Abstract:
The invention(s) relates to semiconductor test system and method that isolates and counteracts forces that bend test equipment resulting in improved manufacturing yield and throughput. The system includes a force retainer fixedly mounted on a material handler and a force locator positioned between the force retainer and a circuit board. Together, the force retainer and locator prevent the circuit board from bending. Other embodiments are illustrated and described.

Description:
BACKGROUND OF THE INVENTION(S)  
       [0001]     1. Field of the Invention(s)  
         [0002]     The invention(s) relates to a semiconductor test system and method. More particularly, the invention(s) relates to a semiconductor test system and method that isolates and counteracts forces that bend test equipment resulting in improved manufacturing yield and throughput.  
         [0003]     2. Description of the Related Art  
         [0004]     Semiconductor devices, e.g., wafers and integrated circuits, are typically tested at various points in their manufacture. Testing ensures the devices—and the manufacturing processes used to produce them—are working properly and within acceptable quality ranges.  
         [0005]     A typical test is as follows. The wafer or integrated circuit under test (DUT) is placed on a chuck or similar mechanical tool that brings the DUT into contact with the test system. The DUT electrically connects to the test equipment through contact pins, often spring-loaded. The aggregate force of the spring-loaded pins is high, often exceeding 100 pounds. This aggregate force might cause the test equipment to flex or bow, damaging the test equipment and the DUT and causing inconsistent electrical contact between them. Inconsistent electrical contact increases test failures, lowering yield and throughput.  
         [0006]     Accordingly, a need remains for semiconductor test system and method that reduces test equipment bending resulting in improved yield and throughput. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The foregoing and other objects, features, and advantages of the invention(s) will become more readily apparent from the detailed description of an embodiment that references the following drawings.  
         [0008]      FIG. 1  is a side view of a conventional test system.  
         [0009]      FIG. 2  is a side view of a test system.  
         [0010]      FIG. 3  is an exploded view of a test system.  
         [0011]      FIG. 4  is a flowchart of a test method.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]      FIG. 1  is a side view of a conventional test system  100 . Referring to  FIG. 1 , a test system  100  includes an interface unit  105  mounted on a top plate  104  of a material handler  101 . A person of reasonable skill in the art should recognize that the material handler  101  is known by various names depending on the type of the DUT. For example, the material handler  101  is a prober where the DUT is a wafer or a part handler where the DUT is a packaged integrated circuit. The top plate  104  might have a variety of different shapes and sizes and be made of different materials depending on the application.  
         [0013]     The interface unit  105  is mounted on the top plate  104  using a variety of fasteners, e.g., clamps  114 A and  114 B. A person of reasonable skill in the art should recognize other fasteners used for mounting the interface unit  105  to the top plate  104 , including screws, clips, hinges, tacks, nails, and the like. The interface unit  105  interfaces the DUT  111 , e.g., a wafer, to the test head  102 . A person of reasonable skill in the art should recognize that the interface unit  105  is known by various names depending on the type of DUT. For example, the interface unit  105  is a sort interface unit (SIU) where the DUT is a wafer and a test interface unit (TIU) where the DUT is a packaged integrated circuit.  
         [0014]     The interface unit  105  is unique to each DUT model under test. For example, one interface unit tests wafers having one design and another interface unit tests wafers having another design. Thus, the interface unit  105  changes at least every time the DUT model being tested changes. And the interface unit  105  might be replaced if it fails or otherwise stops functioning properly within a single DUT production run.  
         [0015]     The interface unit  105  includes a probe head  106  mounted on a printed circuit board (PCB)  112 . The probe head  106  is alternatively termed a socket or contactor in packaged test. The probe head  106  is mounted on the PCB  112  using a variety of fasteners, e.g., screws  118 . A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the probe head  106  to the PCB  112 , including clamps, clips, hinges, tacks, nails, and the like. Contact pins  107  extend outwardly from the probe head  106 . The contact pins  107  might be spring loaded.  
         [0016]     The PCB  112  includes electronics used to interface the test head  102  to the DUT  111  such that test head  102  is capable of loading, stressing, and otherwise testing the DUT  111 . The PCB  112  includes traces, power planes, and a variety of components, e.g., relays, integrated circuits, capacitors, resistors, and the like. The PCB  112  might have any of a variety of shapes and come in any of a variety of sizes depending on the particular interface unit  105  and DUT  111 . The PCB  112  is made of a variety of well-known materials including fiberglass FR4 and the like.  
