JP6650660B2 - Electromagnetic wave shielding sheet for flexible printed wiring board and flexible printed wiring board with electromagnetic wave shielding sheet - Google Patents

Description

  The present invention relates to an electromagnetic wave shielding sheet used by being attached (joined) to a wiring board such as a printed wiring board, and a printed wiring board with an electromagnetic wave shielding layer formed by joining a magnetic wave shielding sheet to a wiring board.

Electronic devices such as digital cameras and mobile phones are becoming smaller and thinner. Accordingly, printed wiring boards mounted on these electronic devices have also been required to be reduced in size and thickness. Further, a printed wiring board generally has an electromagnetic wave shielding layer for reducing noise (hereinafter, a printed wiring board provided with an electromagnetic wave shielding layer is referred to as a "printed wiring board with an electromagnetic wave shielding layer").
In recent years, a wiring circuit (signal wiring) of a printed wiring board has been required to transmit a high-speed and large-capacity signal, and a signal to be passed through the wiring circuit needs to have a higher frequency. Therefore, even when a high-speed digital signal having a frequency of several tens of GHz is used, a high shielding property and a low transmission loss are required.
Furthermore, the international standard “CISPR22” concerning radiated electromagnetic noise (EMI) has been revised, and the upper limit frequency of electromagnetic noise to be suppressed has been expanded from the conventional 1 GHz to 6 GHz, and further measures against electromagnetic noise are required. Have been.

JP 2011-07139 A JP-A-2013-77108

However, the electromagnetic wave shielding sheet of Patent Document 1 has a vapor deposited film as an essential configuration. When a high-frequency signal is passed through a wiring circuit of a printed wiring board with an electromagnetic shielding sheet using an ultra-thin evaporated film of about submicron, conductor loss increases. On the other hand, the electromagnetic wave shield sheet of Patent Document 2 has a metal layer as an essential configuration. For this reason, the electromagnetic wave shielding sheet becomes rigid, and processing adequacy (punching, pressing, etc.) is reduced.
By the way, a printed wiring board with an electromagnetic wave shielding sheet undergoes a lead-free solder reflow process. Further, when the printed wiring board with the electromagnetic wave shielding sheet is placed under high humidity, the insulating layer or the adhesive layer absorbs moisture from the peripheral portion even if it has a vapor deposition film or a metal layer having a high gas barrier property. The water in the adhesive layer volatilizes explosively during short-time heating in the reflow step. When the electromagnetic wave shielding sheet has a vapor-deposited film or a metal layer, there is a problem that the vapor-deposited film or the metal layer becomes a “lid” and foams.

  An object of the present invention is to provide a printed wiring board with an electromagnetic wave shielding sheet that has excellent transmission characteristics and does not foam even when exposed to high temperatures during lead-free solder reflow after moisture absorption.

The present invention is an electromagnetic wave shielding sheet including an insulating layer, a conductive layer, and an adhesive layer,
The conductive layer contains a resin and a conductive filler, and the conductive layer has a surface resistance of 100 [mΩ / □] or less and a conductivity of 1 × 10 ⁶ [S / m] or more. To an electromagnetic wave shielding sheet.

  The present invention also relates to a printed wiring board with an electromagnetic wave shielding sheet, wherein the electromagnetic wave shielding sheet is attached to at least one surface of the printed wiring board.

  Furthermore, the present invention relates to an electronic device using the printed wiring board with the electromagnetic wave shielding sheet described above. It is preferable that the electronic device transmits a signal having a frequency in a range of 1 MHz to 20 GHz.

  According to the present invention, in addition to sufficient adhesive properties, it is possible to provide an electromagnetic wave shielding sheet having excellent transmission characteristics and excellent flexibility and workability, and a print with an electromagnetic wave shielding sheet that does not foam at high temperatures during lead-free solder reflow even if it absorbs moisture. A wiring board can be provided.

The electromagnetic wave shielding film of the present invention includes an insulating layer, a conductive layer, and an adhesive layer. The adhesive layer is located on one surface of the electromagnetic wave shielding film.
First, the insulating layer will be described.
It is preferable to use an insulating resin for the insulating layer. For example, a film formed from an acrylic resin, a urethane resin, a polyester resin, an epoxy resin, a phenol resin, a polycarbonate resin, or the like, or a plastic film such as polyester, polycarbonate, polyimide, or polyphenylene sulfide can be used. Further, two or more insulating layers may be used for the electromagnetic wave shielding film.

