Electromagnetic wave shielding film and shielded printed wiring board

Abstract

Provided is an electromagnetic wave shielding film in which cracks are less likely to occur in a shielding layer when the electromagnetic wave shielding film is affixed to a step portion. An electromagnetic wave shielding film according to the present invention comprises an adhesive layer, a shielding layer that is laminated on the adhesive layer and includes a metal layer, and a protective layer that is laminated on the shielding layer on the side opposite from the adhesive layer, wherein when a cross section of the electromagnetic wave shielding film along the lamination direction of the adhesive layer, the shielding layer, and the protective layer is viewed, L1 / L2 is greater than 1.00 in a target region of the cross section having a discretionary width M in a width direction perpendicular to the lamination direction, where L1 is the length of a first main surface on the adhesive-layer side of the shielding layer, and L2 is the length of a second main surface on the protective-layer side of the shielding layer.

Description

Electromagnetic wave shielding film and shielded printed wiring board

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

[0002] Patent Document 1 discloses an electromagnetic wave shielding sheet including a conductive layer and an insulating layer, the insulating layer containing a thermosetting resin, a curing agent, and a black colorant, and the black colorant having an average primary particle size of 20 to 100 nm.

[0003] JP 2016-143751 A

[0004] Conventional electromagnetic shielding films, such as the electromagnetic shielding sheet described in Patent Document 1, generally have a configuration in which a shielding layer (a conductive layer in Patent Document 1) and a protective layer (an insulating layer in Patent Document 1) are laminated together. Conventional electromagnetic shielding films sometimes use a metal layer such as copper as the shielding layer. Furthermore, conventional electromagnetic shielding films sometimes use an adhesive layer laminated on the side of the shielding layer opposite the protective layer to enable attachment (adhesion) to other components.

[0005] However, when a conventional electromagnetic wave shielding film is attached (adhered) to a stepped portion from the adhesive layer side, there is a problem in that cracks occur in the shielding layer due to the poor conformability of the shielding layer, which includes a metal layer.

[0006] The present invention has been made to solve the above problems, and aims to provide an electromagnetic wave shielding film that is less likely to cause cracks in the shielding layer when attached to a stepped portion. Another aim of the present invention is to provide a shielded printed wiring board having an electromagnetic wave shielding film that is less likely to cause cracks in the shielding layer when attached to a stepped portion.

[0007] The electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film comprising an adhesive layer, a shielding layer laminated on the adhesive layer and including a metal layer, and a protective layer laminated on the shielding layer on the opposite side to the adhesive layer, wherein when a cross section of the electromagnetic wave shielding film is viewed along the lamination direction of the adhesive layer, the shielding layer, and the protective layer, in a target region of the cross section having an arbitrary width M in a width direction perpendicular to the lamination direction, where L1 is the length of a first main surface of the shielding layer facing the adhesive layer and L2 is the length of a second main surface of the shielding layer facing the protective layer, L1 / L2 is greater than 1.00.

[0008] In the electromagnetic wave shielding film of the present invention, L1 / L2 is greater than 1.00. Therefore, it can be said that in the electromagnetic wave shielding film of the present invention, the first main surface of the shielding layer facing the adhesive layer is rougher than the second main surface of the shielding layer facing the protective layer. As a result, when the electromagnetic wave shielding film of the present invention is attached to a stepped portion from the adhesive layer side, the roughness of the first main surface of the shielding layer facing the adhesive layer, i.e., the first main surface of the shielding layer facing the stepped portion, makes it easier for the shielding layer to conform to the stepped portion even if the shielding layer includes a metal layer. Therefore, when the electromagnetic wave shielding film of the present invention is attached to a stepped portion from the adhesive layer side, cracks are less likely to occur in the shielding layer.

[0009] In the electromagnetic wave shielding film of the present invention, L1 / L2 is preferably greater than 1.00 and equal to or less than 1.05.

[0010] In the electromagnetic wave shielding film of the present invention, if L1 / L2 is 1.00 or less, the step-conforming ability of the shielding layer is poor, and cracks are likely to occur in the shielding layer when the electromagnetic wave shielding film of the present invention is attached to a step.

[0011] In the electromagnetic wave shielding film of the present invention, if L1 / L2 is greater than 1.05, the first main surface of the shielding layer becomes too rough, which may make it difficult to obtain sufficient shielding properties of the electromagnetic wave shielding film of the present invention.

[0012] In the electromagnetic wave shielding film of the present invention, L1 / M is preferably 1.01 or more and 1.06 or less.

[0013] In the electromagnetic wave shielding film of the present invention, if L1 / M is smaller than 1.01, the step-conforming ability of the shielding layer is unlikely to be sufficiently improved, and therefore, when the electromagnetic wave shielding film of the present invention is attached to a step, the effect of making cracks less likely to occur in the shielding layer may not be fully achieved.

[0014] In the electromagnetic wave shielding film of the present invention, if L1 / M is greater than 1.06, the first main surface of the shielding layer becomes too rough, which may make it difficult to obtain sufficient shielding properties of the electromagnetic wave shielding film of the present invention.

[0015] In the electromagnetic wave shielding film of the present invention, L2 / M is preferably 1.00 or more and 1.03 or less.

[0016] In the electromagnetic wave shielding film of the present invention, L2 / M cannot be smaller than 1.00 by definition.

[0017] In the electromagnetic wave shielding film of the present invention, if L2 / M is greater than 1.03, not only the second main surface of the shielding layer but also the first main surface, which is rougher than the second main surface of the shielding layer, will become too rough, and it may be difficult to obtain sufficient shielding properties of the electromagnetic wave shielding film of the present invention.

