Shield-equipped flexible printed wiring board

Abstract

This shield-equipped flexible printed wiring board comprises: a flexible printed wiring board that has a base material layer on which a ground circuit is formed; a first electromagnetic wave shield layer that is deposited on a first surface of the flexible printed wiring board; a second electromagnetic wave shield layer that is deposited on a second surface on the opposite side from the first surface of the flexible printed wiring board; a first electrically conductive adhesive layer that electrically connects the first electromagnetic wave shield layer to the ground circuit while bonding the first electromagnetic wave shield layer to the first surface; and a second electrically conductive adhesive layer that electrically connects the second electromagnetic wave shield layer to the ground circuit while bonding the second electromagnetic wave shield layer to the second surface. The shield-equipped flexible printed wiring board has a through-hole that penetrates the base material layer in the thickness direction, and an electrically conductive material is disposed in the through-hole.

Description

Flexible Printed Wiring Board with Shield Cross - reference to Related Applications

[0001] This application claims the priority of Japanese Patent Application No. 2025 - 009007, which is incorporated herein by reference.

[0002] The present invention relates to a flexible printed wiring board with a shield.

[0003] Conventionally, in order to take EMC countermeasures in electronic devices, an electromagnetic wave shield has been formed on a flexible printed wiring board using an electromagnetic wave shield film. Generally, a flexible printed wiring board includes a base material layer on which a wiring pattern including a ground circuit is formed on the surface, and a coverlay laminated on the base material layer so as to cover the wiring pattern. On the other hand, an electromagnetic wave shield film includes an electromagnetic wave shield layer formed of a metal foil or the like, and a conductive adhesive layer containing conductive particles. And, in order to exhibit sufficient shielding characteristics in the shielded flexible printed wiring board, the electromagnetic wave shield film is adhered to the flexible printed wiring board so that the electromagnetic wave shield layer and the ground circuit are electrically connected through the conductive adhesive layer.

[0004] As a specific method of forming such electrical connection, after forming through - holes in the coverlay to expose the ground circuit, the electromagnetic wave shield film is thermocompression - bonded to the coverlay in a state where the coverlay and the conductive adhesive layer are in contact. As a result, the conductive adhesive flows into the through - holes from the conductive adhesive layer, and a conduction path is formed between the ground circuit and the electromagnetic wave shield layer through the conductive adhesive filled in the through - holes and the conductive adhesive layer formed between the coverlay and the electromagnetic wave shield layer.

[0005] Furthermore, electromagnetic shielding is being formed not only on the first surface (one side) of the flexible printed circuit board, but also on both the first and second surfaces (both sides). Regarding such a flexible printed circuit board, Patent Document 1 describes forming a first through-hole in the coverlay to expose the ground circuit in the same manner as described above, and further forming a second through-hole that penetrates the coverlay and the substrate layer. Then, with the coverlay and the conductive adhesive layer in contact, the first electromagnetic shielding film is heat-pressed onto the coverlay, and with the substrate layer and the conductive adhesive layer in contact, the other electromagnetic shielding film is heat-pressed onto the substrate layer. As a result, conductive adhesive flows from the conductive adhesive layers on both the first and second surfaces into the second through-hole. Then, a conductive path is formed between the ground circuit and the electromagnetic shielding layer on the second surface through the conductive adhesive filling the second through-hole and the conductive adhesive layer formed on the second surface.

[0006] Japanese Patent Application Publication No. 2010-177472

[0007] Incidentally, in order to further miniaturize electronic devices, it may be desirable to reduce the thickness of shielded flexible printed circuit boards that serve as components. However, forming electromagnetic shielding on both sides inevitably increases the thickness. To address the demand for thickness reduction, one option is to reduce the thickness of the conductive adhesive layer. However, in order to allow a sufficient amount of conductive adhesive to flow into the through-holes and form a stable conductive path between the ground circuit and the electromagnetic shielding layer, it is necessary to use a conductive adhesive layer with a certain thickness or more. For this reason, it is considered difficult to satisfy the demand for thickness reduction with conventional conductive paths using through-holes as described in Patent Document 1, etc.

[0008] In view of the above circumstances, the object of the present invention is to provide a shielded flexible printed circuit board that has conductive paths that can reduce the thickness while forming electromagnetic wave shields on both sides.

