Inverter apparatus and method of manufacturing the same

In an inverter apparatus in which a three-phase inverter main circuit having a plurality of arms comprises a plurality of semiconductor chips for electric power, one arm of the three-phase inverter main circuit includes IGBTs and diodes of semiconductor chips having a size of 10 mm by 10 mm or less with the semiconductor chips connected in parallel, while the IGBTs and the diodes are bonded to a conductor having a thickness of 1.5 mm or more and 5 mm or less, and the conductor is glued to a cooler through an insulating resin sheet containing ceramics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-347876, filed Nov. 13, 2001, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inverter apparatus in which a three-phase inverter main circuit having a plurality of arms includes a plurality of semiconductor chips for electric power and a driving circuit and a control circuit are provided, particularly relates to the small inverter apparatus having good cooling efficiency and high reliability for an electric automobile, and a method of manufacturing the same.

2. Description of the Related Art

In the electric automobile, miniaturization and the high reliability of the inverter apparatus are demanded, The inverter apparatus having the good cooling efficiency is required in order to realize the miniaturization and the high reliability of the inverter apparatus.

A structure of a conventional inverter apparatus will be described below referring toFIG. 1to FIG.3.FIG. 1is a sectional plan view of the conventional inverter apparatus,FIG. 2is a sectional side view of the conventional inverter apparatus, andFIG. 3is a partially sectional view of an inside of the conventional inverter apparatus.

In FIG.1andFIG. 2, the inverter apparatus includes a semiconductor device portion2for electric power in which a semiconductor chip constituting a three-phase inverter main circuit is mounted, an aluminum electrolytic capacitor4which is a smoothing capacitor for an electric source fixed on a fixing base5, current detectors101and102which detect current of three-phase output conductors91to93, and a control unit11, the inverter apparatus is fixed on a bottom surface of a inverter apparatus casing1by mounting screws3.

The semiconductor device portion2and the aluminum electrolytic capacitor4are electrically connected by a conductor of positive side7, a conductor of negative side8, and connecting screws6. An inlet12, an outlet13, and a channel15of coolant14are provided on the bottom surface of the inverter apparatus casing1. The semiconductor device portion2is cooled by the coolant14which enters at the inlet12and flows through the channel15, the coolant14goes out from the outlet13. The coolant14is, for example, an anti-freeze solution.

In the semiconductor device portion2, as shown inFIG. 3, an insulating substrate17is laminated and bonded to an upper portion of a metal plate for heat dissipation16mounted on the inverter apparatus casing1, a metal electrode18is laminated and bonded to an upper portion of the insulating substrate17, and an IGBT191and a diode201of the semiconductor chip are stacked and bonded to an upper portion of the metal electrode18. The IGBT191and the diode201, the metal electrode18, and the insulating substrate17are contained by an insulative resin package, the metal plate for heat dissipation16is adhered to the resin package at an end portion of the metal plate for heat dissipation16. An inside of the resin package is filled with an insulating gel.

In the semiconductor device portion2, a thermal conductivity grease21is applied to a rear face of the metal plate for heat dissipation16in order to reduce contact thermal resistance, the semiconductor device portion2is fixed on the bottom surface of the inverter apparatus casing1, in which the channel15is provided, by the mounting screws3.

In the semiconductor device portion for electric power2having the above-described configuration, when the IGBT191and the diode201of the semiconductor chip are conducted, loss is generated. Since the insulating gel of a heat insulator is filled in upper potions of the IGBT191and the diode201, almost part of the loss generated in the IGBT191and the diode201is thermally conducted to the lower metal electrode18. The loss thermally conducted to the metal electrode18is thermally conducted to the metal plate for heat dissipation16through the insulating substrate17. As shown inFIG. 1toFIG. 3, the metal plate for heat dissipation16is pressurized and contacted by the mounting screws3to the bottom surface of the inverter apparatus casing1, the loss is dissipated by the coolant14.

In the above-described conventional inverter apparatus, there are problems as follows.

