US2974761A

US2974761A - Electrical component with improved metal-to-glass end sealing mechanism

Info

Publication number: US2974761A
Application number: US739932A
Authority: US
Inventors: Mihai D Patrichi
Original assignee: Networks Electronic Corp
Current assignee: Networks Electronic Corp
Priority date: 1958-06-04
Filing date: 1958-06-04
Publication date: 1961-03-14
Anticipated expiration: 1978-03-14

Description

2,974,761 ASS M lmw Hmw mm T March 14, 1961 ELECTRICAL COMPONENT WITH IMPROVED METAL-TO-GL 5 r mm M M m w a M m w t Ila United States Patent ELECTRICAL COMPONENT WITH IMPROVED ME'IlsAL-TO-GLASS END SEALING MECH- AN M Mihai D. Patrichi, Chatsworth, Califl, asslgnor to Networks Electronic Corporation, Van Nuys, Califl, a corporation of California Filed June '4, 1958, Ser- No. 739,932

7 Claims. (Cl. 189-365) This application is in part a continuation of my prior applications S.N. 615,981, filed October 15, 1956, for Electrical Resistors and the Like, now abandoned; and SN. 616,091, filed October 15, 1956, now Patent No. 2,897,583, issued August 4, 1959, for Method of Fusing Metal to Glass articles.

This invention relates to electrical. components and especially to miniature electrical components embodying electrical parts sealed within a dielectric envelope, and has as its general object to provide an improved hermetically sealed high temperature electrical component. The invention is applicable to resistors, germanium diodes, rotors, coils, servo mechanisms, antennas, power packs and various electrical instruments wherein electrical parts are required to be sealed within an insulating envelope.

One of the major objects of the invention is to provide such a component wherein the envelope comprises primarily a fully transparent barrel of high temperature dielectric material, preferably glass having the characteristics of Pyrex glass, and wherein headers likewise utilizing a high temperature dielectric material having expansion characteristics matched to those of the barrel, are hermetically sealed to the respective ends of the barrel and in turn are hermetically sealed to terminals projecting t-herethrough into the interior of the envelope.

In the case of the thermal relay, the invention provides the advantage of hermetically sealed, moisture proof, shock resistant enclosure of a pair of operating units in the respective ends of the envelope, one of said operating units comprising an overload-sensitive fuse structure, the other comprising a switch adapted to be activated by the projection of a plunger slidably mounted in the barrel intermediate the fuse parts and the switch parts and constituting the actuator of the switch. Such a switch may be either normally open or normally closed and functions as a relay for actuating a relay circuit when a fuse circuit is overloaded. In the case of a resistor, a resistor coil may be provided with adequate dielectric protection by being mounted within an hermetically sealed envelope embodying the invention, with a filling of insulative potting material or rings of such potting material, partial surrounding of the end parts, or other mechanical supporting device.

Other objects and advantages will become apparent in the ensuing specification and appended drawing in which:

Fig. 1 is a side view of an electrical component embodying the invention;

Fig. 2 is an end view thereof;

Fig. 3 is a longitudinal sectional view of a resistor embodying the invention;

Fig. 4 is a cross sectional view of the resistor;

Fig. 5 is a fragmentary detail sectional view on an enlarged scale, showing the fused joint between the barrel and header of an electrical component embodying the invention;

Fig. 6 is a fragmentary sectional view on a more highly enlarged scale, showing the multiple-layer hermetic sealing joint between the metal and glass part of an electrical component embodying the invention; and

Fig. 7 is a sectional view illustrating the invention as embodied in a thermal relay.

Referring now to the drawing in detail, I have shown therein, in Figs. 3 and 3a, as an example of one general form in which the invention may be embodied, a resistor embodying an inductionless coil 10 (wound in an even number of layers, e.g. two, in a manner such that the inductive field of one layer will neutralize that of the next) supported upon a tubular mandrel 11 on which it is directly wound. The wire of coil 10 is one that will prove satisfactory as to stability of texture and resistance rating under high temperatures, a suitable material being Karma wire or other alloy used in wire resistors. Mandrel 11 with its resistance winding 10 is encased within a barrel 12 of internal diameter slightly larger than the outer diameter of winding 10, so that the Wound mandrel may remain in substantially coaxial relation with the barrel 12 even though it should contact the inner wall thereof at some point around its circumference. The ends of barrel 12 are closed and hermetically sealed by headers 13 each including a metal mounting ring of L- section, consisting in a radial flange 14 (Fig. 5) and an open collar 15 projecting axially from the inner margin of flange 14 into a respective end of barrel 12. Flanges 14 are fused or soldered at 22 to the ends of barrel 12, previously covered with metal as hereinafter described, to provide a very secure hermetically sealed connection, resistant to vibration, shocks, moisture-laden air, etc. Each header 13 includes an insulator plug 18 fused or soldered into collar 15 thereof. Terminal rods 19 are fused or soldered into cylindrical bores in respective plugs 18 and project theret-hrough into the respective ends of mandrel 11, where they are welded or soldered to the respective end portions 20 of winding 10.

