Dec. 21, 1948. D. L. SNOW ET AL 2,456,653 SEAL FOR HIGH-FREQUENCY TRANSMISSION LINES Filed Dec, l0, l942

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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 -nickel- 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 of the type known variously by In securing such alloy members together or to such trade names as and Fernico. This another metal we preferably employ a soldering alloy is used because it has approximately the s operation, using a 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 theOperation, 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. by the following process, Fig. 4 is another enlarged section illustrating First, the surface of each conductor to be the soldered metal to metal joint between the tube Sealed to the glass is heated, as by hydrogen fir barrel and the resonator. 40 ing, until its oxide-coated surface is reduced. Fig. 1 illustrates the invention as applied to a This is a cleaning operation which makes the con tunable high frequency electronic tube of the type ductor surface especially receptive to soldering, employing a hollow resonator and a concentric and results in an improved solder bond between transmission line. the plating and Kovar. The next operation com The hollow resonator comprises a cylindrical prises electroplating the cleaned conductor sur metal barrel 2 and opposite end walls 3 and 4 face with copper or an equivalent conductor. provided with reentrant poles 5 and 6 sup Preferably the copper plating is about 0.001 inch porting Centered and aligned grids T and 8. A thick. It is not, however, material to the inven suitable cathode 9 is located within pole 6 near tion to plate the Kovar in this exact manner. grid 8. 50 Any equivalent plating step may be employed. Wall 4 is an annularly crimped sheet metal The next operation is to hydrogen fire the member of beryllium copper or a like resilient plated copper surface for reducing the oxide there fatigue resistant material having sufficient stiff and cleaning the copper-plated surface for seal ness to normally maintain its shape but being ing with the glass. By hydrogen firing we mean Controllably deformable for tuning. Wall 4 is heating in an atmosphere of hydrogen. In this Secured permanently, preferably by soldering, to step, We probably remove all gases trapped or barrel 2 and pole B. otherwise present in the metal and replace the A metal plate 2 is rigid with pole 6 below wall Sane by hydrogen. As will appear, this step may 4 and parallel to wall f. Wall 3 and plate 2, be eliminated, although it is preferable for prac which may be of steel, copper or any suitable 80 tical purposes. metal, are interconnected by the usual springs If the glass sealing operation were attempted (only one shown) urging them together and by at this point, it would be subject to the same dif adjustable tuning screws such as 22. As screws ficulties as explained above. Hence we have found 22 are rotated, the distance between grids 7 and further treatment needed for insuring good seals. is changed to tune the hollow resonator. Plate 65 The final and most important step before seal 2 is carried by the usual base (not shown). ing is to now heat the copper-plated conductors The wall of barrel 2 is apertured at 23 to re in a vacuum furnace, preferably maintained at ceive a hollow tube 24 comprising the outer con about 900 C. for a duration of approximately ductor of a concentric transmission line. The in five minutes. This heating period is not especial ner conductor 2 is reversely bent within the res 70 ly critical but it must be sufficiently long so that onator to provide an antenna loop 26, and is an the operation releases or removes from the metal, chored, as by soldering, to the inner periphery of especially from the copper-plated surface, mole Outer conductor 24. Conductors 24 and 25 are cules of hydrogen which had been absorbed be preferably made of a nickel-cobalt-iron alloy such fore and during the preliminary firing opera as Kovar, Fernico, or the like, 75 tions. For example, the operation has been car 9,466,668 red out successfully at 400', C. This vacuum 6 heating operation also removes from the metal The phase of the invention related to gs, 3 Surface any other foreign substances which, like and 4 is of especial application and advantage hydrogen, may become liberated during the en where the soldered parts are relatively large or suing glass-to-metal sealing step and form bub subjected to relatively heavy stresses. bles or like structural defects in the seal. Since many changes could be made in the above After the vacuum fring step, the metal con construction and many apparently widely differ ductor and glass elements are assembled as shown, ent embodiments of this invention could be made and heat is supplied to the glass to seal them without departing from the scope thereof, it is together. Careful observation shows that no in intended that all matter contained in the above perfections form in the seal during this opera O description or shown in the accompanying draw tion, which results in perfect glass-to-metal seals. ings shall be interpreted as