Abstract:
An electrical connector, comprising: a frame; and a plurality of modules retained by the frame. Each module has: a housing; a plurality of contacts in the housing; and a plurality of fusible elements secured to the contacts for mounting the connector to a substrate. An electrical connector, comprising: a frame having a plurality of walls defining a perimeter of the connector and defining at least one opening; and a plurality of modules positioned within the at least one opening. Each module has: a housing; a plurality of contacts in the housing; and a plurality of fusible elements secured to the contacts for mounting the connector to a substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/216,574, filed on Dec. 18, 1998, U.S. Pat. No. 6,155,860 which is a continuation-in-part of U.S. Pat. Ser. No. 09/209,132, filed on Dec. 10, 1998, U.S. Pat. No. 6,093,042, both of which claim benefit to U.S. Provisional Patent Application serial No. 60/073,281, filed on Jan. 31, 1998. All three applications are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrical connector. More specifically, the present invention relates to an electrical connector which has a plurality of housings. 
     2. Brief Description of Earlier Developments 
     Improvements in computer systems and communications equipment generally involve miniaturization and increased operating speeds. Designers must adapt the electrical connectors used in these systems to handle such changes. 
     Several types of electrical connectors exist that have adapted to miniaturization and to the increased operating speeds. One type is a zero insertion force (ZIF) connector. ZIF connectors use a mechanism either to spread a contact apart before receiving its mating contact or to provide mechanical advantage to a contact so that it may spread apart and engage its mating contact. 
     While beneficial in larger applications, current ZIF designs may not be preferred in high contact density situations. ZIF connectors can be complex and costly, particularly when miniaturization is required. In addition, the smaller actuators may not have sufficient strength to spread a contact apart or to mate the contacts. The actuators also may not fit within footprint limitations. Finally, ZIF connectors may not provide sufficient contact wipe to ensure a stable electrical contact. 
     Another type of electrical connector uses contacts with differential heights. Some of the contacts reside at one elevation, while the others reside at a different elevation. The taller contacts mate first, followed by the shorter contacts. As a result, the connector exhibits a lower peak insertion force. The peak insertion force is lower because not all of the connectors mate in parallel (i.e. at the same time). 
     Connectors with differential height contacts, however, may not be preferred in high contact density situations. In miniaturized connectors, producing differential height contacts are viewed as impractical, and are likely to be unsuccessful. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a modular electrical connector. 
     It is a further object of the present invention to provide an electrical connector which has a plurality of housings. 
     It is a further object of the present invention to provide an electrical connector with enhanced thermal reliability. 
     It is a further object of the present invention to provide an electrical connector that exhibits a reduced potential for warp. 
     It is a further object of the present invention to provide an electrical connector that offsets the effects of the differences in the coefficient of thermal expansion (CTE) of the connector and the substrate to which the connector mounts. 
     It is a further object of the present invention to provide an electrical connector having an array of fusible elements that are generally coplanar. 
     These and other objects of the present invention are achieved in one aspect of the present invention by an electrical connector, comprising: a frame; and a plurality of modules retained by the frame. Each module has: a housing; a plurality of contacts in the housing; and a plurality of fusible elements secured to the contacts for mounting the connector to a substrate. 
     These and other objects of the present invention are achieved in another aspect of the present invention by an electrical connector, comprising: a frame having a plurality of walls defining a perimeter of the connector and defining at least one opening; and a plurality of modules positioned within the at least one opening. Each module has: a housing; a plurality of contacts in the housing; and a plurality of fusible elements secured to the contacts for mounting the connector to a substrate. 
     These and other objects of the present invention are achieved in another aspect of the present invention by a surface mount electrical connector having a housing with contacts therein. The improvement comprises a plurality of modules forming the housing. 
