Power semiconductor module, power conversion device, and method for manufacturing power semiconductor module

Abstract

This power semiconductor module is provided with: a power semiconductor element (20); and a lead frame (10) or a substrate (11) on which the power semiconductor element (20) is mounted. At least one of the power semiconductor element (20), the lead frame (10), and the substrate (11) and the adherend bonded thereto are bonded via a metal sintered material (30) containing a metal oxide.

Description

Power semiconductor module, power conversion device, and method for manufacturing power semiconductor module

[0001] The present disclosure relates to a structure and manufacturing method of a power semiconductor module.

[0002] Semiconductor modules for power control are called power semiconductor modules and are used in a wide range of products, from industrial equipment to home appliances and information terminals. Power semiconductor modules are required to have high productivity and reliability.

[0003] In addition, semiconductor elements formed from wide bandgap semiconductors such as SiC have a high operating temperature and are highly efficient, so it is highly likely that power semiconductor elements formed from wide bandgap semiconductors will become mainstream in the future. Therefore, power semiconductor modules are also required to have a package form that can be applied to power semiconductor elements formed from wide bandgap semiconductors.

[0004] Power semiconductor modules handle large currents and high voltages, generating a lot of heat. Because power semiconductor elements can experience thermal runaway when they get too hot, power semiconductor modules generally use heat dissipation structures that use copper or aluminum heat dissipation fins, which have excellent thermal conductivity. Aluminum and copper are also used for the conductor layers of ceramic substrates that mount power semiconductor elements. Aluminum, in particular, is lightweight and highly corrosion-resistant, so ceramic substrates with aluminum fins and aluminum conductor layers are often used for power semiconductor modules for automobiles.

[0005] Aluminum and aluminum alloys are also often used for the surface electrodes of power semiconductor elements. Because aluminum does not wet well with common tin-based solders, surface electrodes containing aluminum are often plated with nickel or other materials. However, aluminum forms a dense surface oxide film in the atmosphere, making aluminum plating technically difficult. For example, Patent Document 1 listed below proposes a joining method using a silver oxide reduction reaction as a method for joining aluminum conductor layers and aluminum electrodes as is.

[0006] On the other hand, anodic bonding has traditionally been used as a method for joining glass and metal, etc. To perform normal anodic bonding, the surfaces of both adherends must be smoothed to a surface roughness of about several nanometers. For example, Patent Document 2 listed below proposes a method in which a bonding material is applied to one adherend and baked, and then the other adherend is placed on top of it and heated while applying an electric current to join them. In this method, it is considered that the surface roughness of the adherends can be as low as several hundred nanometers.

[0007] JP 2022-059274 A JP 2002-145676 A

[0008] The joining method of Patent Document 1 can obtain a certain degree of joining strength with aluminum, but the conditions of the load and heating temperature during joining are strict, and the heat resistance is somewhat poor.

[0009] The conductor layer of a ceramic substrate has a surface roughness of more than several hundred nanometers due to recrystallization caused by heat treatment, etc., so it is difficult to apply the bonding method of Patent Document 2 to the conductor layer of a ceramic substrate. Furthermore, there is a trend toward thinner power semiconductor elements to reduce loss, and thinner power semiconductor elements tend to warp by several hundred nanometers, so it is difficult to apply the bonding method of Patent Document 2 to a power semiconductor module.

[0010] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a power semiconductor module that can obtain strong and highly reliable bonding even when the power semiconductor elements or the lead frame or substrate on which they are mounted have significant warpage or surface roughness.

[0011] The power semiconductor module according to the present disclosure comprises a power semiconductor element and a lead frame or a substrate on which the power semiconductor element is mounted, and at least one of the power semiconductor element, the lead frame, and the substrate is bonded to an adherend via a metal sintered material containing a metal oxide.

[0012] According to the present disclosure, even when the power semiconductor element or the lead frame or substrate on which it is mounted has significant warpage or surface roughness, a strong and reliable bond can be obtained.

[0013] FIG. 1 is a conceptual diagram showing the structure of a power semiconductor module according to a first embodiment. FIG. 2 is a conceptual diagram showing the structure of a power semiconductor module according to the first embodiment. FIG. 3 is a cross-sectional view showing a manufacturing process of a power semiconductor module according to the first embodiment. FIG. 4 is a cross-sectional view showing the manufacturing process of a power semiconductor module according to the first embodiment. FIG. 5 is a cross-sectional view showing the manufacturing process of a power semiconductor module according to the first embodiment. FIG. 6 is a cross-sectional view showing the manufacturing process of a power semiconductor module according to the first embodiment. FIG. 7 is an explanatory diagram of a silver sintered material according to the first embodiment. FIG. 8 is an explanatory diagram of a silver sintered material according to the first embodiment. FIG. 9 is a conceptual diagram showing the structure of a power semiconductor module according to a second embodiment. FIG. 10 is a conceptual diagram showing the structure of a power semiconductor module according to the second embodiment. FIG. 11 is a conceptual diagram showing the structure of a power semiconductor module according to the second embodiment. FIG. 12 is a conceptual diagram showing the structure of a power semiconductor module according to the second embodiment. FIG. 13 is a conceptual diagram showing the structure of a modified example of the power semiconductor module according to the second embodiment. FIG. 14 is a conceptual diagram showing the structure of a power semiconductor module according to a third embodiment. FIG. 15 is a schematic diagram showing a manufacturing process of a power semiconductor module according to the third embodiment. Fig. 16 is a schematic diagram showing a process for manufacturing a power semiconductor module according to embodiment 3. Fig. 17 is a schematic diagram showing a process for manufacturing a power semiconductor module according to embodiment 3. Fig. 18 is a schematic diagram showing a process for manufacturing a power semiconductor module according to embodiment 3. Fig. 19 is a schematic diagram showing a process for manufacturing a power semiconductor module according to embodiment 3. Fig. 20 is a block diagram showing a configuration of a power conversion system to which a power conversion device according to embodiment 4 is applied.

