Abstract:
A socket assembly is provided for receiving electronic packages including a cover and a base slidably engaging one another and movable between open and closed positions. The base includes a contact array. The socket assembly also includes a cam member received by the cover and base. Rotation of the cam member actuates a sliding motion between the cover and base. The socket assembly further includes a load bearing member mounted to one of the cover and base, and a wear plate mounted about the load bearing member. The wear plate has a cam reception hole accepting the cam member. The load bearing member and the cam member are located different distances from the contact array to reduce the moment caused by the sliding motion between the cover and base.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a socket assembly that is designed to reduce bowing during actuation. 
     Pin grid array (PGA) sockets are used to accept electronic packages on printed circuit boards. PGA sockets facilitate electrical communication between a large number of pins born on an electronic processor and electrical components to which the PGA sockets are mounted (such as circuit boards). Zero insertion force (ZIF) PGA sockets utilize a cover that is slidably movable on a base between open and closed positions. The sliding movement may be actuated, for example, by a cam that is rotated by a hand tool. The cover has a hole array configured to match a pin array on a processor. Similarly, the base has an array of pin receiving chambers configured to accept the pin array of the processor. The processor is mated to the socket by first placing the processor such that its pins penetrate the holes of the cover. With the cover in the open position, the pins penetrate through the holes of the cover and into the pin receiving chambers of the base but are not electrically connected to the pin receiving chambers of the base. When the cover is slid to the closed position, the pins are electrically connected to the base via the pin receiving chambers. 
     Because there may be hundreds of pins in the array, moving the cover to the closed position can require a considerable force to move the pins into their fully mated position. This force can cause the socket assembly to bow, resulting in inadequate actuation and/or de-actuation. 
     FIG. 1 illustrates an example of a prior art socket system  10  with a cam actuation mechanism. The socket system  10  includes a cover  12  slidably mounted to a housing  14 . The housing  14  is mounted to a board (not shown) by solderballs  16 . The socket system  10  includes a cam  18  that is accepted by both the cover  12  and the housing  14 . Rotation of the cam  18  results in the cover  12  moving along direction A relative to the housing  14 . The cover  12  moves to the right in FIG. 1 when closed (or actuation) and to the left when opened (or de-actuation). The socket system  10  also includes a housing wear plate  20  that nests in the housing  14  and contacts the cam  18  along a bearing surface of the cam  18  as the cam  18  is rotated, and a cover wear plate  21  that nests in the cover  12  and also contacts the cam  18  along a bearing surface as the cam  18  is rotated. The cam  18  includes an eccentric portion that contacts the cover wear plate  21 , causing the cover  12  to move laterally as the cam  18  is rotated. 
     When the cam  18  is rotated, resultant forces are exerted on the housing  14  from the cam  18  via the housing wear plate  20 . When the cover  12  is being actuated, a resultant force occurs at closing push surface  22 . When the cover  12  is being de-actuated, a resultant force occurs at opening push surface  24 . These resultant forces create a moment about the solderballs  16  at which the housing  14  is mounted. The horizontal portions of the moment arms are the opening moment arm  26  and the closing moment arm  28 , and correspond to the opening push surface  24  and closing push surface  22 , respectively. The moments caused by the resultant forces cause bowing and deflection along bowing direction B. Further, the resultant forces at the opening push surface  24  can cause wear and cracking at a back edge  30  of the housing  14 . 
     For the socket system  10  illustrated in FIG. 1, closing or actuation causes deflection downward along bowing direction B. In this circumstance, the socket system  10  may be supported by a board to which it is mounted and engagement may be achieved. However, opening or de-actuation causes bowing upward along bowing direction B. Because there is no support available above the socket system  10 , the resulting bowing can prevent disengagement of the socket. 
     A need remains for a socket assembly that overcomes the above-noted and other disadvantages of existing PGA sockets. 
