Electromagnetic wave shield film and shield printed wiring board

Abstract

The present invention relates to an electromagnetic wave shield film that can sufficiently exhibit a shielding effect even at high frequencies and that can be made to be thin, and to a shield printed wiring board including the same. An electromagnetic wave shield film according to the present invention has a shield layer containing a binder component and first conductive particles and satisfies T / δ ≥ 45 / Rs, T ≤ 30, and T / δ ≥ 1 (in the formulas, T represents the thickness [μm] of the shield layer, Rs represents the sheet resistance value [mΩ / sq.] of the shield layer, and δ represents the skin depth [μm] of the shield layer at 10 GHz).

Description

Electromagnetic wave shielding film and shielded printed wiring board

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

[0002] Electromagnetic wave shielding films are often attached to printed wiring boards. Patent Document 1 proposes a shielding member in which the thickness of the metal film is equal to or less than the skin depth of the frequency. Patent Document 2 discloses a composite magnetic material in which the average thickness of soft magnetic powder is smaller than the skin depth of the operating frequency. Patent Document 3 proposes making the thickness of the shielding material greater than the skin depth from the viewpoint of magnetic flux leakage. Patent Document 4 proposes making the thickness of the conductive sheet greater than 10 times the skin depth of the magnetic resonance wavelength. Patent Document 5 proposes making the thickness of the alloy-based magnetic material in the electromagnetic wave absorbing sheet 1 / 10 to 10 times the skin depth.

[0003] JP 2001-156491, JP 10-97913, JP 2004-289213, Special table 2013-513410, JP 7-249888

[0004] In recent years, high-speed transmission circuits such as 5G installed in electronic devices are being required to exhibit shielding effects in even higher frequency bands. In addition, as electronic devices become smaller and thinner, there is a demand for even thinner electromagnetic wave shielding films.

[0005] An object of the present invention is to provide an electromagnetic wave shielding film that exhibits sufficient shielding effect even at high frequencies and that can be made thinner, and a shielded printed wiring board including the same.

[0006] The present invention provides the following electromagnetic wave shielding film and shielding printed wiring board. [1] An electromagnetic wave shielding film having a shielding layer containing a binder component and first conductive particles, and satisfying the following formulas (1) to (3): (1) T / δ≧45 / Rs (2) T≦30 (3) T / δ≧1 (where T represents the thickness [μm] of the shielding layer, Rs represents the sheet resistance [mΩ / sq.] of the shielding layer, and δ represents the skin depth [μm] of the shielding layer at 10 GHz.) [2] The electromagnetic wave shielding film according to [1], in which the sheet resistance Rs of the shielding layer is 1000 mΩ or less. [3] The electromagnetic wave shielding film according to [1] or [2], in which the content of the first conductive particles in the shielding layer is 45% by mass or more and 85% by mass or less. [4] The electromagnetic wave shielding film according to any of [1] to [3], in which the first conductive particles include flaky conductive particles. [5] The conductivity σ of the shield layer is 2.0×10 ７ The electromagnetic shielding film according to any one of [1] to [4], wherein the electrical conductivity σ of the conductive adhesive layer is 2.0 × 10 S / m or less. [6] The electromagnetic shielding film according to any one of [1] to [5], further comprising a protective layer. [7] The electromagnetic shielding film according to [6], wherein the protective layer is laminated in contact with the shielding layer. [8] The electromagnetic shielding film according to any one of [1] to [7], further comprising a conductive adhesive layer containing second conductive particles. [9] The electromagnetic shielding film according to [8], wherein the content of the second conductive particles in the conductive adhesive layer is 10% by mass or more and 30% by mass or less.

[10] The electromagnetic shielding film according to [8] or [9], wherein the second conductive particles include flaky conductive particles.

[11] The electromagnetic shielding film according to any one of [8] to

[10] , wherein the thickness of the conductive adhesive layer is 1 μm or more and 30 μm or less.

