Fluoropolymer films, copper-clad laminates, and circuit boards

Abstract

To obtain a fluororesin film which reduces defects during lamination and has good adhesion to copper foil, and a copper-clad laminate using the same. A film made of a fluorine-containing composition, After heat treatment at 180°C for 3 minutes, the surface condition of one or both sides is measured using a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) to find that the oxygen element ratio is 1.35 atomic % or more, and when the film is heat treated at 180°C for 10 minutes, cooled to room temperature, and then measured, the absolute value of the dimensional change rate in MD and TD before and after heat treatment is 2% or less. Fluoropolymer film.

Description

[Technical Field]

[0001] This disclosure relates to fluoropolymer films, copper-clad laminates, and circuit boards. [Background technology]

[0002] Epoxy resins and polyimide resins are widely used as insulating layers in circuit boards. In recent years, several configurations have been proposed for high-frequency circuit boards used in high-frequency range applications at the tens of gigahertz level, in which a fluororesin insulating layer is formed on copper foil from the viewpoint of dielectric properties and hygroscopicity (Patent Documents 1-3).

[0003] In such printed circuit boards, adhesion to copper foil is sometimes achieved by surface-treating a fluororesin film (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2016 / 021666 [Patent Document 2] International Publication No. 2019 / 203243 [Patent Document 3] International Publication No. 2020 / 145133 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The present disclosure aims to provide a fluororesin film and a copper-clad laminate using the same that reduce defects during lamination and exhibit good adhesion to copper foil. [Means for solving the problem]

[0006] This disclosure is, A film comprising a composition containing a fluororesin, After heat treatment at 180°C for 3 minutes, the oxygen element ratio measured on one or both sides of the surface using scanning X-ray photoelectron spectroscopy (XPS / ESCA) is 1.35 atomic% or higher. When the film was heat-treated at 180°C for 10 minutes and then cooled to 25°C, the absolute value of the dimensional change rate of MD and TD before and after heat treatment was 2% or less. It is a fluoropolymer film.

[0007] The above oxygen element ratio is preferably 1.5 atomic% or higher. The above-mentioned fluororesin film preferably contains tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) or tetrafluoroethylene-hexafluoropropylene (FEP).

[0008] The above fluororesin film is It is preferable that the difference between the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) on the surface state of one or both sides of the film and the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) after etching the film with an argon gas cluster ion beam at an incident angle of 45° in the depth direction for 15 minutes is 1.0 atomic% or more.

[0009] The above-mentioned fluororesin film is preferably characterized by an adhesive strength greater than 30 N / m when two films on the same surface are bonded together at 200°C, either on one side or both sides.

[0010] The above-mentioned fluororesin film preferably has a dielectric loss tangent of less than 0.0015 at 10 GHz. The above-mentioned fluororesin film preferably has a dielectric loss tangent of less than 0.0015 at 40 GHz. The above fluororesin film has an unstable end group number of carbon atoms in the main chain of the fluororesin. 6 It is preferable that the number per unit be less than 10.

[0011] The fluororesin film preferably has an adhesive strength of 0.8 N / mm or more when adhered to a copper foil with a surface roughness Rz of 1.5 μm or less. The fluororesin film is preferably used for a copper-clad laminate.

[0012] The present disclosure is also a copper-clad laminate having a copper foil and any of the above-described fluororesin films as essential layers. The copper-clad laminate further has layers other than the copper foil and the fluororesin film. The layers other than the copper foil and the fluororesin film are preferably at least one selected from the group consisting of polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, and polybutadiene. The copper foil preferably has a surface roughness Rz of 1.5 μm or less. The copper-clad laminate preferably has an adhesive strength between the copper foil and the fluororesin film of 0.8 N / mm or more.

[0013] The present disclosure is also a circuit board having the copper-clad laminate described in any of the above.

[0014] The present disclosure is also a method for manufacturing the copper-clad laminate described in any of the above, characterized in that the fluororesin film is preheated at a temperature not lower than the glass transition temperature and lower than the melting point of the film, and then laminated with a copper foil or / and a fluororesin film and a substrate other than the copper foil.

Effects of the Invention

[0015] The fluororesin film of the present disclosure has an effect of less occurrence of defects during lamination and also obtaining good adhesion to the copper foil.

Modes for Carrying Out the Invention

[0016] Hereinafter, the present disclosure will be described in detail. When manufacturing copper-clad laminates by laminating fluororesin film and copper foil using a roll-to-roll method, the challenges are to reduce defects in the lamination process and to achieve high adhesion between the fluororesin and copper foil. One of the causes of defects in the lamination process is that if there are wrinkles (crumpling) in the roll of film, these wrinkles will remain when the film is laminated. Such wrinkles (crumpling) are believed to be caused by changes in the shape of the film over time while it is in a roll.

[0017] Such changes in film shape over time are thought to be due to residual stress within the film. To suppress this, possible methods include annealing to relieve residual stress in the fluororesin film, and adjusting manufacturing conditions such as melt extrusion conditions (T-die lip opening, air gap, etc.) and film winding conditions during the film manufacturing process to minimize residual stress.

[0018] Furthermore, fluororesins are generally difficult to bond to copper foil. Therefore, it is preferable to surface-treat the fluororesin film to improve its lamination properties. Such surface treatments generally involve methods that increase the amount of oxygen atoms on the resin surface.

[0019] It has become clear that the effect of surface treatment of fluororesin films to improve adhesion tends to decrease with heating. This is presumed to be because oxygen atoms on the surface detach when heated, reducing the amount of oxygen atoms on the surface. In the lamination process, to improve productivity, the film is sometimes preheated to a temperature above the glass transition temperature but below the melting point before lamination. In such cases, for a fluororesin film that has undergone a thermal history to be bonded to copper foil, it has become clear that the oxygen atom ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) on the surface of the film that will be bonded to the copper foil after heat treatment at 180°C for 3 minutes must be 1.35 atomic% or higher.

[0020] From the above perspective, (1) When measured after heat treatment at 180°C for 10 minutes and then cooling to 25°C, the absolute value of the dimensional change rate of MD and TD before and after heat treatment is 2.0% or less. and (2) After heat treatment at 180°C for 3 minutes, the oxygen atom ratio of the surface to be bonded to the copper foil was measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) and was 1.35 atomic% or higher. By using a fluororesin film that simultaneously satisfies these two requirements, it is possible to obtain a fluororesin film that reduces defects during lamination and also exhibits excellent adhesion to copper foil.

[0021] To obtain a fluororesin film that satisfies both of the above performance requirements (1) and (2), the post-molding processing conditions of the fluororesin film are crucial. As mentioned above, annealing can be cited as one example of a method for reducing the shrinkage rate in order to achieve the objectives of this disclosure. Annealing of fluoropolymer films is generally a heat treatment. Therefore, if annealing is performed after surface treatment, the oxygen atom content decreases, leading to a reduction in adhesive strength. Furthermore, a reduction in adhesive strength also occurs due to the preheating process during lamination. Therefore, when performing annealing, it is necessary to select appropriate conditions for both surface treatment and annealing. In addition, to avoid such problems caused by annealing, methods such as reducing internal stress by adjusting the film manufacturing process may be employed. In this disclosure, by adjusting the above-mentioned conditions and creating a fluororesin film that satisfies (1) and (2) above, defects during lamination are reduced, and good adhesion is obtained at the same time.

