Metal paste for bonding, bonded body, and manufacturing method for bonded body

Abstract

Provided is a metal paste for bonding that contains metal particles, a reducing agent, and a dispersion medium, and that has a yield stress measured via the procedure described here of 2.0 MPa or less.　Yield stress measurement procedure: (1) Apply the metal paste for bonding on a copper substrate, dry at 90°C for 30 minutes, and form a 3x3x0.05 mm thick metal-particle-containing layer. (2) Use a die shear testing machine to press the metal-particle-containing layer in the horizontal direction 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 between the tip of the tool and the copper substrate of 0.02 mm, thereby obtaining a stress (MPa)-strain (%) curve. (3) Define the stress when the permanent strain becomes 0.2% in the stress (MPa)-strain (%) curve as the yield stress (MPa).

Description

Metal paste for bonding, bonded body, and method for manufacturing the bonded body

[0001] The present disclosure relates to a metal paste for bonding, a bonded body, and a method for manufacturing the bonded body.

[0002] When manufacturing semiconductor devices, various bonding materials are used to form a bonding layer that bonds a semiconductor element to a lead frame or the like (supporting member). For example, high-lead solder has been used to form the bonding layer for bonding power semiconductors, LSIs, and the like that operate at temperatures up to about 150°C. In recent years, semiconductor elements have become higher capacity and more space-saving, and there is an increasing demand for semiconductors to operate at high temperatures of 175°C or higher. In order to ensure the operational stability of such semiconductor devices, the bonding layer must have connection reliability and high thermal conductivity. However, in the temperature range of 175°C or higher, the bonding layers of the high-lead solder and lead-free solder that have been used in the past have problems with connection reliability and also have insufficient thermal conductivity (30 Wm －１ K －１ ) and therefore alternative materials are needed.

[0003] As a joining method using an alternative material, a joining method utilizing the low-temperature sintering phenomenon of copper fine particles has been proposed. The sintered copper layer formed by this method has excellent mechanical strength, is likely to achieve connection reliability at high temperatures, and can keep 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).

[0004] Patent No. 5006081

[0005] T. Morita, Y. Yasuda: Materials Transactions, 56(6), 2015, 878-882

[0006] Power modules and the like in which a support member and a semiconductor element are bonded 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. This copper paste is then applied to a support member to form a copper paste coating. Next, the coating is dried to form a copper particle-containing layer, and the semiconductor element is placed on top of this. The resulting laminate is then transported to a sintering furnace or the like, and the copper particle-containing layer is sintered to bond the support member and the semiconductor element.

[0007] Conventional copper pastes, when dried, are difficult to obtain the property (hereinafter also referred to as tackiness) that allows them to temporarily bond semiconductor elements, etc. If the semiconductor elements fall off during transportation of the laminate, this leads to a decrease in yield in the production of bonded bodies such as power modules.

[0008] Therefore, the present disclosure aims to provide a joining metal paste that can sufficiently suppress the detachment of components in the production of a joined body using a metal paste, a joined body using the joining metal paste, and a method for producing the joined body.

[0009] The present disclosure relates to the following [1] to [9].

[0010] [1] A metal bonding paste containing metal particles, a reducing agent, and a dispersion medium, the yield stress of which measured by the following procedure is 2.0 MPa or less. Yield stress measurement procedure: (1) The metal bonding 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 x 3 mm x 0.05 mm thick. (2) Using a die shear tester, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool at 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 stress at which the permanent strain in the stress (MPa)-strain (%) curve is 0.2% is defined as the yield stress (MPa). [2] The metal paste for joining according to [1], wherein the metal particles have, on their surfaces, 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, the reducing agent is a polyhydric alcohol, and the metal paste for joining further contains a second fatty acid having 18 or less carbon atoms. [3] The metal paste for joining according to [2], wherein the content of the second fatty acid is 5 mass% or less based on the total amount of the metal paste for joining. [4] The metal paste for joining according to [2] or [3], wherein the second fatty acid has a weight loss rate of 2 mass% or less when heated at 90°C for 30 minutes in a nitrogen atmosphere. [5] The metal paste for joining according to any one of [1] to [4], wherein the metal paste for joining contains a gelling agent. [6] A joined body comprising a first member, a second member, and a joining portion joining them, wherein the joining portion comprises a sintered body of the metal paste for joining according to any one of [1] to [5]. [7] A method for manufacturing a bonded body, comprising: a first step of applying the bonding metal paste according to any one of [1] to [5] 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 arranging 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. [8] The method for manufacturing a bonded body according to [7], wherein in the third step, the second member is pressure-bonded onto the metal particle-containing layer, which has been heated to 90°C or higher, at a pressure of 0.5 to 2 MPa for a pressure-bonding time of 3 seconds or less.[9] A method comprising: a first step of applying a bonding metal paste onto a first member to form a coating film of the bonding metal paste; and a second step of drying the coating film to form a metal particle-containing layer. １ The second member is applied to the metal particle-containing layer heated to 0.5° C. or higher under a pressure of Y １ a third step of pressing the metal particles together at a pressure of 100 MPa or more to obtain a laminate; and a fourth step of sintering the metal particle-containing layer of the laminate, wherein the bonding metal paste contains metal particles, a reducing agent, and a dispersion medium, and the yield stress X of the bonding metal paste measured by the following procedure is １ is 2.0 MPa or less, and X １ / Y １ The yield stress of the bonded body is 4.0 or less. (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 of 3 mm x 3 mm x 0.05 mm thick. (2) A die shear tester is used to heat the metal particle-containing layer with a 4 mm wide tool at a heating temperature T １ The tool is pressed horizontally under the conditions of 100°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 stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2% is defined as the yield stress X １ (MPa).