[12] The electromagnetic shielding film according to any one of [8] to

[11] , wherein the electrical conductivity σ of the conductive adhesive layer is 2.0 × 10 S / m or less.

[13] A shielded printed wiring board comprising the electromagnetic wave shielding film according to any one of [1] to

[12] and a printed wiring board.

[0007] According to the present invention, it is possible to provide an electromagnetic wave shielding film that exhibits sufficient shielding effect even at high frequencies and that can be made thinner, and a shielded printed wiring board including the same.

[0008] Fig. 1 is a schematic cross-sectional view for schematically explaining the shielding effect. Fig. 2 is a graph showing the relationship between the shielding effect (absorption loss) and the ratio of thickness to skin depth for each conductivity. Fig. 3 is a graph showing the relationship between the sheet resistance value and the ratio of thickness to skin depth for each conductivity. Fig. 4 is a graph showing the relationship between the shielding effect and frequency for each conductivity. Fig. 5 is a schematic cross-sectional view showing an example of the layer structure of an electromagnetic wave shielding film. Fig. 6 is a schematic cross-sectional view showing another example of the layer structure of an electromagnetic wave shielding film. Fig. 7 is a schematic cross-sectional view showing an example of the layer structure of a shielded printed wiring board.

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all of the drawings, the scales of the components are appropriately adjusted to make them easier to understand, and the scales of the components shown in the drawings do not necessarily match the scales of the actual components.

[0010] <Electromagnetic Wave Shielding Film> The electromagnetic wave shielding film of the present invention has a shielding layer containing a binder component and first conductive particles, and satisfies the following formulas (1) to (3): (1) T / δ≧45 / Rs (2) T≦30 (3) T / δ≧1 (where T represents the thickness [μm] of the shielding layer, Rs represents the sheet resistance value [mΩ / sq.] of the shielding layer, and δ represents the skin depth [μm] of the shielding layer at 10 GHz.)

[0011] It is known that in order to exert a shielding effect, the thickness of the shielding layer must be equal to or greater than the skin depth at the frequency. However, if the thickness of the shielding layer is increased in order to improve the shielding performance in the high frequency band, it becomes difficult to reduce the thickness of the electromagnetic wave shielding film. According to the present invention, by satisfying formulas (1) to (3), an electromagnetic wave shielding film that exerts a sufficient shielding effect even at high frequencies and can be reduced in thickness can be obtained.

[0012] The shielding effect SE of the shield layer is expressed by the following formula (i): As shown in Figure 1, the incident wave Pin on the shield layer becomes the transmitted wave Pout from the shield layer due to reflection loss (plane wave R, near electric field Re or near magnetic field Rm), absorption loss A, and multiple reflection effect B. The shielding effectiveness SE, reflection loss (plane wave R, near electric field Re or near magnetic field Rm), absorption loss A, and multiple reflection effect B are respectively expressed by the following formulas (ii) to (vii) (see HW Ott, "Noise reduction techniques in electronic systems", Wiley-Interscience, 1988).

[0013] The inventors have focused on absorption loss A and conducted research, and have found that when skin depth δ is less than material thickness T, absorption loss A can suddenly increase (Fig. 2). This phenomenon occurs because, when the sheet resistance Rs of the shield layer is constant, fluctuations in conductivity σ result in fluctuations in both the thickness T of the shield layer and the skin depth δ [formulas (I) to (III) below], but it is presumed that this is because the fluctuation ratio of thickness T to conductivity σ is greater than the fluctuation ratio of skin depth δ. (I) Rs = 1 / (σ·T) (II) δ = 1 / (π×f×μ ０ ×μ ｒ ×σ) １／２ (III) ρ=1 / σ [wherein Rs represents the sheet resistance value, σ represents the conductivity of the shield layer, T represents the thickness of the shield layer, δ represents the skin depth, ρ represents the resistivity of the shield layer, f represents the frequency, μ ０ represents the magnetic permeability in a vacuum, and μ ｒ represents the relative permeability of the shielding material.]

