Electromagnetic wave shielding film and shielding printed wiring board

Abstract

The present invention relates to an electromagnetic wave shielding film capable of sufficiently exerting a shielding effect and achieving thinning even at a high frequency, and a shielded printed wiring board provided with the electromagnetic wave shielding film. The electromagnetic wave shielding film of the present invention has a shielding layer containing an adhesive component and first conductive particles, and satisfies T / δ ≥ 45 / Rs, T ≤ 30, T / δ ≥ 1 (in the formulae, T represents the thickness of the shielding layer [μm], Rs represents the sheet resistance value of the shielding layer [mΩ / sq.], and δ represents the skin depth at 10 GHz of the shielding layer [μm]).

Description

Technical Field

[0001] This invention relates to electromagnetic wave shielding films and also to shielded printed circuit boards. Background Technology

[0002] Printed circuit boards often have electromagnetic wave shielding films adhered to them. Patent Document 1 discloses a shielding component where the thickness of the metal film is below the skin depth of the frequency. Patent Document 2 discloses a composite magnetic material where the average thickness of the soft magnetic powder is less than the skin depth of the operating frequency. Patent Document 3 proposes a shielding material thickness greater than the skin depth from the viewpoint of magnetic flux leakage. Patent Document 4 proposes a conductive sheet thickness greater than ten times the skin depth of the magnetic resonance wavelength. Patent Document 5 proposes an electromagnetic wave absorbing sheet with an alloy-type magnetic material thickness ranging from one-tenth to ten times the skin depth.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2001-156491

[0004] Patent Document 2: Japanese Patent Application Publication No. 10-97913

[0005] Patent Document 3: Japanese Patent Application Publication No. 2004-289213

[0006] Patent Document 4: Japanese Patent Publication No. 2013-513410

[0007] Patent Document 5: Japanese Patent Application Publication No. 7-249888

[0008] In recent years, high-speed transmission circuits such as 5G used in electronic devices have required shielding effects at higher frequency bands. In addition, the miniaturization and thinning of electronic devices have necessitated further thinning of electromagnetic wave shielding films. Summary of the Invention

[0009] The purpose of this invention is to provide an electromagnetic wave shielding film that can fully exert its shielding effect even at high frequencies and achieve thin-film processing, as well as a shielded printed circuit board having the electromagnetic wave shielding film.

[0010] This invention provides the following electromagnetic wave shielding film and shielding printed circuit board.

[0011] [1] An electromagnetic wave shielding film, wherein,

[0012] It has a shielding layer containing an adhesive component and first conductive particles, and satisfies the following equations (1) to (3):

[0013] (1) T / δ≥45 / Rs

[0014] (2) T≤30

[0015] (3) T / δ≥1

[0016] (In the formula, T represents the thickness of the shielding layer [μm], Rs represents the thin-film resistance of the shielding layer [mΩ / sq.], and δ represents the skin depth of the shielding layer at 10GHz [μm]).

[0017] [2] According to the electromagnetic wave shielding film described in [1], wherein,

[0018] The sheet resistance value Rs of the aforementioned shielding layer is below 1000mΩ.

[0019] [3] According to the electromagnetic wave shielding film described in [1] or [2], wherein,

[0020] The content of the first conductive particles in the shielding layer is 45% by mass or more and 85% by mass or less.

[0021] [4] According to any one of [1] to [3], the electromagnetic wave shielding film, wherein,

[0022] The aforementioned first conductive particle comprises sheet-like conductive particles.

[0023] [5] According to any one of [1] to [4], the electromagnetic wave shielding film, wherein,

[0024] The conductivity σ of the aforementioned shielding layer is 2.0 × 10⁻⁶. 7 Below S / m.

[0025] [6] According to any one of [1] to [5], the electromagnetic wave shielding film, wherein,

[0026] It also has a protective layer.

[0027] [7] According to the electromagnetic wave shielding film described in [6], wherein,

[0028] The aforementioned protective layer and the aforementioned shielding layer are stacked together in a grounded manner.

