Percussion drilling of polyimide using VUV and UV solid state lasers

Percussion drilling of blind holes and vias in Kapton® film was investigated using Q-switched solid state lasers operating at UV (355nm) and VUV (266nm) wavelengths. Holes were analyzed using different methods such as scanning electron microscopy (SEM) and surface profilometry. Ablation rates for the two wavelengths are compared. No abrupt thresholds were found and there was no evidence of an incubation effect within the first few pulses. Introducing pauses during the drilling increased the number of shots required for perforation of the film. The effects of fluence on diameter, depth and taper of the holes are presented. Smaller and neater holes are achieved more accurately with a lower fluence. An observed skin effect brought about by long exposure to low fluence VUV laser light is also discussed.