Patent Publication Number: US-2007095555-A1

Title: Cable assembly and method of preparing cable assembly

Description:
This application claims priority under 35 USC 119 from U.S. Provisional application Ser. No. 60/731,607, filed Oct. 28, 2005, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Technical Field of the Invention  
      This invention is in the field of cable assemblies for use in high-speed electronic devices such as computers, and in methods of fabricating such devices.  
      2. Description of the Related Art  
      The high-speed computer industry makes use of coaxial cables for the transmission of high-frequency signals. When many cables are required, it is advantageous to handle multiples of the cables simultaneously. To this end, manufacturers have prepared a product with cables bonded side by side to form a ribbon of coaxial cables. This ribbon cable configuration allows for simultaneously handling as many cables as are bonded together. Termination of the cables can be done in a step-and-repeat planar fashion. However, equipment for simultaneously stripping the ends of ribbons of coaxial cables is unavailable, although equipment for stripping one or both ends of a single cable is readily available. This lack of a convenient way of stripping ends of ribbons of coaxial cable makes use of such ribbon cables problematic.  
      In addition, some kinds of coaxial cables, such as cables with braided shields or cables having served shields, utilize a multiplicity of fine wires for their shielding. Such shields lack mechanical unity, and are thus not suitable for welding to cable terminations.  
      From the foregoing it will be appreciated that improved methods are desirable with regard to high-speed cables and method of making assemblies of such cables.  
     SUMMARY OF THE INVENTION  
      According to another aspect of the invention, a method of making a cable assembly includes placing coaxial cables between a pair of solder-coated conductive material ribbons, and heating the cables and/or ribbons to solder together the coaxial cables and the ribbons.  
      According to still another aspect of the invention, a cable assembly includes plural coaxial cables, each including conductive shielding consisting of many fine wires. The conductive shielding of the cables are secured to a conductive material ribbon or strip.  
      According to a further aspect of the invention, a cable assembly includes plural cables having ends placed in half-cylindrical portions of a conductive material ribbon or strip. The cable ends are soldered or otherwise secured to the conductive material strips.  
      According to a still further aspect of the invention, a cable assembly includes: a plurality of coaxial cables, each including a signal conductor circumferentially surrounded by a conductive shield; and a pair of ribbons of conductive material attached to the shields of coaxial cables.  
      According to another aspect of the invention, a method of forming a cable assembly, the method includes: stripping portions of a plurality of coaxial cables, to thereby expose conductive shielding of the cables, wherein for each of the cables the exposed conductive shielding surrounds a signal conductor of the cable; placing the exposed conductive shielding of the cables between a pair of conductive ribbons; and attaching the exposed conductive shielding to the conductive ribbons, thereby forming the cable assembly.  
      To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the annexed drawings, which are not necessarily to scale:  
       FIG. 1  shows an oblique view of a cable assembly in accordance with the present invention;  
       FIG. 2  shows an exploded view of the cable assembly of  FIG. 1 ;  
       FIG. 3  shows an oblique view of a conductive ribbon used in the cable assembly of  FIG. 1 ;  
       FIG. 4  is a high-level flowchart showing steps in the manufacture of the cable assembly of  FIG. 1 ;  
       FIGS. 5 and 6  are oblique views illustrating operations in the method of  FIG. 4 ;  
       FIG. 7  is an oblique view illustrating connection of the cable assembly of  FIG. 1  to an electrical connector; and  
       FIG. 8  is an oblique view of an alternate embodiment of the cable assembly in accordance with the present invention, with a plurality of cables linked by conductive ribbons at both ends of the cables. 
