JP2021061365A - Electromagnetic wave shield film, circuit board, and manufacturing method thereof - Google Patents

Abstract

To provide an electromagnetic wave shield film with reduced connection resistance between a shield layer and a wiring for ground or ground layer, a circuit board using the electromagnetic wave shield film, and a manufacturing method thereof.SOLUTION: An electromagnetic wave shield film 1D includes an insulating resin layer 10, and a shield layer 22 adjacent to the insulating resin layer 10 and having at least the outermost layer on the opposite side of the insulating resin layer 10 as a metal thin film layer, and a conductive adhesive layer 24 provided on the side of the shield layer 22 opposite to the insulating resin layer 10, and the conductive adhesive layer 24 contains flaky conductive particles 24b, and the minimum storage elastic modulus at 100 to 190°C is 1.0×103 to 1.0×105 Pa, and there is also provided a circuit board 2 using the electromagnetic wave shield film.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electromagnetic wave shielding film, a circuit board, and a method for manufacturing a circuit board.

In order to shield electromagnetic wave noise generated from the printed wiring board and electromagnetic wave noise from the outside, an electromagnetic wave shielding film having an insulating resin layer and a conductive layer is applied to the surface of the printed wiring board via an insulating film (coverlay film). It may be provided (see, for example, Patent Document 1). The conductive layer is, for example, a conductive adhesive for electrically connecting a shield layer made of a metal thin film layer for shielding electromagnetic waves and a ground wiring or a ground layer in a printed circuit of the shield layer and a printed wiring board. Has a layer.

A circuit board provided with an electromagnetic wave shielding film is manufactured by stacking a printed wiring board with an insulating film and an electromagnetic wave shielding film so that the insulating film and the conductive adhesive layer are in contact with each other and heat-pressing them.
The insulating film is provided with a through hole in a portion overlapping the ground wiring or the ground layer. The conductive adhesive layer penetrates into this penetrating term by a hot press and comes into contact with the gland wiring or the gland layer.

Japanese Unexamined Patent Publication No. 2016-086120

The electromagnetic wave shield film is required to further improve the shielding effect. For that purpose, it is necessary to reduce the connection resistance between the shield layer and the ground wiring or the ground layer.
The present invention has been made in view of the above circumstances, and is an electromagnetic wave shield film in which the connection resistance between the shield layer and the ground wiring or the ground layer is reduced, a circuit board using this electromagnetic wave shield film, and its manufacture. Provide a method.

In order to achieve the above problems, the present invention has adopted the following configuration.
[1] The insulating resin layer, the shield layer adjacent to the insulating resin layer and at least the outermost layer on the side opposite to the insulating resin layer is a metal thin film layer, and the insulating resin layer of the shield layer are opposite to each other. With a conductive adhesive layer provided on the side,
The conductive adhesive layer comprises a flaky conductive particles, the lowest value of the storage elastic modulus at 100 to 190 ° C. is ^{1.0 × 10 3 ~1.0 × 10 5} Pa, an electromagnetic wave shielding film.
[2] The electromagnetic wave shielding film according to [1], wherein the conductive particles have a volume average particle diameter of 1 to 100 μm.
[3] The electromagnetic wave shielding film according to [1] or [2], wherein the ratio of the conductive particles to 100% by mass of the conductive adhesive layer is 1% by mass or more and 50% by mass or less.
[4] The electromagnetic wave according to any one of [1] to [3], wherein the ratio of the average thickness of the conductive particles to the layer thickness of the conductive adhesive layer is 0.002 to 0.3. Shield film.
[5] A circuit board main body provided with a ground wiring or a circuit including a ground layer on at least one surface of the board.
An insulating film having a through hole formed in a portion adjacent to the one surface and overlapping the ground wiring or the ground layer.
The electromagnetic wave shielding film according to any one of [1] to [4], which is adjacent to the insulating film on the side opposite to the circuit board main body, is provided.
A circuit board in which the conductive adhesive layer in the electromagnetic wave shielding film adheres to the insulating film and penetrates into the through hole to be in contact with the ground wiring or the ground layer.
[6] For a circuit board main body provided with a ground wiring or a circuit including a ground layer on at least one surface of the substrate, an insulating film having through holes formed in a portion overlapping the ground wiring or the ground layer is provided. After stacking, the electromagnetic wave shielding film according to any one of [1] to [4] is laminated so that the conductive adhesive layer is in contact with the insulating film and the conductive adhesive layer, and then heat-pressed. How to manufacture a circuit board.

According to the method for manufacturing an electromagnetic wave shield film, a circuit board, and a circuit board of the present invention, it is possible to reduce the connection resistance between the shield layer and the ground wiring or the ground layer in the circuit board main body. Therefore, a high shielding effect can be obtained.

It is sectional drawing which shows one Embodiment of the electromagnetic wave shielding film in this invention. It is sectional drawing which shows one Embodiment of the circuit board in this invention. It is sectional drawing which shows the manufacturing process of the circuit board of FIG. It is sectional drawing which shows the circuit board when the storage elastic modulus of a conductive adhesive layer is large. It is sectional drawing which shows the circuit board when the conductive particle of the conductive adhesive layer is spherical.

The definitions of the following terms apply throughout the specification and claims.
The "isotropic conductive adhesive layer" means a conductive adhesive layer having conductivity in the thickness direction and the surface direction.
The "anisotropic adhesive layer" means a conductive adhesive layer that has conductivity in the thickness direction and does not have conductivity in the surface direction.
The “conductive adhesive layer having no conductivity in the plane direction” means a conductive adhesive layer having a surface resistance of 1 × 10 ⁴ Ω / □ or more.

For the average thickness of conductive particles, 30 particles were randomly selected from the magnified image of the particles with an electron microscope, the thickness of each particle was measured, and the measured thicknesses of the 30 particles were arithmetically averaged. It is obtained from the obtained value.
The volume average particle diameter of the conductive particles is a volume-based cumulative 50% diameter (d50) obtained by a laser diffraction / scattering method.

Use a digital length measuring machine (Mitutoyo, Lightmatic VL-50-B) to determine the thickness of the film (release film, insulating film, etc.) and coating film (insulating resin layer, conductive adhesive layer, etc.). The thickness of 5 randomly selected points was measured and averaged. However, the layer thickness in the circuit board is a value obtained by measuring and averaging the thicknesses of five randomly selected parts from the portion where the through holes are not formed.
The thickness of the metal thin film layer is a value obtained by measuring the thicknesses of five randomly selected points using an eddy current type film thickness meter and averaging them.

The storage elastic modulus is a value measured using a dynamic viscoelasticity measuring device (RSAII manufactured by Leometric Scientific Co., Ltd., USA) under the conditions of frequency: 1 Hz and heating rate: 5 ° C./min.
Surface resistance, if it is less than 10 ⁶ Ω / □, low resistivity resistivity meter (e.g., Mitsubishi Chemical Co., Loresta GP, ASP probe) using a four-terminal method (JIS K 7194: 1994 and JIS R 1637: a surface resistivity as measured by the method) that conforms to 1998, in the case of 10 ⁶ Ω / □ or more, high resistance resistivity meter (e.g., Mitsubishi Chemical Co., Hiresta UP, a URS probe) using double The surface resistivity measured by the ring method (a method conforming to JIS K 6911: 2006).
The dimensional ratios in FIGS. 1 to 5 are different from the actual ones for convenience of explanation. In addition, the numerical range represented by using "~" in the present specification means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

<Electromagnetic wave shield film>
FIG. 1 is a cross-sectional view showing an electromagnetic wave shielding film 1A according to an embodiment of the present invention.
The electromagnetic wave shield film 1A of the present embodiment includes an insulating resin layer 10, a shield layer 22 adjacent to the insulating resin layer 10, and a conductive adhesive layer 24 provided on the opposite side of the shield layer 22 from the insulating resin layer 10. Has.
Further, in the present embodiment, the first release film 30 is attached to the side of the insulating resin layer 10 opposite to the shield layer 22. Further, a second release film 40 is attached to the side of the conductive adhesive layer 24 opposite to the shield layer 22.

The thickness of the electromagnetic wave shielding film 1A excluding the release film is preferably 5 μm or more and 50 μm or less, and more preferably 8 μm or more and 30 μm or less. If the thickness of the electromagnetic wave shielding film 1A excluding the release film is at least the lower limit of the above range, it is unlikely to break when the first release film 30 is peeled off. If the thickness of the electromagnetic wave shielding film 1A excluding the release film is equal to or less than the upper limit of the above range, the circuit board can be thinned.