[0014] 1 and 2 are conceptual diagrams showing the structure of a power semiconductor module according to embodiment 1. Fig. 1 is a cross-sectional view of the switching element control device, and Fig. 2 is a top view of the switching element control device.

[0015] The power semiconductor module according to the first embodiment comprises a lead frame 10, a power semiconductor element 20 mounted on the lead frame 10, and a sealing resin 70 that seals them (in FIG. 2, only the outline of the sealing resin 70 is shown by a dotted line).

[0016] In this embodiment, the power semiconductor element 20 is an insulated gate bipolar transistor (IGBT) made of silicon, measuring 10 mm x 8 mm and having a thickness of 0.1 mm. However, the power semiconductor element 20 is not limited to an IGBT, and may be, for example, a metal-oxide-semiconductor field-effect transistor (MOSFET), a Schottky barrier diode (SBD), or a PN junction diode. The material of the power semiconductor element 20 may also be a wide bandgap semiconductor such as silicon carbide (SiC). When the material of the power semiconductor element 20 is a wide bandgap semiconductor, superior characteristics can be obtained in high voltage, large current, and high temperature operation compared to silicon. Wide bandgap semiconductors include silicon carbide, gallium nitride (GaN)-based materials, diamond, and the like.

[0017] The power semiconductor element 20 has a source electrode 20s and a gate electrode 20g as surface electrodes on its upper surface (front surface), and a drain electrode 20d as a back surface electrode on its lower surface (back surface). The source electrode 20s, the gate electrode 20g, and the drain electrode 20d are made of aluminum or an aluminum alloy.

[0018] The lead frame 10 comprises a source terminal 10s, a drain terminal 10d, and a gate terminal 10g. The power semiconductor element 20 is mounted on the drain terminal 10d, and the drain electrode 20d on the underside of the power semiconductor element 20 is joined to the drain terminal 10d of the lead frame 10 by a silver sintered material 30, which is a metal sintered material. That is, in this embodiment, the adherend joined to the power semiconductor element 20 via the silver sintered material 30 is the lead frame 10. Conversely, it can also be said that the adherend joined to the lead frame 10 via the silver sintered material 30 is the power semiconductor element 20. The silver sintered material 30 preferably contains a metal oxide. A copper sintered material may be used instead of the silver sintered material 30.

[0019] The source electrode 20s of the power semiconductor element 20 is connected to the source terminal 10s via a wire 41, and the gate electrode 20g of the power semiconductor element 20 is connected to the gate terminal 10g via a wire 42. In this embodiment, the lead frame 10 is made of copper and has a thickness of 0.6 mm. The wire 41 is made of an aluminum alloy and has a diameter (φ) of 0.3 mm. The wire 42 is made of an aluminum alloy and has a diameter of 0.15 mm.

[0020] However, the material of the lead frame 10 is not limited to copper and may be, for example, 42 alloy or aluminum. The material of the wires 41 and 42 is not limited to aluminum alloy and may be, for example, pure aluminum or copper. A ribbon may be used instead of the wire 41.

[0021] The sealing resin 70 insulates and seals the lead frame 10, the power semiconductor element 20, the silver sintered material 30, the wire 41, and the wire 42. However, the source terminal 10s, the source terminal 10s, and the gate terminal 10g of the lead frame 10 each partially protrude from the sealing resin 70. The portions of the source terminal 10s, the source terminal 10s, and the gate terminal 10g protruding from the sealing resin 70 function as external connection terminals. The sealing resin 70 is made of epoxy resin with alumina filler dispersed therein.

[0022] A method for manufacturing a power semiconductor module according to the first embodiment will now be described. First, as shown in Fig. 3, a silver oxide paste 30p composed of a metal compound and an organic solvent, which will be the material for the silver sintered material 30, is applied to a lead frame 10 using a dispenser, and the power semiconductor element 20 is then positioned and placed on top. The silver oxide paste 30p can be, for example, a silver oxide powder with a particle size of 2 to 3 µm dispersed in an organic solvent (for example, a mixture of ethylene glycol and terpineol (concentration: approximately 10 wt%)).

[0023] Next, as shown in FIG. 4 , the lead frame 10, silver oxide paste 30p, and power semiconductor element 20 are sandwiched between the base heater 60b and collet heater 60c of a current-applying heating press 60. A load is applied to the power semiconductor element 20 to pressurize the silver oxide paste 30p, while a current is applied from a DC power supply 60e. In this embodiment, a load of 1 MPa is applied to the power semiconductor element 20, and a voltage and current of 15 V and 4 A are applied from the DC power supply 60e. The heating process was performed by first heating at 100°C for 600 seconds, then at 300°C for 1800 seconds, and then slowly cooling. As a result, the silver oxide paste 30p becomes the silver sintered material 30, and the drain electrode 20d of the power semiconductor element 20 and the lead frame 10 are bonded by the silver sintered material 30.

