Abstract:
A tray transfer arm which is widely used regardless of kinds of customer trays and capable of maintaining the stability of holding ICs to be tested. The tray transfer arm for transferring customer trays KST loaded with a plurality of ICs to be tested comprises a cover plate for covering the opening surface of a pocket of the tray.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an electronic component testing apparatus for testing a variety of electronic components, such as semiconductor integrated circuit devices (hereinafter referred to as an “IC” or “ICs”), a tray transfer arm used therefor and a tray transfer method, more particularly relates to a tray transfer arm of fully general-purposed and able to maintain stability in holding electronic components regardless of kinds of customer trays, electronic component testing apparatus and a tray transfer method.  
           [0003]    2. Description of the Related Art  
           [0004]    An electronic component testing apparatus called a “handler” conveys a large number of ICs held on a tray to the inside of a testing apparatus where the ICs are made to electrically contact a test head, then the IC testing unit is made to perform the test. When the test is ended, the ICs are conveyed out from the test head and reloaded on trays in accordance with the results of the tests so as to classify them into categories of good ICs and defective ones.  
           [0005]    In a handler of the related art, the trays for holding the DUTs (Devices under test) to be tested or the tested DUTs (hereinafter referred to the “customer trays”) and the trays conveyed inside the Electronic component testing apparatus (hereinafter referred to as the “test trays”) are different, therefore, the ICs are switched between the customer trays and the test trays before and after the test.  
           [0006]    When switching the tested ICs from the test trays to the customer trays, empty customer trays are prepared for the number of categories of good ICs and defective ones, etc., to which the tested ICs are reloaded from the test trays. When the customer trays are filled up, it is necessary to convey the reloaded ICs to prepare new empty customer trays. Thus, a transfer apparatus called a tray transfer arm is comprised in the electronic component testing apparatus.  
           [0007]    In the tray transfer arms of the related art, as shown in FIG. 12, a customer tray KST loaded with a large number of ICs to be tested is held beneath a tray magazine plate  34 . And the magazine plate  34  moves in the directions of X, Y and Z axises at this state, and thereby, the customer tray KST is transferred to a desired position.  
           [0008]    The above test tray is regarded to be a part exclusively for the handler, while the customer tray KST varies in the shape, particularly, the illustrated thickness H (substantially, H 1 ) and the depth D of a pocket KST 1  for carrying ICs to be tested in accordance with kinds of the customer tray KST.  
           [0009]    Accordingly, when preparing the tray transfer arm of the handler, it has been a general way to prepare it to be fit to a customer tray having the thickest thickness H, or to switch a hook  40  for holding the tray transfer arm in accordance with kinds of the customer tray.  
           [0010]    If the tray transfer arm is made to be fit to a shape of the customer tray having the thickest thickness H, however, the pocket KST 1  is too deep as shown in FIG. 12 when holding a customer tray having thinner thickness H, consequently, a space S between the IC to be tested and the bottom surface of the magazine plate  34  becomes large and the IC to be tested is liable to be out of its position on the pocket KST 1  during transferring the customer tray.  
           [0011]    Also, there has been a disadvantage that switching the holding hook  40  to an exclusive one in accordance with the kinds of the customer trays KST brings extremely burdensome works and requires a long time for the arrangements.  
         SUMMARY OF THE INVENTION  
         [0012]    It is an object of the present invention to provide a tray transfer arm, an electronic component testing apparatus and a tray transfer method of fully general-purposed and able to maintain stability in holding electronic components to be tested regardless of kinds of customer trays.  
           [0013]    (1-1) According to the first aspect of the present invention, there is provided a tray transfer arm for holding and transferring a tray having a pocket for loading an electronic component therein, comprising a cover plate for covering an opening surface of the pocket.  
           [0014]    In the present invention, it is possible to cover with the cover plate the opening surface of the pocket regardless of kinds of a tray when the tray transfer arm holds and transfer the tray. As a result, the electronic components to be tested become stable without jumping out from their correctly held positions and a high speed transfer becomes attainable and disadvantages, such as a pick-up mistake in the next process, can be prevented beforehand.  
           [0015]    The cover plate according to the present invention is not particularly limited. It also includes the tray itself other than exclusive plates. Namely, the tray can be used also as a cover plate.  
           [0016]    (1-2) In the above invention, the position of attaching the cover plate is not particularly limited. It can be attached to the respective trays and also to the tray transfer arm. The jumping out of the DUTs from the electronic component magazine easily occurs mainly during transferring at a high speed, which can be prevented simply by attaching the cover plate to the tray transfer arm.  
