Abstract:
A top loaded burn-in socket for forming a plurality of electrical connections between a ball gird array (BGA) package having a plurality of conductive ball leads and an electrical component is provided. The socket assembly includes a plurality of resilient electrical contacts; a cam being configured to position the contacts from a first position to a second position; a device guide plate including a plurality of openings for receiving the ball leads; and an actuating mechanism configured to interact with the cam to position the contacts, wherein an upper portion of the contacts engages the ball leads between the upper portion and an inclined surface of the device guide plate openings. Each ball is thus held in a manner that does not require the use of a hold down mechanism for effecting electrical continuity between the BGA package and the contacts of the subject burn-in socket.

Description:
PRIORITY  
       [0001]     This application is a continuation of application Ser. No. 11/210,322, filed Aug. 24, 2005, which claims the benefit of U.S. Provisional Application No. 60/605,321 filed Aug. 27, 2004, the contents of both of which are hereby incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     1. Field  
         [0003]     The present disclosure relates to a universal burn-in ball grid array socket, and more particularly, a top loaded burn-in socket which eliminates the need for hold down devices when the ball grid array package is inserted into the subject socket.  
         [0004]     2. Description of the Related Art  
         [0005]     Integrated circuits are typically housed within a package which is designed to protect the integrated circuit from damage, provide adequate heat dissipation during operation, and provide electrical connection between the integrated circuit and the leads of a printed circuit board. Several conventional packages are in the prior art including land grid array (LGA), pin grid array (PGA), ball grid array (BGA), column grid array (CGA) and quad flat pack (QFP).  
         [0006]     Referring to  FIG. 1A , a ball grid array (BGA) package  102  typically consists of a semi-conductor device  104  and a plurality of conductive ball leads  106  extending downwardly from the bottom surface  108  of the semi-conductor device  104 . The BGAs generally place conductive ball leads over an entire surface of a chip, instead of just around the edges. Thus, BGA packages allow system designers to place more leads in a given package size using looser tolerances than peripheral lead type packages such as the quad flat pack (QFP). Therefore, board producers are not required to use the fine pitch spacings that are now necessary for high lead count packages. Also, BGAs have finer pitch spacings than pin grid arrays (PGA), since the solder balls do not have the coplanarality problem associated with through-hole PGAs.  
         [0007]     In the prior art, the electrical connection between the BGA package and underlying printed circuit board (PCB), or electrical component, was generally provided by soldering the ball leads which are located underneath the BGA package onto pads which are provided on the upper surface of printed circuit boards.  
         [0008]     In many applications, the soldering of the ball leads of the ball grid array package to the printed circuit board is undesirable. For example, it is impossible to visually locate a short or ground between the ball grid array package and printed circuit board. Usually, an expensive X-ray technique is required to inspect the connections since the ball leads are hidden under the ball grid array package. Further, the increasing number of ball leads being provided by ball grid array packages makes the soldering of the ball grid array packages to printed circuit boards more difficult.  
         [0009]     Accordingly, in the prior art and disclosed in various patent publications, connectors have been developed which are designed to eliminate the need for the soldering the ball leads of a BGA package to a printed circuit board. More particularly, applicant is the inventor of U.S. Pat. No. 5,887,344 entitled “Method of Mounting a Plurality of Ball Leads onto a BGA Socket” which issued on Mar. 30, 1999 and is assigned to the assignee of the subject patent application. Applicant is also the inventor of U.S. Pat. No. 5,730,606 which issued on Mar. 24, 1998 and is entitled “Universal Production Ball Grid Array Socket”. U.S. Pat. No. 5,887,344 is a divisional application of U.S. Pat. No. 5,730,606. In turn, applicant is also the inventor of U.S. Pat. No. 5,984,694 which issued on Nov. 16, 1999 and is entitled “Universal Production Ball Grid Array Socket”, and said patent is a divisional application of U.S. Pat. No. 5,887,344. Applicant is also the inventor of U.S. Pat. No. 6,045,416 which issued on Apr. 4, 2000 and is entitled “Universal Production Ball Grid Array Socket”, and this patent is a continuation-in-part of U.S. Pat. No. 5,730,606. All of the above-mentioned patents are assigned to the assignee of the subject patent application. U.S. Pat. Nos. 5,730,606; 5,887,344; 5,984,694 and 6,045,416 are all incorporated herein by reference.  
