Study on Electromechanical Properties of Solder Jointed YBCO Coated Conductors With Etched Copper Stabilizer Under Axial Tension

Sintering Nano-Silver Paste by Resistive Joule Heating Process for 2G HTS Tape Joints

“…The samples in the third show property of low I c retention percentage (<80%), indicating that their HTS superconductivity was affected by the relative high temperature process and some oxidation has occurred on the tape surface, which was observed in the test sample heated at 250 • C (furnace heating) (Figure 4c). Generally, some studies [9,13] have suggested a heating temperature below 250 • C can avoid the low I c retention percentage problem of the 2G HTS tape. Our heating temperature was below 250 • C, but two samples are still found in this block.…”

“…However, the Sn-alloy formed Cu 6 Sn 5 and Cu 3 Sn IMC (intermetallic compound) on the cupper-solder interface at a temperature as low as 125 • C. The formation of IMC reduces the reliability of joints used in high power electronics for operations carried out over long time periods [32]. Most studies [9,10,33] have reported that the HTS joining process using Sn-alloy solder is heated at 190-230 • C, which means that the IMC will form at the solder-Cu interface. The use of the indium foil as solder has shown relatively low specific resistance; however, this may be due to the high compressive stress of about 100 MPa that was used [11].…”

“…According to previous studies, there are three types of joining processes: the solder joint method, the diffusion joint method, and the superconducting joint method. The solder joint method uses low melting point solder, such as Sn-alloy, to join (weld) the 2G HTS tapes; the specific resistance of the joint is about 0.02-1 µΩ•cm 2 [8][9][10][11][12][13]. The diffusion joint method requires a relatively high temperature and compression pressure to cause inter-diffusion at the joint, such as Cu or Ag of the protective layer of 2G HTS tape, with the specific resistance of about 0.067 µΩ•cm 2 [13,14].…”

“…For the solder joint method, Huang et al [9] used Sn 36 Pb 37 as the solder for the 2G HTS tape joining and sintered at 190 • C with a bonding pressure of 10MPa; the specific resistance of the joint was about 0.034 µΩ•cm 2 . He also mentioned that if the thickness of the copper protective layer of the wire is reduced (from 20 µm to 5 µm) through a proper etching method, the specific resistance of the joint would be reduced to about 0.025-0.027 µΩ•cm 2 without affecting the superconducting properties of the 2G HTS tape.…”

Thermal Cycling of (RE)BCO-Based Superconducting Tapes Joined by Lead-Free Solders

“…They experimented with different joint geometries and surface preparation processes, with and without application of pressure during the soldering process. In their follow-up study [ 14 ], they also investigated the mechanical properties of joints (tensile stress); similar measurements were published by [ 11 ], in which they found that etching out the SCT Cu stabilizer reduced both the R j. A j and I c degradation upon axial load.…”