Abstract:
An electrical connector having an insulating housing, a plurality of first contacts ( 139 ), a plurality of second contacts ( 141,143 ), wherein the connector exhibits a desired characteristic impedance. The second contacts are angled relative to the first contacts and each has an edge ( 151 ) disposed adjacent to an edge or side of first contacts. An electrical connector as described above where the first contacts are signal contacts, the second contacts are power or ground contacts, and the desired impedance is approximately less than 50 ohms.

Description:
This Application contain benefit of provisional application Ser. No. 60/070,820 filed Jan. 8, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrical connector. More specifically, the present invention relates to a high speed electrical connector. 
     2. Brief Description of Earlier Developments 
     Technological advances in computer processors and memory impact the interconnection systems that couple the processors or memory to other components. One such technological advance is the increased speed of computer systems. The interconnect system must precisely control the electrical characteristics in order to interact properly with the processors or memory of these high speed computer systems. 
     While precisely controlling the electrical characteristics of the connector for compatibility, the design of the connector must also consider mechanical requirements such as high pin count, high pin density, low insertion force and low profile. The design of the connector must also be compatible with the processes used in making electronic assemblies, such as surface mount technology (SMT). Also important, the interconnection system must be cost effective. 
     One affect of these technological advances involves the desired characteristic impedance of the interconnection system. Current technology generally demands that the interconnection system exhibit a technology generally demands that the interconnection system exhibit a characteristic impedance of approximately 50 ohms. Future requirements, however, may require certain interconnection systems to exhibit lower characteristic impedance values, such as approximately 25-30 ohms. The interconnection system must match the characteristic impedance of the entire system, or risk the integrity of the signals that pass through. Mismatch can cause reflections that degrade the sub-nanosecond edge rates of the signals. 
     One solution to lowering the characteristic impedance of the connector utilizes bent contacts. The bend creates different pitch values on the mounting side and mating side of the connector. On the mounting side, for example, the contacts could have a common pitch, such as 0.050′ for attachment to a printed circuit board (PCB). On the mating side, the pitch could have a smaller value. While the smaller pitch value may decrease the characteristic impedance of the connector, this solution introduces other problems. In order to accommodate the bend, the contact must be longer. The longer contact could exhibit a greater inductance and could potentially create an impedance mismatch with other parts of the contact. The longer contact sacrifices the profile height of the connector. Finally, the bending process could potentially fracture the contact. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved electrical connector. 
     It is a further object of the present invention to provide an electrical connector compatible with future electronic systems. 
     It is a further object of the present invention to provide a tunable electrical connector. 
     It is a further object of the present invention to provide a controlled impedance electrical connector. 
     It is a further object of the present invention to provide an electrical connector with a low characteristic impedance. 
     It is a further object of the present invention to provide a high speed electrical connector that maintains a common contact pitch. 
     It is a further object of the present invention to provide a surface mounted, high speed electrical connector. 
     It is a further object of the present invention to provide a high pin count, high speed electrical connector. 
     It is a further object of the present invention to provide a high contact density, high speed electrical connector. 
     It is a further object of the present invention to provide a low profile, high speed electrical connector. 
     It is a further object of the present invention to provide a cost effective high speed electrical connector. 
     These and other objects are achieved, in one aspect of the present invention, by an electrical connector having an insulative housing, a plurality of signal contacts, and a plurality of ground or power contacts, wherein the connector exhibits a characteristic impedance of less than approximately 50 ohms. 
     These and other objects are achieved, in another aspect of the present invention, by an electrical connector, comprising: an insulative housing; a plurality of first contacts; and a plurality of second contacts angled relative to the first contacts. 
     These and other objects are achieved in another aspect of the present invention by an electrical connector, comprising: an insulative housing; a plurality of first contacts; a plurality of second contacts, each having an edge disposed adjacent an edge or side of one of the first contacts. 
