WO1998002890A1

WO1998002890A1 - Method of manufacturing ribbon cable having an internal drain conductor

Info

Publication number: WO1998002890A1
Application number: PCT/US1997/012146
Authority: WO
Inventors: Robert Gordon Truxes
Original assignee: W.L. Gore & Associates, Inc.
Priority date: 1996-07-15
Filing date: 1997-07-14
Publication date: 1998-01-22
Also published as: AU3600597A

Abstract

A method for manufacturing ribbon cable includes disposing a plurality of conductors within a layer of insulating material. The conductors are in aligned parallel relation with one another in a direction along the length of the cable. At least one of the conductors has a strand of material located adjacent thereto in such a manner that the conductor and strand are in stacked relation. The layer of insulating material is notched adjacent the stacked conductor and strand at an end of the layer. The strand of material beginning at the notches formed in the insulating layer is peeled back for removing a strip of insulating material above the strand and exposing the other conductor. The exposed conductor serves as the drain conductor for the ribbon cable upon laminating a shield on the insulating layer in a position in which the shield engages the exposed conductor.

Description

TITLE OF THE INVENTION

METHOD OF MANUFACTURING RIBBON CABLE HAVING AN INTERNAL DRAIN CONDUCTOR

FIELD OF THE INVENTION

This invention generally relates to ribbon cable and methods for manufacturing the same More particularly, the present invention relates to a novel method of manufacturing ribbon cable having at least one internal drain conductor for grounding the ribbon cable

BACKGROUND OF THE INVENTION

In the past, flat or ribbon cable has been manufactured by laminating copper conductors between layers of insulating tape (polyester or other polymer materials) To alter electrical performance of the ribbon cable, it is well-known to add or laminate a thin layer of conducting material to one or both sides of the cable This thin layer is commonly known as a shield, and is usually designed with a "drain" wire which is in contact with the shield The drain wire allows easy grounding of the shield to circuitry Due to the limitations in the laminating technique, the placement of these "drain conductors" is usually limited to the outside edge margins of the cable Figure 1 illustrates a well-known, commercially available ribbon cable, generally indicated at 10 As shown, the cable 10 comprises a plurality of conductors, each indicated at 12, which are in parallel relation with one another, and a layer of insulating matenal 14 in which the conductors are embedded Another layer of insulating material 16 is laminated on layer 14 A thin metallic layer or shield 18 is laminated on layer 16, the shield engaging a dram wire 20 positioned adjacent the lateral edge margin of the cable 10 Due to manufacturing constraints of the presently known methods for manufacturing ribbon cable, the drain wire 20 must be positioned adjacent one of the lateral edge margins of the ribbon cable It is the desire of cable manufactures to locate the drain conductors

"internally" with respect to the lateral edges of the cable to obtain electrical isolation between individual or groups of conductors By providing such internal drain conductors, the overall electrical characteristics of the cable can be modified, and signal interference between one group of conductors to the adjacent conductors can be minimized Many solutions to this problem have been tried with various degrees of success Most of these approaches have focused on individually applying a shield to each conductor prior to the making of the cable, or the mechanical connection of the shield and the drain wire after the cable has been completed Each of the options currently available is an expensive alternative to the continuous and automated manufacture of cable with a drain wire in contact with the shield

The most common technique for modifying the electrical properties of the material is to make cables from individual "primaries" consisting of insulated conductors with a shield wrapped around the core construction These individual "primaries" are then combined to form cables by laminating the primaries within an outer insulation This process is undesirable for several reasons, including the time involved in the manufacture of the individual primaries, and the labor intensive termination steps involved in the individual termination of each conductor and the corresponding shield Certain of these limitations have been addressed by specialized constructions, such as the ribbon cable disclosed in U S Patent No 4,972,041 to Crawley et al While this patent discloses a cable with an improved electrical performance, and a significantly reduced termination cost (mass termination is possible), material and processing costs are significant Other mechanical means of connecting the shield to drain conductors include the use of pins, staples, or rivets that are applied after the manufacture of the cable by piercing the insulation to connect the shield to the drain conductors Such mechanical fasteners create faults in the insulation that are subject to tearing or physical damage, especially in applications where the cable is undergoing cyclic flexure over thousands of cycles The repeated stress on the point where the insulation has been penetrated rapidly results in insulation failure

