Abstract: Methods and apparatus for manufacturing an improved ribbon cable comprising a plurality of insulated wires juxtaposed in fixed relationship to each other and an improved transposed cable in which each conductor of the cable of the invention is in the form of a continuous helix. The electromagnetic device of the invention has the ribbon cable of the invention as its magnetic windings.

Abstract: A flat cable bus with fan-out patterns which provide equal length wires to eliminate clock skew is disclosed.

Abstract: A nickel-plated metal terminal to be spot welded has a contact part plated with nickel and a spot welding part to be spot welded to a metal part not plated with nickel thereby improving the weld characteristic of the spot welded terminal.

Abstract: An electrical power distribution system is disclosed which includes flat undercarpet power cable. The cable includes portions of the cables spliced to one another to effect a continuation of the power distribution. A covering for the spliced joint of the two cables includes two foam layers having double backed adhesive thereon which, when placing the two facing surfaces together, adhesively affixes the two foam layers together. The outer surfaces, which include adhesive, adhere a protective sheet of insulative material thereto.

Abstract: A flexible beam lead tape having three layers having trace conductors, a dielectric and a ground plane. Vias extend through the dielectric layer at the first and second ends of the electrical conductors for providing versatile connections to either ends of the conductors. The ends of the conductors may be provided with electrical connections on either or both sides of the tape and may be connected by pressure contact or by bonding.

Abstract: A computer and switching mainframe connection system and flat cable connection elements therefor. The elements are a flat cable "S" circuit, FIG. 1, and a bus circuit, FIG. 8. The "S" circuit has an elongated run (68) and a "S" portion (43). The bus circuit has "U" elements (61) and a linear portion (58) with the signal lines of the "U" elements (61) connected to the signal lines of the bus circuit (80). The mainframe is formed of an array of circuit boards (100) bearing a wafer (90) and header (99) for the wafer which in turn is connected to ports (101) to which tab connectors (57, 56, FIG. 3) of the bus circuit and "S" circuit are connected.

Abstract: A flexible coaxial cable capable of high frequency signal propagation formed from a multilayer configuration having a plurality of adjacent signal traces etched in dielectric material and surrounded by a protective ground layer. Selected ones of the signal traces are designated to be conducting signal lines. A 360-degree signal return line is formed around each of the designated conducting signal traces utilizing signal traces adjacent those serving as conducting signal lines as part of the return line conductor. A 360-degree shield is also formed around the return line, again employing selected signal traces as part of the shield. The return line and shield are created using photo and laser etching, chemical milling and electroplating techniques. The cable allows electrical signal propagation in the gigahertz frequency range without appreciable signal loss and provides high density packaging. The flexible nature of the cable and its structure combine to provide an even variable standing wave ratio.

Abstract: In accordance with one embodiment of the invention, a process for interconnecting the circuitry of two substrates comprises the step of terminating the circuitry on bonding pads that are arranged in parallel rows with the first row of each substrate being nearest an edge of the substrate. The bonding pads of the two first rows of the two substrates are joined by conductors of a dielectric tape that bridges the two substrates. The conductors overlap the edges of the dielectric tape and are organized to permit them to be bonded to corresponding bonding pads of the two substrates, for example, by soldering. The two second rows of bonding pads are joined by conductors on a second dielectric tape which is wide enough to cover two first rows of bonding pads and thereby provide electrical insulation.

Abstract: A probe for an in-circuit emulator comprising a flexible substrate composed of a base film, a pattern provided on a central portion of the base film, plastic parts mounted on both ends of the base film, a connecting element detachably provided at one end of the flexible substrate, and reinforcing members mounted on the plastic parts.

Abstract: Flexible electrical connectors are employed to connect rigid members, such as plugs and printed circuit boards. Such connectors have a tendency to tear, especially in the region near the rigid member, and this can prove expensive to remedy. The invention provides reinforcing thread members, for example, along the connector which prevent any tear which may develop from growing further.

Abstract: An electric contact arrangement for a multi-strand cable having at least one connection position for receiving a contact plug, comprises a plurality of spaced openings extending through the cable insolation and defining the connection position, and a respective plurality of plug contacts received in the openings. Each contact comprises a contact element that in engaged position thereof makes electrical contact with a cable strand intersecting the end zone of a respective opening.

