JP6645610B1 - Electromagnetic wave shielding sheet and electromagnetic wave shielding wiring circuit board - Google Patents

Abstract

An electromagnetic wave shielding sheet having solder reflow resistance and excellent thermal cycle reliability, excellent high-frequency shielding properties, and excellent bending resistance, and a wiring circuit board using the electromagnetic wave shielding sheet. An interface between the metal layer and the metal layer in contact with the conductive adhesive layer of the metal layer has a 60 ° specular gloss of 10 according to ISO 7668. To 800, and wherein the metal layer has a plurality of openings and an aperture ratio of 0.10 to 20%. [Selection diagram] Fig. 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 being used by being joined to a part of a component that emits an electromagnetic wave, and an electromagnetic wave using the electromagnetic wave shielding sheet The present invention relates to a shielded wiring circuit board.

  2. Description of the Related Art Various electronic devices such as portable terminals, PCs, servers, and the like have built-in printed 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 electric signals.

  With the transmission of transmission signals at higher speeds, the electromagnetic wave shielding sheet is also required to reduce electromagnetic wave shielding properties (hereinafter referred to as high frequency shielding properties) corresponding to high frequency noise and to reduce transmission loss (hereinafter sometimes referred to as transmission characteristics) in a high frequency region. ing. Patent Document 1 discloses a configuration in which a metal layer having a thickness of 0.5 to 12 μm and an anisotropic conductive adhesive layer are provided in a laminated state. In addition, it describes that the configuration appropriately shields an electric wave, a magnetic wave, and an electromagnetic wave traveling from one surface side to the other surface side of the electromagnetic wave shielding sheet and reduces transmission loss.

WO 2013/077108 JP 2013-168463 A

2. Description of the Related Art In recent years, with high-speed transmission of transmission signals in electronic devices typified by mobile phones, an electromagnetic wave shielding sheet on a printed circuit board incorporated therein has also been required to have high-frequency shielding properties and transmission characteristics. Therefore, it has been considered 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, an electromagnetic wave shielding printed circuit board in which an electromagnetic wave shielding sheet using a metal layer is adhered to a printed circuit board has a layer between layers due to volatile components generated from inside the printed circuit board when a heating process such as solder reflow is performed. There has been a problem that floating occurs, resulting in poor appearance and poor connection due to foaming or the like (hereinafter, sometimes referred to as solder reflow resistance). To solve this problem, for example, Patent Document 2 discloses that a metal foil having a plurality of pinholes in a metal thin film layer is used, and that volatile components are transmitted through the pinholes of the metal thin film layer, thereby suppressing floating and foaming between layers. ing.
In addition, the thicker the metal layer of the electromagnetic wave shielding sheet, the higher the shielding performance, while the higher the repulsive force. Therefore, when a shielded printed wiring board in which an electromagnetic wave shielding sheet is adhered to a printed wiring board, cracks in bent portions, poor appearance, poor insulation, noise leakage, and the like have become problems when assembled in a housing. Was.
On the other hand, with the worldwide spread of electronic devices such as smartphones and tablet terminals in recent years, reliability under all temperature conditions is required. The printed circuit boards provided with the electromagnetic wave shielding sheets of Patent Document 1 and Patent Document 2 have a problem that when exposed to an extreme temperature change, the printed circuit boards are peeled off from the printed circuit boards or disconnected from the ground circuit. (Hereinafter, thermal cycle reliability).

  The present invention has been made in view of the above background, and aims to have solder reflow resistance and excellent cooling / heating cycle reliability, and have an excellent high-frequency shielding property and a good bending resistance. An object of the present invention is to provide an electromagnetic wave shield sheet and a wiring circuit board using the electromagnetic wave shield sheet.

As a result of intensive studies by the present inventors, they have found that the following aspects can solve the problems of the present invention, and have completed the present invention.
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 surface of the metal layer in contact with the conductive adhesive layer conforms to ISO 7668. The obtained 60 ° specular gloss is 10 to 800, the metal layer 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, showing excellent high-frequency shielding properties even when used in a high-frequency transmission circuit, and having good bending resistance and high connection reliability even after exposure to a thermal cycle, In addition, an excellent effect that an electromagnetic wave shielding wiring circuit board can be provided.

It is sectional drawing which illustrated the electromagnetic wave shielding sheet which concerns on this embodiment. It is the figure which illustrated the ratio comparison of the specular reflection light / diffuse reflection light of the surface from which a roughness degree 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 schematic plan view of a thermal cycle reliability evaluation, and a sectional view of a cut part. It is a dynamic viscoelasticity curve of a laminated hardened material (Example 5).

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

<Electromagnetic wave shield sheet>
The electromagnetic wave shielding sheet of the present invention has a laminate having at least a conductive adhesive layer, a metal layer, and a protective layer in this order. FIG. 1 is a cross-sectional view illustrating 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 laminate 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. 3 are 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 surface of the metal layer in contact with the conductive adhesive layer is determined in accordance with ISO 7668. Since a metal layer having a 60 ° specular gloss of 10 to 800 is provided, excellent transmission characteristics and the like can be exhibited particularly in a printed circuit board that transmits a high-frequency (for example, 100 MHz to 50 GHz) signal. .
For example, the electromagnetic wave shielding sheet 10 forms an electromagnetic wave shielding layer by bonding a surface of the conductive adhesive layer 1 side to a wiring circuit substrate, which is an adherend, to produce an electromagnetic wave shielding wiring circuit substrate. That is, of the surface of the metal layer 2, the surface facing the signal wiring in the printed circuit board is the surface in close contact with the conductive adhesive layer 1.

