Laminate for electronic circuit boards and method for manufacturing the same

Abstract

To provide a laminate for an electronic circuit board, with which a flexible circuit board low in transmission loss of high frequency electric signals can be manufactured.SOLUTION: There is provided a laminate 10 for an electronic circuit board in which a metal foil 17 is laminated on one or both faces of a base material film 15 through an adhesive layer 16. The base material film contains, as a main component, syndiotactic polystyrene, is biaxially oriented, and has a melting point of 260-290°C, a glass transition temperature of 230-260°C, a dielectric constant at a frequency of 10 GHz of 2.6 or less, a dielectric tangent of 0.002 or less, and peel strength in peeling off the metal foil of 3 N / 10 mm or more through before and after a heating test at 260°C for 30 seconds.SELECTED DRAWING: Figure 1

Description

[[Technical Field]]

[0001] The present invention relates to a laminate for manufacturing a flexible circuit board. [[Background Art]]

[0002] For manufacturing flexible circuit boards and the like, a flexible copper clad laminate (FCCL) obtained by bonding and laminating copper foil on one side or both sides of a synthetic resin film is used. The transmission loss of an electrical signal consists of conductor loss and dielectric loss, and the higher the signal frequency, the greater the proportion of dielectric loss. In recent years, with the rapid progress of higher frequency of electrical signals, reduction of dielectric loss caused by materials in the vicinity of copper foil has become an issue. Patent Documents 1 to 5 describe FCCLs aimed at reducing dielectric loss, which are three-layer or five-layer copper-clad laminates composed of a synthetic resin film, an adhesive layer, and copper foil. Patent Document 6 describes a laminate for an electronic circuit board in which a metal layer is formed by plating on the surface of a syndiotactic polystyrene-based resin film. In addition, Patent Document 7 describes a film containing a syndiotactic polystyrene-based resin as a base film for a flat cable for efficiently transmitting high-frequency signals. [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2021-038281 [[Patent Document 2]] International Publication No. WO 2018 / 030026 [[Patent Document 3]] Japanese Unexamined Patent Application Publication No. 2017-121807 [[Patent Document 4]] Japanese Patent No. 6539404 [[Patent Document 5]] International Publication No. WO 2016 / 017473 [[Patent Document 6]] Japanese Unexamined Patent Application Publication No. 2015-002334 [[Patent Document 7]] International Publication No. 2019 / 049922 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] This invention has been made in consideration of the above circumstances, and aims to provide a laminate for electronic circuit boards that can manufacture flexible circuit boards with low transmission loss of high-frequency electrical signals. [Means for solving the problem]

[0005] The laminate for electronic circuit boards of the present invention is a laminate for electronic circuit boards in which a metal foil is laminated on one or both sides of a base film via an adhesive layer. The base film is mainly composed of syndiotactic polystyrene, is biaxially oriented, has a melting point of 260-290°C, a glass transition temperature of 230-260°C, a relative permittivity of 2.6 or less at a frequency of 10 GHz, and a dielectric loss tangent of 0.002 or less. Furthermore, the peel strength when peeling off the metal foil is 3 N / 10 mm or more before and after a heating test of 260°C for 30 seconds.

[0006] Here, the glass transition temperature Tg is a value measured by thermomechanical analysis (TMA). Specifically, it can be measured in accordance with JISC6481-1996. Peel strength refers to the 90-degree peel strength as specified in JISC5016-1994.

[0007] This configuration provides a laminate for electronic circuit boards that offers high strength and heat resistance, and enables the manufacture of flexible circuit boards with low transmission loss of high-frequency electrical signals.

[0008] Preferably, the base film is substantially composed of syndiotactic polystyrene and a styrene-based thermoplastic elastomer, and more preferably, the styrene-based thermoplastic elastomer is a polystyrene-poly(ethylene / butylene)-polystyrene copolymer. This makes it possible to increase the peel strength while keeping the transmission loss of the laminate for electronic circuit boards low.

[0009] Preferably, the laminate for the electronic circuit board has an S21 parameter, which indicates the transmission loss when the metal foil is pattern-etched to produce a microstrip line, that is -5 dB / 100 mm or more and 0 or less at 40 GHz.

[0010] Preferably, the maximum height roughness Rz at the interface between the metal foil and the adhesive layer is 2.0 μm or less. Here, the maximum height roughness Rz is the maximum height roughness specified in JIS B0601-2013. This makes it possible to further reduce the transmission loss of the flexible circuit board.

