Power semiconductor module and method of manufacturing the same

A power semiconductor module and a method of manufacture thereof includes a lead frame carrying lead having inner and outer lead portions. The outer lead portions, which are connected by soldering to semiconductor chips simultaneously, eliminate the need for using bonding wires. Since no bonding wire is used for connecting the leads and the semiconductor chips, a sufficient current capacity is obtained. The bonding between an insulating circuit board and the semiconductor chips and the bonding between the semiconductor chips and the leads can be made simultaneously in a single step of reflow-soldering. As a result, the mounting time can be shortened and the power semiconductor module can be manufactured more efficiently.

BACKGROUND

Power semiconductor modules are used in inverters, uninterruptive power supplies, machine tools, industrial robots, and such apparatuses in the form of packages, independent from these industrial apparatuses. Such a power semiconductor module houses therein one or more semiconductor chips insulated gate bipolar transistors (hereinafter referred to as “IGBTs”) and such power semiconductor devices constituting the power converter circuit. The power semiconductor module is mounted on a predetermined control circuit board for controlling any of the apparatuses described above. See for instance JP 2002-50722 A.

The following describes such a power semiconductor module that houses a plurality of semiconductor chips. Typically, the power semiconductor module mounts the semiconductor chips on an insulating circuit board by soldering. The power semiconductor module has the leads connected to the control circuit board and the semiconductor chips by wire bonding using metal wires. Then, the power semiconductor module incorporating therein the semiconductor chips, mounted on the insulating circuit board and connected to the leads by wire bonding, is packaged by molding in a resin casing. A radiator plane arranged on the side opposite to the side of the resin casing, on which outer leads are mounted, is in contact with a cooling fin so that the heat generated in the power semiconductor devices can be dissipated to the outside.

Since the cross sectional area of the metal wires connecting the outer leads and the semiconductor chips in the power semiconductor module described above is relatively small, the module is limited in its current capacity. While a thick metal wire can improve the current capacity, it is difficult to bond the thick metal wire by ultrasonic bonding or by welding.

The manufacturing process for manufacturing the power semiconductor module includes soldering the semiconductor chip to the insulating circuit board and connecting the semiconductor chips and the outer lead portions by wire bonding. The metal wire bonding is conducted wire by wire. Since from 200 to 500 metal wires are typically used for manufacturing the power semiconductor module, it takes a long time to bond the metal wires.

Accordingly, there remains a need to provide a power semiconductor module that is manufactured more efficiently. The present invention addresses this need.

SUMMARY OF THE INVENTION

The present invention relates to a power semiconductor module that houses therein one or more semiconductor chips mounting power semiconductor devices thereon, and a method of manufacturing the same.

One aspect of the present invention is a power semiconductor module that can be mounted to a control circuit board of an electronic device. The power semiconductor module can include at least one power semiconductor device, and leads having outer lead portions that can be connected to the control circuit board of the electronic device and inner lead portions connected to the at least one semiconductor chip. The module can further include a terminal casing housing part of the leads, and an insulating circuit board housed in the terminal casing. One major surface of the insulating circuit board forms a radiator plane. The at least one semiconductor chip is mounted on the other major surface, on the side opposite to the radiator plane, of the insulating circuit board, and the inner lead portions are connected to the at least one semiconductor chip on the side opposite to the insulating circuit board.

The at least one semiconductor chip can be surface-mounted on the insulating circuit board by brazing or soldering and the inner lead portions can be surface-mounted on the at least one semiconductor chip by brazing or soldering. The at least one semiconductor chip can comprises two or more semiconductor chips, which can have an equal thickness, mounted on the insulating circuit board.

The terminal casing can comprise a main body and a pair of fastener mounting plates extending in the opposite directions from the main body thereof to facilitate fasteners into a cooling fin such that the radiator plane of the insulating circuit board can be brought into contact with the cooling fin. The radiator plane of the insulating circuit board protrudes for a predetermined length from the contact planes of the fastener mounting plates, across which the fastener mounting plates can be brought into contact with the cooling fin, to enable the radiator plane of the insulating circuit board to make contact with the cooling fin.

The terminal casing can be filled with a thermosetting resin, such as epoxy resin, that hardens for insulating sealing. The terminal casing can have cutouts formed between the fastener mounting plates and the main body of the terminal casing such that portions remaining below the cutouts are thin. Slits can be disposed in the thin portions of the fastener mounting plates. The contact plane on each of the fastener mounting plates can have a boss protruding from each of the fastener mounting plates.