[0024] Next, as shown in FIG. 5, a wire 41 is used to connect the source electrode 20s of the power semiconductor element 20 to the source terminal 10s of the lead frame 10, and a wire 42 is used to connect the gate electrode 20g of the power semiconductor element 20 to the gate terminal 10g of the lead frame 10, thereby forming a desired circuit.

[0025] Finally, as shown in FIG. 6, the lead frame 10 carrying the power semiconductor element 20 is fixed between the upper mold die 70u and the lower mold die 70d, and the sealing resin 70 is injected and heated to harden, thereby forming the power semiconductor module shown in FIGS. 1 and 2.

[0026] In this embodiment, the silver sintered material 30 that bonds the lead frame 10 and the power semiconductor element 20 is formed by sandwiching a silver oxide paste 30p, which is a bonding material, between the lead frame 10 and the power semiconductor element 20, and applying a current to the power semiconductor element 20 while applying pressure and heat. As will be described later, the silver sintered material 30 formed by this method has high bonding strength. Therefore, even if the power semiconductor element 20 is significantly warped or the source electrode 20s and the drain electrode 20d have significant surface roughness, or even if the lead frame 10 on which the power semiconductor element 20 is mounted has significant warpage or surface roughness, it is possible to ensure adhesion and increase bonding strength. This allows for a highly reliable bond, improving the reliability of the power semiconductor module.

[0027] Furthermore, as in the present embodiment, the use of a paste (silver oxide paste 30p) made of a powdered metal compound and an organic solvent as the bonding material improves the ability to absorb warpage of the power semiconductor element 20 and the surface roughness of the source electrode 20s and the drain electrode 20d. Furthermore, the presence of a liquid component in the bonding material also has the effect of facilitating migration of metal ions generated in the bonding material during the bonding process.

[0028] The configuration and mechanism of the silver sintered material 30 will be described below.

[0029] The silver sintered material 30 is bonded using a sintering bonding technology that combines the decomposition reaction of a metal precursor (silver oxide) with current control during bonding, achieving a low-temperature, low-pressure process for difficult-to-bond materials (such as aluminum, which is difficult to solder) and non-metallic materials (such as silicon in power semiconductor elements and ceramic insulating substrates). During the decomposition process of silver oxide by reaction with an organic solvent, atomic-scale metals containing silver ions are generated. By applying an electric current during this process, the generated metals are transported to the difficult-to-bond material (the surface of the material), achieving highly efficient interfacial bonding.

[0030] Here, the sintering material will be described. The aforementioned metal precursor (silver oxide) decomposes at a specific temperature either alone or when mixed with a reducing organic solvent. The metal precursor is, for example, a silver precursor or a copper precursor. The silver precursor is, for example, a silver compound containing silver oxide or a silver salt of an organic acid, and the copper precursor is, for example, a copper compound containing copper oxide or a copper salt of an organic acid.

[0031] The bonding material can be used not only as a metal precursor alone but also as a mixture with a metal powder. For example, the metal powder preferably contains at least one selected from the group consisting of silver, copper, nickel, tin, zinc, gold, palladium, platinum, and alloys thereof. Furthermore, the metal powder preferably contains silver or copper from the above metal group. In this case, the bonding layer can achieve higher electrical conductivity and heat dissipation properties. The shape of the metal powder may be spherical, flake-like, ball-like, or needle-like. In this case, the average particle diameter of the metal particles is preferably 0.02 μm or more and 10 μm or less, and more preferably 0.05 μm or more and 30 μm or less. The mixed bonding material preferably contains 1% by mass or more but less than 100% by mass of the metal precursor, and more preferably 30% by mass or more and 100% by mass or less of the metal precursor (e.g., metal oxide).

[0032] Next, the organic solvent will be described. The bonding material is in the form of a solution or paste and contains an organic solvent. For example, a monohydric alcohol or a polyhydric alcohol, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, or terpineol, is used as the organic solvent. In this case, it is desirable that the metal precursor in the bonding material is sufficiently dispersed in the organic solvent and has good applicability. The organic solvent may also contain an organic acid. Examples of organic acids include formic acid, oxalic acid, stearic acid, acetic acid, citric acid, myristic acid, and benzoic acid, as well as lauric acid, palmitic acid, oleic acid, linoleic acid, acetone dicarboxylic acid, phthalic acid, silver glycolate, and malonic acid.

[0033] Next, energization will be described. As shown in FIG. 7 , assume that a first substrate 91 and a second substrate 92 of different types are joined. The first substrate 91 can be selected from a metallic material, and the second substrate 92 can be selected from a metallic material (including plated, difficult-to-bond metals and non-metallic materials), difficult-to-bond metal materials, and non-metallic materials. The aforementioned paste-like joining material 93 is inserted between the first substrate 91 and the second substrate 92. The structure consisting of the first substrate 91, the second substrate 92, and the joining material 93 is fixed and pressed by a jig 94. The first substrate 91 side serves as a positive electrode and the second substrate 92 side serves as a negative electrode, and is connected to an external constant-current power supply. The constant-current power supply connection may be made via another material or a conductive jig. 7 shows an example in which a jig 94 is a conductive jig connected to a constant current power supply, and a structure consisting of a first substrate 91, a second substrate 92, and a bonding material 93 is sandwiched between a positive electrode member 94p and a negative electrode member 94n of the jig 94. During bonding, a current is applied at a temperature of 100°C or higher, a pressure of 0.1 MPa or higher (for fixing), and a bonding time of 10 minutes or longer (larger values ​​result in a stronger joint). The current density is 6 mA / mm ２ ~1 A / mm ２ More specifically, the current can be selected from the range of 25 mA / mm ２ ~250mA / mm ２ It is desirable to select from the range of

