Abstract:
A cable-circuit board assembly is disclosed for use in providing a high speed transmission line for connecting electronic devices together. The circuit board is joined to a ground extension member that extends rearwardly of the circuit board and between sets of wires that are terminated to respective surfaces of the circuit board. The extension portion places a ground plane in the termination area of the connector, rear of the trailing edge of the circuit board to provide shielding between pairs of wires on opposite sides of the paddle card where the cable shields are cut back.

Description:
BACKGROUND OF THE PRESENT DISCLOSURE 
     The Present Disclosure relates generally to cable interconnection systems, and more particularly, to improved cable terminations in such assemblies for use in high speed data transmission applications. 
     Conventional cable interconnection systems are found in electronic devices such as routers and servers and the like, and are used to form signal transmission lines. These transmission lines may extend between chip members and connectors, connectors in two different devices, and between devices themselves. Often, differential signal wires are used for each such transmission line in a cable and although it is easy to maintain a desired impedance profile along the length of the cable due to the cable geometry, it is difficult to maintain such a profile at the termination ends of the wires. In some instances, these terminations occur at circuit board that takes the form of an edge, or paddle, card. The wires are terminated to contact pads along the trailing edge of the circuit board. In such a situation, the exterior insulation is stripped back and the bare conductors are terminated to solder pads or the like. The outer shields of the cable wires are also removed for an extent to facilitate the attachment of the cable wire free ends to the circuit card. As such, this termination area is left without a ground plane from the rea of the solder pads to the end of the cable wire outer shields. This ungrounded area has been known to contribute to and increase the crosstalk between the cable wires, especially in high speed applications. It is desirable to therefore have a cable termination with a structure that lessens the crosstalk in the termination area. 
     The Present Disclosure is therefore directed to a cable assembly that is particularly suitable for high speed data transmission applications. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     Accordingly, there is provided an improved high speed cable assembly that has an improved termination structure that is suitable for beneficial termination in high speed data transmission applications. 
     In accordance with an embodiment as described in the following Present Disclosure, a cable assembly is disclosed that utilizes a circuit board, preferably in the form of a paddle card, to which the wires of the multi-wire cable are terminated. The circuit board includes front contact pads which engage terminals of an opposing mating connector, as well as rear, or termination contact pads to which free ends of the cable wires are terminated. The cable wires have their free ends stripped of insulation, their outer grounding shield peeled back upon themselves and their free ends soldered to the termination contact pads. In order to provide grounding and shielding in the area rearward of the circuit board, a conductive extension member is provided in the form of a metal ground plate. The ground plate is disposed exterior of the circuit board and extends widthwise of the circuit board and has a length sufficient to extend underneath the cable wire insulation which is peeled back upon the cable wire. 
     The ground plate extends from close to the rear, or trailing, edge of the circuit board and underneath the cable wires, which are arranged in pairs for connection to contact pads or the like disposed on the top and bottom sides of the circuit board. The cable wires have their insulation coverings stripped from the ends thereof. The wires are usually arranged in pairs of wires that are enclosed within outer grounding shields in the form of either a conductive braid or foil wrapping. The wire insulation and outer shield are trimmed back so that the wire conductors are exposed in a fashion for easy termination to the circuit board. When stripped, the cable wire outer shield is usually peeled back over the wire insulation and a bare (non-shielded) extent of the cable wire insulation is exposed that extends between the leading edge of the insulative covering and the leading edge of the exterior shield. As the wire pairs are arranged in rows along the top and bottom surfaces of the circuit board and the wire pair conductors are terminated to contact pads on the top and bottom surfaces of the circuit board, a gap occurs between the top and bottom sets of wire pairs respectively attached to the circuit board. This gap area is prone to increased crosstalk between the top and bottom sets of wire pairs, and it also introduces discontinuities in the impedance profile of the cable assembly. 
