Patent ID: 11950365
Assignee: SUMITOMO ELECTRIC INDUSTRIES, LTD.
Field: Audio-visual technology (Electrical engineering)
Classification: CPC H  C | IPC H

Claim 4:
5. A method of manufacturing a flexible printed circuit board including a base film having a hole for forming a through hole; and a coil-shaped wiring layer layered on at least one surface side of the base film,
wherein the wiring layer includes a land portion arranged at an inner peripheral surface of the hole and at a peripheral portion of the hole of the base film, and a winding portion arranged in a spiral shape with the land portion as an inside end portion or an outside end portion,
wherein the winding portion includes a first winding portion that is an outermost circumference and a second winding portion that is inside relative to the outermost circumference,
wherein a ratio of an average thickness of the land portion to an average thickness of the second winding portion is 1.1 or more and 5 or less, and
wherein the average thickness of the land portion is greater than or equal to 20 μm,
wherein the method comprises:
forming a first plating body including a lower land layer of the land portion and a lower winding layer of the winding portion by electroplating a first metal material on a conductive underlayer of the base film having the hole for forming the through hole using a resist pattern, the conductive underlayer being layered on at least one surface side of the base film;
removing, after the forming of the first plating body, the resist pattern and a region of the conductive underlayer on which the first plating body is not layered; and
forming, after the removing, a second plating body including an upper land layer of the land portion and an upper winding layer of the winding portion by electroplating a second metal material on the first plating body;
wherein in the forming of the first plating body, the first metal material is electroplated on the conductive underlayer so that a second plating amount for forming the lower land layer is greater than a first plating amount for forming an inside relative to the outermost circumference of the lower layer winding layer,
wherein the land portion is formed by a portion of the conductive underlayer, the lower land layer and the upper land layer, and
wherein the winding portion is formed by another portion of the conductive underlayer, the lower winding, layer and the upper winding layer.