Characteristic impedance planning in PCB design

This paper discusses some of the practical implications of not accounting for differences in characteristic impedance values found by the PCB Manufacturer and those found in a major Signal Integrity (SI) analysis tool. In the first part, the reasons for differences in characteristic impedances values are discussed. The second part, discusses some of the possible workarounds to the differences and methods to minimize the differences as to obtain values that are consistent with IPC approximated values for symmetrical stripline, assymetrical stripline, and microstrips. Snapshots of the feature changes are shown to facilitate necessary adjustments in the simulation runs through step by step changes.