Resin film, metal-clad laminate, printed wiring board, and method for producing resin film

Abstract

The purpose of the present invention is to provide a resin film or a metal-clad laminate which is capable of producing a printed wiring board having excellent dimensional stability and reduced transmission loss. The purpose of the present invention is also to provide a method for producing a resin film which enables the production of a printed wiring board having excellent dimensional stability and reduced transmission loss. The present invention relates to a resin film (7) comprising a polyimide film (70) and a PTFE film (71) directly laminated on the polyimide film (70). In the resin film (7), the peel strength when the PTFE film (71) is peeled off is 0.5 N / mm or more.

Description

Technical Field

[0001] The present invention relates to a resin film, a metal-clad laminate, a printed circuit board and a method for manufacturing the resin film. Background Art

[0002] In order to enable large-scale and high-speed communication of information, printed circuit boards are required to reduce transmission loss. Transmission loss is composed of conductor loss and dielectric loss. Dielectric loss can be reduced by reducing the relative dielectric constant and dielectric loss tangent of the dielectric. On the other hand, dielectric loss increases with higher signal frequency. With the development of high-frequency band utilization, the importance of reducing the relative dielectric constant and dielectric loss tangent of the resin film used in the manufacture of printed circuit boards is increasing.

[0003] To reduce the relative dielectric constant and dielectric loss tangent, polytetrafluoroethylene (PTFE) is sometimes used as a material for printed circuit boards (see, for example, Patent Documents 1 and 2). PTFE exhibits the lowest dielectric constant and dielectric loss tangent among fluororesins. This is because PTFE has a repeating structure of -(CF2-CF2)-.

[0004] On the other hand, polyimide is sometimes used as a material for printed wiring boards (see, for example, Patent Document 3). This is because polyimide has excellent heat resistance, insulation properties, dimensional stability, etc. Polyimide is particularly suitable as a material for the insulating substrate of flexible printed circuit boards.

[0005] In the technology of Patent Document 3 using polyimide, in order to reduce the relative dielectric constant and dielectric loss tangent, a fluororesin other than PTFE, specifically a fluororesin such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (i.e., PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (i.e., FEP), is provided on both sides of the polyimide layer. Prior art literature Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-307611 Patent Document 2: Japanese Patent Application Laid-Open No. 2005-163006 Patent Document 3: Patent No. 5625906 Patent Document 4: Japanese Patent Application Laid-Open No. 2012-233038 Summary of the Invention Problems to be solved by the invention

[0007] The printed wiring board manufactured using the technology of Patent Document 3 comprises a resin film comprising a first fluororesin layer, a polyimide layer, and a second fluororesin layer. While this exhibits excellent dimensional stability and reduced transmission loss, there is still room for improvement. In particular, there is room for improvement in reducing transmission loss.

[0008] The present invention aims to provide a resin film or metal-clad laminate capable of producing a printed wiring board having excellent dimensional stability and reduced transmission loss. Furthermore, the present invention aims to provide a method for producing a resin film capable of producing a printed wiring board having excellent dimensional stability and reduced transmission loss. Technical solutions to the problem

[0009] In order to solve this problem, the present invention has the following structure [1]. [1] A resin film comprising: a polyimide film and a first polytetrafluoroethylene film directly laminated on the polyimide film, The peel strength when the first polytetrafluoroethylene film is peeled off is 0.5 N / mm or more.

[0010] According to [1], since the resin film includes a polyimide film, the dimensional stability of the resin film can be improved.

[0011] Furthermore, since the resin film includes the first polytetrafluoroethylene film (i.e., the first PTFE film), the relative dielectric constant and dielectric loss tangent of the resin film can be reduced. This is because PTFE exhibits the lowest dielectric constant and dielectric loss tangent among fluororesins such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (i.e., PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (i.e., FEP).

[0012] Moreover, since the first PTFE film is directly laminated on the polyimide film, the relative dielectric constant and dielectric loss tangent of the resin film can be further reduced. This is explained. Assuming that when PTFE and polyimide are bonded with an adhesive, it is believed that the relative dielectric constant and dielectric loss tangent are increased due to the adhesive. In this regard, according to [1], the first PTFE film is directly laminated on the polyimide film, that is, the first PTFE film is bonded to the polyimide film without an adhesive. Thus, the increase in relative dielectric constant and dielectric loss tangent that may be caused by the adhesive can be avoided. Therefore, the relative dielectric constant and dielectric loss tangent of the resin film can be further reduced.

[0013] Furthermore, since the peel strength is 0.5 N / mm or more, it is possible to suppress undesired peeling of the first PTFE film. Thus, it is possible to suppress the first PTFE film from peeling from the polyimide film, which may be caused by impact, temperature change, humidity change, etc. that the resin film may be subjected to.

[0014] Therefore, according to the resin film of [1], a printed wiring board having excellent dimensional stability and reduced transmission loss can be manufactured.

[0015] The present invention preferably has the following configurations [2] to [7]. [2] The resin film according to [1], further comprising a second polytetrafluoroethylene film directly laminated on the polyimide film, The first polytetrafluoroethylene film, the polyimide film, and the second polytetrafluoroethylene film are arranged in this order in the thickness direction of the resin film. The peel strength when the second polytetrafluoroethylene film is peeled off is 0.5 N / mm or more.

[0016] [3] The resin film according to [2], wherein the relative dielectric constant at 28 GHz is 3.0 or less.

[0017] [4] The resin film according to [2] or [3], wherein the dielectric loss tangent at 28 GHz is 0.004 or less.

[0018] [5] The resin film according to any one of [2] to [4], wherein the total thickness of the first polytetrafluoroethylene film and the second polytetrafluoroethylene film is greater than or equal to 60% and less than or equal to 90% of the total thickness of the first polytetrafluoroethylene film, the polyimide film, and the second polytetrafluoroethylene film (100%).

[0019] [6] The resin film according to any one of [1] to [5], wherein the polyimide film comprises a polyimide containing a polyimidebenzoxazole component.

[0020] [7] The resin film according to any one of [1] to [6], which is used for producing at least one of a metal-clad laminate and a printed wiring board.

[0021] [8] The resin film according to any one of [1] to [7], wherein the linear expansion coefficient at 50°C to 200°C is 30 ppm / °C or less.

[0022] The present invention also relates to the following structure [9]. [9] A metal-clad laminate comprising: The resin film according to any one of [1] to [8], and a metal foil provided on the first polytetrafluoroethylene film of the resin film.

[0023] The present invention also relates to the following structure

[10] .

[10] A printed wiring board produced using the resin film described in any one of [1] to [8].

[0024] The present invention also relates to the following structure

[11] .

[11] A method for producing the resin film according to any one of [1] to [8], comprising the following steps: a step of plasma-treating the surface of the first polytetrafluoroethylene film at an oxygen concentration of less than 0.5% by volume; a step of thermocompression bonding the first polytetrafluoroethylene film treated with the plasma to the polyimide film in a state where the surface of the first polytetrafluoroethylene film treated with the plasma faces the polyimide film; In the step of performing the plasma treatment, the temperature of the surface of the first polytetrafluoroethylene film is 180° C. or higher.

[0025] According to

[11] , since the surface of the first PTFE film is subjected to plasma treatment, the carbon-fluorine bonds of the PTFE molecules can be cut.

[0026] Furthermore, since the plasma treatment is performed at a surface temperature of 180°C or higher on the first PTFE membrane, the mobility of the PTFE molecules on the surface of the first PTFE membrane can be increased, thereby effectively bonding PTFE molecules having carbon atoms whose carbon-fluorine bonds have been severed by plasma irradiation to other PTFE molecules having similarly severed carbon atoms. In other words, the formation of carbon-carbon bonds between PTFE molecules can be actively promoted. In other words, the cross-linking reaction can be actively promoted. Therefore, the surface hardness of the first PTFE membrane can be increased (this can be said to be able to repair or remove the fragile layer on the surface of the first PTFE membrane). As a result, the adhesion of the first PTFE membrane to the polyimide membrane, i.e., the peel strength, can be improved.

