TWI889599B - Electromagnetic wave shielding sheet, printed wiring board with electromagnetic wave shielding sheet, and electronic equipment - Google Patents

Abstract

The present invention provides an electromagnetic wave shielding sheet which does not peel off during punching and has excellent transmission characteristics, shielding properties and degassing properties, and a printed circuit board having the electromagnetic wave shielding sheet. An electromagnetic wave shielding sheet is provided, wherein a protective layer, a conductive layer and an adhesive layer are sequentially stacked, wherein the conductive layer contains a metal filler and an adhesive, and a peeling test is performed at a peeling angle of 180° between the protective layer and the adhesive layer and a peeling speed of 300 mm/min. When the conductive layer undergoes cohesive failure, the peeling force is 50 [gf/25 mm] to 2500 [gf/25 mm]. In the peeling test, the cohesive failure rate of the conductive layer is greater than 10%.

Description

Electromagnetic wave shielding sheet, printed circuit board having electromagnetic wave shielding sheet, and electronic device

The present invention relates to an electromagnetic wave shielding sheet, a printed circuit board having the electromagnetic wave shielding sheet, and an electronic device.

Various electronic devices such as mobile terminals, personal computers (PCs), and servers have built-in substrates such as printed circuit boards. In order to prevent malfunctions caused by external magnetic fields or radio waves, and to reduce unnecessary radiation from electrical signals, electromagnetic wave shielding structures are provided on these substrates.

With the high-speed transmission of transmission signals, printed circuit boards with electromagnetic wave shielding sheets are required to have electromagnetic wave shielding properties against high-frequency noise (hereinafter referred to as high-frequency shielding properties) and reduce transmission losses in high-frequency regions (hereinafter sometimes referred to as transmission characteristics). International Publication No. 2013/077108 discloses a shielding film including a metal layer with a thickness of 0.5 μm to 12 μm and an anisotropic conductive adhesive layer in a laminated state. It is also described that, with this structure, electric field waves, magnetic field waves, and electromagnetic waves traveling from one side of the electromagnetic wave shielding sheet to the other side can be well shielded, and transmission losses can be reduced.

[The problem that the invention wants to solve]

However, an electromagnetic shielding printed circuit board having an electromagnetic shielding sheet using a metal layer attached to the printed circuit board has the following problem: when performing a heat treatment such as reflow soldering, volatile components generated from the inside of the printed circuit board float between the layers, resulting in poor appearance and poor connection due to foaming. The reason is that outgassing such as water vapor generated from the printed circuit board is retained by the dense metal layer of the electromagnetic shielding sheet, so the electromagnetic shielding sheet is required to have permeability of the outgassing (hereinafter referred to as degassing property).

On the other hand, when using the electromagnetic wave shielding sheet, it is sometimes stamped into a desired size and shape. In this case, there is a stamping method that is as follows: the electromagnetic wave shielding sheet is bonded to a tape carrier and stamped, and the tape carrier is peeled off after being attached to a printed circuit board, etc. In the case of this method, when the tape carrier is peeled off, sometimes the electromagnetic wave shielding sheet is not peeled off at the interface between the tape carrier and the electromagnetic wave shielding sheet, but peeling occurs inside the electromagnetic wave shielding sheet (hereinafter referred to as carrier stamping adaptability).

The purpose of the present invention is to provide an electromagnetic shielding sheet that suppresses peeling in the electromagnetic shielding sheet during punching and has excellent transmission characteristics, shielding properties and degassing properties, a printed circuit board having the electromagnetic shielding sheet, and an electronic device. [Means for solving the problem]

The inventors of this case have repeatedly made efforts to study and found that the problem of the present invention can be solved in the following form, thereby completing the present invention. [1]: An electromagnetic wave shielding sheet, which is stacked with a protective layer, a conductive layer and an adhesive layer in sequence, wherein the conductive layer of the electromagnetic wave shielding sheet contains a metal filler and an adhesive, and a peeling test is carried out at a peeling angle of 180° between the protective layer and the adhesive layer and a peeling speed of 300 mm/min. The peeling force when the conductive layer undergoes cohesive failure is 50 [gf/25 mm] to 2500 [gf/25 mm], and in the peeling test, the cohesive failure rate of the conductive layer is more than 10%. [2]: The electromagnetic shielding sheet according to [1], wherein the conductivity of the conductive layer is 2.4×10 ⁶ [S/m] to 3.0×10 ⁷ [S/m]. [3]: The electromagnetic shielding sheet according to [1] or [2], wherein the surface resistivity of the conductive layer is 4.0×10 ^-3 [Ω/□] to 2.0×10 ^-1 [Ω/□]. [4]: The electromagnetic shielding sheet according to any one of [1] to [3], wherein the area of the metal filler in a cross-section after the electromagnetic shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes, when the cross-sectional area of the conductive layer is 100, is 23 to 95. [5]: The electromagnetic shielding sheet as described in any one of [1] to [4], wherein the thickness of the conductive layer in the cross section after the electromagnetic shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes is 1 μm to 12 μm. [6]: The electromagnetic shielding sheet as described in any one of [1] to [5], 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 the electromagnetic shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes is 10 to 70. [7]: An electromagnetic shielding sheet as described in any one of [1] to [6], wherein the metal filler comprises 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 30 minutes, the mass ratio of the silver element when the total mass of copper and silver elements is set to 100% obtained by energy dispersive X-ray analysis is greater than 3% and less than 25%. [8]: A printed circuit board having an electromagnetic shielding sheet, comprising the electromagnetic shielding sheet as described in any one of [1] to [7]. [9]: An electronic device comprising the printed circuit board having the electromagnetic shielding sheet as described in [8]. [Effect of the invention]

According to the present invention, it is possible to provide an electromagnetic shielding sheet which suppresses peeling in the electromagnetic shielding sheet during punching and has excellent transmission characteristics, shielding properties and degassing properties, a printed circuit board having the electromagnetic shielding sheet, and an electronic device.

<Electromagnetic wave shielding sheet> The electromagnetic wave shielding sheet of the present invention (hereinafter, also referred to as the sheet) has a protective layer, a conductive layer and an adhesive layer in sequence. The electromagnetic wave shielding sheet is attached to the adherend through the adhesive layer by heat pressing, thereby forming an electromagnetic wave shielding layer, and shielding and reflecting electromagnetic waves on the attached surface. The electromagnetic wave shielding sheet is characterized in that the peeling angle between the protective layer and the adhesive layer of the electromagnetic wave shielding sheet is 180°, and the peeling force (hereinafter, sometimes referred to as the peeling force) in the peeling test at a peeling speed of 300 mm/min is 50 [gf/25 mm] to 2500 [gf/25 mm]. The peeling force is preferably 100 [gf/25 mm] to 2500 [gf/25 mm], more preferably 180 [gf/25 mm] to 2500 [gf/25 mm].

