This application claims the benefit of the Korean Application No. P2002-13539 filed on Mar. 13, 2002, which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for recognizing a working height of a carrier in a semiconductor device test handler, and more particularly, to an apparatus and method for recognizing a working height of a carrier in a semiconductor device test handler enabling to measure to reset the working height of the carrier in accordance with a species of the semiconductor devices and replacing components such as a tray and a change kit fast and precisely when various kinds of semiconductor devices are tested in the handler. 
   2. Discussion of the Related Art 
   Generally, semiconductor devices produced in a production line undergo tests for checking whether to be good or fail before shipment. 
   A handler is a device for testing such semiconductor devices. The handler uses a semiconductor device carrier to transfer semiconductor devices received on a tray to another process line automatically, loads the semiconductor devices on a test socket of a test site to carry out a demanded test thereon, and classifies the tested semiconductor devices into various levels to unload them on the tray. The handler carries out such steps repeatedly to perform the tests. 
     FIG. 1  illustrates a layout of a general handler for semiconductor device test. 
   Referring to  FIG. 1 , in a front part of a handler body  1 , formed are a loading unit  2  on which trays receiving test-expecting semiconductor devices thereon are loaded and an unloading unit  3  having a plurality of trays receiving test-completed semiconductor devices classified into good products and fail products in accordance with test results. And, a soaking plate  7  is installed in rear of the loading unit  2 . The soaking plate  7  includes a heating means (not shown in the drawing) and a cooling means (not shown in the drawing) inside to heat or cool the test-expecting semiconductor devices to a predetermined temperature for temperature test. 
   And, a reject multi-stacker  5 , on which a plurality of trays are loaded to receive the semiconductor devices classified by grade into the fail product&#39;s according to the test results, is installed in rear of the unloading unit  3 . 
   In a test site  10  located at the foremost rear part of the handler body  1 , at least one test socket  11  connected electrically to an external testing device is installed to test a performance of each of the semiconductor devices. Over the test socket  11 , formed are first and second index heads  12   a  and  12   b  installed to move horizontally to pick up to load the semiconductor devices, which are transferred to standby positions at both sides of the test socket  11 , on the test sockets  11  as well as to pick up to retransfer the tested semiconductor devices on the test sockets  11  to the standby positions at both sides. 
   In the very front of the test site  10 , first and second shuttles  8   a  and  8   b  are installed to move back and forth. The first and second shuttles  8   a  and  8   b  receive to transfer the semiconductor devices from the loading unit  2  or the soaking plate  7  to the standby positions at both sides of the test sockets  11  of the test site  10 . At one sides of the first and second shuttles  8   a  and  8   b , third and fourth shuttles  9   a  and  9   b  are installed to move back and forth, respectively. The third and fourth shuttles  9   a  and  9   b  receive to transfer the test-completed semiconductor devices from the test site  10  to an outside of the test site  10 . 
   Fixing frames  13  are installed at the front end of the handler body  1  and over the very front side of the test site  10  across the handler body  1 , respectively. A pair of movable frames  14   a  and  14   b  are installed at the fixing frames  13  to move right and left along the fixing frames  13 . And, two device transfer unit  15  are installed at the movable frames  14   a  and  14   b  to move along the movable frames  14   a  and  14   b  to pick up semiconductor devices, respectively. Each of the device transfer unit  15  includes a plurality of pickers (not shown in the drawing) to transport a plurality of the semiconductor devices simultaneously. 
   Meanwhile, a handler is constituted to carry out a test on such semiconductor devices as QFP, BGA, SOP, and the like. After one species of the semiconductor devices have been tested, another species of the semiconductor devices are tested. In such a case, the tray and change kits including the soaking plate  7 , shuttles  8   a ,  8   b ,  9   a , and  9   c , test sockets  11 , and the like are replaced by another change kits fitting to the semiconductor device species to carry out the test. 
   In this case, the change kits replaced according to the species of the test-expecting semiconductor devices differ from each other in sizes and thickness and the semiconductor device species differ from each other in thickness. Hence, working sections of the device transfer unit  15  should be reset. 
