JP7620644B2 - Electromagnetic wave shielding film and shielded printed wiring board - Google Patents

Description

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

Mobile devices such as smartphones and tablet terminals use shielded flexible printed wiring boards (hereinafter also referred to as "shielded printed wiring boards") with an electromagnetic wave shielding film attached to them to block electromagnetic waves generated from inside or entering from the outside. The shielding layer used in the electromagnetic wave shielding film is made of a thin metal layer formed by deposition, sputtering, plating, etc., or a conductive paste with a high loading of conductive filler. As 5G and other technologies become more widespread in the future, high frequencies and high speed transmission will progress in order to communicate large volumes of data, and noise countermeasures for electronic devices will become even more necessary.

As such an electromagnetic shielding film, Patent Document 1 discloses an electromagnetic shielding material (electromagnetic shielding film) in which a shielding layer having a thickness of 1 to 8 μm and consisting of one selected from the group consisting of Ni, Fe, Co, Ti, Zn, Cr, Sn, Cu, and alloys containing at least one of these metals is formed in one or more layers on the surface of a polymer film by either a sputtering method, a vapor deposition method, or a plating method, and between the surface of the polymer film and the shielding layer, a base layer having a thickness of 1 μm or less and consisting of one selected from the group consisting of Ni, Co, Zn, Fe, Cu, Ti, Cr, oxides and nitrides of these metals, and alloys containing at least one of these metals is formed in one or more layers by either a sputtering method or a vapor deposition method.

Furthermore, Patent Document 2 discloses an electromagnetic wave shielding film (electromagnetic wave shielding film) that is applied to molded products made from either ABS resin, PC, or ABS/PC polymer alloy, and is characterized in that it comprises a first layer of Cu and a second layer of Sn-Cr coating.

JP 2004-128158 A Patent No. 3826756

In the case of the electromagnetic wave shielding film mentioned above, multiple metal layers are laminated in a state of contact with each other, so there was a problem that the adhesion between the shielding layers was insufficient and cracks were likely to occur when repeatedly bent.

The present invention has been made to solve the above problems, and the object of the present invention is to provide an electromagnetic wave shielding film having high adhesion strength of the shielding layer and excellent bending resistance.

In other words, the electromagnetic wave shielding film of the present invention is characterized in that an isotropic conductive adhesive layer, an insulating layer, and a metal layer are laminated in that order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm.

In the electromagnetic wave shielding film of the present invention, both the isotropically conductive adhesive layer and the metal layer have the effect of shielding electromagnetic waves.
In the electromagnetic wave shielding film of the present invention, an insulating layer is formed between the isotropic conductive adhesive layer and the metal layer. Therefore, the metal layer is not easily peeled off. Furthermore, even if the electromagnetic wave shielding film of the present invention is repeatedly folded, cracks are not easily generated in the metal layer.

In the electromagnetic wave shielding film of the present invention, the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm.
When the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm, the metal layer is less likely to peel off, and cracks are less likely to occur in the metal layer even if the electromagnetic wave shielding film is repeatedly folded.

In the electromagnetic wave shielding film of the present invention, the metal layer preferably has a thickness of 0.1 to 8 μm.
If the thickness of the metal layer is less than 0.1 μm, the strength of the metal layer is weakened and the metal layer becomes susceptible to breakage.
If the thickness of the metal layer exceeds 8 μm, the flexibility of the metal layer decreases, and therefore the metal layer is more likely to crack when repeatedly bent.

In the electromagnetic wave shielding film of the present invention, the insulating layer preferably has a thickness of 0.5 to 10 μm.
If the thickness of the insulating layer is less than 0.5 μm, the amount of the insulating layer is so small that the metal layer is easily peeled off.
If the thickness of the insulating layer exceeds 10 μm, the insulating layer is too thick and stress is likely to be applied to the metal layer when the electromagnetic shielding film is folded, which makes the metal layer more likely to crack when folded repeatedly.

In the electromagnetic wave shielding film of the present invention, the metal layer preferably contains at least one selected from the group consisting of copper, silver, and aluminum.
These metals are inexpensive, and when the metal layer is made of these metals, it exhibits excellent electromagnetic wave shielding properties.

In the electromagnetic wave shielding film of the present invention, the metal layer preferably has through holes formed therein.
The electromagnetic shielding film is placed on a printed wiring board and is heat-pressed to bond the film to the printed wiring board, which may generate volatile components between the insulating layer and the metal layer.
If the metal layer does not have through holes, the volatile components may expand due to heat, causing the metal layer and the insulating layer to peel off. However, if the metal layer has through holes, the volatile components can pass through the through holes, preventing the metal layer and the insulating layer from peeling off.

