Patent Publication Number: US-7223919-B2

Title: Flat flexible cable with integrated stiffener

Description:
TECHNICAL FIELD 
   The present application generally relates generally to flat flexible cable. 
   BACKGROUND 
   Flat flexible cable is commonly used for connecting electrical devices. Flat flexible cable may provide a structure including multiple conductive pathways and may be easily and reversibly bent and twisted in a narrow and crowded space. Various advantages may be provided by flat flexible cable as compared to other cable types. For example, using rectangular conductors as conductive pathways may allow greater amounts of current to be transferred at equal cross-sectional area in comparison with round conductors. This may allow a weight reduction and a reduction in space required for the cable. These advantages have found particular utility in the electronics and automotive industries. The flat configuration of flat flexible cable also allows this type of cable to be mounted behind coverings with limited design depth. Because of these advantages, flexible flat cable is being used to an increasing degree in automobile manufacture as a replacement for cable consisting of round conductors. 
   Flat flexible cable may generally be provided as a laminated structure or an extruded structure. As a laminated structure, flat flexible cable may generally include a plurality of parallel conductors laminated between opposed insulating sheets or strips. Laminated electrical flat conductors may generally be provided as individual conductors in spool form. The individual conductors may be arranged into a conductor set during the process of lamination using slotted guides. The conductor set consists of individual conductive pathways. The individual conductive pathways may be individually insulated from each other, i.e., arranged at a spacing relative to each other and have a rectangular cross section. The tops of the conductive pathways may be electrically insulated, for example by an insulating sheet, which is laminated onto the conductive pathways. Similarly, a bottom insulator may also be laminated onto the bottom of the conductive pathways. The top insulator and bottom insulator may be laminated together in the regions between adjacent conductive pathways and on the edges outside of the conductive pathways. 
   Extruded flat flexible cable may be formed by conductive pathways in an insulating sheath by an extrusion process with an electrically insulating plastic sheath. The plurality of conductors may pass through an extrusion die, such as a wire coating, cross-head extrusion die with the conductors maintained in a desired spaced-apart and parallel arrangement. The resultant flat flexible cable may, therefore, include a plurality of conductive pathways that are electrically isolated, but encased in a unitary sheathing. The shape and properties of the finished extruded flat flexible cable may correspond at least essentially to the shape and properties of a laminated flat flexible cable and the sheathing material. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Features and advantages of the claimed subject matter will be apparent from the following description of embodiments consistent therewith, which description should be considered in conjunction with the accompanying drawings, wherein: 
       FIG. 1  illustrates an embodiment of a flat flexible cable in plan view; 
       FIG. 2  is an end view of the flat flexible cable shown in  FIG. 1 ; 
       FIG. 3  shows the embodiment of the flat flexible cable of  FIG. 1  from a side elevation; 
       FIG. 4  is a side elevation exploded view of the flat flexible cable of  FIG. 1 ; and 
       FIG. 5  illustrates another embodiment of a flat flexible cable in plan view. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , an end portion of an embodiment of a flat flexible cable  10  is shown in plan view. In the illustrated embodiment, the flat flexible cable  10  is shown including a plurality of conductive pathways  12   a–e  that may extend generally parallel to one another. It should be noted that while five conductive pathways  12   a–e  are illustrated, the flat flexible cable  10  may include greater of fewer conductive pathways. The plurality of conductive pathways  12   a–e  may be separated across the width of the flat flexible cable  10  by a plurality of respective insulating partitions  14   b–e . The two outer conductive pathways  12   a  and  12   e  may be insulated on the outside edges thereof by respective insulating partitions  14   a  and  14   f . With additional reference to  FIG. 3 , the flat flexible cable  10  may also include a top insulating layer  16  and a bottom insulating layer  18 , thereby electrically isolating the conductive pathways on the upper and lower surfaces thereof. 
   Consistent with the present disclosure, the plurality of conductive pathways  12   a–e  may each be a flexible conductive foil or wire. The conductive foil or wire may include a metallic material, or a conductive or semi-conductive material, for example a conductive polymer, like polyacetylene, or polymer filled with a conductive filler, such as silver. According to one embodiment, each of the plurality of conductive pathways  12   a–e  may include a copper foil, although, as previously mentioned, other conductive materials may suitable be employed herein. Additionally, while the plurality of conductive pathways  12   a–e  are shown as being generally similarly dimensioned this is not a necessary feature. For example, one or more of the conductive pathways  12   a–e  may have a larger or smaller cross-sectional area to suit specific current capacities, etc. 