(Insulating resin layer)
The insulating resin layer 10 becomes a protective layer of the shield layer 22 after the second release film 40 and the first release film 30 are peeled from the electromagnetic wave shield film 1A.

As the insulating resin layer 10, a coating film containing a photocurable resin and a photoradical polymerization initiator is applied, and a coating film formed by semi-curing or curing; a coating material containing a thermosetting resin and a curing agent is applied. A coating film formed by semi-curing or curing; a coating film formed by applying a coating material containing a thermoplastic resin and drying it; a layer composed of a film obtained by melt-molding a composition containing a thermoplastic resin, or the like. Can be mentioned. From the viewpoint of heat resistance when subjected to the solder reflow process, a coating film or thermosetting resin formed by applying a paint containing a photocurable resin and a photoradical polymerization initiator and semi-curing or curing it. A coating film formed by applying a coating material containing a curing agent and a curing agent and semi-curing or curing the coating film is preferable.

Examples of the photocurable resin include compounds having a (meth) acryloyl group.
Examples of the photoradical polymerization initiator include known photoradical polymerization initiators depending on the type of photocurable resin.
Examples of the thermosetting resin include amide resin, epoxy resin, phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, and ultraviolet curable acrylate resin.
As the thermosetting resin, an amide resin and an epoxy resin are preferable from the viewpoint of excellent heat resistance.
Examples of the curing agent include known curing agents depending on the type of thermosetting resin.
Examples of the thermoplastic resin include aromatic polyetherketone, polyimide, polyamideimide, polyamide, polysulfone, polyethersulfone, polyphenylene sulfide, polyphenylene sulfide, polyphenylene sulfide sulfone, and polyphenylene sulfide ketone.

The insulating resin layer 10 contains one or both of a colorant (pigment, dye, etc.) and a filler in order to conceal the printed circuit of the printed wiring board and impart designability to the circuit board. May be good.
As one or both of the colorant and the filler, a pigment or a filler is preferable from the viewpoint of weather resistance, heat resistance and concealing property, and a black pigment or a black pigment is used from the viewpoint of concealing property and design property of a printed circuit. Combinations with other pigments or fillers are more preferred.
The insulating resin layer 10 may contain a flame retardant. The insulating resin layer 10 may contain other components, if necessary, as long as the effects of the present invention are not impaired.

The surface resistance of the insulating resin layer 10 ^{is preferably 1 × 10 6} Ω / □ or more from the viewpoint of electrical insulation. The surface resistance of the insulating resin layer 10 ^{is preferably 1 × 10 19} Ω / □ or less from a practical point of view.
The thickness of the insulating resin layer 10 is preferably 0.1 μm or more and 30 μm or less, and more preferably 0.5 μm or more and 20 μm or less. When the thickness of the insulating resin layer 10 is at least the lower limit of the above range, the insulating resin layer 10 can sufficiently exert the function as a protective layer. When the thickness of the insulating resin layer 10 is not more than the upper limit of the above range, the thickness of the electromagnetic wave shielding film 1A excluding the release film can be reduced.

(Shield layer)
The shield layer 22 has one or a plurality of metal thin film layers formed so as to spread in the plane direction. The metal thin film layer is a layer made of only metal. At least the outermost layer of the shield layer 22 opposite to the insulating resin layer 10 is a metal thin film layer.

Examples of the metal thin film layer include a vapor deposition film formed by physical vapor deposition (vacuum vapor deposition, sputtering, ion beam deposition, electron beam deposition, etc.) or CVD (chemical vapor deposition), a plating film formed by plating, a metal foil, and the like. Can be mentioned. The metal thin film layer is preferably a vapor-deposited film or a plated film in terms of excellent surface conductivity. A thin-film metal film layer is more preferable, and a thin-film film by physical vapor deposition is more preferable because the shield layer 22 can be made thin, has excellent conductivity in the plane direction even if the thickness is thin, and can be easily formed by a dry process. preferable.

Examples of the metal constituting the metal thin film layer include aluminum, silver, copper, gold, and conductive ceramics. From the viewpoint of electrical conductivity, silver or copper is preferable.
Among the metal thin-film layers, a metal-deposited layer is preferable, and a silver-deposited layer or a copper-deposited layer is more preferable, because the metal thin-film layer has high electromagnetic shielding properties and the metal thin film can be easily formed.

The surface resistance of the metal thin film layer is preferably 0.001 Ω / □ or more and 1 Ω / □ or less, and more preferably 0.001 Ω / □ or more and 0.5 Ω / □ or less. When the surface resistance of the metal thin film layer is equal to or higher than the lower limit of the above range, the shield layer 22 can be sufficiently thinned. If the surface resistance of the metal thin film layer is not more than the upper limit of the above range, it can sufficiently function as an electromagnetic wave shielding layer.

When the shield layer 22 is composed of one metal thin film layer, the thickness of the shield layer 22, that is, the thickness of the metal thin film layer is preferably 0.01 μm or more and 1 μm or less, and more preferably 0.05 μm or more and 1 μm or less. When the thickness of the shield layer 22 is 0.01 μm or more, the conductivity in the plane direction is further improved. When the thickness of the shield layer 22 is 0.05 μm or more, the shielding effect of electromagnetic noise is further improved. When the thickness of the shield layer 22 is not more than the upper limit of the above range, the thickness of the electromagnetic wave shield film 1A excluding the release film can be reduced. In addition, the productivity and flexibility of the electromagnetic wave shielding film 1A are improved.

When the shield layer 22 has a plurality of metal thin film layers, the shield layer 22 is configured as a laminated body in which a non-metal layer is inserted between the metal thin film layers.
The number of metal thin film layers is preferably 2 to 10, more preferably 2 to 6 layers, and even more preferably 2 to 4 layers. By having a plurality of metal thin film layers, the number of reflection interfaces of electromagnetic waves is larger than that in the case of providing one metal thin film layer, and even if the thickness of each metal thin film layer is thin, the electromagnetic wave shielding property is excellent.
The thickness, constituent materials, physical properties, etc. of each metal thin film layer may be the same as or different from each other.

When the shield layer 22 has a plurality of metal thin film layers, the thickness of each metal thin film layer is preferably 1 μm or less. Independently, 0.01 μm or more and 1 μm or less is preferable, 0.05 μm or more and 0.6 μm or less is more preferable, and 0.1 μm or more and 0.4 μm or less is further preferable. The thickness of each metal thin film layer may be the same or different.
When the thickness of each metal thin film layer is not more than the upper limit of the above range, the gas permeability in each metal thin film layer is increased, and the gas generated during the solder reflow treatment (for example, the gas generated from the conductive adhesive layer 24). Can be easily permeated, so that delamination and swelling due to the retention of gas can be prevented.
When the thickness of each metal thin film layer is at least the lower limit of the above range, the electromagnetic wave shielding property at the interface of each metal thin film layer is improved.

When the shield layer 22 has a plurality of metal thin film layers, the total thickness of the plurality of metal thin film layers is preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm or more and 2 μm or less, and more preferably 0.3 μm or more. It is more preferably 1.2 μm or less, and most preferably 0.5 μm or more and 1 μm or less.
When the total thickness is not more than the lower limit of the above range, the gas permeability in the shield layer 22 is enhanced, and the gas generated during the solder reflow treatment (for example, the gas generated from the conductive adhesive layer 24) is permeated. Since it becomes easy, it is possible to prevent delamination and swelling due to the retention of gas.
When the total thickness is not more than the upper limit of the above range, the electromagnetic wave shielding film can be made thinner.

When the shield layer 22 has a plurality of metal thin film layers, a non-metal layer is always interposed between the metal thin film layers. In other words, when a group of metal thin film layers is multi-layered without interposing a non-metal layer (for example, when the metal thin film layer B is laminated on the metal thin film layer A by vapor deposition or the like), this A group of metal thin film layers is regarded as one metal thin film layer.

The metal thin film layer of the shield layer 22 is a layer made of only metal. On the other hand, the non-metal layer interposed between the metal thin film layers is not a layer composed only of metal, but a layer containing at least a resin. Examples of the non-metal layer include an insulating layer made of an insulating resin (resin that is electrically insulating), a conductive layer containing conductive particles or a conductive polymer.

The thickness of the non-metal layer is preferably 0.01 μm or more and 5 μm or less, more preferably 1 μm or more and 4 μm or less, and further preferably 2 μm or more and 3 μm or less.
When the thickness of the non-metal layer is not less than the lower limit of the above range, the adhesive force to the adjacent metal thin film layer is increased, and when it is not more than the upper limit of the above range, the gas permeability in the non-metal layer is increased, and as a result, soldering is performed. It is preferable because it improves heat resistance.

