Implementation substrate

Abstract

To provide a mounting board that can mitigate thermal stress and has excellent connection reliability.SOLUTION: A mounting substrate has an insulating substrate, a sintered copper layer disposed on the insulating substrate, and a bonding layer between the insulating substrate and the sintered copper layer that bonds the insulating substrate and the sintered copper layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a mounting substrate.

Background Art

[0002] DBC (Direct Bonded Copper) substrates and AMC (Active Metal Brazed Copper) substrates in which copper plates are bonded to both sides of a fine ceramics plate are used as mounting substrates for power devices in power electronics. These mounting substrates not only serve as a mounting substrate for insulating a conductor pattern and a heat sink that constitute a power electronics circuit from the power electronics circuit, but also function as a heat dissipation path taking advantage of the high thermal conductivity of fine ceramics and copper. Furthermore, by taking advantage of the low thermal expansion property of the fine ceramics plate, the thermal stress of the bonding layer with the power device can be reduced, and the reliability of the power circuit can be improved. For this reason, the above-mentioned mounting substrates are widely adopted particularly in the field of power electronics that requires reliability (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, power devices using SiC or GaN have attracted attention from the perspective of high-temperature operation. However, due to the increase in thermal stress associated with high-temperature operation, as well as the increase in thermal stress due to the higher Young's modulus of SiC (Young's modulus: about 440 GPa) and GaN (Young's modulus: about 200 GPa) compared to that of conventional Si (Young's modulus: about 130 GPa), a decrease in connection reliability has become a problem. In DBC substrates and AMC substrates, ceramic plates (Young's modulus of alumina: about 380 GPa, Young's modulus of AlN: about 320 GPa, Young's modulus of SiN: about 300 GPa) and copper plates (Young's modulus: 110 - 130 GPa) are also materials with a high Young's modulus, making it difficult to relieve thermal stress. In addition, DBC substrates and AMC substrates require advanced manufacturing technologies and are expensive, which is also an issue.

[0005] The present invention has been made in view of the problems of the above prior art, and an object thereof is to provide a mounting substrate capable of relieving thermal stress and having excellent connection reliability.

Means for Solving the Problems

[0006] In order to achieve the above object, the present invention provides a mounting substrate including an insulating substrate, a sintered copper layer disposed on the insulating substrate, and a bonding layer disposed between the insulating substrate and the sintered copper layer for bonding the insulating substrate and the sintered copper layer.

[0007] In the above mounting substrate, the thickness of the sintered copper layer may be 50 μm or more and 1000 μm or less.

[0008] In the above mounting substrate, the thermal conductivity of the sintered copper layer may be 120 W / m·K or more.

[0009] In the above mounting substrate, the Young's modulus of the sintered copper layer may be 10 GPa or more and 70 GPa or less.

[0010] In the above mounting substrate, the density of the sintered copper layer may be 60% by volume or more and 90% by volume or less.

[0011] In the mounting substrate described above, the insulating substrate may be a ceramic substrate or a glass substrate.

[0012] The mounting substrate may further include a metal foil layer disposed on a surface of the sintered copper layer opposite to the bonding layer.

[0013] In the mounting substrate, the thickness of the bonding layer may be 10 μm or less.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a mounting substrate that can relieve thermal stress and has excellent connection reliability.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. Also, the dimensional ratios in the drawings are not limited to the ratios shown.

[0017] The mounting substrate according to this embodiment includes an insulating substrate, a sintered copper layer disposed on the insulating substrate, and a bonding layer disposed between the insulating substrate and the sintered copper layer for bonding the insulating substrate and the sintered copper layer. The mounting substrate having the above configuration is a high thermal conductivity and low thermal stress mounting substrate that can be used as a mounting substrate for high heat generation devices.

[0018] Figs. 1(a) and (b) are schematic cross-sectional views showing an embodiment of the mounting substrate. The mounting substrate 100 shown in Fig. 1(a) includes an insulating substrate 2, sintered copper layers 1 disposed on both surfaces of the insulating substrate 2, and a bonding layer 3 disposed between the insulating substrate 2 and the sintered copper layers 1 for bonding the insulating substrate 2 and the sintered copper layers 1. In the mounting substrate 100, the sintered copper layer 1 and the bonding layer 3 disposed on one surface of the insulating substrate 2 form a predetermined conductor pattern. The mounting substrate 200 shown in Fig. 1(b) further includes a metal foil layer 4 on the sintered copper layer 1 of the mounting substrate 100 shown in Fig. 1(a). In the mounting substrate 200, the sintered copper layer 1, the bonding layer 3, and the metal foil layer 4 disposed on one surface of the insulating substrate 2 form a predetermined conductor pattern.

[0019] Figs. 2(a) and (b) are schematic cross-sectional views showing another embodiment of the mounting substrate. The mounting substrate 300 shown in Fig. 2(a) includes an insulating substrate 2, a sintered copper layer 1 disposed on one side of the insulating substrate 2, and a bonding layer 3 disposed between the insulating substrate 2 and the sintered copper layer 1 for bonding the insulating substrate 2 and the sintered copper layer 1. In the mounting substrate 300, the sintered copper layer 1 and the bonding layer 3 form a predetermined conductor pattern. The mounting substrate 400 shown in Fig. 2(b) further includes a metal foil layer 4 on the sintered copper layer 1 of the mounting substrate 300 shown in Fig. 2(a). In the mounting substrate 400, the sintered copper layer 1, the bonding layer 3, and the metal foil layer 4 form a predetermined conductor pattern.

