Electromagnetic wave shielding sheets and printed wiring boards

Abstract

The electromagnetic shielding sheet of the present invention comprises a protective layer, a metal layer and a conductive adhesive layer. The metal layer has a plurality of openings, and the opening ratio of the openings is 0.1% to 20%. Moreover, the electromagnetic shielding sheet has a tensile strength of 10N / 20mm to 80N / 20mm.

Description

[0001] [References]

[0002] This application is based upon and claims the benefit of priority of Japanese patent application No. 2019-101051 filed on May 30, 2019, the disclosure of which is incorporated herein in its entirety by reference. Technical Field

[0003] The present invention relates to an electromagnetic wave shielding sheet suitable for being joined to a part of a component emitting electromagnetic waves and a printed wiring board with the electromagnetic wave shielding sheet. Background Art

[0004] Various electronic devices such as mobile terminals, personal computers (PCs), and servers have built-in substrates such as printed wiring boards. In order to prevent malfunctions caused by external magnetic fields or radio waves and to reduce unnecessary radiation from electrical signals, electromagnetic wave shielding structures are provided on these substrates.

[0005] In International Publication No. 2013 / 077108, the subject is to provide a shielding film, a shielding printed wiring board, and a method for manufacturing a shielding film that can well shield electric field waves, magnetic field waves, and electromagnetic waves traveling from one side of the shielding film to the other side, and have good transmission characteristics even when used in a high-frequency signal system, and the following structure is disclosed. That is, a shielding film is disclosed, including a metal layer and an anisotropic conductive layer with a layer thickness of 0.5μm to 12μm in a laminated state. In addition, it is recorded that: the structure of grounding through the grounding (GND) circuit of the printed wiring board and the anisotropic conductive layer can well shield electric field waves, magnetic field waves, and electromagnetic waves traveling from one side of the shielding film to the other side.

[0006] International Publication No. 2014 / 192494 describes a method of including a metal thin film layer of an electromagnetic wave shielding sheet having a diameter of 0.1 μm to 100 μm and a number of 10 / cm 2 ~1000pcs / cm 2 The invention discloses a shielding film for a printed wiring board having a metal foil with pinholes and a conductive adhesive layer, so as to solve the problem that the interlayer adhesion of the shielded printed wiring board is destroyed due to the volatile components generated in the heating pressing or reflow soldering steps. Summary of the invention

[0007] As transmission signals are transmitted at higher speeds, electromagnetic shielding sheets are also required to have high shielding properties and transmission characteristics for high frequencies. Therefore, it has been considered that it is preferable to use a metal layer in the conductive layer of an electromagnetic shielding sheet as described in International Publication No. 2013 / 077108.

[0008] However, a shielded printed wiring board formed by pasting an electromagnetic wave shielding sheet having a metal layer onto a printed wiring board has the following problem: during a heating treatment such as reflow soldering, floating occurs between layers due to volatile components generated from the inside of the printed wiring board, and foaming, etc., leads to poor appearance and poor connection (hereinafter sometimes referred to as reflow soldering resistance).

[0009] In order to solve this problem, International Publication No. 2014 / 192494 proposes to use a metal layer having pinholes in an electromagnetic wave shielding sheet. However, depending on the diameter and number of the pinholes, the reflow resistance cannot exhibit acceptable performance.

[0010] Furthermore, when an electromagnetic shielding sheet having pinholes is heat-pressed, cracks may occur in the metal layer starting from the pinholes, thereby deteriorating the electromagnetic shielding properties (hereinafter referred to as crack resistance).

[0011] Moreover, as electronic devices become smaller, the circuit area of ​​printed wiring boards is also reduced, and the opening area of ​​vias used for GND grounding is being miniaturized. However, the electromagnetic wave shielding sheets of International Publication No. 2013 / 077108 and International Publication No. 2014 / 192494 have poor reliability for GND grounding of the small opening vias, and there is a problem of deterioration in electromagnetic wave shielding properties.

[0012] The present invention is made in view of the above background, and its purpose is to provide an electromagnetic wave shielding sheet which has good reflow resistance and crack resistance, can perform GND grounding with high reliability even for a small opening path, and has high electromagnetic wave shielding properties when used in a high-frequency transmission circuit, and a printed wiring board using the electromagnetic wave shielding sheet.

[0013] The present inventors have made intensive studies and have found that the problems of the present invention can be solved by the following embodiments, thereby completing the present invention.

[0014] That is, the electromagnetic wave shielding sheet of the present invention includes a protective layer, a metal layer and a conductive adhesive layer, the metal layer has a plurality of openings, the opening ratio of the openings is 0.1% to 20%, and the tensile strength is 10N / 20mm to 80N / 20mm.

[0015] According to the present invention, an electromagnetic shielding sheet can be provided which has excellent reflow resistance and crack resistance, can perform highly reliable GND grounding even for vias with small openings, and has high electromagnetic shielding properties when used in high-frequency transmission circuits.

[0016] The above and other objects, features and advantages of the present invention will be more fully understood from the detailed description given below and the accompanying drawings which are given by way of illustration only and therefore should not be considered to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic cross-sectional view of a cut portion showing an example of a printed wiring board according to the present embodiment.

[0018] Figure 2 It is a schematic plan view of the main surface side of the printed wiring board of the Example and the comparative example.

[0019] Figure 3 It is a schematic plan view of the back side of the printed wiring board of the Example and the comparative example.

[0020] Figure 4 It is a schematic plan view of the back side of the printed wiring board of the Example and the comparative example.

[0021] Figure 5 This is a schematic plan view of the main surface side of a printed wiring board having a microstripline circuit for crosstalk measurement.

[0022] Figure 6 This is a schematic plan view of the back side of a printed wiring board having a microstrip line circuit for crosstalk measurement.

[0023] Figure 7 yes Figure 2 Cross-sectional view of the XI-XI cut portion.

[0024] Figure 8 yes Figure 2 Cross-sectional view of the XII-XII cut portion.

[0025] Figure 9(1) to Figure 9(6) It is a schematic plan view of the connection reliability evaluation to the small opening via.

[0026] [Explanation of Symbols]

[0027] 1, 8b, 25b, 31b: Conductive adhesive layer

[0028] 2: Metal layer

[0029] 3.25a: Protective layer

[0030] 4: Opening

[0031] 5.54: Ground wiring

[0032] 6, 35, 53: Signal wiring

[0033] 7: Printed wiring board

[0034] 8: Top coating

[0035] 8a, 21, 31a, 33, 50: Polyimide film

[0036] 9: Insulating substrate

[0037] 10, 25: Electromagnetic wave shielding sheet

[0038] 11, 24: Passage

[0039] 20: Wiring board with coplanar circuit (flexible printed wiring board with coplanar circuit)

[0040] 22A, 22B: Copper foil circuit

[0041] 23: Polyimide cover

[0042] 30: Wiring board with microstrip circuit

[0043] 31: Overlay

[0044] 34: Ground layer

[0045] 51: Through hole

[0046] 52: Copper film

[0047] 55: Ground pattern (i)

[0048] 56: Back side ground pattern (ii) DETAILED DESCRIPTION

[0049] Hereinafter, an example of an embodiment of the present invention will be described. In addition, the size or ratio of each component in the following figures is for the convenience of explanation and is not limited thereto. Moreover, in this specification, the description of "arbitrary number A to arbitrary number B" means that the range includes number A as the lower limit and number B as the upper limit. Moreover, the "sheet" in this specification not only includes the "sheet" defined in Japanese Industrial Standards (JIS), but also includes "film". Moreover, the numerical values ​​specified in this specification are values ​​obtained by the method disclosed in the embodiment or examples.

