Surface-treated copper foil, copper-clad laminate, and printed wiring board

Abstract

Provided is a surface-treated copper foil that has excellent adhesion between a resin substrate and the surface-treated copper foil, has low transmission loss, and can be used to manufacture a printed circuit board or the like with good laser workability. This surface-treated copper foil has, on at least one side, a roughened surface on which roughened particles have been formed, and measured physical values for the roughened surface fulfill the following (a), (b), and (c).　(a) The true reflectance of the roughened surface, measured using a spectrophotometer with a light source that emits 45° polarized light at a wavelength of 600 nm, and on condition that the incidence angle and the reflection angle are both 70°, is at least 0.20% and no greater than 0.90%.　(b) The Y value for the brightness of the roughened surface is at least 10.0 and no greater than 15.5.　(c) The Ssk of the roughened surface, measured using a laser microscope, is at least 0.30 and no greater than 0.80.

Description

Surface-treated copper foil, copper-clad laminates, and printed wiring boards

[0001] The present invention relates to a surface-treated copper foil that can be suitably used in the production of printed wiring boards and the like, and to a copper-clad laminate and a printed wiring board that use the surface-treated copper foil.

[0002] In recent years, electronic circuit boards have been required to transmit electrical signals at high speeds in order to accommodate improvements in information processing speeds of electronic devices and high-speed wireless communications, leading to the increasing use of high-frequency circuit boards. High-frequency circuit boards require reduced transmission loss to achieve high-speed electrical signal transmission. Methods for reducing transmission loss include lowering the dielectric constant and dielectric dissipation factor of resin substrates and reducing transmission loss in conductor circuit wiring (particularly copper foil). One method for reducing the dielectric constant and dielectric dissipation factor of resin substrates is to select a resin with a low dielectric constant and dielectric dissipation factor (e.g., liquid crystal polymer) as the resin substrate material. However, depending on the type of resin, it has been difficult to achieve sufficient chemical adhesion between the resin substrate and copper foil, even with the use of a coupling agent or the like. Another method for reducing transmission loss in copper foil involves reducing surface roughness using roughening particles or the like. However, reducing surface roughness has been problematic in that it has been difficult to achieve sufficient physical adhesion (anchor effect) between the resin substrate and copper foil.

[0003] As described above, there is a trade-off between the adhesion between a resin substrate and a copper foil and the transmission loss. Therefore, a conventional method has been to achieve adhesion between a resin substrate and a copper foil by using surface irregularities on the copper foil while reducing the dielectric constant and dielectric loss tangent of the resin substrate. For example, Patent Document 1 discloses a method of adjusting the surface roughness and lightness (brightness) of the copper foil to improve adhesion to a liquid crystal polymer film. Patent Document 2 also discloses a method of adjusting the height and aspect ratio of roughening particles on the copper foil surface to improve adhesion to a liquid crystal polymer film. However, while the techniques disclosed in Patent Documents 1 and 2 improve adhesion to a liquid crystal polymer film by increasing the surface irregularities of the copper foil, they do not sufficiently reduce transmission loss, and there is a risk that they will not be able to meet the recent demand for low transmission loss.

[0004] While reducing transmission loss and improving adhesion have traditionally been emphasized in high-frequency circuit boards, the miniaturization and thinning of electronic devices has led to a demand for highly integrated, compact, and high-density printed wiring boards, particularly for various electronic components used in mobile devices such as mobile phones. In such compact, high-density printed wiring boards, blind via holes are sometimes used for interlayer connections, and manufacturing processes for forming via holes by laser irradiation are becoming increasingly common. Because roughening particles are inevitably formed at the bottom of via holes, when blind via holes are formed by laser irradiation, resin derived from the resin substrate may remain at the bottom of the formed blind via holes. Residual resin may prevent sufficient conductivity even after plating and reduce connection reliability during interlayer connection, so minimal resin residue is preferable. Therefore, copper foils have been required to have the property of easily removing resin adhered to their surface from the surface by laser irradiation (hereinafter referred to as "laser processability"). Excellent laser processability of copper foils reduces the likelihood of resin derived from the resin substrate remaining at the bottom of blind via holes formed by laser irradiation. At the bottom of the bottomed via hole where the interlayer connection conductor is formed, the metal constituting the interlayer connection conductor is integrated with the copper foil and the roughening particles, making it difficult to clearly identify the surface of the copper foil or the interface of the roughening particles in the interlayer connection conductor portion of the printed wiring board.

[0005] In order to achieve both good adhesion between a resin substrate and copper foil and good laser processability, a method has been proposed in which copper foil is used that can suppress the residue of resin derived from the resin substrate (Patent Document 3).The technology disclosed in Patent Document 3 makes it possible to suppress the residue of resin derived from the resin substrate at the bottom of a blind via hole formed by laser irradiation by providing a blackening treatment layer with high laser absorption on the surface of the copper foil.

[0006] However, in the technology disclosed in Patent Document 3, a laser absorption layer or a blackening treatment layer with a large transmission loss is present at the interface between the resin substrate and the copper foil in an area other than the area where the blind via hole is formed, which may increase the transmission loss, and therefore may not be able to meet the low transmission loss that has been required in recent years.

[0007] JP 2005-219379 A International Publication No. 2012 / 020818 JP 11-284309 A

[0008] An object of the present invention is to provide a surface-treated copper foil and a copper-clad laminate that have excellent adhesion between a resin substrate and the surface-treated copper foil, have low transmission loss, and are suitable for producing printed wiring boards, etc. Another object of the present invention is to provide a printed wiring board that has excellent adhesion between a resin substrate and the surface-treated copper foil, have low transmission loss, and are suitable for laser processability.

[0009] A surface-treated copper foil according to one embodiment of the present invention is a surface-treated copper foil having a roughened surface on at least one side on which roughening particles are formed, and wherein physical property values ​​measured on the roughened surface satisfy the following (a), (b), and (c): (a) The specular reflectance of the roughened surface, measured using a spectrophotometer having a light source emitting 45° polarized light with a wavelength of 600 nm, at an incident angle and a reflection angle of 70°, is 0.20% or more and 0.90% or less; (b) The brightness Y value of the roughened surface is 10.0 or more and 15.5 or less; and (c) The Ssk of the roughened surface, measured using a laser microscope, is 0.30 or more and 0.80 or less.

[0010] According to another aspect of the present invention, there is provided a surface-treated copper foil having a roughened surface on at least one side thereof on which roughening particles are formed, wherein when the surface-treated copper foil is cut to expose a cross section perpendicular to the roughened surface, the physical properties of the roughened surface measured by observing the cross section with a scanning electron microscope satisfy the following (f), (g), and (h): (f) the average cross-sectional particle height h_ave of the roughening particles is 0.35 μm or more and 0.70 μm or less; (g) the standard deviation w_σ of the cross-sectional particle width of the roughening particles is 0.05 μm or more and 0.10 μm or less; and (h) the skewness h_sk of the cross-sectional particle height of the roughening particles is 0.80 or more and -2.50 × h_ave + 3.50 or less.

[0011] Furthermore, a copper-clad laminate according to yet another aspect of the present invention comprises the surface-treated copper foil according to the one aspect or another aspect described above, and a resin substrate bonded to the roughened surface of the surface-treated copper foil. Furthermore, a printed wiring board according to yet another aspect of the present invention comprises the copper-clad laminate according to the yet another aspect described above.

[0012] The surface-treated copper foil and copper-clad laminate of the present invention have excellent adhesion between the resin substrate and the surface-treated copper foil, and can be used to produce printed wiring boards, etc. that have low transmission loss and good laser processability. The printed wiring board of the present invention has excellent adhesion between the resin substrate and the surface-treated copper foil, and has low transmission loss and good laser processability.

[0013] 1 is a cross-sectional view illustrating the configuration of a copper-clad laminate according to an embodiment of the present invention; FIG. 2 is a cross-sectional view illustrating the configuration of a printed wiring board in which a surface-treated copper foil and a resin base material are integrally bent; FIG. 3 is a cross-sectional view illustrating the configuration of a printed wiring board constituting a stripline-type transmission line; FIG. 4 is a view illustrating a process for forming via holes, forming a circuit pattern, and forming an interlayer connector in a copper-clad laminate; FIG. 5 is a view illustrating a method for forming blind via holes in a double-sided copper-clad laminate by laser irradiation; FIG. 6 is a view illustrating a method for forming blind via holes in a single-sided copper-clad laminate by laser irradiation; FIG. 7 is a cross-sectional view of a via hole in a copper-clad laminate using a conventional surface-treated copper foil; FIG. 8 is a cross-sectional view of a via hole in a copper-clad laminate using the surface-treated copper foil of the first and second embodiments; FIG. 9 is an SEM image of a cross section of a surface-treated copper foil; FIG. 10 is a view illustrating a method for measuring the average value h_ave of the cross-sectional particle height, the standard deviation w_σ of the cross-sectional particle width, and the skewness h_sk of the cross-sectional particle height of roughening particles. 10A and 10B are diagrams illustrating a method for measuring the average value h_ave of cross-sectional particle heights, the standard deviation w_σ of cross-sectional particle widths, and the skewness h_sk of cross-sectional particle heights of roughening particles having special shapes.

[0014] An embodiment of the present invention will be described. Note that the embodiment described below is merely an example of the present invention. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0015] [Surface-Treated Copper Foil According to the First Embodiment] The surface-treated copper foil according to the first embodiment is a surface-treated copper foil having a roughened surface on at least one side on which roughening particles are formed, and the physical property values ​​measured on the roughened surface satisfy the following (A), (B), and (C): (A) The specular reflectance of the roughened surface, measured using a spectrophotometer having a light source emitting 45° polarized light with a wavelength of 600 nm, at an incident angle and a reflection angle of 70°, is 0.20% or more and 0.90% or less; (B) The brightness Y value of the roughened surface is 10.0 or more and 15.5 or less; (C) The Ssk of the roughened surface, measured using a laser microscope, is 0.30 or more and 0.80 or less.

[0016] The surface-treated copper foil according to the first embodiment has been subjected to a surface treatment such as a roughening treatment (e.g., copper plating) on ​​at least one of the front and back surfaces. The roughened surface has a roughened surface on which roughening particles are formed by the roughening treatment. The entire surface of the surface-treated copper foil may be a roughened surface, or a portion of the surface may be a roughened surface. When producing the surface-treated copper foil, the raw material copper foil is subjected to a roughening treatment. Examples of the raw material copper foil include electrolytic copper foil and rolled copper foil.

