Laminate, method for manufacturing same, and circuit board

Abstract

Provided is a laminate demonstrating low transmission loss and excellent properties when used as a circuit board. The laminate unconditionally comprises a metal layer and a fluororesin-containing layer adjacent to the metal layer, wherein the arithmetic average surface roughness Sa on the metal side of an adhesion surface between the metal layer and the fluororesin-containing layer is 0.05 μm or less.

Description

Laminate, its manufacturing method, and circuit board

[0001] The present disclosure relates to a laminate, a method for manufacturing the same, and a circuit board.

[0002] In the field of circuit boards, laminates having a fluororesin-containing layer and a metal layer are widely known (see, for example, Patent Documents 1 and 2). Such laminates are produced by heating and bonding a fluororesin film and a metal foil.

[0003] In such laminates, metal foils with roughened surfaces have been used as the metal foil layers to improve adhesion between the fluororesin film and the metal. In recent years, the use of metal foils with high surface smoothness has also been investigated to reduce transmission loss.

[0004] JP 2023-3106 WO 2016 / 104297

[0005] An object of the present disclosure is to provide a laminate that has low transmission loss and excellent properties when used as a circuit board.

[0006] The present disclosure relates to a laminate essentially comprising a metal layer and a fluororesin-containing layer adjacent to the metal layer, wherein the arithmetic mean surface roughness Sa of the metal side of the adhesive surface between the metal layer and the fluororesin-containing layer is 0.05 μm or less.

[0007] The laminate preferably has an adhesive strength of 0.1 N / mm or more between the metal layer and the fluororesin-containing layer. The laminate is preferably a long laminate having a width of 200 mm or more. The laminate preferably has an oxygen element ratio of 1.35 atomic% or more when the surface of the fluororesin-containing layer is measured using a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA). The oxygen element ratio is preferably 1.5 atomic% or more.

[0008] In the laminate of the present disclosure, the difference between the oxygen element ratio when the surface of the fluororesin-containing layer on the side not facing the metal layer is measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) and the oxygen element ratio when the fluororesin-containing layer is etched in the depth direction with an argon gas cluster ion beam at an incident angle of 45° for 15 minutes and then measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) is preferably 1.0 atomic % or more.

[0009] The laminate preferably has a dynamic friction coefficient between the metal layer surface and the fluororesin-containing layer surface of 0.70 or less, and an adhesive strength of more than 30 N / m when the fluororesin-containing layer surfaces of two laminates are bonded together at 200°C.

[0010] The fluororesin-containing layer is preferably a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer or a tetrafluoroethylene / hexafluoropropylene copolymer. ６ It is preferable that the fluororesin-containing layer is composed of less than 10 particles of fluororesin per particle. It is preferable that the fluororesin in the fluororesin-containing layer has a melt flow rate of 1 to 50 g / 10 min at 372°C and a load of 49 N.

[0011] The laminate of the present disclosure may further include a layer (A) other than the metal layer and the fluororesin-containing layer, and the layer (A) may contain 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, divinylbenzene, and polybutadiene.

[0012] The metal layer is preferably formed using a metal foil having a surface roughness Rz of 1.5 μm or less.

[0013] The present disclosure also provides a method for producing the above-mentioned laminate, which is characterized by having a step of laminating a fluororesin film and a metal foil by roll-to-roll lamination at a temperature of 280°C or less.

[0014] In the method for producing the laminate, the oxygen element ratio of at least one surface of the fluororesin film is preferably 1.35 atomic % or more when the surface state of the fluororesin film is measured by a scanning X-ray photoelectron spectroscopy / analysis (XPS / ESCA).The oxygen element ratio of the fluororesin film is preferably 1.5 atomic % or more.

[0015] In the method for producing the laminate, the fluororesin film preferably has a difference of 1.0 atomic % or more between the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) of the surface condition of one or both sides thereof and the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) of the film after etching the film in the depth direction at an incident angle of 45° for 15 minutes. The present disclosure also relates to a circuit substrate comprising the above fluororesin laminate.

[0016] The laminate of the present disclosure has a high degree of smoothness at the bonding surface between the fluororesin-containing layer and the metal layer, and therefore has low transmission loss, making it suitable for use as a circuit substrate.

[0017] 1 is a schematic diagram showing a manufacturing apparatus for a laminate according to the present disclosure used in Examples. FIG. 2 is a diagram showing a laminate structure of an example of a laminate according to the present disclosure.

[0018] The present disclosure will be described in detail below. As described above, the adhesion between the fluororesin-containing layer and the metal layer is improved as the surface roughness increases, but in order to reduce transmission loss, it is desirable that the adhesion surface be smooth. In the present disclosure, we have investigated this issue.

[0019] Known methods for obtaining a laminate in which a fluororesin-containing layer and a metal layer are bonded include a method of bonding a metal foil to a fluororesin film, a method of metal deposition on a fluororesin film, etc. Among these, when bonding a metal foil to a fluororesin film, a metal foil with high smoothness is used as the material, and at the same time, the bonding conditions are examined to obtain a laminate with excellent surface smoothness of the bonding surface.

[0020] Furthermore, when a laminate is obtained by metal vapor deposition, a laminate with excellent surface smoothness of the bonding surface can be obtained by bringing the film into close contact with the cooling roll during vapor deposition.

[0021] In the case of a laminate obtained by a method of bonding a metal foil and a fluororesin film, the bonding conditions are important. If the bonding conditions are not appropriate, it will be impossible to achieve both surface smoothness and adhesion at the bonding surface. In other words, even if a metal foil with high smoothness is used as a material, if the bonding conditions are inappropriate, either the adhesive strength or the surface smoothness of the bonding surface will deteriorate. In the present disclosure, the above-mentioned object has been achieved by using a metal foil with excellent smoothness and by examining the bonding conditions with the fluororesin film (the raw material for the fluororesin-containing layer in the laminate).

[0022] When metal deposition is performed on a fluororesin film, the surface smoothness of the adhesive surface is such that adhesion to the cooling roll during deposition is ensured, thereby achieving the above-mentioned object.

