Femtosecond laser-based surface gold removal and its applications in flip chip bonding

Femtosecond laser processing was utilized to thin Au platings from 3.0 μm to 0.3 μm. This study investigated the effects of processing parameters on thinning quality. Results demonstrate that laser processing significantly improves solder wettability, achieving an average spreading coefficient above 95%. It also homogenizes solder joint composition and effectively controls intermetallic compound (IMC) growth, reducing its thickness by over 75% after 500 h of aging. The process suppresses brittle Pb-rich layer formation and curbs void growth, maintaining a void ratio below 1.0% and doubling the shear load after aging. Fracture analysis confirms maintained ductility. This study demonstrates a femtosecond-laser-based localized interfacial engineering strategy for thick-Au pads, in which localized Au reduction primarily suppresses excessive Au–Sn interfacial reactions, while the laser-induced micro-groove topology improves solder spreading and local interfacial contact.