Surface-treated copper foil, copper-cladded laminate plate, and printed wiring board

Abstract

A surface-treated copper foil having a copper foil and a surface-treated layer formed on at least one surface of the copper foil. The surface-treated layer has a rate of change of Vmc of 23.00 to 40.00%, the rate of change of Vmc being represented by the following equation: the rate of change of Vmc = (P2 - P1) / P2 × 100 (1) in which P1 is Vmc calculated by applying a λs filter having a cutoff value λs of 2 μm, and P2 is Vmc calculated without applying the λs filter.

Description

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

[0001] The present disclosure relates to a surface-treated copper foil, a copper-clad laminate, and a printed wiring board.

[0002] Copper-clad laminates are widely used in various applications, such as flexible printed wiring boards. Flexible printed wiring boards are manufactured by etching the copper foil of a copper-clad laminate to form a conductor pattern (also called a "wiring pattern") and then mounting electronic components on the conductor pattern by connecting them with solder.

[0003] In recent years, in electronic devices such as personal computers and mobile terminals, the frequency of electrical signals has been increasing in line with the increase in communication speed and capacity, and flexible printed wiring boards that can accommodate this have been in demand. In particular, the higher the frequency of the electrical signal, the greater the loss (attenuation) of signal power, making it easier for data to become unreadable, and therefore there has been a demand for reducing the loss of signal power.

[0004] The causes of signal power loss (transmission loss) in electronic circuits can be broadly divided into two categories. The first is conductor loss, i.e., loss due to copper foil, and the second is dielectric loss, i.e., loss due to the resin substrate. Conductor loss is characterized by the skin effect in the high-frequency range, where current flows along the surface of the conductor. Therefore, if the copper foil surface is rough, the current will flow along a complex path. Therefore, to reduce the conductor loss of high-frequency signals, it is desirable to reduce the surface roughness of the copper foil. Hereinafter, when the terms "transmission loss" and "conductor loss" are simply used in this specification, they primarily mean "transmission loss of high-frequency signals" and "conductor loss of high-frequency signals."

[0005] On the other hand, since dielectric loss depends on the type of resin substrate, it is desirable to use a resin substrate made of a low-dielectric material (e.g., liquid crystal polymer, low-dielectric polyimide) for circuit boards through which high-frequency signals pass. Furthermore, since dielectric loss is also affected by the adhesive used to bond the copper foil to the resin substrate, it is desirable to bond the copper foil to the resin substrate without using an adhesive. Therefore, forming a surface treatment layer on at least one side of the copper foil has been proposed to bond the copper foil to the resin substrate without using an adhesive. For example, Patent Document 1 proposes a method in which a roughening treatment layer made of roughening particles is provided on the copper foil and a silane coupling treatment layer is formed on the outermost layer.

[0006] JP 2012-112009 A

[0007] The surface of copper foil on which a surface treatment layer is formed generally has minute irregularities. For example, in the case of rolled copper foil, oil pits formed by rolling oil during rolling form minute irregularities on the surface. In addition, in the case of electrolytic copper foil, polishing streaks formed by the rotating drum during polishing cause minute irregularities on the rotating drum side surface of the electrolytic copper foil deposited on the rotating drum. If minute irregularities exist on the copper foil surface, for example, when forming a roughening treatment layer, current concentrates on the convex parts of the copper foil surface, causing overgrowth of roughening particles, while insufficient current is supplied to the concave parts of the copper foil surface and their surroundings, making it difficult for the roughening particles to grow. As a result, coarse roughening particles are formed on the convex parts of the copper foil surface, while the concave parts of the copper foil surface and their surrounding concave parts have too small roughening particles. In particular, the adhesion of roughening particles is insufficient near the edges of the oil pits, i.e., the roughening particles are not uniformly formed on the copper foil surface. When surface-treated copper foil containing a large number of coarse roughening particles is bonded to a resin substrate, applying a force to peel the surface-treated copper foil can cause stress to concentrate on the coarse roughening particles, making the foil more likely to break, resulting in reduced adhesion to the resin substrate. Furthermore, when the roughening particles are insufficiently large, the anchoring effect of the roughening particles is reduced, and sufficient adhesion between the copper foil and the resin substrate can be insufficient. In particular, resin substrates made from low-dielectric materials such as liquid crystal polymers and low-dielectric polyimides are more difficult to bond to copper foil than conventional resin substrates, so there is a need for a method to improve adhesion between copper foil and the resin substrate. Furthermore, although a silane coupling treatment layer has the effect of improving adhesion between the copper foil and the resin substrate, depending on the type of silane coupling treatment layer, the effect of improving adhesion may not be sufficient.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide, in one aspect, a surface-treated copper foil that can improve adhesion to a resin substrate, particularly a resin substrate suitable for high-frequency applications. Another aspect of the present invention aims to provide a copper-clad laminate that has excellent adhesion between a resin substrate, particularly a resin substrate suitable for high-frequency applications, and the surface-treated copper foil. Another aspect of the present invention aims to provide a printed wiring board that has excellent adhesion between a resin substrate, particularly a resin substrate suitable for high-frequency applications, and a circuit pattern.

[0009] In order to solve the above problems, the present inventors have conducted extensive research on surface-treated copper foils, and have found that adding a trace amount of a tungsten compound to a plating solution used to form a roughened layer can suppress the overgrowth of roughening particles formed on the convex parts of the copper foil surface and facilitate the formation of roughening particles around the concave parts of the copper foil surface.The present inventors then analyzed the surface shape of the surface-treated copper foil obtained in this way and found that the rate of change in Vmc of the surface treatment layer is closely related to this surface shape, leading to the completion of an embodiment of the present invention.

[0010] That is, one aspect of an embodiment of the present invention relates to a surface-treated copper foil having a copper foil and a surface treatment layer formed on at least one surface of the copper foil, wherein the surface treatment layer has a rate of change in Vmc expressed by the following formula (1) of 23.00 to 40.00%: Rate of change in Vmc=(P2-P1) / P2×100 (1) In the formula, P1 is Vmc calculated by applying a λs filter with a cutoff value λs of 2 μm, and P2 is Vmc calculated without applying the λs filter.

