Improvement of Chip Evacuation in Drilling of Lead-Free Brass Using Micro Drill

As the miniaturization of integrated circuits has progressed, the penetration holes of bonding jigs have become smaller. However, micro drills have a tendency to break when drilling small holes with high aspect ratios. Moreover, to reduce the impact on the environment, there has been a recent trend towards the use of lead-free brass as jig materials, but these are very difficult to drill. In the present study, small holes are drilled in lead-free brass using a micro drill, and the effects of web thinning, the helix angle, and the nick geometry on chip evacuation are investigated. The results indicate that drills with a helix angle of 15° have the longest tool life. The formation of a nick on the cutting edge is found to help decrease the thrust force during deep drilling. A drill with a relatively shallow nick perpendicular to the cutting edge have excellent chip discharge performance, and its cutting force is stable. Nick treatment effectively decreases the thrust force at a deep drilling position.