     The ground plate extends axially rearwardly from the circuit board into this gap between the leading edge of the wire shield and the trailing edge of the circuit board. It fills the intervening space of the gap between the top and bottom pairs of cable wires with a ground plane, and this ground plane provides shielding between the top and bottom wire pairs. This shielding reduce crosstalk in the termination area. A series of mounting arms are provided and these mounting arms are attached, such as by soldering, to the ground circuits on the circuit board via selected contact pads. The mounting arms may be stamped and formed from the same metal blank as the ground plate. The mounting arms are spaced apart widthwise, a sufficient distance to accommodate a wire pair between pairs of mounting arms. Moreover, the extension member can assist in providing strain relief to the cable assembly when the circuit board is overmolded with an insulative material at least in the termination area. Suitable overmolding materials include plastics and/or epoxies. 
     These and other objects, features and advantages of the Present Disclosure will be clearly understood through a consideration of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The organization and manner of the structure and operation of the Present Disclosure, together with further objects and advantages thereof, may best be understood by reference to the following Detailed Description, taken in connection with the accompanying Figures, wherein like reference numerals identify like elements, and in which: 
         FIG. 1  illustrates a sectional view taken through the termination area of a conventional cable-circuit board assembly; 
         FIG. 2  is a perspective view of typical cable connector housing in which cable-circuit board assemblies of the type illustrated in  FIGS. 1 and 5  are housed; 
         FIG. 3  is a perspective view of the cable-circuit board assembly of  FIG. 1  and which is used in combination with the Present Disclosure; 
         FIG. 4  is a top plane view of the cable-circuit board assembly of  FIG. 3 ; 
         FIG. 5  is a perspective view of a cable-circuit board assembly constructed in accordance with the principles of the Present Disclosure, showing the top of the circuit board; 
         FIG. 6  is an exploded view of the cable-circuit board assembly of  FIG. 5 ; 
         FIG. 7  is the same view as  FIG. 5 , but with the top set of wire pairs and ground plate extension member removed for clarity; 
         FIG. 8  is the same view as  FIG. 7  but with the ground plate extension member attached to the trailing edge of the circuit board; 
         FIG. 9  is a cross-sectional view of the cable-circuit board assembly of  FIG. 5 , taken along Line  9 - 9  thereof and illustrating the relative locations of the top and bottom wire pairs and ground plate extension member; and 
         FIG. 10  is a cross-sectional view of the cable-circuit board assembly of  FIG. 5 , taken along Line  10 - 10  thereof, illustrating the relative locations of the wire pairs and ground plate extension member in the lengthwise direction. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the Present Disclosure may be susceptible to embodiment in different forms, there is shown in the Figures, and will be described herein in detail, specific embodiments, with the understanding that the Present Disclosure is to be considered an exemplification of the principles of the Present Disclosure, and is not intended to limit the Present Disclosure to that as illustrated. 
     As such, references to a feature or aspect are intended to describe a feature or aspect of an example of the Present Disclosure, not to imply that every embodiment thereof must have the described feature or aspect. Furthermore, it should be noted that the description illustrates a number of features. While certain features have been combined together to illustrate potential system designs, those features may also be used in other combinations not expressly disclosed. Thus, the depicted combinations are not intended to be limiting, unless otherwise noted. 
     In the embodiments illustrated in the Figures, representations of directions such as up, down, left, right, front and rear, used for explaining the structure and movement of the various elements of the Present Disclosure, are not absolute, but relative. These representations are appropriate when the elements are in the position shown in the Figures. If the description of the position of the elements changes, however, these representations are to be changed accordingly. 
       FIGS. 1-4  illustrate a conventional cable connector  10  ( FIG. 2 ) that has an outer connector housing  11  with a hollow termination end  13  that receives an end of a multiple-wire cable  14 , and a smaller mating end  12  and partially encloses a circuit board  15 . The mating end  12  of the connector holds a mating blade, shown as the circuit board  15 , shown in the form of a paddle card, in an orientation that is suitable for mating with an opposing, mating receptacle connector (not shown) which has a slot that receives the forward, mating end of the circuit board  15 . In order to provide a means for ensuring engagement with the opposing connector after mating, the connector  10  is also preferably provided with an elongated latch member  17  with engagement hooks or the like disposed at its forward end. These hooks are received in openings disposed in the opposing connector. The latch member  17  is actuated by the manipulation of an actuator  18 , shown as a pull tab. 
