Abstract:
A handler for a device under test (“DUT”) includes a rotating table which supports up to eight DUTs. The DUTs are held in place over openings in the table and separate heat exchangers contact the individual DUTs through the openings and conductively control the temperature of the DUTs. Six of the DUTs are in conditioning stations and are lifted off of the rotary table until they contact separate spring-loaded pads. One of the DUTs is in a test station and it is lifted off of the rotary table until it contacts a test head, at which point testing is performed. The temperature of each of the DUTs is controlled throughout the process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of previously filed provisional application No. 60/110,829, filed on Dec. 2, 1998, which is hereby fully incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to the field of transporting and controlling the temperature of integrated circuits (“ICs”) and more particularly to an improved apparatus, system, and method of transporting ICs and controlling the temperature of ICs for testing. 
     2. Description of the Related Art 
     Previous systems for transporting IC devices to a test site use a carrier-conveyor system. The IC device is taken from a tray on which the IC device is resting in a “live bug” position (connections down) by a “pick and place” handling system. Typically, the pick and place handling system uses a vacuum handling device to pick up the IC device from its tray and place the IC device on a carrier, still in a live bug position. The carrier slides or moves through the conveyor towards the test site. 
     For testing at non-ambient temperature conditions, the carrier passes through or is contained within a passive convection heating or cooling apparatus, such as a convection oven or “soak site.” The number of carriers in the conveyor, combined with the time spent at the test site, defines how long the convection apparatus is used to bring the IC device to the temperature desired for testing. A characterization process is typically used to determine whether the IC device has reached the desired test temperature by the time it reaches the test site. The characterization process usually requires the use of special thermal test devices with an external temperature measuring apparatus. The external temperature measuring apparatus may include thermocouple sensors which can read a thermocouple voltage and translate it into a temperature reading. Once the carrier reaches the test site, the IC device is typically removed from the carrier by a second vacuum handling device and is placed into a test site socket, with the necessary socketing force. In some systems, the IC device is not removed from the carrier. Instead, the carrier is placed under a contactor and the IC device is pressed against the test site socket, using a pressing mechanism. This approach is popular with memory IC handling systems or systems which achieve a high degree of parallel testing. 
     After testing, the IC device is placed back into the carrier by the vacuum handling device and the carrier continues to move through the conveyor system. In some systems, the conveyor system continues through a second convection apparatus, called a “de-soak chamber.” The de-soak chamber is used to force the temperature of the IC device back to a safe handling temperature or above the dew point temperature. 
     That is, back to a safe handling temperature when the testing is hot, and above the dew point temperature when the testing is cold. 
     After exiting the de-soak chamber, if any, the vacuum handling device removes the IC device from the carrier and places it into a tray, typically a JEDEC (Joint Electronic Device Engineering Council) compliant tray. The particular tray used depends on whether the IC device successfully passed the testing process. Depending on the test results, the trays are dispatched to their next process location. 
     A disadvantage of such a system is that there is no provision to maintain the device under test (“DUT”) temperature while the test is underway. Heat can be lost in some cases through the test site socket. The test can also cause the IC device to heat itself. For some critical, speed dependent tests, the resulting variation in the test temperature setpoint can frequently impair the quality of the test result. 
     Another disadvantage is that the complexity of and the number of moving parts of the soak and de-soak chambers can impair reliability of the handling system. Exposing moving parts, which may have different thermal expansion coefficients, to test temperatures complicates the design of the parts and subjects the operation to considerable wear. Passive convection heating and cooling apparatuses require that the moving parts of the apparatus be exposed to the sometimes extreme temperatures experienced by the IC device. These temperatures may affect the conveyor mechanism and further impair reliable operation. To remove an obstacle, clear a jam or service the system requires that the soak chamber be brought to safe handling temperatures. This consumes valuable production equipment utilization time. In the case of IC devices with a large thermal capacitance, the capacity requirements for the soak chamber are increased, which further aggravates the complexity and temperature exposure reliability concerns. 
