Composition for bonding materials and method for manufacturing the same

Abstract

To provide a bonding material composition having sufficiently high bonding strength. [Solution] The bonding material composition comprises copper particles having formic acid attached to their surface and having an average particle diameter of 0.5 μm to 100 μm, a complex or complex salt containing copper ions, formate ions, and a basic group-containing compound, and a solvent. The molar ratio of the basic group-containing compound to the formic acid in the entire bonding material composition (amount of substance of the basic group-containing compound / amount of substance of the formic acid) is less than 0.5.

Description

Technical Field

[0001] The present invention relates to a composition for a bonding material and a method for producing the same.

Background Art

[0002] When manufacturing a semiconductor device, various bonding materials are used to bond a semiconductor element and a lead frame or the like (support member). Among semiconductor devices, high-lead solder has been used as a bonding material for power semiconductors that operate at high temperatures. On the other hand, since high-lead solder does not have sufficient thermal conductivity, a bonding material containing silver particles with high thermal conductivity has been studied as an alternative material.

[0003] Although the sintered product of the bonding material containing silver particles shows higher thermal conductivity than high-lead solder, it is necessary to apply pressure at a high pressure during bonding to obtain bonding strength. In addition, the bonding material containing silver particles also has a high material cost. Therefore, instead of the bonding material containing silver particles, the use of a bonding material containing copper particles has been studied.

[0004] As a bonding material containing copper particles, for example, Patent Document 1 discloses a sintering paste containing copper particles having D10 of 100 nm or more and D90 of 500 nm or less coated with triethanolamine, an epoxy methacrylate urethane (binder), malonic acid (activator), a dispersant, and an organic solvent.

[0005] Further, Patent Document 2 discloses a conductive paste containing nano-sized copper particles, micron-sized copper particles, and a mixed solvent having formic acid and a basic compound, and having a molar ratio of the basic group-containing compound to formic acid (amount of substance of the basic group-containing compound / amount of substance of formic acid) of 0.5 or more.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] However, the bonding materials described in Patent Documents 1 and 2 did not exhibit sufficient cohesiveness during sintering, and therefore could not achieve sufficient bonding strength.

[0008] Therefore, a bonding material that provides sufficient bonding strength through sintering is desired. In particular, from the viewpoint of reducing damage to semiconductor devices, it is desirable that the material can be sintered at lower temperatures and pressures while still achieving sufficient bonding strength.

[0009] This invention has been made in view of the above circumstances, and aims to provide a bonding material composition having sufficiently high bonding strength and a method for manufacturing the same. [Means for solving the problem]

[0010] [1] A bonding material composition comprising formic acid-coated copper particles having formic acid attached to their surface and having an average particle diameter of 0.5 μm or more and 100 μm or less, a complex or complex salt containing copper ions, formate ions, and a basic group-containing compound, and a solvent, wherein the molar ratio of the basic group-containing compound to the formic acid in the entire bonding material composition (amount of substance of the basic group-containing compound / amount of substance of the formic acid) is less than 0.5. [2] The bonding material composition according to [1], wherein the hydrogen ion concentration (pH) is 5.0 or less. [3] The bonding material composition according to [1] or [2], further comprising liberated formic acid. [4] The bonding material composition according to any one of [1] to [3], wherein the basic group-containing compound comprises an alkanolamine. [5] The bonding material composition according to [4], wherein the alkanolamine comprises 3-(diethylamino)-1,2-propanediol or 3-(dimethylamino)-1,2-propanediol. [6] A bonding material composition according to any one of [1] to [5], further comprising copper particles having an average particle diameter of less than 0.5 μm. [7] The bonding material composition according to any one of [1] to [6], wherein the formic acid-coated copper particles include copper particles A-1 having an average particle diameter of 1.0 μm or more and 100 μm or less, and copper particles A-2 having an average particle diameter of 0.5 μm or more and less than 1.0 μm. [8] A bonding material composition according to any one of [1] to [7], wherein when the formic-coated copper particles are subjected to thermomass differential thermal analysis (TG-DTA analysis), no exothermic peak is detected in the 180-300°C range originating from the surface protective agent. [9] A composition for bonding materials according to any one of [1] to [8], further comprising a curable compound.

[10] The bonding material composition according to [9], comprising a (meth)acrylic compound and a polymerization initiator as the curable compound.

[11] The bonding material composition according to [9], comprising an epoxy compound as the curable compound and a curing agent.

[12] The solvent comprises a polyalkylene glycol-based solvent, the composition for bonding materials according to any one of [1] to

[11] . A bonding material obtained by sintering any of the bonding material compositions described in

[13] [1] to

[12] .

[14] A method for producing a bonding material composition, comprising the step of obtaining a bonding material composition using formic acid-coated copper particles having an average particle diameter of 0.5 μm or more and 100 μm or less with formic acid adhering to the surface, a complex or complex salt containing copper ions, formate ions and a basic group-containing compound, and a solvent.

[15] The formic acid-coated copper particles are obtained by treating copper particles having an average particle diameter of 0.5 μm or more and 100 μm or less with formic acid, and the method for producing the bonding material composition according to

[14] .

[16] The method for producing the bonding material composition according to

[14] or

[15] , wherein the formic acid-coated copper particles include copper particles A-1 having an average particle diameter of 1.0 μm or more and 100 μm or less, and copper particles A-2 having an average particle diameter of 0.5 μm or more and less than 1.0 μm.

[17] In the step of obtaining the composition for bonding material, copper particles having an average particle diameter of less than 0.5 μm are further used, which is the method for manufacturing the composition for bonding material according to any one of

[14] to

[16] .

[18] In the step of obtaining the composition for bonding material, formic acid is further used, which is the method for manufacturing the composition for bonding material according to any one of

[14] to

[17] .

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a composition for bonding material having a sufficiently high bonding strength and a method for manufacturing the same.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a bonded body according to an embodiment of the present invention. [Figure 2] FIGS. 2A and 2B are measurement results showing the heat generation behavior and weight change before and after treatment of copper particles (copper particles 1). [Figure 3] FIGS. 3A and 3B are measurement results showing the heat generation behavior and weight change before and after treatment of copper particles (copper particles 3). [Figure 4] FIG. 4 is a SEM observation photograph of a cross-section of a cured product of Composition 3.

Embodiments for Carrying Out the Invention

[0013] Copper particles are usually coated with a surface protective agent such as a higher fatty acid on the surface in order to enhance dispersibility. According to the study by the present inventors, the sinterability can be enhanced by removing a part of the surface protective agent coating the copper particle surface by formic acid treatment.

[0014] Then, after formic acid treatment, copper particles with most of the formic acid remaining attached to the particle surface (formic acid-attached copper particles) are used, and in combination with a predetermined copper complex or copper complex salt, by setting the molar ratio of the basic group-containing compound to formic acid within a predetermined range, it has been found that a joining material with high sinterability and good joining strength can be obtained. That is, a composition containing formic acid-attached copper particles and a copper complex salt containing copper ions, formic acid, and a basic group-containing compound, with a molar ratio of the basic group-containing compound to formic acid (amount of substance of the basic group-containing compound / amount of substance of formic acid) less than 0.5, has been found to have high sinterability and exhibit good joining strength.

[0015] The reason for this is not clear, but it is presumed as follows. The carboxy group of formic acid in the formic acid-attached copper particles and the basic group of the basic group-containing compound contained in the copper complex or copper complex salt form a hydrogen bond to form a pseudo-crosslink. Thereby, when sintering, the formic acid-attached copper particles can interact with each other via the copper complex or copper complex salt, so that the sinterability can be enhanced. Also, since the composition contains a large amount of formic acid, the pH of the composition becomes low, making it difficult to oxidize the copper particles. Thereby, the surface of the copper particles is activated, so that the sinterability can be enhanced. Thereby, high joining strength can be obtained.