Examples of the insulating resin constituting the insulating layer include known thermosetting resins and thermoplastic resins, and thermosetting resins are preferable from the viewpoint of heat resistance. The thermosetting resin constituting the non-metal layer may be in any of an uncured state, a B-staged state, and a cured state.
The insulating layer may contain components other than the insulating resin, if necessary.

Examples of the thermosetting resin include epoxy resin, phenol resin, imide resin, urethane resin, condensation-curing silicone, addition-curing silicone, and thermosetting acrylic resin. Of these, epoxy resin is preferable because it has excellent heat resistance.
The insulating resin may contain a curing agent of a thermosetting resin. Examples of the curing agent include an isocyanate compound having two or more isocyanate groups, an epoxy compound having two or more epoxy groups, and the like, which are appropriately selected depending on the type of the thermosetting resin.

Examples of the thermoplastic resin include a thermoplastic acrylic resin, an ethylene-vinyl acetate copolymer, an ethylene-acrylic copolymer, a polyvinyl chloride, a polyvinyl acetate, a polyamide, chloroprene, a styrene-butadiene copolymer, and a styrene-. Examples thereof include a butadiene-styrene block copolymer or a hydrogenated product thereof, a styrene-isoprene-styrene block copolymer or a hydrogenated product thereof, and the like.

Examples of the resin contained in the conductive layer include the above-mentioned thermosetting resin and thermoplastic resin, and a thermosetting resin is preferable from the viewpoint of heat resistance. Further, a conductive polymer is also suitable in that it imparts conductivity to the conductive layer.

When the conductive layer contains conductive particles and an insulating resin, the volume average particle diameter of the conductive particles is preferably 0.2 μm or more and 10 μm or less, more preferably 0.5 μm or more and 8 μm or less, and 0.8 μm or more and 5 μm or less. More preferred. The thickness of the conductive layer can be maintained as long as it is equal to or higher than the lower limit of the above range. When it is not more than the upper limit of the above range, the adhesive strength between the metal thin film layers can be increased.

The proportion of the conductive particles in the conductive layer is preferably 1% by volume or more and 30% by volume or less, and more preferably 2% by volume or more and 15% by volume or less, out of 100% by volume of the conductive layer. When it is at least the lower limit of the above range, the conductivity of the conductive layer becomes good. When it is not more than the upper limit value of the above range, the adhesiveness of the conductive layer becomes good. In addition, the flexibility of the electromagnetic wave shielding film 1A is improved.

The thickness of the conductive layer containing the conductive particles is preferably 0.2 μm or more and 10 μm or less, more preferably 0.5 μm or more and 8 μm or less, and further preferably 0.8 μm or more and 5 μm or less. When it is at least the lower limit of the above range, the adhesive strength between the metal thin film layers can be increased. If it is not more than the upper limit of the above range, the electromagnetic wave shielding film 1A can be thinned. In addition, the flexibility of the electromagnetic wave shielding film 1A is improved.

When the conductive layer contains a conductive polymer, the conductive layer may or may not contain a resin other than the conductive polymer. Examples of the resin other than the conductive polymer include the thermosetting resin and the thermoplastic resin. The conductive layer may contain the conductive particles in addition to the conductive polymer.
Examples of the conductive polymer include a conductive composite containing a known π-conjugated conductive polymer and polyanion.
When there are a plurality of non-metal thin film layers constituting the shield layer 22, the thickness, constituent materials, physical properties, etc. of each non-metal layer may be the same as or different from each other.

(Conductive adhesive layer)
The conductive adhesive layer 24 contains an adhesive component 24a and conductive particles 24b.
The adhesive component 24a contains an adhesive resin. It may also contain a flame retardant. The adhesive component 24a may contain a cellulose resin, microfibrils (glass fiber, etc.) in order to increase the strength of the conductive adhesive layer 24 and improve the punching characteristics. The adhesive component 24a may contain other components, if necessary, as long as the effects of the present invention are not impaired.

As the adhesive resin, a thermosetting resin is used because it can exhibit heat resistance after curing.
The thermosetting resin may be in an uncured state or in a B-staged state. Examples of the thermosetting resin include epoxy resin, phenol resin, amino resin, alkyd resin, urethane resin, synthetic rubber, ultraviolet curable acrylate resin and the like. Epoxy resin is preferable because it has excellent heat resistance. The epoxy resin may contain a rubber component (carboxy-modified nitrile rubber, acrylic rubber, etc.) for imparting flexibility, a tackifier, and the like.
Examples of other components in the adhesive component 24a include a curing agent, a curing accelerator, a low stress agent (stress relaxation agent), and the like.

As the curing agent, an aromatic carboxylic acid having one or more hydroxy groups is preferable, and 4-hydroxybenzoic acid or gallic acid is more preferable, from the viewpoint of further improving the adhesiveness of the conductive adhesive layer 24.
The content of the curing agent in the adhesive component 24a is preferably 1 part by mass or more and 100 parts by mass or less, more preferably 5 parts by mass or more and 50 parts by mass or less, and 10 parts by mass or more and 30 parts by mass with respect to 100 parts by mass of the adhesive resin. More preferably, it is by mass or less. When the content of the curing agent is at least the lower limit of the above range, the conductive adhesive layer 24 has excellent curability and further excellent adhesiveness. When the content of the curing agent is not more than the upper limit of the above range, the curing rate of the conductive adhesive layer 24 becomes appropriate.

When the curing agent is an aromatic carboxylic acid having one or more hydroxy groups and the adhesive resin is an epoxy resin, the number of moles of active hydrogen groups of the curing agent with respect to 1 mol of epoxy groups is 0.5 mol or more and 1 It is preferably 5.5 mol or less. When the number of moles of active hydrogen groups in the curing agent is not less than the lower limit of the above range, the conductive adhesive layer 24 has excellent curability and further excellent adhesiveness. When the number of moles of active hydrogen groups in the curing agent is not more than the upper limit of the above range, the curing rate of the conductive adhesive layer 24 becomes appropriate. Here, the active hydrogen group of the curing agent is a hydroxyl group and a carboxy group.

Examples of the low stress agent include vinyl acetate resin and silicone compounds.
The content of the low stress agent in the adhesive component 24a is preferably 10% by mass or more and 80% by mass or less, and more preferably 30% by mass or more and 70% by mass or less, based on 100% by mass of the adhesive component 24a (solid content). .. When the content of the low stressing agent is within the above range, the flexibility of the conductive adhesive layer 24 is excellent.

In order to reduce the "minimum storage elastic modulus at 100 to 190 ° C." (hereinafter referred to as "minimum storage elastic modulus during hot pressing"), a resin having a low storage elastic modulus is used as the adhesive resin in the adhesive component 24a. You can use it. In order to prevent the "minimum storage elastic modulus at 100 to 190 ° C." from becoming too low, a filler such as resin fine particles or inorganic fine particles is added, or the product is cured at 100 to 190 ° C. and stored after curing. The type and amount of the thermosetting resin and the curing agent having a high elastic modulus may be selected.

The conductive particles 24b are in the form of flakes with both surfaces flattened. The flake-shaped conductive particles used in the present invention refer to leaf-shaped particles having a thickness of 1/10 or less of the volume average particle size.
The volume average particle diameter of the conductive particles 24b is preferably 1 μm to 100 μm, more preferably 3 μm to 80 μm, and further preferably 5 μm to 50 μm. The thickness of the conductive particles 24b is preferably in the range of 0.05 μm to 1 μm.
Further, it is preferable that the lengths of one conductive particle in the longitudinal direction of the flat portion and in the lateral direction of the flat portion are independently in the range of 1 μm to 100 μm.

Examples of the material constituting the conductive particles 24b include silver, platinum, gold, copper, nickel, palladium, and aluminum. Of these, silver is preferable because of its high conductivity.
Further, the particles may have a metal coat layer on the surface of the core particles containing the metal oxide.
The metal oxide is preferably one or more selected from the group consisting of alumina, silica, zirconia, and magnesia.
Examples of the metal contained in the metal coat layer include silver, platinum, gold, copper, nickel, palladium, and aluminum. Of these, silver is preferable because of its high conductivity.