[Loss tangent of laminated cured product]
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 laminate 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 preferably 0.10 or more.
Thereby, the cooling / heating cycle reliability can be further improved.

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

The laminated cured product is obtained by removing the peelable sheet from the electromagnetic wave shielding sheet before or after hot pressing, and heat-pressing only one electromagnetic wave shielding sheet, or laminating a plurality of electromagnetic wave shielding sheets with a laminator or the like And hot pressing.
That is, the laminated cured product is the same laminated component of the electromagnetic wave shielding sheet as the electromagnetic wave shielding layer used for the electromagnetic wave shielding wiring circuit board.

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

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

Formula (3)
(Loss tangent of the cured laminate) =
(Loss modulus E '' of the cured laminate) / (Storage modulus E '' of the cured laminate)
As an example, FIG. 5 shows a dynamic viscoelasticity curve of the cured laminate (Example 5). By reading the loss elastic modulus E ″ and the storage elastic modulus E ′ at a certain temperature and applying those numerical values to the above-described equation (3), the loss tangent at the corresponding temperature can be calculated. It is preferable that the loss tangent of the laminated cured product at 125 ° C. after hot pressing at 170 ° C. for 30 minutes is 0.1 or more from the viewpoint of cooling / heating cycle reliability. When the loss tangent at 125 ° C. after hot pressing at 170 ° C. for 30 minutes of the laminated cured product is 0.1 or more, it is possible to sufficiently relax the stress generated by expansion at the time of high-temperature exposure. The loss tangent of the laminated cured product 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 is determined by the loss elastic modulus E ″ and the storage elastic modulus of any of the conductive adhesive layer, the metal layer, the protective layer, and other layers included in the laminated cured product, or two or more layers. It can be controlled by changing E '. By changing the loss modulus E ″ and the storage modulus E ′ of one or more layers included in the laminated cured product, the loss modulus E ″ and the storage modulus of the laminated cured product are changed. This is because the rate E ′ changes and the loss tangent of the cured laminate 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, there is control of the amount of a curing agent in the protective layer. 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 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 of controlling the loss tangent of the laminated cured product is not particularly limited, and the type and the mixing ratio of the thermoplastic resin or the thermosetting resin and the curing agent are changed, the thickness of each layer is changed, and the thickness of the metal layer is changed. A conventionally known method such as changing the type can be applied.

《Metal layer》
The metal layer of the present invention has a function of providing a high-frequency shielding property to the electromagnetic wave shielding sheet. The surface of the interface between the conductive adhesive layer and the metal layer on the side where the metal layer is in contact with the conductive layer has a 60 ° specular gloss of 10 to 800 determined in accordance with ISO 7668. By controlling the 60 ° specular gloss so as to be in the range of 10 to 800, both bending resistance and cooling / heating cycle reliability can be achieved. The details of the 60 ° specular gloss and the effects obtained by controlling the 60 ° specular gloss will be described later.
Further, the metal layer of the present invention has a plurality of openings, and the opening ratio is 0.10 to 20%. As a result, solder reflow resistance is improved, and occurrence of poor appearance and reduction in connection reliability can be suppressed.

[60 ° mirror gloss]
The 60 ° mirror gloss is a parameter standardized in ISO 7668 and represents the gloss of the surface to be measured. The specular gloss can be measured by irradiating light (incident light) to the surface of the object to be measured at a certain incident angle, detecting light reflected at a certain degree of accuracy (specular reflected light) by a detector, and digitizing the light.
The incident light applied to the surface to be measured is reflected, transmitted or absorbed when reaching the surface to be measured. The reflection includes specular reflection and diffuse reflection, and light reflected at the same angle (reflection angle) as the incident angle is specular reflection light, which is light detected by specular gloss measurement. The 60 ° specular gloss is a value measured at an incident angle and a reflection angle of 60 °.
When the surface to be measured is a metal layer, most of the incident light is reflected. Which ratio of the reflected light becomes specular reflection and diffuse reflection depends on the roughness of the surface of the metal layer. FIG. 2 is a cross-sectional view of two types of surfaces to be measured having different degrees of roughness. On the measurement target surface having a small degree of roughness, the ratio of the specular reflected light is large, while the diffuse reflected light is small, and the value of the specular gloss is large. On the other hand, on the measurement target surface having a large degree of roughness, the ratio of the specular reflected light is small, while the diffuse reflected light is large, and the value of the specular gloss is small. That is, the specular gloss can be used as an index for measuring the degree of roughness of the surface to be measured.

  It should be noted that the value of the 60 ° specular gloss of the metal layer is not changed by the step of forming the electromagnetic wave shielding layer such as a hot press. Therefore, the 60 ° specular glossiness of the surface of the metal layer in contact with the conductive adhesive layer in the electromagnetic wave shielding layer is also 10 to 800.

