Patent ID: 12224220

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below. The same configuration is denoted by the same reference number and a description thereof will not be repeated.

First Embodiment

Referring toFIG.1toFIG.3, a semiconductor module1in a first embodiment will be described. Semiconductor module1mainly includes a first power semiconductor device20, a second power semiconductor device25, conductive wires35and36, a resin film40, a first electrode terminal32, and a second electrode terminal33. Semiconductor module1may further include an insulated circuit board10, a case45, and a sealing member50.

Insulated circuit board10includes an insulating substrate11. Insulating substrate11includes a front surface and a rear surface on the side opposite to the front surface. Insulating substrate11is formed of a ceramic material such as alumina (Al2O3), aluminum nitride (AlN), or silicon nitride (Si3N4). Insulated circuit board10includes a conductive circuit pattern12and a conductive plate13. Conductive circuit pattern12is provided on the front surface of insulating substrate11. Conductive plate13is provided on the rear surface of insulating substrate11. Conductive circuit pattern12and conductive plate13are formed of, for example, a metal material such as copper (Cu) or aluminum (Al).

First power semiconductor device20is, for example, a switching element such as an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field-effect transistor (MOSFET), or a diode such as a freewheeling diode. First power semiconductor device20is mainly formed of a semiconductor material such as silicon, silicon carbide, gallium nitride, or diamond.

First power semiconductor device20includes a first back electrode21and a first front electrode22. First back electrode21is provided on a first back face of first power semiconductor device20. First back electrode21is joined to conductive circuit pattern12using a conductive joint member (not illustrated) such as solder or sintered metal nanoparticles. First front electrode22is provided on a first front face of first power semiconductor device20on the side opposite to the first back face. First front electrode22and the second back electrode are formed of, for example, aluminum or an Al alloy containing Si.

First power semiconductor device20may further include a first guard ring23. First guard ring23is provided in a peripheral region of the first front face of first power semiconductor device20. In a plan view of the first front face, first guard ring23surrounds first front electrode22. First guard ring23is formed of, for example, the same conductive material as first front electrode22.

Second power semiconductor device25is, for example, a switching element such as an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field-effect transistor (MOSFET), or a diode such as a freewheeling diode. Second power semiconductor device25is mainly formed of a semiconductor material such as silicon, silicon carbide, gallium nitride, or diamond.

Second power semiconductor device25includes a second back electrode26and a second front electrode27. Second back electrode26is provided on a second back face of second power semiconductor device25. Second back electrode26is joined to conductive circuit pattern12using a conductive joint member (not illustrated) such as solder or sintered metal nanoparticles. Second front electrode27is provided on a second front face of second power semiconductor device25on the side opposite to the second back face. Second front electrode27and second back electrode26are formed of, for example, aluminum or an Al alloy containing Si.

Second power semiconductor device25may further include a second guard ring28. Second guard ring28is provided in a peripheral region of the second front face of second power semiconductor device25. In a plan view of the second front face, second guard ring28surrounds second front electrode27. Second guard ring28is formed of, for example, the same conductive material as second front electrode27.

First electrode terminal32and second electrode terminal33are provided at an enclosure47that constitutes case45. First electrode terminal32and second electrode terminal33are formed of, for example, a metal material such as copper or aluminum.

As illustrated inFIG.1andFIG.2, conductive wire35is joined to a surface22aof first front electrode22. Conductive wire35is joined to first front electrode22of first power semiconductor device20at a first joint30. First joint30is a joint surface between surface22aof first front electrode22and a surface35aof conductive wire35. As illustrated inFIG.1andFIG.3, conductive wire35is joined to a surface27aof second front electrode27. Conductive wire35is joined to second front electrode27of second power semiconductor device25at a second joint31. Second joint31is a joint surface between surface27aof second front electrode27and surface35aof conductive wire35. Conductive wire35is joined to first electrode terminal32by wire bonding.

Conductive wire36is joined to second electrode terminal33and conductive circuit pattern12by wire bonding. Conductive wires35and36are formed of, for example, copper, iron, nickel, cobalt, aluminum, or an alloy thereof.