[0009] The shielded flexible printed circuit board according to the present invention is as follows: (1) A flexible printed circuit board having a ground circuit; a first electromagnetic wave shielding layer laminated on a first surface of the flexible printed circuit board; a second electromagnetic wave shielding layer laminated on a second surface of the flexible printed circuit board opposite to the first surface; a first conductive adhesive layer that adheres the first electromagnetic wave shielding layer to the first surface while providing electrical conductivity with the ground circuit; and a second conductive adhesive layer that adheres the second electromagnetic wave shielding layer to the second surface while providing electrical conductivity with the ground circuit, wherein the flexible printed circuit board includes a base material layer having a first surface on which the ground circuit is formed, has through holes penetrating the base material layer in the thickness direction, a conductive material is disposed in the through holes, and the second electromagnetic wave shielding layer and the ground circuit are electrically connected via the conductive material.

[0010] (2) The shielded flexible printed circuit board according to (1) above, wherein the through hole extends through the ground circuit, and the conductive material is arranged to connect with the circumferential surface of the ground circuit.

[0011] (3) The shielded flexible printed circuit board according to (1) or (2) above, wherein a plating is formed on the wall surface of the through hole as the conductive material, and the plating forms a conductive peripheral wall on the wall surface of the through hole.

[0012] (4) The shielded flexible printed circuit board according to any one of (1) to (3) above, wherein the flexible printed circuit board has a conductive bottom that closes the through hole on the side of the second electromagnetic wave shielding layer, and the conductive material in the through hole is arranged to be connected to the conductive bottom.

[0013] (5) The shielded flexible printed circuit board as described in (4) above, wherein the conductive bottom portion is embedded in the second conductive adhesive layer.

[0014] According to the present invention, it is possible to provide a shielded flexible printed circuit board that has conductive paths that can reduce thickness while forming electromagnetic wave shields on both sides.

[0015] This is a schematic cross-sectional view showing the layer structure and conduction paths of a shielded flexible printed circuit board according to one embodiment. This is a schematic cross-sectional view of a copper-clad laminate used in the manufacture of the shielded flexible printed circuit board shown in Figure 1. This is a schematic cross-sectional view showing that a second through-hole has been formed in the copper-clad laminate shown in Figure 2 to form a conduction path in the thickness direction. This is a schematic cross-sectional view showing that the portion of the second copper foil exposed by the formation of the second through-hole (exposed surface) in Figure 3 has been plated. This is a schematic cross-sectional view showing that the second copper foil has been etched so as to leave a conductive bottom portion in Figure 4. This is a schematic cross-sectional view showing that a coverlay has been laminated over the ground circuit shown in Figure 5 via an insulating adhesive layer. This is a schematic cross-sectional view showing that a first through-hole has been formed in the coverlay and insulating adhesive layer to form a conduction path in the thickness direction in Figure 6.

[0016] Hereinafter, with reference to the drawings, a shielded flexible printed circuit board according to one embodiment of the present invention will be described.

[0017] The shielded flexible printed circuit board of this embodiment is manufactured by bonding an electromagnetic wave shielding film, which comprises an electromagnetic wave shielding layer and a conductive adhesive layer, to a flexible printed circuit board. In other words, in the manufacture of the shielded flexible printed circuit board of this embodiment, the electromagnetic wave shielding film is used as the material. The conductive adhesive layer in the electromagnetic wave shielding film contains a thermosetting resin composition and conductive particles. In the manufacture of the shielded flexible printed circuit board of this embodiment, the first electromagnetic wave shielding film is heat-pressed onto the flexible printed circuit board with the conductive adhesive layer in contact with the first surface of the flexible printed circuit board. The second electromagnetic wave shielding film is heat-pressed onto the flexible printed circuit board with the conductive adhesive layer in contact with the second surface (the surface opposite to the first surface) of the flexible printed circuit board. This results in a double-sided shielded flexible printed circuit board in which electromagnetic wave shielding layers are laminated on both the first and second surfaces of the flexible printed circuit board. In the following, with respect to the surfaces of each layer constituting the flexible printed circuit board, the surface that is located on the side of the first electromagnetic shielding film in the thickness direction of the flexible printed circuit board will be referred to as the first surface, and the surface that is located on the side of the second electromagnetic shielding film will be referred to as the second surface.

