KR20200145812A - Electromagnetic shielding sheet, printed circuit board having electromagnetic shielding structure - Google Patents

Abstract

The present invention provides an electromagnetic wave shielding sheet which has reflow soldering resistance, reduces transmission loss even when used in a high-frequency transmission circuit to exhibit excellent high-frequency shielding properties, and has high connection reliability after exposure to a cold/heat cycle, and an electromagnetic wave shielding wiring circuit board. The problem is solved through the electromagnetic wave shielding sheet. The electromagnetic wave shielding sheet includes a conductive adhesive layer, a metal layer, and a protective layer, a root-mean-square slope (Sdq) of a surface of the metal layer in contact with the conductive adhesive layer as determined in accordance with ISO 25178-2:2012 is 0.0001-0.5, and the metal layer has a plurality of openings and an aperture ratio of 0.10%-20%.

Description

Electromagnetic shielding sheet, and electromagnetic shielding wiring circuit board {ELECTROMAGNETIC SHIELDING SHEET, PRINTED CIRCUIT BOARD HAVING ELECTROMAGNETIC SHIELDING STRUCTURE}

The present invention relates to an electromagnetic wave shielding (SHIELD) sheet, and an electromagnetic wave shielding wiring circuit board, for example, an electromagnetic wave shielding sheet suitable for bonding to a part of a component emitting electromagnetic waves, and an electromagnetic wave shielding property using an electromagnetic wave shielding sheet It relates to a wiring circuit board.

In various electronic devices such as mobile phones, PCs, servers, etc., wiring circuit boards such as printed wiring boards are incorporated. Such a wiring circuit board is provided with an electromagnetic wave shielding structure to prevent malfunction due to external magnetic fields or radio waves, and to reduce unnecessary radiation from electric signals.

In accordance with the high-speed transmission of the transmission signal, the electromagnetic wave shielding sheet also has electromagnetic wave shielding properties corresponding to high-frequency noise (hereinafter, referred to as high-frequency shielding properties), and reduction of transmission loss in the high-frequency region (hereinafter, improved transmission characteristics). There is) is required. In Patent Document 1, a configuration comprising a metal layer having a thickness of 0.5 to 12 μm and an anisotropic conductive adhesive layer in a laminated state is disclosed. Further, it is described that, by the configuration, electric field waves, magnetic field waves, and electromagnetic waves traveling from one side of the electromagnetic wave shielding sheet to the other side are satisfactorily shielded while reducing transmission loss at the same time.

International Publication No. 2013/077108 Japanese Patent Laid-Open Publication No. 2013-168643

BACKGROUND ART In recent years, in electronic devices typified by mobile phones, high-frequency shielding properties and transmission characteristics are also required for electromagnetic wave shielding sheets on wiring circuit boards incorporated therein in accordance with high speed transmission of transmission signals. For this reason, it has become preferable 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, by simply using a metal layer with a thickness of 0.5 to 12 μm, the electromagnetic wave shielding sheet cannot express sufficient transmission characteristics in the high frequency band, and further research on the metal layer to give the electromagnetic wave shielding sheet more excellent transmission characteristics. Has been required to do.

In addition, the electromagnetic wave shielding wiring circuit board in which the electromagnetic wave shielding sheet using a metal layer is affixed to the wiring circuit board is interlayered by volatile components generated inside the wiring circuit board when heat treatment such as solder reflow is performed. There is a problem in that lift occurs in the device, resulting in poor appearance and poor connection due to foaming or the like. Regarding this problem of resistance to solder reflow (hereinafter referred to as solder reflow resistance), for example, in Patent Document 2, a volatile component is pinned to the metal thin film layer by using a metal foil having a plurality of pinholes in the metal thin film layer. By permeating through the hole, lifting or foaming between layers is suppressed.

On the other hand, with the worldwide spread of electronic devices such as smart phones and tablet terminals, reliability in all temperature conditions is required. When the wiring circuit board provided with the electromagnetic wave shielding sheet of Patent Document 1 and Patent Document 2 is exposed to extreme temperature changes, problems such as peeling from the wiring circuit board and disconnection of the connection to the ground circuit have occurred. The electromagnetic wave shielding sheet is required to improve reliability against such temperature changes (hereinafter, referred to as cooling and heating cycle reliability).

The present invention has been made in view of the above background, and an object thereof is an electromagnetic wave shielding sheet having solder reflow resistance and excellent cooling and heating cycle reliability, excellent high-frequency shielding property, and transmission properties suitable for high-frequency signals, and the It is to provide a wiring circuit board using an electromagnetic wave shielding sheet.

As a result of intensive examination of the present inventor, it was found that the subject of the present invention can be solved in the following aspects, and the present invention was completed.

That is, the electromagnetic wave shielding 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 interface of the metal layer in contact with the conductive adhesive layer is ISO 25178-2:2012. Based on the root mean square slope (Sdq) of 0.0001 to 0.5, the metal layer is characterized in that it has a plurality of openings, and the opening ratio is 0.10 to 20%.

According to the present invention, an electromagnetic wave shielding sheet having excellent solder reflow resistance, excellent high frequency shielding property by reducing transmission loss even when used in a high frequency transmission circuit, and having high connection reliability even after exposure to a cold heat cycle, and an electromagnetic wave shielding wiring circuit board Exhibits an excellent effect that can provide.

1 is a cross-sectional view illustrating an electromagnetic wave shielding sheet according to the present embodiment,
FIG. 2 is a diagram for comparing examples of two surfaces having different root mean square slopes (Sdq),
3 is a schematic cutaway cross-sectional view showing an example of the electromagnetic wave shielding wiring circuit board according to the present embodiment,
4 is a schematic plan view of a main surface side of a wiring board having a coplanar circuit according to an embodiment and a comparative example,
5 is a schematic plan view of a rear side of a wiring board having a coplanar circuit according to an example and a comparative example;
6 is a schematic plan view of a main surface side of a wiring board having a coplanar circuit provided with an electromagnetic wave shielding sheet according to an embodiment and a comparative example,
7 is a schematic plan view of the reliability evaluation of a cooling/heating cycle and a cross-sectional view of a cut portion,
8 is a dynamic viscoelastic curve of an electromagnetic wave shielding sheet (Example 5).

