Electromagnetic wave shielding film and printed wiring board with electromagnetic wave shielding film

Abstract

The present invention provides a practical electromagnetic wave shielding film which exhibits good adhesion and maintains a low connection resistance value even after being placed in a high-temperature, high-humidity environment, and which is highly versatile. The electromagnetic wave shielding film is formed by sequentially stacking an insulating resin layer, a shielding layer, and a conductive adhesive layer, the conductive adhesive layer being formed using a conductive adhesive composition containing an adhesive component and conductive particles, the adhesive component having a water absorption of less than 2.0%, the adhesive component containing a thermosetting resin, the thermosetting resin containing an epoxy resin having a structural formula represented by the following general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g / eq. (In the above formula (1), R1 represents a hydrocarbon group having 1 to 35 carbon atoms, R2 represents hydrogen or a methyl group, and n represents an integer of 1 to 10.)

Description

TECHNICAL FIELD

[0001] The present application relates to an electromagnetic wave shielding film and a printed wiring board with an electromagnetic wave shielding film printed thereon. BACKGROUND

[0002] In order to shield electromagnetic wave noise generated from a flexible printed wiring board (hereinafter also referred to as FPC), electromagnetic wave noise from the outside, a method is known in which an electromagnetic wave shielding film having an insulating resin layer, a metal thin film layer (hereinafter also referred to as a shielding layer or an electromagnetic wave shielding layer), and a conductive adhesive layer is attached to a flexible printed wiring board via an insulating film (hereinafter, also referred to as a cover film).

[0003] In such a method, the conductive adhesive layer of the electromagnetic wave shielding film of the printed wiring board is connected to a ground circuit of the printed wiring board through an opening portion provided in the insulating film covering the ground circuit and is shielded.

[0004] As a conductive adhesive composition constituting the conductive adhesive layer of the electromagnetic wave shielding film, various conductive adhesive compositions are known (for example, refer to Patent Documents 1 and 2).

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: JP Patent Publication No. 2019-196458

[0008] Patent Document 2: JP Patent No. 5854248 SUMMARY

[0009] (PROBLEMS TO BE SOLVED BY THE INVENTION)

[0010] In addition, for the electromagnetic wave shielding film, in addition to the bending resistance and heat resistance required for the entire flexible printed wiring board, durability of maintaining high adhesion and low connection resistance value under a high temperature and high humidity environment is also required.

[0011] However, when the electromagnetic wave shielding film is left under a high temperature and high humidity environment, the adhesion decreases due to the degradation of the adhesive layer over time, and the conductive particles made of metal and the shielding layer are oxidized, and thus there is a problem that the low connection resistance value cannot be maintained after being left under a high temperature and high humidity environment.

[0012] In the above-described Patent Document 1, it is described that the adhesion under a high temperature and high humidity environment is improved by using a specific ratio of an adhesive composition, but there is no particular mention of the connection resistance value when left under a high temperature and high humidity environment. From the viewpoint of providing an electromagnetic wave shielding film that can exhibit good adhesion and maintain a low connection resistance value even after being left under a high temperature and high humidity environment, there is room for improvement.

[0013] In addition, in the above-described Patent Document 2, it is described that by using surface-coated conductive fine particles, it is possible to provide a conductive adhesive having high connection reliability even after hygrothermal aging, but in the technology of the above-described Patent Document 2, there is a problem that the selection of the conductive fine particles becomes complicated and the manufacturing cost is increased, and there is a lack of versatility.

[0014] Therefore, an object of the present application is to provide a practical electromagnetic wave shielding film having high versatility, which can exhibit good adhesion and maintain a low connection resistance value even after being placed in a high-temperature high-humidity environment.

[0015] (Technical Solution for Solving the Problem)

[0016] As a result of repeated diligent studies by the inventors of the present application in order to solve the above-described problem, it was found that an electromagnetic wave shielding film which solves the above-described problem by using an adhesive component exhibiting a specific water absorption as a conductive adhesive composition used in a conductive adhesive layer constituting an electromagnetic wave shielding film and containing a thermosetting resin including a specific epoxy resin, thereby completing the present application.

[0017] The present application includes the following modes.

[0018] [1] An electromagnetic wave shielding film which is formed by sequentially stacking an insulating resin layer, a shielding layer, and a conductive adhesive layer, the conductive adhesive layer being formed using a conductive adhesive composition containing an adhesive component and conductive particles, the adhesive component having a water absorption of less than 2.0%, the adhesive component containing a thermosetting resin, the thermosetting resin containing an epoxy resin having a structural formula represented by the following general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g / eq.

[0019]

Chemical Formula 1

[0020]

[0021] (In the above-described formula (1), R1 represents a hydrocarbon group having 1 to 35 carbon atoms, R2 represents hydrogen or a methyl group, and n represents an integer of 1 to 10.)

[0022] [2] The electromagnetic wave shielding film described in [1], further containing 30 to 70% by mass of the epoxy resin in the adhesive component.

[0023] [3] The electromagnetic wave shielding film described in [1] or [2], wherein the epoxy equivalent is 215 to 400 g / eq.

[0024] [4] The electromagnetic wave shielding film described in any one of [1] to [3], wherein R1 in the general formula (1) is a hydrocarbon group including a structure of an alicyclic hydrocarbon or an aromatic hydrocarbon.

[0025] [5] The electromagnetic wave shielding film described in [3] or [4], wherein the epoxy equivalent is 250 to 400 g / eq.

[0026] [6] The electromagnetic wave shielding film described in any one of [1] to [5], wherein a rubber component is contained in the adhesive component.

[0027] [7] The electromagnetic wave shielding film described in [6], wherein the acid value of the rubber component is 20 mgKOH / g or less.

[0028] [8] The electromagnetic wave shielding film described in [6] or [7], wherein the epoxy equivalent of the rubber component is 0.05 eq / kg or more.

[0029] [9] The electromagnetic wave shielding film described in any one of [6] to [8], wherein the glass transition temperature of the rubber component is 10°C or more.

[0030]

[10] An electromagnetic wave shielding film-printed wiring board having: a printed wiring board provided with a printed circuit on at least one side of a substrate; an insulating film adjacent to the side of the printed wiring board on which the printed circuit is provided; and the electromagnetic wave shielding film described in any one of [1] to [9] provided so that the electrically conductive adhesive layer is adjacent to the insulating film.

[0031] (EFFECT OF INVENTION)

[0032] According to the present application, a practical electromagnetic wave shielding film having high versatility, which exhibits good adhesion and maintains a low connection resistance value even after being placed in a high-temperature high-humidity environment, can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a cross-sectional view showing an embodiment of the electromagnetic wave shielding film.

[0034] Figure 2 is a cross-sectional view showing another embodiment of the electromagnetic wave shielding film.

[0035] Figure 3 is a cross-sectional view showing a manufacturing process of the electromagnetic wave shielding film as Figure 1

[0036] Figure 4 is a cross-sectional view showing another embodiment of the manufacturing process of the electromagnetic wave shielding film as Figure 1

[0037] ​​Figure 5 is a cross-sectional view showing a manufacturing process of the electromagnetic wave shielding film of Figure 1

[0038] Figure 6 Figure 1 is a cross-sectional view showing a manufacturing process of the electromagnetic wave shielding film of

[0039] Figure 7 is a cross-sectional view showing an embodiment of the printed wiring board with the electromagnetic wave shielding film.

[0040] Figure 8 is a cross-sectional view showing a manufacturing process of the printed wiring board with the electromagnetic wave shielding film of Figure 7 DETAILED DESCRIPTION

[0041] Hereinafter, the electromagnetic wave shielding film of the present application will be described in detail, but the description of the constituent elements described below is an example as one embodiment of the present application, and is not limited to these contents.

[0042] The definitions of the following terms are applicable in the present specification and claims.

[0043] "The isotropic conductive adhesive layer" means a conductive adhesive layer having conductivity in the thickness direction and the surface direction.

[0044] "The anisotropic conductive adhesive layer" means a conductive adhesive layer having conductivity in the thickness direction, but not having conductivity in the surface direction.

[0045] "The conductive adhesive layer not having conductivity in the surface direction" means a conductive adhesive layer having a surface resistance of 1 x 10 4 Ω or more.

[0046] The average particle diameter of the conductive particles is a value obtained by randomly selecting 30 conductive particles from a microscope image of the conductive particles, measuring the minimum diameter and the maximum diameter of each of the conductive particles, taking the central value of the minimum diameter and the maximum diameter as the particle diameter of one particle, and performing an arithmetic mean of the particle diameters of the 30 conductive particles measured.

[0047] The film thickness of the film (release film, insulating film, etc.), the coated film (insulating resin layer, conductive adhesive layer, etc.), the shielding layer (electromagnetic wave shielding layer), etc. is a value obtained by observing the cross section of the measurement object using a microscope and measuring the thickness at 5 places and performing an average.

