Ultralarge-taper microhole arrays in polyimide films fabricated via UV picosecond laser spiral scanning with sequential coupling to fixed-point pulsing

As a polymer material, polyimide (PI) features high-temperature resistance, excellent electrical insulation, high mechanical strength, and stable chemical properties, making PI processing technologies highly promising for a wide range of applications. This study investigates the ablation characteristics of PI films under ultraviolet (UV) picosecond laser irradiation, focusing on the effects of laser pulse repetition frequency on the ablation and carbonization behavior of PI. It is found that the higher the pulse repetition frequency, the more severe the degree of ablation and carbonization of PI. Both photothermal and photochemical ablation mechanisms are observed during laser processing of PI. A novel laser spiral-scanning processing technique, termed sequentially coupled fixed-point pulsing, is proposed and systematically studied to fabricate high-quality tapered microhole arrays. The relationships among hole morphology, hole-wall quality, scanning speed, and spiral pitch are investigated, and the spiral-scanning processing method significantly reduces carbonization on the PI film surface. Ultralarge-taper microhole arrays with entrance diameters of 40–60 μm and exit diameters of 2–4 μm were fabricated on 25-μm-thick PI films, with no detectable changes in the composition and content of the material in the processed area.