In the electromagnetic wave shielding film of the present invention, the opening area of each of the through holes is preferably 10 to 80,000 ^μm2 .
When the opening area of the through hole formed in the metal layer is within the above range, the bending resistance is sufficient, and the accumulation of volatile components between the metal layer and the insulating layer can be prevented.

In the electromagnetic wave shielding film of the present invention, the aperture ratio of the through holes is preferably 0.05 to 30%.
When the aperture ratio of the through holes formed in the metal layer is within the above range, the bending resistance is sufficient, and it is possible to prevent volatile components from accumulating between the metal layer and the insulating layer.

The shielded printed wiring board of the present invention is a shielded printed wiring board comprising a printed wiring board consisting of a base film, a printed circuit including a ground circuit arranged on the base film, and a coverlay covering the printed circuit, and an electromagnetic wave shielding film in which an isotropic conductive adhesive layer, an insulating layer, and a metal layer are laminated in that order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm, and is characterized in that the electromagnetic wave shielding film is arranged on the printed wiring board so that the isotropic conductive adhesive layer is in contact with the coverlay.

The shielded printed wiring board of the present invention includes an electromagnetic wave shielding film in which an isotropic conductive adhesive layer, an insulating layer, and a metal layer are laminated in this order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm. That is, the shielded printed wiring board of the present invention includes the above-mentioned electromagnetic wave shielding film of the present invention.
Therefore, in the shielded printed wiring board of the present invention, the metal layer is less likely to peel off, and cracks are less likely to occur in the metal layer even if the shielded printed wiring board is repeatedly bent.

In the shielded printed wiring board of the present invention, it is preferable that the coverlay has an opening that exposes the ground circuit, and the opening is filled with the isotropic conductive adhesive layer so that the isotropic conductive adhesive layer and the ground circuit are in contact with each other.
In such a shielded printed wiring board, the isotropic conductive adhesive layer and the ground circuit are in sufficient contact with each other and electrically connected. In the shielded printed wiring board of the present invention, the isotropic conductive adhesive layer has a function of shielding electromagnetic waves, so that the electromagnetic wave shielding effect is enhanced.

In the shielded printed wiring board of the present invention, the metal layer is electrically connected to an external ground.
In the shielded printed wiring board of the present invention, the metal layer has the function of shielding electromagnetic waves, so that if the metal layer is electrically connected to an external ground, the electromagnetic wave shielding effect is enhanced.

In the electromagnetic wave shielding film of the present invention, an insulating layer is formed between the isotropic conductive adhesive layer and the metal layer. Therefore, the metal layer is not easily peeled off. Furthermore, even if the electromagnetic wave shielding film of the present invention is repeatedly folded, cracks are not easily generated in the metal layer.
In the electromagnetic wave shielding film of the present invention, the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm.
When the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm, the metal layer is less likely to peel off, and cracks are less likely to occur in the metal layer even if the electromagnetic wave shielding film is repeatedly folded.

FIG. 1 is a cross-sectional view that illustrates an example of the electromagnetic wave shielding film of the present invention. FIG. 2A is a process diagram that illustrates an example of a metal layer forming step in the method for producing an electromagnetic wave shielding film of the present invention. FIG. 2B is a process diagram that illustrates an example of an insulating layer forming step in the method for producing the electromagnetic wave shielding film of the present invention. FIG. 2C is a process diagram that illustrates an example of an isotropic conductive adhesive layer forming step in the method for producing an electromagnetic wave shielding film of the present invention. FIG. 3 is a cross-sectional view showing a schematic example of a shielded printed wiring board according to the present invention. FIG. 4A is a cross-sectional view that illustrates a schematic diagram of another example of the shielded printed wiring board of the present invention. FIG. 4B is a cross-sectional view that illustrates a schematic diagram of another example of the shielded printed wiring board of the present invention. FIG. 4C is a cross-sectional view that illustrates a schematic diagram of another example of the shielded printed wiring board of the present invention. FIG. 4D is a cross-sectional view illustrating a schematic diagram of another example of the shielded printed wiring board of the present invention.

The electromagnetic wave shielding film of the present invention is described in detail below. However, the present invention is not limited to the following embodiments, and can be modified and applied as appropriate within the scope that does not change the gist of the present invention.