Resin film40has electrical insulating properties. As illustrated inFIG.2, resin film40is formed to be continuous on an end portion30aof first joint30between first front electrode22and conductive wire35in the longitudinal direction (the horizontal direction inFIG.2) of conductive wire35, surface22aof first front electrode22, and surface35aof conductive wire35. Resin film40is formed to be continuous on an end portion30bof first joint30between first front electrode22and conductive wire35in the longitudinal direction of conductive wire35, surface22aof first front electrode22, and surface35aof conductive wire35.

As illustrated inFIG.3, resin film40is formed to be continuous on an end portion31aof second joint31between second front electrode27and conductive wire35in the longitudinal direction of conductive wire35, surface27aof second front electrode27, and surface35aof conductive wire35. Resin film40is formed to be continuous on an end portion31bof second joint31between second front electrode27and conductive wire35in the longitudinal direction of conductive wire35, surface27aof second front electrode27, and surface35aof conductive wire35.

As illustrated inFIG.1, resin film40may be formed on the entire conductive wire35between first joint30and second joint31. Resin film40is formed to be continuous on at least one of the end portions of the joint between first front electrode32and conductive wire35in the longitudinal direction of conductive wire35, a surface of first electrode terminal32, and surface35aof conductive wire35. Resin film40is formed to be continuous on at least one of the end portions of the joint between second electrode terminal33and conductive wire36in the longitudinal direction of conductive wire36, a surface of second electrode terminal33, and a surface of conductive wire36. Resin film40is formed to be continuous on at least one of the end portions of the joint between conductive circuit pattern12and conductive wire36in the longitudinal direction of conductive wire36, a surface of conductive circuit pattern12, and a surface of conductive wire36. Resin film40may be formed on the entire conductive wires35and36.

As illustrated inFIG.1, resin film40further covers first guard ring23and second guard ring28. Resin film40is in contact with sealing member50and first guard ring23. Resin film40is in contact with sealing member50and second guard ring28.

Resin film40may be further formed on a surface of insulated circuit board10exposed from first power semiconductor device20and second power semiconductor device25. Resin film40may be further formed on a portion of first electrode terminal32to which conductive wire35is joined. Resin film40may be further formed on a portion of second electrode terminal33to which conductive wire36is joined. Resin film40may be further formed on a surface of a base plate46exposed from insulated circuit board10. Resin film40may be further formed on a surface of enclosure47located between the electrode terminal (first electrode terminal32, second electrode terminal33) and base plate46. Resin film40is formed by, for example, dispensing, electrodeposition, electrostatic spray deposition, spin coating, liquid immersion, or spray coating.

Resin film40is softer than first front electrode22, second front electrode27, and conductive wires35and36. The elastic elongation rate of resin film40is 4.5% to 10.0%. The elastic elongation rate of resin film40is defined by the strain rate of resin film40at the yield point of resin film40(seeFIG.4) in a tensile test defined in JIS K7161. It is noted that the plastic elongation rate of resin film40is different from the elastic elongation rate of resin film40. The plastic elongation rate of resin film40is defined by the strain rate of resin film40at the break point of resin film40(seeFIG.4) in a tensile test defined in JIS K7161. Resin film40is formed of, for example, a polyimide resin, an epoxy resin, or a silicone resin. An example of the epoxy resin applicable to resin film40is an underfill U8443-14 available from NAMICS CORPORATION. An example of the silicone resin applicable to resin film40is a silicone resin KE-210 available from Shin-Etsu Silicones.

The shear bond strength of resin film40to conductive wire35,36is 8.0 MPa to 13.0 MPa. The shear bond strength of resin film40to first front electrode22of first power semiconductor device20is 8.0 MPa to 13.0 MPa. The shear bond strength of resin film40to second front electrode27of second power semiconductor device25is 8.0 MPa to 13.0 MPa. In the present description, the shear bond strength of a first member to a second member is the tensile stress at a point of time when the first member becomes separated from the second member when tensile stress is applied to the first member and the second member in a direction along the bonded interface between the first member and the second member and in directions opposite to each other. The shear bond strength is measured by the method defined in Japanese Industrial Standards (JIS) K6850.