The terminal casing can have at least one protrusion protruding toward the insulating circuit board in the bonding areas between the terminal casing and the insulating circuit board, to enable the thermosetting resin to flow around the at least one protrusion into a gap between the terminal casing and the insulating circuit board. The terminal casing can include an adhesion strengthening structure that strengthens the adhesion of the thermosetting resin.

The outer lead portions are adapted to be surface-mounted on the control circuit board by soldering on the side opposite to the side of the radiator plane. At least one protrusion can be formed at least on the surface that is adapted to face the control circuit board, of any of the terminal casing and the fastener mounting plates, to secure a predetermined solder thickness for soldering the outer lead portions to the control circuit board.

Each of the fastener mounting plates can include a fastener insertion hole, through which a fastener can be inserted, for fastening the power semiconductor module and the control circuit board to the cooling fin. Each of the fastener mounting plates can include a boss-shaped fastener insertion holder having the fastener insertion hole formed through the boss-shaped fastener insertion holder. The boss-shaped fastener insertion holder is insertable into an insertion hole formed in the control circuit board, to position the power semiconductor module on the control circuit board.

The portions of the leads to be soldered can include protrusions that protrude toward the solder. Polyimide layers can be formed the at least one semiconductor chip except on the electrodes thereof.

Another aspect of the present invention is a method of manufacturing the power semiconductor module described above. The method can includes the following steps: (a) providing at least one semiconductor chip; (b) providing the insulating circuit board, which can comprise an insulator layer, electrode layers constituting electrodes on one major surface of the insulator layer, and a radiator layer constituting a radiator plane on the other major surface of the insulator layer; (c) forming first solder layers on the respective electrodes; (d) mounting the at least one semiconductor chip on the first solder layers; (e) forming second solder layers on the at least one semiconductor chip; (f) stamping a predetermined metal plate to form the lead frame having leads, with the inner and outer lead portions, connected to each other via tie-bars; (g) forming a terminal casing by injection molding a resin using a predetermined molding die for housing part of the leads therein; (h) mounting the insulating circuit board on the terminal casing by bringing the inner lead portions into contact with the respective second solder layers; (i) reflowing the first and second solder layers to solder the insulating circuit board and the at least one semiconductor chip to each other and to solder the at least one semiconductor chip and the inner lead portions to each other; (j) filling the terminal casing with a hardening thermosetting resin, which can be epoxy resin, for insulating sealing; and (k) separating the outer lead portions.

The step (a) can include equalizing the two or more semiconductor chips in the thickness thereof. The step (a) can include forming polyimide layers on the at least one semiconductor chip except on the electrodes thereof and forming plating layers on the electrode surfaces thereof.

The step (c) or (e) or both steps can include dispersing core balls having a predetermined diameter into the first solder layers or the second solder layers.

The inner lead portions can be formed on the lead frame after the step (g). Insulation tests can be conducted on the leads before the step (k), and the outer lead portions that have passed the insulation tests can be identified. The step (f) can include forming the lead frame as a flat member and integrating the flat lead frame into the terminal casing, and the inner and outer lead portions can be formed by press works. The inner and outer lead portions can be formed by applying a coining work for partially shaping the portions of the lead frame to be soldered with respective protrusions protruding toward the solder.

The step (g) can include forming a pair of fastener mounting plates integrated into a main body of the terminal casing such that the fastener mounting plates extend in the opposite directions from the main body of the terminal casing, and fastening into a cooling fin through the fastener mounting plates to bring the radiator plane of the insulating circuit board into contact with the cooling fin.

The step (g) also can includes forming cutouts between the fastener mounting plates and the main body of the terminal casing such that the portions of the cutouts remaining between the fastener mounting plates and the main body of the terminal casing are thin. The step (g) also can include forming at least one protrusion protruding from the terminal casing toward the insulating circuit board in the bonding areas between the terminal casing and the insulating circuit board, integrally on the terminal casing. The step (g) also can include forming the adhesion strengthening structure integrally into the terminal casing, the adhesion strengthening structure strengthening the adhesion of the thermosetting resin.