         [0010]     One of the possible shortcomings associated with prior art burn-in sockets is the requirement to have, as part of the socket, a means for holding down the chip scale package (CSP) or ball grid array (BGA) package in the socket, because of the spring forces acting to bias the respective package out of the socket. Such hold down means usually incorporates a plurality of individual pieces, in order to lock the ball grid array package to the socket. The additional locking means adds cost, as well as possible mechanical problems in connection with the mounting of a ball grid array package to a burn-in socket of the prior art type.  
         [0011]     One example of a prior art type burn-in socket employs a spring pogo “Z” axis type of contact  110  which pushes up against the solder balls  106  of the BGA package as shown in  FIG. 1B . Because of the spring structure of the pogo contact  110 , the package  102  requires an opposite and reactive force to maintain contact between the pogo sockets and balls. The reactive force is provided by a hold down means which adds parts and complexity to the socket. Similarly, a spring type contact  112  shown in  FIG. 1C  results in the same disadvantages.  
         [0012]     In another type of device as illustrated in  FIG. 1D , stamped pins  114  are provided in the socket with a force directed in the “Z” axis direction, and again a hold down means must be provided for maintaining the ball grid array package in the burn-in socket of this prior art type.  
         [0013]     A still further type of a prior art socket is shown in  FIG. 1E . This type of socket uses dual pinch pins  116 , and that type of contact also requires a hold down mechanism that adds parts and complexity to the burn-in socket. Furthermore, since the pinch pins engage a lower portion of the solder balls  106 , damage may result to the solder balls.  
         [0014]     Furthermore, another one of the possible shortcomings associated with prior art CSP/BGA production sockets is the possible wicking of the fluid materials used during the bonding of the ball leads onto an underside of a ball grid array socket. More particularly, it is important that the contact which extends through a hole in the substrate is tightly supported in the hole so as to ensure that no wicking of fluid materials takes place.  
         [0015]     Accordingly, it is an object of the present disclosure to provide a top loaded, burn-in socket which does not require a hold down mechanism as part of the socket.  
         [0016]     It is a further object of the present disclosure to provide a top loaded, burn-in socket which inherently includes structure for maintaining the interengagement of the ball grid array package in the burn-in socket, and thereby obviates the requirement for a hold down mechanism as part of the socket.  
         [0017]     It is still a further object of the present disclosure to provide a top loaded, burn-in socket which does not require a hold down mechanism as part thereof, thereby eliminating unnecessary structural components within the burn-in socket and reducing the complexity of the socket structure.  
         [0018]     It is another object of the present disclosure to provide a contact for a CSP/BGA production socket which is mounted to the socket in a manner to prevent wicking of fluid materials used for bonding a solder ball to the socket.  
       SUMMARY  
       [0019]     A top loaded burn-in socket assembly for forming a plurality of electrical connections between a ball grid array (BGA) package having a plurality of conductive ball leads and an electrical component is provided. The socket assembly includes a plurality of resilient electrical contacts; a cam being configured to position the contacts from a first position to a second position; a device guide plate including a plurality of openings for receiving the ball leads; and an actuating mechanism configured to interact with the cam to position the contacts, wherein an upper portion of the contacts engages the ball leads between the upper portion and an inclined surface of the device guide plate openings. Each ball is thus held in a manner that does not require the use of a hold down mechanism for effecting electrical continuity between the BGA package and the contacts of the subject burn-in socket.  
         [0020]     According to one aspect of the present disclosure, a socket assembly includes a generally rectangular housing including a base having a plurality of apertures; a plurality of resilient electrical contacts disposed in the plurality of apertures; a cam having a plurality of openings corresponding to the plurality of contacts disposed in the housing, the cam being configured to position the plurality of electrical contacts from a first closed position to a second open position; a generally rectangular device guide plate disposed on the an upper surface of the housing, the device guide plate having a base including a plurality of openings for receiving the ball leads and a plurality of side walls extending upwardly from the base defining an insert area for the package; and an actuating mechanism configured to interact with the cam to position the plurality of electrical contacts from the first closed position to the second open position.  
         [0021]     In another aspect, each electrical contact includes a lower portion for contacting the electrical component below the socket assembly, an intermediate portion for securing the electrical contact to the housing and an upper portion for contacting a ball lead of the package, wherein the upper portion of the electrical contact includes a dual pin configuration for contacting an upper hemisphere of the ball lead.  
