Patent Publication Number: US-2005142944-A1

Title: High speed shielded internal cable/connector

Description:
BACKGROUND INFORMATION  
      Typically, internal cable/connectors are unshielded and do not require metal shielding around connectors. One example of an internal cable/connector that is unshielded is ATA. However, if there is a certain amount of EMI emission being generated from the internal cable/connector, then the cable/connector has to meet FCC open box EMI containment requirement. This open box EMI containment requirement states that if a certain amount of EMI emission is being generated then the internal cable/connector will require metal shielding. Thus, a need exists for a low cost, shielded internal cable/connector that meets FCC EMI containment requirement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Various features of the invention will be apparent from the following description of preferred embodiments as illustrated in the accompanying drawings, in which like reference numerals generally refer to the same parts throughout the drawings. The drawings are not necessarily to scale, the emphasis instead being placed upon illustrating the principles of the inventions.  
       FIG. 1  is a perspective view of a cable assembly of the present invention;  
       FIG. 2  is a perspective view of a metal can on the cable assembly.  
       FIG. 3  is an exploded view of edge fingers.  
       FIG. 4  is an exploded view of the metal can connecting to the edge fingers.  
       FIG. 5  is a cross-section view of a board header. 
    
    
     DETAILED DESCRIPTION  
      In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular structures, architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the various aspects of the invention. However, it will be apparent to those skilled in the art having the benefit of the present disclosure that the various aspects of the invention may be practiced in other examples that depart from these specific details. In certain instances, descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.  
       FIG. 1  is a perspective view of a cable assembly of the present invention. A motherboard  10  includes edge fingers  15  and a daughter card  20  includes edge fingers  25 . The edge fingers  15 ,  25  are located directly on the motherboard  10  and the daughter card  20 . A cable assembly  30  includes connectors  35  on either end of the cable assembly  30 . These connectors  35  are also known as metal cans  35 . The connectors  35  directly mate with the edge fingers  15 ,  25  on the motherboard  10  and the daughter card  20 . By having the cable assembly  30  directly mating with the motherboard  10  and the daughter card  20 , this eliminates the cost of connectors on the motherboard and the daughter card and the associated assembly cost.  
      The cable assembly  30  may be shielded with a stamped and formed metal can  35 . The cable shielding braid is terminated onto the metal can  35  with the same termination process currently being done for most shielded external cables. This forms a continuous shielding throughout the cable assembly  35 .  
      The metal can  35  on the cable assembly  30  must also be connected to the ground planes on the system motherboard  10  and on the daughter card  20  to complete a return path.  FIGS. 2-4  illustrate how the metal can  35  is terminated to the motherboard  10  and the daughter card  20 .  FIG. 2  illustrates a perspective view of the metal can  35  on the cable assembly  30 . The metal can  35  includes compliant spring members  40  that may be stamped and formed on the metal can  35 . It should be noted that there are multiple ways to stamp and form spring members  40  out of the metal can, and  FIG. 2  illustrates one way.  
       FIG. 3  is an exploded view of the edge fingers  15 ,  25  on the motherboard  10  and the daughter card  20 . The taller fingers are the ground connections  45  on the edge fingers  15 ,  25 . These ground connections  45  connect to the spring members  40  of the metal can  35  on the cable assembly  30 . In this particular example, there are three ground connections  45  on each edge finger  15 ,  25  to connect to the metal can  35  on the cable assembly  30 . However, the number of ground connections  45  can vary depending on the EMI containment needs. The shorter fingers  50  are the contacts for signals, such as the clock signal. There is a difference between the signal contact  50  and the ground connection  45 , with the ground connection  45  being extended beyond the signal contacts  50  towards the front end of the cable assembly  30 . This is to maximize the EMI performance by containing the electromagnetic field with the metal can  35  as much as possible.  
       FIG. 4  illustrates how the metal can terminates to the edge fingers on the motherboard and the daughter card. When the cable assembly  30  is plugged into the motherboard  10  or the daughter card  20 , the spring members  40  on the metal can  35  mate with the edge finger ground connections  45 . These ground connections  45  are connected to a ground plane through vias  55  located on the ground connections  45 . When the edge finger  15 ,  25  is being plugged into the metal can  35 , the spring member  40  retracts and enables the edge finger  15 ,  25  inside the metal can  35 . Once inside, various connections can be established between the metal can and ground. These connections may be contact points for shielding  60 , contact point for the signal  65  and the contained EMI field  70 .  
       FIG. 5  illustrates an alternative to the cable assembly of  FIG. 1 . In some instances it may be desirable to bring the interface to the middle of the system board, instead of from the board edge. In these situations, a board header  75  can be made with contact pads  80  similar to the edge fingers shown in  FIG. 3 . The board header  75  may be placed on the motherboard  10  where it is desirable. The contact pads  80  mate the board header  75  to the cable assembly  30 . A solder tail  85  connects the board header  75  to the motherboard  10 . Although  FIG. 5  illustrates a through-hole mounted connector, a surface mounted connector would work as well. This enables the current cable assembly  30  to connect to any motherboard  10  no matter where the edge fingers  15  are located.  
      This invention provides a viable way to design an EMI shielded internal cable interconnect with the lowest possible cost to enable implementation of Intel&#39;s EXPRESSCARD in desktops. The one piece card edge style for the cable assembly makes it possible to eliminate the connectors on the motherboard or on the daughter card. The innovative scheme of terminating the metal can to the system ground makes it possible to shield only the cable assembly. All the shielding is on the cable assembly  30  and no shielding is on the edge fingers  15 ,  25  or the header  75 .  
      In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular structures, architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the various aspects of the invention. However, it will be apparent to those skilled in the art having the benefit of the present disclosure that the various aspects of the invention may be practiced in other examples that depart from these specific details. In certain instances, descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.