JP4416633B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device that radiates heat with a radiating fin attached to a bottom surface.

  Conventionally, a power module in which a power semiconductor element (power MOSFET, IGBT, etc.) is connected on an insulating substrate and incorporated in one package is known. The power module has a configuration in which a power semiconductor element is provided on the front main surface side and heat is released from the back main surface side to which the heat sink is joined. Silicone grease is applied to the back main surface of the power module, and the power module is fixed to the heat radiation fins with screws through the silicone grease.

  When the power module is fixed to the heat radiating fins, pressure is applied in order to improve the familiarity between the silicone grease and the heat radiating fins, and the power modules are further tightened and fixed with screws. For this reason, after tightening the screws, a part of the silicone grease between the power module and the heat radiating fin may gradually protrude outward. As a result, the power module sinks slightly, and as a result, there is a gap between the screw fastening portion and the screw head of the power module, and looseness occurs.

  Here, when the screw is loosened, the adhesion between the power module and the heat radiating fin is lowered, and there is a problem that the heat radiating capability of the entire apparatus is lowered. When the heat dissipation capability is significantly reduced, the power semiconductor element in the power module may be thermally destroyed.

  By the way, in the assembly process of the conventional power module, when tightening the screw for screwing the power module on the heat radiating fin, the work is divided into two stages such as temporarily tightening the screw first and then finally tightening. Yes. This is because the insulating layer crack of the insulating metallized substrate in the power module is not generated. Since the excess silicone grease protrudes to the outside by this temporary tightening, there is an effect that the occurrence of the loosening of the screws can be partially reduced as a result of the two-stage operation of performing the final tightening thereafter. However, such a two-stage screw tightening operation does not necessarily improve work efficiency, and is not necessarily performed. Further, just because the screw tightening operation is divided into two stages, it does not mean that the screws are not loosened due to the protrusion of the silicone grease.

The invention described in Patent Document 1 is such that in a power module fixed to a cooler via a heat conductive grease, a groove is formed between the application portion of the heat conductive grease and the screw hole. is there. The groove is for preventing the heat conductive grease from entering the screw hole.
JP 2003-168772 A

  An object of the present invention is to prevent loosening of a screw when a power module is screwed onto a heat radiating fin.

The present invention has been made to achieve the above object. A semiconductor device according to the present invention includes:
A heat sink with a semiconductor element mounted on the front surface,
A heat dissipating fin having a facing surface facing the back main surface of the heat radiating plate, wherein the back main surface of the heat radiating plate and the facing surface are disposed facing each other;
Grease formed over the entire facing region where the back main surface of the heat sink and the facing surface face each other;
A screw provided at a peripheral portion of the heat radiating plate and press-contacting a back main surface of the heat radiating plate and a facing surface of the heat radiating fin via the grease;
With
A screw hole for screwing the screw is formed in the peripheral portion of the heat radiating plate, and a screw hole is formed at a corresponding position of the heat radiating fin,
The heat radiating plate is provided with a relief portion for escaping the excess amount of the grease at the time of the pressure contact,
The escape portion is a slit provided around a screw hole of the heat sink;
The slit penetrates from the back main surface to the front main surface and penetrates into the screw hole,
The semiconductor device is characterized in that the slit has a portion in which a width of the slit penetrating from the back main surface to the front main surface is smaller than a diameter of the screw hole .

  By utilizing the present invention, it is possible to prevent the screw portion for the solid from being loosened even if the heat radiation fin is screwed to the bottom surface of the power module and a considerable time elapses.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments according to the present invention will be described below with reference to the drawings. In the following description, the terms “upper”, “lower”, “right”, “left”, “front”, “back” and other terms including those terms (for example, “upper surface”) indicating a specific direction. , “Bottom surface”, “right side”, “left side”, “front main surface”, “back main surface”), are used as appropriate to facilitate the understanding of the invention with reference to the drawings. However, the technical scope of the invention is not limited by these terms. Accordingly, embodiments of the specific invention described below are upside down or rotated 90 ° in any direction (for example, clockwise direction or counterclockwise direction) as a matter of course. It is included.

  First, FIG. 7 shows a schematic perspective view of a general power module 2. Inside the power module 2, one or more semiconductor elements (not shown) are joined on an insulating substrate (not shown) by solder or the like. These semiconductor elements and insulating substrate are completely covered with a case 4 which is usually made of resin. Further, a heat sink 6 made of copper, aluminum or the like is joined to the lower surface of the insulating substrate. The case 4 covers the substantially entire upper surface of the heat sink 6 on which the semiconductor element and the insulating substrate are mounted, and is fixed to the upper surface of the heat sink. The power module 2 usually has main electrode terminals and signal terminals, which are connected to the semiconductor element and protrude outward from the inside of the case 4, but these terminals are omitted in FIG.

  As described above, the case 4 covers substantially the entire upper surface of the heat radiating plate 6, but does not cover the four corners of the upper surface of the heat radiating plate 6, and the surfaces of the four corners are exposed. Screw holes 8 are formed in the four corners. These screw holes 8 are for screws 14 for screwing the power module 2 to the radiating fins. In addition, the part of the heat sink 6 in which the screw hole 8 is formed and the surface is exposed is not limited to four corners, but may be a peripheral part that is not a corner.

