Metal paste for joining, joined body, and method for manufacturing the joined body

Abstract

A bonding metal paste containing metal particles, a reducing agent, and a dispersion medium, wherein the yield stress measured by the following procedure is 2.0 MPa or less. Procedure for measuring yield stress: (1) Apply bonding metal paste to the copper substrate and dry at 90°C for 30 minutes to form a metal particle-containing layer with a thickness of 3 mm × 3 mm × 0.05 mm. (2) Using a die-shear type testing machine, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool under the conditions of a heating temperature of 90°C, a speed of 100 μm / s, and a distance of 0.02 mm between the tip of the tool and the copper substrate, to obtain a stress (MPa)-strain (%) curve. (3) The yield stress (MPa) is defined as the stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2%.

Description

[Technical Field]

[0001] This disclosure relates to a metal paste for joining, a joined body, and a method for manufacturing a joined body. [Background technology]

[0002] When manufacturing semiconductor devices, various bonding materials are used to form a bonding layer that joins semiconductor elements to lead frames and other support members. For example, high-lead solder has been used to form the bonding layer for power semiconductors, LSIs, etc., that operate at temperatures up to about 150°C. In recent years, with the increasing capacitance and space-saving of semiconductor elements, there has been a growing demand for high-temperature operation of semiconductors at 175°C or higher. To ensure the operational stability of such semiconductor devices, the bonding layer needs to have connection reliability and high thermal conductivity. However, in the temperature range above 175°C, conventionally used high-lead solder and lead-free solder bonding layers have connection reliability issues and insufficient thermal conductivity (30Wm²). -1 K -1 Therefore, alternative materials are needed.

[0003] One proposed joining method using alternative materials is one that utilizes the low-temperature sintering phenomenon of copper nanoparticles. The sintered copper layer formed by this method has excellent mechanical strength, provides reliable connections at high temperatures, and keeps material costs low. As such a sintered copper layer, a sintered copper layer obtained by reducing and sintering copper oxide particles has been proposed (see Patent Document 1 and Non-Patent Document 1 below). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5006081 [Non-patent literature]

[0005] [Non-Patent Document 1] T. Morita, Y. Yasuda: Materials Transactions, 56(6), 2015, 878-882 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Power modules and the like, in which a support member and a semiconductor element are joined via a sintered copper layer, are typically manufactured through the following process: First, a copper paste is prepared by dispersing copper particles in a liquid dispersion medium, and this copper paste is applied to the support member to form a copper paste coating. Next, the semiconductor element is placed on the copper particle-containing layer formed by drying the coating. The resulting laminate is then transported to a sintering furnace or the like, and the copper particle-containing layer is sintered to join the support member and the semiconductor element.

[0007] Conventional copper pastes, once dry, do not easily acquire the property (hereinafter also referred to as tackiness) necessary to temporarily fix semiconductor elements. If semiconductor elements fall off during the transport of the laminated structure, it leads to a decrease in yield in the manufacturing of bonded components such as power modules.

[0008] Therefore, the present disclosure aims to provide a metal paste for joining that can sufficiently suppress the detachment of members in the manufacture of a joint using a metal paste, a joint using the metal paste for joining, and a method for manufacturing the joint. [Means for solving the problem]

[0009] This disclosure relates to the following [1] to [9].

[0010] [1] It contains metal particles, a reducing agent, and a dispersion medium. A bonding metal paste having a yield stress of 2.0 MPa or less, as measured by the following procedure. Procedure for measuring yield stress: (1) Apply the bonding metal paste onto the copper substrate and dry it at 90 °C for 30 minutes to form a metal particle-containing layer with a thickness of 3 mm × 3 mm × 0.05 mm. (2) Using a die shear tester, push the metal particle-containing layer horizontally with a tool having a width of 4 mm under the conditions of a heating temperature of 90 °C, a speed of 100 μm / s, and a distance of 0.02 mm between the tip of the tool and the copper substrate to obtain a stress (MPa)-strain (%) curve. (3) Define the stress when the permanent strain in the stress (MPa)-strain (%) curve reaches 0.2% as the yield stress (MPa). [2] The metal particles have a carboxylic acid compound with a molecular weight of 300 g / mol or less or an alcohol compound with a molecular weight of 300 g / mol or less on the surface, the reducing agent is a polyhydric alcohol, and the bonding metal paste according to [1], further containing a second fatty acid having 18 or less carbon atoms. [3] The content of the second fatty acid is 5% by mass or less based on the total amount of the bonding metal paste, the bonding metal paste according to [2]. [4] The second fatty acid has a weight loss rate of 2% by mass or less when heated at 90 °C for 30 minutes in a nitrogen atmosphere, the bonding metal paste according to [2] or [3]. [5] The bonding metal paste according to any one of [1] to [4], containing a gelling agent. [6] A joined body including a first member, a second member, and a joint portion joining these, where the joint portion includes a sintered body of the bonding metal paste according to any one of [1] to [5], the joined body. [7] A first step of applying the bonding metal paste according to any one of [1] to [5] onto the first member to form a coating film of the bonding metal paste, a second step of drying the coating film to form a metal particle-containing layer, a third step of disposing the second member on the metal particle-containing layer to obtain a laminate A fourth step of sintering the metal particle-containing layer of the laminate; A method for manufacturing a joined body, comprising: [8] In the third step, the second member is pressure-bonded onto the metal particle-containing layer heated to 90°C or higher under a pressure-bonding pressure of 0.5 to 2 MPa and a pressure-bonding time of 3 seconds or less. The method for manufacturing a joined body according to [7]. [9] A first step of applying a joining metal paste onto a first member to form a coating film of the joining metal paste; A second step of drying the coating film to form a metal particle-containing layer; A third step of obtaining a laminate by pressure-bonding a second member onto the metal particle-containing layer heated to T1°C or higher under a pressure of Y1 MPa or higher; A fourth step of sintering the metal particle-containing layer of the laminate; Comprising: The joining metal paste contains metal particles, a reducing agent, and a dispersion medium; A method for manufacturing a joined body, wherein a yield stress X1 of the joining metal paste measured by the following procedure is 2.0 MPa or less, and X1 / Y1 is 4.0 or less. Procedure for measuring the yield stress: (1) Apply the joining metal paste onto a copper substrate and dry it at 90°C for 30 minutes to form a metal particle-containing layer having a thickness of 3 mm × 3 mm × 0.05 mm. (2) Using a die shear type testing machine, horizontally push the metal particle-containing layer with a tool having a width of 4 mm under the conditions of a heating temperature of T1°C, a speed of 100 μm / s, and a distance of 0.02 mm between the tip of the tool and the copper substrate to obtain a stress (MPa)-strain (%) curve. (3) Define the stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2% as the yield stress X1 (MPa).

Advantages of the Invention

[0011] According to this disclosure, it is possible to provide a metal paste for joining that can sufficiently suppress the detachment of members in the manufacture of a joint using a metal paste, a joint using the metal paste for joining, and a method for manufacturing the joint. [Brief explanation of the drawing]

[0012] [Figure 1] This is a diagram illustrating the definition of yield stress. [Figure 2] This is a schematic diagram illustrating the method for measuring yield stress. [Figure 3] This is a schematic diagram illustrating the method for measuring tack strength. [Modes for carrying out the invention]

[0013] The following describes in detail the embodiments for implementing this disclosure (hereinafter referred to as "this embodiment"). This disclosure is not limited to the following embodiments.

[0014] <Metal paste for bonding> The bonding metal paste of this embodiment contains metal particles, a reducing agent, and a dispersion medium. The bonding metal paste has a yield strength of 2.0 MPa or less, as measured by the following procedure.

[0015] [Procedure for measuring yield stress] (1) Apply bonding metal paste to the copper substrate and dry at 90°C for 30 minutes to form a metal particle-containing layer with a thickness of 3 mm × 3 mm × 0.05 mm. (2) Using a die-shear type testing machine, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool under the conditions of a heating temperature of 90°C, a speed of 100 μm / s, and a distance of 0.02 mm between the tip of the tool and the copper substrate, and a stress (MPa)-strain (%) curve is obtained. (3) The yield stress (MPa) is defined as the stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2%.

