Joint structure, joining material, and method for manufacturing a joint structure

Abstract

To prevent reduction in bonding strength even after prolonged use in high temperature environments.SOLUTION: A bonding structure (100) includes a first bonding object (110), a second bonding object (120), and a bonding layer (130). The bonding layer (130) bonds the first bonding object (110) and the second bonding object (120). The first bonding object (110) is non-metallic. The bonding layer (130) contains a metal precursor that decomposed at a predetermined temperature and metal particles that did not decompose at the predetermined temperature.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a joined structure, a joining material, and a method for manufacturing a joined structure.

Background Art

[0002] It is known to integrally join a plurality of members to each other. For example, in a semiconductor device, a semiconductor chip is mounted on a substrate via a joining layer. In recent years, it has been considered to mount a semiconductor element (particularly, a power semiconductor element) often used in a high-temperature environment on a substrate using a silver joining layer obtained by sintering silver particles (see Patent Document 1).

[0003] Patent Document 1 discloses a joining material containing, in addition to silver particles, a solvent, 2-butoxyethoxyacetic acid as a dispersant, and benzotriazole as a reaction inhibitor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in a joined structure produced using a conventional joining material, when used for a long time in a high-temperature environment, the joining strength of the joining material may significantly decrease.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a joined structure, a joining material, and a method for manufacturing a joined structure capable of suppressing a decrease in joining strength even when used for a long time in a high-temperature environment.

Means for Solving the Problems

[0007] The bonding structure according to the present invention comprises a first object to be bonded, a second object to be bonded, and a bonding layer that bonds the first object to be bonded and the second object to be bonded. The first object to be bonded is nonmetallic. The bonding layer contains a metal precursor that has decomposed at a predetermined temperature and metal particles that have not dissolved at the predetermined temperature.

[0008] In one embodiment, the second object to be joined is made of metal or is made of non-metal.

[0009] In one embodiment, the bonding layer contains 1% by mass or more and less than 100% by mass of metal particles.

[0010] In one embodiment, the particle size of the metal particles is 0.02 μm or more and 10 μm or less.

[0011] In one embodiment, the metal precursor includes a silver precursor.

[0012] The bonding material according to the present invention contains a metal precursor that decomposes at a predetermined temperature and metal particles that do not decompose at the predetermined temperature.

[0013] A method for manufacturing a bonded structure according to the present invention includes the steps of: preparing a first object to be joined; preparing a second object to be joined; preparing a joining material; forming a laminate by stacking the first object to be joined and the second object to be joined via the joining material; and forming a joining layer from the joining material that joins the first object to be joined and the second object to be joined by heating the laminate at a predetermined temperature. The joining material contains a metal precursor that decomposes at the predetermined temperature and metal particles that do not decompose at the predetermined temperature. [Effects of the Invention]

[0014] According to the present invention, even when the bonded structure is used in a high-temperature environment for a long period of time, the decrease in the bonding strength of the bonded structure can be suppressed. [Brief explanation of the drawing]

[0015] [Figure 1]It is a schematic diagram of the joining structure according to this embodiment. [Figure 2] It is a figure showing a scanning electron micrograph of the joining layer according to this embodiment. [Figure 3] It is a schematic diagram of the joining material according to this embodiment. [Figure 4] (a) to (e) are schematic diagrams showing the manufacturing method of the joining structure according to this embodiment. [Figure 5] It is a figure showing a scanning electron micrograph of the joining material according to this embodiment. [Figure 6] It is a figure showing a scanning electron micrograph of the joining layer according to this embodiment. [Figure 7] It is a figure showing the shear strength of the joining layer according to this embodiment. [Figure 8] It is a figure showing the shear strength of the joining layer according to this embodiment.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of a joining structure, a joining material, and a method for manufacturing a joining structure according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0017] FIG. 1 shows a schematic diagram of a joining structure 100 of this embodiment. As shown in FIG. 1, the joining structure 100 includes a first joining object 110, a second joining object 120, and a joining layer 130. The joining layer 130 joins the first joining object 110 and the second joining object 120.

