Electromagnetic wave shielding sheet, printed wiring board with electromagnetic wave shielding sheet, and electronic device

Abstract

To provide: an electromagnetic wave shielding sheet which is excellent in transmission characteristics, shielding properties and degassing properties, and in which peeling does not occur during punching: and a printed wiring board with the electromagnetic wave shielding sheet.SOLUTION: An electromagnetic wave shielding sheet comprises a protective layer, a conductive layer and an adhesive layer laminated in this order, where the conductive layer contains a metal filler and a binder. In a peeling test conducted at a peeling angle of 180° and a peeling speed of 300 mm / min between the protective layer and the adhesive layer, the peeling strength when cohesive failure occurs in the conductive layer is 50 to 2500 [gf / 25 mm], and the cohesive failure rate in the peeling test is 10% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electromagnetic shielding sheet, a printed wiring board with an electromagnetic shielding sheet, and an electronic device.

Background Art

[0002] Various electronic devices such as mobile terminals, PCs, and servers incorporate substrates such as printed wiring boards. These substrates are provided with an electromagnetic shielding structure to prevent malfunction due to external magnetic fields and radio waves, and also to reduce unnecessary radiation from electrical signals.

[0003] With the high-speed transmission of transmission signals, printed wiring boards with electromagnetic shielding sheets are required to have electromagnetic shielding properties (hereinafter referred to as high-frequency shielding properties) corresponding to high-frequency noise and to reduce transmission losses (hereinafter sometimes referred to as transmission characteristics) in the high-frequency region. Patent Document 1 discloses a shielding film having a metal layer with a layer thickness of 0.5 to 12 μm and an anisotropic conductive adhesive layer in a laminated state. And it is described that with this configuration, electric field waves, magnetic field waves, and electromagnetic waves traveling from one surface side to the other surface side of the electromagnetic shielding sheet are well shielded and transmission losses are reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in an electromagnetic shielding printed wiring board with an electromagnetic shielding sheet using a metal layer attached to a printed wiring board, when heat treatment such as solder reflow is performed, lifting occurs between layers due to volatile components generated from the inside of the printed wiring board, resulting in problems such as appearance defects and connection failures due to foaming and the like. This is because outgassing such as water vapor generated from the printed wiring board stays in the dense metal layer of the electromagnetic shielding sheet, and the electromagnetic shielding sheet is required to have permeability to outgassing. (Hereinafter, gas permeability)

[0006] On the other hand, when the electromagnetic shielding sheet is used, it may be punched into a desired size and shape. In that case, there is a punching method in which the electromagnetic shielding sheet is bonded to a carrier tape, punched, and after being attached to a printed wiring board or the like, the carrier tape is peeled off. In this method, when the carrier tape is peeled off, peeling may occur not at the adhesion interface between the carrier tape and the electromagnetic shielding sheet, but inside the electromagnetic shielding sheet. (Hereinafter, carrier punching suitability)

[0007] An object of the present invention is to provide an electromagnetic shielding sheet that does not peel during punching and is excellent in transmission characteristics, shielding properties, and gas permeability, and a printed wiring board with an electromagnetic shielding sheet.

Means for Solving the Problems

[0008] As a result of intensive studies by the present inventors, it has been found that the problems of the present invention can be solved in the following aspects, and the present invention has been completed. [1]: An electromagnetic shielding sheet in which a protective layer, a conductive layer, and an adhesive layer are laminated in this order, wherein the conductive layer contains a metal filler and a binder, and a peeling test is performed at a peeling angle of 180° and a peeling speed of 300 mm / min between the protective layer and the adhesive layer, and the peeling force when the conductive layer undergoes cohesive failure is 50 to 2500 [gf / 25 mm], and in the peeling test, the cohesive failure rate is 10% or more. [2]: The electromagnetic shielding sheet according to [1], wherein the conductivity of the conductive layer is 2.4×106 to 3.0×107 [S / m]. [3]: The electromagnetic shielding sheet according to [1], wherein the surface resistivity of the conductive layer is 4.0×10-3 to 2.0×10-1 [Ω / sq]. [4]: The electromagnetic shielding sheet according to [1], wherein, when the cross-sectional area of the conductive layer is taken as 100 in the cross-section of the electromagnetic shielding sheet after heat-pressing at 170 °C, 2 MPa for 30 minutes, the area occupied by the metal filler is 23 to 95. [5]: The electromagnetic shielding sheet according to [1], wherein the thickness of the conductive layer in the cross-section of the electromagnetic shielding sheet after heat-pressing at 170 °C, 2 MPa for 30 minutes is 1 to 12 μm. [6]: The electromagnetic shielding sheet according to [1], wherein the metal filler includes a flaky metal filler, and the average aspect ratio of the flaky metal filler in the cross-section of the conductive layer after heat-pressing the electromagnetic shielding sheet at 170 °C, 2 MPa for 30 minutes is 10 to 70. [7]: The electromagnetic shielding sheet according to [1], wherein the metal filler includes silver-coated copper powder, and in the cross-section of the conductive layer after heat-pressing the electromagnetic shielding sheet at 170 °C, 2 MPa for 30 minutes, the mass ratio of the silver element is 3% or more and 25% or less when the total mass of the copper and silver elements by energy dispersive X-ray analysis is 100%. [8]: A printed wiring board with an electromagnetic shielding sheet, comprising the electromagnetic shielding sheet according to [1] to [7]. [9]: An electronic device, comprising the printed wiring board with an electromagnetic shielding sheet according to [8].

Advantages of the Invention

[0009] According to the present invention, it is possible to provide an electromagnetic shielding sheet that does not peel during punching, and has excellent transmission characteristics, shielding properties, and gas permeability, and a printed wiring board with an electromagnetic shielding sheet.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0011] <Electromagnetic wave shielding sheet> The electromagnetic wave shielding sheet of the present invention has a protective layer, a conductive layer, and an adhesive layer in this order. The electromagnetic wave shielding sheet forms an electromagnetic wave shielding layer by being attached to an adherend through the adhesive layer by heat pressing, and shields and reflects electromagnetic waves on the attached surface. The peel strength (hereinafter sometimes referred to as peel strength) of the peel test at a peel angle of 180° and a peel speed of 300 mm / min between the protective layer and the adhesive layer of the electromagnetic wave shielding sheet is 50 to 2500 [gf / 25 mm]. The peel strength is preferably 100 to 2500 [gf / 25 mm], more preferably 180 to 2500 [gf / 25 mm].

[0012] Further, the electromagnetic wave shielding sheet of the present invention is characterized in that the cohesive failure rate is 10% or more. The cohesive failure rate is the ratio of the area of the cohesive failure portion of the conductive layer to the entire area of the peel surface in the peel test for measuring the above-mentioned peel strength. The cohesive failure rate is preferably 10% or more, more preferably 40% or more, and even more preferably 70% or more.

[0013] By setting the peel strength and the cohesive failure rate within the above ranges, the interfaces of the protective layer / conductive layer and the conductive layer / adhesive layer can be strongly adhered, and the cohesive force of the conductive layer can also be maintained at a high level, so that the carrier punching suitability can be set at a suitable level.

