Drill breakage is one of the dominant factors in micro drilling performance for printed circuit boards (PCBs). PCBs are composite material, and it makes drilling behavior more complicate in the chip formation and evacuating mechanism, which might correlate with drill breakage. This paper presents experimental analysis of a chip evacuation behavior in dependence on drill wear and cutting torque, focusing on copper foils, woven glass fiber and fillers. Evacuated chips during drilling PCBs were observed using a high-speed video camera, and evacuating criteria of chips were discussed. These were examined using φ0.25mm drills at a rotational speed of 16×10
4min
-1. The conclusions obtained are as follows. As regards chip formation and evacuating behavior, a) cutting torque has a strong correlation with chip evacuation. Chip evacuation is getting worse gradually to increase cutting torque through the elapse of drilling. b) When chips are frozen in a deeper hole, it results in drill breakage by the cutting torque beyond drill strength. As regards influence of composite materials, a) glass cloth is one of the dominant factors in drill wear. And drill wear deteriorates chip evacuation. b) External copper foils scarcely affect drill wear, but they bring chips freezing to increase cutting torque. c) Harder filler silica increases drill wear, and chip evacuation deteriorates. Though easy-to-vaporize aluminum hydroxide causes scarcely drill wear, it generates freezing chip evacuation and makes maximum cutting torque increased.
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