Abstract:
A reusable burn-in/test fixture for discrete TAB die consists of two halves. The first half of the test fixture contains cavity in which die is inserted. When the two halves are assembled, the fixture establishes electrical contact with the die and with a burn-in oven. The test fixture need not be opened until the burn-in and electrical test are completed. The fixture permits the die to be characterized prior to assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of Ser. No. 08/192,023, filed Feb. 3, 1994, U.S. Pat. No. 6,091,250, which is a division of Ser. No. 07/973,931, filed Nov. 10, 1992, U.S. Pat. No. 5,302,891, which is a continuation of Ser. No. 07/709,858, filed Jun. 4, 1991, abandoned. 
   This application is related to Ser. No. 08/888,448, filed Jul. 7, 1997, U.S. Pat. No. 6,091,251, and to Ser. No. 788,065, filed Nov. 5, 1991, U.S. Pat. No. 5,440,240, and to Ser. No. 73,005, filed Jun. 7, 1993, U.S. Pat. No. 5,408,190. 

   FIELD OF THE INVENTION 
   This invention relates to electrical test equipment for semiconductor devices. More specifically, the invention relates to an apparatus and method to perform dynamic burn-in and full electrical/performance/speed testing on discrete nonpackaged or semi-packaged dice. 
   BACKGROUND OF THE INVENTION 
   Semiconductor devices are subjected to a series of test procedures in order to assure quality and reliability. This testing procedure conventionally includes “probe testing”, in which individual dice, while still on a wafer, are initially tested to determine functionality and speed. Probe cards are used to electrically test die at that level. The electrical connection interfaces with only a single die at a time in wafer; not discrete die. 
   If the wafer has a yield of functional dice which indicates that quality of the functional dice is likely to be good, each individual die is assembled in a package to form a semiconductor device. Conventionally, the packaging includes a lead frame and a plastic or ceramic housing. 
   The packaged devices are then subjected to another series of tests, which include burn-in and discrete testing. Discrete testing permits the devices to be tested for speed and for errors which may occur after assembly and after burn-in Burn-in accelerates failure mechanisms by electrically exercising the devices (UUT) at elevated temperatures, thus eliminating potential failures which would not otherwise be apparent at nominal test conditions. 
   Variations on these procedures permit devices assembled onto circuit arrangements, such as memory boards, to be burned-in, along with the memory board in order to assure reliability of the circuit, as populated with devices. This closed assembly testing assumes that the devices are discretely packaged in order that it can then be performed more readily. 
   It is proposed that multiple integrated circuit devices be packaged as a single unit. This can be accomplished with or without conventional lead frames. This creates two problems for conventional test methods. Firstly, discrete testing is more difficult because the conventional lead frame package is not used. Furthermore, when multiple devices are assembled into a single package, the performance of the package is reduced to that of the die with the lowest performance. In other words, the ability to presort the individual dice is limited over that obtained through probe testing. Secondly, the packaging may have other limitations which are aggravated by burn-in stress conditions so that the packaging becomes a limitation for burn-in testing. 
   A form of hybrid integrated circuit incorporates a plurality of dice in a single package. This increases density of packaging and permits matched components on different dice to be packaged as a single part. The yield rate of such an assembly is likely to be at least a multiple of the yield rates of its component dice. As mentioned, if performance of the dice is factored in, the yield is likely to become significantly lower than the multiple of the component yield rates. 
   On the other hand, if the test results of burned in dice are available, the component yield rates can be increased. It is further possible to match components by matching various characterizations (such as signal timing and response times), thereby providing more margin for proper response. 
   Such hybrid integrated circuits, as well as other configurations establish a need for burned in semiconductor dice. Ideally, it would be desirable to permit testing of individual dice in a manner similar to that accomplished with discrete packaged semiconductor devices. 