[0020] The mounting substrate having the configuration as described above includes a sintered copper layer 1 on an insulating substrate 2, and the sintered copper layer 1 is joined to the insulating substrate 2 via a joining layer 3, so that thermal stress can be sufficiently relaxed and excellent connection reliability can be obtained. This is because the sintered copper layer 1 has excellent electrical conductivity and excellent thermal conductivity, so that it can exhibit a power supply function to components mounted on the mounting substrate including high heat-generating devices and a function of quickly diffusing and exhausting the generated heat. Further, since the sintered copper layer 1 is joined by a metallic bond, it is difficult to directly join it to the insulating substrate 2 joined by a covalent bond. However, by providing a joining layer 3 between the two, the sintered copper layer 1 and the insulating substrate 2 can be joined.

[0021] Hereinafter, each member constituting the above-described mounting substrate will be described in detail.

[0022] (Sintered copper layer 1) The sintered copper layer (sintered Cu layer) 1 has high electrical conductivity and high thermal conductivity, and exhibits a power supply function to components mounted on a mounting substrate including high heat-generating devices and a function of quickly diffusing and exhausting the generated heat.

[0023] The thickness of the sintered copper layer 1 is, for example, 50 μm or more and 1000 μm or less, preferably 70 μm or more and 700 μm or less, and more preferably 100 μm or more and 500 μm or less. If the thickness is 50 μm or more, heat can be quickly diffused and dissipated from the high heat-generating device, and it tends to be able to withstand thermal stress. If the thickness is 1000 μm or less, the sintered copper layer 1 is easily formed, and it is also advantageous in terms of material cost.

[0024] The Young's modulus of the sintered copper layer 1 is, for example, 70 GPa or less, preferably 60 GPa or less, and more preferably 50 GPa or less. If the Young's modulus is lower, the thermal stress can be suppressed, and thus the reliability against temperature cycles tends to be further improved. The lower limit of the Young's modulus is, for example, 10 GPa or more, preferably 15 GPa or more, and more preferably 20 GPa or more. If the Young's modulus is this high or more, it is less likely that the sintered copper layer 1 will become fragile, and the possibility of the sintered copper layer 1 being destroyed by thermal stress can be reduced. The Young's modulus can be measured by a nanoindenter, a microforce tester, a universal material tester, a four-point bending tester, a three-point bending tester, a tensile tester, etc.

[0025] The yield stress of the sintered copper layer 1 is, for example, 80 MPa or more, preferably 120 MPa or more, and more preferably 130 MPa or more. The yield stress is related to the fracture resistance against thermal stress, and the higher it is, the more preferable it is. The yield stress can be measured by a microforce tester, a universal material tester, a four-point bending tester, a three-point bending tester, a tensile tester, etc.

[0026] The density of the sintered copper layer 1 is, for example, 60% by volume or more, preferably 64% by volume or more, and more preferably 67% by volume or more. The upper limit of the density is 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. When the density is 60% by volume or more, the thermal cycle reliability is improved, and the destruction of the sintered copper layer 1 when repeated thermal strain is applied is suppressed, and the reliability tends to be high. When the density is 90% by volume or less, the Young's modulus becomes low, and the thermal stress fracture of the device is likely to be suppressed. The density can be measured by density measurement from the outer shape and mass, fluorescent X-ray intensity measurement, three-dimensional FIB / SEM image, etc.

[0027] The thermal conductivity of the sintered copper layer 1 is, for example, 120 W / m·K or more, preferably 150 W / m·K or more, and more preferably 160 W / m·K or more. From the perspective of heat dissipation, the higher the thermal conductivity, the more preferable. However, since the thermal conductivity of dense copper is 401 W / m·K, this value is the upper limit. The thermal conductivity can be measured by a flash method thermal diffusivity measuring device, thermowave analysis, combination by thermal simulation of transient heat measurement results, etc.

[0028] The thermal conductivity of the sintered copper layer 1 may have a difference between the thermal conductivity in the thickness direction and the surface direction. When the value of (thermal conductivity in the surface direction) / (thermal conductivity in the thickness direction)×100(%) is greater than 100%, it is preferable because the effect of quickly spreading and diffusing the heat generated in the high-heat-generation device in the surface direction can be obtained. This value is preferably 105% or more, and more preferably 120% or more.

[0029] Such a sintered copper layer 1 can be formed by sintering copper particles. The sintered copper layer 1 can also be formed by directly depositing dry copper particles and then sintering them. Further, it can also be formed by applying a Cu paste in which copper particles are made into a paste state with a dispersion medium, drying, and then sintering. The Cu paste is composed of, for example, copper particles, a dispersion medium, other metal particles, and additives, and at least copper particles and a dispersion medium are essential components.

[0030] There are various types of copper particles depending on the particle size, shape, surface treatment agent, and composition, and their configurations are also various. However, as long as they can be sintered, their types and configurations are not limited.

[0031] The smaller the particle size of the copper particles, the lower the sintering temperature can be. On the other hand, the larger the particle size, the more advantageous in terms of dispersibility and increasing the Cu paste concentration. In order to make the sintering temperature 300°C or lower, it is preferable that a part of the copper particles is composed of particles of 1 μm or less. Further, from the viewpoints of dispersibility and concentration, the proportion of Cu particles of 100 nm or less is preferably from 0 mass% to 30 mass% based on the mass of all metal particles. Also, from the viewpoints of increasing the Cu paste concentration and suppressing volume shrinkage during sintering, copper particles larger than 1 μm may be included.

[0032] The shapes of the copper particles include spherical, quasi-spherical, flake-shaped, oval-shaped, needle-shaped, and dendritic. It may contain copper particles of multiple shapes.

