Abstract:
A purpose of the invention is to provide a socket and a socket base, capable of holding the retainers outside the viewing field of the camera in spite of the size and/or shape of the retainers when measuring contact gaps, for example.

Description:
TECHNICAL FIELD 
     The present invention relates to a socket with a plurality of contacts corresponding to a plurality of terminals provided on a bottom surface of an integrated circuit device such as a ball grid array (BGA) device. Also, the present invention relates to a socket base for use with the socket. Further, the present invention relates to a method for using and operating the socket and the socket base and a method for testing the socket. 
     BACKGROUND 
     A patent document 1 discloses a socket for a temporal connection of a ball grid array (BGA) integrated circuit device to a test circuit. The socket includes a pattern of contacts corresponding to a pattern of terminals, e.g., solder balls provided on a bottom surface of the integrated circuit device. Each of the contacts has a pair of tips for resiliently nipping an associated one of the solder balls of the integrated circuit device. The socket also has structures for moving each pair of contact tips between an opened position in which the contact tips are spaced apart from each other to accommodate the associated solder ball therebetween and a closed position in which the contact tips resiliently hold the associated solder ball therebetween. 
     A patent document 2 discloses another socket including one or more pairs of retainers for forcing the integrated circuit device against the contacts to attain reliable contacts between the contacts of the socket and the associated solder balls of the integrated circuit device. Each of the retainers is supported for rotation between a protruded position in which each of the retainers is protruded above the upper surface of the integrated circuit to force the integrated circuit device against the contacts and a retracted position in which the retainer is fully retracted from above the integrated circuit device. A spring is provided for each retainer to force the retainer toward the protruded position. 
     The sockets have various advantages. Among other things, the retainers ensure reliable electrical contacts between the solder balls of the integrated circuit device and the associated contacts of the socket. However, when optically checking whether a sufficient opening or gap necessary for receiving the solder ball is formed between the opened contact tips and/or whether a predetermined physical condition is provided to each contact, the protruded retainers can intervene between the camera and a part of the contacts, inhibiting the measurement of the gaps of those contacts, depending upon the size and/or shape of the retainers. This requires that the retainers are retained in the retracted positions by means of exclusively designed tools before mounting the socket onto the test site. Also, a fitting and unfitting of the tool requires an extra effort and time. 
     In view of foregoing, a purpose of the present invention is to provide a socket, a socket base and methods for operating and testing the sockets, capable of holding the retainers outside the viewing field of the camera in spite of the size and/or shape of the retainers. 
     SUMMARY OF THE INVENTION 
     To attain this, the present invention is to provide a socket for an integrated circuit device, the socket having a plurality of contacts corresponding to a plurality of terminals mounted on a major surface of the integrated circuit device, comprising: 
     a base for supporting the contacts; 
     a plurality of retainers, each of the retainers being mounted on the base for movement between a projected position in which the retainer is projected into a region above the integrated circuit device mounted on the contacts to make a contact with an upper surface portion of the integrated circuit device and a retracted position in which the retainer is retracted out of the region above the integrated circuit device; 
     a plurality of springs, each of said springs being provided for biasing the retainer from the retracted position to the projected position; 
     wherein the base has a plurality of through-holes extending through the base, the through-holes being so positioned that, when pins are passed upwardly through the through-holes, respectively, the retainers are forced by the pins from the projected positions to the retracted positions. 
     Another aspect of the present invention is to provide a socket base for supporting the socket, wherein the socket base has the pins. 
     Another aspect of the present invention is to provide a method for operating retainers of a socket for an integrated circuit device, comprising the steps of: 
     (a) providing a socket including a base having through-holes extending through the base, a plurality of contacts mounted in the base, retainers mounted for movement between respective first positions in which the retainers are positioned above an integrated circuit device mounted on the contacts to retain the integrated circuit device on the contacts and respective second positions in which the retainers are retracted from above the integrated circuit device to release the integrated circuit device and springs for biasing the retainers from the respective second positions to the respective first positions; 
     (b) providing a socket base for supporting the socket, the socket base having pins corresponding to the through-holes; 
     (c) mounting the socket on the socket base so that the pins of the socket base are passed through the corresponding through-holes of the base to force the retainers from the respective first positions to the respective second positions against the springs; and 
     (d) removing said socket from said socket base. 