[0022] Further details regarding this disclosure are provided below. This disclosure relates to a fluoropolymer film. The resin constituting the fluoropolymer film is not particularly limited and may be any polymer that partially contains fluorine atoms. There may be two or more types of polymers that partially contain fluorine atoms, and the polymer may also contain other resins other than fluoropolymers, rubber, additives, fillers, etc. Furthermore, the fluoropolymer may contain at least one functional group selected from carbonyl group-containing groups (for example, acid anhydride groups, groups having carbonyl groups between carbon atoms of hydrocarbon groups, carbonate groups, carboxyl groups, haloformyl groups, alkoxycarbonyl groups, etc.), hydroxyl groups, epoxy groups, amide groups, amino groups, and isocyanate groups.

[0023] The method for introducing the above functional group is not particularly limited, but for example, it can be introduced when manufacturing fluororesins. In this case, the functional group is derived from at least one selected from the group consisting of monomers, chain transfer agents, and polymerization initiators used in the manufacturing process. Examples of the above monomers include itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, and maleic anhydride. Examples of chain transfer agents include those derived from methanol, acetic acid, acetic anhydride, methyl acetate, ethylene glycol, propylene glycol, etc. Examples of polymerization initiators include ammonium persulfate, potassium persulfate, di-n-propyl peroxydicarbonate, diisopropyl peroxycarbonate, tert-butyl peroxyisopropyl carbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, and di-2-ethylhexyl peroxydicarbonate.

[0024] The fluororesin is more preferably a melt-mold fluororesin, and examples include tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), copolymer having chlorotrifluoroethylene (CTFE) units (CTFE copolymer), tetrafluoroethylene hexafluoropropylene copolymer (FEP), tetrafluoroethylene ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF), tetrafluoroethylene hexafluoropropylene vinylide fluoride copolymer (THV), and tetrafluoroethylene vinylidene fluoride copolymer. Among these melt-mold fluororesins, tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) and tetrafluoroethylene hexafluoropropylene copolymer (FEP) are preferred.

[0025] By using the above-mentioned melt-mold fluororesin, melt molding can be performed, thus reducing processing costs compared to using PTFE. Furthermore, it is possible to improve adhesion when bonding with copper foil.

[0026] The resin constituting the above-mentioned fluororesin film preferably has a glass transition temperature of 40°C or higher. A temperature of 40°C or higher is preferable because, for example, when storing a roll film at room temperature, deformation at ambient temperature is less likely to occur. A temperature of 60°C or higher is more preferable, and a temperature of 80°C or higher is even more preferable. The above upper limit is not particularly limited, but from the viewpoint of adhesion, a temperature of 200°C or lower is preferable, a temperature of 160°C is more preferable, and a temperature of 120°C or lower is even preferable.

[0027] The above PFA preferably has a melting point of 180 to 340°C, more preferably 230 to 330°C, and even more preferably 280 to 320°C. The above melting point corresponds to the temperature of the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10°C / min using a differential scanning calorimeter (DSC).

[0028] The above PFA is not particularly limited, but a copolymer in which the molar ratio of TFE units to PAVE units (TFE units / PAVE units) is 70 / 30 or more and less than 99.5 / 0.5 is preferred. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and an even more preferred molar ratio is 80 / 20 or more and 98.5 / 1.5 or less. If there are too few TFE units, the mechanical properties tend to decrease, and if there are too many, the melting point tends to become too high and the moldability tends to decrease. The above PFA may be a copolymer consisting only of TFE and PAVE, or it is also preferable that the monomer units derived from monomers copolymerizable with TFE and PAVE are 0.1 to 10 mol%, and the total of TFE units and PAVE units is 90 to 99.9 mol%. Examples of monomers copolymerizable with TFE and PAVE are HFP and CZ3Z4=CZ5(CF2). nExamples include vinyl monomers represented by Z6 (wherein Z3, Z4, and Z5 are the same or different, representing a hydrogen atom or a fluorine atom; Z6 represents a hydrogen atom, a fluorine atom, or a chlorine atom; and n represents an integer from 2 to 10), and alkyl perfluorovinyl ether derivatives represented by CF2=CF-OCH2-Rf7 (wherein Rf7 represents a perfluoroalkyl group having 1 to 5 carbon atoms). Other copolymerizable monomers include, for example, cyclic hydrocarbon monomers having an acid anhydride group. Examples of acid anhydride monomers include itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, and maleic anhydride. Acid anhydride monomers may be used individually or in combination of two or more.

[0029] The above PFA preferably has a melt flow rate (MFR) of 0.1 to 100 g / 10 min, more preferably 0.5 to 90 g / 10 min, and even more preferably 1.0 to 85 g / 10 min. In this specification, the MFR is a value obtained by measuring under conditions of 372°C and a load of 5.0 kg in accordance with ASTM D3307.

[0030] The above-mentioned FEP is not particularly limited, but copolymers in which the molar ratio of TFE units to HFP units (TFE units / HFP units) is 70 / 30 or more and less than 99 / 1 are preferred. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and an even more preferred molar ratio is 80 / 20 or more and 97 / 3 or less. If there are too few TFE units, the mechanical properties tend to decrease, and if there are too many, the melting point tends to become too high and the moldability tends to decrease. It is also preferable that the FEP is a copolymer in which monomer units derived from monomers copolymerizable with TFE and HFP are 0.1 to 10 mol%, and the total of TFE units and HFP units is 90 to 99.9 mol%. Examples of monomers copolymerizable with TFE and HFP include alkyl perfluorovinyl ether derivatives. Other copolymerizable monomers include, for example, cyclic hydrocarbon monomers having an acid anhydride group. Examples of acid anhydride monomers include itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, and maleic anhydride. Acid anhydride monomers may be used individually or in combination of two or more.

[0031] The above FEP preferably has a melting point of 150 to 320°C, more preferably 200 to 300°C, and even more preferably 240 to 280°C. The above melting point is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10°C / min using a differential scanning calorimeter (DSC). The above FEP preferably has an MFR of 0.01 to 100 g / 10 min, more preferably 0.1 to 80 g / 10 min, even more preferably 1 to 60 g / 10 min, and particularly preferably 1 to 50 g / 10 min.

[0032] The above-mentioned fluororesin is preferable to have fewer functional groups, and in particular, a lower number of unstable end groups. Such fluororesins can be produced by adjusting the conditions during manufacturing (polymerization reaction), or by reducing the number of unstable end groups by performing fluorine gas treatment, heat treatment, or supercritical gas extraction treatment on the polymerized fluororesin. Fluorine gas treatment is preferred because it offers excellent processing efficiency and some or all of the unstable end groups are converted to -CF3, which becomes a stable end group. Using a fluororesin with a reduced number of unstable end groups in this way is preferable because it lowers the electrostatic loss tangent and reduces the loss of electrical signals.

[0033] The number of unstable end groups mentioned above is not particularly limited, but for fluororesins with a main chain of 10 carbon atoms... 6 The value per unit is preferably 450 or less, more preferably 250 or less, even more preferably 100 or less, and most preferably 50 or less. Considering the effect of reducing dielectric loss tangent, it is preferably less than 10, and even more preferably 5 or less.

[0034] Examples of unstable end groups include functional groups such as -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), hydroxyl groups (-CH2OH, etc.), -CONH2, -COOR (R=CH3, etc.), -CF2H, and -OCOO-R (n-propyl carbonate, etc.).

[0035] The number of unstable end groups is measured specifically by the following method. First, the above-mentioned fluororesin is melted and compressed to produce a film with a thickness of 0.25 to 0.3 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain the infrared absorption spectrum of the above-mentioned fluororesin, and a difference spectrum is obtained from the base spectrum, which is completely fluorinated and does not contain any functional groups. From the absorption peak of a specific functional group that appears in this difference spectrum, the number of carbon atoms in the above-mentioned fluororesin is calculated according to the following formula (A): 1 × 10 6 Calculate the number of unstable terminals per unit. N = I × K / t (A) I: Absorbance K: Correction coefficient t: Film thickness (mm)

[0036] For reference, Table 1 shows the absorption frequency, molar extinction coefficient, and correction factor for the unstable end groups used in this specification. The molar extinction coefficient was determined from FT-IR measurement data of a small molecule model compound.