[0033] The surface treatment agent for copper particles is used to suppress the oxidation and aggregation of copper particles. For example, aliphatic carboxylic acids such as dodecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, linoleic acid, linolenic acid, oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, o-phenoxybenzoic acid; aliphatic alcohols such as cetyl alcohol, stearyl alcohol, isobornyl cyclohexanol, tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, stearylamine; aliphatic nitriles such as stearonitrile, decanenitrile; silane coupling agents such as alkylalkoxysilane; polymer treatment agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, silicone oligomer, etc. The surface treatment agent may be used alone or in combination of two or more.

[0034] The composition of the copper particles is mainly composed of metallic copper, copper oxide, and cuprous oxide. In particular, even if they are metallic copper particles, the surface may be naturally oxidized and contain copper oxide and cuprous oxide randomly. From the viewpoint of improving the physical properties of copper, the copper particles may contain elements other than copper and oxygen in an amount of 5% by mass or less. Such elements include Si, Mg, Al, Ag, Ni, Fe, Zr, Ge, Mn, Sn, Zn, P, S, Mo, Ta, etc.

[0035] The dispersion medium of the Cu paste is not particularly limited as long as it is mixed with copper particles to impart flexibility and is removed during drying or firing. Such dispersion media include decane, dodecane, tetradecane, hexadecane, butyl cellosolve, carbitol, butyl cellosolve acetate, carbitol acetate, ethylene glycol diethyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-methyl ether, isobornyl cyclohexanol, tributyrin, terpineol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, 4-methyl-1,3-dioxolan-2-one, diethylene glycol monobutyl ether, isobornyl cyclohexanol (e.g., "MTPH" manufactured by Nippon Terpene Chemical Co., Ltd.), isooctadecanol (e.g., "Fine Oxocol 180" and "Fine Oxocol 180T" manufactured by Nissan Chemical Industries, Ltd.), 1-hexadecanol (cetyl alcohol), 2-hexadecanol (e.g., "Fine Oxocol 1600" manufactured by Nissan Chemical Industries, Ltd.), 9-octadecenol (oleyl alcohol), and other alkyl alcohols;Octyl octanoate, methyl myristate, ethyl myristate, methyl linoleate, methyl stearate, butyl stearate (e.g., "Exceparl BS" manufactured by Kao Corporation), stearyl stearate (e.g., "Exceparl SS" manufactured by Kao Corporation), 2-ethylhexyl stearate (e.g., "Exceparl EH-S" manufactured by Kao Corporation), isotridecyl stearate (e.g., "Exceparl TD-S" manufactured by Kao Corporation), tetraethylene glycol, triethylene glycol bis(2-ethylhexanoic acid), tributyl citrate, dibutyl sebacate, tributyrin, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, methylheptadecane, tridecylcyclohexane, tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, pentylphenol, benzylphenol, 2-(4-methoxyphenyl)ethanol (methoxyphenethyl alcohol), benzyl benzoate, hexadecanenitrile, heptadecanenitrile, symmetriline, etc. may be mentioned.;

[0036] Examples of other metal particles of the Cu paste include particles such as zinc, tin, nickel, silver, gold, palladium, platinum, etc. The volume average particle diameter of the other metal particles may be 0.01 to 10 μm, may be 0.01 to 5 μm, or may be 0.05 to 3 μm. The shape of the other metal particles is not particularly limited. The content of the other metal particles may be less than 20% by mass, may be 10% by mass or less, or may be 0% by mass based on the total mass of the metal particles from the viewpoint of obtaining sufficient bondability.

[0037] When metal particles composed of metal species with a low melting point are used as other metal particles, a tendency to obtain an effect of reducing the sintering temperature is observed. Furthermore, since a sintered body in which multiple types of metals are solid-solved or dispersed can be obtained, mechanical properties such as the yield stress and fatigue strength of the sintered body are improved, and the connection reliability is likely to be enhanced. Also, by adding multiple types of metal particles, the sintered body (sintered copper layer) of the bonding material can have sufficient bonding strength with respect to a specific adherend. When the sintered copper layer is used for bonding microdevices, the die shear strength and connection reliability of the microdevices are likely to be improved.

[0038] Examples of additives for the Cu paste include reducing agents, viscosity modifiers, surface tension modifiers, shape retention agents, and the like.

[0039] By adding a reducing agent, sintering can be performed in a gas atmosphere with low or no reducibility, such as in an inert gas containing 5% or less hydrogen, nitrogen, or argon. Such a reducing agent needs to be a reducing agent that can remain in the Cu paste up to 200°C or higher, which is the sintering temperature. Examples of such reducing agents include polyhydric alcohols such as glycerin, diglycerin, hexanetriol, and phloroglucinol; glycols such as tetraethylene glycol and polyethylene glycol; saccharides such as glucose; carboxylic acids such as oxalic acid and 2,2-bis(hydroxymethyl)propionic acid; hydrazides such as adipic acid dihydrazide; and polyhydric alcohols or ether polymers such as polyethylene glycol and polyvinyl alcohol.

[0040] For the purpose of improving the printability of the Cu paste and the shape stability after printing, a viscosity modifier, a surface tension modifier, and a shape retention agent may be added. Examples of the surface tension modifier include nonionic surfactants, fluorosurfactants, and the like. Examples of the viscosity modifier include alkylamines, alkylcarboxylic acids, silicones, polyacrylic acids, polysaccharides, and the like. As the shape retention agent, at least one selected from the group consisting of polycarbonate, poly(meth)acrylic acid, poly(meth)acrylate, and polyester is preferable, and polycarbonate is more preferable. Examples of the polycarbonate include poly(alkylene carbonate) such as poly(propylene carbonate), poly(ethylene carbonate), and poly(butylene carbonate).

