Abstract
I. INTRODUCTION With the recent improvement in the performance and miniaturization of computers, communication equipment, and various other pieces of electronic apparatus, multi-layer printed-circuit boards have attained wide usage. The need for drilling such boards has been increasing. A multi-layer printed-circuit board used in the computer is usually provided with 2,000 to 3,000 holes 0.5-0.9 mm in diameter, each made by a NC high-speed automatic drilling machine. It is estimated that the number of holes made for the drilling of printed-circuit boards might well have reached 200 billion in 1971. Drilling printed-circuit boards is accomplished by using a drill, a punch, a laser beam, an electron beam and liquid jet, or by other methods. It is considered that the use of a drill is most suitable from the point of view of surface quality of drilled holes, reliability of their plating through holes, workability, and so forth.
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