JP4685039B2 - Power semiconductor device - Google Patents

Description

  The present invention relates to a power semiconductor device, and more particularly to improvement of a heat dissipation structure when the power semiconductor device is attached to a heat sink such as a heat sink via grease.

  Conventionally, a power semiconductor device generates a large amount of heat from elements constituting the power semiconductor device. Therefore, a heat radiator such as a heat sink is attached to dissipate heat to suppress an increase in temperature. In the power semiconductor device, grease is interposed between the base plate and the heat sink, and the base plate is fastened and fixed to the heat sink with screws.

  Here, the thermal conductivity of grease is inferior to that of metal by about two orders of magnitude. If the grease layer is thick, the thermal resistance between the power semiconductor device and the heat sink is significantly increased, resulting in poor heat dissipation. There was a problem.

  As a conventional device for solving such problems, a protrusion is formed on the outer peripheral portion on the bottom surface side of the base plate, so that a gap is formed between the bottom surface of the base plate and the upper surface of the heat sink. There is a structure in which the base plate is warped so that the base plate becomes convex toward the heat sink side by tightening.

  In such a structure, as the base plate is warped so that the vicinity of the central portion of the base plate becomes convex as it is tightened with screws, when attaching the power semiconductor device to the heat sink, especially the grease in the central portion is used. It can be eliminated (see Patent Document 1).

JP 2000-58727 A

  Since the conventional power semiconductor device is configured as described above, there is a problem in that the screw is loosened due to deformation due to creep because the screw does not fit in the screw hole over the entire length.

  In addition, since the contact surface between the screw head and the case is reduced, a moment acts on the screw when the power semiconductor device and the heat sink are fixed with the screw. In order to counteract this moment force and reduce the maximum normal stress generated in the cross section of the screw, the section modulus of the screw has to be increased, and there is a problem that the screw cannot be miniaturized.

  The present invention has been made to solve the above-described problems, and securely attaches a heat sink to the power semiconductor device with screws, and reduces the thickness of the grease interposed between the power semiconductor device and the heat sink. It is for the purpose.

The power semiconductor device according to the present invention is such that grease is interposed between the base plate and the heat sink, and the base plate is fixed to the heat sink by inserting a screw into a mounting hole provided in the base plate, Protruding portions with mounting holes in the vicinity of the corners of the base plate are configured to be higher than the bottom surfaces of the other base plates, and projecting near the center between the corners of the base plate. The base plate is deformed so as to have a convex shape toward the heat sink side by tightening a screw inserted into the mounting hole not provided with the projecting portion and provided with the protruding portion. .

According to the power semiconductor device of the present invention, the base plate is fixed to the heat sink by inserting grease between the base plate and the heat sink and inserting screws into the mounting holes provided in the base plate. Te, along with a configured to be higher than the bottom surface of the other of the base plate by providing the projecting portion mounting holes provided in the vicinity of the corner portions of the base plate, in the vicinity of the center between the corners of the base plate Since the base plate was deformed so as to have a convex shape toward the heat sink by tightening the screw inserted in the mounting hole without the protrusion, and the mounting hole without the protrusion. The lower surface portion of the screw head and the upper surface portion of the projecting portion are in contact with each other in a planar manner, and the lower surface portion of the projecting portion and the upper surface portion of the heat sink are also in contact with each other in a planar shape. It can be fixed to the mounting hole screws stably.

  Even if the base plate is tightened so that the base plate is convex toward the heat sink, the screw is securely seated in the periphery of the mounting hole. No creep deformation occurs and the screws do not loosen even after long-term use.

  Furthermore, since it is not necessary to use a large screw as in the prior art, the power semiconductor device can be miniaturized and the cost can be reduced.

Embodiment 1 FIG.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is an exploded perspective view showing a power semiconductor device according to Embodiment 1 of the present invention. The power semiconductor device 1 has a case 2 and a base plate 3, and a semiconductor element mounted on a substrate (not shown) is built in the case 2, and the base plate 3 is made of copper, aluminum, or a synthetic material containing them. It is composed of

  Further, usually, a mounting hole 4 is provided in the outer peripheral portion of the base plate 3, and the power semiconductor device 1 is fixed to the heat sink 5 with screws 6. The attachment holes 4a are provided at four locations near the corners of the base plate 3, and the attachment holes 4b are provided at four locations near the center between the corners.