[0041] (Insulating substrate 2) The insulating substrate 2 is preferably a low thermal expansion insulating substrate. The insulating substrate 2 has low thermal expansion, insulation, and thermal conductivity, and exhibits functions of adjusting the thermal expansion rate of the high thermal conductivity and low thermal stress mounting substrate, insulating the current flowing through the sintered copper layer 1, and exhausting the heat generated from the high heat generation device.

[0042] Such a low thermal expansion insulating substrate is preferably a ceramic substrate, a glass substrate, or a single crystal substrate, and a ceramic substrate is more preferable from the viewpoint of cost.

[0043] Examples of the material of the ceramic substrate include alumina, aluminum nitride, silicon nitride, silicon carbide, zirconia, yttria, boron nitride, mullite, cordierite, steatite, forsterite, cermet, etc. from the viewpoint of achieving both high thermal conductivity and low thermal expansion rate, and alumina, aluminum nitride, and silicon nitride are particularly preferable.

[0044] Examples of the material of the glass substrate include quartz glass, crystallized glass, borosilicate glass, etc.

[0045] Examples of the material of the single crystal substrate include alumina, diamond, quartz, etc.

[0046] In addition, by making the coefficient of thermal expansion of the insulating substrate 2 closer to that of the high-heat-generation device, the thermal stress can be reduced and the connection reliability can be improved. Many high-heat-generation devices are composed of Si, SiC, GaN, GaP, GaAs, InP, GaO, Al2O3, etc., and their coefficients of thermal expansion are Si: 2.4, SiC: 4.2 (4.7), GaN: 5.6 (3.2), GaP: 5.3, GaAs: 6.0, InP: 4.5, GaO, Al2O3: 5.0 (all units are ppm / K). These coefficients of thermal expansion are lower than those of copper (16.8 ppm / K) and aluminum (23.0 ppm / K) which constitute the heat sink. Therefore, by making the combined coefficient of thermal expansion of the insulating substrate 2 and the sintered copper layer 1 closer to that of the high-heat-generation device, or by setting the combined coefficient of thermal expansion of the insulating substrate 2 and the sintered copper layer 1 to be intermediate between the coefficient of thermal expansion of the high-heat-generation device and that of the heat sink, the overall thermal stress can be reduced. For this reason, the lower the coefficient of thermal expansion of the insulating substrate 2, the more preferable it is. For example, it is preferable to use SiN ceramic (2.8 ppm / K), SiC ceramic (3.7 ppm / K), AlN ceramic (4.6 ppm / K), etc. Also, in the mounting substrate of this embodiment, since the wiring layer is formed by the sintered copper layer 1 with a low Young's modulus compared to dense copper, the thermal stress can be reduced. As the insulating substrate 2 with a larger coefficient of thermal expansion than the conventional DBC substrate and AMC substrate, for example, alumina (7.2 ppm / K), zirconia (10.5 ppm / K), etc. may be used.

[0047] The thickness of the insulating substrate 2 is balanced with the thickness of the sintered copper layer 1 in terms of adjusting insulation and thermal cycle reliability.

[0048] (Bonding layer 3) It is difficult to directly bond between the sintered copper layer 1 bonded by metallic bonding and the insulating substrate 2 bonded by covalent bonding, and a bonding layer 3 is required between the two. Examples of the method for forming the bonding layer 3 include a method of directly bonding a copper foil or copper plate onto the insulating substrate 2 at high temperature and high pressure (DBC method), a method of bonding a copper foil or copper plate to the insulating substrate 2 with a brazing material (AMC method), a method of forming a bonding layer on the insulating substrate 2 by vapor deposition or sputtering, etc.

[0049] In the DBC method, the insulating substrate 2 and the copper foil or copper plate are stacked and subjected to high temperature and high pressure for bonding. At this time, the copper oxide on the surface of the copper foil or copper plate and the oxide of the insulating substrate 2 are mixed at the interface, and a glass transition layer is formed for bonding. When the insulating substrate 2 is not an oxide such as AlN, etc., after forming an oxide layer by heating in an oxidizing atmosphere, etc., it is bonded by the DBC method.

[0050] The AMC method is a method of bonding under high temperature and high pressure through a brazing material that can bond to both the copper foil or copper plate and the insulating substrate 2. Examples of the brazing material include active metals such as Ti and Cr that can bond to both the copper foil or copper plate and the insulating substrate 2, and Ag and Cu, etc. that adjust the melting point.

[0051] Such DBC substrates bonded by the DBC method and AMC substrates bonded by the AMC method are commercially available, and such commercially available substrates may be purchased and used. By forming the sintered copper layer 1 on the copper foil or copper plate of the DBC substrate and the AMC substrate to the required thickness, the mounting substrate of the present embodiment is formed, and the effects of improving the connection reliability and the heat dissipation performance from the device can be obtained.

[0052] In the method of forming the bonding layer 3 by vapor deposition or sputtering, a metal (such as Ti and Cr, etc.) having bonding properties with the insulating substrate 2 is formed by vapor deposition or sputtering, and then Cu and Ni, etc. having connectivity with the sintered copper layer 1 are formed by vapor deposition or sputtering, whereby the bonding layer 3 can be formed.

[0053] The thickness of the bonding layer 3 is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 1 μm or less.