The barrel 12 and headers 13 cooperatively provide an hermetically sealed casing or envelope within which the electrical parts of the device are enclosed and protected, such electrical parts, in the case of a resistor, comprising the Winding 10 and its connections to terminals 19. As shown in Fig. 3, the space within the envelope 12, 13 may be completely filled with a cushioning and insulating core body 21 of latex potting material in which the mandrel 11 and winding 10 are embedded and suspended with an almost complete shock and vibration insulation. Alternatively, as shown in Fig. 3a, the envelope may be only partly filled with potting material, for example in just the end regions thereof. In such arrange ments, the potting material may function to absorb shocks and vibration imposed upon the terminals 19 and envelope, protecting the winding 10 and its connections to the terminais, against the destructive effect thereof.

Barrel 12, mandrel 11 and plugs 18 are of high temperature heat-resistant glass of high lead content, such as Pyrex glass. The

mounting rings

14, 15, of headers 13 are drawn sheet metal parts, of a corrosion resistant metal, such as Kovar (an alloy of iron, nickel and cobalt) having substantially the same coeflicient of thermal expansion as the glass parts.

The glass and metal parts are joined to one another by strong, durable hermetically sealed joints permanently resisting leaking and mechanical breakdown (from the effect of shocks and vibration). This is attained through the use of improved composite laminated fused joints indicated at 22 and 24 (Figs. 5 and 6). Each of said joints consists in three or four separate coatings, including: a very thin molecular film of noble metal fused to the glass surface; an electro-deposited coating of a good binding metal such as copper, joined to such noble metal film; a film of noble metal upon the surface of the

mounting ring

14, 15; and a film of solder interposed between the noble metal surface of the metal part and the electro-deposited coating on the glass part and bonding the same together.

, In the preferred form of the invention, the mounting ring is of Kovar metal and the noble metal films on the glass part and upon the surface of the metal part are of silver.

Silver solder is used in the solder coating wherever the component is required to withstand temperatures exceeding 400 F. However, for those cases Where the temperature range is below a maximum limit of approximately 400 (e.g. 390 F. or under) I find that satisfactory results can be obtained by utilizing a tin-lead solder of a high temperature type, i.e., having a higher melting point (higher lead content) than the solder commonly used in establishing electrical connections. Either of these solders are regarded as a high temperature solder, the silver solder having the higher range.

In the case of the resistor as shown in Fig. 3 and in Fig. 5, the joint 22 is interposed largely between flange 14 and an opposed end of barrel 12; and the joint 24 is interposed between the periphery of plug 18 and the in ternal surface of mounting ring collar 15. The same may be true in the case of the resistor shown in Fig. 3a. A joint 23 is interposed between a terminal 19 and the bore of plug 18. This joint may be of the same type as

joints

22 and 24, or may be a plain fused joint as described hereinafter.

In the modified form of electrical component shown in Fig. 7, the headers 13a, having a diameter just slightly less than the internal diameter of barrel 12, are joined to the respective ends of the barrel by end joints 22; and by annular cylindrical joints 30 interposed directly between the cylindrical outer surfaces of headers 13a and the cylindrical inner surface of barrel 12a as shown; there being no potting material used in this type of device.

In the modified form of the invention shown in Fig. 7, an assembly of fuse and relay parts may be sealed Within the envelope, including a plunger 31 slidably mounted within the barrel 12a, a coil spring 32 for projecting the plunger to a position in which a switch part 33 on one end of the plunger may close the circuit between a pair of terminals 19a sealed in and extending through one of the headers 13a; and a fuse element 34 anchored between the plunger 31 and a second pair of terminals 1% mounted in the other header, whereby the plunger 31 is normally held in a retracted position but will be released upon burning of the fuse element 34 when subjected to overload, thereby causing the plunger 31 to be spring projected to close the circuit between the terminals 19a.