[0011] According to the present disclosure, it is possible to provide a joining metal paste that can sufficiently suppress the falling off of components in the production of a joined body using a metal paste, a joined body using the joining metal paste, and a method for producing a joined body.

[0012] It is a figure showing a graph for explaining the definition of yield stress, It is a schematic diagram for explaining a method for measuring yield stress, It is a schematic diagram for explaining a method for measuring tack strength.

[0013] Hereinafter, an embodiment for carrying out the present disclosure (hereinafter referred to as the "present embodiment") will be described in detail. The present disclosure is not limited to the following embodiment.

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

[0015] [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 x 3 mm x 0.05 mm thick. (2) Using a die shear tester, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool at 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 stress at which the permanent strain in the stress (MPa)-strain (%) curve is 0.2% is defined as the yield stress (MPa).

[0016] When a tool is applied to a metal particle-containing layer, the metal particle-containing layer undergoes elastic deformation depending on the magnitude of the external force, and plastic deformation occurs when the stress reaches a certain level. Elastic deformation refers to deformation that occurs as a result of the application of an external force, but returns to its original shape when the external force is removed. Plastic deformation refers to deformation that occurs as a result of the application of an external force, but does not return to its original shape when the external force is removed. The stress at which elastic deformation begins to transition to plastic deformation is called the yield point. Before the yield point, there is a roughly proportional relationship (linear correlation) between the magnitude of the external force and the degree of deformation of the metal particle-containing layer, but 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] FIG. 1 is a diagram showing a stress (MPa)-strain (%) curve for explaining the definition of yield stress. As shown in FIG. 1, when the metal particle-containing layer is pressed horizontally with a tool, the strain (%) of the metal particle-containing layer increases. In the present disclosure, the strain (%) of the metal particle-containing layer refers to the ratio of the tool movement distance to the measured length of the metal particle-containing layer in the tool movement direction (3 mm) (100 × tool movement distance (mm) / 3 mm). In the present disclosure, the stress X (MPa) at which the permanent strain becomes 0.2% is defined as the yield stress (MPa).

[0018] The stress at which the permanent strain becomes 0.2% is the approximate straight line (R ２ >95%) on the horizontal axis so that it passes through the point where the permanent set (%) is 0.2%, and it can be found from the intersection of the approximation line and the curve. ２ An approximate straight line is obtained for the rise of the stress (MPa)-strain (%) curve so that the coefficient of determination is 95% or more, and the length of the approximate straight line in the direction in which the tool moves in the metal particle-containing layer before measurement is L ０ (In this embodiment, L ０ = 3 mm), the tool movement distance is 0.002 × L ０ The stress at which the permanent strain becomes 0.2% can be determined from the intersection of the approximate straight line obtained by translating (offsetting) the curve so that it passes through point 1 and the original curve.

[0019] The above-mentioned bonding metal paste can sufficiently prevent components from falling off when manufacturing a bonded body using the metal paste. The inventors speculate as follows about the reason for this effect. Because 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 placing the components under predetermined conditions of temperature and pressure (for example, conditions under which the yield stress is 4.0 times or less the pressure at the temperature at which the yield stress is measured) and by performing compression bonding for a predetermined time, it is possible to prevent voids from occurring between the components to be bonded and the metal particle-containing layer, thereby improving tack strength.

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

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

[0022] Hereinafter, each component used in the metal bonding paste of this embodiment will be described in detail.

[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 semi-metal particles, as well as alloy particles made by combining two or more of these.

[0024] The alloy particles may be copper alloy particles formed from an alloy of copper and a metal other than copper, such as 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 a monovalent or divalent copper compound. Examples of the monovalent or divalent copper compound include cuprous oxide, cupric oxide, cuprous hydroxide, cupric hydroxide, cuprous carbonate, cupric carbonate, copper nitride, and copper(I) phosphide. From the viewpoint of cost and availability as particles, the copper compound particles may contain 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 or higher and 300°C or lower.

[0027] The metal particles may have, on the surface thereof, 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.

[0028] The carboxylic acid compound having a molecular weight of 300 g / mol or less is a compound having at least one carboxy group in the molecule and having a molecular weight of 300 g / mol or less. Examples of the carboxylic acid compound having a molecular weight of 300 g / mol or less include fatty acids (hereinafter sometimes referred to as first fatty acids) having 10 to 18 carbon atoms (including the carbon atoms of the carboxyl group). Examples of the first fatty acid include capric acid (decanoic acid), methyl nonanoic acid, ethyl octanoic acid, propyl heptanoic acid, butyl hexanoic acid, undecanoic acid, methyl decanoic acid, ethyl nonanoic acid, propyl octanoic acid, butyl heptanoic acid, 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, pentyl decanoic acid, hexyl nonanoic acid, palmitic acid, methyl pentadecanoic acid, ethyl tetradecanoic acid, Saturated fatty acids such as ladecanoic 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 such as octenoic acid, nonenoic acid, methylnonenoic 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.

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

[0030] The carboxylic acid compounds having a molecular weight of 300 g / mol or less may be used alone or in combination of two or more.

[0031] Examples of alcohol compounds having 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 the 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 it possible to sinter the material under mild conditions of low temperature (300°C or less) and low pressure (10 MPa or less).