[0054] (Metal foil layer 4) The mounting substrate of this embodiment has a bonding layer 3 and a sintered copper layer 1 laminated in this order on an insulating substrate 2, but it may have a metal foil layer 4 outside the sintered copper layer 1. Since the sintered copper layer 1 is a porous sintered body, when solder or a bonding paste is used thereon, it may be absorbed into the sintered copper layer 1 and it may become difficult to bond the device. Providing the metal foil layer 4 on the sintered copper layer 1 can solve this problem. When simultaneously bonding the device elements necessary during the formation of the sintered copper layer 1, or when bonding with a sintered bonding material, etc., if there are no problems with bonding, this metal foil layer 4 is not necessary.

[0055] As the material of the metal foil layer 4, a metal excellent in conductivity and thermal conductivity can be used. From that viewpoint, copper, silver, and aluminum are preferable, and copper is more preferable in terms of price and being the same metal as the sintered copper layer 1. A metal foil of an alloy in which 5 mass% or less of a different element is mixed with these metals may also be used. In order to improve the bonding property with the sintered copper layer 1 and prevent oxidation and discoloration of the surface, a different metal may be plated on the metal foil layer 4. Examples of the metal to be plated include copper, nickel, palladium, gold, silver, and alloys mainly composed of these.

[0056] The thickness of the metal foil layer 4 is preferably thin from the viewpoint of reducing thermal stress, preferably 32 μm or less, more preferably 16 μm or less, and even more preferably 12 μm or less. However, since the metal foil layer 4 becomes difficult to handle and the price also increases when it becomes thin, 1 μm or more is preferable, 3 μm or more is more preferable, and 5 μm or more is even more preferable.

[0057] The surface of the metal foil layer 4 may be roughened to improve adhesion.

[0058] (Manufacturing method of mounting substrate) The manufacturing method of the mounting substrate according to this embodiment includes a step of forming a bonding layer 3 on an insulating substrate 2 and a step of forming a sintered copper layer 1 on the bonding layer 3. When forming the metal foil layer 4 on the surface of the sintered copper layer 1, the metal foil layer 4 can be bonded simultaneously in the step of forming the sintered copper layer 1.

[0059] As a process of forming the bonding layer 3 on the insulating substrate 2, an active metal that bonds to both the insulating substrate 2 and a metal, such as Ti, Cr, Zr, W, Mo, V, Nb, Ta, is deposited or sputtered on the insulating substrate 2 to form a film, and then a metal having adhesiveness to the sintered copper layer 1, such as Cu, Ni, Pd, Ag, Au, Pt, is deposited or sputtered to form the bonding layer 3.

[0060] The thickness of the active metal layer is, for example, 5 nm or more, preferably 10 nm or more. When the thickness is more than this, film defects tend to be reduced. The thickness of the active metal layer is, for example, 200 nm or less, preferably 100 nm or less. An unnecessarily thick active metal layer increases costs and manufacturing time, which is not preferable.

[0061] For the layer of the metal having adhesiveness to the sintered copper layer 1, Cu, Ni, Pd, Ag, Au, Pt may be formed into a film alone on the active metal layer, or a plurality of different metals such as Ni / Au, Ni / Ag, Ni / Pd, Ni / Pd / Au, Ni / Pd / Ag, Ni / Pt, Ni / Pt / Au, Ni / Pt / Ag may be provided in multiple layers. By adopting such a configuration, it is possible to prevent the active metal layer from diffusing into other metal layers and reducing the bonding strength.

[0062] From the viewpoint of preventing the diffusion of the active metal, the thickness of the layer of the metal having adhesiveness to the sintered copper layer 1 is, for example, 10 nm or more, preferably 50 nm or more. Also, the upper limit of the thickness is about 1000 nm. When the thickness is less than this, it is easy to suppress peeling or cracking due to internal stress.

[0063] Alternatively, a DBC substrate or an AMC substrate having the bonding layer 3 formed on the insulating substrate 2 as described above may be purchased and used.

[0064] The process of forming the sintered copper layer 1 can be realized by disposing the above-described Cu paste on the bonding layer 3 formed on the insulating substrate 2 and sintering it to form the sintered copper layer 1.

[0065] The method of disposing the Cu paste on the bonding layer 3 may be any method capable of adhering the Cu paste, and known methods can be adopted. Specific examples of the method of disposing the Cu paste on the bonding layer 3 include methods by printing such as screen printing, transfer printing, offset printing, relief printing, intaglio printing, gravure printing, stencil printing, jet printing, etc., dispensers (e.g., jet dispensers, needle dispensers, screw dispensers), comma coaters, slit coaters, die coaters, gravure coaters, slit coaters, bar coaters, applicators, spray coaters, spin coaters, dip coaters, etc., methods by soft lithography, particle deposition methods, methods by electrodeposition coating, and the like.

[0066] The disposed Cu paste may be dried from the viewpoint of suppressing the flow during sintering and the generation of voids. That is, the manufacturing method of the present embodiment may further include a drying step of drying the Cu paste before the step of sintering to form sintered copper.

[0067] Drying may be performed in the air, in an oxygen-free atmosphere such as nitrogen or a noble gas, or in a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving at room temperature (e.g., 25 °C), heating drying, or vacuum drying. For heating drying or vacuum 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. can be used. The drying conditions (drying temperature and time) may be appropriately set according to the type and amount of the volatile components (e.g., components other than metal particles such as organic solvents and thermally decomposable resins) used in the Cu paste. As the drying conditions (drying temperature and time), for example, conditions of drying at 50 °C or higher and less than 130 °C for 1 to 120 minutes may be used.

[0068] Next, the Cu paste is sintered to form a sintered copper layer 1. As a result, the particles in the sintered copper layer 1 are sintered together to form a metallic bond, thereby forming a layer with excellent thermal conductivity and electrical conductivity. At this time, a metallic bond is also formed by sintering on the surface of the bonding layer 3 to achieve strong bonding. The sintering of the Cu paste can be carried out by heat treatment or heat and pressure treatment.