FIG. 1 is a cross-sectional view that illustrates an example of the electromagnetic wave shielding film of the present invention.
In the electromagnetic wave shielding film 10 shown in FIG. 1, an isotropically conductive adhesive layer 20, an insulating layer 30, and a metal layer 40 are laminated in this order.
In the electromagnetic wave shielding film 10, the total thickness of the insulating layer 30 and the metal layer 40 is 0.5 μm or more and less than 20 μm.

The electromagnetic wave shielding film 10 is to be disposed on a printed wiring board.
In the electromagnetic wave shielding film 10, both the isotropic conductive adhesive layer 20 and the metal layer 40 have the effect of shielding electromagnetic waves, so that in a shielded printed wiring board in which the electromagnetic wave shielding film 10 is arranged, electromagnetic waves can be shielded by the isotropic conductive adhesive layer 20 and the metal layer 40.

In the electromagnetic wave shielding film 10, an insulating layer 30 is formed between the isotropic conductive adhesive layer 20 and the metal layer 40. Therefore, the metal layer 40 is not easily peeled off. In addition, even if the electromagnetic wave shielding film 10 is repeatedly folded, cracks are not easily generated in the metal layer 40.

In the electromagnetic wave shielding film 10, the total thickness of the insulating layer 30 and the metal layer 40 is 0.5 μm or more and less than 20 μm, and preferably 1 to 12 μm.
When the total thickness of the insulating layer 30 and the metal layer 40 is 0.5 μm or more and less than 20 μm, the metal layer 40 is less likely to peel off, and cracks are less likely to occur in the metal layer 40 even if the electromagnetic wave shielding film 10 is repeatedly folded.

The following describes each component of the electromagnetic wave shielding film 10.

(Metal Layer)
The material constituting the metal layer 40 is not particularly limited as long as it can shield electromagnetic waves, but it is preferable that the material contains at least one selected from the group consisting of copper, silver, and aluminum.
These metals are inexpensive, and when the metal layer 40 is made of these metals, it exhibits excellent electromagnetic wave shielding properties.

As described above, in the electromagnetic wave shielding film 10, the thickness of the metal layer 40 is preferably 0.1 to 8 μm, and more preferably 0.1 to 4 μm.
If the thickness of the metal layer is less than 0.1 μm, the strength of the metal layer is weakened and the metal layer becomes susceptible to breakage.
If the thickness of the metal layer exceeds 8 μm, the flexibility of the metal layer decreases, and therefore the metal layer is more likely to crack when repeatedly bent.

The metal layer 40 may be a vapor-deposited metal layer, a plated metal layer, or may consist of a rolled or electrolytic metal foil.

It is preferable that the metal layer 40 has a through hole formed therein.
The electromagnetic wave shielding film 10 is placed on a printed wiring board. At this time, the electromagnetic wave shielding film 10 is thermocompression bonded. At this time, volatile components may be generated between the insulating layer 30 and the metal layer 40.
If no through holes are formed in the metal layer 40, the volatile components may expand due to heat, causing the metal layer 40 to peel off from the insulating layer 30. However, if through holes are formed in the metal layer 40, the volatile components can pass through the through holes, thereby preventing the metal layer 40 from peeling off from the insulating layer 30.

The shape of the through hole is not particularly limited, but may be a polygonal shape such as a triangle or a rectangle, a circle, or an ellipse.

In the metal layer 40, the opening area of each of the through holes is preferably 10 to 80,000 μm ² , and more preferably 10 to 8,000 μm ² .
If the opening area of the through hole formed in the metal layer 40 is within the above range, the bending resistance is sufficient, and the accumulation of volatile components between the metal layer 40 and the insulating layer 30 can be prevented.

In the metal layer 40, the aperture ratio of the through holes is preferably 0.05 to 30%, and more preferably 0.1 to 10%.
If the aperture ratio of the through holes formed in the metal layer 40 is within the above range, the bending resistance is sufficient, and accumulation of volatile components between the metal layer 40 and the insulating layer 30 can be prevented.

The through holes may be equally spaced in the metal layer 40. If the through holes are equally spaced, it is preferable that the through holes are continuously arranged in a uniform pattern.
The arrangement pattern of the through holes may be such that, when the metal layer 40 is viewed in plan, equilateral triangles are continuously arranged in a plane, and the centers of the through holes are located at the vertices of the equilateral triangles. Also, when the metal layer 40 is viewed in plan, the arrangement pattern may be such that, when the metal layer 40 is viewed in plan, squares are continuously arranged in a plane, and the centers of the through holes are located at the vertices of the squares. Also, when the metal layer 40 is viewed in plan, the arrangement pattern may be such that, when the metal layer 40 is viewed in plan, the centers of the through holes are located at the vertices of a regular hexagon.

