Transient liquid phase diffusion bonding preform including unidirectional porous metal body, and transient liquid phase diffusion bonding method and power module using same

Abstract

The present invention provides a transient liquid phase diffusion bonding preform, and a transient liquid phase diffusion bonding method and a power module using same, the preform having a unidirectional porous metal body applied thereto and thus facilitating high-temperature bonding. The transient liquid diffusion bonding preform to which a unidirectional porous metal body is applied, according to an embodiment of the present invention, comprises: a unidirectional porous metal body having a plurality of unidirectional pores extending in one direction from a first surface to a second surface and made of a high-melting point metal; a first surface layer disposed on the first surface of the unidirectional porous metal body and made of a low-melting point metal; a second surface layer disposed on the second surface of the unidirectional porous metal body and made of the low-melting point metal; and a pore-filling layer for filling at least a portion of the plurality of unidirectional pores of the unidirectional porous metal body and made of the low-melting point metal.

Description

Transient liquid phase diffusion bonding preform including a unidirectional porous metal body, a method for transient liquid phase diffusion bonding using the same, and a power module

[0001] The technical idea of ​​the present invention relates to a metal bonding method, and more specifically, to a transition liquid phase diffusion bonding preform including a unidirectional porous metal body that is easy to bond at high temperatures, a transition liquid phase diffusion bonding method using the same, and a power module.

[0002] Higher performance, miniaturization, and weight reduction of electronic devices require higher density and integration of semiconductor packages. However, higher integration generates more heat, which degrades semiconductor device performance and can lead to defects such as substrate deterioration, thereby reducing product reliability and lifespan. In particular, high-voltage power conversion electrical components for eco-friendly automobiles are used in extremely harsh operating environments, including high-temperature heat generation and thermal shock conditions. Therefore, securing more efficient heat-dissipating materials and structures is essential. Therefore, research on heat-dissipating materials and technologies that can effectively dissipate generated heat while improving semiconductor device performance and suppressing degradation of product performance and reliability is increasingly important.

[0003] Power modules integrate multiple power semiconductor devices to transmit or convert high power. Wide bandgap semiconductors, such as SiC and GaN, are known as excellent materials for power modules. Conventional silicon suffers from reduced efficiency at high temperatures, leading to the adoption of SiC and GaN. Because these wide bandgap semiconductors operate at higher temperatures than silicon-based semiconductors, long-term, high-temperature reliability at the junction is required.

[0004] Soldering is widely used in the semiconductor industry as a joining process. Soldering is a method of joining components by melting only solder with a melting point below 450°C without melting the base metal. Lead-free solder pastes based on tin (Sn) are commonly used. However, residual tin can remelt after soldering. To prevent this, gold-based high-temperature solder pastes have been proposed. However, these pastes suffer from the high cost of gold and the complex nature of gold-tin intermetallic compounds. Furthermore, SiC-based power semiconductors operate at temperatures exceeding 200°C on average, necessitating the use of alternative solders with melting points below 250°C.

[0005] Sintering is a method of joining nanometer- or micrometer-sized powder particles by heat treatment to form a single mass. This sintering method is performed using a metal powder paste with various compositions and mixing ratios of metal powder and binder. The metal powders are mainly silver (Ag) and copper (Cu). The sintering method using the metal powder paste enables sintering between metal powders at a temperature lower than the melting point of the metal powders themselves. Furthermore, the sintered joint has the same melting point as the metal powders, preventing remelting in high-temperature environments. Therefore, reliability issues that arise in high-temperature environments of power modules can be resolved.

[0006] For example, sintering bonding using silver (Ag) powder paste can provide excellent thermal conductivity and high electrical conductivity, but has limitations such as high price and long sintering process time. Sintering bonding using copper (Cu) powder paste can provide excellent thermal conductivity and high electrical conductivity, and is possible at a relatively low price, but has difficulty with copper oxidation problem. A core-shell structured bonding material formed by coating silver on copper particles can solve the copper oxidation problem, but the manufacturing of the bonding material requires a complex process, so there may be limitations in commercialization.

[0007] The technical problem to be achieved by the technical idea of ​​the present invention is to provide a transition liquid phase diffusion bonding preform including a unidirectional porous metal body that is easy to bond at high temperatures, a transition liquid phase diffusion bonding method using the same, and a power module.

[0008] However, these tasks are exemplary and the technical idea of ​​the present invention is not limited thereto.

[0009] According to one aspect of the present invention, a transition liquid phase diffusion bonding preform including a unidirectional porous metal body that is easy to bond at high temperatures, a transition liquid phase diffusion bonding method using the same, and a power module are provided.

[0010] According to one embodiment of the present invention, the transition liquid phase diffusion bonding preform may include: a unidirectional porous metal body having a plurality of unidirectional pores extending in one direction from a first surface to a second surface, and made of a high-melting-point metal; a first surface layer disposed on a first surface of the unidirectional porous metal body and made of a low-melting-point metal; a second surface layer disposed on a second surface of the unidirectional porous metal body and made of the low-melting-point metal; and a pore-filling layer filling at least a portion of the plurality of unidirectional pores of the unidirectional porous metal body and made of the low-melting-point metal.

[0011] According to one embodiment of the present invention, at least one of the first surface layer, the second surface layer, and the pore filling layer may be formed as a plating layer formed by plating.

[0012] According to one embodiment of the present invention, the high-melting-point metal may include copper or a copper alloy, and the low-melting-point metal may include tin or a tin alloy.

[0013] According to one embodiment of the present invention, the one-way porous metal body may have a porosity in the range of 1% by volume to 70% by volume.

[0014] According to one embodiment of the present invention, the one-way porous metal body may be formed as a metal casting body using a mold casting method, a continuous melting zone method, a continuous casting method, or a centrifugal casting method.

[0015] According to one embodiment of the present invention, the one-way porous metal body may be formed as a metal molded body formed by press forming, rolling, and then perforating, laser processing, or selective etching a metal material in the shape of a sheet, plate, sheet, or foil.

