JP7654579B2 - Electromagnetic wave shielding film and printed wiring board with electromagnetic wave shielding film - Google Patents

Description

The present invention relates to an electromagnetic wave shielding film and a printed wiring board with an electromagnetic wave shielding film.

In order to shield electromagnetic noise generated from a flexible printed wiring board (hereinafter also referred to as FPC) or from external electromagnetic noise, a method is known in which an electromagnetic 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 bonded to the flexible printed wiring board via an insulating film (hereinafter also referred to as a coverlay film).
In such a method, the printed wiring board is shielded by connecting the conductive adhesive layer of the electromagnetic wave shielding film and the ground circuit of the printed wiring board through an opening provided in an insulating film covering the ground circuit.

Various types of conductive adhesive compositions are known as conductive adhesive compositions that constitute the conductive adhesive layer of an electromagnetic wave shielding film (see, for example, Patent Documents 1 and 2).

JP 2019-196458 A Patent No. 5854248

Incidentally, the electromagnetic wave shielding film is required to have the bending resistance and heat resistance required for the entire flexible printed wiring board, as well as high adhesion in a high-temperature and high-humidity environment and durability capable of maintaining a low connection resistance value.
However, when the electromagnetic wave shielding film is placed in a high-temperature, high-humidity environment, the adhesive layer deteriorates over time, reducing adhesion, and the metallic conductive particles and shielding layer are oxidized, resulting in the problem that a low connection resistance value cannot be maintained after being placed in the high-temperature, high-humidity environment.
The above-mentioned Patent Document 1 reports that the use of an adhesive composition with a specific formulation improves adhesion in a high-temperature, high-humidity environment, but does not particularly mention the connection resistance value after being placed in a high-temperature, high-humidity environment. From the viewpoint of providing an electromagnetic wave shielding film that shows good adhesion and maintains a low connection resistance value even after being placed in a high-temperature, high-humidity environment, there is room for improvement.
In addition, Patent Document 2 reports that by using surface-coated conductive fine particles, it is possible to provide a conductive adhesive that has high connection reliability even after moist heat aging treatment. However, the technology of Patent Document 2 has problems such as the need to complexly select the conductive fine particles and increased manufacturing costs, making it less versatile.

Therefore, the present invention aims to provide a versatile and practical electromagnetic shielding film that exhibits good adhesion and maintains low connection resistance even after being placed in a high-temperature, high-humidity environment.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that it is possible to provide an electromagnetic shielding film that can solve the above problems by using an adhesive component that exhibits a specific water absorption rate as a conductive adhesive composition used in the conductive adhesive layer that constitutes the electromagnetic shielding film, and by making the adhesive component contain a thermosetting resin that includes a specific epoxy resin, and thus completed the present invention.

The present invention includes the following aspects.
[1] An electromagnetic wave shielding film comprising an insulating resin layer, a shielding layer, and a conductive adhesive layer laminated in this order,
The conductive adhesive layer is formed using a conductive adhesive composition containing an adhesive component and conductive particles,
The water absorption rate of the adhesive component is less than 2.0%;
The adhesive component contains a thermosetting resin,
The electromagnetic wave shielding film, wherein the thermosetting resin has a structural formula represented by the following general formula (1) and contains an epoxy resin exhibiting an epoxy equivalent of 170 to 400 g/eq.

（上記式（１）中、Ｒ_１は炭素数１～３５の炭化水素基を、Ｒ_２は水素又はメチル基を、ｎは１～１０の整数を表す）
［２］前記接着剤成分中に、前記エポキシ樹脂が３０～７０質量％含有される、［１］に記載の電磁波シールドフィルム。
［３］前記エポキシ当量が２１５～４００ｇ／ｅｑである、［１］又は［２］に記載の電磁波シールドフィルム。
［４］前記一般式（１）中のＲ_１が脂環式炭化水素、又は、芳香族炭化水素を含む構造からなる炭化水素基である、［１］～［３］のいずれかに記載の電磁波シールドフィルム。
［５］前記エポキシ当量が２５０～４００ｇ／ｅｑである、［３］又は［４］に記載の電磁波シールドフィルム。
［６］前記接着剤成分にゴム成分を含有する、［１］～［５］のいずれかに記載の電磁波シールドフィルム。
［７］前記ゴム成分の酸価が２０ｍｇＫＯＨ／ｇ以下である、［６］に記載の電磁波シールドフィルム。
［８］前記ゴム成分のエポキシ当量が０．０５ｅｑ／ｋｇ以上である、［６］又は［７］に記載の電磁波シールドフィルム。
［９］前記ゴム成分のガラス転移温度が１０℃以上である、［６］～［８］のいずれかに記載の電磁波シールドフィルム。
［１０］基板の少なくとも片面にプリント回路が設けられたプリント配線板と、
前記プリント配線板の前記プリント回路が設けられた側の面に隣接する絶縁フィルムと、
前記導電性接着剤層が前記絶縁フィルムに隣接するように設けられた［１］～［９］のいずれかに記載の電磁波シールドフィルムと、
を有する、電磁波シールドフィルム付きプリント配線板。

(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.)
[2] The electromagnetic wave shielding film according to [1], wherein the adhesive component contains 30 to 70 mass % of the epoxy resin.
[3] The electromagnetic wave shielding film according to [1] or [2], wherein the epoxy equivalent is 215 to 400 g/eq.
[4] The electromagnetic wave shielding film according to any one of [1] to [3], wherein R ₁ in the general formula (1) is a hydrocarbon group having a structure containing an alicyclic hydrocarbon or an aromatic hydrocarbon.
[5] The electromagnetic wave shielding film according to [3] or [4], wherein the epoxy equivalent is 250 to 400 g/eq.
[6] The electromagnetic wave shielding film according to any one of [1] to [5], wherein the adhesive component contains a rubber component.
[7] The electromagnetic wave shielding film according to [6], wherein the acid value of the rubber component is 20 mg KOH/g or less.
[8] The electromagnetic wave shielding film according to [6] or [7], wherein the rubber component has an epoxy equivalent of 0.05 eq/kg or more.
[9] The electromagnetic wave shielding film according to any one of [6] to [8], wherein the rubber component has a glass transition temperature of 10° C. or higher.
[10] A printed wiring board having a printed circuit provided on at least one surface of a substrate;
an insulating film adjacent to a surface of the printed wiring board on which the printed circuit is provided;
[1] to [9], in which the conductive adhesive layer is provided adjacent to the insulating film; and
A printed wiring board with an electromagnetic wave shielding film.

The present invention provides a versatile and practical electromagnetic shielding film that exhibits good adhesion and maintains low connection resistance even after being placed in a high-temperature, high-humidity environment.

FIG. 1 is a cross-sectional view showing one embodiment of an electromagnetic wave shielding film. FIG. 2 is a cross-sectional view showing another embodiment of the electromagnetic wave shielding film. FIG. 3 is a cross-sectional view showing steps (A1-1) to (A1-4) of the production process as one embodiment of the production process for the electromagnetic wave shielding film of FIG. FIG. 4 is a cross-sectional view showing the steps (A2-1) and (A2-2) of the production process of the electromagnetic wave shielding film of FIG. 1 according to another embodiment. FIG. 5 is a cross-sectional view showing a production process of step (A2-3) as another embodiment of the production process for the electromagnetic wave shielding film of FIG. FIG. 6 is a cross-sectional view showing a production process of step (A2-4) as another embodiment of the production process for the electromagnetic wave shielding film of FIG. FIG. 7 is a cross-sectional view showing one embodiment of a printed wiring board with an electromagnetic wave shielding film. 8A to 8C are cross-sectional views showing the manufacturing process of the printed wiring board with the electromagnetic shielding film of FIG.

