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.

1. [1] J. Chae, S. S. Park, and T. Freiheit, “Investigation of microcutting operations,” Int. J. of Machine Tools & Manufacture, Vol.46, pp. 313-332, 2006.
2. [2] H. Watanabe, H. Tsuzaka, and M. Masuda, “Micro Drilling for Printed Circuit Boards – Influence of Radial Run-out on Characteristics of Micro Drilling –,” J. of the Japan Society for Precision Engineering, Vol.74, No.11, pp. 1204-1209, 2008. (in Japanese)
3. [3] T. Terabayashi, Y. Daikou, Y. Maeda, and M. Masuda, “Microdrilling of Printed Circuit Boards (3rd Report) – Non-contact Measurement of Small Cutting Torque Using Deformation of Thin-Walled Elastic Cylinder –,” J. of the Japan Society for Precision Engineering, Vol.67, No.6, pp. 927-931, 2001. (in Japanese)
4. [4] D. Bellinger, Ph.D., A. Leviton, M.D., C. Waternaux, H. Needleman, M. Rabinowitz, Ph.D., “Longitudinal analyses of prenatal and postnatal lead exposure and early cognitive development,” New England J. of Medicine, Vol.316, pp. 1037-1043, 1987.
5. [5] A. J. McMichAel, et al., “Port pirie Cohort Study: Environmental Exposure to Lead and Children’s Abilities at the Age of Four Years,” New England J. of Medicine, Vol.319, pp. 468-475, 1988.
6. [6] Water legal committee, “Water practical of six major laws Heisei 24 version,” p. 166, Corporation Gyosei, 2012. (in Japanese)
7. [7] H. Takeyama and E. Usui, “Machinability of Leaded Brass,” J. of the Japan Society for Precision Engineering, Vol.25, No.298, pp. 461-467, 1959. (in Japanese)
8. [8] O. Okubo, T. Aoyama, I. Inasaki, and T. Shimizu, “A study on the Cutting Tool Breakage and Its Prediction in Micro Hole Drilling,” Trans. of the Japan Society of Mechanical Engineers, Vol.51, No.471(C Series), pp. 2929-2935, 1985. (in Japanese)
9. [9] R. Heinemann, S. Hinduja, G. Barrow, and G. Petuelli, “The Performance of Small Diameter Twist Drills in Deep-Hole Drilling,” J. of Manufacturing Science and Engineering, Vol.128, No.4, pp. 884-892, 2006.
10. [10] T. Takagaki, T. Nikaido, and J. Tagami, “Nanostructural analysis with using focus ion beam systems,” The J. of the Japanese Society for Dental Materials and Devices, Vol.30, No.4, pp. 249-251, 2011. (in Japanese)
11. [11] H. Kubota and H. Tabei, “Drilling of a Small and Deep Hole Using a Twist Drill,” Trans. of the Japan Society of Mechanical Engineers, Vol.62, No.601(C Series), pp. 3691-3697, 1996. (in Japanese)