Electromagnetic wave shielding film

Abstract

Provided is an electromagnetic wave shielding film in which shielding performance against electromagnetic waves is unlikely to deteriorate even when an opening is provided in a shielding layer. An electromagnetic wave shielding film according to the present invention comprises, in a lamination direction, an adhesive layer, a shielding layer laminated onto the adhesive layer and provided with an opening, and a protective layer laminated onto the opposite side of the shielding layer from the adhesive layer, the electromagnetic wave shielding film being characterized in that the adhesive layer includes, in the laminating direction, a first adhesive layer laminated onto the opposite side of the shielding layer from the protective layer, and a second adhesive layer laminated onto the opposite side of the first adhesive layer from the shielding layer, the first adhesive layer is a conductive adhesive layer containing a conductive filler, and the thickness of the first adhesive layer is 200% or less of the maximum thickness of the conductive filler in the first adhesive layer.

Description

Electromagnetic wave shielding film

[0001] The present invention relates to an electromagnetic wave shielding film.

[0002] Patent Document 1 discloses an electromagnetic wave shielding sheet including a layered product provided with a conductive adhesive layer, a metal layer, and a protective layer in this order, wherein a surface of the metal layer in contact with the conductive adhesive layer has a 60° specular glossiness of 10 to 800 determined in accordance with ISO 7668, the metal layer has a plurality of openings, and an aperture ratio is 0.10 to 20%.

[0003] Japanese Unexamined Patent Publication No. 2021-27313

[0004] In the electromagnetic wave shielding sheet described in Patent Document 1, since the metal layer has openings, when an electromagnetic wave shielding wiring circuit board obtained by attaching the electromagnetic wave shielding sheet to a wiring circuit board is subjected to solder reflow processing, volatile components contained in a polyimide film or a coverlay adhesive of the wiring circuit board are released to the outside, and it is stated that occurrence of poor appearance due to interfacial delamination between the coverlay adhesive and the electromagnetic wave shielding sheet can be suppressed.

[0005] However, the electromagnetic wave shielding sheet described in Patent Document 1 has a problem that since electromagnetic waves transmit through the openings of the metal layer, the shielding performance of shielding electromagnetic waves tends to decrease. Such a problem is particularly likely to become apparent with respect to electromagnetic waves in a high frequency band (for example, 1 GHz or higher).

[0006] On the other hand, in the electromagnetic wave shielding sheet described in Patent Document 1, since the conductive adhesive layer is laminated on the metal layer having openings, a method of shielding electromagnetic waves transmitted through the openings of the metal layer by the conductive filler in the conductive adhesive layer is conceivable. However, in the electromagnetic wave shielding sheet described in Patent Document 1, since the conductive filler is randomly positioned in the conductive adhesive layer, there is room for improvement in providing a configuration in which the conductive filler is easily positioned near the openings of the metal layer, so that the conductive filler easily shields electromagnetic waves transmitted through the openings of the metal layer.

[0007] The present invention was made to solve the above problems, and aims to provide an electromagnetic shielding film in which the shielding performance against electromagnetic waves does not deteriorate even when an opening is provided in the shielding layer.

[0008] The electromagnetic wave shielding film of the present invention comprises, in the lamination direction, an adhesive layer, a shielding layer laminated on the adhesive layer and having an opening, and a protective layer laminated on the side of the shielding layer opposite to the adhesive layer, wherein the adhesive layer includes, in the lamination direction, a first adhesive layer laminated on the side of the shielding layer opposite to the protective layer, and a second adhesive layer laminated on the side of the first adhesive layer opposite to the shielding layer, the first adhesive layer being a conductive adhesive layer containing a conductive filler, and the thickness of the first adhesive layer being 200% or less of the maximum thickness of the conductive filler in the first adhesive layer.

[0009] In the electromagnetic shielding film of the present invention, the thickness of the first adhesive layer is 200% or less of the maximum thickness of the conductive filler in the first adhesive layer. Thus, in the electromagnetic shielding film of the present invention, because the thickness of the first adhesive layer is small, the range in which the conductive filler in the first adhesive layer can move is limited during the formation of the first adhesive layer, and as a result, the movement of the conductive filler in the first adhesive layer is easily suppressed. Specifically, in the electromagnetic shielding film of the present invention, because the thickness of the first adhesive layer is small, the conductive filler in the first adhesive layer is more likely to be aligned in the width direction perpendicular to the lamination direction than in the lamination direction. More specifically, in the electromagnetic shielding film of the present invention, because the thickness of the first adhesive layer is 200% or less of the maximum thickness of the conductive filler in the first adhesive layer, it is less likely that two conductive fillers will overlap in the lamination direction in the first adhesive layer, and as a result, the conductive fillers are more likely to be aligned in the width direction rather than the lamination direction. In the electromagnetic shielding film of the present invention, the movement of conductive fillers in the first adhesive layer is more easily suppressed during the formation of the first adhesive layer, and the conductive fillers in the first adhesive layer are more easily aligned in the width direction. As a result, the probability that the conductive fillers in the first adhesive layer are located near the opening of the shielding layer laminated on the first adhesive layer increases. Consequently, in the electromagnetic shielding film of the present invention, the probability that the conductive fillers in the first adhesive layer will shield electromagnetic waves that have passed through the opening of the shielding layer also increases. Therefore, it can be said that the electromagnetic shielding film of the present invention does not easily experience a decrease in shielding performance against electromagnetic waves even if an opening is provided in the shielding layer. In particular, it can be said that the electromagnetic shielding film of the present invention does not easily experience a decrease in shielding performance against electromagnetic waves in the high frequency band (for example, 1 GHz or higher).

[0010] Furthermore, there is a concern that sufficient adhesive performance may not be obtained from the first adhesive layer due to its small thickness. Therefore, if only the first adhesive layer is provided, there is a concern that sufficient adhesive performance may not be obtained from the adhesive layer. In contrast, in the electromagnetic shielding film of the present invention, the adhesive layer includes a second adhesive layer in addition to the first adhesive layer, so that sufficient thickness (total thickness) of the adhesive layer is ensured. Thus, in the electromagnetic shielding film of the present invention, even if an opening is provided in the shielding layer, sufficient thickness of the adhesive layer is ensured by the further provision of the second adhesive layer, thereby obtaining sufficient adhesive performance for the entire adhesive layer, in order to obtain the effect that the shielding performance against electromagnetic waves does not easily decrease.

[0011] If the thickness of the first adhesive layer is greater than 200% of the maximum thickness of the conductive filler in the first adhesive layer, the thickness of the first adhesive layer becomes too large. As a result, the range in which the conductive filler can move within the first adhesive layer is not easily restricted during its formation, and consequently, the movement of the conductive filler within the first adhesive layer is not easily suppressed. When the movement of the conductive filler within the first adhesive layer is not easily suppressed in this way, the probability that the conductive filler within the first adhesive layer will be located near the opening of the shielding layer and shield electromagnetic waves that have passed through the opening of the shielding layer becomes less likely.

[0012] The thickness of the first adhesive layer may be, for example, 50% or more of the maximum thickness of the conductive filler in the first adhesive layer. If the thickness of the first adhesive layer is less than 50% of the maximum thickness of the conductive filler in the first adhesive layer, the thickness of the first adhesive layer may become too small, making it difficult to obtain sufficient adhesive performance for the adhesive layer including the first and second adhesive layers, even if a second adhesive layer is provided. For example, if the thickness of the first adhesive layer becomes too small, the conductive filler in the first adhesive layer is more likely to be exposed from the surface of the first adhesive layer, making it difficult to form the second adhesive layer laminated on the first adhesive layer. As a result, it becomes difficult to ensure sufficient thickness for the second adhesive layer, and consequently, it may be difficult to obtain sufficient adhesive performance for the adhesive layer including the first and second adhesive layers. Furthermore, if the thickness of the first adhesive layer is less than 50% of the maximum thickness of the conductive filler in the first adhesive layer, the conductive filler in the first adhesive layer may be more easily exposed from the surface of the first adhesive layer, and may also be more easily detached from the first adhesive layer.

[0013] In the electromagnetic wave shielding film of the present invention, it is preferable that the maximum length of the conductive filler in the first adhesive layer is 50% or more and 200% or less of the average opening diameter of the opening in the shielding layer.

[0014] In the electromagnetic wave shielding film of the present invention, if the maximum length of the conductive filler in the first adhesive layer is less than 50% of the average opening diameter of the opening in the shielding layer, the maximum length of the conductive filler in the first adhesive layer becomes too small. This can make it difficult for the conductive filler in the first adhesive layer to shield electromagnetic waves that have passed through the opening in the shielding layer, even if the probability of the conductive filler in the first adhesive layer being located near the opening in the shielding layer increases during the formation of the first adhesive layer.

[0015] In the electromagnetic wave shielding film of the present invention, if the maximum length of the conductive filler in the first adhesive layer is greater than 200% of the average opening diameter of the shielding layer's opening, the maximum length of the conductive filler in the first adhesive layer becomes too large. As a result, when the conductive filler in the first adhesive layer is exposed from the surface of the first adhesive layer, the exposed area tends to become larger, making it difficult to form the second adhesive layer laminated on the first adhesive layer. When it becomes difficult to form the second adhesive layer, it becomes difficult to ensure a sufficient thickness for the second adhesive layer, and consequently, it may become difficult to obtain sufficient adhesive performance for the adhesive layer including the first and second adhesive layers.

[0016] In the electromagnetic shielding film of the present invention, it is preferable that the conductive filler in the first adhesive layer is flake-shaped or spherical. In particular, in the electromagnetic shielding film of the present invention, it is more preferable that the conductive filler in the first adhesive layer is flake-shaped.

