Electromagnetic wave shielding sheet and manufacturing method thereof, shielding wiring substrate, and electronic device

Abstract

The present invention provides an electromagnetic wave shielding sheet and its manufacturing method, a shielding wiring substrate, and an electronic device that can suppress curling and burrs and has electromagnetic wave shielding properties, easy deformability, and air permeability. The electromagnetic wave shielding sheet of the present invention includes an adhesive layer (A) and a shielding layer (B) stacked on the adhesive layer (A). The shielding layer (B) has a metal layer (C) stacked on the adhesive layer (A), and a conductive filler high-filling layer (D) containing an adhesive component (d-1) and a conductive filler (d-2) and stacked on the metal layer (C), and the content of the conductive filler (d-2) is set to 75% by mass to 95% by mass relative to 100% by mass of the conductive filler high-filling layer (D).

Description

[0001] This application claims the benefit of priority based on Japanese Patent Application No. 2021-46610, filed on March 19, 2021, the disclosure of which is incorporated herein in its entirety. Technical Field

[0002] The present invention relates to an electromagnetic wave shielding sheet having an adhesive layer and a shielding layer and a method for producing the same. The present invention also relates to a shielding wiring board and an electronic device. Background Art

[0003] Various electronic devices, including mobile devices, personal computers (PCs), and servers, incorporate substrates such as printed wiring boards. These substrates are equipped with electromagnetic shielding structures to prevent malfunctions caused by external magnetic fields and radio waves, and to reduce unwanted radiation from electrical signals.

[0004] Patent Document 1 discloses a shielding film for a printed wiring board, aiming to provide a shielding film for a printed wiring board that is less susceptible to damage to the metal layer even when subjected to repeated flexing and sliding. The film comprises an insulating layer having an arithmetic mean roughness of 0.5 μm to 5.0 μm on one surface, and a metal layer formed into a bellows structure along the surface of the insulating layer. Furthermore, Patent Document 2 discloses an electromagnetic wave shielding film, aiming to provide an electromagnetic wave shielding film that is less susceptible to degradation of shielding properties and exhibits sufficient flex resistance during the manufacture of a shielded printed wiring board. The film comprises a conductive adhesive layer, a shielding layer including a metal layer having multiple openings whose opening area and porosity fall within specific ranges, and an insulating layer, laminated in this order. Furthermore, Patent Document 3 discloses a conductive layer having a laminated structure comprising at least a conductive adhesive layer, an electromagnetic wave absorbing layer, and an electromagnetic wave shielding layer (metal layer) from the side of the flexible printed wiring board 50. Patent Document 4 discloses a shape-retaining film including a plastically deformable metal layer and an adhesive layer for bonding to a flexible wiring board, which can also be used as a shielding film.

[0005] A representative substance that blocks electromagnetic waves is metal. In the electromagnetic wave shielding film disclosed in Patent Document 1 and the like, the metal layer functions as a shielding layer that blocks electromagnetic waves.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-38278

[0009] Patent Document 2: International Publication No. 2018 / 147298

[0010] Patent Document 3: Japanese Patent Application Publication No. 2019-021837

[0011] Patent Document 4: International Publication No. 2014 / 192490 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] Electromagnetic shielding sheets are typically wound into a roll for storage during manufacture and unwound for use. Furthermore, electromagnetic shielding sheets are sometimes punched into the desired size and shape before use. However, this can lead to stress accumulation in the electromagnetic shielding sheet during roll storage, resulting in residual strain and warping (hereinafter referred to as curling) during unwinding. Furthermore, during this punching process, the end surfaces of the electromagnetic shielding sheet are prone to curling up (hereinafter referred to as burrs). When curling or burring occurs in an electromagnetic shielding sheet, it is found that the yield is reduced and the reliability of the product is lowered. Therefore, there is a need for an electromagnetic shielding sheet that can suppress curling and burring.

[0014] When an electromagnetic wave shielding sheet is bonded to, for example, a flexible printed wiring board, it is sometimes held in a bent state within the electronic device. Therefore, there is a demand in the market for an electromagnetic wave shielding sheet that exhibits excellent electromagnetic wave shielding properties and excellent deformability even when bent. Furthermore, when a printed wiring board to which the electromagnetic wave shielding sheet is bonded undergoes high-temperature processing such as a reflow process, gases generated from the printed wiring board may not be able to pass through the electromagnetic wave shielding sheet, resulting in partial delamination between layers or floating, which may cause poor appearance. Therefore, there is a demand for an electromagnetic wave shielding sheet that can address air permeability issues.

[0015] The present invention has been made in view of the above background, and an object of the present invention is to provide an electromagnetic shielding sheet that can suppress curling and burrs and has electromagnetic shielding properties, easy deformability, and air permeability, a method for manufacturing the same, a shielding wiring board, and an electronic device.

[0016] Technical means to solve the problem

[0017] As a result of diligent research, the present inventors have found that the problems of the present invention can be solved by the following aspects, thereby completing the present invention.

[0018] [1]: An electromagnetic wave shielding sheet comprising an adhesive layer (A) and a shielding layer (B) laminated on the adhesive layer (A).

[0019] The shielding layer (B) comprises a metal layer (C) laminated on the adhesive layer (A), and a highly conductive filler-filled layer (D) containing a binder component (d-1) and a conductive filler (d-2) and laminated on the metal layer (C), wherein no metal layer is formed on the side of the highly conductive filler-filled layer (D) opposite to the side on which the metal layer (C) is formed.

[0020] The content of the conductive filler (d-2) is 75% by mass to 95% by mass relative to 100% by mass of the conductive filler-rich layer (D).

[0021] [2]: The electromagnetic shielding sheet according to [1], wherein the adhesive layer (A) contains an adhesive component (a-1),

[0022] The adhesive component (a-1) was press-treated at 170° C. for 30 minutes. The relative dielectric constant of the pressed product (a′-1) was 1.0 to 3.5 at 23° C. and a frequency of 28 GHz. The dielectric loss tangent of the pressed product (a′-1) was 0.0001 to 0.02 at 23° C. and a frequency of 28 GHz.

[0023] [3]: The electromagnetic shielding sheet according to [1] or [2], wherein the adhesive layer (A) contains a conductive filler (a-2),

[0024] The content of the conductive filler (d-2) is 84% to 95% by mass relative to 100% by mass of the conductive filler-rich layer (D).

[0025] The content of the conductive filler (a-2) is 15% by mass to 45% by mass relative to 100% by mass of the adhesive layer (A).

[0026] [4]: The electromagnetic shielding sheet according to any one of [1] to [3], further comprising a protective layer (E) laminated on the shielding layer (B).

[0027] The protective layer (E) contains a binder component (e-1),

[0028] The sheet-shaped pressed product (e'-1) obtained by pressing the adhesive component (e-1) at 170° C. for 30 minutes has a breaking strength of 15 MPa or more.

[0029] [5]: The electromagnetic shielding sheet according to any one of [1] to [4], wherein the repulsive force of the pressed product after being pressed at 170° C. for 30 minutes is 0.01 mN / cm to 30 mN / cm.

[0030] [6]: A shielded wiring substrate comprising: a wiring circuit substrate including an insulating base material, a circuit pattern formed on the insulating base material, and an outer coating layer formed on the insulating base material and the circuit pattern; and

[0031] Electromagnetic wave shielding sheet,

[0032] The electromagnetic shielding sheet is bonded to the overcoat layer using the adhesive layer (A) of the electromagnetic shielding sheet according to any one of [1] to [5].

[0033] [7]: An electronic device comprising the shielded wiring substrate according to [6].

[0034] [8]: A method for manufacturing an electromagnetic wave shielding sheet, the electromagnetic wave shielding sheet comprising a laminated structure of an adhesive layer (A) and a shielding layer (B), the method comprising:

[0035] A step of forming an adhesive layer (A);

[0036] a step of forming a metal layer (C) that functions as a part of the shielding layer (B); and

[0037] A step of applying a conductive filler-containing composition containing a binder component (d-1) and a conductive filler (d-2) to form a highly conductive filler-filled layer (D) functioning as a part of the shielding layer (B),

[0038] The content of the conductive filler (d-2) is set to 75% to 95% by mass relative to 100% by mass of the highly conductive filler-filled layer (D), and the adhesive layer (A), the metal layer (C), and the highly conductive filler-filled layer (D) are stacked in this order, with no metal layer formed on the side of the highly conductive filler-filled layer (D) opposite to the side on which the metal layer (C) is formed.

[0039] Effects of the Invention

[0040] The present invention provides an electromagnetic shielding sheet that can suppress curling and burring and has electromagnetic shielding properties, easy deformability, and air permeability, a method for producing the same, a shielded wiring board, and an electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic cross-sectional view showing an example of the electromagnetic shielding sheet according to the present embodiment.

[0042] Figure 2 This is a schematic cross-sectional view showing an example of the main portion of the shielded wiring board according to the present embodiment.

[0043] Figure 3 This is a schematic cross-sectional view for explaining a method for evaluating curling of the electromagnetic shielding sheet of the example.

[0044] Figure 4 This is a schematic cross-sectional view for explaining a method for evaluating the deformability of the electromagnetic shielding sheet of the example.

[0045] Figure 5 It is a schematic plan view of the main surface side of the printed circuit board of the embodiment.

[0046] Figure 6 This is a schematic plan view of the back side of the printed circuit board of the embodiment.

[0047] Figure 7 This is a schematic plan view of the back surface side of the shielded wiring substrate of the embodiment.

[0048] Explanation of symbols

[0049] 1, 2, 6: electromagnetic wave shielding sheet,

[0050] 5: Evaluation samples,

[0051] 8: outer coating,

[0052] 10, 15: Wiring circuit board,

[0053] 11: Insulating substrate,

[0054] 12: Circuit pattern,

[0055] 12a: Signal wiring,

[0056] 12b: Ground wiring,

[0057] 13: outer coating,

[0058] 14: passage,

[0059] 20, 21: Shielded wiring substrate,

[0060] 41a: bending part,

[0061] 41b: Left,

[0062] 41c: right,

[0063] 42: laminated body,

[0064] 44: Substrate,

[0065] 45: Silicone rubber sheet,

[0066] 50: Polyimide film,

[0067] 51: copper plating film,

[0068] 52: through hole,

[0069] 53: Signal wiring,

[0070] 54: Ground wiring,

[0071] 55: ground pattern,

[0072] 56: Back side ground pattern,

[0073] 60: Taiwan. DETAILED DESCRIPTION

[0074] Hereinafter, an example of an embodiment to which the present invention is applied will be described. In addition, as long as they are consistent with the gist of the present invention, other embodiments are also included in the scope of the present invention. In addition, the numerical range determined by using "to" in this specification includes the numerical values recorded before and after the "to". In addition, in this specification, "film" or "sheet" is not distinguished according to thickness. In addition, the various components appearing in this specification may be independently a single type or two or more types may be used in combination unless otherwise noted. In addition, the so-called "β layer stacked on the α layer" includes, in addition to a stacked structure in which the β layer is stacked directly above the α layer, a stacked structure in which the β layer is stacked on the α layer via other layers. In addition, the numerical values determined in this specification are values obtained according to the method disclosed in the examples.

