Esd protection for universal grid type test fixtures

Abstract

A test fixture provides ESD protection to electronic switching circuitry in a universal grid type fixture having test probes arranged for electrical contact with a printed circuit board under test and in which test signals are sent between the circuit board and a high speed electronic test analyzer through intervening switching circuits. The test fixture includes a movable probe plate, a test probe mounted in the probe plate, the test probe including a movable plunger for making electrical contact with a printed circuit board during a test cycle, the plunger being movable between a first position and a second position, and a ground plane on the movable probe plate connected to electrical ground, the probe plunger having a ground plane contact element that contacts the ground plane in said first position of the plunger and which moves out of the contact with the ground plane when the plunger moves to the second position. The probe plate, is moved to a pre-test position in which the plunger is in the first position and in an electrical contact with the circuit board so that electrostatic charges on the board are dissipated to electrical ground through the ground plane via contact between the ground plane contact element of the plunger and the ground plane. The probe plate is moved to a test position after a preset time delay in which the plunger is compressed under a test force that moves the plunger to the second position out of contact with the ground plane to electrically isolate the plunger for conducting the test after electrostatic charges have been dissipated.