[0017] In the electromagnetic wave shielding film of the present invention, when the conductive filler in the first adhesive layer is flake-shaped or spherical, the conductive filler in the first adhesive layer is located near the opening of the shielding layer, making it easier for the conductive filler to shield electromagnetic waves that have passed through the opening of the shielding layer. In particular, when the conductive filler in the first adhesive layer is flake-shaped, the conductive filler bends more easily even when the electromagnetic wave shielding film is bent, making it easier to maintain contact between the conductive fillers, and consequently, the conductivity of the first adhesive layer does not easily decrease. Therefore, when the conductive filler in the first adhesive layer is flake-shaped, the shielding performance of the first adhesive layer against electromagnetic waves that have passed through the opening of the shielding layer does not easily decrease even when the electromagnetic wave shielding film is bent.

[0018] In the electromagnetic wave shielding film of the present invention, it is preferable that the maximum thickness of the conductive filler in the first adhesive layer is 0.1 μm or more and 1.5 μm or less.

[0019] In the electromagnetic wave shielding film of the present invention, if the maximum thickness of the conductive filler in the first adhesive layer is less than 0.1 μm, the thickness of the first adhesive layer, which is 200% or less of the maximum thickness of the conductive filler in the first adhesive layer, becomes too small. As a result, even if a second adhesive layer is provided, it may be difficult to obtain sufficient adhesive performance for the adhesive layer including the first and second adhesive layers.

[0020] In the electromagnetic wave shielding film of the present invention, if the maximum thickness of the conductive filler in the first adhesive layer is greater than 1.5 μm, the thickness of the first adhesive layer, which is 200% or less of the maximum thickness of the conductive filler in the first adhesive layer, becomes too large. As a result, the range in which the conductive filler can move in the first adhesive layer during its formation becomes less restricted, and consequently, the movement of the conductive filler in the first adhesive layer becomes less suppressed. When the movement of the conductive filler in the first adhesive layer becomes less suppressed in this way, the probability that the conductive filler in the first adhesive layer will be located near the opening of the shielding layer and shield electromagnetic waves that have passed through the opening of the shielding layer becomes less likely to occur.

[0021] In the electromagnetic wave shielding film of the present invention, the thickness of the first adhesive layer is preferably 0.2 μm or more and 3 μm or less.

[0022] In the electromagnetic wave shielding film of the present invention, if the thickness of the first adhesive layer is less than 0.2 μm, the thickness of the first adhesive layer becomes too small, which can make it difficult to obtain sufficient adhesive performance for the adhesive layer including the first and second adhesive layers, even if a second adhesive layer is also provided.

[0023] In the electromagnetic wave shielding film of the present invention, if the thickness of the first adhesive layer is greater than 3 μm, the thickness of the first adhesive layer becomes too large, making it difficult to restrict the range in which the conductive filler in the first adhesive layer can move during its formation. As a result, the movement of the conductive filler in the first adhesive layer may not be effectively suppressed. When the movement of the conductive filler in the first adhesive layer is not effectively suppressed in this way, the probability that the conductive filler in the first adhesive layer will be located near the opening of the shielding layer and shield electromagnetic waves that have passed through the opening of the shielding layer may decrease.

[0024] In this specification, "film" is synonymous with "sheet," and the two are not distinguished by their thickness. In other words, "electromagnetic shielding film" is synonymous with "electromagnetic shielding sheet."

[0025] According to the present invention, it is possible to provide an electromagnetic wave shielding film in which the shielding performance against electromagnetic waves does not easily deteriorate even if an opening is provided in the shielding layer.

[0026] Figure 1 is a schematic cross-sectional view showing an example of the electromagnetic shielding film of the present invention. Figure 2 is a schematic cross-sectional view showing an enlarged portion of the electromagnetic shielding film in Figure 1. Figure 3 is a schematic cross-sectional view showing an enlarged portion of another example of the electromagnetic shielding film of the present invention. Figure 4 is a schematic cross-sectional view showing an example of a shielded printed circuit board having the electromagnetic shielding film of the present invention.

[0027] The following describes specific examples of the electromagnetic shielding film of the present invention. However, the present invention is not limited to the following configurations, and may be modified as appropriate without departing from the spirit of the invention. Furthermore, a combination of several of the preferred configurations described below also constitutes the present invention.

[0028] The drawings shown below are schematic representations, and their dimensions, aspect ratios, and scales may differ from those of the actual product.

[0029] In this specification, unless otherwise specified, terms describing relationships between elements (e.g., "same," "parallel," "perpendicular," etc.) and terms describing the shapes of elements mean not only the literal, exact form, but also a range of substantially equivalent forms, for example, a range including differences of a few percent (e.g., 5% or less).

[0030] [Electromagnetic Shielding Film] Figure 1 is a schematic cross-sectional view showing an example of the electromagnetic shielding film of the present invention. Figure 2 is a schematic cross-sectional view showing an enlarged portion of the electromagnetic shielding film in Figure 1.

[0031] The electromagnetic wave shielding film 1 shown in Figure 1 comprises an adhesive layer 10, a shielding layer 20 with an opening 21, and a protective layer 30.

[0032] The shield layer 20 is laminated on the adhesive layer 10.

[0033] The protective layer 30 is laminated on the side of the shield layer 20 opposite to the adhesive layer 10.

[0034] As described above, in the electromagnetic wave shielding film 1, the adhesive layer 10, the shielding layer 20, and the protective layer 30 are laminated in order in the lamination direction (up and down in Figures 1 and 2).

[0035] In the electromagnetic wave shielding film 1, the adhesive layer 10 includes a first adhesive layer 10A laminated on the side of the shielding layer 20 opposite to the protective layer 30 in the lamination direction, and a second adhesive layer 10B laminated on the side of the first adhesive layer 10A opposite to the shielding layer 20. In other words, in the electromagnetic wave shielding film 1, the first adhesive layer 10A and the second adhesive layer 10B are laminated sequentially with respect to the shielding layer 20 in the lamination direction.

[0036] In the electromagnetic wave shielding film 1, the first adhesive layer 10A is a conductive adhesive layer containing a conductive filler 11A.

[0037] In the electromagnetic shielding film 1, the thickness (dimension in the lamination direction) T10A of the first adhesive layer 10A is 200% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A. Thus, in the electromagnetic shielding film 1, because the thickness T10A of the first adhesive layer 10A is small, the range in which the conductive filler 11A can move in the first adhesive layer 10A is limited during the formation of the first adhesive layer 10A, and as a result, the movement of the conductive filler 11A in the first adhesive layer 10A is easily suppressed. Specifically, in the electromagnetic shielding film 1, because the thickness T10A of the first adhesive layer 10A is small, the conductive filler 11A in the first adhesive layer 10A is more likely to align in the width direction perpendicular to the lamination direction (for example, the left-right direction in Figures 1 and 2) rather than in the lamination direction. More specifically, in the electromagnetic shielding film 1, the thickness T10A of the first adhesive layer 10A is 200% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A. As a result, it becomes difficult for two conductive fillers 11A to overlap in the lamination direction in the first adhesive layer 10A, and consequently, the conductive fillers 11A tend to align in the width direction rather than the lamination direction. In the electromagnetic shielding film 1, the movement of the conductive fillers 11A in the first adhesive layer 10A is suppressed when the first adhesive layer 10A is formed, and the conductive fillers 11A in the first adhesive layer 10A tend to align in the width direction. Therefore, the probability that the conductive fillers 11A in the first adhesive layer 10A are located near the opening 21 of the shielding layer 20 laminated on the first adhesive layer 10A increases. As a result, in the electromagnetic shielding film 1, the probability that the conductive fillers 11A in the first adhesive layer 10A will shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20 also increases. Based on the above, it can be said that the electromagnetic shielding film 1 is less likely to experience a decrease in shielding performance against electromagnetic waves even when an opening 21 is provided in the shielding layer 20. In particular, it can be said that the electromagnetic shielding film 1 is less likely to experience a decrease in shielding performance against electromagnetic waves in the high frequency band (for example, 1 GHz or higher).

[0038] Furthermore, with respect to the first adhesive layer 10A, there is a concern that sufficient adhesive performance may not be obtained due to its small thickness T10A. Therefore, if only the first adhesive layer 10A is provided as the adhesive layer 10, there is a concern that sufficient adhesive performance of the adhesive layer 10 may not be obtained. In contrast, in the electromagnetic wave shielding film 1, the adhesive layer 10 includes a second adhesive layer 10B in addition to the first adhesive layer 10A, so that the thickness (total thickness) T10 of the adhesive layer 10 is sufficiently secured. Thus, in the electromagnetic wave shielding film 1, even if an opening 21 is provided in the shielding layer 20, the shielding performance against electromagnetic waves does not decrease easily. In order to obtain this effect, even if a first adhesive layer 10A with a small thickness T10A is provided, the thickness T10 of the adhesive layer 10 is sufficiently secured by the further provision of the second adhesive layer 10B, so that sufficient adhesive performance of the adhesive layer 10 as a whole can be obtained.

[0039] If the thickness T10A of the first adhesive layer 10A is greater than 200% of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, the thickness T10A of the first adhesive layer 10A becomes too large, making it difficult to restrict the range in which the conductive filler 11A can move during the formation of the first adhesive layer 10A. As a result, the movement of the conductive filler 11A in the first adhesive layer 10A is not easily suppressed. When the movement of the conductive filler 11A in the first adhesive layer 10A is not easily suppressed in this way, the probability that the conductive filler 11A in the first adhesive layer 10A will be located near the opening 21 of the shielding layer 20 and shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20 becomes less likely.

[0040] The thickness T10A of the first adhesive layer 10A may, for example, be 50% or more of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A. If the thickness T10A of the first adhesive layer 10A is smaller than 50% of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, the thickness T10A of the first adhesive layer 10A becomes excessively small, and thus even if the second adhesive layer 10B is further provided, it may become difficult to sufficiently obtain the adhesive performance of the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B. For example, if the thickness T10A of the first adhesive layer 10A becomes excessively small, the conductive filler 11A in the first adhesive layer 10A is likely to be exposed from the surface of the first adhesive layer 10A, which makes it difficult to form the second adhesive layer 10B laminated on the first adhesive layer 10A. As a result, it becomes difficult to sufficiently secure the thickness of the second adhesive layer 10B, and consequently, it may become difficult to sufficiently obtain the adhesive performance of the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B. Furthermore, if the thickness T10A of the first adhesive layer 10A is smaller than 50% of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, the conductive filler 11A in the first adhesive layer 10A is likely to be exposed from the surface of the first adhesive layer 10A, and in some cases, the conductive filler 11A in the first adhesive layer 10A is likely to fall off from the first adhesive layer 10A.