  When the electromagnetic wave shielding sheet, the laminated cured product obtained by curing them, and the electromagnetic wave shielding wiring circuit board are bent, the contained metal layer is also bent. At that time, if the surface of the metal layer has steep irregularities, the metal layer may be cracked. That is, when the metal layer is bent, stress concentrates on the concave portions of the unevenness, and cracks occur in the metal layer starting from the concave portions. Cracks in the metal layer cause problems such as a decrease in shielding properties due to poor conductivity of the metal layer and poor appearance caused by crack end portions breaking through other layers. Therefore, from the viewpoint of bending resistance, the 60 ° specular gloss of the surface of the metal layer in contact with the conductive adhesive layer is preferably 10 or more, more preferably 20 or more, and preferably 40 or more. More preferred.

  On the other hand, from the viewpoint of the thermal cycle reliability, as a result of intensive studies, it was found that the thermal cycle reliability was improved by setting the 60 ° specular gloss of the metal layer in the range of 10 to 800. This is because even if the conductive adhesive layer undergoes a shape change due to expansion and contraction in the cooling and heating cycle, the conductive filler in the conductive adhesive layer and the metal layer are formed by appropriately roughening the irregularities formed on the metal layer surface. This is considered to be due to the fact that the contact with the substrate is maintained and the deterioration of the connection resistance value is suppressed. As a result of the examination, the 60 ° specular gloss of the metal layer is more preferably in the range of 20 to 750, and further preferably in the range of 40 to 700.

[Control method of 60 ° mirror gloss]
A method of controlling the 60 ° specular gloss of the metal layer surface is, for example, a method of forming a roughened surface by attaching roughened particles on a copper foil surface, which is described in JP-A No. 2017-13473. Polishing the metal surface using a buff, polishing the metal surface using abrasive cloth paper, forming a metal layer on a carrier material having irregularities by plating or the like to transfer the irregularities of the carrier material And a shot blast method in which an abrasive is blown onto a metal surface by compressed air. The method for controlling the 60 ° specular gloss of the surface of the metal layer is not limited to the illustrated method, and a conventionally known method can be applied.

[Metal layer thickness]
The thickness of the metal layer is preferably 0.3 μm or more. By setting the thickness of the metal layer to 0.3 μm or more, it is possible to suppress the transmission of the electromagnetic wave noise generated from the printed circuit board, to achieve a sufficient high-frequency shielding property, and to reduce the bending time. Of the metal layer can be suppressed. The thickness of the metal layer is more preferably 0.5 μm or more. On the other hand, the thickness of the metal layer is preferably 5.0 μm or less. 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 thermal cycle reliability is improved. The upper limit of the thickness of the metal layer is more preferably 3.5 μm or less.

[Components of metal layer]
As the metal layer, for example, a metal foil, a metal deposition film, and a metal plating film can be used.
The metal used for the metal foil is preferably, for example, a conductive metal such as aluminum, copper, silver, or gold, and any one of a metal or an alloy of a plurality of metals can be used. Copper, silver, and aluminum are more preferred in terms of high-frequency shielding properties and cost, and copper is still more preferred. As the copper, for example, a rolled copper foil or an electrolytic copper foil is preferably used.
As the metal used for the metal deposition film and the metal plating film, 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, the metal deposition film, and the metal plating film may be coated with a metal or an organic substance such as a rust preventive.

[Aperture]
The metal layer has a plurality of openings, and the opening ratio is 0.10 to 20%. Having the opening improves solder reflow resistance. By having the opening, when the electromagnetic wave shielding wiring circuit board is subjected to the solder reflow treatment, the volatile components contained in the polyimide film and the coverlay adhesive of the wiring circuit board escape to the outside, and the coverlay adhesive and the electromagnetic wave shielding sheet Can be prevented from occurring due to interface peeling.

  The shape of the opening as viewed from the surface of the metal layer may be any shape such as a perfect circle, an ellipse, a square, a polygon, a star, a trapezoid, a branch, or the like, if necessary. The shape of the opening is preferably a perfect circle and an ellipse from the viewpoint of manufacturing cost and securing the toughness 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).
Formula (2)
(Aperture ratio [%]) = (Area of opening per unit area) / (Area of opening per unit area + Area of non-opening per unit area) × 100

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

  In particular, in the range where the 60 ° specular gloss of the metal layer is 700 or more, in an electromagnetic wave shielding sheet having a smooth interface with the conductive adhesive layer, the adhesion between the metal layer and the conductive adhesive layer is weak, and during the solder reflow treatment, Volatile components expand at the interface between the metal layer and the conductive adhesive layer, which may cause poor appearance such as delamination or floating, but the aperture ratio is 0.10% or more, preferably 0.50% or more. Thereby, the volatile components can be sufficiently released, and the occurrence of delamination or floating can be further suppressed.

