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

Abstract

One purpose of the present invention is to provide a resin film and a metal-clad laminate, each of which enables the production of a printed wiring board that has excellent dimensional stability, while being reduced in transmission loss. Another purpose of the present invention is to provide a method for producing a resin film that enables the production of a printed wiring board that has excellent dimensional stability, while being reduced in transmission loss. The present invention relates to a resin film 7 which comprises a polyimide film 70 and a PTFE film 71 that is directly superposed on the polyimide film 70. With respect to the resin film 7, the peeling strength at the time when the PTFE film 71 is peeled is 0.5 N / mm or more.

Description

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

[0001] The present invention relates to a resin film, a metal-clad laminate, a printed wiring board, and a method for producing a resin film.

[0002] To enable the transmission of large amounts of information and high-speed communication, printed wiring boards are required to reduce transmission loss. Transmission loss consists of conductor loss and dielectric loss. Dielectric loss can be reduced by reducing the relative permittivity and dielectric loss tangent of the dielectric. On the other hand, dielectric loss increases as the signal frequency increases. As the use of high-frequency bands progresses, it is becoming increasingly important to reduce the relative permittivity and dielectric loss tangent of the resin films used in the production of printed wiring boards.

[0003] In order to reduce the relative dielectric constant and the dielectric loss tangent, polytetrafluoroethylene (PTFE) is sometimes used as one of the materials for printed wiring boards (see, for example, Patent Documents 1 and 2). PTFE exhibits the lowest dielectric constant and the lowest dielectric loss tangent among fluororesins. This is because PTFE has a -(CF ２ -CF ２ )- repeating structure.

[0004] On the other hand, polyimide is sometimes used as one of the materials for printed wiring boards (see, for example, Patent Document 3). This is because polyimide has excellent heat resistance, insulating properties, dimensional stability, etc. Polyimide is particularly suitable for use as one of the materials for insulating substrates of flexible printed wiring 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 a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (i.e., PFA) or a tetrafluoroethylene-hexafluoropropylene copolymer (i.e., FEP), is provided on both sides of a polyimide layer.

[0006] JP 2002-307611 A JP 2005-163006 A JP 5625906 A JP 2012-233038 A

[0007] The printed wiring board manufactured using the technology of Patent Document 3 includes a resin film including a first fluororesin layer, a polyimide layer, and a second fluororesin layer, and therefore has excellent dimensional stability and reduced transmission loss, but there is room for improvement, particularly in reducing transmission loss.

[0008] The present invention aims to provide a resin film or metal-clad laminate that can be used to produce a printed wiring board having excellent dimensional stability and reduced transmission loss. Another object of the present invention is to provide a method for producing a resin film that can be used to produce a printed wiring board having excellent dimensional stability and reduced transmission loss.

[0009] In order to solve this problem, the present invention has the following configuration [1]: [1] A resin film comprising: a polyimide film; and a first polytetrafluoroethylene film directly laminated on the polyimide film, wherein 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 contains a polyimide film, the resin film can have excellent dimensional stability.

[0011] Furthermore, since the resin film contains the first polytetrafluoroethylene film (i.e., the first PTFE film), the dielectric constant and dielectric loss tangent of the resin film can be reduced 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] Furthermore, since the first PTFE film is directly laminated on the polyimide film, the dielectric constant and dielectric loss tangent of the resin film can be further reduced. This will be explained. If PTFE and polyimide were bonded with an adhesive, the adhesive would likely increase the dielectric constant and dielectric loss tangent. In contrast, according to [1], the first PTFE film is directly laminated on the polyimide film, i.e., the first PTFE film is bonded to the polyimide film without an adhesive. Therefore, it is possible to avoid an increase in the dielectric constant and dielectric loss tangent that may be caused by the adhesive. Therefore, the 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, undesired peeling of the first PTFE film from the polyimide film, which may occur due to an impact to which the resin film may be subjected, or a change in temperature or humidity, can be suppressed.

[0014] Therefore, the resin film according to [1] makes it possible to manufacture a printed wiring board that is excellent in dimensional stability and has reduced transmission loss.

[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, wherein 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, and 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], having a relative dielectric constant at 28 GHz of 3.0 or less.

[0017] [4] The resin film according to [2] or [3], having a dielectric loss tangent at 28 GHz of 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 60% or more and 90% or less 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 contains a polyimide containing a polyimide benzoxazole component.

[0020] [7] The resin film according to any one of [1] to [6], which is used to produce 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], having a linear expansion coefficient of 30 ppm / °C or less from 50°C to 200°C.

[0022] The present invention also relates to the following configuration [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 configuration

[10] :

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

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

[11] :

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

[0025] According to

[11] , the surface of the first PTFE film is subjected to plasma treatment, which makes it possible to break the carbon-fluorine bonds of the PTFE molecules.

[0026] Furthermore, because the plasma treatment is performed at a surface temperature of 180°C or higher, it is possible to improve the mobility of PTFE molecules on the surface of the first PTFE film, and therefore PTFE molecules having carbon atoms with carbon-fluorine bonds broken by plasma irradiation can be effectively bonded to other PTFE molecules having similarly broken carbon atoms. This means that the formation of carbon-carbon bonds between PTFE molecules can be actively promoted. This means that the crosslinking reaction can be actively promoted. This improves the surface hardness of the first PTFE film (which could also be said to repair or remove the brittle layer on the surface of the first PTFE film). As a result, the adhesion of the first PTFE film to the polyimide film, i.e., the peel strength, can be improved.

[0027] Furthermore, because the plasma treatment is performed at an oxygen concentration of less than 0.5% by volume, it is possible to avoid inhibition of carbon-carbon bond formation by oxygen (hereinafter sometimes referred to as "oxygen inhibition"), and therefore the surface hardness of the first PTFE film can be further improved, thereby further improving the adhesion of the first PTFE film to the polyimide film, i.e., the peel strength.

[0028] According to the present invention, it is possible to provide a resin film or a metal-clad laminate that can be used to manufacture a printed wiring board having excellent dimensional stability and reduced transmission loss. According to the present invention, it is also possible to provide a method for manufacturing a resin film that can be used to manufacture a printed wiring board having excellent dimensional stability and reduced transmission loss.

