Bonding composition and bonded structure

Abstract

Provided is a bonding composition that has an outflow inhibition effect and that enables a bonded structure having a bonding site with high shear strength. The bonding composition contains copper powder and a solvent. The solvent contains a first solvent having a boiling point of 150°C or higher and 300°C or lower and a surface tension of 30 mN / m or higher, and a second solvent having a surface tension of less than 30 mN / m. The content of the first solvent is 0.1% by mass or more and 20% by mass or less relative to the copper powder, and the content of the second solvent is 1.5% by mass or more and 20% by mass or less relative to the copper powder.

Description

Technical Field

[0001] This invention relates to a bonding composition and a bonding structure. Background Technology

[0002] In recent years, semiconductor devices, known as power devices, have been widely used in power conversion / control devices such as inverters. These semiconductor devices are mounted (bonded) onto substrates such as circuit boards, ceramic substrates, or wiring elements such as lead frames. Traditionally, solder has been used extensively in the mounting of semiconductor devices. However, with increasing environmental awareness in recent years, there is a growing demand for lead-free solder.

[0003] However, power devices generate a lot of heat during operation due to their high current control characteristics. In contrast, lead-free solder has low heat resistance, which can lead to insufficient installation of power devices.

[0004] Therefore, a paste-like bonding composition containing metal powder such as copper powder has been proposed to replace solder. During bonding (mounting), the bonding composition is applied to the surface of one of the substrates (such as a substrate) to form a coating. Then, another substrate (such as a power device) is placed on the coating to form a laminate. If the laminate is heat-treated, the metal powder in the bonding composition sinters to form bonding areas, thereby obtaining a bonding structure in which the substrates are bonded together.

[0005] Patent Documents 1 and 2 are examples of documents that disclose such bonding compositions. Patent Document 1 discloses a copper paste for bonding, which comprises metal particles and a dispersion medium, wherein the metal particles comprise submicron copper particles and micron copper particles (claim 1 of Patent Document 1). This copper paste for bonding is used to bond a first component and a second component such as a semiconductor element (

[0072] to

[0085] of Patent Document 1). In addition, Patent Document 2 discloses a copper paste for bonding, which contains copper particles, a solvent, and an additive composed of a phosphate ester (claim 1 of Patent Document 2).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2022-180400

[0009] Patent Document 2: Japanese Patent Application Publication No. 2022-128185 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] Thus, although bonding compositions containing metal powders such as copper powder have been proposed in the past (hereinafter, sometimes simply referred to as "compositions"), there is room for improvement in the conventional compositions.

[0012] As described above, during bonding, a paste-like bonding composition is applied to the surface of the substrate or other objects to be bonded. The application is performed by means such as printing. At this time, the solvent contained in the bonding composition sometimes wets and spreads on the substrate, reaching areas outside the printed area. This phenomenon of solvent wetting and spreading is called exudation.

[0013] For example, such as Figure 1 and 2 As shown, taking the bonding of a substrate 2 (the substrate to be bonded) and a semiconductor element 6 as an example, a bonding composition 4 is coated on the substrate 2, and the semiconductor element 6 is placed on it. It should be noted that... Figure 1 This is a top view showing the state in which the semiconductor element 6 is placed. Figure 2 This is a side view. At this time, sometimes the solvent separates from the coated bonding composition 4 and wets and spreads on the upper surface of the substrate 2. This is exudation. In this case, an area of ​​solvent wetting and spreading (exudation area) 8 is formed beyond the area coated with the bonding composition 4 (paste area). It should be noted that the exudation area 8 is the area of ​​solvent wetting and spreading, and is the area outside the paste area.

[0014] Exudation occurs frequently. However, if significant exudation occurs, the metal powder (such as copper powder) contained in the bonding composition flows out along with the solvent and adheres to the insulating parts of the bonded object (such as a substrate), potentially causing problems such as poor insulation. Therefore, it is important to suppress exudation to prevent such problems.

[0015] In addition, although it is desirable to improve the shear strength (joint strength) of the joint between the joined bodies to ensure the reliability of the joint structure, it is difficult to achieve both exudation suppression and improved shear strength in the prior art.

[0016] The inventors conducted in-depth research in view of these problems. As a result, they obtained the following insight: in a bonding composition containing copper powder and a solvent, by replacing a portion of the solvent with a high surface tension solvent having specified properties, it is possible to suppress exudation and obtain a bonding structure with a bonding portion having high shear strength.

[0017] The present invention was made based on the following insight, and its objective is to provide a bonding composition that has the effect of inhibiting exudation and can produce a bonding structure with a bonding portion having high shear strength.

[0018] Solution for solving the problem

[0019] This invention includes the methods described in (1) to (7) below. It should be noted that in this specification, the expression "~" includes the values ​​at both ends. That is, "X~Y" is synonymous with "X and above and Y and below".

[0020] (1) A bonding composition comprising copper powder and a solvent,

[0021] The solvents mentioned above include a first solvent with a boiling point of 150°C or higher and 300°C or lower and a surface tension of 30 mN / m or higher, and a second solvent with a surface tension of less than 30 mN / m.