[0050] The electromagnetic wave shielding sheet 10 of the present invention comprises a laminated body in which a conductive adhesive layer 1, a metal layer 2, and a protective layer 3 are laminated in this order (see Figure 1 ). The electromagnetic wave shielding sheet 10 can arrange the conductive adhesive layer 1 on the part (not shown) and join it with the part through a joining process. The joining process can be any process as long as it can join the conductive adhesive layer 1 with the part. For example, heat treatment or thermocompression bonding can be preferably used. The protective layer 3 plays the role of protecting the conductive adhesive layer 1 and the metal layer 2, and is arranged at a position closer to the surface side than the metal layer 2. The metal layer 2 is a layer sandwiched between the protective layer 3 and the conductive adhesive layer 1, and mainly plays the role of shielding electromagnetic waves. In the printed wiring board, the metal layer 2 plays the role of shielding the electromagnetic noise generated by the signal wiring inside the part, etc., and shielding the signal from the outside.

[0051] The metal layer 2 has a plurality of openings 4, and the opening ratio of the openings 4 is 0.1% to 20%. The electromagnetic shielding sheet 10 of the present embodiment has a tensile strength of 10 N / 20 mm to 80 N / 20 mm.

[0052] The opening 4 is also the part where the protective layer 3 and the conductive adhesive layer 1 are bonded, and plays a role in improving the reflow resistance. Moreover, by setting the opening ratio calculated based on the area of ​​the opening 4 and the non-opening portion to 0.1% to 20%, both the reflow resistance and the high electromagnetic wave shielding performance can be taken into account. By further setting the tensile strength of the electromagnetic wave shielding sheet 10 to 10N / 20mm to 80N / 20mm, the crack resistance is improved, and the degradation of the electromagnetic wave shielding performance can be suppressed.

[0053] Hereinafter, the electromagnetic shielding sheet and the printed wiring board of the present embodiment will be described in detail. First, the metal layer, the conductive adhesive layer, and the protective layer constituting the electromagnetic shielding sheet of the present embodiment will be described in detail.

[0054] Metal Layer

[0055] The metal layer of the present invention has a plurality of openings, and the opening ratio of the openings is 0.1% to 20%. By setting the opening ratio of the openings to such a range, high electromagnetic wave shielding properties can be maintained, and both reflow resistance and crack resistance can be taken into account. The opening ratio can be adjusted according to the area and number of the openings. Moreover, the opening ratio is calculated according to the following formula (1).

[0056] Opening ratio (%) = opening area per unit area / (opening area per unit area + non-opening area per unit area) × 100 ... Formula (1)

[0057] The lower limit of the aperture ratio is more preferably 0.3%, and still more preferably 0.5%. The upper limit of the aperture ratio is more preferably 15%, and still more preferably 6.5%.

[0058] Furthermore, by setting the aperture ratio to a range of 0.1% to 20%, it is possible to maintain reflow resistance, high electromagnetic wave shielding performance, and connection reliability of small-opening vias.

[0059] The aperture ratio can be determined, for example, by using an image obtained by magnifying the metal layer 500 to 5000 times vertically from the surface direction using a laser microscope and a scanning electron microscope (SEM), binarizing the openings and non-openings, and taking the number of pixels of the binarized color per unit area as the respective areas.

[0060] Furthermore, in the openings of the metal layer of the present invention, the average value of the circularity coefficient of the openings calculated using the formula (2) may be 0.5 or more.

[0061] Circularity coefficient = (area × 4π) / (circumference) 2 ...Equation (2)

[0062] Among them, the circumference refers to the length of the periphery when the extracted opening is two-dimensionally projected by extracting an image obtained by observing the metal layer using any one of an optical microscope, a laser microscope and an electron microscope, in which the plane of the opening is extracted to be perpendicular to the observation viewpoint and the opening as a whole can be confirmed; the area refers to the width of the area defined by the periphery when the extracted opening is two-dimensionally projected.

[0063] As described above, the metal layer of the present invention has a plurality of openings. It is preferred that the metal layer has openings on the entire surface. The openings are responsible for allowing volatile components contained in the polyimide film or the cover layer adhesive of the printed wiring board to escape to the outside when the printed wiring board is subjected to a heat treatment such as reflow soldering. This can suppress the poor appearance and the decrease in connection reliability caused by the interface peeling between the cover layer adhesive and the electromagnetic wave shielding sheet. By further Figure 1 As shown in the cross-sectional schematic diagram of , the protective layer and the conductive adhesive layer are bonded inside the opening, the adhesive strength of the interface between the protective layer / metal layer / conductive adhesive layer is further improved, and the reflow resistance is further improved.

[0064] The shape of the opening is preferably a circle, and the average value of the circularity coefficient calculated according to formula (2) is greater than 0.5. By setting the average value of the circularity coefficient to be greater than 0.5, even if tension in the surface direction is applied to the metal layer, cracks are not easily generated in the peripheral wall of the opening, thereby improving crack resistance. The average value of the circularity coefficient is more preferably greater than 0.7.

[0065] In addition, by making the circularity coefficient within the above range, the electromagnetic wave shielding property after time at high temperature and high humidity can be improved. This is because, when the value of the circularity coefficient is small, the opening is deformed, and when the conductive layer and the protective layer are attached, an incompletely filled void portion is generated in the opening. When the electromagnetic wave shielding sheet is stored for a long time in a high temperature and high humidity environment, moisture will penetrate into the void and rust will be generated around the opening. As a result, the conductivity is locally deteriorated, so it is believed that the electromagnetic wave shielding property is also deteriorated.

[0066] By using the circularity coefficient of the formula (2), the degree of concavity (undulation) of the outer edge of the opening can be grasped. The circularity coefficient of a perfect circle is 1, and as the concavity and convexity increase, the circularity coefficient decreases. That is, the circularity coefficient is greater than 0 and less than 1. The circularity coefficient in this specification is obtained by using the analysis software of Mac-View Ver.4 (Mountech), and the image (about 500 to 10,000 times) is read by a laser microscope or an electron microscope for the opening of the metal layer, and about 20 openings are selected using the manual recognition mode. The circularity coefficient is calculated based on the setting that the particle reference data is the equivalent diameter of the projection area circle and the distribution is the volume distribution, and the average value of 20 is obtained. In the formula (2), the area is the area inside the line of the outer periphery when forming a two-dimensional projection as a flat surface, and the outer periphery of the opening when the flat surface is two-dimensionally projected is the length of the perimeter.

[0067] The area of ​​each opening is preferably 0.7 μm 2 ~5000μm 2 , more preferably 10 μm 2 ~4000μm 2 , and more preferably 20 μm 2 ~2000μm 2 By setting the opening area to 0.7 μm 2 As a result, the protective layer and the conductive adhesive layer are well bonded, and the reflow resistance is further improved. 2 The following are preferred because they can provide high and excellent electromagnetic wave shielding properties.