[0029] Fig. 1 is a schematic cross-sectional view of a resin film in this embodiment. Fig. 2 is a conceptual diagram of an atmospheric pressure plasma treatment apparatus that can be used in this embodiment. Fig. 3 is a conceptual diagram showing a partially enlarged view of the periphery of an electrode that constitutes the atmospheric pressure plasma treatment apparatus that can be used in this embodiment. Fig. 4 is a schematic cross-sectional view of a metal-clad laminate in this embodiment.

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

[0031] 1, the resin film 7 of this embodiment includes a polyimide film 70, a polytetrafluoroethylene film (i.e., a PTFE film) 71, and a polytetrafluoroethylene film (i.e., a 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 laminated in this order. Because these are arranged in this order, the resin film 7 can have excellent low moisture absorption.

[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 have excellent dimensional stability.

[0033] It is preferable that both surfaces of the polyimide film 70, i.e., the surface 701 and the surface 702, are surface-modified. By modifying the surfaces, it is possible to increase the peel strength when the PTFE film 71 or the PTFE film 72 is peeled from the polyimide film 70, and therefore it is possible to further suppress undesired peeling of the PTFE film 71 or the PTFE film 72.

[0034] The thickness of the polyimide film 70 is preferably 1 μm or more, more preferably 5 μm or more, and 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 device and conditions: Device name: Rheogel-E4000 manufactured by UBM Corporation Jig: Stretching jig Sample length: 14 mm Sample width: 5 mm Frequency: 10 Hz Heat-up starting temperature: 0° C. Heat-up rate: 5° C. / min Atmosphere: Nitrogen

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

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

[0038] With regard to polyimides, the following examples can be given as preferred combinations of aromatic tetracarboxylic acids and aromatic diamines: A. A combination of an aromatic tetracarboxylic acid having a pyromellitic acid residue and an aromatic diamine having a benzoxazole structure; B. A combination of an aromatic diamine having a phenylenediamine skeleton and an aromatic tetracarboxylic acid having a biphenyltetracarboxylic acid skeleton; C. A combination of an aromatic diamine having a diphenyl ether skeleton and an aromatic tetracarboxylic acid having a pyromellitic acid residue. Of these, combination A is preferred.

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

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053] Among these, from the viewpoint of ease of synthesis, each isomer of amino(aminophenyl)benzoxazole is preferred, and 5-amino-2-(p-aminophenyl)benzoxazole is more preferred. Here, "each isomer" refers to each isomer determined depending on the coordination positions of the two amino groups in amino(aminophenyl)benzoxazole (e.g., each compound described in "Chemical Formula 1" to "Chemical Formula 4" above). These diamines may be used alone or in combination of two or more.

[0054] Furthermore, one or more of the diamines exemplified below may be used in combination. 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, ...-1,1,1,3,3,3-hexafluoropropane, m-phenylenedi diamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl 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, 1,1-bis[4-(4-aminophenoxy)phenyl]ethane )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]-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]ane ter, 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,4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 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-cyanophenoxy)-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-phenoxybenzof phenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3'-diamino-4,4'-diviphenoxybenzophenone, 4,4'-diamino-5,5'-diviphenoxybenzophenone, 3,4'-diamino-4,5'-diviphenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 4,4'-diamino-5-biphenoxybenzophenone, 3,4'-diamino-4-biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 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-biphenoxybenzoyl)benzene, 1,4-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,3-bis(4-amino-5-biphenoxybenzoyl)benzene, 1,Examples include 4-bis(4-amino-5-biphenoxybenzoyl)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 have been substituted with halogen atoms, alkyl or alkoxy groups having 1 to 3 carbon atoms, cyano groups, or halogenated alkyl or alkoxy groups having 1 to 3 carbon atoms in which some or all of the hydrogen atoms of the alkyl or alkoxy groups have been substituted with halogen atoms. These diamines preferably account for 30 mol % or less, more preferably 20 mol % or less, of the total diamines.

[0055] Examples of aromatic tetracarboxylic acid anhydrides 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]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] The aromatic tetracarboxylic acid anhydrides may be used alone or in combination of two or more kinds.

[0063] Furthermore, one or more of the non-aromatic tetracarboxylic dianhydrides exemplified below may be used in combination. Examples of such tetracarboxylic acid anhydrides include butane-1,2,3,4-tetracarboxylic acid dianhydride, pentane-1,2,4,5-tetracarboxylic acid dianhydride, cyclobutane tetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydride, cyclohexane-1,2,4,5-tetracarboxylic acid dianhydride, cyclohex-1-ene-2,3,5,6-tetracarboxylic acid dianhydride, 3-ethylcyclohex-1-ene-3-(1,2),5,6-tetracarboxylic acid dianhydride, 1-methyl-3-ethylcyclohexane-3-(1,2),5,6-tetracarboxylic acid dianhydride, 1-methyl-3-ethylcyclohex-1-ene-3-(1,2),5,6-tetracarboxylic acid dianhydride, 1-ethylcyclohexane-1-(1,2),3,4-tetracarboxylic acid dianhydride, 1-propylcyclohexane-1-( 2,3),3,4-tetracarboxylic acid dianhydride, 1,3-dipropylcyclohexane-1-(2,3),3-(2,3)-tetracarboxylic acid dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic acid dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid dianhydride, 1-propylcyclohexane-1-(2,3),3,4-tetracarboxylic acid dianhydride, 1,3-dipropylcyclo Examples include hexane-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, etc. The content of these tetracarboxylic dianhydrides, i.e., non-aromatic tetracarboxylic dianhydrides, is preferably 30 mol % or less, and 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 dissolves both the raw material monomer and the resulting polyamic acid. However, polar organic solvents are preferred, such as N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoric amide, ethyl cellosolve acetate, diethylene glycol dimethyl ether, sulfolane, and halogenated phenols. These solvents can be used alone or in combination. The amount of solvent used should be sufficient to dissolve the raw material monomer. Specific examples of the amount used include an amount in which the weight of the monomer in the solution containing the dissolved monomer is typically 5 to 40% by weight, and preferably 10 to 30% by weight.

