CN114945268A - Electromagnetic wave shielding film and printed wiring board with electromagnetic wave shielding film - Google Patents

Abstract

The invention provides a practical electromagnetic wave shielding film which can show good sealing property and maintain low connection resistance value after being placed in a high-temperature high-humidity environment, and has high universality. The electromagnetic wave shielding film is formed by sequentially laminating an insulating resin layer, a shielding layer and a conductorThe conductive adhesive layer is formed by using a conductive adhesive composition containing an adhesive component and conductive particles, wherein the water absorption rate of the adhesive component is less than 2.0%, the adhesive component contains a thermosetting resin, and the thermosetting resin contains an epoxy resin which has a structural formula shown in the general formula (1) and presents an epoxy equivalent of 170-400 g/eq.

(in the above formula (1), R ₁ Represents a hydrocarbon group having 1 to 35 carbon atoms, R ₂ Represents hydrogen or methyl, and n represents an integer of 1 to 10).

Description

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

Technical Field

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

Background

In order to shield (shield) electromagnetic wave noise generated from a flexible printed wiring board (hereinafter, also referred to as FPC) and electromagnetic wave noise from the outside, a method of bonding 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 to a flexible printed wiring board via an insulating film (hereinafter, also referred to as a cover film) is known.

In such a method, the conductive adhesive layer of the electromagnetic wave shielding film of the printed wiring board and the ground circuit of the printed wiring board are connected to each other through an opening provided in an insulating film covering the ground circuit, and are shielded.

As a conductive adhesive composition constituting a conductive adhesive layer of an electromagnetic wave shielding film, various conductive adhesive compositions are known (for example, see patent documents 1 and 2).

Prior art documents

Patent document

Patent document 1: JP-A2019-196458

Patent document 2: JP 5854248A

Disclosure of Invention

(problems to be solved by the invention)

In addition to the bending resistance and heat resistance required for the entire flexible printed wiring board, the electromagnetic shielding film is required to have durability capable of maintaining high adhesion and low connection resistance in a high-temperature and high-humidity environment.

However, when the electromagnetic wave shielding film is placed in a high-temperature and high-humidity environment, the adhesive layer deteriorates with time, the adhesion decreases, and the metal conductive particles and the shielding layer are oxidized, so that there is a problem that a low connection resistance value cannot be maintained after the electromagnetic wave shielding film is placed in a high-temperature and high-humidity environment.

Patent document 1 describes that the adhesion under a high-temperature and high-humidity environment is improved by using an adhesive composition having a specific compounding ratio, but does not particularly mention the connection resistance value when placed under a high-temperature and high-humidity environment. There is room for improvement from the viewpoint of providing an electromagnetic wave shielding film that can exhibit good adhesion even after being left in a high-temperature and high-humidity environment and maintain a low connection resistance value.

Further, patent document 2 describes that a conductive adhesive having high connection reliability even after wet heat aging treatment can be provided by using surface-coated conductive fine particles, but the technique of patent document 2 has a problem that selection of conductive fine particles is complicated, production cost is increased, and versatility is poor.

Accordingly, an object of the present invention is to provide a highly versatile and practical electromagnetic wave shielding film that exhibits good adhesion and maintains a low connection resistance value even after being placed in a high-temperature and high-humidity environment.

(means for solving the problems)

As a result of intensive studies to solve the above problems, the present inventors have found that an electromagnetic wave shielding film capable of solving the above problems can be provided by using an adhesive component exhibiting a specific water absorption rate as a conductive adhesive composition used in a conductive adhesive layer constituting an electromagnetic wave shielding film and by including a thermosetting resin containing a specific epoxy resin in the adhesive component, and have completed the present invention.

The present invention includes the following embodiments.

[1] An electromagnetic wave shielding film is formed by sequentially laminating an insulating resin layer, a shielding layer and a conductive adhesive layer, wherein the conductive adhesive layer is formed by 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 the thermosetting resin contains an epoxy resin which has a structural formula shown in the general formula (1) and presents 170-400 g/eq of epoxy equivalent.

[ CHEM 1]

(in the above formula (1), R ₁ Represents a hydrocarbon group having 1 to 35 carbon atoms, R ₂ Represents hydrogen or methyl, and n represents an integer of 1 to 10. )

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

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

[4]In [1]]～[3]The electromagnetic wave shielding film according to any one of the above general formulae (1), wherein R is ₁ Is a hydrocarbon group having a structure containing an alicyclic hydrocarbon or 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 rubber component has an acid value of 20mgKOH/g or less.

[8] The electromagnetic wave shielding film according to [6] or [7], wherein the rubber component has an epoxy equivalent of 0.05eq/kg or more.

[9] The electromagnetic wave shielding film according to any one of [6] to [8], wherein a glass transition temperature of the rubber component is 10 ℃ or higher.

[10] A printed wiring board with an electromagnetic wave shielding film, comprising: 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; and the electromagnetic wave-shielding film according to any one of [1] to [9], which is provided so that the conductive adhesive layer is adjacent to the insulating film.

(effect of the invention)

According to the present invention, a highly versatile and practical electromagnetic wave shielding film can be provided which exhibits good adhesion and maintains a low connection resistance value even after being placed in a high-temperature and high-humidity environment.

Drawings

Fig. 1 is a cross-sectional view showing an 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 the manufacturing steps of steps (a1-1) to (a1-4) as an embodiment of the manufacturing step of the electromagnetic wave shielding film of fig. 1.

Fig. 4 is a cross-sectional view showing the manufacturing steps of steps (a2-1) to (a2-2) as another embodiment of the manufacturing step of the electromagnetic wave shielding film of fig. 1.

Fig. 5 is a cross-sectional view showing a manufacturing process of the process (a2-3) as another embodiment of the manufacturing process of the electromagnetic wave shielding film of fig. 1.

Fig. 6 is a cross-sectional view showing a manufacturing process of the process (a2-4) as another embodiment of the manufacturing process of the electromagnetic wave shielding film of fig. 1.

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

Fig. 8 is a cross-sectional view showing a manufacturing process of the printed wiring board with an electromagnetic wave shielding film of fig. 7.

Detailed Description

The electromagnetic wave shielding film of the present invention will be described in detail below, but the description of the constituent elements described below is an example of one embodiment of the present invention and is not limited to these contents.

The following definitions of terms apply throughout the present specification and claims.

The "isotropic conductive adhesive layer" refers to a conductive adhesive layer having conductivity in the thickness direction and the surface direction.

The "anisotropic conductive adhesive layer" refers to a conductive adhesive layer having conductivity in the thickness direction and not having conductivity in the surface direction.

