A printed circuit board having prescribed conductive patterns formed on an insulating layer is provided about 20 mm apart from an AC electrode provided in a plasma etching device. An earth electrode is provided on the side opposing the AC electrode. More specifically, the printed circuit board is provided outside a sheath layer that is a region having a high plasma density generated in the vicinity of the AC electrode. The frequency of an AC power supply is preferably not more than 1 GHz. The pressure in the device is preferably in the range from 1.33×10−2 Pa to 1.33×102 Pa. The inter-electrode distance between the AC electrode and the earth electrode is preferably not more than 150 mm, more preferably from 40 mm to 100 mm.