Abstract:
A backplane cabling interconnect scheme is provided that includes a wafer based cable termination and an organizer shroud. The shroud complements existing backplane connectors and provides positioning and polarization for the cable terminated wafer. The wafer cable ends can be stacked or arranged in various arrays and are held in place with an integral latch. A permanent latch is provided for high vibration environments.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 to U.S. Provisional Application No. 61/296,635, filed Jan. 20, 2010, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to cable interconnection at the backplane of computers. 
     2. Description of the Related Art 
     Modern electronic systems such as computer systems, telephonic switches and the like, often include large circuit boards called backplane boards that are rack mounted or retained in cabinets and are electrically connected to a number of smaller circuit boards called daughter cards. Various functions on the daughter cards are transferred between cards via the backplane. Examples of such configurations may be found in U.S. Pat. Nos. 6,824,391, 6,267,604, and 6,171,115. 
       FIGS. 1 and 2  show an example of a connection scheme  1  that allows multiple daughter cards to be connected to a common backplane or motherboard  3 . Interconnections from one daughter card to another run through this backplane  3 . Connectors  6  may be used to make the interconnections. Additionally, the backplane  3  can be configured with the same connector  6  on the side opposite the daughter cards to allow a unit called the rear transition module to be added. Often during development, there is a need to either probe certain connection points on the backplane or to change the routing of the circuitry, and rear transition modules may be used to make such connections. Rear transition modules may be a circuit board with a first connector that mates with the connector  6 , a second connector for connecting to other devices, and conductive traces on the rear transition module circuit board for making connections between its first connector and second connector. Optional connectivity may be added to the rear transition module to allow cable input-output I/O and the like. Such modules are expensive, allow limited flexibility, and take up considerable space behind the backplane  3 . 
     It will be appreciated that improvements in making connections to backplanes would be desirable. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, a low electrical loss interconnection is provided at a backplane. 
     According to another aspect of the invention, an interconnection provides ability to enhance the existing backplane capability by allowing additional circuitry external of the backplane. 
     According to yet another aspect of the invention, custom configuration capability is added by point-to-point ordering. 
     According to still another aspect of the invention, an interconnection allows easy changes to the backplane circuitry in the laboratory during product development. 
     According to a further aspect of the invention, an interconnection provides a low profile, allowing close panel enclosure. 
     According to a still further aspect of the invention, an interconnection reduces the backplane complexity, allowing for lower backplane cost. 
     According to another aspect of the invention, an interconnection enables cabling to the front panel of the enclosure as well as the backpanel or external direct. 
     According to yet another aspect of the invention, an interconnection provides the ability to attach a high bandwidth probe to the backplane circuitry. 
     According to still another aspect of the invention, an interconnection provides point-to-point interconnect capability. 
     According to a further aspect of the invention, an interconnection enhances existing backplane capabilities. 
     According to a still further aspect of the invention, an interconnection provides low attenuation in point-to-point connection. 
     According to other aspects, permanent holddowns are provided for deployment in vibration environs, a low profile allows close panel enclosure, an interconnection could reduce complexity of backplane thus lowering cost, and an interconnection allows cabling to front panel as well as backpanel or I.O. direct. 
     According to other aspects, an interconnection includes one or more cable wafer captures (holddowns) that have one or more of a radius limit, a retention function, retention by screws, and the ability to disable a latching function. 
     According to yet other aspects, an interconnection includes a shroud that has one or more of polarization left and right, polarization of power, and elevation to allow circuit board use up to (adjacent to) a backplane connector. 
     According to still other aspects, a wafer of an interconnection includes one or more of a snap feature for coupling together multiple wafers, cable egress and strain relief, stacking of latch arms of stacked wafers, polarization features, a latch feature for engaging a shroud, such as apertures in the shroud, a stress limiter, and an alignment feature using pins or posts. 