   In U.S. Pat. No. 4,899,107, commonly assigned, a reusable burn-in/test fixture for discrete TAB die is provided. The fixture consists of two halves, one of which is a die cavity plate for receiving semiconductor dice as the units under test (UUT); and the other half establishes electrical contact with the dice and with a burn-in oven The first half of the test fixture contains cavities in which die are inserted circuit side up. The die will rest on a floating platform. The second half has a rigid high temperature rated substrate, on which are mounted probes for each corresponding die pad. Each of a plurality of probes is connected to an electrical trace on the substrate (similar to a P.C. board) so that each die pad of each die is electrically isolated from one another for high speed functional testing purposes. The probe tips are arranged in an array to accommodate eight or sixteen dice. 
   The two halves of the test fixture are joined so that each pad on each die aligns with a corresponding probe tip. The test fixture is configured to house groups of 8 or 16 die for maximum efficiency of the functional testers. 
   There are some testing and related procedures when the parts are singulated. For this reason, it is inconvenient to retain multiple die in a single test fixture. 
   TAB tape is normally bonded at bondpads in order to establish electrical connections which exhibit long term reliability without requiring that external pressure be applied to the assembly. The bonding of the TAB tape establishes a mechanical connection which can cause the bond pads to lift off of (become detached from) the die when the TAB tape is removed. 
   The bondpads are conductive areas on the face of the die which are used as an interconnect for connecting the circuitry on the die to the outside world. Normally, conductors are bonded to the bondpads, but it is possible to establish electrical contact through the bondpads by biasing conductors against the bondpads without actual bonding. 
   SUMMARY OF THE INVENTION 
   It has been found desireable to perform testing and related procedures in discrete fixtures prior to final assembly. In order to accomplish this, a two piece reusable burn-in/test fixture for discrete die is provided. The fixture consists of two halves, one of which is a die cavity plate for receiving a semiconductor die as the units under test (UUT). 
   In a first embodiment, a die is placed face up in a cavity in a first half of the fixture. A die contact member is used to establish contact with bondpads on the die, and to conduct between the bondpads and external connector leads on the fixture. 
   The contact between the bondpads and the external connector leads is preferably established by utilizing non-bonded TAB (tape automated bonding) technology. Conductors on the non-bonded TAB tape extend from the bondpads to connection points, and the connection points conduct to contacts, which are in turn in communication with the external connector leads. 
   The non-bonded TAB tape is essentially similar to conventional TAB interconnect methods, except that its connection function may be performed without permanently bonding the TAB tape to the die. In order to maintain contact with circuitry on the die, the non-bonded TAB tape is biased against the die when the burn-in/test fixture is assembled. The non-bonded contact of the non-bonded TAB tape applies primarily to the die pads. Contact between the tape and other conductors may also be non-bonded contact, although the attachment of the TAB tape to the fixture may be effected either without permanent bonding, or by bonding techniques. The non-bonded TAB tape is biased against the die, preferably by a compressible elastomeric pad. 
   In the preferred form of that embodiment, the external connector leads are connector pins, which preferably are in a DIP (dual inline plug) or QFP (quad flat pack) configuration. The pins terminate as the connection points. 
   In an alternate form of that embodiment, the conductors on the non-bonded TAB tape conduct to the top of the tape, and attachment of the second half of the fixture establishes an electrical connection between the conductors and the external connection leads, either through the second half or through a separate conductor. 
   The fixture establishes electrical contact with a single die and with a burn-in oven, as well as permitting testing of dice in discretely packaged form. 
   In another embodiment of the invention, a two piece reusable burn-in/test fixture for discrete die is provided. The first half of the test fixture contains a cavity in which a die is inserted circuit side up. The die will rest on a floating platform. The second half has a probe for each die pad. Each probe is connected to an electrical connector which can be used for attachment to a burn-in board and may be used for connection to a discrete circuit tester. 
   The probes can take several forms. Deposited conductors would be similar to the use of non-bonded TAB tape, except that the deposited conductors could be located on a fixed substrate. Conductive elastomers may be used, in which the conductive elastomer is used to establish electrical communication between the die, at the bondpads, and the external connection leads. Biased metal probes, such as probe wires, may be used. 
