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

Abstract

A semiconductor module according to the present disclosure is characterized by comprising: a semiconductor device (1); a heat sink (12) on which the semiconductor device (1) is placed; an external case (14) that has, at the bottom thereof, a protruding part (14e) protruding outward, and that forms, together with the heat sink (12), an internal space in which the semiconductor device (1) is housed; a fixing member (13b) that fixes the external case (14) to the heat sink (12) at the protruding part (14e); and a sealing member (15a) that is provided between the heat sink (12) and the protruding part (14e) of the external case (14), to maintain the air pressure in the internal space, in which the protruding part (14e) is pressed toward the heat sink (12) by the fixing member (13b) to fix the external case (14) to the heat sink (12).

Description

Semiconductor Module, Method for Manufacturing Semiconductor Module, and Power Converter

[0001] The present disclosure relates to a semiconductor module incorporating a semiconductor device, a method for manufacturing a semiconductor module, and a power converter.

[0002] As a conventional technique for a semiconductor module in which a semiconductor device is housed in a housing, for example, there is a semiconductor module disclosed in Patent Document 1. Specifically, a structure of a semiconductor module is disclosed in which a semiconductor device is fixed onto a heat sink with a screw, and the heat sink and the housing are joined so as to seal the semiconductor device.

[0003] Japanese Unexamined Patent Publication No. 2019-75415

[0004] When a semiconductor device is used in a high-altitude environment such as that of an aircraft, the ambient atmospheric pressure becomes low. In a low atmospheric pressure environment, the discharge inception voltage decreases compared to that under atmospheric pressure, making discharge more likely to occur. Therefore, when a high voltage is applied to the terminals of the semiconductor device, discharge may occur between the high-voltage terminal and the low-voltage terminal, or between the high-voltage terminal and a member such as the heat sink. In the conventional prior art, airtightness is not taken into consideration, and there has been a risk that the atmospheric pressure around the semiconductor element decreases in a low atmospheric pressure environment, leading to a decrease in insulation performance.

[0005] An object of the present disclosure is to provide a semiconductor module, a method for manufacturing a semiconductor module, and a power converter capable of suppressing a decrease in insulation performance even in a low atmospheric pressure environment.

[0006] A semiconductor module according to the present disclosure includes: a semiconductor device; a heat sink on which the semiconductor device is mounted; an outer case having, at a bottom portion thereof, a protruding portion protruding outward, the outer case forming an internal space together with the heat sink in which the semiconductor device is housed; a fixing member that fixes the outer case to the heat sink at the protruding portion; and a sealing member provided between the heat sink and the protruding portion of the outer case, the sealing member maintaining the atmospheric pressure in the internal space, wherein the protruding portion is pressed toward the heat sink by the fixing member, so that the outer case is fixed to the heat sink.

[0007] The power conversion device according to this disclosure comprises a main conversion circuit and a control circuit. The main conversion circuit has the above-mentioned semiconductor device and converts and outputs the input power. The control circuit outputs a control signal to the main conversion circuit to control the main conversion circuit.

[0008] The method for manufacturing a semiconductor module according to this disclosure includes the steps of: placing a semiconductor device on a heat sink; placing an external case before lid attachment on the heat sink via a sealing member; fastening the semiconductor device and the external case before lid attachment to the heat sink with fixing members; and joining a lid to the external case to seal the semiconductor device inside the external case so as to maintain the air pressure in the internal space. The fastening of the heat sink and the external case is characterized by pressing a protruding portion at the bottom of the external case toward the heat sink with a fixing member.

[0009] According to the configuration of this disclosure, a semiconductor module capable of suppressing the deterioration of insulation performance even in a low-pressure environment, a method for manufacturing a semiconductor module, and a power conversion device are provided.

[0010] This is a cross-sectional view of a semiconductor module according to Embodiment 1. This is an enlarged view of the portion where the external case 14 is fixed to the heat sink 12 in Figure 1. This is a cross-sectional view of a case in Embodiment 1 where multiple semiconductor devices 1 are arranged in parallel. This is a cross-sectional view showing the internal structure of the semiconductor device 1 in Embodiment 1. This is a flowchart of the manufacturing method of a semiconductor module according to Embodiment 1. This is a cross-sectional view showing the S1 step in the flowchart of Figure 5. This is a cross-sectional view showing the S2 step in the flowchart of Figure 5. This is a cross-sectional view showing the S3 step in the flowchart of Figure 5. This is a cross-sectional view showing the S4 step in the flowchart of Figure 5. This is a cross-sectional view of a semiconductor module according to Embodiment 2. This is a cross-sectional view of a semiconductor module according to Embodiment 3. This is a cross-sectional view of a semiconductor module according to a modified example of Embodiment 3. This is a cross-sectional view of a semiconductor module according to Embodiment 4. This is a cross-sectional view of a semiconductor module according to Embodiment 5. This is a block diagram showing the configuration of a power conversion system to which the power conversion device according to Embodiment 6 is applied.

