Electromagnetic wave shielding film

Abstract

The present invention provides an electromagnetic wave shielding film which has excellent economical efficiency, excellent bonding with a printed circuit board, can exert excellent shielding performance after being subjected to a high-heat environment, and has excellent connection stability between an electromagnetic wave shielding layer and a grounding circuit. The electromagnetic wave shielding film 1 includes an electromagnetic wave shielding layer 2 and a conductive adhesive layer 3 provided on one side of the electromagnetic wave shielding layer 2; the electromagnetic wave shielding layer 2 includes aluminum as a constituent material; the conductive adhesive layer 3 includes nickel particles as conductive particles, the average value of the roundness of the nickel particles is less than 0.85, and the 10% cumulative value of the roundness is less than 0.65.

Description

Technical Field

[0001] The present disclosure relates to an electromagnetic wave shielding film. Background Art

[0002] Conventionally, in portable devices such as smartphones and tablets, flexible printed circuits (FPCs) with electromagnetic wave shielding films attached are used to shield electromagnetic waves generated from the inside and electromagnetic waves intruding from the outside.

[0003] Electromagnetic wave shielding films are known to include, for example, an electromagnetic wave shielding layer including a metal film and a conductive adhesive layer including conductive particles. The conductive adhesive layer of the electromagnetic wave shielding film is overlapped with the insulating layer of the printed circuit board covering the circuit pattern, and hot pressing is performed to bond the electromagnetic wave shielding film to the printed circuit board to produce a shielded printed circuit board.

[0004] The insulating layer is provided with an opening for exposing the grounding circuit, and the electromagnetic wave shielding film is placed on the printed circuit board and hot pressed, so that the conductive adhesive layer flows and the opening is filled with the conductive adhesive. Thus, the electromagnetic wave shielding layer and the grounding circuit contained in the circuit pattern of the printed circuit board are electrically connected via the conductive adhesive, and the electromagnetic wave shielding film can exert its shielding performance.

[0005] After that, the components are mounted on the shielded printed wiring board through a solder reflow process. In the solder reflow process, the components are exposed to a high temperature of, for example, about 270°C.

[0006] In recent years, from the viewpoint of cost reduction, an electromagnetic wave shielding film using aluminum as an electromagnetic wave shielding layer has been known (for example, refer to Patent Documents 1 and 2).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent document 1: Japanese Patent Laid-Open No. 7-122883;

[0010] Patent document 2: International Publication No. 2017 / 164174. Summary of the invention

[0011] Technical problem to be solved by the invention

[0012] However, the combination of the electromagnetic wave shielding layer and the conductive particles using aluminum in the electromagnetic wave shielding film described in Patent Document 1 has the following problems: after passing through the above-mentioned solder reflow process, the on-resistance between the electromagnetic wave shielding layer and the grounding circuit increases, and the original shielding performance cannot be exerted. In addition, the combination of the electromagnetic wave shielding layer and the conductive particles using aluminum in the electromagnetic wave shielding film described in Patent Document 2 has the following problems: poor bonding with the printed circuit board, and after passing through the above-mentioned solder reflow process, the connection stability between the electromagnetic wave shielding layer and the grounding circuit cannot be obtained. Therefore, there is a need for an electromagnetic wave shielding film that has excellent bonding with a printed circuit board, can exert excellent shielding performance after being subjected to a high-heat environment, and has excellent connection stability between the electromagnetic wave shielding layer and the grounding circuit.

[0013] Therefore, the purpose of the present disclosure is to provide an electromagnetic wave shielding film that has excellent economic efficiency, excellent bonding with a printed wiring board, can exert excellent shielding performance after being exposed to a high-temperature environment, and has excellent connection stability between the electromagnetic wave shielding layer and the ground circuit.

[0014] Technical means to solve technical problems

[0015] The inventors of the present disclosure have conducted intensive discussions to achieve the above-mentioned purpose, and found that an electromagnetic wave shielding film using aluminum in an electromagnetic wave shielding layer and using specific nickel particles as conductive particles in a conductive adhesive layer can achieve excellent economic efficiency and excellent bonding with a printed circuit board, and can exert excellent shielding performance after being subjected to a high-temperature environment, and the connection stability between the electromagnetic wave shielding layer and the grounding circuit is excellent. The present disclosure was completed based on this discovery.

[0016] The present invention provides an electromagnetic wave shielding film, which includes an electromagnetic wave shielding layer and a conductive adhesive layer provided on one side of the electromagnetic wave shielding layer.

[0017] The electromagnetic wave shielding layer includes aluminum as a constituent material.

[0018] The conductive adhesive layer includes nickel particles as conductive particles, and the average value of the circularity of the nickel particles is 0.85 or less, and the 10% cumulative value of the circularity is 0.65 or less.

