Electromagnetic wave shield film

Abstract

Provided is an electromagnetic wave shield film that is not susceptible to swelling of an electroconductive adhesive layer due to heating and has sufficiently high solder float resistance. An electromagnetic wave shield film according to the present invention is obtained by sequentially layering a protective layer, a metal layer, and an electroconductive adhesive layer, wherein the electromagnetic wave shield film is characterized in that the electroconductive adhesive layer contains an epoxy resin having a weight-average molecular weight Mw of 50,000 or higher, a carboxy-group-containing curing agent, a nitrogen-containing organic filler, a phosphorus-containing liquid flame retardant, and an electroconductive filler.

Description

Electromagnetic wave shielding film

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

[0002] 2. Description of the Related Art Conventionally, an electromagnetic wave shielding film has been attached to a printed wiring board such as a flexible printed wiring board (FPC) to shield it from external electromagnetic waves.

[0003] Known electromagnetic wave shielding films include those in which a protective layer, a metal layer, and an adhesive layer are laminated in this order. Such electromagnetic wave shielding films are superimposed on a printed wiring board and then hot-pressed in this state. The electromagnetic wave shielding film is then bonded to the printed wiring board by the adhesive layer, producing a shielded printed wiring board. Components are then mounted on the shielded printed wiring board by solder reflow. The printed wiring board is configured such that a printed pattern on a base film is covered with an insulating film.

[0004] As such an electromagnetic wave shielding film, Patent Document 1 discloses an electromagnetic wave shielding film formed by laminating an insulating resin layer, a shielding layer, and a conductive adhesive layer in this order, wherein the insulating resin layer and the conductive adhesive layer contain a flame retardant containing phosphorus or nitrogen, and the electromagnetic wave shielding film contains a predetermined amount of a flame retardant containing phosphorus and a flame retardant containing nitrogen.

[0005] Japanese Patent Application Laid-Open No. 2022-21641

[0006] When electromagnetic wave shielding films are subjected to heat during the heat press and solder reflow processes used to manufacture shielded printed wiring boards, the conductive adhesive layer can swell. This is thought to be caused by gases generated from the conductive adhesive layer itself and moisture absorbed by the conductive adhesive layer volatilizing and expanding due to the heat.

[0007] Furthermore, in the electromagnetic wave shielding film described in Patent Document 1, a flame retardant containing solid phosphorus is added to the adhesive layer as a flame retardant in order to improve the heat resistance of the conductive adhesive layer. However, an electromagnetic wave shielding film having such a configuration has the problem of insufficient solder float resistance.

[0008] 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 in which the conductive adhesive layer is less likely to bulge due to heating and which has sufficiently high solder float resistance.

[0009] The present inventors have found that the inclusion of a phosphorus-containing liquid flame retardant in a conductive adhesive layer improves solder float resistance. That is, the electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film having a protective layer, a metal layer, and a conductive adhesive layer laminated in this order, wherein the conductive adhesive layer contains an epoxy resin having a weight-average molecular weight Mw of 50,000 or more, a curing agent having a carboxy group, a nitrogen-containing organic filler, a phosphorus-containing liquid flame retardant, and a conductive filler.

[0010] The electromagnetic wave shielding film of the present invention contains an epoxy resin having a weight-average molecular weight Mw of 50,000 or more and a liquid flame retardant containing phosphorus, and therefore the conductive adhesive layer is less likely to swell when heated and has sufficiently high solder float resistance.

[0011] If the weight-average molecular weight Mw of the epoxy resin contained in the conductive adhesive layer is less than 50,000, the conductive adhesive layer will swell due to heating and will have poor solder float resistance. Furthermore, if the conductive adhesive layer does not contain a curing agent having a carboxyl group, the solder float resistance will also be poor. Furthermore, if the conductive adhesive layer does not contain a nitrogen-containing organic filler, the solder float resistance will also be poor.

[0012] In the electromagnetic wave shielding film of the present invention, the epoxy resin preferably has an epoxy equivalent of 7,000 to 10,000 g / eq. When the epoxy equivalent of the epoxy resin is within this range, the conductive adhesive layer is less likely to blister due to heating, and solder float resistance is sufficiently high.

