Abstract:
An improved test socket for use in testing integrated circuits. The test socket includes a housing having one or more slots formed therein. Contacts can be received within respective slots and maintained therein with rear ends of the contacts in engagement with traces on a load board. Mounting is accomplished by means of a pair of elastomers, and the elastomers maintain each contact such that, when the front end of a contact is engaged by the lead or pad of the device to be tested and urged into its corresponding slot, an arcuate surface at a rear end of each contact rolls across its corresponding trace with virtually no translational or rotational sliding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of application Ser. No. 11/482,644 filed on Jul. 7, 2006 now U.S. Pat. No. 7,445,465, which claims priority of the following provisional applications filed under 35 U.S.C. §111(a) claiming priority, under 35 U.S.C. §119(e) (1): provisional application Ser. No. 60/697,693, previously filed Jul. 8, 2005, under 35 U.S.C. §111(b); provisional application Ser. No. 60/776,654, previously filed on Feb. 24, 2006, under 35 U.S.C. §111(b); and provisional application Ser. No. 60/697,721, previously filed on Jul. 8, 2005, under 35 U.S.C. §111(b). 

   TECHNICAL FIELD 
   The present invention deals with electronic component testing technologies. More specifically, however, the invention deals with test sockets which employ contacts for testing an electronic component. A test socket includes contacts which interconnect and provide an electronic path between a lead or pad of the electronic component to be tested and a corresponding trace on a load board. The invention focuses upon control and regulation of forces applied to a device lead or pad and a load board trace by a corresponding contact of the test socket. 
   BACKGROUND OF THE INVENTION 
   Integrated circuit device testing is a procedure which has been observed for many years in order to obtain as high a degree of quality control as possible for electronic devices. A tester typically includes a plurality of conductive traces formed on a load board associated with the tester apparatus. It is necessary to interconnect a lead, of a leaded device, or a pad, of a non-leaded device, to a corresponding trace on the load board in order to effectuate testing. A test socket having a plurality of contacts is interposed between the device under test and the load board in order to effectuate interconnection. One contact engages, at a front end, the lead or pad of a device under test with its corresponding trace on the load board. 
   Over the years, shape and construction of such contacts have evolved in response to the construction of test sockets, load boards, and architecture of devices to be tested. Formerly, it was considered necessary to have a wiping action at the various locations of engagement at the contact ends in order to provide a good transmission path. As technology has progressed, however, it has become apparent that less wiping action is necessary to maintain a good transmission path than what was formerly believed. Furthermore, it has become apparent that excessive wiping action damages component parts at the various points of engagement and significantly decreases the life of the test socket and tester load board. Consequently, various attempts have been made to minimize abrading of one surface relative to another. The current state of the art, however, has been unable to define a construction adequate to both maximize efficiency of the test socket and minimize abrasion and consequent deterioration of component parts. 
   It is to these problems and dictates of the prior art that the present invention is directed. Its advantages will become more apparent with reference to the Summary of the Invention, Detailed Description of the Invention, appended claims and accompanying drawing figures. 
   SUMMARY OF THE INVENTION 
   The present invention is an improved test socket. It includes a housing which has a first surface that is placed into engagement with a surface of a tester load board. The housing has a second surface which is generally parallel to, and spaced from, the housing first surface. The second surface of the housing faces in a direction opposite that in which the first surface faces. At least one slot, extending through the housing between the first and second surfaces thereof, is formed in the housing. A contact is received in a corresponding slot. Such a contact has a front end which normally extends beyond the second surface of the housing to be engaged by a corresponding lead or pad of a device to be tested. The contact further has a rear end which defines an arcuate surface, the arcuate surface engaging a corresponding trace formed on the surface of the tester load board. The contact is elastomerically mounted in its slot such that, when the front end of the contact is engaged by the lead or the pad of the device to be tested and urged into its slot, the arcuate surface of the contact rolls across its corresponding trace on the surface of the tester load board with virtually no translational or rotational sliding. Abrasion between the contact and the load board is, thereby, substantially eliminated. 
