Electromagnetic shielding film and insulated printed circuit board.

Abstract

Invention details;

Description

Electromagnetic wave shielding film and shielded printed wiring board

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

[0002] Mobile devices such as smartphones and tablet terminals use shielded flexible printed wiring boards (hereinafter also referred to as "shielded printed wiring boards") with an electromagnetic wave shielding film attached to them to block electromagnetic waves generated internally and electromagnetic waves entering from the outside. The shielding layer used in the electromagnetic wave shielding film is formed from a thin metal layer formed by vapor deposition, sputtering, plating, etc., or a conductive paste with a high loading of conductive filler. As 5G and other technologies become more widespread in the future, higher frequencies and faster transmissions will become necessary to communicate large volumes of data, making noise countermeasures for electronic devices even more necessary.

[0003] As such an electromagnetic wave shielding film, Patent Document 1 discloses an electromagnetic wave shielding material (electromagnetic wave shielding film) in which a shielding layer having a thickness of 1 to 8 μm and made of one or more elements selected from the group consisting of Ni, Fe, Co, Ti, Zn, Cr, Sn, Cu, and alloys containing at least one of these metals is formed on the surface of a polymer film by either sputtering, vapor deposition, or plating, and one or more underlayers having a thickness of 1 μm or less and made of one or more elements selected from the group consisting of Ni, Co, Zn, Fe, Cu, Ti, Cr, oxides and nitrides of these metals, and alloys containing at least one of these metals are formed between the surface of the polymer film and the shielding layer by either sputtering or vapor deposition.

[0004] Furthermore, Patent Document 2 discloses an electromagnetic wave shielding film that is applied to a molded product made of any of ABS resin, PC, and ABS / PC polymer alloy, and that is characterized by comprising a first layer of Cu and a second layer of Sn—Cr coating.

[0005] Japanese Patent Publication No. 2004-128158

[0006] In the case of the electromagnetic wave shielding film, since a plurality of metal layers are laminated in contact with each other, there is a problem that the adhesion between the shielding layers is insufficient and cracks are likely to occur when the film is repeatedly bent.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide an electromagnetic wave shielding film having a shielding layer with high adhesive strength and excellent bending resistance.

[0008] That is, the electromagnetic wave shielding film of the present invention is characterized in that an isotropically conductive adhesive layer, an insulating layer, and a metal layer are laminated in this order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm.

[0009] In the electromagnetic wave shielding film of the present invention, both the isotropically conductive adhesive layer and the metal layer have the effect of shielding electromagnetic waves. In the electromagnetic wave shielding film of the present invention, an insulating layer is formed between the isotropically conductive adhesive layer and the metal layer. Therefore, the metal layer is less likely to peel off. Furthermore, even if the electromagnetic wave shielding film of the present invention is repeatedly folded, cracks are less likely to occur in the metal layer.

[0010] In the electromagnetic wave shielding film of the present invention, the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm. When the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm, the metal layer is less likely to peel off, and cracks are less likely to occur in the metal layer even when the electromagnetic wave shielding film is repeatedly folded.

[0011] In the electromagnetic wave shielding film of the present invention, the thickness of the metal layer is preferably 0.1 to 8 μm. If the thickness of the metal layer is less than 0.1 μm, the strength of the metal layer is weakened and the metal layer is easily damaged. If the thickness of the metal layer exceeds 8 μm, the flexibility of the metal layer is reduced, and the metal layer is easily cracked when repeatedly bent.

[0012] In the electromagnetic wave shielding film of the present invention, the thickness of the insulating layer is preferably 0.5 to 10 μm. If the thickness of the insulating layer is less than 0.5 μm, the amount of the insulating layer is reduced, making the metal layer more likely to peel off. If the thickness of the insulating layer exceeds 10 μm, the insulating layer is so thick that stress is more likely to be applied to the metal layer when the electromagnetic wave shielding film is folded. As a result, cracks are more likely to occur in the metal layer when the film is folded repeatedly.

[0013] In the electromagnetic wave shielding film of the present invention, the metal layer preferably contains at least one metal selected from the group consisting of copper, silver, and aluminum. These metals are inexpensive, and when the metal layer is made of these metals, it exhibits excellent electromagnetic wave shielding properties.

[0014] In the electromagnetic wave shielding film of the present invention, it is preferable that through holes are formed in the metal layer. The electromagnetic wave shielding film is placed on a printed wiring board. At this time, the electromagnetic wave shielding film is thermocompression bonded. At this time, volatile components may be generated between the insulating layer and the metal layer. If through holes are not formed in the metal layer, these volatile components may expand due to heat, causing peeling between the metal layer and the insulating layer. However, if through holes are formed in the metal layer, the volatile components can pass through the through holes, preventing peeling between the metal layer and the insulating layer.