[0016] When a metal particle-containing layer is pressed with a tool, the layer undergoes elastic deformation in proportion to the magnitude of the external force, and plastic deformation occurs when the stress exceeds a certain level. Elastic deformation refers to deformation that returns to its original shape when the external force is removed, while plastic deformation refers to deformation that does not return to its original shape when the external force is removed. The stress at which the transition from elastic to plastic deformation begins is called the yield point. Before the yield point, there is an almost proportional relationship (linear correlation) between the magnitude of the external force and the degree of deformation of the metal particle-containing layer, while after the yield point, there is a nonlinear correlation between the magnitude of the stress and the degree of deformation of the metal particle-containing layer.

[0017] Figure 1 shows a stress (MPa)-strain (%) curve to illustrate the definition of yield stress. As shown in Figure 1, when a metal particle-containing layer is pushed horizontally with a tool, the strain (%) of the metal particle-containing layer increases. In this disclosure, the strain (%) of the metal particle-containing layer refers to the ratio of the tool's travel distance (100 × tool travel distance (mm) / 3 mm) to the length of the metal particle-containing layer being measured in the direction of tool movement (3 mm). In this disclosure, the yield stress (MPa) is defined as the stress X (MPa) when the permanent strain reaches 0.2%.

[0018] The stress when the permanent strain reaches 0.2% is the approximate straight line (R) of the slope of the rising edge of the stress (MPa)-strain (%) curve shown in Figure 1. 2 The value of >95% can be determined by drawing a line that passes through the point where the permanent strain (%) on the horizontal axis is 0.2%, and finding the intersection point of the approximate line and the curve. Specifically, using the least squares method, R 2 An approximate straight line is found for the rise of the stress (MPa)-strain (%) curve so that the coefficient of determination is 95% or higher. When this approximate straight line is translated (offset) so that it passes through a point where the tool's movement distance is 0.002 × L0, where L0 is the length in the direction the tool moves in the metal particle-containing layer before measurement (L0 = 3 mm in this embodiment), the stress at which the permanent strain reaches 0.2% can be determined from the intersection point of the approximate straight line and the original curve.

[0019] The above-mentioned metal paste for joining can sufficiently suppress the detachment of members in the manufacturing of joined bodies using the metal paste. The inventors speculate that the reason for this effect is as follows: Since the metal particle-containing layer formed from the metal paste having the above-mentioned specific yield stress is capable of plastic deformation, the inventors speculate that by setting the temperature and pressure when placing the members to predetermined conditions (for example, the yield stress being 4.0 times or less of the pressure at the temperature at which the yield stress is measured) and pressing them together for a predetermined time, it is possible to suppress the formation of voids between the members to be joined and the metal particle-containing layer, thereby improving the tack strength.

[0020] By using the above-mentioned metal bonding paste, sufficient tack strength can be achieved even when mounting a component to a metal particle-containing layer under mild conditions that do not place stress on the components to be bonded (for example, bonding conditions of 90°C, 0.5-2 MPa pressure, and a bonding time of 3 seconds or less).

[0021] The bonding metal paste may have a yield strength of 0.5 to 2.0 MPa, 0.5 to 1.9 MPa, or 0.5 to 1.8 MPa.

[0022] The following describes in detail each component used in the bonding metal paste of this embodiment.

[0023] (metal particles) Examples of metal particles include copper particles, silver particles, gold particles, platinum group particles (platinum, palladium, rhodium, iridium), magnetic particles (iron, cobalt, nickel), light metal particles (aluminum, beryllium, magnesium, titanium, alkali metals, alkaline earth metals), low melting point particles (tin, indium, lead, germanium), other common transition metal particles, and metalloid particles, as well as alloy particles formed by combining two or more of these.

[0024] The alloy particles may also be copper alloy particles formed from an alloy of copper and a metal other than copper. Examples of copper alloy particles include copper-gold alloy particles, copper-silver alloy particles, copper-zinc alloy particles, and copper-tin alloy particles.

[0025] The bonding metal paste of this embodiment may contain copper compound particles as metal particles. The copper compound particles include monovalent or divalent copper compounds. Examples of monovalent or divalent copper compounds include cuprous oxide, cupric oxide, cuprous hydroxide, cupric hydroxide, cuprous carbonate, cupric carbonate, copper nitride, and copper(I) phosphide. From the viewpoint of price and availability as particles, the copper compound particles may include at least one compound selected from the group consisting of cuprous oxide, cupric oxide, cuprous hydroxide, cupric hydroxide, and cupric carbonate.

[0026] The metal particles may be sinterable in a temperature range of 200°C to 300°C.

[0027] The metal particles may have carboxylic acid compounds or alcohol compounds with a molecular weight of 300 g / mol or less on their surface.

[0028] Carboxylic acid compounds with a molecular weight of 300 g / mol or less are compounds that have at least one carboxyl group in their molecule and have a molecular weight of 300 g / mol or less. Examples of carboxylic acid compounds with a molecular weight of 300 g / mol or less include fatty acids (hereinafter sometimes referred to as first fatty acids) with 10 to 18 carbon atoms (including the carbon atoms of the carboxyl group). Examples of the first fatty acid include capric acid (decanoic acid), methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanoic acid, tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid, methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyl tetra Examples of saturated fatty acids include radicanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, and nonylcyclohexanecarboxylic acid; and unsaturated fatty acids include octenoic acid, nonenic acid, methylnonenic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sapienic acid, oleic acid, vaccenoic acid, linoleic acid, linolenic acid, and linolenic acid.

[0029] The carboxylic acid compound with a molecular weight of 300 g / mol or less may be a carboxylic acid with a molecular weight of 210 g / mol or less, from the viewpoint of dispersion stability of metal particles and oxidation prevention, and may also be lauric acid or decanoic acid, from the viewpoint of exhibiting low-temperature sinterability due to low-temperature decomposition.

[0030] Carboxylic acid compounds with a molecular weight of 300 g / mol or less may be used individually or in combination of two or more.

[0031] Examples of alcohol compounds with a molecular weight of 300 g / mol or less include glycols such as triethylene glycol and diethylene glycol, and α-terpineol.

[0032] The metal paste may contain copper particles as metal particles. In this case, the metal oxide film on the particle surface is easily reduced by the reducing solvent used in the paste, making sintering possible even under mild conditions of low temperature (below 300°C) and low pressure (below 10 MPa).

[0033] Examples of copper particles include submicro copper particles and micro copper particles. Copper particles refer to particles that contain copper as the main component, for example, particles in which the copper content is 80% by mass or more. The copper content in copper particles may be 85% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 100% by mass.

[0034] The submicro copper particles may be copper particles that are sinterable in a temperature range of 200°C to 380°C. Examples of submicro copper particles include those containing copper particles with a particle size of 0.05 μm to 0.8 μm. For example, copper particles with a volume average particle size of 0.05 μm to 0.8 μm can be used. If the volume average particle size of the submicro copper particles is 0.05 μm or more, it is easier to obtain effects such as suppression of the synthesis cost of the submicro copper particles, good dispersibility, and suppression of the amount of organic protective agent used. If the volume average particle size of the submicro copper particles is 0.8 μm or less, it is easier to obtain the effect of excellent sinterability of the submicro copper particles. From the viewpoint of achieving the above effects even more, the volume average particle size of the submicro copper particles may be 0.6 μm or less, 0.5 μm or less, or 0.4 μm or less. In addition, the volume average particle size of the submicro copper particles may be 0.05 μm or more, 0.07 μm or more, or 0.1 μm or more. The volume-average particle size of the submicro copper particles may be, for example, 0.05 μm or more and 0.5 μm or less, 0.07 μm or more and 0.8 μm or less, 0.08 μm or more and 0.8 μm or less, 0.08 μm or more and 0.6 μm or less, 0.1 μm or more and 0.5 μm or less, or 0.2 μm or more and 0.45 μm or less.

[0035] In this disclosure, volume-average particle size refers to the 50% volume-average particle size. To determine the volume-average particle size of metal particles, the raw material metal particles, or dried copper particles obtained by removing volatile components from a metal paste, can be dispersed in a dispersion medium using a dispersant, and then measured using a light scattering particle size distribution analyzer (for example, a Shimadzu nanoparticle size distribution analyzer (SALD-7500nano, manufactured by Shimadzu Corporation)). When using a light scattering particle size distribution analyzer, hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, water, etc., can be used as the dispersion medium.

[0036] The submicro copper particle content may be 20% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 90% by mass or less, 85% by mass or less, 80% by mass or less, 20% by mass or more and 90% by mass or less, 30% by mass or more and 90% by mass or less, 35% by mass or more and 85% by mass or less, 40% by mass or more and 80% by mass or less, or 60% by mass or more and 80% by mass or less, based on the total mass of the metal particles. If the submicro copper particle content is within the above range, it becomes easier to ensure the bonding strength of the joint, and if the members to be joined are semiconductor elements, the semiconductor device tends to exhibit good die-shear strength and connection reliability.

