Joining paste and joined article

Abstract

To provide a joining paste that, under non-pressurized conditions, suppresses voids in a coating film after sintering to exhibit high thermal conductivity, has excellent joining strength, and can suppress a decrease in joining strength due to thermal cycles, and a joined article using the joining paste.SOLUTION: A joining paste contains metal particles (A) and a dispersion medium (B), the metal particles (A) containing metal particles (a) having an average particle diameter of 100 nm or more and 500 nm or less in an amount of 50 mass% or more based on the total mass of the metal particles (A). When the joining paste is heated at a rate of 3°C / min, and when the weight loss at 650°C (M650) is defined as 100, the weight loss at 200°C (M200) is between 88 and 98.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a paste for bonding that has excellent thermal conductivity and bonding strength under non-pressurized conditions and can suppress a decrease in bonding strength associated with thermal cycling, and a bonded body using the bonding paste.

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As joining processes using such a joining material, there are a method performed under no pressure (hereinafter referred to as non-pressure joining) and a method performed under pressure (hereinafter referred to as pressure joining). Pressure joining is effective for void reduction, improves thermal conductivity, and promotes sintering of metal particles, so strong joining is possible, and it has the advantage of excellent joining strength and thermal cycle characteristics. However, pressure joining requires dedicated equipment, and furthermore, the object to be joined must be able to withstand the pressure environment, so the joining object and applications are limited. Therefore, it is required to reduce voids and exhibit high thermal conductivity in non-pressure joining, and to achieve strong joining and improve joining strength and thermal cycle characteristics. On the other hand, in recent years, the area of semiconductor elements has been increasing. However, it is known that as the area of the element increases, it becomes more difficult for internal gas, etc. to escape, and voids tend to occur. In addition, the difference in the linear expansion coefficient between Si elements or SiC elements and the linear expansion coefficient of copper used as silver particles and the base material is very large. During the thermal cycle test, strain occurs between the copper base material / silver particle-containing joining layer / Si or SiC element layers, cracks tend to occur, and the thermal cycle characteristics tend to deteriorate. Furthermore, although the SiC element has a linear expansion coefficient similar to that of the Si element, it has a higher hardness than the Si element. Therefore, compared with the Si element, the strain applied during the thermal cycle is larger, and cracks tend to occur in the joining layer. That is, the required level for improving the joining strength and thermal cycle characteristics of SiC semiconductor elements has been increasing year by year.

[0006] However, the inventions described in Patent Document 1 and Patent Document 2 do not satisfy the constituent requirements of the present invention and cannot solve the problems of joining strength and thermal cycle characteristics when joining a large-area SiC element by non-pressure joining.

[0007] Accordingly, the problem to be solved by the present disclosure is to provide a joining paste that can suppress voids in the sintered coating film, exhibit high thermal conductivity, have excellent joining strength, and suppress a decrease in joining strength due to thermal cycling even under non-pressurized conditions, and a joined body using the joining paste.

Means for Solving the Problem

[0008] As a result of intensive studies, the present inventors have found that the above problems can be solved. [1]: A joining paste containing metal particles (A) and a dispersion medium (B), wherein the metal particles (A) contain metal particles (a) having an average particle diameter of 100 nm or more and 500 nm or less in an amount of 50% by mass or more based on the total mass of the metal particles (A), and when the weight loss M650 at 650 °C when the temperature of the joining paste is increased at a heating rate of 3 °C / min is taken as 100, the weight loss M200 at 200 °C is 88 or more and 98 or less. [2]: When the weight loss at 150 °C is designated as M150 with the weight loss M650 taken as 100, the ratio (M150 / M200) of the weight loss M150 to the weight loss M200 is 0.975 or more, the joining paste according to [1]. [3]: The joining paste according to [1] or [2], wherein the dispersion medium (B) has a content of a dispersion medium (b1) having a boiling point of 250 °C or more and 300 °C or less of 50% by mass or more based on the total mass of the dispersion medium (B). [4]: The joining paste according to [3], wherein the dispersion medium (b1) contains at least one selected from the group consisting of terpene-based and glycol ether-based. [5]: The joining paste according to any one of [1] to [4], wherein the dispersion medium (B) has a content of a dispersion medium (b2) having a boiling point exceeding 300 °C of 10% by mass or less based on the total mass of the dispersion medium (B). [6]: The joining paste according to any one of [1] to [5], wherein the dispersion medium (B) has a content of a dispersion medium having a hydroxyl group of 90% by mass or more based on the total mass of the dispersion medium (B). [7]: 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 [1] to [6]. [8]: The joined body according to [7], wherein the first joined part is an untreated base material. [9]: The joined body according to [7] or [8], wherein the second joined part is SiC.

Advantages of the Invention

[0009] According to the present invention, even under non-pressure conditions, it is possible to suppress voids in the coating film after sintering, exhibit high thermal conductivity, have excellent joining strength, and suppress a decrease in joining strength due to thermal cycling. A joining paste and a joined body using the joining paste can be provided.

