SEMICONDUCTOR MODULE, POWER CONVERTER, AND POWER CONVERTER MANUFACTURING METHOD

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2022-135375, filed on Aug. 26, 2022, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION
1. Field of the Invention

The embodiments discussed herein relate to a semiconductor module, a power converter, and a power converter manufacturing method.

2. Background of the Related Art

A semiconductor module includes power devices, and for example, forms an inverter. Such a semiconductor module is used in a power converter. Examples of the power devices include insulated gate bipolar transistors (IGBTs) and power metal-oxide-semiconductor field-effect transistors (MOSFETs). The semiconductor module is constituted by laminating semiconductor chips including power devices, an insulated circuit substrate, and a heat dissipation base.

In the semiconductor module used in the power converter, a cooling module is provided on the rear surface of the heat dissipation base via a thermal grease. Examples of the cooling module include a cooling fin and a cooing device using a coolant. The heat dissipation base of the semiconductor module and the cooling module are joined to each other by screws.

The semiconductor module in which the thermal grease is applied to the heat dissipation base in advance may be shipped, and the cooling module may be attached to the semiconductor module at the shipping destination. In this case, if the thermal grease is in a paste form, the thermal grease may make its surroundings dirty during the shipment. To avoid this, a phase change thermal grease is used instead of such a thermal grease. The phase change thermal grease keeps its solid state at room temperature and, when heated, changes into a paste.

See, for example, the following documents.

- Japanese Laid-open Patent Publication No. 2006-332479.
- Japanese Laid-open Patent Publication No. 2013-251473.
- International Publication Pamphlet No. WO 2019/239997.
- Japanese Laid-open Patent Publication No. 2022-073478.
- Japanese Laid-open Patent Publication No. 2009-277976.
- “Fuji Electric Journal,” Vol. 82, No. 6, 2009, pages 67-71.

At the shipping destination of the semiconductor module that is provided in the above-mentioned power converter, the cooling module is joined to the semiconductor module by screws, and then the phase change thermal grease is changed into a paste. According to the phase change of the phase change thermal grease from solid to liquid, the gap between the heat dissipation base and the cooling module becomes smaller. Therefore, a gap may be generated between the heat dissipation base and each screw, which may reduce the tightening torque between the semiconductor module and the cooling module.

SUMMARY OF THE INVENTION

According to one aspect, there is provided a semiconductor module, including: a semiconductor chip; an insulated circuit substrate including a wiring board on a front surface thereof, the wiring board having the semiconductor chip bonded thereto; a heat dissipation base having a front surface and a rear surface opposite to each other, the front surface having a substrate region to which the insulated circuit substrate is bonded, the rear surface having a heat dissipation region overlapping the substrate region in a plan view of the semiconductor module and a loop-shaped region surrounding the heat dissipation region, the heat dissipation base having a plurality of fastening holes through which fastening members are to be inserted, the fastening holes being located outside the substrate region and being surrounded by the loop-shaped region; a solid heat dissipation member made of a phase change material, provided on the rear surface of the heat dissipation base in the heat dissipation region; and an elastic member on the rear surface of the heat dissipation base in the loop-shaped region.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the basic configuration of a power conversion system according to a first embodiment;

FIG. 2 is an appearance view of a semiconductor module according to the first embodiment;

FIG. 3 is a sectional view of the semiconductor module according to the first embodiment;

FIG. 4 is a plan view (without a case) of the semiconductor module according to the first embodiment;

FIG. 5 is a plan view (without a case or terminals) of the semiconductor module according to the first embodiment;

FIG. 6 is a rear surface view of the semiconductor module according to the first embodiment;

FIG. 7 is an equivalent circuit diagram representing functions of the semiconductor module according to the first embodiment;

FIG. 8 is a flowchart illustrating a power converter manufacturing method according to the first embodiment;

FIG. 9 is a view for describing a cooling module attachment step included in the power converter manufacturing method according to the first embodiment;

FIG. 10 is a view for describing a melting step included in the power converter manufacturing method according to the first embodiment;

FIG. 11 illustrates a cooling module attachment step included in a power converter manufacturing method according to a reference example;

FIG. 12 illustrates a melting step included in the power converter manufacturing method according to the reference example;

FIG. 13 is a rear surface view of a semiconductor module according to the first embodiment (variation);

FIG. 14 is a rear surface view of a semiconductor module according to a second embodiment;

FIG. 15 is a rear surface view of a semiconductor module according to a third embodiment;

FIG. 16 is a rear surface view of a semiconductor module according to a fourth embodiment; and

FIG. 17 is a rear surface view of a semiconductor module according to the fourth embodiment (variation).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments will be described with reference to the accompanying drawings. In the following description, the terms “front surface” and “upper surface” refer to an X-Y surface facing up (in the +Z direction) in a semiconductor module 10 of drawings. Similarly, the term “up” refers to an upward direction (the +Z direction) in the semiconductor module 10 of the drawings. The terms “rear surface” and “lower surface” refer to an X-Y surface facing down (in the −Z direction) in the semiconductor module 10 of the drawings. Similarly, the term “down” refers to a downward direction (the −Z direction) in the semiconductor module 10 of the drawings. The same directionality applies to other drawings, as appropriate. The terms “front surface,” “upper surface,” “up,” “rear surface,” “lower surface,” “down,” and “side surface” are used for convenience to describe relative positional relationships, and do not limit the technical ideas of the embodiment. For example, the terms “up” and “down” are not always related to the vertical directions to the ground. That is, the “up” and “down” directions are not limited to the gravity direction. In addition, in the following description, the term “main component” refers to a component contained at a volume ratio of 80 vol % or more.

First Embodiment

The basic configuration of a power conversion system will be described with reference to FIG. 1. FIG. 1 illustrates the basic configuration of a power conversion system according to a first embodiment. The power conversion system 1 includes a power converter 2, a power supply 3, and a load 4.

The power converter 2 converts direct current power supplied from the power supply 3 to alternating current power that is then supplied to the load 4. This power converter 2 includes a voltage smoothing unit 2a, an inverter unit 2b, and a cooling unit 2c. The voltage smoothing unit 2a smooths a direct current voltage supplied from the power supply 3. The voltage smoothing unit 2a may include a smoothing circuit that has this function. The inverter unit 2b converts the direct current voltage smoothed by the voltage smoothing unit 2a to an alternating current voltage that is then applied to the load 4. The inverter unit 2b may include an inverter circuit that has this function. The inverter unit 2b includes a semiconductor module 10, which will be described later. In addition to this, the inverter unit 2b includes a control driving circuit that controls the semiconductor module 10, and others. In this connection, the load 4 is a motor, for example. The cooling unit 2c cools the voltage smoothing unit 2a and the inverter unit 2b. For example, the cooling unit 2c is a cooling fin or a cooling device that achieves the cooling through circulation of a coolant therein. The cooling unit 2c corresponds to a cooling module 90, which will be described later.