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

[Method of Manufacturing Metal Layer Having Opening]
As a method for producing a metal layer having an opening, a conventionally known method can be applied. A method of forming a pattern resist layer on a metal foil and etching the metal foil to form an opening (i), screen printing (Ii) a method of printing a conductive paste in a predetermined pattern by a method, screen printing of an anchor agent in a predetermined pattern and metal plating only on the anchor agent printed surface, and JP-A-2015-63730. The manufacturing method (iv) and the like that have been used can be applied.
That is, a water-soluble or solvent-soluble ink is pattern-printed on a support, a metal deposition film is formed on the surface thereof, 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 electrolytic plating. Among them, an opening forming method of forming a pattern resist layer and etching a metal foil (i) However, it is preferable because the shape of the opening can be precisely controlled. However, the shape of the opening may be controlled by other methods, and the method of manufacturing the metal layer is not limited to the etching method (i).

《Conductive adhesive layer》
The conductive adhesive layer can be formed using a conductive resin composition. The conductive resin composition contains a binder resin and a conductive filler. As the binder resin, either a thermoplastic resin or a thermosetting resin and a curing agent can be used. As the conductive adhesive layer, either an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer can be used. The isotropic conductive adhesive layer has conductivity in the vertical and horizontal directions with the electromagnetic wave shielding sheet placed horizontally. In addition, the anisotropic 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 either isotropically conductive or anisotropically conductive, and the anisotropically conductive layer is preferable because the cost can be reduced.

[Thermoplastic resin]
As the thermoplastic resin, 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 Polymers, fluororesins and the like can be 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 a liquid crystal polymer and a fluorine-based resin.
The 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. The functional group includes, for example, a hydroxyl group, a phenolic hydroxyl group, a methoxymethyl group, a carboxyl group, an amino group, an epoxy group, an oxetanyl group, an oxazoline group, an oxazine group, an aziridine group, a thiol group, an isocyanate group, a blocked isocyanate group, and a blocked group. Examples include a carboxyl group and a silanol group. Thermosetting resin, for example, acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane resin, polyurethane urea resin, epoxy resin, oxetane resin, phenoxy resin, polyimide resin, polyamide resin, polyamide imide resin, phenolic resin Known resins such as resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzoxazine resin, silicone resin, and fluororesin are exemplified.
The 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.
The curing agents 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 either alone or as a mixture of both.

[Conductive filler]
The conductive filler has a function of giving conductivity to the conductive adhesive layer. As the material of the conductive filler, for example, conductive metals such as gold, platinum, silver, copper and nickel and alloys thereof, and fine particles of a conductive polymer are preferable, and silver is more preferable in terms of price and conductivity. From the viewpoint of cost reduction, composite fine particles having not a single material fine particle but a metal or resin as a core and a coating layer covering the surface of the core are also preferable. Here, it is preferable that the core is appropriately selected from inexpensive nickel, silica, copper and alloys thereof, and resin. The covering layer is preferably made of a conductive metal or a conductive polymer. Examples of the conductive metal include gold, platinum, silver, nickel, manganese, and indium, and alloys thereof. Examples of the conductive polymer include polyaniline and polyacetylene. Among these, silver is preferred from the viewpoint 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 bar shape, and a grape shape are preferable. Further, two kinds of conductive fillers having different shapes may be mixed.
The conductive fillers 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. D ₅₀ average particle diameter of the conductive filler that is 2μm or more, also for the expansion of the conductive adhesive layer during thermal cycling test, conductive fillers with each other sufficiently in contact, it is possible to secure the conduction path . On the other hand, from the viewpoint of achieving compatibility with the thickness of the conductive adhesive layer, the thickness is preferably 30 μm or less, more preferably 20 μm or less, and still more preferably 15 μm or less. By D ₅₀ average particle diameter and 30μm or less, it is possible to suppress the phenomenon that the conductive filler breaks through a protective layer during bending. D ₅₀ average particle size can be determined by a laser diffraction scattering method particle size distribution measuring apparatus or the like.

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

  For the purpose of improving the desired physical properties and imparting functions, the conductive resin composition has, as other optional components, a silane coupling agent, a rust inhibitor, a reducing agent, an antioxidant, a pigment, a dye, a tackifier resin, a plasticizer, UV absorbers, defoamers, leveling regulators, fillers, flame retardants, and the like can be added. For example, carbon particles can be added for the purpose of adjusting the viscoelasticity of the conductive adhesive layer. Examples of the carbon particles include carbon black, Ketjen black, acetylene black, carbon nanotube, and graphene.

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

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

  Coating methods include, for example, gravure coating, kiss coating, die coating, lip coating, comma coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, dip coating. A known coating method such as a method can be used. At the time of coating, a drying step is preferably performed. 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, the reliability of the cooling / heating cycle and the solder reflow resistance can be improved.

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

  Further, as the protective layer, a film formed of an insulating resin such as polyester, polycarbonate, polyimide, polyamide imide, polyamide, polyphenylene sulfide, and polyether ether ketone can be used.

