Laminate for electronic circuit boards and method for manufacturing the same

Abstract

To provide a laminate for electronic circuit boards with high adhesive strength between a film substrate and an adhesive layer. [Solution] A laminate for an electronic circuit board in which a metal foil 18 is laminated on one or both sides of a base film 15 via an adhesive layer 17, wherein the base film is mainly composed of syndiotactic polystyrene, is biaxially oriented, has a melting point of 230-290°C, a glass transition temperature of 180-260°C, a relative permittivity of 2.6 or less at a frequency of 10 GHz, a dielectric loss tangent of 0.002 or less, and the arithmetic mean roughness Ra of the surface 16 of the base film in contact with the adhesive layer is 0.5-1.0 μm or the maximum height roughness Rz is 4.0-7.0 μm.

Description

[Technical Field]

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

[0002] For producing flexible circuit boards and the like, a flexible copper clad laminate (FCCL) has been proposed which is formed by laminating a syndiotactic polystyrene (SPS) film, which is a synthetic resin film with low transmission loss, and a copper foil adhered to one or both sides of the SPS film via an adhesive layer. However, when an SPS film is used as a base film, there has been a problem that the adhesive strength between the SPS film and the adhesive layer is low. To address this problem, for example, Patent Document 1 describes activating the surface of an SPS film by treating it with atmospheric pressure nitrogen plasma. Regarding the adhesive layer, for example, Patent Document 2 describes an adhesive having improved adhesion to a base film made of a resin with low dielectric properties and low polarity such as SPS. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2024-072480 [Patent Document 2] International Publication No. WO 2018 / 030026 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laminate for an electronic circuit board in which the adhesive strength between an SPS film base material and an adhesive layer is improved. [Means for Solving the Problem]

[0005] The present invention relates to 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, wherein the base film is mainly composed of syndiotactic polystyrene, is biaxially oriented, has a melting point of 230 to 290°C, a glass transition temperature of 180 to 260°C, a relative permittivity of 2.6 or less at a frequency of 10 GHz, a dielectric loss tangent of 0.002 or less, and the arithmetic mean roughness Ra of the surface of the base film in contact with the adhesive layer is 0.5 to 1.0 μm or the maximum height roughness Rz is 4.0 to 7.0 μm.

[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 peel strength in the 90-degree direction as specified in JISC5016-1994. Arithmetic mean roughness Ra and maximum height roughness Rz are the arithmetic mean roughness and maximum height roughness as specified in JISB0601-2013.

[0007] 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.

[0008] 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.

[0009] Preferably, the maximum height roughness Rz of the surface of the metal foil that is in contact with the adhesive layer is 2.0 μm or less.

[0010] 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 230°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; roughening at least one side of the base film to roughen the arithmetic mean roughness Ra to 0.5 to 1.0 μm or the maximum height roughness Rz to 4.0 to 7.0 μm; forming an adhesive layer on the roughened surface; and laminating a metal foil on the adhesive layer.

[0011] Preferably, in the method for manufacturing the laminate for electronic circuit boards described above, the surface roughening treatment is performed by sandblasting. [Effects of the Invention]

[0012] According to the laminate for electronic circuit boards or the method for manufacturing the laminate for electronic circuit boards of the present invention, a laminate for electronic circuit boards can be obtained that has high heat resistance and can manufacture flexible circuit boards with low transmission loss of high-frequency electrical signals. Furthermore, by roughening the surface of the SPS base film on the side in contact with the adhesive layer, a laminate for electronic circuit boards with high adhesive strength between the base film and the adhesive layer can be obtained.