     BRIEF SUMMARY OF THE INVENTION 
     At least one preferred embodiment of the present invention is provided including a socket assembly for receiving electronic packages. The socket assembly includes a cover and a base slidably engaging one another and movable between open and closed positions. The base includes a contact array. The socket assembly also includes a cam member received by the cover and base. Rotation of the cam member actuates a sliding motion between the cover and base. The socket assembly also includes a load bearing member mounted to one of the cover and base. The socket assembly further includes a wear plate mounted about the load bearing member. The wear plate has a cam reception hole accepting the cam member. The load bearing member and the cam member are located different distances from the contact array to reduce the moment caused by the sliding motion between the cover and base. 
     Optionally, the load bearing feature may extend from a wear plate cavity formed in the base. The distance between the cam member and the contact array is greater than the distance between the load bearing member and the contact array. The load bearing member may include an opening push surface and a closing push surface. The opening push surface transmits a resultant force when the cover is moved toward the open position, and the closing push surface transmits a resultant force when the cover is moved toward the closed position. 
     The load bearing member may include an oblong raised element including an opening push surface and a closing push surface on opposing sides of the load bearing member. The wear plate may include an opening forming an oblong slot accepting the oblong raised element. The opening includes an opening surface contacting the opening push surface of the load bearing member, and a closing surface contacting the closing push surface of the load bearing member. 
     In accordance with at least one preferred embodiment, a socket assembly is provided including a housing, a cover, a cam pin, and a housing wear plate. The housing includes an array of contacts. The contacts are mountable to a circuit board at a mounting feature. The housing also includes an opening push surface and closing push surface. The cover is slidably mounted to the housing and movable relative to the housing between an actuated and a de-actuated position. The housing includes a pin grid corresponding to the array of contacts. The cam pin is received by the housing and the cover, and rotation of the cam pin moves the cover between the actuated and de-actuated positions. The cam pin is located farther from the array of contacts than the opening and closing push surfaces. The housing wear plate includes a cam reception hole that receives the cam pin. The cam reception hole has a bearing surface that contacts the cam pin. The housing wear plate transfers actuation forces from the cam pin to the opening and closing push surfaces. The housing wear plate cooperates with the opening push surface and the closing push surface to reduce a resultant moment caused by a sliding motion between the cover and the base. 
     Optionally, the housing may include a load bearing member extending from a housing wear plate cavity that is formed in the housing. The load bearing member includes at least one of the opening push and closing push surfaces. The housing wear plate includes an opening including at least one of the opening and closing surfaces. The opening receives the load bearing member. The opening may extend through the housing wear plate. 
     In accordance with at least one preferred embodiment, a socket assembly is provided including a housing, a cover, a cam pin, a cover wear plate, and a housing wear plate. The housing includes an array of contacts that are mountable to a circuit board at a mounting feature. The housing also includes a housing wear plate cavity including a load bearing member extending from the housing wear plate cavity. The load bearing member has an opening push surface and a closing push surface. The cover is slidably mounted to the housing and movable between an actuated and de-actuated position. The cover includes a pin grid corresponding to the array of contacts. The housing and the cover receive the cam pin, and rotation of the cam pin actuates the housing between the actuated and the de-actuated positions. The cam pin is located further from the mounting feature than the opening and closing push surfaces. The cover wear plate is received by the cover and includes a cam reception hole having a bearing surface that contacts the cam pin. The cover wear plate cooperates with the cam pin to transmit resultant forces from the movement of the cover from the cover to the cam pin. The housing wear plate is received by the housing wear plate cavity and has a cam reception hole that receives the cam pin. The cam reception hole has a bearing surface that contacts the cam pin. The housing wear plate includes an opening that includes an opening surface corresponding to the opening push surface of the load bearing member, and a closing surface corresponding to the closing push surface of the load bearing member. The opening receives the load bearing member. The opening and closing surfaces cooperate with the opening push and closing push surfaces, respectively, to reduce the resultant moment cause by the sliding motion between the cover and the base. 
     Certain embodiments of the present invention thus provide a socket assembly that reduces bowing and improves actuation and de-actuation effectiveness. Certain embodiments of the present invention also provide a socket assembly that reduces wear, damage, and cracking to components of the socket assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an example of a prior art socket system  10  with a cam actuation mechanism. 
     FIG. 2 illustrates an exploded view of a PGA socket assembly formed in accordance with an embodiment of the present invention. 
