The Influence of Power/Ground Resonance to Via´s SSN Noise Coupling in Multilayer Package and Three Mitigating Ways

When the high-frequency signal is transmitted through parallel plane by via, it encounters discontinuities at its reference planes, where the high frequency TEM waves are not guided smoothly between signal trace and the reference plane. As a result, the electromagnetic wave energy between the signals and return currents are redistributed, and electromagnetic waves at the parallel planes cavity are excited due to the absence of continuous return current plane at the via neck. The loaded energy is a main source of PCB edge radiation, and at the same time, at resonance frequencies of the resonator formed by the package´s parallel planes, the noise electromagnetic energy in parallel plane cavity, such as SSN (simultaneous switching noise), is more easily to be coupled into via too, which may cause the deterioration of the signal on the via. To thoroughly study this phenomenon, this paper makes theoretical investigation of the influence of parallel plane resonance to via´s SSN coupling based on cavity resonator theory and coupling mechanism to get the theoretical support for the influence of parallel plane resonance, especially the power/ground resonant impedance to SSN coupling. Because the SSN coupling above is maximized, when the impedance of the power/ground system is maximized, the ways to mitigate the coupling should be based on reducing the impedance of avoid the impedance. Three ways to mitigate this SSN coupling including 1) adding anti-via (shorting via) near the initial via; 2) reducing overall parallel plane impedance; 3) adding capacitor the reduce the parallel plane impedance near the location of the via are investigated. Finally, the effect of the three ways above are simulated and compared with the structures without these three improvements.