[0017] Furthermore, by using a surface-treated copper foil whose roughened surface satisfies all of the above-mentioned configurations (A), (B), and (C), it is possible to manufacture a printed wiring board or the like that has excellent adhesion between the resin substrate and the surface-treated copper foil, small transmission loss, and good laser processability. Furthermore, since the transmission loss is small even when a high-frequency signal is transmitted to the circuit of the manufactured printed wiring board, the surface-treated copper foil according to the first embodiment can be suitably used for manufacturing a printed wiring board used in a high-frequency band (a printed wiring board having a high-frequency circuit).

[0018] The surface-treated copper foil according to the first embodiment will be described in more detail. The mechanism by which the above-described effects are obtained is not entirely clear, but is presumed to be as follows.

[0019] (A) Specular Reflectance: First, because the specular reflectance is measured under geometric conditions similar to those of the surface, with both the incident angle and reflection angle at 70°, it allows for evaluation that is sensitive to the surface shape. Furthermore, by spectrally analyzing the incident light and using the reflectance of light with lower energy (longer wavelength) than the copper plasma frequency, light absorption by the copper is suppressed, and reflection from the copper surface becomes dominant. The reflection angle is largely dependent on the copper surface shape, and it is speculated that the specular reflection component, in particular, where the incident angle and reflection angle are the same, is influenced by the shape of the roughening particles formed on the surface. Therefore, we found that by using a spectrum with a wavelength of 600 nm, which is close to the average cross-sectional particle height h_ave of the roughening particles, evaluation that sensitively reflects the shape of the roughening particles is possible. Therefore, the higher the specular reflectance, the smaller the transmission loss, and the lower the specular reflectance, the stronger the adhesion between the resin substrate and the surface-treated copper foil.

[0020] (A) Y Value of Brightness The Y value of brightness, which is the reflectance at an incident angle of 45° and a reflection angle of 0° of white light, is presumed to be a value that sensitively reflects the shape of the roughening particles when the sample surface is viewed from above in a direction perpendicular to the sample surface, i.e., the particle width of the roughening particles, particularly since the reflection angle is 0°, which is perpendicular to the sample surface. The higher the Y value of brightness, the larger the particle width of the roughening particles, and therefore the greater the powder shedding resistance of the surface-treated copper foil (powder shedding is less likely to occur), and the lower the Y value of brightness, the better the laser processability (reduction of resin residue at the bottom of via holes).

[0021] (c) Ssk The Ssk of the roughened surface can be used to evaluate the bias in the distribution of particle heights of the roughened particles when observed from the surface. The larger the Ssk, the easier it is for the laser light to reach the base of the roughened particles, resulting in better laser processability (reduced resin residue at the base of the roughened particles), and the smaller the Ssk, the better the resistance to powder shedding.

[0022] Although these three items (a), (b), and (c) each have a trade-off relationship, it has been found that by controlling them within a predetermined range, copper foil exhibiting the above-mentioned effects can be obtained. One method for controlling these three items within a predetermined range is, for example, to perform a two-stage electroplating process using different electrolytic solutions during the roughening treatment and control the vertical temperature ratio in the electrolytic bath in the second stage of electroplating. By controlling the vertical temperature ratio in the electrolytic bath within a certain range, the growth rate of the roughening particles during the second stage of roughening treatment changes. Therefore, it is believed that roughening particles can be formed with a predetermined distribution of specular reflectance and brightness Y value, while having a biased distribution.

[0023] The specular reflectance of the roughened surface is measured using a spectrophotometer. Light from a light source is split into wavelengths of 600 nm, and the light is emitted at 45° polarized light, with both the incident angle and the reflection angle being 70°. The specular reflectance of the roughened surface is measured under these conditions. "45° polarized light" refers to placing a polarizer in front of the sample, with s-polarized light at 0° and p-polarized light at 90°, and emitting light from the light source with the polarizer at 45°. The specular reflectance of the roughened surface must be 0.20% or more and 0.90% or less, but the lower limit may be 0.26% or more. The upper limit may be 0.78% or less.

[0024] In this specification, the Y value of brightness refers to the Y value representing reflectance in the XYZ color system defined by the International Commission on Illumination (CIE). The method for measuring the Y value of brightness of a roughened surface is not particularly limited, but it can be measured, for example, using a colorimeter. For example, the Y value of brightness of the roughened surface can be measured by irradiating the roughened surface with white light under conditions of an incident angle of 45° and a reflection angle of 0°. The Y value of brightness of the roughened surface must be 10.0 or more and 15.5 or less, but the lower limit may be 11.0 or more. The upper limit may be 15.0 or less, or 14.5 or less.

[0025] In the surface-treated copper foil according to the first embodiment, the Ssk of the roughened surface measured using a laser microscope is 0.30 or more and 0.80 or less. The Ssk of the roughened surface is measured by irradiating the roughened surface with a laser of a specific wavelength using a laser microscope. An example of the wavelength of the irradiated laser is 404 nm.

[0026] The numerical range of Ssk of the roughened surface must be 0.30 or more and 0.80 or less, but the lower limit may be 0.35 or more, and the upper limit may be 0.70 or less.

[0027] In the surface-treated copper foil according to the first embodiment, a nickel coating may be formed on the roughened surface, and the amount of nickel (Ni) deposited by the nickel coating is 0.20 mg / dm 2 0.40mg / dm or more 2If the surface-treated copper foil has a nickel coating, the rust prevention and heat resistance of the surface-treated copper foil will be improved.

[0028] At least one of a nickel coating, a zinc coating, and a chromium coating may be laminated on the roughened surface. The coating formed by laminating at least one of a nickel coating, a zinc coating, and a chromium coating functions as a rust-proofing layer, thereby further enhancing the rust prevention of the surface-treated copper foil.

[0029] A chemical adhesive layer containing a chemical adhesive may be further laminated on the rust-proofing layer. The chemical adhesive layer can be formed by a chemical adhesive treatment using a chemical adhesive such as a silane coupling agent. The chemical adhesive layer further enhances the adhesion between the surface-treated copper foil and the resin substrate. Note that the rust-proofing layer and the chemical adhesive layer are very thin, so they do not affect the shape of the roughening particles on the roughened surface of the surface-treated copper foil.

[0030] Further, as a method for forming the chemical adhesive layer, for example, a method of applying a silane coupling agent solution directly or indirectly via a rust-proofing layer or the like to the roughened surface of the surface-treated copper foil, followed by air drying (natural drying) or heat drying can be mentioned. The applied silane coupling agent solution can be dried by evaporating water, but heat drying at a temperature of 50°C or higher and 180°C or lower is preferable because it promotes the reaction between the silane coupling agent and the copper foil.

[0031] The chemical adhesive layer preferably contains one or more silane coupling agents selected from the group consisting of epoxy silane, amino silane, vinyl silane, methacrylic silane, acrylic silane, styryl silane, ureido silane, mercapto silane, sulfide silane and isocyanate silane.These silane coupling agents have different effects depending on the interaction with the reactive functional group contained in the resin of the resin substrate, so it is necessary to select an appropriate one in consideration of its compatibility with the resin.

[0032] Specific examples of the silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, p-styryltrimethoxysilane, p-styryltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and bis(3-(triethoxysilyl)propyl)disulfide. However, other silane coupling agents can also be appropriately selected and used. These silane coupling agents may be used alone or in combination of two or more.

[0033] [Surface-Treated Copper Foil According to a Second Embodiment] The surface-treated copper foil according to a second embodiment is a surface-treated copper foil having, on at least one side thereof, a roughened surface on which roughening particles are formed, and when the surface-treated copper foil is cut to expose a cross section perpendicular to the roughened surface, the roughened surface has physical properties measured by observing the cross section with a scanning electron microscope that satisfy the following (F), (G), and (H): (F) The average cross-sectional particle height h_ave of the roughening particles is 0.35 μm or more and 0.70 μm or less. (G) The standard deviation w_σ of the cross-sectional particle width of the roughening particles is 0.05 μm or more and 0.10 μm or less. (H) The skewness h_sk of the cross-sectional particle height of the roughening particles is 0.80 or more and -2.50 × h_ave + 3.50 or less.

[0034] The surface-treated copper foil according to the second embodiment has a surface treatment, such as a roughening treatment (e.g., copper plating), applied to at least one of the front and back surfaces. The roughened surface has a roughened surface on which roughening particles are formed by the roughening treatment. The entire surface of the surface-treated copper foil may be a roughened surface, or a portion of the surface may be a roughened surface. When producing the surface-treated copper foil, the raw copper foil is subjected to a roughening treatment. Examples of the raw copper foil include electrolytic copper foil and rolled copper foil.

[0035] Furthermore, by using a surface-treated copper foil whose roughened surface satisfies the above-mentioned configurations (f), (g), and (h), it is possible to manufacture a printed wiring board or the like that has excellent adhesion between the resin substrate and the surface-treated copper foil, small transmission loss, and good laser processability. Furthermore, since the transmission loss is small even when a high-frequency signal is transmitted to the circuit of the manufactured printed wiring board, the surface-treated copper foil according to the second embodiment can be suitably used for manufacturing a printed wiring board used in a high-frequency band (a printed wiring board having a high-frequency circuit).

[0036] The surface-treated copper foil according to the second embodiment will be described in more detail. The above-mentioned effect can be achieved if the roughening particles on the roughened surface have a shape that satisfies the above-mentioned features (f), (g), and (h). While the mechanism is not entirely clear, it is presumed that the above-mentioned effect can be achieved by defining the ranges of parameters obtained from the distribution of the cross-sectional particle height and width of the roughening particles, which can only be accurately determined by observing a scanning electron microscope (SEM) image of the cross section of the surface-treated copper foil.

[0037] More specifically, the roughening particles have a cross-sectional particle height average value h_ave of 0.35 μm or more and 0.70 μm or less, and the larger the cross-sectional particle height average value h_ave of the roughening particles, the better the adhesion between the resin substrate and the surface-treated copper foil, and the smaller the cross-sectional particle height average value h_ave of the roughening particles, the smaller the transmission loss. Furthermore, the roughening particles have a cross-sectional particle width standard deviation w_σ of 0.05 μm or more and 0.10 μm or less, and the larger the cross-sectional particle width standard deviation w_σ of the roughening particles, the better the adhesion between the resin substrate and the surface-treated copper foil, and the smaller the cross-sectional particle width standard deviation w_σ of the roughening particles, the better the laser processability (reduction of resin residue at the bottom of a via hole).