[0018] The shielded printed wiring board of the present invention is a shielded printed wiring board comprising a printed wiring board having a base film, a printed circuit provided on the base film, and a coverlay provided to cover the printed circuit, and an electromagnetic wave shielding film provided on the coverlay side of the printed wiring board, characterized in that the electromagnetic wave shielding film is the electromagnetic wave shielding film of the present invention, and the adhesive layer side faces the coverlay.

[0019] As described above, when the electromagnetic wave shielding film of the present invention is attached to a stepped portion from the adhesive layer side, cracks are less likely to occur in the shielding layer. Therefore, in the shielded printed wiring board of the present invention including the electromagnetic wave shielding film of the present invention, cracks are less likely to occur in the shielding layer even when the electromagnetic wave shielding film of the present invention is attached to a stepped portion of the printed wiring board from the adhesive layer side.

[0020] In this specification, the term "film" is synonymous with the term "sheet," and the two are not distinguished by thickness. In other words, the term "electromagnetic wave shielding film" is synonymous with the term "electromagnetic wave shielding sheet."

[0021] According to the present invention, it is possible to provide an electromagnetic wave shielding film that is less likely to cause cracks in the shielding layer when attached to a stepped portion.Furthermore, according to the present invention, it is possible to provide a shielded printed wiring board having an electromagnetic wave shielding film that is less likely to cause cracks in the shielding layer when attached to a stepped portion.

[0022] FIG. 1 is a cross-sectional view schematically showing an example of an electromagnetic wave shielding film of the present invention. FIG. 2 is an enlarged cross-sectional view of the electromagnetic wave shielding film in FIG. 1 , illustrating a method for determining L1 and L2. FIG. 3 is a cross-sectional view schematically showing an example of a shielded printed wiring board of the present invention. FIG. 4 is an original image showing a target area of ​​a cross section of the electromagnetic wave shielding film of Example 1. FIG. 5 is an adjusted image showing the target area of ​​a cross section of the electromagnetic wave shielding film of Example 1. FIG. 6 is an extracted image showing the target area of ​​a cross section of the electromagnetic wave shielding film of Example 1. FIG. 7 is an original image showing the target area of ​​a cross section of the electromagnetic wave shielding film of Comparative Example 4. FIG. 8 is an adjusted image showing the target area of ​​a cross section of the electromagnetic wave shielding film of Comparative Example 4. FIG. 9 is an extracted image showing the target area of ​​a cross section of the electromagnetic wave shielding film of Comparative Example 4.

[0023] Specific examples of the electromagnetic wave shielding film of the present invention and the shielded printed wiring board of the present invention are described below. Note that the present invention is not limited to the following configurations and may be modified as appropriate without departing from the gist of the present invention. In addition, a combination of multiple individual preferred configurations described below also constitutes the present invention.

[0024] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0025] In this specification, unless otherwise specified, terms indicating the relationship between elements (e.g., "parallel," "perpendicular," etc.) and terms indicating the shape of elements not only mean the literal strict form, but also mean a range that is substantially equivalent, for example, a range that includes a difference of about a few percent.

[0026] [Electromagnetic Wave Shielding Film] FIG. 1 is a cross-sectional view schematically showing an example of the electromagnetic wave shielding film of the present invention.

[0027] The electromagnetic wave shielding film 1 shown in FIG. 1 has an adhesive layer 10 , a shielding layer 20 including a metal layer, and a protective layer 30 .

[0028] The shielding layer 20 is laminated on the adhesive layer 10 .

[0029] The protective layer 30 is laminated on the shielding layer 20 on the side opposite to the adhesive layer 10 .

[0030] As described above, the electromagnetic wave shielding film 1 has the adhesive layer 10, the shielding layer 20, and the protective layer 30 laminated in this order.

[0031] In the electromagnetic wave shielding film 1, when a cross section of the electromagnetic wave shielding film 1 is viewed along the stacking direction (vertical direction in FIG. 1 ) of the adhesive layer 10, the shielding layer 20, and the protective layer 30, in a target region of the cross section having an arbitrary width M in the width direction (horizontal direction in FIG. 1 ) perpendicular to the stacking direction, where L1 is the length of the first main surface 21a of the shielding layer 20 facing the adhesive layer 10 and L2 is the length of the second main surface 21b of the shielding layer 20 facing the protective layer 30, L1 / L2 is greater than 1.00. Therefore, it can be said that in the electromagnetic wave shielding film 1, the first main surface 21a of the shielding layer 20 facing the adhesive layer 10 is rougher than the second main surface 21b of the shielding layer 20 facing the protective layer 30. As a result, when the electromagnetic wave shielding film 1 is attached to the stepped portion from the adhesive layer 10 side, the first main surface 21 a of the shielding layer 20 on the adhesive layer 10 side, i.e., the first main surface 21 a of the shielding layer 20 on the stepped portion side, is rough, so that the step-conforming ability of the shielding layer 20 is likely to be improved even if the shielding layer 20 includes a metal layer. Therefore, when the electromagnetic wave shielding film 1 is attached to the stepped portion from the adhesive layer 10 side, cracks are less likely to occur in the shielding layer 20.

[0032] In the electromagnetic wave shielding film 1, for example, one main surface of the shielding layer 20 is roughened by a conventionally known method such as etching, and then the shielding layer 20 is positioned so that the roughened main surface faces the adhesive layer 10, thereby achieving a configuration in which L1 / L2 is greater than 1.00.

[0033] L1 / L2 is preferably greater than 1.00 and equal to or less than 1.05, and more preferably equal to or greater than 1.01 and equal to or less than 1.04.

[0034] If L1 / L2 is 1.00 or less, the step conformability of the shielding layer 20 will be poor, and cracks will be more likely to occur in the shielding layer 20 when the electromagnetic wave shielding film 1 is attached to a stepped portion.

[0035] If L1 / L2 is greater than 1.05, the first main surface 21a of the shielding layer 20 becomes too rough, and it may become difficult to obtain sufficient shielding properties from the electromagnetic wave shielding film 1.