[0011] The present invention provides a method for manufacturing a laminate for electronic circuit boards, comprising the steps of: melting and kneading a resin composition mainly composed of syndiotactic polystyrene having a melting point of 260°C or higher to form a precursor film; biaxially stretching the precursor film and performing relaxation heat treatment at a temperature of 230°C or higher to produce a base film; forming an adhesive layer on at least one side of the base film; and laminating a metal foil on the adhesive layer. [Effects of the Invention]

[0012] According to the laminate for electronic circuit boards of the present invention, since a base film mainly composed of syndiotactic polystyrene is used as the substrate, a flexible circuit board with lower transmission loss even for high-frequency electrical signals can be manufactured at a lower cost compared to cases using liquid crystal polymers or polyimides. Furthermore, because syndiotactic polystyrene has low water absorption, the transmission characteristics of the flexible circuit board do not deteriorate easily even when used in a humid environment. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows the layer configuration of a laminate for an electronic circuit board according to one embodiment of the present invention. A: 5-layer structure, B: 3-layer structure. [Figure 2] This figure shows the measurement results of A: relative permittivity Dk and B: dielectric loss tangent Df for the substrate film used in the laminate for the electronic circuit board of the example. [Figure 3] It is a figure showing the measurement results of S21 parameters of laminates for electronic circuit boards in Examples and Comparative Examples. Mode for Carrying Out the Invention

[0014] Referring to FIG. 1A, the laminate 10 for an electronic circuit board according to the present embodiment has a 5-layer structure in which metal foils 17 are laminated on both surfaces of a base film 15 via adhesive layers 16. Referring to FIG. 1B, another laminate 11 for an electronic circuit board according to the present embodiment has a 3-layer structure in which a metal foil 17 is laminated on one surface of a base film 15 via an adhesive layer 16. A flexible circuit board can be manufactured by a subtractive method in which the metal foil 17 of the laminates 10 and 11 for electronic circuit boards is etched into a circuit pattern. Furthermore, a build-up substrate can also be manufactured by combining the laminates 10 and 11 for electronic circuit boards with other resin films, glass cloth, or the like. In the following, the characteristics, materials, and the like of each layer will be described with reference to the 5-layer structure laminate 10 for electronic circuit boards, but the description also applies to the 3-layer structure laminate 11 for electronic circuit boards.

[0015] The base film 15 contains syndiotactic polystyrene (SPS) as a main component and is biaxially oriented.

[0016] Biaxial orientation means that in the plane direction, polymers are oriented in two mutually different directions, for example, the extrusion direction (MD) of the film and the direction perpendicular thereto (TD). Required strength and heat resistance can be imparted by biaxially orienting the base film 15. Biaxial orientation can be achieved by biaxially stretching an unstretched precursor film.

[0017] SPS is a styrene-based polymer having a syndiotactic structure. A syndiotactic structure refers to a stereostructure in which phenyl groups or substituted phenyl groups, which are side chains, are alternately positioned in opposite directions relative to the main chain formed from carbon-carbon bonds. The degree of stereoregularity (tacticity) of SPS can be quantified by nuclear magnetic resonance (13C-NMR) spectroscopy using isotopic carbon. The tacticity of SPS-based resins measured by 13C-NMR can be indicated by the proportion of syndiotactic chains (such as racemic dyads) in which the stereoconfiguration of the constituent units is reversed, among chains consisting of several monomer units, for example, a dyad in the case of 2 units, a triad in the case of 3 units, or a pentad in the case of 5 units. In this embodiment, SPS is a styrene-based polymer having a syndiotacticity of 75% or more, preferably 85% or more, for racemic dyads, or 60% or more, preferably 75% or more, for racemic triads, or 30% or more, preferably 50% or more, for racemic pentads. Furthermore, the base film 15 may be made by mixing two or more different types of SPS.

[0018] Examples of styrene-based polymers used as SPS include polystyrene, poly(alkylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), poly(vinylbenzoic acid ester), hydrogenated polymers thereof, mixtures thereof, or copolymers mainly composed of these. Examples of poly(alkylstyrene) include poly(methylstyrene), poly(ethylstyrene), poly(isopropylstyrene), poly(tert-butylstyrene), poly(phenylstyrene), poly(vinylnaphthalene), and poly(vinylstyrene). Examples of poly(halogenated styrene) include poly(chlorostyrene), poly(bromostyrene), and poly(fluorostyrene). Examples of poly(halogenated alkylstyrene) include poly(chloromethylstyrene). Examples of poly(alkoxystyrene) include poly(methoxystyrene) and poly(ethoxystyrene). Polystyrene is preferred as the styrene-based polymer used as SPS.