[0022] The content of the first solvent mentioned above is 0.1% by mass or more and 20% by mass or less relative to the copper powder mentioned above.

[0023] The content of the second solvent is 1.5% by mass or more and 20% by mass or less relative to the copper powder.

[0024] (2) The bonding composition according to (1) above, wherein the surface tension of the first solvent is 30 mN / m or more and 65 mN / m or less, and the surface tension of the second solvent is 20 mN / m or more and less than 30 mN / m.

[0025] (3) The bonding composition according to (1) or (2) above, wherein the first solvent is selected from one or more solvents selected from the group consisting of alcohol solvents, glycol solvents, ketone solvents and ester solvents.

[0026] (4) The bonding composition according to any one of (1) to (3) above, wherein the second solvent is a liquid carboxylic acid.

[0027] (5) The bonding composition according to any one of (1) to (4) above, wherein the content of the copper powder in the bonding composition is 80% by mass or more and 96% by mass or less.

[0028] (6) The bonding composition according to any one of (1) to (5) above, wherein the paste viscosity of the bonding composition is 10 Pa·s or more and 800 Pa·s or less.

[0029] (7) A joining structure comprising a first joined body, a second joined body, and a sintered body of a joining composition comprising any one of (1) to (6) above, wherein the first joined body and the second joined body are joined together.

[0030] The effects of the invention

[0031] According to the present invention, a bonding composition is provided that has the effect of inhibiting exudation and can obtain a bonding structure with a bonding portion having high shear strength. Attached Figure Description

[0032] Figure 1 It is a diagram (top view) used to illustrate the seepage phenomenon.

[0033] Figure 2 It is a diagram (side view) used to illustrate the efflux phenomenon. Detailed Implementation

[0034] Specific embodiments of the present invention (hereinafter referred to as "this embodiment") will be described below. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made without changing the spirit of the present invention.

[0035] <<1. Composition for bonding>>

[0036] The bonding composition of this embodiment comprises copper powder and a solvent. The solvent comprises a first solvent having a boiling point of 150°C or higher and 300°C or lower and a surface tension of 30 mN / m or higher, and a second solvent having a surface tension of less than 30 mN / m. The content of the first solvent is 0.1% by mass or higher and 20% by mass or lower relative to the copper powder. The content of the second solvent is 1.5% by mass or higher and 20% by mass or lower relative to the copper powder. Detailed descriptions of each component are provided below.

[0037] Copper powder

[0038] Copper powder is a powder containing copper as its main component, which becomes a constituent material of the bonding part obtained by sintering the bonding composition. That is, the sintered body of copper powder contained in the composition constitutes the bonding part. It should be noted that in this specification, powder or powder refers to an aggregate of multiple particles. It can also be said that multiple particles constitute powder or powder.

[0039] Copper powder can have a composition containing copper and the balance being unavoidable impurities. Unavoidable impurities can be, for example, oxides that inevitably form on the surface of the copper particles constituting the copper powder. Typically, the content of elements other than copper in the copper powder is 5% by mass or less. Alternatively, the copper powder may contain copper in a proportion of 50% by mass or more, with the balance being other elements. Copper alloy powder is an example of such copper powder. From the viewpoint of improving conductivity, the copper content in the copper powder is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The content of each element in the copper powder can be determined, for example, by ICP emission spectroscopy or non-dispersive infrared absorption spectrometry.

[0040] The shape of the copper particles constituting the copper powder is not particularly limited. For example, they can have various shapes such as spherical, flake-like, polyhedral, dendritic, and columnar. However, from the viewpoint of improving particle filling and obtaining a joint with high shear strength, spherical copper particles are preferred. Whether copper particles are spherical can be determined based on the particle roundness coefficient. Specifically, copper powder is observed using a scanning electron microscope (SEM), and the area S and perimeter L of randomly selected copper particles are measured, from which the roundness coefficient 4πS / L is calculated. 2 The roundness coefficients of multiple copper particles are calculated, and their average value is determined. Copper particles are defined as spherical when the arithmetic mean of the roundness coefficients is above 0.85.

[0041] Preferably, the copper powder content in the bonding composition is 80% by mass or more and 96% by mass or less. By moderately increasing the amount of copper powder, the conductivity and shear strength of the bonding site are further improved. In addition, by moderately suppressing the amount of copper powder, the aggregation of copper particles in the composition can be suppressed, resulting in improved coatability of the composition. It should be noted that the content refers to the total amount of copper powder contained in the bonding composition. That is, as described later, in the case where the copper powder includes a first copper powder and a second copper powder, it is the total amount of the first copper powder and the second copper powder.

[0042] The average particle size of copper powder (D) 50 The particle size of the copper powder is preferably 0.03 μm or more, and more preferably 0.05 μm or more. By appropriately increasing the particle size of the copper powder, particle aggregation in the composition can be prevented, and particle dispersibility can be improved. On the other hand, the average particle size (D) of the copper powder is... 50 The particle size is preferably 20 μm or less, and more preferably 10 μm or less. By appropriately reducing the particle size of the copper powder, the sinterability of the copper powder can be improved.