[0019] In the above-mentioned electromagnetic wave shielding film, aluminum, which is cheaper than silver or copper, is used as the constituent material of the electromagnetic wave shielding layer, so it is economically superior. The conductive particles in the conductive adhesive layer use nickel particles with an average roundness of less than 0.85 and a 10% cumulative value of the roundness of less than 0.65. The above-mentioned roundness is an index indicating the approximation of the two-dimensional shape of the nickel particles to the circle. The higher the two-dimensional shape is, the closer the circle is. The roundness of 1.0 indicates that its shape is a perfect circle. That is, the average roundness of the nickel particles is less than 0.85, indicating that the two-dimensional shape of the nickel particles is different from the perfect circle to a certain extent, and the 10% cumulative value of the roundness of the nickel particles is less than 0.65, indicating that the proportion of nickel particles with small roundness is more to a certain extent. By using the above nickel particles as conductive particles, in the above-mentioned electromagnetic wave shielding film, aluminum is used as the constituent material of the electromagnetic wave shielding layer, and the bonding property with the printed wiring board is excellent. After experiencing a high-temperature environment, it can exert excellent shielding performance, and the connection stability between the electromagnetic wave shielding layer and the grounding circuit is excellent.

[0020] Preferably, the nickel particles are in a filamentous shape.

[0021] It is preferable that the average aspect ratio of the nickel particles is 0.70 or less.

[0022] It is preferable that the 10% cumulative value of the aspect ratio of the nickel particles is 0.50 or less.

[0023] Preferably, the median diameter of the nickel particles is 1 to 30 μm.

[0024] It is preferred that the content of the nickel particles in the conductive adhesive layer is 2 to 80% by mass.

[0025] Effects of the Invention

[0026] The electromagnetic wave shielding film disclosed in the present invention has excellent economic efficiency and excellent bonding properties with a printed wiring board. It can exert excellent shielding performance after being exposed to a high-temperature environment, and has excellent connection stability between the electromagnetic wave shielding layer and the ground circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027]

Figure 1

[0028] [Electromagnetic wave shielding film]

[0029] The electromagnetic wave shielding film disclosed in the present invention comprises at least: an electromagnetic wave shielding layer, and a conductive adhesive layer provided on at least one side of the electromagnetic wave shielding layer. The electromagnetic wave shielding film may also include other layers other than the electromagnetic wave shielding layer and the conductive adhesive layer. As the other layer, an insulating layer may also be included on the opposite side of the electromagnetic wave shielding layer to the conductive adhesive layer.

[0030] An embodiment of the electromagnetic wave shielding film will be described below. Figure 1 It is a schematic cross-sectional view of one embodiment of the electromagnetic wave shielding film.

[0031] Figure 1 The electromagnetic wave shielding film 1 shown includes: an electromagnetic wave shielding layer 2, a conductive adhesive layer 3 disposed adjacent to one side of the electromagnetic wave shielding layer 2, and an insulating layer 4 disposed adjacent to the other side of the electromagnetic wave shielding layer 2. In other words, the electromagnetic wave shielding film 1 includes the conductive adhesive layer 3, the electromagnetic wave shielding layer 2, and the insulating layer 4 in sequence.

[0032] (Electromagnetic wave shielding layer)

[0033] The electromagnetic wave shielding layer includes aluminum as a constituent material. The electromagnetic wave shielding layer including aluminum as a constituent material can include: a metal layer composed of metals such as an aluminum layer (a layer composed of aluminum) or an alloy layer composed of an alloy of aluminum and other metals, and a layer formed on the surface of other layers (films, other metal layers, etc.) (a layer with metal plating applied), etc. In addition, there is no particular limitation on the method for forming the above-mentioned aluminum layer, the above-mentioned alloy layer and other metal layers, and for example, electrolysis, evaporation (such as vacuum evaporation), sputtering, chemical vapor deposition (CVD) method, metal organic growth (MO) method, plating, rolling processing, etc. can be listed. The electromagnetic wave shielding layer can be a single layer or a plurality of layers (for example, a layer with metal plating applied).

[0034] The thickness of the electromagnetic wave shielding layer is not particularly limited, but is preferably 0.01 μm or more, and more preferably 0.1 μm or more. If the thickness is 0.01 μm or more, the shielding performance is better. From the perspective of superior flexibility and superior transmission characteristics of high-frequency signals above 10 MHz and better electromagnetic wave shielding performance, the thickness is preferably 12 μm or less, more preferably 10 μm or less, and further preferably 3 μm or less. The thickness of the aluminum layer is preferably within the above range.

[0035] (Conductive adhesive layer)

[0036] The conductive adhesive layer has bonding properties and conductivity for bonding the electromagnetic wave shielding film to a printed wiring board, for example. The conductive adhesive layer is preferably formed adjacent to the electromagnetic wave shielding layer. The conductive adhesive layer may be a single layer or multiple layers.

