Abstract:
An electrical connector mountable to a substrate, including: a frame mountable to the substrate; a housing supported by the frame; and a plurality of contacts extending through said housing and mountable to the substrate. A socket for connecting an electrical component to a substrate, including: a housing; a frame; and a cover. The housing includes: a contact mountable to the substrate and adapted to engage a terminal of the electrical component, and guidance structure. The frame is mountable to the substrate and supports the housing. The cover movably secures to the frame and includes: guidance structure that corresponds to the guidance structure on the housing so that the cover aligns with the housing and can move between a first and a second position; and an opening so that the contact can engage the terminal of the electrical component.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority to Provisional Patent Application No. 60/147,120, filed on Aug. 04, 1999, and Provisional Patent Application No. 60/147,118, filed on Aug. 04, 1999, both of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electrical connectors. More specifically, the present invention relates to zero insertion force (ZIF) sockets. 
     2. Brief Description of Earlier Developments 
     A common application for ZIF sockets involves connecting a microprocessor to a circuit board. Each subsequent microprocessor generation poses greater demands on the socket design. For example, new microprocessors may require smaller centerline spacing between contacts, greater pin count or increased coplanarity. While conventional socket designs provide suitable results for existing microprocessors, these socket designs may not prove adequate in future generations of microprocessors. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrical connector that exhibits reduced stress levels at the solder joints. 
     It is a further object of the present invention to provide an electrical connector capable of accommodating mismatches in the coefficients of thermal expansion (CTE) of the various materials used in the electronic device. 
     It is a further object of the present invention to provide a socket that does not transmit forces caused by actuation of the socket to the solder joints. 
     It is a further object of the present invention to provide an electrical connector having satisfactory coplanarity. 
     It is a further object of the present invention to provide an electrical connector with improved manufacturability. 
     It is a further object of the present invention to provide an electrical connector exhibiting improved mold flow characteristics. 
     It is a further object of the present invention to provide an electrical connector with improved reliability. 
     It is a further object of the present invention to provide an electrical connector that exhibits greater flexibility. 
     It is a further object of the present invention to provide an electrical connector with a contact housing having greater compliancy. 
     It is a further object of the present invention to provide an electrical connector modularly assembled from several components. 
     It is a further object of the present invention to provide an electrical connector formed from loosely coupled components. 
     These and other objects of the present invention are achieved in one aspect of the present invention by an electrical connector mountable to a substrate, comprising: a frame mountable to the substrate; a housing supported by the frame; and a plurality of contacts extending through the housing and mountable to the substrate. 
     These and other objects of the present invention are achieved in another aspect of the present invention by a socket for connecting an electrical component to a substrate, comprising: a housing; a frame; and a cover. The housing includes: a contact mountable to the substrate and adapted to engage a terminal of the electrical component, and guidance structure. The frame mounts to the substrate and supports the housing. The cover movably secures to the frame and includes: guidance structure that corresponds to the guidance structure on the housing so that the cover aligns with the housing and can move between a first and a second position; and an opening so that the contact can engage the terminal of the electrical component. 
     These and other objects of the present invention are achieved in another aspect of the present invention by an electrical system, comprising: an electrical component having a terminal; a substrate having a conductive element; and an electrical connector mounted to the substrate and adapted to removably secure the electrical component to the substrate. The connector comprises: a housing; a frame; and a cover. The housing includes: a contact mounted to the substrate and adapted to engage a terminal of the electrical component, and guidance structure. The frame mounts to the substrate and supports the housing. The cover movably secures to the frame and includes: guidance structure that corresponds to the guidance structure on the housing so that the cover aligns with the housing and can move between a first and a second position; and an opening so that the contact can engage the terminal of the electrical component. 