         [0017]     The test head  102  includes electronics used to test the DUT  111 . The test head  102  simulates a variety of load and other stress conditions designed to identify faulty or marginally operative DUTs  111 . The test head  102  includes connectors  1   13 A and  1   13 B. The connectors  113 A and  113 B are connected to the test head  102  at one end and to the PCB  112  at another end. A person of reasonable skill in the art knows well the design of the probe head  106 , PCB  112 , and test head  102 , and, thus, we will not discuss them in any further detail.  
         [0018]     The test system  100  operates as follows. Before testing begins, the interface unit  105  is mounted on the top plate  104  using clamps  114 A and  114 B. The connectors  113 A and  113 B on the test head  102  are connected to the PCB  112 . A chuck or other material handling equipment  109  brings the DUT  111  into contact with the probe head  106  and, more particularly, the contact pins  107 . The contact pins  107  electrically connect the DUT  111  to the PCB  112  to the test head  102 . As the chuck  109  pushes the DUT  111  into the contact pins  107 , it exerts a probe force  114  on the interface unit  105  and the test head  102 . The probe force  114  can exceed 100 pounds for high pin count packaged integrated circuits.  
         [0019]     If left unchecked, the probe force  114  might cause the interface unit  105  and the probe head  102  to bend, flex, or bow resulting in damage to the system  100  and/or the DUT  111 . In particular, the probe force  114  might cause the probe head  106  and PCB  112  to bend resulting in intermittent electrical contact between them and the DUT  111 , which, in turn, results in lowering yield and throughput.  
         [0020]     The probe force  114  must be counteracted to prevent it from bending the test system  100 . In one embodiment, the interface unit  105  includes a stiffener plate  110  fixedly mounted on the underside of the PCB  112 . The stiffener plate  110  is mounted on the PCB  112  using a variety of fasteners, e.g., screws  117 A and  117 B. A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the stiffener plate  110  to the PCB  112 , including clamps, clips, hinges, tacks, nails, and the like. The stiffener plate  110  might have a variety of shapes and sizes depending on the interface unit  105  (and, more particularly the PCB  112 ). In one embodiment, the stiffener plate  110  surrounds the probe head  106 . The stiffener plate  110  might be made of a variety of materials. In one embodiment, the stiffener plate  110  is stainless steel allowing the stiffener plate  110  to be both thin and strong.  
         [0021]     In one embodiment, the interface unit  105  includes a stiffener ring  108  mounted on the topside of the PCB  112  using a variety of fasteners, e.g., screws  117 A and  117 B. A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the stiffener ring  108  to the PCB  112 , including clamps, clips, hinges, tacks, nails, and the like. The stiffener ring  108  is positioned between the test head  102  and the PCB  112 . The stiffener ring  108  might have a variety of shapes and sizes. In one embodiment, the stiffener ring  108  includes a plurality of concentric rings interconnected with support members (not shown). The connectors  113 A and  113 B access the PCB  112  through open spaces between the support members. The inner most concentric ring supports the center of the PCB  112 . The stiffener ring  108  might be made of a variety of materials. In one embodiment, the stiffener ring  108  is aluminum.  
         [0022]     The stiffener plate  110  and the stiffener ring  108  prevent the probe force  114  from bending the interface unit  105  and, more particularly, the PCB  112 . The interface unit  105  must be light since operators often replace it. It follows that the stiffener plate  110  and the stiffener ring  108  must also be light. And the stiffener ring  108  is height constrained by the connectors  113 A and  113 B and the position of the test head  102 .  
         [0023]     The addition of the stiffener plate  110  and the stiffener ring  108  increases the cost of the interface unit  105  since each interface unit  105  is a consumable that includes these additional components. And the stiffener plate  110  and the stiffener ring  108  only partially prevent bending of the interface unit  105  because of their designs&#39; weight and height constraints that result in stiffness limits.  
         [0024]     Finally, simulation and testing of the system  100  is difficult. This is because the test head  102  and the interface unit  105  form an integral part of the system  100 . Simulation is made difficult because different manufacturers design and develop the different components of the system  100 , e.g., the interface unit  105  and the test head  102 . Getting modeling data from each of these manufacturers is at best cumbersome. Testing does not reasonably approximate the system  100 &#39;s true performance without the test head  102 . But with the test head  102  in place, data collection equipment cannot be properly attached to the system  100  to measure the system  100 &#39;s bend.  