[0029] [8] An electromagnetic wave shielding film according to any one of [1] to [7], wherein,

[0030] It also has a conductive adhesive layer containing second conductive particles.

[0031] [9] According to the electromagnetic wave shielding film described in [8], wherein,

[0032] The content of the second conductive particles in the conductive adhesive layer is 10% by mass or more and 30% by mass or less.

[0033]

[10] According to the electromagnetic wave shielding film described in [8] or [9], wherein,

[0034] The aforementioned second conductive particle comprises sheet-like conductive particles.

[0035]

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

[10] , wherein,

[0036] The thickness of the aforementioned conductive adhesive layer is 1 μm or more and 30 μm or less.

[0037]

[12] According to any one of [8] to

[11] , the electromagnetic wave shielding film, wherein,

[0038] The conductivity σ of the above-mentioned conductive adhesive layer is less than 2.0 × 10 S / m.

[0039]

[13] A shielded printed circuit board, wherein,

[0040] It possesses an electromagnetic wave shielding film and a printed circuit board as described in any one of [1] to

[12] .

[0041] According to the present invention, an electromagnetic wave shielding film that can fully exert its shielding effect even at high frequencies and achieve thin-film processing, as well as a shielded printed circuit board having the electromagnetic wave shielding film, can be provided. Attached Figure Description

[0042] Figure 1 It is a simplified cross-sectional view used to illustrate the shielding effect.

[0043] Figure 2 It is a graph showing the relationship between the shielding effect (absorption loss) and the ratio of thickness to skin depth according to each conductivity.

[0044] Figure 3 It is a graph showing the relationship between the resistance value of the thin film and the ratio of the thickness to the skin depth according to each conductivity.

[0045] Figure 4 It is a graph showing the relationship between shielding effect and frequency according to each conductivity.

[0046] Figure 5 This is a simplified cross-sectional view illustrating an example of the layered structure of an electromagnetic wave shielding film.

[0047] Figure 6 This is a simplified cross-sectional view, schematically representing another example of the layered structure of an electromagnetic wave shielding film.

[0048] Figure 7 This is a simplified cross-sectional view illustrating an example of the layer structure of a shielded printed circuit board. Detailed Implementation

[0049] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited to the following embodiments. In all the following drawings, the scale has been appropriately adjusted for easy understanding of the constituent elements, and the scale of each constituent element shown in the drawings may not be consistent with the actual scale of the constituent elements.

[0050] Electromagnetic wave shielding film

[0051] The electromagnetic wave shielding film of the present invention has a shielding layer comprising an adhesive component and a first conductive particle, and satisfies the following formulas (1) to (3).

[0052] (1) T / δ≥45 / Rs

[0053] (2) T≤30

[0054] (3) T / δ≥1

[0055] [Where, T represents the thickness of the shielding layer [μm], Rs represents the thin-film resistance of the shielding layer [mΩ / sq.], and δ represents the skin depth of the shielding layer at 10 GHz [μm].]

[0056] It is known that the thickness of the shielding layer is set to be above the skin depth of the frequency in order to achieve the shielding effect. However, if the thickness of the shielding layer is increased in order to improve the shielding performance at high frequencies, it is difficult to achieve the thin-film nature of the electromagnetic wave shielding film. According to the present invention, by satisfying equations (1) to (3), an electromagnetic wave shielding film that can fully exert the shielding effect and achieve thin-film nature even at high frequencies can be obtained.

[0057] The shielding effect SE of the shielding layer is defined as the ratio of the transmitted wave Pout to the incident wave Pin, as shown in the following equation (i).

[0058] [Mathematical Formula 1]

[0059]

[0060] like Figure 1 As shown, the incident wave Pin towards the shielding layer becomes the transmitted wave Pout from the shielding layer due to reflection loss (plane wave R, near-field electric field Re or near-field magnetic field Rm), absorption loss A, and multiple reflection effect B. The shielding effect SE, reflection loss (plane wave R, near-field electric field Re or near-field magnetic field Rm), absorption loss A, and multiple reflection effect B are respectively represented by the following equations (ii) to (vii) (refer to HW Ott, "Noise reduction techniques in electronic systems", Wiley-interscience, 1988.).

