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 have a substrate such as a printed wiring board built therein. These substrates are provided with an electromagnetic shielding structure in order to prevent malfunction due to an external magnetic field or radio wave, and also to reduce unnecessary radiation from an electric signal.

[0003] With the high-speed transmission of transmission signals, a printed wiring board with an electromagnetic shielding sheet is required to have electromagnetic shielding properties (hereinafter referred to as high-frequency shielding properties) corresponding to high-frequency noise and to reduce transmission loss (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 shielded well and transmission loss is 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, floating 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 outgases such as water vapor generated from the printed wiring board are retained in the dense metal layer of the electromagnetic shielding sheet, and the electromagnetic shielding sheet is required to have permeability to outgases. (Hereinafter, gas permeability)

[0006] On the other hand, when an electromagnetic shielding sheet is used, it may be punched into a desired size and shape. In this 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 peeling the carrier tape, peeling may occur not at the adhesive 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 performance, 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 2.4×106~3.0×107 [S / m]. [3]: The electromagnetic shielding sheet according to [1], wherein the surface resistivity of the conductive layer is 4.0×10-3~2.0×10-1 [Ω / sq]. [4]: The electromagnetic shielding sheet according to [1], wherein when the cross-sectional area of the conductive layer is set to 100 at the cut surface after heat-pressure bonding the electromagnetic shielding sheet under the conditions of 170°C, 2 MPa, and 30 minutes, the area occupied by the metal filler is 23~95. [5]: The electromagnetic shielding sheet according to [1], wherein the thickness of the conductive layer at the cut surface after heat-pressure bonding the electromagnetic shielding sheet under the conditions of 170°C, 2 MPa, and 30 minutes is 1~12 μm. [6]: The electromagnetic shielding sheet according to [1], wherein the metal filler includes flaky metal fillers, and the average aspect ratio of the flaky metal fillers at the cut surface of the conductive layer after heat-pressure bonding the electromagnetic shielding sheet under the conditions of 170°C, 2 MPa, and 30 minutes is 10~70. [7]: The electromagnetic shielding sheet according to [1], wherein the metal filler includes silver-coated copper powder, and at the cut surface of the conductive layer after heat-pressure bonding the electromagnetic shielding sheet under the conditions of 170°C, 2 MPa, and 30 minutes, when the total mass of copper and silver elements by energy dispersive X-ray analysis is 100%, the mass ratio of silver element is 3% or more and 25% or less. [8]: A printed wiring board with an electromagnetic shielding sheet, comprising the electromagnetic shielding sheet according to [1]~[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 is excellent in transmission characteristics, shielding properties, and outgassing properties, 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 hot pressing, and shields and reflects electromagnetic waves on the attached surface. The peeling force (hereinafter sometimes referred to as the peeling force) in the peeling test at a peeling angle of 180° and a peeling 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 peeling force is preferably 100 to 2500 [gf / 25 mm], and 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 peeling surface in the peeling test for measuring the above-described peeling force. 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 peeling force and the cohesive failure rate within the above ranges, the interfaces of the protective layer / conductive layer and the conductive layer / adhesive layer are strongly adhered, and the cohesive force of the conductive layer can also be maintained at a high level. Therefore, the suitability for carrier punching 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. Methods for increasing the peel strength of the protective layer and the adhesive layer are mentioned. 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 it is preferable that the binder contains at least resin. By containing a metal filler and resin in the conductive layer, the air permeability can be made good.

[0017] Preferable examples of the resin can include a thermoplastic resin or a curable resin. 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 network structure of high molecules and hardens and cannot return to its original state. There are a type that cures with a thermosetting resin alone and a type that cures by using a thermosetting resin and a curing agent in combination.

[0018] When a thermoplastic resin is used for the resin of the binder, the contained thermoplastic resin exists in a solid state, and when heat-pressing with an adherend such as an FPC, the thermoplastic resin melts and solidifies again after cooling, so that a desired adhesive strength can be obtained. Also, when a thermosetting resin is used for the resin of the binder, the contained thermosetting resin and curing agent exist in an uncured or semi-cured state (B stage), and by curing with an adherend such as an FPC by heat pressing or the like (C stage), a desired adhesive strength can be obtained. 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 the 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 in one molecule that can be used for a crosslinking reaction by heating, such as 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., and it preferably contains a carboxyl group or a phenolic hydroxyl group.

[0021] The total of the acid value and the phenolic hydroxyl group 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 group 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 resin, polybutadiene-based 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 adhesive strength, polyurethane resin, polyurethane-urea resin, addition-type ester resin, epoxy compound, phenoxy resin, polyimide resin, polyamide resin, piperazine polyamide resin, polyamide-imide 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 metal fillers becomes strong, the peeling force is improved, and thus 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 "curing 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 curing 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 curing 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 curing agent can be used alone or in combination of two or more kinds. Note that the curing agent may be a low molecular compound or a high molecular compound, but is a compound different from the above-mentioned thermosetting resin.