The following describes the semiconductor module 10 of the inverter unit 2b provided in the power converter 2 with reference to FIG. 2. FIG. 2 is an appearance view of a semiconductor module according to the first embodiment. Components, which will be described later, of the semiconductor module 10 are housed in a case 60, as illustrated in FIG. 2. In this connection, a heat dissipation base 30, which is rectangular in plan view, is provided on the rear surface (on the rear surface side of the case 60) of the semiconductor module 10 (see FIGS. 3 and 4).

The case 60 includes a lid 61, sidewalls 62a to 62d, and terminal ports 63 and 64. The lid 61 has terminal blocks 61a, 61b, and 61c arranged at the center thereof in the long-side direction thereof. Screw holes 61a1, 61b1, and 61c1 are respectively formed in the front surfaces of the terminal blocks 61a, 61b, and 61c. First to third wiring members 71, 72, and 74 extend upward from the terminal blocks 61a, 61b, and 61c, respectively. FIG. 2 illustrates the case where the first to third wiring members 71, 72, and 74 extend upward (in the +Z direction). The extending first to third wiring members 71, 72, and 74 are bent toward the front surfaces of the terminal blocks 61a, 61b, and 61c, respectively, so that opening holes formed in the first to third wiring members 71, 72, and 74 face the screw holes 61a1, 61b1, and 61c1, respectively, and screws are tightened into the opening holes and the corresponding screw holes 61a1, 61b1, and 61c1 together. In addition, the case 60 surrounds fastening holes 31a to 31d formed in the heat dissipation base 30, and has fixing holes 65 at the four corners thereof in plan view so that the fixing holes 65 face the fastening holes 31a to 31d, respectively.

The sidewalls 62a to 62d surround in order the four sides of the heat dissipation base 30. The sidewalls 62a to 62d surround the components disposed on the heat dissipation base 30 (see FIG. 3). In this connection, the sidewalls 62a to 62d are firmly attached to the heat dissipation base 30 using an adhesive. The terminal ports 63 and 64 are provided in the sidewall 62d. Control terminals 75 and 76 are exposed from the terminal ports 63 and 64, respectively. In this connection, the fixing holes 65 are formed in the vicinity of the corners each defined by two of the sidewalls 62a to 62d. The semiconductor module 10 may be screwed to a cooling module, which will be described later, through the fixing holes 65.

The sidewalls 62a to 62d, terminal ports 63 and 64, and fixing holes 65 included in the case 60 are integrally molded using a resin. In addition, the lid 61 is also integrally molded using the resin. The resin here contains a thermoplastic resin as a main component. Examples of the thermoplastic resin include a polyphenylene sulfide resin, a polybutylene terephthalate resin, a polybutylene succinate resin, a polyamide resin, and an acrylonitrile butadiene styrene resin. The case 60 may be formed by attaching the lid 61 that is separately made to the opening formed by the sidewalls 62a to 62d using an adhesive.

The following describes the components housed in the semiconductor module 10 with reference to FIGS. 3 to 6. FIG. 3 is a sectional view of the semiconductor module according to the first embodiment. FIG. 4 is a plan view (without a case) of the semiconductor module according to the first embodiment. FIG. 5 is a plan view (without a case or terminals) of the semiconductor module according to the first embodiment. FIG. 6 is a rear surface view of the semiconductor module according to the first embodiment. In this connection, FIG. 3 is a sectional view taken along a dash-dotted line Y-Y of FIG. 2. FIG. 4 is a plan view of the semiconductor module 10 of FIG. 2 without the case 60. FIG. 5 is a plan view of the semiconductor module 10 of FIG. 2 without the case 60 or the first to third wiring members 71, 72, and 74.

As illustrated in FIGS. 3 to 5, the semiconductor module 10 includes insulated circuit substrates 20a and 20b and the heat dissipation base 30 having the insulated circuit substrates 20a and 20b disposed on the front surface thereof. In the semiconductor module 10, these components are housed in the case 60. Semiconductor chips 41a to 44a and 41b to 44b are disposed on the insulated circuit substrates 20a and 20b, respectively. In addition, the semiconductor module 10 includes the first to third wiring members 71, 72, and 74. For example, the first to third wiring members 71, 72, and 74 are plate-like lead frames.

The case 60 is provided on the periphery of the heat dissipation base 30. This case 60 has the sidewalls 62a to 62d that surround the insulated circuit substrates 20a and 20b, and the lid 61 provided at the top of the opening formed by the sidewalls 62a to 62d. The semiconductor chips 41a to 44a and 41b to 44b, insulated circuit substrates 20a and 20b (and bonding wires 51a to 55a, 51b to 56b, and 57 to 59) are housed in the space surrounded by the case 60 and heat dissipation base 30. In addition, the semiconductor chips 41a to 44a and 41b to 44b, insulated circuit substrates 20a and 20b (and bonding wires 51a to 55a, 51b to 56b, and 57 to 59) may be sealed by a sealing member 80. The sealing member 80 is silicone, for example. In addition, end portions of the first to third wiring members 71, 72, and 74 for electrical connection with an external device are exposed on the lid 61. In this connection, the illustration of the control terminals 75 and 76 illustrated in FIG. 2 is omitted in FIGS. 3 to 5.

One end portion of each of the first to third wiring members 71, 72, and 74 is connected to the insulated circuit substrate 20a or the insulated circuit substrate 20b inside the case 60. In addition, the other end portion thereof extends to the outside from the lid 61. The other end portion may be connected to the power supply 3 or load 4, not illustrated.

More specifically, the one end portion of the first wiring member 71 is electrically and mechanically connected to the wiring boards 23a3 and 23a5 of the insulated circuit substrate 20a. The one end portion of the first wiring member 71 is electrically connected to the semiconductor chips 41a, 42a, 43a, and 44a via the wiring boards 23a3 and 23a5 and the bonding wires 53a and 54a. The other end portion (first external connection portion 71d) of the first wiring member 71 extends to the outside from the lid 61 and is bent toward the front surface of the lid 61.

The one end portion of the second wiring member 72 is electrically and mechanically connected to the wiring board 23b2 of the insulated circuit substrate 20b. The one end portion of the second wiring member 72 is electrically connected to the semiconductor chips 41b, 42b, 43b, and 44b via the wiring board 23b2. The other end portion (second external connection portion 72d) of the second wiring member 72 extends to the outside from the lid 61 and is bent toward the front surface of the lid 61.