[0037] The conductive adhesive layer includes nickel particles as conductive particles. The aluminum used in the electromagnetic wave shielding layer is easily oxidized and forms an oxide film on the surface, and the nickel particles can break through the oxide film due to the effects of their hardness, etc., and can stably maintain a good electrical connection. If other soft metal particles are used, even if they are in a shape with protrusions, it is difficult to break through the oxide film and it is difficult to obtain a good electrical connection. The above-mentioned nickel particles can be used only one type, or two or more types can be used within the scope of not damaging the purpose of the present disclosure.

[0038] The average value of the roundness of the nickel particles is 0.85 or less, preferably 0.84 or less, and more preferably 0.83 or less. The average value of the roundness is preferably small, and from the viewpoint of obtaining better conductivity in the thickness direction and the surface direction of the conductive adhesive layer, it is, for example, 0.60 or more, preferably 0.70 or more, and more preferably 0.75 or more.

[0039] The 10% cumulative value of the roundness of the nickel particles is 0.65 or less, preferably 0.64 or less, and more preferably 0.63 or less. The 10% cumulative value of the roundness is preferably small, and from the viewpoint of obtaining better conductivity in the thickness direction and the surface direction of the conductive adhesive layer, it is, for example, 0.40 or more, preferably 0.45 or more, and more preferably 0.50 or more.

[0040] The circularity is the value obtained by dividing the circumference of a circle having the same area as the projected image of the particle by the circumference of the projected image of the particle. The 10% cumulative value of the circularity is the value equivalent to 10% cumulative when the cumulative frequency is 100%. The various values ​​related to the circularity can be measured by the method described in the examples.

[0041] In the above-mentioned electromagnetic wave shielding film, aluminum, which is cheaper than silver and copper, is used as a constituent material of the electromagnetic wave shielding layer, thereby having excellent economic efficiency. In addition, as the conductive particles in the conductive adhesive layer, nickel particles having an average value of roundness of less than 0.85 and a 10% cumulative value of the above-mentioned roundness of less than 0.65 are used. The above-mentioned roundness is an index indicating the approximation of the projected image (two-dimensional shape) of the nickel particles to the circle. The higher the two-dimensional shape is, the closer the circle is. The roundness of 1.0 indicates that its shape is a perfect circle. That is, the average value of the roundness of the nickel particles is less than 0.85, indicating that the two-dimensional shape of the nickel particles is different from the perfect circle to a certain extent, and the 10% cumulative value of the roundness of the nickel particles is less than 0.65, indicating that the proportion of nickel particles with small roundness is more to a certain extent. By using the above nickel particles as conductive particles, in the above-mentioned electromagnetic wave shielding film, aluminum is used as a constituent material of the electromagnetic wave shielding layer, and the bonding property with the printed circuit board is excellent. After experiencing a high-temperature environment, it can exert excellent shielding performance, and the connection stability between the electromagnetic wave shielding layer and the grounding circuit is excellent.

[0042] The average aspect ratio of the nickel particles is preferably 0.70 or less, more preferably 0.69 or less. The average aspect ratio is, for example, 0.60 or more, preferably 0.65 or more.

[0043] The 10% cumulative value of the aspect ratio of the nickel particles is preferably 0.50 or less, more preferably 0.49 or less. The 10% cumulative value of the aspect ratio is, for example, 0.35 or more, preferably 0.40 or more.

[0044] The aspect ratio is the ratio of the length to the width (aspect ratio) of the circumscribed rectangle when the smallest rectangle when the particle pattern of the nickel particles in the projected image is surrounded by a rectangle is used as the circumscribed rectangle. The above average aspect ratio is less than 0.70, which means that in the above minimum rectangle, the length is longer to a certain extent relative to the width, and the 10% cumulative value of the above aspect ratio is less than 0.50, which means that the proportion of nickel particles with a small aspect ratio is larger to a certain extent. When the above nickel particles are used as conductive particles, in the conductive adhesive layer, each conductive particle extending in the thickness direction is in contact, so that the conductivity in the thickness direction is better. In addition, it is speculated that this is because in the conductive adhesive layer, the above nickel particles are also arranged in the surface direction, which results in an increase in the connection between the electromagnetic wave shielding layer and the grounding circuit, thereby being able to exert excellent shielding performance after experiencing a high heat environment, so that the resistance value is stable. The various values ​​related to the aspect ratio can be measured by the method described in the embodiment.

[0045] The shape of the nickel particles is preferably filamentous. The filamentous nickel particles are, for example, particles with nickel as the main component, in which 10 to 1000 primary particles are connected in a chain to form filamentous secondary particles. If the nickel particles are filamentous, the effect of this shape is that it is easier to break through the oxide film, and the connection stability after being exposed to a high heat environment is better.

