JP6597927B1 - Electromagnetic shielding sheet and electromagnetic shielding wiring circuit board - Google Patents

Abstract

An electromagnetic wave shielding sheet and an electromagnetic wave shield that have solder reflow resistance, reduce transmission loss even when used in a high frequency transmission circuit, exhibit excellent high frequency shielding properties, and have high connection reliability even after exposure to a thermal cycle. To provide a conductive circuit board. A root mean square slope Sdq determined in accordance with ISO 25178-2: 2012 on a surface of a metal layer that is in contact with the conductive adhesive layer is 0. 0.001 to 0.5, and the metal layer has a plurality of openings and has an opening ratio of 0.10 to 20%. [Selection] Figure 1

Description

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

  Various electronic devices such as portable terminals, PCs, servers, and the like have built-in wiring circuit boards such as printed wiring boards. These printed circuit boards are provided with an electromagnetic wave shielding structure in order to prevent malfunctions due to external magnetic fields and radio waves and to reduce unnecessary radiation from electrical signals.

  With the increase in transmission speed of transmission signals, electromagnetic wave shielding sheets are also required to reduce electromagnetic wave shielding properties (hereinafter referred to as high frequency shielding properties) corresponding to high frequency noise and transmission losses in the high frequency region (hereinafter sometimes referred to as transmission characteristics). 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. And it is described by the said structure that an electric field wave, a magnetic field wave, and electromagnetic waves which advance from the one surface side of the electromagnetic wave shielding sheet to the other surface side are well shielded and transmission loss is reduced.

International Publication No. 2013/077108 JP 2013-168643 A

2. Description of the Related Art In recent years, in electronic devices typified by mobile phones, with the increase in transmission speed of transmission signals, an electromagnetic wave shielding sheet on a printed circuit board built in them is required to have high frequency shielding properties and transmission characteristics. For this reason, it has been considered suitable to use a metal layer having a thickness of 0.5 to 12 μm as described in Patent Document 1 for the conductive layer of the electromagnetic wave shielding sheet.
However, simply by using a metal layer having a thickness of 0.5 to 12 μm, 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. Therefore, it has been required to further devise the metal layer.
In addition, an electromagnetic wave shielding wiring circuit board in which an electromagnetic wave shielding sheet using a metal layer is affixed to the wiring circuit board is subjected to a volatile component generated from the inside of the wiring circuit board when heat treatment such as solder reflow is performed. There was a problem in that floating occurred and foaming or the like caused poor appearance and poor connection (hereinafter sometimes referred to as solder reflow resistance). For example, in Patent Document 2, a metal foil having a plurality of pinholes is used in the metal thin film layer, and volatile components are transmitted through the pinholes in the metal thin film layer to suppress floating and foaming between the layers. ing.
On the other hand, with the recent widespread use of electronic devices such as smartphones and tablet terminals in recent years, reliability under all temperature conditions is required. When the printed circuit board provided with the electromagnetic wave shielding sheet of Patent Document 1 and Patent Document 2 is exposed to an extreme temperature change, there has been a problem that peeling from the printed circuit board or disconnection from the ground circuit is interrupted. (Hereinafter, reliability of thermal cycle).

  The present invention has been made in view of the above-described background, and its object is to have solder reflow resistance and excellent thermal cycle reliability, and excellent high-frequency shielding properties and transmission suitable for high-frequency signals. An electromagnetic wave shielding sheet having characteristics and a printed circuit board using the electromagnetic wave shielding sheet are provided.

As a result of intensive studies by the inventor, it has been found that the problems of the present invention can be solved in the following modes, and the present invention has been completed.
That is, the electromagnetic wave shielding sheet according to the present invention has a laminate including a conductive adhesive layer, a metal layer, and a protective layer in this order, and the interface of the metal layer in contact with the conductive adhesive layer is ISO 25178-2: 2012. The root mean square slope Sdq determined in accordance with the above is 0.0001 to 0.5,
The metal layer has a plurality of openings and has an opening ratio of 0.10 to 20%.

  According to the present invention, an electromagnetic wave shielding sheet that 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. And the outstanding effect that an electromagnetic wave shielding wiring circuit board can be provided is produced.

It is sectional drawing which illustrated the electromagnetic wave shield sheet which concerns on this embodiment. It is the figure which illustrated the comparison of the surface from which a root mean square inclination Sdq differs. It is a typical cut section sectional view showing an example of an electromagnetic wave shielding wiring circuit board concerning this embodiment. It is a typical top 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 typical top 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 typical top view of the main surface side of the wiring board which has a coplanar circuit with an electromagnetic wave shield sheet which concerns on an Example and a comparative example. It is the typical top view of a thermal cycle reliability evaluation, and a cutting part sectional view. It is a dynamic viscoelastic curve of an electromagnetic wave shield sheet (Example 5).

Hereinafter, an example of an embodiment to which the present invention is applied will be described. In addition, the size and ratio of each member in the following drawings are for convenience of explanation, and are not limited to this. In the present specification, the description “any number A to any number B” includes the number A as a lower limit and the number B as an upper limit in the range. The “sheet” in this specification includes not only “sheet” defined in JIS but also “film”. Moreover, the numerical value specified in this specification is a value calculated | required by the method disclosed by embodiment or an Example.

<Electromagnetic wave shield sheet>
The electromagnetic wave shielding sheet of the present invention has a laminate including at least a conductive adhesive layer, a metal layer, and a protective layer in this order. FIG. 1 is a cross-sectional view illustrating an electromagnetic wave shielding sheet 10 according to an embodiment of the invention. As shown in FIG. 1, the electromagnetic wave shielding sheet 10 has a laminated body including a conductive adhesive layer 1, a metal layer 2, and a protective layer 3 in this order, and the metal layer 2 includes the conductive adhesive layer 1 and the protective layer. 3 is arranged.
The electromagnetic wave shielding sheet of the present invention has a plurality of openings 4 and an opening ratio of 0.10 to 20%, and the root mean square Sdq of the surface in contact with the conductive adhesive layer is 0.0001 to 0. Since it has a metal layer in the range of .5, excellent transmission characteristics and the like can be expressed particularly in a printed circuit board that transmits a high-frequency signal (for example, 100 MHz to 50 GHz).
For example, the electromagnetic wave shielding sheet 10 forms an electromagnetic wave shielding layer by bonding a wiring circuit board as an adherend and a surface on the conductive adhesive layer 1 side to produce an electromagnetic wave shielding wiring circuit board. That is, of the surface of the metal layer 2, the surface that is in close contact with the conductive adhesive layer 1 is opposite to the signal wiring in the printed circuit board.