[0015] In the electromagnetic wave shielding film of the present invention, the opening area of ​​each of the through holes is 10 to 80,000 μm ２ When the opening area of ​​the through hole formed in the metal layer is within the above range, the bending resistance is sufficient, and it is possible to prevent volatile components from accumulating between the metal layer and the insulating layer.

[0016] In the electromagnetic wave shielding film of the present invention, the aperture ratio of the through holes is preferably 0.05 to 30%. When the aperture ratio of the through holes formed in the metal layer is in this range, the bending resistance is sufficient and it is possible to prevent volatile components from accumulating between the metal layer and the insulating layer.

[0017] The shielded printed wiring board of the present invention is a shielded printed wiring board comprising a printed wiring board consisting of a base film, a printed circuit including a ground circuit arranged on the base film, and a coverlay covering the printed circuit, and an electromagnetic wave shielding film in which an isotropically conductive adhesive layer, an insulating layer, and a metal layer are laminated in that order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm, and is characterized in that the electromagnetic wave shielding film is arranged on the printed wiring board so that the isotropically conductive adhesive layer is in contact with the coverlay.

[0018] The shielded printed wiring board of the present invention includes an electromagnetic wave shielding film in which an isotropically conductive adhesive layer, an insulating layer, and a metal layer are laminated in this order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm. That is, the shielded printed wiring board of the present invention includes the electromagnetic wave shielding film of the present invention. Therefore, in the shielded printed wiring board of the present invention, the metal layer is less likely to peel off, and cracks are less likely to occur in the metal layer even when the shielded printed wiring board is repeatedly bent.

[0019] In the shielded printed wiring board of the present invention, it is preferable that the coverlay has an opening that exposes the ground circuit, and the opening is filled with the isotropically conductive adhesive layer so that the isotropically conductive adhesive layer and the ground circuit are in contact with each other. In such a shielded printed wiring board, the isotropically conductive adhesive layer and the ground circuit are in sufficient contact with each other and electrically connected. In the shielded printed wiring board of the present invention, the isotropically conductive adhesive layer has the function of shielding electromagnetic waves, so that the electromagnetic wave shielding effect is enhanced.

[0020] In the shielded printed wiring board of the present invention, the metal layer is electrically connected to an external ground. In the shielded printed wiring board of the present invention, the metal layer has the function of shielding electromagnetic waves, so when the metal layer is electrically connected to an external ground, the electromagnetic wave shielding effect is enhanced.

[0021] In the electromagnetic wave shielding film of the present invention, an insulating layer is formed between the isotropically conductive adhesive layer and the metal layer. Therefore, the metal layer is less likely to peel off. Furthermore, even if the electromagnetic wave shielding film of the present invention is repeatedly folded, cracks are less likely to occur in the metal layer. Furthermore, in the electromagnetic wave shielding film of the present invention, the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm. When the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm, the metal layer is less likely to peel off, and cracks are less likely to occur in the metal layer even if the electromagnetic wave shielding film is repeatedly folded.

[0022] FIG. 1 is a cross-sectional view schematically showing an example of an electromagnetic wave shielding film of the present invention. FIG. 2A is a process diagram schematically showing an example of a metal layer formation step in the method for producing an electromagnetic wave shielding film of the present invention. FIG. 2B is a process diagram schematically showing an example of an insulating layer formation step in the method for producing an electromagnetic wave shielding film of the present invention. FIG. 2C is a process diagram schematically showing an example of an isotropically conductive adhesive layer formation step in the method for producing an electromagnetic wave shielding film of the present invention. FIG. 3 is a cross-sectional view schematically showing an example of a shielded printed wiring board of the present invention. FIG. 4A is a cross-sectional view schematically showing another example of a shielded printed wiring board of the present invention. FIG. 4B is a cross-sectional view schematically showing another example of a shielded printed wiring board of the present invention. FIG. 4C is a cross-sectional view schematically showing another example of a shielded printed wiring board of the present invention. FIG. 4D is a cross-sectional view schematically showing another example of a shielded printed wiring board of the present invention.

