydroxyl groups in the polyamide (A) can be adjusted depending on the purpose, but is preferably 1 to 80 mgKOH/g, more preferably 5 to 60 mgKOH/g, and even more preferably 5 to 30 mgKOH/g. When the phenolic hydroxyl value is 1 mgKOH/g or more, a dense crosslinked structure can be formed, and the resistance, hardness, and heat resistance of the cured coating film can be improved. When the phenolic hydroxyl value is 80 mgKOH/g or less, a cured coating film with good adhesion and flexibility can be obtained. When the phenolic hydroxyl value is within the range of 1 to 80 mgKOH/g, the adhesion, flexibility, and heat resistance of the resulting coating film are improved, which is preferable.

The phenolic hydroxyl value can be adjusted by the blending composition of monomers having a phenolic hydroxyl group among all the monomers constituting the polyamide (A-1), or the polyamide (a-1) and the polyamide (a-2).
For example, in the case of polyamide (A) obtained by reacting only 5-hydroxyisophthalic acid having a phenolic hydroxyl group as the polybasic acid compound and only dimer diamine having a C20 to C60 hydrocarbon group and no phenolic hydroxyl group as the polyamine compound, the phenolic hydroxyl value is close to 80 mgKOH/g, and the heat resistance of the thermoset product is further improved.

When polyamide (A) is polyamide (A-3), its phenolic hydroxyl value is the phenolic hydroxyl value of the mixture of polyamide (a-1) and polyamide (a-2).

[Mass average molecular weight]
The mass average molecular weight of the polyamide (A-1) is preferably from 3,000 to 1,000,000, more preferably from 5,000 to 550,000, and even more preferably from 10,000 to 300,000, from the viewpoints of handleability and dispersibility of metal particles through interaction with the metal particles.
The mass average molecular weight of the polyamide (a-1) is preferably 500 to 30,000, more preferably 1,000 to 20,000, and even more preferably 1,000 to 10,000, from the viewpoint of solubility in general-purpose solvents described below.
The weight average molecular weight of the polyamide (a-2) is preferably in the same range as that of the polyamide (A-1).

[Glass transition temperature]
The glass transition temperature of the polyamide (A) is preferably −40° C. to 120° C., and more preferably −30° C. to 80° C. By setting the glass transition temperature of the polyamide (A) in the range of −40° C. to 120° C., it is possible to suppress extrusion during bonding, and further to achieve good embedding properties in the substrate, thereby further improving the adhesiveness.

The above glass transition temperature can be adjusted by the blending ratio of monomers having C20-60 hydrocarbon groups. For example, by increasing the blending ratio of monomers having C20-60 hydrocarbon groups, the concentration of amide bonds with high water absorption decreases, and the flexibility characteristic of dimerized fatty acids is imparted, so that the glass transition temperature becomes close to -40°C.

When polyamide (A) is polyamide (A-3), its glass transition temperature is the glass transition temperature of a mixture of polyamide (a-1) and polyamide (a-2).

<Synthesis of polyamide (A)>
The polymerization method of the polyamide (A) used in the present invention is not particularly limited, and known methods such as melt polymerization, interfacial polymerization, solution polymerization, bulk polymerization, solid-phase polymerization, and combinations of these methods can be used. Industrially, the reaction is generally carried out at 150 to 300°C for about 1 to 24 hours in the presence or absence of a catalyst, and it is preferable to carry out the reaction at 180 to 270°C under reduced pressure of atmospheric pressure or less in order to promote the dehydration or dealcoholization reaction and to avoid coloration and decomposition reactions due to high temperatures.

Examples of the catalyst that can be used in the polymerization include inorganic phosphorus compounds such as phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, polyphosphoric acid, and alkali metal salts and alkaline earth metal salts thereof; phosphites such as triphenyl phosphite and diphenyl phosphite; titanium-based catalysts such as tetrabutyl orthotitanate and tetraisopropyl orthotitanate; tin-based catalysts such as dibutyltin oxide, dibutyltin laurate and monobutylhydroxytin oxide; and zirconium-based catalysts such as tetrabutoxyzirconium, zirconium acetate and zirconium octylate.
These catalysts may be used in combination of two or more kinds.