The phrase "a conductive adhesive layer having no conductivity in the in-plane direction" means that the surface resistance is 1X 10 ⁴ And a conductive adhesive layer having an omega or higher.

The average particle diameter of the conductive particles is a value obtained as follows: the conductive particle size is obtained by randomly selecting 30 conductive particles from a microscopic image of the conductive particles, measuring the minimum diameter and the maximum diameter of each conductive particle, and arithmetically averaging the measured particle sizes of the 30 conductive particles with the median value of the minimum diameter and the maximum diameter as the particle size of one particle.

The film thickness of the film (release film, insulating film, etc.), coating film (insulating resin layer, conductive adhesive layer, etc.), shielding layer (electromagnetic wave shielding layer), etc. is a value obtained by observing the cross section of the measurement object with a microscope, measuring the thickness at 5 points, and averaging the thickness.

Surface resistance of less than 10 ⁶ In the case of Ω/□, the surface resistivity was measured by a four-terminal method (method in accordance with JIS K7194: 1994 and JIS R1637: 1998) using a low-resistance resistivity meter (for example, Loresta GP, ASP Probe manufactured by Mitsubishi chemical corporation) at 10 ⁶ The term "Ω/□" or higher means the surface resistivity measured by a double loop method (method according to JIS K6911: 2006) using a high resistivity meter (for example, Hiresta UP, URS probe manufactured by Mitsubishi chemical corporation).

(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 containing an adhesive component and conductive particles.

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

The adhesive component contains a thermosetting resin.

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.

[ CHEM 2]

(in the above formula (1), R ₁ Represents a C1-35 hydrocarbon group, R ₂ Represents hydrogen or methyl, and n represents an integer of 1 to 10. )

Fig. 1 is a cross-sectional view showing one embodiment of an 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 shield layer 20 adjacent to the insulating resin layer 10; a conductive adhesive layer 22 adjacent to the side of the shield layer 20 opposite to the insulating resin layer 10; a first release film 30 adjacent to the side of the insulating resin layer 10 opposite to the shielding layer 20; and a second release film 40 adjacent to the conductive adhesive layer 22 on the side opposite to the shield 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 isotropic conductive adhesive layer 26.

< insulating resin layer >

The insulating resin layer 10 is a protective layer for the shield layer 20, which is formed by attaching the electromagnetic wave shielding film 1 to the surface of the insulating film provided on the surface of the printed wiring board and peeling off the first release film 30.

Examples of the insulating resin layer 10 include: a coating film formed by coating a composition containing a thermosetting resin and a curing agent and semi-curing or curing the composition; a coating film formed by applying a coating liquid containing a thermosetting resin, a curing agent and a solvent and drying, semi-curing or curing the coating liquid, and the like. The insulating resin layer 10 is preferably a coating film formed by applying a coating solution containing a resin material (a combination of a thermosetting resin and a curing agent) and a solvent, drying the coating solution, and semi-curing or curing the coating solution as necessary, from the viewpoint of further improving the adhesion between the insulating resin layer 10 and the shield layer 20.

Examples of the thermosetting resin include amide resins, epoxy resins, phenol resins, amino resins, alkyd resins, urethane resins, synthetic rubbers, and ultraviolet-curable acrylate resins. As the thermosetting resin, an amide resin and an epoxy resin are preferable in terms of excellent heat resistance.

Examples of the curing agent include known curing agents corresponding to the type of the thermosetting resin.

In order to hide a printed circuit of a printed wiring board with an electromagnetic wave shielding film or to impart design properties to a printed wiring board with an electromagnetic wave shielding film, the insulating resin layer 10 may contain either or both of a colorant (pigment, dye, or the like) and a filler.

Either or both of the colorant and the filler are preferably a pigment or a filler from the viewpoint of weather resistance, heat resistance and concealing properties, and more preferably a black pigment or a combination of a black pigment and another pigment or a filler from the viewpoint of concealing properties and designing properties of a printed circuit.

The insulating resin layer 10 may contain other components as necessary within a range not impairing the effects of the present invention.

The surface resistance of the insulating resin layer 10 is preferably 1 × 10 from the viewpoint of electrical insulation ⁶ Omega or more. From the practical viewpoint, the surface resistance of the insulating resin layer 10 is preferably 1 × 10 ¹⁹ Omega is less than or equal to.

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 greater 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 not more than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thin.

< Shielding layer (electromagnetic wave shielding layer)) >

The shield layer 20 is not particularly limited as long as it has conductivity, 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 plane direction, and therefore has conductivity in the plane direction, and functions as an electromagnetic wave shield layer or the like.

Examples of the metal constituting the metal film include 1 kind selected from nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, and zinc, or an alloy containing any 1 or more kinds of these. Among them, copper and copper-containing alloys are preferable from the viewpoint of shielding properties and economy.

Examples of the method for forming a metal film include a vapor deposition film formed by physical vapor deposition (vacuum vapor deposition, sputtering, ion beam vapor deposition, electron beam vapor deposition, or the like) or chemical vapor deposition, a plating film formed by plating, and a metal foil. Among them, a vacuum vapor deposition film or a sputtering film formed by a vacuum film formation method (such as a vacuum vapor deposition method or a sputtering method), or a plating film formed by an electroplating method is preferable in terms of excellent conductivity in the plane direction. A vapor deposited film by a vacuum deposition method is more preferable in that the film can be made thin, has excellent conductivity in the plane direction even if the film is thin, and can be easily formed by a dry process. The metal film may be a metal foil formed by rolling, a metal foil produced by electrolysis (for example, a special electrolytic copper foil), or the like.

When the shield layer is a conductive film made of conductive particles, the conductive particles may be particles of carbon, silver, copper, nickel, solder, or the like, for example. The conductive particles may be silver-coated copper particles obtained by plating copper powder with silver, particles obtained by plating insulating particles such as resin balls or glass beads with metal, or the like. These conductive particles can be used alone or in a mixture of 2 or more.

The shape of the conductive particles may be any of spherical, needle-like, fibrous, flake-like, or dendritic, and from the viewpoint of forming a layer, a flake-like shape is preferable.

The thickness of the shield 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. When 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 equal to or less than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thin. In addition, the productivity and flexibility of the electromagnetic wave shielding film 1 are improved.

The surface resistance of the shield layer 20 is preferably 0.001 Ω to 1 Ω, and more preferably 0.001 Ω to 0.1 Ω. If the surface resistance of the shield layer 20 is equal to or higher than the lower limit of the above range, the shield layer 20 can be made sufficiently thin. When the surface resistance of the shielding layer 20 is not more than the upper limit of the above range, it can sufficiently function as an electromagnetic wave shielding layer.