     FIG. 3 illustrates a sectional view of a PGA socket assembly formed in accordance with an embodiment of the present invention in an open, or de-actuated position. 
     FIG. 4 illustrates a perspective view of a cam pin formed in accordance with an embodiment of the present invention. 
     FIG. 5 illustrates an elevation view of the cam pin of FIG.  4 . 
     FIG. 6 illustrates a perspective view of a cover formed in accordance with an embodiment of the present invention with a cam and an indicator in place. 
     FIG. 7 illustrates a perspective view of a housing formed in accordance with an embodiment of the present invention. 
     FIG. 8 illustrates a perspective view of a housing wear plate formed in accordance with an embodiment of the present invention. 
    
    
     The foregoing summary, as well as the following detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, embodiments which are presently preferred. It should be understood, however, that the present invention is not limited to the precise arrangements and instrumentality shown in the attached drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 illustrates an exploded view of an embodiment of a PGA socket assembly  40 , and FIG. 3 illustrates a sectional view of the socket assembly  40  in an open, or de-actuated position. The socket assembly  40  includes a cover  42 , a cam pin  44 , and a housing, or base,  46 . The cover  42  and housing  46  are socket halves. The cover  42  slidably engages the housing  46 . The cam pin  44  is rotatable, and rotation of the cam pin  44  actuates the sliding movement of the cover  42  on the housing  46 . Interposed between the cam  44  and the cover  42  is an indicator  48  that indicates whether the socket assembly  40  is actuated or de-actuated. An example of such an indicator is more fully described in U.S. patent application Ser. No. 10/113,540, filed Apr. 1, 2002. 
     The cam pin  44  is made out of metal, while the cover  42  and housing  46  are made out of plastic. If the cam pin  44  were in direct contact with either the cover  42  or the housing  46 , the cam pin  44  could wear or damage the plastic surfaces. Instead, the socket assembly  40  includes a cover wear plate  50  and a housing wear plate  52 , each made out of metal. The cover wear plate  50  nests in the cover  42  and accepts the cam pin  44 . Similarly, the housing wear plate  52  nests in the housing  46  and accepts the cam pin  44 . The socket assembly  40  further includes a retaining plate  54  that retains the cam pin  44  in the socket assembly  40 . 
     As illustrated in FIG. 3, the socket assembly  40  also includes an interposer  56  having pins  58 . The interposer  56  is mounted to and in electrical communication with a processor (not shown). The interposer  56  rides on top of the cover  42 , and the pins  58  of the interposer  56  are accepted by a pin grid  96  (FIG. 2) of the cover  42 , which correspond to a contact array  126  (FIG. 2) of contacts  128  (FIG. 3) of the housing  46 . In FIG. 3, the cover  42  is shown in an open position, meaning that the socket assembly  40  is de-actuated. In the open position, the pins  58  of the interposer  56  penetrate through the pin grid  96  of the cover  42  and into the contact array  126  of the housing  46 , but the pins  58  are not in electrical communication with the contacts  128 . Moving the cover  42  (and the interposer along with the cover  42 ) to the right along opening/closing direction C results in the pins  56  being brought into electrical contact with the contacts  128 . Similarly, moving the cover  42  to the left along opening/closing direction C terminates the electrical communication between the pins  58  and the contacts  128 . 
     FIG. 4 illustrates a perspective view of the cam pin  44 , and FIG. 5 illustrates an elevation view of the cam pin  44 . The cam pin  44  includes a top portion  60 , a cover portion  66 , a housing portion  68 , and a bottom portion  70 . The top portion  60  adjoins the cover portion  66 , the cover portion  66  adjoins the housing portion  68 , and the housing portion  68  adjoins the bottom portion  70 . Further, the top portion  60 , the housing portion  68 , and the bottom portion  70  are all concentric with one another. The cover portion  66  is eccentric with respect to the other portions. 
     The top portion  60  includes a hexagonal socket  62 . The hexagonal socket  62  is sunken into the top portion  60  and accepts a hexagonal head wrench to facilitate actuation. Additionally, the top portion  60  also includes a tab  63  extending laterally from the top portion  60 . The top portion  60  terminates at a top lip  64  that extends inward laterally to meet the cover portion  66 . 