[0016] According to one embodiment of the present invention, the transition liquid phase diffusion bonding method may include the steps of: providing a transition liquid phase diffusion bonding preform including a unidirectional porous metal body and at least one surface layer made of a low-melting-point metal; arranging a metal member made of a high-melting-point metal on at least one surface of the transition liquid phase diffusion bonding preform; heat-treating the transition liquid phase diffusion bonding preform; and bonding the metal member to the transition liquid phase diffusion bonding preform by transition liquid phase diffusion of the high-melting-point metal and the low-melting-point metal.

[0017] According to one embodiment of the present invention, the unidirectional porous metal body may include: a unidirectional porous metal body having a plurality of unidirectional pores extending in one direction from a first surface to a second surface, and made of a high-melting-point metal; a first surface layer disposed on the first surface of the unidirectional porous metal body and made of a low-melting-point metal; a second surface layer disposed on the second surface of the unidirectional porous metal body and made of the low-melting-point metal; and a pore-filling layer filling at least a portion of the plurality of unidirectional pores of the unidirectional porous metal body and made of the low-melting-point metal.

[0018] According to one embodiment of the present invention, at least one of the first surface layer, the second surface layer, and the pore filling layer may be formed as a plating layer formed by plating.

[0019] According to one embodiment of the present invention, the heat treatment step can be performed at a temperature ranging from 100°C to 400°C for 1 minute to 120 minutes.

[0020] According to one embodiment of the present invention, the joining step may be performed by causing the high-melting-point metal and the low-melting-point metal to react with each other to form at least one of a eutectic alloy, a permeable alloy, and an intermetallic compound.

[0021] According to one embodiment of the present invention, the power module comprises: a ceramic circuit board including a ceramic layer, a first substrate copper layer, and a second substrate copper layer; at least one semiconductor element disposed on the first substrate copper layer; a mold layer covering the semiconductor element; and a heat sink disposed on the second substrate copper layer, wherein the heat sink can be joined by a heat sink joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0022] According to one embodiment of the present invention, the present invention further includes a base plate disposed on the second substrate copper layer, and the base plate can be joined by a base plate joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0023] According to one embodiment of the present invention, the power module comprises: an upper ceramic substrate including an upper ceramic layer, an upper first substrate copper layer, and an upper second substrate copper layer; an upper first spacer disposed on a portion of the upper first substrate copper layer; and an upper second spacer disposed on a portion of the upper first substrate copper layer and having a greater height than the upper first spacer; a lower ceramic circuit board including a lower ceramic substrate including a lower ceramic layer, a lower first substrate copper layer, and a lower second substrate copper layer; a first semiconductor element disposed between the upper first spacer and the lower first substrate copper layer; a second semiconductor element disposed between the upper second spacer and the lower first substrate copper layer and having a smaller thickness than the first semiconductor element; a mold layer filling a space between the upper ceramic circuit board and the lower ceramic circuit board to cover the first semiconductor element and the second semiconductor element; an upper heat sink disposed on the upper second substrate copper layer; And a lower heat sink disposed on the lower second substrate copper layer, wherein at least one of the upper heat sink and the lower heat sink can be joined by a heat sink joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0024] According to one embodiment of the present invention, at least one of an upper base plate disposed on the upper second substrate copper layer and a lower base plate disposed on the lower second substrate copper layer is further included, and at least one of the upper base plate and the lower base plate can be joined by a base plate joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0025] According to one embodiment of the present invention, at least one of the upper first spacer and the upper second spacer can be joined by a spacer joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0026] The present invention relates to a transition liquid phase diffusion bonding preform including a unidirectional porous metal body and a transition liquid phase diffusion bonding method using the same, wherein, in a transition liquid phase diffusion bonding based on a copper-tin (Cu-Sn) system, a unidirectional porous metal body is plated with tin to form a transition liquid phase diffusion bonding preform, and a transition liquid phase diffusion bonding method is performed using the same.

[0027] The transition liquid phase diffusion bonding preform according to the present invention and the transition liquid phase diffusion bonding method using the same have the effects of improving properties such as oxidation prevention, thermal conductivity enhancement, bonding strength enhancement, and thermomechanical stress relief compared to conventional methods, and have the effects of process improvement such as simplification of the pretreatment process and shortening of the process time.

[0028] The above-described transition liquid phase diffusion bonding preform has a lower vertical elastic modulus than conventional porous metals, thereby reducing thermal stress. Furthermore, its vertical thermal conductivity is higher than that of conventional porous metals. Furthermore, when the above-described transition liquid phase diffusion bonding preform has a thickness of 0.1 mm, all or most of the pores are open apertures. Therefore, tin is injected into all pores during plating, enabling faster and more predictable bonding.

[0029] Compared to conventional silver sintering methods, the bonding method using the above-described transition liquid phase diffusion bonding preform uses Cu-Sn, so it is inexpensive and does not cause silver migration (Ag sintering). In addition, compared to conventional copper sintering methods, the bonding method using the above-described transition liquid phase diffusion bonding preform can fundamentally prevent copper oxidation problems and overcome the problems of weak bonding strength between copper particles and difficulty in controlling microstructure.

[0030] The transition liquid phase diffusion bonding preform according to the present invention and the transition liquid phase diffusion bonding method using the same can be applied to bonding processes of substrates, such as die attach processes and substrate attach processes, in various fields, such as automobiles and power semiconductors.

[0031] The effects of the present invention described above are illustrative, and the scope of the present invention is not limited by these effects.

[0032] FIG. 1 is a top view illustrating a unidirectional porous metal body applied to a transition liquid phase diffusion bonding preform according to one embodiment of the present invention.

[0033] FIG. 2 is a cross-sectional view taken along line AA of the one-way porous metal body of FIG. 1 according to one embodiment of the present invention.

[0034] FIG. 3 is a cross-sectional view illustrating a transition liquid diffusion bonding preform according to one embodiment of the present invention.

[0035] FIG. 4 is a cross-sectional view showing a joint formed using a transition liquid diffusion bonding preform according to one embodiment of the present invention.

[0036] FIG. 5 is a flowchart illustrating a transition liquid phase diffusion bonding method using a transition liquid phase diffusion bonding preform according to one embodiment of the present invention.

[0037] FIG. 6 is an optical microscope photograph showing the bonding cross-sectional area of ​​a bond formed by a transitional liquid diffusion bonding method using a transitional liquid diffusion bonding preform according to an embodiment of the present invention, compared to a comparative example.

