Etching of polyimide by a Q-switched CO2 laser

High-speed etching of polyimide films used as insulators for multi-layered printed circuit boards has been investigated using a Q-switched CO2 laser tuned at 9.3 mu m. A mechanical chopper inserted in the cavity realizes the Q-switching operation. The pulse repetition rate of the laser is as high as several tens of kHz, so that continuous processing of certain width is possible without beam aiming to each hole. The laser beam is scanned by a galvano-mirror and then focused to the work by a telecentric lens. Metal layer on the top of the printed-circuit board is used as a contact mask, and it works as a multi-reflector in conjunction with a reflector placed above. Multi-reflection increases the processing speed by a factor of 2.5. Overall processing speed is 1.5 m/min for 0.1 m width or 0.15 m(2)/min.