[0043] It should be noted that the average particle size of copper powder (D) 50 The following steps can be taken: First, add 10 times the mass of 2-propanol relative to the bonding composition and stir thoroughly. Repeat the washing operation, removing only the supernatant while removing the remaining solid components (filter cake). Allow the obtained filter cake to stand at room temperature and dry thoroughly. Observe the obtained dried product (copper powder) using SEM. During SEM observation, obtain SEM images at magnifications of 1000x to 100,000x. Then, randomly select more than 50 particles from the SEM images where particle outlines are observed to determine the particle size (Heywood diameter). Calculate the particle volume in the case of spherical particles from the Heywood diameter, and determine the particle size distribution based on the volume criterion from the obtained data. Next, in the obtained particle size distribution, calculate the particle size at 50% capacity (cumulative volume 50% particle size) that accumulates from the side with the smaller particle size (cumulative volume 50% particle size), and define this as the average particle size (D). 50 ).

[0044] More preferably, the preferred copper powder comprises 50% of the cumulative volumetric particle size (D) of the region smaller than 1 μm in the particle size distribution as determined by SEM observation. 50 The first copper powder with a particle size greater than 0.11 μm and less than 1 μm, and the cumulative volume 50% particle size (D) in the region of this particle size distribution greater than 1 μm. 50 It is a second copper powder with a diameter of 1 μm or larger and a diameter of 10 μm or smaller.

[0045] From the viewpoint of achieving good particle dispersibility by preventing aggregation in the bonding composition, the D of the first copper powder 50 Preferably, the micrometer size is 0.11 μm or larger. Furthermore, from the viewpoint of fully ensuring the sinterability of the copper powder, the D0 of the first copper powder is... 50 Preferably, the micrometer diameter is 0.9 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. From the viewpoint of improving the shear strength of the joint obtained by sintering copper powder, the D0.05 of the second copper powder is... 50 Preferably, the particle size is 1 μm or larger. Furthermore, from the viewpoint of improving the coatability of the composition, the D2 of the second copper powder... 50 Preferably, it is 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less.

[0046] It should be noted that the D of the first copper powder and the second copper powder 50 The particle size distribution can be determined as follows: First, the overall particle size distribution of the copper powder is determined using the method described above. Then, the obtained particle size distribution is divided into a region with a particle size less than 1 μm (the first copper powder region) and a region with a particle size greater than 1 μm (the second copper powder region). Furthermore, when measuring the particle size, at least 50 particles are measured in both the first and second copper powder regions. Then, the cumulative volume 50% particle size (D) is determined from the particle size distribution of the first copper powder region. 50 The particle size of the first copper powder was determined based on the particle size distribution in the second copper powder region. Additionally, the cumulative 50% volume particle size (D) was determined from the particle size distribution in the second copper powder region. 50 ), and set it as the particle size of the second copper powder.

[0047] The proportion of the first copper powder in the bonding composition relative to the total mass of the first copper powder and the second copper powder is preferably 10% by mass or more and 95% by mass or less, more preferably 15% by mass or more and 90% by mass or less, and even more preferably 20% by mass or more and 80% by mass or less. Furthermore, the proportion of the second copper powder relative to the total mass of the first copper powder and the second copper powder is preferably 5% by mass or more and 90% by mass or less, more preferably 10% by mass or more and 85% by mass or less, and even more preferably 20% by mass or more and 80% by mass or less. By setting the mixing ratio within the above range, the filling properties of the particles can be improved, and the shear strength of the bonding site can be sufficiently improved. It should be noted that the mass of the first copper powder and the second copper powder can be calculated as follows: By observing with SEM, the dried material (copper powder) prepared as described above is divided into a region with a particle size distribution of less than 1 μm and a region with a particle size distribution of 1 μm or more. The mass of the copper powder in the former region is defined as the mass of the first copper powder, and the mass of the copper powder in the latter region is defined as the mass of the second copper powder. Specifically, the average particle size of the copper powder in regions with a particle size distribution less than 1 μm and regions with a particle size distribution greater than 1 μm is calculated. Then, the volume of the copper powder is calculated from the average particle size, and the mass of the copper powder in each region is calculated by multiplying the volume by the density.

[0048] The copper powder may also be untreated copper powder (untreated copper powder). Alternatively, surface treatment may be performed to a extent that does not impair the effects of this embodiment (surface-treated copper powder). As surface-treated copper powder, examples include surface-treated copper powder on which a surface treatment layer formed of fatty acids, copper salts of fatty acids, aliphatic amines, silane coupling agents, titanate coupling agents, aluminate coupling agents, etc., is provided on the surface of the copper powder.

[0049] <Solvent>

[0050] The solvent imparts an appropriate viscosity to the bonding composition, resulting in good coatability. Furthermore, by uniformly dispersing the copper particles in the composition, it ensures good electrical conductivity and shear strength at the bonded joint obtained after firing the composition.