[0013] In the electromagnetic wave shielding film of the present invention, the epoxy resin preferably contains at least one selected from the group consisting of bisphenol A epoxy resins, bisphenol F epoxy resins, and bisphenol A / bisphenol F copolymer epoxy resins. The epoxy resin preferably contains a polymer having a polymer unit represented by the following general formula (1). The epoxy resin may also contain a polymer represented by the following general formula (2).

[0014] (In formula (1), R １ and R ２ are each hydrogen or a methyl group, and R １ and R ２ may be the same or different.)

[0015] (In formula (2), R １ , R ２ , R ３ and R ４ are each hydrogen or a methyl group, and R １ , R ２ , R ３ and R ４ may be the same or different.)

[0016] In the electromagnetic wave shielding film of the present invention, when the epoxy resin is of the above type, swelling of the conductive adhesive layer due to heating is unlikely to occur, and solder float resistance is sufficiently high.

[0017] In the electromagnetic wave shielding film of the present invention, the content of the epoxy resin is preferably 20 to 50 wt %. When the content of the epoxy resin is in this range, the solder float resistance is sufficiently high.

[0018] In the electromagnetic wave shielding film of the present invention, the content of the liquid flame retardant is preferably 10 to 19 wt %. If the content of the liquid flame retardant is less than 10 wt %, it becomes difficult for the conductive adhesive layer to achieve sufficient flame retardancy. If the content of the liquid flame retardant is more than 19 wt %, the weight percentages of the epoxy resin and the conductive filler become relatively small, making it difficult for the conductive adhesive layer to achieve sufficient adhesion or conductivity.

[0019] According to the present invention, it is possible to provide an electromagnetic wave shielding film in which the conductive adhesive layer is less likely to bulge due to heating and which has sufficiently high resistance to solder float.

[0020] Fig. 1 is a cross-sectional view schematically showing an example of an electromagnetic wave shielding film of the present invention. Fig. 2 is a cross-sectional view schematically showing an example of a shielded printed wiring board of the present invention in which the electromagnetic wave shielding film of the present invention is used. Fig. 3 is a schematic diagram of a method for measuring the resistance value of an electromagnetic wave shielding film in a heat resistance test.

[0021] 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.

[0022] Fig. 1 is a cross-sectional view schematically showing an example of the electromagnetic wave shielding film of the present invention. The electromagnetic wave shielding film 10 shown in Fig. 1 is formed by laminating a protective layer 40, a metal layer 30, and a conductive adhesive layer 20 in this order.

[0023] In the electromagnetic wave shielding film (10), the conductive adhesive layer (20) contains an epoxy resin having a weight-average molecular weight (Mw) of 50,000 or more, a curing agent having a carboxy group, a nitrogen-containing organic filler, a phosphorus-containing liquid flame retardant, and a conductive filler.

[0024] As described below, the electromagnetic wave shielding film 10 is superimposed on a printed wiring board and then hot-pressed in this state. As a result, the electromagnetic wave shielding film 10 is adhered to the printed wiring board by the adhesive layer, producing a shielded printed wiring board. Components are then mounted on the shielded printed wiring board by solder reflow. Even when subjected to such heat, the electromagnetic wave shielding film 10 is resistant to swelling of the conductive adhesive layer and has sufficiently high solder float resistance. The mechanism by which this effect is achieved is not fully understood, but the phosphorus-containing liquid flame retardant is thought to be important.

[0025] Preferred embodiments of each of the components of the electromagnetic wave shielding film 10 will be described in detail below.

[0026] (Epoxy Resin Contained in the Conductive Adhesive Layer) The conductive adhesive layer 20 contains an epoxy resin having a weight-average molecular weight Mw of 50,000 or more. The weight-average molecular weight Mw of the epoxy resin is preferably 50,000 to 80,000, and more preferably 50,000 to 70,000. If the weight-average molecular weight Mw of the epoxy resin contained in the conductive adhesive layer is less than 50,000, the conductive adhesive layer will swell when heated and will have poor solder float resistance.

