Electromagnetic wave shielding film and shielding printed circuit board

Abstract

Provided is an electromagnetic wave shielding film in which expansion does not readily occur between a ground circuit and an adhesive layer, even if the electromagnetic wave shielding film is used for a long period of time in a high-temperature, high-humidity environment, in which the adhesive layer of the electromagnetic wave shielding film and the ground circuit of the printed circuit board are brought into contact with each other. This electromagnetic wave shielding film is provided with an adhesive layer and a first protective layer disposed on the adhesive layer, and is characterized in that the first protective layer contains a urethane resin having an acid value of 2000-4000 g / eq and silica particles, and the adhesive layer contains a urethane resin having an acid value of 2000-4000 g / eq, an imidazole compound, and a flame retardant containing phosphorus.

Description

Technical Field

[0001] The invention relates to an electromagnetic wave shielding film and a shielding printed circuit board. Background Art

[0002] Conventionally, an electromagnetic wave shielding film is attached to a printed circuit board such as a flexible printed circuit board (FPC) to shield electromagnetic waves from the outside.

[0003] Electromagnetic wave shielding films typically have a structure comprising a conductive adhesive layer, a shielding layer composed of a metal film, etc., and a protective layer laminated in this order. The electromagnetic wave shielding film is laminated onto a printed circuit board and then hot-pressed, thereby bonding the electromagnetic wave shielding film to the printed circuit board via the conductive adhesive layer, thereby producing a shielded printed circuit board.

[0004] The printed circuit board has a structure in which a printed pattern on a base film is covered with an insulating film, and the printed pattern also includes a printed pattern serving as a ground circuit.

[0005] When manufacturing a shielded printed circuit board as described above, it is known that an opening is provided on the insulating film to expose the ground circuit, and when the electromagnetic shielding film is arranged on the printed circuit board in such a manner that the conductive adhesive layer of the electromagnetic shielding film contacts the ground circuit, the shielding properties are good.

[0006] As such an electromagnetic wave shielding film, patent document 1 discloses an electromagnetic wave shielding film, which is characterized in that it is an electromagnetic wave shielding film formed by stacking an insulating resin layer, a shielding layer and a conductive adhesive layer in sequence, and the insulating resin layer and the conductive adhesive layer contain a flame retardant containing only a specified amount of phosphorus or nitrogen, and the insulating resin layer contains 10 to 100 parts by mass of the flame retardant containing phosphorus or nitrogen relative to 100 parts by mass of the thermosetting resin in the insulating resin layer, and the conductive adhesive layer contains 10 to 100 parts by mass of the flame retardant containing phosphorus or nitrogen relative to 100 parts by mass of the thermosetting resin in the conductive adhesive layer.

[0007] Patent Document 1 discloses a shielded flexible printed circuit board in which a conductive adhesive layer of an electromagnetic shielding film is brought into contact with a ground circuit of a printed circuit board.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2022-21641 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] When a printed circuit board (a shielded flexible printed circuit board) with an electromagnetic wave shielding film described in Patent Document 1, in which the conductive adhesive layer (adhesive layer) of the film contacts the ground circuit of the printed circuit board, is used for a long time in a high-temperature, high-humidity environment, there is a problem in which metal or other precipitates are generated between the ground circuit of the printed circuit board and the adhesive layer, causing expansion, deterioration of the appearance, or reduction in connection reliability. This problem is particularly prominent when the adhesive layer contains phosphorus and the thickness of the adhesive layer after being applied to the printed circuit board is thin.

[0013] Furthermore, when a protective nickel-gold plating layer is formed on the surface of the ground circuit, phosphorus contained in the adhesive layer reacts with surrounding moisture and nickel, causing nickel to precipitate on the surface of the nickel-gold plating layer. This nickel precipitation on the surface of the nickel-gold plating layer can cause expansion between the ground circuit and the adhesive layer.

[0014] The present invention is completed to solve the above-mentioned problems. The purpose of the present invention is to provide an electromagnetic wave shielding film that is not prone to expansion between the ground circuit and the adhesive layer even when a shielded printed circuit board is used for a long time in a high temperature and high humidity environment so that the adhesive layer of the electromagnetic wave shielding film is in contact with the ground circuit of the printed circuit board.

[0015] Solutions for solving problems

[0016] The inventors discovered that the reason for the precipitation and expansion of metals etc. between the ground circuit and the adhesive layer is the moisture between the ground circuit and the adhesive layer. If the water resistance of the adhesive layer and the protective layer is improved, the precipitation of metals etc. can be prevented, thus completing the present invention.

[0017] That is, the electromagnetic wave shielding film of the present invention is characterized in that it has an adhesive layer and a first protective layer arranged on the above-mentioned adhesive layer, the above-mentioned first protective layer contains an urethane resin with an acid value of 2000 to 4000 g / eq and silica particles, and the above-mentioned adhesive layer contains an urethane resin with an acid value of 2000 to 4000 g / eq, an imidazole compound and a flame retardant containing phosphorus.

[0018] In the electromagnetic shielding film of the present invention, the adhesive layer contains a urethane resin having an acid value of 2000 to 4000 g / eq and an imidazole compound.

[0019] The electromagnetic shielding film of the present invention is placed on a printed circuit board by hot pressing. During this process, the urethane resins in the adhesive layer crosslink, causing the adhesive layer to cure. During this curing reaction, the imidazole compound functions as a curing accelerator.

[0020] If the acid value of the urethane resin contained in the adhesive layer is within the above range, the crosslinking density increases during curing of the adhesive layer, thereby improving the moisture resistance of the adhesive layer. Therefore, even when a shielded printed circuit board equipped with the electromagnetic wave shielding film of the present invention is used for a long time in a high temperature and high humidity environment, metal precipitates, etc., are unlikely to form between the ground circuit and the adhesive layer, and expansion is unlikely to occur.

[0021] If the acid value of the urethane resin contained in the adhesive layer is less than 2000 g / eq, the crosslinking density of the adhesive layer after curing becomes high, which reduces embedding properties. In addition, when stress is generated, it becomes difficult to absorb the stress.

[0022] When the acid value of the urethane resin contained in the adhesive layer exceeds 4000 g / eq, the crosslinking density becomes low and the moisture resistance decreases.

[0023] In the electromagnetic shielding film of the present invention, the adhesive layer contains a flame retardant containing phosphorus.

[0024] Therefore, the adhesive layer is less likely to burn.

[0025] It should be noted that flame retardants containing phosphorus easily absorb moisture. Therefore, if the adhesive layer contains a flame retardant containing phosphorus, the moisture content of the adhesive layer increases.

[0026] If the moisture content of the adhesive layer increases, metal and other precipitates are likely to form between the ground circuit and the adhesive layer, which can easily cause expansion. However, as described above, in the electromagnetic wave shielding film of the present invention, the adhesive layer after curing has a high crosslinking density and high moisture resistance.

[0027] Therefore, even if the adhesive layer contains a flame retardant containing phosphorus, swelling is unlikely to occur.

[0028] In the electromagnetic shielding film of the present invention, the first protective layer contains a urethane resin having an acid value of 2000 to 4000 g / eq.

[0029] The electromagnetic wave shielding film of the present invention is placed on a printed circuit board by heat pressing. At this time, the urethane resin contained in the first protective layer is cross-linked, and the first protective layer is cured.

[0030] If the acid value of the urethane resin contained in the first protective layer is within the above range, the crosslinking density increases during curing of the first protective layer, thereby improving the moisture resistance of the first protective layer. High moisture resistance of the first protective layer reduces the formation of metal and other precipitates between the ground circuit and the adhesive layer, thereby preventing expansion.