     The cover portion  66  is eccentric to the other portions, and is sized to be accepted by the cover wear plate  50 . The cover portion  66  is joined to the housing portion  68 . The housing portion  68  is cylindrical and concentric with the top portion  66 , and is accepted by the housing wear plate  52 . The housing portion  68  is joined to the bottom portion  70 . 
     The bottom portion  70  of the cam pin  44  includes a retention lobe  72 , a retention lip  74 , and a bottom lobe  76 . The diameter of the retention lobe  72  is less than the diameter of the housing portion  68 , and less than the diameter of the bottom lobe  76 . The retention lip  74  joins the retention lobe  72  to the bottom lobe  76 . 
     FIG. 6 illustrates a perspective view of the cover  42  with the cam  44  and the indicator  48  in place. The cover  42  is slidably mounted to the housing  46 . The cover  42  includes a top portion  90 , a bottom portion  92 , and a back portion  94 . The cover  42  includes a pin grid  96  of openings extending from the top portion  90  through the bottom portion  92 . The pin rid  96  corresponds to the arrangement of pins  58  of the interposer  56  as well as to the contact array  126  of the housing  46 . The cover also includes a cam reception hole  104  (see FIG. 2) extending from the top portion  90  through the bottom portion  92  through which the cam pin  44  extends. 
     The cover  42  also includes a cam recess  98  extending into the top portion  90  proximal to the back portion  94 . The cam recess  98  accepts the cam pin  44  and the indicator  48 . The cam recess  98  includes a cam shelf  100  upon which the cam pin  44  and indicator  48  rest when the ring  82  of the indicator  48  abuts the cam shelf  100 . The top portion  90  of the cover  42  also includes positive stops  102  that cooperate with the tab  63  of the cam pin  44  to limit the range of rotation of the cam pin  44  to approximately 180° to prevent the cam pin  44  from rotating beyond the actuated or de-actuated positions. 
     With reference to FIGS. 2 and 6, the indicator  48  includes a through hole  80 , a ring  82 , and an arm  84 . The through hole  80  accepts the cam pin  44 , and the indicator  48  is interposed between the cam pin  44  and the cover  42  such that the top lip  64  of the cam pin  44  abuts the ring  82  which abuts the cam shelf  100  of the cover  42 . The indicator  48  moves between an actuated and a de-actuated position when the cam pin  44  is rotated so that the position of the arm  48  provides a visual cue as to the position of the cam pin  44 , thus indicating whether the socket assembly  40  is in an actuated or de-actuated position. 
     With reference to FIGS. 2 and 3, the cover  42  includes a recess  106  that extends into the bottom portion  92  of the cover  42  and accepts the cover wear plate  50 . The cover wear plate  50  nests snugly into the wear plate recess  106  so that it will not rotate along with the cam pin  44  when the cam pin  44  is actuated. The cover wear plate includes an oblong cam reception hole  110  that accepts the cover portion  66  of the cam pin  44  with minimal clearance. The inside of the oblong cam reception hole  110  is defined by a bearing surface  112  that contacts the outer surface of the cover portion  66  of the cam pin  44 . Further, the cover wear plate  50  also includes push surfaces  114  that contact corresponding push surfaces  115  (see FIG. 3) of the wear plate recess  106  to transmit a sliding force caused by rotation of the cam pin  44  to move the cover  42 . The cover wear plate  50  also includes void holes  116  to reduce weight. 
     As previously mentioned, the cover  42  is slidably mounted to the housing  46 . FIG. 7 illustrates a perspective view of the housing  46 . The housing  46  includes a top portion  120 , a bottom portion  122 , and a back portion  124 . The housing  46  includes a contact array  126  corresponding to the array of pins  58  on the interposer  56  as well as the pin grid  96  of the cover  42 . The contact array  126  includes individual contacts  128  terminating in solderballs  130  proximal to the bottom portion  122 . The contacts  128  typically contain a fork, or fingers, (not shown) such that the pins  58  may be advanced into the fingers to electrically communicate with the contacts  128 , and retracted out of the fingers to terminate the electrical communication. The solderballs  130  are soldered to a board (not shown), thereby providing a mounting feature and facilitating electrical communication between components connected to the interposer  56  and the board. 
