High frequency measurement techniques for vias in printed circuit boards

This article provides an overview of some multiport measurement techniques for dense via arrays, which play an important role in high-speed links as package and connector footprints in multilayer printed circuit boards. Advantages, challenges, and limitations of three approaches for high-frequency measurements up to 50 GHz are discussed: launches with fan-out traces and on-board coaxial connectors, double-sided direct surface probing with RF microprobes, and recessed probe launches with extension traces and microprobes. The measurement results obtained by the presented measurement techniques are then compared to simulation results computed using full-wave and physics-based via models. Finally, the multiport probing approach with interposers is addressed through a case study of simultaneous access for up to 12 vias in a 1 mm pitch via array that can be applied for measurements in the frequency range up to 10-15 GHz.