a flexible printed circuit comprising a substrate , a plurality of function lines , and a plurality of first dummy lines . the substrate comprises at least two periphery areas and an intermediate area . each periphery area comprises a first layout region , a second layout region and a first rough region disposed between the first and second layout regions . the intermediate area is disposed between the periphery areas . the function lines are disposed on the substrate and within the intermediate area . the first dummy lines are disposed on the substrate and within the first or second layout area .