E3 M.5 FIG. 3

Dec. 21, 1948. D. L. SNOW ET AL 2,456,653 SEAL FOR HIGH-FREQUENCY TRANSMISSION LINES Filed Dec, l0, l942 NNSS S N - N raxx as as X x rary ox as a X x X x X won a 27 s Š 2 - 22222 12ZYZZY NRSNNNNNN F.G. 2 24 4 E3 m.5 FIG. 3 S-3 33 % 8 INVENTORS, D. L. SNOW, W. W. HANSEN; 2/66,AORNEY Patented Dec. 21, 1948 2,456,653 UNITED STATES PATENT OFFICE 2,456,653 SEAL FOR HIGH-FREQUENCY TRANSMISSION LINES, Donald L. Snow, Hempstead, and william W. Hansen, Garden City, N. Y., assignors to The Sperry Corporation, a corporation of Delaware Application December 10, 1942, serial No. 468,603 3 Claims. (C. 174-28) 1. This invention relates to seals and methods of . further important part of our-invention, as will . making them and is particularly concerned with be described below, includes methods for prevent the making of efficient seals in electronic and like ing bubbling and similar defects in the seal. devices. According to another phase of the invention phasein itsof thepreferred invention embodiment will be described an important with re we have solved problems encountered during the : gard to the formation of an efficient insulating operations of soldering members made of the seal between the inner and outer conductors of above-consideredmetal parts. These cobalt-nickel-iron joints must be alloymechanically to other a concentric transmission line. ... strong and vacuum tight. The features of metal . In electronic apparatus we prefer to make both 10 to-metal seal are particularly claimed in copend inner and outer conductors of an ultra high fre ing application S.N. 54,872, filed October 16, 1948, ... quency concentric transmission line of a cobalt entitled Metal-to-metal seals. nickel-iron alloy of the type known variously by In securing such alloy members together or to such trade names as Kovar and Fernico. This another metal we preferably employ a soldering alloy is used because it has approximately the s operation, using a solder having an appreciable 'same low coefficient of thermal expansion as silver content and a relatively high melting point. borosilicate glass for normal Operating temper We have found that this silver solder has an ex atures and therefore appears especially adapted tremely high affinity for the nickel-cobalt-iron for use with insulating glass seals. For the con alloy, and rapidly enters into combination with position of such an alloy, see U. S. Letters Patent 20 it. This high affinity of silver solder for the alloy No. 1,942,260. apparently results in an alloying action between The use of such alloy conductors has, however, the nickel-cobalt-iron alloy and the silver in the raised an unexpected problem because the alloy solder, whereby the alloy member develops a rel is a relatively poor electrical conductor, especially atively large newly alloyed and relatively brittle for ultra high frequency currents. Thus, al 25 though gas-tight seals may readily be provided weakened section which may crack to destroy the between such alloy conductors and glass, such vacuum when subjected to temperature variations a transmission line construction has not proved and other stresses during normal operation. to be electrically efficient, especially at high fre According to another important phase of the quencies, and its losses may usually be relatively 30 invention, we have developed new methods for large. silver soldering a member made of nickel-cobalt We have discovered that if the current cOn iron alloy whereby the mechanical strength of ducting surfaces of the conductors are electro Operation,the member is not impaired by the soldering plated, or similarly coated, with a layer of copper or some other excellent electrical conductor, such 35 With the above in mind it is a major object greatly increases the electrical efficiency of the of the invention to provide a novel method of transmission line and reduces the losses therein. connecting a metal member in gas tight relation This is an important part of the invention. But with another metal member and a glass' body. considerable difficulty has often been encountered It is a further object of the invention to provide in embodying the glass seals in such plated-alloy 40 a high frequency device having efficient durable conductor transmission lines. Apparently as a novel sealed joints, which are resistant to the result of the relatively high temperatures neces thermal and mechanical stresses encountered sary for the sealing operations, Severe mechanical during normal operation of the device. defects in the seal have been encountered. These It is a further object of this invention to pro defects usually comprise bubbles in the glass, and Wide a novel method of sealing glass to metal pockets between