[0026] The photocurable resin may be any resin having one or more unsaturated bonds in one molecule that cause a crosslinking reaction by 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 4.0×10 -3 ~2.0×10 -1 [Ω / □], preferably 4.0×10 -3 ~1.0×10 -1 [Ω / □], more preferably. By setting the surface resistivity of the conductive layer within this range, high-frequency shielding performance can be made good.

[0028] The surface resistivity of the conductive layer in the present invention is in accordance with JIS K7194-1994 and is, for example, the resistance value measured using a four-probe probe of "Loresta GP" manufactured by Mitsubishi Chemical multiplied by a predetermined constant. Specifically, from the central part of the adhesive layer of the electromagnetic wave shielding sheet (a rectangular sample piece of 80 mm × 50 mm) of the present invention, four conductive bumps linearly provided at 5 mm intervals are inserted 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 2.4×10 6 ~3.0×10 7 [S / m], preferably 5.0×10 6 ~3.0×10 7 [S / m], more preferably. 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 making the conductivity fall 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 making the surface resistivity fall 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 these, silver powder and silver-coated copper powder with high conductivity are preferable. 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, when the total mass of copper and silver elements by energy-dispersive X-ray analysis is set to 100%, the mass ratio of silver elements is preferably 3% to 25%, and more preferably 6 to 15%. By setting it within this range, while making the suppression effect of transmission loss during high-speed transmission and the high-frequency shielding property good, the cost can be reduced by increasing the ratio of copper, which is cheaper than silver, to 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-shaped (including leaf-shaped particles described later), dendritic, plate-shaped, needle-shaped, rod-shaped, and grape-shaped can be mentioned, but flake-shaped is preferable from the viewpoints of improving conductivity and increasing the aggregation breakdown rate. The flake-shaped particles shall also include leaf-shaped particles having a plurality of cuts at the outer edge (for example, particles obtained by flattening dendritic particles).

[0034] After heat-pressing the electromagnetic shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes, the average aspect ratio ([major axis (μm)] / [thickness (μm)]) of the flaky metal filler on the cross-section of the conductive layer 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 a high level of 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 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, 95% by mass or less is preferable. 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 strength is improved.

[0037] When the area of the conductive layer on the cross-section of the electromagnetic shielding sheet after heat-pressing 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] After heat-pressing the electromagnetic shielding sheet under the conditions of 170 °C, 2 MPa, and 30 minutes, the thickness of the conductive layer on the cross-section 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 shielding sheet becomes good. <Protective layer> The protective layer preferably contains at least resin. As the resin, the same resin as that of the aforementioned conductive layer can be used, and it is preferable to use a thermosetting resin and a curing agent in combination. Further, the protective layer may have a laminated structure of two or more layers. By setting the total ratio 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-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 can be achieved. Further, 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. As the resin, the same resin as that of the aforementioned conductive layer can be used, and it is preferable to use a thermosetting resin and a curing agent in combination. From the viewpoint of transmission loss, materials with low dielectric constant and low dielectric tangent are preferable for the resin and the curing agent, and from the viewpoint of characteristic impedance, materials with low dielectric constant are preferable. For example, a structure containing many fluorine atoms or hydrocarbons with a small polarizability, or a liquid crystal alignment or crystal alignment material that fixes dipoles is preferable. Similar to the protective layer, by setting the total ratio 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-pressing 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, and 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.

[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% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 30% by mass with respect to 100% by mass of the adhesive layer. When the thickness of the formed adhesive layer is taken as a reference (100), the average particle diameter D50 of the metal filler is preferably about 100 to 300. By containing 10 to 45% by mass of the conductive filler having 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 agent, 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 polyetheretherketone 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 peelable sheet, and laminating these 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 punching out the carrier is improved. It is preferable that a peelable sheet is laminated on the surfaces of the protective layer and the adhesive layer.

[0051] <Printed Wiring Board with Electromagnetic Wave Shielding Sheet> A printed wiring board with an electromagnetic wave shielding sheet includes an electromagnetic wave shielding layer formed from the electromagnetic wave shielding 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 wave shielding sheet on the cover coat layer, the electromagnetic wave shielding 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 wave shielding 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 permittivity 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 also 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. 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 an electromagnetic shielding sheet of the present invention can be used as a ground circuit in addition to shielding electromagnetic waves, thereby omitting a part of the ground circuit and reducing the area of the printed wiring board, making it possible to reduce costs and incorporate it into a narrow area within the housing.