     Therefore, a need has arisen for a system for transporting an IC device to a position for being tested which reduces the complexity of the transfer system. A further need exists for a system for transporting an IC device to a position for being tested which reduces the temperature exposure of the transport mechanism. A further need exists for a system which reduces the lost utilization time when the transport mechanism requires servicing. Another need exists for a system for efficiently bringing an IC device to a desired temperature for testing. 
     SUMMARY OF THE INVENTION 
     Briefly, in accordance with one aspect of the present invention, there is provided a system for handling a device under test (“DUT”). The system includes a carrier, a receptacle, a tooling system, and a lift mechanism. The carrier is for supporting the DUT, and the carrier has an aperture which is adapted to be disposed below at least a portion of the DUT. The receptacle is for supporting the carrier. The receptacle also has an aperture, and the receptacle is adapted to maintain the alignment of the carrier such that the carrier aperture overlaps at least part of the receptacle aperture. The tooling system is for conductively controlling a temperature of the DUT and for supporting the DUT. The lift mechanism is coupled to the tooling system. 
     The lift mechanism is for raising and lowering the tooling system when both the receptacle aperture and the carrier aperture are vertically aligned with the tooling system such that at least a portion of the tooling system can penetrate both the receptacle aperture and the carrier aperture and contact the DUT. The lift mechanism is further coupled to the receptacle to facilitate the vertical alignment. When the tooling system is raised to contact the DUT, the lift mechanism further raises the tooling system to raise the DUT above the carrier such that the DUT is not in direct contact with the carrier. 
     Briefly, in accordance with another aspect of the present invention, there is provided a method of handling a device under test (“DUT”). The method includes (i) supporting the DUT with a structure adapted to support the weight of the DUT, (ii) contacting the DUT with a conductive temperature control system, (iii) vertically raising the supported DUT off of the structure so that the DUT is not in direct contact with the structure, and (iv) maintaining contact between the DUT and the conductive temperature control system while the DUT is not in direct contact with the structure. 
     Briefly, in accordance with another aspect of the present invention, there is provided a system for handling a device under test (“DUT”). The system includes support means, a transport device, temperature controlling means, and lifting means. The support means is for supporting the DUT and it includes an aperture. The transport device is coupled to the support means and is for moving the DUT. The temperature controlling means is for controlling the temperature of the DUT with conduction. The lifting means is for lifting the DUT above the support means such that the DUT is not in direct contact with the support means. 
     Briefly, in accordance with another aspect of the present invention, there is provided a tooling system for handling a device under test (“DUT”). The tooling system includes a heat exchanger and a contact pad. The tooling system is adapted to apply a first force for contacting the heat exchanger to the DUT. The tooling system is adapted to apply a second force for contacting the contact pad to the DUT to secure the DUT in a fixed location for testing. 
     Briefly, in accordance with another aspect of the present invention, there is provided a method for positioning a semiconductor device under test (“DUT”). The method includes measuring a distance traveled by the DUT, providing feedback on the distance traveled, and utilizing the distance traveled to control the position of the DUT. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a top view of an embodiment of the present invention. 
     FIG. 1B is an exploded view of the rotary section of FIG.  1 A. 
     FIG. 2A depicts an IC device in a “live bug” position. 
     FIG. 2B depicts an IC device in a “dead bug” position. 
     FIG. 3A depicts an IC device in a carrier, which in turn is in a receptacle in accordance with an embodiment of the present invention. 
     FIG. 3B depicts an IC device in a carrier, which in turn is in a receptacle in accordance with another embodiment of the present invention. 
     FIG. 4 depicts a soak station of an embodiment of the present invention. 
     FIG. 5A depicts a cross view of a test actuator assembly in accordance with an embodiment of the present invention. 
     FIG. 5B depicts a side-view of a test actuator assembly in accordance with an embodiment of the present invention. 
     FIG. 5C depicts a top view of a test actuator assembly in accordance with an embodiment of the present invention. 
     FIG. 5D is an exploded view of a portion of FIG.  5 A. 
     FIG. 5E is an exploded view of a portion of FIG.  5 B. 
     FIG. 6A depicts a perspective bottom view of a rotary transport device in accordance with an embodiment of the present invention. 