The step (h) comprises mounting the insulating circuit board on the terminal casing such that the radiator plane of the insulating circuit board protrudes for a predetermined length from the contact planes of the fastener mounting plates, across which the fastener mounting plates are brought into contact with the cooling fin, toward the cooling fin.

The step (i) can include aligning the at least one semiconductor chip in an self-aligning manner.

The step (j) can include flowing the thermosetting resin around the at least one protrusion into the gap between the terminal casing and the insulating circuit board. The step (j) also can include making the adhesion strengthening structure hold the thermosetting resin.

DETAILED DESCRIPTION

Referring to the drawings, the present power semiconductor module is described in connection with controlling an inverter. In the following descriptions, the vertical positional relations are described sometimes with reference to the orientation of the power semiconductor module shown inFIG. 1.

Referring now toFIG. 1, a power semiconductor module1includes a resin terminal casing2housing an insulating circuit board (described later) and at least one semiconductor chip mounted on the insulating circuit board. Since the terminal casing2is filled and sealed with an epoxy resin (thermosetting resin)3, the insulating circuit board and the semiconductor chips are not illustrated inFIG. 1.

Fastener mounting plates4for bonding the power semiconductor module1to a cooling fin (described later) with screw or fasteners extend from a pair of side faces on the main body of the terminal casing2. A protrusion5for positioning the power semiconductor module1in mounting the power semiconductor module1to the control circuit board of an inverter is disposed on the upper surface of each fastener mounting plate4. A plurality of outer lead portions6, which will be connected to the control circuit board described, extend outwardly from the other pair of side faces of the terminal casing2.

Referring toFIG. 3(B), the power semiconductor module1includes the terminal casing2housing therein an insulating circuit board7, a plurality of semiconductor chips8mounted on the insulating circuit board7, and a lead frame9connecting the semiconductor chips8to the control circuit board. The terminal casing2is filled and sealed with an epoxy resin3. The outer lead portions6are formed of the end portions of the lead frame9. As shown inFIGS. 2(A)-2(C), the terminal casing2includes a main body11shaped as a rectangular frame. As clearly shown inFIG. 3(C), a step12is formed in the upper opening of the main body11along the inner periphery of the rectangular frame thereof. The step12strengthens the adhesion of the epoxy resin3to the terminal casing2and holds the hardened epoxy resin3. The lower opening of the main body11is widened such that a step13for housing the insulating circuit board7is formed. The step13is slanting upwardly and inwardly. Protrusions14protruding toward the insulating circuit board7are disposed in the vicinity of the four corners of the step13. The functions of the protrusions14will be described later.

As clearly shown inFIG. 3(B), the frame width of the main body11for holding the loaded epoxy resin3is a little bit larger than the frame width thereof for housing the insulating circuit board7, and the inner surface of the frame-shaped main body11is step-shaped in the height direction thereof. As shown inFIGS. 2(A)-2(C), a pair of flanges15is disposed on both end portions of each long side face of the portion in the main body11filled with the epoxy resin3. The flanges15on one side face protrude opposite to the flanges15on the other side face, and perpendicularly to the longitudinal direction of the main body11. The flanges15disposed as described above improve the rigidity of portion in the main body11filled with the epoxy resin3. In contrast, fine trenches16for substantially thinning the bottom of the main body11are formed therein such that the rigidity of the portion in the main body11for housing the insulating circuit board7is reduced. The fastener mounting plates4described above extend outwardly from the end faces along the width of the portion in the main body11for housing the insulating circuit board7.

A fastener insertion holder21for inserting a screw or fastener described later is disposed at a position of the fastener mounting plate4spaced part from the main body11of the terminal casing2. A fastener insertion hole22is bored vertically in the central part of the fastener insertion holder21. A circular boss23is arranged on the bottom face of the fastener mounting plate4such that the circular boss23is protruding from the bottom surface of the fastener mounting plate4. The fastener insertion hole22is formed through the center of the protruding circular boss23. The distal end face of the circular boss23works as a contact plane contacting with a cooling fin described later. A U-shaped cutout24is formed between the fastener insertion holder21and the main body11of the terminal casing2such that the portion of the fastener mounting plate4left below the cutout24between the fastener insertion holder21and the main body11of the terminal casing2(hereinafter referred to as the “bottom of the cutout24”) is thin. A long slit25extending in the width direction of terminal casing2is formed in the central part of the bottom of the cutout24to raise the flexibility thereof.