[0038] Furthermore, the skewness h_sk of the cross-sectional particle height of the roughening particle is 0.80 or more and -2.50 × h_ave + 3.50 or less, and the larger the skewness h_sk of the cross-sectional particle height of the roughening particle, the better the laser processability (suppression of resin remaining at the base of the roughening particle), and the smaller the skewness h_sk of the cross-sectional particle height of the roughening particle, the better the powder shedding resistance. Note that "h_ave" in "0.80 or more and -2.50 × h_ave + 3.50 or less" is the average value h_ave of the cross-sectional particle height of the roughening particle.

[0039] Although these three items (F), (G), and (H) each have a trade-off relationship, it has been found that controlling them within a predetermined range can produce copper foil with the above-mentioned effects. One method for controlling these three items within a predetermined range is, for example, performing a two-stage electroplating process using different electrolytic solutions during the roughening treatment and controlling the vertical flow rate ratio of the electrolytic solution in the electrolytic bath in the second stage of electroplating. By controlling the vertical flow rate ratio of the electrolytic solution in the electrolytic bath within a certain range, it is expected that a height distribution will occur in the flow rate of the electrolytic solution near the cathode during the second stage of roughening treatment, which will affect the growth rate of the roughening particles. This will change the growth rate of the roughening particles during the second stage of roughening treatment. Therefore, while the average value h_ave of the cross-sectional particle height of the roughening particles and the standard deviation w_σ of the cross-sectional particle width of the roughening particles are within the above-mentioned predetermined range, a certain bias will occur in the distribution of the cross-sectional particle height of the roughening particles, and it is believed that roughening particles can be formed in which the skewness h_sk of the cross-sectional particle height of the roughening particles is within the above-mentioned predetermined range.

[0040] The cross-sectional particle height of the roughening particles in the surface-treated copper foil according to the second embodiment is the length of a specific roughening particle in the direction in which the roughening particle protrudes from the roughened surface of the surface-treated copper foil. The average cross-sectional particle height of the roughening particles must be 0.35 μm or more and 0.70 μm or less, but the lower limit may be 0.40 μm or more. The upper limit may be 0.60 μm or less.

[0041] The cross-sectional particle width of the roughening particle in the surface-treated copper foil according to the second embodiment is the length of a specific roughening particle in a direction perpendicular to the direction in which the roughening particle protrudes from the roughened surface of the surface-treated copper foil. The standard deviation of the cross-sectional particle width of the roughening particle must be 0.05 μm or more and 0.10 μm or less, but the lower limit may be 0.06 μm or more. The upper limit may be 0.09 μm or less.

[0042] At least one of a nickel coating, a zinc coating, and a chromium coating may be laminated on the roughened surface. The coating formed by laminating at least one of a nickel coating, a zinc coating, and a chromium coating functions as a rust-proofing layer, thereby further enhancing the rust prevention of the surface-treated copper foil.

[0043] A chemical adhesive layer containing a chemical adhesive may be further laminated on the rust-proofing layer. The chemical adhesive layer can be formed by a chemical adhesive treatment using a chemical adhesive such as a silane coupling agent. The chemical adhesive layer further enhances the adhesion between the surface-treated copper foil and the resin substrate. Note that the rust-proofing layer and the chemical adhesive layer are very thin, so they do not affect the shape of the roughening particles on the roughened surface of the surface-treated copper foil.

[0044] Further, as a method for forming the chemical adhesive layer, for example, a method of applying a silane coupling agent solution directly or indirectly via a rust-proofing layer or the like to the roughened surface of the surface-treated copper foil, followed by air drying (natural drying) or heat drying can be mentioned. The applied silane coupling agent solution can be dried by evaporating water, but heat drying at a temperature of 50°C or higher and 180°C or lower is preferable because it promotes the reaction between the silane coupling agent and the copper foil.

[0045] The chemical adhesive layer preferably contains one or more silane coupling agents selected from the group consisting of epoxy silane, amino silane, vinyl silane, methacrylic silane, acrylic silane, styryl silane, ureido silane, mercapto silane, sulfide silane and isocyanate silane.These silane coupling agents have different effects depending on the interaction with the reactive functional group contained in the resin of the resin substrate, so it is necessary to select an appropriate one in consideration of its compatibility with the resin.

[0046] Specific examples of the silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, p-styryltrimethoxysilane, p-styryltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and bis(3-(triethoxysilyl)propyl)disulfide. However, other silane coupling agents can also be appropriately selected and used. These silane coupling agents may be used alone or in combination of two or more.

[0047] [Copper-clad laminate] As shown in FIG. 1 , the copper-clad laminate 30 according to this embodiment comprises the surface-treated copper foil 10 according to the first or second embodiment, and a resin substrate 20 bonded to the roughened surface 10 a of the surface-treated copper foil 10.

[0048] The copper-clad laminate 30 according to this embodiment includes the surface-treated copper foil 10 according to the first or second embodiment. Therefore, by using the copper-clad laminate 30 according to this embodiment, it is possible to manufacture a printed wiring board or the like that has excellent adhesion between the resin substrate 20 and the surface-treated copper foil 10, small transmission loss, and good laser processability.

[0049] The type of resin forming the resin substrate is not particularly limited, but examples include thermoplastic resins such as liquid crystal polymer, polyether ether ketone, polyphenylene sulfide, polyphenylene ether, polyphenylene oxide, polyetherimide, polyethersulfone, polyethylene naphthalate, polyethylene terephthalate, thermoplastic polyimide, and cyclic polyolefin, as well as thermosetting resins such as polyimide, heat-resistant epoxy resin, cyanate-based resin (e.g., bismaleimide triazine), and thermosetting modified polyphenylene ether.

[0050] Among these resins, preferred are liquid crystal polymers such as thermotropic liquid crystal polymers, rheotropic liquid crystal polymers, etc. Examples of thermotropic liquid crystal polymers include liquid crystal polyesters, and examples of liquid crystal polyesters include aromatic polyesters obtained by reacting an aromatic hydroxycarboxylic acid as an essential monomer with an aromatic dicarboxylic acid or an aromatic diol.

[0051] Specific examples of aromatic polyesters include polyesters synthesized from parahydroxybenzoic acid (PHB), phthalic acid, and 4,4'-biphenol, polyesters synthesized from PHB and 2,6-hydroxynaphthoic acid, and polyesters synthesized from PHB, terephthalic acid, and ethylene glycol.

[0052] [Printed Wiring Board] The printed wiring board according to this embodiment includes the copper-clad laminate according to the above-described embodiment. Since the printed wiring board according to this embodiment includes the surface-treated copper foil according to the first or second embodiment, the adhesion between the resin substrate and the surface-treated copper foil is excellent, the transmission loss is small, and the laser processability is good.

[0053] In the printed wiring board according to the present embodiment, the surface-treated copper foil and the resin substrate may be plastically deformed. The printed wiring board according to the present embodiment is composed of a metal foil and a resin substrate (e.g., a thermoplastic resin film), and therefore is easily plastically deformed. When heated, the plastic deformation becomes even easier.

[0054] Furthermore, in the printed wiring board according to this embodiment, the surface-treated copper foil and the resin base material may be integrally bent. Fig. 2 is a cross-sectional view showing an example of a printed wiring board in which the surface-treated copper foil and the resin base material are integrally bent. In the printed wiring board according to this embodiment, the resin base material and the surface-treated copper foil have excellent adhesion to each other, so that the resin base material and the surface-treated copper foil can be integrally bent without peeling off when deformed.

[0055] The printed wiring board according to this embodiment can be subjected to various stresses and deformations within the scope of the present invention depending on the configuration of the electronic circuit board and the manufacturing conditions, but the printed wiring board according to this embodiment may or may not be bent when incorporated into an electronic device.

[0056] The printed wiring board according to this embodiment may form a transmission line. The printed wiring board according to this embodiment may also form a stripline, microstrip, or coplanar transmission line. Since the printed wiring board according to this embodiment has low transmission loss, it has good characteristics even when the roughened surfaces are opposed to each other, and can form transmission lines of any shape.

[0057] 3 is a cross-sectional view showing an example of a printed wiring board constituting a stripline transmission line. At least one of the multiple surface-treated copper foils of the printed wiring board in FIG. 3 is the surface-treated copper foil according to the first embodiment or the second embodiment. The surface-treated copper foil according to the first embodiment or the second embodiment has excellent adhesion to a resin substrate, low transmission loss, and excellent laser processability, and therefore can be used as any of the multiple surface-treated copper foils of the printed wiring board. That is, it can be used as the surface-treated copper foil located in the outermost layer of the printed wiring board, or as the surface-treated copper foil located inside the printed wiring board.

[0058] [Examples] The present invention will be explained in more detail below with reference to examples and comparative examples. [Examples and Comparative Examples of Surface-Treated Copper Foil According to the First Embodiment] [1] Preparation of Copper Foil Substrate An electrolytic copper foil was prepared as the copper foil that will be the raw material for the surface-treated copper foil. This electrolytic copper foil will serve as the copper foil substrate for roughening treatment. The electrolytic copper foil was produced by electrolysis under the following conditions. The electrolytic copper foil produced under the following conditions had a thickness of 12 μm and a surface roughness (ten-point average roughness Rzjis in accordance with JIS B0601-2001) of 1.1 μm. The surface roughness was measured on the surface of the electrolytic copper foil using a contact surface roughness measuring instrument ("Surfcorder SE1700" manufactured by Kosaka Laboratory Co., Ltd.).

[0059] <Production conditions for electrolytic copper foil> Copper concentration in electrolytic solution: 80 g / L H2SO4 concentration in electrolytic solution: 70 g / L Chlorine concentration in electrolytic solution: 25 mg / L Bath temperature: 55°C Current density: 45 A / dm 2

[0060] <Additives to the electrolyte and their concentrations> Sodium 3-mercapto-1-propanesulfonate: 2 mg / L Hydroxyethyl cellulose: 10 mg / L Low molecular weight glue (molecular weight 3000): 50 mg / L

[0061] [2] Roughening Treatment Next, one side of the copper foil substrate prepared in [1] above was subjected to a plating treatment as a roughening treatment to form a roughened surface, thereby producing a surface-treated copper foil. This plating treatment was a two-stage electroplating treatment. For the first-stage plating treatment (1), a first-stage treatment solution having the following composition was used, and the current density and current application time were as shown in Table 1. For the second-stage plating treatment (2) performed subsequent to the first-stage plating treatment (1), a second-stage treatment solution having the following composition was used, and the current density, current application time, and vertical temperature ratio in the electrolytic cell were as shown in Table 1. The vertical temperature ratio in the electrolytic cell was determined by dividing the liquid temperature (K) of the electrolytic solution above the opening position in the electrolytic cell by the liquid temperature (K) of the electrolytic solution below the opening position in the electrolytic cell. If necessary, additional treatments may be performed before the first-stage plating treatment (1) and after the second-stage plating treatment (2).