Embodiments for Carrying Out the Invention

[0010] The joining paste of the present disclosure is a joining paste containing metal particles (A) and a dispersion medium (B), wherein the metal particles (A) have a proportion of metal particles (a) having an average particle diameter of 100 nm or more and 500 nm or less of 50% by mass or more, and when the weight loss M650 at 650 °C when the joining paste is heated at a heating rate of 3 °C / min is taken as 100, the weight loss M200 at 200 °C is 88 or more and 98 or less. The joining paste of the present disclosure contains 50% by mass or more of metal particles (a) having an average particle diameter of 100 nm or more and 500 nm or less in the metal particles (A), and the ratio of the weight loss M200 at 200 °C to the weight loss M650 at 650 °C is within a predetermined range, so that it is a severe joining condition of non-pressure, and even when the joined member is an untreated base material such as non-plated or it is difficult to achieve stable joining such as in a SiC semiconductor element, excellent joining strength and joining strength after thermal cycling can be exhibited. Specifically, as described above, it is possible to provide a pressureless-bondable bonding paste having high thermal conductivity, high bonding strength at the bonded portion, and suppression of a decrease in bonding strength due to thermal cycling, and a bonded body using the bonding paste. Further, thereby, even when a large-area SiC element is bonded without pressure, high thermal conductivity, excellent bonding strength, and thermal cycling characteristics can be exhibited.

[0011] <(Metal particles (A))> The metal particles (A) play a role in expressing the conductivity and thermal conductivity of the bonded body and bonding the objects to be bonded in the sintering process, and include silver, copper, an alloy containing silver and / or silver, silver oxide, copper oxide, and coated particles having a metal (excluding silver and copper) as a core body and its surface coated with silver and / or silver. By using the metal particles (A), a bonded body having excellent strength can be obtained. Further, it can correspond to a wide range of firing temperatures and can also correspond to various firing environments such as under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere.

[0012] The metal particles (A) contain a predetermined amount or more of metal particles (a) (hereinafter referred to as metal particles (a)) having an average particle diameter of 100 nm or more and 500 nm or less, so that the particles are melted or bound (hereinafter also referred to as sintered) to each other in the temperature range of 200°C to 350°C at which the bonding paste is heated and sintered, and it becomes possible to change into a bulk metal. As a result, the objects to be bonded are bonded. Hereinafter, the portion formed by sintering the metal particles (A) present between the objects to be bonded is called a bonding layer. From the viewpoints of conductivity and thermal conductivity, the metal particles (A) and the metal particles (a) are preferably particles using silver or copper, and more preferably silver particles from the viewpoint of oxidation resistance.

[0013] In the present disclosure, it is important that the metal particles (A) contain 50 mass% or more of the metal particles (a) having a specific average particle diameter. The "average particle diameter" as used herein means the volume-based 50% integrated particle diameter distribution particle diameter (d50) determined by the measurement method described in the examples. The d50 of the metal particles (a) is 100 nm or more and 500 nm or less, preferably 150 nm or more, more preferably 200 nm or more. Also, the d50 of the metal particles (a) is preferably 400 nm or less, more preferably 300 nm or less.

[0014] The metal particles (A) and the metal particles (a) may have their surfaces coated with an organic component. For example, the silver particles (A) and the silver particles (a) may be particles in which the surfaces of the silver particles are coated with an organic component. The organic component is also referred to as a protective agent. When coated with an organic component, the storage stability of the joining paste is improved. Examples of the organic component include fatty acids, aliphatic amines, aliphatic alcohols, etc., but saturated or unsaturated fatty acids are preferred, more preferably saturated or unsaturated fatty acids having 3 to 18 carbon atoms, and even more preferably saturated or unsaturated fatty acids having 6 to 18 carbon atoms. The organic component may contain one kind or two or more kinds.

[0015] The content of the metal particles (a) having a specific average particle diameter in the metal particles (A) is preferably 70 mass% or more, more preferably 85 mass% or more. The metal particles (A) and the metal particles (a) may each independently be used alone or in combination of a plurality. The metal particles (A) can contain metal particles other than the metal particles (a) as long as the effects of the present invention are not impaired. The metal particles (A) may contain metal particles having an average particle diameter exceeding 500 nm, may be combined with metal particles having an average particle diameter exceeding 1000 nm, and may have different metal species.

[0016] <Dispersion medium (B)> The joining paste of the present disclosure contains a dispersion medium (B). The dispersion medium (B) plays a role of dispersing the metal particles (A) and imparting fluidity to the coating film in the sintering process of silver. Examples of the dispersion medium (B) include terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersorb TOE100, Tersorb MTPH (manufactured by Nippon Terpene 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 diacetate, dipropylene glycol methyl ether acetate, 1,3-butylene glycol, 1,3-butanediol, 1,4-butanediol, 2-ethyl-1,3-hexanediol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, polyethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and isoparaffin-based dispersion media contained in hydrocarbon-based dispersion media. One kind may be used alone, or two or more kinds may be used in combination.

[0017] The dispersion medium (B) preferably contains 50% by mass or more of a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower (hereinafter referred to as the dispersion medium (b1)) based on the total mass of the dispersion medium (B). By containing 50% by mass or more of the dispersion medium (b1), the dispersion medium is likely to remain in the silver sintering process, and it becomes easy to make the value of the weight loss M200 at 200°C be 88 or more and 98 or less. The content of the dispersion medium (b1) is preferably 60% by mass or more, more preferably 70% by mass or more, based on the total mass of the dispersion medium (B). The boiling point of the dispersion medium (b1) is preferably 260°C or higher.

[0018] Further, the dispersion medium (B) preferably has a proportion of a dispersion medium (b2) (hereinafter referred to as the dispersion medium (b2)) having a boiling point exceeding 300°C, based on the total mass of the dispersion medium (B), of 10% by mass or less. When the proportion of the dispersion medium (b2) is 10% by mass or less, the dispersion medium does not excessively remain in the silver sintering process, and it becomes easy to make the value of the weight loss M200 at 200°C be 88 or more and 98 or less. When the value of the weight loss M200 at 200°C is 88 or more and 98 or less, since the dispersion medium remains in the sintering stage, the fluidity of the coating film increases, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity can be exhibited. Further, the wettability with respect to the joint portion is improved and the contact area is increased, so that a strong joint can be formed. Thereby, excellent joint strength and thermal cycle properties can be exhibited.

