Analysis Of High Frequency Characteristics Of The Vertical Via Structure In Multilayer PCB

The vias are the most common vertical interconnect structures in packages and multilayer PCBs,enabling electrical connections between layers or between components and traces.When the operating frequency rises to RF or microwave segment,vias as a discontinuity can cause very serious signal integrity problems.In the existing research,the influence of sidewall roughness on the electrical performance of via is rarely studied.In the case of high frequency,reflection and crosstalk problem analysis of differential via interconnect structure is not sufficient.In order to solve above problems,this paper studies the high frequency characteristics of vertical via structure in multilayer PCB board.The paper focuses on the study of equivalent circuit modeling of vias with rough sidewall,differential vias transmission characteristics and crosstalk problem.Firstly,influence of the sidewall roughness on high frequency performance(>10GHz)of via interconnect structures is studied.The paper describes basic principle of the effect of sidewall roughness of via on the conductor loss.The parasitic parameters of the equivalent circuit of the via with rough sidewall are deduced.An electrical model of via is proposed considering the effect of via sidewall roughness.And the relationship between the high frequency characteristic of via and sidewall roughness is obtained.The proposed circuit model is analytically calculated and validated with CST full wave electromagnetic simulation.Then the transmission characteristics of differential vias in high speed circuits is studied.The influence of via diameter,antipad,ground via return,stub and wiring way on transmission characteristics of differential via is analyzed in detail.Optimize the design parameters using full wave simulation and experimental measurements.A typical chip-chip high speed differential channel model is established.The purpose of improving the channel transmission performance is achieved by optimizing the differential via interconnect structure in the channel.Presents a modeling and simulation methodology through chip package-PCB co-design and co-optimization in 25 Gbps.The simulation results show that the optimized transmission performance of the system is much better than that of the previous system.Finally,the crosstalk problem between the differential vias is studied.The physical model of three pairs of differential via interconnection structures is established by using CST full wave simulation software.The signal distribution mode,S:G ratio are designed and optimized to explore the crosstalk performance of differential vias.The impact of PCB routing layer selection and via stub are also considered.The optimal design scheme for reduce via crosstalk in the BGA and PCB interconnection area is proposed.Both frequency domain and time domain simulation results show that above methods are validated to effectively reduce the crosstalk between differential vias.The research results of this paper can be applied to the accurate modeling and signal integrity analysis of the vias at high frequencies,and provide the theoretical basis for the design and manufacture of high-speed circuits.