JP6706654B2 - Electromagnetic wave shield film, flexible printed wiring board with electromagnetic wave shield film, and methods for manufacturing the same - Google Patents

Description

The present invention relates to an electromagnetic wave shielding film, a flexible printed wiring board provided with the electromagnetic wave shielding film, and a method for manufacturing them.

An electromagnetic wave shield film may be provided on the surface of the flexible printed wiring board in order to shield electromagnetic noise generated from the flexible printed wiring board and electromagnetic noise from the outside (see, for example, Patent Document 1).

FIG. 9: is sectional drawing which shows an example of the manufacturing process of the conventional flexible printed wiring board with an electromagnetic wave shield film.
The flexible printed wiring board 101 with an electromagnetic wave shield film includes a flexible printed wiring board 130, an insulating film 140, and an electromagnetic wave shield film 110 from which a release film 118 is peeled off.
The flexible printed wiring board 130 has a printed circuit 134 provided on one surface of a base film 132.
The insulating film 140 is provided on the surface of the flexible printed wiring board 130 on the side where the printed circuit 134 is provided.
The electromagnetic wave shield film 110 includes an insulating protective layer 112, a metal thin film layer 114 that covers the first surface of the insulating protective layer 112, an anisotropic conductive adhesive layer 116 that covers the surface of the metal thin film layer 114, and an insulating layer. Release film 118 (carrier film) that covers the second surface of the protective layer 112.
The anisotropic conductive adhesive layer 116 of the electromagnetic wave shielding film 110 is adhered and cured on the surface of the insulating film 140. Further, the anisotropic conductive adhesive layer 116 is electrically connected to the printed circuit 134 through the through hole 142 formed in the insulating film 140.

The flexible printed wiring board 101 with an electromagnetic wave shielding film is manufactured through the following steps, for example, as shown in FIG.
(I) A step of providing an insulating film 140 having a through hole 142 formed at a position corresponding to the ground of the printed circuit 134 on the surface of the flexible printed wiring board 130 where the printed circuit 134 is provided.
(Ii) The electromagnetic wave shielding film 110 is superposed on the surface of the insulating film 140 so that the anisotropic conductive adhesive layer 116 of the electromagnetic wave shielding film 110 is in contact with the surface of the insulating film 140. A step of adhering the anisotropic conductive adhesive layer 116 and electrically connecting the anisotropic conductive adhesive layer 116 to the ground of the printed circuit 134 through the through hole 142.
(Iii) A step of obtaining the flexible printed wiring board 101 with the electromagnetic wave shielding film by peeling and removing the release film 118 that has finished the role as a carrier film from the insulating protective layer 112 after hot pressing.

However, in the flexible printed wiring board 101 with the electromagnetic wave shielding film, the electromagnetic wave shielding film 110 is bent and deformed along the shape of the unevenness at the portion having the unevenness such as the through hole 142, so that the metal thin film layer 114. Is likely to crack. The anisotropic conductive adhesive layer 116 has conductivity in the thickness direction, but does not have conductivity in the plane direction. Therefore, when a crack occurs in the metal thin film layer 114, the metal thin film layer 114 and the anisotropic conductive adhesive layer 116 have a conductive property. The resistance of the electromagnetic wave shield layer formed of the adhesive layer 116 increases, and the electromagnetic wave noise shielding effect of the electromagnetic wave shield layer decreases.

JP, 2014-112576, A

The present invention provides an electromagnetic wave shielding film and a flexible printed wiring board with an electromagnetic wave shielding film, which can maintain the electromagnetic wave noise shielding effect even if a crack occurs in the metal thin film layer, and a method for producing them.

The present invention has the following aspects.
(1) An insulating protective layer, a metal thin film layer having a surface resistance of 0.01 to 0.3Ω, and an isotropic conductive adhesive layer containing a conductive filler and having a surface resistance of 1 to 100Ω in this order. An electromagnetic wave shielding film, wherein the isotropic conductive adhesive layer contains conductive particles and conductive fibers as the conductive filler.
(2) The electromagnetic wave shielding film according to (1), wherein the ratio of the conductive filler is 30 to 80% by volume based on 100% by volume of the isotropic conductive adhesive layer.
(3) The electromagnetic wave shielding film according to (1) or (2), further including a first release film provided on the surface of the insulating protective layer.
(4) The electromagnetic wave shielding film according to (3), further including a second release film provided on the surface of the isotropic conductive adhesive layer.
(5) A method for producing the electromagnetic wave shielding film according to (4) above, which has the following steps (a) to (d).
(A) A step of forming an insulating protective layer on one surface of the first release film.
(B) A first release film, an insulating protective layer, and a metal thin film layer by forming a metal thin film layer having a surface resistance of 0.01 to 0.3Ω on the surface of the insulating protective layer. And a step of obtaining a first laminated body including in order.
(C) Isotropic conductivity containing a second release film and a conductive filler by forming an isotropic conductive adhesive layer on one surface of the second release film, and having a surface resistance of 1 to 100Ω. Obtaining a second laminated body provided with a conductive adhesive layer in order.
(D) The first laminated body and the second laminated body are brought into contact with each other by the metal thin film layer of the first laminated body and the isotropic conductive adhesive layer of the second laminated body. Process to bond.
(6) Flexible printed wiring board having a printed circuit provided on at least one surface of a base film, an insulating film provided on a surface of the flexible printed wiring board on which the printed circuit is provided, and a surface of the insulating film The electromagnetic shielding film of (1) or (2), to which the isotropic conductive adhesive layer is adhered, the isotropic conductive adhesive layer passing through a through hole formed in the insulating film. A flexible printed wiring board with an electromagnetic wave shielding film electrically connected to the printed circuit.
(7) A method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film, which has the following steps (e) to (g).
(E) An insulating film having through holes formed at positions corresponding to the printed circuit is provided on the surface of the flexible printed wiring board having the printed circuit on at least one surface of the base film on the side where the printed circuit is provided, and insulation is provided. The process of obtaining a flexible printed wiring board with a film.
(F) After the step (e), the flexible printed wiring board with an insulating film and the electromagnetic wave shielding film according to any one of (1) to (3) are bonded to the surface of the insulating film by the isotropic conductive bonding. Layered so as to contact the agent layer, by hot pressing these, the isotropic conductive adhesive layer is adhered to the surface of the insulating film, and the isotropic conductive adhesive layer, the through hole Through and electrically connecting to the printed circuit.
(G) When the electromagnetic wave shielding film includes a first release film, a step of peeling the first release film after the step (f).

The electromagnetic wave shielding film of the present invention can maintain the electromagnetic wave noise shielding effect even if a crack occurs in the metal thin film layer.
According to the method for producing an electromagnetic wave shield film of the present invention, it is possible to produce an electromagnetic wave shield film that can maintain the electromagnetic wave noise shielding effect even if a crack occurs in the metal thin film layer.
The flexible printed wiring board with an electromagnetic wave shielding film of the present invention can maintain the electromagnetic wave noise shielding effect even if a crack occurs in the metal thin film layer.
ADVANTAGE OF THE INVENTION According to the manufacturing method of the flexible printed wiring board with an electromagnetic shielding film of this invention, the flexible printed wiring board with an electromagnetic shielding film which can maintain the electromagnetic-wave noise shielding effect can be manufactured, even if a crack occurs in a metal thin film layer.