     Another aspect of the present invention is to provide a method for testing a socket for an integrated circuit device, comprising the steps of: 
     (a) providing a socket having a base having through-holes extending through the base, a plurality of contacts mounted in the base, retainers mounted for movement between respective first positions in which the retainers are positioned above an integrated circuit device mounted on the contacts to retain the integrated circuit device on the contacts and respective second positions in which the retainers are retracted from above the integrated circuit device to release the integrated circuit device and springs for biasing the retainers from the respective second positions to the respective first positions; 
     (b) providing a socket base for supporting the socket, the socket base having pins corresponding to the through-holes; 
     (c) mounting the socket on the socket base while the pins of the socket base are passed through the corresponding through-holes of the base to force the retainers from the respective first positions to the respective second positions against the springs; and 
     (d) removing the socket from the socket base. 
     According to the socket, socket base and the combination thereof, when the socket is mounted on the socket base, the pins of the socket base are passed through the corresponding through-holes of the base to force the corresponding retainers from the projected positions to the retracted positions. This allows that, when measuring the gaps of the contacts and/or the physical conditions of the contacts such as heights of the contact tips relative to the base, the optical device such as camera are capable of viewing and measuring the gaps and/or physical conditions of all contacts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the socket according to the present invention; 
         FIG. 2  is a plan view of the socket according to the present invention; 
         FIG. 3  is an exploded perspective view of the socket according to the present invention; 
         FIG. 4  is a perspective view of the base and the retainers of socket shown in  FIG. 1 ; 
         FIG. 5  is an enlarged perspective view of the contacts provided in the socket shown in  FIG. 1 ; 
         FIG. 6A  is a partial enlarged perspective view showing a movement of a nest assembly and contacts, in which the contact tips take a free state; 
         FIG. 6B  is a partial enlarged perspective view showing a movement of the nest assembly and contacts, in which the contact tips take an open state; 
         FIG. 6C  is a partial enlarged perspective view showing a movement of the nest assembly and contacts, in which the contact tips are moving from the free state to the closed state; 
         FIG. 6D  is a partial enlarged perspective view showing a movement of the nest assembly and contacts, in which the contact tips are moving from the closed state to the open state; 
         FIG. 7  is a perspective view of a part of the socket and the socket base; 
         FIG. 8  is a partial perspective view showing the socket mounted on the socket base; and 
         FIG. 9  is a diagram showing a movement for mounting the socket onto the socket base. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the accompanying drawings, several embodiments of the socket will be described below in connection with a specific operation for measuring contact gaps. Referring to  FIGS. 1-3 , in particular  FIG. 3 , a socket generally indicated by reference numeral  10  has an alignment plate  100 , a base  200 , retainers  300 , a nest assembly  400 , a guide frame  500 , a lever assembly  600  and a top cover  700 . 
     The alignment plate  100 , which is in the form of substantially rectangular plate of electrically non-conductive material, has a rectangular, contact alignment region  102 . The region  102  has a number of contact alignment holes  104  arranged in a grid, at regular intervals in the orthogonal X- and Y-directions. The plate  100  also has through-holes  106  each extending vertically between top and bottom surfaces of the alignment plate  100  and provided adjacent and outside the central portion of the opposite edges of the rectangular region  102  (one of the through-holes is omitted from the drawing.) 
     As indicated in  FIG. 4 , the base  200 , which is made of electrically non-conductive material, has a rectangular bottom portion  202  and peripheral walls  204  surrounding the bottom portion  202 . The bottom portion  202  has a rectangular contact alignment region  206  corresponding to the contact alignment region  102  of the alignment plate  100 . Similar to the contact alignment region  102  of the alignment plate  100 , the contact alignment region  206  has a number of contact alignment holes  208  arranged in a grid, at the regular intervals in the orthogonal X- and Y-directions. 
       FIG. 5  shows an embodiment of the contact  800 . The illustrated contact  800 , which is made of electrically conductive material, has a central portion  802  in the form of “U” when viewed from above. The opposite ends of the central portion  802  are extended upward to form a pair of cantilever arms  804  each of which terminate at tip portions  806 . A part of the central portion  802  is extended downward to form a leg  808 . Each contact  800  is securely held by the base  200  with the central portion  802  fitted within the contact alignment hole  208 , so that the cantilever arms  804  and the tips  806  are projected from the top surface of the base and the legs  808  are projected from the bottom surface of the base. 