[0038] FIG. 7 is an optical microscope photograph showing the change in the joint cross-sectional area of ​​a joint formed by a transitional liquid phase diffusion bonding method using a transitional liquid phase diffusion bonding preform according to an embodiment of the present invention, compared to a comparative example, according to aging treatment after bonding.

[0039] FIG. 8 is an optical microscope photograph showing the change in the joint cross-sectional area of ​​a joint formed by a transitional liquid phase diffusion bonding method using a transitional liquid phase diffusion bonding preform according to an embodiment of the present invention, compared to a comparative example, according to a corrosion test after bonding.

[0040] Figure 9 is a graph showing the bonding strength of a bond formed by a transition liquid phase diffusion bonding method using a transition liquid phase diffusion bonding preform according to one embodiment of the present invention compared to a comparative example.

[0041] FIGS. 10 and 11 are cross-sectional views illustrating a power module having a joint formed by performing transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform according to one embodiment of the present invention.

[0042] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Embodiments of the present invention are provided to more completely explain the technical idea of ​​the present invention to those skilled in the art. The following embodiments may be modified in various different forms, and the scope of the technical idea of ​​the present invention is not limited to the following embodiments. Rather, these embodiments are provided to more faithfully and completely convey the technical idea of ​​the present invention to those skilled in the art. Like reference numerals throughout this specification denote like elements. Furthermore, various elements and areas in the drawings are schematically drawn. Therefore, the technical idea of ​​the present invention is not limited by the relative sizes or intervals drawn in the attached drawings.

[0043] In this specification, a layer formed "on" another layer may refer to a layer formed directly above the other layer, or may refer to an intermediate layer or layers formed on another layer. It should be noted that the meanings of "upper" and "lower" in this specification are relative, and the direction upward from the ceramic substrate is described as "upper", and the direction downward is described as "lower."

[0044] In the semiconductor industry, transient liquid phase (TLP) bonding has been proposed for bonding processes, which is relatively inexpensive and forms an intermetallic compound with a high melting point. The TLP bonding is a technology that combines soldering and diffusion bonding, in which a low-melting-point metal layer is interposed between high-melting-point metal layers, and the low-melting-point metal layer melts at a certain temperature and diffuses into the high-melting-point metal layer to form an intermetallic compound, thereby bonding the layers. The intermetallic compound formed may vary depending on the types of the high-melting-point and low-melting-point metal layers. The high-melting-point metal layer may be made of copper (Cu) or nickel (Ni), and the low-melting-point metal layer may be made of a Sn-based material with a low melting point. For example, intermetallic compounds such as Cu6Sn5 or Cu3Sn in a Cu-Sn system, Ni3Sn4 in a Ni-Sn system, and Ag3Sn in a Ag-Sn system may be formed in the bonding region. Since the melting point of these intermetallic compounds is generally around 400℃ or higher, remelting does not occur at the joints even when the power module is exposed to a high-temperature environment. However, the typical TLD process has a very long process time, which is limited by the thickness of the joint and the type of intermetallic compound formed. In other words, the TLD process has a limitation in that it takes a long time for the low melting point material to melt and the diffusion reaction to occur. To shorten this long process time, a method of bonding while applying pressure can be considered, but high pressure can damage the power module during the bonding process. In addition, conventional solders have limitations such as low thermal conductivity and poor mechanical properties.

[0045] According to the technical idea of ​​the present invention, a transition liquid phase diffusion bonding preform including a unidirectional porous metal body can be configured to include a unidirectional porous metal body composed of a high-melting-point metal such as copper, and a surface layer formed on the surface thereof by plating or the like with a low-melting-point metal such as tin. In addition, a low-melting-point metal such as tin can penetrate into the pores of the unidirectional porous metal body. Accordingly, the diffusion area of ​​tin can be increased, thereby shortening the process time required for bonding. In addition, the thermal conductivity of the bonded portion can be increased compared to the prior art. In addition, since the formation of Kirkendall voids due to the difference in diffusion rates of two metals with different melting points can be suppressed, the mechanical properties can be improved. In addition, since the fracture path can be deformed along the unidirectional porous metal body after heat treatment due to the unidirectional porous metal body remaining after the bonding process, a decrease in shear strength can be prevented.

[0046] Although thermal conductivity is expected to be improved by using a bulk metal without pores rather than a unidirectional porous metal, it is predicted that the diffusion rate will not be increased, and thus the process time will not be able to be shortened. In addition, a foam-type metal body with non-directional pores is also predicted to provide a similar effect to the unidirectional porous metal body to some extent, but the unidirectional porous metal body has a structure in which pores are formed in one direction, and therefore the modulus of elasticity in the vertical direction is lower than that of a conventional porous metal body, and accordingly, thermomechanical stress caused by thermal shock can be alleviated, and long-term reliability at high temperatures can be improved.

[0047] In addition, when the unidirectional porous metal body is composed of copper, an acid removal process may be required during the bonding process due to the high oxidation capacity of copper. However, the transition liquid phase diffusion bonding preform of the present invention forms a surface layer composed of tin or the like having oxidation resistance on the surface of the unidirectional porous metal body, thereby solving this copper oxidation problem.

[0048] In addition, since the transition liquid phase diffusion bonding preform of the present invention is manufactured in the form of a preform, it can provide the advantage of shortening the pretreatment process.

[0049] Hereinafter, a one-way porous metal body according to the technical idea of ​​the present invention will be described in detail.

[0050] FIG. 1 is a top view illustrating a unidirectional porous metal body applied to a transition liquid phase diffusion bonding preform according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA of the unidirectional porous metal body of FIG. 1 according to an embodiment of the present invention.

[0051] Referring to FIGS. 1 and 2, a unidirectional porous metal body (1) has a metal body (2) and a plurality of unidirectional pores (3) formed to extend along a pore extending direction within the metal body (2). The unidirectional porous metal body (1) may be referred to as a lotus structure. The unidirectional pores (3) may be formed to a depth that penetrates the metal body (2) or may be formed to a depth that does not penetrate the metal body (2).

[0052] The unidirectional porous metal body (1) can exhibit anisotropic properties, unlike conventional porous metals that include pores in an isotropic manner, since it includes unidirectional pores (3) arranged in one direction. In particular, it has excellent heat transfer performance in the pore direction and a thermal stress relief effect.

