Laser drilling of AlN ceramics using nanosecond pulses

Laser drilling of aluminum nitride (AlN) ceramics by 6 ns SHG (lambda = 532 nm) Nd:YAG laser pulses is studied. The drilling rate, quality of the holes, and the effects related to plasma formation are investigated. Numerical model based on the heat-transfer equation is developed to describe the drilling process. Different mechanisms of material decomposition are found to be realized, which depend on the laser fluence. They determine the quality of the holes produced. Below 5 GW/cm(2) the material ejection is realized by decomposition of ceramics into sold or liquid Al and gaseous N-2. The letter blows away clusters and flakes from the irradiated area and the holes drilled have irregular shape. At higher laser intensities, the decomposition into gaseous Al and N-2 or direct evaporation of the ceramics results in good hole quality. A saturation of the ablation rate as a function of the laser intensity is observed above 15 GW/cm(2). The calculated depths of the holes drilled are in agreement with the experimental data when absorption of the laser radiation from the plasma plume is taken into account.