The invention also contemplates an envelope construction such as that shown in Fig. 7, in a resistor having no potting material at all, the winding fitting within the barrel 12 with sufficient snugness to support it in substantially coaxial relation thereto; the ends of terminals 19 extending loosely into the ends of mandrel 11; and the headers 13 being fitted within the ends of the barrel 12 with direct bonded joints 30 between the peripheral surfaces of the headers and the internal surface of the barrel as in Fig. 7. v Kovar is a preferred material for the

headers

13, 13a, since it is especially well matched to hard glass such as Pyrex in its expansion characteristics. Where such a metal is used, the coating of noble metal thereon is an essential element'of the device. Alternatively, in some cases the metal part may be of solid noble metal, in which case the surface thereof constitutes the fourth coating.

The term molecular film" as applied to the noble metal film on the glass surface is not necessarily restricted to a film of single molecule thickness. Instead, the term is intended to designate a coating having a thinness within the range of approximately .0005 inch to .005 inch.

As shown in Fig. 6, the several layers of the bonding joint, beginning withthe layer attached to the glass 4 surface, are arranged in the following order and indi cated by the following reference characters:

( 1) Noble metal (silver) film on glass surface;

(2) Electro-coating (copper) on silver film;

(3) Solder binding layer;

(4) Noble metal surface (silver electro-deposited on Kovar) on metal part.

The noble metal coatings on the metal parts and the metal films and copper coatings on the glass parts are deposited on the surfaces of the respective parts prior to assembly into the finished component. In the coating process for the glass parts, the latter are preliminarily prepared by thorough cleansing. If they are dirty, they may be first water washed (e.g-. in adetergent solu tion) and rinsed or may be preliminarily washed in methanol. Two main cleaning steps are then performed namely (a) soaking in chromic acid solution and (b) soaking in methanol. The parts are preferably rinsed between the chromic acid and methanol baths. The parts are then dried.

As a second main step following the cleaning step, a silver paste paint (e.g. a mixture of powdered silver in 40% toluene) is applied by brushing or dipping, to the areas of the glass that are to be fused to the metal parts.

As a third step, the coated parts are heat treated (e.g. in an electric oven) to anneal the glass parts and fuse the silver coatings thereto, temperatures in the range of 1140 F. to 1150 F. being reached. For example, in a preferred practice of the process, the parts are cured for three hours at 1150 F. to fully vaporize and dissipate all traces of the toluene carrier and to leave the silver particles in the form of a continuous film (l) of silver metal which is fused to the glass surfaces. At the conclusion of the curing operations, the parts are allowed to cool slowly to room temperature to avoid shattering of the glass.

As a fourth step in the process, silvered surfaces (1) of the glass parts are coated with copper by an electroplating step. In the electro-plating step, substantial copper coatings (2) are built up upon the glass parts, to a thickness in the range of .0005 inch to .005 inch.

In a separate series of steps, header plugs 18 are prepared by pressure molding bodics of powdered glass in the form of the plugs 18 around

respective terminals

19 or 19a; then fusing these assemblies by heat treating at temperatures in the fusing range of the glass to fuse the powdered glass particles into a solid body of glass for each of the plug elements 18, with the terminals fused therein.

In the final step of the process, the previously coated glass and metal parts are assembled and soldered to one another through the medium of the solder films (3) of Fig. 6, these films uniting with the previously deposited coatings to constitute the

joints

22, 30 joining the

headers

13, 13a etc. to the barrel 12 (and to constitute the joints 24 between the mounting rings 14 and the insulator plug 18 where it is soldered into the collar 15). The soldering step may be performed by the application of rings of solder wire to the joints at the ends thereof and the subsequent heating of the assembly to melt the solder and cause it to seep by capillary action into the joints, or by other known soldering processes. For example, in the solder-ing of a previously assembled header 13 (including the insulator plug 18 and the mounting ring 14 already attached thereto as by soldering), the header may be loosely inserted into a respective end of the barrel 12, previously coated with the silver film (1) and the electro-copper coating (2), the latter facing 'at the joint (e.g. resting against the end of the glass tube around the periphery of ring 14) and the assembly then heated to cause the solder to seep inwardly between the ring 14 and the end of the glass tube to complete the outer portion 22 of the joint, and thence into the cylindrical space between the collar 15 and the internal surface of the glass tube to form the cylindrical joint 30.

