Abstract:
A calibration unit for a semiconductor integrated circuit tester includes a frame, a manipulator arm which extends in cantilever fashion from the frame, and a calibration head attached to the manipulator arm at its distal end and having a downwardly directed test interface for mating with a test head in DUT up orientation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a calibration unit for a semiconductor integrated circuit tester. 
     A conventional semiconductor integrated circuit tester includes a test head having multiple terminals for engaging respective terminals of a device under test (DUT) for carrying out test activities at the terminals of the DUT. The terminals of the test head are distributed over a DUT interface of the test head. The test head is conventionally carried by a manipulator which allows the test head to be positioned in several different orientations, including the so-called DUT down orientation in which the DUT interface is directed downwards, for engaging a DUT from above. 
     U.S. Pat. No. 4,724,378 discloses a calibration unit for a semiconductor integrated circuit tester. A practical implementation of the calibration unit shown in U.S. Pat. No. 4,724,378 includes a wheeled trolley or cart having a frame and an XYZ table mounted to the frame in a manner allowing movement of the table relative to the frame along horizontal (X and Y) and vertical (Z) axes. The test head of the tester that is to be calibrated is positioned over the calibration unit in the DUT down orientation and is docked to the calibration unit. The XYZ table executes a sequence of movements relative to the frame of the trolley to engage sequentially each terminal of the test head. While the XYZ table is in engagement with a given terminal, the calibration unit and the tester execute a calibration operation. 
     The practical implementation of the known calibration unit can only operate with a tester whose test head can be positioned in the DUT down orientation. This is not a severe disadvantage with a tester having a manipulator that provides a full range of movement of the test head. However, it has been proposed that semiconductor integrated circuit testers should be designed so that the test head has a limited range of movement and cannot be positioned in the DUT down orientation, even though it can be positioned in the DUT up orientation, in which the DUT interface is directed downwards. The conventional calibration unit cannot be used to calibrate such testers. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention there is provided a calibration unit for a semiconductor integrated circuit tester comprising a frame, a manipulator arm having a proximal end at which it is attached to the frame and extends in cantilever fashion from the frame, the manipulator arm also having a distal end, and a calibration head attached to the manipulator arm at the distal end thereof and having a downwardly directed test interface for mating with a test head in DUT up orientation. 
     In accordance with a second aspect of the invention there is provided a semiconductor integrated circuit tester including a frame, a manipulator arm having a proximal end at which it is attached to the frame and extends in cantilever fashion from the frame, the manipulator arm also having a distal end, and a test head attached to the manipulator arm at the distal end thereof and having a downwardly directed test interface, and wherein the manipulator arm includes a parallelogram linkage allowing vertical movement of the test head relative to the frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which 
     FIG. 1 is a perspective view of a calibration unit in accordance with the invention, 
     FIG. 2 is a side view at an enlarged scale of a part of the calibration unit shown in FIG. 1, and 
     FIG. 3 is an enlarged sectional view of a detail of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     The calibration unit shown in FIG. 1 comprises a wheeled cart  10  including a rectangular frame  12  to which a support plate  14  is attached. A post  16  extends upward from the support plate  14  at one end of the cart. The post is held in a vertical orientation by gusset plates  18 , which are welded to the post and to the support plate  14 . Vertical side plates  20  attached to three of the sides of the frame extend upward, above the support plate  14  and define a storage compartment  22 . 
     A manipulator arm  24  is attached to the upper end of the post  16 . The manipulator arm  24  includes an inner arm segment  26  which is supported on the post  16  by a bearing which constrains the inner arm segment to extend substantially radially from the post  16  and allows the inner arm segment  26  to pivot relative to the post  16  about a vertical axis. 
     The manipulator arm also includes an outer arm assembly  28  formed as a parallelogram linkage composed of inner and outer vertical links  30 ,  32  and upper and lower links  34 ,  36  which connect the vertical links. The inner vertical link  30  includes a body  38  in which a shaft  40 , only the lower end of which can be seen in the drawings, is held. The shaft  40  is journalled in a bearing which is housed in the outer end of the inner arm segment  26  and constrains the shaft to a vertical orientation. Suitable thrust bearings (not shown) support the body  38  relative to the inner arm segment  26  and allow the vertical link  30 , and the parallelogram linkage of which the vertical link  30  is a part, to pivot relative to the arm segment  26  about the axis of the vertical shaft  40 . 
     The upper link  34  is composed of two parallel rods  34 A,  34 B. Similarly, the lower link  36  is composed of two parallel rods  36 A,  36 B. 