[0034] Figure 8 shows an example of joining of SiC and Ag-plated metal test pieces. The joining method of the prior art (without current application) exhibited a strength characteristic of 22.4 MPa at 250°C, and 47 MPa at 300°C, a high-temperature condition that produces a stronger joint. In contrast, the joining method of the present disclosure (with current application) exhibited a strength characteristic of 69.8 MPa at 250°C, approximately three times that of the prior art. Furthermore, the joining method of the present disclosure exhibited a strength of 53.2 MPa even at 200°C, a temperature at which joint strength is believed to decrease, exceeding the strength obtained under the high-temperature condition (300°C) of the prior art. Furthermore, a strength index of 30.5 MPa was obtained even under low-pressure conditions at 250°C, demonstrating the effectiveness of the joining method of the present disclosure.

[0035] Furthermore, by reversing the polarity of the power supply during the pressure and heat application process, it is possible to reverse the migration direction of silver ions, for example, thereby generating dense nuclei on the surfaces of both adherends and improving the bonding strength.

[0036] 9 and 10 are conceptual diagrams showing the structure of a power semiconductor module according to embodiment 2. Fig. 9 is a cross-sectional view of the power semiconductor module. Fig. 10 is a top view of the power semiconductor module.

[0037] The power semiconductor module according to the second embodiment includes a resin-insulated metal substrate 11, a diode 21 and an IGBT 22 which are power semiconductor elements mounted on the resin-insulated metal substrate 11, a case 50 for accommodating these elements, and a liquid sealing resin 71 filled in the case 50 (the liquid sealing resin 71 is not shown in FIG. 10 ).

[0038] Resin insulated metal substrate 11 comprises aluminum base layer 11b, heat dissipation insulation layer 11i on aluminum base layer 11b, and aluminum conductor layer 11c on heat dissipation insulation layer 11i. In this embodiment, resin insulated metal substrate 11 measures 40 mm x 18 mm and is 3.5 mm thick, aluminum conductor layer 11c is 0.4 mm thick, heat dissipation insulation layer 11i is 0.1 mm thick, and aluminum base layer 11b is 3 mm thick. Instead of aluminum base layer 11b and aluminum conductor layer 11c, a base layer and conductor layer made of copper may be used.

[0039] The diode 21 is made of silicon, has a size of 8 mm x 8 mm and a thickness of 0.1 mm, and includes an anode electrode 21a made of an aluminum alloy as a surface electrode on the upper surface and a cathode electrode 21c made of an aluminum alloy as a back electrode on the lower surface.

[0040] The IGBT 22 is made of silicon, has dimensions of 10 mm x 8 mm and a thickness of 0.1 mm, and includes a source electrode 22s and a gate electrode 22g made of an aluminum alloy as surface electrodes on the top surface, and a drain electrode 22d on the back surface.

[0041] The cathode electrode 21c of the diode 21 and the drain electrode 22d of the IGBT 22 are each joined to the aluminum conductor layer 11c of the resin insulated metal substrate 11 by a silver sintered material 30. That is, in this embodiment, the adherends joined to the diode 21 and IGBT 22, which are power semiconductor elements, via the silver sintered material 30 are the resin insulated metal substrate 11. Conversely, it can also be said that the adherends joined to the resin insulated metal substrate 11 via the silver sintered material 30 are the diode 21 and the IGBT 22. A copper sintered material may be used instead of the silver sintered material 30.

[0042] A case 50 is mounted on the periphery of resin insulated metal substrate 11, and a source terminal 51s, a drain terminal 51d, and a signal terminal 51g such as a gate terminal are insert-molded into case 50. The source terminal 51s is connected to the anode electrode 21a of diode 21 and the source electrode 22s of IGBT 22 via wire 41. The drain terminal 51d is connected to aluminum conductor layer 11c via wire 41, thereby electrically connecting the drain terminal 51d to the cathode electrode 21c of diode 21 and the drain electrode 22d of IGBT 22. The signal terminal 51g is connected to the gate electrode 22g of IGBT 22 and the like via wire 42.

[0043] In this embodiment, the case 50 is made of PPS (Poly Phenylene Sulfide) resin and measures 44 mm x 22 mm x 8 mm. The source terminal 51s and the drain terminal 51d are made of copper and have a thickness of 0.6 mm. The signal terminal 51g is made of copper and have a thickness of 0.3 mm. The wire 41 is made of an aluminum alloy and has a diameter of 0.3 mm, and the wire 42 is made of an aluminum alloy and has a diameter of 0.15 mm. The liquid sealing resin 71 is made of epoxy resin with alumina filler dispersed therein. The source terminal 51s, the drain terminal 51d, and the signal terminal 51g may be made of copper or aluminum with nickel plating on the surface. The filler in the liquid sealing resin 71 may be silica. The liquid sealing resin 71 may also be a mixture of epoxy resin and silicone resin, or a silicone gel.

[0044] 11 , a bus bar 52 may be used instead of a wire 41 as a member connecting a source terminal 51s to the anode electrode 21a of the diode 21 and the source electrode 22s of the IGBT 22. In this case, the bus bar 52 may be joined to the source terminal 51s, the anode electrode 21a, and the source electrode 22s using a silver sintered material 30 (or a copper sintered material). In other words, in FIG. 11 , the adherends joined to the diode 21 and the IGBT 22, which are power semiconductor elements, via the silver sintered material 30 include the bus bar 52 in addition to the lead frame 10. The bus bar 52 is, for example, made of copper and has a thickness of 0.6 mm.

