Joining paste and joined article

Abstract

To provide a joining paste that, under 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 more than 500 nm and at most 10 μm in an amount of 50 mass% or more based on the total mass of the metal particles (A), the dispersion medium (B) containing a dispersion medium (b1) having a boiling point of 250°C or more and 300°C or less in an amount of 55 mass% or more based on the total mass of the dispersion medium (B). 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 joining that has excellent thermal conductivity and bonding strength under pressure conditions and can suppress a decrease in bonding strength associated with thermal cycling, and a joined body using the paste for joining.

Background Art

[0002] Conventionally, solder has been used as a joining 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 joining 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, joining materials such as pastes for joining using sinterable metal particles have been proposed.

[0003] Patent Document 1 discloses a joining 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 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 joining 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 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 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 in reducing voids, improving thermal conductivity, and promoting sintering of metal particles. Therefore, it has the advantage of enabling strong joining and being excellent in 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 becomes larger, it becomes more difficult for internal gas, etc. to escape, and there is a tendency for voids to be easily generated. In addition, the difference in the coefficient of linear expansion between Si elements or SiC elements and the coefficient of linear expansion 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 / joining layer containing silver particles / Si or SiC element layers, cracks are likely 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 are likely 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 even in the case of pressure joining, the problems of joining strength and thermal cycle characteristics in large-area SiC elements cannot be solved.

[0007] Therefore, the problem to be solved by the present disclosure is to provide a joining paste capable of suppressing voids in the sintered coating film under pressure conditions, exhibiting high thermal conductivity, having excellent joining strength, and suppressing a decrease in joining strength accompanying thermal cycles, and a joined body using the joining paste.

Means for Solving the Problems

[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 exceeding 500 nm and not exceeding 10 μm, in an amount of 50% by mass or more based on the total mass of the metal particles (A), and the dispersion medium (B) has a content of a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower of 55% by mass or more based on the total mass of the dispersion medium (B), and when the temperature of the joining paste is raised at a rate of temperature increase of 3°C / min, when the weight loss M650 at 650°C is taken as 100, the weight loss M200 at 200°C is 88 or more and 98 or less. A joining paste. [2]: When the weight loss at 150°C is denoted as M150 with respect to 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 (b1) contains at least one selected from the group consisting of terpene-based and glycol ether-based. [4]: The joining paste according to any one of [1] to [3], 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). [5]: The joining paste according to any one of [1] to [4], 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). [6]: A joined body in which a first joined part and a second joined part are joined by the joining paste according to [1] to [5]. [7]: The joined body according to [6], wherein the first joined part is an untreated base material. [8]: The joined body according to [6] or [7], wherein the second joined part is SiC.

Effect of the Invention

[0009] According to the present invention, under pressure conditions, a joining paste capable of suppressing voids in a sintered coating film to exhibit high thermal conductivity, having excellent joining strength, and suppressing a decrease in joining strength due to thermal cycling, 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 proportion of metal particles (a) having an average particle diameter exceeding 500 nm and being 10 μm or less is 50% by mass or more, and in the dispersion medium (B), the content of a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower is 55% by mass or more based on the total mass of the dispersion medium (B), 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. By having the above configuration, under pressure conditions, excellent joining strength and joining strength after thermal cycling can be exhibited even when the members to be joined are non-treated base materials such as those without plating or when stable joining is difficult such as in the case of SiC semiconductor elements. Specifically, as described above, a joining paste capable of pressure joining, having high thermal conductivity, high joining strength at the joined portion, and suppressed decrease in joining strength due to thermal cycling, and a joined body using the joining paste can be provided. Further, thereby, even when a large-area SiC element is joined, high thermal conductivity, excellent joining strength, and thermal cycling characteristics can be exhibited.