[0053] The manufacturing method for forming a one-way porous metal body (1) can be carried out in various ways. For example, in the case of a casting method, there are a mold casting method, a continuous melt zone method, a continuous casting method, a centrifugal casting method, etc., and in the case of a forming method, there are press forming, rolling, perforation, laser processing, or selective etching of a metal material in the shape of a sheet, plate, sheet, or foil.

[0054] The one-way porous metal body (1) can be formed as a metal casting body using a mold casting method, a continuous melting zone method, a continuous casting method, or a centrifugal casting method.

[0055] Alternatively, the one-way porous metal body (1) may be formed as a metal molded body formed by using press forming, rolling, and then perforating, laser processing, or selective etching of a metal material in the shape of a sheet, plate, sheet, or foil.

[0056] The pore characteristics of a unidirectional porous metal body (1) of a casting method can be controlled by the pressure of the injected hydrogen gas, the solidification speed, etc. As the hydrogen gas pressure and the solidification speed increase, the porosity and pore size can decrease. The unidirectional porous metal body (1) can have a porosity in the range of, for example, 1 vol% to 70 vol%.

[0057] A unidirectional porous metal body (1) refers to a metal in which cylindrical pores are arranged in one direction. In addition, if necessary, the unidirectional porous metal body can be utilized as a composite material composed of other materials.

[0058] A unidirectional porous metal body (1) is a form in which unidirectional pores are contained within the metal. It has the characteristic of anisotropic thermal, electrical, and mechanical properties. This anisotropic characteristic is what differentiates it from other porous metals. For example, the unidirectional porous metal body (1) may have anisotropic elastic modulus, thermal conductivity, and electrical conductivity.

[0059] The one-way porous metal body (1) may include various metals, may include a high-melting point metal, and may include, for example, copper or a copper alloy.

[0060] Table 1 shows the anisotropic thermal, electrical, and mechanical properties of a unidirectional porous metal body (1) composed of copper according to the porosity. In Table 1, “∥” means a direction parallel to the extension direction of the pores, and “⊥” means a direction parallel to the extension direction of the pores.

[0061] Porosity (%)Elasticity modulus (GPa)Thermal conductivity (W / mK)Electrical conductivity (x10 6 Ω -1 m -1 )E ∥ E ⊥ K ∥ K ⊥ σ ∥ σ ⊥ 0759534034015.015.01067~7480~9430527013.512.02060~6660~7927022012.09.73052~5943~5923517010.57.84045~5130~422001409.05.25037~4420~291651207.54.06030~3613~19130806.02.27022~298~1295504.51.28015~214~760303.00.7

[0062] Referring to Table 1, the elastic modulus, thermal conductivity, and electrical conductivity of a unidirectional porous metal body (1) composed of copper decrease as the porosity increases. In addition, the elastic modulus, thermal conductivity, and electrical conductivity exhibit anisotropy in that they decrease more in the vertical direction than in the direction parallel to the extension direction of the pores as the porosity increases.

[0063] When comparing a copper structure without pores and a unidirectional porous metal body composed of copper, their coefficients of thermal expansion are almost the same. On the other hand, the thermal stress of the unidirectional porous metal body composed of copper is significantly reduced for the same strain, so that mechanical thermal stress can be alleviated. In addition, since the elastic modulus of the unidirectional porous metal body in both the vertical and horizontal directions decreases with respect to external stress, the shock absorption capacity can be improved. Although the thermal conductivity and electrical conductivity of the unidirectional porous metal body composed of copper decrease as the porosity increases, they are higher than those of molybdenum.

[0064] The unidirectional porous metal body described above can hinder the propagation path of cracks occurring at the joint through the pores provided therein. When a crack propagating along the interface encounters the pores, the direction of the path changes, thereby increasing the joint strength.

[0065] By inserting other materials into the pores of the above-mentioned one-way porous metal body, the properties of a composite material can be obtained. Accordingly, properties such as elastic modulus, thermal conductivity, electrical conductivity, and parasitic inductance can be changed, and if necessary, improved.

[0066] FIG. 3 is a cross-sectional view illustrating a transition liquid diffusion bonding preform according to one embodiment of the present invention.

[0067] Referring to FIG. 3, the transition liquid phase diffusion bonding preform (4) may include a unidirectional porous metal body (1), a first surface layer (5a), a second surface layer (5b), and a pore filling layer (5c).

[0068] A unidirectional porous metal body (1) has a metal body (2) and a plurality of unidirectional pores (3) extending in one direction within the metal body (2).

[0069] The first surface layer (5a) is arranged on the first surface (1a) of the one-way porous metal body (1) and may be made of a low-melting-point metal.

[0070] The second surface layer (5b) is disposed on the second surface (1b) of the one-way porous metal body (1) and may be made of the low melting point metal.

[0071] The pore filling layer (5c) fills at least a portion of the plurality of unidirectional pores (3) of the unidirectional porous metal body (1) and may be made of the low melting point metal.

[0072] At least one of the first surface layer (5a), the second surface layer (5b), and the pore-filling layer (5c) may be formed as a plating layer formed by plating.

[0073] The high melting point metal may have a relatively high melting point, for example, may have a melting point in the range of 400°C to 1100°C, and may include, for example, copper or a copper alloy.

[0074] The low melting point metal may have a relatively low melting point, for example, may have a melting point in the range of 100°C to 400°C, and may include, for example, tin or a tin alloy.

[0075] The high-melting-point metal and the low-melting-point metal can react with each other to form at least one of a eutectic alloy, a peritectic alloy, a eutectoid alloy, and an intermetallic compound.

[0076] However, these materials are exemplary and the technical idea of ​​the present invention is not limited thereto.

[0077] The unidirectional porous metal body (1) may have a porosity ranging from 1% by volume to 70% by volume. The unidirectional porous metal body (1) may be formed of a metal casting, or may be manufactured by various methods such as press forming and laser processing. The unidirectional porous metal body (1) may be formed of the high-melting-point metal.

[0078] FIG. 4 is a cross-sectional view showing a joint formed using a transition liquid diffusion bonding preform according to one embodiment of the present invention.