[0036] L1 / M is preferably 1.01 or more and 1.06 or less, and more preferably 1.01 or more and 1.05 or less.

[0037] If L1 / M is smaller than 1.01, the step-following ability of the shielding layer 20 is unlikely to be sufficiently improved, and therefore, when the electromagnetic wave shielding film 1 is attached to a step, the effect of making cracks less likely to occur in the shielding layer 20 may not be fully achieved.

[0038] If L1 / M is greater than 1.06, the first main surface 21a of the shielding layer 20 becomes too rough, and it may become difficult to obtain sufficient shielding properties from the electromagnetic wave shielding film 1.

[0039] L2 / M is preferably 1.00 or more and 1.03 or less, and more preferably 1.01 or more and 1.02 or less.

[0040] By definition, L2 / M cannot be less than 1.00.

[0041] If L2 / M is greater than 1.03, not only the second main surface 21b of the shielding layer 20 but also the first main surface 21a, which is rougher than the second main surface 21b of the shielding layer 20, will become too rough, and it may be difficult to obtain sufficient shielding characteristics of the electromagnetic wave shielding film 1.

[0042] A method for determining L1 and L2 in the electromagnetic wave shielding film 1 will be described below.

[0043] FIG. 2 is an enlarged cross-sectional view of the electromagnetic wave shielding film in FIG. 1, illustrating a method for determining L1 and L2.

[0044] First, a cross section of the electromagnetic wave shielding film 1 along the stacking direction (vertical direction) of the adhesive layer 10, the shielding layer 20, and the protective layer 30 is exposed. Then, an original image of a target region (e.g., FIG. 2 ) having an arbitrary width M in the width direction (horizontal direction) perpendicular to the stacking direction is obtained from the cross section. Specifically, the original image of the target region is obtained using a scanning electron microscope (SEM). The magnification of the scanning electron microscope used to obtain the original image of the target region is not particularly limited as long as the target region can be included in the field of view, and may be, for example, 3000x.

[0045] The width M of the target region is arbitrary and is not particularly limited, but is, for example, 40 μm or more and 50 μm or less.

[0046] In the example shown in FIG. 2, the target area having the width M is a partial area in the width direction of the electromagnetic wave shielding film 1, but it may be the entire area in the width direction of the electromagnetic wave shielding film 1.

[0047] Next, an adjusted image of the target region is obtained by changing the brightness and contrast of the original image of the target region obtained as described above in order to clarify the first principal surface 21 a and the second principal surface 21 b of the shield layer 20. The extent to which the brightness and contrast of the original image of the target region are changed is not particularly limited as long as the intended first principal surface 21 a and second principal surface 21 b of the shield layer 20 can be clearly identified; for example, the brightness may be reduced by 25% (also written as "-25%) and the contrast may be increased by 75% (also written as "+75%)."

[0048] Next, the first principal surface 21a and the second principal surface 21b of the shield layer 20 are extracted from the adjusted image of the target area obtained as described above using image editing software, thereby obtaining an extracted image of the target area.

[0049] Next, in the image of the target region obtained as described above after extraction, image analysis software is used to enlarge a line P1 representing the first main surface 21a of the shield layer 20, and calculate the circumference Q1 of the line P1 based on the pixel size of the image. Here, because the line P1 has a certain thickness in the enlarged state, the outline of the line P1 (including the outlines on the adhesive layer 10 side and the protective layer 30 side) becomes visible. Then, the length along the outline of the line P1 is calculated based on the pixel size of the image, thereby calculating the circumference Q1 of the line P1. Half of the circumference Q1 of the line P1 obtained in this manner is defined as the length L1 of the first main surface 21a of the shield layer 20 (the length L1 along the first main surface 21a of the shield layer 20).

[0050] Similarly, in the image of the target region obtained as described above after extraction, image analysis software is used to enlarge a line P2 representing the second main surface 21b of the shield layer 20, and calculate the circumference Q2 of the line P2 based on the pixel size of the image. Here, because the line P2 has a certain thickness in the enlarged state, the outline of the line P2 (including the outlines on the adhesive layer 10 side and the protective layer 30 side) becomes visible. Then, the length along the outline of the line P2 can be calculated based on the pixel size of the image. Half of the circumference Q2 of the line P2 obtained in this manner is defined as the length L2 of the second main surface 21b of the shield layer 20 (the length L2 along the second main surface 21b of the shield layer 20).

[0051] Furthermore, in the image obtained after extraction of the target region as described above, the width M of the target region is measured using image analysis software.

[0052] In the electromagnetic wave shielding film 1, L1 / L2 is greater than 1.00, i.e., the length L1 of the first main surface 21a of the shielding layer 20 is greater than the length L2 of the second main surface 21b of the shielding layer 20, and therefore it can be said that the first main surface 21a of the shielding layer 20 is rougher than the second main surface 21b of the shielding layer 20.

[0053] Each of the components of the electromagnetic wave shielding film 1 will be described below.

[0054] <Adhesive Layer> The adhesive layer 10 can be used when attaching (bonding) the electromagnetic wave shielding film 1 to another member, such as a printed wiring board. The adhesive layer 10 makes it easy to attach the electromagnetic wave shielding film 1 to another member, such as a printed wiring board, from the adhesive layer 10 side (the side opposite to the protective layer 30). This makes it easy to manufacture a shielded printed wiring board in which the electromagnetic wave shielding film 1 is provided on a printed wiring board.