    
    
     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 a  is a top perspective view of one alternative embodiment of a he present invention in an assembled state; 
     FIG. 1 b  is a bottom perspective view of the electrical connector in FIG. 1 a;    
     FIG. 2 is an exploded view all of the components and sub-assemblies forming the electrical connector in FIG. 1 b;    
     FIG. 3 a  is a top perspective view of one sub-assembly of the electrical connector in FIG. 1 a;    
     FIG. 3 b  is a bottom perspective view of the sub-assembly in FIG. 3 a;    
     FIG. 4 a  is a top perspective view of another sub-assembly of the electrical connector in FIG. 1 a;    
     FIG. 4 b  is a bottom perspective view of the sub-assembly in FIG. 4 a;    
     FIG. 5 a  is a detailed view of the sub-assembly shown in FIG. 4 a;    
     FIG. 5 b  is a bottom perspective view of one of the components in FIG. 4 a;    
     FIG. 5 c  is a cross-sectional view of the component in FIG. 5 a  taken along lines Vc—Vc; 
     FIG. 6 a  is a top perspective view of another component of the electrical connector in FIG. 1 a;    
     FIG. 6 b  is a detailed view of the component in FIG. 6 a;    
     FIG. 6 c  is a cross-sectional view of the component in FIG. 6 b  taken along lines VIb—VIb; 
     FIG. 7 a  is a perspective view of one component of the electrical connector in FIG. 2 a;    
     FIG. 7 b  is an opposite perspective view of the component in FIG.  7   a;    
     FIG. 7 c  is a cross-sectional view of the sub-assembly in FIG. 4 a  taken along lines VIIb—VlIb; 
     FIG. 8 a  is a top perspective view of another sub-assembly of the electrical connector in FIG. 1 a;    
     FIG. 8 b  is a bottom perspective view of the sub-assembly in FIG. 6 a;    
     FIG. 9 a  and  10   a  are a detailed view and a cross-sectional view (taken along line Xa—Xa), respectively, of the electrical connector in FIG. 1 a  in an open position; 
     FIGS. 9 b  and  10   b  are a detailed view and a cross-sectional view (taken along line Xa—Xa) of the electrical connector in FIG. 1 a  in a closed position; and 
     FIG. 11 is a perspective view of several components of an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Generally speaking, the present invention is an electrical connector used to connect a first electrical component to a second electrical component. More specifically, the present invention is a socket that connects a microprocessor interposer I having pins P disposed in an array (e.g. PGA) to a motherboard M. The socket receives interposer pins P with zero insertion force (ZIF). Preferably, the socket surface mounts to motherboard M, although other mounting methods could be used. Ball grid array (BGA) technology is the preferred surface mounting technique. 
     The socket is modular, with several sub-assemblies forming the socket. The components of the socket are designed to be flexible. When compared to a comparable unitary structure, the modular socket of the present invention is less rigid. Accordingly, the present invention can better handle stress build up caused by CTE differential between the various materials used in the interposer I, motherboard M and the socket. The present invention can also better handle stresses caused by the mating of the interposer pins P and the socket contacts than a comparable unitary structure. FIGS. 1 a - 10   b  present a first alternative embodiment of the present invention while FIG. 11 presents a second alternative embodiment. 
     FIGS. 1 a  and  1   b  provide a top and a bottom perspective view, respectively, of a socket  100 . A top  101  of socket  100  faces, and receives, interposer I. A bottom  103  of socket  100  faces, and mounts to, motherboard M. Although the various figures demonstrate socket  100  as being actuated by a hand tool T, such as a screwdriver, other actuation mechanisms (e.g. a lever rotating an eccentric cam) could be used. 
     As seen in FIG. 2, numerous components form socket  100 . Socket  100  could include, for example, a cover  201 , a plurality of contacts  303 , a spacer  305 , a contact housing contact housing  307 , a plurality of solder masses  309  and a base frame  401 . Contacts  303 , housing  305 , contact housing  307  and solder masses  309 , when assembled together, form contact housing sub-assembly  301 . As described in more detail below, assembly of socket  100  involves placing contact housing sub-assembly into base frame  401 , then securing cover  201  over base frame  401 . 