[Loss tangent of laminated cured product]
Further, the electromagnetic wave shielding sheet of the present invention has a loss tangent at 125 ° C. of a laminated cured product obtained by hot pressing a laminated body provided with at least a conductive adhesive layer, a metal layer, and a protective layer in this order at 170 ° C. for 30 minutes. It is preferable that it is 0.10 or more.
Thereby, cooling cycle reliability can be improved more.

  The laminated cured product can be formed by curing the electromagnetic wave shielding sheet by hot 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 among them, the layer having a curing component refers to a cured laminate.

Laminated cured product is a product obtained by removing a peelable sheet from an electromagnetic wave shield sheet before or after hot pressing, and performing hot pressing on only one electromagnetic wave shield sheet, or laminating a plurality of electromagnetic wave shield sheets, etc. Can be obtained by any of the methods of laminating and hot pressing.
That is, the laminated cured product is a laminated component similar to the electromagnetic wave shielding layer used for the electromagnetic wave shielding wiring circuit board in the electromagnetic wave shielding sheet.

  Specifically, for example, two electromagnetic wave shielding sheets are prepared, the peelable sheets on the respective conductive adhesive layer sides are peeled off, the exposed conductive adhesive layers are bonded together, and hot pressed under conditions of 170 ° C. for 30 minutes. A laminate comprising at least a conductive adhesive layer, a metal layer, and a protective layer in this order can be thermally cured to obtain a cured laminate.

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

Formula (3)
(Loss tangent of laminated cured product) =
(Loss elastic modulus E ″ of laminated cured product) / (storage elastic modulus E ′ of laminated cured product)
The laminated cured product preferably has a loss tangent at 125 ° C. after hot pressing at 170 ° C. for 30 minutes of 0.1 or more from the viewpoint of cooling cycle reliability. When the loss tangent at 125 ° C. after heat pressing of the laminated cured product at 170 ° C. for 30 minutes is 0.1 or more, it is possible to sufficiently relieve the stress generated by expansion during high temperature exposure. The laminated cured product preferably has a loss tangent at 125 ° C. after hot pressing at 170 ° C. for 30 minutes of 0.13 or more, more preferably 0.15 or more.

  The loss tangent of the laminated cured product is the loss elastic modulus E ″ and the storage elastic modulus of any one of the conductive adhesive layer, metal layer, protective layer, other layers provided in the laminated cured product, or two or more layers. 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 elasticity 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 for 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, the storage elastic modulus E ′ of the protective layer is increased or decreased by increasing or decreasing the amount of the curing agent in the protective layer. 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 or blending ratio of the thermoplastic resin or the thermosetting resin and the curing agent is changed. The thickness of each layer is changed. A conventionally known method such as changing the type can be applied.

《Metallic layer》
The metal layer of the present invention has a function of imparting high-frequency shielding properties to the electromagnetic wave shielding sheet. As for the interface of the metal layer on the side in contact with the conductive adhesive layer, the root mean square slope Sdq defined by ISO 25178-2: 2012 is 0.0001 to 0.5. By controlling the root mean square slope Sdq to be in the range of 0.0001 to 0.5, both transmission characteristics and cooling cycle reliability can be achieved. Details of the root mean square slope Sdq and details of the effects obtained by controlling the root mean square slope Sdq will be described later.
Furthermore, the metal layer of the present invention has a plurality of openings and an opening ratio of 0.10 to 20%. Thereby, the solder reflow resistance is improved, and appearance defects and a decrease in connection reliability can be suppressed.

[Root mean square slope Sdq]
The root mean square slope Sdq is a surface property parameter defined by the following formula (1) in ISO 25178-2: 2012. A represents the area of the defined surface, ∂x represents the x-axis direction, ∂y represents the y-axis direction, and ∂z (x, y) represents the minute displacement in the z-axis direction.

The root mean square slope Sdq can be calculated by processing surface shape coordinate data obtained by any one of an optical microscope, a laser microscope, and an electron microscope using analysis software. The root mean square slope Sdq represents the root mean square of the slope at all points on the definition surface, and is a parameter expressing the steepness of the irregularities on the definition surface. As the parameters expressing the surface properties, the arithmetic average height Sa and the maximum height Sz are generally used, but these are parameters that represent only the height of the unevenness, and accurately represent the surface state. Is not appropriate.
FIG. 2 illustrates two surfaces having different root mean square slopes Sdq. The larger the value of the root mean square slope Sdq, the steeper the surface unevenness. That is, the degree of surface irregularity can be determined by the numerical value of the root mean square slope Sdq.

  Note that the value of the root mean square slope Sdq of the metal layer does not change depending on the formation process of the electromagnetic shielding layer such as a heating press. Therefore, the root mean square slope Sdq of the interface of the metal layer in contact with the conductive adhesive layer in the electromagnetic wave shielding layer is also 0.0001 to 0.5.

  Further, in the metal layer of the electromagnetic wave shielding sheet, due to the nature of the current, the current flows on the surface of the metal layer at a high frequency. The transmission characteristics of the signal wiring in the printed circuit board are affected by the current flowing in the nearby conductor. Therefore, if the surface of the metal layer adjacent to the signal wiring is rough, the distance from the current flowing on the metal surface varies. However, transmission characteristics become unstable. Therefore, from the viewpoint of transmission characteristics, the root mean square Sdq of the surface of the metal layer in contact with the conductive adhesive layer is preferably 0.5 or less, more preferably 0.4 or less, and 0.3 More preferably, it is as follows.