[0023] (Arithmetic mean surface roughness Sa) The laminate of the present disclosure is characterized in that the arithmetic mean surface roughness Sa of the metal side of the bonding surface between the metal layer and the fluororesin interlayer is 0.05 μm or less. Regarding Sa, refer to FIG. 2. FIG. 2 is a diagram showing an example of a laminate of the present disclosure, which is a laminate having a structure in which a fluororesin-containing layer (3-A) and a metal layer (3-B) are bonded together. In such a laminate, the metal side of the bonding surface (3-C) between the metal layer (3-B) and the fluororesin-containing layer (3-A) is the surface to be measured for Sa in the present disclosure. The arithmetic mean surface roughness Sa is a parameter defined in ISO 25178 and is a measurement of three-dimensional surface properties. A laminate satisfying these parameters has an extremely smooth surface of the metal layer and reduced transmission loss.

[0024] More specifically, Sa is a parameter that extends the line roughness parameter Ra (arithmetic mean height of the line) to three dimensions (surface). It represents the average of the absolute values ​​of the height differences (z(x, y)) from the average plane of each measurement point in the reference area A, and is calculated using the following formula:

[0025]

[0026] The arithmetic mean surface roughness Sa of the metal side of the adhesive surface between the metal layer and the fluororesin-containing layer was calculated by observing the adhesive surface between the metal layer and the fluororesin-containing layer with a laser microscope VK-X1000 (manufactured by Keyence Corporation) and calculating the arithmetic mean roughness (Sa) in accordance with ISO 25178. The measurement area had a two-dimensional surface area of ​​60091 μm. 2 In particular, the measurement of the adhesive surface between the metal layer and the fluororesin-containing layer is carried out as follows: The laminate is placed in the device with the fluororesin side facing up and the metal side facing down. Since a laser microscope is an instrument that applies laser light and performs surface analysis from the reflected light, there are two reflection points on the laminate when the laser irradiation position is lowered. The reflection from the outermost surface comes from the resin surface, and the reflection from the second layer comes from the adhesive surface between the metal layer and the fluororesin-containing layer. The reflection data from the second layer at this time is analyzed and taken as the arithmetic mean surface roughness Sa of the metal side of the adhesive surface between the metal layer and the fluororesin-containing layer.

[0027] Laminates in which a metal layer and a fluororesin-containing layer are bonded to each other are known. However, a laminate that maintains high surface smoothness of the bonded surfaces after bonding has not been known until now. The present disclosure makes it possible to obtain a laminate that exhibits a small decrease in transmission loss when comparing transmission loss before and after bonding, thereby providing a circuit board with excellent performance.

[0028] The value Sa is more preferably 0.10 μm or less, and even more preferably 0.05 μm or less. The lower limit of the value Sa is not particularly limited, but can be, for example, 0.01 μm or more.

[0029] (Surface roughness Rz) In terms of the surface shape of the metal side of the adhesive surface between the metal layer and the fluororesin-containing layer, it is preferable that the surface roughness Rz of the metal before lamination is 1.5 μm or less. Rz is a parameter in the height direction called "maximum height." A portion of the roughness curve measured with a laser microscope is extracted over a reference length (282 μm), and the Rz is calculated as the sum of the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv).

[0030] The specific measurement method is as follows: Rz was calculated by analyzing the reflection data of the metal layer surface on the bonding surface before bonding to the resin side.

[0031] (Adhesion strength between metal layer and fluororesin-containing layer) The laminate of the present disclosure preferably has an adhesion strength between the metal layer and the fluororesin-containing layer of 0.1 N / mm or more. That is, it is preferable that the laminate has the smoothness of the adhesive surface as described above and has sufficient adhesive strength. Note that the adhesive strength in the present disclosure is a value measured by the method described in the examples.

[0032] The adhesive strength is more preferably 0.1 N / mm or more, more preferably 0.2 N / mm or more, and even more preferably 0.4 N / mm or more.

[0033] (Increase in transmission loss relative to unroughened copper foil) The laminate of the present disclosure preferably has an increase in transmission loss relative to unroughened copper foil of 2% or less at 28 GHz. Preferably, it is 1.5% or less, and more preferably, it is 1% or less. Preferably, it is 4% or less at 80 GHz. Preferably, it is 3% or less, and more preferably, it is 2% or less.

[0034] The rate of increase in transmission loss relative to the unroughened copper foil was measured using the following methods (1) to (3). (1) A printed circuit board was fabricated by forming a transmission line on one of the copper foil surfaces of a laminate in which copper foil was bonded to both sides of a fluororesin-containing layer. The transmission line constituted a microstrip line, and a pattern with a characteristic impedance of 50 Ω was selected, and the transmission loss (S21: dB / cm) at 28 GHz and 80 GHz was measured. (2) Next, the transmission loss of a laminate with the same configuration but in an ideal bonding state (unroughened copper foil: Sa 0.02 μm) was calculated (28 GHz and 80 GHz) using an electromagnetic field simulator (ideal value). (3) The difference between the measured value and the ideal value divided by the ideal value was used as the rate of increase in transmission loss.

[0035] (Long Film) The laminate of the present disclosure is preferably a long film. A long film produced continuously is particularly preferable from the viewpoint of production costs. The width of the long film is preferably 200 mm or more. Furthermore, the length is preferably 1 m or more, more preferably 3 m or more, more preferably 5 m or more, and even more preferably 10 m or more.

[0036] (Oxygen Element Ratio) In the laminate of the present disclosure, the oxygen element ratio is preferably 1.35 atomic % or more when the surface of the fluororesin-containing layer is measured using a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA: PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.)).

[0037] Here, the oxygen element ratio was measured using a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) PHI5000 VersaProbe II (manufactured by ULVAC-PHI, Inc.). Carbon, oxygen, fluorine, nitrogen, and silicon were detected, and the oxygen element ratio was determined from the composition ratio of C1s, O1s, F1s, N1s, and Si2p. Details of the surface treatment method will be described later.

[0038] Furthermore, in the laminate of the present disclosure, the difference between the oxygen element ratio when the surface state of the fluororesin-containing layer is measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) and the oxygen element ratio when the fluororesin-containing layer is etched in the depth direction with an argon gas cluster ion beam at an incident angle of 45° for 15 minutes and then measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) is preferably 1.0 atomic % or more. A larger difference in the oxygen element ratio from the surface in the depth direction is preferable in that a predetermined transmission loss can be obtained while maintaining adhesion.