[0019] The weight average molecular weight of SPS is 10,000 to 3,000,000, preferably 30,000 to 1,500,000, and particularly preferably 50,000 to 500,000.

[0020] The melting point of SPS is 260°C or higher. This makes it possible to increase the glass transition temperature Tg of the base film and improve the heat resistance of the laminate 10 for electronic circuit boards. On the other hand, there is no particular problem even if the melting point of SPS is high, but the melting point of SPS usually does not exceed 290°C.

[0021] Preferably, the base film 15 is substantially composed of SPS and a styrenic thermoplastic elastomer (TPS). Among thermoplastic elastomers (TPE), TPS is one whose hard segment is formed of polystyrene. The expression "substantially composed of SPS and TPS" means that even when a resin other than SPS and TPS is contained, the content thereof is within a range where the required transmission loss and heat resistance can be obtained for the laminate 10 for electronic circuit boards. Specifically, the sum of the proportion of SPS and the proportion of TPS in the total resin of the base film 15 is 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 100% by mass. When the base film 15 contains TPS, the peel strength can be increased while suppressing deterioration of the dielectric properties of the base film.

[0022] Various commercially available products can be used as TPS. Further, as TPS, hydrogenated products are preferably used. This improves the heat resistance of TPS and can prevent unexpected reactions from occurring in the melting and extrusion step of the base film raw material performed at high temperature.

[0023] As hydrogenated TPS, various types with different soft segments can be used, such as polystyrene-poly(ethylene / butylene)-polystyrene (TPS-SEBS), polystyrene-poly(ethylene / propylene)-polystyrene (TPS-SEPS), polystyrene-poly(ethylene-ethylene / propylene)-polystyrene (TPS-SEEPS), and polystyrene-poly(ethylene / propylene)-polystyrene (TPS-SEP). Among these, it is particularly preferable to use TPS-SEBS in which the soft segment consists of poly(ethylene / butylene). The TPS contained in the base film 15 may be a mixture of two or more different resins.

[0024] The amount of TPS blended is preferably such that the weight ratio of SPS(a) to TPS(b) is (a) / (b) = 97 / 3 to 60 / 40, and more preferably 95 / 5 to 70 / 30 or 90 / 10 to 80 / 20. This preferred blending ratio is the same even when TPS-SEBS is used as all or part of the TPS. If the amount of TPS blended is too low, the effect of improving the peel strength of the laminate 10 for electronic circuit boards will be small. On the other hand, if the amount of TPS blended is too high, the deterioration of the dielectric properties of the base film 15 will become significant.

[0025] The base film 15 may contain additives other than polymers, such as plasticizers, antioxidants, UV absorbers, light stabilizers, lubricants, antistatic agents, inorganic fillers, colorants, nucleating agents, and flame retardants.

[0026] The melting point of the base film 15 is 260°C or higher, regardless of whether the base film consists solely of SPS or substantially of SPS and TPS. This allows for a higher glass transition temperature (Tg) of the base film, thereby improving the heat resistance of the laminate 10 for the electronic circuit board. On the other hand, while a high melting point of the base film 15 does not pose any particular problem, base films with SPS as the main component typically do not exceed 290°C.

[0027] The glass transition temperature Tg of the base film 15 is 230°C or higher, preferably 240°C or higher. This increases the heat resistance of the laminate 10 for the electronic circuit board. On the other hand, a high glass transition temperature Tg does not pose any particular problem, but for base films mainly composed of SPS, it does not usually exceed 260°C. In this specification, the glass transition temperature Tg refers to the temperature measured by thermomechanical analysis (TMA). The glass transition temperature Tg can be measured by several methods, but the TMA method is superior as a practical indicator of heat resistance. Specifically, the glass transition temperature Tg by TMA can be determined from the TMA curve measured in accordance with JISC6481-1996. Although the SPS material itself has a low glass transition temperature Tg, the glass transition temperature Tg can be increased by biaxial orientation, thereby improving heat resistance.