[0041] The thickness T10A of the first adhesive layer 10A is preferably 50% or more and 150% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, more preferably 75% or more and 125% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, and particularly preferably 80% or more and 100% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A.

[0042] When the thickness T10A of the first adhesive layer 10A is 80% or more and 100% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, the conductive filler 11A in the first adhesive layer 10A will not be exposed from the surface of the first adhesive layer 10A, or will be slightly exposed. In this way, when the conductive filler 11A in the first adhesive layer 10A is slightly exposed from the surface of the first adhesive layer 10A on the side of the second adhesive layer 10B, the conductivity between the first adhesive layer 10A and the second adhesive layer 10B is more likely to increase due to the exposed conductive filler 11A, compared to the case where the conductive filler 11A in the first adhesive layer 10A is not exposed from the surface of the first adhesive layer 10A on the side of the second adhesive layer 10B. Furthermore, if the thickness T10A of the first adhesive layer 10A is 80% or more and 100% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, and the conductive filler 11A in the first adhesive layer 10A is only slightly exposed from the surface of the first adhesive layer 10A on the second adhesive layer 10B side, it will have little effect when forming the second adhesive layer 10B that is laminated on the first adhesive layer 10A.

[0043] The thickness T10A of the first adhesive layer 10A is determined in the electromagnetic wave shielding film 1 as follows. First, the cross-section of the electromagnetic wave shielding film 1 along the lamination direction is exposed. Next, a scanning electron microscope (SEM) is used to acquire an image of the cross-section at a magnification of 3000x. Then, in the acquired image, the thickness (dimension in the lamination direction) of the portion of the first adhesive layer 10A that does not extend into the opening 21 of the shielding layer 20 is measured at five arbitrary locations. The average of these measured values ​​is then defined as the thickness T10A of the first adhesive layer 10A. Thus, the thickness T10A of the first adhesive layer 10A refers to the thickness of the portion of the first adhesive layer 10A that does not extend into the opening 21 of the shielding layer 20.

[0044] The maximum thickness of the conductive filler 11A in the first adhesive layer 10A is determined in the electromagnetic wave shielding film 1 as follows. First, in the above-mentioned image (magnification of 3000 times) obtained when determining the thickness T10A of the first adhesive layer 10A, an ellipse with the minimum area circumscribing the conductive filler 11A is drawn using image analysis software. Then, the dimension of the minor axis (minor diameter) of this ellipse is defined as the thickness of the conductive filler 11A. Next, the thickness of the conductive filler 11A determined by the above-described method is measured for any 5 conductive fillers 11A. Then, the maximum value among these measured values is defined as the maximum thickness of the conductive filler 11A in the first adhesive layer 10A.

[0045] The above feature that the thickness T10A of the first adhesive layer 10A is 200% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A only needs to be satisfied when at least one cross-section of the electromagnetic wave shielding film 1 along the lamination direction is observed.

[0046] It is preferable that the thickness T10A of the first adhesive layer 10A is 90% or more and 110% or less of the average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A.

[0047] When the thickness T10A of the first adhesive layer 10A is smaller than 90% of the average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A, the thickness T10A of the first adhesive layer 10A becomes too small, so even if the second adhesive layer 10B is further provided, it may become difficult to sufficiently obtain the adhesive performance of the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B.

[0048] If the thickness T10A of the first adhesive layer 10A is greater than 110% of the average value of the dimension T11A of the conductive filler 11A in the lamination direction within the first adhesive layer 10A, the thickness T10A of the first adhesive layer 10A may become too large, making it difficult to restrict the range in which the conductive filler 11A can exist within the first adhesive layer 10A. When the range in which the conductive filler 11A can exist within the first adhesive layer 10A becomes less restricted in this way, the probability that the conductive filler 11A in the first adhesive layer 10A will be located near the opening 21 of the shielding layer 20 and shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20 may decrease.

[0049] The thickness T10A of the first adhesive layer 10A is more preferably 95% to 105% of the average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A, and is particularly preferably 98% to 102% of the average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A.

[0050] The average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A is determined as follows. First, in the above image (magnified 3000 times) obtained when determining the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, points P1 and P2 located at both ends in the lamination direction on the contour line of the conductive filler 11A in the first adhesive layer 10A are determined. Here, on the contour line of the conductive filler 11A in the first adhesive layer 10A, point P1 is defined as the point furthest from the shield layer 20 in the lamination direction, and point P2 is defined as the point furthest from the shield layer 20 in the lamination direction. Next, a straight line Q1 (dashed line in Figure 2) passing through point P1 and extending in the width direction (left-right direction in Figures 1 and 2) and a straight line Q2 (dashed line in Figure 2) passing through point P2 and extending in the width direction are defined. Then, the distance between straight line Q1 and straight line Q2 in the lamination direction is defined as the dimension T11A of the conductive filler 11A in the first adhesive layer 10A in the lamination direction. Next, the dimension T11A of the conductive filler 11A in the first adhesive layer 10A in the lamination direction, as defined by the method described above, is measured for any five conductive fillers 11A. The average of these measured values ​​is then defined as the average value of the dimension T11A of the conductive filler 11A in the lamination direction in the first adhesive layer 10A.

[0051] The above-mentioned characteristic, that the thickness T10A of the first adhesive layer 10A is 90% or more and 110% or less of the average value of the dimension T11A of the conductive filler 11A in the lamination direction within the first adhesive layer 10A, is preferably met when viewing at least one cross-section of the electromagnetic wave shielding film 1 along the lamination direction.

[0052] In the examples shown in Figures 1 and 2, the average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A is the same as the maximum thickness of the conductive filler 11A in the first adhesive layer 10A. However, the average value of the dimension T11A in the lamination direction of the conductive filler 11A in the first adhesive layer 10A may be different from the maximum thickness of the conductive filler 11A in the first adhesive layer 10A.

[0053] The maximum length of the conductive filler 11A in the first adhesive layer 10A is preferably 50% or more and 200% or less of the average opening diameter of the opening 21 of the shield layer 20.

[0054] If the maximum length of the conductive filler 11A in the first adhesive layer 10A is less than 50% of the average aperture diameter of the opening 21 of the shielding layer 20, the maximum length of the conductive filler 11A in the first adhesive layer 10A becomes too small. This can make it difficult for the conductive filler 11A in the first adhesive layer 10A to shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20, even if the probability of the conductive filler 11A in the first adhesive layer 10A being located near the opening 21 of the shielding layer 20 increases during the formation of the first adhesive layer 10A.

[0055] If the maximum length of the conductive filler 11A in the first adhesive layer 10A is greater than 200% of the average opening diameter of the opening 21 in the shield layer 20, the maximum length of the conductive filler 11A in the first adhesive layer 10A becomes too large. As a result, if the conductive filler 11A in the first adhesive layer 10A is exposed from the surface of the first adhesive layer 10A, the exposed area tends to become larger, which can make it difficult to form the second adhesive layer 10B that is laminated on the first adhesive layer 10A. If it becomes difficult to form the second adhesive layer 10B, it becomes difficult to ensure a sufficient thickness of the second adhesive layer 10B, and as a result, it may become difficult to obtain sufficient adhesive performance for the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B.

[0056] The maximum length of the conductive filler 11A in the first adhesive layer 10A is more preferably 75% to 150% of the average opening diameter of the openings 21 of the shield layer 20, even more preferably 90% to 120%, and particularly preferably 95% to 105%.

[0057] The maximum length of the conductive filler 11A in the first adhesive layer 10A is determined in the electromagnetic wave shielding film 1 as follows. First, using the image (at a magnification of 3000x) obtained when determining the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, an ellipse with the smallest area circumscribing the conductive filler 11A is drawn using image analysis software. The dimension of the major axis (major diameter) of this ellipse is then determined as the length of the conductive filler 11A. Next, the length of the conductive filler 11A determined by the method described above is measured for five conductive fillers 11A selected when determining the maximum thickness of the conductive filler 11A. The maximum value among these measured values ​​is then determined as the maximum length of the conductive filler 11A in the first adhesive layer 10A.

[0058] The average aperture diameter of the openings 21 in the shielding layer 20 is determined in the electromagnetic wave shielding film 1 as follows: First, the equivalent circle diameter, calculated from the area of ​​the end of the opening 21 on the first adhesive layer 10A side of the shielding layer 20 when the electromagnetic wave shielding film 1 (shielding layer 20) is viewed from the lamination direction, is measured for any five openings 21. Then, the average of these measured values ​​is determined as the average aperture diameter of the openings 21 in the shielding layer 20.

[0059] Furthermore, the average aperture diameter of the openings 21 in the shielding layer 20 can also be the average value of the aperture diameters (equivalent circle diameters) of the openings 21 formed in the shielding layer 20 during the manufacturing process of the electromagnetic wave shielding film 1.

[0060] Preferably, the average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A is 50% or more and 200% or less of the average opening diameter of the opening 21 of the shield layer 20.

[0061] If the average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A is smaller than 50% of the average opening diameter of the opening 21 of the shielding layer 20, the average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A becomes too small, which can make it difficult for the conductive filler 11A in the first adhesive layer 10A to shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20, even if the conductive filler 11A in the first adhesive layer 10A is located near the opening 21 of the shielding layer 20.