illustrative and not Although the invention has been described by in a limiting sense, way of example for sealing copper-plated Kovar What is claimed is: to borosilicate glass, it will be understood that it 1. In combination, a nickel-cobalt-iron alloy is applicable to the formation of perfect seals 15 tube, a degasified coating of copper on the inner between substantially any equivalent metal and surface of said tube, a nickel-cobalt-iron alloy glass combinations. For example, the conductors wire having a degasified coating of copper and may comprise any metal or alloy having about positioned coaxially within said tube, and a boro the same coefficient of thermal expansion as any silicate glass cylinder positioned on said wire arbitrarily chosen glass suitable for the seal glass, 20 within said tube and sealed to said copper coated and surface platings 2 and may be of any surfaces whereby a vacuum-tight, mechanically suitable metal having the property of being high rigid coaxial line assembly is provided. ly electrically conductive and of being attached 2. In an eficient high frequency transmission to glass. line, two conductors made of nickel-cobalt-iron The essential Operation of this phase of the in 25 alloy, a sealing body of glass between said con vention is the removal of the released gaseous ductors, said alloy having the same low thernal substances. The invention is therefore of suf coefficient of thermal expansion as said glass, and client scope to include application of this opera a degasified coating of copper between each of tion to conductors plated or coated in any manner, said conductors and the glass body. and independently of whether they are prepared 30 3. A coupling for efficient conduc by the above-outlined preferred process steps. tion of ultra high frequency energy comprising a We have thus provided an electrically eficient, degasified internally copper-plated cylinder of mechanically sound and vacuum tight seal for a . nickel-cobalt-iron alloy adapted to be bonded at concentric transmission line. The plated Kovar one end to a wall of a vacuum tube, a degasified conductors are just as electrically eficient as 35 copper-plated nickel-cobalt-iron alloy wire posi would be solid copper conductors, and at the same tioned coaxially within said cylinder and extend time the low thermal expansion and other struc tural advantages of Kovar are retained to keep ing beyond said one end of said cylinder, and a the seal intact during operating conditions. borosilicate glass element sealed to the copper While the chief importance of our sea is in 40 plated surfaces of said cylinder and said wire ultra high frequency conductor structure, it is whereby said coupling is rendered gas tight and very useful for lower frequency applications as said wire and cylinder are rigidly spaced. well. DONAD, SNOW. Fig. 3 is an exaggerated sectional represent WALAM. W. HANS:N. tion of the metal to metal joint between the Kovar tube barrel 2 and wall . The lower edge REFERENCES C TED and periphery of collar 2 are coated, as by dis The following references are of record in the tillation or electrodeposition, with a layer of fle of this patent: nickel 3D. The nickel-plated end of collar 2 is UNITED STATES PATENTS inserted and silver soldered in the usual manner in groove 28, the hardened older body being Number Name Date indicated at in Fig. 3. . 789,515 Whitney ------May 9, 1905 This above soldiered joint is sound and fin, 1458,110 Mackay ------May 22, 1923 and the barrel does not fracture under repeated 1498,908 Fink ------June 24, 1924 temperature stress. The nickel coating does not 55 1547,395 Hoyt ------July 28, 1925 rapidly alloy with the silver in the solder, and 1,639,575 Robinson ------Aug. 16, 1927 prevents the silver from reaching the covar. 1879,518 Fowle ------Aug. 7, 1928 1740,448 Donat ------Dec. 24, 1929 It is obvious that any suitable metal other than 1893,286 Iredell ------Jan. 3, 1933 nickel may be used to plate the Kovar. It is e 2,057,452 Scott ------Oct. 13, 1936 sential, however, that such metal be capable of 2,082335 Scott ------Dec. 1, 1936 forming a good solder bond and also serve as a 2,119,608 Stewart ------June 7, 1938 protective shield for preventing the silver solder 2,121,598 Kerschbaum et al. -- June 21, 1938 from alloying with the Kovar. The metal plating 2,133,492 Watter ------Oct. 18, 1938 should, of course, have a higher melting point 2,163,410 Pulfrich et al. --- June 20, 1939 than the solder. 2,169,570 Ronci ------Aug. 15, 1939 Fig. 4 is an exaggerated sectional illustration 2,172,978 Kirch ------Sept. 12, 1939 of the manner in which Kovar conductor 24 is 2,273,135 Ohnesorge ------Feb. 17, 1942 mounted on barrel 2. Prior to insertion into 2273488 Hofman ------Feb. 17, 1942 aperture 23, the associated end of conductor 24 O is coated on its external periphery, preferably by 2,394,398 Mouromtse? et al.---- Feb. 5, 1946 electrodeposition, with a layer of ricked. The FOREIGN PATENTs plated end of conductor 24 is thrust irts aperture Number Country Date 23 as stily?'" 2reri in the usual manner, the 249,084 Great Britain ------July 1, 1920 hardered 5.3ide; being indicated at .