     Rather than rigidly assembling all of the sub-assemblies together, the present invention loosely couples the sub-assemblies. In other words, the sub-assemblies are not interference fit together. Rather, the various surfaces of the sub-assemblies abut without interference. 
     Without interference fitting, the present invention encourages some movement between the sub-assemblies. The relative movement of the sub-assemblies as a result of loose coupling helps absorb the stress caused by CTE differential and by the mating of interposer pins P and contacts  303 . Whereas a rigid socket would transmit the stresses to the solder joint, a loosely coupled connector does not transmit all of the forces between connected components. Rather, the loosely coupled components individually absorb any stresses. Any stress that might be transmitted between adjacent components is generally an insignificant amount. 
     The movement between loosely coupled components, while large enough to prevent stress build up in the solder joints, should also be sufficiently small to ensure and maintain proper orientation between the respective sub-assemblies. 
     FIGS. 3 a  and  3   b  display cover  201 . Preferably made from a suitable insulative material such as a high temperature thermoplastic, cover  201  has an upper wall  203  and opposed sidewalls  205 . 
     Since cover  201  must move across base frame  401 , the longitudinal axes of sidewalls  205  define the actuation direction indicated by line A. The top surface of upper wall  203  could include printed indicia  207  to assist the socket actuation process discussed below. 
     Upper wall  203  receives interposer I. Upper wall  203  includes a plurality of apertures  209  sized large enough to allow interposer pins P to pass freely therethrough, but sized small enough to provide lateral support to pins P during mating with contacts  303 . The pattern of apertures  209  on cover  201  corresponds to the pattern of interposer pins P. The present invention could, however, have patterns arranged differently than that shown in FIG. 3 a  in order to receive other interposers (such as an interposer with an interstitial pin grid array). 
     If designed for one specific interposer, the number of apertures  209  preferably equals the number of interposer pins. In order to, for example, accommodate interposers with differing pin counts, socket  100  could have more apertures  209  than interposer pins P. 
     As seen in FIG. 3 a , cover  201  could include a central opening  211 . Generally, cover  201  could have central opening  211  when the interposer provides pins only along its periphery (i.e. no pins at the center). Central opening  211  improves heat dissipation through socket  100  and helps make cover  201  more flexible. 
     Sidewalls  205  preferably act as latches to secure cover  201  to base frame  401 . Assembling socket  100  involves snap fitting sidewalls  205  over latch structure on base frame  401 . In order to allow cover  201  to snap fit onto base frame  401 , upper wall  203  could include relief slits  229 . 
     Once properly fitted over base frame  401 , recesses  213  on the inner surfaces of sidewalls  205  can accept the latch structure on base frame  401  without interference. Recesses  213  communicate with slits  229  in upper wall  203 . The lower surface of upper wall  203  rests upon the upper surface of base frame  401  when cover  201  successfully latches to base frame  401 . 
     The latch structure on base frame  401  freely travels within recesses  213  during actuation of socket  100  between an open and a closed position. In other words, the latch structure generally does interfere with the sidewalls that define recesses  213 . This loose coupling, along with the loose coupling of the various sub-assemblies of socket  100 , helps prevent 
     stresses from building up in the solder joints. The latch structure, while not interfering with recesses  213 , is sized so as to ensure proper alignment between cover  201  and base frame  401 . 
     Ribs  215  extend from a bottom surface of upper wall  203  as seen in FIG. 3 b  . Ribs  215  each have an outwardly directed face  217 . Face  217  engages actuating tool T used to urge socket  100  between the open and closed positions. Ribs  215  reside within correspondingly shaped openings in base frame  401  to aid in aligning cover  201  and contact housing sub-assembly  301  without interference. 