[0011] In another aspect, the present invention relates to a copper-clad laminate comprising the surface-treated copper foil and a resin substrate adhered to the surface treatment layer of the surface-treated copper foil. Furthermore, in another aspect, the present invention relates to a printed wiring board comprising a circuit pattern formed by etching the surface-treated copper foil of the copper-clad laminate.

[0012] According to an embodiment of the present invention, in one aspect, a surface-treated copper foil capable of improving adhesion to a resin substrate, particularly a resin substrate suitable for high-frequency applications, can be provided. According to another aspect, according to an embodiment of the present invention, a copper-clad laminate having excellent adhesion between a resin substrate, particularly a resin substrate suitable for high-frequency applications, and the surface-treated copper foil can be provided. According to another aspect, according to an embodiment of the present invention, a printed wiring board having excellent adhesion between a resin substrate, particularly a resin substrate suitable for high-frequency applications, and a circuit pattern can be provided.

[0013] 1 is a typical load curve of a surface treatment layer, FIG. 2 is a schematic diagram for explaining roughening particles constituting a surface treatment layer and Vmc, and FIG. 3 is a schematic enlarged cross-sectional view of a surface-treated copper foil having a roughening treatment layer on one side of the copper foil.

[0014] Preferred embodiments of the present invention will be described in detail below, but the present invention should not be construed as being limited thereto, and various modifications and improvements can be made based on the knowledge of those skilled in the art without departing from the gist of the present invention. The multiple components disclosed in the following embodiments can be appropriately combined to form various inventions. For example, some components may be deleted from all the components shown in the following embodiments, or components from different embodiments may be appropriately combined.

[0015] The surface-treated copper foil according to the embodiment of the present invention has a copper foil and a surface treatment layer formed on at least one side of the copper foil. The surface treatment layer may be formed on only one side of the copper foil, or may be formed on both sides of the copper foil. When a surface treatment layer is formed on both sides of the copper foil, the types of the surface treatment layers may be the same or different.

[0016] The surface shape of the surface treatment layer can be identified using surface texture parameters obtained by measuring the surface texture in accordance with ISO 25178-2:2012 and analyzing the load curve calculated from the measurement data. Before explaining the load curve, we will first explain the load area ratio. The load area ratio is the ratio obtained by dividing the area corresponding to the cross section of a three-dimensional object when the object is cut at a plane of a certain height by the area of ​​the measurement field. In this disclosure, the object to be measured is assumed to be a copper foil or a surface treatment layer of a surface-treated copper foil. The load curve is a curve that represents the load area ratio at each height. The area ratio near 0% represents the height of the highest part of the object to be measured, and the height near 100% represents the height of the lowest part of the object to be measured.

[0017] Next, a typical load curve of a surface treatment layer is shown in FIG. 1. The load curve can be used to express the volume of the solid portion and the volume of the void portion of the surface treatment layer. The volume of the solid portion corresponds to the volume of the portion occupied by the solid portion of the object in the measurement field of view, and the volume of the void portion corresponds to the volume occupied by the space between the solid portions in the measurement field of view. The load curve described in the present disclosure is divided into a valley portion, a core portion, and a peak portion, with the areal load ratios of 10% and 80% as boundaries. Referring to FIG. 1 and describing the surface treatment layer according to an embodiment of the present invention, Vvv refers to the volume of the void portion in the valley portion of the surface treatment layer, Vvc refers to the volume of the void portion in the core portion of the surface treatment layer, Vmp refers to the volume of the solid portion in the peak portion of the surface treatment layer, and Vmc refers to the volume of the solid portion in the core portion of the surface treatment layer. Note that a peak portion refers to a high portion of the object to be measured. A valley portion refers to a low portion of the object to be measured. A core portion refers to the portion of the object to be measured other than the peak portion and the valley portion, i.e., a portion with a height close to the average.

[0018] The peak volume Vmp is the volume of the peak, i.e., the volume of the solid body at the high height of the object being measured, and refers to the volume of the solid body at the particularly high height of the surface treatment layer. Here, the solid body at the particularly high height of the surface treatment layer can be interpreted as the volume resulting from overgrown particles (particularly, roughening particles). The core volume Vmc is the volume of the solid body at the core, i.e., the part of the object being measured that is close to the average height, and refers to the volume of the solid body at the average height of the surface treatment layer. Here, the solid body at the average height of the surface treatment layer can be interpreted as the volume resulting from average-sized particles (particularly, roughening particles) formed in a relatively smooth portion of the copper foil surface. In summary, as a result of the above analysis, the present inventors have found that, in the surface-treated copper foil according to the embodiment of the present invention, Vmp correlates with the solid body volume of overgrown large particles, and Vmc correlates with the solid body volume of average-sized particles. In the following description, the case where the particles are roughening particles may be taken as an example, but it should be noted that the particles are not limited to roughening particles.

[0019] Measurement data for measuring the surface texture of the surface-treated copper foil according to the embodiment of the present invention can be obtained using a laser microscope such as a confocal laser microscope. Here, by applying a Fourier transform to the measurement data, the measurement data can be separated into waveforms with various periods and amplitudes. The inventors considered that it would be possible to calculate surface texture parameters of interest from the measurement data by applying a filter to each separated waveform, which attenuates the amplitude of waveforms within a specific frequency range, and then analyzing the data obtained by synthesizing all the waveforms again.

