Composition for joining

Abstract

To provide a composition for joining, which comprises silver fine particles having a small average particle diameter and silver particles having a large average particle diameter, wherein large-diameter silver particles can be closely joined without requiring a complicated manufacturing process.SOLUTION: A composition for joining comprises: silver fine particles (a) having a predetermined average particle diameter and having a surface partially or entirely coated with an amine; silver particles (b) having a predetermined average particle diameter and having a surface partially or entirely coated with a fatty acid; an organic solvent group (c) composed of one or more organic solvents having a boiling point of 270 to 350°C; and an organic solvent group (d) composed of one or more organic solvents having a boiling point of 150 to 270°C, wherein a total of three or more organic solvents are contained in the organic solvent group (c) and the organic solvent group (d). Using the composition for joining can form a dense and strong joining layer due to the interaction between the silver particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bonding composition used mainly for bonding metal members, particularly electronic components such as semiconductor elements. [Background technology]

[0002] Conventionally, bonding compositions such as lead solder have been used to bond metal members to each other. For example, the inside of semiconductor devices such as LEDs and power modules has a structure in which a semiconductor element is bonded onto a substrate. When electronic components such as semiconductor elements are bonded to a circuit, a method using lead solder is widely used.

[0003] Silicon carbide (SiC) semiconductors, which have been actively developed as semiconductor materials in recent years, can generate a large amount of heat when a large current is applied to the semiconductor element during use. In this case, if the semiconductor element is joined with solder as in the past, the melting point of the solder becomes lower than the operating temperature of the semiconductor device, which can lead to failure of the semiconductor device, making mounting difficult.

[0004] Therefore, conductive adhesives using metal particles such as silver have been proposed as an alternative to solder. For example, Patent Document 1 discloses a bonding composition made of metal nanoparticles, particularly silver nanoparticles, with an average particle size of 100 nm or less. A bonding composition made of silver nanoparticles with such a small average particle size can be sintered at relatively low temperatures, and the melting point of the bonding layer formed after sintering is equivalent to that of elemental silver. Therefore, a bonding layer made of a sintered body of a bonding composition using silver nanoparticles has excellent heat resistance and can be used stably even in high-temperature environments or under large current loads.

[0005] In bonding compositions made of silver particles, compositions have been devised that contain not only nanoparticles with a small average particle size, but also silver particles with a larger average particle size of several hundred nanometers to several tens of micrometers, as shown in Patent Document 2. By adjusting the particle size of the silver particles in the bonding composition in this way, it is expected that the density of the bonding layer after sintering will be increased, and the bonding strength and thermal reliability will be improved accordingly.

[0006] However, large-sized silver particles have lower surface energy than nanoparticles, making them less susceptible to low-temperature sintering, potentially resulting in problems such as poor sintering between silver particles or between silver particles and bonding members. Furthermore, large-sized silver particles have lower fluidity within the bonding composition than small-sized nanoparticles. Therefore, they are less able to migrate to the interface between the bonding members and the bonding composition during sintering, diffuse into the bonding members, and form bonds, potentially resulting in a decrease in the bonding strength between the silver and the bonding members.

[0007] On the other hand, using a large amount of small nanoparticles can mitigate the deterioration of sinterability due to particle size, but due to their high surface energy, a large amount of surface protection agents such as resins and polymer dispersants are required to ensure storage stability, which may result in a decrease in sinterability due to the surface protection agents.In addition, as the proportion of solvents and additives in the paste increases and the proportion of silver decreases, there is a risk that shrinkage of the silver bonding layer during sintering and the resulting distortion may occur more significantly than with pastes using silver particles with large particle sizes. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2011 / 007402 [Patent Document 2] International Publication No. 2019 / 142633 Summary of the Invention [Problem to be solved by the invention]

[0009] As SiC semiconductors become more widely used and bonding compositions containing silver particles for high-temperature environments begin to be used, improving the sinterability of pastes containing large-sized silver particles, which are less expensive than nanoparticles and less susceptible to thermal stress due to shrinkage, has become a critical issue. The present invention has been made in light of this issue, and aims to provide a formulation and manufacturing method for a bonding composition that can tightly bond large-sized silver particles without requiring a complex manufacturing process. [Means for solving the problem]

[0010] In order to solve the above problems, the bonding composition of the present invention comprises silver microparticles (a) having a volume average diameter of 10 nm to 200 nm as measured by a dynamic light scattering particle size distribution analyzer and having a part or all of their surfaces coated with an amine; silver particles (b) having a volume average diameter of 1,000 nm to 30,000 nm and having a part or all of their surfaces coated with a fatty acid; a group of organic solvents (c) consisting of one or more organic solvents with a boiling point of 270 to 350°C; and a group of organic solvents (d) consisting of one or more organic solvents with a boiling point of 150 to 270°C, wherein the group of organic solvents (c) and the group of organic solvents (d) contain a total of three or more organic solvents.