[0046] The median diameter (D50) of the nickel particles is preferably 1 to 30 μm, more preferably 2 to 20 μm, and further preferably 3 to 13 μm. If the median diameter is 1 μm or more, the resistance value described below becomes lower and the shielding performance is better. If the median diameter is 30 μm or less (especially 13 μm or less), the nickel particles are more dispersed in the conductive adhesive layer, the bonding property with the printed wiring board is better, and the connection stability of the electromagnetic wave shielding layer and the grounding circuit is better after being subjected to a high heat environment. The median diameter is a circle equivalent diameter measured by a laser diffraction particle size analyzer.

[0047] The content ratio of nickel particles in the conductive adhesive layer is not particularly limited, and is preferably 2 to 60% by mass, more preferably 3 to 50% by mass, further preferably 4 to 40% by mass, further preferably 4.5 to 30% by mass, and particularly preferably 5 to 25% by mass, relative to the total amount of 100% by mass of the conductive adhesive layer. If the above content ratio is 2% by mass or more, the conductivity is better. In addition, even in the case of a large amount of compounding with a content ratio of 30% or more, the electromagnetic wave shielding film can still exhibit adhesion to the printed circuit board after experiencing a high heat environment. If the above content ratio is 60% by mass or less, the adhesive component can be fully contained, and the adhesion to the printed circuit board is better. In addition, even if the above content ratio is a small amount of compounding with a content ratio of 25% or less, the electromagnetic wave shielding film can exhibit excellent shielding performance and connection stability between the electromagnetic wave shielding layer and the grounding circuit after experiencing a high heat environment.

[0048] The conductive adhesive layer preferably contains a binder component that can function as an adhesive. Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray-curable compounds. The binder component may be used alone or in combination of two or more.

[0049] Examples of the thermoplastic resin include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (e.g., polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, acrylic resins, etc. The thermoplastic resins may be used alone or in combination of two or more.

[0050] The thermosetting resin may include a thermosetting resin (thermosetting resin) and a resin obtained by curing the thermosetting resin. Examples of the thermosetting resin include phenolic resins, epoxy resins, polyurethane resins, melamine resins, alkyd resins, and the like. The thermosetting resin may be used alone or in combination of two or more.

[0051] Examples of the epoxy resins include bisphenol epoxy resins, spiro epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, terpene epoxy resins, glycidyl ether epoxy resins, glycidyl amine epoxy resins, and (linear) phenolic epoxy resins.

[0052] Examples of the bisphenol epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, and tetrabromobisphenol A epoxy resins. Examples of the glycidyl ether epoxy resins include tris(glycidyloxyphenyl)methane and tetra(glycidyloxyphenyl)ethane. Examples of the glycidylamine epoxy resins include tetraglycidyldiaminodiphenylmethane. Examples of the (linear) novolac epoxy resins include cresol (linear) novolac epoxy resins, phenol (linear) novolac epoxy resins, α-naphthol (linear) novolac epoxy resins, and brominated phenol (linear) novolac epoxy resins.

[0053] The active energy ray-curable compound can include compounds that can be cured by irradiation with active energy rays (active energy ray-curable compounds) and compounds obtained by curing the active energy ray-curable compounds. The active energy ray-curable compound is not particularly limited, and examples thereof include polymerizable compounds containing one or more (preferably two or more) free radical reactive groups (e.g., (meth)acryloyl groups) in the molecule. The active energy ray-curable compound can be used alone or in combination of two or more.

[0054] The above-mentioned adhesive component is preferably a thermosetting resin. In this case, after the electromagnetic wave shielding film is arranged on the printed wiring board, the adhesive component can be cured by applying pressure and heat, and the bonding property is further improved.

[0055] When the binder component includes a thermosetting resin, a curing agent for promoting a thermosetting reaction may be included as a component constituting the binder component. The curing agent may be appropriately selected according to the type of the thermosetting resin. The curing agent may be used alone or in combination of two or more.

[0056] The content of the binder component in the conductive adhesive layer is not particularly limited, but is preferably 40 to 98% by mass, more preferably 50 to 97% by mass, further preferably 60 to 96% by mass, further preferably 70 to 95.5% by mass, and particularly preferably 75 to 95% by mass, relative to the total amount of 100% by mass of the conductive adhesive layer. If the content is 40% by mass or more, the bonding property to the printed wiring board is better. If the content is 98% by mass or less, the conductive particles can be fully contained.

[0057] The conductive adhesive layer may be a layer having isotropic conductivity or anisotropic conductivity as required, and preferably has anisotropic conductivity from the viewpoint of improving the transmission characteristics of high-frequency signals transmitted by the signal circuit of the printed wiring board.

[0058] In the range that does not damage the effect of the present disclosure, the above-mentioned conductive adhesive layer may contain other ingredients other than the above-mentioned components. The above-mentioned other ingredients can list well-known and even commonly used adhesive layer components. The above-mentioned other ingredients can, for example, list curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, colorants, leveling agents, coupling agents, ultraviolet absorbers, tackifying resins, anti-adhesion agents, etc. The above-mentioned other ingredients can be used only one, or two or more. Among all the conductive particles contained in the conductive adhesive layer, the proportion of nickel particles whose average value of roundness and 10% cumulative value are within the above range is preferably 90% by mass or more, more preferably 95% by mass or more, and further preferably 98% by mass or more.

