抄録
Increase in aspect ratio, the ratio of hole length to hole diameter, inevitably results in difficulties with micro drilling of multilayered printed circuit boards (PCBs) such as damage to inner walls of holes, drill breakage and reduction in yield rate and productivity. This paper presents the experimental analysis of a chip flow mechanism for micro drilling of typical composite material PCBs consisting of copper foil, woven glass fiber and polyimide resin, from the view point of the cutting force. Measurement of the cutting force revealed that a complex chip flow peculiar to composite materials results in a sudden increase in cutting torque and thrust, bringing about the above-mentioned damage. This damage can be diminished by smoothing the chip flow during drilling. As a result, through-holes with superior quality inner walls have been achieved, which are free from resin smear on the cut surface of the copper foil, tears at the drilling end, deformation of the copper foil and scoops on the inner walls.