In addition, the electromagnetic wave shielding sheet of the present invention is characterized in that the cohesive failure rate is 10% or more. The so-called cohesive failure rate refers to the ratio of the area of the cohesive failure portion of the conductive layer to the total area of the peeling surface in the peeling test for measuring the peeling force. The cohesive failure rate is preferably 10% or more, more preferably 40% or more, and further preferably 70% or more.

By setting the peeling force and the cohesive failure rate to the above ranges, the interfaces of the protective layer/conductive layer and the conductive layer/adhesive layer are strongly bonded, and the cohesive force of the conductive layer can also be maintained at a high state, thereby achieving an optimal level of carrier impact adaptability.

As a method for making the peeling force fall within a desired range, for example, there can be cited a method of appropriately selecting the types of resins contained in the conductive layer, protective layer, and adhesive layer, or adjusting the amount of metal filler contained in the conductive layer. The details will be described later.

As a method to increase the cohesive failure rate, the type of adhesive of the conductive layer and the shape and content of the metal filler are adjusted. There are also methods to increase the peeling force of the protective layer and adhesive layer. The details of each method will be described later.

<Conductive layer> Next, the conductive layer used in the present invention is described. The conductive layer used in the present invention contains a metal filler and an adhesive, and the adhesive preferably contains at least a resin. By including a metal filler and a resin in the conductive layer, the degassing property can be improved.

Preferred examples of resins include thermoplastic resins and hardening resins. The hardening resin is preferably a thermosetting resin or a photocurable resin, and more preferably a thermosetting resin. A thermoplastic resin is a resin that becomes soft when heated to a glass transition temperature or a melting point, and a thermosetting resin is a resin that forms a macromolecular mesh structure by crosslinking when heated, and hardens and cannot be restored to its original state. There are types in which a thermosetting resin is hardened alone, and types in which a thermosetting resin and a hardener are used together.

When a thermoplastic resin is used as the resin of the adhesive, the contained thermoplastic resin exists in a solid state. When hot-pressing with an adherend such as a flexible printed circuit (FPC), the thermoplastic resin melts and solidifies again after cooling, thereby obtaining the required bonding strength. In addition, when a thermosetting resin is used as the resin of the adhesive, the contained thermosetting resin and the curing agent exist in an uncured or semi-cured state (B stage), and harden by hot-pressing with an adherend such as an FPC (C stage), thereby obtaining the required bonding strength. Among them, as adhesive components, it is preferred to use a thermosetting resin and a hardener, and it is more preferred to semi-harden them after using the thermosetting resin and the hardener. The semi-hardening method is not particularly limited, and examples include: a method of applying heat to the extent that the hardener does not react completely, a method of using multiple hardeners with different reaction temperatures, and a method of using multiple hardeners with different reaction times. Among them, the method of using multiple hardeners with different reaction temperatures is preferred. That is, it is preferred to include a second hardener that promotes the hardening reaction when reaching the B stage in addition to a first hardener that promotes the hardening reaction when reaching the C stage. As a result, the bonding between the metal fillers becomes stronger, the peeling force is improved, and the carrier impact pressure adaptability becomes better.

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, and fluororesins.

The thermosetting resin may be any resin having one or more functional groups that can be used for cross-linking reaction by heating, such as hydroxyl group, phenolic hydroxyl group, methoxymethyl group, carboxyl group, amino group, epoxy group, oxacyclobutyl group, oxazoline group, oxazine group, aziridine group, thiol group, isocyanate group, blocked isocyanate group, blocked carboxyl group, silanol group, etc. in one molecule, and preferably contains carboxyl group or phenolic hydroxyl group.

The total of the acid value and the phenolic hydroxyl value of the thermosetting resin is preferably 3 mgKOH/g to 100 mgKOH/g, more preferably 3 mgKOH/g to 70 mgKOH/g, and further preferably 5 mgKOH/g to 40 mgKOH/g. By setting the total of the acid value and the phenolic hydroxyl value of the thermosetting resin to this range, the metal fillers are firmly bonded to each other, the peeling force is increased, and the carrier impact pressure adaptability is improved.

Preferred examples of the thermosetting resin include acrylic resins, maleic acid resins, polybutadiene resins, polyester resins, polyurethane resins, epoxy resins, cyclohexane resins, phenoxy resins, polyimide resins, polyamide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, and fluororesins. Among them, polyurethane resins, polyurethane urea resins, addition ester resins, epoxy compounds, phenoxy resins, polyimide resins, polyamide resins, piperazine polyamide resins, and polyamide imide resins are preferred in terms of dispersion stability of metal fillers and bonding strength. Thermosetting resins may be used alone or in combination of two or more.

The weight average molecular weight of the thermosetting resin is preferably 20,000 to 300,000, more preferably 50,000 to 300,000, and further preferably 100,000 to 300,000. By setting the weight average molecular weight of the thermosetting resin to this range, the metal fillers are firmly bonded to each other, the peeling force is increased, and thus the carrier pressure adaptability is improved.

In addition, the thermosetting resin in the present invention preferably contains, in addition to the above resin, a so-called "hardener" such as a resin or a low molecular compound that reacts with the above functional group to form a chemical crosslink, if necessary.

The hardener is not particularly limited as long as it has two or more functional groups that can react with the functional groups of the thermosetting resin. Examples of hardeners include epoxy compounds, compounds containing anhydride groups, isocyanate compounds, aziridine compounds, amine compounds, phenol compounds, organic metal compounds (metal chelate compounds), polyol compounds, melamine compounds, silane compounds, carbodiimide compounds, benzoxazine compounds, maleimide compounds, and compounds containing β-hydroxyalkylamide groups. Hardeners can be used alone or in combination of two or more. In addition, the hardener can be a low molecular weight compound or a high molecular weight compound, but it is a compound different from the thermosetting resin.

The photocurable resin is any resin having one or more unsaturated bonds in one molecule that undergo crosslinking reaction by light, and examples thereof include acrylic resins, maleic acid resins, polybutadiene resins, polyester resins, polyurethane resins, epoxy resins, cyclohexane resins, phenoxy resins, polyimide resins, polyamide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, and fluororesins.