   However, in measuring the working height according to the semiconductor species and the options of the change kits to be replaced, an operator moves the device transfer unit  15  to pick &amp; place positions one by one and then moves the device transfer unit  15  upward and downward to set up the working height. In such a case, a probability of error occurrence during input is high and a working height setup takes too much time. Hence, daily productivity is reduced and overall efficiency of the test work is decreased. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to an apparatus and method for recognizing a working height of a carrier in a semiconductor device test handler that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
   An object of the present invention is to provide an apparatus and method for recognizing a working height of a carrier in a semiconductor device test handler enabling to measure the working height of the carrier fast and precisely to reset with a simplified structure of the apparatus. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may 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 objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, in a device transfer system for picking up to transfer semiconductor devices between a tray and a change kit by a command of a control unit of a handler, the device transfer system installed on a handler body to move horizontally and vertically, the device transfer system having a plurality of vertically movable pickers absorbing the semiconductor devices by suction, an apparatus for recognizing a working height in a semiconductor device test handler according to the present invention includes an elevating block installed at one side of the device transfer system to move upward and downward, a touch probe installed vertical to the elevating block to move upward and downward in accordance with a contact with an under target object, a detecting means for detecting ascendance of the touch probe by the contact between the touch probe and the target object, and a driving means for driving the elevating block upward and downward. 
   In another aspect of the present invention, in the above-explained apparatus for recognizing the working height, a method of recognizing the working height in a semiconductor device test handler includes the steps of finding an offset value ΔZ by a height difference between a lower end of a picker and a lower end of a touch probe and an offset value ΔZ 0  by a detecting means to store the offset values ΔZ and ΔZ 0  in a handler control unit, moving a device transfer system to a position of a recognizing object and actuating a driving means to lower an elevating block and the touch probe, lowering the device transfer system until the detecting means detects ascendance of the touch probe, acquiring a vertical position value h of the device transfer system when the detecting means detects a contact member; and calculating a work position value ΔH by compensating an offset value existing between a measuring means and a picker of the device transfer system for the vertical position value h. 
   Preferably, the step of finding the offset value ΔZ by the height difference between the lower end of a picker and the lower end of the touch probe and the offset value ΔZ 0  by the detecting means includes a first step of installing a measuring jig on the handler body, disposing the device transfer system on the measuring jig, and lowering the touch probe, a second step of lowering the device transfer system until the touch probe touches the measuring jig to acquire a vertical position value Z 1  at a moment that the touch probe touches the measuring jig, a third step of further lowering the device transfer system until the detecting means detects the touch probe to acquire a vertical position value Z 0  at a moment that the detecting means detects the touch probe, a fourth step of elevating the elevating block and touch probe but lowering a picker, a fifth step of acquiring a vertical position value Z 2  at a moment that the picker touches the measuring jig by lowering the device transferring means until the picker touches the measuring jig, and a sixth step of calculating the offset values ΔZ and ΔZ 0  by the vertical position values Z 1 , Z 0  and Z 2  acquired in the second, third, and fifth steps to store in the handler control unit. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention 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 application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
       FIG. 1  illustrates a layout of a related art handler for semiconductor device test; 
       FIG. 2  illustrates a bird&#39;s-eye view of a carrier in a handler having an apparatus for recognizing a working height according to the present invention; 
       FIG. 3  illustrates a bird&#39;s-eye view of an apparatus for recognizing a working height according to the present invention; 
       FIG. 4  illustrates a front view of an apparatus for recognizing a working height in  FIG. 3  for explaining its operation; 
       FIG. 5  illustrates a flowchart of a method of recognizing a working height according to the present invention; and 
       FIG. 6  illustrates a flowchart of finding an offset value to carry out the method of recognizing a working height in FIG.  5 . 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 2  illustrates a bird&#39;s-eye view of a carrier in a handler having an apparatus for recognizing a working height according to the present invention. 
   Referring to  FIG. 2 , a support block  143  is installed at one side of a movable block  141 , which is installed to move along a movable frame  14   a  (cf.  FIG. 1 ) of a handler, to move upward and downward through a guide member such as an LM guide  142 . And, a device transfer unit  15  is fixed to the support block  143  to pick up a semiconductor device. 