[0037] The sub-micro copper particle content may be 20% by mass or more and 90% by mass or less, based on the total mass of the copper particles. If the sub-micro copper particle content is 20% by mass or more, when used in combination with micro copper particles such as flake-shaped micro copper particles, the spaces between the copper particles can be sufficiently filled, making it easier to ensure the bonding strength of the joint, and if the members to be joined are semiconductor elements, the semiconductor device tends to exhibit good die-shear strength and connection reliability. If the sub-micro copper particle content is 90% by mass or less, the in-plane volume shrinkage (XY direction) of the sintered layer when sintered without pressure or under pressure can be sufficiently suppressed, making it easier to ensure the bonding strength of the joint, and if the members to be joined are semiconductor elements, the semiconductor device tends to exhibit good die-shear strength and connection reliability. From the perspective of achieving the above effects even more effectively, the submicro copper particle content may be 30% by mass or more, 35% by mass or more, 40% by mass or more, 85% by mass or less, 83% by mass or less, 80% by mass or less, 30% by mass or more and 85% by mass or less, 35% by mass or more and 85% by mass or less, 40% by mass or more and 80% by mass or less, or 60% by mass or more and 80% by mass or less, based on the total mass of copper particles.

[0038] The shape of the sub-micro copper particles is not particularly limited. Examples of the shape of the sub-micro copper particles include spherical, massive, needle-like, flaky, substantially spherical, and aggregates thereof. From the viewpoints of dispersibility and filling property, the shape of the sub-micro copper particles may be spherical, substantially spherical, or flaky, and from the viewpoints of flammability, dispersibility, miscibility with flaky micro-particles, etc., it may be spherical or substantially spherical. In the present disclosure, "flaky" includes flat plate-like shapes such as plate-like and scaly shapes.

[0039] From the viewpoints of dispersibility, filling property, and miscibility with flaky micro-particles, the aspect ratio of the sub-micro copper particles may be 5 or less, may be 4 or less, or may be 3 or less. In the present disclosure, "aspect ratio" refers to the ratio of the long side (major axis) / thickness of the particle. The measurement of the long side (major axis) and thickness of the particle can be obtained, for example, from the SEM image of the particle.

[0040] The sub-micro copper particles may be treated with a surface treatment agent containing a carboxylic acid compound having a molecular weight of 300 g / mol or less or an alcohol compound having a molecular weight of 300 g / mol or less as described above.

[0041] The treatment amount of the surface treatment agent may be an amount that adheres to one to three molecular layers on the surface of the sub-micro copper particles. This amount can be calculated from the number of molecular layers (n) adhered to the surface of the sub-micro copper particles, the specific surface area (A p )(unit: m 2 / g) of the sub-micro copper particles, the molecular weight (M s )(unit: g / mol) of the surface treatment agent, the minimum covering area (S S )(unit: m 2 / piece) of the surface treatment agent, and Avogadro's number (N A )(6.02×10 23 pieces). Specifically, the treatment amount of the surface treatment agent is calculated according to the formula of the treatment amount (mass%) of the surface treatment agent = {(n·A p ·M s ) / (S S ·N A +n·A p ·M s )}×100%.

[0042] The specific surface area of ​​submicro copper particles can be calculated by measuring the specific surface area of ​​dried submicro copper particles using the BET specific surface area measurement method. The minimum coating area of ​​a surface treatment agent is 2.05 × 10⁻⁶ when the surface treatment agent is a linear saturated fatty acid. -19 m 2 It is / 1 molecule. For other surface treatment agents, it can be measured, for example, by calculation from a molecular model, or by the method described in "Chemistry and Education" (Katsuhiro Ueeda, Sumio Inafuku, Iwao Mori, 40(2), 1992, pp. 114-117). An example of a quantitative method for surface treatment agents is shown. Surface treatment agents can be identified by thermal desorption gas / gas chromatography-mass spectrometry of the dried powder obtained by removing the dispersion medium from the metal paste, thereby determining the carbon number and molecular weight of the surface treatment agent. The carbon content of the surface treatment agent can be analyzed by carbon content analysis. An example of a carbon content analysis method is high-frequency induction heating furnace combustion / infrared absorption spectroscopy. From the identified carbon number, molecular weight and carbon content of the surface treatment agent, the amount of surface treatment agent can be calculated using the above formula.

[0043] The amount of surface treatment agent used may be 0.1 to 15% by mass, 1 to 15% by mass, 5 to 15% by mass, or 8 to 12% by mass, based on the mass of the submicro copper particles having the surface treatment agent.

[0044] Commercially available submicro copper particles can be used. Examples of commercially available submicro particles include CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd.) and Tn-Cu100 (manufactured by Taiyo Nippon Sanso Corporation).

[0045] As micro-copper particles, copper particles with a particle size of 2 μm or more and 50 μm or less can be used. For example, copper particles with a volume-average particle size of 2 μm or more and 50 μm or less can be used. If the volume-average particle size of the micro-copper particles is within the above range, volume shrinkage in the in-plane direction (XY direction) of the sintered layer and the generation of voids when sintered without pressure or under pressure can be sufficiently reduced, making it easier to ensure the bonding strength of the joined body. If the members to be joined are semiconductor elements, the semiconductor device tends to exhibit good die-shear strength and connection reliability. From the viewpoint of achieving the above effects even more effectively, the volume-average particle size of the micro-copper particles may be 2 μm or more, 3 μm or more, 20 μm or less, 15 μm or less, 10 μm or less, 2 μm or more and 20 μm or less, 2 μm or more and 10 μm or less, 3 μm or more and 20 μm or less, or 3 μm or more and 10 μm or less.

[0046] The shape of the micro-copper particles is preferably flake-shaped. By using flake-shaped micro-copper particles, the micro-copper particles in the metal particle-containing layer are oriented substantially parallel to the bonding surface, which suppresses volume shrinkage when the metal particle-containing layer is sintered, making it easier to ensure the bonding strength of the bonded body. When the members to be bonded are semiconductor elements, the semiconductor device tends to exhibit good die-shear strength and connection reliability. From the viewpoint of achieving the above effects even more effectively, the aspect ratio of the flake-shaped micro-copper particles may be greater than 2, 4 or more, 6 or more, 10 or more, or 50 or more.

[0047] The content of micro-copper particles may be 10% to 90% by mass, 15% to 65% by mass, or 20% to 60% by mass, based on the total mass of copper particles. If the content of micro-copper particles is within the above range, it becomes easier to ensure the bonding strength of the bonded body, and if the members to be bonded are semiconductor elements, the semiconductor device tends to exhibit good die-shear strength and connection reliability.

[0048] In the case of micro-copper particles, there is no particular limitation on whether or not they are treated with a surface treatment agent, but from the viewpoint of dispersion stability and oxidation resistance, the micro-copper particles may be treated with the first surface treatment agent containing the fatty acid described above.

[0049] The amount of surface treatment agent applied may be one molecular layer or more on the particle surface. This amount of surface treatment agent varies depending on the specific surface area of ​​the micro-copper particles, the molecular weight of the surface treatment agent, and the minimum coverage area of ​​the surface treatment agent. The amount of surface treatment agent may be 0.1-15% by mass, 1-15% by mass, 5-15% by mass, or 8-12% by mass, based on the mass of the micro-copper particles containing the surface treatment agent. The specific surface area of ​​the micro-copper particles, the molecular weight of the surface treatment agent, and the minimum coverage area of ​​the surface treatment agent can be calculated using the same method as described above for sub-micro copper particles.

[0050] Commercially available micro-copper particles can be used. Examples of commercially available spherical micro-particles include the Cu-HWQ series (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.), 1100Y (manufactured by Mitsui Mining & Smelting Co., Ltd.), 1200Y (manufactured by Mitsui Mining & Smelting Co., Ltd.), 1300Y (manufactured by Mitsui Mining & Smelting Co., Ltd.), MA-C08J (manufactured by Mitsui Mining & Smelting Co., Ltd.), and MA-CJU (manufactured by Mitsui Mining & Smelting Co., Ltd.).

[0051] Examples of commercially available flake-shaped microparticles include 1100YP (manufactured by Mitsui Mining & Smelting Co., Ltd.), 1200YP (manufactured by Mitsui Mining & Smelting Co., Ltd.), and 3L3N (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.).

