Metal layer and electromagnetic wave shielding film

Abstract

The present invention provides a metal layer for an electromagnetic wave shielding film that can make it difficult for volatile components to destroy the interlayer tight adhesion of the electromagnetic wave shielding film. The metal layer for an electromagnetic wave shielding film of the present invention is a metal layer comprising a first main surface and a second main surface on the opposite side of the first main surface, characterized in that: the metal layer is formed with a plurality of openings that penetrate from the first main surface through the second main surface, the opening area of ​​the opening in the first main surface is 70 to 71000 μm², and the opening rate of the opening in the first main surface is 0.1 to 20%, and the opening area of ​​the opening in the second main surface is larger than the opening area of ​​the opening in the first main surface.

Description

Technical Field

[0001] The invention relates to a metal layer and an electromagnetic wave shielding film. Background Art

[0002] Conventionally, electromagnetic wave shielding films have been attached to printed circuit boards such as flexible printed circuit boards (FPCs) to shield electromagnetic waves from the outside.

[0003] Generally, the electromagnetic wave shielding film contains a structure in which a conductive adhesive layer, a shielding layer composed of a metal film, etc., and an insulating layer are stacked in sequence. The electromagnetic wave shielding film is hot pressed while being overlapped with a printed circuit board, whereby the electromagnetic wave shielding film is bonded to the printed circuit board through the adhesive layer, thereby making a shielded printed circuit board. After the bonding, the components are mounted on the printed circuit board by solder reflow. In addition, the printed circuit board is a structure in which the printed pattern on the base film is covered by an insulating film.

[0004] When manufacturing a shielded printed circuit board, if the shielded printed circuit board is heated by hot pressing or solder reflow, gas will be generated from the conductive adhesive layer in the electromagnetic wave shielding film or the insulating film in the printed circuit board. In addition, when the base film of the printed circuit board is formed by a highly hygroscopic resin such as polyimide, water vapor is sometimes generated from the base film due to heating. These volatile components generated from the conductive adhesive layer, the insulating film, and the base film cannot pass through the shielding layer, and thus accumulate between the shielding layer and the conductive adhesive layer. Therefore, when the shielding layer is heated rapidly by the solder reflow process, the volatile components accumulated between the shielding layer and the conductive adhesive layer sometimes destroy the interlayer tight adhesion between the shielding layer and the conductive adhesive layer, resulting in reduced shielding properties.

[0005] Patent document 1 discloses an electromagnetic wave shielding film for solving the above-mentioned problem, wherein the electromagnetic wave shielding film is composed of a conductive adhesive layer, a shielding layer stacked on the conductive adhesive layer, and an insulating layer stacked on the shielding layer. The electromagnetic wave shielding film is characterized in that a plurality of openings are formed in the shielding layer, the opening area of ​​the openings is 70 to 71000 μm², and the opening ratio of the openings is 0.05 to 3.6%.

[0006] In addition, patent document 2 discloses an electromagnetic wave shielding sheet (electromagnetic wave shielding film), which is characterized in that it is composed of a protective layer, a metal layer and a conductive adhesive layer, and has a tensile strength of 10 to 80 N / 20 mm. The metal layer contains several openings, and the average value of the roundness coefficient of the openings calculated according to a certain formula is greater than 0.5, and the opening rate of the metal layer is 0.1 to 20%.

[0007] As shown in the electromagnetic wave shielding films described in Patent Documents 1 and 2, if an opening having a certain shape is provided in the shielding layer, even if volatile components are generated, the volatile components can pass through the shielding layer through the opening. Therefore, it is possible to prevent the volatile components from accumulating between the shielding layer and the conductive adhesive layer, and to prevent the shielding properties from being reduced due to the loss of close adhesion between the layers.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2018 / 147298;

[0011] Patent document 2: Japanese Patent No. 6544466. Summary of the invention

[0012] Technical problem to be solved by the invention

[0013] However, there is still room for improvement in the technical effect of preventing volatile components from destroying the interlayer adhesion.

[0014] The present invention has been made in view of the above-mentioned technical problems, and an object of the present invention is to provide a metal layer for an electromagnetic wave shielding film which can make it difficult for volatile components to destroy the interlayer adhesion of the electromagnetic wave shielding film.

[0015] Technical means to solve technical problems

[0016] To solve the above technical problems, the inventors of the present invention have conducted intensive studies and found that the interlayer adhesion of the electromagnetic wave shielding film can be less likely to be damaged by controlling the shape of the openings formed in the metal layer of the electromagnetic wave shielding film, thereby completing the present invention.

[0017] That is, the metal layer for electromagnetic wave shielding film of the present invention is a metal layer comprising a first main surface and a second main surface on the opposite side of the first main surface, and the metal layer for electromagnetic wave shielding film is characterized in that: a plurality of openings are formed in the metal layer extending from the first main surface through the second main surface, the opening area of ​​the openings in the first main surface is 70 to 71000 μm², and the opening rate of the openings in the first main surface is 0.1 to 20%, and the opening area of ​​the openings in the second main surface is larger than the opening area of ​​the openings in the first main surface.

[0018] An electromagnetic wave shielding film is formed by placing an insulating layer on the first main surface of the metal layer for an electromagnetic wave shielding film of the present invention and placing a conductive adhesive layer on the second main surface. The electromagnetic wave shielding film is attached to a printed wiring board.

[0019] When the printed circuit boards are heated (reflow) to mount electronic components, volatile components are mainly generated from the printed circuit boards.

