JPH08125070A - Semiconductor device - Google Patents

Abstract

PURPOSE: To improve the reliability of a semiconductor device by altering the disposition of a pin mark and hence by removing the thin part of the resin which is easily cut out from the periphery of a screw hole. CONSTITUTION: Pin marks to be formed by a pressing pin for pressing a radiating plate 1 to the mold surface are disposed on the inner periphery of screw holes 4 provided at the holes 4 at both short sides 21 of the plate 1. The pin marks 5a, 5d of the side in which a force for tearing off resin 3 is operated are shifted or removed reversely to the rotating direction with respect to the rotating direction to clamp a mounting screw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to cracking of resin of a semiconductor device which is equipped with a heat sink and is screwed to an external heat sink.
About prevention of call.

[0002]

2. Description of the Related Art In many semiconductor devices for encapsulating high-power circuit elements, a heat-dissipating plate is used and resin-encapsulated so that the back surface of the heat-dissipating plate is exposed (for example, Japanese Patent Laid-Open No. 1994-140541). ). An example of such a semiconductor device will be described with reference to FIG. 3A is a plan view, and FIG. 3B is a bottom view. In these figures, 1 is a heat sink, 2 is a lead for external connection, 3 is a mold resin, 4 is a screw hole for mounting a device, and 5 is a pin mark of a pressing pin of the heat sink 1 at the time of molding.

A heating element such as a power transistor or a power IC is fixed on the surface of the heat sink 1 inside the resin 3, and the back surface of the heat sink 1 is exposed on the surface of the resin 3. When this semiconductor device is mounted, the back surface of the heat dissipation plate 1 is brought into close contact with an external heat dissipation fin (not shown), and a mounting screw that penetrates the screw hole 4 is screwed to fix the semiconductor device to the external heat dissipation. Fix it on the fin. The heat generated during the operation of the semiconductor device is conducted to the heat radiation fins via the heat radiation plate 1.

FIGS. 4A and 4B are plan views of the semiconductor device, and FIG. 4B is a plan view of the semiconductor device.
It is a line sectional view. In the molding step, the circuit element is fixed to the surface of the heat sink 1, the circuit element and the lead 2 are wire-bonded, and then the lead frame is installed inside the cavity 7 which is a space having the same shape as the outer shape of the resin 3 of the mold 6. Then, the resin is injected into the cavity 7. At this time, since the back surface of the heat sink 1 is not exposed when the heat sink 1 is molded in a state of being floated from the mold 6, the heat sink 1 should be placed in the mold 6.
It needs to be pressed against the surface. Therefore, the resin is injected while the heat dissipation plate 1 is pressed against the surface of the lower mold 6 by the pressing pin 8 protruding from the upper mold 6. The pin mark 5 in FIGS. 3A and 3B is formed by the pressing pin 8. Since the heat sink 1 is exposed on the surface of the pin mark 5, the pin mark 5 is formed on the inner peripheral surface of the screw hole 4 for the purpose of avoiding unnecessary short circuit with other members.

FIGS. 5A and 5B are a plan view and a side view showing an example in which the semiconductor device is mounted on a radiation fin 9. The screw holes 4 of the device body 10 and the screw holes 11 formed in the heat radiation fins 9 are aligned, and the mounting screws 12 are inserted into the screw holes 4 and 11 so that the back surface of the heat radiation plate 1 and the heat radiation fins 9 are brought into close contact with each other. Screw both to. 13 is a screw hole 4
A washer having a diameter larger than that of 14 is a nut corresponding to the screw 12. A female screw may be directly cut in the screw hole 11. Further, the washer 13 may be omitted by using the mounting screw 12 whose head is larger than the diameter of the screw hole 4.

[0006]

[Problems to be Solved by the Invention] Ordinary bolt (screw)
Is tightened clockwise unless otherwise specified. Due to this peculiar directionality, it was revealed that the resin 3 of the apparatus main body 10 was cracked and cracked when the mounting screw 12 was tightened. 6 (A) and 6 (B) are plan views (A) and (B) BB showing a state in which such a crack is generated.
It is a line sectional view. The pin mark 5 is not formed as a bottomed hole whose periphery is completely surrounded by the resin 3, but is formed as a bottomed hole having an opening 15 on the inner peripheral surface of the screw hole 4. Therefore, the regions 16a and 16b in which the resin 3 is thin are generated in the screw hole 4.

The washer 1 is inserted into the screw hole 4 having such a structure.
When the contact of 3 and the tightening force of the mounting screw 12 are applied,
A moment force in the directions of the arrows 17a and 17b shown in the drawing is applied to the resin 3 in a direction along the rotation direction of the screw 12. At the pin mark 5b, the moment 17b becomes a force in the direction of compressing the resin 3, and the moment 17b
Since a large amount of the resin 3 exists in the direction in which is applied, this serves as a support, and the thin portion 16b does not crack or crack. However, at the pin mark 5a, the moment 17a is
Force in the direction of pulling the persimmon, and the moment 17a
There is no support in the direction of addition of. Therefore, there is a defect that the resin 3 is cracked 18 and impairs the reliability of the semiconductor device. In FIG. 3A, the thin portion 5a corresponds to the thin portion 5d, and the thin portion 5b corresponds to the thin portion 5c.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. By removing the thin portion 17a by shifting the pin mark 5a to which the force in the pulling direction is applied, the resin is removed. It is intended to provide a semiconductor device which is free from cracking and chipping.

[0009]

According to the present invention, since the thin portion 16a does not exist, cracking and chipping of the resin can be prevented.