< conductive adhesive layer >

The conductive adhesive layer 22 is a layer for adhering the electromagnetic wave shielding film 1 to the 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 the printed wiring board.

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

Examples of the conductive adhesive layer include an anisotropic conductive adhesive layer 24 having conductivity in the thickness direction and not having conductivity in the surface direction, and an isotropic conductive adhesive layer 26 having conductivity in the thickness direction and the surface direction. The conductive adhesive layer is preferably an anisotropic conductive adhesive layer 24 in view of not having conductivity in the plane direction and having good transmission characteristics and good flexibility of the electromagnetic wave shielding film 1. The isotropic conductive adhesive layer 26 is preferable as the conductive adhesive layer in that it can sufficiently function as an electromagnetic wave shielding layer.

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.

< adhesive component >

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

The adhesive component contains a thermosetting resin.

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.

[ CHEM 3]

(in the above formula (1), R ₁ Represents a hydrocarbon group having 1 to 35 carbon atoms, R ₂ Represents hydrogen or methyl, and n represents an integer of 1 to 10. )

As R in the above formula (1) ₁ The 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 composed of an appropriate combination thereof.

As R ₁ For example, the following groups can be exemplified.

[ CHEM 4]

R in the above formula (1) ₂ Methyl groups are more hydrophobic than hydrogen, and therefore can reduce the hygroscopicity of the adhesive component, and are more preferred.

The epoxy resin having the structural formula represented by the general formula (1) and exhibiting an epoxy equivalent of 170 to 400g/eq (in the present specification, the epoxy resin is also referred to as a "specific epoxy resin") may contain 1 or 2 or more species.

By using an epoxy resin having a polyfunctional structure represented by the above formula (1) as the epoxy resin, the crosslinking density of the conductive adhesive layer at the time of curing can be increased, and the conductive particles are stably immobilized, so that the conductive adhesive layer can secure excellent adhesiveness.

The adhesive component preferably contains 30 to 70 mass% of a specific epoxy resin.

If the content of the specific epoxy resin in the adhesive component is 30% by mass or more, the problem that the adhesiveness cannot be secured due to curing failure can be effectively prevented. If the content is 70% by mass or less, the problem that the connectivity cannot be ensured due to the influence of moisture absorption can be effectively prevented.

The epoxy equivalent of the specific epoxy resin is 170 to 400 g/eq.

By limiting the epoxy equivalent, the OH group (hydrophilic) and the functional group R of the epoxy group which can be opened at the time of curing can be formed ₁ (hydrophobicity) optimization.

If the epoxy equivalent is too small, the functional group R ₁ The effect of (2) is insufficient, and the conductive particles may be oxidized by moisture absorption, resulting in poor connectivity. On the other hand, if the epoxy equivalent is too large, the number of OH groups is small, and adhesion and crosslinking properties are deteriorated, and there is a possibility that the connectivity is deteriorated.

The epoxy equivalent is preferably 190g/eq or more, more preferably 215g/eq or more, still more preferably 245g/eq or more, particularly preferably 250g/eq or more, and further preferably 300g/eq or less.

The epoxy equivalent can be measured according to JIS K7236: 2001, respectively.

In the present invention, by making the water absorption rate of the adhesive component in the conductive adhesive layer less than 2.0%, and blending a specific epoxy resin in the adhesive component, it is possible to suppress deterioration of the conductive adhesive layer and oxidation due to moisture absorption of the conductive particles and the shield layer, and it is possible to form an electromagnetic wave shield film capable of maintaining a low connection resistance value even in a high-temperature and high-humidity environment.

The adhesive component may contain an epoxy resin other than the specific epoxy resin and a thermosetting resin other than the epoxy resin as long as the effects of the present invention are not impaired.

Examples of the other thermosetting resin include a phenol resin, an amino resin, an alkyd resin, a urethane resin, a synthetic rubber, and an ultraviolet-curable acrylate resin.

The adhesive component further contains a curing agent in addition to the thermosetting resin.

Examples of the curing agent include latent curable adhesives that are cured by reaction with a thermosetting resin upon heating.

The curing agent includes an addition type curing agent having a plurality of functional groups capable of reacting with the thermosetting resin, and a catalyst type curing agent such as a cation or anion which releases the strain energy of the epoxy group. The catalyst-type curing agent is preferable because the storage stability of the binder component is good.

The content of the catalyst-type curing agent in the adhesive component is preferably 0.1 part by mass or more and 50 parts by mass or less, more preferably 0.5 part by mass or more and 30 parts by mass or less, and still more 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.

In addition to the above-mentioned curing agent, various components such as a rubber component, a tackifier, a curing accelerator, and a stress reducer (stress relaxation agent) can be used as other components than the thermosetting resin that can be contained in the adhesive component.

The adhesive component may contain a rubber component (carboxyl-modified nitrile rubber, acrylic rubber, etc.) for imparting flexibility, a tackifier, and the like. The adhesive component may contain a curing accelerator, a stress reducer (stress relaxation agent), and the like.

The acid value of the rubber component contained in the adhesive component is preferably 20mgKOH/g or less from the viewpoint of adhesiveness and water absorption. The epoxy equivalent of the rubber component is preferably 0.05eq/kg or more and 1eq/kg or less from the viewpoint of reactivity with an epoxy resin. The glass transition temperature of the rubber component is preferably 10 ℃ or higher.

By containing a rubber component satisfying the above requirements in the adhesive component, an electromagnetic wave shielding film exhibiting good adhesion and capable of maintaining a low connection resistance value for a longer period of time can be provided even after being placed in a high-temperature and high-humidity environment.

Examples of the stress reducing agent include acrylonitrile butadiene rubber (NBR), acrylic rubber, styrene butadiene rubber, vinyl acetate resin, silicone resin, and the like.

The content of the stress reducer in the adhesive component is preferably 10 mass% or more and 80 mass% or less, and more preferably 30 mass% or more and 70 mass% or less, out of 100 mass% of the adhesive component (solid component) before curing. When the content of the stress reducing agent is within the above range, the flexibility of the conductive adhesive layer is excellent.

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

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

If the water absorption rate of the adhesive component is too high, for example, oxidation of the conductive particles is promoted, and the connectivity is deteriorated, and further, expansion is generated by vaporization of moisture, and the heat resistance is also deteriorated. On the other hand, if the water absorption of the adhesive component is too low, the compatibility with the epoxy resin is deteriorated.

The water absorption of the adhesive component can be determined in accordance with JIS K7209 as follows.

[ Water absorption ]

The adhesive component was coated on a PET substrate and heated at 150 ℃ for 1 hour to prepare a cured layer.