[0013] While common surface modification methods for polymer films, such as corona treatment and plasma treatment, are known to lose their surface modification effect over time, physical surface roughening treatments do not have this concern. Roughening the surface of SPS substrate films is an effective processing method for stably achieving high adhesive strength in copper-clad laminates using SPS films. [Brief explanation of the drawing]

[0014] [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 the S21 parameter of the laminated electronic circuit boards of the examples and comparative examples. [Modes for carrying out the invention]

[0015] Referring to Figure 1A, the laminate 10 for electronic circuit boards in this embodiment has a five-layer structure in which metal foil 18 is laminated on both sides of a base film 15 via an adhesive layer 17. Referring to Figure 1B, another laminate 11 for electronic circuit boards in this embodiment has a three-layer structure in which metal foil 18 is laminated on one side of a base film 15 via an adhesive layer 17. Flexible circuit boards can be manufactured by a subtractive method in which the metal foil 18 of the laminates 10 and 11 for electronic circuit boards is etched into a circuit pattern. Furthermore, build-up substrates can be manufactured by compounding the laminates 10 and 11 for electronic circuit boards with other resin films, glass cloths, etc. In the following, the characteristics and materials of each layer will be explained using the five-layer laminate 10 for electronic circuit boards as an example, but the explanation is also applicable to the three-layer laminate 11 for electronic circuit boards.

[0016] The base film 15 is mainly composed of syndiotactic polystyrene (SPS), is biaxially oriented, and has a roughened surface on the adhesive layer side.

[0017] Biaxial orientation means that, in the planar direction, the polymers are oriented in two different directions, for example, the extrusion direction of the film (MD) and the direction perpendicular to it (TD). By biaxially oriented the base film 15, the required strength and heat resistance can be imparted. Biaxial orientation can be achieved by biaxially stretching an unstretched precursor film.

[0018] The surface 15a of the base film 15 that is in contact with the adhesive layer 17 has an arithmetic mean roughness Ra of 0.5 to 1.0 μm or a maximum height roughness Rz of 4.0 to 7.0 μm, as specified in JIS B0601-2013. If the surface roughness expressed by these parameters is too small, the effect of improving adhesive strength will be small. On the other hand, if the surface roughness is too large, stress concentration may reduce the tensile strength of the film base material, or abrasive particles may remain, potentially causing adverse effects.

[0019] 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.

[0020] Examples of styrenic polymers as SPS include polystyrene, poly(alkylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), poly(vinyl benzoate), hydrogenated polymers of the foregoing, mixtures of the foregoing, and copolymers containing these as main components. Examples of poly(alkylstyrene) include poly(methylstyrene), poly(ethylstyrene), poly(isopropylstyrene), poly(tertiary butylstyrene), poly(phenylstyrene), poly(vinylnaphthalene), poly(vinylstyrene) and the like. Examples of poly(halogenated styrene) include poly(chlorostyrene), poly(bromostyrene), poly(fluorostyrene) and the like. Examples of poly(halogenated alkylstyrene) include poly(chloromethylstyrene) and the like. Examples of poly(alkoxystyrene) include poly(methoxystyrene), poly(ethoxystyrene) and the like. As the styrenic polymer for SPS, polystyrene is preferred.

[0021] The weight average molecular weight of SPS is 10,000 to 3,000,000, preferably 30,000 to 1,500,000, particularly preferably 50,000 to 500,000.

[0022] The melting point of SPS is 230°C or higher, preferably 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.

[0023] Preferably, the base film 15 consists substantially of SPS and a styrene-based thermoplastic elastomer (TPS). Among thermoplastic elastomers (TPE), TPE is one in which the hard segment is formed of polystyrene. The expression "consists substantially of SPS and TPS" means that even when a resin other than SPS and TPS is contained, the content thereof falls within a range where the required transmission loss and heat resistance can be obtained as the laminate 10 for an electronic circuit board. Specifically, a value obtained by adding the ratio of SPS and the ratio of TPS to 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.

[0024] Various commercially available products can be used as TPS. Further, as TPS, it is preferable to use a hydrogenated product. 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 a high temperature.

[0025] As the hydrogenated TPS, various products having 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 whose soft segment is formed of poly(ethylene / butylene). Note that the TPS contained in the base film 15 may be a mixture of two or more different types of resins.

[0026] 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.

[0027] 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.

[0028] The melting point of the base film 15 is 230°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.

[0029] The glass transition temperature Tg of the base film 15 is 180°C or higher, preferably 230°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.

[0030] 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.

[0031] 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.