It is sectional drawing which shows an example of the electromagnetic wave shield film of this invention. It is sectional drawing which shows an example of process (a)-(b) in the manufacturing method of the electromagnetic wave shield film of this invention. It is sectional drawing which shows an example of a process (c) in the manufacturing method of the electromagnetic wave shield film of this invention. It is sectional drawing which shows an example of a process (d) in the manufacturing method of the electromagnetic wave shield film of this invention. FIG. 6 is a perspective view showing a model case of an electromagnetic wave shield layer used to roughly estimate the total resistance of the electromagnetic wave shield layer before a crack is generated in the metal thin film layer. FIG. 6 is a perspective view showing a model case of an electromagnetic wave shield layer used to roughly estimate the overall resistance of the electromagnetic wave shield layer after a crack has occurred in the metal thin film layer. It is sectional drawing which shows an example of the flexible printed wiring board with an electromagnetic wave shield film of this invention. It is sectional drawing which shows an example of process (e)-(g) in the manufacturing method of the flexible printed wiring board with an electromagnetic wave shielding film of this invention. It is sectional drawing which shows an example of the manufacturing process of the conventional flexible printed wiring board with an electromagnetic wave shield film.

The following definitions of terms apply throughout the specification and claims.
For the average particle diameter of the conductive particles, 30 conductive particles are randomly selected from the electron microscopic image of the conductive particles, the minimum diameter and the maximum diameter of each conductive particle are measured, and the minimum diameter and the maximum diameter are measured. It is a value obtained by arithmetically averaging the measured particle diameters of 30 conductive particles with the median value of and as the particle diameter of one particle.
The average fiber length of the conductive fibers was determined by randomly selecting 30 conductive fibers from the electron microscope image of the conductive fibers, measuring the fiber length of each conductive fiber, and measuring 30 conductive fibers. Is a value obtained by arithmetically averaging the fiber lengths of.
For the average fiber diameter of the conductive fibers, randomly select 30 conductive fibers from the electron microscope image of the conductive fibers, measure the minimum diameter and the maximum diameter of each conductive fiber, and calculate the minimum diameter and the maximum diameter. Is the value obtained by arithmetically averaging the measured fiber diameters of the 30 conductive fibers, with the median value of and as the fiber diameter of one fiber.
The specific surface area of the conductive particles and the conductive fibers is a value calculated from the value obtained by immersing degassed particles and the like in liquid nitrogen and measuring the amount of adsorbed nitrogen.
For the thickness of the film (release film, insulating film, etc.), coating film (insulating protective layer, conductive adhesive layer, etc.), metal thin film layer, etc., observe the cross section of the measurement object using a transmission electron microscope. It is a value obtained by measuring and averaging the thickness at five points.
The storage elastic modulus is calculated as one of the viscoelastic properties using a dynamic viscoelasticity measuring device which is calculated from the stress applied to the measurement target and the detected strain and outputs as a function of temperature or time.
For the surface resistance, two thin-film metal electrodes (length 10 mm, width 5 mm, inter-electrode distance 10 mm) formed by vapor-depositing gold on quartz glass were used. The resistance between the electrodes is measured by pressing a region of 10 mm×20 mm of the object to be measured with a load of 0.049 N from above the object and measuring with a measuring current of 1 mA or less.

<Electromagnetic wave shield film>
FIG. 1 is a sectional view showing an example of the electromagnetic wave shielding film of the present invention.
The electromagnetic wave shielding film 10 includes an insulating protective layer 12, a metal thin film layer 14 that covers the first surface of the insulating protective layer 12, an isotropic conductive adhesive layer 16 that covers the surface of the metal thin film layer 14, and an insulating layer. The first release film 18 covering the second surface of the property protection layer 12 and the second release film 20 covering the surface of the isotropic conductive adhesive layer 16 are provided.

(Insulating protective layer)
The insulating protective layer 12 serves as a base (base) when forming the metal thin film layer 14, and after the electromagnetic wave shielding film 10 is attached to the surface of the insulating film provided on the surface of the flexible printed wiring board, Protect the thin film layer 14.
The surface resistance of the insulating protective layer 12 is preferably 1×10 ⁶ Ω or more from the viewpoint of electrical insulation. The surface resistance of the insulating protective layer 12 is preferably 1×10 ¹⁹ Ω or less from the practical point of view.

As the insulating protective layer 12, a coating film formed by applying a coating material containing a thermosetting resin and a curing agent and curing it, a coating film formed by applying a coating material containing a thermoplastic resin, a thermoplastic resin Examples thereof include a layer made of a film obtained by melt-molding a resin. From the viewpoint of heat resistance when soldering or the like, a coating film formed by applying and curing a coating material containing a thermosetting resin and a curing agent is preferable.

Examples of the thermosetting resin include amide resin, epoxy resin, phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, and UV-curable acrylate resin. From the viewpoint of excellent heat resistance, amide resin and epoxy resin are preferable. preferable.

The storage elastic modulus at 160° C. of the insulating protective layer 12 is preferably 5×10 ⁶ to 1×10 ⁸ Pa, more preferably 8×10 ⁶ to 2×10 ⁷ Pa. Usually, a cured product of a thermosetting resin is hard, and thus a coating film made of such a resin has poor flexibility, and particularly when the thickness is reduced, it is very brittle and does not have sufficient strength to exist as a self-supporting film. The insulating protective layer 12 preferably has sufficient strength under the temperature at which the first release film 18 is peeled off (the temperature at which the conductive adhesive is cured, usually 150 to 200° C.). .. When the storage elastic modulus at 160° C. of the insulating protective layer 12 is 5×10 ⁶ Pa or more, the insulating protective layer 12 does not soften. If the storage elastic modulus at 160° C. of the insulating protective layer 12 is 1×10 ⁸ Pa or less, flexibility and strength will be sufficient. As a result, when the first release film 18 is peeled off, not only the insulating protective layer 12 but also the electromagnetic wave shielding film 10 is unlikely to break.

The insulating protective layer 12 may be colored in order to impart a design property to the flexible printed wiring board with the electromagnetic wave shielding film.
The insulating protective layer 12 may be composed of two or more types of layers having different properties such as storage elastic modulus and materials.

The thickness of the insulating protective layer 12 is preferably 1 to 10 μm, more preferably 1 to 5 μm. When the thickness of the insulating protective layer 12 is 1 μm or more, the heat resistance becomes good. If the thickness of the insulating protective layer 12 is 10 μm or less, the electromagnetic wave shielding film 10 can be made thin.

(Metal thin film layer)
The metal thin film layer 14 is a layer made of a metal thin film. Since the metal thin film layer 14 is formed so as to spread in the plane direction, it has conductivity in the plane direction and functions as an electromagnetic wave shield layer or the like.

Examples of the metal thin film layer 14 include a metal thin film formed by physical vapor deposition (vacuum vapor deposition, sputtering, ion beam vapor deposition, electron beam vapor deposition, etc.), CVD, plating, and the like, and can be made thin, and A metal thin film (vapor deposited film) formed by physical vapor deposition is preferable because it has excellent conductivity in the surface direction even if the thickness is thin and can be easily formed by a dry process.

Examples of the material of the metal thin film forming the metal thin film layer 14 include aluminum, silver, copper, gold, conductive ceramics and the like. Copper is preferable in terms of electrical conductivity, and conductive ceramics are preferable in terms of chemical stability.