    
    
     DETAILED DESCRIPTION  
      A cable assembly includes a plurality of coaxial cables and a pair of conductive material ribbons or strips that are placed on opposite sides of the cables, and that are soldered to conductive shields of the cables. The ends of the cables are stripped in order to expose portions of a central signal conductor and a conductive shield that circumferentially surrounds the central signal conductor. The stripped portions are placed between the conductive material ribbons, with the shield portions of the stripped ends in contact with the conductive ribbons. The conductive ribbons may have suitable depressions or indentations, such as substantially half-cylindrical shaped indentations, to better secure the stripped ends of the cables, and to maintain the cables in a predetermined spaced configuration. For instance, the cables may be substantially parallel to one another, and may be evenly spaced from one another. The conductive ribbons may be substantially identical to one another, and may form a series of holes or pockets in which individual of the cables are substantially surrounded. One side of each of the conductive ribbons, the side in contact with the shield material of the cables, may be coated with solder. After the cables have been placed between the conductive material ribbons, the conductive ribbons and/or the cable ends may be heated to melt and reflow the solder, thereby soldering the conductive ribbons to the shields of the coaxial cables. The ribbons may thus mechanically couple a plurality of cables together in a desired configuration, for example with all the cables being substantially evenly spatially separated from one another. In addition, the conductive ribbon electrically links the shields of all the cables together. The conductive ribbons may be coupled to other contacts or shield plates, such as by a welded connection with the conductive ribbon. Thus the use of the conductive ribbons facilitates making electrical connection to the braided or served shields of the cables. The conductive ribbons may be made of a suitable electrically conductive material, such as copper. The conductive ribbons may have suitable cable-receiving portions, for example, substantially half-cylindrical portions, between flat portions that are used to separate adjacent of the cables. Both of the conductive ribbons may be substantially identical, and both may be coated on one side with a coating of solder.  
       FIGS. 1 and 2  show a cable assembly  10  that includes a plurality of cables  12  joined together by conductive ribbons  14  and  16 . The cables  12  are coaxial cables, each including a signal wire  22  and conductive shielding  24  circumferentially surrounding the signal wire  22 . An inner insulation layer  26  separates the signal wire  22  from the conductive shield  24 . Outer insulation  28  surrounds the conductive shielding  24  and makes an outer casing for the cable  12 . The conductive shielding  24  may consist of a multitude of fine wires twisted or braided together. Thus, the cables  12  may be cables with braided shields or served shields. Any of a variety of sizes of cables may be used.  
      The conductive ribbons  14  and  16  mechanically and electrically couple together stripped ends  29  of the cables  12 . The ribbons  14  and  16  mechanically couple the cables together in a desired spacing relative to one another. The ribbons  14  and  16  also electrically couple together portions of the shields  24  of the cables  12 .  
       FIG. 3  shows a more detailed view of the configuration of one of the ribbons, the lower ribbon  16 . The upper ribbon  14  may be substantially identical to the lower ribbon  16 . The ribbon  16  may be formed from a rectangular sheet of a conductive material, for example, from suitable sheet copper having a thickness of from 0.005 to 0.015 inches (0.13 to 0.38 mm). The ribbon  16  has a plurality of flat portions  30  interspersed between a plurality of depressions or indentations  32 . The depressions  32  may be substantially half-cylindrical, cable-receiving portions  34 , defining axes  36 . The axes  36  of adjacent of the depressions  32  may be spaced apart with spacing  40 . The ribbons  14  and  16  may line up with their respective flat portions  30  in contact with one another. The substantially half-cylindrical portion  34  of the ribbons  14  and  16  may thereby define a plurality of cable-receiving cylindrical openings  42  ( FIG. 1 ). The half-cylindrical portions  34  of the ribbons  14  and  16  may substantially surround the inserted portions (stripped ends) of the cable  12 . The cable-receiving portions  34  may substantially surround the stripped ends of each of the cables  12 .  
      Each of the ribbons  14  and  16  may have a solder layer  44  on one side thereof, the concave side of the half-cylindrical, cable-receiving portions  34 . Once the stripped ends  29  of the cables  12  are placed between the ribbons  14  and  16 , the ribbons  14  and  16  and/or the stripped ends  29  are heated to cause the solder layer  44  to melt and reflow partially into the conductive shield material  24  of the cables  12 . After subsequent cooling, the solder solidifies again, making a mechanical and electrical bond between the conductive ribbons  14  and  16  and the conductive shield material  24  of the cables  12 . In addition, the soldering may mechanically couple together the conductive ribbons  14  and  16 , for example, by soldered connections made between the flat portion  30  of one of the conductive ribbons, and the flat portion  30  of the other of the conductive ribbons.  