[0045] 12, a ceramic substrate 12 may be used instead of the resin insulated metal substrate 11. In this case, the adherend bonded to the diode 21 and the IGBT 22 via the silver sintered material 30 is the ceramic substrate 12. The ceramic substrate 12 comprises an aluminum conductor layer 12b, a ceramic layer 12i on the aluminum conductor layer 12b, and an aluminum conductor layer 12c on the ceramic layer 12i. A fin base 80 may be bonded to the aluminum conductor layer 12b of the ceramic substrate 12 via the silver sintered material 30. In other words, the adherend bonded to the ceramic substrate 12 via the silver sintered material 30 may include the fin base 80 in addition to the diode 21 and the IGBT 22. The fin base 80 comprises a base portion 80b and a plurality of pin fin portions 80p.

[0046] In the example of Figure 12, the ceramic substrate 12 is 40 mm x 18 mm in size and 2.1 mm in thickness, the aluminum conductor layers 12c and 12b are 0.8 mm in thickness, and the ceramic layer 12i is made of SiN and 0.6 mm in thickness. The fin base 80 is made of aluminum and is 52 mm x 24 mm in size, the base portion 80b is 3 mm in thickness, and each of the pin fin portions 80p is 1.5 mm in diameter and 6 mm in height. The surfaces of the aluminum conductor layers 12b and 12c may be nickel-plated. Alternatively, copper conductor layers may be used instead of the aluminum conductor layers 12b and 12c.

[0047] Furthermore, as in this embodiment, when there are multiple locations where silver sintered material 30 can be used, some of it may be replaced with solder (for example, solder containing 96.5% tin, 3% silver, and 0.5% copper with a melting point of 217°C), brazing material, conductive adhesive, etc.

[0048] Fig. 13 is a cross-sectional view showing the structure of a modified example of the power semiconductor module according to embodiment 2. The configuration of Fig. 13 differs from the configuration of Fig. 9 in that a copper plate 34 as a metal plate and solder 35 are interposed between the diode 21 and the IGBT 22 and the silver sintered material 30.

[0049] The power semiconductor module of this modified example includes a resin-insulated metal substrate 11, a diode 21 and an IGBT 22 which are power semiconductor elements mounted on the resin-insulated metal substrate 11, a case 50 that houses them, and a liquid sealing resin 71 filled in the case 50.

[0050] Resin insulated metal substrate 11 is made up of aluminum base layer 11b, heat dissipation insulating layer 11i on aluminum base layer 11b, and aluminum conductor layer 11c on heat dissipation insulating layer 11i. In this modification, resin insulated metal substrate 11 also has a size of 40 mm x 18 mm and a thickness of 3.5 mm, aluminum conductor layer 11c is 0.4 mm thick, heat dissipation insulating layer 11i is 0.1 mm thick, and aluminum base layer 11b is 3 mm thick.

[0051] The diode 21 is made of silicon, has a size of 8 mm x 8 mm, and a thickness of 0.1 mm, and includes an anode electrode 21a made of an aluminum alloy as a surface electrode on the upper surface and a cathode electrode 21c made of an aluminum alloy and plated with nickel as a back electrode on the lower surface.

[0052] The IGBT 22 is made of silicon, has dimensions of 10 mm x 8 mm, and a thickness of 0.1 mm, and includes a source electrode 22s and a gate electrode 22g made of an aluminum alloy as surface electrodes on the top surface of the IGBT 22, and a nickel-plated drain electrode 22d on the back surface.

[0053] The cathode electrode 21c of the diode 21 and the drain electrode 22d of the IGBT 22 are each joined to a copper plate 34 (thickness: 0.3 mm) by solder 35. The copper plate 34 is joined to the aluminum conductor layer 11c of the resin insulated metal substrate 11 by a silver sintered material 30. In other words, in this modification, the adherend joined to the resin insulated metal substrate 11 via the silver sintered material 30 is the copper plate 34.

[0054] In this modification, the diodes 21 and the IGBTs 22 are mounted on the copper plate 34 arranged on the resin insulated metal substrate 11, and therefore the diodes 21 and the IGBTs 22 can be mounted using solder 35. Specifically, the manufacture of the power semiconductor module includes a step of sandwiching silver oxide paste between the resin insulated metal substrate 11 and the copper plate 34 and sintering the silver oxide paste to bond the resin insulated metal substrate 11 and the copper plate 34, and a step of bonding the diodes 21 and the IGBTs 22 to the copper plate 34 with the solder 35.

[0055] Since the solder 35 is a softer material than the silver sintered material 30, the use of the solder 35 can alleviate stress caused by the difference in thermal expansion coefficient between the diode 21 and the IGBT 22 and the resin insulated metal substrate 11 compared to the second embodiment (FIG. 9), thereby contributing to improving the reliability of the power semiconductor module.

[0056] This modification can also be applied to Embodiment 1. That is, in the power semiconductor module of Fig. 1 , a copper plate 34 as a metal plate and solder 35 may be interposed between the power semiconductor element 20 and the silver sintered material 30, and the power semiconductor element 20 may be mounted on the copper plate 34 arranged on the lead frame 10.

[0057] Third Preferred Embodiment FIG. 14 is a conceptual diagram showing the structure of a power semiconductor module according to a third preferred embodiment, showing a cross section of the power semiconductor module.