[0031] When the acid value of the urethane resin contained in the first protective layer is less than 2000 g / eq, the strength of the first protective layer after curing becomes too high, and the bending resistance (toughness) becomes low.

[0032] When the acid value of the urethane resin contained in the first protective layer exceeds 4000 g / eq, the strength is reduced, and the first protective layer may be damaged during heat pressing of the electromagnetic shielding film.

[0033] In the electromagnetic shielding film of the present invention, the first protective layer contains silica particles. The silica particles function as a filler, thereby increasing the strength of the first protective layer.

[0034] In the electromagnetic shielding film of the present invention, the melting point of the imidazole compound is preferably 150 to 220°C.

[0035] Such an imidazole compound functions suitably as a curing accelerator for the adhesive layer.

[0036] In the electromagnetic shielding film of the present invention, the adhesive layer preferably contains an epoxy resin having an epoxy value of 1000 g / eq or less.

[0037] When the adhesive layer contains such an epoxy resin, the crosslinking density of the cured adhesive layer can be increased.

[0038] In particular, when the epoxy resin is a phenol novolac type, the adhesive layer has heat resistance and low hydrolysis properties.

[0039] In the electromagnetic shielding film of the present invention, the adhesive layer is preferably a conductive adhesive.

[0040] When the adhesive layer is a conductive adhesive, when the electromagnetic shielding film of the present invention is placed on a printed circuit board, the ground circuit of the printed circuit board can be electrically connected to the conductive adhesive layer by bringing the ground circuit into contact with the conductive adhesive layer.

[0041] In the electromagnetic shielding film of the present invention, it is preferable that a metal layer is disposed between the adhesive layer and the first protective layer.

[0042] Such a metal layer functions as a shielding layer that absorbs and reflects electromagnetic waves, thereby improving the shielding properties of the electromagnetic shielding film of the present invention.

[0043] In the electromagnetic shielding film of the present invention, it is preferable that a second protective layer is formed on the main surface of the first protective layer opposite to the main surface facing the adhesive layer, and the second protective layer is harder than the first protective layer.

[0044] When the electromagnetic shielding film of the present invention has such a second protective layer, it is possible to prevent damage due to external impact or the like and damage due to abrasion.

[0045] In addition, in this specification, the "hardness" of the first protective layer and the second protective layer refers to the Young's modulus measured by an indentation test using a nanoindenter in accordance with ISO14577.

[0046] In the electromagnetic shielding film of the present invention, preferably, the thickness of the adhesive layer is 5 μm to 14 μm, and when the electromagnetic shielding film is hot-pressed at 3 MPa, 170° C., and 30 minutes, the thickness of the adhesive layer is 2 μm to 10 μm.

[0047] In a shielded printed circuit board configured with an electromagnetic wave shielding film by hot pressing, when the thickness of the adhesive layer of the electromagnetic wave shielding film is relatively thin, if the shielded printed circuit board is used for a long time in a high temperature and high humidity environment, metal precipitates such as metal will be generated between the ground circuit and the adhesive layer, which is prone to expansion.

[0048] However, the electromagnetic shielding film of the present invention has high moisture resistance as described above. Therefore, even if the thickness of the adhesive layer after hot pressing is 2 μm to 10 μm, metal and other precipitates are unlikely to form between the ground circuit and the adhesive layer, and swelling can be prevented.

[0049] The shielded printed circuit board of the present invention is characterized in that it includes a printed circuit board and an electromagnetic wave shielding film arranged on the above-mentioned printed circuit board, the above-mentioned printed circuit board has a base film, a printed circuit arranged on the above-mentioned base film, and a covering layer arranged in a manner covering the above-mentioned printed circuit, the above-mentioned printed circuit includes a grounding circuit, and an opening portion is formed on the above-mentioned covering layer to expose the above-mentioned grounding circuit, the above-mentioned electromagnetic wave shielding film has an adhesive layer and a first protective layer arranged on the above-mentioned adhesive layer, the above-mentioned first protective layer includes a cured product of a urethane resin with an acid value of 2000 to 4000 g / eq and silica particles, the above-mentioned adhesive layer includes a cured product of a urethane resin with an acid value of 2000 to 4000 g / eq, an imidazole compound and a flame retardant containing phosphorus, the above-mentioned adhesive layer of the above-mentioned electromagnetic wave shielding film fills the above-mentioned opening portion of the above-mentioned printed circuit board and is in contact with the above-mentioned grounding circuit.

[0050] The shielded printed circuit board of the present invention is obtained by disposing the electromagnetic wave shielding film of the present invention on a printed circuit board.

[0051] Therefore, even when the shielded printed circuit board of the present invention is used for a long time in a high-temperature and high-humidity environment, metal and other precipitates are unlikely to form between the ground circuit of the printed circuit board and the adhesive layer of the electromagnetic shielding film, thereby preventing expansion.

[0052] Effects of the Invention

[0053] According to the present invention, it is possible to provide an electromagnetic shielding film that is less likely to expand between the ground circuit and the adhesive layer even when a shielded printed circuit board is used for a long time in a high temperature and high humidity environment in which the adhesive layer of the electromagnetic shielding film is in contact with the ground circuit of the printed circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a cross-sectional view schematically showing an example of the electromagnetic shielding film according to the first embodiment of the present invention.

[0055] Figure 2 It is a cross-sectional view schematically showing an example of a modification of the electromagnetic shielding film according to the first embodiment of the present invention.

[0056] Figure 3A This is a process diagram schematically showing an example of a printed circuit board preparation step in the method for manufacturing a shield printed circuit board according to the first embodiment of the present invention.

[0057] Figure 3B This is a process diagram schematically showing an example of an electromagnetic shielding film placement step in the method for manufacturing a shielded printed wiring board according to the first embodiment of the present invention.

[0058] Figure 3C This is a process diagram schematically showing an example of a hot pressing step in the method for manufacturing a shield printed wiring board according to the first embodiment of the present invention.

[0059] Figure 4 It is a cross-sectional view schematically showing an example of a shield printed circuit board according to the first embodiment of the present invention.

[0060] Figure 5 It is a cross-sectional view schematically showing an example of the electromagnetic shielding film according to the second embodiment of the present invention.

[0061] Figure 6 It is a cross-sectional view schematically showing the method of the bendability test.

[0062] Figure 7A This is a photograph of the appearance of the electromagnetic shielding film according to Example 1 after 1000 hours of the expansion confirmation test.

[0063] Figure 7B This is a photograph of the appearance of the electromagnetic shielding film according to Comparative Example 1 after 1000 hours of the expansion confirmation test.

[0064] Figure 8A This is an SEM image of a cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Example 1.

[0065] Figure 8B This is an SEM image of a cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of the expansion confirmation test conducted using the electromagnetic shielding film according to Comparative Example 1.

[0066] Figure 9A This is an image showing nickel distribution in a cross section of a contact portion between an adhesive layer and a printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Example 1.

[0067] Figure 9B This is an image showing nickel distribution in a cross section of a contact portion between an adhesive layer and a printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Comparative Example 1.

[0068] Figure 10A This is an image showing the distribution of phosphorus in a cross section of a contact portion between an adhesive layer and a printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Example 1.

[0069] Figure 10B This is an image showing the distribution of phosphorus in the cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of the expansion confirmation test conducted using the electromagnetic shielding film according to Comparative Example 1.

[0070] Figure 11A It is a cross-sectional view schematically showing a method of a connection resistance value measurement test.