After the one header has been attached to the barrel, the assembly of internal electrical parts is inserted, in the case of the thermal relay of Fig. 7, and the other header is then assembled to the open end of the barrel and is bonded thereto in the same manner as the first header. In the case of a resistor, the assembly of mandrel 11 and winding 10, with one end thereof attached to the terminal of the first header, is inserted into the barrel prior to the attachment of the first header thereto. The first header is then bonded to the barrel in the manner described above. The terminal of the other header may then be soldered to the free end of the winding "10, and the header may be arranged atone side of the barrel while the assembly of barrel and internal parts is placed in an upright position in a suitable tray or holder, with its open end at the top. The barrel 12 may then be filled with the potting material, the other header assembled loosely in place with an interposed ring of solder, and the entire assembly then processed for curing the potting material and subsequently subjected to fusing heat applied to the open end thereof to bond the second header to the barrel.

I claim:

1. An hermetically sealed moisture and shock resistant electrical component of small dimensions and of high electrical and mechanical requirements, comprising: a cylindrical tubular barrel of high temperature hard glass, a header comprising a plug of high temperature glass having a cylindrical periphery and a substantially rigid mounting ring of metal having a co-etficient of expansion matched to that of said barrel and of said plug, said mounting ring being of L-section, including a cylindrical collar of greater diameter than its axial length, fitted within an end portion of said barrel in concentric relation thereto and a flange extending radially outwardly from the outer end of said collar; and a conductor terminal extending through and sealed in said plug, said plug being sealed within said collar; and a joint of laminated structure and of thin cylindrical sleeve form, interposed between and united to the periphery of said collar and the inner surface of said barrel, said collar and joint solidly interposed between said plug and barrel, said joint further including an integral flat radial ring portion extending outwardly from the cylindrical portion thereof and solidly interposed between and united to the end surface of said barrel and to the back surface of said radial flange, said joint being of laminated structure including a film of noble metal fused on the end of said barrel, a coating of copper on said noble metal film, a surface of noble metal on said mounting ring, and a layer of solder interposed between and bonded to said noble metal surface and to said coating of copper.

2. An hermetically sealed moisture and shock resistant electrical component of small dimensions and of high electrical and mechanical requirements, comprising: a cylindrical tubular barrel of high temperature hard glass having thermal and shock resistant characteristics equivalent to those of Pyrex glass; a header comprising a plug of high temperature glass having a cylindrical periphery and a substantially rigid mounting ring of metal having the characteristics of Kovar, with a coefficient of expansion matched to that of said barrel and of said plug, said mounting ring being of L-section, including a cylindrical collar of greater diameter than axial length extending into an end portion of said barrel in concentric relation thereto and a flange extending radially outwardly from the outer end of said collar, and a conductor terminal extending through and sealed in said plug; and metallic joints of laminated structure and of cylindrical ring form, one being an inner joint interposed between and united to the periphery of said plug and the inner surface of said collar, and the other being an outer joint interposed between and united to the periphery of said collar and the inner surface of said barrel, said collar and joints solidly interposed between said plug and barrel, the outer joint further including an integral flat radial ring portion extending outwardly from the cylindrical portion thereof and solidly interposed between and united to the end surface of said barrel and to the back surface of said radial flange, each of said joints being of laminated structure including a film of silver fused to a respective glass surface, a coating of electro'copper on said silver film, a surface of silver on said mounting ring, and a layer of solder interposed between and bonded to said silver surface and said coating of copper.

3. An electrical component as defined in claim 2, wherein said solder layer is of silver solder.

4. An electrical component as defined in claim 3, wherein said silver surface consists in a film of silver electroplated on the respective metal part.

5. An electrical component as defined in claim 2, wherein said plug is generally in the form of a thick flat disc having a cylindrical periphery.

6. An electrical component as defined in claim 2, wherein said silver film and said copper coating are each of a thinness within the range of approximately .0005 inch and .005 inch thickness.

7. An electrical component as defined in claim 2,

, wherein said plug is of fused powdered glass, and wherein said terminal is fused therein.

References Cited in the file of this patent UNITED STATES PATENTS 760,065 Gilmore May 17, 1904 1 2,053,765 Dana Sept. 8, 1936 2,334,631 Johnson Nov. 16, 1943 2,446,277 Gordon Aug. 3, 1948 2,451,847 Madden et a1. Oct. 19, 1948 7 2,477,372 Herzog July 26, 1949 2,490,776 Braunsdorif Dec. 13, 1949 2,812,466 Murdock Nov. 5, 1957