           [0017]    (1-3) In the above invention, the cover plate may be provided exclusively in accordance with the shapes, etc. of the respective trays, and more preferably, the cover plate is provided movably in the vertical direction with respect to the opening surface of the tray. By doing so, one cover plate can be widely used for the trays having different shapes, such as the thickness, etc., as well. Namely, in providing a cover plate to the tray transfer arm, by giving a room (space) in the vertical direction with respect to the opening surface, the cover plate covers by contacting with the opening surface of the tray due to its own wight both when holding a thick tray and a thin tray. Accordingly, it can be used widely to different kinds of trays as far as the room permits.  
           [0018]    (1-4) As explained above, the cover plate according to the present invention can be an exclusive part in accordance with kinds of the trays. In this case, although it is not particularly limited, it is preferable that the cover plate is provided removably to the tray transfer arm and forms a projection portion projecting toward the electronic component pocket of the tray.  
           [0019]    In this way, even in the case of using exclusive parts in accordance with kinds of the tray, only the cover plate is parts which should be switched. Thus, comparing with the case of switching the holding hook, time for arrangements and increase in cost can be suppressed. Also, in the case of using exclusive parts, the projection portion in accordance with the electronic component to be tested can be formed on the cover plate, and it becomes possible to attain the state where stability of the electronic component to be tested can be maintained most.  
           [0020]    (1-5) Furthermore, in the above invention, the cover plate is not necessarily a separate parts. It may be the tray magazine plate itself constituting the tray transfer arm. In this case, it is preferable that, along with holding the tray, a hook mechanism for pressing the tray in the direction toward the tray magazine plate is provided.  
           [0021]    By doing so, the opening surface of trays having different shapes, such as the thickness, etc., can be pressed against to contact with the tray magazine plate, and the electronic components to be tested become stabilized without jumping out from the correctly held position. Therefore, a high speed transfer becomes possible and disadvantages, such as a pick-up mistake, etc. in the next process, can be prevented beforehand.  
           [0022]    Also, by forming on the tray magazine plate a projection portion projecting toward the electronic component pocket of the tray, stability of the loaded electronic components to be tested increases furthermore.  
           [0023]    (2) According to the second aspect of the present invention, there is provided an electronic component testing apparatus, comprising a tray magazine for carrying therein a tray having a pocket for loading an electronic component to be tested therein and a tray transfer arm for transferring the tray carried in the tray magazine to a loader section, wherein the tray transfer arm comprises a cover plate for covering an opening surface of the pocket.  
           [0024]    Also, there is provided an electronic component testing apparatus, comprising a tray magazine for carrying therein a tray having a pocket for loading an electronic component therein, and a tray transfer arm for transferring a tray loaded with post-test electronic components at an unloader section to said tray magazine, wherein the tray transfer arm comprises a cover plate for covering an opening surface of the pocket.  
           [0025]    (3) According to the third aspect of the present invention, there is provided a tray transfer method comprising a step for transferring a tray loaded with an electronic component to be tested in a pocket thereof, wherein the tray is transferred in a state that at least an opening surface of the pocket is covered.  
           [0026]    In the present invention, a tray is transferred in a state that at least an opening surface of the electronic component pocket is covered when transferring the tray loaded with electronic components in the pocket wherein one primary surface has the opening, therefore, it is possible to prevent the electronic components from jumping. As a result, the electronic components are stabilized without jumping out of the correct held position, so that a high speed transfer becomes possible and disadvantages, such as a pick-up mistake, etc. in the next process, can be prevented beforehand.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    These and other objects and features of the present invention will be explained in more detail below with reference to the attached drawings, wherein:  
         [0028]    [0028]FIG. 1 is a perspective view of an embodiment of an Electronic component testing apparatus according to the present invention;  
         [0029]    [0029]FIG. 2 is a schematic diagram of a methods of handling a tray in the Electronic component testing apparatus shown in FIG. 1;  
         [0030]    [0030]FIG. 3 is a perspective view of the structure of an IC stocker of the Electronic component testing apparatus of FIG. 1;  
         [0031]    [0031]FIG. 4 is a perspective view of a customer tray used in the Electronic component testing apparatus of FIG. 1;  
         [0032]    [0032]FIG. 5 is a sectional view along the line V-V of FIG. 1.  
         [0033]    [0033]FIG. 6 is a perspective view of an embodiment of a tray transfer arm of the present invention;  
         [0034]    [0034]FIGS. 7A and 7B are disassembled perspective views of an embodiment of a tray transfer arm of the present invention;  
         [0035]    [0035]FIGS. 8A to  8 C are sectional views (corresponding to the sectional view along the line VIII-VIII in FIG. 6) for explaining a function of the tray transfer arm of the present invention;  
         [0036]    [0036]FIGS. 9A and 9B are sectional views of another embodiment of the tray transfer arm of the present invention;  
         [0037]    [0037]FIGS. 10A and 10B are sectional views of another embodiment of the tray transfer arm of the present invention;  
         [0038]    [0038]FIG. 11 is a front view of a hook shown in FIGS. 9A and 9B; and  
         [0039]    [0039]FIG. 12 is a sectional view of a tray transfer arm of the related art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    Embodiments of the present invention will be explained below based on the drawings.  