[0068] The number of openings is preferably 100 / cm 2 ~200000 pieces / cm 2 , more preferably 1000 pieces / cm 2 ~150000 pieces / cm 2 , and preferably 1000 pcs / cm 2 ~20000pcs / cm 2 By setting the number of openings to 100 / cm 2As a result, the volatile components can be easily removed to the outside efficiently, so the reflow resistance can be further improved. 2 The following are preferred because high electromagnetic wave shielding properties can be ensured.

[0069] The thickness of the metal layer is preferably 0.5 μm to 5 μm. The thickness of the metal layer is more preferably 1.0 μm to 4.5 μm, and further preferably 1 μm to 4 μm. By setting the thickness of the metal layer to be in the range of 0.5 μm to 5 μm, a balance between high electromagnetic wave shielding performance and crack resistance can be achieved.

[0070] As the metal layer, for example, metal foil, metal vapor-deposited film, or metal plating film can be used.

[0071] The metal used in the metal foil is preferably a conductive metal such as aluminum, copper, silver, gold, etc., and copper, silver, aluminum, and copper are more preferred in terms of electromagnetic wave shielding and cost. For example, rolled copper foil or electrolytic copper foil is preferably used as copper, and electrolytic copper foil is more preferred. If electrolytic copper foil is used, the thickness of the metal layer can be further reduced. In addition, the metal foil can also be formed by plating.

[0072] The metal used in the metal vapor-deposited film and the metal-plated film is preferably aluminum, copper, silver, or gold, and more preferably copper or silver. From the perspective of thin film formation, the metal layer is preferably a vapor-deposited film. From the perspective of electromagnetic wave shielding properties, a metal foil is preferably used.

[0073] <Method for producing metal layer>

[0074] The method for manufacturing a metal layer having an opening can be applied by a previously known method, and can be applied by a method of forming a patterned resist layer on a metal foil and etching the metal foil to form an opening (i), a method of printing a conductive paste in a predetermined pattern by screen printing (ii), a method of screen printing a primer (Anchor Agent) in a predetermined pattern and metal-plating only the primer-printed surface (iii), and a manufacturing method described in Japanese Patent Gazette No. 2015-63730 (iv), etc.

[0075] That is, a pattern printing of a water-soluble or solvent-soluble ink is carried out on a support, a metal vapor-deposited film is formed on its surface, and the pattern is removed. By forming a release layer on its surface and performing electrolytic plating, a metal layer with an opening of a carrier can be obtained. Among these, the opening forming method (i) in which a pattern resist layer is formed and a metal foil is etched can precisely control the shape of the opening, so it is preferred. However, the manufacturing method of the metal layer is not limited to the etching method (i), as long as the shape of the opening can be controlled, other methods can also be used.

[0076] 《Conductive adhesive layer》

[0077] The conductive adhesive layer can be formed using a conductive resin composition. The conductive resin composition includes a thermosetting resin and a conductive filler. The conductive adhesive layer can use either an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. The isotropic conductive adhesive layer has conductivity in the vertical direction and the horizontal direction when the electromagnetic wave shielding sheet is placed horizontally. Moreover, the anisotropic conductive adhesive layer has conductivity only in the vertical direction when the electromagnetic wave shielding sheet is placed horizontally.

[0078] The conductive adhesive layer may be either isotropically conductive or anisotropically conductive, but anisotropically conductive is preferred because it can reduce costs.

[0079] <Thermosetting resin>

[0080] Thermosetting resins are resins having multiple functional groups that can react with a curing agent. Functional groups include, for example, hydroxyl, phenolic hydroxyl, methoxymethyl, carboxyl, amino, epoxy, oxetane, oxazoline, oxazine, aziridine, thiol, isocyanate, block isocyanate, block carboxyl, silanol, etc. Thermosetting resins include, for example, acrylic resins, maleic acid resins, polybutadiene resins, polyester resins, polyurethane resins, polyurethane urea 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, silicone resins, fluororesins, and other known resins.

[0081] The thermosetting resins may be used alone or in combination of two or more.

[0082] Among these, polyurethane resins, polyurethane urea resins, polyester resins, epoxy resins, phenoxy resins, polyimide resins, polyamide resins, and polyamideimide resins are preferred in terms of reflow resistance.

[0083] The acid value of the thermosetting resin is preferably 1 mgKOH / g to 50 mgKOH / g, and more preferably 3 mgKOH / g to 30 mgKOH / g. When the acid value is 1 mgKOH / g to 50 mgKOH / g, the reflow resistance is further improved.

[0084] The content of the thermosetting resin in the solid content of the conductive adhesive layer is preferably 10 to 80% by weight, more preferably 15 to 80% by weight. By setting the content within the above range, reflow resistance and crack resistance can be improved.

[0085] <Hardener>

[0086] The curing agent has a plurality of functional groups that can react with the functional groups of the thermosetting resin. Examples of the curing agent include known compounds such as epoxy compounds, compounds containing anhydride groups, isocyanate compounds, aziridine compounds, amine compounds, phenol compounds, and organic metal compounds.

[0087] The hardeners may be used alone or in combination of two or more.

[0088] The various curing agents are preferably contained in an amount of 7 to 50 parts by weight, more preferably 9 to 40 parts by weight, and still more preferably 10 to 30 parts by weight, based on 100 parts by weight of the thermosetting resin.

[0089] <Conductive filler>

[0090] The conductive filler has the function of imparting conductivity to the conductive adhesive layer. Among the conductive fillers, conductive metals such as gold, platinum, silver, copper, and nickel, and alloys thereof, and conductive polymer particles are preferred as raw materials, and silver is more preferred in terms of price and conductivity.

[0091] Moreover, from the viewpoint of reducing costs, it is also preferred that the microparticles of non-single raw materials are composite microparticles that use metal or resin as the core body and have a coating layer that coats the surface of the core body. Here, the core body is preferably appropriately selected from cheap nickel, silicon dioxide, copper and its alloys, and resin. The coating layer is preferably a conductive metal or a conductive polymer. For example, conductive metals can include: gold, platinum, silver, nickel, manganese, and indium, and their alloys. And conductive polymers can include polyaniline, polyacetylene, etc. Among these, silver is preferred in terms of price and conductivity.

[0092] The shape of the conductive filler is not limited as long as the desired conductivity can be obtained. Specifically, for example, spherical, flake, leaf, dendrite, plate, needle, rod, or grape shape is preferred. Moreover, two conductive fillers of different shapes may be mixed.

[0093] The conductive filler may be used alone or in combination of two or more.

[0094] The average particle size of the conductive filler is D 50 The average particle size is preferably 2 μm or more, more preferably 5 μm or more, and further preferably 7 μm or more from the viewpoint of sufficiently ensuring conductivity. On the other hand, from the viewpoint of taking into account the thinness of the conductive adhesive layer, it is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. 50 The average particle size can be determined using a laser diffraction / scattering particle size distribution measuring apparatus or the like.

[0095] The content of the conductive filler in the conductive adhesive layer is preferably 35% to 90% by weight, more preferably 39% to 85% by weight, and further preferably 40% to 80% by weight. By setting it to 35% by weight or more, the connection reliability of the small opening passage is improved. On the other hand, by setting it to 90% by weight or less, the adhesive force of the conductive adhesive layer increases, so the reflow resistance is improved.

[0096] The conductive resin composition may further contain a silane coupling agent, a rust preventive, a reducing agent, an antioxidant, a pigment, a dye, a tackifier resin, a plasticizer, an ultraviolet absorber, a defoamer, a leveling agent, a filler, a flame retardant, and the like as optional components.