[0048] The surface resistance is less than 10 6 ​​​In the case of Ω / □, the surface resistivity is measured using a low-resistivity resistivity meter (e.g., Mitsubishi Chemical Corporation, Loresta GP, ASP probe) via the four-terminal method (according to JIS K 7194:1994 and JIS R 1637:1998), at 10 6 For values ​​above Ω / □, the surface resistivity is measured using a high-resistivity resistivity meter (e.g., Mitsubishi Chemical Corporation, Hiresta UP, URS probe) via the double-ring method (according to the method in JIS K 6911:2006).

[0049] (Electromagnetic wave shielding film)

[0050] The electromagnetic wave shielding film of the present invention is formed by sequentially stacking an insulating resin layer, a shielding layer, and a conductive adhesive layer.

[0051] The conductive adhesive layer is formed using a conductive adhesive composition containing adhesive components and conductive particles.

[0052] The water absorption rate of the adhesive components is less than 2.0%.

[0053] The adhesive contains thermosetting resin.

[0054] Thermosetting resins contain epoxy resins having the structure shown in the following general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g / eq.

[0055]

Chemistry 2

[0056]

[0057] (In the above formula (1), R1 represents a hydrocarbon group with 1 to 35 carbon atoms, R2 represents hydrogen or methyl, and n represents an integer from 1 to 10.)

[0058] Figure 1 This is a cross-sectional view showing one embodiment of the electromagnetic wave shielding film of the present invention.

[0059] Figure 2 This is a cross-sectional view showing another embodiment of the electromagnetic wave shielding film of the present invention.

[0060] The electromagnetic wave shielding film 1 has: an insulating resin layer 10; a shielding layer 20 adjacent to the insulating resin layer 10; a conductive adhesive layer 22 adjacent to the shielding layer 20 on the opposite side of the insulating resin layer 10; a first release film 30 adjacent to the insulating resin layer 10 on the opposite side of the shielding layer 20; and a second release film 40 adjacent to the conductive adhesive layer 22 on the opposite side of the shielding layer 20.

[0061] The electromagnetic wave shielding film 1 of the first embodiment is an example in which the adhesive layer 22 is an anisotropic conductive adhesive layer 24.

[0062] The electromagnetic wave shielding film 1 of the second embodiment is an example in which the adhesive layer 22 is an isotropic conductive adhesive layer 26.

[0063] <Insulating resin layer>

[0064] The insulating resin layer 10 is a protective layer of the shielding layer 20 after the electromagnetic wave shielding film 1 is attached to the surface of the insulating film provided on the surface of the printed wiring board and the first release film 30 is peeled off.

[0065] As the insulating resin layer 10, a coating film formed by coating a composition containing a thermosetting resin and a curing agent and semi-curing or curing it, a coating film formed by coating a coating liquid containing a thermosetting resin, a curing agent and a solvent and drying, semi-curing or curing it, and the like can be given. As the insulating resin layer 10, from the viewpoint of further improving the adhesiveness of the insulating resin layer 10 to the shielding layer 20, a coating film formed by coating a coating liquid containing a resin material (combination of a thermosetting resin and a curing agent) and a solvent and drying it, and semi-curing or curing it as necessary is preferred.

[0066] As the thermosetting resin, an amide resin, an epoxy resin, a phenol resin, an amino resin, an alkyd resin, a polyurethane resin, a synthetic rubber, an ultraviolet curing acrylate resin, and the like can be given. As the thermosetting resin, from the aspect of excellent heat resistance, an amide resin, an epoxy resin is preferred.

[0067] As the curing agent, a publicly known curing agent corresponding to the type of the thermosetting resin can be given.

[0068] In order to hide the printed circuit of the printed wiring board with the electromagnetic wave shielding film or to impart designability to the printed wiring board with the electromagnetic wave shielding film, the insulating resin layer 10 can contain either or both of a colorant (pigment, dye, and the like) and a filler.

[0069] As either or both of the colorant and the filler, from the viewpoint of weather resistance, heat resistance, and hiding property, a pigment or a filler is preferred, and from the viewpoint of hiding property and designability of the printed circuit, a black pigment or a combination of a black pigment and another pigment or filler is more preferred.

[0070] The insulating resin layer 10 can contain other components as necessary within a range not impairing the effects of the present application.

[0071] From the viewpoint of electrical insulation, the surface resistance of the insulating resin layer 10 is preferably 1 x 10 6 Ω or more. From the practical viewpoint, the surface resistance of the insulating resin layer 10 is preferably 1 x 10 19Ω or less.

[0072] The thickness of the insulating resin layer 10 is preferably 0.1 μm or more and 30 μm or less, more preferably 0.5 μm or more and 20 μm or less, and further preferably 3 μm or more and 15 μm or less. If the thickness of the insulating resin layer 10 is equal to or more than the lower limit of the above range, the insulating resin layer 10 can sufficiently function as a protective layer. If the thickness of the insulating resin layer 10 is equal to or less than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thin.

[0073] <Shielding layer (electromagnetic wave shielding layer)>

[0074] The shielding layer 20 is not particularly limited as long as it has conductivity, and can be a metal film or a conductive film composed of conductive particles, or the like.

[0075] The shielding layer 20 is formed so as to extend in the planar direction, and thus has conductivity in the planar direction and functions as an electromagnetic wave shielding layer or the like.

[0076] As the metal constituting the metal film, for example, one selected from nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, and zinc, or an alloy containing any one or more of these, or the like can be given. Among these, from the viewpoints of shielding properties and economy, copper and a copper-containing alloy are preferable.

[0077] As the method of forming the metal film, for example, an evaporation film formed by physical evaporation (vacuum evaporation, sputtering, ion beam evaporation, electron beam evaporation, or the like), a plating film formed by plating, a metal foil, or the like can be given. Among these, from the aspect that the conductivity in the planar direction is excellent, a vacuum evaporation film or a sputtering film formed by a vacuum film formation method (vacuum evaporation method, sputtering method, or the like), or a plating film formed by an electroplating method is preferable. From the viewpoints that the thickness can be made thin, and even if the thickness is thin, the conductivity in the planar direction is excellent, and the film can be formed simply by a dry process, an evaporation film using a vacuum evaporation method is more preferable. In addition, the metal film can also be a metal foil formed by rolling processing, or an electrolytic-based metal foil (for example, a special electrolytic copper foil, or the like), or the like.

[0078] In the case where the shielding layer is a conductive film composed of conductive particles, the conductive particles can be, for example, carbon, silver, copper, nickel, solder, or the like. In addition, the conductive particles can be silver-coated copper particles in which silver plating is performed on copper powder, particles in which metal plating is performed on insulating particles such as resin balls or glass beads, or the like. These conductive particles can be used alone or two or more kinds can be mixed and used.

[0079] The shape of the conductive particles can be any one of a spherical shape, a needle shape, a fibrous shape, a flaky shape, or a dendritic shape, and from the viewpoint of forming a layer, a flaky shape is preferable.

[0080] The thickness of the shielding layer 20 is preferably 0.01 μm or more and 3 μm or less, more preferably 0.05 μm or more and 2 μm or less, and even more preferably 0.1 μm or more and 1.5 μm or less. If the thickness of the shielding layer 20 is 0.01 μm or more, the shielding effect of electromagnetic wave noise becomes better. If the thickness of the shielding layer 20 is the upper limit value of the above range or less, the electromagnetic wave shielding film 1 can be made thinner. In addition, the productivity and flexibility of the electromagnetic wave shielding film 1 become better.

[0081] The surface resistance of the shielding layer 20 is preferably 0.001 Ω or more and 1 Ω or less, and more preferably 0.001 Ω or more and 0.1 Ω or less. If the surface resistance of the shielding layer 20 is the lower limit value of the above range or more, the shielding layer 20 can be made sufficiently thin. If the surface resistance of the shielding layer 20 is the upper limit value of the above range or less, the function as an electromagnetic wave shielding layer can be sufficiently exerted.

[0082] <Conductive adhesive layer>

[0083] The conductive adhesive layer 22 is a layer for adhering the electromagnetic wave shielding film 1 to a printed wiring board with an insulating film.

[0084] The conductive adhesive layer 22 is a conductive adhesive layer having conductivity for electrically connecting the electromagnetic wave shielding film 1 to a printed wiring board.

[0085] The conductive adhesive layer has conductivity at least in the thickness direction and has adhesiveness.

[0086] As the conductive adhesive layer, an anisotropic conductive adhesive layer 24 having conductivity in the thickness direction and not having conductivity in the planar direction, or an isotropic conductive adhesive layer 26 having conductivity in the thickness direction and the planar direction can be given. As the conductive adhesive layer, from the viewpoint that the transmission characteristics are good and the flexibility of the electromagnetic wave shielding film 1 becomes good because the conductivity is not present in the planar direction, the anisotropic conductive adhesive layer 24 is preferable. As the conductive adhesive layer, from the viewpoint that the function as an electromagnetic wave shielding layer can be sufficiently exerted, the isotropic conductive adhesive layer 26 is preferable.