[0051] In this embodiment, a mixture of a first solvent and a second solvent is used as the solvent. The first solvent is a component with a relatively large surface tension of 30 mN / m or more. By using the first solvent with a high surface tension, exudation suppression can be achieved. This is believed to be because the increased surface tension of the solvent as a whole (the mixture of the first and second solvents) reduces the wettability to the bonded object, thereby suppressing the wetting spread of the solvent when the bonding composition is applied to the bonded object. Conversely, if the surface tension of the first solvent is less than 30 mN / m, the wetting spread of the solvent intensifies, and therefore the exudation suppression effect becomes insufficient. From the viewpoint of the dispersibility of the bonding composition, the surface tension of the first solvent is preferably 30.2 mN / m or more and 65 mN / m or less, more preferably 30.4 mN / m or more and 50 mN / m or less. It should be noted that the surface tension measurement is performed by the method described in the embodiments below or a method based thereon.

[0052] The content of the first solvent in the bonding composition is 0.1% by mass or more and 20% by mass or less relative to the copper powder. Here, the content of the first solvent is the mass ratio of the first solvent to the copper powder. If the content is less than 0.1% by mass, the effect based on the first solvent, i.e., the effect of exudation suppression, becomes insufficient. If the content exceeds 20% by mass, the total amount of solvent becomes excessive. Since the paste viscosity of the bonding composition becomes too low, exudation may still occur. In addition, the shear strength of the joint obtained by firing the bonding composition may decrease. From the viewpoint of achieving higher levels of shear strength improvement and exudation suppression, the content of the first solvent relative to the copper powder is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less.

[0053] The boiling point of the first solvent is 150°C or higher and 300°C or lower. If the boiling point exceeds 300°C, the volatilization removal during firing of the bonding composition becomes insufficient. If volatilization removal is insufficient, organic matter may remain at the resulting bonding site, resulting in reduced shear strength and conductivity. On the other hand, if the boiling point is lower than 150°C, the composition may boil violently during firing, creating pores at the bonding site, which reduces the conductivity and shear strength of the bonding site. From the viewpoint of further improving the conductivity and shear strength of the bonding site, the boiling point of the first solvent is preferably 150°C or higher and 290°C or lower, more preferably 150°C or higher and 280°C or lower.

[0054] The second solvent is a relatively small component with a surface tension of less than 30 mN / m. This second solvent improves the wettability of the copper powder, thereby increasing the dispersibility of the copper powder. This, in turn, improves the shear strength of the joint in the bonded structure. On the other hand, while the first solvent with a high surface tension has an exudation suppression effect, the desired shear strength of the joint cannot be obtained using only the first solvent. Therefore, by combining the second solvent with a low surface tension as described in this invention, exudation suppression can be maintained while improving shear strength. If the surface tension of the second solvent is 30 mN / m or more, the effect of improving shear strength becomes insufficient. From the viewpoint of exudation suppression, the surface tension of the second solvent is preferably 20 mN / m or more and 29.5 mN / m or less, more preferably 22 mN / m or more and 29 mN / m or less.

[0055] The content of the second solvent in the bonding composition is 1.5% by mass or more and 20% by mass or less relative to the copper powder. Here, the content of the second solvent is the mass ratio of the second solvent to the copper powder. If the content is less than 1.5% by mass, the effect of the second solvent becomes insufficient, and the effect of improving shear strength becomes insufficient. If the content exceeds 20% by mass, the total amount of solvent becomes excessive. Since the paste viscosity of the bonding composition becomes too low, exudation may occur. In addition, the shear strength of the joint obtained by firing the bonding composition may decrease. From the viewpoint of improving shear strength, the content of the second solvent relative to the copper powder is preferably 2% by mass or more. On the other hand, from the viewpoint of achieving a higher level of shear strength improvement and exudation suppression, the content of the second solvent relative to the copper powder is preferably 15% by mass or less, more preferably 10% by mass or less.

[0056] The boiling point of the second solvent is not limited. However, it is preferably 150°C or higher and 300°C or lower. By setting the boiling point to 300°C or lower, organic matter residue at the joint is prevented, and a decrease in conductivity and shear strength is easily prevented. On the other hand, by setting the boiling point to 150°C or higher, a decrease in conductivity and shear strength at the joint is also easily prevented. From the viewpoint of further improving the conductivity and shear strength of the joint, the boiling point is preferably 150°C or higher and 290°C or lower, and more preferably 150°C or higher and 280°C or lower.

[0057] Preferably, the surface tension of the first solvent is 30 mN / m or more and 65 mN / m or less, and the surface tension of the second solvent is 20 mN / m or more and less than 30 mN / m. This achieves a higher balance between improved shear strength and exudation suppression.

[0058] The types of the first and second solvents are not limited within the range that satisfies the above requirements. Examples include alcohols, ketones, esters, ethers, hydrocarbons, and organic acids. Specifically, examples include alcohols such as propylene glycol, ethylene glycol, hexanediol, diethylene glycol, 1,3-butanediol, 1,4-butanediol, dipropylene glycol, tripropylene glycol, and dihydroterpineol; ethers such as vinyl carbitol and butyl carbitol; and organic acids such as carboxylic acids. However, the first and second solvents are preferably compatible solvents. The presence or absence of compatibility can be determined by investigating whether phase separation occurs when the mixture of the first and second solvents is allowed to stand.