     Two vertically-spaced ears  42  project from the body  38  and horizontal shafts  44  pass through the ears and project at each end from the ears  42 . The inner ends of the upper rods  34 A,  34 B are journalled on the projecting ends of the upper shaft by bearings  48  and the inner ends of the lower rods  36 A,  36 B are journalled on the projecting ends of the lower shaft by bearings  50 . 
     The outer vertical link  32  includes a body  52  from which two vertically-spaced ears  54  project. As in the case of the inner link  30 , horizontal shafts  56  pass through the ears  54  and project at each end from the ears. The outer ends of the upper rods  34 A,  34 B are journalled on the projecting ends of the upper shaft by bearings  60  and the outer ends of the lower rods  36 A,  36 B are journalled on the projecting ends of the lower shaft by bearings  62 . 
     As shown in FIG. 2, body  52  accommodates a shaft  64 , the lower end of which projects downwards from the body  52 . The shaft  64  is journalled in a bearing which constrains the shaft  64  to a vertical orientation and allows rotational movement of the shaft  64  relative to the body  52 . Suitable bearings retain the shaft  64  in the body  52 . 
     As shown in FIG. 3, the shaft  64  is provided at its lower end with a two-part bushing  66  which is made of rubber or other resiliently deformable material and is held on the shaft  64  by nuts  68  and washers  70 . A mounting element  72  is attached to the shaft  64  by the bushing  66 . Specifically, the mounting element  72  is composed of an annular disk portion and a skirt depending from the rim of the disk portion, and the shaft  64  passes through the hole in the annular disk portion and the annular disk portion is clamped between the two parts of the bushing  66 . The skirt has an external flange  76  and a carrier plate  74  is secured to the flange  76  by screws  78  (FIG.  2 ). 
     The carrier plate  74  is nominally horizontal, but the deformable bushing  66  allows a limited range of angular movement of the carrier plate  74  relative to the outer arm assembly  28  about horizontal axes. A calibration head  80  including an XYZ table  81  is attached to the underside of the plate  74  and is oriented with its test interface downwards. The calibration head  80  includes docking bars  82  for docking to a test head in DUT up orientation. 
     When the calibration unit is not in use, the manipulator arm can be turned about the post  16  to position the calibration head over the storage compartment  22  and the calibration head can then be lowered so that the docking bars  82  are positioned in the storage compartment. In this condition, the test interface is protected effectively from damage by inadvertent impacts. 
     A leg  84  extends downward from the inner body  30  and is provided at its lower end with a foot  86 . A linear actuator  88  is attached at one end to the foot  86  and extends upward from the foot  86 , passing between the lower rods  36 A,  36 B and between the upper rods  34 A,  34 B, and is attached to the upper rods  34 A,  34 B. The linear actuator may be, for example, a gas cylinder or a compressed air cylinder connected to a regulated source of compressed air. By virtue of its connection between the inner body  30  and the upper rods  34 A,  34 B, the linear actuator is able to exert a force resisting the force exerted on the outer body  32  by the weight of the carrier plate  74  and the calibration head  80 . Accordingly, even though the weight of the calibration head might be as much as 250 kg, an operator can easily raise and lower the carrier plate  74  and the calibration head using one hand, and can position the calibration head precisely over the test head prior to docking with the test head. 
     The pivotal connections of the inner arm segment  24  allow a wide range of horizontal movement of the calibration head without influencing the vertical position of the calibration head, and the parallelogram linkage allows vertical movement of the calibration head without influencing the orientation of the carrier plate  74 . The mounting of the calibration head to the outer link  32  allows the calibration head to turn about a vertical axis and allows limited angular movement of the calibration head about horizontal axes. 
     When the calibration unit is not in use, the manipulator arm can be turned about the post  16  to position the calibration head over the storage compartment  22  and the calibration head can then be lowered so that the docking bars  82  are positioned in the storage compartment. In this condition, the tester interface is protected effectively from damage by inadvertent impacts. 
     It will be appreciated that the invention is not restricted to the particular embodiment that has been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, although the invention has been described with reference to a calibration unit to be used with a tester having a test head which can be positioned in the DUT up orientation but not in the DUT down orientation, the invention can also be used to provide a semiconductor integrated circuit tester having a test head which can be positioned only in the DUT down orientation. In this case, the element  80  shown in FIG. 1 is the test head of a tester rather than the calibration head of a calibration unit and the test head can be used in conjunction with a device handler or wafer prober that can present devices to be tested to a test head in DUT down orientation. A manipulator that provides a limited range of movement for the test head is advantageous because it is less expensive to manufacture than a conventional manipulator that not only allows the test head to be moved vertically and horizontally but also allows the test head to be positioned selectively in the DUT up orientation or in the DUT down orientation.