FLEXIBLE SHIELDED CABLE

Abstract: A flexible shielded cable including a flexible metallic conductor, a layer of dielectric material disposed around the flexible metallic conductor, a flexible metallic shield about the layer of dielectric material, and a metallic coating enclosing the flexible metallic shield to completely seal the surface of the metallic shield. The flexible metallic shield is applied longitudinally with abutting longitudinal edges which are soldered together by the metallic coating.

Description: FLEXIBLE SHIELDED CABLE BACKGROUND OF THE INVENTION This invention relates generally to electrical cables, and more particularly to shielded coaxial cables widely used in the electronic industry for signal transmission. Shielded cables are normally of three types, namely, rigid, semi-rigid or flexible. Flexible shielded cables are available in a variety of sizes, and are widely used where 5 requirements relative to permissible energy transfer are matched to cable size. One type of flexible cable known in the prior art is disclosed in U.S. Patent No. 4,694,122 granted September 15, 1987 to L.J. Visser. The cable includes one or more centrally located conductors surrounded by a synthetic resinous dielectric material. The dielectric material is covered by a layer of copper foil, the edges of which are overlapped, and in turn covered by a l o layer of copper braid woven about the foil, following which the cable is dipped in a bath of molten solder or tin to completely seal any openings. The foil is applied either as a spiral winding or an axially applied curved strip to form overlapping edges in either case. Because of the relatively slow speed of the braiding operation, the cable is manufactured in two stages, with the final solder or tin coating performed as a separate operation. The braiding operation is 15 normally performed immediately adjacent the application of the foil in order to retain the foil in position, particularly where the foil is applied in non-spiraled manner. This procedure, while effective, requires a relatively slowly moving continuous process limited by the speed of the braiding operation, which is substantially slower than any of the other steps. 20 SUMMARY OF THE INVENTION Briefly stated, the invention contemplates the provision of an improved shielded cable and process for manufacturing it. This is accomplished by applying the foil covering axially or longitudinally of or spiraling in such manner that the edges of the foil are substantially abutted, and immediately thereafter soldered together, eliminating the need for overlapping edges and 25 fixing the foil in position so that it may be conveniently covered by a braided shield and then coated with a separate solder or via a tin dip operation, thus each manufacturing step may proceed at the maximum speed consistent with the nature of the operation performed. BRIEF DESCRIPTION OF THE DRAWINGS 30 In the drawings, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding arts throughout the several views. Figure 1 is an enlarged cross sectional view of an embodiment of the invention. Figure 2 is a fragmentary perspective view thereof with certain of the component parts removed for purpose of clarity. Figure 3 is a block diagram showing the application of the foil layer over a conductor and surrounding dielectric material prior to braiding for a subsequent soldering operation. Figure 4 is a diagrammatic view showing the solder or tin dipping operation. DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT In accordance with the invention, the device, generally indicated by reference character 10, is in the form of a flexible cable having at least one central conductor 1 1 , a surrounding layer of dielectric material 12, a copper foil wrapping 13, a braided copper cover 14, and a sealing layer 15 applied as molten solder or tin. The copper foil wrapping 13 is applied as a longitudinal strip to form first and second abutting edges 21 and 22 defining a small interstice in the order of several thousandths of an inch. The foil is preferably of a thickness ranging between .0005 to .0025 inches in thickness. While it is possible to apply a narrow strip of molten solder (not shown) to cover the interstice, it has been determined that it is possible to obtain an equivalent result using a portion of the sealing layer 15 to penetrate the interstices in the braided copper 14. Referring to Figure 3, there is illustrated an apparatus for performing a process wherein the foil layer is applied over the dielectric material. The conductor is fed from a conductor supply reel 30. The foil is fed from a supply roll 31. A die 32 applies the foil about the conductor. The assembly passes through braiding operation 33 and over an idler pulley 34 to take-up reel 35. Figure 4 shows an apparatus for performing a final solder or tin dipping operation with a supply spool 48 feeding braided cable 49 through a flux bath 50, a tin bath 51 , a cooling bath 52, and a take-up reel 53. During this operation, the molten metal saturates the braid to fill the voids therein, and bonds the wire braid to the copper foil, sealing the abutted edges of the foil and leaving a sealed surface on the cable. A variety of materials may be used for this purpose, usually tin or a tin-lead amalgam. By applying the copper tape longitudinally to form abutted edges, both the tape and braid operations may be continuous, permitting the cables to be manufactured in long lengths. These operations, as with multiple shields on flexible cables, are usually performed in the same operation by forming the tape around the dielectric using the die device 32 positioned below the braiding operation 33, as illustrated in Fig. 3. The completed cable, which has been dipped in a molten metal, has many desirable properties. The shield, even after application of the molten metallic layer, remains very supple, much more so than would be possible when using solid copper tubes and, therefore, can be formed by hand into three dimensional configurations. The time required to accomplish this is a small fraction of that required in the case of semi-rigid cables, since no tools or jigs are required. Because of the smooth non-overlapping configuration of the copper foil against the dielectric, transmission characteristics have proven adequate to allow the cable to meet the Mil- C-17 requirements for corresponding semi-rigid cables. A wide range of dielectric materials are compatible with the present invention. The preferred dielectric materials in common use for coaxial cable applications include polyethylene, polypropylene, polytetrafluoroethylene and fluorinated ethylene-propylene. The latter two resins are in what is referred to as "the Teflon family". (Teflon is a registered trademark of DuPont). There are other fluorocarbon resins which are suitable, and in fact, where desired, a non- fluorinated thermosetting synthetic resin may also be used. The preferred dielectric in accordance with the invention is polytetrafluoroethylene in both expanded and non-expanded form, because of its superior dielectric properties, high temperature resistance, and rather than a shaφ melt point, it has a transition temperature at which it softens but retains its shape should the melt point be exceeded during processing. When using low temperature thermoplastic material, care must be taken not to deform the dielectric while it is above the melt point. It may thus be seen that the present provides an improvement in the production of coaxial cables, in which the need to overlap longitudinal edges of the copper tape has been eliminated. Instead, the flexible cable of the present invention includes a copper tape layer of substantially uniform thickness having longitudinal abutted edges which are sealed subsequently with the application of a layer of molten solder and tin which penetrates the voids in the braid and seals the abutted edges. Having thus described several particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is limited only as defined in the following claims and the equivalents thereto. What is claimed is:

