SI/PI degradation due to package-common-mode resonance caused by parasitic capacitance between package and PCB

Package-common-mode resonance which is caused by a parasitic capacitance and parasitic inductances between package and PCB grounds makes degradation of signal and power integrity. A parasitic capacitance between a package ground and a PCB ground anti-resonates with a parasitic inductance at ground connections such as solder balls in a BGA package. In this resonance, currents flow on power and ground lines in the package with the same phase. Thus, the authors name this antiresonance “Package-common-mode resonance”. The package-common-mode resonance causes the power and/or ground bounce and increase of jitter of the output signal. According to measurement results of test boards, the resonance frequency is depend on the number of ground connection because the parasitic inductance is decreased by increasing ground connection. For example, the resonance frequency was changed from 575 MHz to 862 MHz in the test board when the number of the ground connection was decupled.