Abstract:
The automatic loading and unloading of devices for burn-in testing is facilitated by loading burn-in boards in a magazine with the stacked boards in the magazine moved into and out of a burn-in oven by means of a trolley. The trolley can include an elevator whereby a plurality of magazines can be stacked in the oven for the simultaneous burn-in testing of devices mounted on the burn-in boards. Each board has rollers on one end which are engagable by pneumatically actuated cam mechanisms for inserting the board into an electrical contact in the oven for burn-in tests. Preferably, the cam mechanisms allow for extraction of a single board for inspection. The cam mechanisms may be mounted on a door of the oven.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a Divisional application of U.S. application Ser. No. 12/055,141, now U.S. Pat. No. 7,567,076, entitled “Automated Loading/Unloading of Devices for Burn-In Testing”, by Teoh et al., filed Mar. 25, 2008, which is a Divisional application of U.S. application Ser. No. 11/424,934, now U.S. Pat. No. 7,378,836, entitled “Automated Loading/Unloading of Devices for Burn-In Testing”, by Teoh et al., filed Jun. 19, 2006, which claims the benefit of U.S. Provisional Patent Application No. 60/766,316, entitled “Automated Loading/Unloading of Devices for Burn-In Testing”, filed Jan. 10, 2006, which are incorporated herein by reference. 
    
    
     BACKGROUND 
     This invention relates generally to the fabrication of semiconductor devices, and more particularly the invention relates to the loading and unloading of cycler boards into an oven for burn-in testing. 
     Literally millions of semiconductor devices are fabricated each year. A final step in the fabrication is a burn-in test of each packaged device to identify defective devices. 
     In carrying out the burn-in tests, a plurality of multi-layer printed circuit boards or “burn-in” boards are provided with each board having a plurality of test sockets for receiving packaged devices for testing. One end of each board has contacts for mating with connectors of the test apparatus to facilitate the testing of each device. One such test apparatus is the AEHR Corporation MTX oven which receives a plurality of stacked boards for burn-in testing of devices in a heated environment. 
     Heretofore, packaged devices had been loaded automatically into a burn-in board at a Loader/Unloader Station with a human operator sequentially providing the burn-in boards for device insertion into the test sockets. After a full stack of burn-in boards have been loaded with packaged devices, the human operator physically and sequentially moves each board to the AEHR burn-in oven for testing. The process is time consuming and the placement of the loaded burn-in boards can be physically taxing. Other burn-in systems employ a magazine for holding a plurality of burn-in boards which can be loaded into an oven in one operation. However, known systems employ a board latching mechanism at the back of the oven for engaging board contacts with oven connectors. The mechanism is manually actuated, and the location at the back of the oven complicates routine maintenance of the mechanism. 
     The present invention is directed to alleviating these difficulties found in prior art burn-in systems. 
     SUMMARY 
     In accordance with the invention, a magazine or carrier is provided for a plurality of stacked burn-in boards, and a trolley is employed to move the magazine from the Loader/Unloader Station to the burn-in oven for testing and for returning tested devices on the burn-in boards back to Loader/Unloader Station. 
     In one embodiment, the magazine has a plurality of rails for slidably receiving the burn-in boards with the top of the magazine being open to allow the insertion and removal of devices in the board sockets at the Loader/Unloader Station. The magazine has a bottom support surface which can move over rollers in the Loader/Unloader Station and in the oven to facilitate movement into and out of the Loader/Unloader Station and the oven. 
     The trolley or cart is provided for moving a loaded magazine between the Loader/Unloader Station and the oven. The trolley has wheels to facilitate the movement, and a support surface of the trolley has rollers for receiving the bottom support surface of the magazine as a loaded magazine is moved into or out of the oven or the Loader/Unloader Station. 
     In one embodiment, the trolley has an elevator for raising and lowering the support surface of the trolley whereby a plurality of loaded magazines can be stacked in the oven and in the Loader/Unloader Station. The trolley has alignment mechanisms such as rollers for physically engaging alignment members of the oven and the Loader/Unloader Station in horizontal alignment. Optical sensors are employed for vertical alignment of the magazines, using the trolley elevator, in the oven and Loader/Unloader Station. 
     In accordance with an important feature of the invention, a loaded magazine is moved to a position inside the oven with the board contacts abutting electrical connectors in the oven but not engaging the connectors. A door of the oven, when closed, has mechanisms for inserting the burn-in board contacts into the oven connectors and for extracting the contacts from the connectors. Preferably, all boards can be inserted together or separately. In one embodiment, each board has cam follower rollers at one end opposite from the contacts, and the rollers engage cam surfaces of the pneumatically actuated mechanism. When actuated, the cam surfaces engage the rollers and slidably move one or more boards in the magazine to engage the contacts or remove the contacts from the connectors. 