[0020] In analyzing surface roughness measurement data, the inventors discovered that detailed information on the characteristic surface shape of the surface treatment layer according to an embodiment of the present invention (particularly, the adhesion state of the roughening particles that make up the surface treatment layer) can be obtained by combining surface texture parameters calculated using a λs filter with a cutoff value λs of 2 μm and surface texture parameters calculated without using this λs filter. Here, the λs filter is a profile filter that significantly attenuates the amplitude of waveforms with wavelengths smaller than the cutoff value λs. The λs filter corresponds to the S filter in ISO 25178-2:2012. The amount by which the λs filter attenuates the amplitude varies depending on the wavelength of the waveform. For wavelengths with the cutoff value λs, the amplitude is attenuated to 50% of the original value, and for waveforms with smaller wavelengths, the amplitude is attenuated even more. The cutoff value λs of 2 μm is between the size of the roughening particles that make up the surface treatment layer and the size of the oil pits. The measurement data obtained by setting the cutoff value λs to 2 μm is data derived from waveforms with a shorter period than the cutoff value λs, and can therefore be understood as data from which data derived from roughening particles has been removed. Based on this, the difference between the surface texture parameter calculated without applying a λs filter with a cutoff value λs of 2 μm and the surface texture parameter calculated with this λs filter can be said to be information on the surface treatment layer from which information on oil pits has been removed, i.e., information on the roughening particles that make up the surface treatment layer.

[0021] Based on the above findings, the inventors analyzed various surface quality parameters obtained from the load curve and found that the rate of change in Vmc in the surface treatment layer, expressed by the following formula (1), is closely related to the adhesion amount of roughening particles of average size that make up the surface treatment layer: Rate of change in Vmc=(P2-P1) / P2×100 (1) In the formula, P1 is Vmc calculated using a λs filter with a cutoff value λs of 2 μm, and P2 is Vmc calculated without using the λs filter.

[0022] Here, a schematic diagram illustrating the roughening particles and Vmc constituting the surface treatment layer is shown in Figure 2. As shown in Figure 2, the surface treatment layer contains average-sized roughening particles A and overgrown roughening particles B. As already explained above, Vmc corresponds to the volume of average-sized roughening particles A formed on a relatively smooth portion of the copper foil surface and is thought to correlate with the amount of average-sized roughening particles A attached. Vmc is significantly influenced by macroscopic shapes such as oil pits. To more accurately read the information on the surface treatment layer, it is necessary to remove the contribution of macroscopic shapes. P1 can be interpreted as the value of Vmc from which information derived from roughening particles has been removed, in other words, the value of Vmc from which information derived from oil pits and the like remains. Taking the difference between P2 and P1 means removing information derived from macroscopic shapes such as oil pits contained in Vmc. As a result, information correlated with the amount of average-sized roughening particles A attached can be accurately extracted. The average size of roughening particles A formed on relatively smooth portions of the copper foil surface is thought to be closely related to the adhesive strength between the resin substrate and the surface treatment layer. Overgrown (coarse) roughening particles B lead to roughening breakage, while excessively small roughening particles are thought to not penetrate the resin substrate at all. Therefore, by producing a surface-treated copper foil in which the rate of change in Vmc of the surface treatment layer, which correlates with the average adhesion amount of roughening particles A, is controlled within an appropriate range, it is possible to improve adhesion to the resin substrate. From this perspective, surface-treated copper foils according to embodiments of the present invention, in which the rate of change in Vmc is 23.00 to 40.00%, exhibit sufficient adhesive strength to the resin substrate. To stably obtain this effect, the rate of change in Vmc is preferably 23.00 to 32.00%, more preferably 23.00 to 31.00%.

[0023] The surface treatment layer preferably has an Sku (kurtosis) calculated without applying the λs filter of 2.50 to 4.50. Sku is a parameter that expresses the degree of peaking (kurtosis) of a height histogram created based on the average height. For example, Sku = 3.00 means that the height distribution is a normal distribution. Furthermore, when Sku > 3.00, the larger the value, the more concentrated the height distribution. Conversely, when Sku < 3.00, the smaller the value, the more dispersed the height distribution.

[0024] The surface-treated copper foil according to an embodiment of the present invention has a surface irregularity, which contributes to improving the adhesion between the copper foil and the resin substrate. The Sku of the surface treatment layer is an index for evaluating the height distribution of the irregularities. An Sku of 2.50 to 4.50 of the surface treatment layer means that the height distribution is normal or close to normal. On the other hand, an Sku of less than 2.50 means that the height of the surface treatment layer (height from the copper foil surface) is a mixture of low and high parts, resulting in a uniform height distribution. An Sku of the surface treatment layer greater than 4.50 means that the height distribution is uneven, i.e., the surface of the surface treatment layer is dominated by parts of a certain height. A height distribution of the surface treatment layer that is normal or close to normal means, for example, that when a roughening treatment layer is formed on the surface of a copper foil, there are few areas where roughening particles have overgrown on the convex portions of the copper foil surface, i.e., there are few roughening particles, and there are few areas around the concave portions of the copper foil surface (the ends of the convex portions) where roughening particles have not formed. Therefore, an Sku of 2.50 to 4.50 for the surface treatment layer means that the overgrowth of roughening particles formed on the convex portions of the copper foil surface is suppressed, and that roughening particles are also formed around the concave portions of the copper foil surface.

[0025] Neither surface-treated copper foils with many roughening particles nor surface-treated copper foils with areas where no roughening particles are formed are preferable from the viewpoint of adhesion to the resin substrate. For example, when a surface-treated copper foil with many roughening particles is bonded to a resin substrate and a force is applied to peel the surface-treated copper foil, stress is concentrated on the coarse roughening particles, making the foil more likely to break, which is thought to result in a decrease in adhesion to the resin substrate. Furthermore, when a surface-treated copper foil with areas where no roughening particles are formed is bonded to the resin substrate, the anchoring effect of the roughening particles cannot be fully secured, and the adhesion between the surface-treated copper foil and the resin substrate is thought to decrease. Therefore, from the viewpoint of stably obtaining adhesion to the resin substrate, the lower limit of Sku of the surface-treated layer is preferably 2.90 and the upper limit is preferably 4.10. The Sku of the surface-treated layer can be determined by measuring the surface roughness in accordance with ISO 25178-2:2012 and analyzing the profile curve calculated from the measurement data.

