TWI837383B - Electromagnetic wave shielding sheet and electromagnetic wave shielding wiring circuit board - Google Patents

Abstract

The present invention provides an electromagnetic wave shielding sheet and an electromagnetic wave shielding wiring circuit substrate that have reflow resistance, reduce transmission loss even when used in a high-frequency transmission circuit, exhibit excellent high-frequency shielding, and still have high connection reliability after exposure to cold and hot cycles. The electromagnetic wave shielding sheet is solved by an electromagnetic wave shielding sheet, which is characterized in that it includes a conductive adhesive layer, a metal layer and a protective layer, the surface of the metal layer in contact with the conductive adhesive layer has a root mean square slope Sdq of 0.0001 to 0.5 calculated according to ISO 25178-2:2012, and the metal layer has a plurality of openings, and the opening rate is 0.10% to 20%.

Description

Electromagnetic wave shielding sheet and electromagnetic wave shielding wiring circuit substrate

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

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

As the transmission signal is transmitted at a higher speed, electromagnetic wave shielding sheets are also required to have electromagnetic wave shielding properties against high-frequency noise (hereinafter, sometimes referred to as high-frequency shielding properties) and reduce transmission losses in high-frequency regions (hereinafter, sometimes referred to as improved transmission characteristics). Patent document 1 discloses a structure having a metal layer with a thickness of 0.5μm to 12μm and an anisotropic conductive adhesive layer in a laminated state. It is also described that according to this structure, electric field waves, magnetic field waves, and electromagnetic waves traveling from one side of the electromagnetic wave shielding sheet to the other side can be well shielded while reducing transmission losses.

[Prior art literature]

[Patent Literature]

[Patent Document 1] International Publication No. 2013/077108

[Patent Document 2] Japanese Patent Publication No. 2013-168643

In recent years, with the high-speed transmission of transmission signals in electronic devices such as mobile phones, the electromagnetic shielding sheets on the wiring circuit boards built into these devices are also required to have high-frequency shielding and transmission characteristics. Therefore, it has been considered that it is better to use a metal layer with a thickness of 0.5μm to 12μm in the conductive layer of the electromagnetic shielding sheet as described in Patent Document 1.

However, if only a metal layer with a thickness of 0.5μm to 12μm is used, the electromagnetic wave shielding sheet cannot exhibit sufficient transmission characteristics in the high-frequency band. In order to make the electromagnetic wave shielding sheet have better transmission characteristics, further research on the metal layer is required.

In addition, the electromagnetic wave shielding wiring circuit board formed by attaching an electromagnetic wave shielding sheet with a metal layer to the wiring circuit board has the following problem: when performing a heat treatment such as reflow soldering, floating occurs between layers due to volatile components generated from the inside of the wiring circuit board, and poor appearance and poor connection are caused due to foaming, etc. In order to solve the problem of resistance to reflow soldering (hereinafter, sometimes referred to as reflow soldering resistance), for example, in Patent Document 2, a metal foil having multiple pinholes in the metal thin film layer is used to allow volatile components to pass through the pinholes of the metal thin film layer, thereby suppressing floating or foaming between layers.

On the other hand, with the global popularity of electronic devices such as smartphones and tablet terminals in recent years, reliability under all temperature conditions is required. When the wiring circuit substrates with electromagnetic wave shielding sheets of Patent Documents 1 and 2 are exposed to extreme temperature changes, problems such as peeling off from the wiring circuit substrate or disconnection from the ground circuit occur. The electromagnetic wave shielding sheet is required to improve the reliability of such temperature changes (hereinafter, sometimes referred to as hot and cold cycle reliability).

The present invention is made in view of the above background, and its purpose is to provide an electromagnetic wave shielding sheet having reflow resistance and excellent hot and cold cycle reliability, excellent high-frequency shielding and transmission characteristics suitable for high-frequency signals, and a wiring circuit substrate using the electromagnetic wave shielding sheet.

The inventor of the present invention has conducted diligent research and found that the problem of the present invention can be solved in the following implementation form, thereby completing the present invention.

That is, the electromagnetic wave shielding sheet of the present invention is characterized in that it has a laminate having a conductive adhesive layer, a metal layer, and a protective layer in sequence, and the root mean square slope Sdq of the interface of the metal layer connected to the conductive adhesive layer is 0.0001~0.5 according to the International Organization for Standardization (ISO) 25178-2:2012, and the metal layer has a plurality of openings, and the opening ratio is 0.10%~20%.

The electromagnetic wave shielding wiring circuit substrate of the present invention is characterized by comprising: an electromagnetic wave shielding layer formed by the electromagnetic wave shielding sheet, a surface coating layer, and a wiring board having signal wiring and an insulating substrate.

According to the present invention, the following excellent effects are achieved, namely: an electromagnetic wave shielding sheet and an electromagnetic wave shielding wiring circuit substrate having excellent reflow resistance, reducing transmission loss even when used in a high-frequency transmission circuit, exhibiting excellent high-frequency shielding, and having high connection reliability after exposure to hot and cold cycles can be provided.

1: Conductive adhesive layer

2: Metal layer

3: Protective layer

4: Opening

5: Ground wiring

6: Signal wiring

7: Electromagnetic wave shielding wiring circuit substrate

8: Top coating

9: Insulating substrate

10: Electromagnetic wave shielding sheet

11: Passageway

12: Electromagnetic wave shielding layer

20: Wiring board with coplanar circuits

21: Wiring board with coplanar circuit and electromagnetic wave shielding sheet

22A, 22B: Copper foil circuit

23: Polyimide coating

24: Circular passage

25: Sample (electromagnetic wave shielding sheet)

25a: Protective layer

25b: Conductive adhesive layer

50: Polyimide film

51:Through hole

52: Copper-plated film

53:Signal wiring

54: Ground wiring

55: Grounding pattern (i)

56: Ground pattern on the back side (ii)

FIG1 is a cross-sectional view illustrating an electromagnetic wave shielding sheet according to this embodiment.

Figure 2 is a graph comparing two examples of surfaces with different root mean square slopes Sdq.

FIG3 is a schematic cross-sectional view showing an example of an electromagnetic wave shielding wiring circuit substrate of the present embodiment.

FIG4 is a schematic plan view of the main surface side of a wiring board having a coplanar circuit in an embodiment and a comparative example.

FIG5 is a schematic plan view of the back side of a wiring board having a coplanar circuit according to an embodiment and a comparative example.

FIG6 is a schematic plan view of the main surface side of a wiring board having a coplanar circuit with an electromagnetic wave shielding sheet according to an embodiment and a comparative example.

Figure 7 (1) to Figure 7 (6) are schematic plan views and cross-sectional views of the hot and cold cycle reliability evaluation.

