Fluororesin film, method for producing laminate, laminate, and method for producing circuit board

Abstract

To join a metal foil without using fusion or an adhesive.SOLUTION: The fluororesin film has a modified surface subjected to a vacuum plasma treatment in an oxygen-containing gas atmosphere on at least one surface of the film. When the modified surface is observed using time-of-flight secondary ion mass spectrometry, at least one of the mass-to-charge ratios 31, 41, 43, 51, 55, 59, and 77 of the positive secondary ion intensity or at least one of the mass-to-charge ratios 45, 59, 205, 217, and 229 of the negative secondary ion intensity is detected more than when the vacuum plasma treatment is not performed.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a fluororesin film, a method for manufacturing a laminate in which a fluororesin film and a metal foil are bonded together, a laminate manufactured by the laminate manufacturing method, and a method for manufacturing a circuit board using the laminate in which a fluororesin film and a metal foil are bonded together. [Background technology]

[0002] Fluororesin films have excellent chemical resistance and heat resistance and are therefore used in a wide range of industrial fields. For example, fluororesin films are widely used as lining materials for chemical equipment and insulating materials for electronic components. However, the surface of fluororesin films is highly hydrophobic, resulting in poor adhesion to other materials. Therefore, when bonding a fluororesin film to a metal foil, for example, the surface of the fluororesin film is typically melted and fused, or an adhesive is used. However, fusion or adhesive bonding results in significant signal transmission loss when the film is used in high-frequency applications such as high-frequency transmission lines and antenna circuit components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-110193 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, the present invention provides a fluororesin film that can be bonded to metal foil without using fusion or an adhesive, a method for manufacturing a laminate in which a fluororesin film and a metal foil are bonded, a laminate manufactured by the laminate manufacturing method, and a method for manufacturing a circuit board using a laminate in which a fluororesin film and a metal foil are bonded. [Means for solving the problem]

[0005] The fluororesin film of the present disclosure has a modified surface on at least one surface of the film that has been subjected to vacuum plasma treatment in an oxygen-containing gas atmosphere. When observed using time-of-flight secondary ion mass spectrometry (hereinafter referred to as TOF-SIMS), the modified surface exhibits a higher concentration of at least one of the positive secondary ion intensities with mass-to-charge ratios (hereinafter sometimes referred to as m / z) of 31, 41, 43, 51, 55, 59, and 77, or at least one of the negative secondary ion intensities with m / z of 45, 59, 205, 217, and 229, than in a surface that has not been subjected to the vacuum plasma treatment.

[0006] The fluororesin film of the present disclosure has a modified surface on at least one side of the film, in which the composition ratio of fluorine atoms to carbon atoms (hereinafter referred to as F / C) is 2.3 or less when measured using a scanning X-ray photoelectron spectroscopy analyzer (hereinafter referred to as ESCA / XPS).

[0007] The fluororesin film of the present disclosure has a modified surface provided on at least one surface of the film, which has a contact angle with water of less than 90° and 60° or more at room temperature and can be directly bonded to a metal foil at a temperature lower than the melting point.

[0008] The method for producing a laminate according to the present disclosure is a method for producing a laminate in which a fluororesin film and a metal foil are bonded together, and includes a surface modification step of performing a surface modification treatment to modify the surface of the fluororesin film by vacuum plasma treatment to produce the fluororesin film having the modified surface on the surface of the fluororesin film, and a bonding step of contacting the fluororesin film with a smooth surface of a metal foil having a smooth surface with a surface roughness Rz of 1.2 μm or less and pressing the smooth surface at a temperature lower than the melting point of the fluororesin film, thereby bonding the fluororesin film and the metal foil together without using fusion or an adhesive.

[0009] The laminate of the present disclosure is a laminate in which the above-mentioned fluororesin film and metal foil are bonded together, and no welding layer in which the fluororesin film is melted or any adhesive is provided between the fluororesin film and the metal foil, and the fluororesin film and the metal foil are directly bonded together via the modified surface, and the peel strength in the 90-degree direction between the fluororesin film and the metal foil is 0.8 N / cm or more.

[0010] The method for manufacturing a circuit board according to the present disclosure includes an etching step of removing by etching part or all of the metal foil from the laminate obtained by the above-described method for manufacturing a laminate, and a rejoining step that is carried out after the etching step and that joins a fluororesin film or metal foil having the modified surface different from the fluororesin film to the part of the laminate where the fluororesin film is exposed, without using fusion or an adhesive. [Brief explanation of the drawings]

