Femtosecond Laser Drilling of Alumina Wafers

The topography, radial spread, and chemical composition of the slag produced during percussion and trepanning hole drilling techniques using femtosecond laser were investigated. Results of analyses by optical microscopy, scanning electron microscopy, and energy dispersion spectroscopy are presented. While there were no significant differences in the average ablation rates observed when a near infrared femtosecond laser was used, when compared with the ultraviolet nanosecond laser ablation of alumina (Al 2 O 3 ) ceramics, that of the femtosecond laser provided much cleaner holes. There was an absence of particulates due to re-solidification of molten material around the periphery of the hole. The slag consisted of ultrafine powders formed during condensation of the supersaturated ablation plume. This slag can easily be removed in an ultrasonic bath with a mixture of acetone and water. In combination with trepanning hole drilling, the femtosecond laser produced micro-via holes, in alumina wafers, that were free of cracks and re-cast molten material.