Abstract: A shielded printed circuit board system is described in which a microstrip transmission line secured to the surface of a dielectric substrate between ground planes is shielded to isolate the microstrip and inhibit the escape of electromagnetic radiation. This system reduces crosstalk in printed circuit boards and also reduces coupling of external fields into the signal path, thus allowing more sensitive measurements. The shield member is conductive and includes a body section and downwardly depending leg members. The leg members are secured to ground planes on each side of the microstrip transmission line. In another embodiment a dimensionally stable support plate (e.g., an aluminum plate) is secured over the shield member.

Abstract: A high density flexible circuit for coupling electrical devices. The flexible circuit has signal and ground traces on both sides of the flexible circuit. Each signal trace is surrounded by ground traces. There is a ground trace on either side of each signal trace and two ground traces located below each signal trace. This system of placing ground traces surrounding each signal trace reduces electrical noise between the signal traces and reduces the electrical capacitance of the circuit.

Abstract: A flat multi-conductor power cable is disclosed which includes a plurality of generally parallel, spaced apart, flat conductors which are surrounded by two layers of insulation material. An internal layer is extruded around each of the flat conductors and is intimately bonded to each conductor. A single external layer is extruded around all of the internal layers and is intimately joined to all of the internal layers. Preferably, the external layer comprises a thermoplastic elastomer and the internal layer comprises a polyolefinic ionomer. A method and apparatus for making such a flat multi-conductor power cable is also disclosed.

Abstract: Improved method and apparatus for manufacturing transposed ribbon cable, an improved ribbon cable in which a plurality of insulated wires are juxtaposed in fixed relationship to each other, and an improved transposed ribbon cable in which each conductor of the cable of the invention is in the form of a continuous helix. The transposed ribbon cable is manufactured by the method and apparatus of the invention by folding a ribbon cable angularly with respect to the longitudinal axis repeatedly while advancing the ribbon cable incrementally.

Abstract: Flat electrical connecting cable with controlled electrical and thermal resistances.It comprises a flat insulating support, on which are installed connecting lines constituted by two superimposed layers. The first of them is constituted by a poor heat conducting material, such a manganin, while the second is discontinuous andis formed from a very good electric conducting material, such as copper. The segments on which the second layer is installed are thermally insulated an at uniform temperature. It is possible to vary the conductivity of the different layers by acting on the thickness and width thereof.This invention is applicable in industries such as cryogenics and space, as well as all applications functioning between a cold source and hot source, where it is wished to control the heat exchanges.

Abstract: A flexible cable has a grounding pattern or patterns provided therein. Thereby, when an object having static electricity of high voltage is caused to approach the flexible cable, dielectric breakdown of a base and cover of a high polymer material of the cable, to a conducting portion of the cable which is not exposed at the interior of the flexible cable is prevented, and damage to an electronic circuit connected with the not exposed portion, due to electric discharge, can be prevented by causing the static electricity to be discharged to the exposed grounding pattern.

Abstract: Electrical interconnection between a leadthrough in a cathode ray tube envelope wall and terminals for internal, electrically operable, components such as an electron gun, is established by flexible conductor means comprising a flexible circuit consisting of one or more polyimide films with conductive tracks deposited thereon and, secured to the film(s) to form a single assembly, a further one or more superposed polyimide films having spaced apertures through which at least one conductor element, for example of metal wire or tape, is woven. The conductor element(s) can carry high currents safely and the conductor means is sufficiently thin and flexible to be routed round internal components easily.

Abstract: An electrically conducting hot melt adhesive is located at limited contact regions of a flexible circuit support, which typically carries a large scale integrated circuit (LSI) chip. A non-conducting hot melt adhesive is disposed between the limited contact regions at the non-contact regions. The resulting electrical connector can then be brought into contact with the corresponding areas of flexible or rigid circuit supports and through the application of heat and pressure, fuse the respective members so as to establish circuit paths between their limited contact regions via the electrically conducting hot melt adhesive. Heat and pressure are applied to the conducting hot melt adhesive in the same way as for an electrically non-conducting hot melt adhesive after contacting limited contact regions of another flexible circuit support or a rigid circuit support with the molten adhesive. Subsequently, the molten adhesive is left to cool so as to solidify.

