Via pattern design and optimization for differential signaling 25Gbps and above

Ground via design rules may need to be re-visited to support high-speed signaling for 25Gbps and above, according to our experience. In this paper, the study begins with some basic via patterns with different ground via placement to investigate loss, crosstalk, common mode, and electromagnetic field distribution to help understand the underlying physics. The benefit of joint anti-pad is also analyzed for signaling at 25Gbps and above. Impact of adjacent vias to the modeled via pair of interest is studied and it is found that the adjacent vias should be properly terminated and included in the modeling. Finally crosstalk study is performed for the given via patterns.