US 3212169 A
Description (OCR text may contain errors)
1955 H. K. GLASER ETAL 3,212,169
GRID ELECTRODE STRUCTURE AND MANUFACTURING METHOD THEREFOR Filed Feb. 9, 1962 Fig.|.
WITNESSESI ldlNxEgiToRs d CFO OSEI Ofl ,7 E cYhorles F. Emery. CZMZA [g ATTOR United States Patent 3,212,169 GRID ELECTRODE STRUCTURE AND MANU- FACTURING METHOD THEREFOR Harold K. Glaser and Charles F. Emery, Horseheads, N.Y., assignors to Westinghouse Electric Corporation,
East Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 9, 1962, Ser. No. 172,192 Claims. (Cl. 29-1555) This invention relates to electronic discharge devices and more particularly to electrodes for such devices and methods of manufacturing thereof.
The characteristics of electronic discharge devices determine the scope of its use and the elliciency of its operation. The requirements of an electronic discharge device at very high frequencies impose conditions which can only be satisfied by extremely precise constructional features to produce the essential electrical constants whereby the highest efliciency is attained. The most important characteristic of an electron discharge tube is normally in transconductance. The transconductance depends on the spacing between the cathode, control grid and the diameter of the grid lateral wire and the spacing between the adjacent lateral wires. In order to attain a high transconductance, it is necessary to reduce the diameter of the control grid lateral wire to a point where the wire is not self-supporting when wound in a conventional grid form. Therefore, the fragile lateral wire must be wound on a support frame which maintains the spacing between the grid and cathode substantially constant within its operational range. In addition, of course, the grid laterals should be of uniform diameter and uniform spacing.
To overcome the problem of support of this fragile wire, it is necessary to resort to a rigid frame on which the thin helix wire can be wound and fixed thereto. This type of grid structure is referred to in the art as the frame or planar type grid construction.
The economical mass production of frame grids is a serious problem. Previous solutions have utilized a frame of molybdenum coated with gold. Lateral wires of unplated tungsten are wound onto the coated frame or frames. The wound assembly is then heated in a suitable atmosphere to melt the gold which in turn solders the lateral tungsten wires to the molybdenum frame. The individual grids are then gold plated to provide the proper finish on the lateral wires to prevent secondary emission problems. Gold plated tungsten wires cannot be used in this process because good adherence between the gold and tungsten is hard to achieve and the gold tends to form beads at the soldering temperature. Another problem that exists with some lower temperature solders is that it tends to flow out over the laterals and thereby change its dimensions and the secondary emission properties of the lateral wire.
It is accordingly an object of the present invention to provide an improved electron discharge device.
It is another object to provide an improved grid electrode structure.
It is another object to provide an improved method of manufacturing a grid electrode structure to provide uniform diameter lateral members.
It is another object to provide an improved method of manufacturing an electrode that is easy to control and will tolerate a wide latitude of variation.
Stated briefly, the present invention provides a rigid frame or planar grid structure for an electron discharge device and the method of manufacturing so as to provide uniform spacing and diameter of the lateral grid members. These features are realized in the method of manufacturing by providing a brazing material in which a coating 3,212,169 Patented Oct. 19, 1965 of copper is applied to the frame member and a coating of gold is applied over the copper coating. The lateral wires with a gold coating thereon are wound over the frame. In the brazing of the lateral members to the frame member, the gold coating on the lateral wire does not flow and as a result a uniform diameter of wire is obtained in the final product.
Further objects and advantages of the invention will become apparent as the following description proceeds and the features of the novelty which characterize the invention will be pointed out in particularly in the claims annexed to and forming a part of this specification.
For a better understanding of the invention, reference may be had to the accompanying drawings, in which:
FIGURE 1 is an electron discharge device partially broken away and incorporating a grid electrode made in accordance with the teachings of the invention;
FIG. 2 is a perspective view of the grid electrode incorporated in FIG. 1;
FIG. 3 is a perspective view of a grid winding jig used for winding the grid lateral wire onto a frame grid support member; and,
FIG. 4 is a cross section of the grid structure taken along line IV-IV of FIG. 2 prior to the brazing operation.
Referring in detail to FIG. 1, there is shown an electron discharge device embodying the present invention. The device is comprised of an envelope 10 of suitable material such as glass with an electrode assembly or cage indicated generally by the character 12 enclosed therein. The envelope 10 shown is of conventional design and includes a tipped off exhaust tube 14 on top of the envelope 10 and a button stem header 16 closing off the bottom portion of the envelope 10. A plurality of lead-in members 18 are provided through the button stem 16 for provoding the necessary voltages to the electrodes therein. The electrode assembly within the envelope 10 consists of a cathode 20 illustrated as an indirectly heated type cathode. Positioned adjacent to the cathode 20 is a control grid 22 which is described in more detail later within the specification. Positioned on the opposite side of the control grid 22 with respect to the cathode 20 is an anode member 21 for collecting the electrons from the cathode 2t The unit or mount includes a pair of spacer insulating discs 19 of a suitable material such as mica which supports the electrodes in a fixed position within the electrode cage 12.
