Laser induced recast and the formation of porous carbonized conductive micro-via on polymer thin film

Abstract

Laser micro-drilling of polymer substrate is widely used for multilayer interconnected circuits. In this study, an analytical model of the chopped-laser micro-drilling process on polyimide substrates was developed to elucidate the mechanism that leads to the formation of conductive porous structures on the surface of the micro-via. The results revealed that the conductive porous structure and its surface morphology at the orifice have resulted from a combined effect of thermal decomposition and thermocapillary recast effects, which are simultaneously affected by the attenuation of laser energy due to extinction by the soot and the augmentation of thermal impact due to micro-combustion at the orifice. Experimental results showed that the deformed area around the orifice is reduced with increasing chopped-laser frequency due to the reduced characteristic length of thermal diffusion. In contrast, the increased temperature gradient caused the maximum height of the porous structure at the orifice to become more prominent. A modified attenuation factor is proposed to simulate this dual laser-material thermal interaction resulting from the combined laser attenuation and micro-combustion augmentation on the polymer surface, the drilling speed, the size of the orifice, and the profile of the porous structure. The simulation results matched the drilling speed from experiments, and the maximum relative error in the overall profile of the drilled micro-vias was <11 %. The proposed multi-physics model effectively captures complex laser-material interactions, providing accurate predictions for surface morphology and micro-via dimensions essential for improving the quality of laser-fabricated multilayer 3D electronics, leading to sustainable manufacturing.