[0011] The embodiments of this disclosure will be described in detail with reference to the drawings. In the following drawings, the same or corresponding parts will be denoted by the same reference numerals, and redundant descriptions will not be repeated. The embodiments described below are illustrative, and the scope of this disclosure is not limited to the embodiments described below.

[0012] Semiconductor devices are designed to maintain insulation under atmospheric pressure, but if insulation measures are not taken for the structure of the semiconductor device, high-voltage discharge may occur in low-pressure environments, potentially leading to malfunctions. For example, the design of the space distance between terminals and creepage distance constitutes insulation measures. However, changing the structure of the semiconductor device and implementing insulation measures according to the application of the semiconductor module in which it is used (for example, for high-altitude environments or normal-pressure environments) is cumbersome, as it requires individual optimization design based on the performance, type, and size of the semiconductor device. As an alternative to avoid such hassles, the inventors of this application have devised a semiconductor module that can maintain the operating environment of the semiconductor device at atmospheric pressure even in low-pressure environments by sealing the semiconductor device within an external case.

[0013] Embodiment 1. <Configuration of Semiconductor Module> The semiconductor module according to Embodiment 1 will be described below.

[0014] Figure 1 is a cross-sectional view of a semiconductor module according to Embodiment 1. In the semiconductor module 10, the semiconductor device 1 is housed in an internal space (referred to as a sealed space S in this embodiment) surrounded by an external case 14 and a heat sink 12. This internal space is sealed and maintained at an internal pressure adjusted to approximately atmospheric pressure. The internal pressure in the sealed space S does not need to be strictly maintained and may be reduced to an extent that suppresses discharge, as will be described later. Because the sealed space S is maintained at approximately atmospheric pressure, even if the external space is in a low-pressure environment, the discharge generated from the high-voltage terminal 8a of the semiconductor device 1 when a high voltage is applied is suppressed compared to the environment of the external space. In order to maintain the internal pressure of the sealed space S, it is sufficient that the space formed by the external case 14 and the heat sink 12, or the external case 14 itself, has a gap-free structure. Specifically, sealing members such as gaskets can be inserted between the external case 14 and the heat sink 12, or between members if the external case 14 is composed of multiple members.

[0015] As shown in Figure 1, the outer case 14 is composed of a wall portion 14a and a lid 14b. It is preferable to use an insulating material such as epoxy resin or polyphenylene sulfide (PPS) resin for the outer case 14. A packing 15b, which is a sealing member, is interposed between the wall portion 14a and the lid 14b of the outer case, and the two are fastened together by a screw 13c, which is a fixing member. In the example shown in Figure 1, the wall portion 14a of the outer case 14 is joined to the heat sink 12, and the wall portion 14a is shaped to surround the semiconductor device 1. The lid 14b is placed on the upper surface of the end of the wall portion 14a, opposite to the part where the heat sink 12 and the wall portion 14a are joined, and is joined to it, creating a structure that covers the top of the semiconductor device 1 and puts a lid on it.

[0016] The wall portion 14a of the outer case 14 is in contact with the heat sink 12 on which the semiconductor device 1 is mounted, via the sealing member 15. Also, since Figure 1 is a schematic cross-sectional view of the semiconductor module 10, the wall portion 14a is shown as being divided into left and right sides in the figure, but (in reality) the wall portion 14a has a shape that surrounds the semiconductor device 1. Therefore, the area in which the wall portion 14a is in contact with the heat sink 12 surrounds the semiconductor device 1. For convenience, the end of the wall portion 14a that is in contact with the heat sink 12 will be referred to as the "bottom" of the wall portion 14a.

[0017] The outer case 14 is fixed to the heat sink 12 at its bottom (for convenience, this refers to the protruding portion 14e, which is not shown in Figure 1 but will be explained in Figure 2) by a screw 13b, which is a fixing member. A packing 15a, which is a sealing member, is interposed between the bottom of the outer case 14 (protruding portion 14e) and the heat sink 12. As a result, the internal space formed by the outer case 14 and the heat sink 12 becomes a sealed space, and an internal pressure of approximately atmospheric pressure is maintained (here, the gas filling the sealed space S is air).

[0018] The semiconductor device 1 is placed on a heat sink 12 that defines a sealed space S together with the outer case 14. A heat dissipation grease may be placed between the heat sink 5 of the semiconductor device and the heat sink 12. The semiconductor device 1 and the heat sink 12 are fastened together by screws 13a, which are fixing members.