The control electrode 22 comprises a frame or disc member 24 of a suitable material such as molydenum with a plurality of lateral wires 30 of tungsten wire 31 with a gold coating 32 thereon. The frame or disc member 24 is normally formed by punching sheet metal into the form illustrated in FIG. 2 with an aperture 36 provided in the central region thereof and which is the active area of the control grid 22.
The molybdenum frame 24 is then plated with copper so as to deposit a coating 26 of copper over the molyb denum frame of a thickness of about .00003 to .00005 inch. A coating 28 of gold is then deposited onto the copper plated frame by electroplating, for example. The gold coating is a thickness of about .00009 to .00011 inch.
Two frames 24 are then secured as indicated in FIG. 3 and a tungsten wire having a gold coating of about 4% by weight is wound about the frame members. A suitable method of winding the lateral wires 30 onto the frame members 24 is illustrated in FIG. 3 and simply consists of a jig member 40 to which two disc members 24 are secured by the clamping members 42 and 44. The frame members 24 are then rotated and the lateral wire 30 fed thereto to wind the lateral wires 30 about the two frame members 24. The cut ends of the lateral wire 30 are secured to the frame 24 by use of a volatile bonding agent such as Lucite and then the unit is inserted into a brazing furnace. FIG. 4 illustrates the structure of the grid 22 prior to insertion in the furnace. The unit is heated in the presence of Ammogas (a Westinghouse Electric Corporation trademark, now assigned to the Sunbeam Corporation, for a non-oxidizing atmosphere of disassociate-d ammonia, i.e. 3H +N or a hydrogen atmosphere for two minutes at 930 C. This heat treatment produces a gold-copper solid solution which is rich enough in gold to minimize dissolving the gold coating 32 from the lateral wire 30. The proper thickness of coatings 26 and 28 as specified above also permits the brazing operation to be carried out at a temperature which is low enough to preclude recrystallization of the molybdenum frame. The molybdenum frame, therefore, retains its ductility.
Because of the negature of the gold-copper solid solution, the bond will not remelt unless it is heated above the original bonding temperature. Another advantage of the structure shown above is that the grid, by providing the plating on the lateral ends of the frame 24, is also capable of suppressing secondary emission.
While there has been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.
We claim as our invention:
1. The method of manufacturing a grid electrode which comprises winding a series of turns of a fine wire of gold plated tungsten onto a frame support member of molybdenum, said support member having a coating of copper on said support member and a gold coating on said copper coating, placing said support member and said turns of wire in a non-oxidizing atmosphere, subjecting said turns of Wire and said support member to a temperature sufiicient to produce a gold-copper solid solution on said support member, and cooling said support member and said turns of wire whereby said turns of wire are secured to said support member.
2. The method of manufacturing a grid electrode which comprises providing a molybdenum support member having a coating of copper on said support member and said copper coating having a coating of gold thereon, placing a plurality of tungsten lateral wires having thereon a coating of gold on said support member, placing said support member and said lateral wires in a non-oxidizing atmosphere, subjecting said lateral wires and said support member to a temperature suflicient to produce a gold-copper solid solution on said support member, and cooling said lateral wires and said support member whereby said coatings of gold and copper secure said lateral wires to said support member.
3. The method of manufacturing an electrode including a tungsten wire coated with gold and a frame member of molybdenum, said method comprising the steps of disposing a first layer of copper upon said frame member, disposing a second layer of gold upon said first layer, placing said wire onto said frame member, subjecting said wire and said frame member to a temperature sufiicient to produce a gold-copper solid solution on said frame member, and cooling said frame member and said wire to thereby secure said wire to said frame member.
4. The method of manufacturing as claimed in claim 3, wherein said steps of disposing said first and second layers is performed by electroplating.
5. The method of manufacturing as claimed in claim 3, wherein said first layer is disposed upon said frame member to a thickness in the range of .00003 to .00005 inch, and said second layer is disposed on said first layer to a thickness in the range of .00009 to .00011 inch.
References Cited by the Examiner UNITED STATES PATENTS 2,678,486 5/54 Chick et al 313-348 X 2,897,395 7/59 Miller 29-25.14 X 2,961,759 11/60 Weissfloch 29-2514 X 3,069,585 12/62 Katz 2925.14 X
WHITMORE A. WILTZ, Primary Examiner.
LEON PEAR, Examiner.