[0087] The conductive adhesive layer is formed using a conductive adhesive composition containing an adhesive component and conductive particles, the adhesive component containing a thermosetting resin.

[0088] <<Adhesive component>>

[0089] The water absorption of the adhesive component is less than 2.0%.

[0090] The adhesive component contains a thermosetting resin.

[0091] The thermosetting resin contains an epoxy resin having a structural formula represented by the following general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g / eq.

[0092] [Chem. 3]

[0093]

[0094] (In the above formula (1), R1 represents a hydrocarbon group having 1 to 35 carbon atoms, R2 represents hydrogen or a methyl group, and n represents an integer of 1 to 10.)

[0095] As R1 in the above formula (1) (a hydrocarbon group having 1 to 35 carbon atoms), there is no particular limitation, and it can be, for example, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a hydrocarbon group composed of an appropriate combination thereof.

[0096] As R1, for example, the following groups can be exemplified.

[0097] [Chem. 4]

[0098]

[0099] R2 in the above formula (1) is more hydrophobic than hydrogen, and thus can reduce the hygroscopicity of the adhesive component, and is more preferable.

[0100] Note that the epoxy resin having a structural formula represented by the above general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g / eq (hereinafter, this epoxy resin will also be referred to as "specific epoxy resin") can contain one or two or more kinds.

[0101] As the epoxy resin, by using an epoxy resin having a multifunctional structure represented by the above formula (1), the crosslinking density of the conductive adhesive layer at the time of curing can be increased, and the conductive particles can be stably immobilized, and thus the conductive adhesive layer can ensure excellent connectivity.

[0102] In the adhesive component, it is preferable to contain 30 to 70 mass% of the specific epoxy resin.

[0103] If the content of the specific epoxy resin in the adhesive component is 30 mass% or more, the problem of being unable to ensure connectivity due to poor curing can be effectively prevented. In addition, if it is 70 mass% or less, the problem of being unable to ensure connectivity due to the influence of moisture absorption can be effectively prevented.

[0104] The specific epoxy resin exhibits an epoxy equivalent of 170 to 400 g / eq.

[0105] By limiting the epoxy equivalent, the OH group (hydrophilicity) of the ring-opened epoxy and the functional group R1 (hydrophobicity) at the time of curing can be optimized.

[0106] If the epoxy equivalent weight is too small, the hydrophobic effect of the functional group R1 is not sufficient, and the conductive particles can be oxidized due to moisture absorption, and the connectivity can be poor. On the other hand, if the epoxy equivalent weight is too large, the OH group is small, the adhesion and crosslinking are poor, and the connectivity can be poor.

[0107] As the epoxy equivalent weight, it is preferable to be 190 g / eq or more, more preferable to be 215 g / eq or more, further preferable to be 245 g / eq or more, particularly preferable to be 250 g / eq or more, and in addition, preferable to be 300 g / eq or less.

[0108] The measurement of the epoxy equivalent weight can be performed in accordance with JIS K7236:2001.

[0109] In the present application, by making the water absorption of the adhesive component in the conductive adhesive layer be less than 2.0%, and by incorporating a specific epoxy resin into the adhesive component, the degradation of the conductive adhesive layer, and the oxidation due to moisture absorption of the conductive particles and the shielding layer can be suppressed, and an electromagnetic wave shielding film that can maintain a low connection resistance value even in a high temperature and high humidity environment can be formed.

[0110] The adhesive component can also contain an epoxy resin other than the specific epoxy resin, and other thermosetting resins other than the epoxy resin, within a range that does not affect the effects of the present application.

[0111] As the other thermosetting resins, for example, phenol resin, amino resin, alkyd resin, polyurethane resin, synthetic rubber, ultraviolet-curable acrylate resin, and the like can be mentioned.

[0112] In addition, the adhesive component contains a curing agent in addition to the above-mentioned thermosetting resins.

[0113] The curing agent can be a latent curing adhesive that is cured by reacting with the thermosetting resin by heating.

[0114] As the curing agent, there are a curing agent of the polyfunctional type that has multiple functional groups that can react with the thermosetting resin, and a catalyst type curing agent that releases strain energy of an epoxy group, or the like. Since the storage stability of the adhesive component is good, a catalyst type curing agent is preferable.

[0115] The content of the catalyst type curing agent in the adhesive component is preferably 0.1 parts by mass or more and 50 parts by mass or less, more preferably 0.5 parts by mass or more and 30 parts by mass or less, and further preferably 1 part by mass or more and 10 parts by mass or less, with respect to 100 parts by mass of the thermosetting resin.

[0116] In addition, as other components than the thermosetting resin that can be contained in the adhesive component, various components such as a rubber component, a tackifier, a curing accelerator, a low-stress agent (stress relaxer), and the like can be exemplified in addition to the above-described curing agent.

[0117] The adhesive component can contain a rubber component (carboxyl-modified nitrile rubber, acrylic rubber, or the like) for imparting flexibility, a tackifier, or the like. In addition, the adhesive component can also contain a curing accelerator, a low-stress agent (stress relaxer), or the like.

[0118] The acid value of the rubber component contained in the adhesive component is preferably 20 mgKOH / g or less from the viewpoints of adhesion and water absorption. In addition, the epoxy equivalent of the rubber component is preferably 0.05 eq / kg or more and 1 eq / kg or less from the viewpoint of reactivity with the epoxy resin. In addition, the glass transition temperature of the rubber component is preferably 10°C or more.

[0119] By causing the adhesive component to contain a rubber component satisfying the above-described requirements, an electromagnetic wave shielding film that exhibits good adhesion and can maintain a low connection resistance value for a longer period of time even after being left in a high-temperature high-humidity environment can be provided.

[0120] As the low-stress agent, acrylonitrile butadiene rubber (NBR), acrylic rubber, styrene butadiene rubber, vinyl acetate resin, silicone resin, or the like can be exemplified.

[0121] The content of the low-stress agent in the adhesive component is preferably 10% by mass or more and 80% by mass or less, and more preferably 30% by mass or more and 70% by mass or less, in 100% by mass of the adhesive component (solid content) before curing. If the content of the low-stress agent is within the above-described range, the flexibility of the conductive adhesive layer is excellent.

[0122] The water absorption of the adhesive component is less than 2.0%.

[0123] By limiting the water absorption of the adhesive component, the compounding conditions are also limited for other components than the specific epoxy resin.

[0124] If the water absorption of the adhesive component is too high, for example, the oxidation of the conductive particles is promoted, the connectivity becomes poor, and in addition, expansion occurs due to the vaporization of moisture, and the heat resistance also deteriorates. On the other hand, if the water absorption of the adhesive component is too low, the compatibility with the epoxy resin becomes poor.

[0125] The water absorption of the adhesive component can be found in accordance with JIS K 7209 in the following manner.

[0126] [Water Absorption]

[0127] The adhesive components are coated onto a PET substrate and heated at 150°C for 1 hour to create a cured layer.

[0128] The test piece consisting of the cured layer was exposed to 85°C for 48 hours at a relative humidity of 85%. Then, the change in mass of the test piece, i.e., the difference between the initial mass and the mass after exposure to water, was measured and expressed as a percentage of the initial mass.

[0129] <<Conductive Particles>>

[0130] In the conductive adhesive composition that forms the conductive adhesive layer, in addition to the adhesive components mentioned above, conductive particles are also contained.

[0131] like Figure 1 As shown, the anisotropic conductive adhesive layer 24 includes, for example, an adhesive 24a containing the above-mentioned resin and conductive particles 24b.

[0132] like Figure 2 As shown, the isotropic conductive adhesive layer 26 includes, for example, an adhesive 26a containing the above-mentioned resin and conductive particles 26b.

[0133] Examples of conductive particles include metal particles (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, etc.), graphite powder, sintered carbon particles, plated sintered carbon particles, and core-shell resin particles coated with metal. From the perspective of high conductivity, metal particles are preferred; from the perspective of low cost, copper particles are more preferred.

[0134] The average particle size of the conductive particles 24b in the anisotropic conductive adhesive layer 24 is preferably 2 μm or more and 26 μm or less, more preferably 4 μm or more and 16 μm or less. If the average particle size of the conductive particles 24b is at or above the lower limit of the above range, the stability of the electrical connection is improved, and the conductive particles 24b are less likely to impair the flowability of the resin in the anisotropic conductive adhesive layer 24. Therefore, the conformability of the insulating film of the anisotropic conductive adhesive layer 24 to the shape of the through hole can be ensured. If the average particle size of the conductive particles 24b is at or below the upper limit of the above range, the conductive particles 24b will not hinder the contact between the resin of the anisotropic conductive adhesive layer 24 and the surface of the bonded object, and sufficient adhesion can be ensured.