[0011] The bonding composition of the present invention contains silver particles (a) whose surface is partially or entirely coated with an amine and whose volume average diameter measured by a dynamic light scattering particle size distribution analyzer is 10 nm to 200 nm, and silver particles (b) whose surface is partially or entirely coated with a fatty acid and whose volume average diameter measured by a dynamic light scattering particle size distribution analyzer is 1,000 nm to 30,000 nm, wherein cationic positive charges derived from the amine are distributed on the surface of the silver particles (a), and anionic negative charges derived from the fatty acid are distributed on the surface of the silver particles (b). The positive charges on the surface of the silver particles (a) and the negative charges on the surface of the silver particles (b) cause electrostatic attraction during sintering, causing the silver particles (a), which have high surface energy and good sinterability, to approach and adhere to the silver particles (b) before sintering, thereby enabling the silver particles (b), which have inherently low surface energy and poor sinterability, to be densely and firmly bonded within the silver bonding layer.

[0012] The bonding composition of the present invention is characterized in that it contains an organic solvent group (c) consisting of one or more organic solvents with a boiling point of 270 to 350° C. and an organic solvent group (d) consisting of one or more organic solvents with a boiling point of 150 to 270° C., and that the organic solvent groups (c) and (d) contain a total of three or more organic solvents. By using a mixture of multiple organic solvents with boiling points higher and lower than the sintering temperature in this way, the volatilization of the organic solvents during sintering is slowed, thereby suppressing the generation of large voids.

[0013] Furthermore, by preventing the solvent from completely evaporating even after the low-boiling point solvent has volatilized, the distance between the silver particles narrows as the solvent evaporates, and the electrostatic attraction is strengthened, allowing the silver microparticles to flow within the high-boiling point solvent.This promotes adhesion of the silver microparticles to the silver powder due to electrostatic attraction, making it possible to form a stronger bonding layer.

[0014] In the present invention, the amine coating a part or the whole of the surface of the silver fine particles (a) preferably contains a secondary amine.

[0015] In the present invention, the secondary amine is preferably a secondary amino alcohol.

[0016] In addition, in the present invention, it is preferable that the silver microparticles (a) are produced by a method for producing silver microparticles, characterized by comprising: a first step of mixing a fatty acid silver salt capable of producing metallic silver by reduction with the secondary amine to prepare a solution containing a silver amine complex; a second step of adding a reducing liquid containing a reducing component to the complex solution to reduce the silver complex, thereby producing silver microparticles having a secondary amine coating on part or all of their surfaces; and a third step of washing the silver microparticles with an organic solvent.

[0017] The bonding composition of the present invention preferably contains a primary amine having 8 to 20 carbon atoms.

[0018] The bonding composition of the present invention preferably further contains a nonionic surfactant. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a bonding composition that can form a strong bonding layer even when silver powder having a low surface energy and a large particle size is used. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram summarizing the formulations and measurement results of bonding compositions of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0021] In this specification, "silver fine particles (a) having a volume average diameter of 10 nm to 200 nm as measured by a dynamic light scattering particle size distribution analyzer and whose surface is partially or entirely coated with an amine" may be abbreviated as "silver fine particles (a)," "silver particles (b) having a volume average diameter of 1,000 nm to 30,000 nm and whose surface is partially or entirely coated with a fatty acid" may be abbreviated as "silver particles (b)," "a group of organic solvents (c) consisting of one or more organic solvents with a boiling point of 270 to 350°C" may be abbreviated as "group of organic solvents (c)," and "a group of organic solvents (d) consisting of one or more organic solvents with a boiling point of 150 to 270°C" may be abbreviated as "group of organic solvents (d)."

[0022] The bonding composition of the present invention is characterized by containing amine-coated silver particles (a), fatty acid-coated silver particles (b), and organic solvents (c) and (d). When a predetermined amount of amine-coated silver particles (a) and fatty acid-coated silver particles (b) are combined, electrostatic attraction due to the difference in the silver surface treatment agent occurs during sintering of the bonding composition, resulting in hetero-aggregation of the silver particles (a) and (b). This allows the relatively low-sinterability silver particles (b) to bond via the highly sinterable silver particles (a), forming a strong silver bonding layer and exhibiting excellent bonding strength and thermal reliability. Furthermore, using a combination of solvents with different boiling points allows the bonding composition to have good printability on the bonding member when printed. Furthermore, the high-boiling-point solvent can impart fluidity to the silver particles (a) during sintering, thereby promoting the hetero-aggregation effect.

