Laminate, method for producing the same, and circuit board

Abstract

To provide a laminate having low transmission loss and excellent properties when used as a substrate for a circuit.SOLUTION: The laminate essentially 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 the bonding surface between the metal layer and the fluororesin-containing layer is 0.05 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2023-3106 [Patent Document 2] International Publication No. 2016 / 104297 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[0006] The present disclosure relates to a laminate essentially comprising a metal layer and a fluororesin-containing layer adjacent to the metal layer, characterized in that 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] In the laminate, the adhesive strength between the metal layer and the fluororesin-containing layer is preferably 0.1 N / mm or more. 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 with 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 measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) on the surface of the fluororesin-containing layer on the side not facing the metal layer and the oxygen element ratio measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) after etching the fluororesin-containing layer in the depth direction with an argon gas cluster ion beam at an incident angle of 45° for 15 minutes is preferably 1.0 atomic % or more.

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

[0010] The fluororesin-containing layer is preferably a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer or a tetrafluoroethylene / hexafluoropropylene copolymer. The fluororesin-containing layer has an unstable terminal group content of 1×10 6 It is preferable that each of the electrodes is made of less than 10 fluororesin particles. In the fluororesin-containing layer, the fluororesin preferably 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 have 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, it is preferable that the oxygen element ratio is 1.35 atomic % or more when the surface state of at least one surface of the fluororesin film is measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA). The fluororesin film preferably has an oxygen element ratio of 1.5 atomic % or more.

[0015] In the method for producing the laminate, it is preferable that the difference between the oxygen element ratio when the surface condition of one or both sides of the fluororesin film is measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) and the oxygen element ratio when the film 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 1.0 atomic % or more. The present disclosure also provides a circuit board comprising the above-described fluororesin laminate. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing a manufacturing apparatus for a laminate according to the present disclosure used in the examples. [Figure 2] FIG. 2 is a diagram showing a laminate structure in an example of a laminate according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[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 better when the surface roughness is higher, but in order to reduce transmission loss, it is desirable that the adhesion surface be highly 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 is vapor-deposited on a fluororesin film, the surface smoothness of the adhesive surface is such that adhesion to the cooling roll is ensured during vapor deposition, 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 the above 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) into 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]

number

[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 a device 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 above Sa is more preferably 0.10 μm or less, and even more preferably 0.05 μm or less. There is no particular lower limit to the above Sa, but it 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 bonding 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 it is calculated as the sum of the highest point (maximum peak height: Rp) and the deepest point (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 adhesive strength of 0.1 N / mm or more between the metal layer and the fluororesin-containing layer. That is, it is preferable that the adhesive surface has the smoothness described above and has sufficient adhesive strength. 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 compared to un-roughened copper foil) The laminate of the present disclosure preferably has an increase in transmission loss of 2% or less at 28 GHz relative to unroughened copper foil, preferably 1.5% or less, and more preferably 1% or less, and at 80 GHz, preferably 4% or less, preferably 3% or less, and more preferably 2% or less.

[0034] The rate of increase in transmission loss relative to the non-roughened copper foil was measured by the following measurement 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 attached 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 of the same configuration in an ideal bonding state (unroughened copper foil: Sa 0.02 μm) was calculated (28 GHz and 80 GHz) (ideal value) using an electromagnetic field simulator. (3) The difference between the measured value and the ideal value divided by the ideal value was taken as the increase rate of transmission loss.

[0035] (long film) The laminate of the present disclosure is preferably a long film. A continuously produced long film 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 spectrometer (XPS / ESCA: PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.)).

[0037] The oxygen element ratio was measured using a scanning X-ray photoelectron spectrometer (XPS / ESCA) PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.) The detection targets were carbon, oxygen, fluorine, nitrogen, and silicon, and the oxygen element ratio was determined from the composition ratios of C1s, O1s, F1s, N1s, and Si2p. The surface treatment method will be described in detail 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. The greater the difference in oxygen element ratio from the surface to the depth direction, the more preferable it is in that a predetermined transmission loss can be obtained while maintaining adhesiveness.