The thickness of the metal thin film layer 14 is preferably 0.01 to 1 μm, more preferably 0.05 to 1 μm. When the thickness of the metal thin film layer 14 is 0.01 μm or more, the conductivity in the plane direction is further improved. When the thickness of the metal thin film layer 14 is 0.05 μm or more, the effect of shielding electromagnetic noise is further improved. When the thickness of the metal thin film layer 14 is 1 μm or less, the electromagnetic wave shielding film 10 can be thinned. Further, the productivity and flexibility of the electromagnetic wave shielding film 10 are improved.

The surface resistance of the metal thin film layer 14 is 0.01 to 0.3Ω, preferably 0.02 to 0.2Ω, and more preferably 0.05 to 0.1Ω. If the surface resistance of the metal thin film layer 14 is 0.01 Ω or more, the metal thin film layer 14 can be made sufficiently thin. If the surface resistance of the metal thin film layer 14 is 0.3Ω or less, it can sufficiently function as an electromagnetic wave shield layer.

(Isotropic conductive adhesive layer)
The isotropic conductive adhesive layer 16 has conductivity in the thickness direction and the surface direction and also has adhesiveness.
The isotropic conductive adhesive layer 16 can sufficiently function as an electromagnetic wave shield layer as compared with an anisotropic conductive adhesive layer that has conductivity in the thickness direction and does not have conductivity in the plane direction.

The isotropic conductive adhesive layer 16 contains a conductive filler. The isotropic conductive adhesive layer 16 preferably contains the conductive particles 22 as a conductive filler from the viewpoint of the conductivity in the thickness direction and the surface direction, and the conductivity in the surface direction is further improved, resulting in surface resistance. It is more preferable to include the conductive particles 22 and the conductive fibers 24 as the conductive filler from the standpoint that the ratio is low, and that the strength of the isotropic conductive adhesive layer 16 is high and cracks are less likely to occur.

Further, in the isotropic conductive adhesive layer 16, the conductivity in the plane direction is further improved and the surface resistance is lowered, and the strength of the isotropic conductive adhesive layer 16 is increased, and cracks are generated. From the standpoint of difficulty, the fiber direction of the conductive fiber 24 is biased in the plane direction of the isotropic conductive adhesive layer 16 rather than in the thickness direction of the isotropic conductive adhesive layer 16, that is, the conductive fiber. It is preferable that 24 is oriented in the plane direction of the isotropic conductive adhesive layer 16.

The isotropic conductive adhesive layer 16 is preferably a thermosetting isotropic conductive adhesive layer from the viewpoint of exhibiting heat resistance after curing.
The thermosetting isotropic conductive adhesive layer 16 includes, for example, a thermosetting adhesive, conductive particles 22, and conductive fibers 24. The isotropic conductive adhesive layer 16 may be in an uncured state or in a B-staged state.

Examples of the thermosetting adhesive include epoxy resin, phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, and UV curable acrylate resin. Epoxy resin is preferable from the viewpoint of excellent heat resistance. The epoxy resin may contain a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility, a tackifier or the like.
The thermosetting adhesive may contain a cellulose resin or microfibril (glass fiber or the like) in order to increase the strength of the isotropic conductive adhesive layer 16 and improve the punching property.

Examples of the conductive particles 22 include graphite powder, baked carbon particles, particles of metal (silver, platinum, gold, copper, nickel, palladium, aluminum, solder, etc.), plated baked carbon particles, and the like. From the viewpoint of the fluidity of the isotropic conductive adhesive layer 16, the hard carbon particles having a spherical shape are preferable.

The average particle diameter of the conductive particles 22 is preferably 0.1 to 10 μm, more preferably 0.2 to 1 μm. When the average particle diameter of the conductive particles 22 is 0.1 μm or more, the number of contact points of the conductive particles 22 increases, and the conductivity in the three-dimensional direction can be stably increased. If the average particle diameter of the conductive particles 22 is 10 μm or less, the fluidity of the isotropic conductive adhesive layer 16 (following the shape of the through hole of the insulating film) can be secured, and the inside of the through hole of the insulating film can be secured. It can be sufficiently filled with a conductive adhesive.

The specific surface area of the conductive particles 22 is preferably ^{0.2~50m 2 / g, 0.5~20m 2 /} g is more preferable. When the specific surface area of the conductive particles 22 is 0.2 m ² /g or more, the conductive particles 22 are easily available. When the specific surface area of the conductive particles 22 is 50 m ² /g or less, the oil absorption amount of the conductive particles 22 does not become too large, and as a result, the viscosity of the conductive adhesive does not become too high and the coating property is further improved. Becomes Further, the fluidity of the isotropic conductive adhesive layer 16 (following the shape of the through hole of the insulating film) can be further secured.

When the conductive filler is only the conductive particles 22, the ratio of the conductive particles 22 is preferably 30 to 80% by volume, more preferably 50 to 70% by volume, out of 100% by volume of the isotropic conductive adhesive layer 16. preferable. When the proportion of the conductive particles 22 is 30% by volume or more, the conductivity of the isotropic conductive adhesive layer 16 is stabilized. When the proportion of the conductive particles 22 is 80% by volume or less, the adhesiveness and fluidity of the isotropic conductive adhesive layer 16 (the conformability to the shape of the through hole of the insulating film) are improved. In addition, the flexibility of the electromagnetic wave shielding film 10 is improved.

Examples of the conductive fibers 24 include carbon nanofibers, metal (copper, platinum, gold, silver, nickel, etc.) nanowires, and the like, because the thickness of the isotropic conductive adhesive layer 16 is as thin as the micron level, the fiber diameter Thin carbon nanofibers are preferred. As the carbon nanofiber, a vapor grown carbon fiber is preferable because it has excellent dispersibility and secures the fluidity of the isotropic conductive adhesive layer 16 (following the shape of the through hole of the insulating film). preferable.

The average fiber length of the conductive fibers 24 is preferably 0.5 to 5 μm, more preferably 1 to 3 μm. When the average fiber length of the conductive fibers 24 is 0.5 μm or more, the conductivity and strength of the isotropic conductive adhesive layer 16 are further improved. When the average fiber length of the conductive fibers 24 is 5 μm or less, the adhesiveness and fluidity of the isotropic conductive adhesive layer 16 (the conformability to the shape of the through holes of the insulating film) are improved.

The average fiber diameter of the conductive fibers 24 is preferably 0.01 to 0.5 μm, more preferably 0.05 to 0.3 μm. When the average fiber diameter of the conductive fibers is 0.01 μm or more, the conductivity and strength of the isotropic conductive adhesive layer 16 are further improved. When the average fiber diameter of the conductive fibers 24 is 0.5 μm or less, the adhesiveness and fluidity of the isotropic conductive adhesive layer 16 (the conformability to the shape of the through holes of the insulating film) are improved.

The aspect ratio of the conductive fibers 24 is preferably 5 to 300, more preferably 10 to 100. When the aspect ratio of the conductive fiber is 5 or more, the conductivity and strength of the isotropic conductive adhesive layer 16 are further improved. When the aspect ratio of the conductive fiber is 300 or less, the adhesiveness and fluidity of the isotropic conductive adhesive layer 16 (the conformability to the shape of the through hole of the insulating film) are improved.