[0071] Figure 11B It is a cross-sectional view schematically showing a method of a connection resistance value measurement test. DETAILED DESCRIPTION

[0072] Hereinafter, the electromagnetic shielding film of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0073] (First embodiment)

[0074] Figure 1 It is a cross-sectional view schematically showing an example of the electromagnetic shielding film according to the first embodiment of the present invention.

[0075] Figure 1 The electromagnetic shielding film 10 shown includes an adhesive layer 20 , a first protective layer 41 disposed on the adhesive layer 20 , and a metal layer 30 disposed between the adhesive layer 20 and the first protective layer 41 .

[0076] In the electromagnetic shielding film 10 , the first protective layer 41 contains a urethane resin having an acid value of 2000 to 4000 g / eq and silica particles.

[0077] The adhesive layer 20 contains a urethane resin having an acid value of 2000 to 4000 g / eq, an imidazole compound, and a flame retardant containing phosphorus.

[0078] Each component is described in detail below.

[0079] (Adhesive layer)

[0080] The electromagnetic wave shielding film 10 is placed on the printed circuit board by hot pressing. During this process, the urethane resin in the adhesive layer 20 crosslinks, causing the adhesive layer 20 to cure. During this curing reaction, the imidazole compound functions as a curing accelerator. Furthermore, the adhesive layer 20 is in contact with the ground circuit.

[0081] If the acid value of the urethane resin contained in the adhesive layer 20 is between 2000 and 4000 g / eq, the crosslinking density increases during curing of the adhesive layer 20, thereby improving the moisture resistance of the adhesive layer 20. Therefore, even when the shielded printed circuit board equipped with the electromagnetic shielding film 10 is used for a long period of time in a high-temperature, high-humidity environment, metal and other precipitates are less likely to form between the ground circuit and the adhesive layer 20, thus preventing expansion. The acid value of the urethane resin contained in the adhesive layer 20 is preferably between 2100 and 3900 g / eq.

[0082] If the acid value of the urethane resin contained in the adhesive layer is less than 2000 g / eq, the crosslinking density of the adhesive layer after curing becomes high, which reduces embedding properties. In addition, when stress is generated, it becomes difficult to absorb the stress.

[0083] When the acid value of the urethane resin contained in the adhesive layer exceeds 4000 g / eq, the crosslinking density becomes low and the moisture resistance decreases.

[0084] In this specification, the "acid value of the resin" refers to the reciprocal of the molar equivalent of potassium hydroxide required to neutralize the free fatty acids present in 1 g of the resin, and the unit is "g / eq".

[0085] It should be noted that in the field to which the present invention pertains, "resin acid value" is sometimes also expressed as the number of milligrams of potassium hydroxide required to neutralize the free fatty acids present in 1 g of resin, in which case the unit is "mgKOH / g." These can be converted using the following formula (1).

[0086] [mgKOH / g]=56.11 / [g / eq]×1000···(1)

[0087] In addition, in this specification, "the acid value of a resin" can be measured according to JIS K0070:1992.

[0088] In the adhesive layer 20 , the content of the urethane resin having an acid value of 2000 to 4000 g / eq is preferably 30 to 80% by weight, more preferably 30 to 70% by weight.

[0089] When the content of the urethane resin having an acid value of 2000 to 4000 g / eq is within the above range, the crosslinking density of the adhesive layer 20 during curing becomes high, and the moisture resistance of the cured adhesive layer 20 can be improved.

[0090] The number average molecular weight of the urethane resin is preferably 10000 to 20000. The number average molecular weight of the urethane resin can be measured by gel permeation chromatography (GPC) under the following conditions.

[0091] Measuring instrument: Alliance GPC System (manufactured by Waters)

[0092] Column: Shodex GPC KF-806L (Showa Denko)

[0093] Column temperature: 40°C

[0094] Sample concentration: 0.05wt% / THF

[0095] Injection volume: 10 μL

[0096] Standard specimens: Tosoh: Standard PS500, Shodex Standard PS SM-105 (kit)

[0097] The glass transition temperature of the urethane resin is preferably 40° C. to 60° C. The glass transition temperature is determined by differential scanning calorimetry.

[0098] The adhesive layer 20 preferably contains an epoxy resin having an epoxy value of 1000 g / eq or less, and more preferably contains an epoxy resin having an epoxy value of 90 to 900 g / eq.

[0099] When the adhesive layer 20 contains such an epoxy resin, the crosslinking density of the cured adhesive layer 20 can be increased.

[0100] In addition, in this specification, "epoxy value of epoxy resin" can be measured according to JIS K7236:2001.

[0101] The melting point of the imidazole compound contained in the adhesive layer 20 is preferably 150 to 220°C, more preferably 160 to 210°C.

[0102] Such an imidazole compound functions suitably as a curing accelerator for the adhesive layer 20 .

[0103] The content of the imidazole compound in the adhesive layer 20 is preferably 0.1 to 10% by weight, more preferably 0.2 to 9.9% by weight.

[0104] If the content of the imidazole compound is less than 0.1% by weight, the adhesive layer is difficult to cure due to the small amount of the imidazole compound.

[0105] When the content of the imidazole compound exceeds 10% by weight, the effect as a curing catalyst approaches the upper limit, which is uneconomical.

[0106] The imidazole compound is not particularly limited, and 2-phenyl-4-methylimidazole (manufactured by Shikoku Chemicals, Ltd., model: 2P4MZ, melting point 174-184° C.), 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine (manufactured by Shikoku Chemicals, Ltd., model: 2MZ-A, 2MZA-PW, melting point 248-268° C.), 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine (manufactured by Shikoku Chemicals, Ltd., model: C11Z-A, melting point 187-195° C.), 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine (manufactured by Shikoku Chemicals, Ltd., model:

[0014] Examples of the present invention include oxazolyl-(1')-ethyl-s-triazine (manufactured by Shikoku Chemicals, Inc., model number: 2E4MZ-A, melting point 215-225°C), 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct (manufactured by Shikoku Chemicals, Inc., models: 2MA-OK, 2MAOK-PW, melting point 260°C), 2-phenyl-4,5-dihydroxymethylimidazole (manufactured by Shikoku Chemicals, Inc., model number: 2PHZ-PW, melting point 230°C), and 2-phenyl-4-methyl-5-hydroxymethylimidazole (manufactured by Shikoku Chemicals, Inc., model number 2P4MZ-PW, melting point 191-195°C). These may be used alone or in combination of two or more. Among them, 2-phenyl-4-methyl-5-hydroxymethylimidazole is particularly preferred.

[0107] In the electromagnetic shielding film 10 , the adhesive layer 20 contains a flame retardant containing phosphorus.

[0108] Therefore, the adhesive layer 20 is less likely to burn.

[0109] Furthermore, flame retardants containing phosphorus easily absorb water. Therefore, if the adhesive layer 20 contains a flame retardant containing phosphorus, the moisture content of the adhesive layer increases.

[0110] If the moisture content of the adhesive layer increases, metal and other precipitates are likely to form between the ground circuit and the adhesive layer 20, which can easily cause expansion. However, as described above, in the electromagnetic shielding film 10, the adhesive layer 20 after curing has a high crosslinking density and high moisture resistance.

[0111] Therefore, even if the adhesive layer 20 contains a flame retardant containing phosphorus, expansion is unlikely to occur between the ground circuit and the adhesive layer 20 .

[0112] The content of the phosphorus-containing flame retardant in the adhesive layer 20 is preferably 10% by weight to 40% by weight.

[0113] If the content of the phosphorus-containing flame retardant is less than 10% by weight, it is difficult to obtain a flame retardant effect.