[0018] The first joining object 110 is made of a non-metal. The first joining object 110 may be an insulating member, a conductive member, or alternatively, the first joining object 110 may be a semiconductor member.

[0019] For example, the first bonding object 110 is an insulating substrate, and the first bonding object 110 may be a semiconductor chip. As an example, the semiconductor chip is a power semiconductor chip containing Si, SiC, or GaN. Also, as an example of other applicable non-metallic materials, SiO2, Si3N4, SnO2, In2O3, ITO (indium tin oxide), etc. can be mentioned.

[0020] The second bonding object 120 is made of non-metal or metal. The second bonding object 120 may be an insulating member or a conductive member. Alternatively, the second bonding object 120 may be a semiconductor member.

[0021] For example, the second bonding object 120 is an insulating substrate, and the second bonding object 120 may be a semiconductor chip. As an example, the semiconductor chip is a power semiconductor chip containing Si, SiC, or GaN. Also, as an example of other applicable non-metallic materials, SiO2, Si3N4, SnO2, In2O3, ITO (indium tin oxide), etc. can be mentioned.

[0022] In the bonding structure 100 of the present embodiment, the bonding layer 130 contains a metal precursor decomposed at a predetermined temperature and metal particles (cores) not decomposed at the predetermined temperature. The predetermined temperature is, for example, 20°C to 300°C, and preferably about 200°C to 300°C.

[0023] The metal precursor decomposes at a predetermined temperature. The metal precursor is, for example, a silver precursor. The silver precursor is, for example, a silver compound or an organic acid silver salt. The silver compound is, for example, silver(I,II) oxide, silver carbonate, or silver hydroxide. The organic acid silver salt is, for example, a silver salt of saturated fatty acids (1 to 24 carbon atoms) such as formic acid, acetic acid, lauric acid, myristic acid, palmitic acid, and stearic acid; a silver salt of unsaturated fatty acids (24 or less carbon atoms) such as oleic acid and linoleic acid; a silver salt of dicarboxylates (2 to 6 carbon atoms) such as oxalic acid, malonic acid, and acetonedicarboxylic acid; a silver silver salt of aromatic carboxylates such as benzoic acid and phthalic acid; a silver salt of hydroxy acids (2 to 6 carbon atoms) such as silver glycolate and citric acid. In particular, silver salt of formate, silver salt of oxalate, silver acetate, or silver salt of stearate is preferred. The silver precursor generates atomic to nanoscale silver through a decomposition reaction during thermal decomposition. Silver at the atomic to nanoscale can be interfacially bonded to nonmetallic surfaces at the atomic level.

[0024] The metal particles do not decompose at a predetermined temperature. Preferably, the metal particles contain at least one selected from the group consisting of silver, copper, nickel, zinc, gold, palladium, platinum, and alloys thereof. Furthermore, it is preferable that the metal particles contain silver or copper from the above metal group; in this case, the bonding layer 130 can achieve higher conductivity and higher heat dissipation characteristics.

[0025] Furthermore, it is even more preferable that the metal particles contain silver.

[0026] The metal particles may be spherical or flake-shaped. In this case, the average particle size of the metal particles is preferably 0.02 μm or more and 10 μm or less, and more preferably 0.05 μm or more and 30 μm or less.

[0027] The bonding layer 130 preferably contains 1% by mass or more and less than 100% by mass of metal particles, and more preferably contains 10% by mass or more and 70% by mass of metal particles.

[0028] The bonding layer 130 will now be described with reference to Figure 2. Figure 2 is a scanning electron microscope image of the bonding layer 130. The black areas represent metal particles. The white areas represent metal precursors. As shown in Figure 2, metal precursors were observed between the metal particles in the bonding layer 130.