[0058] The circuit configuration of the power semiconductor module of FIG. 14 is the same as that of the power semiconductor module of FIG. 1 . However, a bus bar 52 is used instead of a wire 41 to connect the source terminal 10s and the source electrode 20s of the power semiconductor element 20. A silver sintered material 30, which is a metal sintered material, is provided to cover the surfaces of the source electrode 20s and the drain electrode 20d of the power semiconductor element 20. The front or back electrode of the power semiconductor element 20 covered with the silver sintered material 30 is bonded to an adherend by solder 31. Specifically, the drain electrode 20d covered with the silver sintered material 30 and the drain terminal 10d are bonded together, the source electrode 20s covered with the silver sintered material 30 and the bus bar 52 are bonded together, and the bus bar 52 and the source terminal 10s are bonded together by solder 31. For example, the solder 31 may be 96.5% tin, 3% silver, 0.5% copper, and has a melting point of 217°C.

[0059] The other configurations are the same as those of the power semiconductor module shown in FIG. 1, and therefore will not be described here.

[0060] A method for manufacturing a power semiconductor module according to embodiment 3 will now be described. First, as shown in Fig. 15, conductive silicone rubber 60f is attached to each of base heater 60b and collet heater 60c of current application heating press device 60, and silver oxide paste 30p, which is the material for silver sintered material 30, is applied to base heater 60b and source electrode 20s of power semiconductor element 20.

[0061] Next, as shown in FIG. 16 , a heat treatment is performed by applying a load and heat to the power semiconductor element 20 while applying a current from a DC power supply 60e. In this embodiment, a load of 1 MPa is applied to the power semiconductor element 20, and a voltage and current of 15 V and 4 A are applied from the DC power supply 60e. The heat treatment is performed by first heating at 100°C for 600 seconds, then heating at 300°C for 1800 seconds, and then slowly cooling. As a result, the silver oxide paste 30p becomes the silver sintered material 30, and the source electrode 20s and the drain electrode 20d of the power semiconductor element 20 are covered with the silver sintered material 30, as shown in FIG. 17 .

[0062] 18, the gate electrode 20g of the power semiconductor element 20 is connected to the gate terminal 10g of the lead frame 10 using a wire 42. In addition, the drain electrode 20d coated with the silver sintered material 30 and the drain terminal 10d, the source electrode 20s coated with the silver sintered material 30 and the bus bar 52, and the bus bar 52 and the source terminal 10s are joined using solder 31.

[0063] Finally, similarly to the first embodiment, the lead frame 10 on which the power semiconductor elements 20 are mounted is fixed between the upper mold die 70u and the lower mold die 70d, and the sealing resin 70 is injected and heated to harden, thereby forming the power semiconductor module according to the third embodiment as shown in FIG.

[0064] In this embodiment, the source electrode 20s and the drain electrode 20d are covered with the silver sintered material 30, and the warpage of the power semiconductor element 20 and the surface roughness of the source electrode 20s and the drain electrode 20d are absorbed by the silver sintered material 30. In addition, the silver sintered material 30 has high adhesion to the source electrode 20s and the drain electrode 20d. Therefore, even if the warpage of the power semiconductor element 20 or the surface roughness of the source electrode 20s and the drain electrode 20d is large, or even if the warpage or surface roughness of the ceramic substrate 12 on which it is mounted is large, a highly reliable bond can be obtained with the solder 31.

[0065] <Fourth Embodiment> In this embodiment, the power semiconductor module according to any one of the above-described first to third embodiments is applied to a power conversion device. The application of the power semiconductor modules according to the first to third embodiments is not limited to a specific power conversion device, but hereinafter, as the fourth embodiment, a case where the power semiconductor modules according to the first to third embodiments are applied to a three-phase inverter will be described.

[0066] FIG. 20 is a block diagram showing the configuration of a power conversion system to which the power conversion device according to this embodiment is applied.

[0067] The power conversion system shown in Fig. 20 is composed of a power supply 100, a power conversion device 200, and a load 300. The power supply 100 is a DC power supply and supplies DC power to the power conversion device 200. The power supply 100 can be composed of various components, such as a DC system, a solar cell, or a storage battery, or it may be composed of a rectifier circuit connected to an AC system or an AC / DC converter. The power supply 100 may also be composed of a DC / DC converter that converts DC power output from a DC system into a predetermined power.

[0068] The power conversion device 200 is a three-phase inverter connected between the power source 100 and the load 300, and converts DC power supplied from the power source 100 into AC power and supplies the AC power to the load 300. As shown in Fig. 20 , the power conversion device 200 includes a main conversion circuit 201 that converts DC power into AC power and outputs it, and a control circuit 203 that outputs a control signal to the main conversion circuit 201 to control the main conversion circuit 201.

[0069] The load 300 is a three-phase electric motor driven by AC power supplied from the power conversion device 200. The load 300 is not limited to a specific application, but is an electric motor mounted on various electrical devices, and is used as an electric motor for, for example, a hybrid vehicle, an electric vehicle, a railroad car, an elevator, or an air conditioning device.