       FIG. 3  is a perspective view of a conventional termination structure used in the connector of  FIG. 2  and which terminate individual wires  25  of the cable  14  to circuits on the circuit board  15 . As shown in  FIG. 3  the cable  14  encloses a plurality of wires  24 . The wires illustrated are of the twin-ax construction, meaning that they have a pair of conductors  27  running along their lengths and in a spaced apart fashion. The conductors  27  are held in place by an outer insulative and dielectric covering  26 . The dielectric covering  26  is itself enclosed by an outer shield member  29 . The dielectric covering  26  may enclose the pair of conductors  27 , as shown best in  FIGS. 3-4 , or the dielectric covering  26  may be a pair of coverings, with one of the coverings enclosing one of the conductors. An outer shield member  29  is shown as extending around the dielectric covering and this shield member may take the form of a braided wire or a copper foil or the like. A drain wire  30  is commonly provided that extends for the length of the wire pair in a spiral pattern therearound and underneath the outer shield  29 . The cable wires  24  are arranged in two rows, with a first set of cable wires attached to first termination contact pads and the second set of cable wires being attached to second termination contact pads of the circuit board. 
     Turning to  FIG. 4 , which is a plan view of the termination structure shown in  FIG. 3 , it can be seen that the circuit board  15  takes the general form of a rectangle and has a leading edge  20  and a trailing edge  22 . The leading edge  20  is the forwardmost edge of the circuit board  15  and is that portion of the circuit board that is inserted into the card-receiving slot of an opposing, mating connector. The circuit board  15  is typically formed with an array of conductive first contact pads  21  disposed proximate to the circuit board leading edge  20  that mate with terminals of the opposing connector. The circuit board  15  further includes a plurality of conductive second termination contact pads  23  disposed proximate the trailing edge  22  thereof. The free ends  25  of the cable wire conductors  27  are terminated to the termination contact pads  23  as by soldering. 
     For termination, the free ends  25  of the cable wire conductors  27  are exposed by removing a given length of their outer covering(s)  26 , and their associated outer shield member(s)  29 . The removal of these materials defines respective leading edges  28 ,  31  of the wire insulation coverings  26  and the shield members  29 . Both of these leading edges are spaced apart from the free ends  25  of the cable wire conductors  27 . These leading edges  28 ,  31 , as shown best in  FIG. 4 , also are spaced rearwardly of the circuit board contact pads  23  and the trailing edge  22  of the circuit board  15 . The distance between the circuit board trailing edge  22  and the leading edge of the outer shield member(s)  29  defines a gap “G” having a lengthwise distance of L 2  through which the cable wire conductors  27  extend, partly in an insulated condition and partly in a bare, exposed condition ( FIG. 10 ). In this area, the wire conductors  27  have no ground with which to reference. Drain wires  30  associated with each twin-ax pair may be provided and they are separately attached to the circuit board termination contact pads  23  that are connected to ground circuits or an internal ground plane layer of the circuit board  15 . 
     In the gap area, the cable wires  24  are arranged in first and second sets of wire pairs. The first set of cable wire pairs are terminated to the termination contact pads on the top surface of the circuit board  15 , the second set of cable wire pairs are attached to the termination contact pads on the bottom surface of the circuit board  15 . The wire pairs are arranged in side-by-side order and further arranged in two vertically spaced apart and generally horizontal planes. These two sets of cable wires are separated from each other by a vertical spacing. In the gap, G, where the outer shielding  29  has been removed from over the signal wire conductors, no ground plane is present as any ground plane of the circuit board construction ends at or near the trailing edge of the circuit board  15 . Hence, there is no shielding in this gap area between the first and second sets of wire pairs. Even though the gap distance is relatively small, typically less than one inch, crosstalk will occur between the first and second sets of wire pairs at high data transfer speeds, such as between about 6 and about 10 Gigabits per second (Gbps) and this crosstalk inhibits efficient signal transmission and may lead to discontinuities in the impedance profile of the cable assembly. 
