A flexible circuit board comprises a substrate which has a polyimide layer recessed to define at least a compartment. The compartment includes an inner wall surface having a side wall and a bottom wall. The compartment is for containing a multilayer unit, wherein the multilayer unit includes an adhesion enhancing layer formed on the wall of the compartment, a first electrically conducting layer disposed on the adhesion enhancing layer, and a second electrically conducting layer formed on the first electrically conducting layer. The adhesion enhancing layer is palladium. The first electrically conducting layer is nickel. The substrate is composed of polyimide (PI).