Joining paste and joined article

Abstract

To provide a joining paste that 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, not only in pressure joining but also in non-pressure joining, and a joined article using the joining paste.SOLUTION: A joining paste contains metal particles (A) and a dispersion medium (B), wherein the content of dispersion medium (b2) with a boiling point exceeding 300°C in the dispersion medium (B) is 20 mass% or less. When 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 100°C, 150°C, 200°C, and 250°C satisfies all of the conditions (1) to (4): (1) M100 is between 10 and 70, (2) M150 is between 85 and 96, (3) M200 is between 88 and 98, and (4) M250 is between 93 and 99.5.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a bonding paste having excellent thermal conductivity and bonding strength and capable of suppressing a decrease in bonding strength due to 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 (LEC) element, and the like. In recent years, in the technical field of next-generation power electronics, devices such as SiC that can operate at high temperatures have been demanded. As a bonding material for manufacturing such devices, 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 heating 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 adhering to at least a part of the surface of the inorganic particles, and specifying the values of the weight loss rate when heating from room temperature to 200 ° C. and when heating 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 joining materials, 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 objects and applications are limited. Therefore, not only in pressure joining but also in non-pressure joining, it is required to reduce voids, exhibit high thermal conductivity, 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 element area increases, it becomes more difficult for internal gas, etc. to escape, and voids tend to occur easily. Also, the difference in the coefficient of linear expansion between Si elements or SiC elements and that 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 / the joining layer containing silver particles / the Si or SiC element layer, cracks tend to occur, and the thermal cycle characteristics tend to deteriorate. Furthermore, although the SiC element has a coefficient of linear expansion similar to that of the Si element, since it has a higher hardness than the Si element, the strain applied during the thermal cycle is larger than that of the Si element, 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 large-area SiC elements.

[0007] Accordingly, the problem to be solved by the present disclosure is to provide a joining paste that can 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, not only in pressure bonding but also in non-pressure bonding, 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 content of the dispersion medium (b2) having a boiling point exceeding 300°C in the dispersion medium (B) is 20% by mass or less based on the total mass of the dispersion medium (B), 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, and the weight losses at 100°C / 150°C / 200°C / 250°C are taken as M100 / M150 / M200 / M250 respectively, the joining paste is characterized by satisfying all of the following (1) to (4). (1) M100 is 10 or more and 70 or less. (2) M150 is 85 or more and 96 or less. (3) M200 is 88 or more and 98 or less. (4) M250 is 93 or more and 99.5 or less. [2]: When the weight loss at 150°C is taken as M150 with the weight loss M650 at 650°C being 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 content of the dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower in the dispersion medium (B) is 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 paste for joining according to any one of [1] to [4], 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 joining according to any one of [1] to [5], 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 joined body in which a first joined part and a second joined part are joined by the paste for joining 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, in both pressure joining and non-pressure joining, 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 paste for joining and a joined body using the joining paste can be provided.

Embodiments for Carrying Out the Invention

[0010] The paste for joining of the present disclosure is a paste for joining containing metal particles (A) and a dispersion medium (B), wherein the content of the dispersion medium (b2) having a boiling point exceeding 300°C in the dispersion medium (B) is 20% by mass or less based on the total mass of the dispersion medium (B), and when the weight loss M650 at 650°C when the temperature of the paste for joining is raised at a rate of 3°C / min is set to 100, and the weight losses at 100°C / 150°C / 200°C / 250°C are set to M100 / M150 / M200 / M250, respectively, it is characterized by satisfying the following (1) to (4). (1) M100 is 10 or more and 70 or less. (2) M150 is 85 or more and 96 or less. (3) M200 is 88 or more and 98 or less. (4) M250 is 93 or more and 99.5 or less. By having the above configuration, the disclosed bonding paste can exhibit excellent bonding strength and bonding strength after thermal cycling regardless of pressure application or non-pressure application, even in cases where the members to be bonded are non-treated base materials such as non-plated ones or where stable bonding is difficult, such as in SiC semiconductor elements. Specifically, according to the above, it is possible to provide a bonding paste having high thermal conductivity, high bonding strength at the bonded portion, and suppression of a decrease in bonding strength accompanying thermal cycling, and a bonded body using the bonding paste. Further, thereby, even when a large-area SiC element is bonded, 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 members to be bonded during the sintering process, and include silver, copper, alloys containing silver and / or silver, silver oxide, copper oxide, and coated particles having a metal (excluding silver and copper) as a core 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) exhibit a function in which the particles melt or adhere to each other (hereinafter also referred to as sintering) in the temperature range of 200°C to 350°C at which the bonding paste is heated and sintered, and can change into a bulk metal. As a result, the members to be bonded are joined. Hereinafter, the portion formed by sintering of the metal particles (A) present between the members to be bonded is referred to as a bonding layer. From the viewpoints of conductivity and thermal conductivity, the metal particles (A) are preferably particles using silver or copper, and more preferably silver particles from the viewpoint of oxidation resistance.

