WO1996007185A1

WO1996007185A1 - Fluoro-polymer insulated ribbon cable for insulation displacement connector

Info

Publication number: WO1996007185A1
Application number: PCT/US1995/008403
Authority: WO
Inventors: Wayne Paul Harris; Gary Wayne Paddison; Michael Wayne Bricker
Original assignee: The Whitaker Corporation
Priority date: 1994-09-01
Filing date: 1995-07-05
Publication date: 1996-03-07

Abstract

A ribbon cable for an insulation displacement connector having a plurality of tin plated copper wire conductors enclosed within an insulating material that has a low dielectric constant and a processing temperature above the melt temperature of the tin plated wire conductors.

Description

FLUORO-POLYMER INSULATED RIBBON CABLE FOR INSULATION DISPLACEMENT CONNECTOR

The present invention relates to an improved ribbon cable for an insulation displacement connector ("IDC") . IDC ribbon cables are useful in a variety of applications in which multiple discrete signals are carried on separate wires in a restricted space. IDC ribbon cable is characterized by the presence of ridges on the outer surface of the cable. Generally, IDC ribbon cables include a plurality of wire conductors lying in a common plane and enclosed by an insulating material. The number of wire conductors can vary and can depend on, among other things, the use to which the cable will be put. The wire conductor is typically made of copper or copper alloys that can be unplated or plated with nickel, silver, or tin and can be solid or made from two or more twisted strands. Examples of insulating material are plastic polymers and copolymers such as polyvinyl chloride ("PVC"), cross-linked olefins, fluorinated ethylenepropylene ("FEP"), polytetrafluoroethylene ("PTFE"), polyimide, composites of polyester and PVC, and composites of polyester and polyethylene. The cable may be terminated by a connector. One such connector is an insulation displacement connector ("IDC") which is well known in the art. IDCs require the center of each conductor in the cable to be substantially evenly spaced apart so that each conductor can be easily terminated within a single contact in the connector without touching adjacent conductors. In addition, IDCs typically use a piercing action through the insulation to establish a contact between the connector and the conductor. As a result, IDC ribbon cable is used with IDCs to minimize the amount of insulation through which the connector must pierce to establish contact with the conductor. The ridges in the IDC ribbon cable also aid in aligning the cable and its conductors within the contacts of the connector.

One method of producing ribbon cable is in a lamination process where sheets of insulation film are bonded by rollers under heat and pressure with the conductors placed between the films. In an attempt to obtain substantially evenly spaced conductors across the width of the cable, the rollers often times have grooves machined on their surface and the conductors are guided to the grooved area of the rollers. Nevertheless, it is difficult to produce ribbon cable in this manner where the pitch, i.e., the distance between the center of two adjacent conductors, is small, for example less than 1 millimeter. In addition, since the rollers are heated to accomplish bonding of the films, the insulating material is restricted to lower processing temperature polymers such as PVC₃ or to the use of higher melt temperature plating materials such as nickel or silver. As a result, the lamination process using tin plated conductors for ribbon cable has been limited to the lower processing temperature films such as PVC. The processing temperature refers to that temperature at which the films can be extruded or bonded together by heat.

The high processing temperature required to bond PTFE or FEP films would melt the tin plating in a ribbon cable lamination process; therefore, the use of PTFE or FEP with tin plated conductors in a lamination process has been restricted to flat or block ribbon cable. Another method of producing ribbon cable is by pressure extrusion. In this process, the conductor and films meet and are joined just prior to the exit of the die head. The advantage to this process as compared to the lamination process is that it is easier to provide substantially even pitch across the width of the cable. A particular problem with this process is that the plating of the conductor can melt near the exit of the die due to the high processing temperature required for the polymer and clog the wire guide near the exit of the die. Therefore, the use of this process for tin plated conductors has also been limited to the lower processing temperature films such as PVC.

Because it is desired to provide ribbon cables that have faster signal bussing with less signal degradation as well as other improved thermal, chemical and physical characteristics, insulation using polymers such as FEP and PTFE are desired. Unfortunately, only unplated, nickel and silver plated conductors for IDC ribbon cable have been available to date.

Since tin plated conductors offer advantages, for example cost, as compared to unplated, silver or nickel plated conductors, it is desired to be able to use tin plated conductors in IDC ribbon cable having FEP as the insulating material. The present invention solves present problems by providing an IDC ribbon cable for an insulation displacement connector comprising a plurality of tin plated wire conductors enclosed within an insulating material that has an extrusion processing temperature above the melt temperature of the tin plated wire conductors. The present invention provides an IDC ribbon cable for an insulation displacement connector comprising a plurality of tin plated wire conductors enclosed within an insulating material that has a processing temperature above the melt temperature of the tin plated wire conductors. Preferably, the insulating material has a low dielectric constant and is a fluorinated ethylenepropylene polymer.

In a preferred embodiment, the plurality of wire conductors lie in the same plane and have a pitch, i.e., the distance between the center of adjacent conductors, that is substantially the same along the width of the cable. Each wire conductor can be solid or at least two twisted solid wires.

Figure 1 is a plan view of an IDC ribbon cable according to the present invention with a portion of the insulation stripped away at the end.

Figure 2 is an end view of a portion of an IDC ribbon cable according to the present invention wherein each conductor is a twisted strand.

Figure 3 is an end view of a portion of an IDC ribbon cable according to the present invention wherein each conductor is a solid wire.

