Surface-treated copper foil and copper-clad laminate

Abstract

Provided is a surface-treated copper foil comprising a copper foil and a chromate layer that is provided on at least one surface of the copper foil. The chromate layer contains Ag, Cr, and at least one element selected from the group consisting of P, S, and N. When the surface of the chromate layer is measured by XPS, the ratio AgCr of the total atomic ratio of Ag and Cr to the total atomic ratio of Ag, Cr, P, S, and N is 0.400-0.999.

Description

Surface-treated copper foil and copper-clad laminates

[0001] This disclosure relates to surface-treated copper foil and copper-clad laminates, and more particularly to surface-treated copper foil and copper-clad laminates used in the formation of circuits requiring high-frequency characteristics.

[0002] Copper-clad laminates consist of copper foil and a resin layer on the surface of the copper foil, and are widely used in various applications such as flexible printed circuit boards. Flexible printed circuit boards are manufactured by chemically etching the copper foil of a copper-clad laminate to form circuits (also called "conductor patterns"), and then soldering electronic components onto these circuits.

[0003] As a copper foil provided in a copper-clad laminate, a surface-treated copper foil is known in which a roughening treatment layer is provided on the surface of the copper foil (for example, Patent Document 1). When this surface-treated copper foil is heat-pressed and bonded to a resin substrate which will become the resin layer, the molten resin flows around the roughened particles on the surface of the surface-treated copper foil, thereby firmly maintaining the interface between the copper foil surface and the resin layer (anchor effect). This suppresses the delamination of the circuit from the resin layer.

[0004] In recent years, with the increasing speed and capacity of communications in electronic devices such as personal computers and mobile terminals, electrical signals have become more high-frequency, creating a demand for flexible printed circuit boards capable of handling these frequencies. In particular, as the frequency of an electrical signal increases, signal power loss (attenuation) becomes greater, making data difficult to read. Therefore, reducing signal power loss is essential.

[0005] 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 the copper foil. The second is dielectric loss, i.e., loss due to the resin layer. In the high-frequency range, current has the characteristic of flowing along the surface of the conductor (i.e., the skin effect). Therefore, if the surface of the copper foil is rough, the current will flow along a complex path. Consequently, from the viewpoint of reducing conductor loss of high-frequency signals, forming a roughened layer on the surface of the copper foil is disadvantageous. On the other hand, regarding the resin layer, by using low-dielectric materials such as PTFE (materials with a relative permittivity of less than 2.5 and a dielectric loss tangent of less than 0.001), transmission loss when high-frequency (especially above 5 GHz) AC current flows through the circuit can be suppressed.

[0006] Japanese Patent Publication No. 2012-112009

[0007] As described above, in conventional technology, the adhesion between the copper foil and the resin layer depends on a roughened layer applied to the surface of the copper foil, but the formation of a roughened layer is disadvantageous for reducing conductor loss of high-frequency signals. Against this backdrop, there has been a desire for the development of a technology that can improve adhesion with the resin layer without relying on a roughened layer.

[0008] Embodiments of the present invention have been made to solve the above-mentioned problems, and in one aspect, aim to provide a surface-treated copper foil with excellent adhesion to a resin layer. Furthermore, embodiments of the present invention aim to provide a copper-clad laminate with excellent adhesion to a resin layer.

[0009] In order to solve the above problems, the inventors conducted intensive research on surface-treated copper foil and found that by providing a predetermined chromate layer on at least one surface of the copper foil, the adhesion to the resin layer is improved, thus completing the embodiments of the present invention.

[0010] In other words, an embodiment of the present invention comprises, in one aspect, a copper foil and a chromate layer provided on at least one surface of the copper foil, wherein the chromate layer contains at least one element selected from the group consisting of P, S, and N, Ag, and Cr, and when the surface of the chromate layer is measured by XPS, the ratio of the sum of the atomic ratios of Ag and Cr to the sum of the atomic ratios of Ag, Cr, P, S, and N AgCr However, this relates to surface-treated copper foil, where the coefficient is between 0.400 and 0.999.

[0011] Furthermore, embodiments of the present invention relate to a copper-clad laminate comprising the surface-treated copper foil and a resin layer provided on the surface of the chromate layer of the surface-treated copper foil.

[0012] According to embodiments of the present invention, in one respect, a surface-treated copper foil with excellent adhesion to a resin layer can be provided. Furthermore, according to embodiments of the present invention, in another respect, a copper-clad laminate with excellent adhesion to a resin layer can be provided.

