Package to board interconnect design for minimum return loss

Return loss from impedance discontinuities severely limits the bandwidth and power efficiency of chip-to-chip copper interconnects. Among the more frequently found discontinuities are vertical transitions connecting signals in different layers in the system. In this work, we present a general condition to improve return loss in vertical package to board transitions in high speed links. The relationship involves the impedance of on-package and on-board transmission lines as well as the via model. Experimental results that apply the proposed method show a 10-dB improvement in return loss. The proposed method can be applied in the design of copper interconnects with minimum reflection, which is a requirement of high-speed and low-power signaling systems.