A GHz multi-channel cryogenic test fixture for superconducting integrated circuit testing

We have designed a cryogenic test fixture for functional testing of digital and analogue superconducting integrated circuits (IC) in the GHz frequency range. The test fixture consists of a ball grid array (BGA) chip carrier, a detachable BGA socket, a coaxial printed wiring board, and 40 long coaxial cables with SMA connectors. The chip carrier has a microstrip wiring and solder balls. On the chip carrier, a superconducting IC chip is connected using Al wire bonding. The wiring board has a coaxial wiring structure. The wiring characteristic impedance of the chip carrier and the print wiring board was designed to be 50 Ω. In the BGA socket, the BGA chip carrier is electrically connected to the printed wiring board using anisotropic conductive rubber sheet. The coaxial cables are connected to the printed wiring board with soldering. All parts of the system were made with nonmagnetic materials. The high frequency characteristics were partially evaluated by TDR measurement and vector impedance measurement at 4.2 K, 77 K and room temperature.