   The support block  143  moves upward and downward along the LM guide  142  by a ball screw  144  installed vertical to the movable block  141  and a vertical axis servomotor  145  driving the ball screw  144 . 
   And, the device transfer unit  15  includes a rectangular frame  151  and a plurality of pickers  152  installed to move inside the frame  151  wherein pitches of the pickers  152  are variable reciprocally. And, each of the pickers  152  is elevated upward or downward by an air-pressure cylinder  153  coupled inside the frame  151 . 
   Moreover, an apparatus for recognizing a working height to measure the working height of the device transfer unit  15  is installed at one side of the frame  151 . The apparatus for recognizing the working height, as shown in  FIG. 2  to  FIG. 4 , includes an air pressure cylinder  161  fixed to one side of the frame  151 , an elevating block  163  fixed to a lower end of a cylinder rod  162  of the air pressure cylinder  161 , a touch probe  164  moving upward and downward through a ball bush (not shown in the drawing) coupled with the elevating block  163 , and a limit sensor  166  installed at one upper side end of the elevating block  163  to detect elevation of an upper end of the touch block  164 . 
   The touch probe  164  is supported elastically by a compression spring  165  coupled with a lower end of the elevating block  163 . When the device transfer unit  15  descends so that the lower end of the touch probe  164  comes into contact with a certain object such as a measurement jig, the touch probe  164  goes up. If the contact is released, the touch probe  164  returns to its initial position by an elastic force of the compression spring  165 . 
   Besides, the limit sensor  166  is an LED sensor including a light-emitting unit  166   a  emitting a beam and a light-receiving unit  166   b  installed to leave a predetermined interval from the light-emitting unit  166   a  wherein the beam emitted from the light-emitting unit  166   a  becomes incident on the light-receiving unit  166   b . When the touch probe  164  ascends so that the upper end of the touch probe  164  is disposed between the light-emitting and light-receiving units  166   a  and  166   b , a propagating path of the beam is blocked so that the limit sensor  166  detects the elevation of the touch probe  164 . 
   Operation of the apparatus for recognizing the working height according to the present invention is explained as follows. 
   First of all, the vertical axis servomotor  145  is operated to lift the device transfer unit  15  to a reference height, the air pressure cylinder  153  for driving the picker is actuated to elevate the picker  152 , and then the device transfer unit  15  is moved to a working height measuring position, i.e. an upper side of the change kits such as the tray  200  and the shuttles  8   a ,  8   b ,  9   a , and  9   c.    
   Subsequently, the air pressure cylinder  161  of the apparatus for recognizing the working height is operated to lower the cylinder rod  162  so that the lower end  164  of the touch probe  164  is disposed lower than that of the picker  152 . 
   The vertical axis servomotor  145  is then driven to lower the cylinder rod  162  slowly. The descent of the device transfer unit  15  proceeds until the sensor  166  detects the upper end of the touch probe  164  as the touch probe  164  comes into contact with the tray  200  or the semiconductor device  100  on the change kit. 
   Once the sensor  166  detects the upper end of the touch probe  164 , a detecting signal is transferred to a control unit (not shown in the drawing). The control unit then reads a position value of the device transfer unit to calculate a working height. 
   Yet, such a position value found through the above-explained height measuring process is for the height between the semiconductor device  100  mounted on the handler body and the touch probe  164  of the recognizing apparatus. Between the picker  152  and the recognizing apparatus, one offset value by the installed positions and the other offset value by the ascendance amount of the touch probe  164  of which upper end is detected by the limit sensor  166  exist. Hence, the actual working height of the picker  152  is calculated by compensating theses offset values. 
   A method of recognizing a working height accomplished by the apparatus for recognizing the working height according to the present invention is explained in detail as follows. 
   First of all, the information about the offset values should be inputted previously to the control unit (not shown in the drawing) of the handler before the actual working height is calculated. A height offset between the picker  152  and touch probe  164  and an offset of the limit sensor  166  are found in a following manner. 
   First of all, a measuring jig (not shown in the drawing) is put on a random point on the handler body and the device transfer unit  15  is disposed right over the measuring jig. 
   The air pressure cylinder  153  of the device transfer unit  15  is actuated to lower the picker  152 , and then the other air pressure cylinder  161  of the apparatus for recognizing the working height is lowered so that the lower end of the touch probe  164  is disposed below that of the picker  152 . 
