Proximity effects between striplines and vias

This paper presents initial results on spurious trace-via interactions, i.e. the coupling between striplines and vias that are routed in close proximity in printed circuit boards. It is shown that the primary interaction is mediated by a capacitive coupling. Moreover, antipads of signal vias act as discontinuities in the return current path of striplines. The relevance of this effect is increased by layer misregistration in fabricated PCB laminates. For differential traces, imbalances in antipad to trace overlap margin lead to imbalances in the differential pairs, resulting in mode conversion and degradation of differential noise margins. Finally, crosstalk between striplines on different signal layers, even widely separated ones, can be mediated through capacitive coupling to and from signal vias.