Thermosetting resin compositions, coverlay films, and flexible printed circuit boards

Abstract

This thermosetting resin composition contains: a polyamideimide resin having an acrylonitrile-butadiene skeleton; an epoxy resin that is not solid at 25ºC; fine rubber particles dispersed in the non-solid epoxy resin; an inorganic filler; and a curing agent. The content of the non-solid epoxy resin is 30-70 parts by mass relative to 100 parts by mass of the polyamideimide resin. The content of the fine rubber particles is 5-20 parts by mass relative to 100 parts by mass of the polyamideimide resin. The content of the inorganic filler is 20-40 parts by mass relative to 100 parts by mass of the polyamideimide resin.

Description

[Technical Field]

[0001] The present invention relates to a thermosetting resin composition, a coverlay film, and a flexible printed circuit board. [Background technology]

[0002] Patent Document 1 discloses a flexible printed circuit board comprising a coverlay film with an adhesive layer, and a substrate on which wiring is formed, and a coverlay film covering the wiring, which are intended to be placed in a high-temperature environment for a long period of time. It also discloses an adhesive resin composition that can be used for the adhesive layer constituting the coverlay film. Specifically, it discloses an adhesive resin composition containing a siloxane-containing polyimide resin and a bisphenol-type vinyl ester resin. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-43925 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The bisphenol-type vinyl ester resin contained in this adhesive resin composition is prone to degradation and oxidation due to heat. Therefore, when a coverlay film using this adhesive resin composition as the adhesive layer is exposed to high-temperature environments for a long period of time, the adhesive layer is likely to degrade, and the adhesive strength between the adhesive layer and the adherend is likely to decrease.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a coverlay film that has excellent adhesion even when exposed to high-temperature environments for a long period of time, a flexible printed circuit board equipped with this coverlay film, and a thermosetting resin composition that can be used in the adhesive layer of this coverlay film. [Means for solving the problem]

[0006] The present invention is as follows: [1] A polyamide-imide resin having an acrylonitrile butadiene rubber skeleton, An epoxy resin that is non-solid at 25°C, The aforementioned non-solid epoxy resin contains fine rubber particles, Inorganic fillers and, Contains a hardening agent, The content of the non-solid epoxy resin is 30 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The content of the fine rubber particles is 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The inorganic filler is a thermosetting resin composition comprising 20 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the polyamide-imide resin.

[0007] [2] The thermosetting resin composition according to [1] above, wherein the fine-particle rubber comprises a core layer and a shell layer covering its surface.

[0008] [3] Oxygen permeability at 30°C is 35.0 × 10⁻⁶ -6 m 3 / m 2 • Polyimide film with an atm of 24hr or less, The adhesive layer comprises the thermosetting resin composition described in [1] or [2] above, The adhesive layer is laminated on at least one surface of the polyimide film, forming a coverlay film.

[0009] [4] The coverlay film according to [3], wherein a gas barrier layer that suppresses oxygen permeation is laminated on at least one surface of the polyimide film.

[0010] [5] The oxygen permeability of the polyimide film on which the gas barrier layer is laminated at 30°C is 5.0 × 10 -6 m 3 / m 2·atm·24 hours or less, the coverlay film according to [4] above.

[0011] [6] A coverlay film according to any one of [3] to [5] above, and a substrate on which wiring is formed. A flexible printed wiring board in which the coverlay film is laminated on the substrate such that the adhesive layer and the wiring are in contact with each other.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a coverlay film having excellent adhesiveness even when placed in a high-temperature environment for a long period of time, a flexible printed wiring board including this coverlay film, and a thermosetting resin composition that can be used for the adhesive layer of this coverlay film.

Modes for Carrying Out the Invention

[0013] Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail. The embodiments are examples for explaining the present invention and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and implemented within the scope of its gist. Also, the parts by mass used in the present invention mean the parts by mass of the resin excluding volatile components such as organic solvents contained in the resin, that is, the parts by mass of the non-volatile components. Further, the semi-cured state (B-stage) means a state in which the curing reaction of the thermosetting resin composition has proceeded halfway.