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

The surface resistivity of the conductive layer in the present invention is obtained by multiplying the resistance value measured in accordance with Japanese Industrial Standards (JIS) K7194-1994 using a four-probe probe such as "Loresta GP" manufactured by Mitsubishi Chemical by a prescribed constant. Specifically, four conductive bumps arranged in a straight line at intervals of 5 mm are inserted from the center of the adhesive layer of the electromagnetic wave shielding sheet of the present invention (a rectangular sample sheet of 80 mm×50 mm) until the conductive layer is reached. The positions of the four conductive bumps are parallel to the long sides of the sample sheet. A current flows between two points on the outer side of the four conductive bumps, and the voltage between two points on the inner side is measured to obtain the resistance value = voltage/current. Then, multiply the measured value by the constant "4.239" to obtain the value of "surface resistivity".

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

The conductivity of the conductive layer in the present invention can be obtained from the thickness t (μm) of the conductive layer and the surface resistivity. The details are described in the embodiments.

As a method for making the conductivity within the desired range, for example, a method of forming a good conductive path by containing the preferred metal filler described below in the preferred amount described below. As a method for making the surface resistivity within the desired range, in addition to the same method as for the conductivity, a method of increasing the thickness of the conductive layer can also be cited.

As metal fillers, there can be listed: metal powders of gold, silver, copper, nickel, etc.; alloy powders of solder, etc.; copper powder coated with silver (silver-coated copper powder); glass fiber or carbon filler that has been metal-plated, etc. Among them, silver powder and silver-coated copper powder with high conductivity are preferred. The amount of copper or silver in the conductive layer can be evaluated by observing the cross-section of the electromagnetic wave shielding sheet. In the cross-section, the mass ratio of the silver element when the total mass of copper and silver elements is set to 100% obtained by energy dispersive X-ray analysis is preferably 3% to 25%, and more preferably 6% to 15%. By setting the above range, the transmission loss suppression effect during high-speed transmission and high-frequency shielding properties can be improved while increasing the proportion of copper, which is cheaper than silver, thereby reducing costs. As a method for controlling the amount of silver element within the required range, for example, the amount of silver coating is controlled when preparing silver-coated copper powder.

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 metal fillers of different shapes may be mixed. For example, spherical, flaky (including leaf-shaped particles described later), dendrite, plate, needle, rod, and grape shapes may be listed. From the perspective of improving conductivity and increasing the cohesive failure rate, flaky particles are preferred. The flaky particles may also include leaf-shaped particles having a plurality of cuts on the outer edge (for example, particles obtained by flattening dendrite particles).

The average aspect ratio ([length (μm)]/[thickness (μm)]) of the flaky metal filler in the cross section of the conductive layer after the electromagnetic shielding sheet is heat-pressed at 170°C and 2 MPa for 30 minutes is preferably in the range of 10 to 70, more preferably in the range of 15 to 60. By setting the aspect ratio of the flaky particles in the above range, the transmission loss suppression effect during high-speed transmission, high-frequency shielding properties, and carrier pressure adaptability can be achieved with high dimensionality.

The average particle size D50 of the metal filler is preferably 1 μm to 100 μm, more preferably 3 μm to 50 μm, and further preferably 5 μm to 20 μm. By setting it within the above range, the transmission loss suppression effect during high-speed transmission and the high-frequency shielding property can be improved, and the bendability of the printed circuit board having the electromagnetic wave shielding sheet can be improved.

The content of the metal filler is preferably 75% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more, in the solid content of 100% by mass of the conductive layer. In addition, it is preferably 95% by mass or less. By setting the content of the metal filler to 75% by mass or more, the cohesive failure rate is improved, and by setting the content of the metal filler to 95% by mass or less, the peeling force is improved.

The area of the metal filler in the cross section of the conductive layer after the electromagnetic wave shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes is preferably 23% to 95%, more preferably 30% to 95%, and further preferably 45% to 95%, when the area of the conductive layer is 100%. By setting it within these ranges, the transmission loss suppression effect during high-speed transmission and high-frequency shielding properties can be improved.

The thickness of the conductive layer in the cross section after the electromagnetic wave shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes is preferably 1 μm to 12 μm, and more preferably 1 μm to 8 μm. By setting the thickness to 1 μm or more, a conductive layer with high shielding properties can be obtained. In addition, by setting the thickness to 12 μm or less, the bendability of the printed circuit board with the electromagnetic wave shielding sheet becomes good. <Protective layer> The protective layer preferably contains at least a resin. The resin can use the same resin as the conductive layer, and preferably uses a thermosetting resin and a hardener. In addition, the protective layer can also be a laminated structure of two or more layers. By setting the combined ratio of the resin and the hardener in the protective layer to more than 50%, the peeling force and cohesive failure rate of the protective layer are improved, and the impact pressure adaptability of the carrier is improved.

The thickness of the protective layer in the cross section after the electromagnetic wave shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes can be appropriately designed according to the application, but 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 protective layer to 0.5 μm or more, the protective property becomes sufficient. In addition, by setting the thickness of the protective layer to 25 μm or less, the bendability of the printed circuit board having the electromagnetic wave shielding sheet becomes good.

In the protective layer, silane coupling agents, antioxidants, pigments, dyes, adhesive imparting resins, plasticizers, ultraviolet absorbers, defoamers, leveling agents, fillers, flame retardants, etc. can also be added as needed.

<Adhesive layer> The adhesive layer is located on one side of the electromagnetic wave shielding sheet and is responsible for bonding with the printed circuit board described later. The adhesive layer preferably contains at least a resin. The resin can be the same resin as the conductive layer, and preferably a thermosetting resin and a hardener are used together. From the perspective of transmission loss, the resin or hardener is preferably a material with a low dielectric constant and a low dielectric loss tangent. From the perspective of characteristic impedance, a material with a low dielectric constant is preferably used, such as a structure containing a large number of fluorine atoms or hydrocarbons with a small polarizability, and a liquid crystal orientation or crystal orientation material that fixes the dipole. The adhesive layer also has a combined ratio of resin and hardener of 50% or more, similar to the protective layer. This improves the peeling force and cohesive failure rate, and improves the carrier impact pressure adaptability.

The thickness of the adhesive layer in the cross section after the electromagnetic wave shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes can be appropriately designed according to the application, but 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 bonding force to the printed circuit board can be increased. In addition, by setting the thickness of the adhesive layer to 25 μm or less, the bendability of the printed circuit board with the electromagnetic wave shielding sheet becomes good.

The adhesive layer may be insulating or conductive. When it is conductive, the adhesive composition forming the adhesive layer may further contain the metal filler exemplified in the conductive layer. In addition, microparticles of conductive polymers such as polyaniline and polyacetylene may also be used. When the adhesive layer is conductive, it may be isotropically conductive or anisotropically conductive. In addition, the so-called isotropic conductivity means that the adhesive layer has conductivity in any direction of its thickness direction and surface direction, and the so-called anisotropic conductivity means that the adhesive layer has conductivity substantially only in its thickness direction. From the perspective of improving the transmission characteristics in the high-frequency range and reducing costs, it is preferred to use anisotropic conductivity.