[0055] When the electromagnetic wave shielding film 1 is attached to the stepped portion from the adhesive layer 10 side, it is preferable that the adhesive layer 10 have high flexibility so that the adhesive layer 10 can conform to the stepped portion. In this case, when the electromagnetic wave shielding film 1 is attached to the stepped portion from the adhesive layer 10 side, the adhesive layer 10 can conform to the stepped portion more easily, making the shielding layer 20 laminated on the adhesive layer 10 more susceptible to the effects of the stepped portion. In contrast, in the electromagnetic wave shielding film 1, L1 / L2 is greater than 1.00. In other words, the first main surface 21 a of the shielding layer 20 facing the adhesive layer 10 is rougher than the second main surface 21 b of the shielding layer 20 facing the protective layer 30. This makes it easier for the shielding layer 20 to conform to the stepped portion. Therefore, even if the shielding layer 20 is more susceptible to the effects of the stepped portion when the electromagnetic wave shielding film 1 is attached to the stepped portion, cracks are less likely to occur in the shielding layer 20.

[0056] The material of the adhesive layer 10 is not particularly limited as long as it is an adhesive material that can attach (adhere) the electromagnetic wave shielding film 1 to another member, such as a printed wiring board.

[0057] The adhesive layer 10 is preferably a conductive adhesive layer.

[0058] When the adhesive layer 10 is a conductive adhesive layer, it becomes possible to electrically connect, for example, the shielding layer 20 of the electromagnetic wave shielding film 1 to a ground circuit included in the printed circuit of a printed wiring board via the conductive adhesive layer, which tends to improve the shielding properties of the electromagnetic wave shielding film 1.

[0059] The conductive adhesive layer may be an isotropically conductive adhesive layer or an anisotropically conductive adhesive layer, and is preferably an anisotropically conductive adhesive layer.

[0060] When the conductive adhesive layer is an anisotropic conductive adhesive layer, the transmission characteristics of high-frequency signals transmitted through signal circuits included in the printed circuit of the printed wiring board are more likely to be improved compared to when the conductive adhesive layer is an isotropic conductive adhesive layer.

[0061] When the adhesive layer 10 is a conductive adhesive layer, the adhesive layer 10 preferably contains a conductive filler and an adhesive resin.

[0062] The conductive filler is not particularly limited, and examples thereof include silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by silver-plating copper powder, polymer fine particles, metal-coated fine particles obtained by coating glass beads or the like with a metal, carbon fiber, graphite, etc. Among these, from the viewpoint of production cost, the conductive filler is preferably copper powder or silver-coated copper powder, which are inexpensive and easily available.

[0063] The adhesive layer 10 may contain only one type of the conductive filler described above, or may contain two or more types.

[0064] The shape of the conductive filler is not particularly limited, and examples thereof include spherical, flake, scale, dendritic, rod, and fibrous shapes. Among these, the conductive filler preferably has a dendritic shape. When the conductive filler has a dendritic shape, the conductive filler bends easily even when the electromagnetic wave shielding film 1 is bent, and therefore contact between the conductive filler particles is more likely to be maintained, and as a result, the conductivity of the conductive adhesive layer is less likely to decrease.

[0065] The average particle size of the conductive filler is not particularly limited, but is preferably 0.5 μm or more and 15 μm or less, and more preferably 5 μm or more and 13 μm or less.

[0066] If the average particle size of the conductive filler is smaller than 0.5 μm, it may be difficult to obtain sufficient conductivity in the conductive adhesive layer.

[0067] If the average particle diameter of the conductive filler is larger than 15 μm, the conductive adhesive layer will become too thick and difficult to bend, which may make it difficult to obtain sufficient bendability of the conductive adhesive layer, and ultimately the bendability of the electromagnetic wave shielding film 1.

[0068] The weight ratio of the conductive filler in the conductive adhesive layer is preferably 10% by weight or more and 80% by weight or less.

[0069] When the conductive adhesive layer is an anisotropic conductive adhesive layer, the weight proportion of the conductive filler in the conductive adhesive layer is preferably 5% by weight or more and 40% by weight or less, and more preferably 10% by weight or more and 35% by weight or less.

[0070] Examples of adhesive resins include thermoplastic resins and thermosetting resins.

[0071] Examples of thermoplastic resins include styrene-based resins, vinyl acetate-based resins, polyester-based resins, polyethylene-based resins, polypropylene-based resins, imide-based resins, amide-based resins, and acrylic-based resins.

[0072] Examples of thermosetting resins include phenolic resins, epoxy resins, urethane resins, melamine resins, alkyd resins, and polyester resins.

[0073] The adhesive layer 10 may contain only one type of adhesive resin, or may contain two or more types of adhesive resins.

[0074] The adhesive layer 10 does not have to be a conductive adhesive layer. Specifically, the adhesive layer 10 may be a non-conductive adhesive layer. In this case, the adhesive layer 10 may contain the adhesive resin described above without containing the conductive filler described above.

[0075] The thickness of the adhesive layer 10 is not particularly limited, but is preferably 0.5 μm or more and 30 μm or less.

[0076] If the thickness of the adhesive layer 10 is less than 0.5 μm, the adhesive layer 10 becomes too thin, and it may be difficult to obtain sufficient adhesive performance from the adhesive layer 10 .

[0077] If the thickness of the adhesive layer 10 is greater than 30 μm, the adhesive layer 10 may become too thick and difficult to handle, and the electromagnetic wave shielding film 1 may also become too thick and difficult to handle.

[0078] <Shielding Layer> The shielding layer 20 exhibits shielding performance of shielding electromagnetic waves. For example, when the electromagnetic wave shielding film 1 is mounted on a mobile device such as a smartphone or a tablet terminal, the shielding layer 20 can block electromagnetic waves generated from inside the mobile device and electromagnetic waves entering from outside the mobile device.

[0079] The shield layer 20 includes a metal layer, which makes it easier for the shield layer 20 to shield electromagnetic waves.

[0080] The shield layer 20 is preferably a metal layer.