[0027] In the electromagnetic wave shielding film of the present invention, the epoxy equivalent of the epoxy resin is preferably 7,000 to 10,000 g / eq, more preferably 7,500 to 10,000 g / eq. When the epoxy equivalent of the epoxy resin is within the above range, swelling of the conductive adhesive layer due to heating is unlikely to occur, and solder float resistance is sufficiently high. In this specification, the "epoxy equivalent of the epoxy resin" can be measured in accordance with JIS K7236:2001. The epoxy resin preferably contains at least one selected from the group consisting of bisphenol A epoxy resins, bisphenol F epoxy resins, and bisphenol A / bisphenol F copolymer epoxy resins. Of these, bisphenol A / bisphenol F copolymer epoxy resins are preferred. The epoxy resin preferably contains a polymer having a polymer unit represented by the following general formula (1). The epoxy resin may also contain a polymer represented by the following general formula (2).

[0028] (In formula (1), R １ and R ２ are each hydrogen or a methyl group, and R １ and R ２ may be the same or different.)

[0029] (In formula (2), R １ , R ２ , R ３ and R ４ are each hydrogen or a methyl group, and R １ , R ２ , R ３ and R ４ may be the same or different.)

[0030] In the electromagnetic wave shielding film 10, if the epoxy resin is of the above type, the conductive adhesive layer is less likely to swell due to heating, and the resistance to solder float is sufficiently high.

[0031] In the electromagnetic wave shielding film 10, the content of the epoxy resin in the conductive adhesive layer 20 is preferably 20 to 50 wt %, and more preferably 27 to 42 wt %. When the content of the epoxy resin is within the above range, the solder float resistance is sufficiently high.

[0032] (Curing agent contained in conductive adhesive layer) The curing agent having a carboxy group contained in the conductive adhesive layer 20 is not particularly limited as long as it can cure the epoxy resin, but examples include polyester-modified urethane having a carboxy group, polyolefin having a carboxy group, etc. By using such a curing agent, swelling of the conductive adhesive layer due to heating is less likely to occur, and solder float resistance is sufficiently improved.

[0033] In the electromagnetic wave shielding film 10, the content of the curing agent having a carboxy group in the conductive adhesive layer 20 is preferably 5 to 25 wt %, and more preferably 7 to 24 wt %. When the content of the epoxy resin is within the above range, the solder float resistance is sufficiently high.

[0034] In addition to the curing agent having a carboxy group, the electromagnetic wave shielding film 10 may contain a curing agent such as a polyfunctional glycidyl amine or a phenolic novolac resin. When such a curing agent is contained, the solder float resistance is further improved.

[0035] (Nitrogen-containing organic filler contained in the conductive adhesive layer) Examples of the nitrogen-containing organic filler contained in the conductive adhesive layer 20 include melamine cyanurate, polyurethane, etc. When the conductive adhesive layer 20 contains such an organic filler, the solder float resistance is further improved.

[0036] The content of the nitrogen-containing organic filler in the conductive adhesive layer 20 is preferably 15 to 35 wt %, and more preferably 25 to 35 wt %.

[0037] (Phosphorus-containing liquid flame retardant contained in conductive adhesive layer) The phosphorus-containing liquid flame retardant contained in the conductive adhesive layer 20 is preferably a phosphate ester, and examples of the phosphate ester include bisphenol A bis(diphenyl phosphate), resorcinol bis(diphenyl phosphate), phosphoric acid, mixed esters with [1,1'-biphenyl]-4,4'-diol and Examples of suitable flame retardants include phenol (CAS No. 1003300-73-9), triethyl phosphate, tributyl phosphate, tri(2-ethylhexyl) phosphate, tributoxyethyl phosphate, tris(isopropylphenyl) phosphate, tricresyl phosphate, tributoxyethyl phosphate, trixylenyl phosphate, tris(2-ethylhexyl) phosphate, cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, cresyl 2,6-xylenyl phosphate, tris(chloropropyl) phosphate, tris(dichloropropyl) phosphate, resorcinol bis-dixylenyl phosphate, cresyl diphenyl phosphate, and diphenyl(2-ethylhexyl) phosphate. These flame retardants impart flame retardancy to the conductive adhesive layer and can also sufficiently enhance solder float resistance. In this specification, the term "liquid flame retardant" refers to a flame retardant that is liquid at 23°C.