[0037] [Table 1]

[0038] The above fluorination treatment can be carried out by bringing an unfluorinated fluororesin into contact with a fluorine-containing compound.

[0039] The fluorine-containing compounds mentioned above are not particularly limited, but include fluorine radical sources that generate fluorine radicals under fluorination treatment conditions. Examples of fluorine radical sources include F2 gas, CoF3, AgF2, UF6, OF2, N2F2, CF3OF, and halogenated fluorides (e.g., IF5, ClF3).

[0040] The fluorine radical source, such as F2 gas, may be at 100% concentration, but for safety reasons, it is preferable to mix it with an inert gas and dilute it to 5-50% by mass, and more preferably to 15-30% by mass. Examples of the inert gas include nitrogen gas, helium gas, and argon gas, but nitrogen gas is preferred for economic reasons.

[0041] The conditions for the above fluorination treatment are not particularly limited, and the fluororesin may be brought into contact with a fluorine-containing compound in a molten state. However, it is usually carried out at a temperature below the melting point of the fluororesin, preferably 20 to 220°C, and more preferably 100 to 200°C. The above fluorination treatment is generally carried out for 1 to 30 hours, preferably 5 to 25 hours. The above fluorination treatment preferably involves bringing an unfluorinated fluororesin into contact with fluorine gas (F2 gas).

[0042] In this specification, the content of each monomer unit constituting the fluororesin can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0043] The fluororesin film of this disclosure may contain components other than fluororesin. The components that can be contained are not particularly limited, but include fillers such as silica particles and glass short fibers, and thermosetting resins and thermoplastic resins that do not contain fluorine.

[0044] The fluororesin-containing composition of this disclosure may also contain spherical silica particles. This results in good fluidity of the resin, and facilitates molding even when a large amount of silica is incorporated.

[0045] The spherical silica particles described above refer to particles whose shape is close to a perfect sphere. Specifically, a sphericity of 0.80 or higher is preferred, 0.85 or higher is more preferred, 0.90 or higher is even more preferred, and 0.95 or higher is most preferred. Sphericity is calculated by taking a picture with a scanning electron microscope (SEM) and using the observed area and perimeter of the particle as follows: (Sphericity) = {4π × (Area) ÷ (Perimeter)²}. The closer the value is to 1, the closer it is to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (Spectris Corporation: FPIA-3000) is adopted.

[0046] The spherical silica particles described above preferably have a D90 / D10 ratio of 2 or more (preferably 2.3 or more and 2.5 or more) and a D50 ratio of 10 μm or less when the volume is accumulated from the smallest particle size. Furthermore, it is preferable that the D90 / D50 ratio is 1.5 or more (more preferably 1.6 or more). It is also preferable that the D50 / D10 ratio is 1.5 or more (more preferably 1.6 or more). This allows smaller spherical silica particles to fill the gaps between larger spherical silica particles, resulting in excellent packing properties and high fluidity. In particular, it is preferable that the frequency of smaller particle sizes is higher in the particle size distribution compared to a Gaussian curve. The particle size can be measured using a laser diffraction scattering particle size distribution analyzer. It is also preferable that coarse particles with a predetermined particle size or larger are removed by filtering or the like.

[0047] The spherical silica particles described above preferably have a water absorption of 1.0% or less, and more preferably 0.5% or less. Water absorption is based on the mass of the silica particles when dry. Water absorption is measured by leaving a dry sample at 40°C and 80% RH for 1 hour, and then measuring the moisture generated by heating to 200°C using a Karl Fischer moisture analyzer.

[0048] Alternatively, the spherical silica particles can be obtained by heating the fluororesin composition at 600°C for 30 minutes in an atmospheric environment to burn off the fluororesin, extracting the spherical silica particles, and then measuring each of the above parameters using the method described above.

[0049] The silica powder of the present invention may be surface-treated. By pre-treating the surface, aggregation of silica particles can be suppressed, and the silica particles can be well dispersed in the resin composition.

[0050] The above surface treatment is not particularly limited, and any known treatment can be used. Specifically, examples include treatment with silane coupling agents such as epoxysilane, aminosilane, vinylsilane, acrylicsilane, hydrophobic alkylsilane, phenylsilane, and fluorinated alkylsilane having reactive functional groups, plasma treatment, and fluorination treatment.

[0051] Examples of the silane coupling agents mentioned above include epoxysilanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, aminosilanes such as aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane, vinylsilanes such as vinyltrimethoxysilane, and acrylicsilanes such as acryloxytrimethoxysilane.

[0052] The spherical silica used may be commercially available silica particles that satisfy the properties described above. Examples of commercially available silica particles include Denka Fused Silica FB Grade (manufactured by Denka Co., Ltd.), Denka Fused Silica SFP Grade (manufactured by Denka Co., Ltd.), Excelica (manufactured by Tokuyama Corporation), High Purity Synthetic Spherical Silica AdmaFine (manufactured by Admatex Co., Ltd.), Admanano (manufactured by Admatex Co., Ltd.), AdmaFuse (manufactured by Admatex Co., Ltd.), and the like.

[0053] The film of this disclosure has an oxygen atom ratio of 1.35 atomic% or more when the surface condition of one or both sides is measured by ESCA after heat treatment at 180°C for 3 minutes. More preferably, the oxygen atom ratio is 1.5 atomic% or more, even more preferably 1.8 atomic% or more, and most preferably 2.0 atomic% or more.

[0054] The film disclosed herein may be a fluorine film in which the difference between the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) on its surface and the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) after etching the film with an argon gas cluster ion beam at an incident angle of 45° in the depth direction for 15 minutes is 1.0 atomic% or more. By increasing only the oxygen element ratio on the surface that contributes to adhesion in this way, sufficient adhesive strength can be obtained without impairing dielectric properties.

[0055] The above heat treatment of 180°C for 3 minutes means that the film was placed on a metal tray and treated in an electric furnace under an air atmosphere.

[0056] The fluororesin film of this disclosure exhibits an absolute value of 2.0% or less in the dimensional change rate of MD and TD before and after heat treatment, when measured after cooling to 25°C following heat treatment at 180°C for 10 minutes. The above dimensional change rate is more preferably 1.8% or less, and most preferably 1.5% or less. In this disclosure, the dimensional change rate is 180 mm for a film sample cut to a 300 mm square. The film was marked with gauge points at intervals, heat-treated for 10 minutes in an electric furnace under an air atmosphere set to 180°C without applying any load, and then cooled to 25°C. The gauge spacing in the MD and TD directions of the film was measured, and the change in gauge spacing before and after heat treatment was used to calculate the result.

[0057] The resin film of this disclosure preferably has a dielectric loss tangent of less than 0.0015 at 10 GHz. This is preferable because it can keep the loss of electrical signals in the circuit low. The dielectric loss tangent is more preferably less than 0.0013, even more preferably less than 0.0010, and most preferably 0.00050 or less. Furthermore, assuming that signals are transmitted at higher frequencies and antennas are transmitted and received, the dielectric loss tangent at 40 GHz is preferably less than 0.0015, more preferably less than 0.0013, even more preferably less than 0.0010, and most preferably 0.00050 or less. In order to keep the dielectric loss tangent within the above range, it is preferable to use a resin with few unstable end groups, and more preferably to use a fluororesin that has undergone end fluorination treatment.

