Patent Publication Number: US-6712648-B2

Title: Laminate electrical interconnect system

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electrical connectors, and more particularly, to a composite layered interconnect system. Even more particularly, the present invention relates to a high density electrical interconnect system having multiple shielded electrical paths. 
     BACKGROUND OF THE INVENTION 
     Backplane systems are comprised of a complex printed circuit board which is referred to as a backplane or motherboard, and several smaller printed circuit boards which are referred to as daughtercards which plug into the backplane. Each of the daughtercards includes one or more chips which are referred to as the driver/receiver, The driver/receiver sends and receives signals from the drivers/receivers on other daughtercards. A signal path is formed between the driver/receiver on a first daughtercard and the driver/receiver on the second daughtercard. The signal path includes an electrical connector that connects the first daughtercard to the backplane, a second electrical connector that connects the second daughtercard to the backplane and the second daughtercard having the driver/receiver that receives the carriage signals. Various drivers/receivers being used today can transmit signals to data rates between 5-10 Gb/second and greater. The limiting factor (data transfer rate) in the signal path are the electrical connectors which connect each daughtercard to the backplane. A need exists in the art for a high speed electrical connector capable of handling the required high speed transfer data. 
     Further, the receivers are capable of discriminating signals having only 5% of the original signal strength sent by the driver. Reduction in signal strength increases the importance of minimizing cross-talk between signal paths to avoid signal degradation or errors being introduced into digital data streams. With high speed, high density electrical connectors, it is even more important to minimize cross-talk. Most high density electrical connectors use stamped copper components for carrying electrical signals. These copper components are usually unshielded and thus there is cross-talk between signal carrying paths. 
     Thus, need exists in the art for a high speed electrical connector capable of handling high speed signals that reduces cross-talk between signal paths. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an electrical connector in which separate signal paths are shielded from each other. 
     Another object of the present invention is to provide a low cost, high density electrical interconnect system which is simple to manufacture. 
     Yet another object of the present invention is to provide an electrical interconnect system having a dense array of signal carrying contacts and a shielded signal carrying path. 
     These and other objects of the present invention are achieved by an electrical connector including a plurality of layers wherein each layer has a first side and a second side. Each layer has longitudinal grooves in the first side and the second side. The longitudinal grooves are electrically conductive and each of the plurality of layers is adjacent to at least one other layer. A first layer has a first side not adjacent to another layer. A last layer has a second side not adjacent to another layer. A first side of each other layer is adjacent to a second side of another layer. A plurality of contacts is each engaged with a respective groove. 
     The foregoing and other objects of the present invention are achieved by an electrical connector including a first layer and a last layer and a plurality of intermediate layers. Each layer has a first surface and a second surface and each layer has a plurality of conductive traces on at least one of said first surface and the second surface. A plurality of contacts is each engaged with a respective groove. 
     The present invention is directed to an electrical connector having a laminate structure. The laminate structure has multiple parallel grooves. The laminate structure is electrically conductive and is coated with an electrically non-conductive material. Each groove has a signal carrying path which is advantageously surrounded by the laminate structure, thereby forming a type of Faraday cage around the signal carrying path and creating a completely shielded electrical path. 
    
    
     Still other objects and advantages of the present invention will become readily apparent to those killed in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by limitation, in the figure of the accompanying drawings, wherein elements having the same reference numeral designation represent like elements throughout and wherein: 
     FIG. 1 is an exploded view of a first embodiment of the present invention and a laminated electrical interconnect system according to the principles of the present invention; 
     FIG. 2 is a perspective view of the electrical interconnect system of FIG. 1 fully assembled; 
     FIG. 3 is a plan view of a lance type electrical contact used with the electrical interconnect system; 
     FIG. 4 is a cross-sectional view of the lance-type electrical contact engaged with the laminate structure; 
     FIG. 5 is a perspective view of a second embodiment of the present invention in a horizontal configuration; 
     FIG. 6 is a perspective view of a laminate used in the FIG. 5 electrical connectors; 
     FIG. 7 is a ground spring used in the FIG. 5 electrical connector; 
     FIG. 8 is another perspective view of a layer of the second embodiment of FIG. 5 with electrical contacts engaged with the laminate; 
     FIG. 9 is a perspective view of a layer of the second embodiment of FIG. 5 with an electrical contact engaged with a compressible conductive pad in a groove in the laminate; and 
     FIG. 10 is a perspective view of two layers of the second embodiment of FIG. 5 with a micro-strip positioned between the layers. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Refer first to FIG. 1, which is an exploded view of a horizontal first embodiment of an electrical connector according to the principles of the present invention. Electrical connector  20  includes a first layer  22 , a second layer  24 , a third layer  26 , and a fourth layer  28  which together form a laminate structure  29 . It is envisioned that the electrical connector would include many more layers than are shown in FIG.  1  and it is possible to have approximately 3000 signal lines in each electrical connector. Most preferably, the first embodiment of the electrical connector would have 15 layers each having 200 grooves for a total of 3000 signal paths. Each signal path has opposed contacts at opposite ends of the signal path. 