[0033] The copper particles include submicro copper particles and micro copper particles. The copper particles refer to particles containing copper as a main component, for example, particles having a copper content of 80% by mass or more. The copper content of the 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 submicron copper particles may be copper particles that are sinterable in a temperature range of 200°C to 380°C. Examples of submicron copper particles include copper particles having a particle size of 0.05 μm to 0.8 μm. For example, copper particles having a volume average particle size of 0.05 μm to 0.8 μm can be used. When the volume average particle size of the submicron copper particles is 0.05 μm or more, effects such as reduced synthesis costs, good dispersibility, and reduced amounts of organic protective agents used are easily achieved. When the volume average particle size of the submicron copper particles is 0.8 μm or less, the effect of excellent sinterability of the submicron copper particles is easily achieved. From the viewpoint of further achieving the above effects, the volume average particle size of the submicron copper particles may be 0.6 μm or less, 0.5 μm or less, or 0.4 μm or less. Furthermore, the volume average particle size of the submicron 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 submicron 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 the present disclosure, the volume average particle size refers to the 50% volume average particle size. The volume average particle size of metal particles can be determined by, for example, dispersing raw material metal particles or dried copper particles obtained by removing volatile components from a metal paste in a dispersion medium using a dispersant, and measuring the resulting dispersion medium with 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, examples of dispersing media that can be used include hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, and water.

[0036] The content of the submicron copper particles 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, or 80% by mass or less, based on the total mass of the metal particles, 20% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 80% by mass or less, 20% by mass or more, 30% by mass or more, 35% by mass or more, 85% by mass or less, 40% by mass or more, 80% by mass or less, or 60% by mass or more, 80% by mass or less. If the content of the submicron copper particles is within the above range, it is easy to ensure the bonding strength of the bonded body, and when the bonded members are semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability.

[0037] The content of the submicron copper particles may be 20% by mass or more and 90% by mass or less, based on the total mass of the copper particles. If the content of the submicron copper particles is 20% by mass or more, when used in combination with microcopper particles such as flaky microcopper particles, the spaces between the copper particles can be sufficiently filled, making it easier to ensure the bonding strength of the bonded body. When the bonded members are semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. If the content of the submicron copper particles is 90% by mass or less, the volume shrinkage in the in-plane direction (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 bonded body. When the bonded members are semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. From the viewpoint of further achieving the above-mentioned effect, the content of the submicron copper particles 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 the copper particles.

[0038] The shape of the submicron copper particles is not particularly limited. Examples of the shape of the submicron copper particles include spherical, blocky, needle-like, flake-like, approximately spherical, and aggregates thereof. From the viewpoint of dispersibility and packing ability, the shape of the submicron copper particles may be spherical, approximately spherical, or flake-like. From the viewpoint of combustibility, dispersibility, mixability with flaky microparticles, etc., the shape may be spherical or approximately spherical. In the present disclosure, the term "flake-like" includes flat shapes such as plate-like and scale-like.

[0039] From the viewpoints of dispersibility, packing property, and mixability with flaky microparticles, the aspect ratio of the submicron copper particles may be 5 or less, 4 or less, or 3 or less. In the present disclosure, the "aspect ratio" refers to the long side (major axis) / thickness of the particle. The long side (major axis) and thickness of the particle can be measured, for example, from an SEM image of the particle.

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

[0041] The amount of the surface treatment agent to be used for the treatment may be an amount that allows one to three molecular layers to adhere to the surface of the submicron copper particles. This amount depends on the number of molecular layers (n) attached to the surface of the submicron copper particles, the specific surface area (A ｐ ) (unit m 2 / g) and the molecular weight of the surface treatment agent (M ｓ ) (unit: g / mol) and the minimum coverage area of ​​the surface treatment agent (S Ｓ ) (unit m ２ / piece) and Avogadro's number (N Ａ ) (6.02 x 10 ２３ Specifically, the amount of surface treatment agent can be calculated from the following formula: Treatment amount of surface treatment agent (mass%) = {(n·A ｐ ・M ｓ ) / (S Ｓ ・N Ａ +n・A ｐ ・M ｓ )} × 100%.

[0042] The specific surface area of ​​the submicron copper particles can be calculated by measuring the dried submicron copper particles using the BET specific surface area measurement method. When the surface treatment agent is a linear saturated fatty acid, the minimum coverage area of ​​the surface treatment agent is 2.05 × 10 －１９ m ２ / 1 molecule. In the case of 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" (Kamieda Katsuhiro, Inafuku Sumio, Mori Iwao, 40(2), 1992, pp. 114-117). An example of a method for quantifying the surface treatment agent is shown below. The surface treatment agent can be identified by a thermal desorption gas / gas chromatograph mass spectrometer for the dried powder obtained by removing the dispersant 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. Examples of carbon content analysis methods include high-frequency induction heating furnace combustion / infrared absorption method. The amount of the surface treatment agent can be calculated using the above formula from the carbon number, molecular weight, and carbon content of the identified surface treatment agent.

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

[0044] Commercially available submicron copper particles can be used, such as CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd.) and Tn-Cu100 (manufactured by Taiyo Nippon Sanso Co., Ltd.).

[0045] As the micro copper particles, copper particles having a particle size of 2 μm to 50 μm can be used, for example, copper particles having a volume average particle size of 2 μm to 50 μm. When 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 during sintering without pressure or under pressure can be sufficiently reduced, making it easier to ensure the bonding strength of the bonded body. When the bonded components are semiconductor elements, the semiconductor device tends to exhibit good die shear strength and connection reliability. To further achieve the above effects, 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 to 20 μm, 2 μm to 10 μm, 3 μm to 20 μm, or 3 μm to 10 μm.