Other possibilities are envisioned which would depend upon the placement of "strips" of insulation over the conductors which are to be isolated, leaving the conductors that are to be in contact with the shield exposed Such a method would result in a process similar to the method of the present invention, but the method would require exact alignment of conductors and several strips of insulation which would be difficult to manage in a large volume manufacturing environment Further, the removal of insulation over the selected conductors by abrasive or laser stripping would again be an expensive option that would result in a prohibitive cost for all except in the most critical application The need exists for a reliable, low cost, continuous process to manufacture a shielded cable where the drain wires are not located at the lateral edge margins of the cable

The foregoing illustrates limitations known to exist in present methods of manufacturing πbbon cable Thus, it is apparent that it would be advantageous to provide an improved method directed to overcoming one or more of the limitations set forth above Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter SUMMARY OF THE INVENTION

The present invention advances the art of ribbon cables, and the methods of manufacturing ribbon cable having internally located drains, beyond which is known to date In one aspect of the present invention, a method for manufacturing ribbon cable comprises the steps of

(a) disposing a plurality of conductors within a layer of insulating material, the conductors being in aligned parallel relation with one another in a direction along the length of the cable, at least one of the conductors having a strand of material located adjacent thereto in such a manner that the conductor and strand are in stacked relation,

(b) notching the layer of insulating material adjacent the stacked conductor and strand at an end of the layer, and

(c) peeling back the strand of material beginning at the notches formed in the layer of insulating material for removing a strip of insulating material above the strand and exposing the conductor, the exposed conductor serving as the dram conductor for the ribbon cable

It is, therefore, a purpose of the present invention to provide a method for manufacturing ribbon cable having at least one drain conductor internally with respect to the lateral edges of the ribbon cable Another purpose of the present invention is to provide a method for manufacturing ribbon cable having internal drain conductors which is less expensive than the other prior art methods discussed above

A further purpose of the present invention is to provide a method for manufacturing ribbon cable, having internal drain conductors, which positions the conductors and drain conductors precisely within the cable

Another purpose of the present invention is to provide a method for manufacturing πbbon cable, having internal dram conductors, which is less time consuming than the other prior art methods BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of a preferred embodiment of the invention, will be better understood when read in conjunction with the appended drawings For purposes of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred It should be understood, however, that the invention is not limited to the precise arrangement and instrumentality shown In the drawings

Figure 1 is a perspective view of a prior art ribbon cable having a drain wire located adjacent a lateral edge margin of the cable,

Figure 2 is a perspective view of a ribbon cable manufactured in accordance with the method of the present invention, the ribbon cable having internally located drain wires,

Figure 3 is a front elevational view of the ribbon cable in a stage of its manufacturing process after laminating a pair of polymeric sheets to one another with a plurality of conductors disposed therebetween, and

Figure 4 is a perspective view of the ribbon cable after notching one of the polymeric sheets adjacent a stacked conductor and strand of material at an end of the sheet and peeling back the strand for removing a strip of insulating material above the strand thereby exposing the conductor the exposed conductor serving as the drain conductor for the ribbon cable

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein similar reference characters designate corresponding parts throughout the several views, the ribbon cable manufactured pursuant to the method of the present invention is generally illustrated at 30 in Figure 2 As shown, the ribbon cable 30 includes a plurality of conductors, each indicated at 32, which are disposed within a layer of insulating material, generally indicated at 34 Insulating material 34 is generally comprised of two polymeric sheets (not shown) laminated to one another with the conductors 32 disposed therebetween

At least one layer of shielding material 40, referred to as a "shield", which is fabricated from metallic material, is bonded to an upper surface of the layer of insulating material 34 As shown in Figure 2, there are two shields 40 laminated to the insulation layer 34 The shields 40 are preferably applied on the insulating layer 34 during a separate manufacturing step which will be described in greater detail hereinafter As shown in Figure 2, the top shield 40 engages several conductors wherein these conductors constitute drain conductors, which, as described above, allow easy grounding of the shield to intended circuitry. The drain conductors are designated by reference numerals 42 and 44 in Figure 2. It should be noted that the drain conductors 42 located adjacent the lateral edge margins of the ribbon cable 30 may be manufactured in the well-known manner described above. The internally located drain conductors 44 are manufactured pursuant to the novel method of the present invention.