       FIGS. 5-10  illustrate our solution to this problem. The circuit board  15  of  FIGS. 5-10  has eight distinct signal transmission channels that each include a pair of cable wires  24 . Four of the transmission channels are located, figuratively speaking, on the top surface of the circuit board while the remaining four transmission channels are located on the bottom surface of the circuit board  15 . The four transmission channels are illustrated in  FIG. 6  as TX 1  through TX 4  and the three termination contact pads that make up the transmission channel (positive, negative and ground) are shown grouped together by the dashed lines  60 . 
     In order to reduce crosstalk between the first (upper) and second (lower) sets of wires, we provide a ground extension member  50  in the form of an elongated ground plate  52  which has a planar base portion  54  having a front to back length of L 1 , and a plurality of individual mounting arms  56 . The ground plate  52  is disposed exterior of the circuit board and it has a width that is preferably equal or less than the width of the circuit board  15  and it has a leading (front) edge  57  and a trailing (rear) edge  58 . In order to attach the ground plate  52  to the circuit board  15 , a the mounting arms  56  are preferably stamped and formed to define offset arms that are arranged along the leading edge  57  of the ground plate  52 . The mounting arms  56  rise up from the plane of the ground plate  52  and extend forwardly of the ground plate leading edge  57  past the trailing edge  22  of the circuit board  15 . Preferably, the mounting arms  56  have a length (from the ground plate to the tip end) that is about 20% to about 50% of the length L 1  of the ground plate  52 , and most preferably a length of about 30% to about 40% of L 1 . This relationship provides a suitable length that eliminates crosstalk in the gap, but also provides a suitable length for reliable attachment to the circuit board termination contact pads. Preferably, when assembled in a framework for holding the ground plate  52  and the circuit board  15  together, the leading edge  57  of the ground plate  52  abuts the trailing edge  22  of the circuit board  15 . 
     Preferably, the mounting arms  56  are spaced apart widthwise of the ground plate  52  in a spacing such that each space between the mounting arms  52  accommodate not only a cable wire pair, but also roughly aligns the cable wire pair with their associated signal termination contact pads on the circuit board  15 . 
     The ground plate  52  may be considered as an extension of the ground planes formed within the circuit board  15  and extends from the circuit board trailing edge  22  through the gap area G for a given length which ends at a location rearwardly of the leading edge  31  of the cable wires outer shield(s)  29 , whether the shield  29  is cut or peeled-back upon the of the cable wire pairs. As such, the ground plate member fills the gap G as well as provides a conductive surface that the cable wire outer shields  29  of at least one of the sets of wire pairs contact when the wire pairs are attached to the circuit board  15  as illustrated in  FIG. 5 . To some extent, the ground plate  52  also facilitates the attachment of the wire pairs on the top surface of the circuit board  15  as it tends to position the wire conductors  27  of the wire pairs in line with the signal termination contact pads  23  of the circuit board  15 . Although not necessary, the length of the ground plate  15  permits the exterior shields  29  of the wire pairs to be soldered thereto. 
     Such a structure reduces the crosstalk that occurs in this area, especially at high data transfer speeds of about 6 Gbs up to about 10 Gbps and above. The use of the circuit board extension portion  35  to solve this problem does so without increasing the complexity of assembly. This new development also provides the user with the ability to integrate a strain relief aspect into the termination area. This may be done by forming a body portion utilizing a suitable material such as a plastic or an epoxy that is molded over the cable wires  24 , the ground plate  52 , the termination contact pads  23  and a portion of the circuit board  15 . 
     Finally, while a preferred embodiment of the Present Disclosure is shown and described, it is envisioned that those skilled in the art may devise various modifications without departing from the spirit and scope of the foregoing Description and the appended Claims.