Hereinafter, an example of an embodiment to which the present invention is applied will be described. In addition, the size or ratio of each member in the drawings below is for convenience of description and is not limited thereto. In addition, in the description of "arbitrary number A-arbitrary number B" in this specification, the number A is included as a lower limit in the range, and the number B is included as an upper limit. In addition, "sheet" in this specification shall include not only "sheet" defined by JIS, but also "film". In addition, the numerical value specified in this specification is a value calculated|required by an embodiment or the method disclosed in an Example.

<Electromagnetic shielding sheet>

The electromagnetic wave shielding sheet of the present invention has a laminate comprising at least a conductive adhesive layer, a metal layer, and a protective layer in this order. 1 is a cross-sectional view illustrating an electromagnetic wave shielding sheet 10 according to an embodiment of the present invention. As shown in Fig. 1, the electromagnetic wave shielding sheet 10 has a laminated body comprising a conductive adhesive layer 1, a metal layer 2, and a protective layer 3 in this order, and the metal layer 2 is conductive. It is disposed between the adhesive layer 1 and the protective layer 3.

The electromagnetic wave shielding sheet of the present invention has a plurality of openings 4, has an opening ratio of 0.10 to 20%, and has a root mean square slope (Sdq) of the surface in contact with the conductive adhesive layer in the range of 0.0001 to 0.5. Since the metal layer is provided, excellent transmission characteristics and the like can be exhibited particularly in a wiring circuit board that transmits a signal of high frequency (eg, 100 MHz to 50 GHz).

The electromagnetic wave shielding sheet 10 comprises, for example, a wiring board as an adherend and a surface on the side of the conductive adhesive layer 1, and further cured as necessary to form an electromagnetic wave shielding layer of the electromagnetic wave shielding wiring circuit board. In this case, the interface of the metal layer in contact with the conductive adhesive layer of the electromagnetic wave shielding sheet is disposed on the signal wiring side.

[Loss tangent of laminated cured product]

In addition, the electromagnetic wave shielding sheet of the present invention is a laminated cured product obtained by hot 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, and a loss tangent at 125° C. of 0.10 or more. It is desirable.

Accordingly, it is possible to further improve the reliability of the cooling and heating cycle.

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, the laminated cured product refers to a laminate in which a layer having a cured component among the conductive adhesive layer, metal layer, protective layer, and other functional layers constituting the electromagnetic wave shielding sheet is cured.

In the laminated cured product, the peelable sheet is removed from the electromagnetic wave shielding sheet before or after hot pressing, and only one electromagnetic wave shielding sheet is hot pressed; Alternatively, several electromagnetic wave shielding sheets are laminated by a laminator or the like to perform hot pressing; Etc. can be obtained in any way.

Specifically, for example, two electromagnetic wave shielding sheets were prepared, the peelable sheet on the respective conductive adhesive layer side was peeled off, the exposed conductive adhesive layers were bonded together, and hot pressed under conditions of 170°C for 30 minutes, at least The laminate provided with the conductive adhesive layer, the metal layer, and the 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 determined by the following equation (3), and serves as an index of the stress relaxation ability generated when the electromagnetic wave shielding sheet is deformed.

Equation (3)

(Loss tangent of laminated cured product) =

(Loss modulus of cured laminate (E')) / (Storage modulus of cured laminate (E'))

The laminated cured product preferably has a loss tangent of 0.1 or more at 125°C after hot pressing at 170°C for 30 minutes from the viewpoint of reliability of the cooling and heating cycle. When the loss tangent at 125°C after hot pressing at 170°C for 30 minutes is 0.1 or more, it becomes possible to sufficiently alleviate the stress caused by expansion during high temperature exposure. In the laminated cured product, the loss tangent at 125°C after hot pressing at 170°C for 30 minutes is more preferably 0.13 or more, and even more preferably 0.15 or more.

The loss tangent of the laminated cured product can be controlled by changing any of the layers constituting the laminated cured product, or the loss modulus (E") and storage modulus (E') of two or more layers. The loss modulus of the laminated cured product (E''), and the storage modulus (E') of the laminated cured product by varying the loss modulus (E'') and storage modulus (E') of one layer or two or more layers constituting the laminated cured product ) Changes, and the loss tangent of the laminated cured product changes.

As an example of a method of changing the loss modulus (E") and storage modulus (E'), the amount of the curing agent in the protective layer is controlled. 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 increases or decreases. As a result, the storage modulus (E') of the laminated cured product increases or decreases, and the loss tangent of the laminated cured product decreases or increases.

The method of controlling the loss tangent of the laminated cured product is not particularly limited, and conventionally known methods such as changing the type or blending ratio of the thermoplastic resin or thermosetting resin and the curing agent, changing the thickness of each layer, or changing the type of metal layer. The method can be applied.

<<metal layer>>

The metal layer has a function of imparting high frequency shielding properties to the electromagnetic wave shielding sheet. The interface of the metal layer on the side in contact with the conductive adhesive layer has a root mean square slope (Sdq) of 0.0001 to 0.5 specified in ISO 25178-2:2012. By controlling the root mean square slope (Sdq) to be in the range of 0.0001 to 0.5, it is possible to achieve both transmission characteristics and cooling/heat cycle reliability. Details of the root mean square slope Sdq and detailed effects obtained by controlling the root mean square slope Sdq will be described later.

Further, the metal layer has a plurality of openings, and the opening ratio is 0.10 to 20%. For this reason, solder reflow resistance is improved, and occurrence of appearance defects and a decrease in connection reliability can be suppressed.

[Square Mean Square Root Slope (Sdq)]

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

[Equation 1]

The root mean square slope (Sdq) can be calculated by processing coordinate data of a surface shape obtained by any one of an optical microscope, a laser microscope, and an electron microscope by an analysis software. The root mean square slope Sdq represents the root mean square of the slope at all points of the positive surface, and is a parameter expressing the roughness of irregularities on the positive surface. As parameters for expressing the properties of the surface, arithmetic mean height (Sa) and maximum height (Sz) are generally used, but these are parameters representing only the height of the unevenness, and are not suitable for accurately representing the state of the surface.

2 illustrates two surfaces having different slopes of the root mean square (Sdq). The larger the value of the root mean square slope (Sdq), the more rough the surface irregularities become. That is, the degree of roughness of the surface irregularities can be determined by the value of the root mean square slope Sdq.

In addition, the value of the root mean square slope (Sdq) of this metal layer does not change by a forming process of an electromagnetic wave shielding layer such as a hot 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.