[0019] Examples of the dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower include terpene-based ones such as Tersorb TOE-100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol) (manufactured by Nippon Terpene Chemical Co., Ltd.); glycol ether-based ones such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether; Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate), and 1,6-diacetoxyhexane. Among them, at least one selected from the group consisting of terpene-based and glycol ether-based ones is preferably used.

[0020] The dispersion medium (B) preferably contains a dispersion medium containing a hydroxyl group. Since the dispersion medium (B) has a hydroxyl group, it adsorbs to the metal particles (A) and the dispersibility is improved. Further, since the volatilization of the dispersion medium becomes gentle, the film shrinkage that occurs during sintering becomes gentle. Thereby, the fluidity of the coating film increases, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity is exhibited. Further, the wettability with respect to the joint portion is improved and the contact area is increased, so that a strong joint can be formed. Thereby, excellent joint strength and thermal cycle properties can be exhibited. From the above viewpoints, the content rate of the dispersion medium containing a hydroxyl group is preferably 90% by mass or more, more preferably 95% by mass or more, based on the total mass of the dispersion medium (B).

[0021] Examples of the dispersion medium containing a hydroxyl group include terpineol-based ones such as terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersorb TOE-100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol), Tersorb MTPH (isobornyl cyclohexanol); glycol ether-based ones such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, polyethylene glycol monobutyl ether.

[0022] <Weight loss> As described above, it is important that when the weight loss M650 at 650°C when the temperature of the joining paste of the present disclosure is raised at a heating rate of 3°C / min is taken as 100, the weight loss M200 at 200°C is 88.0 or more and 98.0 or less. When it is within the above range, since the dispersion medium remains in the sintering stage, the fluidity of the coating film increases, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity can be exhibited. In addition, the wettability with respect to the joined portion is improved and the contact area is increased, so that a strong joint can be formed. Thereby, excellent joint strength and thermal cycle resistance can be exhibited. The value of M200 when M650 is taken as 100 is preferably 90.0 or more and 96.0 or less. In this specification, when the weight loss M650 at 650°C is taken as 100, the weight losses at 150°C / 250°C / 300°C are defined as M150 / M250 / M300, respectively. The weight loss can be measured using thermogravimetry-differential thermal analysis method (hereinafter also referred to as TG-DTA analysis method). For example, using a thermogravimetry-differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)), 10 mg of the sample is heated at a heating rate of 3°C / min in a nitrogen atmosphere under the condition of a start temperature of 30°C to obtain the result.

[0023] From the viewpoints of the thermal conductivity, joint strength, and thermal cycle characteristics described above, the paste for joining of the present disclosure may have M150 of 85.0 or more and 96.0 or less, M250 of 93.0 or more and 98.5 or less, and M300 of 96.0 or more and 99.0 or less.

[0024] Further, for the paste for joining of the present disclosure, the ratio of M150 to M200 (M150 / M200) is preferably 0.975 or more. When the value of M150 / M200 is 0.975 or more, in the sintering process between 150°C and 200°C, the rapid volatilization of the dispersion medium and other organic substances is suppressed, and the shrinkage of the coating film generated during sintering becomes gentle. As a result, the fluidity of the coating film is increased, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity is exhibited. In addition, the wettability with respect to the joint portion is improved and the contact area is increased, so that a strong joint can be formed. Thereby, excellent joint strength and thermal cycle properties can be exhibited.

[0025] From the viewpoints of the thermal conductivity, joint strength, and thermal cycle characteristics described above, the paste for joining of the present disclosure may have a ratio of M200 to M250 (M200 / M250) of 0.95 or more, and a ratio of M150 to M250 (M150 / M250) of 0.93 or more.

[0026] <Compound (C)> The paste for joining of the present disclosure may contain a compound (C) having 20 to 80 carbon atoms and having two or more functional groups (c) selected from the group consisting of a hydroxyl group, a carboxyl group, and an amino group (hereinafter referred to as compound (C)). By including such a compound (C), even after part or all of the dispersion medium (B) has volatilized, it can exist as a liquid composition, so that a good joint interface integrated with the joint portion can be formed. In addition, each functional group (c) has a high binding property with metal particles and exhibits excellent dispersibility. The number of carbon atoms in compound (C) represents the numerical value including the carbon atoms in functional group (c). Therefore, when the functional group (c) in compound (C) is a carboxy group, the number of carbon atoms including the carbon atoms in this carboxy group is regarded as the number of carbon atoms in compound (C).

[0027] In compound (C), the skeleton (partial structure) excluding functional group (c) is an organic residue, and it is preferably a hydrocarbon group or a group in which a plurality of hydrocarbon groups are bonded by a linking group containing a heteroatom. Examples of such a linking group 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). Compound (C) preferably has no functional groups other than functional group (c).

[0028] When the number of functional groups (c) in compound (C) is denoted as n, compound (C) preferably has an n-valent hydrocarbon group. In compound (C), the skeleton excluding functional group (c) is more preferably composed only of an n-valent hydrocarbon group in terms of obtaining a strong conjugate.