[0062] If the average value of the widthwise dimension W11A of the conductive filler 11A in the first adhesive layer 10A is greater than 200% of the average opening diameter of the opening 21 of the shield layer 20, the average value of the widthwise dimension W11A of the conductive filler 11A in the first adhesive layer 10A becomes too large. As a result, if the conductive filler 11A in the first adhesive layer 10A is exposed from the surface of the first adhesive layer 10A, the exposed area tends to become larger, making it difficult to form the second adhesive layer 10B laminated on the first adhesive layer 10A. If it becomes difficult to form the second adhesive layer 10B, it becomes difficult to ensure a sufficient thickness of the second adhesive layer 10B, and consequently, it may become difficult to obtain sufficient adhesive performance for the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B.

[0063] The average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A is more preferably 75% or more and 150% or less of the average opening diameter of the opening 21 of the shield layer 20, even more preferably 90% or more and 120% or less of the average opening diameter of the opening 21 of the shield layer 20, and particularly preferably 95% or more and 105% or less of the average opening diameter of the opening 21 of the shield layer 20.

[0064] The average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A is determined as follows. First, in the above image (magnified 3000 times) obtained when determining the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, points R1 and R2 located at both ends in the width direction on the contour line of the conductive filler 11A in the first adhesive layer 10A are determined. Next, a straight line S1 (dashed line in Figure 2) extending in the lamination direction passing through point R1 and a straight line S2 (dashed line in Figure 2) extending in the lamination direction passing through point R2 are determined. Then, the distance in the width direction between the straight line S1 and the straight line S2 is determined as the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A. Next, the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A, determined by the method described above, is measured for any five conductive fillers 11A. The average of these measurements is then defined as the average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A.

[0065] In the examples shown in Figures 1 and 2, the average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A is the same as the maximum length of the conductive filler 11A in the first adhesive layer 10A. However, the average value of the dimension W11A in the width direction of the conductive filler 11A in the first adhesive layer 10A may be different from the maximum length of the conductive filler 11A in the first adhesive layer 10A.

[0066] The following describes each component of the electromagnetic wave shielding film 1.

[0067] <Adhesive Layer> The adhesive layer 10 can be used when attaching (adhering) the electromagnetic shielding film 1 to other components, such as a printed circuit board. The adhesive layer 10 makes it easy to attach the electromagnetic shielding film 1 to other components, such as a printed circuit board, from the adhesive layer 10 side (opposite side of the protective layer 30). This makes it easy to manufacture a shielded printed circuit board in which the electromagnetic shielding film 1 is provided on the printed circuit board.

[0068] The adhesive layer 10 includes a first adhesive layer 10A and a second adhesive layer 10B, in that order from the shield layer 20 side.

[0069] The first adhesive layer 10A may or may not be inserted into the opening 21 of the shield layer 20.

[0070] When the first adhesive layer 10A is embedded in the opening 21 of the shield layer 20, the first adhesive layer 10A may be embedded in the entire opening 21 of the shield layer 20, or in a part of the opening 21 of the shield layer 20. In other words, the first adhesive layer 10A may be embedded in at least a part of the opening 21 of the shield layer 20.

[0071] The first adhesive layer 10A is a conductive adhesive layer containing a conductive filler 11A.

[0072] The first adhesive layer 10A may be an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. In particular, the first adhesive layer 10A is preferably an anisotropic conductive adhesive layer.

[0073] The conductive filler 11A in the first adhesive layer 10A is not particularly limited in type and may be, for example, 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 etc. with metal, carbon fiber, graphite, etc. Among these, the conductive filler 11A in the first adhesive layer 10A is preferably copper powder or silver-coated copper powder, which are inexpensive and readily available, from the viewpoint of manufacturing cost.

[0074] The first adhesive layer 10A may contain only one type of conductive filler 11A from the above-mentioned conductive fillers, or it may contain two or more types.

[0075] The conductive filler 11A in the first adhesive layer 10A is preferably in the shape of flakes or spheres. In particular, the conductive filler 11A in the first adhesive layer 10A is more preferably in the shape of flakes.

[0076] When the conductive filler 11A in the first adhesive layer 10A is flake-shaped or spherical, if the conductive filler 11A in the first adhesive layer 10A is located near the opening 21 of the shielding layer 20, the conductive filler 11A in the first adhesive layer 10A will be more effective at shielding electromagnetic waves that have passed through the opening 21 of the shielding layer 20. In particular, when the conductive filler 11A in the first adhesive layer 10A is flake-shaped, even if the electromagnetic wave shielding film 1 is bent, the conductive filler 11A will be more flexible, making it easier to maintain contact between the conductive fillers 11A, and consequently, the conductivity of the first adhesive layer 10A will not be reduced. Therefore, when the conductive filler 11A in the first adhesive layer 10A is flake-shaped, even if the electromagnetic wave shielding film 1 is bent, the shielding performance of the first adhesive layer 10A against electromagnetic waves that have passed through the opening 21 of the shielding layer 20 will not be reduced.

[0077] The shape of the conductive filler 11A in the first adhesive layer 10A is not limited to flake or spherical shapes, but may be, for example, flake-shaped, dendrite-shaped, rod-shaped, fibrous, etc. In particular, when the shape of the conductive filler 11A in the first adhesive layer 10A is dendrite-shaped, the conductive filler 11A becomes more flexible even when the electromagnetic wave shielding film 1 is bent, making it easier to maintain contact between the conductive fillers 11A, and as a result, the conductivity of the first adhesive layer 10A is less likely to decrease. Therefore, when the shape of the conductive filler 11A in the first adhesive layer 10A is dendrite-shaped, the shielding performance of the first adhesive layer 10A against electromagnetic waves transmitted through the opening 21 of the shielding layer 20 is less likely to decrease even when the electromagnetic wave shielding film 1 is bent.

[0078] The maximum thickness of the conductive filler 11A in the first adhesive layer 10A is preferably 0.1 μm or more and 1.5 μm or less.

[0079] If the maximum thickness of the conductive filler 11A in the first adhesive layer 10A is less than 0.1 μm, the thickness T10A of the first adhesive layer 10A, which is 200% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, becomes too small. As a result, even if a second adhesive layer 10B is provided, it may be difficult to obtain sufficient adhesive performance for the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B.

[0080] If the maximum thickness of the conductive filler 11A in the first adhesive layer 10A is greater than 1.5 μm, the thickness T10A of the first adhesive layer 10A, which is 200% or less of the maximum thickness of the conductive filler 11A in the first adhesive layer 10A, becomes too large. As a result, the range in which the conductive filler 11A can move in the first adhesive layer 10A is not easily restricted during its formation, and consequently, the movement of the conductive filler 11A in the first adhesive layer 10A is not easily suppressed. When the movement of the conductive filler 11A in the first adhesive layer 10A is not easily suppressed in this way, the probability that the conductive filler 11A in the first adhesive layer 10A will be located near the opening 21 of the shielding layer 20 and shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20 may not increase.

[0081] The maximum length of the conductive filler 11A in the first adhesive layer 10A is preferably 0.5 μm or more and 30 μm or less.

[0082] If the maximum length of the conductive filler 11A in the first adhesive layer 10A is less than 0.5 μm, the maximum length of the conductive filler 11A in the first adhesive layer 10A becomes too small. This can make it difficult for the conductive filler 11A in the first adhesive layer 10A to shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20, even if the probability of the conductive filler 11A in the first adhesive layer 10A being located near the opening 21 of the shielding layer 20 increases during the formation of the first adhesive layer 10A.

[0083] If the maximum length of the conductive filler 11A in the first adhesive layer 10A is greater than 30 μm, the maximum length of the conductive filler 11A in the first adhesive layer 10A becomes too large, and if the conductive filler 11A in the first adhesive layer 10A is exposed from the surface of the first adhesive layer 10A, the exposed area tends to become large, which can make it difficult to form the second adhesive layer 10B that is laminated on the first adhesive layer 10A. If it becomes difficult to form the second adhesive layer 10B, it becomes difficult to ensure a sufficient thickness of the second adhesive layer 10B, and as a result, it may become difficult to obtain sufficient adhesive performance for the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B.

[0084] The average particle size of the conductive filler 11A in the first adhesive layer 10A 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.

[0085] If the average particle size of the conductive filler 11A in the first adhesive layer 10A is smaller than 0.5 μm, it may be difficult to obtain sufficient conductivity in the first adhesive layer 10A.

[0086] If the average particle size of the conductive filler 11A in the first adhesive layer 10A is greater than 15 μm, the first adhesive layer 10A may become too thick and difficult to bend, making it difficult to obtain sufficient flexibility for the first adhesive layer 10A, and consequently for the electromagnetic wave shielding film 1.

[0087] The weight percentage of conductive filler 11A in the first adhesive layer 10A is preferably 10% by weight or more and 80% by weight or less.

[0088] When the first adhesive layer 10A is an anisotropic conductive adhesive layer, the weight percentage of conductive filler 11A in the first adhesive layer 10A 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.

[0089] The aspect ratio of the conductive filler 11A in the first adhesive layer 10A is not particularly limited, but is preferably 7 or more, more preferably 15 or more, and even more preferably 18 or more. Alternatively, the aspect ratio of the conductive filler 11A in the first adhesive layer 10A may be, for example, 150 or less.

[0090] The aspect ratio of the conductive filler 11A in the first adhesive layer 10A is determined as average length / average thickness, using the average thickness and average length of the conductive filler 11A.

[0091] The average thickness of the conductive filler 11A in the first adhesive layer 10A is determined as the average of the thickness measurements of five conductive fillers 11A selected when determining the maximum thickness of the conductive filler 11A in the first adhesive layer 10A.

[0092] The average length of the conductive filler 11A in the first adhesive layer 10A is determined as the average of the measured lengths of five conductive fillers 11A selected when determining the maximum length of the conductive filler 11A in the first adhesive layer 10A.

[0093] The density of the conductive filler 11A in the first adhesive layer 10A is not particularly limited.

[0094] When the electromagnetic wave shielding film 1 is viewed from the lamination direction, it is preferable that at least a portion of the conductive filler 11A in the first adhesive layer 10A overlaps the opening 21 of the shielding layer 20. In this case, the conductive filler 11A in the first adhesive layer 10A can more easily shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20.