The 10% compressive strength of the conductive particles 24b is preferably 30 MPa or more and 200 MPa or less, more preferably 50 MPa or more and 150 MPa or less, and further preferably 70 MPa or more and 100 MPa or less. When the 10% compressive strength of the conductive particles 24b is equal to or higher than the lower limit of the above range, the conductive adhesive layer 24 penetrates the insulating film without significantly losing the pressure applied to the shield layer 22 during hot pressing. It is securely electrically connected through the holes by the printed circuit of the printed wiring board. When the 10% compressive strength of the conductive particles 24b is equal to or less than the upper limit of the above range, the contact with the shield layer 22 is improved and the electrical connection is ensured.

The ratio of the conductive particles 24b to 100% by mass of the conductive adhesive layer 24 is preferably 1% by mass or more and 50% by mass or less, and more preferably 1% by mass or more and 40% by mass or less. It is more preferably mass% or more and 30 mass% or less.
When the content of the conductive particles 24b in the conductive adhesive layer 24 is not more than a preferable upper limit value, the conductive adhesive layer 24 has conductivity in the thickness direction and conductivity in the surface direction. It tends to be an anisotropic conductive adhesive layer. When the conductive adhesive layer 24 becomes an anisotropic conductive adhesive layer, the cost can be reduced while maintaining the conductivity as compared with the case where the conductive adhesive layer 24 becomes an isotropic adhesive layer.
When the content of the conductive particles 24b in the conductive adhesive layer 24 is at least a preferable lower limit value, the conductivity of the conductive adhesive layer 24 becomes good.

Storage modulus of the storage modulus at 100 to 190 ° C. of the conductive adhesive layer 24 (lowest storage modulus during hot pressing) is ^{1.0 × 10 3 ~1.0 × 10 5} Pa. The minimum storage elastic modulus during hot pressing ^{is preferably 1.0 × 10 3 to} 5.0 × 10 ⁴ Pa, and more preferably 1.0 × 10 ^{3 to} 1.0 × 10 ⁴ Pa.
When the minimum storage elastic modulus during hot pressing is not more than a preferable upper limit value, the conductive particles 24b are likely to be oriented along the surface direction of the substrate when the printed wiring board with an insulating film and the electromagnetic wave shielding film 1A are hot pressed. If the minimum storage elastic modulus during hot pressing is equal to or higher than the preferable lower limit value, the adhesive component 24a is less likely to elute from the conductive adhesive layer 24 when the printed wiring board with an insulating film and the electromagnetic wave shielding film 1A are hot pressed. ..

The surface resistance of the conductive adhesive layer 24 ^{is preferably 1 × 10 4} Ω / □ or more and 1 × 10 ¹⁶ Ω / □ or less, and more preferably 1 × 10 ⁶ Ω / □ or more and 1 × 10 ¹⁴ Ω / □ or less. When the surface resistance of the conductive adhesive layer 24 is at least the lower limit of the above range, the content of the conductive particles 24b can be suppressed low. If the surface resistance of the conductive adhesive layer 24 is not more than the upper limit of the above range, there is no problem in anisotropy in practical use.

The thickness of the conductive adhesive layer 24 is preferably 3 to 25 μm, more preferably 3 to 15 μm, and even more preferably 5 to 10 μm.
When the thickness of the conductive adhesive layer 24 is equal to or greater than the lower limit of the above range, the fluidity of the conductive adhesive layer 24 (following the shape of the through hole of the insulating film) can be ensured, and the insulating film penetrates. The inside of the hole can be sufficiently filled with the conductive adhesive. When the thickness of the conductive adhesive layer 24 is not more than the upper limit of the above range, the electromagnetic wave shielding film 1A can be thinned. In addition, the flexibility of the electromagnetic wave shielding film 1A is improved. Further, when the printed wiring board with the insulating film and the electromagnetic wave shielding film 1A are hot-pressed, the adhesive component 24a is less likely to be eluted from the conductive adhesive layer 24.

The ratio of the average thickness of the conductive particles 24b to the layer thickness of the conductive adhesive layer 24 is preferably 0.002 to 0.3, more preferably 0.01 to 0.3, and is 0. It is more preferably .04 to 0.2.
When the above ratio is not more than the preferable lower limit value, the conductive particles are oriented in the plane direction in the through holes of the insulating film in the circuit board, and the conductive particles are easily conducted in the thickness direction, so that the connection resistance is easily lowered.

(First release film)
The first release film 30 serves as a carrier film for the insulating resin layer 10 and the shield layer 22, and improves the handleability of the electromagnetic wave shield film 1A. The first release film 30 is peeled off from the insulating resin layer 10 after the electromagnetic wave shielding film 1A is attached to a printed wiring board or the like.

The first release film 30 has, for example, a release film main body 32 and an adhesive layer 34 provided on the surface of the release film main body 32 on the insulating resin layer 10 side.

As the resin material of the release film main body 32, polyethylene terephthalate (hereinafter, also referred to as “PET”), polyethylene naphthalate, polyethylene isophthalate, polybutylene terephthalate, polyolefin, polyacetate, polycarbonate, polyvinylidene sulfide, polyamide, ethylene- Examples thereof include vinyl acetate copolymers, polyvinyl chlorides, polyvinylidene chlorides, synthetic rubbers, and liquid crystal polymers. As the resin material, PET is preferable from the viewpoint of heat resistance (dimensional stability) and price when manufacturing the electromagnetic wave shielding film 1A.

The release film body 32 may contain one or both of a colorant (pigment, dye, etc.) and a filler.
Either one or both of the colorant and the filler is different from the insulating resin layer 10 in that it can be clearly distinguished from the insulating resin layer 10 and it is easy to notice the unpeeled residue of the first release film 30 after hot pressing. Colored ones are preferred, and white pigments, fillers, or combinations of white pigments with other pigments or fillers are more preferred.

The storage elastic modulus of the release film main body 32 at 180 ° C. ^{is preferably 8 × 10 7} Pa or more and 5 × 10 ⁹ Pa, and more preferably 1 × 10 ⁸ Pa or more and 8 × 10 ⁸ Pa. When the storage elastic modulus of the release film main body 32 at 180 ° C. is equal to or higher than the lower limit of the above range, the first release film 30 has an appropriate hardness, and the first release during hot pressing. The pressure loss in the mold film 30 can be reduced. When the storage elastic modulus of the release film main body 32 at 180 ° C. is equal to or less than the upper limit of the above range, the flexibility of the first release film 30 becomes good.

The thickness of the release film main body 32 is preferably 3 μm or more and 75 μm or less, and more preferably 12 μm or more and 50 μm or less. When the thickness of the release film main body 32 is at least the lower limit of the above range, the handleability of the electromagnetic wave shield film 1A is good. When the thickness of the release film main body 32 is equal to or less than the upper limit of the above range, heat is likely to be transferred to the conductive adhesive layer when the conductive adhesive layer of the electromagnetic wave shielding film 1A is hot-pressed on the surface of the insulating film. ..

The pressure-sensitive adhesive layer 34 is formed by applying, for example, a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive to the surface of the release film main body 32. Since the first release film 30 has the pressure-sensitive adhesive layer 34, when the second release film 40 is peeled off from the conductive adhesive layer, or the electromagnetic wave shield film 1A is attached to a printed wiring board or the like by hot pressing. At that time, the release of the first release film 30 from the insulating resin layer 10 is suppressed, and the first release film 30 can sufficiently serve as a protective film.

The pressure-sensitive adhesive is such that the first release film 30 can be peeled from the insulating resin layer 10 after the hot pressing without the first release film 30 being easily peeled from the insulating resin layer 10 before the hot pressing. It is preferable that the pressure-sensitive adhesive layer 34 is provided with an appropriate degree of adhesiveness.
Examples of the pressure-sensitive adhesive include an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, and a rubber-based pressure-sensitive adhesive. The glass transition temperature of the pressure-sensitive adhesive is preferably −100 ° C. or higher and 60 ° C. or lower, and more preferably −60 ° C. or higher and 40 ° C. or lower.

The thickness of the first release film 30 is preferably 25 μm or more and 125 μm or less, and more preferably 38 μm or more and 100 μm or less. When the thickness of the first release film 30 is at least the lower limit of the above range, the handleability of the electromagnetic wave shielding film 1A is good. When the thickness of the first release film 30 is equal to or less than the upper limit of the above range, heat is applied to the conductive adhesive layer when the conductive adhesive layer of the electromagnetic wave shielding film 1A is hot-pressed on the surface of the insulating film. Easy to convey.

(Second release film)
The second release film 40 protects the conductive adhesive layer and improves the handleability of the electromagnetic wave shielding film 1A. The second release film 40 is peeled off from the conductive adhesive layer before the electromagnetic wave shielding film 1A is attached to the printed wiring board or the like.