[0079] Referring to Fig. 4, a bonded body is illustrated in which a first metal layer (6a) is disposed on the upper side of a transition liquid phase diffusion bonding preform (1), i.e., on the first surface layer (5a), and a second metal layer (6b) is disposed on the lower side of the transition liquid phase diffusion bonding preform (1), i.e., on the second surface layer (5b). When the bonded body is heat-treated, the high-melting-point metal and the low-melting-point metal undergo transition liquid phase diffusion, so that the first metal layer (6a) and the second metal layer (6b) are each bonded to the transition liquid phase diffusion bonding preform (1).

[0080] The first metal layer (6a) and the second metal layer (6b) may be made of various metals, and may be made of the aforementioned high-melting-point metals, for example, copper or a copper alloy. However, these materials are exemplary and the technical concept of the present invention is not limited thereto.

[0081] FIG. 5 is a flowchart illustrating a transition liquid phase diffusion bonding method using a transition liquid phase diffusion bonding preform according to one embodiment of the present invention.

[0082] Referring to FIG. 5, the transition liquid phase diffusion bonding method (S100) may include the steps of: providing a transition liquid phase diffusion bonding preform including a unidirectional porous metal body and at least one surface layer made of a low-melting-point metal (S110); arranging a metal member made of a high-melting-point metal on at least one surface of the transition liquid phase diffusion bonding preform (S120); heat-treating the transition liquid phase diffusion bonding preform (S130); and bonding the metal member to the transition liquid phase diffusion bonding preform by transition liquid phase diffusion of the high-melting-point metal and the low-melting-point metal (S140).

[0083] The above unidirectional porous metal body may include a unidirectional porous metal body having a plurality of unidirectional pores extending in one direction from a first surface to a second surface, and made of a high-melting-point metal; a first surface layer disposed on the first surface of the unidirectional porous metal body and made of a low-melting-point metal; a second surface layer disposed on the second surface of the unidirectional porous metal body and made of the low-melting-point metal; and a pore-filling layer filling at least a portion of the plurality of unidirectional pores of the unidirectional porous metal body and made of the low-melting-point metal.

[0084] The high melting point metal may have a relatively high melting point, for example, may have a melting point in the range of 400°C to 1100°C, and may include, for example, copper or a copper alloy.

[0085] The low melting point metal may have a relatively high melting point, for example, may have a melting point in the range of 100°C to 400°C, and may include, for example, tin or a tin alloy.

[0086] At least one of the first surface layer, the second surface layer, and the pore-filling layer may be formed as a plating layer formed by plating.

[0087] The above heat treatment step (S130) can be performed, for example, at a temperature in the range of 100°C to 400°C for 1 minute to 120 minutes.

[0088] The above bonding step (S140) can be performed by allowing the high-melting-point metal and the low-melting-point metal to react with each other to form at least one of a eutectic alloy, a permeable alloy, and an intermetallic compound.

[0089] Experimental example

[0090] Below, preferred experimental examples are presented to aid understanding of the present invention. However, the following experimental examples are provided solely to aid understanding of the present invention, and the present invention is not limited to the following experimental examples.

[0091] The examples were prepared as follows. A unidirectional porous metal body having multiple unidirectional pores and made of copper as a high-melting-point metal was prepared. Thereafter, the unidirectional porous metal body was plated with tin to form a first surface layer, a second surface layer, and a pore-filling layer made of tin, thereby forming a transition liquid phase diffusion bonding preform. Subsequently, copper foil as a metal member was placed on both surfaces of the transition liquid phase diffusion bonding preform, i.e., on the first surface layer and the second surface layer made of tin. Subsequently, heat treatment for transition liquid phase diffusion was performed at about 260°C for 10 to 30 minutes.

[0092] A comparative example was prepared as follows. Instead of the aforementioned unidirectional porous metal body, a tin plate was prepared. Next, copper foil was placed on both surfaces of the tin plate. Subsequently, heat treatment was performed at approximately 260°C for 30 minutes.

[0093] FIG. 6 is an optical microscope photograph showing the bonding cross-sectional area of ​​a bond formed by a transitional liquid diffusion bonding method using a transitional liquid diffusion bonding preform according to an embodiment of the present invention, compared to a comparative example.

[0094] In Fig. 6, “porous Cu” represents a structure provided by a one-way porous metal body, and “Cu” on the upper and lower sides represents copper foil.

[0095] Referring to (a) to (c) of FIG. 6, in the embodiment, a copper-tin intermetallic compound, such as Cu3Sn or Cu6Sn5, was formed on the surface and inside of the unidirectional porous metal body in contact with the copper foil. It can be seen that the area where the copper-tin intermetallic compound was formed increased as the heat treatment time elapsed. On the other hand, referring to (d) of FIG. 6, in the comparative example, a copper-tin intermetallic compound, such as Cu3Sn or Cu6Sn5, was formed only on the surface portion of the tin plate.

[0096] At the same heat treatment time of 30 minutes, the example is analyzed to have improved bonding strength because the formation area of ​​the intermetallic compound is increased compared to the comparative example.

[0097] In addition, the embodiment is analyzed to have increased the tin-copper diffusion area by filling the pores of the unidirectional porous metal body with tin, thereby causing transition liquid phase diffusion to occur more rapidly. Therefore, the process time for transition liquid phase diffusion is expected to be shortened.

[0098] FIG. 7 is an optical microscope photograph showing the change in the joint cross-sectional area of ​​a joint formed by a transitional liquid phase diffusion bonding method using a transitional liquid phase diffusion bonding preform according to an embodiment of the present invention, compared to a comparative example, according to aging treatment after bonding.

[0099] Referring to Fig. 7, this is the result after aging treatment at a temperature of 150°C after performing bonding. In the example, no Kirkendall voids were observed up to an aging time of 500 hours, and were observed at an aging time of 1000 hours. On the other hand, in the comparative example, Kirkendall voids were observed even at an aging time of 300 hours. The Kirkendall voids are formed due to the difference in diffusion rates of copper and tin, and can weaken the mechanical and chemical properties of the bond. It is analyzed that the example suppresses the formation of the Kirkendall voids by filling the pores of the unidirectional porous metal body with tin.