[0029] The number of functional groups (c) in compound (C) is preferably 2 or 3. Compound (C) may have a linear structure, or may have 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 be in a liquid state with good fluidity.

[0030] Examples of the compound (C) having a linear structure include eicosanedioic acid, heneicosanedioic acid, docosanedioic acid, tetracosanedioic acid, triacontanedioic acid, dotriacontanedioic acid, tetracontanedioic acid, pentacontanedioic acid, hexacontanedioic acid, and batyl alcohol. Examples of the compound (C) having a branched and / or cyclic structure include dimer acid, trimer acid, tetramer acid, dimer diol, trimer triol, tetramer tetraol, dimer diamine, trimer triamine, tetramer tetramine, and phytantriol. The compound (C) is more preferably a compound selected from the group consisting of dimer acid, trimer acid, dimer diol, trimer triol, dimer diamine, and trimer triamine.

[0031] In the bonding paste of the present disclosure, from the viewpoints of initial bonding strength and thermal cycle characteristics, the content of the compound (C) is preferably 0.05 to 2.0% by mass, more preferably 0.1 to 1.0% by mass, based on the mass of the metal particles (A).

[0032] <Compound (D)> The bonding paste of the present disclosure may contain a compound (D) (hereinafter referred to as compound (D)) having at least one nitrogen atom selected from the group consisting of secondary nitrogen atoms and tertiary nitrogen atoms and having 4 or more hydroxyl groups. From the viewpoints of bonding strength and thermal cycle characteristics, the compound (D) preferably has a tertiary nitrogen atom. 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 binding property with the metal particles (A) is enhanced and the dispersibility is remarkably improved. In addition, the tertiary nitrogen atom has a function of reducing the metal particles (A) and the bonded portion, and when the number of tertiary nitrogen atoms is 2 or more, the reducing function is enhanced. Further, from the viewpoints of dispersibility and reducing function, the number of hydroxyl groups in the compound (D) is preferably 4 to 6. In particular, since the hydroxyl groups are excellent in the binding property with the metal particles (A), they tend to improve the dispersibility. When the number of hydroxyl groups is 4 or more, the binding property with the metal particles (A) is enhanced, and the dispersibility is remarkably improved. In addition, the hydroxyl groups have a function of reducing the metal particles (A) and the joint portion, and when the number of hydroxyl groups is 4 or more, the reducing function is greatly improved.

[0033] The content of the compound (D) is preferably 0.02% by mass or more based on the mass of the metal particles (A). When it is 0.02% by mass or more, the dispersibility of the metal particles (A) is improved, and sintering proceeds with the compound (D) remaining in the coating film, and sintering proceeds in a state where the coating film has fluidity. Therefore, the adhesion to the joint portion and the defects of the joint layer are reduced. From the viewpoints of dispersibility, adhesion to the joint portion, and reduction of joint layer defects, it is more preferably 0.05% by mass or more, and still more preferably 0.10% by mass or more. Also, the content of the compound (D) is preferably 2.00% by mass or less based on the mass of the metal particles (A). By being 2.00% by mass or less, the residual amount in the coating film after sintering can be reduced, and the joint strength and thermal cycle characteristics are excellent. From the viewpoint of reducing the residual amount, it is more preferably 1.0% by mass or less, and still more preferably 0.5% by mass or less.

[0034] <Manufacture of the joining paste> The joining paste of the present disclosure only needs to contain at least the metal particles (A) and the dispersion medium (B), and its manufacturing method is not particularly limited and can be adjusted using a known method. Examples of the apparatus for preparing the joining paste from the metal particles (A) and the dispersion medium (B) include a disper, a three-roll mill, a bead mill, an ultrasonic disperser, a planetary stirrer, and the like.

[0035] The proportion of the mass of the metal particles (A) based on the mass of the paste for bonding is preferably 80% by mass to 95% by mass, more preferably 85% by mass to 94% by mass. By including the metal particles (A) within the above range, good printability as a paste for bonding can be exhibited, while suppressing the residue of the dispersion medium (B) in the bonded body, suppressing the generation of voids derived from the dispersion medium (B), and good bonding strength can be exhibited.

[0036] The paste for bonding of the present disclosure can contain additives, for example, it can contain a sintering accelerator, a binder resin, a resin-type dispersant, a reducing agent, and the like.

[0037] <Bonded body and method for manufacturing a bonded body> By using the paste for bonding of the present disclosure, a first bonded portion and a second bonded portion can be bonded to obtain a bonded body. The bonded body can be manufactured, for example, by the following manufacturing method (I) by non-pressure bonding or manufacturing method (II) by pressure bonding. The paste for bonding of the present disclosure has its weight loss during sintering controlled, and even under non-pressure conditions, it can suppress voids in the coating film after sintering and exhibit high thermal conductivity. Also, it has excellent bonding strength and can suppress a decrease in bonding strength due to thermal cycling.

[0038] [Manufacturing method (I)] Manufacturing method (I) is a method by non-pressure bonding, and preferably includes, for example, the following steps (1) to (3). (1) A step of applying the paste for bonding to the first bonded body. (2) A step of placing the second bonded portion on the first bonded portion to which the paste for bonding has been applied. (3) A step of sintering the placed laminate in a non-pressure environment.

[0039] (1) Coating step As a method of applying the joining paste to the object to be joined, there is no particular limitation as long as it can be uniformly applied on the member. For example, various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, gravure offset printing, etc., and a dispensing method using a dispenser can be mentioned. Since the joining paste of the present disclosure has excellent fluidity even when containing metal particles at a high concentration, it is particularly preferably used in combination with metal mask printing.