[0010]

An embodiment of the present invention will be described in detail below with reference to FIG. 1A is a plan view and FIG. 1B is a bottom view. In these drawings, 1 is a heat sink, 2 is a plurality of leads for external connection, 3 is a molding resin, 4 is a screw hole portion for mounting a device, and 5 is a heat sink 1 at the time of molding.
It is a pin mark of the pressing pin.

The heat dissipation plate 1 has a rectangular shape having short sides 21 and long sides 22, and the leads 2 are led out in a direction orthogonal to the long sides 22. A circuit element (not shown) is fixed to the surface of the heat sink 1, the circuit element is connected to the tip of the lead 2 by wire bonding, and the circuit element, the wire, and the tip portion of the lead 2 are sealed inside the resin 3. It The heat dissipation plate 1 is sealed so that its back surface side is exposed on the surface of the resin 3.

A screw hole 4 is formed on both short sides 21 of the heat dissipation plate 1 by recessing a part thereof. The shape of the screw hole 4 is a semicircle with a diameter slightly larger than the diameter of the mounting screw 4 to be inserted,
The pattern is a combination of a straight line obtained by drawing a tangent to the semicircle perpendicularly to the short side 21. This is to allow a margin for the positioning accuracy of the screw 12 and the screw holes 4 and 11 when mounting the device. The outer shape of the resin 3 corresponds to the shape of the heat sink 1.

It is assumed that the mounting screw 12 is a screw that is normally tightened clockwise. With respect to this clockwise rotation direction, the pin marks 5b and 5c forming the thin portion 16b on the side where the force for compressing the resin 3 is applied are arranged at the same positions as in FIG. And, the pin mark 5a forming a thin portion (reference numeral 16a in FIG. 6A) on the side where the force in the pulling direction is applied to the resin 3
5b is shifted in a direction opposite to the rotation direction. With this, the distance from the ends of the pin marks 5a, 5b to the short side of the resin 3 becomes large, and the thickness of the resin 3 becomes large.
It is possible to prevent the resin from cracking or breaking when a clockwise force is applied.

How much the pin marks 5a and 5b are shifted depends on how much tightening pressure is applied to the mounting screw 12, but the center line connecting the center points of the semicircles of the screw holes 4 (see FIG. 1 (A It was confirmed that when the resin was shifted to the position of 23), cracking or chipping of the resin did not occur. This is because in the upper half of the center line 23 in FIG.
It is estimated that a force in the direction of compression is applied to the resin 3 in the lower half.

The pressing pin (reference numeral 8 in FIG. 4) may be provided integrally with the mold 6, but since it is worn due to contact with the heat dissipation plate 1, it is used as a separation pin which is replaceably attached to the mold 6. Is also good. Further, in order to absorb the variation in the plate pressure of the heat dissipation plate 1 and also to be used as a peeling pin for peeling the resin 3 from the mold 6 after molding, a movement for sliding while contacting the surface of the mold 6 It may be a pin. When the separating pin and the moving pin are used, it is more advantageous in terms of accuracy to form the surface for fixing the pin and the mold 6 or the sliding surface with respect to the flat surface of the mold. For this reason, the pin marks 5 in FIG. 3 are all formed by the separating pins, and therefore the pressing pin 8 is not formed in the semicircular portion of the screw hole 4 pattern, but in the straight line portion. It is arranged.
In FIG. 1, the pin marks 5a and 5d are formed by the pressing pin 8 which is integrated with the curved surface of the mold 6, and the pin marks 5b and 5c are formed by the separation type pressing pin 8 which is formed on the flat surface of the mold 6. There is.

FIG. 2 shows a second embodiment of the present invention. The pin marks 5a and 5b are shifted in the previous embodiment, whereas the pin marks 5a and 5b are completely removed in this embodiment. According to this embodiment, the pin marks 5a, 5
Since it can be implemented by controlling the separation type or movable type pressing pin 8 corresponding to b so as not to be removed or moved, immediate implementation is possible.

[0017]

As described above, according to the present invention,
The thin portion of the resin 3 located in a region where the force generated by the rotation of the mounting screw 12 acts in the direction of pulling the resin 3 (Fig. 6).
Since the reference numeral 16a) is removed, there is an advantage that the resin 3 can be prevented from cracking or chipping when the semiconductor device is mounted. Further, according to the second embodiment of the present invention, there is an advantage that it can be carried out immediately by only removing one of the pressing pins 8.

[Brief description of drawings]

FIG. 1 is a plan view (A) for explaining the present invention.
It is a bottom view.

FIG. 2 is a plan view for explaining a second embodiment of the present invention.

FIG. 3 is a plan view (A) for explaining a conventional example.
It is a bottom view.

FIG. 4A is a plan view showing a state during molding, and FIG.
It is an AA line sectional view.

5 (A) is a plan view and FIG. 5 (B) is a side view showing a state at the time of mounting.

FIG. 6A is a plan view for explaining a conventional example, and FIG.
It is a BB line sectional view.

Claims (2)

[Claims] 1. A rectangular heat radiating plate having a screw hole for mounting a screw on its short side, a molding resin for sealing the back surface of the heat radiating plate so as to expose the back surface of the heat radiating plate, and a metal heat radiating plate for molding the heat radiating plate. In a semiconductor device having a pin mark formed in the screw hole portion by a pressing pin that presses against a mold, the pin mark is formed from the pin mark to an end surface of the molding resin in a direction along the rotation direction of the mounting screw. A semiconductor device characterized in that it is positionally shifted so as to increase the distance between the two. 2. The semiconductor device according to claim 1, wherein the pin mark is arranged only in a region where a force applied by the tightening pressure of the mounting screw is applied to the resin in a compression direction.