   It is envisioned that the rear end of the contact, in addition to defining the arcuate surface in engagement with the load board, also defines a gradually arcing surface which is angularly spaced from the arcuate surface thereof. The housing, in this embodiment, defines a wall within the slot. The wall is engaged by the gradually arcing surface of the rear end of the contact, and the spatial relationship between the gradually arcing surface and the wall is such that, as the front end of the contact is engaged by the lead or pad of the device to be tested and urged into the corresponding slot, the gradually arcing surface moves along the wall and causes the arcuate surface of the contact to roll across its corresponding trace. It is envisioned that the wall defined by the housing would be angularly spaced at an acute angle relative to the first surface of the housing. This would enable the arcuate surface of the contact to roll across the trace of the tester load board with virtually no translational or rotational sliding. 
   A preferred embodiment of the invention employs a pair of elastomers, crossing perpendicularly across the slots, to effect the elastomeric mounting of the contacts. A front elastomer is positioned in a channel between the surface of the tester load board and the contacts. The front elastomer is pre-compressed in view of the fact that a shoulder defined by the housing can be employed to engage the contacts and limit the distance they extend beyond the second surface of the housing. Pre-compression is, thereby, accomplished by the contacts and the load board sandwiching the front elastomer therebetween. The front elastomer becomes further compressed by the contacts as they are engaged by the leads or pads of the device to be tested and urged into their respective slots. 
   The rear elastomer pre-loads the rear end of the contact. It thereby maintains contact between the rear end of each contact against its corresponding trace on the surface of the tester load board. 
   The present invention can employ contacts made of precious metals. Such contacts extend load board life. A Neyoro G contact is a solid gold alloy contact without any plating. While it has been found that such a material extends the life of the contact, it also extends load board life. By using Neyoro G material for the contacts, load board life can, it has been found, be at least doubled over load board life in mechanisms known in the prior art. 
   The present invention is thus an improved test socket which addresses the dictates of the prior art and solves problems thereof. More specific features and advantages obtained in view of those features will become apparent with reference to the Detailed Description of the Invention, appended claims and accompanying drawing figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a test socket in accordance with the present invention showing contact and elastomer response to engagement of a contact by a lead of a device under test; and 
       FIG. 2  is a perspective view of a contact for use in the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawing figures, wherein like reference numerals denote like elements throughout the several views,  FIG. 1  illustrates a test socket  10  in accordance with the present invention. The test socket  10  is intended for use with a tester typically employed for ascertaining quality of integrated circuit devices used in electronic appliances. The tester interfaces with a tester load board  12  which has electrically conductive traces  14  formed on a surface  16  thereof to enable electronic communication between the tester and an integrated circuit device  18  to be tested. That is, electrical signals are transmitted between the device under test  18  and the test apparatus through the test socket  10 . 
     FIG. 1  illustrates a DUT package which is provided with a plurality of leads  20 , only one of which is shown.  FIG. 1  illustrates only a portion of the device under test  18 , but it will be understood that substantially identical leads extend along both of opposite sides of the device package  18 . 
     FIG. 1  further illustrates a lead backer which, when the device under test  18  is brought into engagement with its leads  20  in contact with corresponding contacts  24  of the test socket  10 , deters bending of the leads  20 . Downward pressure is brought to bear upon the device  18  under test by a plunger mechanism (not shown). The plunger depresses, when testing is to be conducted, the contacts  24  to overcome an upward bias imparted by the elastomerically-mounted contacts  24 .  FIG. 1  illustrates the normal position of the contacts  24  prior to a device under test  18  being brought into engagement with the contacts  24 . That figure also illustrates, in phantom, a position of the contact when the plunger has depressed the device under test to its test position. Typically, the distance of travel of the front end  26  of a contact  24  along an axis along which the plunger moves is on the order of 0.3 mm. It will be understood that, in view of the construction of the contacts  24  as will be discussed hereinafter, an arcuate surface  28  at a rear end  30  of the contact  24  on a lower edge thereof will roll across a corresponding trace  14  on the load board  12  with virtually no translational or rotational sliding of that surface along the trace  14 . Optimally, arcuate surface  28  would have as great a radius of curvature as possible to limit the impact brought to bear upon trace  14 . Further, it has been found that, in view of the construction of the contact  24 , translational sliding of the front end  26  of the contact  24  along the lead  20  of the device under test  18  to which the contact corresponds will be adequate to effect significant scrub on the front end of the contact but minimal scrub on a lead  20  of the device  18 . For example, in one embodiment of the invention, the translational sliding is on an order of 0.041 mm on the device  18 . 