[0065] The polymerization reaction conditions for obtaining polyamic acid (hereinafter simply referred to as "polymerization reaction") may be conventionally known conditions. Specific examples include continuous stirring and / or mixing in an organic solvent at a temperature range of 0 to 80°C for 10 minutes to 30 hours. The polymerization reaction may be divided into sections or the temperature may be adjusted as needed. In this case, the order of addition of the two monomers is not particularly limited, but it is preferable to add the aromatic tetracarboxylic acid anhydride to the aromatic diamine solution. The viscosity of the polyamic acid solution obtained by the polymerization reaction, measured at 25°C using a Brookfield viscometer, is preferably 10 to 2,000 Pa·s, more preferably 100 to 1,000 Pa·s, from the viewpoint of liquid delivery stability.

[0066] Vacuum degassing during the polymerization reaction is effective in producing a high-quality polyamic acid solution. Furthermore, a small amount of an end-capping agent may be added to the aromatic diamines before the polymerization reaction to control the polymerization. Examples of end-capping agents include compounds having a carbon-carbon double bond, such as maleic anhydride. When maleic anhydride is used, the amount used is preferably 0.001 to 1.0 mole per mole of the aromatic diamines.

[0067] To form the polyimide film 70 from the polyamic acid solution obtained by the polymerization reaction, the polyamic acid solution may be applied to a support and dried to obtain a green film (self-supporting precursor film), which is then subjected to a heat treatment to cause the imidization reaction. The application of the polyamic acid solution to the support includes, but is not limited to, casting from a slit die or extrusion using an extruder, and any conventionally known solution application means may 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. Examples of suitable drying conditions include a temperature of 70 to 150°C and a drying time of 5 to 180 minutes. Conventional drying devices can be used to achieve these conditions, including hot air, hot nitrogen, far-infrared radiation, and high-frequency induction heating. Next, an imidization reaction is carried out to obtain a polyimide film 70 from the resulting green sheet. A specific method for this reaction can be any conventional imidization reaction. For example, a method using a polyamic acid solution that does not contain a ring-closing catalyst or a dehydrating agent, optionally stretching the solution, and then subjecting it to a heat treatment to promote the imidization reaction (the so-called thermal ring-closing method) can be used. In this case, the heating temperature can be 100 to 500°C. From the viewpoint of film physical properties, a more preferable two-stage heat treatment is a treatment at 150 to 250°C for 3 to 20 minutes, followed by a treatment at 350 to 500°C for 3 to 20 minutes.

[0069] Another example of an imidization reaction is the chemical ring-closure method, in which a polyamic acid solution is pre-mixed with a ring-closure catalyst and a dehydrating agent, and the imidization reaction is carried out by the action of the ring-closure catalyst and the dehydrating agent. In this method, the polyamic acid solution is applied to a support, and the imidization reaction is partially carried out to form a self-supporting film, after which the imidization is fully carried out by heating. In this case, the partial imidization reaction is preferably carried out by heat treatment at 100 to 200°C for 3 to 20 minutes, and the complete imidization reaction is preferably carried out by heat treatment at 200 to 400°C for 3 to 20 minutes.

[0070] 1.2 PTFE Film 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, it is possible to reduce the relative dielectric constant and dielectric loss tangent of the resin film 7. This is because PTFE exhibits 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] The PTFE film 71 is laminated directly on the polyimide film 70. Because the PTFE film 71 is laminated directly on the polyimide film 70, the dielectric constant and dielectric dissipation factor of the resin film 7 can be further reduced. This will be explained. If the PTFE film 71 and the polyimide film 70 were bonded together with an adhesive, the adhesive would likely increase the dielectric constant and dielectric dissipation factor. In contrast, according to this embodiment, the PTFE film 71 is laminated directly on the polyimide film 70, i.e., the PTFE film 71 is bonded to the polyimide film 70 without an adhesive. Therefore, it is possible to avoid an increase in the dielectric constant and dielectric dissipation factor that may be caused by an adhesive. Therefore, the dielectric constant and dielectric dissipation factor of the resin film 7 can be further reduced. Meanwhile, the PTFE film 72 is also laminated directly on the polyimide film 70. Because the PTFE film 72 is laminated directly on the polyimide film 70, the dielectric constant and dielectric dissipation factor of the resin film 7 can be further reduced.

[0072] Of both surfaces of the PTFE film 71, at least the surface facing the polyimide film 70 is preferably surface-modified. By surface-modifying this surface, it is possible to increase the peel strength when peeling the PTFE film 71 from the polyimide film 70, and therefore it is possible to further suppress undesired peeling of the PTFE film 71. Note that both surfaces of the PTFE film 71 may be surface-modified.

[0073] Of both surfaces of the PTFE film 72, it is preferable that at least the surface facing the polyimide film 70 is also surface-modified. By surface-modifying this surface, it is possible to increase the peel strength when peeling the PTFE film 72 from the polyimide film 70, and therefore it is possible to further suppress undesired peeling of the PTFE film 72. Note that both surfaces of the PTFE film 72 may be surface-modified.

[0074] The thickness of the PTFE film 71 and the PTFE film 72 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and even more preferably 20 μm or more. On the other hand, the thickness of the PTFE film 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 thicknesses of the PTFE film 71 and the PTFE film 72 can be independent of each other. Therefore, the thicknesses of the two films may be the same or different.

[0075] It may go without saying that the PTFE film 71 and the PTFE film 72 contain polytetrafluoroethylene, i.e., PTFE.

[0076] <1.3. Physical Properties, Uses, etc. of Resin Film> In the resin film 7, the peel strength when peeling the PTFE film 71 from the polyimide film 70 is 0.5 N / mm or more. A peel strength of 0.5 N / mm or more can suppress undesired peeling of the PTFE film 71. Therefore, peeling of the PTFE film 71 from the polyimide film 70, which may occur due to impacts to which the resin film 7 may be subjected, temperature changes, humidity changes, etc., can be suppressed. The peel strength is preferably 0.6 N / mm or more, more preferably 0.7 N / mm or more, even more preferably 0.8 N / mm or more, and even more preferably 0.9 N / mm or more. On the other hand, the peel strength may 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.

[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, even more preferably 0.7 N / mm or more, even more preferably 0.8 N / mm or more, and even more preferably 0.9 N / mm or more. A peel strength of 0.5 N / mm or more can suppress undesired peeling of the PTFE film 72. Therefore, peeling of the PTFE film 72 from the polyimide film 70, which may occur due to impacts to which the resin film 7 may be subjected, temperature changes, humidity changes, etc., can be suppressed. On the other hand, the peel strength may 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, even more preferably 2.6 or less, still more preferably 2.55 or less, and even more preferably 2.50 or less.