     The bottom surface of upper wall  203  also includes channels  219 . Channels  219  accept projections that extend upwardly from base frame  401 . The projections travel freely within channels  219  as socket moves between the open and closed positions. In other words, the projections generally do not interfere with the sidewalls defining channels  219 . While not interfering with channels, the projections do ensure adequate alignment between cover  201  and base frame  401 . Although shown in FIG. 3 b  as only a recess in cover  201 , channels  219  could extend entirely through upper wall  203  of cover  201 . 
     Upper wall  203  also has keyways  221 . Keyways  221  accept splines extending from contact housing sub-assembly  301  without interference. Keyways  221  have a guidance surface  223  extending between opposed stop surfaces  225 ,  227 . A corresponding surface on each spline abuts guidance surface  223  to ensure proper alignment between cover  201  (and, necessarily, interposer pins P) and contact housing sub-assembly (and, necessarily, the contacts) as socket  100  travels between the open and closed position. 
     In the closed position, a corresponding surface of each spline abuts stop surface  225 . In the open position, an opposite surface of each spline abuts stop surface  227 . In other words, stop surfaces  225 ,  227  determine the travel limits of cover  201 , while guidance surface  223  maintains alignment during movement. In order to have suitable flexibility, cover  201  could be manufactured as follows. Cover  201  could be injection molded using a liquid crystal polymer (LCP). Upper wall  203 , which has a 25×31 array of apertures  209  with 0.050″ centerline spacing that receive 0.12″ diameter interposer pins P, could have a thickness of approximately 1.00 mm. In addition, the thickness of sidewalls  205  could be 1.75 mm. 
     FIGS. 4 a  and  4   b  display assembled contact housing sub-assembly  301 . As discussed above, contact housing sub-assembly  301  includes contacts  303 , spacer  305 , contact housing  307  and solder masses  309 . If surface mounting of socket  100  is not required or if a different type of surface mount technique is used, solder masses  309  may not be required. Each component of contact housing sub-assembly  301  will now be described. 
     FIGS. 4 a ,  5   a ,  5   b  and  5   c  display spacer  305 , which is preferably used to increase the mating height of socket  100 . Spacer  305 , preferably made from a suitable insulative material such as a high temperature thermoplastic, has a planar base  311  with an array of apertures  313  therethrough. A peripheral wall  315  extends around, and upwardly from, base  311 . A peripheral recess  365  extends around base  311 . 
     Each aperture  313  frictionally retains a corresponding contact  303  therein. As shown in FIGS. 5 a  and  5   c , aperture  313  preferably has a tapered lead-in surface. The lead-in aids in the insertion of contacts  303  into spacer  305  and allows the arms of contact  303  to flex during insertion of interposer pin P. 
     As seen in FIG. 5 a , spacer  305  helps retain and stabilize contacts  303  using deformable ribs  331 . Preferably located at the four corners of aperture  313 , ribs  331  deform upon insertion of contact  303 , but have sufficient rigidity to prevent rotation of contact  303  during mating with interposer pin P. 
     While providing some rigidity to spacer  305 , the geometry of, and various features on, wall  315  also allow spacer  305  to flex. For instance, the inner surface of wall  315  includes channels  317  that correspond to the locations of cut-out sections on the outer wall of contact housing  307 . Channels  317  provide a reduced thickness section to wall  315 . This allows wall  315  to resile during insertion of contact housing sub-assembly  101  into base frame  401 , which is described in more detail below. As discussed earlier, a flexible spacer  305  is desired so that spacer  305 , rather than solder masses  309 , absorb stresses resulting from CTE mismatch or from interposer pins P mating with contacts  303 . 
     On opposed sides of spacer  305 , the outer surface of wall  315  includes blocks  319 . Blocks  319  extend past wall  315  as shown in FIG. 4 a  and reside within notches in base frame  401 . 
     Blocks  319  can have different sizes in order to prevent incorrect placement of contact housing sub-assembly in base plate  401 . That way, contact housing sub-assembly  301  could only mount on base plate  401  when blocks  319  align with correspondingly sized notches on base frame  401 . 
