Abstract:
A method of assembling a test contactor is described. The method includes aligning an interposer and an electrical contactor wherein resilient interconnection elements of the interposer are resiliently deformed into a deformed state to make electrical contact with corresponding electrical terminals on the electrical contactor; and securing the interposer and the electrical contactor together to lock the resilient interconnection elements in said deformed state.

Description:
This Application is a divisional of U.S. patent application Ser. No. 10/197,133, filed on Jul. 16, 2002, which issued as U.S. Pat. No. 6,853,209 on Feb. 8, 2005. 

   FIELD OF THE INVENTION 
   This invention relates to test equipment. In particular, it relates to test equipment for testing electrical circuits including integrated circuits. 
   BACKGROUND 
   When fabrication of electronic devices, such as computer processors and memories, have been completed, the electronic devices are subjected to burn-in and electrical testing in order to identify and eliminate defective devices before shipment. The term “burn-in” relates to operation of an integrated circuit at a predetermined temperature or temperature profile, typically an elevated temperature in an oven. Certain operating electrical bias levels and/or signals are supplied to the electronic devices while they are at the elevated temperature. The use of the elevated temperature accelerates stress to which the devices are subjected during burn-in, so that marginal devices that would otherwise fail shortly after being placed in service fail during burn-in, and are therefore not shipped. 
   Test equipment for burn-in testing of electrical circuits generally comprise a connection arrangement for electrically connecting an electrical circuit to be tested such as an integrated circuit on a wafer or test substrate, to a test probe circuit. 
   SUMMARY 
   In one embodiment, the invention provides a contactor assembly for use in testing electrical circuits. The contactor assembly comprises an electrical contactor including a contactor substrate, and a plurality of electrical terminals; an interposer including an interposer substrate having first and second sides, a plurality of first and second resilient interconnection elements extending respectively from the first and second sides of the interposer substrate, wherein the interposer is positioned in a predetermined position relative to the electrical contactor in which predetermined position each first resilient interconnection element makes electrical contact with an electrical terminal of the electrical contactor, the interposer substrate having been moved relatively towards the contactor substrate to resiliently deform the first resilient interconnection spring elements; and a retaining component having a first portion secured to the electrical contactor and a second portion in contact with the interposer to retain the interposer in the predetermined position relative to the electrical contactor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described by way of example with reference to the accompanying drawings wherein: 
       FIG. 1  is a block diagram of an interposer, an electrical contactor and a wafer comprising circuits to be tested; 
       FIG. 2  is a block diagram of a contactor assembly in accordance with one embodiment of the invention; 
       FIG. 3  is a block diagram illustrating a stage in the formation of the contactor assembly of  FIG. 2 ; 
       FIG. 4  is a perspective view of a vacuum plate connected to a ring, in accordance with one embodiment of the invention; 
       FIG. 5  is a top plan view of the vacuum plate and ring of  FIG. 4 ; 
       FIG. 6  is a section on  6 - 6  in  FIG. 5 ; 
       FIG. 7  is a block diagram illustrating how a ring and interposer seated therein may be aligned with a contactor, in accordance with one embodiment of the invention; 
       FIG. 8  is a perspective view of an alignment machine in accordance with one embodiment of the invention; 
       FIG. 9  is an end view of the alignment machine shown in  FIG. 8  of the drawings with a microscope mounted thereon; 
       FIG. 10  is a perspective view of the alignment machine of  FIG. 8  mounted on a probe plate; 
       FIG. 11  is an end view of  FIG. 10 ; and 
       FIG. 12  is a block diagram of a test probe assembly in accordance with one embodiment of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  of the accompanying drawings illustrates an interposer  10  and an electrical contactor  26  which together form a contactor assembly, according to an embodiment of the invention, used to test electrical circuits, for example, on a wafer  32 . 
   As will be seen from  FIG. 1 , the interposer  10  includes a substrate having a first side  12  and a second side  14 . The interposer  10  includes a number of electrical terminals  16  on the first side  12 . The interposer  10  also includes resilient interconnection elements in the form of interconnection spring elements  18 . Each interconnection spring element  18  extends from an electrical terminal  16  on the side  12  and terminates in a free end. The purpose of each interconnection spring elements  16  is to make good electrical contact with corresponding electrical terminals on the electrical contactor  26 . In other embodiments, the resilient interconnection elements include pogo pins and compliant conductive bumps. 
   The interposer  10  also has an interconnection spring element  20  on each electrical terminal  16  on side  14 . The interconnection spring elements  20  are similar to the interconnection spring elements  18  except that the interconnection spring elements  20  are for making electrical contact with corresponding electrical terminals on the wafer  32 . 
   The interposer also includes mechanical stops  22  on the sides  12  and  14  to prevent overtravel of the interconnection spring elements  18  and to prevent the interposer from touching certain areas of the wafer  32 . 
   The electrical contactor  26  includes a contactor substrate which includes a side  28 . Electrical contactor  26  also includes electrical terminals  30  on the side  28 . 
   The wafer  32  is shown to include a side  34  which has the electrical circuits to be tested. The wafer  32  has electrical terminals  36  on the side  34  whereby electrical connection to the electrical circuits may be made. 