A first problem is that the thermal conductivity grease21is applied to the rear face of the metal plate for heat dissipation16in order to reduce the contact thermal resistance, the metal plate for heat dissipation16is pressurized and contacted to the bottom surface of the inverter apparatus casing1in which the channel15is provided by the mounting screws3disposed about a periphery of the semiconductor device portion2, so that an applied pressure is not uniformly applied to the whole metal plate for heat dissipation16.

For this reason, the contact thermal resistance between the metal plate for heat dissipation16and the inverter apparatus casing1becomes as quite large as thermal resistance of an inside of the semiconductor device portion2, which results in the bad cooling efficiency.

In addition to the first problem, a second problem is that the thermal conductivity grease21applied to the rear face of the metal plate for heat dissipation16might deteriorate on a long-term basis, which causes reliability to be decreased.

These problems can not finally contribute to improvement of current-carrying capacity of the inverter apparatus, furthermore, the above-described problems generates another problem that the inverter apparatus increases in size as a cooler and the like increase in size and it is difficult that the reliability is not secured presupposing a long-term service of the inverter apparatus.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an inverter apparatus which the current-carrying efficiency is improved by increasing the cooling efficiency in an inverter main circuit, the miniaturization is contributed, and the high reliability can be exercised and a method of manufacturing the same.

In order to achieve the above-described object, according to an aspect of the invention, there is provided an inverter apparatus in which a three-phase inverter main circuit having a plurality of arms comprises a plurality of semiconductor chips, wherein one arm of the three-phase inverter main circuit includes a plurality of semiconductor chips having a size of 2 mm by 2 mm or more and 10 mm by 10 mm or less which are connected in parallel, the plurality of semiconductor chips are connected to a conductor having a thickness of 1.5 mm or more and 5 mm or less, and the conductor is connected to a cooler through an insulating resin sheet containing ceramics.

In order to achieve the above-described object, according to another aspect of the invention, there is provided a method of manufacturing an inverter apparatus in which one arm of a three-phase inverter main circuit comprises a plurality of semiconductor chips having a size of 2 mm by 2 mm or more and 10 mm by 10 mm or less which are connected in parallel, the plurality of semiconductor chips are connected to a conductor having a thickness of 1.5 mm or more and 5 mm or less, and the conductor is connected to a cooler through an insulating resin sheet, wherein an epoxy resin sheet is used as the insulating resin sheet, the epoxy resin sheet is interposed between the conductor and the cooler, and the conductor and the cooler are pressurized and adhered with heating.

According to the inverter apparatus of the invention, the chip size is 2 mm by 2 mm or more and 10 mm by 10 mm or less arid the chips are connected in parallel, so that a value of non-linear strain of solder is small, several tens kW of current-carrying capacity required for the electric automobile can be secured.

The semiconductor chip is directly adhered to the cooler with the insulating resin sheet, so that the thermal resistance is decreased and the high reliability can be secured.

According to the method of manufacturing an inverter apparatus of the invention, after the semiconductor chip is bonded by the solder to the conductor, the epoxy resin sheet is interposed between the conductor and the cooler, and the conductor and the cooler are pressurized and adhered with heating, which allows characteristics of the epoxy resin sheet not to be deteriorated.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described below referring to the drawings.

A first embodiment of the invention will be described referring toFIG. 4to FIG.7.

InFIG. 4, the semiconductor device portion for electric power in the inverter apparatus constitutes a three-phase inverter main circuit, one arm of the three-phase inverter main circuit includes IGBTs191A,191B,191C, and191D of a semiconductor chip having size of 10 mm by 10 mm or less and diodes201A,201B, and201C having size of 10 mm or less, the IGBTs191A,191B,191C, and191D and the diodes201A,201B, and201C are connected in parallel.

FIG. 4shows the embodiment in case that the IGBT is four parallels and the diode is three parallels. The IGBTs191A,191B,191C, and191D of a semiconductor chip and diodes201A,201B, and201C are disposed on a conductor22made of copper having a thickness of 1.5 mm or more and 5 mm or less, while IGBTs and diodes are dispersed each other with a distance no less than a double thickness of the conductor22. The conductor22and IGBTs191A,191B,191C, and191D and diodes201A,201B, and201C are bonded by a bonding material of a low-melting solder such as Sn/Pb or a high-melting solder such as Sn/Ag/Cu. The conductor22is further glued to a cooler24made of copper or aluminum with an insulating resin sheet25containing ceramics.

