Patent Publication Number: US-2009230985-A1

Title: Burn-in system with measurement block accomodated in cooling block

Description:
This application is a Divisional of co-pending application Ser. No. 12/116,599, filed on May 7, 2008, which is a Divisional of application Ser. No. 11/226,408, filed on Sep. 15, 2005, now U.S. Pat. No. 7,397,258. The entire contents of each of the above-identified applications are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a burn-in system for conducting a burn-in test for extracting initial defects of semiconductor integrated circuits and other various types of electronic devices, more particularly relates to a burn-in system for simultaneously conducting a burn-in test on a large number of electronic devices. In countries where incorporation by reference of other documents is allowed, the content described in the following application is incorporated into the present application by reference and made part of the description of this application. 
     Japanese Patent Application No. 2004-079623, filed on Mar. 19, 2004. 
     2. Description of the Related Art 
     As a burn-in system used for burn-in tests—a type of screening test for extracting initial defects of electronic devices and removing initially malfunctioning devices, there is known a system holding a burn-in board mounting a large number of devices under test in a burn-in chamber, applying a predetermined voltage to impart electrical stress, and heating the air in this burn-in chamber to impart a predetermined temperature of thermal stress or a system not heating the air in the burn-in chamber, but instead providing heater blocks and bringing the heater blocks into direct contact with the devices under test to impart thermal stress for a burn-in test. 
     In such a burn-in system, since a burn-in test is conducted over a long period of time from several hours to several tens of hours, the test efficiency is raised by conducting the burn-in test simultaneously for a large number of electronic devices. At this time, the test is desirably performed in a state giving as uniform a thermal stress as possible to the large number of devices under test. 
     However, in actuality, even with the same lot of electronic devices, inherent defects, manufacturing variations, etc. result in each electronic device differing in consumed power, so the electronic devices sometimes vary in amounts of self generated heat as well. Therefore, even if simply heating the air in the burn-in chamber or bringing heater blocks into contact with the devices, it is sometimes difficult to apply a uniform thermal stress to the simultaneously tested plurality of electronic devices. 
     In particular, recent IC chips have become larger in capacity, higher in performance, and faster in speed. Along with this, the amount of self generated heat has been increasing as a general trend. Along with this, the variation in amount of self generated heat has also become larger as a general trend. Therefore, accurate control of the temperature of each electronic device in a burn-in test is being demanded. 
     SUMMARY OF THE INVENTION 
     The present invention has as its object the provision of a burn-in system enabling the temperature of a large number of electronic devices differing in amount of self generated heat to be simultaneously reliably adjusted to a predetermined temperature. 
     To achieve this object, according to a first aspect of the present invention, there is provided a burn-in system bringing heating blocks having heating means for heating a plurality of devices under test mounted on a burn-in board and cooling blocks formed with channels able to carry a coolant for cooling the devices under test into contact with the devices under test and simultaneously conducting a burn-in test on the plurality of devices under test, wherein each cooling block is formed with a first accommodating space for accommodating the heating block, and each heating block is accommodated in a first accommodating space in a state with a layer of air formed with the cooling block so as to be insulated from the cooling block. 
     In the present invention, there is provided a burn-in system adjusting the temperatures of a plurality of devices under test mounting on a burn-in board by heating blocks and cooling blocks and simultaneously performing a burn-in test of those devices under test, wherein each cooling block is formed with a first accommodating space and accommodates the heating block in that first accommodating space in a state maintaining clearance. 
     Due to this, a layer of air is formed between each cooling device for cooling a device under test and the heating block for heating that device under test, the heating block is insulated from the cooling block, and the heating block is made thermally floating in state with respect to the cooling block, so heat is not directly conducted from the heating block to the cooling block. For this reason, the heating means of each heating block can positively and easily raise the temperature of the individual electronic device and coolant flowing through the channels formed in each cooling block can be used to positively and easily cool the individual electronic device, so when simultaneously performing a burn-in test on a plurality of electronic devices, it is possible to independently and accurately control the temperatures of the individual electronic devices. 
     While not particularly limited in the present invention, preferably each heating block is supported with play with respect to the cooling block, and when a heating block is not in contact with a device under test, a front end face of the heating block sticks out relative to a front end face of the cooling block. 
     By making the front end face of the heating block stick out from the front end face of the cooling block, when contacting a device under test, the heating block contacts the device under test before the cooling block. Further, as explained above, each heating block is supported with play with respect to the cooling block in a state maintaining clearance between the heating block and the inside wall surfaces of the first accommodating space, that is, the heating block is in a mechanically floating state with respect to the cooling block, so the heating block contacting the device under test before the cooling block operates fit against that device under test. Due to this, since the front end face of the heating block is in close contact with the device under test, the device under test can be efficiently raised in temperature. 
     While not particularly limited in the present invention, preferably each heating block and cooling block have provided between them first biasing means for biasing the heating block to a front end side. 
     By providing first biasing means between each heating block and cooling block, when the heating block contacts a device under test, that heating block is suitably pushed against and closely contacts the device under test, so the device under test can be raised in temperature more efficiently. 
     While not particularly limited in the present invention, preferably when a heating block is not in contact with the device under test, the first biasing means cause the heating block to be biased to a contact surface side and cause part of the heating block to contact the cooling block. 
     Due to this, the heat of the heating means of the heating block can be utilized to raise the temperature of the coolant flowing through the channels of the cooling block, so there is no longer a need to separately provide a heater for heating the coolant separate from that heating means. 
     While not particularly limited in the present invention, preferably the system is further provided with measurement blocks having measuring means for measuring temperatures of the devices under test, each cooling block is formed with a second accommodating space for accommodating the measurement block, and each measurement block is accommodated in the second accommodating space in the state with a layer of air formed with the cooling block so as to be insulated from the cooling block. 
     Due to this, a layer of air is formed between each cooling block for cooling a device under test and the measurement block for measuring the temperature of the device under test, the measurement block is insulated from the cooling block, and the measurement block is made thermally floating in state with respect to the cooling block, so the temperature of the device under test can be accurately measured and the precision of temperature adjustment is improved. 
     To achieve the object, according to a second aspect of the invention, there is provided a burn-in system bringing cooling blocks formed with channels able to carry a coolant for cooling a plurality of devices under test mounted on a burn-in board and measurement blocks having measuring means for measuring the temperatures of the devices under test into contact with the plurality of devices under test and simultaneously conducting a burn-in test on the plurality of devices under test, wherein the system is further provided with variable flow rate means for varying the flow rate of the coolant flowing through the channels formed in the cooling blocks, each cooling block is formed with a second accommodating space for accommodating the measurement block, and each measurement block is accommodated in the second accommodating space in a state with a layer of air formed with the cooling block so as to be insulated from the cooling block. 
     In the present invention, there is provided a burn-in system adjusting the temperatures of a plurality of devices under test mounted on a burn-in board by cooling blocks and simultaneously performing a burn-in test on those devices under test, wherein the system is further provided with variable flow rate means for varying the flow rates of coolant flowing through channels formed in the cooling blocks, each cooling block is formed with a second accommodating space, and a measurement block is accommodated in this second accommodating space in a state maintaining clearance. 