[0095] When the electromagnetic wave shielding film 1 is viewed from the lamination direction, if at least a portion of the conductive filler 11A in the first adhesive layer 10A overlaps the opening 21 of the shielding layer 20, it is preferable that the conductive filler 11A in the first adhesive layer 10A overlaps the opening area of ​​the opening 21 of the shielding layer 20 by 80% or more and 100% or less.

[0096] When the electromagnetic shielding film 1 is viewed from the lamination direction, if at least a portion of the conductive filler 11A in the first adhesive layer 10A overlaps with the opening 21 of the shielding layer 20, it is preferable that the conductive filler 11A in the first adhesive layer 10A is separated from the shielding layer 20 (not in contact with the shielding layer 20). In other words, when the electromagnetic shielding film 1 is viewed from the lamination direction, if at least a portion of the conductive filler 11A in the first adhesive layer 10A overlaps with the opening 21 of the shielding layer 20, it is preferable that a gap exists between the conductive filler 11A in the first adhesive layer 10A and the shielding layer 20. In this case, the opening 21 of the shielding layer 20 is less likely to be blocked by the conductive filler 11A in the first adhesive layer 10A, so even if the conductive filler 11A in the first adhesive layer 10A is located near the opening 21 of the shielding layer 20, the permeability for volatile components (gases), described later, to pass through the opening 21 of the shielding layer 20 is more easily maintained.

[0097] It is preferable that the conductive fillers 11A in the first adhesive layer 10A are in contact with each other. In this case, the conductivity of the first adhesive layer 10A is less likely to decrease, especially in the width direction, and the shielding performance of the first adhesive layer 10A against electromagnetic waves transmitted through the opening 21 of the shield layer 20 is less likely to decrease.

[0098] As shown in Figure 2, the conductive filler 11A in the first adhesive layer 10A may be oriented in the width direction. Specifically, as shown in Figure 2, the long axis direction of the conductive filler 11A in the first adhesive layer 10A may be parallel to the width direction.

[0099] The conductive filler 11A in the first adhesive layer 10A may be oriented in a direction other than the width direction. In other words, the long axis direction of the conductive filler 11A in the first adhesive layer 10A does not have to be parallel to the width direction.

[0100] Figure 3 is a schematic, enlarged cross-sectional view showing a part of another example of the electromagnetic wave shielding film of the present invention.

[0101] As shown in Figure 3, the conductive filler 11A in the first adhesive layer 10A may be oriented in a direction that forms an acute angle with respect to the width direction. Specifically, as shown in Figure 3, the long axis direction of the conductive filler 11A in the first adhesive layer 10A may form an acute angle with respect to the width direction.

[0102] In the examples shown in Figures 1, 2, and 3, the first adhesive layer 10A contains a plurality of conductive fillers 11A. Of the plurality of conductive fillers 11A, all may be oriented in the width direction, all may be oriented in a direction other than the width direction, or some may be oriented in the width direction and the remainder in a direction other than the width direction.

[0103] The first adhesive layer 10A preferably further contains an adhesive resin in addition to the conductive filler 11A.

[0104] The adhesive resin in the first adhesive layer 10A may be, for example, a thermoplastic resin, a thermosetting resin, or the like.

[0105] The thermoplastic resin in the first adhesive layer 10A may be, for example, a styrene resin, a vinyl acetate resin, a polyester resin, a polyethylene resin, a polypropylene resin, an imide resin, an amide resin, an acrylic resin, or the like.

[0106] The thermosetting resin in the first adhesive layer 10A may be, for example, a phenolic resin, epoxy resin, urethane resin, melamine resin, alkyd resin, polyester resin, or the like.

[0107] The first adhesive layer 10A may contain only one type of adhesive resin from the above-mentioned adhesive resins, or it may contain two or more types.

[0108] The thickness T10A of the first adhesive layer 10A is preferably 0.2 μm or more and 3 μm or less.

[0109] If the thickness T10A of the first adhesive layer 10A is less than 0.2 μm, the thickness T10A of the first adhesive layer 10A becomes too small, which can make it difficult to obtain sufficient adhesive performance for the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B, even if a second adhesive layer 10B is also provided.

[0110] If the thickness T10A of the first adhesive layer 10A is greater than 3 μm, the thickness T10A of the first adhesive layer 10A becomes too large, making it difficult to restrict the range in which the conductive filler 11A can move during the formation of the first adhesive layer 10A. As a result, the movement of the conductive filler 11A in the first adhesive layer 10A may not be suppressed. When the movement of the conductive filler 11A in the first adhesive layer 10A is not suppressed in this way, the probability that the conductive filler 11A in the first adhesive layer 10A will be located near the opening 21 of the shielding layer 20 and shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20 may not increase.

[0111] The type of the second adhesive layer 10B is not particularly limited, as long as it is capable of exhibiting adhesive performance.

[0112] The second adhesive layer 10B is preferably a conductive adhesive layer.

[0113] When the second adhesive layer 10B is a conductive adhesive layer, and the adhesive layer 10 consists of the first adhesive layer 10A and the second adhesive layer 10B, the adhesive layer 10 becomes a conductive adhesive layer. For example, it becomes possible to electrically connect the shielding layer 20 of the electromagnetic shielding film 1 and the ground circuit included in the printed circuit of the printed wiring board via the conductive adhesive layer 10. As a result, the shielding performance of the electromagnetic shielding film 1 tends to improve.

[0114] When the second adhesive layer 10B is a conductive adhesive layer, the second adhesive layer 10B may be an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. In particular, it is preferable that the second adhesive layer 10B is an anisotropic conductive adhesive layer.

[0115] If the second adhesive layer 10B is a conductive adhesive layer, it is preferable that the second adhesive layer 10B contains a conductive filler 11B.

[0116] The conductive filler 11B in the second adhesive layer 10B is not particularly limited in type and may be, for example, 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 etc. with metal, carbon fiber, graphite, etc. Among these, from the viewpoint of manufacturing cost, it is preferable that the conductive filler 11B in the second adhesive layer 10B is copper powder or silver-coated copper powder, which are inexpensive and readily available.

[0117] The second adhesive layer 10B may contain only one type of conductive filler 11B from the above-mentioned conductive fillers, or it may contain two or more types.

[0118] The type of conductive filler 11B in the second adhesive layer 10B may be the same as the type of conductive filler 11A in the first adhesive layer 10A, or it may be different from the type of conductive filler 11A in the first adhesive layer 10A.

[0119] The shape of the conductive filler 11B in the second adhesive layer 10B is not particularly limited and may be, for example, flake-shaped, spherical, flaky, dendrite-shaped, rod-shaped, fibrous, etc. In particular, when the conductive filler 11B in the second adhesive layer 10B is flake-shaped or dendrite-shaped, the conductive filler 11B bends more easily even when the electromagnetic wave shielding film 1 is bent, so that contact between the conductive fillers 11B is more easily maintained, and as a result, the conductivity of the second adhesive layer 10B does not decrease easily. For this reason, when the conductive filler 11B in the second adhesive layer 10B is flake-shaped or dendrite-shaped, the shielding performance of the second adhesive layer 10B against electromagnetic waves transmitted through the opening 21 of the shielding layer 20 does not decrease easily even when the electromagnetic wave shielding film 1 is bent.

[0120] The shape of the conductive filler 11B in the second adhesive layer 10B may be the same as the shape of the conductive filler 11A in the first adhesive layer 10A, or it may be different from the shape of the conductive filler 11A in the first adhesive layer 10A.

[0121] The average particle size of the conductive filler 11B in the second adhesive layer 10B 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.

[0122] If the average particle size of the conductive filler 11B in the second adhesive layer 10B is smaller than 0.5 μm, it may be difficult to obtain sufficient conductivity in the second adhesive layer 10B.

[0123] If the average particle size of the conductive filler 11B in the second adhesive layer 10B is greater than 15 μm, the second adhesive layer 10B may become too thick and difficult to bend, making it difficult to obtain sufficient flexibility for the second adhesive layer 10B, and consequently for the electromagnetic shielding film 1.

[0124] The average particle size of the conductive filler 11B in the second adhesive layer 10B may be the same as the average particle size of the conductive filler 11A in the first adhesive layer 10A, or it may be different from the average particle size of the conductive filler 11A in the first adhesive layer 10A.

[0125] If the average particle diameter of the conductive filler 11B in the second adhesive layer 10B is different from the average particle diameter of the conductive filler 11A in the first adhesive layer 10A, the average particle diameter of the conductive filler 11B in the second adhesive layer 10B may be larger than or smaller than the average particle diameter of the conductive filler 11A in the first adhesive layer 10A.

[0126] The weight percentage of conductive filler 11B in the second adhesive layer 10B is preferably 10% by weight or more and 80% by weight or less.

[0127] When the second adhesive layer 10B is an anisotropic conductive adhesive layer, the weight percentage of conductive filler 11B in the second adhesive layer 10B 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.

[0128] The weight ratio of conductive filler 11B in the second adhesive layer 10B may be the same as the weight ratio of conductive filler 11A in the first adhesive layer 10A, or it may be different from the weight ratio of conductive filler 11A in the first adhesive layer 10A.

[0129] The aspect ratio of the conductive filler 11B in the second adhesive layer 10B is not particularly limited, but is preferably 7 or more, more preferably 15 or more, and even more preferably 18 or more. Alternatively, the aspect ratio of the conductive filler 11B in the second adhesive layer 10B may be, for example, 150 or less.

[0130] The aspect ratio of the conductive filler 11B in the second adhesive layer 10B may be the same as the aspect ratio of the conductive filler 11A in the first adhesive layer 10A, or it may be different from the aspect ratio of the conductive filler 11A in the first adhesive layer 10A.

[0131] If the aspect ratio of the conductive filler 11B in the second adhesive layer 10B is different from the aspect ratio of the conductive filler 11A in the first adhesive layer 10A, the aspect ratio of the conductive filler 11B in the second adhesive layer 10B may be greater than or less than the aspect ratio of the conductive filler 11A in the first adhesive layer 10A.

