Characteristics of drill damage and hole quality in microdrilling of printed circuit boards

The present paper investigates the characteristics of drill damage and hole quality when microdrilling printed circuit boards consisting of laminated layers of glass-fibre reinforced resins and copper. A CNC-based microdrilli ng apparatus is developed for this purpose. It is found that the feed patte rn and feed rates play an important role in the efficiency of the drilling. An optimum cutting feed rate satisfying the minimum-cost criterion is eval uated using the Taylor tool-life equation. To investigate hole quality a me thod of measuring instantaneous drill temperature is proposed and temperatu re rise is compared with a finite-element result. The maximum temperature i s Limited to below 150 degrees C because the copper inserted between the ep oxy layers plays an important role as a good heat sink. An SEM observation and the temperature consideration lead to the conclusion that resin smear d oes not take place under the recommended cutting conditions.