    
    
     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 perspective view of a first alternative embodiment of the present invention in an unmated condition; 
     FIG. 2 is a perspective view of the first alternative embodiment in a mated, open condition; 
     FIG. 3 is a perspective view of the first alternative embodiment in a mated, closed condition; 
     FIG. 4 is a plan view of one component of the first alternative embodiment of the present invention; 
     FIG. 5 is a plan view of another component of the first alternative embodiment of the present invention; 
     FIG. 6 is a side view of the first alternative embodiment in a mated, closed condition; 
     FIG. 7 is a perspective view of a second alternative embodiment of the present invention in an unmated condition; 
     FIG. 8 is a perspective view of a second alternative embodiment of the present invention in a mated, open condition; 
     FIG. 9 is a perspective view of a second alternative embodiment of the present invention in a mated, closed condition; 
     FIG. 10 is a plan view of one component of the second alternative embodiment of the present invention; 
     FIG. 11 is a plan view of another component of the second alternative embodiment of the present invention; 
     FIG. 12 is a side view of the second alternative embodiment in a mated, closed condition; 
     FIG. 13 is a graph depicting the insertion forces for mating a conventional connector compared to mating a connector of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-12 display several alternative embodiments of the present invention. In general, the present invention is a board-to-board electrical connector having plug and receptacle portions. Rather than mating the contacts in parallel (i.e. all of the contacts at the same time), the plug and receptacle portions sequentially mate the contacts. The present invention achieves sequential mating of the contact by preferably rotating the plug portion relative to the receptacle portion. Hinge assemblies on the plug and receptacle portions interface to allow rotation and to precisely align the contacts on the plug and receptacle portions. The sequential mating of the contacts in the present invention preferably exhibits a lower peak mating force that electrical connectors that mate the contacts in parallel. 
     FIGS. 1-6 display one alternative embodiment of the present invention. An electrical connector  100  includes a plug portion  101  and a receptacle portion  103 . Connector  100  preferably interconnects two substrates S such as printed circuit boards (PCBs) as seen in FIG.  6 . Plug  101  and receptacle  103  are removably engageable as shown in FIGS. 1-3. Once engaged, plug  101  can rotate relative to receptacle  103  from the open position shown in FIG. 2 to the closed position shown in FIG.  3 . Rotation of plug  101  relative to receptacle  103  allows the sequential mating of the contacts. Plug  101  and receptacle  103  will now be individually described in greater detail. 
     As seen in FIGS. 1 and 4, plug  101  has a generally planar insulative housing  105 , preferably manufactured from a plastic, such as liquid crystal polymer (LCP). Housing  105  has a mounting end  107  that faces substrate S and a mating end  109  that faces receptacle  103 . An array of apertures  147  extend through housing  105  from mounting end  107  to mating end  109 . 
     An array of contacts  111  reside within apertures  147  in housing  105 . Apertures  147  preferably retain contacts  111  within housing  105  using, for example, a projection  149  extending into aperture  147  from a side wall. Contacts  111  remain within apertures  147  by an interference fit with projection  149 . As seen in FIG. 4, each contact  111  generally parallels sides  113 ,  115  of housing  105 , and is generally perpendicular to a leading edge  117  and a trailing edge  119  of housing  105 . Since plug  101  and receptacle  103  mate along an axis that is generally parallel to trailing edge  119 , contacts  111  are also generally perpendicular to the mating axis of connector  100 . 
     Contacts  111  form a series of rows and columns on housing  105 . As used throughout, a row refers to a group of contacts  111  that extend along the length of housing  105  from leading edge  117  to trailing edge  119 . A columns refer to a group of contacts  111  that extend along the width of housing  105  between sides  113 ,  115 . 
     Although the figures display blade-type contacts on the plugs, other types of contacts, such as round pins, could be used with the present invention. In addition, the connector could employ several different types of contacts at one time. For example, some contacts could carry a signal or ground, while others carry power. This, for example, allows the connectors of the present invention to be hot matable. 
     Housing  105  has a wall  121  extending around the perimeter to protects contacts  111  from damage. As seen in FIG. 1, wall  121  could extend around the entire perimeter of housing  105 . 
     Leading edge  117  of housing  105  includes a tab  123  to assist the user in rotating plug  101  to mate and to unmate with receptacle  103 . Trailing edge  119  of housing  105  includes a hinge assembly  125  that allows plug  101  to rotate relative to receptacle  103  and to properly align the contacts on plug  101  and receptacle  103 . Hinge assembly  125  extends generally parallel to the plane of housing  105 . A description of the components of hinge assembly  125  follows. 
     A pair of extensions  127  project outwardly from trailing edge  119  of housing  105 , each adjacent a respective side  113 ,  115 . Each extension  127  has a curved element  129  flanked by a pair of arms  131 . As seen in FIG. 1, curved elements  129  have a first surface  133  shaped to engage a hinge pin on receptacle  103  and a second surface  135  opposite first surface  133  shaped to interact with a block  183  on receptacle  103 . 
