PATENT ABSTRACT
The present invention provides a high-speed electrical interconnection system designed to overcome the drawbacks of conventional interconnection systems. That is, the present invention provides an electrical connector capable of handling high-speed signals effectively.

PATENT DESCRIPTION
[0001]     The present application is a continuation of U.S. patent application Ser. No. 10/893,430, filed on Jul. 19, 2004 (Status: Pending), which claims the benefit of U.S. Provisional Patent Application No. 60/487,580, filed on Jul. 17, 2003, and which is also a continuation-in-part of U.S. patent application Ser. No. 10/234,859, filed Sep. 5, 2002 (Now U.S. Pat. No. 6,910,897), which is a continuation-in-part of U.S. patent application Ser. No. 10/036,796, filed Jan. 7, 2002 (Now U.S. Pat. No. 6,843,657), which claims the benefit of U.S. Provisional Patent Application No. 60/260,893, filed on Jan. 12, 2001 and U.S. patent application No. 60/328,396, filed on Oct. 12, 2001. Each above identified application is incorporated herein by this reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to electrical interconnection systems, and more specifically, to a high speed, high-density interconnection system for differential and single-ended transmission applications.  
         [0004]     2. Discussion of the Background  
         [0005]     Backplane systems are comprised of a complex printed circuit board that is referred to as the backplane or motherboard, and several smaller printed circuit boards that are referred to as daughtercards or daughterboards that plug into the backplane. Each daughtercard may include a chip that is referred to as a driver/receiver. The driver/receiver sends and receives signals from driver/receivers on other daughtercards. A signal path is formed between the driver/receiver on a first daughtercard and a driver/receiver on a second daughtercard. The signal path includes an electrical connector that connects the first daughtercard to the backplane, 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 carried signal.  
         [0006]     Various driver/receivers being used today can transmit signals at data rates between 5-10 Gb/sec and greater. The limiting factor (data transfer rate) in the signal path is the electrical connectors that connect each daughtercard to the backplane. Further, the receivers are capable of receiving signals having only 5% of the original signal strength sent by the driver. This 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 eliminate or reduce cross-talk. Thus, a 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  
       [0007]     The present invention provides a high-speed electrical interconnection system designed to overcome the drawbacks of conventional interconnection systems. That is, the present invention provides an electrical connector capable of handling high-speed signals effectively.  
         [0008]     In one aspect the present invention provides an interconnect system having a first circuit board, a second circuit board and a connector for connecting the first circuit board to the second circuit board.  
         [0009]     The first circuit board includes (a) a first differential interconnect path, (b) a first signal pad on a surface of the first circuit board and (c) a second signal pad also on the surface of the first circuit board, wherein the first differential interconnect path includes a first signal path electrically connected to the first signal pad and a second signal path electrically connected to the second signal pad. The second circuit board includes a second differential interconnect path.  
         [0010]     The connector electrically connects the first differential interconnect path with the second differential interconnect path. The connector may include the following: an interposer having a first face and a second face opposite the first face, the first face facing the surface of the first circuit board; a first conductor having an end adjacent to the second surface of the interposer; a second conductor parallel with and equal in length to the first conductor, the second conductor also having an end adjacent to the second surface of the interposer; a dielectric material disposed between the first conductor and the second conductor; a first elongated contact member having a conductor contact section, a board contact section and an interim section between the conductor contact section and the board contact section, the conductor contact section being in physical contact with the end of the first conductor, the board contact section being in physical contact with and pressing against a surface of the first signal pad, but not being secured to the first signal pad, and the interim section being disposed in a hole extending from the first face of the interposer to the second face of the interposer, wherein the first signal pad exerts a force on the first contact member and the first contact member is free to move in the direction of the force to a limited extent.  
         [0011]     In another aspect, the present invention provides a connector for electrically connecting a signal path on a first circuit board with a signal path on a second circuit board. The connector may include: a first, a second and a third spacer; a first circuit board disposed between the first and second spacers; and a second circuit board disposed between the second and third spacers.  
         [0012]     The first circuit board has a first face abutting a face of the first spacer and a second face abutting a face of the second spacer. The second face has a set of signal conductors disposed thereon. Each of the signal conductors disposed on the second face has a first end adjacent a first edge of the second face, a second end adjacent a second edge of the second face, and an interim section between the first end and the second end.  
         [0013]     The second circuit board has a first face abutting a face of the second spacer and a second face abutting a face of the third spacer. The first face of the second circuit board having a set of signal conductors disposed thereon. Each of the signal conductors disposed on the first face having a first end adjacent a first edge of the first face, a second end adjacent a second edge of the first face, and an interim section between the first end and the second end.  
         [0014]     The first edge of the second face of the first circuit board is parallel and spaced apart from the first edge of the first face of the second circuit board. Advantageously, to reduce cross-talk, none of the first ends of the signal conductors on the first circuit board are aligned with any of the first ends of the signal conductors on the second circuit board.  
         [0015]     In another aspect, the present invention provides a spacer for a connector. The spacer may include a first face having a set of M grooves disposed thereon, each of the M grooves extending from a first edge of the first face to a second edge of the first face; a second face having a set of N grooves disposed thereon, each of the N grooves extending from a first edge of the second face to a second edge of the second face; and an elongate finger projecting outwardly from a side of the spacer for attaching the spacer to a part of the connector.  