[0081] The constituent material of the metal layer is not particularly limited as long as it is a conductive material capable of shielding electromagnetic waves, and examples thereof include copper, silver, gold, aluminum, nickel, tin, palladium, chromium, titanium, zinc, and alloys containing at least one of these. Among these, the constituent material of the metal layer is preferably copper. In other words, the metal layer is preferably a copper layer. When the metal layer is a copper layer, the shielding performance of the shielding layer 20 is more likely to be sufficiently exhibited even against high-frequency electromagnetic waves.

[0082] The thickness of the metal layer is preferably 0.1 μm or more and 50 μm or less.

[0083] If the thickness of the metal layer is less than 0.1 μm, the metal layer may not be able to exhibit sufficient shielding performance, and if the thickness of the metal layer is less than 0.1 μm, the metal layer may be too thin and have reduced strength, which may result in the metal layer and, ultimately, the electromagnetic wave shielding film 1 not being able to exhibit sufficient bending resistance.

[0084] If the thickness of the metal layer is greater than 50 μm, the metal layer may become too thick and difficult to handle, which may also result in an excessively thick and difficult to handle electromagnetic wave shielding film 1. Furthermore, if the thickness of the metal layer is greater than 50 μm, the metal layer may become too thick and difficult to bend, which may make it difficult to obtain sufficient bendability of the metal layer, and therefore of the electromagnetic wave shielding film 1.

[0085] The metal layer may be a metal foil layer.

[0086] When a conventional electromagnetic wave shielding film is attached to a stepped portion, if the metal layer contained in the shielding layer is a metal foil layer, the film is likely to have poor conformability to uneven surfaces compared to, for example, a metal vapor-deposited layer formed by vapor deposition. In contrast, in the electromagnetic wave shielding film 1, L1 / L2 is greater than 1.00, meaning that the first main surface 21 a of the shielding layer 20 facing the adhesive layer 10 is rougher than the second main surface 21 b of the shielding layer 20 facing the protective layer 30. This means that even if the metal layer contained in the shielding layer 20 is a metal foil layer, the film is likely to have high conformability to uneven surfaces. Therefore, even if the metal layer contained in the shielding layer 20 is a metal foil layer, cracks are less likely to occur in the shielding layer 20 when the electromagnetic wave shielding film 1 is attached to a stepped portion.

[0087] The metal foil layer may be a copper foil layer.

[0088] In the electromagnetic wave shielding film 1, L1 / L2 is greater than 1.00, meaning that the first main surface 21a of the shielding layer 20 facing the adhesive layer 10 is rougher than the second main surface 21b of the shielding layer 20 facing the protective layer 30, which tends to improve the conformability to unevenness of the shielding layer 20. Therefore, in the electromagnetic wave shielding film 1, even if the metal foil layer included in the shielding layer 20 is a copper foil layer containing copper, which is a material that is prone to cracking, cracks are less likely to occur in the shielding layer 20 when the electromagnetic wave shielding film 1 is attached to an uneven area.

[0089] The copper foil layer may be made of rolled copper foil or electrolytic copper foil.

[0090] The metal foil layer may be a layer other than a copper foil layer.

[0091] The metal layer may be formed by a method other than a metal foil layer. In this case, the metal layer may be formed by a method such as a vapor deposition method (vacuum vapor deposition, electron beam vapor deposition, etc.), a plating method (electrolytic plating, electroless plating, etc.), a sputtering method, a chemical vapor deposition (CVD) method, a metal organic method, etc. Furthermore, the metal layer may be formed from a material such as metal nanoparticles or flaky metal particles.

[0092] When the metal layer is formed by a vapor deposition method, the metal layer is a vapor-deposited metal layer. For example, when the metal layer is formed by vapor-depositing copper, the metal layer is a vapor-deposited copper layer.

[0093] The thickness of the shield layer 20 is not particularly limited, but is preferably 0.1 μm or more and 50 μm or less, more preferably 0.5 μm or more and 10 μm or less, and even more preferably 1 μm or more and 6 μm or less.

[0094] If the thickness of the shielding layer 20 is less than 0.1 μm, it may be difficult to fully exhibit the shielding performance of the shielding layer 20. Furthermore, if the thickness of the shielding layer 20 is less than 0.1 μm, the shielding layer 20 may be too thin and the strength of the shielding layer 20 may be reduced. As a result, it may be difficult to obtain sufficient bending resistance of the shielding layer 20, and therefore of the electromagnetic wave shielding film 1.

[0095] If the thickness of the shielding layer 20 is greater than 50 μm, the shielding layer 20 may become too thick and difficult to handle, which may also result in the electromagnetic wave shielding film 1. Furthermore, if the thickness of the shielding layer 20 is greater than 50 μm, the shielding layer 20 may become too thick and difficult to bend, which may make it difficult to obtain sufficient bendability of the shielding layer 20, and therefore the bendability of the electromagnetic wave shielding film 1.

[0096] <Protective Layer> The protective layer 30 exhibits a protective function of protecting other layers such as the shield layer 20 .

[0097] The constituent material of the protective layer 30 is not particularly limited as long as it is an insulating material that can protect other layers, and examples thereof include a thermoplastic resin composition, a thermosetting resin composition, and an active energy ray curable composition.

[0098] The thermoplastic resin composition is not particularly limited, and examples thereof include an amide-based resin composition, a styrene-based resin composition, a vinyl acetate-based resin composition, a polyester-based resin composition, a polyethylene-based resin composition, a polypropylene-based resin composition, an imide-based resin composition, and an acrylic-based resin composition.

[0099] The thermosetting resin composition is not particularly limited, and examples thereof include a urethane-based resin composition, a phenol-based resin composition, an epoxy-based resin composition, a melamine-based resin composition, an alkyd-based resin composition, and a polyester-based resin composition.

