A reliable molding technique by using epoxy-based resin for thin-film superconducting quantum interference devices

A reliable package is necessary for superconducting devices fabricated with thin films and wirebonds to maintain stable operation and good performance of the devices. In particular, prevention of wirebond disconnection due to thermal cycles is very important. We have developed a reliable epoxy resin and molding technique, which works as a stable package at extremely low temperature. Using this resin to package low-Tc superconducting quantum interference devices (SQUIDs) with aluminum and niobium wirebonds, so far 94.2% of more than 1500 SQUIDs have shown no disconnection of wirebond after ten thermal cycles at 77 K plus once at 4.2 K. We also confirmed that this resin does not generate any magnetic noise and a SQUID can be detrapped with a magnetic flux through thermal conduction from a resistor packaged together with the SQUID.