[0070] The power conversion device 200 will be described in detail below. The main conversion circuit 201 includes switching elements and freewheel diodes (not shown). The switching elements convert DC power supplied from the power source 100 into AC power, which is supplied to the load 300. While the main conversion circuit 201 can have a variety of specific circuit configurations, the main conversion circuit 201 according to this embodiment is a two-level, three-phase full-bridge circuit that can be configured with six switching elements and six freewheel diodes connected in anti-parallel to each switching element. At least one of the switching elements and freewheel diodes of the main conversion circuit 201 is configured using a semiconductor module 202 corresponding to any one of the first to third embodiments described above. Two of the six switching elements are connected in series to form upper and lower arms, which constitute a respective phase (U phase, V phase, and W phase) of the full-bridge circuit. The output terminals of each upper and lower arm, i.e., the three output terminals of the main conversion circuit 201, are connected to the load 300.

[0071] The main conversion circuit 201 also includes a drive circuit (not shown) that drives each switching element, but the drive circuit may be built into the semiconductor module 202, or may be provided separately from the semiconductor module 202. The drive circuit generates drive signals that drive the switching elements of the main conversion circuit 201 and supplies them to the control electrodes of the switching elements of the main conversion circuit 201. Specifically, in accordance with control signals from a control circuit 203 (described later), the drive circuit outputs to the control electrodes of each switching element a drive signal that turns the switching element on and a drive signal that turns the switching element off. To maintain a switching element in the on state, the drive signal is a voltage signal (on signal) that is equal to or greater than the threshold voltage of the switching element, and to maintain a switching element in the off state, the drive signal is a voltage signal (off signal) that is equal to or less than the threshold voltage of the switching element.

[0072] The control circuit 203 controls the switching elements of the main conversion circuit 201 so that the desired power is supplied to the load 300. Specifically, it calculates the time (on time) that each switching element of the main conversion circuit 201 should be in the on state based on the power to be supplied to the load 300. For example, the main conversion circuit 201 can be controlled by PWM control, which modulates the on time of the switching elements according to the voltage to be output. The control circuit 203 then outputs a control command (control signal) to a drive circuit included in the main conversion circuit 201 so that an on signal is output to a switching element that should be in the on state at each time point, and an off signal is output to a switching element that should be in the off state at each time point. In accordance with this control signal, the drive circuit outputs an on signal or an off signal as a drive signal to the control electrode of each switching element.

[0073] In the power conversion device according to this embodiment, the semiconductor modules according to the first to third embodiments are applied as the switching elements and free wheel diodes of the main conversion circuit 201, thereby achieving improved reliability.

[0074] In the present embodiment, an example has been described in which the power semiconductor modules according to the first to third embodiments are applied to a two-level three-phase inverter, but the application of the power semiconductor modules according to the first to third embodiments is not limited to this and can be applied to various power conversion devices. In the present embodiment, a two-level power conversion device is described, but a three-level or multi-level power conversion device may also be used. In addition, when power is supplied to a single-phase load, the power semiconductor modules according to any of the first to third embodiments may be applied to a single-phase inverter. Furthermore, when power is supplied to a DC load or the like, the power semiconductor modules according to the first to third embodiments can also be applied to a DC / DC converter or an AC / DC converter.

[0075] Furthermore, the power conversion device to which the power semiconductor module according to any one of the first to third embodiments is applied is not limited to the case where the load described above is an electric motor, but can also be used, for example, as a power supply device for an electric discharge machine, a laser processing machine, an induction heating cooker, or a contactless power supply system, and can also be used as a power conditioner for a solar power generation system, a power storage system, etc.

[0076] It should be noted that the embodiments can be freely combined, and the embodiments can be modified or omitted as appropriate.

[0077] <Supplementary Notes> Various aspects of the present disclosure will be summarized below as supplementary notes.

[0078] (Supplementary Note 1) A power semiconductor module comprising: a power semiconductor element; and a lead frame or a substrate on which the power semiconductor element is mounted, wherein at least one of the power semiconductor element, the lead frame, and the substrate is bonded to an adherend via a metal sintered material containing a metal oxide.

[0079] (Supplementary Note 2) The power semiconductor module according to Supplementary Note 1, wherein the metal sintered material is a silver sintered material or a copper sintered material.

[0080] (Supplementary Note 3) The power semiconductor module according to Supplementary Note 1 or Supplementary Note 2, wherein the metal sintered material bonds a front electrode or a back electrode of the power semiconductor element to the adherend.

[0081] (Supplementary Note 4) The power semiconductor module according to Supplementary Note 1 or Supplementary Note 2, wherein the metal sintered material is provided so as to cover a front electrode or a back electrode of the power semiconductor element, and the front electrode or the back electrode covered with the metal sintered material is joined to the adherend by solder.

[0082] (Supplementary Note 5) A power conversion device comprising: a main conversion circuit having the power semiconductor module according to any one of Supplementary Note 1 to Supplementary Note 4, which converts input power and outputs the converted power; and a control circuit which outputs a control signal for controlling the main conversion circuit to the main conversion circuit.

[0083] (Supplementary Note 6) A method for manufacturing a power semiconductor module including a power semiconductor element and a lead frame or a substrate on which the power semiconductor element is mounted, the method comprising: a step of sandwiching and pressurizing a bonding material containing a metal compound and an organic solvent between at least one of the power semiconductor element, the lead frame, and the substrate and an adherend to be bonded thereto; a step of applying current to the bonding material; and a step of performing a heat treatment to sinter the bonding material while pressurizing the bonding material and applying current to it, thereby bonding at least one of the power semiconductor element, the lead frame, and the substrate to the adherend.