[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 approximately parallel to the bonding surface, thereby suppressing 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 further achieving the above effects, the flake-shaped micro copper particles may have an aspect ratio of more than 2, 4 or more, 6 or more, 10 or more, or 50 or more.

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

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

[0049] The amount of the surface treatment agent may be an amount equivalent to one molecular layer or more on the particle surface. The amount of such a 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 the surface treatment agent may be 0.1 to 15 mass%, 1 to 15 mass%, 5 to 15 mass%, or 8 to 12 mass% based on the mass of the micro copper particles having 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 in the case of the submicro copper particles described above.

[0050] Commercially available micro copper particles can be used. Examples of commercially available spherical micro particles include Cu-HWQ series (manufactured by Fukuda Metal Foil & Powder 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 Co., Ltd.).

[0052] The metal paste may contain submicron copper particles and micron copper particles as metal particles, which can suppress volume shrinkage and sintering shrinkage that accompany drying of the dispersion medium, and facilitate preventing peeling between the joining surfaces of the members and the sintered body of the metal particle-containing layer.

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

[0054] In order to improve sinterability, the metal paste may contain spherical submicro copper particles and spherical micro copper particles as metal particles, in which the mass ratio of the spherical submicro copper particles to the spherical micro copper particles may be 30:70 to 90:10, or 40:60 to 80:20.

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

[0056] To prevent cracking after drying of the metal paste, the metal paste may contain spherical submicro copper particles and flaky micro copper particles as metal particles, in which the mass ratio of the spherical submicro copper particles to the flaky micro copper particles may be 30:70 to 90:10, or 40:60 to 80:20.

[0057] The metal paste may contain submicro copper particles, flaky micro copper particles, and spherical micro copper particles from the viewpoints of low-temperature sintering properties, suppression of volumetric shrinkage in the XY directions (directions parallel to the joining surface), and improving the packing of metal particles in the metal particle-containing layer.

[0058] From the above viewpoint, the metal paste comprises submicro copper particles having a volume average particle size of 0.05 μm to 0.8 μm, spherical micro copper particles having a volume average particle size of 2 μm to 50 μm and an aspect ratio of 2 or less, and flaky micro copper particles having an aspect ratio of more than 2, wherein the total content of the submicro copper particles, the spherical micro copper particles, and the flaky 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 the submicro copper particles, the spherical micro copper particles, and the flaky micro copper particles may be 20% by mass to 80% by mass, 5% by mass to 50% by mass, and 5% by mass to 50% by mass, respectively, based on the total mass thereof, or may be 60% by mass to 80% by mass, 10% by mass to 20% by mass, and 10% by mass to 20% by mass.

[0059] The metal paste containing copper particles may contain metal particles containing metal elements other than copper (other metal particles). The other metal particles may include, for example, particles of zinc, gold, palladium, silver, nickel, platinum, brass, manganese, tin, antimony, indium, aluminum, vanadium, etc. The other metal particles may have a volume average particle size of 0.01 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, or 0.05 μm or more and 3 μm or less.

[0060] When a metal paste containing copper particles contains other metal particles, a sintered body in which multiple types of metals are dissolved or dispersed can be obtained, which improves the mechanical properties of the sintered body, such as yield stress and fatigue strength, and tends to improve connection reliability. Furthermore, by adding multiple types of metal particles, the sintered body of the metal particle-containing layer can have sufficient bonding strength to a predetermined adherend. When the member to be bonded is a semiconductor element, the die shear strength and connection reliability of the semiconductor device are likely to be improved.

[0061] When the metal paste containing copper particles contains other metal particles, the content of the other metal particles may be less than 5 mass % or may be 3 mass % or less based on the total mass of the metal particles, from the viewpoint of obtaining sufficient bonding properties. The 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 the metal paste.

[0063] (Reducing Agent) Examples of the reducing agent include polyhydric alcohols. Examples of the polyhydric alcohols include pentaethylene glycol, hexaethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polyethylene glycols such as polyethylene glycol 200, polyethylene glycol 300, and polyethylene glycol 400, polypropylene glycols 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] The polyhydric alcohol may be polyethylene glycol, or may be polyethylene glycol 200, polyethylene glycol 300, or polyethylene glycol 400, from the viewpoint that it functions as a highly polar solvent, can exhibit a reducing effect at the heating temperature of the metal paste, and can easily ensure sufficient sinterability.

[0065] The polyhydric alcohols can be used alone or in combination of two or more.

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

[0067] (Dispersion medium) Examples of the dispersion medium include monohydric and polyhydric alcohols such as pentanol, hexanol, heptanol, octanol, decanol, dihydroterpineol, terpineol, isobornylcyclohexanol (MTPH), 1,5-pentanediol, 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, and diethylene glycol isopropyl methyl ether. Ethers such as triethylene glycol dimethyl ether, 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;Examples of mercaptans having an alkyl group having 1 to 18 carbon atoms include mercaptans having a cycloalkyl group having 5 to 7 carbon atoms. Examples of mercaptans having an alkyl group having 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 having 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, or 5% by mass or more, or 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. Furthermore, 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 the 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 the metal particles due to low viscosity and sintering inhibition due to residue during sintering can be suppressed.

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

[0070] The metal paste of this embodiment may further contain a second fatty acid when 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 surfaces and contain a reducing agent that is a polyhydric alcohol.