[0075] [[Electromagnetic wave shielding sheet]]

[0076] An example of an electromagnetic shielding sheet according to an embodiment of the present invention (hereinafter also referred to as "this sheet") is shown in FIG. Figure 1 .like Figure 1 As shown, this sheet 1 includes an adhesive layer (A) and a shielding layer (B) laminated on the adhesive layer (A). The shielding layer (B) includes a metal layer (C) laminated on the adhesive layer (A), and a highly conductive filler-filled layer (D) containing a binder component (d-1) and a conductive filler (d-2) laminated on the metal layer (C). Furthermore, no metal layer is formed on the side of the highly conductive filler-filled layer (D) opposite to the side on which the metal layer (C) is formed. The content of the conductive filler (d-2) in the highly conductive filler-filled layer (D) is set to a range of 75% to 95% by mass relative to 100% by mass of the highly conductive filler-filled layer (D). This sheet is bonded to an adherend such as a printed wiring board via the adhesive layer (A) and functions as an electromagnetic wave shielding member for the adherend.

[0077] According to this sheet, by not constituting the shielding layer (B) solely with a metal layer (C) but by combining the metal layer with a highly conductive filler-filled layer (D) containing a binder component (d-1), it is possible to achieve excellent electromagnetic shielding properties while suppressing curling and burring, and to combine excellent deformability with air permeability. Specifically, while the shielding layer (B) provides excellent electromagnetic shielding properties, the combination of the metal layer (C) and the highly conductive filler-filled layer (D) suppresses curling and burring, thereby achieving excellent deformability. Furthermore, compared to a shielding layer consisting solely of a metal layer, the present shielding layer (B) comprising a metal layer (C) and a highly conductive filler-filled layer (D) containing a binder component (d-1) allows the thickness of the metal layer, which is highly dense but presents challenges with air permeability, to be reduced, thereby improving air permeability.

[0078] Electromagnetic shielding sheets are typically produced and stored in rolls for reasons such as ease of transport and continuous production. However, because the metal layer is formed on the electromagnetic shielding sheet, residual strain is generated during roll storage, and curling occurs during unwinding. This curling reduces handling during cutting or stamping. Furthermore, dimensional accuracy deteriorates.

[0079] On the other hand, according to this sheet, the curling can be effectively suppressed by the stress relaxation effect of the binder component (d-1) of the highly conductive filler-filled layer (D) functioning as a part of the shielding layer (B).

[0080] In addition, electromagnetic shielding sheets wound into a roll are sometimes unwound and punched into the desired size and shape before use. However, since the electromagnetic shielding sheet has a metal layer, punching such sheets can easily produce burrs on the end surfaces.

[0081] By combining a metal layer and a highly conductive filler-filled layer containing a binder component (d-1) as the shield layer (B), this sheet can reduce the thickness of the metal layer, which can cause burrs. Furthermore, the binder component (d-1) in the highly conductive filler-filled layer (D) mitigates stress applied to the sheet during stamping. Consequently, this sheet effectively reduces the occurrence of burrs.

[0082] For example, a flexible printed circuit (FPC) with an electromagnetic shielding sheet attached is sometimes incorporated into an electronic device in a bent state. However, since the electromagnetic shielding sheet contains a metal layer, its rigidity generates a springback force when bent. Therefore, there is a demand for an electromagnetic shielding sheet with excellent deformability.

[0083] This sheet utilizes a metal layer (C) and a highly conductive filler-filled layer (D) containing a binder component (d-1) and having a specific conductive filler content as the shield layer (B). This allows the thickness of the metal layer, which contributes to its rigidity, to be designed to be thin. Furthermore, by using the highly conductive filler-filled layer (D), the layer of the shield layer (B) that is positioned on the outside during bending and that is subject to further stress, as the highly conductive filler-filled layer (D), the metal layer (C) can be effectively prevented from breaking, cracking, and poor appearance.

[0084] FPCs bonded with electromagnetic shielding sheets undergo high-temperature processing steps, such as reflow soldering. During this process, the electromagnetic shielding sheet must be permeable to outgassing, such as water vapor, generated from the FPC. However, because the electromagnetic shielding sheet contains a dense metal layer, outgassing can be trapped in the metal layer, potentially causing blistering, bubbling, partial delamination between layers, and poor appearance.

[0085] By combining a metal layer with a highly conductive filler-filled layer containing the binder component (d-1) as the shielding layer (B), this sheet can reduce the thickness of the metal layer, which can hinder air permeability. This thinner metal layer facilitates the formation of fine pores that provide air permeability. Alternatively, additional pores can be provided in the metal layer for air permeation, but this increases the number of production steps.

[0086] In this sheet, the metal layer (C) in the shield layer (B) is positioned closer to the electronic component (adherend) incorporating signal wiring and other components. The conductive filler (d-2) in the highly conductive filler-filled layer (D) is dispersed in the binder component (d-1). Therefore, focusing on the portion exhibiting conductivity, the highly conductive filler-filled layer (D) alone exhibits a certain degree of surface irregularities.

[0087] On the other hand, when this sheet is used in an FPC for high-frequency applications, in the shield layer (B) of this sheet, if the current becomes high-frequency due to its nature, the current will flow through the surface of the metal layer (C). The transmission characteristics of signal wiring in a printed circuit board are affected by the current flowing through nearby conductors. Therefore, if the surface of the metal layer (C) near the signal wiring has steep irregularities, the distance from the current flowing through the metal surface will fluctuate, causing unstable transmission characteristics. Therefore, from the perspective of transmission characteristics, the shield layer (B) is preferably smooth.

[0088] This sheet smoothes the electronic component (adherend) side of the shield layer (B), improving transmission characteristics. For example, when forming the metal layer (C) by vapor deposition or plating, the metal layer (C) can be formed to fill recessed areas on the surface of the highly conductive filler-filled layer (D). Furthermore, when the metal layer (C) is a metal foil such as copper foil, the surface irregularities of the highly conductive filler-filled layer (D) can be covered with the smooth metal layer (C).

[0089] (Rebound force of electromagnetic wave shielding sheet)

[0090] To achieve excellent deformability, the sheet preferably exhibits a rebound force of 0.01 mN / cm to 30 mN / cm after a press treatment at 170°C for 30 minutes. This range provides excellent deformability and more effectively suppresses curling and burring. Furthermore, the method for measuring the rebound force of the sheet after a press treatment is intended to refer to the values determined in the Examples described below. Each layer is described below in detail.

[0091] [Adhesive layer (A)]

[0092] The adhesive layer (A) serves to bond the sheet to the adherend. Bonding of the sheet to the adherend is typically performed by thermocompression bonding. The layer after bonding to the adherend is referred to as the bonding layer (A'), to distinguish it from the adhesive layer (A) of the sheet before bonding to the adherend.

[0093] The adhesive layer (A) can be formed using an adhesive composition. The adhesive composition includes a binder component (a-1). The binder component (a-1) includes at least a resin. Preferred examples of the resin include thermoplastic resins and thermosetting resins. A thermoplastic resin is a resin that softens when heated to a temperature above its glass transition temperature or melting point, while a thermosetting resin is a resin that crosslinks when heated to form a polymer network structure and hardens to a point where it cannot return to its original shape. There are types in which a thermosetting resin is cured alone, and types in which a thermosetting resin and a hardener are used in combination. Of these, it is preferred to use a thermosetting resin and a hardener as the binder component (a-1).

[0094] When a thermoplastic resin is used as the resin in the adhesive component (a-1), the contained thermoplastic resin is in a solid state. During hot pressing with an adherend such as an FPC, the thermoplastic resin melts and solidifies again after cooling, thereby achieving the desired bond strength. Alternatively, when a thermosetting resin is used as the resin in the adhesive component (a-1), the contained thermosetting resin and curing agent are in an uncured state (stage B). The desired bond strength can be achieved by hot pressing with an adherend such as an FPC, etc., thereby curing the adhesive component (stage C). Furthermore, prior to bonding the adherend, the adhesive component (a-1) may be in a semi-cured state, where part of the adhesive component (a-1) is cured.

[0095] From the perspective of achieving good adhesion with the shielding layer (B) and further improving adhesion with adherends such as the cover film of the FPC (e.g., a polyimide resin), the adhesive layer (A) preferably contains a thermosetting resin or / and a thermoplastic resin containing at least one of a hydroxyl group and a carboxyl group in the adhesive component (a-1).

[0096] When the present sheet is used in a member that transmits signals, such as an FPC, in order to reduce the transmission loss of high-frequency signals transmitted through electronic components such as the FPC, it is preferred that the pressed product (a'-1) obtained by press-treating the adhesive component (a-1) of the adhesive layer (A) of the present sheet at 170°C for 30 minutes has a relative dielectric constant of 1.0 to 3.5 and a dielectric loss tangent of 0.0001 to 0.02 at 23°C and a frequency of 28 GHz.

[0097] In the case of a thermosetting resin as the binder component (a-1), the press-treated product (a'-1) forms a hardened layer. A hardened layer is typically formed by treatment at 170°C for 30 minutes. However, for binder components (a-1) that do not form a hardened layer under these conditions, the heating temperature and / or time are adjusted to form a hardened layer before measurement. Hardening here refers to complete hardening, which is stage C, and not semi-hardening, which is stage B.

[0098] Among the transmission losses generated during signal transmission in electronic components such as FPCs, dielectric loss is expressed by the following formula (1).

[0099] [Number 1]

[0100]

[0101] In the formula (1), α is the transmission loss of the dielectric, K is the proportional constant, f is the frequency, and ε r is the relative dielectric constant, and tanδ is the dielectric loss tangent.

[0102] By reducing the relative dielectric constant and dielectric loss tangent of the pressed product (a'-1) of the adhesive component (a-1) of the adhesive layer (A), dielectric loss can be reduced as shown in the formula (1), thereby reducing transmission loss.

[0103] By combining the shielding layer (B) in this sheet with an adhesive layer (A) containing a binder component (a-1) that produces a press-treated material (a'-1) with a relative dielectric constant and dielectric loss tangent within the specific ranges, transmission loss can be more effectively reduced. In particular, with the recent trend toward higher-speed transmission (higher frequencies) in electronic devices, there is a demand for reducing transmission loss in the frequency ranges known as the sub-6 band (3.6 GHz to 6 GHz) and the 5G millimeter wave band (28 GHz to 300 GHz). However, this method can also effectively reduce transmission characteristics in these frequency ranges. The upper limit of the relative dielectric constant is more preferably 3.0, and a further preferred upper limit is 2.5. Furthermore, the upper limit of the dielectric loss tangent is more preferably 0.01, and a further preferred upper limit is 0.005.

[0104] The bonding layer (A') of this sheet after bonding to the adherend can be insulating or conductive. In the case of being conductive, it is sufficient as long as the adhesive composition forming the adhesive layer (A) further contains a conductive filler (a-2). When the bonding layer (A') is conductive, it can be isotropic or anisotropic. In addition, the so-called isotropic conductivity means that the bonding layer (A') has conductivity in both the thickness direction and the surface direction, and the so-called anisotropic conductivity means that the bonding layer (A') has conductivity only in the thickness direction. From the perspective of improving the transmission characteristics in the high-frequency range and reducing costs, it is preferably anisotropic conductivity.

[0105] Furthermore, when the conductive filler (a-2) is included in the adhesive layer (A), the relative dielectric constant and dielectric loss tangent values increase compared to those without the conductive filler. However, by setting the relative dielectric constant of the pressed product (a'-1) of the adhesive component (a-1) to 1.0 to 3.5 and the dielectric loss tangent to 0.0001 to 0.02 at 23°C and a frequency of 28 GHz, excellent transmission characteristics are achieved even with the addition of the conductive filler (a-2). This is believed to be due to the synergistic effect of the improved shielding properties of the added conductive filler (a-2) and the low dielectric effect of the adhesive component (a-1) by controlling the dielectric properties of the pressed product (a'-1) of the adhesive component (a-1) in the adhesive layer (A).

[0106] The thickness of the adhesive layer (A) is not particularly limited and can be appropriately designed depending on the intended use. From the perspective of thinning, the thickness of the adhesive layer (A) is preferably about 4 μm to 10 μm.

