Abstract:
An index head assembly for a semiconductor device test handler is provided which allows for precise positioning of a device in a test socket, as well as accurate testing of the device once properly positioned in the test socket. The head portion of the index head assembly includes a holding part which absorbs and holds the device using a vacuum force, a heating part which generates heat to maintain the device at the appropriate temperature, and a compliance part which accurately aligns and positions the index head relative to the test socket so that the device may be properly connected to the test socket. The downward force used to connect the semiconductor device to the test socket is controlled by a force transducer, and the temperature of the semiconductor device is accurately controlled through direct heat transfer from an electric heater provided within the head portion of the index head assembly. A plurality of ball plungers and guide members, as well as the particular installation of various parts of the head portion relative to one another ensure proper alignment of the device within the test socket.

Description:
This application is a Divisional of U.S. patent application Ser. No. 10/033,981 filed Jan. 3, 2002 now U.S. Pat. No. 6,925,706, which is hereby incorporated by reference and which claimed the benefit of Korean application No. P2001-1118 filed Jan. 9, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an index head in a semiconductor device test handler, and more particularly, to an index head in a semiconductor device test handler for mounting semiconductor device in a test socket at a test site. 
   2. Background of the Related Art 
   In general, modular ICs, in which memory, and/or non-memory semiconductor devices are fabricated on one substrate appropriately in circuit basis, are main components that serve important functions in computers or home appliances, which are shipped after various testing. As known, the handler is equipment required for automatic testing of the semiconductor device and modular RAM. 
   In general, many of the handlers are designed to carry out, not only a general performance tests under a room temperature, but also high temperature tests, and low temperature tests in which the semiconductor devices, the modular ICs, and the like are tested if they are operative normally under an extremely high temperature, or low temperature environment formed by using electric heater or liquefied nitrogen spraying system into a enclosed chamber at the test site. 
   In the meantime, the index head in the handler serves holding semiconductor devices in the test site under such an extremely high or low temperature, and mounting/dismounting to/from test sockets, as well as pressing down the semiconductor devices in a state the semiconductor devices are mounted in the test sockets for reducing contact resistances between the sockets and leads on the semiconductor devices. 
   The index head also serves to prevent a temperature drop of the semiconductor devices in the sockets during temperature testing by blowing hot air to the semiconductor devices in a state the index head presses down the semiconductor devices. However, the foregoing related art index head has the following problems. 
   First, in the hot air blowing for prevention of the temperature drop of the semiconductor devices, an accurate temperature control has been difficult, and even parts that require no heating are heated. 
   Second, the related art index head is provided with a compliance mechanism (or a floating mechanism) for an exact alignment between the held semiconductor devices and the sockets, which becomes shaky in high speed operation of the index head, that limits an operation speed of the index head. 
   Third, because a pressing down force of the index head on the semiconductors in the sockets influences a result of the test, it is required to control and monitor the pressing down force. However, the related art index head is not provided with devices for automatic control and monitoring the pressing down force, such that a worker is required to make sure and adjust the force, personally. Accordingly, an accurate control of the force has been difficult, and if the force is excessive, the semiconductor devices are damaged. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to an index head in a semiconductor device test handler that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
   An object of the present invention is to provide an index head in a semiconductor device test handler, which permits an accurate temperature control, a stable operation of the compliance mechanism, and an automatic accurate control of a pressing down force. 
   Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the index head in a semiconductor device test handler, for holding semiconductor devices, and mounting/dismounting to/from test sockets, includes a carrier base fixedly fitted to a transfer device movable in any direction, an elevating carrier coupled to the carrier base to be movable in up and down directions, elevating means for moving the elevating carrier in up and down directions with respect to the carrier base, a head holder under the elevating carrier coupled to the elevating carrier via a guide member for making relative movement with respect to the elevating carrier in up and down directions, and a plurality of heads each including a holding part fixedly fitted to a bottom of the head holder for holding the semiconductor device by vacuum, a heating part on top of the holding part for transfer of a heat to the semiconductor device directly when the semiconductor device is mounted in the test socket, and a compliance part fitted over the heating part for providing degrees of freedom for an alignment between the semiconductor device held by the holding part and the test socket. 