   In a third embodiment, the die is placed face up in a cavity in a first half of the fixture. A second half of the fixture includes external connector leads and is used to establish contact with bondpads on the die. Attachment of the die to the external connection leads is established either through contact points on the second half, or through an intermediate member, such as a non-bonded TAB tape. 
   In a fourth embodiment, the die is placed face down in a fixture which includes a die receiving cavity. Contact with bondpads on the die are established in order that the bondpads are in electrical communication with external connector leads on the fixture. 
   In that embodiment, the probes and the electrical connector are located on the second half. In the preferred form of that embodiment, the electrical connector extends upward from the face of the circuit side of the die, so that the fixture is normally connected to a tester with the integrated circuit side of the die facing down. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  show a preferred embodiment of the inventive burn-in fixture; 
       FIG. 3  shows details of non-bonded TAB tape used with the invention; 
       FIG. 4  shows a modification to the embodiment of  FIGS. 1 and 2 , in which a modified cover plate has conductive polymer contacts. 
       FIG. 5  shows an embodiment in which a die cavity housing is used for connections between the die and external connection pins; 
       FIG. 6  shows an alternate embodiment of a test package, in which an upper portion is used to connect the die to external test circuitry; 
       FIG. 7  shows a modification to the embodiment of  FIGS. 1 and 2 , in which a modified cover plate has conductive polymer contacts; and 
       FIG. 8  shows a modification of the invention, in which flexible tape is used to directly connect the die to an external connector connected to external test circuitry. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 and 2 , the inventive burn-in fixture  11  includes a die cavity plate  13  and a cover  15 . The die cavity plate  13  includes a die receiving cavity  17 . 
   The die receiving cavity  17  has dimensions which are at least sufficient to accommodate a die  21 . The die  21  is to be connected at bondpads  27 , which are typically 0.1 mm wide. For this reason, it is advantageous to provide a spacer plate  29  which fits within the die receiving cavity  17  and precisely positions the die  21  for subsequent alignment. The die cavity plate  13  also has a slot  31  which permits convenient access to the bottom of the die  21  in order that the die  21  may be lifted out of the die receiving cavity  17 . 
   A plurality of external connector leads  33  extend from the burn in fixture  11 . As can be seen in  FIG. 2 , in the preferred embodiment, the external connector leads  33  are attached to the die cavity plate  13 , and extend therefrom. The external connector leads  33  are shown as connector pins, which preferably are in a DIP (dual inline plug) or QFP (quad flat pack) configuration. 
   The external connector leads  33  are secured by the die cavity plate  13  and terminate on the die cavity plate  13  with contact pads  37 . The contact pads  37  are in approximate planar alignment with the bondpads  27 . 
   Referring to  FIGS. 1 and 2 , contact between the bondpads  27  and the external connector leads  33  is established by non-bonded TAB (tape automated bonding) tape  41 , shown in  FIG. 3 . 
   The non-bonded TAB tape  41  is essentially similar to conventional TAB tape methods, except that its connection function may be performed without bonding the TAB tape  41  to the die  21 . In order to maintain contact with the bondpads  27 , the non-bonded TAB tape  41  is biased against the die  21  when the burn-in/test fixture  11  is assembled. This enables the non-bonded TAB tape  41  to be lifted from the die  21  without destroying the bondpads  27 . 
   The non-bonded TAB tape  41  includes a plastic film  43 , preferably formed of polyimide, onto which are formed a plurality of conductive traces  45 . The conductive traces  45  have bumps  47 ,  48  which are intended for registration with a bondpad  27  or a contact pad  37 . The conductive traces  45  therefore are able to conduct signals between the bondpads  27  and the contact pads  37 . 
   It is possible to bond the TAB tape  41  to the bondpads  27 , if such a bond could be made reversible. That would require that the bond be generally weaker than the attachment of the bondpad  27  to the die  21 . This would necessitate a weak bond, or another means to permit the die to be separated from the fixture  11 . 
   It is also possible to permanently bond the TAB tape  41  to the die  21 , and to retain the attachment to the TAB tape  41  to the die  21  subsequent to burn in. 