[0084] (Supplementary Note 7) A method for manufacturing a power semiconductor module, comprising: a step of sandwiching and pressurizing a bonding material containing a metal compound and an organic solvent between at least one of a front electrode and a back electrode of a power semiconductor element and a jig; a step of applying current to the bonding material; a step of sintering the bonding material by performing a heat treatment while pressurizing and applying current to the bonding material, thereby coating at least one of the front electrode and the back electrode with a metal sintered material; and a step of joining at least one of the front electrode and the back electrode coated with the metal sintered material to an adherend with solder.

[0085] (Supplementary Note 8) The method for manufacturing a power semiconductor module according to Supplementary Note 6 or Supplementary Note 7, wherein the bonding material is a paste made of the powdered metal compound and the organic solvent.

[0086] (Supplementary Note 9) The method for manufacturing a power semiconductor module according to any one of Supplementary Note 6 to Supplementary Note 8, wherein the metal compound includes a silver compound or a copper compound.

[0087] (Supplementary Note 10) The method for manufacturing a power semiconductor module according to any one of Supplementary Note 6 to Supplementary Note 9, wherein the organic solvent contains a monohydric or polyhydric alcohol.

[0088] 10 lead frame, 10s source terminal, 10g gate terminal, 10d drain terminal, 11 resin insulated metal substrate, 11c aluminum conductor layer, 11i heat dissipation insulation layer, 11b aluminum base layer, 12 ceramic substrate, 12c aluminum conductor layer, 12i ceramic layer, 12b aluminum conductor layer, 20 power semiconductor element, 20s source electrode, 20g gate electrode, 20d drain electrode, 21 diode, 21a anode electrode, 21c cathode electrode, 22 IGBT, 22s source electrode, 22g gate electrode, 22d drain electrode, 30 silver sintered material, 30p silver oxide paste, 31, 35 solder, 34 copper plate, 41, 42 wire, 50 case, 51s source terminal, 51d drain terminal, 51g signal terminal, 52 bus bar, 60 current application heating press device, 60b Base heater, 60c collet heater, 60e DC power supply, 70 sealing resin, 70u, 70d mold, 71 liquid sealing resin, 80 fin base, 80b base portion, 80p pin fin portion, 91 first substrate, 92 second substrate, 93 bonding material, 94 jig, 94p positive electrode side member of jig, 94n negative electrode side member of jig, 100 power supply, 200 power conversion device, 201 main conversion circuit, 202 semiconductor module, 203 control circuit, 300 load.

Claims

1. A power semiconductor module comprising a power semiconductor element and a lead frame or a substrate on which the power semiconductor element is mounted, wherein at least one of the power semiconductor element, the lead frame, and the substrate and an adherend joined thereto are joined via a metal sintered material containing a metal oxide.

2. The power semiconductor module according to claim 1, wherein the metal sintered material is a silver sintered material or a copper sintered material.

3. The power semiconductor module according to claim 1 or 2, wherein the metal sintered material joins a surface electrode or a back surface electrode of the power semiconductor element to the adherend.

4. The power semiconductor module according to claim 1 or 2, wherein the metal sintered material is provided so as to cover a surface electrode or a back surface electrode of the power semiconductor element, and the surface electrode or the back surface electrode covered with the metal sintered material and the adherend are joined by solder.

5. A power conversion device comprising the power semiconductor module according to any one of claims 1 to 4, a main conversion circuit that converts input power and outputs the converted power, and a control circuit that outputs a control signal for controlling the main conversion circuit to the main conversion circuit.

6. A method for manufacturing a power semiconductor module comprising a power semiconductor element and a lead frame or a substrate on which the power semiconductor element is mounted, the method comprising: a step of pressing with a joining material containing a metal compound and an organic solvent sandwiched between at least one of the power semiconductor element, the lead frame, and the substrate and an adherend joined thereto; a step of applying a current to the joining material; and a step of sintering the joining material by performing a heat treatment in a state where the joining material is pressed and a current is applied, thereby joining at least one of the power semiconductor element, the lead frame, and the substrate to the adherend.

7. A method for manufacturing a power semiconductor module including a power semiconductor element, a metal plate on which the power semiconductor element is mounted, and a lead frame or a substrate on which the metal plate is mounted, the method comprising: a step of pressing with a bonding material containing a metal compound and an organic solvent sandwiched between the lead frame or the substrate and the metal plate as an adherend bonded thereto; a step of applying an electric current to the bonding material; a step of performing a heat treatment in a state where the bonding material is pressed and an electric current is applied to sinter the bonding material, thereby bonding the lead frame or the substrate and the metal plate; and a step of bonding the power semiconductor element and the metal plate with solder.

8. A method for manufacturing a power semiconductor module, the method comprising: a step of pressing with a bonding material containing a metal compound and an organic solvent sandwiched between at least one of a front surface electrode and a back surface electrode of a power semiconductor element and a jig; a step of applying an electric current to the bonding material; a step of performing a heat treatment in a state where the bonding material is pressed and an electric current is applied to sinter the bonding material, thereby coating at least one of the front surface electrode and the back surface electrode with a metal sintered material; and a step of bonding at least one of the front surface electrode and the back surface electrode coated with the metal sintered material and an adherend with solder.

9. The method for manufacturing a power semiconductor module according to any one of claims 6 to 8, wherein the bonding material is a paste composed of the powdery metal compound and the organic solvent.

10. The method for manufacturing a power semiconductor module according to any one of claims 6 to 9, wherein the metal compound contains a silver compound or a copper compound.

11. The method for manufacturing a power semiconductor module according to any one of claims 6 to 10, wherein the organic solvent contains a monohydric or polyhydric alcohol.

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