[0019] A weak point may be provided in either or both of the wall portion 14a and the lid 14b of the outer case. The weak point can be provided by designing or processing a thin section or notch in any part of the wall portion 14a and the lid 14b of the outer case. In this way, when the semiconductor device 1 short-circuits and an excessively large current flows, causing a rapid rise in internal pressure accompanied by a rise in temperature, the weak point will be preferentially destroyed, resulting in the effect of releasing the pressure at a lower pressure than in a case where no weak point is provided.

[0020] In Figure 1, the internal structure of the semiconductor device 1 is omitted for convenience. The semiconductor device 1 can be a standard one that maintains insulation under atmospheric pressure, and there is no need to implement special insulation measures based on the structure of the semiconductor device 1 for use in low-pressure environments.

[0021] The type of semiconductor device 1 is not particularly limited and may include, for example, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), bipolar transistors, and packages for their integrated circuits.

[0022] The semiconductor device 1 has a heat sink 5 on its bottom surface. The heat generated during the operation of the semiconductor device 1 is dissipated from the heat sink 5 to the heat sink 12. However, the semiconductor device 1 does not necessarily have to have a heat sink 5 on its bottom surface.

[0023] The semiconductor device 1 has a high-voltage terminal 8a and a low-voltage terminal 8b (hereinafter referred to as terminal 8 when neither is distinguished). The high-voltage terminal 8a is a terminal to which a high voltage is applied, and the low-voltage terminal 8b is a terminal to which a voltage lower than that of the high-voltage terminal 8a is applied. An insulated conductor 16 is connected to each terminal, and the insulated conductor 16 passes through the outer case 14 and is brought out to the outside. The insulated conductor 16 is configured such that the conductor 17 is insulated with an insulating material 18 in the portion that passes through the outer case 14 and on the outside of the outer case. The number of terminals 8 is not particularly limited, and the semiconductor device 1 only needs to have terminals 8. In addition, the terminals and connecting conductors for inputting switching signals to the semiconductor device 1 are omitted.

[0024] Figure 2 is an enlarged view of the portion in Figure 1 where the outer case 14 is fixed to the heat sink 12. As shown in Figure 2, the outer case 14 (wall portion 14a) has a protruding portion 14e at its bottom that protrudes outward at the point of fixation to the heat sink 12. Here, "outward direction" refers to the direction toward the external space, opposite to the internal space (sealed space S) formed by the outer case 14 and the heat sink 12, as viewed from the wall portion 14a of the outer case. The protruding portion 14e is shaped to bend and protrude outward at the point where the outer case 14 is connected to the heat sink 12. It can also be described as a flange or girdle shape. It is effective in strengthening the connection between parts and ensuring airtightness at the connection point. For convenience, the protruding portion 14e is shown enclosed by a dotted line. The protruding portion 14e is pressed toward the heat sink 12 by a screw 13b via a packing 15a. This fixes the outer case 14 to the heat sink 12.

[0025] As described above, since the protruding portion 14e of the outer case protrudes outward, it does not affect the arrangement or design of the semiconductor device 1 housed in the internal space, compared to the case where it protrudes inward, and the outer case 14 can be made smaller. This reduces the amount of air filled inside and reduces the amount of deformation of the outer case 14 due to air expansion.

[0026] Figure 3 is a cross-sectional view of the semiconductor device 1 in this embodiment when multiple devices are arranged in parallel. As shown in Figure 3, multiple semiconductor devices 1 may be arranged in parallel and sealed inside the external case 14. In this case, the high-voltage terminals 8a of each semiconductor device 1 are connected in parallel to one conductor 17, and the low-voltage terminals 8b are also connected in parallel to the other conductor 17. Alternatively, each high-voltage terminal 8a and each low-voltage terminal 8b may be connected to an independent conductor 17.

[0027] Figure 4 is a cross-sectional view showing the internal structure of the semiconductor device 1. The internal structure of the semiconductor device 1 shown in Figure 4 is just one example, and the internal structure of the semiconductor device 1 is not particularly limited as long as it is the module structure of the semiconductor module 10 described in Figure 1.

[0028] As shown in Figure 4, the semiconductor device 1 has a heat sink 5 on its bottom surface, an insulating layer 4 is bonded to the upper surface of the heat sink 5, and two metal layers 3a and 3b are bonded to the upper surface of the insulating layer 4, respectively. A semiconductor chip 2 is mounted on the upper surface of one metal layer 3a, and the semiconductor chip 2 is connected to the other metal layer 3b by a wire 9. The internal structure of the semiconductor device 1 is covered by a semiconductor case 6, and the inside is sealed with an insulating encapsulant 7. High-voltage terminals 8a are connected to metal layer 3a, and low-voltage terminals 8b are connected to metal layer 3b, and these are brought out to the outside of the semiconductor case 6. When the semiconductor device 1 is operating, heat is generated from the semiconductor chip 2, and the heat is dissipated by passing through the metal layer 3a, insulating layer 4, and heat sink 5 in that order. The semiconductor device 1 also has a through hole 11, through which a screw 13a is passed to fasten it to a heat sink 12 (for convenience, the reference numerals for the screw 13a, heat sink 12, and outer case 14 are not shown in Figure 4).