[0028] The thermal expansion coefficient of the base film 15 is preferably 80 ppm / °C or less, and more preferably 70 ppm / °C or less, in both the MD and TD directions. While a lower thermal expansion coefficient is preferable, for base films mainly composed of SPS, it is usually not below 10 ppm / °C. Furthermore, the absolute value of the difference between the MD and TD thermal expansion coefficients is preferably 50 ppm / °C or less, and more preferably 20 ppm / °C or less.

[0029] The thickness of the base film 15 is preferably 10 to 100 μm, more preferably 12 to 50 μm. This allows for a good balance between the strength and flexibility of the laminate 10 for the electronic circuit board.

[0030] The relative permittivity Dk of the base film 15 is 2.6 or less at a frequency of 10 GHz. Furthermore, the dielectric loss tangent Df of the base film 15 is 0.002 or less, preferably 0.001 or less, at a frequency of 10 GHz. While all layers—the base film 15, adhesive layer 16, and metal foil 17—affect the transmission loss of the laminate 10 for electronic circuit boards, the low relative permittivity Dk and dielectric loss tangent Df of the base film 15 make it possible to keep the transmission loss of high-frequency electrical signals low even when using commercially available adhesives or copper foil. Note that for base films mainly composed of SPS, the relative permittivity is typically 2.0 or higher, and the dielectric loss tangent is typically 0.00001 or higher.

[0031] The relative permittivity Dk of the adhesive layer 16 is preferably 2.6 or less at a frequency of 10 GHz. Furthermore, the dielectric loss tangent Df of the adhesive layer is preferably 0.005 or less, more preferably 0.003 or less at a frequency of 10 GHz. Such an adhesive layer can be formed using commercially available adhesives such as AF-700 manufactured by Toagosei Co., Ltd. or SAFY manufactured by Nikkan Kogyo Co., Ltd.

[0032] The components of the adhesive layer 16 are not particularly limited as long as they have the required adhesive strength to the base film 15 and the metal foil 17, and various known adhesives, such as those described in Patent Documents 2, 3, or 5, can be used. The adhesive layer may be formed by coating the surface of the base film 15 or the metal foil 17 with a liquid adhesive, or it may be formed using an adhesive formed into a film (hereinafter referred to as "adhesive film"). Preferably, the adhesive layer is formed using an adhesive film.

[0033] The thickness of the adhesive layer 16 is preferably 3 to 50 μm, more preferably 5 to 30 μm. If the adhesive layer is too thin, sufficient adhesive performance may not be obtained. On the other hand, if the adhesive layer is too thick, solvent residue is likely to remain, which may cause foaming during the manufacturing process of the flexible circuit board.

[0034] The type of metal foil 17 is not particularly limited; for example, foils of copper, gold, aluminum, or alloys mainly composed of these can be used, and copper foil is preferred. Various commercially available copper foils can be used as the copper foil.

[0035] The smoother the interface between the metal foil 17 and the adhesive layer 16, the lower the transmission loss of the flexible circuit board can be. For this reason, it is preferable that the surface of the metal foil 17 that comes into contact with the adhesive layer 16 be smooth, and the maximum height roughness Rz of the surface of the metal foil is preferably 2.0 μm or less, more preferably 1.0 μm or less. Here, the maximum height roughness Rz is the maximum height roughness specified in JIS B0601-2013. On the other hand, the maximum height roughness Rz of the surface of the metal foil that comes into contact with the adhesive layer is preferably 0.2 μm or more. This ensures sufficient adhesive strength with the adhesive layer. The maximum height roughness Rz of the surface of the metal foil that comes into contact with the adhesive layer is the maximum height roughness Rz of the interface between the metal foil 17 and the adhesive layer 16 in the laminate 10 for electronic circuit boards.

[0036] The thickness of the metal foil 17 can be determined within a range that provides the required conductivity, depending on the type of metal. When the metal foil is copper foil, it is preferably 1 to 100 μm, more preferably 1 to 40 μm. A thickness within this range allows for a high level of both sufficient conductivity and the flexibility required for flexible circuit boards.

[0037] The laminate 10 for electronic circuit boards is required to have various performance characteristics, but particularly important ones include transmission loss, peel strength, heat resistance, and thermal shock resistance.

[0038] The transmission loss of the laminate 10 for electronic circuit boards can be evaluated by the S21 parameter obtained when a microstrip line is fabricated by pattern etching of the metal foil 17, preferably -5 dB / 100 mm or more and 0 or less at 40 GHz. A negative value for the S21 parameter indicates that there is transmission loss, and a smaller absolute value of the S21 parameter indicates smaller transmission loss.