(Insulating layer)
The material of the insulating layer 30 is not particularly limited as long as it can sufficiently bond the metal layer 40, and may be a thermosetting resin composition or a thermoplastic resin composition.
The electromagnetic wave shielding film 10 is thermocompression bonded when it is disposed on a printed wiring board. Whether a thermosetting resin composition or a thermoplastic resin composition is used as the insulating layer 30 is preferably determined depending on the conditions for thermocompression bonding.
From the viewpoint of heat resistance, the insulating layer 30 is preferably made of a thermosetting resin composition.

Examples of the thermoplastic resin contained in the thermoplastic resin composition include urethane resins, polystyrene-based resins, vinyl acetate-based resins, polyester-based resins, polyolefin-based resins (e.g., polyethylene-based resins, polypropylene-based resin compositions, etc.), acrylic-based resins, and the like.
The insulating layer 30 may be made of only one type of these resins, or may be made of two or more types.

Examples of the thermosetting resin contained in the thermosetting resin composition include phenol-based resins, epoxy-based resins, urethane-based resins, melamine-based resins, alkyd-based resins, and polyimide-based resins.
The insulating layer 30 may be made of only one type of these resins, or may be made of two or more types.

The thickness of the insulating layer 30 is preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.
If the thickness of the insulating layer is less than 0.5 μm, the amount of the insulating layer is so small that the metal layer is easily peeled off.
If the thickness of the insulating layer exceeds 10 μm, the insulating layer is too thick and stress is likely to be applied to the metal layer when the electromagnetic shielding film is folded, which makes the metal layer more likely to crack when folded repeatedly.

(Isotropic conductive adhesive layer)
The isotropically conductive adhesive layer 20 is made of conductive particles and a resin composition.

Examples of the conductive particles include silver particles, copper particles, nickel particles, aluminum particles, and silver-coated copper particles obtained by plating copper with silver.
These conductive particles have excellent conductivity and can therefore suitably impart conductivity to the isotropically conductive adhesive layer 20 .
The isotropically conductive adhesive layer 20 may contain one type of conductive particles alone or multiple types of conductive particles.

The size of the conductive particles is not particularly limited, but it is preferable that the average particle size (d ₅₀ ) is 0.5 to 20 μm.
When the average particle size (d ₅₀ ) is 0.5 μm or more, the conductive particles have good dispersibility, aggregation can be suppressed, and they are less likely to be oxidized.
When the average particle size (d ₅₀ ) is 20 μm or less, the connectivity with the ground circuit is good.

The weight percentage of the conductive particles contained in the isotropically conductive adhesive layer 20 is preferably 40 to 80 wt %, and more preferably 50 to 70 wt %.
If the weight ratio of the conductive particles is less than 40 wt %, it becomes difficult to obtain isotropic conductivity.
If the weight ratio of the conductive particles exceeds 80 wt %, the isotropically conductive adhesive layer becomes brittle, and the electromagnetic wave shielding film becomes more susceptible to breakage.

The material for the resin composition is not particularly limited, but examples of the resin composition that can be used include thermoplastic resin compositions such as a styrene-based resin composition, a vinyl acetate-based resin composition, a polyester-based resin composition, a polyethylene-based resin composition, a polypropylene-based resin composition, an imide-based resin composition, an amide-based resin composition, and an acrylic-based resin composition; and thermosetting resin compositions such as a phenol-based resin composition, an epoxy-based resin composition, a urethane-based resin composition, a melamine-based resin composition, and an alkyd-based resin composition.
Among these, epoxy resin compositions are preferred.
The adhesive resin composition may contain one of these materials alone or a combination of two or more of them.

In addition, the isotropic conductive adhesive layer 20 may further contain flame retardants, flame retardant assistants, curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, UV absorbers, defoamers, leveling agents, fillers, viscosity adjusters, etc.

The thickness of the isotropically conductive adhesive layer 20 is preferably 3 to 20 μm, and more preferably 5 to 10 μm.
When the thickness of the isotropically conductive adhesive layer 20 is 3 μm or more, the filling property into the openings provided in the coverlay of the printed wiring board is improved.
When the thickness of the isotropically conductive adhesive layer 20 is 20 μm or less, it is possible to meet the demand for thinner electromagnetic wave shielding films.

In the electromagnetic wave shielding film 10 , a protective layer may be further formed on the metal layer 40 .
The protective layer can prevent the metal layer 40 from being damaged by external impact or the like.
In the electromagnetic wave shielding film of the present invention, a protective layer may not be formed.