[0016] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the embodiments.

[0017] 1. Composition for joining material The composition for joining material of the present embodiment (hereinafter also simply referred to as "composition") includes copper particles having an average particle diameter of 0.5 μm or more and 100 μm or less with formic acid attached to the surface (formic acid-attached copper particles), a complex or complex salt (copper complex or copper complex salt) containing copper ions, formic acid ions, and a basic group-containing compound, and a solvent. And the molar ratio of the basic group-containing compound and formic acid in the whole composition (amount of substance of the basic group-containing compound / amount of substance of formic acid) is less than 0.5.

[0018] If the above molar ratio is less than 0.5, the amount of formic acid in the composition is large, and a sufficient amount of formic acid adheres to the surface of the copper particles. Preferably, at least a portion of the surface of the copper particles is coated with formic acid. As a result, hydrogen bonding occurs between the carboxyl groups of the formic acid on the surface of the copper particles and the basic groups of the basic group-containing compound of the copper complex or copper complex salt. This improves the dispersibility of the copper particles and facilitates the formation of pseudo-crosslinks between the copper particles via the copper complex during sintering, thereby facilitating sintering. This increases the bonding strength. From a similar viewpoint, it is preferable that the above molar ratio is 0.3 or less. The lower limit of the above molar ratio is not particularly limited, but from the viewpoint of making it less likely for free formic acid to volatilize into the working environment and further improving safety during the manufacture and use of the material, it is preferable that it be 0.05 or more. That is, it is preferable that the above molar ratio is 0.05 or more and less than 0.5.

[0019] The "amount of substance of the basic group-containing compound" in the above molar ratio refers to the amount of substance of the basic group-containing compound contained in the composition, and is derived, for example, from the basic group-containing compound contained in the copper complex or copper complex salt. The "amount of substance of formic acid" in the above molar ratio refers to the amount of substance of formic acid contained in the composition, and is derived, for example, from the formic acid attached to the surface of the copper particles, the formic acid contained in the complex, and the formic acid liberated in the composition.

[0020] The above molar ratio is determined by the absorption spectrum obtained by FT-IR measurement of the above composition, where the peak originating from the NH group of the basic group-containing compound in the composition (e.g., 3400-3350 cm⁻¹) is observed. -1 , 3330~3250cm -1 The height of the peak appearing in the region and the C=O stretching peak derived from the carboxyl group of formic acid (e.g., 1720-1700 cm) -1 It can be calculated from the ratio of the height of the peak that appears in the region. in particular, 1) For samples with a known molar ratio of NH groups to carboxyl groups, measure the ratio of peak heights in the absorption spectra obtained by FT-IR measurement, and prepare a calibration curve showing the relationship between the molar ratio and the peak height ratio. 2) The above molar ratio is calculated by comparing the ratio of peak heights obtained from the absorption spectrum when an FT-IR measurement is performed on an unknown sample with the calibration curve.

[0021] FT-IR measurements are performed using either transmission or reflection methods, or the ATR method if the peak intensity is weak, under a nitrogen atmosphere, in a measurement range of 400-4000 cm². -1 It can be done under these conditions.

[0022] Furthermore, the above molar ratio can also be calculated from the charging ratio of formic acid-attached particles, copper complex or copper complex salt, and formic acid during the preparation of the composition.

[0023] The above molar ratio can be adjusted, for example, by the ratio of formic acid-coated copper particles to copper complexes or copper complex salts, the amount of formic acid attached to the formic acid-coated copper particles, the amount of free formic acid, etc. For example, if the amount of formic acid attached to copper particles is increased or the amount of free formic acid is increased while using formic acid-coated copper particles and copper complexes or copper complex salts in combination, the above molar ratio will decrease.

[0024] The hydrogen ion concentration (pH) of the composition is not particularly limited, but is preferably 5.0 or less, and more preferably 2.0 to 4.5. When the pH of the composition is 5.0 or less, the surface of the copper particles can be made less susceptible to oxidation. Therefore, it is easier to improve the sinterability and the conductivity of the sintered product.

[0025] The hydrogen ion concentration (pH) of the composition can be measured by the following procedure. First, the composition is diluted with pure water to a concentration of 10% by mass to prepare a pure water suspension. Then, the solid material is centrifuged (2000 rpm, 5 min), and the pH of the supernatant is measured at room temperature (20°C) using a pH meter (AS ONE AS700). The pH of the composition can be adjusted mainly by the formic acid content in the composition and the amount of formic acid attached to the copper particles.

[0026] The following provides a detailed explanation of each component.

[0027] 1-1. Formic acid-coated copper particles Formic acid-coated copper particles are copper particles with an average particle diameter of 0.5 μm to 100 μm on which formic acid is attached to the surface. Preferably, the formic acid-coated copper particles are copper particles obtained by treating copper particles with an average particle diameter of 0.5 μm to 100 μm on which a surface protective agent such as a higher fatty acid is attached with formic acid. In such formic acid-coated copper particles, at least a portion of the surface protective agent on the surface is removed, and at least a portion of the surface is coated with formic acid.

[0028] Whether or not formic acid is adhering to the surface of copper particles can be confirmed during manufacturing by measuring the weight change before and after formic acid treatment (the weight increase after treatment is considered the amount of formic acid adhering). It can also be confirmed by TG-DTA measurement of copper particles sampled from the composition.

[0029] When confirming by TG-DTA (Differential Thermal Analysis-Calorie Analysis), a TG-DTA instrument (e.g., Seiko Instruments TA-7000) is used, and the differential heat and weight change are measured from 30°C to 300°C under a nitrogen atmosphere at a heating rate of 10°C / min. If there is a weight decrease from around 150°C and the weight change is small and stable from around 230°C (see "After Treatment" in Figures 2B and 3B described later), it can be confirmed that the surface deposit is formic acid. Furthermore, if higher fatty acids, which act as surface protectants, remain, weight loss will continue above 230°C (see "Before Treatment" in Figures 2B and 3B below). Also, if weight loss is observed below 150°C, presumably due to water adhering during the process, the amount of formic acid adhering will be calculated by subtracting that amount from the weight loss at a stable point around 230°C.

[0030] The amount of formic acid attached is, for example, 1.0% by mass or more and 20% by mass or less, preferably 2.0% by mass or more and 15% by mass or less, relative to the copper particles. When the amount of formic acid attached is 1.0% by mass or more, it is easy to crosslink with the copper complex or copper complex salt via hydrogen bonding, thereby further improving the dispersibility and sinterability of the copper particles. When the amount of formic acid attached is 20% by mass or less, the release and volatilization of formic acid are suppressed, allowing for safe work without inhaling formic acid during operation.

[0031] Furthermore, as described above, it is preferable that at least a portion of the surface protective agent is removed from the formic acid-coated copper particles. This is because the aggregation of copper particles during sintering is less likely to be inhibited by the surface protective agent, thereby improving sinterability. Whether or not the surface protective agent has been removed can be confirmed by the absence of an exothermic peak in the 180-300°C, preferably 200-250°C, and more preferably 240-250°C range, which originates from the surface protective agent (e.g., higher fatty acids), in the TG-DTA measurement described above. Specifically, the absence of an exothermic peak means that no exothermic peak accompanied by a weight change of 2% by mass or more (an exothermic peak that reaches more than 100 μV with a sample amount of 12 mg in the exothermic behavior) is detected (see "After Treatment" in Figures 2A and 3A described later). The TG-DTA measurement can be performed in the same manner as described above.

