High Throughput Laser Drilling with High Power Lasers Using a Two-Dimensional Polygon Mirror Scanner

Abstract

The throughput of laser processes is typically limited by the available average laser power or the distribution speed of the laser energy onto the workpiece. In the last years, the development of laser sources brought out high average power laser sources. Thus, the distribution speed becomes the lim-iting factor. The development of industry ready polygon mirror scanners addresses this problem. In this study, a 1 kW nanosecond pulsed fiber laser is used to drill silicon wafers of 180 μm thickness and stainless-steel of 200 μm thickness in multi pass ablation. The laser energy is distributed with a two-dimensional polygon mirror scanner with a free aperture of 30 mm. Scan speeds up to 400 m/s has been utilized with high precision. In the used process, every drilling hole is hit only once per scan and must be hit again in every repetition until the holes is finished. This is achieved by pulse synchro-nization, whereby the laser adapts its pulse repetition rate to the scanner generated position frequency signal. In different processing conditions, between 25 and 220 pulses are required to drill through. With pulse repetition rates in the MHz range, drill rates of up to 15,000 holes/s are achievable. The accuracy of the process is evaluated using the drilling hole diameter at the laser entrance and exit side of the material. Furthermore, it is shown, how the diameter is influenced by variable processing pa-rameters