  In the present embodiment, the peripheral portion of the mounting hole 4 a located at the four corners is configured to be higher than the bottom surface of the other base plate 3 by the protruding portion 7. As will be described later, the protruding portion 7 may be constituted by a component different from the base plate 3 as a spacer, or may be integrally formed with the base plate 3 as a protruding portion of the base plate 3. good. Further, grease (not shown) is inserted between the base plate 3 and the heat sink 5.

  FIGS. 2A and 2B are cross-sectional views taken along line AA in FIG. 1. FIG. 2A shows that when the power semiconductor device 1 is attached to the heat sink 5, screws 6 are inserted into the attachment holes 4b. FIG. 2 is a cross-sectional view showing a state before the screw 6 is tightened, and FIG. 2B is a cross-sectional view showing a state after the screw 6 is tightened. FIG. 2 shows an example in which the protruding portion 7 is provided integrally with the base plate 3.

  When the screw 6 inserted into the mounting hole 4b is tightened from the state of FIG. 2A, the base plate 3 is shown in FIG. To curve. Since a bending force as shown in FIG. 2B is exerted on the entire surface of the base plate 3, a bending moment for deforming the base plate 3 in the normal direction of the base surface is provided at the center of the base plate 3. Power works.

  Due to this bending moment force, the grease in the center is swept out, and the thickness of the grease in this portion can be reduced. Further, in the mounting hole 4a, the lower surface portion of the head of the screw 6 and the upper surface portion of the projecting portion 7 are in contact with each other in a planar shape, and the lower surface portion of the projecting portion 7 and the upper surface portion of the heat sink 5 are also in contact with each other in a planar shape. Therefore, the screw 6 can be stably fixed in the mounting hole 4a.

  Further, since the mounting hole 4b is provided at a substantially central portion between the projecting portions 7, the distance between the corner portion of the projecting portion 7 serving as a fulcrum and the mounting hole 4b is sufficiently large. The screw 6 can be tightened, and the screw 6 can be stably fixed in the mounting hole 6b.

  Moreover, since the protrusion part 7 in which the attachment hole 4a was provided is provided in the corner | angular part vicinity of the base board 3, it becomes possible to change the whole base board 3 in convex shape toward the heat sink 5 side, More grease can be discharged.

  In FIG. 3, as in the conventional apparatus, a protrusion is formed on the outer peripheral portion on the bottom surface side of the base plate 3, thereby forming a gap between the bottom surface of the base plate 3 and the upper surface of the heat sink 5. It is an expanded sectional view which shows the structure which warps so that the base board 3 may become convex toward the heat sink 5 side by tightening with the screw | thread 6 inside.

  In such a structure, since a force as indicated by M works, the screw 6 does not fit in the screw hole over the entire length, and thus there is a problem that the screw 6 is loosened due to deformation due to creep. In this case, since the force indicated by M does not work, such a problem is less likely to occur.

  As described above, according to the present invention, even if the screw 6 is tightened so that the base plate 3 is convex toward the heat sink 5, the screw 6 is securely seated in the periphery of the mounting hole 4a. As in the prior art, a large axial force is not applied to the screw thread, and the screw 6 is not creep-deformed, and the screw does not loosen even after a long period of use.

  In addition, since it is not necessary to use a large screw as in the prior art, the power semiconductor device can be downsized and the cost can be reduced.

  The protrusion 7 can be formed integrally with the base plate 3 by plating. In this case, the bottom surface of the base plate 3 other than the periphery of the attachment hole 4a where the protrusion 7 is formed is masked with a resist or a metal plate, and the protrusion 7 is formed by plating only the periphery of the attachment hole 4a. Form.

  As the plating, tin plating, nickel plating, or the like is adopted, and nickel plating containing nickel plating and phosphorus is preferably applied particularly when strength against tightening by screws is required.

  Moreover, the protrusion part 7 can also be formed by press work. In this case, when the base plate 3 is formed, the projecting portion 7 can be formed by plastic working at the same time, and the projecting portion can be simultaneously formed in the pressing process without requiring a step of forming the projecting portion 7 in particular. 7 can be formed. In addition, the protrusion 7 can be formed by machining.