     As indicated in  FIGS. 3 and 4 , the base  200  further has a pair of retainer supports  210  positioned outside the contact alignment region  206  to oppose to each other across the region  206 . Each retainer support  210  has a pair of vertical walls  212  positioned in line and parallel to the adjacent peripheral edge of the region  206 , defining a vertical slot  212  therebetween. Each of the walls  212  has on its back an upper engagement portion  216  and a lower engagement portion  218 , both projected rearward therefrom. In addition, provided below the vertical slot  214  and outside the contact alignment region  206  is a through-hole  220  extending vertically through the bottom portion  202  of the base. 
     As shown in  FIG. 3 , the alignment plate  100  and the base  200  are assembled with each other. In this assembling, the legs  808  of the contacts projected from the bottom surface of the base are each passed through the associated contact alignment holes  104  of the alignment plate  100  to protrude downward. When assembled, the through-holes  220  of the bottom portion  202  of the base are properly aligned in line with the associated through-holes  106  of the alignment plate  100 . This in turn means that the through-holes  106  of the alignment plate  100  and the through-holes  220  are so positioned that they oppose to each other in the assembled condition. 
     Preferably, the assembling of the alignment plate  100  and the base  200  is attained by means of a snap-fit mechanism made of, for example, four vertical legs  108  of the alignment plate  100  and the corresponding four recesses or through-holes  222  of the base  200  into each of which the legs  108  are inserted for engagement. 
     As shown in  FIG. 4 , the retainer  300  has a main portion  302  in the form of substantially inversed “J” or “L” with a distal end  304  projected forwardly from its top portion. The main portion  302  has a proximal end portion  306  with a pair of bearing shafts  308  projecting from its left and right edges. The proximal end  306  further has a front projection  310  which projects from a central, front surface portion thereof and a rear projection  312  which projects from a central, rear surface portion thereof. 
     Each of the retainer  300  is assembled to the retainer support  210  of the base  200  with the main portion  302  positioned behind the vertical walls  212  and each of the left and right bearing shafts  308  engaged between the upper and lower engagements  216  and  218 , so that the retainer  300  is supported for rotation between a first position or projected position in which the distal end  304  projects above the contact alignment region  208  of the base  200  (see  FIG. 2 ) and a second position or retracted position the distal end  304  stays outside the contact alignment region  208  (see  FIG. 7 ). In the assembled state, the forward projection  310  stays within the vertical slot  214  and above the through-hole  220  when the retainer  300  takes the projected position. A biasing means or spring  314  is provided for each retainer and positioned between the base  200  and the rear projection  310  of the retainer so that the retainer  300  is biased and retained in the projected position while the main portion  302  is forced against the vertical walls  212 . 
     As indicated in  FIG. 3 , the nest assembly  400  has a pair of comb structures  402  as described in U.S. Pat. No. 5,498,970. Each of the comb structures  402 , which is made of electrically non-conductive material, has an end frame portion  404  and a plurality of parallel cantilever racks  406  extending orthogonally therefrom. A gap defined between the neighboring racks  406  is slightly larger than the width of the cantilever rack so that the comb structures  402  can be assembled to each other with each of the cantilever racks of one comb structure  402  positioned between the neighboring cantilever racks of the other comb structure  402 . 
     The nest structures  402  are oriented in opposite directions and then assembled with each of the cantilever arms  406  of one nest structure  402  positioned between the each neighboring cantilever arms  406  of the other nest structure  402  to form the nest assembly  400 . The nest assembly  400  so assembled is placed on the base  200  with the cantilever arms  406  oriented in the X-direction. As indicated in  FIG. 6A , ones of the contact tips  806  are located between the neighboring projections  408  of the racks  406  of one comb structure  402  and the other ones of the tips  806  are located between the neighboring projections  408  of the racks  406  of the other comb structure  402 . As indicated in  FIGS. 6A-6D , this allows that, by forcing the comb structures  402  close to each other in the X-direction against the resiliency of the cantilever arms  804 , each pair of contact tips  806  is forced from a free state (see  FIG. 6A ) to an open state (see  FIG. 6B ), creating a larger space therebetween having a size sufficient for receiving a terminal or solder ball  902  provided on the major surface (e.g., bottom surface) of the integrated circuit device  900 . 