[0011] [Figure 1] In one embodiment, S11 is a cross-sectional view schematically showing a fluororesin film having a modified surface, S12 is a cross-sectional view schematically showing a laminate in which a fluororesin film and a metal foil are bonded, and S13 is a cross-sectional view schematically showing a circuit board formed by removing a part of the metal foil from the laminate. [Figure 2] 1 shows a cross section of an example circuit board according to an embodiment, where S14 is a cross section that schematically shows a state before a laminate having a circuit pattern and a fluororesin film are bonded together, and S15 is a cross section that schematically shows a circuit board in which another fluororesin film is bonded to the laminate. [Figure 3] 1 shows a cross section of a circuit board of another example different from that of FIG. 2 according to an embodiment, in which S14 is a cross section that schematically shows a state before a laminate having a circuit pattern is bonded to another laminate having a circuit pattern, and S15 is a cross section that schematically shows a circuit board in which another laminate is bonded to the laminate. [Figure 4] FIG. 1 is a diagram showing the physical properties of PFA and PTFE used in a fluororesin film according to one embodiment. [Figure 5]FIG. 1 shows the F / C value of the modified surface of a fluororesin film, the contact angle of the modified surface, the E value in plasma treatment, the peel strength of the fluororesin film bonded to a metal foil, and the bonding conditions for the fluororesin film and the metal foil for an example and a comparative example according to one embodiment. [Figure 6] FIG. 10 is a diagram showing a comparison of the peak intensities of main positive and negative secondary ions obtained by time-of-flight secondary ion mass spectrometry for a fluororesin film according to one embodiment. [Figure 7] FIG. 10 is a diagram showing a comparison of the detection depth of main positive secondary ions by time-of-flight secondary ion mass spectrometry for a fluororesin film according to one embodiment. [Figure 8] FIG. 1 is a flow chart showing an example of a method for manufacturing a laminate according to an embodiment. [Figure 9] FIG. 1 is a diagram schematically illustrating an example of a vacuum plasma treatment machine used in the production of a fluororesin film according to one embodiment. [Figure 10] FIG. 1 shows the peel strength of a laminate according to one embodiment to which a metal foil was bonded several days after the surface modification process was performed, and the F / C value 1.5 years after the surface modification process was performed. [Figure 11] FIG. 10 is a diagram comparing transmission loss between a laminate according to an embodiment and a commercially available high-frequency substrate. [Figure 12] 1 is a flow chart showing an example of a method for manufacturing a circuit board according to an embodiment; [Figure 13] FIG. 1 is a diagram showing an example of a sample used in an experiment on re-bonding of a fluororesin film after etching a metal foil according to one embodiment. [Figure 14] FIG. 1 is a diagram showing the peel strength of each sample in an experiment on re-bonding of a fluororesin film after etching a metal foil, for one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a fluororesin film, a method for manufacturing a laminate, a laminate, a method for manufacturing a circuit board, and a circuit board according to embodiments will be described with reference to the drawings.

[0013] The fluororesin film 10 shown in FIG. 1 (S11) is a fluororesin film made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or polytetrafluoroethylene. The fluororesin film 10 is formed into a film shape by, for example, melt extrusion molding or skiving. In the following description, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer will sometimes be referred to as PFA, and polytetrafluoroethylene will sometimes be referred to as PTFE. The melting points, viscosities, continuous use temperatures, and relative dielectric constants of PFA and PTFE are as shown in FIG. 4.

[0014] The thickness of the fluororesin film 10 may be selected depending on the intended use, and is preferably approximately 100 μm or less for high-frequency transmission lines or antenna circuits, for example. As shown in Figure 4, the relative dielectric constant of the fluororesin film 10 is 2.1 or less in the low- to high-frequency range for both PFA and PTFE.

[0015] The fluororesin film 10 shown in FIG. 1 (S11) has a modified surface 11. The modified surface 11 is a surface of the fluororesin film 10 modified by, for example, vacuum plasma treatment. In this embodiment, the modified surface 11 may include not only the surface region of the fluororesin film 10 but also a region in the depth direction, i.e., the thickness direction of the fluororesin film 10. In this case, the modified surface 11 may also be referred to as a modified layer 11. Furthermore, the term "vacuum" in the "vacuum plasma treatment" of this embodiment does not mean a complete vacuum, but rather a state of reduced pressure below atmospheric pressure. The vacuum plasma treatment of this embodiment is performed in an atmosphere containing, for example, water vapor, Ar, N2, O2, CO2, HO, methyl alcohol, or other oxygen-containing gases, either alone or in combination. The modified surface 11 is provided on at least one side of the fluororesin film 10. In this embodiment, the modified surface 11 is provided on one side of the fluororesin film 10, but may be provided on both sides.

[0016] The modified surface 11 is a surface of the fluororesin film 10 that has been modified by vacuum plasma treatment in an oxygen-containing gas atmosphere, thereby changing the atomic ratio of fluorine atoms to carbon atoms as measured by a scanning X-ray photoelectron spectroscopy analyzer compared to an untreated surface. Here, the scanning X-ray photoelectron spectroscopy analyzer is generally referred to as XPS, which stands for X-ray Photoelectron Spectroscopy, or ESCA, which stands for Electron Spectroscopy for Chemical Analysis. In this specification, the scanning X-ray photoelectron spectroscopy analyzer is sometimes referred to as XPS. In the following description, the atomic ratio of fluorine atoms to carbon atoms is sometimes referred to as F / C.

[0017] 5 shows the experimental results for each example and comparative example of the fluororesin film 10. Of these, Examples 1 to 7 and Comparative Examples 1 to 4 are examples in which the fluororesin film 10 is made of PFA. In Examples 1 to 7 and Comparative Examples 1 to 4, the F / C of the modified surface 11 is set to be different. In Examples 8 and 9 and Comparative Example 5, the fluororesin film 10 is set to be different. In Examples 8 and 9 and Comparative Example 5, the F / C of the modified surface 11 is also set to be different.

[0018] In Figure 5, "F / C" indicates the F / C value measured by XPS for the modified surface 11 of each example and comparative example. In this case, in all of Examples 1 to 9, the F / C value of the modified surface 11 is 2.3 or less. In addition, in all of Examples 1 to 7, in which the fluororesin film 10 is made of PFA, the F / C value of the modified surface 11 is 0.5 or more. In all of Examples 8 and 9, in which the fluororesin film 10 is made of PTFE, the F / C value of the modified surface 11 is 1.5 or more.

