Cost-effective SIW band-pass filters for millimeter wave applications a method to combine low tolerances and low prices on standard pcb substrates

The fabrication of passive RF structures in the millimeter wave frequency range with conventional printed circuit technology is subjected to some disadvantages (available design rules, dimensional accuracy and tolerances) compared to ceramic circuit carriers. The here presented SPE (sequential pre etching) process technology allows a significant reduction of these disadvantages, without diminishing the robustness of the PCB against environmental influences (IPC-A-600 class 3). The tolerance of the up to now dominating etching process is reduced from ±15 μm (at a copper height of 35 μm) to ±5 μm (at a copper height of 15 μm). For filters the new technology provides two benefits. Due to the lower copper thickness, the permitted design rules are significantly improved (line/space 50/50 μm at all layers - even at electroplated copper layers). Therefore structures with minimized dimensions can be realized. In addition the reduced etching tolerance allows fabricating filters with accurate and constant filter edges. In order to demonstrate the advantages, a high-slope SIW (substrate integrated waveguide) band-pass filter in the V-Band is presented. It is shown how the characteristic and tolerances of the filter are changed positively by the SPE technology.