Electromagnetic wave shielding film and shielded printed wiring board

Abstract

The purpose of the present invention is to provide an electromagnetic wave shielding film in which a crack is not generated in a protective layer even if the film is repeatedly bent, and shield performance is not susceptible to deterioration. This electromagnetic wave shielding film according to the present invention is obtained by sequentially laminating a protective layer, a shield layer, and an adhesive layer, and is characterized in that the ratio (hardness / Young's modulus) of the hardness to the Young's modulus of the protective layer as measured by a nanoindentation test conforming to ISO 14577 is 0.05-0.10.

Description

Electromagnetic wave shielding film and shielded printed wiring board

[0001] The present invention relates to an electromagnetic wave shielding film and a shielded printed wiring board.

[0002] Mobile devices such as smartphones and tablet terminals use printed wiring boards with electromagnetic wave shielding film attached (hereinafter simply referred to as "shielded printed wiring boards") to block electromagnetic waves generated from inside and electromagnetic waves entering from outside.

[0003] As such an electromagnetic wave shielding film, Patent Document 1 discloses an electromagnetic wave shielding sheet comprising a conductive layer and an insulating layer, the insulating layer containing a thermosetting resin, a curing agent, and a black colorant, and the black colorant having an average primary particle diameter of 20 to 100 nm.

[0004] JP 2016-143751 A

[0005] Until now, smartphones and other devices have been straight-type devices with no moving parts. However, due to the need for larger screens and higher functionality, foldable phones have emerged, and demand for this type of smartphone is expected to increase further in the future. In foldable phones, flexible printed wiring boards with electromagnetic wave shielding film attached are placed even in the moving parts. Foldable phones have a structure in which the moving parts can bend nearly 180 degrees. Conventional electromagnetic wave shielding films have poor resistance to repeated bending at such moving parts, and cracks are likely to occur in the protective layer of the electromagnetic wave shielding film when folded. Cracks in the protective layer also make it easier for cracks to occur in the shielding layer, which causes the problem of reduced shielding performance.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide an electromagnetic wave shielding film that does not develop cracks in the protective layer even when repeatedly bent and is less likely to lose shielding performance.

[0007] The electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film in which a protective layer, a shielding layer, and an adhesive layer are laminated in this order, and is characterized in that the ratio (hardness / Young's modulus) of the hardness of the protective layer (hereinafter also simply referred to as "hardness of the protective layer") to the Young's modulus of the protective layer (hereinafter also simply referred to as "Young's modulus of the protective layer") measured by a nanoindentation test in accordance with ISO 14577 is 0.05 to 0.10.

[0008] When the ratio of the hardness of the protective layer to the Young's modulus of the protective layer is within the above range, the protective layer has appropriate elasticity and hardness, and cracks are unlikely to occur in the protective layer even when the electromagnetic wave shielding film is bent at a steep angle.

[0009] In the electromagnetic wave shielding film, the protective layer preferably contains a particulate filler, which can adjust the hardness and Young's modulus of the protective layer.

[0010] In the electromagnetic wave shielding film, the particulate filler preferably includes inorganic particles and / or resin particles. The inorganic particles preferably include at least one selected from the group consisting of carbon, silica, and alumina. These particulate fillers are suitable for adjusting the hardness and Young's modulus of the protective layer.

[0011] In the electromagnetic wave shielding film, the weight percentage of the particulate filler in the protective layer is preferably 2 to 22 wt %. If the weight percentage of the particulate filler is less than 2 wt %, the protective layer becomes too soft. If the weight percentage of the particulate filler is more than 22 wt %, the protective layer becomes too hard.

[0012] In the electromagnetic wave shielding film, the protective layer preferably contains at least one resin selected from the group consisting of polyimide resin, acrylic resin, epoxy resin, polyester resin, polyamide-imide resin, and urethane resin. These resins have sufficient insulating properties and are suitable materials for protecting the shielding layer and adhesive layer. Furthermore, when the protective layer contains such a resin, cracks are less likely to occur in the protective layer when the electromagnetic wave shielding film is bent at a steep angle.

[0013] In the electromagnetic wave shielding film, the adhesive layer is preferably a conductive adhesive layer. When the adhesive layer is a conductive adhesive layer, the shielding layer of the electromagnetic wave shielding film can be electrically connected to the ground circuit of the printed wiring board. In this case, the shielding performance of the electromagnetic wave shielding film is improved.