[0014] (Thermosetting Resin Composition) The thermosetting resin composition of the embodiment includes a polyamideimide resin having an acrylonitrile-butadiene rubber skeleton, an epoxy resin that is non-solid at 25°C, fine particle rubber dispersed in the non-solid epoxy resin, an inorganic filler, and a curing agent.

[0015] The thermosetting resin composition of the embodiment has excellent heat resistance and adhesiveness by including the above components. This thermosetting resin composition is suitable as a resin composition constituting the adhesive layer of a coverlay film.

[0016] The following describes the components contained in the thermosetting resin composition.

[0017] (Polyamide-imide resin with an acrylonitrile butadiene rubber backbone) The polyamide-imide resin used in the embodiment consists of (a) a polycarboxylic acid derivative having an acid anhydride group, (b) an isocyanate compound, and (c) acrylonitrile butadiene rubber having carboxyl groups at both ends. Hereinafter, acrylonitrile butadiene rubber will also be referred to as NBR.

[0018] (a) component Examples of polycarboxylic acid derivatives having an acid anhydride group include trimellitic anhydride, pyromellitic dianhydride, ethylene glycol bisanhydrotrimellitate, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride. These may be used individually or in combination of two or more.

[0019] (b) Component Examples of isocyanate compounds include diphenylmethane-4,4'-diisocyanate, torylene-2,4-diisocyanate, m-xylylene diisocyanate, 2,2'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, and torylene-2,4'-diisocyanate. These may be used individually or in combination of two or more.

[0020] (c) Component Acrylonitrile butadiene rubber having carboxyl groups at both ends imparts adhesion and flexibility to thermosetting resin compositions. From the viewpoint of imparting adhesion and flexibility to thermosetting resin compositions, the weight-average molecular weight of NBR having carboxyl groups at both ends is preferably 1000 to 4000.

[0021] The polyamide-imide resin used in the embodiment is obtained by the isocyanate method. Specifically, components (a), (b), and (c) are added to a container in such a way that the following formula is satisfied, and condensed by heating at, for example, 100°C to 180°C. Organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and γ-butyrolactone may be added during condensation. (b) Number of isocyanate groups in component (b) / {Number of acid anhydride groups in component (a) + Number of carboxyl groups in component (c)} = 0.8 or more and 1.2 or less

[0022] The polyamide-imide resin obtained by the above method improves the film-forming properties of the thermosetting resin composition of the embodiment.

[0023] Furthermore, the glass transition temperature of the obtained polyamide-imide resin is between 150°C and 200°C. This polyamide-imide resin improves the heat resistance of the thermosetting resin composition of the embodiment. The glass transition temperature can be determined by measuring the dynamic viscoelasticity of the polyamide-imide resin.

[0024] (An epoxy resin that is non-solid at 25°C) An epoxy resin that is non-solid at 25°C is fluid at 25°C. This epoxy resin has two or more epoxy groups in one molecule. The epoxy equivalent of this epoxy resin is preferably 100 g / eq to 400 g / eq, and more preferably 150 g / eq to 350 g / eq. This epoxy resin can improve the dispersibility of fine rubber particles in a thermosetting resin composition and improve the adhesion between the substrate and the adhesive layer constituting the coverlay film.

[0025] Examples of epoxy resins that are non-solid at 25°C include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol A novolac type epoxy resin, phenol novolac type epoxy resin, amine type epoxy resin, and alicyclic epoxy resin. From the viewpoint of heat resistance, bisphenol A type epoxy resin is preferred as the non-solid epoxy resin at 25°C, and bisphenol A novolac type epoxy resin and phenol novolac type epoxy resin are more preferred. Two or more epoxy resins may be used in combination as the non-solid epoxy resin at 25°C.

[0026] The content of the non-solid epoxy resin at 25°C is 30 parts by mass or more and 70 parts by mass or less per 100 parts by mass of polyamide-imide resin, from the viewpoint of improving adhesion between the substrate and the adhesive layer constituting the coverlay film.

[0027] (Microparticle rubber) The fine-particle rubber can be any fine-particle rubber that disperses in a non-solid epoxy resin at 25°C, and from the viewpoint of improving dispersibility, fine-particle rubber composed of a core layer and a shell layer covering its surface is preferred.