[0023] <Silver fine particles (a)> The silver fine particles (a) have a specific average particle size range, and therefore have the function of sintering together at a temperature range of 150°C to 350°C, which is the sintering temperature of the bonding composition, thereby bonding the bonding members together. Hereinafter, the region formed by sintering the silver fine particles (a) and silver particles (b) present between the bonding members will be referred to as the bonding layer.

[0024] In the present invention, it is important to use silver microparticles (a) having a specific average particle size. The term "average particle size" as used herein refers to the 50% cumulative distribution particle size (d50) on a volume basis determined by the measurement method described in the Examples. The average particle size of the silver microparticles (a) is 10 nm to 200 nm, preferably 30 nm or more, and more preferably 50 nm or more. The average particle size of the silver microparticles (a) is preferably 150 nm or less, and more preferably 130 nm or less. If the average particle size of the silver microparticles (a) is 10 nm or less, the surface energy of the silver microparticles (a) becomes high, requiring a large amount of additives to ensure stability over time. If the average particle size of the silver microparticles (a) is 200 nm or more, the surface energy becomes low, resulting in a loss of low-temperature sinterability.

[0025] The fine silver particles (a) may be of any shape, but are preferably spherical.

[0026] The silver fine particles (a) have a surface partially or entirely coated with an amine. Coating the surface with an amine suppresses aggregation of the silver fine particles (a) and increases the storage stability of the bonding composition. Coating with an amine also enables the formation of a strong bonding layer through the hetero-aggregation described above. Any amine can be used as the amine coating the surface. One or more types of amines may be used in combination to coat the surface. The amine coating the surface partially or entirely of the silver fine particles (a) may be attached during the production of the silver fine particles (a) described below, or may be attached by mixing the amine during the preparation of the bonding composition.

[0027] The amine coating the surface of the silver fine particles (a) partially or entirely preferably includes an aliphatic amine having one amino group having 3 to 20 carbon atoms. The aliphatic amine having one amino group having 3 to 20 carbon atoms may be linear or have a side chain as long as the carbon number is in the range of 3 to 20. It may also have a functional group other than an amino group. Examples of the aliphatic amine include, but are not limited to, octylamine, decylamine, dodecylamine, hexadecylamine, oleylamine, cyclopentylamine, cyclohexylamine, stearylamine, 2-aminoethanol, 2-(methylamino)ethanol, 2-(methylamino)ethanol, and triethylamine. From the viewpoints of good protection performance for the silver fine particles (a) and good volatility during sintering, primary aliphatic amines having 8 to 20 carbon atoms, such as octylamine, dodecylamine, and hexadecylamine, are preferred.

[0028] Due to their high surface energy, silver microparticles (a) are preferably produced by a wet reduction method, which allows the surface to be protected with an amine simultaneously during production. An example of the production process is given below. An amine complex of silver is synthesized by adding an amine to an organic silver salt such as silver acetate. A reducing solution containing a reducing component such as formic acid or ascorbic acid is added to this amine complex and heated, producing silver microparticles coated with an amine as a surface protective agent. Repeating the process of adding water or an organic solvent to these silver microparticles, stirring, and discarding the supernatant makes it possible to produce amine-coated silver microparticles from which excess salts and other impurities have been removed.

[0029] The amine used in the above-mentioned silver fine particle production process is preferably a secondary amine, which is easy to handle and requires a reaction temperature within the range of 50 to 100°C due to the influence of basicity and the stability of the amine complex. Furthermore, secondary amino alcohols containing hydroxyl groups are more preferred in terms of their boiling point and ease of removal during washing of the silver fine particles. Examples of secondary amino alcohols include, but are not limited to, diethanolamine, 2-methylaminoethanol, and 2-isopropylaminoethanol.

[0030] <Silver particles (b)> The silver particles (b) have a specific average particle size range, which allows them to form a strong silver bonding layer when sintered with the silver particles (a). Furthermore, by adding silver particles (b) with an average particle size larger than that of the silver particles (a), tiny voids are created between the silver particles (b), and the organic solvent evaporates from these voids, which makes it possible to suppress the generation of voids due to the volatilization of the solvent during sintering.