[0097] The conductive resin composition can be obtained by mixing and stirring the materials described above. For stirring, a known stirring device such as a dispermat or a homogenizer can be used.

[0098] The conductive adhesive layer can be prepared by a known method, for example, by applying a conductive resin composition on a removable sheet and drying it to form a conductive adhesive layer, or by extruding the conductive resin composition into a sheet using an extruder such as a T-die.

[0099] The coating method may be, for example, a gravure coating method, a kiss coating method, a die coating method, a lip coating method, a notch wheel coating method, a doctor blade method, a roller coating method, a knife coating method, a spray coating method, a rod coating method, a spin coating method, a dip coating method, or the like. It is preferred that a drying step be performed during coating. For example, a known drying device such as a hot air dryer or an infrared heater may be used for the drying step.

[0100] The thickness of the conductive adhesive layer is preferably 2 μm to 30 μm, more preferably 3 μm to 15 μm, and still more preferably 4 μm to 9 μm. Furthermore, by setting the thickness within the range of 2 μm to 30 μm, reflow resistance and connection reliability of small via openings can be improved.

[0101] Protective layer

[0102] The protective layer can be formed using a conventionally known resin composition.

[0103] The resin composition may contain the thermosetting resin and curing agent described in the conductive resin composition and the optional components as required. In addition, the thermosetting resin and curing agent used in the protective layer and the conductive adhesive layer may be the same or different.

[0104] The resin composition can be obtained by the same method as the conductive resin composition.

[0105] Furthermore, a film formed of an insulating resin such as polyester, polycarbonate, polyimide, or polyphenylene sulfide may be used as the protective layer.

[0106] The thickness of the protective layer is usually about 2 μm to 12 μm.

[0107] 《Electromagnetic wave shielding sheet》

[0108] The electromagnetic shielding sheet of the present invention includes at least a protective layer, a metal layer having an opening, and a conductive adhesive layer.

[0109] The electromagnetic shielding sheet of the present invention includes a metal layer having a plurality of openings and an opening ratio of 0.1% to 20%, and thus can further suppress crosstalk, etc., particularly in a wiring board transmitting high-frequency (eg, 100 MHz to 50 GHz) signals.

[0110] The electromagnetic wave shielding sheet of the present invention has a tensile strength of 10 N / 20 mm to 80 N / 20 mm. By setting the range, crack resistance is improved and degradation of electromagnetic wave shielding properties can be suppressed. The tensile strength is more preferably in the range of 20 N / 20 mm to 70 N / 20 mm, and further preferably in the range of 30 N / 20 mm to 65 N / 20 mm.

[0111] In the present invention, the tensile strength of the electromagnetic shielding sheet can be controlled using, for example, the opening ratio and thickness of the openings in the metal layer and the circularity coefficient of the openings.

[0112] Specifically, the smaller the opening ratio of the metal layer, the higher the tensile strength, and the larger the opening ratio of the metal layer, the lower the tensile strength. This is because: the smaller the opening ratio of the metal layer, the larger the contact area between the metal layer and the conductive adhesive layer, and the less likely the metal layer and the conductive adhesive layer are to peel off.

[0113] Moreover, the thinner the metal layer is, the lower the tensile strength is, and the thicker the metal layer is, the higher the tensile strength is. This is because the thicker the metal layer is, the higher the strength of the metal layer is.

[0114] Moreover, the lower the circularity coefficient of the opening of the metal layer, the lower the tensile fracture strength, and the higher the circularity coefficient of the opening, the higher the tensile fracture strength. This is because: the higher the circularity coefficient of the opening, the closer the shape of the opening is to a circle, and the fewer the starting points of cracks when tensile deformation stress is applied to the electromagnetic wave shielding sheet.

[0115] Furthermore, in the present invention, in addition to these, the tensile strength of the electromagnetic wave shielding sheet can also be controlled by the composition or structure of the protective layer and the conductive adhesive layer. For example, by increasing the content of the hardener in the conductive adhesive layer, the degree of hardening of the hardening system including the resin and the hardener can be increased, thereby increasing the strength of the conductive adhesive layer and improving the tensile strength of the electromagnetic wave shielding sheet.

[0116] In addition, the method of improving the strength of the conductive adhesive layer is not limited to the above method, and methods such as changing the type of resin or the type of hardener, adding fillers, etc. can also be used. Moreover, the strength of the protective layer can also be controlled by the same method as the conductive adhesive layer.

[0117] Moreover, the electromagnetic wave shielding sheet of the present invention can have the following excellent electromagnetic wave shielding properties, namely: it is attached to a wiring board with a coplanar circuit, the signal wiring of the wiring board with a microstrip line circuit is laminated with the protective layer of the electromagnetic wave shielding sheet, and when a 10GHz sinusoidal wave flows through the signal wiring of the microstrip line circuit, the crosstalk of the coplanar circuit is less than -45dB.

[0118] Specifically, the electromagnetic wave shielding property can be evaluated as follows, for example.

[0119] First, prepare the coplanar circuit.

[0120] A coplanar circuit is a planar transmission circuit in which a signal wiring is printed on one side of an insulating substrate such as a polyimide film. In the present invention, a coplanar circuit uses a circuit in which a ground wiring is formed in parallel on a polyimide film in the form of sandwiching two signal wirings. In addition, the coplanar circuit is provided with a ground pattern for GND grounding via a through hole on the facing surface.

[0121] The electromagnetic shielding layer is formed by attaching the conductive adhesive layer of the electromagnetic shielding sheet to the insulating substrate surface of the coplanar circuit opposite to the signal wiring by thermocompression bonding. At this time, the electromagnetic shielding sheet is electrically connected to the partially exposed ground pattern.

[0122] Next, the signal wiring of a separately prepared printed wiring board with a microstrip line circuit is arranged on the protective layer of the electromagnetic wave shielding layer formed on the coplanar circuit to obtain a test piece for measurement. A network analyzer is connected to the coplanar circuit and microstrip line circuit of this test piece, and the crosstalk in the coplanar circuit is measured when a sine wave of 10MHz to 20GHz flows through the signal wiring of the microstrip line circuit, so that the electromagnetic wave shielding property can be evaluated.

[0123] In addition, although a polyimide cover film with an adhesive is attached to the coplanar circuit and the microstrip line circuit, a part of the circuit used for connecting a probe of a network analyzer is exposed.

[0124] In the present invention, when a 10 GHz sine wave flows through the signal wiring of the microstrip line circuit, the crosstalk of the coplanar circuit is preferably less than -45 dB, more preferably less than -50 dB, and even more preferably less than -55 dB. By making the crosstalk less than -45 dB, high electromagnetic wave shielding properties can be obtained.

[0125] The electromagnetic shielding sheet of the present invention has a plurality of openings, and the opening ratio of the openings is 0.1% to 20%. Moreover, the tensile strength of the electromagnetic shielding sheet is 10N / 20mm to 80N / 20mm. As a result, the reflow resistance and crack resistance are excellent. As a result, the resistance value in the surface direction of the metal layer changes less, and the high electromagnetic shielding performance can be stably maintained, and the defective condition of the electronic components is reduced when encapsulated in a narrow frame.

[0126] The electromagnetic wave shielding sheet can obtain the desired bonding strength by allowing the thermosetting resin and curing agent contained in the conductive adhesive layer to exist in an uncured state (B stage) and curing with the wiring board by hot pressing (C stage). In addition, the uncured state includes a semi-cured state in which a part of the curing agent is cured.