The electromagnetic wave shielding film of the present invention will be described in detail below, but the explanation of the constituent elements described below is one example of one embodiment of the present invention, and the present invention is not limited to these contents.
The following definitions of terms apply throughout the specification and claims.
The term "isotropically conductive adhesive layer" refers to a conductive adhesive layer that has conductivity in the thickness direction and the surface direction.
The term "anisotropically conductive adhesive layer" refers to a conductive adhesive layer that has conductivity in the thickness direction but not in the surface direction.
The term "conductive adhesive layer having no conductivity in the planar direction" means a conductive adhesive layer having a surface resistance of 1×10 ⁴ Ω or more.
The average particle diameter of the conductive particles is a value obtained by randomly selecting 30 conductive particles from a microscopic image of the conductive particles, measuring the minimum and maximum diameters of each conductive particle, defining the median of the minimum and maximum diameters as the particle diameter of one particle, and calculating the arithmetic mean of the measured particle diameters of the 30 conductive particles.
The film thickness of a film (e.g., release film, insulating film), coating (e.g., insulating resin layer, conductive adhesive layer), shield layer (electromagnetic wave shielding layer), etc. is determined by observing the cross section of the measurement target using a microscope, measuring the thickness at five points, and averaging the measured thickness.
When the surface resistance is less than 10 ⁶ Ω/□, it is the surface resistivity measured using a low resistance resistivity meter (e.g., Loresta GP, ASP Probe, manufactured by Mitsubishi Chemical Corporation) by the four-terminal method (a method conforming to JIS K 7194:1994 and JIS R 1637:1998), and when it is 10 ⁶ Ω/□ or more, it is the surface resistivity measured using a high resistance resistivity meter (e.g., Hiresta UP, URS Probe, manufactured by Mitsubishi Chemical Corporation) by the double ring method (a method conforming to JIS K 6911:2006).

(Electromagnetic wave shielding film)
The electromagnetic wave shielding film of the present invention is formed by laminating an insulating resin layer, a shielding layer, and a conductive adhesive layer in this order.
The conductive adhesive layer is formed using a conductive adhesive composition that contains an adhesive component and conductive particles.
The water absorption rate of the adhesive component is less than 2.0%.
The adhesive component contains a thermosetting resin.
The thermosetting resin has a structural formula represented by the following general formula (1) and contains an epoxy resin exhibiting an epoxy equivalent of 170 to 400 g/eq.

（上記式（１）中、Ｒ_１は炭素数１～３５の炭化水素基を、Ｒ_２は水素又はメチル基を、ｎは１～１０の整数を表す）

(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.)

FIG. 1 is a cross-sectional view showing one embodiment of the electromagnetic wave shielding film of the present invention.
FIG. 2 is a cross-sectional view showing another embodiment of the electromagnetic wave shielding film of the present invention.
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 side opposite the insulating resin layer 10; a first release film 30 adjacent to the insulating resin layer 10 on the side opposite the shielding layer 20; and a second release film 40 adjacent to the conductive adhesive layer 22 on the side opposite the shielding layer 20.

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

<Insulating resin layer>
The insulating resin layer 10 becomes a protective layer for the shielding layer 20 after the electromagnetic wave shielding film 1 is attached to the surface of an insulating film provided on the surface of a printed wiring board and the first release film 30 is peeled off.

Examples of the insulating resin layer 10 include a coating film formed by applying a composition containing a thermosetting resin and a curing agent, and semi-curing or curing the coating film; a coating film formed by applying a coating liquid containing a thermosetting resin, a curing agent, and a solvent, drying the coating liquid, and semi-curing or curing the coating film. As the insulating resin layer 10, a coating film formed by applying a coating liquid containing a resin material (a combination of a thermosetting resin and a curing agent) and a solvent, drying the coating liquid, and semi-curing or curing the coating film as necessary is preferable, because it provides better adhesion between the insulating resin layer 10 and the shield layer 20.

Examples of the thermosetting resin include amide resin, epoxy resin, phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, ultraviolet-curable acrylate resin, etc. As the thermosetting resin, amide resin and epoxy resin are preferred from the viewpoint of excellent heat resistance.
The curing agent may be a known curing agent suitable for the type of thermosetting resin.

The insulating resin layer 10 may contain either or both of a colorant (pigment, dye, etc.) and a filler in order to conceal the printed circuit of the printed wiring board with the electromagnetic shielding film or to impart design features to the printed wiring board with the electromagnetic shielding film.
As either or both of the colorant and the filler, from the viewpoints of weather resistance, heat resistance, and hiding power, a pigment or a filler is preferable, and from the viewpoints of hiding power and design of the printed circuit, a black pigment or a combination of a black pigment with another pigment or a filler is more preferable.
The insulating resin layer 10 may contain other components as necessary within the range that does not impair the effects of the present invention.

From the viewpoint of electrical insulation, the surface resistance of the insulating resin layer 10 is preferably 1×10 ⁶ Ω or more, and from the viewpoint of practical use, the surface resistance of the insulating resin layer 10 is preferably 1×10 ¹⁹ Ω or less.
The thickness of the insulating resin layer 10 is preferably 0.1 μm to 30 μm, more preferably 0.5 μm to 20 μm, and even more preferably 3 μm to 15 μm. If the thickness of the insulating resin layer 10 is equal to or greater than the lower limit of the above range, the insulating resin layer 10 can fully 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.

<Shield layer (electromagnetic wave shielding layer)>
The shield layer 20 is not particularly limited as long as it is conductive, and may be a metal film, a conductive film made of conductive particles, or the like.
The shield layer 20 is formed so as to extend in the planar direction, and is therefore conductive in the planar direction, and functions as an electromagnetic wave shield layer or the like.

Examples of metals constituting the metal film include one selected from the group consisting of nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium and zinc, or alloys containing at least one of these. Among these, copper and alloys containing copper are preferred from the standpoint of shielding properties and economic efficiency.

Methods for forming the metal film include, for example, deposition films formed by physical vapor deposition (vacuum deposition, sputtering, ion beam deposition, electron beam deposition, etc.) or chemical vapor deposition, plating films formed by plating, metal foils, etc. Among them, vacuum deposition films or sputtering films formed by vacuum film formation methods (vacuum deposition method, sputtering method, etc.), or plating films formed by electrolytic plating methods are preferred because they have excellent conductivity in the plane direction. Deposition films by vacuum deposition are more preferred because they can be made thin, have excellent conductivity in the plane direction even when thin, and can be easily formed by a dry process. The metal film may also be a metal foil formed by rolling processing, or a metal foil by electrolysis (for example, special electrolytic copper foil, etc.).

When the shield layer is a conductive film made of conductive particles, the conductive particles may be, for example, particles of carbon, silver, copper, nickel, solder, etc. The conductive particles may also be silver-coated copper particles obtained by silver plating copper powder, or particles obtained by metal plating insulating particles such as resin balls or glass beads. These conductive particles may be used alone or in combination of two or more kinds.

The conductive particles may be spherical, needle-like, fibrous, flake-like, or dendritic in shape, with flake-like particles being preferred from the viewpoint of layering.

The thickness of the shielding layer 20 is 0.01 μm or more and 3 μm or less, preferably 0.05 μm or more and 2 μm or less, and 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 electromagnetic noise shielding effect is better. If the thickness of the shielding layer 20 is equal to or less than the upper limit of the above range, the electromagnetic shielding film 1 can be made thinner. In addition, the productivity and flexibility of the electromagnetic shielding film 1 are improved.

