Electromagnetic wave shielding film and shielded printed wiring board

Abstract

The present invention relates to an electromagnetic wave shielding film that exhibits sufficient shielding effect even at high frequencies and can be made thinner, and a shielded printed wiring board including the same. The electromagnetic wave shielding film of the present invention has a shielding layer containing a binder component and first conductive particles, and satisfies the relationships T / δ≧45 / Rs, T≦30, and T / δ≧1 (where T represents the thickness of the shielding layer [μm], Rs represents the sheet resistance of the shielding layer [mΩ / sq.], and δ represents the skin depth of the shielding layer at 10 GHz [μm]).

Description

[Technical Field]

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

[0002] Electromagnetic wave shielding films are often attached to printed wiring boards. Patent Document 1 proposes a shielding material 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 perspective 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-156491 [Patent Document 2] Japanese Patent Application Publication No. 10-97913 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-289213 [Patent Document 4] Special Publication No. 2013-513410 [Patent Document 5] Japanese Patent Application Publication No. 7-249888 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, high-speed transmission circuits such as 5G installed in electronic devices are being required to exhibit shielding effects at 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. [Means for solving the problem]

[0006] The present invention provides the following electromagnetic wave shielding film and shielded printed wiring board. [1] A shield layer including a binder component and first conductive particles, An electromagnetic wave shielding film that satisfies the following formulas (1) to (3). (1) T / δ≧45 / Rs (2) T≦30 (3) T / δ≧1 (In the formula, 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.) [2] The electromagnetic wave shielding film according to [1], wherein the sheet resistance value Rs of the shielding layer is 1000 mΩ or less. [3] The electromagnetic wave shielding film according to [1] or [2], 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 wave shielding film according to any one of [1] to [3], wherein the first conductive particles include flaky conductive particles. [5] The conductivity σ of the shield layer is 2.0×10 7 The electromagnetic wave shielding film according to any one of [1] to [4], wherein the electromagnetic wave shielding film has a saturation of 0.5 S / m or less. [6] The electromagnetic wave shielding film according to any one of [1] to [5], further comprising a protective layer. [7] The electromagnetic wave shielding film according to [6], wherein the protective layer is laminated in contact with the shielding layer. [8] The electromagnetic wave shielding film according to any one of [1] to [7], further comprising a conductive adhesive layer containing second conductive particles. [9] The electromagnetic wave 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 wave shielding film according to [8] or [9], wherein the second conductive particles include flaky conductive particles.

[11] The electromagnetic wave 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 wave 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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view for illustrating the shielding effect. [Figure 2] 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. [Figure 3] FIG. 3 is a graph showing the relationship between the sheet resistance value and the ratio of thickness to skin depth for each conductivity. [Figure 4] FIG. 4 is a graph showing the relationship between the shielding effect and frequency for each conductivity. [Figure 5]FIG. 5 is a schematic cross-sectional view showing an example of the layer structure of an electromagnetic wave shielding film. [Figure 6] FIG. 6 is a schematic cross-sectional view showing another example of the layer structure of the electromagnetic wave shielding film. [Figure 7] FIG. 7 is a schematic cross-sectional view showing an example of the layer structure of a shielded printed wiring board. DETAILED DESCRIPTION OF THE INVENTION

[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 [In the formula, 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.]

[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 made thinner can be obtained.

[0012] The shielding effectiveness SE of the shield layer is calculated by the following formula (i):

number

number

number

number

number

number

number

[0013] The inventors conducted research focusing on absorption loss A and found that a phenomenon can occur in which absorption loss A increases suddenly when skin depth δ is smaller than material thickness T (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 and skin depth δ of the shield layer [formulas (I) to (III) below], but it is presumed that this is because the fluctuation ratio of thickness T to conductivity σ is larger than the fluctuation ratio of skin depth δ. (I) Rs=1 / (σ·T) (II) δ=1 / (π×f×μ0×μ r ×σ) 1 / 2 (III) ρ=1 / σ [In the formula, 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, μ0 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] Figure 3 shows a graph plotting the relationship between the sheet resistance Rs and the ratio of skin depth δ to thickness T (T / δ) for each conductivity σ of the shield layer. In Figure 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 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 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 6 S / m or less. The inventors have found that the shielding effectiveness in the high frequency band tends to be improved as the conductivity is lower. As shown in Figure 4, when the sheet resistance value Rs is the same, the shielding effectiveness 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 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 an 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 can include a protective layer 20 on one side of the shielding layer 10. The electromagnetic wave shielding film 100 can also 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 particle) 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 heating and pressing the electromagnetic wave shielding film under conditions of 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 heating and pressing the electromagnetic wave shielding film under conditions of 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 heated and pressed at 150° C., 2 MPa, and 30 minutes and the shielding layer is cut in the thickness direction. 2 More than 900μm 2 may be less than or equal to 100 μm 2 More than 400μm 2 If the average area of ​​the first conductive particles is within the above range, the electromagnetic wave shielding film tends to be easily thinned and the shielding effect tends to be easily exhibited at high frequencies.