[0127] The releasable sheet is a sheet obtained by subjecting a substrate such as paper or plastic to a known releasable treatment.

[0128] Furthermore, in order to prevent adhesion of foreign matter, the electromagnetic shielding sheet is usually stored in a state where the removable sheet is attached to the conductive adhesive layer and the protective layer.

[0129] The electromagnetic shielding sheet may include other functional layers in addition to the protective layer, metal layer and conductive adhesive layer. Other functional layers are layers having functions such as hard coating, water vapor barrier, oxygen barrier, thermal conductivity, low dielectric constant, high dielectric constant or heat resistance.

[0130] The electromagnetic wave shielding sheet of the present invention can be used for various purposes that require shielding electromagnetic waves. For example, it can be used for flexible printed wiring boards, rigid printed wiring boards, chip on film (COF), tape automated bonding (TAB), flexible connectors, liquid crystal displays, touch screens, etc. Moreover, it can also be used as a housing of a personal computer, a wall of a building material, a window glass, and other building materials, and a component for shielding electromagnetic waves from vehicles, ships, airplanes, etc.

[0131] <Method for producing electromagnetic wave shielding sheet>

[0132] In the production of the electromagnetic shielding sheet, a known method can be used for laminating the conductive adhesive layer and the metal layer.

[0133] For example, the following methods (i) to (v) can be mentioned.

[0134] Method (i) A conductive adhesive layer is formed on a removable sheet, and after laminating the conductive adhesive layer on the electrolytic copper foil surface side of an electrolytic copper foil with an opening having a copper carrier, the copper carrier is peeled off. Then, the surface from which the copper carrier is peeled off is overlapped with a protective layer formed separately on the removable sheet and laminated. Method (ii) A protective layer is formed on a removable sheet, and after laminating the protective layer on the electrolytic copper foil surface side of an electrolytic copper foil with an opening having a copper carrier, the copper carrier is peeled off. Then, the surface from which the copper carrier is peeled off is overlapped with a conductive adhesive layer formed separately on the removable sheet and laminated. Method (iii) A resin composition is applied to the electrolytic copper foil surface side of an electrolytic copper foil with an opening having a copper carrier to form a protective layer, and a removable sheet is attached. Thereafter, the copper carrier is peeled off, and a conductive adhesive layer formed separately on the removable sheet is overlapped and laminated. Method (iv) A conductive adhesive layer is formed on a removable sheet, and after laminating the conductive adhesive layer on the electrolytic copper foil surface side of the electrolytic copper foil with a copper carrier, the copper carrier is peeled off. Then, the surface from which the copper carrier is peeled off is overlapped with a protective layer formed separately on the removable sheet and laminated, and then an opening is formed in the electromagnetic wave shielding sheet using a needle-shaped jig. Method (v) After laminating the protective layer formed on the removable sheet on the electrolytic copper foil surface side of the electrolytic copper foil with an opening having a copper carrier, the copper carrier is peeled off. Then, a conductive adhesive layer is formed on the surface from which the copper carrier is peeled off.

[0135] 《Printed wiring board》

[0136] The printed wiring board of the present invention comprises: an electromagnetic wave shielding sheet, a top coating layer, and a wiring board comprising a circuit pattern having a signal wiring and a ground wiring and an insulating substrate. The electromagnetic wave shielding sheet comprises a protective layer, a metal layer and a conductive adhesive layer, the metal layer has a plurality of openings, the opening rate of the openings is 0.1% to 20%, and the tensile strength of the electromagnetic wave shielding sheet is 10N / 20mm to 80N / 20mm.

[0137] In the printed wiring board of the present invention, the electromagnetic wave shielding layer is formed by hot pressing an electromagnetic wave shielding sheet including a protective layer, a metal layer and a conductive adhesive layer. The metal layer has a plurality of openings, the opening ratio of the openings is 0.1% to 20%, and the tensile strength of the electromagnetic wave shielding sheet is 10N / 20mm to 80N / 20mm.

[0138] The wiring board includes a circuit pattern having a signal wiring and a ground wiring on the surface of an insulating substrate. On the wiring board, a top coating layer is formed to insulate and protect the signal wiring and the ground wiring and to have a passage on at least a portion of the ground wiring. After the conductive adhesive layer of the electromagnetic wave shielding sheet is arranged on the top coating layer, the electromagnetic wave shielding sheet is thermally pressed to allow the conductive adhesive layer to flow into the passage and bond to the ground wiring, thereby manufacturing the sheet.

[0139] Reference Figure 1 , an example of the printed wiring board 7 of the present invention will be described.

[0140] The electromagnetic shielding sheet 10 includes a protective layer 3 , a metal layer 2 having a plurality of openings, and a conductive adhesive layer 1 .

[0141] The top coat layer 8 is an insulating material that covers the signal wiring 6 of the wiring board and protects the signal wiring 6 from the external environment.

[0142] The top coat 8 is preferably a polyimide film with a thermosetting adhesive, a thermosetting or ultraviolet curing solder resist, or a photosensitive cover film. For micro-machining, a photosensitive cover film is more preferred. Moreover, the top coat is usually made of a known resin having heat resistance and flexibility such as polyimide. The thickness of the top coat 8 is usually about 10 μm to 100 μm.

[0143] The circuit pattern includes a ground wiring 5 for grounding and a signal wiring 6 for transmitting an electrical signal to an electronic component. Both are usually formed by etching a copper foil. The thickness of the circuit pattern is usually about 1 μm to 50 μm.

[0144] The insulating substrate 9 is a support for the circuit pattern, and is preferably a bendable plastic such as polyester, polycarbonate, polyimide, polyphenylene sulfide, or liquid crystal polymer, and more preferably a liquid crystal polymer and polyimide. Among these, if the use of a printed wiring board that transmits high-frequency signals is considered, a liquid crystal polymer with a low relative dielectric constant and dielectric loss tangent is further preferred.

[0145] When the wiring board is a rigid wiring board, the constituent material of the insulating substrate is preferably glass epoxy. By including such an insulating substrate, the wiring board obtains high heat resistance.

[0146] The electromagnetic wave shielding sheet 10 and the wiring board are usually hot-pressed at a temperature of about 150°C to 190°C, a pressure of about 1MPa to 3MPa, and a time of about 1 minute to 60 minutes. Through hot pressing, the conductive adhesive layer 1 is in close contact with the top coat 8, and the conductive adhesive layer 1 flows and fills the passage 11 formed in the top coat 8, thereby achieving conduction with the grounding wiring 5. Through hot pressing, the thermosetting resin reacts and hardens.

[0147] In order to accelerate hardening, post-curing may be performed at 150° C. to 190° C. for 30 to 90 minutes after hot pressing. In addition, the electromagnetic shielding sheet after hot pressing is sometimes called an electromagnetic shielding layer.

[0148] The opening area of ​​the passage 11 is preferably 0.008 mm 2 Above and 0.8mm 2 More preferably 0.3 mm 2 Below, especially preferably 0.03mm 2 By setting it as the above range, the reliability of ground connection is ensured, and the area of ​​the ground wiring can be narrowed while maintaining high electromagnetic wave shielding properties, thereby achieving miniaturization of the printed wiring board.