Abstract: An electrical transmission unit line is provided comprising a porous dielectric layer having positioned on one side thereof a pair of narrow, parallel elongated electrical conductors and on the other side thereof, opposite the pair of conductors and extending transversely across both wires of the pair and parallel thereto, a wide ground conductor. An electrical transmission line having a plurality of such unit lines is also provided. The porous dielectric is preferably porous, expanded polytetrafluoroethylene. The transmission lines are covered with an electrically insulating material, preferably a nonporous plastic.

Abstract: An orientable lamp adjustable both in elevation and angle to properly illuminate an area of interest. The lamp includes a low-voltage, high-intensity light bulb housing attached to the end of an extensible arm cantilevered from a base. The arm is constituted by a pair of superposed electrically-insulated metal tapes that are arched to resist flexure and are interconnected to the bulb terminals to function as a two-wire line. The tapes are windable on a spring-biased reel rotatable within a cylindrical casing mounted on the base and having a projecting nose from which the tapes emerge. The angle of the casing relative to the base is adjustable, whereby the angle of the cantilevered arm may be varied to adjust the angle assumed by the fixture. Also supported on the base is a step-down transformer connected by sliding contacts to the tapes on the rotatable reel to supply low-voltage power to the two-wire line to energize the bulb.

Abstract: In wafer-scale-integrated assemblies, microminiature transmission lines are utilized as interconnects on the wafer. The extremely small cross-sectional area of a typical such line results in its total line resistance being relatively large. Such a line exhibits signal reflections and resonances. In practice, it is not feasible to eliminate these effects by conventional load termination techniques. As a result, the frequency at which digital signals can be transmitted over such a line is typically limited to well below its so-called resonance limit. In accordance with a feature of the invention, the structural parameters of each line are selected to meet specified design criteria that ensure optimal high-frequency performance of the line.

Abstract: The flat multiconductor cable contains live, neutral and ground conductors lying generally parallel to each other and in side by side, single-plane relation. The live and neutral conductors are sealably surrounded by a relatively hard, polyetherimide material that is substantially free from attack from calcium hydroxide. An outer jacket or casing of polyvinylchloride (PVC) sealably surrounds the polyetherimide layers and contacts the ground conductor. The PVC is substantially free from attack in an alkaline environment. As such, the cable construction provides an enhanced resistance to puncture, particularly in alkaline environments which may be encountered in undercarpet wiring system applications.

Abstract: A backplane power distribution system characterized by generally uniform current densities so as to be capable of handling very high levels of current. This is achieved with a stepped backplane construction. For example, in a system having, in order, a first conductive layer, a first dielectric layer, a second conductive layer, and a second dielectric layer, the second conductive and dielectric layers extend transversely beyond the first conductive and dielectric layers to present a substantial exposed area of the second conductive layer. Typically, a rectangular metal bus bar is bolted to the backplane to make contact with the exposed area, and power supply connections to the bus bar are made in any convenient manner.

Abstract: An improved ribbon cable comprising a plurality of insulated wires in a fixed relationship to each other. The conductors have an axis in a common plane, and extend the full length of the cable. The conductors are bonded to a ribbon of flexible insulation material in a spaced apart relation with the longitudinal axes of the ribbon material and the conductors generally parallel to each other. In specific embodiments, the conductors may be foil, strips or depositions of conductive material. In other specific embodiments, a coating of flexible insulation material is superimposed on the ribbon material between the conductors and/or the conductors are overcoated with a continuous and uniform coat of flexible insulation or bonding material. An improved transposed ribbon cable is also provided.

Abstract: A microstrip transmission line comprises a plurality of signal-carrying lines disposed along a dielectric ribbon and separated by a predetermined spacing. Ground-plane conductors are disposed on the opposite side of the ribbon in staggered relation to the signal-carrying lines such that the ground-plane conductors occupy spaces corresponding to the gaps between adjacent signal-carrying lines. This arrangement lowers the capacitance and raises the impedance of the transmission line while maintaining high signal line density.

Abstract: The flat multiconductor cable contains live, neutral and ground conductors lying generally parallel to each other and in side by side, single-plane relation. The live and neutral conductors are sealably surrounded by a relatively hard, polyetherimide material that is substantially free from attack from calcium hydroxide. An outer jacket or casing of polyvinylchloride (PVC) sealably surrounds the polyetherimide layers and contacts the ground conductor. The PVC is substantially free from attack in an alkaline environment. The polyetherimide layers are extruded over the live and neutral conductors providing a seal therearound and thereby a barrier to moisture. The PVC layer is then extruded over the conductors providing a further seal around the polyetherimide layers.

