Gate lead for center gate pressure assembled thyristor

The gate lead for a center gate thyristor consists of a contact disk connected to the end of an elongated flexible conductive lead wire which is insulated over its major length. The lead is threaded through the central opening in a plunger which is received in a central opening in the pole piece and terminates in a contact disk which is captured against the bottom of the plunger. A compression spring is captured between the other end of the cylinder and the plunger, thereby to press the contact disk into high pressure contact with the gate electrode on the junction when the device is assembled. The opposite end of the gate lead wire is connected to a terminal which can be easily connected to the interior end of the gate pin which extends through the insulation housing of the assembly.

BACKGROUND OF THE INVENTION 
This invention relates to high power compression assembled thyristors, and 
more specifically relates to a novel spring biased center gate lead 
structure for such devices. 
Compression assembled housings for high power semiconductor housings are 
well known, and generally comprise a pair of massive copper pole pieces 
coaxially fixed to the opposite ends of a support ceramic cylinder and 
projecting into the cylinder. A semiconductor wafer having the necessary 
P-N junctions therein to define a thyristor is then fixed in position 
between the opposite flat, parallel interior surfaces of the respective 
pole pieces. This wafer is commonly termed a "junction". The junction has 
main electrodes on its opposite surfaces, and these are engaged with high 
pressure by the respective pole pieces when they are put under clamping 
pressure. 
The gate or control electrode for the thyristor is commonly located at the 
center of the top of the wafer or junction. Thus, a gate lead must be 
fixed to the center gate electrode and attached to a gate pin which 
extends through the ceramic insulator during the assembly of the housing. 
Such gate leads can break during assembly or can make poor contact to the 
center junction electrode or pin. The assembly operation is therefore 
tedious and the gate connection unreliable. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with the invention, a novel spring biased contact system is 
provided for making contact to the center gate of a thyristor junction. 
The contact system is carried totally in the upper pole piece and has a 
free contact end to be connected to the interior of the gate pin before 
the pole pieces and cylinder are fixed together. 
The gate contact consists of an insulation cylinder which is fixed in an 
opening in the top pole. A spring plunger is movably mounted within the 
cylinder, and a compression spring presses the plunger away from the pole 
piece and toward the junction. The lead wire extends through an opening 
along the axis of the plunger and terminates at one end with an enlarged 
contact disk which is pressed between the outer end of the plunger and the 
center gate electrode on the junction. The gate lead then extends along a 
slot in the top pole piece and terminates in a connector which is easily 
connected to the interior end of the gate which extends through the wall 
of the ceramic insulator. 
The novel gate lead structure is fully supported in the upper pole piece, 
and permits easy assembly of the pole pieces, ceramic insulator and 
junction in a reliable manner, and ensures good contact to the gate 
electrode of the junction when the pole pieces are assembled.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring first to FIGS. 1 and 2, there is shown therein the outline of a 
typical pressure assembled power semiconductor device, and shows the 
device as having an upper copper pole piece 20, a lower copper pole piece 
21 (FIG. 1) and a ceramic insulator 22 (FIG. 1) which receives the two 
pole pieces 20 and 21. The top and bottom surfaces of the pole pieces 20 
and 21 are flat and parallel and are mounted between housing heat sinks 
(not shown) which press the pole pieces toward one another by conventional 
means. 
The lower pole piece 21 has a copper flange 19 (FIG. 11) which connects it 
to the bottom of insulator 22. The top of insulator 22 has a flange 23 
(FIGS. 1, 2 and 11). The upper pole piece 20 has a mounting flange 24 
which is welded to flange 23 to assemble the package and seal the interior 
of the package. A gate pin 25 extends through the ceramic insulator 22 and 
can be connected to the gate electrode of a junction connected to the 
interior of the housing. The gate pin 25 must be connected to the gate 
electrode of the junction before the package is sealed at flanges 23 and 
24. 