Figure 8 is the dynamic viscoelasticity curve of the electromagnetic wave shielding sheet (Example 5).

Hereinafter, an example of an implementation method of the present invention will be described. In addition, the size or ratio of each component in the following figure is for the convenience of explanation and is not limited thereto. Moreover, in this specification, the description of "any number A to any number B" means that the range includes number A as the lower limit and number B as the upper limit. Moreover, the "sheet" in this specification includes not only the "sheet" defined in Japanese Industrial Standards (JIS), but also "film". Moreover, the numerical values specified in this specification are values obtained by using the methods disclosed in the implementation method or examples.

<Electromagnetic wave shielding sheet>

The electromagnetic wave shielding sheet of the present invention has a laminated body having at least a conductive adhesive layer, a metal layer, and a protective layer in sequence. FIG. 1 is a cross-sectional view of an electromagnetic wave shielding sheet 10 illustrating an embodiment of the present invention. As shown in FIG. 1 , the electromagnetic wave shielding sheet 10 has a laminated body having a conductive adhesive layer 1, a metal layer 2, and a protective layer 3 in sequence, and the metal layer 2 is arranged between the conductive adhesive layer 1 and the protective layer 3.

The electromagnetic wave shielding sheet of the present invention has a metal layer with a plurality of openings 4, and an opening ratio of 0.10% to 20%, and 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, so it can exhibit excellent transmission characteristics, especially in a wiring circuit substrate that transmits high-frequency signals (for example, from 100MHz to 50GHz).

Regarding the electromagnetic wave shielding sheet 10, for example, the surface of the conductive adhesive layer 1 is bonded to a wiring board as an adherend, and then hardened as needed to form an electromagnetic wave shielding layer of an electromagnetic wave shielding wiring circuit substrate. At this time, the interface of the metal layer in contact with the conductive adhesive layer of the electromagnetic wave shielding sheet is arranged on the signal wiring side.

[Loss tangent of layer-hardened materials]

Furthermore, the electromagnetic wave shielding sheet of the present invention preferably has a loss tangent of 0.10 or more at 125°C of a laminated body having at least a conductive adhesive layer, a metal layer, and a protective layer in sequence, which is heat-pressed at 170°C for 30 minutes.

This can further improve the reliability of the hot and cold cycles.

The laminated cured product can be formed by hot pressing the electromagnetic wave shielding sheet at 170°C for 30 minutes for curing. That is, the laminated cured product refers to a laminated body obtained by curing the layer having a curing component among the conductive adhesive layer, metal layer, protective layer and other functional layers constituting the electromagnetic wave shielding sheet.

The laminated hardened product can also be obtained by removing the release sheet from the electromagnetic wave shielding sheet before or after the heat pressing and heat pressing only one electromagnetic wave shielding sheet; or by laminating a plurality of electromagnetic wave shielding sheets using a laminating machine and heat pressing; etc.

Specifically, for example, two electromagnetic wave shielding sheets are prepared, the release sheets on the respective conductive adhesive layer sides are peeled off, and the exposed conductive adhesive layers are bonded to each other, and heat-pressed at 170°C for 30 minutes to heat-cure the laminated body having at least a conductive adhesive layer, a metal layer, and a protective layer in sequence to produce a laminated cured product.

The loss tangent of a layer-hardened product is a value obtained by the following formula (3), and is an indicator of the ability to relax the stress generated when the electromagnetic shielding sheet is deformed.

Formula (3) (Loss tangent of the layer-hardening material) = (Loss elastic coefficient E") of the layer-hardening material / (Storage elastic coefficient E' of the layer-hardening material)

From the perspective of thermal cycle reliability, the laminated hardener preferably has a loss tangent of 0.1 or more at 125°C after hot pressing at 170°C for 30 minutes. If the loss tangent of the laminated hardener at 125°C after hot pressing at 170°C for 30 minutes is 0.1 or more, the stress caused by expansion during high temperature exposure can be sufficiently alleviated. The laminated hardener preferably has a loss tangent of 0.13 or more at 125°C after hot pressing at 170°C for 30 minutes, and preferably 0.15 or more.

The loss tangent of the laminated hardened material can be controlled by changing the loss elastic coefficient E" and storage elastic coefficient E' of any one of the layers or two or more layers constituting the laminated hardened material. This is because by changing the loss elastic coefficient E" and storage elastic coefficient E' of one or more layers constituting the laminated hardened material, the loss elastic coefficient E" and storage elastic coefficient E' of the laminated hardened material will change, thereby changing the loss tangent of the laminated hardened material.

As an example of a method for changing the loss elastic coefficient E" and the storage elastic coefficient E', the amount of hardener in the protective layer can be controlled. That is, by increasing or decreasing the amount of hardener in the protective layer, the storage elastic coefficient E' of the protective layer increases or decreases. As a result, the storage elastic coefficient E' of the laminated hardened material increases or decreases, thereby decreasing or increasing the loss tangent of the laminated hardened material.

There is no particular limitation on the method for controlling the loss tangent of the laminated hardened product, and it is possible to apply conventionally known methods such as changing the type or mixing ratio of the thermoplastic resin or thermosetting resin and the hardener, changing the thickness of each layer, changing the type of the metal layer, etc.

《Metal Layer》

The metal layer has the function of imparting high-frequency shielding properties to the electromagnetic wave shielding sheet. In the interface of the metal layer on the side contacting the conductive adhesive layer, the root mean square slope Sdq specified by ISO 25178-2:2012 is 0.0001~0.5. By controlling the root mean square slope Sdq to the range of 0.0001~0.5, both transmission characteristics and thermal cycle reliability can be taken into account. The details of the root mean square slope Sdq and the details of the effect obtained by controlling the root mean square slope Sdq will be described later.

Furthermore, the metal layer has multiple openings, and the opening rate is 0.10% to 20%. As a result, the reflow resistance is improved, thereby suppressing the occurrence of poor appearance and the decrease in connection reliability.

[Root mean square slope Sdq]

x表示x軸方向，

y表示y軸方向，

z(x，y)表示z軸方向的微小位移。 The root mean square slope Sdq is a surface property parameter defined by the following formula (1) in ISO 25178-2:2012. A represents the area of the defined surface,

x represents the x-axis direction,

y represents the y-axis direction,

z(x, y) represents a small displacement in the z-axis direction.

The root mean square slope Sdq can be calculated by processing the coordinate data of the surface shape obtained by any of the optical microscope, laser microscope and electron microscope through analytical software. The root mean square slope Sdq represents the root mean square of the slopes at all points defining the surface, and is a parameter that expresses the steepness of the concavities and convexities in the defined surface. As parameters that express the properties of the surface, the arithmetic mean height Sa or the maximum height Sz is usually used, but these are parameters that only express the height of the concavities and convexities, and are not suitable for accurately expressing the state of the surface.