     Due to this, without providing a heater or other heating means, each variable flow rate means can vary the flow rate of the coolant to adjust the cooling thermal resistance of the cooling block and therefore the temperature of each device under test can be easily adjusted, so when simultaneously performing a burn-in test on a plurality of electronic devices, it is possible to independently and accurately control the temperature of each electronic device. 
     Further, a layer of air is formed between each cooling block for cooling a device under test and a measurement block for measuring the temperature of the device under test, the measurement block is insulated from the cooling block, and the measurement block is made thermally floating in state with respect to the cooling block, so the temperature of the device under test can be accurately measured and the precision of temperature adjustment is improved. 
     Further, to achieve the object, according to a third aspect of the present invention, there is provided a burn-in system provided with at least cooling blocks formed with channels able to carry a coolant for cooling a plurality of devices under test mounted on a burn-in board and formed with openings communicating with the channels at their front end faces, measurement blocks having measuring means for measuring temperatures of the devices under test, variable flow rate means for varying flow rates of the coolant through channels formed in the cooling blocks, and coolant recovering means for recovering coolant flowing through the channels, each cooling block formed with a second accommodating space for accommodating a measurement block, each measurement block accommodated in a second accommodating space in a state with a layer of air formed with the cooling block so as to be insulated from the cooling block, and pushing against the devices under test mounted on the burn-in board the cooling blocks and the measurement blocks to bring the coolant into direct contact with the devices under test through the openings and simultaneously conducting a burn-in test on the plurality of devices under test and, when the burn-in test ends, using the coolant recovering means to recover the coolant. 
     In the present invention, there is provided a burn-in system adjusting the temperatures of a plurality of devices under test mounted on a burn-in board and simultaneously performing a burn-in test on the devices under test, wherein the system is further provided with variable flow rate means for varying the flow rates of coolant flowing through channels formed in the cooling blocks and the front end faces of the cooling blocks are formed with openings communicating with the channels. Further, when pushing a cooling block against an electronic device, the coolant supplied through the opening is made to directly contact the surface of the device under test so as to cool the device under test when performing the burn-in test. After the burn-in test, the coolant recovering means recovers the coolant from the surface of the device under test. 
     Due to this, without providing a heater or other heating means, each variable flow rate means can vary the flow rate of the coolant to adjust the temperature of the individual device under test directly and easily, so when simultaneously performing a burn-in test on a plurality of electronic devices, it is possible to independently and accurately control the temperature of each electronic device. 
     While not particularly limited in the invention, preferably each measurement block is supported with play with respect to the cooling block, and in the state where a measurement block is not in contact with the device under test, the front end face of the measurement block sticks out relative to the front end face of the cooling block. 
     By making the front end face of each measurement block stick out from the front end face of the cooling block, when contacting a device under test, the measurement block contacts the device under test before the measurement block. Further, as explained above, since each measurement block is supported with play with respect to the cooling block in a state with a clearance maintained between the measurement block and the inside wall surface of the second accommodating space, that is, the measurement block is in a mechanical floating state with respect to the cooling block, the measurement block contacting the device under test before the cooling block operates fit against that device under test. Due to this, the front end face of the measurement block closely contacts the device under test, so the temperature of the device under test can be more accurately measured. 
     While not particularly limited in the invention, preferably each measurement block and cooling block are provided between them with second biasing means for biasing the measurement block to the front end face side. 
     By providing second biasing means between the measurement block and the cooling block, when the measurement block contacts a device under test, that measurement block is suitably pushed against and closely contacts the device under test, so the temperature of the device under test can be more accurately measured. 
     While not particularly limited in the invention, preferably in a state where a measurement block is not in contact with the device under test, the second biasing means cause the measurement block to be biased to the front end side and cause part of the measurement block to contact the cooling block. 
     By bringing part of the measurement block into contact with the cooling block before contacting a device under test, it becomes possible to monitor the temperature of the cooling block or the state of operation of the heating means of the heating block or to enable self-diagnosis of that measuring means. 
     While not particularly limited in the invention, preferably the system is further provided with temperature adjustment boards supporting a plurality of the cooling blocks at frames with play and a burn-in chamber able to hold each burn-in board and having the temperature adjustment boards, each temperature adjustment board being provided in the burn-in chamber so that each cooling block faces a device under test mounted on the burn-in board. 
     By further providing temperature adjustment boards supporting a plurality of cooling blocks at a frame with play, the cooling blocks are set in a mechanically floating state with respect to the temperature adjustment boards. 
     Due to this, the variations in height of inclination of the devices under test mounted on the burn-in board can be absorbed, so the cooling blocks can be made to closely contact the devices under test and the temperature of the devices under test can be accurately adjusted. 
     While not particularly limited in the invention, preferably each cooling block is supported on a frame through third biasing means biasing the cooling block toward a burn-in board facing it in the burn-in chamber. 
     By providing third biasing means between each cooling block and the frame, when a cooling block contacts a device under test, that cooling block is suitably pushed against and closely contacts the device under test, so the temperature of the device under test can be more accurately adjusted. 
     While not particularly limited in the invention, preferably at least part of the channels formed at the plurality of cooling blocks are connected in series. 
     By connecting the channels in series in this way, compared with when connecting all of them in parallel, it is possible to keep down the increase in the number of connection points of the pipes in the temperature adjustment boards and possible to improve the reliability of the pipes. 
     While not particularly limited in the invention, preferably each cooling block is provided with a bypass for making the coolant bypass the channels. 
     By providing such a bypass in each cooling block, when adjusting the temperature of a device under test with a relatively low power consumption and not that large an amount of self generated heat, the flow rate of the coolant flowing through the channels can be suitably secured and the temperature of the device under test can be suitably adjusted. 
     While not particularly limited in the invention, preferably each variable flow rate means is provided in a channel or a bypass. Further, while not particularly limited in the invention, preferably the system is further provided with a chiller able to adjust the temperature and flow rate of the coolant. 
     While not particularly limited in the invention, preferably the temperature adjustment boards have first cooling blocks formed with the bypasses and second cooling blocks not formed with the bypasses. 
     By providing the same temperature adjustment board with two different types of cooling blocks with different cooling performances due to the presence/absence of bypasses, a single burn-in system can handle DUTs with a wide range of amounts of self-generated heat. 
     While not particularly limited in the invention, preferably the burn-in chamber has a plurality of the temperature adjustment boards, one temperature adjustment board among the plurality of temperature adjustment boards has first cooling blocks formed with the bypasses and the other temperature adjustment boards have second cooling blocks not formed with the bypasses. Due to this, a single burn-in system can handle DUTs with a wide range of amounts of self-generated heat. 
     While not particularly limited in the invention, preferably each temperature adjustment board has at least two types of cooling blocks having different thermal resistances between the coolant and the devices under test. 
     By providing each temperature adjustment board with at least two types of cooling blocks with different thermal resistances between the coolant and the devices under test, a single burn-in system can handle DUTs with a wide range of amounts of self-generated heat. 
