Katsuhiro Minamida

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 micrometer. 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 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 m2/min.

Development of Optical System for Controlling Spatial Profile of Laser Beam.

A new optical system for controlling spatial profile of laser beam has been developed. The principle of the system controls independently transverse and longitudinal diameters of the laser beam. The system consists of cylindrical mirrors and integration mirrors which focus the beam in directions perpendicularly intersecting with each other. In order to investigate the focusing property of the optical system, a calculating model for predicting beam paths through the optical system has beendeveloped using the ray tracing method. According to the model, three typical optical systems for a line shape focused beam have been designed-(1), two cylindrical mirrors, (2) one cylindrical mirror and one integration mirror, and (3) one cylindrical mirror and one integration mirror with convex segments. After laser heating experiments of steel by using these optical systems, it has been proved that they are useful in actual industrial applications.