         [0016]     The above and other features, embodiments and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The accompanying drawings, which are incorporated herein and form part of the specification, help illustrate various embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.  
         [0018]      FIG. 1  is an exploded view of a connector in accordance with an example embodiment of the present invention.  
         [0019]      FIG. 2  is a view of a printed circuit board according to an embodiment of the present invention.  
         [0020]      FIG. 3  is a front side view of the printed circuit board shown in  FIG. 2 .  
         [0021]      FIG. 4  is a perspective view of a spacer in accordance with an example embodiment of the present invention.  
         [0022]      FIG. 5  is a top view of a first face of the spacer shown in  FIG. 4 .  
         [0023]      FIG. 6  is a top view of a second face of the spacer shown in  FIG. 4 .  
         [0024]      FIG. 7  is a front side view of the spacer shown in  FIG. 4 .  
         [0025]      FIG. 8  is a top view of a first face of a second spacer.  
         [0026]      FIG. 9  is a top view of a second face of the second spacer.  
         [0027]      FIG. 10  is a perspective view of an apparatus consisting of a circuit board sandwiched between two spacers.  
         [0028]      FIG. 11  is a front side view of the apparatus shown in  FIG. 10 .  
         [0029]      FIG. 12  illustrates an arrangement of multiple circuit boards and multiple spacers according to an example embodiment of the present invention.  
         [0030]      FIG. 13  is a top view of a first face of a circuit board according to an embodiment of the present invention.  
         [0031]      FIG. 14  illustrates how the alignment of the conductors on an A type circuit board differs from alignment of the conductors on a B type circuit board.  
         [0032]      FIG. 15  illustrates a contact member according to one embodiment of the invention.  
         [0033]      FIGS. 16 and 17  illustrate a cell according to one embodiment of the invention.  
         [0034]      FIGS. 18 and 19  illustrate that cells may be configured to fit into an aperture of an interposer.  
         [0035]      FIG. 20  illustrates a finger of a spacer inserted into a corresponding notch of an interposer.  
         [0036]      FIG. 21  illustrates the arrangement of the interposers  180  in relation to board  120  and in relation to boards  2190  and  2180 , according to one embodiment  
         [0037]      FIG. 22  is a cross-sectional view of an embodiment of the connector  100 .  
         [0038]      FIG. 23  illustrates an embodiment of backbone  150 .  
         [0039]      FIG. 24  illustrates an embodiment of an end cap  199 .  
         [0040]      FIG. 25  is an exploded view of backbone  150  and an end cap  199 .  
         [0041]      FIG. 26  is a view of a backbone  150  and an end cap  199  assembled together.  
         [0042]      FIG. 27  is a view of a spacer connected to backbone  150 .  
         [0043]      FIG. 28  illustrates an embodiment of mounting clip  190   b.    
         [0044]      FIG. 29  is an exploded view of clip  190   b  and end cap  199 .  
         [0045]      FIG. 30  is a view of clip  190   b  having an end cap  199  attached thereto.  
         [0046]      FIG. 31  illustrates an embodiment of shield  160 .  
         [0047]      FIG. 32  is an exploded view of shield  160  and an interposer  180 .  
         [0048]      FIG. 33  is a view of shield  160  being connected to an interposer  180 .  
         [0049]      FIG. 34  is a view of an assembled connector with an interposer  180  and clip  190   a  omitted.  
         [0050]      FIGS. 35 and 36  are different views of an almost fully assembled connector  100  according to one embodiment assembled without cells in  FIG. 35  and with  2  cells in  FIG. 36 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0051]      FIG. 1  is an exploded view of a connector  100  in accordance with an example preferred embodiment of the present invention. Some elements have been omitted for the sake of clarity. As illustrated in  FIG. 1 , connector  100  may include at least one printed circuit board  120  having electrical conductors printed thereon. In the embodiment shown, connector  100  may further include a pair of spacers  110   a  and  110   b , a pair of interposers  180   a  and  180   b , a pair of end-caps  190   a  and  190   b , a backbone  150 , a shield  160 , and a pair of endplates  190   a  and  190   b . Although only one circuit board and only two spacers are shown in  FIG. 1 , one skilled in the art will appreciate that in typical configurations connector  100  will include a number of circuit boards and spacers, with each circuit board being disposed between two spacers, as will be described herein.  
         [0052]      FIG. 2  is a view of printed circuit board  120 . In the embodiment shown, circuit board  120  is generally rectangular in shape. As shown, circuit board  120  may have one or more electrical conductors disposed on a face  220  thereof. In the embodiment shown, board  120  has four conductors  201 ,  202 ,  203 , and  204  disposed on face  220 . Each conductor  201 - 204  has a first end, a second and an interim section between the first and second ends. The first end of each conductor is located at a point on or adjacent a first edge  210  of face  220  and the second end of each conductor is located at a point on or adjacent a second edge  211  of face  220 . In many embodiments, second edge  211  of face  220  is perpendicular to first edge  210 , as shown in the embodiment illustrated in  FIG. 2 .  
         [0053]     Although not shown in  FIG. 2 , there are corresponding electrical conductors on the opposite face of circuit board  120 . More specifically, for each conductor  201 - 204 , there is a conductor on the opposite face that is a mirror image of the conductor. This feature is illustrated in  FIG. 3 , which is a front side view of board  120 . As shown in  FIG. 3 , conductors  301 - 304  are disposed on face  320  of board  120 , which face  320  faces in the opposite direction of face  220 . As further illustrated, conductors  301 - 304  correspond to conductors  201 - 204 , respectively.  