   The index head further includes a force transducer between the elevating carrier and the head holder for automatic measurement of a load applied by the elevating carrier in proportion to displacement of the elevating carrier with respect to the head holder when the semiconductor device mounted in the test socket is pressed down. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: 
     In the drawings: 
       FIG. 1  illustrates a perspective view of an index head in accordance with a preferred embodiment of the present invention; 
       FIGS. 2A and 2B  illustrate side sections of key parts of the index head in  FIG. 1 , each showing a system and operation of the index head; 
       FIG. 3  illustrates a perspective view of a head holder part of the index head of the present invention; 
       FIG. 4  illustrates a flow chart of control of the index head operation by using the load cell in  FIG. 2A ; 
       FIG. 5  illustrates a disassembled perspective view of a head part of the index head in  FIG. 1 ; 
       FIG. 6  illustrates a perspective view of a bottom of a holding part in the head part in  FIG. 5 ; 
       FIG. 7  illustrates a longitudinal section of key parts of disassembled head part in  FIG. 5 ; 
       FIGS. 8A–8D  explain an operation principle of the compliance part in the head part in  FIG. 6 , wherein, 
       FIG. 8A  illustrates a state in which an alignment is made by the compliance part; 
       FIG. 8B  illustrates an operation principle of the compliance part in a state an offset is occurred; 
       FIG. 8C  illustrates an operation principle of the compliance part in a state a tilting is occurred; and, 
       FIG. 8D  illustrates an operation principle of the compliance part in a state a rotation is occurred. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  FIGS. 1 , and  2 A and  2 B illustrate an entire system and operation an index head in accordance with a preferred embodiment of the present invention. 
   Referring to the drawings, the index head includes a carrier base  10  fitted to a transfer device (not shown) movable in X-Y-Z directions and/or a ‘θ’ direction, a rotation direction, within a test site (not shown), an elevating carrier  20  coupled to the carrier base  10  with an LM guide  11  in between, a ball screw  13  fitted to the carrier base  10  to be coupled to the elevating carrier  20  for transmission of an up/down driving force to the elevating carrier  20 , and a servo motor  12  for driving the ball screw  13 . 
   There is a head holder  30  under the elevating carrier  20  coupled thereto via an LM guide  21  for making relative movement with respect to the elevating carrier  20 , and there are a plurality of heads  40  under the head holder  30  fixedly coupled thereto for holding the semiconductor devices  1  by vacuum and mounting/dismounting to/from the test sockets  2 . 
   There is a load cell  35  in a central part of a top of the head holder  30  as a force transducer for measuring a load applied to the elevating carrier  20  in proportion to a displacement of the elevating carrier  20  with respect to the head holder  30  when the head  40  mounts the semiconductor device  1  to the test socket  2  and applies a pressure thereto, thereby controlling operation of the servo motor  12 . 
   Accordingly, referring to  FIG. 4 , if the elevating carrier  20  moves down with respect to the head holder  30  in a state the index head  40  of the present invention mounts the semiconductor devices  1  to the test sockets  2 , the load is measured in proportion to a degree of compression as the load cell  35  is compressed by the downward movement of the elevating carrier  20 . When the load applied to the load cell  35  reaches to a preset point, i.e., to an appropriate load, a control part (not shown) which controls operation of the servo motor  12  senses it, and stops operation of the servo motor  12 , under which condition the test of the semiconductor device is carried out. 
   By the way, referring to  FIG. 3 , the head holder  130  may be provided with one pair of guide pins  131  fitted on both sides of a top part thereof to couple with coupling holes correspondingly formed in the elevating carrier  20 , thereby coupling the head holder  130  to the elevating carrier  20 . 
   In the meantime, with regard the head structures illustrated in  FIGS. 2A and 2B , the head  40  includes a holding part  41  fixedly fitted to a bottom of the head holder  30  for holding the semiconductor device by vacuum, a heating part  42  on top of the holding part  41  for transfer of a heat to the semiconductor device directly when the semiconductor device is mounted in the test socket  2 , and a compliance part  43  fitted over the heating part  42  spaced therefrom for providing degrees of freedom for an alignment between the semiconductor device held by the holding part  41  and the test socket  2 . 
