Abstract:
An improved test socket for testing or connecting an integrated circuit is disclosed having a platform for receiving the integrated circuit and adapted to overlay a piece of test equipment or other board, the platform formed with an array of slots each locating a portion of a two-piece connector assembly. The socket includes a conforming groove that captures an elastomer member therein while providing exposure of the elastomer member to a link assembly. The socket, with the capture groove, provides improved contact of the link assembly and reliability in locating and maintaining positioning of the elastomer member.

Description:
BACKGROUND 
     The present invention relates to a socket that electrically connects an integrated circuit with an IC board. More particularly, the present invention is directed to a socket, such as those used for testing or connecting an integrated circuit, that incorporates an array of two-piece connectors that achieve a positive connection between an IC device under test (DUT) and a board, such as a load board of a piece of test equipment or other fixture. 
     Integrated circuit tester devices have long been used in the semiconductor industry to test and evaluate the quality of the chips off the manufacturing line. Signal integrity is a critical aspect of chip design and testing. To this end, it is desirable to maintain impedance through a conducting portion of a contact interconnecting the integrated circuit lead to its corresponding load board pad at a particular desired level. The effective impedance of the design is a function of a number of factors. These include width and length of conduction path, material of which the conductive structure is made, material thickness, etc. 
     When testing the electrical characteristics of a packaged or molded semiconductor device such as an integrated circuit (IC), it is common to utilize a specialized test socket that secures and connects the IC to the equipment that evaluates its performance, i.e. a load board. Many different test sockets have been devised for quickly and temporarily connecting integrated circuit leads of a chip to be tested to a load board of a tester. Automated test apparatus in particular use a number of such sockets. Typical socket arrangements use force brought to bear upon a contact positioned between a lead of the IC and the load board to deform a probe tip of the contact and engage a pad on the load board. Such a configuration provides for positive connection between the pins or contact pads of the DUT and corresponding leads of a test apparatus. Examples of this type of connection can be found, for example, in U.S. Pat. No. 6,409,521 to Rathburn, and U.S. Pat. No. 7,737,708 to Sherry, the teachings and contents of both of which are fully incorporated herein by reference. 
     U.S. Pat. No. 7,918,669 to Tiengtum discloses a socket system that uses a linkage to urge the connectors of the test circuit upward where it can make contact with the test equipment. This test socket was found to be very successful in ensuring good contact with the test apparatus while reducing force on the circuit itself. However, the configuration shown in the &#39;669 patent did not adequately secure the link member or properly direct its force against the PCB. The elastomer member could slip out of its groove or twist out of alignment. The present invention utilizes the benefits of the &#39;669 socket but overcomes the shortcomings set forth above. 
     SUMMARY OF THE INVENTION 
     The present invention is a socket for an integrated circuit having a series of contact pads or other electrical connection sites linearly arranged, for example, along at least one peripheral edge, the socket including a platform that supports the IC and houses a plurality of connectors that when engaged with the integrated circuit&#39;s contact pads, complete an electrical connection between the contact pads and the associated fixture&#39;s contacts below the platform. The socket&#39;s platform may have a plurality of generally parallel slots for aligning and receiving a corresponding plurality of electrical contacts, one in each slot. Each electrical contact path is formed of a two piece linkage that cooperates to form an electrical connection between the contact pad and the fixture&#39;s contact. The two pieces of the contact cooperate together to form a non-deforming, reliable electrical connection between the IC and the board. The socket includes a semi-circular groove to house a cylindrical elastomer member, the profile providing both lateral, upward, and downward support to resist movement of the elastomer member and better position the connector against the PCB. 
     These and many other features of the present invention will best be understood by reference to the following descriptions and figures. However, it is to be understood that while the inventor&#39;s best mode has been described and shown, the invention is not to be limited to any particular drawing or description. Rather, it is understood that there may be many variations of the present invention that would be readily appreciated by one of ordinary skill in the art, and the invention encompasses all such variations and modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevated, perspective view of an embodiment of the test socket of the present invention; 
         FIG. 2  is an elevated, perspective view of the socket and cylindrical capture groove; 
         FIG. 3  is an enlarged, elevated cut-away view of a portion of a test socket illustrating the connector and cylindrical capture groove; 
         FIG. 4  is below view of the socket showing the elastomer member and circular capture groove; 
         FIG. 5  is an enlarged, perspective view of the link and mount in the engaged position; 
         FIG. 6  is an enlarged, cross-sectional view of the contact between the integrated circuit and the connector link; and 
         FIG. 7  is an elevated view of the connection between the PCB and the connectors under the influence of the elastomer member. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The description below is presented in the environment of a test board and a test IC. However, it is to be understood that the invention is not so limited in application, and that other uses of the socket are anticipated and contemplated by the inventors. Thus, no limitation should be implied by the use of terms such as “test socket” or “load board.” Rather, the invention may be used for any and all applications for which it is appropriate. 
