US2814165A - Vacuum-tight electrical connections for electron-discharge devices - Google Patents

Description

Nov, 26, 1957 R. K. GOODWIN 1 VACUUM-TIGHT ELECTRICAL CONNECTIONS FOR ELECTRON-DISCHARGE DEVICES Filed June 12, 1952 JNVENTOR. RONALD KENNETH Gooowm Hi5 ATTQRN United States Patent 6 f VACUUM-TIGHT ELECTRICAL CONNECTIONS F OR ELECTRON-DISCHARGE DEVICES Ronald Kenneth Goodwin, Hiliingdon, England, assignor to Cinema-Television Limited, London, England, a British company Application June 12, 1952, Serial No. 293,090

Claims priority, application Great Britain July 6, 1951 1 Claim. (Cl. 49-78) This invention relates to improvements in vacuum-tight electrical connections for electron discharge devices having vitreous envelopes and is more especially concerned with such devices in which it is required to make electrical connection between a conducting layer on the inner surface of an element of the envelope of the device and an external circuit.

The invention is especially applicable to devices in which one element of the envelope comprises a disc or spherical shell of glass or other vitreous insulating material which is sealed to another vitreous portion of the envelope during the manufacture of the device and which carries on its inner face a conducting layer to which electrical contact must be made from outside the device. As a specific example, the invention is especially useful for forming vacuum-tight connections to a metal-backing layer deposited over the fluorescent screen of a cathoderay tube, image converter, or the like.

A known method of making such connections consists of rounding the edge of a portion of the periphery of such an element, applying to the rounded edge a layer of a material known in the art as platinum paste-which comprises finely divided platinum mixed with a small quantity of a finely divided binding material such as lead borosilicate and with a volatile carrier vehicle such as turpentineheating the element in an oven to burn away or bake out the carrier vehicle from the paste, and then locally heating the paste residue by means of a small flame to cause the binder component of the paste to melt and to sinter the platinum firmly to the glass. The element is thus provided with a conductor extending from the inner to the outer face and is then sealed to the remainder of the envelope of the device.

This known method suffers from the serious disadvantage that a large proportion of seals made in this manner are found to leak, owing to the fact that chains of small bubbles tend to form or are trapped in the space between the two portions of the envelope and the edges of the sintered metallic layer. These bubbles are not removed during the normal process of sealing, because the glass does not become sufficiently fluid during this process to flow into this space. Tooling of the outer component of the envelope to force it into the space usually results in breakage of the paste layer and a useless seal.

It is, therefore, an object of the present invention to provide an improved method of making vacuum-tight electrical connections in electron-discharge devices constructed with vitreous envelopes, by the use of which method the disadvantages of known techniques may be avoided at little or no increase in cost.

According to the present invention there is provided a method of making a vacuum-tight electrical connection to the interior of a vitreous envelope which comprises the steps of applying to a component member of the envelope a layer of paste comprising a finely divided metal mixed with a binding agent and a volatile carrier vehicle and extending continuously from an inward to an out 2,814,165 Patented Nov. 26, 1957 ward portion of the member, bevelling the lateral edges of the paste layer over at least such portions as are to be enclosed within the seal between the member and a mating component member of the envelope, heating the paste layer to volatilize the carrier vehicle and to sinter the metal and binder to the member, assembling the component member to its mating member, and sealing the members together.

This method results in a great reduction in the proportion of leaky seals produced, as the glass is able to flow smoothly on to the platinum, making a vacuum-tight joint, without the necessity for excessive tooling and consequent risk of breaking the conductor.

Where a metal is referred to in the specification and claims it is to be understood that a metal must be chosen which will not be attacked either by the atmosphere at the high temperatures to which it will be subjected in the sealing process or by metallic vapours or gases which may be used within the discharge device, and which will form a conductive layer when the finely divided metal is sintered to the glass in the presence of a binder such as lead borate.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken in connection with the accompanying drawings in the several figures of which like reference numerals indicate like elements and in which:

Figures 1-5 illustrate the preparation of an envelope element for a known type of connection;

Figures 68 illustrate the construction of a joint using an element prepared as described in relation to Figures 1-5; and

Figure 9 illustrates the form of a vacuum-tight connection prepared according to the present invention.