The test piece composed of the cured layer was exposed to 85 ℃ for 48 hours at a relative humidity of 85%. Then, the mass change of the test piece, i.e., the difference between the initial mass and the mass after exposure to water, was measured and found and characterized as a percentage of the initial mass.

< conductive particles >)

The conductive adhesive composition for forming the conductive adhesive layer contains conductive particles in addition to the above adhesive component.

As shown in fig. 1, the anisotropic conductive adhesive layer 24 includes, for example, an adhesive 24a containing the above resin and conductive particles 24 b.

As shown in fig. 2, the isotropic conductive adhesive layer 26 includes, for example, an adhesive 26a containing the resin and conductive particles 26 b.

Examples of the conductive particles include particles of a metal (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, or the like), graphite powder, fired carbon particles after plating, core-shell resin particles coated with a metal, and the like. The metal particles are preferable from the viewpoint of high conductivity, and the copper particles are more preferable from the viewpoint 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. When the average particle diameter of the conductive particles 24b is equal to or larger than the lower limit of the above range, the stability of electrical connection is improved, and the conductive particles 24b hardly impair the fluidity of the resin of the anisotropic conductive adhesive layer 24, so that the following property of the insulating film of the anisotropic conductive adhesive layer 24 to the shape of the through-hole can be secured. When the average particle diameter of the conductive particles 24b is not more than the upper limit of the above range, the conductive particles 24b do not inhibit the contact between the resin of the anisotropic conductive adhesive layer 24 and the surface of the adherend, and sufficient adhesion can be secured.

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. When the average particle diameter of the conductive particles 26b is equal to or larger than the lower limit of the above range, the contact frequency of the conductive particles 26b increases, and the conductivity in the 3-dimensional direction can be stably improved. When the average particle diameter of the conductive particles 26b is not more than the upper limit of the above range, the conductive particles 26b do not inhibit contact between the resin of the isotropic conductive adhesive layer 26 and the surface of the adherend, and sufficient adhesion can be secured.

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, out of 100 vol% of the anisotropic conductive adhesive layer 24. When the ratio of the conductive particles 24b is not less than the lower limit of the above range, the conductivity of the anisotropic conductive adhesive layer 24 becomes good. When the ratio of the conductive particles 24b is not more than the upper limit of the above range, the adhesiveness and fluidity (following ability to the shape of the through-hole of the insulating film) of the anisotropic conductive adhesive layer 24 become good. In addition, the flexibility of the electromagnetic wave shielding film 1 becomes good.

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, out of 100 vol% of the isotropic conductive adhesive layer 26. When the ratio of the conductive particles 26b is equal to or higher than the lower limit of the above range, the conductivity of the isotropic conductive adhesive layer 26 becomes good. When the ratio of the conductive particles 26b is not more than the upper limit of the above range, the adhesiveness and fluidity (following ability to the shape of the through-hole of the insulating film) of the isotropic conductive adhesive layer 26 become good. In addition, the flexibility of the electromagnetic wave shielding film 1 becomes good.

The surface resistance of the anisotropic conductive adhesive layer 24 is preferably 1 × 10 ⁴ Omega is 1 × 10 or more ¹⁶ Omega or less, more preferably 1X 10 ⁶ Omega and 1 × 10 ¹⁴ Omega is less than or equal to. When the surface resistance of the anisotropic conductive adhesive layer 24 is equal to or higher than the lower limit of the above range, the content of the conductive particles 24b is suppressed to be low. When the surface resistance of the anisotropic conductive adhesive layer 24 is not more than the upper limit of the above range, there is no problem in practical anisotropy.

The surface resistance of the isotropic conductive adhesive layer 26 is preferably 0.05 Ω to 2.0 Ω, and more preferably 0.1 Ω to 1.0 Ω. When the surface resistance of the isotropic conductive adhesive layer 26 is equal to or higher than the lower limit of the above range, 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 becomes further good. In addition, the fluidity of isotropic conductive adhesive layer 26 (the ability to follow the shape of the through-hole of the insulating film) can be further ensured. When the surface resistance of the isotropic conductive adhesive layer 26 is not more 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. When the thickness of the anisotropic conductive adhesive layer 24 is equal to or more than the lower limit of the above range, the flowability of the anisotropic conductive adhesive layer 24 (the ability to follow the shape of the through hole of the insulating film) can be ensured, and the through hole of the insulating film can be sufficiently filled with the conductive adhesive. Further, the distance between the electromagnetic wave shielding layer 20 and the printed circuit can be increased, and the transmission characteristics are improved. When the thickness of the anisotropic conductive adhesive layer 24 is not more than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thin. In addition, the flexibility of the electromagnetic wave shielding film 1 becomes good.

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. When the thickness of the isotropic conductive adhesive layer 26 is equal to or more than the lower limit of the above range, the adhesiveness is good. Further, the flowability of isotropic conductive adhesive layer 26 (following property to the shape of the through hole of the insulating film) can be ensured, the through hole of the insulating film can be sufficiently filled with the conductive adhesive, the bending resistance can be ensured, and isotropic conductive adhesive layer 26 is not broken even when repeatedly bent. When the thickness of the isotropic conductive adhesive layer 26 is not more than the upper limit of the above range, the electromagnetic wave shielding film 1 can be made thin. In addition, the flexibility of the electromagnetic wave shielding film 1 becomes good. Further, the isotropic conductive adhesive layer 26 having a higher surface resistance than the electromagnetic wave shielding layer 20 is thin, and transmission characteristics are improved.

< first mold Release film >

The first release film 30 serves as a protective film for the insulating resin layer 10, and improves the workability 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 insulating-film-equipped printed wiring board.

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

The first release film 30 may be formed by directly providing the adhesive layer/release agent layer 34 on the surface of the base layer 32, or may be formed by providing the adhesive layer/release agent layer 34 on the surface of the insulating resin layer 10 and then bonding the base layer 32 to the surface of the adhesive layer/release agent layer 34 to provide the adhesive layer/release agent layer 34 on the surface of the base layer 32.

Examples of the resin material of 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, and liquid crystal polymer. As the resin material, PET is preferable from the viewpoint of heat resistance (dimensional stability) and price in the production of the electromagnetic wave shielding film 1.

Substrate layer 32 may contain colorants or fillers.

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 further preferably 25 μm or more and 100 μm or less. When the thickness of the base layer 32 is equal to or greater than the lower limit of the above range, the electromagnetic wave shielding film 1 has good handleability. When the thickness of the base layer 32 is not more 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 hot-pressed on the 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.