[0032] The surface protective agent includes an organic compound having functional groups (e.g., carboxyl groups, phosphate groups, and amino groups) that can adhere to the surface of copper particles, and preferably includes an aliphatic amine or a fatty acid or its ester.

[0033] Aliphatic amines are, for example, aliphatic amines having 8 or more carbon atoms, preferably aliphatic amines having 8 to 16 carbon atoms. Examples of aliphatic amines include octylamine and dodecylamine. Fatty acids or their esters are, for example, fatty acids or their esters having 8 or more carbon atoms, preferably higher fatty acids or their esters (saturated or unsaturated fatty acids with 12 to 24 carbon atoms or their alkyl esters). Examples of fatty acids or their esters include myristyl acid, palmitic acid, stearic acid, oleic acid, and linoleic acid, as well as their methyl esters.

[0034] As described above, the formic acid-coated copper particles are submicron to micron-sized copper particles with an average particle diameter of 0.5 μm to 100 μm. Because such copper particles have a small surface area, they disperse easily in the solvent when used in combination with copper complexes. Furthermore, since the volume shrinkage of the sintered product is small, the bonding strength can be further increased. From a similar viewpoint, the average particle diameter of the formic acid-coated copper particles is preferably 0.5 μm to 10 μm, and more preferably 0.5 μm to 5 μm.

[0035] In this specification, the average particle diameter refers to the volume-based cumulative 50% particle diameter obtained by particle diameter distribution measurement using laser diffraction. The above average particle diameter represents the particle diameter of the copper particles themselves, without any formic acid or surface protective agents attached.

[0036] The formic acid-coated copper particles may contain multiple copper particles with different average particle sizes. For example, the formic acid-coated copper particles may contain micron-sized copper particles A-1 with an average particle size of 1.0 μm or more and 100 μm or less, and submicron-sized copper particles A-2 with an average particle size of 0.5 μm or more and less than 1.0 μm. In this case, whether the composition contains micron-sized copper particles A-1 and submicron-sized copper particles A-2 can be confirmed by observing a cross-section of the cured product of the composition using a scanning electron microscope (SEM) at an acceleration voltage of 5.0 kV and a magnification of 5000x or more, and observing the image obtained, for example, by the presence of copper particles with a particle size of less than 1.0 μm and copper particles with a particle size of 1.0 μm or more (see Figure 4).

[0037] When the formic-coated copper particles contain micron-sized copper particles A-1 and submicron-sized copper particles A-2, the mass ratio of copper particles A-1 to copper particles A-2 (copper particles A-1 / copper particles A-2) is preferably 0.25 or more and 1.2 or less, and more preferably 0.4 or more and 1.0 or less. When the above mass ratio is 0.25 or more, the content ratio of micron-sized copper particles A-1 is moderately high, resulting in less volume shrinkage during sintering, making it easier to adjust according to the desired coating film thickness. When the above mass ratio is 1.2 or less, the content ratio of submicron-sized copper particles A-2 is moderately high, making it easier to increase the packing density of the sintered product, and thus easier to increase the bonding strength and conductivity. The total amount of micron-sized copper particles A-1 and submicron-sized copper particles A-2 in the formic-coated copper particles may be 100% by mass of the total mass of the formic-coated copper particles.

[0038] The shape of the copper particles is not particularly limited and may be spherical, lumpy, needle-shaped, or flake-shaped (flat, plate-like, or scale-like), but spherical is preferred from the viewpoint of dispersibility and packing properties.

[0039] The content of formic acid-coated copper particles in the above composition is, for example, 30 parts by mass or more and 80 parts by mass or less, preferably 50 parts by mass or more and 70 parts by mass or less, and more preferably 55 parts by mass or more and 65 parts by mass or less, per 100 parts by mass of the total mass of copper particles in the composition. Note that the copper particle content refers to the content of copper particles after subtracting the amount of formic acid. Furthermore, in this specification, "total mass of copper particles in the above composition" refers to the total mass of all copper particles contained in the above composition. For example, in this embodiment, it refers to the total mass of copper particles after subtracting the amount of formic acid and other copper particles (e.g., copper particles that have not been treated with formic acid) described later.

[0040] 1-3. Copper complexes or copper complex salts A copper complex or copper complex salt is a complex or complex salt containing a copper ion, a formate ion, and a basic group-containing compound. The formate ion and the basic group-containing compound are ligands that coordinate to the copper ion.

[0041] The basic group-containing compound is a ligand that coordinates to the copper ion, and is preferably a reducing compound, and more preferably a compound having an optionally substituted amino group. The optionally substituted amino group includes not only the amino group (-NH2) but also a substituted amino group in which at least some of the hydrogen atoms of the amino group are replaced with alkyl groups such as methyl or ethyl groups. In the compound having the optionally substituted amino group, the amino group portion coordinates with the divalent copper ion of the copper-containing compound. In this way, the compound not only readily forms a coordinate bond with the copper ion, but also reduces the copper ion to copper particles during sintering, thereby improving sinterability. The optionally substituted amino group is preferably an alkanolamine or alkylenediamine.

[0042] Alkanolamines are compounds having one or more hydroxyl groups and one or more optionally substituted amino groups in their molecule. Alkanolamines may be primary amines, secondary amines, or tertiary amines.

[0043] Examples of alkanolamines include compounds having one hydroxyl group, such as 1-amino-2-propanol, 1-amino-2-butanol, 2-amino-1-butanol, 2-amino-2-methyl-1-propanol, ethanolamine, 3-amino-1-propanol, 4-amino-1-butanol, and 2-amino-2-ethyl-1,3-propanediol; and compounds having two or more hydroxyl groups, such as 3-(diethylamino)-1,2-propanediol and 3-(dimethylamino)-1,2-propanediol.

[0044] Alkylenediamines are compounds that contain an aliphatic hydrocarbon chain and two amino groups within their molecule. Examples of alkylenediamines include ethylenediamine, N,N'-dimethylethylenediamine, 1,3-propanediamine, and 1,4-butanediamine.

[0045] Among these, the ligand preferably contains an alkanolamine. The hydroxyl group of the alkanolamine readily forms hydrogen bonds with copper ions of the copper complex or copper complex salt contained in the above composition, or with formic acid-attached copper particles, and readily reduces the copper surface. It also readily removes the oxide film on the metal surface of the member to be joined. This makes it easier to increase the bonding strength. The alkanolamine is preferably an alkanolamine having two or more hydroxyl groups in one molecule, more preferably an alkanolamine having two or more hydroxyl groups and an alkylamino group, and 3-(diethylamino)-1,2-propanediol or 3-(dimethylamino)-1,2-propanediol is particularly preferred.

[0046] For example, the copper formate complex is preferably represented by the following formula (1). [ka]

[0047] In formula (1), Cu represents divalent copper. L1 and L2 are the above-mentioned alkanolamine or alkylenediamine, and preferably the above-mentioned alkanolamine.

[0048] For example, in the complex represented by formula (1) above, during sintering, the divalent copper is reduced to zero-valent copper by the reducing action of alkanolamines, etc., forming copper particles, which together with the copper particles on which formic acid was attached to the surface, constitute the sintered material. The formic acid ligand is oxidized by carbon dioxide and outgassed. In addition, since the alkanolamine also reduces the copper surface of the joined member, the oxide film on that surface can also be removed, thereby further increasing the bonding strength.

