An Analysis of Conductor Surface Roughness Effects on Signal Propagation for Stripline Interconnects

Conductors with a roughened surface have significant effects on high-speed signal propagation on backplane traces designed for a 10+ Gb/s network. An accurate approach to evaluate these effects, including the signal attenuation and the phase delay, is proposed in this paper. A differential extrapolation roughness measurement technique is first used to extract the dielectric properties of the substrate used for lamination, and then a periodic model is used to calculate an equivalent roughened conductor surface impedance, which is then used to modify the transmission line per-unit-length parameters R and L. The results indicate that the conductor surface roughness increases the conductor loss significantly as well as noticeably increasing the effective dielectric constant. This approach is validated using both a full-wave simulation tool and measurements, and is shown to be able to provide robust results for the attenuation constant within +/- 0.2 Np/m up to 20 GHz.