US2988665A

US2988665A - Coated contact members for electric discharge tubes

Info

Publication number: US2988665A
Application number: US698720A
Authority: US
Inventors: Duran Johannes Christiaan; Bakker Martinus Antonius Maria
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1952-12-05
Filing date: 1957-11-25
Publication date: 1961-06-13
Anticipated expiration: 1978-06-13
Also published as: GB731588A; NL174361B; DE963013C; NL87131C; BE524826A; CH317668A; FR1089039A

Description

June 13, 1961 J. c. DURAN ET AL COATED CONTACT MEMBERS FOR ELECTRIC DISCHARGE TUBES Original Filed Dec. 2, 1953 2 Sheets-Sheet 1 FIGJ INVENTORS JOHANNES CHRISTIAAN DURAN MARTINUS ANTONIUS MARIA BAKKER June 13, 1961 J. c. DURAN ETAL 2,988,665

COATED CONTACT MEMBERS FOR ELECTRIC DISCHARGE TUBES Original Filed Dec. 2, 1953 2 Sheets-Sheet 2 JOHANNES CHRISTIAAN DURAN MARTINUS ANTONIUS MARIA BAKKER hile. g AG\NT I Ufl ed States Pa m- 2,988,665 COATED CONTACT MEMBERS FOR ELECTRIC DISCHARGE TUBES Johannes Christiaan Duran and Martinus Antonius Maria -Bakker, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Continuation of application Ser. No. 395,707, Dec. 2, 1953. This application Nov. 25, 1957, Ser. No.

698,720 Claims priority, application Netherlands Dec. 5, 1952 '3 Claims. (Cl. 313-311) This invention relates to coated contact members for an electric discharge tube and to a method of providing such coatings.

. This application is a continuation of application Ser. No. 395,707, filed December 2, 1953, .now abandoned.

For certain purposes, it is necessary for contact pins of electric discharge tubes to be coated with a thin layer of gold before being sealed into the base of the tube, so that not only is a permanent reliable contact afforded with the receiving contact members of a tube holder, but, also, the high-frequency resistance of the pins is considerably reduced. However, for this purpose, it is essential that the gold'layer be wholly intact at least on the contact, members themselves after the pins have been sealed into the base of thetube. In view of the large number of contact membersrequired, a popular technique often employed is the so-called drum method, in which the objectsv to "be coated are. poured in bulk into a rotatable drum, and coatedby --a conventional electro-chemical Process However,"coating' thecontact pins with a thin gold layer in thisway does not generally give satisfactory results, especially when the gold layer is to be kept rather thin to minimize the cost. In fact, it has been found that a gold layer thinner than 5 microns does not remain intact during the sealing of the pins even on portions of the pins projecting from the glass base. More particularly, if the pin consists of nickel, the gold and the nickel are found to diffuse into one another, so that the advantages offered by the use of a gold layer are lost. When chrome-iron pins are used, in connection with the drum method of plating, an additional difilculty arises that the gold layer poorly adheres to the chrome-iron base; further a leak may occur if such pins are to be hermetically sealed-in to the base.

An intermediate layer may be employed to avoid diffusion of the gold into the metal of the substratum. However, for the purpose desired, such an intermediate layer must not only avoid diffusion in two directions, but, also,

satisfactory adherence of this layer both to the core metal and to the gold layer must be insured, even when both the said layer and the gold layer have been provided by the drum method. Further, the intermediate layer must not be chemically attacked by the cyanide alkaline solution before the gold has deposited thereon. Still further, the intermediate layer must not give off gas when the pins are heated during the sealing into glass, otherwise, a vacuum-tight joint could not be effected.

According to the invention, the foregoing conditions are completely fulfilled and the desired results attained by employing an intermediate layer containing cobalt between the outer gold layer and the contact member. An intermediate layer which consists of pure cobalt, or of an alloy of cobalt with iron and/0r nickel, such as fernico, is particularly suitable for this purpose. The use of such a cobalt-containing intermediate layer not only prevents diffusion of the gold into the intermediate layer, or conversely, but also insures highly satisfactory adherence of the gold layer. Moreover, both the gold layer and the intermediate layer may be provided by use of the drum ice.

method. It has been found that gold layers having a thickness of less than 1 micron, e.g. a few tenths of a micron, provided on top of a cobalt-containing intermediate layer keep wholly intact even under the usual unfavorable conditions to which the contact members are exposed during sealing and during operation of the tube. The more cobalt present in the intermediate layer, the thinner the gold layer which may be provided. However, it is not objectionable to provide thicker gold layers if desired, or a copper or silver layer, since the cobaltcontaining intermediate layer afiords the same advantages when providing a copper or silver layer.

Other cobalt-containing layers which are suitable are cobalt-iron; cobalt-nickel or cobalt-manganese layers. The proportions of the cobalt in a cobalt alloy should preferably be at least 20%, better results being attained as the quantity of cobalt is increased. The contact members themselves are preferably constituted of chromeiron. By chrome-iron is meant an alloy of chromium and iron containing between ,10% to 35% of chromium.

Other metals suitable for the contact member are nickel,

iron, alloys of nickel-iron with copper and/ or chromium, cobalt or manganese; and further tungsten.