         [0054]     When the interconnection system  100  of the present invention is used to transmit differential signals, one of the electrical conductors  201 - 204  and its corresponding electrical conductor on the opposite face may be utilized together to form the two wire balanced pair required for transmitting the differential signal. Since the length of the two electrical conductors is identical, there should be no skew between the two electrical conductors (skew being the difference in time that it takes for a signal to propagate the two electrical conductors).  
         [0055]     In configurations where connector  100  includes multiple circuit boards  120 , the circuit boards are preferably arranged in a row in parallel relationship. Preferably, in such a configuration, each circuit board  120  of connector  100  is positioned between two spacers  110 .  
         [0056]      FIG. 4  is a perspective side view of spacer  110   a  according to one embodiment of the invention. As shown, spacer  110   a  may have one or more grooves disposed on a face  420  thereof, which face  420  faces away from board  120 . In the embodiment shown, face  420  of spacer  110   a  has three grooves  401 ,  402  and  403  disposed thereon. Each groove  401 - 403  extends from a point at or near a first edge  410  of face  420  to a point at or near second edge  411  of face  420 . In many embodiments, second edge  411  of face  420  is perpendicular to first edge  410 , as shown in the embodiment illustrated in  FIG. 4 .  
         [0057]     As further shown, face  420  of spacer  110   a  may have one or more recesses disposed at an edge of face  420 . In the embodiment shown, there are two sets of four recesses disposed at an edge on face  420 . The first set of recesses includes recesses  421   a - d , and the second set of recesses includes recesses  431   a - d . Each recess  421   a - d  is positioned directly adjacent to the end of at least one groove and extends from a point on edge  410  of face  420  to a second point spaced inwardly from edge  410  a short distance. Similarly, each recess  431   a - d  is positioned directly adjacent to the end of at least one groove and extends from a point on edge  411  of face  420  to a second point spaced inwardly from edge  411  a short distance. Accordingly, in the embodiment shown, there is at least one recess between the ends of all the grooves. Each recess  421 ,  431  is designed to receive the end of spring element (see  FIG. 16 , elements  1520 ).  
         [0058]     Although not shown in  FIG. 4 , there may be grooves and recesses on the opposite face  491  of spacer  110   a . In a preferred embodiment, the number of grooves on the first face of a spacer  110  is one less (or one more) than the number of grooves on the second face of the spacer  110 , but this is not a requirement. Similarly, in the preferred embodiment, the number of recesses on the first face of a spacer  110  is two less (or two more) than the number of recesses on the second face of the spacer  110 . This feature is illustrated in  FIGS. 5-7 , where  FIG. 5  is a top view of face  420 ,  FIG. 6  is a top view of the opposite face (i.e., face  491 ), and  FIG. 7  is a front side view of spacer  110   a.    
         [0059]     As shown in  FIG. 5 , grooves  401 - 403 , recesses  421   a - d , and recesses  431   a - d  are disposed on face  420  of spacer  110   a . Similarly, as shown in  FIG. 6 , grooves  601 - 604 , recesses  621   a - c,  and recesses  631   a - c  are disposed on face  491  of spacer  110   a , which face  491  faces in the opposite direction of face  420 .  
         [0060]     Grooves  601 - 604  are similar to grooves  401 - 404  in that each groove  601 - 604  extends from a point on a first edge  610  of face  491  to a point on a second edge  611  of face  491 . Likewise, recesses  621  and  631  are similar to recesses  421  and  431 . Like each recess  421 , each recess  621  extends from a point on edge  610  of face  491  to a second point spaced inwardly from edge  610  a short distance. Similarly, each recess  631  extends from a point on edge  611  of face  491  to a second point spaced inwardly from edge  611  a short distance. Each recess  621 ,  631  is designed to receive the end of a spring element (see  FIG. 16 , elements  1520 ).  
         [0061]     The figures illustrate that, in some embodiments, the number of grooves on one face of a spacer  110  is one less (or one more) than the number of grooves on the opposite face of the spacer. And also show that the number of recesses on one face may be two less (or two more) than the number of recesses on the opposite face.  
         [0062]     In the embodiment shown in  FIGS. 4-6 , each recess on one face is positioned so that it is generally directly opposite an end of a groove on the other face. For example, recess  421   a  is generally directly opposite an end of groove  604  and recess  621   a  is generally directly opposite an end of groove  403 . This feature can be more easily seen by examining  FIG. 7 , which is a front side view of the spacer.  
         [0063]     Referring back to  FIG. 4-6 ,  FIG. 4  shows that spacer  110   a  may further include three fingers  435 ,  437 , and  440 . It also shows that that spacer  110   a  may also include a slot  444  and a first pair of bosses  450  disposed on and projecting outwardly from face  420  and a second pair of bosses  650  disposed on and projecting outwardly from face  491 . Bosses  650  are provided to fit in the apertures  244  of circuit board  120 . This feature enables board  120  to be properly aligned with respect to the adjacent spacers  110   a  and  110   b.    