[0026] The surface treatment layer preferably has an Sq (root mean square height) of 0.20 to 0.60 μm calculated without applying the λs filter. Sq is a height-direction parameter defined in ISO 25178-2:2012 and represents the variation in the height of the convex portions on the surface of the surface treatment layer. A large Sq of the surface treatment layer means that the variation in the height of the convex portions on the surface of the surface treatment layer is large. An excessively large Sq (too large variation in the height of the convex portions) can be problematic from the perspective of quality control as an industrial product. Therefore, by setting the Sq of the surface treatment layer within the above range, it is possible to ensure productivity while allowing for some variation in the height of the convex portions, thereby enabling appropriate quality control. From the perspective of stably achieving these effects, the lower limit of the Sq of the surface treatment layer is preferably 0.26 μm, more preferably 0.30 μm, and even more preferably 0.34 μm, and the upper limit is preferably 0.53 μm, more preferably 0.48 μm, and even more preferably 0.43 μm. The Sq of the surface treatment layer can be determined by measuring the surface roughness in accordance with ISO 25178-2:2012 and analyzing the profile curve calculated from the measurement data.

[0027] The surface treatment layer preferably has an arithmetic mean height (Sa) of 0.20 to 0.40 μm, calculated without applying the λs filter. Sa is a height parameter defined in ISO 25178-2:2012 and represents the average height difference from the mean plane. If the Sa of the surface treatment layer is large, the surface of the surface treatment layer becomes rough, making it easier to demonstrate the anchor effect when the surface-treated copper foil is bonded to a resin substrate. On the other hand, if the Sa of the surface treatment layer is too large, transmission loss increases due to the skin effect of the surface-treated copper foil when a circuit board is fabricated by processing a copper-clad laminate in which the surface-treated copper foil is bonded to a resin substrate. Therefore, by setting the Sa of the surface treatment layer within the above range, a balance can be achieved between ensuring the adhesion of the surface-treated copper foil to the resin substrate and suppressing transmission loss. From the viewpoint of stably obtaining such effects, the lower limit of the Sa of the surface treatment layer is preferably 0.23 μm, more preferably 0.24 μm, and the upper limit is preferably 0.35 μm. Furthermore, when prioritizing suppression of transmission loss due to the skin effect and ease of quality control as an industrial product, it is preferable that the surface treatment layer has Sa of 0.20 to 0.32 μm and Sq of 0.26 to 0.40 μm. Note that Sa of the surface treatment layer can be determined by measuring the surface roughness in accordance with ISO 25178-2:2012 and analyzing the profile curve calculated from the measurement data.

[0028] The surface treatment layer preferably has an Ssk (skewness) calculated without applying the λs filter of -1.10 to 0.60. Ssk is a parameter that expresses the degree of bias (skewness) of a height histogram created based on the average height. For example, Ssk = 0.00 means that the height distribution is symmetrical with respect to the average line. Furthermore, when Ssk > 0.00, the larger the value, the more the height distribution is biased downward relative to the average line. Conversely, when Ssk < 0.00, the smaller the value, the more the height distribution is biased upward relative to the average line. Therefore, Ssk of the surface treatment layer, like Sku, is an index for evaluating the height distribution of the unevenness of the surface treatment layer. An Ssk of -1.10 to 0.60 means, for example, that when a roughening treatment layer is formed on the surface of a copper foil, there are few areas where roughening particles, i.e., coarse roughening particles, overgrow on the convex portions of the copper foil surface, and there are few areas where roughening particles are not formed around the concave portions of the copper foil surface (the ends of the convex portions). On the other hand, if the Ssk is less than -1.10, there are many areas where roughening particles are not formed around the concave portions of the copper foil surface. Furthermore, if the Ssk exceeds 0.60, there are many areas where roughening particles overgrow on the convex portions of the copper foil surface. From the viewpoint of obtaining stable adhesion to the resin substrate, the upper limit of the Ssk of the surface treatment layer is preferably 0.40, and the lower limit is preferably -0.80. The Ssk of the surface treatment layer can be determined by measuring the surface roughness in accordance with ISO 25178-2:2012 and analyzing the profile curve calculated from the measurement data.

[0029] The type of surface treatment layer is not particularly limited, and various surface treatment layers known in the art can be used. Examples of surface treatment layers include a roughening treatment layer, a heat-resistant treatment layer, a rust-proofing treatment layer, a chromate treatment layer, and a silane coupling treatment layer. These layers can be used alone or in combination of two or more. Among them, it is preferable that the surface treatment layer contains a roughening treatment layer from the viewpoint of adhesion to the resin substrate. Furthermore, when the surface treatment layer contains one or more layers selected from the group consisting of a heat-resistant treatment layer, a rust-proofing treatment layer, a chromate treatment layer, and a silane coupling treatment layer, it is preferable that these layers are provided on the roughening treatment layer.

[0030] As an example, FIG. 3 shows a schematic enlarged cross-sectional view of a surface-treated copper foil having a roughened layer on one side of the copper foil. As shown in FIG. 3, the roughened layer formed on one side of the copper foil 10 includes roughened particles 20 and a cover plating layer 30 that covers at least a portion of the roughened particles 20. The roughened particles 20 are formed not only near the center of the convex portions 11 on the surface of the copper foil 10 but also around the concave portions 12 (the ends of the convex portions 11). Furthermore, the overgrowth of the roughened particles 20 formed on the convex portions 11 on the surface of the copper foil 10 is suppressed by adding a trace amount of a tungsten compound to the plating solution. Therefore, the roughened particles 20 do not overgrow into large particles, but rather have a complex shape that grows in all directions. It is believed that such a structure can be achieved by controlling the rate of change in Vmc of the surface treatment layer within the above range.

[0031] The roughening particles 20 are not particularly limited, but may be formed from a single element selected from the group consisting of copper, nickel, cobalt, phosphorus, tungsten, arsenic, molybdenum, chromium, and zinc, or an alloy containing two or more of these elements. Among these, the roughening particles 20 are preferably formed from copper or a copper alloy, particularly copper. The cover plating layer 30 is not particularly limited, but may be formed from copper, silver, gold, nickel, cobalt, zinc, etc.