[0071] (Second Fatty Acid) The second fatty acid may be a fatty acid having a carbon number (including the carbon of the carboxyl group) of 18 or less. 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 saturated fatty acids such as 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 such as octenoic acid, nonenoic acid, methylnonenoic 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] From the viewpoints of storage stability and affinity with the reducing agent, the second fatty acid may be a fatty acid having 8 to 18 carbon atoms, a fatty acid having 10 or less carbon atoms, or a fatty acid having 8 to 10 carbon atoms. Furthermore, from the viewpoint of reducing residue after the drying step, the second fatty acid may be decanoic acid, lauric acid, myristic acid, palmitic acid, or stearic acid.

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

[0074] From the viewpoint of improving tackiness, the weight loss rate of the second fatty acid when heated at 90°C for 30 minutes in a nitrogen atmosphere may be 2% by mass or less, 1% by mass or less, or 0.5% by mass or less. In such cases, the tackiness can be further improved by leaving a larger amount of the second fatty acid 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 carried out, for example, using a simultaneous differential thermal analysis (TG-DTA) measuring device, and the weight loss rate can be calculated from the TG-DTA measurement results using the following formula: Weight loss rate (mass%) = 100 × (Z １ -Z ２ ) / Z １ During the ceremony, Z １ represents the mass (g) of the second fatty acid before heating, Z ２ represents the mass (g) of the second fatty acid after heating at 90°C for 30 minutes under a nitrogen atmosphere.

[0075] The TG-DTA measurement conditions may be, for example, the following: <Measurement conditions> Apparatus: NEXTA STA200RV (manufactured by Hitachi High-Tech Science Corporation) Atmosphere: Nitrogen atmosphere Heating conditions: The temperature is raised from room temperature (25°C) to 90°C at a rate of 10°C / min, and the sample is heated at 90°C for 30 minutes, after which heating is stopped and the temperature is lowered 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 that metal sintering inhibition (e.g., copper sintering inhibition) will occur due to residual components.

[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 less, or 20 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the 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 mass% or more, 1 mass% or more, 5 mass% or less, 3 mass% or less, 0.5 mass% or more and 5 mass% or less, or 1 mass% or more and 3 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 having 10 or more carbon atoms on the surface, a reducing agent which is a polyhydric alcohol, and a second fatty acid having 10 or less carbon atoms.

[0080] The inventors speculate as follows as to why the tackiness of the above-mentioned metal paste is further improved. The surfaces of metal particles protected with a first fatty acid having 10 or more carbon atoms exhibit hydrophobic properties because the long-chain alkyl groups are arranged outward. The polyhydric alcohol added as a reducing agent is hydrophilic, and therefore has poor wettability with metal particles protected with a fatty acid. However, it is believed that the second fatty acid, a fatty acid having 10 or less carbon atoms, coordinates in multiple layers on the surfaces of the metal particles, buffering the hydrophobicity and improving the wettability between the metal particles and the polyhydric alcohol. The inventors speculate that this results in the formation of a liquid film of the polyhydric alcohol on the surfaces of the metal particles, making the metal particle-containing layer more susceptible to plastic deformation, thereby improving the tackiness.

[0081] (Gelling Agent) In order to further improve 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 content of the gelling agent in the metal paste may be 0.1 to 1 mass % or 0.3 to 0.5 mass % based on the total mass of the metal paste.

[0083] (Other Components) The metal paste may contain additives such as wetting improvers such as nonionic surfactants and fluorine-based surfactants; surface tension adjusters; dispersants such as alkylamines and alkylcarboxylic acids; antifoaming agents such as silicone oils; and ion trapping agents such as inorganic ion exchangers. The content of the additives may be adjusted appropriately within a range that does not impair the effects of the present invention. Furthermore, the metal paste may have a total content of nonmetallic inorganic particles (e.g., glass particles) of 1% by mass or less, or 0.1% by mass or less, based on the total amount of metal particles. Furthermore, the metal paste may not contain nonmetallic inorganic particles.

[0084] Examples of nonionic surfactants include polyether compounds, which are amphiphilic, such as 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. The polyoxyalkylene alkyl ether is preferably polyoxyethylene oleyl ether, from the viewpoint of preventing copper sintering from being inhibited by residual components.

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

[0087] The polyether compounds can be used alone or in combination of two or more.

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

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

[0090] The metal paste may not contain a nonionic surfactant.

[0091] The viscosity of the metal paste is not particularly limited, and when it is applied by a method 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 be composed 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 of the first liquid, the second liquid is applied to the surface of the coating film or dried film, and the coating film can be further dried as necessary to form a metal particle-containing layer.

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

[0094] When the metal paste is composed of a plurality of chemical liquids, the yield stress of the mixture of the chemical liquids can be determined in the same manner as described above.

[0095] <Method for manufacturing a metal paste for bonding> The metal paste can be prepared by mixing the above-mentioned metal particles (e.g., submicro 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 the components, a stirring process or a dispersion process may be performed. The maximum particle size of the metal paste dispersion may be adjusted by a classification operation.

[0096] The above method may include a step of surface treating the metal particles with 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.

[0097] The stirring treatment can be carried out using a stirrer, such as an Ishikawa stirrer, a Silverson stirrer, a cavitation stirrer, a rotation-revolution type stirrer, an ultra-thin film high-speed rotary disperser, an ultrasonic disperser, a Raikai mixer, a twin-screw kneader, a bead mill, a ball mill, a three-roll mill, a homomixer, a planetary mixer, an ultra-high pressure type disperser, a thin layer shear disperser, or a dispersizer.