     The invention and object and features thereof will be more readily apparent from the following detailed description and appended claims when taken with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a burn-in board including cam-engaging rollers in accordance with one embodiment of the invention. 
         FIG. 2  is a perspective view of a burn-in oven as used in one embodiment of the invention. 
         FIG. 3  is a perspective view of a Loader/Unloader Station as used in one embodiment of the invention. 
         FIG. 4  is a perspective view of a magazine for supporting a plurality of burn-in boards. 
         FIG. 5  is a perspective view of a trolley for use in transporting magazines. 
         FIG. 6  is a top view illustrating a trolley receiving or unloading a magazine at a Loader/Unloader Station. 
         FIGS. 7   a ,  7   b  are a top view and side view of a trolley loading or unloading magazines in a burn-in oven. 
         FIGS. 8   a ,  8   b  are plan views of a burn-in board in an oven with contacts of the board abutting an oven connector and with contacts inserted into the connector, respectively, and further illustrating pneumatically actuated mechanisms in the oven door for inserting the burn-in board contacts into oven connectors and for extracting the contacts from the connectors, respectively, in accordance with an embodiment of the invention. 
         FIG. 9  is a schematic of a controller for the pneumatically actuated mechanism. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a burn-in board  10  which comprises a multi-layer printed circuit board. Mounted on one surface of board  10  and connected with the multi-layer conductive layers of the printed circuit board are sockets  12  which receive packaged integrated circuit devices  14  for burn-in testing. At one end of board  10  are conductors  16  which mate with connectors of a burn-in test apparatus for applying electrical signals to a device undergoing test. At an opposite end of board  10  are rollers  18  which as will be described are engaged by cam surfaces for the insertion and retraction of conductors  16  in and from connectors of the burn-in apparatus. 
       FIG. 2  is a perspective view of a conventional burn-in oven such as the AEHR MTX oven which has been modified to receive a burn-in board magazine assembly in accordance with the invention. Oven  20  includes an outer door  22  which provides a heat seal during burn-in testing and an inner door  24  which inserts and retracts burn-in boards in the oven board contacts or with conductors engaging connectors during the test. A lower support surface  26  and an upper support surface  28  are provided for each receiving a magazine loaded with burn-in boards whereby the magazines can be stacked in the oven during test. Lower support surface  26  has rollers  27  and upper support surface  28  has rollers  29  for engaging the magazine assembly during loading and unloading of the magazines in the oven. Guides  30  protrude from the base of oven  20  and facilitate the horizontal alignment of a magazine with the oven for loading and unloading magazines. 
       FIG. 3  is a perspective view of a conventional board loader/unloader elevator station  40  which withdraws boards from a magazine for the automatic insertion and retraction of devices into burn-in boards in preparation for burn-in testing or for final unloading and packaging of acceptable devices. Station  40  includes a top support frame  42  including rollers  44  for receiving a magazine and a bottom support frame  46  including rollers  48  for receiving a magazine in a stacked arrangement. Guides  50  protrude from the loader/unloader station and provide horizontal alignment for a trolley when receiving or unloading magazines at the loader/unloader station. 
       FIG. 4  is a perspective view of a magazine  60  for supporting a plurality of burn-in boards in a stacked array. Magazine  60  includes a plurality of vertical support frames  62  to which are mounted board support guides  64  with opposing guides  64  slidably receiving burn-in boards in a stacked array. Rails  67 ,  68  on the bottom surface  66  supports the magazine when placed in the loader/unloader station or in the burn-in oven. Rails  68  on the bottom are received in an alignment guide on a trolley when loading the magazine from the oven or the loader/unloader station to the trolley for transport. In operation, unloaded burn-in boards are sequentially removed from magazine  60  when in the loader/unloader station for the automatic insertion of packaged devices into sockets of the board and automatic extraction of devices from the boards. In one embodiment, the magazine (or carrier)  60  includes an optical alignment mechanism  69  for vertically aligning the magazine with the oven  20  and the load/unload station  40 . 