On the other hand, from the viewpoint of cooling cycle reliability, as a result of intensive studies, it was found that the cooling cycle reliability is improved by setting the root mean square slope Sdq of the metal layer in the range of 0.0001 to 0.5. This is because the conductive filler in the conductive adhesive layer is formed by making the angle of the irregularities formed on the surface of the metal layer moderately sharp even when the shape change due to expansion and contraction of the conductive adhesive layer occurs in the cold cycle. This is probably because the contact between the metal layer and the metal layer is maintained, and the deterioration of the connection resistance value is suppressed. As a result of the study, the root mean square slope Sdq of the metal layer is more preferably in the range of 0.001 to 0.4, and still more preferably in the range of 0.01 to 0.3.

[Method of controlling root mean square slope Sdq]
The method for controlling the root mean square slope Sdq of the surface of the metal layer is described in, for example, a method of forming a roughened surface by attaching roughened particles on a copper foil surface, Japanese Patent Application Laid-Open No. 2017-13473. A method for polishing a metal surface using a buff, a method for polishing a metal surface using a polishing cloth, a shot blasting method in which an abrasive is sprayed onto the metal surface with compressed air, and a carrier material having a predetermined root mean square slope Sdq A method of forming a metal layer on the surface and transferring irregularities on the surface of the carrier material to the metal layer, a film having a predetermined root mean square slope Sdq and a metal layer are pressure-bonded, and the irregularities on the film surface are transferred to the metal layer A method is mentioned. The method for controlling the root mean square slope Sdq on the surface of the metal layer is not limited to the exemplified method, and a conventionally known method can be applied.

[Metal layer thickness]
The thickness of the metal layer is preferably 0.3 to 5.0 μm. By setting the thickness of the metal layer to 0.3 μm or more, it is possible to suppress transmission with respect to the wavelength of electromagnetic noise generated from the printed circuit board and to exhibit sufficient high-frequency shielding properties. The lower limit of the thickness of the metal layer is more preferably 0.5 μm. 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 cooling cycle reliability is improved. The upper limit of the thickness of the metal layer is more preferably 3.5 μm.

[Components of metal layer]
For example, a metal foil, a metal vapor deposition film, or a metal plating film can be used for the metal layer.
The metal used for the metal foil is preferably, for example, a conductive metal such as aluminum, copper, silver, or gold, and any one kind of metal or an alloy of a plurality of metals can be used. Copper, silver, and aluminum are more preferable in terms of high-frequency shielding properties and cost, and copper is more preferable. As for copper, it is preferable to use a rolled copper foil or an electrolytic copper foil, for example.
As the metal used for the metal vapor deposition film and the metal plating film, for example, one kind of conductive metal such as aluminum, copper, silver, and gold, or an alloy of a plurality of metals is preferably used, and copper and silver are more preferable. One surface or both surfaces of the metal foil, metal vapor deposition film, and 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 opening ratio is 0.10 to 20%. By having the opening, solder reflow resistance is improved. By having an opening, when the electromagnetic shielding wiring circuit board is subjected to solder reflow processing, the volatile components contained in the polyimide film and coverlay adhesive of the wiring circuit board are released to the outside, and the coverlay adhesive and electromagnetic shielding sheet Occurrence of poor appearance due to the interfacial peeling can be suppressed.

The shape of the opening viewed from the surface of the metal layer can be formed as necessary, for example, a perfect circle, an ellipse, a quadrangle, a polygon, a star, a trapezoid, and a branch. From the viewpoint of ensuring manufacturing cost and toughness of the metal layer, the shape of the opening is preferably a perfect circle and an ellipse.
In addition, the measurement of the root mean square slope Sdq is a result of measurement using a surface portion having no opening of the metal layer.

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

When the aperture ratio is 0.10 or more, volatile components during the solder reflow process can be sufficiently released, resulting in poor appearance due to interface peeling between the coverlay adhesive and the electromagnetic shielding sheet, and a decrease in connection reliability. Since it can suppress, it is preferable.
On the other hand, it is preferable that the aperture ratio be 20% or less because the amount of electromagnetic noise passing through the opening can be reduced and the shielding property can be improved. The range of the aperture ratio that achieves both solder reflow resistance and high-frequency shielding performance at a high level is more preferably 0.30 to 15%, and further preferably 0.50 to 6.5%.

  In particular, in an electromagnetic wave shield sheet having a smooth interface with the conductive adhesive layer in a range where the root mean square slope Sdq of the metal layer is 0.001 or less, the adhesion between the metal layer and the conductive adhesive layer is weak, and solder reflow treatment Occasionally, the volatile component expands at the interface between the metal layer and the conductive adhesive layer, resulting in poor appearance such as delamination and floating, but the aperture ratio is 0.10% or more, preferably 0.50% or more. By doing so, volatile components can be sufficiently released, and the occurrence of peeling and floating can be further suppressed.

  The measurement of the aperture ratio is, for example, using an image enlarged by a magnification of 500 to 2000 times with a laser microscope and a scanning electron microscope (SEM) perpendicularly from the plane direction of the metal layer, and straightening the opening and the non-opening, It can be obtained by setting the number of pixels of the birectified color per unit area as each area.

[Method for producing metal layer having opening]
As a method for producing a metal layer having an opening, a conventionally known method can be applied. A method (i) for forming an opening by forming a pattern resist layer on a metal foil and etching the metal foil, screen printing A method (ii) for printing a conductive paste in a predetermined pattern by the method (ii), a method (iii) for screen printing an anchor agent in a predetermined pattern and metal plating only on the anchor agent printing surface, and JP-A-2015-63730 The manufacturing method (iv) etc. currently applied can be applied.
That is, water-soluble or solvent-soluble ink is pattern-printed on the support, a metal vapor deposition film is formed on the surface, and the pattern is removed. 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 the metal foil is etched 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 includes 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 direction and the horizontal direction with the electromagnetic wave shielding sheet placed horizontally. The anisotropic conductive adhesive layer has conductivity only in the vertical direction with the electromagnetic wave shielding sheet placed horizontally.
The conductive adhesive layer may be either isotropic conductive or anisotropic conductive, and anisotropic conductive is preferable because cost can be reduced.

