JP2021027311A - Electromagnetic wave shielding sheet and electromagnetic wave shielding wiring circuit board - Google Patents

Abstract

To provide: an electromagnetic wave shielding sheet which has solder reflow resistance, superior hot-cold cycle reliability, high chemical resistance, excellent high-frequency shielding properties, and transmission characteristics suitable for high-frequency signals; and a wiring circuit board based on the electromagnetic wave shielding sheet.SOLUTION: The electromagnetic wave shielding sheet comprises a conductive adhesive layer, a metal layer, and a protective layer. The Flop Index (FI), calculated with the formula (1), of an interface of the metal layer in contact with the conductive adhesive layer is from 10 to 90. The metal layer has multiple apertures with a numerical aperture of 0.10 to 20%.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electromagnetic wave shield sheet and an electromagnetic wave shielded wiring circuit board. For example, an electromagnetic wave shield sheet suitable for joining and using a part of a component that emits an electromagnetic wave, and an electromagnetic wave using the electromagnetic wave shield sheet. Shielded wiring circuit board.

Various electronic devices such as mobile terminals, PCs, and servers have built-in wiring circuit boards such as printed wiring boards. These wiring circuit boards are provided with an electromagnetic wave shield structure in order to prevent malfunction due to an external magnetic field or radio wave, and to reduce unnecessary radiation from an electric signal.

With the increase in high-speed transmission of transmission signals, the electromagnetic wave shield sheet is also required to have electromagnetic wave shielding properties (hereinafter, high frequency shielding properties) corresponding to high frequency noise and reduction of transmission loss (hereinafter, sometimes referred to as transmission characteristics) in the high frequency region. ing. Patent Document 1 discloses a configuration in which a metal layer having a thickness of 0.5 to 12 μm and an anisotropic conductive adhesive layer are provided in a laminated state. It is described that the configuration satisfactorily shields electric field waves, magnetic field waves, and electromagnetic waves traveling from one side to the other side of the electromagnetic wave shield sheet and reduces transmission loss.

International Publication No. 2013/077108 Japanese Unexamined Patent Publication No. 2013-168643

In recent years, in electronic devices typified by mobile phones, high-frequency shielding properties and transmission characteristics are required for electromagnetic wave shield sheets on wiring circuit boards built therein as transmission signals are transmitted at high speed. Therefore, as described in Patent Document 1, it has been preferable to use a metal layer having a thickness of 0.5 to 12 μm as the conductive layer of the electromagnetic wave shield sheet.
However, if a metal layer having a thickness of 0.5 to 12 μm is simply used, the electromagnetic wave shield sheet cannot exhibit sufficient transmission characteristics in the high frequency band, and the electromagnetic wave shield sheet has better transmission characteristics. Has been required to make further efforts for the metal layer.
In addition, the electromagnetic wave shielding property wiring circuit board in which the electromagnetic wave shielding sheet using the metal layer is attached to the wiring circuit board is layered by the volatile components generated from the inside of the wiring circuit board when the heat treatment such as solder reflow is performed. There was a problem that the floating occurred and the appearance was poor and the connection was poor due to foaming etc. (hereinafter, it may be referred to as solder reflow resistance). To solve this problem, for example, in Patent Document 2, a metal foil having a plurality of pinholes in the metal thin film layer is used, and a volatile component is permeated through the pinholes of the metal thin film layer to suppress floating and foaming between layers. ing.
Further, in the mounting process of an electronic device, the electromagnetic wave shielded wiring circuit board may be exposed to the cleaning process mainly for the purpose of removing dirt, dust and the like. At that time, there is a problem that the resistance to decomposition / dissolution of the electromagnetic wave shield layer to cleaning chemicals is not sufficient and the electromagnetic wave shield layer is damaged.

On the other hand, with the worldwide spread of electronic devices such as smartphones and tablet terminals in recent years, reliability under all temperature conditions is required. When the wiring circuit board provided with the electromagnetic wave shield sheet of Patent Document 1 and Patent Document 2 is exposed to an extreme temperature change, there are problems such as peeling from the wiring circuit board and disconnection from the ground circuit. (Hereinafter, cold cycle reliability).

The present invention has been made in view of the above background, and an object of the present invention is to have solder reflow resistance, excellent thermal cycle reliability, high chemical resistance, excellent high frequency shielding property, and high frequency wave. It is an object of the present invention to provide an electromagnetic wave shield sheet having transmission characteristics suitable for a signal and a wiring circuit board using the electromagnetic wave shield sheet.

As a result of diligent studies by the present inventor, 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.
That is, the electromagnetic wave shield sheet according to the present invention has a laminate having a conductive adhesive layer, a metal layer, and a protective layer in this order, and the surface of the metal layer in contact with the conductive adhesive layer is calculated by the formula (1). The Flop Index (FI) is 10 to 90, the metal layer has a plurality of openings, and the aperture ratio is 0.10 to 20%.

According to the present invention, it has excellent solder reflow resistance, reduces transmission loss even when used in a high-frequency transmission circuit, exhibits excellent high-frequency shielding properties, and has high connection reliability even after exposure to a thermal cycle. It has an excellent effect of being able to provide an electromagnetic wave shield sheet exhibiting chemical resistance and an electromagnetic wave shielded wiring circuit board.

It is sectional drawing which illustrates the electromagnetic wave shield sheet which concerns on this embodiment. It is a figure which showed the FI measurement system, and the FI behavior of two surfaces which differed in the steepness and order of unevenness. It is a schematic cut section sectional view which shows an example of the electromagnetic wave shielded wiring circuit board which concerns on this embodiment. It is a schematic plan view of the main surface side of the wiring board which has a coplanar circuit which concerns on an Example and a comparative example. It is a schematic plan view of the back surface side of the wiring board which has a coplanar circuit which concerns on an Example and a comparative example. It is a schematic plan view of the main surface side of the wiring board which has the coplanar circuit with the electromagnetic wave shield sheet which concerns on Example and the comparative example. It is a schematic plan view of the cold cycle reliability evaluation, and is the sectional view of the cut part. It is a dynamic viscoelastic curve of the laminated cured product (Example 5).

Hereinafter, an example of an embodiment to which the present invention is applied will be described. The sizes and ratios of the members in the following figures are for convenience of explanation and are not limited thereto. Further, in the present specification, the description "arbitrary number A to arbitrary number B" includes the number A as the lower limit value and the number B as the upper limit value in the range. Further, the term "sheet" in the present specification includes not only "sheet" defined in JIS but also "film". In addition, the numerical value specified in the present specification is a value obtained by the method disclosed in the embodiment or the embodiment.

<Electromagnetic wave shield sheet>
The electromagnetic wave shield sheet of the present invention has a laminate having at least a conductive adhesive layer, a metal layer, and a protective layer in this order. FIG. 1 is a cross-sectional view illustrating the electromagnetic wave shield sheet 10 according to the embodiment of the present invention. As shown in FIG. 1, the electromagnetic wave shielding sheet 10 has a laminate having a conductive adhesive layer 1, a metal layer 2, and a protective layer 3 in this order, and the metal layer 2 is a conductive adhesive layer 1 and a protective layer. It is arranged between three.
The electromagnetic wave shield sheet of the present invention has a plurality of openings 4, has an aperture ratio of 0.10 to 20%, and the surface of the metal layer in contact with the conductive adhesive layer is calculated by the formula (1). Since the metal layer having a Flop Index (FI) of 10 to 90 is provided, excellent transmission characteristics and the like can be exhibited particularly in a wiring circuit board that transmits a high frequency (for example, 100 MHz to 50 GHz) signal. ..
For the electromagnetic wave shield sheet 10, for example, a wiring circuit board which is an adherend and a surface on the conductive adhesive layer 1 side are bonded to form an electromagnetic wave shield layer to produce an electromagnetic wave shielded wiring circuit board. That is, of the surface of the metal layer 2, the surface facing the signal wiring in the wiring circuit board is the surface in close contact with the conductive adhesive layer 1.