[0059] The thickness of the conductive adhesive layer is preferably 3 to 20 μm, more preferably 5 to 15 μm. In order to make the conductive adhesive layer anisotropic, the thickness of the conductive adhesive layer is preferably less than the median diameter of the nickel particles. In this case, the electromagnetic wave shielding film and the printed wiring board are electrically connected well.

[0060] (Insulation layer)

[0061] The insulating layer has a function of protecting the conductive adhesive layer and / or the electromagnetic wave shielding layer in the electromagnetic wave shielding film.

[0062] The insulating layer preferably includes a binder component. Examples of the binder component include thermoplastic resins, thermosetting resins, and active energy ray-curable compounds. Examples of the thermoplastic resins, thermosetting resins, and active energy ray-curable compounds include those that can be included in the conductive adhesive layer. The binder component may be used alone or in combination of two or more.

[0063] The insulating layer may contain other components other than the binder component as long as the effects of the present disclosure are not impaired. Examples of the other components include curing agents, curing accelerators, plasticizers, flame retardants, defoamers, viscosity modifiers, antioxidants, diluents, anti-settling agents, fillers, colorants, levelers, coupling agents, ultraviolet absorbers, tackifying resins, anti-adhesion agents, etc. The other components may be used alone or in combination of two or more.

[0064] The above-mentioned insulating layer can be a single layer or multiple layers. When the above-mentioned insulating layer is multiple layers, for example, it can be a laminate of more than two layers with different physicochemical properties such as material, hardness or elastic modulus. For example, in a laminate of an outer layer with low hardness and an inner layer with high hardness, the outer layer has a cushioning effect, so the pressure applied to the electromagnetic wave shielding layer can be alleviated in the process of heating and pressurizing the electromagnetic wave shielding film on the printed circuit board. Therefore, it is possible to suppress the electromagnetic wave shielding layer from being destroyed due to the height difference provided on the printed circuit board.

[0065] The thickness of the insulating layer is not particularly limited and can be appropriately set as needed, preferably 1 to 20 μm, more preferably 2 to 15 μm, and further preferably 3 to 10 μm. If the thickness is 1 μm or more, the electromagnetic wave shielding layer and the conductive adhesive layer can be more fully protected. If the thickness is 20 μm or less, the softness and flexibility are excellent, and it is also economically advantageous.

[0066] The electromagnetic wave shielding film may also include a separator (peeling film) on the insulating layer side and / or the conductive adhesive layer side. The separator is laminated in a manner that allows it to be peeled off from the electromagnetic wave shielding film. The separator is an element for covering and protecting the insulating layer and the conductive adhesive layer, and is peeled off when the electromagnetic wave shielding film is used.

[0067] Examples of the separator include polyethylene terephthalate (PET) films, polyethylene films, polypropylene films, and plastic films and papers whose surfaces are coated with a release agent such as a fluorine-based release agent or a long-chain alkyl acrylate-based release agent.

[0068] The thickness of the separator is preferably 10 to 200 μm, more preferably 15 to 150 μm. When the thickness is 10 μm or more, the protective performance is better. When the thickness is 200 μm or less, the separator is easy to peel off during use.

[0069] The electromagnetic wave shielding film may further include an anchor coating layer formed between the insulating layer and the electromagnetic wave shielding layer. With the above structure, the bonding property between the electromagnetic wave shielding layer and the insulating layer is further improved.

[0070] The materials forming the above-mentioned adhesion-promoting coating layer include polyurethane resin, acrylic resin, core-shell composite resin with polyurethane resin as shell and acrylic resin as core, epoxy resin, polyimide resin, polyamide resin, melamine resin, phenol resin, urea-formaldehyde resin, blocked isocyanate obtained by reacting blocking agents such as phenol with polyisocyanate, polyvinyl alcohol, polyvinyl pyrrolidone, etc. The above-mentioned materials may be used alone or in combination of two or more.

[0071] The resistance value (initial resistance value) of the electromagnetic shielding film obtained by the following conductivity test is not particularly limited, but is preferably 500 mΩ or less, more preferably 400 mΩ or less, and further preferably less than 300 mΩ. When the initial resistance value is 500 mΩ or less, the electromagnetic shielding film and the ground circuit are well conductive.

[0072] [Conductivity test]

[0073] The following printed circuit board was used as the printed circuit board: two copper foil patterns simulating the ground circuit were formed on a base member composed of a polyimide film, and an insulating adhesive layer and a covering film composed of a polyimide film with a thickness of 25 μm were formed thereon. A circular opening with a diameter of 1 mm simulating the ground connection portion was formed on the covering film. Then, the electromagnetic wave shielding film and the printed circuit board were vacuumed for 60 seconds under the conditions of temperature: 170°C and pressure: 3.0 MPa by a pressing machine, and then heated and pressed for 180 seconds to join, and heated in an oven at 150°C for 60 minutes, and the resistance value between the two copper foil patterns was measured with a resistance meter, and it was used as the resistance value.