[0149] The shape of the passage is not particularly limited, and any of circular, square, rectangular, triangular, and irregular shapes can be used depending on the application.

[0150] In terms of being able to more effectively suppress the leakage of electromagnetic waves, it is preferred that the electromagnetic wave shielding layer is formed on both sides of the wiring substrate. The electromagnetic wave shielding sheet of the present invention includes a protective layer, a metal layer and a conductive adhesive layer, the metal layer having a plurality of openings, and the opening ratio of the openings is 0.1% to 20%. Moreover, in the openings of the metal layer, the average value of the circularity coefficient calculated according to formula (2) can be greater than 0.5. Since the electromagnetic wave shielding sheet of the present invention includes such a structure, after the electromagnetic wave shielding layer is formed on both sides of the wiring substrate, when the reflow treatment is performed, the internal residual gas will also be discharged to the outside through the opening 4, so that no foaming will occur. In addition, the electromagnetic wave shielding sheet 10 in the printed wiring board of the present invention can be used as a grounding circuit in addition to shielding electromagnetic waves. Therefore, by omitting a part of the grounding circuit, the area of ​​the printed wiring board can be reduced, and the cost can be reduced, and it can be assembled into a small area in the frame.

[0151] Furthermore, there is no particular limitation on the signal wiring, and the signal wiring can be used in any circuit including a single-ended circuit including one signal wiring and a differential circuit including two signal wirings, but preferably a differential circuit. On the other hand, when there is a restriction in the circuit pattern area of ​​the printed wiring board and it is difficult to form a ground circuit in parallel, the ground circuit may not be provided in the lateral direction of the signal circuit, and an electromagnetic wave shielding sheet may be used as the ground circuit to form a printed wiring board structure having grounding in the thickness direction.

[0152] The printed wiring board of the present invention is preferably provided (mounted) in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet terminals in addition to liquid crystal displays, touch panels, and the like.

[0153] [Example]

[0154] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. In the examples, "parts" means "parts by weight" and "%" means "% by weight".

[0155] The acid value, weight average molecular weight (Mw), glass transition temperature (Tg) of the resin, average particle size of the conductive filler, circularity coefficient of the opening of the metal layer, and tensile strength of the electromagnetic shielding sheet were measured by the following method.

[0156] <Measurement of the acid value of resin>

[0157] The acid value is measured in accordance with JIS K0070. Accurately weigh about 1g of the sample in a stoppered conical flask, add 100ml of a mixture of tetrahydrofuran / ethanol (volume ratio: tetrahydrofuran / ethanol = 2 / 1) to dissolve it. Add phenolphthalein test solution as an indicator, titrate with 0.1N alcoholic potassium hydroxide solution, and the end point is when the indicator remains light red for 30 seconds. The acid value (unit: mgKOH / g) is calculated according to the following formula.

[0158] Acid value (mgKOH / g) = (5.611×a×F) / S

[0159] in,

[0160] S: Sample quantity (g)

[0161] a: Consumption of 0.1N alcoholic potassium hydroxide solution (ml)

[0162] F: Titer of 0.1N alcoholic potassium hydroxide solution

[0163] <Measurement of weight average molecular weight (Mw) of resin>

[0164] The weight average molecular weight (Mw) is measured using a gel permeation chromatograph (GPC) "HPC-8020" manufactured by Tosoh Co., Ltd. GPC is a liquid chromatograph that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on differences in their molecular sizes. The measurement in the present invention is performed by connecting two "LF-604" (manufactured by Showa Denko Co., Ltd.: GPC column for rapid analysis: 6mmID×150mm size) in series and using them as columns, and is performed under the conditions of a flow rate of 0.6ml / min and a column temperature of 40°C. The weight average molecular weight (Mw) is determined by polystyrene conversion.

[0165] <Glass transition temperature (Tg) of resin>

[0166] The Tg was measured by differential scanning calorimetry ("DSC-1" manufactured by Mettler Toledo).

[0167] <Measurement of average particle size of conductive filler>

[0168] D 50 The average particle size is a value obtained by measuring the conductive filler using a laser diffraction / scattering particle size distribution measuring device LS13320 (manufactured by Beckman Coulter) and a tornado dry powder sample module, and is the particle size at which the cumulative value in the particle size cumulative distribution is 50%. In addition, the refractive index is set to 1.6.

[0169] <Measurement of the circularity coefficient of the opening>

[0170] A planar image of the metal layer was acquired at a magnification of 2000 to 5000 times using a reflection electron microscope JSM-IT100 (JEOL Ltd.) so that the number of openings in the metal layer was about 20, and the analysis was performed by the above method.

[0171] <Determination of tensile breaking strength>

[0172] Prepare two electromagnetic wave shielding sheets, peel off the release films on the conductive adhesive layer side of each sheet, and use a hot roll laminator to bond the conductive adhesive layers of each other to obtain a laminate. After cutting the laminate into a size of 20 mm in width × 60 mm in length, peel off both sides of the peelable film on the protective layer side to prepare a test sample. For the test sample, a small desktop tester EZ-TEST (manufactured by Shimadzu Corporation) was used to perform a tensile test (test speed 50 mm / min) at a temperature of 25°C and a relative humidity of 50%. The tensile breaking strength (N / 20mm) of the electromagnetic wave shielding sheet was calculated based on the obtained SS curve (stress-strain curve).

[0173] Next, the raw materials used in Examples are shown below.

[0174] "raw material"

[0175] Conductive filler: composite fine particles (dendritic fine particles in which 100 parts by weight of copper as a core is coated with 10 parts by weight of silver), average particle size D 50 :11.0μm Made by Fukuda Metal Foil Powder Industry Co., Ltd.

[0176] Thermosetting resin: polyurethane urea resin having an acid value of 5 mgKOH / g, a weight average molecular weight of 54,000, and a Tg of -7°C (manufactured by Toyo Chemical Co., Ltd.)

[0177] Epoxy compound: "JER828" (bisphenol A type epoxy resin epoxy equivalent = 189 g / eq) manufactured by Mitsubishi Chemical Corporation

[0178] Aziridine compound: "Chemitite PZ-33" manufactured by Japan Catalyst Co., Ltd.

[0179] <Production of Conductive Resin Composition 1>

[0180] In terms of solid content, 100 parts of thermosetting resin, 52 parts of conductive filler, 10 parts of epoxy compound and 0.5 parts of aziridine compound are placed in a container, a mixed solvent (toluene: isopropanol = 2:1 (weight ratio)) is added in such a way that the concentration of non-volatile components becomes 40%, and the mixture is stirred for 10 minutes using a disperser to obtain a conductive resin composition.

[0181] The conductive resin composition was applied onto the 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 a conductive resin composition (conductive adhesive layer) 1 .

[0182] <Manufacturing of Conductive Resin Compositions 2 to 15>

[0183] Conductive resin compositions (conductive adhesive layer) 2 to 15 shown in Tables 1 and 2 were prepared in the same manner as in Conductive Resin Composition 1 except that the addition amounts of the conductive filler and the epoxy compound were changed.

[0184] Table 1

[0185]

[0186] Table 2

[0187]

[0188] [Example 1]

[0189] 100 parts of thermosetting resin, 10 parts of epoxy compound and 1 part of aziridine compound were added in terms of solid content, and stirred for 10 minutes using a disperser to obtain a resin composition. The obtained resin composition was applied to copper foil using a bar coater to a dry thickness of 5 μm, and dried in an electric oven at 100° C. for 2 minutes, and then a slightly adhesive release sheet was attached to the protective layer.