[Loss tangent of laminated cured product]
Further, the electromagnetic wave shield sheet of the present invention has a loss tangent at 125 ° C. of a laminated cured product obtained by heat-pressing a laminate having at least a conductive adhesive layer, a metal layer, and a protective layer in this order at 170 ° C. for 30 minutes. It is preferably 0.10 or more.
Thereby, the reliability of the thermal cycle can be further improved.

The laminated cured product can be formed by curing the electromagnetic wave shield sheet by heat pressing at 170 ° C. for 30 minutes. That is, it is composed of a conductive adhesive layer, a metal layer, a protective layer, and other functional layers, and the layer having a curing component among them refers to a cured laminate.

The laminated cured product is obtained by removing the peelable sheet from the electromagnetic wave shield sheet before or after heat pressing, and heat pressing only one electromagnetic wave shield sheet, or using a plurality of electromagnetic wave shield sheets as a laminator or the like. It can be obtained by any method of laminating and hot pressing.
That is, the laminated cured product is a laminated component of the electromagnetic wave shielding sheet similar to the electromagnetic wave shielding layer used for the electromagnetic wave shielding wiring circuit board.

Specifically, for example, two electromagnetic wave shield sheets are prepared, the peelable sheets on the conductive adhesive layer side of each are peeled off, the exposed conductive adhesive layers are bonded to each other, and heat pressed at 170 ° C. for 30 minutes. A laminate having at least a conductive adhesive layer, a metal layer, and a protective layer in this order can be thermally cured to obtain a laminated cured product.

The loss tangent of the laminated cured product is a numerical value obtained by the following mathematical formula (3), and is an index of the stress relieving ability generated when the electromagnetic wave shield sheet is deformed.

Formula (3)
(Loss tangent of laminated cured product) =
(Loss elastic modulus of laminated cured product E ″) / (Storage elastic modulus of laminated cured product E ″)
As an example, FIG. 8 shows a dynamic viscoelastic curve of the laminated cured product (Example 5). By reading the loss elastic modulus E ″ and the storage elastic modulus E ″ at a certain temperature and applying these numerical values to the above-mentioned mathematical formula (3), the loss tangent at the corresponding temperature can be calculated. From the viewpoint of thermal cycle reliability, it is preferable that the laminated cured product has a loss tangent of 0.1 or more at 125 ° C. after heat pressing at 170 ° C. for 30 minutes. When the loss tangent at 125 ° C. after heat pressing at 170 ° C. for 30 minutes of the laminated cured product is 0.1 or more, the stress generated by expansion during high temperature exposure can be sufficiently relaxed. The laminated cured product has a loss tangent of 0.13 or more, more preferably 0.15 or more at 125 ° C. after heat pressing at 170 ° C. for 30 minutes.

The loss tangent of the laminated cured product is the loss elastic modulus E ″ of any one of the conductive adhesive layer, the metal layer, the protective layer, and other layers provided in the laminated cured product, or two or more layers, and the storage elastic modulus. It can be controlled by changing E'. By changing the loss elastic modulus E ″ and the storage elastic modulus E ″ of one layer or two or more layers included in the laminated cured product, the loss elastic modulus E ″ and the storage elastic modulus of the laminated cured product are changed. This is because the rate E'changes and the loss tangent of the laminated cured product changes.

As an example of a method of changing the loss elastic modulus E ″ and the storage elastic modulus E ″ of one layer or two or more layers included in the laminated cured product, control of the amount of the curing agent in the protective layer can be mentioned. That is, by increasing or decreasing the amount of the curing agent in the protective layer, the storage elastic modulus E'of the protective layer is increased or decreased. As a result, the storage elastic modulus E'of the laminated cured product increases or decreases, and the loss tangent of the laminated cured product decreases or increases.
The method for controlling the loss tangent of the laminated cured product is not particularly limited, and the type and compounding ratio of the thermoplastic resin or the thermosetting resin and the curing agent are changed, the thickness of each layer is changed, and the metal layer is used. Conventionally known methods such as changing the type can be applied.

《Metal layer》
The metal layer of the present invention has a function of imparting high-frequency shielding property to the electromagnetic wave shielding sheet. At the interface between the conductive adhesive layer and the metal layer, the surface on the side where the metal layer is in contact with the conductive layer has a Flop Index (FI) of 10 to 90 calculated by the formula (1). By controlling the FI to be in the range of 10 to 90, both transmission characteristics and thermal cycle reliability can be achieved. Details of the FI and the effects obtained by controlling the FI will be described later.
Further, the metal layer of the present invention has a plurality of openings and an aperture ratio of 0.10 to 20%. As a result, the solder reflow resistance is improved, and it is possible to suppress the occurrence of poor appearance and the deterioration of connection reliability.

[Flop Index (FI)]
Flop Index (FI) is a parameter calculated by the equation (1).

The FI measurement system is shown in FIG. 2 (a). The FI irradiates light (incident light) at an incident angle of 45 ° with respect to the perpendicular direction of the surface to be measured, detects the light reflected at a certain angle (specular reflected light) by a detector, and quantifies it. Calculated using lightness L ^*. L ^* is the brightness L ^* in the ^{L *} a ^* b ^* color system defined by JIS Z8729, ^{and L *} _{15 °} , L ^* _{45 °} , and L ^* _{110 °} are in the perpendicular direction of the surface to be measured, respectively. ^{On the other hand, L *} is observed at offset angles of 15 °, 45 °, and 110 ° from the specularly reflected light of the light incident at an angle of 45 °.
FI is an index for evaluating the unevenness of the surface to be measured and the order of the surface unevenness. As shown in FIG. 2B, when the surface of the measurement target surface is severely uneven and disordered, the incident light is reflected (scattered) at all angles, so that the angle dependence of the detected light amount becomes small. As a result, the FI value calculated by the equation (1) becomes a small value. On the other hand, as shown in FIG. 2C, when the unevenness of the surface to be measured is gentle and the order is high, the incident light is strongly reflected at a certain angle, so that the amount of light detected depends on the angle. Becomes larger. In particular, among the light observed at the offset angles of 15 °, 45 °, and 110 °, the amount of light at 15 ° is large, so that the FI is a large value.

The FI value of this metal layer does not change due to the process of forming the electromagnetic wave shield layer such as a heating press. Therefore, the FI of the surface of the metal layer in contact with the conductive adhesive layer in the electromagnetic wave shielding layer is also 10 to 90.

Further, in the metal layer of the electromagnetic wave shield sheet, due to the nature of the electric current, the electric current flows on the surface of the metal layer at a high frequency. Since the transmission characteristics of signal wiring in a wiring circuit board are affected by the current flowing through a nearby conductor, if the surface of the metal layer adjacent to the signal wiring is uneven, the distance from the current flowing through the metal surface will fluctuate. However, the transmission characteristics become unstable. Therefore, from the viewpoint of transmission characteristics, the FI of the surface of the metal layer in contact with the conductive adhesive layer is preferably 10 or more, more preferably 15 or more, and further preferably 20 or more.

On the other hand, from the viewpoint of the reliability of the cold cycle, as a result of diligent studies, it was found that the reliability of the cold cycle is improved by setting the FI of the metal layer in the range of 10 to 90. This is because even when the shape of the conductive adhesive layer changes due to expansion and contraction in the thermal cycle, the unevenness formed on the surface of the metal layer is made moderately steep, and the unevenness pattern is given appropriate disorder. It is considered that this is because the contact between the conductive filler in the adhesive layer and the metal layer is maintained and the deterioration of the connection resistance value is suppressed. As a result of the examination, the FI of the metal layer is more preferably in the range of 15 to 85, and further preferably in the range of 20 to 80.

[FI control method]
As a method for controlling the FI on the surface of the metal layer, for example, a method of adhering roughened particles on the surface of a copper foil to form a roughened surface, using a buff described in Japanese Patent Application Laid-Open No. 2017-13473. A method of polishing the metal surface using a polishing cloth, a method of polishing the metal surface using a polishing cloth, a method of forming a metal layer on a carrier material having irregularities and transferring the irregularities of the carrier material, compression. An example is a shot blast method in which an abrasive is sprayed onto a metal surface by air. The method for controlling the FI on the surface of the metal layer is not limited to the illustrated method, and a conventionally known method can be applied.