[0032] The roughened layer can be formed by electroplating. In particular, the roughening particles 20 can be formed by electroplating using a plating solution containing a trace amount of a tungsten compound. The tungsten compound is not particularly limited, but sodium tungstate (Na2WO4) can be used, for example. The content of the tungsten compound in the plating solution is preferably 1 ppm or more. This content can suppress overgrowth of the roughening particles 20 formed on the protrusions 11 and facilitate the formation of the roughening particles 20 around the recesses 12. The upper limit of the tungsten compound content is not particularly limited, but is preferably 20 ppm from the viewpoint of suppressing an increase in electrical resistance.

[0033] The electroplating conditions for forming the roughened layer are not particularly limited and may be adjusted depending on the electroplating apparatus used, but typical conditions are as follows. Each electroplating may be performed once or multiple times. (Conditions for forming roughened particles 20) Plating solution composition: 5 to 15 g / L Cu, 40 to 100 g / L sulfuric acid, 1 to 6 ppm sodium tungstate Plating solution temperature: 20 to 50°C Electroplating conditions: current density 30 to 90 A / dm 2 , time 0.1 to 8 seconds

[0034] (Conditions for forming the cover plating layer 30) Plating solution composition: 10 to 30 g / L of Cu, 70 to 130 g / L of sulfuric acid Plating solution temperature: 30 to 60°C Electroplating conditions: current density 4.8 to 15 A / dm 2 , time 0.1 to 8 seconds

[0035] The heat-resistant treatment layer and the rust-proofing treatment layer are not particularly limited and can be formed from materials known in the art. Since the heat-resistant treatment layer may also function as a rust-proofing treatment layer, a single layer having both the functions of a heat-resistant treatment layer and a rust-proofing treatment layer may be formed. The heat-resistant treatment layer and / or the rust-proofing treatment layer may be a layer containing one or more elements (which may be in the form of metal, alloy, oxide, nitride, sulfide, etc.) selected from the group consisting of nickel, zinc, tin, cobalt, molybdenum, copper, tungsten, phosphorus, arsenic, chromium, vanadium, titanium, aluminum, gold, silver, platinum group elements, iron, and tantalum. Among these, the heat-resistant treatment layer and / or the rust-proofing treatment layer is preferably a Ni-Zn layer.

[0036] The heat-resistant treatment layer and the rust-proofing treatment layer can be formed by electroplating. The conditions are not particularly limited and can be adjusted depending on the electroplating equipment used. However, the conditions for forming the heat-resistant treatment layer (Ni-Zn layer) using a general electroplating equipment are as follows. Note that electroplating may be performed once or multiple times. Plating solution composition: 1 to 30 g / L Ni, 1 to 30 g / L Zn Plating solution pH: 2 to 5 Plating solution temperature: 30 to 50°C Electroplating conditions: current density 0.1 to 10 A / dm 2 , time 0.1 to 5 seconds

[0037] The chromate-treated layer is not particularly limited and can be formed from materials known in the art. In this specification, the term "chromate-treated layer" refers to a layer formed from a solution containing chromic anhydride, chromic acid, dichromate, chromate salt, or dichromate salt. The chromate-treated layer can be a layer containing elements such as cobalt, iron, nickel, molybdenum, zinc, tantalum, copper, aluminum, phosphorus, tungsten, tin, arsenic, and titanium (which may be in the form of a metal, alloy, oxide, nitride, sulfide, or the like). Examples of chromate-treated layers include chromate-treated layers treated with an aqueous solution of chromic anhydride or potassium dichromate, and chromate-treated layers treated with a treatment solution containing chromic anhydride or potassium dichromate and zinc.

[0038] The chromate treatment layer can be formed by known methods such as immersion chromate treatment and electrolytic chromate treatment. The conditions are not particularly limited, but for example, the conditions for forming a general chromate treatment layer are as follows. The chromate treatment may be performed once or multiple times. Chromate solution composition: 1 to 10 g / L K2Cr2O7, 0.01 to 10 g / L Zn Chromate solution pH: 2 to 5 Chromate solution temperature: 30 to 55°C Electrolysis conditions: current density 0.1 to 10 A / dm 2 , time 0.1 to 5 seconds (in the case of electrolytic chromate treatment)

[0039] The silane coupling treatment layer is not particularly limited and can be formed from materials known in the art. In this specification, the term "silane coupling treatment layer" refers to a layer formed with a silane coupling agent. The silane coupling agent is not particularly limited, and any known agent in the art can be used. Examples of silane coupling agents include amino-based silane coupling agents, epoxy-based silane coupling agents, mercapto-based silane coupling agents, methacryloxy-based silane coupling agents, vinyl-based silane coupling agents, imidazole-based silane coupling agents, and triazine-based silane coupling agents. Among these, amino-based silane coupling agents and epoxy-based silane coupling agents are preferred. The above silane coupling agents can be used alone or in combination of two or more. A typical method for forming a silane coupling treatment layer includes applying a 1 to 3% by volume aqueous solution of the above-mentioned silane coupling agent and drying it to form a silane coupling treatment layer.

[0040] The copper foil 10 is not particularly limited and may be either an electrolytic copper foil or a rolled copper foil. Electrolytic copper foil is generally produced by electrolytically depositing copper from a copper sulfate plating bath onto a titanium or stainless steel drum. It has a flat S-side (shine side) formed on the rotating drum side and an M-side (matte side) formed on the opposite side of the S-side. The M-side of electrolytic copper foil generally has minute irregularities. Furthermore, the S-side of electrolytic copper foil has minute irregularities due to the transfer of polishing streaks formed on the rotating drum during polishing. Furthermore, rolled copper foil has minute irregularities on its surface due to the formation of oil pits by rolling oil during rolling.

[0041] The material of the copper foil 10 is not particularly limited. However, when the copper foil 10 is a rolled copper foil, high-purity copper such as tough pitch copper (JIS H3100 alloy number C1100) or oxygen-free copper (JIS H3100 alloy number C1020 or JIS H3510 alloy number C1011), which are commonly used for circuit patterns on printed wiring boards, can be used. Furthermore, copper alloys such as Sn-containing copper, Ag-containing copper, copper alloys containing Cr, Zr, or Mg, and Corson copper alloys containing Ni and Si can also be used. In this specification, the term "copper foil 10" is intended to encompass copper alloy foils.