     While not particularly limited in the invention, preferably the burn-in chamber has a plurality of the temperature adjustment boards, and a thermal resistance between the coolant and the devices under test in coolant blocks in one temperature adjustment board among the plurality of temperature adjustment boards and a thermal resistance between the coolant and the devices under test in coolant blocks of the other temperature adjustment boards are different. Due to this, a single burn-in system can handle DUTs with a wide range of amounts of self-generated heat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein: 
         FIG. 1  is a front view of an overall burn-in system according to a first embodiment of the present invention; 
         FIG. 2  is a side view of the overall burn-in system shown in  FIG. 1 ; 
         FIG. 3  is a conceptual view of the system configuration of the burn-in system shown in  FIG. 1 ; 
         FIG. 4  is a plan view of an overall burn-in board mounting DUTs in the first embodiment of the present invention; 
         FIG. 5  is a plan view of a temperature adjustment board used in a burn-in system according to the first embodiment of the present invention; 
         FIG. 6  is a side view of a first temperature adjustment head supported on the temperature adjustment board shown in  FIG. 5 ; 
         FIG. 7  is a top plan view of the first temperature adjustment head shown in  FIG. 6 ; 
         FIG. 8  is a bottom plan view of the first temperature adjustment head shown in  FIG. 6 ; 
         FIG. 9  is a cross-sectional view of the first temperature adjustment head along the line IX-IX of  FIG. 8 ; 
         FIG. 10  is a cross-sectional view of the first temperature adjustment head along the line X-X of  FIG. 8 ; 
         FIG. 11  is a heat conduction model of a temperature adjustment head in the first embodiment of the present invention; 
         FIG. 12  is a graph of the adjustable range of temperature of first to third temperature adjustment heads in a burn-in system according to the first embodiment of the present invention; 
         FIG. 13  is a view of the state of temperature adjustment of a DUT by a first temperature adjustment head in the first embodiment of the present invention; 
         FIG. 14  is a side view of a second temperature adjustment head used in a burn-in system according to the first embodiment of the present invention; 
         FIG. 15  is a bottom plan view of the second temperature adjustment head shown in  FIG. 14 ; 
         FIG. 16  is a view of the state of temperature adjustment of a DUT by a second temperature adjustment head in the first embodiment of the present invention; 
         FIG. 17  is a side view of a temperature adjustment head in a second embodiment of the present invention; 
         FIG. 18  is a side view of a temperature adjustment head in a third embodiment of the present invention; 
         FIG. 19  is a bottom plan view of the temperature adjustment head shown in  FIG. 18 ; and 
         FIG. 20  is a schematic view of a coolant recovering means of a burn-in system according to a third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, embodiments of the present invention will be explained based on the drawings. 
     First Embodiment 
       FIG. 1  is a front view of an overall burn-in system according to a first embodiment of the present invention,  FIG. 2  is a side view of the overall burn-in system shown in  FIG. 1 ,  FIG. 3  is a conceptual view of the system configuration of the burn-in system shown in  FIG. 1 , and  FIG. 4  is a plan view of an overall burn-in board mounting DUTs in the first embodiment of the present invention. 
     First, explaining the overall configuration of the burn-in system  1  according to the first embodiment of the present invention, this burn-in system  1 , as shown in  FIG. 1  to  FIG. 3 , is provided with a burn-in chamber  100  which can hold burn-in boards  200  on which for example DUTs (devices under test) such as IC chips (corresponding to “device under test” in the claims) are mounted and has temperature adjustment boards  300  with temperature adjustment heads  400  for adjusting the DUTs in temperature arranged facing the burn-in boards  200 ; a DUT power source  600  for supplying the DUTs with power voltage; a heater power source  700  for driving heaters of the temperature adjustment heads  400  of the temperature adjustment boards  300 ; a burn-in controller  800  for controlling the DUTs in temperature and controlling the supply of the power voltage or signals etc.; and a chiller  900  for supplying a coolant to the temperature adjustment heads  400  of the temperature adjustment board  300 . 
     This burn-in system  1  is a monitored burn-in system which pushes the temperature adjustment heads  400  of the temperature adjustment boards  300  against the DUTs, uses heaters and coolants to adjust the DUTs in temperature and apply thermal stress, and supplies power voltage and supplies the input circuits of the DUTs with signals close to those of actual operation for screening and for monitoring of the characteristics of the output circuits of the DUTs. 
     Further, this burn-in system  1 , for example, can simultaneously conduct burn-in tests on 640 DUTs with different amounts of self-generated heat such as 0 to 100 W level medium heat emitting types, 100 to 200 W level high heat emitting types, or, 200 to 300 W level superhigh heat emitting types. 
     The burn-in chamber  100  of the burn-in system  1  according to the present embodiment, as shown in  FIG. 1  and  FIG. 2 , has an inside chamber defined by heat insulating walls etc. and a door able to be opened and closed for loading and unloading burn-in boards to and from the inside chamber. Further, the inside chamber of this burn-in chamber  100  is provided with 16 levels and two rows of slots  110  for supporting the burn-in boards  200  and therefore can hold a total of 32 burn-in boards  200 . Note that the number and arrangement of the slots  110  in this burn-in chamber  100  are not particularly limited in the present invention and can be freely set in consideration of the test efficiency etc. 
     Further, as shown in  FIG. 2 , the back of each slot  110  is provided with a connector  120  into which an edge connector  202  of a burn-in board  200  (see  FIGS. 3 and 4 ) can be inserted. This connector  120 , as shown in  FIG. 3 , is electrically connected to the DUT power source  600  and the burn-in controller  800 . Note that  FIG. 3  only illustrates one set of the burn-in board  200  and temperature adjustment board  300 , but the other 31 sets of burn-in boards  200  and temperature adjustment boards  300  are similarly connected to the DUT power source  600 , heater power source  700 , burn-in controller  800 , and, chiller  900 . Further, the air in the burn-in chamber  100  is circulated by a fan (not shown) etc. so as to keep heated air around the DUTs from stagnating there, but is not controlled to the extent of adjusting the DUTs in temperature. 
     Here, a burn-in board  200  held in the burn-in chamber  100  will be explained. This burn-in board  200 , as shown in  FIG. 4 , is comprised of 20 burn-in sockets  201  able to mount DUTs arranged on a board with superior heat resistance in four rows and five columns. One side edge of that board is formed with an edge connector  202  able to be inserted into a connector  120  formed in the burn-in chamber  100 . Note that the number and arrangement of the burn-in sockets  201  on the burn-in board  200  are not particularly limited in the present invention and can be freely set in consideration of the test efficiency etc. 
     That board is further formed with a printed circuit (not shown) electrically connecting this edge connector  202  and the burn-in sockets  201 . When the edge connector  202  of the burn-in board  200  is inserted into the connector  120  of the burn-in chamber  100 , the DUTs mounted on the burn-in board  200  are electrically connected to the DUT power source  600  and the burn-in controller  800  through this printed circuit and the burn-in sockets  201 . Note that while not particularly illustrated, the work for insertion and removal of DUTs to and from the burn-in sockets  201  of this burn-in board  200  is performed for example outside of the burn-in system  1  using an inserter/remover, loader/unloader, etc. 
     The burn-in chamber  100 , as shown in  FIG. 1  to  FIG. 3 , further is provided with 32 temperature adjustment boards  300  for adjusting the DUTs in temperature arranged so as to face the burn-in boards  200  supported at the slots  110 . Each temperature adjustment board  300  is able to be raised and lowered in the vertical direction by air cylinders  130  (see  FIG. 3 ) under the control of the burn-in controller  800  so that, at the time of a burn-in test, the temperature adjustment heads  400  can be brought into contact with the DUTs and, at the time of non-contact, the temperature adjustment heads  400  can be moved away from the DUTs. Note that temperature adjustment board  300  will be explained later in detail. 