The insulating resin sheet25is, for example, a sheet in which epoxy resin is filled with a ceramic filler such as boron nitride, thermal conductivity of the insulating resin sheet25is in the range from 2 to 4 W/mK and a thickness of the insulating resin sheet25is in the range from about 0.1 to about 0.15 mm.

In the conductor22, plating treatment26is carried out on a surface on which the IGBTs191A to191D and the diodes201A to201C are bonded. In the conductor22, plating treatment is not carried out on a reverse surface on which the cooler24is adhered by the insulating resin sheet25containing ceramics.

Since the IGBT191and the diode201are made of silicon and the conductor22is made of copper, when the heat cycle is loaded, difference in coefficient of linear expansion between the IGBT191and the diode201and the conductor22causes generation of shear stress and non-linear strain in the solder23. When heat cycle is loaded, larger value of non-linear strain causes generation of crack in solder. A smaller value of non-linear strain increases reliability and durability.

In case that the heat cycle is loaded on the semiconductor device portion for electric power in the inverter apparatus of the embodiment, the shear stress is generated in the solder23and the non-linear strain is generated. This is because the IGBT191and the diode201are made of silicon and the conductor22is made of copper, so that the coefficients of linear expansion of the IGBT191and the diode201and the conductor22are different.

FIG. 5is the analytic result of the correlation between the maximum value of non-linear strain of the solder23as a bonding material and the chip size when the heat cycle test holding temperatures ranging from −40° C./1 hr to 125° C./1 hr is carried out on the semiconductor device portion for electric power according to the first embodiment of the invention.

According toFIG. 5, it is recognized that there is a remarkable difference in non-linear strain of solder bordered on the chip size in 10 mm by 10 mm.

That is to say, when the chip size exceeds 10 mm by 10 mm, it is found that the non-linear strain of the solder is increased. Therefore, when the upper limitation of the chip size in 10 mm by 10 mm, it is found that the reliability and the durability of the inverter apparatus can be secured. On the other hand, when the lower limitation of the chip size ranging from 5 mm by 5 mm showed inFIG. 5to 2 mm by 2 mm inspected by inventors, it is found that the reliability and the durability of the inverter apparatus can be secured.

The current-carrying capacity per one chip is decreased when the chip size in 10 mm by 10 mm or less similarly to the embodiment. In this case, several tens kW of current-carrying capacity required for the electric automobile can be secured by connecting the chips in parallel.

In the inverter apparatus having a configuration shown inFIG. 4, the IGBTs191A to191D and the diodes201A to201C bonded to the conductor22are directly adhered to the cooler24by using the insulating resin sheet25, so that the contact thermal resistance at a contact portion to the cooler like the conventional semiconductor device portion for electric power shown inFIG. 3is eliminated, the thermal resistance is decreased.

Furthermore, the insulating resin sheet25has low thermal conductivity, compared with the conventional insulating substrate17, for example, alumina substrate (thermal conductivity is 21 W/mK and thickness is 0.32 mm), the conductor22on the insulating resin sheet25is made of copper whose thermal conductivity is good, a thickness of the conductor22is 1.5 mm or more and 5 mm or less, and the IGBTs191A to191D and the diodes201A to201C are disposed on the conductor22while the IGBT191and the diode201are dispersed on the conductor22. Accordingly, heat generated in the IGBTs191A to191D and the diodes201A to201C is diffused by heat conduction of the conductor22and absorbed by heat capacity of the conductor22. This permits the thermal resistance to be further decreased in the semiconductor device portion for electric power of the embodiment.

FIG. 6is the analytic result of a temperature change of the IGBT191and the diode201during the conducting period of the inverter apparatus when the thickness of the conductor22is 3 mm. In the starting period of the inverter apparatus, IGBT loss and diode loss become large, and temperature rise of both the IGBT and the diode particularly becomes large.