2-50 m< ² >/g is preferable and, as for the specific surface area of the electroconductive fiber 24, 2-40 m< ² >/g is more preferable. When the specific surface area of the conductive fiber 24 is 2 m ² /g or more, the conductive fiber 24 is easily available. When the specific surface area of the conductive fibers 24 is 50 m ² /g or less, the oil absorption amount of the conductive fibers 24 does not become too large, and as a result, the viscosity of the conductive adhesive does not become too high and the coating property is further improved. Becomes Further, the fluidity of the isotropic conductive adhesive layer 16 (following the shape of the through hole of the insulating film) can be further secured.

When the conductive filler is the conductive particles 22 and the conductive fibers 24, the ratio of the conductive fibers 24 is preferably 3 to 30% by volume in 100% by volume of the isotropic conductive adhesive layer 16, and 5 to 5%. 20% by volume is more preferred. However, the total of the conductive particles 22 and the conductive fibers 24 is 30 to 80% by volume (preferably 50 to 70% by volume). When the proportion of the conductive fibers 24 is 3% by volume or more, the conductivity and strength of the isotropic conductive adhesive layer 16 are further improved. When the proportion of the conductive fibers 24 is 30% by volume or less, the viscosity of the conductive adhesive does not become too high and the coatability becomes good. Further, the fluidity of the isotropic conductive adhesive layer 16 (following 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 isotropic conductive adhesive layer 16. You can

The thickness of the isotropic conductive adhesive layer 16 is preferably 5 to 20 μm, more preferably 7 to 17 μm. When the thickness of the isotropic conductive adhesive layer 16 is 5 μm or more, the conductivity of the isotropic conductive adhesive layer 16 is further improved, and the isotropic conductive adhesive layer 16 can sufficiently function as an electromagnetic wave shield layer. In addition, the fluidity of the isotropic conductive adhesive layer 16 (following the shape of the through hole of the insulating film) can be secured, and the inside of the through hole of the insulating film can be sufficiently filled with the conductive adhesive to improve the resistance. Foldability can be ensured and the isotropic conductive adhesive layer 16 will not be broken even if it is repeatedly bent. If the thickness of the isotropic conductive adhesive layer 16 is 20 μm or less, the electromagnetic wave shielding film 10 can be made thin. In addition, the flexibility of the electromagnetic wave shielding film 10 is improved.

The surface resistance of the isotropic conductive adhesive layer 16 is 1 to 100 Ω, preferably 1 to 50 Ω, more preferably 1 to 10 Ω. When the surface resistance of the isotropic conductive adhesive layer 16 is 1 Ω or more, the isotropic conductive adhesive layer 16 has high fluidity and high strength and toughness. If the surface resistance of the isotropic conductive adhesive layer 16 is 100 Ω or less, even if a crack occurs in the metal thin film layer 14, the resistance of the electromagnetic wave shield layer composed of the metal thin film layer 14 and the isotropic conductive adhesive layer 16 The rise is suppressed, and as a result, the electromagnetic wave shielding film 10 can maintain the electromagnetic wave noise shielding effect.

(First release film)
The first release film 18 serves as a carrier film when the insulating protective layer 12 and the metal thin film layer 14 are formed, and improves the handleability of the electromagnetic wave shielding film 10. The first release film 18 is peeled from the insulating protective layer 12 after the electromagnetic wave shielding film 10 is attached to a flexible printed wiring board or the like.

Examples of the resin material of the first release film 18 include polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polyolefin, polyacetate, polycarbonate, polyphenylene sulfide, polyamide, ethylene-vinyl acetate copolymer, polychlorinated. Examples thereof include vinyl, polyvinylidene chloride, synthetic rubber, liquid crystal polymer, and the like, and polyethylene terephthalate is preferable from the viewpoint of heat resistance (dimensional stability) and cost when manufacturing the electromagnetic wave shielding film 10.

The storage elastic modulus at 160° C. of the first release film 18 is preferably 0.8×10 ⁸ to 4×10 ⁸ Pa, more preferably 0.8×10 ^{8 to} 3×10 ⁸ Pa. When the storage elastic modulus at 160° C. of the first release film 18 is 0.8×10 ⁸ Pa or more, the electromagnetic wave shielding film 10 has good handleability. If the storage elastic modulus at 160° C. of the first release film 18 is 4×10 ⁸ Pa or less, the flexibility of the first release film 18 will be good.

The thickness of the first release film 18 is preferably 5 to 500 μm, more preferably 10 to 150 μm, and further preferably 25 to 100 μm. When the thickness of the first release film 18 is 5 μm or more, the electromagnetic wave shielding film 10 has good handleability. Further, the first release film 18 works sufficiently as a cushioning material, and the isotropic conductive adhesive layer 16 of the electromagnetic wave shielding film 10 is formed on the surface of the insulating film provided on the surface of the flexible printed wiring board by hot pressing. At the time of sticking, the isotropic conductive adhesive layer 16 easily follows the uneven shape of the surface of the insulating film. When the thickness of the first release film 18 is 500 μm or less, when the isotropic conductive adhesive layer 16 of the electromagnetic wave shielding film 10 is hot pressed onto the surface of the insulating film, the isotropic conductive adhesive layer 16 is formed. Heat is easily transmitted.

(Release agent layer)
The surface of the release film main body 18a on the insulating protective layer 12 side is subjected to a release treatment with a release agent to form a release agent layer 18b. Since the first release film 18 has the release agent layer 18b, when the first release film 18 is peeled from the insulating protective layer 12 in the step (g) described below, the first release film 18 18 is easily peeled off, and the insulating protective layer 12 and the cured isotropic conductive adhesive layer 16 are less likely to break.
As the release agent, a known release agent may be used.

The thickness of the release agent layer 18b is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm. When the thickness of the release agent layer 18b is within the above range, the first release film 18 is more easily peeled off in the step (g) described later.

(Second release film)
The second release film 20 protects the isotropic conductive adhesive layer 16 and improves the handleability of the electromagnetic wave shielding film 10. The second release film 20 is peeled from the isotropic conductive adhesive layer 16 before the electromagnetic wave shielding film 10 is attached to a flexible printed wiring board or the like.

The resin material of the second release film 20 may be the same as the resin material of the first release film 18.
The thickness of the second release film 20 is preferably 5 to 500 μm, more preferably 10 to 150 μm, and further preferably 25 to 100 μm.

(Release agent layer)
The surface of the release film main body 20a on the side of the isotropic conductive adhesive layer 16 is subjected to a release treatment with a release agent to form a release agent layer 20b. Since the second release film 20 has the release agent layer 20b, when the second release film 20 is released from the isotropic conductive adhesive layer 16 in the step (g) described below, The release film 20 is easily peeled off, and the isotropic conductive adhesive layer 16 is less likely to break.
As the release agent, a known release agent may be used.

The thickness of the release agent layer 20b is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm. When the thickness of the release agent layer 20b is within the above range, the second release film 20 is more easily peeled off in the step (g) described later.

(Thickness of electromagnetic wave shield film)
The thickness of the electromagnetic wave shielding film 10 (excluding the release film) is preferably 10 to 45 μm, more preferably 10 to 30 μm. When the thickness of the electromagnetic wave shielding film 10 (excluding the release film) is 10 μm or more, the first release film 18 is less likely to break when peeled off. When the thickness of the electromagnetic wave shielding film 10 (excluding the release film) is 45 μm or less, the flexible printed wiring board with the electromagnetic wave shielding film can be made thin.