     Proximal to the back portion  124 , the housing  46  includes a wear plate cavity  132  recessed into the top portion  120 . The wear plate cavity  132  houses the housing wear plate  52 . The wear plate cavity  132  is defined by a cavity base  134  and cavity sides  136 . The housing  46  also includes a cam reception hole  138  penetrating through the wear plate cavity  132 , through which the cam pin  44  passes. 
     The wear plate cavity  132  includes a load bearing feature  140 . The load bearing feature  140  is an oblong projection extending upward from the cavity base  134 . The load bearing feature  140  is located nearer to the contact array  126  than the cam reception hole  138  is to the contact array  126 . The load bearing feature  140  includes an opening push surface  142  and a closing push surface  144 , which as a result are also nearer to the contact array  126  than the cam reception hole  138  is. Consequently, the opening and closing push surfaces  142 ,  144  of the housing  46  are closer to the solderballs  130  of the socket assembly  40  than the closing and opening push surfaces  22 ,  24  are to the solderballs  16  of the prior art system  10 . This results in a reduced moment arm and reduced bowing. The load bearing feature  140  also includes cuts  146  sunk into the closing push surface  144  to control the location of force transmission to the load bearing feature  140  along the closing push surface  144 . 
     The wear plate cavity  132  also includes a recess  148  surrounding the area where the load bearing feature  140  meets the cavity base  134 . The recess  148  extends below the cavity base  134  and insures that there are no radii surrounding the junction of the load bearing feature  140  and the cavity base  134  that would prevent the housing wear plate  52  from resting flat on the cavity base  134  of the wear plate cavity  132  of the housing  46 . The wear plate cavity  132  further includes a keying feature  150  extending upward from the cavity base  134  that helps properly align the housing wear plate  52  in the wear plate cavity  132 . 
     FIG. 8 illustrates a perspective view of the housing wear plate  52 . The housing wear plate  52  includes a top portion  160  and a bottom portion  162  joined by sides  164 , and is sized to be accepted by the wear plate cavity  132  of the housing  46 . The housing wear plate  52  includes a slot  166  extending from the top portion  160  through the bottom portion  162 . The slot  166  is oblong and snugly accepts the load bearing feature  140  of the housing  46 . The slot  166  includes an opening surface  168  and a closing surface  170  that correspond to the opening push surface  142  and the closing push surface  144 , respectively, of the housing  46 . The opening surface  168  and closing surface  170  cooperate with the opening push surface  142  and the closing push surface  144 , respectively, to transmit resultant forces from the movement of the cover  42  from the cam pin  44  to the housing  46 . 
     Extending through the housing wear plate  52  is a cam reception hole  172  that accepts the cam pin  44 . The interior of the cam reception hole  172  is defined by a bearing surface  174 . The bearing surface  174  contacts the outer surface of the housing portion  68  of the cam pin  44 . Also extending through the housing wear plate  52  is a keying hole  176 . The keying hole  176  accepts the keying feature  150  of the wear plate cavity  132  of the housing  46 . When the housing wear plate is manufactured, a burr can be created on the top portion  160 . The keying hole  176  and. keying feature  150 , which are located laterally off center of the cover wear plate  52 , cooperate to ensure that the housing wear plate  52  is placed in the wear plate cavity  132  with the burr side up, or facing the cover wear plate  50  (which is made of metal) instead of the cavity base  134  (which is made of plastic). The housing wear plate  52  also includes a void hole  178 . The void hole  178  reduces the overall weight of the housing wear plate  52  and the socket assembly  40 . The void hole  178  is sized and configured so that it will not accept the keying feature  150 . 