     According to another aspect of the invention, a backplane cable interconnection includes: a shroud for surrounding contacts of a backplane; cable end modules installed in slots of the shroud, wherein each of the cable end modules includes: a printed circuit board having contact pads for engaging the contacts of the backplane; one or more cables having conductors that are coupled to the contact pads; and an overmold on the printed circuit board that mechanically couples the one or more cables to the printed circuit board; and holddowns that are mechanically coupled to the shroud to retain the cable end modules in the slots. The holddowns disable a release feature of the cable end modules that would allow release of the cable end modules from the slot. 
     According to yet another aspect of the invention, a cable end module including: a printed circuit board having contact pads; one or more cables having conductors that are coupled to the contact pads; and an overmold on the printed circuit board that mechanically couples the one or more cables to the printed circuit board. The overmold includes a protrusion and a protrusion-receiving recess on opposite sides. The protrusion snaps into the protrusion-receiving recess of an adjacent of an adjacent cable end module. 
     According to still another aspect of the invention, a shroud for surrounding contacts of a backplane, the shroud including: a main body having slots therein for receiving stacked cable end modules; and a pair of side brackets at opposite ends of the main body. The main bodies has pairs of latch windows corresponding to respective of the slots, for receiving protrusions of the cable end modules when the modules are inserted into the slots. The side brackets keep the main body away from the backplane when the shroud is installed on the backplane. 
     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 
       The annexed drawings, which are not necessarily to scale, show various aspects of the invention. 
         FIG. 1  is an oblique view of part of a backplane. 
         FIG. 2  is a plan view of the backplane. 
         FIG. 3  is an oblique view of an interconnection in accordance with an embodiment of the present invention, installed on a backplane. 
         FIG. 4  is an oblique view of part of the shroud of the interconnection of  FIG. 3 . 
         FIG. 5  is a top view of a cable end module of the interconnection of  FIG. 3 . 
         FIG. 6  is a back view of the cable end module of  FIG. 5 . 
         FIG. 7  is an oblique view of part of the interconnection of  FIG. 3 , highlighting further details. 
         FIG. 8  shows a stack of cable end modules used as part of the interconnection of  FIG. 3 . 
         FIG. 9  is an exploded view showing a pair of the modules of the stack of  FIG. 8 . 
         FIG. 10  is a side view of the connection between two of the modules of the stack of  FIG. 8 . 
         FIG. 11  is an oblique view showing connection of contacts of connectors on a backplane. 
         FIG. 12  is a plan view of an interconnection according to an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A backplane cable interconnection is used to engage a backplane connector on a backplane. The backplane cable interconnection includes a shroud that that fits around the backplane connector, and a series of cable end modules that are inserted into the shroud. The shroud and the modules are used in place of rear transition modules. Such rear transition modules are fundamentally very expensive because of size and complexity; and, therefore, are not easily replaced with new designs. Also, backplane circuitry, such as that in rear transition modules, has electrical losses that are greater than cable losses. The present interconnection satisfies a need that exists for a connection method that will allow backplane circuit rerouting with small electrical losses, while allowing the ability to be easily changed without large investment. Also, a need exists for a backplane interconnection that will allow direct cabling between the backplane and the enclosure or between the backplane and an adjacent enclosure. Additionally, a need exists for a backplane interconnection that allows discrete probing of backplane circuitry by providing access at the backplane position. All of these advantages are provided by the interconnection described below. 
     The present cable interconnection allows ultimate flexibility when either cabling daughter-card position to daughter-card position, point-to-point, or when incorporating cable I/O from the backplane. This utility recognized the need for laboratory development experimentation and for ultimately deployable product having certain unique functions. 
     For example, it has long been recognized that circuit board attenuation exceeds cable attenuation by a large margin-sometimes 10:1. Certain critical electrical paths would benefit from cable interconnection. Also, products can be easily reconfigured by cabling rather than redoing an expensive backplane circuit board. Additionally, cables can go from the backplane to the enclosure panel, either front or back, and then to the outside world. Alternatively cables can go directly from the backplane to the outside world. Obviously, these improvements are of substantial value. 