[0028] The core layer constituting the fine-particle rubber is composed of a polymer having rubber-like elasticity. Examples of polymers having rubber-like elasticity include diene rubber, acrylic rubber, styrene rubber, and polysiloxane rubber. The core layer may be composed of two or more polymers. The shell layer covering the surface of the core layer is composed of a copolymer obtained by copolymerizing one or more components selected from (meth)acrylic acid ester monomers, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated acid derivatives, (meth)acrylamide derivatives, and maleimide derivatives.

[0029] The polymer constituting the core layer and the copolymer constituting the shell layer are bonded together by graft polymerization. The shell layer covers part or all of the surface of the core layer. Preferably, the copolymer constituting this shell layer has functional groups that react with non-solid epoxy resin and curing agent at 25°C. Fine particle rubber having such a structure has increased affinity with non-solid epoxy resin at 25°C and improved dispersibility. Examples of functional groups that react with non-solid epoxy resin and curing agent at 25°C include hydroxyl groups, carboxyl groups, and epoxy groups, with epoxy groups being preferred from the viewpoint of improving dispersibility.

[0030] From the viewpoint of improving dispersibility, the size of the fine rubber particles is preferably such that the average particle size is between 0.05 μm and 1 μm.

[0031] The content of fine rubber particles is 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of polyamide-imide resin, from the viewpoint of improving adhesion between the substrate and the adhesive layer constituting the coverlay film.

[0032] Rather than directly adding the fine rubber particles to the thermosetting resin composition, it is preferable to add a non-solid epoxy resin at 25°C, in which the fine rubber particles are dispersed, to the thermosetting resin composition. This allows for uniform dispersion of the fine rubber particles within the thermosetting resin composition. Examples of non-solid epoxy resins at 25°C in which the fine rubber particles are already dispersed include MX-136, MX-153, MX-154, MX-170, MX-217, MX-257, MX-416, MX-451, MX-551, MX-960, and MX-965, all manufactured by Kaneka Corporation. Two or more types of non-solid epoxy resins at 25°C in which the fine rubber particles are already dispersed may be used in combination.

[0033] (Hardening agent) The curing agent should be capable of curing the non-solid epoxy resin at 25°C. Examples include diaminodiphenylmethane (DDM), diaminodiphenylsulfone (DDS), diaminodiphenyl ether (DDE), hexamethylenediamine, dicyandiamide, and phenol novolac. Among these, dicyandiamide is preferred, and diaminodiphenylsulfone is more preferred, from the viewpoint of ease of controlling the curing reaction. Two or more curing agents may be used in combination.

[0034] The equivalent amount of curing agent is preferably 0.3 to 0.8 equivalents, and more preferably 0.3 to 0.6 equivalents, relative to one equivalent of epoxy groups in the non-solid epoxy resin at 25°C. By using an equivalent amount of curing agent less than one equivalent of epoxy groups in the non-solid epoxy resin at 25°C, the adhesion between the substrate and the adhesive layer constituting the coverlay film can be improved. Furthermore, the thermosetting resin composition can be spread into the gaps between the wiring formed on the substrate. In addition, the insulation reliability of the thermosetting resin composition itself after curing can be improved.

[0035] (Inorganic fillers) Examples of inorganic fillers include aluminum hydroxide, magnesium hydroxide, and silica. From the viewpoint of improving heat resistance and exhibiting flame retardancy, aluminum hydroxide is preferred as the inorganic filler, and magnesium hydroxide is more preferred. Furthermore, two or more types of inorganic fillers may be used.

[0036] The inorganic filler content is 20 to 40 parts by mass per 100 parts by mass of polyamide-imide resin, from the viewpoint of improving adhesion between the substrate and the adhesive layer constituting the coverlay film.

[0037] A thermosetting resin composition can be obtained by adding predetermined amounts of each of the above-mentioned components, namely polyamide-imide resin, epoxy resin that is non-solid at 25°C, fine rubber particles dispersed in the non-solid epoxy resin, inorganic filler, and curing agent, to a container and mixing them. Such a thermosetting resin composition has excellent heat resistance and adhesion.

