JPS6244408B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a semiconductor device.

For example, in a semiconductor device such as a resin-molded power transistor, a lead frame on which a semiconductor chip (hereinafter simply referred to as a chip) is placed is exposed on the surface of a resin-molded package, and heat from the chip is transferred to the exposed lead frame (which is used as a heat dissipation section). ). A semiconductor device having such a structure has conventionally been manufactured as shown in FIG. In the figure, 1 and 2 are a pair of molding dies (here, 1 is called the lower mold 2 and the upper mold is called the upper mold), 3 is a chip,
Reference numeral 4 designates a lead integrated with the heat dissipation portion 4A to which the chip 3 is die-bonded, 5 a lead, and 6 a wire such as a gold wire that connects the chip 3 and the lead 5.

When manufacturing a transistor, a heat dissipating section 4A with a chip 3 disposed on its surface is placed on the bottom surface 1A of a lower mold 1, and an upper mold 2 is placed on the lower mold 1. Each lead 4, 5 is led out from this overlapping portion. Then, molding resin is injected into the cavity between the two molds 1 and 2. By the way, in such a manufacturing process, the injected resin covers the bottom surface 1A and the heat dissipation part 4.
If something flows into the gap between A and A,
After completion, burrs begin to form around the heat dissipation part 4A, impairing the heat dissipation effect and lowering the product value. Therefore, when burrs are formed around the heat dissipating section 4A, the burrs are peeled off each time, but the addition of such a step significantly impairs the workability.

In order to prevent burrs from forming around the heat dissipating section 4A, press the surface of the heat dissipating section 4A against the bottom surface 1A so that no gap is created between the heat dissipating section 4A and the bottom surface 1A. good. Therefore, a push pin 8 that penetrates the upper mold 2 is prepared. 9 is a pressing plate for pressing the push pin 8, and 10 is a spacer. By pressing the heat radiating part 4A from the surface with the push pin 8 in this way, the heat radiating part 4A and the bottom surface 1
This makes it possible to prevent a gap from forming between A and A.

However, if a push pin 8 with a flat tip end surface as shown in FIG. 1 is used, the following problem will occur. The first case is when there is variation in the thickness of the heat dissipation section 4A. For example, if the thickness of heat dissipation part 4A is 1.5 mm, the tolerance is ±0.05 mm.
It is said that Therefore, as push pin 8, the thickness is 1.5 mm.
If we set the length necessary to hold down the heat dissipation part 4A of mm, for example, the heat dissipation part 4A is (1.5-
0.05=1.45 mm), a gap of 0.05 mm will be created between the tip end surface of the push pin 8 and the heat dissipation part 4A, and the heat dissipation part 4 by the push pin 8 will
It becomes impossible to hold A.

Conversely, if the heat radiation part 4A has a thickness of (1.5 + 0.05 = 1.55 mm), when the push pin 8 presses down the heat radiation part 4A, the abutment surface between the lower mold 1 and the upper mold 2
A gap of 0.05mm is created, and the existence of this gap causes burrs to form on the peripheral wall of the product after molding. Therefore, in this case, a step to remove this burr becomes necessary.

The second problem is a decrease in moisture resistance. Since the push pin 8 is installed and resin molded as described above,
A hole, which is the mark of the push pin 8, will be formed in the product after molding. The surface of the heat dissipation section 4A is exposed at the bottom of this hole. If the push pin 8 has a flat end surface as described above, the exposed area of the heat dissipation portion 4A will be approximately the same as the end surface of the push pin 8. Therefore, if moisture accumulates in these holes, the surface area that comes into contact with the moisture increases, and the risk of damage increases. Moreover, if such a large amount of moisture comes into contact with the heat dissipating portion 4A, the moisture easily enters the interior through the interface between the heat dissipating portion 4A and the molded resin. It is clear that if such moisture enters, the chip 3, wire 6, etc. will be damaged.

An object of the present invention is to manufacture a semiconductor device so that burrs are not formed around a heat dissipation part or on the peripheral wall of the product.

Another object of the present invention is to manufacture a semiconductor device so that moisture resistance is not impaired.

This invention has a push pin 8 that presses down the heat dissipation part 4A.
As shown in FIG. 2, the tip 8A is shaped like a cone. When a round bar-shaped push pin 8 is used, the tip 8A may be conical, and when a square bar-shaped push pin 8 is used, it may be pyramid-shaped. Then, resin for the package is poured into the mold with the heat dissipating portion 4A pressed against the inner surface of the mold by the push pins 8.