[0074] The resistance value (resistance value after reflow soldering) of the electromagnetic wave shielding film obtained by the conductivity test after the reflow soldering process of the temperature curve set to be exposed to hot air at 265°C for 5 seconds through 3 cycles is not particularly limited, and is preferably 1000mΩ or less, more preferably 700mΩ or less, and further preferably less than 500mΩ. If the above resistance value is 1000mΩ or less, the electromagnetic wave shielding film and the grounding circuit after being subjected to a high temperature environment are well connected. The above resistance value after reflow soldering is measured in the same manner as the conductivity test of the above initial resistance value for the electromagnetic wave shielding film after the above reflow soldering process through 3 cycles.

[0075] The bonding strength of the electromagnetic wave shielding film obtained by the following bonding test is not particularly limited, but is preferably 3.0 N / 10 mm or more, more preferably 3.5 N / 10 mm or more, and further preferably more than 4.0 N / 10 mm. If the bonding strength is 3.0 N / 10 mm or more, the bonding property with the printed wiring board after being exposed to a high temperature environment is excellent.

[0076] [Joinability test]

[0077] A polyimide film with a thickness of 25 μm is attached to the conductive adhesive layer of the electromagnetic wave shielding film, and a press machine is used to evacuate the film for 60 seconds at a temperature of 170°C and a pressure of 3.0 MPa, and then heated and pressed for 180 seconds for bonding. After that, a heat treatment is performed at 150°C for 60 minutes to prepare a test sample. Next, the test sample is cut into 10 mm widths, and a tensile tester is used to peel off the contact surface of the conductive adhesive layer and the polyimide film at a peeling speed of 50 mm / min and a peeling angle of 180°, thereby measuring the bonding strength, which is used as the bonding force.

[0078] The electromagnetic wave shielding film is preferably used for a printed wiring board, and is particularly preferably used for a flexible printed wiring board (FPC).

[0079] (Method for producing electromagnetic wave shielding film)

[0080] An embodiment of a method for producing the electromagnetic wave shielding film is described below. Figure 1 In the production process of the electromagnetic wave shielding film 1 shown, first, a laminate of the insulating layer 4 and the electromagnetic wave shielding layer 2 and a conductive adhesive layer 3 are separately produced. Thereafter, the separately produced laminate and conductive adhesive layer 3 are bonded together (lamination method).

[0081] When producing the laminate, the insulating layer 4 is formed, for example, by applying (coating) a resin composition for forming the insulating layer 4 onto a temporary substrate such as a release film or onto a substrate, and removing the solvent and / or partially curing the resin composition as required.

[0082] The resin composition may include, for example, a solvent in addition to the components included in the insulating layer. Examples of the solvent include toluene, acetone, methyl ethyl ketone, methanol, ethanol, propanol, dimethylformamide, etc. The solid content concentration of the resin composition may be appropriately set according to the thickness of the insulating layer to be formed.

[0083] The resin composition can be applied by a well-known coating method, for example, a coating machine such as a gravure roll coater, a reverse roll coater, an oiling roll coater, a lip coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, a direct coater, or a slit coater can be used.

[0084] Next, the electromagnetic shielding layer 2 is formed on the surface of the insulating layer 4 formed on the separator. The electromagnetic shielding layer 2 is preferably formed by evaporation or sputtering. The evaporation and sputtering methods can be well-known and commonly used methods. In this way, a laminate of the insulating layer 4 / electromagnetic shielding layer 2 is produced.

[0085] On the other hand, when the conductive adhesive 3 is prepared, the conductive adhesive layer 3 is formed, for example, by applying (coating) an adhesive composition for forming the conductive adhesive layer 3 onto a temporary substrate such as a release film or onto a substrate, and removing the solvent and / or partially curing the adhesive composition as required.

[0086] The adhesive composition may further include a solvent (solvent) in addition to the components contained in the conductive adhesive layer. The solvent may include those exemplified as solvents that may be contained in the resin composition. The solid content concentration of the adhesive composition may be appropriately set according to the thickness of the conductive adhesive layer to be formed.

[0087] The adhesive composition can be applied by a known coating method, for example, a coating machine used for coating the resin composition can be used.

[0088] Next, the exposed surface (the electromagnetic wave shielding layer 2 side) of the laminated body produced separately and the conductive adhesive layer 3 are bonded together to produce the electromagnetic wave shielding film 1 .

[0089] As another form other than the above-mentioned lamination method, the electromagnetic wave shielding film 1 can be manufactured by a method of sequentially laminating each layer (direct coating method). Figure 1 The electromagnetic wave shielding film 1 can be produced by applying (coating) an adhesive composition for forming the conductive adhesive layer 3 on the surface of the electromagnetic wave shielding layer 2 of the laminate, and, if necessary, performing desolvation and / or partial curing to form the conductive adhesive layer 3 .