[0107] When bonding this sheet to components such as FPCs, it requires heat resistance sufficient to withstand heating in a reflow oven or similar process. In such cases, it is preferable to include a thermosetting resin and a hardener in the adhesive component (a-1), so that the bonding layer (A') of the sheet after bonding to the adherend serves as a cured layer. The components of the adhesive layer (A) are described in detail below.

[0108] (Binder component (a-1))

[0109] As a preferred example of thermoplastic resin, polyolefin resin, vinyl resin, acrylic resin, styrene-acrylic resin, diene resin, terpene resin, petroleum resin, cellulose resin, polyamide resin, polyurethane resin, polyester resin, polycarbonate resin, polyimide resin, fluororesin etc. can be listed. With regard to the viewpoint of transmission loss, it is preferably a material that satisfies the relative dielectric constant and dielectric loss tangent, and with regard to the viewpoint of characteristic impedance, it is preferably a material that satisfies the relative dielectric constant. As a preferred example, fluororesin etc. can be listed. In addition, the material that is classified as liquid crystal polymer can be listed as a preferred example. Thermoplastic resin can be used alone or in combination of two or more.

[0110] Examples of the thermosetting functional group contained in the thermosetting resin include a hydroxyl group, a phenolic hydroxyl group, an acid anhydride 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, a blocked carboxyl group, and a silanol group.

[0111] Examples of thermosetting resins include acrylic resins, maleic acid resins, polyolefin resins, polybutadiene resins, polyester resins, polyurethane resins, polyurethane urea resins, polycarbonate resins, epoxy resins, oxetane resins, phenoxy resins, polyimide resins, polyamide resins, polyamideimide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, polyimidebenzoxazole resins, polybenzoxazole resins, silicone resins, and fluororesins. The thermosetting resins may be used alone or in combination of two or more.

[0112] The hardener is not particularly limited as long as it is a substance having two or more functional groups that can react with the functional groups of the thermosetting resin. As an example of a hardener, there are: epoxy compounds, compounds containing anhydride groups, isocyanate compounds, aziridine compounds, amine compounds, phenolic compounds, organic metal compounds (metal chelate compounds), polyol compounds, melamine compounds, silane compounds, carbodiimide compounds, benzoxazine compounds, maleimide compounds, and compounds containing β-hydroxyalkylamide groups. The hardener can be used alone or in combination of two or more. In addition, the hardener can be a low molecular weight compound or a high molecular weight compound. In addition, when a high molecular weight compound is used as a hardener, the component with a larger amount of the hardener is set as the thermosetting resin, and the component with a smaller amount of the hardener is set as the hardener.

[0113] When the curable functional group of the thermosetting resin is a hydroxyl group, the curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, or an organometallic compound. Furthermore, when the curable functional group of the thermosetting resin is an amino group, the curing agent is preferably an isocyanate compound, an epoxy compound, an aziridine compound, a carbodiimide compound, or an organometallic compound. Furthermore, when the curable functional group of the thermosetting resin is a carboxyl group, the curing agent is preferably an epoxy compound or an organometallic compound.

[0114] Preferred combinations when using two or more curing agents include epoxy compounds and organometallic compounds, epoxy compounds and aziridine compounds and organometallic compounds, etc. Using these together can increase the crosslinking density, effectively improving the adhesive layer (A) from bleeding out during heat and pressure bonding and improving its heat resistance.

[0115] Examples of the isocyanate compound include polyisocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, hydrogenated xylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate; adducts of these polyisocyanate compounds with polyol compounds such as trimethylolpropane; biuret or isocyanurate of these polyisocyanate compounds; and adducts of these polyisocyanate compounds with existing polyether polyols or polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, and the like.

[0116] Examples of the epoxy compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A-epichlorohydrin epoxy resin, N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N-diglycidylaniline, and N,N-diglycidyltoluidine.

[0117] Examples of the polycarbodiimide include the Carbodilite series manufactured by Nisshinbo Co., Ltd. Among them, Carbodilite V-01, 03, 05, 07, and 09 are preferred due to their excellent compatibility with organic solvents.

[0118] Examples of the aziridine compound include 2,2′-bishydroxymethylbutanol tris[3-(1-aziridinyl)propionate] and 4,4′-bis(ethyleneiminocarbonylamino)diphenylmethane.

[0119] The organometallic compound is a compound containing a metal and an organic compound, which reacts with the functional groups of the thermosetting resin to form crosslinks. The type of organometallic compound is not particularly limited, and examples thereof include organoaluminum compounds, organotitanium compounds, and organozirconium compounds. Furthermore, the bond between the metal and the organic compound may be a metal-oxygen bond, not limited to a metal-carbon bond. Furthermore, the bonding between the metal and the organic compound may be chemical, coordinate, or ionic.

[0120] The organoaluminum compound is preferably an aluminum chelate compound. Examples of the aluminum chelate compound include ethyl acetoacetate aluminum diisopropoxide, tris(ethyl acetoacetate)aluminum, alkyl acetoacetate aluminum diisopropoxide, bis(ethyl acetoacetate)aluminum monoacetylacetonate, tris(acetoacetate)aluminum, bis(ethyl acetoacetate)aluminum monoacetoacetate, di-n-butoxide monomethyl acetoacetate aluminum, diisobutoxide monomethyl acetoacetate aluminum, di-sec-butoxide monomethyl acetoacetate aluminum, aluminum isopropoxide, mono-sec-butoxyaluminum diisopropoxide, aluminum sec-butoxide, and aluminum ethoxide.

[0121] The organic titanium compound is preferably a titanium chelate compound. Examples of the titanium chelate compound include titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate, titanium octanediol, titanium ethylacetoacetate, 1,3-propanedioxybis(ethylacetoacetate)titanium, polyacetylacetoacetonate titanium, tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetraoctyl titanate, tert-amyl titanate, tetra-tert-butyl titanate, tetrastearyl titanate, titanium isostearate, tri-n-butoxy titanium monostearate, di-isopropoxy titanium distearate, titanium stearate, di-isopropoxy titanium diisostearate, (2-n-butoxycarbonylbenzoyloxy)tributoxy titanium, and the like.

[0122] The organic zirconium compound is preferably a zirconium chelate compound. Examples of the zirconium chelate compound include zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, zirconium monobutoxyacetylacetonate bis(ethylacetoacetate), zirconium dibutoxybis(ethylacetoacetate), n-propyl zirconate, n-butyl zirconate, zirconium stearate, and zirconium octanoate. Of these, organic titanium compounds are preferred in terms of thermal curing reactivity and heat resistance after curing.

[0123] The content of the hardener can be appropriately designed, but is preferably 1 to 50 parts by mass per 100 parts by mass of the thermosetting resin. By setting this range, the crosslinking density can be adjusted appropriately, maintaining good hygroscopicity and adhesion. Furthermore, the elastic modulus of the cured product can be appropriately maintained. The hardener content is more preferably 3 to 40 parts by mass, and even more preferably 3 to 30 parts by mass, per 100 parts by mass of the thermosetting resin.

[0124] From the perspective of providing a sheet that maintains excellent transmission properties and exhibits superior adhesive properties even when used in high-frequency components, the press-treated product (a'-1) of the adhesive component (a-1) at 170°C for 30 minutes preferably has the aforementioned relative permittivity and dielectric loss tangent. Preferred examples of the adhesive component (a-1) include a combination of a thermosetting resin having a carboxyl group and a hardener containing an epoxy compound and an organometallic compound, a combination of a thermosetting resin having a phenolic hydroxyl group and a hardener containing a polyisocyanate group, and a combination of a thermosetting resin having an epoxy group and a hardener containing an organometallic compound.

[0125] Among these, it is particularly preferred that thermosetting resin comprises carboxyl-containing resin, comprises epoxy compound as curing agent, and then comprises at least one of organometallic compound and isocyanate compound.Epoxy compound is allocated with respect to 1 equivalent of carboxylic acid and is preferably 0.5 times to 10 times, more preferably 1 times to 5 times epoxy equivalent.The total curing agent equivalent of organometallic compound and isocyanate compound is allocated with respect to 1 equivalent of carboxylic acid, preferably 0.1 times to 5 times, more preferably 0.5 times to 3 times scope is allocated.By using curing agent as described, the unreacted functional group number after heat curing can be suppressed, so relative dielectric constant and dielectric loss tangent are further reduced.

[0126] Furthermore, the reactive functional group value (acid value) of the resin in the binder component (a-1) is preferably set to 20 mgKOH / g or less, and more preferably to 10 mgKOH / g or less. From the perspective of reacting with a large amount of curing agent during curing to form a strong crosslinked structure, the lower limit of the reactive functional group value (acid value) is preferably 1 mgKOH / g.

[0127] (Conductive filler (a-2))

[0128] The conductive filler (a-2) has the function of imparting conductivity to the bonding layer (A'). In the case of a conductive bonding layer (A'), whether or not the adhesive layer (A) of the sheet is conductive does not matter. Examples of the conductive filler (a-2) include metal powders such as gold, platinum, silver, copper, nickel, aluminum, tin, palladium, chromium, titanium, zinc, manganese, and indium, alloy powders, and low-melting-point metal powders such as solder. In addition, composite microparticles having a coating layer covering the surface of the core are also preferred. For example, silver-plated copper powder, metal-plated glass fiber or carbon filler, etc. can be listed. In addition, microparticles of conductive polymers such as polyaniline and polyacetylene can also be used. Among these, silver powder with high conductivity, silver-plated copper powder, or low-melting-point metal powders such as solder are preferred. The conductive filler can be used alone or in combination of two or more.

[0129] Regarding the shape of the conductive filler (a-2), there is no limitation as long as the desired conductivity is obtained in the bonding layer (A'). For example, spherical, flake-shaped (including leaf-shaped particles described later), dendritic, plate-shaped, needle-shaped, rod-shaped, and grape-shaped shapes can be listed. It is also possible to mix two or more conductive fillers (a-2) of different shapes. In order to exhibit anisotropic conductivity, it is preferably set to a spherical or dendritic shape. In addition, from the perspective of making the outgas permeability good, dendritic particles and spherical particles are better than flake-shaped particles. When dendritic particles are used as the conductive filler (a-2), the number of contact points between the conductive fillers increases, which can further improve the grounding connectivity when the sheet is bonded to an FPC, etc. The details will be described later.

[0130] From the perspective of ensuring sufficient conductivity, the average particle size of the conductive filler (a-2) is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 7 μm or more. On the other hand, from the perspective of achieving a balance between the thinness of the adhesive layer (A) and conductivity, it is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. The average particle size can be determined using a laser diffraction-scattering particle size distribution measuring device or the like. In addition, the average particle size is D 50 Average particle size, D 50 The average particle size of the conductive filler (a-2) was measured using a laser diffraction-scattering particle size distribution analyzer LS13320 (Beckman-Coulter) using a tornado dry powder sample module. This value represents the particle size at 50% of the cumulative value in the cumulative particle size distribution. The refractive index was set to 1.6.

[0131] The content of the conductive filler (a-2) can be appropriately designed. It is preferably 45% by mass or less, more preferably 15% to 40% by mass, and even more preferably 20% to 30% by mass, relative to 100% by mass of the adhesive layer (A). A content of 45% by mass or less improves outgassing permeability and transmission properties. Furthermore, a content of 15% by mass or greater further enhances grounding connectivity when the sheet is bonded to a printed circuit board such as an FPC. Details are described below.

[0132] (Other ingredients)

[0133] A solvent may be suitably used in the adhesive composition used to form the adhesive layer (A). In addition to the aforementioned components, silane coupling agents, curing aids, rust inhibitors, reducing agents, antioxidants, pigments, dyes, tackifier resins, plasticizers, UV absorbers, defoamers, leveling agents, fillers, flame retardants, and the like may be added as optional ingredients for the purpose of improving desired physical properties or imparting desired functions.