     Each of the layers  22 ,  24 ,  26 , and  28  has an inner surface  42 ,  44 ,  46  and  48  respectively. Each layer  22 ,  24 ,  26 , and  28  has an outer surface  52 ,  54 ,  56 , and  58 , respectively. Each of the layers  42 ,  44 ,  46  and  48  is preferably made from an electrically conductive material such as aluminum, brass or copper. Each of the layers  22 ,  24 ,  26 , and  28  can either be molded or stamped from a metallic material and suitably insulated by plating with an appropriate dielectric material. Alternatively, each of the layers can be molded from a non-conductive material and suitably plated for shielding and then insulated with the appropriate dielectric material. The first layer  22  has a front edge  62  and an opposite back edge  72 , both transverse to the longitudinal direction. The second layer  24  has a front edge  64  and a back edge  74  transverse to the longitudinal direction. The third layer  26  has a front edge  66  and a back edge  76 . The fourth layer  28  has a front edge  68  and a back edge  78 . 
     The first layer has a left side edge  73  and a right side edge  75 . The second layer has a left side edge  83  and a right side edge  85 . The third layer has a left side edge  87  and a right side edge  89 . The fourth layer has a left side edge  91  and a right side edge  93 . The first layer  22  has a smaller radius of curvature and each succeeding layer  24 ,  26  and  28  has a slightly larger radius of curvature such that the layers  22 ,  24 ,  26 , and  28  are stackable on one another. Each layer  22 ,  24 ,  26 , and  28  is aligned with the other layers such that right side edges  75 ,  85 ,  89 ,  93  are aligned and the left side edges  73 ,  83 ,  87 ,  91  are aligned. 
     Each of the four layers  72 - 78  is coated with an electrically non-conductive dielectric material such as anodize Teflon™, or ceramic. Layers  22 ,  24 ,  26 , and  28  can be bonded together with a non-conductive epoxy placed in between layers or mechanically. It is important that the layers  22 ,  24 ,  26 , and  28  are not electrically in contact with one another except that each of the layers  22 ,  24 ,  26 , and  28  is connected to ground. Each of the layers  22 ,  24 ,  26 , and  28  has an exposed portion  82 - 88 , for example, on the right side edges  75 ,  85 ,  89 ,  93  thereof, respectively, which are connected to ground as discussed below. 
     As depicted in FIG. 1, layer  22  has three longitudinally inwardly extending lower grooves  102  (not shown),  104  and  106  which extend from the front edge  62  to the back edge  72 . Although the grooves are depicted as semi-circular any shape can be used for ease of manufacture. The layer  22  also has three inwardly upper grooves  108 ,  110 ,  112 . As depicted in FIG. 1, grooves  108 ,  110  and  112  each have a conductive trace  122 ,  124 ,  126 , respectively, in a lower part of the groove. The conductive traces are placed in the grooves after the layers have been insulated and in this manner each of the traces is electrically separate from adjacent traces. For example, with respect to groove  108  a gap  132  exists between the conductive trace  122  and surface  52  so that there is no possibility of electrical contact between layer  22  and layer  24 . As depicted in FIG. 1, the grooves  102 ,  104 ,  106  in the lower surface  42  can have conductive traces and a junction can be formed between a respective trace and an inserted electrical contact. 
     The layer  24  has lower longitudinal grooves  142 ,  144  and  146 . The remaining grooves or layers  24 ,  26 , and  28  are not discussed for clarity. The grooves  142 ,  144  and  146  can either have conductive traces or not depending on the application. 
     As depicted in FIG. 1, groove  142  can also have a conductive trace placed therein, for example, and the same signal can be carried by conductive traces  122  and  142  forming a single signal path through the conductor. Alternatively, each of the conductive traces  122 ,  142  can carry different signals permitting the use of differential-pairs of lines on each side of the conductive contact. 