[Thickness of metal layer]
The thickness of the metal layer is preferably 0.3 μm or more. By setting the thickness of the metal layer to 0.3 μm or more, transmission of electromagnetic noise generated from the wiring circuit board can be suppressed, and sufficient high-frequency shielding properties can be exhibited. The thickness of the metal layer is more preferably 0.5 μm or more. On the other hand, the thickness of the metal layer is preferably 5.0 μm or less. By setting the thickness of the metal layer to 5.0 μm or less, the loss tangent of the laminated cured product can be increased, and the reliability of the thermal cycle is improved. The upper limit of the thickness of the metal layer is more preferably 3.5 μm or less.

[Components of metal layer]
As the metal layer, for example, a metal foil, a metal vapor deposition film, or a metal plating film can be used.
The metal used for the metal foil is preferably a conductive metal such as aluminum, copper, silver, or gold, and any one type of metal or an alloy of a plurality of metals can be used. Copper, silver and aluminum are more preferable, and copper is even more preferable from the viewpoint of high frequency shielding property and cost. As copper, for example, it is preferable to use rolled copper foil or electrolytic copper foil.
As the metal used for the metal vapor deposition film and the metal plating film, it is preferable to use one kind of conductive metal such as aluminum, copper, silver and gold, or an alloy of a plurality of metals, and copper and silver are more preferable. One surface of the metal foil, the metal vapor deposition film, and the metal plating film may be coated with a metal or an organic substance such as a rust preventive.

[Aperture]
The metal layer has a plurality of openings, and the aperture ratio is 0.10 to 20%. Having an opening improves solder reflow resistance. By having an opening, when the electromagnetic wave shielding wiring circuit board is soldered, the volatile components contained in the polyimide film and the coverlay adhesive of the wiring circuit board are released to the outside, and the coverlay adhesive and the electromagnetic wave shielding sheet are released. It is possible to suppress the occurrence of poor appearance due to the peeling of the interface.

The shape of the opening seen from the surface of the metal layer can be, for example, a perfect circle, an ellipse, a quadrangle, a polygon, a star, a trapezoid, a branch, or the like, if necessary. From the viewpoint of manufacturing cost and ensuring the toughness of the metal layer, the shape of the opening is preferably a perfect circle and an ellipse.

[Aperture ratio of metal layer]
The aperture ratio of the metal layer is in the range of 0.10 to 20% and can be calculated by the following mathematical formula (2).
Formula (2)
(Aperture ratio [%]) = (Area of opening per unit area) / (Area of opening per unit area + Area of non-opening per unit area) x 100

When the aperture ratio is 0.10 or more, the volatile components during the solder reflow treatment can be sufficiently released, and the appearance deterioration due to the interfacial peeling of the coverlay adhesive and the electromagnetic wave shield sheet and the deterioration of the connection reliability can be prevented. It is preferable because it can be suppressed.
On the other hand, when the aperture ratio is 20% or less, the amount of electromagnetic noise passing through the opening portion can be reduced and the shielding property can be improved, which is preferable. The range of the aperture ratio that achieves both solder flow resistance and high frequency shielding property at a high level is more preferably 0.30 to 15%, and further preferably 0.50 to 6.5%.

In particular, in the electromagnetic wave shield sheet having a smooth interface with the conductive adhesive layer in the range where the FI of the metal layer is 80 or more, the adhesion between the metal layer and the conductive adhesive layer is weak, and the metal layer and the conductive adhesive layer are conductive during the solder reflow treatment. Volatile components may expand at the interface with the adhesive layer, causing appearance defects such as delamination and floating. However, volatile by setting the opening ratio to 0.10% or more, preferably 0.50% or more. The components can be sufficiently released, and the occurrence of delamination and floating can be further suppressed.

The aperture ratio is measured, for example, by binarizing the openings and non-openings using an image magnified 500 to 2000 times with a laser microscope and a scanning electron microscope (SEM) perpendicular to the plane direction of the metal layer. It can be obtained by setting the number of binarized color pixels per unit area as each area.

[Manufacturing method of metal layer having openings]
As a method for producing a metal layer having an opening, a conventionally known method can be applied. A method of forming a pattern resist layer on a metal foil and etching the metal foil to form an opening (i), screen printing. A method of printing a conductive paste on a predetermined pattern (ii), a method of screen-printing an anchoring agent with a predetermined pattern and metal-plating only the anchoring agent printed surface (iii), and JP-A-2015-63730. The manufacturing method (iv) and the like described above can be applied.
That is, a water-soluble or solvent-soluble ink is pattern-printed on the support, and a metal vapor-deposited film is formed on the surface of the support to remove the pattern. A metal layer having an opening with a carrier can be obtained by forming a release layer on the surface and electroplating. Among these, an opening forming method (i) in which a pattern resist layer is formed and a metal foil is etched. However, it is preferable because the shape of the opening can be precisely controlled. However, the shape of the opening may be controlled by other methods, and the method for manufacturing the metal layer is not limited to the etching method (i).

《Conductive adhesive layer》
The conductive adhesive layer can be formed using a conductive resin composition. The conductive resin composition contains a binder resin and a conductive filler. As the binder resin, either a thermoplastic resin or a thermosetting resin and a curing agent can be used. As the conductive adhesive layer, either an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer can be used. The isotropic conductive adhesive layer has conductivity in the vertical and horizontal directions when the electromagnetic wave shield sheet is placed horizontally. Further, the anisotropic conductive adhesive layer has conductivity only in the vertical direction when the electromagnetic wave shield sheet is placed horizontally.
The conductive adhesive layer may be either isotropically conductive or anisotropically conductive, and in the case of anisotropically conductive, the cost can be reduced, which is preferable.

[Thermoplastic resin]
The thermoplastic resins 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, and liquid crystals. Examples include polymers and fluororesins. Although not particularly limited, a material having a low dielectric constant and a low dielectric loss tangent is preferable from the viewpoint of transmission loss, and a material having a low dielectric constant is preferable from the viewpoint of characteristic impedance, and liquid crystal polymers, fluororesins and the like can be mentioned.
The thermoplastic resin can be used alone or in combination of two or more.

[Thermosetting resin]
A thermosetting resin is a resin having a plurality of functional groups capable of reacting with a curing agent. Functional groups include, for example, hydroxyl groups, phenolic hydroxyl groups, methoxymethyl groups, carboxyl groups, amino groups, epoxy groups, oxetanyl groups, oxazoline groups, oxazine groups, aziridine groups, thiol groups, isocyanate groups, blocked isocyanate groups and blocked functional groups. Examples thereof include a carboxyl group and a silanol group. The thermosetting resin includes, for example, acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane resin, polyurethane urea resin, epoxy resin, oxetane resin, phenoxy resin, polyimide resin, polyamide resin, polyamideimide resin, and phenolic resin. Known resins such as resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins and fluororesins can be mentioned.
The thermosetting resin can be used alone or in combination of two or more.

Among these, polyurethane resin, polyurethane urea resin, polyester resin, epoxy resin, phenoxy resin, polyimide resin, polyamide resin, and polyamideimide resin are preferable from the viewpoint of solder reflow resistance.

[Hardener]
The curing agent has a plurality of functional groups capable of reacting with the functional groups of the thermosetting resin. Examples of the curing agent include known compounds such as epoxy compounds, acid anhydride group-containing compounds, isocyanate compounds, aziridine compounds, amine compounds, phenol compounds, and organic metal compounds.
The curing agent can be used alone or in combination of two or more.

The curing agent is preferably contained in an amount of 1 to 50 parts by weight, more preferably 3 to 40 parts by weight, still more preferably 3 to 30 parts by weight, based on 100 parts by weight of the thermosetting resin.

The thermoplastic resin and the thermosetting resin can be used alone or in combination of both.