     Referring to FIG. 2, the socket assembly  40  also includes a retaining plate  54  that acts to retain the cam pin  44  in place. The retaining plate is accepted by a retaining plate cavity  180  (see FIG. 3) that extends into the bottom portion  122  of the housing  46 . The retaining plate  54  includes a slot  192  that has a first width  194  and a second width  196 . The first width  194  is greater than the diameter of the bottom lobe  76  of the cam pin  44 , and the second width  196  is greater than the diameter of the retention lobe  78  but less than the diameter of the bottom lobe  76 . Thus, when the slot  192  is aligned such that the first width  194  aligns with the bottom lobe  76 , the cam pin  44  may be lowered into the socket assembly until the retaining plate  54  surrounds the retention lobe  72 . With the retaining plate  54  and cam pin  44  thus aligned, the retaining plate  54  may be slid laterally with respect to the cam pin  44  so that the second width  196  surrounds the retention lobe  72  of the cam pin  44 . Because the second width  196  is less than the diameter of the bottom lobe  76 , any attempts to remove the cam pin  44  from the socket assembly  44  will be prevented by the interaction of the retention lip  74 , the retaining plate  54 , and the retaining plate cavity  180  of the housing  46 . 
     FIG. 3 illustrates the socket assembly  40  in an open, or de-actuated position. The pins  58  have been accepted by the contact array  126 , but are not in electrical communication with the individual contacts  128 . For the pins  58  to achieve electrical communication with the contacts  128 , the cover must be moved to the right along opening/closing direction C. 
     This movement is accomplished by rotation of the cam pin  44 . An operator places a hexagonal wrench in the hexagonal socket  62  and rotates the cam pin  44 . As the cam pin  44  rotates, the cover portion  66  of the cam pin  44  presses against the bearing surface  112  of the cover wear plate  50  and the housing portion  68  of the cam pin  44  presses against the bearing surface  174  of the housing wear plate  52 . Because the cover portion of the cam pin  44  is off-center from the housing portion  68  of the cam pin  44  and the housing wear plate  52  maintains the cam pin  44  in place relative to the housing  46 , the cover  42  is forced to slide relative to the housing  46  into the closed or actuated position. 
     The movement of the cover  42  into the closed position is opposed by the sum of the forces required to insert each pin  58  into each contact  128 . Because there are hundreds of contacts, the total force required may be quite large. This required actuation force results in a resultant force being placed on the cam pin  44 . That resultant force is transmitted from the cam pin  44  to the bearing surface  174  of the housing wear plate  52 , and in turn from the housing wear plate  52  to the load bearing feature  140  of the housing  46  via the interaction of the closing surface  170  of the housing wear plate  52  and the closing push surface  144  of the housing  46 . The transmission of the resultant force at the load bearing feature  140  results in a moment about the solderball  130 . The horizontal component of the moment arm is shown by closing moment arm  200 . Similarly, sliding the cover to the open position from the closed position results in the transmission of a resultant force via the interaction of the opening surface  168  of the housing wear plate  52  and the opening push surface  142  of the load bearing feature  140  of the housing  46 . Opening moment arm  202  is the horizontal component of the moment arm corresponding to the moment caused by moving the cover  42  to the open position. The moments caused by opening and closing the cover  42  can cause bowing along bowing direction D. 
     For the embodiment illustrated in FIG. 3, the opening moment arm  202  is the largest moment arm corresponding to the sliding of the cover  42  along direction C. Opening moment arm  202  is significantly less than either the opening moment arm  26  or the closing moment arm  28  of the prior art socket system  10  illustrated in FIG.  1 . For example, for similarly sized sockets, the opening moment arm  202  may be 6.86 mm, whereas the opening moment arm  26  may be 19.02 mm. Because the moment is directly proportional to the length of the moment arm, the socket system  40  will experience considerably less bowing than the prior art socket system  10 . Also, because the transmission of the resultant forces has been moved away from the back of the socket assembly  40 , there will be reduced cracking of the housing  46  caused by the forces involved with opening and closing the cover  46  compared to the prior art socket system  10 . 
     While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. For example, multiple load bearing features, or a load bearing feature of a different shape may be used. Also, the wear plate could include a load bearing feature that extends into the housing. It is therefore contemplated by the appended claims to cover such modifications as incorporate those features which come within the spirit and scope of the invention.