[0013] Preferred embodiments of the present invention will be described 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 spirit of the invention. The multiple components disclosed in the following embodiments can be combined in appropriate ways to form various inventions. For example, some components may be removed from all the components shown in the following embodiments, or components from different embodiments may be combined in appropriate ways. In this specification, "A to B" means "A or greater and B or less," where A and B represent numerical values.

[0014] The surface-treated copper foil according to an embodiment of the present invention comprises a copper foil and a chromate layer provided on at least one surface of the copper foil. The chromate layer contains at least one element selected from the group consisting of P, S, and N, Ag, and Cr, and when the surface of the chromate layer is measured by XPS (X-ray photoelectron spectroscopy), the ratio of the sum of the atomic ratios of Ag and Cr to the sum of the atomic ratios of Ag, Cr, P, S, and N AgCrHowever, this is between 0.400 and 0.999. By having such a configuration, the surface-treated copper foil according to the embodiment of the present invention can be provided with excellent adhesion to the resin layer. Furthermore, since the chromate layer has a rust-preventive effect, there is no need to apply rust-preventive treatment to the surface of the chromate layer.

[0015] The chromate layer may be provided on only one side of the copper foil, or it may be formed on both sides of the copper foil. When the chromate layer is formed on both sides of the copper foil, the types of chromate layers may be the same, or they may be different as long as the above conditions are met. Furthermore, it is preferable that the chromate layer be located as the outermost layer. By making the chromate layer the outermost layer, it can be brought into direct contact with the resin layer, thereby improving adhesion with the resin layer.

[0016] The chromate layer can be applied directly to the surface of the copper foil. By applying the chromate layer in this way, adhesion between the chromate layer and the copper foil can also be ensured.

[0017] The chromate layer comprises at least one element selected from the group consisting of P, S, and N, as well as Ag and Cr. Hereinafter, in this specification, "containing a predetermined element" means that the predetermined element is detected when the surface of the chromate layer is measured by XPS (i.e., the atomic ratio of the predetermined element is above the detection limit). The chromate layer may optionally contain other elements (e.g., impurity elements).

[0018] The chromate layer, when its surface is measured by XPS, is the ratio of the sum of the atomic ratios of Ag and Cr to the sum of the atomic ratios of Ag, Cr, P, S, and N. AgCr However, it is 0.400 to 0.999, preferably 0.516 to 0.949. AgCr By controlling this, the adhesion to the resin layer can be improved.

[0019] Here, in this specification, AgCrThe atomic ratios of each element used in the calculation are obtained by measuring the surface of the chromate layer using XPS. The XPS measurement shall be performed under the following conditions. If the instrument operation software or data analysis software is updated, the software shall be operated and set to be equivalent to the conditions described herein. Instrument: PHI 5000 VersaProbe II manufactured by ULVAC, Inc. Ultimate vacuum: 8.2 × 10⁻⁶ -8 Pa Excitation source: Monochromatic AlKα Output: 25.0W Beam diameter: 100 μmφ Incident angle: 90 degrees Extraction angle: 45 degrees Neutralization gun: None In addition, the following orbitals are used in the calculations for XPS measurements. That is, the elements to be measured in XPS are N, P, S, Cr and Ag. N: 1s (400 eV) P: Sum of 2p³ / ² (130 eV) and 2p¹ / ² (131 eV) of P²p S: Sum of 2p³ / ² (167 eV) and 2p¹ / ² (168 eV) of S²p Cr: 3p (44 eV) Ag: Sum of 3d⁵ / ² (368 eV) and 3d³ / ² (374 eV) of 3d Furthermore, in calculating the peak area of ​​each element, the peak area having a peak at the bond energy closest to the above bond energy is calculated after background removal using the Shirley method. Also, since it is difficult to separate the two peaks above for P, S and Ag, the sum of the peak areas of both peaks is calculated. Furthermore, in XPS measurements, for each element, the spectrum is acquired in a range of 6 eV before and after the above bond energy (for example, a range of 44 eV ± 6 eV for Cr) under the narrow scan conditions shown below. Pass energy: 117.4 eV (common to N, P, S, Cr, and Ag) Step energy: 0.5 eV (common to N, P, S, Cr, and Ag) Number of integrations: 120 times for N and Cr, 144 times for P, 168 times for S, and 96 times for Ag. The quantitative value is calculated from the calculated peak area using the relative sensitivity coefficient method. The sensitivity coefficient for each element is the value recommended by the instrument manufacturer. No corrections such as matrix correction are made during the calculation. Before performing the XPS measurement, the surface of the object to be measured is not decontaminated. Decontamination means, for example, removing the surface of the object to be measured by sputtering.