The second release film 40 has, for example, a release film main body 42 and a release agent layer 44 provided on the surface of the release film main body 42 on the conductive adhesive layer side.

Examples of the resin material of the release film main body 42 include the same resin materials as those of the release film main body 32.
The release film main body 42 may contain a colorant, a filler and the like.
The thickness of the release film body 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 is formed, for example, by treating the surface of the release film main body 42 with a release agent. 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, the second release film 40 can be easily peeled off and is conductive. The release adhesive layer is less likely to break.
As the release agent, a known release agent may be used.

The thickness of the release agent layer 44 is preferably 0.05 μm or more and 30 μm or less, and more preferably 0.1 μm or more and 20 μm or less. When the thickness of the release agent layer 44 is within the above range, the second release film 40 can be more easily peeled off.

<Other Embodiments of Electromagnetic Wave Shield Film>
For example, if the insulating resin layer 10 has sufficient flexibility and strength, the first release film 30 may be omitted.
When the adhesive force on the surface of the conductive adhesive layer 24 is small, the second release film 40 may be omitted.
The first release film 30 does not have to have the pressure-sensitive adhesive layer 34 when the release film main body 32 is a self-adhesive film.
The first release film 30 may have a release agent layer instead of the pressure-sensitive adhesive layer 34.
The second release film 40 does not have to have the release agent layer 44 when the release film main body 42 alone has sufficient releasability.

<Manufacturing method of electromagnetic wave shield film>
The electromagnetic wave shield film in the present invention has, for example, a first laminate having a first release film, an insulating resin layer and a shield layer in this order, and a second release film and a second release film having a conductive adhesive layer in order. It can be manufactured by stacking and crimping the laminated body of the above so that the shield layer and the conductive adhesive layer are in contact with each other.

Specifically, the following method (A1) or method (A2) can be mentioned.
However, the method for producing the electromagnetic wave shielding film in the present invention is not limited to the method (A1) or the method (A2).

The method (A1) is a method having the following steps (A1-1) to (A1-4).
Step (A1-1): A step of preparing a metal thin film with a carrier film provided with a shield layer 22 on the surface of the carrier film.
Step (A1-2): The insulating resin layer 10 is formed on the surface of the shield layer 22 of the metal thin film with a carrier film, the first release film 30 is attached to the surface of the insulating resin layer 10, and the carrier film is peeled off. The process of obtaining the first laminate.
Step (A1-3): A step of forming a conductive adhesive layer 24 on one side of the second release film 40 to obtain a second laminate.
Step (A1-4): The first laminated body and the second laminated body are bonded so that the shield layer 22 of the first laminated body and the conductive adhesive layer 24 of the second laminated body are in contact with each other. Process.
Hereinafter, each step of the method (A-1) will be described in detail.

The metal thin film with a carrier film in the step (A1-1) may be produced by forming a shield layer 22 on the surface of the carrier film, or a commercially available metal thin film with a carrier film may be obtained.
Examples of the carrier film include those in which a release agent layer is formed on the surface of a carrier film (PET film or the like).
As a method of forming the shield layer 22 in the step (A1-1), when the shield layer 22 is composed of one metal thin film layer, a method of forming a vapor deposition film by physical vapor deposition, CVD (chemical vapor deposition), or plating. Examples thereof include a method of forming a plating film and a method of attaching a metal foil. From the viewpoint that the shield layer 22 having excellent conductivity in the plane direction can be formed, a method of forming a vapor-deposited film by physical vapor deposition or CVD, or a method of forming a plating film by plating is preferable. Physical vapor deposition and CVD can be performed because the thickness of the shield layer 22 can be reduced, the shield layer 22 having excellent surface conductivity can be formed even if the thickness is thin, and the shield layer 22 can be easily formed by a dry process. A method of forming a thin-film deposition film by physical vapor deposition is more preferable, and a method of forming a thin-film deposition film by physical vapor deposition is further preferable.

Examples of the method for forming the insulating resin layer 10 in the step (A1-2) include the following methods.
A method in which a paint containing a photocurable resin and a photoradical polymerization initiator is applied to the surface of a shield layer 22 of a metal thin film with a carrier film to be semi-cured or cured.
A method of semi-curing or curing a paint containing a thermosetting resin and a curing agent on the surface of a shield layer 22 of a metal thin film with a carrier film.
A method in which a paint containing a thermoplastic resin is applied to the surface of a shield layer 22 of a metal thin film with a carrier film and dried.
A method of directly laminating a film formed by extrusion molding a composition containing a thermoplastic resin on the surface of a shield layer 22 of a metal thin film with a carrier film.
Among these methods, from the viewpoint of heat resistance during soldering or the like, a paint containing a photocurable resin and a photoradical polymerization initiator is applied to the surface of the shield layer 22 of the metal thin film with a carrier film. A method of semi-curing or curing, or a method of applying a coating material containing a thermosetting resin and a curing agent to the surface of the shield layer 22 of the metal thin film with a carrier film and semi-curing or curing is preferable.

Examples of the paint application method include die coater, gravure coater, roll coater, curtain flow coater, spin coater, bar coater, reverse coater, kiss coater, fountain coater, rod coater, air doctor coater, knife coater, blade coater, and cast. A method using various coaters such as a coater and a screen coater can be applied.
When the photocurable resin is semi-cured or cured, it may be irradiated with light (ultraviolet rays or the like).
When the thermosetting resin is semi-cured or cured, it may be heated using a heater such as a heater or an infrared lamp.

In the step (A1-3), the conductive adhesive paint is applied to the surface of the second release film 40 provided with the release agent layer 44.
The conductive adhesive coating material contains an adhesive component 24a, conductive particles 24b, and a solvent.
Solvents contained in conductive adhesive paints include esters (butyl acetate, ethyl acetate, methyl acetate, isopropyl acetate, ethylene glycol monoacetate, etc.) and ketones (methyl ethyl ketone, methyl isobutyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, etc.). , Alcohol (methanol, ethanol, isopropanol, butanol, propylene glycol monomethyl ether, propylene glycol, etc.) and the like.

Examples of the method of applying the conductive adhesive paint include a die coater, a gravure coater, a roll coater, a curtain flow coater, a spin coater, a bar coater, a reverse coater, a kiss coater, a fountain coater, a rod coater, an air doctor coater, and a knife coater. A method using various coaters such as a blade coater, a cast coater, and a screen coater can be applied.
The conductive adhesive layer 24 is formed by volatilizing the solvent from the applied conductive adhesive paint.

In the bonding of the first laminated body and the second laminated body in the step (A1-4), crimping is performed in order to improve the adhesion between the first laminated body and the second laminated body.
The pressure at the time of crimping is preferably 0.1 kPa or more and 100 kPa or less, more preferably 0.1 kPa or more and 20 kPa or less, and further preferably 1 kPa or more and 10 kPa or less.
The temperature at the time of crimping (temperature of the hot plate) is preferably 50 ° C. or higher and 100 ° C. or lower.

The method (A2) is a method having the following steps (A2-1) to (A2-4).
Step (A2-1): A step of forming the insulating resin layer 10 on one side of the first release film 30.
Step (A2-2): A step of forming a shield layer 22 on the surface of the insulating resin layer 10 opposite to the first release film 30 to obtain a first laminate.
Step (A2-3): A step of forming a conductive adhesive layer 24 on one side of the second release film 40 to obtain a second laminate.
Step (A2-4): The first laminated body and the second laminated body are bonded so that the shield layer 22 of the first laminated body and the conductive adhesive layer 24 of the second laminated body are in contact with each other. Process.

In the step (A2-1), the insulating resin layer 10 is formed on the surface of the first release film 30 on the pressure-sensitive adhesive layer 34 side. The coating and coating method is the same as the step (A1-2) in the method (A1).
In the step (A2-2), the shield layer 22 is formed on the surface of the insulating resin layer 10 opposite to the first release film 30. The method for forming the shield layer 22 is the same as the step (A1-1) in the method (A1).
The step (A2-3) and the step (A2-4) are the same as the step (A1-3) and the step (A1-4) in the method (A1).

<Circuit board>
The circuit board in the present invention includes a circuit board main body in which a circuit including a ground wiring or a ground layer is provided on at least one surface of the substrate, and a portion adjacent to the one surface and overlapping the ground wiring or the ground layer. An insulating film having through holes formed therein and an electromagnetic wave shielding film of the present invention adjacent to the side of the insulating film opposite to the circuit board main body are provided.
The conductive adhesive layer in the electromagnetic wave shielding film adheres to the insulating film and penetrates into the through hole to be in contact with the ground wiring or the ground layer.

