Head assembly for printed circuit board test fixture

Claim 1

In a head assembly for a vacuum actuated test fixture for a printed circuit board including a top plate having top and bottom sides and a perimeter, said top plate being adapted for receiving said printed circuit board in sealed relation thereon, a probe plate having a perimeter and having a plurality of test probes thereon, and support means for supporting said top plate in upwardly spaced relation to said probe plate and for sealing between said top plate and said probe plate so that said top plate is nevertheless downwardly movable toward said probe plate for effecting electrical contact between said test probes and said printed circuit board, the improvement comprising said support means comprising a rigid peripheral support member including a substantially horizontally extending support wall extending adjacent the perimeter of said top plate in downwardly spaced relation thereto, said support wall having a top side and being received in sealed relation on said probe plate, and resilient seal means between said top plate and said support wall extending along the perimeter of said top plate, said resilient seal means including a primary seal member received in sealed engagement with one of either the bottom side of said top plate or the top side of said support wall, and a resilient secondary seal member received in sealed engagement with the other of the bottom side of said top plate or the top side of said support wall, said primary and secondary seal members being positioned one atop the other and cooperating for supporting said top plate on said support wall, said primary seal member normally being maintained in spaced relation to said other of the bottom side of said top plate or the top side of said support wall by said secondary seal member, said secondary seal member being resiliently compressible to draw said primary seal member into sealed engagement with both the bottom side of said top plate and the top side of said support wall.