[0114] When the content of the phosphorus-containing flame retardant exceeds 40% by weight, the adhesive layer is likely to contain moisture and swell.

[0115] As the flame retardant containing phosphorus, phosphate compounds such as melamine phosphate, polyphosphate melamine, guanidine phosphate, polyphosphate guanidine, ammonium phosphate, polyphosphate, ammonium amide, polyphosphate amide, phosphoric acid carbamate, polyphosphate carbamate, polyphosphate carbamate, polyphosphate compounds, red phosphorus, organophosphate compounds, phosphazene compounds, phosphonic acid compounds, diethyl phosphinate aluminum, methyl ethyl phosphinate aluminum, diphenyl phosphinate aluminum, ethyl butyl phosphinate aluminum, methyl butyl phosphinate aluminum, polyethylene phosphinate aluminum, phosphine oxide compounds, phosphorus ortho compounds, phosphoramide compounds etc. can be used. They can be used alone or in combination of two or more. Wherein, diethyl phosphinate aluminum is particularly preferred.

[0116] In the electromagnetic shielding film 10 , the adhesive layer 20 is preferably a conductive adhesive.

[0117] When the adhesive layer 20 is a conductive adhesive, when the electromagnetic shielding film 10 is placed on a printed circuit board, the ground circuit of the printed circuit board can be electrically connected to the adhesive layer 20 by bringing the conductive adhesive layer into contact with the ground circuit.

[0118] Furthermore, in the electromagnetic shielding film 10 , the adhesive layer 20 is also in contact with the metal layer 30 , and thus the ground circuit of the printed circuit board can be electrically connected to the metal layer 30 .

[0119] The metal layer 30 functions as a shielding layer for shielding electromagnetic waves, and thus the shielding characteristics are improved by being electrically connected to the ground circuit of the printed circuit board.

[0120] When the adhesive layer 20 is a conductive adhesive layer, it may have isotropic conductivity or anisotropic conductivity, preferably anisotropic conductivity. When the adhesive layer 20 has anisotropic conductivity, the transmission characteristics of high-frequency signals transmitted by the signal circuit of the printed circuit board are improved.

[0121] Such a conductive adhesive layer can be produced by adding conductive particles to the adhesive layer 20 .

[0122] The conductive particles are not particularly limited, and may be metal fine particles, carbon nanotubes, carbon fibers, metal fibers, or the like.

[0123] When the conductive particles are metal fine particles, the metal fine particles are not particularly limited and may be silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-coated copper powder obtained by silver-plating copper powder, fine particles obtained by coating polymer fine particles, glass beads, etc. with metal, etc.

[0124] Among them, from the viewpoint of economic efficiency, copper powder or silver-coated copper powder, which are available at low cost, is preferred.

[0125] The shape of the conductive particles is not particularly limited, and may be appropriately selected from spherical, flat, scaly, dendritic, rod-like, fibrous, and the like.

[0126] The particle size of the conductive particles (D 50 ) is preferably 4.0 μm to 30.0 μm, more preferably 4.0 μm to 20.0 μm.

[0127] The particle size of the conductive particles (D 50 ) is within the above range, the conductivity of the adhesive layer 20 becomes good.

[0128] It should be noted that the particle size (D 50 ) can be measured using a laser diffraction particle size distribution analyzer (SALD-2200 manufactured by Shimadzu Corporation).

[0129] When the adhesive layer 20 is a conductive adhesive layer, the content of the conductive particles is preferably 10% by weight to 70% by weight.

[0130] When the content of the conductive particles is within the above range, the conductivity of the conductive adhesive layer becomes good.

[0131] When the content of the conductive particles is less than 10% by weight, it becomes difficult for the adhesive layer to obtain conductivity.

[0132] When the content of the conductive particles exceeds 70% by weight, the adhesive layer becomes hard and the flexibility decreases.

[0133] In addition, when imparting anisotropic conductivity to the conductive adhesive layer, the content of the conductive particles is preferably 10% by weight to 40% by weight.

[0134] In the electromagnetic shielding film 10 , the thickness of the adhesive layer 20 before curing is preferably 5 μm to 14 μm, more preferably 6 μm to 14 μm.

[0135] Furthermore, when the electromagnetic shielding film 10 is hot-pressed under the conditions of 3 MPa, 170° C., and 30 minutes, the thickness of the adhesive layer 20 is preferably 2 μm to 10 μm.

[0136] In a shielded printed circuit board configured with an electromagnetic wave shielding film 10 by hot pressing, when the thickness of the adhesive layer of the electromagnetic wave shielding film is relatively thin, if the shielded printed circuit board is used for a long time in a high temperature and high humidity environment, metal precipitates such as the like are likely to be generated between the ground circuit and the adhesive layer, and expansion is likely to occur.

[0137] However, the electromagnetic shielding film 10 has high moisture resistance as described above. Therefore, even if the thickness of the adhesive layer 20 after hot pressing is 2 μm to 10 μm, expansion is unlikely to occur between the ground circuit and the adhesive layer 20 .

[0138] In the electromagnetic shielding film 10 , the adhesive layer 20 may further contain a resin component, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, an ultraviolet absorber, a defoaming agent, a leveling agent, a filler, a viscosity modifier, a dispersant, and the like.

[0139] Examples of the resin component include thermoplastic resin compositions such as styrene resin compositions, vinyl acetate resin compositions, polyester resin compositions, polyethylene resin compositions, polypropylene resin compositions, imide resin compositions, amide resin compositions, and acrylic resin compositions; and thermosetting resin compositions such as phenolic resin compositions, melamine resin compositions, and alkyd resin compositions.

[0140] (Metal layer)

[0141] In the electromagnetic shielding film 10 , the metal layer 30 functions as a shielding layer that absorbs and reflects electromagnetic waves. The formation of the metal layer 30 can improve the shielding properties of the electromagnetic shielding film 10 .

[0142] The metal layer preferably contains at least one metal selected from copper, silver, gold, aluminum, nickel, tin, palladium, chromium, titanium, and zinc. Alternatively, the metal layer may be formed of an alloy of at least two metals selected from this group.

[0143] The metal layer 30 formed of these metals can appropriately shield electromagnetic waves.

[0144] The metal layer 30 may be a rolled metal foil, a metal plating layer, or a metal vapor-deposited layer.

[0145] The thickness of the metal layer 30 is preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 6 μm.

[0146] When the thickness of the metal layer is less than 0.1 μm, the metal layer is too thin, resulting in reduced strength. Consequently, bending resistance is reduced. Furthermore, it is difficult to fully reflect and absorb electromagnetic waves, which can lead to reduced electromagnetic shielding properties.

[0147] When the thickness of the metal layer exceeds 10 μm, the entire electromagnetic shielding film becomes thick and difficult to handle.

[0148] (First protective layer)

[0149] In the electromagnetic shielding film 10 , the first protective layer 41 includes a urethane resin having an acid value of 2000 to 4000 g / eq.

[0150] The electromagnetic shielding film 10 is placed on the printed circuit board by heat pressing. At this time, the urethane resins contained in the first protective layer 41 are cross-linked, and the first protective layer 41 is cured.

[0151] If the acid value of the urethane resin contained in the first protective layer 41 is between 2000 and 4000 g / eq, the crosslinking density increases during curing of the first protective layer 41, thereby improving the moisture resistance of the first protective layer 41. High moisture resistance of the first protective layer reduces the formation of metal and other precipitates between the ground circuit and the adhesive layer, thus preventing expansion. The acid value of the urethane resin contained in the first protective layer 41 is more preferably between 2100 and 3900 g / eq.