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

[0080] The linear expansion coefficient of resin film 7 from 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 resin film 7 is to the linear expansion coefficient of metal foil (copper foil as an example), the more likely it is that the metal foil will be prevented from peeling from resin film 7. On the other hand, the linear expansion coefficient of resin film 7 from 50°C to 200°C may be, for example, 5 ppm / °C or more.

[0081] The thickness of the resin film 7 is preferably 5 μm or more, more preferably 10 μm or more. The thickness of the resin film 7 may be 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, or 60 μm or more. 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. Being 60% or more allows the relative dielectric constant and dielectric loss tangent of the resin film 7 to be further reduced. On the other hand, from the viewpoint 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] Resin film 7 can be suitably used to manufacture printed wiring boards, metal-clad laminates, etc. This is because printed wiring boards with excellent dimensional stability and reduced transmission loss can be manufactured using resin film 7. An example of a printed wiring board is a flexible printed wiring board (for example, a single-sided flexible printed wiring board, a double-sided flexible printed wiring board, or a multilayer flexible printed wiring board).

[0084] 2. Manufacturing Method of Resin Film The manufacturing method of resin film 7 includes a step of modifying the surfaces of PTFE film 71 and PTFE film 72 (hereinafter sometimes referred to as "step A"), a step of modifying the surface of polyimide film 70 (hereinafter sometimes referred to as "step B"), and a step of thermocompression bonding the PTFE film 71 and PTFE film 72 together with the modified surface of the PTFE film 71 facing the polyimide film 70 and the modified surface of the PTFE film 72 facing the polyimide film 70 (hereinafter sometimes referred to as "step C"). Either step A or step B may be performed first, or they may be performed in parallel.

[0085] <2.1. Step A> In step A, the surfaces of the PTFE film 71 and the PTFE film 72 are modified. Step A includes a step of performing plasma treatment on the surface of the PTFE film 71 (hereinafter sometimes referred to as "step A1") and a step of performing plasma treatment on the surface of the PTFE film 72 (hereinafter sometimes referred to as "step A2"). Steps A1 and A2 may be performed separately, or may be performed together using a single plasma treatment device. When steps A1 and A2 are performed separately, they may be performed in parallel, or one may 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 film 71 is subjected to plasma treatment. This can cleave the carbon-fluorine bonds in the PTFE molecules. Examples of plasma treatment include vacuum plasma treatment (i.e., low-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 film 71. In this specification, "atmospheric pressure plasma treatment" refers to plasma treatment at 700 hPa to 1300 hPa.

[0087] It is preferable to use a dielectric barrier discharge for the plasma treatment, which allows a glow discharge to be generated stably under atmospheric pressure (i.e., under 700 hPa to 1300 hPa).

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

[0089] In step A1, the surface of the PTFE film 71 is subjected to plasma treatment at an oxygen concentration of less than 0.5% by volume. By performing the plasma treatment at an oxygen concentration of less than 0.5% by volume, it is possible to avoid inhibition of carbon-carbon bond formation by oxygen (i.e., oxygen inhibition), thereby improving the surface hardness of the PTFE film 71. This improves the adhesion of the PTFE film 71 to the polyimide film 70, i.e., the peel strength. The oxygen concentration may be, for example, 0.4% by volume or less, 0.3% by volume or less, 0.2% by volume or less, or 0.1% by volume or less.

[0090] In step A1, the surface temperature of the PTFE film 71 is 180°C or higher. Plasma treatment at 180°C or higher improves the mobility of PTFE molecules on the surface of the PTFE film 71, thereby effectively bonding PTFE molecules with carbon atoms of carbon-fluorine bonds broken by plasma irradiation to other PTFE molecules with similarly broken carbon atoms. This actively promotes the formation of carbon-carbon bonds between PTFE molecules. This actively promotes cross-linking reactions. This improves the surface hardness of the PTFE film 71 (which could be rephrased as repairing or removing the brittle layer on the surface of the PTFE film 71). As a result, the adhesion of the PTFE film 71 to the polyimide film 70, i.e., the peel strength, can be improved. The surface temperature of the PTFE film 71 may be 190°C or higher, 195°C or higher, 200°C or higher, or 205°C or higher. On the other hand, the surface temperature of the PTFE film 71 may be, for example, 320° C. or less, 280° C. or less, 260° C. or less, 240° C. or less, or 220° C. The surface temperature of the PTFE film 71 can be adjusted, for example, by the power input to a high-frequency power source (described later) or by heating with a halogen heater (described later).

[0091] The time during which the surface temperature of the PTFE film 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 may be 400 seconds or longer or 500 seconds or longer. On the other hand, the time during which the surface temperature of the PTFE film 71 is 180°C or higher may be 6000 seconds or shorter, 3000 seconds or shorter, 2000 seconds or shorter, or 1000 seconds or shorter.

[0092] To generate plasma, for example, a high frequency power supply with an applied voltage 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 generally stated, but if forced, it is 15 W / cm ２ More than 40W / cm ２ The following is preferred:

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

[0094] The opposing electrodes can be cylindrical or flat metals with at least one side coated with a dielectric. The distance between the opposing electrodes cannot be generally determined, but from the viewpoint 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 may be, for example, 0.2 mm or more, 0.4 mm or more, or 0.5 mm or more.

[0095] Gases that can be used to generate plasma include, for example, rare gases such as helium, argon, and neon, and reactive gases such as oxygen, nitrogen, and hydrogen. It is preferable to use only non-polymerizable gases. Among these gases, only one or more rare gases may be used. A mixed gas of one or more rare gases and an appropriate amount of one or more reactive gases may also be used. When using a dielectric barrier discharge, helium is preferred because it is easy to obtain a glow discharge and has a low discharge inception voltage. When using a dielectric barrier discharge, argon and nitrogen are preferred because they are easy to obtain a glow discharge and are inexpensive.

[0096] Regarding the generation of plasma, plasma may be generated under conditions in which the gas atmosphere is controlled using a chamber, or plasma may be generated under conditions in which the plasma is completely open to the atmosphere by flowing a rare gas through the electrode portion.