[0040] (2) Placement step Next, the second object to be joined is placed on the first object to be joined coated with the joining paste of the present disclosure. When the joining paste of the present disclosure is used, it can be placed without pressure. In non-pressure joining, it is preferable that this placement step is also performed without pressure, but it is also possible to place it while applying pressure. When applying pressure, the pressure is appropriately set according to the viscosity of the joining paste and the drying state of the paste, but it is preferably 0.001~40 MPa, more preferably 0.003~30 MPa.

[0041] (3) Sintering step The sintering conditions for non-pressure joining of the laminate with the second object to be joined placed on the first object to be joined are appropriately changed. For example, conditions such as 200~350 °C under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere can be mentioned. Examples of the firing apparatus include a hot air oven, a firing furnace, an electric furnace, an infrared oven, a reflow oven, a microwave oven, a hot plate, a light firing apparatus, etc. These apparatuses can be used alone or in combination as appropriate. The non-pressure sintering conditions are preferably such that after heating to the set temperature at a heating rate of 2 °C~30 °C per minute, it is maintained at a temperature equal to or higher than the set temperature for about 10 minutes to 2 hours. The set temperature is preferably 200~350 °C, more preferably 230 °C~300 °C, and even more preferably 250~280 °C.

[0042] (2a) Preliminary drying step In the manufacturing method (I) using non-pressure bonding, it is preferable to provide a preliminary drying step (2a) between step (2) and step (3) for the purpose of removing the organic components in the bonding coating film. Since the paste for bonding of the present disclosure contains the compound (B), the coating film can flow and form a bonding interface even after the dispersion medium (B) is preliminarily dried and removed, so the preliminary drying step can be provided. By providing the preliminary drying step, the residual of the dispersion medium (B), which is one of the causes of defects (voids) in the bonding layer, can be suppressed, and the bonding layer has excellent denseness, which is preferable. The preliminary drying can be carried out, for example, using a device similar to a firing device under the conditions of 60 to 220 °C for 1 minute to 300 minutes. Preferably, it is in the range of 70 to 100 °C for 30 minutes to 120 minutes.

[0043] That is, as the manufacturing method (I), it particularly preferably includes the following steps. (1) Step of applying the paste for bonding to the first adherend. (2) Step of placing the second adherend on the first adherend portion coated with the paste for bonding. (2a) Step of heating and preliminarily drying the placed laminate. (3) Step of sintering the placed laminate in a non-pressure environment.

[0044] [Manufacturing method (II)] The manufacturing method (II) is a method by pressure bonding, and preferably includes, for example, the following steps (10) to (30). (10) Step of applying the paste for bonding to the first adherend. (10a) Step of heating and preliminarily drying the applied laminate. (20) Step of placing the second adherend on the first adherend portion coated and preliminarily dried with the paste for bonding. (30) Step of sintering the placed laminate in a pressure environment.

[0045] (10) Coating step As a method of applying the joining paste to the joined body, there is no particular limitation as long as it can be uniformly applied on the member. For example, various printing methods such as screen printing, flexographic printing, offset printing, gravure printing, metal mask printing, gravure offset printing, etc., and a discharging method using a dispenser can be mentioned. Since the joining paste of the present disclosure has excellent fluidity even when containing metal particles at a high concentration, it is particularly preferably used in combination with metal mask printing.

[0046] (10a) Preliminary drying step In the manufacturing method (II) using pressure joining, a preliminary drying step (10a) can be provided between the step (10) and the step (20) for the purpose of removing the organic components in the joining coating film. By providing the preliminary drying step, the preliminary drying can be carried out, for example, under the conditions of 60 to 220 °C for 1 minute to 300 minutes using an apparatus similar to a firing apparatus.

[0047] (20) Placement step Next, the second joined part is placed on the first joined part to which the joining paste of the present disclosure has been applied and preliminarily dried. In the case of pressure joining, the placement step may also be carried out under pressure. The pressure is appropriately set according to the viscosity of the joining paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, more preferably 0.3 to 30 MPa.

[0048] (30) Sintering step The sintering conditions for pressure joining the laminate in which the second joined part is placed on the first joined part are appropriately changed, and examples thereof include conditions such as 200 to 350 °C under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere. The pressure is appropriately set according to the viscosity of the joining paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, more preferably 1 to 30 MPa.

[0049] In any of the manufacturing methods, the thickness of the bonding layer formed when bonding the parts to be bonded with the bonding paste is not limited, 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.

[0050] [Parts to be bonded] The type of the parts to be bonded is not particularly limited, and examples thereof include metal materials, semiconductor materials, plastic materials, ceramic materials, and electronic elements. Examples of the metal include copper, gold, and aluminum. Examples of the semiconductor material include silicon, germanium, gallium arsenide, gallium phosphide, cadmium sulfide, silicon nitride, graphite, yttrium oxide, magnesium oxide, silicon carbide, and gallium nitride. Examples of the plastic material include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate. Examples of the ceramic material include glass and silicon. Examples of the electronic element include semiconductor elements, LED elements, and power device elements.