         [0064]     Finger  435  is located towards the top of the front side of spacer  110   a  and finger  437  is located towards the front of the bottom side of spacer  110   a . Finger  435  projects outwardly from the front side of spacer  110   a  in a direction that is perpendicular to the front side of the spacer. Similarly, finger  437  projects outwardly from the bottom side of spacer  110   a  in a direction that is perpendicular to the bottom side of the spacer. Fingers  435 ,  437  function to attach spacer  110   a  to interposers  180   b ,  180   a , respectively. More specifically, interposer  180   a  includes a recess  1810  (see  FIG. 18 ) for receiving and retaining finger  437 . Similarly interposer  180   b  includes a recess for receiving and retaining finger  435 . Fingers  435 ,  437  each include a protrusion  436  and  438 , respectively. The protrusions are sufficiently resilient to allow them to snap into corresponding recesses in the corresponding interposers.  
         [0065]     Slot  444  is located towards but spaced apart from the backside of spacer  110   a . Slot  444  extends downwardly from the top side of spacer  110  to form finger  440 . Finger  440  and slot  444  function together to attach spacer  110   a  to backbone  150 .  
         [0066]     Referring back to spacer  10   b  (see  FIG. 1 ), in the embodiment shown, spacer  10   b  is similar but not identical to spacer  110   a . Accordingly, in some embodiments connector  100  includes two types of spacers: type A and type B. In other embodiments, more or less than two types of spacers may be used.  FIGS. 8 and 9  further illustrate spacer  110   b  (the type B spacer) according to one embodiment.  FIG. 8  is a top view of a face  820  of spacer  110   b . Face  820  faces circuit board  120 . As shown in  FIG. 8 , face  820  is similar to face  491  of spacer  110   a , which also faces board  120 . Like face  491 , face  820  has four grooves  801 - 804 , a first set of three recesses  821   a - c , and a second set of three recesses  831   a - c.    
         [0067]     Grooves  801 - 804  are similar to grooves  601 - 604  in that each groove  801 - 804  extends from a point on a first edge  810  of face  820  to a point on a second edge  811  of face  820 . Likewise, recesses  821  and  831  are similar to recesses  621  and  631 . Like each recess  621 , each recess  821  extends from a point on edge  810  of face  820  to a second point spaced inwardly from edge  810  a short distance. Similarly, each recess  831  extends from a point on edge  811  of face  820  to a second point spaced inwardly from edge  811  a short distance.  
         [0068]      FIG. 9  is a top view of a face  920  of spacer  110   b . Face  920  faces away from circuit board  120  in the opposite direction of face  820 . As shown in  FIG. 9 , face  920  is similar to face  420  of spacer  110   a , which also faces away from board  120 . Like face  420 , face  920  has three grooves  901 - 903 , a first set of four recesses  921   a - d , and a second set of four recesses  931   a - d.    
         [0069]     Grooves  901 - 903  are similar to grooves  401 - 403  in that each groove  901 - 903  extends from a point on a first edge  910  of face  920  to a point on a second edge  911  of face  920 . Likewise, recesses  921  and  931  are similar to recesses  421  and  431 . Each recess  421  extends from a point on edge  910  of face  920  to a second point spaced inwardly from edge  910  a short distance, and each recess  931  extends from a point on edge  911  of face  920  to a second point spaced inwardly from edge  911  a short distance.  
         [0070]     Spacer  110   b  also includes three fingers  835 ,  837 , and  840 , a slot  844 , and a pair apertures  850  extending through spacer  110   b . Apertures  850  are provided to receive bosses  650 . This feature enables spacer  110   b  to be properly aligned with respect to spacers  110   a.    
         [0071]     Unlike finger  435 , which is located towards the top of the front side of spacer  110   a , finger  835  is located towards the bottom of the front side of spacer  110   b . Similarly, unlike finger  437 , which is located towards the front of the bottom side of spacer  110   a , finger  837  is located towards the back of the bottom side of spacer  110   b . Finger  835  projects outwardly from the front side of spacer  110   a  in a direction that is perpendicular to the front side of the spacer, and finger  437  projects outwardly from the bottom side of spacer  110   a  in a direction that is perpendicular to the bottom side of the spacer. Like fingers  435 ,  437 , fingers  835 ,  837  function to attach spacer  110   b  to interposers  180   b ,  180   a , respectively.  
         [0072]     As discussed above, board  120  is positioned between spacers  110   a  and  10   b . This feature is illustrated in  FIG. 10 . Although not shown in  FIG. 10 , bosses  650  of spacer  110   a  protrude though apertures  244  of board  120  and through apertures  850  of spacer  110   b . This use of bosses  650  facilitates the proper alignment of spacers  110   a,b  and board  120 . When board  120  is properly aligned with the spacers, conductors  201 - 204  and  301 - 304  are aligned with grooves  601 - 604  and  801 - 804 , respectively. This feature is illustrated in  FIG. 11 .  
         [0073]     As shown in  FIG. 11 , grooves  601 - 604 , which are disposed on the side of spacer  110   a  facing board  120 , are positioned on the spacer to mirror electrical conductors  201 - 204  on printed circuit board  120 . Likewise, grooves  801 - 804 , which are disposed on the side of spacer  110   b  facing board  120 , are positioned on the spacer to mirror electrical conductors  301 - 304 . Grooves  601 - 604  and  801 - 804 , among other things, prevent electrical conductors  201 - 204  and  301 - 304  from touching spacer  110   a  and  110   b , respectively. In this way, the electrical conductors disposed on board  120  are insulated by the air caught between board  120  and the grooves.  
