JPS599946A - Structure of cap for metal seal type semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the generation of the leakage of an internally enclosed gas and the exfoliation, etc. of a welding section by forming an annular groove to the unbonded surface of a flange through press work while forming an annular projecting section to the unbonded surface with the formation of the annular groove. CONSTITUTION:With the cap 10, the high annular projecting section 10B is formed to the unbonded surface of the flange 10A for the cap while the annular groove 10C generated with the formation of the projecting section 10B is formed on the unbonded surface side of the flange 10A. Accordingly, even when an inner jig and an outer jig are worn away unequally and a stem is bent and molded, a clearance is not generated between the projecting section 10B and the stem, and a bead and the stem can be pressure-welded by adequate contact pressure at all times. The height of such a projecting section 10B can only be realized by molding the groove 10C through press work.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a cap structure for a metal-sealed semiconductor device.

[Technical background of the invention]

Individual semiconductor elements such as power transistors are generally enclosed in metal packages, and are configured as metal-sealed semiconductor devices that can maintain high reliability even during long-term use. As is well known, this metal package consists of a flat stem on which a semiconductor element is mounted, and a metal cap fixed onto the stem by resistance welding. is filled with an inert gas such as N2. A metal-sealed semiconductor device with such a configuration can operate stably over a long period of time as long as the welding between the cap and stem is reliable and the internal gas does not leak. In the manufacturing process, for the reasons described below, there is a considerable number of defective products due to poor welding, and it is necessary to improve this situation.

[Problems with background technology]

Below, the structure of a conventional metal-sealed semiconductor device and its sealing method will be explained with reference to the drawings, and the reason why welding defects occur will be explained.

1 and 2 show the schematic structure of a known metal-sealed semiconductor device, in which 1 is a stem and 2 is a stem.
is a cap, 6 is a heat dissipation plate fitted to a part of stem 1, 4
6 is a semiconductor element having a brazing material 5 fixed on the heat dissipation plate 6 with a wire (not shown), 6 is a lead-out lead connected to the electrode V of the semiconductor element 4 via a wire (shown), and 7 is a part of the lead-out part. This is the brazing material that fixes 6.

As seen in the figure, the cap 2 is provided with a flange 2A' (i-) along the outer peripheral edge of its end;
A = i The cap 2 is fixed on the stem 1 by resistance welding to the stem 1.

Conventionally, the cap 2 and the stem 1 have been welded using a jig shown in FIG. In FIG. 3, reference numeral 8 denotes an inner jig made of copper that supports the cap 2 in an inverted state, and this inner jig 8 also serves as an electrode during welding. Reference numeral 9 denotes an outer jig that horizontally supports the stem 1 in an upside-down state, and this outer jig 9 is made of a synthetic resin insulator such as Teflon. Place stem 1 and cap 2 on these jigs as shown by the two-dot chain line, and press a welding electrode (not shown) against the back surface of stem 1 corresponding to the position of cap 2 on flange 2. The cap 2 is fixed to the stem 1 by welding. As shown in Fig. 4, a low-height annular bead 2B is formed on the flange 2A of the cap 2 by press working, and the bead 2B is pressed against the surface of the stem 1 to concentrate the welding current there. The bead 2B' is melted to form a welded portion.

When welding the cap 2 and the stem 1 using such a jig, it is necessary that the bead 2B is completely melted around the entire circumference of the cap 2 in order for the welded portion of both to be complete. For this purpose, it is necessary that the entire end surface of the bead 2B is always pressed against the surface of the stem 1 with uniform pressure over its entire circumference. However, with the above-mentioned jig, it is not possible to maintain such conditions for the following reasons, and this may lead to defective welding of the cap 2, which immediately causes a defective package of the semiconductor device. It has become.

Since the entire surface of the bead 2B is always welded to the stem 1 in the jig, K is (i) the cap support surface 8A of the inner jig 8;
and the stem support surface 9A of the outer jig 9 are always completely parallel, and (11) the amount of wear on each of the surfaces 8A and 9A is equal, and the shaft is worn uniformly over the entire circumference. Although certain conditions are required, parts of both jigs 8 and 9 that are made of different materials, and the cap support surface 8 of the inner jig 8
Since it also serves as an aid welding electrode, the relationship between the height positions of both sides and the parallelism of both sides change as the stem support surface of the external jig 9 changes θ, and as a result, the entire surface of the bead 2B comes into contact with the surface of the stem 1. Otherwise, the contact pressure between the bead 2B and the stem 1 becomes uneven. Therefore, in areas where the contact pressure between bead 2B and stem 1 is insufficient, welding strength may be insufficient due to insufficient penetration, and in areas where bead 2B and stem 1 are not in contact, welding No current flows and no welding occurs.