     These and other objects are achieved in another aspect of the present invention by a method of making an electrical connector. The method includes the steps of: providing an insulative housing; providing a plurality of signal contacts; providing a plurality of ground or power contacts; inserting the signal contacts into the insulative housing; inserting the ground or power contacts into the insulative housing so that an edge of each ground or power contact is positioned adjacent one of the signal contacts. The electrical connector exhibits a desired characteristic impedance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other uses and advantages of the present invention will become apparent to those skilled in the art upon reference to the specification and the drawings, in which: 
     FIG. 1 is a bottom view of one component of a first alternative embodiment of the present invention; 
     FIG. 2 is a perspective view of the component shown in FIG. 1; 
     FIG. 3 is a top view of the component shown in FIG. 1; 
     FIG. 4 is a perspective view of another component of the first alternative embodiment of the present invention; 
     FIG. 5 a  is a top view of the component shown in FIG. 4; 
     FIG. 5 b  is a top view of an alternative arrangement of the component  25  shown in FIG. 4; 
     FIG. 6 is a perspective view of one component of a second alternative embodiment of the present invention; 
     FIG. 7 is a top view of the component shown in FIG. 6; 
     FIG. 8 is a perspective view of another component of the second alternative embodiment of the present invention; 
     FIG. 9 is a top view of the component shown in FIG. 8; 
     FIG. 10 is a perspective view of one component of a third alternative embodiment of the present invention; 
     FIG. 11 is a top view of the component shown in FIG. 10; 
     FIG. 12 is a perspective view of another component of the third alternative embodiment of the present invention; 
     FIG. 13 is a top view of the component shown in FIG. 12; 
     FIG. 14 is a top view of one component of a fourth alternative embodiment of the present invention; 
     FIG. 15 is a top view of another component of the fourth alternative embodiment of the present invention; 
     FIGS. 16 a-c  are schematics of the contact arrangement in the first alternative embodiment of the present invention; the second and a portion of the fourth alternative embodiment of the present invention; and the third alternative embodiment of the present invention, respectively; 
     FIGS. 17 a-c  demonstrate the estimated characteristic impedance at a central location and at an outer region of the first alternative embodiment of the present invention; the second and a portion of the fourth alternative embodiment of the present invention; and the third alternative embodiment of the present invention, respectively; 
     FIGS. 18 a-c  demonstrate the estimated near end cross-talk (NEXT) and far end cross-talk (FEXT) between contacts in a row of the first alternative embodiment of the present invention; the second and a portion of the fourth alternative embodiment of the present invention; and the third alternative embodiment of the present invention, respectively; 
     FIGS. 19 a-c  demonstrate the estimated near end cross-talk (NEXT) and far end cross-talk (FEXT) between contacts in a column of the first alternative embodiment of the present invention; the second and a portion of the fourth alternative embodiment of the present invention; and the third alternative embodiment of the present invention, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention generally relates to an electrical connector having an insulative housing and a plurality of contacts arranged thereon. To operate at high speeds, such as greater than 500 MHz, the signal contacts are surrounded by ground or power contacts. Each alternative embodiment of the present invention has a different arrangement of the contacts in order to achieve certain objectives. 
     The first alternative embodiment of the present invention will now be described with reference to FIGS. 1-4,  5   a ,  5   b  and  16   a . The connector includes a receptacle  101  and a plug  103 . A discussion of receptacle  101  and plug  103  follows. 
     With reference to FIGS. 1-3, receptacle  101  has an insulative housing  105  made from a suitable plastic, such as liquid crystal polymer  20  (LCP). Housing  105  can have a generally planar base  107  with a wall  109  extending around the perimeter. 
     Apertures  111  extend through housing  105  from a mating end  113  that faces plug  103  to a mounting end  115  that faces a substrate (not shown) to which receptacle  101  attaches. Contacts  117 ,  119  reside within apertures  111 , preferably by an interference fit. Contacts  117 ,  119  form an array of rows and columns on housing  105 . Rows align with arrow R in the figures and columns align with arrow C in the figures. Although FIGS. 2 and 3 display dual beam contacts  117 ,  119 , receptacle  101  could use other types of contacts. 