In addition, in the metal layer of the electromagnetic wave shielding sheet, due to the nature of the current, the current flows through the surface of the metal layer when it becomes a high frequency. Since the transmission characteristics of the signal wiring in the wiring circuit board are affected by the current flowing through the conductor in the vicinity, if the surface of the metal layer adjacent to the signal wiring is rough, the distance to the current flowing through the metal surface fluctuates and transmits. The characteristics become unstable. Therefore, from the viewpoint of transmission characteristics, the root mean square slope (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 even more preferably 0.3 or less.

On the other hand, as a result of intensive examination, it was found that the reliability of the cooling and heating cycle 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 even when the shape change occurs due to the expansion and contraction of the conductive adhesive layer in the cooling and heating cycle, contact between the conductive filler in the conductive adhesive layer and the metal layer is maintained by making the angle of the irregularities formed on the surface of the metal layer appropriately acute. It is thought that it is because deterioration is being suppressed. As a result of the examination, it is more preferable that the root mean square slope (Sdq) of the metal layer is in the range of 0.001 to 0.4, and still more preferably in the range of 0.01 to 0.3.

[Control method of root mean square slope (Sdq)]

The method of controlling the root-mean-square slope (Sdq) of the surface of the metal layer includes, for example, a method of forming a roughened surface by attaching roughened particles on the surface of a copper foil; A method of polishing a metal surface using a buff described in Japanese Patent Laid-Open No. 2017-13473; A method of polishing a metal surface using a polishing cloth; A shot blast method in which an abrasive is blown onto a metal surface with compressed air; Forming a metal layer on the carrier material having a predetermined root mean square slope (Sdq); A method of transferring irregularities on the surface of a carrier material to a metal layer; A method of transferring the unevenness of the film surface to the metal layer by compressing the film and the metal layer having a predetermined root mean square slope (Sdq); And the like. The method for controlling the root mean square slope Sdq of 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]

It is preferable that the thickness of the metal layer is 0.3 to 5.0 μm. When the thickness of the metal layer is 0.3 μm or more, transmission of electromagnetic wave noise generated from the wiring circuit board can be suppressed, and sufficient high-frequency shielding properties can be expressed. The lower limit of the thickness of the metal layer is more preferably 0.5 μm. When the thickness of the metal layer is 5.0 μm or less, the loss tangent of the laminated cured product can be increased, and the reliability of the cooling and heating cycle is improved. The upper limit of the thickness of the metal layer is more preferably 3.5 μm.

[Component 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, and gold, and 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 more preferable from the viewpoint of high frequency shielding property and cost. 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, it is preferable to use one kind of conductive metal such as aluminum, copper, silver, gold, or an alloy of several metals, and more preferably copper and silver. The metal foil, metal vapor deposition film, and metal plating film may be coated on one or both surfaces with an organic substance such as a metal or a rust inhibitor.

[Opening]

The metal layer has a plurality of openings, and the opening ratio is 0.10 to 20%. By having an opening, solder reflow resistance is improved. It has an opening, and when the electromagnetic wave shielding wiring circuit board is subjected to solder reflow treatment, volatile components contained in the polyimide film or coverlay adhesive of the wiring circuit board are removed to the outside, and the coverlay adhesive and the electromagnetic wave shielding sheet are separated from the interface. It is possible to suppress the occurrence of appearance defects.

The shape of the opening viewed from the surface of the metal layer includes, for example, a round circle, an ellipse, a square, a polygon, a star shape, a trapezoid shape, and a tree branch shape. From the viewpoint of manufacturing cost and securing the toughness of the metal layer, the shape of the opening is preferably a round circle or an ellipse.

Further, the root mean square slope Sdq is calculated excluding the 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 equation (2).

Equation (2)

(Opening rate [%]) = (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 treatment can be sufficiently removed, and occurrence of appearance defects due to interfacial peeling between the coverlay adhesive and the electromagnetic wave shielding sheet, and a decrease in connection reliability can be suppressed.

On the other hand, since the aperture ratio is less than 20%, shielding properties can be improved by reducing the amount of electromagnetic wave noise passing through the opening portion. The range of the aperture ratio is preferably 0.30 to 15%, and more preferably 0.50 to 6.5%, from the viewpoint of achieving both solder reflow resistance and high frequency shielding at a high level.

In particular, in the electromagnetic wave shielding sheet having a relatively smooth interface with a root mean square slope (Sdq) of 0.001 or less of the metal layer, the adhesion between the metal layer and the conductive adhesive layer is weak, and solder reflow resistance may decrease. Even with such an electromagnetic shielding sheet, by setting the aperture ratio of the metal layer to 0.10% or more, preferably 0.50% or more, volatile components can be sufficiently removed, further suppressing the occurrence of delamination or lifting, and suppressing the decrease in solder reflow resistance. do.

The measurement of the aperture ratio is, for example, using an image magnified 500 to 2000 times vertically in the plane direction of the metal layer with a laser microscope and a scanning electron microscope (SEM), and binarizing the opening and the non-opening portion and binarizing the pixels per unit area. It can be calculated by taking the number as each area.

[Method of manufacturing a metal layer having an opening]

A method for producing a metal layer having an opening may be applied to a conventionally known method, comprising: a method (i) of forming a pattern resist layer on the metal foil and etching the metal foil to form the opening; (Ii) a method of printing a conductive paste on a predetermined pattern by screen printing; A method (iii) of metal plating only on the printing surface of the anchor agent by screen printing the anchor agent in a predetermined pattern; The manufacturing method (iv) described in Japanese Patent Application Laid-Open No. 2015-63730, that is, pattern printing a water-soluble or solvent-soluble ink on a support to form a metal vapor deposition film on the surface thereof to remove the pattern. A method of obtaining a metal layer having an opening provided with a carrier material by forming a release layer on the surface and electrolytic plating; Etc. may be applied.

Among these, the method (i) 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 of manufacturing the metal layer is not limited to the 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, any of a thermoplastic resin, 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 isotropically conductive adhesive layer has conductivity in the vertical and horizontal directions in a state where the electromagnetic wave shielding sheet is placed horizontally. Further, the anisotropically conductive adhesive layer has conductivity only in the vertical direction in a state where the electromagnetic wave shielding sheet is placed horizontally.

The conductive adhesive layer may be any of isotropic conductivity or anisotropic conductivity, and in the case of anisotropic conductivity, cost can be reduced, so it is preferable.