[0190] Next, the copper carrier of the copper foil is peeled off, and the conductive adhesive layer is bonded to the copper foil surface, thereby obtaining an electromagnetic wave shielding sheet including "peelable sheet / protective layer / copper foil / conductive adhesive layer / peelable sheet". The bonding of the copper foil and the conductive adhesive layer is carried out at a temperature of 90°C and a pressure of 3kgf / cm 2 Next, pass through the heat laminator to bond.

[0191] In addition, copper foil has Figure 3 The openings of the copper foil are formed by forming a pattern resist layer on the copper foil formed on the copper carrier via a release layer and etching the copper foil.

[0192] [Example 2 to Example 33, Comparative Example 1 to Comparative Example 3]

[0193] The electromagnetic shielding sheets of Examples 2 to 33 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 except that the types of the conductive adhesive layer and the copper foil were changed.

[0194] In addition, the copper foils of the examples and comparative examples were obtained by forming a pattern resist layer on the copper foil formed on the copper carrier via a release layer and forming openings by etching, as in Example 1. The circularity coefficient and aperture ratio of the openings of the copper foils in the examples and comparative examples are shown in Tables 3 to 6.

[0195] The following evaluations were performed using the obtained electromagnetic shielding sheet. The results are shown in Tables 3 to 6.

[0196] <Reflow resistance>

[0197] Reflow resistance is evaluated by whether the electromagnetic shielding sheet changes in appearance after contacting molten solder. The appearance of an electromagnetic shielding sheet with high reflow resistance does not change, but an electromagnetic shielding sheet with low reflow resistance foams or peels off.

[0198] First, peel off the removable sheet of the conductive adhesive layer of the electromagnetic wave shielding sheet with a width of 25mm and a length of 70mm, and crimp the exposed conductive adhesive layer to the gold-plated surface of the gold-plated copper-clad laminate (gold plating 0.3μm / nickel plating 1μm / copper foil 18μm / adhesive 20μm / polyimide film 25μm) with a total thickness of 64μm at 150℃, 2.0MPa, and 30 minutes to thermally cure it to obtain a laminate. The obtained laminate was cut into a size of 10mm in width and 65mm in length to prepare a sample. The obtained sample was placed in a gas environment of 40℃ and 90%RH for 72 hours. After that, the polyimide film surface of the sample was floated on the molten solder at 250℃ for 1 minute with the polyimide film surface facing down, and then the sample was taken out and its appearance was visually observed. The presence of abnormalities such as foaming, bulging, and peeling was evaluated according to the following criteria.

[0199] ◎: No change in appearance.

[0200] ○: A small amount of small foaming was observed.

[0201] △: A large number of small bubbles were observed.

[0202] △△: Small bubbles were observed on the entire surface of the sample.

[0203] ×: Severe foaming or peeling was observed.

[0204] <Electromagnetic wave shielding properties>

[0205] The electromagnetic wave shielding property was evaluated by measuring the crosstalk. The crosstalk was evaluated using the following measurement samples.

[0206] (Manufacture of wiring boards having coplanar circuits)

[0207] Figure 2 2 is a schematic plan view of the main surface side of a flexible printed wiring board with a coplanar circuit (hereinafter, also referred to as a wiring board with a coplanar circuit) 20 used in the measurement, Figure 3A schematic plan view of the back side is shown in the figure. First, prepare a double-sided CCL "R-F775" (manufactured by Panasonic) formed by laminating 12μm thick rolled copper foil on both sides of a 50μm thick polyimide film 50. Then, 6 through holes 51 (diameter 0.1mm) are provided near each of the four corners of the rectangular shape. In addition, for the convenience of illustration, only two through holes 51 are shown at each corner. Subsequently, after an electroless plating treatment, an electrolytic plating treatment is performed to form a 10μm copper-plated film 52, and conduction between the two main surfaces is ensured via the through holes 51. Afterwards, as Figure 2 As shown, two signal wirings 53 with a length of 10 cm, a ground wiring 54 on the outside thereof parallel to the signal wiring 53, and a ground pattern (i) 55 extending from the ground wiring 54 and including a through hole 51 in the short side direction of the polyimide film 50 are formed on the main surface of the polyimide film 50.

[0208] Thereafter, the copper foil formed on the back side of the polyimide film 50 is etched to obtain a ground pattern (i) 55 at a position corresponding to the ground pattern (i). Figure 3 The back side grounding pattern (ii) 56 as shown. The inspection specifications for the appearance and tolerance of the circuit are set to the Japan Electronics Packaging and Circuit Association (JPCA) standard (JPCA-DG02). Next, a top coating 8 "CISV1215 (Nikkan Industries Co., Ltd.)" comprising a polyimide film 8a (thickness 12.5μm) and a conductive adhesive layer 8b (thickness 15μm) is attached to the main surface side of the polyimide film 50 (refer to Figure 2 ). In addition, Figure 2 In the figure, the top coat layer 8 is shown in a perspective view so that the structure of the signal wiring 53 and the like can be clearly understood. Thereafter, the copper foil pattern exposed from the top coat layer 8 is subjected to nickel plating (not shown) and then to gold plating (not shown).

[0209] Secondly, if Figure 4 As shown, an electromagnetic wave shielding sheet 10 including a laminate of a conductive adhesive layer 1, a metal layer 2, and a protective layer 3 is prepared, and a peelable sheet (not shown) provided on the conductive adhesive layer 1 of the electromagnetic wave shielding sheet 10 is peeled off. Then, the conductive adhesive layer 1 of the electromagnetic wave shielding sheet 10 is placed inside and crimped onto the entire back side of a wiring board 20 having a coplanar circuit under the conditions of 150°C, 2.0 MPa, and 30 minutes, thereby obtaining a wiring board 20 having a coplanar circuit with an electromagnetic wave shielding sheet. Figure 4 , the back side ground pattern (ii) 56 is shown in a perspective view.

[0210] (Manufacture of wiring board with microstrip line circuit)

[0211] picture Figure 5 and Figure 6 In that way, a wiring board 30 having a microstrip line circuit is separately manufactured. First, prepare a double-sided CCL "R-F775" (manufactured by Panasonic Corporation) formed by laminating rolled copper foil with a thickness of 12 μm. Then, two signal wirings 35 with a length of 10 cm are formed on one of the surfaces by etching. The inspection specifications for the appearance and tolerance of the circuit are set to the JPCA standard (JPCA-DG02). Secondly, a covering layer 31 "CISV1215 (manufactured by Nikkan Industries Co., Ltd.)" (refer to Figure 5 ). In addition, Figure 5 In the figure, the cover layer 31 is shown in a perspective view so that the structure of the signal wiring 35 and the like can be clearly understood. Then, the signal wiring 35 exposed from the cover layer 31 is plated with nickel (not shown) and then with gold (not shown). Figure 6 As shown, a ground layer 34 is provided on the back side of the polyimide film 33 .

[0212] (Test piece preparation)

[0213] Then, the signal wiring 35 side of the wiring board 30 having the microstrip line circuit is laminated in such a manner as to contact the electromagnetic wave shielding sheet 10 side of the wiring board 20 having the coplanar circuit, and fixed with a jig. A schematic cross-sectional view of the laminate is shown in FIG. Figure 7 and Figure 8 . Figure 7 Equivalent to Figure 2 The XI-XI cut section diagram, Figure 8 Equivalent to Figure 2 Cross-sectional view of the XII-XII cut portion.