[0132] The density of the conductive filler 11B in the second adhesive layer 10B is not particularly limited.

[0133] The density of the conductive filler 11B in the second adhesive layer 10B may be the same as the density of the conductive filler 11A in the first adhesive layer 10A, or it may be different from the density of the conductive filler 11A in the first adhesive layer 10A.

[0134] If the density of the conductive filler 11B in the second adhesive layer 10B is different from the density of the conductive filler 11A in the first adhesive layer 10A, the density of the conductive filler 11B in the second adhesive layer 10B may be greater than or less than the density of the conductive filler 11A in the first adhesive layer 10A.

[0135] When the electromagnetic wave shielding film 1 is viewed from the lamination direction, it is preferable that at least a portion of the conductive filler 11B in the second adhesive layer 10B overlaps the opening 21 of the shielding layer 20. In this case, the conductive filler 11B in the second adhesive layer 10B can more easily shield electromagnetic waves that have passed through the opening 21 of the shielding layer 20.

[0136] When the electromagnetic wave shielding film 1 is viewed from the lamination direction, if at least a portion of the conductive filler 11B in the second adhesive layer 10B overlaps the opening 21 of the shielding layer 20, it is preferable that the conductive filler 11B in the second adhesive layer 10B overlaps the opening area of ​​the opening 21 of the shielding layer 20 by 80% or more and 100% or less.

[0137] It is preferable that the conductive fillers 11B in the second adhesive layer 10B are in contact with each other. In this case, the conductivity of the second adhesive layer 10B is less likely to decrease, especially in the width direction, and the shielding performance of the second adhesive layer 10B against electromagnetic waves transmitted through the opening 21 of the shield layer 20 is less likely to decrease.

[0138] The conductive filler 11B in the second adhesive layer 10B may be oriented in the width direction or in a direction other than the width direction. Specifically, the long axis direction of the conductive filler 11B in the second adhesive layer 10B may be parallel to the width direction or not.

[0139] In the examples shown in Figures 1, 2, and 3, the second adhesive layer 10B contains a plurality of conductive fillers 11B. Of the plurality of conductive fillers 11B, all may be oriented in the width direction, all may be oriented in a direction other than the width direction, or some may be oriented in the width direction and the remainder in a direction other than the width direction.

[0140] The second adhesive layer 10B preferably further contains an adhesive resin in addition to the conductive filler 11B.

[0141] The adhesive resin in the second adhesive layer 10B may be, for example, a thermoplastic resin, a thermosetting resin, or the like.

[0142] The thermoplastic resin in the second adhesive layer 10B may be, for example, a styrene resin, a vinyl acetate resin, a polyester resin, a polyethylene resin, a polypropylene resin, an imide resin, an amide resin, an acrylic resin, or the like.

[0143] The thermosetting resin in the second adhesive layer 10B may be, for example, a phenolic resin, epoxy resin, urethane resin, melamine resin, alkyd resin, polyester resin, or the like.

[0144] The second adhesive layer 10B may contain only one type of adhesive resin, or it may contain two or more types.

[0145] The type of adhesive resin in the second adhesive layer 10B may be the same as the type of adhesive resin in the first adhesive layer 10A, or it may be different from the type of adhesive resin in the first adhesive layer 10A.

[0146] The second adhesive layer 10B does not have to be a conductive adhesive layer. Specifically, the second adhesive layer 10B may be a non-conductive adhesive layer. In this case, the second adhesive layer 10B may contain the above-mentioned adhesive resin without containing the conductive filler 11B.

[0147] The thickness T10B of the second adhesive layer 10B is preferably 1 μm or more and 20 μm or less.

[0148] If the thickness T10B of the second adhesive layer 10B is less than 1 μm, the thickness T10B of the second adhesive layer 10B becomes too small, and the thickness T10 of the adhesive layer 10 including the first adhesive layer 10A and the second adhesive layer 10B becomes too small, which can make it difficult to obtain sufficient adhesive performance of the adhesive layer 10.

[0149] If the thickness T10B of the second adhesive layer 10B is greater than 20 μm, the thickness T10B of the second adhesive layer 10B becomes too large, and the total thickness T10 of the adhesive layer 10, including the first adhesive layer 10A and the second adhesive layer 10B, becomes too large, making the adhesive layer 10 difficult to handle, and thus the electromagnetic wave shielding film 1 may also become difficult to handle.

[0150] The thickness T10B of the second adhesive layer 10B is determined in the electromagnetic wave shielding film 1 as follows. First, in the image obtained when determining the thickness T10A of the first adhesive layer 10A, the thickness of the second adhesive layer 10B (dimension in the lamination direction) is measured at five arbitrary locations. Then, the average of these measured values ​​is determined as the thickness T10B of the second adhesive layer 10B.

[0151] The thickness T10B of the second adhesive layer 10B may be the same as the thickness T10A of the first adhesive layer 10A, or it may be different from the thickness T10A of the first adhesive layer 10A.

[0152] If the thickness T10B of the second adhesive layer 10B is different from the thickness T10A of the first adhesive layer 10A, the thickness T10B of the second adhesive layer 10B may be greater than or less than the thickness T10A of the first adhesive layer 10A.

[0153] The adhesive layer 10 may include a first adhesive layer 10A and a second adhesive layer 10B, and may also include other adhesive layers besides the first adhesive layer 10A and the second adhesive layer 10B, or it may not include any other adhesive layers besides the first adhesive layer 10A and the second adhesive layer 10B. In other words, the number of adhesive layers constituting the adhesive layer 10 is not particularly limited as long as there are multiple layers, it may be two layers, or it may be three or more layers.

[0154] The adhesive layer 10 is preferably a conductive adhesive layer as a whole. In other words, it is preferable that the multiple adhesive layers constituting the adhesive layer 10 (including the first adhesive layer 10A and the second adhesive layer 10B) include a conductive adhesive layer, and it is particularly preferable that they be conductive adhesive layers.

[0155] If the adhesive layer 10 is a conductive adhesive layer, for example, it becomes possible to electrically connect the shielding layer 20 of the electromagnetic shielding film 1 and the ground circuit included in the printed circuit of the printed wiring board via the adhesive layer 10. As a result, the shielding performance of the electromagnetic shielding film 1 tends to improve.

[0156] When the adhesive layer 10 is a conductive adhesive layer, the adhesive layer 10 as a whole may be an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. In particular, it is preferable that the adhesive layer 10 as a whole is an anisotropic conductive adhesive layer.

[0157] When the adhesive layer 10 is an anisotropic conductive adhesive layer, the transmission characteristics of high-frequency signals transmitted in the signal circuits included in the printed circuit of the printed wiring board tend to improve compared to when the adhesive layer 10 is an isotropic conductive adhesive layer.

[0158] The thickness T10 of the adhesive layer 10 is preferably 1.2 μm or more and 23 μm or less.

[0159] If the thickness T10 of the adhesive layer 10 is less than 1.2 μm, the adhesive performance of the adhesive layer 10 may not be sufficiently obtained due to the thickness T10 being too small. Also, if the thickness T10 of the adhesive layer 10 is less than 1.2 μm, the adhesive layer 10 may not be sufficiently small, making it difficult to embed the adhesive layer 10 into stepped areas of the printed circuit board when placing the electromagnetic shielding film 1 on other components, such as a printed circuit board.

[0160] If the thickness T10 of the adhesive layer 10 is greater than 23 μm, the adhesive layer 10 becomes too thick, making it difficult to handle, and consequently, the electromagnetic shielding film 1 may also become difficult to handle.

[0161] The thickness T10 of the adhesive layer 10 is determined as follows. First, in the image obtained when determining the thickness T10A of the first adhesive layer 10A, the thickness (dimension in the lamination direction) of the portion of the adhesive layer 10 that does not extend into the opening 21 of the shield layer 20 is measured at five arbitrary locations. Then, the average of these measured values ​​is determined as the thickness T10 of the adhesive layer 10.

[0162] <Shielding Layer> The shielding layer 20 exhibits shielding performance by blocking electromagnetic waves. For example, when the electromagnetic wave shielding film 1 is installed in a mobile device such as a smartphone or tablet, the shielding layer 20 can block electromagnetic waves generated from inside the mobile device and electromagnetic waves entering from outside the mobile device.

[0163] The shield layer 20 is provided with an opening 21.

[0164] In this case, when a shielded printed circuit board, in which an electromagnetic wave shielding film 1 is provided on a printed circuit board, is heated in a heating press process, a solder reflow process, etc., volatile components (gases) may be generated from the adhesive layer 10 of the electromagnetic wave shielding film 1, the coverlay of the printed circuit board, etc. Also, if the base film of the printed circuit board contains a highly hygroscopic resin such as polyimide, when the shielded printed circuit board is heated, volatile components (in this case, water vapor) may be generated from the base film of the printed circuit board. When volatile components (gases) are generated from the components of the shielded printed circuit board in this way, these volatile components (gases) may not be able to pass through the shielding layer 20 and may accumulate between the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shielding layer 20. In this case, if the shielded printed circuit board is rapidly heated, for example, during a solder reflow process, the volatile components (gas) accumulated between the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shielding layer 20 may expand, causing the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shielding layer 20 to peel off at the interface between them.

[0165] In contrast, in the electromagnetic wave shielding film 1, since an opening 21 is provided in the shielding layer 20, as described above, even if volatile components (gases) are generated from the components of the shielding printed circuit board when the shielding printed circuit board having the electromagnetic wave shielding film 1 is heated, these volatile components (gases) can pass through the opening 21 in the shielding layer 20. As a result, volatile components (gases) are less likely to accumulate between the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shielding layer 20, so delamination at the interface between the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shielding layer 20 due to volatile components (gases) is less likely to occur.

[0166] The planar shape of the opening 21 of the electromagnetic wave shielding film 1 (shielding layer 20) when viewed from the stacking direction is not particularly limited and may be circular, elliptical, racetrack-shaped, polygonal (e.g., triangular, square, pentagonal, hexagonal, octagonal, etc.), star-shaped, etc. Among these, the planar shape of the opening 21 of the shielding layer 20 is preferably circular because it is easy to form the opening 21.