The surface resistance of the shield 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 shield layer 20 is equal to or greater than the lower limit of the above range, the shield layer 20 can be made sufficiently thin. If the surface resistance of the shield layer 20 is equal to or less than the upper limit of the above range, the shield layer 20 can function satisfactorily as an electromagnetic wave shield layer.

<Conductive adhesive layer>
The conductive adhesive layer 22 is a layer for attaching the electromagnetic wave shielding film 1 to a printed wiring board with an insulating film.
The conductive adhesive layer 22 is a conductive adhesive layer having conductivity for electrically connecting the electromagnetic wave shielding film 1 and a printed wiring board.

The conductive adhesive layer has electrical conductivity at least in the thickness direction and has adhesiveness.
The conductive adhesive layer may be an anisotropic conductive adhesive layer 24 that has conductivity in the thickness direction but not in the surface direction, or an isotropic conductive adhesive layer 26 that has conductivity in the thickness direction and in the surface direction. The conductive adhesive layer is preferably anisotropic conductive adhesive layer 24 in that it has good transmission characteristics due to its lack of conductivity in the surface direction and improves the flexibility of the electromagnetic wave shielding film 1. The conductive adhesive layer is preferably isotropic conductive adhesive layer 26 in that it can function sufficiently as an electromagnetic wave shielding layer.
The conductive adhesive layer is formed using a conductive adhesive composition that contains an adhesive component including a thermosetting resin and conductive particles.

<<Adhesive Components>>
The water absorption rate of the adhesive component is less than 2.0%.
The adhesive component contains a thermosetting resin.
The thermosetting resin has a structural formula represented by the following general formula (1) and contains an epoxy resin exhibiting an epoxy equivalent of 170 to 400 g/eq.

（上記式（１）中、Ｒ_１は炭素数１～３５の炭化水素基を、Ｒ_２は水素又はメチル基を、ｎは１～１０の整数を表す）
上記式（１）中のＲ_１（炭素数１～３５である炭化水素基）としては、特に制限はなく、例えば、脂肪族炭化水素基でも、脂環式炭化水素基でも、芳香族炭化水素基でも、またこれらの適宜組み合わせからなる炭化水素基であってもよい。
Ｒ_１としては、例えば、下記の基が例示できる。

(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.)
R ₁ in the above formula (1) (a hydrocarbon group having 1 to 35 carbon atoms) is not particularly limited and may be, for example, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a hydrocarbon group consisting of an appropriate combination of these.
Examples of _R1 include the following groups.

For _R2 in the above formula (1), a methyl group is more preferred than a hydrogen atom because it is more hydrophobic and can reduce the hygroscopicity of the adhesive component.
The epoxy resin having the structural formula represented by the above general formula (1) and exhibiting an epoxy equivalent of 170 to 400 g/eq (such an epoxy resin is also referred to as a "specific epoxy resin" in this specification) may contain one or more types.
By using an epoxy resin having a multifunctional structure such as that shown in the above formula (1) as the epoxy resin, the crosslink density of the conductive adhesive layer when hardened can be increased, and the conductive particles can be stably fixed, thereby ensuring excellent connectivity of the conductive adhesive layer.
The adhesive component preferably contains the specific epoxy resin in an amount of 30 to 70 mass %.
If the content of the specific epoxy resin in the adhesive component is 30% by mass or more, the problem of insufficient connectivity due to insufficient curing can be effectively prevented, while if it is 70% by mass or less, the problem of insufficient connectivity due to the influence of moisture absorption can be effectively prevented.
The epoxy equivalent weight of the particular epoxy resin is from 170 to 400 g/eq.
By limiting the epoxy equivalent, it is possible to optimize the OH group (hydrophilicity) of the epoxy ring-opened during curing and the functional group R ₁ (hydrophobicity).
If the epoxy equivalent is too small, the hydrophobic effect of the functional group _R1 is insufficient, and the conductive particles may be oxidized due to moisture absorption, resulting in a deterioration in connectivity. On the other hand, if the epoxy equivalent is too large, there may be few OH groups, resulting in poor adhesion and crosslinking, resulting in a deterioration in connectivity.
The epoxy equivalent is preferably 190 g/eq or more, more preferably 215 g/eq or more, even more preferably 245 g/eq or more, particularly preferably 250 g/eq or more, and is preferably 300 g/eq or less.
The epoxy equivalent can be measured in accordance with JIS K7236:2001.

In the present invention, the water absorption rate of the adhesive component in the conductive adhesive layer is set to less than 2.0%, and a specific epoxy resin is blended into the adhesive component, thereby making it possible to suppress deterioration of the conductive adhesive layer and oxidation of the conductive particles and shielding layer due to moisture absorption, and to form an electromagnetic wave shielding film that can maintain a low connection resistance value even in a high-temperature, high-humidity environment.

The adhesive component may contain epoxy resins other than the specific epoxy resins and thermosetting resins other than epoxy resins, provided that the effects of the present invention are not adversely affected.
Other examples of the thermosetting resin include phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, and ultraviolet-curable acrylate resin.

The adhesive component contains a curing agent in addition to the above-mentioned thermosetting resin.
The curing agent may be a latent curing adhesive that reacts with a thermosetting resin and cures when heated.
The curing agent includes polyaddition type curing agents that have multiple functional groups that can react with thermosetting resins, and catalytic type curing agents such as cationic or anionic curing agents that release the distortion energy of epoxy groups. Catalytic type curing agents are preferred because they provide good storage stability to the adhesive components.
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 even more preferably 1 part by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the thermosetting resin.

In addition, components other than the thermosetting resin that can be contained in the adhesive component include various components such as a rubber component, a tackifier, a curing accelerator, and a stress reducing agent (stress relaxation agent) in addition to the above-mentioned curing agent.
The adhesive component may contain a rubber component (such as a carboxy-modified nitrile rubber or an acrylic rubber) for imparting flexibility, a tackifier, etc. The adhesive component may also contain a curing accelerator, a stress reducing agent (stress relaxation agent), etc.

The acid value of the rubber component contained in the adhesive component is preferably 20 mgKOH/g or less from the viewpoint of adhesion and water absorption. 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. The glass transition temperature of the rubber component is preferably 10° C. or more.
By incorporating a rubber component that satisfies the above requirements into the adhesive component, it is possible to provide an electromagnetic wave shielding film that exhibits good adhesion and can maintain a low connection resistance value for a long period of time even after being placed in a high-temperature, high-humidity environment.

Examples of the stress reducing agent include acrylonitrile butadiene rubber (NBR), acrylic rubber, styrene butadiene rubber, vinyl acetate resin, and silicone resin.
The content of the stress reducing 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, based on 100% by mass of the adhesive component (solid content) before curing. If the content of the stress reducing agent is within the above range, the flexibility of the conductive adhesive layer is excellent.

The water absorption rate of the adhesive component is less than 2.0%.
By limiting the water absorption rate of the adhesive components, the compounding conditions for the components other than the specific epoxy resin are also limited.
If the water absorption rate of the adhesive component is too high, for example, the oxidation of the conductive particles is accelerated, resulting in poor connectivity, and the evaporation of moisture causes swelling, resulting in poor heat resistance.On the other hand, if the water absorption rate of the adhesive component is too low, the compatibility with the epoxy resin is poor.
The water absorption rate of the adhesive component can be determined in accordance with JIS K 7209 as follows.

[Water absorption rate]
The adhesive component is applied onto a PET substrate and heated to 150° C. for 1 hour to produce a hardened layer.
A test piece made of the cured layer is exposed to conditions of 85° C., 48 hours, and 85% relative humidity, and the mass change of the test piece, i.e., the difference between the initial mass and the mass after exposure to water, is measured and expressed as a percentage of the initial mass.