     Each outermost arm  131  has an outwardly facing, or exterior surface  187 ,  189 . Surfaces  187 ,  189  interact with corresponding surfaces on the hinge assembly of receptacle  103  to ensure proper alignment of the contacts during mating. 
     A centrally located extension  137  also projects outwardly from a central location on trailing edge  119  of housing  105 , but extends in a direction opposite of extensions  127 . Central extension  137  has a curved element  139  flanked by a pair of arms  141 . Curved elements  139  have a first surface  143  shaped to engage a hinge pin on receptacle  103  and a second surface  145  opposite first surface  133  shaped to interact with a block on receptacle  103 . 
     As seen in FIG. 6, connector  100  provides a board-to-board interconnection. Accordingly, plug  101  must mount to substrate S, preferably prior to mating with receptacle  103 . Plug  101  preferably mounts to substrate S using reflow techniques, in particular Ball Grid Array (BGA) technology. As seen in FIG. 3, a fusible element  151 , such as a solder ball, secures to a tail portion (not shown) of contact  111 . 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. Fusible element  151  resides, at least partially, within an enlarged portion  153  of aperture  147 . 
     FIG. 5 shows receptacle  103  having a generally planar insulative housing  155 , preferably manufactured from a plastic such as LCP. Housing  151  has a mounting end  157  facing substrate S and a mating end  159  facing plug  101 . An array of apertures  161  extend through housing  151  from mounting end  153  to mating end  155 . 
     An array of contacts  163  reside within apertures  161  in housing  155 . Contacts  163  can be dual beam contacts and can be retained by the apertures in the same manner as described earlier and as described in International Publication number WO 98/15989. As seen in FIG. 5, each contact  163  generally parallels sides  165 ,  167  and is generally perpendicular to a leading edge  169  and a trailing edge  171  of housing  155 . Since plug  101  and receptacle  103  mate along an axis that is generally parallel to trailing edge  171 , contacts  163  are also positioned generally perpendicular to the mating axis of connector  100 . 
     In order to mate with contacts  111  of plug  101 , contacts  163  of receptacle  103  form a series of rows and columns on housing  155 . As seen in FIGS. 1 and 2, contacts  163  preferably all have the same elevation. This simplifies the assembly of receptacle  103 . 
     Also shown in FIGS. 1 and 2, the individual beams of each dual beam contact  163  preferably have the same length as the other beam. This reduces the amount of material required to form the contact and simplifies the contact forming process. 
     Housing  155  can have a wall  173  extending around the perimeter to protect contacts  163  from damage. As seen in FIG. 5, wall  173  does not extend around the entire perimeter of housing  155 . Wall  173  has a discontinuity at trailing edge  165 . The discontinuity in wall  173  allows hinge assembly  125  of plug  101  to interact with the hinge assembly of receptacle  103  for complete mating of plug  101  and receptacle  103 . 
     Wall  173  includes a recessed portion  175  at leading edge  163  of housing  151 . Recessed portion  175  receives tab  123  on plug  101  when in the mated, closed condition shown in FIGS. 3 and 6. 
     Trailing edge  171  of housing  155  includes a hinge assembly  177  that allows plug  101  to rotate relative to receptacle  103 . Hinge assembly  177  extends generally parallel to the plane of housing  155 . Hinge assembly  177  includes a hinge pin  179  braced by a series of supports  181  along trailing edge  171  of housing  155 . 
     A series of blocks  183  extend from trailing edge  171  between adjacent supports  181 . Blocks  183  have curved surfaces  185  that correspond to second surfaces  133 ,  143  of extensions  127  and central extension  137 , respectively. Curved surfaces  185  of blocks  183  have substantially the same shape as second curved surfaces  135 ,  145  of extensions  127  and central extension  137 . Specifically, curved surfaces  135 ,  145 ,  185  are circular and have generally the same radius of curvature to ensure proper meshing of hinge assemblies  125 ,  177  along the entire mating path. Precise movement of hinge assemblies  125 ,  177  ensures proper alignment of contacts  111 ,  163  in plug  101  and receptacle  103  during mating. 