[Thermoplastic resin]

As thermoplastic resins, 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 , A liquid crystal polymer, a fluororesin, and the like. Although not particularly limited, from the viewpoint of transmission loss, a material having a low dielectric constant and a low dielectric loss tangent is preferably a material having a low dielectric constant from the viewpoint of a characteristic impedance, and a liquid crystal polymer or a fluorine-based resin may be mentioned.

Thermoplastic resins can be used alone or in combination of two or more.

[Thermosetting resin]

The thermosetting resin is a resin having a plurality of functional groups capable of reacting with a curing agent. Functional groups are, for example, hydroxyl group, phenolic hydroxyl group, methoxy methyl group, carboxyl group, amino group, epoxy group, oxetanyl group, oxazoline group, oxadine group, aziridine group, thiol group, isocyanate group, blocked isocyanate group, blocked carboxyl group, Silanol group, etc. are mentioned. Thermosetting resins are, for example, acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane resin, polyurethaneurea resin, epoxy resin, oxetane resin, phenoxy resin, polyimide resin, polyamide Known resins such as resin, polyamideimide resin, phenolic resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzooxadine resin, silicone resin, and fluorine resin are mentioned.

Thermosetting resins can be used alone or in combination of two or more.

Among these, polyurethane resins, polyurethaneurea resins, polyester resins, epoxy resins, phenoxy resins, polyimide resins, polyamide resins, and polyamideimide resins 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 group 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.

The curing agent can be used alone or in combination of two or more.

The curing agent preferably contains 1 to 50 parts by weight, more preferably 3 to 40 parts by weight, and even 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 imparts conductivity to the conductive adhesive layer. The conductive filler is preferably made of a conductive metal such as gold, platinum, silver, copper and nickel, and alloys thereof, and fine particles of a conductive polymer, and more preferably silver from the viewpoint of cost and conductivity.

In addition, composite fine particles having a coating layer covering the surface of the nucleus body by using metal or resin as the nucleus, not the fine particles of a single material, are also preferable from the viewpoint of cost reduction. At this time, the nucleus is preferably appropriately selected from inexpensive nickel, silica, copper, and alloys thereof, and resin. The coating layer is preferably a conductive metal or a conductive polymer. Examples of the conductive metal include gold, platinum, silver, nickel, manganese, and indium, and alloys thereof. Further, examples of the conductive polymer include polyaniline and polyacetylene. Among these, silver is preferable in terms of cost and conductivity.

The shape of the conductive filler is not particularly limited as long as desired conductivity can be obtained. Specifically, for example, a spherical shape, a flake shape, a leaf shape, a branch shape, a plate shape, a needle shape, a rod shape, and a grape shape are preferable. Further, you may mix two types of conductive fillers of such different shapes.

Conductive fillers can be used alone or in combination of two or more.

The average particle diameter of the conductive filler is a D50 average particle diameter, and from the viewpoint of sufficiently securing conductivity, 2 μm or more is preferable, 5 μm or more is more preferable, and 7 μm or more is even more preferable. On the other hand, from the viewpoint of making it compatible with the thinness of the conductive adhesive layer, 30 μm or less is preferable, 20 μm or less is more preferable, and 15 μm or less is even more preferable. The D50 average particle diameter can be determined by a laser diffraction/scattering method particle size distribution measuring device 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 it as 35% by weight or more, the connection between the conductive adhesive layer and the ground wiring is improved, and the high-frequency shielding property and the reliability of the cooling and heating cycle are improved. On the other hand, by setting it to 90% by weight or less, solder reflow resistance and transmission characteristics are further improved.

The conductive resin composition may contain a silane coupling agent, a rust inhibitor, a reducing agent, an antioxidant, a pigment, a tackifier resin, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling adjuster, a filler, a flame retardant, and the like as other optional components.

The conductive resin composition can be obtained by mixing and stirring the materials described so far. As 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 coating and drying a conductive resin composition on a peelable sheet; A method of extruding the conductive resin composition into a sheet using an extrusion molding machine such as a T-die; And the like.

Coating methods include, for example, gravure coat method, kiss coat method, die coat method, lip coat method, comma coat method, blade method, roll coat method, knife coat method, spray coat method, bar coat method, spin coat method. And a known coating method such as a dip coating method can be used. It is preferable to perform a drying process after coating. For the drying step, for example, a known drying device such as a hot air dryer and 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. As the thickness is in the range of 2 to 30 μm, it can improve the reliability of the cooling cycle and solder reflow resistance.

<<protective layer>>

The protective layer can be formed using a conventionally known resin composition.

The resin composition may contain the thermoplastic resin or thermosetting resin described in the conductive resin composition, and the above-described optional component as needed, and a curing agent. In addition, the thermosetting resin and 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 the conductive resin composition.

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

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

<<Manufacturing method of electromagnetic wave shielding sheet>>

In the manufacture 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, and a conductive adhesive layer is laminated on the electrolytic copper foil side of an electrolytic copper foil having an opening provided with a carrier material, and then the carrier material is peeled off. And, the method of laminating by overlapping the surface from which the carrier material was peeled off and the protective layer separately formed on the peelable sheet;

(ii) A protective layer is formed on the peelable sheet, and a protective layer is laminated on the electrolytic copper foil surface side of the electrolytic copper foil having an opening provided with the carrier material, and then the carrier material is peeled off. And a method of laminating the surface from which the carrier material is peeled off and a conductive adhesive layer separately formed on the releasable sheet.

(iii) A resin composition is applied to the electrolytic copper foil surface side of the electrolytic copper foil having an opening provided with a carrier material to form a protective layer, and a peelable sheet is attached thereto. Thereafter, the carrier material is peeled off, and the conductive adhesive layer separately formed on the releasable sheet is stacked and laminated;

(iv) A conductive adhesive layer is formed on the peelable sheet, and the conductive adhesive layer is laminated on the side of the electrolytic copper foil side of the electrolytic copper foil provided with the carrier material, and then the carrier material is peeled off. And, a method of forming an opening in the electromagnetic wave shielding sheet with a needle-shaped jig after laminating the surface from which the carrier material is peeled off and the protective layer separately formed on the peelable sheet;

(v) After laminating the protective layer formed on the peelable sheet on the side of the electrolytic copper foil surface of the electrolytic copper foil having an opening provided with the carrier material, the carrier material is peeled off. And, a method of forming a conductive adhesive layer on the surface of the carrier material peeled off;

