Determining the Machining Parameters for Femtosecond Laser Helical Drilling by Effect of Chemical Composition of Glass Substrates

Abstract

This work proposes a new femtosecond laser helical drilling method with a high geometrical accuracy for various glass substrate materials. This new helical drilling method was performed from the bottom of the substrate with water flow for the increase of roundness accuracy in thru-holes. The theoretical correlation between the machining parameters is presented and experimentally investigated. The femtosecond laser at a wavelength of 1552 nm with a pulse duration of 800 fs was adopted in the experimental system. The used glass substrates were an aluminosilicate glass (ASG) substrate, a soda-lime glass (SLG) substrate, and a borosilicate glass (BSG) substrate. By applying this suggested method, thru-holes in each glass substrate can be fabricated with good surface qualities, such as small taper angle, no cracks, and no chippings. This work intensively investigates the characteristics of drilling conditions for each glass substrate. The chemical components contained in each glass substrate were quantitatively analyzed by laser ablation-inducted chemical plasma mass spectrometry (LA-ICP MS). As the WT% of Al2O3 and MgO components contained in the glass substrates is higher, the ablation threshold energy of each glass substrate is lower. This results in faster vertical speed of a laser head. The ablation threshold energy of the glass substrates was found to depend on the Al2O3 and MgO contents. When the weight percentages of both components were higher, the ablation threshold energy was lower. The effect of these components on the ablation threshold energy was theoretically investigated using self-trapped exciton analysis.