[0058] The above-mentioned fluororesin film preferably has an adhesive strength of 0.8 N / mm or more, more preferably 0.9 N / mm or more, and even more preferably 1.0 N / mm or more when bonded to copper foil with a surface roughness Rz of 1.5 μm or less using a vacuum heat press under the conditions of a temperature above the melting point and below the melting point + 30°C, a pressure of 1.5 to 3.0 MPa, and a time of 300 to 600 seconds. Here, adhesive strength refers to the adhesive strength measured under the conditions described in the examples for a laminate bonded under the above conditions.

[0059] Preferably, the above-mentioned fluororesin film has an adhesive strength greater than 30 N / m when two films on the same surface are bonded together at 200°C, either on one side or both sides. Having such an adhesive strength ensures that the fluororesin film maintains excellent adhesion when used in combination with various other substrates, even after heat treatment. It is more preferable that the adhesive strength is greater than 50 N / m, and even more preferable that it is greater than 100 N / m.

[0060] (Method for manufacturing fluororesin film) The following details an example of a method for manufacturing the fluoropolymer film described above. However, the fluoropolymer film described above is not limited to those manufactured by the following methods. The fluororesin film of this disclosure is not limited in terms of the molding method used to form the film, but examples include melt molding methods such as extrusion molding, and casting methods in which a solution or dispersion containing fluororesin is prepared and then applied and dried on a substrate. Furthermore, the film may be stretched by uniaxial stretching or biaxial stretching, or it may be an unstretched film.

[0061] By performing surface treatment and annealing on one or both sides of the fluororesin film obtained by this method under appropriate conditions, a fluororesin film that satisfies the requirements of (1) and (2) above can be obtained.

[0062] The specific method for the surface modification described above is not particularly limited and can be carried out by any known method. Surface modification of fluororesin films can be performed using conventional discharge treatments such as corona discharge, glow discharge, plasma discharge, and sputtering. For example, the surface free energy can be controlled by introducing oxygen, nitrogen, or hydrogen gas into the discharge atmosphere. Alternatively, the surface to be modified can be exposed to an atmosphere of an inert gas containing organic compounds, and a high-frequency voltage can be applied between electrodes to induce a discharge. This generates active species on the surface, and then the surface can be modified by introducing functional groups of organic compounds or by graft polymerization of polymerizable organic compounds. Examples of such inert gases include nitrogen, helium, and argon.

[0063] Examples of organic compounds in the inert gas containing the organic compound include polymerizable or nonpolymerizable organic compounds containing oxygen atoms, such as vinyl esters like vinyl acetate and vinyl formate; acrylic acid esters like glycidyl methacrylate; ethers like vinyl ethyl ether, vinyl methyl ether, and glycidyl methyl ether; carboxylic acids like acetic acid and formic acid; alcohols like methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones like acetone and methyl ethyl ketone; carboxylic acid esters like ethyl acetate and ethyl formate; and acrylic acids like acrylic acid and methacrylic acid. Of these, vinyl esters, acrylic acid esters, and ketones are preferred because the modified surface is less likely to deactivate, i.e., has a long lifespan, and is easy to handle in terms of safety, with vinyl acetate and glycidyl methacrylate being particularly preferred.

[0064] The concentration of the organic compound in the inert gas containing the organic compound varies depending on its type and the type of fluororesin to be surface modified, but is usually 0.1 to 3.0% by volume, preferably 0.1 to 1.0%, more preferably 0.15 to 1.0%, and even more preferably 0.30 to 1.0%. The discharge conditions should be appropriately selected depending on the desired degree of surface modification, the type of fluororesin, and the type and concentration of the organic compound. Typically, the discharge rate is 50 to 1500 W·min / m 2 Preferably 70 W·min / m 2 More than 1400W min / m 2The discharge treatment is performed within the following range. The treatment temperature can be any temperature within the range of 0°C to 100°C. It is preferable that the temperature be 80°C or lower due to concerns about film stretching and wrinkling. The degree of surface modification is such that, considering that the adhesive ability of the surface decreases due to heat during post-processing, the oxygen element abundance ratio observed by ESCA is 2.6% or higher, preferably 2.8% or higher, more preferably 3.0% or higher, and even more preferably 3.5% or higher. There is no particular upper limit, but considering the impact on productivity and other physical properties, it is preferable that it be 25.0% or lower. There is no particular limit on the nitrogen element abundance ratio, but it is preferable that it be 0.1% or higher. The thickness of one fluororesin film is preferably 2.5 to 1000 μm, more preferably 5 to 500 μm, and even more preferably 12.5 to 150 μm.

[0065] In the manufacturing of the fluororesin film according to this disclosure, it is preferable to perform an annealing treatment after the above surface treatment. Furthermore, heat treatment may be performed in the process of laminating the film with other materials such as copper foil. As a result of these heat treatments, the amount of oxygen on the surface of the fluororesin film decreases. Therefore, it is preferable to perform surface modification under conditions that ensure a sufficient amount of surface oxygen is obtained at the time when the fluororesin film and other materials such as copper foil are actually laminated together.

[0066] (Annealing treatment) Annealing can be carried out by heat treatment. This heat treatment can be performed, for example, by passing the material through a heating furnace in a roll-to-roll manner.

[0067] The annealing temperature is preferably above the glass transition temperature - 20°C and below the melting point, more preferably above the glass transition temperature and below the melting point - 20°C, and even more preferably above the glass transition temperature and below the melting point - 60°C. The annealing time is not particularly limited, but can be adjusted as appropriate, for example, between 0.5 and 60 minutes. Furthermore, if the film that has passed through the annealing furnace comes into contact with the rolls of the winding device while still hot, deformation (wavy) of the film is likely to occur due to thermal shrinkage caused by the temperature change. To prevent this, the film may be cooled by passing it through a cooling zone after the high-temperature annealing zone before being wound by the winding device. There are no particular limitations on the cooling method, but it can be cooled with cold air or a cooling roll, and it is preferable to keep the film temperature below the glass transition temperature.

[0068] When heating using the roll-to-roll method described above, the tension can be adjusted appropriately depending on the film thickness and set temperature, but it is preferable to keep it at 20 N / m or less. Heating under these conditions is preferable because it allows for sufficient relaxation of internal stress and prevents dimensional changes.

[0069] The above-mentioned surface treatment and annealing treatments are not limited to a specific order, nor are they limited to being performed only once; they may be performed two or more times. Since tension is applied during the surface treatment process, it is preferable to perform the surface treatment before the annealing treatment in order to control the thermal shrinkage rate. Furthermore, the film may be slit to a predetermined width and length before or after these treatments, and in that case, it is preferable to adjust the tension so that the film does not stretch.

[0070] The fluororesin film of this disclosure can be used as a sheet for printed circuit boards, laminated with other substrates. The fluororesin film of this disclosure preferably has a thickness of 2.5 to 1000 μm, more preferably 5 to 500 μm, and even more preferably 12.5 to 150 μm. The thickness can be selected considering the balance between the electrical properties of the laminate and the coefficient of thermal expansion.

[0071] This disclosure also relates to a laminate characterized by having copper foil adhered to one or both sides of the fluororesin film described above. As described above, the fluororesin-containing film of this disclosure has excellent adhesive properties. The copper foil preferably has an Rz of 1.5 μm or less. That is, the fluororesin composition of this disclosure also has excellent adhesion to copper foil with a high smoothness of Rz of 1.5 μm or less. Furthermore, the copper foil only needs to have an Rz of 1.5 μm or less on at least the surface that adheres to the fluororesin film described above, and the Rz value of the other surface is not particularly limited.

[0072] The thickness of the copper foil is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm, and even more preferably in the range of 9 to 35 μm.

[0073] The copper foils mentioned above are not particularly limited; for example, rolled copper foil, electrolytic copper foil, etc., are examples.