[0029] <Method for Manufacturing Semiconductor Modules> The method for manufacturing semiconductor modules according to this embodiment will be described below. Figure 5 is a flowchart showing the steps of the semiconductor module manufacturing method. Figures 6 to 9 show the steps of each step in the flowchart of Figure 5. The following explanation will follow the steps shown in the flowchart of Figure 5, with reference to Figures 6 to 9 which show each step.

[0030] First, as shown in Figure 6, prepare the outer case 14 before attaching the lid 14b. Before attaching the lid 14b, the insulating wire 16 penetrates the wall portion 14a of the outer case 14 (Step S1).

[0031] Next, as shown in Figure 7, the outer case 14, before attaching the lid 14b prepared in step S1, is placed on the upper surface of the heat sink 12 via the packing 15a, and the semiconductor device 1 is then placed inside the outer case 14 (step S2). The order in which the outer case 14 and the semiconductor device 1 are placed does not matter, but if the outer case 14 is placed first, it is preferable to bend the insulating wires 16 so as not to interfere with the later placement of the semiconductor device 1. If it is difficult to bend the insulating wires 16, the semiconductor device 1 can be placed first. Although not shown in the figure, the outer case 14 and the semiconductor device 1 have through holes for inserting screws in step S3, and the heat sink 12 has corresponding screw holes. When placing them, ensure that the through holes and screw holes overlap.

[0032] Subsequently, as shown in Figure 8, the semiconductor device 1 and the heat sink 12 are fastened together with screws 13a, and the outer case 14 and the heat sink 12 are fastened together with screws 13b (step S3).

[0033] Next, as shown in Figure 9, the insulated conductor 16 is connected to the high-voltage terminal 8a and the low-voltage terminal 8b of the semiconductor device 1 (step S4).

[0034] Finally, the lid 14b is installed on the upper surface of the wall portion 14a of the outer case via the packing 15b and fastened with screws 13c (step S5). Since the inside of the outer case 14 is sealed by the wall portion 14a and the lid 14b of the outer case, the gas pressure inside the outer case 14 is maintained even if the outside air pressure drops after this step. As a result, the semiconductor module according to the embodiment shown in Figure 1 is manufactured.

[0035] <Effects of the Embodiment> In the semiconductor module according to this embodiment, the semiconductor device 1 is housed inside the external case 14 and sealed with internal pressure, so that the internal pressure is kept constant and terminal discharge is suppressed in a low-pressure environment. Therefore, it is possible to use a general-purpose semiconductor device without having to prepare a separate semiconductor device specifically designed for low-pressure environments. Accordingly, the semiconductor module according to this embodiment has the effect of suppressing terminal discharge in a low-pressure environment.

[0036] Furthermore, the semiconductor module according to this embodiment can secure a contact area between the heat sink 12 and the external case 14 equal to the width of the protruding portion 14e of the external case 14, thereby improving airtightness.

[0037] Furthermore, in the semiconductor module according to this embodiment, the protruding portion 14e of the outer case 14 protrudes outward, making it easy to fasten the outer case 14 and the heat sink 12 at this portion. Therefore, the semiconductor module according to this embodiment is easy to assemble.

[0038] Embodiment 2. <Configuration of Semiconductor Module> The semiconductor module according to Embodiment 2 will be described below. In this embodiment, the shape of the inner surface of the wall portion 14a and the lid 14b of the outer case conforms to the shape of the semiconductor device 1. In this embodiment, as in Embodiment 1, the protruding portion 14e of the outer case is fixed to the heat sink 12 via a packing 15a to maintain the internal air pressure, and the same reference numerals are used for parts that are the same as or equivalent to those in Embodiment 1, and their description is omitted.

[0039] Figure 10 is a cross-sectional view of a semiconductor module according to Embodiment 2. As shown in Figure 10, the shape of the inner surfaces of the outer case wall 14a and lid 14b conforms to the shape of the semiconductor device 1. That is, the shape of the inner surfaces of the outer case wall 14a and lid 14b is matched to the shape of the semiconductor device 1, and is designed to reduce the gap between the semiconductor device 1 and the outer case 14. The wire penetration portion 17a that penetrates the outer case wall 14a is aligned with the position of the terminal 8 to which it will be connected, so that when the outer case 14 is installed, the tip portion 17b of the wire overlaps with the terminal 8. Furthermore, the shape of the inner surface of the outer case 14 may be molded integrally with the outer case wall 14a and lid 14b from the beginning, or separate components may be bonded together afterward. If separate components are used, they may be made of a different material than the outer case 14.