     FIG. 6B depicts a perspective top view of a rotary transport device in accordance with an embodiment of the present invention. 
     FIG. 6C depicts an exploded perspective top view of a rotary transport device in accordance with an embodiment of the present invention. 
     FIG. 7A shows the general orientation of the test head, the carrier, and the test actuator assembly prior to testing of a DUT, according to an embodiment of the present invention. 
     FIG. 7B shows the test head comprising the socket, according to an embodiment of the present invention. 
     FIG. 8 illustrates a thermal control circuit connected to a tooling system. 
     FIG. 9 is a heat exchanger assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The above-noted and other aspects of the present invention will become more apparent from a description of the preferred embodiment, when read in conjunction with the accompanying drawings. The drawings illustrate the preferred embodiment of the invention. In the drawings, the same members have the same reference numerals. 
     1. Rotary Transport Device 
     Referring to FIG. 1A, in a preferred embodiment of the present invention, an IC device  20  in a tray  22  is transported by a Cartesian robot (not illustrated) to an active tray nest  29  in a staging area  30 . The IC device  20  is positioned in the tray  22  in a “live bug” position, that is, with its connections  24 , pointing down towards the tray  22 . The live bug position is illustrated in FIG.  2 A. In the active tray nest  29 , the IC device  20  is picked up by a vacuum handler (not illustrated), which places the IC device  20  in an inversion handler  35 , still in a live bug position (connections  24  pointing down towards the inversion handler). As described in co-pending provisional application U.S. Ser. No. 60/110,827 (attorney docket number  42811-107 ), filed on Dec. 2, 1998, and fully incorporated herein by reference, the inversion handler transfers the IC device  20  to a carrier  40  in a rotary table  44  of a rotary transport device  45  (also illustrated in FIG.  6 ), in a manner so that the IC device  20  is in the carrier  40  in a “dead bug” position, with connections  24  pointed up, away from the carrier  40 . 
     The inversion handler is the preferred apparatus for placing the IC device  20  in the carrier  40  because it places the IC device  20  in the carrier  40  in the dead bug position, with connections  24  pointed up. The dead bug position, illustrated in FIG. 2B, is the preferred position for the IC device  20  while in the carrier  40  for the purposes of the present invention. The carrier  40  may hold one or more IC devices  20 . 
     Referring to FIG. 3A, in an exploded view, the IC device  20  rests in the carrier  40 , which in turn rests in a receptacle  46  of the rotary table  44  of the rotary transport device (not illustrated in this figure). The receptacle  46  has a first aperture  47  which lines up with a second aperture  48  in the carrier  40 . More generally, the receptacle  46  refers to any device or part of a device which is used to acquire, guide, stabilize, align, contain, support, or hold the carrier  40  on the table  44 . Another embodiment is shown in FIG. 3B, in which the table  44  comprises the receptacle  46 , which includes the aperture  47  as well as a pair of locating pins  49 . The locating pins  49  line up with and are inserted into locating holes  41  in the carrier  40 . 
     Referring to FIGS. 1A,  1 B, and  6 A- 6 C, the carrier  40  preferably does not slide along a track nor is it moved along a conveyor belt. Instead, as illustrated in FIGS. 1A and 1B, the rotary table  44  of the rotary transport device  45  rotates around a shaft  247  (illustrated in FIG. 6C) to place the carrier  40  holding the IC device  20  in one or more positions or stations. The rotation of the rotary table  44  is preferably driven by a direct servo motor  246 . Pneumatic brake  248  is used for normal load/unload. For example, in FIGS. 1A and 1B, the rotary transport device  45  has a staging station  50 , six soak (or temperature control) stations  52 ,  53 ,  54 ,  55 ,  56 ,  57 , and a test station  60 , which, in the embodiment illustrated, is 180 degrees from the pick up, or staging, station  50 . The rotary transport device  45  may have a plurality of carriers  40 , such as one at every station, with each carrier holding one or more IC devices  20 . 
