Testing of integrated circuit components of the silicon wafer type for grading purposes is accomplished by supporting the wafer matrix on a platform type work table which is indexed in an x-y coordinate fashion, with the work table being moved vertically to a test position such that the test probes make contact with a precise predetermined position corresponding to the precise location of that portion of the integrated circuit to be tested. The work table is movable vertically with reference to a predetermined axis and rotatable with respect thereto such that the surface of the table remains perpendicular to the reference axis. The chuck assembly for moving the table includes a housing having a bore whose center forms the axis, with a chuck plate mounted for sliding movement in the bore. The end of the chuck plate is in the form of a flanged spool which receives bearing-eccentric assembly for effecting vertical movement while permitting rotation of the spool and the attached chuck plate. A multiphase stepping motor is used to drive the chuck plate through the bearing-eccentric assembly, the motor including optical limit switches sensing the motor shaft position and controlling the motor operation. The motor has a sinusoidal speed characteristic and uniformly decelerates as the table reaches the predetermined reference position. A vacuum assembly is used to provide a pressure differential across the table, the chuck assembly being electrically grounded to prevent interference with testing of wafers. Also described is an angular orientation system by which the rotation of the table may be controlled.
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