[0069] For heat treatment, for example, a hot plate, a hot air dryer, a hot 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, etc. can be used.

[0070] For heat and pressure treatment, a hot plate press device, a thermocompression bonding device, etc. may be used, or the above heat treatment may be carried out while applying pressure by placing a weight, or the above heat treatment may be carried out while applying pressure with a spring jig or the like.

[0071] Note that the step of forming the sintered copper layer 1 on the bonding layer 3 may be carried out by a method of transferring a Cu paste layer formed in advance on a base film onto the bonding layer 3. In this case, for example, a mounting substrate can be manufactured by the following method. First, a mask 30 is placed on a base film 20, and a Cu paste is applied from above the mask 30 to form a Cu paste layer 11 (see (a) of FIG. 3). Then, the mask 30 is peeled off to obtain a laminate (first laminate) having a patterned Cu paste layer 11 on the base film 20 (see (b) of FIG. 3). The first laminate and a second laminate having a bonding layer 3 formed on an insulating substrate 2 are positioned and bonded so that the Cu paste layer 11 of the first laminate and the bonding layer 3 of the second laminate are in contact with each other, and dried and sintered while applying pressure (see (c) of FIG. 3). As a result, the Cu paste layer 11 is sintered to form a sintered copper layer 1. Then, by peeling off the base film 20, a mounting substrate including the insulating substrate 2, the bonding layer 3 formed on the insulating substrate 2, and the sintered copper layer 1 formed on the bonding layer 3 can be obtained (see (d) of FIG. 3). In the above method, by sintering the Cu paste layer 11 in a pressurized state, it is possible to further prevent cracks from occurring in the sintered copper layer 1 after sintering.

[0072] In the above method, the base film 20 is not particularly limited. For example, an aluminum foil, a stainless steel plate, a heat-resistant resin film such as polyimide, a polytetrafluoroethylene-coated metal plate, etc. can be used. Also, the mask 30 is not particularly limited. For example, a SUS stencil mask, a screen printing plate, etc. can be used. Further, as the Cu paste, from the viewpoint of maintaining the shape of the Cu paste layer 11, it is preferable to use a Cu paste with a relatively high viscosity. Also, before bonding the first laminate and the second laminate, from the viewpoint of maintaining the shape of the Cu paste layer 11, the Cu paste layer 11 may be dried.

[0073] In the above method, as means for drying and sintering the first laminate and the second laminate while applying pressure as shown in FIG. 3(c), for example, an atmosphere-controlled oven heating using a jig having a spring-based pressing mechanism, an atmosphere-controlled thermocompression bonding device, a hot plate press, a pressure sintering bonding device, a hydrostatic pressure thermocompression bonding device, etc. can be used. Here, the pressure during pressing can be 0.1 MPa or more and 20 MPa or less. Note that the methods and conditions for drying and sintering can adopt the same methods and conditions as those described above. Also, the drying may be performed before bonding the first laminate and the second laminate as described above.

[0074] (Mounting example using a mounting substrate) On one side of the mounting substrate of the present embodiment, a heat sink or a water-cooling plate is connected, and on the other side, a high heat-generating device element, a passive element, electrode terminals, etc. are mounted.

[0075] FIG. 4 is a schematic cross-sectional view showing an example of mounting using the mounting substrate of the present embodiment. The mounting example 500 shown in FIG. 4 is obtained by mounting a device chip (semiconductor chip) 5, an electrode terminal 7, and a metal wire (metal frame) 9 on a sintered copper layer 1 having a conductor pattern formed thereon in the mounting substrate 100 shown in FIG. 1(a). The metal wire 9 electrically connects the device chip 5 and a sintered copper layer 1 different from the sintered copper layer 1 on which the device chip is mounted. Further, in the mounting example 500, a heat sink or a water-cooled plate 8 is provided on the sintered copper layer 1 on which no conductor pattern is formed.

[0076] FIG. 5 is a schematic cross-sectional view showing an example of mounting using the mounting substrate of the present embodiment. The mounting example 600 shown in FIG. 5 is obtained by mounting a device chip (semiconductor chip) 5 and an electrode terminal 7 via a die bonding material 6 on a metal foil layer 4 having a conductor pattern formed thereon in the mounting substrate 200 shown in FIG. 1(b), removing the metal foil layer 4 other than the portions where the device chip 5 and the electrode terminal 7 are mounted, and then mounting a metal wire (metal frame) 9 that electrically connects the device chip 5 and a sintered copper layer 1 different from the sintered copper layer 1 on which the device chip is mounted. Further, in the mounting example 600, a heat sink or a water-cooled plate 8 is provided via a die bonding material 6 on the metal foil layer 4 on which no conductor pattern is formed.

Example

[0077] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[0078] [Example 1] (Formation of Insulating Substrate and Bonding Layer) As a low thermal expansion insulating substrate, an alumina plate having a size of 50 mm in length × 50 mm in width × 0.25 mm in thickness was purchased and used. A layer of Ti(50 nm) / Ni(100 nm) (the Ti layer is on the side of the alumina plate) was formed on both surfaces of the alumina plate by sputtering to form a bonding layer. Hereinafter, the bonding layer formed on one surface of the insulating substrate is referred to as the first bonding layer, and the bonding layer formed on the other surface is referred to as the second bonding layer.