     Referring again to FIGS. 1A and 1B, once the IC device  20  is placed in the carrier  40  at the staging station  50 , the rotary transport device  45  rotates, placing the IC device and its carrier  40  in temperature control station  52 . (While this rotation happens to be clockwise in the pictured embodiment, an alternative embodiment could rotate in some other manner, such as counterclockwise or may rotate in both clockwise and counterclockwise directions.) 
     2. The Temperature Control 
     Referring to FIG. 4, at temperature control station  52 , the carrier  40  is positioned inside a soak station assembly  61 . The carrier  40  is positioned above a lift pad  62  and below a spring-loaded pad  64  (springs not illustrated) on the underside roof  66  of an arm  68  of a framework  70  for the soak station assembly  61 . If the IC device has connections (not illustrated in this figure), the spring-loaded pad  64  has small holes (not illustrated) for receiving those connections. 
     The lift pad  62  is part of a soak site actuator  72  of the soak station assembly  61 . The soak site actuator  72  is preferably controlled by a fixed-stroke pneumatic cylinder  96  and includes the lift pad  62 , soak tooling  74  (a tooling system), the soak station housing  76 , pneumatic system (not illustrated), and end-of-travel sensors  77 . 
     The lift pad  62  is supported on top of the soak station housing  76  by four shafts  80 . The shafts  80  have a pre-loaded spring  81  on the outside of them, although many other variations on the number and placement of springs, or other impact absorbing devices is possible. The spring loading depends on the system and IC chip design but is generally less than 20 PSI. Bushings  83  are included for each of the shafts  80 . 
     The soak tooling  74  as illustrated in FIG. 4 extends through an aperture  82  in the lift pad  62  and includes a heat exchanger housing  84 , heating element  002  (see FIG.  9 ), a heat exchanger element  001  (see FIG. 9) (preferably a heat sink adapted to be cooled by a liquid), integrated temperature sensor  301  (see FIG.  9 ), a feedback loop (not fully illustrated), and a contact pad  90 . In an alternative embodiment, the springs which are located in the spring-loaded pad  64  could be positioned under the soak tooling  74 . 
     FIG. 9 illustrates a heat exchanger assembly. In the preferred embodiment, the heat exchanger assembly is inside of heat exchanger housing  84 . As described above, the heat exchanger assembly of FIG. 9 includes heat exchanger element  001 , heating element  002 , and integrated temperature sensor  301 . The heat exchanger assembly of FIG. 9 also includes a variety of other components including screw  201 , washer  202 , and bracket  302 . 
     There are two upwardly-pointing precising pins  92  on the lift pad  62  as well as two downwardly-pointing precising pins  94  on the underside roof  66  of the arm  68  of the framework  70 . 
     Once the carrier  40  is in place, the soak site actuator  72  activates and lifts the lift pad  62  until it is touching the bottom of the carrier  40 . The carrier  40  has holes (not illustrated) in its underside which engage the upwardly-pointing precising pins  92 . 
     As the soak station actuator  72  continues to lift the carrier  40 , holes  93  in the top of the carrier engage the downwardly-pointing pins  94  until the carrier is placed against the underside roof  66 . The end of travel sensors  77  limit the movement of the soak station actuator  72 . 
     The arm  68  contacts the stationary carrier  40  and compresses springs  81 , allowing the soak tooling  74  to continue to travel through aperture  47  (not illustrated here, see FIG. 3A) in receptacle  46  (not illustrated here, see FIG. 3A) and through the second aperture  48  (not illustrated here, see FIG. 3A) in the carrier  40  until the contact pad  90  contacts the bottom of the IC device  20 . The soak tooling  74  continues to lift the IC device  20  above the carrier  40  until the IC device  20  is in contact with the spring-loaded pad  64  on the underside roof  66  of the arm  68  of the framework  70 . 
     Upon initial contact of the IC device  20  and the spring-loaded pad  64 , a spring (not illustrated, but analogous to spring  137  in FIG. 5D) within the heat exchanger assembly (see FIG. 9) compresses. This compression allows the contact pad  90  to continue to rise and to make contact with the bottom of the IC device  20 . The compression continues until the heat exchanger assembly (see FIG. 9) is below the surface of the contact pad  90  (contact pad  90  is at the top of soak tooling  74 ). Then, different springs (not illustrated, but analogous to springs  139  in FIG. 5B) above spring-loaded pad  64 , and below the arm  68 , compress and exert the required force against the IC device  20  needed to hold the device  20  in place during the soak/de-soak. 
