Abstract
This paper represents the drilling of dense printed circuit boards (PCBs) using microdrills. Although ultrahigh rotational drilling is known as empirically effective to improve tool breakage, it causes microdrills’ radial run-out as it has some disadvantages. Hence, the correlation between the radial run-out of drills and the hole quality was examined experimentally using 0.1-mm diameter drills at a rotational speed of 3 × 105 min−1. The drilling behavior at contact with a work surface was dynamically observed using a high-speed video camera. It was concluded that: (1) Orbital revolving drills with the radial run-out substantially move toward the centripetal direction, just after starting contact with a work surface. (2) The entry sheet effectively intensifies the centripetal action. (3) The radial run-out is insensitive to drill wear as well as hole quality, because of the centripetal action.
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