[0167] When viewing a cross-section of the electromagnetic wave shielding film 1 (shielding layer 20) along the lamination direction, the cross-sectional shape of the opening 21 of the shielding layer 20 is not particularly limited and may be rectangular, mortar-shaped (trapezoidal), etc.

[0168] The number of openings 21 in the shield layer 20 may be one or multiple.

[0169] If there are multiple openings 21 in the shield layer 20, the planar shapes of the multiple openings 21 may be the same as each other, different from each other, or partially different.

[0170] If there are multiple openings 21 in the shielding layer 20, when the electromagnetic wave shielding film 1 (shielding layer 20) is viewed from the stacking direction, the multiple openings 21 may be arranged regularly or irregularly.

[0171] When multiple openings 21 are arranged regularly, the arrangement of the multiple openings 21 is not particularly limited and may be, for example, a grid pattern or a staggered pattern.

[0172] When the electromagnetic wave shielding film 1 (shielding layer 20) is viewed from the stacking direction, the opening area of ​​each opening 21 of the shielding layer 20 is not particularly limited, but is 50 μm. ２ More than 75000μm ２ Preferably, it is 60 μm ２ More than 35000μm ２ More preferably, the following: 70 μm ２ More than 10000μm ２ The following is even more preferable:

[0173] The opening area of ​​each opening 21 in the shield layer 20 is 50 μm². ２ If the amount is smaller than this, the volatile components (gases) mentioned above may tend to accumulate between the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shield layer 20.

[0174] The opening area of ​​each opening 21 in the shield layer 20 is 75,000 μm². ２ If the value is greater than this, electromagnetic waves may be more likely to pass through the opening 21 of the shielding layer 20.

[0175] The total opening ratio of the openings 21 in the shield layer 20 is not particularly limited, but is preferably 2.0% or more and 30% or less, more preferably 3.6% or more and 15% or less, and even more preferably 3.6% or more and 8.0% or less.

[0176] If the total opening ratio of the openings 21 in the shield layer 20 is lower than 2.0%, the volatile components (gases) mentioned above may tend to accumulate between the adhesive layer 10 (in this case, the first adhesive layer 10A) and the shield layer 20.

[0177] If the sum of the aperture ratios of the openings 21 in the shielding layer 20 is higher than 30%, electromagnetic waves may be more likely to pass through the openings 21 in the shielding layer 20. Also, if the sum of the aperture ratios of the openings 21 in the shielding layer 20 is higher than 30%, the strength of the shielding layer 20 may be more likely to decrease.

[0178] The constituent material of the shielding layer 20 is not particularly limited as long as it is a conductive material capable of shielding electromagnetic waves.

[0179] The shielding layer 20 preferably includes a metal layer. In this case, the shielding layer 20 becomes more effective at shielding electromagnetic waves.

[0180] The shield layer 20 is preferably a metal layer.

[0181] The constituent material of the metal layer in the shielding layer 20 is not particularly limited as long as it is a metal material capable of shielding electromagnetic waves, and may be, for example, copper, silver, gold, aluminum, nickel, tin, palladium, chromium, titanium, zinc, or an alloy containing at least one of these. Among these, the constituent material of the metal layer in the shielding layer 20 is preferably copper. In other words, the metal layer in the shielding layer 20 is preferably a copper layer. When the metal layer in the shielding layer 20 is a copper layer, the shielding performance of the shielding layer 20 is more likely to be fully exhibited even against high-frequency electromagnetic waves.

[0182] The thickness of the metal layer in the shield layer 20 (dimension in the stacking direction) is not particularly limited, but is preferably 0.1 μm or more and 50 μm or less.

[0183] If the thickness of the metal layer in the shielding layer 20 is less than 0.1 μm, the shielding performance of the metal layer may not be fully realized. Also, if the thickness of the metal layer in the shielding layer 20 is less than 0.1 μm, the strength of the metal layer may decrease due to its excessive thickness, and as a result, the bending resistance of the metal layer, and consequently the bending resistance of the electromagnetic wave shielding film 1, may not be fully realized.

[0184] If the thickness of the metal layer in the shielding layer 20 is greater than 50 μm, the metal layer becomes too thick and difficult to handle, which may also make the electromagnetic shielding film 1 difficult to handle. Furthermore, if the thickness of the metal layer in the shielding layer 20 is greater than 50 μm, the metal layer becomes too thick and difficult to bend, which may make it difficult to obtain sufficient flexibility for the metal layer, and consequently for the electromagnetic shielding film 1.

[0185] The metal layer in the shield layer 20 may be a metal foil layer.

[0186] The metal foil layer in the shield layer 20 may be a copper foil layer.

[0187] The copper foil layer in the shield layer 20 may be made of rolled copper foil or electrolytic copper foil.

[0188] Furthermore, the metal foil layer in the shield layer 20 may be something other than a copper foil layer.

[0189] The metal layer in the shield layer 20 may be other than a metal foil layer. In this case, the metal layer in the shield layer 20 may be formed by methods such as vapor deposition (vacuum deposition, electron beam deposition, etc.), plating (electrolytic plating, electroless plating, etc.), sputtering, chemical vapor deposition (CVD), or metal-organic deposition. Furthermore, the metal layer in the shield layer 20 may be formed from materials such as metal nanoparticles or flaky metal particles.

[0190] When the metal layer in the shield layer 20 is formed by a vapor deposition method, the metal layer becomes a metal vapor-deposited layer. For example, when the metal layer in the shield layer 20 is formed by vapor deposition of copper, the metal layer becomes a copper vapor-deposited layer.

[0191] The thickness of the shield layer 20 (dimensions in the stacking direction) 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.

[0192] If the thickness of the shielding layer 20 is less than 0.1 μm, the shielding performance of the shielding layer 20 may not be fully realized. Also, if the thickness of the shielding layer 20 is less than 0.1 μm, the strength of the shielding layer 20 may decrease due to its thinness, and as a result, the bending resistance of the shielding layer 20, and consequently the bending resistance of the electromagnetic wave shielding film 1, may not be fully realized.

[0193] If the thickness of the shielding layer 20 is greater than 50 μm, the shielding layer 20 becomes too thick and difficult to handle, which may also make the electromagnetic shielding film 1 difficult to handle. Furthermore, if the thickness of the shielding layer 20 is greater than 50 μm, the shielding layer 20 becomes too thick and difficult to bend, which may make it difficult to obtain sufficient flexibility for the shielding layer 20, and consequently for the electromagnetic shielding film 1.

[0194] <Protective Layer> The protective layer 30 provides protection by protecting other layers such as the shield layer 20.

[0195] The constituent material of the protective layer 30 is not particularly limited as long as it is an insulating material capable of protecting the other layers, and may be, for example, a thermoplastic resin composition, a thermosetting resin composition, an active energy ray curable composition, etc.

[0196] The thermoplastic resin composition in the protective layer 30 is not particularly limited in type and may be, for example, an amide resin composition, a styrene resin composition, a vinyl acetate resin composition, a polyester resin composition, a polyethylene resin composition, a polypropylene resin composition, an imide resin composition, an acrylic resin composition, or the like.

[0197] The thermosetting resin composition in the protective layer 30 is not particularly limited in type and may be, for example, a urethane resin composition, a phenolic resin composition, an epoxy resin composition, a melamine resin composition, an alkyd resin composition, a polyester resin composition, or the like.

[0198] The active energy ray curable composition in the protective layer 30 is not particularly limited in type and may be, for example, a polymerizable compound having multiple (meth)acryloyloxy groups in its molecule.

[0199] The protective layer 30 may contain only one of the above compositions, or it may contain two or more.

[0200] The protective layer 30 may contain at least one of urethane resin and amide resin.

[0201] The protective layer 30 may optionally contain curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, UV absorbers, defoamers, leveling agents, fillers, flame retardants, flame retardant aids, viscosity modifiers, anti-blocking agents, etc.

[0202] The thickness of the protective layer 30 (dimensions in the lamination direction) 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.

[0203] If the thickness of the protective layer 30 is less than 1 μm, the protective performance of the protective layer 30 may not be fully realized due to the thickness becoming too small.

[0204] 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 can make it difficult to obtain sufficient flexibility for the protective layer 30, and consequently for the electromagnetic shielding film 1.

[0205] The electromagnetic wave shielding film 1 is manufactured, for example, as follows.

[0206] (Process for producing a protective layer) A protective layer 30 is produced. For example, a protective layer composition containing an insulating material is applied to a transfer film, and then the coated product is heated to produce the protective layer 30.

[0207] (Process for laminating the shield layer) The shield layer 20 is laminated onto the protective layer 30. For example, by placing a metal foil on the protective layer 30, the shield layer 20, which consists of a metal foil layer, is placed on the protective layer 30. Then, the shield layer 20 is laminated onto the protective layer 30 by laminating the shield layer 20.

[0208] (Process of forming an opening in the shield layer) An opening 21 is formed in the shield layer 20. For example, by performing laser processing on the shield layer 20, an opening 21 is formed that penetrates the shield layer 20 in the stacking direction and reaches the protective layer 30.

[0209] When forming the opening 21 in the shield layer 20, the shield layer 20 may be drilled or etched.

[0210] The above describes a method of forming the opening 21 in the shield layer 20 after laminating the shield layer 20 onto the protective layer 30. However, the opening 21 may also be formed in the shield layer 20 before laminating the shield layer 20 onto the protective layer 30. In other words, a shield layer 20 with the opening 21 already provided may be laminated onto the protective layer 30.

[0211] (Step of laminating adhesive layer) The adhesive layer 10 is laminated on the side of the shield layer 20 opposite to the protective layer 30.