[0152] When the acid value of the urethane resin contained in the first protective layer is less than 2000 g / eq, the strength of the first protective layer after curing becomes too high, and the bending resistance (toughness) becomes low.

[0153] When the acid value of the urethane resin contained in the first protective layer exceeds 4000 g / eq, the strength is reduced, and the first protective layer may be damaged during heat pressing of the electromagnetic shielding film.

[0154] In the first protective layer 41 , the content of the urethane resin having an acid value of 2000 to 4000 g / eq is preferably 50 to 90% by weight, more preferably 60 to 80% by weight.

[0155] When the content of the urethane resin having an acid value of 2000 to 4000 g / eq is within the above range, the crosslinking density of the first protective layer 41 during curing becomes high, and the moisture resistance of the cured first protective layer 41 can be improved.

[0156] In the electromagnetic shielding film 10 , the first protective layer 41 includes silica particles. The silica particles function as a filler, thereby increasing the strength of the first protective layer 41 .

[0157] The particle size of silica particles (D 50 ) is preferably 0.1 μm to 10 μm, more preferably 0.1 μm to 9 μm.

[0158] It should be noted that the particle size of the silica particles (D 50 ) can be measured using a laser diffraction particle size distribution analyzer (SALD-2200 manufactured by Shimadzu Corporation).

[0159] The content of the silica particles in the first protective layer 41 is preferably 5% by weight to 40% by weight, and more preferably 5% by weight to 30% by weight.

[0160] When the content of the silica particles is less than 5% by weight, it is difficult to sufficiently increase the strength of the first protective layer.

[0161] When the content of the silica particles exceeds 40% by weight, the first protective layer becomes too hard and its flexibility decreases.

[0162] In the electromagnetic shielding film 10 , the thickness of the first protective layer 41 is preferably 1 μm to 15 μm, and more preferably 3 μm to 10 μm.

[0163] If the thickness of the first protective layer is less than 1 μm, it is too thin to sufficiently protect the metal layer and the adhesive layer.

[0164] If the thickness of the first protective layer exceeds 15 μm, the electromagnetic shielding film becomes difficult to bend due to the excessive thickness, and the toughness of the first protective layer 41 decreases. Therefore, it is difficult to apply the film to a member requiring resistance to bending.

[0165] In the electromagnetic shielding film 10 , the first protective layer 41 may further include resin components, curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, ultraviolet absorbers, defoamers, leveling agents, flame retardants, viscosity modifiers, anti-blocking agents, dispersants, and the like.

[0166] Examples of the resin component include thermoplastic resins such as styrene resin compositions, vinyl acetate resin compositions, polyester resin compositions, polyethylene resin compositions, polypropylene resin compositions, imide resin compositions, and acrylic resin compositions; thermosetting resins such as phenolic resin compositions, epoxy resin compositions, urethane resin compositions, melamine resin compositions, and alkyd resin compositions; and active energy ray-curable compositions.

[0167] In the electromagnetic wave shielding film 10, the ratio of the acid value of the urethane resin contained in the adhesive layer 20 to the acid value of the urethane resin contained in the first protective layer 41 is preferably [acid value of the urethane resin contained in the adhesive layer (g / eq)]: [acid value of the urethane resin contained in the first protective layer (g / eq)] = 1:2 to 2:1, more preferably 1:1.5 to 1.5:1, and particularly preferably the same.

[0168] When the ratio of the acid value of the urethane resin contained in the adhesive layer 20 to the acid value of the urethane resin contained in the first protective layer 41 is within the above range, the difference in crosslink density between the cured adhesive layer 20 and the cured first protective layer 41 becomes smaller, and the degree of moisture resistance is also close.

[0169] It should be noted that in the electromagnetic wave shielding film 10, the acid value (g / eq) of the urethane resin contained in the adhesive layer 20 is preferably lower than the acid value (g / eq) of the urethane resin contained in the first protective layer. In this case, the crosslinking density of the cured adhesive layer 20 is higher than the crosslinking density of the cured first protective layer 41.

[0170] In this case, the moisture resistance of the cured adhesive layer 20 becomes higher, so that metal or the like is less likely to be deposited between the ground circuit and the adhesive layer 20 , and expansion can be further prevented.

[0171] In the electromagnetic shielding film 10 , the urethane resin contained in the adhesive layer 20 and the urethane resin contained in the first protective layer 41 may be of different types, but are preferably of the same type.

[0172] Next, modifications of the electromagnetic shielding film of the first embodiment will be described.

[0173] Figure 2 This is a cross-sectional view schematically showing an example of a modification of the electromagnetic shielding film according to the first embodiment of the present invention.

[0174] Figure 2 The electromagnetic shielding film 110 shown has a second protective layer 42 formed on the main surface of the first protective layer 41 opposite to the main surface facing the adhesive layer 20 . The second protective layer 42 is harder than the first protective layer 41 , which is different from the electromagnetic shielding film 10 described above.

[0175] When the electromagnetic shielding film 110 includes such a second protective layer 42 , it is possible to prevent damage due to external impact or the like, and damage due to abrasion.

[0176] The second protective layer 42 is preferably made of polyester resin.

[0177] The second protective layer 42 made of such a material is excellent in impact resistance and abrasion resistance, and also has high blocking resistance.

[0178] The thickness of the second protective layer 42 is preferably 0.1 μm to 5 μm, and more preferably 0.1 μm to 4 μm.

[0179] Next, a method for producing the shielded printed wiring board of the present invention using the electromagnetic shielding film of the first embodiment of the present invention will be described.

[0180] The method for manufacturing a shielded printed circuit board of the present invention comprises the following steps: (1) a printed circuit board preparation step, (2) an electromagnetic wave shielding film placement step, and (3) a hot pressing step.

[0181] Each step is described below.

[0182] (1) Printed circuit board preparation process

[0183] Figure 3A This is a process diagram schematically showing an example of a printed circuit board preparation step in the method for manufacturing a shield printed circuit board according to the first embodiment of the present invention.

[0184] First, if Figure 3A As shown, a printed circuit board 50 is prepared.

[0185] Figure 3A The printed wiring board 50 shown includes a base film 51 , a printed circuit 52 arranged on the base film 51 , and a cover layer 53 arranged so as to cover the printed circuit 52 .

[0186] The printed circuit 52 includes a ground circuit 52 a , and the cover layer 53 has an opening 53 a formed therein for exposing the ground circuit 52 a .

[0187] (2) Electromagnetic wave shielding film configuration process

[0188] Figure 3B This is a process diagram schematically showing an example of an electromagnetic shielding film placement step in the method for manufacturing a shielded printed wiring board according to the first embodiment of the present invention.

[0189] Then, if Figure 3B As shown, the electromagnetic shielding film 10 is placed on the printed circuit board 50 so that the adhesive layer 20 of the electromagnetic shielding film 10 is in contact with the coverlay 53 of the printed circuit board 50 .

[0190] (3) Hot pressing process

[0191] Figure 3C This is a process diagram schematically showing an example of a hot pressing step in the method for manufacturing a shield printed wiring board according to the first embodiment of the present invention.

[0192] Then, if Figure 3C As shown, the electromagnetic wave shielding film 10 is bonded to the printed circuit board 50 by heat pressing.

[0193] As a result, the urethane resin contained in the first protective layer 41 of the electromagnetic shielding film 10 is cross-linked, and the first protective layer 41 is cured.

[0194] Furthermore, the urethane resin contained in the adhesive layer 20 of the electromagnetic shielding film 10 is also cross-linked, and the adhesive layer 20 is cured.