[0020] When the surface of the chromate layer is measured by XPS, the ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S and N P may be less than 0.20. In this case, the ratio of the chromate layer AgCr is preferably 0.700 to 0.980, more preferably 0.750 to 0.949, still more preferably 0.801 to 0.949. The ratio in the chromate layer P when it is less than 0.20, the ratio AgCr by controlling as described above, the effect of improving adhesion to the resin layer can be stably ensured. Note that the ratio in the chromate layer P varies depending on the formation conditions of the chromate layer (for example, the type of pH adjuster for the plating solution used). Here, in the present specification, the ratio P the atomic ratio of each element used for calculation of is the above ratio AgCr can be measured by the same method as the atomic ratio of each element used for calculation of .

[0021] When the surface of the chromate layer is measured by XPS, the ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S and N P may be 0.20 or more. In this case, the ratio of the chromate layer AgCr is preferably 0.450 to 0.800, more preferably 0.516 to 0.749, still more preferably 0.601 to 0.749. The ratio in the chromate layer P when it is 0.20 or more, the ratio AgCr by controlling as described above, the effect of improving adhesion to the resin layer can be stably ensured.

[0022] The chromate layer can be formed by electroplating. The conditions are not particularly limited and can be adjusted according to the electroplating equipment used, but the conditions for forming a chromate-treated layer using a general electroplating equipment are as follows. Note that the chromate treatment may be performed once or multiple times. Plating solution composition: 1 to 10 g / L of Cr salt (e.g., K2Cr2O7), 0.03 to 2.0 g / L of Ag salt (e.g., AgNO3) Plating solution pH: 1.5 to 3.2 Plating solution temperature: 25 to 60°C Plating conditions: Current density 0.50 to 1.40 A / dm 2 , time 0.1 to 5 seconds

[0023] Furthermore, the chromate layer can also be formed simply by immersing the part in the plating solution. When forming the chromate layer by immersion, the same plating solution used for electroplating can be used. The immersion time is not particularly limited, but is typically 0.1 to 60 seconds.

[0024] The copper foil is not particularly limited and may be either electrolytic copper foil or rolled copper foil. Electrolytic copper foil is generally manufactured by electrolytically ejecting copper from a copper sulfate plating bath onto a titanium or stainless steel drum, and has a flat S-surface (shine surface) formed on the rotating drum side and an M-surface (matte surface) formed on the opposite side of the S-surface. The M-surface of electrolytic copper foil generally has minute irregularities. The S-surface of electrolytic copper foil also has minute irregularities because polishing marks from the rotating drum formed during polishing are transferred to it. The chromate layer may be provided on either the S-surface or the M-surface of the electrolytic copper foil. Rolled copper foil has minute irregularities on its surface because oil pits are formed by the rolling oil during rolling.

[0025] The material of the copper foil is not particularly limited. When the copper foil is a rolled copper foil, high-purity copper such as tough pitch copper (JIS H3100, alloy number C1100) and oxygen-free copper (JIS H3100, alloy number C1020 or JIS H3510, alloy number C1011) that are commonly used for circuit patterns of printed wiring boards can be used. In addition, copper alloys such as Sn-containing copper, Ag-containing copper, copper alloys added with Cr, Zr or Mg, and Corson copper alloys added with Ni, Si and the like can also be used. In this specification, the term "copper foil" is a concept that also includes copper alloy foil.

[0026] The thickness of the copper foil is not particularly limited, and may be, for example, 1 to 1000 μm, 1 to 500 μm, 1 to 300 μm, 3 to 100 μm, 5 to 70 μm, 6 to 35 μm, or 9 to 18 μm.

[0027] The surface-treated copper foil according to an embodiment of the present invention may further include an underlayer provided between the copper foil and the chromate layer. The underlayer preferably contains Ni and W. An underlayer containing such elements can improve heat resistance without impairing the adhesion between the copper foil and the chromate layer.