  The thickness of the insulating layer can be appropriately designed depending on the application, but is preferably in the range of 0.5 μm to 25 μm, and more preferably 2 μm to 10 μm. When the thickness of the insulating layer is 0.5 μm or more, the insulating property becomes sufficient. When the thickness is 25 μm or less, the flexibility of the flexible printed wiring board with the electromagnetic wave shielding sheet is improved.

  Add silane coupling agent, antioxidant, pigment, dye, tackifier resin, plasticizer, ultraviolet absorber, defoamer, leveling regulator, filler, flame retardant, etc. as necessary in the insulating layer You may.

  Next, the adhesive layer used in the present invention will be described. For the adhesive layer used in the present invention, a thermoplastic resin or a curable resin can be used. The curable resin is preferably a thermosetting resin or a photocurable resin.

  As the thermoplastic resin, polyolefin resin, vinyl resin, styrene / acrylic resin, diene resin, terpene resin, petroleum resin, cellulose resin, polyamide resin, polyurethane resin, polyester resin, polycarbonate resin, polyimide resin, Liquid crystal polymers, fluororesins and the like can be mentioned. Although not particularly limited, a material having a low dielectric constant and a low dielectric loss tangent is preferable from the viewpoint of transmission loss, and a material having a low dielectric constant is preferable from the viewpoint of characteristic impedance, and examples thereof include a liquid crystal polymer and a fluorine-containing resin.

  The thermosetting resin is a functional group that can be used for a crosslinking reaction by heating, for example, a hydroxyl group, a phenolic hydroxyl group, a methoxymethyl group, a carboxyl group, an amino group, an epoxy group, an oxetanyl group, an oxazoline group, an oxazine group, an aziridine group, and a thiol. Any resin having at least one group, isocyanate group, blocked isocyanate group, blocked carboxyl group, silanol group, etc. in one molecule may be used. For example, acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane Resins, epoxy resins, oxetane resins, phenoxy resins, polyimide resins, polyamide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, fluorine resins, and the like. In addition, the thermosetting resin in the present invention may contain a so-called “curing agent” such as a resin or a low-molecular compound that reacts with the above-described functional group to form a chemical crosslink, if necessary, in addition to the above-mentioned resin. preferable.

  The photocurable resin may be any resin having one or more unsaturated bonds in one molecule that cause a cross-linking reaction by light. For example, acrylic resin, maleic acid resin, polybutadiene resin, polyester resin, polyurethane resin, epoxy resin Resin, oxetane resin, phenoxy resin, polyimide resin, polyamide resin, phenolic resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzoxazine resin, silicone resin, fluorine resin and the like.

  The thickness of the adhesive layer can be appropriately designed depending on the application, but is preferably in the range of 0.5 μm to 25 μm, and more preferably 2 μm to 10 μm. When the thickness of the adhesive layer is 0.5 μm or more, the adhesive strength to the printed wiring board can be increased. When the thickness is 25 μm or less, the flexibility of the flexible printed wiring board with the electromagnetic wave shielding sheet is improved.

The adhesive layer is located on one surface of the electromagnetic wave shielding sheet and serves to adhere to a printed wiring board described later.
The adhesive layer is preferably an anisotropic conductive adhesive layer exhibiting conductivity only in the thickness direction or an insulating adhesive. If an anisotropic conductive adhesive layer is used as the adhesive layer and the anisotropic conductive adhesive layer and a conductive layer described later are brought into contact with each other, a special member is used for the ground circuit of the printed wiring board and the conductive layer. It can be electrically connected without using. By using an anisotropic conductive adhesive layer as the adhesive layer, more efficient electrical bonding can be achieved.

The anisotropic conductive adhesive layer contains a resin and a conductive filler H, and preferably contains 30% by mass or less of the conductive filler H. When the thickness of the formed adhesive layer is defined as a reference (100), the size of the conductive filler H is preferably about 100 to 300. By containing 30% by mass or less of the conductive filler H having the above-described size, a conductive adhesive layer that is not isotropic but is anisotropic can be formed.
Examples of the conductive filler H to be used include metal powder such as gold, silver, copper, and nickel; alloy powder such as solder; silver-plated copper powder; metal-plated glass fiber and carbon filler. Of these, silver powder having high conductivity and silver-plated copper powder are preferred.
Examples of the shape of the conductive filler include a sphere, a flake, a dendrite, and a fiber, and a sphere or a dendrite is particularly preferable because anisotropic conductivity is easily obtained.
Examples of the resin used include the same resins as those for forming the insulating layer described above.