[0019] That is, in Examples 1 to 7 in which the fluororesin film 10 was made of PFA, the F / C value of the modified surface 11 was 0.5 or more and 2.3 or less. In addition, in Examples 8 and 9 in which the fluororesin film 10 was made of PTFE, the F / C value of the modified surface 11 was 1.5 or more and 2.3 or less. Note that vacuum plasma treatment was not performed on Comparative Examples 1 and 5.

[0020] In FIG. 5, "contact angle (°)" indicates the contact angle of water with the modified surface 11 at room temperature of 25°C. In this case, in Examples 1 to 7 and Comparative Examples 1 to 4 made of PFA, the contact angle decreases as the F / C decreases. As shown in FIG. 5, in Examples 1 to 7, the contact angle of the modified surface 11 is less than 90° and not less than 60°. Meanwhile, the contact angle of Comparative Example 1, which was not surface-modified, is 95.5°, which is not less than 90°. Therefore, the contact angles of Examples 1 to 7 are smaller than the contact angle of PFA that was not surface-modified.

[0021] The inventors of the present application measured the peel strength between the fluororesin film 10 and the metal foil 20 in each example and comparative example. The laminate 30 was obtained by bonding the metal foil 20 to the modified surface 11 without using fusion or adhesive, as shown in (S12) of FIG. 1 . The peel strength was measured based on a 90-degree peel strength test in accordance with JIS-C-6481. The metal foil 20 can be, for example, a copper foil. In each example and comparative example, the fluororesin film used was a fluororesin film without adhesive functional groups, such as "Neoflon PFA" manufactured by Daikin Industries, Ltd. or "Naflon PTFE" manufactured by Nichias Corporation. The metal foil 20 was "CD-T9DA-SV" manufactured by Fukuda Metal Foil Co., Ltd. This metal foil 20 had a nominal thickness of 10 μm and a smooth surface 21 with a surface roughness Rz of 1.2 μm or less, e.g., 1.2 μm or 0.85 μm. The smooth surface 21 is the surface that comes into direct contact with and is bonded to the modified surface 11 of the fluororesin film 10 .

[0022] In this embodiment, the metal foil 20 is not limited to copper foil. It is also possible to use a tough-pitch rolled copper foil, an oxygen-free rolled copper foil, an electrolytic copper foil, or a high-strength copper alloy foil. The metal foil 20 may also be a highly conductive metal foil whose main component is aluminum, a copper or aluminum alloy, stainless steel, or a 42 alloy, other than copper. The thickness of the metal foil 20 is not particularly limited and may be selected depending on the purpose. However, for high-frequency applications, a thickness of 18 μm or less is preferable. In particular, for fine patterns, a thickness of 12 μm or less can be used.

[0023] The fluororesin film 10 and the metal foil 20 are bonded to each other without fusion or adhesive by heating and pressing them at a temperature lower than the melting point of the fluororesin film 10 using a high-temperature, high-pressure press or the like. That is, in the laminate 30, no layer of molten fluororesin film 10 or adhesive layer is provided between the fluororesin film 10 and the metal foil 20, and the fluororesin film 10 and the metal foil 20 are bonded together by direct contact.

[0024] The bonding conditions for the fluororesin film 10 and the metal foil 20 in each example and comparative example are as shown in "Bonding Conditions" in Fig. 5. When the fluororesin film 10 is made of PFA, the bonding conditions are set to a heating temperature of 190°C and a pressurizing pressure of 10 MPa. In this case, the heating temperature of 190°C is lower than the melting point of PFA, which is 290°C to 310°C. When the fluororesin film 10 is made of PTFE, the bonding conditions are set to a heating temperature of 310°C and a pressurizing pressure of 10 MPa. In this case, the heating temperature of 310°C is also lower than the melting point of PFA, which is 327°C.

[0025] As shown in FIG. 5 , a certain correlation was observed between the F / C value of the surface of the fluororesin film 10, i.e., the modified surface 11, and the peel strength, regardless of whether the fluororesin film 10 was made of PFA or PTFE. According to the results shown in FIG. 5 , when the F / C value of the modified surface 11 of the fluororesin film 10 was reduced from the value in the untreated case, i.e., the value in Comparative Examples 1 and 5, adhesive strength was generated. Furthermore, when the F / C value of the modified surface 11 of the fluororesin film 10 was reduced, the peel strength increased to a predetermined value, for example, the values ​​in Examples 2 and 8. Further reduction of the F / C value subsequently reduced the peel strength. Note that in FIG. 5 , when the F / C values ​​are similar, as in Examples 1 and 8, for example, the peel strength of PTFE was lower than that of PFA. This is thought to be because a fragile layer exists near the surface of PTFE, and during peeling, peeling occurs at this fragile layer before the interface between PTFE and the metal foil.

[0026] The laminate 30 shown in Fig. 1 and other figures is manufactured by a manufacturing method according to this embodiment. As shown in Fig. 8, the manufacturing method for this laminate 30 includes a surface modification step S11 and a bonding step S12. The surface modification step S11 is a step of forming a modified surface 11 on the surface of the fluororesin film 10 by performing a surface modification treatment that modifies the surface of the fluororesin film 10 using a low-temperature vacuum plasma treatment. In this case, "low temperature" means a temperature below the melting point of the fluororesin film 10, which is the raw material.

[0027] In this embodiment, vacuum plasma treatment is a process in which a high DC or AC voltage is applied between electrodes in a vacuum or reduced-pressure environment, and the substrate is exposed to the glow discharge generated thereby, thereby modifying the surface of the substrate. The treatment gas used in the vacuum plasma treatment is preferably water vapor, Ar, N2, O2, CO2, HO, or an oxygen-containing gas such as methyl alcohol, either alone or in combination. The treatment pressure is not particularly limited, but is preferably in the range of 0.1 Pa to 1330 Pa, and more preferably in the range of 1 Pa to 133 Pa.