[0023] The electromagnetic wave shielding film of the present invention will be specifically described below. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0024] Fig. 1 is a cross-sectional view schematically showing one example of the electromagnetic wave shielding film of the present invention. The electromagnetic wave shielding film 10 shown in Fig. 1 includes an isotropically conductive adhesive layer 20, an insulating layer 30, and a metal layer 40 laminated in this order. In addition, in the electromagnetic wave shielding film 10, the total thickness of the insulating layer 30 and the metal layer 40 is 0.5 µm or more and less than 20 µm.

[0025] The electromagnetic wave shielding film 10 is disposed on a printed wiring board. In the electromagnetic wave shielding film 10, both the isotropically conductive adhesive layer 20 and the metal layer 40 have the effect of shielding electromagnetic waves, so that in a shielded printed wiring board on which the electromagnetic wave shielding film 10 is disposed, electromagnetic waves can be shielded by the isotropically conductive adhesive layer 20 and the metal layer 40.

[0026] In the electromagnetic wave shielding film 10, an insulating layer 30 is formed between the isotropic conductive adhesive layer 20 and the metal layer 40. This makes it difficult for the metal layer 40 to peel off. Furthermore, even if the electromagnetic wave shielding film 10 is repeatedly folded, cracks are unlikely to occur in the metal layer 40.

[0027] In the electromagnetic wave shielding film 10, the total thickness of the insulating layer 30 and the metal layer 40 is 0.5 μm or more and less than 20 μm. This thickness is preferably 1 to 12 μm. When the total thickness of the insulating layer 30 and the metal layer 40 is 0.5 μm or more and less than 20 μm, the metal layer 40 is less likely to peel off, and cracks are less likely to occur in the metal layer 40 even when the electromagnetic wave shielding film 10 is repeatedly folded.

[0028] Each component of the electromagnetic wave shielding film 10 will be described below.

[0029] (Metal Layer) The material constituting the metal layer 40 is not particularly limited as long as it can shield electromagnetic waves, but it preferably contains at least one selected from the group consisting of copper, silver, and aluminum. These metals are inexpensive, and when the metal layer 40 is made of these metals, it exhibits excellent electromagnetic wave shielding properties.

[0030] As described above, in the electromagnetic wave shielding film 10, the thickness of the metal layer 40 is preferably 0.1 to 8 μm, and more preferably 0.1 to 4 μm. If the thickness of the metal layer is less than 0.1 μm, the strength of the metal layer is weakened and the metal layer is easily damaged. If the thickness of the metal layer exceeds 8 μm, the flexibility of the metal layer is reduced, and the metal layer is more likely to crack when repeatedly bent.

[0031] The metal layer 40 may be a vapor-deposited metal layer, a plated metal layer, or a rolled or electrolytic metal foil.

[0032] It is preferable that through holes are formed in the metal layer 40. The electromagnetic wave shielding film 10 is placed on a printed wiring board. At this time, the electromagnetic wave shielding film 10 is thermocompression bonded. At this time, volatile components may be generated between the insulating layer 30 and the metal layer 40. If through holes are not formed in the metal layer 40, these volatile components may expand due to heat, causing the metal layer 40 and the insulating layer 30 to peel off. However, if through holes are formed in the metal layer 40, the volatile components can pass through the through holes, preventing the metal layer 40 and the insulating layer 30 from peeling off.

[0033] The shape of the through-hole is not particularly limited, but may be a polygonal shape such as a triangle or a rectangle, a circular shape, or an elliptical shape.

[0034] In the metal layer 40, the opening area of ​​each of the through holes is 10 to 80,000 μm ２ It is preferable that the thickness is 10 to 8000 μm. ２ If the opening area of ​​the through hole formed in the metal layer 40 is within the above range, the bending resistance is sufficient, and it is possible to prevent volatile components from accumulating between the metal layer 40 and the insulating layer 30.

[0035] The aperture ratio of the through holes in the metal layer 40 is preferably 0.05 to 30%, and more preferably 0.1 to 10%. If the aperture ratio of the through holes formed in the metal layer 40 is within the above range, the bending resistance is sufficient, and it is possible to prevent volatile components from accumulating between the metal layer 40 and the insulating layer 30.

[0036] In the metal layer 40, the through holes may be arranged at equal intervals. When the through holes are arranged at equal intervals, it is preferable that the through holes are arranged continuously in a fixed pattern. The arrangement pattern of the through holes may be such that, when the metal layer 40 is viewed in plan, equilateral triangles are arranged continuously in the vertical and horizontal directions, and the centers of the through holes are located at the vertices of the equilateral triangles. Alternatively, when the metal layer 40 is viewed in plan, the arrangement pattern may be such that, when squares are arranged continuously in the vertical and horizontal directions, and the centers of the through holes are located at the vertices of the squares. Alternatively, when the metal layer 40 is viewed in plan, the arrangement pattern may be such that, when the metal layer 40 is viewed in plan, the centers of the through holes are located at the vertices of a regular hexagon.