The material of the protective layer is not particularly limited as long as it has insulating properties and can protect the metal layer 40, but it is preferable that it is composed of a thermoplastic resin composition, a thermosetting resin composition, an active energy ray curable composition, etc.

Thermoplastic resin compositions for the protective layer include, but are not limited to, styrene-based resin compositions, vinyl acetate-based resin compositions, polyester-based resin compositions, polyethylene-based resin compositions, polypropylene-based resin compositions, polyamide-based resin compositions, acrylic-based resin compositions, etc.

Thermosetting resin compositions for the protective layer include, but are not limited to, phenol-based resin compositions, epoxy-based resin compositions, urethane-based resin compositions, melamine-based resin compositions, alkyd-based resin compositions, polyimide-based resin compositions, etc.

The active energy ray curable composition for the protective layer is not particularly limited, but examples include polymerizable compounds having at least two (meth)acryloyloxy groups in the molecule.

The protective layer may be composed of a single material or two or more materials.

The protective layer may contain, as necessary, curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, UV absorbers, defoamers, leveling agents, fillers, flame retardants, viscosity adjusters, anti-blocking agents, etc.

The thickness of the protective layer is not particularly limited and can be set appropriately as needed, but it is preferably 1 to 15 μm, and more preferably 3 to 10 μm.

Next, a method for producing the electromagnetic wave shielding film of the present invention will be described.
When producing the electromagnetic wave shielding film of the present invention, a metal layer forming step, an insulating layer forming step, and an isotropic conductive adhesive layer forming step are carried out.

FIG. 2A is a process diagram that illustrates an example of a metal layer forming step in the method for producing an electromagnetic wave shielding film of the present invention.
First, as shown in FIG. 2A, a release film 50 is prepared, and a metal layer 40 is formed thereon.
The type of release film 50 is not particularly limited, and a conventionally used non-silicon release film, a slightly adhesive film, or the like can be used.
The method for forming the metal layer 40 is not particularly limited, and it may be formed by disposing a rolled or electrolytic metal foil, by vapor deposition, or by plating.

FIG. 2B is a process diagram that illustrates an example of an insulating layer forming step in the method for producing the electromagnetic wave shielding film of the present invention.
Next, as shown in FIG. 2B, the insulating layer 30 is formed on the metal layer 40.
The method for forming the insulating layer 30 is not particularly limited, and may be, for example, coating with a bar coater.

FIG. 2C is a process diagram that illustrates an example of an isotropic conductive adhesive layer forming step in the method for producing an electromagnetic wave shielding film of the present invention.
Next, as shown in FIG. 2C, an isotropic conductive adhesive layer 20 is formed on the insulating layer 30.
The method for forming the isotropically conductive adhesive layer 20 is not particularly limited, and may be, for example, coating with a bar coater.

When the laminate produced through the above steps is inverted by 180°, the electromagnetic wave shielding film 10 shown in FIG. 1 is obtained.
The release film 50 can be peeled off when in use.

Next, a shielded printed wiring board 1 including an electromagnetic wave shielding film 10 will be described.
The shielded printed wiring board 1 is also an example of a shielded printed wiring board of the present invention.

FIG. 3 is a cross-sectional view showing a schematic example of a shielded printed wiring board according to the present invention.
The shielded printed wiring board 1 shown in Figure 3 comprises a printed wiring board 60 consisting of a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 10.
In the shielded printed wiring board 1 , the electromagnetic wave shielding film 10 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 contacts the coverlay 63 .

The shielded printed wiring board 1 includes an electromagnetic wave shielding film 10. Therefore, in the shielded printed wiring board 1, the metal layer 40 is not easily peeled off, and even if the shielded printed wiring board 1 is repeatedly bent, the metal layer 40 is not easily cracked.

In addition, in the shielded printed wiring board 1 shown in FIG. 3, an opening 63a is formed in the coverlay 63 to expose the ground circuit 62a.
The opening 63a is filled with the isotropically conductive adhesive layer 20 so that the isotropically conductive adhesive layer 20 and the ground circuit 62a are in contact with each other.
In this shielded printed wiring board 1, the isotropic conductive adhesive layer 20 and the ground circuit 62a are in sufficient contact with each other and electrically connected. In the shielded printed wiring board 1, the isotropic conductive adhesive layer 20 has a function of shielding electromagnetic waves, so that the electromagnetic wave shielding effect is enhanced.

In the shielded printed wiring board of the present invention, the coverlay does not need to have an opening for exposing the ground circuit.
In this case, the ground circuit and the isotropic conductive adhesive layer may be electrically connected by a conductive bump or a conductive pin.