         [0022]     In a further aspect, the housing of the socket assembly includes a plurality of side walls extending upwardly from the base defining a second insert area for the cam and the cam being dimensioned to be smaller than the second insert area to allow the cam to slide within the second insert area from a first position to a second position. The upper portion of the electrical contact is bent relative to the intermediate portion to bias the cam in the first position. Furthermore, the cam includes a plurality of inclined walls extending downward from a top surface of the cam to guide the upper portion of the electrical contact from the first closed position to the second open position.  
         [0023]     In another aspect of the present disclosure, each opening of the device guide plate includes a circular inclined surface that tapers outward from an upper surface of the base of the device guide plate to a lower surface of the base of the device guide plate, wherein the upper portion of the electrical contact extends into the opening of the device guide plate to engage the ball lead between the upper portion and the inclined surface.  
         [0024]     In a further aspect, at least three openings of the device guide plate are formed in a key lock configuration, the key lock configuration including a circular opening portion for each of the three openings for receiving a ball lead and a connector portion between at least two of the circular opening portions to allow the upper portion of the electrical contact open wide enough to allow the ball lead to enter the circular opening portion.  
         [0025]     According to another aspect of the present disclosure, an electrical contact for a test socket assembly, the test socket assembly for forming a plurality of electrical connections between a ball grid array package having a plurality of conductive ball leads and an electrical component, includes a lower portion for contacting the electrical component below the socket assembly, an intermediate portion for securing the electrical contact to the socket assembly and an upper portion for contacting a ball lead of the package, wherein the upper portion is movable from a first closed position to a second open position.  
         [0026]     Furthermore, each contact has molded thereon at one end, preferably by an insert molding technique, a plastic sleeve, which sleeve is of a diameter slightly greater than the diameter of the aperture in the housing to achieve an interference fit for maintaining the contact within the aperture, in a manner which prevents wicking of fluid materials into the contact. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0028]      FIG. 1A  is a cross sectional view of a conventional ball grid array (BGA) device;  
         [0029]      FIGS. 1B, 1C ,  1 D and  1 E illustrate four different types of prior art, burn-in sockets which use different types of contacts;  
         [0030]      FIG. 2  is an exploded perspective view of the top loaded, burn-in socket of the present disclosure;  
         [0031]      FIG. 3  is a perspective view of a housing employed in the top loaded burn-in socket of the present disclosure;  
         [0032]      FIG. 4A  is a front elevational view of an electrical contact for the socket of the present disclosure,  FIG. 4B  is a side elevational view of the contact in  FIG. 4A  and  FIG. 4C  is a side elevational view of the contact formed for use in the housing according to an embodiment of the present disclosure;  
         [0033]      FIG. 5A  is a top plan view of a cam employed in the socket of the present disclosure,  FIG. 5B  is a side elevational view of the cam taken along line  5 B- 5 B in  FIG. 5A ,  FIG. 5C  is bottom perspective view of the cam and  FIG. 5D  is a side elevational view of the cam;  
         [0034]      FIG. 6A  is a perspective view of a device guide plate;  
         [0035]      FIG. 6B  is a top plane view of the device guide plate with an enlarged view of openings formed therein;  
         [0036]      FIG. 6C  is a cross-sectional view of the device guide plate with an enlarged view of one opening of the device guide plate;  
         [0037]      FIG. 7  is a bottom perspective view of an actuating mechanism;  
         [0038]      FIGS. 8A, 8B ,  8 C and  8 D are cross-sectional views of the socket and corresponding top plan views illustrating the sequential positions of the dual contact pins relative to the side walls of the device guide plate of the present disclosure, where  FIG. 8A  shows the contacts in a normally closed position,  FIG. 8B  shows the contacts in an open position,  FIG. 8C  shows the contact in the open position with the BGA device inserted into the socket, and  FIG. 8D  shows the contacts in contact with the solder ball leads of the BGA device;  
         [0039]      FIG. 9A  is a front elevational view of an electrical contact and  FIG. 9B  is a side elevational view of the contact in  FIG. 9A  formed for use in the housing according to another embodiment of the present disclosure;  
         [0040]      FIG. 10A  is a front elevational view of an electrical contact and  FIG. 10B  is a side elevational view of the contact in  FIG. 10A  formed for use in the housing according to a further embodiment of the present disclosure;  
         [0041]      FIGS. 11A and 11B  are respectively front elevational and side elevational views of a socket contact of the present disclosure, with a plastic sleeve molded thereon, and with the contact being formed and still connected to a carrier strip;  
         [0042]      FIG. 11C  is a front elevational view of the plastic sleeve;  
         [0043]      FIG. 11D  is a top elevational view of  FIG. 11C ; and  
         [0044]      FIG. 11E  is a top plan view of an alternate configuration of the plastic sleeve. 