[Conductive filler]
The conductive filler has a function of imparting conductivity to the conductive adhesive layer. As the material of the conductive filler, for example, conductive metals such as gold, platinum, silver, copper and nickel and alloys thereof, and fine particles of the conductive polymer are preferable, and silver is more preferable from the viewpoint of cost and conductivity. Further, composite fine particles having a coating layer covering the surface of the nuclei with a metal or resin as the nuclei instead of the fine particles of a single material are also preferable from the viewpoint of cost reduction. Here, the nucleolus is preferably selected from nickel, silica, copper and alloys thereof, and resins, which are inexpensive. The coating layer is preferably a conductive metal or a conductive polymer. Examples of the conductive metal include gold, platinum, silver, nickel, manganese, indium and the like, and alloys thereof. Examples of the conductive polymer include polyaniline and polyacetylene. Among these, silver is preferable from the viewpoint of price and conductivity.

The shape of the conductive filler is not limited as long as the desired conductivity can be obtained. Specifically, for example, spherical, flake-shaped, leaf-shaped, dendritic-shaped, plate-shaped, needle-shaped, rod-shaped, and grape-shaped are preferable. Further, two kinds of conductive fillers having different shapes may be mixed.
The conductive filler may be used alone or in combination of two or more.

The average particle diameter of the conductive filler, D is a ₅₀ average particle size, from the viewpoint of sufficiently ensuring conductivity is preferably at least 2 [mu] m, more preferably at least 5 [mu] m, and more preferably be 7μm or more. On the other hand, from the viewpoint of achieving compatibility with the thinness of the conductive adhesive layer, it is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. D ₅₀ average particle size can be determined by a laser diffraction scattering method particle size distribution measuring apparatus or the like.

The content of the conductive filler in the conductive adhesive layer is preferably 35 to 90% by weight, more preferably 39 to 70% by weight, still more preferably 40 to 65% by weight. When the content is 35% by weight or more, the connection between the conductive adhesive layer and the ground wiring is improved, so that the high frequency shielding property and the reliability of the thermal cycle are improved. On the other hand, when it is 90% by weight or less, the solder reflow resistance and the transmission characteristics are improved.

The conductive resin composition has other optional components such as a silane coupling agent, a rust preventive, a reducing agent, an antioxidant, a pigment, a dye, a tackifier resin, and a plasticizer for the purpose of improving desired physical properties and imparting functions. UV absorbers, antifoaming agents, leveling adjusters, fillers, flame retardants, etc. can be blended. For example, carbon particles can be added for the purpose of adjusting the viscoelasticity of the conductive adhesive layer. Examples of carbon particles include carbon black, ketjen black, acetylene black, carbon nanotubes, graphene and the like.

The conductive resin composition can be obtained by mixing and stirring the materials described above. For stirring, a known stirring device such as a dispermat or a homogenizer can be used.

A known method can be used for producing the conductive adhesive layer. For example, a method of forming a conductive adhesive layer by applying a conductive resin composition on a peelable sheet and drying it, or using an extrusion molding machine such as a T-die to obtain a conductive resin composition. It can also be formed by extruding into a sheet.

The coating method is, for example, gravure coating method, kiss coating method, die coating method, lip coating method, comma coating method, blade method, roll coating method, knife coating method, spray coating method, bar coating method, spin coating method, dip coating method. A known coating method such as a method can be used. It is preferable to carry out a drying step at the time of coating. For the drying step, for example, a known drying device such as a hot air dryer or an infrared heater can be used.

The thickness of the conductive adhesive layer is preferably 2 to 30 μm, more preferably 3 to 15 μm, and even more preferably 4 to 9 μm. When the thickness is in the range of 2 to 30 μm, the reliability of the thermal cycle and the resistance to solder reflow can be improved.

《Protective layer》
The protective layer can be formed using a resin composition. The resin composition contains a binder resin. As the binder resin, either a thermoplastic resin or a thermosetting resin and a curing agent can be used.

The weight average molecular weight of the binder resin is preferably 10,000 or more. When the weight average molecular weight of the thermosetting resin is 10,000 or more, decomposition and dissolution of the coating film when exposed to cleaning chemicals can be suppressed, and chemical resistance is improved. The weight average molecular weight of the thermosetting resin is more preferably 30,000 or more, and further preferably 50,000 or more.

[Thermoplastic resin]
The thermoplastic resins 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, and liquid crystals. Examples include polymers and fluororesins. Although not particularly limited, a material having a low dielectric constant and a low dielectric loss tangent is preferable from the viewpoint of transmission loss, and a material having a low dielectric constant is preferable from the viewpoint of characteristic impedance, and liquid crystal polymers, fluororesins and the like can be mentioned.
The thermoplastic resin can be used alone or in combination of two or more.

[Thermosetting resin]
A thermosetting resin is a resin having a plurality of functional groups capable of reacting with a curing agent. Functional groups include, for example, hydroxyl groups, phenolic hydroxyl groups, methoxymethyl groups, carboxyl groups, amino groups, epoxy groups, oxetanyl groups, oxazoline groups, oxazine groups, aziridine groups, thiol groups, isocyanate groups, blocked isocyanate groups and blocked functional groups. Examples thereof include a carboxyl group and a silanol group. The thermosetting resin includes, for example, acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane resin, polyurethane urea resin, epoxy resin, oxetane resin, phenoxy resin, polyimide resin, polyamide resin, polyamideimide resin, and phenolic resin. Known resins such as resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins and fluororesins can be mentioned.
The thermosetting resin can be used alone or in combination of two or more.

Among these, polyurethane resin, polyurethane urea resin, polyester resin, epoxy resin, phenoxy resin, polyimide resin, polyamide resin, and polyamideimide resin are preferable from the viewpoint of solder reflow resistance.

[Hardener]
The curing agent has a plurality of functional groups capable of reacting with the functional groups of the thermosetting resin. Examples of the curing agent include known compounds such as epoxy compounds, acid anhydride group-containing compounds, isocyanate compounds, aziridine compounds, amine compounds, phenol compounds, and organic metal compounds.
The curing agent can be used alone or in combination of two or more.

The curing agent is preferably contained in an amount of 1 to 50 parts by weight, more preferably 3 to 40 parts by weight, still more preferably 3 to 30 parts by weight, based on 100 parts by weight of the thermosetting resin.

The thermoplastic resin and the thermosetting resin can be used alone or in combination of both.

Other optional components of the resin composition include silane coupling agents, rust preventives, reducing agents, antioxidants, pigments, dyes, tackifier resins, plasticizers, UV absorbers, defoamers, leveling adjusters, and fillings. Can contain agents, flame retardants, etc.

The resin composition can be obtained by mixing and stirring the materials described above. For stirring, a known stirring device such as a dispermat or a homogenizer can be used.

A known method can be used to prepare the protective layer. For example, a method of forming a protective layer by applying a resin composition on a peelable sheet and drying it, or by extruding the resin composition into a sheet using an extrusion molding machine such as a T-die. It can also be formed.

The coating method is, for example, gravure coating method, kiss coating method, die coating method, lip coating method, comma coating method, blade method, roll coating method, knife coating method, spray coating method, bar coating method, spin coating method, dip coating method. A known coating method such as a method can be used. It is preferable to carry out a drying step at the time of coating. For the drying step, for example, a known drying device such as a hot air dryer or an infrared heater can be used.

Further, as the protective layer, a film formed of an insulating resin such as polyester, polycarbonate, polyimide, polyamideimide, polyamide, polyphenylene sulfide, and polyetheretherketone can also be used.

The thickness of the protective layer is preferably 2 to 20 μm. When the thickness of the protective layer is 2 to 20 μm, dissolution of the protective layer and peeling from the metal layer after exposure to the cleaning chemical can be suppressed.