[0052] The metal paste may contain sub-micro copper particles and micro copper particles as metal particles. In this case, volume shrinkage and sintering shrinkage associated with the drying of the dispersion medium can be suppressed, and delamination between the bonding surface of the components and the sintered body of the metal particle-containing layer can be easily prevented.

[0053] From the above perspective, the metal paste may contain sub-micro copper particles with a volume average particle size of 0.05 μm or more and 0.8 μm or less, and spherical micro copper particles with a volume average particle size of 2 μm or more and 50 μm or less, wherein the total content of sub-micro copper particles and micro copper particles is 80% by mass or more or 90% by mass or more based on the total mass of metal particles, and the content of sub-micro copper particles may be 30% by mass or more and 90% by mass or less based on the total mass of sub-micro copper particles and micro copper particles.

[0054] From the viewpoint of improving sinterability, the metal paste may contain spherical submicro copper particles and spherical micro copper particles as metal particles. In this case, the mass ratio of spherical submicro copper particles to spherical micro copper particles may be 30:70 to 90:10, or 40:60 to 80:20.

[0055] When the metal paste contains spherical sub-micro copper particles and spherical micro copper particles as metal particles, the volume average particle size of the sub-micro copper particles is preferably 0.1 μm or more and 0.8 μm or less, more preferably 0.1 μm or more and 0.6 μm or less, and even more preferably 0.1 μm or more and 0.5 μm or less. The volume average particle size of the micro copper particles is preferably 2 μm or more and 50 μm or less, more preferably 2 μm or more and 20 μm or less, even more preferably 2 μm or more and 15 μm or less, and even more preferably 2 μm or more and 10 μm or less.

[0056] From the viewpoint of preventing cracking after the metal paste dries, the metal paste may contain spherical sub-micro copper particles and flake-shaped micro copper particles as metal particles. In this case, the mass ratio of spherical sub-micro copper particles to flake-shaped micro copper particles may be 30:70 to 90:10, or 40:60 to 80:20.

[0057] The metal paste may contain sub-micro copper particles, flake-shaped micro copper particles, and spherical micro copper particles, from the viewpoint of low-temperature sinterability, suppression of volume shrinkage in the XY direction (direction parallel to the bonding surface), and improvement of the packing of metal particles in the metal particle-containing layer.

[0058] From the above perspective, the metal paste contains submicro copper particles with a volume average particle size of 0.05 μm or more and 0.8 μm or less, spherical micro copper particles with a volume average particle size of 2 μm or more and an aspect ratio of 2 or less, and flake-shaped micro copper particles with an aspect ratio greater than 2, wherein the total content of submicro copper particles, spherical micro copper particles, and flake-shaped micro copper particles is 80% by mass or more or 90% by mass or more, based on the total mass of the metal particles, and the content of submicro copper particles, spherical micro copper particles, and flake-shaped micro copper particles may be 20% by mass or more and 80% by mass or less, 5% by mass or more and 50% by mass or less, and 5% by mass or more and 50% by mass or less, based on the sum of their masses, or 60% by mass or more and 80% by mass or less, 10% by mass or more and 20% by mass or less, and 10% by mass or more and 20% by mass or less.

[0059] A metal paste containing copper particles may also contain metal particles containing metal elements other than copper (other metal particles). These other metal particles may include, for example, particles of zinc, gold, palladium, silver, nickel, platinum, brass, manganese, tin, antimony, indium, aluminum, vanadium, etc. The volume-average particle size of these other metal particles may be 0.01 μm to 10 μm, 0.01 μm to 5 μm, or 0.05 μm to 3 μm.

[0060] When a metal paste containing copper particles also contains other metal particles, a sintered body can be obtained in which multiple types of metals are dissolved or dispersed. This improves the mechanical properties of the sintered body, such as yield stress and fatigue strength, and enhances connection reliability. Furthermore, by adding multiple types of metal particles, the sintered body with the metal particle-containing layer can have sufficient bonding strength to a given adherend. When the components to be bonded are semiconductor elements, the die-shear strength and connection reliability of the semiconductor device tend to improve.

[0061] If the metal paste containing copper particles also contains other metal particles, the amount of these other metal particles may be less than 5% by mass or 3% or less by mass, based on the total mass of the metal particles, from the viewpoint of obtaining sufficient bonding properties. Other metal particles may not be included. The shape of the other metal particles is not particularly limited.

[0062] The content of inorganic particles other than metal particles in the metal paste may be 30% by mass or less, 20% by mass or less, or 0% by mass, based on the total amount of metal paste.

[0063] (Reducing agent) Examples of reducing agents include polyhydric alcohols. Examples of polyhydric alcohols include polyethylene glycol such as pentaethylene glycol, hexaethylene glycol, dipropylene glycol, tripylene glycol, tetrapropylene glycol, polyethylene glycol such as polyethylene glycol 200, polyethylene glycol 300 and polyethylene glycol 400, polypropylene glycol such as polypropylene glycol 200, polypropylene glycol 300, polypropylene glycol 400, polypropylene glycol 700 and polypropylene glycol 4000, polyethylene glycol monooleate, polyethylene glycol monostearate, polyethylene glycol monolaurate, polyoxyethylene sorbitan monolaurate, polyoxyethylene polyoxypropylene glycol, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, 2-amino-2-(hydroxymethyl)-1,3-propanediol and 1,3-bis(tris(hydroxymethyl)methylamino)propane.

[0064] From the viewpoint of functioning as a highly polar solvent and exhibiting a reducing effect at the heating temperature of the metal paste, and from the viewpoint of easily ensuring sufficient sinterability, the polyhydric alcohol may be polyethylene glycol, and may be polyethylene glycol 200, polyethylene glycol 300, or polyethylene glycol 400.

[0065] Polyhydric alcohols can be used individually or in combination of two or more types.

[0066] The amount of polyhydric alcohol used as a reducing agent in the metal paste may be 5 to 10 parts by mass or 3 to 5 parts by mass per 100 parts by mass of the total mass of metal particles, from the viewpoint of suppressing sintering defects and ensuring bonding strength.

[0067] (dispersion medium) Examples of dispersion media include monohydric and polyhydric alcohols such as pentanol, hexanol, heptanol, octanol, decanol, dihydroterpineol, terpineol, isobornylcyclohexanol (MTPH), 1,5-pentadiol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, tetraethylene glycol, α-terpineol (α-terpineol), dihydroterpineol (dihydroterpineol), and geraniol; ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, diethylene glycol isopropyl methyl ether, and triethylene glycol dimethyl ether. Ethers such as triethylene glycol butyl methyl ether, propylene glycol propyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol dimethyl ether, tripropylene glycol methyl ether, and tripropylene glycol dimethyl ether; esters such as ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate (DPMA), ethyl lactate, butyl lactate, γ-butyrolactone, and propylene carbonate; acid amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; aliphatic hydrocarbons such as cyclohexanone, octane, nonane, decane, and undecane; aromatic hydrocarbons such as benzene, toluene, xylene, and 1-methylnaphthalene; mercaptans having alkyl groups with 1 to 18 carbon atoms;Examples of mercaptans include those having a cycloalkyl group with 5 to 7 carbon atoms. Examples of mercaptans having an alkyl group with 1 to 18 carbon atoms include ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, hexyl mercaptan, and dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group with 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan, and cycloheptyl mercaptan.

[0068] The content of the dispersion medium in the metal paste may be 2% by mass or more, 5% by mass or more, 50% by mass or less, 30% by mass or less, or 20% by mass or less, based on the total mass of the metal paste. For example, the content of the dispersion medium may be 2 to 50% by mass, 5 to 30% by mass, or 5 to 20% by mass, based on the total mass of the metal paste. Also, the content of the metal paste may be 5 to 50 parts by mass, 5 to 40 parts by mass, or 7 to 35 parts by mass, based on 100 parts by mass of the total mass of metal particles contained in the metal paste. If the content of the dispersion medium is within the above range, the viscosity of the metal paste can be adjusted to a more appropriate level, and uneven dispersion of metal particles due to low viscosity and inhibition of sintering due to residue during sintering can be suppressed.

[0069] In this embodiment, two or more dispersion media can be used in combination.

[0070] In this embodiment, the metal paste may further contain a second fatty acid if the metal particles have a carboxylic acid compound or an alcohol compound with a molecular weight of 300 g / mol or less on their surface, and the paste contains a reducing agent that is a polyhydric alcohol.