         [0041]    [0041]FIG. 1 is a partially notched perspective view of an Electronic component testing apparatus wherein a tray transfer arm of the present invention is comprised, and FIG. 2 is a schematic view for explaining the method of handling a tray in the Electronic component testing apparatus. Note that FIG. 2 is a view for understanding the method of handling the tray in the Electronic component testing apparatus of the present embodiment, in which members actually aligned in the vertical direction is partially shown by a plan view. Therefore, the mechanical (three-dimensional) structure will be explained with reference to FIG. 1.  
         [0042]    The Electronic component testing apparatus  1  of the present embodiment  1  comprises, as shown in FIG. 1 and FIG. 2, a chamber section  100  including a test head, a tray magazine  200  for storing ICs to be tested from now and also classifying and storing tested ICs, a loader section  300  for conveying the IC to be tested to the chamber section  100 , and an unloader portion  400  for classifying and taking out the ICs tested in the chamber section  100 .  
         [0043]    Note that, in the following explanation, a case where the tray transfer arm  205  of the present invention is applied to an Electronic component testing apparatus  1  of a chamber form will be shown, however, the tray transfer arm of the present invention can be applied to any handlers as far as they transfer a tray loaded with ICS to be tested (hereinafter also referred to as a customer tray KST), and which is not limited to the chamber form Electronic component testing apparatus described below and can be applied, for example, to an Electronic component testing apparatus in a heat plate form.  
         [0044]    Chamber Section  100   
         [0045]    The Electronic component testing apparatus  1  of the present embodiment tests (inspects) whether an IC operates suitably in a state applying a high temperature or low temperature thermal stress to the DUT or not applying, and classifies the DUTs in accordance with the test results. The operating test in the state with thermal stress applied is performed by reloading the DUTs from the customer tray KST carrying a large number of DUTs to be tested to a test tray TST conveyed through the inside of the Electronic component testing apparatus  1 .  
         [0046]    The test tray TST is conveyed into the chamber section  100  after being loaded with the DUTs by the loader section  300 , then the DUTs are tested in a state carried on the test tray TST. Then after conveying out the tested ICs to the unloader section  400 , the respective DUTs are reloaded at the unloader portion  400  to the customer tray KST in accordance with the test results.  
         [0047]    The chamber section  100  is comprised of a constant temperature chamber  101  for giving a desired high temperature or low temperature thermal stress, or no thermal stress to the DUTs loaded on the test tray TST, a test chamber  102  for making the DUTs contact the test head in a state given the thermal stress or no thermal stress by the constant temperature chamber  101 , and a soak chamber  103  for removing the given thermal stress from the DUTs tested in the test chamber  102 .  
         [0048]    In the soak chamber  103 , when a high temperature was applied in the constant temperature chamber  101 , the DUTs are cooled by blowing in air to return them to room temperature. Alternatively, when a low temperature of about −30° C. has been applied in the constant temperature chamber  101 , it heats the DUTs by hot air or a heater etc. to return them to a temperature where no condensation occurs. Next, the thus treated DUTs are conveyed out to the unloader section  400 .  
         [0049]    As shown in FIG. 1, the constant temperature chamber  101  and soak chamber  103  of the chamber section  100  are arranged so as to project upward from the test chamber  102 . Here, a test tray TST is loaded with the DUTs at the loader section  300  and conveyed to the constant temperature chamber  101 . The constant temperature chamber  101  is provided with a vertical conveyor, illustration of which is omitted. A plurality of test trays TST stand by in a state supported by the vertical conveyor until the test chamber  102  becomes empty. While standing by, a high temperature or low temperature thermal stress is applied to the DUTs.  
         [0050]    The test chamber  102  has a test head  104  arranged at its center. A test tray TST is conveyed above the test head  104  and the DUTs are tested by bringing them into electrical contact with the test head  104 . The test tray TST finished being tested is treated in the soak chamber  103  to return the temperature of the ICS to room temperature, then is discharged to the unloader section  400 .  
         [0051]    In front of the constant temperature chamber  101  and the soak chamber  103  is provided a board  105  as shown in FIG. 1. This board  105  has a test tray conveyor  108  mounted on it. The test tray TST discharged from the soak chamber  103  by the test tray conveyor  108  provided on the board  105  is returned to the constant temperature chamber  101  through the unloader section  400  and the loader section  300 .  
         [0052]    Tray Magazine  200   
         [0053]    The tray magazine  200  is provided with a pre-test IC stocker  201  for holding DUTs to be tested and a post-test IC stocker  202  for holding DUTs classified in accordance with the test results.  