[0214] A network analyzer E5071C (manufactured by Agilent Japan) was connected to the signal wiring 35 exposed on the wiring board 30 having a microstrip line circuit and the signal wiring 53 exposed on the wiring board 20 having a coplanar circuit. Then, a sine wave of 10 MHz to 20 GHz was input to the signal wiring 35 of the wiring board 30 having a microstrip line circuit, and the crosstalk in the wiring board 20 having a coplanar circuit was measured at this time, and the influence of electromagnetic wave shielding properties was confirmed by this value.

[0215] The L / S (line / space) of the signal wiring 35 was appropriately adjusted so that the characteristic impedance was ±10Ω. 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.

[0216] The measured crosstalk was evaluated based on the following criteria. The evaluation results (electromagnetic wave shielding properties) are shown in Tables 3 to 6.

[0217] ◎: Insufficient crosstalk at 10GHz -55dB

[0218] ○: Crosstalk at 10GHz is -55dB or more and less than -50dB

[0219] △: Crosstalk at 10GHz is -50dB or more and less than -45dB

[0220] ×: Crosstalk at 10 GHz is -45 dB or more

[0221] <Electromagnetic wave shielding properties after aging at high temperature and high humidity>

[0222] The wiring board 20 with a coplanar circuit having an electromagnetic shielding sheet was placed in a high temperature and high humidity environment of 85°C and 85% for 500 hours, and then the crosstalk at 10 GHz was measured. The electromagnetic shielding property was measured in the same manner as above except that it was placed in a high temperature and high humidity environment for 500 hours.

[0223] ◎: Insufficient crosstalk at 10GHz -55dB

[0224] ○: Crosstalk at 10GHz is -55dB or more and less than -50dB

[0225] △: Crosstalk at 10GHz is -50dB or more and less than -45dB

[0226] ×: Crosstalk at 10 GHz is -45 dB or more

[0227] <Crack resistance>

[0228] For an electromagnetic wave shielding sheet with a width of 50 mm and a length of 50 mm, a releasable sheet without peeling off the conductive adhesive layer was heat pressed at 150°C and 5.0 MPa for 30 minutes. After that, the releasable sheet was peeled off and the presence or absence of cracks in the metal layer was confirmed from the conductive adhesive side using an optical microscope. The evaluation criteria are as follows.

[0229] ◎: No cracks, which is a very good result.

[0230] ○: One to five crack sites are considered good results.

[0231] △: There are 6 to 10 crack sites, which is not a problem in practical use.

[0232] ×: The device has 11 or more cracks and cannot be used practically.

[0233] <Connection reliability to small opening passages>

[0234] like Figure 9(1) to Figure 9(3) As shown, a copper foil circuit 22A and a copper foil circuit 22B having a thickness of 18 μm and not electrically connected to each other are formed on a polyimide film 21 having a thickness of 25 μm. Next, a copper foil circuit 22A having a thickness of 37.5 μm and a diameter of 1.1 mm (the passage area is 1.0 mm 2 ) of the circular passage 24 with an adhesive polyimide cover layer 23 to form a flexible printed wiring board.

[0235] Furthermore, an electromagnetic wave shielding sheet 25 having a width of 20 mm and a length of 50 mm is prepared. Figure 9(4) to Figure 9(6) As shown, the removable sheet is peeled off from the electromagnetic shielding sheet 25, and the exposed conductive adhesive layer 25b is pressure-bonded to the flexible printed wiring board formed as described above under the conditions of 150°C, 2 MPa, and 30 minutes, and the conductive adhesive layer 25b and the protective layer 25a of the electromagnetic shielding sheet are cured.

[0236] Next, the peelable sheet on the protective layer 25a side of the sample is removed, and the "Loresta GP" BSP probe manufactured by Mitsubishi Chemical is used to measure the initial connection resistance value between 22A-22B shown in the plan view of Figure 9 (4). In addition, Figure 9 (2) is a D-D' cross-sectional view of Figure 9 (1), and Figure 9 (3) is a C-C' cross-sectional view of Figure 9 (1). Similarly, Figure 9 (5) is a D-D' cross-sectional view of Figure 9 (4), and Figure 9 (6) is a C-C' cross-sectional view of Figure 9 (4). For the diameter of the passage, from 1.1mm (the passage area is 1.0mm 2 ) to 0.1mm (the passage area is 0.008mm 2 ) were produced with a scale of 0.1 mm, and for each, a connection reliability test was carried out in the same manner as described above to confirm the minimum via diameter at which the connection resistance value became 200 mΩ or less.

[0237] The evaluation criteria for connection reliability are as follows.

[0238] ◎: Minimum passage diameter is 0.2mm (passage area is 0.03mm 2 ) or less. This is a very good result.

[0239] ○: Minimum passage diameter is 0.3mm (passage area is 0.07mm 2 ) and above 0.6mm (the passage area is 0.3mm 2 ) or less. This is a good result.

[0240] △: Minimum passage diameter is 0.7mm (passage area is 0.4mm 2 ) and above 1.0mm (the passage area is 0.8mm 2) or less. There is no problem in practical use.

[0241] ×: Minimum passage diameter is 1.1 mm (passage area is 1.0 mm 2 ) or is not less than 200mΩ. Not practical.

[0242] Table 3

[0243]

[0244] Table 4

[0245]

[0246] Table 5

[0247]

[0248] Table 6

[0249]

[0250] From the disclosure set forth, it is obvious that the embodiments of the present disclosure can be modified in many ways. Such variations should not be regarded as departing from the spirit and scope of the present disclosure, and all such modifications obvious to those skilled in the art are intended to be included within the scope of the claims.

Claims

1. An electromagnetic wave shielding sheet, characterized in that: It includes a protective layer, a metal layer and a conductive adhesive layer. The metal layer has a plurality of openings, and the opening ratio of the openings is 0.1% to 20%. The tensile breaking strength is 30N / 20mm~80N / 20mm, The thickness of the metal layer is 0.5 μm to 5 μm, The conductive adhesive layer contains a thermosetting resin and a conductive filler. The content of the conductive filler in the conductive adhesive layer is 35% by mass to 90% by mass.

2. The electromagnetic wave shielding sheet according to claim 1, characterized in that The average value of the circularity coefficient of the opening of the metal layer calculated according to the following formula is greater than 0.5; Circularity coefficient = (area × 4π) / (circumference) 2 The circumference refers to the length of the periphery when the opening is two-dimensionally projected by extracting an image obtained by observing the metal layer using any one of an optical microscope, a laser microscope and an electron microscope, in which the plane of the opening is extracted to be perpendicular to the observation viewpoint and the opening as a whole can be confirmed; the area refers to the width of the area defined by the periphery when the extracted opening is two-dimensionally projected.

3. A printed wiring board, characterized in that include: An electromagnetic shielding sheet, a top coat layer, and a wiring board having a signal wiring and an insulating substrate according to claim 1 or 2.

4. The printed wiring board according to claim 3, wherein The signal wiring has a signal circuit and a ground circuit. A passage is provided in the topcoat layer for exposing the ground circuit, The passage area is 0.008 mm 2 Above and 0.8mm 2 the following.

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