The invention will now be described with reference to the accompanyingdrawing in which:

FIG. 1 shows a tube containing contact pins according to the invention, and

FIG. 2 shows one embodiment of a contact member according to 'the invention.

FIG. 3 shows a diagram of the process.

Referring to FIG. 1, an envelope 1 of an electric discharge tube is closed by a glass base 2. Sealed into the base 2 are a plurality of chrome-iron contact pins 3, of which at leas't'the portions projecting externally from the tube 1 are coated with a gold layer 5 having a thickness of less than a micron. A layer 4 consisting of fernico material, i.e. an alloy of cobalt-iron-nickel containing about 28% nickel and 18% cobalt is provided between the gold layer 5 and the conductor 3. If the gold layer 5 must also serve to afford satisfactory high-frequency conduction, a greater thickness, for example, 2 microns or upwards, may be used. A layer of such thickness keeps intact even within the seal and the tube. Although, through use of the drum method, the whole pin is coated with an intermediate layer and a gold layer, the gold layer, if it is of great thinness, might have a tendency to be interrupted wholly or in part at the sealing area as a result of the difiusion which still occurs at the high temperature during sealing. However, such thin gold layers are provided mainly for obtaining a highly satisfactory and reliable contact between the pin and the contact spring of a tube holder, and need therefore be provided only on the part of the pins projecting from the tube.

FIG. 2 shows a so-called triple sealing pin which is very common in the field consisting of a lower core 8 of nickel, iron, nickel-iron, chrome-iron or similar material. The central core 7 consists of copper-clad wire and the upper core 6 of iron, molybdenum or a metal similar to that of the core 8. According to the invention, the whole of this pin is coated with a cobalt-containing intermediate layer 4 at least 5 microns in thickness, and preferably 10 to 12 microns in thickness and on top thereof a gold layer 5 of, for example, 0.5 micron thick. After this pin has been sealed into the base of the tube it will still be intact at least on the core 8 to insure satisfactory contact with the contact members of a receiving tube holder. The process is shown in FIG. 3.

To provide the intermediate layer, 1 kg. of chromeiron pins is poured in bulk into a container and overspread with hydrochloric acid for cleaning the surface. The pins are then rinsed in water, transferred into a rotary drum, and overspread with an acid cobalt-containa ing bath, e.g., C080 312.5 grammes, NaCl 19.6 grammes, H BO 50 grammes, H 1000 cm. having a temperature of 60 to 70 C. An electrode is provided extending into the heap of pins, and another in contact with the bath only. During rotation of the drum, a voltage is applied between the electrodes so that a current of 35 amps.

passes through the bath during 3 hours and the pins are coated with a cobalt-containing layer of the desired thickness. After further rinsing, the pins in the drum are suffused with an alkaline cyanide-bath for plating out a gold layer using a current of 4 amps. during 2 /2 hours. Since the chrome-iron core of the pins is protected from the alkaline bath by the intermediate layer, the chromeiron is not chemically attacked. It has been found that the drum method thus yields highly satisfactory results. The cobalt-containing intermediate layer adheres very well both to the core and the gold layer, and does not give off any appreciable amount of gas during sealing in of the pins in the tube. After a rinse with water the pins can be stored.

It will be evident that the invention is not limited to the coating of contact members, by the drum method since other methods are equally suitable but the drum method, in the case of large quantities of pins, is much preferable to the others.

The term substantially pure cobalt as it appears in the claims shall be understood to mean cobalt of such purity that dififusion between the outer layer and the core is prevented.

While we have described our invention in connection With specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. An electric discharge tube comprising an envelope and at least one contact member sealed therein, said member consisting essentially of a base of a metal selected from the group consisting of nickel, iron, chromium and alloys thereof, an outer layer thereover of a metal selected from the group consisting of copper, gold, and silver, and a layer intermediate said base and said outer layer, said intermediate layer consisting of substantially pure cobalt about 10 microns in thickness.

2. An electric discharge tube comprising an envelope and at least one contact member sealed therein, said member consisting essentially of a base metal selected from the group consisting of nickel, iron, chromium, and alloys thereof, an outer layer of gold thereover, and a layer intermediate said base and said gold layer, said intermediate layer consisting of substantially pure cobalt about 10 microns in thickness.

3. An electric discharge tube comprising an envelope and at least one contact member sealed therein, said member consisting essentially of a base metal selected from the group consisting of nickel, iron, chromium, and alloys thereof, an outer layer thereover having a thickness of less than about one micron and consisting of gold, and a layer intermediate said gold layer and said base, said intermediate layer consisting of substantially pure cobalt about 10 microns in thickness.

References Cited in the file of this patent UNITED STATES PATENTS 58,037 Thompson Sept. 11, 1866 2,284,151 Kingston May 26, 1942 2,300,558 Driggs Nov. 31, 1942 2,429,222 Ehrhardt Oct. 21, 1947 2,819,207 Shepard June 22 1953 FOREIGN PATENTS 238,227 Switzerland Oct. 1, 1945 OTHER REFERENCES Metal Finishing, September 1951, pages -85. Fiat Final Report 785, Electrical Contacts.