     Each outermost support  181  includes an interior, or inwardly facing surface  195 ,  197  of an adjacent block  183 . Surfaces  195 ,  197  interact with surfaces  187 ,  189  of hinge assembly  125  to ensure proper alignment of the contacts during mating. Specifically, surfaces  187 ,  189  abut surfaces  195 ,  197  to laterally align plug  101  relative to receptacle  103 . This helps ensure proper alignment of contacts  111 ,  163  during mating. 
     As previously discussed, connector  100  provides a board-to-board interconnection. Receptacle  103  preferably mounts to substrate S using reflow techniques, in particular BGA technology. A fusible element, such as a solder ball, secures to a tail portion (not shown) of contact  163  using, for instance, the methods described in the aforementioned International Publication number WO 98/15989. The fusible element resides, at least partially, within an enlarged portion (not shown) of aperture  161  similar to enlarged portion  153  of plug  101 . 
     The mating of plug  101  and receptacle  103  will now be described with reference to FIGS. 1-3. Initially, plug  101  and receptacle  103  are separate, or unmated, as shown in FIG.  1 . To interface plug  101  and receptacle  103 , hinge assemblies  125 ,  177  must mesh as shown in FIG.  2 . The features of hinge assemblies  125 ,  177 , plug  101  and receptacle enhance the ease of blind mating plug  101  and receptacle  103 . 
     Describing the mating in particular, extensions  127  and central extension  139  enter the openings formed between hinge pin  179 , extensions  181  and trailing edge  171  of housing  155 . Arms  131 ,  141  of hinge assembly  125  enter the areas flanking blocks  183  of hinge assembly  177 . Outer surfaces  187 ,  189  of arms  131  abut inner surfaces  195 ,  197  of supports  181  to laterally align plug  101  with receptacle  103  along an axis parallel to trailing edges  119 ,  171 . 
     In the mated, open condition shown in FIG. 2, curved surfaces  185  of blocks  183  begin to abut second surfaces  135 ,  145  of extensions  127  and central extension  137 . Surfaces  135 ,  145 ,  185  help longitudinally align plug  101  and receptacle  103  along an axis parallel to sides  113 ,  115 ,  165 ,  167  of plug  101  and receptacle  103 . Preferably, the other adjacent surfaces of arm  131 , supports  181  and blocks  185  have a clearance therebetween to reduce the amount of force required to rotate plug  101 . 
     Extensions  127  and central extension  137  provide a retaining force on opposite sides of hinge pin  179  due to the opposite orientation of central extension  137  relative to extensions  127 . The retaining forces, along with the placing of extensions  127  and central extension  137  between hinge pin  179  and trailing edge  119  of housing  105  prevents separation of plug  101  from receptacle  103 . In other words, plug  101  can only separate from receptacle  103  by reversing the mating process (i.e. rotating plug  101  away from receptacle  103 ). 
     The rotation of plug  101  begins the mating of contacts  111 ,  163 . Each contact  111  progressively enters into the space between the opposed arms of the dual beam contacts  163  during rotation. Each arm of the dual beam contact  163  interacts with an opposite surface of blade contact  111 . Contact  163  retains contact  111  between its resilient dual beams. The area between the dual beams of each contact  163  is generally parallel to the mating axis of plug  101  and receptacle  103 . 
     The column of contacts  111 ,  163  closest to trailing edges  119 ,  171  of plug  101  and receptacle  103  mate first. Mating progresses with each subsequent column away from trailing edges  119 ,  171  of plug  101  and receptacle  103 . 
     FIGS. 3 and 6 shows connector  100  in a fully mated and closed condition. While mated, wall  173  of receptacle  103  can surround wall  121  of plug  101  and tab  123  rests within recess  175  in leading edge  169  of receptacle  103 . 
     The difference in CTE of the substrates and the connector, and coplanarity of the fusible elements are two important considerations with large scale array connectors. CTE differential can introduce stress into the solder joints that couple the connector and the substrate. Solder joint stress potentially reduces the thermal reliability of the connector. CTE differential can also warp the connector. Connector warp potentially misaligns the mating connectors, increasing the required peak insertion force. Connector warp may also affect the coplanarity of the fusible elements that couple the connector to the substrate. 