[0040] <Effects of the Embodiment> Similar to Embodiment 1, the semiconductor module according to this embodiment has a configuration in which the protruding portion 14e of the outer case is fixed to the heat sink 12 via a packing 15a, thereby maintaining the internal pressure, and has the effect of suppressing terminal discharge in a low-pressure environment. Furthermore, the semiconductor module according to this embodiment has the following effects.

[0041] When the internal space is sealed by the outer case 14 and the outside is placed in a low-pressure environment, the difference in pressure between the air pressure inside the sealed space S and the outside air pressure generates pressure in the direction that causes the air inside to expand. Therefore, if the strength of the outer case 14 is low, there is a risk that the outer case 14 may break due to this pressure. In this embodiment, by making the inner surfaces of the wall portion 14a and lid 14b of the outer case conform to the shape of the semiconductor device 1, the amount of air filled inside the outer case 14 can be reduced, and the amount of deformation of the outer case 14 due to air expansion can be reduced. Therefore, this embodiment has the effect of suppressing damage to the outer case 14.

[0042] Embodiment 3. <Configuration of Semiconductor Module> The semiconductor module according to Embodiment 3 will be described below. In this embodiment, an insulating filler 19 is sandwiched between the outer case 14 and the semiconductor device 1. In this embodiment, as in Embodiments 1 and 2, the protruding portion 14e of the outer case is fixed to the heat sink 12 via a packing 15a to maintain the internal air pressure, and the same reference numerals are used for parts that are the same as or corresponding to these embodiments, and their description is omitted.

[0043] Figure 11 is a cross-sectional view of a semiconductor module according to Embodiment 3. As shown in Figure 11, an insulating filler 19 is sandwiched between the outer case 14 and the semiconductor device 1. The inner surface of the outer case 14 has a shape that protrudes toward the semiconductor device 1. The insulating filler 19 is preferably a flexible insulator, such as silicone rubber. For convenience, Figure 11 shows a gap between the insulating filler 19, the outer case 14, and the semiconductor device 1, but it is preferable that the insulating filler 19 and each component be in contact. Note that the structure of sandwiching the insulating filler 19 in this embodiment may also be applied to Embodiments 1 and 2.

[0044] FIG. 12 is a cross-sectional view of a semiconductor module according to a modification of the third embodiment. In the modification shown in FIG. 12, unlike FIG. 11, the shape of the inner surface side of the outer case 14 does not protrude toward the semiconductor device 1. That is, the inner surface of the outer case 14 is flat, and since it does not protrude as in FIG. 11, the volume occupied by the insulating filler 19 in the internal space of the outer case 14 increases. In this modification, since the inner surface of the outer case 14 is flat and has a simple structure, molding of the outer case 14 is easier compared to the embodiment shown in FIG. 11. Further, the outer case 14 can be molded regardless of the shape of the semiconductor device 1, and it is only necessary to appropriately change the insulating filler 19.

[0045] <Operational Effects of the Embodiment> Similar to the first embodiment, the semiconductor module according to the present embodiment has a configuration in which the protruding portion 14e of the outer case is fixed to the heat sink 12 via the packing 15a to maintain the internal air pressure, and has an effect of suppressing discharge of terminals in a low-pressure environment. Further, the semiconductor module according to the present embodiment has the following operational effects.

[0046] In the present embodiment, by filling the gap between the outer case 14 and the semiconductor device 1 with the insulating filler 19, the amount of air inside the outer case 14 can be reduced. Therefore, the present embodiment has an effect of reducing the deformation amount of the outer case 14 caused by the expansion of the internal air under a low-pressure environment. Further, by bringing the insulating filler 19 into direct contact with the outer case 14 and the semiconductor device 1, there is an effect of improving heat dissipation from the upper surface and side surfaces of the semiconductor device 1 via the insulating filler 19 and the outer case 14.

[0047] Embodiment 4. <Configuration of Semiconductor Module> Hereinafter, a semiconductor module according to Embodiment 4 will be described. In the present embodiment, an insulated conductive wire 16 penetrates through the top surface portion 14c of an integrated outer case 14, and the connection between the insulated conductive wire 16 and the terminal 8 of the semiconductor device is assisted via a connection electrode by the pressing force of a spring 21 provided between the two. Note that, similar to Embodiments 1 to 3, the present embodiment has a configuration in which the protruding portion 14e of the outer case is fixed to the heat sink 12 via a packing 15a to maintain internal air pressure, and portions identical or corresponding to those in those embodiments are denoted by the same reference numerals, and description thereof is omitted.

[0048] FIG. 13 is a cross-sectional view of the semiconductor module according to Embodiment 4. As shown in FIG. 13, unlike Embodiment 1, the outer case 14 according to the present embodiment is not divided into a wall portion 14a and a lid 14b but is formed integrally. The outer case 14 is open only on the bottom side, and the inside of the outer case 14 is sealed by being joined to the heat sink 12 via the packing 15a. Further, the insulated conductive wire 16 penetrates through the top surface portion 14c of the outer case 14.

