Abstract:
A testing scheme for ball-grid array devices of different sizes where the same ball-grid pattern may be tested using the same set of test adapters. A testing scheme includes providing a plurality of devices having a predetermined pattern of solder balls attached, providing a plurality of adapters secured to a test board, each of the adapters including a plurality of test contacts arranged in a pattern corresponding to the predetermined pattern of solder balls, removably attaching the plurality of devices to a device holding apparatus such that the predetermined pattern of solder balls on the devices corresponds to the predetermined pattern of test contacts on the plurality of adapters, then positioning the device holding apparatus to bring the plurality of solder balls in contact with the plurality of test contacts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from Singapore Application No. 200204962-5, filed Aug. 16, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates, generally, to testing and burn-in of semiconductor devices and, more particularly, to an improved test and burn-in fixture for use with bare die and high-density packages such as ball grid arrays. 
   2. Background Information 
   Modern semiconductor fabrication techniques have dramatically increased the density and speed of semiconductor devices, leading to a parallel effort in the field of semiconductor packaging, where increased device density gives rise to many challenges related to electrical connectivity, heat-transfer, manufacturability, and the like. One such challenge relates to the burn-in and testing of ball-grid array (BGA) packages, chip-scale packages (CSP), bumped die, and other such devices using an array of solder balls as contacts. 
   With such devices, edge-of-package to solder ball location is a critical dimension, and is easily influenced by substrate tolerance issues, processing machinery, test machinery, and other factors. The BGA ball pad location tolerance might be approximately +/−25 microns, while the singulation tolerance of the edges of finished devices may vary by +/−50 microns. Any such errors in alignment may result in erroneous rejection due to poor contacts during electrical tests—errors which will only become more significant as ball pitch becomes smaller and effects such as thermal expansion and the like become more and more dominant. 
   Furthermore, while ball-grid array patterns may be standardized, the dimensions of the packages or die themselves often vary greatly. Referring to  FIG. 1 , for example, while the two BGA devices  102  and  106  exhibit the same pattern of solder balls  104 , their external package or die dimensions are different, and would therefore require different test adapters for burn-in or functional testing. Specifically, the distance x′ from corner  116  to ball  114  on device  106  is significantly larger than dimension x from corner  112  to ball  110  on device  102 . Similarly, the dimension y′ of device  106  is greater than dimension y of device  102 . Traditional BGA test systems would rely on registration of the external package of the devices to corners within a rectangular fixture. As a result, any fixture designed for use with device  102  could not be used with device  106 . 
   Similarly, any wafer-level testing would require refixturing of the test board to accommodate different die geometries. As it is desirable to achieve 100% utilization of burn-in boards, current test systems are inadequate in that rejects during wafer-level testing can not easily be removed after each stage. 
   Methods are therefore needed in order to overcome these and other limitations of the prior art. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides systems and methods which overcome the shortcomings of the prior art by providing a testing scheme wherein ball-grid array devices of different sizes but the same ball-grid pattern may be efficiently and cost-effectively tested using the same set of test adapters. 
   In accordance with one aspect of the present invention, a testing scheme includes the following steps: providing a plurality of devices having a predetermined pattern of terminals (for example, solder balls) attached thereto; providing a plurality of adapters secured to a test board, each of said adapters including a plurality of test contacts arranged in a pattern corresponding to said predetermined pattern of terminals; removeably attaching said plurality of devices to a device holding apparatus such that said predetermined pattern of terminals on said devices corresponds to said predetermined pattern of test contacts on said plurality of adapters; and positioning said device holding apparatus to bring said plurality of terminals in contact with said plurality of test contacts. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The subject invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and: 
       FIG. 1  is a schematic view of typical packages or dice having an array of solder bonds arranged in a grid; 
       FIG. 2  is schematic cross-sectional view of a testing scheme in accordance with the present invention; 
       FIG. 3  is a schematic cross-sectional view of the scheme shown in  FIG. 2  wherein the ball grid is brought into contact with the test contact array; 
       FIG. 4  depicts an array of adapters in accordance with the present invention used to test devices of varying sizes; 
       FIGS. 5A and 5B  show top and side views of an adapter in accordance with one embodiment of the present invention; 
       FIGS. 6 and 7  shows a schematic cross-sectional view of an adapter in accordance with another embodiment of the present invention; and 
       FIG. 8  shows a test assembly in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Systems and methods in accordance with the present invention provide a testing scheme wherein ball-grid array devices of different sizes but the same ball-grid pattern may be efficiently and cost-effectively tested using the same set of test adapters. 