[0029] In the bonded structure 100 of this embodiment, the bonding layer 130 contains not only metal particles that did not decompose at a predetermined temperature, but also metal precursors that did decompose at a predetermined temperature, thereby improving the bonding strength of the bonding layer 130. Furthermore, even when the bonded structure 100 is used at high temperatures for a long period of time (for example, 250°C or higher), the decrease in the bonding strength of the bonding layer 130 is suppressed.

[0030] Next, with reference to Figure 3, the bonding material S for forming the bonding layer 130 will be described. Figure 3 is a schematic diagram of the bonding material S. As shown in Figure 3, the bonding material S contains a metal precursor 134 that decomposes at a predetermined temperature and metal particles 132 that do not decompose at a predetermined temperature.

[0031] The metal precursor 134 decomposes at a predetermined temperature. The metal precursor 134 is a silver compound or an organic acid silver salt. The silver precursor is, for example, a silver compound or an organic acid silver salt. The silver compound is, for example, silver(I,II) oxide, silver carbonate, or silver hydroxide. The organic acid silver salt is, for example, a silver salt of saturated fatty acids (1 to 24 carbon atoms) such as formic acid, acetic acid, lauric acid, myristic acid, palmitic acid, and stearic acid; a silver salt of unsaturated fatty acids (24 or fewer carbon atoms) such as oleic acid and linoleic acid; a silver salt of dicarboxylates (2 to 6 carbon atoms) such as oxalic acid, malonic acid, and acetonedicarboxylic acid; a silver salt of aromatic carboxylates such as benzoic acid and phthalic acid; a silver salt of hydroxy acids (2 to 6 carbon atoms) such as silver glycolate and citric acid.

[0032] The metal precursor 134 may be spherical or flake-shaped. In this case, the average particle size of the metal precursor 134 is preferably 0.01 μm or more and 5 μm or less, and more preferably 0.1 μm or more and 2 μm or less.

[0033] The metal particles 132 do not decompose at a predetermined temperature. Preferably, the metal particles 132 contain at least one selected from the group consisting of silver, copper, nickel, zinc, gold, palladium, platinum, and alloys thereof. Furthermore, it is preferable that the metal particles 132 contain silver or copper from the above group of metals.

[0034] The metal particles 132 may be spherical or flake-shaped. In this case, the average particle diameter of the metal particles 132 is preferably 0.2 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 30 μm or less.

[0035] The surface of the metal particles 132 may be compounded with fatty acids. In this case, the sintering reaction can be promoted. Alternatively, the surface of the metal particles 132 may be compounded with a metal precursor 134.

[0036] For example, the bonding material S is a solution or a paste. The bonding material S further contains an organic solvent M. For example, a monohydric alcohol or a polyhydric alcohol can be used as the organic solvent M, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, or terpineol. In this case, it is preferable that the metal particles 132 and the metal precursor 134 are sufficiently dispersed in the organic solvent M within the bonding material S. For example, it is preferable that the metal particles 132 and the metal precursor 134 are thoroughly stirred in the organic solvent M or before being added to the organic solvent M.

[0037] The bonding material S preferably contains, for example, 1% by mass or more and less than 100% by mass of metal particles 132, and more preferably contains 10% by mass or more and 70% by mass of metal particles.

[0038] The bonding material S may contain an organic acid instead of the metal precursor 134. Examples of organic acids include formic acid, oxalic acid, stearic acid, acetic acid, citric acid, myristic acid, benzoic acid, as well as lauric acid, palmitic acid, oleic acid, linoleic acid, acetone dicarboxylic acid, phthalic acid, silver glycolate, or malonic acid. In this case, the reaction between the metal particles 132 and the organic acid can generate the metal precursor 134 on the surface of the silver particles during the bonding process.

[0039] The bonding material S of this embodiment contains not only metal particles 132 that do not decompose at a predetermined temperature, but also metal precursors 134 that decompose at a predetermined temperature, thereby improving the bonding strength of the bonding layer 130. Furthermore, even when the bonding structure 100 is used at high temperatures for a long period of time (for example, 250°C or higher), the decrease in the bonding strength of the bonding layer 130 is suppressed.