The insulating circuit board7is shaped as a rectangular plate fitting the lower inner circumference of the main body11of the terminal casing2as shown inFIGS. 2(B) and 2(C). As clearly shown inFIG. 3(C), the insulating circuit board7includes a main substrate26made of aluminum or copper, an insulator resin layer27made of an epoxy resin containing a filler exhibiting an excellent thermal conductivity (such as aluminum nitride powder and silicon dioxide powder), and copper foil patterns28printed on the insulator resin layer27. The semiconductor chip8is surface-mounted on the copper foil via a solder layer29. A narrow gap is formed between the insulating circuit board7and the main body11of the terminal casing2so that the insulating circuit board7can be held stably inside the main body11with the epoxy resin3filling the gap. As clearly shown inFIG. 3(A), the lower surface of the insulating circuit board7is exposed below the terminal casing2such that a radiator plane is formed. The radiator plane of the insulating circuit board7protrudes downwardly for a certain length from the distal end faces of the circular bosses23.

The lead frame9is a long copper plate molded to the main body11of the terminal casing2such that the lead frame9extends parallel to the main body11of the terminal casing2. One end of the lead frame9extends outwardly from the main body11such that an outer lead portion6, the longitudinal cross section thereof having an L shape, is formed, and the other end of the lead frame9extends into the main body11such that an inner lead portion30, the longitudinal cross section thereof also having an L-shape, is formed. The end portion of the outer lead portion6is almost on the same plane with the upper surface of the main body11and extends parallel to the upper surface of the main body11. The end portion of the outer lead portion6is bonded by soldering to the control circuit board of an inverter described later. The end portion of the inner lead portion30extends parallel to the upper surface of the semiconductor chip8and connects to the electrode of the semiconductor chip8via a solder layer31.

The power semiconductor module1configured as described above can be mounted on the control circuit board of an inverter and a cooling fin is attached to the power semiconductor module1. Referring toFIG. 4, which shows a partial cross sectional view, in mounting the power semiconductor module1on a control circuit board101, the power semiconductor module1is set at a predetermined position of the control circuit board101by inserting the positioning protrusions5on the power semiconductor module1into positioning holes102formed through the control circuit board101. Solder layers103are formed by screen printing in advance at the positions corresponding to the outer lead portion6of the power semiconductor module1. In setting the power semiconductor module1, the outer lead portions6are placed on the solder layers103. The fastener insertion holes22of the power semiconductor module1are placed at the positions corresponding to insertion holes104formed in advance through the control circuit board101. In this state, reflow-soldering is conducted to bond the power semiconductor module1to the control circuit board101. Small protrusions17can be formed near the four corners on the upper surface of the main body11of the terminal casing2to secure a certain solder layer thickness at the time when the solder layers are made to reflow.

The unit, in which the power semiconductor module1and the control circuit board101are combined, is mounted on a cooling fin110, the upper surface thereof is flat. A fastener hole111is formed at the position of the cooling fin110corresponding to the fastener insertion hole22of the power semiconductor module1. The unit combining the power semiconductor module1and the control circuit board101therein is fixed to the cooling fin110by inserting a screw or fastener120from the side of the control circuit board101into the fastener insertion holes104and22and by fastening the fastener120into the fastener hole111. Since the radiator plane of the insulating circuit board7protrudes downward for a certain length from the distal end faces of the circular bosses23as described earlier, the bottoms of the cutouts24are bent by the fastening due to the height difference. Since the radiator plane of the insulating circuit board7is pressed strongly to the cooling fin110, excellent heat conduction is obtained between the insulating circuit board7and the cooling fin110. Therefore, sufficient heat radiation effects are obtained.

Now the method for manufacturing the power semiconductor module will be described in detail below.FIG. 5is a flow chart describing the steps for manufacturing the power semiconductor module according to the first embodiment.FIGS. 6(A)-14illustrate the manufacturing steps. In the following, the manufacturing process is described in the descending order of the step numbers (S11through S37) described inFIG. 5.