     The DUT power source  600  of the burn-in system  1  according to the present embodiment, as shown in  FIG. 3 , is connected to the DUTs through the connectors  120  of the burn-in chamber  100  and the edge connectors  202 , printed circuits, and burn-in sockets  201  of the burn-in boards  200  to be able to supply power voltage to the DUTs and is controlled by the burn-in controller  800 . Further, the heater power source  700 , as shown in  FIG. 3 , is connected so as to be able to supply power to the heaters (explained later) provided at the temperature adjustment boards  300  in the burn-in chamber  100  and is controlled by the burn-in controller  800 . 
     The burn-in controller  800  of the burn-in system  1  according to the present embodiment controls the temperatures of the DUTs during the burn-in test, the voltages supplied to the DUTs, and the signals supplied to them. In addition, it judges any DUT exhibiting abnormal reactions during the burn-in tests to be defective, for example, holds the serial number of the DUT linked with the number of the slot in the burn-in chamber  100  and the position on the burn-in board  200 , and feeds back the test results. 
     This burn-in controller  800 , as shown in  FIG. 3 , is connected to temperature sensors (explained later) provided at the temperature adjustment boards  300  in the burn-in chamber  100  so as to enable detection of the temperatures of the DUTs and is connected to the heater power source  600  and chiller  900  so as to enable control of the temperatures of the DUTs. Further, it is connected to the DUT power source  700  so as to enable control of the power voltage supplied to the DUTs. 
     These DUT power source  600 , heater power source  700 , and burn-in controller  800  are held in an instrument rack  500  shown in  FIG. 1 . 
     The chiller  900  of the burn-in system  1  according to the present embodiment causes a fluorine-based inert liquid (for example, 3M Fluorinert FC-323) or other coolant to circulate to the cooling blocks (explained later) of the temperature adjustment board  300  in the burn-in chamber  100  and can adjust the coolant in temperature and flow rate under the control of the burn-in controller  800 . Note that the coolant in the present invention is not limited to the above liquid and for example may also be a gas. 
     Below, a temperature adjustment board  300  used in the burn-in system  1  according to the present embodiment will be explained. 
       FIG. 5  is a plan view of a temperature adjustment board used in a burn-in system according to the first embodiment of the present invention,  FIG. 6  is a side view of a first temperature adjustment head supported on the temperature adjustment board shown in  FIG. 5 ,  FIG. 7  is a top plan view of the first temperature adjustment head shown in  FIG. 6 ,  FIG. 8  is a bottom plan view of the first temperature adjustment head shown in  FIG. 6 ,  FIG. 9  is a cross-sectional view of the first temperature adjustment head along the line IX-IX of  FIG. 8 ,  FIG. 10  is a cross-sectional view of the first temperature adjustment head along the line X-X of  FIG. 8 ,  FIG. 11  is a heat conduction model of a temperature adjustment head in the first embodiment of the present invention,  FIG. 12  is a graph of the adjustable range of temperature of first to third temperature adjustment heads in a burn-in system according to the first embodiment of the present invention,  FIG. 13  is a view of the state of temperature adjustment of a DUT by a first temperature adjustment head in the first embodiment of the present invention,  FIG. 14  is a side view of a second temperature adjustment head used in a burn-in system according to the first embodiment of the present invention,  FIG. 15  is a bottom plan view of the second temperature adjustment head shown in  FIG. 14 , and  FIG. 16  is a view of the state of temperature adjustment of a DUT by a second temperature adjustment head in the first embodiment of the present invention. 
     The temperature adjustment board  300  of the present embodiment, as shown in  FIG. 5  and  FIG. 6 , is provided with 20 temperature adjustment heads  400  for adjusting the DUTs in temperature, a frame  301  for supporting the temperature adjustment head  400   s , and main pipes  302  and branch pipes  303  for supplying the cooling blocks of the temperature adjustment heads  400  with coolant from the chiller  900 . 
     The frame  301  of this temperature adjustment board  300 , as shown in  FIG. 5 , is a flat plate member formed with four rows and five columns, or a total of 20, openings  3011  corresponding to the arrangement of the DUTs mounted on a burn-in board  200  (arrangement of burn-in sockets  201 ). Further, as shown in  FIG. 6 , each opening  3011  has a temperature adjustment head  400  inserted into it. As shown in  FIG. 9  and  FIG. 10 , each temperature adjustment head  400  is supported with play with respect to the frame  301  by supporting parts  304  of the frame  301  via third springs  305  (third biasing means) pressing that temperature adjustment head  400  to the facing burn-in board  200  side. 
     By setting each of the temperature adjustment heads  400  in a mechanical floating state with respect to the temperature adjustment board  300  in this way, variations in height or inclination of the DUTs mounted on the burn-in board  200  can be absorbed by the temperature adjustment heads  400 . 
     Further, by having each of the temperature adjustment heads  400  supported by the frame  301  via third springs  305  pushing the temperature adjustment heads  400  to the burn-in board  200  side, when each temperature adjustment head  400  contacts a DUT, that temperature adjustment head  400  can be made to be suitably pushed against and closely contact the DUT. 
     The temperature adjustment head  400  in the first embodiment of the present invention includes a first temperature adjustment head  400   a  for example for 0 to 100 W level medium heat emitting types of DUTs, a second temperature adjustment head  400   b  for example for 100 to 200 W level high heat emitting types of DUTs, and a third temperature adjustment head for example for 200 to 300 W level superhigh heat emitting types of DUTs. By selecting the suitable type from among the total three types of temperature adjustment heads by considering the amount of self generated heat of the DUTs in question, it becomes possible to handle DUTs of a broad range of amount of self generated heat by a single burn-in system  1  (see  FIG. 12 ). Note that the second and third temperature adjustment heads will be explained in detail later, but no matter which temperature adjustment heads are employed, the temperature adjustment board  300  is configured the same except for the temperature adjustment heads. 
     Each first temperature adjustment head  400 , as shown in  FIG. 6 , is provided with a cooling block  410   a  for cooling a DUT, a heater block  420   a  for heating a DUT, and a sensor block  430   a  for measuring the temperature of a DUT. 
     The cooling block  410   a  of this first temperature adjustment head  400   a  is made of aluminum, copper, or another material superior in heat conductivity. As shown in  FIG. 6  and  FIG. 7 , this cooling block  410   a  is formed inside it with an inside space  412   a  for circulation of the coolant supplied from the chiller  900 . Further, this cooling block  410   a  is formed inside it with an entrance side channel  41   a  connecting a branch pipe  303  and the inside space  412   a  so as to extend downward at an angle along the direction of progression of the coolant and is formed inside it with an exit side channel  413   a  connecting the inside space  412   a  and a branch pipe  303  so as to extend upward at an angle along the direction of progression of the coolant. The flow of the coolant is utilized for circulating it through the inside space  412   a.    
     Further, in this first temperature adjustment head  400   a , the coolant supplied from the chiller  900  through a main pipe  302  and branch pipe  303  to a cooling block  410   a  flows from the branch pipe  303  through the entrance side channel  411   a  to the inside space  412   a  so can cool the DUT contacting that cooling block  410   a.    