[0098] Examples of the dispersion treatment include a thin layer shear disperser, a dispersizer, a bead mill, an ultrasonic homogenizer, a high shear mixer, a narrow gap three-roll mill, a wet ultra-atomizer, a supersonic jet mill, and an ultra-high pressure homogenizer.

[0099] The classification can be carried out by, for example, filtration, natural sedimentation, or centrifugation. Examples of filters for filtration include a water comb, a metal mesh, a metal filter, and a nylon mesh.

[0100] <Jointed body> The joined body of this embodiment is a joined body including a first member, a second member, and a joining portion that joins them, and the joining portion includes a sintered body of the above-mentioned joining metal paste. In the joined body of this embodiment, since the joining portion includes the above-mentioned sintered body of the above-mentioned joining metal paste, falling off of the members is sufficiently suppressed.

[0101] <Method for manufacturing a bonded body> A first embodiment of the method for manufacturing a bonded body of the present disclosure includes a first step of applying the above-described 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 arranging 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 producing a bonded body according to the present embodiment, the metal particle-containing layer has excellent tackiness, which improves the tack strength between the first and second members in the laminate, thereby preventing the first or second member from falling off during transport of the laminate.

[0103] Examples of the first member and the second member include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, MOS-FETs, thyristors, logic, sensors, analog integrated circuits, LEDs, semiconductor lasers, and oscillators; lead frames, metal plate-attached ceramic substrates (e.g., DBCs), and substrates for mounting semiconductor elements such as LED packages; power supply members such as copper ribbons, metal blocks, and terminals; heat sinks; and water-cooled plates.

[0104] The first member and the second member may have a metal layer on their joining surfaces that forms a metal bond with the sintered body of the metal paste. Examples of metals constituting the metal layer include copper, nickel, silver, gold, palladium, platinum, lead, tin, and cobalt. These metals may be used alone or in combination of two or more. The metal layer may also be an alloy containing the above metals. In addition to the above metals, examples of metals used in the alloy include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, and molybdenum. Examples of members having a metal layer include members plated with various metals, wires, chips plated with metals, heat spreaders, ceramic substrates with metal plates attached, lead frames plated with various metals or made of various metals, copper plates, and copper foils.

[0105] (First Step) In the first step, the above-described bonding metal paste is applied onto a first member to form a coating film of the bonding metal paste.

[0106] Methods that can be used to apply the metal paste onto the first member include inkjet printing, super inkjet printing, screen printing, transfer printing, offset printing, jet printing, a dispenser, a jet dispenser, a needle dispenser, a comma coater, a slit coater, a die coater, a gravure coater, a slit coat, letterpress printing, intaglio printing, gravure printing, stencil printing, soft lithography, a bar coater, an applicator, a particle deposition method, a spray coater, a spin coater, a dip coater, and electrodeposition coating.

[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. 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] (Second Step) In the second step, the coating film is dried to form a metal particle-containing layer. Methods for drying the coating film include heat drying and vacuum drying.

[0109] The gas atmosphere during heat drying or reduced pressure drying may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing atmosphere such as hydrogen or formic acid.

[0110] For heat drying or reduced pressure drying, for example, a hot plate, a warm air dryer, a warm air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, a hot plate press device, etc. The drying temperature and time may be appropriately adjusted depending on the type and amount of the dispersion medium used.

[0111] In the second step, the metal particle-containing layer may be dried so that the content of the dispersion medium in the metal particle-containing layer 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 may be dried so that the dispersion medium is substantially absent (e.g., 0% by mass). Also, the metal particle-containing layer may be dried so that the content of the dispersion medium in the metal particle-containing layer 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 may be dried so that the dispersion medium is substantially absent (e.g., 0% by mass).

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

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

[0114] In the second step, the contents of the dispersion medium, the reducing agent, and the 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, the reducing agent, and the second fatty acid to be added, respectively.

[0115] (Third Step) In the third step, a second member is disposed on the metal particle-containing layer to obtain a laminate.

[0116] Examples of methods for placing the second member on the metal particle-containing layer include using a chip mounter, a flip chip bonder, and a carbon or ceramic positioning jig.

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

[0118] The metal particle-containing layer can be heated using, for example, a hot plate, a flip-chip bonder, etc. A flip-chip bonder can heat the substrate side and the member side separately.

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

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

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

[0122] The obtained laminate can be transported to a sintering furnace or the like for carrying out the fourth step. Examples of transporting means include manual transport, an automatic conveyor, a transport machine, an automatic cart, a robot arm, etc. In the laminate, the second member is sufficiently temporarily fixed by the metal particle-containing layer having excellent tackiness, so that the problem of the second member falling off during the transport is unlikely to occur.

[0123] (Step 4) In step 4, 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 containing no hydrogen or having a hydrogen concentration of 10% or less. Note that the oxygen-free atmosphere refers to an atmosphere having an oxygen concentration of 1% by volume or less, and the oxygen concentration may be 0.1% by volume or less, 0.01% by volume or less, or 0.001% by volume or less.

[0124] The heat treatment can be performed using a heating device having a pressure bonding mechanism, such as a hot plate, a warm air dryer, a warm air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, or a steam heating furnace.

[0125] The hydrogen-free atmosphere may be a non-oxidizing gas such as nitrogen, a rare gas, a heat-resistant organic gas, water vapor, or a mixture thereof, or may be under vacuum.

