Ultrasonic-assisted wetting behaviors of Sn solder on (111) nano-twinned Cu electroplating films for UBM

Excellent wetting performance is critical to achieving reliable Cu/Sn interconnections. By optimizing the microstructure of the under bump metallization (UBM) layers and incorporating ultrasonic assistance, the solder-free wetting performance of Sn on Cu surfaces can be significantly enhanced. Experimental results demonstrate that electroplating can be employed to fabricate nanotwinned Cu (Nt-Cu) coatings with preferred orientations along (111) and (220) crystallographic planes. The (111)Nt-Cu surface exhibits the optimal wetting performance for Sn. Furthermore, the application of ultrasonic energy leads to a notable improvement in low-temperature wetting behavior, accompanied by the intermetallic compound (IMC) growth being detached from the interface and the distinct cut-off region characteristics appearing in the three-phase zone.