[0049] The content of the copper complex or copper complex salt is, for example, 1 to 10 parts by mass, preferably 3 to 7 parts by mass, based on 100 parts by mass of the total mass of copper particles in the composition. When the content of the copper complex is 1 part by mass or more, hydrogen bonding interactions are more likely to occur between the formic acid-coated copper particles and the copper complex or copper complex salt, thereby improving the dispersibility of the formic acid-coated copper particles and further promoting sintering through reduction. When the content of the copper complex is 10 parts by mass or less, sinterability is less likely to be impaired by outgassing due to the reduction of the copper complex.

[0050] Copper complexes or copper complex salts can be obtained, for example, by mixing a copper-containing compound (e.g., copper formate) with a desired alkanolamine or alkylenediamine in a solvent such as an alcohol, and then removing the liberated formic acid and the solvent.

[0051] 1-4. Solvent The solvent is not particularly limited, and alcohol-based solvents, glycol-based solvents, acetate-based solvents, and hydrocarbon-based solvents can be used. Examples of alcohol-based solvents include α-terpineol and isopropyl alcohol. Examples of glycol-based solvents include ethylene glycol, diethylene glycol, polyethylene glycol, and polypropylene glycol. Examples of acetate-based solvents include butyl acetate carbitate. Examples of hydrocarbon-based solvents include decane, dodecane, and tetradecane.

[0052] In particular, polyalkylene glycol-based solvents such as polyethylene glycol and polypropylene glycol are preferred from the viewpoint of improving packing properties during sintering to obtain a dense sintered product, and from the viewpoint of preventing unintended oxidation of copper particles during sintering due to their high reducing effect. The number average molecular weight of the polyalkylene glycol-based solvent may be, for example, 120 to 400, and preferably 180 to 400.

[0053] The solvent content is not particularly limited, but is, for example, 1 to 15 parts by mass, preferably 3 to 12 parts by mass, per 100 parts by mass of total copper particles in the composition. When the solvent content is within the above range, the viscosity of the composition can be further reduced. Furthermore, when a highly reducing solvent is used, the oxide film on the copper surface of the members to be joined can be removed more effectively, thereby increasing the bonding strength.

[0054] 1-5. Other ingredients The above composition may further contain other components as needed. For example, the above composition may further contain other copper particles other than the formic acid-coated copper particles described above, formic acid, and binder components (curable compounds, polymerization initiators, curing agents, etc.).

[0055] 1-5-1. Other copper particles The other copper particles are preferably copper particles with an average particle diameter of less than 0.5 μm. These copper particles may be copper particles to which a surface protective agent is attached but which have not been treated with formic acid; that is, copper particles to which a surface protective agent is attached but which do not have formic acid attached. Furthermore, free formic acid may be attached to these copper particles.

[0056] The shape of the other copper particles is not particularly limited, but is preferably spherical. The average particle diameter of the other copper particles is not particularly limited, but is preferably less than 0.5 μm, and more preferably between 0.1 μm and 0.4 μm. Because such nano-sized copper particles have a large surface area, they tend to aggregate during sintering. Therefore, it is easy to increase the packing density of the sintered product and improve its conductivity.

[0057] The content of other copper particles is, for example, 20 parts by mass or more and 70 parts by mass or less, preferably 30 parts by mass or more and 50 parts by mass or less, and more preferably 35 parts by mass or more and 45 parts by mass or less, based on 100 parts by mass of the total mass of copper particles in the above composition. If the content of other copper particles is 20 parts by mass or more, the cohesiveness during sintering can be further improved. If the content of other copper particles is 50 parts by mass or less, the volume shrinkage during sintering can be further reduced. There may be one type of other copper particle or two or more types.

[0058] The total mass of copper particles in the above composition is not particularly limited, but it is preferably 85% by mass or more and 98% by mass or less relative to the total mass of non-volatile components of the above composition. If the total mass is 85% by mass or more, the conductivity of the resulting sintered product can be further enhanced. If the total mass is 98% by mass or less, for example, if a curable compound is further included, its content increases, which can further enhance the curability and bonding strength.

[0059] Other copper particles may be commercially available. Examples of commercially available products include CH-0200L1 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.36 μm), HT-14 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.41 μm), and Tn-Cu100 (manufactured by Taiyo Nissan Co., Ltd., volume average particle size 0.12 μm).

[0060] 1-5-2. Formic acid The above composition may further contain liberated formic acid as needed. The liberated formic acid is derived from the formic acid used in the preparation process of the above composition, as described later. By further containing such formic acid, the pH of the above composition can be lowered. This makes the surface of the copper particles in the above composition less susceptible to oxidation and more activating.

[0061] The amount of formic acid in the above composition should be such that the pH falls within the above range. For example, it can be 4.0% by mass or less, preferably 3.2% by mass or less, relative to the total mass of copper particles in the composition.

[0062] 1-5-3. Curing compound The curable compound may be a radical polymerizable compound or a cationic polymerizable compound. It may also be a compound containing both radical polymerizable and cationic polymerizable groups.

[0063] (1) (meth)acrylic compounds The curable compound may include, for example, a compound having a (meth)acryloyl group ((meth)acrylic compound). In this specification, (meth)acryloyl refers to acryloyl, methacryloyl, or both. The (meth)acrylic compound (E) may be one type or two or more types may be used in combination.

[0064] The (meth)acrylic compound is not particularly limited, but from the viewpoint of further increasing bonding strength, it may include urethane (meth)acrylate or epoxy (meth)acrylate.

[0065] The urethane (meth)acrylate or epoxy (meth)acrylate is preferably an oligomer. An oligomer is a polymer in which monomer units are repeated, for example, 2 to several tens of times, and is a polymer whose weight-average molecular weight (Mw) in polystyrene equivalent values, as measured by the GPC method, is preferably 400 or more and less than 10,000, more preferably 450 to 7,500, and even more preferably 500 to 5,000. Because such urethane (meth)acrylate or epoxy (meth)acrylate has an appropriate chain length, it is easy to impart flexibility to the sintered product and can further increase the bonding strength.

[0066] (Urethane (meth)acrylate) Urethane (meth)acrylates are compounds having a urethane bond and a (meth)acryloyl group, and are, for example, addition reaction products of an isocyanate compound, a hydroxyl group-containing (meth)acrylate, and any polyhydric alcohol.

[0067] Examples of isocyanate compounds include aliphatic isocyanates such as butane diisocyanate, pentane diisocyanate, and hexamethylene diisocyanate; alicyclic isocyanates such as cyclohexyl isocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate; and aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, and diphenylmethane diisocyanate.

[0068] Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2,3-hydroxypropyl (meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritol penta(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerin di(meth)acrylate, etc.

[0069] Examples of polyhydric alcohols include glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol, pentanediol, butanediol, hexanediol, and cyclohexanedimethanol; polyether polyols obtained by addition polymerization of these glycols with ethylene oxide or propylene oxide; polyester polyols obtained by reacting these glycols with carboxylic acids such as adipic acid or phthalic acid; and polycarbonate polyols.

[0070] Examples of urethane (meth)acrylates include Aronics M-1100, M-1200, M-1210, M-1310, M-1600, and M-1960 from Toagosei Co., Ltd., and R1204, R1211, R1213, R1217, R1218, R1301, R1302, R1303, R1304, R1306, R1308, R1901, and R1150 from Daiichi Kogyo Seiyaku Co., Ltd. This includes EBECRYL230, 270, 4858, 8402, 8804, 8807, 8803, 9260, 1290, 1290K, 5129, 4842, 8210, 210, 4827, 6700, 4450, 220 manufactured by Daicel-Scytec Corporation, and NK Oligo U-4HA, U-6HA, U-15HA, U-108A, U200AX, etc. manufactured by Shin-Nakamura Chemical Industry Co., Ltd.

