Abstract:
There is provided a system for connecting signals between at least two electronic modules. The interconnection conduits are provided via one or more blades, which are equipped with connection areas along their edge toward the modules. This structure opens up more room for high frequency signaling connections. The blades used for the interconnect can be replaced in a live system during operational conditions.

Description:
BACKGROUND OF THE INVENTION 
     Backplanes are used in rack mounted systems to provide interconnections between electronic devices mounted within the rack. Specifically, electronic devices such as processors, interfaces, switches, etc., are supported within a slot of the rack. The said devices are prepared to be inserted into one of the said slots provisioned with connections to the backplane mounted within the rack. Commonly, the electronic device will have a connector, which mates with the corresponding connector of the backplane. The backplane provides interconnection of signals between the devices mounted within the rack and devices external to the rack. 
     However, prior art backplanes do not provide a good solution for high speed differential signaling above 2.5 Gb/s. The prior art backplane may include ten to thirty layers for interconnections between different slots of the rack system. The problems is that the higher the signaling frequency the higher the losses in signal strength. Specifically, anytime a single interconnect is switched, there is a pulse to the signal trace in the backplane and the material surrounding the trace reacts to this electromagnetic change. The molecules surrounding the trace change orientation due to the pulse in the trace such that heat is generated, thereby causing the amplitude of the signals to decrease. Accordingly, the signals will exhibit a loss in signal strength and be more susceptible to interference. 
     The prior art backplane is a per se non-exchangeable component of the systems built with them. This specifically prohibits the installation of active or even passive components on the backplanes for high availability systems. 
     The present invention addresses the above-mentioned deficiencies in the prior art backplane by providing a backplane that minimizes losses in the signals. Specifically, the rear interconnect system of the present invention provides a point to point interconnect method, which supports higher frequency interconnect protocols by reducing the signal loss. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a system for transferring signals between at least two electronic modules. The system includes at least one interconnect blade in communication with each of the electronic modules or a subset thereof. The signal or signal pair traces implemented on the interconnect blades may connect to exactly two electronic modules, or they may form a bus connecting to several electronic modules. 
     Each of the interconnect blades has a substrate and at least two contact areas formed on the substrate. Each contact area connects to a respective one of the electronic modules. Disposed on each of the substrates is at least one conduit operative to transfer the signals. The conduits may comprise wires or optical fibers. Each interconnect blade may include an insulating layer surrounding the conduits. The insulating layer facilitates the transfer of high frequency signals by a conduit comprising a wire. 
     The substrate of the blade may be a printed circuit board fabricated from a fiberglass material such as FR4. The blade may further include a carrier foil with interconnect traces formed by an etching process on its surface. The insulating area surrounding the wires may be a material such as air, gas or foam, which guarantee a separation distance for the wire from the surrounding substrate such that the high frequency signals flowing through the wires do not waste their energy into heating the substrate. In the case of using wire pairs for differential signaling, the energy loss will decrease significantly, because the symmetrical signaling waves zero out with increasing distance. 
     The required room for a better suited environment of the signals within the rear interconnect blade is achieved by the invention of said blade being mounted perpendicular to the plane of a conventional backplane. Several interconnect networks, including full mesh interconnects can be partitioned in a way which is compatible to the solution with an array of interconnect blades built according to the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
     FIG. 1 is a perspective view of a single interconnect blade constructed in accordance with the present invention and operative to receive multiple electronic modules; 
     FIG. 2 is a cross-section of the interconnect blade shown in FIG. 1; 
     FIG. 3 is a plan view of an interconnect blade with multiple fingers; 
     FIG. 4 is a perspective view of vertically mounted electronic modules interconnected by multiple horizontal interconnect blades; 
     FIG. 5 is a perspective view of horizontally mounted electronic modules interconnected by multiple vertical interconnect blades; 
     FIG. 6 is a perspective view of multiple vertical interconnect blades with module connectors on both sides; and 
     FIG. 7 is a perspective view of an electronic module having a flexible printed circuit board for connectors that mate with interconnect blades. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same, FIG. 1 is a perspective view of a rear interconnect blade  10  operative to interconnect electronic modules  12  in a high speed and low loss manner. Each of the modules  12  is an electronic device, which may support a different technology. In this regard, a module  12  may be a processor module, memory module, power supply, etc. The blade  10  provides a multitude of scenarios for the utilization of high-speed interconnection of modules  12  with electrical or optical medium. An architecture using the blade  10  allows a scalable, configurable rear interconnect having simultaneous support of different technologies. In this regard, the blade  10  provides the basis for a family of possible electromechanical interconnect standards. The blade  10  is typically installed within a chassis (not shown) that provides physical support for the modules  12  inserted therein. 