     This method allows separate forces to be applied for contacting the heat exchanger assembly to the IC device  20  and for holding the IC device  20  against the spring-loaded pad  64 . Other embodiments may utilize different mechanisms to apply the different forces, including without limitation, flat springs, rubber or some other compressible material, and shock absorbers. 
     The soak tooling  74  is designed for the particular IC device to be tested, so that the soak tooling  74  travels the proper distance (“the stroke”) for that particular IC device and then it activates the end of travel sensors  77 . The end of travel sensors  77  are activated by a flag which is coupled to the soak tooling housing  76 . 
     After the IC device  20  is engaged against the spring-loaded pad  64  and the heat exchanger assembly is in contact with the IC device  20 , the heating or cooling cycle may begin. The integrated temperature sensor (not illustrated) measures the temperature of the heat exchanger element (not illustrated) and uses the measured temperature of the heat exchanger element to change the temperature of the heating element (not illustrated), the temperature sensor determines how much the temperature of the heat exchanger element is lowered/raised by the transfer of heat to/from the IC device  20 . The feedback loop (not illustrated) sends this information to a thermal control circuit  160  (see FIG.  8 ), which adjusts the energy to the heating element to optimize the temperature of the IC device  20 . 
     Referring to FIG. 8, there is shown a thermal control circuit  160  connected to a tooling system  162 . The tooling system  162  may be a soak tooling  74  (see FIG. 4) or a test tooling  130  (see FIGS.  5 A and  5 D), for example. The tooling system  162  is shown with a dashed line to a DUT  20 , indicating that the tooling system  162  is adapted to be coupled to the DUT  20 . 
     After the desired temperature is reached, the pneumatically-controlled soak station actuator  72  retracts. Then the springs  81  relax, allowing the IC device  20  to return to the carrier  40 . The rotary transport device  45  rotates to the next position. 
     In the preferred embodiment of the invention pictured in FIG. 1A, there are three temperature control stations  52 - 54  for the IC device  20  to rotate through before reaching the test station  60 . Each temperature control station  52 - 54  raises the temperature of the IC device  20  by a pre-defined value. The temperature of the air inside of the temperature control stations  52 - 54  is preferably maintained close to ambient. 
     In the embodiment of the invention pictured in FIGS. 1A and 1B, there is also a fourth temperature control station  55  which the IC device  20  rotates through after completing the test at the test station  60 . At this fourth temperature control station  55 , the temperature of the IC device  20  is brought below a safe “touch” temperature or above the dew point temperature, as explained earlier. In alternate embodiments there could be more than one post-test temperature control station  55 . There are two additional stations  56 - 57  which are not used at this time, but which could be used to further heat or cool the device  20 . 
     The total number of temperature control stations used in alternative embodiments may vary, depending upon test times, number of devices in parallel, and the time required to soak the particular IC device that the embodiment is targeting. 
     When the soak tooling  74  lifts the IC device  20  above the carrier  40 , the thermal isolation between the IC device  20  and the carrier  40  is increased. This enables the soak tooling  74  to more effectively control the temperature of the IC device and also minimizes the thermal stress to the carrier  40  and other parts. 
     The Test Station 
     After rotating the IC device  20  through the temperature adjustment stations  52 - 54 , the rotary transport device  45  rotates again, placing the IC device  20  into the test station  60 . At the test station  60 , the carrier  40  is positioned above a test actuator assembly  100  (illustrated in FIGS. 5A-5E) and below a test head  250 , as illustrated in FIG.  7 A. 