[0014] As a method for setting the peel strength within a desired range, for example, there are methods such as appropriately selecting the types of resins contained in the conductive layer, the protective layer, and the adhesive layer, or adjusting the amount of metal filler contained in the conductive layer. Details will be described later.

[0015] As a method for improving the cohesive failure rate, the type of binder in the conductive layer and the shape and content of the metal filler are adjusted. Examples include methods for increasing the peel strength of the protective layer and the adhesive layer. Details of each method will be described later. <Conductive layer>

[0016] Next, the conductive layer used in the present invention will be described. The conductive layer used in the present invention contains a metal filler and a binder, and the binder preferably contains at least a resin. By containing a metal filler and a resin in the conductive layer, the gas permeability can be improved.

[0017] Preferable examples of the resin include thermoplastic resins or curable resins. The curable resin is preferably a thermosetting resin or a photocurable resin, and more preferably a thermosetting resin. A thermoplastic resin refers to a resin that softens when heated to a temperature equal to or higher than its glass transition temperature or melting point, and a thermosetting resin refers to a resin that crosslinks when heated to form a three-dimensional network structure of polymers and hardens and cannot return to its original state. There are types that cure with a thermosetting resin alone and types that cure by using a thermosetting resin and a curing agent in combination.

[0018] When a thermoplastic resin is used as the resin of the binder, the contained thermoplastic resin exists in a solid state, melts during hot pressing with an adherend such as an FPC, and solidifies again after cooling, thereby obtaining a desired adhesive strength. When a thermosetting resin is used as the resin of the binder, the contained thermosetting resin and curing agent exist in an uncured or semi-cured state (B-stage), and cure by hot pressing or the like with an adherend such as an FPC (C-stage), thereby obtaining a desired adhesive strength. Among these, it is preferable to use a thermosetting resin and a curing agent as the binder component, and a semi-cured state after using the thermosetting resin and the curing agent is more preferable. The method of semi-curing is not particularly limited, and examples include a method of applying heat to such an extent that the curing agent does not completely react, a method of using a plurality of curing agents having different reaction temperatures, and a method of using a plurality of curing agents having different reaction times. Among these, a method of using a plurality of curing agents having different reaction temperatures is preferable. That is, in addition to the first curing agent in which the curing reaction proceeds during C-stage formation, it is preferable to include a second curing agent in which the curing reaction proceeds during B-stage formation. By these, the bonding between the metal fillers becomes strong, the peeling force is improved, and the suitability for carrier punching is improved.

[0019] Examples of the thermoplastic resin include polyolefin resins, vinyl resins, styrene-acrylic resins, diene resins, terpene resins, petroleum resins, cellulose resins, polyamide resins, polyurethane resins, polyester resins, polycarbonate resins, polyimide resins, liquid crystal polymers, fluororesins, and the like.

[0020] The thermosetting resin may be a resin having one or more functional groups that can be used for a crosslinking reaction by heating, for example, a hydroxyl group, a phenolic hydroxyl group, a methoxymethyl group, a carboxyl group, an amino group, an epoxy group, an oxetanyl group, an oxazoline group, an oxazine group, an aziridine group, a thiol group, an isocyanate group, a blocked isocyanate group, a blocked carboxyl group, a silanol group, etc. in one molecule, and preferably contains a carboxyl group or a phenolic hydroxyl group.

[0021] The total of the acid value and the phenolic hydroxyl value of the thermosetting resin is preferably 3 to 100 mgKOH / g, more preferably 3 to 70 mgKOH / g, and even more preferably 5 to 40 mgKOH / g. By setting the total of the acid value and the phenolic hydroxyl value of the thermosetting resin within this range, the bonding between the metal fillers becomes strong, the peeling force is improved, and the suitability for carrier punching is improved.

[0022] Preferable examples of the thermosetting resin include acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane resin, epoxy resin, oxetane resin, phenoxy resin, polyimide resin, polyamide resin, phenolic resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzoxazine resin, silicone resin, fluororesin, etc. Among these, from the viewpoints of dispersion stability of the metal filler and adhesion strength, polyurethane resin, polyurethane-urea resin, addition-type ester resin, epoxy compound, phenoxy resin, polyimide resin, polyamide resin, piperazine polyamide resin, polyamideimide resin are preferable. The thermosetting resin can be used alone or in combination of two or more kinds.

[0023] The weight-average molecular weight of the thermosetting resin is preferably 20,000 to 300,000, more preferably 50,000 to 300,000, and even more preferably 100,000 to 300,000. By setting the weight-average molecular weight of the thermosetting resin within this range, the bonding between the metal fillers becomes strong, the peeling force is improved, and the suitability for carrier punching is improved.

[0024] In addition, the thermosetting resin in the present invention preferably contains, in addition to the above resins, a so-called "hardening agent" such as a resin or a low-molecular compound that reacts with the above functional groups to form a chemical crosslink as necessary.

[0025] The hardening agent only needs to have two or more functional groups capable of reacting with the functional groups of the thermosetting resin and is not particularly limited. As an example of the hardening agent, epoxy compound, acid anhydride group-containing compound, isocyanate compound, aziridine compound, amine compound, phenol compound, organometallic compound (metal chelate compound), polyol compound, melamine compound, silane-based compound, carbodiimide-based compound, phenol compound, benzoxazine compound, maleimide compound, β-hydroxyalkylamide group-containing compound can be exemplified. The hardening agent can be used alone or in combination of two or more kinds. Note that the hardening agent may be a low-molecular compound or a high-molecular compound, but it is a compound different from the above-described thermosetting resin.

[0026] The photocurable resin may be any resin having one or more unsaturated bonds that cause a crosslinking reaction upon exposure to light. Examples thereof include acrylic resins, maleic acid resins, polybutadiene-based resins, polyester resins, polyurethane resins, epoxy resins, oxetane resins, phenoxy resins, polyimide resins, polyamide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, fluorine resins, and the like.

[0027] The surface resistivity of the conductive layer is preferably 4.0×10 -3 ~2.0×10 -1 [Ω / □], and more preferably 4.0×10 -3 ~1.0×10 -1 [Ω / □]. By setting the surface resistivity of the conductive layer within this range, good high-frequency shielding performance can be achieved.

[0028] The surface resistivity of the conductive layer in the present invention is obtained by multiplying the resistance value measured using a four-probe probe of "Loresta GP" manufactured by Mitsubishi Chemical Corporation in accordance with JIS K7194-1994 by a predetermined constant. Specifically, four conductive bumps linearly provided at 5 mm intervals are inserted from the central portion of the adhesive layer of the electromagnetic wave shielding sheet (a rectangular sample piece of 80 mm×50 mm) of the present invention until they reach the conductive layer. The positions of the four conductive bumps are parallel to the long side of the sample piece. A current is passed between the two outer points of the four conductive bumps, the voltage between the two inner points is measured, and the resistance value = voltage / current is obtained. Then, the value obtained by multiplying the measured value by the constant "4.239" is defined as the "surface resistivity".