     FIG. 2  of the drawings shows a contactor assembly  40  in accordance with one embodiment of the invention. The assembly  40  includes an interposer  10  and a retaining component in the form of a ring  42 . The interposer  10  is secured or held in a predetermined z position relative to the electrical contactor  26  by a ring  42 . It will be seen that in the predetermined or aligned position, each interconnection spring element  18  has been deformed against a spring force thereof to make electrical contact with a corresponding electrical terminal  30  of electrical contactor  26 . The predetermined z position is reached by moving the ring  42  and the interposer  10  seated therein until the stops  22  bear against the side  28  of the electrical contactor  26 . In other embodiments, the predetermined position is reached when sufficient pressure is exerted by the interconnection spring elements  18  (or the pogo pins or compliant conductive bumps in other embodiments) to keep the contactor  26  in place. The stops  22  are thus optional. A spacing between the interposer  10  and the electrical contactor  26  is such that each of the interconnection spring elements  18  is under compression. 
   The ring  42  is formed with a recessed surface  44  which defines a seat for the interposer  10 . The ring  42  has a flat flange-like face  46  which bears against side  28  of electrical contactor  26 . The ring  42  is secured to the electrical contactor  26  by means of fasteners  43 , for example screws, extending through screw holes  48  (see  FIG. 4 ). The holes  48  are dimensioned to accommodate the fasteners  43  with some degree of play to permit alignment of fiducial markings on the interposer  10  and contactor  26 , respectively. 
     FIG. 3  of the drawings shows a first stage in the formation of the contactor assembly  40 . Referring to  FIG. 3 , a vacuum plate  50  is releasably secured to a side of the ring  42  opposing face  46  to form a sub-assembly  51 . The vacuum plate  50  can be connected to a pump (not shown) by means of a coupling  54  and a hose  52  connected to the coupling  54 . In use, the pump creates a vacuum in a region  56  between the vacuum plate  50  the interposer  10 . The vacuum retains interposer  10  against the recessed surface  44 . As can be seen from  FIGS. 4 and 5 , the vacuum plate  50  is shaped and dimensioned to provide access to the fasteners  43 . 
   As can be seen from  FIG. 6  which shows a sectional view through sub-assembly  51  taken at  6 - 6  in  FIG. 5 , the interposer  10  seats snugly in the ring  42 . 
     FIG. 7  of the drawings shows a block diagram of how alignment of the interposer  10  with the electrical contactor  26  is achieved. The interposer  10  is seated in the ring  42  and moved in an x, y, or θ) direction such that a fiducial marking  58  on the side  14  of the interposer  10  is aligned with a fiducial marking  60  on the side  28  of the electrical contactor  26 . Once the fiducial marking  58  is aligned with the fiducial marking  60 , the ring  42  together with the interposer  10  is displaced in a z direction so that the ring  42  makes contact with the electrical contactor  26 . A screw  43  located in hole  48  is then screw-threaded into a complementary threaded socket  68  formed in electrical contactor  26 . The fiducial markings  58 ,  60  allow for alignment for the electrical terminals  30  on the electrical contactor  26  with the ends of the interconnection spring elements  18  without having to take an image of the interconnection spring elements  18 . Tolerances in the position of each interconnection spring element in the x-y plane or the angle at which it projects from the x-y plane do not effect the alignment process. The mechanical stops  22  on the side  18  of the interposer  10  may be used to limit movement of the interposer  10  towards the electrical contactor  26  when forming the assembly  40 , such that each of the interconnection spring elements  18  is under the desired compression. 
     FIG. 8  of the drawings shows a perspective view of an alignment machine  70 , in accordance with one embodiment of the invention, which may be used to align the ring  42  and interposer  10  combination with the electrical contactor  26 . The alignment machine  70  includes a base  72  which is shaped and dimensioned to rest on a probe plate  152  which, in use, houses the electrical contactor  26 . The alignment machine  70  also includes a raised platform or plate  74  which is secured to the base  72  by means of mounting brackets  76 . The platform  74  supports a carriage  78 . The carriage  78  is seen in  FIG. 9  of the drawings which shows a side view of the alignment machine  70 . The carriage  78  is secured to an underside of the platform  74  by means of a mounting arrangement comprising angle brackets  88  and horizontal springs  90 . The angle brackets  88  are secured to the platform  74  and provide an anchor for one end of the springs  90 , the other end of the springs  90  being secured to a floating plate  80  of carriage  78  as can be seen in  FIG. 9  of the drawings. 
   The carriage  78  further includes ring holders  82  which are secured to the floating plate  80  of vertical members  84  extending between the ring holders  82  and the floating plate  80 . 