[0028] The surface modification step of step S11 can be performed using, for example, an internal electrode type vacuum plasma treatment machine 1 as shown in Fig. 8. The vacuum plasma treatment machine 1 performs low-temperature plasma treatment on a fluororesin film material F, which is the starting material, to obtain a fluororesin film 10 having a modified surface 11. As shown in Fig. 8, the vacuum plasma treatment machine 1 includes, for example, a treatment chamber 2, a supply unit 3a, a take-up unit 3c, a treatment roller 3b, a guide roller 4, an electrode 5, a high-frequency power supply 6, a vacuum valve 7a, a gas valve 7b, and a pressure gauge 8.

[0029] The treatment chamber 2 is an airtight chamber capable of reducing and increasing the pressure inside. The supply unit 3a, winding unit 3c, treatment roller 3b, guide roller 4, and electrode 5 are provided inside the treatment chamber 2. The supply unit 3a is configured by winding a fluororesin film material F into a roll before vacuum plasma treatment. The supply unit 3a has the function of supplying the fluororesin film material F to the treatment roller 3b side. The winding unit 3c has the function of winding up the fluororesin film 10 after vacuum plasma treatment.

[0030] The processing roller 3b is used to perform vacuum plasma treatment on the fluororesin film material F supplied from the supply unit 3a. The processing roller 3b is connected to earth (not shown). The guide roller 4 applies tension to the fluororesin film material F and the fluororesin film 10, thereby guiding the movement of the fluororesin film material F and the fluororesin film 10. The electrode 5 is a rod-shaped electrode and is arranged to surround the upper periphery of the processing roller 3b with a small gap therebetween. A high-frequency power source 6 is connected to the electrode 5. In this configuration, the space between the processing roller 3b and the electrode 5 functions as a processing region S for performing vacuum plasma treatment.

[0031] The vacuum valve 7a connects the inside of the processing chamber 2 to a vacuum pump (not shown). When the vacuum valve 7a is opened, the vacuum pump reduces the pressure inside the processing chamber 2. The gas valve 7b connects the inside of the processing chamber 2 to a gas supply source (not shown). When the gas valve 7b is opened, gas from the gas supply source is supplied to the vicinity of the electrode 5 inside the processing chamber 2. The gas supplied from the gas supply source into the processing chamber 2 can be, for example, an oxygen-containing gas such as H2O, alcohol, or CO2, either alone or mixed with N2, Ar gas, or the like. The pressure inside the processing chamber 2 is measured appropriately by a pressure gauge 8.

[0032] In this configuration, the fluororesin film material F wound in a roll is drawn out from the supply unit 3a and wound nearly one full turn around the processing roller 3b while being guided by a plurality of guide rollers 4 in the processing chamber 2. The fluororesin film material F passes through the processing region S between the processing roller 3b and the electrode 5, where a modified surface 11 is formed by vacuum plasma treatment. Thereafter, the fluororesin film 10 having the modified surface 11 formed by vacuum plasma treatment is wound up in the winding unit 3c while being guided by the guide rollers 4.

[0033] In this embodiment, for example, the pressure in the processing chamber 2 is 35 Pa, the gas supply rate is 20 cc / min, and the feed speed of the fluororesin film material F is 2 m / min. The processing intensity (E value) of the vacuum plasma processing is 50 W·min / m 2 ~2000W·min / m 2 In this case, the F / C value can be reduced by increasing the treatment intensity (E value) of the vacuum plasma treatment.

[0034] Here, functional groups such as COOH groups are added to the modified surface 11 of the fluororesin film 10 by vacuum plasma treatment, thereby imparting low-temperature bondability to the fluororesin film 10. When the metal foil 20 to be bonded is brought into contact with the surface of the fluororesin film 10 to which functional groups such as COOH groups have been added and then heated and pressed, a condensation reaction occurs at the interface between the fluororesin film 10 and the metal foil 20, which is presumably responsible for a strong direct bond between the two.

[0035] Here, the inventors of the present application used time-of-flight secondary ion mass spectrometry (hereinafter referred to as TOF-SIMS) to observe the modified surface 11 of each fluororesin film 10. As a result, as shown in Fig. 6, at least one of the mass-to-charge ratios (m / z) of positive secondary ion intensity of 31, 41, 43, 51, 55, 59, and 77, or at least one of the mass-to-charge ratios (m / z) of negative secondary ion intensity of 45, 59, 63, 205, 217, and 229 was detected in a larger amount from the surface layer of the modified surface 11 of the fluororesin film 10 that had been subjected to the vacuum plasma treatment, compared to an untreated product that had not been subjected to the vacuum plasma treatment.

[0036] In this case, at least one of the mass-to-charge ratios (m / z) of positive secondary ions of 31, 41, 43, 51, 55, 59, and 77 and at least one of the mass-to-charge ratios (m / z) of negative secondary ions of 45, 59, 63, 205, 217, and 229 were detected in greater quantities from the surface layer of the modified surface 11 of the fluororesin film 10 that had been subjected to the vacuum plasma treatment, compared to the untreated product that had not been subjected to the vacuum plasma treatment. In this embodiment, at least one of the mass-to-charge ratios (m / z) of positive secondary ions of 41, 43, 51, 55, 59, and 77 and the mass-to-charge ratios (m / z) of negative secondary ions of 45, 59, 63, 205, 217, and 229 were detected in greater quantities from the surface layer of the modified surface 11 of each of Examples 1 to 9 that had been subjected to the vacuum plasma treatment, compared to the untreated product that had not been subjected to the vacuum plasma treatment.