     The test actuator assembly  100  is driven by a servo motor  105  (see FIGS. 5B and 5C) and includes a test liftplate  110 , with an aperture  111 , and resting on four hafts  115  with springs  120  outside. Referring to FIGS. 5A and 5D, the shafts  115  are attached to the framework  125  of the test actuator assembly  100  at a base plate  128  and extend through the bottom. Inside the four shafts  115 , below an aperture (not illustrated in FIGS. 5A or  5 D) in the test lift plate  110  and above the base plate  128 , is a test tooling  130  (a tooling system). As illustrated in FIGS. 5B and 5E, the test tooling  130  includes a heat exchanger housing  134 , a heating element  136  (see also  002  in FIG.  9 ), a heat exchanger element (preferably a liquid cooled heat sink)  138  (see also  001  in FIG. 9) an integrated temperature sensor ( 301  in FIG.  9 ), a feedback loop (not fully illustrated), a test precising pin  112 , and a contact pad  140 . 
     The heat exchanger assembly of FIG. 9 was described earlier in the section on temperature control. A heat exchanger assembly, as in FIG. 9, is also inside of heat exchanger housing  134 . Thus, the heat exchanger assembly of FIG. 9 is preferably inside of each of the six soak stations  52 - 54 ,  55 - 57 , and the test station  60 . 
     In operation, the servo motor  105  drives a pulley (not illustrated), which turns a ballscrew  113 , which causes the base plate  128  to move upwards, until the test lift plate  110  is placed against the carrier  40 . Once contact with the carrier  40  is made, the base plate  128  continues to move upwards, until the test lift plate  110  is pressed against the carrier  40  which in turn is pressed against a socket  255  in the test head  250  (see FIGS.  7 A and  7 B). 
     Then the base plate  128  continues to move upward, allowing the test tooling  130  to pass through the aperture  111  in the test lift plate  110 . This continued movement of the base plate  128  compresses the springs  120  inside the shafts  115 , as the shafts  115  extend out the bottom of the base plate  128 . The test tooling  130  passes through the second aperture  48  in carrier  40  to be pressed against the IC device  20 . Note that the IC device  20  is in a dead bug position with the connections pointing upward to the test head  250  (see FIGS.  7 A and  7 B). 
     The base plate  128  continues to extend, lifting the IC device  20 , until the connectors of the IC device  20  are in contact with socket  255  in the test head  250  (see FIGS.  7 A and  7 B). Upon initial contact of the IC device  20  and the socket  255  connections, spring  137  (see FIG. 5D) compresses. This compression allows the contact pad  140  to continue to rise and to make contact with the bottom of the IC device  20 . The compression continues until the heat exchanger assembly (see FIG. 9) is below the surface of the contact pad  140  (see FIG.  5 B). 
     Then, springs  139  (see FIG. 5B) compress and exert the required force against the IC device  20 , through the contact pad  140 , needed to fully mate the IC device  20  with the socket  255 . This method allows separate forces to be applied for contacting the heat exchanger assembly to the IC device  20  and for socketing the IC device  20 . 
     When the test tooling  130  lifts the IC device  20  above the carrier  40 , the thermal isolation between the IC device  20  and the carrier  40  is increased. This enables the test tooling  130  to more effectively control the temperature of the IC device  20  and also minimizes the thermal stress to the carrier  40  and other parts. 
     To limit the movement of the IC device  20  or for calibration, a linear variable displacement transducer  145  may be used. A part such as an IC device of a known thickness is cycled through the system to the test station  60 . The part would be set up to socket with the test head while measurements of the linear variable displacement transducer  145  are being read upon an output. The linear variable transducer  145  will move some distance in the vertical or Z direction, that is, moving the part towards being socketed with the test head. The linear variable displacement transducer  145  tells when the part has “bottomed out” in the test head socket. Software controlling the apparatus of the invention has a database with part-specific thickness values and the desired gap between the package bottom and the test head base. These values will be used to program the Z axis position of the part. If the mechanism shifts for some reason (e.g., thermal expansion, variable spring Constants) the Z axis distance can be adjusted to maintain the desired gap. 
     Thus, through the use of the linear variable displacement transducer  145  (a distance measurer), the IC device  20  can be brought to desired gap (for example, 1/1000 inch), bottomed-out, or past the point of bottoming out by further compressing the spring inside of the linear variable displacement transducer  145 . This allows the measurement of the distance traveled by the IC device  20  in relation to the socket  255 , for example and without limitation, to be measured directly. Other embodiments can utilize different techniques and/or devices, known in the art, to measure this distance, or can apply a calibrated amount of force to achieve a desired distance. 