[0058] Regarding the signal wiring, it is not particularly limited and can be used in 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, the ground circuit may not be provided beside the signal circuit, and the electromagnetic shielding layer may 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 an electromagnetic shielding sheet of the present invention is preferably provided (mounted) in electronic devices such as displays, touch panels, notebook PCs, mobile phones, smartphones, and tablet terminals.

[0060] In addition, 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 in 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 "%" shall respectively mean "parts by mass" and "mass%". 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, where S: Sampling amount of the sample (g) a: Consumption amount of the 0.1 N alcoholic potassium hydroxide solution (mL) F: Normality of the 0.1 N alcoholic potassium hydroxide solution

[0063] 《Measurement of Phenolic Hydroxyl Value of Resin》 The phenolic hydroxyl value was measured in accordance with JIS K0070. The phenolic hydroxyl value is represented by the amount (mg) of potassium hydroxide required to neutralize acetic acid bound to the phenolic hydroxyl group when the phenolic hydroxyl group contained in 1 g of the phenolic hydroxyl group-containing resin is acetylated. When calculating the phenolic hydroxyl value of the phenolic hydroxyl group-containing resin, it was calculated taking into account the acid value as shown in the following formula. Specifically, approximately 1 g of the sample was precisely weighed into a conical flask with a stopper, and 100 mL of a mixed solution of tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1) 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 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. Thereafter, 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 amount (mL) of the 0.5 N alcoholic potassium hydroxide solution b: Consumption amount (mL) of the 0.5 N alcoholic potassium hydroxide solution in the blank experiment F: Normality of the 0.5 N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

[0064] 《Measurement of the weight average molecular weight (Mw) of the resin as the binder component》 The measurement of Mw was performed by GPC (gel permeation chromatography) "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: size 6 mm ID × 150 mm) were connected in series to the column and used, with a flow rate of 0.6 mL / min and a column temperature of 40 °C of the column temperature. It was carried out under conditions. 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 measuring device LS13320 (manufactured by Beckman Coulter) was used. It is the D50 average particle diameter obtained by measuring the filler with a Turbinedry Powder Sample Module, which is the particle diameter at which the cumulative value in the particle size 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 mgKOH / g, a phenolic hydroxyl value of 0 mgKOH / g, and Mw of 54,000 (manufactured by Toyochem Co., Ltd.) A-2: Polyurethane polyurea resin with an acid value of 0 mgKOH / g, a phenolic hydroxyl value of 10 mgKOH / g, and Mw of 120,000 (manufactured by Toyochem Co., Ltd.) A-3: Polyurethane polyurea resin with an acid value of 10 mgKOH / g, a phenolic hydroxyl value of 0 mgKOH / g, and Mw of 122,000 (manufactured by Toyochem Co., Ltd.) A-4: Polyurethane polyurea resin with an acid value of 8 mgKOH / g, a phenolic hydroxyl value of 0 mgKOH / 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) 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 a 10 mass% silver coating to flaky copper powder with an average particle diameter of 13 μm 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) 《Production of 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 the resin composition was obtained by stirring with a disper for 10 minutes. 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). 《Production of 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). 《Production of 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. 《Production of Electromagnetic Shielding Sheet》 The protective layer (I) surface of the produced film (1) and the conductive layer (II) surface of the film (2) were laminated using a laminator (100°C, pressure 2 MPa, lamination speed 1 m / min). After lamination, 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 the conductive layer (II), the protective layer (I), and the 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 and thickness described in Tables 1 to 3 were used instead of the raw materials used in Example 1.

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

[0071] 《Peeling 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. For 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 compliant with JIS Z0237, the peeling force was measured under the conditions of a peeling angle of 180° and a peeling speed of 300 mm / min, and the average value of the two test pieces was taken as the peeling force. Furthermore, the peeled surface after the peeling 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 bonded to 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.), the cross-section was platinum-evaporated, 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] "Measurement of Thickness" The cross-section of the measurement sample was observed with a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus), and the thickness of each layer was measured. The magnification was set to 500 - 5000 times, and the average of 10 locations 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. Note that the aspect ratio is [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, due to the atomic number effect, a contrast difference occurs between the resin layer and the metal layer, and the shape of the metal can be recognized. Specifically, since the metal is 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 with the image analysis free software "GIMP2.6.11", and the number of black and white pixels was counted to calculate the area ratio of the metal filler in the conductive layer to the components other than the metal filler. When the area of the conductive layer (the number of black and white pixels) was set to 100, the area of the filler (the number of white pixels) was taken as the area occupied by the filler.