[0135] The average particle diameter of the conductive particles 26b in the isotropic conductive adhesive layer 26 is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.2 μm or more and 1 μm or less. If the average particle diameter of the conductive particles 26b is the lower limit value of the above range or more, the contact frequency of the conductive particles 26b increases, and the conductivity in the 3-dimensional direction can be stably improved. If the average particle diameter of the conductive particles 26b is the upper limit value of the above range or less, the conductive particles 26b do not hinder the contact of the resin of the isotropic conductive adhesive layer 26 with the surface of the adherend, and sufficient adhesion can be ensured.

[0136] The proportion of the conductive particles 24b in the anisotropic conductive adhesive layer 24 is preferably 1 vol% or more and 30 vol% or less, and more preferably 2 vol% or more and 10 vol% or less, in 100 vol% of the anisotropic conductive adhesive layer 24. If the proportion of the conductive particles 24b is the lower limit value of the above range or more, the conductivity of the anisotropic conductive adhesive layer 24 becomes good. If the proportion of the conductive particles 24b is the upper limit value of the above range or less, the adhesion, the flowability (the followability to the shape of the through-hole of the insulating film) of the anisotropic conductive adhesive layer 24 becomes good. In addition, the flexibility of the electromagnetic wave shielding film 1 becomes good.

[0137] The proportion of the conductive particles 26b in the isotropic conductive adhesive layer 26 is preferably 50 vol% or more and 80 vol% or less, and more preferably 60 vol% or more and 70 vol% or less, in 100 vol% of the isotropic conductive adhesive layer 26. If the proportion of the conductive particles 26b is the lower limit value of the above range or more, the conductivity of the isotropic conductive adhesive layer 26 becomes good. If the proportion of the conductive particles 26b is the upper limit value of the above range or less, the adhesion, the flowability (the followability to the shape of the through-hole of the insulating film) of the isotropic conductive adhesive layer 26 becomes good. In addition, the flexibility of the electromagnetic wave shielding film 1 becomes good.

[0138] The surface resistance of the anisotropic conductive adhesive layer 24 is preferably 1 x 10 4 Ω or more and 1 x 10 16 Ω or less, and more preferably 1 x 10 6 Ω or more and 1 x 10 14 Ω or less. If the surface resistance of the anisotropic conductive adhesive layer 24 is the lower limit value of the above range or more, the content of the conductive particles 24b is suppressed to be low. If the surface resistance of the anisotropic conductive adhesive layer 24 is the upper limit value of the above range or less, the anisotropy is not a problem in practice.

[0139] The surface resistance of the isotropic conductive adhesive layer 26 is preferably 0.05 Ω or more and 2.0 Ω or less, and more preferably 0.1 Ω or more and 1.0 Ω or less. If the surface resistance of the isotropic conductive adhesive layer 26 is the lower limit value of the above range or more, the content of the conductive particles 26b is suppressed to be low, the viscosity of the conductive adhesive does not become too high, and the coatability is further improved. In addition, the flowability (the followability to the shape of the through-hole of the insulating film) of the isotropic conductive adhesive layer 26 can be further improved. If the surface resistance of the isotropic conductive adhesive layer 26 is the upper limit value of the above range or less, the entire surface of the isotropic conductive adhesive layer 26 has uniform conductivity.

[0140] The thickness of the anisotropic conductive adhesive layer 24 is preferably 2 μm or more and 25 μm or less, and more preferably 5 μm or more and 20 μm or less. If the thickness of the anisotropic conductive adhesive layer 24 is the lower limit value of the above range or more, the flowability (the followability to the shape of the through-hole of the insulating film) of the anisotropic conductive adhesive layer 24 can be improved, and the through-hole of the insulating film can be sufficiently filled with the conductive adhesive. In addition, the distance between the electromagnetic wave shielding layer 20 and the printed circuit can be increased, and the transmission characteristics can be improved. If the thickness of the anisotropic conductive adhesive layer 24 is the upper limit value of the above range or less, the electromagnetic wave shielding film 1 can be made thinner. In addition, the flexibility of the electromagnetic wave shielding film 1 can be improved.

[0141] The thickness of the isotropic conductive adhesive layer 26 is preferably 2 μm or more and 20 μm or less, and more preferably 3 μm or more and 10 μm or less. If the thickness of the isotropic conductive adhesive layer 26 is the lower limit value of the above range or more, the adhesion can be improved. In addition, the flowability (the followability to the shape of the through-hole of the insulating film) of the isotropic conductive adhesive layer 26 can be improved, the through-hole of the insulating film can be sufficiently filled with the conductive adhesive, and the bending resistance can be improved, and the isotropic conductive adhesive layer 26 can not be broken even if it is repeatedly bent. If the thickness of the isotropic conductive adhesive layer 26 is the upper limit value of the above range or less, the electromagnetic wave shielding film 1 can be made thinner. In addition, the flexibility of the electromagnetic wave shielding film 1 can be improved. In addition, the film thickness of the isotropic conductive adhesive layer 26, which has a higher surface resistance than the electromagnetic wave shielding layer 20, can be made thinner, and the transmission characteristics can be improved.

[0142] <First Release Film>

[0143] The first release film 30 serves as a protective film for the insulating resin layer 10, and improves the handleability of the electromagnetic wave shielding film 1. The first release film 30 is peeled from the insulating resin layer 10 after the electromagnetic wave shielding film 1 is attached to the printed wiring board with the insulating film.

[0144] The first release film 30 has, for example, a base material layer 32 and an adhesive layer or release agent layer 34 provided on the surface of the base material layer 32 on the side of the insulating resin layer 10. Note that the adhesive layer or release agent layer 34 is also referred to as an adhesive / release agent layer 34 in this specification.

[0145] The adhesive / release agent layer 34 can be provided directly on the surface of the base material layer 32, or the base material layer 32 can be attached to the surface of the adhesive / release agent layer 34 after the adhesive / release agent layer 34 is provided on the surface of the insulating resin layer 10, whereby the adhesive / release agent layer 34 is provided on the surface of the base material layer 32.

[0146] As the resin material of the base material layer 32, polyethylene terephthalate (hereinafter also referred to as PET), polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polyolefin, polyacetate, polycarbonate, polyphenylene sulfide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, synthetic rubber, liquid crystal polymer, and the like can be given. From the viewpoint of heat resistance (dimensional stability) and price when manufacturing the electromagnetic wave shielding film 1, PET is preferable as the resin material.

[0147] The base material layer 32 can contain a coloring agent or a filler.

[0148] The thickness of the base material layer 32 is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 150 μm or less, and further preferably 25 μm or more and 100 μm or less. If the thickness of the base material layer 32 is equal to or more than the lower limit of the above range, the handleability of the electromagnetic wave shielding film 1 becomes good. If the thickness of the base material layer 32 is equal to or less than the upper limit of the above range, heat is easily transmitted to the conductive adhesive layer 22 when the electromagnetic wave shielding film 1 is thermally compressed to a printed wiring board with an insulating film.

[0149] The adhesive layer 34 or the release agent layer 34 is provided between the base material layer and the insulating resin layer.

[0150] The first release film 30 has the adhesive layer or release agent layer 34, whereby the first release film 30 can be prevented from peeling from the insulating resin layer 10 when the second release film 40 is peeled from the conductive adhesive layer 22 or when the electromagnetic wave shielding film 1 is thermally attached to a printed wiring board or the like, and the first release film 30 can sufficiently function as a protective film.

[0151] As the adhesive, a publicly known adhesive can be used.

[0152] Further, the release agent layer 34 is formed on the surface of the base material layer 32 by performing a release treatment using a release agent. The first release film 30 has the release agent layer 34, so that the first release film 30 is easily peeled off when the first release film 30 is peeled off from the insulating resin layer 10, and the insulating resin layer 10 is not easily broken.

[0153] As the release agent, a publicly known release agent can be used.

[0154] The thickness of the adhesive layer 34 is preferably 0.05 μm or more and 50.0 μm or less, and more preferably 0.1 μm or more and 25.0 μm or less. If the thickness of the adhesive layer 34 is within the above range, the surface of the first release film 30 has moderate adhesiveness.

[0155] The thickness of the release agent layer 34 is preferably 0.05 μm or more and 2.0 μm or less, and more preferably 0.1 μm or more and 1.5 μm or less. If the thickness of the release agent layer 34 is within the above range, the first release film is easily further peeled off.

[0156] <Second Release Film>

[0157] The second release film 40 is used to protect the conductive adhesive layer 22, so that the electromagnetic wave shielding film 1 has good workability. The second release film 40 is peeled off from the conductive adhesive layer 22 before the electromagnetic wave shielding film 1 is attached to the printed wiring board with an insulating film.

[0158] The second release film 40 has, for example, a base material layer 42, and a release agent layer or an adhesive layer 44 provided on the surface of the base material layer 42 on the side of the conductive adhesive layer.

[0159] Note that, in the present specification, the release agent layer or the adhesive layer 44 is also referred to as a release agent layer / adhesive layer 44.