The anisotropic conductive adhesive layer contains a resin and a metal filler, which can be achieved by setting the content and size of the metal filler within the range described below. The content of the metal filler can be appropriately designed, preferably 10% to 45% by mass relative to 100% by mass of the adhesive layer, more preferably 15% to 40% by mass, and further preferably 20% to 30% by mass. When the thickness of the adhesive layer to be formed is taken as the reference (100), the average particle size 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 size D50, an anisotropic conductive adhesive layer can be formed instead of an isotropic conductive adhesive layer. The shape of the metal filler used is preferably spherical or branch-like, which can easily obtain anisotropic conductivity.

In the adhesive layer, silane coupling agents, rust inhibitors, reducing agents, antioxidants, pigments, dyes, adhesive imparting resins, plasticizers, ultraviolet absorbers, defoaming agents, leveling agents, fillers, flame retardants, etc. can also be added as needed.

<Method for manufacturing electromagnetic wave shielding sheet> Below, an example of the method for manufacturing the present sheet is described. However, the manufacturing method of the present invention is not limited to the following manufacturing method. The present sheet has: a step of forming a conductive layer, a step of forming a protective layer, and a step of forming an adhesive layer.

<Conductive layer formation step> Prepare a composition containing a metal filler for forming a conductive layer. Specifically, the composition containing a metal filler can be obtained by mixing and stirring a binder, a metal filler, and a solvent as required. For stirring, a known stirring device such as a dispermat or a homogenizer can be used. After preparing the composition containing a metal filler, the conductive layer is formed by applying the composition containing a metal filler on a release sheet and drying it. Examples of coating methods include gravure coating, kiss coating, die coating, lip coating, notch wheel coating, scraper coating, roller coating, knife coating, spray coating, rod coating, spin coating, and dip coating. The drying step may use a well-known drying device such as a hot air dryer or an infrared heater. In addition, an extrusion molding machine such as a T-die may be used to form a sheet-shaped conductive layer.

<Protective layer formation step> The protective layer can be formed from a resin composition containing a resin by the same method as the conductive layer. In addition, the protective layer can also use a film formed from an insulating resin such as polyester, polycarbonate, polyimide, polyamide imide, polyamide, polyphenylene sulfide, polyetheretherketone, etc.

<Step of forming the adhesive layer> The adhesive layer can be formed by a resin composition including a resin and, if necessary, a conductive filler by the same method as the conductive layer.

The lamination sequence of this sheet is set to be the sequence of protective layer/conductive layer/adhesive layer. As for the lamination method of each layer, the protective layer, conductive layer and adhesive layer are prepared on the release sheet, and they are laminated in the above-mentioned lamination sequence. As for lamination, for example, lamination can be performed under the conditions of a temperature of about 80°C to 130°C, a pressure of about 0.2 MPa to 5.0 MPa, and a lamination speed of about 0.5 m/min to 20 m/min. By setting it to this range, the adhesion between the layers is improved, and the cohesive failure rate is improved. In addition, the peeling force is improved and the carrier's impact pressure adaptability is improved. Preferably, a structure in which a peeling sheet is laminated on the surface of the protective layer and the adhesive layer.

<Printed circuit board with electromagnetic wave shielding sheet> The printed circuit board with electromagnetic wave shielding sheet includes: an electromagnetic wave shielding layer formed by the electromagnetic wave shielding sheet of the present invention; an outer coating layer; and a printed circuit board including a circuit pattern including signal wiring and ground wiring and an insulating substrate. The printed circuit board includes a circuit pattern including signal wiring and ground wiring on the surface of the insulating substrate, and can be manufactured in the following manner: an outer coating layer is formed on the printed circuit board to insulate and protect the signal wiring and the ground wiring, and a through hole is formed on at least a portion of the ground wiring, and after the adhesive layer surface of the electromagnetic wave shielding sheet is arranged on the outer coating layer, the electromagnetic wave shielding sheet is heat-pressed so that the adhesive layer flows into the through hole and is bonded to the ground wiring.

The electromagnetic wave shielding layer is a structure including an adhesive layer, a conductive layer, and a protective layer. The outer coating is an insulating material that covers the signal wiring of the printed circuit board to protect it from the influence of the external environment. The outer coating is preferably a polyimide film with a thermosetting adhesive, a thermosetting or UV-curing solder resist, or a photosensitive cover film. In order to perform fine processing, a photosensitive cover film is more preferably used. In addition, the outer coating generally uses a known resin with heat resistance and flexibility such as polyimide. The thickness of the outer coating is usually about 10 μm to 100 μm.

The circuit pattern includes ground wiring for grounding and signal wiring for sending electrical signals to electronic components. Both are generally formed by etching copper foil. The thickness of the circuit pattern is usually around 1 μm to 50 μm.

The insulating substrate is a support for the circuit pattern, and is preferably a bendable plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, liquid crystal polymer, and more preferably a liquid crystal polymer and polyimide. Among them, if the use of printed circuit boards for transmitting high-frequency signals is considered, liquid crystal polymers with low relative dielectric constants and dielectric loss tangents are further preferred. In the case where the printed circuit board is a rigid circuit board, the constituent material of the insulating substrate is preferably glass epoxy. By including an insulating substrate such as these, the printed circuit board can obtain high heat resistance.

The heat pressing of electromagnetic shielding sheets and printed circuit boards is generally performed at a temperature of about 150℃ to 190℃, a pressure of about 1 MPa to 3 MPa, and a time of about 1 minute to 60 minutes. By heat pressing, the agent layer flows and fills the through hole formed in the outer coating, thereby achieving conductivity with the ground wiring. Sometimes, post-curing is performed at 150℃ to 190℃ for 30 minutes to 90 minutes after heat pressing.

The opening area of the through hole is preferably 0.8 ^mm2 or less, and preferably 0.008 ^mm2 or more. By setting it within the above range, the area of the ground wiring can be narrowed, thereby miniaturizing the printed circuit board. The shape of the through hole is not particularly limited, and any of a circle, square, rectangle, triangle, and amorphous shapes can be used according to the application.

In terms of more effectively suppressing the leakage of electromagnetic waves, it is preferred that the electromagnetic wave shielding layers are stacked on both sides of the printed circuit board. In addition, the electromagnetic wave shielding layer in the printed circuit board with the electromagnetic wave shielding sheet of the present invention can not only shield the electromagnetic waves, but also be used as a grounding circuit. Thus, it is possible to reduce costs by omitting part of the grounding circuit and reducing the area of the printed circuit board, and further, it can be assembled in a small area in a frame.