[0020] The metal layer of the present invention has a feature that the opening area of ​​the second main surface opening is larger than the opening area of ​​the first main surface opening, so that volatile components can easily escape from the second main surface to the first main surface side.

[0021] Therefore, in the electromagnetic wave shielding film using the metal layer of the present invention, the interlayer adhesion is less likely to be impaired.

[0022] Preferably, in the metal layer of the present invention, the opening is tapered.

[0023] If the opening is tapered, volatile components can escape more easily.

[0024] Preferably, in the metal layer of the present invention, the ratio of the longest diameter A of the opening in the first main surface to the longest diameter B of the opening in the second main surface is: longest diameter A / longest diameter B=0.65 to 0.95.

[0025] If the ratio of the longest diameter A to the longest diameter B is less than 0.65, when an electromagnetic wave shielding film is made using a metal layer and a shielded printed circuit board is manufactured using the electromagnetic wave shielding film, it is easy to form unevenness on the surface of the electromagnetic wave shielding film. The unevenness is the cause of poor appearance and also causes a decrease in shielding properties.

[0026] If the ratio of the longest diameter A to the longest diameter B exceeds 0.95, the difference between the size of the opening on the first main surface and the size of the opening on the second main surface is small, making it difficult to obtain the effect of facilitating the escape of volatile components.

[0027] Preferably, in the metal layer of the present invention, the shape of the opening is circular or elliptical in a plan view of the metal layer for an electromagnetic wave shielding film.

[0028] The circular or elliptical opening has no corners, so the metal layer will not be damaged starting from the corners.

[0029] Preferably, the thickness of the metal layer of the present invention is 0.5 to 10.0 μm.

[0030] If the thickness of the metal layer of the present invention is less than 0.5 μm, the metal layer is easily damaged and the shielding property is insufficient.

[0031] If the thickness of the metal layer of the present invention exceeds 10.0 μm, the flexibility of the metal layer decreases.

[0032] The metal layer of the present invention is preferably composed of at least one metal selected from the group consisting of copper, silver, nickel, aluminum and titanium.

[0033] When a metal layer composed of the above metal is used for an electromagnetic wave shielding film, the shielding property is improved.

[0034] The electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film formed by stacking an insulating layer, a metal layer and a conductive adhesive layer in sequence, and is characterized in that: the metal layer is the metal layer of the present invention mentioned above, the first main surface of the metal layer is in contact with the insulating layer, and the second main surface of the metal layer is in contact with the conductive adhesive layer.

[0035] The electromagnetic wave shielding film of the present invention uses the metal layer of the present invention. Therefore, the electromagnetic wave shielding film of the present invention can be said to be an electromagnetic wave shielding film in which the interlayer adhesion is not easily destroyed by volatile components.

[0036] Effects of the Invention

[0037] In the metal layer of the present invention, the opening area of ​​the second main surface opening is larger than the opening area of ​​the first main surface opening.

[0038] The electromagnetic wave shielding film is formed by disposing an insulating layer on the first main surface of the metal layer of the present invention and disposing a conductive adhesive layer on the second main surface. In the electromagnetic wave shielding film, volatile components are mainly generated from the conductive adhesive layer.

[0039] The metal layer of the present invention has a feature that the opening area of ​​the second main surface opening is larger than the opening area of ​​the first main surface opening, so that volatile components can easily escape from the second main surface to the first main surface side.

[0040] Therefore, in the electromagnetic wave shielding film using the metal layer of the present invention, the interlayer adhesion is less likely to be impaired. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] [ Figure 1A ] Figure 1A is a perspective schematic diagram of an example of a metal layer for an electromagnetic wave shielding film according to the first embodiment of the present invention;

[0042] [ Figure 1B ] Figure 1B is along Figure 1A A-A line cross-sectional view;

[0043] [ Figure 2 ] Figure 2 It is a schematic cross-sectional view of an example of an electromagnetic wave shielding film using the metal layer for an electromagnetic wave shielding film according to the first embodiment of the present invention;

[0044] [ Figure 3A ] Figure 3A is a schematic cross-sectional view showing an example of a cross section obtained by cutting the opening portion in a direction perpendicular to the first main surface when the opening portion of the metal layer is tapered;

[0045] [ Figure 3B ] Figure 3Bis a schematic cross-sectional view showing an example of a cross section obtained by cutting the opening portion in a direction perpendicular to the first main surface when the opening portion of the metal layer is tapered;

[0046] [ Figure 4A ] Figure 4A This is an explanatory diagram for explaining the principle that when the ratio of the longest diameter A to the longest diameter B is less than 0.65, it is easy to form unevenness on the surface of the electromagnetic wave shielding film;

[0047] [ Figure 4B ] Figure 4B This is an explanatory diagram for explaining the principle that when the ratio of the longest diameter A to the longest diameter B is less than 0.65, it is easy to form unevenness on the surface of the electromagnetic wave shielding film;

[0048] [ Figure 4C ] Figure 4C This is an explanatory diagram for explaining the principle that when the ratio of the longest diameter A to the longest diameter B is less than 0.65, it is easy to form unevenness on the surface of the electromagnetic wave shielding film;

[0049] [ Figure 5A ] Figure 5A is a top view schematic diagram of an example of an array pattern of openings in a metal layer of the present invention;

[0050] [ Figure 5B ] Figure 5B is a top view schematic diagram of an example of an array pattern of openings in a metal layer of the present invention;

[0051] [ Figure 5C ] Figure 5C is a top view schematic diagram of an example of an array pattern of openings in a metal layer of the present invention;

[0052] [ Figure 6 ] Figure 6 is a photograph showing a cross-sectional view in a direction perpendicular to the first main surface of the copper layer involved in Example 1;

[0053] [ Figure 7 ] Figure 7 This is a schematic diagram of the structure of the system used in the KEC method. DETAILED DESCRIPTION

[0054] The metal layer for an electromagnetic wave shielding film of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and can be applied after being appropriately modified within the scope of the present invention.