[0160] As the resin material of the base material layer 42, the same material as the resin material of the base material layer 32 of the first release film 30 can be used.

[0161] The base material layer 42 can contain a coloring agent or a filler.

[0162] The thickness of the base material layer 42 is preferably 5 μm or more and 500 μm or less, more preferably 10 μm or more and 150 μm or less, and further preferably 25 μm or more and 100 μm or less.

[0163] The release agent layer 44 or the adhesive layer 44 is provided between the base material layer 42 and the conductive adhesive layer 22.

[0164] The release agent layer 44 is formed by applying a release treatment using a release agent to the surface of the base material layer 42. The second release film 40 has the release agent layer 44, so that the second release film 40 is easily peeled off when the second release film 40 is peeled off from the conductive adhesive layer 22, and the conductive adhesive layer 22 is not easily broken.

[0165] As the release agent, a publicly known release agent can be used.

[0166] The thickness of the release agent layer 44 is preferably 0.05 μm or more and 2.0 μm or less, and more preferably 0.1 μm or more and 1.5 μm or less. If the thickness of the release agent layer 44 is within the above range, the second release film 40 is easily further peeled off.

[0167] As the adhesive layer 44, the same adhesive layer as the adhesive layer 34 described in the column of the "first release film" above can be used.

[0168] <Configuration of electromagnetic wave shielding film>

[0169] In the present application, the electromagnetic wave shielding film can have at least an insulating resin layer, a shielding layer, and a conductive adhesive layer. In the electromagnetic wave shielding film, there are cases where the first release film and the second release film are included, and there are cases where they are not included.

[0170] For this reason, in the present specification, there are cases where the first release film and / or the second release film are included in the insulating resin layer, the shielding layer, and the conductive adhesive layer and are referred to as the electromagnetic wave shielding film, and there are cases where they are not included and are referred to as the electromagnetic wave shielding film.

[0171] <Thickness of electromagnetic wave shielding film>

[0172] The thickness of the electromagnetic wave shielding film 1 (excluding the release films) is preferably 5 μm or more and 45 μm or less, and more preferably 5 μm or more and 30 μm or less. If the thickness of the electromagnetic wave shielding film 1 (excluding the release films) is the lower limit value of the above range or more, the first release film 30 is not easily broken when it is peeled off. If the thickness of the electromagnetic wave shielding film 1 (excluding the release films) is the upper limit value of the above range or less, the printed wiring board with the electromagnetic wave shielding film can be made thin.

[0173] <Method for manufacturing electromagnetic wave shielding film>

[0174] As the first embodiment of the method for manufacturing the electromagnetic wave shielding film of the present application, for example, a method based on the following method (Al) can be given. Note that in the following method (Al), as the electromagnetic wave shielding film, a film having the insulating resin layer, the shielding layer, and the conductive adhesive layer is used. Figure 1The adhesive layer shown is an anisotropic conductive adhesive layer 24, but the present application is not limited to this adhesive layer. The manufacturing method described below is equally applicable whether the adhesive layer is an isotropic conductive adhesive layer 27 or an adhesive layer 22 that does not contain conductive particles.

[0175] Method (A1) is specifically a method having the following steps (A1-1) to (A1-4).

[0176] Hereinafter, based on the above Figure 3 Method (A1) will be described.

[0177] Step (A1-1): a step of forming the insulating resin layer 10 on one face of the first release film 30.

[0178] Step (A1-2): a step of forming the shielding layer 20 on the face of the insulating resin layer 10 opposite the first release film 30.

[0179] Step (A1-3): a step of forming the anisotropic conductive adhesive layer 24 on the face of the shielding layer 20 opposite the insulating resin layer 10.

[0180] Step (A1-4): a step of laminating the second release film 40 on the face of the anisotropic conductive adhesive layer 24 opposite the shielding layer 20.

[0181] Hereinafter, each step of method (A1) will be described in detail.

[0182] As the method of forming the insulating resin layer 10 in step (A1-1), for example, a method in which the adhesive layer / release agent layer 34 side of the first release film 30 is coated with a coating material containing a thermosetting resin and a curing agent, and is semi-cured or cured is preferred from the viewpoint of heat resistance at the time of soldering or the like.

[0183] As the coating method of the coating material, for example, a method using various coaters such as a die coater, a gravure coater, a roll coater, a curtain flow coater, a spin coater, a bar coater, a reverse coater, a kiss coater, a jet coater, a blade coater, an air knife coater, a doctor blade coater, a flow coater, a screen coater, and the like can be applied.

[0184] When semi-curing or curing the thermosetting resin, heating using a heater, an infrared lamp, or the like can be performed.

[0185] In step (A1-2), the shielding layer 20 is formed on the face of the insulating resin layer 10 opposite the first release film 30.

[0186] As a method of forming the shield layer 20, a method using a vacuum film forming method (vacuum evaporation, sputtering), a method using an electroplating method, a method of sticking a metal foil (copper foil), and the like can be given.

[0187] In the case where the film thickness of the shield layer 20 is less than 3 μm, from the viewpoint of being able to form the shield layer 20 having a desired film thickness and surface shape, a method of forming an evaporation film by vacuum evaporation or a method of forming a plated film by electroplating is preferred. From the viewpoint of being able to form the shield layer 20 having high gas permeability and easily discharging gas generated inside to the outside under high temperature conditions, and being able to easily form the shield layer 20 by a dry process, a method of forming an evaporation film by vacuum evaporation is more preferred.

[0188] In the case where the film thickness of the shield layer 20 is 3 μm or more, from the viewpoint of not causing deterioration of the insulating resin layer 10 based on a thermal process of vacuum evaporation, and being able to easily form the shield layer 20 having a desired film thickness, a method of performing lamination treatment using pressurization and / or heating to bring the insulating resin layer 10 into contact with a metal foil (copper foil) is preferred.

[0189] Here, the pressure in the pressurization treatment is preferably 0.1 kPa or more and 100 kPa or less, more preferably 0.1 kPa or more and 20 kPa or less, and further preferably 1 kPa or more and 10 kPa or less.

[0190] The heating can be performed simultaneously with the pressurization treatment. The heating temperature at this time is preferably -30°C or more and +50°C or less from the glass transition temperature of the semi-cured or cured insulating resin layer, and more preferably 50°C or more and 150°C or less.

[0191] In the process (Al-3), a conductive adhesive paint containing an adhesive 24a, a conductive particle 24b, and a solvent is applied to the surface of the shield layer 20 on the side opposite to the insulating resin layer 10.

[0192] The conductive adhesive paint applied is allowed to volatilize the solvent, thereby forming an anisotropic conductive adhesive layer 24.

[0193] As the solvent contained in the adhesive paint, esters (butyl acetate, ethyl acetate, methyl acetate, isopropyl acetate, ethylene glycol monoacetate, and the like), ketones (methyl ethyl ketone, methyl isobutyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, and the like), alcohols (methanol, ethanol, isopropyl alcohol, butanol, propylene glycol monomethyl ether, propylene glycol monomethyl ether, and the like), and the like can be given.

[0194] The method of applying the conductive adhesive is the same as the method of applying the paint in the process (Al-1).

[0195] In the process (A1-4), the second release film 40 is laminated to the anisotropic conductive adhesive layer 24 on the side opposite to the electromagnetic wave shielding layer 20, with the release agent layer / adhesive layer 44 in contact with the anisotropic conductive adhesive layer 24.

[0196] After the second release film 40 is laminated to the anisotropic conductive adhesive layer 24, in order to improve the adhesion between the layers, the laminate composed of the first release film 30, the insulating resin layer 10, the shielding layer 20, the anisotropic conductive adhesive layer 24, and the second release film 40 can also be subjected to a lamination treatment using pressure and / or heat.

[0197] The pressure conditions are the same as in the pressure treatment in the process (A1-2). Also in the process (A1-4), the heat treatment can be performed similarly to the process (A1-2).

[0198] Also in the method (A1), examples are described in which the lamination treatment is performed in the processes (A1-2), (A1-4), but the stage at which the lamination treatment is performed is not limited thereto.

[0199] As a second embodiment of the method of manufacturing the electromagnetic wave shielding film of the present application, for example, a manufacturing method based on the following method (A2) can be given.

[0200] The method (A2) is specifically a method having the following processes (A2-1) to (A2-4).

[0201] Hereinafter, the method (A2) will be described based on Figures 4-6 The method (A2) will be described. The processes (A2-1) to (A2-2) are shown in Figure 4 The process (A2-3) is shown in Figure 5 The process (A2-4) is shown in Figure 6 .

[0202] Process (A2-1): A process of forming the insulating resin layer 10 on one face of the first release film 30.

[0203] Process (A2-2): A process of forming the shielding layer 20 on the face of the insulating resin layer 10 opposite to the first release film 30 to form a laminate (p1).

[0204] Process (A2-3): A process of forming the anisotropic conductive adhesive layer 24 on the second release film 40 to form a laminate (p2).

