An analysis of copper surface roughness effects on signal propagation in PCB traces

Conductor loss due to the roughened metal foil surface has significant effects on high-speed signals propagation on backplane traces designed for 10+ Gbps network. A practical method to evaluate these effects, including the signal attenuation and the propagation phase velocity, is proposed in this paper. A periodic structure is used to model the morphology of the roughness profile. The equivalent surface impedance is extracted from the grating surface wave propagation constant to model the roughness. This modified surface impedance can hence be used in the traditional attenuation constant formula to calculate the actual conductor loss. This approach is validated using measurement, and is shown to be able to provide robust result within 0.2 dB/m relative error in attenuation constant.