Low-Resistance Soldered Joints of Commercial 2G HTS Wire Prepared at Various Values of Applied Pressure

Abstract

In this study, we prepared soldered joints of 2G HTS wires from three different manufacturers: SuNAM, SuperPower, and SuperOx. We used Pb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">39</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">61</sub> solder and varied the pressure applied on the joint during soldering in the 3.9-10.5 MPa range. We found that for all samples, joint resistivity decreased with increasing applied pressure. Practically important, very low joint resistivity values in the 10-15 nΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> range were reproducibly achieved in joints made with SuperPower and SuperOx wire. Resistivity of joints made with SuNAM wire was rather high, in the 40-90 nΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> range. No degradation in I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> across joints occurred in joints made at up to 8 MPa applied pressure. In joints made with SuperOx wire at applied pressure above 8 MPa, there was I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation comparing to the initial I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of individual wires before joining. We speculate on the possible reasons for the different resistivity and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation behavior of joints made with wires from different manufacturers.