Differential vias transition modeling in a multilayer printed circuit board

A 26-layer printed circuit board including several test sites has been analyzed. All the sites have a transition from coupled microstrips to coupled striplines through signal vias. Differential measurements have been performed on some of these test sites to estimate the effect on S-parameters and eye diagrams due to via and antipad radius variation, and different lengths of via stub. The focus of this paper is on a test site with a transition from top to the sixth layer. At the same time, a physics based circuit model has been assembled in a spice-based simulation tool and a full-wave model has been generated as well. The paper will show that the process of modeling can require a series of adjustments to get reasonable results. A brief discussion about possible issues associated with fabrication tolerances is presented in the last chapter.