Package analysis tool based on a method of moments/surface formulation

Abstract

A package analysis tool is described which is based on a method of moments analysis and surface formulation. The surface formulation replaces ideal conductors by electric currents on their surfaces; electric and magnetic currents are used for lossy conductors. These currents are then discretized using triangular linear current approximations, with the primary advantage of being able to represent arbitrary shapes. Frequency dependent inductance and resistance are computed using a novel approach. The capacitance is also computed using piecewise constant charge distributions on each triangle. The current and charge distributions are compatible, and therefore transmission line modelling can be done accurately. The algorithm enables use of the tool for both transmission line and discontinuity modelling, as well as inductance evaluation for analysis of simultaneous switching noise. The tool has a graphical pre- and post-processor, which allows analysis of highly irregular structures, as are found in most practical packaging configurations. In this paper, algorithms for the tool are described. Comparisons are shown between results obtained using the approach of the paper and analytical and approximate calculations. Comparison is also shown with measured capacitance for irregular shapes. The analysis of the simultaneous switching noise for a 304 lead, six layer single chip module is described.