US2768490A - Apparatus for evacuating and sealing - Google Patents

Description

Oct. 30, 1956 J. w. DAWSON ET AL 2,768,490

' APPARATUS FOR EVACUATING AND SEALING Filed Dec. 29, 1953 PULSE RESISTANCE 52- WELDER I INVENTORS JOHN w. DAWSON geBERT C. INGRAHAM ATTORNEY United States Patent "ice 2,768,490 APPARATUS FOR EVACUATING AND SEALING John W. Dawson, Winchester, and Robert C. Ingraham,

Danvers, Mass, assignors to Sylvania Electric Products Inc., a corporation of Massachusetts Application December 29, 1953, Serial 400,997

2 Claims. (Cl. 553-101) The present invention is drawn to methods and apparatus for sealing electrical devices in hermetically sealed and evacuated envelopes and more particularly for evacuating and sealing the envelopes ofv semiconduotor devices such as diodes for rectification and transistors for amplification and the like. Such devices usually include one or more rectifying contacts on a body of semiconductor which ordinarily h a-s connection.

It has for some time been apparent that even amount of ordinary atmosphere enclosed in the sealed envelopes of such devices might in time have deleterious possible the thorough evacuation of such envelopes for sealing and, if desirable, the filling of such devices with a rare or other inert gas. V I

Diodes and transistors employing germanium and like semiconductive materials are inherently susceptible to fiabrication as very 'tiny units. The space that might be occupied and the complexity that might be introduced by an exhaust tubul-ation is objectionable from the point of view of compactness and simplicity of manufiacture; and accordingly it is a further object of the invention to avoid the need for suchexhaust tubulation in fabricating evacuated (and optionally refilled) sealed units. The envelope 'of an inherently tiny device could have no more than a small exhaust tubulation. A protracted time is required for exhausting an envelope to any specified highorder vacuum through a very small-diameter tube; or, viewed otherwise, the degree of vacuum resulting when a small-bore exhaust tubulation is used isrelatively poor. By virtue of the present invention which avoids the exhaust tubulation entirely, a high-grade vacuum may be effected quickly.

As will be seen, the illustrative embodiment of the apparatus aspect of the invention includes a two-element chamber wherein locating and holding portions are pro vided for respective parts of a two-part envelope; and the part-holding portion of one element of the chamber is movable relative to the chamber in the way to appreach the envelope part held by the other element of the chamber. The chamber incorporates sealing means effective to unite and hermetically seal the envelope parts together, optionally by induction-heating to melt solder or the like on the opposed envelope parts (as in copending application Serial No. 390,068, filed November 3, 1953, by Frederic Koury); or the envelope parts, evacuated while separated, are brought into assembled contact and resistance-welded, as detailed below or they may be united by a cold-flow process now well known.

The nature of the invention and its further features of novelty will be better appreciated from the following detailed disclosure of an illustrative embodiment. In the drawings,

Fig. 1 is a fragmentary view, greatly reduced in scale,

2,768,490 Patented Oct. 30, 1956 of novel apparatus embodying features of the invention;

Fig. .2 is a longitudinal cross-sectional view, somewhat reduced, of a part of the apparatus of Fig. 1, cmbodying features of the invention;

Fig. 3 is a view similar to Fig. 2 of the same device at another phase of its operation;

Fig. 4 is an enlarged detail of the apparatus in Fig. 3; and

Fig. 5 is an enlarged cross sectional view of a typical device fabricated by means of the present invention.

Referring now to Figs. 2-4 inclusive it is seen that a two-element chamber 10A and 10B is shown in which the lower element 10B has an exhaust line 12 which branches int- o passages 14 and 16 communicating with the hollow18 in chamber element 10A. A rubber ring 20 which is suitable for forming a seal between elements 10A and 10B of the chamber also introduces electrical insulation between those chamber elements. A rigid ring 22 of suitable insulation is carried by chamber element 103 for guiding element 10A along the vertical axis of chamber element 10B. Ring 22 is received in relief 24 of chamber element 10A. A key 26, also of insulation, is secured to chamber element 10B, and is slidably received in groove 28in the upper chamber element 10A.

At the top of element 10A is a metal sylphon bellows 30 having an internal stiff helical compression spring 32 and a vertically slidable shaft 34 therein, this shaft being held against rotation in its support by-a pin and slot connection 36.

As seen in Fig. 4, chamber element 10 B includes an insert 38 of any suitable electrically conducting material which is formed with a seat shaped to receive lower part 40 of a typical device to be evacuated and sealed. The upper part 42 of the device is received in a recess 44 within slide member 34; and member 42 is held frictionally in place by a spring-ball detent 46. Member 34 is also electrically conductive. I

In Fig. 5 the illustrative device being fabricated in the apparatus of Figs. 2-4 is seen to be a point contact transistor including a flanged metal ring 40a, three leads 40b extending through a glass seal 40c; and sharp rectifying contacts 40d are carried by two of the leads 40b, bearing against a semiconductor body 40:: which is carried by and ohmically united to the third lead 401;. Glass seal 40c and flanged metal ring 40a constitute the lower envelope part, received in element 10A of the chamber.