<<Conductive particles>>
The conductive adhesive composition that forms the conductive adhesive layer contains conductive particles in addition to the adhesive components described above.
The anisotropic conductive adhesive layer 24 includes, for example, an adhesive 24a containing the above-mentioned resin and conductive particles 24b as shown in FIG.
The isotropically conductive adhesive layer 26 includes, for example, an adhesive 26a containing the above-mentioned resin and conductive particles 26b as shown in FIG.

Conductive particles include metal (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, etc.) particles, graphite powder, baked carbon particles, plated baked carbon particles, metal-coated core-shell type resin particles, etc. Metal particles are preferred in terms of high conductivity, and copper particles are more preferred in terms of low cost.

The average particle diameter of the conductive particles 24b in the anisotropic conductive adhesive layer 24 is preferably 2 μm or more and 26 μm or less, and more preferably 4 μm or more and 16 μm or less. If the average particle diameter of the conductive particles 24b is equal to or more than 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 fluidity of the resin of the anisotropic conductive adhesive layer 24, so that the conformability of the anisotropic conductive adhesive layer 24 to the shape of the through holes of the insulating film can be ensured. If the average particle diameter of the conductive particles 24b is equal to or less than the upper limit of the above range, the conductive particles 24b do not hinder the contact between the resin of the anisotropic conductive adhesive layer 24 and the surface of the adherend, and sufficient adhesion can be ensured.

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 equal to or greater than the lower limit of the above range, the contact frequency of the conductive particles 26b increases, and the conductivity in the three-dimensional direction can be stably improved. If the average particle diameter of the conductive particles 26b is equal to or less than the upper limit of the above range, the conductive particles 26b do not hinder the contact between the resin of the isotropic conductive adhesive layer 26 and the surface of the adherend, and sufficient adhesion can be ensured.

The proportion of conductive particles 24b in the anisotropic conductive adhesive layer 24 is preferably 1% by volume to 30% by volume, and more preferably 2% by volume to 10% by volume, of 100% by volume of the anisotropic conductive adhesive layer 24. If the proportion of conductive particles 24b is equal to or greater than the lower limit of the above range, the conductivity of the anisotropic conductive adhesive layer 24 will be good. If the proportion of conductive particles 24b is equal to or less than the upper limit of the above range, the adhesion and fluidity (ability to conform to the shape of the through holes in the insulating film) of the anisotropic conductive adhesive layer 24 will be good. In addition, the flexibility of the electromagnetic wave shielding film 1 will be improved.

The proportion of conductive particles 26b in the isotropic conductive adhesive layer 26 is preferably 50% by volume or more and 80% by volume or less, and more preferably 60% by volume or more and 70% by volume or less, out of 100% by volume of the isotropic conductive adhesive layer 26. If the proportion of conductive particles 26b is equal to or greater than the lower limit of the above range, the conductivity of the isotropic conductive adhesive layer 26 will be good. If the proportion of conductive particles 26b is equal to or less than the upper limit of the above range, the adhesion and fluidity (ability to conform to the shape of the through holes in the insulating film) of the isotropic conductive adhesive layer 26 will be good. In addition, the flexibility of the electromagnetic wave shielding film 1 will be improved.

The surface resistance of the anisotropic conductive adhesive layer 24 is preferably 1×10 ⁴ Ω or more and 1×10 ¹⁶ Ω or less, and more preferably 1×10 ⁶ Ω or more and 1×10 ¹⁴ Ω or less. If the surface resistance of the anisotropic conductive adhesive layer 24 is equal to or more than the lower limit of the above range, the content of the conductive particles 24b can be kept low. If the surface resistance of the anisotropic conductive adhesive layer 24 is equal to or less than the upper limit of the above range, there is no practical problem with anisotropy.

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 equal to or more than the lower limit of the above range, the content of the conductive particles 26b is kept low, the viscosity of the conductive adhesive does not become too high, and the applicability is further improved. In addition, the fluidity of the isotropic conductive adhesive layer 26 (the ability to follow the shape of the through holes in the insulating film) can be further ensured. If the surface resistance of the isotropic conductive adhesive layer 26 is equal to or less than the upper limit of the above range, the entire surface of the isotropic conductive adhesive layer 26 has uniform conductivity.

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 equal to or more than the lower limit of the above range, the fluidity (ability to conform to the shape of the through-holes in the insulating film) of the anisotropic conductive adhesive layer 24 can be ensured, and the through-holes in 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, improving the transmission characteristics. If the thickness of the anisotropic conductive adhesive layer 24 is equal to or less than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thinner. In addition, the flexibility of the electromagnetic wave shielding film 1 is improved.

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 equal to or more than the lower limit of the above range, the adhesion is improved. In addition, the fluidity (ability to follow the shape of the through-holes of the insulating film) of the isotropic conductive adhesive layer 26 can be ensured, the through-holes of the insulating film can be sufficiently filled with the conductive adhesive, and the folding resistance is also ensured, so that the isotropic conductive adhesive layer 26 will not break even if it is repeatedly folded. If the thickness of the isotropic conductive adhesive layer 26 is equal to or less than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thinner. In addition, the flexibility of the electromagnetic wave shielding film 1 is improved. In addition, the transmission characteristics are improved by making the film thickness of the isotropic conductive adhesive layer 26, which has a higher surface resistance than the electromagnetic wave shielding layer 20, thinner.

<First Release Film>
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 off from the insulating resin layer 10 after the electromagnetic wave shielding film 1 is attached to the printed wiring board with an insulating film.

The first release film 30 has, for example, a base layer 32 and an adhesive layer or release agent layer 34 provided on the surface of the base layer 32 facing the insulating resin layer 10. In this specification, the adhesive layer or release agent layer 34 is also referred to as an adhesive layer/release agent layer 34.
The first release film 30 may be one in which an adhesive layer/release agent layer 34 is provided directly on the surface of a substrate layer 32; or it may be one in which an adhesive layer/release agent layer 34 is provided on the surface of an insulating resin layer 10, and then a substrate layer 32 is attached to the surface of the adhesive layer/release agent layer 34, thereby providing an adhesive layer/release agent layer 34 on the surface of the substrate layer 32.

Examples of the resin material for the base layer 32 include 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, etc. As the resin material, PET is preferable from the viewpoints of heat resistance (dimensional stability) during production of the electromagnetic wave shielding film 1 and cost.
The substrate layer 32 may contain a colorant or a filler.

The thickness of the base 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 even more preferably 25 μm or more and 100 μm or less. If the thickness of the base layer 32 is equal to or more than the lower limit of the above range, the handling properties of the electromagnetic wave shielding film 1 are good. If the thickness of the base layer 32 is equal to or less than the upper limit of the above range, heat is easily transferred to the conductive adhesive layer 22 when the electromagnetic wave shielding film 1 is heat-pressed onto a printed wiring board with an insulating film.

An adhesive layer 34 or a release agent layer 34 is disposed between the base layer and the insulating resin layer.
Because the first release film 30 has an adhesive layer or release agent layer 34, the first release film 30 is prevented from peeling off from the insulating resin layer 10 when the second release film 40 is peeled off from the conductive adhesive layer 22 or when the electromagnetic wave shielding film 1 is attached to a printed wiring board or the like by hot pressing, and the first release film 30 can fully fulfill its role as a protective film.
As the adhesive, a known adhesive may be used.
In addition, the release agent layer 34 is formed by performing a release treatment with a release agent on the surface of the base layer 32. Since the first release film 30 has the release agent layer 34, when the first release film 30 is peeled off from the insulating resin layer 10, the first release film 30 is easily peeled off and the insulating resin layer 10 is less likely to break.
As the release agent, a known release agent may be used.