[0059] Preferably, the first solvent is one or more selected from the group consisting of alcohol-based solvents, glycol-based solvents, ketone-based solvents, and ester-based solvents. The first solvent is not limited, and examples include one or more selected from the group consisting of cyclohexanol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, glycerol, acetone-acetone, acetophenone, glyceryl monoacetate, glyceryl triacetate, diethylene glycol, triethylene glycol, triethylene glycol methyl ether, γ-butyrolactone, dipropylene glycol, terpineol, dihydroterpineol, octyl glycol, benzyl alcohol, ethoxyethoxyethanol, butoxyethoxyethanol, tripropylene glycol, isophorone, and butylcarbidol acetate. The first solvent may be a single solvent or a mixture of multiple solvents. When using a mixed solvent, it is preferable that the solvents contained in the mixed solvent are compatible with each other. In addition, the total amount of each solvent contained in the mixed solvent is sufficient as long as it meets the preferred range of the first solvent amount (more than 0.1% by mass and less than 20% by mass relative to copper powder).

[0060] The second solvent is preferably liquid carboxylic acid. Liquid carboxylic acid is a carboxylic acid that is liquid at 1 atmosphere and 20°C. When carboxylic acid is used as a solvent, the copper particles are activated by surface etching, and copper carboxylate with a sintering-promoting effect is generated. Therefore, the sinterability of the copper powder is improved, and the shear strength of the bonding site can be significantly enhanced. In addition, by using liquid carboxylic acid, the copper particles are uniformly dispersed, resulting in a composition with good coatability.

[0061] Examples of liquid carboxylic acids include branched aliphatic saturated monocarboxylic acids with 4 or more and 18 or fewer carbon atoms, preferably selected from one or more secondary and tertiary saturated aliphatic monocarboxylic acids that are liquid at 1 atmosphere and 20°C. Preferably, such carboxylic acids are selected from one or more of 2,2-dimethylbutyric acid, neodecanoic acid, and 2-ethylhexanoic acid, more preferably from one or more of the group consisting of neodecanoic acid and 2-ethylhexanoic acid. Using such carboxylic acids can further improve the shear strength of the bonding site. The second solvent can be a single solvent or a mixture of multiple solvents. When using a mixed solvent, it is preferable that the solvents contained in the mixed solvent are compatible with each other. Furthermore, the total amount of each solvent contained in the mixed solvent only needs to meet the preferred range for the amount of the second solvent (1.5% by mass or more and 20% by mass or less relative to copper powder).

[0062] Preferably, the total content of the first solvent and the second solvent in the bonding composition is 4% by mass or more and 20% by mass or less, more preferably 4% by mass or more and 15% by mass or less, and particularly preferably 4% by mass or more and 10% by mass or less.

[0063] Preferably, the surface tension of the mixed solvent of the first solvent and the second solvent is 20 mN / m or more and 40 mN / m or less. Here, the mixed solvent refers to a solvent obtained by mixing the first solvent and the second solvent in the same proportion as in the liquid composition. By setting the surface tension of the mixed solvent within the above-mentioned range, the exudation suppression effect can be more significantly achieved.

[0064] In particular, the following combination is preferred for the first solvent and the second solvent.

[0065] • First solvent: terpineol; Second solvent: neodecanoic acid

[0066] • First solvent: dipropylene glycol; Second solvent: neodecanoic acid

[0067] • First solvent: Octanediol; Second solvent: Neodecanoic acid

[0068] • First solvent: diethylene glycol; Second solvent: neodecanoic acid

[0069] • First solvent: terpineol; Second solvent: 2-ethylhexanoic acid

[0070] • First solvent: dipropylene glycol; Second solvent: 2-ethylhexanoic acid

[0071] • First solvent: Octanediol; Second solvent: 2-Ethylhexanoic acid

[0072] • First solvent: diethylene glycol; Second solvent: 2-ethylhexanoic acid

[0073] <Other Ingredients>

[0074] In addition to copper powder, the first solvent, and the second solvent, the bonding composition of this embodiment may also contain other additives. Examples of other additives include sintering aids, binder resins, reducing agents, surface tension modifiers, defoamers, and viscosity modifiers. However, the bonding composition may also be composed only of copper powder, the first solvent, and the second solvent, without any other additives. Even without other additives, the effects of improving shear strength and inhibiting exudation can be fully realized.

[0075] <Viscosity>

[0076] The paste viscosity of the bonding composition is preferably 10 Pa·s or more and 800 Pa·s or less. Increasing the viscosity to a certain level allows for more reliable exudation suppression. Furthermore, it enables uniform dispersion of copper particles in the composition, suppressing their sedimentation. Consequently, the filling capacity of copper particles in the coating film obtained by coating the composition is improved, resulting in a bonding site with superior conductivity and shear strength. From the same viewpoint, the paste viscosity of the bonding composition is preferably 30 Pa·s or more, more preferably 50 Pa·s or more. On the other hand, moderately suppressing the viscosity improves the coatability of the composition. Additionally, if copper particles are densely packed in the composition, they tend to aggregate. Suppressing the viscosity suppresses the aggregation of copper particles, resulting in a bonding site with particularly superior conductivity and shear strength. From the same viewpoint, the paste viscosity of the bonding composition is preferably 600 Pa·s or less, more preferably 400 Pa·s or less. It should be noted that the viscosity measurement is performed by the method described in the examples below or a method based thereon.

