Understanding the mechanism of ultrasonic vibration-assisted drilling (UVAD) for micro-hole formation on silicon wafers using numerical and analytical techniques

This study investigated the mechanism of UVAD using numerical and analytical techniques. Silicon wafers possess challenging cutting properties due to their inherent brittleness and susceptibility to cracking along specific crystal orientation. Hence, non-traditional cutting methods like UVAD hold promise for precision micro-hole drilling in silicon wafers. In order to comprehend the mechanism of UVAD, the numerical technique utilized a direct brittle micro-cracking model within a 2D finite element (FE) method. This facilitated a comparative analysis between conventional drilling (CD) and UVAD, with a specific focus on understanding the micro-cracking mechanisms during the mechanical process. This study examined primarily the cutting force, micro-fracture analysis, and cutting energy. The numerical technique effectively predicted micro-cracks within the brittle regime, a task that is challenging to accomplish using analytical methods alone. In parallel, an analytical technique was developed to predict brittle-ductile transition (BDT) lines by analyzing the thrust force and specific cutting energy (SCE), combined with the numerical technique. Various feed rates per revolution were tested to validate the analytical force predictions. The analytical results demonstrate that the force profile corresponds to the transient cutting depth, while the numerical results indicated that the direct brittle micro-cracking model effectively demonstrated the fracture mechanisms, particularly at greater depths of cut. The SCE graph can predict the formation of a ductile regime on the cutting surface of the drilled micro-hole, although predicting micro-fractures on the side edges of the drilled micro-holes remains challenging. Additionally, UVAD demonstrated a reduction in micro-fractures on the sides of drilled micro-holes, particularly at very low feed rates per revolution.