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 appropriate adhesiveness.
The thickness of the release agent layer 34 is preferably from 0.05 μm to 2.0 μm, and more preferably from 0.1 μm to 1.5 μm. If the thickness of the release agent layer 34 is within the above range, the first release film can be peeled off more easily.

<Second Release Film>
The second release film 40 protects the conductive adhesive layer 22 and improves the handleability of the electromagnetic wave shielding film 1. 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.

The second release film 40 has, for example, a base layer 42 and a release agent layer or adhesive layer 44 provided on the surface of the base layer 42 on the conductive adhesive layer side.
In this specification, the release agent layer or the adhesive layer 44 is also referred to as a release agent layer/adhesive layer 44.

Examples of the resin material of the base material layer 42 include the same resin material as that of the base material layer 32 of the first release film 30 .
The substrate layer 42 may include a colorant or a filler.
The thickness of the base 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 even more preferably 25 μm or more and 100 μm or less.

A release agent layer 44 or a pressure-sensitive adhesive layer 44 is disposed between the base material layer 42 and the conductive adhesive layer 22 .
The release agent layer 44 is formed by performing a release treatment with a release agent on the surface of the base layer 42. Since the second release film 40 has the release agent layer 44, when the second release film 40 is peeled off from the conductive adhesive layer 22, the second release film 40 is easily peeled off and the conductive adhesive layer 22 is less likely to break.
As the release agent, a known release agent may be used.

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 becomes even easier to peel off.

The adhesive layer 44 can be the same as the adhesive layer 34 described above in the section "First release film."

<Configuration of electromagnetic wave shielding film>
In the present invention, the electromagnetic wave shielding film has at least an insulating resin layer, a shielding layer, and a conductive adhesive layer, and may or may not include a first release film and a second release film.
Therefore, in this specification, the term "electromagnetic wave shielding film" may refer to the insulating resin layer, shielding layer, and conductive adhesive layer as well as the first release film and/or second release film, and may also refer to the electromagnetic wave shielding film without including these release films.

<Thickness of electromagnetic shielding film>
The thickness of the electromagnetic wave shielding film 1 (excluding the release film) is preferably 5 μm to 45 μm, more preferably 5 μm to 30 μm. If the thickness of the electromagnetic wave shielding film 1 (excluding the release film) is equal to or greater than the lower limit of the above range, the film is less likely to break when the first release film 30 is peeled off. If the thickness of the electromagnetic wave shielding film 1 (excluding the release film) is equal to or less than the upper limit of the above range, the printed wiring board with the electromagnetic wave shielding film can be made thinner.

(Method of manufacturing electromagnetic wave shielding film)
An example of a first embodiment of the method for producing an electromagnetic shielding film of the present invention is a production method by the following method (A1). In the following method (A1), an electromagnetic shielding film in which the adhesive layer is an anisotropic conductive adhesive layer 24 shown in Fig. 1 is used as an example of the electromagnetic shielding film, but the adhesive layer is not limited to this adhesive layer. The production method described below is similarly applicable whether the adhesive layer is an isotropic conductive adhesive layer 27 or an adhesive layer 22 that does not contain conductive particles.
Specifically, the method (A1) is a method having the following steps (A1-1) to (A1-4).
Hereinafter, the method (A1) will be described with reference to FIG.
Step (A1-1): A step of forming an insulating resin layer 10 on one surface of a first release film 30.
Step (A1-2): A step of forming a shield layer 20 on the surface of the insulating resin layer 10 opposite to the first release film 30.
Step (A1-3): A step of forming an anisotropic conductive adhesive layer 24 on the surface of the shield layer 20 opposite to the insulating resin layer 10.
Step (A1-4): A step of laminating a second release film 40 on the surface of the anisotropic conductive adhesive layer 24 opposite to the shield layer 20.
Each step of the method (A1) will be described in detail below.

As a method for forming the insulating resin layer 10 in the step (A1-1), for example, from the viewpoint of heat resistance during soldering or the like, a method in which a paint containing a thermosetting resin and a curing agent is applied to the surface of the first release film 30 on the pressure-sensitive adhesive layer/release agent layer 34 side, and then semi-cured or cured is preferable.
Examples of a method for applying the coating material include methods 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 fountain coater, a rod coater, an air doctor coater, a knife coater, a blade coater, a cast coater, and a screen coater.
When semi-curing or curing the thermosetting resin, it is sufficient to heat it using a heater such as a heater or an infrared lamp.

In the step (A1-2), a shield layer 20 is formed on the surface of the insulating resin layer 10 opposite to the first release film 30 .
The shield layer 20 can be formed by a vacuum film forming method (vacuum deposition, sputtering), an electrolytic plating method, or a method of attaching a metal foil (copper foil).
When the thickness of the shield layer 20 is less than 3 μm, a method of forming a vapor deposition film by vacuum deposition or a method of forming a plated film by electrolytic plating is preferred from the viewpoint of forming a shield layer 20 having a desired thickness and surface shape. A method of forming a vapor deposition film by vacuum deposition is more preferred from the viewpoints of forming a shield layer 20 having high gas permeability, easily releasing gas generated inside under high temperature conditions to the outside, and easily forming the shield layer 20 by a dry process.
When the thickness of the shielding layer 20 is 3 μm or more, a method of performing a lamination process by applying pressure and/or heat so that the insulating resin layer 10 and the metal foil (copper foil) are in contact is preferable, because deterioration of the insulating resin layer 10 due to the thermal history of the vacuum deposition does not occur and the shielding layer 20 having the desired thickness can be easily formed.
Here, the pressure in the pressurizing treatment is preferably from 0.1 kPa to 100 kPa, more preferably from 0.1 kPa to 20 kPa, and even more preferably from 1 kPa to 10 kPa.
The heating temperature may be -30°C to +50°C from the glass transition temperature of the semi-cured or cured insulating resin layer, and preferably 50°C to 150°C.

In the step (A1-3), a conductive adhesive paint containing adhesive 24a, conductive particles 24b, and a solvent is applied to the surface of shield layer 20 opposite insulating resin layer 10.
The solvent is evaporated from the applied conductive adhesive paint to form an anisotropic conductive adhesive layer 24 .
Examples of solvents contained in the adhesive coating material include esters (butyl acetate, ethyl acetate, methyl acetate, isopropyl acetate, ethylene glycol monoacetate, etc.), ketones (methyl ethyl ketone, methyl isobutyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, etc.), alcohols (methanol, ethanol, isopropanol, butanol, propylene glycol monomethyl ether, propylene glycol, etc.), and the like.
The method for applying the conductive adhesive is the same as the method for applying the paint in the step (A1-1).

In step (A1-4), the second release film 40 is laminated on the side of the anisotropic conductive adhesive layer 24 opposite the electromagnetic wave shielding layer 20 so that the release agent layer/adhesive layer 44 is in contact with the anisotropic conductive adhesive layer 24.
After laminating the second release film 40 onto the anisotropic conductive adhesive layer 24, the laminate consisting 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 may be subjected to a lamination process using pressure and/or heat in order to increase the adhesion between the layers.
The pressure conditions are the same as those in the pressure treatment in the step (A1-2). Also in the step (A1-4), a heat treatment may be carried out in the same manner as in the step (A1-2).
In the method (A1), the lamination process is performed in steps (A1-2) and (A1-4) by way of example, but the stage at which the lamination process is performed is not limited to this.