     Further, between the entrance side channel  411   a  and the exit side channel  413   a , a bypass  414   a  is formed branching off from the entrance side channel  411   a  and the exit side channel  413   a  to make the coolant bypass the inside space  412   a.    
     The medium heat emitting type of DUT covered by this first temperature adjustment head  400   a  has a relatively low amount of self generated heat compared with the above-mentioned high heat emitting or superhigh heat emitting type of DUT, so if circulating a similar amount of coolant as with the second and third temperature adjustment heads for other types of DUTs through the inside space  412   a , the head will be overcooled and may not be able to impart the predetermined thermal stress to the DUT. As opposed to this, in the first temperature adjustment head  400   a  of the present embodiment, the excess flow of coolant is made to bypass the space by the bypass  414   a  so as to limit the flow of coolant passing through the inside space  412   a . Due to this, when adjusting the temperature of a DUT with a relatively low amount of self generated heat, it is possible to make the flow of the coolant through the inside space suitable and possible to suitably adjust the DUT in temperature. 
     This cooling block  410   a  is formed with a first accommodating space  415   a  for accommodating the heater block  420   a  and a second accommodating space  416   a  for accommodating the sensor block  430   a.    
     This first accommodating space  415   a , as shown in  FIG. 6 ,  FIG. 8 , and  FIG. 9 , has a size enabling a predetermined clearance to be secured between the heater block  420   a  and the inside wall surfaces of that first accommodating space  415   a . Further, this first accommodating space  415   a  is formed to open at the surface of the cooling block  410   a  contacting the DUT. 
     Further, the second accommodating space  416   a  similarly, as shown in  FIG. 6 ,  FIG. 8 , and  FIG. 10 , has a size enabling a predetermined clearance to be secured between the sensor block  430   a  and the inside wall surfaces of that second holding space  416   b . Further, this second holding space  416   a  is formed to open at the surface of the cooling block  410   a  contacting the DUT. 
     The heater block  420   a  of the first temperature adjustment head  400   a , like the cooling block  410   a , is comprised of aluminum, copper, or another material superior in heat conductivity. As shown in  FIG. 9 , it has a substantially projecting shape overall, is formed at its front end with a projecting part  422   a  projecting outward, and has for example a 100 W level heat generating heater  421   a  embedded inside it. This heater  421   a , as shown in  FIG. 3 , is connected to the heater power source  700  so as to be able to be supplied with power from it. 
     This heater block  420   a , as shown in  FIG. 6  and  FIG. 8 , is accommodated in the first accommodating space  415   a  in a state with a clearance maintained from the inside wall surfaces of the first accommodating space  415   a  of the cooling block  410   a.    
     Therefore, this heater block  420   a  is accommodated in a state maintaining clearance from the first accommodating space  415   a , a layer of air is formed between the heater block  420   a  and the cooling block  410   a , the cooling block  410   a  is insulated from the heater block  420   a , and the heater block  420   a  is in a thermally floating state with respect to the cooling block  410   a , so heat will not be directly conducted from the heater block  420   a  to the cooling block  410   a.    
     This heater block  420   a , as shown in  FIG. 9 , is supported at its top two ends through first springs  423   a  (first biasing means) with respect to the cooling block  410   a  and is pushed in the downward direction in the figure by the first springs  423   a . Due to this, when the heater block  420   a  is not in contact with the DUT, the heater block  420   a  is pushed by the first springs  423   a  so that the shoulders  424  of the heater block  420   a  contact the cooling block  410   a . Further, the pushing action of the first springs  423   a  causes the front end face of the projecting part  422   a  to stick out relative to the front end face of the cooling block  410   a.    
     By making the front end face of the projecting part  422   a  of the heater block  420   a  stick out relative to the front end face of the cooling block  410   a  in this way, when contacting the DUT, the heater block  420  contacts it earlier than the cooling block  410   a . Further, the heater block  420   a  is supported with play with respect to the cooling block  410   a  in a state securing clearance from the inside wall surfaces of the first accommodating space  415   a , that is, the heater block  420   a  is in a mechanically floating state with respect to the cooling block  410   a , so the heater block  420   a  contacting the DUT earlier than the cooling block  410   a  can operate fit against the DUT. 
     Further, by providing the first springs  423   a  between the heater block  420   a  and the cooling block  410   a  so as to push the heater block  420   a  to the DUT side, when the heater block  420   a  contacts the DUT, that heater block  420   a  can be made to be suitably pushed against and closely contact the DUT. 
     The sensor block  430   a  of the first temperature adjustment head  400   a , like the cooling block  410   a , is comprised of aluminum, copper, or another material superior in heat conductivity. As shown in  FIG. 10 , it has a substantially projecting shape overall, is formed at its front end with a projecting part  432   a  projecting outward, and has for example a platinum sensor or other temperature sensor  431   a  embedded inside it. This temperature sensor  431   a , as shown in  FIG. 3 , is connected to the above-mentioned burn-in controller  800  so as to be able to transmit the detected temperature of the DUT to it. 
     This sensor block  430   a , as shown in  FIG. 6  and  FIG. 8 , is accommodated in the second accommodating space  416   a  in a state maintaining clearance with the inside wall surfaces of the second accommodating space  416   a  of the cooling block  410   a.    
     Therefore, this sensor block  430   a  is accommodated in a state maintaining clearance with respect to the second accommodating space  416   a , a layer of air is formed between the sensor block  430   a  and the cooling block  410   a , the sensor block  430   a  is insulated from the cooling block  410   a , and the sensor block  430   a  is in a thermally floating state with respect to the cooling block  410   a , so heat will not be directly conducted from the cooling block  410   a  to the sensor block  430   a , and the temperature of the DUT can be accurately measured. 
     This sensor block  430   a , as shown in  FIG. 10 , is supported at its top two ends through second springs  433   a  (second biasing means) with respect to the cooling block  410   a  and is pushed in the downward direction in the figure by the second springs  433   a . Due to this, when the sensor block  430   a  is not in contact with the DUT, the sensor block  430   a  is pushed by the second springs  433   a  so that the shoulders  434  of the sensor block  430   a  contact the cooling block  410   a . Further, the pushing action of the second springs  433   a  causes the front end face of the projecting part  433   a  to stick out relative to the front end face of the cooling block  410   a.    
     By making the front end face of the projecting part  432   a  of the sensor block  430  stick out relative to the front end face of the cooling block  410   a  in this way, when contacting the DUT, the sensor block  430   a  contacts it earlier than the cooling block  410   a . Further, the sensor block  430   a  is supported with play with respect to the cooling block  410   a  in a state securing clearance from the inside wall surfaces of the second accommodating space  416   a , that is, the sensor block  430   a  is in a mechanically floating state with respect to the cooling block  410   a , so the sensor block  430   a  contacting the DUT earlier than the cooling block  410   a  can operate fit against the DUT. 
     Further, by providing the second springs  433   a  between the sensor block  430   a  and the cooling block  410   a  so as to push the sensor block  430   a  to the DUT side, when the sensor block  423   a  contacts the DUT, that sensor block  430   a  can be made to be suitably pushed against and closely contact the DUT. 