     The other opposed sides of wall  315  include splines  323 . Similar to blocks  319 ,  321 , splines  323  extend past wall  315  and reside within keyways  221  when cover  201  snap fits onto base frame  401 . Splines include a guidance surface  325  flanked by opposed stop surfaces  327 ,  329 . 
     In the closed position, stop surfaces  225 ,  327  abut. In the open position, stop surfaces  227 ,  329  abut. During actuation of socket  100  between the open and closed positions, guidance surface  223  of cover  201  travels along guidance surface  325  of contact housing sub-assembly  301 . This arrangement provides direct alignment between cover  201  (containing interposer pins P) and contact housing sub-assembly  301  (containing contacts  303 ). In other words, the manufacturing tolerances of base frame  401  do not affect the ability of interposer pins P and contacts  303  to align properly. 
     In addition, splines  323  also reside in notches  415  in base frame  401 . Since splines  323  are not interference fitted into notches  415 , no stress accumulation occurs. However, the splines are suitably sized relative to notches  415  in order to provide guidance. 
     Beneath blocks  319  and splines  321 , posts  367  extend past the lower surface of base  311  of spacer  305 . During the build up of contact housing sub-assembly  301 , posts  367  enter corresponding openings in the contact housing  307 . 
     Spacer  305  could be injection molded using a liquid crystal polymer (LCP). While the presence of the number apertures  313  helps increase the flexibility of housing  305 , additional flexibility may be required. Flexibility could be increased by adjusting the relative dimensions of housing  305 . For example, base  311  could have a thickness of 1.28 mm and peripheral wall  315  could have a height of 0.95 mm and a thickness of 0.75 mm. 
     FIGS. 4 b ,  6   a ,  6   b  and  6   c  display contact housing  307 . Similar to spacer  305 , contact housing  307  is made from a suitable insulative material such as a high temperature thermoplastic and includes a planar base  333  with an array of apertures  335  therethrough. A peripheral wall  337  extends around base  333 . 
     Each aperture  335  frictionally retains a corresponding contact  303  therein. As shown in FIGS. 6 b  and  6   c , aperture  335  preferably has a tapered lead-in surface. The lead-in aids in the insertion of contacts  303  into contact housing  307  and acts as a stop for shoulders  359 . Once shoulder  359  engages the lead-in portion of aperture  335 , contact  303  cannot extend further into aperture  335 . 
     Deformable ribs  361  in aperture  335  help contact housing  307  retain contacts  303 . Preferably, ribs  361  are centrally located on opposite side walls of aperture  335 . 
     Aperture  335  should also have a recess  363  at a mounting end. Recess  363  allows a portion of solder mass  309  to reside therein. 
     The outer surface of peripheral wall  337  includes various features that interact with corresponding features on base frame  401  to retain contact housing subassembly  301  in base frame  401 . Opposite sides of peripheral wall  337  include cut-out sections  339 . Cut-out sections  339  allow contact housing  307  to pass freely by latch structure on base frame  401  during placement of contact housing sub-assembly  301  into base frame  401 . The other opposite sides of peripheral wall  337  include notches  341 . When inserting contact housing  307  into base frame  401 , notches  341  rest on an upper surface of a ledge projects inwardly from a wall defining a central opening. 
     Each side of the inner surface of peripheral wall  337 , along with a corresponding portion of base  333 , includes an opening  369 . Openings  369  receive posts  367  on spacer  305 . 
     Contact housing  307  could be injection molded using a liquid crystal polymer (LCP). While the apertures help increase the flexibility of contact housing  307 , additional flexibility may be required. As with spacer  305 , the flexibility could be increased by adjusting the relative dimensions of contact housing  307 . For example, base  333  could have a thickness of 1.02 mm and peripheral wall  337  could have a height of 0.78 mm and a thickness of 0.75 mm. 
