A solid-state UV laser was used to make arrays of reproducible percussion-drilled micron-sized holes in polyimide. An optical switch was employed as a pulse picker to select specific patterns of pulses from the high repetition rate laser beam. The ability to control and vary the number of pulses per burst and the time between bursts enhanced the drilling rate while minimizing thermal damage around the holes. The optimum pulse patterns were determined experimentally. A photodiode acted as a breakthrough sensor to end the drilling and optimize the exit hole size and quality. Results were compared with computer simulations of the drilling process based on modeling of the laser/material interaction.
Polymers play an important role in many applications such as microelectronics and medical devices. Micro-channels and shaped holes can be produced by 2.5D micro-structuring with excimer laser sources using mask projection. The industrial cost associated with these processes can be greatly reduced by the use of solid-state lasers due to their lower cost and maintenance. For this purpose, we investigate the interaction of polyimide (Kapton) with solid-state lasers emitting in the UV (266 & 355 nm) spectral range. The study presents a comparison of the ablation profiles obtained for different laser sources and these are discussed in term of roughness and efficiency. Limitations on the actual motion system (scan-head) are evident and the need to control the material removed by a small Gaussian beam in terms of overlapping for the direct writing process will be highlighted.
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.