[0014] Therefore, by focusing on the sheet resistance value Rs and the ratio (T / δ) of the skin depth δ to the thickness T, it was found that when the above formulas (2) and (3) are satisfied, if the sheet resistance value Rs and the ratio (T / δ) of the skin depth δ to the thickness T satisfy formula (1), an electromagnetic wave shielding film can be obtained that exhibits sufficient shielding effect even at high frequencies and has excellent flexibility.

[0015] Fig. 3 shows a graph plotting the relationship between the sheet resistance Rs and the ratio of the skin depth δ to the thickness T (T / δ) for each conductivity σ of the shield layer. In Fig. 3, the shaded area is the area that satisfies formulas (1) to (3).

[0016] From the viewpoint of shielding effect in the high frequency band, the sheet resistance value Rs of the shield layer is preferably 1000 mΩ / sq. or less, and more preferably 100 mΩ / sq. or less. Also, it is usually 0 mΩ / sq. or more, and may be more than 0 mΩ / sq., for example, 20 mΩ / sq. or more.

[0017] The thickness T of the shielding layer is 30 μm or less, and may be, for example, 3 μm or more and 25 μm or less, and is preferably 5 μm or more and 20 μm or less, more preferably 10 μm or more and 20 μm or less, from the viewpoint of thinning and ease of handling. Note that the thickness T of the shielding layer in the present invention is the thickness of the shielding layer obtained by heating and pressing the electromagnetic wave shielding film under conditions of 150° C., 2 MPa, and 30 minutes and observing the cross section.

[0018] The conductivity σ of the shield layer is preferably 2.0×10 from the viewpoint of the shielding effect in the high frequency band. ７ S / m or less, and more preferably 1.0×10 ７ S / m or less, more preferably 3.0 × 10 ６ S / m or less, particularly preferably 2.8 × 10 ６S / m or less. The inventors have found that the shielding effect in the high frequency band tends to be improved as the conductivity is lower. As shown in FIG. 4, when the sheet resistance Rs is the same, the shielding effect SE in the high frequency band tends to be higher as the conductivity σ is lower. It is presumed that this tendency occurs because the variation ratio of the thickness T to the conductivity σ is larger than the variation ratio of the skin depth δ. The conductivity σ of the shielding layer is usually 1×10 ５ S / m or more, for example, 5×10 ５ It may be S / m or more.

[0019] The electromagnetic wave shielding film can exhibit a shielding effect in the high frequency band, and the electromagnetic wave shielding effect of the electromagnetic wave shielding film at 10 GHz may be, for example, 60 dB or more, and preferably 70 dB or more.

[0020] The shield layer may be isotropically conductive.

[0021] The electromagnetic wave shielding film may be composed of only the shielding layer, or may be a laminated film composed of the shielding layer and other layers. From the viewpoint of reducing the thickness, the electromagnetic wave shielding film may be composed of only the shielding layer.

[0022] Fig. 5 shows an example of the layer structure of the electromagnetic wave shielding film of the present invention. The electromagnetic wave shielding film 100 shown in Fig. 5 includes a shielding layer 10. The shielding layer 10 includes a binder component 11 and first conductive particles 12. As shown in Fig. 5, the electromagnetic wave shielding film 100 may include a protective layer 20 on one side of the shielding layer 10. The electromagnetic wave shielding film 100 may include other components such as a conductive adhesive layer, a metal layer, and a release substrate.

[0023] The shield layer 10 can be formed using a shield layer-forming composition. The shield layer-forming composition can include first conductive particles 12 and a binder component 11. The shield layer-forming composition can include, 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 filler, a flame retardant, a viscosity adjuster, an antiblocking agent, etc. The shield layer-forming composition can be, for example, a thermoplastic resin composition, a thermosetting resin composition, an active energy ray-curable composition, etc.