     Each module  12  may comprise a rigid printed circuit board (PCB) typically manufactured from a fiberglass material and having a predetermined size. In this regard, the modules  12  may all be the same size in order to meet a desired form factor of the chassis. However, it will be recognized that the modules  12  do not need to be the same size for operation with the interconnect blade  10 . Furthermore, modules  12  may consist of more than one board. The module  12  may also be a fully enclosed unit with integrated cooling and power conversion structures. 
     Each of the modules  12  includes a connector receptacle  14 , which mates with a connector  16  available at the edge of the blade  10 . Referring to FIG. 1, the connector receptacle  14  is installed perpendicular to the plane of the module  12  and parallel to the plane of the blade  10 . In this regard, for the configuration shown in FIG. 1, each of the modules  12  are plugged in from the front of the chassis containing the blade  10  with each of the modules  12  perpendicular to the blade  10 . 
     Connector  16  may be realized as an edge connector that is formed as an extension of the blade  10  and is insertable into the connector receptacle  14 . In this regard, the connector receptacle  14  contains a recess for receiving the edge connector  16 . As will be further explained below, the edge connector  16  is operative to transfer signals to/from the connector receptacle  14 . When the module  12  is inserted into the chassis containing the blade  10 , the connector receptacle  14  mates with the edge connector  16  in order to provide the interconnect between the module  12  and the blade  10 , as will be further explained below. 
     Embodiments of the invention may use state of the art techniques for the implementation of the rear interconnect blade. The following exemplary embodiment shows a possible more elaborate implementation. Referring to FIG. 2, a cross-sectional view of the blade  10  is shown. The blade  10  has a core  17  fabricated from a fiberglass material used in circuit board construction such as FR4. The core  17  forms the edge connector  16  and also has a generally planar body portion  18 . The edge connector  16  has a thickness which is slightly less than the body portion  18 . As previously discussed, the edge connector  16  is sized according to the requirements of the connector receptacle  14 . 
     Formed on the edge connector  16  is a contact area  20 , which makes an electrical connection with the connector receptacle  14  when inserted therein. Specifically, the contact area  20  connects with a conductive area of the connector receptacle  14  in order to transfer electrical signals therebetween. The contact area  20  is etched on the surface of a carrier foil  22 , which extends from the edge connector  16  through the body portion  18 , as seen in FIG.  2 . The carrier foil  22  and the contact area  20  are formed using circuit board construction and etching techniques. The contact area  20  may be gold plated copper or some other type of conductive material. A signal wire  24  is formed on the carrier foil  22  and extends into the interior of the body portion  18  from the edge connector  16 . The wire  24  transfers the signal from the contact area  20  to the interior of the body portion  18  and to other edge connectors  16 . The wire  24  may be constructed from a copper trace etched on the surface of the carrier foil  22 . Multiple wires  24  may be formed in order to transfer multiple signals. 
     The blade  10  further includes an insulating layer  26  in contact with each signal wire  24 . The insulating layer  26  may be formed from air, foam, gas, or any other material that does not absorb high frequency energy. As seen in FIG. 2, the insulating layer  26  may be disposed adjacent to the wire  24  such that the wire is in contact with the insulating layer  26  instead of the core  17 . The insulating layer  26  prevents the high frequency energy from the signals transmitted in the wire  24  from heating the core  17  and thereby prevents losses in the signals carried by the wire  24 . The insulating layer  26  provides a guaranteed minimum distance from the signal conduits (i.e., wire  24 ) from the core  17  or other carrier material. 