[0061] [Mathematical Formula 2]

[0062]

[0063] [Mathematical Formula 3]

[0064]

[0065] [Mathematical Formula 4]

[0066]

[0067] [Mathematical Formula 5]

[0068]

[0069] [Mathematical Formula 6]

[0070]

[0071] [Mathematical Expression 7]

[0072]

[0073] After conducting research on absorption loss A, the inventors discovered that when the skin depth δ is less than the material thickness T, the absorption loss A sometimes increases sharply. Figure 2 The reason for the above phenomenon is that, if the conductivity σ changes while keeping the thin-layer resistance Rs of the shielding layer constant, the thickness T and skin depth δ of the shielding layer will also change [as shown in equations (I) to (III) below]. However, the change rate of the thickness T relative to the conductivity σ is greater than the change rate of the skin depth δ.

[0074] (I) Rs = 1 / (σ·T)

[0075] (II) δ=1 / (π×f×μ0×μ r ×σ) 1／2

[0076] (III) ρ = 1 / σ

[0077] [In the formula, Rs represents the thin-film resistance, σ represents the conductivity of the shielding layer, T represents the thickness of the shielding layer, δ represents the skin depth, ρ represents the resistivity of the shielding layer, f represents the frequency, μ0 represents the permeability in vacuum, and μ...] r This represents the relative permeability of the shielding material.

[0078] Therefore, focusing on the ratio of the thin layer resistance value Rs and the skin depth δ to the thickness T (T / δ), it was found that when the above equations (2) and (3) are satisfied, and when the ratio of the thin layer resistance value Rs and the skin depth δ to the thickness T (T / δ) satisfies equation (1), an electromagnetic wave shielding film that fully exerts its shielding effect even at high frequencies and has excellent buckling properties can be obtained.

[0079] exist Figure 3 The graph shows the relationship between the thin-film resistance Rs and the ratio (T / δ) of the skin depth δ to the thickness T, plotted according to the conductivity σ of each shielding layer. Figure 3 In the diagram, the area marked with diagonal lines is the region that satisfies equations (1) to (3).

[0080] From the viewpoint of shielding effectiveness at high frequencies, the sheet resistance Rs of the shielding layer is preferably 1000 mΩ / sq. or less, and more preferably 100 mΩ / sq. or less. Alternatively, it is typically 0 mΩ / sq. or more, and exceeding 0 mΩ / sq. is acceptable; for example, it is 20 mΩ / sq. or more.

[0081] The thickness T of the shielding layer is 30 μm or less, for example, it can be 3 μm or more and 25 μm or less. From the viewpoint of thin film production and operability, it is preferably 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less. Furthermore, the thickness T of the shielding layer in this invention is obtained by heating and pressurizing the electromagnetic wave shielding film at 150°C, 2 MPa, and 30 min and observing the cross-section.

[0082] From the perspective of shielding effectiveness at high frequencies, the conductivity σ of the shielding layer is preferably 2.0 × 10⁻⁶. 7 S / m or less, more preferably 1.0 × 10 7 S / m or less, more preferably 3.0 × 10 6 S / m or less, especially preferably 2.8 × 10 6 Below S / m. The inventors have discovered that the lower the conductivity, the easier it is to improve the shielding effect at high frequencies. For example... Figure 4 As shown, with the same thin-layer resistance value Rs, the shielding effect SE in the high-frequency band tends to increase as the conductivity σ decreases. This trend is presumably because the change rate of thickness T relative to conductivity σ is greater than the change rate of skin depth δ. The conductivity σ of the shielding layer is typically 1 × 10⁻⁶. 5 S / m or higher, for example, 5×10 5 S / m or higher.