[0024] (Binder Component) The binder component 11 may contain, for example, a cured product of a thermoplastic resin, a thermosetting resin, or an active energy ray-curable resin. Examples of the thermoplastic resin include styrene-based, vinyl acetate-based, polyester-based, polyethylene-based, polypropylene-based, imide-based, amide-based, and acrylic-based thermoplastic resins. Examples of the thermosetting resin include phenol-based, epoxy-based, urethane-based, melamine-based, and alkyd-based thermosetting resins. Examples of the active energy ray-curable composition may include, for example, a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule. These may be used alone or in combination of two or more.

[0025] (First conductive particles) The content of the first conductive particles 12 in the shield layer 10 may be, for example, 45% by mass or more and 85% by mass or less. From the viewpoint of shielding effect in the high frequency band, the content of the first conductive particles 12 in the shield layer 10 is preferably 60% by mass or more and 85% by mass or less, and more preferably 70% by mass or more and 85% by mass or less.

[0026] The first conductive particles 12 may be flake-shaped conductive particles, spherical conductive particles, dendritic conductive particles, rod-shaped conductive particles, fibrous conductive particles, etc. From the viewpoint of thinning the electromagnetic wave shielding film and improving the sheet resistance, the first conductive particles 12 are preferably flake-shaped conductive particles. The first conductive particles 12 may be used alone or in combination of two or more types. When two or more types are used in combination, for example, a combination of flake-shaped conductive particles and spherical conductive particles can be used.

[0027] The flaky conductive particles may have an aspect ratio of, for example, 18 or more in a cross section of the shielding layer cut in the thickness direction after the electromagnetic wave shielding film has been heated and pressurized at 150°C, 2 MPa, and 30 minutes. The spherical conductive particles may have an aspect ratio of, for example, 1 to 1.5 in a cross section of the shielding layer cut in the thickness direction after the electromagnetic wave shielding film has been heated and pressurized at 150°C, 2 MPa, and 30 minutes.

[0028] The first conductive particles 12 have an average area (hereinafter also referred to as average area) of, for example, 25 μm when the electromagnetic wave shielding film is cut in the thickness direction of the shielding layer after being heated and pressed under conditions of 150° C., 2 MPa, and 30 minutes. ２ 900 μm or more ２ may be less than or equal to 100 μm ２ 400 μm or more ２ If the average area of ​​the first conductive particles is within the above range, the electromagnetic wave shielding film tends to be easily thin and to exhibit a high-frequency shielding effect.

[0029] The first conductive particles 12 may have an average thickness (hereinafter also referred to as average thickness) of, for example, 100 nm to 400 nm, or 150 nm to 300 nm, measured at a cross section of the electromagnetic wave shielding film after heating and pressing the film at 150°C, 2 MPa, and 30 minutes, and the average thickness is measured at a cross section of the electromagnetic wave shielding film after cutting the film in the thickness direction. When the average thickness of the first conductive particles is within the above range, the electromagnetic wave shielding film tends to be thin and the electromagnetic wave shielding effect tends to be easily exhibited at high frequencies.

[0030] The average particle size of the first conductive particles 12 may be, for example, 1 to 30 μm, preferably 5 to 20 μm, and more preferably 10 to 15 μm.

[0031] When the first conductive particles 12 are flaky conductive particles, the major axis direction of the flaky conductive particles can be in the range of 0 to 30° in the direction perpendicular to the thickness direction from the viewpoint of thinning and sheet resistance value.

[0032] When the first conductive particles 12 include flaky conductive particles and spherical conductive particles, the mass ratio of the flaky conductive particles to the spherical conductive particles can be, for example, 6:4 to 8:2 from the viewpoint of thinning and sheet resistance.