Resin film40having an elastic elongation rate of 4.5% to 10.0% and a shear bond strength of 8.0 MPa to 13.0 MPa is formed of, for example, a polyimide resin defined by Formula (I) below. This polyimide resin is obtained by polymerizing an acid dihydrate including an alkyl group and a diamine including a benzene ring, an ether bond, and an alkyl group. Here, R1 represents CnH2n+1(n is a natural number), and R2 represents CmH2m+1(m is a natural number). The polyimide resin defined by Formula (I) has a long molecular chain and the molecular chain can rotate about the ether bond. The polyimide resin defined by Formula (I) below therefore is soft and has a high shear bond strength.

Case45includes base plate46and enclosure47. Base plate46is formed of, for example, a metal such as copper or aluminum or an alloy such as aluminum-silicon carbide alloy (AlSiC) or copper-molybdenum alloy (CuMo). Conductive plate13of insulated circuit board10is joined to base plate46. Base plate46can function as a heatsink. In a modification of the present embodiment, base plate46may be omitted and conductive plate13may serve the function of base plate46in the present embodiment.

Enclosure47has electrical insulating properties. Enclosure47is formed of an electrically insulating resin such as polyphenylene sulfide (PPS) resin or polybutylene terephthalate (PBT) resin. Base plate46and enclosure47are affixed to each other using an adhesive (not illustrated). This adhesive is formed of, for example, a silicone resin or an epoxy resin.

Sealing member50seals first power semiconductor device20, second power semiconductor device25, conductive circuit pattern12, conductive wires35and36, and resin film40. Sealing member50may further seal insulating substrate11. In the present embodiment, sealing member50is formed of a gel such as silicone gel. The second tensile modulus of the gel forming sealing member50is lower than the first tensile modulus of the resin material forming resin film40. In the present description, the tensile modulus is measured by a tensile test defined in JIS K7161.

Referring toFIG.5, the operation of semiconductor module1in the present embodiment will be described in comparison with comparative examples.FIG.5illustrates the power cycling lifetime of semiconductor modules of Comparative Examples A to C and semiconductor modules1of Examples D to G. A semiconductor module of Comparative Example A has a configuration similar to semiconductor module1in the present embodiment but does not include resin film40. Semiconductor modules of Comparative Examples B and C have a configuration similar to semiconductor module1in the present embodiment, but resin film40included in the semiconductor modules of Comparative Examples B and C is a polyimide resin film having an elastic elongation rate of less than 4.5%. In semiconductor modules1of Examples D to G, resin film40is a polyimide resin film having an elastic elongation rate of 4.5% or more. Resin film40in semiconductor module1of Example G is a polyimide resin film represented by Formula (I) above.

A power cycling test of semiconductor module1is a test in which the lifetime (power cycling lifetime) of semiconductor module1is measured by alternately repeating a first step of feeding current to first power semiconductor device20or second power semiconductor device25and a second step of feeding no current to first power semiconductor device20and second power semiconductor device25. As illustrated inFIG.5, the power cycling lifetime of semiconductor module1has a correlation to the elastic elongation rate of resin film40.

Specifically, when the semiconductor module does not include resin film40(Comparative Example A) or when the semiconductor module includes resin film40having an elastic elongation rate of less than 4.5% (Comparative Examples B and C), the power cycling lifetime of the semiconductor module is short. The reason is as follows. During a power cycling test of the semiconductor module, the members such as first front electrode22, second front electrode27, and conductive wire35included in the semiconductor module repeats thermal expansion and thermal shrinkage. Thus, thermal stress is repeatedly applied to first joint30between first front electrode22and conductive wire35and to second joint31between second front electrode27and conductive wire35. Since the semiconductor module of Comparative Example A does not include resin film40, this thermal stress causes cracking in first joint30or second joint31or peeling of conductive wire35from first front electrode22or second front electrode27. The power cycling lifetime of the semiconductor module of Comparative Example A is therefore shortest.