[0051] The first part to be bonded and the second part to be bonded may be not only of the same type but also of different types of members. In order to increase the bonding strength of the bonded portion, the surface of the part to be bonded may be subjected to corona treatment, plating treatment, or the like. Since the bonding paste of the present disclosure can achieve void reduction and strong bonding, it can also achieve high thermal conductivity, excellent bonding strength, and thermal cycle characteristics for a substrate (also referred to as a non-treated substrate or a non-plated substrate) that has not been subjected to treatments such as corona treatment or plating treatment. For example, the bonding paste of the present disclosure is suitable when the first part to be bonded is a non-treated substrate (for example, a non-treated copper substrate). In addition, since the joining paste of the present disclosure can achieve void reduction and strong joining, it can also achieve high thermal conductivity, excellent joining strength, and thermal cycle characteristics even in a structure such as "copper base material / joining layer containing silver particles / SiC element" where strain is likely to occur during the thermal cycle test. For example, the joining paste of the present disclosure is suitable when the second joined part is SiC.

Example

[0052] Hereinafter, the present disclosure will be described in detail using examples and comparative examples, but the technical scope of the present disclosure is not limited thereto. In the examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "mass%", respectively. The numerical values in the tables represent "parts" unless otherwise specified.

[0053] [Weight loss] The weight loss of the joining paste of the present disclosure was determined by heating 10 mg of the sample from an initial temperature of 30°C to 650°C at a heating rate of 3°C / min in a nitrogen atmosphere using a thermogravimetric differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)) to obtain the weight loss at each temperature. When the weight loss M650 at 650°C was set to 100, the weight loss at 150°C was designated as M150, the weight loss at 200°C as M200, the weight loss at 250°C as M250, and the weight loss at 300°C as M300.

[0054] <Manufacture of metal particles> (Production Example 1) Metal particle A1 Under a nitrogen atmosphere, 200 parts of toluene and 22.3 parts of silver hexanoate were mixed while stirring at 25 °C to form a 0.5 M solution. Then, 1.6 parts of diethylaminoethanol and 0.28 parts of oleic acid were added as a dispersant and dissolved. Thereafter, 73.1 parts of an aqueous solution of 20% succinic acid dihydrazide (hereinafter referred to as SUDH) was added dropwise as a reducing agent, and the color of the solution changed from light yellow to dark brown. Further, the temperature was raised to 40 °C to promote the reaction and allow the reaction to proceed. After standing and separating, the aqueous phase was taken out to remove excess reducing agent and impurities. Further, distilled water was added to the toluene layer several times, and washing and separation were repeated. 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. When the particle diameter of the metal particles A1 was determined by the method described below, d50 was 210 nm.

[0055] (Production Example 2) Metal Particles A2 Metal particles A2 were obtained in the same manner as in Production Example 1, except that 1.8 parts of diethylaminoethanol and 0.31 parts of oleic acid were used. d50 was 185 nm.

[0056] (Production Example 3) Metal Particles A3 Metal particles A3 were obtained in the same manner as in Production Example 1, except that 1.2 parts of diethylaminoethanol and 0.18 parts of oleic acid were used. d50 was 290 nm.

[0057] (Production Example 4) Metal Particles A4 Metal particles A4 were obtained in the same manner as in Production Example 1, except that 1.0 parts of diethylaminoethanol and 0.14 parts of oleic acid were used. d50 was 390 nm.

[0058] (Production Example 5) Metal Particles A5 Metal particles A5 were obtained in the same manner as in Production Example 1, except that 2.4 parts of diethylaminoethanol and 0.42 parts of oleic acid were used. d50 was 120 nm.

[0059] (Production Example 6) Metal Particles A6 Silver diethylaminoethanol 0.7 part, except that the amount of oleic acid was 0.12 part, metal particles A6 were obtained in the same manner as in Production Example 1. The d50 was 450 nm.

[0060] (Production Example 7) Metal particles A7 Silver hexanoate was 17.0 parts of copper pentanoate, and metal particles A7 were obtained in the same manner as in Production Example 1, except that 1.8 parts of diethylaminoethanol and the amount of oleic acid was 0.45 part. The d50 was 150 nm.

[0061] (Production Example 8) Metal particles A10 Metal particles A10 were obtained in the same manner as in Production Example 1, except that 2.1 parts of diethylaminoethanol and the amount of oleic acid was 0.71 part. The d50 was 85 nm.

[0062] (Production Example 9) Metal particles A11 Metal particles A11 were obtained in the same manner as in Production Example 1, except that 1.4 parts of diethylaminoethanol and the amount of oleic acid was 0.09 part. The d50 was 600 nm.

[0063] (Production Example 10) Metal particles A12 Metal particles A12 were obtained in the same manner as in Production Example 1, except that 0.6 part of diethylaminoethanol and the amount of oleic acid was 0.07 part. The d50 was 1100 nm.

[0064] [Method for Measuring Average Particle Diameter of Metal Particles] Isopropyl alcohol was added to each metal particle and dispersed with an ultrasonic disperser to obtain a 0.5 mass% dispersion. The particle diameter of the metal particles in the dispersion was measured using a NanoTrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.), and the average particle diameter (d50) was determined. Among the metal particles produced by the above method, metal particles A1 - A7 correspond to the metal particles (a) of the present disclosure, and metal particles A10 - A12 correspond to metal particles that are not the metal particles (a).