[0071] (Second fatty acid) The second fatty acid may be a fatty acid with 18 or fewer carbon atoms (including the carbon atoms of the carboxyl group). Examples of the second fatty acid include acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, caprylic acid, methylheptanoic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanoic acid, propylhexanoic acid, capric acid (decanoic acid), methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, and lauric acid. Methyl undecanoic acid, ethyl decanoic acid, propyl nonanoic acid, butyl octanoic acid, pentyl heptanoic acid, tridecanoic acid, methyl dodecanoic acid, ethyl undecanoic acid, propyl decanoic acid, butyl nonanoic acid, pentyl octanoic acid, myristic acid, methyl tridecanoic acid, ethyl dodecanoic acid, propyl undecanoic acid, butyl decanoic acid, pentyl nonanoic acid, hexyl octanoic acid, pentadecanoic acid, methyl tetradecanoic acid, ethyl tridecanoic acid, propyl dodecanoic acid, butyl undecanoic acid Examples of saturated fatty acids include pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid (stearic acid), isostearic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, and nonylcyclohexanecarboxylic acid; and unsaturated fatty acids include octenoic acid, nonenic acid, methylnonenic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sapienic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, and linolenic acid.

[0072] The second fatty acid may be a fatty acid with 8 to 18 carbon atoms, a fatty acid with 10 or fewer carbon atoms, or a fatty acid with 8 to 10 carbon atoms, from the viewpoint of storage stability and affinity with reducing agents. Furthermore, the second fatty acid may be decanoic acid, lauric acid, myristic acid, palmitic acid, or stearic acid, from the viewpoint of reducing residue after the drying process.

[0073] The second fatty acid may be used alone or in combination of two or more types.

[0074] From the viewpoint of improving tackiness, the second fatty acid may have a weight loss rate of 2% by mass or less, 1% by mass or less, or 0.5% by mass or less when heated at 90°C for 30 minutes under a nitrogen atmosphere. In such cases, the tackiness can be further improved by allowing more of the second fatty acid to remain in the metal particle-containing layer formed by heating and drying the coating film of the metal paste. Heating of the second fatty acid can be performed, for example, by differential thermal-thermogravimetric analysis (TG-DTA) measuring instrument, and the weight loss rate can be calculated from the TG-DTA measurement results using the following formula. Weight reduction rate (mass%)=100×(Z1-Z2) / Z1 In the formula, Z1 represents the mass (g) of the second fatty acid before heating, and Z2 represents the mass (g) of the second fatty acid after heating at 90°C for 30 minutes under a nitrogen atmosphere.

[0075] The measurement conditions for TG-DTA may be, for example, the following: <Measurement conditions> Equipment: NEXTA STA200RV (manufactured by Hitachi High-Tech Science Co., Ltd.) Atmosphere: Nitrogen atmosphere Heating conditions: Heat from room temperature (25°C) to 90°C at a rate of 10°C / minute, heat at 90°C for 30 minutes, then stop heating and allow to cool down to room temperature (25°C).

[0076] The content of the second fatty acid in the metal paste may be 0.5% by mass or more, 1% by mass or more, 5% by mass or less, 3% by mass or less, 0.5% by mass or more and 5% by mass or less, or 1% by mass or more and 3% by mass or less, based on the total mass of the metal particles. If the content of the second fatty acid is within the above range, it is possible to impart flexibility to the metal paste while making it less likely for residual components to inhibit metal sintering (for example, inhibit copper sintering).

[0077] From the same viewpoint as above, the content of the second fatty acid in the metal paste may be 10 parts by mass or more and 100 parts by mass or 20 parts by mass or more and 60 parts by mass per 100 parts by mass of polyhydric alcohol blended as a reducing agent.

[0078] From the same viewpoint as above, the content of the second fatty acid in the metal paste may be 0.5% by mass or more, 1% by mass or more, 5% by mass or less, 3% by mass or less, 0.5% by mass or more and 5% by mass or less, or 1% by mass or more and 3% by mass or less, based on the total amount of the metal paste.

[0079] From the viewpoint of further improving tackiness, the metal paste may contain metal particles having a first fatty acid with 10 or more carbon atoms on its surface, a reducing agent which is a polyhydric alcohol, and a second fatty acid which has 10 or fewer carbon atoms.

[0080] The inventors speculate that the reason for the improved tackiness in the above-mentioned metal paste is as follows: The surface of the metal particles protected by the first fatty acid with 10 or more carbon atoms exhibits hydrophobic properties because the long-chain alkyl groups are arranged outward. The polyhydric alcohol added as a reducing agent is hydrophilic, so its wettability with the fatty acid-protected metal particles is poor. However, it is thought that the wettability between the metal particles and the polyhydric alcohol is improved because the fatty acid with 10 or fewer carbon atoms, acting as a second fatty acid, forms a multilayer coordination on the surface of the metal particles, buffering the hydrophobicity. As a result, the inventors speculate that a liquid film of polyhydric alcohol is formed on the surface of the metal particles, making the metal particle-containing layer more easily plastically deformable, thereby improving the tack strength.

[0081] (Gelling agent) From the viewpoint of further improving tackiness, the metal paste may contain a gelling agent. Examples of gelling agents include 1,3,2,4-dibenzylidene-D-sorbitol and 12-hydroxystearic acid.

[0082] The gelling agent content in the metal paste may be 0.1 to 1% by mass or 0.3 to 0.5% by mass, based on the total mass of the metal paste.

[0083] (Other ingredients) The metal paste may contain, as additives, wetting agents such as nonionic surfactants and fluorinated surfactants; surface tension modifiers; dispersants such as alkylamines and alkylcarboxylic acids; defoamers such as silicone oils; and ion trapping agents such as inorganic ion exchangers. The content of the additives can be adjusted as appropriate within a range that does not hinder the effects of the present invention. Furthermore, the total content of non-metallic inorganic particles (e.g., glass particles) in the metal paste may be 1% by mass or less, or 0.1% by mass or less, based on the total amount of metal particles. Moreover, the metal paste may not contain any non-metallic inorganic particles.

[0084] Examples of nonionic surfactants include polyether compounds. Polyether compounds are amphiphilic. Examples of polyether compounds include polyoxyalkylene alkyl ethers.

[0085] Examples of polyoxyalkylene alkyl ethers include polyoxyethylene-lauryl ether, polyoxyethylene-cetyl ether, polyoxyethylene-oleyl ether, polyoxyethylene-stearyl ether, polyoxyethylene-behenyl ether, polyoxyethylene-2-ethylhexyl ether, and polyoxyethylene-isodecyl ether. From the viewpoint of reducing the likelihood of copper sintering inhibition by residual components, polyoxyethylene-oleyl ether is preferred.

[0086] The HLB value of the polyether compound may be 10-16, 11-15, or 12-14.

[0087] Polyether compounds can be used individually or in combination of two or more.

[0088] The polyether compound content in the metal paste may be 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 3.0% by mass or less, 2.0% by mass or less, 1.0% by mass or less, or 0.3% by mass or more and 1.0% by mass or less, based on the total mass of the metal particles. If the polyether compound content is within the above range, it is possible to impart flexibility to the metal paste while suppressing the occurrence of copper sintering inhibition by residual components.

[0089] From the same viewpoint as above, the content of the polyether compound in the metal paste may be 6 to 60 parts by mass, 10 to 40 parts by mass, or 15 to 20 parts by mass, per 100 parts by mass of the polyhydric alcohol blended as a reducing agent.

[0090] The metal paste may not contain nonionic surfactants.

[0091] The viscosity of the metal paste is not particularly limited, and when applied by methods such as printing, it may be adjusted to a viscosity suitable for the application method. The Casson viscosity of the metal paste at 25°C may be 1 Pa·s or more or 100 Pa·s or more, and may be 10 Pa·s or less or 50 Pa·s or less.

[0092] The metal paste of this embodiment may consist of a first liquid containing metal particles, a dispersion medium, and optionally a reducing agent, and a second liquid containing a second fatty acid, a reducing agent, and optionally a dispersion medium. In this case, after forming a coating film or a dried film thereof of the first liquid, the second liquid can be applied to their surfaces and, if necessary, further dried to form a layer containing metal particles.

