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.
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