<Joint paste>
The bonding paste of the present invention can be produced by uniformly mixing and dispersing the above-mentioned polyamide (A), metal particles (B), and dispersion medium (C) by a conventionally known method. The method for mixing and dispersing the bonding paste is not particularly limited, and for example, a disperser, a three-roll mill, a bead mill, an ultrasonic disperser, or a self-revolving stirrer dispenser can be used.

The bonding paste of the present invention preferably contains polyamide (A) in the range of 0.01 to 1.70 mass% based on the mass of the metal particles (B). When the content of polyamide (A) is 0.01 mass% or more, the fluidity of the paste is improved and the bonding coating film is densified. This suppresses the generation of voids during heating during bonding, and allows the development of good bonding strength and thermal cycle characteristics. When the content is 1.70 mass% or less, the amount of organic matter that causes voids in the bonding coating film is suppressed. This suppresses the generation of voids during heating during bonding, and allows the development of good bonding strength and thermal cycle characteristics.
The content of polyamide (A) is more preferably 0.02% by mass or more, further preferably 0.04% by mass or more, particularly preferably 0.10% by mass or more. The content of polyamide (A) is more preferably 1.30% by mass or less, further preferably 1.00% by mass or less, particularly preferably 0.50% by mass or less.

The bonding paste of the present invention preferably has a metal particle (B)/dispersion medium (C) ratio in the range of 80/20 to 98/2 (mass ratio), more preferably in the range of 85/15 to 96/4 (mass ratio), and even more preferably in the range of 90/10 to 94/6 (mass ratio). By being in the above range, it is possible to ensure good application suitability as a bonding paste, suppress the residue of organic components in the dried coating film, suppress the generation of voids when heated during bonding, and achieve good bonding strength.

<Other ingredients>
The bonding paste of the present invention may contain known components such as a hardener, a sintering accelerator, a binder resin (excluding polyamide (A)), a dispersant, and additives, within the range that does not impair the effects of the present invention.

[Curing agent]
The curing agent that may be used in the present invention may be, for example, a compound having a functional group capable of reacting with the phenolic hydroxyl group of the polyamide (A). Examples of such a compound include an epoxy group-containing compound, an isocyanate group-containing compound, a carbodiimide group-containing compound, a metal chelate compound, a metal alkoxide, and a metal acylate.
Furthermore, when the polyamide resin (A) has a carboxy group or an amino group as a terminal functional group, the polyamide resin (A) contains a mixture of functional groups such as a phenolic hydroxyl group, a carboxy group, and/or an amino group, and by selecting the above-mentioned curing agent, the processability and adhesiveness can be adjusted by utilizing the difference in reactivity with each functional group.

<Joint>
The bonding paste of the present invention can bond a first body to a second body to obtain a bonded body. The method of applying the bonding paste to the body to be bonded is not particularly limited as long as it can apply the paste uniformly to the member, and examples of the method include various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, gravure offset printing, and dispenser coating.
The thickness of the bonding coating is not limited, but is usually 3 μm to 500 μm, preferably 10 μm to 200 μm, and more preferably 20 μm to 100 μm.

Sintering conditions in the bonding step can be appropriately selected, and examples of the conditions include atmospheric pressure, a nitrogen atmosphere, a vacuum, pressurized, and a reducing atmosphere at 200 to 300° C. Sintering devices include, for example, hot air ovens, infrared ovens, reflow ovens, microwave ovens, hot plates, and light sintering devices. These devices may be used alone or in combination.
A preliminary drying step may be provided before the baking step in order to remove organic components from the bonding coating film. For example, such a preliminary drying step may involve heating at a temperature in the range of 60 to 220° C. and drying under reduced pressure using an apparatus similar to the baking apparatus described above.

In addition, when placing a second object to be joined on a first object to be joined coated with the joining paste of the present invention, the second object to be joined can be placed while applying pressure. The pressure is set appropriately depending on the viscosity of the joining paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, and more preferably 0.3 to 30 MPa.