[0055] The metal layer for an electromagnetic wave shielding film of the present invention and the electromagnetic wave shielding film using the metal layer will be described with reference to the drawings.

[0056] Furthermore, an electromagnetic wave shielding film using the metal layer for an electromagnetic wave shielding film of the present invention is also one aspect of the present invention.

[0057] Figure 1A It is a perspective schematic diagram of an example of the metal layer for electromagnetic wave shielding films according to the first embodiment of the present invention. Figure 1B is along Figure 1A Cross-sectional view of line A-A.

[0058] Figure 2 This is a schematic cross-sectional view of an example of an electromagnetic wave shielding film using the metal layer for an electromagnetic wave shielding film according to the first embodiment of the present invention.

[0059] like Figure 1A and Figure 1B As shown, the metal layer 10 includes a first main surface 11 and a second main surface 12 on the opposite side to the first main surface 11 .

[0060] The metal layer 10 has a plurality of openings 20 formed therein, the openings 20 penetrating from the first main surface 11 to the second main surface 12 .

[0061] also, Figure 1B In the figure, for convenience, the end of the opening 20 on the first principal surface 11 side is referred to as the opening 21 , and the end of the opening 20 on the second principal surface side is referred to as the opening 22 .

[0062] like Figure 2 As shown, the electromagnetic wave shielding film 50 includes a metal layer 10 , an insulating layer 60 disposed on the first main surface 11 , and a conductive adhesive layer 70 disposed on the second main surface 12 .

[0063] That is, in the electromagnetic wave shielding film 50 , the insulating layer 60 , the metal layer 10 , and the conductive adhesive layer 70 are sequentially stacked. In the electromagnetic wave shielding film 50 , the first main surface 11 of the metal layer 10 is in contact with the insulating layer 60 , and the second main surface 12 of the metal layer 10 is in contact with the conductive adhesive layer 70 .

[0064] The opening area of ​​the opening 21 is 70 to 71000 μm², preferably 70 to 32000 μm², more preferably 70 to 10000 μm², and further preferably 80 to 8000 μm².

[0065] The opening ratio of the opening 21 is 0.1 to 20%, and more preferably 0.1 to 10.0%.

[0066] If the opening area and opening ratio of the opening 21 formed in the metal layer 10 are within the above ranges, the metal layer 10 has sufficient folding resistance. In addition, in the electromagnetic wave shielding film using the metal layer 10 of the present invention, volatile components can be prevented from accumulating between the metal layer 10 and the conductive adhesive layer.

[0067] In addition, in this specification, the "aperture ratio" of the opening 21 refers to the ratio of the total opening area of ​​the openings 21 to the total area of ​​the first main surface 11 of the metal layer 10. In addition, in this specification, the "aperture ratio" of the opening 22 refers to the ratio of the total opening area of ​​the openings 22 to the total area of ​​the second main surface 12 of the metal layer 10.

[0068] If the opening area of ​​the opening in the first main surface is less than 70 μm², the opening is too narrow and it is difficult for volatile components to pass through the metal layer. Therefore, volatile components are easily accumulated between the metal layer and the conductive adhesive layer. Therefore, when an electromagnetic wave shielding film containing the above-mentioned metal layer is used to manufacture a shielded printed circuit board, the interlayer tight adhesion between the metal layer and the conductive adhesive layer is easily destroyed. This will cause blistering during reflow soldering.

[0069] If the opening area of ​​the opening in the first main surface exceeds 71000 μm², the opening is too wide, the metal layer is weak, and the folding resistance is reduced. In addition, the shielding properties are reduced.

[0070] If the opening ratio of the openings in the first main surface is less than 0.1%, the opening ratio is too small, and the volatile components are difficult to pass through the metal layer, which makes it easy for the volatile components to accumulate between the metal layer and the conductive adhesive layer, and cause blistering during reflow.

[0071] If the opening ratio of the openings in the first main surface exceeds 20%, the ratio of the openings is too large, the metal layer is weak, the folding resistance is reduced, and the shielding properties are reduced.

[0072] In the metal layer 10 , the opening area of ​​the opening 22 on the second main surface 12 is larger than the opening area of ​​the opening 21 .

[0073] As described above, the insulating layer 60 is disposed on the first main surface 11 of the metal layer 10, and the conductive adhesive layer 70 is disposed on the second main surface 12, thereby forming the electromagnetic wave shielding film 50. The electromagnetic wave shielding film 50 is attached to a printed wiring board.

[0074] In order to mount electronic components, the printed wiring board is heated (reflow soldering), and at this time, volatile components are mainly generated from the printed wiring board.

[0075] The metal layer 10 has a feature that the opening area of ​​the opening 22 is larger than the opening area of ​​the opening 21 , and therefore, volatile components can easily escape from the second main surface 12 to the first main surface 11 side.