In the circuit board of the present invention, the conductive adhesive of the electromagnetic wave shielding film contains flake-shaped particles and has a low minimum storage elastic coefficient at the time of hot pressing. In this case, the conductive particles 24b are likely to be oriented along the surface direction of the substrate. Therefore, the contact area between the shield layer 22 and the conductive particles 24b, the conductive particles 24b overlapping in the thickness direction of the conductive adhesive layer 24, and the conductive particles 24b and the ground wiring 54a becomes large. Further, the heat press makes it easy to bring the shield layer 22 closer to the ground wiring 54a. For example, the distance between the shield layer 22 and the ground wiring 54a can be reduced to about the thickness of the conductive particles 24b.

Therefore, the shield layer and the ground wiring or the ground layer in the circuit board main body can be made conductive with a small connection resistance. Therefore, a high shielding effect can be obtained.
Further, since the side of the oriented conductive particles 24b in contact with the shield layer 22 is flat, inconveniences such as the conductive particles 24b breaking through the shield layer 22 are unlikely to occur even if the pressure of a hot press is applied.

FIG. 2 is a cross-sectional view showing an embodiment of the circuit board of this embodiment.
The circuit board 2 is a first release film 30 and a second release film 40 from the flexible printed wiring board 50 which is an example of the substrate body, the insulating film 60, and the electromagnetic wave shielding film 1A of the first embodiment. It is provided with an electromagnetic wave shielding film 1D from which the and is peeled off.
The flexible printed wiring board 50 is provided with a printed circuit 54 on at least one side of a base film 52, which is an example of a substrate. The print circuit 54 includes a ground wiring 54a and a signal circuit.

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 conductive adhesive layer 24 of the electromagnetic wave shielding film 1D is adhered to and cured on the surface of the insulating film 60. Further, the conductive adhesive layer 24 is electrically connected to the ground wiring 54a of the print circuit 54 through the through hole 62 formed in the insulating film 60.

In the vicinity of the printed circuit 54 excluding the portion having the through hole 62, the shield layer 22 of the electromagnetic wave shield film 1D is arranged so as to face each other with the insulating film 60 and the conductive adhesive layer 24 interposed therebetween.
The separation distance between the printed circuit 54 and the shield layer 22 excluding the portion having the through hole 62 is substantially equal to the sum of the thickness of the insulating film 60 and the thickness of the conductive adhesive layer 24. The separation distance is preferably 30 μm or more and 200 μm or less, and more preferably 60 μm or more and 200 μm or less. If the separation distance is smaller than 30 μm, the impedance of the signal circuit becomes low. Therefore, in order to have a characteristic impedance such as 100Ω, the line width of the signal circuit must be reduced, and the variation in the line width is the variation in the characteristic impedance. Therefore, the reflected resonance noise due to the impedance mismatch can easily get on the electric signal. If the separation distance is larger than 200 μm, the circuit board 2 becomes thick and the flexibility becomes insufficient.

(Flexible printed wiring board)
The flexible printed wiring board 50 is a printed circuit 54 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 or both sides of the base film 52 via an adhesive layer (not shown); a resin solution or the like forming the base film 52 is cast on the surface of the copper foil. Things etc. can be mentioned.
Examples of the material of the adhesive layer include epoxy resin, polyester, polyimide, polyamide-imide, polyamide, phenol resin, urethane 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.

As the base film 52, a film having heat resistance is preferable, a polyimide film, a polyetherimide film, a polyphenylene sulfide film, and a liquid crystal polymer film are more preferable, and a polyimide film is further preferable.
The surface resistance of the base film 52 ^{is preferably 1 × 10 6} Ω / □ or more from the viewpoint of electrical insulation. The surface resistance of the base film 52 ^{is preferably 1 × 10 19} Ω / □ or less from a practical point of view.
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 50 μm or less, and more preferably 10 μm or more and 25 μm or less from the viewpoint of flexibility.

Examples of the copper foil constituting the printed circuit 54 include rolled copper foil and electrolytic copper foil, and rolled copper foil is preferable from the viewpoint of flexibility. The print circuit 54 is used as a signal circuit, a ground circuit, a ground layer, and the like.
The thickness of the copper foil is preferably 1 μm or more and 50 μm or less, and more preferably 18 μm or more and 35 μm or less.
The end portion (terminal) of the print circuit 54 in the length direction is not covered with the insulating film 60 or the electromagnetic wave shielding film 1D and is exposed because of solder connection, connector connection, component mounting, and the like.

(Insulation film)
The insulating film 60 (coverlay film) is formed by forming an adhesive layer (not shown) on one side of an insulating film main body (not shown) by applying an adhesive, attaching an adhesive sheet, or the like.
The surface resistance of the insulating film body ^{is preferably 1 × 10 6} Ω / □ or more from the viewpoint of electrical insulation. The surface resistance of the insulating film body ^{is preferably 1 × 10 19} Ω / □ or less from a practical point of view.
As the insulating film main body, a film having heat resistance is preferable, a polyimide film, a polyetherimide film, a polyphenylene sulfide film, and a liquid crystal polymer film are more preferable, and a polyimide film is further preferable.
The thickness of the insulating film 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, polyamide-imide, polyamide, phenol resin, urethane resin, acrylic resin, melamine resin, polystyrene, polyolefin and the like. The epoxy resin may contain a rubber component (carboxy-modified nitrile rubber, etc.) 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 62 formed in the insulating film 60 is not particularly limited. Examples of the shape of the opening of the through hole 62 include a circle, an ellipse, and a quadrangle. The through hole 62 is formed in a portion overlapping the ground wiring 54a or the ground layer.

(Other embodiments)
The circuit board in the present invention is not limited to the embodiment shown in the illustrated example.
For example, the flexible printed wiring board 50 may have a ground layer on the back side, and the ground layer may be connected to the ground wiring 54a on the front side by a via hole. Further, the flexible printed wiring board 50 may have printed circuits 54 on both sides, and an insulating film 60 and an electromagnetic wave shielding film 1D may be attached to both sides.
Instead of the flexible printed wiring board 50, an inflexible rigid printed circuit board may be used.

<Manufacturing method of circuit board>
In the method for manufacturing a circuit board of the present invention, a through hole is provided in a portion of a circuit board body in which a circuit including a ground wiring or a ground layer is provided on at least one surface of the board, in a portion overlapping the ground wiring or the ground layer. The insulating film on which the above-mentioned material is formed is laminated, and then the electromagnetic wave shielding film of the present invention is laminated so that the conductive adhesive layer is in contact with the insulating film and the conductive adhesive layer, and then heat-pressed to manufacture a circuit board. The method.

The circuit board 2 can be manufactured, for example, by a method having the following steps (a) to (d) (see FIG. 4).
Step (a): An insulating film 60 having a through hole 62 formed at a position corresponding to the ground wiring 54a is provided on the surface of the flexible printed wiring board 50 on the side where the printed circuit 54 is provided, and the printed wiring with the insulating film is provided. The process of obtaining the plate 3.
Step (b): After the step (a), the printed wiring board 3 with an insulating film and the electromagnetic wave shielding film 1C obtained by peeling the second release film 40 from the electromagnetic wave shielding film 1A are separated from each other by the insulating film 60. A step of stacking the conductive adhesive layer 24 so as to be in contact with the surface of the film and heat-pressing them.
Step (c): A step of peeling the first release film 30 from the electromagnetic wave shielding film 1C when the first release film 30 is no longer needed after the step (b).
Step (d): A step of main curing the conductive adhesive layer 24 between the steps (a) and the step (b), or after the step (c), if necessary.
Hereinafter, each step will be described in detail with reference to FIG.

Step (a):
The step (a) is a step of laminating the insulating film 60 on the flexible printed wiring board 50 to obtain the printed wiring board 3 with the insulating film.
Specifically, first, an insulating film 60 having a through hole 62 formed at a position corresponding to the printed circuit 54 is superposed on the flexible printed wiring board 50. The through hole 62 may be formed after the flexible printed wiring board 50 and the insulating film 60 on which the through hole 62 is not formed are overlapped with each other.
Next, 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 printed wiring board 3 with the 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 mainly cured in the step (d).
The adhesive layer is adhered and cured by, for example, hot pressing with a press machine (not shown) or the like.

