Via Transition Optimization Using a Domain Decomposition Approach

A method to minimize the return loss for via interconnects on printed circuit boards (PCB), based on the domain decomposition of traces, via barrels, and trace-to-via transitions is presented. This decomposition allows to optimize different via lengths, by separating the via barrel as an independent domain. The method is demonstrated by full-wave simulations. It starts by optimizing the via impedance, matching the traces by an appropriate size of the via environment followed by a subsequent compensation of trace-to-via transition discontinuities. Equivalent circuits of each domain are used to corroborate the performance improvement. Three pad geometries are proposed to compensate the discontinuities of a trace-to-via transition. For a long via on a PCB with eleven metal layers, using four ground vias, it was possible to achieve a wide-band low-reflection response below -30 dB from DC up to 32 GHz for microstrip traces and -37 dB from DC up to 20 GHz for stripline traces.