[0076] Therefore, in the electromagnetic wave shielding film 50 using the metal layer 10 , the interlayer adhesion is less likely to be impaired.

[0077] In the metal layer 10 , the shape of the opening 22 is not particularly limited as long as the opening area is larger than the opening area of ​​the opening 21 , but is preferably a tapered shape.

[0078] If the opening 20 is tapered, volatile components can escape more easily.

[0079] Figure 3A and Figure 3B This is a schematic cross-sectional view of an example of a cross section obtained by cutting the opening in a direction perpendicular to the first main surface when the opening of the metal layer is tapered.

[0080] like Figure 3A As shown, when the opening 20 is tapered, in a cross section obtained by cutting the opening 20 in a direction perpendicular to the first main surface 11 , the side surface 13 of the opening 20 forms an acute angle α with the first main surface 11 .

[0081] The acute angle α is preferably 5 to 85°, more preferably 15 to 75°, and even more preferably 20 to 60°.

[0082] In addition, if Figure 3B As shown, in the metal layer 10 , the tip of the opening 20 on the first main surface 11 side may be an R surface.

[0083] At this time, in the cross section of the metal layer 10 obtained by cutting in a direction perpendicular to the first main surface 11, the angle formed by the imaginary straight line 13' extending the straight line portion of the side surface 13 of the opening 20 and the imaginary straight line 11' extending the straight line portion of the first main surface 11 is taken as the acute angle α.

[0084] In the metal layer 10 , the ratio of the longest diameter A of the opening 21 to the longest diameter B of the opening 22 is preferably longest diameter A / longest diameter B=0.65 to 0.95, more preferably 0.7 to 0.85.

[0085] If the ratio of the longest diameter A to the longest diameter B is less than 0.65, when an electromagnetic wave shielding film is made using a metal layer and a shielded printed circuit board is manufactured using the electromagnetic wave shielding film, it is easy to form unevenness on the surface of the electromagnetic wave shielding film. The unevenness is the cause of poor appearance and also leads to reduced shielding properties.

[0086] If the ratio of the longest diameter A to the longest diameter B exceeds 0.95, the difference between the size of the opening on the first main surface and the size of the opening on the second main surface is small, making it difficult to obtain the effect of facilitating the escape of volatile components.

[0087] The principle that when the ratio of the longest diameter A to the longest diameter B is less than 0.65, irregularities are easily formed on the surface of the electromagnetic wave shielding film will be described below using the drawings.

[0088] Figure 4A , Figure 4B and Figure 4C This is an explanatory diagram for explaining the principle that when the ratio of the longest diameter A to the longest diameter B is less than 0.65, irregularities are easily formed on the surface of the electromagnetic wave shielding film.

[0089] like Figure 4A As shown, when the ratio of the longest diameter A to the longest diameter B is less than 0.65, that is, when the opening area of ​​the opening 22 is much larger than the opening area of ​​the opening 21, the peripheral portion 10a of the opening 21 of the metal layer 10 is very thin.

[0090] like Figure 4B As shown, the insulating layer 60 is disposed on the first main surface 11 of the metal layer 10 , and the conductive adhesive layer 70 is disposed on the second main surface 12 , thereby forming the electromagnetic wave shielding film 50 .

[0091] like Figure 4C As shown, after the electromagnetic wave shielding film 50 is arranged on the printed wiring board, the electromagnetic wave shielding film 50 is heated and pressurized ( Figure 4C The arrow indicates the direction of pressure).

[0092] At this time, since the portion 10a around the opening 21 of the metal layer 10 is thin, it is easy to break.

[0093] When the portion 10a around the opening 21 of the metal layer 10 is broken, irregularities are likely to be formed on the surface of the electromagnetic wave shielding film.

[0094] In the metal layer 10 , the shape of the opening 20 when looking down at the metal layer 10 is not particularly limited, and the opening 20 may be polygonal, circular, or elliptical.

[0095] Among them, a circular shape or an elliptical shape is preferred.

[0096] The circular or elliptical opening 20 has no corners, so the metal layer will not be damaged starting from the corners.

[0097] In the metal layer 10 , a plurality of openings 20 may be arranged in an array at equal intervals when looking down at the metal layer 10 .

[0098] When a plurality of openings 20 are arranged in an array at equal intervals, the interval is preferably 10 to 10000 μm, more preferably 25 to 2000 μm, and even more preferably 250 to 2000 μm.

[0099] If the interval between the openings is less than 10 μm, the proportion of the openings in the entire metal layer is high, which makes the metal layer weak, reduces the folding resistance, and also reduces the shielding properties.

[0100] If the interval between the openings exceeds 10,000 μm, the proportion of the openings in the entire metal layer is low, which makes it difficult for volatile components to pass through the metal layer. Therefore, in an electromagnetic wave shielding film using a metal layer, volatile components are easily accumulated between the metal layer and the conductive adhesive layer, and blistering occurs during reflow soldering.

[0101] In the metal layer 10 , the openings 20 may be randomly dispersed or dispersed with a fixed regularity.

[0102] In the metal layer 10 , when the openings 20 are dispersed according to a fixed regularity, the openings 20 may be in a zigzag array or a grid array.

[0103] An example of an array pattern in which the openings 20 in the metal layer 10 are dispersed with a fixed regularity will be described with reference to the drawings.

[0104] Figure 5A , Figure 5B and Figure 5C Each is a top view schematically showing an example of an array pattern of openings in the metal layer of the present invention.