In the semiconductor modules of Comparative Examples B and C, the elastic elongation rate of resin film40is less than 4.5% and relatively small. Resin film40therefore fails to sufficiently follow thermal expansion and thermal shrinkage of the members such as first front electrode22, second front electrode27, and conductive wire35included in semiconductor module1. Resin film40peels off from end portions30a,30bof first joint30, end portions31a,31bof second joint31, surface22aof first front electrode22, surface27aof second front electrode27, or surface35aof conductive wire35in fewer power cycles. Resin film40fails to alleviate thermal stress applied to first joint30and second joint31in fewer power cycles. The thermal stress causes cracking in first joint30or second joint31or peeling of conductive wire35from first front electrode22or second front electrode27. The power cycling lifetime of the semiconductor modules of Comparative Examples B and C is longer than the power cycling lifetime of the semiconductor module of Comparative Example A, but the power cycling lifetime of the semiconductor modules of Comparative Examples B and C is still relatively short.

In comparison, when semiconductor module1includes resin film40having an elastic elongation rate of 4.5% to 10% (Examples D to G), the power cycling lifetime of semiconductor module1increases sharply with increase of the elastic elongation rate of resin film40. The reason is as follows. In semiconductor modules1of Examples D to G, since the elastic elongation rate of resin film40is 4.5% or more, resin film40can sufficiently follow thermal expansion and thermal shrinkage of the members such as first front electrode22, second front electrode27, and conductive wire35included in semiconductor module1. Resin film40does not peel off from end portions30a,30bof first joint30, end portions31a,31bof second joint31, surface22aof first front electrode22, surface27aof second front electrode27, and surface35aof conductive wire35over more power cycles. Resin film40can alleviate thermal stress applied to first joint30and second joint31over more power cycles. Resin film40can prevent thermal stress from causing cracking in first joint30or second joint31or peeling of conductive wire35from first front electrode22or second front electrode27. The power cycling lifetime of semiconductor modules1of Examples D to G is long.

The effects of semiconductor module1in the present embodiment will be described.

Semiconductor module1in the present embodiment includes first power semiconductor device20, conductive wire35, and resin film40. First power semiconductor device20include a first electrode (first front electrode22). Conductive wire35is joined to a first surface (surface22a) of the first electrode (first front electrode22). Resin film40is formed to be continuous on a first end portion (at least one of end portion30aor end portion30b) of first joint30between the first electrode (first front electrode22) and conductive wire35in the longitudinal direction of conductive wire35, the first surface (surface22a) of the first electrode (first front electrode22), and a second surface (surface35a) of conductive wire35. Resin film40has an elastic elongation rate of 4.5% to 10.0%.

Since resin film40has an elastic elongation rate of 4.5% or more, resin film40can follow thermal expansion and thermal shrinkage of the members such as the first electrode (first front electrode22) of first power semiconductor device20and conductive wire35included in semiconductor module1. Resin film40does not peel off from the first end portion (at least one of end portion30aor end portion30b) of first joint30, the first surface (surface22a) of the first electrode (first front electrode22), and the second surface (surface35a) of conductive wire35. Resin film40keeps alleviating thermal stress applied to first joint30. Resin film40can prevent cracking in first joint30or peeling of conductive wire35from the first electrode (first front electrode22). The lifetime of semiconductor module1is prolonged and semiconductor module1has improved reliability.

In semiconductor module1in the present embodiment, the shear bond strength of resin film40to conductive wire35is 8.0 MPa to 13.0 MPa.

Since the shear bond strength of resin film40to conductive wire35is 8.0 MPa or more, resin film40is even less likely to peel off from surface35aof conductive wire35during use of semiconductor module1. Resin film40keeps alleviating thermal stress applied to first joint30. Resin film40can prevent cracking in first joint30or peeling of conductive wire35from the first electrode (first front electrode22). The lifetime of semiconductor module1is prolonged and semiconductor module1has improved reliability.