[0032] 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 17, and metal foil 18—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.

[0033] The relative permittivity Dk of the adhesive layer 17 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.

[0034] The components of the adhesive layer 17 are not particularly limited as long as they have the required adhesive strength to the base film 15 and the metal foil 18. The adhesive layer may be formed by coating the surface of the base film 15 or the metal foil 18 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.

[0035] The thickness of the adhesive layer 17 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.

[0036] The type of metal foil 18 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.

[0037] The smoother the interface between the metal foil 18 and the adhesive layer 17, 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 18 that comes into contact with the adhesive layer 17 be smooth, and the maximum height roughness Rz of the metal foil surface 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 18 and the adhesive layer 17 in the laminate 10 for electronic circuit boards.

[0038] The thickness of the metal foil 18 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.

[0039] Various performance characteristics are required for the laminate 10 for electronic circuit boards, but important ones include transmission loss and peel strength.

[0040] 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 18. The S21 parameter is 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 for the S21 parameter indicates smaller transmission loss.

[0041] The peel strength of the laminate 10 for electronic circuit boards is the peel strength when peeling the metal foil 18 from the laminate 10, and the 90-degree peel strength specified in JISC5016-1994 is 3N / 10mm or more, preferably 5N / 10mm or more.

[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, increase 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 more preferably 230°C or higher, and even more 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] Both sides of the heat-treated film are roughened. The roughening is preferably performed by sandblasting. Sandblasting can be done either dry or wet. Wet sandblasting is a method in which an abrasive and water mixture is sprayed from a nozzle. The SPS resin used in this embodiment has high hardness, and the sandblasting process creates steep irregularities, which greatly improves the adhesive strength with the adhesive layer.

[0047] Surface roughening can be performed by embossing or sanding, but embossing does not easily create sufficiently large irregularities, and sanding does not allow for continuous processing, resulting in low productivity.

[0048] Furthermore, preferably, after the surface roughening treatment, the surface of the substrate film is activated using methods such as corona discharge treatment, ozone oxidation treatment, UV-ozone treatment, plasma discharge treatment, or electron beam irradiation.

[0049] Next, an adhesive layer 17 and a metal foil 18 are laminated onto the base film 15 manufactured as described above. In a five-layer laminate 10 for electronic circuit boards, the adhesive layer 17 and metal foil 18 are laminated on both sides of the base film 15. In a three-layer laminate 11 for electronic circuit boards, the adhesive layer 17 and metal foil 18 are laminated on only one side of the base film 15.

[0050] When using a liquid adhesive to form the adhesive layer 17, the adhesive is applied to both sides of the base film 15, the metal foil 18 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 18 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 17 and metal foil 18 may be laminated on the other side in the same manner.

[0051] When an adhesive film is used to form the adhesive layer 17, 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.

[0052] As a result, all the layers are integrated, and the laminate 10 for electronic circuit boards is manufactured. According to the manufacturing method for the laminate for electronic circuit boards of this embodiment, high adhesive strength can be obtained between the adhesive layer and the SPS substrate film by roughening the surface of the SPS substrate film. [Examples]

[0053] Laminated structures for electronic circuit boards were fabricated according to the examples and comparative examples, and their performance was evaluated.

[0054] All of the fabricated samples consisted of five layers, but in the example of the laminate for electronic circuit boards, only one side of the base film was roughened, and the transmission loss and peel strength of the roughened side were evaluated.

[0055] (Base film) 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, 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 film with a thickness of 50 μm. The glass transition temperature Tg of the relaxation heat-treated film was 240°C. Furthermore, the relative permittivity Dk and dielectric loss tangent Df of the relaxation heat-treated film were measured at 1 GHz and 10 GHz using the equilibrium disk resonator method. Dk was 2.4 and Df was 0.0004.

[0056] Films that had undergone relaxation heat treatment were used as base films, either after sandblasting and / or surface activation treatment, or without any treatment. Both dry and wet sandblasting were performed on one side of the film at a line speed of 10 m / min using 40 μm particles. Surface activation treatment was performed at a line speed of 10 m / min using atmospheric pressure nitrogen plasma or vacuum plasma with an output of 4 kW / width of 500 mm. Surface activation treatment was performed on both sides of the film.

