Roughness characterization for interconnect analysis

A novel method for practical prediction of interconnect conductor surface roughness effect on multi-gigabit digital signals is proposed. A differential impedance operator of a conductor is constructed with Trefftz finite elements and locally adjusted with a correction coefficient to account for the roughness effect. Any correction coefficient derived for the additional power loss due to roughness can be used with the proposed method. Modified Hammerstad's correction coefficient is proposed and used here as an example. A test board is manufactured and investigated up to 50 GHz. Parameters of the conductor roughness model are identified with generalized modal S-parameters. An increase of effective dielectric constant due to conductor surface roughness is observed and explained by capacitive effect of spikes on the surface of conductor. It is shown that the constructed interconnect models are consistent with the measured data.