Closure for semiconductor device and method of construction

DETAILED DESCRIPTION OF THE INVENTION A semiconductor device constructed according to the invention is shown in FIG.
1 as a silicon controlled rectifier.
The silicon controlled rectifier includes three subassemblies; a base pellet assembly 1 shown in FIG.
2, a cathode gate tube assembly 3 shown in FIG.
3 and an anode diaphragm assembly 5 shown in FIG.
4.
The cathode gate tube assembly 3 and the anode diaphragm assembly 5 are assembled into a subassembly shown in FIG.
5 and this subassembly is assembled to the base pellet assembly 1 as shown in FIG.
1.
The base pellet assembly 1 comprises a triangular base 7 having holes 9 at the apices of the angles for attaching the base with screws 10 and bushings 12 to a heat sink (not shown).
The base has a planar mounting surface for good heat conduction.
An externally threaded flange 11 extends upwardly from the base.
A semiconductor pellet 14 is centered in flange 11 on base 7 by an insulating ring 16.
An annealed silver wetting wafer 15 serves to wet the pellet-base interface to assure intimate electrical and thermal contact at final assembly.
The cathode gate tube assembly 3 shown in FIG.
3 comprises a cathode tube 17 of copper having a flange 19 at one end.
A gate tube 21 of nickel iron is centered in cathode tube 17 and is secured thereto by a compression bonded glass seal 23.
A steel tube 25 is soldered or brazed to the inner surface of cathode tube 17 for better adherence of the glass seal 23 and to strengthen the bond.
The anode diaphragm assembly 5 shown in FIG.
4 comprises a relatively thin metallic diaphram 27 with a flanged center 29 having a diameter large enough to fit over cathode tube 17.
An anode ring 31 of steel having a cylindrical skirt 30 depending therefrom is arranged concentrically to diaphragm 27 and an annular ceramic insulator 33 metalized on both flat surfaces 34 and 36 is assembled between diaphragm 27 and anode ring 31 and the metalized surfaces are soldered or brazed to the diaphragm and anode ring.
The lower portion of cylindrical skirt 30 is threaded at 32 for attachment to flange 11 on base 7