[0038] (Other components) The thermosetting resin composition may further contain other additives or the like. Examples of the other additives include imidazole-based accelerators such as 2-methylimidazole, N-benzyl-2-methylimidazole, and 2-undecylimidazole; Lewis acid complexes such as boron trifluoride monoethylamine; curing accelerators such as polyamine and melamine resin; dispersants, softeners, anti-aging agents, pigments, dyes, and silane coupling agents. Also, two or more additives or the like may be used.

[0039] (Coverlay film) The coverlay film of the embodiment is composed of, for example, a polyimide film and an adhesive layer laminated on one side thereof. The coverlay film of the embodiment is used to protect the wiring formed on the substrate. From the viewpoint of reducing deterioration due to oxygen when the adhesive layer is placed in a high-temperature environment for a long time, it is preferable that the oxygen permeability of the polyimide film is low. The oxygen permeability of the polyimide film at 30 °C is preferably 35.0×10 -6 m 3 / m 2 ·atm·24 hr or less. Thereby, since the oxygen permeating through the polyimide film is reduced, the deterioration of the adhesive layer due to oxygen is reduced, and the decrease in the adhesive strength between the adhesive layer and the wiring is suppressed. Also, since the glass transition temperature of the thermosetting resin composition after curing is 130 °C or higher and 200 °C or lower, the adhesive layer also has excellent heat resistance. Therefore, the coverlay film has excellent adhesiveness even when placed in a high-temperature environment for a long time.

[0040] The thickness of the polyimide film only needs to have the function as a coverlay film, and from the viewpoint of workability, it is, for example, 2 μm or more and 75 μm or less. Also, from the viewpoint of reducing oxygen permeability, the thickness of the polyimide film is preferably 12.5 μm or more.

[0041] The thickness of the adhesive layer should be sufficient to protect the wiring formed on the substrate, for example, 5 μm to 50 μm after drying. The curing state of the adhesive layer before lamination to the substrate, i.e., the curing state of the thermosetting resin composition, is semi-cured (stage B). The adhesive layer may be formed on both sides of the polyimide film. With a coverlay film having this configuration, since the adhesive layer is formed on both sides of the polyimide film, the wiring surface of one substrate and the wiring surface of another substrate can be protected with a single coverlay film, enabling multilayering of substrates.

[0042] Next, an example of a method for producing a coverlay film will be described. First, the thermosetting resin composition of the embodiment is prepared. The thermosetting resin composition is applied to one side of a polyimide film using a coating apparatus. Next, the film coated with the thermosetting resin composition is heated until the thermosetting resin composition reaches a semi-cured state (stage B), and then cooled. In this way, a coverlay film is obtained in which an adhesive layer is laminated on one side of a polyimide film. The heating conditions are, for example, 100°C to 250°C and 5 seconds to 30 minutes, and can be adjusted depending on the thickness of the adhesive layer. In addition, an organic solvent may be added to the thermosetting resin composition to improve the coatability.

[0043] Any organic solvent that can adjust the viscosity of the thermosetting resin composition is acceptable, and examples include glycols such as ethylene glycol and propylene glycol; glycol monoalkyl ethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; glycol dialkyl ethers such as ethylene glycol dimethyl ether and ethylene glycol diethyl ether; alkyl esters such as methyl acetate, ethyl acetate, propyl acetate, and methyl acetoacetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; aliphatic hydrocarbons such as hexane, cyclohexane, and octane; amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and cyclic ethers such as tetrahydrofuran and dioxane. Two or more organic solvents may be used in combination.

[0044] The coating apparatus can be any apparatus capable of laminating a thermosetting resin composition onto a film to a predetermined thickness. Examples of coating apparatus include die coaters, comma coaters, and gravure coaters.

[0045] (Flexible printed circuit board) The flexible printed circuit board of this embodiment comprises a substrate on which wiring is formed and a coverlay film having an adhesive layer, with the coverlay film laminated on the substrate so as to be in contact with the wiring and the adhesive layer.