In addition, there is no particular limitation on the signal wiring, and any circuit including a single end circuit including one signal wiring or a differential circuit including two signal wirings can be used, but a differential circuit is more preferred. On the other hand, when there are restrictions on the circuit pattern area of the printed circuit board and it is difficult to form a ground circuit in parallel, the ground circuit may not be provided next to the signal circuit, and the electromagnetic wave shielding layer may be used as the ground circuit to produce a printed circuit board structure having a ground in the thickness direction.

The printed circuit board with the electromagnetic wave shielding sheet of the present invention is preferably equipped (mounted) in electronic devices such as displays, touch screens, etc., as well as notebook PCs, mobile phones, smart phones, tablet terminals, etc.

In addition, the electromagnetic wave shielding sheet of the present invention is preferably used for applications requiring high-speed transmission due to its excellent shielding performance and high-speed transmission characteristics. Specifically, it can be preferably used in electronic devices that transmit signals in the frequency range of 1 MHz to 20 GHz. [Example]

Next, the present invention is described in more detail by showing examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively. In addition, the acid value, phenolic hydroxyl value, weight average molecular weight (Mw) of the resin, and the average particle size of the metal filler were measured by the following method.

《Determination of the acid value of resin》 The acid value is measured in accordance with JIS K0070. Accurately weigh about 1 g of the sample in a stoppered Erlenmeyer flask and add 100 mL of a mixture of tetrahydrofuran/ethanol (volume ratio: tetrahydrofuran/ethanol = 2/1) to dissolve it. Add phenolphthalein test solution as an indicator and titrate with 0.1 N alcoholic potassium hydroxide solution. The end point is when the indicator remains light red for 30 seconds. The acid value (unit: mgKOH/g) is calculated according to the following formula. Acid value (mgKOH/g) = (5.611×a×F)/S Wherein, S: Sample collection amount (g) a: Consumption of 0.1 N alcoholic potassium hydroxide solution (mL) F: Titer of 0.1 N alcoholic potassium hydroxide solution

《Determination of phenolic hydroxyl value of resin》 The phenolic hydroxyl value is measured in accordance with JIS K0070. The phenolic hydroxyl value is a value expressed as the amount of potassium hydroxide (mg) required to neutralize the acetic acid bonded to the phenolic hydroxyl groups when acetylation is performed on the phenolic hydroxyl groups contained in 1 g of the phenolic hydroxyl-containing resin. When calculating the phenolic hydroxyl value of the phenolic hydroxyl-containing resin, the acid value is taken into consideration as shown in the following formula. Specifically, about 1 g of the sample is accurately weighed in a co-stoppered Erlenmeyer flask, and 100 mL of a mixed solution of tetrahydrofuran/ethanol (volume ratio: tetrahydrofuran/ethanol = 2/1) is added to dissolve it. Then, accurately add 5 mL of acetylation agent (a solution of 100 mL made by dissolving 25 g of acetic anhydride in pyridine) and stir for about 1 hour. Add phenolphthalein test solution as an indicator and continue stirring for 30 seconds. Then, titrate with 0.5 N alcoholic potassium hydroxide solution until the solution turns light red. Calculate the phenolic hydroxyl value according to the following formula. Phenolic hydroxyl value (mgKOH/g) = [{(b-a)×F×28.05}/S]+D Where, S: Sample collection amount (g) a: Consumption of 0.5 N alcoholic potassium hydroxide solution (mL) b: Consumption of 0.5 N alcoholic potassium hydroxide solution in blank experiment (mL) F: Titer of 0.5 N alcoholic potassium hydroxide solution D: Acid value (mgKOH/g)

《Determination of the weight average molecular weight (Mw) of the resin as an adhesive component》 The Mw was measured using a gel permeation chromatograph (GPC) "HPC-8020" (manufactured by Tosoh Corporation). GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on their molecular size differences. This measurement was performed using two "LF-604" (manufactured by Showa Denko: GPC column for rapid analysis: 6 mm inner diameter (ID) × 150 mm size) connected in series and used as the column, and was performed at a flow rate of 0.6 mL/min and a column temperature of 40°C. Mw was determined by polystyrene conversion.

《Measurement of average particle size of metal fillers》 The average particle size was measured using the laser diffraction-scattering method fine distribution measuring device LS13320 (manufactured by Beckman-Coulter). The D50 average particle size was obtained by measuring the filler using the cyclone drying powder sample module, and is the particle size with a cumulative value of 50% in the cumulative distribution of particle sizes. In addition, the refractive index was set to 1.6.

《Raw materials》 The raw materials used in the embodiments and comparative examples are shown below. The adhesives in Tables 1 to 3 correspond to the following adhesives respectively. The same applies to other hardeners and metal fillers. 《Adhesive》 A-1: Acid value 6 mgKOH/g, phenolic hydroxyl value 0 mgKOH/g, Mw 54,000 polyimide resin (manufactured by Toyo Chemical (TOYO CHEM) Co., Ltd.) A-2: Acid value 0 mgKOH/g, phenolic hydroxyl value 10 mgKOH/g, Mw 120,000 polyurethane polyurea resin (manufactured by Toyo Chemical (TOYO CHEM) Co., Ltd.) A-3: Acid value 10 mgKOH/g, phenolic hydroxyl value 0 mgKOH/g, Mw 122,000 polyurethane polyurea resin (manufactured by Toyo Chemical (TOYO CHEM) Co., Ltd.) A-4: Acid value 8 mgKOH/g, phenolic hydroxyl value 0 mgKOH/g, polyurethane polyurea resin with Mw of 54,000 (manufactured by TOYO CHEM) 《Hardener》 B-1: Bisphenol A epoxy resin "jER828" (manufactured by Mitsubishi Chemical Corporation) B-2: Multifunctional epoxy resin "TETRAD-X" (manufactured by Mitsubishi Gas Chemical Corporation) B-3: Aziridine compound "Chemitite PZ-33" (manufactured by Nippon Catalyst Co., Ltd.) B-4: Multifunctional epoxy resin "jER1031S" (manufactured by Mitsubishi Chemical Corporation) B-5: Bisphenol A epoxy resin "jER1001" (manufactured by Mitsubishi Chemical Corporation) 《Metal filler》 C-1: Silver-coated copper powder with an average particle size of 13 μm and coated with 10% silver by mass C-2: Silver-coated copper powder with an average particle size of 11 μm and coated with 10% silver by mass C-3: Silver-coated copper powder with an average particle size of 9 μm and coated with 10% silver by mass C-4: Silver-coated copper powder with an average particle size of 16 μm and coated with 10% silver by mass C-5: Silver-coated copper powder with an average particle size of 15 μm flaky copper powder coated with 10% silver by mass C-6: 10% silver-coated flaky copper powder with an average particle size of 10 μm C-7: 13 μm flaky copper powder coated with 1% silver by mass C-8: 13 μm flaky copper powder coated with 5% silver by mass C-9: 14 μm flaky copper powder coated with 8% silver by mass C-10: Silver-coated copper powder with an average particle size of 13 μm and coated with 20% by mass of silver C-11: Silver-coated copper powder with an average particle size of 12 μm C-12: Silver-coated copper powder with an average particle size of 8 μm and coated with 5% by mass of silver

