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EP-4742842-A1 - METHOD FOR MANUFACTURING FLEXIBLE PRINTED WIRING BOARD, AND FLEXIBLE PRINTED WIRING BOARD

EP4742842A1EP 4742842 A1EP4742842 A1EP 4742842A1EP-4742842-A1

Abstract

A method of manufacturing a flexible printed wiring board 1A includes a preparing step of preparing a double-sided substrate 100 having an insulating base material 10 and metal foil layers 102a, 102b laminated on an insulating layer, a hole formation step of forming a through hole 50 in the insulating base material 10 and the metal foil layers 102a, 102b, and a plating step of forming first and second plating layers 103 around and inside the through hole. The plating step includes a first plating step of forming the first plating layer 103 around and inside the through hole by a panel plating method, and a second plating step of forming a second plating layer 104 around and inside the through hole by a pattern plating method.

Inventors

  • OGAWA, AKIKO
  • OKADA, JUN

Assignees

  • Fujikura Printed Circuits Ltd.

Dates

Publication Date
20260513
Application Date
20240613

Claims (7)

  1. A method of manufacturing a flexible printed wiring board, comprising: a preparing step of preparing a substrate having an insulating layer and a metal foil layer laminated on the insulating layer; a hole formation step of forming a hole in the insulating layer and the metal foil layer; and a plating step of forming a plating layer around and inside the hole, wherein the plating step includes: a first plating step of forming a first plating layer around and inside the hole by a panel plating method; and a second plating step of forming a second plating layer around and inside the hole by a pattern plating method.
  2. The method of manufacturing the flexible printed wiring board according to claim 1, wherein the first plating step includes forming the first plating layer such that the first plating layer has a thickness of 1/2 or less of a thickness of the metal foil layer, and the second plating step includes forming the second plating layer such that the second plating layer has a thickness of 1/2 or less of the thickness of the metal foil layer.
  3. The method of manufacturing the flexible printed wiring board according to claim 1 or 2, wherein the second plating step is performed after the first plating step and includes forming the second plating layer on the first plating layer.
  4. The method of manufacturing the flexible printed wiring board according to claim 1 or 2, wherein the first plating step is performed after the second plating step and includes forming the first plating layer on the second plating layer.
  5. The method of manufacturing the flexible printed wiring board according to any one of claims 1 to 4, further comprising a patterning step of etching the second plating layer, the first plating layer, and the metal foil layer to form a wiring pattern and a land portion surrounding the hole, wherein in the land portion, a diameter of the second plating layer is smaller than a diameter of the first plating layer.
  6. A flexible printed wiring board comprising: an insulating layer; and a land portion laminated on the insulating layer, wherein the land portion includes: a metal foil layer; a third plating layer laminated on the metal foil layer; and a fourth plating layer laminated on the third plating layer, the flexible printed wiring board has a hole formed in the insulating layer and the metal foil layer and surrounded by the land portion, the third and fourth plating layers are formed around and inside the hole, and in the land portion, a diameter of the third plating layer is different from a diameter of the fourth plating layer.
  7. The flexible printed wiring board according to claim 6, wherein a thickness of the third plating layer is 1/2 or less than a thickness of the metal foil layer, and a thickness of the fourth plating layer is 1/2 or less than the thickness of the metal foil layer.

Description

Technical Field The present invention relates to a method of manufacturing a flexible printed wiring board as well as a flexible printed wiring board. In designated states where incorporation of documents by reference is accepted, the contents described in Japanese Patent Application No. 2023-109563 filed on July 3, 2023 in Japan are incorporated by reference into this specification and are regarded as a portion of the description of this specification. Background Art An increase in the total thickness of electrode layers that form a wiring circuit is disadvantageous for forming fine wiring (see, for example, paragraph [0004] of Patent Document 1). In contrast to this, it has been known to manufacture a printed wiring board using a button plating method in which plating is applied thickly only to an interlayer connection portion to ensure connection reliability (see, for example, paragraphs [0006] to [0016] and FIG. 5 of Patent Document 1). In the button plating method, the printed wiring board is usually manufactured by the following steps. First, a double-sided copper clad laminate having copper foils on both sides of an insulating base material is prepared (see, for example, FIG. 5(1) of Patent Document 1). Next, a through hole is formed in the double-sided copper clad laminate, and subsequently, desmear treatment and conductive treatment are performed as pretreatment for achieving interlayer connection by electrolytic plating (see, for example, FIG. 5(2) of Patent Document 1). Next, a photosensitive dry film to be used as a plating resist is laminated, followed by exposure and development, whereby an opening of the photosensitive dry film is formed at and around the through hole. Next, a copper plating layer is formed over the through hole of the double-sided copper clad laminate and the opening of the photosensitive dry film using an electrolytic copper plating process to achieve electrical interlayer connection. Subsequently, by peeling off the photosensitive dry film, the double-sided copper clad laminate in which plating is applied thickly only to the interlayer connection portion is obtained (see, for example, FIG. 5(3) of Patent Document 1). Next, photosensitive dry films to be used as etching resists are laminated on both sides of the double-sided copper clad laminate, followed by exposure and development (see, for example, FIG. 5(4) of Patent Document 1). Next, a wiring circuit is formed on the copper foil using etching by a subtractive method, and the photosensitive dry film is peeled off (see, for example, FIG. 5(5) of Patent Document 1). Through the above steps, a double-sided printed wiring board in which plating is applied thickly only to the interlayer connection portion is obtained. Prior Art Document Patent Document Patent Document 1: JP 2009-88334 A Summary of Invention Problems to Be Solved by Invention In the above conventional technique using the button plating method, a level difference formed between the copper foil as a base and the plating applied thickly only to the interlayer connection portion becomes large. Accordingly, when the photosensitive dry film to be used as the etching resist is laminated on the double-sided copper clad laminate, the photosensitive dry film may tear due to the level difference, causing poor formation in the wiring circuit. On the other hand, when the plating formed by the button plating method is thinned to make the level difference small, the interlayer connection portion becomes thinner, leading to a possibility of a reduction in electrical connection reliability. A problem to be solved by the present invention is to provide a method of manufacturing a flexible printed wiring board as well as a flexible printed wiring board that is capable of suppressing poor formation of a wiring pattern and improving connection reliability. Means for Solving Problems [1] An aspect 1 of the present invention is a method of manufacturing a flexible printed wiring board, the method including a preparing step of preparing a substrate having an insulating layer and a metal foil layer laminated on the insulating layer, a hole formation step of forming a hole in the insulating layer and the metal foil layer, and a plating step of forming a plating layer around and inside the hole, the plating step including a first plating step of forming a first plating layer around and inside the hole by a panel plating method, and a second plating step of forming a second plating layer around and inside the hole by a pattern plating method.[2] An aspect 2 of the present invention may be the method of manufacturing the flexible printed wiring board according to the aspect 1, in which the first plating step may include forming the first plating layer such that the first plating layer has a thickness of 1/2 or less of a thickness of the metal foil layer, and the second plating step may include forming the second plating layer such that the second plating layer has a thickness of 1/2 or