EMI Investigation and Mitigation of Flexible Flat Cables and Connectors

In modern mobile devices, as a result of the increase in data rate, requirement for higher density signal and cost-effective solution, the flexible flat cable (FFC) now plays an important role to connect separated printed circuit boards (PCBs). Due to the low-cost fabrication and varied shielding structure, FFC has been identified as a noise source for electromagnetic interference (EMI) and desense issues. In this paper, the common mode noise generated from FFC and related connectors is investigated. With the assistance of full wave and circuit simulation, main cause of the common mode noise has been identified as the ground discontinuity and the related voltage difference between the PCB ground and the FFC ground. By providing better shielding and improving ground continuity, 11 dB reduction of total radiation power (TRP) is observed at 5 GHz.