     To ensure the relative movement of the comb structures  402 , the nest assembly  400  is connected to the base  200  so that at least one of the comb structures  402  can move to and from the other. For example, as shown in  FIG. 3 , each of the comb structures  402  has engagement legs  410  at opposite ends of the end frame portion  40 . The base  200 , on the other hand, has four engagement holes  222  to each of which the engagement legs  410  are inserted. The size of the engagement holes  222  in the X-direction is larger than that of the legs  41  so that the legs  410  can move in that direction within the associated engagement holes  222 . This allows the relative movement of the comb structures  402  between two positions corresponding to the free and open states. 
     The package guide  500 , which is made of electrically non-conductive material and is used for guiding the BGA integrated circuit device into a proper position of the nest assembly  400 , has a rectangular frame  502  defining a rectangular opening region  504  which corresponds to the external configuration of the integrated circuit device. The package guide  500  is assembled to the base  200  to which the nest assembly  400  has been mounted. In this assembled state, the tips  806  of the contacts held by the nest assembly  400  are exposed within the opening region  504 , allowing the contacts  800  to hold the corresponding solder balls  902  on the bottom surface of the integrated circuit device  900  placed within the opening  504  ( FIGS. 6A to 6D ). Preferably, four inner edges of the rectangular frame  502  have respective surface portions  506  each inclined downwardly and inwardly to ease the insertion of the integrated circuit device into the opening  504 . Also preferably, the frame portions  508  running in the X-direction have downwardly extended cutouts  510  to ensure rearward rotations of the retainers  300 . Further preferably, the package guide  500  has restrictions  512  which restrict the rearward movements of the bearing shafts  308  retained by the retainer supports  210  of the base  200 . Furthermore, the package guide  500  is preferably secured to the nest assembly  400  using the legs  514  of the package guide  500  (only two of which are illustrated in  FIG. 3 ) and the recesses  224  of the base  200  into which the legs  514  are engaged. 
     Referring to  FIG. 3 , the lever assembly  600  has a pair of substantially U-shaped brackets  602 . Each bracket  602  has a transverse member  604  in the form of place extending in the Y-direction and sides arms  606  each extending substantially perpendicularly from either end of the transverse member  602 . The brackets  602  are so assembled with each other that the arms  604  of one bracket intersect obliquely with those of the other. The assembled lever assembly  600  is then mounted on the base  200  so that each of the transverse members  604  is positioned between the end frame  404  of the nest assembly  400  on the base  200  and the opposed side wall of the base  200 , with the arms  606  oriented obliquely and upwardly. This ensures that, when the distal ends of the arms  606  are depressed downward, the transverse members  604  rotate about their longitudinal axes to force the end frames  404  of the nest assembly  400  toward each other, which results in that the tips  806  of each contact  800  are changed from the free state to the open state. When, on the other hand, the depressing force is eliminated, the tips  806  of each contact  800  are moved from the open state to the free state due to the resiliency of the contacts. 
     The top cover  700 , which is made of electrically non-conductive material, has a rectangular frame  702  defining therein an opening  704  which is so sized and shaped that the integrated circuit device  900  can pass therethrough and is assembled on the base  200  on which the nest assembly  400 , the guide frame  500  and the lever assembly have been already assembled thereto. To allow the top cover  700  to move vertically between an elevated position (see  FIG. 1 ) and a lowered position (not shown), relative to the base  200 , the top cover  700  has a plurality of downwardly extending legs  706  and the base  200  has in its outer peripheral surfaces a plurality of vertical grooves  226  in each of which the legs  706  of the top cover  700  are slidably engaged. The inner surface of each leg  706  has an engagement portion  712  and the associated base groove  226  has in its top portion a projection  228  to which the engagement portion  712  will be engaged to inhibit the top cover  700  from elevating beyond its elevated position. A plurality of biasing springs  708  are provided between the top cover  700  and the base  200 , so that the top cover  700  is normally forced in the elevated position. The top cover  700  further has a pair of downwardly extending actuators  710  capable of engaging with the rearward projections  312  of the retainers  300  to move the retainer  300  from the projected position back to the retracted position due to the downward movement of the top cover  700  from the elevated position to the lowered position. 