     
    
     DETAILED DESCRIPTION  
       [0045]     Preferred embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.  
         [0046]     The new and improved top loaded burn-in socket of the present disclosure is intended for use in a chip scale package or ball grid array package (CSP/BGA) burn-in sockets.  
         [0047]     Referring to  FIG. 2 , a top loaded, burn-in socket of the present disclosure is generally designated by the numeral  10 . The socket  10  includes a base plate or bottom  12  having openings  24  for coupling the socket to a printed circuit board (PCB), an electrical component or the like, a generally rectangular housing  14  having a plurality of apertures, a plurality of resilient electrical contacts  16  disposed in the plurality of apertures and a cam  18  having a plurality of openings corresponding to the plurality of contacts  16  disposed in the housing  14 , the cam being configured to position the plurality of electrical contacts  16  from a first closed position to a second open position. The socket  10  also includes a generally rectangular device guide plate  20  disposed on an upper surface of the housing  14 . The device guide plate  20  includes a base including a plurality of openings for receiving solder ball leads or contacts of an integrated circuit (IC) device and a plurality of side walls extending upwardly from the base defining an insert area for the IC package or device  102 . Further, the socket  10  includes an actuating mechanism or cam pusher  22  configured to interact with the cam  18  to position the plurality of electrical contacts  16  from the first closed position to the second open position.  
         [0048]     The base plate  12  is formed from a generally flat piece of non-conductive material which in use will be securely fastened to a PCB or the like. The base plate also includes a plurality of apertures for enabling the contacts of the socket  10  to be coupled to corresponding connections of a PCB or the like. The base plate  12  further includes two latches  26 ,  28  for coupling to corresponding openings  26 - 1 ,  28 - 1  of the device guide plate  20  for containing intermediate components of the socket together.  
         [0049]     Referring to  FIG. 3 , the housing  14  is illustrated without the electrical contacts disposed therein. The non-conductive housing  14  is generally rectangular having a base  30  including a plurality of apertures  32  for receiving the contacts  16  and a plurality of side walls  34 ,  36 ,  38 ,  40  extending upwardly from the base  30  defining an insert area  42  for the cam  18 . The housing  14  further includes a plurality of annular recesses  44  for receiving springs  46  which bias the cam pusher  22  in its most upright position.  
         [0050]     Referring to  FIGS. 4A and 4B , an electrical contact  16  to be employed in the socket  10  of the present disclosure is illustrated. The contact  16  includes a lower portion  48  which extends through the base plate  12  for coupling to an electrical component, underlying PBC or the like, an intermediate portion  50  including a barb  51  and an upper portion  52  for contacting a solder ball lead. The intermediate portion  50  is configured with the barb  51  to form an interference fit when placed in an aperture  32  of the housing  14  to secure the contact  16 . The upper portion  52  includes a dual contact pin configuration  54  for contacting an upper hemisphere of a solder ball. Preferably, the contact  16  is stamped from a single piece of sheet material, e.g., a blank, which will add only a small thickness to the openings in the device guide plate for receiving the ball leads.  
         [0051]     As shown in  FIG. 4C , the upper portion  52  of contact  16  is bent at a deflection point  56  of intermediate portion  50  at a predetermined angle a. The contact  16  may be formed from any known resilient conductive material. Preferably, the contact  16  is made of a brush beryllium copper alloy and has resilient properties which allow the upper portion  52  to move from a first position as shown in  FIG. 4C  to a second position as shown in  FIG. 4B . The resiliency of the contact and the configuration of the device guide plate  20  will enable the socket to retain a BGA device without a hold down mechanism, the details of which will be described below.  