     The wire  24  can be routed in the proper direction on the blade  10  in order to connect other edge connectors  16 . Specifically, referring to FIG. 3, a plan view of the blade  10  is shown illustrating how the wires  24  may be routed. The wires  24  may be routed from different edge connectors  16  of a single blade  10  as a differential signal pair  32  if desired. Referring back to FIG. 2, a cross-sectional view of the differential signal pair  32  is shown. The signal pairs  32  are routed along the length of the blade  10  and are surrounded by the insulating layer  26 . Differential pairs may be routed side by side on the same surface of the carrier foil as shown in FIG. 3 or an opposite sides of the carrier foil forming the so called broad side coupling. 
     The blade  10  further includes ground layers  28  disposed on either side of the body portion  18 . The ground layer  28  is made from a conductive material such as copper for EMC containment. The ground layers  28  on both sides of the blade  10  must be interconnected around the perimeter using regularly placed plated vias (through-holes)  30 . Each via  30  contains a conductive material-which electrically connects the top and bottom ground layers  28  together. The ground layers  28  are then electrically connected to a ground of the system in order to provide EMC shielding. 
     As seen in FIG. 2, the wires  24  may be routed on both sides of the carrier foil  22 . The wires  24  distribute the signals along the blade  10  between the modules  12 . Typically, backplane signal interfaces do not require a random interconnect of the backplane connections of all slots. Bus interconnect signal groups can be easily partitioned to several blades  10 , as will be further explained below. Alternatively, the signal groups may be partitioned to separate carrier foils  22  of a single blade  10  without interconnection between the foils  22 . Even full mesh interconnects of differential pair signaling connections can be partitioned so that the rear interconnect blades  10  can be used without interconnection between multiple blades  10  or carrier foils  22  within the blades  10  carrying the interconnection. Accordingly, by using multiple blades  10  it is possible to provide interconnect between multiple modules  12  without having a backplane with multiple layers. 
     The blades  10  support a modular approach to rear interconnect blades. For example, multiple blades  10  can be mounted from the front or the rear of a system enclosure (i.e., chassis). The enclosure and the blades  10  are equipped with matching mounting supports, which provide high position accuracy. The mounting support of the rear interconnect blade  10  includes castellations and guides in the chassis corresponding to castellations on the blade  10  thereby allowing the insertion of the blade  10  to support contiguous subsets of module slots. An example of the modularity of the blade  10  is where a blade  10  can support a full mesh interconnect of all modules by one rear interconnect blade  10  and pair-wise interconnects of the neighboring slots via another rear interconnect blade  10 . The interconnects of neighboring modules may be implemented using a number of short blades  10  installed in line instead of one large rear interconnect blade. 
     As previously discussed above, an edge connector  16  is used to connect with the module  12 . The connector  16  may also be any specifically designed indirect connector resembling a standard edge connector. It is also possible to use two part connectors for the edge connector  16 . For example, two 90 degree surface mount connectors on both sides of the blade  10  could be used. In this instance, the thickness of the blade  10  has to be within the tolerance requirements of the connectors. 
     Referring to FIG. 4, a constellation of multiple modules  12  and blades  10  is shown. The modules  12  are inserted vertically, while the blades are horizontal. As seen in FIG. 3, each module  12  is inserted into multiple blades  10  which interconnect the modules  12  together. As mentioned above, each blade  10  can provide interconnection for differential signaling pairs between the modules  12 . 
     By using multiple blades  10  in a system configuration it is possible to provide interconnections between multiple modules  12  without using a single common backplane. For instance, a single blade  10  can be used to interconnect data signals, while another blade  10  can be used to interconnect control signals. In this regard, it is possible to assign signals to certain blades  10 . 
     Referring to FIG. 5, rear mounted vertical interconnect blades  10  are shown. In this configuration, the blades  10  are vertical and the modules  12  are horizontal. The benefit of this configuration is that front to back cooling of the modules  12  is possible by the blades providing a path for vertical airflow. Furthermore, this configuration can be implemented as an interconnect architecture for 1U (1.75 inches high) module enclosures. 