[0212] First, the first adhesive layer 10A is laminated on the side of the shield layer 20 opposite to the protective layer 30. For example, the first adhesive layer 10A is laminated on the side of the shield layer 20 opposite to the protective layer 30 by coating the conductive adhesive layer composition containing the conductive filler 11A on the side of the shield layer 20 opposite to the protective layer 30. In this case, the conductive adhesive layer composition is coated on the side of the shield layer 20 opposite to the protective layer 30 to form the first adhesive layer 10A such that the thickness T10A (thickness of the portion of the shield layer 20 that does not penetrate into the opening 21) is 200% or less of the maximum thickness of the conductive filler 11A. Here, the maximum thickness of the conductive filler 11A in the conductive adhesive layer composition may be determined in advance, for example, by coating the conductive adhesive layer composition containing the conductive filler 11A on a suitable substrate and then measuring the cross-section in the same manner as the method for determining the "maximum thickness of the conductive filler 11A in the first adhesive layer 10A" described above. As a result, when the first adhesive layer 10A is formed, the range in which the conductive filler 11A can move in the first adhesive layer 10A is limited, and consequently, the movement of the conductive filler 11A in the first adhesive layer 10A is more easily suppressed. Specifically, because the thickness T10A of the first adhesive layer 10A is small, the conductive filler 11A in the first adhesive layer 10A is more likely to align in the width direction than in the lamination direction. More specifically, it becomes less likely that two conductive fillers 11A will overlap in the lamination direction in the first adhesive layer 10A, and consequently, the conductive fillers 11A are more likely to align in the width direction rather than the lamination direction. As a result, in the electromagnetic wave shielding film 1 obtained later, the probability that the conductive filler 11A in the first adhesive layer 10A is located near the opening 21 of the shielding layer 20 laminated on the first adhesive layer 10A is increased.

[0213] Next, the second adhesive layer 10B is laminated on the side of the first adhesive layer 10A opposite to the shield layer 20. For example, the second adhesive layer 10B is laminated on the side of the first adhesive layer 10A opposite to the shield layer 20 by coating a conductive adhesive layer composition containing a conductive filler 11B on the side of the first adhesive layer 10A opposite to the shield layer 20.

[0214] As described above, the adhesive layer 10, including the first adhesive layer 10A and the second adhesive layer 10B, is laminated on the side of the shield layer 20 opposite to the protective layer 30.

[0215] Through the above process, electromagnetic wave shielding film 1 is manufactured.

[0216] The electromagnetic shielding film 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 regarding the structure, manufacturing conditions, etc. of the electromagnetic shielding film.

[0217] [Shielded Printed Wiring Board] Figure 4 is a schematic cross-sectional view showing an example of a shielded printed wiring board having the electromagnetic wave shielding film of the present invention.

[0218] The shielded printed circuit board 100 shown in Figure 4 comprises a printed circuit board 51 and an electromagnetic wave shielding film 1.

[0219] The following describes each component of the shielded printed circuit board 100.

[0220] <Printed Wiring Board> The printed wiring board 51 has a base film 60, a printed circuit 70, and a coverlay 80.

[0221] The printed circuit board 51 is preferably a flexible printed circuit board. In this case, the printed circuit board 51 can be easily bent, making the shielded printed circuit board 100 usable in a wider range of applications.

[0222] (Base film) The base film 60 preferably contains engineering plastic, and more preferably consists of engineering plastic.

[0223] The engineering plastic contained in the base film 60 is not particularly limited in type and may be, for example, a resin such as polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, or polyphenylene sulfide.

[0224] (Printed circuit) The printed circuit 70 is provided on the base film 60.

[0225] The printed circuit 70 may be bonded to the base film 60 via an adhesive, or it may be joined without an adhesive, for example, in the same way as an adhesive-free copper-clad laminate.

[0226] The printed circuit 70 may include a ground circuit 71.

[0227] The printed circuit 70 may include a signal circuit (not shown).

[0228] The materials used to make up the printed circuit 70 are not particularly limited in type and may include, for example, circuit materials such as copper.

[0229] (Coverlay) The coverlay 80 is provided so as to cover the printed circuit 70.

[0230] The coverlay 80 may be provided with an exposure hole 81 that exposes the ground circuit 71 from the coverlay 80.

[0231] The coverlay 80 does not necessarily need to have an exposure hole 81.

[0232] The coverlay 80 preferably contains engineering plastic, and more preferably consists of engineering plastic.

[0233] The engineering plastic in the coverlay 80 may be, for example, a resin such as polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, or polyphenylene sulfide.

[0234] If the base film 60 and the coverlay 80 contain engineering plastics, the types of engineering plastics in the base film 60 and the coverlay 80 may be the same or different.

[0235] The coverlay 80 may be made by bonding multiple flexible insulating films together with an adhesive.

[0236] The coverlay 80 may be formed by a series of methods such as coating, drying, exposure, developing, and heat treatment of a photosensitive insulating resin.

[0237] <Electromagnetic wave shielding film> The electromagnetic wave shielding film 1 has the configuration described above (see Figures 1 and 2).

[0238] The electromagnetic shielding film 1 is provided on the coverlay 80 side of the printed circuit board 51.

[0239] The electromagnetic shielding film 1 has its adhesive layer 10 side (opposite to the protective layer 30) facing the coverlay 80. In the example shown in Figure 4, the electromagnetic shielding film 1 is provided on the printed circuit board 51 such that the adhesive layer 10 located on the opposite side of the protective layer 30 is in contact with the coverlay 80.

[0240] It is preferable that the adhesive layer 10 (second adhesive layer 10B in Figure 4) penetrates the exposed hole 81 and is in contact with the ground circuit 71. In this case, it is more preferable that the adhesive layer 10 fills the inside of the exposed hole 81 and is in contact with the ground circuit 71. In either case, if the adhesive layer 10 as a whole is a conductive adhesive layer, the shielding layer 20 and the ground circuit 71 will be electrically connected via the conductive adhesive layer. This makes it easier to improve the shielding performance of the electromagnetic shielding film 1.

[0241] The electromagnetic shielding film 1 is provided on the printed circuit board 51 by a conventionally known method. For example, it is preferable to place the electromagnetic shielding film 1 on the printed circuit board 51 so that the adhesive layer 10 side (opposite side from the protective layer 30) faces the coverlay 80 (in Figure 4, so that it is in contact with the coverlay 80), and then heat-press the electromagnetic shielding film 1 and the printed circuit board 51 together. The temperature during heat-pressure bonding is preferably 150°C or higher and 200°C or lower. The pressure during heat-pressure bonding is preferably 2 MPa or higher and 5 MPa or lower. The pressurizing time during heat-pressure bonding is preferably 1 minute or higher and 60 minutes or less.

[0242] The shielded printed circuit 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 regarding the configuration, manufacturing conditions, etc., of the shielded printed circuit board.

[0243] This specification discloses the following:

[0244] <1> An electromagnetic wave shielding film comprising an adhesive layer, a shield layer laminated on the adhesive layer and having an opening, and a protective layer laminated on the side of the shield layer opposite to the adhesive layer, wherein the adhesive layer includes, in the lamination direction, a first adhesive layer laminated on the side of the shield layer opposite to the protective layer, and a second adhesive layer laminated on the side of the first adhesive layer opposite to the shield layer, the first adhesive layer being a conductive adhesive layer containing a conductive filler, and the thickness of the first adhesive layer being 200% or less of the maximum thickness of the conductive filler in the first adhesive layer.

[0245] <2> The electromagnetic wave shielding film according to <1>, wherein the maximum length of the conductive filler in the first adhesive layer is 50% or more and 200% or less of the average opening diameter of the opening in the shielding layer.

[0246] <3> The electromagnetic wave shielding film according to <1> or <2>, wherein the shape of the conductive filler in the first adhesive layer is flake-shaped or spherical.

[0247] <4> An electromagnetic wave shielding film according to any one of <1> to <3>, wherein the maximum thickness of the conductive filler in the first adhesive layer is 0.1 μm or more and 1.5 μm or less.

[0248] <5> An electromagnetic wave shielding film according to any one of <1> to <4>, wherein the thickness of the first adhesive layer is 0.2 μm or more and 3 μm or less.

[0249] 1 Electromagnetic shielding film 10 Adhesive layer 10A First adhesive layer 10B Second adhesive layer 11A, 11B Conductive filler 20 Shielding layer 21 Opening 30 Protective layer 51 Printed circuit board 60 Base film 70 Printed circuit 71 Ground circuit 80 Coverlay 81 Exposed hole 100 Shielded printed circuit board P1, P2, R1, R2 Points Q1, Q2, S1, S2 Lines T10 Thickness of adhesive layer T10A Thickness of first adhesive layer T10B Thickness of second adhesive layer T11A Dimension of conductive filler in the first adhesive layer in the lamination direction W11A Dimension of conductive filler in the first adhesive layer in the width direction

Claims

1. An electromagnetic wave shielding film comprising, in the lamination direction, an adhesive layer, a shield layer laminated on the adhesive layer and having an opening, and a protective layer laminated on the side of the shield layer opposite to the adhesive layer, wherein the adhesive layer includes, in the lamination direction, a first adhesive layer laminated on the side of the shield layer opposite to the protective layer, and a second adhesive layer laminated on the side of the first adhesive layer opposite to the shield layer, the first adhesive layer being a conductive adhesive layer containing a conductive filler, and the thickness of the first adhesive layer being 200% or less of the maximum thickness of the conductive filler in the first adhesive layer.

2. The electromagnetic wave shielding film according to claim 1, wherein the maximum length of the conductive filler in the first adhesive layer is 50% or more and 200% or less of the average opening diameter of the opening in the shielding layer.

3. The electromagnetic wave shielding film according to claim 1 or 2, wherein the shape of the conductive filler in the first adhesive layer is flake-shaped or spherical.

4. The electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the maximum thickness of the conductive filler in the first adhesive layer is 0.1 μm or more and 1.5 μm or less.

5. The electromagnetic wave shielding film according to any one of claims 1 to 4, wherein the thickness of the first adhesive layer is 0.2 μm or more and 3 μm or less.

Images