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2010
Journal Article
Titel
Modeling, quantification, and reduction of the impact of uncontrolled return currents of vias transiting multilayered packages and boards
Abstract
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.