<< Manufacturing method of electromagnetic wave shield sheet >>
In the production of the electromagnetic wave shield sheet, a known method can be used as a method of laminating the conductive adhesive layer and the metal layer.
For example, (i) a conductive adhesive layer is formed on a peelable sheet, and a conductive adhesive layer is provided on the electrolytic copper foil surface side of an electrolytic copper foil (also referred to as a copper foil with a carrier material) having an opening with a carrier material. After laminating and laminating, the carrier material is peeled off. Then, a method in which the surface from which the carrier material has been peeled off and a protective layer separately formed on the peelable sheet are laminated and laminated, (ii) electrolysis in which the protective layer is formed on the peelable sheet and has an opening with the carrier material. After laminating a protective layer on the electrolytic copper foil surface side of the copper foil and laminating it, the carrier material is peeled off. Then, a method of laminating the surface from which the carrier material has been peeled off and the conductive adhesive layer separately formed on the peelable sheet in layers, (iii) on the electrolytic copper foil surface side of the electrolytic copper foil having an opening with the carrier material. The resin composition is applied to form a protective layer, and a peelable sheet is attached. After that, the carrier material is peeled off, and the conductive adhesive layer separately formed on the peelable sheet is laminated and laminated. (Iv) The conductive adhesive layer is formed on the peelable sheet, and the electrolytic copper of the copper foil with the carrier material is electrolytic copper. After laminating the conductive adhesive layer on the foil surface side, the carrier material is peeled off. Then, after laminating the surface from which the carrier material has been peeled off and the protective layer separately formed on the peelable sheet are laminated, a method of forming an opening in the electromagnetic wave shield sheet with a needle-shaped jig, (v) peelability. The protective layer formed on the sheet is laminated on the electrolytic copper foil surface side of the electrolytic copper foil having the opening with the carrier material, and then the carrier material is peeled off. Then, a method of forming a conductive adhesive layer on the surface from which the carrier material has been peeled off, (vi) a method of forming a conductive adhesive layer on a peelable sheet, and among the surfaces of a rolled copper foil having openings, the FI is 10 to 10. A method of laminating a surface of 90, a conductive adhesive layer on top of each other, and then laminating the other surface laminated with the conductive adhesive layer and a protective layer separately formed on a peelable sheet, (vii). ) After forming a protective layer on the peelable sheet and laminating the conductive adhesive layer on the other surface of the rolled copper foil having an opening, which has an FI of 10 to 90, is laminated. A method of laminating the other surface laminated with the protective layer and a conductive adhesive layer separately formed on a peelable sheet. (Viii) Of the surfaces of the rolled copper foil having an opening, the FI is 10 to 10. A resin composition is applied to the other surface of the surface of 90 to form a protective layer, and a peelable sheet is attached. After that, a method of superimposing and laminating the other surface and a conductive adhesive layer separately formed on a peelable sheet, (ix) of the surfaces of the rolled copper foil having an opening, the FI is 10 to 90. A conductive resin composition is applied to the surface to form a conductive adhesive layer, and a peelable sheet is attached. After that, a method of superimposing and laminating the other surface and a protective layer separately formed on the peelable sheet can be mentioned.

The electromagnetic wave shield sheet may include other functional layers in addition to the conductive adhesive layer, the metal layer, and the protective layer. The other functional layer is a layer having functions such as hard coat property, water vapor barrier property, oxygen barrier property, thermal conductivity, low dielectric constant, high dielectric constant, and heat resistance.

The electromagnetic wave shield sheet of the present invention can be used for various purposes in which electromagnetic waves need to be shielded. For example, it can be used not only for flexible printed wiring boards, but also for rigid printed wiring boards, COFs, TABs, flexible connectors, liquid crystal displays, touch panels, and the like. It can also be used as a member for blocking electromagnetic waves of building materials such as personal computer cases, walls of building materials and window glass, and vehicles, ships and aircraft.

Further, the electromagnetic wave shield sheet of the present invention can have an excellent transmission characteristic that the transmission loss when a sine wave of 15 GHz is passed through the signal wiring of the coplanar circuit is less than 8 dB.

Specifically, the transmission characteristics can be evaluated, for example, as follows.
First, a coplanar circuit is prepared.
The coplanar circuit is one of the flat transmission circuits in which signal wiring is printed on one side of an insulating base material such as a polyimide film. In the present invention, the coplanar circuit has two signal wirings sandwiched on the polyimide film. Use a circuit in which ground wiring is formed in parallel. In the coplanar circuit described above, a ground pattern for grounding is installed on the opposite surface via a through hole.
The conductive adhesive layer of the electromagnetic wave shield sheet is attached to the insulating base material surface on the opposite side of the signal wiring of the coplanar circuit, and the electromagnetic wave shield sheet is laminated by heat pressing. At this time, the electromagnetic wave shield sheet conducts with the partially exposed ground pattern. By the method described above, a test piece for evaluating transmission characteristics can be obtained.

A network analyzer is connected to the coplanar circuit of this test piece, and the ratio of input power and output power when a sine wave of 100 MHz to 20 GHz is passed through the signal wiring of the coplanar circuit is calculated, and the transmission loss is calculated and evaluated. Can be done. The voltage and current ratio may be used instead of electric power.

In the present invention, when a 15 GHz sine wave is passed through the signal wiring of the coplanar circuit, the transmission loss is preferably less than 8 dB, more preferably less than 7.5 dB, still more preferably less than 7 dB. When the transmission loss is less than 8 dB, it is possible to reduce the transmission loss at a high level.

In the electromagnetic wave shield sheet of the present invention, when a thermoplastic resin is used as the binder resin in the conductive adhesive layer, the contained thermoplastic resin exists in a solid state, and the thermoplastic resin is melted by the wiring circuit board and the thermal press. The desired adhesive strength can be obtained by solidifying again after cooling.

In the electromagnetic wave shield sheet of the present invention, when a thermosetting resin is used as the binder resin in the conductive adhesive layer, the contained thermosetting resin and the curing agent are present in an uncured state (B stage), and the wiring circuit board and the wiring circuit board. By curing by hot pressing (C stage), the desired adhesive strength can be obtained. The uncured state includes a semi-cured state in which a part of the curing agent is cured.

The electromagnetic wave shield sheet is generally stored in a state where a peelable sheet is attached to the conductive adhesive layer and the protective layer in order to prevent foreign matter from adhering.

The peelable sheet is a sheet obtained by performing a known peeling treatment on a base material such as paper or plastic.

<Electromagnetic wave shielded wiring circuit board>
The electromagnetic wave shielded wiring circuit board includes an electromagnetic wave shield layer and a cover coat layer formed from the electromagnetic wave shield sheet of the present invention, and a wiring circuit board having a circuit pattern having signal wiring and ground wiring and an insulating base material. ..
The wiring circuit board has a circuit pattern having signal wiring and ground wiring on the surface of the insulating base material, and insulates and protects the signal wiring and ground wiring on the wiring circuit board, and at least one on the ground wiring. A cover coat layer having vias is formed in the portion, the conductive adhesive layer surface of the electromagnetic wave shield sheet is arranged on the cover coat layer, and then the electromagnetic wave shield sheet is hot-pressed to form a conductive adhesive layer inside the vias. It can be manufactured by flowing in and adhering to the ground wiring.

An example of the electromagnetic wave shielding wiring circuit board of the present invention will be described with reference to FIG.
The electromagnetic wave shield layer 12 has a configuration including a conductive adhesive layer 1, a metal layer 2, and a protective layer 3.

The cover coat layer 8 is an insulating material that covers the signal wiring of the wiring circuit board and protects it from the external environment. As the cover coat layer, a polyimide film with a thermosetting adhesive, a thermosetting or ultraviolet curable solder resist, or a photosensitive coverlay film is preferable, and a photosensitive coverlay film is more preferable for fine processing. Further, as the cover coat layer, a known resin having heat resistance and flexibility such as polyimide is generally used. The thickness of the cover coat layer is usually about 10 to 100 μm.

The circuit pattern includes a ground wiring 5 for grounding and a signal wiring 6 for sending an electric signal to an electronic component. Both are generally formed by etching a copper foil. The thickness of the circuit pattern is usually about 1 to 50 μm.

The insulating base material 9 is a support for a 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, a liquid crystal polymer having a low relative permittivity and a dielectric loss tangent is more preferable in consideration of the use of a wiring circuit board for transmitting a high frequency signal.
When the wiring circuit board is a rigid wiring board, glass epoxy is preferable as the constituent material of the insulating base material. By providing an insulating base material such as these, the wiring circuit board can obtain high heat resistance.