[0077] By using the bonding composition of this embodiment, seepage after coating is less likely to occur. Therefore, problems such as poor insulation caused by seepage can be suppressed. In addition, the shear strength (bond strength) of the joint formed using this bonding composition is high. Therefore, a highly reliable joint structure can be manufactured.

[0078] <<2. Method for manufacturing the bonding composition>>

[0079] The bonding composition of this embodiment is manufactured by mixing copper powder, a first solvent, a second solvent, and other additives as needed. The copper powder can be copper powder manufactured by various methods such as wet reduction, atomization, and electrolytic reduction. For example, when using wet reduction or atomization, spherical particles are easily obtained. When using electrolytic reduction, dendritic or columnar particles are easily obtained. Flaky particles are obtained, for example, by applying mechanical force to spherical particles to plastically deform them. Furthermore, when using copper powder containing fine first copper powder and coarse second copper powder, the first copper powder and the second copper powder are prepared separately and mixed. Mixing can be performed using a known mixing apparatus such as a roller mill.

[0080] <<3. Manufacturing method of joint structure>>

[0081] The manufacturing method of the bonding structure in this embodiment includes: a step of coating the bonding composition described above onto the surface of a first substrate to form a coating film, and then placing a second substrate on the coating film to obtain a laminate (coating and lamination step); and a step of heat-treating the obtained laminate to sinter the copper powder contained in the coating film, thereby bonding the first substrate and the second substrate and obtaining a bonding structure having a bonding portion originating from the bonding composition (heating step).

[0082] <Coating and Lamination Process>

[0083] In the coating and lamination process, a bonding composition is applied to the surface of a first substrate to form a coating film, and then a second substrate is placed on the coating film to obtain a laminate. The coating film can be formed using known coating methods such as screen printing, dot printing, gravure printing, reverse coating, or doctor blade coating. The coating film can be applied to the entire surface area of ​​the first substrate, or it can be applied discontinuously to a portion of the surface. Furthermore, from the viewpoint of more reliably ensuring high shear strength, the coating film can be applied not only to the surface of the first substrate but also to the surface of the second substrate.

[0084] By placing a second bonded object on a coating film, a laminate having a first bonded object, a second bonded object, and a coating film between them can be obtained. The first and second bonded objects can be made of the same material or different materials. From the viewpoint of obtaining a stable joint with high shear strength, the thickness of the coating film portion when the first and second bonded objects overlap is preferably 1 μm or more and 500 μm or less, more preferably 5 μm or more and 300 μm or less.

[0085] <Heating Process>

[0086] In the heating process, the obtained laminate is heat-treated to sinter the copper powder contained in the coating, thereby bonding the first and second substrates and obtaining a bonded structure with bonding portions derived from the bonding composition. If necessary, the coating can be dried at a low temperature before heat treatment. As bonding portions of the copper powder sintered body formed by heat treatment, the first and second substrates are mechanically bonded and electrically and thermally connected. Therefore, a bonded structure with bonding portions exhibiting excellent electrical conductivity, shear strength, and thermal conductivity can be obtained.

[0087] The heat treatment is preferably carried out in a reducing gas atmosphere such as hydrogen or formic acid, or an inert gas atmosphere such as nitrogen or argon. Furthermore, the heating temperature is preferably less than 300°C, more preferably 150°C or higher but less than 300°C, and can be 180°C or higher but less than 300°C, or 200°C or higher but less than 300°C. Provided the heating temperature is within the above range, the heating time (firing time) is preferably 20 minutes or more, more preferably 20 minutes or more but less than 120 minutes, and even more preferably 30 minutes or more but less than 120 minutes.

[0088] The heat treatment is performed under no pressure or under pressure. No-pressure treatment is performed without applying any pressure other than the weight of the joined parts and atmospheric pressure, while pressure treatment is performed with applied pressure. When pressure treatment is performed, a pressure of 0.001 MPa or more, more preferably 0.001 MPa or more and 20 MPa or less, and even more preferably 0.01 MPa or more and 15 MPa or less is applied.

[0089] <Joint Structure>

[0090] The bonding structure of this embodiment comprises a first bonded body, a second bonded body, and a sintered body of a bonding composition that bonds the first bonded body and the second bonded body. Here, the bonded bodies (the first bonded body and the second bonded body) are the objects to be bonded, and examples include spacers made of various conductive metals such as gold, silver, or copper, heat sinks, metal wires, substrates with metal wires on their surfaces, or conductive materials such as semiconductor chips. Specifically, examples include semiconductor elements such as power modules, transmitters, amplifiers, and LED modules, lead frames, metal plate-attached ceramic substrates, semiconductor element mounting substrates, metal wiring, bulk materials, power supply components, heat sinks, water-cooled plates, and metal clips.

[0091] Specific examples of bonding structures include semiconductor devices formed by bonding a semiconductor element mounting substrate as the first bonded body, a semiconductor chip as the second bonded body, and a sintered body of a bonding composition. Other examples include: a bonded body formed by bonding a semiconductor element mounting substrate as the first bonded body, a heat sink as the second bonded body, and a sintered body of a bonding composition; and a bonded body formed by bonding a semiconductor chip electrode as the first bonded body, a metal clip as the second bonded body, and a sintered body of a bonding composition.