[0029] The conductivity of the conductive layer is preferably 2.4×10 6 ~3.0×10 7 [S / m], and more preferably 5.0×10 6 ~3.0×10 7 [S / m]. By setting the conductivity of the conductive layer within this range, transmission loss during high-speed transmission can be suppressed.

[0030] The conductivity of the conductive layer in the present invention is determined from the thickness t (μm) of the conductive layer and the surface resistivity described above. Details will be described in the examples.

[0031] As a method for setting the conductivity within a desired range, for example, a method of containing a suitable metal filler described later in a suitable amount described later to form a good conductive path can be mentioned. As a method for setting the surface resistivity within a desired range, in addition to those similar to the conductivity, a method of increasing the thickness of the conductive layer can be mentioned.

[0032] Examples of the metal filler include metal powders such as gold, silver, copper, and nickel, alloy powders such as solder, silver-coated copper powder (silver-coated copper powder), metal-plated glass fibers, and carbon fillers. Among them, silver powder and silver-coated copper powder with high conductivity are preferred. The amount of copper or silver elements in the conductive layer can be evaluated by observing the cross-section of the electromagnetic shielding sheet. In the cross-section, the ratio of the mass of silver element when the total mass of copper and silver elements by energy dispersive X-ray analysis is 100% is preferably 3% to 25%, and more preferably 6 to 15%. By setting it within this range, while suppressing the transmission loss during high-speed transmission and making the high-frequency shielding property good, the cost can be reduced by increasing the proportion of copper, which is cheaper than silver. As a method for controlling the amount of the silver element within a desired range, for example, when producing silver-coated copper powder, the amount of silver coating is controlled.

[0033] The shape of the metal filler is not limited as long as the desired conductivity can be obtained in the conductive layer, and two or more types of metal fillers with different shapes may be mixed. For example, spherical, flake-like (including leaf-like particles described later), dendritic, plate-like, needle-like, rod-like, and grape-like shapes can be mentioned, but flake-like is preferred from the viewpoint of improving conductivity and increasing the aggregation breakdown rate. The flake-like particles shall also include leaf-like particles having a plurality of cuts at the outer edge (for example, particles obtained by flattening dendritic particles).

[0034] The average aspect ratio ([major axis (μm)] / [thickness (μm)]) of the flaky metal filler on the cut surface of the conductive layer after heat-pressing the electromagnetic wave shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes is preferably in the range of 10 to 70, and more preferably in the range of 15 to 60. By setting the aspect ratio of the flaky particles within this range, it is possible to achieve high-dimensional compatibility between the suppression effect of transmission loss during high-speed transmission, high-frequency shielding performance, and carrier punching suitability.

[0035] The average particle size of the metal filler is preferably 1 to 100 μm, more preferably 3 to 50 μm, and even more preferably 5 to 20 μm. By setting it within this range, while making the suppression effect of transmission loss during high-speed transmission and high-frequency shielding performance good, the flexibility of the printed wiring board with the electromagnetic wave shielding sheet can be improved.

[0036] The content of the metal filler is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 90% or more in 100% by mass of the solid content of the conductive layer. Also, it is preferably 95% by mass or less. By setting the content of the metal filler to 75% by mass or more, the aggregation breakdown rate is improved, and by setting it to 95% by mass or less, the peel force is improved.

[0037] When the area of the conductive layer on the cut surface after heat-pressing the electromagnetic wave shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes is taken as 100%, the area occupied by the metal filler is preferably 23 to 95%, more preferably 30 to 95%, and even more preferably 45 to 95%. By setting it within these ranges, the suppression effect of transmission loss during high-speed transmission and high-frequency shielding performance can be made good.

[0038] The thickness of the conductive layer on the cut surface after heat-pressing the electromagnetic wave shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes is preferably 1 to 12 μm, and more preferably 1 to 8 μm. By setting the above thickness to 1 μm or more, a conductive layer with high shielding performance can be obtained. Also, by setting the thickness to 12 μm or less, the flexibility of the printed wiring board with the electromagnetic wave shielding sheet becomes good.​ <Protective layer> The protective layer preferably contains at least resin. The resin can be the same resin as the aforementioned conductive layer, and it is preferable to use a thermosetting resin in combination with a curing agent. Also, the protective layer may have a laminated structure of two or more layers. By setting the total proportion of the resin and the curing agent in the protective layer to 50% or more, the peel strength and the cohesive failure rate of the protective layer are improved, and the suitability for carrier punching is improved.

[0039] The thickness of the protective layer at the cut surface after heat and pressure bonding the electromagnetic shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes can be appropriately designed according to the application, but it is preferably in the range of 0.5 μm to 25 μm, and more preferably 2 μm to 10 μm. When the thickness of the protective layer is 0.5 μm or more, sufficient protection is achieved. Also, when it is 25 μm or less, the flexibility of the printed wiring board with the electromagnetic shielding sheet is improved.

[0040] In the protective layer, a silane coupling agent, an antioxidant, a pigment, a dye, a tackifier resin, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, etc. may be added as necessary. <Adhesive layer>

[0041] The adhesive layer is located on one surface of the electromagnetic shielding sheet and is responsible for adhering to the printed wiring board described later. The adhesive layer preferably contains at least resin. The resin can be the same resin as the aforementioned conductive layer, and it is preferable to use a thermosetting resin in combination with a curing agent. From the perspective of transmission loss, materials with low dielectric constant and low dielectric tangent are preferable for the resin and the curing agent, and from the perspective of characteristic impedance, materials with low dielectric constant are preferable. For example, structures containing many fluorine atoms or hydrocarbons with a small polarizability, or liquid crystal alignment or crystal alignment materials that fix dipoles are preferable. Similar to the protective layer, by setting the total proportion of the resin and the curing agent in the adhesive layer to 50% or more, the peel strength and the cohesive failure rate are improved, and the suitability for carrier punching is improved.

[0042] After heat - press bonding the electromagnetic shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes, the thickness of the adhesive layer at the cut surface can be appropriately designed according to the application, but it is preferably in the range of 0.5 μm to 25 μm, more preferably 2 μm to 10 μm. By setting the thickness of the adhesive layer to 0.5 μm or more, the adhesive force to the printed wiring board can be increased. Also, by setting it to 25 μm or less, the flexibility of the printed wiring board with the electromagnetic shielding sheet becomes good. The flexibility of the printed wiring board becomes good.

[0043] The adhesive layer may be insulating or conductive. In the case of making it conductive, the metal filler exemplified in the conductive layer may be further contained in the adhesive composition forming the adhesive layer. Also, fine particles of conductive polymers such as polyaniline and polyacetylene may be used. When the adhesive layer is made conductive, it may be isotropically conductive or anisotropically conductive. Note that isotropic conductivity means that the adhesive layer has conductivity in both its thickness direction and surface direction, and anisotropic conductivity means that the adhesive layer has conductivity substantially only in its thickness direction. From the viewpoints of improving the transmission characteristics in the high - frequency band and cost reduction, it is preferable to make it anisotropically conductive.