Next, the conductive layer used in the present invention will be described. It is important that the conductive layer used in the present invention contains a resin and a conductive filler, has a surface resistance of 100 [mΩ / □] or less, and has a conductivity of 1 × 10 ⁶ [S / m] or more. It is preferable that the surface resistance is as small as possible. Since the conductivity of metals such as gold, silver, and copper is about 5 × 10 ⁷ [S / m], the conductivity of the conductive layer used in the present invention should be as close to 5 × 10 ⁷ [S / m] as possible. preferable.
By setting the surface resistance of the conductive layer to 100 [mΩ / □] or less and the conductivity to 1 × 10 ⁶ [S / m] or more, conductor loss can be reduced and deterioration of the data signal waveform during high-speed transmission can be suppressed. .

The surface resistance value of the conductive layer in the present invention is obtained by multiplying a resistance value measured using a four-probe probe of “Lorester GP” manufactured by Mitsubishi Chemical Corporation by a predetermined constant according to JIS K7194-1994.
Specifically, four conductive bumps linearly provided at 5 mm intervals from the center of the adhesive layer of the electromagnetic wave shielding sheet (80 mm × 50 mm rectangular sample piece) of the present invention until the conductive layer is reached. insert. The positions of the four conductive bumps are parallel to the long sides of the sample piece. A current is applied between the two outside points of the four conductive bumps, and the voltage between the two inside points is measured to obtain resistance = voltage / current. Next, a value obtained by multiplying the measured value by a constant “4.239” is defined as “surface resistance value”.

The conductivity of the conductive layer in the present invention is determined from the thickness t (μm) of the conductive layer and the above-described surface resistance.
That is, when the thickness of the conductive layer is t (μm) and the above-described surface resistance R (mΩ / □) is obtained by observing the cross section of the electromagnetic wave shielding sheet of the present invention, the conductivity σ (S / m) of the conductive layer is as follows. It is obtained by the formula.
σ = 10 ⁹ / R / t

  The thickness of the conductive layer can be appropriately designed depending on the application, but is preferably in the range of 2 μm to 20 μm, and more preferably 3 μm to 10 μm. By setting the thickness to 2 μm or more, a strong conductive layer having sufficient cohesion can be obtained. When the thickness is 20 μm or less, the flexibility of the flexible printed wiring board with the electromagnetic wave shielding sheet is improved.

Such a conductive layer can be obtained by various methods. For example, the conductive layer E preferably contains 70% by mass or more, more preferably 80% by mass or more, and more preferably 85% by mass or more. Is more preferable. Examples of the conductive filler E to be used include metal powder such as gold, silver, copper and nickel, alloy powder such as solder, silver-plated copper powder, metal-plated glass fiber and carbon filler. Of these, silver powder having high conductivity and silver-plated copper powder are preferred.
Examples of the shape of the conductive filler include a spherical shape, a flake shape, a dendritic shape, and a fibrous shape. In particular, the flake shape and the dendritic shape, in which the fillers can easily come into contact with each other, are particularly preferable.
Examples of the resin used include the same resins as those for forming the insulating layer described above.

Electromagnetic wave shielding sheet produced as described above is preferably water vapor permeability is 1cc / m 2 · ^24h or more. Even if the printed wiring board with an electromagnetic wave shielding sheet is heated suddenly in the reflow process in a state where it absorbs moisture, it is easy for water vapor to permeate, so explosive vaporized water is not retained in the electromagnetic wave shielding sheet, so foaming Does not occur.
In the present invention, the water vapor transmission rate can be measured by a water vapor transmission rate measuring device (PERMATRAN-W, manufactured by Mocon Corporation).

The electromagnetic wave shielding sheet manufactured as described above can be used by being attached to various wiring boards such as a flexible printed wiring board. Further, the electromagnetic wave shielding sheet according to the present invention can be widely applied to various electronic devices, devices, appliances, etc., in addition to wiring boards. Since the electromagnetic wave shielding sheet according to the present invention is excellent in shielding performance and high-speed transmission characteristics, it is particularly advantageous in applications requiring high-speed transmission.
INDUSTRIAL APPLICABILITY The printed wiring board with an electromagnetic wave shielding sheet of the present invention can be suitably used for an electronic device that transmits a signal in a frequency range of 1 MHz to 20 GHz, for example, an electronic device such as a digital camera or a mobile phone.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In Examples and Comparative Examples, "parts" and "%" mean "parts by mass" and "% by mass", respectively.
The weight average molecular weight of the polyurethane polyurea resin and the number average molecular weight of the polyester resin described in the examples are the weight average molecular weight and the number average molecular weight in terms of polystyrene determined by GPC measurement. Are as follows.
Apparatus: Shodex GPC System-21 (Showa Denko)
Column: A total of three Shodex KF-802, KF-803L, and KF-805L (manufactured by Showa Denko) were connected and used.
Solvent: tetrahydrofuran Flow rate: 1.0 ml / min
Temperature: 40 ° C
Sample concentration: 0.3% by mass
Sample injection volume: 100 μl