[0100] The active energy ray-curable composition is not particularly limited, and examples thereof include polymerizable compounds having a plurality of (meth)acryloyloxy groups in the molecule.

[0101] The protective layer 30 may contain only one type of the above-mentioned compositions, or may contain two or more types of the above-mentioned compositions.

[0102] The protective layer 30 may contain at least one of a urethane resin and an amide resin.

[0103] The protective layer 30 may contain, as necessary, 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 flame retardant assistant, a viscosity adjuster, an antiblocking agent, etc.

[0104] The thickness of the protective layer 30 is not particularly limited, but is preferably 1 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less.

[0105] If the thickness of the protective layer 30 is less than 1 μm, the protective layer 30 becomes too thin, and the protective performance of the protective layer 30 may not be fully exhibited.

[0106] If the thickness of the protective layer 30 is greater than 15 μm, the protective layer 30 becomes too thick and difficult to bend, which may make it difficult to obtain sufficient bendability of the protective layer 30, and ultimately the bendability of the electromagnetic wave shielding film 1.

[0107] The electromagnetic wave shielding film of the present invention is not limited to the above-mentioned embodiment, and various applications and modifications can be made within the scope of the present invention with respect to the configuration, production conditions, etc. of the electromagnetic wave shielding film.

[0108] For example, the electromagnetic wave shielding film of the present invention may further include an anchor layer laminated between the shielding layer and the protective layer.

[0109] Examples of materials constituting the anchor layer include urethane resin, acrylic resin, core-shell composite resin with urethane resin as the shell and acrylic resin as the core, epoxy resin, imide resin, amide resin, melamine resin, phenol resin, urea-formaldehyde resin, blocked isocyanate resin obtained by reacting polyisocyanate with a blocking agent such as phenol, polyvinyl alcohol resin, polyvinylpyrrolidone resin, and polyester resin.

[0110] [Shielded Printed Wiring Board] FIG. 3 is a cross-sectional view schematically showing an example of a shielded printed wiring board of the present invention.

[0111] The shielded printed wiring board 100 shown in FIG. 3 includes a printed wiring board 51 and an electromagnetic wave shielding film 1 .

[0112] Each component of the shielded printed wiring board 100 will be described below.

[0113] <Printed Wiring Board> The printed wiring board 51 has a base film 60 , a printed circuit 70 , and a coverlay 80 .

[0114] The printed wiring board 51 is preferably a flexible printed wiring board, which makes it easier to bend the printed wiring board 51, allowing the shielded printed wiring board 100 to be used in a wider range of applications.

[0115] (Base Film) The base film 60 preferably contains an engineering plastic, and more preferably is made of an engineering plastic.

[0116] Examples of the engineering plastic contained in the base film 60 include resins such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide.

[0117] (Printed Circuit) The printed circuit 70 is provided on the base film 60 .

[0118] The printed circuit 70 may be adhered to the base film 60 via an adhesive, or may be joined without an adhesive, for example, in the same manner as an adhesiveless copper clad laminate.

[0119] The printed circuit 70 may include a ground circuit 71 .

[0120] The printed circuit 70 may include signal circuits (not shown).

[0121] The material of which the printed circuit 70 is made is not particularly limited, and examples thereof include circuit materials such as copper.

[0122] (Coverlay) The coverlay 80 is provided to cover the printed circuit 70 .

[0123] The coverlay 80 may have an exposure hole 81 that exposes the ground circuit 71 from the coverlay 80 .

[0124] The coverlay 80 does not necessarily have to have the exposure holes 81 .

[0125] The coverlay 80 preferably includes an engineering plastic, and more preferably is made of an engineering plastic.

[0126] Examples of the engineering plastic contained in the coverlay 80 include resins such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide.

[0127] When the base film 60 and the coverlay 80 contain engineering plastics, the engineering plastics contained therein may be the same as or different from each other.

[0128] The coverlay 80 may be formed by bonding a plurality of flexible insulating films together with an adhesive.

[0129] The coverlay 80 may be formed by a series of methods such as coating a photosensitive insulating resin, drying, exposing, developing, and heat treating.

[0130] <Electromagnetic Wave Shielding Film> The electromagnetic wave shielding film 1 has the above-described configuration (see FIG. 1).

[0131] The electromagnetic wave shielding film 1 is provided on the coverlay 80 side of the printed wiring board 51 .

[0132] The adhesive layer 10 side (the side opposite the protective layer 30) of the electromagnetic wave shielding film 1 faces the coverlay 80. In the example shown in Fig. 3, the electromagnetic wave shielding film 1 is provided on the printed wiring board 51 so that the adhesive layer 10 located on the side opposite the protective layer 30 contacts the coverlay 80.

[0133] It is preferable that the adhesive layer 10 enters the exposure hole 81 and contacts the ground circuit 71. In this case, it is more preferable that the adhesive layer 10 fills the inside of the exposure hole 81 and contacts the ground circuit 71. In either case, if the adhesive layer 10 is a conductive adhesive layer, the shielding layer 20 and the ground circuit 71 are electrically connected via the conductive adhesive layer. This tends to improve the shielding characteristics of the electromagnetic wave shielding film 1.

[0134] The electromagnetic wave shielding film 1 is provided on the printed wiring board 51 by a conventionally known method. For example, it is preferable to place the electromagnetic wave shielding film 1 on the printed wiring board 51 so that the adhesive layer 10 side (the side opposite the protective layer 30) faces the coverlay 80 (so that it is in contact with the coverlay 80 in FIG. 3 ), and then thermocompression bond the electromagnetic wave shielding film 1 and the printed wiring board 51 together. The temperature during thermocompression bonding is preferably 150° C. or higher and 200° C. or lower. The pressure during thermocompression bonding is preferably 2 MPa or higher and 5 MPa or lower. The pressure application time during thermocompression bonding is preferably 1 minute or higher and 60 minutes or lower.