   The top and bottom insulating layers  16 ,  18  of the flat flexible cable  10  may be formed from any electrically insulating film, sheet, or coating. According to one embodiment, the top and bottom insulating layers  16 ,  18  may be formed from a polymeric sheet or film. Examples of suitable polymeric films or sheets may include polyester film, for example biaxially oriented polyester film available from E. I. du Pont de Nemours and Company under the name Mylar®, polyamide film, as well as numerous other polymeric film and sheet materials. The top and bottom insulating layers  16 ,  18  may be formed from the same material. Alternatively, the top and bottom insulating layers  16 ,  18  may be formed from different materials. Additionally, the top and bottom insulating layers  16 ,  18  may be provided having the same thickness as one another, but may alternatively be provided having different thicknesses. 
   As most clearly shown in  FIG. 3 , the conductive pathways, generally indicated by  12 , as well as the bottom insulating layer  18 , may extend beyond the top conductive layer  16 , thereby providing an exposed region E of the conductive pathways  12 . The exposed region E may facilitate electrical coupling between the flat flexible cable  10  and a mating connector (not shown) or other device. For example, the flat flexible cable  10  may be electrically coupled with a connector, such as a zero insertion force (ZIF) connector, which may have a plurality of electrical contacts positioned to provide electrical connection with the respective conductive pathways  12   a–e  in the exposed region E of the conductive pathways  12 . Consistent with an embodiment herein, each end of the flat flexible cable  10  may include an exposed region E, allowing each end of the flat flexible cable  10  to be electrically coupled to a connector as generally described above. In an embodiment in which each end of the flat flexible cable  10  is provided with an exposed region E, the exposed regions may be provided on the same side of the flat flexible cable  10 , or may be provided on opposed sides of the flat flexible cable  10 . Alternative arrangements for electrically coupling the flat flexible cable  10  may be utilized herein. According to alternative arrangements, one, or both, ends of the flat flexible cable  10  may be provided without an exposed region E or the conductive pathways  12 . 
   A flat flexible cable  10  consistent with the present disclosure may also include a stiffening element  24 . In the illustrated embodiment the stiffening element  24  is disposed in a stiffened region S, located at an end of the flat flexible cable  10 . The stiffening element  24  may be a member extending across at least a portion of the width of the flat flexible cable  10 . In one embodiment, the stiffening element  24  may extend across the entire width of the flat flexible cable  10 . 
   As best shown in  FIGS. 2 and 3 , the stiffening element  24  may be disposed between an outer insulating layer, such as the bottom insulating layer  18 , and the conductive pathways  12 . Accordingly, as shown in  FIG. 3 , the stiffening member  24  may be integrated into the structure of the flat flexible cable  10 . Integrating the stiffening member  24  into the structure of the flat flexible cable  10  may, to some degree, prevent the stiffening member from becoming inadvertently separated, e.g. peeled, from the remainder of the flat flexible cable  10 . For example, in the illustrated embodiment, the bottom insulating layer  18  may be stepped over the stiffening element  24 , thereby providing a continuous bottom surface to the flexible flat cable  10  and covering the rearward edge of the stiffening element  24 . The incorporated stiffening element  24  and the continuous bottom surface may prevent the stiffening element  24  from inadvertently separating form the flexible flat cable  10 , at least in part, by eliminating the exposure of the free rearward edge of the stiffening element  24  to possible snagging or peeling action. 
   Consistent with the present disclosure, stiffening member  24  may be formed from any suitable material. According to one embodiment, the stiffening member  24  may be formed from a polymeric material. For example, the stiffening member  24  may be formed from the same material as the top and bottom insulating layers  16 ,  18 . Accordingly, the stiffening member  24  may be formed from, for example, a polymeric sheet or film such as polyester, polyamide, etc. It is not necessary, however, for the stiffening member  24  to be formed from the same material as either or both of the insulating layers  16 ,  18 . Furthermore, it is contemplated herein that the stiffening element  24  may be a composite structure including two or more materials. In an embodiment employing a composite stiffening element  24 , the two or more materials may be provided as a mixed structure, a layered structure, etc. 
