Size Effect of Drill Bit on Coupled Vibrations during High Speed Micro-Drilling Process of Composite Printed Circuit Board

This paper presents a comprehensive method to consider the size effect of the drill bit on the lateral and torsional vibrations of micro-drill tool accurately. Based on the Euler angles, and Lagrange’s equation, the dynamic micro-drilling spindle model including micro-drilling tool is derived. To express more realistic behaviors of the model, the Timoshenko beam model is employed. The dynamic responses of the micro-drill tool are obtained by utilizing the finite element method and Newmark’s method. The influences of the drill bit with high length to diameter are investigated in three cases as 15:1, 18:1, and 20:1 using the same 0.1 mm diameter drill at a rotational speed of 5×104 rpm during air cutting and cutting of the 6-layer FR-4 composite board. The hole-quality is used to discuss the influences of those drill bit aspect ratios.