[0135] As described above, when the electromagnetic wave shielding film 1 is attached to a stepped portion from the adhesive layer 10 side, cracks are less likely to occur in the shielding layer 20. Therefore, in a shielded printed wiring board 100 having the electromagnetic wave shielding film 1, cracks are less likely to occur in the shielding layer 20 even when the electromagnetic wave shielding film 1 is attached to a stepped portion of the printed wiring board 51 from the adhesive layer 10 side. For example, in the shielded printed wiring board 100, cracks are less likely to occur in the shielding layer 20 even when the electromagnetic wave shielding film 1 is attached from the adhesive layer 10 side to a stepped portion of the coverlay 80 caused by an exposure hole 81 for exposing the ground circuit 71.

[0136] The shielded printed wiring board of the present invention is not limited to the above-described form, and various applications and modifications can be made within the scope of the present invention with respect to the configuration, manufacturing conditions, etc. of the shielded printed wiring board.

[0137] EXAMPLES Hereinafter, examples will be given that more specifically disclose the electromagnetic wave shielding film of the present invention, but the present invention is not limited to the following examples.

[0138] Example 1 An electromagnetic wave shielding film of Example 1 was produced by the following method.

[0139] (Step of Producing Protective Layer) A protective layer composition containing a urethane resin was applied to a transfer film, and then heated at 108° C. for 3 minutes using an electric oven to produce a protective layer.

[0140] (Step of Laminating Shield Layer) A 2 μm-thick copper foil was placed on the protective layer, thereby forming a shield layer made of a copper foil layer. One main surface of the shield layer (copper foil layer) was roughened by etching, and the shield layer was then placed on the protective layer so that the roughened main surface faced the opposite side of the protective layer (the adhesive layer side to be laminated in the step described below). The shield layer was then laminated on the protective layer under conditions of 115°C, 0.5 MPa, and 20 rpm. This resulted in a configuration in which the first main surface of the shield layer opposite the protective layer (the adhesive layer side to be laminated in the step described below) was rougher than the second main surface of the shield layer facing the protective layer.

[0141] (Step of laminating adhesive layer) A conductive adhesive layer composition containing copper particles and a urethane resin was applied to the side of the shielding layer opposite the protective layer, thereby laminating an adhesive layer that is a conductive adhesive layer on the side of the shielding layer opposite the protective layer.

[0142] In this manner, an electromagnetic wave shielding film of Example 1 was produced.

[0143] [Examples 2 to 6] Electromagnetic wave shielding films of Examples 2 to 6 were produced in the same manner as the electromagnetic wave shielding film of Example 1, except that the roughness of the roughened main surface of the shielding layer (copper foil layer) was changed.

[0144] [Comparative Examples 1 to 6] The electromagnetic shielding films of Comparative Examples 1 to 6 were produced in the same manner as the electromagnetic shielding film of Example 1, except that the shielding layer (copper foil layer) was laminated on the protective layer so that the roughened main surface of the shielding layer faced the protective layer. In producing the electromagnetic shielding films of Comparative Examples 1 to 6, the roughness of the roughened main surfaces of the shielding layers (copper foil layers) was made different from one another.

[0145] [Evaluation] <Roughness of Shielding Layer> The length L1 of the first main surface of the shielding layer on the adhesive layer side and the length L2 of the second main surface of the shielding layer on the protective layer side were determined for the electromagnetic wave shielding films of Examples 1 to 6 and Comparative Examples 1 to 6. The results are shown in Tables 1 and 2.

[0146] The specifics for determining L1 and L2 are as follows:

[0147] First, a cross section of the electromagnetic wave shielding film along the stacking direction of the adhesive layer, the shielding layer, and the protective layer was exposed. Then, an original image of a target area of ​​the cross section having an arbitrary width M in the width direction perpendicular to the stacking direction was obtained. At this time, a scanning electron microscope "JSM-6510LA" manufactured by JEOL Ltd. was used to obtain the original image of the target area at a magnification of 3000x.

[0148] Next, in order to clarify the first and second principal surfaces of the shield layer for the original image of the target area obtained as described above, the bmp data of the original image of the target area was pasted into Microsoft's PowerPoint, and the brightness and contrast of the original image of the target area were changed (brightness: -25%, contrast: +75%) to obtain an adjusted image of the target area.

[0149] Next, the first principal surface and the second principal surface of the shield layer were extracted from the adjusted image of the target area obtained as described above using image editing software "GIMP (Ver. 2.10.36)" manufactured by "The GIMP Development Team," thereby obtaining an extracted image of the target area.

[0150] Next, in the image of the target region obtained as described above after extraction, a line P1 indicating the first main surface of the shield layer was enlarged and a length Q1 of one circumference of the line P1 was calculated based on the pixel size of the image using image analysis software "WinROOF2018" manufactured by Mitani Corporation. Half of the length Q1 of one circumference of the line P1 obtained in this manner was defined as the length L1 of the first main surface of the shield layer (the length L1 along the first main surface of the shield layer).

[0151] Similarly, in the image after extraction of the target region obtained as described above, a line P2 indicating the second main surface of the shield layer was enlarged and a length Q2 of one circumference of the line P2 was calculated based on the pixel size of the image using image analysis software "WinROOF2018" manufactured by Mitani Corporation. Half of the length Q2 of one circumference of the line P2 obtained in this manner was defined as the length L2 of the second main surface of the shield layer (the length L2 along the second main surface of the shield layer).

[0152] Furthermore, in the image after extraction of the target region obtained as described above, the width M of the target region was measured using image analysis software "WinROOF2018" manufactured by Mitani Shoji Co., Ltd.