[0037] (Insulating Layer) The material of the insulating layer 30 is not particularly limited as long as it can sufficiently bond the metal layer 40, and may be a thermosetting resin composition or a thermoplastic resin composition. The electromagnetic wave shielding film 10 is thermocompression bonded when disposed on a printed wiring board. Whether a thermosetting resin composition or a thermoplastic resin composition is used as the insulating layer 30 is preferably determined based on the conditions for thermocompression bonding. From the viewpoint of heat resistance, the insulating layer 30 is preferably made of a thermosetting resin composition.

[0038] Examples of the thermoplastic resin contained in the thermoplastic resin composition include urethane resin, polystyrene resin, vinyl acetate resin, polyester resin, polyolefin resin (e.g., polyethylene resin, polypropylene resin composition, etc.), acrylic resin, etc. The insulating layer 30 may be made of only one of these resins, or two or more of them.

[0039] Examples of the thermosetting resin contained in the thermosetting resin composition include phenolic resins, epoxy resins, urethane resins, melamine resins, alkyd resins, and polyimide resins. The insulating layer 30 may be made of only one of these resins, or two or more of them.

[0040] The thickness of the insulating layer 30 is preferably 0.5 to 10 μm, and more preferably 1 to 5 μm. If the thickness of the insulating layer is less than 0.5 μm, the amount of insulating layer is reduced, making the metal layer more likely to peel off. If the thickness of the insulating layer exceeds 10 μm, the insulating layer is so thick that stress is more likely to be applied to the metal layer when the electromagnetic wave shielding film is folded. As a result, cracks are more likely to occur in the metal layer when the film is folded repeatedly.

[0041] (Isotropically Conductive Adhesive Layer) The isotropically conductive adhesive layer 20 is made of conductive particles and a resin composition.

[0042] Examples of conductive particles include silver particles, copper particles, nickel particles, aluminum particles, and silver-coated copper particles obtained by plating copper with silver. These conductive particles have excellent conductivity and can therefore suitably impart conductivity to the isotropically conductive adhesive layer 20. The isotropically conductive adhesive layer 20 may contain one type of these conductive particles alone, or may contain multiple types.

[0043] The size of the conductive particles is not particularly limited, but the average particle diameter (d ５０ The average particle diameter (d ５０ When the average particle diameter (d) is 0.5 μm or more, the conductive particles have good dispersibility, aggregation can be suppressed, and the conductive particles are less likely to be oxidized. ５０ When the thickness is 20 μm or less, the connectivity with the ground circuit is good.

[0044] The weight percentage of the conductive particles contained in the isotropically conductive adhesive layer 20 is preferably 40 to 80 wt %, and more preferably 50 to 70 wt %. If the weight percentage of the conductive particles is less than 40 wt %, it becomes difficult to obtain isotropic conductivity. If the weight percentage of the conductive particles exceeds 80 wt %, the isotropically conductive adhesive layer becomes brittle, and the electromagnetic wave shielding film becomes more susceptible to damage.

[0045] The material for the resin composition is not particularly limited, but examples thereof include thermoplastic resin compositions such as styrene-based resin compositions, vinyl acetate-based resin compositions, polyester-based resin compositions, polyethylene-based resin compositions, polypropylene-based resin compositions, imide-based resin compositions, amide-based resin compositions, and acrylic-based resin compositions, and thermosetting resin compositions such as phenol-based resin compositions, epoxy-based resin compositions, urethane-based resin compositions, melamine-based resin compositions, and alkyd-based resin compositions. Among these, epoxy-based resin compositions are preferred. The material for the adhesive resin composition may be one of these alone or a combination of two or more.

[0046] The isotropic conductive adhesive layer 20 may further contain a flame retardant, a flame retardant assistant, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a viscosity adjuster, etc.

[0047] The thickness of the isotropically conductive adhesive layer 20 is preferably 3 to 20 μm, and more preferably 5 to 10 μm. When the thickness of the isotropically conductive adhesive layer 20 is 3 μm or more, the filling ability into openings provided in the coverlay of the printed wiring board is improved. When the thickness of the isotropically conductive adhesive layer 20 is 20 μm or less, it is possible to meet the demand for thinner electromagnetic wave shielding films.