[0031] In the present invention, it is important to use silver particles (b) having a specific average particle size. The average particle size of the silver particles (b) is 1,000 to 30,000 nm, preferably 2,000 nm or more. The average particle size of the silver particles (b) is preferably 10,000 nm or less, more preferably 5,000 nm or less. If the average particle size of the silver particles (b) is not within this range, it will be impossible to form a dense bonding layer together with the silver fine particles (a).

[0032] The silver particles (b) may have any shape, but are preferably spherical.

[0033] The silver particles (b) have a surface partially or entirely coated with a fatty acid. Coating the surface with a fatty acid suppresses aggregation, thereby increasing the storage stability of the bonding composition. Furthermore, coating with a fatty acid enables the formation of a strong bonding layer by the hetero-aggregation described above. Any fatty acid can be used as the fatty acid coating the surface, and a fatty acid having 3 to 20 carbon atoms is preferred. Furthermore, one or more fatty acids may be used in combination to coat the surface.

[0034] The fatty acid having 3 to 20 carbon atoms may be linear or may have a side chain, as long as the number of carbon atoms is in the range of 3 to 20. In addition, it may have a functional group other than a carboxy group. Examples include but are not limited to butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, oleic acid, stearic acid, and ricinoleic acid.

[0035] The blending ratio of the silver component consisting of silver fine particles (a) and silver particles (b) in the bonding composition can be any value, but when the mass of the entire bonding composition is taken as 100%, the silver component is preferably 80% or more, more preferably 90% or more. Furthermore, the silver component is preferably 95% or less. When the silver component is contained in this range by mass of the entire composition, it becomes possible to prepare a bonding composition with a viscosity suitable for mounting by printing.

[0036] The blending ratio of silver particles (a) to silver particles (b) in the silver component is preferably in the range of silver particles (a) / silver particles (b) = 10 / 90 to 90 / 10 (mass ratio), and more preferably silver particles (a) / silver particles (b) = 30 / 70 to 70 / 30 (mass ratio). When the silver component is within this range, the silver particles (a) can enter between the silver particles (b) and can be densely sintered due to the effect of hetero-coagulation.

[0037] In the present invention, silver is used as the metal particles in the bonding composition. However, for any metal particles such as copper or gold, the metal component ratio and solvent ratio in the bonding composition can be appropriately adjusted according to the density of the metal component, thereby making it possible to obtain the effect of improving sinterability by utilizing the hetero-coagulation.

[0038] <Organic solvent group (c)> Next, the organic solvent group (c) will be described. The organic solvent group (c) is a mixture of organic solvents composed of one or more organic solvents with a boiling point of 270 to 350°C. Because the organic solvent group (c) has a boiling point higher than the sintering temperature of the bonding composition, it volatilizes slowly during sintering and is less likely to produce large voids. This has the effect of making it easier to densely form a silver bonding layer. In addition, the flow of silver fine particles (a) in the high-boiling point solvent promotes hetero-aggregation of silver fine particles (a) on the surfaces of silver particles (b), thereby improving sinterability. The boiling point of the organic solvent contained in the organic solvent group (c) is preferably 320°C or lower.

[0039] As the organic solvent included in the organic solvent group (c), any organic solvent having a boiling point of 270 to 350° C. can be used. Specific examples include, but are not limited to, isobornylcyclohexanol, benzyl benzoate, 2-(1-methyl-1-(4-methyl-3-cyclohexenyl)ethoxy)ethanol, glycerin, polyethylene glycol, polyethylene glycol monomethyl ether, terpinyloxyethanol, and isoparaffin solvents.

[0040] <Organic solvent group (d)> Next, we will explain the organic solvent group (d). The organic solvent group (d) is a mixture of organic solvents composed of one or more organic solvents with a boiling point of 150 to 270°C. This organic solvent group (d) has a lower boiling point than the organic solvent group (c) and volatilizes earlier during sintering than the organic solvent group (c). Therefore, when the organic solvent group (d) volatilizes, the distance between the silver fine particles (a) and the silver particles (b) decreases, making electrostatic attraction more likely to occur. In addition, the organic solvents contained in the organic solvent group (d) generally have lower viscosity than the organic solvents contained in the organic solvent group (c), which also improves the handleability of the bonding composition. The boiling point of the organic solvents contained in the organic solvent group (d) is preferably 180°C or higher, more preferably 200°C or higher. The boiling point of the organic solvents contained in the organic solvent group (d) is preferably 250°C or lower.

[0041] As the organic solvent contained in the organic solvent group (d), any organic solvent having a boiling point of 150 to 270° C. can be used. Specific examples include, but are not limited to, terpineol, dihydroterpineol, dihydroterpinyl acetate, dihydroterpinyloxyethanol, isophorone, γ-butyrolactone, dipropylene, octyl propionate, 1,3-butanediol, 1,4-butanediol, 2-ethyl-1,3-hexanediol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and polyethylene glycol monobutyl ether.

