GB2135119A - Self-aligning, self-loading semiconductor clamp - Google Patents

Abstract

A self-aligning clamp for a compression bonded semiconductor device 66 and that can be assembled without the use of a press, uses a ball and socket component 36,46 and the compression is controlled by the use of Belleville washers 28 designed for a specific force. Bolts 94 force down a pressure plate 16 until the plate abuts a sleeve 102. The clamp holds the semi- conductor device to its leads/electrodes 64/72. <IMAGE>

Description

SPECIFICATION Self aligning, seif loading semiconductor clamp The present invention relates generally to discrete power semiconductor devices and more specifically to a self-aligning, self-loading clamp for a discrete power semiconductor device.

Clamps which first require jigging to align discrete semiconductor devices in the clamp and then require a press to compress the device within the clamp are known. The principal object of the invention is to maintain a given uniform force on a semiconductor device.

The invention resides broadly in a clamp for holding a semiconductor device (66), structure (28) within said clamp, for originating and maintaining a compressive force within said clamp and structure (36,46) for transmitting said compressive force to said semiconductor device characterized in that the compressive force structure originates and maintains a given force (102, 94, 28,72, 12) and the force transmitting structure (36,46) transmits a uniform compressive force.

The present invention is directed to a clamp for a semiconductor device, said clamp comprising means for positioning and holding a semiconductor device in a predetermined position within said clamp, means integral with said clamp for originating and maintaining a predetermined compressive force within said clamp and means for uniformly transmitting said compressive force to said semiconductor device.

For a better understanding of the nature of the present invention reference should be had to the following detailed discussion and drawing of which: Figure 1 is a top view of a clamp embodying the teachings of this invention; and Figure 2 is a cross-sectional side view of the clamp of Figure 1 taken aiong the line 1 1-11.

With reference to Figures 1 and 2, there is shown a clamp 10 embodying the teachings of the present invention.

The clamp 10 is comprised of a metal clamp plate 12 preferably of a hardened steel. The metal clamp plate 12 is triangular in shape and has an aperture 14 at its midpoint. The aperture 14 extends entirely through the plate 12 from top surface 16 to bottom surface 18.

A A metal locator 20 is disposed in contact with bottom surface 18 of the clamp plate 12. The locator 20 is preferably of aluminium with a thickness of from 0.0020 to 0.0030 inch. The locator 20 has an inverted cylindrical shape. Bottom portion 22 of the cylinder is disposed along and in physical contact with bottom surface 18 Gf the clamp plate 12. Side portion 24 of the cylindrical shaped locator 20 is disposed away from the bottom surface 18 of the clamp plate 12. There is an aperture 26 extending entirely through bottom portion 22 of the locator 20.

The aperture 26 in bottom portion 22 of locator 20 is vertically aligned with the aperture 14 in clamp plate 12.

A disc spring 28, preferably comprised of steel Belleville washers is disposed inside side portion 24 of locator 20. The disc spring 28 has a portion of top surface 30 in contact with the bottom 22 of locator 20 and a portion of bottom surface 32 in contact with a shoulder 34 of a ball member 36.

The ball member 36 is comprised of a metal preferably aluminum or steel. The ball member 36 has a top surface consisting of a flag central portion 38 and the shoulder portion 34. The central portion 38 and the shoulder portion 34 are joined by a vertical portion 40.

Bottom surface 42 of ball member 36 is a curved surface that mates with top surface 44 of socket member 46.

There is a first aperture 48 and a second and wider aperture 49, concentric with the first aperture, which together extend entirely through the ball member 36 from top surface 38 to bottom surface 42.

The socket member 46 is comprised of a metal, as for example, aluminum or steel and is preferably comprised of the same metal as ball member 36.

The socket member 46 has an essentially flat bottom surface 50, a vertical side 52 and a curved top surface 54. The curved top surface 54 mates with curved bottom surface 42 of ball member 36.

There is an aperture 56 extending through the socket member 46 from top surface 54 to bottom surface 50.

There is a washer 56 of an electrically insulating material as for example mica disposed in physical contact with bottom surface 50 of socket member 46.

The washer 56 has an aperture 58 therein.

A metal electrical lead 60, preferably having an "L" shape configuration, has a first portion 62, the base of the "L", disposed in contact with washer 56 and a second portion 64, the vertical portion of the"L", disposed vertically outside of the perimeter of the clamp plate 12. In Figures 1 and 2, the vertical portion 64 is shown extending vertically upward toward, but outside of the perimeter of, the clamp plate 12. It will be understood of course that the vertical portion can extend downward away from the clamp plate 12 if desired.

There is an aperture 65 in the lead 60 to facilitate making contact to other external circuit components not shown.

The electrical lead 60 is preferably of copper or aluminum.

A flat, compression bonded semiconductor device 66 is disposed with a first diaphram electrode 68 in electrical ohmic contact with base portion 62 of electrical lead 60.

The semiconductor 66 shown is a transistor of the type designated JEDEC D62T. It will be understood that any flat type, compression bonded semiconductor device can be used in the clamp of this invention and that the device may be a transistor, rectifier or thyristor.

A second diaphragm electrode 70 of device 66 is in ohmic electrical contact with a metal collector plate 72.

The collector plate 72 is preferably of copper.

There is an aperture 73 in collector plate 72.

The electrical lead 60 and the collector plate 72 provide electrical contact means: to the emitter and collector regions of a transistor; to the cathode emitter and anode emitter of a thyristor; and to the anode and cathode of a rectifier. If it is necessary to make electrical contact to a third region of the device as for example to the base region of a transistor or thyristor, means 74 can be brought out through side wall 76 of the device.