     Referring now to  FIG. 3 , an interconnection  10  is shown mounted to the backplane  3  that has the connector  6  on it. The interconnection  10  includes a shroud or shell  14  that fits around the connector  6 , cable end modules (cable wafers or wafers)  16  that are installed in the shroud  14  and engage electrical contacts of the connector  6 , and cable wafer capture brackets (holddowns)  18  and  20  that are used to retain the cable end modules  16  in the shroud  14 . 
     With reference now in addition to  FIG. 4 , the shroud  14  is a die cast metal part that is used to hold secure the interconnection  10  to the backplane  3 , and to allow the wafers  16  and the brackets  18  and  20  to be secured to it. Alternatively the shroud  14  may be a plastic part, such as a molded plastic part. The shroud  14  has a pair of side brackets at either end, such as the bracket  24 , for receiving screws, such as the screw  26 , for securing the shroud  14  to the backplane  3 . The brackets  24  keep a main body  30  of the shroud  14  off of the surface of the backplane  3 . The main body  30  may be about 0.125″ above the backplane  3 . Having the main body  30  spaced above the backplane  3  prevents interference with components that might be located on the backplane  3  close to the connector  6 . The underside of the brackets  24  have protruding bosses around the bracket screw holes. The bosses are configured to engage holes in the backplane  3 , to aid in properly locating the shroud  14  relative to the backplane holes. 
     The shroud main body  30  has a series of vertical slots  34  separated by partitions  36  extending into the interior space of the main body  30  from side walls  38  of the main body  30 . Each of the slots  34  is configured to receive one of the wafers  16 , for engagement with the contacts of the connector  6  at the bottom of the slot  34 . The separate slots  34  aid in keeping the wafers  16  properly spaced and positioned, even when several wafers  16  are stacked together and inserted as a unit. 
     The side walls  38  of the shroud body  30  have latch windows  44 , a series of rectangular (square) holes in the side walls for receiving a latching mechanism of the waters  16 , as described further below. Each of the slots  34  has one of the latch windows on each side, for securing the wafer  16  placed in that slot  34 . 
     Corners of a top wall  46  of the body  30  have tapped holes  48  therein. The tapped holes  48  are for receiving screws  52  that secure the brackets  18  and  20  to the shroud  14 . 
       FIGS. 5-7  show further details of the wafer  16  and its securement to the shroud  14 . The wafer  16  has a printed circuit board  60  that has a series of the conductive contact pads  62  for engaging the contacts of the backplane connector  6  ( FIG. 3 ). Conductors  66  of cables  68  are soldered or otherwise electrically connected to conductive traces in contact with some of the contact pads  62 . In the illustrated embodiment two of the cables are twin coaxial cables, while a third is a single coaxial, but it will be appreciated that a variety of cable configurations are possible. After the cables  68  are coupled to the circuit board  60  a polymer overmold covers the ends of the cables  68  and the connections of the conductors  66  to the circuit board  60 . The overmold provides a good strain relief for the ends of the cables  68 . 
     Other pads  62  are coupled to a conductive shield plane or ground plane  72  that is on a back side of the circuit board  60 . The ground plane  72  is a conductive material that is placed on the back side of the circuit board, in a manner similar to the placement of the contact pads  62  and conductive traces on the front side of the circuit board  60 . Electrical contact between the ground plane  72  and some of the contact pads  62  is made through vias in the circuit board  60  that are filled with conductive material. 
     A molded plastic piece or body  76  is heat staked onto the circuit board  60 . The plastic piece  76  includes a central body portion  78 , and a pair of arms  82  and  84 . The plastic piece or body  76  may be made of any of a variety of suitable plastics, for example suitable thermoplastics. In addition the arms  82  and  84  provide features to secure the wafer  16  to the shroud  14 . Further, there are locating features on both the central body portion  78  and the arms  82  and  84  to aid in stacking multiple of the wafers  16  together, and to move the arms  82  and  84  of a stack of wafers  16  together. 