     Preferably, the end of contacts  117 ,  119  adjacent mounting end  115  has a fusible element, such as a solder ball  121 , secured thereto for surface mounting the connector to the substrate. International Publication number WO 98/15989 (International Application number PCT/US97/18066), herein incorporated by reference, describes methods of securing a solder ball to a contact and of securing a connector having solder balls to a substrate. Contacts  117 ,  119  could, however, secure to the substrate using other techniques. 
     Contact  117  preferably carries a signal, while contacts  119  carry ground or power. For high speed operations, four contacts  119  surround each contact  117  as shown in FIG.  2 . Two of the four contacts  119  reside in the same row as contact  117 , while the other two of the four contacts  119  reside in adjacent rows. 
     Contacts  119  that reside in the same row as contact  117  have generally the same orientation as contact  117 . Contacts  119  that reside in adjacent rows are angled relative to contact  117 . Preferably, contacts  119  that reside in adjacent rows are generally perpendicular to contact  117 . 
     Each contact  117 ,  119  has major surfaces defining sides  123  and minor surfaces defining edges  125 . As shown in FIGS. 2 and 3, an edge  125  of each contact  119  is adjacent contact  117 . Placing edge  125  of contact  119  nearest contact  117  more strongly couples contacts  117 ,  119  than when side  123  of contact  119  is placed adjacent contact  117 . 
     With reference to FIGS. 4 and 5 a , plug  103  has an insulative housing  127  made from a suitable plastic, such as liquid crystal polymer (LCP). Housing  127  can have a generally planar base  129  with a wall  131  extending around the perimeter. 
     Apertures  133  extend through housing  127  from a mating end  135  that faces receptacle  101  to a mounting end  137  that faces a substrate (not shown) to which plug  103  attaches. Contacts  139 ,  141 ,  143  reside within apertures  133 , preferably by an interference fit. Contacts  139 ,  141 ,  143  form an array of rows (aligned with arrow R) and columns (aligned with arrow C) on housing  127 . 
     Due to the close proximity of contacts  143  to contacts  139 , contacts  143  can have bent portions  145  to avoid interference with the beams of contacts  117  as they engage contacts  139  during mating. Although FIGS. 3 and 4 display blade-type contacts, plug  103  could use other types of contacts. 
     A series of projections  147  can extend from mating end  135  of housing  127 . Projections  147  are preferably formed during the injection molding step that forms housing  127 . In the embodiment shown in FIG. 5 a , projections  147  abut sides  123  of contacts  139 ,  141 ,  143 . Projections  147  can serve, for example, two purposes. First, projections  147  can help control the coupling between contacts  139  and contacts  141 ,  143 . Second, projections  147  can laterally support contacts  139 ,  141 ,  143  to improve rigidity. 
     In the alternative embodiment shown in FIG. 5 b , projections  147  can also reside in the area between contacts  139 ,  143 . The placement of a material between a ground and a signal contact controls characteristic impedance. Selecting a specific material, including air, helps tune characteristic impedance of the connector as a result of the dielectric constant of the material. 
     As with receptacle  101 , the end of contacts  139 ,  141 ,  143  adjacent mounting end  137  has a fusible element, such as a solder ball (not shown), secured thereto for surface mounting the connector to the substrate using, for example, ball grid array (BGA) technology. Contacts  139 ,  141 ,  143  could, however, secure to the substrate using other techniques. 
     Contact  139  preferably carries a signal, while contacts  141 ,  143  carry ground or power. For high speed operations, four contacts  141 ,  143  surround each contact  139  as shown in FIG.  4 . Contacts  141  reside in the same row as contact  139 , while contacts  143  reside in adjacent rows. 
     Contacts  141  have generally the same orientation as contact  139  since they reside in the same row. Contacts  143 , however, are angled relative to contacts  139 . Preferably, contacts  143  are generally perpendicular to contacts  139 . 