A preferred method for joining two objects to be joined is to apply the joining paste of the present invention to a first object to be joined, place a second object to be joined on the applied surface, and heat the paste to about 200-300°C at a heating rate of about 1°C/min to 15°C/min to perform sintering. After heating is complete, it is preferable to maintain the temperature higher than the temperature at the end of heating for about 10 minutes to 2 hours.

The type of the object to be joined is not particularly limited, and examples thereof include metal members, electronic elements, plastic materials, and ceramic materials.
It is preferable to join metal members together, a metal member and a semiconductor element, or a metal member and an LED element.

Examples of the metal member include a copper substrate, a gold substrate, an aluminum substrate, etc. Examples of the electronic element include a semiconductor element, an LED element, and a power device element.
Semiconductor elements include silicon and germanium, as well as gallium arsenide, gallium phosphide, cadmium sulfide, etc. LED elements include aluminum, silicon nitride, diamond, graphite, yttrium oxide, magnesium oxide, etc.
In particular, it is possible to use power device elements of silicon carbide, gallium nitride, etc. Examples of the plastic material include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, polyethylene naphthalate, etc.
Examples of the ceramic material include glass and silicon.
The first and second objects to be joined may be members of different kinds, not just the same kind. The members may be appropriately processed by corona treatment, plating, or the like in order to increase the joining strength.
Examples of the metal member include a copper substrate, a gold substrate, and an aluminum substrate.
Examples of the electronic element include a semiconductor element and an LED element.
Examples of semiconductor elements include silicon, germanium, gallium arsenide, gallium phosphide, and cadmium sulfide. Examples of LED elements include aluminum, silicon nitride, diamond, graphite, yttrium oxide, and magnesium oxide. In particular, power device elements such as silicon carbide and gallium nitride can be used.
Examples of plastic materials include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate.
Examples of ceramic materials include glass and silicon.

The first and second objects to be joined may be members of different types, not just the same type. The members may be subjected to a corona treatment or plating treatment to increase the joining strength.

The present invention will be described in detail below using examples and comparative examples, but the technical scope of the present invention is not limited thereto. In the examples, "parts" means "parts by mass" and "%" means "% by mass" unless otherwise specified. In addition, the numerical values in the tables mean "parts" unless otherwise specified.

[Measurement of particle size]
Isopropyl alcohol was added to the metal particles, and the mixture was dispersed using an ultrasonic disperser to obtain a 0.5% by mass dispersion. The particle diameters of the metal particles in the dispersion were measured using a Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.) to determine d1, d50, and d99.

[Calculation of mass reduction rate]
For each metal particle (B), a differential thermal-thermogravimetric simultaneous measurement device (TG-DTA, EXSTAR TG/DTA6200, manufactured by Seiko Instruments Inc.) was used to raise the temperature from 25° C. at a heating rate of 5° C./min, and the mass reduction rate of the metal particle (B) at Te was determined when the mass of the metal particle (B) at Ts, Te, and Ts was taken as 100 mass%. As shown in FIG. 1, the extrapolated start temperature of the exothermic peak on the lowest temperature side shown in the DTA curve was taken as Ts, and the extrapolated end temperature of the exothermic peak on the highest temperature side shown in the DTA curve was taken as Te.
Mass reduction rate=[(mass of metal particles (B) at Ts−mass of metal particles (B) at Te)/mass of metal particles (B) at Ts]×100

<Production of Metal Particles>
(Production Example 1) Metal particles B1
Under a nitrogen atmosphere, 200 parts of toluene and 21.5 parts of silver hexanoate were mixed while stirring at 25 ° C., and 2.3 parts of diethylaminoethanol and 0.25 parts of oleic acid were added as dispersants and dissolved. Then, 70.0 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, toluene was added, and the process of removing the supernatant after centrifugation was repeated twice. The precipitate was dried to obtain metal particles B1 in which silver particles were coated with hexanoic acid and oleic acid. The particle size of metal particles B1 was determined by the above-mentioned method, and d1 was 100 nm, d50 was 250 nm, and d99 was 450 nm.