Figure 2 shows two surfaces with different root mean square slopes Sdq. The larger the value of the root mean square slope Sdq, the steeper the surface unevenness becomes. In other words, the degree of surface unevenness steepness 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 due to the formation steps of the electromagnetic wave shielding layer such as heating and pressing. 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 0.0001~0.5.

Moreover, in the metal layer of the electromagnetic wave shielding sheet, when the current becomes high frequency due to the nature of the current, it will flow through the surface of the metal layer. The transmission characteristics of the signal wiring in the wiring circuit board are affected by the current flowing in the nearby conductor. Therefore, when the surface of the metal layer close to the signal wiring is steep, the distance from the current flowing through the metal surface will change, making the transmission characteristics unstable. Therefore, from the perspective 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 further preferably 0.3 or less.

On the other hand, as a result of active research, it was found that the reliability of hot and cold cycles is improved by setting the root mean square slope Sdq of the metal layer to the range of 0.0001~0.5. It is believed that this is because even in the case of shape changes due to the expansion and contraction of the conductive adhesive layer during hot and cold cycles, the contact between the conductive filler in the conductive adhesive layer and the metal layer is maintained by making the angle of the concave and convex formed on the surface of the metal layer appropriately sharp, thereby suppressing the deterioration of the connection resistance value. As a result of the research, it is more preferable to set the root mean square slope Sdq of the metal layer to the range of 0.001~0.4, and further preferably to the range of 0.01~0.3.

[Control method of root mean square slope Sdq]

Methods for controlling the root mean square slope Sdq of the metal layer surface include: a method of attaching roughening particles to the surface of the copper foil to form a roughened surface; a method of polishing the metal surface using a buff as described in Japanese Patent Publication No. 2017-13473; a method of polishing the metal surface using abrasive cloth; a shot blast method of blowing an abrasive material onto the metal surface by compressed air; a method of forming a metal layer on a carrier material having a specified root mean square slope Sdq and transferring the concavo-convex surface of the carrier material to the metal layer; a method of laminating a film having a specified root mean square slope Sdq with a metal and transferring the concavo-convex surface of the film to the metal layer, etc. The method for controlling the root mean square slope Sdq of the metal layer surface is not limited to the exemplified method, and conventionally known methods can be applied.

[Thickness of metal layer]

The thickness of the metal layer is preferably 0.3μm~5.0μm. By setting the thickness of the metal layer to 0.3μm or more, the wavelength of electromagnetic noise generated from the wiring circuit board can be suppressed from penetrating, thereby demonstrating sufficient high-frequency shielding. The lower limit of the thickness of the metal layer is more preferably 0.5μm. By setting the thickness of the metal layer to 5.0μm or less, the loss tangent of the laminated hardened material can be increased, thereby improving the reliability of hot and cold cycles. The upper limit of the thickness of the metal layer is more preferably 3.5μm.

[Metal layer composition]

The metal layer may be, for example, metal foil, metal vapor-deposited film, or metal-plated film.

The metal used in the metal foil is preferably a conductive metal such as aluminum, copper, silver, gold, etc., and a single metal or an alloy of multiple metals can be used. In terms of high-frequency shielding and cost, copper, silver, and aluminum are more preferred, and copper is more preferred. For example, copper is preferably used in the form of rolled copper foil or electrolytic copper foil.

The metal used in the metal vapor deposition film and the metal plating film is preferably an alloy of one or more conductive metals such as aluminum, copper, silver, and gold, and copper and silver are more preferred. One or both surfaces of the metal foil, metal vapor deposition film, and metal plating film can be coated with metal or organic substances such as rustproofing agents.

[Opening]

The metal layer has a plurality of openings, and the opening ratio is 0.10% to 20%. The openings improve reflow resistance. The openings allow volatile components contained in the polyimide film or cover adhesive of the wiring circuit board to escape to the outside during reflow treatment of the electromagnetic wave shielding wiring circuit board, thereby suppressing the occurrence of poor appearance caused by interface peeling of the cover adhesive and the electromagnetic wave shielding sheet.

The shape of the opening observed from the surface of the metal layer can be, for example, a perfect circle, an ellipse, a quadrilateral, a polygon, a star, a trapezoid, a dendrite, etc. From the perspective of manufacturing cost and ensuring the toughness of the metal layer, the shape of the opening is preferably a perfect circle or an ellipse.

In addition, the root mean square slope Sdq is calculated excluding the opening of the metal layer.

[Opening ratio of metal layer]

The opening ratio of the metal layer is in the range of 0.10% to 20%, which can be calculated using the following formula (2).

Formula (2) (Opening ratio [%]) = (Area of openings per unit area) / (Area of openings per unit area + Area of non-openings per unit area) × 100

By setting the opening ratio to 0.10% or more, volatile components can be fully released during the reflow process, thereby suppressing the appearance defects and the decrease in connection reliability caused by the interface peeling between the cover adhesive and the electromagnetic shielding sheet.

On the other hand, by making the opening ratio less than 20%, the amount of electromagnetic wave noise passing through the opening portion can be reduced, thereby improving shielding properties. In order to be able to take into account both reflow resistance and high-frequency shielding properties at a high level, the opening ratio range is preferably 0.30%~15%, and more preferably 0.50%~6.5%.

In particular, in electromagnetic shielding sheets with a relatively smooth interface and a metal layer RMS slope Sdq of 0.001 or less, the metal layer and the conductive adhesive layer have weak adhesion, and the reflow resistance may decrease. Even in such electromagnetic shielding sheets, by setting the opening rate of the metal layer to 0.10% or more, preferably 0.50% or more, the volatile components can be fully escaped, thereby further suppressing the occurrence of interlayer peeling or floating and suppressing the decrease in reflow resistance.

The opening ratio can be determined, for example, by using an image obtained by magnifying the metal layer vertically by 500 to 2000 times using a laser microscope and a scanning electron microscope (SEM), binarizing the opening and non-opening parts, and taking the number of binarized pixels per unit area as the area of each part.

[Method for manufacturing a metal layer having an opening]

The method for manufacturing the metal layer having an opening can be applied by a conventionally known method, and can be applied by a method (i) of forming a patterned anti-etching agent layer on a metal foil and etching the metal foil to form the opening; a method (ii) of printing a conductive paste in a predetermined pattern by screen printing; a method (iii) of applying an anchor coating in a predetermined pattern. Agent) screen printing and metal plating only the primer printing surface (iii); and the manufacturing method (iv) described in Japanese Patent Publication No. 2015-63730, that is, printing a water-soluble or solvent-soluble ink pattern on a support, forming a metal vapor-deposited film on its surface, and removing the pattern; a method of obtaining a metal layer with an opening portion of a carrier material by forming a release layer on its surface and performing electrolytic plating, etc.