[0100] FIG. 8 is an optical microscope photograph showing the change in the joint cross-sectional area of ​​a joint formed by a transitional liquid phase diffusion bonding method using a transitional liquid phase diffusion bonding preform according to an embodiment of the present invention, compared to a comparative example, according to a corrosion test after bonding.

[0101] In Fig. 8, the corrosion test was performed using a salt spray test. The internal microstructure was observed at 24, 48, 72, and 96 salt spray hours while spraying a 5 wt% NaCl aqueous solution at 35°C onto the joint.

[0102] Referring to Fig. 8, in the embodiment, no corrosion products were observed up to 48 hours of salt spray time, and corrosion products were observed at 72 hours of salt spray time. However, the amount of the corrosion products was observed to be relatively small. On the other hand, in the comparative example, corrosion products were observed at 24 hours of salt spray time, and the corrosion products increased as the spray time increased. A significantly large amount of corrosion products was observed at salt spray times exceeding 72 hours. Therefore, it can be seen that the embodiment has excellent corrosion resistance because it can suppress the formation of corrosion products compared to the comparative example.

[0103] Figure 9 is a graph showing the bonding strength of a bond formed by a transition liquid phase diffusion bonding method using a transition liquid phase diffusion bonding preform according to one embodiment of the present invention compared to a comparative example.

[0104] Fig. 9 (a) shows the change in bonding strength according to the high-temperature aging treatment time of Fig. 7, and Fig. 9 (b) shows the change in bonding strength according to the salt spray time of Fig. 8.

[0105] Referring to Fig. 9, the initial bonding strength of the Example is higher than that of the Comparative Example, which is consistent with the results described above with reference to Fig. 6. As the aging treatment time and salt spray time increase, the bonding strength of the Example and Comparative Example decreases, but the Comparative Example shows a greater decrease in bonding strength, which is consistent with the results described above with reference to Figs. 7 and 8.

[0106] Therefore, it is analyzed that the embodiment can provide higher bonding strength than the comparative example while providing improved durability and corrosion resistance.

[0107] The embodiment can provide a thermal conductivity that is about 2 to 3 times higher than that of the comparative example. In addition, the embodiment can alleviate the decline in shear strength compared to the comparative example, and this is analyzed to be because the crack propagation path is changed by the unidirectional porous metal body having a pore structure, that is, because the crack propagation path is increased by the heterogeneous structure of tin filling the pores and copper forming the pores. In addition, the embodiment can alleviate thermal stress because the unidirectional porous metal body has a lower elastic modulus in the vertical direction than the existing porous metal.

[0108] Additionally, the transition liquid phase diffusion bonding preform can prevent copper oxidation by plating the surface with tin. In addition to the above tin, the formation of an oxidation-resistant metal on the surface is also included within the technical concept of the present invention.

[0109] In addition, the transition liquid phase diffusion bonding preform can simplify the bonding process and shorten the pretreatment process by being formed in advance in the form of a preform.

[0110] Application: Power modules

[0111] The transition liquid phase diffusion bonding method using the transition liquid phase diffusion bonding preform according to the present invention can be applied to various fields. Among these, a power module will be described as an example.

[0112] FIGS. 10 and 11 are cross-sectional views illustrating a power module having a joint formed by performing transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform according to one embodiment of the present invention.

[0113] Referring to FIG. 10, a power module (3000) may include a ceramic circuit board (300), a first semiconductor element (370), a second semiconductor element (380), a mold layer (390), a heat sink (340), and a base plate (350).

[0114] The ceramic circuit board (300) may include a ceramic substrate (310) including a ceramic layer (311), a first substrate copper layer (312), and a second substrate copper layer (313).

[0115] The ceramic layer (311) may have excellent thermal conductivity and electrical insulation. The ceramic layer (311) may be made of a ceramic material and may include, for example, at least one of Al2O3, AlN, ZTA (Zirconia Toughened Alumina), and Si3N4.

[0116] The first substrate copper layer (312) can be patterned to function as a circuit structure for a semiconductor device. The first substrate copper layer (312) can be formed as a single layer or as multiple layers. The first substrate copper layer (312) can have a total thickness in the range of, for example, 100 μm to 1000 μm, and can have a total thickness of, for example, about 300 μm.

[0117] The second substrate copper layer (313) can function as a warpage prevention layer that prevents the ceramic layer (311) from warping. In addition, the second substrate copper layer (313) can provide a path for dissipating heat generated from the semiconductor element to the outside. For this purpose, a heat dissipation structure can be attached to the second substrate copper layer (313). The second substrate copper layer (313) can be formed as a single layer or as a plurality of layers. The second substrate copper layer (313) can have a total thickness of, for example, 100 μm to 1000 μm, and can have a total thickness of, for example, about 300 μm.

[0118] The first substrate copper layer (312) and the second substrate copper layer (313) may include the same material, may be formed by the same method, and may be formed simultaneously. At least one of the first substrate copper layer (312) and the second substrate copper layer (313) may be formed by a DBC copper layer formed by bonding copper foil on a ceramic layer (311) through a high-temperature oxidation process, a DPC copper layer formed by forming a seed layer on the ceramic layer (311) and then plating the seed layer with copper, or an AMB copper layer formed by bonding copper foil using an active metal foil to the ceramic layer (311). However, this is exemplary, and the first substrate copper layer (312) and the second substrate copper layer (313) may include different materials, be formed by different methods, or be formed at different process points, and this is also within the technical scope of the present invention.

[0119] Additionally, the case where the ceramic substrate (310) is an AMB (active metal brazing) substrate including an active metal brazing layer is also included in the technical concept of the present invention.

[0120] At least one semiconductor element may be arranged on a first substrate copper layer (312). The first semiconductor element (370) may be bonded to the first substrate copper layer (312) by a first element adhesive layer (372). The second semiconductor element (380) may be bonded to the first substrate copper layer (312) by a second element adhesive layer (382). The first element adhesive layer (372) and the second element adhesive layer (382) may be solder layers or adhesive layers, which are exemplary and the technical idea of ​​the present invention is not limited thereto.

