Rapid formation of high aspect ratio through holes in thin glass substrates using an engineered, QCW laser approach

As communication networks advance toward higher frequency bands (e.g. 5G), glass has become a promising candidate for low-loss materials in packaging and interconnect applications. While current techniques for through hole (through glass via, TGV) formation allow for drilling of >40 µm diameter holes, there are currently limited commercially viable options for smaller TGVs. Herein we report, using a single laser source and no post-processing, the formation of high aspect ratio TGVs in 10–20 µs for 50 and 100 µm thick glass. This is accomplished by exploiting a novel laser parameter space consisting of high power quasi-continuous wave (QCW) pulse trains of ∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim$$\end{document} 28 ps pulses with Gaussian beam profile. Crucially, this approach is compatible with high bandwidth beam steering technologies (galvanometers and acousto-optic deflectors (AODs)), allowing for simple scaling to an industrially viable throughput of tens of thousands of vias per second for high-density drill patterns. The TGVs have straight, smooth sidewalls, minimal splash, and high uniformity. Multi-physical simulations show that the drilling process is initiated by multi-photon absorption of laser energy and cascade ionization within an incubation period of several microseconds. After this incubation period, rapid material removal occurs via strong vaporization along with hydrodynamic ejection of molten glass.