     FIGS. 7-12 display another alternative embodiment of the present invention. This embodiment helps offset the effects of CTE differential and helps improve coplanarity by using a modular approach. The alternative embodiment utilizes several smaller components rather than a unitary, larger component. 
     An electrical connector  200  includes a modular plug portion  201  and a modular receptacle portion  203  for interconnecting two substrates S as shown in FIG.  12 . Plug  201  and receptacle  203  are removably engageable from the unmated condition shown in FIG. 7 to the intermediate, mated, open condition shown in FIG. 8, and ending at the mated, closed condition shown in FIG.  9 . Rotation of plug  201  relative to receptacle  203  allows the sequential mating of the contacts. Plug  201  and receptacle  203  will now be described in detail. 
     As shown in FIGS. 7,  9  and  10 , one component of modular plug  201  is a frame  205  that supports the remaining components. Frame  205  is made of a suitable material, including plastic or metal. Frame  205  can secure to substrate S using, for example, solder or a fastener (not shown). Frame  205  can provide additional rigidity to substrate S and may serve as a shield, to nearby electrical components, from electromagnetic interference (EMI). 
     Frame  205  has an outer wall  209  defining an opening sized to receive a desired number of removable housings  207 . As seen in FIG. 10, the opening is slightly larger than housing  207 . When receiving more than one housing  207 , frame  205  may include a web  211  that extends between opposed sides of frame  205 . Webs  211  add rigidity to frame  205  and also help retain housing  207 . In this instance, outer wall  209  and web  211  define the openings for housings  207 . 
     Wall  209  and web  211  have projections  213  extending into the opening. Projections  213  engage side walls of housing  207  and maintain housing  207  away from wall  209 . In other words, projections  213  provide a gap between housing  207  and wall  209  to accommodate any housing size variations and any movement of plug  201  during thermal cycles. 
     Wall  209  also has tabs  215  extending into the opening. In addition to engaging projections  213 , housing  207  rests on tabs  215  when fully inserted within the opening. The combination of housing  207  resting on tabs  215  and projections  213  engaging housing  207  ensures the retention of housing  207  within frame  205 . 
     Frame  205  includes a hinge assembly  217  at a trailing edge  219  to allow rotation of plug  201  relative to receptacle  203 . Frame  205  can be made from metal when, for example, conditions require additional strength from connector  200  or connector  200  will be subjected to numerous mating cycles. 
     Hinge assembly  217  includes extensions  221  projecting from trailing edge  219  of housing  105 . Each extension  221  has a curved element  223  flanked by a pair of arms  225 . Curved elements  223  have a first surface  227  shaped to engage a hinge pin on receptacle  203  and a second surface  229  opposite first curved surface  227  shaped to engage a block  277  on receptacle  203 . 
     Each outermost arm  225  includes an outwardly facing, or exterior surface  283 ,  285 . Surfaces  283 ,  285  interact with corresponding surfaces on the hinge assembly of receptacle  203  to ensure proper alignment of the contacts during mating. 
     A centrally located extension  231  also projects outwardly from a central location on trailing edge  219  of frame  205 , but extends in a direction opposite of extensions  221 . Central extension  231  has a curved element  233  flanked by a pair of arms  235 . Curved elements  233  have a first surface  237  shaped to engage a hinge pin on receptacle  203  and a second surface  239  opposite first curved surface  237  shaped to interact with block  277  on receptacle  203 . 
     Plug  201  includes a wall  241  projecting from a mating end  243  that faces receptacle  203 . Wall  241  at least partially extends around the perimeter of frame  205 . As seen in FIG. 10, wall  241  does not reside along trailing edge  219  so as not to interfere with hinge assembly  217 . Wall  241  can protect contacts  247  on housing  207  from damage. 
     When soldered to substrate S, frame  205  can include solder pads  291 . Solder pads  291  elevate the remainder of frame  205  from substrate S. Solder pads  291  may help transfer heat to the solder balls on housing  207  during the reflow process and may aid in any visual inspection of the solder balls after securing plug  201  to substrate S. In addition, solder pads  291  can aid in any cleaning that must be done between frame  205  and substrate S after securing to substrate S. 
     Frame  205  can also secure to substrate S in other manners. For example, frame  205  could have apertures (not shown) therethrough to receive a fastener (not shown), such as a screw, securable to substrate S. 