[0044] The anisotropic conductive adhesive layer contains a resin and a metal filler, and can be realized by setting the content and size of the metal filler within the ranges described below. The content of the metal filler can be appropriately designed, but it is preferably 10 to 45 mass% with respect to 100 mass% of the adhesive layer, more preferably 15 to 40 mass%, and even more preferably 20 to 30 mass%. When the thickness of the formed adhesive layer is taken as the reference (100), the average particle diameter D50 of the metal filler is preferably about 100 to 300. By containing 10 to 45 mass% of the conductive filler with the average particle diameter D50, an anisotropic conductive adhesive layer rather than an isotropic one can be formed. The shape of the metal filler used is particularly preferably spherical or dendritic, which is easy to obtain anisotropic conductivity.

[0045] In the adhesive layer, a silane coupling agent, a rust preventive, a reducing agent, an antioxidant, a pigment, a dye, a tackifier resin, a plasticizer, an ultraviolet absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, etc. may be added as necessary. <Method for manufacturing an electromagnetic shielding sheet>

[0046] Hereinafter, an example of the manufacturing method of this sheet will be described. However, the manufacturing method of the present invention is not limited to the following manufacturing method. This sheet has a step of forming a conductive layer, a step of forming a protective layer, and a step of forming an adhesive layer.

[0047] <Step of forming a conductive layer> Prepare a metal filler-containing composition used for forming the conductive layer. Specifically, a binder, a metal filler, and a solvent as necessary are mixed and stirred to obtain a metal filler-containing composition. For stirring, known stirring devices such as a dispermat and a homogenizer can be used. After preparing the metal filler-containing composition, the conductive layer can be formed by coating the metal filler-containing composition on a release sheet and drying it. Examples of the coating method include a gravure coating method, a kiss coating method, a die coating method, a lip coating method, a comma coating method, a blade coating method, a roll coating method, a knife coating method, a spray coating method, a bar coating method, a spin coating method, and a dip coating method. For the drying process, known drying devices such as a hot air dryer and an infrared heater can be used. Also, a sheet-like conductive layer may be formed using an extrusion molding machine such as a T-die.

[0048] <Step of forming a protective layer> The protective layer can be formed from a resin composition containing a resin in the same manner as the conductive layer. Also, as the protective layer, a film formed by molding an insulating resin such as polyester, polycarbonate, polyimide, polyamideimide, polyamide, polyphenylene sulfide, or polyether ether ketone can also be used.

[0049] <Step of forming an adhesive layer> The protective layer can be formed from a resin composition containing a resin and, if necessary, a conductive filler in the same manner as the conductive layer.

[0050] The lamination order of this sheet shall be such that it is in the order of protective layer / conductive layer / adhesive layer. The lamination method for each layer can be formed by preparing a structure in which a protective layer, a conductive layer, and an adhesive layer are respectively formed on a release sheet and laminating them in the above lamination order. Lamination can be performed, for example, under conditions of a temperature of about 80 to 130°C, a pressure of about 0.2 to 5.0 MPa, and a lamination speed of about 0.5 to 20 m / min. By setting it within this range, the adhesion between layers is improved, and the cohesive failure rate is improved. Also, the peel strength is improved, and the suitability for carrier punching is improved. It is preferable that a release sheet is laminated on the surfaces of the protective layer and the adhesive layer.

[0051] <Printed Wiring Board with Electromagnetic Shield Sheet> A printed wiring board with an electromagnetic shield sheet includes an electromagnetic shield layer formed from the electromagnetic shield sheet of the present invention, a cover coat layer, and a printed wiring board having a circuit pattern with signal wiring and ground wiring and an insulating substrate. The printed wiring board has a circuit pattern with signal wiring and ground wiring on the surface of an insulating substrate. On the printed wiring board, a cover coat layer that insulates and protects the signal wiring and the ground wiring and has vias on at least a part of the ground wiring is formed. After disposing the adhesive layer surface of the electromagnetic shield sheet on the cover coat layer, the electromagnetic shield sheet is thermally pressed to allow the adhesive layer to flow into the vias and adhere to the ground wiring, thereby enabling manufacturing.

[0052] The electromagnetic shield layer has a configuration including an adhesive layer, a conductive layer, and a protective layer. The cover coat layer is an insulating material that covers the signal wiring of the printed wiring board and protects it from the external environment. The cover coat layer is preferably a polyimide film with a thermosetting adhesive, a thermosetting or ultraviolet curable solder resist, or a photosensitive coverlay film, and a photosensitive coverlay film is more preferable for microfabrication. Also, it is common to use a known resin having heat resistance and flexibility such as polyimide for the cover coat layer. The thickness of the cover coat layer is usually about 10 to 100 μm.

[0053] The circuit pattern includes a ground wiring that takes ground and a signal wiring that sends an electrical signal to an electronic component. It is common to form both by etching a copper foil. The thickness of the circuit pattern is usually about 1 to 50 μm.

[0054] The insulating base material is a support for the circuit pattern, and a flexible plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, or liquid crystal polymer is preferable, and liquid crystal polymer and polyimide are more preferable. Among these, considering the use of a printed wiring board for transmitting high-frequency signals, a liquid crystal polymer having a low relative dielectric constant and dielectric tangent is even more preferable. When the printed wiring board is a rigid wiring board, the constituent material of the insulating base material is preferably glass epoxy. By providing such an insulating base material, the printed wiring board can obtain high heat resistance.

[0055] The thermal press of the electromagnetic wave shielding sheet and the printed wiring board is generally performed under conditions of a temperature of about 150 to 190 °C, a pressure of about 1 to 3 MPa, and a time of about 1 to 60 minutes. Due to the thermal press, the adhesive layer flows to fill the vias formed in the cover coat layer, enabling conduction with the ground wiring. Post-curing may be performed at 150 to 190 °C for 30 to 90 minutes after the thermal press.

[0056] The opening area of the via is preferably 0.8 mm 2 or less, and 0.008 mm 2The above is preferable. By setting it within the above range, the area of the ground wiring can be narrowed, and miniaturization of the printed wiring board can be achieved. It can be realized. The shape of the via is not particularly limited, and any of a circle, square, rectangle, triangle, irregular shape, etc. can be used according to the application.

[0057] It is preferable to laminate the electromagnetic shielding layer on both sides of the printed wiring board because it can more effectively suppress electromagnetic wave leakage. In addition, the electromagnetic shielding layer in the printed wiring board with the electromagnetic shielding sheet of the present invention can be used as a ground circuit in addition to shielding electromagnetic waves. Thereby, a part of the ground circuit can be omitted, and the cost can be reduced by reducing the area of the printed wiring board, and it can be incorporated into a narrow area in the housing.

[0058] Also, regarding the signal wiring, it is not particularly limited, and it can be used for either a single - ended circuit consisting of one signal wiring or a differential circuit consisting of two signal wirings, but a differential circuit is more preferable. On the other hand, when there are restrictions on the circuit pattern area of the printed wiring board and it is difficult to form the ground circuit in parallel, instead of providing a ground circuit beside the signal circuit, the electromagnetic shielding layer can be used as the ground circuit to form a printed wiring board structure having a ground in the thickness direction.

