Adaptive reflow hole optimization suppresses 22-layer PCB impedance mismatch

In this paper, we propose a frequency band adaptive return vias optimization configuration method for the impedance mismatch of high-speed signal layer changing vias in 22-layer high-density PCBs. By establishing a three-dimensional full-wave electromagnetic simulation model, we systematically analyze the influence of the position, number, and arrangement of the return vias on the S-parameters and time-domain reflection characteristics in the range of 0~77 GHz. The experimental results show that in the frequency bands of 0~30 GHz and 55~60 GHz, the symmetric layout of two return vias (55 mil spacing and 90° azimuth) can reduce the return loss by 32%, while in the high-frequency band of 30~77 GHz, the curvilinear distribution scheme of 6~10 return vias can suppress the insertion loss to below 1.5 dB. The study further reveals the nonlinear relationship between return vias spacing and impedance fluctuation, and proposes a hierarchical optimization strategy based on band characteristics, which provides theoretical guidance for PCB design in 5G communication and high-speed computing platforms.