Abstract: The cable of this invention comprises a pair of solid, flat, flexible electrical conductors of beryllium-copper attached to a reinforcing webbing of braided nylon. The ends of the conductors are soldered to electrical connector sockets and pins which are supported by glass reinforced resin disks. The webbing is tensioned while being molded inside a water impermeable elastomer which also encompasses the conductors, disks, and end portion of the sockets and pins. A second molding operation covers the water impermeable elastomer with a tough elastomer to form the cable including integral connector bodies incorporating the sockets and pins.

Abstract: A flat multiconductor cable having a multilayer construction and especially suited for use in establishing interconnections between the cable conductors and a separate conductive array such as a similar flat cable is disclosed. Conductive ink, formed metal conductors or etched conductors can be deposited on a flexible substrate and covered by a dielectric covering in the form of an ultraviolet cured dielectric coating or a separate insulating film. The conductors can be covered by anisotropic conductive adhesive with the conductive adhesive in contact with the underlying conductors at exposed tap locations where no dielectric coating is deposited or where the dielectric coating has been removed. A separate conductive array can be positioned in registry with the tap locations and the conductive adhesive can be used both to secure the conductive array to the cable and to establish electrical continuity between corresponding conductors.

Abstract: Improved method and apparatus for manufacturing transposed ribbon cable, an improved ribbon cable, and an improved transposed ribbon cable. The transposed ribbon cable is manufactured by the method and apparatus of the invention by folding a ribbon cable angularly with respect to the longitudinal axis repeatedly while advancing the ribbon cable incrementally.

Abstract: A flat electrical cable for power distribution is designed for undercarpet use and has two side-by-side live and neutral conductors 12,14 formed into a package 15 by insulation 16,18 around them. In a three-phase construction there are four conductors (FIG. 5). A conductive earthing screen 26 forming the sole earthing conductor overlies the package 15 and is of the same width as the package but is not bonded or only lightly bonded to it. An outer insulating layer 28 tightly surrounds the screen 26 and package 24 and holds them together at the edges, as well as providing protection along the cable edge. The layer 28 is formed of strips 30,32 which can be cut away at X to remove the edges 34 when a connection is to be made, the edge of the screen 26 providing a cutting guide. An insulating plate can be slid between the screen 26 and package 24 so that insulation displacement connections can be made from opposed sides of the cable.

Abstract: A composite tape primarily for use in transformer winding as an electric screen and having a backing layer of Melinex plastics tape (112) folded around a metal foil strip of copper (110), and a strip of adhesive PVC tape (114) applied to the folded round edges, is formed by a machine having a braked spool (48) of PVC tape (52) which is fed around a roller (36) with a copper foil strip (58) from a braked second spool (56), sandwiched between the tape (52) and the roller (36), and guide rollers (40, 42) which turn in the outermost edges of the tape (52) to overlie the foil (58), whereafter adhesive tape (66) from a braked third spool is applied to the overlapping edges of the tape (52) by a roller (68) and the composite tape is fed through an outlet roller guide (74).

Abstract: A shielded multiconductor flexible cable for protection against EMI and/or RFI is disclosed. The shielded cable is comprised of a plurality of conductors disposed between two layers of insulating substrates, said cable having a graphic shield disposed on the exterior surface of at least one of the insulating substrate layers. The graphic shield is comprised of solidified conductive ink. Said ink provides an interference shield against EMI and RFI.

Abstract: An adhesive interconnecting means is comprised of one or more conductors on an insulating substrate, a first adhesive layer, said first layer being anisotropically conductive and disposed over said conductors and substrate and a second adhesive layer said second layer being a flowable adhesive that extends over the first substrate and anisotropically conductive layer. The anisotropically conductive adhesive is comprised of a nonhomogenous mixture of conductive particles in a nonconductive adhesive binder; the conductive particles, of random size and shape, are dispersed randomly throughout the mixture in noncontiguous conductive units, each unit being comprised of one or more individual particles, the units being sufficiently spaced apart to preclude electrical conductivity between adjacent conductive areas on the same substrate.

