Signal integrity: Efficient, physics-based via modeling: Return path, impedance, and stub effect control

In this third paper of the series, physics-based models are used to develop insight into practical aspects of the electrical performance of via interconnects in the frequency range up to 20 GHz. It will be shown that with careful design of the via environment, the current return path can be controlled, which makes it possible to describe vias in terms of transmission line parameters in certain frequency ranges. This implies that via impedance can be controlled to match a specific target in order to minimize reflections. Furthermore, the via stub effect and alternatives to mitigate it by shifting unwanted resonances beyond the range of interest are addressed. Finally, both via impedance matching and stub length reduction methods were applied to a generic link configuration in order to assess the impact on signal integrity.