The heat pressing between the electromagnetic wave shield sheet 10 and the wiring circuit board is generally performed under the 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. The conductive adhesive layer 1 and the cover coat layer 8 are brought into close contact with each other by a hot press, and the conductive adhesive layer 1 flows to fill the vias 11 formed in the cover coat layer 8 to conduct conduction with the ground wiring 5. Can be taken. The thermosetting resin reacts and cures by the heat press to form the electromagnetic wave shield layer 12.
In addition, in order to accelerate curing, post-cure may be performed at 150 to 190 ° C. for 30 to 90 minutes after hot pressing.

The opening area of the via 11 is preferably 0.8 mm ² or less, 0.008 mm ² or more. By setting the above range, the area of the ground wiring can be narrowed, and the size of the printed wiring board can be reduced.
The shape of the via is not particularly limited, and any of them can be used depending on the application such as a circle, a square, a rectangle, a triangle, and an amorphous shape.

It is preferable to laminate the electromagnetic wave shield layer on both sides of the wiring circuit board from the viewpoint of more effectively suppressing the leakage of electromagnetic waves. In addition, the electromagnetic wave shield layer in the electromagnetic wave shielding wiring circuit board 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 wiring circuit board. This makes it possible to reduce costs and incorporate it into a narrow area inside the housing.

Further, the signal wiring is not particularly limited, and can be used for either a single-ended circuit consisting of one signal wiring or a differential circuit consisting of two signal wirings, but the differential circuit is more suitable. preferable. On the other hand, when the circuit pattern area of the wiring circuit board is limited and it is difficult to form the ground circuit in parallel, the ground circuit is not provided next to the signal circuit, and the electromagnetic wave shield layer is used as the ground circuit. A printed wiring board structure having a ground in the thickness direction can also be used.

The electromagnetic wave shielding wiring circuit board of the present invention is preferably provided (mounted) on electronic devices such as notebook PCs, mobile phones, smartphones, and tablet terminals in addition to liquid crystal displays and touch panels.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. Further, in the examples, "part" means "part by weight", and "%" means "% by weight".

The acid value of the resin, the weight average molecular weight (Mw), the glass transition temperature (Tg), and the average particle size of the conductive filler were measured by the following methods.

<< Measurement of acid value of binder resin >>
The acid value was measured according to JIS K0070. Approximately 1 g of the sample is precisely weighed in a stoppered Erlenmeyer flask, and 100 ml of a tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2/1) mixed solution is added and dissolved. To this, a phenolphthalein test solution was added as an indicator, titrated with a 0.1 N alcoholic potassium hydroxide solution, and the end point was when the indicator held a pink color for 30 seconds. The acid value was calculated by the following formula (unit: mgKOH / g).
Acid value (mgKOH / g) = (5.611 × a × F) / S
However,
S: Sample collection amount (g)
a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)
F: Titer of 0.1N alcoholic potassium hydroxide solution

<< Measurement of weight average molecular weight (Mw) of binder resin >>
The weight average molecular weight (Mw) was measured by using GPC (gel permeation chromatography) "HPC-8020" manufactured by Tosoh Corporation. GPC is a liquid chromatography in which a substance dissolved in a solvent (THF; tetrahydrofuran) is separated and quantified according to the difference in molecular size. In the measurement in the present invention, two "LF-604" (manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID x 150 mm size) are connected in series to the column, the flow rate is 0.6 ml / min, and the column temperature is set. It was carried out under the condition of 40 ° C., and the weight average molecular weight (Mw) was determined in terms of polystyrene.

<< Glass transition temperature (Tg) of binder resin >>
The Tg was measured by differential scanning calorimetry (“DSC-1” manufactured by METTLER TOLEDO).

<< Measurement of average particle size of conductive filler >>
D ₅₀ average particle size, using a laser diffraction scattering method particle size distribution measuring apparatus LS13320 (manufactured by Beckman Coulter, Inc.) at Tornado Dry Powder sample module is a numerical value of the conductive filler obtained by measuring the particle The cumulative value in the cumulative diameter distribution is a particle size of 50%. The refractive index was set to 1.6.

Subsequently, the raw materials used in the examples are shown below.
"material"
Conductive filler: Composite fine particles (dendrite-like fine particles in which 10 parts by weight of silver is coated on 100 parts by weight of copper in the core) Average particle size D ₅₀ : 11.0 μm Binder resin manufactured by Fukuda Metal Foil Powder Industry Co., Ltd. 1: Polyurethane urea resin with acid value of 5 mgKOH / g, weight average molecular weight of 70,000, and Tg of -5 ° C (manufactured by Toyochem)
Binder resin 2: Acid value 5 mgKOH / g, weight average molecular weight 2,000, Tg is -14 ° C polyurethane urea resin (manufactured by Toyochem)
Binder resin 3: Polyurethane urea resin having an acid value of 5 mgKOH / g, a weight average molecular weight of 10,500, and a Tg of -11 ° C (manufactured by Toyochem).
Binder resin 4: Polyurethane urea resin having an acid value of 5 mgKOH / g, a weight average molecular weight of 32,000, and a Tg of -9 ° C (manufactured by Toyochem).
Epoxy compound: "JER828" (bisphenol A type epoxy resin epoxy equivalent = 189g / eq) Aziridine compound manufactured by Mitsubishi Chemical Co., Ltd .: "Chemitite PZ-33" Pigment manufactured by Nippon Catalyst Co., Ltd. Pigment: Carbon black "MA100" Carrier material manufactured by Mitsubishi Chemical Co., Ltd .: "Empoxy S25" manufactured by Unitika

Table 1 shows the copper foil with carrier material used.
These copper foils with a carrier material have a thickness, an aperture ratio, etc. shown in Table 1 by a method of forming a pattern resist layer on the copper foil formed on the carrier material and etching the copper foil to form an opening. It is a copper foil that has.

<Manufacturing of conductive adhesive layer 1>
In terms of solid content, 100 parts of binder resin 1, 47 parts of conductive filler, 10 parts of epoxy compound, 0.5 part of aziridine compound are charged in a container, and a mixed solvent (toluene:) is prepared so that the non-volatile content concentration becomes 40%. Isopropyl alcohol = 2: 1 (weight ratio)) was added and stirred with a disper for 10 minutes to obtain a conductive resin composition.

The conductive resin composition was coated on a peelable sheet with a bar coater so that the drying thickness was 10 μm, and dried in an electric oven at 100 ° C. for 2 minutes to obtain a conductive adhesive layer 1.

<Manufacturing of conductive adhesive layers 2 to 8>
The conductive adhesive layers 2 to 8 shown in Tables 2 to 5 were prepared in the same manner as in the conductive adhesive layer 1 except that the amount of the conductive filler added was changed.

[Example 1]
A resin composition 1 was obtained by adding 100 parts of a binder resin 1, 30 parts of an epoxy compound and 7.5 parts of an aziridine curing agent in terms of solid content and stirring with a disper for 10 minutes. The obtained resin composition 1 is coated on a copper foil A1 with a carrier material using a bar coater so that the drying thickness is 5 μm, and dried in an electric oven at 100 ° C. for 2 minutes to form a protective layer 1. Then, a slightly adhesive peelable sheet was attached to the protective layer 1.

Next, the carrier material of the copper foil A1 with the carrier material was peeled off, the copper foil surface was buffed, and the FI of the copper foil surface was adjusted to the values shown in Table 2 to obtain the copper foil 2. By adhering the conductive adhesive layer 4 to the surface of the copper foil after polishing, an electromagnetic wave shield sheet composed of "peeling sheet / protective layer 1 / copper foil 2 / conductive adhesive layer 4 / peelable sheet" was obtained. The copper foil 2 and the conductive adhesive layer 4 were bonded together by a thermal laminator at a ^{temperature of 90 ° C. and a pressure of 3 kgf / cm 2.}

[Examples 2-32, Comparative Examples 1-4]
As shown in Tables 1 to 5, Examples 2 to 32 and Comparative Examples 1 to 4 were carried out in the same manner as in Example 1 except that the types of the conductive adhesive layer, the protective layer, and the copper foil were changed. Electromagnetic wave shield sheets were obtained respectively. When the target value of the FI on the copper foil surface was different from the value of the carrier material, the FI was adjusted by appropriately polishing or roughening the surface by buffing.