      The solder layer  44  on the conductive ribbons  14  and  16  may have any of a wide variety of suitable solder materials, using any of a variety of suitable commercially-available solder alloys. The conductive ribbons  14  and  16  may be made by stamping or by other suitable processes.  
      The conductive ribbons  14  and  16  allow for secure evenly-spaced placement of the ends  29  of the cables  12 , substantially parallel to one another. The conductive ribbons  14  and  16  also provide a way to electrically link together the shields  24  of the various cables  12 , and provide as well a way of making electrical connection, such as a welded electrical connection, to the shields  24 .  
      It will be appreciated that the illustrated embodiment of the cable assembly  10 , with the cables  12  substantially evenly spaced from one another, is but one possible configuration for the cable assembly  10 . It will be appreciated that many other spacings of the cables  12  may be obtained by suitably shaped conductive ribbons. The broad concept of securing coaxial cables between a pair of conductive elements made by applied in any of a wide variety of other suitable configurations.  
       FIG. 4  shows a flowchart of a method  100  for assembling the cable assembly  10  ( FIG. 1 ). First, in step  102 , the ends  29  of a plurality of coaxial cables  12  are stripped.  FIG. 5  shows a single cable  12  with an end  29  stripped to expose portions of the conductive shield  24 , and the signal wire  22 . It will be appreciated that suitable machines for stripping ends of coaxial cables are well known.  
      Thereafter, in step  104  a plurality of the stripped cables  12  are placed on a lower conductive ribbon  16 , as illustrated in  FIG. 6 . The stripped ends  29  of the cable  12  are placed in the cable-receiving portions  34  of the lower conductive ribbon  16  such that the conductive shielding  24  of the cables  12  is in contact with the solder layer  44  of the lower conductive ribbon  16 . Then the top conductive ribbon  14  is placed on the stripped ends  29  in step  106 , and the conductive ribbons  14  and  16  are clamped or otherwise fixtured together. Then, in step  108 , heating is applied to melt and reflow the solder from the solder layers  44  of the conductive ribbons  14  and  16 . The soldering may be by any suitable soldering method, such as conformal hot bar soldering.  
      Referring now to  FIG. 7 , the cable assembly  10  is shown being coupled to a connector  120  by a step-and-repeat automatic welding process. The signal wires  22  of the individual cables  12  of the cable assembly  10  are evenly spaced, and can be terminated by welding to evenly-spaced signal conductors  122  of the connector  120 . Shield contacts  124  of a conductive shield  130  of the connector  120  can be welded to the flat portions  30  of one of the conductive ribbons  14  and  16 . The uniform spacing of the signal wires  22  and the flat portions  30  facilitates use of step-and-repeat automatic welding.  
       FIG. 8  shows a variation of the cable assembly  10  in which both ends  140  and  150  of the cable assembly  10  are joined together with respective pairs of conductive ribbons  14 ,  16  and  14 ′,  16 ′. It will be appreciated that the same steps described above for stripping the ends  29  and  29 ′ of the cables  12 , and for applying the conductive ribbons  14  and  16  to the ends  29  and  29 ′ of the cables  12 , may also be employed to apply the conductive ribbons  14 ′ and  16 ′ to opposite ends  29  and  29 ′ of the cables  12 .  
      The cable assembly  10  and the method  100  provide an effective way to utilize existing machinery for stripping single coaxial cables, to produce cable assemblies that can be reliably secured to electrical connectors using automatic step-and-repeat weld processes. The use of the conductive ribbons  14  and  16  provides both a reliable way of mechanically securing the stripped ends  29  of the cables together, but also provides a way of easily making electrical connections to the fine-wire conductive shields  24  of the cables  12 .  
      Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.