[0097] An example of the plasma treatment according to step A1 will be described below with reference to FIGS. 2A and 2B.

[0098] The surface modification method for a PTFE film 71 using the atmospheric pressure plasma processing device A shown in FIG. 2A is as follows. First, the PTFE film 71 is washed, if necessary, with an organic solvent such as acetone or water such as ultrapure water. Next, as shown in FIG. 2B, the PTFE film 71 is placed on the sample holder of the rotary stage 16 in the chamber 12. Then, as shown in FIG. 2B, the air in the chamber 12 is sucked out from the vacuum exhaust system 13 using a suction device (not shown) to reduce the pressure, and a plasma-generating gas is supplied into the chamber 12 (see the arrow in FIG. 2A). This brings the pressure inside the chamber 12 to atmospheric pressure. Note that the PTFE film 71 is not shown in FIG. 2A, but is shown only in FIG. 2B. Note that atmospheric pressure does not necessarily have to be strictly 1013 hPa; it can be in the range of 700 to 1300 hPa.

[0099] With the apparatus shown in FIG. 2A, plasma treatment can be performed with the oxygen concentration in the vicinity of the surface of the PTFE film 71 (plasma irradiated region) set to less than 0.5% by volume.

[0100] Next, the height of the electrode lifting mechanism 15 (vertical direction in FIG. 2A ) is adjusted to move the electrode 14 to the desired position. Adjusting the height of the electrode lifting mechanism 15 allows adjustment of the distance between the electrode 14 and the surface (top surface) of the PTFE film 71. The distance between the electrode 14 and the surface of the PTFE film 71 is preferably 5 mm or less, and more preferably 2 mm or less. In particular, when the surface temperature of the PTFE film 71 is to be set within a specific range by natural temperature rise due to plasma treatment, a distance of 1.0 mm or less is particularly preferred. Since the PTFE film 71 is moved by rotation of the rotary stage 16, it goes without saying that the electrode 14 must not come into contact with the PTFE film 71.

[0101] By rotating the rotary stage 16, the plasma can be irradiated onto desired portions of the surface of the PTFE film 71. The rotation speed of the rotary stage 16 is preferably 1 mm / sec to 3 mm / sec, but may be outside this range. The plasma irradiation time for the PTFE film 71 can be adjusted, for example, by varying the rotation speed of the rotary stage 16 or by repeatedly rotating the rotary stage 16 a desired number of times.

[0102] While moving the rotary stage 16 to move the PTFE film 71, the high-frequency power supply 10 is operated to generate plasma between the electrode 14 and the rotary stage 16, and the desired area on the surface of the PTFE film 71 is irradiated with the plasma. At this time, by using a high-frequency power supply 10 with the applied voltage frequency and output power density described above, for example, and using an alumina-coated copper electrode and an aluminum alloy sample holder, glow discharge under dielectric barrier discharge conditions can be achieved. Therefore, peroxide radicals can be stably generated on the surface of the PTFE film 71. The peroxide radicals are introduced by radicals, electrons, ions, and the like contained in the plasma, which induce the formation of dangling bonds by defluorination of the surface of the PTFE film 71. These bonds then react with water components present in the air remaining in the chamber or by exposure to clean air after plasma treatment. In addition to peroxide radicals, hydrophilic functional groups such as hydroxyl groups and carbonyl groups can also be spontaneously formed on the dangling bonds.

[0103] The intensity of the plasma irradiated onto the surface of the PTFE film 71 can be adjusted as appropriate by adjusting various parameters of the high-frequency power supply 10, the distance between the electrode 14 and the surface of the PTFE film 71, etc. Note that the surface of the PTFE film 71 may be set to a specific temperature range by adjusting the cumulative irradiation time onto the surface of the PTFE film 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 film 71 is 0.5 mm to 2.0 mm, and the output power density is 15 W / cm ２ ~30 W / cm ２In this case, the cumulative irradiation time for the surface of the PTFE film 71 is preferably 50 to 3,300 seconds, more preferably 250 to 3,300 seconds, and even more preferably 550 to 2,400 seconds. The plasma irradiation time refers to the cumulative time during which the surface of the PTFE film 71 is irradiated with plasma. The surface temperature of the PTFE film 71 may be 180°C or higher for at least half of the plasma irradiation time, and more preferably 180°C or higher for at least two-thirds of the plasma irradiation time. In either embodiment, by keeping the surface temperature of the PTFE film 71 within the above range, the mobility of the PTFE molecules on the surface of the PTFE film 71 is improved, significantly increasing the probability that carbon atoms in the carbon-fluorine bonds of PTFE molecules cleaved by the plasma will bond with carbon atoms in other PTFE molecules similarly formed to form carbon-carbon bonds, thereby improving surface hardness.

[0104] Alternatively, a heating means for heating the PTFE film 71 may be provided separately. As shown in FIG. 2B , a heat ray irradiation device such as a halogen heater 17 may be disposed near the electrode 14 to directly heat the surface of the PTFE film 71. To raise the environmental temperature within the chamber 12, a heating device for heating the gas within the chamber 12 and a circulation device equipped with a stirring blade or the like for circulating the heated gas within the chamber 12 may be disposed within the chamber 12. A heating means may be disposed on the rotating stage 16 to heat the PTFE film 71 from the underside. Of course, these may be combined. It is preferable to preheat the PTFE film 71 before operating the high-frequency power supply 10 so that the desired temperature is reached during plasma irradiation.

[0105] The surface temperature of the PTFE film 71 during the plasma treatment can be measured by a radiation thermometer 21 as shown in Fig. 2B. The surface temperature of the PTFE film 71 may also be measured by a temperature measurement sticker.

[0106] The description of an example of plasma processing based on FIGS. 2A and 2B is as 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 atom of the carbon-fluorine bond cleaved by plasma irradiation may react with oxygen that may be present in the surroundings during plasma irradiation, thereby generating peroxide radicals. The carbon atom of the carbon-fluorine bond cleaved by plasma irradiation may be exposed to the air after plasma treatment, thereby generating peroxide radicals. Of course, the carbon atom of the carbon-carbon bond cleaved by plasma irradiation may react with oxygen that may be present in the surroundings during plasma irradiation, thereby generating peroxide radicals. The carbon atom of the carbon-carbon bond cleaved by plasma irradiation may be exposed to the air after plasma treatment, thereby generating peroxide radicals.