[0062] <First stage treatment solution> Copper (Cu) concentration: 60 g / L Sulfuric acid (H2SO4) concentration: 120 g / L Bath temperature: 60°C

[0063] <Second-stage treatment solution> Copper concentration: 20 to 30 g / L H2SO4 concentration: 150 g / L Molybdenum (Mo) concentration: 0.2 to 0.4 g / L Iron (Fe) concentration: 2 g / L Bath temperature: 30 to 40°C

[0064] [3] Formation of Underlayer and Intermediate Layer Subsequently, the roughened surface of the surface-treated copper foil produced in [2] above was metal-plated in the following order under the conditions below to form an underlayer and an intermediate layer.

[0065] <Ni plating> Ni concentration in plating solution: 40 g / L H3BO3 concentration in plating solution: 5 g / L Bath temperature: 20°C pH of plating solution: 3.6 Current density: as shown in Table 1 Treatment time: 10 seconds

[0066] <Zn plating> Zn concentration in plating solution: 2.5 g / L NaOH concentration in plating solution: 40 g / L Bath temperature: 20°C pH of plating solution: 3.6 Current density: 0.3 A / dm 2 Processing time: 5 seconds

[0067] <Cr plating> Cr concentration of plating solution: 5 g / L Bath temperature: 30°C pH of plating solution: 2.2 Current density: 5 A / dm 2 Processing time: 5 seconds

[0068] [4] Formation of Silane Coupling Agent Layer Finally, a silane coupling agent layer was formed on the intermediate layer (particularly the outermost Cr plating layer) formed in [3] above. The silane coupling agent layer was formed by applying a 3% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane onto the intermediate layer and drying at 100°C. The amount of silane attached was 0.003 mg / dm2 in terms of silicon (Si) atoms.2 is.

[0069]

[0070] The surface-treated copper foils of Examples A1 to A10 and Comparative Examples A1 to A10 were produced as described in [1] to [4] above. Some of the production conditions for the surface-treated copper foils were as described above, and the remaining conditions were as shown in Table 1. Various physical properties were measured for the roughened surface of each of the obtained surface-treated copper foils. In addition, each of the obtained surface-treated copper foils was evaluated for adhesion to the resin substrate, transmission loss, powder shedding resistance, copper foil oxidation, and laser processability. The measurement and evaluation methods are described below. The measurement and evaluation results are also shown in Table 1.

[0071] <Specular Reflectance of Roughened Surface> The specular reflectance of the roughened surface was measured using a spectrophotometer V-780 and an absolute reflectance measurement unit ARSN-918i manufactured by JASCO Corporation. The incident light used for the measurement was 45° polarized light with a wavelength of 600.0 nm and a bandwidth of 5.0 nm, and no aperture was used.

[0072] The surface-treated copper foil was placed in a spectrophotometer so that the incident surface of the incident light was parallel to the transverse direction (TD) perpendicular to the machine direction (MD) of the copper foil during production of the electrodeposited copper foil, and the regular reflectance of the roughened surface was measured under the condition that the incident angle and reflection angle were both 70°. Dark correction and blank correction were performed, and the measurement was repeated once.

[0073] <Y Value of Lightness of Roughened Surface> The Y value of the XYZ color system defined by the CIE was measured using a lightness color meter SM-T45 manufactured by Suga Test Instruments Co., Ltd. The measurement conditions were as follows: the color measurement conditions were a C light source and a 2-degree field of view, the optical conditions were in accordance with condition a of JIS Z8722:2009, and an aperture with a diameter of 30 mm was used.

[0074] <Ssk of Roughened Surface> Using a confocal laser microscope VK-X3100 manufactured by Keyence Corporation, the Ssk of the roughened surface was measured according to the method specified in ISO 25178. The wavelength of the laser light source was 404 nm. Measurements were taken at five randomly selected locations on the roughened surface, and the average value was taken as the Ssk of the roughened surface.

[0075] The magnification of the objective lens of the confocal laser microscope was 100x, the scan mode was laser confocal, the measurement size was 2048 x 1536, the measurement quality was high-resolution, the pitch was 0.06 μm, and the light intensity was automatically adjusted. Ssk was calculated using the following filter processing and calculation conditions.

[0076] Calculation target area: 142 μm (TD direction) x 106 μm (MD direction) Image processing: Reference plane setting (calculation target area: entire) Smoothing processing (Gaussian, size 3 x 3) S filter: None F-operation: None L filter: 0.01 μm (Gaussian, end effect correction: ON)

[0077] <Nickel deposition amount by nickel coating> The roughened surface of the surface-treated copper foil was subjected to fluorescent X-ray analysis using a scanning X-ray fluorescence analyzer ZSX Primus IV manufactured by Rigaku Corporation to measure the nickel deposition amount. The amount of nickel atoms was quantified using a calibration curve obtained using known standard samples.

[0078] <Adhesion to Resin Substrate> A surface-treated copper foil was laminated on one side of a 50 μm-thick liquid crystal polymer film (manufactured by Ise Murata Manufacturing Co., Ltd., thickness precision: 0.7 μm, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0020, ratio of maximum to minimum coefficient of linear thermal expansion: 1.4) so ​​that the roughened surface was in contact with the liquid crystal polymer film, and a polyimide film ("Upilex 20S" manufactured by UBE Corporation) was laminated on the other side as a release material to obtain a laminate.

[0079] This laminate was sandwiched between two 2 mm thick stainless steel plates, and the laminate sandwiched between the stainless steel plates was then sandwiched between two 1 mm thick stainless steel fiber woven fabric cushioning materials, and placed in a vacuum press. The vacuum press was then used to hold the laminate at a temperature of 300°C and a pressure of 3 MPa for 5 minutes. After cooling, the thermocompression-bonded laminate was removed from the vacuum press, and the release material was removed to obtain a single-sided copper-clad laminate.

[0080] Using a tensile tester (Shimadzu Corporation, "AGS-H"), the strength (unit: N / mm) was measured when the surface-treated copper foil was peeled from this single-sided copper-clad laminate in a 180° direction at a speed of 50 mm / min according to the method specified in JIS C6471-1995. Specifically, a 5 mm wide masking tape was attached to the copper foil of the single-sided copper-clad laminate, and the laminate was immersed in a ferric chloride solution to etch and remove unnecessary portions of the copper foil. The single-sided copper-clad laminate was then washed with water, the masking tape was peeled off, and the laminate was dried in a circulating oven at 80°C for 1 hour to form a 5 mm wide linear circuit pattern.

[0081] To prevent the test piece (single-sided copper-clad laminate) from bending and changing the peel angle when peeling the copper foil from the single-sided copper-clad laminate, the test piece was attached to a reinforcing plate with a thickness of 1 mm or more. One end of the formed circuit pattern was peeled off and clamped in the tensile tester. The copper foil was then peeled at an angle of 180° to the test piece at a rate of 50 mm / min for 10 mm or more. The average strength during this period was calculated, and this value was designated as the peel strength (N / mm). The results are shown in Table 1. In the examples and comparative examples, the 180° peel strength was measured as an index of adhesion between the resin substrate and the surface-treated copper foil. A 180° peel strength of 0.70 N / mm or more was evaluated as pass, and a 180° peel strength of less than 0.70 N / mm was evaluated as fail.

[0082] <Transmission Loss> Surface-treated copper foil was bonded to both sides of a 50 μm-thick liquid crystal polymer film (manufactured by Ise Murata Manufacturing Co., Ltd., thickness accuracy: 0.7 μm, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0020, ratio of maximum to minimum coefficient of linear thermal expansion: 1.4) by a heat fusion method to prepare a double-sided copper-clad laminate.

[0083] Next, the surface-treated copper foil on one side of the double-sided copper-clad laminate was etched to form a linear pattern of a predetermined width (110 μm) and length (20 mm and 50 mm) as a signal layer, and the surface-treated copper foil on the other side was used as a ground layer to prepare a circuit board with a microstrip line structure. This circuit board was then dried by being kept in a circulating oven at 50°C for 24 hours, and then cooled to room temperature under the standard environment described in JIS C6481-1996 to prepare a circuit board for evaluating high-frequency characteristics.

[0084] Both ends of the pattern of the circuit board for evaluating high frequency characteristics prepared as described above were sandwiched between test fixtures, and a high frequency signal (40 GHz) was passed through the pattern to measure the strength of the passing signal (S21). The signal strength was measured using a PNA microwave network analyzer N5227B manufactured by Keysight Technologies Inc. and a universal test fixture 3680V manufactured by Anritsu Corporation. The measurement was performed five times using the same pattern, and the average value was taken as the transmission loss amount of each circuit board.

[0085] The transmission loss per unit length was calculated from the difference between the transmission loss of the circuit board for evaluating high-frequency characteristics with a pattern length of 20 mm and the transmission loss of the circuit board for evaluating high-frequency characteristics with a pattern length of 50 mm, and from the difference in the pattern lengths of both circuit boards for evaluating high-frequency characteristics.

[0086] Furthermore, the transmission loss per unit length of the surface-treated copper foils of each of the Examples and Comparative Examples was indexed, with the transmission loss per unit length of Example B2 described later being taken as the reference value (100). The results are shown in Table 1. In the Examples and Comparative Examples, when the transmission loss index exceeded 115, the transmission loss was evaluated as being large and unacceptable, and this is indicated by an x ​​in Table 1. When the transmission loss index was 115 or less, the transmission loss was evaluated as being small and acceptable, and this is indicated by a ∘ in Table 1. When the transmission loss index was 100 or less, the transmission loss was evaluated as being particularly small and acceptable, and this is indicated by a ⊚ in Table 1.

[0087] <Laser processability (reduction of resin residue at the bottom of the via hole)> When forming a blind via hole by laser irradiation, resin derived from the resin substrate may remain at the bottom of the formed blind via hole. If the resin remains, sufficient conductivity may not be obtained even when an interlayer connector is formed, and the connection reliability at the time of interlayer connection may be reduced. Copper-clad laminates were produced using the surface-treated copper foil, and their laser processability, i.e., whether or not resin derived from the resin substrate is less likely to remain at the bottom of the formed blind via hole when formed by laser irradiation, was evaluated.

[0088] A single-sided copper-clad laminate was produced by bonding a 12 μm thick surface-treated copper foil to one side of a 50 μm thick liquid crystal polymer film (manufactured by Ise Murata Manufacturing Co., Ltd., thickness accuracy: 0.7 μm, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0020, ratio of maximum to minimum coefficient of linear thermal expansion: 1.4) using a heat fusion method.

