Electromagnetic interference from printed circuit boards connected by flexible printed circuit board

Flexible printed circuit (FPC) has used for the 3D wiring in the electronic equipment. PCBs are often located in 3D and connected by FPC to make the electronic device small. In this case the PCBs are faced each other in small distance and have electromagnetic interference. This causes deterioration of transmission property at high frequency and electromagnetic noise radiation. In this study, electric radiation and transmission property of the PCBs connected by FPC are calculated using 3D electromagnetic solver. From the results, it is found that resonant frequencies are shifted by mismatch of the characteristic impedance and of balance mode of the lines. And new radiation peak appears at the frequency corresponding to the distance between the faced PCBs.