[0121] The first semiconductor element (370) and the second semiconductor element (380) may include various semiconductor elements such as power semiconductor elements, memory semiconductor elements, switching semiconductor elements, and diode semiconductor elements. The first semiconductor element (370) and the second semiconductor element (380) may be, for example, power semiconductor elements, such as gate turn-off thyristor (GTO) semiconductor elements, insulated gate bipolar mode transistor (IGBT) semiconductor elements, SiC MOSFET (Metal Oxide Semiconductor Field Effect Transistor) semiconductor elements, etc., and may perform an operation of converting and supplying power supplied from a power supply unit such as a battery into power for driving a motor through a switching operation. In addition, the first semiconductor element (370) and the second semiconductor element (380) may include electrode members formed on the upper or lower portions. The second semiconductor element (380) may have a smaller thickness than the first semiconductor element (370). However, this is exemplary, and a case where the power module (3000) includes semiconductor elements of the same height, for example, only the first semiconductor element (370), is also included in the technical idea of ​​the present invention.

[0122] A mold layer (390) may be placed on a ceramic circuit board (300, 300a) to cover the first semiconductor element (370) and the second semiconductor element (380). The mold layer (390) may insulate the first semiconductor element (370) and the second semiconductor element (380). The mold layer (390) may be composed of, for example, EMC (epoxy molding compound).

[0123] A base plate (350) may be disposed on a second substrate copper layer (313). The base plate (350) may function as mechanical support and heat storage management. The base plate (350) may be bonded to the second substrate copper layer (313) by a base plate joint (352). The base plate joint (352) may be formed by transient liquid phase diffusion bonding using a transient liquid phase diffusion bonding preform including a unidirectional porous metal body. The base plate (350) may be formed of a metal plate, for example, a copper plate. In addition, a case where the base plate (350) is formed of the unidirectional porous metal body is also included in the technical concept of the present invention. The base plate (350) is optional and may be omitted.

[0124] The heat sink (340) can be disposed on the second substrate copper layer (313) and can be disposed on the base plate (350). The heat sink (340) can be bonded to the second substrate copper layer (313) or the base plate (350) by a heat sink joint (342). The heat sink joint (342) can be formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body. The heat sink (340) can include a material having excellent heat transfer properties, such as aluminum or copper.

[0125] Referring to FIG. 11, the power module (3000a) may include an upper ceramic circuit board (300b_U), a lower ceramic circuit board (300_D), a first semiconductor element (370), a second semiconductor element (380), a mold layer (390), an upper heat sink (340_U), a lower heat sink (340_D), an upper base plate (350_U), and a lower base plate (350_D).

[0126] The upper ceramic circuit board (300b_U) may include an upper ceramic substrate (310_U) including an upper ceramic layer (311_U), an upper first substrate copper layer (312_U), and an upper second substrate copper layer (313_U); and an upper base plate (350_U). The upper ceramic circuit board (300b_U) may further include an upper first spacer (320_U) and an upper second spacer (330_U).

[0127] The lower ceramic circuit board (300_D) may include a lower ceramic substrate (310_D) including a lower ceramic layer (311_D), a lower first substrate copper layer (312_D), and a lower second substrate copper layer (313_D); and a lower base plate (350_D). Here, the lower ceramic circuit board (300_D) does not include a spacer.

[0128] The upper ceramic circuit board (300b_U) and the lower ceramic circuit board (300_D) can be placed facing each other.

[0129] The upper first spacer (320_U) and the upper second spacer (330_U) may be disposed on a portion of the upper ceramic substrate (310_U), for example, on a portion of the upper first substrate copper layer (312_U). The upper second spacer (330_U) may have a greater height than the upper first spacer (320_U). The upper first spacer (320_U) may be bonded to the upper first substrate copper layer (312_U) by the first spacer bonding portion (322). The upper second spacer (330_U) may be bonded to the upper first substrate copper layer (312_U) by the second spacer bonding portion (332). The upper first spacer (320_U) and the upper second spacer (330_U) may be formed of a metal workpiece that does not include pores inside, such as a copper structure, a copper molybdenum alloy structure, or the like, or may be formed of the above-described one-way porous metal body, and may include, for example, copper or a copper alloy.

[0130] The first spacer joint (322) and the second spacer joint (332) can be formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0131] The first semiconductor element (370) may be placed between the upper first spacer (320_U) and the lower first substrate copper layer (312_D). The first semiconductor element (370) may be bonded to the upper first spacer (320_U) and the lower first substrate copper layer (312_D) by a first element adhesive layer (372).

[0132] The second semiconductor element (380) may be placed between the upper second spacer (330_U) and the lower first substrate copper layer (312_D). The second semiconductor element (380) may be bonded to the upper first spacer (320_U) and the lower first substrate copper layer (312_D) by a second element adhesive layer (382).

[0133] The second semiconductor element (380) may have a smaller thickness than the first semiconductor element (370). Therefore, by placing an upper first spacer (320_U) having a relatively smaller thickness on the upper side of the first semiconductor element (370) and placing an upper second spacer (330_U) having a relatively larger thickness on the upper side of the second semiconductor element (380), the thickness difference between the second semiconductor element (380) and the first semiconductor element (370) can be corrected.

[0134] The first element adhesive layer (372) and the second element adhesive layer (382) may be solder layers or adhesive layers, which are exemplary and the technical idea of ​​the present invention is not limited thereto.

[0135] The mold layer (390) can fill the space between the upper ceramic circuit board (300b_U) and the lower ceramic circuit board (300_D). Accordingly, the first semiconductor element (370) and the second semiconductor element (380) can be covered by the mold layer (390). The mold layer (390) can insulate the first semiconductor element (370) and the second semiconductor element (380). The mold layer (390) can be composed of, for example, EMC (epoxy molding compound).

[0136] The power module (3000b) includes an upper first spacer (320_U) and an upper second spacer (330_U), and does not include a spacer at the bottom, so it may have an asymmetrical structure with respect to the first semiconductor element (370) and the second semiconductor element (380).

[0137] However, this is exemplary and the technical concept of the present invention also includes a case where the lower ceramic circuit board (300_D) includes a spacer. In addition, the technical concept of the present invention also includes a case where the power module has a symmetrical structure.

[0138] The upper base plate (350_U) may be placed on the upper second substrate copper layer (313_U). The upper base plate (350_U) may be bonded to the upper second substrate copper layer (313_U) by the upper base plate joint (352_U). The lower base plate (350_D) may be placed on the lower second substrate copper layer (313_D). The lower base plate (350_D) may be bonded to the lower second substrate copper layer (313_D) by the lower base plate joint (352_D).

