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A comparison of typical surface finishes on the high frequency performances of transmission lines in PCBs

Surface finishes are ubiquitous in printed circuit board (PCB) interconnects to facilitate reliable bonding. The modelling of the HF (high frequency) behavior of these interconnects can be difficult to predict with available modelling techniques, especially when the modelling must simultaneously account for surface finish and surface roughness effects. In this paper, an adapted filament modelling technique has been used to model the resistive losses of the five most commonly used surface finishes in commercial PCB manufacturing up to 70GHz. The results show nearly no difference in HF properties, when compared to no finish, when the finish consists of only one layer. When the finish consists of two layers, it can nearly double the resistive losses in the range of 10GHz to 20GHz, for example, depending on the distribution of surface roughness, the type of finish, and the thicknesses of the finish layers.