[0093] Furthermore, if the metal paste contains metal particles having a first fatty acid with 10 or more carbon atoms on its surface, a reducing agent which is a polyhydric alcohol, a second fatty acid with 10 or fewer carbon atoms, and a dispersion medium, the metal paste may be composed of a first liquid containing the metal particles and dispersion medium, and a second liquid containing the reducing agent, the second fatty acid, and optionally the dispersion medium. In this case, after forming a coating film or a dried film thereof with the first liquid, the second liquid can be applied to their surface and dried further if necessary to form a metal particle-containing layer with excellent tackiness. For example, after forming a coating film or a dried film thereof with the first liquid, the second liquid containing polyethylene glycol and decanoic acid may be applied to its surface.

[0094] Furthermore, if the metal paste is composed of multiple chemical solutions, the yield stress can be determined for each mixture of solutions in the same manner as described above.

[0095] <Method for manufacturing metal paste for bonding> The metal paste can be prepared by mixing the above-mentioned metal particles (e.g., sub-micro copper particles and micro copper particles), the above-mentioned reducing agent, the above-mentioned dispersion medium, and, if necessary, other metal particles, the above-mentioned second fatty acid, and any additives. After mixing each component, stirring or dispersion treatment may be performed. The maximum particle size of the dispersion may be adjusted by classification of the metal paste.

[0096] The above method may include a step of surface-treating the metal particles with a carboxylic acid compound or an alcohol compound having a molecular weight of 300 g / mol or less.

[0097] The stirring process can be carried out using a stirrer. Examples of stirrers include the Ishikawa stirrer, Silverson stirrer, cavitation stirrer, rotational stirring device, ultra-thin film high-speed rotary disperser, ultrasonic disperser, Raikai machine, twin-screw kneader, bead mill, ball mill, three-roll mill, homomixer, planetary mixer, ultra-high pressure disperser, thin-layer shear disperser, and disparizer.

[0098] Examples of dispersion processes include thin-layer shear dispersers, disparizers, bead mills, ultrasonic homogenizers, high-shear mixers, narrow-gap three-roll mills, wet-type ultra-fine atomizers, supersonic jet mills, and ultra-high-pressure homogenizers.

[0099] Classification operations can be carried out, for example, by filtration, natural sedimentation, or centrifugal separation. Examples of filters for filtration include water combs, metal mesh, metal filters, and nylon mesh.

[0100] <zygote> The joint of this embodiment comprises a first member, a second member, and a joint portion that joins them, wherein the joint portion includes a sintered body of the above-mentioned bonding metal paste. In the joint of this embodiment, since the joint portion includes a sintered body of the above-mentioned bonding metal paste, the detachment of the members is sufficiently suppressed.

[0101] <Method for manufacturing a jointed body> A first embodiment of the method for manufacturing a bonded body according to the present disclosure comprises: a first step of applying the above-mentioned bonding metal paste onto a first member to form a coating film of the bonding metal paste; a second step of drying the coating film to form a metal particle-containing layer; a third step of placing a second member on the metal particle-containing layer to obtain a laminate; and a fourth step of sintering the metal particle-containing layer of the laminate.

[0102] In the method for manufacturing the bonded body of this embodiment, the metal particle-containing layer has excellent tack strength, thereby improving the tack strength between the first member and the second member in the laminate. This makes it possible to suppress the detachment of the first member or the second member during the transport of the laminate.

[0103] Examples of the first and second components include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, 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 components such as copper ribbons, metal blocks, and terminals; heat sinks; and water cooling plates.

[0104] The first and second members may have a metal layer at their joint surface that forms a metallic bond with the sintered body of the metal paste. Examples of metals that make up the metal layer include copper, nickel, silver, gold, palladium, platinum, lead, tin, and cobalt. These metals may be used individually or in combination of two or more. The metal layer may also be an alloy containing the above metals. Examples of metals that can be used in alloys, in addition to the above metals, include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, and molybdenum. Examples of members having a metal layer include members with various metal platings, wires, metal-plated chips, heat spreaders, ceramic substrates with metal plates attached, lead frames with various metal platings or lead frames made of various metals, copper plates, and copper foils.

[0105] (1st step) In the first step, the above-mentioned bonding metal paste is applied to the first member to form a coating of the bonding metal paste.

[0106] Methods for applying the metal paste onto the first component include inkjet printing, super inkjet printing, screen printing, transfer printing, offset printing, jet printing, dispensers, jet dispensers, needle dispensers, comma coaters, slit coaters, die coaters, gravure coaters, slit coats, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, bar coating, applicators, particle deposition methods, spray coaters, spin coaters, dip coaters, electrodeposition coating, etc.

[0107] The thickness of the coating film may be 1 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more. Furthermore, the thickness of the coating film may be 3000 μm or less, 1000 μm or less, 500 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, or 150 μm or less.

[0108] (2nd process) In the second step, the coating film is dried to form a layer containing metal particles. Methods for drying the coating film include heat drying and vacuum drying.

[0109] The gas atmosphere during heating and drying or vacuum drying may be air, an oxygen-free atmosphere such as nitrogen or a noble gas, or a reducing atmosphere such as hydrogen or formic acid.

[0110] For heating and drying or vacuum drying, for example, a hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far-infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, heater heating device, steam heating furnace, hot plate press device, etc. may be used. The drying temperature and time may be adjusted as appropriate according to the type and amount of dispersion medium used.

[0111] In the second step, the metal particle-containing layer may be dried so that the content of the dispersion medium is 0.5% by mass or less, 0.1% by mass or less, or 0.05% by mass or less, based on the total amount of the metal particle-containing layer, or it may be dried so that it is substantially absent (for example, 0% by mass). Alternatively, the metal particle-containing layer may be dried so that the content of the dispersion medium is 0.5% by mass or less, 0.1% by mass or less, or 0.05% by mass or less, based on the amount of dispersion medium added, or it may be dried so that it is substantially absent (for example, 0% by mass).

[0112] In the second step, the metal particle-containing layer may be dried so that the reducing agent content is 95-100% by mass, 97-100% by mass, or 99-100% by mass, based on the amount of reducing agent added.

[0113] In the second step, the metal particle-containing layer may be dried so that the content of the second fatty acid is 95-100% by mass, 97-100% by mass, or 99-100% by mass, based on the amount of the second fatty acid added.

[0114] In the second step, the content of the dispersion medium, reducing agent, and second fatty acid in the metal particle-containing layer can be adjusted, for example, by adjusting the drying conditions according to the boiling points of the dispersion medium, reducing agent, and second fatty acid to be added.

[0115] (3rd step) In the third step, a second component is placed on the metal particle-containing layer to obtain a laminate.

[0116] Methods for placing a second component on a metal particle-containing layer include, for example, a chip mounter, a flip-chip bonder, and a positioning jig made of carbon or ceramic.

[0117] From the viewpoint of improving tack strength, the second component may be placed on a metal particle-containing layer heated to 90°C or higher. The heating temperature may be above the melting point of the second fatty acid, and may be 150°C or lower, or 120°C or lower, from the viewpoint of suppressing the volatilization of the second fatty acid and suppressing the oxidation of the metal particles (e.g., copper particles).

[0118] For heating the metal particle-containing layer, for example, a hot plate or a flip-chip bonder can be used. A flip-chip bonder can heat the substrate side and the component side separately.

[0119] In the third step, the second member may be pressed onto the metal particle-containing layer at a predetermined pressure. From the viewpoint of preventing damage to the first and second members and improving the quality of the resulting joint, the pressure applied when pressing the second member onto the metal particle-containing layer may be 2.0 MPa or less or 1.9 MPa or less. From the viewpoint of improving tackiness, the pressure may be greater than or equal to the yield stress of the metal paste in this embodiment, and may be 1.0 MPa or more, 1.5 MPa or more, or 1.9 MPa or more.

[0120] The crimping time in the third step may be adjusted as appropriate depending on the heating temperature and the crimping pressure. For example, in the third step, the second member may be crimped onto the metal particle-containing layer heated to 90°C or higher with a crimping pressure of 0.5 to 2 MPa and a crimping time of 3 seconds or less. The crimping time may be adjusted as appropriate depending on the member to which the joining metal paste is applied, for example, 0.1 to 3.0 seconds, 0.1 to 2.0 seconds, or 0.1 to 1.0 seconds.

[0121] In the third step, when placing the second member on the metal particle-containing layer, the second member may erode in the thickness direction of the metal particle-containing layer, causing the edge of the metal particle-containing layer to extend outward beyond the edge of the second member, resulting in a portion where the metal particle-containing layer and the second member are not in contact. From the viewpoint of connection reliability, it is preferable that in the third step, no portion of the metal particle-containing layer on the second member side surface is not in contact with the second member.