[0090] The electromagnetic wave shielding film can be used to make a shielded printed circuit board. For example, by bonding the conductive adhesive layer of the electromagnetic wave shielding film to a printed circuit board (such as a cover film), a shielded printed circuit board having the electromagnetic wave shielding film bonded to the printed circuit board can be obtained. In the shielded printed circuit board, for example, the conductive adhesive layer can be thermally cured by subsequent heating and pressurization treatment. Example

[0091] An embodiment of the electromagnetic wave shielding film of the present disclosure will be described in further detail below based on examples, but the electromagnetic wave shielding film of the present disclosure is not limited to these examples.

[0092] Example 1

[0093] (Formation of insulating layer)

[0094] In order to make the solid content 20 mass %, 100 mass parts of bisphenol A epoxy resin (trade name "jER1256", manufactured by Mitsubishi Chemical Corporation) and 0.1 mass parts of curing agent (trade name "ST14", manufactured by Mitsubishi Chemical Corporation) were blended into toluene, and stirred and mixed to prepare a resin composition. The obtained resin composition was applied to the release-treated surface of a polyethylene terephthalate (PET) film with a release treatment on the surface, and the solvent was removed by heating, thereby forming an insulating layer (thickness 6 μm).

[0095] (Formation of electromagnetic wave shielding layer)

[0096] An aluminum layer with a thickness of 0.1 μm was formed on the surface of the obtained insulating layer by a vapor deposition method, thereby obtaining a laminate of the insulating layer and the electromagnetic wave shielding layer. Specifically, a PET film with an insulating layer formed thereon was placed in a batch vacuum vapor deposition apparatus (trade name "EBH-800", manufactured by ULVAC Co., Ltd.), and the vacuum degree was adjusted to 5×10 -1 Pa or less, aluminum was deposited by magnetron sputtering (DC power output: 3.0 kW) to a thickness of 0.1 μm.

[0097] (Formation of Conductive Adhesive Layer)

[0098] In the case of making the solid content 20 mass %, 95 mass parts of bisphenol A epoxy resin (trade name "jER1256", manufactured by Mitsubishi Chemical Corporation), 0.1 mass parts of curing agent (trade name "ST14", manufactured by Mitsubishi Chemical Corporation), and 5 mass parts of conductive particles consisting of filamentous nickel particles (No.1) were mixed into toluene, and stirred and mixed to prepare an adhesive composition. The properties of the conductive particles used are shown in Table 2. The obtained adhesive composition was applied to the release-treated surface of a PET film with a release treatment on the surface, and the solvent was removed by heating, thereby forming a conductive adhesive layer (thickness 12 μm).

[0099] (Production of electromagnetic wave shielding film)

[0100] The obtained conductive adhesive layer was bonded to the electromagnetic wave shielding layer surface of the laminate composed of the insulating layer and the electromagnetic wave shielding layer to prepare the electromagnetic wave shielding film of Example 1 having a structure of conductive adhesive layer / electromagnetic wave shielding layer / insulating layer.

[0101] Examples 2 to 4 and Comparative Examples 1 to 8

[0102] An electromagnetic shielding film was produced in the same manner as in Example 1 except that the type and content ratio of the nickel particles in the conductive adhesive layer were changed as shown in Table 1. Table 2 shows the properties of the conductive particles used in each example.

[0103] (evaluate)

[0104] The electromagnetic wave shielding films obtained in Examples and Comparative Examples were evaluated as follows.

[0105] (1) Roundness, aspect ratio, and median diameter

[0106] The roundness, aspect ratio, and median diameter of the conductive particles were measured using a flow particle image analyzer (trade name "FPIA-3000", manufactured by Sysmex Co., Ltd.). Specifically, a 10x objective lens was used in an optical system of bright field, and the conductive particle dispersion with a concentration adjusted to 4000 to 20000 / μl was measured using the LPF measurement mode. The conductive particle dispersion was prepared by adding 0.1 to 0.5 ml of a surfactant to an aqueous solution of sodium hexametaphosphate adjusted to 0.2% by mass, and adding 0.1 ± 0.01 g of conductive particles as a measurement sample. The suspension in which the conductive particles were dispersed was dispersed in an ultrasonic disperser for 1 to 3 minutes and provided for measurement. The average value of the roundness of the conductive particles obtained, the 10% cumulative value of the roundness, the average aspect ratio, the 10% cumulative value of the aspect ratio, and the median diameter are shown in Table 2, respectively.