Since the shear bond strength of resin film40to conductive wire35is 13.0 MPa or less, the thickness of first joint30and conductive wire35on the periphery thereof is not excessively small when conductive wire35is bonded to the first electrode (first front electrode22) of first power semiconductor device20. Breakage of conductive wire35can be prevented when thermal stress is applied to conductive wire35during use of semiconductor module1. The lifetime of semiconductor module1is prolonged and semiconductor module1has improved reliability.

Semiconductor module1in the present embodiment further includes sealing member50. Sealing member50seals first power semiconductor device20, conductive wire35, and resin film40. Sealing member50is formed of a gel. The second tensile modulus of the gel is lower than the first tensile modulus of the resin material forming resin film40. Although sealing member50is formed of a gel, the lifetime of semiconductor module1is prolonged and semiconductor module1has improved reliability, because of the provision of resin film40.

In semiconductor module1in the present embodiment, first power semiconductor device20includes a guard ring (first guard ring23). Resin film40covers the guard ring (first guard ring23) and is in contact with sealing member50and the guard ring (first guard ring23).

Since the guard ring (first guard ring23) is provided in the peripheral region of first power semiconductor device20, the dielectric strength of first power semiconductor device20is improved. Furthermore, resin film40prevents peeling of sealing member50from the guard ring (first guard ring23) and thus formation of a void between sealing member50and the guard ring (first guard ring23). The dielectric strength of first power semiconductor device20is therefore improved. Semiconductor module1has improved reliability.

Semiconductor module1further includes second power semiconductor device25. Second power semiconductor device25includes a second electrode (second front electrode27). Conductive wire35is joined to a third surface (surface27a) of the second electrode (second front electrode27). Resin film40is formed to be continuous on a second end portion (at least one of end portion31aor end portion31b) of second joint31between the second electrode (second front electrode27) and conductive wire35, the third surface (surface27a) of the second electrode (second front electrode27), and the second surface (surface35a) of conductive wire35and is formed on the entire conductive wire35between first joint30and second joint31.

Resin film40is formed to be continuous on a second end portion (at least one of end portion31aor end portion31b) of second joint31between the second electrode (second front electrode27) of second power semiconductor device25and conductive wire35, the third surface (surface27a) of the second electrode (second front electrode27), and the second surface (surface35a) of conductive wire35. Resin film40therefore can follow thermal expansion and thermal shrinkage of the members such as the second electrode (second front electrode27) of second power semiconductor device25and conductive wire35included in semiconductor module1. Resin film40does not peel off from the second end portion (at least one of end portion31aor end portion31b) of second joint31, the third surface (surface27a) of the second electrode (second front electrode27), and the second surface (surface35a) of conductive wire35. Resin film40keeps alleviating thermal stress applied to second joint31. Resin film40can prevent cracking in second joint31or peeling of conductive wire35from the second electrode (second front electrode27). The lifetime of semiconductor module1is prolonged and semiconductor module1has improved reliability.

Resin film40is formed on the entire conductive wire35between first joint30and second joint31. Resin film40is therefore even less likely to peel off from the second surface (surface35a) of conductive wire35. Resin film40can prevent cracking in first joint30and second joint31or peeling of conductive wire35from the first electrode (first front electrode22) and the second electrode (second front electrode27). The lifetime of semiconductor module1is prolonged and semiconductor module1has improved reliability.

Second Embodiment

Referring toFIG.1toFIG.3, a semiconductor module1ain a second embodiment will be described. Semiconductor module1ain the present embodiment has a configuration similar to semiconductor module1in the first embodiment but differs mainly in the following points.

Semiconductor module1a includes a sealing member50ainstead of sealing member50in the first embodiment. Sealing member50ais formed of a thermosetting resin. The thermosetting resin mainly includes, for example, an epoxy resin, a urethane resin, a polyimide resin, or an acrylic resin. The third tensile modulus of the thermosetting resin is higher than the first tensile modulus of the resin material forming resin film40. The thermosetting resin is harder than resin film40and sealing member50(first embodiment) formed of a gel. Sealing member50a(the present embodiment) formed of a thermosetting resin therefore constrains conductive wire35stronger than resin film40and sealing member50(first embodiment) formed of a gel.