[0122] The resulting laminate can be transported to a sintering furnace or the like for carrying out the fourth step. Transport methods include manual transport, automatic conveyors, transport machines, automatic trolleys, and robotic arms. Because the second component is sufficiently temporarily fixed in place by a metal particle-containing layer with excellent tack properties, the problem of the second component falling off during transport is unlikely to occur.

[0123] (4th step) In the fourth step, the metal particle-containing layer of the laminate can be sintered by heat treatment in an oxygen-free atmosphere. The oxygen-free atmosphere may be an atmosphere that does not contain hydrogen or has a hydrogen concentration of 10% or less. Note that an oxygen-free atmosphere refers to an atmosphere with an oxygen concentration of 1 volume% or less, and the oxygen concentration may be 0.1 volume% or less, 0.01 volume% or less, or 0.001 volume% or less.

[0124] For the heat treatment, a heating device having a compression mechanism can be used. Examples of heating devices include hot plates, hot air dryers, hot air heating furnaces, nitrogen dryers, infrared dryers, infrared heating furnaces, far-infrared heating furnaces, microwave heating devices, laser heating devices, electromagnetic heating devices, heater heating devices, steam heating furnaces, and the like.

[0125] Examples of hydrogen-free atmospheres include non-oxidizing gases such as nitrogen, noble gases, heat-resistant organic gases, water vapor, or mixtures thereof, or under vacuum.

[0126] The gas atmosphere during sintering may be a reducing atmosphere. Examples of reducing atmospheres include nitrogen containing formic acid gas, a noble gas containing formic acid gas, and a non-oxidizing gas containing 10% or less hydrogen. Alternatively, the gas atmosphere during sintering may be a forming gas (nitrogen containing hydrogen below the lower explosive limit (e.g., 5% or less or 3% or less)) or low molecular weight alcohol (e.g., methanol, ethanol) vapor.

[0127] The maximum temperature reached during the heat treatment may be between 200°C and 450°C, between 230°C and 400°C, between 240°C and 350°C, or between 250°C and 300°C, from the viewpoint of reducing thermal damage to the members being joined and improving yield.

[0128] The holding time at the maximum temperature reached 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 completely volatilizing the dispersion medium and improving yield. In particular, if the maximum temperature reached is 250°C or higher, sintering can be sufficiently advanced with a holding time of 10 minutes or less.

[0129] After the fourth step, a joined body can be obtained comprising a first member, a second member, and a sintered body of a metal particle-containing layer that joins them.

[0130] The die shear strength of the joint may be 40 MPa or more, 50 MPa or more, 60 MPa or more, or 30 MPa or more, from the viewpoint of sufficiently joining the first member and the second member. The die shear strength can be measured using a universal bond tester (4000 series, manufactured by DAGE Corporation), etc.

[0131] In the above-described assembly, at least one of the first member and the second member 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. In such cases, the assembly becomes a semiconductor device. The resulting semiconductor device can have sufficient die-shear strength and connection reliability.

[0132] Examples of semiconductor devices include power modules consisting of diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, Schottky diodes, fast recovery diodes, etc., as well as oscillators, amplifiers, high-brightness LED modules, semiconductor laser modules, logic, sensors, and the like.

[0133] A second embodiment of the method for manufacturing a bonded body according to the present disclosure comprises: a first step of applying a bonding metal paste onto a first member to form a coating of the bonding metal paste; a second step of drying the coating to form a metal particle-containing layer; a third step of pressing a second member onto the metal particle-containing layer, which has been heated to T1°C or higher, at a pressure of Y1MPa or higher to obtain a laminate; and a fourth step of sintering the metal particle-containing layer of the laminate.

[0134] In the method for manufacturing a bonded body according to the second embodiment, the bonding metal paste contains metal particles, a reducing agent, and a dispersion medium, and the yield stress X1 of the bonding metal paste, measured by the following procedure, is 2.0 MPa or less, and X1 / Y1 is 4.0 or less. Procedure for measuring yield stress: (1) Apply bonding metal paste to the copper substrate and dry at 90°C for 30 minutes to form a metal particle-containing layer with a thickness of 3 mm × 3 mm × 0.05 mm. (2) Using a die-shear type testing machine, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool under the conditions of heating temperature T1°C, speed 100 μm / s, and distance between the tip of the tool and the copper substrate 0.02 mm, to obtain a stress (MPa)-strain (%) curve. (3) The yield stress X1 (MPa) is defined as the stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2%.

[0135] In the second embodiment of the method for manufacturing a joint, the materials constituting the first member, the second member, and the joining metal paste can be the same as those constituting the first member, the second member, and the joining metal paste in the first embodiment described above, and the composition of the joining metal paste can also be the same.

[0136] According to the second embodiment of the method for manufacturing a bonded body, by setting the yield stress X1 of the bonding metal paste to 4.0 times or less Y1, it is possible to suppress the generation of voids between the members to be bonded and the metal particle-containing layer due to plastic deformation of the metal particle-containing layer in the third step, thereby obtaining a laminate with excellent tack strength. From the viewpoint of further improving tack, X1 / Y1 may be 3.0 or less, 2.5 or less, 2.0 or less, or 1.0 or less. From the viewpoint of excellent adhesive strength, X1 / Y1 may be 0.9 or more.

[0137] The heating temperature T1 may be 80-130°C, 85-120°C, or 90-110°C, from the viewpoint of improving tackiness.

[0138] The crimping pressure Y1 may be 0.5 to 2.0 MPa, 0.7 to 1.7 MPa, or 1.0 to 1.5 MPa, from the viewpoint of durability and tackiness of the members to which the joining metal paste is applied.

[0139] The crimping time may be adjusted as appropriate depending on the member to which the bonding metal paste is applied and the pressure of the crimping, for example, it may be 3.0 seconds or less, and may be 0.1 to 3.0 seconds, 0.1 to 2.0 seconds, or 0.1 to 1.0 seconds.

[0140] In the second embodiment, the heating temperature of the metal particle-containing layer and the pressing pressure of the second member in the third step may be set based on the yield stress X1 of the metal paste at the heating temperature T1.

[0141] The bonding metal paste may have a yield strength of 0.5 to 2.0 MPa, 0.5 to 1.9 MPa, or 0.5 to 1.8 MPa at a heating temperature of 90°C. [Examples]

[0142] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples.

[0143] The following materials were prepared. (Submicro copper particles A) Copper particles with a lauric acid treatment amount of 10% by mass and a volume-average particle size of 0.21 μm were prepared as submicro copper particles A.

[0144] (Submicro copper particles B) Copper particles with a volume-average particle size of 0.18 μm and a processing amount of octanoic acid of 2 mass% were prepared as submicro copper particles B.

[0145] (Micro copper particles A) A mixture of spherical copper particles with a volume-average particle size of 7.3 μm and a lauric acid treatment amount of 10% by mass was prepared as micro-copper particles A, and flake-shaped copper particles with a volume-average particle size of 1.7 μm and a lauric acid treatment amount of 10% by mass was prepared.

[0146] (Micro copper particles B) Flake-shaped copper particles with a lauric acid treatment amount of 3% by mass and a volume-average particle size of 5 μm were prepared as micro-copper particles B.

[0147] [Preparation of metal paste] The metal pastes shown in Table 1 (parts by mass) were prepared using the procedure described below. The amounts shown in the table represent the proportion (parts by mass) of each component when the total mass of the metal paste is 100 parts by mass.

[0148] <Example 1> Under conditions of 25°C room temperature and 60% humidity, dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd.) as a dispersion medium, sub-micro copper particles A, and micro copper particles A were mixed and stirred for 30 minutes at a rotation speed of 300 rpm using a planetary mixer (manufactured by Primix). The resulting mixture was dispersed once using a disparizer (manufactured by Shinto Kogyo Co., Ltd.) under conditions of a gap of 50 μm and a rotation speed of 12,000 rpm to obtain a dispersion.

[0149] To the dispersion obtained above, dihydroterpineol was added as the remaining dispersion medium, polyethylene glycol 200 (hereinafter abbreviated as PEG200) (manufactured by NOF Corporation) as a reducing agent, and decanoic acid (manufactured by Shin Nippon Rika Co., Ltd.) as a second fatty acid. The mixture was stirred at 2000 rpm under reduced pressure for 3 minutes using a rotary mixer (Sinky, Awatori Rentaro ARE-310) to obtain metal paste a.