[0039] The peel strength of the laminate 10 for electronic circuit boards is the peel strength when peeling the metal foil 17 from the laminate 10, and the 90-degree peel strength specified in JISC5016-1994 is 3N / 10mm or more, preferably 5N / 10mm or more, and more preferably 6N / 10mm or more.

[0040] The heat resistance of the laminate 10 for electronic circuit boards can be evaluated by the peel strength after a heating test. The laminate 10 for electronic circuit boards typically requires a heat resistance of 260°C or higher, considering the reflow process of flexible circuit boards. Specifically, the heating test can be performed by passing a test piece through a reflow oven and heating it at 260°C for 30 seconds. Alternatively, the heating at 260°C for 30 seconds may be repeated. The number of times the piece is passed through the reflow oven is at least once, preferably six or more times, and the peel strength after the heating test is 3N / 10mm or higher, preferably 5N / 10mm or higher, and more preferably 6N / 10mm or higher.

[0041] The thermal shock resistance of the laminate 10 for electronic circuit boards can be evaluated by the change in conductivity before and after a thermal shock (high-temperature immersion) test as specified in JISC5016-1994. Specifically, the thermal shock test involves subjecting the test specimen to a predetermined number of thermal cycles between 260°C and 20°C. The change in conductivity is preferably 10% or less before and after 100 thermal cycles. Details of the test method will be described later in the examples.

[0042] Next, the manufacturing method for the laminate 10 for electronic circuit boards according to this embodiment will be described.

[0043] The resin composition that will be the raw material for the base film 15 is melted and kneaded to form a precursor film. The precursor film can be formed by, for example, extrusion molding, calendering, or casting, and is preferably formed by extrusion molding.

[0044] The molded, unstretched precursor film is biaxially oriented, for example, by a simultaneous biaxial stretching method or a sequential biaxial stretching method, preferably by a simultaneous biaxial stretching method. The stretching ratio, stretching temperature, and stretching speed for biaxial stretching can be selected according to the thermal properties of the resin, the desired coefficient of thermal expansion, and the tensile fracture nominal strain. In this embodiment, the stretching ratio is preferably 2.0 to 5.0 times for both MD and TD, and more preferably 2.2 to 4.0 times. It is preferable that the stretching ratios for MD and TD are similar. Specifically, the difference between the stretching ratio of MD and the stretching ratio of TD is preferably 0.6 or less, more preferably 0.3 or less.

[0045] Biaxially stretched films are subjected to further relaxation heat treatment. This is to reduce the absolute value of the thermal shrinkage rate, raise the glass transition temperature (Tg), and improve the heat-resistant dimensional stability. The relaxation treatment is performed at a temperature below the melting point of the stretched film, preferably below (melting point - 10°C). The relaxation treatment temperature is 230°C or higher, preferably 240°C or higher. This allows the glass transition temperature (Tg) of the base film to be 230°C or higher. The relaxation ratio for both MD and TD is preferably 0.80 to 1.00 times, more preferably 0.85 to 1.00 times, and most preferably 0.90 to 0.98 times. It is preferable that the relaxation ratios for MD and TD are similar. Specifically, the difference between the relaxation ratio of MD and the relaxation ratio of TD is preferably 0.1 or less, more preferably 0.05 or less, and most preferably 0.02 or less.

[0046] Next, an adhesive layer 16 and a metal foil 17 are laminated onto the base film 15 manufactured as described above. In the five-layer laminate 10 for electronic circuit boards, the adhesive layer 16 and metal foil 17 are laminated on both sides of the base film 15. In the three-layer laminate 11 for electronic circuit boards, the adhesive layer 16 and metal foil 17 are laminated on only one side of the base film 15.

[0047] Since the SPS constituting the base film 15 has poor adhesive properties, the surface of the base film is first activated. The method of activation is not particularly limited, and methods such as corona discharge treatment, ozone oxidation treatment, UV-ozone treatment, plasma discharge treatment, and electron beam irradiation can be used. Preferably, the surface of the base film is treated with atmospheric pressure plasma, and more preferably, the surface of the base film is treated with atmospheric pressure nitrogen plasma. In base films mainly composed of SPS, atmospheric pressure plasma treatment, especially atmospheric pressure nitrogen plasma treatment, is preferable because it can suppress damage to the base material.