   The holding part  41  in the head  40  includes a pocket block  411  of a conductive material with a good heat conductivity having a through hole  412  in a center for close contact coupling with the heating part  42 , a floating nozzle  413  inserted in the through hole  412  in the pocket block  411  for holding the semiconductor device by vacuum, and a plurality of blades  415  of a non-conductive material vertical to a bottom surface of the pocket block for pressing leads of the semiconductor device held under the floating nozzle  413  to contact with terminal part (not shown) of the test socket  2 . 
   The floating nozzle  413  in the holding part  41  is designed to allow a free movement in up/down directions for a distance within the through hole  412 , by forming steps at an upper part and a lower part of the through hole  412  respectively to have diameters greater than an intermediate part thereof, coupling a nut  414  to an upper part of the floating nozzle  413  in a state the floating nozzle  413  is passed through the through hole  412 , and forming an annular rim  413   a  on a lower part of the floating nozzle  413 , to form a gap between the lower part step of the through hole  412  and the rim  413   a  of the floating nozzle  413  when the floating nozzle  413  is set on the through hole  412  by gravity, thereby allowing the free movement in up/down directions for a distance within the through hole  412  as much as the gap. 
   Accordingly, when the head  40  presses down the semiconductor device mounted in the socket  2  (see  FIG. 1 ), a top surface of the semiconductor device is brought into contact with the bottom surface of the pocket block  411  as the floating nozzle  413  move upward. 
   There are positioning holes  416  in opposite side parts of the pocket block  411  in correspondence to, and to be inserted and passed through positioning pins  2   a  (see  FIG. 8A ) in the vicinity of the test socket  2  for accurate guidance of the head  40  to the test socket in a process the head  40  holds the semiconductor device and mounts in the test socket  2 , wherein each of the positioning pins  2   a  on the test socket  2  has a conical peak for easy insertion of the head  40  even if there is a slight misalignment between the head  40  and the socket  2 , for alignment between the head  40  and the test socket  2 , together with the compliance part  43  explained, later. 
   In the meantime, the heating part  42  in the head  40  includes a heating block  421  on top of the holding part  41  having a built-in electric heater  422  for transfer of a heat to the pocket block  411 , a through hole  426  in a central part of the heating block  421 , and a coupling nozzle  423  passed through, and fixed to the through hole  426 . 
   A lower end of the coupling nozzle  423  is fixed to a top end of the floating nozzle  413  in the holding part  41 , and is formed of flexible silicone for free upward movement of the floating nozzle  413 . 
   The heating block  421  has coupling bosses  425  at four corners of the top part for coupling with the compliance part  43 . The coupling bosses  425  are formed of an insulating material for cutting off heat transfer from the heating block  421  to the compliance part  43 . 
   In the meantime, the compliance part  43  includes a lower block  435  fixed to the heating part  42 , and an upper block  431  coupled to the lower block  435  with allowances for having degrees of freedom in X-Y-Z and rotation θ directions. 
   There are a plurality of holes  433  for receiving ball plungers  434 , compression springs  434   a , retainers  434   b  fitted to lower ends of the compression springs  434   a , and balls  434   c  retained under the retainers  434   b  and exposed outside of the bottom surface of the upper block  431 . 
   The lower block  435  has ball buttons  437  of conical recess at positions corresponding to the holes  433  in the upper block  431  for receiving the balls  434   c  in the ball plungers  434 . 
   There is a coupling hole  432  or  436  in each central part of the upper block  431  and the lower block  435 , for coupling with the coupling nozzle  423 , and there is an O-ring  439  between the upper block  431  and the lower block  435  for improvement of air tightness at a contact part of the two coupling holes  432  and  436 . 
   In the meantime, a top part of the coupling hole  432  in the upper block  431  is connected to an external air pump (not shown) for evacuation. 
   The operation of the compliance part  43  will be explained with reference to  FIGS. 8A–8D . 