[0089] Next, a carbon dioxide laser was used to irradiate the liquid crystal polymer film side of the single-sided copper-clad laminate, forming 150 via holes at random locations. The diameter of the via holes was 100 μm. The laser irradiation was performed under the following conditions: pulse width 1 to 5 μs, tip energy 1 to 3 mJ, mask diameter 1 to 3 mm, and number of irradiation shots 5 to 10, depending on the structure of the roughening particles.

[0090] After the via holes were formed, the roughened surface of the surface-treated copper foil at the bottom of the via holes was observed to check for the presence or absence of residual resin. The presence or absence of residual resin was confirmed by removing the surface-treated copper foil by etching after laser processing, and then observing with an optical microscope at a magnification of 10x to check for the presence or absence of residual resin at the bottom of the via holes. Observation with an optical microscope was performed on all 150 via holes, and the number of via holes without residual resin was counted.

[0091] In the examples and comparative examples, when the number of via holes with no residual resin was 80 or more, the processability was very good and the result was evaluated as "pass," which is indicated by a double circle in Table 1. When the number of via holes with no residual resin was 40 to 79, the result was evaluated as "pass," which is indicated by a circle in Table 1. When the number of via holes with no residual resin was 39 or less, the result was evaluated as "fail," which is indicated by an x ​​in Table 1.

[0092] <Laser processability (suppression of resin residue at bases of roughening particles)> The present embodiment aims to provide a printed wiring board having excellent adhesion between a resin substrate and a surface-treated copper foil, low transmission loss, and good long-term connection reliability. Specifically, the present embodiment aims to suppress the resin residue at bases of roughening particles in the surface-treated copper foil, thereby suppressing the occurrence of cracks between the resin substrate and the surface-treated copper foil due to thermal stress during long-term use, which can cause poor connection or cracks, resulting in a decrease in connection reliability.

[0093] According to this embodiment, a printed wiring board can be provided in which the adhesion between the resin substrate and the surface-treated copper foil is excellent, transmission loss is small, and resin is less likely to remain at the base of the roughening particles (excellent laser processability).Since resin is less likely to remain at the base of the roughening particles, long-term connection reliability can be ensured.

[0094] Copper-clad laminates were prepared using surface-treated copper foils, and their laser processability, i.e., whether or not resin derived from the resin substrate was less likely to remain at the base of roughening particles in blind via holes formed by laser irradiation, was evaluated. Single-sided copper-clad laminates were prepared in the same manner as in the above-mentioned "Laser processability (suppression of resin residue at the bottom of via holes)," and then via holes were formed using a carbon dioxide laser. The single-sided copper-clad laminates with via holes formed therein were then analyzed as follows.

[0095] First, the single-sided copper-clad laminate with the via holes formed therein was pretreated. Osmium (Os) or platinum (Pt)-palladium (Pd) was vapor-deposited onto the single-sided copper-clad laminate. This allowed the bottom of the via holes to be observed using a scanning electron microscope (SEM). The single-sided copper-clad laminate was embedded in an embedding resin such as epoxy resin, and then cut so that the maximum diameter cross-section of the via holes could be observed. The exposed cross-section was mirror-polished. Then, polishing marks were removed using flat milling to obtain a sample for scanning electron microscope observation.

[0096] The cross section of the sample was observed using a scanning electron microscope, and secondary electron images (SEM images) were obtained at 5,000x magnification. The acceleration voltage of the scanning electron microscope was 10 kV. SEM images with a width of 25 μm were obtained in one field of view, and SEM images were obtained in ten fields of view. These 10 SEM images were then analyzed to evaluate the degree of resin remaining at the bottom of the via hole. This is explained below.

[0097] First, the contour of the surface shape of the roughened surface is extracted. Then, among the roughening particles present in one field of view, the roughening particle with the highest tip is selected, and that tip is taken as the highest point of that field of view. Furthermore, among the roughening particles present in one field of view, the gap with the lowest bottom between the roughening particles is selected, and that bottom of that gap is taken as the lowest point of that field of view.

[0098] Next, a highest line is drawn that passes through the highest point and is parallel to the surface of the copper foil (i.e., a line parallel to the width of the field of view), and a lowest line is drawn that passes through the lowest point and is parallel to the surface of the copper foil. The area between these two lines is defined as the measurement area. The height (height from the lowest line) that is 25% of the height of this measurement area (the distance between the highest line and the lowest line) is defined as the "reference height."

[0099] At this reference height, gaps between roughening particles with a width of 0.2 μm or more were defined as "valleys" between the roughening particles. If resin remained in the valleys, the degree of resin remaining at the base of the roughening particles was evaluated based on the distance between the bottom of the valley and the surface of the remaining resin.

[0100] The degree of resin remaining at the base of the roughening particles was calculated for all valleys within a 25 μm range centered on the center of the bottom of the via hole, and the degree of resin remaining at the base of the roughening particles was calculated for a total of 10 fields of view. The laser processability (reduction of resin remaining at the base of the roughening particles) was then evaluated using the average value. The results are shown in Table 1.

[0101] In the examples and comparative examples, when the distance between the bottom of the valley and the surface of the remaining resin is 0.6 μm or less, it is evaluated as passing, and is indicated by a circle in Table 1. When the distance between the bottom of the valley and the surface of the remaining resin exceeds 0.6 μm, it is evaluated as failing, and is indicated by an x ​​in Table 1. The bottom of the valley is defined as the intersection of a line perpendicular to the line representing the reference height and passing through the center of the valley with the surface of the copper foil.

[0102] <Powder Fall-Off Resistance> After attaching a reference plate to the non-roughened surface of the surface-treated copper foil, a white dust-free paper was brought into contact with the roughened surface of the surface-treated copper foil. A weight of 1 kg was placed on the white dust-free paper, and the white dust-free paper was moved 50 mm at a speed of 100 mm / min in a direction parallel to the contact surface between the roughened surface and the white dust-free paper.

[0103] The surface of the white dust-free paper was photographed using an optical microscope under reflected illumination to obtain a magnified image. The magnification was 20x. The brightest area of ​​the enlarged image was designated a brightness of 255, and the darkest area a brightness of 0. Areas with a brightness of 200 or less were considered to be copper powder transferred to the white dust-free paper (copper powder resulting from the roughening particles). The area ratio (area rate) of areas with a brightness of 200 or less in the enlarged image was then calculated. The results are shown in Table 1. In the examples and comparative examples, an area rate of less than 0.5% was evaluated as pass, indicated by a circle in Table 1. An area rate of 0.5% or more was evaluated as fail, indicated by an x ​​in Table 1.

[0104] <Oxidation of Copper Foil> The surface-treated copper foil was placed in an oven and heated, and the presence or absence of discoloration after heating was confirmed. The heating conditions were a temperature of 250°C, a heating time of 30 minutes, and an air atmosphere. The results are shown in Table 1. In the examples and comparative examples, when the surface-treated copper foil did not discolor, it was evaluated as passing, and this is indicated by a circle in Table 1. When the surface-treated copper foil did discolor, it was evaluated as failing, and this is indicated by an x ​​in Table 1.

[0105] Comparing Examples A1 to A10 with Comparative Examples A1 to A6, it can be seen that Examples A1 to A10 have excellent laser processability. Residual resin at the bottom of the via hole is suppressed, and residual resin at the base of the roughening particles is also suppressed, reducing the number of fracture points in the via hole for interlayer connection. This allows for a printed wiring board with excellent not only initial connection reliability but also long-term connection reliability.

[0106] Fig. 7 shows a cross-sectional view of a copper-clad laminate using conventional surface-treated copper foil. Fig. 7 shows a cross-section of a via hole, and it can be seen that resin remains at the base of the roughening particles at the bottom of the via hole. Therefore, crack sources are likely to occur at the interface between the interlayer connection conductor in the via hole and the surface-treated copper foil.

[0107] Figure 8 is a cross-sectional view of a copper-clad laminate using the surface-treated copper foil of the first embodiment. Figure 8 shows a cross-section of a via hole, and it can be seen that because laser light is easily introduced to the base of the roughening particles, resin residue at the base of the roughening particles at the bottom of the via hole is suppressed. This strengthens the bond between the interlayer connection conductor in the via hole and the surface-treated copper foil, making it less likely for crack sources to occur at the interface between the interlayer connection conductor and the surface-treated copper foil. The process of forming via holes, circuit patterns, and interlayer connectors in a copper-clad laminate is as shown in Figure 4, and the specific details are as follows.

[0108] An example of a process for forming blind via holes in a double-sided copper-clad laminate 100 by laser irradiation is shown in Figure 5. Also, an example of a process for forming blind via holes in a single-sided copper-clad laminate 100 by laser irradiation is shown in Figure 6. The process for forming blind via holes is almost the same for both double-sided and single-sided copper-clad laminates, so the following explanation will be given using a double-sided copper-clad laminate as an example. Note that the same reference numerals are used to designate corresponding components in Figures 5 and 6.

[0109] A copper clad laminate 100 shown in Fig. 5(a) is irradiated with a laser 130 to form a blind via hole (see Fig. 5(b)). When forming a blind via hole by laser irradiation, residue 120 (metal originating from the surface-treated copper foil 111 and resin originating from the resin substrate 113) may remain at the bottom 140 of the blind via hole after processing by irradiating with the laser 130 (see Fig. 5(b)).

[0110] Therefore, after the blind via holes are formed, the copper-clad laminate 100 is subjected to a desmear process to remove residues 120 in the blind via holes (see FIG. 5C). Then, after the desmear process, an interlayer connector 116 is formed. Methods for forming the interlayer connector 116 include a method for forming a plating film 115 and a method for filling the blind via holes with at least one of plating and metal paste to form the interlayer connector 116. As shown in FIG. 5D, a plating process can be performed to form a plating film 115 on the inner surface of the blind via hole. Alternatively, as shown in FIG. 5E, the interlayer connector 116 can be formed by filling the blind via holes with at least one of plating and metal paste. The top surface of the interlayer connector 116 does not need to be flush with the surfaces of the surface-treated copper foil 111 and the resin substrate 113.

[0111] [Examples and Comparative Examples of Surface-Treated Copper Foil According to the Second Embodiment] [1] Preparation of Copper Foil Substrate An electrolytic copper foil was prepared as the copper foil that would serve as the raw material for the surface-treated copper foil. This electrolytic copper foil would serve as the copper foil substrate for the roughening treatment. The electrolytic copper foil was produced by electrolysis under the following conditions. The electrolytic copper foil produced under the following conditions had a thickness of 12 μm and a surface roughness (ten-point average roughness Rzjis in accordance with JIS B0601-2001) of 1.1 μm. The surface roughness was measured on the surface of the electrolytic copper foil using a contact surface roughness measuring instrument ("Surfcorder SE1700" manufactured by Kosaka Laboratory Co., Ltd.).