[0013] The particle diameter of the metal particles (A) can be appropriately selected according to the application and bonding conditions. Usually, those having an average particle diameter of 100 nm or more and 10 μm or less are preferably used. The "average particle diameter" as used in this specification means the volume-based 50% integrated particle size distribution particle diameter (d50) determined by the measurement method described in the examples. The d50 of the metal particles (A) is preferably 100 nm or more and 10 μm or less, more preferably 150 nm or more, and even more preferably 200 nm or more. Also, the d50 of the metal particles (A) is preferably 8 μm or less, more preferably 5 μm or less.

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

[0015] The metal particles (A) may each independently be used alone or in combination of a plurality.

[0016] <Dispersion medium (B)> The bonding paste of the present disclosure contains a dispersion medium (B). The dispersion medium (B) functions to disperse the metal particles (A) and plays a role of imparting fluidity to the coating film in the silver sintering process. 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 of them may be used alone, or two or more of them may be used in combination.

[0017] In addition, for the bonding paste of the present disclosure, it is important that the content of the dispersion medium (b2) (hereinafter referred to as the dispersion medium (b2)) having a boiling point exceeding 300°C is 20% by mass or less based on the total mass of the dispersion medium (B) and satisfies the following (1) to (4). (1) M100 is 10.0 or more and 70.0 or less. (2) M150 is 85.0 or more and 96.0 or less. (3) M200 is 88.0 or more and 98.0 or less. (4) M250 is 93.0 or more and 99.5 or less. When the above conditions are satisfied, the drying behavior of the dispersion medium in the sintering process can be controlled. Specifically, since the dispersion medium remains appropriately in the sintering stage, the fluidity of the coating film is increased, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity can be 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. As a result, excellent joint strength and thermal cycle resistance can be exhibited.

[0018] The weight loss can be measured using thermogravimetric differential thermal analysis (hereinafter also referred to as TG-DTA analysis). For example, using a thermogravimetric differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)), 10 mg of a sample can be heated at a heating rate of 3 °C / min in a nitrogen atmosphere under the condition of a start temperature of 30 °C.

[0019] From the viewpoint of satisfying the above (1) to (4), the dispersion medium (B) preferably contains a dispersion medium (b1) having a boiling point of 250 °C or higher and 300 °C or lower (hereinafter referred to as dispersion medium (b1)) in an amount of 50% by mass or more 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 satisfy the above conditions. 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.

[0020] In addition, for the dispersion medium (B), the proportion of the dispersion medium (b2) having a boiling point exceeding 300 °C is preferably 15% by mass or less, more preferably 10% by mass or less, based on the total mass of the dispersion medium (B). When the proportion of the dispersion medium (b2) is 15% by mass or less, the dispersion medium does not remain excessively in the silver sintering process, and it becomes easy to satisfy the above conditions.

[0021] As the dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower, for example, terpene-based 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 such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether; and Texanol (2,2,4-trimethylpentane-1,3-diol monoisobutyrate) can be mentioned. Among them, at least one selected from the group consisting of terpene-based and glycol ether-based is preferably used.