[0033] (Protective Layer) The protective layer 20 has insulating properties and can have the function of protecting the shielding layer 10. The protective layer 20 can contain a resin composition for forming a protective layer, such as a cured product of a thermoplastic resin composition, a thermosetting resin composition, or an active energy ray-curable composition. The thermoplastic resin composition can contain, for example, a styrene-based, vinyl acetate-based, polyester-based, polyethylene-based, polypropylene-based, imide-based, acrylic-based, or other thermoplastic resin.

[0034] The thermosetting resin composition may contain, for example, a phenol-based, epoxy-based, urethane-based, melamine-based, or alkyd-based thermosetting resin.

[0035] The active energy ray-curable composition may contain, for example, a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule.

[0036] The protective layer 20 may be made of a single material, or may be made of two or more materials, or may be made of only a thermoplastic resin or a thermosetting resin.

[0037] The protective layer 20 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 filler, a flame retardant, a viscosity adjuster, an antiblocking agent, etc.

[0038] The thickness of the protective layer 20 may be, for example, 1 to 15 μm, and preferably 3 to 10 μm.

[0039] The protective layer 20 may be disposed on the shielding layer 10 in direct contact therewith, or may be disposed on the shielding layer 10 via a metal layer described below. When the electromagnetic wave shielding film 100 is disposed on a printed wiring board, the protective layer 20 can be disposed on the opposite side to the printed wiring board.

[0040] (Conductive Adhesive Layer) The conductive adhesive layer can have the function of bonding the electromagnetic wave shielding film 100 to a printed wiring board, bonding the shielding layer 10 to the protective layer 20, or bonding the shielding layer 10 or the protective layer 20 to a metal layer described below. The conductive adhesive layer may be, for example, anisotropically conductive or isotropically conductive. When the conductive adhesive layer is anisotropically conductive, the effect on transmission loss of high-frequency signals transmitted through the shielded printed wiring board can be reduced. When the conductive adhesive layer is isotropically conductive, the electromagnetic wave shielding film can be well conformed to steps provided on the printed wiring board.

[0041] The conductive adhesive layer may contain a cured product of an adhesive resin composition. Examples of the adhesive resin composition that can be used include thermoplastic resin compositions such as styrene-based resin compositions, vinyl acetate-based resin compositions, polyester-based resin compositions, polyethylene-based resin compositions, polypropylene-based resin compositions, imide-based resin compositions, amide-based resin compositions, and acrylic-based resin compositions, as well as thermosetting resin compositions such as phenol-based resin compositions, epoxy-based resin compositions, urethane-based resin compositions, melamine-based resin compositions, and alkyd-based resin compositions. The adhesive resin composition that constitutes the conductive adhesive layer may be different from the above-described shielding layer-forming composition.

[0042] The conductive adhesive layer contains second conductive particles. The content of the second conductive particles in the conductive adhesive layer may be, for example, 10% by mass or more and 30% by mass or less. When the content of the second conductive particles is 10% by mass or more, the shielding properties are good, and when it is 30% by mass or less, the transmission characteristics of high-frequency signals are good. Furthermore, when the content of the second conductive particles in the conductive adhesive layer is within the above range, the conductive adhesive layer tends to be anisotropically conductive.

[0043] The second conductive particles are the same as those described above for the first conductive particles contained in the shielding layer. From the viewpoint of reducing the thickness and sheet resistance of the electromagnetic wave shielding film, the second conductive particles are preferably flake-shaped conductive particles.

[0044] The thickness of the conductive adhesive layer may be, for example, 30 μm or less, preferably 1 μm to 20 μm, more preferably 2 μm to 20 μm, and even more preferably 3 μm to 10 μm. A conductive adhesive layer thickness of 30 μm or less has the advantage of being thin, while a thickness of 1 μm or more improves adhesive strength.

[0045] (Metal Layer) The electromagnetic wave shielding film may include a metal layer from the viewpoint of shielding effect. The metal layer may include a layer made of a material such as gold, silver, copper, aluminum, nickel, tin, palladium, chromium, titanium, or zinc. Among these, from the viewpoint of electrical conductivity and cost efficiency, a layer made of copper is preferred. The metal layer may also include a layer made of an alloy of the above metals.

