Abstract:
A method of applying a premold to a cable. The cable may have a plurality of shielded pairs, where the shielded pairs have conductors. A premold is applied to the cable, where the shielded pairs are aligned within the premold. A deformable material is wrapped over the premold. A shell is applied over the deformable material. The premold is sufficiently hard so as to protect the conductors from deformation when applying the shell. A portion of the conductors may be deformed before being welded.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The inventions relate to a cable assembly. 
     2. Description of Related Art 
     One concern in data communications is signal integrity. Factors that affect signal integrity include cable design and the process that is used to terminate or attach a cable. Cables are typically made of a plated center conductor covered by a dielectric and a braid or foil shield protector with an overall non-conductive jacket. The termination of the braid onto a device, such as a printed circuit board (PCB) or a connector, can significantly affect cable performance. 
     One way to terminate a braid is to strip the end of the braid and solder the end of the wire onto a PCB/connector termination. One popular method of soldering a wire onto a solder pad is hot bar soldering. One problem with this method in that a large amount of heat must be introduced during the solder. The heat causes the dielectric to melt and subsequently shrink. In addition, a significant amount of time is often consumed by this method. Finally, the solder pad, PCB, or connection material may burn when using hot bar soldering. 
     Laser terminating is another method of terminating a wire onto a PCB/connector, but it also has problems such as a tendency to burn and variable power. Also, the timing of the laser pulse needs to be within very tight tolerances. 
     Parallel gap resistance welding is another method of terminating a wire onto a PCB/connector. One problem with resistance welding is that it is very difficult, and sometimes impossible, to resistance weld a wire of 28 AWG or higher gage size. This is because a large amount of heat is necessary to weld a wire of that thickness, and the heat has a tendency to burn the solder pad on the PCB or the connection material. 
     However, parallel gap resistance welding has advantages over hot bar welding. There is no shrinking of the cable dielectric with parallel gap resistance welding, and the time needed to make the weld is significantly shorter than the time to solder. 
     A common way to terminate a braid is to use a ferrule. One significant problem with a ferrule is that crimping the wire to apply the ferrule tends to crush the cable dielectric. Another problem with existing methods of terminating a braid is that they can tend to rearrange the placement of the differential pair within the cable jacket. Both problems can affect impedance and other electrical parameters, which affect signal integrity. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides methods and systems for improving data transfers within cable assemblies. 
     One embodiment of the invention includes a method of applying a strain relief premold, also called a mold, to a cable, where the premold is sufficiently hard so as to protect the conductors within the shielded pairs within the cable from being crushed. 
     Another embodiment of the invention includes a cable comprising a plurality of shielded pairs, with a mold fastened around the cable, and a clamshell applied over the mold, where the mold protects the cable from being crushed when the clamshell is applied. In some embodiments, the cable comprises a single conductor. 
     In another embodiment, the invention includes a method of attaching a cable to a printed circuit board, where a portion of a 24 AWG or larger size conductor of a wire or cable is deformed and after deforming the thickness of the conductor is substantially the same as the diameter of smaller size cable, and resistance welding the deformed conductor. By way of nonlimiting example, a 24 AWG conductor may be deformed according to the methods provided herein such that the thickness of the resulting deformed portion of the cable is substantially the same as the diameter of a non-deformed 30 AWG cable. 
     These and other features and advantages will become apparent from the drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  illustrates an example of a single wire associated with embodiments of the present invention. 
         FIG. 2  illustrates an example of a cross-sectional view of a single wire of embodiments of the present invention. 
         FIGS. 3 and 3A  illustrate a single shielded pair as may be used with embodiments of the present invention. 
         FIG. 4  illustrates an example of a weld between a single shielded pair and a printed circuit board according to some aspects of the present invention. 
         FIG. 5  illustrates an example of two cables before premolds of embodiments of the present invention are applied. 
         FIG. 6  illustrates an example of a strain relief premold of embodiments of the present invention. 
         FIG. 6A  illustrates a portion of a cable jacket wrapped around a portion of a premold according to embodiments of the present invention. 
         FIG. 6B  illustrates copper tape wrapped over a portion of a premold according to embodiments of the present invention. 
         FIG. 7  illustrates a method of applying a premold to a cable. 
     
    
    
     DETAILED DESCRIPTION 
     A cable  100  is illustrated in  FIG. 1 . Cable  100  has a cable jacket  110 , dielectric  122 , and center conductor  120 . Cable jacket  110  may, for example, be made up of a single braid of material, or may contain both an outer braid and an inner braid. Cable  100  includes a proximal portion  125  and a distal portion  130 . Cable  100  can transfer data between and among storage devices, switches, routers, printed circuit boards (PCBs), analog to digital converters, connectors, and other devices. In various embodiments, cable  100  can support data transfer rates of 100 Mbps and higher. In some embodiments, cable  100  can support data transfer rates of approximately 4.25 Gbps to approximately 25 Gbps, including by way of non-limiting examples, approximately 4.25 Gbps, approximately 10 Gbps, and approximately 25 Gbps. Cable  100  also can be used with data transfer rates above or below these exemplary rates. 
       FIG. 2  illustrates a cross-sectional view of a proximal portion  125  of cable  100 .  FIG. 2  shows center conductor  120 , which extends substantially the length of cable  100 , and in some aspects extends past cable jacket  110  in a direction along the length of cable  100 . 