[0059] The printed wiring board with the electromagnetic shielding sheet of the present invention is preferably provided (mounted) in electronic devices such as displays, touch panels, as well as notebook PCs, mobile phones, smartphones, tablet terminals, etc.

[0060] Also, since the electromagnetic shielding sheet according to the present invention is excellent in shielding performance and high - speed transmission characteristics, it is preferably applied to applications that require high - speed transmission. Specifically, it can be suitably used for electronic devices that transmit signals in the frequency range of 1 MHz to 20 GHz.

Examples

[0061] Next, examples are shown to explain the present invention in more detail, but the present invention is not limited thereto. In the examples and comparative examples, "parts" and "%" mean "parts by mass" and "mass %", respectively. In addition, the acid value, phenolic hydroxyl value, weight average molecular weight (Mw) of the resin, and the average particle diameter of the metal filler were measured by the following methods.

[0062] 《Measurement of Acid Value of Resin》 The acid value was measured according to JIS K0070. Approximately 1 g of the sample was precisely weighed into a conical flask with a stopper, and 100 mL of a tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1) mixed solution was added and dissolved. To this, a phenolphthalein test solution was added as an indicator, and it was titrated with a 0.1 N alcoholic potassium hydroxide solution. The end point was determined when the indicator maintained a light red color for 30 seconds. The acid value was determined by the following formula (unit: mgKOH / g). Acid value (mgKOH / g) = (5.611 × a × F) / S However, S: Sampling amount of the sample (g) a: Consumption amount of 0.1 N alcoholic potassium hydroxide solution (mL) F: Normality of 0.1 N alcoholic potassium hydroxide solution F: Normality of 0.1 N alcoholic potassium hydroxide solution

[0063] 《Measurement of Phenolic Hydroxyl Value of Resin》 The phenolic hydroxyl value was measured according to JIS K0070. The phenolic hydroxyl value is represented by the amount (mg) of potassium hydroxide required to neutralize acetic acid bonded to the phenolic hydroxyl group when the phenolic hydroxyl group contained in 1 g of the phenolic hydroxyl group-containing resin is acetylated. The phenolic hydroxyl value of the phenolic hydroxyl group-containing resin When calculating, it was calculated considering the acid value as shown in the following formula. Specifically, about 1 g of the sample was precisely weighed into a conical flask with a stopper, and 100 mL of a tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1) mixed solution was added and dissolved. Further, exactly 5 mL of an acetylating agent (a solution prepared by dissolving 25 g of acetic anhydride in pyridine to make a volume of 100 mL) was added, and the mixture was stirred for about 1 hour. To this, a phenolphthalein test solution was added as an indicator and maintained for 30 seconds. Then, it was titrated with a 0.5 N alcoholic potassium hydroxide solution until the solution showed a light pink color. The phenolic hydroxyl value was determined by the following formula. Phenolic hydroxyl value (mgKOH / g) = [{(b - a)×F×28.05} / S] + D However, S: Sampling amount of the sample (g) a: Consumption of 0.5 N alcoholic potassium hydroxide solution (mL) b: Consumption of 0.5 N alcoholic potassium hydroxide solution in the blank experiment (mL) F: Normality of 0.5 N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

[0064] 《Measurement of Weight-Average Molecular Weight (Mw) of the Resin of the Binder Component》 The measurement of Mw was carried out by GPC (Gel Permeation Chromatograph) "HPC-8020" (manufactured by Tosoh Corporation). GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on the difference in their molecular sizes. In this measurement, two "LF-604" (manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID × 150 mm size) columns were connected in series and used, and the measurement was carried out under the conditions of a flow rate of 0.6 mL / min and a column temperature of 40°C. The determination of Mw was carried out in terms of polystyrene conversion.

[0065] 《Measurement of Average Particle Diameter of Metal Filler》 For the measurement of the average particle diameter, a laser diffraction / scattering particle size distribution analyzer LS13320 (manufactured by Beckman Coulter) was used. The D50 average particle diameter was obtained by measuring the filler with a Turbula dry powder sample module, which is the particle diameter at which the cumulative value in the particle diameter cumulative distribution is 50%. The refractive index was set to 1.6.

[0066] 《Raw Materials》 The raw materials used in the examples and comparative examples are shown below. The binders in Tables 1 to 3 correspond to the following binders respectively. The same applies to other curing agents and metal fillers. 《Binder》 A-1: Polyimide resin with an acid value of 6 mg KOH / g, a phenolic hydroxyl value of 0 mg KOH / g, and Mw of 54,000 (manufactured by Toyochem Co., Ltd.) A-2: Polyurethane-polyurea resin with an acid value of 0 mg KOH / g, a phenolic hydroxyl value of 10 mg KOH / g, and Mw of 120,000 (manufactured by Toyochem Co., Ltd.) A-3: Polyurethane-polyurea resin with an acid value of 10 mg KOH / g, a phenolic hydroxyl value of 0 mg KOH / g, and Mw of 122,000 (manufactured by Toyochem Co., Ltd.) A-4: Polyurethane-polyurea resin with an acid value of 8 mg KOH / g, a phenolic hydroxyl value of 0 mg KOH / g, and Mw of 54,000 (manufactured by Toyochem Co., Ltd.) 《Curing Agent》 B-1: Bisphenol A type epoxy resin "jER828" (manufactured by Mitsubishi Chemical Corporation) B-2: Polyfunctional epoxy resin "TETRAD-X" (manufactured by Mitsubishi Gas Chemical Company, Inc.) B-3: Aziridine compound "Chemitite PZ-33" (manufactured by Nippon Shokubai Co., Ltd.) B-4: Polyfunctional epoxy resin "jER1031S" (manufactured by Mitsubishi Chemical Corporation) B-5: Bisphenol A type epoxy resin "jER1001" (manufactured by Mitsubishi Chemical Corporation) 《Metal Filler》 C-1: Silver-coated copper powder obtained by applying 10 mass% silver coating to flaky copper powder with an average particle diameter of 13 μm powder C-2: Silver-coated copper powder obtained by applying a 10 mass% silver coating to flaky copper powder with an average particle diameter of 11 μm C-3: Silver-coated copper powder obtained by applying a 10 mass% silver coating to flaky copper powder with an average particle diameter of 9 μm C-4: Silver-coated copper powder obtained by applying a 10 mass% silver coating to flaky copper powder with an average particle diameter of 16 μm C-5: Silver-coated copper powder obtained by applying a 10 mass% silver coating to flaky copper powder with an average particle diameter of 15 μm C-6: Silver-coated copper powder obtained by applying a 10 mass% silver coating to flaky copper powder with an average particle diameter of 10 μm C-7: Silver-coated copper powder obtained by applying a 1 mass% silver coating to flaky copper powder with an average particle diameter of 13 μm C-8: Silver-coated copper powder obtained by applying a 5 mass% silver coating to flaky copper powder with an average particle diameter of 13 μm C-9: Silver-coated copper powder obtained by applying an 8 mass% silver coating to flaky copper powder with an average particle diameter of 14 μm C-10: Silver-coated copper powder obtained by applying a 20 mass% silver coating to flaky copper powder with an average particle diameter of 13 μm C-11: Flaky silver powder with an average particle diameter of 12 μm C-12: Silver-coated copper powder obtained by applying a 5 mass% silver coating to dendritic copper powder with an average particle diameter of 8 μm