     FIGS. 7 a  and  7   b  display contact  303 . Contact  303 , preferably stamped and formed from a carrier strip of conductive material such as a copper alloy, has dual beams  343 ,  345  extending from one end of a base section  347 . The opposite end of base section  347  includes a mounting section  357  flanked by shoulders  359 . 
     Each beam  343 ,  345  has a respective lead-in portion  349 ,  351  between which pin P enters when socket receives interposer I on cover  201  in an open position (shown in phantom in FIG. 7 a ). Actuation of socket  100  towards a closed position moves pin P towards respective mating portions  353 ,  355  of beams  343 ,  345  (shown in phantom in FIG. 7 a ). Mating portions  353 ,  355  engage opposite sides of interposer pin P. 
     As seen in FIG. 7 b , beam  343  is shorter than beam  345 . Although engaging opposite sides of interposer pin P, beams  343 ,  345  engage pin P at different elevations on pin P. In order to balance the spring rates of beams  343 ,  345 , the width of long beam  345  can be greater than the width of short beam  343 . 
     A mounting section  357  extends from an opposite end of base section  347 . Preferably, mounting section  357  is a surface mount section. Although any surface mount termination could be used, FIG. 7 a  shows the preferred contact  303  capable of surface mounting to motherboard M using BGA technology. Furthermore, other mounting techniques (e.g. pin-in-paste, press-fit) could be used. International Publication numbers WO 98/15989 and WO 98/15991, herein incorporated by reference, describe methods of securing a solder mass  309 , such as a fusible solder ball, to a contact retained by an insulative housing and to a pad on a circuit substrate. 
     Preferably, constructing contact housing sub-assembly  301  involves the following. First, spacer  305  and contact housing  307  are stacked so that posts  367  enter and engage openings  369 . When stacked, peripheral recess  365  of spacer  305  rests on the upper surface of peripheral wall  337  and the bottom surface of base  311  of spacer  305  rests on the upper surface of base  333  of contact housing  307 . 
     Second, contacts  303  are inserted into apertures  313 ,  335  until shoulders  359  abut the tapered lead-in of aperture  335  of contact housing  307 . In that position, beams  343 ,  345  extend upwardly from spacer  305  and mounting portion  357  extends downwardly from contact housing  307 . 
     Finally, solder mass  309  is secured to contact  303  using, for example, the reflow techniques described in International Publication numbers WO 98/15989 and WO 98/15991. The combination of shoulder  357  of contact  303  abutting the tapered lead-in of aperture  313  and of solder mass  309  securing to mounting end  357  of contact  303  serves to lock connector housing sub-assembly  301  together. 
     FIGS. 8 a  and  8   b  display base frame  401 . As with the other components of socket  100 , base frame  401  is made from a suitable insulative material such as a high temperature thermoplastic. In order to have sufficient flexibility, base frame  401  has a generally rectangular shape with a central opening  403  along with various recessed areas. Base frame  401  secures to motherboard M independently of contact housing sub-assembly  301 . Specifically, a lower surface of base frame  401  can have solder pads  431  to surface mount to motherboard M. 
     Opposed ends of base frame  401  each include an opening  405  that receives a corresponding rib  215  on cover  201 . Openings  405  are appropriately sized to allow ribs  215  to travel freely therein as socket  100  travels between an open and a closed position. Opening  405  communicates with a notch  407 . A projection  409  extends from base frame  401  and encloses notch  407 . When cover  201  snap fits onto base frame  401 , openings  411  form between an edge of cover  201  and projection  409 . 
     Openings  411  are sized to allow entry of tool T to actuate socket  100 . Tool T enters and engages a bottom surface of opening  411 . The bottom surface of opening  411  provides the leverage point for tool T to move cover  201 . Since base frame  401  secures to motherboard M separately from contact housing sub-assembly  301 , any forces caused by tool T during actuation do not transfer to contact housing sub-assembly  301 . 
