Determining the machining parameters for femtosecond laser helical drilling of aluminosilicate glass substrate

In this work, a new laser helical drilling method with high geometrical accuracy is proposed for aluminosilicate glass (ASG) substrates. Laser drilling was performed from the bottom of the substrate to reduce the taper angle. The 400 mu m-thick ASG substrates were drilled via a femtosecond laser beam with a wavelength of 1552 nm and a pulse duration of 800 fs. By applying this newly suggested method, thru-holes can be produced with a high roundness accuracy that is less than 20 mu m, a small taper angle, low surface roughness of the sidewall, and high quality laser-drilled edges without cracks or chippings for hole diameters of 0.5, 1, 2, and 3 mm. Correlations are proposed between laser drilling parameters, such as ablation depth, scanning speed, vertical motion speed, and helical layer pitch, each of which are critical variables in drilling thru-holes in ASG substrates. Good surface quality of thru-holes can be experimentally obtained using the machining parameter values estimated by the proposed theory.