[0067] (Example 1) 《Preparation of the protective layer》 100 parts of binder A-1 and 15 parts of curing agent B-1 were charged into a container in terms of solid content, and stirred with a disper for 10 minutes to obtain a resin composition. The obtained resin composition was coated on a release sheet with a bar coater and dried in an electric oven at 100 °C for 2 minutes to produce a film (1) having a protective layer (I). 《Preparation of the conductive layer》 100 parts of binder A-2, 20 parts of curing agent B-2, 1 part of curing agent B-3, and 363 parts of metal filler C-1 were charged into a container in terms of solid content, and stirred with a disper for 10 minutes to obtain a metal filler-containing composition. The obtained metal filler-containing composition was coated on a release sheet with a bar coater and dried in an electric oven at 100 °C for 2 minutes to produce a film (2) having a conductive layer (II). 《Preparation of the adhesive layer》 100 parts of binder A-3, 40 parts of curing agent B-4, 1.5 parts of curing agent B-3, and 61 parts of metal filler C-12 were charged into a container in terms of solid content, and stirred with a disper for 10 minutes to obtain a resin composition. The obtained resin composition was coated on a release sheet with a bar coater and dried in an electric oven at 100 °C for 2 minutes to produce a film (3) having an adhesive layer (III) in the form of a release sheet. 《Fabrication of Electromagnetic Shielding Sheet》 After laminating the protective layer (I) surface of the produced film (1) and the conductive layer (II) surface of the film (2) using a laminator (100 °C, pressure 2 MPa, lamination speed 1 m / min), the space between the conductive layer (II) of the film (2) and the release sheet was peeled off to produce a film (4) composed of a conductive layer (II), a protective layer (I), and a release sheet. The conductive layer (II) surface of the produced film (4) and the adhesive layer (III) surface of the film (3) were laminated using a laminator (100 °C, pressure 2 MPa, lamination speed 1 m / min) to obtain an electromagnetic shielding sheet covered with release sheets on both sides.

[0068] (Examples 2 to 19, Comparative Examples 1 to 2) An electromagnetic shielding sheet covered with release sheets on both sides was obtained in the same manner as in Example 1, except that the raw materials used in Example 1 were changed to the raw materials and thicknesses described in Tables 1 to 3.

[0069] (Comparative Example 4) An electromagnetic shielding sheet covered with release sheets on both sides was obtained in the same manner as in Example 1, except that a copper foil was used for the conductive layer.

[0070] (Comparative Example 5) An electromagnetic shielding sheet covered with release sheets on both sides was obtained in the same manner as in Example 1, except that a conductive layer was formed by vacuum copper evaporation on the protective layer (I) surface of the film (1).

[0071] 《Peel Test》 An electromagnetic shielding sheet with a width of 60 mm and a length of 80 mm was prepared. The release sheet on the adhesive layer side was peeled off to expose the adhesive layer, and an adhesive tape (DF715 manufactured by Toyochem Co., Ltd.) with a width of 70 mm and a length of 140 mm was attached to the exposed surface. After attaching the adhesive tape (DF715 manufactured by Toyochem Co., Ltd.) to the release sheet laminated on the protective layer, the electromagnetic shielding sheet with the adhesive tape laminated on both sides was cut into 25-mm widths, and two test pieces were prepared. Regarding the obtained test pieces, a 2-kg roller was used to apply pressure for one round trip to closely adhere the electromagnetic shielding sheet and the adhesive tape. Using a tensile testing machine conforming to JIS Z0237, the peel force was measured under the conditions of a peel angle of 180° and a peel speed of 300 mm / min, and the average value of the two test pieces was taken as the peel force. Furthermore, the peeled surface after the peel test was visually observed, and the area of the conductive layer that had cohesive failure and transferred to the protective layer and the adhesive layer was measured. When the conductive layer peeled off together with the protective layer or the adhesive layer without cohesive failure, the cohesive failure rate was set to 0%.

[0072] 《Cross-section evaluation》 The release sheet on the adhesive layer side of the electromagnetic shielding sheet was peeled off, and the exposed adhesive layer was laminated with a polyimide film (“Kapton 200EN” manufactured by Toray DuPont Co., Ltd.) and heat-pressed at 2 MPa and 170 °C for 30 minutes. After cutting this into a size of about 5 mm in width and 5 mm in length, 0.05 g of an epoxy resin (Petropoxy 154, manufactured by Maruto Co., Ltd.) was dropped in a slide glass shape and adhered to the electromagnetic shielding sheet to obtain a laminate having a structure of slide glass / electromagnetic shielding sheet / polyimide film. The obtained laminate was cut by ion beam irradiation from the polyimide film side using a cross-section polisher (SM-09010, manufactured by JEOL Ltd.) to deposit platinum on the cross-section, and a cross-section of the electromagnetic shielding sheet after heat pressing (hereinafter referred to as “the cross-section of the measurement sample”) was obtained.

[0073] 《Thickness measurement》 The cross-section of the measurement sample was observed with a scanning electron microscope (JSM-6010Plus, manufactured by JEOL Ltd.), and the thickness of each layer was measured. The magnification was set to 500 to 5000 times, and the average of 10 places was taken as the thickness of each layer.

[0074] "Measurement of Aspect Ratio of Metal Filler" The cross-section of the measurement sample was observed with a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus), and the aspect ratio of the metal filler was measured. The magnification was set to 3000 - 5000 times, and the average of 30 metal fillers was taken as the aspect ratio. The aspect ratio is defined as [major axis (μm)] / [thickness (μm)].

[0075] "Measurement of Area Occupied by Metal Filler" The cross-section of the measurement sample was observed at a magnification of 500 - 5000 times using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus), and the area of the filler in the conductive layer was measured. In the observation with the electron microscope, a contrast difference occurs between the resin layer and the metal layer due to the atomic number effect, and the shape of the metal can be recognized. Specifically, since the metal appears white and the resin layer is color-coded from gray to black, the resin part and the metal part can be distinguished and identified. The image of the electron microscope was binarized into black and white using the image analysis free software "GIMP2.6.11", and the ratio of the area of the metal filler in the conductive layer to the area of the components other than the metal filler was calculated by counting the number of black and white pixels. The area of the filler (number of white pixels) was taken as the area occupied by the filler when the area of the conductive layer (number of black and white pixels) was set to 100.