[0205] Process (A2-4): A process of joining the laminate (p1) and the laminate (p2) with the shielding layer 20 of the laminate (p1) in contact with the anisotropic conductive adhesive layer 24 of the laminate (p2).

[0206] The process (A2-1) and the process (A2-2) are the same as the process (A1-1) and the process (A1-2), respectively.

[0207] The process (A2-3) is the same as the process (A1-3) except that the anisotropic conductive adhesive layer 24 is formed by coating the thermosetting adhesive 24a and the conductive adhesive paint containing the conductive particles 24b on the surface of the second release film 40 provided with the release agent layer / adhesive layer 44 instead of the shielding layer 20.

[0208] In the lamination of the laminate (p1) and the laminate (p2) in the process (A2-4), a pressurization-based lamination treatment for improving the adhesion of the laminate (p1) and the laminate (p2) can be performed. The pressurization conditions are the same as those in the pressurization treatment in the process (A1-4). In addition, in the process (A2-4), a heating treatment can be performed as in the process (A1-4).

[0209] <Effects>

[0210] The electromagnetic wave shielding film 1 of the present embodiment uses an adhesive composition for use in an electrically conductive adhesive layer constituting an electromagnetic wave shielding film, which exhibits a specific water absorption rate, and contains a thermosetting resin containing a specific epoxy resin in the adhesive component, whereby even after being placed in a high-temperature high-humidity environment, good adhesion and a low connection resistance value can be exhibited and maintained.

[0211] <Other Embodiments>

[0212] The electromagnetic wave shielding film of the present embodiment can have only an insulating resin layer, a shielding layer adjacent to the insulating resin layer, and an electrically conductive adhesive layer adjacent to the opposite side of the shielding layer from the insulating resin layer, and is not limited to the illustrated embodiments.

[0213] For example, the insulating resin layer can be two or more layers.

[0214] The first release film can have a release agent layer instead of an adhesive layer.

[0215] The second release film can have an adhesive layer instead of a release agent layer.

[0216] The first release film or the second release film can not have an adhesive layer or a release agent layer, but can be composed only of a base material layer.

[0217] In the case where the insulating resin layer has sufficient softness and strength, the first release film can be omitted.

[0218] In the case where the surface of the electrically conductive adhesive layer has little tackiness, the second release film can be omitted.

[0219] Printed wiring board with electromagnetic wave shielding film

[0220] The printed wiring board with electromagnetic wave shielding film of the present application has: a printed wiring board provided with a printed circuit on at least one side of a substrate; an insulating film adjacent to the side of the printed wiring board on which the printed circuit is provided; and the electromagnetic wave shielding film of the present application described above provided so that the electrically conductive adhesive layer is adjacent to the insulating film.

[0221] Figure 7 is a cross-sectional view showing a first embodiment of a printed wiring board with electromagnetic wave shielding film obtained by the manufacturing method of the present application.

[0222] The flexible printed wiring board 2 with electromagnetic wave shielding film is provided with a flexible printed wiring board 50, an insulating film 60, and the electromagnetic wave shielding film 1 of the first embodiment.

[0223] The flexible printed wiring board 50 is provided with a printed circuit 54 on at least one side of a base film 52.

[0224] The insulating film 60 is provided on the surface of the side of the flexible printed wiring board 50 on which the printed circuit 54 is provided.

[0225] The anisotropic conductive adhesive layer 24 of the electromagnetic wave shielding film 1 is adhered to the surface of the insulating film 60. In addition, the anisotropic conductive adhesive layer 24 is electrically connected to the printed circuit 54 through a through hole (omitted from the drawing) formed in the insulating film 60.

[0226] In the flexible printed wiring board 2 with electromagnetic wave shielding film, the second release film 40 is peeled off from the anisotropic conductive adhesive layer 24.

[0227] In the flexible printed wiring board 2 with electromagnetic wave shielding film, when the first release film 30 is not needed, the first release film 30 is peeled off from the insulating resin layer 10.

[0228] In the vicinity of the printed circuit 54 (signal circuit, ground circuit, ground layer, etc.) except for the portion having the through hole, the shielding layer 20 of the electromagnetic wave shielding film 1 is disposed in opposition separately through the insulating film 60 and the anisotropic conductive adhesive layer 24.

[0229] The separation distance of the printed circuit 54 from the shielding layer 20, excluding the portion having the through-hole, and the thickness of the insulating film 60 and the thickness of the anisotropic conductive adhesive layer 24 are substantially equal to the sum of the thickness of the anisotropic conductive adhesive layer 24. The separation distance is preferably 15 μm or more and 200 μm or less, and more preferably 30 μm or more and 200 μm or less. If the separation distance is less than 15 μm, in order to adjust the characteristic impedance of the signal circuit, it is necessary to reduce the line width of the signal circuit, and it will be technically difficult to achieve stable manufacturing of the printed circuit 54. If the separation distance is more than 200 μm, the flexible printed wiring board 2 with the electromagnetic wave shielding film becomes thick, and the flexibility is also insufficient.

[0230] <Flexible Printed Wring Board>

[0231] The flexible printed wiring board 50 forms a printed circuit (power supply circuit, ground circuit, ground layer, etc.) by processing the copper foil of the copper-clad laminate into a desired pattern by a known etching method.

[0232] As the copper-clad laminate, there can be mentioned a laminate in which a copper foil is attached to one side or both sides of a base film 52 via an adhesive layer (not shown); a laminate obtained by casting a resin solution or the like for forming the base film 52 on the surface of a copper foil; and the like.

[0233] As the material of the adhesive layer, there can be mentioned an epoxy resin, a polyester, a polyimide, a polyamide-imide, a polyamide, a phenol resin, a polyurethane resin, an acrylic resin, a melamine resin, and the like.

[0234] The thickness of the adhesive layer is preferably 0.5 μm or more and 30 μm or less.

[0235] <<Base Film>>

[0236] As the base film 52, a film having heat resistance is preferable, and a polyimide film, a liquid crystal polymer film, and further a polyimide film are more preferable.

[0237] From the viewpoint of electrical insulation, the surface resistance of the base film 52 is preferably 1 x 10 6 Ω or more. From the practical viewpoint, the surface resistance of the base film 52 is preferably 1 x 10 19 Ω or less.

[0238] The thickness of the base film 52 is preferably 5 μm or more and 200 μm or less, and from the viewpoint of flexibility, more preferably 6 μm or more and 25 μm or less, and further preferably 10 μm or more and 25 μm or less.

[0239] <<Printed Circuit>>

[0240] As the copper foil constituting the printed circuit 54 (signal circuit, ground circuit, ground layer, etc.), there can be mentioned a rolled copper foil, an electrolytic copper foil, and the like, and from the viewpoint of flexibility, a rolled copper foil is preferable.

[0241] The thickness of the copper foil is preferably 1 μm or more and 50 μm or less, and more preferably 7 μm or more and 35 μm or less.

[0242] The end portion (terminal) of the printed circuit 54 in the length direction is not covered with the insulating film 60 and the electromagnetic wave shielding film 1 for soldering, connector connection, component mounting, and the like.

[0243] <Insulating Film>

[0244] The insulating film 60 is obtained by forming an adhesive layer (not shown) on one surface of an insulating film main body (not shown) by applying an adhesive, adhering an adhesive sheet, or the like.

[0245] From the viewpoint of electrical insulation, the surface resistance of the insulating film main body is preferably 1 x 10 6 Ω or more. From the practical viewpoint, the surface resistance of the insulating film main body is preferably 1 x 10 19 Ω or less.

[0246] As the insulating film main body, a film having heat resistance is preferable, and a polyimide film, a liquid crystal polymer film, and further a polyimide film are more preferable.

[0247] The thickness of the insulating film main body is preferably 1 μm or more and 100 μm or less, and more preferably 3 μm or more and 25 μm or less from the viewpoint of flexibility.

[0248] As the material of the adhesive layer, an epoxy resin, a polyester, a polyimide, a polyamide-imide, a polyamide, a phenol resin, a polyurethane resin, an acrylic resin, a melamine resin, a polystyrene, a polyolefin, or the like can be given. The epoxy resin can contain a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility.

[0249] The thickness of the adhesive layer is preferably 1 μm or more and 100 μm or less, and more preferably 1.5 μm or more and 60 μm or less.

[0250] The shape of the opening portion of the through hole is not particularly limited. As the shape of the opening portion of the through hole 62, for example, a circular shape, an elliptical shape, a quadrangular shape, or the like can be given.

[0251] (Method for manufacturing printed wiring board with electromagnetic wave shielding film)

[0252] The method for manufacturing a printed wiring board with an electromagnetic wave shielding film of the present application has a step of pressure bonding a printed wiring board in which a printed circuit is provided on at least one surface of a substrate and the above-described electromagnetic wave shielding film of the present application with an insulating film interposed therebetween, and at the time of pressure bonding, the insulating film is made to adhere to the surface of the printed wiring board on which the printed circuit is provided, and the insulating film is made to adhere to the adhesive layer of the electromagnetic wave shielding film.