[0040] The manufacturing method of the bonded structure 100 of this embodiment will now be described with reference to Figures 4 to 6. Figures 4(a) to 4(d) are schematic diagrams showing the manufacturing method of the bonded structure 100 according to this embodiment. Figure 5 is a scanning electron microscope image of the bonded material S. Figure 6 is a scanning electron microscope image of the bonded layer 130.

[0041] First, prepare the first object to be joined, 110, as shown in Figure 4(a).

[0042] Next, as shown in Figure 4(b), the second object to be joined, 120, is prepared.

[0043] Next, prepare the bonding material S as shown in Figure 4(c). The bonding material S may be stored in a refrigerator, and it is preferable to thoroughly stir the bonding material S before use. For example, stirring is preferably carried out for 5 minutes to 2 hours.

[0044] Next, as shown in Figure 4(d), a laminate L is formed by stacking the first object to be joined 110 and the second object to be joined 120 via a bonding material S. For example, the laminate L may be formed by applying the bonding material S to the surface of the first object to be joined 110, and then positioning the second object to be joined 120 opposite the first object to be joined 110 via the bonding material S. Alternatively, the bonding material S may be applied to the surface of the second object to be joined 120. The laminate L may also be formed by injecting the bonding material S between the first object to be joined 110 and the second object to be joined 120, which are positioned at a predetermined distance apart so that their main surfaces face each other. Note that instead of applying the bonding material S, the bonding material S may be sprayed.

[0045] Now, with reference to Figure 5, the bonding material S in the laminate L will be explained. Figure 5 is a scanning electron microscope image of the bonding material S. As shown in Figure 5, multiple metal particles and multiple metal precursors were identified.

[0046] As shown again in Figure 3(e), by heating the laminate L to the heating temperature, a bonding layer 130 that joins the first object to be joined 110 and the second object to be joined 120 is formed from the bonding material S. When the laminate L is heated, the bonding layer 130 is sintered and the bonding layer 130 is formed.

[0047] For example, the heating temperature is a predetermined temperature. Specifically, the heating temperature is 100°C to 600°C, preferably 150°C to 300°C, and more preferably 200°C to 300°C. The heating time is preferably, for example, 1 minute to 5 hours, more preferably 5 minutes to 3 hours, even more preferably 10 minutes to 2 hours, and particularly preferably 30 minutes to 1 hour. This forms a bonding layer 130 that joins the first object to be joined 110 and the second object to be joined 120.

[0048] When forming the bonding layer 130, pressure may be applied to the laminate L when heating it so that the first object to be bonded 110 and the second object to be bonded 120 are bonded with sufficient strength through the bonding layer 130. The pressure is, for example, 0.37 MPa. However, the laminate L may be heated without applying pressure to it.

[0049] The bonding material S of this embodiment contains not only metal particles 132 that do not decompose at a predetermined temperature, but also metal precursors 134 that decompose at a predetermined temperature, thus reducing the energy required for bonding (process conditions: temperature, pressure, time).

[0050] Now, with reference to Figure 6, the bonding layer 130 in the bonding structure 100 will be explained. Figure 6 is a scanning electron microscope image of the bonding layer 130. As shown in Figure 6, it was confirmed that the metal particles and the metal precursor are firmly bonded together.

[0051] Next, we will explain the bonding strength of the bonding layer 130 by referring to Figure 7. Figure 7 is a diagram showing the shear strength of the bonding layer 130. Specifically, Figure 7(a) is a diagram showing the shear strength of the bonding layer 130 formed from the bonding material S by heating the laminate L at 250°C. Figure 7(b) is a diagram showing the shear strength of the bonding layer 130 formed from the bonding material S by heating the laminate L at 300°C. The vertical axis represents the shear strength.