     The first temperature adjustment head  400   a  configured in this way can be expressed by a heat conduction model such as shown in  FIG. 11  since the heater block  420   a  is thermally floating with respect to the cooling block  410   a . When the amount of heat generated by a DUT is Hd [W], the temperature of the coolant is Tw [° C.], the amount of heat generated by the heater  421   a  is Hh [W], and the thermal resistance between the DUT and coolant is θ [° C./W], the temperature Tc [° C.] of the DUT is expressed by Tc=Tw+θcw(Hh+Hd). From this heat conduction model and equation as well, it is learned that the flow of heat from the heater block  420   a  having the heater  421   a  to the surrounding air is extremely small and that the majority of the heat generated at the heater block  420   a  flows to the DUT, so the heater block  420   a  can positively raise the temperature of the DUT. 
     Note that the thermal resistance θ cw spoken of here is comprised of the contact thermal resistance at the contact part of the cooling block  410   a  and DUT surface, the thermal resistance of that cooling block  410   a  itself, and the coolant thermal resistance based on the heat conduction area of the coolant, etc. 
     Note that in the first temperature adjustment head  400   a  in this embodiment, as shown in  FIG. 12 , when the coolant temperature can be changed in a range of 27° C.≦Tw≦80° C., by setting the thermal resistance θ cw to 0.6° C./W, it is possible to adjust the temperature Tc of a DUT varying in amount of self generated heat in the range of 0 W to 100 W by the heater  421   a  and set the DUT temperature to the range of about 87° C. to about 140° C. 
     Four rows and five columns of such first temperature adjustment heads  400   a , as shown in  FIG. 5 , are supported by the frame  301 . This frame  301  is provided with main pipes  302  and branch pipes  303  for supplying coolant from the chiller  900  to the first temperature adjustment heads  400   a . One main pipe  302  splits into five parallel branch pipes  303 . Each branch pipe  303  serially connects the inside spaces  412   a  of the four heads  400   a  arranged in the same line in the frame  301 . Note that while not particularly shown, the pressure of the coolant is adjusted by orifices etc. so that the pressures of the coolant at the first temperature adjustment heads  400   a  become substantially uniform. 
     By serially connecting the inside spaces  412   a  of the first temperature adjustment heads  400   a  in this way, compared with when connecting all temperature adjustment heads in parallel, it is possible to keep down the increase in the number of connection points of the pipes at the temperature adjustment board  300  and possible to improve the reliability of the pipes. 
     Next, the action of the burn-in system  1  using this first temperature adjustment head  400   a  will be explained. 
     Each slot  110  of the burn-in chamber  100  holds a burn-in board  200  mounting DUTs. An edge connector  202  of each burn-in board  200  is inserted into a connector  120  of the burn-in chamber  100 . When the door of the burn-in chamber  100  is closed and a start button (not shown) is pushed etc. to start the burn-in test, first the air cylinders  130  are driven to descend based on a control signal from the burn-in controller  800 , each temperature adjustment board  300  in the burn-in chamber  100  descends with respect to the burn-in board  200  held in the slot  110 , and first temperature adjustment heads  400   a  arranged on that temperature adjustment board  300  contact the DUTs arranged on the burn-in board  200 . 
     At the time of this contact, the front end face of the projecting part  422   a  of each heater block  420   a  sticks out relative to the front end face of the cooling block  410   a , so the heater block  420   a  contacts the device under test before the cooling block  410   a . Further, each heater block  420   a  is in a mechanically floating state with respect to the cooling block  410   a , so the heater block  420   a  contacting the DUT before the cooling block  410   a  operates fit against the DUT and the front end face of the heater block  420   a  closely contacts the DUT, so the DUT can be efficiently raised in temperature. 
     Further, by providing pushing the heater block  420   a  to the DUT side between each heater block  420   a  and cooling block  410   a  first springs  423   a , when a first temperature adjustment head  400   a  contacts a DUT, that heater block  420   a  is suitably pushed against and closely contacts the DUT, so the DUT can be more efficiently raised in temperature. 
     Similarly, since the front end face of the projecting part  432   a  of each sensor block  430   a  sticks out relative to the front end face of the cooling block  410   a , when a first temperature adjustment head  400   a  contacts a DUT, the sensor block  430   a  contacts the DUT before the cooling block  410   a . Further, the sensor block  430   a  is in a mechanically floating state with respect to the cooling block  410   a , so the sensor block  430   a  contacting the DUT before the cooling block  410   a  operates fit against the DUT and the front end face of the sensor block  430   a  closely contacts the DUT, so the temperature of the DUT can be more accurately measured. 
     Further, by providing second springs  433   a  between each sensor block  430   a  and cooling block  410   a , when a first temperature adjustment head  400   a  contacts a DUT, that heater block  420   a  is suitably pushed against and closely contacts the DUT, so the temperature of the DUT can be accurately measured. 
     Further, since each first temperature adjustment head  400   a  is supported with play with respect to the temperature adjustment board  300 , when a first temperature adjustment head  400   a  contacts a DUT, variations in height or inclination of the DUT mounted on the burn-in board  200  can be absorbed by the first temperature adjustment head  400   a , and the first temperature adjustment heads  400   a  can be made to closely contact the DUT, so this first temperature adjustment head  400   a  enables the temperature of the DUT to be more accurately adjusted. 
     Further, by having each first temperature adjustment head  400   a  supported on a frame  301  through third springs  305 , when a first temperature adjustment head  400   a  contacts a DUT, it is possible to make that first temperature adjustment head  400   a  be suitably pushed against and closely contact the DUT, so this first temperature adjustment head  400   a  enables the temperature of the DUT to be more accurately adjusted. 
     Note that up until right before a first temperature adjustment head  400   a  contacts a DUT, the shoulders  424  of the heater block  420   a  contact the cooling block  410   a  due to the action of the first springs  423   a . Due to this, the heater  421   a  of the heater block  420   a  can be used to raise the temperature of the coolant flowing through the channels of the cooling block  410   a , so there is no longer a need to provide the chiller  900  with a heater etc. for heating the coolant. 
     Similarly, up until right before the first temperature adjustment head  400   a  contacts a DUT, the shoulders  434  of the sensor block  430   a  contact the cooling block  410  due to the action of the second springs  433   a . Due to this, the temperature of the cooling block  410   a  or the operating state of the heater  421   a  of the heater block  420   a  can be monitored or the temperature sensor  431   a  itself can be diagnosed. 
     As shown in  FIG. 13 , when a first temperature adjustment head  400   a  contacts a DUT, the burn-in controller  800  monitors the temperature of the DUT by the temperature sensor  431   a  of the sensor block  430   a  and heats the heater  321   a  of the heater block  420   a  so as to apply thermal stress to the DUT and raise it to a predetermined DUT temperature. This DUT temperature is for example 125° C. 
     When the temperature of the DUT reaches a predetermined temperature, the burn-in controller  800  supplies that DUT with power voltage and a signal close to that of actual operation through the connector  120  of the burn-in chamber  200  and the edge connector  202  of the burn-in board  200  for screening. Due to the supply of this power voltage, the DUT generates heat by itself and so the DUT changes in temperature, so the temperature sensor  431   a  is used to monitor the DUT for temperature and the heater  421   a  is turned on/off so as to adjust the temperature of the DUT to a predetermined temperature. 
     When applying this thermal stress, since each heater block  420   a  is in a thermally floating state with respect to the cooling block  410   a , heat is not directly conducted from the heater block  420   a  to the cooling block  410   a , the heater block  420   a  can be used to positively raise the temperature of the individual DUT, the cooling block  410   a  can be used to positively cool that DUT, when simultaneously performing a burn-in test on a plurality of electronic devices, it is possible to independently and accurately control the temperature of each DUT. 
