Flexible cryo-packages for Josephson devices

We have developed a method of bonding superconductive integrated-circuit chips to interchangeable, microwave-compatible, flexible cryo-packages. This "flip-chip on flex" technology will greatly improve the service life and reliability of our Josephson systems because the present press-contacts to the chip are replaced with directly soldered connections. The new method eliminates the most common failure mode for our Josephson chips, which has been the degradation and variation of the contact resistances of the chip pads due to mechanical wear upon repeated thermal cycles from 4°K to room temperature. The superior microwave properties of this packaging provide improved operating margins for our devices. We have demonstrated the reliability of the bonds with repeated thermal cycling for 100% operational chips with 40 connections (67 410 Josephson junctions).