   More particularly, referring to  FIG. 2 , a test apparatus in accordance with one embodiment of the present invention includes a series of adapters  204  connected to a test board  214 , wherein each of the adapters  204  includes a number of test contacts  208  which electrically communicate with test board  214 . The test contacts  208  are aligned with an array of terminals  206  attached to a corresponding series of devices  202 . That is, test contacts  208  are arranged in a grid which matches the terminal pattern (e.g., ball grid pattern) of devices  202 . Devices  202  are attached to an adhesive surface  211  of flexible tape  210  which, in the illustrated embodiment, is anchored by a frame or “carrier”  212 . 
   As shown in  FIG. 3 , when carrier  212  and tape  210  are lowered, terminals  206  are brought into contact with corresponding test contacts  208 . Because the alignment of terminals  206  with contacts  208  is achieved by proper placement of devices  202  on flexible adhesive tape  210 , the dimensions of the device  202  are not critical to achieving good test contact. In the illustration, for example, devices  202 ( a ),  202 ( b ), and  202 ( c ) vary in width, but their respective arrays of terminals  206  properly contact adapters  204 . 
   This advantage can also be seen in  FIG. 4 , which shows a top view of a series of adapters  204  configured in a rectilinear pattern. Without loss of generality, the terms “solder balls,” “ball grid array,” or “balls” are used to describe terminals  206  in the description that follows. Those skilled in the art will recognize that the present invention may be used in connection with any form of terminal, including, for example, various balls, bumps, and the like. 
   A total of twelve devices  202  with ball grid arrays  206  are shown in FIG.  4 . Although the exterior dimensions of devices  202  are different (note, for example, devices  202 ( a ),  202 ( b ), and  202 ( c )) the ball grid array  206  for each device  202  is similarly situated with respect to adapters  204  (and their corresponding test contacts, not shown). In this illustration, the ball grid array for each device  202  is centered with respect to the rectangular outline of the device. Although this centered array position would typically be the case, the present invention may be used in connection with other configurations, i.e., configuration where the ball grid pattern is not necessarily centered with respect to the package. The pattern itself may be arbitrary, and need not be simply rectangular. 
   It should be appreciated that the term “device” as used herein is intended to encompass a wide range of package-level, die-level, and wafer-level applications where an array of solder balls or the like are used to provide electrical connectivity to any external boards or components. 
   In the event device  202  is a semiconductor package, it may comprise, for example, a chip-scale package (CSP) or a ball grid array (BGA) package, including conventional as well as high-lead pitch BGA packages, i.e., plastic ball grid arrays (PBGA), fine-pitch ball grid arrays (FBGA), and thin fine-pitch ball grid arrays (TFBGA). 
   In the event device  202  corresponds to an individual semiconductor die, either in wafer or sawn form, it may comprise any suitable semiconductor material upon which or within which electronic components may be formed. Suitable materials for devices  202  include, for example, group IV semiconductors (i.e., Si, Ge, and SiGe), group III-V semiconductors (i.e., GaAs, InAs, and AlGaAs), and other less-conventional materials, such as SiC, diamond, and sapphire. Devices  202  may comprise single crystal material, a silicon-on-insulator material (SOI), or one or more polycrystalline or amorphous epitaxial layers formed on a suitable base material. It will be appreciated that devices  202  will also include various electronic components incorporated into the semiconductor material as well as interconnect structures consisting of conductive paths and various dielectrics for isolating these conductive paths. Such electronic components and processing methods are well known and therefore will not be discussed in detail herein. 
   Solder balls  206  and, consequently, test contacts  208 , may be configured in a variety of grid patterns with a wide range of ball-pitch. In one embodiment, the ball grid has a pitch of about 0.5 to 2.0 mm. As is known in the art, solder balls  206  may comprise a variety of materials, e.g., various lead alloys (Sn63Pb37, Sn62Pb36Ag2, Sn10Pb90, etc.), lead-free alloys (Sn95Ag5, Sn65Ag25Sb10, Au80Sn20, Sn95.5Ag4Cu0.5, etc.), and various Cu-core and Ag-core balls. 