It is important to decrease the temperature rise of the IGBT and the diode particularly during the starting period of the inverter apparatus in order to improve the reliability of the IGBT191and the diode201, reduce the number of parallel, and miniaturize the semiconductor device portion for electric power and the inverter apparatus.

FIG. 7is a temperature change of the IGBT191and the diode201during the starting period of the inverter apparatus when the thickness of the conductor22is used as a parameter. When the thickness of the conductor22is 1.5 mm or less, the temperatures of the IGBT191and the diode201are particularly increased. The temperatures of the IGBT and the diode is are not largely decreased, even though the thickness of the conductor22is more than 5 mm. When the thickness of the conductor22is 1.5 mm or more and 5 mm or less, the temperatures of the IGBT and the diode during the starting period of the inverter apparatus are decreased by an effect of the heat capacity of the conductor22.

When the thickness of the conductor22is 3 mm, in the semiconductor device portion for electric power of the invention, steady heat resistance per IGBT chip is 0.46 K/W for the IGBT chip size of 7.8 mm by 7.8 mm, the steady heat resistance per IGBT chip is decreased to an almost half value, compared with the conventional semiconductor device portion for electric power having the steady heat resistance per IGBT chip of 1.11 K/W.

In the insulating resin sheet25, adhesiveness to a more active surface such as a copper surface is stronger than the adhesiveness to an inactive surface, for example, a Ni plated surface. On the contrary, in wire bonding which is electric wire of the IGBT and the diode, the adhesiveness to a plated surface is stronger than the adhesiveness to the active surface.

Accordingly, in the conductor22of the embodiment, since the surface bonded to the IGBTs191A to191D and the diodes201A to201C is carried out by the plating treatment26, bonding strength between the wire bonding and the conductor22is increased. The plating treatment is not carried out on the reverse of the conductor22, which1s adhered to the cooler24by the insulating resin sheet25containing ceramics, so that the bonding strength between the conductor22and the insulating resin sheet25is increased.

As described above, in the inverter apparatus of the embodiment shown inFIG. 4toFIG. 7, the heat resistance of the semiconductor chip caused by the IGBT and the diode is decreased halt inside the semiconductor device portion for electric power2, the cooling efficiency is increased, the reliability of the inverter apparatus1s improved, and the miniaturization of the inverter apparatus is realized. Furthermore, since the thermal conductive grease which might deteriorate on a long-term basis, the reliability and the durability are improved

A second embodiment of the invention will be described below referring to FIG.4and FIG.8.

The second embodiment defines a solder thickness in the semiconductor device portion for electric power of the first embodiment.

InFIG. 4, in the inverter apparatus, the semiconductor chips of the IGBTs191A,191B,191C, and191D and the diodes201A,201B, and201C are bonded to the copper conductor22having a thickness of 1.5 mm or more and 5 mm or less by the solder23of the low-melting solder such as Sn/Pb or the high-melting solder such as Sn/Ag/Cu.

When the heat cycle is loaded on the semiconductor device portion for electric power, the shear stress is generated in the solder23, the non-linear strain is generated. This is because the IGBT191and the diode201are made of silicon and the conductor22is made of copper, so that the coefficients of linear expansion of the IGBT191and the diode201and the conductor22are different. The lower is a value of the non-linear strain, the more the reliability and the durability are improved.

FIG. 8is the analytic result of the correlation between the maximum value of non-linear strain of the solder and the solder thickness when the heat cycle test holding temperatures ranging from −40° C./1 hr to 125° C./1 hr is carried out on the semiconductor device portion for electric power shown inFIG. 4to FIG.7.

When the thickness of the solder23is lower than 75 μm, the non-linear strain is increased. When the thickness of the solder23is 75 μm or more, the non-linear strain is decreased, because, by increasing the thickness of the solder23, thermal stress of the solder is dispersed to decrease stress concentration. The non-linear strain is not largely decreased even though the thickness of the solder23is 300 μm or less.