       FIG. 1  shows a test socket  10  of the type embodying the present invention having a generally square wall structure defining a well for receiving an integrated circuit component  16 . As shown more effectively in  FIG. 3 , the test socket  10  has a platform  12  that receives the integrated circuit  16  thereon. The socket  10  is shown on a pad  18  that represents a piece of test equipment that can receive electrical signals from the IC  16  and assess the quality, strength, and other characteristics of the signal. The purpose of the test socket  10  is to electrically pass signals from the contact pad  20  of the IC  16  to the test equipment  18  via a connector assembly  22 . The connector assembly  22  pivots between a stand-by or disengaged position where no IC is present, and an engaged position ( FIG. 6 ), where the engaged position corresponds to the completed electrical circuit between the IC and the test equipment through the connector  22 . The platform  12  has a plurality of slots  24  (best shown in  FIG. 2 ) that allow a portion  19  of the connector  22  to emerge from an upper surface. As explained below, when the IC  16  is placed on the platform  12 , the pads  20  of the IC  16  each contact a portion  19  of the connectors  22  protruding through the slots  24 , and cause the connectors  22  to pivot into the engaged position. In this way, the electrical contact is established reliably and automatically when the IC is placed on the test socket platform  12 . 
       FIG. 6  represents the condition of the connector  22  after the IC  16  has been placed on the platform. The connector  22  that establishes an electrical connection is a two piece assembly having a link member  26  and a mount element  28 . A resilient tubular member  30  is housed in the cylindrical capture groove  33  (see also  FIG. 2 ), and serves to bias the connector  22  in the disengaged position. The groove  33  roughly matches the contour of the elastomer member  30  and holds it in place. This allows the elastomer to be embedded in the socket, and provides more evenly applied pressure in a greater range of surface area of the elastomer  30 . By contouring the groove to the contour of the elastomer profile, misalignment is avoided and consistent and reliable pressure is applied by the elastomer to the link  26 . 
     The mount  28  is retained in the platform  12  and includes a generally planar upper surface  32  and a generally planar lower surface  34 . In a preferred embodiment, the platform  12  is sized to compress the mount  28  slightly so that it extends into and slightly embeds the test equipment contact surface  18 . Between the lower and upper surfaces is a laterally opening cavity  36  having a slightly upwardly tilted orientation. The cavity  36  is substantially circular up to a mouth, which then gradually widens toward the link  26 , and the cavity is approximately sized to retain a portion of the link member therein. The upper edge of the mouth  38  transitions to the upper surface  32  through a curved finger-like projection  40 . Similarly, the lower edge of the mouth  38  transitions to the lower surface  34  through a projecting lip member  42 . The lip member  42  has a lower edge that curves upward to a front edge  44 . 
     The link  26  has three main components. The first component is an arcuate contact surface  46  along the upper edge that is shaped to permit rolling contact with the IC above as the IC applies a downward force on the link  26 , causing the link  26  to pivot about the mount  28 . The second component of the link  26  is a rocker arm  48  having a neck portion  51  that terminates in a bulb-shaped distal tip  50 . The cavity  36  of the mount  28  and the bulb-shaped distal tip of the rocker arm  48  are complimentary sized to allow smoothing pivoting of the rocker arm within the cavity of the mount in a controlled manner without undue wobble. The tubular member  30  is resilient and, seated in the circular capture groove  33 , biases the arcuate surface clockwise (upward) so as to project through the slot  24  of the platform  12 . With the link rotated in the position, a leg member  52  is rotated out of contact with the test equipment  18 . This is the disengaged position (not shown), or stand-by position as the connection assembly is ready for the presence of the IC chip. 
     As seen in  FIGS. 3 and 5  through  7 , when the IC  16  is brought to bear against the platform  12 , the lower surface  17  of the IC  16  contacts the protruding arcuate surface  46  of the link  26  and pushes the link down against the bias of the resilient tubular member  30 . This downward force brought to bear by the IC  16  rotates the link counterclockwise against the bias of the resilient member  30 , as the link  26  pivots about the mount via the rocker arm  48 . This rotation of the link  26  continues until the leg member  52  makes solid contact with the test equipment  18 . Further downward force only increases the pressure applied by the rocker arm  48  at the cavity  36  of the mount  28  to bolster the reliability of the contact. This is the engaged position, as there is a direct flow path between the contact pad  20  of the IC  16 , through the arcuate contact surface  48  of the link  26  and through the rocker arm  48  to the mount  28 , which is embedded on and affixed to a lead (not shown) of the load board/test equipment  18 . The flow path being established, signals can then be processed by the test equipment from the IC in the conventional manner. It should be noted that there is no deformation of any component of the connector assembly, and therefore no part of the connector assembly can lose its resiliency and have the contact pressure diminish over time. 
       FIG. 4  illustrates the capture groove  33  as it surrounds and embeds the cylindrical elastomer member  30 . As can be seen in  FIGS. 2 and 4 , the groove  33  is circular and in profile and cylindrical in shape and matches the contour of the elastomer member  30 . When the socket is placed on the test equipment  18 , the elastomer member  30  is locked in place and cannot move or twist out of position. In a first preferred embodiment, the semi-circular profile is approximately 270 degrees of arc, and is at least greater than 180 degrees of arc in a second preferred embodiment. In other embodiments, the capture groove  33  is of a different shape, but still abides by the contour of the resilient elastomer member  30 . The groove  33  improves contact with the links  26 , 28 , and also facilitates assembly and maintenance as the socket can be handled without having the elastomer member become dislodged or fall out. 
     The capture groove  33  is formed in the socket using a special drill that creates a circular cross section. The drill is sized to match the diameter of the elastomer member so that there is a snug, if not press, fit. The groove is cut across the width of the socket in a preferred embodiment, although the opening of the groove may be intermittent and the elastomer member “weaved” into the groove  33 . 
     It will be understood that this disclosure is merely illustrative, and that it is to be further understood that changes may be made in the details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims, and is not limited in any manner by the aforementioned descriptions and drawings.