[0049] A connection electrode 20 is provided between the insulated conductive wire 16 and the terminal 8 of the semiconductor device, and the insulated conductive wire 16 and the terminal 8 of the semiconductor device are electrically connected via the connection electrode 20. Further, a spring 21 is provided between the top surface portion 14c of the outer case and the terminal 8 of the semiconductor device, and the connection electrode 20 is pressed against the terminal 8 of the semiconductor device by compression of the spring 21. Thereby, the connection between the terminal 8 of the semiconductor device and the insulated conductive wire 16 is assisted via the connection electrode 20 by the pressing force of the spring 21. Note that the structure using the spring 21 according to the present embodiment may be applied to Embodiments 1 to 3.

[0050] <Functions and Effects of the Embodiment> Similar to Embodiment 1, the semiconductor module according to the present embodiment has a configuration in which the protruding portion 14e of the outer case is fixed to the heat sink 12 via the packing 15a to maintain internal air pressure, and has an effect of suppressing discharge at the terminal under a low atmospheric pressure environment. Further, the semiconductor module according to the present embodiment has the following functions and effects.

[0051] In this embodiment, the semiconductor module has an outer case 14 that is not divided into a wall portion 14a and a lid 14b but is an integrated unit. Therefore, in its manufacturing, the step of fastening the lid 14b of the outer case to the wall portion 14a (step S5), which was described in the manufacturing method of the semiconductor module according to Embodiment 1, can be omitted. Furthermore, because the outer case 14 is an integrated unit, there is no risk of internal air leakage compared to using an outer case in which the wall portion 14a and lid 14b are fastened together, and the strength of the outer case 14 can be increased.

[0052] Furthermore, in this embodiment, the semiconductor module has a structure in which the connecting electrode 20 contacts the terminal 8 of the semiconductor device by fastening the external case 14 and the heat sink 12 together, and the external case 14 is further pressed against the heat sink 12 and fixed by screws 13b. As a result, the spring 21 is compressed, and the connecting electrode 20 contacts the terminal 8 while a pressing force is acting on it. Therefore, in this embodiment, unlike Embodiment 1, it is not necessary to directly connect the insulating conductor 16 to the terminal 8 of the semiconductor device. In other words, among the steps described in the manufacturing method of the semiconductor module according to Embodiment 1, the step of connecting the insulating conductor 16 to the terminal 8 of the semiconductor device (step S4) can be omitted.

[0053] As described above, in this embodiment, among the steps described in the semiconductor module manufacturing method according to Embodiment 1, the step of fastening the lid 14b of the outer case to the wall portion 14a (step S5) and the step of connecting the insulating conductor 16 to the terminal 8 of the semiconductor device (step S4) can be omitted. Therefore, the semiconductor module according to this embodiment can be manufactured more simply by omitting some steps. In addition, since the wall portion 14a and the lid 14b are integrated, the risk of air leakage from the outer case 14 can be reduced.

[0054] Embodiment 5. <Configuration of Semiconductor Module> The semiconductor module according to Embodiment 5 will be described below. In this embodiment, instead of using an insulated wire 16 to connect to the terminal 8 of the semiconductor device, an insulating coated busbar 22 is used. In this embodiment, as with Embodiments 1 to 4, the protruding portion 14e of the outer case is fixed to the heat sink 12 via a packing 15a to maintain the internal air pressure, and the same reference numerals are used for parts that are the same as or corresponding to these embodiments, and their description is omitted.

[0055] Figure 14 is a cross-sectional view of a semiconductor module according to Embodiment 5. As shown in Figure 14, the outer case 14 is not divided into a wall portion 14a and a lid portion 14b, but is an integrated unit. The outer case 14 is open only at the bottom, and the inside of the outer case 14 is sealed by joining it to the heat sink 12 via a packing 15a. A bus bar 22, which is a conductive member, passes through the side portion 14d of the outer case, and the tip portion 22a of the bus bar is positioned to contact the terminal 8 of the semiconductor device. When the outer case 14 is fastened to the heat sink 12, the tip portion 22a of the bus bar is fixed to the terminal 8 of the semiconductor device. The bus bar 22 is, for example, a copper plate, and it is desirable that it has sufficient thickness. If the contact between the tip portion 22a of the bus bar and the terminal 8 of the semiconductor device is insufficient, a metal plate or the like may be inserted between them to adjust the contact.

[0056] The busbar 22 is covered with an insulating coating 23. The insulating coating 23 is made of a highly heat-dissipating material, such as an inorganic filler-filled resin. As a result, the heat generated from the terminal 8 is conducted through the busbar 22 and dissipated to the outside air from the insulating coating 23. Note that the structure using the busbar 22 in this embodiment may also be applied to embodiments 1 to 4.