[0046] Examples of wiring formed on a substrate include wiring formed by etching the copper layer of a copper-plated laminate or copper-clad laminate, and wiring printed with conductive ink. The materials constituting the wiring are conductive materials, such as copper, silver, and zinc. The thickness of the substrate constituting the flexible printed circuit board is, for example, 15 μm to 200 μm, from the viewpoint of making the flexible printed circuit board flexible. Here, a copper-plated laminate comprises a copper layer made of copper plating. A copper-clad laminate comprises a copper layer made of copper foil.

[0047] An example of a manufacturing method for flexible printed circuit boards is described below. First, a substrate with pre-formed wiring and a coverlay film with an adhesive layer are prepared. Next, the coverlay film is laminated onto the substrate so that the adhesive layer is in contact with the surface of the substrate with the pre-formed wiring, and then heated and pressurized. This yields a flexible printed circuit board. The heating and pressurizing conditions are, for example, 120°C to 250°C, 5 seconds to 120 minutes, and 1 MPa to 10 MPa, and can be adjusted depending on the lamination configuration.

[0048] In the embodiments described above, a coverlay film comprising a polyimide film and an adhesive layer made of a thermosetting resin composition, wherein the adhesive layer is laminated on at least one surface of the polyimide film, was mentioned, but the following modifications are also included as embodiments.

[0049] (A modified example of a coverlay film with a gas barrier layer) A modified version further includes a gas barrier layer that suppresses oxygen permeation. The gas barrier layer is laminated on at least one surface of the polyimide film constituting the coverlay film. The oxygen permeability of the polyimide film with the gas barrier layer laminated on it at 30°C is, for example, 5.0 × 10⁻⁶. -6 m 3 / m 2 ATM hours are less than 24 hours.

[0050] The adhesive layer may be laminated on the polyimide film surface opposite to the surface on which the gas barrier layer is laminated, or it may be laminated on top of the gas barrier layer.

[0051] The gas barrier layer only needs to be able to suppress oxygen permeation, and examples include gas barrier layers composed of silicon dioxide (SiO2), zinc oxide, etc. The thickness of the gas barrier layer is, for example, 10 nm to 100 nm. The polyimide film on which the gas barrier layer is laminated has reduced oxygen permeation. As a result, contact between oxygen and the adhesive layer laminated on the film is reduced, the deterioration of the adhesive layer due to oxygen, i.e., the deterioration of the thermosetting resin composition due to oxygen is reduced, and the decrease in adhesive strength between the adhesive layer and the wiring is suppressed. [Examples]

[0052] The present invention will be further described in detail by the following examples. The present invention is not limited in any way by the following examples.

[0053] The following components were used in the thermosetting resin compositions in the examples and comparative examples. (Polyamide-imide resin) (1) Polyamide-imide resin: It has an acrylonitrile butadiene rubber backbone and a glass transition temperature of 178°C (manufactured by Toyobo Co., Ltd., HR-71DD). The glass transition temperature was measured using an RSA-G2 from TA-instruments. The conditions were tensile mode, in air, 1 Hz, and heating at 10°C / min.

[0054] (An epoxy resin that is non-solid at 25°C) (1) Epoxy resin EA: It has an epoxy equivalent of 231 g / eq, is of the phenol novolac type, and contains 25 parts by mass of fine particulate rubber (polybutadiene rubber, average particle size 0.1 μm) per 100 parts by mass of epoxy resin EA (manufactured by Kaneka Corporation, MX-217). (2) Epoxy resin EB: has an epoxy equivalent of 270 g / eq, is bisphenol A type, and contains 33 parts by mass of fine particulate rubber (polybutadiene rubber, average particle size 0.1 μm) per 100 parts by mass of epoxy resin EB (manufactured by Kaneka Corporation, MX-153). (3) Epoxy resin EC: It has an epoxy equivalent of 270 g / eq, is of the bisphenol A novolac type, and contains 25 parts by mass of fine particulate rubber (styrene-butadiene rubber, average particle size 0.1 μm) per 100 parts by mass of epoxy resin EC (manufactured by Kaneka Corporation, MX-227M75). (4) Epoxy resin ED: has an epoxy equivalent of 243 g / eq, is bisphenol A type, and contains 25 parts by mass of fine rubber particles (silicone rubber, average particle size 0.1 μm) per 100 parts by mass of epoxy resin ED (manufactured by Kaneka Corporation, MX-960). (5) Epoxy resin EE: has an epoxy equivalent of 177 g / eq and is of the phenol novolac type (manufactured by Mitsubishi Chemical Corporation, jER(registered trademark) 152). (6) Epoxy resin EF: has an epoxy equivalent of 190 g / eq and is bisphenol A type (manufactured by DIC Corporation, EPICLON® 850).