[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 to 10,000 times. For the conductive layer, based on the qualitative analysis chart, the mass concentration of each element was calculated. The elemental amount of silver is the relative mass (%) of silver element when the "total mass of copper and silver elements" is 100%, and when no copper element is detected or the elemental amount of silver is 98% or more, the elemental amount of silver was set to 100%. In energy-dispersive X-ray analysis, elements located at a depth of about several μm from the surface may also be detected. Since it is difficult to perform completely perpendicular measurement in cross-section analysis, only 50% of the conductive layer in the thickness direction was analyzed so as not to be affected by the protective layer or the adhesive layer.

[0077] 《Measurement of Surface Resistivity of Conductive Layer》 On the release-treated surface of the heat-resistant polyester film, screen printing of a pattern of 4 points at intervals of 5 mm in a straight line was performed using a conductive paste composed of an epoxy resin and silver powder. 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 overlaid on the heat-resistant polyester film on which the conductive bumps were formed, and pressure bonding was performed under the conditions of 170°C, 2 MPa, and 30 minutes. The four conductive bumps were 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, and the adhesive layer (III) and the conductive bumps were exposed. 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 "Rolesta 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, even if the conductive bumps penetrate the adhesive layer (III), the measured resistance value 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 Carrier Punching Suitability》 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 make the electromagnetic shielding sheet and the micro-adhesive tape adhere closely. It was die-cut into 20 pieces with a total of 20 pieces of 10 mm x 30 mm using a die-cutting machine. The release sheet on the adhesive layer side of the die-cut electromagnetic shielding sheet was peeled off, and the exposed adhesive layer was laminated (90 °C, pressure 0.3 MPa, lamination speed 2 m / min) with a polyimide film (“Kapton 200EN” manufactured by Toray DuPont). 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 defective rate was calculated using the following formula, and the punching processability was evaluated. (Defective rate) = (Number of pieces corresponding to defective products) / (Total number of die-cut 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. ++: Defective rate is 0%. Extremely good. +: Defective rate is 10% or less. Good. NG: Defective rate is greater than 10%. 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 as 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 facing inward, the electromagnetic wave shielding sheet was pressure-bonded to the entire back surface side of the wiring circuit board 1 having a coplanar circuit under the conditions of 170 °C, 2.0 MPa, and 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] Incidentally, 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, and 30 minutes, and the one in the state without 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. Note that the measured attenuation is in decibels (unit: dB). +++: The attenuation when irradiated with electromagnetic waves at 15 GHz is less than -60 dB. It is extremely good. ++: The attenuation when irradiated with electromagnetic waves at 15 GHz is -60 dB or more and less than -55 dB. It is good. +: The attenuation when irradiated with electromagnetic waves at 15 GHz is -55 dB or more and less than -50 dB. It is practical. NG: The attenuation when irradiated with electromagnetic waves at 15 GHz is -50 dB or more. It is not practical.

[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 cannot 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, and for 30 minutes, and then thermally cured to obtain a laminate. 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 change in appearance is visually 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, for Comparative Examples 1 to 4, 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.

Explanation of Reference Numerals

[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: Backside ground pattern 3: Cover coat layer 4: Electromagnetic shielding sheet 5: Printed wiring board with electromagnetic shielding sheet

Claims

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, a peel test is performed at a peel angle of 180° and a peel speed of 300 mm / min between the protective layer and the adhesive layer, and the peel force when the conductive layer undergoes cohesive failure is 50 to 2500 [gf / 25 mm], and in the peel test, an electromagnetic shielding sheet having a cohesive failure rate of 10% or more.

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

3. The surface resistivity of the conductive layer is 4.0×10 －３ to 2.0×10 －１ [Ω / sq], and the electromagnetic shielding sheet according to claim 1.

4. The electromagnetic shielding sheet according to claim 1, wherein when the cross-sectional area of the conductive layer is taken as 100, the area occupied by the metal filler is 23 to 95 in the cross-section of the conductive layer after the electromagnetic shielding sheet is heat-pressed at 170° C., 2 MPa, and for 30 minutes.

5. The electromagnetic shielding sheet according to claim 1, wherein the thickness of the conductive layer is 1 to 12 μm in the cross-section of the conductive layer after the electromagnetic shielding sheet is heat-pressed at 170° C., 2 MPa, and for 30 minutes.

6. wherein the metal filler includes a flaky metal filler, and the electromagnetic shielding sheet according to claim 1, wherein the average aspect ratio of the flaky metal filler in the cross-section of the conductive layer after the electromagnetic shielding sheet is heat-pressed at 170° C., 2 MPa, and for 30 minutes is 10 to 70.

7. wherein the metal filler includes silver-coated copper powder, and in the cross-section of the conductive layer after the electromagnetic shielding sheet is heat-pressed at 170° C., 2 MPa, and 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%. The electromagnetic shielding sheet according to claim 1.

8. A printed wiring board with an electromagnetic shielding sheet, comprising the electromagnetic shielding sheet according to claims 1 to 7.

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

Images