[0046] The thickness of the metal layer can be, for example, 0.01 to 10 μm.

[0047] Electromagnetic wave shielding films tend to exhibit a shielding effect in the high frequency band even without a metal layer, and from the viewpoints of flexibility and thinning, the electromagnetic wave shielding film preferably does not have a metal layer.

[0048] When the electromagnetic wave shielding film has a protective layer and a metal layer, an anchor coat layer may be formed between the protective layer and the metal layer. Examples of materials for the anchor coat layer include urethane resin, acrylic resin, core-shell composite resin with a urethane resin as the shell and an acrylic resin as the core, epoxy resin, imide resin, amide resin, melamine resin, phenol resin, urea-formaldehyde resin, blocked isocyanate obtained by reacting a blocking agent such as phenol with polyisocyanate, polyvinyl alcohol, and polyvinylpyrrolidone.

[0049] Fig. 6 shows another example of the layer structure of the electromagnetic wave shielding film of the present invention. The electromagnetic wave shielding film 200 shown in Fig. 6 comprises a protective layer 20, a metal layer 30, a shielding layer 10, and a conductive adhesive layer 40. The electromagnetic wave shielding film 200 can be disposed on a printed wiring board via the conductive adhesive layer 40.

[0050] (Releasable Substrate) The electromagnetic wave shielding film may or may not have a releasable substrate. The releasable substrate can be peeled and removed, for example, when the electromagnetic wave shielding film is attached to a shielding printed wiring board. The releasable substrate can be, for example, a resin film whose surface has been subjected to a release treatment.

[0051] (Method for producing electromagnetic wave shielding film) The electromagnetic wave shielding film can be formed, for example, by applying a composition for forming a shielding layer onto a release substrate and curing it with heat, active energy rays, etc. Alternatively, the electromagnetic wave shielding film can be formed by applying the above-mentioned resin composition for forming a protective layer onto a release substrate and curing it with heat, active energy rays, etc. to form a protective layer, and then applying a composition for forming a shielding layer onto the surface of the protective layer and curing it.

[0052] The shield layer-forming composition can be cured, for example, by heating. Heating conditions may be, for example, 150 to 200°C and 1 to 10 minutes. When the shield layer is formed between two or more layers, the shield layer-forming composition can also be cured while being pressurized. Pressurization conditions may be, for example, 2 to 5 MPa.

[0053] (Shielded Printed Wiring Board) The shielded printed wiring board of the present invention comprises the above-mentioned electromagnetic wave shielding film and printed wiring board. Shielded printed wiring board 300 shown in Fig. 7 comprises electromagnetic wave shielding film 100 and printed wiring board 400. Printed wiring board 400 comprises base film 51, printed circuit 52 arranged on base film 51, and coverlay 53 arranged to cover printed circuit 52.

[0054] In the printed wiring board 50, the printed circuit 52 includes a ground circuit 52a, and the coverlay 53 has an opening 53a formed therein to expose the ground circuit 52a.

[0055] The materials for the base film 51 and the coverlay 53 are not particularly limited, but examples thereof include engineering plastics. Examples of such engineering plastics include resins such as polyethylene terephthalate, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide. Among these engineering plastics, polyphenylene sulfide film is preferred when flame retardancy is required, and polyimide film is preferred when heat resistance is required. The thickness of the base film 51 may be, for example, 10 to 40 μm. The thickness of the coverlay 53 may be, for example, 10 to 30 μm.

[0056] The printed circuit 52 can be formed by, but not limited to, etching a conductive material, such as copper, nickel, silver, or gold.