(Example 1) 《Preparation of protective layer》 100 parts of adhesive A-1 and 15 parts of curing agent B-1 were placed in a container in terms of solid content and stirred for 10 minutes using a disperser to obtain a resin composition. The obtained resin composition was applied to a release sheet using a rod coater and dried in an electric oven at 100°C for 2 minutes to prepare a film (1) including a protective layer (I). 《Preparation of Conductive Layer》 According to the solid content conversion, 100 parts of adhesive A-2, 20 parts of hardener B-2, 1 part of hardener B-3, and 363 parts of metal filler C-1 were placed in a container and stirred for 10 minutes using a disperser to obtain a composition containing a metal filler. The obtained composition containing a metal filler was applied to a release sheet using a rod coater and dried in an electric oven at 100°C for 2 minutes to prepare a film (2) including a conductive layer (II). 《Preparation of adhesive layer》 Calculated on a solid basis, 100 parts of adhesive A-3, 40 parts of hardener B-4, 1.5 parts of hardener B-3, and 61 parts of metal filler C-12 were placed in a container and stirred for 10 minutes using a disperser to obtain a resin composition. The obtained resin composition was applied to a release sheet using a rod coater and dried in an electric oven at 100°C for 2 minutes to prepare a film (3) including an adhesive layer (III) on the release sheet. 《Production of electromagnetic wave shielding sheet》 The protective layer (I) surface of the produced film (1) and the conductive layer (II) surface of the film (2) are laminated using a laminating press (100°C, pressure 2 MPa, laminating speed 1 m/min), and then peeled between the conductive layer (II) of the film (2) and the peeling sheet to produce a film (4) comprising a conductive layer (II), a protective layer (I), and a peeling sheet. The conductive layer (II) surface of the prepared film (4) is bonded to the adhesive layer (III) surface of the film (3) using a laminating press (100°C, pressure 2 MPa, laminating speed 1 m/min), thereby obtaining an electromagnetic wave shielding sheet covered on both sides with a release sheet.

(Example 2 to Example 19, Comparative Example 1 to Comparative Example 2) Except that the raw materials used in Example 1 were changed to the raw materials and thicknesses described in Tables 1 to 3, the same procedure as in Example 1 was followed to obtain an electromagnetic wave shielding sheet covered on both sides with a releasable sheet.

(Comparative Example 4) Except for using copper foil in the conductive layer, the same procedure as in Example 1 was performed to obtain an electromagnetic wave shielding sheet covered with release sheets on both sides.

(Comparative Example 5) Except that a conductive layer is formed by vacuum copper deposition on the protective layer (I) of the film (1), the same procedure as in Example 1 is performed to obtain an electromagnetic wave shielding sheet covered on both sides with a release sheet.

《Peeling test》 Prepare an electromagnetic wave shielding sheet with a width of 60 mm and a length of 80 mm, peel off the peeling sheet on the adhesive layer side to expose the adhesive layer, and stick an adhesive tape (DF715 manufactured by Toyo Chemical Co., Ltd.) with a width of 70 mm and a length of 140 mm on the exposed surface. After sticking the adhesive tape (DF715 manufactured by Toyo Chemical Co., Ltd.) on the peeling sheet stacked on the protective layer, cut the electromagnetic wave shielding sheet with the adhesive tape stacked on both sides into 25 mm widths to prepare two test pieces. The obtained test piece was pressed back and forth using a 2 kg roller to make the electromagnetic wave shielding sheet and the adhesive tape close to each other. The peeling force was measured using a tensile testing machine in accordance with JIS Z0237 at 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 peeling surface after the peeling test was visually observed to measure the area of the conductive layer that had undergone cohesive failure and transferred to the protective layer and adhesive layer. In the case where the conductive layer is peeled off together with the protective layer or adhesive layer without cohesive failure, the cohesive failure rate is set to 0%.

《Cross-sectional evaluation》 The release sheet on the adhesive layer side of the electromagnetic wave shielding sheet was peeled off, and the exposed adhesive layer was bonded to a polyimide film ("Kapton 200EN" manufactured by Toray-Dupont) and hot-pressed at 2 MPa and 170°C for 30 minutes. After cutting it into pieces of about 5 mm in width and 5 mm in length, 0.05 g of epoxy resin (Petropoxy 154, manufactured by Maruto) was dropped onto a glass slide and bonded to the electromagnetic wave shielding sheet, thereby obtaining a laminate with a structure of glass slide/electromagnetic wave shielding sheet/polyimide film. The obtained laminate was cut from the polyimide film side by ion beam irradiation using a cross section polisher (manufactured by NEC Corporation, SM-09010), and the cross section was platinum evaporated to obtain the cross section of the electromagnetic wave shielding sheet after heat pressing (hereinafter referred to as the "cross section of the test sample").

《Thickness measurement》 The cross section of the sample was observed using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus) to measure the thickness of each layer. The magnification was set to 500x to 5000x, and the average value of 10 points was taken as the thickness of each layer.

《Measurement of the aspect ratio of metal fillers》 The cross section of the sample was observed using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus) to measure the aspect ratio of the metal filler. The magnification was set to 3000 to 5000 times, and the average value of 30 metal fillers was taken as the aspect ratio. In addition, the so-called aspect ratio refers to [length (μm)] / [thickness (μm)].

《Measurement of the area occupied by metal fillers》 Using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6010Plus), the cross section of the sample was observed at a magnification of 500x to 5000x to measure the area of the fillers in the conductive layer. In observation using an electron microscope, due to the atomic number effect, a contrast difference occurs between the resin layer and the metal layer, allowing the shape of the metal to be identified. Specifically, since the metal is classified as white and the resin layer is classified as gray to black, the resin part and the metal part can be distinguished. The electron microscope image was binarized into black and white using the free image analysis software "GIMP2.6.11", and the number of black and white pixels was counted to calculate the area ratio of the metal filler of the conductive layer to the area ratio of the components other than the metal filler. The area of the filler (the number of white pixels) when the area of the conductive layer (the number of black and white pixels) was set to 100 was taken as the area occupied by the filler.