<Resin synthesis example 1>
A polyester polyol obtained from terephthalic acid, adipic acid and 3-methyl-1,5-pentanediol (manufactured by Kuraray Co., Ltd.) was placed in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube. Kuraray polyol P-1011 ", Mn = 1006) 401.9 parts by mass, dimethylolbutanoic acid 12.7 parts by mass, isophorone diisocyanate 151.0 parts by mass, toluene 40.0 parts by mass, 90 ° C. under a nitrogen atmosphere, After reacting for 3 hours, 300.0 parts by mass of toluene was added thereto to obtain a urethane prepolymer solution having an isocyanate group.
Next, a mixture of 27.8 parts by mass of isophoronediamine, 3.2 parts by mass of di-n-butylamine, 342.0 parts by mass of 2-propanol, and 396.0 parts by mass of toluene has the obtained isocyanate group. Add 815.1 parts by mass of a urethane prepolymer solution, react at 70 ° C. for 3 hours, dilute with 144.0 parts by mass of toluene and 72.0 parts by mass of 2-propanol, Mw = 54,000, acid value = 8 mgKOH / G of polyurethane polyurea resin solution A-1 (also referred to as C-1 or F-1).

<Resin synthesis example 2>
292.1 parts by mass of polycarbonate diol (Kuraray polyol C-2090: manufactured by Kuraray Co., Ltd.) and tetrahydrophthalic anhydride were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping device, introduction tube, and nitrogen introduction tube. (Likacid TH: manufactured by Shin Nippon Rika Co., Ltd.) was charged with 44.9 parts by mass, and 350.0 parts by mass of toluene as a solvent, and the mixture was heated to 60 ° C. while stirring under a nitrogen stream to be uniformly dissolved. Subsequently, the temperature of the flask was raised to 110 ° C., and the reaction was performed for 3 hours. Then, after cooling to 40 ° C, 62.9 parts by mass of bisphenol A type epoxy resin (YD-8125: manufactured by Toto Kasei Co., Ltd.) and 4.0 parts by mass of triphenylphosphine as a catalyst were added, and the temperature was raised to 110 ° C. For 8 hours. After cooling to room temperature, the solid content was adjusted to 35% with toluene to obtain a carboxyl group-containing modified ester resin solution A-2 (also referred to as C-2 or F-2) of the present invention.

<Resin synthesis example 3>
98.5 parts by mass of butyl acrylate, 1.5 parts by mass of acrylic acid, and 150.0 parts by mass of ethyl acetate were charged into a four-necked flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel. The mixture was heated to 70 ° C. under substitution, and 0.15 parts by mass of azobisisobutyronitrile was added to initiate polymerization. From 3 hours after the start of the polymerization to 5 hours after every 1 hour, 0.15 parts by mass of azobisisobutyronitrile was added, and the polymerization was further carried out for 2 hours. Thereafter, 150.0 parts by mass of ethyl acetate was added to terminate the polymerization, and an acrylic resin solution A-3 (also referred to as C-3 or F-3) was obtained.