either the plating and the glass wherein imperfections in the seal are completely or the plating and the alloy surface. Often the avoided. copper plating is entirely removed Over large A further object of the invention is to provide sections, thus destroying the advantage of elec a novel method of sealing glass to metal wherein trical conductivity for which it was employed, absorbed gaseous or gas forming substances are and even more often the glass itself is cracked removed from the metal before assembly with or becomes easily broken, thereby destroying the the glass. Preferably this removal is effected by vacuum and the insulating qualities of the seal. a vacuum firing Operation. , According to our observation, these bubbles and A further object of the invention is to provide pockets are caused by gaseous substances released 5 5 a novel method of sealing glass to a plated nickel from the metal during the heat of the sealing cobalt-iron alloy member wherein imperfections Operation. Wery probably these gaseous sub completelyin the seal avoided.and the resultant novel product. are . stances come mainly from the copper plating, A further object of the invention is to provide wherein they are probably absorbed or otherwise a novel method of Sealing glass to a copper-plated contained until released by the sealing heat. A nickel-cobalt-iron alloy element wherein sub 2,458,658 3 4. stances absorbed or otherwise contained on or Conductor 2 is a relatively stiff wire held firm in the plating which may liberate to form bubbles ly centrally in the transmission line assembly by in the seal upon the application of sealing heat an annular seal 27 of glass or some other rigid are removed prior to incorporation of the element highly insulating material, which also forms a gas with the glass. tight seal for the conductor, A further object of the invention is to provide Wall is formed with an annular groove 2 a novel high frequency energy transmission line in which is seated and soldered one end of a and method of making the same. cylindrical barrel 29, preferably of Kovar or its A further object of the invention is to provide above mentioned equivalents. The other end of a novel joint between two metal surfaces Con O barrel 29 is enclosed by a glass envelope 30 sealed nected by a solder containing a metal which is thereto along rim 3 so that the interior of the readily alloyable with one or both of said surfaces, tube is gas tight for evacuation to operating con wherein formation of the alloy is avoided, and dition. methods of making such a joint. The above discussed problems of making ef A further object of the invention is to provide a 5 ficient gas tight joints capable of withstanding the novel joint between two metal surfaces connected thermal and other mechanical strains attendant by a solder containing a metal which is readily to operation of such ultra high frequency appa alloyable with at least one of said surfaces, where ratus have chiefly been solved by the invention, in formation of the alloy is avoided by first coat as embodied in the above, and the solutions will ing said one surface with a metal which prevents 20 be explained in detail below. the solder from contacting said one surface. Fig. 2 illustrates a greatly enlarged section A further object of the invention is to pro through the glass-to-metal seal 27 in the concen vide a novel method of silver soldering a nickel tric transmission line of Fig.1. cobalt-iron alloy wherein the alloy surface is coat Referring to the drawings, the central con ed before soldering with a layer of nickel or an 25 ductor rod or wire 25, of nickel-cobalt-iron alloy equivalent protective coat. is suitably coated with a copper plating 32. The Further objects of the invention will presently surface of copper plating 32 is heat sealed to the appear as the description proceeds in connection body of glass 27, which in a specific embodiment with the appended claims and the annexed draw Successfully tested and used is a borosilicate glass ings wherein: 30 known in the trade as G705AJ glass, made by the Fig. 1 is a sectional view illustrating an elec Corning Glass Company. The outer annular tron tube embodying the invention. Kovar conductor 24 is internally copper-plated Fig. 2 is an enlarged section of the Kovar-glass at 33 and also heat-sealed to glass body 27. joint in the transmission line of Fig. 1. According to our invention we have discovered Fig. 3 is an enlarged section illustrating the 35 that perfect seals can be almost universally ob soldered metal to metal joint where the trans tained between the conductor and glass elements mission line of Fig. 1 enters the resonator.

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