         [0054]    These pre-test IC stocker  201  and post-test IC stocker  202 , as shown in FIG. 3, are each comprised of a frame-shaped tray support frame  203  and an elevator  204  able to enter from under the tray support frame  203  and move toward the top. The tray support frame  203  supports in it a plurality of stacked customer trays KST as shown in the enlarged view of FIG. 4. The stacked customer trays KST are moved up and down by the elevator  204 .  
         [0055]    The pre-test IC stocker  201  holds stacked customer trays KST on which the DUTs to be tested are held, while the post-test IC stocker  202  holds stacked customer trays KST on which DUTs finished being tested are suitably classified.  
         [0056]    Note that since the pre-test IC stocker  201  and the post-test IC stocker  202  are structured the same, the numbers of the pre-test IC stocker  201  and the post-test IC stocker  202  may be suitably set in accordance with need. In the example shown in FIG. 1 and FIG. 2, the pre-test IC stocker  201  is provided with two stockers STK-B and provided next to that with two empty stockers STK-E to be sent to the unloader section  400 , while the post-test IC stocker  202  is provided with eight stockers STK- 1 , STK- 2 , . . . , STK- 8  and can hold ICS sorted into a maximum of eight classes according to the test results. That is, in addition to classifying ICS as good and defective, it is possible to divide the good ICS into ones with high operating speeds, ones with medium speeds, and ones with low speeds and the defective ICS into ones requiring retesting etc.  
         [0057]    Loader Section  300   
         [0058]    The above-mentioned customer tray KST is conveyed to the loader section  300 , where the DUTs loaded on the customer tray KST are reloaded on the test tray TST stopped at the loader section  300 .  
         [0059]    The X-Y conveyor  304  is used as an IC conveying apparatus for reloading the DUTs from the customer tray KST to the test tray TST, as shown in FIG. 1, which is provided with two rails  301  laid over the top of the board  105 , a movable arm  302  able to move back and forth (this direction designated as the Y-direction) between the test tray TST and a customer tray KST by these two rails  301 , and a movable head  303  supported by the movable arm  302  and able to move in the X-direction along the movable arm  302 .  
         [0060]    The movable head  303  of the X-Y conveyor  304  has suction heads attached facing downward. The suction heads move while drawing out air to pick up the DUTs from the customer tray KST and reload the DUTs on the test tray TST. For example, about eight suction heads are provided for the movable head  303 , so it is possible to reload eight DUTs at one time on the test tray TST.  
         [0061]    Note that in a general customer tray KST, indentation pocket KST 1  for loading the DUTs are formed relatively larger than the shapes of the DUTS, so the positions of the DUTs in a state held on the customer tray KST can vary largely. Therefore, if the DUTs are picked up by the suction heads and conveyed directly to the test tray TST in this state, it becomes difficult for the ICS to be dropped accurately into the IC receiving indentations formed in the test tray TST.  
         [0062]    Therefore, in the Electronic component testing apparatus  1  of the present embodiment, an IC position correcting means called a preciser  305  is provided between the set position of the customer tray KST and the test tray TST. This preciser  305  has relatively deep indentations surrounded with inclined surfaces at their circumferential edges, so when DUTs picked up by the suction heads are dropped into these indentations, the drop positions of the DUTs are corrected by the inclined surfaces. Due to this, the positions of the eight DUTs with respect to each other are accurately set and it is possible to pick up the correctly positioned DUTs by the suction heads once again and reload them on the test tray TST and thereby reload the DUTs precisely in the IC receiving indentations formed in the test tray TST.  
         [0063]    [0063]FIG. 5 is a sectional view along with the line V-V of FIG. 1, a vertical sectional view of a board  105 , a tray transfer arm  205  and a tray magazine  200  which will be explained later on. As shown in FIG. 1, the board  105  of the loader section  300  is provided with a pair of openings  306 ,  306  arranged so that the customer trays KST carried to the loader section  300  can be brought close to the top surface of the board  105 . Each of the openings  306  are provided with a holding hook  306   a  for holding the customer tray conveyed to the opening  306 , and the customer tray KST is held in the position that the top surface thereof faces the surface of the board  105  via the opening  306 .  
         [0064]    Further, an elevator table  307  for elevating or lowering a customer tray KST is provided below the openings  306 . A customer tray KST emptied after reloading of the DUTs to be tested is placed on here and lowered and the empty tray is passed to the lower tray magazine of the tray transfer arm  205 .  
         [0065]    Unloader Section  400   
         [0066]    The unloader section  400  is provided with two X-Y conveyors  404 ,  404  of the same structure as the X-Y conveyor  304  provided at the loader section  300 . The X-Y conveyors  404 ,  404  reload the post-test ICS from the test tray TST carried out to the unloader section  400  to the customer tray KST.  