The one end portion of the third wiring member 74 is electrically and mechanically connected to the wiring board 23a2 of the insulated circuit substrate 20a. The one end portion of the third wiring member 74 is electrically connected to the semiconductor chips 41a, 42a, 43a, and 44a via the wiring board 23a2. The other end portion (third external connection portion 74d) of the third wiring member 74 extends to the outside from the lid 61 and is bent toward the front surface of the lid 61.

A wiring unit 70 includes the above-described first and second wiring members 71 and 72 and a wiring holding unit 73. In the wiring unit 70, parts of the first and second wiring members 71 and 72 are integrally formed with the wiring holding unit 73. Note that the wiring holding unit 73 enables the first and second wiring members 71 and 72 to keep insulation therebetween.

The insulated circuit substrates 20a and 20b include insulating plates 21a and 21b, metal plates 22a and 22b formed on the rear surfaces of the insulating plates 21a and 21b, and wiring boards 23a1 to 23a5 and 23b1 to 23b5 formed on the front surfaces of the insulating plates 21a and 21b, respectively. In this connection, the insulating plates 21a and 21b and metal plates 22a and 22b are rectangular in plan view. In addition, the corners of the insulating plates 21a and 21b and metal plates 22a and 22b may be rounded or chamfered. In plan view, the metal plates 22a and 22b are smaller in size than the insulating plates 21a and 21b and are formed inside the insulating plates 21a and 21b, respectively.

The insulating plates 21a and 21b are made of a ceramic material with high thermal conductivity as a main component. The ceramic material contains aluminum oxide, aluminum nitride, or silicon nitride as a main component, for example.

The metal plates 22a and 22b are made of a metal with high thermal conductivity as a main component. Examples of the metal here include copper, aluminum, and an alloy containing at least one of these. Plating may be performed on the surfaces of the metal plates to improve their corrosion resistance. Examples of the plating material used here include nickel, a nickel-phosphorus alloy, and a nickel-boron alloy.

The wiring boards 23a1 to 23a5 and 23b1 to 23b5 are made of a metal with high electrical conductivity as a main component. Examples of the metal here include copper, aluminum, and an alloy containing at least one of these. Plating may be performed on the surfaces of the wiring boards 23a1 to 23a5 and 23b1 to 23b5 to improve their corrosion resistance. Examples of the plating material used here include nickel, a nickel-phosphorus alloy, and a nickel-boron alloy.

For example, the above-described wiring boards 23a1 to 23a5 and 23b1 to 23b5 are obtained by forming a metal layer on each front surface of the insulating plates 21a and 21b and performing etching or the like on the metal layer. Alternatively, the wiring boards 23a1 to 23a5 and 23b1 to 23b5 cut out of a metal layer in advance may be press-bonded to the front surfaces of the insulating plates 21a and 21b. In this connection, the shapes and quantity of the wiring boards 23a1 to 23a5 and 23b1 to 23b5 illustrated in FIGS. 3 to 5 are just an example.

As the insulated circuit substrates 20a and 20b configured as above, direct copper bonding (DCB) substrates and active metal brazed (AMB) substrates may be used, for example. The insulated circuit substrates 20a and 20b are able to conduct heat generated by the semiconductor chips 41a to 44a and 41b to 44b through the wiring boards 23a2 and 23b2, insulating plates 21a and 21b, and metal plates 22a and 22b to the outside.

In addition, the one end portion (first leg portion 71a (see FIG. 3)) of the first wiring member 71 is connected to the wiring boards 23a3 and 23a5 of the insulated circuit substrate 20a via a solder (not illustrated). The one end portion (second leg portion 72a (see FIG. 3)) of the second wiring member 72 is connected to the wiring board 23b2 of the insulated circuit substrate 20b via the solder (not illustrated). The one end portion (third leg portion 74a (see FIG. 3)) of the third wiring member 74 is connected to the wiring board 23a2 of the insulated circuit substrate 20a via the solder (not illustrated). The solder may be a lead-free solder. For example, the lead-free solder contains, as a main component, at least any one of a tin-silver-copper alloy, a tin-zinc-bismuth alloy, a tin-copper alloy, and a tin-silver-indium-bismuth alloy. In addition, the solder may contain an additive. Examples of the additive include nickel, germanium, cobalt, antimony, and silicon. The solder containing the additive exhibits improved wettability, gloss, and bonding strength, which results in improving the reliability. In this connection, rectangles depicted in the wiring boards 23a2, 23a3, 23a5, 23b2 represent the bonding areas of the third, first, and second wiring members 74, 71, and 72. In addition, for example, ultrasonic bonding may be performed for the bonding, instead of using the solder.

The semiconductor chips 41a to 44a and 41b to 44b are made of silicon as a main component. The semiconductor chips 41a, 42a, 41b, and 42b are switching elements. A switching element is an IGBT or a power MOSFET, for example. The semiconductor chips 41a, 42a, 41b, and 42b of this type each have a drain electrode or collector electrode serving as an input electrode (main electrode) on the rear surface thereof. In addition, the semiconductor chips 41a, 42a, 41b, and 42b each have a gate electrode 41a1, 42a1, 41b1, or 42b1 serving as a control electrode and a source electrode or emitter electrode serving as an output electrode (main electrode) on the front surface thereof. The rear surfaces of these semiconductor chips 41a, 42a, 41b, and 42b are bonded to the wiring boards 23a2 and 23b2 using the above-described solder (not illustrated). In addition, a sintered metal may be used, instead of the solder. The sintered metal contains silver or a silver alloy as a main component. The above solder and sintered metal may be used not only for the bonding between the semiconductor chips 41a to 44a and 41b to 44b and the wiring boards 23a2 and 23b2 but also for bonding the first to third wiring members 71, 72, and 74 to the wiring boards 23a3, 23a5, 23b2, and 23a2.

The semiconductor chips 43a, 44a, 43b, and 44b are diode elements. The diode elements are free wheeling diodes (FWDs). For example, such a diode element includes a Schottky barrier diode (SBD) or a PN junction diode. The semiconductor chips 43a, 44a, 43b, and 44b of this type each have a cathode electrode serving as an output electrode (main electrode) on the rear surface thereof, and an anode electrode serving as an input electrode (main electrode) on the front surface thereof. The rear surfaces of these semiconductor chips 43a, 44a, 43b, and 44b are bonded to the wiring boards 23a2 and 23b3 using the solder (not illustrated).