[0105] also, Figure 5A , Figure 5B and Figure 5C Each of these drawings is a plan view of the metal layer 10 from the first main surface 11 side.

[0106] like Figure 5A As shown, the array pattern of the openings 20 may be an array pattern in which the centers of the openings 20 are located at the vertices of the equilateral triangles in a plane in which equilateral triangles are continuously arranged horizontally and vertically. This array pattern is a form of a Z-shaped array pattern.

[0107] also, Figure 5A In the embodiment, the angle formed by the line segment connecting the adjacent openings 20 is 60°. In the metal layer of the present invention, the angle is not particularly limited and may be 45°, for example.

[0108] In addition, if Figure 5B As shown, the array pattern of the openings 20 may be an array pattern in which the centers of the openings 20 are located at the vertices of the squares in a plane where squares are continuously arranged horizontally and vertically. This array pattern is a form of a grid-shaped array pattern.

[0109] also, Figure 5B In the embodiment, the array is arranged in such a way that the center of the opening 20 is located at the vertex of the square, and in the metal layer of the present invention, the array pattern can also be such that the center of the opening 20 is located at the vertex of the rectangle.

[0110] In addition, if Figure 5CAs shown, the array pattern of the openings 20 may be an array pattern in which, in a plane where regular hexagons are continuously arranged horizontally and vertically, the centers of the openings 20 are located at the vertices of the regular hexagons.

[0111] The thickness of the metal layer 10 is preferably 0.5 to 10.0 μm, more preferably 1.0 to 6.0 μm, and even more preferably 2.0 to 6.0 μm.

[0112] If the thickness of the metal layer 10 is less than 0.5 μm, the metal layer is easily damaged and the shielding property is insufficient.

[0113] If the thickness of the metal layer 10 exceeds 10.0 μm, the flexibility of the metal layer decreases.

[0114] In addition, if the thickness of the metal layer is greater than or equal to 0.5 μm, the metal layer has good transmission characteristics in a signal transmission system that transmits high-frequency signals with a frequency greater than or equal to 1 GHz.

[0115] In addition, when the metal layer is not formed with an opening, if the metal layer is thick, when the electromagnetic wave shielding film including the metal layer is used to manufacture a shielded printed circuit board, the interlayer tight adhesion between the metal layer and the conductive adhesive layer is easily damaged. In particular, if the thickness of the metal layer exceeds 10.0 μm, the interlayer tight adhesion will be significantly damaged. However, the opening 20 is formed in the metal layer 10, so that the interlayer tight adhesion between the metal layer 10 and the conductive adhesive layer 70 can be prevented from being damaged.

[0116] The metal layer 10 is not particularly limited, but is preferably composed of at least one metal selected from the group consisting of copper, silver, nickel, aluminum, and titanium. In addition, the metal layer may be an alloy of these metals.

[0117] If a metal layer composed of these metals is used for an electromagnetic wave shielding film, the shielding properties are improved.

[0118] The method for producing the metal layer of the present invention is not particularly limited, and examples thereof include: a method of forming openings by etching a metal foil without openings; a method of producing by metal plating, vacuum deposition, sputtering, etc.

[0119] Furthermore, when the metal layer of the present invention is produced by etching, the metal foil can be etched by adjusting the composition of the etchant or the etching time so that the opening area of ​​the second main surface opening can be made larger than the opening area of ​​the first main surface opening.

[0120] In addition, when the metal layer of the present invention is produced by metal plating, for example, a spindle-shaped (hammer-shaped) or truncated cone-shaped (cone-shaped) convex portion or the like composed of a resin composition or the like is formed on the substrate in advance, and the metal layer is formed by metal plating, etc. to such an extent that the substrate and the spindle-shaped or truncated cone-shaped convex portion or the like are not completely buried. In addition, the bottom surface of the spindle-shaped or truncated cone-shaped convex portion is preferably circular or elliptical.

[0121] By forming the metal layer as described above, the opening area of ​​the second main surface opening can be made larger than the opening area of ​​the first main surface opening.

[0122] Next, the insulating layer 60 in the electromagnetic wave shielding film 50 will be described.

[0123] The insulating layer 60 is not particularly limited as long as it has sufficient insulating properties and can protect the metal layer 10 and the conductive adhesive layer 70. For example, the insulating layer 60 is preferably composed of a thermoplastic resin composition, a thermosetting resin composition, an active energy ray-curable composition, or the like.

[0124] The thermoplastic resin composition is not particularly limited, and examples thereof include styrene-based resin compositions, vinyl acetate-based resin compositions, polyester-based resin compositions, polyethylene-based resin compositions, polypropylene-based resin compositions, imide-based resin compositions, and acrylic resin compositions.

[0125] The thermosetting resin composition is not particularly limited, and examples thereof include phenolic resin compositions, epoxy resin compositions, polyurethane resin compositions, melamine resin compositions, and alkyd resin compositions.

[0126] The active energy ray-curable composition is not particularly limited, and examples thereof include polymerizable compounds having at least two (meth)acryloyloxy groups in a molecule.

[0127] The insulating layer 60 may be composed of a single material or may be composed of two or more materials.

[0128] The insulating layer 60 may contain a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling agent, a filler, a flame retardant, a viscosity improver, an anti-blocking agent, etc. as required.

[0129] The thickness of the insulating layer 60 is not particularly limited and can be appropriately set as needed, but is preferably 1 to 15 μm, and more preferably 3 to 10 μm.

