EMI Analysis of via stub resonance in a Multi-layer PCB design

As the speed and volume of digital data transmission increases, the need to minimize the overall insertion loss in printed circuit boards becomes more important. The design of the via structure in modern circuit boards has a significant impact on the insertion loss, in addition to the transmission line itself. One approach to optimize the via is to reduce the length of the stubs. Long stubs can result in reflections and potentially add fractional wavelength antennas to the circuit, negatively affecting the signal. This paper aims to investigate the impact of via stub resonance and determine ways to avoid the related issues. By routing high-speed signals on layers with shorter via stubs, the effects of remaining stub lengths are studied and the insertion loss profile and FFS are evaluated. The study reveals that the resonance frequency of the via stub has a significant effect on the insertion loss of the signal and hence intends to the EMI problems.