Abstract:
An electrical socket for supporting an integrated circuit chip on a circuit board mainly includes a dielectric base, a number of conductive contacts retained in the base, a cover and an actuation member for movably attaching to the cover with respect to the base. The actuation member includes a cam shaft whose one end has a step-shaped face and forms an upper portion and a lower portion. The base defines a receiving hole for receiving the end of the cam shaft. The receiving hole has a step-shaped mating face forming an upper portion and a lower portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an electrical socket connector, and more particularly to a zero insertion force (ZIF) socket for electrically assembling an integrated circuit chip to a printed circuit board (PCB), wherein the ZIF socket has an actuation member for motivating a cover relative to a base of the ZIF socket. 
     2. Description of Related Art 
     Conventional ZIF sockets normally comprise a cover defining a plurality of upper passageways therein and slidably engaging with a base having a corresponding number of lower passageways retaining contacts therein. Optionally, the cover is driven to move with respect to the base by a screwdriver. U.S. Pat. Nos. 5,730,615 and 6,347,951 disclose such a driving mechanism for driving the cover to move on the base by inserting a screwdriver into slots defined in the cover and the base and pivoting the screwdriver to drive the cover to move. Such operation of the screwdriver is inconvenient. Furthermore, the screwdriver which is made of hard material (usually steel) can cause damage to either the cover or the base which is made of relatively soft material (usually plastics) when the screwdriver is used to drive the cover to move relative to the base. 
     In order to prevent the above-mentioned shortcoming, another ZIF socket having an actuation device for moving the cover attached with a CPU component relative to the base is provided. For instance, U.S. Pat. Nos. 4,498,725, 5,489,218 and 5,454,727, as well as page 35, page 5 and pages 2˜3 of periodical entitled “CONNECTOR SPECIFIER” published respectively on November 1998, May 1998 and February 1995 all disclose such a typical ZIF socket including an actuation device. The actuation device consists of an exposed lever and an embedded rotation bar wherein the rotation bar joins the lever at one end and the bar further includes multiple cam sections or crank shaft sections. When the bar is oriented vertically to the base, the pins of the CPU component can be freely inserted into the socket. Successively, the operator manually pushes the lever downward to a horizontal position, during which the cam sections or the crank shaft sections of the rotation bar move the cover together with the CPU component horizontally and the pins of the CPU component are moved to engage with the corresponding contacts of the socket. Reversely, when the lever is moved from the horizontal position back to the vertical position, the cover together with the CPU component is moved horizontally in a reverse direction. Therefore, the engagement between the contacts of the socket and the pins of the CPU component is released, and the CPU component can be detached from the socket. Above-mentioned socket uses an actuation lever located along one side of the socket. However, the actuation lever increases the width of the socket. This is unfavorable in view of the minimization and compact trend of electronic components. 
     U.S. Pat. No. 6,338,639 discloses a socket having an actuation member configured to move a cover when the actuation member is rotated about a rotational axis. The actuation member is so designed that the rotational axis of the actuation member is parallel to the longitudinal sides of the socket along which the cover is moved relative to the base. The actuation member includes a cam assembly and an actuation lever. The actuation lever includes a handle and a leg. The actuation member is complicated in structure, which is disadvantageous from a cost consideration. 
     U.S. Pat. No. 6,280,223 discloses another socket having a simple driving mechanism. Nevertheless, when the socket is at a closed position, a high stress exists between the cam and a cover plate of the cover. The cam is made of zinc alloy. When the socket is exposed to an elevated temperature due to the operation of the CPU component mounted on the cover, the high stress causes the cam to creep because of the poor creep strength of zinc alloy. The creep of the cam causes the cam to deform from its original configuration whereby the cam can no longer achieve its requested stroke when it is rotated to move the cover relative to the base. Accordingly, the pins of the CPU component can not be moved to correctly engage with the contacts at the closed position or totally disengage from the contacts at the open position of the socket. 
     Hence, it is requisite to provide an electrical socket with an improved driving mechanism to overcome the above-mentioned disadvantages. 
     SUMMARY OF THE INVENTION 
     Accordingly, a first object of the present invention is to provide an electrical socket having an improved actuation member which can provide a effective stroke for the socket to ensure a reliable connection between the pins of an integrated circuit chip and conductive contacts of the socket. 
     A second object of the present invention is to provide an improved actuation member for a ZIF socket wherein the actuation member is convenient to manipulate by a user without increasing the width of the socket. 
     A third object of the present invention is to provide an improved actuation member for a ZIF socket which has a simple structure, thereby reducing cost. 