[0195] At this time, the adhesive layer 20 of the electromagnetic shielding film 10 fills the opening 53 a of the printed circuit board 50 and is in contact with the ground circuit 52 a.

[0196] The hot pressing conditions are not particularly limited, and may be, for example, 2 to 3 MPa, 160 to 180° C., and 3 to 60 minutes.

[0197] Figure 4 It is a cross-sectional view schematically showing an example of a shield printed circuit board according to the first embodiment of the present invention.

[0198] After the above process, it can be manufactured Figure 4 A shielded printed circuit board 60 is shown.

[0199] Figure 4 The shielding printed circuit board 60 shown is a shielding printed circuit board including a printed circuit board 50 and an electromagnetic wave shielding film 10 disposed on the printed circuit board 50 .

[0200] The printed wiring board 50 includes a base film 51 , a printed circuit 52 disposed on the base film 51 , and a cover layer 53 disposed so as to cover the printed circuit 52 .

[0201] In addition, the printed circuit 52 includes a ground circuit 52 a.

[0202] The cover layer 53 is formed with an opening 53 a that exposes the ground circuit 52 a.

[0203] The electromagnetic shielding film 10 includes an adhesive layer 20 , a first protective layer 41 disposed on the adhesive layer 20 , and a metal layer 30 disposed between the adhesive layer 20 and the first protective layer 41 .

[0204] The first protective layer 41 includes a cured product of a urethane resin having an acid value of 2000 to 4000 g / eq and silica particles.

[0205] The adhesive layer 20 contains a cured product of a urethane resin having an acid value of 2000 to 4000 g / eq, an imidazole compound, and a flame retardant containing phosphorus.

[0206] Furthermore, the adhesive layer 20 of the electromagnetic shielding film 10 fills the opening 53a of the printed circuit board 50 and is in contact with the ground circuit 52a.

[0207] The shielding printed circuit board 60 is formed by disposing the electromagnetic wave shielding film 10 on the printed circuit board 50 .

[0208] Therefore, even if the shielded printed circuit board 60 is used for a long time in a high-temperature and high-humidity environment, metal or the like is unlikely to precipitate between the ground circuit 52a of the printed circuit board 50 and the adhesive layer 20 of the electromagnetic shielding film 10, and expansion is unlikely to occur.

[0209] In the printed circuit board 50, both the base film 51 and the cover layer 53 are preferably formed of engineering plastics, such as polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyimide, polyimide amide, polyetherimide, and polyphenylene sulfide (PPS).

[0210] In the printed circuit board 50 , the printed circuit 52 and the ground circuit 52 a can be made of common circuit materials such as copper.

[0211] A nickel-gold plating layer may be formed on the surfaces of the printed circuit 52 and the ground circuit 52a for protection.

[0212] It should be noted that when a nickel-gold plating layer is formed on the surface of the grounding circuit, since the adhesive layer contains a flame retardant containing phosphorus, water, phosphorus and nickel react at the contact portion between the adhesive layer and the grounding circuit, and nickel may be precipitated on the surface of the nickel-gold plating layer.

[0213] However, in the shielded printed circuit board of the present invention, as described above, the cured adhesive layer 20 has a high crosslink density and high moisture resistance. Therefore, moisture is less likely to accumulate between the cured adhesive layer 20 and the ground circuit 52a. Consequently, nickel can be prevented from precipitating on the surface of the nickel-gold plating layer.

[0214] (Second embodiment)

[0215] Next, an electromagnetic shielding film according to a second embodiment of the present invention will be described.

[0216] Figure 5 It is a cross-sectional view schematically showing an example of the electromagnetic shielding film according to the second embodiment of the present invention.

[0217] Figure 5 The electromagnetic shielding film 210 shown has the same structure as the electromagnetic shielding film 10 , except that the adhesive layer 220 is an isotropic conductive adhesive layer and the metal layer 30 is not provided.

[0218] In the electromagnetic wave shielding film 210 , the adhesive layer 220 has isotropic conductivity, and therefore the adhesive layer 220 functions as a shielding layer that absorbs and reflects electromagnetic waves.

[0219] It should be noted that a preferred configuration of the adhesive layer 220 is the same as that of the adhesive layer 20 of the electromagnetic shielding film 10 described above, except that it is an isotropic conductive adhesive layer.

[0220] In the electromagnetic shielding film 210 , a second protective layer that is harder than the first protective layer 41 may be formed on the first protective layer 41 .

[0221] When the second protective layer is formed on the electromagnetic shielding film 210 , a preferred configuration of the second protective layer is the same as the preferred configuration of the second protective layer 42 of the electromagnetic shielding film 110 .

[0222] The following matters are described in this manual.

[0223] The present disclosure (1) is an electromagnetic wave shielding film, characterized in that it comprises an adhesive layer and a first protective layer arranged on the above-mentioned adhesive layer, the above-mentioned first protective layer comprises a urethane resin with an acid value of 2000 to 4000 g / eq and silica particles, and the above-mentioned adhesive layer comprises a urethane resin with an acid value of 2000 to 4000 g / eq, an imidazole compound and a flame retardant containing phosphorus.

[0224] The present invention (2) is the electromagnetic wave shielding film according to the present invention (1), wherein the melting point of the imidazole compound is 150°C to 220°C.

[0225] The present invention (3) is the electromagnetic shielding film according to the present invention (1) or (2), wherein the adhesive layer contains an epoxy resin having an epoxy value of 1000 g / eq or less.

[0226] The present invention (4) is the electromagnetic shielding film according to any one of the present inventions (1) to (3), wherein the adhesive layer is a conductive adhesive.

[0227] The present disclosure (5) is the electromagnetic shielding film according to any one of the present disclosures (1) to (4), wherein a metal layer is disposed between the adhesive layer and the first protective layer.

[0228] The present disclosure (6) is an electromagnetic wave shielding film described in any one of the present disclosures (1) to (5), wherein a second protective layer is formed on the main surface opposite to the main surface of the first protective layer opposite to the adhesive layer, and the second protective layer is harder than the first protective layer.

[0229] The present invention (7) is the electromagnetic wave shielding film described in any one of the present inventions (1) to (6), wherein the thickness of the adhesive layer is 5 μm to 14 μm, and when the electromagnetic wave shielding film is hot pressed under the conditions of 3 MPa, 170°C, and 30 minutes, the thickness of the adhesive layer is 2 μm to 10 μm.

[0230] The present disclosure (8) provides a shielded printed circuit board, characterized in that it includes a printed circuit board and an electromagnetic wave shielding film arranged on the above-mentioned printed circuit board, the above-mentioned printed circuit board includes: a base film, a printed circuit arranged on the above-mentioned base, and a covering layer arranged in a manner covering the above-mentioned circuit, the above-mentioned printed circuit includes a grounding circuit, and an opening portion is formed on the above-mentioned covering layer to expose the above-mentioned grounding circuit, the above-mentioned electromagnetic wave shielding film has an adhesive layer and a first protective layer arranged on the above-mentioned adhesive layer, the above-mentioned first protective layer includes a cured product of a urethane resin with an acid value of 2000 to 4000 g / eq and silica particles, the above-mentioned adhesive layer includes a cured product of a urethane resin with an acid value of 2000 to 4000 g / eq, an imidazole compound and a flame retardant containing phosphorus, the above-mentioned adhesive layer of the above-mentioned electromagnetic wave shielding film fills the above-mentioned opening portion of the above-mentioned printed circuit board and is in contact with the above-mentioned grounding circuit.

