JP7023836B2 - Electromagnetic wave shield film - Google Patents

Description

The present invention relates to an electromagnetic wave shielding film.

In recent years, smartphones and tablet-type information terminals are required to have the ability to transmit a large amount of data at high speed. In addition, it is necessary to use a high frequency signal in order to transmit a large amount of data at high speed. However, when a high frequency signal is used, electromagnetic noise is generated from the signal circuit provided on the printed wiring board, and peripheral devices are liable to malfunction. Therefore, in order to prevent such a malfunction, it is important to shield the printed wiring board from electromagnetic waves.

As a method of shielding a printed wiring board, it has been studied to use an electromagnetic wave shielding film having a shield layer made of a metal film and a conductive adhesive layer containing a conductive filler (for example, Patent Documents 1 to 3). See.).

In the electromagnetic wave shielding film, the conductive adhesive layer is opposed to the insulating layer covering the printed wiring board, and the film is heated and pressed to be bonded. The insulating layer is provided with an opening that exposes the ground circuit, and when the electromagnetic wave shield film placed on the printed wiring board is heated and pressed, the opening is filled with the conductive adhesive. As a result, the shield layer and the ground circuit of the printed wiring board are connected via the conductive adhesive, and the printed wiring board is shielded. After that, the shielded printed wiring board is exposed to a high temperature of about 270 ° C. in the reflow process in order to connect the printed wiring board and the electronic component.

Japanese Unexamined Patent Publication No. 2004-095566 WO2006 / 088127 Pamphlet WO2009 / 019963 Pamphlet

As the shield layer in the conventional electromagnetic wave shield film, a metal film made of a thin film vapor-deposited with silver or a copper foil is used. Since silver and copper are expensive materials, it is preferable to use an inexpensive material such as aluminum in order to reduce the cost of the shield layer. However, a high-resistance oxide film is likely to be formed on the surface of the aluminum film, and when a normal conductive adhesive cannot electrically connect the aluminum film which is a shield layer and the ground circuit, it does not function as a shield. There is. Further, even if continuity can be ensured in the initial state, the problem that the resistance value increases due to the reflow process has been clarified.

An object of the present disclosure is to make it possible to realize an electromagnetic wave shielding film in which an electrical connection with a printed wiring board is stably maintained without using an expensive material.

One aspect of the electromagnetic wave shielding film of the present disclosure comprises a shield layer made of an aluminum film and a conductive adhesive layer, and the conductive adhesive layer contains a conductive filler made of spike-shaped or filament-shaped nickel particles. ..

In one aspect of the electromagnetic wave shielding film, the conductive filler has a median diameter (D50) of 5 μm or more and 30 μm or less, a mode diameter of 3 μm or more and 50 μm or less, and a cumulative distribution in the mode diameter of 35% or more, preferably 60% or more. Can be.

In one aspect of the electromagnetic wave shielding film, the conductive filler can have a maximum particle size of 90 μm or less.

In one aspect of the electromagnetic wave shielding film, the thickness of the conductive adhesive layer can be equal to or less than the median diameter of the conductive filler.

In one aspect of the electromagnetic wave shielding film, the conductive adhesive layer can contain 20% by mass or more and 50% by mass or less of the conductive filler.

One aspect of the conductive filler for an electromagnetic wave shielding film of the present disclosure is nickel particles which are spike-shaped or filament-shaped, have a mode diameter of 3 μm or more and 50 μm or less, and have a cumulative distribution of 35% or more in the mode diameter.

In one aspect of the conductive filler for an electromagnetic wave shielding film, the nickel particles can have a maximum diameter of 90 μm or less.

According to the electromagnetic wave shielding film of the present disclosure, it is possible to stably maintain an electrical connection with a printed wiring board without using an expensive material.

It is sectional drawing which shows the electromagnetic wave shielding film of this embodiment. It is sectional drawing which shows the shield printed wiring board using the electromagnetic wave shield film of this embodiment.

Hereinafter, embodiments of the electromagnetic wave shielding film of the present invention will be specifically described. The present invention is not limited to the following embodiments, and can be appropriately modified and applied without changing the gist of the present invention.