[0018] As shown in Figure 1, the shielded flexible printed circuit board 1 of this embodiment comprises a flexible printed circuit board 10, a first electromagnetic wave shielding layer 20a laminated on the first surface of the flexible printed circuit board 10, and a second electromagnetic wave shielding layer 20b laminated on the second surface of the flexible printed circuit board 10. The first electromagnetic wave shielding layer 20a is bonded to the first surface of the flexible printed circuit board 10 by a first conductive adhesive layer 21a. The second electromagnetic wave shielding layer 20b is bonded to the second surface of the flexible printed circuit board 10 by a second conductive adhesive layer 21b. Optionally, the shielded flexible printed circuit board may also include a first protective layer laminated on the first surface of the first electromagnetic wave shielding layer, or a second protective layer laminated on the second surface of the second electromagnetic wave shielding layer. The protective layer is, for example, an insulating resin layer.

[0019] The flexible printed circuit board 10 of this embodiment comprises a base layer 11 which is a first insulating layer having insulating properties, a wiring pattern 12 formed on the first surface of the base layer 11 which includes a ground circuit 121, and a second insulating layer 13 which includes a coverlay 131 that covers the wiring pattern 12.

[0020] The base layer 11 of this embodiment is composed of an insulating base sheet 11s, a first insulating adhesive layer 11a laminated on the first surface of the base sheet 11s, and a second insulating adhesive layer 11b laminated on the second surface of the base sheet 11s. The wiring pattern 12 is bonded to the first surface of the base sheet 11s by the first insulating adhesive layer 11a. The flexible printed circuit board 10 of the present invention is a single-sided flexible printed circuit board in which the wiring pattern 12 is formed only on the first surface of the base layer 11. Therefore, the flexible printed circuit board 10 of this embodiment has a second insulating layer 13 (coverlay 131) only on the first surface side via the base layer 11, and does not have an insulating layer (coverlay) on the second surface side via the base layer 11. This reduces the thickness.

[0021] The second insulating layer 13 in this embodiment is composed of a coverlay 131 and a third insulating adhesive layer 132 formed between the wiring pattern 12 and the coverlay 131.

[0022] The flexible printed circuit board 10 of this embodiment has a first through-hole 15 that penetrates the second insulating layer 13 in the thickness direction and extends to the ground circuit 121 in order to form a conductive path between the ground circuit 121 and the first conductive adhesive layer 21a. The flexible printed circuit board 10 of this embodiment also has a second through-hole 16 that penetrates the base layer 11 in the thickness direction and extends to the ground circuit 121 in order to form a conductive path between the ground circuit 121 and the second conductive adhesive layer 21b.

[0023] Due to the layer structure described above, the second conductive adhesive layer 21b is positioned away from the ground circuit 121 by the thickness of the base layer 11. Typically, because the thickness of the base layer 11 is relatively large, the distance of the second conductive adhesive layer 21b from the ground circuit 121 in the thickness direction is greater than that of the first conductive adhesive layer 21a. Therefore, in order to form a conductive path between the second electromagnetic shield layer and the ground circuit using the conventional method employing through holes, it is necessary to form through holes that extend long in the thickness direction and fill such long through holes with conductive adhesive. In such filling, it is necessary to use an electromagnetic shield film equipped with a thick conductive adhesive layer, and consequently, the thickness of the second conductive adhesive layer also increases.

[0024] In contrast, the second through-hole is filled with a conductive material such as plating or conductive paste. When plating is used as the conductive material, the shielded flexible printed circuit board is highly productive and costs can be reduced. When conductive paste is used as the conductive material, the second through-hole is closed, which increases the area on which components can be mounted. Specifically, in the flexible printed circuit board 10 of this embodiment, plating is formed as the conductive material on the wall surface defining the second through-hole 16, and this plating forms a conductive peripheral wall portion 16p on the peripheral wall of the second through-hole 16. Alternatively, a conductive paste may be used as the conductive material, and this conductive paste may be filled into the second through-hole 16. The conductive paste usually contains a thermosetting resin composition and conductive particles such as metal particles. By forming a conductive path extending in the thickness direction by the conductive peripheral wall portion 16p, the second conductive adhesive layer 21b and the ground circuit 121 can be made electrically connected without increasing the thickness of the conductive adhesive layer of the electromagnetic wave shielding film. Therefore, the conductive peripheral wall portion 16p makes it possible to reduce the thickness of the second conductive adhesive layer 21b.