[0037] The present inventors also performed depth profile analysis of the modified surface 11 of the fluororesin film 10 using TOF-SIM to determine the depth of the modification, i.e., the depth of the modified layer. As a result, as shown in FIG. 7 , it was found that at least one of the mass-to-charge ratios (m / z) of 31, 41, 43, and 51 of the positive secondary ion intensity was detected within 20 nm from the surface of the modified surface 11. In the present embodiment, all of the mass-to-charge ratios (m / z) of 31, 41, 43, and 51 were detected within 20 nm from the surface of the modified surface 11. The fluororesin films 10 shown in FIGS. 6 and 7 are the same. When the fluororesin film 10 used in FIGS. 6 and 7 was bonded to a metal foil at a heating temperature of 190°C and a pressure of 12 MPa, a peel strength of 7.2 N / cm was obtained.

[0038] The bonding step of step S12 shown in Fig. 8 is a step of bonding the fluororesin film 10 and the metal foil 20 together without using fusion or adhesive by bringing the modified surface 11 of the fluororesin film 10 obtained through the surface modification step of step S11 into contact with the smooth surface 21 of a metal foil 20 having a surface roughness Rz of 1.2 µm or less and applying pressure. The bonding conditions in the bonding step of step S12 are as shown in "Bonding Conditions" in Fig. 5. The peel strengths for each example and each comparative example are also shown in Fig. 5.

[0039] Whether or not fusion bonding or adhesive is used in the laminate 30 can be determined as follows: That is, the fluororesin film 10 and the metal foil 20 are peeled off, and the interface between the fluororesin film 10 and the metal foil 20 is analyzed by the ATR method (Attenuated Total Reflection method) of FT-IR (Fourier Transform Infrared Spectroscopy) and measured by XPS (X-ray Photoelectron Spectroscopy), thereby making it possible to determine whether or not fusion bonding or adhesive is used.

[0040] The fluororesin film 10 according to this embodiment has a modified surface 11 on at least one surface thereof, which has been subjected to a vacuum plasma treatment in an oxygen-containing gas atmosphere. The present inventors discovered that, when the modified surface 11 is observed using TOF-SIMS as shown in Fig. 6, at least one of the mass-to-charge ratios (m / z) of positive secondary ions of 31, 41, 43, 51, 55, 59, and 77, or at least one of the m / z of negative secondary ions of 45, 59, 205, 217, and 229, is detected more frequently than in a case without vacuum plasma treatment. The present inventors then discovered that, with this fluororesin film 10, the modified surface 11 of the fluororesin film 10 can be bonded to a metal foil 20 without fusion or adhesive and at a temperature lower than the melting point. Therefore, according to this configuration, the modified surface 11 of the fluororesin film 10 and the metal foil 20 can be joined together at a temperature lower than the melting point without using fusion or adhesive.

[0041] Furthermore, the present inventors found that, when the modified surface 11 was observed using TOF-SIMS as shown in Fig. 6, at least one of the mass-to-charge ratios m / z of the positive secondary ion intensity of 31, 41, 43, and 51 was detected within 20 nm from the surface of the modified surface 11. The present inventors then found that by using such a fluororesin film 10, the modified surface 11 of the fluororesin film 10 and the metal foil 20 can be bonded together at a temperature lower than the melting point without using fusion or an adhesive. Therefore, according to this configuration, the modified surface 11 of the fluororesin film 10 and the metal foil 20 can be bonded together at a temperature lower than the melting point without using fusion or an adhesive.

[0042] It was confirmed that the fluororesin films 10 of Examples 1 to 9 above could achieve a peel strength, i.e., a bonding strength, of 0.8 N / cm or more with the metal foil 20 when the F / C value of the modified surface 11 was 2.3 or less. Thus, by setting the F / C value of the modified surface 11 to 2.3 or less, the fluororesin films 10 of Examples 1 to 9 could be bonded to the metal foil 20 without fusion or adhesive and at a temperature lower than the melting point.

[0043] That is, in the laminates 30 obtained by bonding the fluororesin film 10 and the metal foil 20 in Examples 1 to 9, no welding layer in which the fluororesin film 10 is melted or any adhesive is provided between the fluororesin film 10 and the metal foil 20, and the fluororesin film 10 and the metal foil 20 are directly bonded to each other. In this embodiment, "directly bondable" means that bonding is possible without fusion or adhesive. The peel strength in the 90-degree direction between the fluororesin film 10 and the metal foil 20 is 0.8 N / cm or more. In contrast, when the F / C value of the modified surface 11 of the fluororesin film 10 is 2.4 or more, as in Comparative Examples 1, 2, and 5, the peel strength between the fluororesin film 10 and the metal foil 20 is 0.2 N / cm or less, or no bondability is obtained.

[0044] Furthermore, when the fluororesin film 10 is made of PFA, it was confirmed that a high peel strength of 1.0 N / cm or more can be obtained between the fluororesin film 10 and the metal foil 20 by setting the F / C value of the modified surface 11 to 0.5 or more, as shown in Examples 1 to 7. Furthermore, when the fluororesin film 10 is made of PTFE, it was confirmed that a high peel strength of 0.8 N / cm or more can be obtained between the fluororesin film 10 and the metal foil 20 by setting the F / C value of the modified surface 11 to 1.5 or more, as shown in Examples 8 and 9.