         [0074]     Spacers  110  may be fabricated either from an electrically conductive material or from a dielectric material and coated with an electrically conductive layer to electromagnetically shield the electrical conductors of the printed circuit board  120 . Furthermore, the complex impedances of the electrical conductors and their associated grooves can be adjusted by varying the dimensions thereof. Still furthermore, the grooves can include a layer of a dielectric material, such as Teflon, to further adjust the complex impedances of the electrical conductors and their associated channels as well as adjusting the breakdown voltage thereof.  
         [0075]     Referring now to  FIG. 12 ,  FIG. 12  illustrates an example arrangement of spacers  110  and circuit boards  120  when multiple circuit boards are used in connector  100 . As shown, boards  120  and spacers  110  are aligned in a row in parallel relationship and each circuit board  120  is sandwiched between two spacers  110 . In the example shown, there are two types of circuit boards (A) and (B), as well as the two types of spacers (A) and (B) discussed above. The A type circuit boards are identical to each other and the B type circuit boards are identical to each other. Similarly, The A type spacers are identical to each other and the B type spacers are identical to each other.  
         [0076]     In the embodiment shown, spacers  110  and boards  120  are arranged in an alternating sequence, which means that between any two given A type spacers there is a B type spacer and vice-versa, and between any two given A type boards there is a B type board and vice-versa. Thus, an A type spacer is not adjacent to another A type spacer and an A type board is not adjacent to another A type board. Accordingly, in this example configuration, each board  120  is disposed between an A type spacer and a B type spacer.  
         [0077]     As can be seen from  FIG. 12 , each face of each board  120   b  (the B type board) has three conductors thereon.  FIG. 13  is a top view of one face  1320  of a B type board (the other face not shown is a mirror image of face  1320 ). As shown in  FIG. 13 , there are three conductors  1301 ,  1302 , and  1303  disposed on face  1320 . By comparing  FIG. 13  to  FIG. 2  (which is a top view of a face of an A type board), one can see that the A and B type boards are nearly identical. One difference being the number of conductors on each face and the alignment of the conductors on the face. In the embodiment shown, the B type boards have one less electrical conductor than do the A type boards.  
         [0078]     Referring to  FIG. 14 ,  FIG. 14  illustrates how the alignment of the conductors  1301 - 1303  on the B type boards differs from alignment of the conductors  201 - 204  on the A type boards.  FIG. 14  shows representative boards  120   a  and  120   b  in a side by side arrangement so that a front edge  1401  on board  120   a  is spaced apart from and parallel with a corresponding front edge  1402  on board  120   b . From  FIG. 14 , one can clearly see that the ends of the conductors on the B type board located at edge  1402  are not aligned with the ends of the conductors on the A type board located at edge  1401 . For example, in the example shown, the end of any given conductor on the B type board is interstitially aligned with respect to the ends of two adjacent conductors on the A type board. That is, if one were to draw the shortest line from the end of each conductor on the B board to the adjacent face of the A board, each line would terminate at a point that is between the ends of two conductors on the A board. For example, the shortest line from the end of conductor  1301  to the adjacent face of board  120   a  ends at a point that is between the ends of conductors  204  and  203 . An advantage of having the conductors be misaligned is that it may reduce cross-talk in the connector.  
         [0079]     Referring back to  FIG. 12 , one can clearly see that each conductor on each board  120  is aligned with a groove on the spacer directly adjacent the conductor. That is, each groove on each spacer  110  is designed to mirror a corresponding conductor on an adjacent board  120 . Because each conductor is aligned with a corresponding groove, there is a space between the conductor and the spacer.  
         [0080]     when connector  100  is fully assembled, each conductor on a board  120  comes into physical and electrical contact with two contact members (see FIG.  15  for a representative contact member  1530   a ), an end of each of which fits into the space between the adjacent spacer and the conductor. More specifically, the first end of each conductor comes into physical and electrical contact with the contact portion of a first contact member and the second end of each conductor comes into physical and electrical contact with the contact portion second contact member, and the contact portions of the first and second contact members are each disposed in the space between the corresponding end of the conductor and the spacer. Each contact member functions to electrically connect the conductor to which it makes contact to a trace on a circuit board-to which the connector  100  is attached.  
         [0081]      FIG. 15  illustrates a contact member  1530   a , according to one embodiment of the invention, for electrically connecting a conductor  201  on a board  120  to trace on a circuit board (not shown in  FIG. 15 ) to which the connector  100  is attached. Only a portion of contact member  1530   a  is visible in  FIG. 15  because a portion is disposed within a housing  122 .  
         [0082]     As shown in  FIG. 15 , contact member  1530   a  contacts an end of conductor  201  (the spacers and interposers are not shown to better illustrate this feature). In some embodiments, the ends of the conductor  201  are wider than the interim portions so as to provide more surface area for receiving the contact portion of the contact members.  
         [0083]     Partially shown in  FIG. 15  is another contact member  1530   b . Contact member  1530   b  has a bottom portion that is also housed in housing  122 . Contact member  1530   b  contacts an end of conductor  301 , which can&#39;t be seen in  FIG. 15 . Housing  122  is preferably fabricated of an electrically insulative material, such as a plastic. The electrical contacts  1530  of each housing  122  can either be disposed within the housing during fabrication or subsequently fitted within the housing.  