[0092] The bonding structure obtained by the method of this embodiment has a bonding portion formed by a sintered body of the bonding composition. The copper powder in this composition has good sinterability, and the bonding portion formed by its sintered body has high conductivity and shear strength. This bonding structure with such advantages is suitable for various electronic circuits, especially those used in high-temperature environments, such as electronic circuits for automotive applications and power devices.

[0093] Example

[0094] The invention is illustrated in more detail using the following embodiments. However, the invention is not limited to the following embodiments.

[0095] (1) Preparation of the bonding composition

[0096] [Example 1]

[0097] As copper powder, a copper powder prepared by mixing a first copper powder (Mitsui Metals Mining Co., Ltd., CH-0200L1) and a second copper powder (Mitsui Metals Mining Co., Ltd., CS-20) in a mass ratio of first copper powder: second copper powder = 3:7 is used. The D of the first copper powder and the second copper powder... 50 After the bonding composition is adjusted into a paste as described below, the determination is performed using the method described above. The D of the first copper powder... 50 The D of the second copper powder is 0.14 μm. 50 The thickness is 2.2 μm. Both the first and second copper powders are spherical powders.

[0098] Terpineol is used as the primary solvent, and neodecanoic acid (Hexion Corporation, Versatic 10) is used as the secondary solvent. Neodecanoic acid (Versatic 10) is a tertiary saturated aliphatic monocarboxylic acid with 10 carbon atoms, which is liquid at 1 atmosphere and 20°C.

[0099] Two parts by mass of a first solvent (terpineol) and three parts by mass of a second solvent (neodecanonical acid) were added to 95 parts by mass of copper powder. The resulting mixture was pre-mixed with a scraper and then gelatinized using a rotary vacuum mixer (THINKY ARE-500, Co., Ltd.). During gelatinization, two cycles were performed, one at stirring mode (1000 rpm × 1 minute) and the other at degassing mode (2000 rpm × 30 seconds). The resulting paste was then dispersed and mixed using a three-roll mill to prepare a paste-like binding composition.

[0100] (2) Fabrication of the joint structure

[0101] In the center of the chip mounting portion of a copper leadframe (2.0 mm thick), which serves as the first bonding substrate, a bonding composition is applied using a dispensing printing method. Next, a 3 mm square SiC (0.2 mm thick, gold-plated on the back side), serving as the second bonding substrate, is placed on the back side of the bonding composition to obtain a laminate. The thickness of the bonding composition at this point is 50 μm. In this state, the laminate is sintered at 150°C for 90 minutes under a formic acid atmosphere to fabricate the bonding structure.

[0102] [Example 2]

[0103] Dipropylene glycol was used instead of terpineol as the first solvent. Otherwise, the bonding composition and bonding structure were prepared following the same steps as in Example 1.

[0104] [Example 3]

[0105] Octylene glycol was used instead of terpineol as the first solvent. Otherwise, the bonding composition and bonding structure were prepared following the same steps as in Example 1.

[0106] [Example 4]

[0107] The amount of the first solvent (terpineol) added was changed to 3.5 parts by weight, and the amount of the second solvent (neodecanonical acid) added was changed to 1.5 parts by weight. Otherwise, the bonding composition and bonding structure were prepared according to the same steps as in Example 1.

[0108] [Example 5]

[0109] The amount of copper powder was changed to 93.5 parts by mass, the amount of the first solvent (terpineol) was changed to 3.5 parts by mass, and the amount of the second solvent (neodecanonical acid) was changed to 3 parts by mass. Otherwise, the bonding composition and bonding structure were prepared according to the same steps as in Example 1.

[0110] [Example 6]

[0111] 2-Ethylhexanoic acid was used instead of neodecanoic acid as the second solvent. Otherwise, the bonding composition and bonding structure were prepared following the same steps as in Example 1.

[0112] [Comparative Example 1]

[0113] The first solvent (terpineol) was not added. Furthermore, the amount of the second solvent (neodecanonical acid) added was changed to 5 parts by weight. Otherwise, the bonding composition and bonding structure were prepared following the same steps as in Example 1.

[0114] [Comparative Example 2]

[0115] Dodecane was used instead of terpineol as the first solvent. Otherwise, the bonding composition and bonding structure were prepared following the same steps as in Example 1.

[0116] [Comparative Example 3]

[0117] 1-Hexanol was used instead of terpineol as the first solvent. Otherwise, the bonding composition and bonding structure were prepared following the same steps as in Example 1.

[0118] [Comparative Example 4]

[0119] The amount of the first solvent (terpineol) added was changed to 4 parts by mass, and the amount of the second solvent (neodecanonical acid) added was changed to 1 part by mass. Otherwise, the bonding composition and bonding structure were prepared according to the same steps as in Example 1.

[0120] The physical properties (surface tension, boiling point) of the first solvent, the second solvent, and their mixtures used in Examples 1-6 and Comparative Examples 1-4, as well as the contents of the first solvent and the second solvent in the composition (mass ratio relative to copper powder, mass proportion in the composition) are shown in Table 1 below.