[0042] If an organic solvent contains structural isomers and the range between the upper and lower limits of the boiling points of the structural isomers includes 270°C, the boiling point of the structural isomer that is most abundant is the boiling point of the organic solvent, and the number of solvents is considered to be one.

[0043] By including a total of three or more types of organic solvents in organic solvent group (c) and organic solvent group (d), it is possible to suppress the generation of voids due to volatile solvents during sintering, and to further promote the formation of a strong, thermally reliable bonding layer through hetero-coagulation.

[0044] The organic solvent group (c) and the organic solvent group (d) may be contained in the bonding composition in any ratio, but the organic solvent group (c) / organic solvent group (d) ratio is preferably in the range of 90 / 10 to 10 / 90 (mass ratio), and more preferably 80 / 20 to 20 / 80 (mass ratio).

[0045] In addition to the above components, the bonding composition of the present invention may contain optional components such as silver complexes, surfactants, and thickeners to impart appropriate viscosity, adhesion, drying properties, printability, and other properties depending on the intended use, as long as the effects of the present invention are not impaired. Such optional components are not particularly limited. However, it is preferable that the composition does not contain any components that are nonvolatile at sintering temperatures, as these may inhibit bonding of silver particles during sintering.

[0046] The silver complex may be, for example, a complex obtained by mixing any fatty acid silver salt with an aliphatic amine, but is not limited to these. This complex is easily thermally decomposed during sintering to produce minute silver components, which improves the sinterability of the joining material and gives the silver joining layer a denser structure. One type of complex may be contained, or two or more types of complexes may be contained.

[0047] The surfactant may be an anionic surfactant, a cationic surfactant, or a nonionic surfactant, and examples thereof include, but are not limited to, alkyltrimethylammonium salts, alkyldimethylamine oxides, monoalkyl sulfates, and acetylenic diols. Nonionic surfactants are preferred, and acetylenic diols are more preferred, to maintain the charge balance between the silver fine particles (a) and the silver particles (b). These surfactants may be used alone or in combination of two or more.

[0048] Examples of the thickener include, but are not limited to, natural thickeners such as acrylic polymers, xanthan gum, and cellulose, etc. These may be used alone or in combination of two or more.

[0049] Representative embodiments of the method for preparing the bonding composition of the present invention will be described below, but the present invention is not limited to these.

[0050] <Preparation of Bonding Composition> Methods for preparing the bonding composition of the present invention include, but are not limited to, steps such as producing silver fine particles (a) and silver particles (b), and mixing these silver components with organic solvent group (c), organic solvent group (d), and other additives that are added as needed.

[0051] The method for producing silver microparticles (a) of this embodiment, which have an average particle size of 10 nm to 200 nm and are partially or entirely coated with an amine, is not particularly limited, but examples thereof include a method in which a solution containing silver microparticles is prepared by reducing an amine complex containing silver, and the silver microparticles are then washed.

[0052] There are no particular limitations on the production of silver particles (b) having an average particle diameter of 1,000 nm to 30,000 nm and having a partial or entire surface coated with a fatty acid. As in the case of the above-mentioned silver microparticles (a), an example of the method is to prepare a solution containing silver particles by reducing a silver complex in the presence of a fatty acid, and then wash the silver particles.

[0053] For both the silver component of the silver fine particles (a) and the silver particles (b), commercially available silver powder can be used as long as it satisfies the conditions of the surface protective agent, average particle size, etc. Alternatively, a silver component that satisfies the conditions may be produced by substituting the surface protective agent of commercially available silver powder with an amine or a fatty acid by any method.

[0054] Examples of a method for preparing a bonding composition by mixing the above-mentioned silver fine particles (a) and silver particles (b) with the organic solvent group (c), the organic solvent group (d), and other additives added as needed include mixing using an apparatus such as a planetary mixer, a rotary mixer, a three-roll mill, a bead mill, an ultrasonic disperser, or a planetary mixer.

[0055] <Method for joining members using a joining composition> By using the bonding composition of this embodiment, a bonding layer having high bonding strength and thermal reliability can be obtained when bonding bonding members. The bonding composition of the present invention can be applied between a first bonding member and a second bonding member by any method in a bonding composition application step, and the bonding step can be performed by sintering the bonding composition applied between the first bonding member and the second bonding member at a temperature of 200°C or higher and 300°C or lower to bond them together. In this case, bonding members made of any material can be used, and metal substrates plated with gold, silver, copper, etc. can be used.