[0045] Furthermore, research by the inventors of the present application has confirmed that the good bonding properties of the fluororesin film 10 continue for a long period of time, starting immediately after the vacuum plasma treatment. In Figure 10, the fluororesin film 10 that has not been subjected to the vacuum plasma treatment and has not been provided with the modified surface 11 is shown as an "untreated product," and the fluororesin film 10 that has been subjected to the vacuum plasma treatment and has been provided with the modified surface 11 is shown as a "treated product."

[0046] Figure 10 shows the results of measuring the F / C value of an untreated product, the F / C value of a treated product several days after vacuum plasma treatment, and the F / C value of a treated product 1.5 years after vacuum plasma treatment. According to the results in Figure 10, the F / C value of untreated fluororesin film 10 is 2.59. On the other hand, the F / C value of fluororesin film 10 several days after vacuum plasma treatment is 0.71.

[0047] Thus, it was confirmed that functional groups were formed by the vacuum plasma treatment, since the F / C value of the fluororesin film 10 several days after the vacuum plasma treatment was lower than that of the untreated fluororesin film 10. When the fluororesin film 10 several days after the vacuum plasma treatment was bonded to the above-mentioned metal foil 20 under bonding conditions of a heating temperature of 210°C and a pressure of 10 MPa, a peel strength of 8.1 N / cm was obtained.

[0048] Furthermore, the F / C value was 0.87 1.5 years after the vacuum plasma treatment. This result confirmed that the F / C value had not returned to that of the untreated product even 1.5 years after the vacuum plasma treatment, and functional groups remained. Therefore, it is presumed that the adhesive strength with the metal foil 20 remains even for the fluororesin film 10 1.5 years after the vacuum plasma treatment.

[0049] It is generally known that the effective period of adhesive ability of a fluororesin film that has been subjected to corona discharge or plasma treatment is several hours to several days. In contrast, with the fluororesin film 10 of this configuration, it was found that the bonding step of step S12 can be carried out even one month or more after the surface modification step of step S11 has been carried out, meaning that the adhesive ability remains. Therefore, with the method for producing the laminate 30 according to this embodiment, the bonding step can be carried out one month or more after the surface modification step has been carried out.

[0050] The inventors of the present application have found that there is a very high correlation between the F / C value and the water contact angle of the modified surface 11, as shown in Fig. 5. Furthermore, as shown in Fig. 5, the water contact angle corresponding to an F / C range of 2.3 to 0.5 corresponds to approximately 90° to 60°. That is, in a fluororesin film 10 having a modified surface 11, if the contact angle of the modified surface 11 with water at room temperature is less than 90° and equal to or greater than 60°, it can be estimated that the F / C value is within the range of 2.3 to 0.5. Furthermore, such a fluororesin film 10 can be directly bonded to a metal foil 20 at a temperature lower than the melting point.

[0051] That is, the F / C value must be observed using XPS, which requires a lot of money and time. On the other hand, the water contact angle can be easily and quickly observed at the production site using simple equipment such as a microscope, making it possible to quickly evaluate the quality of the modified surface 11 of the fluororesin film 10 at low cost. As a result, when the fluororesin film 10 having the modified surface 11 is put into practical use, quality control during the manufacturing process can be carried out easily and efficiently, which is expected to reduce the overall production cost of the fluororesin film 10 and stabilize the product quality.

[0052] As described above, the method for producing a laminate according to this embodiment includes a surface modification step and a bonding step. The surface modification step is a step of performing a surface modification treatment to modify the surface of the fluororesin film 10 by vacuum plasma treatment, thereby obtaining a fluororesin film 10 having a modified surface 11 on the surface of the fluororesin film 10. The bonding step is a step of bringing the fluororesin film 10 having the modified surface 11 into contact with the smooth surface 21 of a metal foil 20 having a surface roughness Rz of 1.2 μm or less, and applying pressure to bond the fluororesin film 10 and the metal foil 20 together without using fusion or an adhesive.

[0053] This allows the fluororesin film 10 and the metal foil 20 to be bonded together without fusion or adhesive, thereby reducing the transmission loss of the laminate 30 obtained by bonding the fluororesin film 10 and the metal foil 20 together.

[0054] Furthermore, according to the laminate manufacturing method of this embodiment, bonding can be performed immediately after the surface modification step, or it can be performed one month or more after the surface modification step. This eliminates the need to perform the bonding step of step S12 immediately after the surface modification step of step S11, and the surface modification step of step S11 and the bonding step of step S12 can be performed in different locations or at different times. As a result, for example, it becomes possible to store fluororesin films 10 that have undergone the surface modification step as inventory or to sell fluororesin films 10 that have undergone the surface modification step as a product.

[0055] The inventors of the present application also used a laminate manufactured by the laminate manufacturing method of the present disclosure as an example and a commercially available high-frequency board as a comparison example to measure transmission loss at several frequencies, including 90 GHz, for this example and comparative example using a microstrip line method. As shown in FIG. 11, the example of the present disclosure uses Neoflon PFA manufactured by Daikin Industries, Ltd., with a thickness of 100 μm, as the fluororesin. Furthermore, T9DA manufactured by Fukuda Metals Co., Ltd. is used as the metal foil. The example shown in FIG. 11 is a laminate in which the surface of a PFA film is subjected to vacuum plasma treatment so that the F / C value of the surface is set to a range of 2.3 to 0.5, and a copper foil (T9DA manufactured by Fukuda Metals Co., Ltd.) is bonded to the PFA film by heating and pressing it without using fusion or adhesive.