[0153] Examples of images of the target areas used to determine L1 and L2 are shown in Figures 4, 5, 6, 7, 8, and 9. Figure 4 is an original image showing the target area of ​​the cross section of the electromagnetic shielding film of Example 1. Figure 5 is an adjusted image showing the target area of ​​the cross section of the electromagnetic shielding film of Example 1. Figure 6 is an extracted image showing the target area of ​​the cross section of the electromagnetic shielding film of Example 1. Figure 7 is an original image showing the target area of ​​the cross section of the electromagnetic shielding film of Comparative Example 4. Figure 8 is an adjusted image showing the target area of ​​the cross section of the electromagnetic shielding film of Comparative Example 4. Figure 9 is an extracted image showing the target area of ​​the cross section of the electromagnetic shielding film of Comparative Example 4.

[0154] <Presence or Absence of Cracks> When the electromagnetic shielding films of Examples 1 to 6 and Comparative Examples 1 to 6 were attached from the adhesive layer side to a stepped portion of a printed wiring board, specifically, a stepped portion of the coverlay caused by an exposure hole for exposing the ground circuit (see FIG. 3), it was confirmed by image observation whether cracks occurred in the shielding layer. The results are shown in Tables 1 and 2.

[0155]

[0156]

[0157] As shown in Tables 1 and 2, the electromagnetic wave shielding films of Examples 1 to 6, in which the ratio L1 / L2 was greater than 1.00 (the length L1 of the first main surface of the shielding layer was greater than the length L2 of the second main surface of the shielding layer), i.e., the first main surface of the shielding layer was rougher than the second main surface of the shielding layer, were less likely to develop cracks in the shielding layer when attached to a stepped portion, compared to the electromagnetic wave shielding films of Comparative Examples 1 to 6, in which the ratio L1 / L2 was less than 1.00 (the length L2 of the second main surface of the shielding layer was greater than the length L1 of the first main surface of the shielding layer), i.e., the second main surface of the shielding layer was rougher than the first main surface of the shielding layer. Specifically, when the electromagnetic wave shielding films of Examples 1 to 6 were attached to a stepped portion of the coverlay on a printed wiring board, no cracks originating from the stepped portion developed in the shielding layer. On the other hand, when the electromagnetic wave shielding films of Comparative Examples 1 to 6 were attached to a stepped portion of the coverlay on a printed wiring board, cracks originating from the stepped portion developed in the shielding layer.

[0158] The present specification discloses the following:

[0159] <1> An electromagnetic wave shielding film comprising: an adhesive layer; a shielding layer laminated on the adhesive layer and including a metal layer; and a protective layer laminated on the shielding layer on the side opposite to the adhesive layer, wherein, when a cross section of the electromagnetic wave shielding film is viewed along a lamination direction of the adhesive layer, the shielding layer, and the protective layer, in a target region of the cross section having an arbitrary width M in a width direction perpendicular to the lamination direction, L1 is a length of a first main surface of the shielding layer facing the adhesive layer, and L2 is a length of a second main surface of the shielding layer facing the protective layer, where L1 is a length of a first main surface of the shielding layer facing the adhesive layer, and L2 is a length of a second main surface of the shielding layer facing the protective layer, the electromagnetic wave shielding film being characterized in that

[0160] <2> The electromagnetic wave shielding film according to <1>, wherein L1 / L2 is greater than 1.00 and equal to or less than 1.05.

[0161] <3> The electromagnetic wave shielding film according to <2>, wherein L1 / M is 1.01 or more and 1.06 or less.

[0162] <4> The electromagnetic wave shielding film according to <2> or <3>, wherein L2 / M is 1.00 or more and 1.03 or less.

[0163] <5> A shielded printed wiring board comprising: a printed wiring board having a base film, a printed circuit provided on the base film, and a coverlay provided so as to cover the printed circuit; and an electromagnetic wave shielding film provided on the coverlay side of the printed wiring board, wherein the electromagnetic wave shielding film is the electromagnetic wave shielding film according to any one of <1> to <4>, and the adhesive layer side faces the coverlay.

[0164] REFERENCE SIGNS LIST 1 Electromagnetic wave shielding film 10 Adhesive layer 20 Shielding layer 21a First main surface of shielding layer 21b Second main surface of shielding layer 30 Protective layer 51 Printed wiring board 60 Base film 70 Printed circuit 71 Ground circuit 80 Coverlay 81 Exposure hole 100 Shielded printed wiring board M Width of target area P1, P2 Line

Claims

1. An electromagnetic wave shielding film comprising: an adhesive layer; a shielding layer laminated on the adhesive layer and including a metal layer; and a protective layer laminated on the shielding layer on the side opposite the adhesive layer, wherein, when a cross section of the electromagnetic wave shielding film is viewed along the lamination direction of the adhesive layer, the shielding layer, and the protective layer, in a target region of the cross section having an arbitrary width M in the width direction perpendicular to the lamination direction, where L1 is the length of a first main surface of the shielding layer facing the adhesive layer and L2 is the length of a second main surface of the shielding layer facing the protective layer, L1 / L2 is greater than 1.

00.

2. The electromagnetic wave shielding film according to claim 1, wherein L1 / L2 is greater than 1.00 and not greater than 1.

05.

3. The electromagnetic wave shielding film according to claim 2, wherein L1 / M is 1.01 or more and 1.06 or less.

4. The electromagnetic wave shielding film according to claim 2 or 3, wherein L2 / M is 1.00 or more and 1.03 or less.

5. A shielded printed wiring board comprising: a printed wiring board having a base film, a printed circuit provided on said base film, and a coverlay provided so as to cover said printed circuit; and an electromagnetic wave shielding film provided on the coverlay side of said printed wiring board, wherein said electromagnetic wave shielding film is an electromagnetic wave shielding film according to any one of claims 1 to 4, and said adhesive layer side faces said coverlay.

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