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In this article, the particle concentration of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS) is optimized on the basis of rheological investigations. For this metallization process, a smooth, homogeneous and defect-free precursor layer is a prerequisite for adherent and reproducible copper structures. The knowledge of the rheological properties of an ink is crucial for the selection of a suitable coating technology as well as for the adjustment of the ink formulation. Different dilutions of the nanosuspension were examined for their rheological behavior by recording flow curves. A strong shear thinning behavior was found and the viscosity decreases exponentially with increasing dilution. The viscoelastic behavior was investigated by a simulated doctor blade coating process using three-interval thixotropy tests. An overshoot in viscosity is observed, which decreases with increasing thinning of the precursor. As a comparison to these results, doctor blade coating of planar glass and polymer substrates was performed to prepare precursor layers for reductive laser sintering. Surface morphology measurements of the resulting coatings using laser scanning microscopy and rheological tests show that homogeneous precursor layers with constant thickness can be produced at a particle–solvent ratio of 1.33. A too-high particle content results in an irregular coating layer with deep grooves and a peak-to-valley height S z of up to 7.8 μm. Precise dilution control allows the fabrication of smooth surfaces with a S z down to 1.5 μm. [ABSTRACT FROM AUTHOR]

Laser ablation in liquids offers some key advantages over conventional laser processing under gaseous or inert conditions. A significant volumetric reduction of the heat affected zone minimizes the risk of damaging adjacent regions during processing. Due to complex physicochemical interactions the interactions in the ablation zone and their impact need to be investigated. For this study, titanium was chosen as a base material, as it is widely used in a broad range of micromachining applications. The results of the change of ablation rate, surface roughness and surface oxidation for thin titanium foils in both purified water and argon are presented and compared respectively. Processing in the much denser liquid medium reveals differences in the fluence dependant ablation characteristics and an overall reduction in the ablation rate, supposedly caused by plasma-shielding. Favourable aspects are given by the higher surface quality and improved dimensional tolerances, making the process a promising alternative in micromachining applications. [ABSTRACT FROM AUTHOR]

In times of digitalization, multilayer composite materials became central components in an increasing number of application fields. Thus, there is a need for optimization of the cost-intensive and time-consuming processing of multilayer composites. In this contribution, an ultrashort pulse laser-based method is presented for precise and flexible ablation of a printed circuit board base material. Therefore, an 800 nm Gaussian laser beam was transformed into a Bessel beam by an axicon to get a small spot size and an ablation result with a high aspect ratio. The influence of the average laser power, the number of exposure cycles, and the pulse duration on the geometry as well as the surface quality of ablated structures was investigated and compared to Gaussian beam ablation. Furthermore, it is shown that the results can be transferred to microdrilling processes. With the presented method, it was possible to ablate the copper top layer of the printed circuit boards as well as the FR4 layer below with a precisely adjustable depth. [ABSTRACT FROM AUTHOR]