  FIG. 8 is a side view showing the work contents for attaching the power module 2 to the heat radiation fin 20. First, silicone grease (grease in which silicone oil is mainly blended with metal soap or the like) 16 is applied to the entire lower surface of the heat sink 6 of the power module 2 as heat-resistant grease. Of course, you may apply | coat to the area | region surface which opposes the whole lower surface of the heat sink 6 of the power module 2 among the upper surfaces of the radiation fin 20. FIG. Next, the power module 2 is mounted on the upper surface of the radiation fin 20. Further, screws 14 are inserted into screw holes 8 formed in the vicinity of the four corners of the heat radiation plate 6 of the power module 2, and are tightened with, for example, an electric torque driver, and the power module 2 is fixed on the upper surface of the heat radiation fin 20. The Of course, screw holes 22 are also formed at positions corresponding to the radiation fins 20 (see FIG. 10).

  After this screw tightening, as described in the “Background Art” section, there may be a problem that a part of the silicone grease 16 between the power module 2 and the radiation fin 20 gradually protrudes to the outside. . That is, when a screw is inserted into the screw hole 8 formed as shown in FIG. 9 and tightened, the repulsive force of the silicone grease temporarily brings a stable state as shown in the sectional view of FIG. As time passes, as shown in the cross-sectional view of FIG. 10B, the silicone grease 16 protrudes outward, the heat sink 6 sinks slightly, and the screw tightening torque is slightly loosened. In the following embodiment of the invention, an appropriate measure is applied to the vicinity of the screw hole 8 of the heat radiating plate 6, that is, the portion A corresponding to the region surrounded by the dotted line in FIG.

Embodiment 1

  FIG. 3 is a perspective view of the power module 2 according to Embodiment 1 of the present invention, and FIG. 4 is a perspective view as seen from the back main surface of the power module. Further, FIG. 1 shows an enlarged perspective view of the vicinity of the screw hole 8 of the heat radiating plate 6 of the power module 2 according to Embodiment 1 in the upper half, and a perspective view of the vicinity of the screw hole 8 from the back side below the chain line. The figure is shown. In the first embodiment, as best shown in FIG. 1, a plurality of slits (first recesses) 10 near the screw holes 8 and at the edge of the back surface of the heat sink 6, and screws on the back surface of the heat sink 6. A plurality of dimples (second recesses) 12 are provided near the hole 8. In other words, the heat radiating plate 6 is provided with a relief portion for excess silicone grease 16.

  In FIG. 1, FIG. 3 and FIG. 4, the slit 10 and the dimple 12 are provided as the escape portion of the silicone grease 16, but the shape of the escape portion is not limited to these. However, in order to improve the problem of screw loosening, it is preferable that the relief portion is provided in the vicinity of the screw hole 8. Further, if the relief portion is provided in the vicinity of the screw hole 8, the relief portion is formed at a certain distance from the semiconductor element inside the case 4. Therefore, the relief portion such as a slit / dimple can radiate heat from the semiconductor element. There will be no obstruction.

  When slits and dimples are not formed, as shown in FIG. 10, a repulsive force is generated in the silicone grease 16 immediately after screw tightening (see FIG. 10 (1)), and the silicone grease 16 protrudes after a lapse of a corresponding time (see FIG. 10). 10 (2)). Therefore, slits and dimples as shown in Fig. 1 are used to reduce the repulsive force of the silicone grease immediately after screw tightening (reduction of the area of the surface where the heat sink receives stress from the silicone grease) and to secure an escape space for excess silicone grease. It is effective to provide.

  That is, as shown in FIG. 2, the slit 10 allows the excess silicone grease 16 to escape at the same time as the screws 14 are tightened, and the flow of the silicone grease 16 after the screws are tightened can be suppressed.

  Further, the dimple 12 reduces the repulsive force of the silicone grease 16 by reducing the stress surface perpendicular to the stress that the silicone grease 16 receives when screwing. Accordingly, the silicone grease 16 becomes easy to conform simultaneously with the screw tightening by the dimple 12, and as a result, the screw 14 is hardly loosened.

  Note that relief portions such as slits and dimples may be provided on the front main surface of the radiating fin 20 facing the vicinity of the screw holes 8 of the radiating plate 6. 1, 3, and 4 are not provided with a plurality of slits 10 and a plurality of dimples 12, but may be provided with at least one of the slits 10 and the dimples 12. Good.

Embodiment 2

  FIG. 5 is an enlarged perspective view of the vicinity of the screw hole 8 of the heat sink 6 of the power module 2 according to Embodiment 2 of the present invention. The power module 2 according to the second embodiment is substantially the same as the power module 2 according to the first embodiment. Therefore, the same parts are denoted by the same reference numerals and the description thereof is omitted.

  In the power module 2 according to the second embodiment, one of the slits 10 ′ provided in the vicinity of the screw hole 8 penetrates from the back main surface to the front main surface of the heat radiating plate 6 and penetrates into the screw hole 8. is doing.