[0074] The copper foil with an Rz of 1.5 μm or less is not particularly limited, and commercially available foils can be used. Examples of commercially available copper foils with an Rz of 1.5 μm or less include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.).

[0075] The copper foil described above may be surface-treated to enhance its adhesive strength with the fluororesin film of this disclosure.

[0076] The above surface treatment is not particularly limited, but may include silane coupling treatment, plasma treatment, corona treatment, UV treatment, electron beam treatment, etc. The reactive functional group of the silane coupling agent is not particularly limited, but from the viewpoint of adhesion to the resin substrate, it is preferable that it has at least one selected from amino groups, (meth)acrylic groups, mercapto groups, and epoxy groups at its terminal end. The hydrolyzable group is not particularly limited, but may include alkoxy groups such as methoxy groups and ethoxy groups. The copper foil used in this disclosure may have a rust-preventive layer (such as an oxide film like chromate), a heat-resistant layer, etc. formed on it.

[0077] Surface-treated copper foil having a surface treatment layer of the above-mentioned silane compound on the surface of the copper foil can be manufactured by preparing a solution containing the silane compound and then surface-treating the copper foil with this solution.

[0078] The copper foil described above may have a roughened layer on its surface, for example, to improve adhesion to the resin substrate. Furthermore, if the roughening treatment is likely to degrade the performance required in this disclosure, the amount of roughening particles electrodeposited onto the copper foil surface may be reduced or the roughening treatment may be omitted as necessary.

[0079] Between the copper foil and the surface treatment layer, one or more layers selected from the group consisting of a heat-resistant treatment layer, a rust-preventive treatment layer, and a chromate treatment layer may be provided from the viewpoint of improving various properties. These layers may be a single layer or multiple layers.

[0080] The above laminate preferably has an adhesive strength of 0.8 N / mm or more between the copper foil and the fluororesin film. Such an adhesive strength can be achieved by applying the method described above. By increasing the adhesive strength to 0.9 N / mm or more, and further to 1.0 N / mm or more, it can be suitably used as a copper-clad laminate or circuit board. Note that the adhesive strength here refers to the adhesive strength measured under the conditions described in the examples. In the case of a laminate in which copper foil is bonded to the surface-treated surface of a fluororesin film that has been surface-treated on only one side, surface modification may be performed separately on the fluororesin film surface that has not been surface-treated in order to improve the adhesion between the laminate and other materials.

[0081] This disclosure also relates to a laminate characterized by having a copper foil layer, the aforementioned fluororesin film, and a substrate layer. The substrate layer is not particularly limited, but it is preferable to have a fabric layer made of glass fibers or a resin film layer.

[0082] The above-mentioned fabric layer made of glass fibers is a layer made of glass cloth, glass nonwoven fabric, etc. Commercially available glass cloth can be used, and it is preferable that it has been treated with a silane coupling agent to enhance its affinity with the fluororesin. Examples of glass cloth materials include E glass, C glass, A glass, S glass, D glass, NE glass, and low dielectric constant glass, but E glass, S glass, and NE glass are preferred due to their availability. The weave of the fibers can be plain weave or twill weave. The thickness of the glass cloth is usually 5 to 90 μm, preferably 10 to 75 μm, but it is preferable to use one that is thinner than the fluororesin film used.

[0083] The above laminate may use a glass nonwoven fabric as a fabric layer made of glass fibers. A glass nonwoven fabric is made by fixing short glass fibers with a small amount of binder compound (resin or inorganic substance), or by maintaining its shape by entangling the short glass fibers without using a binder compound, and commercially available products can be used. The diameter of the short glass fibers is preferably 0.5 to 30 μm, and the fiber length is preferably 5 to 30 mm. Specific examples of binder compounds include resins such as epoxy resin, acrylic resin, cellulose, polyvinyl alcohol, and fluororesin, as well as inorganic substances such as silica compounds. The amount of binder compound used is usually 3 to 15% by mass relative to the short glass fibers. Examples of materials for the short glass fibers include E glass, C glass, A glass, S glass, D glass, NE glass, and low dielectric constant glass. The thickness of the glass nonwoven fabric is usually 50 μm to 1000 μm, and is preferably 100 to 900 μm. Furthermore, the thickness of the glass nonwoven fabric in this application refers to the value measured using a digital gauge DG-925 (load 110 grams, face diameter 10 mm) manufactured by Ono Sokki Co., Ltd., in accordance with JIS P8118:1998. To improve the affinity with fluororesin, the glass nonwoven fabric may be treated with a silane coupling agent.

[0084] Since most glass nonwoven fabrics have a very high void ratio of 80% or more, it is preferable to use a sheet that is thicker than the sheet made of fluororesin and to compress it by pressure before use.

[0085] The above-mentioned fabric layer made of glass fibers may be a layer formed by laminating glass cloth and glass nonwoven fabric. This allows the properties of each material to be combined to obtain desirable properties. The above-mentioned glass fiber fabric layer may be in the form of a prepreg impregnated with resin.

[0086] The above laminate may have a glass fiber fabric layer and a fluororesin film bonded at the interface, or part or all of the fluororesin film may be impregnated into the glass fiber fabric layer. Furthermore, a prepreg may be prepared by impregnating a glass fiber fabric with a fluororesin composition. A fluororesin film of the present disclosure may be further laminated onto the prepreg obtained in this manner. In this case, the fluororesin composition used to prepare the prepreg is not particularly limited, and the fluororesin film of the present disclosure may also be used.

[0087] As the resin film used as the base material, heat-resistant resin films and thermosetting resin films are preferred. Examples of heat-resistant resin films include polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, and polystyrene. Examples of thermosetting resins include epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, and polybutadiene. The heat-resistant resin film and the thermosetting resin film may contain reinforcing fibers. The reinforcing fibers are not particularly limited, but glass cloth, especially of the low dielectric type, is preferred. The dielectric properties, coefficient of thermal expansion, and water absorption of the heat-resistant resin film and thermosetting resin film are not particularly limited, but for example, the dielectric constant at 20 GHz is preferably 3.8 or less, more preferably 3.4 or less, and even more preferably 3.0 or less. The dielectric loss tangent at 20 GHz is preferably 0.0030 or less, more preferably 0.0025 or less, and even more preferably 0.0020 or less. The coefficient of thermal expansion is preferably 100 ppm / °C or less, more preferably 70 ppm / °C or less, even more preferably 40 ppm / °C or less, and most preferably 20 ppm / °C or less. The water absorption is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

[0088] The fluororesin film of this disclosure can be used in a laminate having a copper foil layer, a substrate layer, and the fluororesin film described above.

[0089] There are no particular limitations on the method for compounding the copper foil, substrate layer, and fluororesin film, but two methods can be cited as examples. (i) A method of lamination using copper foil, a substrate layer, and a pre-formed fluororesin film, by applying pressure under heating using a roll-to-roll process or a press. (ii) A method of manufacturing a laminate by adhering a fluororesin film to one side of a copper foil, and then laminating this laminate with a substrate layer by applying pressure under heating. Furthermore, in the case of method (ii) above, the laminate consisting of copper foil, a base layer, and a fluororesin film may be surface-treated before being bonded to the other layers. Alternatively, the surface of the fluororesin film to be bonded to the base layer may be surface-treated.

[0090] In these methods, when a copper-clad laminate, which requires a fluororesin film and copper foil, is laminated with a base layer such as a glass fiber fabric layer or a resin film layer, the lamination can be achieved by bonding the fluororesin film layer side of the copper-clad laminate to the base layer. In this case, the fluororesin film layer side of the copper-clad laminate may be surface-treated before lamination to improve its adhesive performance. The surface treatment here is not particularly limited and can include the plasma treatment mentioned above.