Semiconductor module1a in the present embodiment has the following effects in addition to the effects of semiconductor module1in the first embodiment.

Semiconductor module1a in the present embodiment further includes sealing member50a. Sealing member50aseals first power semiconductor device20, conductive wire35, and resin film40. Sealing member50ais formed of a thermosetting resin. The third tensile modulus of the thermosetting resin is higher than the first tensile modulus of the resin material forming resin film40.

The thermosetting resin is harder than resin film40and sealing member50(first embodiment) formed of a gel. Sealing member50a(the present embodiment) formed of a thermosetting resin therefore constrains conductive wire35stronger than resin film40and sealing member50(first embodiment) formed of a gel. Cracking in first joint30or peeling of conductive wire35from the first electrode (first front electrode22) due to thermal stress can be prevented. The lifetime of semiconductor module1ais prolonged and semiconductor module1ahas improved reliability.

Third Embodiment

Referring toFIG.6, a semiconductor module1bin a third embodiment will be described. Semiconductor module1bin the present embodiment has a configuration similar to semiconductor module1in the first embodiment but differs mainly in the following points.

As illustrated inFIG.6, at least one of surface22aof first front electrode22of first power semiconductor device20or surface35aof conductive wire35has a coarse surface43. Specifically, coarse surface43is provided at both of surface22aof first front electrode22of first power semiconductor device20and surface35aof conductive wire35. Coarse surface43may be connected to end portions30a,30bof first joint30. Although not illustrated in the drawings, at least one of surface27aof second front electrode27of second power semiconductor device25or surface35aof conductive wire35may also have coarse surface43. Specifically, coarse surface43may be provided at both of surface27aof second front electrode27of second power semiconductor device25and surface35aof conductive wire35. Coarse surface43may be connected to end portions31a,31bof second joint31. Resin film40is formed on coarse surface43.

Semiconductor module1bin the present embodiment has the following effects in addition to the effects of semiconductor module1in the first embodiment.

In semiconductor module1bin the present embodiment, at least one of the first surface (surface22a) of the first electrode (first front electrode22) of first power semiconductor device20or the second surface (surface35a) of conductive wire35has coarse surface43. Resin film40is formed on coarse surface43. Therefore, peeling of resin film40from at least one of the first surface (surface22a) of the first electrode (first front electrode22) of first power semiconductor device20or the second surface (surface35a) of conductive wire35can be prevented. The power cycling lifetime of semiconductor module1bis prolonged and semiconductor module1bhas improved reliability.

Fourth Embodiment

Referring toFIG.7, a semiconductor module1cin a fourth embodiment will be described. Semiconductor module1cin the present embodiment has a configuration similar to semiconductor module1in the first embodiment and has similar effects, but differs mainly in type of the semiconductor module. Specifically, semiconductor module1cis a transfer-molded semiconductor module. Sealing member50is formed by transfer molding.

Semiconductor module1cincludes a heat spreader55, an insulating plate56, and a heatsink57, instead of insulated circuit board10and base plate46(seeFIG.1). Semiconductor module1cincludes a first lead terminal32cand a second lead terminal33c, instead of first electrode terminal32and second electrode terminal33(seeFIG.1). Semiconductor module1cfurther includes a conductive wire37.

First power semiconductor device20and second power semiconductor device25are fixed to a front surface of heat spreader55. For example, first power semiconductor device20and second power semiconductor device25are joined to the front surface of heat spreader55, using a conductive joint member such as solder or sintered metal nanoparticles. Heat spreader55diffuses heat generated from first power semiconductor device20and second power semiconductor device25. Heat spreader55is formed of, for example, a material having a high thermal conductivity, such as copper, aluminum, or graphite.

Heatsink57is provided on a rear surface of heat spreader55with insulating plate56interposed. Heatsink57is formed of, for example, a metal such as copper or aluminum or an alloy such as aluminum-silicon carbide alloy (AlSiC) or copper-molybdenum alloy (CuMo).