The manufacturing method described herein makes it possible to produce ribbon cable 30 with drain conductors 44 located internally with respect to opposing lateral edge margins of the ribbon cable in a continuous and cost- effective fashion. Usually the lamination of the cables, together with any shield, is done in a single pass. For an unshielded cable, the polymeric sheets comprising the insulation material 34, which have been coated on one side with a pressure or heat activated adhesive, are laminated together under pressure and heat with the metallic conductors 32 (and the drain conductors 42, 44) sandwiched between the sheets. The exact placement of the conductors 32 (and the drain conductors 42, 44) with respect to the lateral edge margins of the ribbon cable 30 and to each other is obtained by the use of grooved guide rollers (not shown). The rollers are precisely machined such that the conductors, when laid in the groves of the rollers, are on the exact centeriine spacing required for the cable construction. The result is a laminated cable with precisely spaced metallic conductors. Such rollers are disclosed in U.S. Patent No. 3,833,755 to Soelberg, and are well-known in the art of ribbon manufacturing.

The typical construction of shielded cables is similar, except one or more of the polymeric sheets is coated on both sides with the adhesive. The polymeric sheets then become the "inner" layer of insulating material as an additional layer of metallized film is laminated to the outside. This metallized layer becomes the shield.

The conductors 32, 42 and 44 and the insulation layer 34 are laminated together in one or two passes. The polymeric sheets comprising the insulation layer 34 are coated with adhesive on both sides and are passed over heated drums (not shown) that activate the adhesive. The conductors 32, 42 and 44 are introduced between the polymeric sheets by the use of the guide rollers which provide the exact placement of the conductors relative to each other. If the shield 40 (or shields) is placed onto the insulating layer 34 in a single pass, metallized film (without adhesive) constituting the shield is also fed into the machine so that the metallized side is in contact with the adhesive layer The layer of insulation material and 34 conductors 32, 42 and 44 are then compressed providing intimate contact, and fusing the sheets constituting the layer into a cable

If the ribbon cable 30 is being prepared in a two step process, the outer metallized shield 40 is placed on the cable after the insulating layer by re-heating cable after the first pass in a similar fashion The two step process is most often used when a special step must be taken before the shield is laminated to the cable The method of the present invention provides for the selective removal of a portion of the insulation material 34 from discrete conductors in a step intermediate between the two lamination passes, the removal step constituting the advancement of the present invention over the prior art methods Certain insulation materials, such as polyester for example, possess properties whereby a defect, tear, or notch, once started, will propagate linearly under certain conditions along the length of the material resulting in a clean edge The method of the present invention takes advantage of this property of the material comprising the insulating layer 34 More specifically, the polymeric material used for the sheets which comprise insulating material 34, when notched or torn at an end in a longitudinal direction along the length of the tape, is capable of tearing or being peeled along a straight line along the length of the tape

Referring now to Figure 3, to manufacture the ribbon cable 30 with at least one inwardly located drain conductor 44 in contact with the shield 40

(Figure 2), an additional strand of material 46 is placed above or on top of the conductor 44 which has been designated as an internally located drain Preferably, the strand 46 is fabricated from metallic wire, or another similar material with sufficient tensile strength to withstand the forces applied The location of the strand 46 is provided during the passing of the conductors 32,

42 and 44 through the guide grooves formed on the rollers It is important to note that the shield 40 has not yet been applied