[0056] 11, the transmission loss of the Example at 90 GHz is -3.9 dB / 100 mm, which is smaller than -8 dB / 100 mm. In contrast, the transmission loss of the Example at 90 GHz is -11.8 dB / 100 mm, which is larger than -8 dB / 100 mm. Furthermore, at all frequencies of 60 GHz, 70 GHz, 80 GHz, and 90 GHz, the transmission loss of the Example is smaller than the transmission loss of the Comparative Example.

[0057] As described above, the laminate 30 of the present disclosure can achieve high adhesion between the fluororesin film 10 and the metal foil 20, and furthermore, the transmission loss at 90 GHz measured by the microstrip line method is suppressed to a value less than −8 dB / 100 mm for the laminate 30. In this way, signal transmission loss can be suppressed to a low level when used in high-frequency applications.

[0058] Such a laminate 30 can be used as a material for various electronic circuit boards, such as high-frequency transmission line boards, antenna circuit boards, and high-frequency sensor circuit boards. Since the laminate 30 does not use an adhesive, which increases the dielectric constant, it can achieve a significantly low dielectric constant, making it particularly suitable for use as a wiring board material for processing high-speed signals. It can be used as a material suitable for fifth-generation mobile communication services and even sixth-generation mobile communication services.

[0059] Furthermore, the method for manufacturing a circuit board according to the present disclosure includes, in addition to the surface modification step of step S11 and the bonding step of step S12 shown in the laminate manufacturing method of Fig. 8, an etching step of step S13 and re-bonding steps S14 and S15, as shown in Fig. 12. The etching step of step S13 is a step of removing a portion of the metal foil 20 by etching from the laminate 30 obtained by steps S11 and S12, as shown in (S13) of Fig. 1. This etching step results in the metal foil 20 remaining on the fluororesin film 10 forming a circuit pattern 201. The circuit pattern 201 constitutes an electrical circuit provided on the fluororesin film 10.

[0060] The re-bonding steps S14 and S15 are carried out after the etching step S13, and are steps of bonding, without using fusion or an adhesive, a fluororesin film having a modified surface other than the fluororesin film 10 of the laminate 30 that has been subjected to the etching step, or a metal foil similar to the metal foil 20 to the exposed portion of the laminate 30 where the fluororesin film 10 is exposed. This allows a circuit board to be obtained.

[0061] The rebonding steps S14 and S15 can be, for example, steps of bonding a fluororesin film 10a to the laminate 30, as shown in FIG. 2. In this case, the fluororesin film 10a has a modified surface 11 on one or both sides, as shown in (S14) of FIG. 2, similar to the fluororesin film 10. In the example of FIG. 2, the modified surface 11 of the fluororesin film 10a is arranged toward the portion of the laminate 30 where the fluororesin film 10 is exposed, i.e., toward the circuit pattern 201. The laminate 30 and the fluororesin film 10a are then heated below the melting points of the fluororesin films 10 and 10a and pressurized to be bonded to each other. This results in a circuit board 40a in which the circuit pattern 201 of the laminate 30 is covered with the fluororesin film 10a, as shown in (S15) of FIG. 2.

[0062] Furthermore, the re-bonding steps S14 and S15 can be steps of bonding a laminate 30b to the laminate 30, for example, as shown in Fig. 3. As shown in (S14) of Fig. 3, the laminate 30b is configured to include a fluororesin film 10b and a circuit pattern 201. The fluororesin film 10b has a modified surface 11 on one or both sides, similar to that of the fluororesin film 10. The laminate 30b has circuit patterns 201 on both sides of the fluororesin film 10b. The circuit pattern 201 of the laminate 30b is formed by bonding a metal foil 20 to the modified surface 11 and etching the metal foil 20, similar to that of the laminate 30.

[0063] In this case, in the example of Fig. 3, the surface of the fluororesin film 10b on which the circuit pattern 201 is provided is arranged facing the circuit pattern 201 side of the fluororesin film 10 of the laminate 30. The laminates 30, 30b are then heated below the melting points of the fluororesin films 10, 10b and pressurized to bond them together. As a result, as shown in (S15) of Fig. 3, a circuit board 40b can be obtained in which laminates 30, 30b each having a circuit pattern 201 are further laminated. As such, according to this embodiment, even if the modified surface 11 and the surface of the circuit pattern 201 are exposed to an etching solution, bonded circuit boards 40a, 40b can be obtained without using an adhesive or the like.

[0064] Here, the inventors prepared three samples A to C, as shown in FIG. 13, and measured the peel strength of each sample. Sample A is a laminate 30 obtained by bonding the fluororesin film 10 of Example 2 described above to a metal foil 20 by heating and pressure without using fusion or adhesives. Sample B is obtained by immersing Sample A in an etching solution such as ferric chloride solution, removing the metal foil 20 from Sample A by etching, and then bonding a fluororesin film 10 having a modified surface 11 to the resulting product by heating and pressure without using fusion or adhesives. Sample C is obtained by immersing Sample A in an etching solution such as ferric chloride solution, removing the metal foil 20 from Sample A by etching, and then bonding a metal foil 20a separate from the metal foil 20 by heating and pressure without using fusion or adhesives. Note that EP-XG manufactured by Nippon Denkai Co., Ltd. was used for the metal foils 20 and 20a. As shown in FIG. 14, the bonding conditions for samples A, B, and C were a heating temperature of 210° C. and a pressure of 10 MPa.

