An evaluation of Cu-to-Cu ultrasonic welding bond through thermal cycling

Abstract:
This paper comments on an ultrasonically welded copper busbar terminal to a copper substrate in a power module through thermal cycling. Welded samples were subjected to rapid cycling conditions to better understand the structure of the welds and their failure mechanism. At regular thermal cyclic intervals, the samples were evaluated with 3D X-ray tomography and electron backscatter diffraction (EBSD) to evaluate the microstructural changes. The tomography results show that the busbar continues to maintain its strength and no significant changes are seen until 1500 cycles. The potential significance of changes in grain morphology visible after 1500 cycles is discussed and correlated with the tomography results to help explain the damage observed.