[0025] In this embodiment, the second through-hole 16 extends in the thickness direction so as to penetrate not only the base layer 11 but also the ground circuit 121. The flexible printed circuit board 10 of this embodiment has a conductive peripheral wall portion 16p that extends in the thickness direction, due to plating being formed over the circumferential surface of the base layer 11 defining the second through-hole 16. Furthermore, plating is also formed on the circumferential surface of the ground circuit 121 defining the second through-hole 16. In other words, the flexible printed circuit board 10 of this embodiment has a second through-hole 16 defined from the circumferential surface of the base layer 11 to the circumferential surface of the ground circuit 121, and has a conductive peripheral wall portion 16p whose wall surface defining the second through-hole 16 is plated. In this embodiment, the entire wall surface is plated. This conductive peripheral wall portion 16p makes the conductivity between the second conductive adhesive layer 21b and the ground circuit 121 more stable. The wall surface defining the second through-hole 16 may be flush with the surface. This is thought to allow for the formation of a clean plating.

[0026] Furthermore, as shown in Figure 1, plating may also be formed on the opening edge of the first surface of the ground circuit 121, so that the plating is physically connected to the plating on the circumferential surface of the ground circuit 121. This further stabilizes the conductivity between the second conductive adhesive layer 21b and the ground circuit 121.

[0027] Furthermore, the flexible printed circuit board 10 of this embodiment has a conductive bottom portion 17p that closes the tip of the second through hole 16 on the second surface side. The conductive bottom portion 17p is made of, for example, copper foil. The closing surface of the second through hole 16 in the conductive bottom portion 17p is plated. When the second through hole 16 is viewed in the thickness direction, at least a portion of the outer edge of the conductive bottom portion 17p is located outside the outer edge that defines the tip of the second through hole 16 on the second surface side. Preferably, the entire outer edge of the conductive bottom portion 17p is located outside the outer edge that defines the tip of the second through hole 16 on the second surface side. Since such a conductive bottom portion 17p can increase the contact area with the second conductive adhesive layer 21b, a stable conductive path can be formed between the second conductive adhesive layer 21b and the ground circuit 121.

[0028] The outer edge of the conductive bottom portion 17p, which is located outside the outer edge defining the second through-hole 16, is bonded to the second surface of the base sheet 11s by the second insulating adhesive layer 11b. As a result, the conductive bottom portion 17p is positioned on the second electromagnetic shielding layer 20b side of the base sheet 11s by the thickness of the second insulating adhesive layer 11b and is embedded in the second conductive adhesive layer 21b. This embedding further increases the contact area of ​​the conductive bottom portion 17p with the second conductive adhesive layer 21b, thereby forming a more stable conductive path between the second conductive adhesive layer 21b and the ground circuit 121. Furthermore, since there is no opening for the conductive adhesive to flow into, the options for formulation, such as the material, particle size, and shape of the conductive particles in the second conductive adhesive layer 21b, and the curability of the curable resin composition, can be increased.

[0029] Examples of materials for forming the plating on the conductive peripheral wall portion 16p and the opening edge portion of the ground circuit 121 include nickel, chromium, molybdenum, titanium, vanadium, tin, gold, silver, copper, zinc, palladium, ruthenium, rhodium, iron, and aluminum, or alloys containing two or more of these metals.

[0030] In this embodiment, when laminating the coverlay 131 and the third insulating adhesive layer 132, the coverlay film having the insulating adhesive layer is heat-pressed with the conductive peripheral wall portion 16p and conductive bottom portion 17p exposed. As a result, the insulating adhesive is filled inside the conductive peripheral wall portion 16p, and the conductive peripheral wall portion 16p is covered by the coverlay 131 via the third insulating adhesive layer 132. In other words, the coverlay 131 in this embodiment is arranged to protect the conductive peripheral wall portion 16p by covering it with the insulating adhesive filled in the conductive peripheral wall portion 16p and the third insulating adhesive layer 132.