The first release film 30 has the adhesive layer or the release agent layer 34, so that when the second release film 40 is peeled from the conductive adhesive layer 22 or when the electromagnetic wave shielding film 1 is bonded to a printed wiring board or the like by hot pressing, peeling of the first release film 30 from the insulating resin layer 10 can be suppressed, and the first release film 30 can sufficiently function as a protective film.

As the adhesive, a known adhesive may be used.

The release agent layer 34 is formed by applying a release treatment with a release agent to 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 from the insulating resin layer 10, the first release film 30 is easily peeled, and the insulating resin layer 10 is not easily broken.

As the release agent, a known release agent may be used.

The thickness of 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. When 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 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 further easily peeled.

< second Release film >

The second release film 40 protects the conductive adhesive layer 22 and improves the handling properties of the electromagnetic wave shielding film 1. The second release film 40 is peeled from the conductive adhesive layer 22 before the electromagnetic wave-shielding film 1 is attached to the insulating-film-equipped printed wiring board.

The second release film 40 includes, for example, a base material layer 42, and a release agent layer or adhesive layer 44 provided on the surface of the base material 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 layer 42 include the same resin material as that of the base layer 32 of the first release film 30.

Substrate layer 42 may contain colorants or fillers.

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.

The release agent layer 44 or the adhesive layer 44 is disposed between the base layer 42 and the conductive adhesive layer 22.

The release agent layer 44 is formed by applying a release treatment with a release agent to 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 from the conductive adhesive layer 22, the second release film 40 is easily peeled, and the conductive adhesive layer 22 is not easily broken.

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 is further easily peeled.

As the adhesive layer 44, the same adhesive layer as the adhesive layer 34 described in the above-mentioned column of < first release film > can be used.

< construction of electromagnetic wave-shielding film >

In the present invention, the electromagnetic wave shielding film may include at least an insulating resin layer, a shielding layer, and a conductive adhesive layer. In the electromagnetic wave shielding film, the first release film and the second release film may be included, or may not be included.

Therefore, in the present specification, the first release film and/or the second release film may be included in the insulating resin layer, the shielding layer, and the conductive adhesive layer and may be referred to as an electromagnetic wave shielding film, or the first release film and/or the second release film may be referred to as an electromagnetic wave shielding film without including these release films.

< thickness of electromagnetic wave-shielding film >

The thickness of the electromagnetic wave-shielding film 1 (excluding the release film) is preferably 5 μm or more and 45 μm or less, and more preferably 5 μm or more and 30 μm or less. When 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 first release film 30 is less likely to break when peeled off. If the thickness of the electromagnetic wave shielding film 1 (excluding the release film) is not more than the upper limit of the above range, the printed wiring board having the electromagnetic wave shielding film can be thinned.

(method for producing electromagnetic wave shielding film)

As a first embodiment of the method for producing an electromagnetic wave shielding film of the present invention, for example, a production method by the following method (a1) can be given. In the method (a1) described below, an electromagnetic wave shielding film in which the adhesive layer shown in fig. 1 is the anisotropic conductive adhesive layer 24 is used as an example of the electromagnetic wave shielding film, but the electromagnetic wave shielding film is not limited to this adhesive layer. In the manufacturing method described below, the same applies regardless of whether the adhesive layer is the isotropic conductive adhesive layer 27 or the adhesive layer 22 containing no conductive particles.

The method (A1) specifically includes the following steps (A1-1) to (A1-4).

Hereinafter, the method (a1) will be described with reference to fig. 3.

Step (A1-1): and a step of forming the insulating resin layer 10 on one surface of the first release film 30.

Step (A1-2): and 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): and 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): and 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.

The respective steps 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, the following method is preferable: from the viewpoint of heat resistance at the time of soldering or the like, it is preferable to coat a coating material containing a thermosetting resin and a curing agent on the adhesive layer/release agent layer 34 side of the first release film 30 and semi-cure or cure the coating material.

As a method for applying the coating material, for example, a method using various coating machines such as a die coater, a gravure coater, a roll coater, a curtain coater, a spin coater, a bar coater, a reverse coater, a kiss coater, a jet coater, a bar coater, an air knife coater, a blade coater, a casting coater, and a screen coater can be applied.

When the thermosetting resin is semi-cured or cured, it may be heated by a heater such as a heater or an infrared lamp.

In the step (a1-2), the shield layer 20 is formed on the surface of the insulating resin layer 10 opposite to the first release film 30.

Examples of the method for forming the shield layer 20 include a method using a vacuum film formation method (vacuum deposition, sputtering), a method using an electroplating method, a method of attaching a metal foil (copper foil), and the like.

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 plating film by electroplating is preferable in terms of forming the shield layer 20 having a desired thickness and surface shape. A method of forming a vapor deposition film by vacuum deposition is more preferable in that the shield layer 20 having high gas permeability and easily releasing gas generated inside to the outside under high temperature conditions can be formed, and the shield layer 20 can be easily formed by a dry process.

When the thickness of the shield layer 20 is 3 μm or more, it is preferable to apply a lamination process using pressure and/or heat so that the insulating resin layer 10 and the metal foil (copper foil) are in contact with each other, in view of preventing deterioration of the insulating resin layer 10 due to a thermal process by vacuum deposition and easily forming the shield layer 20 having a desired thickness.

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

Heating may be performed simultaneously with the pressurization treatment. The heating temperature in this case is preferably-30 ℃ or higher and +50 ℃ or lower, and more preferably 50 ℃ or higher and 150 ℃ or lower, from the glass transition temperature of the semi-cured or cured insulating resin layer.

In the step (a1-3), a conductive adhesive coating material containing an adhesive 24a, conductive particles 24b, and a solvent is applied to the surface of the shield layer 20 opposite to the insulating resin layer 10.

The solvent is volatilized by the applied conductive adhesive paint, thereby forming the anisotropic conductive adhesive layer 24.

Examples of the solvent 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, etc.), and the like.

The method of applying the conductive adhesive is the same as the method of applying the coating material in the step (a 1-1).

In the step (a1-4), the second release film 40 is laminated on the surface of the anisotropic conductive adhesive layer 24 opposite to 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 the second release film 40 is laminated on the anisotropic conductive adhesive layer 24, a 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 may be subjected to a lamination treatment by pressing and/or heating in order to improve adhesion between the layers.

The pressing conditions were the same as those in the pressing treatment in the step (A1-2). In the step (A1-4), the heat treatment may be performed in the same manner as in the step (A1-2).

In the method (a1), the lamination process is performed in the steps (a1-2) and (a1-4), but the step of performing the lamination process 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, a production method by the following method (a2) can be given.

The method (A2) specifically includes the following steps (A2-1) to (A2-4).