Among these, method (i) is preferred because the shape of the opening can be precisely controlled. However, the method for manufacturing the metal layer is not limited to method (i), and other methods may be used as long as the shape of the opening can be controlled.

《Conductive adhesive layer》

The conductive adhesive layer can be formed using a conductive resin composition. The conductive resin composition includes an adhesive resin and a conductive filler. The adhesive resin can use either a thermoplastic resin or a thermosetting resin and a hardener. The conductive adhesive layer can use either an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. The isotropic conductive adhesive layer has conductivity in the vertical direction and the horizontal direction when the electromagnetic wave shielding sheet is placed horizontally. Moreover, the anisotropic conductive adhesive layer has conductivity only in the vertical direction when the electromagnetic wave shielding sheet is placed horizontally.

The conductive adhesive layer may be either isotropically conductive or anisotropically conductive. In the case of anisotropic conductivity, cost reduction is possible, so it is preferred.

[Thermoplastic resin]

Examples of thermoplastic resins include polyolefin resins, vinyl resins, styrene-acrylic resins, diene resins, terpene resins, petroleum resins, cellulose resins, polyamide resins, polyurethane resins, polyester resins, polycarbonate resins, polyimide resins, liquid crystal polymers, and fluororesins. Although not particularly limited, from the perspective of transmission loss, materials with low dielectric constants and low dielectric loss tangents are preferred, and from the perspective of characteristic impedance, materials with low dielectric constants are preferred, and examples include liquid crystal polymers and fluororesins.

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

[Thermosetting resin]

Thermosetting resins are resins having multiple functional groups that can react with a hardener. Examples of the functional groups include hydroxyl groups, phenolic hydroxyl groups, methoxymethyl groups, carboxyl groups, amino groups, epoxy groups, cyclohexane groups, oxazoline groups, oxazine groups, aziridine groups, thiol groups, isocyanate groups, blocked isocyanate groups, blocked carboxyl groups, and silanol groups. Examples of thermosetting resins include acrylic resins, maleic acid resins, polybutadiene resins, polyester resins, polyurethane resins, polyurethane urea resins, epoxy resins, cyclohexane resins, phenoxy resins, polyimide resins, polyamide resins, polyamideimide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, fluororesins and other well-known resins.

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

Among these, polyurethane resins, polyurethane urea resins, polyester resins, epoxy resins, phenoxy resins, polyimide resins, polyamide resins, and polyamideimide resins are preferred in terms of reflow resistance.

[Hardener]

The hardener has multiple functional groups that can react with the functional groups of the thermosetting resin. Examples of hardeners include: epoxy compounds, compounds containing acid anhydride groups, isocyanate compounds, aziridine compounds, amine compounds, phenol compounds, organometallic compounds and other well-known compounds.

Hardeners can be used alone or in combination of two or more.

The hardener is preferably contained in an amount of 1 to 50 parts by weight relative to 100 parts by weight of the thermosetting resin, more preferably 3 to 40 parts by weight, and further preferably 3 to 30 parts by weight.

Thermoplastic resins and thermosetting resins can be used alone or in combination.

[Conductive filler]

The conductive filler imparts conductivity to the conductive adhesive layer. Among the conductive fillers, conductive metals such as gold, platinum, silver, copper, and nickel, and alloys thereof, and conductive polymer microparticles are preferred as raw materials, and silver is more preferred in terms of price and conductivity.

Moreover, from the perspective of reducing costs, it is also preferred that the microparticles are not made of a single raw material but are composite microparticles having a metal or resin as the core and a coating layer covering the surface of the core. Here, the core is preferably appropriately selected from inexpensive nickel, silicon dioxide, copper and its alloys, and resin. The coating layer is preferably a conductive metal or a conductive polymer. Examples of conductive metals include gold, platinum, silver, nickel, manganese, and indium, and their alloys. Moreover, conductive polymers include polyaniline, polyacetylene, etc. Among these, silver is preferred in terms of price and conductivity.

There is no limitation on the shape of the conductive filler as long as the desired conductivity can be obtained. Specifically, for example, spherical, flake, leaf, branch, plate, needle, rod, and grape shapes are preferred. Moreover, two types of conductive fillers of different shapes may be mixed.

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

The average particle size of the conductive filler is the _D50 average particle size. From the perspective of sufficiently ensuring conductivity, it is preferably 2 μm or more, more preferably 5 μm or more, and further preferably 7 μm or more. On the other hand, from the perspective of taking the thickness of the conductive adhesive layer into consideration, it is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. _{The D50} average particle size can be obtained using a laser diffraction/scattering 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 further preferably 40% to 65% by weight. By setting it to 35% by weight or more, the connection between the conductive adhesive layer and the ground wiring becomes good, so the high-frequency shielding and hot and cold cycle reliability are improved. On the other hand, by setting it to 90% by weight or less, the reflow resistance and transmission characteristics are further improved.

The conductive resin composition can also be formulated with silane coupling agents, rustproofing agents, reducing agents, antioxidants, pigments, dyes, adhesive imparting resins, plasticizers, ultraviolet absorbers, defoaming agents, leveling agents, fillers, flame retardants, etc. as arbitrary components.

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

The conductive adhesive layer can be prepared by a known method. For example, there are a method of forming a conductive adhesive layer by applying a conductive resin composition on a release sheet and drying it; a method of extruding a conductive resin composition into a sheet using an extrusion molding machine such as a T-die, etc.

The coating method may be a known coating method such as gravure coating, kiss coating, die coating, lip coating, notch wheel coating, scraper coating, roller coating, knife coating, spray coating, rod coating, spin coating, dip coating, etc. It is preferred to perform a drying step after coating. The drying step may be performed using a known drying device such as a hot air dryer or an infrared heater.

The thickness of the conductive adhesive layer is preferably 2μm~30μm, more preferably 3μm~15μm, and further preferably 4μm~9μm. By making the thickness within the range of 2μm~30μm, the hot and cold cycle reliability and reflow resistance can be improved.

《Protective layer》

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

The resin composition may include the thermoplastic resin or thermosetting resin and curing agent described in the conductive resin composition and the optional components as required. In addition, the thermosetting resin and curing agent used in the protective layer and the conductive adhesive layer may be the same or different.

The resin composition can be obtained using the same method as the conductive resin composition.