《Measurement of the mass ratio of silver element》 Using a scanning electron microscope (JSM-6010Plus, manufactured by NEC Corporation) and an energy dispersive X-ray analyzer (JED-2300, manufactured by NEC Corporation), a qualitative analysis chart of each element in the cross section of the measured sample was obtained at an accelerating voltage of 20 kV and a magnification of 3000 to 10000 times. For the conductive layer, the mass concentration of each element was calculated based on the qualitative analysis chart. The element amount of silver is the relative mass (%) of the silver element when the "total mass of copper and silver elements" is set to 100%. When the copper element is not detected or the element amount of silver is 98% or more, the element amount of silver is set to 100%. In addition, in energy dispersive X-ray analysis, elements located at a depth of about several microns from the surface are sometimes detected. It is difficult to measure completely vertically in cross-section analysis. Therefore, only the central 50% of the thickness direction of the conductive layer is used as the analysis object to avoid being affected by the protective layer or adhesive layer.

《Measurement of the surface resistivity of the conductive layer》 On the peeling-treated surface of the heat-resistant polyester film, a conductive paste containing epoxy resin and silver powder was screen-printed in a straight line with a 5 mm interval. After drying, the conductive paste was heated and hardened in an oven at 180°C to form conductive bumps with a diameter of 500 μm and a height of 100 μm. The electromagnetic wave shielding sheet covered with a release sheet on both sides was cut into 80 mm long sides and 50 mm short sides, 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 formed with conductive bumps, and pressure-bonded at 170°C, 2 MPa, and 30 minutes. In addition, the four-point conductive bumps were pressure-bonded in a manner parallel to the long sides of the sample sheet. By pressure bonding, the conductive bumps with a height of 100 μm penetrated the adhesive layer (III) and reached the conductive layer (II). After crimping, the heat-resistant polyester film that has been subjected to a peeling treatment is removed to expose the adhesive layer (III) and the conductive bump. The conductive bump is used as a measurement electrode, and the resistance value is measured in accordance with JIS K7194-1994 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" is used as the surface resistivity. In addition, since the adhesive layer (III) is an anisotropic conductive adhesive layer that exhibits conductivity only in the thickness direction or a non-conductive adhesive layer, even if the conductive bump passes through the adhesive layer (III), the measured resistance value is the resistance value of the conductive layer (II).

《How to calculate the conductivity of the conductive layer》 Based on the thickness t (μm) and surface resistivity R (Ω/□) of the conductive layer measured above, calculate the conductivity σ (S/m) of the conductive layer according to the following formula. σ = 10 ⁶ /R/t

《Evaluation of carrier pressure adaptability》 An electromagnetic wave shielding sheet with a width of 50 mm and a length of 250 mm was prepared. A micro-adhesive tape (LE951 manufactured by Toyo Chemical Co., Ltd.) was attached to the release sheet on the protective layer side, and a 2 kg roller was used to apply pressure in a reciprocating manner to make the electromagnetic wave shielding sheet and the micro-adhesive tape closely adhere to each other. A total of 20 pieces of 10 mm × 30 mm were molded using a press machine. The release sheet on the adhesive layer side of the electromagnetic wave shielding sheet after demolding was peeled off, and the exposed adhesive layer was bonded to a polyimide film ("Kapton 200EN" manufactured by Toray-Dupont) and laminated (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 equivalent to defective products was counted. The defective rate was calculated using the formula shown below, and the punching processability was evaluated. (Defective rate) = (Number of pieces equivalent to defective products) / (Total number of pieces after demolding) × 100 In addition, the so-called defective products refer to products in which the peeling interface is not between the micro-adhesive tape and the electromagnetic wave shielding sheet, but peeling occurs inside the electromagnetic wave shielding sheet when the micro-adhesive tape is peeled off. The evaluation criteria are as follows. ++: Defective rate is 0%. Extremely good. +: Defective rate is less than 10%. Good. NG: Defective rate is greater than 10%. Not practical.

《Evaluation of transmission characteristics》 The transmission characteristics are evaluated using a printed circuit board with an electromagnetic wave shielding sheet having a coplanar circuit. A schematic plan view of the main surface side of the flexible printed circuit board 1 with a coplanar circuit (hereinafter, also referred to as a printed circuit substrate with a coplanar circuit) used in the measurement is shown in FIG1, and a schematic plan view of the back side is shown in FIG2. First, a double-sided CCL "R-F775" (manufactured by Panasonic) is prepared in which a 12 μm thick rolled copper foil is laminated on both sides of a 50 μm thick polyimide film 20. Then, six through holes 22 (diameter 0.1 mm) are provided near the four corners of the rectangular shape. In addition, for the convenience of illustration, only two through holes 22 are shown at each corner. Then, after the electroless plating treatment, the electrolytic plating treatment is performed to form a 10 μm copper-plated film 21, and the copper-plated film formed in the through hole 22 ensures the conduction between the main surface and the back surface. After that, as shown in FIG1, two signal wirings 23 with a length of 10 cm are formed on the main surface of the polyimide film 20, and a ground wiring 24 parallel to the signal wiring 23 is formed on the outer side thereof, and a ground pattern 25 is formed in the area extending from the ground wiring 24 and including the through hole 22 in the short side direction of the polyimide film 20.

After that, the copper foil formed on the back side of the polyimide film 20 is etched to obtain the back side ground pattern 26 shown in FIG. 2 at a position corresponding to the ground pattern 25. The inspection specifications for the appearance and tolerance of the circuit are set to the Japan Electronics Packaging and Circuits Association (JPCA) standard (JPCA-DG02). Next, an outer coating 3 "CISV1215 (manufactured by Nikkan Industries Co., Ltd.)" including a polyimide film (thickness 12.5 μm) and an insulating adhesive layer (thickness 15 μm) is attached to the main surface side of the polyimide film 20. 1, the outer coating layer 3 is shown in a perspective view so as to understand the structure of the signal wiring 23, etc. Thereafter, the copper foil pattern exposed from the outer coating layer 3 is plated with nickel (not shown) and then gold (not shown) is plated.