[0065] According to the results shown in Figure 14, the peel strength of sample A was 11.25 N / cm. The peel strength of sample B was 7.19 N / cm. That is, even after metal foil 20 was bonded to the modified surface 11 of fluororesin film 10 and then the metal foil 20 was removed by etching, another fluororesin film 10 having a modified surface 11 could be bonded to the modified surface 11 exposed by removing the metal foil 20.

[0066] The peel strength of sample C was 3.27. Thus, the modified surface 11 of the fluororesin film 10 still had enough adhesive strength to bond the metal foil 20a, even after the metal foil 20 was bonded and the surface was exposed to an etching solution. That is, it was found that strong functional groups were formed on the modified surface 11 of the fluororesin film 10, enough so that the functional groups remained even after the metal foil 20 was bonded and the surface was exposed to an etching solution.

[0067] 12, the method for manufacturing a circuit board according to this embodiment includes, in addition to a surface modification step in step S11 and a bonding step in step S12, an etching step in step S13 and re-bonding steps in steps S14 and S15. The etching step is a step of removing by etching a portion of the metal foil 20 bonded to the fluororesin film 10. The re-bonding step is performed after the etching step and is a step of bonding a metal foil 20a or a fluororesin film 10a having a modified surface 11 different from that of the fluororesin film 10 to the exposed portion of the laminate 30 without using fusion or an adhesive.

[0068] According to this method, after the metal foil 20 has been removed by etching, another metal foil 20a or a fluororesin film 10a can be bonded to the fluororesin film 10 without fusion or adhesive. As a result, it is possible to form a multi-layered circuit board, even a complex circuit, and the productivity of the circuit board can be improved.

[0069] (Other embodiments) The present invention is not limited to the embodiments described above and illustrated in the drawings, and can be modified, combined, or expanded as desired without departing from the spirit of the invention. The numerical values ​​shown in the above embodiments are merely examples, and the present invention is not limited to these.

[0070] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure. [Explanation of symbols]

[0071] 10, 10a... Fluororesin film, 11... Modified surface, 20, 20a... Metal foil, 21... Smooth surface, 30... Laminate, 40A, 40B... Circuit board

Claims

1. a film-like substrate having a modified surface on at least one side of which a vacuum plasma treatment has been performed in an oxygen-containing gas atmosphere; When the modified surface is observed using time-of-flight secondary ion mass spectrometry (hereinafter sometimes referred to as TOF-SIMS), at least one of the mass-to-charge ratios (hereinafter sometimes referred to as m / z) of positive secondary ions of 31, 41, 43, 51, 55, 59, and 77, or at least one of the m / z of negative secondary ions of 45, 59, 205, 217, and 229, is detected in a larger amount than in a surface not subjected to the vacuum plasma treatment. Fluoropolymer film.

2. When observed using the TOF-SIMS, at least one of the positive secondary ion intensities m / z of 31, 41, 43, and 51 is detected within 20 nm from the surface of the modified surface. The fluororesin film according to claim 1 .

3. a modified surface provided on at least one surface of a film, the modified surface having a composition ratio of fluorine atoms to carbon atoms (hereinafter, sometimes referred to as F / C) of 2.3 or less as measured by a scanning X-ray photoelectron spectroscopy analyzer (hereinafter, sometimes referred to as XPS); Fluoropolymer film.

4. It is composed of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (hereinafter referred to as PFA), The F / C value of the modified surface is 0.5 or more. The fluororesin film according to claim 3.

5. It is made of polytetrafluoroethylene (hereinafter referred to as PTFE), The F / C value of the modified surface is 1.5 or more. The fluororesin film according to claim 3.

6. a modified surface provided on at least one surface of the film, the modified surface having a contact angle with water of less than 90° and 60° or more at room temperature, and capable of directly bonding a metal foil at a temperature lower than the melting point; Fluoropolymer film.

7. A method for producing a laminate in which a fluororesin film and a metal foil are bonded together, comprising the steps of: a surface modification step of obtaining the fluororesin film according to any one of claims 1 to 4, in which the surface of the fluororesin film is modified by a vacuum plasma treatment to provide the modified surface on the surface of the fluororesin film; a joining step of bringing the fluororesin film into contact with a smooth surface of a metal foil having a surface roughness Rz of 1.2 μm or less, and pressing the fluororesin film at a temperature lower than the melting point of the fluororesin film, thereby joining the fluororesin film and the metal foil without using fusion or an adhesive. A method for manufacturing a laminate.

8. The bonding step is carried out one month or more after the surface modification step is carried out. A method for producing the laminate according to claim 7.

9. A laminate in which the fluororesin film according to any one of claims 1 to 6 and a metal foil are bonded together, a welding layer in which the fluororesin film is melted and an adhesive are not provided between the fluororesin film and the metal foil, and the fluororesin film and the metal foil are directly bonded via the modified surface, The peel strength in the 90-degree direction between the fluororesin film and the metal foil is 0.8 N / cm or more. Laminate.

10. A metal foil is bonded to the fluororesin film without using fusion or adhesive, The transmission loss at 90 GHz measured by the microstrip line method is less than -8 dB / 100 mm. The laminate according to claim 9.

11. an etching step of removing a part or all of the metal foil from the laminate obtained by the laminate manufacturing method according to claim 7; a re-bonding step, which is carried out after the etching step, of bonding a fluororesin film or a metal foil having the modified surface other than the fluororesin film to the exposed portion of the laminate without using fusion or an adhesive. A method for manufacturing a circuit board.

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