Hereinafter, the method (a2) will be described with reference to fig. 4 to 6. The steps (A2-1) to (A2-2) are shown in FIG. 4, the step (A2-3) is shown in FIG. 5, and the step (A2-4) is shown in FIG. 6.

Step (A2-1): and forming the insulating resin layer 10 on one surface of the first release film 30.

Step (A2-2): and a step of forming a laminate (p1) by forming the shielding layer 20 on the surface of the insulating resin layer 10 opposite to the first release film 30.

Step (A2-3): and a step of forming the anisotropic conductive adhesive layer 24 on the second release film 40 to form a laminate (p 2).

Step (A2-4): and a step of bonding the laminate (p1) and the laminate (p2) together such that the shield layer 20 of the laminate (p1) is in contact with the anisotropic conductive adhesive layer 24 of the laminate (p 2).

The step (A2-1) and the step (A2-2) are the same as the step (A1-1) and the step (A1-2), respectively.

The step (a2-3) is the same as the step (a1-3) except that the thermosetting adhesive 24a and the conductive adhesive paint containing the conductive particles 24b are applied to the surface of the second release film 40 provided with the release agent layer/adhesive layer 44, not to the shield layer 20, to form the 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 pressure for improving the adhesion between the laminate (p1) and the laminate (p2) can also be performed. The pressing conditions were the same as those in the pressing treatment in the step (A1-4). In the step (A2-4), the heat treatment may be performed in the same manner as in the step (A1-4).

< Effect >

The electromagnetic wave shielding film 1 of the present embodiment uses, as the conductive adhesive composition used in the conductive adhesive layer constituting the electromagnetic wave shielding film, an adhesive component exhibiting a specific water absorption rate, and the adhesive component contains a thermosetting resin containing a specific epoxy resin, whereby it is possible to exhibit good adhesion and maintain a low connection resistance value even after being placed in a high-temperature and high-humidity environment.

< other embodiment >

The electromagnetic wave shielding film of the present invention is not limited to the embodiment illustrated in the drawings 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 side opposite to the insulating resin layer.

For example, the insulating resin layer may be 2 or more layers.

The first release film may have a release agent layer instead of the adhesive layer.

The second release film may have an adhesive layer instead of the release agent layer.

The first release film or the second release film may be composed of only the base layer without having an adhesive layer or a release agent layer.

When the insulating resin layer has sufficient flexibility and strength, the first release film may be omitted.

When the surface of the conductive adhesive layer has low tackiness, the second release film may be omitted.

(printed Wiring Board with electromagnetic wave Shielding film)

The printed wiring board with an electromagnetic wave shielding film of the present invention comprises: 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; and the electromagnetic wave shielding film of the present invention, wherein the 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 wave 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 the side where 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. 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 with electromagnetic wave shielding film 2, the second release film 40 is peeled from the anisotropic conductive adhesive layer 24.

When the first release film 30 is not needed in the flexible printed wiring board with electromagnetic wave shielding film 2, the first release film 30 is peeled off from the insulating resin layer 10.

The shield layer 20 of the electromagnetic wave shielding film 1 is disposed in a spaced-apart opposed relationship with the insulating film 60 and the anisotropic conductive adhesive layer 24 interposed therebetween in the vicinity of the printed circuit 54 (signal circuit, ground layer, etc.) except for the portion having the through-hole.

The separation distance between the printed circuit 54 and the shield layer 20 except for the portion having the through-hole is substantially equal to the sum of the thickness of the insulating film 60 and 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, the line width of the signal circuit must be reduced in order to adjust the characteristic impedance of the signal circuit, and it is technically difficult to realize stable manufacturing of the printed circuit 54. If the separation distance is larger than 200 μm, the flexible printed wiring board 2 having the electromagnetic wave 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 the copper-clad laminate into a desired pattern by a known etching method to form a printed circuit (a power supply circuit, a ground layer, etc.).

Examples of the copper-clad laminate include a laminate in which a copper foil is bonded to one surface or both surfaces of the base film 52 with an adhesive layer (not shown) interposed therebetween; a laminate obtained by casting a resin solution or the like for forming the base film 52 on the surface of the copper foil.

Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane resin, acrylic resin, melamine resin, and the like.

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

< basic film >)

The base film 52 is preferably a film having heat resistance, more preferably a polyimide film or a liquid crystal polymer film, and still more preferably a polyimide film.

The surface resistance of base film 52 is preferably 1 × 10 from the viewpoint of electrical insulation ⁶ Omega or more. From a practical viewpoint, the surface resistance of the base film 52 is preferably 1 × 10 ¹⁹ Omega is less than or equal to.

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

< printed Circuit >)

Examples of the copper foil constituting the printed circuit 54 (signal circuit, ground layer, etc.) include rolled copper foil, electrolytic copper foil, etc., and rolled copper foil is preferable from the viewpoint of bendability.

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.

The end portions (terminals) of the printed circuit 54 in the longitudinal direction are not covered with the insulating film 60 and the electromagnetic wave shielding film 1 for soldering, connector connection, component mounting, and the like.

< insulating film >

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 application of an adhesive, adhesion of an adhesive sheet, or the like.

From the viewpoint of electrical insulation, the surface resistance of the insulating film body is preferably 1 × 10 ⁶ Omega or more. From the practical viewpoint, the surface resistance of the insulating film body is preferably 1 × 10 ¹⁹ Omega is less than or equal to.

The insulating film is preferably a film having heat resistance, more preferably a polyimide film or a liquid crystal polymer film, and still more preferably a polyimide film.

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.

Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane resin, acrylic resin, melamine resin, polystyrene, polyolefin, and the like. The epoxy resin may contain a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility.

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.

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, and a quadrangle.

(method for manufacturing printed Wiring Board with electromagnetic wave Shielding film)

The method for manufacturing a printed wiring board with an electromagnetic wave shielding film according to the present invention includes a step of pressure-bonding a printed wiring board having a printed circuit provided on at least one surface of a substrate and the electromagnetic wave shielding film according to the present invention with an insulating film interposed therebetween, wherein the insulating film is brought into close contact with a surface of the printed wiring board on which the printed circuit is provided and the insulating film is brought into close contact with an adhesive layer of the electromagnetic wave shielding film when the pressure-bonding is performed.

The method for manufacturing a printed wiring board with an electromagnetic wave shielding film of the present invention includes the steps (a) and (b) described below after the electromagnetic wave shielding film is manufactured by the method for manufacturing an electromagnetic wave shielding film of the present invention.

Step (a): and a step of providing an insulating film on the surface of the printed wiring board on which the printed circuit is provided, thereby obtaining a printed wiring board with an insulating film.