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

<< Production method of electromagnetic wave shielding sheet >>
In the production of the electromagnetic wave shielding sheet, a known method can be used for 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 formed on the electrolytic copper foil surface side of an electrolytic copper foil having an opening with a carrier material (also referred to as a copper foil with a carrier material). After stacking and laminating, the carrier material is peeled off. And a method of laminating the surface from which the carrier material has been peeled and a protective layer separately formed on a peelable sheet, and (ii) forming a protective layer on the peelable sheet and having an opening with a carrier material. After laminating and laminating a protective layer on the electrolytic copper foil side of the copper foil, the carrier material is peeled off. Then, a method of laminating and laminating the surface from which the carrier material has been peeled off and a conductive adhesive layer separately formed on a releasable sheet, (iii) on the electrolytic copper foil surface side of the electrolytic copper foil having an opening with a carrier material. A protective layer is formed by coating the resin composition, and a release sheet is attached. After that, the carrier material is peeled off, and a conductive adhesive layer separately formed on the peelable sheet is laminated and laminated. (Iv) The conductive adhesive layer is formed on the peelable sheet, and the electrolytic copper of the copper foil with the carrier material is formed. After laminating the conductive adhesive layer on the foil side, the carrier material is peeled off. Then, after laminating and laminating the surface from which the carrier material has been peeled off and the protective layer separately formed on the releasable sheet, a method of forming an opening in the electromagnetic wave shielding sheet with a needle-like jig, (v) releasability 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 the carrier material, the carrier material is peeled off. Then, a method of forming a conductive adhesive layer on the surface from which the carrier material has been peeled off, (vi) forming a conductive adhesive layer on the peelable sheet, and forming a 60 ° mirror gloss on the surface of the rolled copper foil having openings. After laminating the surface having a degree of 10 to 800 and the conductive adhesive layer, the other surface laminated with the conductive adhesive layer and the protective layer separately formed on a peelable sheet are laminated and laminated. Method, (vii) forming a protective layer on a peelable sheet, and, among the surfaces of the rolled copper foil having openings, the other surface having a 60 ° specular gloss of 10 to 800, and a conductive adhesive A method of laminating the other surface laminated with the protective layer and a conductive adhesive layer separately formed on a releasable sheet after laminating the layers, and (viii) a method of rolling a copper foil having an opening. Of the surface, 60 ° specular gloss The other surface side is 0 to 800 by coating the resin composition to form a protective layer bonded a release sheet. Then, the other surface and a conductive adhesive layer separately formed on a releasable sheet are laminated and laminated. (Ix) Among the surfaces of the rolled copper foil having openings, a 60 ° specular gloss of 10 A conductive resin composition is applied to the surface having a thickness of ~ 800 to form a conductive adhesive layer, and a peelable sheet is bonded. Then, the other surface and the protective layer separately formed on the peelable sheet are laminated and laminated.

  The electromagnetic wave shielding sheet can include another functional layer 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 properties, water vapor barrier properties, oxygen barrier properties, 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 applications that need to shield electromagnetic waves. For example, it can be used not only for a flexible printed wiring board but also for a rigid printed wiring board, COF, TAB, flexible connector, liquid crystal display, touch panel, and the like. In addition, it can be used as a case of a personal computer, a building material such as a wall of a building material and a window glass, and a member for shielding electromagnetic waves of a vehicle, a ship, an aircraft, and the like.

  The electromagnetic wave shielding sheet of the present invention, when using a thermoplastic resin as a binder resin in the conductive adhesive layer, the contained thermoplastic resin is present in a solid state, the thermoplastic resin is melted by a wiring circuit board and hot pressing, By solidifying again after cooling, a desired adhesive strength can be obtained.

  When a thermosetting resin is used as the binder resin in the conductive adhesive layer, the electromagnetic wave shielding sheet of the present invention contains the thermosetting resin and the curing agent in an uncured state (B stage), and causes the printed circuit board to By curing with a hot press (C stage), a desired adhesive strength can be obtained. The uncured state includes a semi-cured state in which a part of the curing agent is cured.

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

  The peelable sheet is a sheet obtained by subjecting a base material such as paper or plastic to a known release treatment.

<Electromagnetic wave shielding 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, a circuit pattern having signal wiring and ground wiring, and a wiring circuit board having an insulating base material. .
The printed circuit board has a circuit pattern having a signal wiring and a ground wiring on a surface of the insulating base material, and insulates and protects the signal wiring and the ground wiring on the printed circuit board; Form a cover coat layer having a via in the portion, the conductive adhesive layer surface of the electromagnetic wave shielding sheet, after arranging on the cover coat layer, hot press the electromagnetic wave shielding sheet, the conductive adhesive layer inside the via It can be manufactured by flowing it and bonding it to the ground wiring.

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

  The cover coat layer 8 is an insulating material that covers the signal wiring of the 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-curing solder resist, or a photosensitive coverlay film, and more preferably a photosensitive coverlay film for fine processing. The cover coat layer is generally formed of 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 line 5 for grounding and a signal line 6 for sending an electric signal to an electronic component. Both are generally formed by etching a copper foil. The thickness of the circuit pattern is usually about 1 to 50 μm.