[0057] (Method for manufacturing a shielding printed wiring board) A shielding printed wiring board can be formed, for example, by applying a shielding layer-forming composition to a printed wiring board and curing it. A shielding printed wiring board can also be formed, for example, by applying a shielding layer-forming composition to a release substrate and curing it, then bonding the shielding layer to the printed wiring board via a conductive adhesive layer, and then peeling off the release substrate. Furthermore, when the electromagnetic wave shielding film has a protective layer or a metal layer, the shielding layer-forming composition can be formed by applying the shielding layer-forming composition to the protective layer or the metal layer and curing it.

[0058] The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" are by mass % and mass parts unless otherwise specified.

[0059] (Evaluation of Shielding Properties) The shielding properties of the electromagnetic wave shielding film were evaluated by the coaxial tube method. The coaxial tube method conforms to ASTM D4935, and the attenuation of electromagnetic waves in the 1 to 10 GHz frequency range by the electromagnetic wave shielding film was measured using a coaxial tube-type shielding effectiveness measurement system manufactured by Keycom Corporation under conditions of a temperature of 25°C and a relative humidity of 30 to 50%. The results are shown in Table 1.

[0060] (Sheet Resistance Measurement Test) The surface resistance R of the shielding layer of an electromagnetic wave shielding film having a long side (L) of 100 mm and a short side (W) of 50 mm was measured. ０ was measured using a tester and calculated using the following formula: Rs = R ０ The sheet resistance value Rs (mΩ / sq.) was calculated by multiplying the ratio of W / L by the formula: × (W / L). Five tests were conducted, and the average value was calculated. If the average sheet resistance value Rs was 100 mΩ / sq. or less, the conductivity was determined to be good. The measurement results are shown in Table 1.

[0061] (Skin depth at 10 GHz) The skin depth is calculated by the following formula: δ=1 / (π×f×μ ０ ×μ ｒ ×σ) １／２ [where δ represents the skin depth, f represents the frequency, and μ ０ represents the magnetic permeability in a vacuum (constant = 1), and μ ｒrepresents the relative permeability of the shielding material (the material characteristic value of copper = 0.999994 ≒ 1), and σ represents the conductivity of the shielding layer. The conductivity σ of the shielding layer was measured using a tester.

[0062] Example 1 - Preparation of Protective Layer - An epoxy resin was applied to a transfer film and heated in an electric oven at 100°C for 2 minutes to prepare a protective layer having a thickness of 5 µm.

[0063] - Preparation of shielding layer - Next, conductive particles [ten conductive particles were observed at 1000 times magnification using a scanning electron microscope, and the area of ​​each conductive particle was measured by image processing from the obtained image data, and the average area (average area) obtained was 213 μm ２ A flake-shaped silver-coated copper powder having an average thickness (average thickness) of 246 nm and a binder component (cresol novolac epoxy resin: "Epiclon N-655-EXP" manufactured by DIC Corporation) were prepared, and these were mixed so that the ratio of the mass of the conductive particles to the total mass of the conductive particles and the binder component was 65 mass %, to prepare a composition for forming a shielding layer.

[0064] Next, a shield layer-forming composition was applied to the protective layer to a thickness of 20 μm. Then, a PET film with a release-treated surface was attached to the surface on which the shield layer-forming composition was applied, and the resulting laminate was heated and pressed at 150° C., 2 MPa, and 30 minutes, and the PET film was peeled off, resulting in a shield layer having a thickness of 15 μm and a conductivity of 2.8×10 ６ (Ω －１ ・m －１ A shielding layer having a sheet resistance of 1.79 mΩ / sq., a skin depth of 3.0 μm at 10 GHz, and a thickness of 1.0 μm was formed, thereby producing an electromagnetic wave shielding film according to Example 1. The thickness of the shielding layer after heating and pressing was measured by cutting the electromagnetic wave shielding film, taking a 1000x SEM image, and using image processing software (SEM Control User Interface Ver. 3.10). The results are shown in Table 1.

[0065] Example 2 and Comparative Example 1 Electromagnetic wave shielding films of Example 2 and Comparative Example 1 were produced in the same manner as in Example 1, except that a shielding layer having a thickness of 30 μm (Example 2) and 60 μm (Comparative Example 1) was formed. The results are shown in Table 1.