[Thermoplastic resin]
Thermoplastic resins include polyolefin resin, vinyl resin, styrene / acrylic resin, diene resin, terpene resin, petroleum resin, cellulose resin, polyamide resin, polyurethane resin, polyester resin, polycarbonate resin, polyimide resin, liquid crystal A polymer, a fluororesin, etc. are mentioned. 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 examples thereof include liquid crystal polymers and fluorine resins.
The thermoplastic resins 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 group, phenolic hydroxyl group, methoxymethyl group, carboxyl group, amino group, epoxy group, oxetanyl group, oxazoline group, oxazine group, aziridine group, thiol group, isocyanate group, blocked isocyanate group, blocked A carboxyl group, a silanol group, etc. are mentioned. Thermosetting resins include, for example, acrylic resins, maleic resins, polybutadiene resins, polyester resins, polyurethane resins, polyurethane urea resins, epoxy resins, oxetane resins, phenoxy resins, polyimide resins, polyamide resins, polyamideimide resins, phenolic resins. Known resins such as resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, and fluorine resins can be used.
Thermosetting resins can be used alone or in combination of two or more.

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

[Curing agent]
The curing agent has a plurality of functional groups that can react with the functional groups of the thermosetting resin. Examples of the curing agent include known compounds such as an epoxy compound, an acid anhydride group-containing compound, an isocyanate compound, an aziridine compound, an amine compound, a phenol compound, and an organometallic compound.
A hardening | curing agent can be used individually or in combination with 2 or more types.

  It is preferable that 1-50 weight part of various hardening | curing agents are included with respect to 100 weight part of thermosetting resins, 3-40 weight part is more preferable, and 3-30 weight part is further more preferable.

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

[Conductive filler]
The conductive filler has a function of imparting conductivity to the conductive adhesive layer. As the material for the conductive filler, for example, conductive metals such as gold, platinum, silver, copper and nickel, and alloys thereof, and fine particles of a conductive polymer are preferable, and silver is more preferable in terms of price and conductivity.
In addition, composite fine particles having a coating layer in which a metal or a resin is used as a core and the surface of the core is covered, are preferable from the viewpoint of cost reduction. Here, the core is preferably selected appropriately from inexpensive nickel, silica, copper and alloys thereof, and resins. 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 alloys thereof. Examples of the conductive polymer include polyaniline and polyacetylene. Among these, silver is preferable from the viewpoints of price and conductivity.

The shape of the conductive filler is not limited as long as desired conductivity can be obtained. Specifically, for example, a spherical shape, a flake shape, a leaf shape, a dendritic shape, a plate shape, a needle shape, a rod shape, and a grape shape are preferable. Moreover, you may mix two types of conductive fillers of these different shapes.
The conductive filler can 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 making the conductive adhesive layer thin, 30 μm or less is preferable, 20 μm or less is more preferable, and 15 μm or less is even more preferable. The D ₅₀ average particle diameter can be determined by a laser diffraction / scattering particle size distribution analyzer 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, and still more preferably 40 to 65% by weight. By setting the content to 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 thermal cycle reliability are improved. On the other hand, the solder reflow resistance and transmission characteristics are further improved by setting the content to 90% by weight or less.

  Other conductive resin compositions include silane coupling agents, rust inhibitors, reducing agents, antioxidants, pigments, dyes, tackifying resins, plasticizers, UV absorbers, antifoaming agents, leveling regulators as optional components. , Fillers, flame retardants, etc.

  The conductive resin composition can be obtained by mixing and stirring the materials described so far. For the stirring, for example, a known stirring device such as a disperse mat or a homogenizer can be used.

  A known method can be used to produce the conductive adhesive layer. For example, a method of forming a conductive adhesive layer by coating a conductive resin composition on a peelable sheet and drying, or using an extruder such as a T-die, the conductive resin composition It can also be formed by extruding into a sheet.

  Coating methods include, 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. A known coating method such as a method can be used. In coating, it is preferable to perform a drying step. In 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 still more preferably 4 to 9 μm. When the thickness is in the range of 2 to 30 μm, cooling cycle reliability and solder reflow resistance can be improved.

《Protective layer》
The protective layer can be formed using a conventionally known resin composition.
The resin composition can contain the above-mentioned optional components as necessary for the thermoplastic resin, thermosetting resin, and curing agent described in the conductive resin composition. The thermosetting resin and the curing agent used for the protective layer and the conductive adhesive layer may be the same or different.

  The resin composition can be obtained by the same method as that for the conductive resin composition.

  The protective layer may be a film formed by molding an insulating resin such as polyester, polycarbonate, polyimide, polyamideimide, polyamide, polyphenylene sulfide, or polyetheretherketone.

  The thickness of the protective layer is usually about 2 to 10 μm.

