NEXT and FEXT characteristics and suppressions in dense 25Gbps+ backplane vias

Abstract

At 25Gbps and beyond, crosstalk noise can degrade a backplane channel signal quality significantly. High density interconnects can generate high crosstalk noise due to the close proximities of the components. In particular, interfacing dense chips and connectors with PCB requires dense implementation of signal via structures. Placing ground via guards can reduce the field overlap between signal via structures but this would also reduce density and create impedance discontinuities; therefore, these guarding via structures need to be placed strategically to reduce their adverse effects. In this study we analyze how near and far end crosstalk (NEXT and FEXT) within the signal via fields are affected by anti-pad, ground via, and ground plane layers. It will be shown that FEXT and NEXT can be affected differently in the presence of ground plane anti-pads. Relationships between these parameters with respect to ground anti-pads and the effectiveness of guarding via structures in reducing crosstalk will be presented.