(Electromagnetic wave shield film)
As shown in FIG. 1, the electromagnetic wave shielding film 100 of the present embodiment includes a shield layer 111 made of an aluminum film, a conductive adhesive layer 112 provided on the first surface side of the shield layer 111, and a shield layer 111. It is provided with an insulating protective layer 113 provided on the second surface side opposite to the first surface of the above.

<Shield layer>
The shield layer 111 of this embodiment is made of an aluminum film. The thickness of the aluminum film is preferably 0.01 μm or more, more preferably 0.1 μm or more, from the viewpoint of improving the shielding characteristics. The thickness is preferably 12 μm or less, more preferably 10 μm or less, still more preferably 3 μm or less, from the viewpoint of flexibility and the transmission characteristics of high frequency signals of 10 MHz or more.

The method for producing the aluminum film is not particularly limited, and the method for producing the aluminum foil by rolling, the vacuum vapor deposition method, the sputtering method, the chemical vapor deposition (CVD) method, and the organic metal deposition (MO) method, which are additive methods, are not particularly limited. , Can be manufactured by plating method or the like.

<Conductive adhesive layer>
The conductive adhesive layer 112 of the present embodiment is a conductive adhesive layer having an adhesive resin composition and a conductive filler. In this embodiment, the conductive filler consists of spike-shaped or filament-shaped nickel particles.

The spike-shaped nickel particles are particles mainly composed of nickel having spike-shaped protrusions on the surface. Examples of the spike-shaped nickel particles include Type 123 manufactured by Vale.

The filament-shaped nickel particles are mainly composed of nickel in which about 10 to 1000 primary particles having an average primary particle diameter of about 0.1 μm to 10 μm are connected in a chain to form filament-like secondary particles. It is a particle that does. Examples of filamentary nickel particles include Type 210, Type 255, Type 270 and Type 287 manufactured by Vale. The description of the particle size and the like of the filamentary nickel particles in the present disclosure is the description of the secondary particles unless otherwise specified.

The spike-shaped or filament-shaped nickel particles preferably have a median diameter (D50) of 5 μm or more, and more preferably 10 μm or more. Further, 30 μm or less is preferable, and 25 μm or less is more preferable. When the median diameter is 5 μm or more, the resistance value described later becomes low and the electromagnetic wave shielding characteristic becomes good. When the median diameter is 30 μm or less, the heat resistance is good. Further, the conductive filler composed of spike-shaped or filament-shaped nickel particles preferably has a mode diameter of 3 μm or more, and more preferably 10 μm or more. Further, it is preferably 50 μm or less, and more preferably 40 μm or less. When the mode diameter is 3 μm or more, the resistance value described later becomes low and the electromagnetic wave shielding characteristic becomes good. When the mode diameter is 50 μm or less, the heat resistance of the electromagnetic wave shielding film becomes good.

Further, the conductive filler composed of spike-shaped or filament-shaped nickel particles preferably has a cumulative distribution of 35% or more, more preferably 60% or more, and further preferably 65% or more in the mode diameter. It is preferably 70% or more, and even more preferably 70% or more. When the cumulative distribution of the mode diameter is 35% or more, the heat resistance of the electromagnetic wave shielding film becomes good.

Further, the conductive filler composed of spike-shaped or filament-shaped nickel particles preferably has a maximum particle diameter (Dmax) of 90 μm or less, more preferably 85 μm or less, still more preferably 80 μm or less. It is more preferably 70 μm or less. When Dmax is 90 μm or less, the heat resistance of the electromagnetic wave shielding film becomes good.

The mode diameter, cumulative distribution, D50 and Dmax can be measured by the methods shown in Examples described later.

It is also possible to mix spike-shaped nickel particles and filamentary nickel particles and use them as a conductive filler.

When the shield layer is a film such as silver or copper, good electrical connection can be obtained by using copper particles, silver particles, silver-coated copper particles, ordinary spherical nickel particles, or the like as a conductive filler. Can be done. However, when the shield layer is an aluminum film, an oxide film is formed on the surface, and it is difficult to obtain a good electrical connection when these particles are used as a conductive filler. Further, even if an electrical connection is obtained in the initial state, the resistance value increases due to the reflow process, and it is difficult to maintain a stable connection.