[0083] Electromagnetic wave shielding films can provide shielding at high frequencies. For example, the shielding effect of an electromagnetic wave shielding film at 10 GHz can be above 60 dB, preferably above 70 dB.

[0084] The shielding layer can be isotropically conductive.

[0085] Electromagnetic wave shielding films can consist of only a shielding layer, or they can be laminated films consisting of a shielding layer and other layers. From a thin-film perspective, electromagnetic wave shielding films can also consist of only a shielding layer.

[0086] Figure 5 An example of the layer structure of the electromagnetic wave shielding film of the present invention is shown. Figure 5 The electromagnetic wave shielding film 100 shown includes a shielding layer 10. The shielding layer 10 comprises an adhesive component 11 and first conductive particles 12. For example... Figure 5 As shown, the electromagnetic wave shielding film 100 may have a protective layer 20 on one side of the shielding layer 10. The electromagnetic wave shielding film 100 may include, for example, a conductive adhesive layer, a metal layer, a release substrate, etc. as other constituent elements.

[0087] The shielding layer 10 can be formed using a shielding layer forming composition. The shielding layer forming composition can include first conductive particles 12 and an adhesive component 11. Depending on the need, the shielding layer forming composition can include curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, ultraviolet absorbers, defoamers, leveling agents, fillers, flame retardants, viscosity modifiers, anti-blocking agents, etc. The shielding layer forming composition can be, for example, a thermoplastic resin composition, a thermosetting resin composition, or an active energy line curable composition.

[0088] (Adhesive components)

[0089] The adhesive component 11 may include, for example, a cured product of a thermoplastic resin, a thermosetting resin, or an active energy line curable resin. Examples of thermoplastic resins include styrene-based, vinyl acetate-based, polyester-based, polyethylene-based, polypropylene-based, imide-based, amide-based, and acrylic-based thermoplastic resins. Examples of thermosetting resins include phenol-based, epoxy-based, polyurethane-based, melamine-based, and alkyd resins. Examples of active energy line curable components include, for example, polymeric compounds having at least two (meth)acryloyloxy groups in their molecules. These components may be used alone or in combination of two or more.

[0090] (First conductive particle)

[0091] The content of the first conductive particles 12 in the shielding layer 10 can be, for example, 45% by mass or more and 85% by mass or less. From the viewpoint of shielding effect at high frequency bands, the content of the first conductive particles 12 in the shielding layer 10 is preferably 60% by mass or more and 85% by mass or less, more preferably 70% by mass or more and 85% by mass or less.

[0092] The first conductive particle 12 can be a sheet-like conductive particle, a spherical conductive particle, a dendritic conductive particle, a rod-like conductive particle, a fibrous conductive particle, etc. From the viewpoint of thinning the electromagnetic wave shielding film and the thin-film resistance value, the first conductive particle 12 is preferably a sheet-like conductive particle. The first conductive particle 12 can be used alone or in combination of two or more types. When using two or more types in combination, for example, a combination of sheet-like conductive particles and spherical conductive particles can be used.

[0093] For sheet-like conductive particles, the aspect ratio of the cross-section when the shielding layer of the electromagnetic wave shielding film, after being heated and pressurized at 150°C, 2MPa, and 30min, is cut along the thickness direction can be, for example, 18 or more. For spherical conductive particles, the aspect ratio of the cross-section when the shielding layer of the electromagnetic wave shielding film, after being heated and pressurized at 150°C, 2MPa, and 30min, is cut along the thickness direction can be, for example, 1 to 1.5.

[0094] For the first conductive particle 12, the average area (hereinafter also referred to as the average area) of the cross-section when the shielding layer is cut along the thickness direction after the electromagnetic wave shielding film has been heated and pressurized at 150°C, 2MPa, and 30min can be, for example, 25μm. 2 Above and 900μm 2 The following can also be 100μm 2 Above and 400μm 2 The following applies. If the average area of ​​the first conductive particle is within the above range, it is easier to thin the electromagnetic wave shielding film and it tends to easily achieve a shielding effect at high frequencies.

