A method for manufacturing a flexible printed circuit board comprising: providing a first flexible precursor board having a layer; adhering a first covering layer with a lower opening, a portion of the circuit layer exposed; adhering a second covering layer with an upper opening to the first covering layer, the upper opening being formed in the lower opening, and a portion of circuit layer being exposed to obtain a second flexible precursor board; providing an upper mound having a protruding portion and a lower mound having a recessed portion, moving the second flexible precursor board between the upper mound and the lower mound, the upper opening being positioned away from the protruding portion and the recessed portion, pressing the upper mound to the lower mound to press the protruding portion into the recessed portion; removing the upper mound and the lower mound to get the flexible printed circuit board.