   The cover  15  includes a rigid cover plate  51  and a resilient compressible elastomeric strip  53 , which serves as a biasing member  53 . When the cover plate  51  is secured to the die cavity plate  13 , the resilient biasing member  53  biases the non-bonded TAB tape  41  against the die  21 . This establishes an ohmic contact between the bondpads  27  and the conductive traces on the non-bonded TAB tape  41 , without the TAB tape  41  being bonded to the bondpads  27 . 
   The non-bonded contact of the non-bonded TAB tape  41  applies primarily to the bondpads  27 . Contact between the TAB tape  41  and the contact pads  37  on the fixture  11  may be effected by bonding techniques. Such bonding is not expected to deteriorate the fixture  11 , even though the fixture is used multiple times. If bonding is used for such contact, then the conductive material from the TAB tape may remain with the fixture  11 , but without detriment to the operation of the fixture  11 . 
   Positioning pins  57  are used to align the cover plate  51  with the die cavity plate  13 . A clamp  61  then secures the cover plate  51  in place over the die cavity plate  13 . The clamp  61  may consist of a wire clasp which may either be latched into place against itself, as shown, or is fitted into parallel horizontal locations in the die cavity plate  13  and the cover plate  51 . With the cover plate  51  in place, conductors on the non-bonded TAB tape  41  extend from the bondpads  27  to the contact pads  37 , so that the bondpads  27  are in electrical communication with the external connector leads  33 . 
     FIG. 4  shows a modification to the embodiment of  FIGS. 1 and 2 , in which a modified cover plate  71  uses conductive polymer contacts  73  in order to establish contact with the bondpads  27 . Contact with the external connector leads  33  is established by electrical contacts  75  on the cover plate  71 , and these contacts  75  may be either conductive polymer or metallic. 
     FIG. 5  shows an embodiment in which a die cavity housing  91  has conductive polymer contacts  93 . The die  27  is placed face down, so as to establish connection between the bondpads  27  and the polymer contacts  93 . 
   In an alternate embodiment of a package  101 , shown in  FIG. 6 , a die receiving housing  103  is used to retain a die  21 , and an upper portion  105  is used to connect the die  21  to external test circuitry, by the use of external connector pins  107 . The die receiving housing  103  contains a die receiving cavity  109 , which supports the die  21  in alignment with electrical contacts  111  which contact bondpads  27  on the die  21 . A biasing plate  115  biases the die  21  against the contacts  111 . In one embodiment of this configuration, the contacts  111  are metallic, although other conductors may be used for the contacts  111 . As an example, it is possible to use conductive polymer for the contacts  111 . 
   In an embodiment shown in  FIG. 7 , contact pins  123  are used to connect to the bondpads  27  on the die  21 . The contact pins  123  are mounted to a dielectric cover  125 , and electrical continuity between the contact pins  123  and base portions  127  of external connector pins  129  is established when the cover  125  is mounted to a die cavity housing  131 . A resilient pad  135  secures the die  21  in position in the housing  131 . 
   The contacts  123  are pin type contacts, which are similar to probe contacts. Because of the relatively precise alignment of the cover  125  with respect to the die  21 , it is possible to design the contacts  123  to have a relatively low biasing force, while still maintaining good ohmic contact between the bondpads  27  and the contacts  123 . 
     FIG. 8  shows a configuration in which a housing fixture  141  merely retains the die  21  in a predetermined positional alignment, and in electrical communication with non-bonded TAB tape  143 . The TAB tape  143  extends beyond the confines of the fixture  141  and terminates in an external connector  147 . 
   While specific locations for bondpads had not been specified, it is possible to test a variety of configurations, including the conventional arrangement of bondpads at the ends of the die  21 . The invention may also be used for testing die configured for LOC (leads over chip), as well as other designs. In each of the above examples, the assembled fixture is adapted into conventional test equipment, such as a burn-in oven. What has been described is a very specific configuration of a test fixture. Clearly, modification to the existing apparatus can be made within the scope of the invention. Accordingly, the invention should be read only as limited by the claims.