[0108] <2.2.2. Process A2—Process of Plasma Treatment on the Surface of the PTFE Film 72> The description of process A2 overlaps with the description of process A1 and will therefore be omitted. Therefore, the description of process A1 can also be used as the description of process A2.

[0109] 2.2. Step B—Step of Modifying the Surface of the Polyimide Film 70 In step B, the surface of the polyimide film 70 is modified, i.e., a surface activation treatment is performed. Step B can include 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 together or separately. When steps B1 and B2 are performed separately, they may be performed in parallel, or one may be performed first.

[0110] For surface activation, the polyimide film 70 may be subjected to a dry surface treatment or a wet surface treatment. Examples of dry surface treatments include plasma treatment, treatments in which the surface is irradiated with active energy rays such as ultraviolet rays, electron beams, and X-rays, corona treatment, flame treatment, and Itro treatment. Examples of wet surface treatments include treatments in which the polymer film surface is brought into contact with an acid and / or alkaline solution. Of these, corona treatment and plasma treatment are more preferred because they can render the surface hydrophilic with relatively low-stress operations.

[0111] When plasma treatment is performed to modify the surface of the polyimide film 70, examples of the plasma treatment include vacuum plasma treatment (i.e., low-pressure plasma treatment) and atmospheric pressure plasma treatment. Gases used to generate plasma include, for example, rare gases such as helium, argon, and neon, and reactive gases such as oxygen, nitrogen, and hydrogen. Of these, oxygen is preferred because it effectively imparts hydrophilicity. One or more of these gases may be used.

[0112] <2.3. Step C—Step of Thermocompression Bonding> In step C, the PTFE film 71 and the PTFE film 72 are thermocompression bonded together with the surface-modified surface of the PTFE film 71 facing the polyimide film 70 and the surface-modified surface of the PTFE film 72 facing the polyimide film 70. In other words, these films are stacked and then thermocompression bonded.

[0113] The heating temperature during thermocompression bonding may be, for example, 200°C to 400°C. The pressure may be, for example, 0.1 MPa to 20 MPa. The thermocompression bonding time may be, for example, 5 minutes to 40 minutes. Thermocompression bonding may be performed using a hot press. It is preferable to evacuate the space to about 10 Pa before thermocompression to remove air present at the interface. In other words, thermocompression bonding is preferably performed under reduced pressure.

[0114] 3 , 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 provided on the PTFE film 71. For example, a method for providing the metal foil 81 on the PTFE film 71 includes forming a monomer-polymerized layer on the PTFE film 71 and then directly or indirectly forming the metal foil 81 on the monomer-polymerized layer (see, for example, Patent Document 4, i.e., JP 2012-233038 A). The monomer-polymerized layer can be a layer formed by polymerizing a monomer through plasma irradiation. The monomer contains a reactive unsaturated bond group. An example of the monomer is an acrylic monomer. Preferred acrylic monomers are acrylic acid or its derivatives, and methacrylic acid or its derivatives. Acrylic acid and methacrylic acid are preferred because they are easily gasified. Alternatively, a method for providing the metal foil 81 on the PTFE film 71 includes dissolving metallic sodium in liquid ammonia, contacting the PTFE film 71 with the solution, and directly or indirectly forming the metal foil 81 on the surface modified with the solution. Another example is a method in which metallic sodium is further dissolved in an ether solvent in which naphthalene has been dissolved, and the solution is then brought into contact with the PTFE film 71, thereby directly or indirectly forming metal foil 81 on the surface modified with the solution.Another example is a method in which a slurry in which finely divided metallic sodium is dispersed in oil is brought into contact with the PTFE film 71, thereby directly or indirectly forming metal foil 81 on the surface modified with the solution.

[0116] The metal foil 82 is provided on the PTFE film 72. The explanation of the method for providing the metal foil 82 on the PTFE film 72 will be omitted because it overlaps with the explanation of the method for providing the metal foil 81 on the PTFE film 71. Therefore, the explanation of the method for providing the metal foil 81 on the PTFE film 71 can also be used as an explanation of the method for providing the metal foil 82 on the PTFE film 72.

[0117] The thickness of 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 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 materials for 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 these, copper and copper alloys are preferred, and copper is more preferred.

[0119] The description of the metal foil 82 will be omitted because it overlaps with the description of the metal foil 81. Therefore, the description of the metal foil 81 can also be used as the description of the metal foil 82.

[0120] As described above, copper and copper alloys are preferable as the materials for the metal foils 81 and 82. In other words, the metal-clad laminate 8 is preferably a copper-clad laminate.

[0121] 4. Various Modifications Can Be Made to This Embodiment Various modifications can be made to the above-described embodiment. For example, one or more of the following modifications can be selected and made to the above-described embodiment.

[0122] In the above embodiment, the resin film 7 includes both the PTFE film 71 and the PTFE film 72. However, the present embodiment is not limited to this configuration. The resin film 7 does not have to include the PTFE film 72.

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

[0124] In the above-described embodiment, the resin film 7 is used to manufacture a printed wiring board or a metal-clad laminate. However, the present embodiment is not limited to this configuration. In other words, the resin film 7 may be used for other purposes.

[0125] In the above embodiment, the PTFE film 71, the polyimide film 70, and the PTFE film 72 are stacked in this order and then thermocompression-bonded together. However, this embodiment is not limited to this configuration. For example, the PTFE film 71 and the polyimide film 70 may be thermocompression-bonded together, and then the polyimide film 70 and the PTFE film 72 may be thermocompression-bonded together.

[0126] In the above embodiment, the polyimide film 70 and the PTFE film 71 are directly laminated together by thermocompression bonding. However, this embodiment is not limited to this configuration. For example, a polyamic acid solution for forming the polyimide film 70 may be applied to the surface-modified surface of the PTFE film 71, followed by drying and heat treatment (imidization).

[0127] In the above embodiment, the polyimide film 70 and the PTFE film 72 are directly laminated together by thermocompression bonding. However, this embodiment is not limited to this configuration. For example, a polyamic acid solution for forming the polyimide film 70 may be applied to the surface-modified surface of the PTFE film 72, followed by drying and heat treatment (imidization).