In this connection, each semiconductor chip 41a to 44a and 41b to 44b may be a reverse-conducting (RC)-IGBT element. An RC-IGBT element is formed by integrating a switching element and a diode element into one semiconductor chip. Alternatively, in place of the semiconductor chips 41a to 44a and 41b to 44b, semiconductor chips that are power MOSFETs made of silicon carbide as a main component may be used. Such a semiconductor chip includes FWD together with power MOSFET.

The above-described insulated circuit substrates 20a and 20b and semiconductor chips 41a to 44a and 41b to 44b are wired using the following bonding wires 51a to 55a, 51b to 56b, and 57 to 59.

The bonding wires 51a and 52a for control wires are electrically connected to the wiring board 23a1 and the gate electrodes 41a1 and 42a1 of the semiconductor chips 41a and 42a. The bonding wires 53a and 54a are electrically connected to the wiring boards 23a3 and 23a5, the main electrodes of the semiconductor chips 41a and 42a, and the main electrodes of the semiconductor chips 43a and 44a.

The bonding wires 51b and 52b for control wires are electrically connected to the wiring board 23b1 and the gate electrodes 41b1 and 42b1 of the semiconductor chips 41b and 42b. The bonding wires 53b and 54b are electrically connected to the wiring boards 23b5 and 23b3, the main electrodes of the semiconductor chips 41b and 42b, and the main electrodes of the semiconductor chips 43b and 44b. The bonding wires 55b and 56b are electrically connected to the wiring board 23b4, the main electrodes of the semiconductor chips 41b and 42b, and the main electrodes of the semiconductor chips 43b and 44b.

In addition, the bonding wires 57 and 58 are electrically connected to the wiring board 23a2 of the insulated circuit substrate 20a and the wiring boards 23b3 and 23b5 of the insulated circuit substrate 20b, respectively. The bonding wires 59 are electrically connected to the wiring board 23a4 of the insulated circuit substrate 20a and the wiring board 23b4 of the insulated circuit substrate 20b.

In this connection, the bonding wires 51a to 55a, 51b to 56b, and 57 to 59 are made of a metal with high electrical conductivity, such as aluminum or copper, or an alloy containing at least one of these.

As illustrated in FIG. 3, the wiring unit 70 includes the above-described first and second wiring members 71 and 72 and the wiring holding unit 73 covering and holding the first and second wiring members 71 and 72. The first and second wiring members 71 and 72 are plate-like lead frames. The wiring holding unit 73 is made of a resin with insulation, for example, a thermoplastic resin. Examples of the resin here include a polyphenylene sulfide resin, a polybutylene terephthalate resin, a polybutylene succinate resin, a polyamide resin, and an acrylonitrile butadiene styrene resin. In addition, an insulating ceramic filler may be added to such a resin. Examples of the ceramic filler here include oxide, nitride, and carbide. Specific examples include silicon, aluminum, and boron.

The first wiring member 71 includes the first leg portion 71a, a first vertical portion 71b, and the first external connection portion 71d. One end portion of the first leg portion 71a of the first wiring member 71 is bonded to the wiring boards 23a3 and 23a5 of the insulated circuit substrate 20a. The first vertical portion 71b is connected to the other end portion of the first leg portion 71a and extends vertically upward (in the +Z direction). The first external connection portion 71d is connected to the first vertical portion 71b, extends to the outside from the lid 61, and is bent toward the front surface of the lid 61. The wiring boards 23a3 and 23a5 are wire-bonded to the main electrodes on the front surfaces of the semiconductor chips 41a, 42a, 43a, and 44a using the bonding wires 53a and 54a. Therefore, the first wiring member 71 is electrically connected to the main electrodes on the front surfaces of the semiconductor chips 41a, 42a, 43a, and 44a, so that a main current flows therethrough.

In addition, the second wiring member 72 includes the second leg portion 72a, a second vertical portion 72b, a second horizontal portion 72c, and the second external connection portion 72d. One end portion of the second leg portion 72a of the second wiring member 72 is bonded to the wiring board 23b2 of the insulated circuit substrate 20b. The second vertical portion 72b is connected to the other end portion of the second leg portion 72a and extends vertically upward (in the +Z direction). The second horizontal portion 72c extends from the second vertical portion 72b in the +X direction. The second external connection portion 72d is connected to the second horizontal portion 72c, extends to the outside from the lid 61, and is bent toward the front surface of the lid 61. The wiring board 23b2 is electrically connected to the main electrodes on the rear surfaces of the semiconductor chips 41b, 42b, 43b, and 44b. Therefore, the second wiring member 72 is electrically connected to the main electrodes on the rear surfaces of the semiconductor chips 41b, 42b, 43b, and 44b, so that a main current flows therethrough.

In addition, the third wiring member 74 is a plate-like lead frame as well. The third wiring member 74 includes the third leg portion 74a, a third horizontal portion 74c, and the third external connection portion 74d. One end portion of the third leg portion 74a of the third wiring member 74 is bonded to the wiring board 23a2 of the insulated circuit substrate 20a. The third horizontal portion 74c is connected to the other end portion of the third leg portion 74a and extends in the +X direction. The third external connection portion 74d is connected to the third horizontal portion 74c, extends to the outside from the lid 61, and is bent toward the front surface of the lid 61. The wiring board 23a2 is electrically connected to the main electrodes on the rear surfaces of the semiconductor chips 41a to 44a. Therefore, the third wiring member 74 is electrically connected to the main electrodes on the rear surfaces of the semiconductor chips 41a to 44a, so that a main current flows therethrough.

In this connection, the control terminals 75 and 76 are electrically connected to the wiring boards 23a1 and 23b1, respectively, although the detailed illustration is omitted. A control signal input from the outside is input to the gate electrodes 41a1, 42a1, 41b1, and 42b1 of the semiconductor chips 41a, 42a, 41b, and 42b via the control terminals 75 and 76, wiring boards 23a1 and 23b1, and bonding wires 51a, 52a, 51b, and 52b.

The first to third wiring members 71, 72, and 74 and control terminals 75 and 76 are made of a metal with high electrical conductivity as a main component. Examples of the metal here include aluminum, copper, iron, nickel, and an alloy containing at least one of these. Plating may be performed on the surfaces of the first to third wiring members 71, 72, and 74 to improve their corrosion resistance. Examples of the plating material used here include nickel, a nickel-phosphorus alloy, and a nickel-boron alloy. In addition, for the bonding between the first to third wiring members 71, 72, and 74 and the wiring boards 23a3, 23a5, 23b2, and 23a2, a solder or sintered metal may be used, as in the case of bonding the semiconductor chips 41a to 44a and 41b to 44b. Alternatively, the first to third wiring members 71, 72, and 74 may be bonded directly to the wiring boards 23a3, 23a5, 23b2, and 23a2 by ultrasonic waves or a laser.

