A simple model for characteristic impedance of wide microstrip lines for flexible PCB

During the last decade, communication technologies of fast digital signals were developed. Popular digital communication interfaces like LVDS format or Hot Link, became very common. Transmission data speeds arrived to some hundreds of MHz and are approaching 1 GHz and transfer of data at such high speed between boards or systems demands a meticulous design of the traces and groundplane, as transmission lines with controlled characteristic impedance. Flat flexible printed circuit boards (PCBs) are the preferred media for data transfer among boards and between a motherboard and external connectors. The flexibility is achieved by producing thin conductors above thin layers of dielectric materials. Because of their dimensions, there is no reliable model for designing transmission lines with controlled impedance for a flexible PCB. This paper attempts to suggest such a model.