[0139] The upper base plate (350_U) and the lower base plate (350_D) can be formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0140] The upper heat sink (340_U) may be disposed on the upper second substrate copper layer (313_U) and may be disposed on the upper base plate (350_U). The upper heat sink (340_U) may be bonded to the upper second substrate copper layer (313_U) or the upper base plate (350_U) by an upper heat sink joint (342_U). The lower heat sink (340_D) may be disposed on the lower second substrate copper layer (313_D) and may be disposed on the lower base plate (350_D). The lower heat sink (340_D) may be bonded to the lower second substrate copper layer (313_D) or the lower base plate (350_D) by a lower heat sink joint (342_D).

[0141] The upper heat sink joint (342_U) and the lower heat sink joint (342_D) can be formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body.

[0142] It will be apparent to a person skilled in the art to which the technical idea of ​​the present invention pertains that the technical idea of ​​the present invention described above is not limited to the above-described embodiments and the attached drawings, and that various substitutions, modifications, and changes are possible within a scope that does not depart from the technical idea of ​​the present invention.

Claims

1. A unidirectional porous metal body having a plurality of unidirectional pores extending in one direction from a first surface to a second surface and made of a high-melting-point metal; A first surface layer formed of a low-melting-point metal and disposed on a first surface of the above-described one-way porous metal body; A second surface layer disposed on the second surface of the one-way porous metal body and made of the low-melting-point metal; and Filling at least a portion of the plurality of one-way pores of the one-way porous metal body, and including a pore-filling layer made of the low-melting-point metal, Transition liquid diffusion bonding preform.

2. In paragraph 1, At least one of the first surface layer, the second surface layer, and the pore filling layer is formed by a plating layer. Transition liquid diffusion bonding preform.

3. In paragraph 1, The above high-melting-point metal includes copper or a copper alloy, The above low melting point metal includes tin or a tin alloy. Transition liquid diffusion bonding preform.

4. In paragraph 1, The above one-way porous metal body is, Having a porosity ranging from 1% by volume to 70% by volume, Transition liquid diffusion bonding preform.

5. In paragraph 1, The above one-way porous metal body is, Consisting of a metal casting formed using a mold casting method, continuous melt casting method, continuous casting method, or centrifugal casting method. Transition liquid diffusion bonding preform.

6. In paragraph 1, The above one-way porous metal body is, A metal body formed by pressing, rolling, and then punching, laser processing, or selective etching a metal material in the shape of a sheet, plate, sheet, or foil. Transition liquid diffusion bonding preform.

7. A step of providing a transition liquid phase diffusion bonding preform comprising a one-way porous metal body and at least one surface layer made of a low melting point metal; A step of placing a metal member made of a high-melting point metal on at least one surface of the above-mentioned transition liquid diffusion bonding preform; A step of heat treating the above transition liquid phase diffusion bonding preform; and A step of bonding the metal member to the transition liquid phase diffusion bonding preform by the transition liquid phase diffusion of the high melting point metal and the low melting point metal, Transition liquid phase diffusion bonding method.

8. In paragraph 7, The above one-way porous metal body is, A unidirectional porous metal body having a plurality of unidirectional pores extending in one direction from a first surface to a second surface and made of a high-melting-point metal; A first surface layer formed of a low-melting-point metal and disposed on a first surface of the above-described one-way porous metal body; A second surface layer disposed on the second surface of the one-way porous metal body and made of the low-melting-point metal; and Filling at least a portion of the plurality of one-way pores of the one-way porous metal body, and including a pore-filling layer made of the low-melting-point metal, Transition liquid phase diffusion bonding method.

9. In paragraph 8, At least one of the first surface layer, the second surface layer, and the pore filling layer is formed by a plating layer. Transition liquid diffusion bonding preform.

10. In paragraph 7, The above heat treatment step is, Performed at a temperature ranging from 100°C to 400°C for 1 to 120 minutes, Transition liquid phase diffusion bonding method.

11. In paragraph 7, The above joining step is, The high melting point metal and the low melting point metal react with each other to form at least one of a eutectic alloy, a permeable alloy, and an intermetallic compound, Transition liquid phase diffusion bonding method.

12. A ceramic circuit board comprising a ceramic layer, a first substrate copper layer, and a second substrate copper layer; At least one semiconductor element disposed on the first substrate copper layer; A mold layer covering the semiconductor element; and including a heat sink disposed on the second substrate copper layer, The above heat sink is joined by a heat sink joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a one-way porous metal body. Power module.

13. In paragraph 12, Further comprising a base plate disposed on the second substrate copper layer, The above base plate is joined by a base plate joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a one-way porous metal body. Power module.

14. An upper ceramic circuit board comprising an upper ceramic layer, an upper first substrate copper layer, and an upper second substrate copper layer; an upper first spacer disposed on a portion of the upper first substrate copper layer; and an upper second spacer disposed on a portion of the upper first substrate copper layer and having a greater height than the upper first spacer. A lower ceramic circuit board comprising a lower ceramic substrate including a lower ceramic layer, a lower first substrate copper layer, and a lower second substrate copper layer; A first semiconductor element disposed between the upper first spacer and the lower first substrate copper layer; A second semiconductor element disposed between the upper second spacer and the lower first substrate copper layer, and having a smaller thickness than the first semiconductor element; A mold layer that fills the space between the upper ceramic circuit board and the lower ceramic circuit board and covers the first semiconductor element and the second semiconductor element; an upper heat sink disposed on the upper second substrate copper layer; and A lower heat sink is disposed on the lower second substrate copper layer, At least one of the upper heat sink and the lower heat sink is joined by a heat sink joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body. Power module.

15. In paragraph 14, Further comprising at least one of an upper base plate disposed on the upper second substrate copper layer and a lower base plate disposed on the lower second substrate copper layer, At least one of the upper base plate and the lower base plate is joined by a base plate joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body. Power module.

16. In paragraph 14, At least one of the upper first spacer and the upper second spacer is joined by a spacer joint formed by transition liquid phase diffusion bonding using a transition liquid phase diffusion bonding preform including a unidirectional porous metal body. Power module.

Images