[0134] [Shield layer (B)]

[0135] The shielding layer (B) prevents malfunctions caused by external magnetic fields or radio waves and / or reduces unwanted radiation from electrical signals. As described above, the shielding layer (B) comprises a metal layer (C) laminated on the adhesive layer (A), and a highly conductive filler-filled layer (D) containing a binder component (d-1) and a conductive filler (d-2) laminated on the metal layer (C). Without departing from the spirit of the present invention, the shielding layer (B) may also include layers other than the metal layer (C) and the highly conductive filler-filled layer (D). In this specification, both the sheet before and after bonding to the adherend are referred to as the shielding layer (B). The same applies to the metal layer (C) and the highly conductive filler-filled layer (D).

[0136] <Metal layer (C)>

[0137] The metal layer (C) functions as part of the shielding layer (B). The type of metal constituting the metal layer (C) is not limited within the scope of the present invention. Examples include gold, platinum, silver, copper, nickel, aluminum, tin, palladium, chromium, titanium, zinc, manganese, and indium. A single conductive metal may be used, or alloys of multiple metals may be used. To achieve superior shielding properties, it is preferred that the metal layer contain 95% or more of a metal selected from gold, platinum, silver, copper, nickel, aluminum, tin, palladium, chromium, titanium, and zinc. Of these, gold, platinum, silver, and copper are preferred, with silver and copper being particularly preferred, to achieve superior shielding properties in a thin layer.

[0138] In terms of high-frequency shielding properties and cost, copper, silver, and aluminum are more preferred, with copper being even more preferred. Preferred examples of copper include rolled copper foil, electrolytic copper foil, vapor-deposited films, and sputtered films. Electrolytic copper foil is more preferred because it allows for a thinner metal layer (C). The metal layer (C) may be a single layer or multiple layers.

[0139] The thickness of the metal layer (C) can be appropriately designed depending on the intended use. However, from the perspective of satisfying shielding and transmission characteristics while also achieving excellent deformability and air permeability, it is preferably 0.05 μm to 2 μm, more preferably 0.1 μm to 1.5 μm, and even more preferably 0.2 μm to 1 μm. By setting the thickness of the metal layer (C) to 0.05 μm to 2 μm, micropores can be easily formed during the formation of the metal layer (C) without requiring a separate pore-forming step. These micropores have the advantage of significantly reducing electromagnetic noise leakage and exhibiting air permeability. In particular, the metal layer (C) obtained by vacuum deposition can easily form micropores, thereby achieving excellent air permeability.

[0140] The surface roughness of the metal layer (C) can be appropriately designed. However, from the perspective of maintaining good transmission characteristics in a high-frequency range, the surface roughness of the interface of the metal layer (C) in contact with the adhesive layer (A) is preferably such that the root mean square slope Sdq calculated using the following formula according to International Organization for Standardization (ISO) 25178-2:2012 is set to 0.0001 to 0.5.

[0141] [Number 2]

[0142]

[0143] A in formula (2) represents the area of the defined surface, represents the x-axis direction, Indicates the y-axis direction, (x, y) represents a small displacement in the z-axis direction.

[0144] The root mean square slope (Sdq) can be calculated by processing the coordinate data of the surface shape obtained using an optical microscope, a laser microscope, or an electron microscope using analysis 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 indicates the steepness of the surface's concavities and convexities.

[0145] Regarding this sheet obtained by bonding to an adherend, when the signal from an FPC or other substrate reaches a high frequency range, the current flows through the surface of the shielding layer (B) due to its nature. Therefore, the transmission characteristics of the signal wiring in the printed wiring board are affected by the current flowing in nearby conductive materials. Therefore, if the surface of the metal layer (C) close to the signal wiring has steep irregularities, the distance from the current flowing through the surface fluctuates, and the transmission characteristics become unstable. By setting the root mean square slope Sdq of the surface of the metal layer (C) on the adhesive layer (A) side within the above range, even better transmission characteristics can be achieved. From the perspective of transmission characteristics, the root mean square slope Sdq of the surface of the metal layer (C) on the adhesive layer (A) side is more preferably 0.4 or less, and even more preferably 0.3 or less.

[0146] Furthermore, the root mean square slope Sdq of the metal layer (C) generally does not change before or after bonding to the adherend by hot pressing or the like. Therefore, the root mean square slope Sdq of the interface between the metal layer (C) and the bonding layer (A') after bonding to the adherend is preferably within a range of 0.0001 to 0.5.

[0147] The metal layer (C) may have a plurality of pores extending through the thickness. The presence of these pores significantly improves reflow resistance and air permeability. To achieve both high levels of reflow resistance and high-frequency shielding properties, the pore opening ratio is preferably 0.10% to 20%.

[0148] <Conductive filler high filling layer (D)>

[0149] The highly conductive filler-filled layer (D) functions as part of the shielding layer (B) and contains a binder component (d-1) and a conductive filler (d-2). The content of the conductive filler (d-2) is 75% to 95% by mass relative to 100% by mass of the highly conductive filler-filled layer (D). This range effectively achieves stress relaxation while maintaining excellent shielding properties. A more preferred range is 80% to 92.5% by mass, a further preferred range is 84% to 90% by mass, and a particularly preferred range is 85% to 90% by mass.

[0150] The thickness of the highly conductive filler-filled layer (D) is not particularly limited, but is preferably 2 μm to 8 μm from the viewpoint of thinning.

[0151] (Binder component (d-1))

[0152] The binder component (d-1) comprises a resin. Preferred examples of the resin include thermoplastic resins and thermosetting resins. The thermosetting resin may be a self-crosslinking resin that cures on its own, but is preferably used in combination with a curing agent. Preferred examples of the thermoplastic resin, thermosetting resin, and curing agent include the compounds exemplified for the binder component (a-1). Either the thermoplastic resin or the thermosetting resin may be used alone or in combination.

[0153] In order to reduce the transmission loss of high-frequency signals transmitted through wiring circuit boards such as FPCs, it is preferred that the adhesive component (d-1) of the highly conductive filler-filled layer (D) of this sheet be subjected to a press treatment at 170°C for 30 minutes. The pressed product (d'-1) has a relative dielectric constant of 1.0 to 3.5 at 23°C and a frequency of 28 GHz, and a dielectric loss tangent of 0.0001 to 0.02. The more preferred upper limit of the relative dielectric constant is 3.0, and the more preferred upper limit is 2.5. In addition, the more preferred upper limit of the dielectric loss tangent is 0.01, and the more preferred upper limit is 0.005. In addition, when a thermosetting resin is included as the adhesive component (d-1), the pressed product (d'-1) becomes a cured layer.

[0154] From the perspective of improving press workability, it is preferred that the loss tangent peak of the pressed sheet (d'-1) in the range of 0°C to 300°C, after pressing the binder component (d-1) at 170°C for 30 minutes, be 0.1 or higher. A loss tangent peak of 0.1 or higher in the range of 0°C to 300°C effectively absorbs and mitigates stress during press working, thereby improving press workability. The loss tangent peak of the pressed sheet (d'-1) in the range of 0°C to 300°C is more preferably 0.3 or higher.

[0155] From the viewpoint of improving the deformability, the rubber-like flat region E' of the sheet-like pressed product (d'-1) after the adhesive component (d-1) is pressed at 170°C for 30 minutes is preferably rub 1.0×10 4 Pa~1.0×10 8 Pa. Rubber-like flat area E' of the sheet-like pressing process (d'-1) rub Within the above range, the conductive filler-rich layer (D) can be given excellent mechanical strength, and damage to the sheet when deformed can be suppressed. Rubber-like flat region E' of the sheet-shaped pressed product (d'-1) rub More preferably, 1.0×10 5 Pa~1.0×10 8 Pa.

[0156] In this specification, the rubber-like flat area E' of the sheet-like pressed object (d'-1) rub It is defined as the average value of the storage elastic coefficient of the sheet-like pressed product (d'-1) at 150° C. to 200° C. The storage elastic coefficient of the sheet-like pressed product (d'-1) at each temperature can be determined using a dynamic viscoelasticity measuring device or the like.

[0157] Compared to using an adhesive layer (A) having a relative permittivity and dielectric loss tangent within the specific ranges, the highly conductive filler-filled layer (D) having a relative permittivity and dielectric loss tangent within the specific ranges is positioned farther from the signal wiring of a printed circuit board such as an FPC. While the effect is less pronounced, a transmission loss reduction effect can still be achieved. From the perspective of more effectively reducing transmission loss, it is more preferable that the pressed product (a'-1) and pressed product (d'-1) of the adhesive component (a-1) and the adhesive component (d-1) each have a relative permittivity of 1.0 to 3.5 and a dielectric loss tangent of 0.0001 to 0.02 at 23°C and a frequency of 28 GHz.

[0158] The preferred content of the hardener relative to 100 parts by mass of the thermosetting resin can be designed as appropriate, but is preferably 1 to 50 parts by mass. This range allows for an appropriate crosslinking density, maintaining good hygroscopicity and adhesion. Furthermore, the elastic modulus of the cured product can be appropriately maintained, resulting in good folding resistance. The hardener content is more preferably 3 to 40 parts by mass, and even more preferably 3 to 30 parts by mass, relative to 100 parts by mass of the thermosetting resin.

[0159] When bonding this sheet to a printed circuit board such as an FPC, heat resistance sufficient to withstand heating in a reflow oven or the like is required. In such cases, it is preferred that the adhesive component (d-1) contain a thermosetting resin and a curing agent, and that the highly conductive filler-filled layer (D) after bonding this sheet to the adherend serve as the cured layer.

[0160] (Conductive filler (d-2))

[0161] From the viewpoint of maintaining good shielding properties, the conductive filler (d-2) is preferably a metal particle. Alternatively, composite fine particles having a metal or resin core and a coating layer covering the surface of the core with the metal may be used.

[0162] Specific examples of metal particles include gold, platinum, silver, copper, nickel, aluminum, tin, palladium, chromium, titanium, zinc, manganese, and indium. Of these, metals selected from the group consisting of gold, platinum, silver, copper, nickel, aluminum, tin, palladium, chromium, titanium, and zinc are preferred for maintaining good shielding properties. The metal particles may be a single type or a mixture of multiple types, or may be alloys. Furthermore, the metal may be the same as or different from the metal used in the metal layer (C).

[0163] The shape of the conductive filler (d-2) is not limited as long as electromagnetic shielding properties such as shielding properties and easy deformability are achieved in the highly filled conductive filler layer (D). Examples include spheres, flakes, dendrites, plates, needles, rods, and grapes. Two or more conductive fillers (d-2) of different shapes may also be mixed. Preferred examples include flaky particles. The flaky particles may further include leaf-shaped particles having multiple cutouts at their outer edges (e.g., particles obtained by flattening dendrite-shaped particles). The aspect ratio of the flaky particles is not limited, but preferably the aspect ratio ([average major diameter (μm)] / [average thickness (μm)]) is in the range of 1.1 to 500.

[0164] (Other ingredients)

[0165] A solvent may be suitably used in the conductive filler-containing composition used to form the highly conductive filler-filled layer (D). In addition to the aforementioned components, optional ingredients such as silane coupling agents, curing aids, rust inhibitors, reducing agents, antioxidants, pigments, dyes, tackifier resins, plasticizers, UV absorbers, defoamers, leveling agents, fillers, and flame retardants may be added for the purpose of improving desired physical properties or imparting desired functions.