[0038] In the electromagnetic wave shielding film of the present invention, the content of the liquid flame retardant is preferably 10 to 19 wt %, and more preferably 10 to 13 wt %. If the content of the liquid flame retardant is less than 10 wt %, it becomes difficult for the conductive adhesive layer to achieve sufficient flame retardancy. If the content of the liquid flame retardant exceeds 19 wt %, the weight percentages of the epoxy resin and the conductive filler become relatively small, making it difficult for the conductive adhesive layer to achieve sufficient adhesion or conductivity.

[0039] (Conductive Filler Included in Conductive Adhesive Layer) The conductive filler included in the conductive adhesive layer 20 is not particularly limited, but examples thereof include metal fine particles, carbon nanotubes, carbon fibers, and metal fibers.

[0040] When the conductive filler is a metal fine particle, the metal fine particle is not particularly limited, but may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by coating copper powder with silver, fine particles obtained by coating polymer fine particles, glass beads, etc. with a metal, etc. Among these, from the viewpoint of economy, copper powder or silver-coated copper powder, which is inexpensively available, is preferred.

[0041] When the conductive filler is metal fine particles, the shape of the conductive filler is not particularly limited, and can be appropriately selected from spherical, flat, scale-like, dendritic, rod-like, fibrous, and other shapes.

[0042] The content of the conductive filler in the conductive adhesive layer 20 is preferably 5 to 40 wt %, and more preferably 5 to 30 wt %. If the content of the conductive filler is less than 5 wt %, it becomes difficult to obtain sufficient conductivity. If the content of the conductive filler exceeds 40 wt %, the conductive adhesive layer becomes hard and is likely to lose flexibility.

[0043] (Metal Layer) The material constituting the metal layer 30 is not particularly limited, but preferably contains at least one metal selected from the group consisting of copper, silver, gold, aluminum, nickel, tin, palladium, chromium, titanium, and zinc. The metal foil may also be made of an alloy of at least two metals selected from this group. Metal foils made of these metals can provide good electromagnetic wave shielding.

[0044] The metal layer 30 may be a rolled metal foil, a metal plated layer, or a metal vapor deposition layer.

[0045] The thickness of the metal layer 30 is preferably 0.1 to 10 μm, and more preferably 0.5 to 6 μm. If the thickness of the metal layer is less than 0.1 μm, the metal layer will be too thin and will have low strength. This will result in reduced bending resistance. In addition, it will be difficult to sufficiently reflect and absorb electromagnetic waves, which will tend to reduce the electromagnetic wave shielding properties. If the thickness of the metal layer exceeds 10 μm, flexibility will tend to decrease. In addition, the entire electromagnetic wave shielding film will become thicker and more difficult to handle.

[0046] (Protective Layer) The material of the protective layer 40 is not particularly limited, but it is preferably composed of a thermoplastic resin composition, a thermosetting resin composition, an active energy ray curable composition, or the like.

[0047] The thermoplastic resin composition 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, an imide-based resin composition, and an acrylic-based resin composition.

[0048] The thermosetting resin composition is not particularly limited, but may include at least one resin composition selected from the group consisting of an epoxy-based resin composition, a urethane-based resin composition, a urethane-urea-based resin composition, a styrene-based resin composition, a phenol-based resin composition, a melamine-based resin composition, an acrylic-based resin composition, and an alkyd-based resin composition.

[0049] The active energy ray-curable composition is not particularly limited, but examples thereof include polymerizable compounds having at least two (meth)acryloyloxy groups in the molecule.

[0050] The protective layer 40 may be made of a single material, or may be made of two or more materials.

[0051] The protective layer 40 may contain, as needed, 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.

[0052] The thickness of the protective layer 40 is not particularly limited and can be set appropriately as needed, but is preferably 1 to 15 μm, and more preferably 3 to 10 μm. If the protective layer is less than 1 μm thick, it is too thin and does not adequately protect the metal layer and the conductive adhesive layer. If the protective layer is more than 15 μm thick, it is too thick and the protective layer is difficult to bend, and the protective layer itself is easily damaged. This makes it difficult to apply to components that require bending resistance.

[0053] Next, a shielded printed wiring board using the electromagnetic wave shielding film of the present invention will be described. Fig. 2 is a cross-sectional view schematically showing an example of a shielded printed wiring board using the electromagnetic wave shielding film of the present invention.