[0065] <Dispersion Medium (B)> The following materials were used as the dispersion medium (B). The manufacturer name, supplementary information, and boiling point obtained are described in parentheses. Dispersion medium B1: Triethylene glycol monobutyl ether (glycol ether-based, hydroxyl group-containing, boiling point 278 °C) Dispersion medium B2: Tersorb TOE-100 (manufactured by Nippon Terpene Chemical Co., Ltd., terpene-based, hydroxyl group-containing, boiling point 268 °C) Dispersion medium B3: 1,6-Diacetoxyhexane (manufactured by Tokyo Chemical Industry Co., Ltd., without hydroxyl group, boiling point 260 °C) Dispersion medium B4: Dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd., terpene-based, hydroxyl group-containing, boiling point 210 °C) Dispersion medium B5: Diethylene glycol monomethyl ether (glycol ether-based, hydroxyl group-containing, boiling point 193 °C) Dispersion medium B6: Tersorb MTPH (manufactured by Nippon Terpene Chemical Co., Ltd., terpene-based, hydroxyl group-containing, boiling point 308 °C)

[0066] <Compound (C)> Compound C1: Priplol 2033 (manufactured by Croda Japan Co., Ltd., a dimer diol with 36 carbon atoms. It consists of two hydroxyl groups and a divalent hydrocarbon group having a branched and cyclic structure. Liquid) Compound C2: Priamine 1071 (manufactured by Croda Japan Co., Ltd., a mixture of a dimer diamine with 36 carbon atoms (consisting of two amino groups and a divalent hydrocarbon group having a branched and cyclic structure, liquid) and a trimer triamine with 54 carbon atoms (consisting of three amino groups and a trivalent hydrocarbon group having a branched and cyclic structure, liquid)) Compound C3: Priplol 1009 (manufactured by Croda Japan Co., Ltd., a hydrogenated dimer acid with 36 carbon atoms. It consists of two carboxy groups and a divalent hydrocarbon group having a branched and cyclic structure. Liquid at 25 °C) Compound C4: Priplol 1040 (manufactured by Croda Japan Co., Ltd., a trimer acid with 54 carbon atoms. It consists of three carboxy groups and a trivalent hydrocarbon group having a branched and cyclic structure. Liquid at 25 °C)

[0067] <Compound (D)> Compound D1: Alkanolamine (number of hydroxyl groups: 4, number of tertiary nitrogen atoms: 2)

[0068] <Manufacture of bonding paste> [Example 1] 88 parts of metal particles A1 and 12 parts of triethylene glycol monobutyl ether were mixed using a planetary stirrer to prepare a bonding paste.

[0069] [Examples 2 to 29, Comparative Examples 1 to 6] Bonding pastes were obtained in the same manner as in Example 1, except that the types and amounts (parts) of the materials were changed according to the compositions shown in Tables 1 to 3. In the tables, blanks indicate that the component was not blended.

[0070] <Evaluation of bonding paste> Using the obtained bonding paste, bonded bodies were produced by the production methods described in Tables 1 to 3. For Examples 1 to 27 and Comparative Examples 1 to 6, Production Method 1 below was used; for Example 28, Production Method 2 below was used; and for Example 29, Production Method 3 below was used. The details of the production methods and the printing conditions of the bonding paste are as follows. [Printing conditions (metal mask printing)] Metal mask: Opening 7.5 mm square, plate thickness 100 μm (manufactured by Ceria Corporation) Metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by Ceria Corporation)

[0071] [Production Method 1] The bonding paste was printed once on the first joint part (copper substrate (unplated): 20 mm × 20 mm × 3 mm) under the above printing conditions. Then, the plated surface of the second joint part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the bonding paste surface, and pressureless bonding was performed under the following sintering conditions 1 to obtain bonded bodies respectively. [Sintering conditions 1] The laminate placed in a firing furnace in a nitrogen atmosphere was heated from 25°C to 80°C at a rate of 5°C / min, and pre-dried at 80°C for 90 minutes. Then, it was heated to 300°C at a rate of 8°C / min, and after reaching 300°C, it was held at 300°C for 2 hours.

[0072] [Manufacturing Method 2] After printing the bonding paste once on the first joint part (non-plated copper substrate: 20 mm × 20 mm × 3 mm) under the above printing conditions, the plated surface of the second joint part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the bonding paste surface, and pressureless bonding was performed under the following sintering conditions to obtain a bonded body. [Sintering Conditions 2] The stacked body placed in a firing furnace in a nitrogen atmosphere was heated from 25°C to 300°C at a rate of 8°C / min, and after reaching 300°C, it was held at 300°C for 2 hours.

[0073] [Manufacturing Method 3] After printing the bonding paste once on the first joint part (non-plated copper substrate: 20 mm × 20 mm × 3 mm) under the above printing conditions, it was placed in a hot air oven and pre-dried at 180°C for 10 minutes. Next, the plated surface of the second joint part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the pre-dried bonding paste surface, and pressure bonding was performed under the following sintering conditions 3 to obtain a bonded body. [Sintering Conditions 3] In a nitrogen atmosphere, while applying pressure of 30 MPa from above the second joint part, the temperature was raised from room temperature to 300°C at a rate of 20°C / min, and after reaching 300°C, it was maintained at the same temperature for 5 minutes.

