LASER BEAM PROCESSING METHOD

PURPOSE: To form a via hole of a desired depth and diameter at a multilayered wiring board with good accuracy by concentrically irradiating this wiring board with a laser beam and detecting the main peak of the intrinsic line spectrum generated in an inner layer conductor formed with this hole. CONSTITUTION: The boring of the surface layer and org. insulating layer of the multilayered wiring board is started by concentrically irradiating the surface of the front layer copper foil of the wiring board with the laser beam. The line spectrum intrinsic to the inner layer conductor material is generated when the laser beam arrives at the surface of the inner layer conductor. Only the desired spectrum is taken out of this plasma emitted light by a band-pass filter 7 via dichroic mirrors 4, 4', is photoelectrically converted by a photodetector 9 through a condenser lens 8 and is inputted to a main controller 10. The inputted data is analyzed by every shot of the laser beam and the number of the times when the line spectrum which is the intrinsic main peak value exceeds the set threshold value is measured. A processing stop signal is outputted when the measured number of times attains the set number of times. The processing end point is determined and the processing of the via hole is ended by this signal.