[0031] In this embodiment, a recessed portion 133 may be formed in the coverlay 131 at a position overlapping with the conductive peripheral wall portion 16p in the thickness direction during the heat-sealing process described above. The recessed portion 133 is recessed toward the conductive bottom portion 17p. The recessed portion 133 in this embodiment is filled with conductive adhesive derived from the conductive adhesive layer of the electromagnetic wave shielding film, and the conductive adhesive within the recessed portion 133 is connected to the first conductive adhesive layer 21a. In addition, the recessed portion 133 may be closed with a filler such as conductive paste. Furthermore, to prevent the formation of the recessed portion 133, a filler such as conductive paste may be filled inside the conductive peripheral wall portion 16p before the heat-sealing of the coverlay film.

[0032] In this embodiment, the first through-hole 15 extends through the coverlay 131 and the third insulating adhesive layer 132 in the thickness direction to the first surface of the ground circuit 121. As a result, the first through-hole 15 in this embodiment is closed by the first surface of the ground circuit 121. The closing surface of the first through-hole 15 in the ground circuit 121 may be plated. On the other hand, in this embodiment, the circumferential surfaces defining the first through-hole 15 of the coverlay 131 and the third insulating adhesive layer 132 are not plated, but these circumferential surfaces may also be plated. That is, the flexible printed circuit board may have conductive circumferential walls formed by plating the circumferential surfaces of each layer defining the first through-hole 15. As a result, the thickness of the first conductive adhesive layer 21a can be reduced in the same way as the second conductive adhesive layer 21b.

[0033] In this embodiment, the first through-hole 15 is formed in a position that does not overlap with the second through-hole 16 in the thickness direction.

[0034] In this embodiment, the thickness of each layer in the flexible printed circuit board 10 is such that the base material layer 11 has the greatest thickness, specifically the base material sheet 11s, and each insulating adhesive layer has the next greatest thickness after the base material sheet 11s. Therefore, forming a second through-hole 16 so that it penetrates the base material layer 11, which serves as a barrier for the conductivity of the second conductive adhesive layer 21b to the ground circuit 121, toward the second conductive adhesive layer 21b, and forming a conductive peripheral wall portion 16p is considered an important technical matter in solving the problems of the present invention. The thickness of the circuit layer including the ground circuit 121 is the smallest. Also, the thickness of the coverlay 131 is smaller than the thickness of the base material layer 11 and each insulating adhesive layer, but larger than the thickness of the circuit layer.

[0035] The thickness of the base layer 11 is, for example, 7 μm to 300 μm. The thickness of the base sheet 11s is, for example, 5 μm to 250 μm. The thickness of the circuit layer is, for example, 0.1 μm to 150 μm. The thickness of each insulating adhesive layer is, for example, 0.5 μm to 30 μm.

[0036] The base sheet 11s is formed from an insulating base film. Examples of the base film include polyimide film, polyethylene terephthalate film (PET film), polyethylene naphthalate film (PEN film), polyether ether ketone film (PEEK film), fluororesin film, and liquid crystal polymer film.

[0037] The wiring pattern 12 forms a circuit layer that includes a ground circuit 121 and a signal circuit.

[0038] The wiring pattern 12 in this embodiment is formed from metal foil. Examples of the metal foil include copper foil such as electrolytic copper foil and rolled copper foil, aluminum foil, nickel foil, and stainless steel foil. When metal foil is used, an insulating adhesive layer (first insulating adhesive layer 11a) is formed between the first surface of the base sheet 11s and the wiring pattern 12. Alternatively, the wiring pattern may be formed from a deposited metal film. Examples of methods for forming the deposited film include sputtering, vacuum deposition, electrolytic plating, and electroless plating. When a deposited film is used, a seed layer may be formed between the first surface of the base sheet 11s and the wiring pattern. The seed layer may be formed by sputtering using a metal such as nickel or a nickel-platinum alloy.