[0056] During this joining, sintering can be performed while applying pressure perpendicular to the joining members, or without applying pressure. Furthermore, sintering can be performed in either a nitrogen atmosphere or air as the environment around the joining members.

[0057] Any method can be used as the application method for applying the bonding composition, and for example, methods such as metal mask printing, dispense printing, screen printing, and stamping printing can be used.

[0058] The present invention will be described in more detail below by way of examples, but the present invention is not limited to the following examples.

[0059] Example 1 <Production of silver particles (a)> A silver complex solution was obtained by adding 18 g of silver acetate (Tokyo Chemical Industry Co., Ltd.) to 18 g of 2-methylaminoethanol (Tokyo Chemical Industry Co., Ltd.) and stirring. Next, a reducing solution containing 3 g of formic acid (Tokyo Chemical Industry Co., Ltd.) was added to the silver complex solution at room temperature, and the mixture was heated to 70°C and reacted for 2 hours. The resulting reaction solution was then mixed with methanol, stirred, and allowed to stand to precipitate silver microparticles. The supernatant was discarded, and the process of mixing methanol again and stirring was repeated to obtain silver microparticles whose surfaces were partially or entirely coated with 2-methylaminoethanol.

[0060] 11 g of the above silver particles and 0.2 g of dodecylamine (Tokyo Chemical Industry Co., Ltd.) were stirred in methanol at room temperature for 2 hours to replace the surface protective agent of the silver particles with dodecylamine. After that, the silver particles were washed by adding methanol, leaving it to stand, and discarding the supernatant. This process was repeated to obtain silver particles (a) whose surfaces were coated with dodecylamine.

[0061] <Silver particles (b)> As silver particles (b), commercially available spherical silver powder (average particle diameter 3 μm) whose surface was coated with a fatty acid was prepared.

[0062] <Measuring the average particle size of silver particles (a)> The silver particles (a) were dispersed in ethanol by ultrasonic irradiation for 35 minutes, and the particle size distribution was measured using a dynamic light scattering particle size distribution analyzer (HORIBA, SZ-100V2). As a result, the average particle size of the silver particles (a) was found to be 104 nm.

[0063] <Preparation of Bonding Composition> The resulting silver particles (a) and silver particles (b) with their surfaces coated with dodecylamine, totaling 26 g of silver components, were mixed with 0.6 g of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.6 g of octyl propionate (manufactured by Nacalai Tesque), and 0.8 g of isobornylcyclohexanol (manufactured by Nippon Terpene Co., Ltd.), and the mixture was stirred under reduced pressure with a planetary stirrer to obtain a bonding composition.

[0064] Example 2 A bonding composition was obtained in the same manner as in Example 1, except that dodecylamine was replaced with 0.3 g of octylamine (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0065] Example 3 A bonding composition was obtained in the same manner as in Example 1, except that dodecylamine was replaced with 0.3 g of hexadecylamine (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0066] Example 4 A bonding composition was obtained in the same manner as in Example 1, except that 0.6 g of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was replaced with 0.6 g of terpinyloxyethanol (manufactured by Nippon Terpene Co., Ltd.).

[0067] Example 5 A bonding composition was obtained in the same manner as in Example 1, except that 0.6 g of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was replaced with 0.6 g of dihydroterpinyloxyethanol (manufactured by Nippon Terpene Co., Ltd.).

[0068] Example 6 A bonding composition was obtained in the same manner as in Example 1, except that 0.01 g of tetramethylacetylenediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was added as a surfactant.

[0069] (Comparative Example 1) A bonding composition was obtained in the same manner as in Example 1, except that dodecylamine was replaced with 0.3 g of oleic acid (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0070] (Comparative Example 2) A bonding composition was obtained in the same manner as in Example 1, except that dodecylamine was replaced with 0.2 g of dodecanoic acid (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0071] (Comparative Example 3) A bonding composition was obtained in the same manner as in Example 1, except that dodecylamine was replaced with 0.3 g of ricinoleic acid (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0072] Comparative Example 4 A bonding composition was obtained in the same manner as in Example 1, except that isobornylcyclohexanol (manufactured by Nippon Terpene) was not used, and 1.0 g of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) and 1.0 g of octyl propionate (manufactured by Nacalai Tesque) were used.

[0073] (Comparative Example 5) A bonding composition was obtained in the same manner as in Example 1, except that octyl propionate (manufactured by Nacalai Tesque) was not used, and 1.0 g of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) and 1.0 g of isobornylcyclohexanol (manufactured by Nippon Terpene) were used.