         [0025]     The system  200  addresses these and other disadvantages. Referring to  FIG. 2 , a test system  200  includes an interface unit  205  mounted on a top plate  204  of a material handler  201 . In one embodiment, the interface unit  205  might be mounted on the top plate  204  using a variety of fasteners, e.g., clamps  214 A and  214 B. In another embodiment, the interface unit  205  might be mounted on the force retainer  216  using a variety of fasteners, e.g., screws. A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the interface unit  205  to the top plate  204  (or the force retainer  216 ), including screws, clips, hinges, tacks, nails, and the like. The top plate  204  might have a variety of different shapes and sizes and be made of different materials depending on the application.  
         [0026]     Like the interface unit  105 , the interface unit  205  is unique to each DUT model under test. For example, one interface unit  205  tests wafers having one design and another interface unit  205  tests wafers having another design. The interface unit  205 , therefore, changes at least every time the DUT model being tested changes. And the interface unit  205  might be replaced if it fails or otherwise stops functioning properly within a single DUT production run.  
         [0027]     The interface unit  205  includes a probe head  206  mounted on a PCB  212  on a first end. The probe head  206  is mounted on the PCB  212  using a variety of fasteners, e.g., screws  218 . A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the probe head  206  to the PCB  212 , including clamps, clips, hinges, tacks, nails, and the like. Contact pins  207  extend outwardly from the probe head  206 . As with contact pins  107 , the contact pins  207  might be spring-loaded.  
         [0028]     The PCB  212  includes electronics used to interface the test head  202  to the DUT  211  such that test head  202  is capable of loading, stressing, and otherwise testing the DUT  211 . The PCB  212  includes traces, power planes, and a variety of components, e.g., relays, integrated circuits, capacitors, resistors, and the like. The PCB  212  might have any of a variety of shapes and come in any of a variety of sizes depending on the particular interface.  
         [0029]     Like the test head  102 , the test head  202  includes electronics used to test the DUT  211 . The test head  202  simulates a variety of load and other stress conditions designed to identify faulty or marginally operative DUTs  211 . The test head  202  includes connectors  213 A and  213 B. The connectors  213 A and  213 B are connected to the test head  202  at one end and to the PCB  212  at another end. A person of reasonable skill in the art knows well the design of the probe head  206 , PCB  212 , and test head  202 , and, thus, we will not discuss them in any further detail.  
         [0030]     The interface unit  205  includes a stiffener ring  208 . The stiffener ring  208  is mounted on the topside of the PCB  212  using a variety of fasteners, e.g., screws  217 A and  217 B. A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the stiffener ring  208  to the PCB  212 , including clamps, clips, hinges, tacks, nails, and the like.  
         [0031]     The stiffener ring  208  might have a variety of shapes and sizes depending on the particular application. Referring to  FIGS. 2 and 3 , in one embodiment, the stiffener ring  308  includes an outer ring  340  surrounding an inner ring  342 . A plurality of ribs  344  connects the outer ring  340  to the inner  342 . Adjacent ribs  344  leave a space  346  through which connectors, e.g., connectors  213 A and  213 B, access the PCB  312  from the test head  202 . The stiffener ring  208  is adapted to stiffen the PCB  212  particularly in the area of the connectors  213 A and  213 B.  
         [0032]     The interface unit  205  includes a force locator  215  fixedly mounted on the PCB  212  with fasteners, e.g., screws  218 . A person of reasonable skill in the art should recognize other fasteners capable of use in mounting the force locator to the PCB  212 , including clamps, clips, hinges, tacks, nails, and the like. The force locator  215  might have a variety of shapes and sizes depending on the application. Referring to  FIGS. 2 and 3 , in one embodiment, the force locator  315  might have a shape similar to that of the probe head  306 . In another embodiment, the force locator  315  might have cutouts (not shown) to allow for component clearance on the PCB  212 . The force locator  215  might be adjusted to accommodate any spacing limitations imposed by the connectors  213 A and  213 B by, e.g., milling or removing extraneous material. The force locator  215  is made of light, inexpensive materials. In one embodiment, the force locator  215  might be made of plastic. In another embodiment, the force locator  215  might be part of a metal plate (not shown) included on the topside of the PCB  212  and used for planarity adjustments. In this later case, the force locator  215  might made of a light metal such as aluminum.  