On the other hand, when spike-shaped or filament-shaped nickel particles are used as the conductive filler, the oxide film on the surface of the aluminum film can be pierced due to the effect of the hardness and shape of the particles, and stable and good electricity can be obtained. It is possible to maintain a target connection. In the case of soft particles made of silver, copper, or the like, even if the particles have protrusions or the like, they cannot penetrate the oxide film, and it is difficult to obtain a good electrical connection.

The amount of the conductive filler added to the entire conductive adhesive layer is preferably 20% by mass or more, more preferably 25% by mass or more, still more preferably 30% by mass or more, from the viewpoint of ensuring good conductivity. Further, from the viewpoint of the adhesiveness of the conductive adhesive layer, it is preferably 50% by mass or less, more preferably 45% by mass or less, and further preferably 40% by mass or less.

The adhesive resin composition is not particularly limited, but is limited to a styrene resin composition, a vinyl acetate resin composition, a polyester resin composition, a polyethylene resin composition, a polypropylene resin composition, an imide resin composition, and the like. A thermoplastic resin composition such as an amide resin composition or an acrylic resin composition, or a phenol resin composition, an epoxy resin composition, a urethane resin composition, a melamine resin composition, or an alkyd resin composition. A thermosetting resin composition or the like can be used. These may be used alone or in combination of two or more.

The conductive adhesive layer may include, if necessary, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoamer, a leveling agent, a filler, a flame retardant, and the like. And at least one of a viscosity modifier and the like may be contained.

The thickness of the conductive adhesive layer is not particularly limited and can be appropriately set as needed, but is preferably 3 μm or more, more preferably 4 μm or more, and preferably 10 μm or less, more preferably 7 μm or less. can do. In order to give anisotropy to the conductive adhesive layer, the thickness of the conductive adhesive layer should be equal to or less than the median diameter (D50) of the conductive filler composed of spike-shaped or filament-shaped nickel particles. Is preferable. When the thickness of the conductive adhesive layer is equal to or less than the median diameter (D50) of the conductive filler, the electrical connection between the electromagnetic wave shield and the printed wiring board is good.

<Insulation protective layer>
The insulating protective layer 113 of the present embodiment is not particularly limited as long as it satisfies predetermined mechanical strength, chemical resistance, heat resistance, etc. that can protect the adhesive layer and the shield layer, and has sufficient insulating properties. For example, a thermoplastic resin composition, a thermosetting resin composition, an active energy ray-curable composition, or the like can be used.

The thermoplastic resin composition is not particularly limited, but is limited to a styrene resin composition, a vinyl acetate resin composition, a polyester resin composition, a polyethylene resin composition, a polypropylene resin composition, an imide resin composition, and the like. Alternatively, an acrylic resin composition or the like can be used. The thermosetting resin composition is not particularly limited, but is limited to a phenol-based resin composition, an epoxy-based resin composition, a urethane-based resin composition having an isocyanate group at the terminal, a urea-based resin having an isocyanate group at the terminal, and a terminal. A urethane urea-based resin having an isocyanate group, a melamine-based resin composition, an alkyd-based resin composition, or the like can be used. The active energy ray-curable composition is not particularly limited, and for example, a polymerizable compound having at least two (meth) acryloyloxy groups in the molecule can be used. These resins may be used alone or in combination of two or more.

The insulating protective layer includes a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, and a viscosity control, if necessary. At least one agent, anti-blocking agent and the like may be contained.

The insulating protective layer may be a laminated body having two or more layers having different physical properties such as material, hardness, and elastic modulus. For example, in the case of a laminate of an outer layer having a low hardness and an inner layer having a high hardness, since the outer layer has a cushioning effect, the pressure applied to the shield layer in the step of heating and pressurizing the electromagnetic wave shield film on the printed wiring board can be relaxed. Therefore, it is possible to prevent the shield layer from being destroyed by the step provided on the printed wiring board.