       FIG. 5  is a perspective view of a trolley for transporting burn-in boards in the magazine  60  of  FIG. 4  to and from the burn-in oven of  FIG. 2  and the loader/unloader station of  FIG. 3 . Trolley  70  includes a handle  72  for physically moving the trolley on rollers  74  between the oven and the loader/unloader station with a motor in housing  76  actuating an elevator  78  for raising and lowering the top surface for the receiving and dispensing of the stacked magazines. The top surface of the elevator includes a guide  80  for receiving rails  68  of the magazine with guide  80  having a stop portion for limiting the travel of the magazine when loaded on the elevator. Rollers  82  receive rails  68  of the magazine. An optical sensor  84  is used for vertical alignment of the elevator with the oven and the loader/unloader station, and roller guide  86  mates with physical guides  50  of the loader/unloader station and guides  30  of the oven for horizontal alignment of the trolley when loading and unloading magazines. 
       FIG. 6  illustrates trolley  70  positioned for receiving a loaded magazine  60  at the loader/unloader station  40 . Roller guides  86  of trolley  70  align with guides  50  of the loader/unloader station for horizontal alignment, vertical alignment is effected by optical sensor  84  of the trolley  70  and laser  52  of the loader/unloader station ( FIG. 3 ) and laser  32  of the oven ( FIG. 2 ). In one embodiment, vertical alignment is effected by optical alignment mechanism  69  of the magazine  60  and laser  52  of the loader/unloader station ( FIG. 3 ) and laser  32  of the oven ( FIG. 2 ). 
     After a magazine is stacked on trolley  70  at the loader/unloader station, the trolley is physically moved to the oven as shown in  FIG. 7   a  with roller guide  30  of the oven engaging roller  86  of the trolley for horizontal alignment.  FIG. 7   b  is a side view illustrating the stacking of a magazine  60  on the upper shelf of oven  20 . Elevator  78  raises magazine  60  until alignment sensor  84  of the trolley and alignment sensor  32  of the oven indicate vertical alignment. Thereupon magazine  60  is pushed into the oven and the trolley is removed. In one embodiment, elevator  78  raises magazine  60  until optical alignment mechanism  69  of the magazine  60  and alignment sensor  32  of the oven indicate vertical alignment. 
     Magazine  60  moves on rollers  29  on top shelf  28  of oven  20  ( FIG. 2 ) until the magazine reaches a physical stop. At this position, the connectors  16  of the burn-in boards are abutting connectors in the oven, but are not inserted therein, as illustrated in  FIG. 8   a . Here the contacts  16  of board  10  are abutting connector  90 , but not inserted therein. Inner door  24  of the oven is then closed with cam surfaces of pneumatic actuated locking devices, for example, shown generally at  92  engaging the rollers. Upon actuation of the pneumatically actuated devices  92 , the cam surfaces urge board  10  through rollers  18  forward with the contacts  16  engaging connector  90 , as shown in  FIG. 8   b.    
     The pneumatic actuators  92  on door  24  are further illustrated in  FIGS. 8   a ,  8   b . In  FIG. 8   a , rollers  18  of board  10  engage cam surfaces  94  of the pneumatic actuators  92 . Upon actuation of pneumatic cylinders  96 , the cam surfaces push rollers  18  and the burn-in board  10  as indicated in  FIG. 8   b , whereupon the contacts of board  10  engage connector  90 . The board contacts are removed from the connector by reverse operation of the pneumatic actuator with cam surface  98  forcing rollers  18  to travel along the cam surface  94  and back to the position in  FIG. 8   a . After the insertion of a magazine in the oven, all boards can be simultaneously moved with contacts engaging connectors or each individual board can be moved by control of the pneumatic actuators for each board. 
       FIG. 9  is a schematic of a controller for the pneumatically actuated board insertion/retraction mechanism. A touch panel PLC  100  selects the board for insertion or retraction. Panel  100  can be a conventional and commercially available programmable logic controller such as the Pro Face™ touch screen controller. A plurality of control lines extend from the panel to control pneumatic valves and air cylinders in the insertion/extraction mechanism. For example, line  102  controls valve  104  which connects a pressure line  106  to line  108  for inserting Board No. 1 into a connector, or which connects line  106  to line  110  for extracting Board No. 1 from the connector. Air cylinder  112  drives cam  114 , and air cylinder  116  drives cam  118  in slidably moving board No. 1 for connector insertion or extraction. 
     The invention facilitates the transfer of burn-in boards from loading/unloading stations to and from a burn-in oven with reduced physical intervention of the human operator. While the invention has been described with reference to specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. For example, actuators other than pneumatic can be employed in the oven door for board insertion and retraction. Various modifications and applications may occur to those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.