As a second embodiment of the method for producing an electromagnetic wave shielding film of the present invention, for example, the following production method (A2) can be mentioned.
Specifically, the method (A2) includes the following steps (A2-1) to (A2-4).
The method (A2) will be described below with reference to Figures 4 to 6. Steps (A2-1) and (A2-2) are shown in Figure 4, step (A2-3) in Figure 5, and step (A2-4) in Figure 6.
Step (A2-1): A step of forming an insulating resin layer 10 on one surface of a first release film 30.
Step (A2-2): A step of forming a shield layer 20 on the surface of the insulating resin layer 10 opposite to the first release film 30 to form a laminate (p1).
Step (A2-3): A step of forming an anisotropic conductive adhesive layer 24 on a second release film 40 to form a laminate (p2).
Step (A2-4): A step of bonding the laminate (p1) and the laminate (p2) together such that the shield layer 20 of the laminate (p1) and the anisotropic conductive adhesive layer 24 of the laminate (p2) are in contact with each other.

The step (A2-1) and the step (A2-2) are the same as the above-mentioned step (A1-1) and step (A1-2), respectively.
Step (A2-3) is similar to the above-described step (A1-3) except that a conductive adhesive paint containing a thermosetting adhesive 24a and conductive particles 24b is applied to the surface of the second release film 40 on which the release agent layer/adhesive layer 44 is provided, rather than to the shielding layer 20, to form an anisotropic conductive adhesive layer 24.
In the bonding of the laminate (p1) and the laminate (p2) in the step (A2-4), a lamination treatment by applying pressure may be performed to enhance adhesion between the laminate (p1) and the laminate (p2). The pressure conditions are the same as those in the pressure treatment in the step (A1-4). Also in the step (A2-4), a heat treatment may be performed as in the step (A1-4).

<Action and effect>
The electromagnetic wave shielding film 1 of this embodiment uses an adhesive component exhibiting a specific water absorption rate as the conductive adhesive composition used in the conductive adhesive layer that constitutes the electromagnetic wave shielding film, and the adhesive component contains a thermosetting resin including a specific epoxy resin, so that the electromagnetic wave shielding film 1 exhibits good adhesion and maintains a low connection resistance value even after being placed in a high-temperature, high-humidity environment.

<Other embodiments>
The electromagnetic wave shielding film of the present invention is not limited to the embodiment shown in the figures, as long as it has an insulating resin layer, a shielding layer adjacent to the insulating resin layer, and a conductive adhesive layer adjacent to the shielding layer on the opposite side to the insulating resin layer.
For example, the insulating resin layer may be two or more layers.
The first release film may have a release agent layer instead of the pressure-sensitive adhesive layer.
The second release film may have a pressure-sensitive adhesive layer instead of the release agent layer.
The first release film or the second release film may not have a pressure-sensitive adhesive layer or a release agent layer, and may be composed of only a base layer.
When the insulating resin layer has sufficient flexibility and strength, the first release film may be omitted.
If the surface of the conductive adhesive layer has little tack, the second release film may be omitted.

(Printed wiring board with electromagnetic shielding film)
The printed wiring board with electromagnetic wave shielding film of the present invention comprises a printed wiring board having 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 invention, in which a conductive adhesive layer is provided adjacent to the insulating film.

FIG. 7 is a cross-sectional view showing a first embodiment of a printed wiring board with an electromagnetic shielding film obtained by the manufacturing method of the present invention.
The flexible printed wiring board 2 with an electromagnetic wave shielding film includes a flexible printed wiring board 50, an insulating film 60, and the electromagnetic wave shielding film 1 of the first embodiment.
The flexible printed wiring board 50 has a printed circuit 54 provided on at least one surface of a base film 52 .
The insulating film 60 is provided on the surface of the flexible printed wiring board 50 on which the printed circuit 54 is provided.
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 (not shown) formed in the insulating film 60.
In the flexible printed wiring board 2 with an electromagnetic wave shielding film, the second release film 40 is peeled off from the anisotropic conductive adhesive layer 24 .
When the first release film 30 becomes unnecessary in the flexible printed wiring board 2 with an electromagnetic wave shielding film, the first release film 30 is peeled off from the insulating resin layer 10 .

In the vicinity of the printed circuit 54 (signal circuit, ground circuit, ground layer, etc.) excluding the portion with the through hole, the shielding layer 20 of the electromagnetic wave shielding film 1 is positioned opposite and spaced apart via the insulating film 60 and the anisotropic conductive adhesive layer 24.
The distance between the printed circuit 54 and the shielding layer 20, excluding the portion with the through holes, is approximately equal to the sum of the thickness of the insulating film 60 and the thickness of the anisotropic conductive adhesive layer 24. The 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 distance is smaller than 15 μm, the line width of the signal circuit must be reduced in order to adjust the characteristic impedance of the signal circuit, making it technically difficult to manufacture a stable printed circuit 54. If the distance is larger than 200 μm, the flexible printed wiring board 2 with the electromagnetic shielding film becomes thick and the flexibility is insufficient.

<Flexible printed wiring board>
The flexible printed wiring board 50 is formed by processing the copper foil of a copper-clad laminate into a desired pattern by a known etching method to form a printed circuit (power supply circuit, ground circuit, ground layer, etc.).
Examples of copper-clad laminates include those in which copper foil is attached to one or both sides of a base film 52 via an adhesive layer (not shown); and those in which a resin solution or the like that forms a base film 52 is cast onto the surface of the copper foil.
Examples of materials for the adhesive layer include epoxy resins, polyesters, polyimides, polyamideimides, polyamides, phenolic resins, urethane resins, acrylic resins, and melamine resins.
The thickness of the adhesive layer is preferably 0.5 μm or more and 30 μm or less.

<<Base film>>
The base film 52 is preferably a film having heat resistance, more preferably a polyimide film or a liquid crystal polymer film, and even more preferably a polyimide film.
The surface resistance of the base film 52 is preferably 1×10 ⁶ Ω or more from the viewpoint of electrical insulation, and is preferably 1×10 ¹⁹ Ω or less from the viewpoint of practical use.
The thickness of the base film 52 is preferably 5 μm or more and 200 μm or less, and from the viewpoint of flexibility, is more preferably 6 μm or more and 25 μm or less, and even more preferably 10 μm or more and 25 μm or less.

<<Printed Circuit>>
Examples of the copper foil constituting the printed circuit 54 (signal circuit, ground circuit, ground layer, etc.) include rolled copper foil and electrolytic copper foil, with rolled copper foil being preferred from the standpoint of flexibility.
The thickness of the copper foil is preferably from 1 μm to 50 μm, and more preferably from 7 μm to 35 μm.
The ends (terminals) of the printed circuit 54 in the longitudinal direction are not covered by the insulating film 60 or the electromagnetic wave shielding film 1 because they are used for soldering, connector connection, component mounting, and the like.

<Insulating film>
The insulating film 60 is an insulating film body (not shown) having an adhesive layer (not shown) formed on one side thereof by applying an adhesive, attaching an adhesive sheet, or the like.
The surface resistance of the insulating film body is preferably 1×10 ⁶ Ω or more from the viewpoint of electrical insulation, and is preferably 1×10 ¹⁹ Ω or less from the viewpoint of practical use.
The insulating film body is preferably a film having heat resistance, more preferably a polyimide film or a liquid crystal polymer film, and even more preferably a polyimide film.
The thickness of the insulating film body is preferably 1 μm or more and 100 μm or less, and from the viewpoint of flexibility, more preferably 3 μm or more and 25 μm or less.
Examples of materials for the adhesive layer include epoxy resins, polyesters, polyimides, polyamideimides, polyamides, phenolic resins, urethane resins, acrylic resins, melamine resins, polystyrene, polyolefins, etc. The epoxy resins may contain a rubber component (such as carboxy-modified nitrile rubber) for imparting flexibility.
The thickness of the adhesive layer is preferably from 1 μm to 100 μm, and more preferably from 1.5 μm to 60 μm.