In the shielded printed wiring board 1, the metal layer 40 is electrically connected to the external ground GND.
In the shielded printed wiring board 1, the metal layer 40 has a function of shielding electromagnetic waves, so that if the metal layer 40 is electrically connected to the external ground GND, the electromagnetic wave shielding effect is enhanced.

The method of electrically connecting the external ground GND and the metal layer 40 is not particularly limited, but the external ground GND and the metal layer 40 can be electrically connected using, for example, a conductive adhesive, a conductive foam, a conductive gasket, etc.

In addition, a case where a protective layer is further formed on the metal layer of the electromagnetic wave shielding film in the shielded printed wiring board of the present invention will be described with reference to the drawings.
4A to 4D are cross-sectional views each showing a schematic diagram of another example of the shielded printed wiring board of the present invention.

The shielded printed wiring board 1A shown in Figure 4A comprises a printed wiring board 60 consisting of a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 11.
In the electromagnetic wave shielding film 11, an isotropically conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order.
In the shielded printed wiring board 1A, the electromagnetic wave shielding film 11 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 contacts the coverlay 63.

The shielded printed wiring board 1A further includes a grounding member 80A having a flat conductive external connection member 81 on top of the protective layer 70 of the electromagnetic wave shielding film 11 and a conductive protrusion 82 protruding from one side of the conductive external connection member 81.
The conductive protrusion 82 penetrates the protective layer 70 and is in contact with the metal layer 40, and the conductive external connection member 81 is electrically connected to the external ground GND.
That is, in shielded printed wiring board 1A, metal layer 40 is connected to external ground GND via ground member 80A.

The conductive external connection member 81 and conductive protrusion 82 of the ground member 80A may be made of any material that is conductive, such as copper, silver, aluminum, etc.

In the ground member 80A, the conductive external connection member 81 and the conductive protrusion 82 may be connected by soldering or welding. The conductive protrusion 82 may be formed by etching, and the conductive external connection member 81 and the conductive protrusion 82 may be integrated.

The shielded printed wiring board 1B shown in Figure 4B comprises a printed wiring board 60 consisting of a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 11.
In the electromagnetic wave shielding film 11, an isotropically conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order.
In the shielded printed wiring board 1B, the electromagnetic wave shielding film 11 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 contacts the coverlay 63 .

The shielded printed wiring board 1B further comprises a grounding member 80B having a flat conductive external connection member 81 on top of the protective layer 70 of the electromagnetic wave shielding film 11 and conductive particles 83 arranged on one side of the conductive external connection member 81.
The conductive particles 83 penetrate the protective layer 70 and are in contact with the metal layer 40, and the conductive external connection member 81 is electrically connected to the external ground GND.
That is, in shielded printed wiring board 1B, metal layer 40 is connected to external ground GND via ground member 80B.

The conductive external connection member 81 of the ground member 80B may be made of any material as long as it has conductivity, and may be made of, for example, copper, silver, aluminum, or the like.
Furthermore, the conductive particles 83 of the ground member 80B may be made of any material as long as it has conductivity, and may be made of, for example, copper, silver, aluminum, or the like.

In the ground member 80B, the conductive particles 83 may be adhered to the conductive external connection member 81 by a conductive adhesive.

The shielded printed wiring board 1C shown in Figure 4C comprises a printed wiring board 60 consisting of a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 11.
In the electromagnetic wave shielding film 11, an isotropically conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order.
In the shielded printed wiring board 1C, the electromagnetic wave shielding film 11 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 contacts the coverlay 63.

The shielded printed wiring board 1C further includes a ground member 80C made of a conductive external connection member 84 on the protective layer 70 of the electromagnetic wave shielding film 11.
The conductive external connection member 84 is formed by bending a flat plate multiple times, and has protruding convex portions 84a.
The protrusion 84a penetrates the protective layer 70 and is in contact with the metal layer 40, and the conductive external connection member 84 is electrically connected to the external ground GND.
That is, in the shielded printed wiring board 1C, the metal layer 40 is connected to the external ground GND via the ground member 80C.

The conductive external connection member 84 of the ground member 80C may be made of any material that is conductive, such as copper, nickel, silver, aluminum, etc.