As described above, in the embodiment, the thickness of the solder23which bonds the IGBT191and the diode201to the conductor22having the thickness of 1.5 mm or more and 5 mm or less is 75 μm or more and 300 μm or less, consequently, the non-linear strain of the solder23can be decreased, and the reliability and the durability of the semiconductor device portion for electric power and the inverter apparatus shown inFIG. 4toFIG. 7can be further improved.

A third embodiment of the invention will be described below referring to FIG.4and FIG.9.

The third embodiment defines a thickness of the cooler24in the semiconductor device portion for electric power of the first embodiment.

FIG. 9is an analytic result of a correlation between a maximum shearing stress of an insulating resin sheet and a cooler thickness/conductor thickness when a heat cycle test holding temperatures ranging from −40° C./1 hr to 125° C./1 hr is carried out on the semiconductor device portion for electric power shown inFIG. 4to FIG.7.

InFIG. 4, the copper conductor22is adhered to the cooler24made of copper or aluminum by the insulating resin sheet25containing ceramics. Though it is thought that a material of the cooler24is copper, aluminum or the like, aluminum is desirable in consideration of productivity, workability, and weight.

When the cooler24is made of aluminum and the heat cycle is loaded on the semiconductor device portion for electric power, the shear stress is generated in the insulating resin sheet by difference in coefficient of linear expansion between the conductor22made of copper and the cooler24made of aluminum. When a value of the shear stress becomes larger, the insulating resin sheet25is peeled. The smaller is the value of the shear stress, the more the reliability and the durability are improved.

FIG. 9is the analytic result of the correlation between the maximum shearing stress of an insulating resin sheet and the cooler thickness/conductor thickness when the cooler24is made of aluminum and the heat cycle test holding temperatures ranging from −40° C./1 hr to 125° C./1 hr is carried out on the semiconductor device portion for electric power shown inFIG. 4to FIG.7.

When the ratio of cooler24thickness/conductor22thickness is lower than 3.3, the maximum shear stress of the insulating resin sheet25is increased. When the ratio of cooler24thickness/conductor22thickness is 3.3 or more, rigidity or the cooler24becomes sufficiently large compared with the conductor22, and deformation of the cooler24is restrained, which allows the deformation of the insulating resin sheet25to be restrained, so that the maximum shear stress of the insulating resin sheet25is decreased. The maximum shear stress is not almost decreased, even though the ratio of cooler24thickness/conductor22thickness is 10 or more.

According to the embodiment, the ratio of the thickness of the cooler24to the thickness of the conductor22having a thickness of 1.5 mm or more and 5 mm or less is 3.3 or more and 10 or less, consequently, the maximum shear stress of the insulating resin sheet25can be decreased, and the reliability and the durability of the semiconductor device portion for electric power and the inverter apparatus of the first and second embodiments of the invention can be further improved.

A fourth embodiment of the invention will be described below referring toFIG. 10to FIG.13.

FIG. 10is a partially perspective view of a semiconductor device portion for electric power in an inverter apparatus according to a fourth embodiment of the invention. In the embodiment, the IGBT per one arm is four parallels and the diode per one arm is two parallels.

FIG. 11is a perspective view illustrating an inside structure of the semiconductor device portion for electric power in the inverter apparatus according to the fourth embodiment of the invention. In the embodiment, the IGBT per one arm is four parallels and the diode per one arm is two parallels.

FIG. 12AtoFIG. 12Cshows the semiconductor device portion for electric power in the inverter apparatus according to the fourth embodiment of the invention,FIG. 12Ais a plan view,FIG. 12Bis a sectional view taken along the line XII-B—XII-B ofFIG. 12A,FIG. 12Cis a sectional view taken along the line XII-C—XII-C of FIG.12A. In the embodiment, the IGBT per one arm is four parallels and the diode per one arm is three parallels.

FIG. 13is a circuit diagram of the inverter apparatus according to the fourth embodiment of the invention.