[0231] Example

[0232] Examples are shown below to more specifically illustrate the present invention, but the present invention is not limited to these examples.

[0233] (Example 1)

[0234] A first release film is prepared, and a polyester resin is coated on the first release film.

[0235] Next, 90 parts by weight of a urethane resin (acid value: 3200 g / eq, number average molecular weight: 18,000, glass transition temperature: 47° C.) and 10 parts by weight of silica particles (particle size D50: 0.1 μm) were mixed to prepare a first protective layer composition.

[0236] Next, the first protective layer composition was applied on the polyester resin and heated in an electric oven at 100° C. for 2 minutes to form the polyester resin and the first protective layer composition as the second protective layer and the first protective layer, respectively.

[0237] The polyester resin and the first protective layer composition were applied so that the thickness of the second protective layer would be 1.5 μm and the thickness of the first protective layer would be 3.0 μm, respectively.

[0238] Next, an anchor coating was applied on the first protective layer, and then a silver layer with a thickness of 0.1 μm was formed by vapor deposition. This silver layer became a shielding layer.

[0239] Next, 40 parts by weight of a urethane resin (acid value: 3200 g / eq, number average molecular weight: 18000, glass transition temperature: 47°C), 4.4 parts by weight of an epoxy resin (phenol novolac type), 30 parts by weight of silver-coated copper powder (particle size D50: 5 μm), 29 parts by weight of aluminum diethylphosphinate as a flame retardant, and 1 part by weight of 2-phenyl-4-methyl-5-hydroxyimidazole as a curing catalyst were mixed to prepare a conductive adhesive composition.

[0240] Next, a second release film was prepared, and a conductive adhesive composition was applied onto the second release film. The film was then heated at 100° C. for 2 minutes in an electric oven to form the conductive adhesive composition as an adhesive layer.

[0241] In addition, the conductive adhesive composition was applied so that the thickness of the adhesive layer would be 8 μm.

[0242] Next, the silver layer formed on the first release film and the adhesive layer formed on the second release film were bonded together to produce the electromagnetic shielding film of Example 1.

[0243] (Example 2) to (Example 5) and (Comparative Example 1) to (Comparative Example 12)

[0244] Except having changed into the material shown in Table 1, the electromagnetic shielding film of Example 2 to Example 5 and Comparative Example 1 to Comparative Example 12 was produced similarly to Example 1.

[0245] In Examples 2 to 5 and Comparative Examples 3, 11, and 12, a urethane-modified polyester resin (number average molecular weight: 18,000, glass transition temperature: 40°C) was used as the adhesive resin. Furthermore, in Comparative Example 8, a conductive adhesive composition was prepared by mixing 40 parts by weight of a polyamide resin, 4.4 parts by weight of an epoxy resin (phenol novolac type), 30 parts by weight of silver-coated copper powder (particle size D50: 5 μm), and 29 parts by weight of aluminum diethylphosphinate as a flame retardant.

[0246] [Table 1]

[0247]

[0248] (Bending resistance test)

[0249] Figure 6 It is a cross-sectional view schematically showing the method of the bendability test.

[0250] The electromagnetic shielding films 10 of Examples and Comparative Examples, with the second release film peeled off, were bonded to both surfaces of a 50 μm polyimide film 71 and cut into a 10 mm×45 mm shape to prepare a test piece 72. Then, the first release film was peeled off.

[0251] Then, if Figure 6 As shown, the test piece 72 was bent and held between two support substrates 73 , and pressure was applied to the support substrates 73 so that the curvature radius of the bent portion 72 a became 0.2 mm.

[0252] Then, the pressure was released and the test piece 72 was observed to evaluate the bending resistance of the electromagnetic shielding film of each Example and each Comparative Example.

[0253] The evaluation criteria are as follows: If the evaluation of the bending resistance is “×”, the bending resistance is low and the film is not practically suitable as an electromagnetic shielding film for a flexible printed circuit board.

[0254] ○: No damage such as cracks was observed in the first protective layer of the electromagnetic shielding film.

[0255] ×: Damage such as cracks was observed in the first protective layer of the electromagnetic wave shielding film.

[0256] [Table 2]

[0257]

[0258] (Measurement of thickness of adhesive layer after pressing and heat resistance test)

[0259] The electromagnetic shielding films of Examples and Comparative Examples, from which the second release film was peeled, were placed on a polyimide film and hot-pressed at 3 MPa, 170° C., for 30 minutes. The thickness of the adhesive layer of each electromagnetic shielding film after hot-pressing was measured.

[0260] The results are shown in Table 2.

[0261] Then, the first release film was peeled off, and heating was performed at 266° C. for 1 minute. This heating simulated reflow heating when electronic components were arranged on a shielded printed circuit board.

[0262] The heat resistance of each electromagnetic shielding film was evaluated by visually observing the state of each electromagnetic shielding film after heating. The results are shown in Table 2.

[0263] In addition, the evaluation criteria are as follows.

[0264] ○: No damage due to heat was observed in the first protective layer of the electromagnetic wave shielding film.

[0265] ×: Damage due to heat was observed in the first protective layer of the electromagnetic wave shielding film.

[0266] [(Expansion confirmation test)

[0267] A printed circuit board was prepared in which a printed circuit composed of copper and having a nickel-gold plated layer formed on the surface was arranged on a base film (thickness: 0.012 mm) composed of polyimide, a cover layer (thickness: 0.0375 mm) composed of polyimide was arranged on the printed circuit, and an opening (0.5 mm×0.5 mm) was formed in the cover layer to expose the printed circuit.

[0268] The second release layer was peeled off from the electromagnetic wave shielding film of each embodiment and each comparative example, and the electromagnetic wave shielding film was placed on the printed circuit board 50 so that the adhesive layer of the electromagnetic wave shielding film of each embodiment and each comparative example was in contact with the cover layer. Heat pressing was then performed at 3 MPa and 170°C for 30 minutes to adhere the electromagnetic wave shielding film to the printed circuit board. This allowed the adhesive layer to enter the opening and come into contact with the printed circuit board.

[0269] Next, the first release film is peeled off to produce a shielded printed circuit board.

[0270] Thereafter, each shielded printed circuit board was left to stand in an environment of temperature: 60° C. and humidity: 95%, and the portion of the electromagnetic shielding film disposed at the opening was observed, and the time required for the portion to swell was measured.

[0271] It should be noted that observations were performed at 250 h, 500 h, 750 h, 1000 h, 1250 h, 2000 h, 2250 h, and 3000 h after the start of the test.

[0272] The results are shown in Table 2.

[0273] In addition, as an example of the expansion confirmation test results, a photograph of the appearance after 1000 hours when the electromagnetic wave shielding film of Example 1 and Comparative Example 1 was used, an SEM image of the cross-section of the contact part between the adhesive layer and the printed circuit, and an image of the nickel and phosphorus distribution analyzed by EDS (energy dispersive X-ray spectroscopy) are shown.

[0274] Figure 7A This is a photograph of the appearance of the electromagnetic shielding film according to Example 1 after 1000 hours of the expansion confirmation test.

[0275] Figure 7B This is a photograph of the appearance of the electromagnetic shielding film according to Comparative Example 1 after 1000 hours of the expansion confirmation test.

[0276] Figure 8A This is an SEM image of a cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Example 1.

[0277] Figure 8B This is an SEM image of a cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of the expansion confirmation test conducted using the electromagnetic shielding film according to Comparative Example 1.

[0278] Figure 9A This is an image showing nickel distribution in a cross section of a contact portion between an adhesive layer and a printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Example 1.