         [0052]     A top plan view of the cam  18  is shown in  FIG. 5A . The cam  18  is formed from a non-conductive material and is generally rectangular and includes a plurality of openings  58  the number of which corresponds to the number of contacts  16 . The cam  18  is dimensioned to be smaller than the insert area  42  of the housing  14  so when disposed in the insert area  42  the cam  18  will be allowed to slide back and forth as indicated by arrow A shown in  FIG. 3 . The sliding motion of the cam  18  will move the upper portion  52  of the contact  16  from a first, closed position to a second, open position. Referring to  FIGS. 5B and 5C , a plurality of inclined walls  60  extend downwardly from a top surface  62  of the cam  18  to guide the upper portion  52  of each contact  16 . Each wall  60  is placed between the rows of openings  58  to allow the contacts  16  to transition smoothly from the first position to the second position.  
         [0053]     The cam  18  further includes a plurality of actuation members  64  configured with at least one inclined surface  66 . As will be described below, the cam pusher  22  will interact with the actuation members  66  to actuate, or slide, the cam, and the contacts, from its first position to a second position. The resilient nature of the contacts will bias the cam  18  to slide back to the first position when pressure is removed from the cam pusher  22 .  
         [0054]     Referring now to  FIG. 6A , a perspective view of the device guide plate  20  is illustrated. The non-conductive device guide plate  20  is generally rectangular device and has a base  68  including a plurality of opening  70  for receiving solder ball leads or contacts  106  of a BGA device  102  and a plurality of side walls  72 ,  74 ,  76 ,  78  extending upwardly from the base  68  defining an insert area  80  for the IC device or package  102 . Each group of three openings  70  is formed in a key lock configuration  82  as shown in the enlarged view of  FIG. 6B . Referring to  FIG. 6C , each key lock configuration  82  includes a circular opening portion  84  for receiving a solder ball contact  106  and a connector portion  86  to allow the upper portion  52  of the electrical contact  16  to open wide enough to allow the solder ball to enter the opening  84 . Each opening  70  includes a circular inclined surface  88  that tapers outward from an upper surface  90  of the base to a lower surface  92  of the base  68 . The operation of the upper portion  52  of the electrical contact  16  and the key lock configuration  82  will be described in more detail below in relation to  FIG. 8 .  
         [0055]     The actuating mechanism or cam pusher  22  is illustrated in  FIG. 7 . The actuating mechanism  22  is formed from a non-conductive material and is generally rectangular and includes a plurality of members for interacting with other components of the socket  10 . Members  120 ,  122 ,  124 ,  126  interact with the plurality of springs  46  recessed in the housing and cause the cam pusher  22  to be biased in its most upright position. Members  128 ,  130 ,  132 ,  134  interact with the actuation members  64  of the cam  18  to slide the cam  18  to the second position to open the contacts  16 . In the second position, the upper portion  52  of the contact  16  is in line with the intermediate portion  50  and lower portion  48 .  
         [0056]     Referring to  FIG. 8A , when the top loaded, burn-in socket  10  is in its initial or rest position, the cam pusher  22  is biased to its most upright position and the cam  18  is in the first position, in the figure, to the right. The dual contact pin portion  54  of each contact  16  engages or is very close to the respective circular opening portion  84  of the opening  70  of the device guide plate  20 . At this time, the spacing between each contact  16 , e.g., the dual contact pin portion  54 , and the inclined wall  88  of the opening  70  prevents a solder ball  106  from entering the respective opening  70 , and thus, the contact  16  is in the closed position.  
         [0057]     As pressure is exerted on the cam pusher  22  in a downward direction as indicated by arrow B, members  120 ,  122 ,  124 ,  126  interact with the plurality of springs  46  and members  128 ,  130 ,  132 ,  134  interact with the actuation members  64  of the cam  18  to slide the cam  18  to the left as indicated by arrow C in  FIG. 8B . The movement of the cam  18  causes the upper portion  52  of each contact  16  to bend at the deflection point  56  so as to open the contact  16 . In this position, the upper portion  52  of the contact  16  is in line with the intermediate portion  50  and lower portion  48 . Here, the upper inclined portion  52  of each contact  16  is sufficiently spaced from the respective inclined wall  88  to create an enlarged opening to allow the solder ball  106  to be received in the opening  70 , e.g., an open contact position. The connector portion  86  of the key lock configuration  82  allows the dual pin contact portion  54  of the contact  16  to move to a position so opening  84  is now larger enough to allow entry of a solder ball.  