In assembling the clamp of this invention, the semiconductor device 66 is disposed on top surface 78 of collector plate 72.

A Adowel pin 80, preferably of steel, is inserted through aperture 73 in the collector plate and into a shallow dimple 82 in the second diaphragm electrode 70. The dowel pin 80 serves to hold the device 66 in place on the collector plate 72.

The electrical lead 60 is then positioned with bottom surface 84 of base portion 62 in physical contact with first diaphragm electrode 68 of the device 66.

Mica washer 66 is disposed over top surface 86 of base portion 62 of electrical lead 60. The mica washer 56 electrically insulates the device 66 from the remainder of the clamp disposed above the lead 60.

Socket member 46 is then disposed on the mica washer 56 with bottom surface 50 of the socket member 46 in physical contact with washer 56.

Bottom curved surface 42 of ball member 36 is disposed in the curved top surface 54 of socket member 46.

Disc spring 28 has its bottom surface 32 disposed on shoulder portion 34 of ball member 36.

Locator member 20 is disposed on top surface 30 of the disc spring 28, with side portions 24 of the locator member 20 extending downwardly and about disc spring 28.

Clamp plate 12 is then disposed on the locator member 20.

A centering pin 88 is then inserted vertically downward through the aperture 14 in clamp plate 12, aperture 26 in locator 20, between the washers of disc spring 28, aperture 48 in ball member 36, aperture 88 in socket member 46, aperture 58 in washer 56, aperture 62 in base portion 62 of electrical lead 60 and into a dimple 92 in diaphragm electrode 68.

The centering pin 38 is preferably comprised of a cured resinous impregnated material as for example, that material sold under the Trademark MICAR TA. Generally, such a material is comprised of a heavy corse paper, such as that sold under the Trademark KRAFT PAPER impregnated with a phenolic or an epoxy resin.

An O# ring 94 of for example, a silicone rubber may be disposed about centering pin 88 atthe point where the centering pin 88 intersects with top surface 16 of clamp plate 12 to hold the components in place.

Three bolts 94 are inserted, one through each aperture 95 in clamp plate 12. The bolts 94 are of steel and have threads 96 on one end which are compatible to threads in apertures 98 in collector plate 72.

An electrical insulating sleeve 100 is shrink fitted around each of the bolts 94 and a bushing 102 preferably of steel is disposed about each bolt 94.

The bolts 94 are screwed into the apertures 98 in the collector plate 72 until the clamp plate 12 comes into physical contact with the bushing 102.

By coordinating the disc spring 28, the length of the bolt 94 and the length of the bushing 102, the desired pressure is transmitted to the device 66. It will be noted that the compressive force is created within the clamp without the use of an external press. That is the force is originated entirely within the clamp itself.

For example, using a disc spring 28 consisting of four Belleville washers, two in series and two in parallel as shown, having a flat load rating of 498 pounds, a bolt length of 1.44 inches with 0.75 inch threaded portion, a bushing have a length of 1.21 inches as measured from the top of collector plate 72, and a clamp plate having a thickness of 0.125 inch a force of 700 pounds can be brought to bear on a D62Ttransistor. This is adequate for the D62T transistor to operate.

The semiconductor fusion which comprises part of the D62T transistor may have, due to the intricate emitter geometry on its top surface, a height differential of up to 0.003 inch. If a compressive force of 700 pounds was transmitted to the top surface of the fusion without any allowance for this height differential, the fusion, due to excessive pressure being applied to the highest spot, may crack or be crushed.

However, a uniform application of force to the fusion is assured by the presence of the ball and socket members 36 and 46 respectively. As the force is applied the ball and socket members adjust to ensure the force is applied equal to the first diaphragm electrode and to the fusion.

If an electrically insulating member 104, as for example a sheet of mica cloth is disposed on bottom surface 106 of collector plate 72, the clamp can be electrically isolated from whatever it is mounted on.

The clamp of this invention can be assembled in a factory or at the users site and does not require any presses or special jigs.

The clamp while described in terms of a transistor can be used for any single semiconductor device or for more than one device i.e., a stack of for example rectifiers. Further, obviously the clamp can also be used for combinations of devices.

Claims (4)

1. A clamp for holding a semiconductor device (66), structure (28) within said clamp, for originating and maintaining a compressive force within said clamp and structure (36,46) for transmitting said compressive force to said semiconductor device characterized in that the compressive force structure originates and maintains a given force (102,94,28, 72,12) and the force transmitting structure (36,46) transmits a uniform compressive force.

2. A clamp according to claim 1, characterized in that said compressive force structure (102, 94, 28, 72, 12) includes a spring member (28) and structure for compressing said spring member a given distance (102,94,72, 12) to originate and maintain said given force.

3. A clamp according to claim 2, characterized in that said compressing structure comprises a first plate (12) and a second plate (72) being disposed to receive said compressive force structure, said force transmitting structure and said semiconductor device therebetween, said compressing structure also comprising bolts (94) for extending between said first and second plate for adjusting the distance between said plates and a bushing (102) having a given length disposed about each of said bolts (94), said given length determining said given compressive force when said bolts are tightened against said bushings.

4. A clamp according to claims 1,2 or 3, characterized in that said force transmitting structure includes ball and socket members (36, 46) disposed between said compressive force structure and the semiconductor device (66).