Abstract: An interconnecting means is comprised of one or more conductive ink conductors screen printed onto a first substrate, the conductive ink being comprised of an insulating polymer medium having first and second groups of conductive particles therein, and an insulating layer of flowable adhesive in covering relationship to the conductors. The first group of particles are finely divided particles which are suspended in the medium and form a continuous conductive path along the length of the conductor. The second group of particles are agglomerates of large particles which are randomly scattered throughout the conductive path and project above the surface of the medium. Interconnection is effected by positioning the first substrate conductors in an overlapping conducting relationship to the conductors on the second substrate such that the flowable adhesive is deposited between the two substrates and applying pressure to the positioned conductors and surrounding areas.

Abstract: An improved strip line cable for transmission of electromagnetic waves in the millimeter wave length range is provided. The cable has a plurality of face to face conductors in pairs, the conductors being separated from their paired counterparts by a porous plastic dielectric insulation material. The cable is jacketed. The improvement comprises the porous plastic dielectric material being, in addition, placed between each conductor and the jacketing material, thereby resulting in each conductor being effectively surrounded by porous plastic dielectric insulating material.

Abstract: A flat cable system includes a flat cable of a first type which has equally spaced flat conductors in a body of insulating material. A cable of a second type has three conductors, the centers of two of which are separated by the same spacing as in the cable of the first type but the third conductor is separated from the second by twice the spacing. A cable of a third type has three conductors which are uniformly spaced by the same center-to-center spacing as in the first type. When the cables are used together, the proper conductors are easily aligned for interconnection by using a reference edge adjacent the first conductor in each cable. The conductors are also color-coded.

Abstract: Connectors are made by applying flat cable techniques. A sheet of conductors (1a-1d) is covered on both faces by respective strips of insulating material which are made to adhere to each other and to the conductors. Gaps are left in the strips to leave portions of the conductors bare. The resulting sandwich is cut up to form connector blanks, which blanks are then shaped to obtain connectors which may have various shapes depending on the intended application.

Abstract: An electrical cable assembly for use in particular with undercarpet wiring systems has a flat multiconductor cable encased in electrical insulation, an insulative film extending lengthwise on the cable and an electrically conductive member overlying the film lengthwise, the conductive member having successive lengthwise extents that are respectively unsecured and secured to the cable. The film is provided with openings therethrough in registry with an exclusive one of the cable conductors through which the conductive member extents are connected to the cable. An electrically conductive shield preferably extends lengthwise with and overlies the conductive member. The shield is selected from material having a hardness greater than that of the conductive member. The material of the conductive member is preferably less cathodic in the electromotive series than the shield material so that in the presence of a corroding medium the shield and not the conductive member will first galvanically corrode.

Abstract: An electromagnetically-decoupled stripline circuit on a conventional circuitboard includes a center groundplane and two coplanar striplines that are sandwiched within a dielectric material between two outer groundplanes. A plurality of connectors conductively interconnect the groundplanes. The center groundplane has a decoupling strip portion lying between the striplines that is split in two by a gap. The gap traverses the direction an electromagnetic field would propagate from one of the striplines toward the other, and a pair of the connectors are positioned to straddle the gap. Z-wires, plated-through holes, and additional gaps may be employed.

Abstract: An adhesive interconnecting means is comprised of one or more conductors on an insulating substrate, a first adhesive layer, said first layer being anisotropically conductive and disposed over said conductors and substrate and a second adhesive layer said second layer being a flowable adhesive that extends over the first substrate and anisotropically conductive layer. The anisotropically conductive adhesive is comprised of a nonhomogenous mixture of conductive particles in a nonconductive adhesive binder; the conductive particles, of random size and shape, are dispersed randomly throughout the mixture in noncontiguous conductive units, each unit being comprised of one or more individual particles, the units being sufficiently spaced apart to preclude electrical conductivity between adjacent conductive areas on the same substrate.

Abstract: Process for manufacturing flat multi-conductor cable having two cable members and peelable internal lamina utilizes a pair of dies which simultaneously align conductors, laminate internal lamina, and extrude external lamina thereon. Each die has a conductor aligning surface with parallel linear conductor-receiving recesses therein and an adjacent extrusion surface. Conductors and internal lamina are drawn between aligning surfaces of mated dies and then between extrusion surfaces where vinyl is extruded through an aperture in each die to form external lamina. A knife-edged die insert adjacent one side of the aligning and extrusion surfaces provides a V-notch in one edge of the cable to facilitate peeling apart cable members for termination to a two-sided connector.