         [0084]     Contact members  1530  may be fabricated by commonly available techniques utilizing any material having suitable electrical and mechanical characteristics. They may be fabricated of laminated materials such as gold plated phosphor bronze. While they are illustrated as being of unitary construction, one skilled in the art will appreciate that they may be made from multiple components.  
         [0085]     As further shown in  FIG. 15 , housing  122  may be configured to hold two elongate springs  1520   a  and  1520   b . Springs  1520  extend in the same direction as contact members  1530  and  1531 . The distal end of a spring  1520  is designed to be inserted into a corresponding spacer recess. For example, distal end of spring  1520   a  is designed to be received in recess  621   c . The combination of the housing  122 , contact members  1530 , and springs  1520  is referred to as a cell  1570 .  
         [0086]      FIGS. 16 and 17  further illustrate cell  1570  according to one embodiment.  FIG. 17  is an exploded view of cell  1570 . As shown, the housing  122  is generally rectangular in shape and includes apertures  1710  for receiving springs  1520  and apertures  1720  for receiving contact members  1530 . Apertures  1720  extend from the top side of housing to bottom side of the housing so that proximal ends  1641  of contact members  1730  can project beyond the bottom side of housing  122 , as shown in  FIG. 16 .  
         [0087]     Apertures  1710  extend from the top surface of housing  122  towards the bottom surface. But do not reach the bottom surface. Accordingly, when a spring  1520  is inserted into an aperture  1710  the proximal end will not project beyond the bottom surface of housing  122 . While open apertures  1710  are illustrated, it is understood that closed apertures can also be used  
         [0088]     As illustrated in  FIG. 17 , each contact member  1530 , according to the embodiment shown, has a proximal end  1641  and a distal end  1749 . Between ends  1641  and  1749  there is a base portion  1743 , a transition portion  1744  and a contact portion  1745 . Base portion  1743  is between proximal end  1641  and transition portion  1744 , transition portion is between base portion  1743  and contact portion  1745 , and contact portion  1745  is between transition portion  1744  and distal end  1749 . In the embodiment shown, base portion  1743  is disposed in aperture  1720  so that generally the entire base portion is within housing  122 , transition portion  1744  is angled inwardly with respect to the base portion, and distal end  1749  is angled outwardly with respect to the transition portion and therefore functions as a lead-in portion.  
         [0089]     In a preferred embodiment, the contact portion of a contact member is not fixed to the end of the conductor with which it makes physical and electrical contact. For example, the contact portions are not soldered or otherwise fixed to the board  120  conductors, as is typical in the prior art. Instead, in a preferred embodiment, a contact member  1630  is electrically connected to its corresponding conductor with a wiping action similar to that used in card edge connectors. That is, the contact portion of the contact member merely presses against the end of the corresponding conductor. For example, referring back to  FIG. 15 , the contact portion of contact member  1530   a  merely presses or pushes against the end portion of conductor  201 . Because it is not fixed to the conductor, the contact portion can move along the length of the conductor while still pressing against the conductor, creating a wiping action. This wiping action may ensure a good electrical connection between the contact members and the corresponding electrical conductors of the printed circuit boards  120 .  
         [0090]     Referring now to  FIGS. 18 and 19 ,  FIGS. 18 and 19  illustrate that each cell  1570  is designed to fit into an aperture  1811  of an interposer  180 . In the embodiment shown, each interposer  180  includes a first set of apertures  1811   a  (see  FIG. 19 ) arranged in a first set of aligned rows to create a first row and column configuration and a second set of apertures  1811   b  arranged in a second set of aligned rows to create second row and column configuration. In the embodiment shown, each row in the second set is disposed between two rows from the first set. For example, row  1931 , which is a row of apertures  1811   b , is disposed between rows  1930  and  1932 , each of which is a row of apertures  1811   a.    
         [0091]     As shown in the figures, the second row and column configuration is offset from the first row and column configuration so that the apertures of the second set are aligned with each other but not aligned with the apertures of the first set, and vice-versa  
         [0092]     An interposer  180  may electromagnetically shield the electrical conductors of the printed circuit boards  120  by being fabricated either of a conductive material or of a non-conductive material coated with a conductive material.  
         [0093]     As also shown in  FIGS. 18 and 19 , interposers  180  include notches  1810  along a top and bottom side. Each notch  1810  is designed to receive the end of a finger of a spacer  110 . Preferably, the finger snaps into a corresponding notch to firmly attach the spacer  110  to the interposer  180 . This feature is illustrated in  FIG. 20 .  
         [0094]     When connector  100  is fully constructed, each aperture in the first and second set receives a cell  1570 . The housing  122  of each cell  1570  has a tab  1633  arranged to fit within a slot  1888  disposed within a corresponding aperture of the interposer  180 , which slot  1888  does not extend the entire length of the aperture. The tab  1633 , therefore, prevents the cell  1570  from falling through the aperture. It is to be understood that the specific shape of the cells and corresponding apertures are merely for exemplary purposes. The present invention is not limited to these shapes.  
         [0095]     Additionally, when connector is fully constructed, the interposers are arranged so that the contact portion  1745  of each contact member  1530  contacts a corresponding conductor.  FIG. 21  illustrates this concept.  