Furthermore, the protective layer may be formed of a film made of insulating resins such as polyester, polycarbonate, polyimide, polyamide imide, polyamide, polyphenylene sulfide, and polyetheretherketone.

The thickness of the protective layer is usually around 2μm~10μm.

"Method for manufacturing electromagnetic wave shielding sheet"

In the production of electromagnetic wave shielding sheets, the method of laminating the conductive adhesive layer and the metal layer can be a known method.

For example, in method (i), a conductive adhesive layer is formed on a release sheet, the conductive adhesive layer is superimposed on the electrolytic copper foil surface of the electrolytic copper foil with an opening portion with a carrier material, and the carrier material is peeled off. Then, the surface from which the carrier material is peeled off is superimposed on a protective layer formed separately on the release sheet, and the protective layer is superimposed on the electrolytic copper foil surface of the electrolytic copper foil with an opening portion with a carrier material, and the carrier material is peeled off. Then, the surface from which the carrier material is peeled is overlapped with a conductive adhesive layer separately formed on a peelable sheet and laminated; method (iii) a resin composition is applied on the electrolytic copper foil surface of the electrolytic copper foil with an opening portion with the carrier material to form a protective layer, and a peelable sheet is attached. Thereafter, the carrier material is peeled off and a conductive adhesive layer formed separately on a release sheet is superimposed and laminated; method (iv) a conductive adhesive layer is formed on a release sheet, the conductive adhesive layer is superimposed and laminated on the electrolytic copper foil side of the electrolytic copper foil with the carrier material, and then the carrier material is peeled off. Then, the surface from which the carrier material is peeled off is overlapped and laminated with a protective layer formed separately on a peelable sheet, and then an opening is formed on the electromagnetic wave shielding sheet using a needle-shaped fixture; method (v) overlaps and laminates the protective layer formed on the peelable sheet on the electrolytic copper foil surface side of the electrolytic copper foil with the opening of the carrier material, and then peels off the carrier material. Then, a conductive adhesive layer is formed on the surface from which the carrier material is peeled off; Method (vi) A conductive adhesive layer is formed on a release sheet, and the surface of the rolled copper foil having an opening, the surface with a root mean square slope Sdq of 0.0001 to 0.5 is overlapped with the conductive adhesive layer and laminated, and then the other surface laminated with the conductive adhesive layer is overlapped with a protective layer formed separately on the release sheet and laminated; Method (vii) A protective layer is formed on a release sheet, and the rolled copper foil having an opening is overlapped with the protective layer formed separately on the release sheet. After laminating the conductive adhesive layer on the other side of the surface of the rolled copper foil with a root mean square slope Sdq of 0.0001 to 0.5, the other side laminated with the protective layer is laminated with a conductive adhesive layer separately formed on a release sheet; method (viii) on the other side of the surface of the rolled copper foil with an opening with a root mean square slope Sdq of 0.0001 to 0.5, a resin composition is applied to form a protective layer, and a release sheet is attached. Then, the other side is overlapped with a conductive adhesive layer formed separately on a release sheet and laminated; Method (ix) On the surface of the rolled copper foil with an opening, a conductive resin composition is applied on the surface with a root mean square slope Sdq of 0.0001 to 0.5 to form a conductive adhesive layer, and a release sheet is attached. Then, the other side is overlapped with a protective layer formed separately on a release sheet and laminated; etc.

In addition to the conductive adhesive layer, metal layer and protective layer, the electromagnetic wave shielding sheet may also include other functional layers. Other functional layers are layers with functions such as hard coating, water vapor barrier, oxygen barrier, 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 that require shielding electromagnetic waves. For example, it can be used for flexible printed wiring boards, rigid printed wiring boards, chip on film (COF), tape automated bonding (TAB), flexible connectors, liquid crystal displays, touch panels, etc. In addition, it can also be used as a personal computer case, building materials such as walls and window glass, and components for blocking electromagnetic waves in vehicles, ships, aircraft, etc.

Moreover, the electromagnetic wave shielding sheet of the present invention can have the following excellent transmission characteristics, namely: the transmission loss is less than 8dB when a 15GHz sine wave flows in the signal wiring of the coplanar circuit.

Specifically, the transmission characteristics can be evaluated as follows, for example.

First, prepare the coplanar circuit.

A coplanar circuit is a type of planar transmission circuit in which a signal wiring is printed on one side of an insulating substrate such as a polyimide film. In this evaluation method, a coplanar circuit uses a circuit in which a ground wiring is formed in parallel on a polyimide film in the form of sandwiching two signal wirings. In addition, a ground pattern for GND grounding is provided on the facing surfaces of the coplanar circuit via a through hole.

The conductive adhesive layer of the electromagnetic shielding sheet is bonded to the insulating substrate surface of the coplanar circuit on the opposite side of the signal wiring, and the electromagnetic shielding sheet is laminated by heat pressing. At this time, the electromagnetic shielding sheet is conductively connected to a part of the exposed ground pattern. According to this method, a test piece for evaluating transmission characteristics can be obtained.

A network analyzer can be connected to the coplanar circuit of this test piece to find the ratio of input power to output power when a 100MHz to 20GHz sine wave flows through the signal wiring of the coplanar circuit, calculate the transmission loss, and perform evaluation. In addition, voltage ratio or current ratio can be used instead of power.

In the present invention, the transmission loss when a 15 GHz sine wave flows through the signal wiring of the coplanar circuit is preferably less than 8 dB, more preferably less than 7.5 dB, and further preferably less than 7 dB. By reducing the transmission loss to less than 8 dB, a high level of transmission loss reduction can be achieved.

When a thermoplastic resin is used in the adhesive resin in the conductive adhesive layer of the electromagnetic wave shielding sheet of the present invention, the desired bonding strength can be obtained by making the contained thermoplastic resin exist in a solid state and utilizing heat pressing with the wiring board to melt the thermoplastic resin and solidify it again after cooling.

When a thermosetting resin is used in the adhesive resin in the conductive adhesive layer of the electromagnetic wave shielding sheet of the present invention, the desired bonding strength can be obtained by allowing the contained thermosetting resin and curing agent to exist in an uncured state (stage B) and curing them by heat pressing with the wiring board (stage C). In addition, the uncured state includes a semi-cured state in which a part of the curing agent is cured.

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

A release sheet is a sheet made by subjecting a substrate such as paper or plastic to a known release treatment.

<Electromagnetic wave shielding wiring circuit board>

The electromagnetic wave shielding wiring circuit substrate includes an electromagnetic wave shielding layer formed by the electromagnetic wave shielding sheet of the present invention, a surface coating layer, and a wiring board including a circuit pattern having signal wiring and ground wiring and an insulating substrate.