     Each contact  139 ,  141 ,  143  has major surfaces defining sides  149  and minor surfaces defining edges  151 . As shown in FIGS. 3 and 4, an edge  151  of each contact  141 ,  143  is adjacent contact  139 . Placing edges  151  of contacts  141 ,  143  nearest contact  139  more strongly couples contacts  139  with contacts  141 ,  143  than when sides  149  of contacts  141 ,  143  are  20  placed adjacent contact  139 . 
     FIG. 16 a  schematically demonstrates the contact arrangement in the first alternative embodiment of the present invention. As discussed above, four ground or power contacts G surround each signal contact S. Except for the ground or power contacts G around the exterior of the connector, each ground or power contact G provides shielding to more than one signal contact S. The use of ground or power contacts G to shield more than one signal contact S provides the first alternative embodiment of the present invention with the highest ratio of signal contacts to ground or power contacts. As an example, a 13×13 array connector with a total pin count of 114 could have 36 signal contacts and 78 ground or power contacts. The remaining alternative embodiments of the present invention described below have lower signal-to-ground ratios. 
     The second alternative embodiment of the present invention will now be described with reference to FIGS. 6-9 and  16   b . Features common to the other alternative embodiments will use the same reference character, save a change in the hundred digit. 
     The connector includes a receptacle  201  and a plug  203 . With reference to FIGS. 6 and 7, receptacle  201  has an insulative housing  205  made from, for example, a suitable plastic. Housing  205  can have a generally planar base  207  with a wall  209  extending around the perimeter. 
     Apertures  211  extend through housing  205  from a mating end  213  that faces plug  203  to a mounting end  215  that faces a substrate (not shown) to which receptacle  201  attaches. Contacts  217 ,  219  reside within apertures  211 , preferably by an interference fit. Contacts  217 ,  219  form an array of rows (aligned with arrow R) and columns (aligned with arrow C) on housing  205 . 
     As with the first alternative embodiment, receptacle  203  preferably surface mounts to the substrate using, for example, ball grid array (BGA) technology. 
     Contact  217  preferably carries a signal, while contacts  219  carry ground or power. This embodiment has six contacts  219  shielding contact  217 . Four of contacts  219  are arranged as described above with respect to the first alternative embodiment. The two additional contacts  219  reside in rows adjacent contacts  217  as shown in FIGS. 6 and 7. In other words, two of the six contacts  219  reside in the same row as contact  217 , while the other four of the six contacts  219  reside in adjacent rows. 
     Contacts  219  that reside in the same row as contact  217  have generally the same orientation as contact  217 . Contacts  219  that reside in adjacent rows are angled relative to contact  217 . Preferably, contacts  219  that reside in adjacent columns are generally perpendicular to contact  217 . 
     Each contact  217 ,  219  has major surfaces defining sides  223  and minor surfaces defining edges  225 . As shown in FIGS. 6 and 7, an edge  225  of each contact  219  is adjacent contact  217 . Placing edge  225  of contact  219  nearest contact  217  more strongly couples contacts  217 ,  219  than when side  223  of contact  219  is placed adjacent contact  217 . 
     With reference to FIGS. 8 and 9, plug  203  has an insulative housing  227  made from, for example, a suitable plastic. Housing  227  can have a generally planar base  229  with a wall  231  extending around the perimeter. 
     Apertures  233  extend through housing  227  from a mating end  235  that faces receptacle  201  to a mounting end  237  that faces a substrate (not shown) to which plug  203  attaches. Contacts  239 ,  241 ,  243  reside within apertures  233 , preferably by an interference fit. Contacts  239 ,  241 ,  243  form an array of rows (aligned with arrow R) and columns (aligned with arrow C) on housing  227 . 
     Due to the close proximity of contacts  243  to contacts  239 ,  241 , contacts  243  can have bent portions  245 . Bent portions  245  allow the beams of contacts  217 ,  219  engage contacts  239 ,  241  without interference. 