[0048] In the electromagnetic wave shielding film 10, a protective layer may be further formed on the metal layer 40. The presence of the protective layer can prevent the metal layer 40 from being damaged by external impacts, etc. Note that the electromagnetic wave shielding film of the present invention does not necessarily need to have a protective layer.

[0049] The material of the protective layer is not particularly limited as long as it has insulating properties and can protect the metal layer 40, but it is preferable that it is composed of a thermoplastic resin composition, a thermosetting resin composition, an active energy ray curable composition, etc.

[0050] The thermoplastic resin composition of the protective layer is not particularly limited, but examples thereof include a styrene-based resin composition, a vinyl acetate-based resin composition, a polyester-based resin composition, a polyethylene-based resin composition, a polypropylene-based resin composition, a polyamide-based resin composition, and an acrylic-based resin composition.

[0051] The thermosetting resin composition of the protective layer is not particularly limited, but examples thereof include a phenolic resin composition, an epoxy resin composition, a urethane resin composition, a melamine resin composition, an alkyd resin composition, and a polyimide resin composition.

[0052] The active energy ray-curable composition for the protective layer is not particularly limited, but examples thereof include polymerizable compounds having at least two (meth)acryloyloxy groups in the molecule.

[0053] The protective layer may be made of a single material or two or more materials.

[0054] The protective layer may contain, as necessary, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, a viscosity adjuster, an antiblocking agent, and the like.

[0055] The thickness of the protective layer is not particularly limited and can be set appropriately as needed, but is preferably 1 to 15 μm, more preferably 3 to 10 μm.

[0056] Next, a method for producing the electromagnetic wave shielding film of the present invention will be described. When producing the electromagnetic wave shielding film of the present invention, a metal layer forming step, an insulating layer forming step, and an isotropically conductive adhesive layer forming step are carried out.

[0057] 2A is a process diagram schematically illustrating an example of a metal layer formation step in the manufacturing method of the electromagnetic wave shielding film of the present invention. First, as shown in FIG. 2A, a release film 50 is prepared, and a metal layer 40 is formed thereon. The type of release film 50 is not particularly limited, and conventionally used non-silicon release films, low-adhesive films, etc. can be used. The method for forming the metal layer 40 is not particularly limited, and it may be formed by rolling or disposing an electrolytic metal foil, by vapor deposition, or by plating.

[0058] 2B is a process diagram schematically illustrating an example of the insulating layer forming step in the method for producing an electromagnetic wave shielding film of the present invention. Next, as shown in FIG. 2B , an insulating layer 30 is formed on the metal layer 40. The method for forming the insulating layer 30 is not particularly limited, and may be, for example, coating with a bar coater.

[0059] 2C is a process diagram schematically illustrating an example of an isotropically conductive adhesive layer forming step in the method for producing an electromagnetic wave shielding film of the present invention. Next, as shown in FIG. 2C , an isotropically conductive adhesive layer 20 is formed on the insulating layer 30. The method for forming the isotropically conductive adhesive layer 20 is not particularly limited, and may be, for example, coating with a bar coater.

[0060] When the laminate manufactured through the above steps is turned over at 180°, it becomes the electromagnetic wave shielding film 10 shown in Fig. 1. The release film 50 can be peeled off when in use.

[0061] Next, a description will be given of a shielded printed wiring board 1 including an electromagnetic wave shielding film 10. The shielded printed wiring board 1 is also an example of a shielded printed wiring board of the present invention.

[0062] Fig. 3 is a cross-sectional view schematically showing an example of a shielded printed wiring board of the present invention. The shielded printed wiring board 1 shown in Fig. 3 includes a printed wiring board 60 including a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 10. In the shielded printed wiring board 1, the electromagnetic wave shielding film 10 is arranged on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 is in contact with the coverlay 63.

[0063] The shielded printed wiring board 1 includes an electromagnetic wave shielding film 10. Therefore, in the shielded printed wiring board 1, the metal layer 40 is less likely to peel off, and cracks are less likely to occur in the metal layer 40 even if the shielded printed wiring board 1 is repeatedly bent.

[0064] 3, an opening 63a that exposes the ground circuit 62a is formed in the coverlay 63. The opening 63a is filled with the isotropically conductive adhesive layer 20 so that the isotropically conductive adhesive layer 20 and the ground circuit 62a come into contact with each other. In this shielded printed wiring board 1, the isotropically conductive adhesive layer 20 and the ground circuit 62a are in sufficient contact with each other and electrically connected. In the shielded printed wiring board 1, the isotropically conductive adhesive layer 20 has the function of shielding electromagnetic waves, thereby improving the electromagnetic wave shielding effect.