     The linear variable displacement transducer  145  can be used to determine the extent of the movement of the IC device  20 , particularly if the IC device  20  is not desired to be “bottomed-out” against the test socket, fully compressing the socket contacts. The linear variable displacement transducer  145  can also be used for error recovery, providing precise feedback on the extent of the IC device travel. 
     Pressure from the heat exchanger housing  134  which is spring loaded and coupled to base plate  128  sockets the IC device  20  in the test head and allows for testing. The temperature of the device  20  is controlled during the test, using any feedback mode such as the one described above for the soak station or the power following feedback mode described in co-pending provisional patent application U.S. Ser. No. 60/092,720 (attorney docket number 42811-104), filed on Jul. 14, 1998 and hereby incorporated by reference. 
     After testing, the servo motor  105  allows the base plate  128  to retract. The IC device  20  de-couples from the test head and returns to the carrier  40 . Then base plate  128  continues to retract until it reaches its original position, allowing the carrier  40  to do the same. The rotary transport device  45  then rotates the IC device  20  through the remaining temperature control stations  55 - 57 , if necessary, to adjust the temperature once more to a safe handling temperature or above the dew point temperature. 
     At the staging station  50 , as described in co-pending application U.S. Ser. No. 60/110,827, the IC device  20  is gripped by the inversion handler and inverted to a live bug position. The vacuum handler retrieves the IC device  20  from the inversion handler and returns it to its JEDEC tray  22 . 
     In the preferred embodiment of the invention, the IC device  20  is sorted into trays identified by bin codes. The bin code may be either a pass bin code or a fail bin code. 
     In an alternative embodiment, a “soft sort” process can be used, whereby a tray map can be maintained for each tray. The tray map is a database which maps the location of each IC device  20  in the tray and the results of the IC device&#39;s test. 
     The device handler described in this disclosure thus includes a variety of advantages. By lifting an IC device  20  off of the carrier  40 , the IC device  20  is no longer in direct contact with the carrier  40 . This lowers the effective thermal mass which must be heated or cooled in order to heat or cool the IC device  20 . A given temperature can, therefore, be achieved in a shorter amount of time. 
     Further, the system is able to respond to self-heating of the IC device  20 . If the system had to heat or cool the larger thermal capacitance of the carrier  40 , it would take longer to respond to self-heating of the IC device  20 . Such delay would make it more difficult, and in some cases prohibitively so, to maintain the temperature of the IC device  20  within specified limits. 
     The carrier  40  is also spared the additional thermal stress of being heated or cooled, sometimes with large, quick temperature deviations. This improves the system&#39;s reliability and reduces both the initial cost to design and manufacture, due to simpler material constraints, as well as the maintenance costs. 
     The system also lifts the IC device  20  off of the carrier  40  in both soak stations and the test station, with the same motion. This reduces the complexity of the system and the number of parts required compared to systems which utilize different motions in soak stations versus test stations. 
     The system is also able to use lower forces when lifting the IC device  20  because the carrier  40  does not need to be lifted. The carrier  40  is usually considerably heavier than the IC device  20 . This allows the system to use smaller, less expensive motors and servos which are also typically easier to maintain. This also reduces the risk of damage and stress to the carrier  40 . Perhaps more importantly, the risk of damage to the IC device  20  and the socket is also lowered. 
     The system also incorporates springs which absorb some of the force and impact. Coil springs are simply one form of impact absorbers. Other impact absorbers include flat springs, compressible materials, and fixtures which are not locked in place. Springs are used in the disclosed embodiment, for example, in the springs  81 , the spring-loaded pad  64 , and the springs  120 . This use of springs further reduces the risk of damage to the IC device  20  and the socket. The springs are used in both the soak stations and the test station. 
     The principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. The invention is not to be construed as limited to the particular forms disclosed, because these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those of ordinary skill in the art without departing from the spirit of the invention.