(vi) After forming a conductive adhesive layer on a peelable sheet and laminating a surface of a rolled copper foil having an opening with a surface having a root mean square slope (Sdq) of 0.0001 to 0.5 and a conductive adhesive layer, the conductive adhesive layer A method of laminating by overlapping another side laminated with the layer and a protective layer formed on a separate peelable sheet;

(vii) After forming a protective layer on the peelable sheet and laminating the other surface of the surface of the rolled copper foil having openings with a root mean square slope (Sdq) of 0.0001 to 0.5 and a conductive adhesive layer, , A method of laminating by overlapping another surface laminated with a protective layer and a conductive adhesive layer formed on a separate peelable sheet;

(viii) Of the surfaces of the rolled copper foil having an opening, a resin composition is applied to another surface of a surface having a root mean square slope (Sdq) of 0.0001 to 0.5 to form a protective layer, and a peelable sheet is attached. Thereafter, a method of laminating by overlapping another surface and a conductive adhesive layer formed on a separate peelable sheet;

(ix) Of the surface of the rolled copper foil having an opening, a conductive resin composition is applied to a surface having a root mean square slope (Sdq) of 0.0001 to 0.5 to form a conductive adhesive layer, and a peelable sheet is attached. Thereafter, a method of laminating by overlapping another surface and a protective layer formed on a separate peelable sheet; And the like.

The electromagnetic wave shielding sheet may include a functional layer other than a conductive adhesive layer, a metal layer, and a protective layer. The other functional layer is a layer having functions of hard coatability, water vapor barrier property, oxygen barrier property, thermal conductivity, low dielectric constant, high dielectric constant, and heat resistance.

The electromagnetic wave shielding sheet of the present invention can be used for various purposes in which it is necessary to shield electromagnetic waves. 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, and touch panels. Further, it can be used as a member for blocking electromagnetic waves such as a case of a PC, a building material such as a wall and a window glass of a building material, and a vehicle, a ship, and an aircraft.

In addition, the electromagnetic wave shielding sheet of the present invention can have excellent transmission characteristics such that a transmission loss when a 15 GHz sine wave is passed through a signal line of a coplanar circuit is less than 8 dB.

Specifically, the transmission characteristics can be evaluated in the following manner, for example.

First, prepare a coplanar circuit.

The coplanar circuit is one of flat transmission circuits in which signal wirings are printed on one side of an insulating substrate such as a polyimide film. In this evaluation method, the coplanar circuit uses a circuit in which ground wirings are formed side by side in the form of sandwiching two signal wirings on a polyimide film. In addition, in the coplanar circuit, a grant pattern for ground grounding is provided on an opposite surface through a through hole.

An electromagnetic wave shielding sheet is laminated by hot pressing by attaching a conductive adhesive layer of an electromagnetic wave shielding sheet to the insulating substrate surface opposite to the signal wiring of the coplanar circuit. At this time, the electromagnetic shielding sheet conducts with the partially exposed ground pattern. By this method, a test piece for evaluation of transmission characteristics can be obtained.

By connecting a network analyzer to the coplanar circuit of this test piece, the ratio of the input power and output power when a sine wave of 100 MHz to 20 GHz is passed through the signal wiring of the co-planar circuit can be calculated and evaluated. . In addition, a voltage ratio and a current ratio can be used instead of power.

In the present invention, the transmission loss when a 15 GHz sine wave is passed 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. Since the transmission loss is less than 8 dB, it is possible to realize a reduction in transmission loss at a high level.

In the case of using a thermoplastic resin for the binder resin in the conductive adhesive layer, the electromagnetic wave shielding sheet of the present invention melts the thermoplastic resin by hot pressing with a wiring board and solidifies again after cooling, so that the thermosetting resin contained therein exists in a solid state. Adhesive strength can be obtained.

In the case of using a thermosetting resin for the binder resin in the conductive adhesive layer, the electromagnetic wave shielding sheet of the present invention is present in an uncured state (Stage B) and cured by heat press with a wiring board (C Stage), the desired adhesive strength can be obtained. Further, the uncured state includes a semi-cured state in which a part of the curing agent is cured.

In addition, since the electromagnetic wave shielding sheet prevents adhesion of foreign substances, it is common to store the conductive adhesive layer and the protective layer in a state where the releasable sheet is attached.

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

<Electromagnetic wave shielding wiring circuit board>

The electromagnetic wave shielding wiring circuit board includes an electromagnetic wave shielding layer formed from the electromagnetic wave shielding sheet of the present invention, a cover coat layer, and a circuit pattern having signal wiring and ground wiring, and a wiring board having an insulating substrate.

In the wiring circuit board, after forming a cover coat layer having a via on at least a part of the ground wiring on the wiring board, placing the conductive adhesive layer side of the electromagnetic wave shielding sheet on the cover coat layer, the electromagnetic wave shielding sheet is By hot pressing, a conductive adhesive layer is introduced into the via to be bonded 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. 3.

The electromagnetic shielding layer 12 is a layer formed of the electromagnetic shielding sheet, and includes a conductive adhesive layer 1, a metal layer 2, a protective layer 3, or a laminated cured product thereof.

The cover coat layer 8 is an insulating material that covers the signal wiring of the wiring board and protects it from the external environment. The cover coat layer is preferably a polyimide film provided with a thermosetting adhesive, a thermosetting or ultraviolet curable solder resist, or a photosensitive coverlay film, and a photosensitive coverlay film is more preferred for fine processing. In addition, for the cover coat layer, it is common to use 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 taking a ground and a signal wiring 6 for sending an electric signal to an electronic component. It is common to form both by etching a copper foil. The thickness of the circuit pattern is usually about 1 to 50 μm.

The insulating substrate 9 is preferably a flexible plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, or liquid crystal polymer, and more preferably a liquid crystal polymer or polyimide as a support for a circuit pattern. Among these, considering the use of a wiring circuit board for transmitting high-frequency signals, a liquid crystal polymer having a low relative permittivity and a dielectric loss tangent is still more preferable.

In the case where the wiring board is a rigid wiring board, the constituent material of the insulating substrate is preferably glass epoxy. By providing such an insulating substrate, the wiring circuit board can obtain high heat resistance.