[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) In the laminate, the coefficient of dynamic friction between the metal layer surface and the fluororesin-containing layer surface is preferably 0.70 or less. In particular, in the case of a long film, the coefficient of dynamic friction 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 problems can be improved and a long film can be wound up well. The dynamic friction coefficient was measured using a Heidon Type: 38 surface tester (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 according to the present disclosure are prepared and the surfaces of the fluororesin-containing layers are bonded together at 200°C, the adhesive strength is preferably greater than 30 N / m. The laminates according to the present disclosure are often subsequently laminated with other materials for use. In such cases, it is preferable that the laminate has excellent adhesiveness. The adhesive strength described above is used as 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 the raw material for the fluororesin-containing layer, and then heat pressing (200°C, 0.1 MPa, 60 s) to create a sample. The sample was then cut into 10 mm wide strips, and the peel strength was measured using a precision universal testing machine, Autograph AGS-X 100N (Shimadzu Corporation), by gripping the unbonded portion of the strip sample with the upper and lower chucks of the Autograph and pulling it at a rate of 100 mm per minute. The value obtained 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] (Per)fluoro(alkyl vinyl ether) (PAVE) may be either a fluoroalkyl vinyl ether or a perfluoro(alkyl vinyl ether). In the present disclosure, a "perfluoro(alkyl vinyl ether)" is an alkyl vinyl ether that does not contain a C-H bond. The PAVE constituting the PAVE unit is represented by the general formula (1): CF2=CFO(CF2CFY 1 O)p -(CF2CF2CF2O) q -R f (1) (where, Y 1 represents F or CF3, and 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 general formula (2): CFX=CXOCF2OR 1 (2) (wherein X may be the same or different and represents H, F or CF3; 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 monomer 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 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 (TFE / HFP) of TFE units to HFP units of 70 to 99 / 1 to 30 (mass %), more preferably 85 to 95 / 5 to 15 (mass %).

[0052] The TFE / HFP copolymer may further contain (per)fluoro(alkyl vinyl ether) (PAVE) units. Examples of PAVE units contained in the TFE / HFP copolymer include the same PAVE units as those described above. The TFE / PAVE copolymer does not contain HFP units, and in this respect, it differs 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 preferably accounts for 25% by mass or less of the total monomer units. The content of HFP units 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 HFP units 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 HFP units is 19 It can be measured by F-NMR.

[0055] The content of PAVE units is more preferably 20% by mass or less, even more 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. Examples 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, 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 70-98 / 0.1-25 / 0.1-25 / 0.1-25 (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 over 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 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 fewer 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, or other methods to reduce the number of unstable terminal groups. Fluorine gas treatment is preferred because it has excellent treatment efficiency and converts some or all of the unstable terminal groups to —CF3, resulting in stable terminal groups. The use of a fluororesin with a reduced number of unstable terminal groups is preferred because it reduces the electrostatic dissipation factor and reduces electrical signal loss.

[0064] The number of unstable terminal groups is not particularly limited, but is preferably 10 or more when the main chain carbon number of the fluororesin is 10. 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 functional groups such as -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), hydroxyl groups (such as -CHOH), -CONH, -COOR (such as R = CH), -CFH, and -OCOO-R (such as normal propyl carbonate).

[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 with 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 the base spectrum, which is completely fluorinated and has no functional groups. 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. N=I×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 FT-IR measurement data of low molecular weight model compounds.

[0068] [Table 1]

[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 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 can also be used. Copper is preferably used from the viewpoints of conductivity and circuit processability. 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. Among 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). A fluororesin-containing layer / metal laminate may be provided on one or both sides of layer (A).

[0077] (Manufacturing method) The method for producing 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 in 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. Thus, using a metal foil with high surface smoothness before bonding is important for achieving the object of the present invention. As a metal foil having an arithmetic mean surface roughness Sa of 0.04 μm or less, a commercially available product can be used, such as 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 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 metal foil, the metal foil will deform due to 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 adhesiveness, thereby enabling adhesion at temperatures below the melting point of the fluororesin by 20°C, for example, 120°C to 280°C. By laminating a metal foil under appropriate conditions to the fluororesin film obtained by this method, 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; and 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. Vinyl acetate and glycidyl methacrylate are particularly preferred.