[0076] "Measurement of Mass Ratio of Silver Element" Using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus) and an energy dispersive X-ray analyzer (manufactured by JEOL Ltd., JED-2300), qualitative analysis charts of each element in the cross-section of the measurement sample were obtained at an acceleration voltage of 20 kV and a magnification of 3000 - 10000 times. For the conductive layer, the mass concentration of each element was calculated based on the qualitative analysis chart. The amount of silver element is the relative mass (%) of the silver element when the "total mass of copper and silver elements" is set to 100%. When no copper element is detected or the amount of silver element is 98% or more, the amount of silver element is set to 100%. ​In energy-dispersive X-ray analysis, elements located at a depth of about several micrometers from the surface may also be detected. Since it is difficult to perform a completely vertical measurement for cross-sectional analysis, only 50% of the conductive layer in the thickness direction was analyzed to avoid being affected by the protective layer and the adhesive layer.

[0077] 《Measurement of Surface Resistivity of Conductive Layer》 On the release-treated surface of the heat-resistant polyester film, using a conductive paste composed of an epoxy resin and silver powder, screen printing was performed in a pattern of four points at intervals of 5 mm in a straight line. After drying this, the conductive paste was heat-cured in an oven at 180 °C to form conductive bumps with a diameter of 500 μm and a height of 100 μm. An electromagnetic shielding sheet covered with release sheets on both sides was cut out to a length of 80 mm and a width of 50 mm. The release sheet on the adhesive layer (III) side was peeled off, and the exposed adhesive layer (III) was overlapped with the heat-resistant polyester film on which the conductive bumps were formed and pressure-bonded under the conditions of 170 °C, 2 MPa, and 30 minutes. Note that the four conductive bumps are pressure-bonded so as to be parallel to the long side of the sample piece. Due to the pressure bonding, the conductive bumps with a height of 100 μm penetrated the adhesive layer (III) and reached the conductive layer (II). After pressure bonding, the release-treated heat-resistant polyester film was removed, exposing the adhesive layer (III) and the conductive bumps. Using this conductive bump as a measurement electrode, in accordance with JIS K7194-1994, the resistance value was measured using a four-probe probe of "Loresta GP" manufactured by Mitsubishi Chemical. The value obtained by multiplying the measured value by the constant "4.239" was taken as the surface resistivity. Note that since the adhesive layer (III) is an anisotropic conductive adhesive layer that exhibits electrical conductivity only in the thickness direction or an adhesive layer that does not have conductivity, the resistance value measured even when the conductive bump penetrates the adhesive layer (III) is the resistance value of the conductive layer (II).

[0078] 《Method for Obtaining Conductivity of Conductive Layer》 From the thickness t (μm) of the conductive layer measured above and the surface resistivity R (Ω / sq), the conductivity σ (S / m) of the conductive layer was obtained according to the following formula. σ = 10 6 / R / t

[0079] "Evaluation of Suitability for Punching Out Careers" An electromagnetic shielding sheet with a width of 50 mm and a length of 250 mm was prepared. A micro-adhesive tape (LE951 manufactured by Toyochem Co., Ltd.) was attached to the release sheet on the protective layer side, and it was pressed once back and forth using a 2 kg roller to closely adhere the electromagnetic shielding sheet and the micro-adhesive tape. Using a punching machine, 20 pieces in total with a size of 10 mm x 30 mm were punched out. The release sheet on the adhesive layer side of the punched electromagnetic shielding sheet was peeled off, and the exposed adhesive layer was bonded to a polyimide film ("Kapton 200EN" manufactured by Toray DuPont Co., Ltd.) and laminated (at 90 °C, pressure 0.3 MPa, lamination speed 2 m / min). Then, the micro-adhesive tape was peeled off, the peeling interface was observed, and the number of pieces corresponding to defective products was counted. The defect rate was calculated using the following formula, The punching processability was evaluated. (Defect rate) = (Number of pieces corresponding to defective products) / (Total number of punched pieces) × 100 Note that defective products refer to those in which, when the micro-adhesive tape is peeled off, the peeling interface is not at the interface between the micro-adhesive tape and the electromagnetic shield, but peeling occurs within the electromagnetic shielding sheet. The evaluation criteria were as follows. ++: The defect rate is 0%. It is extremely good. +: The defect rate is 10% or less. It is good. NG: The defect rate is greater than 10%. It is not practical.

[0080] "Evaluation of Transmission Characteristics" The transmission characteristics were evaluated using a printed wiring board with an electromagnetic shielding sheet having a coplanar circuit. A schematic plan view of the front main surface side of a flexible printed wiring board 1 having a coplanar circuit (hereinafter also referred to as a wiring circuit board having a coplanar circuit) used for measurement is shown in FIG. 1, and a schematic plan view of the back surface side is shown in FIG. 2. First, a double-sided CCL "R-F775" (manufactured by Panasonic Corporation) in which rolled copper foils with a thickness of 12 μm were laminated on both sides of a polyimide film 20 with a thickness of 50 μm was prepared. Then, six through-holes 22 (diameter 0.1 mm) were provided in the vicinity of each of the four rectangular corner portions. In the figure, for the sake of illustration, only two through-holes 22 are shown in each corner portion. Next, after performing electroless plating, electrolytic plating was performed to form a copper plating film 21 with a thickness of 10 μm, and electrical continuity between the front main surface and the back surface was ensured through the copper plating film formed in the through-holes 22. Thereafter, as shown in FIG. 1, two signal wirings 23 with a length of 10 cm were formed on the front main surface of the polyimide film 20, a ground wiring 24 parallel to the signal wiring 23 was formed outside thereof, and a ground pattern 25 was formed in a region including the through-holes 22 in the short side direction of the polyimide film 20 extending from the ground wiring 24.

[0081] Thereafter, the copper foil formed on the back surface of the polyimide film 20 was etched to obtain a back surface side ground pattern 26 as shown in FIG. 2 at a position corresponding to the ground pattern 25. The circuit appearance and tolerance inspection specifications were set according to the JPCA standard (JPCA-DG02). Next, a cover coat layer 3 "CISV1215 (manufactured by Nikkan Kogyo Co., Ltd.)" composed of a polyimide film (thickness 12.5 μm) and an insulating adhesive layer (thickness 15 μm) was attached to the front main surface side of the polyimide film 20. In FIG. 1, the cover coat layer 3 is shown in a perspective view so that the structure of the signal wiring 23 and the like can be understood. Thereafter, nickel plating (not shown) was performed on the copper foil pattern exposed from the cover coat layer 3, and then gold plating (not shown) treatment was performed.

[0082] Next, as shown in FIG. 3, an electromagnetic wave shielding sheet was prepared, and a peelable sheet (not shown) provided on the adhesive layer was peeled off. Then, with the adhesive layer of the electromagnetic wave shielding sheet on the inner side, the electromagnetic wave shielding sheet was pressure-bonded to the entire back surface side of the wiring circuit board 1 having a coplanar circuit at 170° C., 2.0 MPa, for 30 minutes, and the peelable sheet on the protective layer surface was peeled off, thereby obtaining a printed wiring board 5 with an electromagnetic wave shielding sheet having a coplanar circuit for each of the examples and comparative examples. In FIG. 3, the back surface side ground pattern 26 is shown in a perspective view.