The heat dissipation base 30 has a plate shape and is rectangular in plan view. The heat dissipation base 30 has a long side 30a, a short side 30b, a long side 30c, and a short side 30d on the four sides of the front surface 32a and rear surface 32b. A substrate region 32a1 where the insulated circuit substrates 20a and 20b are disposed is set at the center of the front surface 32a of the heat dissipation base 30. In plan view, the fastening holes 31a to 31d that extend from the front surface 32a to the rear surface 32b of the heat dissipation base 30 are formed in order at the respective corners with the substrate region 32a1 therebetween in the heat dissipation base 30. For example, the fastening holes 31a and 31c have the substrate region 32a1 therebetween on the diagonal line.

This heat dissipation base 30 is made of a metal with high thermal conductivity as a main component. Examples of the metal here include copper, aluminum, and an alloy containing at least one of these. Plating may be performed on the surface of the heat dissipation base 30 to improve its corrosion resistance. Examples of the plating material used here include nickel, a nickel-phosphorus alloy, and a nickel-boron alloy.

In addition, a heat dissipation region 32b1 is set at the center of the rear surface 32b of the heat dissipation base 30. The heat dissipation region 32b1 is set on the opposite side of the substrate region 32a1 set on the front surface 32a for disposing the insulated circuit substrates 20a and 20b. A plurality of solid heat dissipation members 33 made of a phase change material are provided in the heat dissipation region 32b1. The heat dissipation members 33 are phase change thermal grease. More specifically, the heat dissipation members 33 are made from a phase change material that is solid and when heated, melts into a paste. Such a material contains a thermoplastic resin as a main component and also contains a phase change material as a binder. Examples of the thermoplastic resin include a polyphenylene sulfide resin, a polybutylene terephthalate resin, a polybutylene succinate resin, a polyamide resin, and an acrylonitrile butadiene styrene resin. The heat dissipation members 33 are solid at room temperature, and are softened (change into a paste) at a temperature ranging from 40° C. to 60° C., inclusive. In the case of FIG. 6, the solid heat dissipation members 33 each have a circular tablet shape in plan view and are arranged vertically and horizontally in a matrix form in the heat dissipation region 32b1. In this connection, the arrangement of the heat dissipation members 33 illustrated in FIG. 6 is an example. The shape of each heat dissipation member 33 in plan view is not limited to be circular, but may be rectangular or triangle. Alternatively, triangular heat dissipation members 33 may be arranged at the corners of the heat dissipation region 32b1, and circular heat dissipation members 33 may be arranged inside the heat dissipation region 32b1.

In addition, a loop-shaped region 32b2 is set on the rear surface 32b of the heat dissipation base 30. The loop-shaped region 32b2 has a continuous loop shape surrounding the fastening holes 31a to 31d and heat dissipation region 32b1. In the case of FIG. 6, the loop-shaped region 32b2 corresponds to the outer periphery of the rear surface 32b of the heat dissipation base 30, includes subregions that are respectively parallel to the long side 30a, short side 30b, long side 30c, and short side 30d in this order, and have rounded corners. Elastic members 34 are provided in the loop-shaped region 32b2 of the heat dissipation base 30. The elastic members 34 contain a low-hardness material with heat dissipation as a main component. For example, such a material is silicone. The heights of the elastic members 34 measured from the rear surface 32b of the heat dissipation base 30 may be substantially equal to or greater than those of the heat dissipation members 33. In addition, the width of the loop-shaped region 32b2 in which the elastic members 34 are provided is set so that, when the elastic members 34 are sandwiched between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 of the cooling module 90, as will be described later, the elastic members 34 do not deform but remain stable.

In addition, in the case of FIG. 6, the elastic members 34 are provided at the four corners of the loop-shaped region 32b2. These elastic members 34 are L-shaped in plan view. In order to keep the gap stable between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 of the cooling module 90, as described later, for example, the elastic member 34 of FIG. 6 adjacent to the fastening hole 31a extends at least to positions corresponding to the boundary points of the fastening hole 31a closest to the long side 30a and short side 30b. The same applies to the other elastic members 34.

The following describes an equivalent circuit representing functions of the semiconductor module 10 with reference to FIG. 7. FIG. 7 is an equivalent circuit diagram representing functions of the semiconductor module according to the first embodiment. As illustrated in FIG. 7, the semiconductor module 10 has a half-bridge circuit with an upper arm part A and a lower arm part B. The upper arm part A of the semiconductor module 10 includes the insulated circuit substrate 20b, the bonding wires 51b to 56b provided on the insulated circuit substrate 20b, the semiconductor chips 41b to 44b, and the second wiring member 72. The upper arm part A also includes the bonding wires 57 to 59, the wiring board 23a2 of the insulated circuit substrate 20a, and the third wiring member 74 disposed on the wiring board 23a2.

The lower arm part B of the semiconductor module 10 includes the insulated circuit substrate 20a, the bonding wires 51a to 55a provided on the insulated circuit substrate 20a, the semiconductor chips 41a to 44a, and the first wiring member 71. The lower arm part B also includes the third wiring member 74. In addition, the two insulated circuit substrates 20a and 20b are connected with the bonding wires 57 to 59. With this configuration, the upper arm part A and the lower arm part B are connected to each other. Thus, the semiconductor module 10 functions as a half-bridge circuit with the upper arm part A and the lower arm part B.

In this semiconductor module 10, a wire connecting a connection point P connected to the positive electrode of the power supply 3 (see FIG. 1) and a connection point C1 connected to the input electrodes of the semiconductor chips 41b and 42b corresponds to the second wiring member 72. That is, the second wiring member 72 is a P terminal forming a positive-electrode input terminal in the half-bridge circuit. A wire connecting a connection point M connected to the terminal of the load 4 (see FIG. 1) and a connection point E1C2 connected to the output electrodes of the semiconductor chips 41b and 42b and the input electrodes of the semiconductor chips 41a and 42a corresponds to the third wiring member 74. That is, the third wiring member 74 is an M terminal forming an output terminal in the half-bridge circuit. A wire connecting a connection point N connected to the negative electrode of the power supply 3 and a connection point E2 connected to the output electrodes of the semiconductor chips 41a and 42a corresponds to the first wiring member 71. That is, the first wiring member 71 is an N terminal forming a negative-electrode input terminal in the half-bridge circuit.

The following describes a method of manufacturing the power converter 2 with the above-described semiconductor module 10 with reference to FIG. 8. FIG. 8 is a flowchart illustrating a power converter manufacturing method according to the first embodiment. FIG. 9 is a view for describing a cooling module attachment step included in the power converter manufacturing method according to the first embodiment. FIG. 10 is a view for describing a melting step included in the power converter manufacturing method according to the first embodiment.