[0014] In the electromagnetic wave shielding film, the conductive adhesive layer is preferably an anisotropically conductive adhesive layer, which improves the transmission characteristics of high-frequency signals transmitted through signal circuits of the printed wiring board compared to when the conductive adhesive layer has anisotropic conductivity.

[0015] The shielded printed wiring board of the present invention is a shielded printed wiring board including a flexible printed wiring board having a base film, a printed circuit arranged on the base film, and a coverlay arranged to cover the printed circuit, and an electromagnetic wave shielding film arranged on the coverlay side of the flexible printed wiring board, characterized in that the electromagnetic wave shielding film is the electromagnetic wave shielding film of the present invention.

[0016] As described above, even when the electromagnetic wave shielding film of the present invention is bent at a steep angle, cracks are unlikely to occur in the protective layer. Therefore, even when the shielded printed wiring board of the present invention including the electromagnetic wave shielding film of the present invention is bent at a steep angle, cracks are unlikely to occur in the protective layer of the electromagnetic wave shielding film.

[0017] According to the present invention, it is possible to provide an electromagnetic wave shielding film in which cracks do not occur in the protective layer even when repeatedly folded, and in which the shielding performance is not easily deteriorated.

[0018] Fig. 1 is a cross-sectional view schematically showing an example of an electromagnetic wave shielding film of the present invention. Fig. 2 is a cross-sectional view schematically showing an example of a cross-section of a shielded printed wiring board using the electromagnetic wave shielding film of the present invention. Fig. 3 is an enlarged photograph (10x) of the protective layer, which is the criterion for "no cracks in the protective layer" in the evaluation of the bending property test of the electromagnetic wave shielding film. Fig. 4 is an enlarged photograph (10x) of the protective layer, which is the criterion for "cracks in the protective layer" in the evaluation of the bending property test of the electromagnetic wave shielding film.

[0019] The electromagnetic wave shielding film of the present invention will be specifically described below. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0020] 1 is a cross-sectional view schematically illustrating an example of an electromagnetic wave shielding film of the present invention. The electromagnetic wave shielding film 10 shown in Fig. 1 is formed by laminating a protective layer 40, a shielding layer 30, and an adhesive layer 20 in this order.

[0021] In the electromagnetic wave shielding film 10, the ratio of the hardness of the protective layer to the Young's modulus (hardness / Young's modulus) measured by a nanoindentation test in accordance with ISO 14577 is 0.05 to 0.10. This ratio is preferably 0.05 to 0.09, and more preferably 0.06 to 0.08. When the ratio of the hardness of the protective layer to the Young's modulus of the protective layer is within the above range, the protective layer has appropriate elasticity and hardness, and cracks are unlikely to occur in the protective layer even when the electromagnetic wave shielding film is bent at a steep angle.

[0022] In the electromagnetic wave shielding film 10, the hardness of the protective layer 40 is preferably 0.05 to 0.80 GPa, more preferably 0.15 to 0.70 GPa, even more preferably 0.20 to 0.60 GPa, even more preferably 0.22 to 0.56 GPa, and particularly preferably 0.27 to 0.44 GPa. If the hardness of the protective layer is less than 0.05 GPa, the protective layer becomes soft and easily deformed. Therefore, when the electromagnetic wave shielding film is repeatedly bent, portions of the protective layer are likely to thin. Cracks are likely to occur in such thinned portions of the protective layer. If the hardness of the protective layer exceeds 0.80 GPa, the toughness of the protective layer decreases, and therefore cracks are likely to occur in the protective layer when the electromagnetic wave shielding film is bent at a steep angle.

[0023] In the electromagnetic wave shielding film 10, the Young's modulus of the protective layer 40 is preferably 3.0 to 6.5 GPa, more preferably 3.25 to 6.25 GPa, and even more preferably 3.5 to 5.5 GPa. If the Young's modulus of the protective layer is less than 3.0 GPa, the protective layer becomes soft and easily deformed. Therefore, when the electromagnetic wave shielding film is repeatedly folded, parts of the protective layer are likely to become thin. Cracks are likely to occur in these thinned parts of the protective layer. If the Young's modulus of the protective layer exceeds 6.5 GPa, the toughness of the protective layer decreases, and therefore cracks are likely to occur in the protective layer when the electromagnetic wave shielding film is folded at a steep angle.

[0024] The hardness and Young's modulus of the protective layer 40 can be adjusted by adding a particulate filler as described below, selecting the material that constitutes the protective layer 40, or adjusting the degree of polymerization of the resin that constitutes the protective layer.