(Method for manufacturing electromagnetic wave shielding film)
The electromagnetic wave shielding film of the present invention can be produced by, for example, a method including the following steps (a) to (d).
(A) A step of forming an insulating protective layer on one surface of the first release film.
(B) A step of forming a metal thin film layer on the surface of the insulating protective layer to obtain a first laminate including the first release film, the insulating protective layer, and the metal thin film layer in this order.
(C) A second laminate having a second release film and an isotropic conductive adhesive layer in that order by forming an isotropic conductive adhesive layer on one surface of the second release film. To obtain.
(D) A step of bonding the first laminate and the second laminate so that the metal thin film layer and the isotropic conductive adhesive layer are in contact with each other.

Hereinafter, a method for manufacturing the electromagnetic wave shielding film 10 shown in FIG. 1 will be described with reference to FIGS.

(Process (a))
As shown in FIG. 2, the insulating protective layer 12 is formed on the surface of the release agent layer 18b of the first release film 18.

The insulating protective layer 12 may be formed by applying a coating material containing a thermosetting resin and a curing agent and curing the coating material, applying a coating material containing a thermoplastic resin, or a film obtained by melt-molding the thermoplastic resin. Examples include a method of sticking. From the viewpoint of heat resistance when soldering or the like, a method of applying a coating material containing a thermosetting resin and a curing agent and curing it is preferable.
The coating material containing the thermosetting resin and the curing agent may contain a solvent and other components as necessary.

When the insulating protective layer 12 is formed by applying a coating material, the insulating protective layer 12 can be made relatively thin. Since the cured product of the thermosetting resin is hard, the strength becomes insufficient when the insulating protective layer 12 is thin. As described above, by setting the storage elastic modulus at 160° C. of the insulating protective layer 12 to be in the range of 5×10 ⁶ to 1×10 ⁸ Pa, good balance between flexibility and strength and heat resistance can be obtained. Become.

The storage elastic modulus of the insulating protective layer 12 is controlled by selecting the type and composition of the thermosetting resin, the curing agent and the like from the viewpoint of the toughness brought about by the crosslink density and the crosslinked structure, and curing the thermosetting resin. This is done by adjusting the storage modulus.
In addition, the storage elastic modulus should be adjusted by adjusting the curing conditions such as temperature and time when curing the thermosetting resin, or by adding a thermoplastic resin such as a thermoplastic elastomer as a non-thermosetting component. Can be adjusted by

(Process (b))
As shown in FIG. 2, the metal thin film layer 14 is formed on the surface of the insulating protective layer 12 to obtain the first stacked body 10a.

Examples of the method of forming the metal thin film layer 14 include a method of forming a metal thin film by physical vapor deposition, CVD, plating and the like, a method of attaching a metal foil, and the like. A method of forming a metal thin film by physical vapor deposition, CVD, plating or the like is preferable from the viewpoint that the metal thin film layer 14 having excellent conductivity in the surface direction can be formed, and the thickness of the metal thin film layer 14 can be made thin and thin. However, the physical vapor deposition method is more preferable because the metal thin film layer 14 having excellent conductivity in the plane direction can be formed and the metal thin film layer 14 can be easily formed by a dry process.

(Process (c))
As shown in FIG. 3, the isotropic conductive adhesive layer 16 is formed on the surface of the release agent layer 20b of the second release film 20 to obtain the second laminate 10b.

Examples of the method for forming the isotropic conductive adhesive layer 16 include a method of applying a conductive adhesive composition.
As the conductive adhesive composition, a composition containing the above-mentioned thermosetting adhesive, conductive particles 22 and conductive fibers 24 is used.

(Process (d))
As shown in FIG. 4, the first laminated body 10a and the second laminated body 10b are attached so that the metal thin film layer 14 and the isotropic conductive adhesive layer 16 are in contact with each other.

The first laminated body 10a and the second laminated body 10b are attached to each other by a pressing machine (not shown) or the like because the conductive fibers 24 are easily oriented in the surface direction of the isotropic conductive adhesive layer 16. It is preferable to carry out by hot pressing according to.

(Effect)
In the electromagnetic wave shielding film 10 described above, the surface resistance of the metal thin film layer 14 is 0.3Ω or less, and the surface resistance of the isotropic conductive adhesive layer 16 is 10Ω or less, and therefore will be described below. As described above, even if the metal thin film layer 14 is cracked, the electromagnetic noise shielding effect can be maintained.

FIG. 5 is a perspective view showing a model case of the electromagnetic wave shield layer including the metal thin film layer 14 and the isotropic conductive adhesive layer 16 before the metal thin film layer 14 is cracked.
The electromagnetic wave shield layer in the model case is a laminate of the metal thin film layer 14 having a width of 10 mm and a length of 20 mm and the isotropic conductive adhesive layer 16 having a width of 10 mm and a length of 20 mm.
Since the surface resistance Rms of the metal thin film layer 14 is a resistance between two electrodes having a length of 10 mm and a distance between electrodes of 10 mm, the total resistance in the length direction (20 mm) of the metal thin film layer 14, that is, the resistance of the circuit is , 2 Rms, which is twice the surface resistance Rms.
The surface resistance Rcs of the isotropic conductive adhesive layer 16 is a resistance between two electrodes having a length of 10 mm and a distance between electrodes of 10 mm. The total resistance is similarly 2Rcs.
When the electromagnetic wave shield layer is regarded as a parallel circuit of the metal thin film layer 14 and the isotropic conductive adhesive layer 16, the overall resistance R1 in the length direction of the electromagnetic wave shield layer before cracks are defined as the resistance of the parallel circuit, That is, it is represented by the following formula (1).
R1=2×Rms·Rcs/(Rms+Rcs) (1)

FIG. 6 is a perspective view showing a model case of the electromagnetic wave shield layer including the metal thin film layer 14 and the isotropic conductive adhesive layer 16 after the metal thin film layer 14 is cracked.
It is assumed that a crack having a gap of 0.2 mm occurs in the widthwise direction at the center of the metal thin film layer 14 in the lengthwise direction.
A parallel circuit composed of a metal thin film layer 14 having a width of 10 mm and a length of 9.9 mm and an isotropic conductive adhesive layer 16 and an isotropic conductive adhesive layer having a width of 10 mm and a length of 0.2 mm. If a circuit composed of 16 and a parallel circuit composed of the metal thin film layer 14 having a width of 10 mm and a length of 9.9 mm and the isotropic conductive adhesive layer 16 are considered to be connected in series, a crack is generated. The total resistance R2 in the length direction of the electromagnetic wave shield layer after being exposed is represented by the following formula (2).
R2=2×0.99×Rms·Rcs/(Rms+Rcs)+0.02×Rcs (2)

When the surface resistance Rms of the metal thin film layer 14 is the maximum value of 0.3Ω and the surface resistance Rcs of the isotropic conductive adhesive layer 16 is the maximum value of 100Ω, the length of the electromagnetic wave shield layer before the crack is generated. The total resistance R1 in the depth direction is 0.598Ω, and the total resistance R2 in the length direction of the electromagnetic wave shield layer after the crack is generated is 2.538Ω. In this way, the increase in resistance of the electromagnetic wave shield layer due to the cracks in the metal thin film layer 14 is suppressed to 10 times or less, and the electromagnetic wave noise shielding effect can be maintained.

