Suppression of noise propagation between power and ground planes using ferrite-plated EBG structure

To confirm the feasibility of suppressing electromagnetic interference (EMI) in the inner layers of multilayered printed wiring boards (PWBs) and sustaining power integrity characteristics, influence of inserting a ferrite-plated thin film between the power and ground planes on the transmission characteristics were evaluated using four types of test boards with the following two conditions: one is the solid test board with a plane copper foil or the EBG (Electromagnetic bandgap) test boards with a one-dimensional lattice-shaped EBG structure consisting of large and small squares 15 mm x 15 mm and 1.5 mm x 1.5 mm in size; the other is whether the 3 or 6 μm-thick ferrite film was deposited or not. The multiple peaks of the transmission coefficient S₂₁ due to parallel plate resonances were observed in the solid test board without ferrite film but the peaks were suppressed over the wide frequency range up to 6 GHz by applying the ferrite film. The EBG test board with the ferrite film provided not only wideband attenuation owing to the ferrite film but also large attenuation in the EBG stopband. The multiple peaks of in the driving point impedance Z₁₁ due to the parallel plate resonances were also successfully suppressed by applying the ferrite film exhibiting favorable power integrity characteristics.