[0074] (Comparative Example 6) A bonding composition was obtained in the same manner as in Example 1, except that octyl propionate (manufactured by Nacalai Tesque), 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.), and isobornylcyclohexanol (manufactured by Nippon Terpene) were not used, and 2.0 g of terpinyloxyethanol (manufactured by Nippon Terpene) was used.

[0075] (Comparative Example 7) A bonding composition was obtained in the same manner as in Example 1, except that octyl propionate (manufactured by Nacalai Tesque) and 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) were not used and 2.0 g of isobornylcyclohexanol (manufactured by Nippon Terpene) was used.

[0076] (Comparative Example 8) A bonding composition was obtained in the same manner as in Example 1, except that octyl propionate (manufactured by Nacalai Tesque) and isobornylcyclohexanol (manufactured by Nippon Terpene) were not used and 2.0 g of 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was used.

[0077] (Comparative Example 9) A bonding composition was obtained in the same manner as in Example 1, except that 2-ethyl-1,3-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) and isobornylcyclohexanol (manufactured by Nippon Terpene Co., Ltd.) were not used and the amount of octyl propionate (manufactured by Nacalai Tesque) was 2.0 g.

[0078] (Comparative Example 10) A bonding composition was obtained in the same manner as in Example 1, except that the silver fine particles (a) described in Example 1 were not used, and commercially available silver particles with an average particle diameter of 260 nm, the surface of which was partially or entirely coated with lauric acid, were used instead.

[0079] (Comparative Example 11) A bonding composition was obtained in the same manner as in Example 1, except that the silver particles (b) described in Example 1 were not used and silver particles with an average particle diameter of 260 nm, the surface of which was partially or entirely coated with hexanoic acid, were used instead.

[0080] (Comparative Example 12) A bonding composition was obtained in the same manner as in Example 1, except that the silver particles (b) described in Example 1 were not used, and commercially available silver particles having an average particle diameter of 260 nm and whose surfaces were partially or entirely coated with lauric acid were used instead.

[0081] The viscosity and bonding strength of the bonding compositions prepared as above were measured by the following methods.

[0082] <Viscosity> 0.5 mL of each bonding composition was measured, and the viscosity (Pa·s) was measured using a cone-plate viscometer (manufactured by Toki Sangyo, TVE-25H cone rotor 3°×R14) at a rotation speed of 5 rpm in an environment of 24°C.

[0083] <Joining strength> Each bonding composition was applied to a copper substrate in a 5 mm × 5 mm square shape using metal mask printing (plate thickness: 100 μm), and a 5 mm × 5 mm Au-plated Kovar chip (chip thickness: 500 μm) was mounted on top of it with a force of 0.8 N. After that, the copper substrate and the Au-plated Kovar chip were bonded by sintering in an oven (manufactured by ESPEC, PHH-202) at 240°C in air for 1 hour.

[0084] The bond strength after sintering was evaluated in terms of shear strength [MPa]. Using a bond strength tester (OLM MFM1500HF), the chip was pressed horizontally at a measurement speed of 170 μm / s and a measurement height of 60 μm to measure the shear strength [MPa].

[0085] The formulations and measurement results of the bonding compositions of Examples 1 to 6 and Comparative Examples 1 to 12 are summarized in Figure 1. Regarding the measurement results, viscosity exceeding 115 Pa s, the limit of the measuring instrument's range, and resulting in poor printability with a metal mask were marked with an X, while viscosity of 115 Pa s or less was marked with an O. Regarding shear strength, those that were worse than the shear strength of 44 MPa in Example 1, the benchmark, were marked with an X, and those that were the same or better were marked with an O.

[0086] 1 are bonding compositions in which the surface protective agent for the silver fine particles (a) was changed. As shown in Table 1, compared to the bonding compositions of Comparative Examples 1, 2, and 3, which used fatty acids, the bonding compositions of Examples 1, 2, and 3, which used amine as the surface protective agent, showed superior results in at least one of printability and shear strength.

[0087] 1 are bonding compositions with different organic solvent formulations. Compared to the bonding compositions of Comparative Examples 4, 5, 6, 7, 8, and 9, which use only one or two types of solvents, the bonding compositions of Examples 1, 4, and 5, which use a total of three types of solvents, a combination of a high-boiling point solvent and a low-boiling point solvent, and the bonding composition of Example 6, which added a surfactant, showed excellent results in at least one of printability and shear strength.