(Production Example 2) Metal particles B2
Metal particles B2 were obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was 2.5 parts and the amount of oleic acid was 0.34 parts. d1 was 35 nm, d50 was 110 nm, and d99 was 250 nm. It was.

(Production Example 3) Metal particles B3
Metal particles B3 were obtained in the same manner as in Production Example 1, except that the amount of silver hexanoate was 23.5 parts and the amount of oleic acid was 0.18 parts. d1 was 180 nm, d50 was 330 nm, and d99 was It was 600 nm.

(Production Example 4) Metal particles B4
Metal particles B4 were obtained in the same manner as in Production Example 1, except that 21.5 parts of silver pentanoate was used instead of 21.5 parts of silver hexanoate, and the amount of oleic acid was 0.3 parts. was 45 nm, d50 was 140 nm, and d99 was 300 nm.

(Production Example 5) Metal particles B5
10 parts of silver nitrate were dissolved in 500 parts of ethylene glycol. Then, 5 parts of polyvinylpyrrolidone were dispersed in the ethylene glycol. Then, the ethylene glycol was heated to 150° C. (reaction temperature), and the reaction temperature was The reaction was carried out for 1 hour while stirring at a rotation speed of 400 rpm and maintaining the temperature at 150° C. During this time, the silver nitrate reacted with ethylene glycol to generate nitrogen oxide gas, and the silver nitrate was reduced to polyvinylpyrrolidone. The dispersion of metal particles was centrifuged, the supernatant was removed, ethylene glycol was added to the precipitate, and the mixture was stirred. The mixture was centrifuged again, and the supernatant was removed. The precipitate was dried to obtain metal particles B5 in which silver particles were coated with polyvinylpyrrolidone. d1 was 160 nm, d50 was 300 nm, and d99 was 650 nm.

(Production Example 6) Metal particles B6
Metal particles B6 were obtained in the same manner as in Production Example 1, except that 32 parts of silver stearate was used instead of 21.5 parts of silver hexanoate and the amount of oleic acid was 0.28 parts. d1 was 240 nm , d50 was 290 nm, and d99 was 420 nm.

(Production Example 7) Metal particles B7
Metal particles B7 were obtained in the same manner as in Production Example 1, except that 18 parts of silver propionate was used instead of 21.5 parts of silver hexanoate and the amount of oleic acid was 0.29 parts. d1 was 140 nm , d50 was 180 nm, and d99 was 250 nm.

(Production Example 8) Metal particles B8
Metal particles B8 were obtained in the same manner as in Production Example 1, except that 33.5 parts of silver myristate was used instead of 21.5 parts of silver hexanoate, and the amount of oleic acid was 0.28 parts. was 70 nm, d50 was 200 nm, and d99 was 750 nm.

(Metal particles b1)
As the metal particles b1, silver particles "LM1" manufactured by Tokusen Kogyo Co., Ltd. were used. d1 was 100 nm, d50 was 1000 nm, and d99 was 3200 nm.

(Production Example 9) Metal particles b2
Metal particles b2 in which silver particles are coated with hexanoic acid and oleic acid are obtained in the same manner as in Production Example 1, except that the amount of diethylaminoethanol was changed to 1.5 parts and the amount of oleic acid was changed to 0.13 parts. The d1 was 110 nm, the d50 was 600 nm, and the d99 was 1100 nm.

(Production Example 10) Metal particles b3
6 parts of oleic acid, 140 parts of n-octylamine, 43 parts of N,N-dimethyl-1,3-diaminopropane, 16 parts of n-dodecylamine, 12 parts of cyclohexylamine, and 64 parts of n-butylamine were added and stirred for 1 minute. Next, 320 parts of silver oxalate was added and stirred for about 10 minutes to obtain a composition for preparing silver particles. After that, the mixture was stirred at 40° C. for 30 minutes, and then further stirred at 90° C. for 30 minutes. After cooling, 1500 parts of methanol was added and stirred, and then centrifuged for 1 minute in a centrifuge to remove the supernatant. The steps of removing the supernatant and removing the supernatant were repeated twice, followed by drying to obtain metal particles b3 in which silver particles were coated with oxalic acid. d1 was 37 nm, d50 was 80 nm, and d99 was 165 nm.