The thickness of the insulating protective layer is not particularly limited and can be appropriately set as needed, but is 1 μm or more, preferably 4 μm or more, and 20 μm or less, preferably 10 μm or less, more preferably 5 μm or less. can do. By setting the thickness of the insulating protective layer to 1 μm or more, the adhesive layer and the shield layer can be sufficiently protected. By setting the thickness of the insulating protective layer to 20 μm or less, the flexibility of the electromagnetic wave shielding film can be ensured, and it becomes easy to apply one electromagnetic wave shielding film to a member that requires flexibility. ..

(Production method)
The method for producing the electromagnetic wave shielding film of the present embodiment is not particularly limited, and the electromagnetic wave shielding film can be produced by various methods. For example, as shown below, a conductive adhesive layer is formed on a supporting base material, an insulating protective layer and a shielding layer are formed on another supporting base material, and a conductive adhesive layer and a shield are formed. It can be manufactured by laminating with layers.

<Conducting adhesive layer forming process>
First, a composition for an adhesive layer is prepared. The composition for the adhesive layer contains a conductive filler, a resin composition, and a solvent. The conductive filler is spike-shaped or filament-shaped nickel particles. The resin composition is not particularly limited, but is a styrene resin composition, a vinyl acetate resin composition, a polyester resin composition, a polyethylene resin composition, a polypropylene resin composition, an imide resin composition, and an amide resin. A thermoplastic resin composition such as a composition or an acrylic resin composition, or a phenol-based resin composition, an epoxy-based resin composition, a urethane-based resin composition, a melamine-based resin composition, an alkyd-based resin composition, or the like. It can be a thermosetting resin composition or the like. These may be used alone or in combination of two or more.

The solvent can be, for example, toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, dimethylformamide, or the like.

In addition, if necessary, a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling agent, a filler, and a flame retardant are added to the composition for the adhesive layer. , And at least one of a viscosity modifier and the like may be contained.

Next, the composition for the adhesive layer is applied to one side of the supporting base material for forming the conductive adhesive layer. The method for applying the protective layer composition to the supporting substrate for forming the conductive adhesive layer is not particularly limited, and known techniques such as lip coating, comma coating, gravure coating, and slot die coating shall be adopted. Can be done.

The supporting base material for forming the conductive adhesive layer can be, for example, a film. The supporting base material for forming the conductive adhesive layer is not particularly limited, and can be formed of, for example, a material such as a polyolefin-based material, a polyester-based material, a polyimide-based material, or a polyphenylene sulfide-based material. A mold release agent layer may be provided between the support base material for forming the conductive adhesive layer and the composition for the adhesive layer.

The prepared composition for an adhesive layer is applied to the surface of a supporting base material for forming a conductive adhesive layer, and the composition for an adhesive layer applied to the surface of a supporting base material for forming a conductive adhesive layer is heated. By drying to remove the solvent, a conductive adhesive layer is formed.

<Insulation protective layer forming process>
First, a composition for a protective layer is prepared. The composition for the protective layer can be prepared by adding an appropriate amount of a solvent and other compounding agents to the resin composition. The solvent can be, for example, toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, dimethylformamide and the like. As other compounding agents, a cross-linking agent, a polymerization catalyst, a curing accelerator, a filler, a colorant and the like can be added. Other compounding agents may be added as needed.

Next, the prepared protective layer composition is applied to one side of the supporting base material for forming the insulating protective layer. The method for applying the protective layer composition to the supporting base material for forming the insulating protective layer is not particularly limited, and known techniques such as lip coating, comma coating, gravure coating, and slot die coating can be adopted. ..

The supporting base material for forming the insulating protective layer can be, for example, in the form of a film. The supporting base material for forming the insulating protective layer is not particularly limited, and can be formed of, for example, a material such as a polyolefin-based material, a polyester-based material, a polyimide-based material, or a polyphenylene sulfide-based material. A release agent layer may be provided between the supporting base material for forming the insulating protective layer and the composition for the protective layer.

The insulating protective layer is formed by heating and drying the protective layer composition applied to the surface of the supporting base material for forming the insulating protective layer to remove the solvent.