         [0033]     The force locator  215  provides mechanical contact between a force retainer  216  and the PCB  212  to thereby create a compressive counter force to the probe force  214 . Put differently, the force locator  215  provides support directly behind the probing force  214  directing it from the PCB  212  to the force retainer  216 .  
         [0034]     The system  200  includes the force retainer  216  fixedly mounted on the top plate  204 . The force retainer  216  is mounted on the top plate with a variety of fasteners, e.g., screws  220 A and  220 B. In the embodiment shown in  FIG. 2 , the force retainer  216  is hinged at one end with hinge  222  and latched at another end with latch  223 . The force retainer  216  might be hinged depending on how and in what sequence the interface unit  205  is mounted on the material handler  201 . The force retainer  216  might also be hinged depending on how and in what sequence the test head  202  is brought into contact with the interface unit  205 .  
         [0035]     The force retainer  216  might have a variety of shapes and sizes depending on the application, including those shown in  FIG. 3 . The last two digits of the reference designators shown in  FIGS. 2 and 3  refer to similar structure. Referring to  FIGS. 2 and 3 , in one embodiment, the force retainer  316  might have a web-like structure where an outer ring  330  surrounds an inner plate  332 . The outer ring  330  and inner plate  332  are connected by a plurality of ribs  334 . Adjacent ribs  334  leave an opening or space  336  through which a connector, e.g., connector  213 A, accesses the PCB  312  from the test head  202 .  
         [0036]     Since the force retainer  216  is fixedly mounted on the top plate  204  and an integral part of the material handler  201  (and not part of the interface unit  205 ) it is not subject to the weight and height limitations imposed on the stiffener ring  108 . The force retainer  216 , therefore, might be made of heavier and stiffer, materials, e.g., steel or cast iron.  
         [0037]     Since the force retainer  216  is not part of the interface unit  205 , but rather fixedly mounted on the material handler  201 , the cost of the interface unit  205  decreases because it no longer integrates stiffening hardware (e.g., stiffener plate  110 ). Relative to the embodiment shown in  FIG. 1 , the system  200  eliminates the stiffener plate  110  and simplifies the stiffener ring  108 . And the test interface unit  205 &#39;s weight is lower improving its handling capability. Bending on the system  200  is not impacted by the test head  202  allowing easier characterization without the test head  202  in place. That is, data collection equipment can be attached to the system  200 . And since the force retainer  216  is fixedly mounted on the test handler  201  and counteracts the probing force  214 , the contribution of the test head  102  to the system&#39;s  200  rigidity is negligible. For modeling and testing purposes, therefore, it is not required or needed. Once the force retainer  216  is simulated and modeled, there is no need to retest with new test interface units  205 .  
         [0038]      FIG. 4  is a flowchart of a method  400  exemplifying an operation of test system  200 . A person of reasonable skill in the art understands that it can modify the invention(s) by exchanging, adding, removing, re-ordering, or otherwise changing the boxes described in  FIG. 4  without departing from the scope and spirit of the present invention(s).  
         [0039]     Referring to  FIG. 4 , at  402 , a force retainer is fixedly mounted directly to a top plate of a material handler using any of a variety of fasteners, e.g., screws. At  404 , an interface unit is mounted on the force retainer from one side (e.g., bottom). At  406 , a test head is brought into proximity with the material handler and the interface unit. Connectors on the test unit are threaded through the force retainer and stiffener ring and connected to the PCB ( 408  and  410 ). At  412 , a chuck or other material handling equipment moves the DUT into contact with the probe head and, more particularly, the contact pins. As the chuck pushes the DUT into the contact pins, it exerts a probe force on the system. At  414 , a force locator directs the probe force from the interface unit to the force retainer. At  416 , the force retainer retains or counteracts the probe force avoids bending the interface unit (and its PCB) and the test head. By doing so, the force retainer prevents intermittent contact between the contact pins and the DUT thereby improving yield and throughput.  
         [0040]     Having illustrated and described the principles of our invention(s), it should be readily apparent to those skilled in the art that the invention(s) can be modified in arrangement and detail without departing from such principles. We claim all modifications coming within the spirit and scope of the accompanying claims.