Stub length prediction for back-drilled vias using a fast via tool

Abstract

This paper presents a fast via tool to predict the via stub length after back-drilling. The fast via tool is developed associated with the physics based via model and is combined with the calculation of plane impedance and via capacitance block by block. The entire via model is built by connecting those via blocks one after another accordingly. The plane impedance is calculated from an analytical formula and the via capacitance is computed from the point of view of energy by solving the potential distribution on each via block using FEM. Via stub length is predicted with the observation of strong resonant trough on the insertion loss, which can be in single-ended mode or mixed mode. Two cases, one signal via surrounded by eight ground vias and four signal vias surrounded by four ground vias, are used to verify the modelling accuracy of the fast via tool by correlating to the measurements. The third case is about via stub length extraction as well as the sensitivity investigation between the stub length and the resonant frequency.