(Production Example 11) Metal particles b4
A metal powder in which silver particles are coated with hexanoic acid and oleic acid was prepared in the same manner as in Production Example 1, except that the amount of silver hexanoate was changed from 21.5 parts to 23 parts and the amount of oleic acid was changed to 0.28 parts. Particles b4 were obtained. d1 was 5 nm, d50 was 10 nm, and d99 was 27 nm.

<Synthesis of polyamide>
(Synthesis Example 1) Polyamide (A-1-1)
In a four-neck flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, inlet tube, and thermometer, 202.9 g (0.35 mol in terms of dibasic acid) of Pripol 1009 as a polybasic acid compound having 36 carbon atoms, 25.7 g (0.14 mol) of 5-hydroxyisophthalic acid as a polybasic acid compound having a phenolic hydroxyl group, 35.1 g (0.21 mol) of terephthalic acid as other polybasic acid compounds, 313.9 g of Priamine 1074 (0.59 mol in terms of diamine) as a polyamine compound having 36 carbon atoms, and 100 g of ion-exchanged water were charged and stirred until the temperature of the heat generation became constant. When the temperature was stabilized, the temperature was raised to 110 ° C., and after confirming the outflow of water, the temperature was raised to 120 ° C. after 30 minutes, and the dehydration reaction was continued while raising the temperature by 10 ° C. every 30 minutes. When the temperature reached 230° C., the reaction was continued at that temperature for 3 hours, and then the mixture was kept under a vacuum of about 2 kPa for 1 hour, and the temperature was then lowered.
Finally, an antioxidant and toluene were added to obtain a solution of a phenolic hydroxyl group-containing polyamide resin having a weight average molecular weight of 9,800, an acid value of 22.8 mgKOH/g, an amine value of 0.3 mgKOH/g, a phenolic hydroxyl value of 13.7 mgKOH/g, a glass transition temperature of 4° C., and a solid content of 40%. The proportion of monomers having C20-60 hydrocarbon groups was 72.7 mol % out of 100 mol % of all monomers subjected to the reaction.

(Synthesis Example 2) Polyamide (A-1-2)
In a four-neck flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, an inlet tube, and a thermometer, 51.4 g of 5-hydroxyisophthalic acid as a polybasic acid compound having a phenolic hydroxyl group, 70.3 g of isophthalic acid as another polybasic acid compound, 313.9 g of Priamine 1074 as a polyamine compound having 36 carbon atoms, and 100 g of ion-exchanged water were charged and stirred until the temperature of the heat generation became constant. When the temperature stabilized, the temperature was raised to 110°C, and after confirming the outflow of water, the temperature was raised to 120°C after 30 minutes, and then the dehydration reaction was continued while raising the temperature by 10°C every 30 minutes. When the temperature reached 230°C, the reaction was continued at that temperature for 3 hours, and the temperature was lowered by holding it under a vacuum of about 2 kPa for 1 hour.
Finally, an antioxidant and toluene were added to obtain a solution of a phenolic hydroxyl group-containing polyamide resin having a weight average molecular weight of 7,400, an acid value of 30.3 mgKOH/g, an amine value of 0.7 mgKOH/g, a phenolic hydroxyl value of 36.3 mgKOH/g, a glass transition temperature of 34° C., and a solid content of 40%. The monomer having a C20-60 hydrocarbon group accounted for 45.5 mol% of the total monomers used in the reaction (100 mol%).