[0253] The manufacturing method of the printed wiring board with the electromagnetic wave shielding film of the present application is a method of manufacturing the printed wiring board with the electromagnetic wave shielding film by the manufacturing method of the electromagnetic wave shielding film of the present application described above, and comprises the following steps (a) and (b).

[0254] Step (a): a step of providing an insulating film on the surface of the printed wiring board on the side where the printed circuit is provided, to obtain a printed wiring board with an insulating film.

[0255] Step (b): a step of, in the case where the electromagnetic wave shielding film has a second release film, peeling the second release film from the electromagnetic wave shielding film, and then superimposing the printed wiring board with the insulating film and the electromagnetic wave shielding film in such a manner that the conductive adhesive layer comes into contact with the surface of the insulating film, and pressing them, to thereby adhere the conductive adhesive layer to the surface of the insulating film, and obtain a printed wiring board with the electromagnetic wave shielding film.

[0256] As a more preferable embodiment, the manufacturing method of the printed wiring board with the electromagnetic wave shielding film of the present application comprises the following steps (a) to (d).

[0257] Step (a): a step of providing an insulating film on the surface of the printed wiring board on the side where the printed circuit is provided, to obtain a printed wiring board with an insulating film.

[0258] Step (b): a step of, in the case where the electromagnetic wave shielding film has a second release film, peeling the second release film from the electromagnetic wave shielding film, and then superimposing the printed wiring board with the insulating film and the electromagnetic wave shielding film in such a manner that the conductive adhesive layer comes into contact with the surface of the insulating film, and pressing them, to thereby adhere the conductive adhesive layer to the surface of the insulating film, and obtain a printed wiring board with the electromagnetic wave shielding film.

[0259] Step (c): a step of, in the case where the electromagnetic wave shielding film has a first release film, peeling the first release film from the electromagnetic wave shielding film after step (b) when the first release film is not needed.

[0260] Step (d): a step of, in the case where the adhesive contained in the conductive adhesive layer is a thermosetting adhesive, as needed, making the conductive adhesive layer substantially cured between step (a) and step (b), or after step (c).

[0261] Hereinafter, the present application will be described with reference to Figure 8 A method of manufacturing a flexible printed wiring board with an electromagnetic wave shielding film will be described.

[0262] <Step (a)>

[0263] As Figure 8As shown, an insulating film 60 with through holes 62 is formed on the flexible printed wiring board 50 at positions corresponding to the printed circuit 54. An adhesive layer of the insulating film 60 is bonded to the surface of the flexible printed wiring board 50 (not shown), and the adhesive layer is cured to obtain a flexible printed wiring board 3 with an insulating film. Alternatively, the adhesive layer of the insulating film 60 can be temporarily bonded to the surface of the flexible printed wiring board 50, and the adhesive layer can be formally cured in step (d).

[0264] The bonding and curing of the adhesive layer are carried out, for example, by hot pressing using a press (illustration omitted).

[0265] <Process (b)>

[0266] like Figure 8 As shown, an electromagnetic wave shielding film 1, on which the second release film 40 has been peeled off, is superimposed on a flexible printed wiring board 3 with an insulating film, and then pressed (preferably hot-pressed) to obtain a flexible printed wiring board 2 with an electromagnetic wave shielding film, on which an anisotropic conductive adhesive layer 24 is pressed onto the surface of the insulating film 60, and the anisotropic conductive adhesive layer 24 is electrically connected to the printed circuit 54 through the through hole 62.

[0267] exist Figure 8 In the diagram of process (b), the printed circuit 54 consists of a ground circuit 54a and a signal circuit 54b (illustrations of 54a and 54b are omitted).

[0268] The bonding of the anisotropic conductive adhesive layer 24 is carried out, for example, by hot pressing using a press (not shown).

[0269] The hot pressing time is preferably 20 seconds or more and 60 minutes or less, more preferably 30 seconds or more and 30 minutes or less.

[0270] The temperature of hot pressing (the temperature of the hot plate of the press) is preferably 140°C or higher and 210°C or lower, more preferably 150°C or higher and 190°C or lower.

[0271] The pressure of hot pressing is preferably 0.5 MPa or more and 20 MPa or less, more preferably 1 MPa or more and 16 MPa or less.

[0272] <Process (c)>

[0273] like Figure 8 As shown, when the first release film 30 is not needed, the first release film 30 is peeled off from the insulating resin layer 10.

[0274] <Effects>

[0275] The printed wiring board 2 with the electromagnetic wave shielding film of the present embodiment has the features of the electromagnetic wave shielding film of the present invention described above, and the shielding layer becomes the printed wiring board with the electromagnetic wave shielding film that is well grounded to the ground circuit of the printed wiring board.

[0276] <Other Embodiments>

[0277] Note that the printed wiring board with the electromagnetic wave shielding film of the present invention can have only the printed wiring board, the insulating film adjacent to the surface of the printed wiring board on which the printed circuit is provided, and the electromagnetic wave shielding film adjacent to the insulating film, and is not limited to the illustrated embodiments.

[0278] For example, the flexible printed wiring board can have a ground layer on the back surface side. In addition, the flexible printed wiring board can have printed circuits on both surfaces, and the insulating film and the electromagnetic wave shielding film can be attached to both surfaces.

[0279] Instead of the flexible printed wiring board, a rigid printed substrate that does not have flexibility can also be used.

[0280] Instead of the electromagnetic wave shielding film 1 of the first embodiment, the electromagnetic wave shielding film 1 of the second embodiment or the like can be used.

[0281]

Embodiments

[0282] Hereinafter, the present invention will be further described with examples, but the scope of the present invention is not limited to these examples.

[0283] Hereinafter, the structural formula of the epoxy resin used in each embodiment is shown.

[0284]

Chemical Formula 5

[0285]

[0286] (Embodiment 1)

[0287] <Composition of the adhesive coating of the insulating resin layer>

[0288] As the adhesive coating contained in the insulating resin layer, 20.6 parts by mass of a bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER (registered trademark) 828), 60.7 parts by mass of a flexible epoxy resin (epoxy resin (manufactured by DIC Corporation, EXA-4816)), 16.7 parts by mass of a curing agent (manufactured by Showa Denko, Sho-amine X (registered trademark)), 2 parts by mass of 2-ethyl-4-methylimidazole (2E4MZ), and 4.9 parts by mass of carbon black were dissolved in 200 parts by mass of a solvent (methyl ethyl ketone) to produce a coating for the insulating resin layer.

[0289] <Composition of the adhesive coating of the conductive adhesive layer>

[0290] As an adhesive coating contained in the conductive adhesive layer, 79 parts by mass of an epoxy resin having the structural formula shown in the above formula (1) (manufactured by DIC Corporation, EPICLON HP7200L (for the specific structural formula, refer to the above formula (a))), 20 parts by mass of an acrylate-based polymer (manufactured by Nagase Chemicals, Ltd., Teisan Resin SG-P3 (Tg 12°C, acid value 0 mgKOH / g, epoxy equivalent 0.21 eq. / kg)), 1 part by mass of an imidazole-based epoxy resin curing agent (manufactured by Shikoku Chemicals Corporation, Curezol 2P4MZ (2-phenyl-4-methylimidazole)), and 20 parts by mass of copper particles (average particle diameter 5.02 μm) were mixed to produce an adhesive coating of the conductive adhesive layer. The blending ratio of the adhesive coating of the conductive adhesive layer is shown in Table 1 below, for example.

[0291] <Manufacture of electromagnetic wave shielding film>

[0292] A first release film was prepared in which an adhesive layer composed of an acrylic adhesive was provided on one side of a PET film (manufactured by Toyobo Co., Ltd., CN200, film thickness 50 μm).

[0293] On the adhesive layer surface of the first release film, the above-mentioned coating for the insulating resin layer was applied using a die coater, and then dried to form an insulating resin layer (10 μm).

[0294] Next, on the surface of the insulating resin layer opposite to the first release film, copper was physically vapor-deposited by an electron beam evaporation method to form a shielding layer composed of a copper vapor-deposited film (film thickness 300 nm).

[0295] Next, on the surface of the shielding layer opposite to the insulating resin layer, the above-mentioned adhesive coating of the conductive adhesive layer was applied using a die coater, and then dried to form a conductive adhesive layer (film thickness 5 μm).

[0296] A second release film was prepared in which a release layer was provided on one side of a PET film (manufactured by Lintec Corporation, T157, thickness of release film main body: 50 μm, thickness of release agent layer: 0.1 μm) by a non-silicone-based release agent.

[0297] The second release film was attached to the surface of the conductive adhesive layer opposite to the shielding layer in such a manner that the above-mentioned release agent layer was in contact with the above-mentioned conductive adhesive layer, to obtain the electromagnetic wave shielding film of Example 1.