[0112] <Production conditions for electrolytic copper foil> Copper concentration in electrolytic solution: 80 g / L H2SO4 concentration in electrolytic solution: 70 g / L Chlorine concentration in electrolytic solution: 25 mg / L Bath temperature: 55°C Current density: 45 A / dm 2

[0113] <Additives to the electrolyte and their concentrations> Sodium 3-mercapto-1-propanesulfonate: 2 mg / L Hydroxyethyl cellulose: 10 mg / L Low molecular weight glue (molecular weight 3000): 50 mg / L

[0114] [2] Roughening Treatment Next, one side of the copper foil substrate prepared in [1] above was subjected to a plating treatment as a roughening treatment to form a roughened surface, thereby producing a surface-treated copper foil. This plating treatment was a two-stage electroplating treatment. For the first-stage plating treatment (1), a first-stage treatment solution having the following composition was used, and the current density and current flow time were as shown in Table 2. For the second-stage plating treatment (2) performed subsequent to the first-stage plating treatment (1), a second-stage treatment solution having the following composition was used, and the current density, current flow time, and vertical flow rate ratio of the electrolyte solution in the electrolytic cell were as shown in Table 2. The vertical flow rate ratio of the electrolyte solution in the electrolytic cell was determined by dividing the flow rate of the electrolyte solution above the opening position in the electrolytic cell by the flow rate of the electrolyte solution below the opening position in the electrolytic cell. If necessary, additional treatments may be performed before the first-stage plating treatment (1) and after the second-stage plating treatment (2).

[0115] <First stage treatment solution> Copper (Cu) concentration: 60 g / L Sulfuric acid (H2SO4) concentration: 120 g / L Bath temperature: 60°C

[0116] <Second-stage treatment solution> Copper concentration: 20 to 30 g / L H2SO4 concentration: 150 g / L Molybdenum (Mo) concentration: 0.2 to 0.4 g / L Iron (Fe) concentration: 2 g / L Bath temperature: 30 to 40°C

[0117] [3] Formation of Underlayer and Intermediate Layer Subsequently, the roughened surface of the surface-treated copper foil produced in [2] above was metal-plated in the following order under the conditions below to form an underlayer and an intermediate layer.

[0118] <Ni Plating> Ni concentration in plating solution: 40 g / L H3BO3 concentration in plating solution: 5 g / L Bath temperature: 20°C pH of plating solution: 3.6 Current density: as shown in Table 2 Treatment time: 10 seconds

[0119] <Zn plating> Zn concentration in plating solution: 2.5 g / L NaOH concentration in plating solution: 40 g / L Bath temperature: 20°C pH of plating solution: 3.6 Current density: 0.3 A / dm 2 Processing time: 5 seconds

[0120] <Cr plating> Cr concentration of plating solution: 5 g / L Bath temperature: 30°C pH of plating solution: 2.2 Current density: 5 A / dm 2 Processing time: 5 seconds

[0121] [4] Formation of Silane Coupling Agent Layer Finally, a silane coupling agent layer was formed on the intermediate layer (particularly the outermost Cr plating layer) formed in [3] above. The silane coupling agent layer was formed by applying a 3% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane onto the intermediate layer and drying at 100°C. The amount of silane attached was 0.003 mg / dm2 in terms of silicon (Si) atoms. 2 is.

[0122]

[0123] The surface-treated copper foils of Examples B1 to B10 and Comparative Examples B1 to B9 were produced as described in [1] to [4] above. Some of the production conditions for the surface-treated copper foils were as described above, and the remaining conditions were as described in Table 2. Various physical properties were measured for the roughened surface of each of the surface-treated copper foils obtained. Furthermore, the adhesion to the resin substrate, transmission loss, powder shedding resistance, copper foil oxidation, and laser processability were evaluated for each of the surface-treated copper foils obtained. The measurement and evaluation methods are described below. The measurement and evaluation results are also shown in Table 2.

[0124] <Average value of cross-sectional particle height h_ave, standard deviation of cross-sectional particle width w_σ, and skewness of cross-sectional particle height h_sk> First, a square test piece with a side length of 5 mm obtained by cutting out a surface-treated copper foil was embedded in an epoxy resin or the like (e.g., an epoxy-based adhesive) and cured. The surface-treated copper foil and resin were then cut to reveal a cross section perpendicular to the roughened surface. The cross section was then precision-polished using an IM4000 ion milling machine manufactured by Hitachi High-Technologies Corporation. The precision polishing conditions were stage mode C1 (swing angle: ±15°, swing speed: 6 round trips / min), acceleration voltage 6 kV, and polishing time 30 minutes. The precision polishing using the ion milling machine was performed at a protrusion amount that did not cause cracking of the resin, deformation of the surface-treated copper foil, or deformation of the roughening particles during cutting. The protrusion amount was, for example, approximately 50 μm.

[0125] The cross section was then observed using a scanning electron microscope (SEM) SU8020 manufactured by Hitachi High-Technologies Corporation, and a secondary electron image at a magnification of 5,000 times (see the SEM image in Figure 9) was obtained. The acceleration voltage of the scanning electron microscope was 3 kV. From the observation of the cross section, an SEM image of a rectangular region measuring 19 μm in length and 500 μm in width was prepared.

[0126] A cross section was randomly produced from one surface-treated copper foil, and an SEM image of a rectangular region measuring 19 μm in length and 500 μm in width was obtained from the cross section. Since one SEM image that can actually be obtained using a scanning electron microscope is an SEM image of a rectangular region measuring 19 μm in length and 25 μm in width, an SEM image of a rectangular region measuring 19 μm in length and 500 μm in width is obtained by acquiring and connecting 20 SEM images of a rectangular region measuring 19 μm in length and 25 μm in width so that the imaged region is continuous. The following image analysis is performed on these 20 consecutive SEM images, and the following image analysis is performed on a region 500 μm in length in the horizontal direction of the SEM image. As a result of performing the following image analysis on this 500 μm long region, the surface-treated copper foil according to the present invention is one that satisfies the constituent elements of the present invention.

[0127] During SEM observation, the surface-treated copper foil is adjusted so that it is horizontal in the cross-sectional SEM image. Note that, if necessary, a copper-clad laminate or a printed wiring board may be used as the observation sample for taking the cross-sectional SEM image. When a copper-clad laminate or a printed wiring board is used, it is not necessary to peel the surface-treated copper foil from the resin substrate, and the copper-clad laminate or the printed wiring board may be cut as is to process and observe the cross section.

[0128] The dimensions of the roughening particles formed on the roughened surface were measured by image analysis of the SEM images obtained by the SEM observation at 5,000x magnification. Specifically, one roughening particle was identified in the SEM image, and the cross-sectional particle height and cross-sectional particle width of that roughening particle were measured. The cross-sectional particle heights and cross-sectional particle widths of multiple roughening particles were then measured, and the average cross-sectional particle height h_ave, the standard deviation of the cross-sectional particle width w_σ, and the skewness of the cross-sectional particle height h_sk were calculated.

[0129] The SEM image was subjected to image processing using image analysis software (open-source free software "ImageJ") to emphasize the contours of the roughening particles, and then to "binarization" processing to color-code the roughening particles. Image processing was then performed to remove noise generated by the "binarization" processing, and further image processing was performed to white out the portions of the roughening particles displayed in black by the "binarization" processing. The contour lines of the roughening particles were then extracted, and the cross-sectional particle height and cross-sectional particle width of the roughening particles at the contour lines were measured using general measurement software (Photo Ruler, etc.).

[0130] The cross-sectional particle height and cross-sectional particle width of the roughening particles can be measured using known processing software such as "WinROOF" and "Photo Ruler," which are general image measurement software. A detailed description will be given later. An example of the simplest method for measuring roughening particles (image analysis method) will be described below with reference to FIG. 10 .

[0131] First, as shown in (a) of FIG. 10 , a straight line L is drawn on the SEM image, the straight line L being parallel to the direction in which the roughening particles protrude from the roughened surface of the surface-treated copper foil and passing through the tip (vertex) V of the roughening particle. Next, as shown in (b) of FIG. 10 , a rectangle Sq having two sides (two vertical sides) parallel to the straight line L and two sides (top and bottom sides) perpendicular to the straight line L is drawn on the SEM image. The rectangle Sq may be a square. The top side of this rectangle Sq passes through the tip V of the roughening particle, and the bottom side contacts the base portion of the roughening particle along the outline of the roughening particle. There are two base portions of the roughening particle along the outline of the roughening particle, and the rectangle Sq is drawn so that the bottom side contacts the base portion with the longer vertical side. The base portion refers to the boundary point between the roughening particle and the surface of the copper foil substrate before roughening treatment, or the boundary point between adjacent roughening particles along the outline of the roughening particle.

[0132] The bottom side of the rectangle Sq may contact the base of the roughening particle on the outline of the roughening particle at one point (when the roughening particle protrudes in a direction not perpendicular to the roughened surface) or at two points (when the roughening particle protrudes in a direction perpendicular to the roughened surface). When the bottom side of the rectangle Sq and the base of the roughening particle on the outline of the roughening particle contact at one point, the contact point becomes one of the two corners on the bottom side of the rectangle Sq, and this corner is designated as R1.

[0133] When the bottom side of the rectangle Sq and the base of the roughening particle's outline meet at two points, the two points of contact are the two corners of the bottom side of the rectangle Sq, so one of the two corners is designated R1. In either the case where the bottom side of the rectangle Sq and the base of the roughening particle's outline intersect at one point or two points, the other of the two corners of the bottom side of the rectangle Sq is designated R2 (see FIG. 10B).

[0134] When the bottom side of the rectangle Sq and the base portion of the roughening particle's outline meet at a single point, the vertical side that passes through the corner R2, one of the two vertical sides connecting the top and bottom sides of the rectangle Sq, intersects with the base portion R2' of the roughening particle's outline. This base portion R2' is the base portion that does not meet the bottom side of the rectangle Sq.

[0135] 10C, the length of the vertical side of the rectangle Sq is defined as the cross-sectional particle height h of the roughening particle. The length of the upper or lower side is defined as the cross-sectional particle width w of the roughening particle. With the exception of the special examples below, a convex portion obtained by drawing one rectangle Sq and measuring the cross-sectional particle height h and cross-sectional particle width w is considered to be one roughening particle.