[0091] In the above-described laminate, the layering order and manufacturing method of the copper foil layer, the substrate layer, and the aforementioned fluororesin film are not particularly limited, and the layer configuration can be adapted to the purpose. Specifically, the aforementioned layering order can be described as consisting of a base layer / fluororesin film / copper foil layer, a copper foil layer / fluororesin film / base layer / fluororesin film / copper foil layer, or a copper foil layer / base layer / fluororesin film / base layer / copper foil layer. Furthermore, it may also have other layers as needed.

[0092] Furthermore, the copper foil in the above-mentioned laminate can be the same as the copper foil detailed in the laminate with the fluororesin film described above.

[0093] In obtaining the laminate structure described above, the fluororesin film of this disclosure is used by adhering copper foil to one or both sides. As described above, the fluororesin film of this disclosure has excellent adhesive properties. Therefore, it also has excellent adhesion to copper foil with a smoothness of Rz 1.5 μm or less. The adhesive strength between the copper foil and the fluororesin film is preferably 0.8 N / mm or more, and by making the adhesive strength 0.9 N / mm or more, and even more preferably 1.0 N / mm or more, it can be suitably used as a copper-clad laminate or circuit board. Note that the adhesive strength here refers to the adhesive strength measured under the conditions described in the examples.

[0094] Copper foil used in circuit boards has conventionally been given a certain degree of surface irregularity to ensure adhesion to the insulating layer. However, in high-frequency applications, the presence of irregularities on the surface of the copper foil causes loss of electrical signals and is therefore undesirable. The above-described laminate can achieve suitable adhesion even to highly smooth copper foil, and is a laminate that can be suitably used as a circuit board.

[0095] The fluororesin film disclosed herein exhibits the advantages of producing fewer defects during lamination and achieving good adhesion to copper foil. Because it possesses adhesion to copper foil with a highly smooth Rz of 1.5 μm or less, it can also provide laminates that are suitable for use in copper-clad laminates, circuit boards, flat cables, coverlays, and the like.

[0096] In this disclosure, a high-frequency circuit includes not only circuits that transmit only high-frequency signals, but also circuits that have transmission lines for transmitting non-high-frequency signals on the same plane, such as transmission lines that convert high-frequency signals to low-frequency signals and output the generated low-frequency signals to the outside, and transmission lines that supply power for driving high-frequency compatible components. It can also be used as a circuit board for antennas, filters, etc. [Examples]

[0097] The present disclosure will be described in detail below based on examples. However, the present invention is not limited to the following examples.

[0098] (Polymer composition) The measurement was performed by 19F-NMR analysis.

[0099] (Melting point) The melting peak was calculated from measurements taken using a DSC device while increasing the temperature at a rate of 10°C / min.

[0100] (Glass transition temperature) The tanδ peak was calculated from measurements taken using a solid dynamic viscoelasticity apparatus (DMA) with a frequency of 10 Hz, a strain of 0.1%, and a heating rate of 5°C / min.

[0101] (Melt Flow Rate (MFR)) Measurements were taken in accordance with ASTM D3307 under conditions of 372°C and a load of 5.0 kg.

[0102] (Thickness of fluororesin film) The measurement was taken using a micrometer.

[0103] (Number of unstable terminal groups) The analysis was performed using an FT-IR Spectrometer 1760X (manufactured by Perkin-Elmer).

[0104] (ESCA analysis of the surface of fluoropolymer film) Measurements were performed using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) analyzer, PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.).

[0105] (Rate of dimensional change) Film samples cut to 300mm square were marked with gauge points at 180mm intervals in both the MD and TD directions. These were placed on a metal plate covered with PTFE-impregnated glass cloth and heat-treated in an electric furnace set to 180°C in an air atmosphere for 10 minutes without any load. After cooling to 25°C (allowing to stand in a 25°C room for at least 30 minutes), the gauge point intervals in both the MD and TD directions of the film were measured with calipers (measurable in mm to two decimal places), and the following formula was used to calculate the change in gauge point intervals before and after heat treatment. Thermal shrinkage rate = {(Length after heat treatment - Length before heat treatment) / Length before heat treatment} × 100 (%)

[0106] (Wrinkles after annealing) Visually check for wrinkles. ○...No deformation (wavy) of the film occurred. ×...Film deformation (wavy) occurred.

[0107] (Wrinkles in the roll film) The appearance of the material was visually inspected after it had been rolled up and stored at room temperature for one month. ○...No wrinkles appear or increase due to tightness during rolling. ×...Wrinkles may appear or increase due to tightness during rolling.

[0108] (Surface roughness of copper foil) The catalog values ​​for electrolytic copper foil CF-T9DA-SV-18 (thickness 18μm / Rz 0.85μm) (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were used.

[0109] (Adhesion strength between copper foil and fluororesin film) Using a fluororesin film without preheating or preheated to a temperature above the glass transition temperature but below the melting point, a laminate was fabricated by stacking copper foil / fluororesin film / copper foil in that order and using a vacuum heat press. An aluminum plate was attached to one side of the laminate with adhesive tape, and the peel strength of the copper foil was measured by gripping and pulling a 10 mm wide copper foil at a 90° angle to the plane of the laminate using a Tensilon universal tester (manufactured by Shimadzu Corporation) at a speed of 50 mm per minute. The obtained value was defined as the adhesive strength.

[0110] (Adhesive strength between fluororesin films) Samples prepared by overlapping the surface-treated surfaces of fluororesin films and performing heat pressing (200 °C, 0.1 MPa, 60 s) were cut into strips with a width of 10 mm. Using a tensilon universal testing machine (manufactured by Shimadzu Corporation), while gripping the non-bonded part of the strip-shaped sample with the upper and lower chucks of the tensilon, the peeling strength was measured by pulling at a speed of 100 mm per minute, and the obtained value was taken as the adhesive strength.

[0111] (Dielectric constant and dielectric loss tangent of fluororesin film) Using a fluororesin film, measurements were taken at 10 GHz, 20 GHz, and 40 GHz (26 °C) using split cylinder resonators CR-710 and CR-740 (EM Lab Co., Ltd.), and analysis was performed using a vector network analyzer P5007A (manufactured by Keysight Technologies Co., Ltd.).

[0112] (Sample 1) The type of fluororesin is PFA (TFE / PPVE copolymer, composition: TFE / PPVE = 95.8 / 4.2 (mass%), MFR: 15.8 g / 10 min, melting point: 305 °C, number of unstable end groups: 297 per 10 main chain carbons 6 A long roll film with a thickness of 50 μm obtained by melt extrusion molding and winding using a T-die method was surface-treated on both sides (while flowing nitrogen gas containing 0.50% by volume of vinyl acetate near the discharge electrode of the corona discharge device and the roll-shaped ground electrode, the film was continuously passed along the roll-shaped ground electrode, and the discharge amount was 1324 W·min / m 2 The film was corona-discharge treated on both sides and the surface-treated long film was wound up. The surface oxygen element ratio of the surface-treated film by ESCA surface analysis was 20.42%. Also, the glass transition temperature of this film was 92 °C.

[0113] (Sample 2) The discharge amount was 265 W·min / m 2Aside from the above, a sample was obtained in the same manner as Sample 1, with both sides of a 50 μm thick film surface-treated. The oxygen element ratio determined by ESCA surface analysis was 11.64%.

[0114] (Sample 3) Discharge rate: 132 w·min / m 2 Aside from the above, a sample was obtained in the same manner as Sample 1, with both sides of a 50 μm thick film surface-treated. The oxygen element ratio determined by ESCA surface analysis was 5.35%.

[0115] (Sample 4) Discharge rate: 88W·min / m 2 Aside from the above, a sample was obtained in the same manner as Sample 1, with both sides of a 50 μm thick film surface-treated. The oxygen element ratio determined by ESCA surface analysis was 3.66%.