         [0067]    As shown in the sectional view of the board  105 , tray transfer arm  205  and tray magazine  200  of FIG. 5, the board  105  of the unloader section  400  is provided with two pairs of openings  406 ,  406  arranged so that the customer trays KST carried to the unloader section  400  can be brought close to the top surface of the test board  105 . Each of the openings  406  is provided with a holding hook  406   a  for holding the customer tray conveyed to the opening  406 , and the customer tray KST is held in the position that the top surface thereof faces the surface of the board  105  via the opening  406 . The specific structure of the holding hook  406   a  is not particularly limited, and, for example, it may mechanically seize the customer tray KST, or the customer tray KST can be held by a pick up means.  
         [0068]    Further, while not illustrated, an elevator table  407  for elevating or lowering a customer tray KST is provided below the openings  406 . A customer tray KST becoming full after being reloaded with the tested DUTs is placed on here and lowered and the full tray is passed to the lower tray magazine of the tray transfer arm  205 . Note that the customer tray KST can be moved up and down or lowered by the elevator  204  of the stocker STK positioned immediately beneath the respective openings in stead of the elevating table  407 .  
         [0069]    Note that in the Electronic component testing apparatus  1  of the present embodiment, while there are a maximum of eight types of sortable categories, it is only possible to arrange a maximum of four customer trays KST at the openings  406  of the unloader section  400 . Therefore, there is a limit of four sortable categories in real time. In general, four categories are sufficient, i.e., good ICS can be classified into high speed response devices, medium speed response devices, and low speed response devices plus defective devices, but there may also arise categories not belonging to these categories such as devices requiring retesting.  
         [0070]    In this way, when DUTs arise which are classified into a different category than the categories given to four customer trays arranged at the openings  406  of the unloader section  400 , one customer tray KST may be returned from the unloader section  400  to the tray magazine  200  and a customer tray KST to hold DUTs of the newly arising category may be transferred to the unloader section  400  in its place so as to hold these DUTs. If customer trays KST are switched in the middle of sorting work, the sorting work has to be interrupted during that time and therefore there is the problem of a reduction in the throughput. Therefore, in the Electronic component testing apparatus  1  of the present embodiment, a buffer section  405  is provided between the test tray TST and the opening  406  of the unloader section  400 , and DUTs of a category rarely appearing are stored temporarily at this buffer section  405 .  
         [0071]    For example, the buffer section  405  is given a capacity able to hold 20 to 30 or so DUTs. A memory is provided for storing the category of ICS held at the IC holding locations of the buffer section  405 . The categories and positions of the DUTs temporarily stored at the buffer section  405  are stored for each DUT. In the intervals of the sorting work or when the buffer section  405  has become full, customer trays KST of the categories to which the DUTs stored at the buffer section  405  belong are called up from the tray magazine  200  and the ICS are loaded on these customer trays KST. At this time, sometimes the DUTs temporarily stored at the buffer section  405  span several categories, but at this time it is sufficient to call up several customer trays KST at one time from the openings  406  of the unloader section  400  when calling up customer trays KST.  
         [0072]    Tray Transfer Arm  205   
         [0073]    As shown in FIG. 1, the upper portion of the pre-test IC stocker  201  and post-test IC stocker  202 , there is provided a tray transfer arm  205  which moves all over the range of the pretest stocker  201  and the post-test stocker  202  in the direction they are aligned between the board  105 . In this example, since openings  306  and  406  of the loader section  300  and the unloader section  400  are formed immediately above the pre-test IC stocker  201  and post-test IC stocker  202  (without deviating in the Y-axis direction), the tray transfer arm  205  is also movable only in the directions of X-axis and Y-axis. Note that in accordance with the positional relationship of the tray magazine  200  and the loader section  300  or the unloader section  400 , the tray transfer arm  205  may be made to be movable in all directions of X, Y and Z axises.  
         [0074]    The tray transfer arm  205  is provided with a pair of tray magazines  205   a  and  205   b  for holding the customer trays KST being in an alignment to the left and the right to each other (in the X-direction), and transfers the customer trays KST between the loader section  300  and the unloader section  400  and between the pre-test IC stocker  201  and post-test IC stocker  202 .  
         [0075]    [0075]FIGS. 6, 7A and  7 B are perspective views of a specific embodiment of the tray transfer arm  205 , in which FIG. 6 shows the state that the whole is combined (note that a cover plate  35  which will be explained later on is not illustrated) and FIGS. 7A and 7B shown the state of combining a magazine plate  34  and the cover plate  35 .  
         [0076]    As shown in FIG. 6, the tray transfer arm  205  is provided with a base plate  32 , which moves in the X-axis direction by a ball screw  31  functioning by being stretched in the X-axis direction, and a tray magazine plate  34  on a primary surface of the base plate  32  via a linear guide  33  being stretched in the Z-axis direction.  