Abstract: A conductor, provided with insulation for forming windings for transformers and other inductive apparatus comprises two substantially rectangular uninsulated conductor strands, which are arranged with a flat side of one conductor strand facing a flat side of the other conductor strand and with an insulating layer arranged between the flat conductor sides, of a material which forms a glued joint between the conductor strands and which contains a spacer of insulating material to ensure that the conductor strands are held at a distance from each other. The glued joint may be provided either before or after the forming of the conductor into a winding. After the glued joint has been achieved, a winding manufactured from the conductor has a high breaking strength and low additional losses. The conductor is suitable for the manufacture of complicated windings as well, such as interleaved disc windings.

Abstract: A flat embedded-shield multiconductor signal transmission cable includes an embedded conformal shield interposed between adjacent conductors to significantly reduce cross-talk by as much as several orders of magnitude over conventional techniques. The shield is forced to a shape in which it is interposed between adjacent conductors by pinch rolling a sandwich of the conductors, insulation and shield between heated rollers, in which the top and bottom sets of conductors are forced inwardly to lie one beside the other with the shield in between. Uniform termination impedance is achieved because the embedded shield is protected during cable stripping. In an alternative embodiment, external shielding may be utilized to completely circumferentially surround the conductors. For improved pitch control, both heated pinch rollers are identical and are provided with resilient surfaces.

Abstract: A flat electrical cable for use under a rug or carpet having a series of regularly spaced elongate apertures in a web of insulating material along one edge of the cable. "U" shaped conductive connectors are used to secure adjacent cables together with an upper segment of the connector passing through an aperture of each cable so as to properly position the cables in respect to each other and electrically connect the cable conductors by means of sharpened pawls on the connector which pierce the plastics insulation of each cable.

Abstract: The moving coil (voice coil) of the loudspeaker is so designed that the loudspeaker will become suitable for automatic production. For this purpose, the moving coil is positioned on a coilform, and as a connecting line extending to the ends of the moving coil there are used flexible ribbon conductors secured to a plastics carrier.

Abstract: An electrical heating device comprises a substrate, an elongated conductor extending longitudinally of the substrate, a semi-conductor pattern carried on the substrate and electrically connected to and extending from the conductor pair, and a sealing layer overlying the conductor and sealed to the substrate at opposite sides of the conductor. The conductor comprises a pair of rectangular in cross-section metallic conductor elements, placed one on top of the other in face-to-face engagement with and unattached to each other. The bottom conductor elements faces towards the substrate and the upper conductor elements faces towards and engaging the sealing layer.

Abstract: A stripline cable is provided comprising a dielectric layer and a plurality of sets of narrow signal conductors and wider ground conductors which are disposed in confronting relation to each other with the dielectric layer sandwiched therebetween. The signal and ground conductors are alternately arranged transversely of the conductors. The dielectric layer is preferably made of porous polytetrafluoroethylene resin. With this arrangement, crosstalk in the stripline can be greatly reduced and signals can be transmitted at higher speeds over the stripline.

Abstract: A thin, flexible, electrically conductive adhesive tape is described suitable for do-it-yourself wiring in low voltage applications including a pair of longitudinally extending parallel electrical conductors each made of a multiplicity of strands of wire enclosed within a backing strip. The backing is paper-thin and can comprise a pair of layers of transparent or translucent plastic material bonded together around the conductors or a single thickness within which the conductors are embedded, the backing being formed for example by co-extrusion of upper and lower layers which are brought together while still in a molten condition so as to fuse together totally enclosing the wires. A stripable cover sheet is preferably provided over a pressure sensitive layer on one surface of the tape. The tape can be separated longitudinally into two tape strips by the provision of a central longitudinally extending line of perforations.

Abstract: An improved multiconductor ribbon cable the conductors having at least two layers of polytetrafluoroethylene (PTFE) insulation, a porous unsintered inner layer, that is, the one closest to the conductors, and an impermeable sintered outer layer. Webs of impermeable sintered PTFE connect the insulated conductors. The process for manufacturing the cable includes embedding the conductors between inner sheets of expanded unsintered PTFE and outer sheets of extruded unsintered PTFE, then compressing the sheets only in the web region to high density, and sintering the webs plus the outer insulation layer.