[0095] For the first conductive particle 12, the average thickness (hereinafter also referred to as average thickness) of the cross-section when the shielding layer after being heated and pressurized at 150°C, 2MPa, and 30min is cut along the thickness direction can be, for example, 100nm or more and 400nm or less, or 150nm or more and 300nm or less. If the average thickness of the first conductive particle is within the above range, it is easier to make the electromagnetic wave shielding film into a thin film and it tends to easily exert a shielding effect at high frequencies.

[0096] The average particle diameter of the first conductive particle 12 can be, for example, 1 to 30 μm, preferably 5 to 20 μm, and more preferably 10 to 15 μm.

[0097] When the first conductive particle 12 is a sheet-like conductive particle, from the viewpoint of thin film formation and sheet resistance, the long axis direction of the sheet-like conductive particle can be in the range of 0 to 30° in the direction perpendicular to the thickness direction.

[0098] When the first conductive particle 12 includes sheet-like conductive particles and spherical conductive particles, from the viewpoint of thin film formation and thin film resistance value, the mass ratio of sheet-like conductive particles to spherical conductive particles can be, for example, 6:4 to 8:2.

[0099] (Protective layer)

[0100] The protective layer 20 is insulating and functions to protect the shielding layer 10. The protective layer 20 may contain a protective layer forming resin composition, such as a thermoplastic resin composition, a thermosetting resin composition, or a cured composition for active energy lines. The thermoplastic resin composition may include, for example, thermoplastic resins such as styrene, vinyl acetate, polyester, polyethylene, polypropylene, imide, and acrylic resins.

[0101] Thermosetting resin compositions may include, for example, thermosetting resins such as phenols, epoxy resins, polyurethane resins, melamine resins, and alkyd resins.

[0102] As a solidified component of active energy lines, for example, it can contain polymeric compounds having at least two (meth)acryloyloxy groups in the molecule.

[0103] The protective layer 20 may be made of a single material, or of two or more materials, or may be formed of only thermoplastic resin or thermosetting resin.

[0104] Depending on the requirements, the protective layer 20 may contain curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, UV absorbers, defoamers, leveling agents, fillers, flame retardants, viscosity modifiers, anti-blocking agents, etc.

[0105] The thickness of the protective layer 20 can be, for example, 1 to 15 μm, preferably 3 to 10 μm.

[0106] The protective layer 20 can be directly grounded onto the shielding layer 10, or it can be disposed on the shielding layer 10 via a metal layer described later. When the electromagnetic wave shielding film 100 is disposed on a printed circuit board, the protective layer 20 can be disposed on the side opposite to the printed circuit board.

[0107] (Conductive adhesive layer)

[0108] The conductive adhesive layer can function to adhere the electromagnetic wave shielding film 100 to the printed circuit board, or to the shielding layer 10 to the protective layer 20, or to the shielding layer 10 or the protective layer 20 to the metal layer described later. The conductive adhesive layer can be, for example, anisotropic or isotropic. When the conductive adhesive layer is anisotropic, the impact on the transmission loss of high-frequency signals transmitted in the shielded printed circuit board can be reduced. When the conductive adhesive layer is isotropic, the electromagnetic wave shielding film's following ability relative to the step difference on the printed circuit board becomes better.

[0109] The conductive adhesive layer can contain a cured adhesive resin composition. Examples of adhesive resin compositions 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, polyurethane-based resin compositions, melamine-based resin compositions, and alkyd-based resin compositions. The adhesive resin composition constituting the conductive adhesive layer can also be a different composition from the composition used to form the shielding layer described above.

[0110] The conductive adhesive layer contains second conductive particles. The content of the second conductive particles in the conductive adhesive layer can be, for example, 10% by mass or more and 30% by mass or less. If the content of the second conductive particles is 10% by mass or more, the shielding performance becomes good; if it is 30% by mass or less, the transmission characteristics of high-frequency signals become good. Furthermore, when the content of the second conductive particles in the conductive adhesive layer is within the above-mentioned range, the conductive adhesive layer tends to easily become anisotropically conductive.

