Welding between rough copper foil and silica glass using green femtosecond laser

The assembly of glass and copper micro devices is widely applied in modern manufacturing industries. Laser welding is an efficient technique. However, weld defects and instability resulting from the low laser absorptivity of copper remain significant challenges. Surface roughness also poses a limitation for optical contact during welding preprocessing. In this work, femtosecond pulse and green light from the second harmonic generation were combined to increase the copper absorptivity. The silica glass and rough copper foil were effectively welded. Under the optimized parameters, a maximum shear strength of 17.19 MPa was obtained. The electron and lattice temperatures during the welding process were simulated using two-temperature model. The microscopical mechanism, element diffusion, and chemical reaction were investigated. A modified region in the glass was formed due to excessive laser energy and scattered subsequent laser pulses. Cu–O-Si bonds were detected on the welds. Welding stability at various temperatures was characterized, with shear strength maintained at approximately 12 MPa after thermal cycling from 0 to 100 °C and heating at 150 °C. This study demonstrated that effective and stable welding of silica glass and rough copper foil can be achieved using green femtosecond lasers.