1. A method of manufacturing flexible circuit board having enhanced bending durability, the method comprising:(a) forming a signal line and a first ground layer on a first dielectric, and forming a second ground layer on the bottom surface of the first dielectric;
(b) preparing a second dielectric;
(c) preparing a first bonding sheet and a first protective sheet connected to one end of the first bonding sheet or positioned to overlap at least a part thereof;
(d) bonding the second dielectric on the first dielectric via the first bonding sheet;
(e) forming a via hole so that the first ground layer and the second ground layer are connected electrically; and
(f) cutting the second dielectric on the first protective sheet in the width direction.