     A series of projections  247  can extend from mating end  235  of housing  227 . Projections  247 , preferably formed during the injection molding step that forms housing  227 , can abut sides  223  of contacts  239 ,  241 ,  243  and could also be placed between contacts  239 ,  243 . Projections  247  can help control the coupling between contacts  239  and contacts  241 ,  243 , and can laterally support contacts  239 ,  241 ,  243  to improve rigidity. 
     As with receptacle  201 , plug  203  can surface mount to the substrate using, for example, BGA technology. 
     Contact  239  preferably carries a signal, while contacts  241 ,  243  carry ground or power. As discussed earlier with respect to contacts  217 ,  219  of receptacle  201 , six contacts  241 ,  243  surround each contact  239  as shown in FIGS. 8 and 9. Contacts  241  reside in the same column as contact  239 , while contacts  243  reside in adjacent columns. 
     Contacts  241  have generally the same orientation as contact  239  since they reside in the same row. Contacts  243 , however, are angled relative to contacts  239 . Preferably, contacts  243  are generally perpendicular to contacts  239 . 
     Each contact  239 ,  241 ,  243  has major surfaces defining sides  249  and minor surfaces defining edges  251 . As shown in FIGS. 8 and 9, an edge  251  of each contact  241 ,  243  is adjacent contact  239  or adjacent another contact  241 . Placing edges  251  of contacts  241 ,  243  nearest contact  239  more strongly couples contacts  239  with contacts  241 ,  243  than when sides  249  of contacts  241 ,  243  are placed adjacent contact  239 . 
     FIG. 16 b  schematically demonstrates the contact arrangement in the second alternative embodiment of the present invention. As discussed above, six ground or power contacts G surround each signal contact S. When compared to the arrangement of the first alternative embodiment shown in FIG. 16 a , the second alternative embodiment places additional ground or power contacts G in the rows adjacent signal contacts S. 
     Most ground or power contacts G provide shielding to more than one signal contact S. However, since the second alternative embodiment uses additional ground or power contacts G than the first alternative embodiment, the signal-to-ground ratio is lower than the first alternative embodiment. As an example, an 11×15 array connector with a total pin count of 165 could have 35 signal contacts and 130 ground or power contacts. As will be discussed in more detail below, the lower signal-to-ground ratio allows the connector to operate at higher speeds. 
     The third alternative embodiment of the present invention will now be described with reference to FIGS. 10-13 and  16   c . Features common to the other alternative embodiments will use the same reference character, save a change in the hundred digit. 
     The connector includes a receptacle  301  and a plug  303 . With reference to FIGS. 10 and 11, receptacle  301  has an insulative housing  305  made from, for example, a suitable plastic. Housing  305  can have a generally planar base  307  with a wall  309  extending around the perimeter. 
     Apertures  311  extend through housing  305  from a mating end  313  that faces plug  303  to a mounting end  315  that faces a substrate (not shown) to which receptacle  301  attaches. Contacts  317 ,  319  reside within apertures  311 , preferably by an interference fit. Contacts  317 ,  319  form an array of rows (aligned with arrow R) and columns (aligned with arrow C) on housing  205 . 
     As with the other alternative embodiments, receptacle  303  preferably surface mounts to the substrate using, for example, ball grid array (BGA) technology. 
     Contact  317  preferably carries a signal, while contacts  319  carry ground or power. As with the other embodiments, contacts  319  surround contact  317  for shielding. Some of contacts  319  reside in the same row as contact  317 , while other contacts  319  reside in adjacent rows. 
     Contacts  319  that reside in the same row as contact  317  have generally the same orientation as contact  317 . However, contacts  319  that reside in adjacent rows are angled relative to contact  317 . Preferably, contacts  319  that reside in adjacent rows are generally perpendicular to contact  317 . 
     Each contact  317 ,  319  has major surfaces defining sides  323  and minor surfaces defining edges  225 . As shown in FIGS. 10 and 11, an edge  325  of each contact  319  that surrounds contact  317  is adjacent contact  317 . Placing edge  325  of contact  319  nearest contact  317  more strongly couples contacts  317 ,  319  than when side  323  of contact  319  is placed adjacent contact  317 . 