(Synthesis Example 3) Polyamide (A-1-3)
In a four-neck flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, inlet tube, and thermometer, 405.7 g of Pripol 1009 as a polybasic acid compound having 36 carbon atoms, 76.2 g of 4,4'-diamino-3,3'-dihydroxybiphenyl as a polyamine compound having a phenolic hydroxyl group, 111.2 g of Wondamin HM as another amine compound, and 100 g of ion-exchanged water were charged and stirred until the temperature of the heat generation became constant. When the temperature was stabilized, the temperature was raised to 110°C, and after confirming the outflow of water, the temperature was raised to 120°C after 30 minutes, and then the dehydration reaction was continued while raising the temperature by 10°C every 30 minutes. When the temperature reached 230°C, the reaction was continued at that temperature for 3 hours, and then the temperature was lowered by holding it under a vacuum of about 2 kPa for 1 hour.
Finally, an antioxidant and toluene were added to obtain a solution of a phenolic hydroxyl group-containing polyamide resin having a weight average molecular weight of 6,800, an acid value of 0.5 mgKOH/g, an amine value of 33.3 mgKOH/g, a phenolic hydroxyl value of 66.7 mgKOH/g, a glass transition temperature of 45° C., and a solid content of 40%. The proportion of monomers having C20-60 hydrocarbon groups was 44.4 mol% out of 100 mol% of all monomers used in the reaction.

(Synthesis Example 4) Polyamide (A-3-1)
In a four-neck flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, inlet tube, and thermometer, 48.6 g (0.21 mol) of dodecanedioic acid as other polybasic acid compounds, 6.9 g (0.03 mol) of 4,4'-diamino-3,3'-dihydroxybiphenyl as a polyamine compound having a phenolic hydroxyl group, 87.6 g (0.42 mol) of Wondamin HM as other amine compounds, and 100 g of ion-exchanged water were charged and stirred until the temperature of the heat generation became constant. When the temperature stabilized, the temperature was raised to 110°C, and after confirming the outflow of water, the temperature was raised to 120°C after 30 minutes, and then the dehydration reaction was continued while raising the temperature by 10°C every 30 minutes. When the temperature reached 230°C, the reaction was continued at that temperature for 3 hours, and the temperature was lowered by holding it under a vacuum of about 2 kPa for 1 hour.
Finally, an antioxidant was added to obtain a phenolic hydroxyl group-containing polyamide (a-1-1) having a mass average molecular weight of 2,800, an acid value of 0.5 mgKOH/g, an amine value of 185.8 mgKOH/g, a phenolic hydroxyl value of 25.1 mgKOH/g and a glass transition temperature of 140°C.

Separately, in a four-neck flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, inlet tube, and thermometer, 284.0 g (0.49 mol in terms of dibasic acid) of Pripol 1009 as a polybasic acid compound with 36 carbon atoms, 102.7 g (0.19 mol in terms of diamine) of Priamine 1074 as a polyamine compound with 36 carbon atoms, and 100 g of ion-exchanged water were charged and stirred until the temperature of the heat generation became constant. When the temperature stabilized, the temperature was raised to 110°C, and after confirming the outflow of water, the temperature was raised to 120°C after 30 minutes, and the dehydration reaction was continued while raising the temperature by 10°C every 30 minutes. When the temperature reached 230°C, the reaction was continued at that temperature for 3 hours, and then the temperature was lowered by holding it under a vacuum of about 2 kPa for 1 hour. Finally, an antioxidant was added to obtain polyamide (a-2-1) having a C20-60 hydrocarbon group with a mass average molecular weight of 8,800, an acid value of 87.4 mg KOH/g, an amine value of 0.3 mg KOH/g, and a glass transition temperature of -30°C. Of the total monomers used in the reaction (100 mol%), the compound having a C20-60 hydrocarbon group was 51 mol%.

Phenolic hydroxyl group-containing polyamide (a-1-1) and C20-60 hydrocarbon group-containing polyamide (a-2-1) were mixed in a ratio of 30:70 (mass ratio), and toluene was added to obtain a polyamide resin solution with a solid content of 40%.

(Synthesis Examples 5 and 6) Comparative Polyamides 1 and 2
Solutions of comparative polyamides 1 and 2 were obtained in the same manner as in Synthesis Example 1, except that the compositions and amounts charged were changed to those shown in Table 1. Comparative polyamide 1 is a polyamide having no phenolic hydroxyl group, and comparative polyamide 2 is a polyamide having no C20-60 hydrocarbon group.

The resulting polyamide resin is shown in Table 1.