   According to one embodiment the stiffening element  24  may be provided to increase the flexural modulus of a region S of the flat flexible cable  10 . The length of the region S may be established by the length of the stiffening element, and may depend on the application for the associated cable. Those skilled in the art will recognize that flat flexible cables may be provided in a variety of dimensions. In one embodiment, where the cable has a width of about 1.1875″, the stiffening element may extend completely or partially across the width of the cable and have a length of about 0.1875.″ 
   The increase in the flexural modulus, or stiffness, of the region S of the flat flexible cable  10  may be a function of a number of characteristics. For example, a more rigid stiffening element  24  may impart a greater stiffness or rigidity on the region S of the flat flexible cable  10  including the stiffening element  24 , as compared to a less stiff or rigid stiffening element  24 . The stiffness or rigidity of the stiffening element  24  may be, at least in part, a function of the mechanical properties of the material used to form the stiffening element  24 . The stiffness of the region S of the flat flexible cable  10  including the stiffening element  24  may also be a function of the thickness of the stiffening element  24 . Generally, a thicker cross-section of a given material may be more rigid than a thinner cross section of the same material. Additionally, a thicker stiffening element  24  may increase the moment of inertia of the region of the flat flexible cable  10  including the stiffening element  24 . 
   Consistent with the foregoing, the stiffening element  24  may be used to increase the flexural modulus, or stiffness, of the region S of the flat flexible cable  10  including the stiffening element. According to one embodiment, the stiffening element  24  may be provided at an end of the flat flexible cable  10 , thereby increasing the stiffness of the end of the cable  10 . Increasing the stiffness of an end of the flat flexible cable  10  may be useful for facilitating the insertion of the end of the flat flexible cable  10  into a connector. The increased stiffness of the end of the flat flexible cable  10  may allow the necessary insertion force to be generated at the end of the flat flexible cable  10  being inserted into a connector without the buckling or bending the cable  10 . Stiffening the end of a flat flexible cable  10  may also be useful even when the cable  10  is being used in combination with a connector requiring minimal insertion force, such as a ZIF connector. Increasing the stiffness of the flat flexible cable  10  may increase the ability to orient and/or position the end of the flat flexible cable  10  in a desired manner in order to achieve an electrical connection between a connector and the flat flexible cable  10 . Increasing the stiffness of a region S of the flat flexible cable  10  may be used to provide other advantages as well. While the stiffening element  24  is disposed at an end of the flat flexible cable  10  in the illustrated embodiments, the stiffening member may be disposed at any location along the length of the flat flexible cable  10 . Furthermore, while the stiffening element  24  is oriented generally transverse to the longitudinal axis of the flat flexible cable  10 , the stiffening element  24  may be disposed in other relationships to the longitudinal axis of the flat flexible cable  10 . 
   A stiffening element  24  herein may also, or alternatively, be used to achieve a desired thickness for a region S of a flat flexible cable  10  including the stiffening element  24 . For example, a connector may require a specific thickness of a mating flat flexible cable  10  in order to generate a desired contact force between an electrical contact of a connector and the conductive pathways  12   a–e  of the flat flexible cable  10 . Similarly, a predetermined thickness may be necessary to generate a desired holding force between the flat flexible cable  10  and a retention feature of the connector. To these ends, the stiffening element  24  may be provided to increase the thickness of the region S of the flat flexible cable  10  including the stiffening element  24  to a desired thickness, or range of thicknesses. Additionally, when the stiffening element  24  is to be used, at least in part, to provide a desired thickness to generate a contact or retention pressure with a cooperating element, the stiffening element  24  may be provided from a material that may be at least somewhat compressible. According to one embodiment, a stiffening element  24  may be provided from a material that is resiliently compressible. Consistent with such an embodiment, a contact force between a flat flexible cable  10  and a cooperating element may include a component related to the spring constant of the resiliently compressible stiffening element  24 , as well as the insulating layers  16 ,  18 , etc. of the cable  10 . 