A step (b): and a step of obtaining the printed wiring board with the electromagnetic wave shielding film by, in the case where the electromagnetic wave shielding film has the second release film, peeling the second release film from the electromagnetic wave shielding film, then laminating 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 the laminated layers to adhere the conductive adhesive layer to the surface of the insulating film.

In a more preferred embodiment, the method for manufacturing a printed wiring board with an electromagnetic wave shielding film according to the present invention includes the following steps (a) to (d).

A step (a): and a step of providing an insulating film on the surface of the printed wiring board on which the printed circuit is provided, thereby obtaining a printed wiring board with an insulating film.

A step (b): and a step of, when the electromagnetic wave shielding film has the second release film, peeling the second release film from the electromagnetic wave shielding film, and then laminating 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 the laminated layers, thereby pressing the conductive adhesive layer against the surface of the insulating film to obtain the printed wiring board with the electromagnetic wave shielding film.

A step (c): in the case where the electromagnetic wave shielding film has the first release film, when the first release film is not necessary after the step (b), the step of peeling the first release film from the electromagnetic wave shielding film.

Step (d): when the adhesive contained in the conductive adhesive layer is a thermosetting adhesive, the step of main-curing the conductive adhesive layer is performed between the steps (a) and (b) or after the step (c), as necessary.

Hereinafter, a method for manufacturing a flexible printed wiring board having an electromagnetic wave shielding film will be described with reference to fig. 8.

< Process (a) >

As shown in fig. 8, an insulating film 60 having a through hole 62 formed at a position corresponding to the printed circuit 54 is stacked on the flexible printed wiring board 50, an adhesive layer (not shown) of the insulating film 60 is adhered to the surface of the flexible printed wiring board 50, and the adhesive layer is cured to obtain the flexible printed wiring board 3 with an insulating film. The adhesive layer of the insulating film 60 may be temporarily adhered to the surface of the flexible printed wiring board 50, and the adhesive layer may be permanently cured in the step (d).

The bonding and curing of the adhesive layer are performed by, for example, hot pressing with a press (not shown) or the like.

< Process (b) >

As shown in fig. 8, electromagnetic wave shielding film 1 from which second release film 40 was peeled off was stacked on flexible printed wiring board with insulating film 3, and pressing (preferably hot pressing) was performed to obtain flexible printed wiring board with electromagnetic wave shielding film 2 in which anisotropic conductive adhesive layer 24 was pressure-bonded to the surface of insulating film 60, and anisotropic conductive adhesive layer 24 was electrically connected to printed circuit 54 through-hole 62.

In the step (b) of fig. 8, the printed circuit 54 is composed of a ground circuit 54a and a signal circuit 54b (54 a and 54b are not shown).

The anisotropic conductive adhesive layer 24 is bonded by, for example, hot pressing with a press (not shown) or the like.

The time for hot pressing is preferably 20 seconds to 60 minutes, more preferably 30 seconds to 30 minutes.

The temperature of hot pressing (temperature of the hot plate of the press) is preferably 140 ℃ or more and 210 ℃ or less, and more preferably 150 ℃ or more and 190 ℃ or less.

The pressure of the hot pressing is preferably 0.5MPa to 20MPa, more preferably 1MPa to 16 MPa.

< step (c) >

As shown in fig. 8, when the first release film 30 is not needed, the first release film 30 is peeled from the insulating resin layer 10.

< Effect >

The printed wiring board with an electromagnetic wave shielding film 2 of the present embodiment has the above-described characteristics of the electromagnetic wave shielding film of the present invention, and the shielding layer is a printed wiring board with an electromagnetic wave shielding film that is well grounded to the ground circuit of the printed wiring board.

< other embodiment >

The printed wiring board with an electromagnetic wave shielding film in the present invention is not limited to the embodiment illustrated in the drawings, 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 with an adhesive layer adjacent to the insulating film.

For example, the flexible printed wiring board may have a ground layer on the back surface side. The flexible printed wiring board may have printed circuits on both surfaces, and an insulating film and an electromagnetic shielding film may be bonded to both surfaces.

A rigid printed substrate having no flexibility may be used instead of the flexible printed wiring board.

The electromagnetic wave shielding film 1 of the second embodiment, etc. may be used instead of the electromagnetic wave shielding film 1 of the first embodiment.

[ examples ] A method for producing a compound

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.

[ CHEM 5]

(example 1)

< formulation of adhesive coating for insulating resin layer >

As the adhesive coating material 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 (EXA-4816, manufactured by DIC corporation), 16.7 parts by mass of a curing agent (Sho-amine X (registered trademark), manufactured by Sho-hei electric corporation), 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 coating material for an insulating resin layer.

< formulation of adhesive coating for conductive adhesive layer >

An adhesive coating material for a conductive adhesive layer was prepared by mixing 79 parts by mass of an epoxy Resin having a structural formula represented by the above formula (1) (product of DIC corporation, EPICLON HP7200L (the specific structural formula is referred to the above formula (a))), 20 parts by mass of an acrylate polymer (product of chanko chemical industries, Teisan Resin SG-P3(Tg12 ℃, acid value 0mgKOH/g, epoxy equivalent 0.21 eq/kg)), 1 part by mass of an imidazole epoxy Resin curing agent (product of seiko chemical industries, Curezol 2P4MZ (2 phenyl 4 methylimidazole)), and 20 parts by mass of copper particles (average particle diameter 5.02 μm). The compounding ratio of the adhesive coating material of the conductive adhesive layer is shown in table 1 below, for example.

< production of electromagnetic wave-shielding film >

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 Toyo Boseki Co., Ltd., CN200, 50 μm in thickness).

The insulating resin layer coating material was applied to the adhesive layer surface 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 shield layer (film thickness 300nm) composed of a copper deposition film.

Next, an adhesive coating of the conductive adhesive layer was applied to the surface of the shield layer opposite to 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 was provided on one side of a PET film (manufactured by Lintec Co., Ltd., T157, thickness of the release film main body: 50 μm, thickness of the release layer: 0.1 μm) with a non-silicone release agent.

The second release film was attached to the surface of the conductive adhesive layer opposite to 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.

< production of printed Wiring Board with electromagnetic wave Shielding film >

An insulating adhesive composition was applied to the surface of a polyimide film (insulating film main body) having a thickness of 25 μm so that the dry film thickness became 25 μm, thereby forming an adhesive layer, thereby obtaining an insulating film (thickness: 50 μm). A through hole (aperture: 800 μm) is formed in the printed circuit at a position corresponding to the ground circuit.

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.