<Shield layer forming process>
Next, a shield layer is formed on the surface of the insulation protection layer to form a laminate of the insulation protection layer and the shield layer. Specifically, a method of laminating an aluminum foil formed to a predetermined thickness in advance to the insulating protective layer, or a method of forming an aluminum film on the surface of the insulating protective layer by vapor deposition or plating can be used.

<Lasting process>
By facing the conductive adhesive layer and the shield layer and laminating the conductive adhesive layer and the laminate, an electromagnetic wave shielding film having an insulating protective layer, a shield layer and a conductive adhesive layer can be obtained.

The supporting base material for forming the conductive adhesive layer may be peeled off immediately before the electromagnetic wave shielding film is attached to the printed wiring board. In this way, the supporting base material for forming the conductive adhesive layer can be used as the protective film for the conductive adhesive layer. Further, the supporting base material for forming the insulating protective layer can be formed after the electromagnetic wave shielding film is attached to the printed wiring board. By doing so, the electromagnetic wave shielding film can be protected by the supporting base material. However, for forming the insulating protective layer, the insulating protective layer may be peeled off at any time after the insulating protective layer is formed.

It is also possible to sequentially form a shield layer and an insulating protective layer on the conductive adhesive layer. It is also possible to sequentially form a shield layer and a conductive adhesive layer on the insulating protective layer.

(Shield printed wiring board)
The electromagnetic wave shielding film of the present embodiment can be used, for example, for the shield printed wiring board 300 shown in FIG. The shield printed wiring board 300 includes a printed wiring board 200 and an electromagnetic wave shielding film 100.

The printed wiring board 200 includes a base layer 211, a printed circuit (ground circuit) 212 formed on the base layer 211, and an insulating adhesive layer 213 provided adjacent to the ground circuit 212 on the base layer 211. And an insulating coverlay 214 provided to cover a part of the ground circuit 212 and to cover the insulating adhesive layer 213. The insulating adhesive layer 213 and the coverlay 214 form an insulating layer of the printed wiring board.

The base layer 211, the insulating adhesive layer 213, and the coverlay 214 are not particularly limited, and may be, for example, a resin film or the like. In this case, it can be formed of a resin such as polypropylene, cross-linked polyethylene, polyester, polybenzoimidazole, polyimide, polyimideamide, polyetherimide, or polyphenylene sulfide. The ground circuit 212 may be, for example, a copper wiring pattern formed on the base layer 211.

The electromagnetic wave shielding film 100 is adhered to the printed wiring board 200 with the conductive adhesive layer 112 on the coverlay 214 side.

Next, a method of manufacturing the shield printed wiring board 300 will be described. The electromagnetic wave shielding film 100 is placed on the printed wiring board 200, and is pressurized while being heated by a press machine. A part of the conductive adhesive layer 112 softened by heating flows into the opening formed in the coverlay 214 by pressurization. As a result, the shield layer 111 and the ground circuit 212 of the printed wiring board 200 are connected via the conductive adhesive, and the shield layer 111 and the ground circuit 212 are connected.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are examples and do not limit the present invention in any way.

<Evaluation of particle size>
The mode diameter, cumulative distribution, D50 and Dmax of the aggregates of the conductive filler particles were measured using a particle size distribution measuring device (MT3300EXII, manufactured by Microtrac Bell) using water as a dispersion medium.

<Evaluation of electrical connection>
The created electromagnetic wave shield film and the printed wiring board for evaluation are overlapped, heated and pressurized at 170 ° C. and 3.0 MPa for 1 minute using a press machine, and then heated and pressurized at the same temperature and pressure for 3 minutes. did. After that, the supporting base material was peeled off from the protective layer to prepare a shielded printed wiring board for evaluation.

The printed wiring board has two copper foil patterns extending in parallel at intervals from each other and an insulating layer (thickness: 25 μm) made of polyimide while covering the copper foil patterns. Each insulating layer has an insulating layer (thickness: 25 μm). An opening (diameter: 1 mm) was provided to expose the copper foil pattern. When the adhesive layer of the electromagnetic wave shielding film and the printed wiring board were overlapped, this opening was completely covered by the electromagnetic wave shielding film.