(Example 1)
<Step 1-1>
Epoxy resin (B-1) (bisphenol A type epoxy resin ("jER1001" manufactured by Mitsubishi Chemical Corporation)) based on 100 parts by solid content of the polyurethane polyurea resin solution (A-1) obtained in Synthesis Example 1. 20 parts were added and mixed by stirring with a disper to obtain an insulating composition, which was coated on a release-treated surface of a 50 μm PET film having been subjected to a release treatment on one side using a comma coater. Then, the film was dried by heating at 100 ° C. for 2 minutes to produce a film (1) having an insulating layer (I) having a dry film thickness of 10 μm.
<Step 1-2>
Epoxy resin (D-1) (bisphenol A type epoxy resin ("jER1001" manufactured by Mitsubishi Chemical Corporation)) based on 100 parts by solid content of the polyurethane polyurea resin solution (C-1) obtained in Synthesis Example 1. 20 parts and 740 parts of conductive filler (E-1) were added thereto and mixed by stirring with a disper to obtain a conductive composition.The conductive filler (E-1) had a 50% particle size of 6.1 μm and a BET. It is a silver-coated copper powder produced by subjecting a flake-like copper powder having a specific surface area of 1.7 m ² / g and an apparent density of 0.53 g / cm ³ to silver plating at a weight ratio of 10%.
Using a comma coater, the obtained conductive composition was applied to the release-treated surface of a 100 μm PET film having one surface subjected to a release treatment, and was dried by heating at 100 ° C. for 2 minutes. A film (2) including the conductive layer (II) having a resistivity of 80 (mΩ / □) was produced. The thickness and surface resistivity of the conductive layer (II) were determined by the methods described below.
<Step 1-3>
After laminating the insulating layer (I) surface of the produced film (1) and the conductive layer (II) surface of the film (2) using a laminator (80 ° C., pressure 2 MPa, line speed 2 m / min), The conductive layer (II) of the film (2) was peeled off from the release-treated polyethylene terephthalate film having a thickness of 100 μm to prepare a film (3) composed of the conductive layer (II), the insulating layer (I), and the 50 μm PET film. .
<Step 1-4>
Epoxy resin (G-1) (bisphenol A type epoxy resin ("jER1001" manufactured by Mitsubishi Chemical Corporation)) 20 per 100 parts of the solid content of the polyurethane polyurea resin solution (F-1) obtained in Synthesis Example 1 Parts and 40 parts of conductive filler (H-1) were added to obtain an anisotropic conductive adhesive resin composition, wherein the conductive filler (H-1) was based on dendritic copper powder produced by an electrolytic method. This is a silver-coated copper powder having an average particle diameter of 12 μm, which is manufactured by applying silver plating at a weight ratio of 10%.
The above-described anisotropic conductive adhesive resin composition was applied on the release-treated surface of a 75 μm PET film having one side subjected to a release treatment, and dried at 100 ° C. for 2 minutes to obtain an adhesive layer (III) having a dry film thickness of 7 μm. ) Was prepared.
<Step 1-5>
The conductive layer (II) surface of the film (3) and the adhesive layer (III) surface of the film (4) are bonded together by using a laminator (80 ° C., pressure 2 MPa, line speed 2 m / min), and the electromagnetic wave is applied. A laminate in which both surfaces of the shield sheet were covered with the PET film was obtained.

(Examples 2 to 13, Comparative Examples 1 to 7)
An electromagnetic wave shielding sheet was prepared in the same manner as in Example 1 except that the raw materials and thickness used in Example 1 were changed to the raw materials and thickness described in Tables 1 and 2.

(Example 13)
Instead of the adhesive composition containing the conductive filler H used in <Step 1-4>, an epoxy was added to 100 parts by solid content of the polyurethane polyurea resin solution (F-1) obtained in Synthesis Example 1. Electromagnetic wave shielding sheet in the same manner as in Example 1 except that an adhesive resin composition containing 20 parts of resin (G-1) (bisphenol A type epoxy resin (“jER1001” manufactured by Mitsubishi Chemical Corporation)) was used. It was created.

(Example 14)
An electromagnetic wave shielding sheet was prepared in the same manner as in Example 1 except that a polyimide film was used instead of the film (1) obtained in <Step 1-1>.
However, Examples 1 to 4 and 12 to 14 are reference examples.

(1) Measurement of thickness t of conductive layer and thickness of adhesive layer A sample having a width of 10 mm and a length of 70 mm was prepared from the laminate obtained in <Step 1-5>, and the adhesive layer ( The release treatment sheet on the III) side was peeled off, and a 50 μm-thick polyimide film (“Kapton 200EN” manufactured by Toray DuPont, hereinafter abbreviated as “Kapton 200EN”) was applied to the adhesive layer (III) at 150 ° C. Crimping was performed under the conditions of 0 MPa and 30 min.
After the pressure bonding, the peelable film on the insulating layer (I) side was removed, a part was cut out, embedded with an epoxy resin, and a cross section in the film thickness direction was cut out with a microtome. The exposed cross section was observed at a magnification of 1000 to 5000 times using a scanning electron microscope, and the thicknesses of the conductive layer t and the adhesive layer were measured.