[0279] Figure 9B This is an image showing nickel distribution in a cross section of a contact portion between an adhesive layer and a printed circuit after 1000 hours of an expansion confirmation test conducted using the electromagnetic shielding film according to Comparative Example 1.

[0280] Figure 10A This is an image showing the distribution of phosphorus in the cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of the expansion confirmation test conducted using the electromagnetic shielding film according to Example 1.

[0281] Figure 10B This is an image showing the distribution of phosphorus in the cross section of the contact portion between the adhesive layer and the printed circuit after 1000 hours of the expansion confirmation test conducted using the electromagnetic shielding film according to Comparative Example 1.

[0282] like Figure 7A and Figure 7B As shown, after 1000 hours of the expansion confirmation test, the electromagnetic shielding film according to Example 1 did not expand, but the electromagnetic shielding film according to Comparative Example 1 expanded.

[0283] In addition, if Figure 8B As shown, in Comparative Example 1, precipitates were present between the adhesive layer of the electromagnetic shielding film and the printed circuit, thereby causing the above-mentioned expansion.

[0284] In addition, if Figure 9B As shown in FIG, it was found that the precipitate was formed by nickel precipitation. Figure 10B As shown, it was found that phosphorus existed around the nickel precipitates.

[0285] according to Figure 10B The phosphorus distribution shown is considered to be caused by the reaction between phosphorus and nickel in Comparative Example 1, whereby nickel of the printed circuit is deposited on the surface of the nickel-gold plating layer.

[0286] (Connection resistance test)

[0287] The electromagnetic shielding films according to the examples and comparative examples were used to measure the electrical resistance of the electromagnetic shielding films according to the examples and comparative examples by the following method.

[0288] Figure 11A and Figure 11B It is a cross-sectional view schematically showing a method of a connection resistance value measurement test.

[0289] like Figure 11A As shown, a printed circuit board 50' for measuring connection resistance values ​​was prepared. The printed circuit board 50' had two disconnected printed circuits 52 formed on a base film 51, and a cover layer 53 covering the base film 51 and the printed circuits 52. The cover layer 53 had openings 53a measuring 0.5 mm x 0.5 mm that partially exposed each printed circuit 52.

[0290] Then, if Figure 11B As shown, the electromagnetic shielding film 10 of each embodiment and comparative example was placed on a printed circuit board 50' for measuring connection resistance, with the adhesive layer 20 of the film 10 in contact with the cover layer 53. Heat pressing was then performed at 3 MPa, 170°C, and 30 minutes to bond the electromagnetic shielding film 10 to the printed circuit board 50' for measuring connection resistance. As a result, the adhesive layer 20 entered the opening 53a, contacted the printed circuit 52, and electrically connected the printed circuits 52 to each other via the adhesive layer 20.

[0291] Then, the resistance value (initial resistance value) between the printed circuits 52 is measured using the resistor 80 .

[0292] Then, the printed circuit board 50' for measuring the connection resistance value with the electromagnetic wave shielding film 10 attached is allowed to stand still in an environment of temperature: 60°C, humidity: 95% and time: 1000h, and the resistance value between the printed circuits 52 (resistance value after high temperature and high humidity load) is measured using the resistor 80 using the same method.

[0293] The results are shown in Table 2.

[0294] In addition, in Table 2, the evaluation of "1Ω or more" in the connection resistance test means a value exceeding the measurement limit.

[0295] As shown in Table 2, the electromagnetic shielding films of the respective Examples all showed good results in the bending resistance test, heat resistance test, expansion confirmation test, and connection resistance test.

[0296] In particular, according to the results of the expansion confirmation test, it is found that even if the shielded printed circuit board in which the adhesive layer of the electromagnetic wave shielding film involved in each embodiment contacts the ground circuit of the printed circuit board is used for a long time in a high temperature and high humidity environment, expansion is not likely to occur between the ground circuit and the adhesive layer.

[0297] As shown in Table 2, it is found that when the acid value of the urethane resin constituting the first protective layer is less than 2000 g / eq, the bending resistance is poor (see Comparative Example 10).

[0298] Furthermore, it was found that when the acid value of the urethane resin constituting the first protective layer exceeds 4000 g / eq, the heat resistance is poor (see Comparative Example 9).

[0299] When the adhesive layer contained no curing accelerator or contained an amine-based liquid latent curing agent as a curing agent, a resistance value exceeding the measurement limit was exhibited in the connection resistance test (see Comparative Examples 2, 7, and 8).

[0300] This is considered to be because the adhesive layer did not sufficiently fill the opening, resulting in a gap between the adhesive layer and the printed circuit.

[0301] Description of Reference Numerals

[0302] 10, 110, 210 electromagnetic wave shielding film

[0303] 20, 220 adhesive layer

[0304] 30 metal layers

[0305] 41 First protective layer

[0306] 42 Second protective layer

[0307] 50 printed circuit boards

[0308] 50' printed circuit board for measuring connection resistance

[0309] 51 basement membrane

[0310] 52 printed circuits

[0311] 52a Grounding circuit

[0312] 53 Covering

[0313] 53a Opening

[0314] 60 Shielded PCB

[0315] 71 polyimide film

[0316] 71a Bend

[0317] 72 test pieces

[0318] 73 Support base plate

[0319] 80 resistor.

Claims

1. An electromagnetic wave shielding film, characterized in that comprising an adhesive layer and a first protective layer disposed on the adhesive layer, The first protective layer comprises a urethane resin having an acid value of 2000 to 4000 g / eq and silica particles. The adhesive layer includes a urethane resin having an acid value of 2000 to 4000 g / eq, an imidazole compound, and a flame retardant containing phosphorus.

2. The electromagnetic wave shielding film according to claim 1, wherein The melting point of the imidazole compound is 150-220°C.

3. The electromagnetic shielding film according to claim 1 or 2, wherein The adhesive layer includes an epoxy resin having an epoxy value of 1000 g / eq or less.

4. The electromagnetic shielding film according to any one of claims 1 to 3, wherein The adhesive layer is a conductive adhesive.

5. The electromagnetic shielding film according to any one of claims 1 to 4, wherein A metal layer is disposed between the adhesive layer and the first protective layer.

6. The electromagnetic shielding film according to any one of claims 1 to 5, wherein A second protective layer is formed on a main surface of the first protective layer opposite to the main surface facing the adhesive layer. The second protective layer is harder than the first protective layer.

7. The electromagnetic shielding film according to any one of claims 1 to 6, wherein The thickness of the adhesive layer is 5 μm to 14 μm, When the electromagnetic shielding film is heat-pressed under conditions of 3 MPa, 170° C., and 30 minutes, the thickness of the adhesive layer is 2 μm to 10 μm.

8. A shielded printed circuit board, characterized in that: The invention comprises a printed circuit board and an electromagnetic wave shielding film arranged on the printed circuit board, The printed circuit board includes: a base film, a printed circuit arranged on the base film, and a cover layer arranged to cover the printed circuit. The printed circuit includes a ground circuit, An opening is formed in the cover layer to expose the ground circuit. The electromagnetic wave shielding film includes an adhesive layer and a first protective layer disposed on the adhesive layer. The first protective layer comprises a cured product of a urethane resin having an acid value of 2000 to 4000 g / eq and silica particles. The adhesive layer comprises a cured product of a urethane resin having an acid value of 2000 to 4000 g / eq, an imidazole compound, and a flame retardant containing phosphorus. The adhesive layer of the electromagnetic wave shielding film fills the opening of the printed circuit board and is in contact with the ground circuit.

Images