First, a semiconductor module manufacturing step of manufacturing the semiconductor module 10 is performed (step S1). In manufacturing the semiconductor module 10, which is included in the power converter 2, first, a preparation step of preparing components of the semiconductor module 10 is performed (step S1a). For example, the components include the semiconductor chips 41a to 44a and 41b to 44b, insulated circuit substrates 20a and 20b, heat dissipation base 30, wiring unit 70, third wiring member 74, case 60, and the raw materials of the heat dissipation members 33 and elastic members 34. In addition to these components, other components needed for manufacturing the semiconductor module 10 and manufacturing equipment are prepared.

Then, an assembly step of assembling the semiconductor module 10 is performed (step S1b). The insulated circuit substrates 20a and 20b are disposed via a solder plate in the substrate region 32al on the front surface 32a of the heat dissipation base 30. The semiconductor chips 41a to 44a and 41b to 44b are each disposed via a solder plate on the wiring board 23a2 of the insulated circuit substrate 20a or the wiring board 23b2 of the insulated circuit substrate 20b. Then, by heating and melting the solder plates into solder and curing the solder, the heat dissipation base 30, insulated circuit substrates 20a and 20b, and semiconductor chips 41a to 44a and 41b to 44b are bonded in order. Then, wiring is performed using the bonding wires 51a to 55a, 51b to 56b, 57, 58, and 59, as illustrated in FIG. 5. In addition, the first to third wiring members 71, 72, and 74 are bonded at predetermined positions on the insulated circuit substrates 20a and 20b. Then, the case 60 is attached to the outer periphery of the heat dissipation base 30 via an adhesive. In this connection, the sealing member 80 is applied to fill the inside of the case 60.

Then, a heat dissipation member arranging step of arranging the plurality of heat dissipation members 33 to the rear surface 32b of the heat dissipation base 30 of the semiconductor module 10 is performed (step S1c). The plurality of heat dissipation members 33 in a solid state are arranged in the heat dissipation region 32b1 on the rear surface 32b of the heat dissipation base 30. For example, this arrangement is performed by a dispensing or printing method.

Then, an elastic member application step of applying the elastic members 34 to the loop-shaped region 32b2 on the rear surface 32b of the heat dissipation base 30 is performed (step S1d). The elastic members 34 are applied to the corners of the loop-shaped region 32b2 on the rear surface 32b of the heat dissipation base 30 by a dispenser. In the manner described above, the semiconductor module 10 illustrated in FIGS. 2 to 6 is manufactured.

Thus manufactured semiconductor module 10 may be shipped to a place where the power converter 2 is to be assembled, for example. Since the heat dissipation members 33 of the semiconductor module 10 to be carried are not in a paste state but in a solid state because of the shipment, the heat dissipation members 33 do not adhere to their surroundings. It is thus possible to carry the semiconductor module 10 reliably, without allowing the heat dissipation members 33 to make their surroundings dirty or reducing the volume of the heat dissipation members 33. In this connection, step S1c and step S1d may be performed simultaneously or in a reversed order.

Then, a cooling module attachment step of attaching thus manufactured semiconductor module 10 to a cooling module is performed (step S2). Here, the semiconductor module 10 is arranged on the cooling surface 91 of the cooling module 90. At this time, the semiconductor module 10 is arranged such that the fastening holes 31a to 31d of the semiconductor module 10 are aligned to the fastening holes (not illustrated) of the cooling module 90. In this connection, for example, the cooling module 90 may be a cooling fin or a cooling device that achieves cooling through circulation of a coolant. In the first embodiment, the cooling module 90 is a cooing fin, for example. The cooling surface 91 of the cooling module 90 may be substantially flat.

The screws 35 are inserted into the fastening holes 31a to 31d of the semiconductor module 10 and are then tightened into the fastening holes of the cooling module 90. By the tightening of the screws 35, the heat dissipation members 33 are sandwiched between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 of the cooling module 90, as illustrated in FIG. 9. In addition, the elastic members 34 are sandwiched between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 of the cooling module 90. In this manner, the cooling module 90 is attached to the semiconductor module 10, thereby obtaining the power converter 2.

After that, a melting step of melting the heat dissipation members 33 is performed (step S3). When heated, the heat dissipation members 33 change from solid to paste (liquid). For example, this heating is achieved by inputting a control signal to the semiconductor chips 41a to 44a and 41b to 44b of the power converter 2 configured at step S2. When a current flows through the semiconductor chips 41a to 44a and 41b to 44b, the semiconductor chips 41a to 44a and 41b to 44b generate heat. The heat from the semiconductor chips 41a to 44a and 41b to 44b is conducted from the heat dissipation base 30 to the heat dissipation members 33, which melts the heat dissipation members 33. At this time, as illustrated in FIG. 10, the heat dissipation members 33 melt, but the gap between the cooling surface 91 of the cooling module 90 and the rear surface 32b of the heat dissipation base 30 is kept by the elastic members 34. Therefore, the gap is not narrowed, but the melting heat dissipation members 33 spread in the gap.

The following describes a reference example in which the elastic members 34 are not provided on the rear surface 32d of the heat dissipation base 30 of the semiconductor module 10, with reference to FIGS. 11 and 12. FIG. 11 illustrates a cooling module attachment step included in a power converter manufacturing method according to the reference example. FIG. 12 illustrates a melting step included in the power converter manufacturing method according to the reference example.

In the case of the reference example as well, a semiconductor module 100 and then a power converter 2 are manufactured according to the flowchart of FIG. 8. However, in the semiconductor module 100 of the reference example, only the heat dissipation members 33 are provided on the rear surface 32b of the heat dissipation base 30, but the elastic members 34 are not provided. The other configuration is the same as that of the semiconductor module 10.

A cooling module attachment step of attaching this semiconductor module 100 to the cooling module 90 is performed (step S2). The semiconductor module 100 is arranged on the cooling surface 91 of the cooling module 90. At this time, the semiconductor module 100 is arranged such that the fastening holes 31a to 31d of the semiconductor module 100 are aligned to the fastening holes (not illustrated) of the cooling module 90. Then, the screws 35 are inserted into the fastening holes 31a to 31d of the semiconductor module 100 and are then tightened into the fastening holes of the cooling module 90. By the tightening of the screws 35, the heat dissipation members 33 are sandwiched between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 of the cooling module 90, as illustrated in FIG. 11. In this manner, the cooling module 90 is attached to the semiconductor module 100, thereby obtaining the power converter 2.

