Abstract

Laser drilling is the most efficient noncontact material removal process. In this research project, a simplified approach using "dual focus" has been proposed to improve the aspect ratio of the drilling. Dual focus drilling not only changes the kerf angle but also increases the depth of drilling due to redistribution of the intensity in the overlapping focusing region. The dual focus is achieved by focusing two wavelengths at two different foci along the optical axis, using a single lens. A theoretical study of dual beam propagation along the optical axis was done for the selection of the radius of curvature of the lens to achieve continuity within the two focusing regions to increase the aspect ratio. Modeling has been done with numerical approach to understand the impact of intensity distribution and optical parameters on the efficiency of dual wavelength drilling. Objective of the research work is to optimize the laser as well as optical parameters theoretically as well as experimentally with respect to dual wavelength drilling for obtaining high aspect ratio drilled holes with minimum power. The microdrilling station was setup with second harmonic generation to achieve dual wavelength with maximum conversion efficiency of 20%. Experiments were done individually with laser wavelengths of 532nm and 1064nm and with focusing both these wavelengths using a single lens at different pulse energies, on 500om thick silicon wafers. SEM observation of results proved that dual frequency drilling is more efficient compared to conventional drilling and results show excellent agreement with the results from the theoretical model.