The shielded printed wiring board 1D shown in Figure 4D comprises a printed wiring board 60 consisting of a base film 61, a printed circuit 62 including a ground circuit 62a arranged on the base film 61, and a coverlay 63 covering the printed circuit 62, and an electromagnetic wave shielding film 12.
In the electromagnetic wave shielding film 12, an isotropically conductive adhesive layer 20, an insulating layer 30, a metal layer 40, and a protective layer 70 are laminated in this order.
In the shielded printed wiring board 1D, the electromagnetic wave shielding film 12 is disposed on the printed wiring board 60 so that the isotropic conductive adhesive layer 20 contacts the coverlay 63.

In the shielded printed wiring board 1D, an opening 71a is formed in a protective layer 71 of an electromagnetic wave shielding film 12, exposing the metal layer 40.
The metal layer 40 is electrically connected to the external ground GND through the opening 71a.

In addition, in the shielded printed wiring board 1D, the opening 71a of the protective layer 71 may be filled with conductive adhesive, and the metal layer 40 may be connected to the external ground GND via the conductive adhesive.

The materials for the base film 61 and the cover layer 63 are not particularly limited, but are preferably made of engineering plastics.
Examples of such engineering plastics include resins such as polyethylene terephthalate, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide.
Among these engineering plastics, polyphenylene sulfide film is preferable when flame retardancy is required, and polyimide film is preferable when heat resistance is required. The thickness of the base film 61 is preferably 10 to 40 μm. The thickness of the coverlay 63 is preferably 20 to 50 μm.

The printed circuit 62 and the ground circuit 62a can be formed by, but not limited to, etching a conductive material.
Conductive materials include copper, nickel, silver, gold, and the like.

An example of a method for manufacturing the shielded printed wiring board 1 is to prepare a printed wiring board 60 and an electromagnetic wave shielding film 10, and to place the electromagnetic wave shielding film 10 on the printed wiring board 60. More specifically, an example of a method is to thermocompression bond the electromagnetic wave shielding film 10 to the printed wiring board 60 so that the isotropic conductive adhesive layer 20 is in contact with the coverlay 63.
The conditions for the thermocompression bonding are not particularly limited, but may be, for example, 150 to 200° C., 2 to 5 MPa, and 1 to 60 minutes.

By carrying out the above-mentioned thermocompression bonding, the isotropic conductive adhesive layer 20 fills the openings 63a.
As a result, the ground circuit 62a is electrically connected to the isotropic conductive adhesive layer 20. This improves the electromagnetic wave shielding effect.

The following examples are provided to explain the present invention in more detail, but the present invention is not limited to these examples.

Example 1
(Metal layer forming process)
Silver (Ag) was vapor-deposited on the surface of the release film on which the non-silicon release agent had been formed, to form a metal layer having a thickness of 0.1 μm.

(Insulating layer forming process)
An epoxy resin was applied onto the metal layer to form an insulating layer having a thickness of 1.0 μm.

(Isotropic conductive adhesive layer formation process)
An isotropic conductive adhesive containing 60 wt % conductive particles made of silver-coated copper powder and 40 wt % epoxy resin was prepared.
The isotropic conductive adhesive layer was applied onto the insulating layer to form an isotropic conductive adhesive layer having a thickness of 15 μm.

Through the above steps, the electromagnetic wave shielding film of Example 1 was produced.

(Examples 2 to 13) and (Comparative Examples 1 to 6)
The electromagnetic wave shielding films of Examples 2 to 13 and Comparative Examples 1 to 3 were produced in the same manner as in Example 1, except that the material and thickness of the metal layer and the thickness of the insulating layer were changed as shown in Table 1.
In addition, electromagnetic wave shielding films according to Comparative Examples 4 to 6 were produced in the same manner as in Example 1, except that the material and thickness of the metal layer were changed as shown in Table 1 and no insulating layer was provided.

(MIT Test)
The bending resistance of the electromagnetic wave shielding films of each of the Examples and Comparative Examples after the release film was peeled off was measured by the following method.
Each electromagnetic wave shielding film was placed on a polyimide film so that the isotropic conductive adhesive layer was in contact with the polyimide film having a thickness of 50 μm, and was attached by thermocompression bonding (170° C., 3 MPa, 30 minutes). Then, the film was cut into a size of length×width=130 mm×15 mm, and the release film was peeled off to obtain a test piece. The bending resistance of each test piece was measured using an MIT folding fatigue tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd., No. 307 MIT type folding fatigue tester) based on the method specified in JIS P8115:2001.
The test conditions are as follows.
Bending clamp tip R: 0.38 mm
Bend angle: ±135°
Bending speed: 175 cpm
Load: 500gf
Detection method: The built-in electrical device detects breaks in the shielding film.