[0116] (Sample 5) Discharge rate: 66 W·min / m 2 A sample was obtained by surface-treating both sides of a 50 μm thick film, in the same manner as Sample 1, except for the following: The oxygen element ratio determined by ESCA surface analysis was 2.54%.

[0117] (Sample 6) A sample was obtained by surface-treating both sides of a 50 μm thick film, in the same manner as Sample 2, except that the type of fluororesin used was fluorinated PFA (TFE / PPVE copolymer, composition: TFE / PPVE = 95.8 / 4.2 (mass%), MFR: 16.2 g / 10 min, melting point: 305°C, number of unstable end groups: undetectable (less than 1 per 106 carbon atoms in the main chain)). The oxygen element ratio determined by ESCA surface analysis was 9.72%. The glass transition temperature of this film was 94°C.

[0118] Table 2 shows the surface treatment conditions and surface analysis results for samples 1 to 6.

[0119] [Table 2]

[0120] (Example 1) Sample 1 film was passed through a 180°C annealing furnace (under an air atmosphere) using a roll-to-roll method, cooled in a cooling zone, and wound into a long roll. At this time, the presence or absence of deformation (wavy) of the film after annealing was visually evaluated. Next, a cut film sampled from this long roll film was placed in an electric furnace at 180°C and heat-treated for 10 minutes, then cooled to room temperature. The dimensional change rate in the MD-TD direction was then measured, and its absolute value was determined. In addition, the film wound onto a core was stored at room temperature for one month, and the tightness of the winding was evaluated.

[0121] (Example 2) Except for using the film from Sample 2, the annealing treatment, subsequent evaluation of film deformation (wavyness), measurement of dimensional change rate, and evaluation of winding tightness were performed in the same manner as in Example 1.

[0122] (Example 3) Except for setting the annealing furnace temperature to 200°C, the annealing process was carried out in the same manner as in Example 2, and the presence or absence of deformation (wavy) of the film, measurement of the dimensional change rate, and evaluation of the winding tightness were performed.

[0123] (Example 4) Except for using the film from Sample 3, the annealing treatment, subsequent evaluation of film deformation (wavyness), measurement of dimensional change rate, and evaluation of winding tightness were performed in the same manner as in Example 1.

[0124] (Example 5) Except for using the film of Sample 4, the annealing treatment, subsequent evaluation of film deformation (wavyness), measurement of dimensional change rate, and evaluation of winding tightness were performed in the same manner as in Example 1.

[0125] (Example 6) Except for using the film of Sample 5, the annealing treatment, subsequent evaluation of film deformation (wavyness), measurement of dimensional change rate, and evaluation of winding tightness were performed in the same manner as in Example 1.

[0126] (Example 7) Except for using the film of Sample 6, the annealing treatment, subsequent evaluation of film deformation (wavyness), measurement of dimensional change rate, and evaluation of winding tightness were performed in the same manner as in Example 1. (Example 8) Except for not including a cooling zone in the annealing process, the annealing treatment, subsequent evaluation of film deformation (wavyness), measurement of dimensional change rate, and evaluation of winding tightness were carried out in the same manner as in Example 1.

[0127] (Comparative Example 1) Except for setting the annealing furnace temperature to 250°C, the annealing process was carried out in the same manner as in Example 2, and the presence or absence of deformation (wavy) of the film, measurement of the dimensional change rate, and evaluation of the winding tightness were performed.

[0128] (Comparative Example 2) The dimensional change rate and coil tightness of Sample 2, which had not undergone annealing, were measured.

[0129] The results for Examples 1-8 and Comparative Examples 1-2 are shown in Table 3.

[0130] [Table 3]

[0131] From the results in Table 3, it is possible to suppress winding tightness due to changes over time by adjusting the annealing conditions and keeping the absolute value of the dimensional change rate after heat treatment at 180°C for 10 minutes below 2%. Furthermore, in Example 8, when a cooling zone was not included in the annealing process, the roll film was deformed (wavy) when unwound after annealing, making it impossible to evaluate winding tightness. In this state, defects occur in the process of laminating with copper foil, etc., so it is preferable to include a cooling step in the annealing process.

[0132] (Example 9) The annealed film from Example 1 (Sample 1:180) was cut into 100mm squares, placed on a metal tray, and heat-treated in an electric furnace (air atmosphere) at 180°C for 3 minutes. The surface of this film that was in contact with air during the heat treatment was analyzed using ESCA. Next, the same side of the heat-treated fluororesin film that had undergone surface analysis was placed in contact with electrolytic copper foil CF-T9DA-SV-18 (thickness 18μm / Rz 0.85μm) (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.). The two films were bonded by heat pressing using a vacuum heat press machine (model: MKP-1000HVWH-S7 / manufactured by Mikado Technos Co., Ltd.) at a press temperature of 320°C, a preheating time of 60 seconds, a pressing pressure of 1.5MPa, and a pressing time of 300 seconds. The bond strength was measured by peeling the film at 90° using a Tensilon universal tester.

[0133] (Example 10) ESCA analysis of the surface of the annealed film (Sample 2:180) in Example 2 revealed an oxygen element ratio of 8.15 atomic%. Furthermore, after etching in the depth direction for 15 minutes using an argon gas cluster ion beam at an incident angle of 45° and sputtering conditions of 2.5kV × 10nA, ESCA analysis of the surface revealed an oxygen element ratio of 0.88 atomic%. The difference between the two results was 7.27 atomic%. The adhesive strength between this annealed film and the copper foil was 1.33 N / mm, and the adhesive strength between the film-treated surfaces was 250 N / m. Next, heat treatment at 180°C for 3 minutes, surface analysis, and adhesive strength measurement were performed in the same manner as in Example 9.

[0134] (Examples 11-12) The evaluation was carried out in the same manner as in Example 9, except that the annealed film from Example 3 (Sample 2: 200) and the annealed film from Example 4 (Sample 3: 180) were used.

[0135] (Example 13) ESCA analysis of the surface of the annealed film (Sample 4:180) in Example 5 revealed an oxygen element ratio of 2.67 atomic%. Furthermore, after etching in the depth direction for 15 minutes using an argon gas cluster ion beam at an incident angle of 45° and sputtering conditions of 2.5kV × 10nA, ESCA analysis of the surface revealed an oxygen element ratio of 0.90 atomic%. The difference between the two results was 1.77 atomic%. The adhesive strength between this annealed film and the copper foil was 1.27 N / mm. Next, heat treatment at 180°C for 3 minutes, surface analysis, and adhesive strength measurement were performed in the same manner as in Example 9.

[0136] (Example 14) Except for using the annealed film (Sample 6:180) from Example 7, the heat treatment at 180°C for 3 minutes, surface analysis, and adhesive strength measurement were performed in the same manner as in Example 9.

[0137] (Example 15) The evaluation was carried out in the same manner as in Example 9, except that the annealed film (Sample 2:180) from Example 2 was heat-treated in an electric furnace (Air atmosphere) at 120°C for 3 minutes.

[0138] (Example 16) The evaluation was carried out in the same manner as in Example 9, except that the annealed film (Sample 2:180) from Example 2 was heat-treated in an electric furnace (Air atmosphere) at 200°C for 3 minutes.

[0139] (Example 17) The evaluation was carried out in the same manner as in Example 9, except that the annealed film (Sample 2:180) from Example 2 was heat-treated in an electric furnace (Air atmosphere) at 250°C for 3 minutes.

[0140] For Examples 10 and 14, the dielectric constant and dielectric loss tangent were measured using a split-cylinder resonator (10 GHz and 40 GHz).

