[WBP1] Conductor Processing & Evaluation

[WBP1-25] [WBP1-25] Thermal Analysis of Solder-Free Sonic Welding Process Using Finite Element Method

*Shinya Sera¹、Takanobu Kiss^1,2、Zeyu Wu¹、Kohei Higashikawa^1,2  (1. Dept. of Electrical Engineering, Kyushu Univ. (Japan), 2. Research Institute of Superconductor Science and Systems, Kyushu Univ. (Japan))

Keywords:

REBCO CC,Sonic Welding,Solder-Free,Low resistive joint

A reproducible low-resistance joint technique is indispensable for the practical application of REBCO coated conductors. Sonic welding enables direct bonding of the surface metallic layers within a short time, offering excellent low-resistive performance and workability. Conventional approaches, however, need to employ intermediate metals such as solder or indium in order to achieve low joint resistivities of 32–39 nΩcm². In contrast, by controlling process parameters precisely such as the input energy E and power P, we achieved a solder-free sonic welding process that achieved a minimum joint resistivity of 17.3 nΩcm² without any degradation of the critical current I_c. We found also that increasing P can further reduce the resistivity, but simultaneously it leads to degradation of I_c. To understand the sonic welding process more in detail and to clarify the mechanism of the joint degradation, it is inevitable to study thermal behavior in the joints during the welding process. In this study, we have performed a thermal analysis of the sonic welding process using the finite element method and studied the influence on joint performance. The analysis revealed that the maximum temperature increases linearly with peak power P, while input energy E also causes a slight increase in the maximum temperature. These results suggest that when the maximum temperature during sonic welding exceeds the thermal tolerance of REBCO, I_c degradation occurs due to thermal damage. Therefore, ensuring that the maximum temperature remains below the tolerance level is crucial for obtaining reliable joints.