Figure 4 is a schematic of the preferred method of manufacturing the IDC ribbon cable of FIG. 1.

Figure 1 shows a ribbon cable 10 for an insulation displacement connector ("IDC") according to the preferred embodiment of the present invention. The IDC ribbon cable has a plurality of tin plated copper wire conductors 12 that are encapsulated within an insulating material 14. The IDC ribbon cable is characterized by a series of ridges or undulations on its top and bottom surfaces defining a crest 16 and a valley 18. As best seen in FIGs. 2 and 3, the wire conductors are preferably aligned in a common plane and the distance between the center of each conductor, defined as the pitch a, is substantially the same across the width of the cable. For example, the pitch can be 1 millimeter, 0.05 millimeter 0.050 inch, or 0.25 inch. Of course, the pitch can be any distance as dictated by, among other things, consumer preferences. The wire conductors can be a strand of at least two twisted solid wires as shown in FIG. 2 or can be a solid wire as shown in FIG. 3.

The insulating material is a polymer that has a processing temperature above the melt temperature of the tin plated wire conductors. The processing temperature refers to that temperature at which the insulating material may be extruded or bonded. The melt temperature refers to that temperature at which the tin begins to soften to obtain amorphous characteristics prior to completely melting. Examples of suitable insulating material are fluoro polymers and copolymers. The fluoro polymers and copolymers may be based on monomers such as tetrafluoroethylene ("TFE"), hexafluoropropylene ("HFP"), monochlorotrifluoroethylene ("CTFE"), as well as others which are known to those skilled in the art. The fluoro polymers and copolymers useful in the present invention may include PTFE, structural derivatives of PTFE containing perfluoroalkoxy ("PFA") side groups, FEP, copolymers of TFE with ethylene ("ETFE"), homopolymers of vinylidene fluoride and copolymers with HFP, and others which will be apparent to those skilled in the art.

Preferably, the insulating material has a low dielectric constant. More preferably, the insulating material is a fluorinated ethylenepropylene polymer. Polymers with similar properties will occur to those skilled in the art.

Figure 4 is a schematic of an apparatus used to manufacture the IDC ribbon cable of the present invention. Preferably, the apparatus is oriented so that the extrusion, bonding, cutting, and take-up processes are conducted horizontally. It will be apparent to one skilled in the art that the apparatus may be designed so that the processes are conducted vertically or some are conducted vertically while others are conducted horizontally. In the preferred process, the insulating material is extruded through slit die heads 30 as two thin films, in a horizontal manner, and directed to a pair of vertically oriented rollers 32a and 32b that join the films with the wire conductors 12 to produce the ribbon cable 10. The slit die heads may be a single unit or may be separate, as shown in FIG. 4, with one head located vertically above the other. In addition, the extruder upstream of the die heads may be a single unit or a separate unit for each die head.

Preferably, the die heads are moveable so that the distance from the die head to the entrance to the rollers may be adjusted for suitable processing conditions. By providing moveable die heads, the temperature of the extrudate prior to entering the rollers may be controlled. For example, when the die heads are placed a distance from the entrance of the rollers, the extrudate may be cooled by ambient air or other means prior to entering the rollers. Such cooling is especially desirable when extruding a polymer such as FEP so that when the tin plated copper conductors are joined with the polymer films, they do not reach their melt temperature. If, however, the extrudate is a polymer such as PVC, such cooling generally is not necessary due to the lower processing temperature. As a result, the die heads can be located closer to the entrance of the rollers. The rollers may also be cooled by any well known means and may also include grooves for further locating the wires laterally.

The wire conductors 12 are guided to the rollers 32 by a wire guide 34 that includes a plurality of apertures, each of which receives a single conductor. In this manner, the pitch of the wire conductors is substantially the same across the width of the cable. Preferably, the guide is moveable toward and away from the rollers. While the ribbon cable is intended to be terminated by an IDC it may also be stripped for soldering as is known in the art. For example, a portion of the cable may be connected to an IDC while another portion may be stripped and soldered to another connector or the like. Of course it should be understood that a wide range of changes and modifications can be made to the embodiments described above. It is therefore intended that the foregoing description illustrates rather than limits this invention, and that it is the following claims, including all equivalents, which define this invention.

Claims

CLAIMS ;

1. A ribbon cable for an insulation displacement connector comprising a plurality of tin plated copper wire conductors enclosed within an insulating material that has a processing temperature above the melt temperature of the tin plated wire conductors.

2. The ribbon cable of claim 1 wherein the insulating material is a polymer having a low dielectric constant.

3. The ribbon cable of claim 1 wherein the insulating material is a fluoro polymer.

4. The ribbon cable of claim 1 wherein the insulating material is a fluorinated ethylenepropylene polymer.

5. The ribbon cable of claim 1 wherein the plurality of wire conductors lie in the same plane.

6. The ribbon cable of claim 1 wherein each wire conductor is a solid wire.

7. The ribbon cable of claim 1 wherein each wire conductor comprises at least two twisted solid wires.

8. The ribbon cable of claim 1 wherein the pitch of the wire conductors is substantially uniform across the width of the cable.

9. The ribbon cable of claim 8 wherein the pitch is 1 millimeter.

10. The ribbon cable of claim 8 wherein the pitch is 0.5 millimeter.

11. The ribbon cable of claim 8 wherein the pitch is 0.050 inches.

12. The ribbon cable of claim 8 wherein the pitch is 0.025 inches.