[0065] In the shielded printed wiring board of the present invention, the coverlay does not necessarily have to have an opening for exposing the ground circuit. In this case, the ground circuit and the isotropic conductive adhesive layer may be electrically connected by a conductive bump or a conductive pin.

[0066] In the shielded printed wiring board 1, the metal layer 40 is electrically connected to the external ground GND. In the shielded printed wiring board 1, the metal layer 40 has a function of shielding electromagnetic waves, and therefore, when the metal layer 40 is electrically connected to the external ground GND, the electromagnetic wave shielding effect is enhanced.

[0067] The method for electrically connecting the external ground GND and the metal layer 40 is not particularly limited, but the external ground GND and the metal layer 40 can be electrically connected using, for example, a conductive adhesive, a conductive foam, a conductive gasket, etc.

[0068] 4A to 4D are cross-sectional views schematically illustrating another example of a shielded printed wiring board according to the present invention, in which a protective layer is further formed on the metal layer of the electromagnetic wave shielding film.

[0069] 4A includes a printed wiring board 60 including a base film 61, a printed circuit 62 including a ground circuit 62a disposed on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 11. In the electromagnetic wave shielding film 11, an isotropic conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order. In the shielded printed wiring board 1A, the electromagnetic wave shielding film 11 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 is in contact with the coverlay 63.

[0070] The shielded printed wiring board 1A further includes a ground member 80A on the protective layer 70 of the electromagnetic wave shielding film 11, the ground member 80A having a flat conductive external connection member 81 and a conductive protrusion 82 protruding from one side of the conductive external connection member 81. The conductive protrusion 82 penetrates the protective layer 70 and contacts the metal layer 40, and the conductive external connection member 81 is electrically connected to the external ground GND. In other words, in the shielded printed wiring board 1A, the metal layer 40 is connected to the external ground GND via the ground member 80A.

[0071] The conductive external connection member 81 and conductive protrusion 82 of the grounding member 80A may be made of any material as long as it is conductive, such as copper, silver, aluminum, etc.

[0072] In the ground member 80A, the conductive external connection member 81 and the conductive protrusion 82 may be connected by soldering or welding. Alternatively, the conductive protrusion 82 may be formed by etching, and the conductive external connection member 81 and the conductive protrusion 82 may be integrated.

[0073] 4B includes a printed wiring board 60 including a base film 61, a printed circuit 62 including a ground circuit 62a disposed on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 11. In the electromagnetic wave shielding film 11, an isotropic conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order. In the shielded printed wiring board 1B, the electromagnetic wave shielding film 11 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 is in contact with the coverlay 63.

[0074] The shielded printed wiring board 1B further includes a ground member 80B on the protective layer 70 of the electromagnetic wave shielding film 11, the ground member 80B having a flat conductive external connection member 81 and conductive particles 83 arranged on one side of the conductive external connection member 81. The conductive particles 83 penetrate the protective layer 70 and contact the metal layer 40, and the conductive external connection member 81 is electrically connected to the external ground GND. In other words, in the shielded printed wiring board 1B, the metal layer 40 is connected to the external ground GND via the ground member 80B.

[0075] The conductive external connection member 81 of the ground member 80B may be made of any material that is conductive, such as copper, silver, aluminum, etc. The conductive particles 83 of the ground member 80B may be made of any material that is conductive, such as copper, silver, aluminum, etc.

[0076] In the ground member 80B, the conductive particles 83 may be adhered to the conductive external connection member 81 with a conductive adhesive.

[0077] 4C includes a printed wiring board 60 including a base film 61, a printed circuit 62 including a ground circuit 62a disposed on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 11. In the electromagnetic wave shielding film 11, an isotropic conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order. In the shielded printed wiring board 1C, the electromagnetic wave shielding film 11 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 is in contact with the coverlay 63.

[0078] The shielded printed wiring board 1C further includes a ground member 80C made of a conductive external connection member 84 on the protective layer 70 of the electromagnetic wave shielding film 11. The conductive external connection member 84 is formed by bending a flat plate multiple times and has a protruding convex portion 84a. The convex portion 84a penetrates the protective layer 70 and contacts the metal layer 40, and the conductive external connection member 84 is electrically connected to the external ground GND. In other words, in the shielded printed wiring board 1C, the metal layer 40 is connected to the external ground GND via the ground member 80C.

[0079] The conductive external connection member 84 of the ground member 80C may be made of any material as long as it is conductive, such as copper, nickel, silver, aluminum, or the like.