(2) Measurement of Surface Resistivity R of Conductive Layer A screen printing of a pattern of four points was made in a straight line at an interval of 5 mm using a conductive paste composed of an epoxy resin and silver powder on the release-treated surface of the heat-resistant polyester film. After drying, the conductive paste was heated and cured in an oven at 180 ° C. to form conductive bumps having a diameter of 500 μm and a height of 100 μm.
The release treatment sheet on the side of the adhesive layer (III) was peeled off from the laminate (a rectangular sample having a long side of 80 mm and a short side of 50 mm) obtained in <Step 1-5>, and the exposed adhesive layer (III) was removed. The heat-resistant polyester film on which the conductive bumps were formed was overlaid and pressed under the conditions of 150 ° C., 1.0 MPa, and 30 minutes. The four conductive bumps are pressure-bonded so as to be positioned parallel to the long side of the sample piece. The conductive bump having a height of 100 μm penetrated the adhesive layer (III) to reach the conductive layer (II) by the pressure bonding.
After the pressure bonding, the heat-resistant polyester film subjected to the peeling treatment was removed to expose the adhesive layer (III) and the conductive bumps.
This conductive bump was used as a measurement electrode, and the resistance value was measured using a four-probe probe of “Lorester GP” manufactured by Mitsubishi Chemical in accordance with JIS K7194-1994. The value obtained by multiplying the measured value by a constant “4.239” is defined as the surface resistance value R. The evaluation criteria are as follows.
In addition, since the adhesive layer (III) is an anisotropic conductive adhesive layer exhibiting electrical conductivity only in the thickness direction or an adhesive layer having no conductivity, the conductive bump penetrates the adhesive layer (III). The measured resistance value is the resistance value of the conductive layer (II).
○: less than 50 mΩ / □ △: 50 mΩ / □ or more and less than 100 mΩ / □ ×: 100 mΩ / □ or more

(3) How to determine the conductivity σ (S / m) of the conductive layer From the film thickness t (μm) and the surface resistance R (mΩ / □) of the conductive layer obtained in (1) and (2) above, It was determined according to the formula.
σ = 10 ⁹ / R / t

(4) Measurement of vapor permeability A sample having a width of 150 mm and a length of 150 mm was prepared from the laminate obtained in <Step 1-5>, and the release treatment sheet on the side of the adhesive layer (III) was peeled off from the sample. The “Kapton 200EN” was pressure-bonded to the adhesive layer (III) under the conditions of 150 ° C., 1.0 MPa, and 30 minutes.
After the pressure bonding, the peelable film on the insulating layer (I) side was removed, and the water vapor transmission rate was measured using a water vapor transmission rate measuring device (PERMATRAN manufactured by MOCON) at 40 ° C. and 100% RH. (Value A)
Further, Kapton 200EN was measured alone (value B), and the water vapor transmission rate was calculated from the following equation (value B).
1 / (A) = 1 / (B) + 1 / (C)
The water vapor permeability was determined according to the criteria described below.
：: 10 g / (m2 · day) or more Δ: 1 g / (m2 · day) or more and less than 10 g / (m2 · day) ×: less than 1 g / (m2 · day)

(5) Evaluation of Adhesive Strength A sample having a width of 10 mm and a length of 70 mm was prepared from the laminate obtained in <Step 1-5>, and the release-treated sheet on the side of the adhesive layer (III) was peeled off from the sample, followed by bonding. The “Kapton 200EN” was pressure-bonded to the agent layer (III) under the conditions of 150 ° C., 1.0 MPa, and 30 minutes.
After the compression bonding, the release film on the insulating layer (I) side is removed, and for the reinforcement for measurement, a polyurethane polyurea-based adhesive sheet is used for the exposed insulating layer (I). It crimped on condition of.
Under an atmosphere of 23 ° C. and a relative humidity of 50%, the cured adhesive layer and the “Kapton 200EN” are peeled off at a pulling rate of 50 mm / min and a peeling angle of 90 °, and the central value of the peeling strength is determined as the adhesive strength ( N / cm).
This test is for evaluating the adhesive strength of the adhesive layer at the time of use at normal temperature, and the result was judged according to the following criteria.
◎: Adhesive strength of 10 (N / cm) or more ：: Adhesive strength of 5 (N / cm) or more and less than 10 (N / cm) △: Adhesive strength of 3 (N / cm) or more and 5 (N / cm) Less than ×): Adhesive strength is less than 3 (N / cm)