[0166] [Protective layer (E)]

[0167] This sheet may further include a protective layer (E) laminated on the shielding layer (B). The protective layer (E) protects the shielding layer (B) or the adhesive layer (A) and prevents electrical connection between the shielding layer (B) and an external conductor.

[0168] The protective layer (E) can be formed using a resin composition. The resin composition includes a binder component (e-1) containing a resin. Preferred examples of the resin include thermoplastic resins and thermosetting resins. The thermosetting resin can be a self-crosslinking resin that cures on its own, but is preferably used in combination with a hardener. Either the thermoplastic resin or the thermosetting resin can be used alone or in combination. In this specification, the protective layer (E) is referred to both before and after bonding to the adherend.

[0169] From the perspective of improving press workability, the sheet-like pressed product (e'-1) obtained by pressing the binder component (e-1) of the protective layer (E) at 170°C for 30 minutes preferably has a breaking strength of 15 MPa or greater. It is more preferably 17 MPa or greater, and even more preferably 20 MPa or greater. The upper limit of the breaking strength is not particularly limited, but is typically 50 MPa or less.

[0170] From the perspective of press workability, the elongation at break of the pressed sheet (e'-1) after pressing the binder component (e-1) of the protective layer (E) at 170°C for 30 minutes is preferably 80% or higher. It is more preferably 150% or higher, and even more preferably 200% or higher. The upper limit of the elongation at break is not particularly limited, but is generally 5000% or lower.

[0171] From the perspective of improving press workability, it is preferred that the loss tangent peak of the pressed sheet (e'-1) in the range of 0°C to 300°C, after the binder component (e-1) of the protective layer (E) is press-treated at 170°C for 30 minutes, be 0.1 or higher. A loss tangent peak of 0.1 or higher in the range of 0°C to 300°C effectively absorbs and mitigates stress during press working, thereby improving press workability. The loss tangent peak of the pressed sheet (e'-1) in the range of 0°C to 300°C is more preferably 0.3 or higher.

[0172] The loss tangent of the sheet-like pressed product (e'-1) can be calculated using the following formula (3). The loss tangent at each temperature in the range of 0°C to 300°C is plotted, and the maximum loss tangent value is defined as the peak. The loss modulus and storage modulus of the sheet-like pressed product (e'-1) can be calculated by dynamic viscoelasticity measurement.

[0173] Equation (3):

[0174] (Loss tangent of sheet-like pressed material (e'-1)) =

[0175] (Loss elastic coefficient of the sheet-like pressed object (e'-1)) / (Storage elastic coefficient of the sheet-like pressed object (e'-1))

[0176] The content of the hardener can be appropriately designed, but is preferably 1 to 50 parts by mass per 100 parts by mass of the thermosetting resin. By setting this range, the crosslinking density can be adjusted appropriately, maintaining good hygroscopicity and adhesion. Furthermore, the elastic modulus of the cured product can be appropriately maintained, resulting in good stamping properties. The hardener content is more preferably 3 to 40 parts by mass, and more preferably 3 to 30 parts by mass, per 100 parts by mass of the thermosetting resin.

[0177] When bonding this sheet to components such as FPCs, heat resistance is required to withstand heating in a reflow oven, etc. In such cases, it is preferable to include a thermosetting resin and a curing agent in the adhesive component (e-1), and to use the protective layer (E) after bonding this sheet to the adherend as a cured layer.

[0178] (Other optional ingredients)

[0179] A solvent can be used as appropriate for the protective layer (E). Furthermore, non-conductive particles may be included as an optional component. These particles enhance the insulating properties of the protective layer (E), increase the pressing force of the sheet against adherends such as FPCs during hot pressing, and improve connectivity with ground wiring. Furthermore, thermally conductive particles may be used to enhance heat dissipation.

[0180] Examples of non-conductive particles include non-conductive ceramics, pigments, and dyes. Ceramics are preferred because they have high hardness and can be transferred to the metal layer without relaxing the pressure applied during hot pressing. Among non-conductive particles, those with a volume resistivity of 1.0×10 10 The volume resistivity of the non-conductive particles is 1.0×10 10 Ω·cm or more, the insulation properties of the protective layer (E) can be further improved. The volume resistivity of the substance contained in the non-conductive particles is more preferably 1.0×10 12 Ω·cm or more, more preferably 1.0×10 14 Ω·cm or more. As volume resistivity is 1.0×10 10 Materials with a resistivity of Ω·cm or higher include ceramics such as aluminum oxide or aluminum trioxide (alumina), zirconium dioxide (zirconia), silicon dioxide (silica), boron carbide, aluminum nitride, boron nitride, magnesium oxide (magnesia), and titanium oxide. Among them, zirconium dioxide (ZrO2; volume resistivity of 1.0×10 12 Ω·cm), and the preferred material is silicon dioxide (SiO2; volume resistivity is 1.0×10 14 Ω·cm). The volume resistivity of the substance contained in the non-conductive particles can be measured in accordance with Japanese Industrial Standards (JIS) C2141. The shape of the non-conductive particles is not limited, and examples thereof include agglomerates, irregular shapes, substantially spherical shapes, spherical shapes, and spherical shapes.

[0181] Pigments may be added to color the protective layer (E) as long as they do not interfere with its function. Examples of pigments include carbon black, carbon graphite, carbon nanotubes, and graphene. Other optional components of the protective layer (E) include silane coupling agents, rust inhibitors, reducing agents, antioxidants, tackifiers, plasticizers, UV absorbers, defoamers, leveling agents, fillers, and flame retardants.

[0182] The thickness of the protective layer (E) is preferably 2 μm to 20 μm. A thickness of the protective layer (E) of 2 μm to 20 μm can suppress dissolution of the protective layer (E) or peeling from the metal layer after exposure to cleaning chemicals.

[0183] (any other layer)

[0184] The sheet may further include other functional layers. Examples of other functional layers include layers having functions such as hard coating, water vapor barrier, oxygen barrier, thermal conductivity, low dielectric constant, high dielectric constant, or heat resistance.

[0185] In order to prevent the adhesion of foreign matter, this sheet is generally stored with a release sheet attached to both main surfaces of the adhesive layer (A) and the protective layer (E). The release sheet is a sheet made of a substrate such as paper or plastic that has been subjected to a conventional release treatment.

[0186] [[Method for manufacturing electromagnetic shielding sheet]]

[0187] The following describes an example of a method for producing this sheet. However, the production method of the present invention is not limited to the following method. This sheet comprises: a step of forming an adhesive layer (A); a step of forming a metal layer (C) that functions as a portion of a shielding layer (B); and a step of applying a conductive filler-containing composition comprising a binder component (d-1) and a conductive filler (d-2) to form a highly conductive filler-filled layer (D) that functions as a portion of the shielding layer (B). The content of the conductive filler (d-2) relative to 100% by mass of the highly conductive filler-filled layer (D) is set to 75% to 95% by mass.

[0188] The lamination order of this sheet is adhesive layer (A) / metal layer (C) / conductive filler-rich layer (D). The order of the process steps for each layer is arbitrary. The lamination method of each layer can be performed arbitrarily using existing methods. For example, it is possible to form a sheet by preparing a sheet having a conductive filler-rich layer (D) formed on a protective layer (E) and a metal layer (C) formed on the conductive filler-rich layer (D), and a sheet having an adhesive layer (A) formed on a releasable sheet, and then laminating these sheets in the order of adhesive layer (A) / metal layer (C) / conductive filler-rich layer (D) / protective layer (E).

[0189] (Adhesive Layer (A) Formation Step)

[0190] An adhesive composition for forming the adhesive layer (A) is prepared. Specifically, the adhesive composition can be obtained by mixing and stirring the formulated components. Stirring can be performed using existing stirring devices such as a dispermat or homogenizer. After preparing the adhesive composition, the adhesive layer (A) is formed using existing methods. For example, the adhesive layer (A) can be formed by applying the adhesive composition to a releasable sheet and drying it. Examples of coating methods include gravure coating, kiss coating, die coating, lip coating, notch wheel coating, doctor blade coating, roll coating, knife coating, spray coating, rod coating, spin coating, and dip coating. The drying step can be performed using existing drying devices such as a hot air dryer and an infrared heater. Alternatively, a sheet-shaped adhesive layer (A) can be formed using an extruder such as a T-die.

[0191] (Metal Layer (C) Formation Step)

[0192] The metal layer (C) may be formed using, for example, metal foil, a metal vapor-deposited film, or a metal-plated film. Furthermore, the metal layer (C) may be formed by vacuum deposition, sputtering, chemical vapor deposition (CVD), or metal organics (MO). The metal layer (C) may also be formed by integrating one or more conductive fillers. Preferred examples of conductive fillers include flaky particles, dendritic particles, and spherical particles. The conductive fillers may be used alone or in combination of two or more. Examples of methods include forming the metal layer (C) on a highly-filled conductive filler layer (D).

[0193] Conventional methods can be applied to control the root mean square slope Sdq of the metal layer (C). Examples include: polishing the metal surface using a buff as described in Japanese Patent Application Laid-Open No. 2017-13473; polishing the metal surface using abrasive cloth; forming the metal layer (C) on a carrier material having a predetermined root mean square slope Sdq and transferring the surface irregularities of the carrier material to the metal layer (C); and press-bonding a film having a predetermined root mean square slope Sdq to the metal layer (C) to transfer the surface irregularities of the film to the metal layer (C).

[0194] By setting the thickness of the metal layer (C) to approximately 0.05 μm to 2 μm, for example, it is possible to easily form air-permeable micropores simultaneously with the formation of the metal layer (C) without requiring a separate pore-forming step. However, a separate pore-forming step may also be employed. Existing methods can be applied to the pore-forming process. Examples include: a method of forming a patterned resist layer on the metal layer (C) and forming pores at the desired locations; a method of screen-printing an anchor agent in a predetermined pattern and then metal-plating the surface where the anchor agent was printed; and the method described in Japanese Patent Application Laid-Open No. 2015-63730.

[0195] (Step of Forming the Highly Conductive Filler-Filled Layer (D))

[0196] A composition containing a conductive filler is prepared for forming the highly conductive filler-filled layer (D). Specifically, the conductive filler-containing composition can be obtained by mixing predetermined amounts of the formulated components and stirring. Stirring can be performed, for example, using the same stirring apparatus as used for the adhesive layer (A). After preparing the conductive filler-containing composition, the highly conductive filler-filled layer (D) is formed using conventional methods. For example, the highly conductive filler-filled layer (D) can be formed by applying the conductive filler-containing composition onto a releasable sheet and drying it. Alternatively, the highly conductive filler-filled layer (D) can be formed by applying it onto a protective layer (E) and drying it. Preferred examples of coating and drying methods include the coating examples described for the adhesive layer (A).

[0197] (Protective Layer (E) Formation Step)

[0198] A resin composition for forming the protective layer (E) is prepared. Specifically, the resin composition can be obtained by mixing and stirring the formulated components. Stirring can be performed, for example, using the same stirring device as used for the adhesive layer (A). After preparing the resin composition, the protective layer (E) is formed using existing methods. For example, the protective layer (E) can be formed by applying the resin composition on a removable sheet and drying it. Preferred examples of the coating method and drying method include the coating example described for the adhesive layer (A). Alternatively, the resin composition can be extruded into a sheet using an extruder such as a T-die. The protective layer (E) can also be formed using a film formed from an insulating resin such as polyester, polycarbonate, polyimide, polyamideimide, polyamide, polyphenylene sulfide, or polyetheretherketone.

[0199] [[Shielded wiring board]]

[0200] An example of the main part of the shielded wiring board according to the embodiment of the present invention is shown in FIG. Figure 2 .like Figure 2As shown, the shielding wiring substrate 20 includes a wiring circuit board 10 and an electromagnetic shielding sheet 2. The wiring circuit board 10 includes an insulating base 11, a circuit pattern 12 formed on the insulating base 11, and an overcoat layer 13 formed on the insulating base 11 and the circuit pattern 12. The electromagnetic shielding sheet 2 is bonded to the insulating base 11 using the adhesive layer (A) of this sheet.