<< Method for producing electromagnetic wave shielding sheet >>
In the production of the electromagnetic wave shielding 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, the conductive adhesive layer is laminated on the electrolytic copper foil surface side of the electrolytic copper foil having an opening with a carrier material, and then the carrier material is peeled off. . And a method of laminating and laminating the surface from which the carrier material has been peeled off and a protective layer separately formed on the peelable sheet, and (ii) electrolysis having a protective layer formed on the peelable sheet and having an opening with a carrier material. After laminating and laminating a protective layer on the electrolytic copper foil surface side of the copper foil, the carrier material is peeled off. And the method of laminating | stacking and laminating | stacking the surface which peeled the carrier material, and the electrically conductive adhesive layer separately formed on the peelable sheet, (iii) On the electrolytic copper foil surface side of the electrolytic copper foil which has an opening part with a carrier material The resin composition is applied to form a protective layer, and a peelable sheet is attached. Thereafter, the carrier material is peeled off and laminated with a conductive adhesive layer separately formed on the peelable sheet, and (iv) a conductive adhesive layer is formed on the peelable sheet to electrolyze the electrolytic copper foil with the carrier material. After laminating the conductive adhesive layer on the copper foil surface side, the carrier material is peeled off. Then, after laminating and laminating the surface from which the carrier material has been peeled off and a protective layer separately formed on the peelable sheet, a method of forming an opening in the electromagnetic wave shield sheet with a needle-like jig, (v) peelability After laminating and laminating the protective layer formed on the sheet on the electrolytic copper foil surface side of the electrolytic copper foil having the opening with carrier material, the carrier material is peeled off. And the method of forming a conductive adhesive layer on the surface from which the carrier material has been peeled off, (vi) forming a conductive adhesive layer on the peelable sheet, and the root mean square slope of the surface of the rolled copper foil having an opening A surface having Sdq of 0.0001 to 0.5, a conductive adhesive layer laminated thereon, the other surface laminated with the conductive adhesive layer, and a protective layer separately formed on the peelable sheet (Vii) A surface of a rolled copper foil having an opening and having a root mean square slope Sdq of 0.0001 to 0.5. (Viii) a method of laminating one surface with a conductive adhesive layer and then laminating another surface laminated with a protective layer and a conductive adhesive layer separately formed on a peelable sheet; Pressure with opening Of the surface of the copper foil, root mean square slope Sdq to form a protective layer by coating a resin composition on the other surface side is 0.0001 bonding a peelable sheet. Thereafter, the other surface and a method of laminating and laminating a conductive adhesive layer separately formed on a peelable sheet, (ix) of the surface of the rolled copper foil having an opening, the root mean square slope Sdq is 0 A conductive resin composition is applied to the surface of .0001 to 0.5 to form a conductive adhesive layer, and a peelable sheet is bonded. Then, the other surface and the method of laminating | stacking the protective layer separately formed on the peelable sheet, etc. are mentioned.

  The electromagnetic wave shielding sheet can 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 or heat resistance.

  The electromagnetic wave shielding sheet of the present invention can be used for various applications where 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, COF, TAB, flexible connectors, liquid crystal displays, touch panels and the like. Moreover, it can also be used as a member for shielding electromagnetic waves from a case of a personal computer, a building material such as a wall of a building material and a window glass, a vehicle, a ship, and an aircraft.

  Moreover, the electromagnetic wave shielding sheet of the present invention can have an excellent transmission characteristic that a 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, for example, transmission characteristics can be evaluated as follows.
First, a coplanar circuit is prepared.
A coplanar circuit is one of planar transmission circuits in which signal wiring is printed on one side of an insulating base material such as polyimide film. In the present invention, a coplanar circuit is formed by sandwiching two signal wirings on a polyimide film. A circuit in which ground wirings are formed in parallel is used. In the coplanar circuit described above, a ground pattern for grounding is provided on the opposite surface through a through hole.
A conductive adhesive layer of an electromagnetic wave shielding sheet is bonded to the surface of the insulating substrate opposite to the signal wiring of the coplanar circuit, and the electromagnetic wave shielding sheet is laminated by hot pressing. At this time, the electromagnetic wave shielding sheet is electrically connected to the partially exposed ground pattern. By the above method, 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 transmission loss is calculated and evaluated. Can do. A voltage / current ratio may be used instead of electric power.

  In the present invention, the transmission loss when a 15 GHz sine wave flows through the signal wiring of the coplanar circuit is preferably less than 8 dB, more preferably less than 7.5 dB, and even more preferably less than 7 dB. When the transmission loss is less than 8 dB, a reduction in transmission loss at a high level can be realized.

  In the electromagnetic wave shielding sheet of the present invention, when a thermoplastic resin is used for the binder resin in the conductive adhesive layer, the contained thermoplastic resin is present in a solid state, and the thermoplastic resin is melted by the printed circuit board and hot press, A desired adhesive strength can be obtained by solidifying again after cooling.

  In the electromagnetic wave shielding 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 exist in an uncured state (B stage), By curing by hot pressing (C stage), desired adhesive strength can be obtained. The uncured state includes a semi-cured state in which a part of the curing agent is cured.

  In addition, in order to prevent adhesion of foreign matter, the electromagnetic wave shielding sheet is generally stored in a state where a peelable sheet is attached to the conductive adhesive layer and the protective layer.

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

<Electromagnetic wave shielding circuit board>
The electromagnetic shielding wiring circuit board includes an electromagnetic shielding layer formed from the electromagnetic shielding sheet of the present invention, a cover coat layer, a circuit pattern having a signal wiring and a ground wiring, and a wiring circuit board having an insulating substrate. .
The wired circuit board has a circuit pattern having a signal wiring and a ground wiring on the surface of the insulating base material. The signal wiring and the ground wiring are insulated and protected on the wired circuit board, and at least one of the ground wiring is provided. After forming a cover coat layer having vias in the part and placing the conductive adhesive layer surface of the electromagnetic wave shield sheet on the cover coat layer, the electromagnetic wave shield sheet is hot pressed, and the conductive adhesive layer is formed inside the via. It can be manufactured by flowing it and bonding it to the ground wiring.

An example of the electromagnetic shielding wiring circuit board of the present invention will be described with reference to FIG.
The electromagnetic shielding sheet layer 12 includes 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 printed circuit board and protects it from the external environment. The cover coat layer is preferably a polyimide film with a thermosetting adhesive, a thermosetting or ultraviolet curable solder resist, or a photosensitive coverlay film, and more preferably a photosensitive coverlay film for fine processing. The cover coat layer generally uses a known resin having heat resistance and flexibility such as polyimide. 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 electrical 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 substrate 9 is a circuit pattern support and is preferably a bendable plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, or liquid crystal polymer, and more preferably a liquid crystal polymer or polyimide. Among these, a liquid crystal polymer having a low relative dielectric constant and dielectric loss tangent is more preferable in consideration of the use of a printed circuit board that transmits a high-frequency signal.
When the printed circuit board is a rigid wiring board, the constituent material of the insulating base material is preferably glass epoxy. By providing such an insulating base material, the printed circuit board can have high heat resistance.