The abbreviations in Table 1 are as follows.
Pripol 1009: Croda Japan, C36 dimer acid, containing a compound having one C6 cyclic structure (acid value: 195 mg KOH/g)
Priamine 1074: Manufactured by Croda Japan, contains a C36 dimer diamine and a compound having one C6 cyclic structure (amine value: 210 mg KOH/g)
5-HIPA: 5-hydroxyisophthalic acid Wondamin HM: New Japan Chemical Co., Ltd., 4,4'-diaminodicyclohexylmethane HAB: 4,4'-diamino-3,3'-dihydroxybiphenyl MXDA: metaxylenediamine

<Synthesis of polyester>
(Polyester Resin 1)
In a four-neck flask equipped with a stirrer, a reflux condenser, a nitrogen inlet pipe, an inlet pipe, and a thermometer, 25.7 parts of 5-hydroxyisophthalic acid as a polybasic acid having a phenolic hydroxyl group, 82.4 parts of adipic acid as another polybasic acid, 332.3 parts of Pripol 2033 as a polyol having a carbon number of 36, and 139.3 parts of toluene were charged, and the mixture was heated to 60°C while stirring under a nitrogen stream to dissolve uniformly. Subsequently, 0.77 parts of tetrabutyl orthotitanate was added as a catalyst, and the mixture was reacted at 110°C for 3 hours. Thereafter, the temperature was raised to 230°C, and the mixture was maintained for 1 hour under a vacuum of about 2 kPa, and then reacted for 2 to 3 hours under a vacuum of about 1 kPa. Finally, an antioxidant and toluene were added to obtain a solution of phenolic hydroxyl group-containing polyester resin 1 having a mass average molecular weight of 9,600, an acid value of 23.4 mgKOH/g, a phenolic hydroxyl value of 18.0 mgKOH/g, a glass transition temperature of 34°C, and a solid content of 40%.

<Production of bonding paste>
[Example 1]
91 parts of metal particles B1, 8.55 parts of dihydroterpineol, and 0.45 parts of polyamide A-1-1 solution (0.20% by mass based on the mass of metal particles B1) were mixed using a planetary stirrer to prepare a joining paste.

[Examples 2 to 24], [Comparative Examples 1 to 8]
A bonding paste was obtained in the same manner as in Example 1, except that the compounding composition was changed according to the contents of Tables 2 to 4.

<Evaluation of bonding paste>
The obtained bonding paste was used to manufacture a bonded body in the following manner, and the obtained bonded body was subjected to the following evaluations. The results are shown in Tables 2 to 4.

[Preparation of Joint]
Each bonding paste was applied once to the plated surface of a substrate 1 described below, and then a substrate 2 described below was placed with the plated surface facing the bonding paste surface, followed by heating and sintering to obtain a bonded body.
The substrate, coating conditions, and sintering conditions are shown below.
<<Substrate>>
Substrate 1 (first bonded body): gold-plated copper substrate (20 x 20 x 3 mm)
Substrate 2 (second bonded body): Gold-plated SiC chip (5 x 5 x 0.3 mm)
<Application conditions>
Metal mask: opening 4 mm square, plate thickness 50 μm (manufactured by Ceria Corporation)
Metal squeegee: 40 mm x 250 mm, thickness 1 mm (manufactured by Seria Corporation)
Sintering conditions
The provisionally bonded body was placed in a hot air oven, and the temperature was raised from 25° C. to 300° C. at a rate of 2° C./min. After reaching 300° C., the temperature was maintained at that temperature for 2 hours.

[Bonding strength (initial, after thermal cycle test)
The initial bond strength (die shear strength) of the bonded body was measured. The bonded body was then subjected to a thermal cycle test, and the bond strength after the thermal cycle was measured in the same manner as the initial bond strength. The bond strength measurement method and thermal cycle test method are described below.
The adhesive strength was evaluated based on the following evaluation criteria. The higher the adhesive strength value, the better the adhesive strength.
<Method of measuring bonding strength>
Measurement device: Universal bond tester (4000 series, manufactured by Daisy Japan Co., Ltd.)
Measurement height: 100 μm
Measurement speed: 500 μm/s
Specifically, the substrate 1 was fixed, and the substrate 1 was pushed toward the substrate 2 at a height of 100 μm from the interface between the substrate 1 and the bonding paste at a speed of 500 μm/s, and the bonding strength at which the bond was destroyed was determined.