[0055] (Hardening agent) Diaminodiphenylsulfone: Has an amine value of 62 g / eq (manufactured by Konishi Chemical Industry Co., Ltd., 3,3'-DAS).

[0056] (Inorganic fillers) (1) Filler FA: Magnesium hydroxide (manufactured by Kyowa Chemical Industry Co., Ltd., KISUMA (registered trademark) 5P), (2) Filler FB: Aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., BF013), (3) Filler FC: Silica (Admatex Corporation, SC2010-MB).

[0057] (Example 1) (Preparation of thermosetting resin composition) 100 parts by mass of polyamide-imide resin, 52 parts by mass of epoxy resin EA, 8.4 parts by mass of curing agent, 30 parts by mass of filler FA, 100 parts by mass of methyl ethyl ketone as an organic solvent, and 260 parts by mass of toluene were added to a container and stirred at room temperature to obtain a thermosetting resin composition.

[0058] (Creation of coverlay film) A thermosetting resin composition was applied to one side of a 25 μm thick polyimide film (Toray DuPont, Kapton® 100EN) using a bar coater so that the thickness after heating was 30 μm, and the film was heated at 150°C for 5 minutes. Then, a release PET film (Toray Industries, Lumirror® #38-S10) was laminated to the film surface coated with the thermosetting resin composition at 100°C, 1 MPa, and 10 seconds to obtain a coverlay film with a release PET film. The oxygen permeability of the polyimide film used in Example 1 at 30°C was 31.0 × 10⁻⁶. -6 m 3 / m 2 The reading was atm·24hr. Oxygen permeability at 30°C was measured in accordance with ASTM D1434.

[0059] (Preparation of the substrate) A copper foil (35 μm thick) constituting an 80 μm thick copper-clad laminate (Arisawa Seisakusho Co., Ltd., LCSE1035EDH(T20)) was soft-etched on its glossy surface with a hydrolyzed sulfuric acid-based soft etching solution (ADEKA Corporation, CL-8) to obtain a substrate from which 1 μm of copper had been removed from the surface of the copper foil.

[0060] <Peel strength (adhesive strength)> The adhesive strength of the obtained coverlay film was measured by the following method. (Sample for measurement) The release PET film was peeled off the coverlay film, and the adhesive layer side was bonded to the copper foil side of the substrate. The sample was then heated and pressurized at 160°C, 3.0 MPa, and for 60 minutes to obtain a sample for measurement. For measurement, the sample was cut to a width of 10 mm and a length of 100 mm.

[0061] (measurement) The peel strength in the 90° direction (perpendicular to the surface of the sample) was measured using a Shimadzu Autograph AGS-500 under the following measurement conditions.

[0062] (Peel strength before heat treatment) After storing the sample at 25°C and 50% relative humidity for 24 hours, the peel strength of the coverlay film and the peel strength of the adherend were measured. The test speed was 50 mm / min. "Coverlay film pulling" refers to pulling the coverlay at a 90° angle (perpendicular direction) to the surface of the sample. "Adhesive pulling" refers to pulling the adherend at a 90° angle (perpendicular direction) to the surface of the sample. The same applies below. The evaluation criteria were as follows: Excellent: Peel strength of 7.0 N / cm or higher. Good: Peel strength of 3.4 N / cm or more and less than 7.0 N / cm. Poor: Peel strength is less than 3.4 N / cm.

[0063] (Peel strength after heat treatment) The sample was placed in a 150°C atmosphere for 250 hours, then stored at 25°C and 50% relative humidity for 24 hours. After this, the peel strength of the coverlay film and the peel strength of the adherend were measured. The test speed was 50 mm / min. The evaluation criteria were as follows: Excellent: Peel strength of 7.0 N / cm or higher. Good: Peel strength of 3.4 N / cm or more and less than 7.0 N / cm. Poor: Peel strength is less than 3.4 N / cm.