[0027] Furthermore, since the plasma treatment is performed at an oxygen concentration of less than 0.5% by volume, the inhibition of carbon-carbon bond formation caused by oxygen (hereinafter sometimes referred to as "oxygen inhibition") can be avoided, thereby further increasing the surface hardness of the first PTFE film. Consequently, the adhesion of the first PTFE film to the polyimide film, i.e., the peel strength, can be further improved. Effects of the Invention

[0028] According to the present invention, a resin film or metal-clad laminate capable of producing a printed wiring board having excellent dimensional stability and reduced transmission loss can be provided. According to the present invention, a method for producing a resin film capable of producing a printed wiring board having excellent dimensional stability and reduced transmission loss can also be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic cross-sectional view of the resin film in this embodiment. Figure 2A FIG. 1 is a schematic diagram of an atmospheric pressure plasma processing apparatus that can be used in this embodiment. Figure 2B It is a schematic diagram showing a partially enlarged view of the periphery of electrodes constituting the atmospheric pressure plasma processing apparatus that can be used in this embodiment. Figure 3 This is a schematic cross-sectional view of a metal-clad laminate in this embodiment. Description of Reference Numerals 7 ...resin film, 70 ...polyimide film, 71 ...PTFE film, 72 ...PTFE film, 701 ...surface of polyimide film, 702 ...surface of polyimide film, 8 ...metal-clad laminate, 81 ...metal foil, 82 ...metal foil; 10...High-frequency power supply, 11...Matching unit, 12...Chamber, 13...Vacuum exhaust system, 14...Electrode, 15...Electrode lifting mechanism, 16...Turntable, 17...Halogen heater, 18...Inner tube, 19...Outer tube, 21...Radiation thermometer. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present invention will be described in detail.

[0031] <1. Resin Film> like Figure 1 As shown, the resin film 7 of this embodiment includes a polyimide film 70, a polytetrafluoroethylene film (i.e., PTFE film) 71, and a polytetrafluoroethylene film (i.e., PTFE film) 72. In the resin film 7, the PTFE film 71, the polyimide film 70, and the PTFE film 72 are arranged in this order in the thickness direction of the resin film 7. In other words, the PTFE film 71, the polyimide film 70, and the PTFE film 72 are stacked in this order. Because these films are arranged in this order, the resin film 7 can achieve excellent low hygroscopicity.

[0032] <1.1. Polyimide Film> The resin film 7 includes a polyimide film 70. The polyimide film 70 includes a surface 701 and a surface 702. The surface 701 faces the PTFE film 71. On the other hand, the surface 702 faces the PTFE film 72. Since the resin film 7 includes the polyimide film 70, it can achieve excellent dimensional stability.

[0033] The polyimide film 70 is preferably surface-modified on both surfaces, namely, the surface 701 and the surface 702. Surface modification can improve the peel strength when peeling the PTFE film 71 or 72 from the polyimide film 70, thereby further suppressing undesired peeling of the PTFE film 71 or 72.

[0034] The thickness of the polyimide film 70 is preferably 1 μm or more, more preferably 5 μm or more. On the other hand, the thickness of the polyimide film 70 is preferably 60 μm or less, more preferably 40 μm or less, and even more preferably 38 μm or less.

[0035] The storage modulus of the polyimide film 70 at 25° C. is preferably 6.0 GPa or more, more preferably 7.0 GPa or more, and even more preferably 8.0 GPa or more. The storage modulus of the polyimide film 70 at 25° C. can be measured using the following apparatus and conditions. Device name: Rheogel-E4000 manufactured by UBM Corporation Clamp: Tensile clamp Sample length: 14mm Sample width: 5mm Frequency: 10Hz Heating starting temperature: 0℃ Heating rate: 5℃ / min Atmosphere: Nitrogen

[0036] The polyimide film 70 includes polyimide. The polyimide film 70 can be formed, for example, by a method comprising casting, drying, and heat-treating (imidization) a polyamic acid solution obtained by reacting aromatic tetracarboxylic acids (hereinafter, aromatic tetracarboxylic anhydrides, acids, and amide-bonding derivatives thereof are collectively referred to as "aromatic tetracarboxylic acids") with aromatic diamines (hereinafter, amines and amide-bonding derivatives thereof are collectively referred to as "aromatic diamines").

[0037] The polyimide preferably contains a polyimide benzoxazole component. Here, "polyimide containing a polyimide benzoxazole component" refers to a polyimide containing a benzoxazole structure. An example of a polyimide containing a polyimide benzoxazole component is a polyimide obtained by polycondensing an aromatic diamine having a benzoxazole structure with an aromatic tetracarboxylic anhydride.

[0038] As preferred combinations of aromatic tetracarboxylic acids and aromatic diamines for polyimide, the following examples can be given. A. Combination of an aromatic tetracarboxylic acid having a pyromellitic acid residue and an aromatic diamine having a benzoxazole structure. B. Combination of aromatic diamines having a phenylenediamine skeleton and aromatic tetracarboxylic acids having a biphenyltetracarboxylic acid skeleton. C. Combination of an aromatic diamine having a diphenyl ether skeleton and an aromatic tetracarboxylic acid having a pyromellitic acid residue. Among them, combination A is preferred.

[0039] Examples of the aromatic diamines having a benzoxazole structure include the following: These diamines preferably account for 70 mol% or more, and more preferably 80 mol% or more, of the total diamines.

[0040] [Chemistry 1] 5-Amino-2-(p-aminophenyl)benzoxazole

[0041] [Chemistry 2] 6-Amino-2-(p-aminophenyl)benzoxazole

[0042] [Chemistry 3] 5-amino-2-(m-aminophenyl)benzoxazole

[0043] [Chemistry 4] 6-amino-2-(m-aminophenyl)benzoxazole

[0044] [Chemistry 5] 2,2'-p-phenylenebis(5-aminobenzoxazole)

[0045] [Chemistry 6] 2,2'-p-phenylenebis(6-aminobenzoxazole)

[0046] [Chemistry 7] 1-(5-aminobenzoxazolyl)-4-(6-aminobenzoxazolyl)benzene

[0047] [Chemistry 8] 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']dioxazole

[0048] [Chemistry 9] 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']dioxazole

[0049] [Chemistry 10] 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:5,4-d']dioxazole

[0050] [Chemistry 11] 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']dioxazole

[0051] [Chemistry 12] 2,6-(3,3'-diaminodiphenyl)benzo[1,2-d:5,4-d']dioxazole

[0052] [Chemistry 13] 2,6-(3,3'-Diaminodiphenyl)benzo[1,2-d:4,5-d']dioxazole

[0053] Among them, from the perspective of ease of synthesis, the isomers of amino(aminophenyl)benzoxazole are preferred, and 5-amino-2-(p-aminophenyl)benzoxazole is more preferred. Here, "isomers" refer to isomers determined by the coordination positions of the two amino groups possessed by amino(aminophenyl)benzoxazole (for example, the compounds described in "Chemicals 1" to "Chemicals 4" above). These diamines can be used alone or in combination of two or more.

[0054] Furthermore, the diamines exemplified below may be used alone or in combination of two or more. Examples of such diamines include 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether. Diphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]methane, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane, 1,2-bis[4-(4-aminophenoxy)phenyl]ethane phenyl]ethane, 1,1-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,1-bis[4-(4-aminophenoxy)phenyl]butane, 1,3-bis[4-(4-aminophenoxy)phenyl]butane, 1,4-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,3-bis[4-(4-aminophenoxy)phenyl]butane, 2-[4-(4-aminophenoxy)phenyl]butane phenyl]-2-[4-(4-aminophenoxy)-3-methylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3-methylphenyl]propane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-Bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfoxide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4'-bis[(3-aminophenoxy)benzoyl]benzene, 1,1-bis[4-(3-aminophenoxy)phenyl]propane, 1,3-bis [4-(3-aminophenoxy)phenyl]propane, 3,4'-diaminodiphenyl sulfide, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy)phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, bis[4-(3-aminophenoxy)phenyl]sulfoxide, 4,4'-bis[3-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis [4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenylsulfone, bis[4-{4-(4-aminophenoxy)phenoxy}phenyl]sulfone, 1,4-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-trifluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-fluorophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-methylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-cyanopheneoxy)-α, α-dimethylbenzyl]benzene, 3,3'-diamino-4,4'-diphenoxybenzophenone, 4,4'-diamino-5,5'-diphenoxybenzophenone, 3,4'-diamino-4,5'-diphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3'-diamino-4,4'-diphenyloxybenzophenone, 4,4'-diamino-5,5'-diphenyloxybenzophenone, 3,4'-diamino-4,5'-diphenyloxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-Diamino-5-biphenyloxybenzophenone, 3,4'-diamino-4-biphenyloxybenzophenone, 3,4'-diamino-5'-biphenyloxybenzophenone, 1,3-bis(3-amino-4-phenoxybenzoyl)benzene, 1,4-bis(3-amino-4-phenoxybenzoyl)benzene, 1,3-bis(4-amino-5-phenoxybenzoyl)benzene, 1,4-bis(4-amino-5-phenoxybenzoyl)benzene, 1,3-bis(3-amino-4-biphenyloxybenzoyl)benzene, 1,4-bis(3-amino-4-biphenyloxybenzoyl)benzene benzoyl)benzene, 1,3-bis(4-amino-5-biphenyloxybenzoyl)benzene, 1,4-bis(4-amino-5-biphenyloxybenzoyl)benzene, 2,6-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzonitrile, and aromatic diamines in which some or all of the hydrogen atoms on the aromatic ring of the above aromatic diamines are substituted with halogen atoms, alkyl or alkoxy groups having 1 to 3 carbon atoms, cyano groups, or haloalkyl or haloalkoxy groups having 1 to 3 carbon atoms (in which some or all of the hydrogen atoms of the alkyl or alkoxy groups are substituted with halogen atoms). These diamines are preferably present in an amount of 30 mol% or less, more preferably 20 mol% or less, of the total diamines.

