Effect of terminal surface design on bond quality in ultrasonic copper wire welding

Abstract

This study presents a design-oriented experimental investigation of ultrasonic welding between 95 mm² EVR252 copper wire and copper substrates with different terminal surface geometries. Several machined surface designs including flat, curved, angled and half-square configurations were evaluated to examine how terminal geometry influences contact conditions, deformation behavior, and joint performance under identical welding parameters. Mechanical and microstructural characteristics of the welded joints were assessed using tensile testing, Vickers microhardness measurements, optical microscopy, scanning electron microscopy (SEM), laser ultrasonic inspection and energy dispersive X-ray spectroscopy (EDS). The results show that the half-square surface configuration (UHS) exhibited the highest tensile strength, reaching 6876 N, an improvement of approximately 262% compared with the reference flat substrate (UOS). SEM observations indicate that the improved joint performance of UHS is associated with enhanced wire confinement, increased effective contact area and improved interfacial continuity. In contrast, joints produced on the flat substrate exhibited more pronounced voids and discontinuities at the interface. EDS analysis revealed differences in elemental signal distribution at the joint interface, which qualitatively reflect variations in interfacial contact conditions among different surface designs. Overall, the results demonstrate that terminal surface geometry plays an important role in influencing ultrasonic welding performance by modifying contact conditions and deformation behavior, providing practical insights for terminal design optimization rather than proposing a new welding mechanism.