[0083] Note that the L / S (line / space) of the signal wiring 23 was appropriately adjusted so that the characteristic impedance was within ±10 Ω. The width of the ground wiring 24 was 100 μm, and the distance between the ground wiring 24 and the signal wiring 23 was 1 mm.

[0084] A network analyzer E5071C (manufactured by Keysight Technologies) was connected to the exposed signal wiring 23 of the printed wiring board 5 with an electromagnetic wave shielding sheet having a coplanar circuit, a sine wave of 15 GHz was input, and the transmission characteristics were evaluated by measuring the transmission loss. The measured transmission characteristics were evaluated according to the following criteria. +++: The transmission loss at 15 GHz is less than 7.0 dB. It is extremely good. ++: The transmission loss at 15 GHz is 7.0 dB or more and less than 8.0 dB. It is good. +: The transmission loss at 15 GHz is 8.0 dB or more and less than 9.0 dB. It is practical. NG: The transmission loss at 15 GHz is 9.0 dB or more. It is not practical.

[0085] 《Evaluation of Shielding Performance》 The electromagnetic wave shielding sheet was sandwiched between peelable films and heat-pressed at 170° C., 2 MPa, for 30 minutes, and the one in the state excluding the peelable film was used as a measurement sample. The shielding performance was in accordance with ASTM D4935, and electromagnetic wave irradiation was performed under the conditions of 300 MHz to 20 GHz using a coaxial tube type shielding effect measurement system manufactured by Keycom. The attenuation amount by which the electromagnetic wave was attenuated by the electromagnetic wave shielding sheet was measured and evaluated according to the following criteria. The measured attenuation is in decibels (unit: dB). +++: When irradiated with electromagnetic waves at 15 GHz, the attenuation is less than -60 dB. It is extremely good. ++: When irradiated with electromagnetic waves at 15 GHz, the attenuation is -60 dB or more and less than -55 dB. Good. +: When irradiated with electromagnetic waves at 15 GHz, the attenuation is -55 dB or more and less than -50 dB. Practically acceptable. NG: When irradiated with electromagnetic waves at 15 GHz, the attenuation is -50 dB or more. Not practically acceptable.

[0086] 《Evaluation of Gas Leakage Property》 The gas leakage property was evaluated by bringing a test piece obtained by laminating an electromagnetic shielding sheet on a copper-clad laminate simulating a wiring circuit board into contact with molten solder and checking for any change in the appearance of the sample. An electromagnetic shielding sheet with high gas leakage property can efficiently release outgases such as water vapor generated from the wiring circuit board to the outside of the wiring circuit board, so the appearance does not change. However, with an electromagnetic shielding sheet with low gas leakage property, the outgases do not escape efficiently, resulting in foaming and peeling. First, the release sheet on the adhesive layer side of an electromagnetic shielding sheet with a width of 25 mm and a length of 70 mm was peeled off, and the exposed adhesive layer was pressure-bonded to the gold-plated surface of a copper-clad laminate with a total thickness of 64 μm (gold plating 0.3 μm / nickel plating 1 μm / copper foil 18 μm / adhesive 20 μm / polyimide film 25 μm) at 170 °C, 2 MPa for 30 minutes, and a heat-cured laminate was obtained. The obtained laminate was cut into a size of 10 mm in width and 65 mm in length to prepare a sample. The obtained sample was left in an atmosphere of 40 °C and 90% RH for 72 hours. Then, with the polyimide film surface of the sample facing down, it was floated on molten solder at 250 °C for 1 minute. Then, the appearance of the taken-out sample was visually observed and evaluated according to the following criteria. ++: No visual change in appearance is observed. It is extremely good. +: The range of appearance defects is 10% or less of the protective layer area in the sample. It is good. NG: The range of appearance defects is wider than 10% of the protective layer area in the sample.

[0087]

Table 1

[0088] [Table 2]

[0089] [Table 3]

[0090] As shown in Tables 1 to 3, the electromagnetic shielding sheets of Examples 1 to 19 of the present invention had high peel strength, low volume resistivity and surface resistivity, and were excellent in carrier punching suitability, shielding property, and gas permeability with respect to Comparative Examples 1 to 4.

Description of Signs

[0091] 1: Wiring circuit board 20: Polyimide film 21: Copper plating film 22: Through hole 23: Signal wiring 24: Ground wiring 25: Ground pattern 26: Back side ground pattern 3: Cover coat layer 4: Electromagnetic shielding sheet 5: Printed wiring board with electromagnetic shielding sheet

Claims

1. An electromagnetic wave shielding sheet having a protective layer, a conductive layer, and an adhesive layer laminated in this order, The conductive layer includes a metal filler and a binder, a peel test is performed at a peel angle of 180° between the protective layer and the adhesive layer and a peel speed of 300 mm / min, and the conductive layer has a peel force of 50 to 2500 [gf / 25 mm] when the conductive layer has undergone cohesive failure; An electromagnetic wave shielding sheet having a cohesive failure rate of 10% or more in the peel test.

2. The electrical conductivity of the conductive layer is 2.4×10 ６ ~3.0 x 10 ７ 2. The electromagnetic wave shielding sheet according to claim 1, wherein the elastic modulus is [S / m].

3. The surface resistivity of the conductive layer is 4.0×10 －３ ~2.0 x 10 －１ 2. The electromagnetic wave shielding sheet according to claim 1, wherein the resistance is [Ω / □].

4. 2. The electromagnetic wave shielding sheet according to claim 1, wherein, in a cut surface after the electromagnetic wave shielding sheet is heat-pressurized under conditions of 170° C., 2 MPa, and 30 minutes, an area occupied by the metal filler is 23 to 95 when a cross-sectional area of ​​the conductive layer is taken as 100.

5. 2. The electromagnetic wave shielding sheet according to claim 1, wherein the thickness of the conductive layer on a cut surface after the electromagnetic wave shielding sheet is heat-pressed under conditions of 170° C., 2 MPa, and 30 minutes is 1 to 12 μm.

6. The metal filler includes a flake metal filler, 2. The electromagnetic wave shielding sheet according to claim 1, wherein the flake metal filler has an average aspect ratio of 10 to 70 in a cut surface of the conductive layer after the electromagnetic wave shielding sheet is heat-pressed under conditions of 170° C., 2 MPa, and 30 minutes.

7. 2. The electromagnetic shielding sheet according to claim 1, wherein the metal filler comprises silver-coated copper powder, and in a cut surface of the conductive layer after the electromagnetic shielding sheet is heat-pressed under conditions of 170° C., 2 MPa, and 30 minutes, a mass ratio of silver element is 3% or more and 25% or less when the total mass of copper and silver element is taken as 100% as measured by energy dispersive X-ray analysis.

8. A printed wiring board comprising the electromagnetic shielding sheet according to any one of claims 1 to 7.

9. An electronic device comprising the printed wiring board with the electromagnetic shielding sheet according to claim 8.

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