[0025] In the electromagnetic wave shielding film 10, the protective layer 40 preferably contains a particulate filler. The particulate filler allows the hardness and Young's modulus of the protective layer 40 to be adjusted.

[0026] The particulate filler preferably contains inorganic particles and / or resin particles. Materials constituting the inorganic particles include carbon, silica, and alumina. Materials constituting the resin particles include acrylic and urethane. These particulate fillers are suitable for adjusting the hardness and Young's modulus of the protective layer.

[0027] The particulate filler preferably has an average particle size of 0.05 to 5.0 μm.

[0028] The shape of the particulate filler is not particularly limited, and may be spherical, rod-like, flat, or irregular.

[0029] In the electromagnetic wave shielding film 10, the weight percentage of the particulate filler in the protective layer 40 is preferably 2 to 22 wt %, and more preferably 4 to 20 wt %. If the weight percentage of the particulate filler is less than 2 wt %, the protective layer becomes too soft. If the weight percentage of the particulate filler is more than 22 wt %, the protective layer becomes too hard.

[0030] In the electromagnetic wave shielding film 10, the protective layer 40 preferably contains at least one resin selected from the group consisting of polyimide resin, acrylic resin, epoxy resin, polyester resin, polyamide-imide resin, and urethane resin. Of these, it is more preferable that the protective layer 40 contains a polyimide resin. These resins have sufficient insulating properties and are suitable materials for protecting the shielding layer 30 and the adhesive layer 20. Furthermore, when the protective layer 40 contains such a resin, cracks are less likely to occur in the protective layer 40 when the electromagnetic wave shielding film 10 is bent at a steep angle.

[0031] In the electromagnetic wave shielding film 10, the thickness of the protective layer 40 is preferably 1 to 15 mm, and more preferably 3 to 8 mm. If the thickness of the protective layer is less than 1 μm, it is too thin and therefore weak and prone to breakage. If the thickness of the protective layer exceeds 15 μm, it is too thick and therefore difficult to bend, making it difficult to arrange the electromagnetic wave shielding film on a flexible printed wiring board that is bent at a sharp angle.

[0032] The protective layer 40 may contain, as needed, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a flame retardant, a viscosity adjuster, an antiblocking agent, and the like.

[0033] In the electromagnetic wave shielding film 10, the shielding layer 30 may be made of any material that can shield electromagnetic waves, such as a metal layer or a conductive resin material. It is preferable that the shielding layer be a metal layer.

[0034] The material of the metal layer is not particularly limited, but may be nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, zinc, or an alloy containing two or more of these metals, etc. Among these, copper is preferred.

[0035] The material and thickness of the metal layer may be appropriately selected depending on the required electromagnetic wave shielding effect and resistance to repeated bending and sliding. For example, from the viewpoint of obtaining a sufficient electromagnetic wave shielding effect, the thickness of the metal layer is preferably 0.1 μm or more. From the viewpoints of productivity and flexibility, the thickness of the metal layer is preferably 8 μm or less.

[0036] The metal layer can be formed by electrolytic plating, electroless plating, sputtering, electron beam evaporation, vacuum evaporation, CVD, metal organic, etc. The metal layer can also be formed from metal foil, metal nanoparticles, scale-like metal particles, etc.

[0037] The adhesive layer 20 in the electromagnetic wave shielding film 10 may be made of any material as long as it has the function of adhering the electromagnetic wave shielding film 10 to a flexible printed wiring board, but it is preferable that the adhesive layer 20 contains an adhesive resin as an adhesive component.

[0038] Examples of adhesive resins that can be used include thermoplastic resins such as styrene resins, vinyl acetate resins, polyester resins, polyethylene resins, polypropylene resins, imide resins, amide resins, and acrylic resins, and thermosetting resins such as phenol resins, epoxy resins, urethane resins, melamine resins, and alkyd resins. The adhesive layer 20 may contain one of these resins alone, or two or more of them.

[0039] In the electromagnetic wave shielding film 10, the adhesive layer 20 is preferably a conductive adhesive layer. When the adhesive layer 20 is a conductive adhesive layer, the shielding layer 30 of the electromagnetic wave shielding film 10 can be electrically connected to the ground circuit of the printed wiring board. In this case, the electromagnetic wave shielding film 10 has good shielding performance.