     When testing the BGA integrated circuit device  900  using the socket  10 , as shown in  FIGS. 6A to 6D , the legs  808  of the contacts  800  extending from the bottom surface of the alignment plate  100  are electrically connected to the testing circuit not shown. In this state, the top cover  700  is depressed to force the distal ends of the arms  606  of the lever assembly  600  downwardly, which rotates the transverse portions  604  of the lever assembly  600  rotate about respective longitudinal axes to force end frame portions  404  of the nest assembly  400  to each other. This results in that the actuators  710  of the top cover  700  depress the rearward projections  312  of the retainers  300 , which rotates the retainers  300  from the projected positions to the retracted positions. Also, each gap defined by the opposed tips  806  of each contact  800  is enlarged, in which each of the solder balls  902  mounted on the bottom surface of the integrated circuit device  900  is accommodated (see  FIG. 6A-6D ). 
     When the depressing force is removed, the top cover  700  returns to the elevated position due to the biasing force from the springs  708 . As a result, the comb structures  402  are moved back to a closed state due to the resiliency of the cantilever arms  804  of the contacts  800 , in which each solder ball  902  is nipped by the obliquely opposed tips  806  of the contacts and thereby the integrated circuit device  900  is electrically connected to the test circuit not shown. Also, the retainers  300  rotate from the retracted positions to the projected positions where the tips  304  of the retainers make forcing contacts with the respective portions of the integrated circuit device  900 . Preferably, the retainers  300 , in particular the tips  304  are so shaped and sized that the tips  304  are brought into contact with the upper surface portions where the tips  304  oppose the solder balls  902 , which prevents an unwanted upward warpage of the central portion of the integrated circuit device which would otherwise be caused if the tips  304  of the retainer  300  depress a region outside the solder balls and prevents the resultant unreliable connections between the contact tips  806  and the solder balls  902  of the contacts in its central region. 
     After the completion of the test for the integrated circuit device  900 , the top cover  700  is again depressed to lower the distal ends of the arms of the lever assembly  600 , which causes the contact tips  806  to move from the closed state to the open state. At this moment, the retainers  300  rotate from the projected positions to the retracted positions. This allows the integrated circuit device  900  to be removed from the socket  10  to lose contacts with the associated contacts. 
     When testing whether each pair of opposed contact tips  806  defines a predetermined size of gap or opening therebetween, the socket  10  is mounted on a socket base  1000  indicated in  FIG. 7 . The socket base  1000 , which is made of electrically non-conductive material, has, for example, four positioning portions  1002  provided according to the outer configuration of the base  200 . The socket base  1000  also includes two actuation rods or pins  1004  extending upwardly from the socket base  1000  within a region surrounded by the four positioning portions  1002 . The actuation pins  1004  are positioned at respective places where both the through-holes  106  of the alignment plate and the associated through-holes  220  of the base aligned therewith oppose when the socket  10  is positioned on the socket base  1000  by means of the positioning portions  1002 . 
     At measuring gaps of the contact tips, the socket  10  is mounted on the socket base  1000 . At this moment, the socket  10  is properly positioned by the four positioning portions  1002 . As shown in  FIGS. 8 and 9 , this causes that the actuation pins  1004  are passed through the through-holes  106  of the alignment plate and also the through-holes  220  of the base and then projected therefrom above the bottom portion  202  of the base, forcing the retainers  300  on the through-holes  220  of the base upward against the biasing forces derived from the springs  314 . This results in that the retainers  300  rotate from the projected positions back to the retracted positions and the distal end portions  304  of the retainers are moved away from the region positioned above the contacts  800 , which ensures that all the gaps of the contact tips to be reliably measured by means of an image pickup device such as camera (not shown). After the completion of the gap measurement, the socket  10  is removed from the socket base, which returns the retainers  300  into the projected positions due to the biasing forces from the springs  314 . 
     In view of the foregoing, the socket according to the present invention causes the retainers  300  to be moved from the projected positions to the retracted positions simply by mounting the socket  10  onto the socket base  1000 , without using any purpose-built specific tools designed for moving and then keeping the retainers  300  at the retracted positions, before mounting the socket onto the socket base. Also, the measurement of the gaps is significantly simplified. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.