The 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 was peeled was stacked on the printed wiring board with an insulating film, and the heat pressing device was used to heat the electromagnetic wave-shielding film at a hot plate temperature: 180 ℃ and load: and hot-pressing under 3MPa for 30 minutes to adhere the conductive adhesive layer to the surface of the insulating film.

The first release film is peeled from the insulating resin layer to obtain a printed wiring board having an electromagnetic wave shielding film.

< measurement of Water absorption (%) of adhesive component >

The adhesive component was coated on a PET substrate and heated at 150 ℃ for 1 hour to prepare a cured layer.

The test piece composed of the cured layer was exposed to 85 ℃ for 48 hours at a relative humidity of 85%. Then, the mass change of the test piece, i.e., the difference between the initial mass and the mass after exposure to water, was measured and found and characterized as a percentage of the initial mass.

The results of measuring the water absorption of the adhesive component used in example 1 are shown in table 1 below.

< evaluation of printed Wiring Board with electromagnetic wave Shielding film >

The printed wiring board with the electromagnetic wave shielding film of example 1 obtained as described above was measured for connection resistance before and after storage in a high-temperature and high-humidity environment, and the connectivity was evaluated. The storage conditions were 2 modes of 500 hours and 1000 hours in an environment of 85 ℃ and 85% humidity. The connectivity was evaluated by the following method.

[ evaluation of connectivity ]

In the printed wiring board with an electromagnetic wave shielding film, the electrical connection between the wiring, the shielding layer, and the wiring is measured through the electromagnetic wave shielding film existing in the through hole (also referred to as a connection hole).

A tester was brought into contact with the printed wiring board having the electromagnetic wave shielding film to measure the resistance value between the wiring and the shielding layer and between the wirings.

The connection resistance value was evaluated according to the following criteria.

O: less than 300m omega

And (delta): 300m omega or more and less than 1000m omega

X: over 1000m omega

The evaluation results of the connectivity of the printed wiring board with an electromagnetic wave shielding film of example 1 are shown in table 1 below.

(examples 2 to 11)

Printed wiring boards with electromagnetic wave shielding films of examples 2 to 11 were produced in the same manner as in example 1, except that the conditions of the conductive adhesive layer in example 1 were changed as shown in tables 1 and 2.

In example 2, EPICLON HP7200HHH (the specific structural formula is shown in formula (a)) manufactured by DIC corporation was used as the epoxy resin.

In example 3, NC3000 (the specific structural formula is referred to as the formula (b)) manufactured by japan chemical corporation) was used as the epoxy resin.

In example 4, NC2000-L (the specific structural formula is referred to as the formula (c)) manufactured by Nippon chemical Co., Ltd.) was used as an epoxy resin.

In example 5, EPPN-201 (the specific structural formula is shown in formula (d)) manufactured by Nippon chemical company was used as the epoxy resin.

In example 10, Teisan Resin SG-70L (Tg-13 ℃, acid value 5mgKOH/g, no epoxy equivalent) made by Citrix corporation was used as the acrylate polymer.

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.

The printed wiring boards with electromagnetic wave-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 examples 1 to 3

Printed wiring boards with electromagnetic wave shielding films of comparative examples 1 to 3 were produced in the same manner as in example 1, except that the conditions of the conductive adhesive layer in example 1 were changed as shown in table 1.

In comparative example 1, jER1001 manufactured by Mitsubishi chemical corporation (the specific structural formula is referred to as the formula (e)) was used as an epoxy resin.

In comparative example 2, jER157S70 (the specific structural formula is shown by the above formula (f)) manufactured by Mitsubishi chemical corporation was used as the epoxy resin.

In comparative example 3, Teisan Resin SG-280(Tg-29 ℃, acid value 30mgKOH/g, no epoxy equivalent) made by Citrix corporation was used as the acrylate polymer.

The water absorption of the adhesive components used in comparative examples 1 to 3 was measured by the same method as in example 1. The results are shown in Table 2.

The printed wiring boards with electromagnetic wave 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.

[ TABLE 1]

[ TABLE 2]

As is clear from the above examples, the electromagnetic wave shielding film of the present invention can reliably exhibit good adhesion and maintain a low connection resistance value even after 500 hours have elapsed after being placed in a high-temperature and high-humidity environment.

It is also found that when a specific rubber component is contained in the adhesive component, even if the elapsed time is 1000 hours, good adhesion can be exhibited and a low connection resistance value can be maintained in some cases.

(Industrial Applicability)

The electromagnetic wave shielding film of the present invention is useful as an electromagnetic wave shielding member in a flexible printed wiring board for electronic devices such as smart phones, cellular phones, optical modules, digital cameras, game machines, notebook computers, and medical instruments.

(description of reference numerals)

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 mold release film

32 base material layer

34 adhesive/mold release layer

40 second mold release film

42 base material layer

44 mold release layer/adhesive layer

50 flexible printed wiring board

52 base film

54 print circuit

60 insulating film

62 through hole.

Claims (10)

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 by using a conductive adhesive composition containing an adhesive component and conductive particles,

the water absorption of the adhesive component is less than 2.0%,

the adhesive component contains a thermosetting resin,

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 400g/eq,

in the above formula (1), R ₁ Represents a hydrocarbon group having 1 to 35 carbon atoms, R ₂ Represents hydrogen or methyl, and n represents an integer of 1 to 10.

2. The electromagnetic wave-shielding film according to claim 1,

the adhesive component contains 30 to 70 mass% of the epoxy resin.

3. The electromagnetic wave-shielding film according to claim 1 or 2, wherein,

the epoxy equivalent is 215-400 g/eq.

4. The electromagnetic wave shielding film according to any one of claims 1 to 3,

r in the general formula (1) ₁ Is a hydrocarbon group having a structure containing an alicyclic hydrocarbon or an aromatic hydrocarbon.

5. The electromagnetic wave-shielding film according to claim 3 or 4,

the epoxy equivalent is 250 to 400 g/eq.

6. The electromagnetic wave-shielding film according to any one of claims 1 to 5,

the adhesive component contains a rubber component.

7. The electromagnetic wave-shielding film according to claim 6,

the acid value of the rubber component is 20mgKOH/g or less.

8. The electromagnetic wave-shielding film according to claim 6 or 7,

the epoxy equivalent of the rubber component is 0.05eq/kg or more.

9. The electromagnetic wave shielding film according to any one of claims 6 to 8,

the glass transition temperature of the rubber component is 10 ℃ or higher.

10. A printed wiring board with an electromagnetic wave shielding film, comprising:

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; and

the electromagnetic wave-shielding film according to any one of claims 1 to 9, wherein the conductive adhesive layer is provided adjacent to the insulating film.

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