[0071] The number of (meth)acryloyl groups (functional groups) contained in one molecule of urethane (meth)acrylate may be one or two or more.

[0072] (Epoxy (meth)acrylate) Epoxy (meth)acrylate can be an addition reaction product of an epoxy compound and (meth)acrylic acid or a carboxyl group-containing (meth)acrylic acid ester. The hydroxyl groups produced in the above addition reaction may be modified with fatty acids, etc. Also, some of the epoxy groups of the epoxy compound may remain.

[0073] Examples of epoxy compounds include aromatic epoxy compounds such as bisphenol-type epoxys, aliphatic epoxy compounds such as diglycidyl ethers of diols having 2 to 20 carbon atoms, and alicyclic epoxy compounds.

[0074] Examples of (meth)acrylic acid and carboxyl group-containing (meth)acrylic acid esters include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, mono(2-acryloyloxyethyl) succinate, mono(2-methacryloyloxyethyl) succinate, (meth)acrylic acid dimer, and caprolactam-modified (meth)acrylic acid.

[0075] Examples of epoxy (meth)acrylates include bisphenol-type epoxy acrylates, novolac-type epoxy acrylates, aliphatic-type epoxy acrylates, glycidyl ester-type acrylates, and modified versions thereof. Commercially available products include, for example, EBECRYL 3700, 3701, and 3708 (manufactured by Daicel Ornex).

[0076] The number of (meth)acryloyl groups (functional groups) contained in one molecule of epoxy (meth)acrylate may be one or two or more.

[0077] (Meth)acrylate having a hydroxyl group or an acidic group The (meth)acrylic compound may contain (meth)acrylate having a hydroxyl group or an acidic group. The (meth)acrylate having a hydroxyl group or an acidic group can facilitate the removal of surface protective agents from the surface of other copper particles during sintering, and can facilitate the formation of a dense sintered product.

[0078] Examples of acidic groups in (meth)acrylates containing hydroxyl or acidic groups include carboxyl groups and phosphate groups. Hydroxyl or acidic groups have a high affinity for amino groups and carboxyl groups of surface protectants, and are therefore easily substituted for these groups.

[0079] Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2,3-hydroxypropyl (meth)acrylate.

[0080] Examples of (meth)acrylates having an acidic group include (meth)acrylic acid, (meth)acrylic acid β-carboxyethyl (meth)acrylate, mono(2-acryloyloxyethyl) succinate, mono(2-methacryloyloxyethyl) succinate, (meth)acrylic acid dimer, and modified caprolactam (meth)acrylic acid.

[0081] The number of (meth)acryloyl groups (functional groups) contained in one molecule of a (meth)acrylate having a hydroxyl group or an acidic group may be one or two or more.

[0082] (Other (meth)acrylic compounds) The (meth)acrylic compound may include other (meth)acrylic compounds not listed above. The number of (meth)acryloyl groups contained in one molecule of the other (meth)acrylic compound may be one or two or more. In particular, from the viewpoint of further increasing the thermosetting rate, polyfunctional (meth)acrylic compounds are preferred, and 2-6 functional, preferably 2-3 functional (meth)acrylic compounds are more preferred. Furthermore, from the viewpoint of facilitating viscosity adjustment of the above composition, monofunctional (meth)acrylic compounds are preferred.

[0083] Examples of polyfunctional (meth)acrylic compounds include: Difunctional (meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetramethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate, trimethylolethane di(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerol di(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritol di(meth)acrylate, etc.; tetramethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolethaneethane tri(meth)acrylate, tetramethylolethane tri(meth)acrylate, tetramethylolethane tri(meth)acrylate, tetramethylolethane tri(meth This includes trifunctional (meth)acrylates such as toxic-modified trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, propylene oxide-modified glycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, and sorbitol tri(meth)acrylate; tetrafunctional or more (meth)acrylates such as dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, sorbitol tetra(meth)acrylate, sorbitol penta(meth)acrylate, and sorbitol hexa(meth)acrylate; pentaerythritol trialyl ether; and trialyl isocyanurate. In particular, it includes bifunctional or more (meth)acrylates.

[0084] Examples of monofunctional (meth)acrylic compounds include aliphatic alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and aromatic (meth)acrylates such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol (meth)acrylate.

[0085] (2) Epoxy compounds The curable compound may include, for example, a compound having an epoxy group (epoxy compound). There are no particular limitations on the epoxy compound; bisphenol A type epoxy resin, novolac type epoxy resin, cyclic aliphatic type epoxy resin, etc., can be used.

[0086] (3) Common matters The content of the curable compound is not particularly limited, but is, for example, 0.1 parts by mass to 5 parts by mass, preferably 0.3 parts by mass to 3 parts by mass, and more preferably 0.5 parts by mass to 2 parts by mass, per 100 parts by mass of the total mass of copper particles in the above composition. When the content of the curable compound is 0.1 parts by mass or more, the curability and bonding strength can be further enhanced. When the content of the curable compound is 5 parts by mass or less, the conductivity of the sintered product is less likely to be impaired.

[0087] 1-5-4. Polymerization Initiators If the above composition contains, for example, a (meth)acrylic compound, it is preferable to further contain a polymerization initiator. The polymerization initiator is preferably a radical polymerization initiator.

[0088] The radical polymerization initiator is not particularly limited, but may be a compound that generates radicals upon heating and initiates a chain polymerization reaction. Examples of such radical polymerization initiators include organic peroxides (e.g., 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanate, t-butyl peroxy-2-ethylhexanate, t-hexyl peroxy-2-ethruhexanate, 1,1-bis(t-butyl peroxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexyl peroxy)-3,3,5-trimethylcyclohexane, bis(4-t-butylcyclohexyl) peroxydicarbonate, etc.), azo compounds, benzoin compounds (e.g., benzoin, benzoin methyl ether, etc.), benzoin ether compounds, acetophenone compounds (e.g., diethoxyacetophenone, α-aminoalkylphenone, etc.), benzopinacol, and acylphosphine oxide compounds (e.g., bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, etc.).

[0089] The content of the radical polymerization initiator can be, for example, 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the (meth)acrylic compound.

[0090] 1-5-5. Hardener If the above composition includes, for example, an epoxy compound, it is preferable to further include a curing agent. The curing agent is not particularly limited, but may, for example, not generate radicals upon heating, but react nucleophilically through lone pairs of electrons or intramolecular anions. Examples of such curing agents include polyhydric amines, polyhydric phenols, organic acid hydrazide compounds, and the like.

[0091] 2. Method for manufacturing a composition for bonding materials The above composition can be obtained by a process of using formic acid-coated copper particles with an average particle diameter of 0.5 μm to 100 μm on which formic acid is attached to the surface, a complex or complex salt containing copper ions, formate ions, and a basic group-containing compound, and a solvent.

[0092] In the process of obtaining the above composition, existing copper particles with formic acid attached may be used, or prepared ones may be used. In addition, as other copper particles, copper particles with an average particle diameter of less than 0.5 μm (nano-sized copper particles) may also be used.

[0093] For example, when preparing formic acid-coated copper particles, the above composition can be obtained by 1) treating copper particles with an average particle diameter of 0.5 μm or more and 100 μm or less with formic acid to obtain formic acid-coated copper particles, and 2) using the formic acid-coated copper particles, a complex or complex salt containing copper ions, formate ions and basic group-containing compounds, copper particles with an average particle diameter of less than 0.5 μm, and a solvent to obtain the above composition.