<<Cold-heat cycle test method>>
The bonded body was kept at -40°C for 30 minutes, then kept at 25°C for 15 minutes, and then kept at 150°C for 30 minutes, which constituted one cycle, and 500 cycles were performed.

Evaluation Criteria
S: Bonding strength is 30 MPa or more (very good)
A+: Bond strength is 22 MPa or more and less than 30 MPa (good)
A: Bonding strength is 15 MPa or more and less than 22 MPa (fairly good)
B: Bonding strength is 10 MPa or more and less than 15 MPa (practical)
C: Bond strength is less than 10 MPa (not practical)

[Coatability]
Each bonding paste was applied to a substrate 1 (gold-plated copper substrate (20×20×3 mm)) under the following application conditions, and the suitability of application was judged according to the following criteria.
<Application conditions>
Metal mask: opening 4 mm square, plate thickness 50 μm (manufactured by Ceria Corporation)
Metal squeegee: 40 mm x 250 mm, thickness 1 mm (manufactured by Seria Corporation)
Evaluation Criteria
A: The bonding paste is evenly applied to the entire opening (4 mm square) (good)
B: The bonding paste is applied to a part of the opening (2 mm or more and less than 4 mm square) (practical)
C: The bonding paste can only be applied to a part of the opening (less than 2 mm square), or the applied part is cracked (not practical).

As shown in Tables 2 to 4, the bonding paste of the present invention had high initial bonding strength and was able to suppress a decrease in bonding strength after a thermal cycle test, even when the adherend was a material with a small linear expansion coefficient and rigidity, such as silicon carbide. The bonding paste of the examples also had excellent coating properties. In particular, when metal particles B1 having d1 in the range of 50 to 150 nm and d99 in the range of 350 to 600 nm were used, excellent initial bonding strength and bonding strength after a thermal cycle were shown.
On the other hand, the bonding paste of the comparative example was inferior in bonding strength and coatability, particularly after the thermal cycle test.

Claims (6)

A bonding paste comprising: a polyamide (A) which is a polymer of a polybasic acid monomer and a polyamine monomer and has a phenolic hydroxyl group in a side chain; metal particles (B); and a dispersion medium (C),
The polyamide (A) satisfies the following (i) and/or (ii),
The bonding paste, wherein the metal particles (B) are particles having a particle diameter (d50) corresponding to 50% of the cumulative particle diameter distribution of 100 to 350 nm.
(i) The polyamide (A) is a polyamide (A-1) in which the phenolic hydroxyl group and the hydrocarbon group having 20 to 60 carbon atoms (but excluding the aromatic ring to which the phenolic hydroxyl group is bonded) are contained within the same polymer.
(ii) The polyamide (A) is a polyamide (A-3) which is a mixture of a polyamide (a-1) having a phenolic hydroxyl group in a side chain and a polyamide (a-2) having a hydrocarbon group having 20 to 60 carbon atoms. The bonding paste according to claim 1, wherein the content of the polyamide (A) is in the range of 0.01 to 1.70 mass% based on the mass of the metal particles (B). The joining paste according to claim 1 or 2, wherein the metal particles (B) have a particle diameter (d1) corresponding to 1% of the cumulative particle diameter distribution of 30 to 200 nm, and a particle diameter (d99) corresponding to 99% of the cumulative particle diameter distribution of 300 to 900 nm. The joining paste according to any one of claims 1 to 3, wherein the metal particles (B) are particles with a mass reduction rate of 0.5 to 7.0 mass%. A bonded body in which a first object to be bonded and a second object to be bonded are bonded using the bonding paste according to any one of claims 1 to 4. A method for manufacturing a joined body, comprising applying the joining paste according to any one of claims 1 to 4 to a first joined body and placing a second joined body on the applied surface.