   The test socket  10  includes a housing  32  which has a first surface  34  generally in engagement with the surface  16  of the tester load board  12  on which the traces  14  are formed. The housing  32  has a second surface  36  which is generally parallel to, and spaced from, the first surface thereof. The second surface  36  of the housing  32  faces oppositely from the first surface  34 . As previously discussed, the housing  32  carries a plurality of contacts  24 . A plurality of slots  38  are provided, each slot to receive a single one of the contacts  24 . 
     FIG. 2  illustrates, in perspective, an individual contact in accordance with the present invention. The contact  24  includes first, second and third protrusions  40 ,  42 ,  44 . The first protrusion  40  is defined by the rear end  30  of the contact  24  which engages the trace  14  of the load board  12 . The third protrusion  44  is defined by the front end  26  of the contact  24  which is engaged by a lead  20  or pad of the device under test  18 . The second protrusion  42  serves to engage, when mounted by a plurality of elastomers  46 ,  48 , as will be discussed hereinafter, a shoulder  49  defined by the housing  32 . Engagement of the shoulder  49  by the second protrusion  42  serves to limit the degree of upward movement of the contact  24  and the distance the front end  26  of the contact  24  will extend beyond the second surface  36  of the housing  32  when the contact  24  is not engaged by a device to be tested. 
   Referring again to  FIG. 1 , the test socket  10  has a pair of channels  50 ,  52  which extend along axes generally transverse to planes defined by the slots  38  formed in the housing  32 . These channels  50 ,  52  are intended to receive elastomers  46 ,  48  which serve to mount the contacts  24  in their slots  38 .  FIG. 1  shows a generally circular channel  50  receiving a larger, front elastomer  46 , and a rectangular channel  52  receiving a smaller, rear elastomer  48 . The rear elastomer  48  is pre-loaded and, because of the arcuate surface  28  of the rear end  30  of the contact  24  being in engagement with the load board  12 , will engage an upper edge of the rear end  30  of the contact  24  at a location to urge the front end  26  of the contact  24  upwardly. Similarly, the front elastomer  46  is under compression and also serves to urge the contact  24  upward and bias it to a point of initial contact by a lead  24  or pad of an integrated circuit device  18  to be tested. 
   As previously alluded to, the arcuate surface  28  in engagement with the trace  14  on the load board  12  has no, if any, appreciable translational or rotational sliding along the trace  14  of the load board  12 . This is so because of an angled wall  54  defined within the housing  32  proximate its first surface  34  near the end of a slot  38 . The rear end  30  of the contact  24 , in addition to defining the arcuate surface  28 , also has a gradually arcing surface  56  at an edge of the rear end  30  of the contact  24  which engages this angled wall  54  defined by the housing  32 . Disposition of a contact  24  is such that the gradually arcing surface  56  will interact with the angled wall  54  defined by the end of the slot  38  so that the point of contact of the arcuate surface  28 , while it will move across the load board trace  14 , will not slide across that trace  14 . The motion will be virtually totally a rolling action (that is, one in which the relative movement across the trace will be as a wheel rolling on a surface without any slippage). This will result from the gradually arcing surface  56 , because of its contour, permitting the arcuate surface  28  of the rear end  30  of the contact  24  to roll without translational sliding as engagement of the gradually arcing surface  56  is maintained in contact with the angled wall  54 . When the device under test  18  is withdrawn, rolling in a reverse direction will occur. 
   As previously discussed, as withdrawal of the device occurs, the second projection  42  will engage the shoulder  49  defined by the housing  32  in order to limit upward movement of the contacts  24 . 
   It will also be noted that the point of application of force by a device under test  18  is spaced laterally a relatively significant distance from the point of engagement of the rear end  30  of the contact  24  with the trace  14  on the load board  12 . This will augment the beneficial advantage achieved by the rolling action (that is, minimization of likelihood of damage to the load board). 
   Further, contacts made of precious metals can be employed in the present invention. Such contacts tend to extend load board life also. A Neyoro G contact, which is a solid gold alloy contact not having any plating, is envisioned as being used. Such a material, it has been found, not only extends the life of the contact. It also, however, extends load board life by minimizing damage to the traces thereon. It has been found that load board life can be at least doubled over mechanisms constructed as known in the prior art. 
   It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in 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.