Laser induced carbonized nanoporous micro-via on polymer thin films for double sided flexible electronics

Laser micro-drilling of polymer substrate is a widely used technology for multilayered interconnected and Flexible Printed Circuit (FPC) boards. Instead of using ultrafast pulsed laser, chopped continuous-wave laser provides an advantage in greatly reduced cost of equipment and processing. In this study, detailed experimental and numerical analysis of the chopped-laser micro-drilling process on polyimide substrate was conducted. The transient temperature and structure variation during the drilling process were analyzed with a model that included heat transfer, material removal and the deformation of a polyimide film surface exposed to laser heating. The formation and morphology of the porous structure at the orifice of the drilled-hole in the polyimide film was attributed to a combination of thermal-decomposition and a thermocapillary recast effect. The maximum relative error in height deformation and diameter variation of the drilled holes was less than 10%, which demonstrated the effectiveness of the proposed model for laser micro-drilling of polymer thin films.