Step (b):
The step (b) is a step of hot-pressing the electromagnetic wave shield film 1C obtained by peeling the second release film 40 from the electromagnetic wave shield film 1A onto the printed wiring plate 3 with an insulating film.
Specifically, the electromagnetic wave shield film 1C from which the second release film 40 has been peeled off is placed on the printed wiring board 3 with an insulating film and heat-pressed. As a result, the conductive adhesive layer 24 is adhered to the surface of the insulating film 60, and the conductive adhesive layer 24 is pushed into the through hole 62 to fill the through hole 62 and form the ground wiring 54a of the print circuit 54. Connect electrically.

In this heat-pressing step, the conductive adhesive layer 24 is softened to the minimum storage elastic modulus at the time of heat-pressing before curing. At this time, in the softened conductive adhesive layer 24, the conductive particles 24b are oriented along the surface direction of the substrate.
Further, since the minimum storage elastic modulus at the time of hot pressing is low, the thickness of the conductive adhesive layer 24 in the through hole 62 becomes sufficiently thin.

Adhesion and curing of the conductive adhesive layer 24 is performed, for example, by hot pressing with a press machine (not shown) or the like.
The heat pressing time is preferably 20 seconds or more and 60 minutes or less, and more preferably 30 seconds or more and 30 minutes or less. When the heat pressing time is equal to or greater than the lower limit of the above range, the conductive adhesive layer 24 can be easily adhered to the surface of the insulating film 60. When the heat pressing time is equal to or less than the upper limit of the above range, the manufacturing time of the circuit board 2 can be shortened.

The temperature of the hot press is preferably 140 ° C. or higher and 190 ° C. or lower, and more preferably 150 ° C. or higher and 175 ° C. or lower. When the temperature of the hot press is equal to or higher than the lower limit of the above range, the conductive adhesive layer 24 can be easily adhered to the surface of the insulating film 60. Moreover, the time of hot pressing can be shortened. When the temperature of the hot press is not more than the upper limit of the above range, deterioration of the electromagnetic wave shielding film 1C, the flexible printed wiring board 50, and the like can be easily suppressed.

The pressure of the hot press is 0.5 MPa or more and 20 MPa or less, preferably 1 MPa or more and 16 MPa or less. When the pressure of the hot press is equal to or higher than the lower limit of the above range, the conductive adhesive layer 24 is adhered to the surface of the insulating film 60. Moreover, the time of hot pressing can be shortened. When the pressure of the hot press is not more than the upper limit of the above range, damage to the electromagnetic wave shielding film 1C, the flexible printed wiring board 50, etc. can be suppressed. Further, when the printed wiring board 3 with the insulating film and the electromagnetic wave shielding film 1C are hot-pressed, the adhesive component is less likely to be eluted from the conductive adhesive layer.

Step (c):
The step (c) is a step of peeling the first release film 30 from the electromagnetic wave shielding film 1C.
Specifically, when the carrier film is no longer needed, the first release film 30 is peeled off from the insulating resin layer 10, and the electromagnetic wave shield film 1D is laminated on the flexible printed wiring board 50. Get the configuration.

Step (d):
The step (d) is a step of main curing the conductive adhesive layer 24.
When the heat pressing time in the step (b) is as short as 20 seconds or more and 10 minutes or less, the conductive adhesive layer 24 is formed between the steps (b) and the step (c) or after the step (c). It is preferable to perform the main curing.
The main curing of the conductive adhesive layer 24 is performed using, for example, a heating device such as an oven.
The heating time is 15 minutes or more and 120 minutes or less, more preferably 30 minutes or more and 60 minutes or less.
When the heating time is equal to or greater than the lower limit of the above range, the conductive adhesive layer 24 can be sufficiently cured. When the heating time is equal to or less than the upper limit of the above range, the manufacturing time of the circuit board 2 can be shortened.
The heating temperature (atmospheric temperature in the oven) is preferably 120 ° C. or higher and 180 ° C. or lower, and more preferably 120 ° C. or higher and 150 ° C. or lower. When the heating temperature is equal to or higher than the lower limit of the above range, the heating time can be shortened. When the heating temperature is not more than the upper limit of the above range, deterioration of the electromagnetic wave shielding film 1D, the flexible printed wiring board 50, and the like can be suppressed.

FIG. 4 is a diagram showing a circuit board 2X when the minimum storage elastic modulus at the time of hot pressing is too high. In FIG. 4, the same components as those in FIG. 2 are designated by the same reference numerals as those in FIG.
The conductive adhesive layer 27 in the electromagnetic wave shielding film 1X of the circuit board 2X contains an adhesive component 27a and conductive particles 27b.
The conductive particles 27b are flake-shaped conductive particles similar to the conductive particles 24b. From storage modulus during hot pressing of the conductive adhesive layer 27 is beyond the 1.0 × ¹⁰ 5 Pa.

In this case, when the printed wiring board with the insulating film and the electromagnetic wave shielding film are hot-pressed, the conductive particles 27b are difficult to be oriented along the surface direction of the substrate, and as shown in FIG. 4, the adhesive remains in a random direction. It is fixed in the component 27a.
As a result, the contact area between the shield layer 22 and the conductive particles 27b, the conductive particles 27b in the thickness direction of the conductive adhesive layer 24, and the conductive particles 27b and the ground wiring 54a becomes insufficient. Therefore, it is not possible to conduct the shield layer and the ground wiring or the ground layer in the circuit board main body with a small connection resistance. Therefore, a high shielding effect cannot be obtained.

FIG. 5 is a diagram showing a circuit board 2Y when the minimum storage elastic modulus at the time of hot pressing is low as in the embodiment of FIG. 2, but the conductive particles are spherical. In FIG. 5, the same components as those in FIG. 2 are designated by the same reference numerals as those in FIG.
The conductive adhesive layer 28 in the electromagnetic wave shielding film 1Y of the circuit board 2Y contains an adhesive component 28a and conductive particles 28b.
Unlike the conductive particles 24b, the conductive particles 27b are spherical. The minimum storage elastic modulus of the conductive adhesive layer 27 during hot pressing is 1.0 × 10 ^{3 to} 1.0 × 10 ⁵ Pa.

In this case, even if the printed wiring board with the insulating film and the electromagnetic wave shield film are hot-pressed, the contact areas between the shield layer 22 and the conductive particles 28b, and the conductive particles 28b and the ground wiring 54a are insufficient.
Further, since the minimum storage elastic modulus at the time of hot pressing is low, the distance between the shield layer 22 and the ground wiring 54a can be easily brought close by the hot pressing, but if the distance is too close, it exists between the shield layer 22 and the ground wiring 54a. It is considered that the conductive particles 28b are pushed out in the lateral direction, and the connection via the conductive particles 28b cannot be performed. Further, if it is not extruded in the lateral direction, another problem may occur such that the conductive particles 28b break through the shield layer 22.
Therefore, it is not possible to conduct the shield layer and the ground wiring or the ground layer in the circuit board main body with a small connection resistance. Therefore, a high shielding effect cannot be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Measurement of connection resistance)
The connection resistance between the shield layer and the ground wiring in the circuit board obtained in each example was measured using a digital multimeter manufactured by Hioki Electric Co., Ltd.

(raw materials)
The conductive particles, the metal thin film with a carrier film, the first release film, and the second release film used in each example are as follows.
The average length in the longitudinal direction, the average length in the lateral direction, the average thickness in the lateral direction, and the ratios thereof of each conductive particle are shown in Table 1 together with the results of Examples and Comparative Examples using each conductive particle. ..

Conductive particle A: Copper, flaky, volume average particle diameter 8.7 μm, thickness 0.2 μm.
Conductive particles B: silver-coated alumina, flaky, volume average particle diameter 12.4 μm, thickness 0.6 μm.
Conductive particles C: copper, flakes, volume average particle diameter 45 μm, thickness 0.5 μm.
Conductive particle D: copper, spherical, volume average particle diameter 6 μm.

Metal thin film with carrier film: Copper foil with release layer (manufactured by Toray KP Film Co., Ltd., Capy Seduce (registered trademark), copper foil thickness: 0.5 μm, copper foil surface resistance: 0.015 Ω / □, PET film Thickness: 50 μm).
First release film: adhesive film (manufactured by Panac, Panaprotect (registered trademark) GN, adhesive strength: 0.49 N / cm, PET film thickness: 75 μm).
Second release film: Release film (manufactured by Panac, Panapeel (registered trademark) SM-1, PET film thickness: 50 μm).

