Probe plate assembly for high-node-count circuit board test fixtures

Abstract

A probe plate assembly for use in a circuit board test fixture is disclosed. First and second plates are mounted substantially parallel to one another and with a space between them. Probe pins are mounted to the first plate and oriented so that they can contact a device under test on the side of the first plate opposite the space. Electrical contacts are mounted to the second plate and oriented so that they can contact a test head on the side of the second plate opposite the space. Flexible conductors electrically couple the probe pins to the electrical contacts. In a disclosed embodiment, the probe pins are spring probes, and the second plate contains clearance holes disposed adjacent the spring probes. Each of the clearance holes has sufficient diameter to allow the socket tail of one of the spring probes to pass through it without substantial friction. The result is that forces from the test head are mechanically decoupled from the first plate, thus preventing bowing of the first plate. In a further disclosed embodiment, a spacer is disposed between and near the periphery of the first and second plates. The spacer may be one continuous gasket piece forming a vacuum seal around the perimeters of the first and second plates. The spacer, as well as the first and second plates, may be made of fiberglass. The first plate may be thinner or less rigid than the second plate and may alternatively be made, for example, of transparent plexiglass.