[0107] (2) Conductivity test

[0108] The electromagnetic wave shielding film prepared in the embodiment and the comparative example is laminated on the printed circuit board for evaluation, and then a press is used to evacuate for 60 seconds at a temperature of 170°C and a pressure of 3.0 MPa, and then heated and pressed for 180 seconds for bonding. The PET film on the insulating layer is then peeled off, and heated in an oven at 150°C for 60 minutes to prepare an evaluation substrate. The printed circuit board contains two copper foil patterns that are spaced apart and extend in parallel, and an insulating protective layer (thickness: 25 μm) composed of polyimide covering the copper foil patterns, and an opening (diameter: 1 mm) is provided in the insulating protective layer to expose each copper foil pattern. When the conductive adhesive layer of the electromagnetic wave shielding film and the printed circuit board are overlapped, the opening is completely covered by the electromagnetic wave shielding film. Then, the resistance value between the two copper foil patterns of the obtained evaluation substrate is measured using a resistance meter, and it is used as the resistance value (initial resistance value) between the printed circuit board and the electromagnetic wave shielding layer before reflow soldering.

[0109] Next, a heat treatment assuming a reflow process was performed, and the resistance value after reflow (resistance value after reflow) was measured. The heat treatment and resistance value measurement were repeated three times. The heat treatment was assumed to use lead-free solder, and the set temperature profile was such that the electromagnetic wave shielding film in the evaluation substrate was exposed to 265°C for 5 seconds. Then, the initial resistance value and the resistance value after reflow were evaluated based on the following evaluation criteria.

[0110] (Initial resistance value)

[0111] ○ (good): less than 300mΩ

[0112] △ (acceptable): 300mΩ or more and 500mΩ or less

[0113] × (Defective): More than 500mΩ

[0114] (Resistance value after reflow soldering)

[0115] ○ (good): less than 500mΩ

[0116] △ (acceptable): 500mΩ or more and 1000mΩ or less

[0117] × (Defective): Exceeds 1000 mΩ.

[0118] (3) Bonding

[0119] A polyimide film with a thickness of 25 μm (trade name "Kapton 100EN", manufactured by DU PONT-TORAY Co., Ltd.) was bonded to the conductive adhesive layer of the electromagnetic wave shielding film produced in the examples and comparative examples, and a press was used to evacuate the film for 60 seconds at a temperature of 170°C and a pressure of 3.0 MPa, and then heated and pressed for 180 seconds for bonding. After that, a heat treatment was performed in an oven at 150°C for 60 minutes to produce a test sample. Next, in order to measure the bonding strength, the test sample was cut into a 10 mm width, and a tensile tester (trade name "AGS-X50N", manufactured by Shimadzu Corporation) was used to peel off the contact surface of the conductive adhesive layer and the polyimide film at a peeling speed of 50 mm / min and a peeling angle of 180°, thereby measuring the bonding strength.

[0120] ○ (good): more than 4.0N / 10mm

[0121] △ (allowable): 3.0N / 10mm or more 4.0N / 10mm or less

[0122] × (poor): less than 3.0N / 10mm.

[0123]

[0124]

[0125] The electromagnetic wave shielding film of the embodiment has excellent bonding, low initial resistance, and low resistance after reflow soldering when using an aluminum layer as the electromagnetic wave shielding layer. Therefore, the electromagnetic wave shielding film of the embodiment is judged to be economically superior, and has excellent bonding with the printed circuit board. After being subjected to a high-temperature environment, it can exert excellent shielding performance, and the connection stability between the electromagnetic wave shielding layer and the grounding circuit is excellent. On the other hand, when nickel particles whose average value and 10% cumulative value of roundness exceed specific values ​​are used as conductive particles in the conductive adhesive layer (comparative example), even if the content ratio of the conductive particles is changed, both excellent bonding and excellent resistance after reflow soldering cannot be achieved.

[0126] Number Description

[0127] 1Electromagnetic wave shielding film

[0128] 2Electromagnetic wave shielding layer

[0129] 3. Conductive adhesive layer

[0130] 4 Insulation layer

Claims

1. An electromagnetic wave shielding film, characterized in that: It comprises an electromagnetic wave shielding layer and a conductive adhesive layer provided on one side of the electromagnetic wave shielding layer; The electromagnetic wave shielding layer includes aluminum as a constituent material, The conductive adhesive layer includes nickel particles as conductive particles, the average value of the roundness of the nickel particles is less than 0.85, and the 10% cumulative value of the roundness is less than 0.65, The average aspect ratio of the nickel particles is less than 0.70, The 10% cumulative value of the aspect ratio of the nickel particles is less than 0.50, The content ratio of the nickel particles in the conductive adhesive layer is 2 to 60% by mass.

2. The electromagnetic wave shielding film according to claim 1, characterized in that: The nickel particles are in the shape of wires.

3. The electromagnetic wave shielding film according to claim 1, characterized in that: The median diameter of the nickel particles is 1 to 30 μm.

4. The electromagnetic wave shielding film according to claim 1, characterized in that: The content ratio of the nickel particles in the conductive adhesive layer is 4.5 to 30% by mass.

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