[0121] (3) Evaluation

[0122] The bonding compositions and bonding structures obtained in Examples 1-6 and Comparative Examples 1-4 were evaluated for various properties according to the following steps.

[0123] <Surface tension>

[0124] The surface tensions of the first and second solvents were measured using a surface tension meter (Kruss K20 Easy Dyne) via the Pt plate method. Measurements were performed at 25°C. The surface tension of a mixture of the first and second solvents was also measured using the same method. The proportions of the first and second solvents in the mixture were the same as those in the bonding composition.

[0125] <Paste Viscosity>

[0126] The viscosity of the bonding composition paste was determined. The viscosity measurement was performed under the following conditions, yielding a shear rate of 10 s. -1 The viscosity value at that time.

[0127] - Measuring apparatus: MARS III rheometer

[0128] (Made by Thermo Scientific)

[0129] - Measurement mode: Shear rate dependent measurement

[0130] - Sensor: Parallel type (φ20mm)

[0131] - Measurement temperature: 25℃

[0132] - Gap: 0.300mm

[0133] - Shear rate: 0.05~120.01s -1

[0134] - Measurement time: 2 minutes

[0135] <Exudation Rate>

[0136] The copper lead frame used for the effusion test was replaced with a 10mm square AMB substrate; otherwise, the laminate was fabricated in the same manner as in the embodiments and comparative examples. As the AMB substrate, a substrate for which a 0.32mm thick silicon nitride ceramic and a 0.2mm thick copper plate (oxygen-free copper C1020) bonding structure had been rust-resistant using a rust inhibitor primarily composed of benzotriazole was used. Furthermore, the arithmetic mean height Sa of the AMB substrate was 0.13μm. It should be noted that the arithmetic mean height Sa was measured within a 2mm square range using a white light interferometer (Zygo ZeGage Pro).

[0137] An optical microscope was used to observe the upper surface of the laminate and to capture optical microscope images. Then, in the obtained optical microscope images (upper surface field images), the areas coated with the bonding composition were identified. Figure 1 The area of ​​the bonding composition region 4 (bonding composition area) and the area of ​​solvent wetting extension ( Figure 1 The area of ​​the exudation zone 8) (exudation area) is calculated, and its ratio (exudation area / area of ​​the bonding composition × 100) is used as the exudation rate (%).

[0138] <Shear Strength>

[0139] The shear strength of the joint structure was determined using a joint strength tester (XYZTEC, Condor Sigma). It should be noted that shear strength is expressed as fracture load (in N) versus joint area (in mm). 2 It is calculated in the form of the ratio of fracture load to joint area.

[0140] (4) Evaluation Results

[0141] The evaluation results are summarized in Table 1 below.

[0142] The sample examples (Examples 1-6) whose surface tension and content of the first and second solvents meet the ranges specified in this embodiment have an exudation rate of 22.9% or less and a shear strength of 27 MPa or more at the joint. In particular, Examples 1, 2, and 6 have an exudation rate as low as 16.3% or less and a shear strength as high as 50 MPa or more.

[0143] In contrast, the comparative sample (Comparative Example 1) without the first solvent had a high exudation rate of 24.2%. Furthermore, the comparative samples (Comparative Examples 2 and 3) containing the first solvent but with low surface tension had relatively high exudation rates of 23.6% or more. Moreover, the comparative sample (Comparative Example 4) with an excessively low amount of the second solvent had a very low shear strength of 8 MPa.

[0144] As can be understood from the above results, according to this embodiment, a bonding composition that has the effect of exudation suppression and can obtain a bonding structure with a bonding part having high shear strength can be provided.

[0145] [Table 1]

[0146]

[0147] Explanation of reference numerals in the attached figures

[0148] 2. The joined body

[0149] 4. Joining composition (joining composition area)

[0150] 6 Semiconductor components

[0151] 8. Leakage (leakage area)

Claims

1. A bonding composition comprising copper powder and a solvent, The solvent comprises a first solvent with a boiling point above 150°C and below 300°C and a surface tension above 30 mN / m, and a second solvent with a surface tension less than 30 mN / m. The content of the first solvent is more than 0.1% by mass and less than 20% by mass relative to the copper powder. The content of the second solvent is more than 1.5% by mass and less than 20% by mass relative to the copper powder.

2. The joining composition according to claim 1, wherein, The surface tension of the first solvent is above 30 mN / m and below 65 mN / m, and the surface tension of the second solvent is above 20 mN / m and below 30 mN / m.

3. The joining composition according to claim 1 or 2, wherein, The first solvent is selected from one or more solvents chosen from the group consisting of alcohol solvents, glycol solvents, ketone solvents and ester solvents.

4. The joining composition according to claim 1 or 2, wherein, The second solvent is a liquid carboxylic acid.

5. The joining composition according to claim 1 or 2, wherein, The copper powder content in the bonding composition is 80% by mass or more and 96% by mass or less.

6. The joining composition according to claim 1 or 2, wherein, The paste viscosity of the bonding composition is 10 Pa·s or more and 800 Pa·s or less.

7. A joining structure comprising a first joined body, a second joined body, and a sintered body of the joining composition of claim 1 or 2 for joining the first joined body and the second joined body.

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