[0136] For the cross-sectional SEM image, a region of 500 μm in length in the width direction of the SEM image is observed, and the cross-sectional particle height h and cross-sectional particle width w of each roughening particle are measured throughout that region. Then, based on the number of roughening particles measured, the average cross-sectional particle height h_ave, the standard deviation of cross-sectional particle width w_σ, and the skewness of cross-sectional particle height h_sk are calculated for the roughening particles. The standard deviation of cross-sectional particle width w_σ and the skewness of cross-sectional particle height h_sk are defined by the following formulas. In the formulas, there is a symbol with a horizontal bar (-) above x (X bar), which represents the measured values ​​x1, x2, x3, ..., x n means the average value of

[0137]

[0138]

[0139] Next, examples of particles that are not measured as roughening particles and a method for measuring roughening particles having special shapes (the above-mentioned special examples) will be described with reference to FIG. 11 as necessary. The cross section of a roughening particle that protrudes obliquely beyond the cut surface may be partially reflected in the observed cross section. Such roughening particles appear to be floating above the surface-treated copper foil in the observed cross section, but such roughening particles are not included in the measurement of the cross-sectional particle height and cross-sectional particle width.

[0140] Furthermore, although not shown, among the convex portions measured according to the above criteria, those having a cross-sectional particle height of 0.15 μm or less do not affect the transmission characteristics and adhesion that are the focus of the present invention, and accurate measurement is difficult. Therefore, those having a cross-sectional particle height of 0.15 μm or less are not included in the measurement of the cross-sectional particle height and cross-sectional particle width, and in this case are not included in the "roughening particles" of the present invention.

[0141] 11(a), among the convex portions measured according to the above criteria, those having a ratio (h / w) of cross-sectional particle height h to cross-sectional particle width w of less than 0.40 do not affect the transmission characteristics or adhesion of interest in the present invention. Therefore, those having a ratio (h / w) of cross-sectional particle height h to cross-sectional particle width w of less than 0.40 are not subject to measurement of cross-sectional particle height and cross-sectional particle width, and in this case are not included in the "roughening particles" of the present invention.

[0142] Next, FIG. 11B shows an example of measuring a protrusion with two or more tips. In this case, as shown in FIG. 11B, based on the definitions above, each tip is considered to be a single roughening particle, and the cross-sectional particle height and cross-sectional particle width are measured. FIG. 11C also shows an example of measuring a protrusion with two or more tips. However, if the line L' drawn for one protrusion intersects with two vertical sides of the rectangle Sq of another protrusion, that protrusion is not measured. For example, in FIG. 11C, the line L' drawn for the tip V' of one protrusion intersects with two vertical sides of the rectangle Sq of another protrusion having the tip V, so the protrusion having the tip V' is not measured.

[0143] However, when two or more convex portions have a relationship in which the straight lines L' intersect with two vertical sides of the rectangle Sq of another convex portion that is different from each other, the convex portion with the highest cross-sectional particle height h is the object of measurement, and the other convex portions are not the object of measurement because they have little effect on the transmission characteristics and adhesion that are the focus of the present invention.

[0144] Figure 11 (d) shows a measurement example in which a convex portion exists on top of a convex portion whose ratio of cross-sectional particle height h to cross-sectional particle width w (h / w) is less than 0.40 and whose base portion is relatively unclear. In this case, the unclear base portion is not the measurement target, and the focus is on the convex portion with a distinct base portion, and measurement is performed based on the above definition. This is because smooth convex portions with unclear base portions do not affect the transmission characteristics and adhesion that are the focus of this invention. For roughening particles with shapes other than those described above, the cross-sectional particle height h and cross-sectional particle width w are measured in accordance with the above criteria, taking into account the effect on the transmission characteristics and adhesion that are the focus of this invention.

[0145] <Adhesion to Resin Substrate> A surface-treated copper foil was laminated on one side of a 50 μm-thick liquid crystal polymer film (manufactured by Ise Murata Manufacturing Co., Ltd., thickness precision: 0.7 μm, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0020, ratio of maximum to minimum coefficient of linear thermal expansion: 1.4) so ​​that the roughened surface was in contact with the liquid crystal polymer film, and a polyimide film ("Upilex 20S" manufactured by UBE Corporation) was laminated on the other side as a release material to obtain a laminate.

[0146] This laminate was sandwiched between two 2 mm thick stainless steel plates, and the laminate sandwiched between the stainless steel plates was then sandwiched between two 1 mm thick stainless steel fiber woven fabric cushioning materials, and placed in a vacuum press. The vacuum press was then used to hold the laminate at a temperature of 300°C and a pressure of 3 MPa for 5 minutes. After cooling, the thermocompression-bonded laminate was removed from the vacuum press, and the release material was removed to obtain a single-sided copper-clad laminate.

[0147] Using a tensile tester (Shimadzu Corporation, "AGS-H"), the strength (unit: N / mm) was measured when the surface-treated copper foil was peeled from this single-sided copper-clad laminate in a 180° direction at a speed of 50 mm / min according to the method specified in JIS C6471-1995. Specifically, a 5 mm wide masking tape was attached to the copper foil of the single-sided copper-clad laminate, and the laminate was immersed in a ferric chloride solution to etch and remove unnecessary portions of the copper foil. The single-sided copper-clad laminate was then washed with water, the masking tape was peeled off, and the laminate was dried in a circulating oven at 80°C for 1 hour to form a 5 mm wide linear circuit pattern.

[0148] To prevent the test piece (single-sided copper-clad laminate) from bending and changing the peel angle when peeling the copper foil from the single-sided copper-clad laminate, the test piece was attached to a reinforcing plate with a thickness of 1 mm or more. One end of the formed circuit pattern was peeled off and clamped in the tensile tester. The copper foil was then peeled 10 mm or more in a 180° direction relative to the test piece at a rate of 50 mm / min. The average strength during this period was calculated, and the resulting value was designated as the peel strength (N / mm). The results are shown in Table 2. In the examples and comparative examples, the 180° peel strength was measured as an index of adhesion between the resin substrate and the surface-treated copper foil. A 180° peel strength of 0.70 N / mm or more was evaluated as pass, and a 180° peel strength of less than 0.70 N / mm was evaluated as fail.

[0149] <Transmission Loss> Surface-treated copper foil was bonded to both sides of a 50 μm-thick liquid crystal polymer film (manufactured by Ise Murata Manufacturing Co., Ltd., thickness accuracy: 0.7 μm, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0020, ratio of maximum to minimum coefficient of linear thermal expansion: 1.4) by a heat fusion method to prepare a double-sided copper-clad laminate.

[0150] Next, the surface-treated copper foil on one side of the double-sided copper-clad laminate was etched to form a linear pattern of a predetermined width (110 μm) and length (20 mm and 50 mm) as a signal layer, and the surface-treated copper foil on the other side was used as a ground layer to prepare a circuit board with a microstrip line structure. This circuit board was then dried by being kept in a circulating oven at 50°C for 24 hours, and then cooled to room temperature under the standard environment described in JIS C6481-1996 to prepare a circuit board for evaluating high-frequency characteristics.

[0151] Both ends of the pattern of the circuit board for evaluating high frequency characteristics prepared as described above were sandwiched between test fixtures, and a high frequency signal (40 GHz) was passed through the pattern to measure the strength of the passing signal (S21). The signal strength was measured using a PNA microwave network analyzer N5227B manufactured by Keysight Technologies Inc. and a universal test fixture 3680V manufactured by Anritsu Corporation. The measurement was performed five times using the same pattern, and the average value was taken as the transmission loss amount of each circuit board.

[0152] The transmission loss per unit length was calculated from the difference between the transmission loss of the circuit board for evaluating high-frequency characteristics with a pattern length of 20 mm and the transmission loss of the circuit board for evaluating high-frequency characteristics with a pattern length of 50 mm, and from the difference in the pattern lengths of both circuit boards for evaluating high-frequency characteristics.

[0153] Furthermore, the transmission loss per unit length of Example B2 was set as the reference value (100), and the transmission loss per unit length of the surface-treated copper foils of each Example and Comparative Example was indexed. The results are shown in Table 2. In the Examples and Comparative Examples, when the transmission loss index exceeded 115, the transmission loss was evaluated as large and unacceptable, and this is indicated by an x ​​in Table 2. When the transmission loss index was 115 or less, the transmission loss was evaluated as small and acceptable, and this is indicated by a ∘ in Table 2. When the transmission loss index was 100 or less, the transmission loss was evaluated as particularly small and acceptable, and this is indicated by a ⊚ in Table 2.

[0154] <Laser processability (reduction of resin residue at the bottom of the via hole)> When forming a blind via hole by laser irradiation, resin derived from the resin substrate may remain at the bottom of the formed blind via hole. If the resin remains, sufficient conductivity may not be obtained even when an interlayer connector is formed, and the connection reliability at the time of interlayer connection may be reduced. Copper-clad laminates were produced using the surface-treated copper foil, and their laser processability, i.e., whether or not resin derived from the resin substrate is less likely to remain at the bottom of the formed blind via hole when formed by laser irradiation, was evaluated.

[0155] A single-sided copper-clad laminate was produced by bonding a 12 μm thick surface-treated copper foil to one side of a 50 μm thick liquid crystal polymer film (manufactured by Ise Murata Manufacturing Co., Ltd., thickness accuracy: 0.7 μm, relative dielectric constant: 3.4, dielectric dissipation factor: 0.0020, ratio of maximum to minimum coefficient of linear thermal expansion: 1.4) using a heat fusion method.

[0156] Next, a carbon dioxide laser was used to irradiate the liquid crystal polymer film side of the single-sided copper-clad laminate, forming 150 via holes at random locations. The diameter of the via holes was 100 μm. The laser irradiation was performed under the following conditions: pulse width 1 to 5 μs, tip energy 1 to 3 mJ, mask diameter 1 to 3 mm, and number of irradiation shots 5 to 10, depending on the structure of the roughening particles.

[0157] After the via holes were formed, the roughened surface of the surface-treated copper foil at the bottom of the via holes was observed to check for the presence or absence of residual resin. The presence or absence of residual resin was confirmed by removing the surface-treated copper foil by etching after laser processing, and then observing with an optical microscope at a magnification of 10x to check for the presence or absence of residual resin at the bottom of the via holes. Observation with an optical microscope was performed on all 150 via holes, and the number of via holes without residual resin was counted.

[0158] In the examples and comparative examples, when the number of via holes with no residual resin was 80 or more, the processability was very good and the result was evaluated as "pass," which is indicated by a double circle in Table 2. When the number of via holes with no residual resin was 40 to 79, the result was evaluated as "pass," which is indicated by a circle in Table 2. When the number of via holes with no residual resin was 39 or less, the result was evaluated as "fail," which is indicated by an x ​​in Table 2.