[0022] The dispersion medium (B) preferably includes a dispersion medium containing a hydroxyl group. When the dispersion medium (B) has a hydroxyl group, it adsorbs to the metal particles (A) and the dispersibility is improved. Furthermore, since the volatilization of the dispersion medium becomes gentle, the film shrinkage occurring during sintering becomes gentle. As a result, 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. In addition, the wettability with respect to the joint portion is improved and the contact area increases, so that a strong joint can be formed. Thereby, excellent joint strength and thermal cycle resistance can be exhibited. From the above viewpoints, the content 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).

[0023] Examples of the dispersion medium containing a hydroxyl group include terpene alcohol-based such as terpineol, dihydroterpineol, dihydroterpinyl acetate, Tersorb TOE-100 (2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol), and Tersorb MTPH (isobornyl cyclohexanol); and glycol ether-based such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, and polyethylene glycol monobutyl ether.

[0024] <Weight loss> From the perspectives of the thermal conductivity, joint strength, and thermal cycle characteristics described above, for the joining paste of the present disclosure, the value of M100 is preferably 10.0 or more and 50.0 or less, the value of M150 is preferably 87.0 or more and 95.0 or less, the value of M200 is preferably 90.0 or more and 96.0 or less, and the value of M250 is preferably 93.0 or more and 98.5 or less. Further, when the weight loss at 300°C with M650 being 100 is defined as M300, the value of M300 may be 96.0 or more and 99.0 or less.

[0025] Also, for the joining paste 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, during 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 during sintering becomes gentle. As a result, 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. In addition, the wettability with respect to the joint portion is improved and the contact area increases, so that a strong joint can be formed. Thereby, excellent joint strength and thermal cycle properties can be exhibited.

[0026] From the perspectives of the thermal conductivity, joint strength, and thermal cycle characteristics described above, for the joining paste of the present disclosure, the ratio of M200 to M250 (M200 / M250) may be 0.95 or more, and the ratio of M150 to M250 (M150 / M250) may be 0.93 or more.

[0027] <Compound (C)> The bonding paste 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 carboxy 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 bonding interface integrated with the bonded 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 of the compound (C) represents a numerical value including the carbon in the functional group (c). Therefore, when the functional group (c) in the compound (C) is a carboxy group, the number of carbon atoms including the carbon in this carboxy group is regarded as the number of carbon atoms of the compound (C).

[0028] In the compound (C), the skeleton (partial structure) excluding the functional group (c) is an organic residue, but 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). The compound (C) preferably does not have a functional group other than the functional group (c).

[0029] When the number of the functional groups (c) of the compound (C) is n, the compound (C) preferably has an n-valent hydrocarbon group. In the compound (C), the skeleton excluding the functional group (c) is more preferably composed only of an n-valent hydrocarbon group in terms of obtaining a strong bonded body.

[0030] The number of the functional groups (c) in the compound (C) is preferably 2 or 3. The 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 easily becomes a liquid having good fluidity.

[0031] 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.

[0032] In the joining paste of the present disclosure, from the viewpoints of initial joining 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).

[0033] <Compound (D)> The joining 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 joining 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. Further, the tertiary nitrogen atom has a function of reducing the metal particles (A) and the joined portion, and when the number of tertiary nitrogen atoms is 2 or more, the reducing function is enhanced. Also, from the viewpoints of dispersibility and reduction function, the number of hydroxyl groups in the compound (D) is preferably 4 to 6. In particular, since the hydroxyl groups are excellent in 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. Further, the hydroxyl groups have a function of reducing the metal particles (A) and the joint portion. When the number of hydroxyl groups is 4 or more, the reduction function is greatly improved.

[0034] 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 in the joint layer are reduced. From the viewpoints of dispersibility, adhesion to the joint portion, and defect reduction in the joint layer, 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). When it is 2.00% by mass or less, the remaining 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 remaining amount, it is more preferably 1.0% by mass or less, and still more preferably 0.5% by mass or less.

[0035] <Manufacture of the paste for bonding> The paste for bonding 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 it can be adjusted using a known method. Examples of the apparatus for preparing the paste for bonding 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.