On the other hand, when the surface resistance Rms of the metal thin film layer 14 is the maximum value of 0.3Ω, and the surface resistance Rcs of the isotropic conductive adhesive layer 16 is 1000Ω which exceeds the maximum value, the electromagnetic wave shield before cracking occurs. The total resistance R1 in the length direction of the layer is 0.600Ω, and the total resistance R2 in the length direction of the electromagnetic wave shield layer after the crack is generated is 20540Ω. As described above, when the surface resistance Rcs of the isotropic conductive adhesive layer 16 exceeds the maximum value, cracks are generated in the metal thin film layer 14 to greatly increase the resistance of the electromagnetic wave shield layer, and as a result, shield electromagnetic wave noise. The effect decreases.

(Other embodiments)
The electromagnetic wave shield film of the present invention may be any one provided with an insulating protective layer, a metal thin film layer having a specific surface resistance, and an isotropic conductive adhesive layer having a specific surface resistance in this order. It is not limited to the embodiment.
For example, when the tackiness of the surface of the isotropic conductive adhesive layer 16 is small, the second release film 20 may be omitted.
When the insulating protective layer 12 has sufficient flexibility and strength, the first release film 18 may be omitted.
The release film may not have the release agent layer when the release film itself has sufficient release properties.

<Flexible printed wiring board with electromagnetic wave shielding film>
FIG. 7: is sectional drawing which shows an example of the flexible printed wiring board with an electromagnetic wave shielding film of this invention.
The flexible printed wiring board 1 with an electromagnetic wave shielding film includes a flexible printed wiring board 30, an insulating film 40, and an electromagnetic wave shielding film 10 from which a release film is peeled off.
The flexible printed wiring board 30 is provided with a printed circuit 34 on at least one surface of a base film 32.
The insulating film 40 is provided on the surface of the flexible printed wiring board 30 on the side where the printed circuit 34 is provided.
The isotropic conductive adhesive layer 16 of the electromagnetic wave shielding film 10 is adhered and cured on the surface of the insulating film 40. Further, the isotropic conductive adhesive layer 16 is electrically connected to the printed circuit 34 through a through hole (not shown) formed in the insulating film 40.

The metal thin film layer 14 of the electromagnetic wave shielding film 10 includes the insulating film 40 and the isotropic conductive adhesive layer 16 in the vicinity of the printed circuit 34 (a signal circuit, a ground circuit, a ground layer, etc.) excluding a portion having a through hole. They are spaced apart and are opposed to each other.
The distance between the printed circuit 34 and the metal thin film layer 14 excluding the portion having the through hole is the sum of the thickness of the insulating film 40 and the thickness of the isotropic conductive adhesive layer 16. The separation distance is preferably 30 to 200 μm, more preferably 60 to 200 μm. If the separation distance is less than 30 μm, the impedance of the signal circuit becomes low. Therefore, in order to have a characteristic impedance of 100Ω or the like, the line width of the signal circuit must be made small, and the variation in the line width causes the variation in the characteristic impedance. Then, the reflected resonance noise due to the impedance mismatch becomes easy to be carried on the electric signal. When the separation distance is larger than 200 μm, the flexible printed wiring board 1 with the electromagnetic wave shielding film becomes thick and flexibility is insufficient.

(Flexible printed wiring board)
The flexible printed wiring board 30 is a printed circuit 34 (power circuit, ground circuit, ground layer, etc.) obtained by processing a copper foil of a copper clad laminate into a desired pattern by a known etching method.
As the copper-clad laminate, a copper foil is attached to one surface or both surfaces of the base film 32 via an adhesive layer (not shown); a resin solution or the like for forming the base film 32 is cast on the surface of the copper foil. The thing etc. are mentioned.
Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane, acrylic resin, and melamine resin.
The thickness of the adhesive layer is preferably 0.5 to 30 μm.

(Base film)
As the base film 32, a film having heat resistance is preferable, a polyimide film and a liquid crystal polymer film are more preferable, and a polyimide film is further preferable.
The surface resistance of the base film 32 is preferably 1×10 ⁶ Ω or more from the viewpoint of electrical insulation. The surface resistance of the base film 32 is preferably 1×10 ¹⁹ Ω or less from the practical point of view.
The thickness of the base film 32 is preferably 5 to 200 μm, more preferably 6 to 25 μm, and further preferably 10 to 25 μm from the viewpoint of flexibility.

(Printed circuit)
Examples of the copper foil forming the printed circuit 34 (signal circuit, ground circuit, ground layer, etc.) include rolled copper foil, electrolytic copper foil and the like, and rolled copper foil is preferable from the viewpoint of flexibility.
The thickness of the copper foil is preferably 1 to 50 μm, more preferably 18 to 35 μm.
The lengthwise ends (terminals) of the printed circuit 34 are not covered with the insulating film 40 or the electromagnetic wave shielding film 10 because of solder connection, connector connection, component mounting, and the like.

(Insulating film)
The insulating film 40 is formed by forming an adhesive layer (not shown) on one surface of a base film (not shown) by applying an adhesive, attaching an adhesive sheet, or the like.
The surface resistance of the base film is preferably 1×10 ⁶ Ω or more from the viewpoint of electrical insulation. The surface resistance of the base film is preferably 1×10 ¹⁹ Ω or less from the practical point of view.
As the substrate film, a film having heat resistance is preferable, a polyimide film and a liquid crystal polymer film are more preferable, and a polyimide film is further preferable.
The thickness of the base film is preferably 1 to 100 μm, and more preferably 3 to 25 μm from the viewpoint of flexibility.
Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamideimide, polyamide, phenol resin, polyurethane, acrylic resin, melamine resin, polystyrene and polyolefin. The epoxy resin may include a rubber component (carboxyl-modified nitrile rubber or the like) for imparting flexibility.
The thickness of the adhesive layer is preferably 1 to 100 μm, more preferably 1.5 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 include a circle, an ellipse, and a quadrangle.

(Method for manufacturing flexible printed wiring board with electromagnetic wave shielding film)
The flexible printed wiring board with the electromagnetic wave shielding film of the present invention can be produced, for example, by a method including the following steps (e) to (g).
(E) An insulating film having through holes formed at positions corresponding to the printed circuit is provided on the surface of the flexible printed wiring board having the printed circuit on at least one surface of the base film on which the printed circuit is provided. The process of obtaining a flexible printed wiring board.
(F) After the step (e), the flexible printed wiring board with an insulating film and the electromagnetic wave shielding film of the present invention are stacked so that the isotropic conductive adhesive layer is in contact with the surface of the insulating film, and these are heated. A step of adhering the isotropic conductive adhesive layer to the surface of the insulating film by pressing and electrically connecting the isotropic conductive adhesive layer to the printed circuit through the through hole.
(G) A step of peeling the first release film after the step (f) to obtain a flexible printed wiring board with an electromagnetic wave shielding film.

Hereinafter, a method for manufacturing the flexible printed wiring board with the electromagnetic wave shielding film will be described with reference to FIG.