Insulating plate56electrically insulates heat spreader55from heatsink57. Insulating plate56transfers heat generated from first power semiconductor device20and second power semiconductor device25and transmitted to heat spreader55to heatsink57. Insulating plate56is formed of, for example, a ceramic material such as silicon nitride (Si3N4), aluminum nitride (AlN), alumina (Al2O3), or zirconium (Zr)-containing alumina.

Insulating plate56may be a resin insulating plate in which powder is dispersed. The powder may have a higher thermal conductivity than the resin forming the base material of the resin insulating plate. The powder may be, for example, ceramic powder formed of ceramics such as alumina (Al2O3), silicon dioxide (SiO2), aluminum nitride (AlN), boron nitride (BN), or silicon nitride (Si3N4). The powder may be formed of diamond (C), silicon carbide (SiC), or boron oxide (B2O3). The powder may be, for example, powder of a resin such as a silicone resin or an acrylic resin. The base material of the resin insulating plate is, for example, an epoxy resin, a polyimide resin, a silicone resin, or an acrylic resin.

In semiconductor module1c, conductive wire35is joined to first front electrode22of first power semiconductor device20and second front electrode27of second power semiconductor device25but is not joined to first lead terminal32c. Conductive wire36is joined to first front electrode22of first power semiconductor device20and second lead terminal33c. Conductive wire37is joined to second front electrode27of second power semiconductor device25and first lead terminal32c.

Resin film40is formed not only on conductive wires35and36but also on conductive wire37. Specifically, resin film40is formed to be continuous on at least one of the end portions of the joint between first front electrode22and conductive wire36in the longitudinal direction of conductive wire36, a surface of first front electrode22, and a surface of conductive wire36. Resin film40is formed to be continuous on at least one of the end portions of the joint between first lead terminal32cand conductive wire36in the longitudinal direction of conductive wire36, a surface of first electrode terminal32c, and a surface of conductive wire36. Resin film40is formed to be continuous on at least one of the end portions of the joint between second front electrode27and conductive wire37in the longitudinal direction of conductive wire37, a surface of second front electrode27, and a surface of conductive wire37. Resin film40is formed to be continuous on at least one of the end portions of the joint between second lead terminal33cand conductive wire37in the longitudinal direction of conductive wire37, a surface of second electrode terminal33c, and a surface of conductive wire37. Resin film40may be formed on the entire conductive wire37.

Fifth Embodiment

In the present embodiment, any one of semiconductor modules1,1a,1b, and1cin the foregoing embodiments to the fourth embodiment is applied to a power conversion apparatus. Although the present disclosure is not limited to any particular power conversion apparatus, a case in which any one of semiconductor modules1,1a,1b, and1cin the present disclosure is applied to a three-phase inverter will be described below as a fifth embodiment.

A power conversion system illustrated inFIG.8includes a power source100, a power conversion apparatus200, and a load300. Power source100is a DC power source and supplies DC power to power conversion apparatus200. Power source100may be composed of, for example, but not limited to, a DC system, a solar battery, or a storage battery or may be composed of a rectifier circuit or an AC/DC converter connected to an AC system. Power source100may be composed of a DC/DC converter that converts DC power output from a DC system into another DC power.

Power conversion apparatus200is a three-phase inverter connected between power source100and load300, and converts DC power supplied from power source100into AC power and supplies AC power to load300. As illustrated inFIG.8, power conversion apparatus200includes a main conversion circuit201to convert DC power into AC power and output AC power, and a control circuit203to output a control signal for controlling main conversion circuit201to main conversion circuit201.

Load300is a three-phase motor driven by AC power supplied from power conversion apparatus200. Load300is not limited to any particular applications and is a motor installed in a variety of electrical instruments and, for example, used as a motor for hybrid vehicles, electric vehicles, railroad vehicles, elevators, or air conditioners.