The heat pressing of the electromagnetic wave shielding sheet 10 and the printed circuit board is generally performed under conditions of a temperature of about 150 to 190 ° C., a pressure of about 1 to 3 MPa, and a time of about 1 to 60 minutes. The conductive adhesive layer 1 and the cover coat layer 8 are brought into close contact with each other by hot pressing, and the conductive adhesive layer 1 flows to fill the via 11 formed in the cover coat layer 7, thereby conducting electrical continuity with the ground wiring 5. I can take it. The thermosetting resin reacts and is cured by hot pressing to form the electromagnetic wave shielding layer 12.
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 it as the above range, the area of the ground wiring can be narrowed, and the printed wiring board can be downsized.
The shape of the via is not particularly limited, and any shape such as a circle, a square, a rectangle, a triangle, or an indefinite shape can be used.

  The electromagnetic wave shielding layer is preferably laminated on both sides of the printed circuit board from the viewpoint that electromagnetic wave leakage can be more effectively suppressed. In addition, the electromagnetic wave shielding 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. As a result, the cost can be reduced and it can be incorporated in a narrow area in the housing.

  In addition, the signal wiring is not particularly limited, and can be used for either a single-ended circuit composed of one signal wiring or a differential circuit composed of two signal wirings. preferable. On the other hand, when the circuit pattern area of the printed circuit board is limited and it is difficult to form the ground circuit in parallel, the ground circuit is not provided beside the signal circuit, and the electromagnetic wave shielding 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 shielding wiring circuit board of the present invention is preferably provided (mounted) on an electronic device such as a notebook PC, a mobile phone, a smartphone, or a tablet terminal in addition to a liquid crystal display, a touch panel, or the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example. In the examples, “part” means “part by weight”, and “%” means “% by weight”.

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

<Measurement of acid value of binder resin>
The acid value was measured according to JIS K0070. About 1 g of a sample is accurately 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 was added a phenolphthalein test solution as an indicator and titrated with a 0.1N alcoholic potassium hydroxide solution. The end point was when the indicator retained a light red color for 30 seconds. The acid value was determined by the following formula (unit: mgKOH / g).
Acid value (mgKOH / g) = (5.611 × a × F) / S
However,
S: Sample collection amount (g)
a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)
F: Potency 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 liquid chromatography that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on the difference in molecular size. For the measurement in the present invention, “LF-604” (manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID × 150 mm size) is connected in series to the column, the flow rate is 0.6 ml / min, the column temperature. It carried out on the conditions of 40 degreeC, and the determination of the weight average molecular weight (Mw) was performed in polystyrene conversion.

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

<< Measurement of average particle diameter of conductive filler >>
The D ₅₀ average particle diameter is a numerical value obtained by measuring a conductive filler with a tornado dry powder sample module using a laser diffraction / scattering particle size distribution analyzer LS13320 (manufactured by Beckman Coulter, Inc.). The cumulative value in the cumulative particle size distribution is a particle size of 50%. The refractive index was set to 1.6.

Then, the raw material used in the Example is shown below.
"material"
Conductive filler: composite fine particles (dendritic fine particles in which 10 parts by weight of silver is coated on 100 parts by weight of core copper) Average particle diameter D ₅₀ : 11.0 μm Binder resin manufactured by Fukuda Metal Foil Co., Ltd .: Acid 5 mg KOH / g, weight average molecular weight 54,000, Tg is −7 ° C. polyurethane urea resin (manufactured by Toyochem)
Epoxy compound: “JER828” (bisphenol A type epoxy resin epoxy equivalent = 189 g / eq) Aziridine compound manufactured by Mitsubishi Chemical Corporation: “Chemite PZ-33” Nippon Shokubai Co., Ltd. Pigment: carbon black “MA100” Carrier material manufactured by Mitsubishi Chemical Corporation: "Emblet S25" (Sdq = 0.02), manufactured by Unitika

<Manufacture of conductive adhesive layer 1>
100 parts of binder resin, 47 parts of conductive filler, 10 parts of epoxy compound, 0.5 part of aziridine compound are charged into a container in terms of solid content, and mixed solvent (toluene: isopropyl (Alcohol = 2: 1 (weight ratio)) was added and stirred for 10 minutes with a disper to obtain a conductive resin composition.

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

<Manufacture of conductive adhesive layers 2-8>
Except having changed the addition amount of the conductive filler, the conductive adhesive layers 2-8 shown in Tables 1-3 were produced by the same method as the conductive adhesive layer 1.

[Example 1]
A resin composition was obtained by adding 100 parts of binder resin, 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 was coated on copper foil using a bar coater so that the dry thickness was 5 μm, and dried in an electric oven at 100 ° C. for 2 minutes to form protective layer 1. A slightly adhesive peelable sheet was bonded to the substrate.

Next, the copper foil carrier material was peeled off, the copper foil surface was buffed, and the root mean square slope Sdq of the copper foil surface was adjusted to the value shown in Table 1. By attaching the conductive adhesive layer 4 to the polished copper foil surface, an electromagnetic wave shielding sheet composed of “peelable 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 at a temperature of 90 ° C. and a pressure of 3 kgf / cm ² with a thermal laminator.

  In addition, the copper foil 2 has a thickness, an opening ratio, and the like 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. Copper foil.

