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

Claim 3:
4. A flexible printed circuit board comprising:
a base film having a hole for forming a through hole;
a coil-shaped wiring layer layered on at least one surface side of the base film; and
a dummy wiring layer that is arranged in a region outside the wiring layer on the base film with an interval from the wiring layer,
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,
wherein a ratio of an average thickness of the first winding portion to the average thickness of the second winding portion is 1.1 or more and 5 or less, and
wherein a ratio of a second area of a layered region of the dummy wiring layer to a first area of a region up to 2 mm by a shortest distance from the wiring layer toward outside thereof in the base film is 20% or more and less than 50%.