[0159] <Laser processability (suppression of resin residue at bases of roughening particles)> The present embodiment aims to provide a printed wiring board having excellent adhesion between a resin substrate and a surface-treated copper foil, low transmission loss, and good long-term connection reliability. Specifically, the present embodiment aims to suppress the resin residue at bases of roughening particles in the surface-treated copper foil, thereby suppressing the occurrence of cracks between the resin substrate and the surface-treated copper foil due to thermal stress during long-term use, which can cause poor connection or cracks, resulting in a decrease in connection reliability.

[0160] According to this embodiment, a printed wiring board can be provided in which the adhesion between the resin substrate and the surface-treated copper foil is excellent, transmission loss is small, and resin is less likely to remain at the base of the roughening particles (excellent laser processability).Since resin is less likely to remain at the base of the roughening particles, long-term connection reliability can be ensured.

[0161] Copper-clad laminates were prepared using surface-treated copper foils, and their laser processability, i.e., whether or not resin derived from the resin substrate was less likely to remain at the base of roughening particles in blind via holes formed by laser irradiation, was evaluated. Single-sided copper-clad laminates were prepared in the same manner as in the above-mentioned "Laser processability (suppression of resin residue at the bottom of via holes)," and then via holes were formed using a carbon dioxide laser. The single-sided copper-clad laminates with via holes formed therein were then analyzed as follows.

[0162] First, the single-sided copper-clad laminate with the via holes formed therein was pretreated. Osmium (Os) or platinum (Pt)-palladium (Pd) was vapor-deposited onto the single-sided copper-clad laminate. This allowed the bottom of the via holes to be observed using a scanning electron microscope (SEM). The single-sided copper-clad laminate was embedded in an embedding resin such as epoxy resin, and then cut so that the maximum diameter cross-section of the via holes could be observed. The exposed cross-section was mirror-polished. Then, polishing marks were removed using flat milling to obtain a sample for scanning electron microscope observation.

[0163] The cross section of the sample was observed using a scanning electron microscope, and secondary electron images (SEM images) were obtained at 5,000x magnification. The acceleration voltage of the scanning electron microscope was 10 kV. SEM images with a width of 25 μm were obtained in one field of view, and SEM images were obtained in ten fields of view. These 10 SEM images were then analyzed to evaluate the degree of resin remaining at the bottom of the via hole. This is explained below.

[0164] First, the contour of the surface shape of the roughened surface is extracted. Then, among the roughening particles present in one field of view, the roughening particle with the highest tip is selected, and that tip is taken as the highest point of that field of view. Furthermore, among the roughening particles present in one field of view, the gap with the lowest bottom between the roughening particles is selected, and that bottom of that gap is taken as the lowest point of that field of view.

[0165] Next, a highest line is drawn that passes through the highest point and is parallel to the surface of the copper foil (i.e., a line parallel to the width of the field of view), and a lowest line is drawn that passes through the lowest point and is parallel to the surface of the copper foil. The area between these two lines is defined as the measurement area. The height (height from the lowest line) that is 25% of the height of this measurement area (the distance between the highest line and the lowest line) is defined as the "reference height."

[0166] At this reference height, gaps between roughening particles with a width of 0.2 μm or more were defined as "valleys" between the roughening particles. If resin remained in the valleys, the degree of resin remaining at the base of the roughening particles was evaluated based on the distance between the bottom of the valley and the surface of the remaining resin.

[0167] The degree of resin remaining at the base of the roughening particles was calculated for all valleys within a 25 μm range centered on the center of the bottom of the via hole, and the degree of resin remaining at the base of the roughening particles was calculated for a total of 10 fields of view. The laser processability (reduction of resin remaining at the base of the roughening particles) was then evaluated using the average value. The results are shown in Table 2.

[0168] In the examples and comparative examples, when the distance between the bottom of the valley and the surface of the remaining resin is 0.6 μm or less, it is evaluated as passing, and is indicated by a circle in Table 2. When the distance between the bottom of the valley and the surface of the remaining resin exceeds 0.6 μm, it is evaluated as failing, and is indicated by an x ​​in Table 2. The bottom of the valley is defined as the intersection of a line perpendicular to the line representing the reference height and passing through the center of the valley with the surface of the copper foil.

[0169] <Powder Fall-Off Resistance> After attaching a reference plate to the non-roughened surface of the surface-treated copper foil, a white dust-free paper was brought into contact with the roughened surface of the surface-treated copper foil. A weight of 1 kg was placed on the white dust-free paper, and the white dust-free paper was moved 50 mm at a speed of 100 mm / min in a direction parallel to the contact surface between the roughened surface and the white dust-free paper.

[0170] The surface of the white dust-free paper was photographed using an optical microscope under reflected illumination to obtain a magnified image. The magnification was 20x. The brightest area of ​​the enlarged image was designated a brightness of 255, and the darkest area a brightness of 0. Areas with a brightness of 200 or less were considered to be copper powder transferred to the white dust-free paper (copper powder resulting from the roughening particles). The proportion of the area of ​​the enlarged image with a brightness of 200 or less (area ratio) was then calculated. The results are shown in Table 2. In the examples and comparative examples, an area ratio of less than 0.5% was evaluated as pass, and is indicated by a circle in Table 2. An area ratio of 0.5% or more was evaluated as fail, and is indicated by an x ​​in Table 2.

[0171] <Oxidation of Copper Foil> The surface-treated copper foil was placed in an oven and heated, and the presence or absence of discoloration after heating was confirmed. The heating conditions were a temperature of 250°C, a heating time of 30 minutes, and an air atmosphere. The results are shown in Table 2. In the examples and comparative examples, when the surface-treated copper foil did not discolor, it was evaluated as passing, and this is indicated by a circle in Table 2. When the surface-treated copper foil did discolor, it was evaluated as failing, and this is indicated by an x ​​in Table 2.

[0172] Fig. 7 shows a cross-sectional view of a copper-clad laminate using conventional surface-treated copper foil. Fig. 7 shows a cross-section of a via hole, and it can be seen that resin remains at the base of the roughening particles at the bottom of the via hole. Therefore, crack sources are likely to occur at the interface between the interlayer connection conductor in the via hole and the surface-treated copper foil.

[0173] Figure 8 is a cross-sectional view of a copper-clad laminate using the surface-treated copper foil of the first embodiment. Figure 8 shows a cross-section of a via hole, and it can be seen that because laser light is easily introduced to the base of the roughening particles, resin residue at the base of the roughening particles at the bottom of the via hole is suppressed. This strengthens the bond between the interlayer connection conductor in the via hole and the surface-treated copper foil, making it less likely for crack sources to occur at the interface between the interlayer connection conductor and the surface-treated copper foil. The process of forming via holes, circuit patterns, and interlayer connectors in a copper-clad laminate is as shown in Figure 4, and the specific details are as follows.

[0174] An example of a process for forming blind via holes in a double-sided copper-clad laminate 100 by laser irradiation is shown in Figure 5. Also, an example of a process for forming blind via holes in a single-sided copper-clad laminate 100 by laser irradiation is shown in Figure 6. The process for forming blind via holes is almost the same for both double-sided and single-sided copper-clad laminates, so the following explanation will be given using a double-sided copper-clad laminate as an example. Note that the same reference numerals are used to designate corresponding components in Figures 5 and 6.

[0175] A copper clad laminate 100 shown in Fig. 5(a) is irradiated with a laser 130 to form a blind via hole (see Fig. 5(b)). When forming a blind via hole by laser irradiation, residue 120 (metal originating from the surface-treated copper foil 111 and resin originating from the resin substrate 113) may remain at the bottom 140 of the blind via hole after processing by irradiating with the laser 130 (see Fig. 5(b)).

[0176] Therefore, after the blind via holes are formed, the copper-clad laminate 100 is subjected to a desmear process to remove residues 120 in the blind via holes (see (c) in FIG. 5). Then, after the desmear process, an interlayer connector 116 is formed. Methods for forming the interlayer connector 116 include a method of forming a plating film 115 and a method of filling the blind via holes with at least one of plating and metal paste to form the interlayer connector 116.

[0177] As shown in Fig. 5(d), plating can be performed to form a plating film 115 on the inner surface of the blind via hole. Also, as shown in Fig. 5(e), the blind via hole can be filled with at least one of plating and metal paste to form an interlayer connector 116. Note that the top surface of the interlayer connector 116 does not need to be flush with the surfaces of the surface-treated copper foil 111 and the resin base material 113.

[0178] 10: Surface-treated copper foil 10a: Roughened surface 20: Resin substrate 30: Copper-clad laminate

Claims

1. A surface-treated copper foil having a roughened surface on at least one side on which roughening particles are formed, wherein the physical property values ​​measured on the roughened surface satisfy the following (a), (b), and (c): (a) The specular reflectance of the roughened surface, measured using a spectrophotometer having a light source emitting 45° polarized light with a wavelength of 600 nm, at an incident angle and a reflection angle of 70°, is 0.20% or more and 0.90% or less. (b) The brightness Y value of the roughened surface is 10.0 or more and 15.5 or less. (c) The Ssk of the roughened surface, measured using a laser microscope, is 0.30 or more and 0.80 or less.

2. A nickel coating is formed on the roughened surface, and the amount of nickel deposited by the nickel coating is 0.20 mg / dm 2 0.40mg / dm or more 2 2. The surface-treated copper foil according to claim 1, wherein:

3. A surface-treated copper foil having a roughened surface on at least one side on which roughening particles are formed, wherein when the surface-treated copper foil is cut to expose a cross section perpendicular to the roughened surface, the physical properties of the roughened surface, measured by observing the cross section with a scanning electron microscope, satisfy the following (f), (g), and (h): (f) the average cross-sectional particle height h_ave of the roughening particles is 0.35 μm or more and 0.70 μm or less; (g) the standard deviation w_σ of the cross-sectional particle width of the roughening particles is 0.05 μm or more and 0.10 μm or less; and (h) the skewness h_sk of the cross-sectional particle height of the roughening particles is 0.80 or more and -2.50 × h_ave + 3.50 or less.

4. A copper-clad laminate comprising the surface-treated copper foil according to any one of claims 1 to 3 and a resin substrate bonded to the roughened surface of the surface-treated copper foil.

5. The copper clad laminate according to claim 4, wherein said resin substrate is formed from a thermoplastic resin.

6. The copper clad laminate according to claim 4, wherein said resin substrate is formed from a liquid crystal polymer.

7. A printed wiring board comprising the copper clad laminate of claim 4.

8. The printed wiring board according to claim 7, wherein the surface-treated copper foil and the resin base material are plastically deformed.

9. The printed wiring board according to claim 7, wherein the surface-treated copper foil and the resin base material are integrally bent.

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