[0057] <Effects of the Embodiment> Similar to Embodiment 1, the semiconductor module according to this embodiment has a configuration in which the protruding portion 14e of the outer case is fixed to the heat sink 12 via a packing 15a, thereby maintaining the internal pressure, and has the effect of suppressing terminal discharge in a low-pressure environment. Furthermore, the semiconductor module according to this embodiment has the following effects.

[0058] In this embodiment, by using a busbar 22 that is thicker than the insulated conductor 16, the heat dissipation from the terminal 8 of the semiconductor device can be improved. Since the terminal 8 becomes hot due to the heat generated by the conductor chip 2 inside the semiconductor device 1, this embodiment is advantageous from the viewpoint of heat dissipation.

[0059] Embodiment 6. This embodiment applies the semiconductor modules described in Embodiments 1 to 5 above to a power converter. The present invention is not limited to a specific power converter, but below, as Embodiment 6, we will describe the case in which the present invention is applied to a three-phase inverter.

[0060] Figure 15 is a block diagram showing the configuration of a power conversion system to which the power conversion device according to this embodiment is applied.

[0061] The power conversion system shown in Figure 15 consists of a power supply 300, a power conversion device 400, and a load 500. The power supply 300 is a DC power supply and supplies DC power to the power conversion device 400. The power supply 300 can be made up of various components, for example, a DC grid, a solar cell, or a storage battery, or it may be made up of a rectifier circuit or AC / DC converter connected to an AC grid. Alternatively, the power supply 300 may be made up of a DC / DC converter that converts DC power output from a DC grid into a predetermined power.

[0062] The power converter 400 is a three-phase inverter connected between the power supply 300 and the load 500. It converts the DC power supplied from the power supply 300 into AC power and supplies the AC power to the load 500. As shown in Figure 15, the power converter 400 includes a main conversion circuit 401 that converts DC power into AC power and outputs it, and a control circuit 403 that outputs a control signal to the main conversion circuit 401 to control the main conversion circuit 401.

[0063] Load 500 is a three-phase motor driven by AC power supplied from power converter 400. Note that load 500 is not limited to a specific application; it is a motor installed in various electrical devices, such as hybrid vehicles, electric vehicles, railway vehicles, elevators, or air conditioning equipment.

[0064] The details of the power converter 400 are described below. The main conversion circuit 401 is equipped with switching elements and freewheeling diodes (not shown), and by switching the switching elements, it converts the DC power supplied from the power supply 300 into AC power and supplies it to the load 500. There are various specific circuit configurations for the main conversion circuit 401, but the main conversion circuit 401 according to this embodiment is a two-level three-phase full-bridge circuit and can be composed of six switching elements and six freewheeling diodes antiparallel to each switching element. Each switching element and each freewheeling diode of the main conversion circuit 401 is composed of a semiconductor module 402 corresponding to any of the embodiments 1 to 5 described above. The six switching elements are connected in series in pairs to form upper and lower arms, and each upper and lower arm constitutes each phase (U phase, V phase, W phase) of the full-bridge circuit. The output terminals of each upper and lower arm, i.e., the three output terminals of the main conversion circuit 401, are connected to the load 500.

[0065] Furthermore, the main conversion circuit 401 includes a drive circuit (not shown) for driving each switching element. The drive circuit may be built into the semiconductor module 402, or it may be configured to be a separate drive circuit from the semiconductor module 402. The drive circuit generates a drive signal to drive the switching elements of the main conversion circuit 401 and supplies it to the control electrodes of the switching elements of the main conversion circuit 401. Specifically, according to the control signal from the control circuit 403, which will be described later, it outputs a drive signal to turn on the switching element and a drive signal to turn off the switching element to the control electrodes of each switching element. When the switching element is kept in the ON state, the drive signal is a voltage signal (ON signal) that is greater than or equal to the threshold voltage of the switching element, and when the switching element is kept in the OFF state, the drive signal is a voltage signal (OFF signal) that is less than or equal to the threshold voltage of the switching element.

[0066] The control circuit 403 controls the switching elements of the main converter circuit 401 so that the desired power is supplied to the load 500. Specifically, it calculates the time (on time) that each switching element of the main converter circuit 401 should be in the ON state based on the power to be supplied to the load 500. For example, the main converter circuit 401 can be controlled by PWM control, which modulates the on time of the switching elements according to the voltage to be output. The control circuit then outputs a control command (control signal) to the drive circuit of the main converter circuit 401 so that an ON signal is output to the switching elements that should be in the ON state at each point in time, and an OFF signal is output to the switching elements that should be in the OFF state. The drive circuit outputs an ON signal or an OFF signal as a drive signal to the control electrode of each switching element according to this control signal.

[0067] In the power conversion device according to this embodiment, a semiconductor module according to any of Embodiments 1 to 5 is used as the switching element and freewheeling diode of the main conversion circuit 401, thereby realizing a highly reliable power conversion device.