After that, a melting step of melting the heat dissipation members 33 is performed (step S3). The heating for this melting is achieved in the same manner as that in the first embodiment. When the heat dissipation members 33 melt, the melting heat dissipation members 33 are sandwiched between the cooling surface 91 of the cooling module 90 and the rear surface 32b of the heat dissipation base 30, and their thicknesses are reduced, as illustrated in FIG. 12. In addition, the melting heat dissipation members 33 spread over the cooling surface 91 of the cooling module 90. Thereby, a gap G is generated between the front surface 32a of the heat dissipation base 30 and each screw 35. Therefore, the tightening torque of the screws 35 joining the semiconductor module 100 to the cooling module 90 is reduced. This leads to a reduction in the heat dissipation of the semiconductor module 100, and thus may reduce the reliability of the power converter 2.

The above-described semiconductor module 10 includes the following components: the semiconductor chips 41a to 44a and 41b to 44b; the insulated circuit substrates 20a and 20b including the wiring boards 23a2 and 23b2 at the front surfaces thereof, the wiring boards 23a2 and 23b2 having the semiconductor chips 41a to 44a and 41b to 44b bonded thereto; and the heat dissipation base 30 having the substrate region 32a1 set on the front surface 32a thereof and the fastening holes 31a to 31d located outside the substrate region 32a1 with the substrate region 32a1 therebetween in plan view, the substrate region 32a1 having the insulated circuit substrates 20a and 20b bonded thereon, the fastening holes 31a to 31d allowing the screws 35 to go through. In addition, the semiconductor module 10 includes the solid heat dissipation members 33 made of a phase change material provided in the heat dissipation region 32b1 that is set on the opposite side of the substrate region 32a1 on the rear surface 32b of the heat dissipation base 30; and the elastic members 34 provided in the loop-shaped region 32b2 that is set on the rear surface 32b of the heat dissipation base 30 so as to surround the fastening holes 31a to 31d and the heat dissipation region 32b1.

This semiconductor module 10 is arranged on the cooling module 90, and is joined to the cooling module 90 by the screws 35. The cooling module 90 has the cooling surface 91. The cooling surface 91 is provided on the rear surface 32b of the heat dissipation base 30 with the elastic members 34 therebetween, and the screws 35 are inserted into the fastening holes 31a to 31d to fasten the heat dissipation base 30, so that the cooling surface 91 and the heat dissipation base 30 sandwich the elastic members 34 therebetween. The heat dissipation members 33 are sandwiched between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 and are located inside the elastic members 34.

In this case, when the heat dissipation members 33 melt, the gap between the heat dissipation base 30 and the cooling module 90 is kept by the elastic members 34. Therefore, no gap is generated between the heat dissipation base 30 and each screw 35, which prevents a reduction in the tightening torque of the screws 35 joining the semiconductor module 10 to the cooling module 90. In addition, since the gap between the heat dissipation base 30 and the cooling module 90 is kept, the melting heat dissipation members 33 sufficiently spread in the gap. This prevents a reduction in the heat dissipation of the semiconductor module 10, and thus prevents a reduction in the reliability of the power converter 2.

In this connection, the above description relates to the case where the fastening holes 31a to 31d are formed at the four corners of the heat dissipation base 30 of the semiconductor module 10. The locations of the fastening holes 31a to 31d are not limited to the four corners of the heat dissipation base 30 of the semiconductor module 10. For example, fastening holes may be formed at the centers of the short sides 30b and 30d of the heat dissipation base 30 of the semiconductor module 10. This case will be described with reference to FIG. 13. FIG. 13 is a rear surface view of a semiconductor module according to the first embodiment (variation).

Fastening holes 31e and 31f are formed at the centers of the short sides 30b and 30d of the heat dissipation base 30 of the semiconductor module 10 of FIG. 13. In this connection, although not illustrated, fastening holes are also formed in the cooling module 90 so as to face the fastening holes 31e and 31f. In addition, the fastening holes 31e and 31f are formed in the heat dissipation base 30 so that the substrate region 32a1 (the heat dissipation region 32b1 on the opposite side thereof) is located therebetween in plan view.

In this case as well, the loop-shaped region 32b2 may be set so as to surround the fastening holes 31e and 31f and heat dissipation region 32b1 on the rear surface 32b of the heat dissipation base 30. In the case of FIG. 13, the loop-shaped region 32b2 corresponds to the outer periphery of the rear surface 32b of the heat dissipation base 30, includes subregions that are respectively parallel to the long side 30a, short side 30b, long side 30c, and short side 30d, and has rounded corners, as in the case of FIG. 6.

In such a case as well, when the heat dissipation members 33 melt, the elastic members 34 provided in the loop-shaped region 32b2 of the heat dissipation base 30 keep the gap between the heat dissipation base 30 and the cooling module 90. Therefore, no gap is generated between the heat dissipation base 30 and each screw 35, which prevents a reduction in the tightening torque of the screws 35 joining the semiconductor module 10 to the cooling module 90. Since the gap between the heat dissipation base 30 and the cooling module 90 is kept, the melting heat dissipation members 33 sufficiently spread in the gap. This prevents a reduction in the heat dissipation of the semiconductor module 10, and thus prevents a reduction in the reliability of the power converter 2.

Second Embodiment

Second and subsequent embodiments relate to various arrangements of the elastic members 34 formed in the loop-shaped region 32b2 of the heat dissipation base 30. In this connection, the various arrangements of the elastic members 34 in the second and subsequent embodiments are applicable not only to the case of FIG. 6 but also to the case of FIG. 13.

First, as the second embodiment, the following describes the case of arranging the elastic members 34 along each side of the heat dissipation base 30 with reference to FIG. 14. FIG. 14 is a rear surface view of a semiconductor module according to the second embodiment.

In a semiconductor module 10a, the elastic members 34 are provided at locations including the centers of the subregions of the loop-shaped region 32b2 respectively parallel to the long side 30a, short side 30b, long side 30c, and short side 30d of the heat dissipation base 30.

In this configuration, when the semiconductor module 10a is attached to the cooling module 90 by the screws 35 and then the heat dissipation members 33 are melted, the elastic members 34 provided as described above keep the gap between the heat dissipation base 30 and the cooling module 90. Therefore, a reduction in the tightening torque of the screws 35 joining the semiconductor module 10a to the cooling module 90 is prevented. In addition, since the gap between the heat dissipation base 30 and the cooling module 90 is kept, the melting heat dissipation members 33 sufficiently spread in the gap. This prevents a reduction in the heat dissipation of the semiconductor module 10a, and thus prevents a reduction in the reliability of the power converter 2.