[0298] <Manufacture of printed wiring board with electromagnetic wave shielding film>

[0299] An insulating adhesive composition was applied to the surface of a polyimide film (insulating film main body) having a thickness of 25 μm in a manner such that the dry film thickness became 25 μm, to form an adhesive layer, to obtain an insulating film (thickness: 50 μm). A through hole (pore diameter: 800 μm) was formed at a position corresponding to the ground circuit of the printed circuit.

[0300] A printed wiring board having a printed circuit formed on the surface of a polyimide film (base film) having a thickness of 12 μm was prepared.

[0301] The insulating film was attached to the printed wiring board by heat pressing, to obtain a printed wiring board with an insulating film.

[0302] The electromagnetic wave shielding film of Example 1, from which the second release film was peeled off, was overlaid on the printed wiring board with an insulating film, and a heat press device was used to heat press for 30 minutes under the conditions of a hot plate temperature of 180°C and a load of 3 MPa, to adhere the conductive adhesive layer to the surface of the insulating film.

[0303] The first release film was peeled off from the insulating resin layer, to obtain a printed wiring board with an electromagnetic wave shielding film.

[0304] <Measurement of Water Absorption (%) of Adhesive Component>

[0305] The adhesive component was applied to a PET substrate, and heated at 150°C for 1 hour, to produce a cured layer.

[0306] A test piece composed of the cured layer was exposed under the conditions of 85°C, 48 hours, and a relative humidity of 85%. Then, the change in mass of the test piece, i.e., the difference between the initial mass and the mass after exposure to water, was measured and calculated as a percentage of the initial mass.

[0307] The results of the measurement of the water absorption of the adhesive component used in Example 1 are shown in Table 1 below.

[0308] <Evaluation of Printed Wiring Board with Electromagnetic Wave Shielding Film>

[0309] The connection resistance of the printed wiring board with an electromagnetic wave shielding film of Example 1 obtained as described above was measured before and after storage in a high-temperature high-humidity environment, to evaluate the connectivity. The storage conditions were two modes of 500 hours and 1000 hours in an environment of 85°C and a humidity of 85%. The connectivity was evaluated by the following method.

[0310] [Connectivity Evaluation]

[0311] In the printed wiring board with an electromagnetic wave shielding film, the electrical connection between the wiring-shielding layer-wiring was measured via the electromagnetic wave shielding film present in the through hole (also referred to as a connection hole).

[0312] The tester was brought into contact with the printed wiring board with the electromagnetic wave shielding film, and the resistance value between the wiring-shielding layer-wiring was measured.

[0313] The connection resistance value was evaluated in accordance with the following criteria.

[0314] O: less than 300 mΩ

[0315] Δ: 300 mΩ or more and less than 1000 mΩ

[0316] X: 1000 mΩ or more

[0317] The evaluation results of the connectivity of the printed wiring board with the electromagnetic wave shielding film of Example 1 are shown in Table 1 below.

[0318] (Examples 2 to 11)

[0319] The printed wiring boards with the electromagnetic wave shielding film of Examples 2 to 11 were produced in the same manner as in Example 1 except that each condition of the electrically conductive adhesive layer was changed as shown in Tables 1 and 2.

[0320] In Example 2, as the epoxy resin, EPICLON HP7200HHH (refer to the above formula (a) for the specific structural formula) manufactured by DIC Corporation was used.

[0321] In Example 3, as the epoxy resin, NC3000 (refer to the above formula (b) for the specific structural formula) manufactured by Nippon Kayaku Co., Ltd. was used.

[0322] In Example 4, as the epoxy resin, NC2000-L (refer to the above formula (c) for the specific structural formula) manufactured by Nippon Kayaku Co., Ltd. was used.

[0323] In Example 5, as the epoxy resin, EPPN-201 (refer to the above formula (d) for the specific structural formula) manufactured by Nippon Kayaku Co., Ltd. was used.

[0324] In Example 10, as the acrylate-based polymer, Teisan Resin SG-70L (Tg -13°C, acid value 5 mgKOH / g, no epoxy equivalent) manufactured by Nippon Shokubai Co., Ltd. was used.

[0325] The water absorption of the adhesive components used in Examples 2 to 11 was measured by the same method as in Example 1. The results are shown in Tables 1 and 2.

[0326] In addition, the printed wiring boards with the electromagnetic wave shielding film produced in Examples 2 to 11 were evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0327] (Comparative Examples 1 to 3)

[0328] Comparative Examples 1 to 3 were produced in the same manner as in Example 1, except that each condition of the electrically conductive adhesive layer was changed as shown in Table 1.

[0329] In Comparative Example 1, as the epoxy resin, jER1001 (see the formula (e) above for the specific structural formula) manufactured by Mitsubishi Chemical Corporation was used.

[0330] In Comparative Example 2, as the epoxy resin, jER157S70 (see the formula (f) above for the specific structural formula) manufactured by Mitsubishi Chemical Corporation was used.

[0331] In Comparative Example 3, as the acrylate-based polymer, Teisan Resin SG-280 (Tg -29°C, acid value 30 mgKOH / g, no epoxy equivalent) manufactured by Nagase Chemicals, Ltd. was used.

[0332] The water absorption of the adhesive components used in Comparative Examples 1 to 3 was measured in the same manner as in Example 1. The results are shown in Table 2.

[0333] In addition, the printed wiring boards with the electromagnetic wave shielding film produced in Comparative Examples 1 to 3 were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0334] [Table 1]

[0335]

[0336] [Table 2]

[0337]

[0338] As is clear from the above examples, the electromagnetic wave shielding film of the present application can reliably exhibit good adhesion and maintain a low connection resistance value even after being left in a high-temperature high-humidity environment for 500 hours.

[0339] In addition, it was found that if a specific rubber component is contained in the adhesive component, there are cases where good adhesion and a low connection resistance value can be exhibited even after 1000 hours have passed.

[0340] (Industrial applicability)

[0341] The electromagnetic wave shielding film of the present application is useful as an electromagnetic wave shielding member in a flexible printed wiring board for electronic devices such as smartphones, mobile phones, optical modules, digital cameras, game consoles, notebook computers, medical equipment, and the like.

[0342] (Explanation of reference numerals)

[0343] 1 electromagnetic wave shielding film

[0344] 2 flexible printed wiring board with electromagnetic wave shielding film

[0345] 3 flexible printed wiring board with insulating film

[0346] 10 insulating resin layer

[0347] 20 shielding layer

[0348] 22 electrically conductive adhesive layer

[0349] 24 anisotropic electrically conductive adhesive layer

[0350] 24a adhesive

[0351] 24b electrically conductive particles

[0352] 26 isotropic electrically conductive adhesive layer

[0353] 26a adhesive

[0354] 26b electrically conductive particles

[0355] 30 first release film

[0356] 32 substrate layer

[0357] 34 adhesive / release agent layer

[0358] 40 second release film

[0359] 42 substrate layer

[0360] 44 release agent / adhesive layer

[0361] 50 flexible printed wiring board

[0362] 52 base film

[0363] 54 printed circuit

[0364] 60 insulating film

[0365] 62 through hole

Claims

1. An electromagnetic wave shielding film, which is formed by sequentially laminating an insulating resin layer, a shielding layer, and a conductive adhesive layer, the conductive adhesive layer is formed using a conductive adhesive composition containing an adhesive component and conductive particles, a water absorption of the adhesive component is less than 2.0%, the adhesive component contains a thermosetting resin and a rubber component, the thermosetting resin contains an epoxy resin having a structural formula represented by the following general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g / eq, ; in the above formula (1), R1 represents a hydrocarbon group having 1 to 35 carbon atoms, R2 represents hydrogen or a methyl group, and n represents an integer of 1 to 10, an epoxy equivalent of the rubber component is 0.05 eq / kg or more.

2. The electromagnetic wave shielding film according to claim 1, wherein 30 to 70 mass% of the epoxy resin is contained in the adhesive component.

3. The electromagnetic wave shielding film according to claim 1 or 2, wherein the epoxy equivalent is 215 to 400 g / eq.

4. The electromagnetic wave shielding film according to claim 1 or 2, wherein R1 in the general formula (1) is a hydrocarbon group containing a structure of an alicyclic hydrocarbon or an aromatic hydrocarbon.

5. The electromagnetic wave shielding film according to claim 3, wherein the epoxy equivalent is 250 to 400 g / eq.

6. The electromagnetic wave shielding film according to claim 1, wherein an acid value of the rubber component is 20 mgKOH / g or less.

7. The electromagnetic wave shielding film according to claim 6, wherein a glass transition temperature of the rubber component is 10°C or more.

8. An electromagnetic wave shielding film printed wiring board, having: a printed wiring board provided with a printed circuit on at least one side of a substrate; an insulating film adjacent to a side of the printed wiring board on which the printed circuit is provided; and the electromagnetic wave shielding film according to any one of claims 1 to 7, which is provided so that the conductive adhesive layer is adjacent to the insulating film. ​ ​ ​

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