High aspect ratio microstructuring of copper surfaces by means of ultrashort pulse laser ablation

摘要

Laser beam machining (LBM) is capable of almost force-free 2D and 3D machining of any kind of material without tool wear. This process is defined by many parameters, such as pulse energy, frequency, scanning velocity and number of scanning repetitions. Modern laser machines provide high energy at shorter pulse durations and have more precise positioning systems than machines of the past. These can easily fulfil today's continuous changing product requirements. For an overall understanding, an extensive amount of experimentation is required to display the interaction laws and dependencies between process parameters, as well as the resulting shapes and quality of the machined surface. By using an ultrashort pulse (USP) laser, a wide range of customer oriented applications in micrometer scale can be addressed, which leads to precise ablation with minimal thermal damage. This paper provides knowledge on the machining of copper micro features with high aspect ratio and a 532 nm wavelength laser beam. Aspect ratios up to 17 and slot widths smaller than 20 μm were performed with a beam radius ω_0 smaller than 5 μm and pulse duration smaller than 12 ps. For desired slot geometries, necessary process parameters were developed and their physical limits are shown and discussed. The limits of minimum structure size have been analysed by observing the remaining material between slots at decreasing distances. Material debris deposits on the non-machined surface, as well as chemical changes of copper, were analysed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). Special attention was given to the taper angle, which arises due to the Gaussian distribution of energy in the laser beam.