The elastic members 34 may each have any length as long as they are able to keep the gap between the heat dissipation base 30 and the cooling module 90. In this connection, the lengths of the elastic members 34 formed in the subregions of the loop-shaped region 32b2 parallel to the long sides 30a and 30c are lengths measured in the X direction. On the other hand, the lengths of the elastic members 34 formed in the subregions of the loop-shaped region 32b2 parallel to the short sides 30b and 30d are lengths measured in the Y direction. If the elastic members 34 are too short, the elastic members 34 may be unable to support the heat dissipation base 30, which may fail to keep the gap between the heat dissipation base 30 and the cooling module 90.

Third Embodiment

A third embodiment will be described with reference to FIG. 15. FIG. 15 is a rear surface view of a semiconductor module according to the third embodiment. In a semiconductor module 10b, elastic members 34 are provided at the following three locations in the loop-shaped region 32b2: at the corners at both ends of a subregion of the loop-shaped region 32b2 parallel to the short side 30d of the heat dissipation base 30, and at the center of a subregion of the loop-shaped region 32b2 parallel to the short side 30b opposite to the short side 30d.

In this configuration, when the semiconductor module 10b is attached to the cooling module 90 by the screws 35 and then the heat dissipation members 33 are melted, the elastic members 34 provided as described above keep the gap between the heat dissipation base 30 and the cooling module 90. This prevents a reduction in the tightening torque of the screws 35 joining the semiconductor module 10b to the cooling module 90. In addition, since the gap between the heat dissipation base 30 and the cooling module 90 is kept, the melting heat dissipation members 33 sufficiently spread in the gap. This prevents a reduction in the heat dissipation of the semiconductor module 10b, and thus prevents a reduction in the reliability of the power converter 2.

In this case as well, the elastic members 34 may each have any length as long as they are able to keep the gap between the heat dissipation base 30 and the cooling module 90, as in the second embodiment. If the elastic members 34 are too short, the elastic members 34 may deform by being sandwiched between the rear surface 32b of the heat dissipation base 30 and the cooling surface 91 of the cooling module 90.

Considering the second and third embodiments, the elastic members 34 of appropriate length may be discontinuously provided in a loop shape in the loop-shaped region 32b2 so as to keep the gap between the heat dissipation base 30 and the cooling module 90. The locations, quantity, and lengths of the elastic members 34 described in the second and third embodiments are just examples.

For example, in FIG. 14, the elastic members 34 may be provided at a plurality of locations in each of the subregions of the loop-shaped region 32b2 respectively parallel to the long side 30a, short side 30b, long side 30c, and short side 30d of the heat dissipation base 30. These elastic members 34 may have different lengths. Long elastic members 34 may be provided only in the subregions of the loop-shaped region 32b2 parallel to the long sides 30a and 30c (or short sides 30b and 30d) of the heat dissipation base 30.

Another arrangement than that illustrated in FIG. 15 may be possible, in which the elastic members 34 are formed at the following three locations of the loop-shaped region 32b2 of the heat dissipation base 30: at a pair of adjacent corners at both ends of one subregion of the loop-shaped region 32b2 parallel to one of the long sides 30a and 30c and short side 30b, and in another subregion that is opposite to the one subregion with the heat dissipation region 32b1 therebetween and is along one of the long sides 30c and 30a and short side 30d. That is, in the loop-shaped region 32b2 set along the outer periphery of the heat dissipation base 30, elastic members 34 may be formed at a pair of adjacent corners at both ends of one subregion (first side) of the loop-shaped region 32b2 parallel to one of the long sides 30a and 30c and short sides 30b and 30b. In addition, an elastic member 34 may be formed in another subregion (second side) of the loop-shaped region 32b2 that is opposite to the one subregion (first side) with the heat dissipation region 32b1 therebetween and is parallel to one of the long sides 30a and 30c and short sides 30b and 30d. Alternatively, the elastic members 34 are not necessarily formed at the corners in FIG. 15. For example, the elastic members 34 may be formed in the opposite end portions of the subregion of the loop-shaped region 32b2 parallel to the long side 30a and at the center of the subregion of the loop-shaped region 32b2 parallel to the long side 30c.

Fourth Embodiment

A fourth embodiment will be described with reference to FIGS. 16 and 17. FIG. 16 is a rear surface view of a semiconductor module according to the fourth embodiment. FIG. 17 is a rear surface view of a semiconductor module according to the fourth embodiment (variation). In a semiconductor module 10c, an elastic member 34 is continuously provided in a loop shape in the loop-shaped region 32b2 of the heat dissipation base 30.

In this configuration, when the semiconductor module 10c is attached to the cooling module 90 by the screws 35 and then the heat dissipation members 33 are melted, the elastic member 34 provided in this manner keeps the gap between the heat dissipation base 30 and the cooling module 90. This prevents a reduction in the tightening torque of the screws 35 joining the semiconductor module 10c to the cooling module 90. In addition, since the gap between the heat dissipation base 30 and the cooling module 90 is kept, and the gap is surrounded by the elastic member 34, the melting heat dissipation members 33 sufficiently spread in the gap but do not spread beyond the gap. In addition, the heat dissipation members 33 do not make their surroundings dirty or reduce their volume. Thus, a reduction in the heat dissipation of the semiconductor module 10c is prevented, and a reduction in the reliability of the power converter 2 is thus prevented.

The melting heat dissipation members 33 are confined by the heat dissipation base 30, the cooling module 90, and the elastic member 34. When the melting heat dissipation members 33 continue to be heated, they may foam and emit gas. If the heat dissipation members 33 are confined by the heat dissipation base 30, cooling module 90, and elastic member 34, the gas is accumulated inside and may explode. To avoid this explosion, a plurality of cuts 34a are formed in the elastic member 34 of the heat dissipation base 30, as illustrated in FIG. 17. Each cut 34a communicates from the inside to the outside of the elastic member 34. Therefore, the gas emitted from the heat dissipation members 33 and confined by the heat dissipation base 30, cooling module 90, and elastic member 34 is output through the cuts 34a to the outside of the elastic member 34. Therefore, the gas is not accumulated in the space formed by the heat dissipation base 30, cooling module 90, and elastic member 34, which prevents the gas from exploding. The cuts 34a may be formed only to release the gas, and therefore may have a width different from that illustrated in FIG. 17 and may be formed at locations different from those illustrated in FIG. 17.

The disclosed technique makes it possible to prevent loosening of fastening to a cooling module, prevent a reduction in cooling performance, and prevent a reduction in the reliability of a semiconductor module and power converter.

All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

SEMICONDUCTOR MODULE, POWER CONVERTER, AND POWER CONVERTER MANUFACTURING METHOD

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CPC

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