The upper envelope part 42 of the device has a flange 42a which is to be united and hermetically sealed to the flanged ring 40a of the lower part 40. The completed unit as shown in Fig. 5 has a continuous weld, as will be described, and the space occupied by the contacts 40b and body 40c is evacuated or filled with an inert gas to any desired degree pressure and of any desired composition. A very high vacuum -or a very pure rare gas both have features to recommend them.

In Fig. 1 there is shown part of a conveyor 50 on which is carried a series of lower cavity members 10B spaced at regular intervals. This conveyor 50 is suitably provided with an intermittent mechanism (not shown) for "advancing it stepwise, involving details well known and forming no part of the present invention. The conveyor may take the form of an endless belt or it may simply be a stepwise indexed plate or turret. The exhaust line 12 is similarly shown broken away because the mechanisms for connecting such lines to a suitable exhaust system after leaving a first loading station, is Well known in machines that have long been used in exhausting and sealing vacuum tubes. Such machines also connect rare gas supplies to the exhaust lines at suitable times, after evacuation but before sealing in the present instance.

At the third station of Fig. 1 there is shown a resistance welding power supply 52 electrically connected to switch 54 between the conveyor 50 (connected to all of the lower chamber elements 108) and additionally connected to :a ram 56 :slidable in bearing 58 and operated to compress sylphon bellows 30 at an appropriate time in the cycle. The actuating mechanism for arm 60 may take the form of a cam or a solenoid or an air-operated piston or any suitable mechanism and is accordingly not shown in detail.

In operation the two-part chamber is manually separated as shown in first station of Fig. 1, and the two portions of the device of Fig. are separately inserted, manually, into the respective seats in parts 38 and 44. At this first station, chamber element '10A'is physically assembled onto the lower chamber element B to occupy the position illustrated in Fig. 2, with chamber element 10A resting on sealing ring and with the envelope part 42 supported in proper opposed alignment with the lower envelope part 40 by virtue of ring 22 and key 26.

In the second station of Fig. 1 the chamber 10A, 10B isevacuated, to a high degree of vacuum as may be desired, with the interior of hollow member 42 freely exposed to the vacuum system. Effective evacuation is assured and expedited by holding these two parts separated during the evacuating interval. During this time spring 32 maintains slide member 34 in the upper position of Fig. 2.

There may be a sequence of stations represented by the single station at the center of Fig. 1, as may be deemed expedient for progressively perfecting the evacuation of the'device; and an additional station may be used if desired for introducing a rare gas by way of line 12 or by way of a separate tube not shown. Such details are well known in the art of vacuum tubes and are not illustrated.

When the degree of vacuum and optional filling has been completed, the two-part assembly 10A, 10B moves into the position shown at the right of Fig. 1. At this station actuator 60 forces slide 56 against slide 34 and depresses that slide until flanged envelope part 42 bears firmly against metal ring 40a. Closure of switch 54, manually or by suitable automatic means, introduces a burst of welding current by way of rod 56, slide 34, members 42 and 42a, metal insert 38, and lower cavity member 10B. One of the metal parts may be formed with a rib, in order to facilitate forming a continuous projection weld as a hermetic seal. It is significant, perhaps, that the welding is effected in a chamber of minimal size and without manual access to the parts to be united; and it is further significant that the welding heat is developed only in that limited region where it is desired, without unnecessarily exposing the semiconductor to high temperatures. Such devices are susceptible to damage by excessive heat, so that the apparatus illustrated is es- --pecially suitable for sealing such temperature-sensitive devices.

The illustrative embodiment of the invention, and the specific application shown, are naturally susceptible to a latitude of modification and to varied application. Acoordingly the appended claims should be broadly construed, as is consistent with the spirit and scope of the invention.

What is claimed is:

1. Apparatus for evacuating and sealing semiconductor devices, including a chamber having mutually separable elements, electrical insulation separating one of said chamber elements from the other of said elements, retaining means in each chamber element for supporting respective envelope parts of the device in spaced-apart positions, one of said retaining means being movable relative to its chamber element to carry its retained envelope part against the other, means for evacuating the space in and around the envelope parts, and means to impress a welding current on the assembled envelope parts.

2. Apparatus for evacuating and sealing together two parts 'of' a metallic envelope having registering weldable surfaces, including a chamber defined by a pair of separable elements, electrical insulating means separating one of said elements from the other, a vacuum outlet for said chamber in one of said elements, a first retaining means in one of said elements for supporting one of said envelope parts in fixed position with respect to said one element, a second retaining means in the other of said elements for supporting the other of said envelope parts spaced "from said one envelope part during evacuation of said chamber, said second retaining means including a cylindrical slide member movable in an opening in said other element and having a .recess in the end thereof within the chamber to receive at least a portion of said other envelope part, means for moving said slide member toward said first retaining means, thereby to force together'the registering surfaces of the envelope parts, and means for causing a Welding current to flow through both of said retaining means and the envelope parts supported thereby.

References Cited in the file of this patent UNITED STATES PATENTS 1,790,787 Badger Feb. 3, 1931 2,006,818 Zimber July 2, 1935 2,014,597 Staley Sept. 17, 1935 2,223,031 Edwards Nov. 26, 1940 2,274,400 De Margitta Feb. 24, 1942 2,435,747 Larson Feb. 10, 1948

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