[0039] The coverlay 131 is formed from a coverlay film. The coverlay film comprises an insulating resin layer and an insulating adhesive layer laminated on the insulating resin layer. The insulating resin layer is composed of, for example, a polyimide film, a polyethylene terephthalate film (PET film), a polyethylene naphthalate film (PEN film), a polyether ether ketone film (PEEK film), a fluororesin film, and a liquid crystal polymer film. From the viewpoint of facilitating the formation of the opening, the coverlay may be a printed type formed from an ink containing a curable resin composition, or a photosensitive type formed from a photosensitive resin.

[0040] Each insulating adhesive layer contains a binder resin. The binder resin may be a curable resin or a thermoplastic resin. Examples of the curable resin include phenolic resins, epoxy resins, urethane resins, melamine resins, alkyd resins, etc. Examples of the thermoplastic resin include polyester resins, polyolefin resins, polystyrene resins, vinyl acetate resins, polyimide resins, polyamide resins, acrylic resins, etc. The curable resin has reaction curability. The curing reaction of the curable resin may be promoted by, for example, thermal energy or energy rays such as ultraviolet rays and electron beams. That is, the curable resin may be a thermosetting resin or a photocurable resin. Examples of the binder resin include epoxy resins, acrylic resins, and urethane resins.

[0041] Each of the first electromagnetic wave shielding layer 20a and the second electromagnetic wave shielding layer 20b may be composed of a metal foil formed by rolling, or may be a deposited film formed by a deposition method such as electrolytic plating, vacuum evaporation, sputtering, CVD method, etc. Examples of the material for forming each electromagnetic wave shielding layer include copper, nickel, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, and alloys composed of two or more of these.

[0042] Each of the first conductive adhesive layer 21a and the second conductive adhesive layer 21b contains conductive particles contained in the conductive adhesive layer of the electromagnetic wave shielding film and a binder resin.

[0043] Examples of the conductive particles include metal particles such as copper particles, silver particles, nickel particles, silver-coated copper particles, gold-coated copper particles, silver-coated nickel particles, gold-coated nickel particles, silver-coated alloy particles, carbon fillers, and metal-coated resin particles. Examples of the shape of the conductive particles include spherical, plate-like, needle-like, and dendritic.

[0044] As the binder resin, the same one as that contained in the insulating adhesive layer can be used.

[0045] The shielded flexible printed wiring board 1 of the present embodiment can be manufactured using a copper-clad laminate. Hereinafter, a method for manufacturing the shielded flexible printed wiring board 1 using a double-sided copper-clad laminate will be described while referring to FIGS. 2 to 7.

[0046] As shown in FIG. 2, the copper-clad laminate CCL as a material includes a base material layer 11, a first copper foil c1 adhered to the first surface of the base material sheet 11s by a first insulating adhesive layer 11a, and a second copper foil c2 adhered to the second surface of the base material sheet 11s by a second insulating adhesive layer 11b.

[0047] As shown in FIG. 3, in the manufacturing method according to the present embodiment, a second through hole 16 is formed that penetrates in the thickness direction from the first copper foil c1 to the second insulating adhesive layer 11b and has a tip in the penetration direction blocked by the second copper foil c2. Thereby, a second through hole 16 defined by the circumferential surfaces of the first copper foil c1 and the second insulating adhesive layer 11b and having a tip in the penetration direction blocked by the second copper foil c2 is obtained. Also, the second copper foil c2 exposed at the portion where the second through hole 16 is formed is obtained.