The electric resistance value between the two copper foil patterns of the obtained shielded printed wiring board was measured using a resistance meter, and the electrical connection between the printed wiring board and the shield layer before reflow was evaluated.

Next, heat treatment assuming reflow processing was performed, and the electrical connection after reflow was evaluated. The heat treatment and the measurement of the electric resistance value were repeated 3 times. Assuming the use of lead-free solder for the heat treatment, a temperature profile was set so that the shield film on the shield printed wiring board was exposed to 265 ° C. for 1 second.

<Creation of insulation protection layer and shield layer>
100 parts by mass of bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1256) and 0. 1 part by mass was blended to prepare an insulating protective layer composition. This composition is applied to a supporting base material for forming an insulating protective layer made of a polyethylene terephthalate (PET) film whose surface has been mold-released, and dried by heating to cover the surface of the supporting base material for forming an insulating protective layer (an insulating protective layer (). A thickness of 6 μm) was formed.

An aluminum film having a thickness of 0.1 μm was formed on the surface of the obtained insulating protective layer by a thin-film deposition method to obtain a laminate of the insulating protective layer and the shield layer. Specifically, a supporting base material having an insulating protective layer formed in a batch type vacuum vapor deposition apparatus (EBH-800 manufactured by ULVAC) is placed, and the vacuum reach is 5 × 10 -1 Pa or less in an argon gas atmosphere. After adjustment, aluminum was deposited to a thickness of 0.1 μm by a magnetron sputtering method (DC power output: 3.0 kW).

(Example 1)
-Creation of electromagnetic wave shield film-
100 parts by mass of bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1256) and 0.1 parts of curing agent (manufactured by Mitsubishi Chemical Corporation, ST14) in toluene so that the solid content is 20% by mass. 43 parts by mass and 43 parts by mass of a conductive filler composed of filamentous nickel particles were added, and the mixture was stirred and mixed to prepare an adhesive layer composition. The mode diameter of the conductive filler was 34 μm, the cumulative distribution was 76%, the median diameter (D50) was 20 μm, and the maximum particle diameter (Dmax) was 88 μm. Further, the proportion of nickel particles in the obtained adhesive layer composition is 30% by mass. The obtained adhesive layer composition is applied to a supporting base material for forming a conductive adhesive layer made of a PET film whose surface has been mold-released, and heat-dried to support the supporting base material for forming a conductive adhesive layer. A conductive adhesive layer (thickness 12 μm) was formed on the surface of the above.

The obtained conductive adhesive layer was bonded to a laminate of an insulating protective layer and a shield layer separately prepared to obtain an electromagnetic wave shielding film of Example 1.

When the electrical connectivity of the electromagnetic wave shielding film of Example 1 was evaluated, the initial electrical resistance value before reflow was 563 mΩ, the electrical resistance value at the first reflow was 653 mΩ, the electrical resistance value at the second reflow was 740 mΩ, and reflow. The electric resistance value of the third reflow was 797 mΩ, the electric resistance value of the fourth reflow was 842 mΩ, and the electric resistance value of the fifth reflow was 881 mΩ.

(Example 2)
Similar to Example 1 except that a conductive filler composed of filamentous nickel particles having a mode diameter of 31 μm, a cumulative distribution of 79%, a median diameter (D50) of 19 μm, and a maximum particle diameter (Dmax) of 62 μm was used. did.

When the electrical connectivity of the electromagnetic wave shielding film of Example 2 was evaluated, the initial electrical resistance value before reflow was 607 mΩ, the electrical resistance value at the first reflow was 658 mΩ, the electrical resistance value at the second reflow was 691 mΩ, and reflow. The electric resistance value of the third reflow was 711 mΩ, the electric resistance value of the fourth reflow was 726 mΩ, and the electric resistance value of the fifth reflow was 739 mΩ.

(Example 3)
Similar to Example 1 except that a conductive filler composed of filamentous nickel particles having a mode diameter of 23 μm, a cumulative distribution of 68%, a median diameter (D50) of 15 μm, and a maximum particle diameter (Dmax) of 88 μm was used. did.