         [0096]      FIG. 21  illustrates the arrangement of the interposers  180  in relation to board  120  and in relation to boards  2190  and  2180 . The spacers  110  are not shown in the figure to illustrate that board  120  and interposers  180  are arranged so that the front side  2102  of board  120  is aligned with the center line of a column of apertures on spacer  180   b  and so that the bottom side  2104  of board  120  is aligned with the center line of a column of apertures on spacer  180   a .  FIG. 21  also shows two cells  1570 , each disposed in an aperture of an interposer  180 . As shown in  FIG. 21 , a contact member  1530  of each cell  1570  makes physical contact with a corresponding conductor.  
         [0097]     Although not shown in  FIG. 21 , when connector  100  is in use, the proximal end  1641  of each contact member  1530   a,b  contacts a conducting element on a circuit board connected to connector  100 . For example, end  1641  of contact member  1530   b  contacts a conducting element on circuit board  2190  and end  1641  of contact member  1530   a  contacts a conducting element on circuit board  2180 . Accordingly,  FIG. 21  illustrates that there is at least one electrical signal path from board  2190  to board  2180  through connector  100 . This electrical signal path includes conductor  214 , contact member  1530   b  and contact member  1530   a . As is appreciated by one skilled in the art, connector  100  provides multiple electrical signal paths from board  2190  and  2180 , wherein each signal path includes two contact members  1530  and a conductor on a board  120 .  
         [0098]     According to the embodiment illustrated in  FIG. 21 , each interposer is arranged in parallel relationship with one circuit board connected to connector  100 . More specifically, interposer  180   a  is in parallel relationship with circuit board  2180  and interposer  180   b  is in parallel relationship with circuit board  2190 . Accordingly, one face of interposer  180   a  faces board  2180  and one face of interposer  180   b  faces board  2190 .  
         [0099]     Referring now to  FIG. 22 ,  FIG. 22  is a cross-sectional view of the connector  100  and shows that when connector  100  is in use, as described above, each proximal end  1641  of each contact member  1530  contacts a conducting element  2194  on circuit board  2190 . In a preferred embodiment, each conducting element  2194  is a signal pad, and not a via. Accordingly, in a preferred embodiment, connector  100  is a compression mount connector because each proximal end  1641  merely presses against the circuit board and is not inserted into a via in the circuit board. However, in other embodiments, each element  2194  may be a via or other electrically conducting element.  
         [0100]     In a preferred embodiment, the board  2190  includes a differential signal path that includes a first signal path  2196   a  (e.g., a first trace) and a second signal path  2196   b  (e.g., a second trace). As shown, the first pad  2194  is connected to the first signal path  2196   a  and the second conducting element  2194   b  is is connected to the first signal path  2196   b . It should be noted that the second circuit board  2180  may also have a pair of conducting elements, like elements  2194 , electrically connected to a pair of signal paths, like paths  2196 .  
         [0101]     As shown in  FIG. 22 , a cell  1570  is inserted into an aperture of interposer  180 . As further shown, the distal end of each contact member  1530  of cell  1570  extends beyond the upper face  2250  of the interposer and the proximal end  1641  of each contact member  1530  extends beyond the bottom face  2251  of the interposer, which faces board  2190  and is generally parallel thereto. Each proximal end  1641  presses against a conducting element  2194  on board  2190 . Likewise, each contact portion  1745  of contact member  1530  presses against a conductor on board  120 . Thus, a contact member  1530  electrically connects a conductor on board  120  with a conducting element  2194  on board  2190 . As illustrated in  FIG. 22 , the ends of the conductors on board  120  are near the upper face  2250  of interposer.  
         [0102]     When end  1641  of a contact member  1530  presses against a corresponding element  2194  a normal force caused by the element is exerted on the contact member. Because the contact member  1530  is held firmly within housing  1570 , the normal force will cause housing  122  to move in the direction of the normal force (i.e., away from the circuit board  2190 ). However, springs  1520  limit how far housing  122  will move away from board  2190  because when the housing  122  moves away from board  2190 , springs  1520  will compress and exert a force on the housing in a direction that is opposite of the direction of the normal force caused by board  2190 . This is so because the distal ends of the springs abut a surface of a spacer  110  and the spacer is firmly attached to the interposer  180 , which itself does not move relative to the board  2190 . Thus, springs  1502  will compress and exert a force on housing in a direction opposite the normal force.  
         [0103]     Referring back to  FIG. 1 , each spacer  110  may be configured to attach to an elongate backbone  150 . Additionally, connector  100  may include two end caps  100   a  and  100   b , each of which is designed to attach to a respective end of backbone  150 . The backbone  150  and end caps  100  are discussed below.  
         [0104]     Referring to  FIG. 23 ,  FIG. 23  illustrates an embodiment of backbone  150 . Backbone  150 , according to the embodiment shown, includes bosses  2300  arranged to mate with the end caps  100  as well as slots  2320 , each arranged to receive finger  440  of a spacer  110 , as shown in  FIG. 27 . Backbone  150  may further include tines  2330  arranged to mate with the spacers  110 .  
         [0105]     Referring to  FIG. 24 ,  FIG. 24  illustrates an embodiment of an end cap  199 . End cap  199 , according to the embodiment shown, includes apertures  2402  arranged to mate with bosses disposed on adjacent spacers as well as bosses  2300  disposed on the backbone  150 . The end cap  199  further includes both a screw  2420  and a pin  2410  arranged to mechanically interface connector  100  with a circuit board, which may have a large number of layers, for example, more than  30  layers, as well as a tongue  2430  arranged to mate with an end plate  190   b  (see  FIGS. 1 and 25 ).  