The shape of the opening of the through hole is not particularly limited. Examples of the shape of the opening of the through hole 62 include a circle, an ellipse, a rectangle, etc.

(Method of manufacturing a printed wiring board with an electromagnetic wave shielding film)
The method for producing a printed wiring board with an electromagnetic wave shielding film of the present invention includes a step of bonding a printed wiring board having a printed circuit on at least one side of a substrate to the above-mentioned electromagnetic wave shielding film of the present invention via an insulating film, and during the bonding, the insulating film is adhered to the side of the printed wiring board on which the printed circuit is provided and also to the adhesive layer of the electromagnetic wave shielding film.
The method for producing a printed wiring board with an electromagnetic wave shielding film of the present invention includes producing an electromagnetic wave shielding film by the above-mentioned method for producing an electromagnetic wave shielding film of the present invention, and then carrying out the following steps (a) and (b).
Step (a): A step of providing an insulating film on the surface of the printed wiring board on which the printed circuit is provided, to obtain a printed wiring board with an insulating film.
Step (b): When the electromagnetic wave shielding film has a second release film, a step of peeling the second release film from the electromagnetic wave shielding film, then overlapping the printed wiring board with the insulating film and the electromagnetic wave shielding film so that the conductive adhesive layer is in contact with the surface of the insulating film, and pressing them to adhere the conductive adhesive layer to the surface of the insulating film, thereby obtaining a printed wiring board with the electromagnetic wave shielding film.

As a more preferred embodiment, the method for producing a printed wiring board with an electromagnetic wave shielding film of the present invention includes the following steps (a) to (d).
Step (a): A step of providing an insulating film on the surface of the printed wiring board on which the printed circuit is provided, to obtain a printed wiring board with an insulating film.
Step (b): When the electromagnetic wave shielding film has a second release film, a step of peeling the second release film from the electromagnetic wave shielding film, then overlapping the printed wiring board with the insulating film and the electromagnetic wave shielding film so that the conductive adhesive layer is in contact with the surface of the insulating film, and pressing them together to press the conductive adhesive layer onto the surface of the insulating film, thereby obtaining a printed wiring board with the electromagnetic wave shielding film.
Step (c): In the case where the electromagnetic wave shielding film has a first release film, a step of peeling off the first release film from the electromagnetic wave shielding film when the first release film is no longer needed after step (b).
Step (d): If the adhesive contained in the conductive adhesive layer is a thermosetting adhesive, a step of fully curing the conductive adhesive layer, as necessary, between step (a) and step (b) or after step (c).

The method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film is described below with reference to Figure 8.

<Step (a)>
8, an insulating film 60 having through holes 62 formed in positions corresponding to the printed circuits 54 is overlaid on the flexible printed wiring board 50, an adhesive layer (not shown) of the insulating film 60 is bonded to the surface of the flexible printed wiring board 50, and the adhesive layer is cured to obtain a flexible printed wiring board 3 with an insulating film. The adhesive layer of the insulating film 60 may be temporarily bonded to the surface of the flexible printed wiring board 50, and the adhesive layer may be fully cured in step (d).
The adhesive layer is bonded and cured, for example, by hot pressing using a press (not shown) or the like.

<Step (b)>
As shown in Figure 8, the electromagnetic wave shielding film 1 from which the second release film 40 has been peeled off is placed on top of a flexible printed wiring board 3 with an insulating film, and pressed (preferably hot pressed) to obtain a flexible printed wiring board 2 with an electromagnetic wave shielding film in which the anisotropic conductive adhesive layer 24 is pressure-bonded to 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.
In the diagram of step (b) in FIG. 8, the printed circuit 54 comprises a ground circuit 54a and a signal circuit 54b (54a and 54b are not shown).

The anisotropic conductive adhesive layer 24 is bonded by, for example, heat pressing using a press (not shown) or the like.
The time for the heat press is preferably from 20 seconds to 60 minutes, and more preferably from 30 seconds to 30 minutes.
The temperature of the heat press (the temperature of the hot platens of the press) is preferably 140°C or higher and 210°C or lower, and more preferably 150°C or higher and 190°C or lower.
The pressure of the heat press is preferably from 0.5 MPa to 20 MPa, and more preferably from 1 MPa to 16 MPa.

<Step (c)>
As shown in FIG. 8, when the first release film 30 is no longer needed, the first release film 30 is peeled off from the insulating resin layer 10 .

<Action and effect>
The printed wiring board 2 with the electromagnetic shielding film of this embodiment has the characteristics of the electromagnetic shielding film of the present invention described above, and is a printed wiring board with an electromagnetic shielding film in which the shielding layer is satisfactorily grounded to the ground circuit of the printed wiring board.

<Other embodiments>
Incidentally, the printed wiring board with an electromagnetic wave shielding film in the present invention is not limited to the embodiment shown in the figures as long as it has a printed wiring board, an insulating film adjacent to the surface of the printed wiring board on which the printed circuit is provided, and an electromagnetic wave shielding film having an adhesive layer adjacent to the insulating film.
For example, the flexible printed wiring board may have a ground layer on the back side. Also, the flexible printed wiring board may have printed circuits on both sides, and an insulating film and an electromagnetic wave shielding film may be attached to both sides.
Instead of a flexible printed wiring board, a rigid printed circuit board that has no flexibility may be used.
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 may be used.

The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.
The structural formula of the epoxy resin used in each example is shown below.

Example 1
<Formulation of adhesive paint for insulating resin layer>
As the adhesive paint to be contained in the insulating resin layer, 20.6 parts by mass of bisphenol A type epoxy resin (jER (registered trademark) 828 manufactured by Mitsubishi Chemical Corporation), 60.7 parts by mass of flexible epoxy resin (epoxy resin (EXA-4816 manufactured by DIC Corporation)), 16.7 parts by mass of hardener (Showa Denko K.K., Showamine 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 prepare a paint for the insulating resin layer.

<Formulation of adhesive paint for conductive adhesive layer>
As the adhesive paint to be contained in the conductive adhesive layer, 79 parts by mass of an epoxy resin having the structural formula represented by the above formula (1) (DIC Corporation, EPICLON HP7200L (for a specific structural formula, see the above formula (a))), 20 parts by mass of an acrylic acid ester polymer (Nagase ChemteX Corporation, Teisan Resin SG-P3 (Tg 12 ° C., acid value 0 mg KOH / g, epoxy equivalent 0.21 eq. / kg)), 1 part by mass of an imidazole-based epoxy resin hardener (Shikoku Kasei Corporation, Curesol 2P4MZ (2 phenyl 4 methyl imidazole)), and 20 parts by mass of copper particles (average particle diameter 5.02 μm) were mixed to prepare an adhesive paint for the conductive adhesive layer. The blending ratio of the adhesive paint for the conductive adhesive layer is shown in Table 1 below.

<Preparation of electromagnetic wave shielding film>
A first release film was prepared in which an adhesive layer made of an acrylic adhesive was provided on one side of a PET film (manufactured by Toyobo Co., Ltd., CN200, film thickness 50 μm).
The coating material for the insulating resin layer was applied to the surface of the pressure-sensitive adhesive layer of the first release film using a die coater, and then dried to form an insulating resin layer (10 μm).
Next, copper was physically deposited by electron beam deposition on the surface of the insulating resin layer opposite to the first release film to form a shielding layer (thickness 300 nm) made of a copper deposition film.
Next, the adhesive paint for the conductive adhesive layer was applied to the surface of the shield layer opposite the insulating resin layer using a die coater, and then dried to form a conductive adhesive layer (film thickness 5 μm).
A second release film was prepared in which a release layer made of a non-silicone release agent was provided on one side of a PET film (T157, manufactured by Lintec Corporation, release film body thickness: 50 μm, release agent layer thickness: 0.1 μm).
The second release film was attached to the side of the conductive adhesive layer opposite the shielding layer so that the release agent layer was in contact with the conductive adhesive layer, thereby obtaining the electromagnetic wave shielding film of Example 1.