     Further, when applying this thermal stress, since each sensor block  430   a  is in a thermally floating state with respect to the cooling block  410   a , heat is not directly conducted from the cooling block  410   a  to the sensor block  430   a , the temperature of the individual DUT can be accurately measured, and the precision of temperature adjustment of the DUT is improved. 
     The above burn-in test is performed continuously over a long period of several hours to tens of hours. During that burn-in test, any DUT exhibiting an abnormal reaction is judged defective. For example, the serial number of that DUT can be held in the burn-in controller  800  and the test results fed back. 
     Next, for example, a second temperature adjustment head  400   b  for dealing with 100 to 200 W level high heat emitting types of DUTs will be explained. 
     This second temperature adjustment head  400   b , as shown in  FIG. 14  to  FIG. 16 , is provided with a cooling block  410   b  for cooling a DUT, a heater block  420   b  for heating a DUT, and a sensor block  430   b  for measuring a DUT for temperature. Aside from a bypass for making the coolant bypass the inside space not being formed in the cooling block, this is structured similar to the above-mentioned first temperature adjustment head  400   a.    
     This second temperature adjustment head  400   b  deals with relatively large heat emitting 100 to 200 W level high heat emitting types of DUTs and is required to exhibit a higher cooling performance compared with the first temperature adjustment head  400   a , so as shown in that figure is not formed with a bypass like the abovementioned first temperature adjustment head  400   a . The entire amount of the coolant supplied from the branch pipe  303  through the entrance side channel  411   b  and exit side channel  413   b  is designed to flow through the inside space  412   b.    
     Further, this second temperature adjustment head  400   b  makes the thermal resistance θ cw between a DUT and the coolant 0.4° C./W and therefore lowers that thermal resistance θ cw more than the first temperature adjustment head  400   b  to improve the cooling efficiency. Note that as the method for reducing the thermal resistance θ cw, for example, the methods of strengthening the pushing force of the temperature adjustment head, using a material more superior in heat conductivity to make the cooling block, increasing the heat conduction area of the coolant, etc. may be illustrated. 
     Due to this, as shown in  FIG. 12 , when the coolant may vary in temperature in the range of 27° C.≦T w≦80° C., the temperature Tc of a DUT, which may vary in amount of self generated heat in the range of 100 W to 200 W, may be adjusted by the heater  421   b  so as to set the DUT temperature at any temperature in the range of about 107° C. to about 160° C. 
     Next, for example, a third temperature adjustment head for dealing with 200 to 300 W level superhigh heat emitting types of DUTs will be explained. 
     This third temperature adjustment head, while not particularly illustrated, is basically the same in configuration as the second temperature adjustment head  400   b . However, the third temperature adjustment head deals with 200 W to 300 W level superhigh heat emitting types of DUTs, so is required to exhibit a higher cooling performance than the second temperature adjustment head  400   b.    
     Therefore, this third temperature adjustment head makes the thermal resistance θ cw between a DUT and the coolant 0.28° C./W and reduces that thermal resistance θ cw more than the second temperature adjustment head  400   c  so as to further improve the cooling performance. 
     Due to this, as shown in  FIG. 12 , when the coolant may vary in temperature in the range of 27° C.≦T w≦80° C., the temperature Tc of the DUT, which may vary in amount of self generated heat in the range of 200 W to 300 W, may be adjusted by a heater built in the heater block to freely set the DUT temperature in the range of about 111° C. to about 164° C. 
     Further, in the burn-in system  1  according to the present embodiment, among the total three types of temperature adjustment heads explained above changing the cooling performance by the presence/absence of bypasses and changing the thermal resistance between the DUTs and cooling blocks, the one matching the amount of self generated heat of each DUT is selected to enable DUTs of a wide range of amounts of self generated heated of 0 W to 300 W or so to be handled by the same burn-in system. 
     Note that the first to third temperature adjustment heads may be mounted mixed on the same temperature adjustment board  300  or first temperature adjustment heads  400   a  may be mounted on one temperature adjustment board  300 , second temperature adjustment heads  400   b  mounted on another temperature adjustment board  300 , and third temperature adjustment heads mounted on another temperature adjustment board  300 . 
     Second Embodiment 
       FIG. 17  is a side view of a temperature adjustment head in a second embodiment of the present invention. 
     The burn-in system according to the second embodiment of the present invention differs in structure of the temperature adjustment head from the burn-in system  1  according to the first embodiment, but the rest of the configuration is identical to that of the burn-in system  1  according to the first embodiment. Below, the burn-in system according to the second embodiment will be explained only with reference to the points of difference from the burn-in system  1  according to the first embodiment. 
     The temperature adjustment head  400 ′ in the present embodiment, as shown in  FIG. 17 , is not provided with any heater block. Instead, a bypass  414 ′ of the cooling block  410 ′ is provided with a valve  417 ′ (variable flow rate means). The head differs from the first temperature adjustment head  400   a  in the first embodiment on this point, but otherwise is the same in configuration. 
     In the first temperature adjustment head  400   a  in the first embodiment, the heater  421   a  of each heater block  420   a  was used to adjust a DUT in temperature, but in the temperature adjustment head  400 ′ in this embodiment, instead of a heater, the valve  417 ′ is operated to adjust the flow rate of the coolant flow through the inside space  412   a  through the channels  411   a  and  413   a  to thereby adjust the DUT in temperature. 
     The valve  417 ′ provided at this temperature adjustment head  400 ′, while not particularly illustrated, is connected to the burn-in controller to enable control. Based on on/off signals of that burn-in controller, the valve  417 ′ is operated to adjust the flow rate of coolant flowing through the bypass  414 ′. Note that this valve  417 ′ may also be provided not at the bypass  414 ′, but at the entrance side channel  411 ′ or exit side channel  413 ′. 
     As explained above, in the burn-in system according to the second embodiment of the present invention, instead of the heater, a valve  417 ′ is provided at the entrance side channel  411 ′ formed in the cooling block  410 ′ of each temperature adjustment head  400 ′. This valve  417 ′ is used to change the flow rate of the coolant so as to adjust the cooling thermal resistance in the cooling block  410 ′. Due to this, the individual DUTs can be easily adjusted in temperature, so when simultaneously performing a burn-in test on a plurality of electronic devices, it is possible to independently and accurately control the temperatures of the individual DUTs. 
     Third Embodiment 
       FIG. 18  is a side view of a temperature adjustment head in a third embodiment of the present invention,  FIG. 19  is a bottom plan view of the temperature adjustment head shown in  FIG. 18 , and  FIG. 20  is a schematic view of a coolant recovering means of a burn-in system according to a third embodiment of the present invention. 
     In the burn-in systems according to the first and second embodiments explained above, the DUTs were indirectly cooled by coolant through the cooling blocks so as to adjust the DUTs in temperature, but in the burn-in system according to the third embodiment of the present invention, the coolant is made to directly contact the DUTs to adjust the DUTs in temperature. 