[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, in a cross section obtained by cutting the shielding layer in the thickness direction after heating and pressing the electromagnetic wave shielding film under conditions of 150°C, 2 MPa, and 30 minutes. If the average thickness of the first conductive particles is within the above range, it tends to be easier to make the electromagnetic wave shielding film thinner and to more easily exhibit shielding effect 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 may be in the range of 0 to 30° in the direction perpendicular to the thickness direction, from the viewpoint of thinning and sheet resistance.

[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 value.

[0033] (protective layer) The protective layer 20 has insulating properties and can function to protect the shielding layer 10. The protective layer 20 can include a resin composition for forming the 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 include, 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, and 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 directly on and in contact with the shielding layer 10, 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. If the conductive adhesive layer is anisotropically conductive, it can reduce the effect on transmission loss of high-frequency signals transmitted through the shielded printed wiring board. If 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 flaky 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 shell and an acrylic resin 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 placed 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 release substrate. The release substrate can be peeled and removed, for example, when the electromagnetic wave shielding film is attached to a shielding printed wiring board. The release substrate can be, for example, a resin film whose surface has been subjected to a release treatment.

[0051] (Electromagnetic wave shielding film manufacturing method) 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 is not limited to, etching a conductive material, etc. Examples of conductive materials include copper, nickel, silver, and gold.

[0057] (Method of manufacturing a shielded printed wiring board) The shielding printed wiring board can be formed, for example, by applying a shielding layer-forming composition to a printed wiring board and curing it. The 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 laminating 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. [Example]

[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] (Shielding performance evaluation) The shielding properties of the electromagnetic wave shielding film were evaluated using 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 resistance value R0 of the surface 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 using a tester and calculated using the following formula: Rs = R0 × (W / L) The sheet resistance Rs (mΩ / sq.) was calculated using the formula: N=5 tests were conducted and the average value was calculated. If the average sheet resistance Rs was 100mΩ / sq. or less, the conductivity was determined to be good. The measurement results are shown in Table 1.

[0061] (skin depth at 10GHz) Skin depth is calculated using the following formula: δ=1 / (π×f×μ0×μ r ×σ) 1 / 2 [In the formula, δ represents the skin depth, f represents the frequency, μ represents the magnetic permeability in a vacuum (constant = 1), and μ r represents 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 shield layer was measured using a tester.

[0062] Example 1 -Creating a protective layer- Epoxy resin was applied to the transfer film and heated in an electric oven at 100°C for 2 minutes to form a protective layer with a thickness of 5 μm.

[0063] -Making the shielding layer- Next, the conductive particles [10 conductive particles were observed at 1000x magnification using a scanning electron microscope, and the area of ​​each conductive particle was measured using image processing from the image data obtained, 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 pressurized at 150°C, 2 MPa, and 30 min, and the PET film was peeled off, resulting in a shield layer with a thickness of 15 μm and a conductivity of 2.8 × 10 6 (Ω -1 m -1 ), a sheet resistance of 1.79 mΩ / sq., and a skin depth of 3.0 μm at 10 GHz, 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) or 60 μm (Comparative Example 1) was formed. The results are shown in Table 1.

[0066] <Comparative Example 2> -Creating the adhesive layer- A conductive adhesive layer composition was prepared by adding 100 parts by mass of bisphenol A epoxy resin (Mitsubishi Chemical's jER1256), 0.1 parts by mass of a curing agent (Mitsubishi Chemical's ST14), and 25 parts by mass of dendritic silver-coated copper powder (average particle diameter 13 μm) to toluene so that the solid content was 20% by mass, and stirring and mixing. The resulting adhesive layer composition was applied to a PET film with a release-treated surface (which was peeled off and removed before measurement), and then heated and dried to form an anisotropically conductive adhesive layer on the surface of the support film.

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

[0068] -Creating a 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] [Table 1] [Explanation of symbols]

[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 cover lay, 53a opening, 200 electromagnetic wave shielding film, 300 shielded printed wiring board, 400 printed wiring board.

Claims

1. a shield layer including a binder component and first conductive particles; An electromagnetic wave shielding film that satisfies the following formulas (1) to (3): (1) T / δ≧45 / Rs (2) T≦30 (3) T / δ≧1 (In the formula, 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.)

2. 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 wave shielding film according to claim 1 , wherein the first conductive particles include flaky conductive particles.

5. The conductivity σ of the shield layer is 2.0×10 ７ The electromagnetic wave shielding film according to claim 1 , having a modulus of elasticity of 1000 kJ / 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 wave 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 flaky conductive particles.

11. 9. 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. 9. 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 wave shielding film according to claim 1 and a printed wiring board.

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