[0094] 1) Process (Formic acid treatment process) Copper particles with an average particle diameter of 0.5 μm or more and 100 μm or less are treated with formic acid to obtain copper particles to which formic acid has adhered.

[0095] The copper particles used as raw materials may have a surface protective agent attached to them. By treating such copper particles with formic acid, at least a portion of the surface protective agent attached to the surface of the copper particles can be removed by the reducing action of formic acid. Multiple copper particles with different average particle diameters may be used as raw materials, and copper particles with an average particle diameter of 1 μm or more and 100 μm or less may be used, as well as copper particles with an average particle diameter of 0.5 μm or more and less than 1.0 μm.

[0096] Commercially available copper particles can be used as raw materials. Examples of commercially available products include CS-10 (average particle size 1.0 μm, treated with high-grade fatty acids) manufactured by Mitsui Mining & Smelting Co., Ltd., UCS-7 (average particle size 0.7 μm, treated with high-grade fatty acids) manufactured by DOWA Corporation, and CT-500 (average particle size 0.5 μm, treated with high-grade fatty acids) manufactured by Mitsui Mining & Smelting Co., Ltd.

[0097] Treatment with formic acid can be carried out, for example, by immersing the raw copper particles in formic acid. The amount of formic acid should be sufficient to immerse the raw copper particles. The immersion temperature is not particularly limited, but can be between 0°C and 40°C, and is preferably room temperature. The immersion time should be adjusted so that the amount of formic acid adhering is within the desired range, and at room temperature, for example, it can be between 30 minutes and 6 hours. After that, the copper particle slurry immersed in formic acid is filtered under reduced pressure, and the resulting filtrate can be crushed or otherwise processed as needed to remove the higher fatty acids of the protective film and obtain copper particles to which formic acid has adhered.

[0098] It is preferable that the amount of formic acid adhering to the copper particles is adjusted to fall within the range described above. In this process, the amount of formic acid adhering can be determined, for example, from the change in weight of the copper particles before and after the formic acid treatment using the following formula. Formic acid deposition amount (mass %) = (Weight of copper particles after formic acid treatment - Weight of copper particles before formic acid treatment) / (Weight of copper particles before formic acid treatment) × 100

[0099] The amount of formic acid deposited can be adjusted mainly by the immersion time in formic acid and whether or not washing is performed after the formic acid treatment. For example, increasing the immersion time in formic acid can increase the amount of formic acid deposited. In addition, by not washing the filtered material after formic acid treatment with alcohol or other substances, not heating it above the volatilization temperature of formic acid, and not separating it by centrifugation, a larger amount of formic acid can be left on the surface of the copper particles, thereby increasing the amount of formic acid deposited.

[0100] Furthermore, copper particles with an average particle diameter of 0.5 μm or more and 100 μm or less may include multiple copper particles with different average particle diameters. In this case, the formic acid treatment in this process may be performed by treating a mixture of copper particles with different average particle diameters with formic acid, or each copper particle with a different average particle diameter may be treated with formic acid separately and then mixed dry.

[0101] 2) Step (Composition preparation step) Next, the obtained formic acid-coated copper particles, copper particles with an average particle diameter of less than 0.5 μm, a copper complex or copper complex salt, and a solvent are used to obtain the above composition.

[0102] In this embodiment, the above composition can be obtained by mixing these components. The mixing procedure is not particularly limited; these components may be mixed simultaneously, or some may be mixed first and the remainder later. As copper particles with an average particle size of less than 0.5 μm, the commercially available products described above can be used.

[0103] The mixing method is not particularly limited, and mixing can be done using mixers such as homodispersers, homomixers, universal mixers, planetary mixers, kneaders, and three-roll mixers.

[0104] Furthermore, formic acid may also be used. That is, formic acid may be further included in the above composition. This allows the pH of the composition to be lowered to below a certain level. As a result, the surface of the copper particles is less likely to oxidize, and the sinterability can be further improved. The amount of formic acid added should be adjusted so that the pH of the composition falls within the above range. For example, it can be added so that the amount of free formic acid in the composition falls within the above range.

[0105] 3. Joint and method for manufacturing the same 3-1.Zygote Figure 1 is a schematic cross-sectional view showing the configuration of a joint according to one embodiment of the present invention.

[0106] As shown in Figure 1, the joint 10 comprises a first member 1, a second member 2, and a joining layer 3 that joins the first member 1 and the second member 2. The joining layer 3 is a sintered product (joining material) of the above composition.

[0107] The first member 1 has a base material 1a and a metal layer 1b. The second member 2 has a base material 2a and a metal layer 2b. The metal layer 1a and the metal layer 2b are arranged on the surfaces that are in contact with the bonding layer 3. Examples of metals that make up the metal layers 1b and 2b include copper, nickel, silver, gold, palladium, platinum, lead, tin, and cobalt.

[0108] Examples of such first member 1 and second member 2 include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, MOS-FETs (including power MOS-FETs), thyristors, logic circuits, sensors, analog integrated circuits, LEDs, semiconductor lasers, and oscillators; substrates for mounting semiconductor elements such as lead frames, metal-plated ceramic substrates (e.g., DBCs), and LED packages; power supply members such as copper ribbons, metal blocks, and terminals; heat sinks; and water cooling plates.

[0109] At least one of the first member 1 and the second member 2 may be a semiconductor element. Examples of semiconductor elements include power modules, oscillators, amplifiers, LED modules, etc., consisting of diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, Schottky diodes, fast recovery diodes, etc. Among these, power semiconductor elements such as power MOSFETs, IGBTs, and Schottky diodes are preferred.

[0110] 3-2. Method for manufacturing a jointed body The bonded body 10 can be manufactured by 1) preparing a laminate in which a first member, the composition, and the second member are stacked in that order, and 2) sintering the composition.

[0111] 1) Process of preparing the laminate First, a laminate is prepared in which the first member, the composition, and the second member are stacked in this order. For example, the composition can be applied to the first member, and then the second member can be placed on top to obtain the laminate.

[0112] The method for applying the above composition is not particularly limited and may include inkjet printing, dispenser printing, screen printing, gravure printing, tensil printing, stamp printing, etc. Among these, screen printing or dispenser printing is preferred from the viewpoint of excellent handling.

[0113] The coating thickness of the above composition is not particularly limited, but may be, for example, 1 μm to 1000 μm, or 10 μm to 500 μm.

[0114] The composition applied to the first member may be dried as needed, from the viewpoint of adjusting the fluidity during sintering.

[0115] 2) A step of sintering the above composition. Next, the laminate is heat-treated to sinter the above composition.

[0116] Heat treatment can be carried out by any method, such as using a hot plate, a dryer (e.g., a hot air dryer), or a heating furnace (e.g., a hot air heating furnace, a firing furnace).

[0117] The gas atmosphere during sintering may be a reducing atmosphere such as hydrogen or formic acid, an inert gas atmosphere such as nitrogen or argon, or a vacuum, and preferably an inert gas atmosphere such as nitrogen or argon. The oxygen concentration in the inert gas atmosphere is preferably 50 ppm or less, and more preferably 20 ppm or less.

[0118] The maximum temperature reached during the heat treatment may be between 150°C and 400°C, between 160°C and 300°C, or between 170°C and 200°C, from the viewpoint of further reducing thermal damage to the components.

[0119] The holding time at the highest temperature achievable may be between 1 minute and 60 minutes, between 1 minute and 40 minutes, or between 1 minute and 30 minutes, from the viewpoint of further volatilizing the solvent.