[0201] The electromagnetic wave shielding sheet 2 only needs to be attached to the printed circuit board 10, and the bonding area can be appropriately designed. Figure 2 In the example of , the adhesive layer (A) of this sheet is used to bond to the outer coating layer 13. Figure 2 In this example, the electromagnetic shielding sheet 2 comprises a four-layer structure: bonding layer (A'), metal layer (C), conductive filler-rich layer (D), and protective layer (E). The bonding method is arbitrary, but typically involves thermocompression bonding. Through thermocompression bonding, a portion of the adhesive layer (A) is filled within the via 14 provided in the overcoat layer 13, and the via 14 is then bonded to the exposed surface of the ground wiring 12b.

[0202] The insulating substrate 11 has the function of serving as a support for the circuit pattern 12. The insulating substrate 11 is not particularly limited. Examples of preferred resins when flexibility is required include polyester, polycarbonate, polyimide, and polyphenylene sulfide. When considering the use of a wiring circuit substrate for transmitting high-frequency signals, a resin having a low relative dielectric constant and a low dielectric loss tangent is preferred. Among the resins listed as examples of preferred resins, a resin classified as a liquid crystal polymer is further preferred. So-called liquid crystal polymers refer to polymers that exhibit liquid crystallinity when heated and melted. In the case of a rigid insulating substrate, glass epoxy having excellent heat resistance is preferred.

[0203] The circuit pattern 12 includes a signal wiring 12a and a ground wiring 12b. The circuit pattern 12 is formed, for example, from a copper layer having a thickness of several μm to several tens of μm. The signal wiring 12a can be applied to, for example, a single-ended transmission line including one signal wiring or a differential transmission line including two signal wirings. Because a differential transmission line uses two signal wirings, currents of opposite phases flow through them, and the potential difference between the signal wirings is read, the effects of electromagnetic noise applied to the signal wirings are reduced. Combining this with the electromagnetic shielding sheet of the present invention allows for more stable signal transmission. Therefore, it is preferred to use a differential transmission line for the signal wiring 12a.

[0204] The outer coating 13 is an insulating material that covers the circuit pattern 12 of the shielded wiring substrate 20 and protects it from the external environment. The outer coating 13 can be appropriately selected from existing insulating materials. Preferably, it is a resin with heat resistance and flexibility, such as polyimide. As preferred examples, there are polyimide films with thermosetting adhesives, thermosetting or ultraviolet curing solder resists, and photosensitive covering films. The thickness of the outer coating 13 is generally about 10 μm to 100 μm. The opening area of the passage 14 is not particularly limited, but from the perspective of miniaturization of the shielded wiring substrate 20, it is preferably 0.8 mm 2 The lower limit is not particularly limited, but is, for example, 0.008 mm. 2 above.

[0205] This sheet is typically bonded to the wiring circuit board 10 of a shielded wiring board by hot pressing, for example, at a temperature of approximately 150°C to 190°C, a pressure of approximately 1 MPa to 3 MPa, and a time of approximately 1 to 60 minutes. Hot pressing brings the adhesive layer (A) into close contact with the overcoat layer 13, and the adhesive layer (A) flows, forming a bonding layer (A') that fills the vias 14 formed in the overcoat layer 13. If the bonding layer (A') exhibits conductivity, electrical conduction is established between the ground wiring 12b and the electromagnetic shielding sheet 2. If the adhesive component of any or all of the adhesive layer (A), the highly conductive filler-filled layer (D), and the protective layer (E) contains a thermosetting resin, the corresponding layer becomes a hardened layer through hot pressing and / or curing. An example of such curing is post-curing at approximately 150°C to 190°C for 30 to 90 minutes after hot pressing.

[0206] To more effectively suppress electromagnetic wave leakage, electromagnetic shielding sheets 2 can be provided on both surfaces of the wired circuit board 10. In the shielded wired circuit board 20, the electromagnetic shielding sheets 2 not only shield electromagnetic waves but also function as a ground circuit. By using the electromagnetic shielding sheets 2 as a ground circuit, the ground circuit area of the wired circuit board 10 can be reduced, thereby achieving miniaturization and cost reduction. Example

[0207] The present invention will be described in more detail below. However, the following examples do not limit the scope of the present invention in any way. In the examples, "parts" and "%" represent "parts by mass" and "mass %," respectively, and Mw refers to the weight-average molecular weight. The amounts in the tables are in parts by mass. The acid value, weight-average molecular weight (Mw), and glass transition temperature (Tg) of the resin, as well as the average particle size of the conductive filler, were measured using the following methods.

[0208] Determination of the acid value of the resin used as an adhesive component

[0209] Acid value is measured in accordance with JIS K0070. Approximately 1 g of sample is accurately weighed into a stoppered Erlenmeyer flask and dissolved in 100 mL of a mixture of tetrahydrofuran and ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1). Phenolphthalein solution is added as an indicator and titrated with 0.1 N alcoholic potassium hydroxide solution. The endpoint is determined when the indicator remains light red for 30 seconds. The acid value (unit: mgKOH / g) is calculated using the following formula.

[0210] Acid value (mgKOH / g) = (5.611×a×F) / S

[0211] in,

[0212] S: Sample quantity (g)

[0213] a: Consumption of 0.1N alcoholic potassium hydroxide solution (mL)

[0214] F: Titer of 0.1N alcoholic potassium hydroxide solution

[0215] Determination of the weight average molecular weight (Mw) of the resin used as the binder component

[0216] Mw was measured using a gel permeation chromatograph (GPC) HPC-8020 (manufactured by Tosoh Corporation). GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on their molecular size. The measurement was performed using two LF-604 (Showa Denko Co., Ltd., rapid analysis GPC columns: 6 mm ID x 150 mm) connected in series, at a flow rate of 0.6 mL / min and a column temperature of 40°C. Mw was determined using polystyrene conversion.

[0217] Glass transition temperature (Tg) of the resin used as the binder component

[0218] The Tg was measured by differential scanning calorimetry “DSC-1” (manufactured by Mettler Toledo).

[0219] Conductive Filler D 50 Average particle size determination

[0220] About D 50The average particle size was measured using a laser diffraction-scattering particle size distribution analyzer, LS13320 (Beckman-Coulter). This value was obtained by measuring the conductive filler using a cyclone-dried powder sample module and represents the particle size at the 50th percentile of the cumulative value of the particle size distribution. The refractive index was set to 1.6.

[0221] "raw material"

[0222] The following lists the raw materials used in the Examples and Comparative Examples. Fillers 1 through 3 in the conductive filler (a-2) and fillers 1 through 3 in the conductive filler (d-2) in Tables 1 through 3 correspond to Conductive Fillers 1 through 3, respectively. The same applies to other resins and curing agents.

[0223] Conductive filler 1: composite fine particles (dendritic fine particles in which 100 parts of copper as a core is coated with 10 parts of silver) with an average particle size of D 50 : 11.0 μm (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)

[0224] Conductive filler 2: composite fine particles (spherical fine particles with 100 parts of copper as a core coated with 10 parts of silver) with an average particle size of D 50 : 10.0 μm (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)

[0225] Conductive filler 3: composite fine particles (flaky fine particles with 100 parts of copper as a core coated with 10 parts of silver) with an average particle size of D 50 : 17.0 μm (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.)

[0226] Resin 1: Polyimide resin with an acid value of 6 mgKOH / g, an Mw of 54,000, and a Tg of 7°C (manufactured by Toyo Chem)

[0227] Resin 2: Polyurethane resin with an acid value of 5 mgKOH / g, Mw of 61,000, and a Tg of -5°C (manufactured by Toyo Chem Co., Ltd.)

[0228] Resin 3: Polyester resin with an acid value of 10 mgKOH / g, Mw of 47,000, and Tg of 12°C (manufactured by Toyochem)

[0229] Hardener 1: Epoxy compound, "JER828" (bisphenol A epoxy resin, epoxy equivalent = 189 g / eq, manufactured by Mitsubishi Chemical Corporation)

[0230] [Example 1]

[0231] 《Preparation of Adhesive Layer (A)》

[0232] 100 parts of Resin 1, 39 parts of Conductive Filler 1, and 15 parts of Hardener 1 (Epoxy Compound) were placed in a container, based on solid content. A mixed solvent (toluene:isopropyl alcohol = 2:1 (mass ratio)) was added to achieve a non-volatile content concentration of 40%, and the mixture was stirred for 10 minutes using a disperser to obtain an adhesive composition.

[0233] The obtained adhesive composition was applied to a releasable 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 an adhesive layer (A). The dry thickness was measured using an ABS digital indicator ID-CX (manufactured by Mitutoyo Co., Ltd.).

[0234] 《Production of Highly Conductive Filler Filling Layer (D)》

[0235] 100 parts of Resin 1, 1035 parts of Conductive Filler 3, and 15 parts of Hardener 1 (Epoxy Compound) were placed in a container, and a mixed solvent (toluene:isopropyl alcohol = 2:1 (mass ratio)) was added to achieve a non-volatile content concentration of 40%. The mixture was stirred for 10 minutes using a disperser to obtain a conductive filler-containing composition.

[0236] The resulting conductive filler-containing composition was applied to a releasable sheet using a bar coater to a dry thickness of 10 μm and dried in a 100°C electric oven for 2 minutes to obtain a highly conductive filler-filled layer (D). The dry thickness of the highly conductive filler-filled layer (D) was measured using the same method as for the adhesive layer (A).

[0237] 《Production of Metal Layer (C) and Shielding Layer (B)》

[0238] A metal layer (C) was formed by vacuum copper deposition on the exposed surface of the highly conductive filler-filled layer (D) with a releasable sheet, thereby obtaining a shielding layer (B) with a releasable sheet. The surface roughness (Sdq) of the metal layer (C) on the adhesive layer (A) side was measured using the following method. Measurement data was acquired from the surface of the exposed metal layer (C) using a laser microscope (Keyence VK-X100). The acquired measurement data was loaded into analysis software (Analysis Application "VK-H1XA" with ISO 25178 Surface Texture Measurement Module "VK-H1XR", both manufactured by Keyence) to perform ISO 25178 surface texture measurements (under the following conditions: S-filter: 1 μm, L-filter: 0.2 mm). In addition, regarding the metal layer (C) having openings on its surface, when performing surface property measurement according to ISO 25178, the openings are excluded from the measurement range.

[0239] 《Production of Protective Layer (E)》

[0240] 100 parts of Resin 1 and 15 parts of Hardener 1 (epoxy compound) were added, based on solid content, and stirred for 10 minutes using a disperser to obtain a resin composition. The releasable sheet was removed from the shielding layer (B) with a releasable sheet, and the resulting resin composition was applied to the exposed surface of the highly conductive filler layer (D) using a bar coater to a dry thickness of 5 μm. The composition was then dried in a 100°C electric oven for 2 minutes to obtain a protective layer (E). A slightly adhesive releasable sheet was then attached to the protective layer (E) to obtain the electromagnetic shielding sheet of Example 1. The dry thickness was measured using the same method as for the adhesive layer (A).

[0241] [Examples 2 to 30, Comparative Examples 1 to 5]

[0242] As shown in Tables 1 to 3, the same procedures as in Example 1 were followed, except that the types of adhesive layer (A), metal layer (C), highly conductive filler-filled layer (D), and protective layer (E) were changed. Electromagnetic shielding sheets of Examples 2 to 30 and Comparative Examples 1 to 5 were obtained, respectively. The conductive filler content is the percentage per 100% by mass of each layer.