  As in the case of the first embodiment, the slit 10 ′ thus formed allows the excess silicone grease 16 to be released at the same time as the screws 14 are tightened, thereby suppressing the flow of the silicone grease 16 after the screws are tightened. it can. In addition, the working efficiency of processing the slit 10 ′ in the second embodiment is greatly improved as compared with the slit in the first embodiment. This is because the slit 10 ′ can be formed at the same time when the screw hole 8 is punched in the heat radiating plate 6.

  Furthermore, in the slit 10 ′ of the heat radiating plate 6 of the power module 2 according to the second embodiment, the gap for escaping the silicone grease 16 becomes larger, so that the dimple 12 and other slits need not be provided.

Embodiment 3

  FIG. 6 is an enlarged cross-sectional view of the vicinity of the screw hole 8 of the heat radiating plate 6 of the power module 2 according to the third embodiment. The power module 2 according to the third embodiment is also substantially the same as the power module 2 according to the first embodiment. Therefore, the same parts are denoted by the same reference numerals and description thereof is omitted.

  In the power module 2 according to the third embodiment, a counterbore (counter screw hole) 18 having an appropriate size is formed on the edge of the screw hole 8 on the back main surface side of the heat radiating plate 6 in contact with the heat radiating fin 20. Yes. This counterbore 18 can be said to have both the slit and dimple effects in the first embodiment. In other words, the counterbore 18 releases excess silicone grease 16 at the same time as the screw 14 is tightened and suppresses the flow thereof, and at the same time reduces the stress surface perpendicular to the stress that the silicone grease 16 receives when tightening the screw, thereby removing the silicone grease 16 from the silicone grease 16. Reduce repulsion.

  Therefore, if the counterbore 18 is made relatively large, it is not necessary to provide the slit 10 or the dimple 12 in the first or second embodiment. Moreover, since the escape part of the silicone grease 16 exists in all directions when viewed from the center of the screw hole 8, the excess silicone grease 16 can be securely fastened.

  Further, the counterbore 18 is formed concentrated on only the edge of the screw hole 8 on the back main surface of the heat sink 6, so in the power module 2 according to the third embodiment, the heat sink 6 near the screw hole 8 is It has substantially the same strength as that of the prior art (see FIG. 9), and deformation such as torsion hardly occurs at the corners of the heat sink 6.

  The counterbore may also be provided at the edge of the screw hole 22 on the opposing surface (front main surface) of the radiating fin 20 facing the radiating plate 6.

The upper half shows an enlarged perspective view of the vicinity of the screw hole of the heat sink of the power module according to Embodiment 1, and shows a perspective view of the vicinity of the screw hole 8 below the chain line from the back side. It is an expanded sectional view of the screw hole vicinity part of the heat sink of the power module which concerns on Embodiment 1 of this invention, and a cross section passes a slit and a dimple. It is a perspective view of the power module 2 which concerns on Embodiment 1 of this invention. It is the perspective view seen from the back main surface of the power module which concerns on Embodiment 1 of this invention. It is an expansion perspective view of the screw hole vicinity part of the heat sink of the power module which concerns on Embodiment 2 of this invention. It is an expanded sectional view of the screw hole vicinity part of the heat sink of the power module which concerns on Embodiment 3 of this invention. It is a schematic perspective view of a general power module. It is a side view which shows the operation | work content which attaches a power module to a radiation fin. An enlarged perspective view of a screw hole portion of a heat sink of a conventional general power module is shown in the upper half, and a perspective view of the same screw hole portion seen from the back side is shown below the chain line. FIG. 10 is an enlarged cross-sectional view of a portion near a screw hole of a heat sink of a general power module, showing a state immediately after screw tightening [FIG. 10 (1)] and a state after a considerable time has passed [FIG. 2)].

Explanation of symbols

2 power module, 4 case, 6 heat sink, 8 screw hole, 10 slit, 12 dimple, 14 screw, 16 silicone grease.

Claims (1)

A heat sink with a semiconductor element mounted on the front surface,
A heat dissipating fin having a facing surface facing the back main surface of the heat radiating plate, wherein the back main surface of the heat radiating plate and the facing surface are disposed facing each other;
Grease formed over the entire facing region where the back main surface of the heat sink and the facing surface face each other;
A screw provided at a peripheral portion of the heat radiating plate and press-contacting a back main surface of the heat radiating plate and a facing surface of the heat radiating fin via the grease;
With
A screw hole for screwing the screw is formed in the peripheral portion of the heat radiating plate, and a screw hole is formed at a corresponding position of the heat radiating fin,
The heat radiating plate is provided with a relief portion for escaping the excess amount of the grease at the time of the pressure contact,
The escape portion is a slit provided around a screw hole of the heat sink;
The slit penetrates from the back main surface to the front main surface and penetrates into the screw hole,
The semiconductor device according to claim 1, further comprising a portion where a width of the slit through which the slit penetrates from the back main surface to the front main surface is smaller than a diameter of the screw hole .

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