[0039] The oxygen element ratio after etching is the oxygen element ratio at the surface of the fluororesin film that is the raw material for the fluororesin-containing layer before the surface treatment, and therefore the difference in the oxygen element ratio represents the increase in the oxygen element ratio due to the surface treatment.

[0040] (Dynamic friction coefficient between the metal layer surface and the fluororesin-containing layer surface) The laminate preferably has a dynamic friction coefficient between the metal layer surface and the fluororesin-containing layer surface of 0.70 or less. In particular, in the case of a long film, the dynamic friction coefficient is more preferably 0.70 or less, even more preferably 0.50 or less, and even more preferably 0.40 or less.

[0041] Therefore, by setting the dynamic friction coefficient between the metal layer surface and the fluororesin-containing layer surface to 0.70 or less, the above-mentioned problem can be improved and long films can be wound up smoothly. The dynamic friction coefficient was measured using a surface property tester, Heidon Type: 38 (manufactured by Shinto Scientific Co., Ltd.). A roller type indenter with a width of 60 mm and a diameter of 30 mm was used. The laminate was fixed to a base with the metal side facing up, and the laminate was fixed to the roller so that the fluororesin-containing layer was on the surface, and the friction test was performed. A 750 g weight was used as the balancer, and a load of 100 g was applied to the sample.

[0042] (Adhesion strength when the surfaces of the fluororesin-containing layers of two laminates are bonded together at 200°C) When two laminates of the present disclosure are prepared and the surfaces of the fluororesin-containing layers of each laminate are bonded together at 200°C, it is preferable that the adhesive strength is greater than 30 N / m. The laminate of the present disclosure is often subsequently laminated with other materials for use. In such cases, it is preferable that the adhesive strength is excellent. The adhesive strength described above is used as such an index, and it is preferable that the adhesive strength is within the above-mentioned range.

[0043] More specifically, the adhesive strength was measured by overlapping the surface-treated surfaces of fluororesin films, which are raw materials for the fluororesin-containing layer, and heat pressing (200°C, 0.1 MPa, 60 s) to produce a sample, which was then cut into 10 mm wide strips. Using a precision universal testing machine Autograph AGS-X 100N (manufactured by Shimadzu Corporation), the unbonded portion of the strip sample was gripped between the upper and lower chucks of the Autograph and pulled at a rate of 100 mm per minute to measure the peel strength, and the obtained value was taken as the adhesive strength.

[0044] (Fluororesin-containing layer) In the laminate of the present disclosure, the resin constituting the fluororesin-containing layer is not particularly limited as long as it is a resin containing fluorine, and known fluororesins can be used. Among them, those made of tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer (PFA) or tetrafluoroethylene / hexafluoropropylene copolymer (FEP) are preferred.

[0045] The (per)fluoro(alkyl vinyl ether) (PAVE) may be either a fluoroalkyl vinyl ether or a perfluoro(alkyl vinyl ether). In the present disclosure, the term "perfluoro(alkyl vinyl ether)" refers to an alkyl vinyl ether that does not contain a C—H bond. Examples of the PAVE constituting the PAVE unit include those represented by the general formula (1): CF ２ = CFO (CF ２ CFY １ O) ｐ -(CF ２ CF ２ CF ２ O) ｑ -R ｆ (1) (wherein, Y １ is F or CF ３ represents R ｆ represents a perfluoroalkyl group having 1 to 5 carbon atoms, p represents an integer of 0 to 5, and q represents an integer of 0 to 5.) and a monomer represented by the general formula (2): CFX=CXOCF ２ OR １ (2) (Wherein, X may be the same or different and is H, F or CF ３ represents R １ represents a linear or branched fluoroalkyl group having 1 to 6 carbon atoms which may contain 1 to 2 atoms of at least one type selected from the group consisting of H, Cl, Br and I, or a cyclic fluoroalkyl group having 5 or 6 carbon atoms which may contain 1 to 2 atoms of at least one type selected from the group consisting of H, Cl, Br and I.

[0046] Among these, the PAVE is preferably a monomer represented by general formula (1), more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) (PPVE), and even more preferably PPVE.

[0047] The content of PAVE units in the TFE / PAVE copolymer is preferably 1.0 to 10% by mass, more preferably 2.0% by mass or more, even more preferably 3.5% by mass or more, particularly preferably 4.0% by mass or more, most preferably 5.0% by mass or more, more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, particularly preferably 6.5% by mass or less, and most preferably 6.0% by mass or less, based on the total amount of the PAVE units. １９ The TFE / PAVE copolymer may be a copolymer consisting of only TFE units and PAVE units.

[0048] When the fluororesin-containing layer is made of a TFE / PAVE copolymer, the melting point is preferably 280 to 322°C, more preferably 290°C or higher, and more preferably 315°C or lower.

[0049] When the fluororesin-containing layer is made of a TFE / PAVE copolymer, the glass transition temperature (Tg) is preferably 70 to 110° C., more preferably 80° C. or higher, and more preferably 100° C. or lower. The glass transition temperature is a value obtained by measuring dynamic viscoelasticity.

[0050] The TFE / HFP copolymer contains TFE units and HFP units. The content of the TFE units in the TFE / HFP copolymer is preferably 70% by mass or more, more preferably 85% by mass or more, and is preferably 99.8% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less, based on the total monomer units.

[0051] The TFE / HFP copolymer preferably has a mass ratio of TFE units to HFP units (TFE / HFP) of 70 to 99 / 1 to 30 (mass %), more preferably 85 to 95 / 5 to 15 (mass %).

[0052] The TFE / HFP copolymer can further contain (per)fluoro(alkyl vinyl ether) (PAVE) units.The PAVE units contained in the TFE / HFP copolymer can be the same as the PAVE units described above.The TFE / PAVE copolymer does not contain HFP units, so in this respect it is different from the TFE / HFP / PAVE copolymer.