The heat pressing between the electromagnetic shielding sheet 10 and the wiring board is generally performed under conditions of a temperature of about 150 to 190°C, a pressure of about 1 to 3 MPa, and a time of about 1 to 60 minutes. The conductive adhesive layer 1 and the cover coat layer 8 are in close contact with each other by hot pressing, and at the same time, the conductive adhesive layer 1 flows to fill the via 11 formed in the cover coat layer 7 to fill the ground wiring 5 Conductivity is taken between and. The thermosetting resin reacts and cures by hot pressing to form the electromagnetic wave shielding layer 12.

In addition, in order to accelerate the 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, and preferably 0.008 mm 2 or more. By setting it as the said range, the area|region of a ground wiring can be narrowed, and the size reduction of a printed wiring board can be realized.

The shape of the via is not particularly limited, and any shape such as circle, square, rectangle, triangle, and irregular shape may be used depending on the application.

It is preferable to laminate the electromagnetic wave shielding layer on both sides of the wiring board from the viewpoint of more effective suppression of leakage of electromagnetic waves. 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 reducing the area of the wiring circuit board by omitting a part of the ground circuit. And can be assembled in a narrow area within the case body.

Further, the signal wiring is not particularly limited, and can be used for two circuits of a single-ended circuit consisting of one signal wiring and a differential circuit consisting of two signal wirings, but a differential circuit is more preferable. On the other hand, if there is a limitation in the circuit pattern area of the wiring board and it is difficult to form the ground circuit in parallel, the ground circuit is not installed next to the signal circuit, and the electromagnetic wave shielding layer is used as the ground circuit to have a gland in the thickness direction. It can also be made into a printed wiring board structure.

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

[Example]

Hereinafter, the present invention will be described in more detail by examples, but the present invention is not limited to the following examples. In addition, "parts" in the examples represent "parts by weight", and "%" represents "% by weight".

In addition, the acid value, the weight average molecular weight (Mw) of the resin, the glass transition temperature (Tg), and the measurement of the average particle diameter of a conductive filler were performed by the following method.

<<Measurement of acid value of binder resin>>

The acid value was measured according to JIS K0070. About 1 g of a sample is precisely weighed in an orbital Erlenmeyer flask, and 100 ml of a tetrahydrofuran/ethanol (volume ratio: tetrahydrofuran/ethanol = 2/1) mixture is added and dissolved. Here, a phenolphthalein test solution was added as an indicator, and titrated with a 0.1N alcoholic potassium hydroxide solution, and the end point was when the indicator kept a pink color for 30 seconds. The acid value was calculated|required by the following formula (unit: mgKOH/g).

Acid value (mgKOH/g) = (5.611×a×F) / S

but,

S: Sample collection amount (g)

a: Consumption amount 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 using Toso Corporation GPC (gel permeation chromatography) "HPC-8020". GPC is a liquid chromatograph in which a substance dissolved in a solvent (THF; tetrahydrofuran) is separated and quantified by the difference in molecular size. In the measurement in the present invention, two ``LF-604'' (Showa Denko Co., Ltd. product: GPC column for rapid analysis: 6mmID × 150mm size) were connected in series to be used, and the flow rate was 0.6 ml/min, and the column temperature. It carried out under the conditions of 40 degreeC, and the weight average molecular weight (Mw) was determined in terms of polystyrene.

<< glass transition temperature of binder resin (Tg) >>

The measurement of Tg was measured by differential scanning calorimetry ("DSC-1" manufactured by METTLER TOLEDO).

<<Measurement of average particle diameter of conductive filler>>

The D50 average particle diameter is a value obtained by measuring a conductive filler with a tornado dry powder sample module using a laser diffraction/scattering particle size distribution measuring device LS13320 (manufactured by Beckman Coulter), and is a cumulative value in the cumulative particle diameter distribution. This is the particle diameter of 50%. In addition, the setting of the refractive index was set to 1.6.

Next, the raw materials used in the examples are shown below.

<<Material>>

Conductive filler: Composite fine particles (dendritic fine particles coated with 10 parts by weight of silver per 100 parts by weight of copper in the core) Average particle diameter D50: 11.0 μm manufactured by Fukuda Metal Foil Powder Industrial Co., Ltd.

Binder resin: Polyurethane urea resin with acid value of 5mgKOH/g, weight average molecular weight of 54,000, Tg of -7℃ (manufactured by Toyochem)

Epoxy compound: "JER828" (bisphenol A type epoxy resin epoxy equivalent = 189g/eq) manufactured by Mitsubishi Chemical

Aziridine compound: "Chemite PZ-33" manufactured by Nihonshokubai

Pigment: Carbon black "MA100" manufactured by Mitsubishi Chemical

Carrier material: 「EMBLETS25」 (Sdq = 0.02) manufactured by Unityca

<Production of conductive adhesive layer (1)>

In terms of solid content, 100 parts of a binder resin, 47 parts of a conductive filler, 10 parts of an epoxy compound, and 0.5 parts of an aziridine compound were prepared in a container, and a mixed solvent (toluene: isopropyl alcohol = 2) so that the non-volatile content concentration was 40%. :1 (weight ratio)) was added, and it stirred with a disper for 10 minutes, and obtained the conductive resin composition.

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

<Production of conductive adhesive layers 2 to 8>

A conductive adhesive layer 2-8 shown in Table 1-3 was produced in the same manner as the conductive adhesive layer 1 except for changing the amount of the conductive filler added.

[Example 1]

A resin composition was obtained by adding 100 parts of a binder resin, 30 parts of an epoxy compound, and 7.5 parts of an aziridine compound in terms of solid content, and stirring with a disper for 10 minutes. The obtained resin composition was coated on copper foil to a dry thickness of 5 μm using a bar coater, dried in an electric oven at 100° C. for 2 minutes to form a protective layer (1), and a non-adhesive peelable sheet on the protective layer (1) I hit it.

Subsequently, the carrier material of the copper foil was removed, the copper foil surface was buff-polished, and the root mean square slope (Sdq) of the copper foil surface was adjusted to a value shown in Table 1. After polishing, by attaching the conductive adhesive layer 4 to the copper foil surface, an electromagnetic wave shielding sheet made of ``releasable sheet/protective layer (1)/copper foil (2)/conductive adhesive layer (4)/releasable sheet)” Got it. The copper foil 2 and the conductive adhesive layer 4 were pasted together by a thermal laminator at a temperature of 90°C and a pressure of 3 kgf/cm 2.

In addition, the copper foil 2 is a copper foil having a thickness shown in Table 1, an aperture ratio, etc. by a method of forming a pattern resist layer on a copper foil formed on a carrier material and etching the copper foil to form an opening.