[0120] Sintering may be carried out under no pressure or under pressure. When pressurized, the applied pressure is preferably between 0.001 MPa and 10 MPa, and more preferably between 0.01 MPa and 5 MPa. By joining under such low pressure or no pressure, damage to the semiconductor device can be further reduced. [Examples]

[0121] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0122] 1.Material 1-1. Copper particles (1) Raw materials • Commercially available copper particles 1 (average particle size 1.0 μm, treated with high-grade fatty acids, micron size) • Commercially available copper particles 2 (average particle size 0.5 μm, treated with high-grade fatty acids, submicron size) • Commercially available copper particles 3 (average particle size 0.7 μm, treated with high-grade fatty acids, submicron size) • Commercially available copper particles 4 (average particle size 150 nm, treated with high-grade fatty acids, nano-sized)

[0123] (2) Preparation of formic acid-coated copper particles and TG-TDA measurement (removability of surface protective agent) (Preparation of formic acid-coated copper particles A-1) 30 g of copper particles (average particle size 1.0 μm, micron-sized copper particles) were weighed into a 50 mL volume resin centrifuge tube, 25 mL of formic acid (manufactured by Fujifilm / Wako Pure Chemical Industries, Ltd.) was added, the tube was sealed, and the mixture was stirred using a vortex mixer. The tube was then left at room temperature for 1 hour.

[0124] The formic acid-soaked copper particle slurry was filtered under reduced pressure using filter paper (Kiriyama Funnel Co., Ltd. 5C) until all liquid remained. The resulting filtrate was then transferred to a tray and crushed until it became a powder. This yielded formic acid-coated copper particles A-1.

[0125] (Preparation of formic acid-coated copper particles A-2) Formic acid-coated copper particles 2 were obtained in the same manner as above, except that 30 g of copper particles 2 (average particle size 0.5 μm, submicron-sized copper particles) were used instead of copper particles 1.

[0126] (4) TG-DTA measurement For each of copper particles 1 and 2, the exothermic behavior and weight change were measured before and after formic acid treatment using TG-DTA (TA-7000, manufactured by Seiko Instruments), with a sample volume of 12 mg, under a nitrogen atmosphere and a heating rate of 10°C / min, when the temperature was raised from 30°C to 300°C. The exothermic behavior and weight change before and after treatment of copper particle 1 are shown in Figures 2A and 2B, and the exothermic behavior and weight change before and after treatment of copper particle 2 are shown in Figures 3A and 3B.

[0127] As shown in Figures 2A and 3A, the exothermic behavior of TG-DTA revealed an exothermic peak of 240-250°C around the higher fatty acid layer, which is a protective layer for commercially available copper particles, before treatment. However, this peak disappeared after treatment. Furthermore, a weight change was observed around 240-250°C (see Figures 2B and 3B). This confirmed that the surface protective layer (higher fatty acid layer) had been removed.

[0128] 1-2.Copper complex <Preparation of copper complexes> Copper formate hydrate was placed in a metal tray and dried on a hot plate heated to 110°C to remove the hydrate. 15 g of the dried copper formate was dissolved in 25.7 g of methanol, and then 28.8 g of 3-(diethylamino)-1,2-propanediol was added and the reaction was carried out at room temperature for 6 hours. The resulting solution was de-methylated using an evaporator, and dried overnight in a vacuum dryer to obtain a copper complex having the structure shown below. [ka] L1, L2 = 3-(diethylamino)-1,2-propanediol

[0129] 1-3. Solvent • Polyethylene glycol (PEG200 manufactured by Fujifilm and Wako Pure Chemical Industries)

[0130] 1-4. Binder (Preparation of binder composition) A binder composition was prepared by mixing 23.3% by mass of urethane acrylate oligomer (Aronics M-1960, manufactured by Toagosei Co., Ltd., a monofunctional curable compound), 35.0% by mass of 4-hydroxybutyl acrylate (manufactured by Nippon Chemical Corporation, a monofunctional curable compound), 35.0% by mass of trimethylolpropane triacrylate (Light Acrylate TMP-A, manufactured by Kyoeisha Chemical Co., Ltd., a trifunctional curable compound), 2.1% by mass of Ominirad 819 (manufactured by IGM, a radical polymerization initiator), 4.2% by mass of Ominirad 907 (manufactured by IGM, a radical polymerization initiator), and 0.5% by mass of BYK-111 (manufactured by BYK, a polymer dispersant).

[0131] 2. Preparation of compositions for bonding materials 2-1. Preparation of the composition [Preparation of Composition 1] (Formic acid treatment of copper particles) 30g of copper particles 1 (average particle size 1.0 μm, micron-sized copper particles) and 40g of copper particles 2 (average particle size 0.5 μm, submicron-sized copper particles) were weighed into 50 mL volume resin centrifuge tubes, 25 mL of formic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, the tubes were sealed, and the mixture was stirred using a vortex mixer. The tubes were then left at room temperature for 1 hour.

[0132] (Removal of excess formic acid) The formic acid-soaked copper particle slurry was filtered under reduced pressure using filter paper (Kiriyama Funnel 5C) until all liquid remained. The resulting filtrate was then transferred to a tray and crushed until it became a powder. This yielded a mixture of formic acid-coated copper particles A-1 and A-2.

[0133] (Preparation of composition) 30.0 g of copper particles 4 (average particle size 150 nm, nano-sized copper particles), 7.4 g of polyethylene glycol 200 (manufactured by Fujifilm and Wako Pure Chemical Industries), 1.0 g of the above-mentioned binder composition, and 4.8 g of the above-mentioned copper complex were mixed. After adding the above-prepared mixture of formic acid-coated copper particles to this, the mixture was kneaded twice at 2000 rpm for 10 seconds each time using a stirring device (Awatori Rentaro, manufactured by THNKY).

[0134] The obtained composition was kneaded using a small TRM (AIMEX, three-roll mill), and then kneaded again using an agitator (THNKY, Awatori Rentaro) under the same conditions as above to obtain the final composition.

[0135] [Preparation of Composition 2] In preparing the composition, the composition was prepared in the same manner as in Example 1, except that the amount of formic acid attached to the formic acid-attached copper particles and the amount of copper complex were changed as shown in Table 1.

[0136] [Preparation of Compositions 3 and 4] In preparing the compositions, the compositions were prepared in the same manner as compositions 1 and 2, except that they contained the amount of formic acid (manufactured by Fujifilm Corporation) shown in Table 1.

[0137] [Preparation of Composition 5] (Formic acid treatment of copper particles) 30g of copper particles 1 (average particle size 1.0 μm, micron-sized copper particles) and 40g of copper particles 3 (average particle size 0.7 μm, submicron-sized copper particles) were weighed into 50 mL volume resin centrifuge tubes, 25 mL of formic acid (manufactured by Fujifilm / Wako Pure Chemical Industries, Ltd.) was added, the tubes were sealed, and the mixture was stirred using a vortex mixer. The tubes were then left at room temperature for 1 hour.

[0138] (Centrifugal separation and air drying) Next, the slurry after formic acid treatment was centrifuged at 20,000 rpm for 5 minutes, and the supernatant was removed. The resulting solid was dried under atmospheric pressure to obtain a mixture of treated copper particles 1 (copper particles (copper particles B-1) and treated copper particles 3 (copper particles B-2) (without formic acid coating).

[0139] (Preparation of composition) In preparing the composition, the mixture of copper particles B-1 and B-2 prepared above was used instead of the mixture of formic acid-coated copper particles A-1 and A-2, except that the composition was prepared in the same manner as composition 1.