[0036] The proportion of the mass of the metal particles (A) based on the mass of the paste for joining 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 joining can be exhibited, while suppressing the residue of the dispersion medium (B) in the joined body, suppressing the generation of voids derived from the dispersion medium (B), and good joining strength can be exhibited.

[0037] The paste for joining 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.

[0038] <Joined body and method for manufacturing joined body> By using the paste for joining of the present disclosure, a first joined part and a second joined part can be joined to obtain a joined body. The joined body can be manufactured, for example, by the following manufacturing method (I) by non-pressure joining or manufacturing method (II) by pressure joining. The paste for joining of the present disclosure has controlled weight loss during sintering, and even under non-pressure conditions, it can suppress voids in the coating film after sintering and exhibit high thermal conductivity. In addition, it has excellent joining strength and can suppress a decrease in joining strength due to thermal cycling.

[0039] [Manufacturing method (I)] Manufacturing method (I) is a method by non-pressure joining, and preferably includes, for example, the following steps (1) to (3). (1) A step of applying the paste for joining to the first joined body. (2) A step of placing the second joined part on the first joined part coated with the paste for joining. (3) A step of sintering the placed laminate in a non-pressure environment.

[0040] (1) Coating step As a method for 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 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.

[0041] (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 applying pressure. In the non-pressure joining, it is preferable that this placement step is also performed without applying pressure, but it is also possible to place 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 preferably it is 0.001 to 40 MPa, more preferably 0.003 to 30 MPa.

[0042] (3) Sintering step The sintering conditions for non-pressure joining the laminate in which the second object to be joined is placed on the first object to be joined are appropriately changed. For example, conditions such as 200 to 350 °C under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere can be mentioned. Examples of the firing device 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 device, etc. These devices can be used alone or in combination as appropriate. The non-pressure sintering conditions are preferably such that after raising the temperature to the set temperature at a heating rate of 2 °C to 30 °C / min, 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 to 350 °C, more preferably 230 °C to 300 °C, and even more preferably 250 to 280 °C.

[0043] (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 compound (B), the coating film can flow and form a bonding interface even after the dispersion medium (B) is dried and removed in advance, 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.

[0044] 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 adhered 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.

[0045] [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 adhered portion coated and preliminarily dried with the paste for bonding. (30) Step of sintering the placed laminate in a pressure environment.

[0046] (10) 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 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.

[0047] (10a) Preliminary drying process In the manufacturing method (II) using pressure joining, a preliminary drying process (10a) can be provided between the process (10) and the process (20) for the purpose of removing the organic components in the joining coating film. By providing the preliminary drying process, the preliminary drying can be performed, for example, under the conditions of 60 to 220 °C for 1 minute to 300 minutes using an apparatus similar to a firing apparatus.

[0048] (20) Placement process Next, the second object to be joined is placed on the first object to be joined to which the joining paste of the present disclosure has been applied and preliminarily dried. In the case of pressure joining, the placement process may also be performed 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.

[0049] (30) Sintering process The sintering conditions for pressure joining the laminate in which the second object to be joined is placed on the first object to be joined are appropriately changed. For example, conditions such as 200 to 350 °C under atmospheric pressure, in a nitrogen atmosphere, in a vacuum, or in a reducing atmosphere can be mentioned. 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.

[0050] In any manufacturing method, the thickness of the bonding layer formed when joining the parts to be joined 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.

[0051] [Parts to be joined] The type of the parts to be joined 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, LEC elements, and power device elements.

[0052] The first part to be joined and the second part to be joined may be not only of the same type but also of different types of members. In order to increase the bonding strength at the joined portion, the surface of the part to be joined 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 achieve high thermal conductivity, excellent bonding strength, and thermal cycle characteristics even 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 joined is a non-treated substrate (for example, a non-treated copper substrate). In addition, since the paste for bonding 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 even in a structure such as "copper base material / bonding layer containing silver particles / SiC element" where strain is likely to occur during the thermal cycle test. For example, the paste for bonding of the present disclosure is suitable when the second part to be bonded is SiC.