The insulating substrate 9 is a support for a circuit pattern, and is preferably a flexible plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, or a liquid crystal polymer, and more preferably a liquid crystal polymer and a polyimide. Among these, liquid crystal polymers having a low relative dielectric constant and a low dielectric loss tangent are more preferable in consideration of the use of a printed circuit board for transmitting a high-frequency signal.
When the wiring 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 at 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 vias 11 formed in the cover coat layer 8 so that conduction with the ground wiring 5 is established. I can take it. The thermosetting resin reacts and is cured by the hot press to form the electromagnetic wave shielding layer 12.
In some cases, post-curing may be performed at 150 to 190 ° C. for 30 to 90 minutes after hot pressing in order to promote curing.

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

  It is preferable that the electromagnetic wave shielding layer is laminated on both sides of the printed circuit board, since the leakage of the electromagnetic wave 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.

  Further, 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 ground circuits in parallel, a ground circuit is not provided next to the signal circuit, and the electromagnetic wave shielding layer is used as a ground circuit. A printed wiring board structure having a ground in the thickness direction may be used.

  The electromagnetic wave shielding wiring circuit board of the present invention is preferably provided (mounted) on electronic devices such as a notebook PC, a mobile phone, a smartphone, and a tablet terminal in addition to a liquid crystal display and a touch panel.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. In the examples, “parts” means “parts by weight”, and “%” means “% by weight”.

  The acid value, weight average molecular weight (Mw), glass transition temperature (Tg), and average particle size 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 precisely weighed and placed in a stoppered Erlenmeyer flask, and dissolved by adding 100 ml of a mixed solution of tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2/1). To this, phenolphthalein TS was added as an indicator, and titration was performed with a 0.1 N alcoholic potassium hydroxide solution, and the time when the indicator retained the light red color for 30 seconds was defined as the end point. 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: 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 GPC (gel permeation chromatography) “HPC-8020” manufactured by Tosoh Corporation. GPC is liquid chromatography in which a substance dissolved in a solvent (THF: tetrahydrofuran) is separated and quantified according to the difference in molecular size. In the measurement in the present invention, two "LF-604" (manufactured by Showa Denko KK: GPC column for rapid analysis: 6 mm ID x 150 mm size) are connected in series, and the flow rate is 0.6 ml / min and the column temperature is measured. The measurement was performed at 40 ° C., and the weight average molecular weight (Mw) was determined in terms of polystyrene.

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

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

Subsequently, the raw materials used in the examples are shown below.
"material"
Conductive filler 1: Composite fine particles (dendritic fine particles coated with 10 parts by weight of silver with respect to 100 parts by weight of core copper) Average particle diameter D ₅₀ : 12.0 μm Conductive filler manufactured by Fukuda Metal Foil & Powder Co. 2: Composite fine particles (dendritic fine particles coated with 10 parts by weight of silver with respect to 100 parts by weight of core copper) Average particle size D ₅₀ : 1.0 μm Conductive filler 3: manufactured by Fukuda Metal Foil & Powder Co., Ltd. Fine particles (dendritic fine particles coated with 10 parts by weight of silver with respect to 100 parts by weight of core copper) Average particle diameter D ₅₀ : 6.0 μm Conductive filler 4: Fukuda Metal Foil & Powder Co., Ltd .: Composite fine particles (core Dendritic fine particles coated with 10 parts by weight of silver with respect to 100 parts by weight of copper) Average particle diameter D ₅₀ : 17.0 μm Conductive filler 5: composite fine particles (copper of core) manufactured by Fukuda Metal Foil & Powder Co., Ltd. 100 weight Silver 10 parts by weight coated dendritic particles) Average particle diameter _D with respect to Part 50: 32.0Myuemu Fukuda Metal Foil & Powder Co. Ltd. Binder resin: acid value 5 mgKOH / g, weight average molecular weight 54,000, Tg is -7 ° C polyurethane urea resin (Toyochem)
Epoxy compound: "JER828" (bisphenol A type epoxy resin, epoxy equivalent = 189 g / eq) Aziridine compound manufactured by Mitsubishi Chemical Corporation: "Chemite PZ-33" Pigment manufactured by Nippon Shokubai Co., Ltd. Pigment: carbon black "MA100" Carrier material manufactured by Mitsubishi Chemical Corporation: "Emblet S25" manufactured by Unitika

Table 1 shows the copper foil with a carrier material used.
These copper foils with a carrier material are prepared by forming a pattern resist layer on the copper foil formed on the carrier material and etching the copper foil to form openings, and the thickness and aperture ratio shown in Table 1 are obtained. It is a copper foil having the following.

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

  The conductive resin composition was applied 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 12>
Conductive adhesive layers 2 to 12 shown in Tables 2 to 5 were produced in the same manner as in the conductive adhesive layer 1 except that the type and amount of the conductive filler were changed.

[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 curing agent in terms of solid content and stirring with a disper for 10 minutes. The obtained resin composition was coated on a copper foil A1 with a carrier material using a bar coater to a dry thickness of 5 μm, and dried in an electric oven at 100 ° C. for 2 minutes to form a protective layer 1. Then, a slightly adhesive peelable sheet was bonded to the protective layer 1.

Next, the carrier material of the copper foil A1 with a carrier material was peeled off, the copper foil surface was buff-polished, and the 60 ° specular glossiness of the copper foil surface was adjusted to a value shown in Table 2 to obtain a copper foil 2. By bonding 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 bonding between the copper foil 2 and the conductive adhesive layer 4 was performed at a temperature of 90 ° C. and a pressure of 3 kgf / cm ^{2 using} a thermal laminator.

