Design of a modular, mixed-speed, general-purpose test probe

The authors describe a modular, mixed-speed, general-purpose probe designed and used for the testing of integrated circuits and devices at cryogenic temperature. Modularity is emphasized for flexibility, ease of repair, and construction. The key feature of this probe is the use of a microstrip flex circuit with plated-thru-holes and plated-up copper/gold bumps at the chip-pad locations, both of which help reduce inductive discontinuities between chip and second-level packaging. The chip is mounted face down onto the bumps and held in place by an alignment plate and spring assembly. Little or no soldering occurs between any of the modules: flex circuit, coax cables, coax-to-microstrip launch, twisted-pair wiring harness, and alignment/spring assembly. Swept frequency response measurements and time domain reflectometry were carried out on three different flex circuit designs and two different coax-to-microstrip launch designs. Magnetic contamination, if any, was below the resolution of superconducting quantum interference device (SQUID) and junction arrays placed on the chip.<>