Claims: CLAIMS 1. A method of forming a metallic shield about a flexible metallic conductor enclosed within a layer of dielectric material to form a flexible shielded coaxial cable, comprising the steps of: a) applying an elongated strip of metal foil about said layer of dielectric materials so that the foil has a pair of substantially abutted longitudinally oriented edges; b) applying a braided metal over said foil to yield a braided cable; and c) passing said braided cable through a bath of molten sealant materials to close interstices in said braided metal and an interstice between the pair of substantially abutted longitudinal oriented edges of the metal foil. 2. A flexible shielded cable comprising: a) at least one elongate flexible metal conductor; b) a layer of flexible dielectric material surrounding said at least one elongate flexible metal conductor; c) a flexible foil surrounding said flexible dielectric material, said flexible foil forming a longitudinally oriented pair of substantially abutted edges; d) a braid surrounding said flexible foil; and; e) a layer of metallic sealant surrounding and penetrating said braid and said pair of substantially abutted edges of said flexible foil. 3. A semi-flexible coaxial cable comprising: a) at least one central elongated flexible metallic conductor; b) a flexible dielectric layer surrounding said at least one central elongated flexible metallic conductor and in contact therewith; and c) a copper-tin composite shield disposed about and in intimate contact with said flexible dielectric layer, said copper-tin composite shield consisting of a copper tape wrapped about the flexible dielectric layer in such manner that a pair of abutted edges of said copper tape are substantially abutted to form a narrow interstice, a copper braid surrounding said copper tape and in contact therewith, and a third metal layer which, applied in a molten state, saturates the copper braid to fill voids therein, bonds the copper braid to the copper tape, seals the abutted edges of the copper tape and leaves a sealed surface on the semi-flexibie coaxial cable. 4 The cable in accordance with claim 3. wherein the abutted edges of the copper tape are longitudinally oriented. 5. The cable in accordance with claim 3, wherein a thickness of the copper tape is in a range between .0005 to .0025 inches. 6. The cable in accordance with claim 3. wherein the copper braid is formed from a copper alloy. 7. The cable in accordance with claim 3, wherein the third metal layer is formed of tin. 8. The cable in accordance with claim 3. wherein the third metal layer is formed of a tin- lead amalgam. 9. The cable in accordance with claim 3. wherein the flexible dielectric layer is formed of polytetrafluoroethylene . 10. The cable in accordance with claim 3. wherein the flexible dielectric layei is formed of fluorinated ethylene-propylene. 11 The cable in accordance with claim 3. wherein the flexible dielectric layer is formed from a non-fluorinated thermosetting synthetic resinous material.

Inventors: GRIMES WILLIAM F, GRIMES, WILLIAM, F.
Applicants: THERMAX CDT INC, THERMAX/CDT, INC.
Application year: 1997
Main classification: H01B13
IPC codes: H01B11, H01B13