     With reference to FIGS. 12 and 13, plug  303  has an insulative housing  327  made from, for example, a suitable plastic. Housing  327  can have a generally planar base  329  with a wall  331  extending around the perimeter. 
     Apertures  333  extend through housing  327  from a mating end  335  that faces receptacle  301  to a mounting end  337  that faces a substrate (not shown) to which plug  303  attaches. Contacts  339 ,  341 ,  343  reside within apertures  333 , preferably by an interference fit. Contacts  339 ,  341 ,  343  form an array of rows (aligned with arrow R) and columns (aligned with arrow C) on housing  327 . 
     Due to the close proximity of contacts  343  to contacts  339 ,  341 , the end of contact  343  that faces contacts  339 ,  341  can have a bent portion  345 . Bent portions  345  allow the beams of contacts  317 ,  319  to engage contacts  339 ,  341  without interference. 
     A series of projections  347  can extend from mating end  335  of housing  327 . Projections  347 , preferably formed during the injection molding step that forms housing  327 , can abut sides  323  of contacts  339 ,  341 ,  343  and can be placed between contacts  339 ,  343 . Projections  347  can help control the coupling between contacts  339  and contacts  341 ,  343 , and can laterally support contacts  339 ,  341 ,  343  to improve rigidity. 
     As with receptacle  301 , plug  303  can surface mount to the substrate using, for example, BGA technology. 
     Contact  339  preferably carries a signal, while contacts  341 ,  343  carry ground or power. As discussed earlier with respect to contacts  317 ,  319  of receptacle  301 , contacts  341 ,  343  surround each contact  339  as shown in FIGS. 12 and 13. Contacts  341  reside in the same row as contact  339 , while contacts  343  reside in adjacent rows. 
     Contacts  341  have generally the same orientation as contact  339  since they reside in the same row. However, contacts  343  are angled relative to contact  339 . Preferably, contacts  343  are generally perpendicular to contact  339 . 
     Each contact  339 ,  341 ,  343  has major surfaces defining sides  249  and minor surfaces defining edges  251 . As shown in FIGS. 12 and 13, an edge  351  of each contact  341 ,  343  is adjacent contact  339  or adjacent another contact  341 . Placing edges  351  of contacts  341 ,  343  nearest contact  339  more strongly couples contacts  339  with contacts  341 ,  343  than when sides  349  of contacts  341 ,  343  are placed adjacent contact  339 . 
     FIG. 16 c  schematically demonstrates the contact arrangement in the third alternative embodiment of the present invention. As discussed above, ground or power contacts G surround each signal contact S. When compared to the arrangement of the second alternative embodiment shown in FIG. 16 b , the third alternative embodiment places an additional row of ground or power contacts G between rows containing signal contacts S. 
     Since only some ground or power contacts G provide shielding to more than one signal contact S, the signal-to-ground ratio is lower than the first or second alternative embodiment. As an example, a 12×17 array connector with a total pin count of 204 could have 32 signal contacts and 172 ground or power contacts. As will be discussed in more detail below, the lower signal-to-ground ratio allows the connector to operate at higher speeds than the earlier alternative embodiments. 
     The fourth alternative embodiment of the present invention will now be described with reference to FIGS. 14,  15  and  16   b . Features common to the other alternative embodiments will use the same reference character, save a change in the hundred digit. 
     The connector is a hybrid, with both plug  401  and receptacle  403  having high speed sections  453 ,  455  and low speed sections  457 ,  459 , respectively. High speed sections  453 ,  455  can have any of the earlier described alternative arrangements of ground and signal contacts. As specifically shown in FIGS. 14 and 15, high speed sections  453 ,  455  follow the arrangement from the second alternative embodiment. No further discussion of high speed sections  453 ,  455  is needed. 
     Low speed section  457  of receptacle  401  has an array of contacts  461  extending through housing  405 . Contacts  461  can have any arrangement, but FIG. 14 displays all contacts  461  having the same orientation. 