[0066] Comparative Example 2 - Preparation of Adhesive Layer - 100 parts by mass of bisphenol A epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1256), 0.1 parts by mass of a curing agent (manufactured by Mitsubishi Chemical Corporation, ST14), and 25 parts by mass of dendritic silver-coated copper powder (average particle diameter 13 μm) were added to toluene so that the solid content was 20% by mass, and the mixture was stirred and mixed to prepare a conductive adhesive layer composition. The obtained adhesive layer composition was applied to a PET film whose surface had been treated with a release agent (which was peeled and removed before measurement), and then heated and dried to form an anisotropically conductive adhesive layer on the surface of the support film.

[0067] - Preparation of Shielding Layer - A rolled copper foil having a thickness of 2 μm was attached to the surface of the obtained adhesive layer.

[0068] - Preparation of protective layer - A thermosetting resin composition was prepared by blending 100 parts by mass of a bisphenol A epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1256) and 0.1 parts by mass of a curing agent (manufactured by Mitsubishi Chemical Corporation, ST14) into toluene so that the solid content was 20% by mass. The thermosetting resin composition was applied to the obtained shielding layer and dried by heating to form a protective layer with a thickness of 10 μm, thereby obtaining an electromagnetic wave shielding film of Comparative Example 2 having a layer structure in which the protective layer / shielding layer / adhesive layer were laminated in this order.

[0069]

[0070] 10 Shielding layer, 11 Binder component, 12 First conductive particles, 20 Protective layer, 30 Metal layer, 40 Conductive adhesive layer, 51 Base film, 52 Printed circuit, 52a Ground circuit, 53 Coverlay, 53a Opening, 200 Electromagnetic wave shielding film, 300 Shielded printed wiring board, 400 Printed wiring board.

Claims

1. An electromagnetic wave shielding film having a shielding layer containing a binder component and first conductive particles, and satisfying the following formulas (1) to (3): (1) T / δ≧45 / Rs (2) T≦30 (3) T / δ≧1 (wherein T represents the thickness [μm] of the shielding layer, Rs represents the sheet resistance value [mΩ / sq.] of the shielding layer, and δ represents the skin depth [μm] of the shielding layer at 10 GHz.) 2. The electromagnetic wave shielding film according to claim 1, wherein the sheet resistance value Rs of the shielding layer is 1000 mΩ or less.

3. The electromagnetic wave shielding film according to claim 1, wherein the content of the first conductive particles in the shielding layer is 45% by mass or more and 85% by mass or less.

4. The electromagnetic shielding film according to claim 1, wherein the first conductive particles include flake-shaped conductive particles.

5. The electrical conductivity σ of the shield layer is 2.0×10 ７ The electromagnetic wave shielding film according to claim 1 , having a linear modulus of 0.5 S / m or less.

6. The electromagnetic wave shielding film according to claim 1, further comprising a protective layer.

7. The electromagnetic wave shielding film according to claim 6, wherein the protective layer is laminated in contact with the shielding layer.

8. The electromagnetic shielding film according to claim 1, further comprising a conductive adhesive layer containing second conductive particles.

9. The electromagnetic wave shielding film according to claim 8, wherein the content of the second conductive particles in the conductive adhesive layer is 10% by mass or more and 30% by mass or less.

10. The electromagnetic wave shielding film according to claim 8, wherein the second conductive particles include flake-shaped conductive particles.

11. The electromagnetic wave shielding film according to claim 8, wherein the conductive adhesive layer has a thickness of 1 μm or more and 30 μm or less.

12. The electromagnetic wave shielding film according to claim 8, wherein the electrical conductivity σ of the conductive adhesive layer is 2.0 × 10 S / m or less.

13. A shielded printed wiring board comprising the electromagnetic shielding film according to claim 1 and a printed wiring board.

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