[0243] [Comparative Example 6]

[0244] An electromagnetic shielding sheet of Comparative Example 6 was obtained by the same method as in Example 1 except that the components shown in Table 3 were used and the adhesive layer (A), the conductive filler-rich layer (D), the metal layer (C), and the protective layer (E) were laminated in this order.

[0245] Determination of the thickness of the metal layer (C) after hot pressing

[0246] The thickness of the metal layer (C) is measured by the following method.

[0247] The release sheet on the adhesive layer (A) side of the electromagnetic shielding sheet was peeled off, and the exposed adhesive layer (A) was laminated to a polyimide film (Kapton 200EN, manufactured by Toray-Dupont) and hot-pressed at 2 MPa and 170°C for 30 minutes. The sheet was cut into pieces approximately 5 mm wide and 5 mm long. 0.05 g of epoxy resin (Petropoxy 154, manufactured by Maruto) was then dropped onto a glass slide and bonded to the electromagnetic shielding sheet, resulting in a laminate structure consisting of glass slide / electromagnetic shielding sheet / polyimide film. The resulting laminate was cut from the polyimide film side using an ion beam irradiation machine (SM-09010, manufactured by JEOL Ltd.) to obtain a measurement sample of the heat-pressed electromagnetic shielding sheet.

[0248] The cross-section of the obtained measurement sample was observed using a laser microscope (Keyence VK-X100). The thickness of the metal layer (C) after hot pressing was measured based on the magnified image obtained. The magnification was set at 500x to 2000x. The following evaluations were performed using the obtained electromagnetic shielding sheet. The results are shown in Tables 4 and 5.

[0249] 《Relative dielectric constant (ε) and dielectric loss tangent (tanδ) of the pressed object (a'-1)》

[0250] The resin and hardener contained in the adhesive component (a-1) of the adhesive layer (A) in each example and comparative example were added to a mixed solvent (toluene:isopropyl alcohol = 2:1 (mass ratio)) and stirred in a disperser for 10 minutes to obtain an adhesive composition (adhesive component (a-1)). The adhesive composition was then applied to a releasable sheet to a dry thickness of 25 μm and dried in a 100°C electric oven for 2 minutes to obtain an adhesive sheet with a releasable sheet. The releasable sheet was then peeled from the resulting adhesive sheet with a releasable sheet, and four sheets were stacked using a vacuum heat laminator. Heat-treated at 170°C for 30 minutes, the sheets were then cut into 50 mm squares to obtain test pieces with a thickness of 100 μm. The test pieces were stored at 23°C and 50% relative humidity for at least 24 hours. The relative dielectric constant and dielectric loss tangent were determined using a cavity resonator method using a dielectric constant measuring instrument manufactured by AET. The relative dielectric constant (ε) and dielectric loss tangent (tanδ) of the compression-treated sample (d'-1) were also determined using the same method.

[0251] Rubber-like flat area E' of the sheet-like pressed object (d'-1) rub , loss tangent, and loss tangent of sheet-shaped pressed material (e'-1)

[0252] The resin and hardener contained in the binder component (d-1) of the highly conductive filler-filled layer (D) in each Example and Comparative Example were added to a mixed solvent (toluene:isopropyl alcohol = 2:1 (mass ratio)) and stirred in a disperser for 10 minutes to obtain each binder component (d-1). The binder component (d-1) was applied to a releasable sheet using a bar coater to a dry thickness of 30 μm. The sheet was then dried in an electric oven at 100°C for 2 minutes and subjected to a press treatment at 170°C for 30 minutes at 2 MPa. The releasable sheet was then peeled off to obtain a pressed sheet (d'-1) for measuring breaking strength and breaking elongation. The center of the pressed sheet (d'-1) was cut into pieces 5 mm wide and 30 mm long to prepare a sample. The sample was placed in a dynamic viscoelasticity measuring apparatus (Dynamic Viscoelasticity Measuring Apparatus DVA-200, manufactured by IT Measurement Control Co., Ltd.) and subjected to dynamic viscoelasticity measurement under the following conditions: a measuring temperature range of -30°C to 300°C, a heating rate of 10°C / min, a measuring frequency of 1 Hz, and a strain of 0.08%. The loss elastic coefficient E'' and storage elastic coefficient E' at each temperature were read. The average value of the storage elastic coefficients obtained within the range of 150°C to 200°C was calculated as the rubbery flat area E'. rubIn addition, the loss tangent at each temperature was calculated by dividing the loss elastic coefficient E'' by the storage elastic coefficient E', and a loss tangent curve was prepared. The maximum point of the obtained loss tangent curve was defined as the loss tangent peak.

[0253] The loss tangent peak of the sheet-shaped pressed product (e′-1) of the binder component (e-1) of the protective layer (E) was also determined by the same method.

[0254] 《Breaking strength and breaking elongation of pressed products (e'-1)》

[0255] The resin and hardener contained in the adhesive component (e-1) of the protective layer (E) in each example and comparative example were added to a mixed solvent (toluene:isopropyl alcohol = 2:1 (mass ratio)) and stirred in a disperser for 10 minutes to obtain the adhesive component (e-1). The adhesive component (e-1) was applied to a releasable sheet using a bar coater to a dry thickness of 30 μm. The sheet was dried in an electric oven at 100°C for 2 minutes and then pressed at 170°C, 2 MPa for 30 minutes. The releasable sheet was then peeled off to obtain a pressed sheet (e'-1) for measuring breaking strength and elongation. The pressed sheet (e'-1) was cut into pieces measuring 20 mm wide by 60 mm long to prepare test specimens. The test specimens were subjected to a tensile test (testing speed 50 mm / min) using a small tabletop tester, EZ-TEST (Shimadzu Corporation), at 25°C and 50% relative humidity. The breaking strength (N / 20 mm) and breaking elongation (%) of the sheet-shaped pressed product (e'-1) were calculated from the obtained SS curve (Stress-Strain curve).

[0256] Rebound force of electromagnetic wave shielding sheets

[0257] Rebound force was evaluated by measuring stiffness according to the test conditions described in JPCA-TM002 8.4.2. A single-sided copper-clad laminate (CCL) with pattern A (L / S: 1.0 mm / 1.0 mm, number of lines: 3 round trips (six lines)) as described in JPCA-TM002 8.4.2 was prepared. An electromagnetic shielding sheet was then cut into pieces 2 cm wide and 6 cm long to prepare a sample. The release sheet on the adhesive layer (A) side of each example and comparative example electromagnetic shielding sheet was removed, and the exposed adhesive layer (A) was placed over the single-sided CCL. The sheets were then pressure-bonded at 170°C, 2 MPa, and 30 minutes. The sheet was then cut into pieces 1.5 cm wide and 3 cm long, and the releasable sheet on the protective layer (E) side was peeled off. The stiffness value was measured under the test conditions described in JPCA-TM002 8.4.2 to determine the repulsive force of the electromagnetic shielding sheet after bonding to the adherend.

[0258] <Pressing workability>

[0259] The stamping workability was evaluated by the method shown below.

[0260] For the electromagnetic shielding sheets with release films obtained in Examples and Comparative Examples, 50 sheets (10 mm × 30 mm) were punched out using a punching machine. The number of defective sheets was counted. The defect rate was calculated using the following formula (4), and the punching workability was evaluated.

[0261] Equation (4):

[0262] (Defective rate) = (Number of defective pieces) / (Total number of pieces after demolding) × 100

[0263] Defective products are those that have burrs (curling) at the ends of the metal layer (C) after being processed into the die-cut shape.

[0264] The evaluation criteria are as follows.

[0265] +++: The defective rate is less than 10%. Excellent.

[0266] ++: The defective rate is 10% or more and less than 15%. Good.

[0267] +: The defective rate is 15% or more and less than 25%. Practical.

[0268] NG: The defect rate is 25% or more. Not practical.

[0269] Curlability

[0270] An electromagnetic wave shielding sheet (length 1000 mm, width 300 mm) with releasable sheets on both sides is prepared. Then, the electromagnetic wave shielding sheet is wound on a 3.0-inch ABS core (manufactured by Showa Maru Co., Ltd.) in a manner that the length direction of the electromagnetic wave shielding sheet is the winding direction, and a roll sample with a length of 300 mm is obtained. The inner side of the roll sample is the adhesive layer (A), and the outer side is the protective layer (E). After the obtained roll sample is exposed to 40°C and 90%RH for 7 days, the electromagnetic wave shielding sheet with a releasable sheet is unwound. Then, the evaluation sample 5 is obtained by cutting it into a size of 100 mm × 100 mm in a manner that the winding direction (length direction) and the width direction are consistent with the direction of each side, with a point 500 mm in the length direction as the center. After that, the evaluation sample 5 is placed on a horizontal table 60 with the protective layer (E) on the lower side and the adhesive layer (A) on the upper side, and the curl rate of the evaluation sample 5 in the length direction (winding direction) is evaluated. Specifically, as Figure 3 As shown, the horizontal distance L of the electromagnetic shielding sheet in the longitudinal direction (winding direction) of the evaluation sample 5 was measured. Then, the curling rate was calculated using the following formula (5).

[0271] Formula (5) Curl ratio =〔(100-L) / 100〕×100(%)

[0272] The obtained curl ratio was evaluated according to the following criteria.

[0273] +++: Curl rate is less than 10%. Excellent.

[0274] ++: The curl rate is 10% or more and less than 20%. Good.

[0275] +: The curl rate is 20% or more and less than 30%. It is practical.

[0276] NG: The curl rate is over 30%. Not practical.

[0277] <Deformability>

[0278] Deformability is the use of Figure 4 The test apparatus shown in the figure was used for evaluation. First, the releasable sheet of the adhesive layer (A) of the electromagnetic shielding sheet was peeled off. A 50 μm-thick polyimide film ("Kapton 200EN" manufactured by Toray-Dupont) was then press-bonded to the adhesive layer (A) at 150°C, 1 MPa, and 30 minutes to obtain an electromagnetic shielding sheet thermocompressed onto the polyimide film. This yielded a test piece (polyimide film / electromagnetic shielding sheet) laminate 42 with a vertical dimension of 10 mm and a horizontal dimension of 100 mm.

[0279] The laminate 42 was placed on a substrate 44 (made of polypropylene). Furthermore, a pair of roughly parallel stainless steel plates (not shown) were placed on the substrate 44 as spacers, and the test piece was placed between these stainless steel plates. The distance between the pair of stainless steel plates was 3 mm, and the thickness of the stainless steel plates was 0.15 mm. The laminate 42 was then bent into a mountain fold at the bend 41a near the center, forming a fold on one side ( Figure 4 The right side of the polyimide film and the left side of the polyimide film / electromagnetic shielding sheet are in a state where the right portion 41c and the left portion 41b on the other side of the bent portion 41a face each other. Figure 4 The outer side of the shield is an electromagnetic shield.

[0280] With the bent test piece placed on substrate 44 as described above, the laminate 42 was pressed from above with a predetermined pressure (0.1 MPa) for 5 seconds via silicone rubber sheet 45. One minute after the pressure was released, the angle θi formed by the line connecting the right portion 41c and the bent portion 41a and the line connecting the left portion 41b and the bent portion 41a was subtracted from the angle θ formed by the line connecting the right portion 41c and the bent portion 41a. The resulting angle was measured as the return angle and evaluated according to the following evaluation criteria.

[0281] +++: The return angle is less than 10°, and there are no cracks or other defects in the bent area. Excellent.

[0282] ++: The return angle is 10° or more and less than 30°, and there are no defects such as cracks in the bent part. Good.

[0283] +: The return angle is 30° or more and less than 60°, and there are no cracks or other defects in the bending part. It is practical.