[Examples 2-29, Comparative Examples 1-4]
As shown in Tables 1 to 3, Examples 2 to 29 and Comparative Examples 1 to 4 were performed in the same manner as Example 1 except that the types of the conductive adhesive layer, the protective layer, and the copper foil were changed. An electromagnetic wave shielding sheet was obtained. When the target value of the root mean square slope Sdq on the copper foil surface was different from the value of the carrier material, the root mean square slope Sdq was adjusted by appropriately polishing or roughening the surface by buffing.

  About the obtained electromagnetic wave shielding sheet, the thickness of each layer, the root mean square inclination Sdq of the metal layer, and the loss tangent of the electromagnetic wave shielding sheet were measured by the following methods.

<< Measurement of thickness of each layer >>
The thickness of the conductive adhesive layer, the metal layer, and the protective layer of the electromagnetic wave shield sheet was measured by the following method.
The peelable sheet on the side of the conductive adhesive layer of the electromagnetic wave shielding sheet is peeled off, and the exposed conductive adhesive layer and a polyimide film (“Kapton 200EN” manufactured by Toray DuPont) are bonded together and heated for 30 minutes under conditions of 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 Marto) is dropped into a glass slide, and an electromagnetic wave shielding sheet is adhered to the glass. A laminate having a sheet / polyimide film configuration was obtained. The obtained laminate was cut by ion beam irradiation from the polyimide film side using a cross section polisher (manufactured by JEOL Ltd., SM-09010) to obtain a measurement sample of the electromagnetic wave shield sheet after hot pressing.

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

<< Measurement of root mean square Sdq of metal layer >>
The root mean square slope Sdq of the metal layer of the electromagnetic wave shielding sheet was measured by the following method.
The peelable sheet on the conductive adhesive layer side of the electromagnetic shielding sheet is peeled off, and the adhesive tape ("CT1835" manufactured by Nichiban Co., Ltd.) is bonded to the exposed conductive adhesive layer, leaving the end of the adhesive tape, and the end of the adhesive tape Peel from the part to peel the conductive adhesive layer / adhesive tape. The conductive adhesive layer was removed, and the exposed surface of the metal layer was subjected to measurement data acquisition using a laser microscope (manufactured by Keyence Corporation, VK-X100).
The acquired measurement data was imported into analysis software (analysis application “VK-H1XA” equipped with ISO 25178 surface texture measurement module “VK-H1XR”, both manufactured by Keyence Corporation), and ISO 25178 surface texture measurement was executed. (Conditions are S-filter: 1 μm, L-filter: 0.2 mm) For metal layers with openings on the surface, the openings are excluded from the measurement range when performing ISO 25178 surface texture measurement. did.

<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 shielding sheets having a width of 50 mm and a length of 50 mm were prepared, the peelable sheets on the respective conductive adhesive layer sides were peeled off, and the exposed conductive adhesive layers were bonded to each other at 170 ° C., 2.0 MPa, The laminate was pressure-bonded for 30 minutes and thermally cured to obtain a laminated cured product. Thereafter, the central part of the laminated cured product was cut out to have 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.), a heating rate: 10 ° C./min, a measuring frequency: 1 Hz, a strain: 0.00. The dynamic viscoelasticity is measured under the condition of 08%. From the obtained dynamic viscoelasticity curve, the loss elastic modulus E ″ and storage elastic modulus E ′ at 125 ° C. are read, and the loss tangent of the laminated cured product is obtained. Calculated.

  The following evaluation was performed using the obtained electromagnetic wave shielding sheet. The results are shown in Tables 1-3.

<Solder reflow resistance>
Solder reflow resistance was evaluated by the presence or absence of changes in appearance after contacting the electromagnetic wave shielding sheet and the molten solder. The appearance of the electromagnetic wave shielding sheet having high solder reflow resistance does not change, but the electromagnetic wave shielding sheet having low solder reflow resistance causes foaming or 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 copper-clad laminate (gold-plated 0.3 μm / gold plated) having a total thickness of 64 μm. A gold-plated surface of nickel plating 1 μm / copper foil 18 μm / adhesive 20 μm / polyimide film 25 μm) was pressure-bonded under the conditions of 170 ° C. and 2.0 MPa for 30 minutes and thermally cured to obtain a laminate. The obtained laminate was cut into a size of 10 mm width and 65 mm length to prepare a sample. The obtained sample was left for 72 hours in an atmosphere of 40 ° C. and 90% RH. Then, float on the molten solder at 250 ° C. for 1 minute with the polyimide film surface of the sample facing down, then take out the sample, visually observe its appearance, and check for the presence or absence of abnormalities such as foaming, floating, and peeling according to the following criteria. evaluated.

A: No change in appearance. Very good.
A: Small foaming is slightly observed. It is good.
Δ: Many small bubbles are observed. Can be used practically.
X: Vigorous 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 shielding sheet shown in FIG.

  FIG. 4 is a schematic plan view of the main surface side of a flexible printed wiring board (hereinafter, also referred to as a wiring board having a coplanar circuit) 20 having a coplanar circuit used for measurement, and FIG. 5 is a schematic plan view of the back side. Indicates. First, double-sided CCL “R-F775” (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. And six through holes 51 (diameter 0.1 mm) were provided in the vicinity of the four rectangular corner portions. In the drawing, for convenience of illustration, only two through holes 51 are shown at each corner. Next, after performing an electroless plating process, an electroplating process is performed to form a 10 μm copper plating film 52, and conduction between the main surface and the back surface is ensured through the copper plating film formed in the through hole 51. did. Thereafter, as shown in FIG. 3, two signal wirings 53 having a length of 10 cm are formed on the main surface of the polyimide film 50, and a ground wiring 54 parallel to the signal wiring 53 and the ground wiring 54 are extended outside thereof. A ground pattern (i) 55 was formed in a region including the through hole 51 in the short direction of the polyimide film 50.

  Thereafter, the copper foil formed on the back surface of the polyimide film 50 was etched to obtain a back surface side ground pattern (ii) 56 as shown in FIG. 5 at a position corresponding to the ground pattern (i) 55. The inspection specification of the appearance and tolerance of the circuit was the JPCA standard (JPCA-DG02). Next, on the main surface side of the polyimide film 50, a cover coat layer 7 “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. Thereafter, the copper foil pattern exposed from the cover coat layer 8 was subjected to nickel plating (not shown), and then gold plating (not shown).

