Via design in multi-layer PCB

Vias between routing layers induce interconnection discontinuities. Signal reflection on the track is enhanced because of these discontinuities. A via is a noise source as the signal frequency increases. The reflection fraction changes with the via geometry properties, especially via height. The paper focuses on the influence of via height on signal reflection. Via heights from 250 /spl mu/m to 1500 /spl mu/m are studied under high frequency by simulation. The reflection loss caused by a via increases with via height nonlinearly. Considering the reflection, an optimization criterion for via design is provided.