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Modeling, quantification, and reduction of the impact of uncontrolled return currents of vias transiting multilayered packages and boards

: Ndip, I.; Ohnimus, F.; Löbbicke, K.; Bierwirth, M.; Tschoban, C.; Guttowski, S.; Reichl, H.; Lang, K.-D.; Henke, H.


IEEE transactions on electromagnetic compatibility 52 (2010), No.2, pp.421-435
ISSN: 0018-9375
Journal Article
Fraunhofer IZM ()

The returning displacement currents of vias transiting multilayered stack-ups in electronic packages and boards excite parasitic transverse electromagnetic modes in power-ground plane pairs, causing them to behave as parallel-plate waveguides. These waves may cause significant coupling in the power-ground cavity, leading to electromagnetic reliability (EMR) issues such as simultaneous switching noise coupling, high insertion loss degradation of signal vias, and stray radiation from the periphery/edges of the package/board. In this contribution, we model and quantify EMR problems caused by uncontrolled return currents of signal vias in conventional multilayer stack-ups. Traditional methods used to minimize these problems, and their limitations are discussed. We propose a low-cost layer stack-up, which overcomes most of the limitations of conventional stack-ups by providing well-defined return-current paths formicrostrip-to-microstrip via transitions. Test samples of the proposed configuration are designed, fabricated, and measured. Very good correlation is obtained between measurement and simulation. Finally, a circuit model for the microstrip-to-microstrip via transition, considering the return-current paths, is developed and the circuit parameters are analytically calculated. Conventional closed-form expressions used for the extraction of these parameters, particularly the via capacitance, are extended and modified.