     Referring to FIG. 6, a vertical blade configuration wherein the modules  12  are inserted into both sides of the blades  10  is shown. In the configuration of FIG. 6, the modules  12  are inserted into either side of the blades  10  in order to provide more interconnection flexibility. In the configuration shown in FIG. 6, the blades  10  are in the center of the enclosure and the modules  12  are inserted from two opposite sides thereof. The multiple blades  10  form a backbone of the system. Vertical air flow is possible in the middle of the chassis, between the interconnect blades. 
     An implementation of the vertical blade configurations shown in FIGS. 5 and 6 is shown in FIG. 7. A single module  12  is connected to multiple blades  10  through the use of a flexible printed circuit board (PCB)  34 . In this regard, the PCB  34  is operative to provide a rear connection point for the connector receptacles  14  while still maintaining an orientation, which is perpendicular to the module  12 . The rear of each connector receptacle is attached to the PCB  34  such that each of the connector receptacles  14  is then insertable into a respective one of the edge connectors  16 . 
     Depending on the application, electronic components may or may not be used on the blades  10 . If electronic components are used on the blades  10 , they may be passive or active depending upon the complexity of the implementation. Furthermore, the electronic complexity of the blade  10  may be lower than, similar to, or greater than the complexity of the modules  12  depending upon the application. The blades  10  may serve as mediators (adapters) of rear connections for the front inserted module. The blades  10  may further be adapted to carry air movers or mass storage devices that may be replaceable via front or rear access to the system. As a superiority over systems designed with conventional backplanes, a system using the interconnect architecture provided by the invention, can support a live insertion and removal of the blade  10  units. In systems with exchangeable blades the limitations for the usage of active components on the interconnect blades will not be required, especially if the interconnect is partitioned into multiple blades in a way that the system can tolerate the removal of one of these blades under operational conditions. 
     It will be recognized that the modules  12  may be heavy and need to be supported when inserted into the chassis containing the blade(s)  10 . The connector receptacles  14  must be aligned with the edge connectors  16  when the module  12  is inserted. Alignment pins may be used to align the module connector receptacle  14  with the edge connector  16  of the blade  10 . This type of construction adds a mechanical support task to the blade. If the weight of the modules is very high, the blades cannot fulfill the task of supporting them. 
     Alternatively, it is possible to route the transfer wires  24  further from the modules  12  in order to form fingers, which allow flexible alignment of the edge connector  16 . Each of the edge connectors  16  may be lengthened to form individual fingers, as shown in FIG.  7 . Each of the fingers has the capability of being deformed to a certain extent without compromising the structural integrity of the blade  10 . By specific choice of the materials, the signal layout, and the formation of the fingers, it is possible to provide flexibility to the fingers, which allow deformation within mechanical tolerances. The flexibility of the finger allows alignment between the module  12  and the blade  10 . The fingers and module  12  need to have alignment features installed in order to support successful engagement over a wide range of tolerances. In this case, the weight of the modules is supported by mechanical structures and guides designed for the purpose. 
     The interconnect blades  10  can further provide redundant interconnects using separate blades to provide alternate resources. For instance, two blades  10  may be used for redundant power distribution that allow an exchange of a faulted blade under conditions of full or degrade service instead of taking a complete shelf or rack out of service for the replacement procedure. Furthermore, in a full mesh interconnect system, the interconnects can be grouped into subgroups so that one blade  10  can contain one quarter of the interconnect and another blade  10  can take another quarter of the interconnect, and so on. If there is a failure in one of the blades  10 , then the faulted blade  10  could be removed and the performance of the system would only be degraded by one quarter. In systems using conventional backplanes, the entire system needs to be powered down in order to replace a faulted backplane. 
     It will be recognized that the blades  10  allow different module depths at different positions within the system. By custom designing each blade  10 , it is possible to adapt the blade  10  for the desired depth of the module  12 . Furthermore, flexible solutions are achievable by telescopic extender mechanisms if flexible carriers for the conduits are applied. 
     Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art. For example, the blades  10  may be configured to provide optical signal paths for the distribution of optical signals. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices within the spirit and scope of the invention.