Test fixture with adjustable bearings and optical alignment system

Abstract

A test fixture for testing circuit boards has a vacuum chamber between a stationary probe plate and a movable top plate. Separate adjustable linear bearings located in quadrants of the fixture provide parallel alignment between the top plate and the probe plate. A continuous vacuum seal between the probe plate and top plate bypasses the bearings so the bearings are outside the vacuum area. Spring loaded test probes in the probe plate extend through holes in the top plate for access to a circuit board under test. The probes contact the board when the top plate moves down toward the probes under a vacuum. The top plate is secured to the probe plate by separate quick-release latch pins extending through the linear bearings. The moving top plate carries fixed tooling pins for mounting the board to the top plate. Movable bearing blocks support the bearings. The top plate is movable for aligning the board with the test probes. The top plate, latch pins, bearings and bearing blocks are movable as a unit relative to the probe plate. After the top plate is aligned with the probes to compensate for art shift among circuit board lots, the quick-release latches are engaged to retain the alignment. The latches are part of a guide post assembly for guiding vertical travel of the top plate during vacuum cycling of the test fixture. An optical alignment system in combination with the movable bearings provides a quick and easy means of aligning the board and the probes with extremely high accuracy.