[Examples 2-33, Comparative Examples 1-4]
As shown in Tables 1 to 5, except that the types of the conductive adhesive layer, the protective layer, and the copper foil were changed, the same procedures as in Example 1 were performed to obtain Examples 2 to 33 and Comparative Examples 1 to 4. Electromagnetic wave shielding sheets were obtained respectively. When the target value of the 60 ° specular gloss of the copper foil surface was different from the value of the carrier material, the 60 ° specular gloss was adjusted by appropriately buffing or roughening the surface.

  With respect to the obtained electromagnetic wave shielding sheet, the thickness of each layer, the 60 ° specular gloss 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 thicknesses of the conductive adhesive layer, the metal layer, and the protective layer of the electromagnetic wave shielding sheet were measured by the following method.
The release sheet on the conductive adhesive layer side of the electromagnetic wave shielding sheet is peeled off, and the exposed conductive adhesive layer and the polyimide film (“Kapton 200EN” manufactured by Du Pont-Toray Co., Ltd.) are bonded together and heated at 2 MPa and 170 ° C. for 30 minutes. Pressed. After cutting this into a size of about 5 mm in width and about 5 mm in length, 0.05 g of an epoxy resin (Petropoxy 154, manufactured by Maruto Co.) was dropped on a slide glass, and an electromagnetic wave shielding sheet was adhered. 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 (SM-09010, manufactured by JEOL Ltd.) to obtain a measurement sample of the electromagnetic wave shielding sheet after hot pressing.

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

<< Measurement of 60 ° specular gloss >>
The 60 ° specular gloss 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 wave shielding sheet was peeled off, and an adhesive tape (“CT1835” manufactured by Nichiban Co.) was adhered to the exposed conductive adhesive layer except for the end of the adhesive tape. Then, the conductive adhesive layer / adhesive tape is peeled off. The conductive adhesive layer was removed, and the surface of the exposed metal layer was measured for specular gloss using a gloss meter (manufactured by BYK, Micro-Tri-Gloss), and the measured value at a measurement angle of 60 ° was converted to 60 ° specular gloss. Degree.

《Measurement of loss tangent of laminated cured product》
The loss tangent of the cured laminate was measured by the following method.
First, two sheets of an electromagnetic wave shielding sheet having a width of 50 mm and a length of 50 mm are prepared, the peelable sheet on each conductive adhesive layer side is peeled off, and the exposed conductive adhesive layers are bonded together, at 170 ° C., 2.0 MPa, The laminate was pressure-bonded under a condition of 30 minutes and thermally cured to obtain a laminated cured product. Thereafter, the central portion of the cured laminate was cut out to a width of 5 mm and a length of 30 mm to obtain a sample. This sample was set in a dynamic viscoelasticity measuring device (dynamic viscoelasticity measuring device DVA-200, manufactured by IT Measurement Control Co., Ltd.), and the temperature was raised at a rate of 10 ° C./min, the measuring frequency was 1 Hz, and the strain was 0.1 mm. The dynamic viscoelasticity was measured under the condition of 08%, and the loss elastic modulus E ″ and the storage elastic modulus E ′ at 125 ° C. were read from the obtained dynamic viscoelasticity curve, and the loss tangent of the laminated cured product was determined. Calculated.

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

<Solder reflow resistance>
Solder reflow resistance was evaluated based on the presence or absence of a change in appearance after the electromagnetic wave shielding sheet was brought into contact with the molten solder. An electromagnetic wave shield sheet having high solder reflow resistance does not change its appearance, but an electromagnetic wave shield sheet having low solder reflow resistance generates foaming and peeling.
First, 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 was peeled off, and the exposed conductive adhesive layer and a gold-plated copper-clad laminate having a total thickness of 64 μm (gold plating 0.3 μm / A gold-plated surface of nickel plating 1 μm / copper foil 18 μm / adhesive 20 μm / polyimide film 25 μm) was pressure-bonded at 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 in width and 65 mm in length to prepare a sample. The obtained sample was left for 72 hours in an atmosphere of 40 ° C. and 90% RH. Then, float the polyimide film surface of the sample on the molten solder at 250 ° C for 1 minute, then take out the sample, observe its appearance visually, and check for any abnormalities such as foaming, floating, peeling, etc. according to the following criteria. evaluated.

A: No change in appearance. Very good.
〇: Small foaming is slightly observed. Good.
Δ: Many small bubbles are observed. Practical.
×: Vigorous foaming and peeling are observed. Not practical.

