Quantifying thermal deformation upon ultraviolet nanosecond laser micro-drilling of copper foil

While laser micro-drilling is promising for metal foil patterning, the inevitably thermal deformation of metal foil under laser ablation significantly deteriorates the patterning accuracy. In the present work, we investigate the characteristics, mechanisms and suppressing strategy of thermal deformation in ultraviolet nanosecond laser micro-drilling of copper foil with a thickness of 100 μm by means of analytical analysis, numerical simulations and experiments. Specifically, an on-site measurement method based on laser displacement sensors is proposed and developed, which is used to dynamically monitor the deformation degree of ablated area in the on-going laser ablation process, thus providing experimental evidence of thermal deformation characteristics of copper foil. Subsequently, a thermo-mechanical coupled finite element model considering the instantaneous material removal is developed, through which the underlying mechanisms governing the thermal deformation of copper foil are elucidated, and an analytical model correlating internal stress distribution with deformation behavior is derived accordingly. Finally, a novel strategy for suppressing laser ablation-induced thermal deformation of copper foil by applying pre-tension force is proposed, the effectiveness of which is theoretically and experimentally demonstrated. And a critical value of pre-tension force for achieving the maximum reduction of 93.1 % of thermal deformation of copper foil is discovered. This work provides a feasible method to quantify and eliminate thermal deformation of copper foil under laser ablation.