In the configuration shown in Figure 2, the heat dissipation part 4 is thinner (1.45 mm) by the minimum allowable error as the push pin 8.
Let's assume that the length is set to be enough to hold down A. Now, when the heat dissipation part 4A is the standard thickness (1.5 mm) or thicker than this by the maximum allowable value (1.55 mm), the tip of the push pin 8 is cone-shaped. It becomes embedded in the surface of the heat dissipation section 4A. The bite depth at this time is 0.05
~0.1mm. Due to this biting, the heat radiating portion 4A is sufficiently pressed down by the push pin 8. Therefore, both upper and lower molds 1 and 2
There is no possibility that a gap will form on the abutting surfaces. When the heat dissipation section 4A is thin by the minimum allowable error, the push pin 8 is set to a length sufficient to press down the heat dissipation section 4A having such a thickness, so that the push pin 8 is sufficient to hold down the heat dissipation section 4A. In this way, even if there is variation in the thickness of the heat dissipating part 4A, the heat dissipating part 4A
The pressing by the push pin 8 is reliable. This makes it possible to prevent burrs from forming around the heat radiating section 4A or on the peripheral wall of the product.

On the other hand, after molding, a hole 13 is formed in the resin-molded package 12 at the mark of the push pin 8 (see FIGS. 4 and subsequent figures). However, the lower end surface of this hole 13 has a cone shape that is the same shape as the tip of the push pin 8. Therefore, unlike when a push pin 8 with a flat tip surface is used, the heat dissipating portion 4A is not exposed by the same area as the tip surface, but the exposed portion is a point or a small area. As a result, even if moisture enters the hole 13, the area of the heat radiating portion 4A that is in contact with the moisture is extremely small. Therefore, moisture is sufficiently prevented from entering the package 12 through the holes 13.

As shown in Fig. 2, when the push pin 8 is pressed by the pressing plate 9 as in Fig. 1, the first
Although it is no longer necessary to make the dimensions of the push pin 8 more precise than in the case shown in the figure, a certain degree of dimensional precision is still required. Figure 3 shows a further solution to this problem. In this configuration, the push pin 8 is pressed down by a push plate 9 via a spring 14. If the push pin 8 is held elastically in this way, the push pin 8 will rise against the elasticity or fall due to the elasticity depending on the variation in the thickness of the heat radiating part 4A, so that the heat radiating part 4A is always pressed down. It begins to hold down elastically. Therefore, it is no longer necessary to make the length of the push pin 8 highly accurate. Note that the heat dissipation part 4A is placed in the upper mold 2.
It may be placed on the surface and pressed from below by the push pin 8.

4 to 6 are a cross-sectional view, a plan cross-sectional view, and a bottom view of a semiconductor device, such as a power transistor, manufactured according to the present invention. Note that 15 in the figure
A through hole is formed to pass through the package 12 as necessary, and is used for inserting a mounting screw when installing the transistor on a wiring board or the like.

As detailed above, according to the present invention, it is possible to manufacture a product without causing burrs on the peripheral wall or around the heat sink, and it is also possible to improve the moisture resistance of the obtained product. be effective.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining the conventional method, FIG. 2 is a sectional view for explaining the manufacturing method according to the present invention, and FIG. 3 is a sectional view for explaining another manufacturing method of the present invention. FIG. 4 is a cross-sectional view of a transistor manufactured by the manufacturing method according to the present invention;
The figure is a sectional plan view of the same, and FIG. 6 is a bottom view of the same. 1, 2... Mold, 3... Semiconductor chip, 4...
Lead, 4A...Heat radiation part, 8...Push pin, 8A
...Tip, 12...Package, 14...Spring.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a semiconductor device comprising a package made of molded resin and a heat dissipation section exposed on the surface of the package, wherein the heat dissipation section is molded with a push pin having a cone-shaped tip. 1. A method of manufacturing a semiconductor device, characterized in that the molding resin for the package is cast while being pressed against the inner surface of a mold for the package. 2. In a method for manufacturing a semiconductor device comprising a package made of a molded resin and a heat dissipating section exposed on the surface of the package, the heat dissipating section is attached to the inner surface of a molding die using a push pin with a cone-shaped tip. A method of manufacturing a semiconductor device, characterized in that the molding resin for the package is cast while being elastically pressed against the package.