     Therefore, the burn-in system according to the third embodiment of the present invention differs in the structure of the temperature adjustment heads. Further, it differs from the burn-in system  1  according to the first embodiment in the point of being provided with coolant recovering means for recovering the coolant after the burn-in test, but rest of the configuration is identical to that of the burn-in system  1  according to first embodiment. Below, the burn-in system according to the third embodiment will be explained with reference to only the points of difference from the burn-in system  1  according to the first embodiment. 
     First, explaining the temperature adjustment head  400 ″ according to this embodiment, this temperature adjustment head  400 ″, as shown in  FIG. 18  and  FIG. 19 , is similar to the second temperature adjustment head  400   b  according to the first embodiment (see  FIG. 14  to  FIG. 16 ), but differs from the second temperature adjustment head  400   b  according to the first embodiment in the point that the cooling block  410 ″ of this temperature adjustment head  400 ″ does not have any part corresponding to the bottom half of the cooling block  410   b  of that second temperature adjustment head  400   b  and in the point that instead of a heater block, a valve  417 ″ (variable flow rate means) is provided. 
     More specifically, the cooling block  410 ″ of each temperature adjustment head  400 ″ according to this embodiment is shaped as the cooling block  410   b  of the second temperature adjustment head  400   b  cut off so that its inside space  412   b  is open. Due to this, the entrance side channel  411 ″ communicating with the branch pipe  303  opens at the entrance side opening  4111 ″ formed at the bottom end face of the cooling block  410 ″. Similarly, the exit side channel  413 ″ communicating with the branch pipe  303  opens at an exit side opening  4131  formed at the bottom end face of the cooling block  410 ″. 
     Further, the cooling block  410 ″ of this temperature adjustment head  400 ″ is formed with a second holding space  416 ″. A sensor block  430 ″ with a built-in temperature sensor  431 ″ is accommodated in that accommodating space  416 ″ in a state maintaining a clearance. Note that the temperature adjustment head  400 ″ according to this embodiment, like the temperature adjustment head  400 ′ according to the second embodiment, is not provided with any heater block with a built-in heater. 
     Further, the bottom end face of this cooling block  410 ″ is fit with ring shaped packings  481 ″ at its outer periphery and at the periphery of the accommodating space  416 ″ in which the sensor block  430 ″ is accommodated. 
     Therefore, when the temperature adjustment head  400 ″ according to the present embodiment contacts a DUT, as shown in  FIG. 18 , the bottom end face of that temperature adjustment head  400 ″, the packings  418 ″, and the top face of the DUT define a space  419 ″. Coolant CL supplied through the entrance side opening  4111 ″ of the entrance side channel  411 ″ enters this space  419 ″, so that coolant can directly contact the DUT. 
     Further, the temperature adjustment head  400 ″ according to the present embodiment has a valve  417 ″ for adjusting the flow rate of the coolant. That valve  417 ″ is provided inside the entrance side channel  411 ″ formed at the cooling block  410 ″. Note that the mounting position of this valve  417 ″ is not particularly limited in the present invention. For example, the valve may also be provided at the exit side channel. 
     The valve  417 ″ provided at this temperature adjustment head  400 ″, while not particularly limited, is connected to the burn-in controller for control. Based on on/off control of that burn-in controller, the valve  417 ″ is operated to adjust the flow rate of the coolant flowing through the entrance side channel  411 ″. 
     Next, explaining the coolant recovering means according to the burn-in system according to the present embodiment, as shown in  FIG. 20 , the coolant recovering means in this embodiment is provided at the chiller  900 ″. This chiller  900 ″ is provided with a pump  901  for circulating the coolant, a heat exchanger  902  for transferring the heat of the coolant to for example about 20° C. or less cooling water so as to cool the coolant, a tank  903  for holding the recovered coolant, and a compressed gas supply apparatus  904  for recovering the coolant and can form a circulation route from the pump  901  through a temperature adjustment head  400 ″ (more specifically, the channels  411 ″ and  413 ″), tank  903 , and heat exchanger  902  and back to the pump  901 . 
     This circulation route is provided with two valves S 1  and S 2 . The first valve S 1  is provided between the pump  901  and the temperature adjustment head  400 ″, while the second valve S 2  is provided between the temperature adjustment head  400 ″ and the tank  903 . 
     Further, this circulation route is connected through a third valve S 3  to the compressed gas supply apparatus  904 . This compressed gas supply apparatus  904  supplies compressed gas to the circulation route to forcibly recover coolant directly contacting the DUTs in the tank  903  after the burn-in test. As the gas supplied from this compressed gas supply apparatus  904 , for example, nitrogen gas may be mentioned. Further, along with the employment of recovery using this compressed gas, the pressure of the compressed gas is released into the atmosphere after the coolant is recovered, so the tank  903  is provided with a fourth valve S 4 . Note that the first to fourth valves S 1  to S 4  are all, while not particularly shown, connected to the burn-in controller for control. Based on on/off control of that burn-in controller, the valves S 1  to S 4  are operated. 
     Next, the method of recovery of the coolant recovering means provided at this chiller  900 ″ will be explained. 
     First, when adjusting the temperatures of the DUTs in the burn-in test, the first and second valves S 1  and S 2  are opened, the third and fourth valves S 3  and S 4  are closed, and a circulation route is formed. Therefore, in this state, the action of the pump  901  causes the coolant to circulate through the circulation route. The coolant cooled at the heat exchanger  902  is supplied to the temperature adjustment head  400 ″, then the used coolant passes through the tank  903  and is cooled again at the heat exchanger  902 . 
     Next, when the burn-in test ends, the pump  901  is stopped and the second to fourth valves S 2  to S 4  are opened. Therefore, in this state, the circulation route is blocked at the first valve S 1 . Instead, the opening of the second to fourth valves S 2  to S 4  causes the formation of a recovery route from the compressed gas supply apparatus  904  through the temperature adjustment head  400 ″ to the tank  903 . Further, when supplied from the compressed gas supply apparatus  904  to that recovery route, the coolant accumulated in the temperature adjustment head  400 ″ is pushed out by the compressed gas and recovered at the tank  903 . After the coolant finishes being recovered, all of the valves S 1  to S 4  are closed. 
     As explained above, in the burn-in system according to the third embodiment of the present invention, when pushing the cooling block  410 ″ of the temperature adjustment block  400 ″ against a DUT, the coolant supplied through the entrance side opening  4111 ″ of the entrance side channel  411 ″ is made to directly contact the surface of the DUT and the valve  417 ″ is controlled to operate to enable the individual DUT to be directly adjusted in temperature. When simultaneously performing a burn-in test on a plurality of DUTs, it is possible to independently and accurately control the temperature of each DUT. 
     Further, by providing the chiller  900 ″ with the above-mentioned recovering means, it is possible to recover the coolant directly contacting the DUTs after the end of the burn-in tests. 
     Note that the embodiments explained above were given for facilitating understanding of the present invention and were not given for limiting the present invention. Therefore, the elements disclosed in the embodiments include all design changes or equivalents falling under the technical scope of the present invention. 
     In the above embodiments, the burn-in system was explained as a monitored burn-in system, but the present invention is not particularly limited to this. For example, it may also be a dynamic burn-in system which applies power voltage to DUTs under a constant temperature and supplies signals close to actual operation to the input circuits of the DUTs for screening or a static burn-in system which applies power voltage to DUTs under a high temperature and sends a current through the DUTs to apply temperature and voltage stress to the DUTs for screening. General burn-in systems are included.