     In order to achieve the objective set forth, a electrical socket in accordance with the present invention is adapted for supporting an integrated circuit chip on a circuit board. The socket comprises a dielectric base defining an array of terminal cells, a plurality of conductive contacts received in the terminal cells, a cover slidably mounted on the base and an actuation member for moving the cover with respect to the base. The base defines a receiving space in one side thereof for receiving the actuation member and a receiving hole formed in an inner face of a lateral side portion thereof and communicating with the receiving space. The receiving space includes a receiving chamber and a receiving slot. The receiving hole has a step-shaped mating face forming an upper portion and a lower portion. The actuation member includes an operating handle and a cam shaft having a stepped shape and forming a cam member for moving the cover with respect to the base. The cam shaft has a contacting end for interacting with the mating face. The contacting end has a stepped shape and forms an upper portion and a lower portion. When the socket is at an open position, the upper portion of the contacting end of the cam shaft bears against the upper portion of the mating face of the receiving hole. When the socket is at a closed position, the upper and lower position of the contacting end of the cam shaft bear against the lower and upper portion of the mating face of the receiving hole, respectively. 
     Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of the present embodiment when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of an electrical socket in accordance with the present invention; 
     FIG. 2 is an assembled view of FIG. 1; 
     FIG. 3 is an enlarged perspective view of a section of a dielectric base and an actuation member of the electrical socket of FIG. 1 before assembly; 
     FIG. 4 is an enlarged cross-sectional view of an end section of the actuation member and a portion of the dielectric base bearing against the end section of the actuation member when the electrical socket is at an open position; 
     FIG. 5 is similar to FIG. 4 but the electrical socket is moved to a closed position; and 
     FIG. 6 is a diagram illustrating a relation between a displacement of a cover and a rotated angle of the actuation member of the electrical socket of the present invention, wherein the actuation member is rotated from zero degree (vertical orientation) to ninety degrees (horizontal orientation). 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiment of the present invention. 
     Referring to FIG. 1 first, a CPU socket  1 , particularly a ZIF BGA socket, for electrically assembling a CPU package (not shown) to a printed circuit board (not shown) in accordance with the present invention comprises a dielectric base  10  adapted for being securely mounted onto the printed circuit board, a plurality of conductive contacts  70  retained in the base  10 , a cover  20  movably covered on the base  10  and an actuation member  30  assembled between the base  10  and the cover  20 . 
     Referring to FIGS. 1 and 3, the dielectric base  10  defines an array of terminal cells  12  for receiving a corresponding number of the conductive contacts  70 , and an array of through holes  14  around the terminal cells  12 . The holes  14  are devised for an optimal formation of the base  10  by plastics injection molding. A receiving space  16  is defined in a top face  11  of the base  10  for receiving the actuation member  30 . The receiving space  16  includes a receiving chamber  160  among the through holes  14  and a receiving slot  162  extending along a lateral side portion  13  of the base  10  and communicating with the receiving chamber  160 . A receiving hole  164  is defined in an inner face of the lateral side portion  13  and in alignment with the receiving chamber  160 . The receiving hole  164  has a step-shaped mating face  166  (see FIGS. 4 and 5) having an upper portion  1660 , a lower portion  1662  and a slope portion  1664  between the upper and lower portions  1660 ,  1662 . Additionally, the lateral side portion  13  of the base  10  forms an inclined face  17  in the receiving slot  162  for preventing the actuation member  30  from over-rotating. A pair of stopping posts  18  is further formed at opposite ends of the lateral side portion  13 . 
     Referring to FIG. 1 again, the cover  20  defines an array of pin holes  22  vertically corresponding to the terminal cells  12  of the base  10  for insertion of pins of the CPU package (not shown) therethrough. A through aperture  24  is defined in a side of the cover  30  corresponding to the receiving chamber  160  of the base  10 . 
     Referring to FIG. 3, the actuation member  30  includes a cam shaft  32  and an operating handle  34  perpendicularly extending from the cam shaft  32  for respectively inserting into the receiving chamber  160  and the receiving slot  162  of the base  10 . The cam shaft  32  has a cam member  320  for driving the cover  20  to move with respect to the base  10 , a supported end  324  remote from the operation handle and for being rotatably supported on the base  10  and a contacting end  322  opposite the supported end  324  and for having an interaction with the mating face  166  as will be detailed below. The contacting end  322  (see FIGS. 4 and 5) includes an upper portion  3220 , a lower portion  3222  and a slope portion  3224  between the upper and lower portions  3220 ,  3222 . So the contacting end  322  has a stepped shape and is received in the receiving hole  164  to interact with the mating face  166  thereof. The operating handle  34  has a curved portion  340  to engage with the post  18  of the base  10  to retain the actuation member  30  at a closed position. 
