A flexible base includes a main region configured for forming flexible printed circuit board units; and two conveying regions respectively arranged on two sides of the main region. Each of the conveying regions includes an insulating substrate, a plurality of sprocket holes, and a patterned supporting layer. The sprocket holes are defined along a lengthwise direction of the insulating substrate. The patterned supporting layer is formed on the insulating substrate. The patterned supporting layer extends from an edge of each sprocket hole towards a periphery region of the corresponding sprocket.