[0040] In the electromagnetic wave shielding film 10, the conductive adhesive layer may be an isotropically conductive adhesive layer or an anisotropically conductive adhesive layer, but is preferably an anisotropically conductive adhesive layer. When the conductive adhesive layer has anisotropic conductivity, the transmission characteristics of high-frequency signals transmitted through the signal circuit of the printed wiring board are improved compared to when the conductive adhesive layer has isotropic conductivity.

[0041] When the adhesive layer 20 is a conductive adhesive layer, the adhesive layer 20 contains a conductive filler. The conductive filler is not particularly limited, but may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by silver-plating copper powder, fine particles of polymer fine particles or glass beads coated with a metal, or the like. Among these, copper powder or silver-coated copper powder, which are inexpensively available, is preferable from an economical standpoint.

[0042] The shape of the conductive filler is not particularly limited, and can be appropriately selected from spherical, flake, scale, dendrite, rod, fiber, and the like. Among these, flake shape is preferred. When the conductive filler is a flake-shaped conductive filler, the conductive filler also bends when the electromagnetic wave shielding film 10 is bent, making it easier to maintain contact between the conductive filler particles. As a result, the conductivity of the conductive adhesive layer is less likely to decrease.

[0043] The average particle size of the conductive filler is not particularly limited, but is preferably 0.5 to 15.0 μm, and more preferably 5 to 13 μm. When the average particle size of the conductive filler is 0.5 μm or more, the conductivity of the conductive adhesive layer is good. When the average particle size of the conductive filler is 15.0 μm or less, the conductive adhesive layer can be made thin.

[0044] The weight percentage of the conductive filler contained in the conductive adhesive layer is preferably 10 to 80% by weight. When the conductive adhesive layer has anisotropic conductivity, the weight percentage of the conductive filler contained in the conductive adhesive layer is preferably 5 to 40% by weight, and more preferably 10 to 35% by weight.

[0045] The thickness of the adhesive layer 20 is not particularly limited and can be set appropriately as needed, but is preferably 0.5 to 30.0 μm. If the thickness of the adhesive layer is less than 0.5 μm, it becomes difficult to obtain good adhesion. If the thickness of the adhesive layer exceeds 30.0 μm, the entire electromagnetic wave shielding film becomes thick and difficult to handle.

[0046] As explained above, the electromagnetic wave shielding film 10 exhibits the effect of being less susceptible to cracking in the protective layer even when bent at a steep angle. Therefore, the electromagnetic wave shielding film 10 is suitable for applications in which it is disposed in electronic devices that are bent at a steep angle. More specifically, the electromagnetic wave shielding film 10 is suitable for applications in which the radius of curvature at the bent portion when bent is 0.5 to 5 mm.

[0047] Next, a shielding printed wiring board using the electromagnetic wave shielding film of the present invention will be described. Note that the shielding printed wiring board described below will be described in the case where the adhesive layer of the electromagnetic wave shielding film is a conductive adhesive layer.

[0048] 2 is a cross-sectional view schematically showing an example of a cross section of a shielded printed wiring board using the electromagnetic wave shielding film of the present invention. The shielded printed wiring board 1 shown in FIG. 2 includes a flexible printed wiring board 50 and an electromagnetic wave shielding film 10.

[0049] The flexible printed wiring board 50 includes a base film 51, a printed circuit 52 disposed on the base film 51, and a coverlay 53 disposed so as to cover the printed circuit 52. The printed circuit 52 includes a ground circuit 52a. The coverlay 53 has an opening 53a formed therein to expose the ground circuit 52a.

[0050] In the shielded printed wiring board 1, the adhesive layer 20 is disposed so as to be in contact with the coverlay 53. The adhesive layer 20 fills the opening 53a and is in contact with the ground circuit 52a. If the adhesive layer 20 is a conductive adhesive layer, the ground circuit 52a and the shielding layer 30 are electrically connected. This improves the shielding performance of the electromagnetic wave shielding film 10.

[0051] Even when the electromagnetic wave shielding film 10 is bent at a sharp angle, cracks are unlikely to occur in the protective layer 40. Therefore, even when the shielded printed wiring board 1 including the electromagnetic wave shielding film 10 is bent at a sharp angle, cracks are unlikely to occur in the protective layer 40 of the electromagnetic wave shielding film 10.

[0052] Thus, the shielded printed wiring board 1 has high bending resistance. Therefore, the shielded printed wiring board 1 is preferably disposed in a movable part of an electronic device having a movable part that can move from 0 to 180 degrees.

[0053] Examples of electronic devices having such movable parts include foldable phones, tablets, and laptop computers.