On the wiring board, a surface coating layer having a passage is formed on at least a portion of the ground wiring, and after the conductive adhesive layer of the electromagnetic wave shielding sheet is disposed on the surface coating layer, the electromagnetic wave shielding sheet is heat-pressed to allow the conductive adhesive layer to flow into the passage and bond to the ground wiring, thereby manufacturing a wiring circuit substrate.

An example of the electromagnetic wave shielding wiring circuit substrate of the present invention is described with reference to FIG3.

The electromagnetic wave shielding layer 12 is a layer formed by the electromagnetic wave shielding sheet, including a conductive adhesive layer 1, a metal layer 2, a protective layer 3 or a laminated hardened product thereof.

The top coating layer 8 is an insulating material that covers the signal wiring of the wiring board and protects it from damage by the external environment. The top coating layer is preferably a polyimide film with a thermosetting adhesive, a thermosetting or UV-curing solder resist, or a photosensitive cover film. For fine processing, a photosensitive cover film is more preferred. Moreover, the top coating layer is usually made of a known resin such as polyimide that has heat resistance and flexibility. The thickness of the top coating layer is usually about 10μm~100μm.

The circuit pattern includes a ground wiring 5 for grounding and a signal wiring 6 for transmitting electrical signals to electronic components. Both are usually formed by etching copper foil. The thickness of the circuit pattern is usually around 1μm~50μm.

The insulating substrate 9 is a support for the circuit pattern, and is preferably a bendable plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, liquid crystal polymer, etc., and is more preferably a liquid crystal polymer or polyimide. Among these, if the use of a wiring circuit substrate for transmitting high-frequency signals is considered, a liquid crystal polymer with a low relative dielectric constant and dielectric loss tangent is further preferred.

When the wiring board is a rigid wiring board, the constituent material of the insulating substrate is preferably glass epoxy. By including an insulating substrate such as these, the wiring circuit board obtains high heat resistance.

The electromagnetic wave shielding sheet 10 and the wiring board are usually hot-pressed at a temperature of about 150°C to 190°C, a pressure of about 1MPa to 3MPa, and a time of about 1 minute to 60 minutes. Through hot pressing, the conductive adhesive layer 1 is in close contact with the surface coating layer 8, and the conductive adhesive layer 1 flows and fills the passage 11 formed in the surface coating layer 8, thereby achieving conduction with the ground wiring 5. Through hot pressing, the thermosetting resin reacts and hardens to form the electromagnetic wave shielding layer 12.

In addition, in order to accelerate hardening, post-curing is sometimes performed at 150℃~190℃ for 30 minutes~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 the opening area within the above range, the area of the ground wiring can be narrowed, thereby achieving miniaturization of the printed wiring board.

The shape of the passage is not particularly limited, and any of circular, square, rectangular, triangular, and amorphous shapes can be used depending on the application.

In terms of more effectively suppressing the leakage of electromagnetic waves, it is preferred to laminate the electromagnetic wave shielding layer on both sides of the wiring board. In addition, the electromagnetic wave shielding layer in the electromagnetic wave shielding wiring circuit substrate of the present invention can be used as a grounding circuit in addition to shielding electromagnetic waves. Thus, by omitting part of the grounding circuit, the area of the wiring circuit substrate can be reduced, and the cost can be reduced, and it can be assembled into a small area in the frame.

Furthermore, there is no particular limitation on the signal wiring, and the circuit can be used in any circuit including a single-ended circuit including one signal wiring or a differential circuit including two signal wirings, but the differential circuit is preferred. On the other hand, when there are constraints in the circuit pattern area of the wiring board and it is difficult to form a ground circuit in parallel, the ground circuit can be used as the electromagnetic wave shielding layer instead of the signal circuit, to form a printed wiring board structure with grounding in the thickness direction.

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

[Implementation example]

The present invention is described in more detail below through examples, but the present invention is not limited to the following examples. Moreover, "parts" in the examples represent "parts by weight" and "%" represents "% by weight".

In addition, the acid value, weight average molecular weight (Mw), glass transition temperature (Tg) of the resin, and the average particle size of the conductive filler were measured using the following method.

《Determination of acid value of adhesive resin》

The acid value is measured in accordance with JIS K0070. Accurately weigh about 1g of the sample in a stoppered conical flask and add 100ml of a mixture of tetrahydrofuran/ethanol (volume ratio: tetrahydrofuran/ethanol = 2/1) to dissolve it. Add phenolphthalein test solution as an indicator and titrate with 0.1N alcoholic potassium hydroxide solution. The end point is when the indicator remains light red for 30 seconds. The acid value (unit: mgKOH/g) is calculated according to the following formula.

Acid value (mgKOH/g) = (5.611×a×F)/S

Where, S: sample collection amount (g)

a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)

F: Titer of 0.1N alcoholic potassium hydroxide solution

《Determination of weight average molecular weight (Mw) of adhesive resin》

The weight average molecular weight (Mw) was measured using a gel permeation chromatograph (GPC) "HPC-8020" manufactured by Tosoh Co., Ltd. GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on their molecular size differences. The measurement in the present invention uses two "LF-604" (manufactured by Showa Denko Co., Ltd.: GPC column for rapid analysis: 6mmID×150mm size) connected in series as a column, and is performed at a flow rate of 0.6ml/min and a column temperature of 40°C. The weight average molecular weight (Mw) is determined by polystyrene conversion.

《Glass transition temperature (Tg) of adhesive resin》

Tg was measured by differential scanning calorimetry ("DSC-1" manufactured by Mettler Toledo).

《Determination of average particle size of conductive fillers》

The _D50 average particle size is a value obtained by measuring the conductive filler using a laser diffraction/scattering particle size distribution measuring device LS13320 (manufactured by Beckman Coulter) and a tornado dry powder sample module, and is the particle size at which the cumulative value in the cumulative particle size distribution is 50%. In addition, the refractive index is set to 1.6.

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

Raw Materials

Conductive filler: composite fine particles (dendritic fine particles with 100 parts by weight of copper as a core coated with 10 parts by weight of silver), average particle size D ₅₀ : 11.0 μm, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.

Adhesive resin: polyurethane urea resin with an acid value of 5 mgKOH/g, a weight average molecular weight of 54,000, and a Tg of -7°C (manufactured by Toyo Chemical Co., Ltd.)

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

Aziridine compounds: "Chemitite PZ-33" manufactured by Japan Catalyst Co., Ltd.