[0079] (Preparation of Cu Paste) 500.00 g of quasi-spherical copper particles and 49.45 g of terpineol were weighed and mixed at 100 rpm for 30 minutes using a planetary mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). The obtained mixture was processed three times with a three-roll mill to obtain a quasi-spherical copper particle slurry. Next, 510.59 g of the quasi-spherical copper particle slurry, 45.25 g of terpineol, 4.80 g of isobutyl alcohol, 237.95 g of plate-shaped copper particles, and 1.41 g of zinc particles were weighed and mixed with a planetary mixer. The obtained mixture was placed in a plastic container and defoamed at 2000 rpm for 2 minutes using a rotation-revolution mixer (Avatori Rentaro, manufactured by Shinchi Co., Ltd.) to obtain a Cu paste.

[0080] (Fabrication of High Thermal Conductivity and Low Thermal Stress Mounting Substrate and Mounting of Device Chip) A 40 mm × 40 mm square opening was provided in a 500-μm-thick PTFE (polytetrafluoroethylene) plate to obtain a first mask. This first mask was placed on the first bonding layer of an insulating substrate on which a bonding layer was formed, filled with Cu paste in the opening, excess Cu paste was removed with a squeegee, and the first mask was removed to form a flat first Cu paste layer on the first bonding layer. Next, a 45 mm × 45 mm square opening was provided in a 1000-μm-thick PTFE plate to obtain a second mask. This second mask was placed on the second bonding layer of an insulating substrate on which a bonding layer was formed, filled with Cu paste in the opening, excess Cu paste was removed with a squeegee, and the second mask was removed to form a flat second Cu paste layer on the second bonding layer.

[0081] Next, an SiC chip (a chip with a size of 5 mm in length × 5 mm in width × 0.3 mm in thickness, with a Ti / Ni layer sputter-formed on the adhesion surface) was mounted on the first and second Cu paste layers. The obtained sample was dried in an explosion-proof warm air oven at 90 °C for 15 minutes. Then, in a hydrogen furnace (manufactured by Shinko Seiki Co., Ltd.), it was fired at 300 °C in hydrogen for 1 hour to form a sintered copper layer and at the same time bond the SiC chip, obtaining a high thermal conductivity and low thermal stress mounting substrate. A dam was made along the outer periphery of the high thermal conductivity and low thermal stress mounting substrate with an adhesive tape, and silicone gel (SE1880, manufactured by Dow Corning) was poured until the entire SiC chip was covered, and it was cured in an explosion-proof warm air oven under the conditions of 70 °C for 30 minutes and 150 °C for 1 hour to obtain a mounted sample.

[0082] [Example 2] (Fabrication of High Thermal Conductivity and Low Thermal Stress Mounting Substrate) In the same manner as in Example 1, after forming a Ti(50 nm) / Ni(100 nm) layer on both sides of an alumina plate, electroless Ni plating (100 nm) and flash Pd plating (10 nm) were further performed on the Ni layer to form a bonding layer. As a result, the adhesion surface was Pd.

[0083] (Preparation of Cu Paste) 500.00 g of quasi-spherical copper particles and 49.45 g of terpineol were weighed and mixed at 100 rpm for 30 minutes using a planetary mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). The obtained mixture was processed three times with a three-roll mill to obtain a quasi-spherical copper particle slurry. Next, 540.19 g of the quasi-spherical copper particle slurry, 14.60 g of terpineol, 20.78 g of tetraethylene glycol, 123.2 g of plate-shaped Cu particles, and 1.23 g of zinc particles were weighed and mixed with a planetary mixer. The obtained mixture was placed in a plastic container and defoamed at 2000 rpm for 2 minutes using a rotation-revolution mixer (Avatori Rentaro, manufactured by Shinchi Co., Ltd.) to obtain a Cu paste.

[0084] (Fabrication of High Thermal Conductivity and Low Thermal Stress Mounting Substrate and Mounting of Device Chip) A PTFE plate with a thickness of 500 μm was provided with a 15 mm × 15 mm square opening to serve as the first mask. This first mask was placed on the first bonding layer of an insulating substrate on which a bonding layer was formed. The opening was filled with Cu paste, and the excess Cu paste was removed with a squeegee. Then, the first mask was removed to form a flat first Cu paste layer on the first bonding layer. Next, a PTFE plate with a thickness of 1000 μm was provided with a 45 mm × 45 mm square opening to serve as the second mask. This second mask was placed on the second bonding layer of an insulating substrate on which a bonding layer was formed. The opening was filled with Cu paste, and the excess Cu paste was removed with a squeegee. Then, the second mask was removed to form a flat second Cu paste layer on the second bonding layer.

[0085] The insulating substrate with Cu paste layers formed on both sides was dried in an explosion-proof hot air oven at 90 °C for 30 minutes to remove terpineol. A 12-μm-thick copper foil (manufactured by Nilaco Corporation) cut into 15 mm × 15 mm pieces was placed on the dried first and second Cu paste layers respectively. A polyimide sheet and an expanded graphite sheet were placed on top of it. Then, in an atmosphere-controlled pressure bonding apparatus (manufactured by Ayumi Industry Co., Ltd.), thermal pressure bonding was performed at 5 MPa, 300 °C for 30 minutes in nitrogen to form a sintered copper layer and a metal foil layer. Thus, a high thermal conductivity and low thermal stress mounting substrate was obtained.