[0053] When the TFE / HFP copolymer is a copolymer containing TFE units, HFP units, and PAVE units (hereinafter also referred to as "TFE / HFP / PAVE copolymer"), the mass ratio (TFE / HFP / PAVE) is preferably 70-99.8 / 0.1-25 / 0.1-25 (mass%). The mass ratio (TFE / HFP / PAVE) is more preferably 75-98 / 1.0-15 / 1.0-10 (mass%). The TFE / HFP / PAVE copolymer preferably contains 1 mass% or more of HFP units and PAVE units in total relative to all monomer units.

[0054] In the TFE / HFP / PAVE copolymer, the HFP unit is preferably 25% by mass or less of the total monomer units. The content of the HFP unit is more preferably 20% by mass or less, even more preferably 18% by mass or less, and particularly preferably 15% by mass or less. The content of the HFP unit is preferably 0.1% by mass or more, more preferably 1% by mass or more, and particularly preferably 2% by mass or more. The content of the HFP unit is １９ It can be measured by F-NMR.

[0055] The content of PAVE units is more preferably 20% by mass or less, further preferably 10% by mass or less, and particularly preferably 3% by mass or less. The content of PAVE units is preferably 0.1% by mass or more, more preferably 1% by mass or more. The content of PAVE units is １９ It can be measured by F-NMR.

[0056] The TFE / PAVE copolymer and the TFE / HFP copolymer may further contain other ethylenic monomer (α) units. The other ethylenic monomer (α) units are not particularly limited as long as they are monomer units copolymerizable with TFE, HFP, and PAVE, and examples thereof include fluorine-containing ethylenic monomers such as vinyl fluoride (VF), vinylidene fluoride (VdF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE); non-fluorinated ethylenic monomers such as ethylene, propylene, and alkyl vinyl ethers; and ethylenic monomers having a hydroxyl group-containing group or a carbonyl group-containing group, such as itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride. The content of the other ethylenic monomer (α) units is preferably 0 to 25% by mass, and more preferably 0.1 to 25% by mass.

[0057] When the copolymer is a TFE / HFP / PAVE / other ethylenic monomer (α) copolymer, the mass ratio (TFE / HFP / PAVE / other ethylenic monomer (α)) is preferably 70 to 98 / 0.1 to 25 / 0.1 to 25 / 0.1 to 25 (mass %). The TFE / HFP / PAVE / other ethylenic monomer (α) copolymer preferably contains 1 mass % or more of monomer units other than TFE units in total.

[0058] The melting point of the TFE / HFP copolymer is preferably 200 to 322°C, more preferably above 200°C, even more preferably 220°C or higher, more preferably 300°C or lower, and even more preferably 280°C or lower.

[0059] The glass transition temperature (Tg) of the TFE / HFP copolymer is preferably 60 to 110° C., more preferably 65° C. or higher, and more preferably 100° C. or lower. The glass transition temperature is a value obtained by measuring dynamic viscoelasticity.

[0060] The fluororesin can be produced by a conventionally known method, for example, by appropriately mixing monomers that constitute the fluororesin and additives such as a polymerization initiator, followed by emulsion polymerization or suspension polymerization, etc. Among these, the fluororesin obtained by emulsion polymerization is more preferred.

[0061] The fluororesin contained in the fluororesin-containing layer preferably has a melt flow rate of 1 to 50 g / 10 min at 372° C. and a load of 49 N.

[0062] The fluororesin-containing layer has an unstable terminal group content of 1×10 carbon atoms. ６ It is preferable that each of the electrodes is made of less than 10 fluororesin particles.

[0063] The fewer functional groups the fluororesin has, the less unstable terminal groups it has. Such fluororesins can be produced by adjusting the conditions during production (polymerization reaction), or by subjecting the fluororesin after polymerization to fluorine gas treatment, heat treatment, supercritical gas extraction treatment, etc. The number of unstable terminal groups can be reduced by using methods such as: excellent treatment efficiency; ３ The fluorine gas treatment is preferable because the fluorine resin having a reduced number of unstable terminal groups is converted into a stable terminal group. The use of such a fluororesin having a reduced number of unstable terminal groups is preferable because it reduces the electrostatic dissipation factor and the loss of electrical signals.

[0064] The number of unstable terminal groups is not particularly limited, but is preferably 10 or more, and more preferably 10 or more, and most .... ６ The number per particle is preferably 450 or less, more preferably 250 or less, even more preferably 100 or less, and most preferably 50 or less. In consideration of the effect of reducing the dielectric loss tangent, the number per particle is preferably less than 10, and more preferably 5 or less.

[0065] Specific examples of unstable terminal groups include -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), and hydroxyl groups (-CH ２ OH, etc.), -CONH ２ , -COOR(R=CH ３ etc.), -CF ２ Examples of functional groups include H and —OCOO—R (normal propyl carbonate, etc.).

[0066] Specifically, the number of unstable terminal groups is measured by the following method. First, the fluororesin is melted and compression-molded to produce a film having a thickness of 0.25 to 0.3 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain an infrared absorption spectrum of the fluororesin, and a difference spectrum is obtained from a base spectrum in which the fluororesin is completely fluorinated and no functional groups are present. From the absorption peaks of specific functional groups that appear in this difference spectrum, the number of carbon atoms in the fluororesin is calculated according to the following formula (A): ６ The number of unstable terminal groups per unit is calculated as follows: N = I x K / t (A) I: absorbance K: correction coefficient t: film thickness (mm)

[0067] For reference, the absorption frequencies, molar absorption coefficients, and correction coefficients for the unstable terminal groups in this specification are shown in Table 1. The molar absorption coefficients were determined from the FT-IR measurement data of low molecular weight model compounds.

[0068]

[0069] The fluororesin-containing layer in the laminate of the present disclosure may contain components other than the fluororesin. The components that can be contained are not particularly limited, and examples thereof include fillers such as silica particles and short glass fibers, and fluorine-free thermosetting resins and thermoplastic resins. The content of components other than the fluororesin is not particularly limited, but is more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0070] In the laminate of the present disclosure, the fluororesin-containing layer preferably has a thickness of 1 to 100 μm. The upper limit is more preferably 50 μm or less, and even more preferably 30 μm or less. The lower limit is more preferably 3 μm or more, and even more preferably 5 μm or more.