Pigment: Carbon black "MA100" manufactured by Mitsubishi Chemical Corporation

Carrier material: "Emblet S25" (Sdq=0.02) manufactured by UNITIKA Corporation

<Manufacturing of conductive adhesive layer 1>

In terms of solid content, 100 parts of adhesive resin, 47 parts of conductive filler, 10 parts of epoxy compound and 0.5 parts of aziridine compound were placed in a container, a mixed solvent (toluene: isopropyl alcohol = 2:1 (weight ratio)) was added so that the non-volatile component concentration became 40%, and the mixture was stirred for 10 minutes using a disperser to obtain a conductive resin composition.

The conductive resin composition was applied to the release sheet using 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.

<Manufacturing of conductive adhesive layer 2 to conductive adhesive layer 8>

Conductive adhesive layer 2 to conductive adhesive layer 8 shown in Table 1 to Table 3 were prepared in the same manner as conductive adhesive layer 1, except that the amount of conductive filler added was changed.

[Implementation Example 1]

100 parts of adhesive resin, 30 parts of epoxy compound and 7.5 parts of aziridine compound were added in terms of solid content, and stirred for 10 minutes using a disperser to obtain a resin composition. The obtained resin composition was applied to copper foil using a rod 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, and a micro-adhesive release sheet was attached to the protective layer 1.

Next, the carrier material of the copper foil is peeled off, the copper foil surface is polished, and the root mean square slope Sdq of the copper foil surface is adjusted to the value shown in Table 1. The conductive adhesive layer 4 is bonded to the polished copper foil surface, thereby obtaining an electromagnetic wave shielding sheet including "peelable sheet/protective layer 1/copper foil 2/conductive adhesive layer 4/peelable sheet". The bonding of the copper foil 2 and the conductive adhesive layer 4 is performed by a thermal lamination machine at a temperature of 90°C and a pressure of 3kgf/ ^cm2 .

In addition, copper foil 2 is a copper foil having the thickness and opening ratio shown in Table 1 by forming a patterned anti-etching agent layer on the copper foil formed on the carrier material and etching the copper foil to form an opening.

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

Except for changing the types of the conductive adhesive layer, protective layer and copper foil as shown in Tables 1 to 3, the same procedure as in Example 1 was followed to obtain electromagnetic wave shielding sheets of Examples 2 to 29 and Comparative Examples 1 to 4, respectively. When the target value of the root mean square slope Sdq of the copper foil surface is different from that of the carrier material, the root mean square slope Sdq is adjusted by appropriately polishing the surface or roughening the surface.

For the electromagnetic shielding sheet obtained, the thickness of each layer, the root mean square slope Sdq of the metal layer, and the loss tangent of the electromagnetic shielding sheet were measured using the following method.

《Measurement of thickness of each layer》

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

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

The cross section of the obtained test sample is observed using a laser microscope (Keyence, VK-X100), and the thickness of each layer is measured based on the observed magnified image. The magnification is set to 500x to 2000x.

"Determination of the root mean square slope Sdq of the metal layer"

The root mean square slope Sdq of the metal layer of the electromagnetic wave shielding sheet is 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 adhesive tape ("CT1835" manufactured by Nichiban) is attached to the exposed conductive adhesive layer in a manner that leaves the end of the adhesive tape (Nichiban) untouched, and the conductive adhesive layer/adhesive tape is peeled off from the end of the adhesive tape. After removing the conductive adhesive layer, the surface of the exposed metal layer is measured using a laser microscope (Keyence VK-X100).

The acquired measurement data is read into the analysis software (equipped with ISO 25178 surface property measurement module "VK-H1XR", analysis application "VK-H1XA", both manufactured by KEYENCE), and ISO 25178 surface property measurement is performed. (Conditions: S-filter; 1μm, L-filter; 0.2mm) In addition, for metal layers with openings on the surface, the openings are excluded from the measurement range when performing ISO 25178 surface property measurement.

《Determination of loss tangent of layer-hardened materials》

The loss tangent of layer-hardened materials is measured by the following method.

First, prepare two electromagnetic wave shielding sheets with a width of 50mm and a length of 50mm, peel off the release sheets on the conductive adhesive layer sides of each sheet, and bond the exposed conductive adhesive layers to each other. Press-bond them at 170℃, 2.0MPa, and 30 minutes to heat cure them and obtain a laminated hardened product. Then, cut the center of the laminated hardened product into a piece with a width of 5mm and a length of 30mm as a sample. This sample was placed in a dynamic viscoelasticity measuring device (dynamic viscoelasticity measuring device DVA-200, manufactured by IT Measurement Control Co., Ltd.) and subjected to dynamic viscoelasticity measurement under the conditions of heating rate: 10°C/min, measuring frequency: 1Hz, and strain: 0.08%. The loss elasticity coefficient E" and storage elasticity coefficient E' at 125°C were read from the obtained dynamic viscoelasticity curve, and the loss tangent of the laminated hardened material was calculated. An example of a dynamic viscoelasticity curve is shown in FIG8 (Example 5).

The obtained electromagnetic wave shielding sheet was used to carry out the following evaluation. The results are shown in Tables 1 to 3.

<Reflow resistance>

Reflow resistance is evaluated by whether the appearance of the electromagnetic shielding sheet changes after it comes into contact with molten solder. The appearance of an electromagnetic shielding sheet with high reflow resistance does not change, but an electromagnetic shielding sheet with low reflow resistance will bubble or peel off.

First, the conductive adhesive layer of the electromagnetic shielding sheet with a width of 25 mm and a length of 70 mm was peeled off, and the exposed conductive adhesive layer was pressed and bonded to the gold-plated surface of a 64 μm-thick gold-plated copper-clad laminate (gold-plated 0.3 μm/nickel-plated 1 μm/copper foil 18 μm/adhesive 20 μm/polyimide film 25 μm) at 170°C, 2.0 MPa, and 30 minutes, and the laminate was thermally cured to obtain a laminate. The obtained laminate was cut into pieces with a width of 10 mm and a length of 65 mm to prepare a sample. The obtained sample was placed in a gas environment of 40°C and 90% RH for 72 hours. Afterwards, the polyimide film of the sample was floated face down on molten solder at 250°C for 1 minute, and then the sample was taken out and its appearance was visually observed. The presence of abnormalities such as bubbling, bulging, and peeling was evaluated according to the following criteria.

(Evaluation criteria)

◎: No change in appearance. Very good.

○: A small amount of foaming was observed. Good.

△: A large amount of small bubbles were observed. Practical.

×: Severe foaming or peeling was observed. Not practical.

<Transmission characteristics>

The transmission characteristics are evaluated using the wiring board 20 having a coplanar circuit as shown in FIG4.