         [0077]    A rod of a first liquid pressure cylinder  36  fixed to the base plate  32  is fixed on the tray magazine plate  34 , the tray magazine plate  34  moves in the Z-axis direction along with the linear guide  33  due to the operation of the first liquid pressure cylinder  36 .  
         [0078]    Also, guide pins  38  for guiding the peripheral edge of the customer tray KST are provided at proper positions on the bottom surface of the tray magazine plate  34 , and the customer tray KST can be held along with the guide pins  38 .  
         [0079]    Further, since the tray magazine plate  34  holds the customer tray KST on its bottom surface, a holding hook mechanism  39  is provided so as not to drop the customer tray KST. The holding hook mechanism  39  is configured, for example as shown in FIG. 6, to be able to open and close (rotate by 90-degree) the hooks  40  provided at the positions corresponding to four corners of the customer tray KST by a link mechanism  42  operating in a second liquid pressure cylinder  41 . Namely, the customer tray KST can be held by the tray magazine plate  34  by leaving the hook  40  open when receiving the customer tray KST and closing the hook  40  in the state of holding the customer tray KST. In the same way, the customer tray KST can be released by opening the hook  40  after being carried to a designated position in a state the hook  40  is closed.  
         [0080]    Note that a control of the rotation drive of the ball screw  31 , the first liquid pressure cylinder  36  and the second liquid pressure cylinder  41  of the holding hook mechanism  39  are performed by a control apparatus, which is also out of FIG. 6.  
         [0081]    Note that in the example shown in FIG. 6, one tray magazine plate  34  is provided to one base plate  32 . However, it can be configured to provide one more tray magazine plate  34  in the X-axis direction as shown in FIG. 1 in order to enable to transfer two customer trays KST at a time by each of the two tray magazine plates  34 .  
         [0082]    In this case, as shown in FIG. 5, it is preferable that a pitch P 1  of a pair of tray magazine, pitches P 3 , P 4  and P 5  of the openings  306  and  406  of the loader section  300  and the unloader section  400  and pitch P 6  of the stocker STK of the tray magazine  200  are all equally set. By doing so, it is possible to simultaneously transfer two customer trays in the same position, so the switching speed becomes higher.  
         [0083]    Also, in the tray transfer arm  205  shown in FIG. 6, the tray magazine plate  34  is made movable also in the Z-axis direction by the first liquid pressure cylinder  36 . However, the present invention is not limited to this case and the z-axis direction may be fixed, as well.  
         [0084]    Particularly, the tray transfer arm  205  of the present embodiment is provided with a cover plate  35  on the bottom surface of the tray magazine plate  34 . While it is not illustrated in FIG. 6, the cover plate  35  of the present embodiment is, as shown in FIG. 7A and FIG. 7B, board-shaped in which a lengthwise length and a lateral length of almost equal with those of the customer tray KST, and four flanges  35   c  are formed at the side edges. The flange  35   c  is a member used when attaching the cover plate  35  to the tray magazine plate  34  and, as shown in FIG. 7B, fixes a holding angle  35   a  to the tray magazine plate  34  with a volt. The cover plate  35  is held by the tray magazine plate  34  by sandwiching the flange  35   c  between the holding angle  35   a  at this time.  
         [0085]    The cover plate  35  is held by the holding angle  35   a  to the tray magazine plate  34  in this way, while in the state not holding a customer tray KST as shown in FIG. 8C, it is held by a room (space) L. By providing the room L, the cover plate  35  is made movable in the Z-axis direction by exactly the length of the room L.  
         [0086]    Also, in the cover plate  35  according to the present embodiment, as shown in FIG. 7A, FIG. 7B and FIGS. 8A to  8 C, a plurality of projection portions  35   b  are formed on the bottom surface, that is, the primary surface facing the top surface of the customer tray KST. The projection portions  35   b  are formed at positions corresponding to the positions of pockets KST 1  of the customer tray, and they face the DUTs to prevent rattling when holding the customer tray KST, as shown in FIGS. 8A to  8 C.  
         [0087]    Note that the projection portions  35   b  is not essential to the present invention. For example, when using the cover plate  35  widely to all of the customer trays KST, the space between a DUT and a cover plate  35  is not always same in the respective customer trays KST, accordingly, it is not easy to make the projection portion  35   b  to be able to be widely used for all of the customer trays KST. Therefore, the projection portion  35   b  are omitted in such a case. On the other hand, when preparing the cover plate  35  as an exclusive member to a certain kind of customer tray group, DUTs loaded to the customer trays KST are naturally limited and the space between the DUT and the cover plate  35  are fixed. Thus, raffling inside the customer tray KST are completely prevented by forming the projection portion  35   b  in accordance with the shape of the DUT.  