[0130] If the thickness of the insulating layer 60 is less than 1 μm, it is too thin to sufficiently protect the metal layer 10 and the conductive adhesive layer 70 .

[0131] If the thickness of the insulating layer 60 exceeds 15 μm, it is too thick, and thus the electromagnetic wave shielding film 50 is difficult to bend, and the insulating layer 60 itself is easily damaged. Therefore, it is difficult to apply to a member requiring folding resistance.

[0132] Next, the conductive adhesive layer 70 in the electromagnetic wave shielding film 50 will be described.

[0133] In the electromagnetic wave shielding film 50 , the conductive adhesive layer 70 may be made of any material as long as it has conductivity and can function as an adhesive.

[0134] For example, the conductive adhesive layer 70 may be composed of conductive particles and an adhesive resin composition.

[0135] The conductive particles are not particularly limited, and may be metal fine particles, carbon nanotubes, carbon fibers, metal fibers, or the like.

[0136] When the conductive particles are metal particles, there are no particular limitations on the metal particles, and they may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by silver-plating copper powder, particles obtained by coating polymer particles or glass beads with metal, etc.

[0137] Among them, from the viewpoint of economic efficiency, copper powder or silver-coated copper powder which is available at low cost is preferred.

[0138] The average particle size of the conductive particles is not particularly limited, but is preferably 0.5 to 15.0 μm. If the average particle size of the conductive particles is 0.5 μm or more, the conductivity of the conductive adhesive layer is good. If the average particle size of the conductive particles is 15.0 μm or less, a thin conductive adhesive layer can be obtained.

[0139] The shape of the conductive particles is not particularly limited, and can be appropriately selected from spherical, flat, scaly, dendritic, rod-like, fibrous, and the like.

[0140] The material of the bonding resin composition is not particularly limited, and thermoplastic resin compositions such as styrene resin compositions, vinyl acetate resin compositions, polyester resin compositions, polyethylene resin compositions, polypropylene resin compositions, imide resin compositions, amide resin compositions, and acrylic resin compositions as well as thermosetting resin compositions such as phenol resin compositions, epoxy resin compositions, polyurethane resin compositions, melamine resin compositions, and alkyd resin compositions can be used.

[0141] The material of the adhesive resin composition may be one of the above materials alone or a combination of two or more.

[0142] The conductive adhesive layer 70 may contain a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling agent, a filler, a flame retardant, a viscosity improver, etc. as required.

[0143] The amount of the conductive particles blended in the conductive adhesive layer 70 is not particularly limited, but is preferably 15 to 80% by mass, and more preferably 15 to 60% by mass.

[0144] When the amount of the conductive particles is within the above range, the adhesion between the conductive adhesive layer and the printed wiring board is improved.

[0145] The thickness of the conductive adhesive layer 70 is not particularly limited and can be appropriately set as needed, but is preferably 0.5 to 20.0 μm.

[0146] If the thickness of the conductive adhesive layer is less than 0.5 μm, it is difficult to obtain good conductivity. If the thickness of the conductive adhesive layer exceeds 20.0 μm, the entire electromagnetic wave shielding film becomes thick and difficult to handle.

[0147] Furthermore, it is preferred that the conductive adhesive layer 70 has anisotropic conductivity.

[0148] If the conductive adhesive layer 70 has anisotropic conductivity, the transmission characteristics of high-frequency signals transmitted by the signal circuit of the printed wiring board are improved compared to the case where the conductive adhesive layer 70 has isotropic conductivity.

[0149] (Other structures)

[0150] In the electromagnetic wave shielding film 50 , an adhesion promoter coating may be formed between the insulating layer 60 and the metal layer 10 .

[0151] Materials for the adhesion-enhancing coating include polyurethane resin, acrylic resin, core-shell composite resin with polyurethane resin as shell and acrylic resin as core, epoxy resin, imide resin, amide resin, melamine resin, phenol resin, urea formaldehyde resin, blocked isocyanate obtained by reacting phenol and other blocking agents with polyisocyanate, polyvinyl alcohol, polyvinyl pyrrolidone, etc.

[0152] In addition, the electromagnetic wave shielding film 50 may include a support film on the insulating layer 60 side, and may include a release film on the conductive adhesive layer 70 side.

[0153] If the electromagnetic wave shielding film 50 includes a support film or a release film, the electromagnetic wave shielding film 50 can be easily handled during operations such as transporting the electromagnetic wave shielding film 50 and attaching the electromagnetic wave shielding film 50 to a printed wiring board.

[0154] The electromagnetic wave shielding film 50 can be used for any purpose as long as the purpose is to shield electromagnetic waves.

[0155] It is particularly preferable to use the electromagnetic wave shielding film 50 for a printed wiring board, in particular, for a flexible printed wiring board. Example

[0156] The following contents are examples for further illustrating the present invention, but the present invention is not limited to the following examples.

[0157] (Example 1)

[0158] The metal layer including the openings was formed by the following method.

[0159] (1) Preparation of substrate

[0160] The silver layer was formed by printing the silver paste on the release-treated surface of the PET film subjected to release treatment by gravure coating.

[0161] The thickness of the silver layer was 30 nm.

[0162] The silver paste used was the one obtained by the following Preparation Example 1.