[0042] The thickness of the copper foil 10 is not particularly limited, but can be, for example, 1 to 1000 μm, alternatively 1 to 500 μm, alternatively 1 to 300 μm, alternatively 3 to 100 μm, alternatively 5 to 70 μm, alternatively 6 to 35 μm, or alternatively 9 to 18 μm.

[0043] The surface-treated copper foil having the above-described configuration can be produced according to a method known in the art. Here, parameters such as the rate of change in Vmc of the surface-treated layer can be controlled by adjusting the conditions for forming the surface-treated layer, particularly the conditions for forming the roughened layer.

[0044] In the surface-treated copper foil according to the embodiment of the present invention, the change rate of Vmc of the surface treatment layer is controlled to 23.00 to 40.00%, and therefore, the adhesion to a resin substrate, particularly a resin substrate suitable for high frequency applications, can be improved.

[0045] A copper-clad laminate according to an embodiment of the present invention comprises the above-described surface-treated copper foil and a resin substrate bonded to the surface treatment layer of the surface-treated copper foil. This copper-clad laminate can be produced by bonding the resin substrate to the surface treatment layer of the above-described surface-treated copper foil. The resin substrate is not particularly limited, and any substrate known in the art can be used. Examples of the resin substrate include a phenolic resin substrate on a paper substrate, an epoxy resin substrate on a paper substrate, an epoxy resin substrate on a synthetic fiber cloth substrate, an epoxy resin substrate on a glass cloth / paper composite substrate, an epoxy resin substrate on a glass cloth / glass nonwoven fabric composite substrate, an epoxy resin substrate on a glass cloth substrate, a polyester film, a polyimide resin, a liquid crystal polymer, and a fluororesin. Among these, a polyimide resin is preferred as the resin substrate.

[0046] The method for bonding the surface-treated copper foil to the resin substrate is not particularly limited and can be performed according to a method known in the art. For example, the surface-treated copper foil and the resin substrate can be laminated and thermocompression bonded. The copper-clad laminate produced as described above can be used to produce a printed wiring board.

[0047] The copper clad laminate according to the embodiment of the present invention uses the above-mentioned surface-treated copper foil, and therefore can improve adhesion to resin substrates, particularly resin substrates suitable for high frequency applications.

[0048] A printed wiring board according to an embodiment of the present invention includes a circuit pattern formed by etching the surface-treated copper foil of the copper-clad laminate. This printed wiring board can be manufactured by etching the surface-treated copper foil of the copper-clad laminate to form the circuit pattern. The method for forming the circuit pattern is not particularly limited, and known methods such as subtractive and semi-additive methods can be used. Among these, the subtractive method is preferred as the method for forming the circuit pattern.

[0049] When a printed wiring board is manufactured by a subtractive method, it is preferably carried out as follows. First, a resist is applied to the surface of the surface-treated copper foil of a copper-clad laminate, and a predetermined resist pattern is formed by exposing and developing it. Next, the surface-treated copper foil in the areas where the resist pattern is not formed (unnecessary areas) is removed by etching to form a circuit pattern. Finally, the resist pattern on the surface-treated copper foil is removed. Note that the various conditions for this subtractive method are not particularly limited, and the method can be carried out according to conditions known in the technical field.

[0050] The printed wiring board according to the embodiment of the present invention uses the above-mentioned copper-clad laminate, and therefore has excellent adhesion between the resin substrate, particularly a resin substrate suitable for high frequency applications, and the circuit pattern.

[0051] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0052] (Example 1) A rolled copper foil (HA-V2 foil manufactured by JX Nippon Mining & Metals Corporation) having a thickness of 12 μm was prepared, and one side was degreased and pickled. After that, a roughening treatment layer, a heat-resistant treatment layer (Ni—Zn layer), a chromate treatment layer, and a silane coupling treatment layer were sequentially formed as surface treatment layers to obtain a surface-treated copper foil. The conditions for forming each treatment layer were as follows. (1) Roughening Treatment Layer <Conditions for forming roughening particles> Plating solution composition: 11 g / L Cu, 50 g / L sulfuric acid, 5 ppm tungsten (derived from sodium tungstate dihydrate) Plating solution temperature: 27° C. Electroplating conditions: current density 80.0 A / dm 2 , time 0.51 seconds Number of electroplating processes: 2 times

[0053] <Conditions for forming the cover plating layer> Plating solution composition: 20 g / L Cu, 100 g / L sulfuric acid Plating solution temperature: 50°C Electroplating conditions: current density 12.6 A / dm 2 , time 0.96 seconds Number of electroplating processes: 2

[0054] (2) Heat-resistant layer <Conditions for forming Ni-Zn layer> Plating solution composition: 23.5 g / L Ni, 4.5 g / L Zn Plating solution pH: 3.6 Plating solution temperature: 40°C Electroplating conditions: current density 0.83 A / dm 2 , time 0.49 seconds Number of electroplating processes: 1

[0055] (3) Chromate Treatment Layer <Conditions for Forming Electrolytic Chromate Treatment Layer> Chromate solution composition: 3 g / L KCrO, 0.33 g / L Zn Chromate solution pH: 3.7 Chromate solution temperature: 55°C Electrolysis conditions: current density 2.20 A / dm 2 , time 0.49 seconds Number of chromate treatments: 2 times

[0056] (4) Silane Coupling Treatment Layer A 1.2% by volume aqueous solution of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane was applied and dried to form a silane coupling treatment layer.

[0057] (Example 2) A surface-treated copper foil was obtained under the same conditions as in Example 1, except for the following changes: <Conditions for forming roughening particles> Electroplating conditions: current density 46.8 A / dm 2 , time 1.01 seconds <Conditions for forming the cover plating layer> Electroplating conditions: current density 9.6 A / dm 2 , time 1.44 seconds <Conditions for forming Ni—Zn layer> Electroplating conditions: current density 0.88 A / dm 2 , time 0.73 seconds <Conditions for forming electrolytic chromate treatment layer> Electrolysis conditions: current density 1.42 A / dm 2 , time 0.73 seconds

[0058] (Example 3) A surface-treated copper foil was obtained under the same conditions as in Example 1, except for the following changes: <Conditions for forming roughening particles> Electroplating conditions: current density 41.3 A / dm 2 , time 1.15 seconds <Conditions for forming cover plating layer> Electroplating conditions: current density 8.2 A / dm 2 , time 1.44 seconds <Conditions for forming Ni—Zn layer> Electroplating conditions: current density 0.73 A / dm 2 , time 0.73 seconds <Conditions for forming electrolytic chromate treatment layer> Electrolysis conditions: current density 1.51 A / dm2 , time 0.73 seconds

[0059] (Example 4) A surface-treated copper foil was obtained under the same conditions as in Example 1, except for the following changes: <Conditions for forming roughening particles> Electroplating conditions: current density 54.8 A / dm 2 , time 0.90 seconds <Conditions for forming cover plating layer> Electroplating conditions: current density 8.2 A / dm 2 , time 1.44 seconds <Conditions for forming Ni—Zn layer> Electroplating conditions: current density 0.73 A / dm 2 , time 0.73 seconds <Conditions for forming electrolytic chromate treatment layer> Electrolysis conditions: current density 1.51 A / dm 2 , time 0.73 seconds

[0060] (Example 5) A surface-treated copper foil was obtained under the same conditions as in Example 1, except for the following changes: <Conditions for forming roughening particles> Electroplating conditions: current density 46.8 A / dm 2 , time 1.01 seconds <Conditions for forming the cover plating layer> Electroplating conditions: current density 9.6 A / dm 2 , time 1.44 seconds <Conditions for forming Ni—Zn layer> Electroplating conditions: current density 0.88 A / dm 2 , time 0.73 seconds <Conditions for forming electrolytic chromate treatment layer> Electrolysis conditions: current density 1.42 A / dm 2 , time 0.73 seconds

[0061] (Example 6) A rolled copper foil (HG foil manufactured by JX Nippon Mining & Metals Corporation) having a thickness of 12 μm was prepared, and one side was degreased and pickled. After that, a roughening treatment layer, a heat-resistant treatment layer (Ni—Zn layer), a chromate treatment layer, and a silane coupling treatment layer were sequentially formed as surface treatment layers to obtain a surface-treated copper foil. The conditions for forming each treatment layer were as follows. (1) Roughening Treatment Layer <Conditions for forming roughening particles> Plating solution composition: 12 g / L Cu, 50 g / L sulfuric acid, 5 ppm tungsten (derived from sodium tungstate dihydrate) Plating solution temperature: 27° C. Electroplating conditions: current density 48.3 A / dm 2 , time 0.81 seconds Number of electroplating processes: 2 times

[0062] <Conditions for forming the cover plating layer> Plating solution composition: 20 g / L Cu, 100 g / L sulfuric acid Plating solution temperature: 50°C Electroplating conditions: current density 11.9 A / dm 2 , time 1.15 seconds Number of electroplating treatments: 2 times

[0063] (2) Heat-resistant layer <Conditions for forming Ni-Zn layer> Plating solution composition: 23.5 g / L Ni, 4.5 g / L Zn Plating solution pH: 3.6 Plating solution temperature: 40°C Electroplating conditions: current density 1.07 A / dm 2 , time 0.59 seconds Number of electroplating processes: 1

[0064] (3) Chromate Treatment Layer <Conditions for Forming Electrolytic Chromate Treatment Layer> Chromate solution composition: 3 g / L KCrO, 0.33 g / L Zn Chromate solution pH: 3.65 Chromate solution temperature: 55°C Electrolysis conditions: current density 1.91 A / dm 2 , time 0.59 seconds Number of chromate treatments: 2 times

[0065] (4) Silane Coupling Treatment Layer A 1.2% by volume aqueous solution of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane was applied and dried to form a silane coupling treatment layer.

[0066] Comparative Example 1 The rolled copper foil (copper foil not subjected to surface treatment) used in Example 1 was used for comparison.

[0067] (Comparative Example 2) A surface-treated copper foil was obtained under the same conditions as in Example 1, except for the following changes: <Conditions for forming roughening particles> Plating solution composition: 11 g / L Cu, 50 g / L sulfuric acid Electroplating conditions: current density 38.8 A / dm 2 , time 1.27 seconds <Conditions for forming the cover plating layer> Electroplating conditions: current density 8.2 A / dm 2 , time 1.44 seconds <Conditions for forming Ni-Zn layer> Electroplating conditions: current density 0.59 A / dm 2 , time 0.73 seconds <Conditions for forming electrolytic chromate treatment layer> Electrolysis conditions: current density 1.42 A / dm 2 , time 0.73 seconds

[0068] The surface-treated copper foils or copper foils obtained in the above Examples and Comparative Examples were evaluated for the following properties. <Vmc, Sku, Sq, Sa, and Ssk> Measurements (image capture) were performed using a laser microscope (LEXT OLS4000) manufactured by Olympus Corporation in accordance with ISO 25178-2:2012. Analysis of the captured images was performed using analysis software for a laser microscope (LEXT OLS4100) manufactured by Olympus Corporation. The results were calculated by averaging the values ​​measured and analyzed at any five locations. The temperature during measurement was 23 to 25°C. The main settings for the laser microscope and analysis software were as follows: Objective lens: MPLAPON50XLEXT (magnification: 50x, numerical aperture: 0.95, immersion type: air, mechanical lens barrel length: ∞, cover glass thickness: 0, field of view: FN18) Optical zoom magnification: 1x Scanning mode: XYZ high precision (height resolution: 60nm, number of pixels of captured data: 1024 x 1024) Captured image size [number of pixels]: 257µm horizontal x 258µm vertical [1024 x 1024] (Since measurement is performed in the horizontal direction, the evaluation length corresponds to 257µm) DIC: Off Multilayer: Off Laser intensity: 100 Offset: 0 Confocal level: 0 Beam diameter aperture: Off Image averaging: 1 time Noise reduction: On Brightness uniformity correction: On Optical noise filter: On Cutoff: When measuring P1 (Vmc), λc = 200 μm and λs = 2 μm were applied, and λf was not applied. When measuring P2 (Vmc), Sku, Sq, Sa, and Ssk, λc = 200 μm was applied, and λs and λf were not applied. Filter: Gaussian filter. Noise removal: Pre-measurement processing. Surface (tilt) correction: Performed. Brightness: Adjusted to a range of 30 to 50. Brightness should be set appropriately depending on the color tone of the object being measured. The above settings are appropriate for measuring the surface of surface-treated copper foil with L* of -69 to -10, a* of 2 to 32, and b* of 221. The rate of change of Vmc was calculated according to the above formula (1). The λc filter corresponds to the L filter in ISO 25178-2:2012.