For the obtained electromagnetic wave shield sheet, the thickness of each layer, the FI of the metal layer, and the loss tangent of the electromagnetic wave shield sheet were measured by the following methods.

<< Measurement of each layer thickness >>
The thicknesses of the conductive adhesive layer, the metal layer, and the protective layer of the electromagnetic wave shield sheet were measured by the following methods.
Peel off the peelable sheet on the conductive adhesive layer side of the electromagnetic wave shield sheet, attach the exposed conductive adhesive layer and the polyimide film ("Kapton 200EN" manufactured by Toray DuPont), and heat for 30 minutes at 2 MPa and 170 ° C. Pressed. After cutting this into a size of about 5 mm in width and 5 mm in length, 0.05 g of epoxy resin (Petropoxy 154, manufactured by Maruto) is dropped into a slide glass, and an electromagnetic wave shield sheet is adhered to the slide glass / electromagnetic wave shield. A laminate having a sheet / polyimide film composition was obtained. The obtained laminate was cut by ion beam irradiation from the polyimide film side using a cross section polisher (SM-09010 manufactured by JEOL Ltd.) to obtain a measurement sample of an electromagnetic wave shield sheet after hot pressing.

The cross section of the obtained measurement sample was measured with a laser microscope (VK-X100 manufactured by KEYENCE CORPORATION), and the thickness of each layer was measured from the observed enlarged image. The magnification was 500 to 2000 times.

《Measurement of FI》
The FI of the metal layer of the electromagnetic wave shield sheet was measured by the following method.
Peel off the peelable sheet on the conductive adhesive layer side of the electromagnetic wave shield sheet, attach an adhesive tape ("CT1835" manufactured by Nichiban Co., Ltd.) to the exposed conductive adhesive layer, leaving the end of the adhesive tape, and attach the end of the adhesive tape. Peeling was performed from the portion, and the conductive adhesive layer / adhesive tape was peeled off. The conductive adhesive layer was removed, and the surface of the exposed metal layer was measured at L ^* _{15 °} , L ^* _{45 °} , L ^* _{110 ° using a multi-angle colorimeter (BYK-mac i23 mm measurement diameter).} The measurement was performed, and the FI was calculated based on the equation (1). The measurement was performed by arranging the multi-angle colorimeter so that the long axis direction of the multi-angle colorimeter and the MD direction of the electromagnetic wave shield sheet coincide with each other. The MD direction refers to the coating direction when the resin composition is coated. The measurement was performed under the conditions that the light source was D50 and the field of view was 2 °.

<< Measurement of loss tangent of laminated cured product >>
The loss tangent of the laminated cured product was measured by the following method.
First, two electromagnetic wave shield sheets having a width of 50 mm and a length of 50 mm are prepared, the peelable sheets on the conductive adhesive layer side of each are peeled off, and the exposed conductive adhesive layers are bonded to each other, and the temperature is 170 ° C., 2.0 MPa. It was crimped under the condition of 30 minutes and heat-cured to obtain a laminated cured product. Then, the central portion of the laminated cured product was cut out to a width of 5 mm and a length of 30 mm to prepare a sample. This sample was set in a dynamic viscoelasticity measuring device (dynamic viscoelasticity measuring device DVA-200, manufactured by IT Measurement Control Co., Ltd.), and the rate of temperature rise: 10 ° C./min, measurement frequency: 1 Hz, strain: 0. Dynamic viscoelasticity measurement was performed under the condition of 08%, and the loss elastic modulus E ″ and the storage elastic modulus E ″ at 125 ° C. were read from the obtained dynamic viscoelasticity curve, and the loss tangent of the laminated cured product was determined. Calculated.

The following evaluation was performed using the obtained electromagnetic wave shield sheet. The results are shown in Tables 2-5.

<Solder flow resistance>
The solder flow resistance was evaluated by the presence or absence of a change in appearance after the electromagnetic wave shield sheet and the molten solder were brought into contact with each other. The appearance of the electromagnetic wave shield sheet having high solder reflow resistance does not change, but the electromagnetic wave shield sheet having low solder reflow resistance causes foaming and peeling.
First, the peelable sheet of the conductive adhesive layer of the electromagnetic wave shield sheet having a width of 25 mm and a length of 70 mm was peeled off, and the exposed conductive adhesive layer and a gold-plated copper-plated laminated plate having a total thickness of 64 μm (gold-plated 0.3 μm /). The gold-plated surface of nickel-plated 1 μm / copper foil 18 μm / adhesive 20 μm / polyimide film 25 μm) was pressure-bonded at 170 ° C., 2.0 MPa, and 30 minutes, and heat-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 at 40 ° C. and 90% RH for 72 hours. After that, the sample is floated on the molten solder at 250 ° C for 1 minute with the polyimide film side down, then the sample is taken out, the appearance is visually observed, and the presence or absence of abnormalities such as foaming, floating, and peeling is checked according to the following criteria. evaluated.

◎: No change in appearance. Very good.
〇: Small foaming is slightly observed. It is good.
Δ: Many small foams are observed. Practical use is possible.
X: Violent foaming and peeling are observed. Not practical.

<Transmission characteristics>
The transmission characteristics were evaluated using a wiring board 21 having a coplanar circuit with an electromagnetic wave shield sheet shown in FIG.

A schematic plan view of the main surface side of the flexible printed wiring board (hereinafter, also referred to as a wiring board having a coplanar circuit) 20 having a coplanar circuit used for the measurement is shown in FIG. 4, FIG. Is shown. First, a double-sided CCL "RF775" (manufactured by Panasonic Corporation) in which a rolled copper foil having a thickness of 12 μm was laminated on both sides of a polyimide film 50 having a thickness of 50 μm was prepared. Then, six through holes 51 (diameter 0.1 mm) were provided in the vicinity of the four rectangular corners. In the figure, for convenience of illustration, only two through holes 51 are shown at each corner. Next, after performing the electroless plating treatment, the electrolytic plating treatment is performed to form a 10 μm copper plating film 52, and the continuity between the main surface and the back surface is ensured through the copper plating film formed in the through hole 51. did. After that, as shown in FIG. 4, two signal wirings 53 having a length of 10 cm are extended on the main surface of the polyimide film 50, and a ground wiring 54 parallel to the signal wiring 53 and a ground wiring 54 are extended to the outside thereof. , The ground pattern 55 was formed in the region including the through hole 51 in the lateral direction of the polyimide film 50.

Then, the copper foil formed on the back surface of the polyimide film 50 was etched to obtain a back surface side ground pattern 56 as shown in FIG. 5 at a position corresponding to the ground pattern 55. The appearance of the circuit and the inspection specifications of the tolerance are the JPCA standard (JPCA-DG02). Next, on the main surface side of the polyimide film 50, a cover coat layer 8 “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 pasted. In FIG. 4, the cover coat layer 8 is shown in a perspective view so that the structure of the signal wiring 53 and the like can be understood. Then, the copper foil pattern exposed from the cover coat layer 8 was nickel-plated (not shown), and then gold-plated (not shown).

Next, as shown in FIG. 6, an electromagnetic wave shield sheet 10 composed of a laminate of the conductive adhesive layer 1, the metal layer 2, and the protective layer 3 was prepared and provided on the conductive adhesive layer 1 of the electromagnetic wave shield sheet 10. The peeling treatment sheet (not shown) was peeled off. Then, on the entire back surface side of the wiring board 20 having the coplanar circuit with the conductive adhesive layer 1 of the electromagnetic wave shield sheet 10 inside, 170 ° C., 2.0
A wiring board 21 having a coplanar circuit with an electromagnetic wave shielding layer was obtained by crimping under the conditions of MPa and 30 minutes. In FIG. 6, the back surface side ground pattern 56 is shown in a perspective view.

