Electrical performance of high density probe array for testing Josephson circuit chips

An assembly has been constructed and successfully evaluated for contacting 228-pad Josephson test chips. Miniature spring contacts mate with the 228, 100 μm diameter pads arranged on 200 μm centers in a double row about the edge of a 6.35 mm chip. Measurements have been made at 4.2K of contact reliability, resistance, self and mutual inductances, and current capacity. Experimental values of electrical characteristics compare well with computer simulations. This probe array is being incorporated into a non-magnetic cryoinsert for Josephson chip testing. The design uses materials such as pyrex, molybdenum, silicon, machineable ceramic, and aluminum to be consistent with a microgauss ambient magnetic field.