[0111] The description of the first conductive particles included in the shielding layer described above applies to the second conductive particles. From the viewpoint of thinning the electromagnetic wave shielding film and the resistance value of the thin film, sheet-like conductive particles are preferred for the second conductive particles.

[0112] The thickness of the conductive adhesive layer can be, for example, 30 μm or less, preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 20 μm or less, and even more preferably 3 μm or more and 10 μm or less. A thickness of 30 μm or less in the conductive adhesive layer provides the advantage of thinness, while a thickness of 1 μm or more increases the adhesive strength.

[0113] (Metal layer)

[0114] From the viewpoint of shielding effectiveness, electromagnetic wave shielding films can include a metal layer. The metal layer can be composed of materials such as gold, silver, copper, aluminum, nickel, tin, palladium, chromium, titanium, and zinc. From the viewpoint of conductivity and economy, a layer composed of copper is preferred. Alternatively, the metal layer can also include a layer composed of an alloy of the aforementioned metals.

[0115] The thickness of the metal layer can be, for example, 0.01 to 10 μm.

[0116] Electromagnetic wave shielding films, even without a metal layer, tend to provide effective shielding at high frequencies. From the perspective of flexibility and thin-film design, electromagnetic wave shielding films without a metal layer are preferred.

[0117] When an electromagnetic wave shielding film has a protective layer and a metal layer, an anchoring coating can also be formed between the protective layer and the metal layer. Examples of materials for the anchoring coating include polyurethane resin, acrylic resin, core-shell composite resins with polyurethane resin as the shell and acrylic resin as the core, epoxy resin, imide resin, amide resin, melamine resin, phenol resin, urea-formaldehyde resin, end-capped isocyanates obtained by reacting end-capping agents such as phenol with polyisocyanates, polyvinyl alcohol, and polyvinylpyrrolidone.

[0118] Figure 6 Another example of the layer structure of the electromagnetic wave shielding film of the present invention is shown. Figure 6 The electromagnetic wave shielding film 200 shown includes 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 circuit board via the conductive adhesive layer 40.

[0119] (Releasable substrate)

[0120] Electromagnetic wave shielding films may or may not have a peelable substrate. A peelable substrate, for example, can be peeled off when the electromagnetic wave shielding film is adhered to a shielded printed circuit board. The peelable substrate can be, for example, a resin film with a peelable surface.

[0121] (Manufacturing method of electromagnetic wave shielding film)

[0122] Electromagnetic wave shielding films can be formed, for example, by coating a shielding layer forming composition onto a releaseable substrate and curing it using heat, active energy lines, or the like. Alternatively, they can be formed by coating the aforementioned protective layer forming resin composition onto a releaseable substrate, curing it using heat, active energy lines, or the like to form a protective layer, then coating the surface of the protective layer with a shielding layer forming composition and curing it.

[0123] The curing of the composition for forming the shielding layer can be carried out, for example, by heating. Heating conditions can be, for example, 150–200°C for 1–10 minutes. When forming a shielding layer between two or more layers, the composition for forming the shielding layer can also be cured under pressure. The pressure conditions can be, for example, 2–5 MPa.

[0124] (Shielded printed circuit board)

[0125] The shielded printed circuit board of the present invention comprises the electromagnetic wave shielding film and the printed circuit board described above. Figure 7 The shielded printed circuit board 300 shown includes an electromagnetic wave shielding film 100 and a printed circuit board 400. The printed circuit board 400 includes: a base film 51, a printed circuit 52 disposed on the base film 51, and a protective layer 53 disposed to cover the printed circuit 52.

[0126] Furthermore, in the printed circuit board 50, the printed circuit 52 includes a ground circuit 52a, and an opening 53a is formed in the sheath 53 to expose the ground circuit 52a.