[Examples 2 to 29, Comparative Examples 1 to 4]

As shown in Tables 1 to 3, except for changing the types of the conductive adhesive layer, the protective layer, and the copper foil, the same was performed as in Example 1, and the electromagnetic wave shielding sheets of Examples 2 to 29 and Comparative Examples 1 to 4 were prepared. Respectively obtained. When the target value of the root mean square slope (Sdq) of the copper foil surface was different from the value of the carrier material, the graded root mean square slope (Sdq) was adjusted by appropriately grinding or roughening the surface by buffing.

Regarding the obtained electromagnetic wave shielding sheet, the thickness of each layer, the root mean square slope (Sdq) of the metal layer, and the loss tangent of the electromagnetic wave shielding sheet were measured by the following method.

<<Measurement of each layer thickness>>

The thickness of the conductive adhesive layer, the metal layer, and the protective layer of the electromagnetic wave shielding sheet were measured by the following method.

Peel off the peelable sheet on the side of the conductive adhesive layer of the electromagnetic shielding sheet, attach the exposed conductive adhesive layer and polyimide film ("Kafton 200EN" manufactured by Toray DuPont), and heat press for 30 minutes at 2 MPa at 170°C. I did. 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 Corporation) was added dropwise in the form of a slide glass, and the electromagnetic shielding sheet was adhered to the slide glass/electromagnetic shielding sheet/polyee. A laminate of the configuration of a mid film was obtained. The obtained laminate was cut from the polyimide film side by ion beam irradiation using a cross section polisher (SM-09010, manufactured by Nippon Denshi Corporation) to obtain a measurement sample of the electromagnetic wave shielding sheet after hot pressing.

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

<<Measurement of the slope of the class average square (Sdq) of the metal layer>>

The root mean square slope (Sdq) of the metal layer of the electromagnetic wave shielding sheet was measured by the following method.

Peel off the peelable sheet on the side of the conductive adhesive layer of the electromagnetic wave shielding sheet, attach an adhesive tape (Nichi Reflective product ``CT1835'') to the exposed conductive adhesive layer, leaving the end of the adhesive tape, and peel off at the end of the adhesive tape, The conductive adhesive layer/adhesive tape is peeled off. The conductive adhesive layer was removed and the surface of the exposed metal layer was subjected to measurement data acquisition using a laser microscope (VK-X100 manufactured by Keyence Corporation).

The obtained measurement data was imported into analysis software (an analysis application “VK-H1XA” equipped with ISO 25178 surface property measurement module “VK-H1XR”, all manufactured by Keyence Corporation), and ISO 25178 surface property measurement was performed (condition is S- Filter; 1 μm, L-filter; 0.2 mm). In addition, regarding the metal layer having openings on the surface, the openings were excluded from the measurement range when ISO 25178 surface property measurement was performed.

<<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 shielding sheets having a width of 50 mm and a length of 50 mm were prepared, the peelable sheet on the side of each conductive adhesive layer was peeled off, and the exposed conductive adhesive layers were pasted together, under conditions of 170°C, 2.0 MPa, and 30 minutes. It pressed and heat-cured to obtain a laminated cured product. Thereafter, the central portion of the laminated cured product was cut into a width of 5 mm and a length of 30 mm to obtain a sample. This sample is set in a dynamic viscoelasticity measurement device (dynamic viscoelasticity measurement device DVA-200, manufactured by Haiti Measurement and Control Co., Ltd.), and the temperature rise rate: 10°C/min, measurement frequency: 1 Hz, distortion: 0.08%. The dynamic viscoelasticity was measured, and from the obtained dynamic viscoelastic curve, the loss modulus (E") and storage modulus (E') at 125°C were read, and the loss tangent of the laminated cured product was calculated. 8 shows an example of a dynamic viscoelastic curve (Example 5).

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

<Soldering reflow resistance>

The solder reflow resistance was evaluated according to the appearance change after the electromagnetic wave shielding sheet and the molten solder were brought into contact with each other. The electromagnetic wave shielding sheet having high solder reflow resistance does not change its appearance, but the electromagnetic wave shielding sheet having low solder reflow resistance causes foaming and peeling.

First, peel off the peelable sheet of the conductive adhesive layer of the electromagnetic wave shielding sheet having a width of 25 mm and a length of 70 mm, and the exposed conductive adhesive layer and a copper clad laminate (gold plated 0.3 μm/nickel plated 1 μm) with a total thickness of 64 μm. /Copper foil 18 µm/adhesive 20 µm/polyimide film 25 µm) was subjected to pressure bonding under conditions of 170°C, 2.0 MPa, 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 allowed to stand for 72 hours in an atmosphere of 40°C and 90%RH. Thereafter, the polyimide film side of the sample was brought down and floated on a melt soldering at 250° C. for 1 minute, and then the sample was taken out and its appearance was visually observed, and the presence or absence of abnormalities such as foaming, lifting, peeling, etc. Evaluated.

(Evaluation standard)

◎: No change in appearance. Very good.

○: Small foaming was observed slightly. Good.

△: A large number of small foams were observed. Practical.

X: Severe foaming or peeling was observed. Impractical.

<transmission characteristics>

The transmission characteristics were evaluated using the wiring board 20 having a coplanar circuit provided with the electromagnetic wave shielding sheet shown in FIG. 4.

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 measurement is shown in Figs. 4, 5, and the back side. It shows a schematic plan view of the side. First, a double-sided CCL "R-F775" (manufactured by Panasonic) was prepared 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. Then, six through holes 51 (0.1 mm in diameter) were provided in the vicinity of the four rectangular corners. In addition, in the figure, for convenience of illustration, only two through holes 51 are shown in each corner part. Subsequently, after performing the electroless plating treatment, electrolytic plating treatment was performed to form a copper plating film 52 of 10 μm, and conduction between the main surface and the back surface was ensured through the copper plating film formed in the through hole 51. Thereafter, it extends from two signal lines 53 having a length of 10 cm 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 on the outside thereof, A ground pattern (i) 55 was formed in a region of the polyimide film 50 including the through hole 51 in the shorter direction.

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 circuit appearance and tolerance inspection specifications were made in the JPCA standard (JPCA-DG02). Next, on the main surface side of the polyimide film 50, a cover coat layer 7 consisting of a polyimide film (thickness 12.5 μm) and an insulating adhesive layer (thickness 15 μm) ``CISV1215 (manufactured by Nikkan Kogyo)'' was affixed. . In addition, 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, nickel plating (not shown) was applied to the copper foil pattern exposed by the cover coat layer 8, followed by gold plating (not shown) treatment.