[0011] <Metal particles (A)> The metal particles (A) exhibit the electrical conductivity and thermal conductivity of the joined body and play a role in joining the objects to be joined during the sintering process. They include silver, copper, alloys containing silver and / or copper, 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 copper. By using the metal particles (A), a joined body with excellent strength can be obtained. Also, it can correspond to a wide range of firing temperatures and 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 exceeding 500 nm and not exceeding 10 μm. By doing so, the metal particles exhibit a function of melting or binding (hereinafter also referred to as sintering) with each other in the temperature range of 200°C to 350°C where the joining paste is heated and sintered under pressure conditions, and can be changed into a bulk metal. As a result, the objects to be joined are joined. Hereinafter, the site formed by the sintering of the metal particles (A) existing between the objects to be joined is called the joining layer. From the viewpoints of electrical 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% by mass or more of the metal particles (a) having a specific average particle diameter. The "average particle diameter" as used in this specification 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) exceeds 500 nm and does not exceed 10 μm, preferably 600 nm or more, more preferably 700 nm or more. Also, the d50 of the metal particles (a) is preferably 8 μm or less, more preferably 5 μm or less, and even more preferably 3 μm 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 said 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. 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 content of the metal particles (a) having a specific average particle diameter in the metal particles (A) is preferably 70% by mass or more, more preferably 85% by 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 of 500 nm or less, may be combined with metal particles having an average particle diameter exceeding 10 μm, 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) serves to disperse the metal particles (A) and to impart fluidity to the coating film in the silver sintering process. The dispersion medium (B) contains 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)) in an amount of 55% by mass or more based on the total mass of the dispersion medium (B). By containing 55% by mass or more of the dispersion medium (b1), the dispersion medium tends 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 rate 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.

[0017] 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 of 10% by mass or less based on the total mass of the dispersion medium (B). 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 step, 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. 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 resistance can be exhibited.

[0018] Examples of the dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower include 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). Among them, at least one selected from the group consisting of terpene-based and glycol ether-based is preferably used.

[0019] The dispersion medium (B) preferably contains a dispersion medium containing a hydroxyl group. The dispersion medium containing a hydroxyl group includes the case where it is the above-described dispersion medium (b1) or (b2). 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 occurring 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 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).

[0020] Examples of the dispersion medium containing a hydroxyl group include terpineol-based 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 such as diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, polyethylene glycol monobutyl ether.

[0021] <Weight loss> As described above, it is important that for the joining paste of the present disclosure, when the weight loss M650 at 650°C when heated 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 joint portion is improved and the contact area increases, so that a strong joint can be formed. As a result, excellent joint strength and thermal cycle properties can be exhibited. The value of M200 when M650 is taken as 100 is preferably 90.0 or more and 96.0 or less. Also 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 taken as M150 / M250 / M300, respectively. The weight loss can be measured using thermogravimetric differential thermal analysis method (hereinafter also referred to as TG-DTA analysis method). For example, using a thermogravimetric differential thermal analyzer (TG / DTA8122 (manufactured by Rigaku Corporation)), 10 mg of the 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.

[0022] From the viewpoints of the above-described thermal conductivity, joint strength, and thermal cycle characteristics, the joining paste 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.

[0023] In addition, for the bonding paste of the present disclosure, the ratio of M150 to M200 (M150 / M200) with respect to 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 is increased, the generation of voids in the coating film after sintering is suppressed, and high thermal conductivity is exhibited. In addition, by improving the wettability with respect to the joint part and increasing the contact area, a strong joint can be formed. Thereby, excellent joint strength and thermal cycle resistance can be exhibited.

[0024] From the viewpoints of the thermal conductivity, joint strength, and thermal cycle characteristics described above, the ratio of M200 to M250 (M200 / M250) of the bonding paste of the present disclosure may be 0.95 or more, and the ratio of M150 to M250 (M150 / M250) may be 0.93 or more.

[0025] <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 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 bonding interface integrated with the joint part can be formed. In addition, each functional group (c) has a high binding property with metal particles and exhibits excellent dispersibility. The carbon number of the compound (C) represents the numerical value including the carbon in the functional group (c). Therefore, when the functional group (c) in the compound (C) is a carboxyl group, the carbon number including the carbon in this carboxyl group is regarded as the carbon number of the compound (C).

[0026] In the compound (C), the skeleton (partial structure) excluding the functional group (c) is an organic residue, 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 has no functional groups other than the functional group (c).

[0027] When the number of the functional groups (c) in 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 conjugate.

[0028] 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 is likely to be in a liquid state with good fluidity.