[0150] <Examples 2, 3 and Comparative Examples 1-3> As shown in Table 1, metal pastes b to f were obtained in the same manner as in Example 1, except that the types and amounts of each component used in the preparation of the metal paste were changed.

[0151] [Measurement of the weight loss rate of the second fatty acid] For each of the second fatty acids used in the examples, differential thermal-thermogravimetric analysis (TG-DTA) was performed under the following measurement conditions, and the weight loss rate (mass%) when the second fatty acid was heated at 90°C for 30 minutes under a nitrogen atmosphere was determined using the following formula. Weight reduction rate (mass%)=100×(Z1-Z2) / Z1 In the formula, Z1 represents the mass (g) of the second fatty acid before heating, and Z2 represents the mass (g) of the second fatty acid after heating at 90°C for 30 minutes under a nitrogen atmosphere. <Measurement conditions> Equipment: NEXTA STA200RV (manufactured by Hitachi High-Tech Science Co., Ltd.) Atmosphere: Nitrogen atmosphere Heating conditions: Heat from room temperature (25°C) to 90°C at a rate of 10°C / minute, heat at 90°C for 30 minutes, then stop heating and allow to cool down to room temperature (25°C).

[0152] The weight loss rates were measured as follows: 2.0% by mass for decanoic acid and 0.1% by mass for isostearic acid.

[0153] The yield stress and tack strength of the metal pastes a to f obtained from Examples 1 to 3 and Comparative Examples 1 to 3 were measured using the following method.

[0154] [Measurement of yield stress] The metal paste obtained above was printed onto a copper plate (30 mm x 30 mm x 2 mm thick) to form a coating film of 3.0 mm x 3.0 mm x 0.1 mm thickness. Next, the metal paste coating film was dried in the atmosphere on a hot plate heated to 90°C for 30 minutes to volatilize the dihydroterpineol dispersion medium and form a metal particle-containing layer (3 mm x 3 mm x 0.05 mm thickness).

[0155] The yield stress was measured using a die shear tester (Nordson STELLAR4000) following the procedure below. As shown in Figure 2, a 4 mm wide tool 30 was pressed horizontally against a metal particle-containing layer 20 provided on a copper substrate 10 at a heating temperature of 90°C, a measurement speed of 100 μm / s, and a measurement height H1 of 0.02 mm. The strain (%) was defined as the ratio of the tool's travel distance to the length of the metal particle-containing layer being measured (3 mm) in the direction the tool moved, and a stress (MPa)-strain (%) curve was obtained. In the obtained stress-strain curve, the least squares method was used to calculate R 2An approximate straight line was found for the rise of the curve so that the coefficient of determination was 95% or higher. This approximate straight line was then translated (offset) so that it passed through the point where the strain (%) was 0.2% (the point where the tool movement distance was 0.002 × 3 mm). The yield stress (MPa) at which the permanent strain reached 0.2% was determined from the intersection point of the approximate straight line and the original curve. The results are shown in Table 1.

[0156] [Table 1]

[0157] [Measurement of tack strength] The metal paste obtained above was printed onto a copper plate (30mm x 30mm x 2mm thick) to form a coating film of 3.0mm x 3.0mm x 0.1mm thickness. Next, the metal paste coating film was dried in air on a hot plate heated to 90°C for 30 minutes to volatilize the dihydroterpineol dispersion medium, forming a metal particle-containing layer (3mm x 3mm x 0.05mm thick). A dummy chip (3mm x 3mm x 0.4mm thick, with a copper layer as the bonding surface) was mounted on the formed metal particle-containing layer using a desktop hot-mount device (TRESKY, T-3000-FC3) under one of the conditions A to C below to obtain a laminate. At this time, the dummy chip was mounted while the metal particle-containing layer was heated on a heater heated to 90°C. <Installation Requirements> Condition A: Pressure 1.0 MPa, crimping time 3.0 seconds Condition B: Pressure 2.0 MPa, crimping time 1.0 second Condition C: Pressure 2.0 MPa, crimping time 0.15 seconds

[0158] The tack strength of the obtained laminate was measured using a die-shear tester (Nordson STELLAR4000) following the procedure below. As shown in Figure 3, the shear load was measured by pressing the tool 30 horizontally against a dummy chip 40 mounted on a metal particle-containing layer 20 provided on a copper substrate 10 at a measurement speed of 500 μm / s and a measurement height H2 of 0.2 mm. The maximum value of the shear load (N) was defined as the chip area (mm²). 2 The value obtained by dividing by ) was defined as the tack strength (kPa), and the average value of the measurements taken for eight laminates was taken as the tack strength. The results are shown in Table 2.

[0159] [Table 2] [Explanation of Symbols]

[0160] 10... Copper substrate, 20... Metal particle-containing layer, 30... Tool, 40... Dummy chip.

Claims

1. It contains metal particles, a reducing agent, and a dispersion medium. A bonding metal paste having a yield stress of 1.1 to 1.9 MPa, as measured by the following procedure. Procedure for measuring yield stress: (1) A bonding metal paste is applied to a copper substrate and dried at 90°C for 30 minutes to form a metal particle-containing layer measuring 3 mm × 3 mm × 0.05 mm in thickness. (2) Using a die-shear type testing machine, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool under the conditions of a heating temperature of 90°C, a speed of 100 μm / s, and a distance of 0.02 mm between the tip of the tool and the copper substrate, to obtain a stress (MPa)-strain (%) curve. (3) The yield stress (MPa) is defined as the stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2%.

2. The metal particles have a carboxylic acid compound with a molecular weight of 300 g / mol or less or an alcohol compound with a molecular weight of 300 g / mol or less on their surface. The reducing agent is a polyhydric alcohol. The bonding metal paste according to claim 1, further comprising a second fatty acid having 18 or fewer carbon atoms.

3. The bonding metal paste according to claim 2, wherein the content of the second fatty acid is 5% by mass or less based on the total amount of the bonding metal paste.

4. The bonding metal paste according to claim 2, wherein the second fatty acid has a weight loss rate of 2% by mass or less when heated at 90°C for 30 minutes under a nitrogen atmosphere.

5. A bonding metal paste according to claim 1, comprising a gelling agent.

6. A joint comprising a first member, a second member, and a joint that connects them, A joint body wherein the joint portion includes a sintered body of the joining metal paste described in any one of claims 1 to 5.

7. A first step of applying a bonding metal paste according to any one of claims 1 to 5 onto a first member to form a coating film of the bonding metal paste, A second step involves drying the aforementioned coating film to form a metal particle-containing layer, A third step is to arrange a second member on the metal particle-containing layer to obtain a laminate, A fourth step of sintering the metal particle-containing layer of the laminate, A method for manufacturing a joint, comprising:

8. The method for manufacturing a joined body according to claim 7, wherein in the third step, the second member is pressed onto the metal particle-containing layer, which has been heated to 90°C or higher, with a pressing pressure of 0.5 to 2 MPa and a pressing time of 3 seconds or less.

9. A first step involves applying a bonding metal paste onto a first member to form a coating film of the bonding metal paste, A second step involves drying the aforementioned coating film to form a metal particle-containing layer, T １ The second member is subjected to pressure Y on the metal particle-containing layer which has been heated to a temperature of ℃ or higher. １ A third step involves compressing the materials at a pressure of MPa or higher to obtain a laminate, A fourth step of sintering the metal particle-containing layer of the laminate, Equipped with, The aforementioned bonding metal paste contains metal particles, a reducing agent, and a dispersion medium. The yield stress X of the bonding metal paste is measured according to the following procedure. １ However, it is 1.1 to 1.9 MPa, and X １ / Y １ A method for manufacturing a joint, wherein the ratio is 0.55 or more and 4.0 or less. Procedure for measuring yield stress: (1) A bonding metal paste is applied to a copper substrate and dried at 90°C for 30 minutes to form a metal particle-containing layer measuring 3 mm × 3 mm × 0.05 mm in thickness. (2) Using a die-sharing tester, the metal particle-containing layer is heated with a tool with a width of 4 mm at a heating temperature T １ Under the conditions of °C, a speed of 100 μm / s, and a distance of 0.02 mm between the tip of the tool and the copper substrate, the tool is pressed horizontally to obtain a stress (MPa)-strain (%) curve. (3) The yield stress X is the stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2%. １ Let it be (MPa).

Images