Joining of Bi-2212 high-Tc superconductors and metals using indium solders

Abstract

BSCCO tubes can be used as a base material for switching devices such as superconducting fault current limiters (SFCLs) that prevent an electrical problem from occurring in an electrical power system. To apply an BSCCO bulk tube to a switching device, the superconducting tube has to be joined with a metallic part to by the over current to the metal part when the FCL is quenched.In this study, joining between Cu–Ni alloy and BSCCO was accomplished by soldering using In–Sn and In–Bi solders. Additionally, an Sn–Ag–Cu/In–Bi solder was used for the soldering of a different kind. For a better joining of the BSCCO superconductor with the In–Bi solder, the surface of the BSCCO was pre-coated with Ag by electro-plating. From the experiments, an intermetallic compound (IMC) of AgxIny chain was observed to be mainly formed from In–Sn and In–Bi soldering process. In case of the soldering of a different kind, IMC of AgxIny and CuxSny was also developed. Finally, we confirmed that the properties of soldering were enhanced by Sn–Ag–Cu/In–Bi twice-soldering process.