Example

[0053] 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, "parts" and "%" represent "parts by mass" and "mass %", respectively, unless otherwise specified. The numerical values in the tables represent "parts" unless otherwise specified.

[0054] [Weight loss] The weight loss of the paste for bonding 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 taken as 100, the weight loss at 100°C was designated as M100, the weight loss at 150°C 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.

[0055] [Production of metal particles] (Production Example 1) Metal particles A1 Under a nitrogen atmosphere, 200 parts of toluene and 22.3 parts of silver hexanoate were mixed while stirring at 25 °C to form a 0.5 M solution. Then, 1.6 parts of diethylaminoethanol and 0.28 parts of oleic acid were added as dispersants 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 the excess reducing agent and impurities. Further, distilled water was added to the toluene layer several times, and washing and separation were repeated. Then, the step of adding toluene, performing centrifugation, and removing the supernatant was repeated twice. The precipitate was dried to obtain metal particles A1 in which the silver particles were coated with hexanoic acid and oleic acid. When the particle size of the metal particles A1 was determined by the method described below, d50 was 210 nm.

[0056] (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.

[0057] (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.

[0058] (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.

[0059] (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.

[0060] (Production Example 6) Metal Particles A6 Silver hexanoate was used in an amount of 17.0 parts, and copper pentanoate was used in an amount of 17.0 parts. Except that 1.8 parts of diethylaminoethanol and 0.45 parts of oleic acid were used, the same procedure as in Production Example 1 was followed to obtain Metal Particles A7. The d50 was 150 nm.

[0061] (Production Example 7) Metal Particles A7 Except that 0.7 part of diethylaminoethanol and 0.12 part of oleic acid were used, the same procedure as in Production Example 1 was followed to obtain Metal Particles A6. The d50 was 450 nm.

[0062] (Production Example 8) Metal Particles A10 Except that 2.1 parts of diethylaminoethanol and 0.71 part of oleic acid were used, the same procedure as in Production Example 1 was followed to obtain Metal Particles A10. The d50 was 85 nm.

[0063] (Production Example 9) Metal Particles A11 Except that 1.4 parts of diethylaminoethanol and 0.09 part of oleic acid were used, the same procedure as in Production Example 1 was followed to obtain Metal Particles A11. The d50 was 600 nm.

[0064] (Production Example 10) Metal Particles A12 Except that 0.6 part of diethylaminoethanol and 0.070 part of oleic acid were used, the same procedure as in Production Example 1 was followed to obtain Metal Particles A12. The d50 was 1100 nm.

[0065] [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 NanoTRAC UPA-EX150 (manufactured by Nikkiso Co., Ltd.), and the average particle diameter (d50) was determined.

[0066] [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: Telsorb 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., no 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: Telsorb MTPH (manufactured by Nippon Terpene Chemical Co., Ltd., terpene-based, hydroxyl group-containing, boiling point 308 °C)

[0067] <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)

[0068] <Compound (D)> Compound D1: Alkanolamine (number of hydroxyl groups 4, number of tertiary nitrogen atoms 2)

[0069] <Manufacture of bonding paste> [Example 1] Metal particles A1 (88 parts) and triethylene glycol monobutyl ether (12 parts) were mixed using a planetary stirrer to prepare a joining paste.

[0070] [Examples 2 to 32, Comparative Examples 1 to 8] Joining pastes were obtained in the same manner as in Example 1, except that the types and blending amounts (parts) of the materials were changed according to the compositions described in Tables 1 to 3. In the tables, blanks indicate that the component was not blended.