[0052] The bonding layer 130 in Example 1 was formed from a bonding material S containing micro-sized flake-shaped silver particles, silver oxide, and diethylene glycol. The bonding layer 130 in Example 2 was formed from a bonding material S containing micro-sized flake-shaped silver particles, silver oxide, and terpineol.

[0053] As shown in Figure 7, when the laminate L was heated to 250°C, the shear strength of the bonded layer 130 formed from the bonding material S was 20 MPa or more, indicating sufficient strength.

[0054] Next, referring to Figure 8, we will describe the 250°C high-temperature storage test of the bonding layer 130 according to Example 1. Figure 8 is a diagram showing the shear strength of the bonding layer 130. The vertical axis represents the shear strength. The horizontal axis represents the holding time.

[0055] As shown in Figure 8, the bonding layer 130 according to Example 1 maintains the same bonding strength as the initial state even after 1000 hours, indicating that it has heat resistance of 250°C or higher. In other words, the bonding layer 130 according to this embodiment can be applied to the manufacture of power modules. Specifically, it can be used in multiple locations such as power semiconductors / metal-ceramic substrates (DBC (Direct Bonded Copper) or DBA (Direct Bonded Aluminum)), ceramic insulating substrates / heat sinks (aluminum or copper), and to manufacture integrated modules. For example, it has long-term thermal reliability even when used in high-temperature environments such as next-generation power modules for automobiles. Furthermore, by applying the present invention, it can be applied, for example, to conductive materials for flexible and stretchable organic electronics or silver electrodes for solar cells.

[0056] Embodiments of the present invention have been described above with reference to the drawings (Figures 1 to 8). However, the present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention. The drawings schematically show each component in order to facilitate understanding, and the thickness, length, number, etc. of each component shown may differ from the actual dimensions due to the convenience of drawing creation. Furthermore, the material, shape, dimensions, etc. of each component shown in the above embodiments are examples and are not particularly limited, and various modifications are possible without substantially departing from the effects of the present invention. [Industrial applicability]

[0057] According to the present invention, the decrease in bonding strength is suppressed even when exposed to high-temperature environments for extended periods. [Explanation of Symbols]

[0058] 100 Jointed structure 110 First object to be joined 120 Second object to be joined 130 Bonding layer 132 Metal particles 134 Metal Precursors

Claims

1. The first object to be joined, The second object to be joined, A bonding layer that joins the first object to be joined and the second object to be joined. A joint structure comprising, The first object to be joined is non-metallic, The aforementioned bonding layer is Metal precursor decomposed at a predetermined temperature, Metal particles that did not decompose at the predetermined temperature and It contains, The aforementioned metal particles are silver particles, The metal precursor is a silver precursor, A bonded structure in which at least one surface of the metal particles is composited with the metal precursor.

2. The joining structure according to claim 1, wherein the second object to be joined is made of metal or non-metal.

3. The bonding structure according to claim 1 or claim 2, wherein the bonding layer contains 1% by mass or more and less than 100% by mass of metal particles.

4. The bonding structure according to any one of claims 1 to 3, wherein the particle size of the metal particles is 0.02 μm or more and 10 μm or less.

5. A metal precursor that decomposes at a predetermined temperature, Metal particles that do not decompose at the predetermined temperature and It contains, The aforementioned metal particles are silver particles, The metal precursor is a silver precursor, A bonding material in which the surface of the metal particles is composited with the metal precursor.

6. The process of preparing the first object to be joined, The process of preparing the second object to be joined, The process of preparing the joining materials, A step of forming a laminate by stacking the first object to be joined and the second object to be joined via the joining material, A step of forming a bonding layer from the bonding material by heating the laminate at a predetermined temperature to bond the first object to be bonded and the second object to be bonded. It includes, The aforementioned joining material is A metal precursor that decomposes at the predetermined temperature, Metal particles that do not decompose at the predetermined temperature and It contains, The aforementioned metal particles are silver particles, The metal precursor is a silver precursor, A method for manufacturing a bonded structure, wherein the surface of the metal particles is composited with the metal precursor.

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