The detail of power conversion apparatus200will be described below. Main conversion circuit201includes switching elements (not illustrated) and freewheeling diodes (not illustrated). The switching elements switch a voltage supplied from power source100, whereby main conversion circuit201converts DC power supplied from power source100into AC power and supplies AC power to load300. There are a variety of circuit configurations of main conversion circuit201. Main conversion circuit201according to the present embodiment may be a two-level three-phase full bridge circuit and include six switching elements and six freewheeling diodes connected in anti-parallel with the respective switching elements. At least any one of the switching elements and the freewheeling diodes of main conversion circuit201is a switching element or a freewheeling diode included in a semiconductor module202corresponding to any one of semiconductor modules1,1a,1b, and1cin the foregoing first to fourth embodiments. Six switching elements are connected in series two by two to form upper and lower arms, and the upper and lower arm constitutes each phase (U phase, V phase, W phase) of the full bridge circuit. The output terminals of the upper and lower arms, that is, three output terminals of main conversion circuit201are connected to load300.

Main conversion circuit201also includes a drive circuit (not illustrated) to drive each switching element. The drive circuit may be contained in semiconductor module202or may be provided separately from semiconductor module202. The drive circuit generates a drive signal for driving a switching element included in main conversion circuit201and supplies the drive signal to the control electrode of the switching element of main conversion circuit201. Specifically, a drive signal to turn ON a switching element and a drive signal to turn OFF a switching element are output to the control electrode of each switching element, in accordance with the control signal from control circuit203. When the switching element is kept ON, the drive signal is a voltage signal (ON signal) equal to or higher than a threshold voltage of the switching element. When the switching element is kept OFF, the drive signal is a voltage signal (OFF signal) equal to or lower than a threshold voltage of the switching element.

Control circuit203controls the switching elements of main conversion circuit201such that a desired power is supplied to load300. Specifically, the time (ON time) in which each switching element of main conversion circuit201is to be turned ON is calculated based on power to be supplied to load300. For example, main conversion circuit201can be controlled by pulse width modulation (PWM) control that modulates the ON time of switching elements in accordance with the voltage to be output. A control command (control signal) is output to a drive circuit of main conversion circuit201such that an ON signal is output to a switching element to be turned ON and an OFF signal is output to a switching element to be turned OFF at each point of time. The drive circuit outputs an ON signal or an OFF signal as a drive signal to the control electrode of each switching element, in accordance with the control signal.

In power conversion apparatus200according to the present embodiment, any one of semiconductor modules1,1a,1b, and1cin the first to fourth embodiments is applied as semiconductor module202that constitutes main conversion circuit201. Power conversion apparatus200according to the present embodiment therefore achieves improved reliability.

In the present embodiment, the present disclosure is applied to a two-level three-phase inverter. However, the present disclosure is not limited thereto and can be applied to a variety of power conversion apparatuses. The present disclosure is applied to a two-level power conversion apparatus in the present embodiment, but may be applied to a three-level power conversion apparatus or a multi-level power conversion apparatus. When the power conversion apparatus supplies power to a single-phase load, the present disclosure may be applied to a single-phase inverter. When the power conversion apparatus supplies power to a DC load or the like, the present disclosure can also be applied to a DC/DC converter or an AC/DC converter.

The power conversion apparatus to which the present disclosure is applied is not limited to a case in which the load is a motor, and may be used as a power supply device for an electric discharge machine or a laser beam machine, or a power supply device for an induction heating cooker or a wireless charging system. The power conversion apparatus to which the present disclosure is applied can also be used as a power conditioner for photovoltaic systems or power storage systems.

REFERENCE SIGNS LIST

1,1a,1b,1csemiconductor module,10insulated circuit board,11insulating substrate,12conductive circuit pattern,13conductive plate,20first power semiconductor device,21first back electrode,22first front electrode,22asurface,23first guard ring,25second power semiconductor device,26second back electrode,27second front electrode,27asurface,28second guard ring,30first joint,30a,30bend portion,31second joint,31a,31bend portion,32first electrode terminal,32cfirst lead terminal,33second electrode terminal,33csecond lead terminal,35,36,37conductive wire,35asurface,40resin film,43coarse surface,45case,46base plate,47enclosure,50,50asealing member,55heat spreader,56insulating plate,57heatsink,100power source,200power conversion apparatus,201main conversion circuit,203control circuit,300load power supply.