Gallium-effect in a Lead-Free Solder for Silver-Sheathed Superconducting Tape

Solder joints of silver-sheathed superconducting tapes are promising for various commercial applications. In this research, Pb, Ga, and Ga-doped lead-free Sn–Ag–Cu solders are used to study the gallium effect for the low joint resistivity with silver-sheathed DI-BISCCO type H tapes. In Ga-doped Sn–Ag–Cu solder, a smooth interfacial Ag2Ga layer is uniformly formed on the Ag-sheath surface. As a result, the solder joint achieved a very low joint resistivity of 16 nΩcm2 at 40 K. The present gallium-doped lead-free solder can also be applied to general soldering use with Ag materials.