         [0058]     While the downward pressure is maintained on the cam pusher  22 , an IC device or package  102  may now be inserted into the socket  10  as shown in  FIG. 8C . Here, the solder balls  106  of the IC device  102  are in the openings  70  but the dual pin contact portion  54  in not yet in contact with the solder balls  106 .  
         [0059]     After the BGA device  102  is inserted, the pressure is released from the cam pusher  22  and the cam pusher is biased in the direction as indicated by arrow D in  FIG. 8D  by springs  46 . As the cam pusher withdraws, members  128 ,  130 ,  132 ,  134  disengage with actuation members  64  of the cam  64  and the upper portion  52  of the contacts return to their normal or first position driving the cam  18  back to its first position. As the contacts  16  return to their rest position, the dual contact pin portion  54  engages the solder ball  106  on one side while the solder ball comes into contact with the inclined wall  88  of opening  70  of the device guide plate  20 , thereby positively engaging and holding the solder ball  106  within the top loaded, burn-in socket  10  and establishing good electrical contact between the ball grid array package  102  and the top loaded, burn-in socket  10 .  
         [0060]     After the ball grid array package  102  is loaded into the top loaded, burn-in socket  10 , the dual contact pin  54  of each contact  16  engages the upper hemispherical surface of the respective solder ball  106 , and at the same time the inclined wall surface  88  likewise engages the upper hemispherical surface of the ball  106 , thereby restraining movement of the ball  106  from the opening  70 , and thereby effectively locking the ball grid array package  102  within the top loaded, burn-in socket  10 .  
         [0061]     Because of the interengagement of the solder balls  106  with the contacts  16  and the inclined surfaces  88  of the device guide plate  20 , there is no need for a hold down mechanism to form a part of the top loaded, burn-in socket  10 , thereby reducing the number of parts of the socket  10  as well as reducing the complexity of the structure of the socket  10 . Furthermore, since the socket  10  adds thickness only to one side of a solder ball via a single contact, the top loaded burn-in socket of the present disclosure is scaleable from 0.5 mm to 1.27 mm. This results in a very low cost socket since the contact is blanked out from sheet material and has only one simple forming station.  
         [0062]      FIGS. 9A and 9B  illustrate another embodiment of an electrical contact  202  to be employed in the socket  10  in accordance with the present disclosure. In the embodiment as shown in  FIG. 9A , the contacts  202  are still connected to a carrier strip  204 , and the contacts are made of a brush beryllium copper alloy or similar conductive material as in known in the art. In the embodiments of  FIGS. 9A and 9B , each contact  202  includes an intermediate barb  206  for connection to the socket structure, e.g., housing  14 . In  FIG. 9B , the contacts  202  are formed so as to be bent through an angle b, e.g., approximately nineteen degrees, prior to the step of molding a plastic sleeves to the contacts, as will be described below.  
         [0063]     In the embodiments of  FIGS. 10A and 10B , the barbed portion  206  is replaced with an undercut  208  as required in certain applications.  
         [0064]      FIGS. 11A and 11B  respectively illustrate a front elevational view and a side elevational view of the contacts  202  with molded sleeves  206  as attached to the carrier  204 . As shown in  FIGS. 11A-11C , insert molded about one end of each contact  202  is a plastic sleeve  206  including a flat platform portion  208  such that a portion  210  of the contact extends beyond the platform portion  208 . After the plastic sleeves  206  are insert molded about the contacts  202 , the carrier strip  204  may then be broken off from the array of contacts  202 .  
         [0065]      FIGS. 11C and 11D  illustrate one embodiment of the plastic sleeve members  208  which include fins designated by the numerals  212  which assist in achieving a tight interference fit between the sleeve  206  and the opening in the socket, so as to prevent wicking of fluid materials when a socket ball is attached to the end  210  of the contact  202 .  FIG. 11E  illustrates another embodiment of the molded sleeve  214  which is generally circular with extending triangular fins  216 .  
         [0066]     The process by which socket balls may be attached to the bottom portion  210  of contacts  202  is fully disclosed in the above-mentioned patents of the applicant, and which are assigned to the assignee of the present disclosure.  
         [0067]     While the disclosure has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims.