Abstract:
The invention relates to a test socket interposer. The interposer includes a flexible substrate with an upper signal contact and an upper ground contact on its top surface and a lower signal and a lower ground contact on its bottom surface. A portion of an upper surface of the upper signal contact is higher and to the right of an upper surface of the ground contact so that a signal contact of a device contacts the upper signal contact before a device ground slug contacts the upper ground contact. Also, a downward force exercised by the device signal contact causes pivoting of the upper signal contact and the substrate is sufficiently flexible to allow for this pivoting of the upper signal contact.

Description:
BACKGROUND OF THE INVENTION 
     1). Field of the Invention 
     This invention relates to a test socket interposer. 
     2). Discussion of Related Art 
     To ensure the quality of integrated circuit chips after manufacture, various testing methods have been devised to find defects. Frequently, testing of the electronic device is performed by subjecting it to a set of input conditions. The pass/fail response to these inputs will determine whether it can be delivered to a customer. 
     Effective testing of an electronic device requires good contact between a signal and ground contact of the electronic device and corresponding contacts on a test socket. During testing, a poor electrical contact may occur between the test socket and the electronic device. One of the reasons for poor electrical contact is non-uniformity of the dimensions of the signal contacts of the electronic device. One or more of the signal contact leads may fail to make full contact with the signal contact of the test socket. Poor electrical contact lowers the reliability of the testing and may impair the transfer of signals between the electronic device and the tester to the extent that a good chip may test as defective. 
     SUMMARY OF THE INVENTION 
     The invention provides a test socket interposer with a horizontal, nonconductive, flexible substrate with a top and bottom surface, a lower ground contact, and a lower signal contact on the bottom surface of the substrate, positionable on a test socket with the lower ground contact on a socket ground contact and with the lower signal contact on a socket signal contact, an upper ground contact and an upper signal contact on the top surface of the substrate, the upper signal contact having a surface, at least a portion of which (i) is higher than an upper surface of the ground contact so that a signal contact of a device in a common plane as a device ground contact contacts the upper signal contact before the device ground contact contacts the upper ground contact when the device is moved downward, and (ii) is to the right of a lower surface of the lower signal contact so that a downward force exercised by the device signal contact causes pivoting of the upper signal contact that moves the area of contact between the device signal contact and the upper signal contact downward, the substrate being sufficiently compliant to allow for pivoting of the upper signal contact, and for the device ground contact to subsequently contact the upper ground contact, and ground and signal electrical connections, the ground electrical connection linking the upper ground contact with the lower ground contact and the signal electrical connection linking the upper signal contact with the lower signal contact. 
     The substrate may have at least one tooling hole formed through the substrate for positioning over tooling pins, to position the substrate on the test socket. 
     The lower surface of the lower ground contact and the lower surface of the lower signal contact may be in a common plane and an air gap may be defined under a portion of the bottom surface of the substrate and above the test socket that is between the socket ground contact and socket signal contact to allow for flexing of the substrate between the lower ground contact and the lower signal contact. 
     The upper ground contact may be positioned on the top surface of the substrate directly above the lower ground contact. 
     The distance between the lower surface of the lower ground contact and the bottom surface of the substrate may be the same as the distance between the lower surface of the lower signal contact and the bottom surface of the substrate. 
     A downward force exercised by the device signal contact on the upper signal contact may cause the upper signal contact to press down against the substrate and form a depression in the top surface of the substrate material under the upper signal contact for the duration that the downward force is exercised. 
     The depression in the substrate material may be located under the side of the upper signal contact closest to the upper ground contact. 
     The distance between the upper surface of the upper signal contact and the top surface of the substrate may be greater than the distance between the upper surface of the upper ground contact and the top surface of the substrate. 
     At least one of the ground electrical connection linking the upper ground contact with the lower ground contact and the signal electrical connection linking the upper signal contact with the lower signal contact may be a via. 
     The test socket interposer may further include a conductive material filling the void in the via. 
     The test socket interposer may have a plurality of upper signal contacts. 
     One of the upper signal contacts may be positioned on the right side of the upper ground contact and one of the upper signal contacts may be positioned on the left side of the upper ground contact. 
     The upper surface of the upper signal contact on the right side and the upper surface of the upper signal contact on the left side may be the same distance above the top surface of the substrate. 
     The upper surfaces of the upper signal contacts may be higher than the upper surface of the upper ground contact so that a device including a signal contact on the right side of the device, a signal contact on the left side of the device, and a ground contact in a common plane with the device signal contacts, will make contact with the right and left upper signal contacts before the upper surface of the upper ground contact. 
     A downward force exercised by the right and left device signal contacts on the right and left upper signal contacts may cause pivoting of the upper signal contacts that moves the areas of contact between the right and left device signal contacts and the upper signal contacts downward, the substrate being sufficiently compliant to allow for pivoting of the upper signal contacts, and for the device ground contact to subsequently contact the upper ground contact. 
     A plurality of upper signal contacts may be all positioned on a perimeter of an area on the top surface of the substrate and the upper ground contacts may be all positioned on the top surface of the substrate in the area within the upper signal contacts. 
     At least two of the upper signal contacts may be in a line on the right side of the area and at least two of the upper signal contacts may be in a line on the left side of the area. 
     The invention also provides a test socket interposer with a horizontal, non-conductive, flexible substrate with a top and bottom surface, a lower ground contact and a lower signal contact on the bottom surface of the substrate, positionable on a test socket with the lower ground contact on a socket ground contact and with the lower signal contact on a socket signal contact, an upper ground contact and an upper signal contact on the top surface of the substrate, the upper signal contact having a surface, at least a portion of which (i) is higher than an upper surface of the ground contact and so that a signal contact of a device in a common plane as a device ground contact contacts the upper signal contact before the device ground contact contacts the upper ground contact when the device is moved downward, (ii) is located vertically above the top surface of the substrate a greater distance than the height of the upper ground contact measured from the top surface of the substrate, and (iii) is to the right of a lower surface of the lower signal contact so that a downward force exercised by the device signal contact causes pivoting of the upper signal contact by pressing the upper signal contact down against the substrate and forms a depression in the top surface of the substrate material under the upper signal contact allowing the area of contact between the device signal contact and the upper signal contact to move downward, the substrate being sufficiently compliant to allow for pivoting of the upper signal contact, and for the device ground contact to subsequently contact the upper ground contact and a ground and signal electrical connection in the substrate, the ground electrical connection linking the upper ground contact with the lower ground contact and the signal electrical connection linking the upper signal contact with the lower signal contact. 
     The invention further provides a method for testing a device using an interposer, the device having a signal contact and a ground contact, and the interposer having a substrate, a lower ground contact, a lower signal contact, an upper ground contact and an upper signal contact, including positioning the interposer on the test socket, moving a device downward until the device signal contact makes contact with the upper surface of the upper signal contact and before the device ground contact makes contact with the upper ground contact, exerting a downward force on the upper signal contact with the device signal contact to cause pivoting of the upper signal contact, the substrate material being sufficiently compliant to allow for a portion of an area of contact of the device and the upper signal contact to move downward to allow subsequent contact of the device ground contact with the upper ground contact and conducting electricity between the device and the test socket via the contacts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is further described by way of examples with reference to the accompanying drawings, wherein: 
     FIG. 1 is a sectioned side view of a test arrangement including a test socket, an electronic device and a test socket interposer, according to an embodiment of the invention; 
     FIG. 2 is a plan view of the test socket interposer; 
     FIG. 3 is a bottom view of the test socket interposer; 
     FIG. 4 is a side view on  4 — 4  in FIG. 2 of the test socket interposer; 
     FIG. 5A is a view similar to FIG. 1 after the electronic device is moved down to the test socket interposer and makes partial contact with the test socket interposer; and 
     FIG. 5B is a view similar to FIG. 5A after the electronic device is moved further down onto the test socket interposer and makes full contact with the test socket interposer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 of the accompanying drawings illustrates a test arrangement  10 , including a test socket  12 , an electronic device  14 , and a test socket interposer  16 , according to an embodiment of the invention. 
     FIGS. 2 to  4  illustrate the test socket interposer  16  in more detail. The test socket interposer  16  includes a substrate  18 , upper signal contacts  20 , upper ground contacts  22 , lower signal contacts  30 , lower ground contacts  28 , signal vias  36 , and ground vias  38 . 
     The substrate  18  is a multi-layer substrate measuring 14 mm by 14 mm, with a thickness of 125 microns, and is made of a Polytetrafluoroethylene, PTFE, which is non-conductive. Two tooling holes  40  are formed through the substrate  18  near the right and left sides. Holes  41  are formed through the substrate  18  for the signal vias  36  and the ground vias  38 . The substrate  18  is flexible and resilient. Further characteristics of the substrate  18  will be evident from the description that follows. 
     FIG. 2 illustrates that the upper signal contacts  20  include upper signal contacts  20 A through  20 T plated on the substrate  18 . Each upper signal contact  20  is made of copper and is 900 microns in length, 230 microns wide, and is plated to a height of 105 microns above an upper surface  42  of the substrate  18 . 
     The upper signal contacts  20  are positioned in four groups of five each, a rear group including upper signal contacts  20 A through  20 E; a right-side group including upper signal contacts  20 F through  20 J; a front group including upper signal contacts  20 K through  20 O; and a left-side group including upper signal contacts  20 P through  20 T. Each upper signal contact  20  is positioned along a periphery of a square internal area  46 , with the upper signal contacts  20 A through  20 E opposite the upper signal contacts  20 K through  20 O and the upper signal contacts  20 F through  20 J opposite the upper signal contacts  20 P through  20 T. The upper signal contacts  20 A through  20 E and  20 K through  20 O are aligned in a y direction  50 , and the upper signal contacts  20 F through  20 J and  20 P through  20 T are aligned in an x direction  48 . 
     FIG. 2 illustrates that the upper ground contacts  22  include upper ground contacts  22 A through  22 D plated on the substrate  18 . Each upper ground contact  22  is made of copper, measures 690 microns by 690 microns, and is plated to a height of 70 microns above the upper surface  42  of the substrate  18 . The upper ground contacts  22 A through  22 D are positioned within the internal area  46  in a two by two array, with the rows of the array aligned in the x direction  48  and the columns of the array aligned in the y direction  50 . 
     FIG. 3 illustrates that the lower signal contacts  30  include lower signal contacts  30 A through  30 T plated on the substrate  18 . Each lower signal contact  30  is 250 microns in length, 250 microns wide, and is plated to a height of  70  microns below a lower surface  44  of the substrate  18 . Each lower signal contact  30  is paired with one of the upper signal contacts  20  and mirrors the position of the respective upper signal contacts  20  on the lower surface of the substrate  44 . Each lower signal contact  30  is positioned relative to one of the respective upper signal contacts  20  directly below an end  54  of the upper signal contact  20  distant from the square internal area  46 . 
     The lower ground contacts  28  are similar to the upper ground contacts  22 . Each lower ground contact  22  is made of copper, measures 690 microns by 690 microns, and is plated to a height of 70 microns below the lower surface  44  of the substrate  18 . Each lower ground contact  28  is paired with an upper ground contact  22 , and mirrors the position of the respective upper ground contacts  22  on the bottom surface  44  of the substrate  18 . 
     FIG. 2 illustrates the signal vias  36  and the ground vias  38  in more detail. The signal vias  36  provide a direct electrical connection through the substrate  18  between the upper signal contacts  20  and the lower signal contacts  30 . There are  20  signal vias  36 , each connecting one of the upper signal contacts  20  with a respective lower signal contact  30 . 
     The ground vias  38  provide a direct electrical connection through the substrate  18  between the upper ground contacts  22  and the lower ground contacts  28 . There are  16  ground vias  38 , positioned with each one of the ground vias  38  at a different corner of one of the four upper ground contacts  22 . Each ground via  38  is one of a group of four ground vias connecting an upper ground contact  22  with a respective lower ground contact  28 . 
     The signal vias  36  and the ground vias  38  are filled with a silver filler  56 . A respective via as together with a respective silver filler  56  forms a respective electrical connection of the test socket interposer  16 . 
     Referring again to FIG. 1, the electronic device  14  includes a device body  58 , device signal contacts  60  and a device ground contact  62 . The device body  58  houses an integrated circuit, not shown, that needs to be tested before being shipped to a customer. The device signal contacts  60  are made of a conductive material and are electronically connected to the integrated circuit, not shown. There are  20  device signal contacts  60 , which are positioned on the device body  58  similarly to the way the upper signal contacts  20  are positioned on the substrate  18 . The device ground contact  62  is made of a conductive material and is electronically connected to the integrated circuit. The device ground contact  62  is rectangular and is positioned within the device signal contacts  60 . The lower surface  63  of the device ground contact  62  is in the same plane as the ends  61  of the device signal contacts  60 . 
     FIG. 1 also illustrates the test socket  12  in more detail. The test socket  12  includes a socket frame  66 , socket signal contacts  68 , socket ground contacts  70  and tooling pins  39 . 
     The socket frame  66  is made of a non-conductive material, a portion of the socket frame  66  having a flat, upper surface  67 . The socket signal contacts  68  are made of a conductive material and are electronically connected to an electrical circuit, not shown, for testing the electronic device  14 . There are  20  socket signal contacts  68 , positioned on the upper surface  67  of the socket frame  66  similarly to the way that the lower signal contacts  30  are positioned on the substrate  18 . 
     The socket ground contacts  70  are made of a conductive material and are electronically connected to the electrical circuit, not shown. The socket ground contacts  70  are positioned on the upper surface  67  of the socket frame  66  within the socket signal contacts  68 . An upper surface  71  of each of the socket ground contacts  70  is in the same plane as the socket signal contacts  68 . There are two tooling pins  39 , which are cylindrical and oriented vertically. The tooling pins  39  are positioned on the upper surface  67  of the socket frame  66  similarly to the way that the tooling holes  40  are positioned on the substrate  18 . 
     In use, the test socket interposer  16  is positioned on the test socket  12 , as shown in FIG. 1, with each of the tooling pins  39  through the respective tooling holes  40 . In this position, each of the socket signal contacts  68  contact each of the respective lower signal contacts  30  and the socket ground contacts  70  contact each of the respective lower ground contacts  28 . Also in this position, an air gap  84  is defined under a portion of the bottom surface  44  of the substrate  18  and above the upper surface  67  of the socket frame  66  that is between the socket ground contact  70  and socket signal contact  68 . 
     The electronic device  14  is then moved into a preparatory position above the test socket interposer  16  with the device signal contacts  60  facing the test socket interposer  16 . 
     As shown in FIG. 5A, the electronic device  14  is then moved downward until each one of the ends  61  of the device signal contacts  60  move into contact with the end  64  of the respective upper signal contact  20 . With the electronic device  14  and the test socket interposer  16  is this position, an air gap  76  is defined between the lower surface  63  of the device ground contact  62  and an upper surface  24  of the upper ground contact  22 . 
     As shown in FIG. 5B, the electronic device  14  is then moved further downward until the lower surface  63  of the device ground contact  62  moves into contact with the upper surfaces  24  of the upper ground contacts  22 . 
     The movement of the electronic device  14  downward from the first position shown in FIG. 5A to the second position shown in FIG. 5B is caused by a downward force F 1  acting on the electronic device  14 . The force F 1  causes forces F 2  to be exerted by each of the ends  61  of the device signal contacts  60  against the end  64  of the respective upper signal contact  20 . The force F 2  causes the upper signal contacts  20  to press against the substrate  18 . The substrate  18  is sufficiently compliant that depressions  80  are formed underneath the upper signal contacts  20 . The air gap  84  under the lower surface  44  of the substrate  18  allows for flexing of the substrate  18  into the air gap  84 . The movement of the upper signal contacts  20  into the depressions  80  effectively pivots the upper signal contacts  18  in a direction  82 , moving the area of contact between the end  61  of the device signal contact  60  and the upper surface  21  of the upper ground contact  20  downward. Pivoting of the upper signal contacts  20  in the direction  82  allows the lower surface  63  of the device ground contact  62  to move into contact with the upper surfaces  24  of the upper ground contacts  22 . 
     With the test socket interposer  16  in the position illustrated in FIG. 5B, electricity is conducted between the electronic device  14  and the test socket  12 . Electricity for the signal is conducted through a path including the device signal contacts  60 , the upper signal contacts  20 , the signal vias  36 , the lower signal contacts  30  and the socket signal contacts  68 . Electricity for the ground is conducted through a path including the device ground contact  62 , the upper ground contacts  22 , the ground vias  38 , the lower ground contacts  28  and the socket ground contacts  70 . Testing is then performed on the electronic device  14 . 
     After testing is performed, the electricity is turned off. The electronic device  14  is then moved upwards, away from the test socket interposer  16  to the position shown in FIG.  1 . This completes one cycle of testing for the electronic device  14 . 
     After a cycle of testing, the test socket interposer  16  is moved to the position shown in FIG.  1 . The depressions  80  that are formed in the substrate  18  while in the position shown in FIG. 5B are temporary and the substrate  18  will rebound, or spring back, to the entirely flat condition shown in FIG. 1 after the electronic device  12  is moved out of contact with the test socket interposer  16 . 
     The substrate  18  is sufficiently resilient that the test socket interposer  16  will withstand repeated cycles of testing without permanent deformation of the substrate  18 . 
     In a worst case for strain on the substrate  18 , the electronic device  14  might be tested with the ends  61  of the device signal contacts  60  measuring  50  microns below the lower surface  63  of the device ground contact  62 . The electronic device  14  in this configuration will produce deeper depressions  80  in the substrate  18  while the test socket interposer  16  is positioned as in FIG.  5 B. The depressions  80  that are formed in the substrate  18  are temporary and the substrate  18  will rebound, or spring back, to the entirely flat condition shown in FIG. 1 after the electronic device  12  is moved out of contact with the test socket interposer  16 . For the electronic device  14  with these measurements, the substrate  18  is sufficiently resilient that the test socket interposer  16  will withstand, for example, at least 1000 cycles of testing without permanent deformation of the substrate  18 . 
     The electronic device  14  might be tested with the ends  61  of the device signal contacts  60  measuring 35 microns or less above the lower surface  63  of the device ground contact  62 . The ends  61  of the device signal contacts  60  for this electronic device  14  are ensured of intimate contact with the upper signal contacts  20  when the electronic device  14  is positioned on the test socket interposer  16  as shown in FIG.  5 B. 
     It can thus be seen that the test socket interposer  16  may compensate for typical manufacturing variations in the lengths of device signal contacts  60  by allowing the area of contact between each of the ends  61  of the device signal contacts  60  and the respective upper signal contact  20  to adjust downwards. The ability of the test socket interposer  16  to compensate for dimensional variations ensures an intimate connection between the device signal contacts  60  and the upper signal contacts  20  and ultimately a more desirable electrical connection between the device signal contacts  60  and the socket signal contacts  68 . 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art.