         [0088]    Next, the operation will be explained.  
         [0089]    Here, with reference to FIG. 5, a sequence of operations will be explained wherein the customer tray KST loaded with pretest ICs is set from the stocker STK-B to a pair of the openings  306  and  306  (the explanation below starts from the state that the customer tray KST is not set to the opening  306 ). The operation of the tray transfer arm according to the present invention is basically the same also in other sequences, so the explanation will be omitted here.  
         [0090]    First, the tray transfer arm  205  is driven in the X-axis direction and stopped right above the pre-test stocker STK-B. Then, the elevator  204  of the pre-test stocker STK-B is elevated and the stacked customer trays KST are moved up to the tray magazine plate  34 . At this time, the holding hook  40  of the tray transfer arm  205  is left open at first and closes when the customer tray KST is set to the tray magazine plate  34  by the elevator  204 . Due to this, the customer tray KST can be held even if the elevator  204  lowers. The above operations may be carried out on a pair of tray magazines  205   a  and  205   b  to the right and the left to each other and also on only either one of the tray magazines  205   a  and  205   b.    
         [0091]    At the same time with this, or before or after this, an elevator table  307  provided at the opening  306  of the loader section  300  is moved down to be lower than the tray transfer arm  205 . Then, the tray transfer arm  205  is driven in the X-axis direction and stopped right above the elevator table  307  in the lowered state.  
         [0092]    Here, the customer tray KST held by the tray magazine plate is reloaded to the elevator table  307  either by elevating the elevating table  307  or by lowering the tray magazine plate  34  by the drive of the first liquid pressure cylinder  36 . This reloading is carried out by opening the holding hook  40  of the tray transfer arm  205 . Also, the above operations may be carried out on a pair of the tray magazines  205   a  and  205   b  to the right and the left to each other and also only on either one of the tray magazines  205   a  and  205   b.    
         [0093]    When the customer tray KST loaded with the pre-test ICs is reloaded to the elevator table  307 , the elevator table  307  is elevated after moving the tray transfer arm  205  in the X-axis direction in the either way, and the customer tray KST is set to the opening  306  of the loader section  300 .  
         [0094]    Due to the above sequence, the customer tray KST loaded with pre-test ICs to be tested from now is set from the stocker STK-B to the opening  306  of the loader  300 .  
         [0095]    Here, in the tray transfer arm  205  of the DUT testing apparatus  1  of the present embodiment, since the cover plate  35  is attached to the tray magazine plate  34  leaving a room L, even when two kinds of customer trays are used, which are customer trays KST having the thickness of Hll as shown in FIG. 8A and customer trays KST having the thickness of H 12  as shown in FIG. 8B (thinner than that of the customer tray KST shown in FIG.  8 A), the pocket opening of the customer tray KST can be closed by the cover plate  35 , so that it is possible to prevent the DUTs from jumping out.  
         [0096]    Namely, the dimension HO between the bottom surface of the tray magazine plate  34  and the holding hook  40  shown in FIG. 8A is set to be common in the tray transfer arm  205 , and a customer tray KST having the thickest thickness is set to be a reference among the customer trays KST used in the tray transfer arm  205 .  
         [0097]    [0097]FIG. 8A shows the state that the thick customer tray KST is held. At this time, the bottom surface of the tray magazine plate  34  and the top surface of the cover plate  35  is in contact or leaves only a slight space L 1  between them at the holding angle  35   a  portion.  
         [0098]    On the other hand, when holding a customer tray KST of a thin thickness by the same transfer arm  205 , as shown in FIG. 8B, a larger space L 2  than that in FIG. 8A is formed between the bottom surface of the tray magazine plate  34  and the top surface of the cover plate  35  at the holding angle  35   a  portion. Namely, when the board thickness of the cover plate  35  is defined as t, there is a relationship of H 0 =H 11 +t+L 1 =H 12 +t+L 2 .  
         [0099]    In any cases, the cover plate  35  covers over the customer tray KST to be held and contact with the customer tray KST due to the weight of the cover plate  35  itself, so that the DUTs loaded on the pocket KST 1  of the customer tray KST are free from jumping out. Especially, as shown in FIG. 8A and FIG. 8B, when the projection portion  35   b  is formed on the other side of the cover plate  35 , raffling of the DUTs can be more surely prevented.  
         [0100]    Also, since the cover plate  35  of the present embodiment is attached removably only by the holding angle  35   a , when using customer trays KST having largely different thicknesses and when provision of the projection portion  35   b  is inevitable due to the large difference of the depths of the pockets KST 1 , other members, such as tray magazine plate  34 , can be widely used only by making the cover plate  35  exclusive member.  
