Use of the SPP Technique to Account for Inhomogeneities in Differential Printed-Circuit-Board Wiring

The short-pulse propagation (SPP) time-domain technique is shown to be able to easily account for the inhomogeneities found in typical printed-circuit-board wiring. SPP is used to generate broadband predictive models for differential lines with different glass-fiber-to-epoxy-resin ratios and also for the soldermask layers used on top and bottom of typical boards. In both cases, a two-step extraction procedure is employed to obtain the broadband complex permittivity for the inhomogeneous structures and correlation with TDT measurements is used to validate the technique. Some examples of the effect of using different epoxy resin contents on the total loss are shown for 7.0 mil and 10.0 mil pitch differential wiring.