[0088] 1 are bonding compositions in which the average particle size of the silver component was changed. Compared with Comparative Example 10 in which the silver fine particles (a) were changed to a silver component having an average particle size outside the range, and Comparative Examples 11 and 12 in which the silver particles (b) were changed to a silver component having an average particle size outside the range, the bonding composition of Example 1 showed superior results in terms of at least one of viscosity and shear strength.

[0089] The bonding composition of this embodiment contains silver particles (a) whose surface is partially or entirely coated with an amine and whose volume average diameter measured by a dynamic light scattering particle size distribution analyzer is 10 nm to 200 nm, and silver particles (b) whose surface is partially or entirely coated with a fatty acid and whose volume average diameter measured by a dynamic light scattering particle size distribution analyzer is 1,000 nm to 30,000 nm, wherein the surface of the silver particles (a) is distributed with positive charges derived from the cationic amine, and the surface of the silver particles (b) is distributed with negative charges derived from the anionic fatty acid. The positive charges on the surface of the silver particles (a) and the negative charges on the surface of the silver particles (b) cause electrostatic attraction during sintering, allowing the silver particles (a), which have high surface energy and good sinterability, to approach and adhere to the silver particles (b) before sintering, thereby enabling the silver particles (b), which have inherently low surface energy and poor sinterability, to be densely and firmly bonded within the silver bonding layer.

[0090] The bonding composition of this embodiment is characterized in that it contains an organic solvent group (c) consisting of one or more organic solvents with a boiling point of 270 to 350° C. and an organic solvent group (d) consisting of one or more organic solvents with a boiling point of 150 to 270° C., and that the organic solvent groups (c) and (d) contain a total of three or more organic solvents. By using a mixture of multiple organic solvents with boiling points higher and lower than the sintering temperature in this way, the volatilization of the organic solvents during sintering is slowed, thereby suppressing the generation of large voids.

[0091] Furthermore, by preventing the solvent from completely evaporating even after the low-boiling point solvent has volatilized, the distance between the silver particles narrows as the solvent evaporates, and the electrostatic attraction is strengthened, allowing the silver microparticles to flow within the high-boiling point solvent.This promotes adhesion of the silver microparticles to the silver powder due to electrostatic attraction, making it possible to form a stronger bonding layer.

[0092] According to the bonding composition of this embodiment, it is possible to provide a bonding composition that can form a strong bonding layer even when silver powder with a low surface energy and large particle size is used.

[0093] The present invention can be embodied in various other forms without departing from its spirit or main characteristics. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited to the description in the specification. Furthermore, all variations, various improvements, substitutions, and modifications within the equivalent range of the claims are within the scope of the present invention. [Explanation of symbols]

[0094] a: Silver fine particles b: silver particles c: Organic solvents d: Organic solvents

Claims

1. A bonding composition comprising: (a) silver fine particles (a) having a volume average diameter of 10 nm to 200 nm as measured by a dynamic light scattering particle size distribution analyzer, and whose surfaces are partially or entirely coated with an amine; (b) silver particles (b) having a volume average diameter of 1,000 nm to 30,000 nm as measured by a dynamic light scattering particle size distribution analyzer, and whose surfaces are partially or entirely coated with a fatty acid; (c) a group of organic solvents (c) consisting of one or more organic solvents having a boiling point of 270 to 350°C; and (d) a group of organic solvents (c) consisting of one or more organic solvents having a boiling point of 150 to 270°C.

2. 2. The bonding composition according to claim 1, wherein the organic solvent group (c) and the organic solvent group (d) contain a total of three or more organic solvents.

3. 3. The bonding composition according to claim 2, wherein the amine coating a part or the whole of the surface of the silver fine particles (a) includes a secondary amine.

4. 4. The bonding composition according to claim 3, wherein the secondary amine is a secondary amino alcohol.

5. 5. The bonding composition according to claim 1, wherein the amine coating a part or the entire surface of the silver fine particles (a) contains a primary amine having 8 to 20 carbon atoms.

6. The bonding composition according to claim 1 , further comprising a nonionic surfactant.

7. A method for producing silver fine particles (a) having a volume average diameter of 10 nm to 200 nm as measured by a dynamic light scattering particle size distribution analyzer and having a surface that is partially or entirely coated with an amine, comprising the steps of: The silver fine particles (a) are prepared by a first step of mixing a fatty acid silver salt capable of generating metallic silver by reduction with the secondary amine to prepare a solution containing a silver amine complex; a second step of adding a reducing solution containing a reducing component to the complex solution to reduce the silver complex, thereby producing silver fine particles whose surfaces are partially or entirely coated with a secondary amine; a third step of washing the silver fine particles with an organic solvent; A method for producing silver fine particles, comprising:

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