       FIGS. 3 and 3A  illustrate a single shielded pair. Referring to  FIG. 3A , each shielded pair has parallel conductors  310  (indicated as  310   a  and  310   b ) separated by a solid dielectric  335  and surrounded by braided copper tubing  340 . Referring to  FIG. 3 , in some aspects, conductors  310  are each surrounded by insulators  320 . Conductors  310  and insulators  320  extend substantially the length of cable  100 . Conductors  310  extend past insulators  320 , in a direction along the length of conductors  310 , at the proximal end, the distal end, or both ends. 
       FIG. 4  illustrates a single shielded pair  120 , the conductors  310  of which have been welded to PCB trace pads  430  of a printed circuit board  420 . In some embodiments, conductors  310  are 24 AWG. The proximal ends of conductors  310  have been deformed. In some embodiments, each of conductors  310  is deformed. In other embodiments, one or more of conductors  310  are deformed. One way to deform the proximal ends of conductors  310  is to flatten them. One way to flatten the proximal ends of conductors  310  into deformed portions  410  is via a Schmidt press. In some embodiments, the thickness of the deformed portion  410  is substantially the same as the diameter of a 30 AWG conductor. Deformed portions  410  are resistance welded to PCB trace pads  430  of printed circuit board  420 . Detents  440  on deformed portions  410  can result from welding deformed portions  410  onto PCB trace pads  430 . In some embodiments, deformed portions  410  are double welded onto the same joint to more securely connect shielded pair  120  to PCB  420 . The proximal ends of conductors  310  are preferably welded to PCB trace pads  430  such that flattened portions  410  remain within the outline of PCB trace pads  430 . This helps to control impedance issues. 
       FIG. 5  illustrates two cables  100  before molds are applied to them. In some embodiments, cables  100  are cut to a specific length. Shielded pairs  120  extend beyond the proximal end of cable jacket  110 , which have been pulled back from the proximal ends  125  of cables  100 . Shielded pairs  120  are aligned into predetermined fixtures  510 . Fixtures  510  allow shielded pairs  120  to lie substantially parallel to each other and in substantially the same plane near their proximal ends. 
       FIG. 6  illustrates premold  610 . Premold  610  is applied to cable  100 . The distal end of premold  610  has a tubular shape, and surrounds the proximal end of cable jacket  110 . The proximal end of premold  610  surrounds shielded pairs  120  near the proximal ends of shielded pairs  120 . However, shielded pairs  120  extend beyond the proximal end of premold  610 . Premold  610  is secured around the proximal end of cable  100  and a portion of shielded pairs  120  near their proximal ends. 
     In some embodiments, premold  610  is made of a rigid material. Nonlimiting examples of materials from which premold  610  can be made include plastic and polycarbonate. 
       FIG. 6A  illustrates a portion of cable jacket  110  after it has been pulled back from the proximal end of cable  100  and wrapped around a portion of premold  610 . The portion of cable jacket  110  is preferably wrapped around the distal end of premold  610 . As illustrated in  FIG. 6A , the distal end of premold  610  has a tubular shape. 
     After a portion of cable jacket  110  is wrapped around the distal end of premold  610 , copper tape  630  is applied over the wrapped portion of cable jacket  110  and thus over the distal end of premold  610  as illustrated in  FIG. 6B . 
       FIG. 7  is a flowchart illustrating an example of a method of applying premold  610  to cable  100 . Instep  710 , cable  100  is cut to a specific length. Cable jacket  110  is pulled back from the proximal end of cable  100  in step  720 . In step  730 , shielded pairs  120  are aligned into predetermined fixtures  510 . In step  740 , premold  610  is applied to cable  100  and shielded pairs  120  such that shielded pairs  120  are aligned within the proximal end of premold  610 . In step  750 , a portion of cable jacket  110  that was pulled back from the proximal end of cable  100  is wrapped around a portion of premold  610 . In another embodiment, step  750  is omitted. In step  760 , copper tape  630  is wrapped around a portion of premold  610 . If step  750  is performed, copper tape  630  in step  760  is also wrapped around at least a portion of cable jacket  110  that is wrapped around premold  610 . In step  770 , a clamshell or other shell is applied over premold  610 . The clamshell is preferably applied by mechanical force. This mechanical force crushes a portion of cable jacket  110  if step  750  is performed. The mechanical force also crushes and secures copper tape  630  wrapped around premold  610  within the clamshell. The crushing force applied in step  770  tightens the clamshell over the copper tape to tighten around premold  610 . Because premold  610  is hard, the crushing force from the clamshell does not deform premold  610 . Because premold  610  is not deformed, the portion of cable  100  within premold  610  is also not deformed. In step  780 , shielded pairs  120  are cut and stripped. In step  790 , conductors  310  are deformed as described above, using for example a Schmidt press. In other embodiments, steps  780  and/or  790  are omitted. In step  795 , conductors  310  are welded to appropriate PCB trace pads  430  of PCB  420 . In other embodiments, other methods are used to attach conductors  310  to PCB trace pads  430 . 
     Although various embodiments have been described in detail herein by way of illustration, it is understood that such detail is solely for that purpose and variation can be made by those skilled in the art without departing from the spirit and scope of the inventions.