First, semiconductor chips8are formed (step S11). SeeFIG. 6(A)-6(B). In detail, IGBTs, free-wheel diodes (FWDs) and such power semiconductor devices are formed on a predetermined semiconductor substrate. Polyimide layers42are formed on the surfaces of the power semiconductor devices except the electrode surfaces thereof. Nickel (Ni) plating layers43are formed on the respective electrodes of the power semiconductor devices by electroless plating. Gold (Au) plating layers44are formed on the Ni plating layers43by electroless plating. Then, the semiconductor substrate is diced into chips41. The plating treatments described above are conducted to improve the wetness of the solder, since the electrodes of the power semiconductor devices are aluminum layers. The plating treatments make the surfaces of the polyimide layers42repel the solder and make the solder adhere accurately to the electrodes as far as the amount of the solder coated later is appropriate.

An insulating circuit board7can be formed (step S12) at the same time as the formation of the semiconductor chips8. As shown inFIG. 3(C), an insulator resin layer27made of an epoxy resin containing a filler exhibiting an excellent thermal conductivity (such as aluminum nitride powder and silicon dioxide power) is formed on a main substrate26made of aluminum or copper. Then, copper foil patterns28constituting the electrodes can be formed on the insulator resin layer27as shown inFIG. 7(A).

Then, solder layers29(first solder layers) are printed at the predetermined positions on the patterns28by screen printing as shown inFIG. 7(B)(step S13). Then, the semiconductor chips8are mounted on the respective solder layers29as shown inFIG. 7(C)(step S14). Further, a thermistor45for temperature detection can be mounted on the solder layer. Then, solder layers31(second solder layers) can be coated with a dispenser at the predetermined positions on the semiconductor chips8and at the predetermined positions on the patterns28as shown inFIG. 7(D)(step S15).

Independently of the steps described above, the terminal casing2and such parts can be formed. In detail, the lead frame9shown inFIG. 8(A)can be formed by stamping a predetermined rectangular copper plate by press work (step S21). In the lead frame9, leads51can be connected by tie-bars such that the lead frame9remains flat as shown inFIG. 8(B). The adjacent leads can be connected by tie-bars52on the inner lead side thereof and by tie-bars53on the outer lead side thereof such that the adjacent leads are short-circuited.

Then, the lead frame9can be set in a predetermined die and the terminal casing2incorporating the lead frame9therein as shown inFIG. 9(A)can be formed by injection molding of a polyphenylene sulfide resin (hereinafter referred to as a “PPS resin”) (step S22). Protrusions14and the step12shown inFIG. 3(C)can be formed on the terminal casing2by injection molding. The fastener mounting plates4also can be formed by injection molding such that the fastener mounting plates4are integrated into the terminal casing. In this state, the lead frame9still remains flat as shown inFIG. 9(B). For improving the adhesiveness of the PPS resin to the epoxy resin, a predetermined amount of a phenoxy resin or an ester may be added to the PPS resin.

Then, the tie-bars52on the inner lead side of the lead frame9can be cut off and the inner lead portions30can be formed as shown inFIGS. 10(A) and 10(B)by pressing the inner lead side of the lead frame9perpendicularly to the plane thereof (step S23). At the same time, a protrusion61protruding downwardly can be formed in the central part of the end portion of the inner lead portion30as shown inFIG. 10(C)by the coining work applied to the inner lead portion30.

Then, the insulating circuit board7can be mounted on the terminal casing2as shown inFIGS. 11(A) and 11(B), and the inner lead portions30of the leads51can be brought into contact with the solder layer31as shown inFIG. 11(C)(step S31). At this stage, the radiator plane of the insulating circuit board7protrudes downwardly for a certain length from the distal end faces of the circular bosses23of the fastener mounting plates4as described above. Then, reflow-soldering is conducted in this state (step S32). In detail, the first and second solder layers29and31are made to reflow simultaneously, and the semiconductor chips8are soldered to the insulating circuit board7and the inner lead portions30simultaneously. The solder layers, repelled by the polyimide layers, move to the positions between the inner lead portions30and the electrodes of the semiconductor chips8by self alignment. As a result, the semiconductor chips8also move in an self-aligning manner and become bonded at the respective centered or correct positions. Since the necessary solder thickness is secured between the inner lead portions30and the semiconductor chips8by the protrusions61on the inner lead portions30as shown inFIG. 11(C), a sufficient solder bonding strength is obtained.

