Structure Depth Monitoring During Processing of Multi-Layer Materials with a Fiber-Based Ultrashort Pulsed Laser Robot

We report on the laser structuring of multi-layer materials using a fiber-based ultrashort pulsed laser robotic system within a processing area of 800 mm × 600 mm × 200 mm. Structuring was performed on a CuAl foil consisting of copper and aluminium layers, as well as on a two-layer printed circuit board (PCB) material comprising two copper layers separated by a polyimide layer. Experiments at different robot coordinates revealed structure depth deviations of up to 9.5 µm for applying a constant number of laser passes. To improve the accuracy and repeatability of the structure depth for true 3D applications, an inline monitoring method based on laser-induced breakdown spectroscopy (LIBS) was introduced. The method enables the real-time detection of material transitions during each single laser structuring pass by analyzing the optical emission intensities at characteristic wavelengths of the individual layer materials. The process is stopped when the ratio of the LIBS intensities of adjacent material layers falls below a predefined threshold. Laser structuring experiments with the LIBS-based process monitoring showed a reduction in the maximum structure depth deviations down to 2.9 µm and 1.9 µm for the CuAl composite foil and the two-layer PCB material, respectively. These results demonstrate the potential of the LIBS-based monitoring approach for achieving precise structure depth control, the removal of material layers and the minimization of damage to the underlying target layers during the processing of multi-layer materials.