Ultrafast copper bonding joints: an optimised method for connecting REBCO tapes and their bonding characteristics

Abstract Using the warm pressure welding method for copper bonding joints facilitates direct bonding between the REBCO copper-stabilised tapes without solder and under atmospheric conditions. In this study, based on our previous work, we propose an optimised method for fabricating ultrafast copper bonding joints. By pretreating the tape for 5 s and bonding at either 100 °C under 354 MPa or 200 °C under 125 MPa for only 1 s, well-bonded copper bonding joints can be effectively fabricated. The typical resistance of ultrafast copper bonding joints is 12 nΩ·cm 2 ; this value is approximately 30% lower than that of traditional copper bonding joints and less than approximately half that of soldered joints. Additionally, the mechanical performance of ultrafast copper bonding joints under axial tension is comparable to that of soldered joints. Compared with those of conventional copper bonding methods, the bonding time, bonding temperature, and bonding pressure are significantly lower. The resistance of a 1 m long copper bonding joint made by this method is as low as 0.23 nΩ at 77 K. In this work, the influences of four essential factors, namely, the flux selection, set temperature, set pressure, and bonding time, on the production of well-bonded copper bonding joints are further investigated.