  Next, as shown in FIG. 6, an electromagnetic wave shielding 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 shielding sheet 10. The release treatment sheet (not shown) was peeled off. Then, the coplanar circuit with the electromagnetic wave shielding layer is bonded to the entire back surface side of the wiring board 20 having the coplanar circuit with the conductive adhesive layer 1 of the electromagnetic wave shielding sheet 10 inside, under the conditions of 170 ° C., 2.0 MPa, 30 minutes. A wiring board 21 having the following was obtained. In FIG. 6, the back side ground pattern (ii) 56 is shown in a perspective view.

  The L / S (line / space) of the signal wiring 53 was adjusted as appropriate 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.

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

A: Transmission loss at 15 GHz is less than 7.0 dB. Very good.
A: Transmission loss at 15 GHz is 7.0 dB or more and less than 7.5 dB.
Δ: Transmission loss at 15 GHz is 7.5 dB or more and less than 8.0 dB.
X: Transmission loss at 15 GHz is 8.0 dB or more.

<High frequency shielding>
The high frequency shielding property is based on ASTM D4935, and the amount of attenuation by which electromagnetic waves are attenuated by the electromagnetic shielding sheet is measured by irradiating electromagnetic waves under the condition of 100 MHz to 15 GHz using a coaxial tube type shielding effect measuring system manufactured by Keycom. And in accordance with the following criteria. In addition, the measured value of attenuation is a decibel (unit; dB).

(Double-circle): The attenuation amount at the time of electromagnetic wave irradiation of 15 GHz is less than -55 dB. It is very favorable.
A: Attenuation amount at the time of electromagnetic wave irradiation of 15 GHz is −55 dB or more and less than −50 dB.
(Triangle | delta): The attenuation amount at the time of electromagnetic wave irradiation of 15 GHz is more than -50dB and less than -45dB.
X: Attenuation amount at the time of electromagnetic wave irradiation of 15 GHz is −45 dB or more.

<Cooling cycle reliability>
The reliability of the thermal cycle was evaluated by measuring the connection resistance value through the small opening vias before and after the thermal cycle. The specific method of evaluation is shown below.
An electromagnetic wave shielding sheet having a width of 20 mm and a length of 50 mm was prepared as Sample 25. 7A and 7B, the peelable sheet is peeled off from the sample 25, and the exposed conductive adhesive layer 25b is separately formed on the flexible printed wiring board (on the polyimide film 21 having a thickness of 25 μm). In addition, a copper foil circuit 22A and a copper foil circuit 22B having a thickness of 18 μm that are not electrically connected to each other are formed. On the copper foil circuit 22A, a diameter of 1.1 mm (a via area is 37.5 μm) is formed. 1.0 mm ² ) a wiring board on which a polyimide cover lay 23 with an adhesive having a circular via 24 is laminated) under conditions of 170 ° C., 2 MPa, 30 minutes, and the conductive adhesive layer 25b of the electromagnetic wave shielding sheet and protection A sample was obtained by curing the 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 measured using the BSP probe of “Lorester GP” manufactured by Mitsubishi Chemical Analytech. And measured. 7B is a cross-sectional view taken along the line DD ′ of FIG. 7A, and FIG. 7C is a cross-sectional view taken along the line CC ′ of FIG. Similarly, FIG. 7 (5) is a DD ′ sectional view of FIG. 7 (4), and FIG. 7 (6) is a CC ′ sectional view of FIG. 7 (4). The sample was put into a thermal shock apparatus (“TSE-11-A”, manufactured by Espec Corp.), exposed to high temperature: 125 ° C., 15 minutes, low temperature exposure: −50 ° C., 15 minutes under alternating exposure conditions 200 times Carried out. Thereafter, the connection resistance value of the sample was measured in the same manner as in the initial stage.
The evaluation criteria for the reliability of the thermal cycle are as follows.

A: (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.
Δ: (connection resistance value after alternating exposure) / (initial connection resistance value) is 3.0 or more and less than 5.0.
X: (Connection resistance value after alternating exposure) / (Initial connection resistance value) is 5.0 or more.

DESCRIPTION OF SYMBOLS 1 Conductive adhesive layer 2 Metal layer 3 Protective layer 4 Opening part 5 Ground wiring 6 Signal wiring 7 Electromagnetic shielding circuit board 8 Cover coat layer 9 Insulating base material 10 Electromagnetic shielding sheet 11 Via 12 Electromagnetic shielding layer 20 Coplanar circuit Wiring board 21 Wiring board having a coplanar circuit with electromagnetic shielding sheet 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 (5)

It has a laminate comprising a conductive adhesive layer, a metal layer, and a protective layer in this order,
The interface of the metal layer in contact with the conductive adhesive layer has a root mean square slope Sdq determined in accordance with ISO 25178-2: 2012 of 0.0001 to 0.5,
The metal layer has a plurality of openings, and the opening ratio is 0.10 to 20%.   The electromagnetic wave shielding sheet according to claim 1, wherein the laminated cured product obtained by hot pressing the laminated body at 170 ° C for 30 minutes has a loss tangent at 125 ° C of 0.10 or more.   The electromagnetic wave shielding sheet according to claim 1, wherein the metal layer has a thickness of 0.3 to 5.0 μm. The conductive adhesive layer contains a binder resin and a conductive filler,
4. The electromagnetic wave shielding sheet according to claim 1, wherein a content of the conductive filler in the conductive adhesive layer is 35 to 90% by mass. An electromagnetic wave shielding wiring comprising: an electromagnetic wave shielding layer formed from the electromagnetic wave shielding sheet according to any one of claims 1 to 4; a cover coat layer; and a wiring board having a signal wiring and an insulating substrate. Circuit board.