Embodiment 2. FIG.
FIG. 4 is a plan view of base plate 3 in the power semiconductor device according to the second embodiment of the present invention as viewed from the bottom. In the first embodiment, as shown in FIG. 1, the shape of the protruding portion 7 is rectangular, whereas in the present embodiment, the portion facing the center side of the base plate 3 has an arc shape. The protruding portion 11 is provided.

  By forming into such a shape, when the screw inserted into the mounting hole 4b is tightened, the base plate 3 is more toward the center of the bottom surface of the base plate 3 than in the case of the first embodiment. As a result of the deformation, the portion where the bottom surface of the base plate 3 and the top surface of the heat sink 5 come into contact with each other increases the amount of grease present in the vicinity of the center of the bottom surface of the base plate 3, thereby increasing the thermal conductivity. Get better.

  The shape of the protruding portion is not limited to the above-described shape, and the protruding portion can be provided on the bottom surface of the base plate 3 so that the screw and the base plate 3 are securely seated around the mounting hole 4a. Thereby, the screw inserted into the attachment hole 4 b can be tightened so that the bottom surface of the base plate 3 is warped toward the upper surface side of the heat sink 5.

Embodiment 3 FIG.
5 is a perspective view showing a heat sink 5 in a power semiconductor device according to Embodiment 3 of the present invention. In the above-described embodiment, the case where the protruding portion is integrally formed on the back surface side of the base plate 3 has been described. However, as shown in FIG. good.

  In this case, the protruding portion 21 is formed so that the periphery of the mounting hole 22 for inserting the screw 6 for mounting the power semiconductor device is raised. By configuring as described above, the same operation as in the first embodiment can be performed.

  As a method for forming the protruding portion 21, it can be formed on the upper surface side of the heat sink 5 by plating, machining, pressing, or the like, as in the case of the first embodiment. Further, when the heat sink 5 is formed by a die casting method, the protruding portions 21 can also be formed at a time in the heat sink manufacturing process. Thereby, it becomes possible to form the protrusion part 21 without increasing a manufacturing process.

  Furthermore, if the base plate 3 is also manufactured by a die casting method, the projecting portion can be formed simultaneously.

Embodiment 4 FIG.
In the above embodiment, the case where the protruding portion is formed integrally with the base plate 3 and the heat sink 5 has been described. However, a spacer may be installed between the base plate 3 and the heat sink 5 as a separate member.

  With this configuration, as in the case of the above-described embodiment, the screw can be stably fixed in the mounting hole, and the base plate 3 can be warped in a convex shape toward the heat sink 5 to eliminate grease. Will be able to promote.

  In addition, since the number of parts can be reduced by forming the projecting portion integrally with the base plate 3 and the heat sink 5 rather than installing a spacer as a separate member, the efficiency is improved.

1 is an exploded perspective view showing a power semiconductor device according to a first embodiment of the present invention. It is the sectional view on the AA line in FIG. It is a partially expanded sectional view which shows the conventional power semiconductor device. It is the top view which looked at the base board 3 in the electric power semiconductor device by Embodiment 2 of this invention from the bottom face direction. It is a perspective view which shows the heat sink 5 in the electric power semiconductor device by Embodiment 3 of this invention.

Explanation of symbols

1 power semiconductor device, 3 base plate, 4a, 4b mounting hole, 5 heat sink,
6 Screw, 7,21 Protruding part.

Claims (4)

A power semiconductor device in which grease is interposed between a base plate and a heat sink, and a screw is inserted into a mounting hole provided in the base plate to fix the base plate to the heat sink . Protruding portions provided with mounting holes in the vicinity of the corners are configured to be higher than the bottom surfaces of the other base plates, and in the vicinity of the center between the corners of the base plates provided mounting holes are not provided, by tightening the inserted the screw into the mounting hole of the protruding portion is not provided, the base plate is deformed so as to convex toward the heat sink side A power semiconductor device. The power semiconductor device according to claim 1, wherein the protrusion is formed integrally with the base plate. The power semiconductor device according to claim 1, wherein the protrusion is formed integrally with the heat sink. 4. The power semiconductor device according to claim 1, wherein a portion of the protruding portion facing the center side of the base plate is formed in an arc shape. 5.

Images