(6) Evaluation of heat resistance (initial and after moisture absorption) A sample having a width of 10 mm and a length of 70 mm was prepared from the laminate obtained in <Step 1-5>, and the adhesive layer (III) side was peeled from the sample. The treated sheet was peeled off, and the “Kapton 200EN” was pressure-bonded to the adhesive layer (III) under the conditions of 150 ° C., 1.0 MPa, and 30 minutes.
After the pressure bonding, the peelable film on the insulating layer (I) side is removed, and the above-mentioned “Kapton 200EN” is brought into contact with the molten solder at 260 ° C. in an environment of 23 ° C. and 50% relative humidity for 1 minute, and the test is performed. The appearance of the piece was visually observed, and the presence or absence of adhesion abnormality such as foaming, floating, and peeling of the shield sheet was evaluated.
(initial).
Separately, the sample after pressure bonding was left in an atmosphere of 40 ° C. and a relative humidity of 90% for 72 hours to absorb moisture, and then heat resistance was tested and evaluated in the same manner as described above (after moisture absorption).
In this test, the heat resistance of a printed wiring board with an electromagnetic wave shielding sheet in lead-free solder reflow is evaluated by substitution with a solder bath. Good heat resistance has no change in appearance before and after soldering, whereas poor heat resistance has foaming and peeling after soldering. These evaluation results were judged based on the following criteria.
◎: “No change in appearance”
Δ: “Small foaming is slightly observed”
×: “Intense foaming and peeling are observed.”

(7) Evaluation of bending resistance A sample having a width of 10 mm and a length of 70 mm was prepared from the laminate obtained in <Step 1-5>, and the release-treated sheet on the side of the adhesive layer (III) was peeled off from the sample and bonded. In the agent layer (III), the polyimide film surface of a two-layer substrate (“Espanex MC-18-25-00FRM” manufactured by Nippon Steel Chemical Co., Ltd.) of a polyimide film and a copper foil was applied at 150 ° C., 1.0 MPa, and 30 minutes. Crimped.
After the pressure bonding, the peelable film on the insulating layer (I) side is removed, the electromagnetic wave shielding sheet is bent outward by 180 degrees, a 500 g weight is placed on the bent portion for 5 seconds, and then the sample is returned to a flat state. A 500 g weight was placed for 5 seconds, and the number of bending was set to one.
Whether or not cracks occurred in the electromagnetic wave shielding sheet provided on the polyimide film side of the two-layer substrate was observed with a microscope “VHX-900” manufactured by KEYENCE CORPORATION, and the number of times of bending without cracks was evaluated.
A: No crack occurs even if bent 50 times or more.
・ ・ ・: 20 times or more and less than 50 times.
Δ: 5 times or more and less than 20 times.
×: Less than 5 times

(8-1) Measurement of transmission loss (for Examples 1 to 12 and Comparative Examples 1 to 7)
<Flexible printed wiring board for measurement>
According to the following procedure, a flexible printed wiring board having a coplanar structure is obtained.
A double-sided CCL is prepared by laminating a 12 μm thick copper foil on both sides of a polyimide film (25 μm thick), two signal wirings (signal circuits) on one surface, and the signal wirings outside each of the signal wirings. Provide parallel ground wiring (ground circuit). The copper foil on the other surface corresponding to the signal wiring (the copper foil on the back surface of the signal wiring) is removed by etching. A plated through hole is provided in a part of the two ground wirings provided on the one surface to ensure conduction with the copper foil on the other surface.
The coverlays are respectively adhered to both surfaces of the processed double-sided CCL. Note that the opening provided in the cover lay on the side where the signal wiring is provided is located on two ground wirings, and the opening provided in the cover lay on the side where the signal wiring is not provided is left. On the copper foil.
<Sample for measurement>
The release treatment sheet on the side of the adhesive layer (III) was peeled off from the laminate obtained in <Step 1-5>, and the adhesive layer (III) was placed on both sides of the flexible printed wiring board having the coplanar structure at 150 ° C. Crimping was performed under the conditions of 1.0 MPa and 30 min to obtain a printed wiring board with an electromagnetic shielding sheet for measuring transmission loss. The adhesive layer (III) is pressed into the opening provided in the cover lay by the pressure bonding, and comes into contact with the two ground wirings provided on the one surface and the copper foil left on the other surface, Conduction is ensured.
Using a network analyzer E5071C (manufactured by Agilent Japan), a signal in the range of 1 MHz to 20 GHz was sent to the signal wiring, and the transmission loss of the printed wiring board with the electromagnetic wave shielding sheet was measured.