[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. Typically, the discharge rate is 50 to 1500 W·min / m 2 , preferably 70W·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. The degree of surface modification of the fluororesin film is such that the oxygen content 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, considering that heat applied during lamination with a metal foil can deactivate oxygen elements on the surface and reduce adhesive strength. There is no particular upper limit, but considering the impact on productivity and other physical properties, it is preferably 25.0% or less. The nitrogen content is not particularly specified, but is preferably 0.1% or more. The thickness of a single 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 sides 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 because it can impart localized unevenness to the resin surface, thereby reducing the dynamic friction coefficient between the metal foil layer surface and the fluororesin-containing layer surface to 0.4 or less. That is, in addition to improving the adhesive strength, the dynamic friction coefficient can be reduced. This is preferable because it prevents poor winding when a long laminate is produced.

[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 between the glass transition temperature of the fluororesin minus 20° C. and the melting point, more preferably between the glass transition temperature of the fluororesin and the melting point minus 20° C., and even more preferably between the glass transition temperature of the fluororesin and the melting point 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 using 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 because 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. [Example]

[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 nickel filter made of multiple layers of #300 mesh or larger that had been ultrasonically cleaned was inserted between the screw and die. The extruder was heated at 360°C. 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 6 The resulting extrusion was carried out through a 1700 mm wide T-die, taken up on a metal cooling roll, and then wound around a winding 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) Using a similar process, 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. 6 The film using PFA (297 particles per film) is referred to as long roll film 2.

[0101] (Manufacturing method of long films 3 and 4) Next, both sides of the obtained long roll film 1 were subjected to surface treatment (a plasma discharge device). Nitrogen gas containing 0.50% by volume of vinyl acetate was passed between the discharge electrode and the roll-shaped ground electrode of the plasma discharge device, and the film was continuously passed along the roll-shaped ground electrode at a discharge rate of 265 W·min / m. 2 The surface-treated long film 3 was wound into a roll. The film was slit into a width of 500 mm to obtain long film 4.

[0102] (Manufacturing method of long films 5 and 6) Next, both sides of the obtained long roll film 2 were subjected to surface treatment (a plasma discharge device). Nitrogen gas containing 0.50% by volume of vinyl acetate was passed between the discharge electrode and the roll-shaped ground electrode of the plasma discharge device, and the film was continuously passed along the roll-shaped ground electrode at a discharge rate 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 obtain long film 6.

[0103] (Manufacturing method of 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) The obtained long roll film 1 was subjected to surface treatment on both sides (a plasma discharge device). He gas containing 0.5% CO2 by volume and 0.5% O2 by volume was flowed near the discharge electrode and roll-shaped ground electrode of the plasma discharge device. The film was passed continuously along the roll-shaped ground electrode, 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 520 mm wide 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.) were bonded together to obtain a laminate 21. During the bonding, the surface temperature (press temperature) of a 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 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 a 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 a long film 8 was used instead of the long film 2 and the pressing temperature was set to 260°C.

[0110] (Reference examples 1~3) Except for changing the pressing temperature as shown in Table 3, the same procedures as for the above-mentioned laminate 21 were carried out to obtain laminates 33 to 35.

[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 laminate 32 above, except that the pressing temperature was changed as shown in Table 3.

[0113] (Method for measuring and evaluating oxygen element ratio) The oxygen element ratio of the resin surface after surface treatment was measured using a scanning X-ray photoelectron spectrometer (XPS / ESCA) PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.) with 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 of the copper foil side at the adhesive surface between the metal foil and the fluororesin-containing layer after lamination) The adhesive surface between the metal layer and the fluororesin-containing layer was observed using a VK-X1000 laser microscope (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, the measurement of the adhesive surface between the metal layer and the fluororesin was performed as follows: The laminate was placed in the device with the fluororesin side facing up and the metal side facing down. The laser microscope is a device that applies laser light and performs surface analysis based on the reflected light. As the laser irradiation position is lowered, two reflection points are found on the laminate. The reflection from the top surface originates from the resin surface, and the reflection from the second layer originates from the adhesive surface between the metal layer and the fluororesin-containing layer. The reflection data from the second layer was analyzed to determine the arithmetic mean surface roughness Sa of the metal side of the adhesive surface between the metal layer and the fluororesin-containing layer. The measurement conditions are as follows: filter type is Gaussian, S filter is 2.5 μm, and L filter is 0.08 mm. In addition, the correction for Sa during analysis is performed as follows. Surface shape correction: Quadratic curve, waviness removal (strength: 5) Smoothing: Median, Size 3x3