Subsequently, as shown in Fig. 6, the peelable sheet of the electromagnetic wave shielding sheet 10 of each of the above examples is removed, and the conductive adhesive layer 1 is placed on the entire rear side of the wiring board 20 having a coplanar circuit as the inner side at 170°C. , 2.0 MPa and 30 minutes of compression to obtain a wiring board 21 having a coplanar circuit with an electromagnetic wave shielding layer. In Fig. 6, the rear ground pattern (ii) 56 is shown in a perspective view.

In addition, the L/S (line/space) of the signal wiring 53 was appropriately adjusted so that the characteristic impedance falls within ±10 Ω. 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.

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

(Evaluation standard)

◎: Transmission loss at 15GHz is less than 7.0dB, very good.

○: Transmission loss at 15GHz is more than 7.0dB, less than 7.5dB, good.

△: Transmission loss at 15GHz is 7.5dB or more and less than 8.0dB, practical.

×: Transmission loss at 15GHz is 8.0dB or more, not practical.

<High frequency shielding property>

In accordance with ASTM D4935, the amount of attenuation by which electromagnetic waves are attenuated by the electromagnetic wave shielding sheet by irradiating electromagnetic waves under conditions of 100 MHz to 15 GHz using a coaxial tube-type shielding effect measurement system manufactured by Keycom Corporation in accordance with ASTM D4935. Measure and mark according to the following criteria. In addition, the measured value of the attenuation amount is decibel (unit; dB).

(Evaluation standard)

◎: The attenuation at the time of 15GHz electromagnetic wave irradiation is very good, less than -55dB.

○: The attenuation at the time of 15GHz electromagnetic wave irradiation, -55dB or more, less than -50dB, good.

△: Attenuation when irradiated with electromagnetic waves of 15GHz, more than -50dB, less than -45dB, practical.

×: Attenuation of -45 dB or more when irradiating electromagnetic waves at 15 GHz is not practical.

<Cooling cycle reliability>

The reliability of the cooling and heating cycle was evaluated by measuring the connection resistance value through the introduction port via before and after the cooling and heating cycle. A specific method of evaluation is shown below.

An electromagnetic wave shielding sheet was prepared in a size of 20 mm in width and 50 mm in length to obtain a sample 25. 7 (1) and (4) will be described by showing the plan view of the sample 25 by peeling the peelable sheet, the exposed conductive adhesive layer 25b, a separately produced flexible printed wiring board (polyimide film (25 μm thick) ( A copper foil circuit 22A having a thickness of 18 μm and a copper foil circuit 22B that are not electrically connected to each other on the 21) are formed, and on the copper foil circuit 22A, a diameter of 37.5 μm and a diameter of 1.1 mm (via area is 1.0 Mm2) by pressing the wiring board on which the polyimide coverlay 23 is laminated with an adhesive having a circular via 24) under conditions of 170°C, 2 MPa, 30 minutes, and the conductive adhesive layer 25b of the electromagnetic wave shielding sheet and A sample was obtained by curing the protective layer 25a. Subsequently, 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 obtained from ``LORESTA-GP'' manufactured by Mitsubishi Chemical Corporation. It was measured using a probe of BSP. 7(2) is a cross-sectional view taken along line D-D' of FIG. 7(1), and FIG. 7(3) is a cross-sectional view taken along line C-C' of FIG. 7(1). Similarly, FIG. 7(5) is a cross-sectional view taken along line D-D' of FIG. 7(4), and FIG. 7(6) is a cross-sectional view taken along line C-C' of FIG. 7(4). The sample was put into a cold shock device ("TSE-11-A", manufactured by SPEC), and 200 exposures were performed alternately under high temperature exposure: 125℃, 15 minutes, low temperature exposure: -50℃, 15 minutes. did. Then, the connection resistance value of the sample was measured similarly to the initial stage.

The criteria for evaluating the reliability of the cooling and heating cycle are as follows.

(Evaluation standard)

◎: (connection resistance value after exposure alternately)/(initial connection resistance value) is less than 1.5, very good.

○: (Connection resistance value after exposure alternately)/(Initial connection resistance value) is 1.5 or more, less than 3.0, good.

△: (connection resistance value after exposure alternately)/(initial connection resistance value) is 3.0 or more and less than 5.0, practical.

X: (connection resistance value after exposure alternately)/(initial connection resistance value) is 5.0 or more, not practical.

[Table 1]

[Table 2]

[Table 3]

This application claims the priority based on Japanese Patent Application No. 2019-112479 for which it applied on June 18, 2019, and includes all of the indication here.

One; Conductive adhesive layer
2; Metal layer
3; Protective layer
4; Opening
5; Grand wiring
6; Signal wiring
7; Electromagnetic shielding wiring circuit board
8; Cover coat layer
9; Insulating substrate
10; Electromagnetic shielding sheet
11; Via
12; Electromagnetic shielding layer
20; Wiring board with coplanar circuit
21; Wiring board with coplanar circuit with electromagnetic shielding sheet
22A, 22B; Copper foil circuit
23; Polyimide coverlay
24; Circular via
25; Sample (electromagnetic shielding sheet)
25a; Protective layer
25b; Conductive adhesive layer
50; Polyimide film
51; Through hole
52; Copper plated film
53; Signal wiring
54; Grand wiring
55; Grand 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) of 0.0001 to 0.5 determined in accordance with ISO 25178-2:2012,
The metal layer has a plurality of openings, and an electromagnetic wave shielding sheet having an opening ratio of 0.10 to 20%.
The method of claim 1,
An electromagnetic wave shielding sheet, wherein the laminated cured product obtained by hot pressing the laminate at 170° C. for 30 minutes has a loss tangent at 125° C. of 0.10 or more.
The method of claim 1,
The thickness of the metal layer, electromagnetic wave shielding sheet, characterized in that the 0.3 ~ 5.0μm.
The method of claim 1,
The conductive adhesive layer contains a binder resin and a conductive filler,
The electromagnetic wave shielding sheet, wherein the content of the conductive filler in the conductive adhesive layer is 35 to 90% by weight.
An electromagnetic wave shielding wiring circuit board 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 signal wiring and an insulating substrate.

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