         [0106]     While the end cap  199  is illustrated as being symmetrical, that is, can be used on either end of connector  100 , separate left and right-handed end caps may also be used. The screw  2420  and pin  2410  of the end cap  199  may be integrally formed with the end cap  199  or may be attached thereto after fabrication of the end cap  199 . It has been found that it is often necessary to utilize a metal rather than a plastic screw  2420  in view of the mechanical stresses involved. It is understood that the present invention is not limited to the use of a screw  2420  and pin  2410  but rather other fastening means may also be used.  
         [0107]     As noted previously, both the end caps  100  and spacers  110  can be fabricated of an insulative material, such as a plastic, covered with a conductive material to provide electromagnetic shielding or can be fabricated entirely of a conductive material, such as a metal.  
         [0108]      FIG. 25  is an exploded view of backbone  150  and an end cap  199  and  FIG. 26  is a view of a backbone  150  and an end cap  199  assembled together.  
         [0109]     Referring to  FIGS. 25 and 26 , the bosses  2300  of the backbone  150  are disposed within corresponding apertures  2402  in the end caps  100  forming a rigid structure. The use of bosses  2300  and apertures  2402  is for exemplary purposes and the present invention is not limited thereto. That is, other fastening means can be used to mechanically connect the backbone  150  to the end caps  100 .  
         [0110]     Furthermore, as shown in  FIG. 27 , a combination of fingers  440  and mating slots are used to mechanically connect the spacers  110  to the backbone  150 . The illustrated combination is for exemplary purposes and the present invention is not limited thereto. In a similar fashion, as discussed above, the fingers  435 ,  437 ,  835 ,  837  of the spacers  110  are arranged to mate with corresponding slots in the interposer  180 . The illustrated combination of fingers and slots is for exemplary purposes and the present invention is not limited thereto.  
         [0111]     Referring back to  FIG. 1 ,  FIG. 1  shows that connector  100  may also include a two mounting clips  190   a  and  190   b  and a shield  160 . Mounting clips  190  and shield  160  are combined with the above described parts of the connector  100  to form a composite arrangement. The mounting clip  190  and shield  160  may be electrically conductive so as to electromagnetically shield the signal carrying elements of connector  100 . The mounting clip  190  and shield  160  will be discussed in detail below.  
         [0112]      FIG. 28  illustrates an embodiment of mounting clip  190   b . Mounting clip  190   b , according to the embodiment shown, includes: (a) pins  2860  arranged to mate with a hole in a circuit board (e.g., board  2190  or  2180 ) and (b) slots  2870  arranged to receive the tongues and  2430  of the end caps  100 . Pins  2860  function to connect clip  190   b  to a circuit board by mating with the circuit board holes mentioned above. Pins  2860  may be electrically conducting and may electrically and physically connect to a ground plane of the circuit board to which it is connected.  
         [0113]      FIG. 29  is an exploded view of clip  190   b  and end cap  199  and  FIG. 30  is a view of clip  190   b  having an end cap  199  attached thereto. As shown in  FIG. 30 , tongue  2430  of end cap  199  is arranged to mate with a corresponding slot  2870  in clip  190   b . As with the other illustrated fastening means, the present invention is not limited to the use of a tongue and corresponding slot.  
         [0114]     Referring now to  FIG. 31 ,  FIG. 31  illustrates an embodiment of shield  160 . Shield  160 , according to the embodiment shown, includes hooks  3100  arranged to fit in slots in an interposer  180 .  FIG. 32  is an exploded view of shield  160  and an interposer  180 .  FIG. 33  is a view of shield  160  being connected to an interposer  180 .  FIG. 33  illustrates how the hooks  3100  of shield  160  snap into slots in interposer  180 , thereby mechanically connecting the two.  
         [0115]      FIG. 34  is a view of an assembled connector with an interposer  180  and clip  190   a  omitted.  FIGS. 35 and 36  are different views of an almost fully assembled connector  100  according to one embodiment. When fully assembled, each aperture in each interposer holds a cell  1570 . Referring to  FIG. 35 ,  FIG. 35  shows end caps  199   a  and  199   b , shield  160 , interposer  180   a  and clip  190   b.    
         [0116]     Referring to  FIGS. 36 ,  FIG. 36  shows end caps  199   a  and  199   b , interposers  180   a  and  180   b , and clips  190   a  and  190   b . The clip  190   a  may be attached to the overall assembly by any usual fastening means and can include pins or other fastening means to attach the assembled connector  100  to a daughtercard, for example.  
         [0117]     The additional interposer  180   b  and additional clip  190   a  may be identical to the interposer  180   a  and end plate  190   b  or can be different (or not present at all), depending upon the application of the interconnection system assembly.  
         [0118]     While the two interposers  180  have been illustrated as being perpendicular to each other, the present invention is not limited thereto. That is, for some applications, the planes of the two interposers  180  can be at a 45-degree angle or other angle, for example. Thus, connector  100  need not be a “right-angle” connector.  
         [0119]     As can be seen from  FIGS. 34-36 , the entire interconnection system assembly attaches together to form a rigid structure in which the electrical conductors on the printed circuit boards  120  may be entirely electromagnetically shielded.  
         [0120]     While various embodiments/variations of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.