[0086] Next, a sintered Cu bonding material (die bond material) was applied onto the copper foil of the high thermal conductivity and low thermal stress mounting substrate using a 200-μm-thick SUS mask having a 5 mm × 5 mm opening. An SiC chip (a chip with a length of 5 mm, a width of 5 mm, and a thickness of 0.3 mm, on the adhered surface of which a Ti / Ni layer was formed by sputtering) was mounted on it. Then, it was processed in a hydrogen furnace (manufactured by Shinko Seiki Co., Ltd.) at 225 °C for 1 hour in hydrogen to sinter the sintered Cu bonding material, thereby bonding the SiC chip and the high thermal conductivity and low thermal stress mounting substrate. A dam was created along the outer periphery of the high thermal conductivity and low thermal stress mounting substrate with an adhesive tape, and silicone gel (SE1880, manufactured by Dowcorning) was poured until the entire SiC chip was covered. It was cured in an explosion-proof hot air oven under the conditions of 70 °C for 30 minutes and 150 °C for 1 hour to obtain a mounting sample.

[0087] Here, the above-mentioned sintered Cu bonding material (die bond material) was prepared as follows. 2.25 g of dihydroterpineol (manufactured by Nippon Terpene Co., Ltd.) as a dispersion medium and 22.75 g of CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd.) as sub-micro copper particles were mixed and processed three times with a three-roll mill to obtain an intermediate. 20.25 g of the intermediate, 0.39 g of dihydroterpineol, 0.990 g of tributyrin (manufactured by Fujifilm Wako Pure Chemical Corporation), and 8.22 g of 3L3N (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) as micro copper particles were kneaded in an agate mortar until the dry powder disappeared, and the mixed solution was transferred to a plastic bottle. The plastic bottle with the cap sealed was stirred for 2 minutes at 2000 min -1 (2000 revolutions per minute) using a planetary vacuum mixer (Planetary Vacuum Mixer ARV-310, manufactured by Shinki Co., Ltd.). Then, 0.06 g of zinc (product number: 13789, manufactured by Alfa Aesar) and the mixed solution were kneaded in an agate mortar until the dry powder disappeared, and the mixed solution was transferred to a plastic bottle. The plastic bottle with the cap sealed was stirred for 2 minutes at 2000 min -1 (2000 revolutions per minute) using a planetary vacuum mixer (Planetary Vacuum Mixer ARV-310, manufactured by Shinki Co., Ltd.) to obtain the sintered Cu bonding material (die bond material).

[0088] [Comparative Example 1] A high-lead solder sheet with a size of 5 mm × 5 mm × thickness of 0.1 mm was placed on a commercially available DBC substrate (manufactured by Kyocera, size: 22 mm in length × 22 mm in width, alumina plate thickness: 0.4 mm, copper plate thickness on both sides: 0.2 mm each, adherend surface: copper). Then, a SiC chip (a chip with a size of 5 mm in length × 5 mm in width × thickness of 0.3 mm with a Ti / Ni layer sputter-formed on the adherend surface) was placed on it. Subsequently, it was processed in a hydrogen furnace (manufactured by Shinko Seiki Co., Ltd.) at 350 °C in hydrogen to melt the high-lead solder and bond the SiC chip and the DBC substrate. A dam was created along the outer periphery of the DBC substrate with an adhesive tape, and silicone gel (SE1880, manufactured by Dowcorning) was poured until the entire SiC chip was covered, and it was cured in an explosion-proof warm air oven under the conditions of 70 °C for 30 minutes and 150 °C for 1 hour to obtain a mounting sample.

[0089] <Evaluation of Connection Reliability: Temperature Cycle Test> For the mounting samples obtained in the examples and comparative examples, a temperature cycle test was conducted in a temperature cycle test apparatus (TSA-72ES-W, manufactured by Espec Corporation). The temperature cycle conditions were -40°C on the low temperature side, 250°C on the high temperature side, and 30 minutes for each temperature step. The bonding state of each interface before the temperature cycle test, after 500 cycles, after 1000 cycles, and after 2000 cycles was observed with an ultrasonic imaging device (InSight-300, manufactured by Insight). Those without peeling or cracks at the interface were regarded as "good", and those with peeling or cracks were regarded as "bad". The results are shown in Table 1.

[0090]

Table 1

Explanation of Symbols

[0091] 1…Sintered copper layer, 2…Insulating substrate, 3…Bonding layer, 4…Metal foil layer, 5…Device chip, 6…Die bonding material, 7…Electrode terminal, 8…Heat sink or water-cooled plate, 9…Metal wire, 100, 200, 300, 400…Mounting substrate, 500, 600…Mounting example.

Claims

1. An insulating substrate, a sintered copper layer which is a porous sintered body disposed on the insulating substrate, and a bonding layer disposed between the insulating substrate and the sintered copper layer for bonding the insulating substrate and the sintered copper layer. The mounting substrate, wherein the bonding layer is a layer including a Ti sputtering film / Ni sputtering film / Ni plating film / Pd plating film in this order from the insulating substrate side.

2. The mounting substrate according to Claim 1, wherein the thickness of the sintered copper layer is 50 μm or more and 1000 μm or less.

3. The mounting substrate according to Claim 1 or 2, wherein the thermal conductivity of the sintered copper layer is 120 W / m·K or more.

4. The mounting substrate according to any one of Claims 1 to 3, wherein the Young's modulus of the sintered copper layer is 10 GPa or more and 70 GPa or less.

5. The mounting substrate according to any one of Claims 1 to 4, wherein the density of the sintered copper layer is 60% by volume or more and 90% by volume or less.

6. The mounting substrate according to any one of Claims 1 to 5, wherein the insulating substrate is a ceramic substrate or a glass substrate.

7. The mounting substrate according to any one of Claims 1 to 6, further comprising a metal foil layer disposed on a surface of the sintered copper layer opposite to the bonding layer.

8. The mounting substrate according to any one of Claims 1 to 7, wherein the thickness of the bonding layer is 10 μm or less.

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