Investigation of through micropatterns fabrication on C194 copper foil by ultraviolet nanosecond pulsed laser microdrilling

Abstract

While the lead frames of C194 copper alloy widely used in IC packages contain high density of through micropatterns, the method for realizing high precision manufacturing of the micropatterns on copper foil with thickness down to a few hundred micrometers is highly demanded. In the present work, we demonstrate the feasibility of manufacturing high density through micropatterns on C194 copper foil with high precision and high uniformity by using ultraviolet nanosecond pulsed laser microdrilling. Specifically, the absorption coefficient of C194 copper foil for 355 nm wavelength is experimentally derived, based on which the sublimation enthalpy of the material is calibrated by iteratively comparing predicted crater morphology by finite element simulations with experimental data. Then the multi-pulse laser ablation mechanisms of C194 copper foil are investigated jointly by finite element simulations and experiments, which derive the quantitative correlation of ablation crater depth with laser ablation parameters. Finally, high density arrays of through micropatterns with high dimensional accuracy and high uniformity are fabricated on C194 copper foil with a thickness of 100 μm by the proposed ultraviolet nanosecond pulsed laser microdrilling with theoretically predicted repeat scanning number. Furthermore, the effect of pickling on surface quality and resistance of the manufactured copper lead frame is addressed. This work provides a feasible method for manufacturing copper alloy lead frames with high precision through micropatterns in an environmentally friendly manner.