InFIG. 10, in the semiconductor device portion for electric power, the IGBTs191A to191D connected in four parallels and the diodes201A and201B connected in two parallels, which constitute an upper side arm of a W-phase of a three-phase inverter main circuit shown inFIG. 10, are arranged in one line on an upper side arm conductor27which constitute the upper side arm of the three-phase inverter main circuit. In the same way, IGBTs192A to192D connected in four parallels and diodes202A and202B connected in two parallels, which constitute an lower side arm of the W-phase of the three-phase inverter main circuit, are arranged in one line on an lower side arm conductor28which constitute is the lower side arm of the three-phase inverter main circuit.

A three-phase output conductor29, which connects a three-phase output terminal40to the IGBTs191A to191D and the diodes201A and201B arranged on the upper side arm conductor27, is arranged between the upper side arm conductor27and the lower side arm conductor28.

In the embodiment shown inFIG. 10toFIG. 13, the lower side arm conductor28and the three-phase output conductor29are formed by the same conductor. A negative electrode conductor30, which connects a negative electrode terminal39to the IGBTs192A to192D and the diodes202A and202B arranged on the lower side arm conductor28, is arranged between the upper side arm conductor27and the lower side arm conductor28. The IGBTs and the diodes and each conductor are electrically connected by wire bonding31.

In case of the above-described arrangement, an individual current path, which is connected in parallel from a positive electrode terminal38to the three-phase output terminal40through each of the IGBTs191A to191D, becomes uniform. In the same way, an individual current path, which is connected in parallel from the three-phase output terminal40to the negative electrode terminal39through each of the IGBTs192A to192D, becomes uniform. In the same way, an individual current path, which is connected in parallel from the three-phase output terminal40to the positive electrode terminal38through each of the diodes201A and201B, becomes uniform.

In the same way, an individual current path, which is connected in parallel from the negative electrode terminal39to the three-phase output terminal40through each of the diodes202A and202B, becomes uniform. Other configurations are the same as the first to third embodiments.

In FIG.11andFIG. 12AtoFIG. 12C, in the semiconductor device portion for electric power, the insulating resin sheet containing ceramics is divided by each phase of the three-phase inverter main circuit, a W-phase insulating resin sheet32, a V-phase insulating resin sheet33, and a U-phase insulating resin sheet34are separated each other by a certain distance, a control lead35and a control input and output terminal36are provided between each of the U to W-phase insulating resin sheet in order to control the parallel connected IGBTs.

Peripheries of the IGBT and the diode, each conductor, and each insulating resin sheet are glued to the cooler24and encapsulated with insulating gel in a resin package37having the positive electrode terminal38, the negative electrode terminal39, the three-phase output terminal40, and the control input and output terminal36. Other configurations are the same as FIG.10.

In the semiconductor device portion for electric power in the inverter apparatus of the embodiment, in addition to effects of the first to third embodiments, the control lead35from each of the IGBTs connected in parallel can be drawn in perpendicular to current of the main circuit and in the shortest distance, so that malfunction caused by a noise of control is eliminated and the reliability is increased.

In the embodiment, the semiconductor chips used per one phase of the upper side or lower side arm are divided uniformly to all current paths of each of the IGBTs and the diodes which are connected in parallel in a manner that a plurality of semiconductor chips are connected in parallel, so that current share of each of the IGBTs and the diodes becomes uniform and local overheat of semiconductor chips of the IGBTs and the diodes is never generated.

Furthermore, in the embodiment, since the insulating resin sheet is divided into each phase, the shear stress of the insulating resin sheet is decreased, which allows the reliability and the durability to be increased.

A fifth embodiment of the invention will be is described below referring to FIG.11andFIG. 14Ato FIG.14C.

FIG. 14Ais a plan view of a semiconductor device portion for electric power in an inverter apparatus according to the fifth embodiment of the invention,FIG. 14Bis a sectional view taken along the line XIV-B—XIV-B ofFIG. 14A,FIG. 14Cis a sectional view taken along the line XIV-C—XIV-C of FIG.14A. In the embodiment, the IGBT per one arm is four parallels and the diode per one arm is three parallels.