On the other hand, in addition to the problems caused by such uneven wear of the jig, warpage, that is, curvature, of the stem 1 has also been a cause of poor welding between the cap 2 and the stem 1. stem 1
In principle, it is necessary that the stem 1 be flat, but since the stem 1 is manufactured by press working, it is often curved to the bottom side during the press working as shown in Fig. 5. If the key 2 is curved, even if there is no problem with the jig as described above, the key 2 knob 2 will be bent as shown in Figure 5.
A gap g is created between the surface of the bead 2B and the surface of the stem 1, resulting in only a portion of the bead 2B being welded, resulting in defective welding of the cap.

In order to prevent such welding defects, the height of the bead should be made higher than before so that even if the jig wears out now, no gap will be created between the bead 2B and the stem 1. At the same time, it is necessary to ensure that the contact pressure between the two is not insufficient, and by making the tip of the bead thinner, it is necessary to increase the current density at the point of contact with stem 1 so that the entire bead can be reliably melted. . However, cap 2 (l
Conventionally, such a solution has not been considered because the bead height cannot be made very large due to nibless molding.

[Purpose of the invention]

This invention solves the above-mentioned problems, and even if the jig 8.9 is unevenly worn or unevenly worn, the cap will not be defective in welding, and even if the stem 1 is warped or curved, the cap can be fixed. An object of the present invention is to provide an improved cap structure that does not cause poor welding.

[Embodiments of the invention]

This invention was made based on the idea mentioned above,
By making the bead height higher than before, even if the inner jig and the outer jig wear unevenly, a gap is not created between the stem 1 and the bead 2B of the cap 2, and at the same time, the stem 1 The cap is characterized in that the cap is constructed such that an appropriate contact pressure is maintained between the bead 2B of the cap and the bead 2B of the cap. The cap according to the present invention has a higher bead than the conventional cap, and also has an annular groove formed on the non-joining surface of the flange at the same time when this bead is completely formed, and by forming this annular groove, the height of the bead is increased. The size is larger than that of conventional caps. Further, since the tip of the build in the cap of the present invention is thinner than that of a conventional bead, the current density at the joint surface with the stem is increased, so that the bead tip can be reliably melted.

[Embodiments of the invention]

FIG. 6 shows a portion of the cap 10 improved according to the present invention. As shown in the figure, the cap 10F/'i of the present invention
The flange 10A has a high annular protrusion, that is, a bead 10B'e on the joint surface side, and the flange 10
The non-bonded surface side of A has an annular groove 10C that is generated due to the formation of the bead [1B]. The height H of the bead 10B is greater than that of the conventional cap, and the width W of the tip thereof is 1/2 of the value of the conventional cap. Therefore, even if the inner jig 8 and the outer jig 9 wear unevenly or the stem 1 is curved, there will be no gap between the bead 10B and the stem 1, and the bead and stem The stem and cap can always be brought into contact with each other with an appropriate contact pressure, and the bead can be reliably melted and the stem and cap can be welded together.

Such a height can only be achieved by forming the annular groove 10C using force and force when forming the cap by press working. cannot be realized.

〔Effect of the invention〕

When a metal-sealed semiconductor device was manufactured using the cap 10 having the structure described above and a curved stem, and a leakage test of the sealed gas and a destructive test were performed on the device, no defective products were found in any of the tests. I didn't.

On the other hand, when a leakage test and a destructive test were conducted under the same conditions as above for a metal-sealed semiconductor device manufactured using a cap 2 with a conventional structure and a curved stem, 30% of the products were defective in the leakage test. In the destructive test, 6 pieces were found to be defective.

In view of these results, it has become clear that leakage of the internally sealed gas and peeling of the welded portion can be prevented by forming the cap structure as in the present invention.

Therefore, according to the present invention, it is possible to provide an improved cap structure that can prevent the occurrence of defective products as described above without making any major improvements to conventional semiconductor device manufacturing equipment.

Note that although the above embodiments show the case where the present invention is applied to an individual semiconductor device, it goes without saying that the present invention can also be applied to integrated circuit devices such as LSIs and ICs. It is clear that the present invention is applicable not only to the case of a rectangular shape.

[Brief explanation of drawings]

FIG. 1 is a plan view of a conventional semiconductor device, FIG. 2 is a sectional view taken along the line H-II in FIG. 1, FIG. 6 is a longitudinal sectional view of the semiconductor device manufacturing apparatus shown in FIG. 5 is an enlarged vertical sectional view of the flange portion of the cap of the semiconductor device in the state shown in FIG. 3;
This figure is an enlarged sectional view showing the state of contact between the cap and the curved stem in the apparatus of FIG. 6, and FIG. 6 is an enlarged longitudinal sectional view of the flange portion of the cap according to the present invention. 1. Stem, 2.10. Gap, 2A, IOA.
... Nolanji, 2B, 10B... Bead, ioc
...Annular groove, 4...Semiconductor element. Figure 1 Figure 2 Figure 4 ρ Figure 3 Figure 5

Claims (1)

[Claims] 1. In a metal cap for a metal-sealed semiconductor device, the metal cap has an annular groove formed by press working on the non-bonding surface of the flange, and an annular protrusion formed due to the formation of the annular groove. 1. A cap structure for a metal-sealed semiconductor device, characterized in that the joint surface of the flange is provided with: