Adhesives, adhesive sheets and flexible copper-clad laminates

Abstract

To develop an adhesive for a flexible copper-clad laminate that provides FCCL with excellent dimensional stability without copper foil breakage or wrinkles while achieving both properties comparable to those of the casting method 2-layer FCCL and productivity higher than that of the lamination method 2-layer FCCL, an adhesive sheet manufactured by the same, and a lamination method flexible copper-clad laminate.SOLUTION: An adhesive for a flexible copper-clad laminate for bonding a polyimide film substrate and a copper foil that make up a flexible copper-clad laminate includes a solvent soluble polyimide, a phenoxy resin having a glass transition temperature (Tg) of 120°C or less, an epoxy resin, and an epoxy resin hardener, and there are also provided an adhesive sheet using the same, a flexible copper-clad laminate, and a manufacturing method of the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flexible copper clad laminate (FCCL) used in flexible printed wiring boards and the like, and an adhesive and adhesive sheet for producing the same. [Background technology]

[0002] In recent years, the demand for various printed wiring boards has grown in line with the trend toward lighter, smaller, and more dense electronic products, with demand for flexible printed wiring boards growing in particular. The main materials for flexible printed wiring boards include flexible copper-clad laminates, coverlay films, and interlayer insulating materials (bonding sheets). Flexible copper-clad laminates for flexible printed wiring boards are generally made from various insulating materials and are manufactured by using a flexible insulating film, such as polyimide film, as the substrate, and then bonding a metal foil to the surface of this substrate via various adhesive materials using heat and pressure bonding.

[0003] Flexible copper-clad laminates (hereinafter also referred to as "3-layer FCCLs") are available that use thermosetting resins such as epoxy resins or acrylic resins as adhesives between copper foil and polyimide film. These thermosetting adhesives have the advantage of being able to bond at relatively low temperatures. However, as requirements for heat resistance, chemical resistance, electrical reliability, dimensional stability, and thinning become more stringent, 3-layer FCCLs are finding it difficult to meet these requirements. Therefore, flexible copper-clad laminates (hereinafter also referred to as "2-layer FCCLs") that have a metal layer directly attached to the polyimide film or use a thermoplastic polyimide as the adhesive layer are gaining popularity. These 2-layer FCCLs are particularly superior to 3-layer FCCLs in terms of heat resistance, dimensional stability, and electrical reliability, and can also contribute to thinner walls.

[0004] There are three manufacturing methods for two-layer FCCL: lamination, casting, and sputtering, each of which has its own advantages and disadvantages.

[0005] Among the three methods, the laminated two-layer FCCL has the highest productivity because it uses a process in which an adhesive sheet with a thermoplastic polyimide (TPI) adhesive layer formed on one or both sides of a polyimide film is bonded to a conductive metal foil (Patent Documents 1, 3-5). Generally, two-layer FCCLs are required to have high solder heat resistance compatible with lead-free soldering and dimensional stability compatible with high-density mounting. However, because the laminated two-layer FCCL uses a high-melting-point thermoplastic polyimide (TPI) as the adhesive, the lamination process must be carried out at high temperatures and pressures of 300°C or higher, which deteriorates dimensional stability after etching and heating. Although various improvements have been made to improve dimensional stability, dimensional stability is still insufficient. Furthermore, the use of a heat-resistant protective film is necessary to prevent copper foil tearing and wrinkling, which poses cost challenges.

[0006] Casting-method two-layer FCCLs use a process in which a polyimide precursor is cast (applied) onto a conductive metal foil and heated to imidize it (Patent Documents 6 and 7). However, they suffer from the essential drawbacks of poor productivity and the need for large, long equipment. To improve dimensional stability and reliable copper foil adhesion, a new technique has been developed in which a high-adhesion polyimide, which has enhanced adhesion between a low-thermal expansion polyimide and copper foil, is used. This polyimide is then coated onto copper foil in three layers at a thickness ratio such that the thermal expansion coefficient after curing matches that of the copper foil, and then cured. Furthermore, a floating-type wide-width continuous coating and curing process for single-sided two-layer FCCLs and a high-speed, wide-width continuous lamination process for double-sided two-layer FCCLs have also been developed. As a result of these repeated improvements, casting-method two-layer FCCLs currently have the most stable properties of the three methods, but their essential drawbacks of poor productivity and the need for large, long equipment have yet to be overcome.

[0007] Sputtering two-layer FCCL is a process in which a conductive metal is laminated onto a polyimide film by sputtering, and is advantageous for forming fine patterns because it is easy to make the conductor layer thin and the interface between the metal and the film is smooth (Patent Document 2). However, the sputtering method requires vacuum deposition equipment, and because of high production costs and poor productivity, the price of FCCL is also the most expensive of the three methods.

[0008] Meanwhile, methods have been reported in which a film made of a thermosetting resin composition containing a solvent-soluble polyimide resin having a phenylindane structure and an epoxy resin is used as an interlayer insulating material or adhesive for multilayer substrates (Patent Documents 8 and 9). Patent Document 8 discloses the use of a thermosetting resin composition as an interlayer insulating material for a build-up multilayer substrate, whose core material is a rigid substrate such as FR-4. Patent Document 9 discloses the use of a thermosetting resin composition as an adhesive for bonding the copper on the surface of a flexible copper-clad board to the copper foil when a build-up multilayer printed wiring board is fabricated by overlaying copper foil on the flexible copper-clad board, which serves as the core material. The thermosetting resin composition contains a phenoxy resin with a glass transition temperature (Tg) of 130°C or higher. However, the adhesive in Patent Document 9 is not a material for bonding the polyimide film substrate and copper foil that constitute FCCL. Patent Document 10 discloses an adhesive containing a polyimide resin and a crosslinking agent for bonding the polyimide film and copper foil that constitute FCCL. However, although Patent Document 10 discloses that the adhesive exhibits a high softening point (20 to 220° C.), a low dielectric constant, and a low dielectric loss tangent, it makes no mention whatsoever of dimensional stability. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 6-232553 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-280684 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-71982 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-136631 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-198385 [Patent Document 6] Japanese Patent Application Laid-Open No. 2016-215651 [Patent Document 7] Japanese Patent Application Publication No. 2019-081379 [Patent Document 8] Japanese Patent Application Laid-Open No. 2006-328214 [Patent Document 9] Japanese Patent Application Laid-Open No. 2013-35881 [Patent Document 10] Japanese Patent Application Publication No. 2019-172989 Summary of the Invention [Problem to be solved by the invention]

[0010] Among two-layer FCCLs, the laminated two-layer FCCL is the most superior in terms of productivity, while the casted two-layer FCCL is the most superior in terms of properties. Therefore, there has been a demand for a lamination process that can achieve properties comparable to those of the casted two-layer FCCL. Because the lamination temperature for the laminated two-layer FCCL is high (over 300°C), a high-heat-resistant film such as a polyimide film is used during lamination to prevent defects such as copper foil tearing and wrinkling. Furthermore, high-temperature lamination inevitably results in poor dimensional stability. Therefore, there has been a demand for an adhesive that can laminate the adhesive layer and copper foil without these defects and that can provide an FCCL with excellent dimensional stability.

[0011] The present invention has been made in consideration of the above circumstances, and its object is to develop an adhesive for flexible copper-clad laminates that combines properties comparable to those of two-layer FCCLs produced by the casting method with productivity equal to or greater than that of two-layer FCCLs produced by the lamination method, and that provides FCCLs that are free from defects such as copper foil breakage and wrinkling and have excellent dimensional stability, and to provide an adhesive sheet and a flexible copper-clad laminate produced by the lamination method (hereinafter also referred to as "2.2-layer FCCL") using the same. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have discovered that by replacing the thermoplastic polyimide (TPI) adhesive used in a laminated two-layer FCCL with a thermosetting adhesive made of a polymer alloy containing a specific solvent-soluble polyimide, a phenoxy resin with a glass transition temperature (Tg) of 120°C or less, an epoxy resin, and an epoxy resin curing agent, it is possible to improve the dimensional stability, which is an area of ​​improvement in the properties of a laminated two-layer FCCL, achieve properties on a par with those of a casted two-layer FCCL, and eliminate defects such as copper foil tearing and wrinkling during lamination, thereby completing the present invention.

[0013] That is, the present invention provides an adhesive for flexible copper-clad laminates for bonding a polyimide film substrate and a copper foil that constitute a flexible copper-clad laminate, the adhesive comprising a solvent-soluble polyimide having a repeating unit represented by the following general formula [I], a glass transition temperature (Tg) of 90℃~120℃ The present invention provides an adhesive comprising a phenoxy resin, an epoxy resin, and an epoxy resin curing agent.

[0014] [ka] (wherein Z is an aromatic or alicyclic tetracarboxylic acid dianhydride residue, and Ar is an aromatic diamine residue having a phenylindane structure).

[0015] The present invention also provides an adhesive sheet for flexible copper-clad laminates, which comprises an adhesive layer for adhering copper foil laminated on one or both sides of a polyimide film substrate constituting the flexible copper-clad laminate, wherein the adhesive layer contains the adhesive of the present invention.

[0016] The present invention also provides a flexible copper-clad laminate comprising an adhesive layer and a copper foil laminated in that order on one or both sides of a polyimide film substrate, wherein the adhesive layer contains the adhesive of the present invention.

[0017] The present invention further provides a method for producing the flexible copper-clad laminate of the present invention, which comprises laminating a copper foil to the adhesive sheet of the present invention at a temperature of 70 to 120°C, and then curing the adhesive layer at a temperature of 200°C or less. [Effects of the Invention]

[0018] Conventionally, laminating the adhesive layer of an adhesive sheet and copper foil at high temperatures has resulted in problems such as copper foil tearing and wrinkling, particularly when the copper foil is thin (18 μm or less). By using the specific adhesive of the present invention to prepare an adhesive sheet by laminating an adhesive layer on the surface of a polyimide film substrate, the adhesive layer of the adhesive sheet and copper foil can be laminated at relatively low temperatures, even when the copper foil is thin, resulting in a flexible copper-clad laminate free of problems such as copper foil tearing and wrinkling. This eliminates the need for a high-temperature, high-pressure lamination process, which is one of the main causes of dimensional stability degradation. Furthermore, the thermosetting temperature is 200°C or less, significantly improving the dimensional stability of the flexible copper-clad laminate. As a result, a flexible copper-clad laminate can be provided that combines properties comparable to those of a two-layer FCCL produced by a casting method with productivity superior to that of a two-layer FCCL produced by a lamination method. DETAILED DESCRIPTION OF THE INVENTION

[0019] The adhesive for flexible copper-clad laminates of the present invention is an adhesive for bonding the polyimide film substrate and copper foil that constitute a flexible copper-clad laminate, and contains a solvent-soluble polyimide having a repeating unit represented by the following general formula [I], a phenoxy resin having a Tg of 120°C or less, an epoxy resin, and an epoxy resin curing agent.

[0020] [ka]

[0021] In the above general formula, Z is an aromatic or alicyclic tetracarboxylic acid dianhydride residue, and Ar is an aromatic diamine residue having a phenylindane structure.

[0022] (Solvent-soluble polyimide) In the repeating unit represented by the general formula [I] contained in the solvent-soluble polyimide of the present invention, the aromatic tetracarboxylic acid dianhydride for introducing the aromatic tetracarboxylic acid dianhydride residue represented by Z into the polyimide is not particularly limited, but is preferably benzophenone tetracarboxylic acid dianhydride or biphenyl tetracarboxylic acid dianhydride.

[0023] Examples of alicyclic tetracarboxylic acid dianhydrides for introducing the alicyclic tetracarboxylic acid dianhydride residue represented by Z into polyimides include bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, norbornane-2-spiro-α-cycloalkanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic acid dianhydride, 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid dianhydride, 2,3,4,5-tetrahydrofuran tetracarboxylic acid dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5 -dioxo-3-furanyl)-naphtho[1,2-c]-furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]-furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]-furan-1,3-dione ,3-dione, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid dianhydride, bicyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, bicyclo[2,2,1]-heptane-2,3,5,6-tetracarboxylic acid dianhydride, and decahydrodimethanonaphthalene-2,3,6,7-tetracarboxylic acid dianhydride.

[0024] The phenylindane structure in the aromatic diamine residue having a phenylindane structure represented by Ar is a structure in which the indane skeleton shown below is substituted with a phenyl group which may have a substituent, and examples of the substituent include a halogen atom or an alkyl group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms. The aromatic diamine residue (Ar) having a phenylindane structure is preferably a diamine residue containing a structure in which a phenyl group which may have a substituent is substituted at the 1st or 2nd position of the indane skeleton shown below, and particularly preferably a diamine residue represented by the following general formula [II].

[0025] [ka]

[0026] [ka]

[0027] In general formula [II], R1, R2, and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms. Furthermore, each R4 and each R5 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms.

[0028] Examples of aromatic diamines for introducing an aromatic diamine residue (Ar) having a phenylindane structure into a polyimide include 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 5-amino-6-methyl-1-(3'-amino-4'-methylphenyl)-1,3,3-trimethylindane, 5-amino-1-(4'-amino-Ph',Ph'-dichloro ... Examples include 6-amino-1-(4'-amino-Ph',Ph'-dichloro-phenyl)-Ph,Ph-dichloro-1,3,3-trimethylindan, 4-amino-6-methyl-1-(3'-amino-4'-methyl-phenyl)-1,3,3-trimethylindan, and Ph-amino-1-(Ph'-amino-2',4'-dimethylphenyl)-1,3,3,4,6-pentamethylindan. Ph and Ph' in the above example compounds represent unspecified positions on the phenyl ring in the phenylindane structure.

[0029] The content of the aromatic diamine component (Ar component) having a phenylindane structure constituting the solvent-soluble polyimide is 50 mol % or more, preferably 60 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, and particularly preferably 90 mol % or more of the total diamine components, from the viewpoint of improving the compatibility between the solvent-soluble polyimide and the epoxy resin.

[0030] The solvent-soluble polyimide may be a block-lock copolymer having a repeating unit other than the repeating unit represented by the general formula [I], or may have a repeating unit having another aromatic diamine residue, an aliphatic diamine residue, or an alicyclic diamine residue, or a diamine residue having a diaminopolysiloxane in the main chain. Examples of diamines used to introduce diamine residues having a diaminopolysiloxane in the main chain into the polyimide include α,ω-bis(2-aminoethyl)polydimethylsiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(4-aminophenyl)polydimethylsiloxane, α,ω-bis(4-amino-3-methylphenyl)polydimethylsiloxane, α,ω-bis(3-aminopropyl)polydiphenylsiloxane, and α,ω-bis(4-aminobutyl)polydimethylsiloxane.

[0031] The solvent-soluble polyimide having the repeating unit represented by the above general formula (I) can be obtained by subjecting an aromatic or alicyclic tetracarboxylic acid dianhydride and an aromatic diamine having a phenylindane structure to a dehydration condensation reaction.

[0032] Although the method for synthesizing the solvent-soluble polyimide may be any known method and is not particularly limited, the solvent-soluble polyimide can be synthesized by reacting approximately equal amounts of the above-mentioned tetracarboxylic acid dianhydride and aromatic diamine in an organic polar solvent in the presence of a catalyst and a dehydrating agent at 160 to 200°C for several hours. Examples of the organic polar solvent that can be used include N-methylpyrrolidone (NMP), γ-butyrolactone, N,N'-dimethylacetamide, N,N'-dimethylformamide, dimethyl sulfoxide, tetramethylurea, and tetrahydrothiophene-1,1-oxide.

[0033] The solvent-soluble polyimide is preferably a block copolymer, which can be synthesized by a block copolymerization reaction, for example, by a two-stage sequential addition reaction, in which a polyimide oligomer is synthesized from a tetracarboxylic dianhydride and an aromatic diamine in the first stage, and then a tetracarboxylic dianhydride and / or an aromatic diamine is further added in the second stage to carry out polycondensation to form a block copolymerized polyimide.

[0034] The dehydration imidization reaction can be accelerated by using a two-component acid-base catalyst that utilizes the lactone equilibrium reaction as a catalyst for the block copolymerization reaction. Specifically, a two-component catalyst consisting of γ-valerolactone and pyridine or N-methylmorpholine is used. As shown in the following formula, water is generated as the imidization proceeds, and the generated water participates in the lactone equilibrium, acting as an acid-base catalyst and exhibiting catalytic action.

[0035] [ka]

[0036] The water produced by the imidization reaction is removed from the system by azeotropy with a dehydrating agent, such as toluene or xylene, present in the polar solvent. When the reaction is complete, the water in the solution is removed, and the acid-base catalyst is converted into γ-valerolactone and pyridine or N-methylmorpholine, which are then removed from the system. In this way, a high-purity polyimide solution can be obtained.

[0037] Other two-component catalysts that can be used include oxalic acid or malonic acid and pyridine or N-methylmorpholine. In a reaction solution at 160 to 200°C, the oxalate or malonate acts as an acid catalyst to promote the imidization reaction. A catalytic amount of oxalic acid or malonic acid remains in the resulting polyimide solvent. This polyimide solution is applied to a substrate and then heated to 200°C or higher to remove the solvent and form a film. When this film is formed, the oxalic acid or malonic acid remaining in the polyimide undergoes thermal decomposition as shown in the following formula and is removed as a gas from the system.

[0038] [ka]

[0039] By the above method, high-purity solvent-soluble polyimides can be obtained. The oxalic acid-pyridine catalyst is more active than the valerolactone-pyridine catalyst, and can produce high-molecular-weight polyimides in a short time. The molecular weight of the synthesized solvent-soluble polyimide is preferably 10,000 to 400,000 in terms of polystyrene equivalent weight average molecular weight (Mw). When the molecular weight of the solvent-soluble polyimide is within this range, good solvent solubility, film properties, and insulating properties can be achieved, which is preferable.

[0040] The term "solvent-soluble" in the present invention refers to the organic polar solvent used in synthesizing the polyimide and the solvent used in the adhesive composition described below, and means that a solution of the polyimide with a solid content of 20 wt % can be prepared using these solvents. Examples of the solvent include NMP, γ-butyrolactone, DMF, and DMAC. The synthesized polyimide can be used in the form of a solution dissolved in the organic polar solvent or the solvent used in the adhesive composition described below to have a solid content of 10 to 30 wt %, for example.

[0041] Furthermore, since the solvent-soluble polyimide of the present invention is a fully imidized polyimide, it does not require high-temperature heat treatment for imidization after the adhesive is applied to the polyimide film substrate, which has the advantage of being able to provide a flexible copper-clad laminate with high dimensional stability compared to polyamic acid (polyimide precursor), which requires high-temperature heat treatment (300°C or higher) for imidization after the adhesive is applied to the polyimide film substrate.

[0042] (epoxy resin) The epoxy resin in the present invention is not particularly limited, but is preferably a rigid-structured epoxy resin having two or more glycidyl groups. The molecular weight (Mw) of the epoxy resin is usually 200 to 2,000, preferably 280 to 1,000. Particularly preferred are biphenyl-type epoxy resins, naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, bisphenol A-type epoxy resins, etc., which can be used alone or in combination of two or more.

[0043] The epoxy resin in the present invention is an epoxy resin that is compatible with a solvent-soluble polyimide and can change the properties of the solvent-soluble polyimide. Because the epoxy resin and the solvent-soluble polyimide resin are compatible with each other, a compatible polymer alloy is produced by mixing the epoxy resin and the solvent-soluble polyimide.

[0044] (epoxy resin hardener) The curing agent used in the present invention is not particularly limited as long as it can cure the epoxy resin, but examples thereof include novolac phenolic resins and resins having a naphthalene structure and an aralkyl structure. Examples of novolac phenolic resins include phenol novolac resins, cresol novolac resins, triazine-modified novolac resins such as benzoguanamine-modified bisphenol A novolac resins, benzoguanamine-modified cresol novolac phenolic resins, benzoguanamine-modified phenol novolac phenolic resins, melamine-modified bisphenol A novolac resins, melamine-modified cresol novolac phenolic resins, and melamine-modified phenol novolac phenolic resins. Examples of resins having a naphthalene structure and an aralkyl structure include 1-naphthol aralkyl resins, 2-naphthol aralkyl resins, and 1,6-naphthalenediol aralkyl resins.

[0045] The amount of the curing agent used relative to the epoxy resin is preferably 0.5 or more and 1.2 or less equivalents of hydroxyl group equivalent. Since an appropriate Tg may not be obtained if the amount of curing agent used is less than 0.5 equivalents, 0.5 or more equivalents are preferred, with 0.6 or more being more preferred. Furthermore, since the water absorption properties of the resin may decrease if the amount of curing agent used exceeds 1.2 equivalents, 1.2 or less equivalents are preferred, with 1.0 or less being more preferred.

[0046] Aromatic amine resins can also be suitably used as curing agents. The aromatic amine resins are not particularly limited as long as they can promote the curing of epoxy resins, but examples thereof include 4,4'-diaminodiphenylsulfone, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, trimethylenebis(4-aminobenzoate), polytetramethyleneoxide-di-p-aminobenzoate, 3,3'-dimethyl-4, Examples include 4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3aminophenoxy)phenyl]sulfone, 9,9'-bis(4-aminophenyl)fluorene, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and the like, which can be used alone or in combination of two or more.

[0047] Although the amount of aromatic amine resin used is not limited, the optimal amount of aromatic amine compound used is 0.3 to 1.5 moles when the number of moles of epoxy resin is 1. By using an amount (total number of moles) of aromatic amine resin of 0.3 or more, an adhesive layer having an appropriate thermal expansion coefficient can be easily obtained. From this viewpoint, the amount (total number of moles) of aromatic amine resin used is more preferably 0.4 or more. Furthermore, by using an amount (total number of moles) of aromatic amine resin of 1.5 or less, an adhesive layer having an appropriate thermal expansion coefficient can also be easily obtained. From this viewpoint, the amount (total number of moles) of aromatic amine resin used is more preferably 1.2 or less.

[0048] (phenoxy resin) The phenoxy resin in the present invention is a phenoxy resin having a glass transition temperature (Tg) of 120°C or less, and specifically, one having a molecular weight (Mw) of 10,000 or more is preferred. As the resin skeleton, taking into account adhesiveness, BPA type, BPA / BPF type, BPA / BPS type, BP / BPS type, etc. are preferred. Examples of commercially available products include JER1256 (weight average molecular weight (hereinafter referred to as Mw) 48,000, glass transition temperature (hereinafter referred to as Tg) 95°C, manufactured by Mitsubishi Chemical Corporation), PKHJ (Mw 57,000, Tg 98°C, manufactured by Gabriel Phenoxies), PKHH (Mw 52,000, Tg 92°C, manufactured by Gabriel Phenoxies), PKFE (Mw 60,000, Tg 98°C, manufactured by Gabriel Phenoxies), and FX-310 (Mw 45,000, Tg 110°C, manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd.).

[0049] By using a phenoxy resin with a glass transition temperature (Tg) of 120°C or less in combination, similar to solvent-soluble polyimide resins, flexibility and adhesiveness are imparted to the adhesive layer formed from the adhesive, and the adhesive layer can be bonded to copper foil at a relatively low temperature. The Tg of the phenoxy resin is preferably 80 to 115°C, more preferably 85 to 113°C, and most preferably 90 to 110°C, in order to prevent defects such as copper foil tearing and wrinkling when laminating the adhesive layer and copper foil, and to ensure that the Tg of the adhesive layer formed from the adhesive falls within the optimum range described below. The Tg of the phenoxy resin can be measured in accordance with IPC-TM-650-2.4.24.3.

[0050] The weight ratio of the solvent-soluble polyimide resin (solid content) to the phenoxy resin in the adhesive composition is usually 1:1.2 to 12.0, preferably 1:1.3 to 10.0, more preferably 1:1.4 to 9.5, and even more preferably 1:1.5 to 9.0.

[0051] The total content (wt%) of the solvent-soluble polyimide resin and the phenoxy resin relative to the total content of the solvent-soluble polyimide resin, phenoxy resin, epoxy resin, and epoxy resin curing agent in the adhesive composition is typically 10 to 50 wt%. If the total content of the solvent-soluble polyimide resin and the phenoxy resin is less than 10 wt%, the adhesive strength and flexibility of the adhesive layer formed from the adhesive composition may be low. Therefore, the total content is preferably 15 wt% or more, more preferably 20 wt% or more, based on the total weight including the epoxy resin and the epoxy resin curing agent. Furthermore, if the total content of the solvent-soluble polyimide resin and the phenoxy resin exceeds 50 wt%, the breaking strength of the film may decrease. Therefore, the total content is preferably 45 wt% or less, more preferably 40 wt% or less, based on the total weight including the epoxy resin and the epoxy resin curing agent.

[0052] The adhesive of the present invention may be an adhesive composition that contains a curing accelerator, a flame retardant, and the like in addition to the above-mentioned solvent-soluble polyimide, epoxy resin, curing agent, and phenoxy resin.

[0053] (curing accelerator) The adhesive of the present invention can be used in combination with a curing accelerator as needed. Common curing accelerators such as various imidazoles can be used as the curing accelerator. The accelerator can be selected mainly from the viewpoint of reaction speed and pot life.

[0054] (Flame retardant) If necessary, a flame retardant can be added to the adhesive of the present invention to impart flame retardancy. Examples of halogen-free flame retardants that can be used include condensed phosphate esters, phosphazenes, polyphosphates, and HCA (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) derivatives.

[0055] The adhesive (composition) can be produced by mixing the epoxy resin, curing agent, solvent-soluble polyimide, and phenoxy resin, as well as the above resin components as needed, and adding a solvent to the resulting mixture to prepare a resin varnish with a resin solids content of 20 to 60% by weight.

[0056] There are no particular limitations on the solvents that can be used in the adhesive composition of the present invention, but it is preferable to combine a high-boiling point solvent such as NMP, γ-butyrolactone, methyl benzoate, diethylene glycol monomethyl ether acetate, or diethylene glycol monomethyl ether acetate with a medium- to low-boiling point solvent such as cyclohexanone or MEK (methyl ethyl ketone).

[0057] (Tensile modulus and Tg of adhesive film) The adhesive (composition) of the present invention is an adhesive in which a semi-cured film made from the adhesive is heat-cured at 180°C for 90 minutes, and the resulting film has a tensile modulus of 1 to 10.0 GPa and a Tg (glass transition temperature) of 120 to 190°C.

[0058] The film used to measure the tensile modulus and Tg was prepared as follows. The resin varnish prepared as described above was applied to the shiny side of 18 μm electrolytic copper foil using a bar coater and dried at 150°C to produce a semi-cured (state B) adhesive-backed copper foil (adhesive thickness: approximately 21 μm). The solvent volatile content was adjusted to 0.6 wt%. The shiny side of the 18 μm electrolytic copper foil was placed on the adhesive sheet side of this adhesive-backed copper foil, which was then placed in a vacuum press and heated and pressurized at 180°C for 90 minutes at 1 MPa (vacuum level: 5 torr). The copper foil was then completely etched, and the resulting adhesive film (approximately 20 μm thick) was measured for tensile modulus and Tg. The tensile modulus was measured in accordance with IPC-TM-650-2.4.18.3, and Tg was measured in accordance with IPC-TM-650-2.4.24.3.

[0059] Here, the tensile modulus is primarily related to the dimensional stability of FCCL, but it also affects warpage and waviness of printed wiring boards. Warpage occurs due to mismatches, particularly in the tensile modulus and thermal expansion coefficient, between the polyimide film used as the core material and the adhesive layer. Because such mismatches occur even in adhesive sheets with a symmetrical structure on both sides, it is desirable to make the tensile modulus and thermal expansion coefficient equal between the polyimide film and the adhesive layer. However, achieving this has been extremely difficult with solvent-soluble polyimide resins. An effective solution is to make the tensile modulus of the adhesive layer less than that of the core polyimide film substrate. If the tensile modulus of the adhesive layer is equal to or greater than that of the core polyimide film substrate, the core polyimide film substrate will experience increased thermal distortion and a greater rate of dimensional change after heating. Furthermore, if the tensile modulus of the adhesive layer is less than 1 GPa, waviness of the FCCL is likely to occur. The tensile modulus is preferably within the range of 1.1 to 5.0 GPa, more preferably 1.2 to 3.0 GPa, and particularly preferably 1.2 to 2.5 GPa. Furthermore, the Tg (glass transition temperature) of a film made from the adhesive is preferably 125 to 185°C, more preferably 130 to 180°C.

[0060] (adhesive sheet) An adhesive sheet for a 2.2-layer FCCL using the lamination method can be obtained by applying the adhesive (composition) of the present invention to one or both sides of a polyimide film substrate and B-staging it to a semi-cured state (B state). Specifically, as described above, a resin varnish prepared by diluting the adhesive (composition) of the present invention with a suitable mixed organic solvent such as NMP / MEK is applied to one or both sides of the polyimide film substrate, which is the core material, using a gravure coater or thin film die coater. In the present invention, in order to achieve dimensional stability equivalent to that of a 2-layer FCCL using the casting method, it is preferable to set the coating thickness, coating temperature, and heat curing temperature of the adhesive layer within the following specific ranges.

[0061] The coating thickness of the adhesive layer must be at least the minimum thickness required to embed the roughened surface of the copper foil to be laminated. Specifically, a thickness equal to or greater than the surface roughness Rz of the copper foil (measured in accordance with JIS B 0601-2001) is preferred. Because this coating thickness particularly affects dimensional stability, in addition to this condition, the thickness of the single-sided adhesive layer should be no more than 20%, preferably no more than 15%, and more preferably no more than 13% of the thickness of the core polyimide film. The thickness of the adhesive layer of the adhesive sheet preferably satisfies both of the above condition ranges, but the absolute thickness value is preferably 1.6 to 4.0 μm, more preferably 2.0 to 3.5 μm, and particularly preferably 2.5 to 2.9 μm. By keeping the adhesive layer thickness within this range, the adhesive properties can be maintained without the differences in physical properties (mainly tensile modulus and thermal expansion coefficient) between the adhesive layer and the core polyimide film becoming apparent in the physical properties of the FCCL as a composite film. The thickness of the adhesive layer of the adhesive sheet is preferably 1.5 to 3.5 μm when the adhesive sheet is heat-cured in a dryer at 180° C. for 90 minutes.

[0062] By ensuring that the tensile modulus and Tg of a film made from the adhesive (composition) of the present invention are within the above-mentioned specific ranges, and further by ensuring that the thickness of the adhesive layer of the adhesive sheet is 1.6 to 4.0 μm, preferably 1.8 to 2.9 μm, the dimensional stability of the FCCL as a composite layer film can be made nearly equivalent to that of the core polyimide film. This makes it possible to provide an adhesive sheet and a laminated 2.2-layer FCCL that have properties comparable to those of a cast-method 2-layer FCCL and superior productivity to that of a laminated 2-layer FCCL. Furthermore, by achieving these conditions, warping due to mismatches in the thermal expansion coefficients of single-sided 2-layer FCCLs can be prevented, making it possible to suppress warping without relying on the TPI bilateral symmetrical structure that is currently widely used.

[0063] The coating temperature of the adhesive layer (including the drying temperature after coating) is also a factor that causes thermal distortion in the FCCL, so the coating temperature is preferably 150°C or lower.

[0064] (Flexible Copper Clad Laminate (FCCL)) A two-layer flexible copper-clad laminate (FCCL) can be produced by laminating (attaching) copper foil to the surface of the adhesive layer of the adhesive sheet produced as described above and then curing the adhesive layer. The adhesive layer of the adhesive sheet and the copper foil can be laminated using a laminator at 70 to 120°C, preferably 75 to 115°C, and more preferably 80 to 110°C. By performing lamination at such a relatively low temperature, a flexible copper-clad laminate can be produced that is free of defects such as copper foil tearing and wrinkling. The thickness of the copper foil is typically 1.5 to 20 μm, preferably 5 to 18 μm. The curing temperature of the adhesive layer, which is the greatest factor in thermal distortion, is preferably 200°C or less, more preferably 195°C or less, and particularly preferably 190°C or less, and more preferably 150°C or more, and even more preferably 160°C or more. By producing an adhesive sheet and an FCCL in the manner described above, the dimensional change rate after etching and heating can be made equivalent to that of a two-layer FCCL produced by the casting method.

[0065] One of the main reasons for the deterioration of dimensional stability after etching and heating of conventional laminated two-layer FCCLs is the occurrence of distortion during the lamination process with copper foil under high temperatures and pressures of 300°C or higher. In the present invention, by using a polymer alloy adhesive containing a specific solvent-soluble polyimide, which is a thermosetting resin, a phenoxy resin with a Tg of 120°C or lower, an epoxy resin, and an epoxy resin curing agent, copper foil lamination at a relatively low temperature that does not cause copper foil tearing or wrinkles, and thermal curing at 200°C or lower, is possible, reducing distortion that occurs during each process and significantly improving the dimensional shrinkage rate. [Example]

[0066] The present invention will be described in detail below based on examples, but the present invention can be modified into various other embodiments and is not limited to the following examples.

[0067] 1. Synthesis of solvent-soluble polyimide resin Synthesis Example 1 A separable three-neck glass flask was equipped with a stirrer, a nitrogen inlet, and a condenser equipped with a water receiver. 58.84 g (0.2 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter referred to as BPDA), 26.64 g (0.1 mol) of 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane (aromatic diamine containing a phenylindane structure), 1.5 g (0.015 mol) of valerolactone, 2.4 g (0.03 mol) of pyridine, 200 g of NMP, and 30 g of toluene were added. The mixture was stirred at 200 rpm at room temperature under a nitrogen atmosphere for 30 minutes, then heated to 180 °C and stirred for 1 hour. The toluene-water azeotrope was removed during the reaction. After cooling to room temperature, 44.13 g (0.15 mol) of BPDA, 66.60 g (0.25 mol) of 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 360 g of NMP, and 90 g of toluene were added and stirred at room temperature for 30 minutes. The mixture was then heated to 180°C and stirred for 1 hour. The reaction was terminated by heating and stirring at 180°C for 2 hours and 30 minutes while removing the water-toluene azeotropic reflux product from the system. The resulting product was diluted with γ-butyrolactone to obtain a block copolymer polyimide solution with a solids content of 20 wt%.

[0068] Synthesis Example 2 A separable three-neck glass flask was equipped with a stirrer, a nitrogen inlet, and a condenser equipped with a water receiver. 64.45 g (0.2 mol) of 3,4,3',4'-benzophenonetetracarboxylic dianhydride (BTDA), 26.64 g (0.1 mol) of 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane (aromatic diamine containing a phenylindane structure), 1.5 g (0.015 mol) of valerolactone, 2.4 g (0.03 mol) of pyridine, 200 g of NMP, and 30 g of toluene were added. The mixture was stirred at 200 rpm at room temperature under a nitrogen atmosphere for 30 minutes, then heated to 180°C and stirred for 1 hour. The toluene-water azeotrope was removed during the reaction. After cooling to room temperature, 48.33 g (0.15 mol) of BTDA, 66.60 g (0.25 mol) of 6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 360 g of NMP, and 90 g of toluene were added and stirred at room temperature for 30 minutes. After stirring, the mixture was heated to 180°C and stirred for 1 hour. The reaction was terminated by heating and stirring at 180°C for 2 hours and 30 minutes while removing the reflux product of the water-toluene azeotrope from the system. The resulting product was diluted with γ-butyrolactone to obtain a block copolymer polyimide solution with a solids content of 20 wt%.

[0069] Synthesis Example 3 A separable three-neck glass flask was equipped with a stirrer, a nitrogen inlet, and a condenser equipped with a water receiver. 64.45 g (0.2 mol) of 3,4,3',4'-benzophenonetetracarboxylic dianhydride (BTDA), 20.02 g (0.1 mol) of 4,4'-diaminodiphenyl ether, 1.5 g (0.015 mol) of valerolactone, 2.4 g (0.03 mol) of pyridine, 200 g of NMP, and 30 g of toluene were added. The mixture was stirred at 200 rpm at room temperature under a nitrogen atmosphere for 30 minutes, then heated to 180°C and stirred for 1 hour. The toluene-water azeotrope was removed during the reaction. After cooling to room temperature, 48.33 g (0.15 mol) of BTDA, 66.60 g (0.25 mol) of 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 360 g of NMP, and 90 g of toluene were added and stirred at room temperature for 30 minutes. After stirring, the mixture was heated to 180°C and stirred for 1 hour. The reaction was terminated by heating and stirring at 180°C for 2 hours and 30 minutes while removing the water-toluene azeotropic reflux product from the system. The resulting product was diluted with γ-butyrolactone to obtain a block copolymer polyimide solution with a solids content of 20 wt%.

[0070] Synthesis Example 4 A separable three-neck glass flask was equipped with a stirrer, a nitrogen inlet, and a condenser equipped with a water receiver. 64.45 g (0.2 mol) of 3,4,3',4'-benzophenonetetracarboxylic dianhydride (BTDA), 15.98 g (0.06 mol) of 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 9.94 g (0.04 mol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1.5 g (0.015 mol) of valerolactone, 2.4 g (0.03 mol) of pyridine, 200 g of NMP, and 30 g of toluene were added and stirred at room temperature for 30 minutes. The mixture was then heated to 180°C and stirred for 1 hour. The toluene-water azeotrope was removed during the reaction. After cooling to room temperature, 48.33 g (0.15 mol) of BTDA, 66.60 g (0.25 mol) of 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 360 g of NMP, and 90 g of toluene were added and stirred at room temperature for 30 minutes. After stirring, the mixture was heated to 180°C and stirred for 1 hour. The reaction was terminated by heating and stirring at 180°C for 2 hours and 30 minutes while removing the water-toluene azeotropic reflux product from the system. The resulting product was diluted with γ-butyrolactone to obtain a block copolymer polyimide solution with a solids content of 20 wt%.

[0071] 2. Preparation of adhesive composition, adhesive sheet and FCCL fabrication Example 1 347 parts by weight of dicyclopentadiene type epoxy resin "HP-7200H" (DIC Corporation, epoxy equivalent 283, resin solid content 80% by weight), 183 parts by weight of melamine-modified cresol novolak resin "EXB-9854" (DIC Corporation, hydroxyl value 151, resin solid content 80% by weight), 290 parts by weight of soluble polyimide resin (Synthesis Example 1, resin solid content 20% by weight), 91 parts by weight of phenoxy resin "jER1256" (Mitsubishi Chemical Corporation, Mw ≒ 48,000, Tg 95 ° C, resin solid content 100% by weight), 57 parts by weight of phosphazene derivative "FP-100" (Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4-methylimidazole. A resin varnish with a resin solid content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of methylimidazole.

[0072] Example 2 337 parts by weight of biphenyl type epoxy resin "NC-3000H" (manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 275, resin solid content 80% by weight), 202 parts by weight of melamine-modified phenol novolak resin "LA-7054" (manufactured by DIC Corporation, hydroxyl value 125, resin solid content 60% by weight), 98 parts by weight of soluble polyimide resin (Synthesis Example 2, resin solid content 20% by weight), 170 parts by weight of phenoxy resin "jER1256" (manufactured by Mitsubishi Chemical Corporation, Mw ≒ 48,000, Tg 95 ° C., resin solid content 100% by weight), 57 parts by weight of phosphazene derivative "FP-100" (manufactured by Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4 methylimidazole. A resin varnish with a resin solid content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of methylimidazole.

[0073] Example 3 349 parts by weight of naphthol aralkyl type epoxy resin "ESN-165" (manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd., epoxy equivalent 265, resin solids 80% by weight), 177 parts by weight of melamine-modified phenol novolak resin "LA-7054" (manufactured by DIC Corporation, hydroxyl value 125, resin solids 60% by weight), 290 parts by weight of soluble polyimide resin (Synthesis Example 3, resin solids 20% by weight), 91 parts by weight of phenoxy resin "jER1256" (manufactured by Mitsubishi Chemical Corporation, Mw ≒ 48,000, Tg 95 ° C, resin solids 100% by weight), 57 parts by weight of phosphazene derivative "FP-100" (manufactured by Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4 methylimidazole. A resin varnish with a resin solids content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of methylimidazole.

[0074] Example 4 A resin varnish with a resin solids content of 40 wt% was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture of 337 parts by weight of biphenyl-type epoxy resin "NC-3000H" (manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 275, resin solids content 80 wt%), 202 parts by weight of melamine-modified phenol novolak resin "LA-7054" (manufactured by DIC Corporation, hydroxyl value 125, resin solids content 60 wt%), 98 parts by weight of soluble polyimide resin (Synthesis Example 1, resin solids content 20 wt%), 170 parts by weight of phenoxy resin "FX-310" (manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd., Mw ≒ 45,000, Tg 110 ° C, resin solids content 100 wt%), 57 parts by weight of phosphazene derivative "FP-100" (manufactured by Fushimi Pharmaceutical Co., Ltd.), and 0.7 parts by weight of 2-ethyl-4-methylimidazole.

[0075] Example 5 372 parts by weight of dicyclopentadiene type epoxy resin "HP-7200H" (DIC Corporation, epoxy equivalent 283, resin solid content 80% by weight), 128 parts by weight of aromatic amine "Elasmer 250P" (Kumiai Chemical Industry Co., Ltd., MW = 488, resin solid content 100% by weight), 290 parts by weight of soluble polyimide resin (Synthesis Example 4, resin solid content 20% by weight), 91 parts by weight of phenoxy resin "jER1256" (Mitsubishi Chemical Corporation, Mw ≒ 48,000, Tg 95 ° C, resin solid content 100% by weight), 57 parts by weight of phosphazene derivative "FP-100" (Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4 methylimidazole. A resin varnish with a resin solid content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of methylimidazole.

[0076] Example 6 372 parts by weight of dicyclopentadiene type epoxy resin "HP-7200H" (DIC Corporation, epoxy equivalent 283, resin solid content 80% by weight), 128 parts by weight of aromatic amine "Elasmer 250P" (Kumiai Chemical Industry Co., Ltd., MW = 488, resin solid content 100% by weight), 98 parts by weight of soluble polyimide resin (Synthesis Example 3, resin solid content 20% by weight), 170 parts by weight of phenoxy resin "FX-310" (Nippon Steel Epoxy Manufacturing Co., Ltd., Mw ≒ 45,000, Tg 110 ° C, resin solid content 100% by weight), 57 parts by weight of phosphazene derivative "FP-100" (Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4-methylimidazole. A resin varnish with a resin solid content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of.

[0077] The resin varnishes prepared in Examples 1 to 6 were diluted to 20% solids, applied to a 20 μm polyimide film (Kapton® EN) using a gravure coater, and dried at 150°C to produce double-sided coated adhesive sheets in the B state (film thickness on one side: 2.8 μm). The volatile content was adjusted to 0.6 wt%. 12 μm copper foil with an Rz of 1.8 μm was laminated to both sides of this adhesive sheet using a laminator at a lamination temperature of 110°C or 100°C. The adhesive layer was then heated to 180°C for 90 minutes in a dryer to heat-cure the adhesive layer, producing double-sided copper foil FCCLs. Similarly, the resin varnishes in each of the above examples were diluted to 20% solids, applied to a 20 μm polyimide film (Kapton® EN) using a gravure coater, and dried at 150°C to produce single-sided coated adhesive sheets in the B state (film thickness on one side: 2.8 μm). The volatile content was adjusted to 0.6 wt%. A 12 μm copper foil with Rz=1.8 μm was attached to one side of this adhesive sheet using a laminator at a lamination temperature of 110°C or 100°C, and then heated in a dryer at 180°C for 90 minutes to heat-cure the adhesive layer, producing a single-sided copper foil FCCL.

[0078] (Comparative Example 1) 337 parts by weight of biphenyl type epoxy resin "NC-3000H" (manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 275, resin solid content 80% by weight), 202 parts by weight of melamine-modified phenol novolak resin "LA-7054" (manufactured by DIC Corporation, hydroxyl value 125, resin solid content 60% by weight), 190 parts by weight of phenoxy resin "jER1256" (manufactured by Mitsubishi Chemical Corporation, Mw ≒ 48,000, Tg 95 ° C, resin solid content 100% by weight), 57 parts by weight of phosphazene derivative "FP-100" (manufactured by Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4 methylimidazole A resin varnish with a resin solid content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of methylimidazole.

[0079] (Comparative Example 2) 347 parts by weight of dicyclopentadiene type epoxy resin "HP-7200H" (DIC Corporation, epoxy equivalent 283, resin solids 80% by weight), 183 parts by weight of melamine-modified cresol novolak resin "EXB-9854" (DIC Corporation, hydroxyl value 151, resin solids 80% by weight), 290 parts by weight of soluble polyimide resin (Synthesis Example 1, resin solids 20% by weight), 303 parts by weight of phenoxy resin ERF-001M30 (Nitto Epoxy Manufacturing Co., Ltd., Tg 146 ° C., resin solids 30% by weight), 57 parts by weight of phosphazene derivative "FP-100" (Fushimi Pharmaceutical Co., Ltd.), 0.7 parts by weight of 2-ethyl-4-methylimidazole. A resin varnish with a resin solids content of 40% by weight was prepared by adding a γ-butyrolactone / cyclohexanone mixed solvent as a solvent to a mixture consisting of methylimidazole.

[0080] Using the resin varnishes of Comparative Examples 1 and 2, double-sided copper foil FCCLs and single-sided copper foil FCCLs were produced in the same manner as in Examples 1 to 6.

[0081] (Comparative Examples 3 to 5) The following commercially available FCCLs were used: Comparative Example 3: Commercially available casting method two-layer FCCL Comparative Example 4: Commercially available laminated two-layer FCCL Comparative Example 5: Commercially available three-layer FCCL

[0082] (Evaluation of various characteristics) The double-sided copper foil FCCL prepared as described above was used to evaluate peel strength, solder heat resistance, and dimensional stability, and the double-sided copper foil FCCL was used to etch the entire surface of the film to evaluate Tg and CTE by the TMA method (thermomechanical analysis). The test method was in accordance with JIS C 6471. The single-sided copper foil FCCL prepared as described above was also evaluated for warpage. Specifically, a sample cut to 100 mm x 100 mm was placed on a mirror-finished plate with the copper foil side facing up, and the amount of warpage was measured. A warpage of 5 mm or less was considered to be absent. The copper foil was also etched over its entire surface, and the amount of warpage was similarly measured.

[0083] (Tensile modulus and Tg of adhesive film) The tensile modulus and Tg of films made from the resin varnishes (adhesive compositions) prepared in Examples 1 to 6 and Comparative Example 1 were measured by the following methods. A resin varnish (adhesive composition) was applied to the shiny side of 18 μm electrolytic copper foil using a bar coater and dried at 150°C to produce a semi-cured (B-state) adhesive-coated copper foil (adhesive thickness: approximately 21 μm). The solvent volatile content was adjusted to 0.6 wt%. The shiny side of 18 μm electrolytic copper foil was placed on the adhesive sheet side of this adhesive-coated copper foil, which was then placed in a vacuum press and heated and pressurized at 180°C for 90 minutes at 1 MPa (vacuum level: 5 torr). The copper foil was then completely etched, resulting in an adhesive film of approximately 20 μm thickness. The tensile modulus and Tg were measured. The tensile modulus was measured in accordance with IPC-TM-650-2.4.18.3. A 10 mm wide strip sample was placed in a tension-compression tester with a grip distance of 50 mm. The tensile strength was measured at a pulling rate of 50 mm / min, and the tensile stress was calculated from the relationship between tensile stress and strain. Tg was measured in accordance with IPC-TM-650-2.4.24.3. IPC-TM-650-2.4.18.3 and IPC-TM-650-2.4.24.3 were measured according to the method described in the "IPC-TM-650 TEST METHODS MANUAL." The constitutional details and characteristic evaluation results of the FCCLs of Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Tables 1 to 4 below.

[0084] [Table 1]

[0085] [Table 2]

[0086] [Table 3]

[0087] [Table 4]

[0088] The results in Tables 1 to 4 show that the FCCLs (Examples 1 to 6) produced using the adhesive of the present invention have improved dimensional stability and no warping of the single-sided panels compared to an FCCL (Comparative Example 1) produced using an adhesive that uses a phenoxy-modified epoxy resin and produces a film with a Tg of less than 120°C. Furthermore, when an adhesive using a phenoxy resin with a Tg of more than 120°C was used, the polyimide film and copper foil did not adhere to each other at a lamination temperature of 100°C, making lamination impossible, and the copper foil broke at a lamination temperature of 125°C (Comparative Example 2). Furthermore, compared to a commercially available two-layer FCCL produced by a casting method (Comparative Example 3), the FCCLs of Examples 1 to 6 demonstrate properties comparable to those of a two-layer FCCL produced by a casting method, despite being produced by a lamination process. [Industrial Applicability]

[0089] By using the adhesive and adhesive sheet of the present invention, it is possible to provide a flexible copper-clad laminate (2.2-layer FCCL) that combines properties comparable to those of a casting method 2-layer FCCL with productivity equal to or higher than that of a lamination method 2-layer FCCL.

Claims

1. The adhesive for flexible copper-clad laminates is used to bond a polyimide film substrate and copper foil that constitute the flexible copper-clad laminate, and contains a solvent-soluble polyimide having a repeating unit represented by the following general formula [I], a phenoxy resin having a glass transition temperature (Tg) of 90°C to 120°C, an epoxy resin, and an epoxy resin curing agent. 【Chemistry 1】 (wherein Z is an aromatic or alicyclic tetracarboxylic acid dianhydride residue, and Ar is an aromatic diamine residue having a phenylindane structure).

2. The adhesive according to claim 1, wherein a semi-cured film made from the adhesive is heat-cured at 180°C for 90 minutes, and the resulting film has a tensile modulus of 1 to 10.0 GPa and a Tg of 120 to 190°C.

3. 3. The adhesive according to claim 1, wherein the phenoxy resin has a glass transition temperature (Tg) of 90 to 115°C.

4. 4. The adhesive according to claim 3, wherein the glass transition temperature (Tg) of the phenoxy resin is 90 to 110°C.

5. 5. The adhesive according to claim 1, wherein the weight ratio of the solvent-soluble polyimide resin (solid content) to the phenoxy resin contained in the adhesive is 1:1.2 to 12.

0.

6. The adhesive according to any one of claims 1 to 5, wherein the total content of the solvent-soluble polyimide resin and the phenoxy resin is 10 to 50 wt% relative to the total content of the solvent-soluble polyimide resin, the phenoxy resin, the epoxy resin, and the epoxy resin curing agent contained in the adhesive.

7. An adhesive sheet for flexible copper-clad laminates, comprising an adhesive layer for adhering copper foil laminated on one or both sides of a polyimide film substrate constituting the flexible copper-clad laminate, wherein the adhesive layer contains the adhesive according to any one of claims 1 to 6.

8. 8. The adhesive sheet according to claim 7, wherein the tensile modulus of the film obtained by heat-curing a semi-cured film made from the adhesive at 180°C for 90 minutes is less than the tensile modulus of the polyimide film substrate.

9. 9. The adhesive sheet according to claim 7, wherein the adhesive layer has a thickness of 1.6 to 4.0 μm.

10. The adhesive sheet according to any one of claims 7 to 9, wherein the adhesive sheet has an adhesive layer thickness of 1.5 to 3.5 µm when the adhesive sheet is heat-cured at 180°C for 90 minutes.

11. A flexible copper-clad laminate comprising an adhesive layer and a copper foil laminated in that order on one or both sides of a polyimide film substrate, wherein the adhesive layer contains the adhesive according to any one of claims 1 to 6.

12. 12. The flexible copper-clad laminate according to claim 11, wherein the thickness of the copper foil is 1.5 to 18 μm.

13. 13. The flexible copper-clad laminate according to claim 11, wherein the surface roughness Rz of the copper foil surface in contact with the adhesive layer is less than the thickness of the adhesive layer.

14. A method for producing a flexible copper-clad laminate according to any one of claims 11 to 13, comprising laminating a copper foil to the adhesive sheet according to any one of claims 7 to 10 at a temperature of 70 to 120°C, and then curing the adhesive layer at a temperature of 200°C or less.

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