InFIG. 11, in the semiconductor device portion for electric power, the cooler24is a liquid cooled type cooler, an enlarged heat transfer surface41is provided in the channel15in which the coolant14of the liquid cooled type of cooler flows, and the enlarged heat transfer surface41is provided in parallel to the upper side arm conductor27and the lower arm conductor28to which the IGBT and the diode are bonded, the three-phase output conductor29, and the negative electrode30. Other configurations are the same as the first to fourth embodiments.

According to the embodiment, in addition to effects of the first to fourth embodiments, since the enlarged heat transfer surface41is provided in parallel to the conductor, thermal deformation of the cooler24in a longitudinal direction of the conductor cause by the heat cycle during the conducting period of the inverter apparatus can be restrained, the value of the shear stress generated in the insulating resin sheet can be decreased, the reliability and the durability of the insulating resin sheet can be further improved.

A sixth embodiment of the invention will be described below referring toFIG. 15Ato FIG.15C.

FIG. 15Ais a plan view of a semiconductor device portion for electric power in an inverter apparatus according to the sixth embodiment of the invention,FIG. 15Bis a sectional view taken along the line XV-B—XV-B ofFIG. 15A,FIG. 15Cis a sectional view taken along the line XV-C—XV-C of FIG.15A. In the embodiment, the IGBT per one arm is four parallels and the diode per one arm is three parallels.

InFIG. 15AtoFIG. 15C, in the semiconductor device portion for electric power, the cooler24is the liquid cooled type of cooler, an outside shape of the cooler24is the same as the fifth embodiment, and the cooler24has a two-stage arrangement of an upper and lower coolers.

That is to say, the cooler24includes an upper-stage cooler portion and a lover-stage cooler portion. In the upper-stage cooler portion, the enlarged heat transfer surface41is provided in the channel15in which the coolant14of the liquid cooled type of cooler flows, and the enlarged heat transfer surface41is provided in parallel to the upper side arm conductor27and the lower arm conductor28to which the IGBT and the diode are bonded, the three-phase output conductor29, and the negative electrode30.

In the lower-stage cooler portion, an enlarged heat transfer surface42is provided perpendicular to the enlarged heat transfer surface41, the lower-stage cooler portion is the cooler which is opened to a periphery and in which the coolant does not flow. The number of plates of the enlarged heat transfer surface42is smaller than that of the enlarged heat transfer surface41.

In the above-described arrangement, since the outside shape of the cooler24is the same as the fifth embodiment, heat dissipation area of the enlarged heat transfer surface41is half compared with the fifth embodiment, however, in case of the liquid cooled type of cooler, fin efficiency of the enlarged heat transfer surface41of the fifth embodiment is approximately 0.5 and the fin efficiency of the enlarged heat transfer surface41of the sixth embodiment is approximately 1, so that cooling capacity of the sixth embodiment is almost the same as that of the fifth embodiment. Other configurations are the same as the first to fifth embodiments.

According to the sixth embodiment, in addition to effects of the first to fifth embodiments, since the enlarged heat transfer surface41and the enlarged heat transfer surface42are orthogonal, the rigidity of the cooler is increased, the thermal deformation of the cooler24in a longitudinal direction of the conductor cause by the heat cycle during the conducting period of the inverter apparatus can be restrained better than the fifth embodiment, the value of the shear stress generated in the insulating resin sheet can be decreased, the reliability and the durability of the insulating resin sheet can be further improved.

A seventh embodiment of the invention will be described below referring to FIG.16.

FIG. 16is a partially sectional view showing a mounting structure of an inverter apparatus, particularly a semiconductor chip of an inside of a semiconductor device portion for electric power according to the seventh embodiment of the invention.

InFIG. 16, in the semiconductor device portion for electric power, an end portion of the conductor22is formed as a thin plate portion43, the positive terminal38, the negative terminal39, the three-phase output terminal40, and the wire bonding31for electric wiring are connected to the thin plate portion43. Other configurations are the same as the first to sixth embodiments.

In the semiconductor device portion for electric power having the configuration shown inFIG. 16, the shear stress is generated in the insulating resin sheet25which glues the conductor22to the cooler24by the heat cycle during the conducting period of the inverter apparatus. The shear stress becomes the maximum at the end portion of the conductor22.