[0163] (Preparation Example 1: Preparation Example of Silver Paste)

[0164] Silver particles having an average particle diameter of 30 nm were dispersed in a mixed solvent of 35 parts by mass of ethanol and 65 parts by mass of ion-exchanged water using a polyethyleneimine compound as a dispersant, thereby obtaining a silver paste having a silver concentration of 15% by mass.

[0165] (2) Formation of the convex part of the figure

[0166] Next, epoxy resin was used to form convex portions on the silver paste by rotary gravure printing, and the convex portions were arranged in a zigzag array with a top of 30 μm, a bottom of 35 μm, a height of 3 μm, and a pitch of 370 μm. In addition, the angle formed by the line segments connecting adjacent convex portions was 45°.

[0167] The top of the protrusion corresponds to the longest diameter A of the opening in one main surface (first main surface) of the copper layer described later, and the bottom of the protrusion corresponds to the longest diameter B of the opening in the other main surface (second main surface).

[0168] The measured values ​​of the convex parts after printing are 38μm at the top, 42μm at the bottom, and 2μm in height. In addition, the measured values ​​of the convex parts are obtained by measuring any five points on the surface of the silver paste with convex parts formed using a confocal microscope (Lasertec, OPTELICS HYBRID, objective lens 20 times), and then analyzing them using data analysis software (LMeye7). The binarization parameter is the height, and the automatic threshold algorithm uses the Kittler method.

[0169] (3) Formation of copper layer

[0170] Next, a metal layer (copper layer) is formed by copper plating on the silver paste having the pattern-shaped protrusions formed thereon.

[0171] The copper plating process is as follows.

[0172] The film was immersed in an electroless copper plating solution (“ARG copper” manufactured by Okuno Pharmaceutical Co., Ltd., pH 12.5) at 55° C. for 20 minutes to form an electroless copper plating film (thickness 0.2 μm) on the silver layer.

[0173] Next, the surface of the chemical copper plating film obtained in the above process is set as the cathode, the phosphor copper is set as the anode, and the electroplating solution containing copper sulfate is used at a current density of 2.5A / dm 2 The electroplating was performed for 30 minutes, thereby forming a copper-plated layer with a total thickness of 2 μm on the silver layer. The electroplating solution used was a solution containing 70 g / liter of copper sulfate, 200 g / liter of sulfuric acid, 50 mg / liter of chloride ions, and 5 g / liter of TOP LUCINA SF (brightener produced by Okuno Pharmaceutical Co., Ltd.).

[0174] Figure 6 The cross section of the copper layer according to Example 1 in the direction perpendicular to the first main surface is shown.

[0175] Figure 6 It is a cross-sectional view of the copper layer involved in Example 1 in a direction perpendicular to the first main surface.

[0176] In the copper layer according to Example 1, the shape of the opening is circular in a plan view, and the cross section cut in a direction perpendicular to the first main surface is tapered.

[0177] In addition, the longest diameter A of the opening in one main surface (first main surface) of the copper layer is 38 μm, the longest diameter B of the opening in the other main surface (second main surface) is 42 μm, the area of ​​the opening in one main surface (first main surface) of the copper layer is 1114 μm², and the area of ​​the opening in the other main surface (second main surface) is 1417 μm².

[0178] In addition, the opening ratio of the opening portion in one main surface (first main surface) of the copper layer was 1%.

[0179] The thickness of the copper layer is 2 μm.

[0180] (Example 2) to (Example 16) and (Comparative Example 1) to (Comparative Example 5)

[0181] Copper layers according to Examples 2 to 16 and Comparative Examples 1 to 5 were produced in the same manner as in Example 1 except that the parameters were changed to those shown in Tables 1 and 2.

[0182] [Table 1]

[0183]

[0184] [Table 2]

[0185]

[0186] (Production of electromagnetic wave shielding film)

[0187] The epoxy resin composition is applied to a PET film substrate with a release treatment on the surface, and heated and cured at 100°C for 3 minutes to form an insulating layer composed of epoxy resin with a thickness of 5 μm. Then, the above-mentioned insulating layer is attached to the first main surface of the copper layer of each embodiment and each comparative example by heat lamination, and the release film is peeled off to form a metal layer with an insulating layer. Then, a conductive adhesive composition with a thickness of 15 μm is applied to the second main surface of the metal layer, and heated and cured at 100°C for 3 minutes, thereby producing the electromagnetic wave shielding film involved in each embodiment and each comparative example. In addition, the conductive adhesive composition is prepared by adding 20% ​​by mass of dendritic silver-coated copper powder with an average particle size of 12 μm to the epoxy resin.

[0188] (Delamination evaluation (Reflow resistance evaluation))

[0189] Each electromagnetic wave shielding film is attached to the printed circuit board by heat pressing.

[0190] Next, after the shielded printed wiring board was placed in a clean room at 23°C and 63% RH for 7 days, it was exposed to the temperature conditions during reflow soldering and evaluated for delamination. The temperature conditions during reflow soldering were set to lead-free solder and a temperature curve of up to 265°C. In addition, the presence of delamination was evaluated by passing the shielded printed wiring board through atmospheric reflow soldering 5 times and then visually observing for blistering.

[0191] The evaluation criteria are as follows. The results are shown in Tables 1 and 2.

[0192] ○: The shielding film has no bubbles at all.

[0193] ×: The shielding film has bubbles.

[0194] (Evaluation of electromagnetic wave shielding properties)

[0195] The electromagnetic shielding properties of the electromagnetic shielding films of the examples and comparative examples were evaluated by the KEC method using an electromagnetic shielding effect measuring apparatus 80 developed by KEC Kansai Electronics Industry Promotion Center.

[0196] Figure 7 This is a schematic diagram of the structure of the system used in the KEC method.

[0197] The system used in the KEC method includes an electromagnetic shielding effect measuring apparatus 80 , a spectrum analyzer 91 , an attenuator 92 that performs 10 dB attenuation, an attenuator 93 that performs 3 dB attenuation, and a preamplifier 94 .

[0198] like Figure 7 As shown, two measuring jigs 83 are provided facing each other in the electromagnetic shielding effect measuring device 80. The electromagnetic shielding films ( Figure 7 The measuring fixture 83 is symmetrically divided in a plane perpendicular to the transmission axis direction thereof, using the size distribution of a TEM cell (Transverse Electro Magnetic Cell). In addition, in order to prevent a short circuit from being formed by inserting the electromagnetic wave shielding film 50, the flat central conductor 84 is arranged in a manner that leaves a gap between each measuring fixture 83.

[0199] In the KEC method, first, the signal output from the spectrum analyzer 91 is input to the measuring fixture 83 on the transmitting side via the attenuator 92. Next, the signal received by the measuring fixture 83 on the receiving side and passed through the attenuator 93 is amplified by the preamplifier 94, and then the signal level is measured by the spectrum analyzer 91. In addition, the spectrum analyzer 91 outputs the attenuation amount when the electromagnetic wave shielding film 50 is installed in the electromagnetic wave shielding effect measuring device 80, using the state in which the electromagnetic wave shielding film 50 is not installed in the electromagnetic wave shielding effect measuring device 80 as a standard.

[0200] Using the above apparatus, the electromagnetic shielding films of each example and each comparative example were cut into 15 cm squares under the conditions of a temperature of 25° C. and a relative humidity of 30 to 50%, and the electromagnetic shielding properties were measured and evaluated at 200 MHz.

[0201] The evaluation criteria are as follows. The results are shown in Tables 1 and 2.

[0202] ○: 85dB or above.

[0203] △: 80dB or more and less than 85dB.

[0204] ×: Less than 80dB.

[0205] (Evaluation of tight fit)

[0206] For the electromagnetic wave shielding films involved in each embodiment and each comparative example, a polyimide film with a thickness of 25 μm ("Kapton 100EN" produced by DuPont Toray) was heated and pressed at 170°C, 3 MPa, and 30 minutes on the conductive adhesive layer in the electromagnetic wave shielding film to prepare a measurement sample. Next, in order to measure the bonding strength, the measurement sample was cut into 10 mm wide, and the contact surface between the conductive adhesive layer and the polyimide film was peeled off at a peeling speed of 50 mm / min and a peeling angle of 180° using a tensile tester AGS-X50N (produced by Shimadzu Corporation) to measure the bonding strength.

[0207] The evaluation criteria are as follows. The results are shown in Tables 1 and 2.

[0208] 〇: 4N / 10mm or more.

[0209] △: 3N / 10mm or more and less than 4N / 10mm.

[0210] ×: Less than 3N / 10mm.

[0211] As shown in Table 1 and Table 2, the electromagnetic wave shielding films according to Examples 1 to 16 all have good reflow resistance, electromagnetic wave shielding properties, and close adhesion.

[0212] Number Description

[0213] 10 Metal Layer

[0214] 10a: opening 21 peripheral portion

[0215] 11 Main side 1

[0216] 12 2nd main side

[0217] 13 Opening side

[0218] 20 Opening

[0219] 21 First main surface side opening

[0220] 22 Second main surface side opening

[0221] 50 Electromagnetic wave shielding film

[0222] 60 Insulation layer

[0223] 70 Conductive adhesive layer

[0224] 80 Electromagnetic wave shielding effect measuring device

[0225] 83 Measuring fixture

[0226] 84 Center conductor

[0227] 91 Spectrum Analyzer

[0228] 92, 93 Attenuator

[0229] 94 Preamplifier

Claims

1. A metal layer for an electromagnetic wave shielding film, the metal layer comprising a first main surface and a second main surface on the opposite side of the first main surface, characterized in that: The metal layer has a plurality of openings formed therein, the openings penetrating from the first main surface to the second main surface; The opening area of ​​the opening in the first main surface is 70 to 71000 μm²; and The opening ratio of the opening in the first main surface is 0.1 to 20%; The opening area of ​​the opening of the second main surface is larger than the opening area of ​​the opening of the first main surface. The opening is cone-shaped, The ratio of the longest diameter A of the opening in the first main surface to the longest diameter B of the opening in the second main surface is longest diameter A / longest diameter B=0.65 to 0.

95.

2. The metal layer according to claim 1, characterized in that: The opening has a circular or elliptical shape when viewed from above the electromagnetic wave shielding film metal layer.

3. The metal layer according to claim 1, characterized in that: The thickness of the metal layer is 0.5-10.0 μm.

4. The metal layer according to any one of claims 1 to 3, characterized in that: The metal layer is composed of at least one metal selected from the group consisting of copper, silver, nickel, aluminum, and titanium.

5. An electromagnetic wave shielding film, the electromagnetic wave shielding film being formed by sequentially stacking an insulating layer, a metal layer and a conductive adhesive layer, characterized in that: The metal layer is the metal layer according to any one of claims 1 to 4; The first main surface of the metal layer is in contact with the insulating layer, and the second main surface of the metal layer is in contact with the conductive adhesive layer.

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