[0064] ( Reference Example 2) ~ (Example 11), (Comparative Example 1) ~ (Comparative Example 6) (Preparation of thermosetting resin composition) As shown in Tables 1 and 2, thermosetting resin compositions were obtained by preparing them in the same manner as in Example 1, except that the types and contents of each component were changed. Unless otherwise specified, the units of the contents in the tables are parts by mass. Note that in Example 11, only the polyimide film, which will be described later, differs from Example 1; all other components are the same as in Example 1.

[0065] (Creation of coverlay film) Reference Example In Examples 2 to 10 and Comparative Examples 1 to 6, the same 25 μm thick polyimide film (Toray DuPont, Kapton® 100EN) as in Example 1 was used. In Example 11, a film was used in which a 30 nm thick gas barrier layer made of SiO2 was laminated on one side of a 25 μm thick polyimide film (Toray DuPont, Kapton® 100EN). The oxygen permeability of the polyimide film with the gas barrier layer used in Example 11 at 30°C was 5.0 × 10⁻⁶. -6 m 3 / m 2 ATMs are less than 24 hours long, and 2.5 × 10 -6 m 3 / m 2 The temperature was atm for 24 hours. The coverlay film was prepared using the same method as in Example 1. The oxygen permeability at 30°C was measured in accordance with ASTM D1434, the same method as in Example 1. The peel strength was measured using the same method as in Example 1. The measurement results are shown in Tables 1 and 2.

[0066] [Table 1]

[0067] [Table 2]

[0068] In Examples 1 to 11, it was found that coverlay films composed of a polyimide film with low oxygen permeability and an adhesive layer made of a thermosetting resin composition containing an inorganic filler and having high heat resistance exhibited high peel strength after heat treatment. Specifically, the thermosetting resin composition constituting the adhesive layer was found to have excellent adhesion when it contained 30 to 70 parts by mass of non-solid epoxy resin at 25°C, 5 to 20 parts by mass of fine rubber particles, and 20 to 40 parts by mass of inorganic fillers, per 100 parts by mass of polyamide-imide resin.

[0069] Furthermore, as evidence of the high peel strength, observation of the interface between the polyimide film and the adhesive layer after measuring the peel strength revealed cohesive failure, where a portion of the adhesive layer remained on the surface of the polyimide film. Similarly, cohesive failure was also observed at the interface between the adherend and the adhesive layer, just as at the interface between the polyimide film and the adhesive layer.

[0070] Furthermore, the oxygen permeability of the polyimide film constituting the coverlay film at 30°C is 35.0 × 10⁻⁶. -6 m 3 / m 2 It was found that by keeping the atm below 24hr, contact between oxygen and the adhesive layer laminated on the film is reduced, thereby reducing the degradation of the adhesive layer due to oxygen and suppressing the decrease in adhesive strength between the adhesive layer and the adherend such as wiring.

[0071] The sample from Example 11 was subjected to further extended exposure to a high-temperature atmosphere, and its peel strength was measured again. Specifically, the peel strength was measured after 500 hours in a 150°C atmosphere followed by 24 hours of storage at 25°C and 50% relative humidity, and again after 1000 hours in a 150°C atmosphere followed by 24 hours of storage at 25°C and 50% relative humidity. The results were as follows. (Example 11) (1)150℃, 500 hours Coverlay film peel strength: 10.5 N / cm. The peel strength of the adherend is 9.8 N / cm. (2)150℃, 1000 hours Coverlay film peel strength: 9.5 N / cm. The peel strength of the adherend is 8.5 N / cm.

[0072] The high peel strength was achieved because the coverlay film, which included a polyimide film with a gas barrier layer, reduced oxygen permeability and thus reduced degradation of the adhesive layer due to oxygen, and because the thermosetting resin composition, which has high heat resistance, contained an inorganic filler. As further evidence of the high peel strength, cohesive failure was observed in the sample of Example 11 at the interface between the adherend and the adhesive layer, and at the interface between the polyimide film and the adhesive layer, after the peel strength measurement.