<Bending resistance>
The peelable sheet of the adhesive layer of the electromagnetic wave shielding sheet having a width of 20 mm and a length of 100 mm was peeled off, and the exposed adhesive layer and the exposed 20 mm and a length of 100 mm Kapton 500H were pressure-bonded at 150 ° C., 2.0 MPa and 30 minutes, The sample was obtained by heat curing. The obtained sample was bent 180 degrees so that the electromagnetic wave shielding sheet was on the outside, and a 1000 g weight was placed on the bent portion for 10 seconds. Then, the bent portion was returned to the original flat state, and the 1000 g weight was again set to 10 g. This was placed for a second and the number of times of bending was set to one. Whether or not cracks occurred in the electromagnetic wave shield sheet was observed with a microscope "VHX-900" manufactured by KEYENCE CORPORATION, and the number of times of bending without cracks was evaluated.
The number of times of bending until a crack occurred in the bent portion where a load of 1000 g was applied was counted. The evaluation criteria are as follows.

：: 10 times or more. Very good.
：: 7 or more and less than 10 times. Good.
Δ: 2 or more and less than 7 times. Practical.
X: Less than 2 times. Not practical.

<High frequency shielding>
The high-frequency shielding property is measured in accordance with ASTM D4935, using a coaxial tube type shielding effect measurement system manufactured by Keycom Inc. under the conditions of 100 MHz to 15 GHz and irradiating electromagnetic waves, and measuring the attenuation of electromagnetic waves attenuated by the electromagnetic wave shielding sheet. Notation is made according to the following criteria. The measured value of the attenuation is decibel (unit: dB).

A: Attenuation amount at the time of irradiation of electromagnetic wave of 15 GHz is less than -55 dB.
〇: The attenuation at the time of irradiation of the electromagnetic wave of 15 GHz is −55 dB or more and less than −50 dB.
Δ: Attenuation amount at the time of irradiation of 15 GHz electromagnetic wave is −50 dB or more and less than −45 dB.
X: Attenuation amount at the time of irradiation of 15 GHz electromagnetic wave is -45 dB or more.

<Cool and heat cycle reliability>
The thermal cycle reliability was evaluated by measuring a connection resistance value via a small opening via before and after the thermal cycle. The specific method of evaluation is shown below.
A sample 25 was prepared by preparing an electromagnetic wave shielding sheet having a width of 20 mm and a length of 50 mm. Referring to the plan views of FIGS. 4A and 4B, the peelable sheet is peeled from the sample 25, and the exposed conductive adhesive layer 25b is formed on a separately prepared flexible printed wiring board (25 μm thick polyimide film 21). A copper foil circuit 22A and a copper foil circuit 22B each having a thickness of 18 μm, which are not electrically connected to each other, are formed on the copper foil circuit 22A. (A wiring board on which a polyimide coverlay 23 with an adhesive having a 1.0 mm ² ) circular via 24 is laminated) at 170 ° C. for 2 minutes at 30 ° C. to protect the conductive adhesive layer 25b of the electromagnetic wave shielding sheet and the 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. 4 (4) was measured using a BSP probe of “Lorester GP” manufactured by Mitsubishi Chemical Analytech. It measured using. FIG. 4B is a cross-sectional view taken along the line DD ′ of FIG. 4A, and FIG. 4C is a cross-sectional view taken along the line CC ′ of FIG. Similarly, FIG. 4 (5) is a sectional view taken along line DD ′ of FIG. 4 (4), and FIG. 4 (6) is a sectional view taken along line CC ′ of FIG. 4 (4). The sample was put into a thermal shock device (“TSE-11-A”, manufactured by Espec Corporation), and exposed to high temperature: 125 ° C. for 15 minutes; low-temperature exposure: −50 ° C. for 15 minutes, alternately exposed 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 thermal cycle reliability are as follows.

：: (connection resistance value after alternate exposure) / (initial connection resistance value) is less than 1.5, which is extremely good.
Good: (connection resistance value after alternate exposure) / (initial connection resistance value) is 1.5 or more and less than 3.0.
Δ: (connection resistance value after alternate exposure) / (initial connection resistance value) is 3.0 or more and less than 5.0.
X: (connection resistance value after alternate exposure) / (initial connection resistance value) 5.0 or more Not practical.

DESCRIPTION OF SYMBOLS 1 Conductive adhesive layer 2 Metal layer 3 Protective layer 4 Opening 5 Ground wiring 6 Signal wiring 7 Electromagnetic wave shielding wiring circuit board 8 Cover coat layer 9 Insulating base material 10 Electromagnetic wave shielding sheet 11 Via 12 Electromagnetic wave shielding layer

Claims (6)

Having a laminate having a conductive adhesive layer, a metal layer, and a protective layer in this order,
The surface of the metal layer in contact with the conductive adhesive layer has a 60 ° specular gloss of 10 to 800 determined in accordance with ISO 7668,
The metal layer has a plurality of openings and an opening ratio of 0.10 to 20%.   The electromagnetic wave shielding sheet according to claim 1, 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.   3. The electromagnetic wave shielding sheet according to claim 1, wherein the thickness of the metal layer is 0.3 to 5.0 [mu] m. The conductive adhesive layer contains a binder resin and a conductive filler,
The D ₅₀ average particle diameter of the conductive filler, an electromagnetic wave shielding sheet according to any one of claims 1 to 3, characterized in that it is 2~30μm of the conductive adhesive layer. The electromagnetic shielding sheet according to claim 4 , wherein the 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 claim 1, a cover coat layer, and a wiring board having a signal wiring and an insulating base material. Circuit board.