[0069] <Measurement of color tone of object to be measured> Using a MiniScan (registered trademark) EZ Model 4000L manufactured by HunterLab, measurements of L*, a*, and b* of the CIE L*a*b* color system were carried out in accordance with JIS Z8730:2009. Specifically, the surface of the surface-treated copper foil or copper foil to be measured obtained in the above Examples and Comparative Examples was pressed against the photosensitive part of the measuring instrument, and measurements were carried out while preventing light from entering from outside. Furthermore, measurements of L*, a*, and b* were carried out based on geometric condition C of JIS Z8722:2009. The main conditions of the measuring instrument were as follows: Optical system: d / 8°, integrating sphere size: 63.5 mm, observation light source: D65 Measurement method: reflected Illumination diameter: 25.4 mm Measurement diameter: 20.0 mm Measurement wavelength / interval: 400-700 nm / 10 nm Light source: pulsed xenon lamp / 1 flash / measurement Traceability standard: National Institute of Standards and Technology (NIST) calibration based on CIE 44 and ASTM E259 Standard observer: 10° The white tile used as the measurement standard had the following object color. When measured at D65 / 10°, the values ​​in the CIE XYZ color system were X: 81.90, Y: 87.02, and Z: 93.76.

[0070] <Peel Strength> After laminating the surface-treated copper foil to a polyimide resin substrate, a 3 mm-wide circuit was formed in the MD direction (the longitudinal direction of the rolled copper foil). The circuit was formed according to a conventional method. Next, the strength (MD 90° peel strength) when the circuit (surface-treated copper foil) was peeled off from the surface of the resin substrate at a speed of 50 mm / min in a 90° direction, i.e., vertically upward relative to the surface of the resin substrate, was measured in accordance with JIS C6471:1995. The measurement was performed three times, and the average value was taken as the peel strength result. A peel strength of 0.50 kgf / cm or more can be said to indicate good adhesion between the circuit (surface-treated copper foil) and the resin substrate. Note that the copper foil of Comparative Example 1 could not be laminated to a polyimide resin substrate, so this evaluation was not performed.

[0071] The results of the above characteristic evaluation are shown in Table 1.

[0072]

[0073] As shown in Table 1, the surface-treated copper foils of Examples 1 to 6, in which the rate of change in Vmc of the surface treatment layer was within the range of 23.00 to 40.00%, had high peel strength. On the other hand, the surface-treated copper foil of Comparative Example 2, in which the rate of change in Vmc of the surface treatment layer was outside the predetermined range, had low peel strength.

[0074] Based on the above results and the discussion of the embodiments of the present invention described above, it is clear that the embodiments of the present invention can provide a surface-treated copper foil that can enhance adhesion to a resin substrate, particularly a resin substrate suitable for high-frequency applications. Furthermore, the embodiments of the present invention can provide a copper-clad laminate that exhibits excellent adhesion between a resin substrate, particularly a resin substrate suitable for high-frequency applications, and the surface-treated copper foil. Furthermore, the embodiments of the present invention can provide a printed wiring board that exhibits excellent adhesion between a resin substrate, particularly a resin substrate suitable for high-frequency applications, and a circuit pattern.

[0075] REFERENCE SIGNS LIST 10 Copper foil 11 Convex portion 12 Concave portion 20 Roughening particles 30 Cover plating layer

Claims

1. A surface-treated copper foil comprising a copper foil and a surface treatment layer formed on at least one surface of the copper foil, wherein the surface treatment layer has a rate of change in Vmc expressed by the following formula (1) of 23.00 to 40.00%: Rate of change in Vmc = (P2 - P1) / P2 × 100 (1) In the formula, P1 is Vmc calculated by applying a λs filter with a cutoff value λs of 2 μm, and P2 is Vmc calculated without applying the λs filter.

2. The surface-treated copper foil according to claim 1, wherein the rate of change of Vmc is 23.00 to 32.00%.

3. The surface-treated copper foil according to claim 1, wherein the rate of change of Vmc is 23.00 to 31.00%.

4. The surface-treated copper foil according to any one of claims 1 to 3, wherein the surface treatment layer has an Sku of 2.50 to 4.50 calculated without applying the λs filter.

5. The surface-treated copper foil according to claim 4, wherein the Sku is 2.90 to 4.

10.

6. The surface-treated copper foil according to any one of claims 1 to 5, wherein the surface treatment layer has an Sq of 0.20 to 0.60 μm calculated without applying the λs filter.

7. The surface-treated copper foil according to any one of claims 1 to 6, wherein the surface treatment layer has an Sa of 0.20 to 0.40 μm calculated without applying the λs filter.

8. The surface-treated copper foil according to any one of claims 1 to 7, wherein the surface treatment layer contains a roughening treatment layer.

9. A copper clad laminate comprising the surface-treated copper foil according to any one of claims 1 to 8 and a resin substrate adhered to the surface treatment layer of the surface-treated copper foil.

10. A printed wiring board having a circuit pattern formed by etching the surface-treated copper foil of the copper-clad laminate according to claim 9.