[0055] Examples of the aromatic tetracarboxylic anhydride include the following: These acid anhydrides preferably account for 70 mol% or more, more preferably 80 mol% or more, of the total acid anhydrides.

[0056] [Chemistry 14] Pyromellitic anhydride

[0057] [Chemistry 15] 3,3',4,4'-Biphenyltetracarboxylic dianhydride

[0058] [Chemistry 16] 4,4'-Oxydiphthalic anhydride

[0059] [Chemistry 17] 3,3',4,4'-Benzophenonetetracarboxylic dianhydride

[0060] [Chemistry 18] 3,3',4,4'-Diphenylsulfonetetracarboxylic dianhydride

[0061] [Chemistry 19] 2,2-Bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride

[0062] Aromatic tetracarboxylic anhydrides may be used alone or in combination of two or more.

[0063] Furthermore, the non-aromatic tetracarboxylic dianhydrides exemplified below can be used alone or in combination of two or more. Examples of such tetracarboxylic anhydrides include butane-1,2,3,4-tetracarboxylic dianhydride, pentane-1,2,4,5-tetracarboxylic dianhydride, cyclobutane tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride, cyclohex-1-ene-2,3,5,6-tetracarboxylic dianhydride, 3-ethylcyclohex-1-ene-3-(1,2),5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohexane-3-(1,2),5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohex-1-ene-3-(1,2),5,6-tetracarboxylic dianhydride, 1-ethylcyclohexane-1-(1,2),3,4-tetracarboxylic dianhydride, and 1-propylcyclohexane-1-(2,3), 3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane-1-(2,3),3-(2,3)-tetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, 1-propylcyclohexane-1-(2,3),3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane-1-(2,3),3-(2,3)-tetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and the like. The content of these tetracarboxylic dianhydrides, ie, non-aromatic tetracarboxylic dianhydrides, is preferably 30 mol% or less, more preferably 20 mol% or less, of the total acid anhydrides.

[0064] The solvent used when reacting (polymerizing) aromatic tetracarboxylic acids with aromatic diamines to obtain polyamic acid is not particularly limited as long as it is a solvent that can dissolve any one of the monomers as raw materials and the generated polyamic acid, but polar organic solvents are preferred, for example, N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, ethyl acetate cellosolve, diethylene glycol dimethyl ether, cyclopentane, halogenated phenols, etc. These solvents can be used alone or in combination. The amount of solvent used can be an amount sufficient to dissolve the monomers as raw materials. As a specific amount used, the amount of the monomers used in the solution in which the monomers are dissolved can be generally 5 to 40% by mass, preferably 10 to 30% by mass.

[0065] The conditions for the polymerization reaction (hereinafter also referred to as "polymerization reaction") for obtaining polyamic acid can be applied to existing well-known conditions. As a specific example, continuous stirring and / or mixing in an organic solvent within a temperature range of 0 to 80°C for 10 minutes to 30 hours can be cited. The polymerization reaction can also be carried out in batches or the temperature can be raised or lowered as needed. In this case, there is no particular restriction on the order in which the two monomers are added, and it is preferred to add aromatic tetracarboxylic anhydride to the aromatic diamine solution. From the viewpoint of liquid feeding stability, the viscosity of the polyamic acid solution obtained by the polymerization reaction is preferably 10 to 2000 Pa·s, more preferably 100 to 1000 Pa·s, when measured by Brookfield viscosity (25°C).

[0066] Vacuum degassing during the polymerization reaction is very effective for producing high-quality polyamic acid solutions. Alternatively, a small amount of an end-capping agent can be added to the aromatic diamine before the polymerization reaction to control the polymerization. Examples of end-capping agents include compounds with carbon-carbon double bonds, such as maleic anhydride. When maleic anhydride is used, the amount is preferably 0.001 to 1.0 moles per mole of aromatic diamine.

[0067] In order to form the polyimide film 70 from the polyamic acid solution obtained by the polymerization reaction, the following method can be used: the polyamic acid solution is applied to a support and dried to obtain a green film (a self-supporting precursor film), and then the green film is subjected to a heat treatment to perform an imidization reaction. The polyamic acid solution can be applied to the support by casting from a slit gate, extrusion using an extruder, etc., but is not limited to these methods, and any conventionally known solution coating method can be used as appropriate.

[0068] The conditions for drying the polyamic acid coated on the support to obtain a green sheet are not particularly limited. As an example, the temperature can be 70 to 150°C, and as a drying time, 5 to 180 minutes can be exemplified. The drying device that achieves such conditions can also be applied to existing known drying devices, and examples include: hot air, hot nitrogen, far infrared rays, high-frequency induction heating, etc. Next, in order to obtain a polyimide film 70 from the obtained green sheet, an imidization reaction is carried out. As a specific method, an existing known imidization reaction can be appropriately used. For example, the following method can be cited: using a polyamic acid solution that does not contain a ring-closing catalyst or a dehydrating agent, a stretching treatment is performed as needed, and then an imidization reaction is carried out by heat treatment (the so-called thermal ring-closing method). The heating temperature in this case can be exemplified by 100 to 500°C. From the perspective of film properties, it is more preferable to cite a two-step heat treatment: treating at 150 to 250°C for 3 to 20 minutes, and then treating at 350 to 500°C for 3 to 20 minutes.

[0069] As an example of other imidization reactions, a chemical ring closure method can also be cited, which contains a ring closure catalyst and a dehydrating agent in a polyamic acid solution, and an imidization reaction is carried out by the action of the above-mentioned ring closure catalyst and the dehydrating agent. In this method, the polyamic acid solution can be applied to a support, and then an imidization reaction is carried out in part to form a self-supporting film, which is then fully imidized by heating. In this case, as a condition for making the imidization reaction partially carried out, it is preferably heat-treated at 100 to 200 ° C for 3 to 20 minutes, and for the condition for fully carrying out the imidization reaction, it is preferably heat-treated at 200 to 400 ° C for 3 to 20 minutes.

[0070] <1.2. PTFE membrane> The resin film 7 includes a PTFE film 71 and a PTFE film 72. Since the resin film 7 includes the PTFE film 71 and the PTFE film 72, the relative dielectric constant and the dielectric loss tangent of the resin film 7 can be reduced. This is because PTFE has the lowest dielectric constant and the lowest dielectric loss tangent among fluororesins such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (i.e., PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (i.e., FEP).

[0071] PTFE film 71 is directly laminated on the polyimide film 70. Because PTFE film 71 is directly laminated on the polyimide film 70, the relative dielectric constant and dielectric loss tangent of resin film 7 can be further reduced. This is explained. If, when PTFE film 71 and polyimide film 70 are bonded with an adhesive, it is believed that relative dielectric constant and dielectric loss tangent become higher due to the adhesive. To this, according to the present embodiment, PTFE film 71 is directly laminated on the polyimide film 70, that is, PTFE film 71 is joined to the polyimide film 70 without an adhesive. Thereby, the increase of relative dielectric constant and dielectric loss tangent that may be caused by the adhesive can be avoided. Therefore, the relative dielectric constant and dielectric loss tangent of resin film 7 can be further reduced. On the other hand, PTFE film 72 is also directly laminated on the polyimide film 70. Since the PTFE film 72 is directly laminated on the polyimide film 70 , the relative dielectric constant and dielectric loss tangent of the resin film 7 can be further reduced.

[0072] It is preferred that at least the surface facing the polyimide film 70 of the two surfaces of the PTFE film 71 be surface-modified. By surface-modifying this surface, the peel strength when the PTFE film 71 is peeled off from the polyimide film 70 can be improved, thereby further suppressing undesirable peeling of the PTFE film 71. It should be noted that both surfaces of the PTFE film 71 can also be surface-modified.

[0073] Preferably, at least the surface facing the polyimide film 70 of the two surfaces of the PTFE film 72 is also surface-modified. By surface-modifying this surface, the peel strength when the PTFE film 72 is peeled off from the polyimide film 70 can be improved, thereby further suppressing undesirable peeling of the PTFE film 72. It should be noted that both surfaces of the PTFE film 72 can also be surface-modified.

[0074] The thickness of PTFE membrane 71 and PTFE membrane 72 is preferably 5 μm or greater, more preferably 10 μm or greater, even more preferably 15 μm or greater, and even more preferably 20 μm or greater. Meanwhile, the thickness of PTFE membrane 71 is preferably 100 μm or less, more preferably 70 μm or less, even more preferably 60 μm or less, and even more preferably 50 μm or less. The thickness of PTFE membrane 71 and PTFE membrane 72 can be independent of each other. Therefore, the thickness of the two membranes can be the same or different.

[0075] It should be noted that, although it may be self-evident, the PTFE membrane 71 and the PTFE membrane 72 contain polytetrafluoroethylene, that is, PTFE.

[0076] <1.3. Properties and Applications of Resin Films> In the resin film 7, the peel strength when peeling the PTFE film 71 from the polyimide film 70 is 0.5N / mm or more. Since the peel strength is 0.5N / mm or more, it is possible to suppress the undesirable peeling of the PTFE film 71. Thus, it is possible to suppress the peeling of the PTFE film 71 from the polyimide film 70, which may be caused by the impact, temperature change, humidity change, etc. that the resin film 7 may be subjected to. The peel strength is preferably 0.6N / mm or more, more preferably 0.7N / mm or more, further preferably 0.8N / mm or more, and further preferably 0.9N / mm or more. On the other hand, the peel strength can be, for example, 2.0N / mm or less, 1.5N / mm or less, 1.4N / mm or less, 1.3N / mm or less, or 1.2N / mm or less.

[0077] In the resin film 7, the peel strength when peeling the PTFE film 72 from the polyimide film 70 is preferably 0.5 N / mm or more, more preferably 0.6 N / mm or more, further preferably 0.7 N / mm or more, further preferably 0.8 N / mm or more, and further preferably 0.9 N / mm or more. When the peel strength is 0.5 N / mm or more, it is possible to suppress the undesirable peeling of the PTFE film 72. Thus, it is possible to suppress the peeling of the PTFE film 72 from the polyimide film 70, which may be caused by impact, temperature change, humidity change, etc. to which the resin film 7 may be subjected. On the other hand, the peel strength can be, for example, 2.0 N / mm or less, 1.5 N / mm or less, 1.4 N / mm or less, 1.3 N / mm or less, or 1.2 N / mm or less.

[0078] In the resin film 7 , the relative dielectric constant at 28 GHz is preferably 3.0 or less, more preferably 2.8 or less, further preferably 2.6 or less, further preferably 2.55 or less, and further preferably 2.50 or less.

[0079] The dielectric loss tangent of the resin film 7 at 28 GHz is preferably 0.006 or less, more preferably 0.005 or less, and further preferably 0.004 or less. The dielectric loss tangent at 28 GHz may be 0.0035 or less, or even 0.0030 or less.

[0080] The linear expansion coefficient of the resin film 7 at 50°C to 200°C is preferably 30 ppm / °C or less, more preferably 28 ppm / °C or less, and even more preferably 25 ppm / °C or less. This is because the closer the linear expansion coefficient of the resin film 7 is to that of a metal foil (for example, copper foil), the more it is possible to suppress the metal foil from peeling off from the resin film 7. Meanwhile, the linear expansion coefficient of the resin film 7 at 50°C to 200°C can be, for example, 5 ppm / °C or more.

[0081] The thickness of the resin film 7 is preferably 5 μm or greater, more preferably 10 μm or greater. The thickness of the resin film 7 may be 20 μm or greater, 30 μm or greater, 40 μm or greater, 50 μm or greater, or 60 μm or greater. On the other hand, the thickness of the resin film 7 is preferably 150 μm or less, more preferably 100 μm or less.

[0082] Of the total thickness of the PTFE film 71, the polyimide film 70, and the PTFE film 72, 100%, the total thickness of the PTFE film 71 and the PTFE film 72 is preferably 60% or more, more preferably 70% or more, and even more preferably 75% or more. When it is 60% or more, the relative dielectric constant and dielectric loss tangent of the resin film 7 can be further reduced. On the other hand, from the perspective of the dimensional stability of the resin film 7, the total thickness of the PTFE film 71 and the PTFE film 72 is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less.

[0083] The resin film 7 can be suitably used as a printed wiring board, a metal-clad laminate, and the like. This is because the resin film 7 enables the manufacture of a printed wiring board having excellent dimensional stability and reduced transmission loss. An example of a printed wiring board is a flexible printed circuit board (e.g., a single-sided flexible printed circuit board, a double-sided flexible printed circuit board, or a multilayer flexible printed circuit board).

[0084] <2. Method for producing resin film> The method for manufacturing the resin film 7 includes the following steps: a step of modifying the surfaces of the PTFE films 71 and 72 (hereinafter sometimes referred to as "step A"), a step of modifying the surface of the polyimide film 70 (hereinafter sometimes referred to as "step B"), and a step of thermally pressing the PTFE films 71 and 72 together with the modified surface thereof facing the polyimide film 70 and the modified surface thereof facing the polyimide film 70 (hereinafter sometimes referred to as "step C"). Either step A or step B may be performed first, or both steps may be performed in parallel.

[0085] <2.1. Process A> In step A, the surfaces of the PTFE membranes 71 and 72 are modified. Step A includes the following steps: a step of plasma-treating the surface of the PTFE membrane 71 (hereinafter sometimes referred to as "step A1"), and a step of plasma-treating the surface of the PTFE membrane 72 (hereinafter sometimes referred to as "step A2"). Step A1 and step A2 can be performed separately or simultaneously using a single plasma treatment apparatus. When steps A1 and A2 are performed separately, they can be performed in parallel, or one step can be performed first.

[0086] <2.1.1. Step A1_ Step of Plasma-treating the Surface of the PTFE Film 71> In step A1, the surface of the PTFE membrane 71 is subjected to a plasma treatment. This can cut the carbon-fluorine bonds of the PTFE molecules. Examples of plasma treatments include vacuum plasma treatment (i.e., reduced pressure plasma treatment) and atmospheric pressure plasma treatment. Of these, atmospheric pressure plasma treatment is preferred because it can heat the surface of the PTFE membrane 71. In this specification, "atmospheric pressure plasma treatment" refers to plasma treatment at 700 hPa to 1300 hPa.

[0087] For plasma processing, it is preferable to use dielectric barrier discharge. By using dielectric barrier discharge, glow discharge can be stably generated under atmospheric pressure (ie, at 700 hPa to 1300 hPa).

[0088] The pressure of the plasma treatment may be, for example, 700 hPa or higher, 800 hPa or higher, 900 hPa or higher, 950 hPa or higher, or 1000 hPa or higher. The pressure of the plasma treatment may be, for example, 1300 hPa or lower, 1200 hPa or lower, or 1100 hPa or lower.

[0089] In step A1, the surface of the PTFE film 71 is plasma treated at an oxygen concentration of less than 0.5% by volume. Since the plasma treatment is performed at an oxygen concentration of less than 0.5% by volume, the obstruction of carbon-carbon bond formation caused by oxygen (i.e., oxygen inhibition) can be avoided, thereby improving the surface hardness of the PTFE film 71. Therefore, the adhesion of the PTFE film 71 to the polyimide film 70, i.e., the peel strength, can be improved. The oxygen concentration can be, for example, less than 0.4% by volume, less than 0.3% by volume, less than 0.2% by volume, or less than 0.1% by volume.

[0090] In step A1, the temperature of the surface of the PTFE membrane 71 is above 180°C. Since the plasma treatment is performed at a temperature above 180°C, the mobility of the PTFE molecules on the surface of the PTFE membrane 71 can be improved, so that the PTFE molecules having carbon atoms of carbon-fluorine bonds cut by plasma irradiation can be effectively bonded to other PTFE molecules having similarly cut carbon atoms. In other words, the formation of carbon-carbon bonds between PTFE molecules can be actively promoted. In other words, the cross-linking reaction can be actively promoted. Therefore, the surface hardness of the PTFE membrane 71 can be improved (this can be said to be the ability to repair or remove the fragile layer on the surface of the PTFE membrane 71). As a result, the adhesion of the PTFE membrane 71 to the polyimide membrane 70, that is, the peel strength, can be improved. The temperature of the surface of the PTFE membrane 71 can be above 190°C, above 195°C, above 200°C, or above 205°C. On the other hand, the surface temperature of the PTFE membrane 71 can be, for example, 320° C. or less, 280° C. or less, 260° C. or less, 240° C. or less, or 220° C. or less. The surface temperature of the PTFE membrane 71 can be adjusted by, for example, inputting power from a high-frequency power supply, heating with a halogen heater, or the like, as described later.

[0091] The time during which the surface temperature of the PTFE membrane 71 is 180°C or higher is preferably 30 seconds or longer, more preferably 100 seconds or longer, even more preferably 200 seconds or longer, and even more preferably 300 seconds or longer. It can be 400 seconds or longer, or even 500 seconds or longer. On the other hand, the time during which the surface temperature of the PTFE membrane 71 is 180°C or higher can be 6000 seconds or shorter, 3000 seconds or shorter, 2000 seconds or shorter, or even 1000 seconds or shorter.

[0092] To generate plasma, a high-frequency power supply with a voltage applied at a frequency of 50 Hz to 2.45 GHz can be used. The output power density, i.e., the output power per unit area, cannot be determined in general terms, but it is preferably 15 W / cm 2 Above 40W / cm 2 the following.

[0093] When pulse output is used, the pulse modulation frequency is preferably 1 kHz to 50 kHz, more preferably 5 kHz to 30 kHz. The pulse duty ratio is preferably 5% to 99%, more preferably 15% to 80%, and even more preferably 25% to 70%.

[0094] The opposing electrode can be a cylindrical or flat metal plate covered on at least one side with a dielectric. While the distance between the opposing electrodes cannot be generalized, from the perspective of plasma generation and heating, it is preferably 5 mm or less, more preferably 3 mm or less, even more preferably 2 mm or less, and even more preferably 1 mm or less. The lower limit of the distance between the opposing electrodes can be, for example, 0.2 mm or more, 0.4 mm or more, or even 0.5 mm or more.

[0095] As the gas for generating plasma, for example, rare gases such as helium, argon, and neon; reactive gases such as oxygen, nitrogen, and hydrogen can be used. As the gas, it is preferred to use only non-polymerizable gases. It should be noted that among these gases, only one or more rare gases can be used. A mixed gas of one or more rare gases and an appropriate amount of one or more reactive gases can also be used. In the case of using dielectric barrier discharge, helium is preferred because it is easy to obtain glow discharge and the starting discharge voltage is low. In the case of using dielectric barrier discharge, argon and nitrogen are preferred because it is easy to obtain glow discharge and is inexpensive.

[0096] Note that plasma may be generated under conditions where the gas atmosphere is controlled using a chamber, or may be generated under conditions where the plasma is completely open to the atmosphere by flowing a rare gas through the electrode portion.

[0097] The following is based on Figure 2A and Figure 2B , an example of the plasma treatment in step A1 is described.

[0098] Use as Figure 2A The surface modification method of the PTFE membrane 71 of the atmospheric pressure plasma treatment apparatus A shown in FIG. 1 is as follows. First, the PTFE membrane 71 is cleaned with an organic solvent such as acetone or water such as ultrapure water as needed. Figure 2B As shown, after the PTFE film 71 is placed on the sample holder of the rotating table 16 in the chamber 12, the air in the chamber 12 is sucked from the vacuum exhaust system 13 by a suction device (not shown) to reduce the pressure, and the gas for generating plasma is supplied into the chamber 12 (see Figure 2A ). Thus, the pressure in the chamber 12 becomes atmospheric pressure. It should be noted that the PTFE membrane 71 Figure 2A Not shown, only Figure 2B It should be noted that the atmospheric pressure does not necessarily need to be 1013 hPa strictly, and may be within the range of 700 to 1300 hPa.

[0099] As long as Figure 2ASuch an apparatus can perform plasma treatment by reducing the oxygen concentration near the surface of the PTFE film 71 (plasma irradiation area) to less than 0.5% by volume.

[0100] Next, adjust the height of the electrode lifting mechanism 15 ( Figure 2A The electrode 14 is moved to a desired position by adjusting the height of the electrode lifting mechanism 15 (in the up and down directions). By adjusting the height of the electrode lifting mechanism 15, the distance between the electrode 14 and the surface (upper surface) of the PTFE membrane 71 can be adjusted. The distance between the electrode 14 and the surface of the PTFE membrane 71 is preferably less than 5 mm, and more preferably less than 2 mm. In particular, when the surface temperature of the PTFE membrane 71 is set to within a specific range by utilizing the natural temperature rise of plasma treatment, the distance is particularly preferably less than 1.0 mm. It should be noted that since the PTFE membrane 71 is moved by the rotation of the turntable 16, the electrode 14 cannot of course come into contact with the PTFE membrane 71.

[0101] By rotating the rotating table 16, plasma can be irradiated on a desired portion of the surface of the PTFE membrane 71. While the rotation speed of the rotating table 16 is preferably 1 mm / s to 3 mm / s, it may be outside this range. The duration of plasma irradiation on the PTFE membrane 71 can be adjusted, for example, by varying the rotation speed of the rotating table 16 and repeatedly rotating the rotating table 16 a desired number of times.

[0102] While making the PTFE film 71 move by moving the rotating table 16, while running the high-frequency power supply 10, thus generating plasma between the electrode 14 and the rotating table 16 and irradiating plasma in the desired range on the surface of the PTFE film 71. At this time, as the high-frequency power supply 10, for example, after using the high-frequency power supply 10 of the frequency of applied voltage as mentioned above or the output power density, by using the copper electrode and the aluminum alloy sample holder covered with aluminum oxide, it is possible to realize the glow discharge under the dielectric barrier discharge condition. Therefore, it is possible to stably generate peroxide radicals on the surface of the PTFE film 71. The introduction of peroxide radicals causes the formation of dangling bonds by inducing the defluorination of the surface of the PTFE film 71 by free radicals, electrons, ions etc. contained in the plasma, and is carried out by reacting with water components in the air etc. by remaining in the air in the chamber or being exposed to clean air after the plasma treatment. In addition, in the dangling bonds, except for the peroxide radicals, hydrophilic functional groups such as hydroxyl and carbonyl can also be formed spontaneously.

[0103] The intensity of the plasma irradiated on the surface of the PTFE membrane 71 can be appropriately adjusted according to various parameters of the high-frequency power supply 10, the distance between the electrode 14 and the surface of the PTFE membrane 71, etc. It should be noted that the surface of the PTFE membrane 71 can also be set to a specific temperature range by adjusting the cumulative irradiation time on the surface of the PTFE membrane 71 according to the output power density. For example, when the frequency of the applied voltage is 5 to 30 MHz, the distance between the electrode 14 and the surface of the PTFE membrane 71 is 0.5 mm to 2.0 mm, and the output power density is 15 W / cm 2 ~30W / cm 2 When the plasma irradiation time is 50 to 3300 seconds, the cumulative irradiation time of the surface of the PTFE membrane 71 is preferably 250 to 3300 seconds, and further preferably 550 to 2400 seconds. It should be noted that the plasma irradiation time refers to the cumulative time of irradiating the surface of the PTFE membrane 71 with plasma. The surface temperature of the PTFE membrane 71 only needs to be above 180°C for at least a portion of the plasma irradiation time. The surface temperature of the PTFE membrane 71 is preferably above 180°C for more than 1 / 2 of the plasma irradiation time, and more preferably above 180°C for more than 2 / 3 of the plasma irradiation time. In either method, by setting the surface temperature of the PTFE membrane 71 within the above-mentioned range, the mobility of the PTFE molecules on the surface of the PTFE membrane 71 can be improved, and the probability of the carbon atoms in the carbon-fluorine bonds of the PTFE molecules cut by the plasma bonding with the carbon atoms of other PTFE molecules generated in the same manner to generate carbon-carbon bonds will be greatly increased, thereby improving the surface hardness.

[0104] In addition, a heating unit for heating the PTFE film 71 may be additionally provided. Figure 2B As shown, it is also possible to configure a thermal radiation irradiation device such as a halogen heater 17 in the vicinity of the electrode 14 in order to directly heat the surface of the PTFE membrane 71. In order to heat up the ambient temperature in the chamber 12, it is also possible to configure a circulator in the chamber 12, the circulator having: a heating device for heating the above-mentioned gas in the chamber 12, a stirring blade for circulating the heated gas in the chamber 12, etc. In order to heat the PTFE membrane 71 from the lower side, it is also possible to configure a heating unit on a turntable 16. Of course, it is also possible to combine them. It should be noted that, in order to become the desired temperature when plasma irradiation, it is preferred that before operating the high-frequency power supply 10, the PTFE membrane 71 is preheated in advance.

[0105] In addition, the surface temperature of the PTFE film 71 during plasma treatment can be expressed as follows: Figure 2B The surface temperature of the PTFE film 71 can also be measured using a temperature measuring tag.

[0106] based on Figure 2Aand Figure 2B An example of plasma treatment has been described above.

[0107] The surface of the plasma-treated PTFE film 71 may have hydrophilic functional groups. Examples of hydrophilic functional groups include peroxide radicals, hydroxyl groups, carbonyl groups, and carboxyl groups. Regarding the generation of peroxide radicals, the carbon atoms of the carbon-fluorine bond that can be cut by plasma irradiation react with oxygen that can be present in the surroundings during the plasma irradiation to generate peroxide radicals. It is also possible that the carbon atoms of the carbon-fluorine bond that can be cut by plasma irradiation come into contact with the atmosphere after the plasma treatment to generate peroxide radicals. Of course, it is also possible that the carbon atoms of the carbon-carbon bond that can be cut by plasma irradiation react with oxygen that can be present in the surroundings during the plasma irradiation to generate peroxide radicals. It is also possible that the carbon atoms of the carbon-carbon bond that can be cut by plasma irradiation come into contact with the atmosphere after the plasma treatment to generate peroxide radicals.

[0108] <2.2.2. Step A2_ Step of Plasma-treating the Surface of the PTFE Film 72> Since the description of step A2 overlaps with that of step A1, its description will be omitted. Therefore, the description of step A1 can be regarded as the description of step A2.

[0109] <2.2. Step B_ Step of Surface Modification of Polyimide Film 70> In step B, the surface of the polyimide film 70 is modified, i.e., surface activation treatment is performed. Step B may include the following steps: a step of modifying the surface 701 of the polyimide film 70 (hereinafter sometimes referred to as "step B1") and a step of modifying the surface 702 of the polyimide film 70 (hereinafter sometimes referred to as "step B2"). Steps B1 and B2 may be performed simultaneously or separately. When steps B1 and B2 are performed separately, they may be performed in parallel, or one step may be performed first.

[0110] To activate the surface, the polyimide film 70 can be surface treated by a dry method or a wet method. Examples of dry surface treatments include plasma treatment, surface irradiation with active energy rays such as ultraviolet rays, electron beams, or X-rays, corona treatment, flame treatment, and ITRO treatment. On the other hand, wet surface treatments include contacting the polymer film surface with an acid and / or alkaline solution. Corona treatment and plasma treatment are more preferred because they allow for hydrophilization with relatively low-load operations.

[0111] When plasma treatment is performed to modify the surface of the polyimide film 70, examples of such plasma treatments include vacuum plasma treatment (i.e., reduced pressure plasma treatment) and atmospheric pressure plasma treatment. Gases used to generate the plasma include, for example, noble gases such as helium, argon, and neon; and reactive gases such as oxygen, nitrogen, and hydrogen. Of these, oxygen is preferred for its ability to effectively hydrophilize the film. It should be noted that one or more of these gases may be used.

[0112] <2.3. Step C_Thermocompression Bonding Step> In step C, the PTFE film 71 and the PTFE film 72 are thermocompression bonded with the surface-modified surface thereof facing the polyimide film 70 and the surface-modified surface thereof facing the polyimide film 70. That is, they are overlapped and thermocompression bonded.

[0113] The heating temperature during thermocompression bonding can be, for example, 200°C to 400°C. The pressure can be, for example, 0.1 MPa to 20 MPa. The thermocompression bonding time can be, for example, 5 minutes to 40 minutes. The thermocompression bonding can also be performed using a heat press. It should be noted that, prior to thermocompression, the pressure is preferably evacuated to approximately 10 Pa to expel air present at the interface. In other words, thermocompression bonding is preferably performed under reduced pressure.

[0114] <3. Metal-clad laminates and printed wiring boards> like Figure 3 As shown, the metal-clad laminate 8 of this embodiment includes a resin film 7, a metal foil 81, and a metal foil 82. In the metal-clad laminate 8, the metal foil 81, the resin film 7, and the metal foil 82 are arranged in this order in the thickness direction of the metal-clad laminate 8. Specifically, the metal foil 81, the PTFE film 71, the polyimide film 70, the PTFE film 72, and the metal foil 82 are arranged in this order in the thickness direction of the metal-clad laminate 8.

[0115] The metal foil 81 is arranged on the PTFE membrane 71. As a method for arranging the metal foil 81 on the PTFE membrane 71, for example, the following method can be cited: after forming a monomer polymerization layer on the PTFE membrane 71, the metal foil 81 is directly or indirectly formed on the monomer polymerization layer (for example, refer to patent document 4, i.e., Japanese Patent Publication No. 2012-233038). It should be noted that the monomer polymerization layer can be a layer in which monomers are polymerized by plasma irradiation. The monomer contains a reactive unsaturated bonding group. As an example of a monomer, an acrylic acid monomer can be cited. As an acrylic acid monomer, acrylic acid or its derivatives, methacrylic acid or its derivatives are preferred. From the aspect of easy gasification, acrylic acid and methacrylic acid are preferred. On the other hand, as a method for arranging the metal foil 81 on the PTFE membrane 71, the following method can also be cited: after dissolving metallic sodium in liquid ammonia, the solution is brought into contact with the PTFE membrane 71, and the metal foil 81 is directly or indirectly formed on the surface modified with the solution. Another method is to dissolve sodium metal in an ether solvent containing naphthalene, bring the resulting solution into contact with the PTFE membrane 71, and directly or indirectly form the metal foil 81 on the surface modified by the solution. Another method is to bring a slurry containing micronized sodium metal dispersed in oil into contact with the PTFE membrane 71, and directly or indirectly form the metal foil 81 on the surface modified by the solution.

[0116] The metal foil 82 is placed on the PTFE membrane 72. The description of the method for placing the metal foil 82 on the PTFE membrane 72 overlaps with the description of the method for placing the metal foil 81 on the PTFE membrane 71, and thus will be omitted. Therefore, the description of the method for placing the metal foil 81 on the PTFE membrane 71 can be considered as the description of the method for placing the metal foil 82 on the PTFE membrane 72.

[0117] The thickness of the metal foil 81 may be, for example, 1 μm or more, 2 μm or more, or 3 μm or more. On the other hand, the thickness of the metal foil 81 may be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0118] Examples of the material of the metal foil 81 include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among them, copper and copper alloys are preferred, and copper is more preferred.

[0119] Since the description of the metal foil 82 overlaps with the description of the metal foil 81 , the description thereof will be omitted. Therefore, the description of the metal foil 81 can be regarded as the description of the metal foil 82 .

