It has been required that the packaging density of PWB(Printed Wiring Boad)is improved because high packaging density technology has allowed downsizing. Therefore, high-quality micromachinings are necessary for PWB. Especially, it is necessary that a great number of through-holes have to be drilled with high reliability to make a circuit. So it is required to improve the quality of the drilled hole. However, it is inevitabole that the quality of the drilled hole is varied owing to the wear of the cutting edge in a great number of drilling. In this paper, it is shown that the shape of the cutting edge is related to the damages around the drilled hole. And the internal damage, the surface roughness and the smear of the drilled hole are increased, as the number of drilled hole is increased. Additionally, it is cleared how the variation of edge shape due to diamond coating affects the drilled hole quality.