[0029] 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.

[0030] In the paste for joining of the present disclosure, 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), from the viewpoints of initial joining strength and thermal cycle characteristics.

[0031] <Compound (D)> The paste for joining 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. The compound (D) preferably has a tertiary nitrogen atom from the viewpoints of joining strength and thermal cycle characteristics. 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 bonding 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, the number of hydroxyl groups of the compound (D) is preferably 4 to 6 from the viewpoints of dispersibility and reducing function. In particular, since the hydroxyl group has excellent bonding property with the metal particles (A), it tends to improve the dispersibility. When the number of hydroxyl groups is 4 or more, the bonding property with the metal particles (A) is enhanced and the dispersibility is remarkably improved. Further, the hydroxyl group has a function of reducing the metal particles (A) and the joined portion, and when the number of hydroxyl groups is 4 or more, the reducing function is greatly improved.

[0032] The content ratio 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 in a state where the compound (D) remains in the coating film, and sintering proceeds in a state where the coating film has fluidity. Therefore, the adhesion to the joined portion and the defects of the joined layer are reduced. From the viewpoints of dispersibility, adhesion to the joined portion, and reduction of defects in the joined layer, it is more preferably 0.05% by mass or more, and still more preferably 0.10% by mass or more. Also, the content rate 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 remaining amount in the sintered coating film 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.

[0033] <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 it 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.

[0034] The proportion of the mass of the metal particles (A) based on the mass of the joining paste 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 joining paste is exhibited, the remaining of the dispersion medium (B) in the joined body is suppressed, the generation of voids derived from the dispersion medium (B) is suppressed, and good joint strength can be exhibited.

[0035] The joining paste of the present disclosure can contain additives, for example, a sintering accelerator, a binder resin, a resin-type dispersant, a reducing agent, and the like.

[0036] <Joined body and method for manufacturing joined body> By using the joining paste of the present disclosure, a first joined portion and a second joined portion can be joined to obtain a joined body. The joined body can be manufactured, for example, by the following manufacturing method by pressure joining. The joining paste of the present disclosure has its weight loss during sintering controlled, suppresses voids in the coating film after sintering, and can exhibit high thermal conductivity. Also, it has excellent joint strength and can suppress a decrease in joint strength accompanying thermal cycling.

[0037] [Manufacturing method by pressure joining] The manufacturing method by pressure bonding preferably includes, for example, the following steps (10) to (30). (10) A step of applying a bonding paste to a first object to be bonded. (10a) A step of heating and pre-drying the applied laminate. (20) A step of placing a second object to be bonded on the first object to be bonded to which the bonding paste has been applied and pre-dried. (30) A step of sintering the placed laminate in a pressurized environment.

[0038] (10) Coating step As a method of applying the bonding paste to the object to be bonded, 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 discharge method using a dispenser can be mentioned. Since the bonding 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.

[0039] (10a) Pre-drying step In the manufacturing method using pressure bonding, a pre-drying step (10a) can be provided between step (10) and step (20) for the purpose of removing the organic components in the bonding coating film. By providing the pre-drying step, pre-drying can be performed, for example, under the conditions of 60 to 220 °C for 1 minute to 300 minutes using a device similar to a firing device.

[0040] (20) Placement step Next, a second object to be bonded is placed on the first object to be bonded to which the bonding paste of the present disclosure has been applied and pre-dried. In the case of pressure bonding, the placement step may also be performed under pressure. The pressure is appropriately set according to the viscosity of the bonding paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, more preferably 0.3 to 30 MPa.

[0041] (30) Sintering step The sintering conditions for pressure-bonding a laminate in which a second joined part is placed on a first joined part 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 bonding paste and the drying state of the paste, but is preferably 0.1 to 40 MPa, more preferably 1 to 30 MPa.

[0042] In any manufacturing method, the thickness of the bonding layer formed when joining the joined parts 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.