[0120] As described above, copper or a copper alloy is preferably used as the material of the metal foil 81 and the metal foil 82. In other words, the metal-clad laminate 8 is preferably a copper-clad laminate.

[0121] <4. Various modifications may be made to this embodiment> Various modifications may be made to the above-described embodiment. For example, one or more modifications may be selected from the following variations and added to the above-described embodiment.

[0122] In the above embodiment, the resin film 7 is described as including both the PTFE film 71 and the PTFE film 72 . However, the present embodiment is not limited to this configuration. The resin film 7 may not include the PTFE film 72 .

[0123] In the above embodiment, the configuration in which the surface of the polyimide film 70 is modified is described. However, the present embodiment is not limited to this configuration. In other words, the polyimide film 70 does not need to be surface-modified.

[0124] In the above embodiment, the resin film 7 is used for manufacturing a printed wiring board or a metal-clad laminate. However, this embodiment is not limited to this structure. That is, the resin film 7 can also be used for other purposes.

[0125] In the above embodiment, the structure in which the PTFE film 71, the polyimide film 70, and the PTFE film 72 are stacked in sequence and then heat-pressed is described. However, this embodiment is not limited to this structure. For example, after the PTFE film 71 and the polyimide film 70 are heat-pressed, the polyimide film 70 and the PTFE film 72 may be heat-pressed.

[0126] In the above-mentioned embodiment, the structure of directly laminating the polyimide film 70 and the PTFE film 71 and thermocompression bonding them has been described. However, this embodiment is not limited to this structure. For example, the surface of the PTFE film 71 through surface modification can also be coated with a polyamic acid solution for forming the polyimide film 70 and dried and heat-treated (imidized).

[0127] In the above-mentioned embodiment, the structure of directly laminating polyimide film 70 and PTFE film 72 and thermocompression bonding them has been described. However, this embodiment is not limited to this structure. For example, the surface of the PTFE film 72 through surface modification can also be coated with a polyamic acid solution for forming polyimide film 70 and dried and heat-treated (imidized).

[0128] In the above embodiment, the metal-clad laminate 8 includes both the metal foil 81 and the metal foil 82 . However, the present embodiment is not limited to this configuration. The metal-clad laminate 8 may not include the metal foil 82 . Example

[0129] The present invention will be described in more detail below with reference to Examples and Comparative Examples. Hereinafter, "parts" means "parts by mass" and "%" means "% by mass" unless otherwise specified.

[0130] <1. Polyimide Film> A 150 mm x 150 mm polyimide film was cut from Xenomax F38 (38 μm thick polyimide film) manufactured by Xenomax Japan Co., Ltd. The 150 mm x 150 mm polyimide film was placed in a plasma processor manufactured by Nihon Hakuden Electronics Co., Ltd., and after evacuating the system to a vacuum, oxygen was injected to induce discharge, resulting in vacuum plasma treatment. The vacuum plasma treatment conditions were a vacuum of 3 × 10 Pa, a gas flow rate of 1.5 SLM (Standard Liters per Minute), and a discharge power of 12 kW.

[0131] <2.PTFE membrane> <2.1. Cleaning> Cut a 450 mm x 700 mm PTFE membrane from Nittoflon No. 900UL (50 μm thick PTFE membrane) manufactured by Nitto Denko Corporation. Immerse the 450 mm x 700 mm PTFE membrane in acetone and ultrasonically clean it for 1 minute. Next, immerse the PTFE membrane in pure water and ultrasonically clean it for 1 minute. After removing the PTFE membrane from the pure water, blow nitrogen gas with a purity of 99% or greater with an air gun. This blows off the pure water adhering to the PTFE membrane.

[0132] <2.2. Thermally Assisted Plasma Treatment> Use as Figure 2A and Figure 2B The plasma generator shown (product name K2X02L023, manufactured by Meisho Machinery Co., Ltd.) modified the surface of the cleaned PTFE membrane using plasma. Specifically, the plasma treatment (hereinafter sometimes referred to as "thermally assisted plasma treatment") was performed according to the following apparatus and operating procedures. As a high-frequency power supply for the plasma generator, a power supply device with an applied voltage frequency of 13.56 MHz was used. As electrodes, a copper tube with an inner diameter of 1.8 mm, an outer diameter of 3 mm, and a length of 165 mm was covered with an alumina tube with an outer diameter of 5 mm, a thickness of 1 mm, and a length of 145 mm was used. As a turntable, a cylindrical turntable made of aluminum alloy with a diameter of 50 mm and a width of 3.4 cm was used. After a PTFE membrane was placed on the upper surface of the turntable, it was fixed with a sample holder, and the position of the electrode was adjusted so that the distance between the PTFE membrane surface and the electrode was 1.0 mm. After the chamber was sealed, the pressure was reduced to 10 Pa using a rotary pump, and then helium was injected until the pressure in the chamber reached atmospheric pressure (specifically 1013 hPa). 2 The high-frequency power supply was set to a constant frequency, and a rotating stage was positioned directly below the electrode to move the PTFE membrane 30 mm in its longitudinal direction at a rate of 2 mm / second. After the high-frequency power supply was activated, the plasma was irradiated for 600 seconds within an area 1.0 cm wide by 3.4 cm long, while the rotating stage was rotating. The plasma irradiation time was adjusted by the number of reciprocating movements of the rotating stage. Specifically, since each round trip took 30 seconds, the number of reciprocating movements of the rotating stage was set to 20. It should be noted that during the plasma treatment, the oxygen concentration near the surface of the PTFE membrane was measured using a zirconium oxide oxygen concentration meter LC-300 manufactured by Toray Engineering Co., Ltd. The oxygen concentration was 25.7 ppm. Therefore, the oxygen concentration was significantly lower than 0.5% by volume. During the plasma treatment, the surface temperature of the PTFE membrane was measured using a radiation thermometer (FT-H40K and FT-50A, manufactured by Keyence Corporation). The surface temperature of the PTFE membrane was 203°C.

[0133] <2.3. Comparative Plasma Treatment> The surface of the cleaned PTFE membrane was subjected to plasma treatment (hereinafter sometimes referred to as "comparative plasma treatment") according to the following apparatus and operating procedures. As normal temperature atmospheric pressure plasma treatment device, the FPE20 manufactured by Fuji Machine Co., Ltd. was used. Output power is 900W, and working gas is nitrogen 29.7L / minute, air 0.3L / minute. After the upper surface of rotating table carries PTFE film, fix it with sample holder, adjust it by the mode of 10mm with the distance of PTFE film surface and electrode. After making the mode of 8mm / second moving on the length direction of PTFE film directly below electrode set rotating table, by once (that is, so that PTFE film passes through 1 method directly below electrode) carry out plasma irradiation.

[0134] <3. PFA membrane> <3.1. Cleaning> Cut a 450 mm x 700 mm PFA membrane from a Fluon+ EA-2000 (25 μm thickness) manufactured by AGC Corporation. Immerse the 450 mm x 700 mm PFA membrane in acetone and ultrasonically clean it for 1 minute. Next, immerse the PFA membrane in pure water and ultrasonically clean it for 1 minute. After removing the PFA membrane from the pure water, blow nitrogen gas with a purity of 99% or higher with an air gun. This blows off any pure water adhering to the PFA membrane.

[0135] <3.2. Thermally Assisted Plasma Treatment> The thermally assisted plasma treatment was performed in the same manner as described above, except that a cleaned PFA membrane was used instead of the cleaned PTFE membrane.

[0136] <3.3. Comparative Plasma Treatment> A comparative plasma treatment was performed in the same manner as described above, except that a cleaned PFA membrane was used instead of the cleaned PTFE membrane.

[0137] <4. Preparation of two-layer film> <4.1. Preparation of the Two-Layer Film of Example 1> With the thermally assisted plasma-treated surface of the PTFE membrane facing the plasma-treated surface of the polyimide membrane, the two membranes were pressure-bonded at 320°C and 13 MPa in the atmosphere (i.e., without vacuum) for 10 minutes to obtain a two-layer membrane.

[0138] <4.2. Preparation of Two-Layer Film of Comparative Example 1> A two-layer membrane was prepared by the same method as in Example 1, except that a non-plasma-treated polyimide membrane was used instead of the plasma-treated polyimide membrane, and a non-plasma-treated PTFE membrane was used instead of the thermally assisted plasma-treated PTFE membrane.