[0054] In the flexible printed wiring board 50, the base film 51 and the coverlay 53 are preferably both made of engineering plastics, such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide (PPS).

[0055] In the flexible printed wiring board 50, the printed circuit 52 can be made of a common circuit material such as copper.

[0056] The base film 51 and the printed circuit 52 may be bonded together with an adhesive, or may be bonded together without adhesive, similar to a so-called adhesiveless copper-clad laminate. The coverlay 53 may be formed by bonding multiple flexible insulating films together with an adhesive, or may be formed by a series of methods such as coating a photosensitive insulating resin, drying, exposing, developing, and heat treating.

[0057] A conventionally known method can be used to attach the electromagnetic wave shielding film 10 to the flexible printed wiring board 50. For example, it is preferable to place the electromagnetic wave shielding film 10 on the flexible printed wiring board 50 so that the adhesive layer 20 of the electromagnetic wave shielding film 10 contacts the coverlay 53 of the flexible printed wiring board 50, and then perform thermocompression bonding under conditions of 150 to 200°C, 2 to 5 MPa, and 1 to 60 minutes.

[0058] So far, the shielded printed wiring board 1 has been described as having a conductive adhesive layer 20 and an opening 53a in the coverlay 53 of the flexible printed wiring board 50. However, in the shielded printed wiring board of the present invention, the adhesive layer 20 does not have to be conductive. In this case, the coverlay does not have to have an opening.

[0059] This specification describes the following inventions:

[0060] The present invention (1) is an electromagnetic wave shielding film comprising a protective layer, a shielding layer, and an adhesive layer laminated in this order, characterized in that the ratio of the hardness of the protective layer to the Young's modulus (hardness / Young's modulus) measured by a nanoindentation test in accordance with ISO 14577 is 0.05 to 0.10.

[0061] The present invention (2) is the electromagnetic wave shielding film according to the present invention (1), wherein the protective layer contains a particulate filler.

[0062] The present invention (3) is the electromagnetic wave shielding film according to the present invention (2), wherein the particulate filler contains inorganic particles and / or resin particles.

[0063] The present invention (4) is the electromagnetic wave shielding film according to the present invention (3), wherein the inorganic particles contain at least one kind selected from the group consisting of carbon, silica, and alumina.

[0064] The present invention (5) is the electromagnetic wave shielding film according to any one of the present inventions (2) to (4), wherein the weight ratio of the particulate filler in the protective layer is 2 to 22 wt %.

[0065] The present invention (6) is the electromagnetic wave shielding film according to any one of the present inventions (1) to (5), wherein the protective layer contains at least one resin selected from the group consisting of polyimide resin, acrylic resin, epoxy resin, polyester resin, polyamideimide resin, and urethane resin.

[0066] The present invention (7) is a shielded printed wiring board including a flexible printed wiring board having a base film, a printed circuit arranged on the base film, and a cover lay arranged so as to cover the printed circuit, and an electromagnetic wave shielding film arranged on the cover lay side of the flexible printed wiring board, wherein the electromagnetic wave shielding film is the electromagnetic wave shielding film according to any one of the present inventions (1) to (6).

[0067] Examples will be given below to explain the present invention more specifically, but the present invention is not limited to these examples.

[0068] Example 1 A protective layer-forming composition was prepared by mixing carbon particles (average particle diameter: 0.1 μm) with a polyimide resin, so that the protective layer-forming composition contained 4 wt % of the carbon particles.

[0069] Next, the composition for forming a protective layer was applied to the transfer film and heated at 150° C. for 3 minutes using an electric oven to form a protective layer having a thickness of 5 μm.

[0070] Next, a rolled copper foil having a thickness of 2 μm was formed on the protective layer, which served as a shielding layer.

[0071] Next, copper particles were mixed into the adhesive resin (epoxy resin) to prepare a conductive adhesive composition, in which the copper particles were contained in an amount of 20 wt %.

[0072] Next, a conductive adhesive composition was applied onto the copper layer to form an adhesive layer having a thickness of 5 μm. The adhesive layer was an anisotropic conductive adhesive layer.

[0073] Through the above steps, the electromagnetic wave shielding film according to Example 1 was produced.

[0074] (Example 2) to (Example 6) and (Comparative Example 1) to (Comparative Example 10) Electromagnetic wave shielding films according to Examples 2 to 6 and Comparative Examples 1 to 10 were produced in the same manner as in Example 1, except that the type of resin used in the protective layer and the content of carbon particles were changed as shown in Tables 1 and 2.