[0054] 2 is composed of a printed wiring board 50 and an electromagnetic wave shielding film 10. The printed wiring board 50 includes a base film 51, a printed circuit 52 disposed on the base film 51, and a coverlay 53 disposed so as to cover the printed circuit 52. In the printed wiring board 50, the printed circuit 52 includes a ground circuit 52a, and the coverlay 53 has an opening 53a formed therein that exposes the ground circuit 52a.

[0055] In the shielded printed wiring board 1 , the electromagnetic wave shielding film 10 is disposed on the printed wiring board 50 so that the coverlay 53 and the conductive adhesive layer 20 are in contact with each other.

[0056] In the shielded printed wiring board 1, the conductive adhesive layer 20 fills the opening 53a in the coverlay 53 and is in contact with the ground circuit 52a. This configuration can improve the shielding characteristics of the electromagnetic wave shielding film 10.

[0057] Furthermore, both the base film 51 and the coverlay 53 are preferably made of engineering plastics, such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide (PPS).

[0058] The printed circuit 52 may be made of conventional circuit materials such as copper.

[0059] The base film 51 and the printed circuit 52 may be bonded with an adhesive, or may be bonded without adhesive, similar to a so-called adhesiveless copper-clad laminate. The coverlay 53 may be formed by bonding multiple flexible insulating films with an adhesive, or may be formed by a series of methods such as coating a photosensitive insulating resin, drying, exposing, developing, and heat treating.

[0060] This specification describes the following:

[0061] The present disclosure (1) is an electromagnetic wave shielding film in which a protective layer, a metal layer, and a conductive adhesive layer are laminated in this order, and the conductive adhesive layer is characterized in that it contains an epoxy resin having a weight-average molecular weight Mw of 50,000 or more, a curing agent having a carboxy group, a nitrogen-containing organic filler, a phosphorus-containing liquid flame retardant, and a conductive filler.

[0062] The present disclosure (2) is the electromagnetic wave shielding film according to the present disclosure (1), wherein the epoxy equivalent of the epoxy resin is 7,000 to 10,000 g / eq.

[0063] The present disclosure (3) is the electromagnetic wave shielding film according to the present disclosure (1) or (2), wherein the epoxy resin comprises at least one selected from the group consisting of bisphenol A type epoxy resins, bisphenol F type epoxy resins, and bisphenol A / bisphenol F copolymer type epoxy resins.

[0064] The present disclosure (4) is the electromagnetic wave shielding film according to any one of the present disclosures (1) to (3), wherein the epoxy resin contains a polymer having a polymer unit represented by the following general formula (1):

[0065] (In formula (1), R １ and R ２ are each hydrogen or a methyl group, and R １ and R ２ may be the same or different.)

[0066] The present disclosure (5) is the electromagnetic wave shielding film according to any one of the present disclosures (1) to (4), wherein the epoxy resin contains a polymer represented by the following general formula (2):

[0067] (In formula (2), R １ , R ２ , R ３ and R ４ are each hydrogen or a methyl group, and R １ , R ２ , R ３ and R ４ may be the same or different.)

[0068] The present disclosure (6) is the electromagnetic wave shielding film according to any one of the present disclosures (1) to (5), wherein the content of the epoxy resin is 20 to 50 wt %.

[0069] The present disclosure (7) is the electromagnetic wave shielding film according to any one of the present disclosures (1) to (6), in which the content of the liquid flame retardant is 10 to 19 wt %.

[0070] Examples will be given below to explain the present invention more specifically, but the present invention is not limited to these examples.