The housing outline of FIGS. 1 and 2 is typical of a number of different 
package outlines which can be used with the present invention. 
FIG. 3 shows an exploded perspective view of the housing of FIGS. 1, 2 and 
11 (without pole pieces) and shows the use of a junction 30 having a 
center gate electrode 31. Note that junction 30 may be any type of 
semiconductor device, but typically will be a thyristor. A silver washer 
32 (FIGS. 3 and 11) is disposed atop the main upper electrode of junction 
31 (FIG. 11). Washer 32 has a opening 33 large enough to prevent contact 
to the center gate electrode of junction 30. A molybdenum washer 35 having 
an opening 36 is disposed atop the silver washer 32. 
A molded silicone junction locator 40 (FIGS. 3 and 11) encloses the 
junction 30, washers 32 and 35 and the bottom of pole piece 20 as shown in 
FIG. 11, to locate the junction relative to pole piece 20 and insulator 22 
and to keep the junction from moving freely within the housing. FIG. 3 
also shows the novel gate assembly 50 which will be later described in 
detail. 
As shown in FIG. 11, the bottom surface of junction 30 (which is 
metallized) contacts the flat upper surface of pole piece 21. 
FIGS. 4, 5 and 6 show the manner in which pole piece 20 is prepared to 
employ the gate contact assembly 50 of FIG. 3. Thus, a slot 51 is cut 
across the interior diameter of the pole piece 20, and an enlarged central 
opening 52 (FIGS. 5 and 6) is formed along the axis of the pole piece. The 
slot 51 allows room for the gate lead while opening 52 receives the gate 
spring assembly housing. 
Thus, the gate lead assembly 50, as shown in FIG. 10, includes a gate 
locator 60 (FIGS. 7, 8 and 11) (or gate assembly housing cylinder) which 
is of any suitable molded insulation material, for example, an insulator 
having the trade name FORTRON. Housing 60 has a central opening 61 which 
leads to a smaller upper opening 62. A notch 63 extends across the radial 
top of housing 60. 
A ceramic insulator spring plunger 70 is slidably movable within opening 61 
(FIGS. 1 and 11) and has an axial opening 72 therethrough. Compression 
spring 73 is then captured atop plunger 70. The gate lead 80 (FIG. 9), 
which may be silver plated copper, has a contact disk or head 81 formed at 
its end. The diameter of wire 80 for its full length may be about 0.4 
millimeters and the diameter of head 81 may be about 1 millimeter. The 
wire 80 is threaded through opening 71 until head 81 seats on the bottom 
of plunger 70. An insulation sleeve 83 encloses the length of lead wire 80 
as shown in FIGS. 10 and 11. 
The opposite end of lead wire 80 from head end 81 receives a suitable 
connector to enable connection of the lead wire to the interior side of 
pin 25, as shown in FIGS. 10 and 11. Thus, a sleeve 90 (FIG. 10) is 
crimped onto the end of wire 80 and wire 80 is then soft soldered to the 
interior of the sleeve 90 of slide-on connector 91. As shown in FIG. 11, 
the connector makes slide connection over the interior end of pin 25. 
It will now be understood that the novel gate lead assembly 50 permits 
simple and reliable assembly of the gate lead in a pressure assembled 
package or housing. Thus, the lead 80 is simply laid into slot 51 of pole 
piece 20, and housing 60 is pressed into opening 52 in the pole piece. The 
gate lead assembly is now fully subassembled with pole piece 20. The 
connector 91 is then connected to pin 25, and the housing can be 
completely assembled without fear of losing the gate connection. Once the 
housing is assembled, contact head 81 is automatically pressed into 
contact with the center gate of junction 30 by spring 73. 
Although the present invention has been described in relation to particular 
embodiments thereof, many other variations and modifications and other 
uses will become apparent to those skilled in the art. It is preferred, 
therefore, that the present invention be limited not by the specific 
disclosure herein, but only by the appended claims.