[0071] The thickness of the fluororesin-containing layer is a value measured by reflection spectroscopy using a film thickness measurement system F20 (manufactured by Filmetrics).

[0072] (Metal Layer) In the present disclosure, examples of metal species constituting the metal foil layer include copper, aluminum, SUS, nickel, and gold. Alloys of these metals can also be used. From the viewpoints of electrical conductivity and circuit processability, copper is preferably used. A heat-resistant layer (nickel plating, titanium plating, etc.) or a rust-preventive layer (chromate treatment layer, etc.) may be formed on the surface of the copper foil. Furthermore, the surface may be chemically treated with a silane coupling agent. Of these, copper foil is preferably used. The metal foil layer preferably has a thickness of 1 to 100 μm.

[0073] The metal layer may be a metal foil layer, or a metal layer or metal foil vacuum-deposited on a fluororesin-containing layer may be used.

[0074] (Layer Structure of Laminate) The laminate of the present disclosure may have a two-layer structure consisting of the above-mentioned fluororesin-containing layer and metal layer, or may have a three-layer or more structure having two or more layers of either or both of these. Furthermore, it may have a three-layer or more structure having a layer (A) other than the metal layer and the fluororesin-containing layer.

[0075] Examples of the layer (A) other than the metal layer and the fluororesin-containing layer include polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, etc. Examples of the thermosetting resin include those containing epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, divinylbenzene, polybutadiene, etc.

[0076] When the laminate of the present disclosure has the layer (A), the layer structure may be metal / fluororesin-containing layer / layer (A). The fluororesin-containing layer / metal laminate may be provided on one or both sides of the layer (A).

[0077] (Manufacturing Method) A manufacturing method for the laminate of the present disclosure is described in detail below. To obtain the laminate of the present disclosure, it is necessary that the metal foil used as the material has high smoothness, and further that the conditions for the step of bonding it to the fluororesin film are adjusted.

[0078] The metal foil used as a raw material for producing the laminate of the present disclosure preferably has an arithmetic mean surface roughness Sa of 0.3 μm or less, more preferably 0.15 μm or less, and even more preferably 0.04 μm or less. As such, using a metal foil with high surface smoothness before bonding is important in achieving the object of the present invention. As a metal foil having an arithmetic mean surface roughness Sa of 0.04 μm or less, commercially available products can be used, and examples thereof include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm, Rz 0.85 μm, Sa 0.02 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd.)).

[0079] The fluororesin film used as a raw material for producing the laminate of the present disclosure is not particularly limited, and any known, general fluororesin film such as those described above can be used.

[0080] Heating is required when bonding the metal foil and the fluororesin film, and in producing the laminate of the present disclosure, the heating temperature is preferably set to the melting point of the fluororesin minus 20°C or lower. For example, when the fluororesin is PFA, the heating temperature is preferably set to 280°C or lower, and preferably 120 to 280°C. More preferably, it is set to 200 to 280°C, and even more preferably, 220 to 280°C. The heat treatment step may be a roll-to-roll lamination method, or a method in which a fluororesin coated on a metal foil is heat-treated.

[0081] In other words, setting the heating temperature to a low temperature of -20°C below the melting point is preferable because it minimizes the loss of smoothness of the bonding surface during the process of bonding the metal foil layer and the fluororesin-containing layer. The mechanism behind this is unclear, but is presumed to be as follows. Resins have the property of expanding when heated and melted, and shrinking when cooled and solidified. Therefore, when heated at a temperature above the melting point of -20°C to bond to a metal foil, the metal foil is deformed by the shrinkage of the resin. Therefore, bonding at a temperature below the melting point of -20°C can suppress deformation of the metal foil due to shrinkage, and the smoothness of the bonding surface is minimized.

[0082] In the present disclosure, the melting point of a fluororesin is determined by measuring the temperature using a differential scanning calorimeter in accordance with ASTM D-4591 at a temperature increase rate of 10°C / min, and the melting point is determined as the temperature at the peak of the endothermic curve obtained.

[0083] In producing the laminate of the present disclosure, the method for bonding the metal foil and the fluororesin film is not particularly limited, but from the viewpoint of excellent production efficiency, a roll-to-roll lamination method is particularly preferred.

[0084] The roll-to-roll method is also preferable in that it reduces costs and allows a long laminate to be obtained. When producing a laminate by such a method, the width of the laminate is not particularly limited, but is preferably 200 mm or more.

[0085] The fluororesin film is preferably surface-modified on one or both sides to improve its adhesiveness, thereby enabling adhesion at a temperature below the melting point of the fluororesin by −20° C., for example, 120° C. to 280° C. By laminating a metal foil to the fluororesin film obtained in this manner under appropriate conditions, the laminate of the present disclosure can be suitably obtained.

[0086] The specific method for the surface modification is not particularly limited, but specific examples are described in detail below. Surface modification of fluororesin films can be achieved by conventional discharge treatments such as corona discharge treatment, glow discharge treatment, plasma discharge treatment, and sputtering. For example, surface free energy can be controlled by introducing oxygen gas, nitrogen gas, hydrogen gas, carbon dioxide gas, methane gas, ethylene gas, or the like into a discharge atmosphere. Alternatively, the surface to be modified can be exposed to an atmosphere of an organic compound-containing inert gas, which is an inert gas containing an organic compound, and a high-frequency voltage is applied between electrodes to generate a discharge, thereby generating active species on the surface. Subsequently, the surface can be modified by introducing functional groups of the organic compound or graft-polymerizing a polymerizable organic compound. Examples of the inert gas include nitrogen gas, helium gas, and argon gas.

[0087] Examples of the organic compound in the organic compound-containing inert gas include polymerizable or non-polymerizable organic compounds containing oxygen atoms, such as vinyl esters such as vinyl acetate and vinyl formate; acrylic esters such as glycidyl methacrylate; ethers such as vinyl ethyl ether, vinyl methyl ether, and glycidyl methyl ether; carboxylic acids such as acetic acid and formic acid; alcohols such as methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; carboxylic esters such as ethyl acetate and ethyl formate; acrylic acids such as acrylic acid and methacrylic acid. Among these, vinyl esters, acrylic esters, and ketones are preferred because the modified surface is less likely to be deactivated, i.e., has a long life.