[0074] The obtained bonded body was used to evaluate the bonding strength and thermal cycle characteristics. Also, the thermal conductivity was evaluated under the conditions described later. The results are shown in Tables 1 to 3. [Bonding Strength] The bonded body was fixed at the part of the first joint part, and starting from the interface between the first joint part and the bonding layer, a position 100 μm in height toward the second joint part was pushed at a speed of 500 μm / s, and the bonding strength (die shear strength) at which the bonding was broken was obtained and evaluated based on the following evaluation criteria. The larger the numerical value of the die shear strength, the better, and 10 MPa or more is within the practical range. The measurement conditions are shown below. [Measurement Conditions] Measuring device: Universal bond tester (manufactured by Daiji Japan Co., Ltd., 4000 series) Measurement height: 100 μm Measurement speed: 500 μm / s

[0075] (Evaluation criteria) S: Die share strength is 35 MPa or more A: Die share strength is 25 MPa or more and less than 35 MPa B: Die share strength is 15 MPa or more and less than 25 MPa C: Die share strength is 10 MPa or more and less than 15 MPa D: Die share strength is less than 10 MPa

[0076] [Thermal cycle characteristics] Using the bonded body, the following cycle test was conducted. Using the bonded body after the cycle test, the bonding strength (die share strength) was obtained and evaluated in the same manner as the above [Bonding strength]. 10 MPa or more is within the practical range. [Cycle test] A process of holding the bonded body at -40°C for 30 minutes and then at 150°C for 30 minutes was defined as one cycle, and 500 cycles of storage were carried out.

[0077] [Thermal conductivity] The thermal conductivity was obtained according to the following formula from the thermal diffusivity, specific heat, and density. Thermal conductivity (W / m·K) = density (g / cm 3 ) × specific heat (J / kg·K) × thermal diffusivity (mm 2 / s) The thermal diffusivity was determined as follows. On the first joint part (copper substrate (unplated): 20 mm × 20 mm × 3 mm), the joining paste was printed once using a metal squeegee (40 mm × 250 mm, thickness 1 mm (manufactured by Ceria Corporation)) with a metal mask (opening 20 mm square, plate thickness 200 μm). Then, the second joint part (copper substrate (unplated): 20 mm × 20 mm × 3 mm) was placed on it, and the laminate placed in a firing furnace under a nitrogen atmosphere was heated from 25°C to 300°C at a rate of 8°C / min. After reaching 300°C, it was held at 300°C for 2 hours to obtain a joined body. The obtained joined body was carbon-coated with carbon spray. Next, the thermal diffusivity was measured using a xenon flash analyzer LFA447 Nano Flash (manufactured by NETZSCH). The larger the numerical value of the thermal conductivity, the better, and 80 W / (m·K) or more is within the practical range.

[0078] (Evaluation Criteria) S: 250 W / (m·K) or more A: 200 W / (m·K) or more and less than 250 W / (m·K) B: 150 W / (m·K) or more and less than 200 W / (m·K) C: 80 W / (m·K) or more and less than 150 W / (m·K) D: Less than 80 W / (m·K)

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] According to the results of Tables 1 to 3, when using the joining paste of the present disclosure, even in a configuration where stable joining is extremely difficult, such as a non-pressurized and non-plated substrate and a large-area SiC element, the thermal conductivity and the joining strength are very high, and the decrease in the joining strength was suppressed even after the thermal cycle test was carried out. In particular, a joining paste in which the value of M150 / M200 satisfies 0.975 or more, a joining paste in which the dispersion medium (b1) having a boiling point of 250 °C or higher and 300 °C or lower is 50% by mass or more, a joining paste in which the dispersion medium (b1) contains at least one selected from the group consisting of terpene-based and glycol ether-based, a joining paste in which the content of the dispersion medium (b2) having a boiling point exceeding 300 °C is 10% by mass or less, and a joining paste in which the content of the dispersion medium having a hydroxyl group is 90% by mass or more based on the total mass of the dispersion medium (B) exhibited high thermal conductivity with voids in the coating film after sintering suppressed even under non-pressurized conditions, excellent joining strength, and suppression of the decrease in the joining strength associated with thermal cycles (Examples 1 and 7, Examples 7 and 17, Examples 2 and 6, Examples 1 and 13, Examples 2 and 6). On the other hand, when using the joining paste of the comparative example, the thermal conductivity and the joining strength were significantly low, and the joining strength after the thermal cycle test also decreased significantly.

Claims

1. A paste for bonding comprising metal particles (A) and a dispersion medium (B), wherein the metal particles (A) contain, based on the total mass of the metal particles (A), 50% by mass or more of metal particles (a) having an average particle diameter of 100 nm or more and 500 nm or less, A paste for bonding, wherein when the weight loss M650 at 650 °C when the temperature of the paste for bonding is raised at a heating rate of 3 °C / min is taken as 100, the weight loss M200 at 200 °C is 88 or more and 98 or less.

2. The paste for bonding according to claim 1, wherein when the weight loss at 150 °C is defined as M150 with the weight loss M650 taken as 100, the ratio (M150 / M200) of the weight loss M150 to the weight loss M200 is 0.975 or more.

3. The paste for bonding according to claim 1, wherein the content of the dispersion medium (b1) having a boiling point of 250 °C or more and 300 °C or less in the dispersion medium (B) is 50% by mass or more based on the total mass of the dispersion medium (B).

4. The paste for bonding according to claim 3, wherein the dispersion medium (b1) contains at least one selected from the group consisting of terpene-based and glycol ether-based.

5. The paste for bonding according to claim 1, wherein the content of the dispersion medium (b2) having a boiling point exceeding 300 °C in the dispersion medium (B) is 10% by mass or less based on the total mass of the dispersion medium (B).

6. The paste for bonding according to claim 1, wherein the content of the dispersion medium having a hydroxyl group in the dispersion medium (B) is 90% by mass or more based on the total mass of the dispersion medium (B).

7. A bonded body in which a first bonded portion and a second bonded portion are bonded by the paste for bonding according to claim 1.

8. The bonded body according to claim 7, wherein the first bonded portion is an untreated base material.

9. The bonded body according to claim 7 or 8, wherein the second bonded portion is SiC.

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