Figure 1 is a plan view of a circular glass window 11 which is to be sealed into the envelope of an electron discharge device. To form a known vacuum-tight connection the edge of this window, whose cross-section at the edge as exemplified by a section taken at 22 is shown in Figure 2, has a portion 1213 of its edge rounded off with a flame to give the form illustrated by the section at 3--3 shown in Figure 3. A layer of platinum paste is then applied With a brush to the edge of the window as shown at 14 in Figure 4. A section of the paste layer taken at 55 will then appear as shown in Figure 5.

The window is then heated in an oven to a temperature of some 5006()0 C. to burn away the turpentine carrier vehicle and while still hot the paste layer is locally heated with a flame to melt the paste binder and sinter the platinum firmly to the glass. The window is now sealed into the envelope as shown in Figures 68.

Figure 6 shows a partial end view of the window 11 sealed to the body 15 of the envelope, while Figure 7 shows a section through the seal at 7-7 in Figure 6, and Figure 8 is a plan view of the same part of the joint. It will be seen that at the lateral edges 16 of the metal layer there is formed a sharp angle which is the cause of failures in the vacuum seal, for the glass of the envelope does not become fluid enough in the sealing process to penetrate fully into the angle, so that there is a tendency for chains of air bubbles to form and become trapped as shown at 17.

According to the present invention, however, after the platinum paste layer has been applied to the rounded edges of the window, the sharp lateral edges 16 of the paste layer are smoothed down to a bevel, for example by brushing in the direction from the top of the paste layer to the adjacent window edge with a brush just moistened 3 with turpentine or such other carrier vehicle as is used. By this means, the paste layer is caused to assume the form illustrated in Figure 9, which shows a completed seal made in accordance with the present invention. The window 11 has a portion of its edge rounded, and the paste layer 14 applied thereto has its lateral edges bevelled off as shown at 18. The window is then assembled in the body 15 of the envelope and sealed to it in known manner.

While the invention is described as utilizing platinum paste, it is apparent that other preparations of similar nature may be used with equal success, provided that the essential feature of producing bevelled lateral edges for the metal layer before sealing is employed.

In any case, 'a seal of this nature is normally limited in its use to carrying currents of the order of a few microamperes, as the metallic layer produced is very thin and might be broken by the passage of higher currents. If larger currents are to be passed, either a number of connections must be connected in parallel or the peripheral extent of the paste layer must be increased, possibly until it completely encircles the window and thus eliminates the edges at which air bubbles may be trapped.

While a particular embodiment of the present invention has been shown and described, it is apparent that various changes and modifications may be made, and it is therefore contemplated in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

The method of making a vacuum-tight electrical connection to the interior of a vitreous envelope which comprises the steps of: applying to a first vitreous component member of said envelope a layer of paste comprising a finely divided metal mixed with a binding agent and a volatile carrier vehicle, said layer extending continuously from an inward portion, over a peripheral portion and to an outward portion of said member; bevelling the lateral edges of that part of said paste layer which extends over said peripheral portion of said member and which will be enclosed within the seal between said first member and a vitreous mating component member of said envelope; heating said layer to volatilize the vehicle and to sinter the metal and binder to said first member; assembling said first component member to its mating member with said part of said sintered layer sandwiched therebetween; and sealing said members together.

References Cited in the file of this patent UNITED STATES PATENTS 1,293,441 Houskeeper Feb. 4, 1919 2,170,602 Bauer Aug. 22, 1939 2,198,578 Hazleton Apr. 23, 1940 2,235,680 Haven et al Mar. 18, 1941 2,265,352 Corbin Dec. 9, 1941 2,282,106 Underwood May 5, 1942 2,454,270 Braunsdorft Nov. 23, 1948 2,461,878 Christensen Feb. 15, 1949 FOREIGN PATENTS 22,911 Great Britain of 1906

Images