The L / S (line / space) of the signal wiring 53 was appropriately adjusted so that the characteristic impedance was within ± 10Ω. The width of the ground wiring 54 was 100 μm, and the distance between the ground wiring 54 and the signal wiring 53 was 1 mm.

A network analyzer E5071C (manufactured by Agilent Japan) is connected to the exposed signal wiring 53 of the wiring board 20 having a coplanar circuit with an electromagnetic wave shield sheet, a sine wave of 15 GHz is input, and the transmission characteristic is measured by measuring the transmission loss. evaluated. The measured transmission characteristics were evaluated according to the following criteria.

⊚: The transmission loss at 15 GHz is less than 7.0 dB, which is extremely good.
〇: The transmission loss at 15 GHz is 7.0 dB or more and less than 7.5 dB, which is good.
Δ: Transmission loss at 15 GHz is 7.5 dB or more and less than 8.0 dB. Practical use is possible.
X: Transmission loss at 15 GHz is 8.0 dB or more, not practical.

<High frequency shielding property>
The high-frequency shielding property conforms to ASTM D4935, and the electromagnetic wave is irradiated under the condition of 100MHz to 15GHz using the coaxial tube type shield effect measurement system manufactured by Keycom, and the amount of attenuation that the electromagnetic wave is attenuated by the electromagnetic wave shield sheet is measured. However, the notation is made according to the following criteria. The measured value of the attenuation is decibel (unit: dB).

⊚: The amount of attenuation when irradiating electromagnetic waves at 15 GHz is less than −55 dB, which is extremely good.
〇: The amount of attenuation when irradiating electromagnetic waves at 15 GHz is -55 dB or more and less than -50 dB.
Δ: Attenuation amount at the time of electromagnetic wave irradiation of 15 GHz is -50 dB or more and less than -45 dB. Practical use is possible. X: The amount of attenuation when irradiating electromagnetic waves at 15 GHz is -45 dB or more, which is not practical.

<Chemical resistance>
The peelable sheet of the adhesive layer of the electromagnetic wave shield sheet having a width of 40 mm and a length of 40 mm is peeled off, and the exposed adhesive layer and Kapton 500H having a width of 50 mm and a length of 50 mm are crimped under the conditions of 170 ° C., 2.0 MPa and 30 minutes. The sample was obtained by thermosetting. A cross-cut guide was used on the protective layer side of the electromagnetic wave shield sheet of the obtained sample according to JIS K5400, and 100 grids with an interval of 1 mm were prepared. After that, it is immersed in the solvent-based cleaning liquid "Zestron FA +" (manufactured by Zestron) for 20 minutes, and the output is set to 100% using the ultrasonic cleaner "UT-205HS" (manufactured by SHARP), and the ultrasonic treatment is performed for 2 minutes. After that, the sample was taken out, washed with distilled water, and then dried. The adhesive tape was strongly pressure-bonded to the grid portion, and the end of the tape was peeled off at a stretch at an angle of 45 °, and the state of the grid was judged according to the following criteria.

⊚: The eyes of any grid do not come off.
〇: Small peeling of the coating film at the intersection of cuts. Clearly not above 5%.
Δ: The coating film is partially or completely peeled off along the cut line. 15% or more and less than 35%. X: The coating film is partially or completely peeled off along the cut line. 35% or more.

<Cold heat cycle reliability>
The reliability of the cold cycle was evaluated by measuring the connection resistance value through the small opening via before and after the cold cycle. The specific method of evaluation is shown below.
An electromagnetic wave shield sheet was prepared to have a width of 20 mm and a length of 50 mm and used as a sample 25. Explaining by showing the plan views of FIGS. 7 (1) and 7 (4), the peelable sheet was peeled off from the sample 25, and the exposed conductive adhesive layer 25b was separately prepared as a flexible printed wiring board (thickness 25 μm).
A copper foil circuit 22A having a thickness of 18 μm and a copper foil circuit 22B which are not electrically connected to each other are formed on the polyimide film 21 of the above, and the copper foil circuit 22A has a thickness of 37.5 μm and a diameter of 1. A wiring board on which a polyimide coverlay 23 with an adhesive having a circular via 24 of 1 mm (via area 1.0 mm ² ) is laminated) is crimped at 170 ° C., 2 MPa, and 30 minutes, and conductively bonded to the electromagnetic wave shield sheet. A sample was obtained by curing the agent layer 25b and the protective layer 25a. Next, the peelable sheet on the protective layer 25a side of the sample was removed, and the initial connection resistance value between 22A and 22B shown in the plan view of FIG. 7 (4) was set to the BSP probe of "Lorester GP" manufactured by Mitsubishi Chemical Analytech. Measured using. 7 (2) is a cross-sectional view taken along the line DD'of FIG. 7 (1), and FIG. 7 (3) is a cross-sectional view taken along the line CC'of FIG. 7 (1). Similarly, FIG. 7 (5) is a cross-sectional view taken along the line DD'of FIG. 7 (4), and FIG. 7 (6) is a cross-sectional view taken along the line CC'of FIG. 7 (4). The sample was placed in a thermal shock device ("TSE-11-A", manufactured by Espec), and exposed to high temperature: 125 ° C for 15 minutes and exposed to low temperature: -50 ° C for 15 minutes. carried out. After that, the connection resistance value of the sample was measured in the same manner as in the initial stage.
The evaluation criteria for thermal cycle reliability are as follows.

⊚: (connection resistance value after alternating exposure) / (initial connection resistance value) is less than 1.5. Very good.
◯: (connection resistance value after alternating exposure) / (initial connection resistance value) is 1.5 or more and less than 3.0 Good.
Δ: (connection resistance value after alternating exposure) / (initial connection resistance value) is 3.0 or more and less than 5.0. Practical use is possible.
×: (connection resistance value after alternating exposure) / (initial connection resistance value) is 5.0 or more, not practical.

1 Conductive adhesive layer 2 Metal layer 3 Protective layer 4 Opening 5 Ground wiring 6 Signal wiring 7 Electromagnetic wave shielding wiring circuit board 8 Cover coat layer 9 Insulating base material 10 Electromagnetic wave shielding sheet 11 Via 12 Electromagnetic wave shielding layer 20 Coplanar circuit Wiring board 21 Wiring board with coplanar circuit with electromagnetic wave shield sheet 50 Polyimide film 51 Through hole 52 Copper plating film 53 Signal wiring 54 Ground wiring 55 Ground pattern (i)
56 Back side ground pattern (ii)

Claims (6)

It has a laminate having a conductive adhesive layer, a metal layer, and a protective layer in this order.
The surface of the metal layer in contact with the conductive adhesive layer has a Flop Index (FI) of 10 to 90 calculated by the formula (1).
An electromagnetic wave shield sheet characterized in that the metal layer has a plurality of openings and an aperture ratio is 0.10 to 20%.

(L ^* _{15 °} , L ^* _{45 °} , and L ^* _{110 °} are offsets from the specularly reflected light of light incident at an angle of 45 ° with respect to the perpendicular direction of the interface of the metal layer in contact with the conductive adhesive layer, respectively. angle 15 °, 45 °, which is the ^L * ^a * ^{b *} color system defined in JIS Z8729 in 110 ° ^{L *.)} The electromagnetic wave shield sheet according to claim 1, wherein the laminated cured product obtained by heat-pressing the laminated body at 170 ° C. for 30 minutes has a loss tangent of 0.10 or more at 125 ° C. The electromagnetic wave shield sheet according to claim 1 or 2, wherein the thickness of the metal layer is 0.3 to 5.0 μm. The electromagnetic wave shield sheet according to any one of claims 1 to 3, wherein the protective layer contains a binder resin, and the weight average molecular weight of the binder resin is 10,000 or more. The conductive adhesive layer contains a binder resin and a conductive filler, and contains
The electromagnetic wave shield sheet according to any one of claims 1 to 4, wherein the content of the conductive filler in the conductive adhesive layer is 35 to 90% by mass. An electromagnetic wave shielding property comprising an electromagnetic wave shielding layer formed from the electromagnetic wave shielding sheet according to any one of claims 1 to 5, a cover coat layer, and a signal wiring and a wiring board having an insulating base material. Circuit board.