<Preparation of printed wiring board with electromagnetic shielding film>
The insulating adhesive composition was applied to the surface of a 25 μm-thick polyimide film (insulating film body) so that the dry film thickness was 25 μm to form an adhesive layer, and an insulating film (thickness: 50 μm) was obtained. A through hole (hole diameter: 800 μm) was formed at a position corresponding to the ground circuit of the printed circuit.
A printed wiring board was prepared in which a printed circuit was formed on the surface of a 12 μm thick polyimide film (base film).
An insulating film was attached to the printed wiring board by hot pressing to obtain a printed wiring board with an insulating film.
The electromagnetic wave shielding film of Example 1 from which the second release film had been peeled off was placed on top of the printed wiring board with an insulating film, and then hot-pressed for 30 minutes using a hot press device with a hot plate temperature of 180°C and a load of 3 MPa to bond a conductive adhesive layer to the surface of the insulating film.
The first release film was peeled off from the insulating resin layer to obtain a printed wiring board with an electromagnetic wave shielding film.

<Measurement of Water Absorption Rate (%) of Adhesive Component>
The adhesive component is applied onto a PET substrate and heated to 150° C. for 1 hour to produce a hardened layer.
A test piece made of the cured layer is exposed to conditions of 85° C., 48 hours, and 85% relative humidity, and the mass change of the test piece, i.e., the difference between the initial mass and the mass after exposure to water, is measured and expressed as a percentage of the initial mass.
The results of measuring the water absorption rate of the adhesive component used in Example 1 are shown in Table 1 below.

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

[Connectivity evaluation]
In a printed wiring board with an electromagnetic shielding film, the electrical connection between the wiring-shielding layer-wiring was measured via the electromagnetic shielding film present in the through-hole (also called a connection hole).
A tester was placed against the printed wiring board with the electromagnetic shielding film to measure the resistance between the wiring, the shielding layer and the wiring.
The connection resistance was evaluated according to the following criteria.
○ Less than 300mΩ △ 300mΩ to less than 1000mΩ × 1000mΩ or more

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

(Examples 2 to 11)
In Example 1, the conditions of the conductive adhesive layer were changed as shown in Tables 1 and 2, but the printed wiring boards with electromagnetic shielding films of Examples 2 to 11 were produced in the same manner as in Example 1.
In Example 2, EPICLON HP7200HHH (for a specific structural formula, see formula (a) above) manufactured by DIC Corporation was used as the epoxy resin.
In Example 3, NC3000 (for the specific structural formula, see formula (b) above) manufactured by Nippon Kayaku Co., Ltd. was used as the epoxy resin.
In Example 4, NC2000-L (for a specific structural formula, see formula (c) above) manufactured by Nippon Kayaku Co., Ltd. was used as the epoxy resin.
In Example 5, EPPN-201 (for a specific structural formula, see formula (d) above) manufactured by Nippon Kayaku Co., Ltd. was used as the epoxy resin.
In Example 10, Teisan Resin SG-70L (Tg -13°C, acid value 5 mgKOH/g, no epoxy equivalent) manufactured by Nagase Chemtex Corporation was used as the acrylic acid ester polymer.

The water absorption of the adhesive components used in Examples 2 to 11 was measured in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Furthermore, the printed wiring boards with electromagnetic shielding films 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.

(Comparative Example 1 to Comparative Example 3)
In Example 1, the conditions of the conductive adhesive layer were changed as shown in Table 1, and the same procedure as in Example 1 was repeated to prepare printed wiring boards with electromagnetic shielding films of Comparative Examples 1 to 3.
In Comparative Example 1, jER1001 (for a specific structural formula, see formula (e) above) manufactured by Mitsubishi Chemical Corporation was used as the epoxy resin.
In Comparative Example 2, jER157S70 (for a specific structural formula, see formula (f) above) manufactured by Mitsubishi Chemical Corporation was used as the epoxy resin.
In Comparative Example 3, Teisan Resin SG-280 (Tg -29°C, acid value 30 mgKOH/g, no epoxy equivalent) manufactured by Nagase Chemtex Corporation was used as the acrylic acid ester polymer.

The water absorption rates of the adhesive components used in Comparative Examples 1 to 3 were measured in the same manner as in Example 1. The results are shown in Table 2.
Moreover, the printed wiring boards with electromagnetic shielding films produced in Comparative Examples 1 to 3 were evaluated in the same manner as in Example 1. The results are shown in Table 2.

As is clear from the above examples, it has been found that the electromagnetic wave shielding film of the present invention reliably exhibits good adhesion and can maintain a low connection resistance even after 500 hours have passed since being placed in a high-temperature, high-humidity environment.
It was also found that when a specific rubber component is contained in the adhesive component, good adhesion can be exhibited and a low connection resistance can be maintained even after 1000 hours have elapsed.

The electromagnetic wave shielding film of the present invention is useful as an electromagnetic wave shielding component in flexible printed wiring boards for electronic devices such as smartphones, mobile phones, optical modules, digital cameras, game consoles, notebook computers, and medical devices.

1 Electromagnetic wave shielding film 2 Flexible printed wiring board with electromagnetic wave shielding film 3 Flexible printed wiring board with insulating film 10 Insulating resin layer 20 Shielding layer 22 Conductive adhesive layer 24 Anisotropic conductive adhesive layer 24a Adhesive 24b Conductive particles 26 Isotropic conductive adhesive layer 26a Adhesive 26b Conductive particles 30 First release film 32 Base layer 34 Pressure-sensitive adhesive layer/release agent layer 40 Second release film 42 Base layer 44 Release agent layer/pressure-sensitive adhesive layer 50 Flexible printed wiring board 52 Base film 54 Printed circuit 60 Insulating film 62 Through hole

Claims (6)

An electromagnetic wave shielding film comprising an insulating resin layer, a shielding layer, and a conductive adhesive layer laminated in this order,
The conductive adhesive layer is formed using a conductive adhesive composition containing an adhesive component and conductive particles,
The water absorption rate 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,
The epoxy resin contains an epoxy resin having a structural formula represented by the following general formula (1) and exhibiting an epoxy equivalent of 215 to 400 g/eq, and does not contain any epoxy resin other than the structural formula represented by the following general formula (1):
The rubber component has an epoxy equivalent of 0.05 eq/kg or more .

(In the above formula (1), _R1 represents an alicyclic hydrocarbon having 1 to 35 carbon atoms or a hydrocarbon group having a structure containing an aromatic hydrocarbon , _R2 represents hydrogen or a methyl group, and n represents an integer of 1 to 10.) The electromagnetic shielding film according to claim 1, wherein the adhesive component contains 30 to 70 mass % of the epoxy resin. 3. The electromagnetic wave shielding film according to claim 1 , wherein the epoxy equivalent is 250 to 400 g/eq. 4. The electromagnetic wave shielding film according to claim 1, wherein the acid value of the rubber component is 20 mgKOH/g or less. 5. The electromagnetic wave shielding film according to claim 1, wherein the rubber component has a glass transition temperature of 10° C. or higher. A printed wiring board having a printed circuit provided on at least one surface of a substrate;
an insulating film adjacent to a surface of the printed wiring board on which the printed circuit is provided;
The electromagnetic wave shielding film according to any one of claims 1 to 5 , wherein the conductive adhesive layer is provided adjacent to the insulating film;
A printed wiring board with an electromagnetic wave shielding film.

Images