Build-Up Spiral and GND Vias for Improving Signal Integrity of Signal Core Vias

Impedance mismatch of vias is one of the factors most strongly affecting the signal integrity of the signal routing on printed circuit boards and IC packages. As an alternative to current methods, such as the use of voids, tuning the via pad size, or adding a stacked spiral, the present study proposes a build-up (BU) spiral with optimized ground core vias to further improve the impedance matching of the signal core via. Through appropriate designs of the radius and curvature of the BU spiral, the capacitive via can be inductively compensated such that it is close to the required impedance. The simulation results show that the proposed mechanism improves the impedance of the core via. Furthermore, the simulation results are in favorable agreement with the measurement results. Finally, the measurement results indicate an 11% improvement in the eye height in the eye diagram at a data rate of 16 Gb/s compared with the case without voids.