When the electrical connectivity of the electromagnetic wave shielding film of Example 2 was evaluated, the initial electrical resistance value before reflow was 622 mΩ, the electrical resistance value at the first reflow was 741 mΩ, the electrical resistance value at the second reflow was 851 mΩ, and reflow. The electric resistance value of the third reflow was 925 mΩ, the electric resistance value of the fourth reflow was 984 mΩ, and the electric resistance value of the fifth reflow was 1036 mΩ.

(Example 4)
Similar to Example 1 except that a conductive filler composed of spike-shaped nickel particles having a mode diameter of 8 μm, a cumulative distribution of 37%, a median diameter (D50) of 10 μm, and a maximum particle diameter (Dmax) of 105 μm was used. did.

The initial electric resistance value before reflow is 1155 mΩ, the electric resistance value of the first reflow is 2089 mΩ, the electric resistance value of the second reflow is 2967 mΩ, the electric resistance value of the third reflow is 3255 mΩ, and the electric resistance value of the fourth reflow is 4066 mΩ. The electric resistance value at the 5th reflow was 4317 mΩ.

(Comparative Example 1)
The same as in Example 1 except that a conductive filler composed of spherical nickel particles having a mode diameter of 7 μm, a cumulative distribution of 66%, a median diameter (D50) of 6 μm, and a maximum particle diameter (Dmax) of 19 μm was used. .. The initial electrical resistance value before reflow was 7750 mΩ. The electrical resistance values of the first to fifth reflows were infinite (outside the measurement range).

(Comparative Example 2)
Conductivity made of dendrite-like silver-coated copper particles (Ag-Cu, manufactured by Mitsui Kinzoku Co., Ltd.) having a mode diameter of 17 μm, a cumulative distribution of 64%, a median diameter (D50) of 14 μm, and a maximum particle diameter (Dmax) of 52 μm. The procedure was the same as in Example 1 except that the filler was used. The electrical resistance value before reflow was infinite (outside the measurement range). Therefore, the electrical resistance value after reflow was not measured.

The evaluation results of each Example and Comparative Example are summarized in Table 1. The electromagnetic wave shielding films of Examples 1 to 4 using filament-shaped or spike-shaped nickel particles have lower electrical resistance before reflow and after reflow than the electromagnetic wave shielding film of Comparative Example 1 using spherical nickel particles. Also maintains low electrical resistance. Further, the electromagnetic wave shielding film of Comparative Example 2 using the dendrite-like silver-coated copper particles could not confirm the continuity even before the reflow.

The electromagnetic wave shielding film of the present disclosure can stably maintain an electrical connection with a printed wiring board without using an expensive material, and is useful as an electromagnetic wave shielding film for shielding a printed wiring board or the like.

100 Electromagnetic wave shield film 111 Shield layer 112 Conductive adhesive layer 113 Insulation protection layer 200 Printed wiring board 211 Base layer 212 Ground circuit 213 Insulation adhesive layer 214 Coverlay 300 Shield print wiring board

Claims (5)

A shield layer made of an aluminum film and a conductive adhesive layer are provided.
The conductive adhesive layer contains a thermosetting adhesive resin composition and a conductive filler composed of filamentous nickel particles, and is bonded under heating and pressure.
The nickel particles are
Median diameter (D50) is 5 μm or more, 30 μm or less,
Mode diameter is 3 μm or more, 50 μm or less,
Cumulative distribution in mode diameter is 35% or more,
The electromagnetic wave shield film. The conductive filler is
The electromagnetic wave shielding film according to claim 1, wherein the cumulative distribution in the mode diameter is 60% or more. The electromagnetic wave shielding film according to claim 1 or 2, wherein the conductive filler has a maximum particle size of 90 μm or less. The electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the conductive adhesive layer has a thickness equal to or less than the median diameter of the conductive filler. The conductive adhesive layer contains the conductive filler in an amount of 20% by mass or more and 50% by mass or less.
The electromagnetic wave shielding film according to any one of claims 1 to 4.

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