[0284] NG: The return angle is 60° or more, or there is a crack at the bend, resulting in an appearance defect. This product is not suitable for practical use.

[0285] Transmission Characteristics

[0286] The transmission characteristics were evaluated using a wiring circuit board with a coplanar circuit and an electromagnetic wave shielding sheet. A schematic plan view of the main surface side of the flexible printed wiring board 15 with a coplanar circuit (hereinafter also referred to as a wiring circuit board with a coplanar circuit) used in the measurement is shown in FIG. Figure 5 , a schematic plan view of the back side is shown in Figure 6. First, prepare a double-sided CCL "R-F775" (manufactured by Panasonic) in which a rolled copper foil with a thickness of 12 μm is laminated on both sides of a polyimide film 50 with a thickness of 50 μm. Then, six through holes 52 (diameter 0.1 mm) are provided near each of the four corners of the rectangular shape. In addition, for the sake of convenience of illustration, only two through holes 52 are shown at each corner. Then, after the electroless plating treatment, the electrolytic plating treatment is performed to form a 10 μm copper-plated film 51, and the conduction between the main surface and the back is ensured through the copper-plated film formed in the through hole 52. Thereafter, as Figure 5 As shown, two signal wirings 53 with a length of 10 cm are formed on the main surface of the polyimide film 50, and a ground wiring 54 is formed on the outside thereof in parallel with the signal wiring 53, and a ground pattern 55 is formed in an area extending from the ground wiring 54 and including a through hole 52 in the short side direction of the polyimide film 50.

[0287] Thereafter, the copper foil formed on the back surface of the polyimide film 50 is etched to obtain a copper foil at a position corresponding to the ground pattern 55. Figure 6 The back side ground pattern 56 is shown. The inspection standards for the appearance and tolerance of the circuit are set to the Japan Electronics Packaging and Circuit Association (JPCA) standard (JPCA-DG02). Next, an overcoat 8 "CISV1215 (Nikkan Industries Co., Ltd.)" consisting of a polyimide film (thickness 12.5 μm) and an insulating adhesive layer (thickness 15 μm) is attached to the main surface side of the polyimide film 50. In addition, Figure 5 In the figure, the outer coating layer 8 is shown in a perspective view so as to clarify the structure of the signal wiring 53, etc. After that, the copper foil pattern exposed from the outer coating layer 8 is nickel-plated (not shown) and then gold-plated (not shown).

[0288] Next, if Figure 7 As shown, an electromagnetic shielding sheet comprising a laminate of an adhesive layer (A), a shielding layer (B), and a protective layer (E) was prepared, and a release sheet (not shown) provided on the adhesive layer (A) was peeled off. Subsequently, the electromagnetic shielding sheet was pressure-bonded, with the adhesive layer (A) of the electromagnetic shielding sheet facing inward, to the entire back side of a printed circuit board 15 having a coplanar circuit at 170°C, 2.0 MPa, and 30 minutes. This yielded shielded printed circuit boards 21 having a coplanar circuit and an electromagnetic shielding layer, each comprising the electromagnetic shielding sheet 6 of each example and comparative example. Figure 7 , the back-side ground pattern 56 is shown in a perspective view.

[0289] The L / S (line / space) of the signal wiring 53 was appropriately adjusted so that the characteristic impedance was ±10 Ω. The width of the ground wiring 54 was 100 μm, and the distance between the ground wiring 54 and the signal wiring 53 was 1 mm.

[0290] A network analyzer E5071C (manufactured by Agilent Japan) was connected to the exposed signal line 53 of a shielded wiring substrate 21 with a coplanar circuit and an electromagnetic shielding sheet. A 15 GHz sine wave was input and the transmission loss was measured to evaluate the transmission characteristics. The measured transmission characteristics were evaluated according to the following criteria.

[0291] +++: Transmission loss at 15 GHz is less than 7.0 dB. Excellent.

[0292] ++: Transmission loss at 15 GHz is 7.0 dB or higher and less than 7.5 dB. Good.

[0293] +: Transmission loss at 15 GHz is 7.5 dB or more and less than 8.0 dB. Practical.

[0294] NG: Transmission loss at 15 GHz is 8.0 dB or more. Impractical.

[0295] Breathability

[0296] A test piece consisting of an electromagnetic shielding sheet laminated onto a copper-clad laminate simulating a printed circuit board is exposed to molten solder, and the air permeability of the sample is evaluated by observing whether the appearance of the sample changes. An electromagnetic shielding sheet with high air permeability efficiently allows outgassing, such as water vapor, generated from the printed circuit board to escape, thus maintaining its appearance. However, an electromagnetic shielding sheet with low air permeability cannot efficiently escape outgassing, resulting in bubbling or peeling.

[0297] First, the release sheet of the adhesive layer (A) of a 25 mm wide, 70 mm long electromagnetic shielding sheet was peeled off. The exposed adhesive layer (A) was then pressure-bonded to the gold-plated surface of a 64 μm thick, gold-plated copper-clad laminate (gold plating 0.3 μm / nickel plating 1 μm / copper foil 18 μm / adhesive 20 μm / polyimide film 25 μm) at 170°C, 2.0 MPa, and heat-cured for 30 minutes to produce a laminate. The resulting laminate was cut into pieces 10 mm wide and 65 mm long to prepare samples. The resulting samples were left in an environment of 40°C and 90% RH for 72 hours. Then, the samples were floated, polyimide film side down, on molten solder at 250°C for 1 minute. The removed samples were visually inspected for appearance and evaluated according to the following criteria.

[0298] +++: No visual changes or defects in appearance were observed. Excellent.

[0299] ++: The range of defective appearance is 10% or less of the protective layer (E) area in the sample. Good.

[0300] +: The area of defective appearance is greater than 10% and less than 30% of the protective layer (E) area in the sample. Practical application possible.

[0301] NG: The area of poor appearance exceeds 30% of the protective layer (E) area in the sample.

[0302] <High-frequency shielding>

[0303] The electromagnetic shielding sheet was sandwiched between removable films and hot-pressed (cured) at 170°C for 30 minutes at a pressure of 2 MPa. The removable films were then removed and the resulting material was used as a test sample. High-frequency shielding performance was measured in accordance with American Society for Testing and Materials (ASTM) D4935 using a coaxial tube-type shielding effectiveness measurement system manufactured by Keycom. Electromagnetic waves were irradiated at frequencies between 100 MHz and 15 GHz. The attenuation of electromagnetic waves in the electromagnetic shielding sheet was measured and evaluated according to the following criteria. The measured attenuation value is expressed in decibels (dB).

[0304] +++: Attenuation when irradiated with 15 GHz electromagnetic waves is less than -55 dB. Excellent.

[0305] ++: Attenuation when exposed to 15 GHz electromagnetic waves is -55 dB or higher and less than -50 dB. Good.

[0306] +: The attenuation when irradiated with 15 GHz electromagnetic waves is -50 dB or more and less than -45 dB. Practical application possible.

[0307] NG: The attenuation when exposed to 15 GHz electromagnetic waves is -45 dB or more. This is not practical.

[0308] [Table 1]

[0309] [Table 2]

[0310] [Table 3]

[0311] [Table 4]

[0312] [Table 5]

[0313] According to the present invention, as shown in this embodiment, it is possible to provide an electromagnetic shielding sheet that can suppress curling and burring and has electromagnetic shielding properties, easy deformability, and air permeability.

[0314] Industrial applicability

[0315] This electromagnetic wave shielding sheet can be used not only in FPCs but also in rigid printed wiring boards, chip-on-film (COF), tape automated bonding (TAB), flexible connectors, liquid crystal displays, touch screens, and other applications. Furthermore, it can be used in a wide range of applications requiring electromagnetic wave shielding, such as personal computer housings, building materials such as walls and window panes, and electromagnetic wave blocking components in vehicles, ships, and aircraft. The shielding wiring board of the present invention can be used in electronic devices such as laptop computers, mobile phones, smartphones, and tablet computers, in addition to being mounted on liquid crystal displays and touch screens.

Claims

1. An electromagnetic wave shielding sheet comprising an adhesive layer (A), a shielding layer (B) laminated on the adhesive layer (A), and a protective layer (E) laminated on the shielding layer (B). The shielding layer (B) comprises a metal layer (C) laminated on the adhesive layer (A), and a highly conductive filler-filled layer (D) containing a binder component d-1 and a conductive filler d-2 and laminated on the metal layer (C). No metal layer is formed on the side of the conductive filler-rich layer (D) opposite to the side on which the metal layer (C) is formed. The content of the conductive filler d-2 is 75% to 95% by mass relative to 100% by mass of the conductive filler-rich layer (D). The protective layer (E) comprises an adhesive component e-1, and a sheet-like pressed product e'-1 after a pressing process at 170° C. for 30 minutes has a breaking strength of 15 MPa or more. The adhesive layer (A) contains a binder component a-1, The relative dielectric constant of the pressed product a'-1 obtained by press-treating the adhesive component a-1 at 170°C for 30 minutes was 1.0 to 3.5 at 23°C and a frequency of 28 GHz, and the dielectric loss tangent of the pressed product a'-1 was 0.0001 to 0.02 at 23°C and a frequency of 28 GHz.

2. The electromagnetic shielding sheet according to claim 1, wherein The adhesive layer (A) contains a conductive filler a-2, The content of the conductive filler d-2 is 84% to 95% by mass relative to 100% by mass of the conductive filler-rich layer (D). The content of the conductive filler a-2 is 15% by mass to 45% by mass relative to 100% by mass of the adhesive layer (A).

3. The electromagnetic shielding sheet according to claim 1, wherein The repulsive force of the pressed object after the pressing process was performed at 170° C. for 30 minutes was 0.01 mN / cm to 30 mN / cm.

4. A shielded wiring substrate comprising: a wiring circuit substrate comprising an insulating base material, a circuit pattern formed on the insulating base material, and an overcoat layer formed on the insulating base material and the circuit pattern; and Electromagnetic wave shielding sheet, The electromagnetic shielding sheet is bonded to the overcoat layer using the adhesive layer (A) of the electromagnetic shielding sheet according to any one of claims 1 to 3 . 5 . An electronic device comprising the shielded wiring substrate according to claim 4 .

6. A method for manufacturing an electromagnetic shielding sheet, the electromagnetic shielding sheet comprising a laminated structure of an adhesive layer (A) and a shielding layer (B), the method comprising: A step of forming an adhesive layer (A); A step of forming a metal layer (C) that functions as a part of the shielding layer (B); a step of applying a conductive filler-containing composition comprising a binder component d-1 and a conductive filler d-2 to form a highly conductive filler-filled layer (D) functioning as a part of the shielding layer (B); and A step of forming a protective layer (E) laminated on the shielding layer (B), wherein the protective layer (E) comprises an adhesive component e-1, wherein the adhesive component e-1 is pressed at 170°C for 30 minutes, and a sheet-like pressed product e'-1 has a breaking strength of 15 MPa or more. The conductive filler d-2 content is set to 75% to 95% by mass relative to 100% by mass of the conductive filler-rich layer (D), and the adhesive layer (A), the metal layer (C), and the conductive filler-rich layer (D) are laminated in this order, with no metal layer formed on the side of the conductive filler-rich layer (D) opposite to the side on which the metal layer (C) is formed. The adhesive layer (A) contains a binder component a-1, The relative dielectric constant of the pressed product a'-1 obtained by press-treating the adhesive component a-1 at 170°C for 30 minutes was 1.0 to 3.5 at 23°C and a frequency of 28 GHz, and the dielectric loss tangent of the pressed product a'-1 was 0.0001 to 0.02 at 23°C and a frequency of 28 GHz.

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