   More background information regarding BGA technology may be found, for example, in John H. Lau,  BALL GRID ARRAY TECHNOLOGY  (1994), and John H. Lau,  FLIP CHIP TECHNOLOGIES  (1995). Additional information regarding basic packaging techniques may be found in a number of standard texts, e.g., Seraphim, Lasky, and Li,  PRINCIPLES OF ELECTRONIC PACKAGING  (1989); John H. Lau, et al.,  ELECTRONIC PACKAGING: DESIGN, MATERIALS, PROCESS, AND RELIABILITY  (1998). 
   In the illustrated embodiment, flexible tape  210  is used to secure devices  202  through the use of an adhesive surface  211  which lightly bonds to surfaces  220  of the devices and which is attached to a carrier  212 . Flexible tape  210  may be any suitably material, e.g., any of the various tapes used to secure wafers and die for sawing, testing, and the like. For example, tape  210  may consist of a flexible polyvinylchloride material having an adhesive surface  211  comprising a synthetic acrylic adhesive. Such adhesives can be selected in accordance with whether a low-tack, medium tack, or high-tack adhesive is required. 
   In one embodiment, carrier  212  comprises a standard inner and outer hoop set, wherein the inner hoop and tape fit concentrically within the outer hoop. The geometry of carrier  212  may be selected in accordance with the size and number of devices being tested. For example, carrier  212  may comprise a conventional circular frame or hoop-set having a diameter of 5″-12″. The present invention may be used in conjunction with larger carriers, however. 
     FIGS. 5A and 5B  show one embodiment of adapter  204 . Specifically,  FIG. 5A  shows a top view of an adapter  204 , and  FIG. 5B  shows a cross-sectional view. In this embodiment, the array of test contacts  208  are fixed within the body of adapter  204  and each test contact  208  includes a corresponding pin  502  which can be used, for example, to fit into a corresponding socket, either soldered or fixed to the test board or connected to the test board pins&#39; wires in the test board (i.e., test board  214  in FIG.  2 ). The top surface of contacts  208  may be flat, concave, or any other shape suitable for contacting a solder ball. The diameter of contacts  208  are preferably about the same diameter as the solder balls being contacted, but may be slightly larger or smaller. 
     FIGS. 6 and 7  show another embodiment of adapter  204 . In this embodiment the adapter  204  includes a number of holes  602  arranged in a pattern corresponding to the ball grid being contacted. A number of probe pins  604  are provided for contacting balls  206  of device  202  through holes  602 . Referring to  FIG. 7 , device  202  is positioned such that balls  206  fit in a self-aligning matter within holes  602 . Next, during testing or burn-in, probe pins  604  are moved into contact with solder balls  206 . In this embodiment, a flexible tape and adhesive surface may be used as shown in  FIG. 2 , or, alternatively, a non-adhesive surface may be brought down upon devices  202  to keep them in contact with adapters  204  after the devices  202  have been properly positioned. 
   The present invention also comprehends a number of additional embodiments for adapter  204  wherein the array of balls  206  are contacted by test contacts  208  of various designs. For example, contacts  208  may be configured as “tweezer” contacts, side contacts, “Y” contacts, spring and pin contacts, metal contacts formed on an elastomer adapter body, conductive epoxy bump contacts, and any other known or future method of contacting solder balls. 
     FIG. 8  shows an example test assembly in accordance with the present invention. Initially, a number of devices  202  are placed on the adhesive surface of tape  210  with solder balls  206  facing outward. These devices may be a subset of dice or package&#39;s selected from a previous test step, or may be dice as sawn in wafer form (wafer-level testing). Next, the carrier  212  and tape  210  are placed such that balls  206  on the various devices  202  make contact with respective adapters  204  on test board  802 . A clamp subassembly  806  rotateably attached to board  802  via a hinge  808  is closed onto the carrier  212  and suitably held in position. In this embodiment, the flexible tape  210  acts to provide a small amount of pressure to the back of devices  202 , ensuring contact with adapters  204 . A connector  804  is provided along one edge of test board  802  to allow the board to be plugged into an external test system through a back-plane or other similar socket in the burn-in oven, test chamber, or the like. Electrical wiring and/or metallic traces (not shown) are included on test board  802  to provide electrical connectivity from the various adapters to connector  804 . 
   Although the invention has been described herein in conjunction with the appended drawings, those skilled in the art will appreciate that the scope of the invention is not so limited. Modifications in the selection, design, and arrangement of the various components and steps discussed herein may be made without departing from the scope of the invention as set forth in the appended claims.