[0057] (Example 1) A dry sandblasted film was used as the base film. An adhesive film (Toagosei Co., Ltd., AF-700, 5 μm thick) with one side of the separator film peeled off was placed on both sides of the base film 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 copper foil (maximum height roughness Rz = 0.85 μm on the adhesive film side surface, 18 μm thick) was placed on both sides 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 laminate for electronic circuit boards of Example 1.

[0058] (Example 2) Similar to Example 1, however, the laminate for electronic circuit boards of Example 2 was fabricated using a base film that had been dry-sandblasted and then activated with atmospheric pressure nitrogen plasma.

[0059] (Example 3) In the same manner as in Example 1, except that a wet-sandblasted substrate film was used to produce the laminate for electronic circuit boards of Example 3.

[0060] (Example 4) Similar to Example 1, however, the laminate for electronic circuit boards of Example 4 was fabricated using a base film that had been wet-sandblasted and then activated with atmospheric pressure nitrogen plasma.

[0061] (Comparative Example 1) A laminate for electronic circuit boards for Comparative Example 1 was fabricated in the same manner as in Example 1, except that the base film used was one that had not undergone sandblasting or activation treatment.

[0062] (Comparative Example 2) Similar to Comparative Example 1, however, a laminate for electronic circuit boards for Comparative Example 2 was fabricated using a substrate film that had been activated with atmospheric pressure nitrogen plasma.

[0063] (Comparative Example 3) Similar to Comparative Example 2, however, a copper foil with a maximum height roughness Rz of 1.3 μm on the adhesive film side surface was used to fabricate the laminate for the electronic circuit board of Comparative Example 3.

[0064] (Comparative Example 4) Similar to Comparative Example 3, however, a laminate for electronic circuit boards for Comparative Example 4 was fabricated using a base film that had been activated with vacuum plasma.

[0065] Transmission loss 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.

[0066] 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.

[0067] Table 1 shows the preparation conditions and evaluation results for each sample. The peel strength is the average of 2 to 4 test results. Figure 2 shows the S21 parameters for several samples. In Figure 2, the lines for Example 1 and Example 2 overlap almost entirely. Also, the line for Example 3 is slightly below the line for Example 4 (on the side with higher transmission loss).

[0068] [Table 1]

[0069] From the S21 parameters shown in Table 1 and Figure 2, it was found that in Examples 1 to 4, the transmission loss was sufficiently small even when the surface of the substrate film was roughened.

[0070] A comparison of Examples 1 and 3 with Comparative Examples 2 to 4 showed that roughening the surface of the base film resulted in an improvement in peel strength equivalent to that achieved by performing a surface activation treatment.

[0071] 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]

[0072] 10. Laminated structure for electronic circuit boards (5-layer structure) 11. Laminated structure for electronic circuit boards (3-layer structure) 15. Base film 16 Surface of the adhesive layer side of the base film 17 Adhesive layer 18 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 base film is mainly composed of syndiotactic polystyrene, is biaxially oriented, has a melting point of 230 to 290°C, a glass transition temperature of 180 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 arithmetic mean roughness Ra of the surface in contact with the adhesive layer of the base film is 0.5 to 1.0 μm, or the maximum height roughness Rz is 4.0 to 7.0 μm. Laminate for electronic circuit boards.

2. A process of melting and kneading a resin composition mainly composed of syndiotactic polystyrene with a melting point of 230°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, A step of roughening at least one side of the base film to an arithmetic mean roughness Ra of 0.5 to 1.0 μm or a maximum height roughness Rz of 4.0 to 7.0 μm, The step of forming an adhesive layer on the roughened surface, A step of laminating metal foil onto the adhesive layer, A method for manufacturing a laminate for an electronic circuit board having the following characteristics.

3. The aforementioned surface roughening treatment is performed by sandblasting. A method for manufacturing a laminate for an electronic circuit board according to claim 2.

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