[0068] In this embodiment, an example of applying the present invention to a two-level three-phase inverter has been described, but the present invention is not limited to this and can be applied to various power conversion devices. In this embodiment, a two-level power conversion device is used, but a three-level or multi-level power conversion device may also be used, and the present invention may be applied to a single-phase inverter when supplying power to a single-phase load. Furthermore, when supplying power to a DC load, the present invention can also be applied to a DC / DC converter or an AC / DC converter.

[0069] Furthermore, the power conversion device to which the present invention is applied is not limited to cases where the load is an electric motor, but can also be used, for example, as a power supply device for electrical discharge machining equipment, laser processing equipment, induction heating cookers, or non-contact power supply systems, and can even be used as a power conditioner for solar power generation systems, energy storage systems, etc.

[0070] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. At least two of the embodiments disclosed herein can be combined, as long as they do not contradict each other. The scope of the invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[0071] The above embodiments can be combined as appropriate.

[0072] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of equivalents of the claims are intended.

[0073] 1 Semiconductor device, 2 Semiconductor chip, 3a, 3b Metal layer, 4 Insulating layer, 5 Heat sink, 6 Semiconductor case, 7 Insulating encapsulant, 8 Terminals, 8a High voltage terminal, 8b Low voltage terminal, 9 Wire, 10 Semiconductor module, 12 Heat sink, 13a, 13b Screws (fixing members), 14 Outer case, 14a Wall section, 14b Cover, 14c Top section, 14d Side section, 14e Protruding section, 15a, 15b Packing (sealing member), 16 Insulated conductor, 17 Conductor, 17a Through section, 17b Tip section, 18 Insulating member, 19 Insulating filler, 20 Connecting electrode, 21 Spring, 22 Busbar, 22a Tip section, 23 Insulating coating, 300 Power supply, 400 Power converter, 401 Main converter circuit, 402 Semiconductor module, 403 Control circuit, 500 load, S sealed space

Claims

1. A semiconductor module comprising: a semiconductor device; a heat sink on which the semiconductor device is mounted; an external case having a protruding portion at its bottom that protrudes outward and forming an internal space in which the semiconductor device is housed together with the heat sink; a fixing member that fixes the external case to the heat sink at the protruding portion; and a sealing member provided between the heat sink and the protruding portion of the external case to maintain the air pressure in the internal space, wherein the protruding portion is pressed toward the heat sink by the fixing member, and the external case is fixed toward the heat sink.

2. The semiconductor module according to claim 1, characterized in that the external case has a wall and a lid, the lid is joined to the upper surface of the wall, and the bottom of the wall is joined to the heat sink, thereby sealing the inside of the external case.

3. The semiconductor module according to any one of claims 1 to 2, characterized in that the semiconductor device has terminals, the terminals are connected to a conductive member that is insulated or coated, and the conductive member penetrates the outer case.

4. The semiconductor module according to claim 3, characterized in that the shape of the inner side of the wall portion of the outer case and the inner side of the lid conforms to the shape of the side and top surface of the semiconductor device, and the conductive member penetrates the outer case such that the tip of the conductive member is positioned to coincide with the position of the terminals of the semiconductor device.

5. The semiconductor module according to any one of claims 1 to 4, characterized in that an insulator is provided between the outer case and the semiconductor layer.

6. The semiconductor module according to claim 1, characterized in that the external case is a single unit, with an opening only at the bottom, and the inside of the external case is sealed by joining the bottom of the external case to the heat sink.

7. The semiconductor module according to claim 6, characterized in that an insulatingly coated conductive member penetrates the upper surface of the outer case, the conductive member and the terminals of the semiconductor device are joined via a connecting electrode provided between the conductive member and the terminals of the semiconductor device, and the connecting electrode is pressed into the terminals of the semiconductor device by compression of a spring provided between the inner upper surface of the outer case and the terminals of the semiconductor device.

8. The semiconductor module according to claim 6, characterized in that a busbar that can contact the terminals of the semiconductor device penetrates the side of the external case.

9. A power conversion device comprising a semiconductor module according to any one of claims 1 to 8, a main conversion circuit that converts and outputs input power, and a control circuit that outputs a control signal to the main conversion circuit for controlling the main conversion circuit.

10. A method for manufacturing a semiconductor module, comprising the steps of: placing a semiconductor device on a heat sink; placing an external case before lid attachment on the heat sink via a sealing member; fastening the semiconductor device and the external case before lid attachment to the heat sink with fixing members; and joining a lid to the external case to seal the semiconductor device inside the external case so as to maintain the air pressure in the internal space, wherein the fastening of the heat sink and the external case is characterized by pressing an outwardly protruding portion at the bottom of the external case toward the heat sink with the fixing member.

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