[0048] When using a liquid adhesive to form the adhesive layer 16, the adhesive is applied to both sides of the base film 15, the metal foil 17 is placed on top of the applied surface, and the entire assembly is sandwiched in a press or the like and the adhesive is cured by heating. Alternatively, the adhesive may be applied to one side of the base film 15, the metal foil 17 may be placed on top, the adhesive may be cured by heating while sandwiched in a press or the like, and then the adhesive layer 16 and metal foil 17 may be laminated on the other side in the same manner.

[0049] When an adhesive film is used to form the adhesive layer 16, the adhesive film and metal foil are layered on both sides of the base film 15, and the entire assembly is sandwiched in a press or the like, and the adhesive is cured by heating. Alternatively, the adhesive film and metal foil may be laminated on one side of the base film 15, and then the adhesive film and metal foil may be laminated on the other side, or the adhesive film may be laminated on both sides of the base film, and then the metal foil may be laminated on the adhesive films on both sides.

[0050] As a result, all the layers are integrated, and the laminate 10 for the electronic circuit board is manufactured. According to the manufacturing method of the laminate for the electronic circuit board of this embodiment, the base film and the metal foil are bonded together with an adhesive, so the manufacturing is easier compared to forming the conductive layer by plating. [Examples]

[0051] The laminate for electronic circuit boards according to the above embodiment and the laminate for electronic circuit boards according to the comparative example were fabricated and their performance was evaluated.

[0052] First, we prepared the base film SF-1 to be used in the example, and the base films SF-2 and SF-3 to be used in the comparative example.

[0053] (Base film SF-1) A full compound was prepared by pre-mixing 90% by mass of SPS (manufactured by Idemitsu Kosan Co., Ltd., Zarec, glass transition temperature 100°C, melting point 270°C) and 10% by mass of TPS-SEBS (manufactured by Kuraray Co., Ltd., Septon). This compound was melt-extruded at 320°C using an extruder equipped with a T-die at its tip, and then cooled to obtain a precursor film. This precursor film was simultaneously biaxially stretched at 110°C at a stretching speed of approximately 500% / min and a stretching ratio of 3.4 × 3.4 (MD × TD). Subsequently, a relaxation heat treatment was performed at 250°C with a relaxation ratio of 0.95 × 0.95 (MD × TD) to produce a base film with a thickness of 50 μm. The glass transition temperature Tg of this base film SF-1 was 240°C.

[0054] (Base film SF-2) SPS (Idemitsu Kosan Co., Ltd., Zarec, glass transition temperature 95°C, melting point 247°C) was melt-extruded at 320°C using an extruder equipped with a T-die at its tip, and then cooled to obtain a precursor film (approximately 500 μm thick). This precursor film was simultaneously biaxially stretched at 110°C at a stretching speed of 500% / min and a stretching ratio of 3.3 × 3.4 (MD × TD), and then subjected to relaxation heat treatment at 230°C with a relaxation ratio of 0.94 × 0.96 (MD × TD) to produce a base film with a thickness of 50 μm. The glass transition temperature Tg of this base film SF-2 was 200°C.

[0055] (Base film SF-3) A full compound was prepared by pre-mixing 80% by mass of SPS (manufactured by Idemitsu Kosan Co., Ltd., Zarec, glass transition temperature 95°C, melting point 247°C) and 20% by mass of TPS-SEEPS (manufactured by Kuraray Co., Ltd., Septon). This compound was melt-extruded at 320°C using an extruder equipped with a T-die at its tip, and then cooled to obtain a precursor film. This precursor film was simultaneously biaxially stretched at 110°C at a stretching speed of approximately 500% / min and a stretching ratio of 3.4 × 3.4 (MD × TD). Subsequently, a relaxation heat treatment was performed at 210°C with a relaxation ratio of 0.95 × 0.95 (MD × TD) to produce a base film with a thickness of 50 μm. The glass transition temperature Tg of this base film SF-3 was 200°C.