   Roller bearings  94  disposed between the platform  74  and the floating plate  80  allow for slideable displacement of the floating plate  80  relative to the platform  74 . Vertical springs  95  urge the floating plate  80  into contact with roller bearings  94 . It will be appreciated that the spring mounting arrangement of the floating plate  80  to the platform  74  allows for movement of the floating plate  80  in an x-y plane. Such movement in the x y plane is controlled by means of an adjustment mechanism which, in one embodiment, includes micrometers  96 ,  98 , and  100 , each of which can be operated to urge a tip thereof to bear against an edge of the floating plate  80  thereby to cause the displacement of floating plate  80 . For example, as can be seen in  FIG. 9  of the drawings, a tip  98 . 1  of the micrometer  98  may be displaced in a y direction to bear against an edge of the floating plate  80  thereby to cause the floating plate  80  to be displaced in the y direction. Because the ring holders  82  are rigidly connected to the floating plate  80 , displacement of the floating plate  80  also causes corresponding displacement of the ring holders  82 . 
   In use, the interposer  10  which is seated in the ring  42  by means of a suction force created with the aid of the vacuum plate  50  and a pump (not shown) is connected mechanically to the ring holders  82  of the carriage  78 . Thereafter, the alignment machine  70  is positioned on a probe plate  152  as is shown in  FIG. 10 . In this position, the ring  42  and the interposer  10  which is seated in the ring  42  is positioned directly over the electrical connector  26  which is seated in the probe plate  152 . 
   A magnification system comprising a microscope  102  which includes a scope section  104  and a base  106  is secured on the platform  74  as can be seen in  FIG. 9  of the drawings. 
   The microscope  102  magnifies the fiducial markings  58 ,  60  on the interposer  10  and the electrical connector  26 , respectively. The micrometers  96 ,  98  and  100  may then be operated to move the carriage  78 , which carries the ring  42  and the interposer  10  with it, so that the interposer  10  may be positioned over the electrical connector  26  in a predetermined or aligned position in which the fiducial markings,  58 ,  60  on the interposer  10  and the electrical contactor  26 , respectively, are in alignment. 
   The alignment machine  70 , further includes micrometer heads  108  which may be operated to move the carriage  78  in a z direction which causes the interposer and ring combination to be displaced in the z direction towards the electrical contactor  26 . In use, displacement in the z direction is continued until the stops  22  contact the side  28  of electrical contactor  26 , or the desired z position is reached. When this position is reached, the screws  43  are screwed into the sockets  68  in the electrical contactor  26 , thereby to secure the ring  42  and the interposer  10  seated therein to the electrical contactor  26 . 
   Once the ring  42  and the interposer  10  are secured to the electrical contactor  26 , the vacuum plate  50  and the alignment machine  70  are removed. The probe plate  152  may then be aligned to a wafer  32 . Thereafter, the probe pate  152  may be secured to a chuck plate  154  which carries the wafer  32  (see  FIG. 12  of the drawings). 
     FIG. 12  of the drawings illustrates the components of test probe assembly  150  in accordance with one embodiment of the invention. The test probe assembly  150  includes a probe plate  152  and a chuck plate  154  which together define a space therebetween for receiving a contactor assembly such as the contactor assembly  40  shown in  FIG. 2  of the drawings. 
   The chuck plate  154  has a pedestal  156  which provides support for the wafer  32 . The probe plate  152  includes a piston  158  which is displaceable in a cylinder  160  by a pneumatic (air) means which, in use, is introduced into the chamber  160  through a hose  162  which is releasably connectable to the cylinder  160 . The piston  158  is urged against an electrical contactor  26  of the contactor assembly  40 . 
   In use, air is introduced into the chamber  160  through hose  162  to urge the piston  158  to move in a z direction, thereby to displace the contactor assembly  40  towards the chuck plate  154  until the mechanical alignment stops  22  on the side  14  of the interposer  10  make contact with the side  34  of the wafer  32 . A resiliently deformable member in the form of an O-ring  163  positioned between the ring  42  and the chuck plate  154  serves to limit or control how much displacement of the contactor assembly  40  is produced by movement of the piston  158 . Thus, movement of the piston  158  does not require precise control. Further, the O-ring  163  provides a seal between the ring  42  and the chuck plate  154 . The O-ring  163  also allows for variations in which the faces  46  of the ring  42  may not be on the same z-plane by cushioning the ring  42  as it is displaced towards the chuck plate  154 . In some embodiments, the O-ring  163  may be replaced by springs which provide a reaction against movement of the piston  158 . Once the mechanical stops  22  of the side  14  of the interposer  10  contact the side  34  of the wafer  32 , the interconnection spring elements are compressed thereby to achieve good electrical contact between the interconnection spring elements  20  of the interposer  10  and the electrical terminals  36  of the wafer  32 . Thereafter, the hose  162  may be removed. The probe assembly  152  may also include a securing mechanism to releasably secure or fasten the chuck plate  154  to the probe plate  152 . The securing mechanism has not been shown in  FIG. 12 , but includes any suitable clamping arrangement such as the kinematic couplings of U.S. Pat. No. 6,340,895 which is hereby incorporated by reference. The test probe assembly  150  may then be inserted into a test burn-in chamber wherein electrical connection pins  166  of an external interface component  164  are received in complementary electrical sockets. 
   Alternatively, the chuck plate  152  may be an integral part of a test probe unit, and the burn-in testing may be done with the test probe assembly in position above the chuck plate  152  on the test probe unit. 
   Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader spirit of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.