[0141] (Comparative Example 3) ESCA analysis of the surface of the annealed film (Sample 5:180) in Example 6 revealed an oxygen element ratio of 1.78 atomic%. Furthermore, after etching in the depth direction for 15 minutes using an argon gas cluster ion beam at an incident angle of 45° and sputtering conditions of 2.5kV × 10nA, ESCA analysis of the surface revealed an oxygen element ratio of 0.86 atomic%. The difference between the two results was 0.92 atomic%. Next, heat treatment at 180°C for 3 minutes, surface analysis, and adhesion strength measurement were performed, similar to Example 8.

[0142] The results for Examples 9-17 and Comparative Example 3 are shown in Table 4.

[0143] [Table 4]

[0144] (Comparative Example 4) Similar to Sample 1, a 50 μm thick film, melt-extruded using the T-die method, was surface-treated on both sides by discharge treatment without the use of an inert gas containing organic compounds. This film was passed through a 180°C annealing furnace (under an air atmosphere) using a roll-to-roll method, cooled in a cooling zone, and wound into a roll. The oxygen element ratio on the film surface after annealing was 4.16%. The adhesive strength between the treated film surfaces was 28 N / m. Next, similar to Example 9, heat treatment was performed at 180°C for 3 minutes, followed by surface analysis and measurement of the adhesive strength with copper foil. The oxygen element ratio on the film surface after heat treatment was 0.92%, and the adhesive strength with copper foil was 0.23 N / mm.

[0145] From the results in Table 4 and Comparative Example 4, it can be seen that by increasing the oxygen element ratio on the film surface after heat treatment at 180°C for 3 minutes to 1.35 atomic%, an adhesive strength of 0.8 N / mm or more with copper foil can be obtained. In particular, the surface treatment using the organic compound-containing inert gas of this disclosure is suitable because there is little deactivation due to heat. From the above, the fluororesin film of the present invention can obtain sufficient adhesive strength even when preheated before lamination with copper foil. Furthermore, since the dielectric loss tangent is 0.0015 or less, the transmission loss in the high-frequency range of the circuit board can be reduced.

[0146] (Example 18) Fluorinated PFA (TFE / PPVE copolymer, composition: TFE / PPVE = 95.8 / 4.2 (mass%), MFR: 16.2 g / 10 min, melting point: 305°C, number of unstable end groups: undetectable (main chain carbon number 10) 6 Using less than one sample per unit, a sample was obtained in the same manner as in Sample 6, by surface-treating one side of a 50 μm thick film. The oxygen element ratio of the surface-treated surface, as determined by ESCA surface analysis, was 10.18%. Using this film, annealing treatment and dimensional change rate measurement in the MD and TD directions were performed in the same manner as in Example 7. The absolute values ​​of the dimensional change rate were 0.90% for MD and 0.58% for TD. Also, in the same manner as in Example 14, the annealed film was placed on a metal tray with the treated surface in contact with air and heat-treated at 180°C for 3 minutes. ESCA analysis of the surface-treated surface revealed an oxygen element ratio of 6.07%.

[0147] Next, the annealed film and electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd.) were heat-pressed using a vacuum heat press (model: MKP-1000HVWH-S7 / manufactured by Mikado Technos Co., Ltd.) at a press temperature of 320°C, a preheating time of 60 seconds, a pressing pressure of 1.5 MPa, and a pressing time of 300 seconds to bond the surface-treated surface of the fluororesin film to the copper foil. The fluororesin film surface of the obtained single-sided copper-clad laminate was then surface-treated, and the single-sided copper-clad laminate was laminated in the order of one single-sided copper-clad laminate / two sheets of prepreg R-5680 (GN) (thickness 132 μm) (manufactured by Panasonic Corporation) / one single-sided copper-clad laminate so that the surface-treated surface and the prepreg were aligned. The laminates were then bonded using a vacuum heat press at a press temperature of 200°C to obtain a double-sided copper-clad laminate. The adhesive strength between the copper foil and the fluorine film was 13.8 N / cm. After removing the copper foil from the fabricated double-sided copper-clad laminate, the dielectric properties were measured at 20 GHz, resulting in a dielectric constant of 3.03 and a dielectric loss tangent of 0.00208. A sample of prepreg R-5680(GN) (thickness 132 μm) (manufactured by Panasonic Corporation) pressed at 200°C had a dielectric constant of 3.31 and a dielectric loss tangent of 0.00244. Furthermore, when the dielectric properties were measured at 40 GHz, the dielectric constant was 3.02 and the dielectric loss tangent was 0.00252. A sample of prepreg R-5680(GN) (thickness 132 μm) (manufactured by Panasonic Corporation) pressed at 200°C had a dielectric constant of 3.38 and a dielectric loss tangent of 0.00294.

[0148] From Example 18, it is possible to improve the electrical properties of other materials by combining this fluororesin film with other materials, and to control dielectric properties and other physical properties by changing the thickness of the fluororesin film. In addition, because it has a low thermal shrinkage rate and is less prone to creasing, defects are less likely to occur when laminating the fluororesin film and copper foil in a roll-to-roll manner.

[0149] Based on the experimental results described above, the fluororesin film of this disclosure has the advantage of reducing defects during lamination, enabling adhesion with highly smooth copper foil which was previously difficult, and having a low dielectric loss tangent, thereby significantly reducing transmission loss when a laminate with highly smooth copper foil is used as a circuit board material. [Industrial applicability]

[0150] The fluororesin film of this disclosure can be suitably used for copper-clad laminates for circuit boards.

Claims

1. After heat treatment at 180°C for 3 minutes, the oxygen element ratio measured on one or both sides of the surface using scanning X-ray photoelectron spectroscopy (XPS / ESCA) is 1.35 atomic% or higher, and furthermore, A fluororesin film that has been heat-treated at 180°C for 10 minutes and then cooled to 25°C, and a fabric layer made of glass fibers, and / or a resin film layer, The fluororesin film, after being cooled to 25°C, has an absolute value of 2% or less in the dimensional change rate of MD and TD before and after heat treatment. The laminate is characterized in that the resin film layer contains at least one selected from the group consisting of polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, and polybutadiene.

2. It contains a prepreg as a fabric layer made of glass fibers, The laminate according to claim 1, wherein the dielectric loss tangent at 20 GHz is lower than that of the prepreg alone.

3. It contains a prepreg as a fabric layer made of glass fibers, The laminate according to claim 1, wherein the dielectric loss tangent at 40 GHz is lower than that of the prepreg alone.

4. Furthermore, the laminate according to any one of claims 2 to 3, having a copper foil layer.

5. A copper-clad laminate characterized by comprising a laminate according to any one of claims 2 to 3, and copper foil.

6. A circuit board characterized by comprising a laminate according to any one of claims 1 to 3.

7. A circuit board characterized by being made of a copper-clad laminate as described in claim 5.

8. A method for manufacturing a fluororesin film, The process includes a step of surface modifying one or both sides of a fluororesin film, and a step of heat treatment at a temperature of glass transition temperature -20°C or higher but below the melting point. The obtained fluororesin film, after heat treatment at 180°C for 3 minutes, has an oxygen element ratio of 1.35 atomic% or higher when the surface condition of one or both sides is measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA). When the film is heat-treated at 180°C for 10 minutes and then cooled to 25°C, the absolute value of the dimensional change rate of MD and TD before and after heat treatment must be 2% or less. A method for manufacturing a fluororesin film characterized by the following.

9. A method for manufacturing a laminate, characterized by preheating the fluororesin film obtained by the method for manufacturing a fluororesin film according to claim 8 to a temperature above the glass transition temperature of the film but below its melting point, and then laminating the copper foil and / or the copper foil with a substrate other than the fluororesin film.

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