     Similar to receptacle  401 , low speed section  459  of plug  403  has an array of contacts  463 . Contacts  463  can have any arrangement, but FIG. 15 displays all contacts  461  having the same orientation. As with high speed section  455 , low speed section  459  may include projections  447  that extend from mating end  435  of housing  427 . Projections  247  can help control the coupling between contacts and can laterally support the contacts to improve rigidity. 
     The present invention can selectively tune the connector to achieve a desired characteristic impedance in several ways. One manner of achieving a desired characteristic impedance in a connector of the present invention adjusts the distance between the ground contacts and the signal contacts. Generally speaking, the closer a ground contact approaches a signal contact, the lower the characteristic impedance. By selecting a distance between signal and ground contacts, the present invention provides a tunable connector. Numerical methods can determine the distance required to achieve a specific characteristic impedance value. 
     Another manner of achieving a desired characteristic impedance in a connector of the present invention changes the geometric attributes of the ground or signal contacts while maintaining a common pitch. Preferably, the width of the ground contacts are adjusted to achieve the desired characteristic impedance. Adjusting the width of the ground contact changes the size of the edge that faces the signal contact. A larger edge more strongly couples with the signal contact. By selecting an aspect ratio (e.g. by adjusting width), the present invention provides a tunable connector. As discussed above, numerical methods can determine the aspect ratio required to achieve a specific characteristic impedance value. 
     A third manner of achieving a desired characteristic impedance is the placing of a dielectric material between the signal and ground contacts. The dielectric constant of the material placed between a ground and a signal contact determines the characteristic impedance of the connector. Selecting a specific material, including air, to reside between a signal and ground contact provides a tunable connector. As discussed above, numerical methods can determine the type, size and placement of the dielectric material relative to the ground and signal contacts required to achieve a specific characteristic impedance value for the connector. 
     FIGS. 17 a-c ,  18   a-c  and  19   a-c  demonstrate the estimated advantages of the several alternative embodiments of the present invention. 
     PROPHETIC EXAMPLE 1 
     A theoretical electrical connector was created using IFS CONNECT, a boundary element field solver available from Interactive Products Corporation, and the Simulation Program with Integrated Circuit Emphasis (SPICE) simulation program available in the public domain. The connector in this first example resembles the alternative embodiment of the present invention shown in FIGS. 1-4,  5   a ,  5   b  and  16   a.    
     Then, the characteristic impedance of the theoretical connector was estimated by exciting the connector model with a simulated Time Delay Reflectometer (TDR) circuit. FIG. 17 a  displays the estimated characteristic impedance at two locations on the theoretical connector. The first location, associated with the lower impedance value, resides at a central location on the connector. The second location, associated with the higher impedance value, resides along an outer region of the connector. 
     The IFS CONNECT and the SPICE simulation programs then estimated the cross-talk characteristics of the simulated connector. FIG. 17 b  displays the cross-talk performance between contacts residing in the same row. FIG. 17 c  displays the cross-talk performance between contacts residing in the same column. 
     PROPHETIC EXAMPLE 2 
     The same tests were performed on a theoretical electrical connector resembling the alternative embodiment of the present invention shown in FIGS. 6-9 and  16   b . FIG. 17 b  displays the estimated characteristic impedances of the simulated connector. The characteristic impedance values are generally the same as the first alternative embodiment. FIGS. 18 b  and  19   b  display the cross-talk performance of the simulated connector. This embodiment displays improved cross-talk performance over the first alternative embodiment. 
     PROPHETIC EXAMPLE 3 
     The same tests were performed on a theoretical electrical connector resembling the alternative embodiment of the present invention shown in FIGS. 10,  11  and  16   c . FIG. 17 c  displays the estimated characteristic impedances of the simulated connector. The characteristic impedance values are generally the same as the first and second alternative embodiments. FIGS. 18 c  and  19   c  display the cross-talk performance of the simulated connector. This embodiment displays improved cross-talk performance over the first and second alternative embodiments. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.