Then, preheating is conducted (step S33) and molten epoxy resin3is loaded into the terminal casing2as shown inFIGS. 12(A) and 12(B)(step S34). As shown inFIG. 12(C), the epoxy resin3is loaded through the gap formed by the protrusions14between the terminal casing2and the insulating circuit board7. The epoxy resin3filling the terminal casing2is hardened in a curing furnace (step S35). The epoxy resin3is held stably by the step12of the terminal casing2. For preventing the epoxy resin3from peeling off the semiconductor chips8or the lead frame9, it is preferable to select an epoxy resin exhibiting a thermal expansion coefficient substantially the same as those of the semiconductor chips8and the lead frame9.

In this state, insulation tests are conducted by feeding current to a pair of tie-bars53(step S36). Then, the outer lead portions6are formed, as shown inFIGS. 13(A) and 13(B), by pressing the outer-lead-side portions of the leads51, which have passed the insulation tests, perpendicularly to the plane of the leads51to cut off the tie-bars53such that leads51become separated from each other (step S37). Although the invention has been described in connection with the terminal casing2of a DIP-type, one that extends the outer lead portions6from the both side faces thereof, the terminal casing may be an SIP-type, one that extends the outer lead portions from one side face thereof, or a QFP-type, one that extends the outer lead portions from the upper surface thereof. The package thus can have any of the different outer lead portion configurations.

As described above, the lead frame9in the power semiconductor module1according to the first embodiment have the inner lead portions30and the outer lead portions6. The outer lead portions6are bonded to the semiconductor chips8simultaneously by soldering. Therefore, the number of the constituent parts is reduced as compared with bonding the outer lead portions and the semiconductor chips via bonding wires. Since it is not necessary to bond the outer lead portions to the semiconductor chip one by one, the power semiconductor module1is obtained efficiently. Since the outer lead portions and the semiconductor chips are not connected by bonding wires, a sufficient current capacity is secured.

Wire bonding is not employed in manufacturing the power semiconductor module1according to the present invention. The bonding between the insulating circuit board7and the semiconductor chips8and the bonding between the semiconductor chips8and the lead frame9are conducted simultaneously through one step of reflow-soldering. Therefore, the time for mounting is shortened extremely and a power semiconductor module is manufactured very efficiently.

An aluminum insulating board including the aluminum main substrate26and the insulator resin layer27formed on the aluminum main substrate26as shown inFIGS. 3(A) through 3(C)is used for the insulating circuit board7in the first embodiment. Alternatively, a direct-copper-bond (DCB) insulating board can be used instead of the aluminum insulating board with no problem.

Referring toFIG. 14, the second embodiment of the power semiconductor module201mounts thereon an insulating circuit board207including an insulating ceramic substrate211made of aluminum oxide (AL2O3), aluminum nitride (AlN), silicon nitride (SiN), and such ceramics. A radiator plane212can be formed on the lower surface of the insulating ceramic substrate211by laminating copper foils thereon. Copper foil patterns213can be formed on the upper surface of the insulating ceramic substrate211. Semiconductor chips8can be surface-mounted on the copper foil patterns213via the solder layers29. The protrusions14on the terminal casing2can be brought into contact with the ceramic substrate211.

The Ni plating layers43and the Au plating layers44can be formed on the electrodes of the power semiconductor chips8by electroless plating to improve the solder wetness as in the second embodiment, as described with reference toFIGS. 6(A) and 6(B). Alternatively, the Ni layers and the Au layers can be formed by other techniques. For example, plasma CVD, vapor deposition, sputtering and such film deposition methods can be used in substitution for the electroless plating. Stannic (Sn) layers can be deposited instead of the Ni layers.

The step12can be formed on the upper part in the terminal casing2to strengthen the adhesion of the epoxy resin3to the terminal casing2as in the first embodiment, as shown inFIGS. 3(B) and 3(C). Alternatively, a structure that facilitates hooking the epoxy resin3can be employed. The epoxy resin3can be adhered tightly to the terminal casing2, for example, by sharp cutouts302formed in the upper parts on the inner circumference of the terminal casing2as shown inFIG. 15.