As seen in Figure 4, notches or tears 48 are formed in the top sheet of polymeπc material which engages the strand 46 As shown in Figure 4, the notches 48 are formed in the top polymeric sheet at the end of the sheet in a direction parallel to the direction of the conductors 32, 42 and 44 The notches 48 are located in the polymeric sheet adjacent and above the lateral edges of the strand 46 Suitable means is provided for automating this notching step It should be noted that the orientation of the strand 46 being placed above conductor 44 as shown in Figure 3 could be reversed (i e , located below the conductor), or that other strands could be provided above any of the other conductors 32, and still fall within the scope of the present invention

A strip of material 50 from the polymeric sheet is removed from the sheet by peeling back the strand 46 and the strip in the manner illustrated in Figure 4 The strand of material 46 produces stress on the polymeric sheet laminated to the strand, resulting in the propagation of the tear and the subsequent removal of the strip 50 The notches 48 formed in the polymeric sheet enable the initiation of the peeling step of the method Once the strip 50 is peeled back, the strip and strand 46 are removed and discarded This action results in the exposure of the conductor 44 initially positioned below the strand 46 Suitable means are provided for automating the peeling step of the method In a preferred embodiment of the present invention, the polymeric sheets, defining the insulating material 34, are comprised of polyester

Once the insulating material is removed, the metallized shield 40 is then applied in a manner as described above As the strip 50 of the insulation layer 34 has been removed over the dram conductor 44, the conductor will come into intimate and engaging contact with the shield 40, creating the ribbon cable 30 depicted in Figure 2

It should be observed that any number of drain conductors 44 can be provided on the ribbon cable 30 For example, in the cable illustrated in Figure 2, there are two internally located dram conductors 44, whereas in Figures 3 and 4, one drain conductor 44 is formed

Although a few exemplary embodiments of the present invention have been described in detail above, those skilled in the art readily appreciate that many modifications are possible without materially departing from the novel teachings and advantages which are described herein Accordingly, all such modifications are intended to be included within the scope of the present invention, as defined by the following claims

Claims

CLAIMS:

Having described the invention, what is claimed is

1 A method of manufacturing a ribbon cable having a plurality of conductors disposed within a layer of insulating material, and a layer of shielding material applied to a surface of the layer of insulating material, one of said conductors defining an internal drain conductor in engagement with said layer of shielding material, said method comprising the steps of (a) disposing a plurality of conductors within a layer of insulating material, said conductors being in aligned parallel relation with one another in a direction along the length of the cable, at least one of said conductors having a strand of material located adjacent thereto in such a manner that the conductor and strand are in stacked relation, (b) notching the layer of insulating material adjacent the stacked conductor and strand at an end of the layer, and

(c) peeling back the strand of material for removing a strip of insulating material above said strand and exposing the other conductor, said exposed conductor serving as the dram conductor for the ribbon cable

2 A method as set forth in claim 1 further comprising the step of applying a layer of shielding material over a side of the ribbon cable having the exposed conductor in a position in which the layer of shielding material engages the exposed conductor

3 A method as set forth in claim 1 , said step of disposing a plurality of conductors within a layer of insulating material comprising the step of laminating a pair of polymeric sheets to one another with said plurality of conductors being disposed therebetween

4 A method as set forth in claim 3, said step of disposing a plurality of conductors with a layer of insulating material further comprising the step of applying pressure on the polymeric sheets for bonding the sheets to one another thereby creating said layer of insulating material

5 A method as set forth in claim 3, said step of disposing a plurality of conductors with a layer of insulating material further comprising the step of applying heat to the polymeric sheets for bonding the sheets to one another thereby creating said layer of insulating material 6 A method as set forth in claim 4, said step of applying pressure including the step of passing the polymeric sheets through a pair of rollers

7 A method as set forth in claim 3, said step of notching the layer of insulating material at one end thereof including the step of notching one of said polymeric sheets in a direction parallel to the lateral edges of said stacked conductor and strand

8 A method as set forth in claim 7, said step of peeling back said strand of material further comprising the step of peeling back said one polymeric sheet along the lateral edges of the strand