[0073] As described above, the coverlay films having adhesive layers composed of the thermosetting resin compositions of Examples 1 to 11 exhibited excellent adhesion in both coverlay film adhesion and adherend adhesion, even when exposed to high-temperature environments for extended periods. Furthermore, Example 11 exhibited excellent adhesion in both coverlay film adhesion and adherend adhesion even when exposed to high-temperature environments for 500 hours and 1000 hours. Such coverlay films are suitable for use in automotive electronic equipment.

[0074] (Note) The various aspects of this disclosure are summarized below as an appendix. (Note 1) A polyamide-imide resin having an acrylonitrile butadiene rubber skeleton, An epoxy resin that is non-solid at 25°C, The aforementioned non-solid epoxy resin contains fine rubber particles, Inorganic fillers and, Contains a hardening agent, The content of the non-solid epoxy resin is 30 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The content of the fine rubber particles is 5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The inorganic filler is a thermosetting resin composition comprising 20 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the polyamide-imide resin.

[0075] (Note 2) The thermosetting resin composition described in Appendix 1 comprises a core layer and a shell layer covering its surface.

[0076] (Note 3) The oxygen permeability at 30°C is 35.0 × 10⁻⁶. -6 m 3 / m 2 • Polyimide film with an atm of 24hr or less, The present invention comprises an adhesive layer made from the thermosetting resin composition described in Appendix 1 or Appendix 2, The adhesive layer is laminated on at least one surface of the polyimide film, forming a coverlay film.

[0077] (Note 4) The coverlay film according to Appendix 3, wherein a gas barrier layer that suppresses oxygen permeation is laminated on at least one surface of the polyimide film.

[0078] (Note 5) The oxygen permeability of the polyimide film on which the gas barrier layer is laminated at 30°C is 5.0 × 10⁻⁶ -6 m 3 / m 2 Coverlay film as described in Appendix 4, with an operating temperature of 24 hours or less at ATM.

[0079] (Note 6) The device comprises a coverlay film as described in any one of Appendix 3 to Appendix 5, and a substrate on which wiring is formed, A flexible printed circuit board in which the coverlay film is laminated on the substrate such that the adhesive layer and the wiring are in contact.

[0080] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of the invention is indicated by the claims, not by the embodiments. Various modifications made within the scope of the claims and the equivalent meaning of the invention are considered to be within the scope of this invention.

[0081] This application is based on Japanese Patent Application No. 2022-201801, filed on 19 December 2022. The entire specification and claims of Japanese Patent Application No. 2022-201801 are incorporated herein by reference.

Claims

1. A polyamide-imide resin having an acrylonitrile butadiene rubber skeleton, An epoxy resin that is non-solid at 25°C, The aforementioned non-solid epoxy resin contains fine rubber particles, Inorganic fillers and, Contains a hardening agent, The content of the non-solid epoxy resin is 30 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The content of the fine rubber particles is 5 parts by mass or more and 18.2 parts by mass or less per 100 parts by mass of the polyamide-imide resin. The inorganic filler is a thermosetting resin composition comprising 20 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the polyamide-imide resin.

2. The thermosetting resin composition according to claim 1, wherein the fine-particle rubber comprises a core layer and a shell layer covering its surface.

3. The oxygen permeability at 30°C is 35.0 × 10⁻⁶. －６ I understand ３ / m ２ Polyimide film with atm 24hr or less, The present invention comprises an adhesive layer made from the thermosetting resin composition described in claim 1 or 2, The adhesive layer is laminated on at least one surface of the polyimide film, forming a coverlay film.

4. The coverlay film according to claim 3, wherein a gas barrier layer that suppresses oxygen permeation is laminated on at least one surface of the polyimide film.

5. The oxygen permeability of the polyimide film on which the gas barrier layer is laminated at 30°C is 5.0 × 10⁻⁶. －６ I understand ３ / m ２ The coverlay film according to claim 4, wherein the temperature is atm 24hr or less.

6. The invention comprises a coverlay film according to claim 3 and a substrate on which wiring is formed, A flexible printed circuit board in which the coverlay film is laminated on the substrate such that the adhesive layer and the wiring are in contact.

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