     Referring to FIG. 1 again, several components of the socket  1  are shown, such as a cover plate  40 , a shaft clip  50  and a pair of latching plates  60 . The cover plate  40 , made of metal, is fixed to the through aperture  24  of the cover  20  by insert molding. An opening  42  is defined in the cover plate  40  for insertion of the cam member  320  of the actuation member  30  therein. The shaft clip  50  is inserted into a corresponding receiving slit  51  of the base  10  and abuts against the supported end  324  of the cam shaft  32  for fixing the actuation member  30  in position. The pair of latch plates  60  is upwardly inserted into through slots  61  of the base  10  and beside hooks (not shown) on a bottom of the cover  20  for preventing the cover  20  from separating from the base  10 . 
     In use, referring to FIGS. 2 and 4 to  6  and cooperating FIG. 2, when the socket  1  is at an open position, in which the operating handle  34  of the actuation member  30  is in zero degree position and oriented vertically to the cover  20  and the base  10 , the pin holes  22  of the cover  20  are vertically aligned with the terminal cells  12  of the base  10  such that the pins of the CPU package can be freely inserted through the pin holes  22  into the terminal cells  12 . At this position, the displacement of the cover  20  relative to the base  10  is zero, and the upper portion  3220  of the contacting end  322  of the cam shaft  32  bears against the upper portion  1660  of the mating face  166 . When the operating handle  34  of the actuation member  30  is rotated about 10 to 20 degrees from zero degree position to “a” degree position, the cover  20  is not pushed to move due to a clearance between the cam member  320  and the cover plate  40 . Thus the displacement of the cover  20  is still zero. By further rotating the operating handle  34  of the actuation member  30  towards its horizontal direction, the cover  20  is thus pushed to move horizontally with respect to the base  10  along an “N” direction and the displacement of the cover increases gradually. The pins of the CPU package begin to move to mechanically and electrically connect with the conductive contacts  70  of the socket  1 . The pushing force of the cam member  320  acting on the cover plate  40  (accordingly an induced stress of the cam member  320 ) increases following the increase of the displacement of the cover  20  during the rotation of the actuation member  30  from the position “a” to the position “b”. When the operating handle  34  is rotated to “b” degree position, the stress arrives at a top peak and the displacement of the cover  20  attains a maximum at which the upper portion  3220  of the contacting end  322  of cam shaft  32  bears against the upper portion  1660  of the mating face  166 , as shown in FIG.  4 . When the operating handle  34  is further rotated about 10 degrees from “b” degree position to “c” degree position, the stress of the cam member  320  and the displacement of the cover  20  remain unchanged. During the process when the operating handle  34  is rotated from original position to “c” degree position, the upper portion  3220  of the contacting end  322  of the cam shaft  32  bears against the upper portion  1660  of the mating face  166  of the base  10  all the time. When the operating handle  34  is continually rotated from “c” degree position towards its horizontal direction, the upper portion  3220  of the contacting end  322  of the cam shaft  32  starts to slide on the slope portion  1664  of the mating face  166  of the base  10  slowly. The cam shaft  32  begins to move in a direction opposing to the “N” direction and the displacement of the cover  20  relative to the base  10  decreases gradually. The stress of the cam member  320  also reduces gradually. When the operating handle  34  is rotated to “d” degree position or ultimate position, that is, the socket is at a closed position, the contacting end  322  of the cam shaft  32  complementarily overlaps the mating face  166  of the receiving hole  164 ; in other words, the upper position  3220  of the contacting end  322  of the cam shaft  32  bears against the lower portion  1662  of the mating face  166  of the base  10 , while the lower position  3222  of the contacting end  322  of the cam shaft  32  bears against the upper position  1660  of the mating face  166  of the base  10 . The displacement of the cover  20  reduces distinctly compared with the displacement of the cover  20  at “c” degree position and the stress is released. At this situation, even if the socket is subject a high temperature environment, the cam member  320  does not have a problem of creep. Therefore, the CPU socket  1  ensures an effective and reliable connection between the pins of the CPU package and the conductive contacts  70  of the socket  1 . Regarding the structure of the cover plate  40  and the cam member  320  and their interaction to move the cover  20  relative to the base  10 , one can refer to U.S. Pat. No. 6,280,223 B1, which is assigned to the same assignee of the present application. Related disclosures of the &#39;223 patent are incorporated herewith by reference. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.