Next, as shown in FIG3, an electromagnetic wave shielding sheet is prepared, and a release sheet (not shown) disposed on the adhesive layer is peeled off. Then, the electromagnetic wave shielding sheet is pressed on the entire back side of the printed circuit substrate 1 having a coplanar circuit, with the adhesive layer of the electromagnetic wave shielding sheet as the inner side, under the conditions of 170°C, 2.0 MPa, and 30 minutes, and the release sheet of the protective layer is peeled off, thereby obtaining a printed circuit board 5 having a coplanar circuit and an electromagnetic wave shielding sheet having the electromagnetic wave shielding sheet 4 of each embodiment and comparative example. In FIG3, a back side grounding pattern 26 is shown in perspective.

Furthermore, the L/S (line/space) of the signal wiring 23 is appropriately adjusted so that the characteristic impedance is ±10 Ω. The width of the ground wiring 24 is 100 μm, and the distance between the ground wiring 24 and the signal wiring 23 is set to 1 mm.

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

《Evaluation of shielding properties》 The electromagnetic wave shielding sheet was sandwiched between release films and hot-pressed at 170℃, 2 MPa, for 30 minutes. The release film was removed and the product in this state was used as a test sample. The shielding properties were evaluated in accordance with American Society for Testing and Materials (ASTM) D4935, using a coaxial tube type shielding effect measurement system manufactured by Keycom, and electromagnetic waves were irradiated under conditions of 300 MHz to 20 GHz. The attenuation of electromagnetic waves in the electromagnetic wave shielding sheet was measured and evaluated according to the following standards. In addition, the measured value of the attenuation is decibel (unit; dB). +++: The attenuation when irradiated with 15 GHz electromagnetic waves is less than -60 dB. Very good. ++: Attenuation when irradiated with 15 GHz electromagnetic waves is -60 dB or more and less than -55 dB. Good. +: Attenuation when irradiated with 15 GHz electromagnetic waves is -55 dB or more and less than -50 dB. Practical. NG: Attenuation when irradiated with 15 GHz electromagnetic waves is -50 dB or more. Not practical.

"Evaluation of degassing properties" A test piece with an electromagnetic shielding sheet stacked on a copper-clad laminate that simulates a printed circuit board is brought into contact with molten solder, and the degassing properties of the sample are evaluated based on whether there is a change in the appearance of the sample. An electromagnetic shielding sheet with high degassing properties allows outgassing such as water vapor generated from the printed circuit board to escape to the outside of the printed circuit board efficiently, so the appearance does not change. However, in an electromagnetic shielding sheet with low degassing properties, outgassing cannot escape efficiently, and bubbles or peeling may occur. First, the release sheet on the adhesive layer side of the electromagnetic shielding sheet with a width of 25 mm and a length of 70 mm was peeled off, and the exposed adhesive layer was pressed and bonded to the gold-plated surface of a 64 μm-thick gold-plated copper-clad laminate (gold-plated 0.3 μm/nickel-plated 1 μm/copper foil 18 μm/adhesive 20 μm/polyimide film 25 μm) at 170°C and 2 MPa for 30 minutes, and the laminate was thermally cured to obtain a laminate. The obtained laminate was cut into pieces with a width of 10 mm and a length of 65 mm to prepare a sample. The obtained sample was placed in an environment of 40°C and 90% RH for 72 hours. After that, the polyimide film of the sample was floated on molten solder at 250°C for 1 minute with the surface facing downward. The appearance of the sample after removal was then visually observed and evaluated according to the following criteria. ++: No appearance changes were found during visual inspection. Very good. +: The range of poor appearance is less than 10% of the protective layer area in the sample. Good. NG: The range of poor appearance is greater than 10% of the protective layer area in the sample.

[Table 1]

[Table 2]

[Table 3]

As shown in Tables 1 to 3, compared with Comparative Examples 1 to 4, the electromagnetic shielding sheets of Examples 1 to 19 of the present invention have high peeling force, low volume resistivity or surface resistivity, and excellent carrier impact pressure adaptability, shielding properties, and degassing properties.

100: Electronic device 1: Printed circuit board (flexible printed circuit board) 20: Polyimide film 21: Copper-plated film 22: Through hole 23: Signal wiring 24: Ground wiring 25: Ground pattern 26: Back side ground pattern 3: External coating 4: Electromagnetic wave shielding sheet 5: Printed circuit board with electromagnetic wave shielding sheet

FIG. 1 is a schematic plan view of the main surface side of the printed circuit substrate of the embodiment. FIG. 2 is a schematic plan view of the back side of the printed circuit substrate of the embodiment. FIG. 3 is a schematic plan view of the back side of the shielding printed circuit substrate of the embodiment.

1: Printed circuit board (flexible printed circuit board) 3: External coating 20: Polyimide film 21: Copper-plated film 22: Through hole 23: Signal wiring 24: Ground wiring 25: Ground pattern

Claims (9)

An electromagnetic wave shielding sheet, which has a protective layer, a conductive layer and an adhesive layer stacked in sequence, wherein the conductive layer contains a metal filler and an adhesive, and a peeling test is performed at a peeling angle of 180° between the protective layer and the adhesive layer and a peeling speed of 300 mm/min. The peeling force when the conductive layer undergoes cohesive failure is 50 [gf/25mm] to 2500 [gf/25mm]. In the peeling test, the cohesive failure rate of the conductive layer is more than 10%. The electromagnetic shielding sheet according to claim 1, wherein the conductivity of the conductive layer is 2.4×10 ⁶ [S/m] to 3.0×10 ⁷ [S/m]. The electromagnetic shielding sheet according to claim 1, wherein the surface resistivity of the conductive layer is 4.0×10 ^-3 [Ω/□] to 2.0×10 ^-1 [Ω/□]. The electromagnetic shielding sheet as claimed in claim 1, wherein the area occupied by the metal filler in the cross-section after the electromagnetic shielding sheet is heat-pressed at 170°C, 2 MPa, and 30 minutes is 23 to 95 when the cross-sectional area of the conductive layer is set to 100. The electromagnetic shielding sheet as described in claim 1, wherein the thickness of the conductive layer in the cut surface after the electromagnetic shielding sheet is heat-pressed at 170°C, 2MPa, and 30 minutes is 1μm to 12μm. The electromagnetic shielding sheet as described in claim 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 the electromagnetic shielding sheet is subjected to heat compression bonding at 170°C, 2 MPa, and 30 minutes is 10 to 70. The electromagnetic shielding sheet as claimed in claim 1, wherein the metal filler comprises 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 30 minutes, the mass ratio of the silver element when the total mass of copper and silver elements is set to 100% obtained by energy dispersive X-ray analysis is 3% or more and 25% or less. A printed circuit board with an electromagnetic wave shielding sheet, comprising the electromagnetic wave shielding sheet as described in any one of claims 1 to 7. An electronic device comprising a printed circuit board having an electromagnetic wave shielding sheet as described in claim 8.