Pretreatment and Structuring of Spatial Circuit Carriers Based on Alumina for High Temperatures and High Frequencies

This paper shows a fundamentally new way for laser structuring and metallization of aluminum oxide. It allows spatial alumina to be structured by means of low power lasers with a wavelength of 1,064 nm and subsequently metallized, using established processes throughout. This can be achieved through two distinct pretreatment options. One using a permanent marker, which is removed with isopropanol in an ultrasonic bath after laser structuring. The other using an acrylic varnish, which is removed with acetone after laser structuring. The optimum laser parameters are determined by a parameter study including 48 factor levels, which are replicated five times each, resulting in a total of 240 samples. The results are used for the production of specimens which are tested with respect to the adhesion strength of the metallization through hot-pin-pull tests. After laser structuring and cleaning the specimens are chemically electroless metallized with copper, nickel and gold. The marker specimens attain copper layer thicknesses of 4.94 μm and an adhesion strength of 1.85 N/mm
²
. The varnish specimens have similar copper layer thicknesses of 4.72 μm, but achieve significantly higher adhesion strengths of 7.51 N/mm
²
. Finally, scanning electron micrographs of untreated and structured surfaces show the effects of the laser structuring on the surface of marker specimens.