Since the end portion of the conductor22is the thin plate portion43, the rigidity of the end portion of the conductor22can be reduced, and the maximum shear stress of an epoxy resin sheet, which is generated in the end portion of the conductor22by the heat cycle during the conducting period of the inverter apparatus, can be reduced. When the thickness of the conductor22is 3 mm and a thickness of the thin plate portion43is 0.5 mm, the maximum shear stress of the epoxy resin sheet is reduced by about 28%.

According to the embodiment, in addition to effects of the first to sixth embodiments, the reliability and the durability of the insulating resin sheet can be further improved.

An eighth embodiment of the invention will be described below referring to FIG.17.

FIG. 17is a partially sectional view showing a mounting structure of an inverter apparatus, particularly a semiconductor chip of an inside of a semiconductor device portion for electric power according to the eighth embodiment of the invention.

InFIG. 17, in the semiconductor device portion for electric power, a slit44is provided in the conductor22between the IGBTs191A to191D and the diodes201A to201C are bonded, a surface where the slit44is provided is glued to the cooler24by the insulating resin sheet25containing ceramics. Other configurations are the same as the first to seventh embodiments.

In the semiconductor device portion for electric power having the configuration shown inFIG. 17, the shear stress is generated in the lower-melting or high-melting solder23which bonds the IGBTs191A to191D and the diodes201A to201C to the conductor22by the heat cycle during tile conducting period of the inverter apparatus.

In the embodiment, since the slit44is provided in the conductor22, deformation easily occurs in a direction perpendicular to the longitudinal direction of the conductor22, so that the thermal expansion in the longitudinal direction of the conductor22can be restrained, and the shear stress of the lower-melting or high-melting solder23can be reduced. When the thickness of the conductor22is 3 mm and a height of the slit44is 2.5 mm, the shear stress of the lower-melting or high-melting solder23is reduced by about 16%.

According to the embodiment, in addition to effects of the first to seventh embodiments, the reliability and the durability of the lower-melting or high-melting solder23can be further improved.

A ninth embodiment of the invention will be described below referring toFIG. 18Ato FIG.18C.

FIG. 18AtoFIG. 18Cshows a method of manufacturing an inverter apparatus according to a ninth embodiment of the invention.

In the semiconductor device portion for electric power, the IGBTs191A to191D and the diodes201A to201C are bonded are bonded to the conductor22by the low-melting solder23such as Sn/Pb or the high-melting solder23such as Sn/Pb/Cu as shown inFIG. 18A, the insulating resin sheet25is glued tentatively to the cooler24as shown in FIG.18B. As shown in18C, an elastic body45such as silicon rubber is arranged in a position where the IGBTs191A to191D and the diodes201A to201C are not bonded an order to pressurize uniformly, the conductor22is pressurized through a pressure plate46, the conductor22and the cooler24are pressurized and heat-glued while the insulating resin sheet25is put between the conductor22and the cooler24. A pressure temperature is, for example, from 160° C. to 170° C., pressurizing force is from about 20 kgf/cm2to about 30 kgf/cm2.

In the semiconductor device portion for electric power ofFIG. 18AtoFIG. 18C, if the conductor22and the cooler24are glued at first by the insulating resin sheet25, heating for long hours at a temperature more than a glass transition temperature or more of the insulating resin sheet25(for example, about 170° C.) is necessary when the IGBTs191A to191D and the diodes201A to201C are soldered, characteristics of the insulating resin sheet are deteriorated.

On the contrary, in the embodiment, since the above-described manufacturing method is employed, the characteristics of the insulating resin sheet are never deteriorated.

With respect to the solder, for example, a high-melting solder with Pb free such as a Sn/Ag/Cu solder can be also used.

As described above, according to the invention, an increase in the cooling efficiency of the inverter main circuit contributes to an increase in the current-carrying capacity, which allows the miniaturization of the inverter apparatus to be achieved. An increase in the reliability of the inverter main circuit and its semiconductor chips allows the reliability of the inverter apparatus to be increased.