[0071] (Example 1) to (Example 7) and (Comparative Example 1) to (Comparative Example 6) Conductive adhesive compositions were prepared by mixing the materials shown in Table 1. The numbers in Table 1 are in wt %. The materials in Table 1 are as follows. Epoxy resin 1: bisphenol A / bisphenol F copolymer epoxy resin, weight average molecular weight Mw: 60,000, epoxy equivalent: 8,800 g / eq. Epoxy resin 2: bisphenol A type epoxy resin, weight average molecular weight Mw: 470, epoxy equivalent: 250 g / eq. Epoxy resin 3: bisphenol A type epoxy resin, weight average molecular weight Mw: 45,000, epoxy equivalent: 7,300 g / eq. Epoxy resin 4: epoxy resin, weight average molecular weight Mw: 35,000, epoxy equivalent: 12,500 g / eq. Curing agent 1: polyester-modified urethane having a carboxy group, acid value: 20 mg KOH / g. Curing agent 2: polyfunctional glycidyl amine, epoxy equivalent: 100 g / eq. Curing agent 3: imidazole (curing initiation temperature: 90°C). Curing agent 4: imidazole (curing initiation temperature: 130°C). Nitrogen-containing organic filler: melamine cyanurate. Phosphorus-containing liquid flame retardant: phosphate ester (bisphenol A bis(diphenyl phosphate)) Conductive filler: 7% silver-coated atomized copper powder

[0072]

[0073] A protective layer made of epoxy resin with a thickness of 5 μm was prepared. Next, electrolytic plating was performed on the protective layer to form a copper layer with a thickness of 2.0 μm. Thereafter, each of the prepared conductive adhesive compositions was applied to the copper layer to a thickness of 20 μm, thereby producing each electromagnetic wave shielding film.

[0074] [Solder Float Test] A copper-clad laminate (polyimide film substrate / adhesive layer / copper foil or electroless gold-plated copper foil) was baked at 135°C for 60 minutes, and then the electromagnetic wave shielding film according to each Example and Comparative Example was hot-pressed onto the polyimide film substrate side of the copper-clad laminate at 170°C, 3 MPa, and 30 minutes to prepare a test laminate. The test laminate was then baked at 135°C for 60 minutes. The test laminate was then passed through an atmospheric reflow oven with a maximum setting temperature of 267°C twice. Test laminates were prepared in their initial state and in a constant temperature and humidity chamber where they were left for a predetermined period of time (24 hours, 48 ​​hours, and 72 hours) at 30°C and 60% RH. The test laminate was then floated in a solder bath (temperature: 288°C) with the electromagnetic wave shielding film side facing up. The conditions for floating in the solder bath were 10 seconds x 3 times. The test laminate was then removed from the solder bath and observed from the electromagnetic wave shielding film side to determine whether or not any swelling had occurred in the electromagnetic wave shielding film, and the solder float resistance was evaluated. The evaluation criteria were as follows. The results are shown in Table 1. A: No swelling of the electromagnetic wave shielding film was observed even after leaving it in a constant temperature and humidity chamber for 72 hours. B: Swelling of the electromagnetic wave shielding film was observed after leaving it in a constant temperature and humidity chamber for 48 hours. C: Swelling of the electromagnetic wave shielding film was observed after leaving it in a constant temperature and humidity chamber for 24 hours. D: Swelling of the electromagnetic wave shielding film was observed in the initial state.

[0075] [Heat Resistance Test] FIG. 3 is a schematic diagram of a method for measuring the resistance value of an electromagnetic wave shielding film in a heat resistance test. The electromagnetic wave shielding film 110 in FIG. 3 is a schematic representation of the electromagnetic wave shielding film according to each example and comparative example. The electromagnetic wave shielding film 110 is formed by sequentially laminating a protective layer 140, a metal layer 130, and a conductive adhesive layer 120. In addition, for the heat resistance test, a model substrate 150 is prepared, which includes a base film 151, multiple measurement printed circuits 152 formed on the base film 151, and a coverlay 153 covering the measurement printed circuits 152, with an opening 153a formed in the coverlay 153 to expose the measurement printed circuits 152. The opening 153a is a circle with a diameter of 1 mm.

[0076] In the heat resistance test, as shown in FIG. 3 , the electromagnetic wave shielding film 110 was placed on the model substrate 150 so that the conductive adhesive layer 120 of the electromagnetic wave shielding film 110 was in contact with the measurement printed circuit 152, and the film was pressurized and heated under conditions of 170°C, 3 MPa, and for 3 minutes, and then after-cured at 150°C for 1 hour, thereby attaching the electromagnetic wave shielding film 110 to the model substrate 150.

[0077] After leaving the model substrate 150 at 60°C for three days, the resistance value between the measurement printed circuits 152 of the model substrate 150 to which the electromagnetic wave shielding film 110 was attached was measured using a resistance meter 160. This resistance value was defined as the "initial resistance value." The results are shown in Table 1.