     The remaining component of modular plug  201  is at least one housing  207 . Housing  207  is generally planar and preferably manufactured from a suitable plastic, such as liquid crystal polymer (LCP). Housings  207  seat within the opening in frame  205 . 
     An array of apertures  245  extend through housing  207 . Contacts  247  reside within apertures  245 , preferably by interference fit. FIG. 10 displays contacts  247  as blade-type contacts, however other types of contacts, including round pins, could be used. 
     Contacts  247  form a series of rows and columns on housing  205 . Each contact  247  generally parallels a side  249  of plug  201  and is generally perpendicular to a leading edge  251  of plug  201 . 
     At a mounting end  253  of housing  207 , aperture  245  has an enlarged opening  255  to receive at least a portion of a fusible element  257 , such as a solder ball. Fusible element  257  secures to a tail end of contact  247 . As discussed with the first embodiment, International Publication number WO 98/15989 (International Application number PCT/US97/18066) describes methods of securing a solder ball to a contact. 
     Housing  207  can have notches  259  along its outer wall. Some notches  259  are sized to correspond to projections  213  of frame  205 , while other notches  259  are sized to correspond to tabs  215  of frame  205 . Notches  259  help align housing  207  within the opening in frame  205 . 
     Save a few features, receptacle  203  is identical to plug  201 . In order to avoid repetition, the following provides only a brief summary of the features of receptacle  203  that are similar to features in plug  201  and a more detailed description of the features that differ from plug  201 . 
     Modular receptacle  203  uses a frame  261  that receives at least one removable housing  263 . Frame  261  has a wall  265  bordering a portion of the perimeter. Wall  265  can help protect the contacts of housing  263 . To receive wall  241  of plug  201  during mating, frame  261  has a channel  267  located inwardly from wall  265 . 
     Frame  261  includes a hinge assembly  269  similar to the hinge assembly in the first alternative embodiment of the present invention. Hinge assembly  269  includes a hinge pin  271  braced by a series of supports  273  along a trailing edge  275  of frame  261 . 
     A series of blocks  277  extend from trailing edge  275  of frame  261  between adjacent supports  273 . Blocks  277  have curved surfaces  279  that correspond to second curved surfaces  229 ,  239  of extensions  221 ,  231 , respectively. Curved surfaces  279  of blocks  277  have substantially the same shape as second curved surfaces  229 ,  239  of extensions  221 ,  231 . Specifically, curved surfaces  229 ,  239 ,  279  are circular and have generally the same radius of curvature to ensure proper meshing of hinge assemblies  217 ,  269  along the entire mating path. Precise movement of hinge assemblies  217 ,  269  ensures proper alignment of contacts  247 ,  281  in plug  201  and receptacle  203  during mating. 
     Each outermost support  273  includes an interior, or inwardly facing surface  291 ,  293 . Surfaces  291 ,  293  interact with surfaces  283 ,  285  of hinge assembly  217  to ensure proper alignment of the contacts during mating. Specifically, outer surfaces  283 ,  285  abut surfaces  291 ,  293  to laterally align plug  201  relative to receptacle  203 . This helps ensure proper alignment of contacts  247 ,  281  during mating. The mating of plug  201  and receptacle  203  proceeds as shown in FIGS. 7-9 in the manner described above with respect to the first embodiment. 
     Housing  263 , save the type of contact, is identical to housing  207  of plug  201 . FIG. 11 demonstrates housing  263  using a dual beam-type contact  281  to mate with blade-type contact  247  of plug  201 . As with contact  247 , contact  281  can be any suitable type of contact. 
     FIG. 13 compares the estimated insertion forces for a typical connector and a connector of the present invention. As used herein, a typical connector refers to a connector in which all of the contacts mate in parallel. In other words, a typical contact mates all of the contacts at the same time. A typical connector produces the insertion force-versus-time path designated  901  in FIG. 13. A typical connector exhibits a peak at the point designated  903  along path  901 . The peak is located approximately midstream along the time period. 
     A connector of the present invention (using the same number of contacts, but sequentially mated) produces the insertion force-versus-time path designated  905  in FIG.  13 . The connector of the present invention exhibits a peak at the point designated  907  along path  905 . The peak is located approximately at the end of the time period. Clearly, the peak insertion force  907  of a connector of the present invention is well below the peak insertion force  903  of a typical connector. 
     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.