[0080] 4D includes a printed wiring board 60 including a base film 61, a printed circuit 62 including a ground circuit 62a disposed on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 12. In the electromagnetic wave shielding film 12, an isotropic conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order. In the shielded printed wiring board 1D, the electromagnetic wave shielding film 12 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 is in contact with the coverlay 63.

[0081] In the shielded printed wiring board 1D, an opening 71a is formed in the protective layer 71 of the electromagnetic wave shielding film 12 to expose the metal layer 40. The metal layer 40 is electrically connected to the external ground GND through the opening 71a.

[0082] In the shielded printed wiring board 1D, the opening 71a of the protective layer 71 may be filled with a conductive adhesive, and the metal layer 40 may be connected to the external ground GND via the conductive adhesive.

[0083] The materials for the base film 61 and the coverlay 63 are not particularly limited, but are preferably made of engineering plastics. Examples of such engineering plastics include resins such as polyethylene terephthalate, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide. Among these engineering plastics, polyphenylene sulfide film is preferable when flame retardancy is required, and polyimide film is preferable when heat resistance is required. The thickness of the base film 61 is preferably 10 to 40 μm. The thickness of the coverlay 63 is preferably 20 to 50 μm.

[0084] The printed circuit 62 and the ground circuit 62a can be formed by etching a conductive material, although there is no particular limitation to such a material. Examples of the conductive material include copper, nickel, silver, and gold.

[0085] A method for manufacturing the shielded printed wiring board 1 includes preparing a printed wiring board 60 and an electromagnetic wave shielding film 10, and placing the electromagnetic wave shielding film 10 on the printed wiring board 60. More specifically, a method includes thermocompression bonding the electromagnetic wave shielding film 10 to the printed wiring board 60 so that the isotropic conductive adhesive layer 20 contacts the coverlay 63. The conditions for thermocompression bonding are not particularly limited, but examples include conditions of 150 to 200°C, 2 to 5 MPa, and 1 to 60 minutes.

[0086] By performing the thermocompression bonding, the opening 63a is filled with the isotropically conductive adhesive layer 20. As a result, the ground circuit 62a and the isotropically conductive adhesive layer 20 are electrically connected, thereby improving the electromagnetic wave shielding effect.

[0087] Examples will be given below to explain the present invention more specifically, but the present invention is not limited to these examples.

[0088] Example 1 (Metal Layer Forming Step) Silver (Ag) was vapor-deposited on the surface of a release film on which a non-silicon release agent had been formed, to form a metal layer having a thickness of 0.1 μm.

[0089] (Insulating Layer Forming Step) An epoxy resin was applied onto the metal layer to form an insulating layer having a thickness of 1.0 μm.

[0090] (Isotropically conductive adhesive layer formation process) An isotropically conductive adhesive containing 60 wt% conductive particles made of silver-coated copper powder and 40 wt% epoxy resin was prepared. The isotropically conductive adhesive layer was applied onto the insulating layer to form an isotropically conductive adhesive layer with a thickness of 15 μm.

[0091] Through the above steps, the electromagnetic wave shielding film according to Example 1 was produced.

[0092] (Examples 2 to 13) and (Comparative Examples 1 to 6) Electromagnetic wave shielding films according to Examples 2 to 13 and Comparative Examples 1 to 3 were produced in the same manner as Example 1, except that the material and thickness of the metal layer and the thickness of the insulating layer were changed as shown in Table 1. Furthermore, electromagnetic wave shielding films according to Comparative Examples 4 to 6 were produced in the same manner as Example 1, except that the material and thickness of the metal layer were changed as shown in Table 1 and no insulating layer was provided.

[0093]

[0094] (MIT Test) The fold resistance of the electromagnetic wave shielding films of each Example and Comparative Example after peeling off the release film was measured using the following method. Each electromagnetic wave shielding film was placed on a polyimide film with a thickness of 50 μm so that the isotropic conductive adhesive layer was in contact with the polyimide film, and the film was attached by thermocompression bonding (170°C, 3 MPa, 30 minutes). The film was then cut into a size of 130 mm x 15 mm, and the release film was peeled off to obtain a test specimen. The fold resistance of each test specimen was measured using an MIT folding fatigue tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd., No. 307 MIT type folding fatigue tester) according to the method specified in JIS P8115:2001. The test conditions were as follows. Bending clamp tip R: 0.38 mm Bending angle: ±135° Bending speed: 175 cpm Load: 500 gf Detection method: Detects breaks in the shielding film using the built-in electrical device

[0095] The evaluation criteria for the MIT test are as follows. The results are shown in Table 1. ◯: Disconnection of the metal layer was observed after bending 1,000 times or more. Δ: Disconnection of the metal layer was observed after bending 300 times or more but less than 999 times. ×: Disconnection of the metal layer was observed after bending less than 300 times.