[0048] Next, as shown in Figure 4, conductivity is imparted to at least the circumferential surface of the layer located on the side of the second copper foil c2 to the first copper foil c1 among the circumferential surfaces of each layer defining the second through hole 16. In this embodiment, the circumferential surface is plated. In this embodiment, the circumferential surfaces of the first copper foil c1 and the base layer 11 are plated. This gives rise to a conductive circumferential wall portion 16p. At this time, a uniform thickness of plating may be formed across the circumferential surface of each layer, or there may be a difference in the thickness of the plating on the circumferential surface of each layer. For example, by making the plating thickness on the circumferential surface of the second insulating adhesive layer 11b, or on the circumferential surface of the base sheet 11s on the second copper foil c2 side, thicker than the plating thickness on the circumferential surface on the first copper foil c1 side, the wall surface of the conductive circumferential wall portion 16p will have a shape that expands in diameter as it moves from the second copper foil c2 side towards the first copper foil c1 side. Compared to a shape where the wall surface contracts in diameter as it moves from the second copper foil c2 side towards the first copper foil c1 side, it is thought that the filling ability of the filler material (filler material derived from the third insulating adhesive layer 132) that will be placed inside the conductive circumferential wall portion 16p will be improved (it will be easier for the filler material to flow in). Such a shape may also be obtained by forming the wall surface defining the second through hole 16 to expand in diameter as it moves from the second copper foil c2 side towards the first copper foil c1 side, and by forming a plating of uniform thickness on the wall surface. In other words, the wall surface of the conductive peripheral wall portion 16p may be formed so as to increase in diameter from the second copper foil c2 side toward the first copper foil c1 side. Furthermore, in this embodiment, the exposed surface of the second copper foil c2 is plated. In addition, the opening edge on the first surface of the first copper foil c1 may also be plated.

[0049] Next, as shown in Figure 5, the second copper foil c2 is etched so as to leave the conductive bottom portion 17p. At this time, fine irregularities may be formed on the surface of the second insulating adhesive layer 11b that is exposed by the removal of the second copper foil c2. It is believed that such a surface will have excellent adhesion to the second conductive adhesive layer due to the anchoring effect.

[0050] Next, as shown in Figure 6, a coverlay film having an insulating adhesive layer is heat-pressed onto the first surface of the first copper foil c1, the insulating adhesive of the insulating adhesive layer is filled into the inside of the conductive peripheral wall portion 16p, and the circuit layer is covered with a coverlay 131 while laminating a third insulating adhesive layer 132 onto the first surface of the first copper foil c1. At this time, a recessed portion 133 is formed in the coverlay 131.

[0051] Next, as shown in Figure 7, the coverlay 131 is penetrated through to the third insulating adhesive layer 132 in the thickness direction. This creates a first through-hole 15 that is defined by the respective circumferential surfaces of the coverlay 131 and the third insulating adhesive layer 132, and exposes the first surface of the ground circuit 121. In this embodiment, the exposed surface of the first copper foil c1 is plated. Alternatively, the respective circumferential surfaces of the coverlay 131 and the third insulating adhesive layer 132 may be plated to form a conductive circumferential wall portion in the first through-hole 15.

[0052] Finally, as shown in Figure 1, the electromagnetic shielding film is heat-pressed onto the first surface of the coverlay 131, the first through-hole 15 is filled with conductive adhesive, and the first conductive adhesive layer 21a is laminated onto the first surface of the coverlay 131 to form the first electromagnetic shielding layer 20a. Furthermore, with the conductive bottom portion 17p in contact with the conductive adhesive layer of the electromagnetic shielding film, the electromagnetic shielding film is heat-pressed onto the second insulating adhesive layer 11b, and the conductive bottom portion 17p is embedded in the second conductive adhesive layer 21b while the second conductive adhesive layer 21b is laminated onto the second surface of the second insulating adhesive layer 11b to form the second electromagnetic shielding layer 20b. This gives rise to the shielded flexible printed circuit board 1.

[0053] Although one embodiment has been shown as an example, the shielded flexible printed circuit board according to the present invention is not limited to the configuration of the above embodiment. Furthermore, the shielded flexible printed circuit board according to the present invention is not limited by the above-described effects. The shielded flexible printed circuit board according to the present invention can be modified in various ways without departing from the spirit of the present invention.

[0054] 1: Shielded flexible printed circuit board, 10: Flexible printed circuit board, 11: Base layer, 11s: Base sheet, 11a: First insulating adhesive layer, 11b: Second insulating adhesive layer, 12: Wiring pattern, 121: Ground circuit, 13: Second insulating layer, 131: Coverlay, 132: Third insulating adhesive layer, 133: Recessed portion, 15: First through hole, 16: Second through hole, 16p: Conductive peripheral wall portion, 17p: Conductive bottom portion, 20a: First electromagnetic shielding layer, 20b: Second electromagnetic shielding layer, 21a: First conductive adhesive layer, 21b: Second conductive adhesive layer, CCL: Copper-clad laminate, c1: First copper foil, c2: Second copper foil

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