[0127] The materials used for the base film 51 and the protective layer 53 are not particularly limited, but engineering plastics can be listed as examples. Examples of such engineering plastics include polyethylene terephthalate, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimide amide, polyetherimide, and polyphenylene sulfide resins. Furthermore, among the above-mentioned 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 can be, for example, 10 to 40 μm. The thickness of the protective layer 53 can be, for example, 10 to 30 μm.

[0128] The printed circuit 52 is not particularly limited, but it can be formed by etching a conductive material. Examples of conductive materials include copper, nickel, silver, and gold.

[0129] (Manufacturing method of shielded printed circuit board)

[0130] Shielded printed circuit boards (PCBs) can be formed, for example, by coating a shielding layer forming composition onto a PCB and then curing it. Alternatively, a shielded PCB can be formed by coating a shielding layer forming composition onto a release liner, curing it, then attaching the shielding layer to the PCB via a conductive adhesive layer, and finally peeling off the release liner. Furthermore, when the electromagnetic wave shielding film has a protective layer or a metal layer, it can be formed by coating a shielding layer forming composition onto the protective layer or metal layer and then curing it.

[0131] Example

[0132] The present invention will be further described in detail below through examples. Unless otherwise specified, "%" and "parts" in the examples refer to mass percentage and mass parts.

[0133] (A censored evaluation)

[0134] The shielding performance of the electromagnetic wave shielding film was evaluated using the coaxial tube method. The coaxial tube method, based on ASTM D4935, was performed using a coaxial tube-type shielding effectiveness measurement system from KEYCOM at a temperature of 25°C and a relative humidity of 30–50%. The attenuation of electromagnetic waves from 1 to 10 GHz through the electromagnetic wave shielding film was measured. The results are shown in Table 1.

[0135] (Thin-film resistivity measurement test)

[0136] The surface resistance R0 of the shielding layer of an electromagnetic wave shielding film with a long side (L) of 100 mm and a short side (W) of 50 mm is measured using a tester, according to the following formula:

[0137] Rs = R0 × (W / L)

[0138] The resistivity Rs (mΩ / sq.) of the thin film was calculated. An experiment was conducted with N=5, and the average value was determined. If the average resistivity Rs is below 100 mΩ / sq., the film is considered to have good conductivity. The measurement results are shown in Table 1.

[0139] (Skin depth at 10GHz)

[0140] According to the following formula:

[0141] δ = 1 / (π × f × μ0 × μ) r ×σ) 1／2

[0142] [In the formula, δ represents the skin depth, f represents the frequency, μ0 represents the permeability in vacuum (constant = 1), μ] r The skin depth was calculated using the relative permeability of the shielding material (inherent value of copper = 0.999994 ≈ 1) and σ, representing the conductivity of the shielding layer. The conductivity σ of the shielding layer was measured using a testing instrument.

[0143] <Example 1>

[0144] - The creation of the protective layer -

[0145] Epoxy resin was coated onto the transfer film, and the film was heated at 100°C for 2 minutes in an electric oven to create a protective layer with a thickness of 5μm.

[0146] - Fabrication of the shielding layer-

[0147] Next, conductive particles were prepared. [The average area (average area) of each conductive particle was determined by image processing from image data obtained by observing 10 conductive particles at 1000x magnification using a scanning electron microscope. The average area was 213 μm.] 2 A composition for forming a shielding layer was prepared by mixing thin-film silver-coated copper powder with an average thickness of 246 nm and an adhesive component (cresol phenolic epoxy resin: DIC Corporation "EPICLON N-655-EXP").

[0148] Next, a shielding layer forming composition was coated onto the protective layer to achieve a thickness of 20 μm. Then, a PET film with a surface-release treatment was adhered to the surface coated with the shielding layer forming composition. The PET film was then peeled off under heat and pressure at 150°C, 2 MPa, and 30 min, resulting in a shielding layer with a thickness of 15 μm and a conductivity of 2.8 × 10⁻⁶. 6 (Ω) －1 ・m －1 An electromagnetic wave shielding film as described in Example 1 was fabricated using a shielding layer with a thin-film resistivity of 1.79 mΩ / sq. and a skin depth of 3.0 μm at 10 GHz. Furthermore, the electromagnetic wave shielding film was cut, and the thickness of the shielding layer after heating and pressurization was measured using 1000x SEM images and image processing software (SEM Control User Interface Ver3.10). The results are shown in Table 1.