     Although not shown in FIG. 1, additional grooves can be added to each of the layers for alignment between adjacent layers. 
     As depicted in FIG. 1, alignment guides  30  and  32  have a rectangular shape and each has a plurality of holes to align with respective holes at opposite ends of the laminate structure  29 . For example, grooves  108  and  142  form roughly a circle and together provide an engagement area for a pin type contact  36  such as that disclosed in a patent application entitled “COMPLIANT SECTION FOR AN ELECTRICAL CONTACT”, Ser. No. 09/965,869, filed on Oct. 1, 2001, assigned to the instant assignee, the disclosure of which is hereby incorporated by reference into this specification in its entirety. 
     Advantageously, the laminate structure  29  completely surrounds each of the signal carrying traces forming a Faraday cage and preventing cross-talk between adjacent traces and eliminating noise. A Faraday cage is an electrostatic screen. The electrostatic screen is a shield against electric flux consisting of a number of straight, narrowly separated rods or wires joined at only one end. The plurality of layers  22 ,  24 ,  26 , and  28  from a type of Faraday cage for each signal contact by directing all magnetic fields created when a current travels through a wire directly to the underlying conductive layer which is then grounded. 
     The alignment guides are made from an electrically non-conductive material. Alignment guide  30  includes a row of holes  110 ,  112 ,  114  which are aligned with grooves  108 ,  142 ;  110 ,  144 ; and  112 ,  146 , respectively. Contacts  36  are inserted into respective holes in alignment guide  30  and contacts  38  are inserted into alignment guide  32 . The contacts  36 ,  38  serve to retain the alignment guides  30 ,  32  to the laminate structure  29 . 
     The contacts  36 ,  38  are held into the backplane and daughtercard using a compliant section such as the eye of a needle  37 ,  39 , respectively. 
     The preferred contact is a lance style type contact  36 ,  38  as depicted in FIG.  1 . The lance style contact  36  has a lance portion  124 , a hand guard portion  126  and a compliant section  37 . Lance portion  124  of the contact  36  engages and mates with the traces forming a junction between the traces and the contact  36 . For example, trace  122  is found in the groove  108  and is engaged with a contact  36 . The geometry of the lance portion  124  is similar to the compliant section  37  except that the eye of the lance is slightly smaller to allow for smaller forces and one of the beams is not fixed on one end to almost simulate a thumb on a hand. A hand guard portion  126  is located between the lance portion  124  and the compliant section  37 ,  39  and engages with an outer surface  130  of the alignment guide  30 . This connector is not limited to the lance contact. 
     A conductive wire/wire pad can be placed in parallel with each groove in the laminate and electrically connected to that laminate to form a more direct path to ground. For example, a very thin spun wire or flat conductive wire/strip that makes reliable contact, like a gasket, with parallel laminates may be placed between all or some data/signal carrying traces, but must ultimately be connected to ground. 
     The alignment guide  30  is retained as part of the connector by the plurality of contacts  36 . The alignment guide  32  is retained to the plurality of layers by a plurality of contacts  38 . A ground  34  has a hollow rectangular configuration and an inner surface of the ground  34  is in contact with the exposed surfaces  82 ,  84 ,  86  and  88  of the layers  22 ,  24 ,  26 , and  28 , respectively. The inner surface of ground  34  presses, i.e., is formed to mechanically flex against the exposed surfaces  82 ,  84 ,  86  and  88  of layers  22 ,  24 ,  26 , and  28 . 
     Refer now to FIG. 3 where the lance type contact  36  is shown in greater detail. The lance section  124  includes a thumb portion  170  and a springy hand portion  172 . The hand guard section  36  includes a first section  180  and a stepped section  182 . Note that stepped section  182  is wider than first section  180  such that the contact can be keyed into holes  110 ,  112  and  114 . 
     Refer now to FIG. 4 illustrating a cross-sectional view of the electrical connector with a contact inserted through the alignment guide  30  into the laminate structure  29 . The thumb portion  170  is in contact with groove  144  and the hand portion  172  is in contact with the groove  110 . As depicted in FIG. 4, the hand portion  172  deflects in a direction away from groove  110 . Also note that the step portion  182  engages with the alignment guide  30 . The alignment guide  30  geometry is such that the contacts are oriented to mate with the trace in the groove. If only one conductive trace is used then it is preferable to have the hand portion  172  in contact with the one conductive trace. 