     FIG. 8A  illustrates a state in which an alignment between the head  40  and the test socket  2  is made by the compliance part  43 , to mount the semiconductor device  1  in the test socket  2 , wherein, when the holding part  41  in the head  40  moves down onto the test socket  2  in a state the holding part  41  holds the semiconductor device  1 , the head  40  is guided to the test socket  2  to mount the semiconductor device  1  in the socket  2  as the positioning pins  2   a  on the test socket  2  are inserted into the positioning holes  416  in the pocket block  411  of the head  40 . 
   If there is an alignment error between the head  40  and the test socket  2  caused by tolerances in assembly, or fabrication of the index head and/or the test socket, the alignment error is corrected in a process the positioning pins  2   a  are inserted into the pocket block  411  in the head  40  because the upper block  431  and the lower block  435  in the compliance part  43  has coupled with degrees of freedom in X-Y-Z and rotation θ directions. 
   That is, referring to  FIGS. 8B ,  8 C, and  8 D, if there is the alignment error, such as offset error, tilting error, or rotation error, between the head  40  and the test socket  2 , a position is corrected by a relative positional movement between the lower block  435  and the upper block  431  in the compliance part  43  in a process the positioning pins  416  are inserted into the positioning holes  416  in the head  40  when the head  40  moves down toward the test socket  2 . 
   Of course, a limit of the alignment error correction by the compliance part  43  is within a range the positioning holes  416  move down by gravity guided by the conical parts at top ends of the positioning pins  2   a  when the head  40  moves down. The operation of the foregoing index head will be explained. 
   When a test tray or a carrier containing semiconductor devices to be tested comes to a test site of the handler, the holding part  41  in the head  40  of the index head holds the semiconductor device and moves to a position right upper side of the test socket  2 . 
   Thus, when the index head comes to the upper side of the test socket  2 , the servo motor  12  on the carrier base  10  comes into operation to move down the elevating carrier  20  along the LM guide  11 , until the semiconductor device  1  is mounted in the test socket  2  as the positioning holes  416  in the head  40  are inserted into the positioning pins  2   a  at the test socket  2 . 
   As explained, even if there is an alignment error between the head  40  and the test socket  2  caused by tolerances in assembly, or fabrication of the index head and/or the test socket, the semiconductor device can be mounted in the test socket  2  accurately as the alignment between the head  40  and the test socket  2  is made by the compliance part  43  in the head  40 . 
   In this instance, as the floating nozzle  413  in the holding part  41  in the head  40  that holds the semiconductor device moves upward on the same time the semiconductor device  1  is mounted in the test socket  2 , to bring a top surface of the semiconductor device  1  to come into contact with the bottom surface of the pocket block  411 . 
   If the servo motor  12  moves down the elevating carrier  20  further in a state the semiconductor device  1  is mounted in the socket  2 , the elevating carrier  20  moves down with respect to the head holder  30 , to press down the semiconductor device  1 , when, as explained, the elevating carrier  20  presses down the load cell  35  in proportion to the downward movement of the elevating carrier  20  with respect to the head holder  30  until the load on the load cell  35  reaches to a preset point, when operation of the servo motor  12  is stopped, and the test is started. 
   When the test is started in this state, the electric heater  422  in the heating part  42  is put into operation to heat the heating block  421 , the heat is transferred to the pocket block  411 , and to the semiconductor device  1  in contact with the pocket block  411  continuously, thereby preventing temperature drop of the semiconductor device. 
   When the test of the semiconductor device is finished at the test socket  2 , the semiconductor device is dismounted from the test socket  2  in a process reverse of the foregoing mounting process, and placed in an empty tray or carrier. 
   As has been explained, the index head in a semiconductor device test handler of the present invention has the following advantages. 
   The accurate control of the force applied to the semiconductor device may means of the force transducer fitted to the head holder improves a test reliability and permits an easy adjustment of the applied force. 
   The direct transfer of a heat to the semiconductor device, without blowing hot air thereto the same as the related art, for prevention of temperature drop of the semiconductor device permits an easy and accurate temperature control, and protect other parts of the equipment that require no temperature drop prevention. 
   Along with this, the smooth alignment between the index head and/or the test socket by the compliance part permits to progress the test faster than before because the index head has a small vibration even in high speed operation of the index head. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the index head in a semiconductor device test handler of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.