[0043] [Joined part] The type of the joined part is not particularly limited, and examples include metal materials, semiconductor materials, plastic materials, ceramic materials, and electronic elements. Examples of metals include copper, gold, and aluminum. Examples of semiconductor materials include silicon, germanium, gallium arsenide, gallium phosphide, cadmium sulfide, silicon nitride, graphite, yttrium oxide, magnesium oxide, silicon carbide, and gallium nitride. Examples of plastic materials include polyimide, polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, and polyethylene naphthalate. Examples of ceramic materials include glass and silicon. Examples of electronic elements include semiconductor elements, LED elements, and power device elements.

[0044] The first joined part and the second joined part may be not only of the same type but also of different types of members. In order to increase the bonding strength of the joined portion, the surface of the joined part may be subjected to corona treatment, plating treatment, etc. The joining paste of the present disclosure can achieve void reduction and strong joining, so it can also achieve high thermal conductivity, excellent joining strength, and thermal cycle characteristics for a substrate that has not been treated with processes such as corona treatment or plating (also referred to as a non-treated substrate or a non-plated substrate). For example, the joining paste of the present disclosure is suitable when the first joined part 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 in a structure such as "copper substrate / joining layer containing silver particles / SiC element" that is likely to generate strain during the thermal cycle test. For example, the joining paste of the present disclosure is suitable when the second joined part is SiC.

Examples

[0045] 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 table represent "parts" unless otherwise specified.

[0046] [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.

[0047] <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, 1.4 parts of diethylaminoethanol and 0.09 part 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) as a reducing agent was added dropwise, 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 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 600 nm.

[0048] (Production Example 2) Metal Particles A2 Metal particles A2 were obtained in the same manner as in Production Example 1, except that 0.6 part of diethylaminoethanol and 0.070 part of oleic acid were used. d50 was 1.1 μm.

[0049] (Production Example 3) Metal Particles A6 Metal particles A6 were obtained in the same manner as in Production Example 1, except that silver hexanoate was replaced with 17.0 parts of copper pentanoate, 1.0 part of diethylaminoethanol, and 0.12 part of oleic acid were used. d50 was 650 nm.

[0050] (Production Example 4) Metal Particles A10 Metal particles A10 were obtained in the same manner as in Production Example 1, except that 1.6 parts of diethylaminoethanol and 0.29 part of oleic acid were used. d50 was 210 nm.

[0051] (Production Example 5) Metal Particles A11 Metal particles A11 were obtained in the same manner as in Production Example 1, except that 1.0 part of diethylaminoethanol and 0.14 part of oleic acid were used. d50 was 390 nm.

[0052] In addition, the following were used as the metal particles. A3: Manufactured by Fukuda Metal Foil Powder Industry, silver powder silicate AgC-A (average particle size 3.5 μm) A4: Manufactured by Fukuda Metal Foil Powder Industry, silver powder silicate AgC-74T (average particle size 6.2 μm) A5: Manufactured by Fukuda Metal Foil Powder Industry, silver silicate AgC-224 (average particle size 9.0 μm)

[0053] [Method for Measuring the Average Particle Size 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 size of the metal particles in the dispersion was measured using a NanoTRAC UPA-EX150 (manufactured by Nikkiso Co., Ltd.), and the average particle size (d50) was determined. Among the metal particles manufactured by the above method, metal particles A1 - A6 correspond to the metal particles (a) of the present disclosure, and metal particles A10 and A11 correspond to metal particles that are not the metal particles (a).

[0054] <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 type, hydroxyl group-containing, boiling point 278 °C) Dispersion Medium B2: Tersorb TOE-100 (manufactured by Nippon Terpene Chemical Co., Ltd., terpene type, 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 type, hydroxyl group-containing, boiling point 210 °C) Dispersion Medium B5: Diethylene glycol monomethyl ether (glycol ether type, hydroxyl group-containing, boiling point 193 °C) Dispersion Medium B6: Tersorb MTPH (manufactured by Nippon Terpene Chemical Co., Ltd., terpene type, hydroxyl group-containing, boiling point 308 °C)

[0055] <Compound (C)> Compound C1: Pripol 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: Pripol 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: Pripol 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)

[0056] <Compound (D)> Compound D1: Alkanolamine (number of hydroxyl groups 4, number of tertiary nitrogen atoms 2)

[0057] <Manufacture of bonding paste> [Example 1] 90 parts of metal particles A1 and 10 parts of triethylene glycol monobutyl ether were mixed using a planetary stirrer to prepare a bonding paste.