[0088] The concentration of the organic compound in the organic compound-containing inert gas varies depending on the type of organic compound, the type of fluororesin to be surface-modified, etc., but is usually 0.1 to 3.0% by volume, preferably 0.1 to 1.0% by volume, more preferably 0.15 to 1.0% by volume, and even more preferably 0.30 to 1.0% by volume. The discharge conditions may be appropriately selected depending on the desired degree of surface modification, the type of fluororesin, the type and concentration of the organic compound, etc. Usually, the discharge amount 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 between 0°C and 100°C. Due to concerns about film stretching and wrinkling, a temperature of 80°C or less is preferred. Regarding the degree of surface modification of the fluororesin film, taking into consideration that oxygen elements on the surface are deactivated by heat applied during lamination with the metal foil, resulting in a decrease in adhesive ability, the oxygen element abundance ratio observed by ESCA is 1.5% or more, preferably 1.75% or more, more preferably 2.0% or more, and even more preferably 2.5% or more. There is no particular upper limit, but in consideration of the impact on productivity and other physical properties, it is preferably 25.0% or less. The nitrogen element abundance ratio is not particularly specified, but is preferably 0.1% or more. The thickness of one fluororesin film is preferably 1.0 to 1000 μm, more preferably 12.5 to 100 μm, and even more preferably 5 to 30 μm.

[0089] In the above method, it is preferable to perform surface treatment so that the oxygen element ratio is 1.5 atomic % or more when the surface conditions of both surfaces of the fluororesin film are measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA). The oxygen element ratio is more preferably 1.75 atomic % or more.

[0090] In the above method, surface treatment with a gas containing an organic compound is also preferable in that it can impart localized unevenness to the resin surface, thereby making the dynamic friction coefficient between the metal foil layer surface and the fluororesin-containing layer surface 0.4 or less. That is, in addition to improving the adhesive strength, the dynamic friction coefficient can be made small. This is preferable in that when a long laminate is produced, poor winding will not occur.

[0091] The fluororesin film plasma-treated by the above method may be annealed to remove residual stress in advance. This reduces dimensional changes in the fluororesin film due to heat from the pressure roll during the process of laminating it with metal foil to produce a laminate, allowing it to be bonded without wrinkles, thereby suppressing poor appearance of the laminate. Because these heat treatments reduce the amount of oxygen on the surface of the fluororesin film, it is preferable to perform surface modification under conditions that ensure a sufficient amount of surface oxygen at the time the fluororesin film and metal foil are bonded together.

[0092] The annealing treatment can be carried out by heat treatment. The heat treatment can be carried out, for example, by passing the material through a heating furnace using a roll-to-roll method. The heat treatment can also be carried out by placing the material in a batch-type drying furnace.

[0093] The annealing temperature is preferably not less than the glass transition temperature of the fluororesin minus 20° C. and less than the melting point, more preferably not less than the glass transition temperature of the fluororesin minus 20° C., and even more preferably not less than the glass transition temperature of the fluororesin minus 60° C. The annealing time is not particularly limited, but may be adjusted as appropriate within the range of, for example, 0.5 to 60 minutes.

[0094] When heating is performed by the roll-to-roll method, the tension may be adjusted appropriately depending on the film thickness, the set temperature, etc., but is preferably 20 N / m or less. Heating under such conditions is preferable in that it can sufficiently relieve internal stress and does not cause dimensional changes, etc.

[0095] The order of the surface treatment and annealing treatment is not particularly limited, and the number of times each step is performed is not limited to one, but each step may be performed two or more times.

[0096] The laminate of the present disclosure has the advantage of having small surface irregularities at the bonding surface between the metal layer and the fluororesin-containing layer, resulting in low transmission loss. Therefore, the laminate can be suitably used for circuit boards, etc. It can be particularly suitably used for circuit boards for high-frequency circuits.

[0097] In this disclosure, the term "high-frequency circuit" refers not only to a circuit that simply transmits only high-frequency signals, but also to a circuit that also includes a transmission line that converts a high-frequency signal into a low-frequency signal and outputs the generated low-frequency signal to the outside, a transmission line for supplying power to drive high-frequency compatible components, and other transmission lines that transmit signals other than high-frequency signals, all of which are installed on the same plane.The circuit can also be used as a circuit board for an antenna, a filter, etc.

[0098] The present disclosure will be specifically described below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0099] [Film Manufacturing Method] (Manufacturing Method of Long Roll Film 1) A fluorinated terminal TFE / PPVE copolymer (composition: TFE / PPVE=96.1 / 3.9 (mass%), MFR: 16.0 g / 10 min, melting point: 305°C, number of unstable terminal groups: undetectable (main chain carbon number: 10)) was extruded at 360°C in an extruder equipped with a stack of multiple #300 mesh or larger sheets and an ultrasonically cleaned nickel filter inserted between the screw and the die. ６ The resulting extrusion was carried out from a 1700 mm wide T-die, taken up on a metal cooling roll, and further taken up on a take-up core to produce a long roll film 1 having a width of 1300 mm and a thickness of 12.5 μm.

[0100] (Manufacturing Method of Long Roll Film 2) A non-terminally fluorinated TFE / PPVE copolymer (composition: TFE / PPVE=95.4 / 4.6 (mass%), MFR: 15.8 g / 10 min, melting point: 305° C., number of unstable terminal groups: 10 main chain carbon atoms) was prepared as a fluororesin in the same process. ６ The film using PFA (297 particles per film) is designated as long roll film 2.

[0101] (Method of manufacturing long films 3 and 4) Next, both sides of the obtained long roll film 1 were subjected to a surface treatment (a nitrogen gas containing 0.50% by volume of vinyl acetate was flowed near the discharge electrode and roll-shaped ground electrode of a plasma discharge device, and the film was continuously passed along the roll-shaped ground electrode, with a discharge amount of 265 W min / m ２The surface-treated long film 3 was wound into a roll. The film was slit into a width of 500 mm to prepare a long film 4.