[0078] The reflow resistance of the model substrate 150 to which the electromagnetic wave shielding film 110 was attached was evaluated after leaving it at 60°C for three days. The reflow conditions assumed lead-free solder, and a temperature profile was set such that the shielding film on the shielded printed wiring board was exposed to 265°C for 10 seconds. The resistance value between the measurement printed circuits 152 after the reflow process was performed a total of five times under these conditions was measured using a resistance meter 160. This resistance value was designated the "resistance value after five reflows." This heating cycle process simulated the reflow process in which electronic components are mounted after the electromagnetic wave shielding film is attached to a printed wiring board. The results are shown in Table 1.

[0079] Furthermore, after the reflow process was performed a total of five times, each electromagnetic wave shielding film was observed to check whether or not swelling had occurred in the electromagnetic wave shielding film placed in the opening 153a. The results are shown in Table 1.

[0080] [Adhesion Test] The electromagnetic wave shielding films according to each Example and Comparative Example were pressed against the polyimide film substrate side of a copper-clad laminate (polyimide film substrate / adhesive layer / electrolessly gold-plated copper foil) under conditions of 2 MPa, 170°C, 10 seconds, and 180 seconds. Subsequently, each electromagnetic wave shielding film attached to the copper-clad laminate was hot-pressed against the bonding film side of a reinforcing film (a film in which a bonding film is laminated on a polyimide film substrate) under conditions of 3 MPa, 170°C, and 3 minutes to produce a laminate. These laminates were then heated at 150°C and 60 minutes for after-curing. Next, the reinforcing films of these laminates were attached to a fixing plate with double-sided tape to prepare sample laminates. Then, with the sample laminate fixed, the copper-clad laminate was pulled at a pulling speed of 50 mm / min and a pulling angle of 180° to peel the copper-clad laminate and each electromagnetic wave shielding film, and the average peel force at this time was measured. The evaluation test was carried out five times, and the results are shown in Table 1.

[0081] As shown in Table 1, it was found that the electromagnetic wave shielding films according to each example were less likely to experience swelling of the conductive adhesive layer due to heating, and had sufficiently high resistance to solder float.

[0082] REFERENCE SIGNS LIST 1 Shielded printed wiring board 10, 110 Electromagnetic wave shielding film 20, 120 Conductive adhesive layer 30, 130 Metal layer 40, 140 Protective layer 50 Printed wiring board 51, 151 Base film 52, Printed circuit 52a Ground circuit 53, 153 Coverlay 53a, 153a Opening 150 Model board 152 Measurement printed circuit 160 Resistance meter

Claims

1. An electromagnetic wave shielding film comprising a protective layer, a metal layer, and a conductive adhesive layer laminated in that order, the conductive adhesive layer comprising an epoxy resin having a weight average molecular weight Mw of 50,000 or more, a curing agent having a carboxy group, a nitrogen-containing organic filler, a phosphorus-containing liquid flame retardant, and a conductive filler.

2. The electromagnetic wave shielding film according to claim 1, wherein the epoxy equivalent of the epoxy resin is 7,000 to 10,000 g / eq.

3. An electromagnetic wave shielding film as described in claim 1 or 2, wherein the epoxy resin comprises at least one selected from the group consisting of bisphenol A type epoxy resins, bisphenol F type epoxy resins and bisphenol A / bisphenol F copolymer type epoxy resins.

4. An electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the epoxy resin contains a polymer having a polymer unit represented by the following general formula (1): (In formula (1), R １ and R ２ are each hydrogen or a methyl group, R １ and R ２ may be the same or different.) 5. An electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the epoxy resin contains a polymer represented by the following general formula (2): (In formula (2), R １ , R ２ , R ３ and R ４ are each hydrogen or a methyl group, R １ , R ２ , R ３ and R ４ may be the same or different.) 6. An electromagnetic wave shielding film according to any one of claims 1 to 5, wherein the content of the epoxy resin is 20 to 50 wt %.

7. An electromagnetic wave shielding film according to any one of claims 1 to 6, wherein the content of the liquid flame retardant is 10 to 19 wt %.

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