Signal Integrity Analysis Of Via Transition Structure In Multilayer PCB

In multilayer printed circuit board(PCB), via transition structure is widely used in signal connection between different layers. When transmitting high frequency signal, the via will lead to the discontinuity of input impedance in the power/ground plane structure. That will cause signal integrity problems, affect signal transmission in quality, and then get in the way of high speed PCB design.In this paper, the boundary element method of constant element and modes resonance method were mainly used to model, analyze and calculate the power/ground plane structure in multilayer PCB. First of all, the power/ground plane structure containing single and multiple signals via was analyzed and calculated, the input impedance of return path in the power/ground plane was calculated, the equivalent lumped circuit model of via was extracted, and the S parameters of via was simulated through PSpice software, again the influence of signal transmission and crosstalk of via was improved by methods of adding ground vias around the signal via. Then, two cascading methods of solving via transition structure in multilayer PCB, including a cascading method based on the equivalent circuit model of via and that of S parameters based on the [ABCD] matrix of two-port networks, were discussed. And cascading S parameters of via between multiple planes in multilayer PCB were simulated and analyzed. Finally, the influence of signal transmission from the different differential vias structure parameters was simulated and analyzed by HFSS, 3-D full wave electromagnetic field analysis software. The accuracy of the calculation methods was verified by ANSYS and HFSS, 3-D electromagnetic field finite element software.The research results show that the input impedance of return path in the power/ground plane in multilayer PCB was at its maximum at the resonance frequency, causing the low transmission efficiency of high frequency signal in via, and the coupling degree between vias reached the maximum. The cascading method based on the equivalent circuit model of via and the cascading method of S parameters based on the [ABCD] matrix can solve the cascading problems of via transition structure in multilayer PCB. When differential signal was transmitted in differential vias in multilayer PCB, reducing the radius of via and pad, increasing the radius of anti-pad, and reducing the center distance of differential vias can improve the transmission performance of high frequency signal in differential vias.Innovations of the paper:(1) The input impedance in the power/ground plane structure in the multilayer PCB was modeled and analyzed by the boundary element method of constant element, including the superposition of incident and reflected wave in anti-pad;(2) The signal transmission and the influence of crosstalk were analyzed by using the combined method of field-circuit in the power/ground plane of multi vias;(3) The cascading S parameters of via transition structure were calculated by using the [ABCD] matrix of two-port networks.