   Subsequently, the vertical axis servomotor  145  is actuated to lower the device transfer unit  15  slowly. In this case, the descent of the device transfer unit  15  is carried out until the lower end of the touch probe  164  touches the upper surface of the measuring jig. And, a vertical position value Z 1  at this moment is encoded to store in the control unit (not shown in the drawing) of the handler. 
   The device transfer unit  15  is then lowered farther until the limit sensor  166  of the recognizing apparatus detects the touch probe  164 . And, a vertical position value Z 0  at the moment that the limit sensor  166  detects  164  the touch probe  164  is encoded to store in the control unit. 
   And, the air pressure cylinder  161  of the recognizing apparatus is actuated to ascend the touch probe  164  and the picker  152  is descended, whereby the lower end of the picker  152  is disposed below that of the touch probe  164 . The device transfer unit  15  is then lowered until the lower end of the picker  152  touches the upper surface of the measuring jig. And, a vertical position value at the moment that the lower end of the picker  152  touches the upper face of the measuring jig is encoded to store. 
   An offset ΔZ 0  of the limit sensor  166  and a height offset ΔZ between the picker  152  and touch probe  164  are calculated as follows.
 
Δ Z   0 =| Z   0 −Z 1 |
 
Δ Z=|Z   2 − Z   1 |
 
   The above-found offset values are stored in the control unit of the handler to use for finding the actual working height by the recognizing apparatus. 
   Once the offset values are found, the operator enables to find the working height automatically in accordance with the replaced semiconductor device and change kit. 
   For instance, in case the working height of the device transfer unit  15  is to be found in the loading unit  2  (cf.  FIG. 1 ) of the handler, after the device transfer unit  15  has been moved toward an upper side of the tray (not shown in the drawing) of the loading unit  2 , the cylinder rod  162  of the air pressure cylinder  161  of the apparatus for recognizing the working height is lowered to descend the touch probe  164 . 
   Subsequently, the device transfer unit  15  is lowered slowly. Once the touch probe  164  comes into contact with the semiconductor device on the tray so that the limit sensor  166  detects the upper end of the touch probe  164 , a vertical position value h at this moment is encoded to store in the control unit (not shown in the drawing) of the handler. 
   And, the control unit of the handler calculates to recognize an actual working height ΔH of the device transfer unit  15  by the above-found vertical position value h and offset values.
 
Δ H=h+ΔZ−ΔZ   0 
 
   In case that a working height of the device transfer unit  15  in the soaking plate  7  (cf.  FIG. 1 ) and shuttles  8   a ,  8   b ,  9   a , and  9   b  (cf.  FIG. 1 ) of the handler, since the semiconductor devices fail to be mounted on the soaking plate  7  and shuttles  8   a ,  8   b ,  9   a , and  9   b , a height between the soaking plate  7  and a semiconductor device landing surface of the surfaces of the shuttle  8   a ,  8   b ,  9   a , or  9   b  is measured and then a thickness of the semiconductor device is subtracted from this height. 
   In case of calculating to recognize the working height ΔH of the device transfer unit  15  as well as the thickness of the semiconductor device, random necessary factors due to the various reasons of the structure and operation of the handler are added to or subtracted from the above equation to recognize the height precisely. 
   Accordingly, the simple construction of the present invention enables to measure the working height of the device carrier automatically. Therefore, in resetting the height of the device carrier after replacement of the tray and change kit, the present invention reduces time and improves precision, thereby enabling to improve test efficiency. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
An apparatus and method are provided for recognizing a working height of a device transfer system in a semiconductor device test handler which allows the working height of the device transfer system to be quickly measured and/or precisely reset. The device transfer system moves horizontally and vertically on a handler body of the semiconductor device test handler, and moves horizontally and vertically, and includes a plurality of pickers which pick up the semiconductor devices. An elevating block installed at one side of the device transfer system moves upward and downward, and a touch probe installed vertical relative to the elevating block moves upward and downward based on contact with a target object. A detector detects ascendance of the touch probe upon contact with the target object, and a working position is determined based on an initial position, a measured position, and a series of offset values.