[0140] [Preparation of Composition 6] In preparing the composition, a mixture of untreated copper particles 1 and copper particles 2 was used instead of a mixture of formic acid-coated copper particles, and the amount of solvent was changed as shown in Table 1, except that the composition was prepared in the same manner as composition 1.

[0141] 2-2. Evaluation (1) Amount of formic acid attached The weight of the copper particle mixture before and after formic acid treatment was measured, and the amount of formic acid deposited was calculated based on the following formula. Formic acid deposition amount (mass %) = (Weight of copper particle mixture after formic acid treatment - Weight of copper particle mixture before formic acid treatment) / (Weight of copper particle mixture before formic acid treatment) × 100

[0142] (2) Molar ratio of basic group-containing compound to formic acid The amount of the basic group-containing compound was calculated from the amount of copper complex used. The amount of formic acid was calculated as the sum of 1) the amount of formic acid attached, 2) the formic acid ions contained in the copper complex, and 3) the amount of formic acid added if it was added during the preparation of the composition. Then, the amount of the basic group-containing compound divided by the amount of formic acid was calculated.

[0143] (3) pH measurement The above-prepared composition was diluted with pure water to a concentration of 10% by mass to prepare a pure water suspension. The solids were centrifuged using a centrifuge (2000 rpm, 5 min), and the pH of the supernatant was measured at 20°C using a pH meter (AS ONE AS700).

[0144] (4) Measurement of joint strength The above-prepared composition was coated onto two types of copper substrates, a QFN (Quad Flat Non-leaded package) substrate and a TO-247 substrate, using a 5mm square SUS screen with a thickness of 80μm (coating thickness 80μm), and then a Cu-plated Si chip (thickness 220μm) was mounted. Subsequently, the materials were bonded using an inert oven (DN611I, manufactured by Yamato Scientific Co., Ltd., oxygen concentration 50 ppm or less) or a press (MKH10-2520, manufactured by Mikado Kiki Co., Ltd.) by heating and pressurizing at the temperatures and times shown in Table 1. After bonding, the bond strength of the resulting bonded material was measured using a bond tester (Nordson 4000PLUS) under the following conditions: test type: destructive test, test height: 100 μm, descent speed: 1.5 mm / s, test speed: 100 μm / s.

[0145] (5) SEM observation The cross-section of the cured product of composition 3 was observed using a scanning electron microscope (SEM) JEOL JFM-7100 at an acceleration voltage of 5.0 kV and a magnification of 5000x.

[0146] (5) Results and Discussion Table 1 shows the evaluation results for compositions 1 to 6. A "-" in the table indicates that measurement was not performed. Figure 4 is an SEM image of the cross-section of the cured product of composition 3.

[0147] [Table 1]

[0148] As shown in Table 1, composition 5 (Comparative Example 1) had a molar ratio of basic groups to carboxylic acid groups exceeding 0.5, and therefore could not be bonded under low pressure and short time conditions. It can also be seen that the copper particles of composition 5 had very little formic acid attached. This is thought to be because, in the centrifugation supernatant removal method and the air drying method, not only is most of the formic acid removed, but the high-boiling-point surface protective agent that remains in the precipitate and was detached during air drying replaces the formic acid attached to the surface and returns to the surface of the copper particles. Furthermore, composition 6 (Comparative Example 2), which did not contain formic acid-treated copper particles, also had a molar ratio of basic groups to carboxylic acid groups of 1.0, and was unable to bond under any conditions.

[0149] In contrast, compositions 1 to 4 (Examples), which contain formic acid-coated copper particles and have a molar ratio of basic groups to carboxylic acid groups of less than 0.5, were found to exhibit higher bonding strength than composition 5 (Comparative Example).

[0150] In particular, it can be seen that the bonding strength is further increased by moderately increasing the copper complex content (comparison of composition 3 and 4). Furthermore, it can be seen that the bonding strength can be further increased, especially when pressed at low pressures (5 MPa or less) by further including free formic acid (comparison of composition 1 and 3, comparison of composition 2 and 4).

[0151] Furthermore, as shown in Figure 4, the cured product of composition 3 contains micron particles with a particle diameter of approximately 1 μm, submicron particles with a particle diameter of approximately 0.5 μm, and nanoparticles that are smaller than 0.5 μm in particle diameter. [Industrial applicability]

[0152] According to the present invention, it is possible to provide a bonding material composition having sufficiently high bonding strength and a method for producing the same. [Explanation of Symbols]

[0153] 1. First member 1a Base material 1b metal layer 2. Second member 2a Base material 2b metal layer 3 Bonding layer 10 zygote

Claims

1. Formic acid-coated copper particles having formic acid attached to their surface and having an average particle diameter of 0.5 μm or more and 100 μm or less, A complex or complex salt containing copper ions, formate ions, and a basic group-containing compound, Solvent and, A composition for bonding materials containing, The molar ratio of the basic group-containing compound to the formic acid in the entire bonding material composition (amount of substance of the basic group-containing compound / amount of substance of the formic acid) is less than 0.

5. Composition for bonding materials.

2. The hydrogen ion concentration (pH) is 5.0 or less. The bonding material composition according to claim 1.

3. Further containing liberated formic acid, The bonding material composition according to claim 1.

4. The basic group-containing compound includes an alkanolamine. The bonding material composition according to claim 1.

5. The alkanolamine comprises 3-(diethylamino)-1,2-propanediol or 3-(dimethylamino)-1,2-propanediol. The bonding material composition according to claim 4.

6. Further containing copper particles with an average particle diameter of less than 0.5 μm, The bonding material composition according to claim 1.

7. The formic-coated copper particles Copper particles A-1 having an average particle diameter of 1.0 μm or more and 100 μm or less, Copper particles A-2, having an average particle diameter of 0.5 μm or more and less than 1.0 μm, including, The bonding material composition according to claim 1 or 6.

8. When the formic-coated copper particles are subjected to differential thermal analysis (TG-DTA analysis), no exothermic peak is detected in the 180-300°C range, which is believed to be due to the surface protective agent. The bonding material composition according to claim 1.

9. Further containing a curable compound, The bonding material composition according to claim 1.

10. The curable compound includes a (meth)acrylic compound and a polymerization initiator. The bonding material composition according to claim 9.

11. The curable compound includes an epoxy compound and a curing agent. The bonding material composition according to claim 9.

12. The solvent includes a polyalkylene glycol-based solvent. The bonding material composition according to claim 1.

13. A bonding material composition obtained by sintering the bonding material composition described in claim 1, Bonding material.

14. The process includes obtaining a bonding material composition using formic acid-coated copper particles with an average particle size of 0.5 μm to 100 μm and formic acid adhering to their surface, a complex or complex salt containing copper ions, formate ions, and a basic group-containing compound, and a solvent. A method for producing a composition for bonding materials.

15. The formic acid-coated copper particles are copper particles with an average particle diameter of 0.5 μm or more and 100 μm or less that have been treated with formic acid. A method for producing the bonding material composition according to claim 14.

16. The formic acid-coated copper particles include copper particles A-1 having an average particle diameter of 1.0 μm or more and 100 μm or less, and copper particles A-2 having an average particle diameter of 0.5 μm or more and less than 1.0 μm. A method for producing the bonding material composition according to claim 14.

17. In the step of obtaining the aforementioned bonding material composition, copper particles with an average particle diameter of less than 0.5 μm are further used. A method for producing the bonding material composition according to claim 14.

18. In the step of obtaining the aforementioned bonding material composition, formic acid is further used. A method for producing the bonding material composition according to claim 14.

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