[0096] (Adhesion Strength Test) The adhesion strength of the electromagnetic wave shielding film of each Example and Comparative Example after peeling off the release film was measured by the following method. Each electromagnetic wave shielding film was placed on a polyimide film with a thickness of 25 μm so that the isotropic conductive adhesive layer was in contact with the polyimide film, and thermocompression bonding was performed under conditions of a temperature of 170°C, a time of 30 minutes, and a pressure of 3 MPa. The metal layer side of the electromagnetic wave shielding film was fixed with double-sided tape, and the polyimide film was peeled off at room temperature at a tensile speed of 50 mm / min and a peel angle of 180°. The peel strength during peeling was measured, and the average of the maximum and minimum values ​​was taken as the adhesion strength.

[0097] The evaluation criteria for the adhesion strength test are as follows. The results are shown in Table 1. ◯: The metal layer peeled off with a tensile force of 4.0 N / cm or more. Δ: The metal layer peeled off with a tensile force of 3.0 N / cm or more but less than 4.0 N / cm. ×: The metal layer peeled off with a tensile force of less than 3.0 N / cm.

[0098] As shown in Table 1, the electromagnetic wave shielding films according to Examples 1 to 13, which included an insulating layer between the isotropically conductive adhesive layer and the metal layer and had a total thickness of the insulating layer and the metal layer of 0.5 μm or more and less than 20 μm, performed well in both the MIT test and the adhesion strength test.

[0099] On the other hand, the electromagnetic wave shielding films according to Comparative Examples 1 to 3, in which the total thickness of the insulating layer and the metal layer exceeded 20 μm, did not perform well in the MIT test, and it was found that the metal layer was prone to cracking when repeatedly bent. Also, the electromagnetic wave shielding films according to Comparative Examples 4 to 6, which did not include an insulating layer between the isotropically conductive adhesive layer and the metal layer, did not perform well in the adhesion strength test, and it was found that the metal layer was prone to peeling.

[0100] REFERENCE SIGNS LIST 1, 1A, 1B, 1C, 1D Shielded printed wiring board 10, 11, 12 Electromagnetic wave shielding film 20 Isotropically conductive adhesive layer 30 Insulating layer 40 Metal layer 50 Release film 60 Printed wiring board 61 Base film 62 Printed circuit 62a Ground circuit 63 Coverlay 63a Opening 70, 71 Protective layer 71a Opening 80A, 80B, 80C Ground member 81, 84 Conductive external connection member 82 Conductive protrusion 83 Conductive particle 84a Convex portion GND External ground

Claims

DEPCT661. Electromagnetic shielding film composed of an isotropic conductive adhesive layer, an insulating layer, and a metallic layer stacked in sequence, with a combined thickness of not less than 0.5 micrometers but less than 20 micrometers.

2. Electromagnetic shielding film according to claim 1 in which the metallic layer has a thickness of 0.1 to 8 micrometers.

3. Electromagnetic shielding film according to claim 1 in which the insulating layer has a thickness of 0.5 to 10 micrometers.

4. Electromagnetic shielding film according to any one of claims 1 to 3 in which the metallic layer consists of at least one layer selected from a group of copper, silver, and aluminum.

5. Electromagnetic shielding film according to any one of claims 1 to 4 in which the metallic layer has at least one through hole.

6. Electromagnetic shielding film according to claim 5 in which each through hole has an pore area of ​​10 to 80,000 square micrometers.

7. Electromagnetic shielding film according to claim 5 or 6 in which at least one through hole has an pore ratio of 0.05 to 30%. 8.A shielded printed circuit board (PCB) assembled with a printed circuit board base film provided on the base film and including the grounding circuit and a cover that encloses the printed circuit and an electromagnetic shielding film assembled with an isotropic conductive adhesive layer, an insulating layer and a metal layer stacked in sequence, where the total thickness of the insulating and metal layers is not less than 0.5 micrometers but less than 20 micrometers, where the electromagnetic shielding film is provided on the PCB with an isotropic conductive adhesive layer in contact with the cover.

9. A shielded printed circuit board under claim 8 in which the cover has an opening to reveal the grounding circuit and the opening is filled with an isotropic conductive adhesive layer in contact with the grounding circuit.

10. A shielded printed circuit board under claim 8 or 9 in which the metal layer is electrically connected to an external ground.

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