Through-Hole Drilling of Flame-Retardant Polyester-Based Films Using a Short-Pulse CO2 Laser

Through-hole drilling of a 200-µm-thick flame-retardant polyester-based film was investigated using a short-pulse CO2 laser with a pulse width of 304 ns.Percussion drilling was performed at a repetition rate of 200 Hz and a fluence of 10.7 J/cm 2 per pulse.Two irradiation methods were examined.One was conventional continuous irradiation, referred to as Continuous Irradiation in this paper.The other was a method referred to as Divided Pulse Train Irradiation.In this method, a sequence of laser pulses (a pulse train) is followed by a certain time interval before the next pulse train is delivered.The minimum number of pulses required to form a through-hole was 75 in Continuous Irradiation, whereas only 4 pulses were sufficient in Divided Pulse Train Irradiation.In this case, 2 pulses were applied in the first set and 2 in the second set, with a time interval of 0.5 ms or longer.Discoloration was observed around the hole in Continuous Irradiation but was absent in Divided Pulse Train Irradiation, suggesting that thermal effects were effectively suppressed in the latter.