[0058] [Examples 2 to 21, Comparative Examples 1 to 7] 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 described in Tables 1 to 3. In the tables, blanks indicate that they were not blended.

[0059] <Evaluation of bonding paste> Using the obtained bonding paste, bonded bodies were produced by the following manufacturing method. The details of the manufacturing method 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 Ceramics Corporation) Metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by Ceramics Corporation)

[0060] [Manufacturing method] On the first joint part (copper base material (unplated): 20 mm × 20 mm × 3 mm), the bonding paste was printed once under the above printing conditions, and then it was put into a hot air oven and pre-dried at 150°C for 2 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 conditions to obtain a bonded body. [Sintering conditions] In a nitrogen atmosphere, while applying pressure from above the second joint part at a pressure of 30 MPa, 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.

[0061] Using the obtained bonded body, the bonding strength and thermal cycle characteristics were evaluated. 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 position 100 μm in height was pushed at a speed of 500 μm / s from the interface between the first joint part and the bonding layer toward the second joint part to obtain the bonding strength (die shear strength) at which the bonding was broken, and it was evaluated based on the following evaluation criteria. The larger the 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 Dieji Japan Co., Ltd., 4000 series) Measuring height: 100 μm Measuring speed: 500 μm / s

[0062] (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

[0063] [Thermal cycle characteristics] Using the bonded body, the following cycle test was carried out. 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] After holding the bonded body at -40 °C for 30 minutes, the process of holding it at 150 °C for 30 minutes was defined as one cycle, and storage for 500 cycles was carried out.

[0064] [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 obtained as follows. On the first joint part (copper base material (unplated): 20 mm × 20 mm × 3 mm), the bonding paste was printed once with a metal mask (opening 20 mm square, plate thickness 200 μm) and a metal squeegee: 40 mm × 250 mm, thickness 1 mm (manufactured by Ceria Corporation). Then, 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 put in. The temperature was raised 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 bonded body. The obtained bonded body was carbon-coated with carbon spray. Next, the thermal diffusivity was measured with 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.

[0065] (Evaluation criteria) S: 250 W / (m·K) or more A: Above 200 W / (m·K) and less than 250 W / (m·K) B: Above 150 W / (m·K) and less than 200 W / (m·K) C: Above 80 W / (m·K) and less than 150 W / (m·K) D: Less than 80 W / (m·K)

[0066]

Table 1

[0067]

Table 2

[0068]

Table 3

[0069] 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-plated substrate and a large-area SiC element, the thermal conductivity and joining strength are very high, and even after performing a thermal cycle test, a decrease in joining strength was suppressed. In particular, a joining paste in which the value of M150 / M200 satisfies 0.975 or more, a joining paste containing at least one selected from the group consisting of terpene-based and glycol ether-based as the dispersion medium (b1), 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) suppressed voids in the coating film after sintering, exhibited high thermal conductivity, had excellent joining strength, and the decrease in joining strength due to thermal cycling was suppressed (Example 6 and Example 12, Example 5 and Example 7, Example 1 and Example 11). On the other hand, when using the joining paste of the comparative example, the thermal conductivity and joining strength were significantly low, and the joining strength after performing the thermal cycle test also decreased significantly.

Claims

1. A bonding paste containing 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 exceeding 500 nm and being 10 μm or less, the dispersion medium (B) has a content of a dispersion medium (b1) having a boiling point of 250°C or higher and 300°C or lower of 55% by mass or more based on the total mass of the dispersion medium (B), and when the weight loss M650 at 650°C when the bonding 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. A bonding paste.

2. The bonding paste according to claim 1, wherein 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.

3. The bonding paste according to claim 1, wherein the dispersion medium (b1) contains at least one selected from the group consisting of terpene-based and glycol ether-based.

4. The bonding paste according to claim 1, 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).

5. The bonding paste according to claim 1, 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).

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

7. The bonded body according to claim 6, wherein the first bonded portion is an untreated base material.

8. The bonded body according to claim 6 or 7, wherein the second bonded portion is SiC.

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