[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 does not have to include the metal foil 82.

[0129] The present invention will be described in more detail below with reference to examples and comparative examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0130] <1. Polyimide Film> A 150 mm x 150 mm polyimide film was cut out from Xenomax F38 (a 38 μm thick polyimide film) manufactured by Xenomax Japan Co., Ltd. The 150 mm x 150 mm polyimide film was placed in a plasma treatment machine manufactured by Nippo Denshi Co., Ltd., evacuated to a vacuum, and oxygen gas was introduced to generate a discharge, thereby performing a vacuum plasma treatment. The vacuum plasma treatment conditions were a degree of vacuum of 3 x 10 Pa, a gas flow rate of 1.5 SLM (Standard Liter per Minute), and a discharge power of 12 kW.

[0131] <2. PTFE Film> <2.1. Cleaning> A 450 mm x 700 mm PTFE film was cut out from Nitoflon No. 900UL (a 50 μm thick PTFE film) manufactured by Nitto Denko Corporation. The 450 mm x 700 mm PTFE film was immersed in acetone and ultrasonically cleaned for 1 minute. The PTFE film was then immersed in pure water and ultrasonically cleaned for 1 minute. Nitrogen gas with a purity of 99% or higher was sprayed onto the PTFE film removed from the pure water using an air gun. This removed the pure water from the PTFE film.

[0132] 2.2. Thermally Assisted Plasma Treatment The surface of a cleaned PTFE film was modified with plasma using a plasma generator (manufactured by Meisho Kiko Co., Ltd., product name K2X02L023) shown in FIGS. 2A and 2B. Specifically, plasma treatment (hereinafter sometimes referred to as "thermally assisted plasma treatment") was performed using the following equipment and procedure. A power supply with an applied voltage frequency of 13.56 MHz was used as the high-frequency power source for the plasma generator. The electrode used consisted of a copper tube with an inner diameter of 1.8 mm, an outer diameter of 3 mm, and a length of 165 mm, covered with an alumina tube with an outer diameter of 5 mm, a thickness of 1 mm, and a length of 145 mm. The rotating stage used was a cylindrical aluminum alloy rotating stage with a diameter of 50 mm and a width of 3.4 cm. A PTFE film was placed on the top of the rotating stage and fixed with a sample holder, and the electrode position was adjusted so that the distance between the PTFE film surface and the electrode was 1.0 mm. After sealing the chamber, the pressure was reduced to 10 Pa using a rotary pump, and then helium gas was introduced into the chamber until the pressure inside the chamber reached atmospheric pressure (specifically, 1013 hPa). Then, the output power density was adjusted to 19.1 W / cm ２ The high-frequency power supply was set to 1 / 3000 s, and the rotation stage was set so that the PTFE film moved 30 mm in the longitudinal direction of the PTFE film at 2 mm / s directly below the electrode. Then, the high-frequency power supply was activated, and plasma irradiation was performed for 600 seconds within a 1.0 cm wide x 3.4 cm long range while rotating the rotation stage. The plasma irradiation time was adjusted by the number of reciprocating movements of the rotation stage. Specifically, since each reciprocating movement took 30 seconds, the number of reciprocating movements of the rotation stage was set to 20. During the plasma treatment, the oxygen concentration near the surface of the PTFE film was measured using a zirconia 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 film was measured using a radiation thermometer (FT-H40K and FT-50A manufactured by Keyence Corporation). The surface temperature of the PTFE film was 203°C.

[0133] 2.3. Comparative Plasma Treatment The surface of the cleaned PTFE film was subjected to plasma treatment (hereinafter sometimes referred to as "comparative plasma treatment") using the following equipment and procedure. The room temperature atmospheric pressure plasma treatment device used was FPE20 manufactured by Fuji Machine Co., Ltd. The output was 900 W, and the gas used was N ２ The gas flow rate was 29.7 L / min, and air flow rate was 0.3 L / min. A PTFE film was placed on the top surface of the stage and fixed with a sample holder, and the distance between the PTFE film surface and the electrode was adjusted to 10 mm. The stage was set so that the PTFE film moved directly below the electrode at 8 mm / sec in the length direction of the PTFE film, and plasma irradiation was performed in a single pass (i.e., the PTFE film passed directly below the electrode once).

[0134] <3. PFA Film> <3.1. Cleaning> A 450 mm x 700 mm PFA film was cut out from Fluon+ EA-2000 (thickness 25 μm) manufactured by AGC Inc. The 450 mm x 700 mm PFA film was immersed in acetone and ultrasonically cleaned for 1 minute. Next, the PFA film was immersed in pure water and ultrasonically cleaned for 1 minute. Nitrogen gas with a purity of 99% or higher was sprayed onto the PFA film taken out of the pure water using an air gun. This removed the pure water from the PFA film.

[0135] 3.2. Thermally Assisted Plasma Treatment A thermally assisted plasma treatment was carried out in the same manner as described above, except that a cleaned PFA film was used instead of the cleaned PTFE film.

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

[0137] 4. Preparation of Bilayer Film 4.1. Preparation of Bilayer Film According to Example 1 The PTFE film and the polyimide film were pressure-bonded together at 320°C and 13 MPa in the atmosphere (i.e., without vacuuming) for 10 minutes, with the thermally assisted plasma-treated surface of the PTFE film facing the plasma-treated surface of the polyimide film. This gave a bilayer film.

[0138] 4.2. Preparation of bilayer film according to comparative example 1 A bilayer film was prepared in the same manner as in example 1, except that a non-plasma-treated polyimide film was used instead of the plasma-treated polyimide film, and a non-plasma-treated PTFE film was used instead of the thermally assisted plasma-treated PTFE film.

[0139] 4.3. Preparation of a Two-Layer Film According to Comparative Example 2 A two-layer film was prepared in the same manner as in Example 1, except that a non-plasma-treated PTFE film was used instead of the thermally assisted plasma-treated PTFE film.

[0140] <4.4. Preparation of bilayer film according to comparative example 3> A bilayer film was prepared in the same manner as in example 1, except that a comparative plasma-treated PTFE film was used instead of the thermally assisted plasma-treated PTFE film.

