Enhancement of Differential Signal Integrity by Employing a Novel Face Via Structure

This paper proposes a novel differential via structure, which is dubbed as face via, to improve the impedance discontinuities at the via transition. The performance of the proposed face via is verified by simulated and measured impedances in time domain reflection responses and by equivalent circuit modeling. In this paper, the conventional cylinder via and the proposed face via were designed and fabricated to demonstrate the effectiveness of the face via in differential signal channels. The analysis indicates that the proposed differential via structure provides a very effective way to minimize the impedance discontinuities at vias by controlling the size of face in the via. The analysis of the eye diagram identified the improvement of signal integrity in channel characteristics. Furthermore, in order to consider the complexity in digital system at high speed, the performance of face vias in multiple via transitions and the effect of return current vias are also investigated. Finally, the effectiveness of the proposed face via has been successfully validated by the simulation and experiment results.