US2960639A - Semi-conductor rectifier assemblies - Google Patents

Description

Nov. 15, 1960 P. M. TIPPLE 2,950,539

SEMI-CONDUCTOR RECTIFIER ASSEMBLIES Filed June 4, 1959 7 7 fl i I 2 INVENTOE fimm z w 8Y5 Z V?" TTORNEYS SEMI-CONDUCTOR RECTIFIER ASSEMBLIES Peter Moi-land Tipple, Ruisiip, England, assignor to Enghsh Electric Valve Company Limited, London, England, a British company Filed June 4, 1959, Ser. No. 818,187 Claims priority, application Great Britain July 2, 1958 2 Claims. (Cl. 317234) This invention relates to semi-conductor rectifier assemblies and more specifically to semi-conductor rectifier assemblies of the kind in which the rectifier propera germanium or a silicon rectifieris housed within an hermetically sealed, gas filled envelope.

According to this invention a semi-conductor rectifier assembly comprises a rectifier proper mounted in an hermetically sealed envelope which also houses a body of solidified desiccant material.

A preferred desiccant material is aluminum sodium silicate which has been subject to molecular sieving and solidified. Such a body is comparatively free from liability to the formation of desiccant dust.

Preferably the body is a pre-cast ring or cylinder or solidified desiccant material. Where, as is commonly the case in practice, the hermetically sealed envelope comprises metal parts which are brazed or otherwise fixed to one another (to complete the envelope) by a heating process involving the application of high temperature, the desiccant ring or cylinder is preferably positioned between the rectifier proper and the areas at which said parts are so fixed to one another so as to provide a measure of shielding of the said rectifier proper from vapours which may be produced by the high temperature heating process.

The invention is illustrated in the accompanying drawings which show, partly in section, two embodiments thereof. Like references indicate like parts in both figures.

Referring to Figure 1, the assembly therein shown comprises a rectifier junction I mounted in the usual way on the customary heavy copper heat sink base 2 between the upper face of said base and the usual top piece 3. The latter is of rectangular section being narrower in the direction at right angles to the plane of the paper than it is in the direction of said plane. An hermetically sealed envelope is completed by means of metal members 4, 5, 6 and 7 and a glass ring 8. The approximately cylindrical member 4 is welded to the top piece 3 near the bottom edge thereof; the approximately annular member 7 is welded to the underside of a top flange on the member 2; the parts and 6 are fused each at one end into opposite ends of the glass ring 8; and the remaining ends of the parts 4 and 5 and the remaining ends of the parts 6 and 7 are brazed together as shown in a final brazing operation to complete the enevlope. An exhaust tube 9 enables the device to be pumped out and filled with a suitable dry gas.

In accordance with this invention a ring of solid desiccant material, pre-cast to a desired shape, such as that shown, and made, for example, of molecular sieved aluminium sodium silicate pre-cast into the solid body, is provided at it). After pumping out and filling with gas, the tube is, of course, pinched off in the usual way.

The desiccant ring serves the important purpose of maintaining the interior of the envelope in a dry state during the life of the device. Careful research has shown that the maintenance of a high degree of dryness is very important to good performance, probably more important than the choice of the gas used. Known gas filled rectifier assemblies have fallen far short of the desired maintenance of a high degree of dryness principally because it is in practice almost impossible to avoid the release, during the life of the device, of small quantities of water vapour occluded by metal surfaces inside the envelope. Accordingly, even though great care is taken in manufacture of a known device to ensure that the gas filling is dry when it is put into the envelope, it all too often happens that when the device has been in use some time the gas filling is no longer of the required dryness. The ring 10 of solidified desiccant provided in accordance with this invention acts as a getter for water Vapour that may be released during the life of the device. The fact that the ring is of solidified desiccant material eliminates or reduces to negligible proportions the risk of powdered desiccant coming near or in contact with the rectifier proper 1. There will therefore be, in general, no need to provide protective films surrounding the rectifying junction. Further, with the ring 10 positioned as shown, it acts as a shield to prevent brazing vapours produced during the final brazing operations of manufacture from reaching the rectifying junction.

The modification shown in Figure 2 will be largely self-evident from the figure. As will be seen, the essential difference between the arrangement of Figure 2 and that of Figure 1 lies in the somewhat different shape and positioning of the solidified desiccant body which in Figure 2 is referenced to 10 In Figure 2, the desiccant body 10- is a cylinder mounted with one end in a ring recess in the top face of the heat-sink base 2. It projects up between the parts 4 and 5 and as will be observed provides a high degree of protection of the rectifier proper 1 against possible vapours produced during the final brazing operations.

I claim:

1. A semi-conductor rectifier assembly comprising a rectifier proper mounted in a hermetically sealed envelope having metal parts, areas of which have been fixed to one another by a process involving the application of high temperature heating, and wherein a pro-cast body of solidified desiccant material is positioned between the rectifier proper and said areas at which said parts are so fixed to one another.

2. An assembly as claimed in claim 1 wherein the desiccant material is aluminium sodium silicate which has been subject to molecular sieving and solidified.

References Cited in the file of this patent UNITED STATES PATENTS 2,686,279 Barton Aug. 10, 1954 2,820,931 Koury Jan. 21, 1958 2,858,356 Setchell Oct. 28, 1958

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