     Rotation of tool T moves cover  201  along base frame  401 . As shown in FIG. 9 b , when socket  100  is in an open position, pin P can freely enter aperture  209  and the space between dual beams  343 ,  345  of contact  303 . Upon actuation of socket  100  to a closed position as shown in FIG. 9 b , pins P engage mating portions  353 ,  355 . Dual beams  343 ,  345  resile in order to provide a suitable normal force to pins P. 
     The inner walls of base frame  401  that define central opening  403  include various features that help retain contact housing sub-assembly in base frame  401 . One set of opposite walls include ledges  413 . Contact housing sub-assembly  301 , specifically contact housing  307 , rests on the upper surfaces of ledges  413 . In other words, ledges  413  prevent contact housing sub-assembly  301  from exiting base frame  401 . 
     The other set of opposing walls has latching structures  417 . During insertion of contact housing sub-assembly  301  into base frame  101 , the reduced thickness portions of peripheral wall  315  and tapered surface  419  engage one another and deflect. Upon complete insertion, the reduced thickness portion of spacer  305  and tapered surface  419  resile to their normal, unloaded position. Once snap fitted onto base frame  401 , the upper surface of peripheral wall  315  abuts lower surface  421 . In other words, latching structures  417  prevent contact housing subassembly  301  from exiting base frame  401 . 
     As seen in FIG. 8 a , only ledges  413  and latching structure  417  retain contact housing sub-assembly  301  on base frame  401 . In addition, contact housing sub-assembly  301  fits within base frame  401  without interference. This loose coupling between base frame  401  and contact housing sub-assembly  301  helps prevent stresses from accumulating in the solder joints. 
     The inner walls of base frame  401  that define central opening  403  also include notches  415  that can accommodate splines  325 . Although contact housing sub-assembly nests within base frame  401 , splines  325  extend past the upper surface of base frame  401 . This allows splines  325  to enter keyways  221  in cover  201 . 
     The inner walls of base frame also include notches  423  flanked by latching structures  417 . Notches  423  receive blocks  319  on contact housing sub-assembly  301 . Blocks  319 , however, do not extend past the upper surface of base frame  401 . Blocks  319  and splines  325  are not interference fitted in to notches  423 ,  415 , respectively. Notches  415 ,  423  do, however, provide guidance to contact housing sub-assembly  301 . 
     Opposite sides of the outer edge of base frame  401  includes latching structure  425 . Latching structure  425  retains cover  201  on base frame  401 . Sidewalls  205  of cover  201  deflect upon engaging tapered walls  427  of latching structures  425 . Upon full engagement, sidewalls  205  resile to their normal position, with the walls that define recesses  213  engaging lower surface  429 . In this position, cover  201  is secured to base frame  401 , but movable relative therealong between the open and closed position. 
     FIG. 11 displays an alternative embodiment of the present invention. In order to avoid repetition of generally similar features previously described in the first embodiment above, only a discussion of the differences follows. 
     Rather than a single keyway  221  along each side of cover  201  and a single spline  323  along each side of contact housing sub-assembly  301 , this alternative embodiment provides cover  201 ′ with several smaller keyways  221 ′ along each side and contact housing sub-assembly  301 ′ has several smaller splines  323 ′. 
     Providing these smaller features helps distribute stresses more evenly across cover  201 ′and across contact housing sub-assembly  301 ′. In addition, these smaller features provide redundant guide surfaces  325 ′ and stop surfaces  327 ′,  329 ′. For example, if the first spline  323 ′ becomes sufficiently damaged, the stop surfaces  327 ′,  329 ′ may no longer provide accurate alignment between cover  201 ′ and the rest of socket  100 ′. The next spline  323 ′ along the line of splines  323 ′ will, however, provide accurate alignment between cover  201 ′ and the rest of socket  100 ′ with guide surface  325 ′ and stop surfaces  327 ′,  329 ′. 
     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.