Optimized launching pads for investigating transmission line losses for different surface finishes of RF-PCBs up to 110 GHz

Abstract

As surface finishe play allegedly a crucial role in the overall performance of RF-circuits, this paper is dedicated to evaluate the impact of four different platings, as well as plain copper, on insertion loss for commercially manufactured RF-PCBs. The selected surface finishe are Electroless Nickel Immersion Gold (ENIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), Immersion Tin, and a manufacturer specifi "shiny"-gold. Although each finis has different involved processing steps, materials, and price, basically no difference in insertion loss has been measured up to 110 GHz for microstrip (MS) or conductor backed coplanar waveguides (CBCPW). Additionally, the impact of manufacturing tolerances on insertion loss has been quantified These tolerances have shown more variation on insertion loss than for all investigated surface finishes with deviations of -11 % and 14 % in insertion loss at 100 GHz of the overall mean. For obtaining accurate data, appropriate launching pad designs have been evaluated previously for conducting reliable wafer prober measurements of wet etched RF-circuits up to 110 GHz.