[0075]

[0076]

[0077] (Measurement of hardness and Young's modulus of protective layer) For the electromagnetic wave shielding films according to each example and comparative example, the hardness and Young's modulus of the protective layer were measured by a nanoindentation test in accordance with ISO 14577 using a KLM iNano nanoindenter. The test was conducted under the following conditions, and the results are shown in Tables 1 and 2. <Nanoindentation test conditions> Maximum applied load: 50 mN Strain rate: 0.2 Maximum load holding time: 2 seconds

[0078] (Bending Test) The electromagnetic shielding fills according to each example and comparative example were bonded to both sides of a double-sided FPC (coverlay thickness: 27.5 μm, copper foil thickness: 12 μm, base polyimide: 25 μm) by hot pressing at 170°C, 3 MPa, and for 30 minutes to prepare test samples. Next, the test samples were bent under the following conditions. <Bending Conditions> Bending angle: 180° Bending radius (curvature radius): 0.2 mm Load: 1 kg

[0079] Under the above-mentioned folding conditions, the test sample was folded 180° in a mountain fold, then returned to a flat state, and then folded 180° in a valley fold, and then returned to a flat state. This process was defined as "one folding cycle." After each folding cycle, the surface of the protective layer of the test sample was observed under a 10x microscope to check for the occurrence of cracks. This operation was repeated to evaluate the bending resistance of the electromagnetic wave shielding films according to each Example and Comparative Example. The evaluation criteria were as follows: ◯: No cracks occurred in the protective layer after 30 folding cycles. ×: Cracks occurred in the protective layer by the time the folding cycle reached 30 cycles. The evaluation results are shown in Tables 1 and 2.

[0080] Photographs used as criteria for determining whether or not cracks have occurred in the protective layer in the bending test are shown in Figures 3 and 4. Figure 3 is an enlarged photograph (10x magnification) of the protective layer, which is the criterion for determining whether "the protective layer has no cracks" in the bending test of an electromagnetic wave shielding film. Figure 4 is an enlarged photograph (10x magnification) of the protective layer, which is the criterion for determining whether "the protective layer has cracks" in the bending test of an electromagnetic wave shielding film.

[0081] As shown in Tables 1 and 2, in Examples 1 to 6 in which the ratio of hardness to Young's modulus of the protective layer (hardness / Young's modulus) was 0.05 to 0.10, the bending test evaluated that no cracks occurred in the protective layer. Therefore, it was found that the electromagnetic wave shielding films according to Examples 1 to 6 were electromagnetic wave shielding films in which cracks did not occur in the protective layer even when repeatedly bent, and the shielding performance was not easily reduced.

[0082] REFERENCE SIGNS LIST 1 Shielded printed wiring board 10 Electromagnetic wave shielding film 20 Adhesive layer 30 Shielding layer 40 Protective layer 50 Flexible printed wiring board 51 Base film 52 Printed circuit 52a Ground circuit 53 Coverlay 53a Opening

Claims

1. An electromagnetic wave shielding film comprising a protective layer, a shielding layer, and an adhesive layer laminated in that order, wherein the ratio of the hardness of the protective layer to the Young's modulus (hardness / Young's modulus) measured by a nanoindentation test in accordance with ISO 14577 is 0.05 to 0.

10.

2. The electromagnetic wave shielding film according to claim 1, wherein the protective layer contains a particulate filler.

3. The electromagnetic wave shielding film according to claim 2, wherein the particulate filler comprises inorganic particles and / or resin particles.

4. The electromagnetic wave shielding film according to claim 3, wherein the inorganic particles contain at least one kind selected from the group consisting of carbon, silica and alumina.

5. The electromagnetic wave shielding film according to any one of claims 2 to 4, wherein the weight ratio of the particulate filler in the protective layer is 2 to 22 wt %.

6. The electromagnetic wave shielding film according to any one of claims 1 to 5, wherein the protective layer contains at least one resin selected from the group consisting of polyimide resin, acrylic resin, epoxy resin, polyester resin, polyamideimide resin, and urethane resin.

7. A shielded printed wiring board comprising a flexible printed wiring board having a base film, a printed circuit arranged on said base film, and a coverlay arranged to cover said printed circuit, and an electromagnetic wave shielding film arranged on the coverlay side of said flexible printed wiring board, wherein said electromagnetic wave shielding film is an electromagnetic wave shielding film as defined in any one of claims 1 to 6.

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