[0115] (Increase in transmission loss compared to un-roughened copper foil) First, a printed circuit board was fabricated by forming a transmission line on one of the copper foil surfaces of a laminate consisting 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 and ideal values ​​was calculated and used as the rate of 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, which were then laminated on both sides of the prepreg so that the fluororesin surface was in contact with the prepreg, to obtain a copper foil layer / fluororesin-containing layer / prepreg / fluororesin-containing layer / copper foil layer laminate. A measurement sample was then prepared under pressing conditions of a temperature of 200°C, a time of 75 minutes, and a pressure of 3.0 MPa, and then cut to a width of 10 mm. Adhesive tape was attached to one side of the cut sample and attached to an aluminum plate. Then, using a precision universal testing machine Autograph AGS-X 100N (manufactured by Shimadzu Corporation), a 10 mm wide piece of copper foil was gripped and pulled in a direction 90° to the plane of the laminate at a speed of 50 mm per minute to measure the peel strength between the copper foil and the fluororesin-containing layer, 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 taken 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 carried out. 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 coefficient of dynamic friction.

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

[0119] [Table 2]

[0120] [Table 3]

[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. [Industrial Applicability]

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

[0123] 1: Fluorine film 2: Metal foil 21: Laminate 100, 101: Pressure roll 102: Fluorine film supply roll 103: Metal foil supply roll 104a to 104c: Transport rolls 105: Laminate winding 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 essentially comprising a metal layer and a fluororesin-containing layer adjacent to the metal layer, A laminate characterized in that the arithmetic mean surface roughness Sa of the metal side of the bonding surface between the metal layer and the fluororesin-containing layer is 0.05 μm or less.

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

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

4. 3. The laminate according to claim 1, wherein the surface of the fluororesin-containing layer has an oxygen element ratio of 1.35 atomic % or more when measured by a scanning X-ray photoelectron spectroscopy / analysis (XPS / ESCA) analyzer.

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

6. 3. The laminate according to claim 1 or 2, wherein the difference between the oxygen element ratio when the surface 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 1.0 atomic % or more.

7. 3. The laminate according to claim 1, wherein the coefficient of dynamic friction between the surface of the metal layer and the surface of the fluororesin-containing layer is 0.70 or less.

8. 3. The laminate according to claim 1, wherein when the surfaces of the fluororesin-containing layers of two laminates are adhered to each other at 200°C, the adhesive strength is greater than 30 N / m.

9. 3. The laminate according to claim 1, wherein the fluororesin-containing layer is a tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer or a tetrafluoroethylene / hexafluoropropylene copolymer.

10. The fluororesin-containing layer has an unstable terminal group content of 1×10 carbon atoms. ６ 3. The laminate according to claim 1, wherein each of the laminates is made of less than 10 fluororesin particles.

11. 3. The laminate according to claim 1, wherein the fluororesin-containing layer contains a fluororesin having a melt flow rate of 1 to 50 g / 10 min at 372° C. under a load of 49 N.

12. The fluororesin-containing layer is a film whose both sides have been surface-treated by plasma discharge treatment with nitrogen gas containing vinyl acetate, The metal layer uses copper foil with a surface roughness Rz of 1.5 μm or less.

3. The laminate according to claim 1, which is obtained by laminating these materials.

13. Further, it has a layer (A) other than the metal layer and the fluororesin film layer, 3. The laminate according to claim 1, wherein 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.

14. 3. The laminate according to claim 1, 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 producing the laminate according to claim 1 or 2, A method for producing a laminate, comprising a step of heat treating a fluororesin film and a metal foil in a roll-to-roll manner at a temperature of the melting point of the fluororesin minus 20°C or lower.

16. A method for producing the laminate according to claim 1 or 2, A method for producing a laminate, comprising a step of heat treating a fluororesin film and a metal foil at a temperature of 280°C or less in a roll-to-roll manner.

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

18. 16. The method for producing a laminate according to claim 15, wherein the difference between the oxygen element ratio when the surface state of one or both sides of the fluororesin film is measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) and the oxygen element ratio when the film 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 1.0 atomic % or more.

19. A circuit board comprising the laminate according to claim 1 or 2.

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