   According to another aspect, shown in  FIG. 5 , the stiffening element  24   b  may be employed to provide strain relief for the flat flexible cable  10   b . For example, the stiffening element  24   b  may provide localized reinforcement of the flat flexible cable  10   b . The flat flexible cable  10   b  may be anchored to a stationary element  34 . A load applied to a portion of the flat flexible cable  10   b  may not be transmitted across the anchored region to a portion of the flat flexible cable  10   b  on the other side of the anchored region. According to one embodiment, the flat flexible cable  10   b  may be anchored by providing a hole  32  defined through the stiffening element  24   b  and mechanically fastening the flat flexible cable  10   b  to the stationary element  34 , for example using a screw  36 , rivet, or similar fastener. The reinforcement provided by the stiffening element  24   b  may resist pull-out under an applied load. Consistent with the embodiment illustrated in  FIG. 5  a portion of the stiffening element  24   b  may extend beyond an edge of the flat flexible cable  10   b . The portion of the stiffening element  24   b  extending beyond the edge of the flat flexible cable  10   b  may be anchored to a stationary structure  34 . Alternatively, the stiffening element of the flat flexible cable may be anchored to a stationary structure by a mechanical fastener, etc., extending through the flat flexible cable and the stiffening element. Consistent with such an embodiment, the stiffening element may, or may not, extend beyond the edge of the flat flexible cable. 
   According to one embodiment, the flat flexible cable  10  may be produced by laminating the top insulating layer  16 , the conductive pathways  12   a–e  and the bottom insulating layer  18  together with the stiffening element  24  laminated at least partially between the bottom insulating layer  18  and the conductive pathways  12   a–e . Lamination may be achieved by providing an adhesive layer  20  between the top insulating layer  16  and the conductive pathways  12   a–e . Similarly, an adhesive layer  22  may be provided between the bottom insulating layer  18  and the conductive pathways  12   a–e . An adhesive layer  26 ,  28  may also be provided on either side of the stiffening element  24 . Consistent with such an embodiment, the insulating partitions  14   a–f  may be formed by adhesive layers  20  and  22  laminated in between the conductive pathways  12   a–e . In the stiffened region S the insulating partitions  14   a–f  may be formed by the adhesive layers  20  and  26 . Similarly, in the stiffened region S the adhesive layer  28  associated with the stiffening element  24  and the adhesive layer  22  may for a layer of adhesive  30  between the lower insulation element  18  and the stiffening element  24 . The adhesive layers  20 ,  22 ,  26 , and  28  may be any suitable adhesive. According to one embodiment, the adhesive layers  20 ,  22 ,  26 , and  28  may be a thermoset adhesive, for example, a polyester adhesive. Various other adhesives, both thermoset and thermoplastic, may suitably be used to produce a flat flexible cable  10  herein. 
   In a related embodiment, the conductive pathways  12   a–e  may be provided on a support member, such a sheet or film of an insulating material. The top insulating layer  16  may be laminated to the conductive pathways  12   a–e  and the support member in the regions between the conductive pathways  12   a–e . Lamination of the top insulating layer  16  to the support member in the regions in between the conductive pathways  12   a–e  may provide the insulating partitions  14   a–f . Similarly, the bottom insulating layer  18  may be laminated to a bottom of the support member. The stiffening element  24  may be laminated between the support member and the bottom insulating layer  18 , thereby integrating the stiffening element  24  into the flat flexible cable  10 . 
   Therefore, consistent with the present disclosure, there is provided a flat flexible cable having an integrated stiffening element. The integrated stiffening element may resist peeling or other removal of the stiffening element from the remainder of the flat flexible cable. In one embodiment, the flat flexible cable may include a laminated structure including conductive pathways disposed between top and bottom insulating layers. The stiffening element may be laminated between the conductive pathways and one of the top and the bottom insulating layers. Suitable adhesives may be employed between the various layers of the laminated structure. According to varying embodiments, the stiffening element of the flat flexible cable may stiffen a region of the cable, provide a desired thickness to region of the cable, facilitate strain relief, etc. 
   The embodiments herein are susceptible to modification and variation without departing from the invention herein. Accordingly, the described embodiments should not be construed as limiting the invention as set forth in the appended claims.