     As depicted in FIG. 5, a second embodiment of the present invention is illustrated. The advantage to the second embodiment depicted in FIGS. 5-8 is that each of the laminates can be identical. In contrast, in the first embodiment, each of the layers  22 ,  24 ,  26 , and  28  is not identical and would have to be stamped or molded in a different tool thus increasing cost and complexity. Each of the laminates  500 ,  502 ,  504 , etc. is stacked one against another. Each laminate  500 ,  502 ,  504  can be made from either an electrically conductive material such as aluminum, copper or brass and then coated with an electrically non-conductive material or can be made from an electrically non-conductive material and then plated with an electrically conductive material. 
     FIG. 8 is a perspective view of a single laminate  500  according to the second embodiment described above. Multiple contacts are shown inserted into grooves on surface  600 . In assembled form, two or more laminates are stacked side-by-side, as depicted in FIG. 5, and the grooves line up with the traces on surface  610 . Contacts inserted in the grooves on surface  600 , as depicted in FIG. 8, are in contact with the traces on surface  610  of the neighboring laminate (not shown). Each laminate has a plurality of circular segmented grooves  602 ,  604 ,  606  as depicted in FIG.  6 . Grooves  602 ,  604 ,  606  extend inwardly from a surface  600 . At the bottom of each of these grooves  602 ,  604 ,  606  is an electrically conductive trace. The conductive traces or signal lines can be precision stamped or printed on a PC board (single or double sided micro-strip, strip line or the like) or produced in shielded or unshielded flexible circuits. Referring back to FIG. 5, on the back surface  610 , can be placed a plurality of conductive traces  520 ,  522 ,  524  as depicted in FIG.  5 . These conductive traces  520 ,  522 ,  524 , etc. can be used to provide a second signal path opposite a particular groove. 
     Laminate  500  has a through hole  620  in one comer thereof which can be used as an alignment hole. Another through hole  622  is an opposite corner thereof to align the stack of laminates  500 ,  502 ,  504 . A conductive pin can be inserted through each holes  620 ,  622 , through the entire length connector to stiffen up the connector assembly and to serve as a ground for grounding all the laminates together. Laminate  500  also has an exposed comer portion with a pair of holes  640 ,  642  connected by surfaces  644 ,  646 ,  648 , respectively. Surfaces  644 ,  646 ,  648  are slightly within the periphery of laminate  500 . A ground spring depicted in FIG. 7 is used to ground all the laminates together. 
     The conductive signals paths can be placed in the grooves  602 ,  604 ,  606  in each laminate as single sided or double sided, printed on a micro-strip, strip line or equivalent. Wires can also be placed into the grooves. The conductive signal paths can also be configured as a differential pair of signal contacts by having one signal path in groove  602 ,  604 ,  606  and a different signal path on traces  520 ,  522 ,  524 . 
     Instead of a cantilever style contact depicted in FIG. 1, a compressible conductive pad, e.g., a Fuzz Button™, can be placed into the end of each groove making electrical contact with a trace and with the backplane or daughtercard. 
     FIG. 9 is a perspective view of a compressible conductive pad  900  in a groove  902  in a laminate  904  and a pin contact  906  inserted into another groove. Pin contact  906  differs from lance-style contact  36  (FIG. 3) by having an elongated cylindrical portion  910  in place of lance section  124 . In an alternate embodiment, the cylindrical portion  910  may be a chamfered cylindrical piece for sliding beside the compressible pad  900 . Insertion of contact  906  into a groove  908  containing a compressible conductive pad (not shown) creates a large contact area between the contact  906  and the trace (not shown) in the groove  908 . 
     FIG. 10 is a perspective view of two adjacent layers  920 ,  922  in a laminate  500  as described above, wherein a micro-strip  924  is positioned between the adjacent layers  920 ,  922 . An additional micro-strip (not shown) would be positioned on the other side of layer  922  oppose micro-strip  924  and layer  920 . A contact  906  is inserted in a groove  926  of one of the layers  922  for contacting the additional micro-strip (not shown). Contact  906  may be either a lance-style contact, e.g., contact  36  of FIG. 3, or a contact  906  of FIG. 9 contacting a compressible pad (not shown) and thereby being in conductive contact with a micro-strip (not shown). 
     It will be readily seen by one of ordinary skill in the art that the present invention fulfills all of the objects set forth above. After reading the foregoing specification, one of ordinary skill will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.