(Process (e))
As shown in FIG. 8, an insulating film 40 having through holes 42 formed at positions corresponding to the printed circuit 34 is laid on the flexible printed wiring board 30, and an adhesive layer of the insulating film 40 is formed on the surface of the flexible printed wiring board 30. By bonding (not shown) and curing the adhesive layer, the flexible printed wiring board 2 with an insulating film is obtained. The adhesive layer of the insulating film 40 may be temporarily adhered to the surface of the flexible printed wiring board 30, and the adhesive layer may be fully cured in the step (f).
Adhesion and curing of the adhesive layer are performed, for example, by hot pressing using a pressing machine (not shown) or the like.

(Process (f))
As shown in FIG. 8, the electromagnetic shielding film 10 from which the second release film 20 has been peeled off is placed on the flexible printed wiring board 2 with an insulating film, and hot pressed to obtain isotropic conductivity on the surface of the insulating film 40. The flexible printed wiring board precursor 3 with an electromagnetic wave shielding film is obtained in which the adhesive layer 16 is bonded and the isotropic conductive adhesive layer 16 is electrically connected to the printed circuit 34 through the through hole 42.

Adhesion and curing of the isotropic conductive adhesive layer 16 are performed, for example, by hot pressing with a pressing machine (not shown).
The time of hot pressing is 20 seconds to 60 minutes, more preferably 30 seconds to 30 minutes. When the hot pressing time is 20 seconds or more, the isotropic conductive adhesive layer 16 is bonded to the surface of the insulating film 40. If the heat pressing time is 60 minutes or less, the manufacturing time of the flexible printed wiring board 1 with the electromagnetic wave shielding film can be shortened.

The temperature of the hot press (the temperature of the press plate of the press) is preferably 140 to 190°C, more preferably 150 to 175°C. When the temperature of hot pressing is 140° C. or higher, the isotropic conductive adhesive layer 16 is bonded to the surface of the insulating film 40. In addition, the time of hot pressing can be shortened. When the temperature of the hot press is 190° C. or lower, deterioration of the electromagnetic wave shielding film 10, the flexible printed wiring board 30, etc. can be suppressed.

The pressure of the hot press is preferably 10 MPa to 20 MPa, more preferably 10 MPa to 16 MPa. If the pressure of the hot press is 10 MPa or more, the isotropic conductive adhesive layer 16 is bonded to the surface of the insulating film 40. In addition, the time of hot pressing can be shortened. When the pressure of the hot press is 20 MPa or less, damage to the electromagnetic wave shielding film 10, the flexible printed wiring board 30, etc. can be suppressed.

(Process (g))
As shown in FIG. 8, the first release film 18 is peeled from the insulating protective layer 12 to obtain the flexible printed wiring board 1 with the electromagnetic wave shielding film.

When the time of hot pressing in the step (f) is a short time of 20 seconds to 10 minutes, main curing of the isotropic conductive adhesive layer 16 is performed before or after peeling the first release film 18. Preferably.
The main curing of the isotropic conductive adhesive layer 16 is performed using a heating device such as an oven.
The heating time is 15 to 120 minutes, preferably 30 to 60 minutes. If the heating time is 15 minutes or more, the isotropic conductive adhesive layer 16 can be sufficiently cured. If the heating time is 120 minutes or less, the manufacturing time of the flexible printed wiring board 1 with the electromagnetic wave shielding film can be shortened.
The heating temperature (ambient temperature in the oven) is preferably 120 to 180°C, and preferably 120 to 150°C. When the heating temperature is 120° C. or higher, the heating time can be shortened. When the heating temperature is 160° C. or lower, deterioration of the electromagnetic wave shielding film 10, the flexible printed wiring board 30, etc. can be suppressed.
It is preferable to perform heating without pressurization, because a special device does not have to be used.

(Effect)
In the flexible printed wiring board 1 with the electromagnetic wave shielding film described above, the surface resistance of the metal thin film layer 14 is 0.3Ω or less, and the surface resistance of the isotropic conductive adhesive layer 16 is 10Ω or less. Even if the metal thin film layer 14 is cracked, the effect of shielding electromagnetic wave noise can be maintained.

(Other embodiments)
The flexible printed wiring board with the electromagnetic wave shielding film of the present invention is not limited to the embodiment shown in the drawings as long as it includes the flexible printed wiring board, the insulating film and the electromagnetic wave shielding film of the present invention.
For example, the flexible printed wiring board may have a ground layer on the back surface side. Further, 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.

Examples will be shown below. The present invention is not limited to the embodiments.

(Storage elastic modulus)
The storage elastic modulus was measured using a dynamic viscoelasticity measuring device (RSAII, manufactured by Rheometric Scientific, Inc.).

(Example 1)
As the first release film 18 and the second release film 20, a polyethylene terephthalate film whose one surface is release-treated with a non-silicone release agent (T157 manufactured by Lintec Co., thickness: 50 μm, at 160° C.) Storage elastic modulus: 6×10 ⁸ Pa) was prepared.

Step (a):
On the surface of the release agent layer 18b of the first release film 18, a solvent-soluble amide resin (TPAE-617C manufactured by T&K Toka Co., Ltd.) and a curing agent (toluene diisocyanate) are dissolved in N,N-dimethylformamide. The coating composition is applied and heated at 150° C. for 0.4 hours to cure the amide resin, and the insulating protective layer 12 (thickness: 5 μm, storage elastic modulus at 160° C.: 8×10 ⁶ Pa, surface resistance: 8×10 ¹² Ω) was formed.

Step (b):
Copper is physically vapor-deposited on the surface of the insulating protective layer 12 by an electron beam vapor deposition method to form a vapor deposition film (metal thin film layer 14) having a thickness of 0.07 μm and a surface resistance of 0.3Ω. The laminated body 10a was obtained.

Step (c):
On the surface of the release agent layer 20b of the second release film 20, a mixture of an epoxy resin (manufactured by DIC, EXA-4816) as a curable epoxy resin and a curing agent (manufactured by Ajinomoto Fine Techno, PN-23). , Silver particles (AG 6-11, manufactured by DOWA Electronics Co., average particle size: 3.6 μm, specific surface area: 0.21 m ² /g, true density: 10.5 g/cm ³ ) and carbon nano particles as the conductive particles 22. Fiber (Showa Denko KK, VGCF, average fiber length: 6 μm, average fiber diameter: 0.15 μm, aspect ratio: 60, specific surface area: 13 m ² /g, true density: 2.1 g/cm ³ ) was used as a solvent (methyl ethyl ketone). ) Is dissolved or dispersed in a conductive adhesive composition is applied using a die coater, the solvent is volatilized, isotropic conductive adhesive layer 16 (thickness: 10 μm, silver particles: 58% by volume, Carbon nanofibers: 15% by volume, surface resistance: 80Ω) were formed to obtain a second laminated body 10b.

Step (d):
The first laminated body 10a and the second laminated body 10b are overlapped so that the metal thin film layer 14 and the isotropic conductive adhesive layer 16 are in contact with each other, and a hot press machine (VFIG-05R manufactured by VIGOR Co., Ltd.) is used. It was used and hot pressed at a temperature of 90° C. and a pressure of 2 MPa for 3 seconds to obtain an electromagnetic wave shielding film 10.