[0149] <Example 2 and Comparative Example 1>

[0150] In addition to forming shielding layers with thicknesses of 30 μm (Example 2) and 60 μm (Comparative Example 1), electromagnetic wave shielding films of Example 2 and Comparative Example 1 were fabricated in the same manner as in Example 1. The results are shown in Table 1.

[0151] <Comparative Example 2>

[0152] - Formulation of the adhesive layer -

[0153] A conductive adhesive layer composition was prepared by adding 100 parts by weight of bisphenol A type epoxy resin (Mitsubishi Chemical Manufacturing, JER1256), 0.1 parts by weight of curing agent (Mitsubishi Chemical Manufacturing, ST14), and 25 parts by weight of dendritic silver-coated copper powder (average particle diameter 13 μm) to toluene at a solid content of 20% by weight and stirring. The obtained adhesive layer composition was coated on a PET film whose surface had been demolded (and removed during testing), and an anisotropic conductive adhesive layer was formed on the surface of the support film by heating and drying.

[0154] - Fabrication of the shielding layer-

[0155] A rolled copper foil with a thickness of 2 μm is adhered to the surface of the obtained adhesive layer.

[0156] - The creation of the protective layer -

[0157] A thermosetting resin composition was prepared by adding 100 parts by weight of bisphenol A type epoxy resin (Mitsubishi Chemical Manufacturing, jER1256) and 0.1 parts by weight of curing agent (Mitsubishi Chemical Manufacturing, ST14) to toluene with a solid content of 20% by weight. The thermosetting resin composition was coated on the obtained shielding layer and heated and dried to form a protective layer with a thickness of 10 μm, thus obtaining the electromagnetic wave shielding film of Comparative Example 2, which has a layer structure stacked in the order of protective layer / shielding layer / adhesive layer.

[0158]

[0159] Explanation of reference numerals in the attached figures

[0160] 10…Shielding layer; 11…Adhesive component; 12…First conductive particle; 20…Protective layer; 30…Metal layer; 40…Conductive adhesive layer; 51…Base film; 52…Printed circuit; 52a…Grounding circuit; 53…Sheath; 53a…Opening; 200…Electromagnetic wave shielding film; 300…Shielded printed circuit board; 400…Printed circuit board.

Claims

1. An electromagnetic wave shielding film, wherein, It has a shielding layer containing an adhesive component and first conductive particles, and satisfies the following equations (1) to (3): (1) T / δ≥45 / Rs （2）T≤30 (3) T / δ≥1 (In the formula, T represents the thickness of the shielding layer, and its unit is [μm]; Rs represents the thin-film resistance value of the shielding layer, and its unit is [mΩ / sq.]; δ represents the skin depth of the shielding layer at 10GHz, and its unit is [μm]).

2. The electromagnetic wave shielding film according to claim 1, wherein, The thin-film resistance value Rs of the shielding layer is below 1000mΩ.

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 particle comprises sheet-like conductive particles.

5. The electromagnetic wave shielding film according to claim 1, wherein, The conductivity σ of the shielding layer is 2.0 × 10⁻⁶. 7 Below S / m.

6. The electromagnetic wave shielding film according to claim 1, wherein, It also has a protective layer.

7. The electromagnetic wave shielding film according to claim 6, wherein, The protective layer and the shielding layer are stacked together in a grounded manner.

8. The electromagnetic wave shielding film according to claim 1, wherein, It also has 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 more than 10% by mass and less than 30% by mass.

10. The electromagnetic wave shielding film according to claim 8, wherein, The second conductive particle comprises sheet-like conductive particles.

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

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

13. A shielded printed circuit board, wherein, It possesses the electromagnetic wave shielding film and printed circuit board as described in claim 1.

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