A flexible printed circuit board (FPCB) simultaneously coupled to both surfaces of a substrate structure, e.g., a touch screen panel is provided. The FPCB includes a main substrate unit having a first pad unit and an auxiliary substrate unit extending from the main substrate unit to one side of the first pad unit. The auxiliary substrate unit includes a first substrate unit positioned parallel with the first pad unit along a first direction, a second substrate unit including a second pad unit, the second substrate unit spaced apart from the first substrate unit in a second direction, orthogonal to the first direction, and a plurality of third substrate units extending along the second direction between the first and second substrate units.