FIG4 shows a schematic plan view of the main surface side of the flexible printed wiring board with coplanar circuit (hereinafter, also referred to as a wiring board with coplanar circuit) 20 used in the measurement, and FIG5 shows a schematic plan view of the back surface side. First, a double-sided CCL "R-F775" (manufactured by Panasonic) is prepared in which a 12 μm thick rolled copper foil is laminated on both sides of a 50 μm thick polyimide film 50. Then, six through holes 51 (diameter 0.1 mm) are provided near the four corners of the rectangular shape. In addition, for the convenience of illustration, only two through holes 51 are shown at each corner. Next, after the electroless plating treatment, the electrolytic plating treatment is performed to form a 10μm copper-plated film 52, and the copper-plated film formed in the through hole 51 ensures the conduction between the main surface and the back surface. After that, two signal wirings 53 with a length of 10cm are formed on the main surface of the polyimide film 50, and a ground wiring 54 parallel to the signal wiring 53 is formed on the outer side thereof, and a ground pattern (i) 55 is formed in the area extending from the ground wiring 54 and including the through hole 51 in the short side direction of the polyimide film 50.

After that, the copper foil formed on the back side of the polyimide film 50 is etched, and the back side ground pattern (ii) 56 as shown in FIG. 5 is obtained at the position corresponding to the ground pattern (i) 55. The inspection specifications for the appearance and tolerance of the circuit are set to the Japan Electronics Packaging and Circuit Association (JPCA) standard (JPCA-DG02). Next, a surface coating layer 7 "CISV1215 (Nikkan Industries Co., Ltd.)" including a polyimide film (thickness 12.5μm) and an insulating adhesive layer (thickness 15μm) is attached to the main surface side of the polyimide film 50. In addition, in FIG. 4, the surface coating layer 8 is shown in a perspective view to understand the structure of the signal wiring 53, etc. Afterwards, the copper foil pattern exposed from the surface coating 8 is nickel-plated (not shown) and then gold-plated (not shown).

Next, as shown in FIG6 , the release sheet of the electromagnetic wave shielding sheet 10 of each example is peeled off, and the conductive adhesive layer 1 is placed inside and pressed onto the entire back side of the wiring board 20 having a coplanar circuit under the conditions of 170°C, 2.0 MPa, and 30 minutes, thereby obtaining a wiring board 21 having a coplanar circuit with an electromagnetic wave shielding sheet. In FIG6 , the back side grounding pattern (ii) 56 is shown in perspective.

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

The network analyzer E5071C (manufactured by Agilent Japan) was connected to the exposed signal wiring 53 of the wiring board 21 with a coplanar circuit with an electromagnetic wave shielding sheet, and a 15 GHz sine wave was input to measure the transmission loss to evaluate the transmission characteristics. The measured transmission characteristics were evaluated according to the following standards.

(Evaluation criteria)

◎: The transmission loss at 15GHz is less than 7.0dB, which is extremely good.

○: The transmission loss at 15GHz is 7.0dB or more and less than 7.5dB, which is good.

△: The transmission loss at 15GHz is above 7.5dB and below 8.0dB, which is practical.

×: The transmission loss at 15GHz is over 8.0dB, which is not practical.

<High frequency shielding>

High-frequency shielding is based on the American Society for Testing and Materials (ASTM) D4935, using a coaxial tube-type shielding effect measurement system manufactured by Keycom. Electromagnetic waves are irradiated under 100MHz~15GHz conditions, and the attenuation of electromagnetic waves in electromagnetic wave shielding sheets is measured and marked according to the following standards. In addition, the measured value of attenuation is decibel (unit: dB).

(Evaluation criteria)

◎: The attenuation when irradiated with 15GHz electromagnetic waves is less than -55dB, which is very good.

○: The attenuation when irradiated with 15 GHz electromagnetic waves is -55 dB or more and less than -50 dB. Good.

△: When irradiated with 15GHz electromagnetic waves, the attenuation is more than -50dB and less than -45dB, which is practical.

×: The attenuation when irradiated with 15GHz electromagnetic waves is -45dB or more. It is not practical.

<Hot and cold cycle reliability>

The reliability of hot and cold cycles is evaluated by measuring the connection resistance value through a small opening before and after the hot and cold cycles. The specific evaluation method is shown below.

An electromagnetic wave shielding sheet having a width of 20 mm and a length of 50 mm was prepared as a sample 25. As shown in the plan views of FIG. 7 (1) and FIG. 7 (4), the release sheet was peeled off from the sample 25, and the exposed conductive adhesive layer 25b was pressed and bonded to a separately prepared flexible printed wiring board (copper foil circuits 22A and 22B having a thickness of 18 μm and not electrically connected to each other were formed on a polyimide film 50 having a thickness of 25 μm, and a 37.5 μm thick copper foil circuit 22A having a diameter of 1.1 mm (path area of 1.0 mm ² ) was laminated on the copper foil circuit 22A) under the conditions of 170°C, 2 MPa, and 30 minutes. ) is placed on a wiring board having a polyimide coating layer 23 with an adhesive and a circular passage 24 of FIG. 7 , and the conductive adhesive layer 25b and the protective layer 25a of the electromagnetic wave shielding sheet are cured, thereby obtaining a sample. Then, the peeling sheet on the protective layer 25a side of the sample is removed, and the initial connection resistance value between 22A and 22B shown in the plan view of FIG. 7 (4) is measured using a "Loresta GP" BSP probe manufactured by Mitsubishi Chemical Analytech. In addition, FIG. 7 (2) is a D-D' cross-sectional view of FIG. 7 (1), and FIG. 7 (3) is a CC' cross-sectional view of FIG. 7 (1). Similarly, (5) of FIG. 7 is a cross-sectional view taken along the line D-D' of (4) of FIG. 7, and (6) of FIG. 7 is a cross-sectional view taken along the line C-C' of (4) of FIG. 7. The sample was placed in a thermal shock device ("TSE-11-A", manufactured by Espec Corporation) and subjected to 200 alternating exposures under the conditions of high temperature exposure: 125°C, 15 minutes, and low temperature exposure: -50°C, 15 minutes. Afterwards, the connection resistance value of the sample was measured in the same manner as in the initial stage.

The evaluation criteria for hot and cold cycle reliability are as follows.

(Evaluation criteria)

◎: (Connection resistance after alternating exposure)/(initial connection resistance) is less than 1.5, which is very good.

○: (Connection resistance after alternating exposure)/(initial connection resistance) is 1.5 or more and less than 3.0, which is good.

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

×: (Connection resistance after alternating exposure)/(initial connection resistance) is 5.0 or more. Not practical.

This application claims priority based on Japanese patent application No. 2019-112479 filed on June 18, 2019, and all the disclosed contents thereof are incorporated herein.

1: Conductive adhesive layer

2: Metal layer

3: Protective layer

4: Opening

10: Electromagnetic wave shielding sheet

Claims (5)

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