Process (e):
An insulating adhesive composition composed of a nitrile rubber-modified epoxy resin is applied to the surface of a 25 μm-thick polyimide film (surface resistance: 1×10 ¹⁷ Ω) (base film) so that the dry film thickness is 25 μm. Then, an adhesive layer was formed to obtain an insulating film 40 (thickness: 50 μm).

A flexible printed wiring board 30 having a printed circuit 34 formed on the surface of a polyimide film (surface resistance: 1×10 ¹⁷ Ω) (base film 32) having a thickness of 12 μm was prepared.
The insulating film 40 was attached to the flexible printed wiring board 30 by hot pressing to obtain the flexible printed wiring board 2 with the insulating film.

Process (f):
The electromagnetic shielding film 10 from which the second release film 20 has been peeled off is placed on the flexible printed wiring board 30 and a hot press device (VFPC-05R manufactured by VIGOR) is used, and the temperature is 170° C. and the pressure is 15 MPa for 30 seconds. By hot pressing, the isotropic conductive adhesive layer 16 was adhered to the surface of the insulating film 40 to obtain the precursor 3 of the flexible printed wiring board with the electromagnetic wave shielding film.
The isotropic conductive adhesive layer 16 is formed by heating the precursor 3 of the flexible printed wiring board with the electromagnetic wave shielding film at a temperature of 170° C. for 30 minutes using a high temperature incubator (HT210 manufactured by Kusumoto Kasei Co., Ltd.). Cured.

Process (g):
The first release film 18 was peeled from the insulating protective layer 12 to obtain a flexible printed wiring board 1 with an electromagnetic wave shielding film.

(Comparative Example 1)
Steps (a)-(b):
In the same manner as in Example 1, a first laminated body was obtained.

Step (c):
On the surface of the release agent layer of the second release film, a mixture of an epoxy resin (manufactured by DIC, EXA-4816) and a curing agent (manufactured by Ajinomoto Fine-Techno, PN-23) as a curable epoxy resin, and conductive. As fired particles 22, fired carbon particles (CR2-800SR, manufactured by Air Water Bell Pearl Co., average particle diameter: 5.0 μm, specific surface area: 0.8 m ² /g, true density: 1.34 g/cm ³ ) are used as a solvent. The conductive adhesive composition dissolved or dispersed in (methyl ethyl ketone) is applied using a die coater, the solvent is volatilized, and the isotropic conductive adhesive layer (thickness: 10 μm, fired carbon particles: 75 volume) is applied. %, carbon nanofiber: 10% by volume, surface resistance: 620 Ω) to obtain a second laminated body.

Step (d):
An electromagnetic wave shielding film was obtained in the same manner as in Example 1 except that the second laminate obtained in the step (c) of Comparative Example 1 was used as the second laminate.

Steps (e) to (g):
A flexible printed wiring board with an electromagnetic wave shielding film was obtained in the same manner as in Example 1 except that the electromagnetic wave shielding film obtained in the step (d) of Comparative Example 1 was used as the electromagnetic wave shielding film.

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 smartphones, mobile phones, optical modules, digital cameras, game machines, notebook computers and medical instruments.

1 Flexible Printed Wiring Board with Electromagnetic Wave Shielding Film 2 Flexible Printed Wiring Board with Insulating Film 3 Precursor of Flexible Printed Wiring Board with Electromagnetic Wave Shielding Film 10 Electromagnetic Wave Shielding Film 10a First Laminate 10b Second Laminate 12 Insulating Protective Layer 14 Metal Thin Film Layer 16 Isotropic Conductive Adhesive Layer 18 First Release Film 18a Release Film Body 18b Release Agent Layer 20 Second Release Film 20a Release Film Body 20b Release Agent Layer 22 Conductive Particles 24 Conductive Fiber 30 Flexible Printed Wiring Board 32 Base Film 34 Printed Circuit 40 Insulating Film 42 Through Hole 101 Flexible Printed Wiring Board with Electromagnetic Wave Shielding Film 110 Electromagnetic Wave Shielding Film 112 Insulating Protective Layer 114 Metal Thin Film Layer 116 Anisotropic Conductive Adhesive Layer 118 Release film 130 Flexible printed wiring board 132 Base film 134 Printed circuit 140 Insulation film 142 Through hole

Claims (6)

An insulating protective layer,
A metal thin film layer that covers the first surface of the insulating protective layer and has a surface resistance of 0.01 to 0.3Ω;
An isotropic conductive adhesive layer containing a conductive filler and having a surface resistance of 1 to 100 Ω, which covers the surface of the metal thin film layer opposite to the side in contact with the insulating protective layer,
Further comprising a first release film covering the second surface of the insulating protective layer,
The isotropic conductive adhesive layer contains, as the conductive filler, conductive particles and conductive fibers,
The electromagnetic wave shielding film, wherein the ratio of the conductive filler is 50 to 80% by volume based on 100% by volume of the isotropic conductive adhesive layer. The electromagnetic wave shielding film according to claim 1, wherein the conductive fiber is carbon nanofiber. The electromagnetic wave shielding film according to claim 1 or 2 , further comprising a second release film that covers a surface of the isotropic conductive adhesive layer opposite to a side in contact with the isotropic conductive adhesive layer. .. A method for producing the electromagnetic wave shielding film according to claim 3 ,
A method for producing an electromagnetic wave shielding film, which comprises the following steps (a) to (d).
(A) A step of forming an insulating protective layer on one surface of the first release film.
(B) A first release film, an insulating protective layer, and a metal thin film layer by forming a metal thin film layer having a surface resistance of 0.01 to 0.3Ω on the surface of the insulating protective layer. And a step of obtaining a first laminated body including in order.
(C) Isotropic conductivity containing a second release film and a conductive filler by forming an isotropic conductive adhesive layer on one surface of the second release film, and having a surface resistance of 1 to 100Ω. Obtaining a second laminated body that is sequentially provided with a conductive adhesive layer.
(D) The first laminated body and the second laminated body are brought into contact with each other by the metal thin film layer of the first laminated body and the isotropic conductive adhesive layer of the second laminated body. Process to bond. A flexible printed wiring board provided with a printed circuit on at least one surface of the base film,
An insulating film provided on the surface of the flexible printed wiring board on which the printed circuit is provided,
The electromagnetic wave shielding film according to claim 1 or 2, wherein the isotropic conductive adhesive layer is adhered to the surface of the insulating film.
A flexible printed wiring board with an electromagnetic wave shielding film, wherein the isotropic conductive adhesive layer is electrically connected to the printed circuit through a through hole formed in the insulating film. A method for manufacturing a flexible printed wiring board with an electromagnetic wave shielding film, which comprises the following steps (e) to (g).
(E) An insulating film having through holes formed at positions corresponding to the printed circuit is provided on the surface of the flexible printed wiring board having the printed circuit on at least one surface of the base film on the side where the printed circuit is provided, and insulation is provided. The process of obtaining a flexible printed wiring board with a film.
(F) After the step (e), the flexible printed wiring board with an insulating film and the electromagnetic wave shielding film according to claim 1 or 2 are formed on the surface of the insulating film by the isotropic conductive adhesive layer. By stacking them in contact with each other, by hot pressing these, the isotropic conductive adhesive layer is adhered to the surface of the insulating film, and the isotropic conductive adhesive layer is passed through the through hole to The process of electrically connecting to a printed circuit.
(G) When the electromagnetic wave shielding film includes a first release film, a step of peeling the first release film after the step (f).

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