     The arms  82  and  84  are able to flex relative to the central body portion  78 . The arms  82  and  84  have respective latch protrusions  86  and  88  for engaging the latch windows  44  of the shroud  14 . The latch protrusions  86  and  88  have ramped bottom surfaces so that the arms  82  and  84  flex inward on their own as the wafer  16  is inserted into the shroud  14 . The latch protrusions  86  and  88  have squared-off upper surfaces such that once the latch protrusions  86  and  88  are engaged with the latch windows  44  they remain so engaged unless the arms  82  and  84  are pressed inward to disengage. This may be done by pressing inward on upper (distal) arm portions  92  and  94 . The upper arm portions  92  and  94  extend above the shroud side walls  38  when the wafer  16  is installed in the shroud  14 . 
     The arms  82  and  84  are thinner than the central body portion  78 . This is to allow for the thickness of the shroud partitions  36 , which are between the arms  82  and  84  of adjacent of the wafers  16 , but are not between bodies  78  of adjacent of the wafers  16 . The arms  82  and  84  may have about half the thickness of the body portion  78 . 
     A top surface  102  of the plastic piece or body  76  has a pair of body protrusions (pins)  104  that line up with and fit into corresponding body recesses  106  on a bottom surface  108  of the plastic piece or body  76 . The fitting of the body pins  104  into the body recesses  106  of an adjacent wafer  16  aids in aligning the adjacent wafers  16  as the wafers  16  are stacked, as shown in  FIG. 8 . 
     The top surface  102  also has protrusions (pins)  114  on the upper arm portions  92  and  94 , with corresponding recesses  116  on the bottom surface  108 , located at corresponding locations on the upper arm portions  92  and  94 . With reference to  FIG. 9 , the upper arm pins  114  and upper arm recesses  116  are used to mechanically couple together the overlapping upper arm portions  92  and  94  of stacked wafers  16 . This allows a user to move all of the upper portions  92  and  94  of a group of stacked wafers  16 , even by pushing inward on the upper arm portions  92  and  94  of only some (or even one) of the wafers  16 . 
     Considering now in addition  FIG. 10 , the plastic piece or body  76  also has a snap lock feature for assembling a stack of the wafers  16 . The bottom surface  108  has protrusions  124  that snap into and lock in corresponding recesses  126  in the plastic piece or body bottom surface  102 . 
     The wafers  16  can be inserted into the shroud  14  either individually or stacked in groups. Groups of the wafers  16  may be snapped together and inserted as a unit. 
     With the explanation of the features of the shroud  14  and the wafer  16  now complete,  FIG. 3  is referred to again to explain the function of the cable wafer capture brackets (holddowns)  18  and  20 . The holddowns  18  and  20  are coupled to the shroud  14  by use of the screws  52  that engage the holes  48  in the shroud  14 . Between the anchors at their ends, the holddowns  18  and  20  are strips of metal that run along both sides of the central body portion  78  of the wafers  16 . This places the holddowns  18  and  20  between the central body portion  78  and the arms  82  and  84  of the wafer  16 . When the holddowns  18  and  20  are in place the arms  82  and  84  cannot be pressed inward to have their latching protrusions  86  and  88  disengage the shroud latch windows  44 . This prevents unwanted disengagement of the wafers  16 , such as in a high-vibration environment. The holddowns  18  and  20  may have flared upper ends, curved (radiused) away from the center of the shroud  14 . 
       FIG. 11  shows one application of the system described herein, with wafers  16  at either end of cables  68  used to provide point-to-point interconnection between contacts of one or more of the connectors  6  on the backplane  3 . 
       FIG. 12  illustrates additional features, with adjacent wafers  16  have an alternating arrangement of cables  68 . In addition  FIG. 12  shows a polarization feature of the shroud  14 , with one side of the slots  34  having a different thickness than the other side (0.05″ versus 0.035″ in the illustrated embodiment). This resulting in a polarized shell  14 , with the different width slot sides prevent insertion of the wafers  16  the wrong way. 
     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.