[0102] (Method for manufacturing long films 5 and 6) Next, both sides of the obtained long roll film 2 were subjected to a surface treatment (a nitrogen gas containing 0.50% by volume of vinyl acetate was flowed near the discharge electrode and roll-shaped ground electrode of a plasma discharge device, and the film was continuously passed along the roll-shaped ground electrode, with a discharge amount of 265 W min / m ２ The surface-treated long film 5 was wound into a roll. The film was slit into a width of 500 mm to prepare a long film 6.

[0103] (Method for manufacturing long film 7) The long film 4 was passed through an annealing furnace (in an air atmosphere) at 180°C by a roll-to-roll method, cooled in a cooling zone, and wound into a roll. This film was slit into a width of 500 mm to obtain the long film 7.

[0104] (Manufacturing Method of Long Film 8) Surface treatment was performed on both sides of the obtained long roll film 1 (CO 2 was applied near the discharge electrode and the roll-shaped ground electrode of the plasma discharge device). ２ 0.5% by volume, O ２ The film was passed continuously along a roll-shaped ground electrode while flowing He gas containing 0.5% by volume of HCl, and the discharge rate was 1200 W·min / m. ２ The surface-treated long film was wound into a roll. This film was slit into a width of 500 mm to obtain long film 8.

[0105] [Laminating with Copper Foil] Example 1 Using the thermal laminating device shown in FIG. 1 , a long film 4 and a long copper foil 2 (electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm, Sa 0.020 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) having a width of 520 mm were laminated together to obtain a laminate 21. During laminating, the surface temperature (press temperature) of the pair of laminating rolls 100 (metal rolls) was 280° C., the pressure applied by the laminating rolls was 20 kN / m, and the conveying speed of the film and copper foil was 3 m / min.

[0106] Examples 2 to 9 Laminates 22 to 29 were obtained in the same manner as for the laminate 21, except that the pressing temperature was changed as shown in Table 2.

[0107] Example 10 A laminate 30 was obtained in the same manner as the laminate 21, except that the long film 7 was used instead of the long film 2 and the pressing temperature was set to 280°C.

[0108] Example 11 A laminate 31 was obtained in the same manner as the laminate 21, except that a long film 6 was used instead of the long film 2 and the pressing temperature was set to 280°C.

[0109] Example 12 A laminate 32 was obtained in the same manner as the laminate 21, except that the long film 8 was used instead of the long film 2 and the pressing temperature was set to 260°C.

[0110] Reference Examples 1 to 3 Laminates 33 to 35 were obtained in the same manner as in the production of the laminate 21, except that the pressing temperature was changed as shown in Table 3.

[0111] Reference Example 4 A laminate 36 was obtained in the same manner as the laminate 21, except that the long film 7 was used and the pressing temperature was set to 300°C.

[0112] Comparative Examples 1 to 3 Laminates 37 to 3940 were obtained in the same manner as in the production of laminate 32, except that the pressing temperature was changed as shown in Table 3.

[0113] (Method of measuring and evaluating oxygen element ratio) Using a scanning X-ray photoelectron spectrometer (XPS / ESCA) PHI5000 VersaProbe II (manufactured by ULVAC-PHI, Inc.), the oxygen element ratio of the resin surface after surface treatment was measured under the conditions of a monochromated AlKα radiation source and an incident angle of 45°. The detection targets were carbon, oxygen, fluorine, nitrogen, and silicon. The oxygen element ratio was determined from the composition ratio of C1s, O1s, F1s, N1s, and Si2p.

[0114] (Sa on the copper foil side of the adhesive interface between the metal foil and fluororesin-containing layer after lamination) The adhesive interface between the metal layer and fluororesin-containing layer was observed using a laser microscope VK-X1000 (manufactured by Keyence Corporation), and the arithmetic mean roughness (Sa) was calculated in accordance with ISO 25178. The measurement area had a two-dimensional surface area of ​​60091 μm2. Specifically, measurement of the adhesive interface between the metal layer and fluororesin was performed as follows: The laminate was placed in the device with the fluororesin side facing up and the metal side facing down. A laser microscope is a device that applies laser light and performs surface analysis from the reflected light. As the laser irradiation position is lowered, two reflection points are present on the laminate. The reflection from the outermost surface originates from the resin surface, and the reflection from the second layer originates from the adhesive interface between the metal layer and fluororesin-containing layer. Analysis of the reflection data from the second layer was used to determine the arithmetic mean surface roughness Sa of the metal side of the adhesive interface between the metal layer and fluororesin-containing layer. The measurement conditions were Gaussian filter type, S filter 2.5 μm, L filter 0.08 mm. In addition, the corrections during Sa analysis were performed as follows: Surface shape correction: Quadratic curve, waviness removal (strength: 5) Smoothing: Median, size 3 × 3

[0115] (Increase in Transmission Loss Relative to Unroughened Copper Foil) First, a printed circuit board was fabricated by forming a transmission line on one of the copper foil surfaces of a laminate formed by laminating copper foil on both sides of a fluororesin-containing layer (50 μm thick). High-frequency transmission characteristics were evaluated using a vector network analyzer (Keysight Technologies N5290A). The transmission line was a microstrip line, and a pattern with a characteristic impedance of 50 Ω was selected. The transmission loss (S21: dB / cm) at 28 GHz and 80 GHz was measured (actual values). Next, the transmission loss of a laminate with the same configuration but in an ideal bonding state (unroughened copper foil: Sa 0.02 μm) was calculated (28 GHz and 80 GHz) (ideal values) using an electromagnetic field simulator (Ansys). For each example and comparative example, the difference between the actual value and the ideal value was calculated and used as the increase in transmission loss.

[0116] (Adhesion Strength between Copper Foil and Fluororesin-Containing Layer) Prepreg R-5680(J) (thickness: 132 μm) (manufactured by Panasonic Corporation) was prepared, and the laminate 21 prepared in Example 1 was cut into two 200 mm square pieces. These were then laminated on both sides of the prepreg so that the fluororesin surface was in contact with the prepreg, resulting in a copper foil layer / fluororesin-containing layer / prepreg / fluororesin-containing layer / copper foil layer laminate. A measurement sample was then prepared under press conditions of a temperature of 200°C, a time of 75 minutes, and a pressure of 3.0 MPa, and then cut into a 10 mm width. Adhesive tape was attached to one side of the cut sample, which was then attached to an aluminum plate. Using a precision universal testing machine, Autograph AGS-X 100N (manufactured by Shimadzu Corporation), the peel strength between the copper foil and the fluororesin-containing layer was measured by gripping and pulling a 10 mm wide piece of copper foil in a direction 90° to the plane of the laminate at a rate of 50 mm per minute, and the obtained value was taken as the adhesive strength.