[0071] [Evaluation of the joining paste] Using the obtained joining paste, joined bodies were produced by the manufacturing methods described in Tables 1 to 3. For Examples 1 to 30 and Comparative Examples 1 to 8, Manufacturing Method 1 below was used; for Example 31, Manufacturing Method 2 below was used; and for Example 32, Manufacturing Method 3 below was used. The details of the manufacturing methods and the printing conditions of the joining paste are as follows. [Printing conditions (metal mask printing)] Metal mask: Opening 7.5 mm square, plate thickness 100 μm (manufactured by Coesia Corporation) Metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by Coesia Corporation)

[0072] [Manufacturing Method 1] The joining paste was printed once on the first joined part (copper substrate (unplated): 20 mm × 20 mm × 3 mm) under the above printing conditions. Then, the plated surface of the second joined part (gold-plated SiC element: 8 mm × 8 mm × 0.3 mm) was placed facing the joining paste surface, and pressureless joining was performed under the following sintering conditions 1 to obtain joined 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.

[0073] [Manufacturing Method 2] On the first joint part (unplated copper substrate: 20 mm × 20 mm × 3 mm), after printing the bonding paste once 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 unpressurized bonding was performed under the following sintering conditions to obtain a bonded body. 〔Sintering condition 2〕The laminate 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.

[0074] [Manufacturing method 3] On the first joint part (unplated copper substrate: 20 mm × 20 mm × 3 mm), after printing the bonding paste once under the above printing conditions, it was put into 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 bonding paste surface after pre-drying, and pressure bonding was performed under the following sintering condition 3 to obtain a bonded body. 〔Sintering condition 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.

[0075] 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 the bonding strength (die shear strength) at which the joint was broken by pushing at a speed of 500 μm / s to a position 100 μm in height toward the second joint part starting from the interface between the first joint part and the bonding layer was determined 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 type bond tester (manufactured by Daiji Japan Co., Ltd., 4000 series) Measuring height: 100 μm Measuring speed: 500 μm / s

[0076] (Evaluation Criteria) S: Die shear strength is 35 MPa or more A: Die shear strength is 25 MPa or more and less than 35 MPa B: Die shear strength is 15 MPa or more and less than 25 MPa C: Die shear strength is 10 MPa or more and less than 15 MPa D: Die shear strength is less than 10 MPa

[0077] [Thermal Cycle Characteristics] The following cycle test was performed using the bonded body. Using the bonded body after the cycle test, the bonding strength (die shear 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] One cycle consisted of holding the bonded body at -40°C for 30 minutes and then at 150°C for 30 minutes, and 500 cycles of storage were performed.

[0078] [Thermal Conductivity] The thermal conductivity was obtained from the thermal diffusivity, specific heat, and density according to the following formula. 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 base material (unplated): 20 mm × 20 mm × 3 mm), the joining paste was printed once using a metal squeegee (40 mm × 250 mm, 1 mm thick (manufactured by Cerion Corporation)) with a metal mask (20 mm square opening, 200 μm thick plate). After that, the second joint part (copper base material (unplated): 20 mm × 20 mm × 3 mm) was placed, and the laminate placed in a firing furnace in 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.

[0079] (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)

[0080]

Table 1

[0081]

Table 2

[0082]

Table 3

[0083] According to the results of Tables 1 to 3, when using the paste for bonding of the present disclosure, even in a configuration where stable bonding is extremely difficult, such as between a non-plated substrate and a large-area SiC element, the thermal conductivity and the bonding strength are very high, and even after performing a thermal cycle test, a decrease in the bonding strength was suppressed.

Claims

1. A paste for bonding, comprising metal particles (A) and a dispersion medium (B), wherein the content of the dispersion medium (b2) having a boiling point exceeding 300°C in the dispersion medium (B) is 20% by mass or less based on the total mass of the dispersion medium (B), when the temperature of the paste for bonding is raised at a rate of temperature increase of 3°C / min, when the weight loss M650 at 650°C is taken as 100, and the weight losses at 100°C / 150°C / 200°C / 250°C are taken as M100 / M150 / M200 / M250 respectively, the paste for bonding is characterized by satisfying all of the following (1) to (4). (1) M100 is 10 or more and 70 or less. (2) M150 is 85 or more and 96 or less. (3) M200 is 88 or more and 98 or less. (4) M250 is 93 or more and 99.5 or less.

2. The paste for bonding according to claim 1, wherein when the weight loss M150 at 150°C is taken as M150 with the weight loss M650 at 650°C 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 higher and 300°C or lower 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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