Through-Hole Drilling of Polyimide Films Using a Short-Pulse CO₂ Laser and Vapor-Absorption-Based Water Assistance

In the processing of resin materials using CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers with wavelengths of 9-11 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex>, excess thermal effects such as carbonization and melting present significant challenges. This study demonstrates a reduction in the heat-affected zone (HAZ) size during hole-drilling of polyimide (PI) films using a short-pulse CO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser combined with a novel yet simple water-assisted method. The proposed method involves placing water beneath the film sample and irradiating the sample with multiple laser pulses, as shown in Fig. 1(a). Once a through-hole is formed in the film, subsequent laser pulses interact with the water beneath the film. This interaction causes water to evaporate, dispersing water vapor or tiny droplets onto and above the sample surface. The water vapor absorbs laser energy, suppressing heat generation in the sample and preventing the expansion of the HAZ.