The evaluation criteria for the MIT test are as follows. The results are shown in Table 1.
A: Breakage of the metal layer was observed after bending 1000 times or more.
Δ: Breakage of the metal layer was confirmed when the number of bending cycles was 300 or more but less than 999.
x: Breakage of the metal layer was observed after bending less than 300 times.

(Adhesion strength test)
The adhesive strength of the electromagnetic wave shielding film of each Example and Comparative Example after the release film was peeled off was measured by the following method.
Each electromagnetic wave shielding film was placed on a polyimide film having a thickness of 25 μm so that the isotropic conductive adhesive layer was in contact with the polyimide film, and the films were thermocompression bonded under the conditions of a temperature of 170° C., a time of 30 minutes, and a pressure of 3 MPa.
The metal layer side of the electromagnetic wave shielding film was fixed with double-sided tape, and the polyimide film was peeled off at room temperature at a tensile speed of 50 mm/min and a peel angle of 180°. The peel strength during peeling was measured, and the average of the maximum and minimum values was taken as the adhesion strength.

The evaluation criteria for the adhesion strength test are as follows. The results are shown in Table 1.
A: The metal layer peeled off with a tensile force of 4.0 N/cm or more.
Δ: The metal layer peeled off with a tensile force of 3.0 N/cm or more and less than 4.0 N/cm.
x: The metal layer peeled off with a tensile force of less than 3.0 N/cm.

As shown in Table 1, the electromagnetic wave shielding films of Examples 1 to 13, which include an insulating layer between the isotropic conductive adhesive layer and the metal layer and have a total thickness of the insulating layer and the metal layer of 0.5 μm or more and less than 20 μm, performed well in both the MIT test and the adhesion strength test.

On the other hand, in the electromagnetic wave shielding films according to Comparative Examples 1 to 3 in which the total thickness of the insulating layer and the metal layer exceeded 20 μm, the MIT test was not good, and it was found that the metal layer was prone to cracking when repeatedly bent.
Furthermore, in the electromagnetic wave shielding films of Comparative Examples 4 to 6, which do not include an insulating layer between the isotropic conductive adhesive layer and the metal layer, the adhesion strength test was poor, and it was found that the metal layer was easily peeled off.

1, 1A, 1B, 1C, 1D Shielded printed wiring board 10, 11, 12 Electromagnetic wave shielding film 20 Isotropic conductive adhesive layer 30 Insulating layer 40 Metal layer 50 Release film 60 Printed wiring board 61 Base film 62 Printed circuit 62a Ground circuit 63 Coverlay 63a Opening 70, 71 Protective layer 71a Opening 80A, 80B, 80C Ground member 81, 84 Conductive external connection member 82 Conductive protrusion 83 Conductive particle 84a Convex portion GND External ground

Claims (10)

an isotropically conductive adhesive layer;
An insulating layer;
A metal layer is directly laminated in this order.
An electromagnetic wave shielding film, characterized in that the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm. The electromagnetic wave shielding film according to claim 1, wherein the thickness of the metal layer is 0.1 to 8 μm. The electromagnetic wave shielding film according to claim 1 or 2, wherein the thickness of the insulating layer is 0.5 to 10 μm. The electromagnetic shielding film according to any one of claims 1 to 3, wherein the metal layer contains at least one selected from the group consisting of copper, silver, and aluminum. The electromagnetic shielding film according to any one of claims 1 to 4, wherein the metal layer has through holes formed therein. 6. The electromagnetic wave shielding film according to claim 5, wherein the opening area of each of the through holes is 10 to 80,000 ^μm2 . The electromagnetic shielding film according to claim 5 or 6, wherein the aperture ratio of the through holes is 0.05 to 30%. A printed wiring board including a base film, a printed circuit including a ground circuit disposed on the base film, and a coverlay covering the printed circuit;
A shielded printed wiring board comprising an electromagnetic wave shielding film in which an isotropic conductive adhesive layer, an insulating layer, and a metal layer are directly laminated in this order, and the total thickness of the insulating layer and the metal layer is 0.5 μm or more and less than 20 μm,
A shielded printed wiring board, characterized in that the electromagnetic wave shielding film is disposed on the printed wiring board so that the isotropic conductive adhesive layer is in contact with the coverlay. an opening for exposing the ground circuit is formed in the coverlay;
9. The shielded printed wiring board according to claim 8, wherein the opening is filled with the isotropic conductive adhesive layer so that the isotropic conductive adhesive layer and the ground circuit are in contact with each other. A shielded printed wiring board as described in claim 8 or 9, in which the metal layer is electrically connected to an external ground.

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