(8-2) Measurement of transmission loss (for Example 13)
A conductive bump was formed on a part of a copper foil surface of a two-layer substrate of a polyimide film and a copper foil (“ESPANEX MC-18-25-00FRM” manufactured by Nippon Steel Chemical Co., Ltd.) using a conductive paste having a height of 100 μm. A “conductive bump sheet” is prepared.
The release sheet on the side of the adhesive layer (III) is peeled off from the laminate obtained in <Step 1-5>, and the adhesive layer (III) is overlaid on both surfaces of the flexible printed wiring board having the coplanar structure. The copper foil and the conductive bumps of the “conductive bump sheet” are stacked on each outermost layer of the electromagnetic wave shielding sheet, ie, each insulating layer (I), on both surfaces, and pressed at 150 ° C., 1 MPa, and 30 min. . By crimping, the conductive bump having a height of 100 μm penetrates the insulating layer (I) and reaches the conductive layer (II).
Separately, by ensuring conduction between the copper foil of the “conductive bump sheet”, the two ground wirings provided on the one surface of the printed wiring board, and the copper foil left on the other surface, the electromagnetic wave Conduction between the conductive layer (II) in the shield sheet and the ground circuit can be ensured.

As shown in Table 2, in Comparative Example 1, the surface resistance of the conductive layer was 100 [mΩ / □] or less because the thickness of the conductive layer was large. However, since the conductive filler E contained in the conductive layer was small, The conductivity of the conductive layer was less than 1 × 10 ⁶ [S / m], and the transmission loss was large.
On the other hand, in Comparative Example 2, the conductivity of the conductive layer was 1 × 10 ⁶ S / m, but since the thickness of the conductive layer was small, the surface resistance of the conductive layer was larger than 100 mΩ / □, and the transmission loss was large. Was.
In Comparative Examples 3 to 5, the amount of the conductive filler E contained in the conductive layer was small, the conductivity of the conductive layer was less than 1 × 10 ⁶ [S / m], and the thickness of the conductive layer was small. Has a surface resistance value of more than 100 [mΩ / □], so that transmission loss is further increased.
Comparative Example 6 uses a copper foil having a thickness of 9 μm, and thus has a high conductivity and a small surface resistance, so that the transmission loss is small. However, in the heat resistance evaluation after moisture absorption, severe foaming occurs, and the bending resistance is evaluated. Then, cracks occur immediately.
In Comparative Example 7, since the vapor deposition layer was used, the conductivity was high, but the surface resistance was large, so the transmission loss was large, and in the heat resistance evaluation after moisture absorption, severe foaming occurred.

  On the other hand, as shown in Table 1, the electromagnetic wave shielding sheet of the present invention has excellent transmission characteristics, adhesive strength, and bending resistance, and does not foam even when heated or exposed to heat after absorbing moisture.

Claims (5)

Having an insulating layer, a conductive layer, and an adhesive layer in this order,
An electromagnetic wave shielding sheet used by being adhered to a printed wiring board by the adhesive layer,
The adhesive layer contains a thermosetting resin and a curing agent,
The conductive layer contains a resin and a conductive filler E, and the conductive layer has a surface resistance of 47 [mΩ / □] or less and a conductivity of 2.4 × 10 ⁶ [S / m] or more,
The shape of the conductive filler E is a flake or a dendrite,
The content of the conductive filler E is 70% by mass or more in 100% by mass of the conductive layer,
The thickness of the conductive layer is 3 to 20 μm,
The transmission loss at 1 GHz is 2.6 or less, the transmission loss at 10 GHz is 6.9 or less, and the transmission loss at 20 GHz is 11.6 or less;
An electromagnetic wave shielding sheet for a flexible printed wiring board, wherein the electromagnetic wave shielding sheet is used for an electronic device transmitting a signal having a frequency in a range of 1 MHz to 20 GHz. The adhesive layer contains a thermosetting resin, a curing agent, and a conductive filler H,
100% by mass of the adhesive layer contains 30% by mass or less of the conductive filler H,
The electromagnetic wave shielding sheet for a flexible printed wiring board according to claim 1, wherein the conductive layer contains 70% by mass or more of a conductive filler E in 100% by mass of the conductive layer. 40 ° C., according to claim 1 or 2 for flexible printed circuit boards electromagnetic shield sheet, wherein the at steam permeability was measured under the conditions of 90% relative humidity ^{1 [cc / m 2 · 24h} ] or higher.   A flexible printed wiring board with an electromagnetic wave shielding sheet, wherein the adhesive layer of the electromagnetic wave shielding sheet for a flexible printed wiring board according to any one of claims 1 to 3 is attached to at least one surface of the flexible printed wiring board. . An electronic device using the flexible printed wiring board with the electromagnetic wave shielding sheet according to claim 4 , which transmits a signal having a frequency in a range of 1 MHz to 20 GHz.