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

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

[0128] The maximum temperature holding time may be 1 minute or more and 60 minutes or less, 1 minute or more and less than 40 minutes, or 1 minute or more and less than 30 minutes, from the viewpoint of volatilizing all of the dispersion medium and improving the yield. In particular, when the maximum temperature to be reached is 250°C or more, sintering tends to proceed sufficiently with a holding time of 10 minutes or less.

[0129] Through the fourth step, a bonded body including the first member, the second member, and the sintered body of the metal particle-containing layer bonding them together can be obtained.

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

[0131] In the bonded structure, at least one of the first member and the second member may be a semiconductor element. Examples of semiconductor elements include power modules including diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, Schottky diodes, and fast recovery diodes, as well as transmitters, amplifiers, and LED modules. In such cases, the bonded structure 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 including diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, Schottky diodes, and fast recovery diodes, as well as transmitters, amplifiers, high-brightness LED modules, semiconductor laser modules, logic, and sensors.

[0133] A second embodiment of the method for manufacturing a joined body of the present disclosure includes a first step of applying a joining metal paste to 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, and a T １ The second member is applied under pressure Y onto the metal particle-containing layer that has been heated to 500°C or higher. １ The method includes a third step of obtaining a laminate by pressing at a pressure of at least 100 MPa, 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 X of the bonding metal paste measured by the following procedure: １ is 2.0 MPa or less, and X １ / Y １ The yield stress is 4.0 or less. Measurement procedure: (1) The bonding metal paste is applied to a copper substrate and dried at 90°C for 30 minutes to form a metal particle-containing layer of 3 mm x 3 mm x 0.05 mm thick. (2) Using a die shear tester, the metal particle-containing layer is heated with a tool having a width of 4 mm at a heating temperature T １ The tool is pressed horizontally under the conditions of 100°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 stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2% is defined as the yield stress X １ (MPa).

[0135] The materials constituting the first member, the second member and the joining metal paste in the second embodiment of the method for manufacturing a joined body can be the same as the materials 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, the yield stress X of the bonding metal paste １ But Y １ By making the X 4.0 times or less, it is possible to suppress the occurrence of voids between the members to be joined and the metal particle-containing layer due to the plastic deformation of the metal particle-containing layer in the third step, and it is possible to obtain a laminate having excellent tack strength. １ / Y １ may be 3.0 or less, 2.5 or less, 2.0 or less, or 1.0 or less. １ / Y １ may be 0.9 or more.

[0137] Heating temperature T １From the viewpoint of improving tackiness, the temperature may be 80 to 130°C, 85 to 120°C, or 90 to 110°C.

[0138] Crimping pressure Y １ 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 of the member to which the bonding metal paste is applied and from the viewpoint of improving tackiness.

[0139] The pressure-bonding time may be adjusted appropriately depending on the member to which the bonding metal paste is applied and the pressure of the pressure-bonding, and may be, for example, 3.0 seconds or less, 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 T １ Yield stress X of metal paste at １ The heating temperature of the metal particle-containing layer and the pressure for pressing the second member in the third step may be set based on the above.

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

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

[0143] The following materials were prepared: (Submicron Copper Particles A) Copper particles having a volume average particle size of 0.21 μm and a treatment amount of lauric acid of 10% by mass were prepared as submicron copper particles A.

[0144] (Submicron Copper Particles B) Copper particles having a volume average particle size of 0.18 μm and treated with 2% by mass of octanoic acid were prepared as submicron copper particles B.

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

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

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

[0148] Example 1 Dihydroterpineol (manufactured by Nippon Terpene Chemical Co., Ltd.) as a dispersion medium, submicro copper particles A, and micro copper particles A were mixed in an environment of room temperature 25°C and humidity 60%, and the mixture was stirred for 30 minutes at 300 rpm using a planetary mixer (manufactured by Primix Co., Ltd.) The resulting mixture was dispersed once using a dispersizer (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] The dispersion obtained above was mixed with dihydroterpineol as the remainder of the dispersion medium, polyethylene glycol 200 (hereinafter abbreviated as PEG200) (manufactured by NOF Corporation) as a reducing agent, and decanoic acid (manufactured by New Japan Chemical Co., Ltd.) as a second fatty acid, and the mixture was stirred at 2000 rpm under reduced pressure for 3 minutes in a planetary mixer (Thinky's Awatori Rentaro ARE-310) to obtain metal paste a.

[0150] Examples 2 and 3 and Comparative Examples 1 to 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 the components used in preparing the metal paste were changed.

[0151] [Measurement of Weight Loss Rate of Second Fatty Acid] Each second fatty acid used in the examples was subjected to simultaneous differential thermal analysis (TG-DTA) under the following measurement conditions, and the weight loss rate (mass %) when the second fatty acid was heated at 90°C for 30 minutes in a nitrogen atmosphere was calculated using the following formula: Weight loss rate (mass %) = 100 × (Z １ -Z ２ ) / Z １ During the ceremony, Z １ represents the mass (g) of the second fatty acid before heating, Z２ represents the mass (g) of the second fatty acid after heating at 90°C for 30 minutes under a nitrogen atmosphere. <Measurement conditions> Apparatus: NEXTA STA200RV (manufactured by Hitachi High-Tech Science Corporation) Atmosphere: Nitrogen atmosphere Heating conditions: The temperature was raised from room temperature (25°C) to 90°C at a heating rate of 10°C / min, and after heating at 90°C for 30 minutes, heating was stopped and the temperature was lowered to room temperature (25°C).

[0152] The measurement results of the weight loss rate were 2.0% by mass for decanoic acid and 0.1% by mass for isostearic acid.