[0141] 4.5. Preparation of a bilayer film according to Comparative Example 4 With the thermally assisted plasma-treated surface of the PFA film facing the plasma-treated surface of the polyimide film, the PFA film and the polyimide film were pressure-bonded together at 340°C and 3 MPa in the atmosphere (i.e., without vacuuming) for 20 minutes to obtain a bilayer film.

[0142] 4.6. Preparation of bilayer film according to Comparative Example 5 A bilayer film was prepared in the same manner as in Comparative Example 4, except that a PFA film without plasma treatment was used instead of the thermally assisted plasma-treated PFA film.

[0143] <4.7. Preparation of bilayer film according to comparative example 6> A bilayer film was prepared in the same manner as in comparative example 4, except that a comparative plasma-treated PFA film was used instead of the thermally assisted plasma-treated PFA film.

[0144] 5. Peel Strength Measurement A 90-degree peel test was performed using a bilayer film to determine the peel strength. Specifically, the polyimide film of the bilayer film was fixed to two stainless steel rods with an adhesive, and the gripping edge of the fluororesin film (i.e., the PTFE film and PFA film) of the bilayer film was clamped in the upper chuck, and the fluororesin film was pulled up perpendicular to the polyimide film. The load cell was 1 kN, and the pulling rate was 60 mm / min. The force required to peel the fluororesin film from the polyimide film, i.e., the peel force (unit: N), was divided by the sample width (unit: mm) to calculate the peel strength (unit: N / mm). The 90-degree peel test was performed using a digital force gauge (ZP-200N, manufactured by Imada Seisakusho Co., Ltd.) and an electric stand (MX-500N, manufactured by Imada Seisakusho Co., Ltd.). The peel strength measurement results are shown in Table 1.

[0145] In this table, PI film refers to polyimide film. For PI film, "no treatment" means that no vacuum plasma treatment was performed. On the other hand, for PTFE film and PFA film, "no treatment" means that neither thermally assisted plasma treatment nor comparative plasma treatment was performed.

[0146] By subjecting the PTFE film to thermally assisted plasma treatment, the peel strength was significantly improved compared to the untreated PTFE film (i.e., neither thermally assisted nor comparative plasma treatment) or comparative plasma treatment (see Example 1 and Comparative Examples 2 and 3).

[0147] <6. Preparation of Three-Layer Film According to Example 2> Vacuum plasma treatment was performed on both sides of a cleaned polyimide film (specifically, Xenomax F38 manufactured by Xenomax Japan Co., Ltd., a 38 μm thick polyimide film) under the conditions described above (see "1. Polyimide Film"). Meanwhile, a cleaned PTFE film (specifically, Nitoflon No. 900UL manufactured by Nitto Denko Corporation, a 50 μm thick PTFE film) was subjected to thermally assisted plasma treatment under the conditions described above (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 stacked and then pressure-bonded at 320 ° C. and 13 MPa in the atmosphere (i.e., without vacuuming) for 10 minutes. A three-layer film was thus obtained.

[0148] 7. Preparation of Three-Layer Film According to Example 3 A three-layer film was prepared in the same manner as in Example 2, except that Xenomax F12.5 (a polyimide film having a thickness of 12.5 μm) manufactured by Xenomax Japan Co., Ltd. was used instead of Xenomax F38, and MSF-100 (a PTFE film having a thickness of 25 μm) manufactured by Chukoh Chemical Industry Co., Ltd. was used instead of Nitoflon No. 900UL.

[0149] 8. Preparation of Three-Layer Film According to Comparative Example 7 Both sides of a washed Xenomax F15 (15 μm thick polyimide film) manufactured by Xenomax Japan Co., Ltd. were subjected to vacuum plasma treatment under the conditions described above (see "1. Polyimide Film"). A PFA film (Fluon+ EA-2000 manufactured by AGC Inc.), the vacuum plasma-treated polyimide film, and a PFA film (Fluon+ EA-2000 manufactured by AGC Inc.) were stacked and then pressure-bonded at 340°C and 3 MPa for 20 minutes under atmospheric pressure. This yielded a three-layer film.

[0150] <9. Measurement of dielectric constant and dielectric loss tangent> The dielectric constant and dielectric loss tangent of the three-layer film were measured using a split cylinder resonator method. Specifically, the dielectric constant and dielectric loss tangent were measured at 28 GHz using a network analyzer (KEYSIGHT N5290A) and a split cylinder resonator (EM Lab CR type). The relative dielectric constant was calculated from the dielectric constant.

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

[0152] <11. Measurement Results> Table 2 shows the results of measuring the physical properties of the three-layer films according to Examples 2 and 3 and Comparative Example 7. In this table, the "thickness ratio of the fluororesin film" means the total thickness of the fluororesin film when the thickness of the three-layer film is taken as 100%.

[0153] INDUSTRIAL APPLICABILITY The present invention can provide a resin film, a metal-clad laminate, a printed wiring board, and a method for producing a resin film, and is therefore industrially applicable.

[0154] 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

[0155] 10... High frequency power supply, 11... Matching unit, 12... Chamber, 13... Vacuum exhaust system, 14... Electrode, 15... Electrode lifting mechanism, 16... Rotating stage, 17... Halogen heater, 18... Inner tube, 19... Outer tube, 21... Radiation thermometer

Claims

1. A resin film comprising a polyimide film and a first polytetrafluoroethylene film directly laminated to the polyimide film, wherein 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, further comprising a second polytetrafluoroethylene film laminated directly on the polyimide film, the first polytetrafluoroethylene film, the polyimide film and the second polytetrafluoroethylene film being arranged in this order in the thickness direction of the resin film, and the peel strength when the second polytetrafluoroethylene film is peeled off is 0.5 N / mm or more.

3. The resin film described in claim 2, having a relative dielectric constant of 3.0 or less at 28 GHz.

4. The resin film described in claim 2, having a dielectric tangent at 28 GHz of 0.004 or less.

5. The resin film described in 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 the total thickness of the first polytetrafluoroethylene film, the polyimide film, and the second polytetrafluoroethylene film, which is 100%.

6. The resin film according to claim 1, wherein the polyimide film comprises a polyimide containing a polyimide benzoxazole component.

7. The resin film according to claim 1, which is used to produce at least one of a metal-clad laminate and a printed wiring board.

8. A metal-clad laminate comprising: a 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 any one of claims 1 to 7.

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