[0117] (Dynamic friction coefficient between copper foil surface and fluororesin-containing layer surface) Measurements were made using a surface property tester, Heidon Type: 38 (manufactured by Shinto Scientific Co., Ltd.). A roller type indenter with a width of 60 mm and a diameter of 30 mm was used. The laminate was fixed to a base with the metal side facing up, and the laminate was fixed to the roller so that the fluororesin-containing layer was on the surface, and the friction test was performed. A 750 g weight was used as the balancer, and a load of 100 g was applied to the sample. The test force obtained by the load cell of this tester was divided by the load over 500 ms within the stable range, and the average value was taken as the dynamic friction coefficient.

[0118] (Appearance of roll) The appearance of a 500 mm wide laminate rolled up is visually judged and defined as follows: ○: No wrinkles △: 1-2 wrinkles in the roll ×: 3 or more wrinkles in the roll

[0119]

[0120]

[0121] It is clear from the results in Tables 2 and 3 that the laminates of the present disclosure have low transmission loss. Furthermore, it is clear that the laminates of Examples 1 to 12 have low friction and do not cause problems due to poor winding.

[0122] The laminate of the present disclosure can be suitably used as a circuit board.

[0123] 1: Fluorine film 2: Metal foil 21: Laminate 100, 101: Pressure roll 102: Fluorine film supply roll 103: Metal foil supply roll 104a-c: Transport roll 105: Laminate take-up roll 3-A: Fluorine resin-containing layer 3-B: Metal foil layer 3-C: Adhesion surface of fluororesin-containing layer / metal foil layer

Claims

1. A laminate comprising a metal layer and a fluororesin-containing layer adjacent to the metal layer, wherein the arithmetic mean surface roughness Sa on the metal side of the adhesion surface between the metal layer and the fluororesin-containing layer is 0.05 μm or less.

2. The laminate according to claim 1, wherein the adhesion strength between the metal layer and the fluororesin-containing layer is 0.1 N / mm or more.

3. The laminate according to any one of claims 1 to 2, wherein the laminate is a long laminate having a width of 200 mm or more.

4. The laminate according to any one of claims 1 to 3, wherein the oxygen element ratio when the surface of the fluororesin-containing layer is measured by a scanning X-ray photoelectron spectrometer (XPS / ESCA) is 1.35 atomic% or more.

5. The laminate according to claim 4, wherein the oxygen element ratio is 1.5 atomic% or more.

6. The difference between the oxygen element ratio when the surface of the fluororesin-containing layer is measured by a scanning X-ray photoelectron spectrometer (XPS / ESCA) and the oxygen element ratio when the fluororesin-containing layer is etched in the depth direction at an incident angle of 45° for 15 minutes by an argon gas cluster ion beam and then measured by a scanning X-ray photoelectron spectrometer (XPS / ESCA) is 1.0 atomic% or more. The laminate according to any one of claims 1 to 5.

7. The laminate according to any one of claims 1 to 6, wherein the coefficient of kinetic friction between the surface of the metal layer and the surface of the fluororesin-containing layer is 0.70 or less.

8. The laminate according to any one of claims 1 to 7, wherein the adhesion strength is greater than 30 N / m when the surfaces of the fluororesin-containing layers in two laminates are bonded together at 200 °C.

9. The laminate according to any one of claims 1 to 8, wherein the fluororesin-containing layer is a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer or a tetrafluoroethylene / hexafluoropropylene copolymer.

10. The laminate according to any one of claims 1 to 9, wherein the fluororesin-containing layer is composed of a fluororesin having an amount of unstable end groups of less than 10 per 1 × 106 carbon atoms.

11. The laminate according to any one of claims 1 to 11, wherein the fluororesin-containing layer has a melt flow rate of 1 to 50 g / 10 min for the fluororesin at 372 °C and a load of 49 N.

12. The laminate according to any one of claims 1 to 11, wherein the fluororesin-containing layer uses a film whose both surfaces are surface-treated by plasma discharge treatment with nitrogen gas containing vinyl acetate, the metal layer uses a copper foil having a surface roughness Rz of 1.5 μm or less, and these are laminated.

13. Further, it has a layer (A) other than the metal layer and the fluororesin film layer, and the layer (A) 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, divinylbenzene, and polybutadiene. The laminate according to any one of claims 1 to 12.

14. The laminate according to any one of claims 1 to 13, wherein the metal layer is formed using a metal foil having a surface roughness Rz of 1.5 μm or less.

15. A method for manufacturing a laminate according to any one of claims 1 to 14, characterized by having a step of heat-treating a fluororesin film and a metal foil in a roll-to-roll manner at a temperature of -20 °C or lower than the melting point of the fluororesin.

16. A method for manufacturing a laminate according to any one of claims 1 to 14, characterized by having a step of heat-treating a fluororesin film and a metal foil in a roll-to-roll manner at a temperature of 280 °C or lower.

17. The method for manufacturing a laminate according to claim 15 or 16, wherein the oxygen element ratio when the surface state of both surfaces of the fluororesin film is measured by a scanning X-ray photoelectron spectrometer (XPS / ESCA) is 1.5 atomic% or more.

18. The method for manufacturing a laminate according to any one of claims 15 to 17, wherein the difference in the oxygen element ratio when the surface state of one or both surfaces of the fluororesin film is measured by a scanning X-ray photoelectron spectrometer (XPS / ESCA) and the oxygen element ratio when the film is etched in the depth direction at an incident angle of 45° for 15 minutes by an argon gas cluster ion beam and then measured by a scanning X-ray photoelectron spectrometer (XPS / ESCA) is 1.0 atomic% or more.

19. A circuit board characterized by having the laminate according to any one of claims 1 to 14.

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