The power semiconductor module1can be mounted on the control circuit board101as shown inFIG. 4of the first embodiment. Alternatively, the power semiconductor module1can be mounted on the control circuit board101in the modified manner as shown inFIGS. 16(A)-17(B). A boss-shaped fastener insertion hold405as shown inFIG. 16(A)can be disposed for positioning the power semiconductor module to the control circuit board101. The fastener insertion holder405is disposed on a fastener mounting plate404of the power semiconductor module such that the fastener insertion holder405protrudes upwardly. The power semiconductor module is positioned on the control circuit board by inserting the fastener insertion holder405into an insertion hole114formed in the control circuit board. A fastener insertion hole406for fastening the power semiconductor module and the control circuit board101to the cooling fin110is formed through the fastener insertion holder405. The fastener insertion hole406works also for the fastener insertion hole22described earlier. The power semiconductor module1and the control circuit board101are fixed to the cooling fin110by fastening the fastener120through the insertion hole406into the fastener hole111of the cooling fin110.

Alternatively, a boss-shaped fastener insertion holder425protruding from a fastener mounting plate424can be provided with a step427, as shown inFIG. 16(B), such that the fastener insertion holder425is coupled and fixed to the control circuit board101at the height, at which the step427is formed. By setting the height of the step427, the positional relation between the outer lead portions6and the control circuit board101can be adjusted, and further, a certain solder thickness can be secured in the reflow of the solder layers103.

Alternatively, a boss-shaped fastener insertion holder435protruding upwardly from a fastener mounting plate434can be disposed as shown inFIG. 17(A)such that the distal end of the fastener insertion holder435is coupled and fixed to the control circuit board101. By setting the height of the fastener insertion holder435, the positional relation between the outer lead portions6and the control circuit board101can be adjusted, and further, a certain solder thickness can be secured in the reflow of the solder layers103. A fastener insertion hole436for securing the power semiconductor module and the control circuit board101to the cooling fin110can be formed through the fastener insertion holder435. The fastener insertion hole436works also for the fastener insertion hole22described earlier. The power semiconductor module1and the control circuit board101can be fixed to the cooling fin110by securing the fastener120through the insertion hole436into the fastener hole111of the cooling fin110.

Alternatively, a boss-shaped fastener insertion holder445tapered to the distal end thereof and protruding upwardly from a fastener mounting plate444is disposed as shown inFIG. 17(B)such that the fastener insertion holder445is coupled and fixed to the insertion hole114of the control circuit board101at a predetermined position on the taper thereof. By appropriately setting the height and the taper of the fastener insertion holder445, the positional relation between the outer lead portions6and the control circuit board101can be adjusted, and further, a certain solder thickness can be secured in the reflow of the solder layers103. A fastener insertion hole436for securing the power semiconductor module1and the control circuit board101to the cooling fin110is formed through the fastener insertion holder445. The fastener insertion hole436works also for the fastener insertion hole22described earlier. The power semiconductor module1and the control circuit board101can be fixed to the cooling fin110by securing the fastener120through the insertion hole436into the fastener hole111of the cooling fin110.

According to the present power module, the semiconductor chips8are surface-mounted on the insulating circuit board7and the lead frame9is surface-mounted on the semiconductor chips8. Alternatively, the so-called insertion mount can be employed and the semiconductor chips8can be bonded to the insulating circuit board7and lead frame9by soldering. Brazing using a brazing filler metal including silver paste and such an electrically conductive adhesive other than the solder can be used alternatively.

The epoxy resin can be used for an insulating sealant. Alternatively, silicone gel and such a gel loading material can be injected into the terminal casing2and hardened therein with no problem. However, the epoxy resin is still preferable, since the epoxy resin exhibits excellent thermal conduction, excellent heat resistance, and high rigidity. When a gel loading material is used, it is necessary to press the upper surface thereof with a resin plate and to pay close precautions.

Although not described specifically in connection with the foregoing embodiments, it is preferable to equalize the thickness of the semiconductor chips8mounted on the insulating circuit board7. By equalize the thickness of the semiconductor chips8, the bend lengths of the lead frame9on the side of the inner leads30can be standardized. As a result, the press die used for forming the bend by pressing is manufactured easily.

Although not described specifically in connection with the foregoing embodiments, copper core balls or nickel core balls having a certain diameter (e.g. form several tens to several hundreds μ m in diameter) can be dispersed into the solder paste to secure a certain solder layer thickness in the reflow of the solder layers.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the present invention. All modifications and equivalents, attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention accordingly is to be defined as set forth in the appended claims.

This application is based on, and claims priority to, Japanese Application No. 2004-274427, filed on 22 Sep. 2004. The disclosure of the priority application, in its entirety, including the drawings, claims, and the specification thereof, are incorporated herein by reference.