[0056] (Example 1) Both sides of the base film SF-1 were activated with atmospheric pressure nitrogen plasma at a line speed of 10 m / min and an output of 4 kW / width of 500 mm. Then, an adhesive film (Toagosei Co., Ltd., AF-700, thickness 5 μm) with one side of the separator film peeled off was placed on top and bonded using a vacuum press at 120°C × 0.4 MPa × 30 seconds. Next, the separator film on the opposite side of the adhesive film was peeled off, and a copper foil (maximum height roughness Rz = 1.3 μm on the adhesive film side surface, thickness 18 μm) was placed on top and bonded using a vacuum press at 120°C × 0.4 MPa × 30 seconds. Furthermore, it was pressed in a hot press at 180°C × 3 MPa × 30 minutes, and after releasing the press, it was left to stand in a heating oven and heated at 180°C × 30 minutes to produce the laminated structure (5-layer structure) for electronic circuit boards of Example 1.

[0057] (Example 2) An electronic circuit board laminate (5-layer structure) for Example 2 was fabricated using the same method as in Example 1, except that the copper foil used had a maximum height roughness Rz of 0.85 μm on the adhesive film side surface.

[0058] (Example 3) Using the same method as in Example 1, however, both sides of the base film were activated with a vacuum plasma at a line speed of 10 m / min and an output of 4 kW / width of 500 mm to produce the laminated structure (5-layer structure) for electronic circuit boards of Example 3.

[0059] (Comparative Example 1) A laminated structure (5 layers) for an electronic circuit board, Comparative Example 1, was fabricated using the same method as in Example 3, except that SF-2 was used as the base film and copper foil with a maximum height roughness Rz = 0.85 μm on the adhesive film side surface was used.

[0060] (Comparative Example 2) A laminated structure (5 layers) for an electronic circuit board, Comparative Example 2, was fabricated using the same method as in Example 3, except that SF-3 was used as the base film and copper foil with a maximum height roughness Rz = 0.85 μm on the adhesive film side surface was used.

[0061] (Comparative Example 3) A laminated structure (5-layer structure) for an electronic circuit board, Comparative Example 3, was fabricated using the same method as in Example 3, except that SF-3 was used as the base film.

[0062] (Comparative Example 4) A commercially available liquid crystal polymer (LCP) film (50 μm thick) was used as the base film, and the same adhesive film and copper foil as in Examples 1 and 3 were used to fabricate a laminate (5-layer structure) for an electronic circuit board as Comparative Example 4.

[0063] (Comparative Example 5) A commercially available polyimide (PI) film (50 μm thick) was used as the base film, and the same adhesive film and copper foil as in Examples 1 and 3 were used to fabricate a laminate (5-layer structure) for an electronic circuit board as Comparative Example 5.

[0064] Table 1 shows the relative permittivity Dk and dielectric loss tangent Df of the substrate film and adhesive layer. In Table 1, the dielectric properties of the substrate film were measured by the cavity resonator method specified in ASTM D2520. The dielectric properties of the adhesive layer are the manufacturer's catalog values. Figure 2 shows the relative permittivity Dk and dielectric loss tangent Df of the substrate film SF-1 used in the example in the region above 10 GHz. The Dk and Df in Figure 2 are the results of three measurements using the balanced disk resonator method.

[0065] [Table 1]

[0066] The transmission loss of the laminates for electronic circuit boards in the examples and comparative examples was evaluated. In addition, the peel strength, heat resistance, and thermal shock resistance were evaluated for several samples.

[0067] The transmission loss of each sample was evaluated by pattern etching copper foil to create a microstrip line with a line width of approximately 0.2 mm and a length of 100 mm, and measuring the S21 parameter at frequencies up to 40 GHz using a network analyzer (Keysight Technologies, E8363B) and probe (FormFactor, ACP40-GSG250) with a characteristic impedance of 50 Ω. A negative S21 parameter indicates transmission loss, and a smaller absolute value of the S21 parameter indicates lower transmission loss.

[0068] Peel strength was determined by cutting a fabricated laminate for electronic circuit boards into 20mm x 100mm sections, etching the copper foil to a width of 10mm, and then pulling the copper foil at a speed of 50mm / min in accordance with JISC5016-1994 to determine the peel strength in the 90-degree direction.

[0069] For heat resistance, a test specimen of the same shape as the one used in the peel test described above was passed through a reflow oven and heated at 270°C for 30 seconds, repeating this process six times. The peel strength was then measured. While heating tests are often performed at 260°C, this example evaluated the material under slightly more stringent conditions.

[0070] For thermal shock resistance, the test was conducted in accordance with JISC5016-1994, but with varying thermal cycling conditions, and the conductivity resistance was measured before and after the test. Specifically, the following was done: A daisy-chain substrate for thermal shock resistance testing of copper-plated through-holes was prepared, similar to Figure 5 in the JIS standard, and a voltage of 100V was applied to measure the conductivity resistance value between two predetermined points as the initial value. Next, the substrate was immersed in a 260°C silicone oil bath for 15 seconds, transferred within 15 seconds of removal, immersed in a 20°C cooling bath for 15 seconds, and transferred within 15 seconds of removal. This thermal cycle was repeated 100 times, and the conductivity resistance value was measured again in the same manner. The criterion for thermal shock resistance was that the conductivity resistance should not change by more than 10% due to the thermal cycle.

[0071] Table 2 shows the layer structure of each sample along with the evaluation results. Figure 3 shows the S21 parameters of several samples. All samples have a 5-layer structure, with the adhesive layer and copper foil being identical and laminated on both sides of the base film. In Table 2, the maximum height roughness Rz of the copper foil is the value for the surface on the adhesive layer side. The peel strength is the average of the results of 2 to 4 tests. For thermal shock resistance, a change in conductivity resistance before and after thermal cycling of less than 10% was considered "OK".

[0072] [Table 2]

[0073] From the S21 parameters shown in Table 2 and Figure 3, it was confirmed that the transmission losses of Examples 1 to 3 were all smaller than those of Comparative Examples 4 and 5. Furthermore, Example 2 and Comparative Example 2, which had the same maximum height roughness Rz on the adhesive film side surface of the copper foil, had almost the same transmission loss. However, as shown in Table 2, Comparative Example 2 had poor heat resistance and thermal shock resistance.

[0074] Table 2 shows that in Examples 1-3, the peel strength did not decrease even after the 270°C heating test. Comparing Example 1 and Example 3, Example 1 had a higher peel strength. This is thought to be because in Example 1, damage to the substrate film was suppressed by atmospheric pressure plasma treatment. In Comparative Examples 1-3, deformation due to the heating test was severe, and the peel strength after the heating test could not be measured. The failure mode in the peel test was material failure of the substrate film surface layer for all samples in the Examples and Comparative Examples.

[0075] Furthermore, in Examples 1-3, no deformation of the test specimens was observed even after the thermal shock test, and the rate of change in conductivity resistance was 10% or less. In Comparative Examples 1-3, deformation due to the thermal shock test (thermal cycling) was severe, and the conductivity resistance after the thermal shock test could not be measured.

[0076] The present invention is not limited to the embodiments or examples described above, and various modifications are possible within the scope of its technical concept. [Explanation of Symbols]

[0077] 10. Laminated structure for electronic circuit boards (5-layer structure) 11. Laminated structure for electronic circuit boards (3-layer structure) 15. Base film 16 Adhesive layer 17 Metal foil

Claims

1. A laminate for an electronic circuit board, in which a metal foil is laminated on one or both sides of a base film via an adhesive layer, The aforementioned substrate film is mainly composed of syndiotactic polystyrene, is biaxially oriented, has a melting point of 260 to 290°C, a glass transition temperature of 230 to 260°C, a relative permittivity of 2.6 or less at a frequency of 10 GHz, and a dielectric loss tangent of 0.002 or less. The metal foil has a maximum height roughness Rz of 2.0 μm or less at the interface with the adhesive layer. The peel strength when the aforementioned metal foil is peeled off is 3 N / 10 mm or more before and after the heating test at 260°C for 30 seconds. When the aforementioned metal foil is pattern-etched to produce a microstrip line, the S21 parameter is -5 dB / 100 mm or greater and 0 or less at 40 GHz. Laminate for electronic circuit boards.

2. The base film is substantially composed of syndiotactic polystyrene and a styrene-based thermoplastic elastomer. The laminate for electronic circuit boards according to claim 1.

3. The styrene-based thermoplastic elastomer is a polystyrene-poly(ethylene / butylene)-polystyrene copolymer. The laminate for electronic circuit boards according to claim 2.

4. A process of melting and kneading a resin composition mainly composed of syndiotactic polystyrene with a melting point of 260°C or higher to form a precursor film, A process to produce a base film by biaxially stretching the aforementioned precursor film and performing relaxation heat treatment at a temperature of 230°C or higher, The steps include forming an adhesive layer on at least one side of the base film, A step of laminating a metal foil having a maximum surface roughness Rz of 2.0 μm or less on one of its surfaces onto the adhesive layer such that the one surface is in contact with the adhesive layer, A method for manufacturing a laminate for an electronic circuit board having the following characteristics.

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