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

[0154] [Measurement of yield stress] The metal paste obtained above was printed on a copper plate (30 mm × 30 mm × 2 mm thick) to provide a coating film of 3.0 mm × 3.0 mm × 0.1 mm thick. The metal paste coating film was then dried in air on a hot plate heated to 90°C for 30 minutes to form a metal particle-containing layer (3 mm × 3 mm × 0.05 mm thick) in which the dihydroterpineol dispersion medium had been volatilized.

[0155] The yield stress was measured using a die shear tester (STELLAR4000, manufactured by Nordson) according to the following procedure. As shown in Fig. 2, a tool 30 having a width of 4 mm 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, and a stress (MPa)-strain (%) curve was obtained by defining the ratio of the tool movement distance to the length (3 mm) of the metal particle-containing layer being measured in the direction in which the tool moved as strain (%). The obtained stress-strain curve was fitted to R by the least squares method. ２ An approximate straight line was calculated for the rising part of the curve so that the coefficient of determination was 95% or more, and the approximate straight line was translated (offset) so that it passed through the point where the strain (%) was 0.2% (the point where the tool travel distance was 0.002 × 3 mm). From the intersection of the approximate straight line and the original curve, the stress at which the permanent strain was 0.2% was calculated as the yield stress (MPa). The results are shown in Table 1.

[0156]

[0157] [Measurement of Tack Strength] The metal paste obtained above was printed on a copper plate (30 mm x 30 mm x 2 mm thick) to provide a coating film measuring 3.0 mm x 3.0 mm x 0.1 mm. Next, the metal paste coating was dried for 30 minutes on a hot plate heated to 90 ° C. under atmospheric pressure, and the dihydroterpineol dispersion medium was evaporated to form a metal particle-containing layer (3 mm x 3 mm x 0.05 mm thick). A dummy chip (3 mm x 3 mm x 0.4 mm thick, having a copper layer as the adhesion surface (bonding surface)) was mounted on the formed metal particle-containing layer using a desktop hot mount device (TRESKY, T-3000-FC3) under any of the following conditions A to C, 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. <Mounting conditions> Condition A: Pressure 1.0 MPa, compression time 3.0 seconds Condition B: Pressure 2.0 MPa, compression time 1.0 seconds Condition C: Pressure 2.0 MPa, compression time 0.15 seconds

[0158] The tack strength of the obtained laminate was measured using a die shear tester (STELLAR 4000, manufactured by Nordson) according to the following procedure. As shown in Figure 3, the tool 30 was pressed 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, and the shear load was measured. The maximum shear load (N) was calculated as a function of the chip area (mm ２ The value obtained by dividing the measured value by the coefficient of friction coefficient (kPa) was defined as the tack strength (kPa), and the average value of the measured values ​​for eight laminates was taken as the tack strength. The results are shown in Table 2.

[0159]

[0160] 10... copper substrate, 20... metal particle-containing layer, 30... tool, 40... dummy chip

Claims

1. A metal bonding paste containing metal particles, a reducing agent, and a dispersion medium, which has a yield stress of 2.0 MPa or less as measured by the following procedure. Yield stress measurement procedure: (1) The metal bonding 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 x 3 mm x 0.05 mm thick. (2) Using a die shear tester, the metal particle-containing layer is pressed horizontally with a 4 mm wide tool at 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 stress at which the permanent strain in the stress (MPa)-strain (%) curve is 0.2% is defined as the yield stress (MPa).

2. The metal bonding paste according to claim 1, wherein the metal particles have on their surfaces 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, the reducing agent is a polyhydric alcohol, and the paste further contains a second fatty acid having 18 or less carbon atoms.

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

4. A metal joining paste as described in claim 2, wherein the second fatty acid has a weight loss rate of 2 mass% or less when heated at 90°C for 30 minutes in a nitrogen atmosphere.

5. The metal bonding paste according to claim 1, which contains a gelling agent.

6. A joined body comprising a first member, a second member, and a joining portion joining them, wherein the joining portion comprises a sintered body of the joining metal paste according to any one of claims 1 to 5.

7. A method for manufacturing a bonded body, comprising: a first step of applying the 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 of drying the coating film to form a metal particle-containing layer; a third step of arranging 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.

8. The method for producing a joined body according to claim 7, wherein in the third step, the second member is pressure-bonded onto the metal particle-containing layer heated to 90°C or higher at a pressure of 0.5 to 2 MPa for a pressure-bonding time of 3 seconds or less.

9. A first step of applying a 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; １ The second member is applied to the metal particle-containing layer heated to 0.5° C. or higher under a pressure of Y １ a third step of pressing the metal particles together at a pressure of 100 MPa or more to obtain a laminate; and a fourth step of sintering the metal particle-containing layer of the laminate, wherein the bonding metal paste contains metal particles, a reducing agent, and a dispersion medium, and the yield stress X of the bonding metal paste measured by the following procedure is １ is 2.0 MPa or less, and X １ / Y １ The method for producing a bonded body, wherein the bond strength is 4.0 or less. Measurement procedure for yield stress: (1) Apply the bonding metal paste to a copper substrate and dry it at 90°C for 30 minutes to form a metal particle-containing layer of 3 mm x 3 mm x 0.05 mm thick. (2) Using a die shear tester, the metal particle-containing layer is heated with a 4 mm wide tool at a heating temperature T １ The tool is pressed horizontally under the conditions of 100°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 stress at which the permanent strain in the stress (MPa)-strain (%) curve becomes 0.2% is defined as the yield stress X １ (MPa).

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