[0139] <4.3. Preparation of Two-Layer Film of Comparative Example 2> A two-layer membrane was prepared by the same method as in Example 1, except that a PTFE membrane without plasma treatment was used instead of the PTFE membrane treated with thermally assisted plasma.

[0140] <4.4. Preparation of Two-Layer Film of Comparative Example 3> A two-layer membrane was prepared by the same method as in Example 1, except that the PTFE membrane treated with the comparative plasma was used instead of the PTFE membrane treated with the thermally assisted plasma.

[0141] <4.5. Preparation of Two-Layer Film of Comparative Example 4> With the thermally assisted plasma-treated surface of the PFA film facing the plasma-treated surface of the polyimide film, the two films were press-bonded at 340°C, 3 MPa, and atmospheric pressure (i.e., without vacuum) for 20 minutes to obtain a two-layer film.

[0142] <4.6. Preparation of Two-Layer Film of Comparative Example 5> A two-layer film was prepared by the same method as in Comparative Example 4, except that a PFA film without plasma treatment was used instead of the PFA film treated with thermally assisted plasma.

[0143] <4.7. Preparation of Two-Layer Film of Comparative Example 6> A two-layer film was prepared by the same method as in Comparative Example 4, except that the PFA film treated with the comparative plasma was used instead of the PFA film treated with the thermally assisted plasma.

[0144] <5. Determination of Peel Strength> A 90-degree peel test was performed using a two-layer film to determine the peel strength. Specifically, after the polyimide film of the two-layer film was fixed to two stainless steel rods with an adhesive, the clamping part of the fluororesin film (i.e., PTFE film, PFA film) of the two-layer film was clamped on the upper clamp, and the fluororesin film was pulled up in a vertical direction relative to the polyimide film. The load sensor was 1 kN and the tensile speed was 60 mm / min. The peel strength (unit: N / mm) was calculated by dividing the force required to peel the fluororesin film from the polyimide film, i.e., the peel force (unit: N) by the sample width (unit: mm). It should be noted that in the 90-degree peel test, a digital dynamometer (ZP-200N, manufactured by IMADA Manufacturing Co., Ltd.) and an electric motor frame (MX-500N, manufactured by IMADA Manufacturing Co., Ltd.) were used. The results of the peel strength measurement are shown in Table 1.

[0145] [Table 1] In this table, the term "PI film" refers to a polyimide film. For a PI film, "untreated" means that the film was not subjected to vacuum plasma treatment. On the other hand, for the PTFE membrane and the PFA membrane, “no treatment” means that neither the thermal-assisted plasma treatment nor the comparative plasma treatment was performed.

[0146] By subjecting the PTFE membrane to thermally assisted plasma treatment, the peel strength can be significantly improved compared to the case without treatment (i.e., neither thermally assisted plasma treatment nor comparative plasma treatment) and the case with comparative plasma treatment (see Example 1, Comparative Examples 2 and 3).

[0147] <6. Preparation of Three-Layer Film of Example 2> A cleaned polyimide film (specifically, Xenomax F38 manufactured by Xenomax Japan Co., Ltd., a polyimide film with a thickness of 38 μm) was subjected to vacuum plasma treatment on both sides under the above-mentioned conditions (see "1. Polyimide Film"). On the other hand, a cleaned PTFE film (specifically, NITOFLON No. 900UL manufactured by Nitto Denko Corporation, a PTFE film with a thickness of 50 μm) was subjected to thermally assisted plasma treatment under the above-mentioned conditions (see "2.2. Thermally Assisted Plasma Treatment"). The thermally assisted plasma-treated PTFE film, the vacuum plasma-treated polyimide film, and the thermally assisted plasma-treated PTFE film were overlapped and then pressed together at 320°C, 13 MPa, and in the atmosphere (i.e., without vacuuming) for 10 minutes. This resulted in a three-layer film.

[0148] <7. Preparation of Three-Layer Film of Example 3> A three-layer film was produced by the same method as in Example 2, except that Xenomax F12.5 (polyimide film with a thickness of 12.5 μm) manufactured by Xenomax Japan Co., Ltd. was used instead of Xenomax F38, and MSF-100 (PTFE film with a thickness of 25 μm) manufactured by Chuko Chemical Industry Co., Ltd. was used instead of NITOFLON No. 900UL.

[0149] <8. Preparation of Three-Layer Film of Comparative Example 7> Both surfaces of a cleaned Xenomax F15 (15 μm thick polyimide film, manufactured by Xenomax Japan Co., Ltd.) were vacuum plasma treated under the conditions described above (see "1. Polyimide Film"). A PFA film (Fluon+EA-2000, manufactured by AGC Corporation) and the vacuum plasma-treated polyimide film were then overlaid on the PFA film (Fluon+EA-2000, manufactured by AGC Corporation) and pressure-bonded at 340°C, 3 MPa, and atmospheric pressure for 20 minutes. This resulted in a three-layer film.

[0150] <9. Determination of Dielectric Constant and Dielectric Loss Tangent> The dielectric constant and dielectric loss tangent of the three-layer film were measured using the split cylindrical resonant cavity method. Specifically, the dielectric constant and dielectric loss tangent were measured at 28 GHz using a network analyzer (Keysight N5290A) and a split cylindrical resonant cavity (EM Labs CR model). It should be noted that the relative dielectric constant was calculated based on the dielectric constant.

[0151] <10. Determination of Linear Expansion Coefficient> The linear expansion coefficient of the three-layer film was measured using a thermomechanical analyzer. Specifically, a sample cut from the three-layer film was heated to 250°C at 20°C / minute and then cooled to room temperature at 5°C / minute. The average linear expansion coefficient was calculated from the temperature drop from 200°C to 50°C. Equipment: TMA4000S manufactured by Bruker AXS Length between sample clamps: 10mm Sample width: 2mm Atmosphere: Nitrogen

[0152] <11. Measurement Results> Table 2 shows the results of the measurements of the physical properties of the three-layer films of Examples 2 and 3 and Comparative Example 7. [Table 2] In addition, in this table, "the thickness ratio of a fluororesin film" means the total thickness of the fluororesin film when the thickness of the three-layer film is set to 100%. Industrial applicability

[0153] Since the present invention can provide a resin film, a metal-clad laminate, a printed wiring board, and a method for producing a resin film, it can be used industrially.

Claims

1. A resin film, characterized in that Include: a polyimide film and a first polytetrafluoroethylene film directly laminated on the polyimide film, The peel strength when the first polytetrafluoroethylene film is peeled off is 0.5 N / mm or more.

2. The resin film according to claim 1, wherein further comprising a second polytetrafluoroethylene film directly laminated on the polyimide film, The first polytetrafluoroethylene film, the polyimide film, and the second polytetrafluoroethylene film are arranged in this order in the thickness direction of the resin film. The peel strength when the second polytetrafluoroethylene film is peeled off is 0.5 N / mm or more. The resin film according to claim 2 , which has a relative dielectric constant of 3.0 or less at 28 GHz. The resin film according to claim 2 , wherein the dielectric loss tangent at 28 GHz is 0.004 or less. The resin film according to claim 2 , wherein The total thickness of the first polytetrafluoroethylene film and the second polytetrafluoroethylene film is 60% or more and 90% or less of 100% of the total thickness of the first polytetrafluoroethylene film, the polyimide film, and the second polytetrafluoroethylene film. The resin film according to claim 1 , wherein The polyimide film includes polyimide containing a polyimide benzoxazole component. The resin film according to claim 1 , which is used for producing at least one of a metal-clad laminate and a printed wiring board.

8. A metal-clad laminate, characterized in that: Include: The resin film according to any one of claims 1 to 7, and a metal foil provided on the first polytetrafluoroethylene film of the resin film. 9 . A printed wiring board produced using the resin film according to claim 1 .

10. A method for producing the resin film according to any one of claims 1 to 7, wherein: The method comprises the following steps: a step of plasma-treating the surface of the first polytetrafluoroethylene film at an oxygen concentration of less than 0.5% by volume; a step of thermocompression bonding the first polytetrafluoroethylene film treated with the plasma to the polyimide film in a state where the surface of the first polytetrafluoroethylene film treated with the plasma faces the polyimide film; In the step of performing the plasma treatment, the temperature of the surface of the first polytetrafluoroethylene film is 180° C. or higher.

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