(Example 1)
A coating liquid for forming an insulating resin layer was applied to the surface of the metal thin film layer of the metal thin film with a carrier film using a # 4 bar coater. After the coating film is dried at 100 ° C. for 1 minute, the surface of the metal thin film layer is irradiated with ultraviolet rays of 400 mJ to form an insulating resin layer (thickness: 10 μm, surface resistance: 1.0 × 10 ¹² Ω / □ or more). Provided.
The first release film was attached to the surface of the insulating resin layer so that the insulating resin layer and the pressure-sensitive adhesive layer were in contact with each other. The carrier film was peeled off from the metal thin film layer to obtain a first laminate.

As a conductive adhesive paint, 56 parts by mass of a thermosetting adhesive (epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., jER1007), 24 parts by mass of an epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., jER1256) and an epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd.) , JER152) and 3 parts by mass of a curing agent (2E4MZ manufactured by Shikoku Kasei Co., Ltd.) are mixed to form a latent curable epoxy resin. A product dissolved or dispersed in 200 parts by mass was prepared.

A conductive adhesive coating was applied to the surface of the second release film on the release agent layer side to a thickness of 25 μm using a comma coater. The coating film was dried at 100 ° C. for 1 minute to provide a conductive adhesive layer (thickness: 10 μm, surface resistance: 1.0 × 10 ¹² Ω / □ or more) to obtain a second laminate.
The first laminate and the second laminate were laminated so that the metal thin film layer and the conductive adhesive layer were in contact with each other, and pressure-bonded under the conditions of temperature: 95 ° C. and pressure: 5 kPa to obtain an electromagnetic wave shielding film. ..

An insulating adhesive composition is applied to the surface of a polyimide film (insulating film body) having a thickness of 25 μm so that the dry film thickness becomes 25 μm to form an adhesive layer, and an insulating film (thickness: 50 μm) is applied. Obtained. A through hole (hole diameter: 150 μm) was formed at a position corresponding to the ground of the printed circuit.
A flexible printed wiring board in which a printed circuit was formed on the surface of a polyimide film (base film) having a thickness of 12 μm was prepared.
An insulating film was attached to the flexible printed wiring board by a hot press to obtain a flexible printed wiring board with an insulating film.

An electromagnetic wave shield film from which the second release film was peeled off was placed on a flexible printed wiring board with an insulating film, and a hot press device (G-12 manufactured by Orihara Seisakusho Co., Ltd.) was used to heat the hot plate temperature: 170 ° C. and load: 5 MPa. The conductive adhesive layer was adhered to the surface of the insulating film by hot pressing for 1 minute.
After peeling the first release film from the insulating resin layer, it was heated at 150 ° C. for 1 hour to obtain a circuit board.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Example 2)
A circuit board was obtained in the same manner as in Example 1 except that the blending amount of the conductive particles was changed as shown in Table 1.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Example 3)
A circuit board was obtained in the same manner as in Example 1 except that the conductive particles B were blended in the blending amounts shown in Table 1 instead of the conductive particles A.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Example 4)
A circuit board was obtained in the same manner as in Example 1 except that the conductive particles C were blended in the blending amounts shown in Table 1 instead of the conductive particles A.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Example 5)
A circuit board was obtained in the same manner as in Example 1 except that the conductive particles C were blended in the blending amounts shown in Table 1 instead of the conductive particles A.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Example 6)
1 part by mass of the curing agent (2E4MZ manufactured by Shikoku Kasei Co., Ltd.) is used instead of 3 parts by mass of the curing agent (2P4MZ manufactured by Shikoku Kasei Co., Ltd.), and conductive particles B are used instead of the conductive particles A as shown in Table 1. A circuit board was obtained in the same manner as in Example 1 except that the amounts were mixed.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Example 7)
In place of 3 parts by mass of the curing agent (manufactured by Shikoku Kasei Co., Ltd., 2P4MZ), 0.3 parts by mass of the curing agent (manufactured by Shikoku Kasei Co., Ltd., 2MZ-H) is shown. A circuit board was obtained in the same manner as in Example 1 except that the mixture was blended in the blending amount shown in 1.
Table 1 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 1 shows the measurement results of the connection resistance of the obtained circuit board.

(Comparative Example 1)
Table 2 shows 1 part by mass of the curing agent (2MZ-H manufactured by Shikoku Kasei Co., Ltd.) instead of 3 parts by mass of the curing agent (2P4MZ manufactured by Shikoku Kasei Co., Ltd.) and conductive particles B instead of the conductive particles A. A circuit board was obtained in the same manner as in Example 1 except that the amounts were blended as shown.
Table 2 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 2 shows the measurement results of the connection resistance of the obtained circuit board.

(Comparative Example 2)
A circuit board was obtained in the same manner as in Example 1 except that the conductive particles D were blended in the blending amounts shown in Table 2 instead of the conductive particles A.
Table 2 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 2 shows the measurement results of the connection resistance of the obtained circuit board.

(Comparative Example 3)
A circuit board was obtained in the same manner as in Example 1 except that the conductive particles D were blended in the blending amounts shown in Table 2 instead of the conductive particles A.
Table 2 shows the layer thickness of the conductive adhesive layer of the obtained circuit board and the ratio of this layer thickness to the average thickness of the conductive particles. Table 2 shows the measurement results of the connection resistance of the obtained circuit board.

(Comparative Example 4)
An attempt was made to obtain a circuit board in the same manner as in Example 1 except that the curing agent was not blended and the conductive particles B were blended in place of the conductive particles A in the blending amounts shown in Table 2.
However, the adhesive layer was eluted during the hot pressing and could not be adhered. Therefore, the layer thickness of the conductive adhesive layer of the circuit board and the connection resistance could not be measured.

As shown in Table 1, in the circuit board of the example, the connection resistance between the shield layer and the ground wiring was small.
On the other hand, as shown in Comparative Example 1 of Table 2, when the storage elastic modulus at the time of hot pressing was too high, the connection resistance between the shield layer and the ground wiring was large. Further, as shown in Comparative Examples 2 and 3, even if the storage elastic modulus at the time of hot pressing was appropriate, when the conductive particles were spherical, the connection resistance was large.
Further, as shown in Comparative Example 4, it was found that if the storage elastic modulus during hot pressing is too low, the adhesive layer elutes during hot pressing, making adhesion difficult.

1A electromagnetic wave shield film,
1C electromagnetic wave shield film,
1D electromagnetic wave shield film,
2 circuit board,
3 Printed wiring board with insulating film,
10 Insulating resin layer,
22 Shield layer,
24 Conductive adhesive layer,
24a Adhesive component,
24b conductive particles,
30 First release film,
32 Release film body,
34 Adhesive layer,
40 Second release film,
42 Release film body,
44 Release agent layer,
50 Flexible printed wiring board,
52 base film,
54 printed circuit,
54a ground wiring,
60 Insulation film,
62 Through hole.

Claims (6)

The insulating resin layer, the shield layer adjacent to the insulating resin layer and at least the outermost layer on the side opposite to the insulating resin layer is a metal thin film layer, and the shield layer provided on the side opposite to the insulating resin layer. With a conductive adhesive layer
The conductive adhesive layer comprises a flaky conductive particles, the lowest value of the storage elastic modulus at 100 to 190 ° C. is ^{1.0 × 10 3 ~1.0 × 10 5} Pa, an electromagnetic wave shielding film. The electromagnetic wave shielding film according to claim 1, wherein the conductive particles have a volume average particle diameter of 1 to 100 μm. The electromagnetic wave shielding film according to claim 1 or 2, wherein the ratio of the conductive particles to 100% by mass of the conductive adhesive layer is 1% by mass or more and 50% by mass or less. The electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the ratio of the average thickness of the conductive particles to the layer thickness of the conductive adhesive layer is 0.002 to 0.3. A circuit board body in which a circuit including a ground wiring or a ground layer is provided on at least one surface of the board.
An insulating film having a through hole formed in a portion adjacent to the one surface and overlapping the ground wiring or the ground layer.
The electromagnetic wave shielding film according to any one of claims 1 to 4, which is adjacent to the side of the insulating film opposite to the circuit board main body, is provided.
A circuit board in which the conductive adhesive layer in the electromagnetic wave shielding film adheres to the insulating film and penetrates into the through hole to be in contact with the ground wiring or the ground layer. An insulating film having a through hole formed in a portion overlapping the ground wiring or the ground layer is superposed on the circuit board main body provided with the ground wiring or a circuit including the ground layer on at least one surface of the board, and then , A circuit board in which the electromagnetic wave shielding film according to any one of claims 1 to 4 is laminated so that the conductive adhesive layer is in contact with the insulating film and the conductive adhesive layer, and then heat-pressed. Method.

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