         [0101]    Other Embodiments  
         [0102]    A tray transfer arm of the present invention can be modified in a variety of ways.  
         [0103]    [0103]FIGS. 9A, 9B,  10 A and  10 B are sectional views of another embodiment of the tray transfer arm of the present invention, wherein FIGS. 9A and 10A are the views from the A_direction of FIG. 6 and FIGS. 9B and 10B are views from the B direction of FIG. 6. FIG. 11 is a view of a cum groove formed on the hook  40  viewed from the front.  
         [0104]    In the above explained embodiments, the cover plate was comprised by a separate member  35  and attached to the tray magazine plate  34 , while in the present embodiment, the tray magazine plate itself is made to be a cover plate, which forms a projection portion  34   b  corresponding to the projection portion  35   b  shown in the above embodiment on the back surface of the tray magazine plate  34  as shown in FIG. 9B. This projection portion  34   b  is also formed at the position corresponding to the position of the pocket KST 1  of the customer tray and prevents raffling by facing to a DUT when holding a customer tray KST.  
         [0105]    Also, a hook  40  is made to be movable in the vertical direction in order to make a pocket opening contact the back surface of the tray magazine plate  34  even when the thickness of the customer trays KST differs. Namely, a cum groove  401  as shown in FIG. 11 is formed on the hook  40  and a pin  402  jointed to the cam groove  401  is fixed on the tray magazine plate  34 .  
         [0106]    As shown in FIG. 9A, a link mechanism  42  to open and close (to revolve by 90-degree) the hook  40  is provided at the upper end of the shaft  403  provided rotatably to the tray magazine plate  34 , and the hook  40  is inserted to the lower end portion of the shaft  403  formed to have a partially plain surface. When the shaft  403  is rotated by this, the hook  40  also rotates together. Also, beneath the hook  40  is provided with a coil spring  404  to apply a power upward to putting up the hook  40 , and the hook  40  moves upward to the upper portion of the shaft  403  due to the applied power of the coil spring  404  in the condition without a restriction by the cam groove  401  and the pin  402 .  
         [0107]    The relationship between the cam groove  401  and the pin  402  shown in FIG. 11 is as below. Note that FIGS. 9A and 9B shows a state where the hook  40  is rotated from the first  0 -degree to 45-degree in the 90-degree rotation, while FIGS. 10A and 10B show a state of the remaining 45 to 90-degree. When the hook  40  is closed by rotating the shaft  403  by 90-degree by the link mechanism  42 , the customer tray KST is held during the first part of rotation up to 45-degree, the held customer tray KST is gradually put up during the remaining 45-degree rotation, and finally the hook  40  is released, as a result, the customer tray KST is pressed against the back surface of the tray magazine plate  34  due to the elasticity of the coil spring  404 .  
         [0108]    A relative relationship of the cum groove  401  and the pin  402  is shown in FIG. 11, wherein the relative movement of the pin  402  is shown for easier understanding of this figure despite the fact that the pin  402  does not move and the hook  40  rotates on which the cam groove  401  is formed.  
         [0109]    As shown in FIG. 11, when closing the hook  40 , the initial position of the pin is at  402 A. And the position after rotating by 45-degree is  402 B. Since the cam groove  401  is horizontal from the position  402 A to the position  402 B, the hook  40  only rotates together with the shaft  403  and does not move upward nor downward.  
         [0110]    During the rotation from the position  402 B to the position  402 C, the hook  40  elevates by exactly hi with respect to the shaft  403  due to the joints of the cam groove  401  and the pin  402 . When the pin  402  reaches to the position  402 C, it further reaches to the position  402 D due to the elasticity of the coil spring  404 , and the hook  40  is released. As a result, as shown in FIGS. 10A and 10B, the customer tray KST is pressed against the back surface of the tray magazine plate  34 .  
         [0111]    Inversely, when opening the hook  40 , the pin  402  relatively moves from the position  402 D to  402 B to  402 A.  
         [0112]    In this way, according to the tray transfer arm  205  of the present embodiment, the opening surface of customer trays KST having different shapes in the thickness, etc. can be also pressed against the back surface of the tray magazine plate  34 , therefore, the DUTs can be stabilized without jumping out from the pocket. Accordingly, a high speed transfer becomes possible and disadvantages, such as a pick-up mistake, etc. in the next process, can be prevented beforehand.  
         [0113]    Note that the embodiments explained above were described to facilitate the understanding of the present invention and not to limit the present invention. Accordingly, elements disclosed in the above embodiments include all design modifications and equivalents belonging to the technical field of the present invention.  
         [0114]    For example, in the above embodiment, it is necessary to prepare the cover plate  35  as an exclusive member. However, instead of such a cover plate  35 , by installing and using a same kind of customer tray KST itself to the tray magazine plate  34 , it is possible to prevent DUTs from jumping out.