[0028] The underlayer can be formed by electroplating. The conditions may be adjusted according to the electroplating apparatus to be used and are not particularly limited, and the conditions for forming the underlayer using a general electroplating apparatus are as follows. Electroplating may be performed once or multiple times. Plating solution composition: 1 to 30 g / L of Ni salt (e.g., NiSO₄·6H₂O), 1 to 30 g / L of W salt (e.g., Na₂WO₄·2H₂O), 1 to 30 g / L of complexing agent (e.g., trisodium citrate dihydrate, trisodium ammonium citrate) Plating solution pH: 2 to 6 Plating solution temperature: 30 to 60°C Plating conditions: current density 0.1 to 10 A / dm 2 , time 0.1 to 5 seconds

[0029] The surface-treated copper foil according to an embodiment of the present invention may optionally be provided with a roughening treatment layer between the copper foil and the chromate layer (or between the copper foil and the underlayer when an underlayer is provided). Providing the roughening treatment layer can further improve adhesion to the resin layer. However, the surface-treated copper foil according to an embodiment of the present invention can sufficiently secure adhesion to the resin layer even without providing a roughening treatment layer. In addition, a surface-treated copper foil not having a roughening treatment layer does not cause conductor loss resulting from the roughened portion, and therefore is suitable for producing an energy-saving high-frequency circuit.

[0030] A copper-clad laminate according to an embodiment of the present invention includes the above-mentioned surface-treated copper foil, and a resin layer provided on a surface of a chromate layer of the surface-treated copper foil. This copper-clad laminate can be produced by bonding a resin base material that forms the resin layer to the chromate layer of the above-mentioned surface-treated copper foil. The resin base material is not particularly limited, and those known in the art can be used. Examples of the resin base material include paper base phenolic resins, paper base epoxy resins, synthetic fiber cloth base epoxy resins, glass cloth-paper composite base epoxy resins, glass cloth-glass nonwoven fabric composite base epoxy resins, glass cloth base epoxy resins, polyester films, polyimide resins, liquid crystal polymers, fluorine resins such as PTFE, and polyolefin resins. Among these, PTFE and polyolefin resins, which are resin base materials formed of low-dielectric materials (materials having a relative dielectric constant of less than 2.5 and a dielectric loss tangent of less than 0.001), are preferred.

[0031] The method for bonding the surface-treated copper foil and the resin base material is not particularly limited, and can be performed according to methods known in the art. For example, the surface-treated copper foil and the resin base material may be laminated and then hot-pressed. The copper-clad laminate produced as described above can be used for producing printed wiring boards. Since the copper-clad laminate according to an embodiment of the present invention uses the above-mentioned surface-treated copper foil, it has excellent adhesion to the resin layer.

[0032] A copper-clad laminate according to an embodiment of the present invention can be made into a printed circuit board by chemically etching the surface-treated copper foil of the copper-clad laminate to form circuits. The method for forming the circuits is not particularly limited, and known methods such as the subtractive method and the semi-additive method can be used. Among these, the subtractive method is preferred for forming the circuits.

[0033] When manufacturing printed circuit boards by the subtractive method, it is preferable to do so as follows: First, a resist pattern is formed by applying a resist to the surface of the surface-treated copper foil of a copper-clad laminate, exposing it to light, and developing it. Next, the surface-treated copper foil in areas where the resist pattern is not formed (i.e., unwanted areas) is removed by chemical etching to form a circuit. Finally, the resist pattern on the surface-treated copper foil is removed. The various conditions in this subtractive method are not particularly limited and can be carried out in accordance with conditions known in the art. Since the printed circuit board obtained in this way uses the above-mentioned copper-clad laminate, it has excellent adhesion between the resin layer and the circuit.

[0034] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these embodiments.

[0035] (Examples 1-3, 7, 8 and 12-18) Rolled copper foil with a thickness of 18 μm (HG foil manufactured by JX Metals Corporation) was prepared. After electrolytically degreasing one side of the copper foil, a chromate layer was formed on the electrolytically degreased side under the electroplating conditions shown in Table 1. For the electroplating solution to form the chromate layer, K2Cr2O7 was used as the Cr salt and AgNO3 as the Ag salt, and the pH of the plating solution was adjusted using a pH adjuster (sulfuric acid, phosphoric acid, or a mixed acid of phosphoric acid and sulfuric acid). The electroplating was performed twice, and the current density was 1.39 A / dm². 2 The electroplating time was set to 1 second, and the plating solution temperature to 55°C.

[0036] (Examples 4-6 and 9-11) Rolled copper foil with a thickness of 18 μm (HG foil manufactured by JX Metals Corporation) was prepared. After electrolytically degreasing one side of the copper foil, a base layer was formed on the electrolytically degreased side, and a chromate layer was formed on the base layer under the electroplating conditions shown in Table 1. The conditions for forming the base layer were as follows: Plating solution composition: 58.2 g / L NiSO4・6H2O and 17.9 g / L Na2WO4・2H2O, 20 g / L trisodium citrate dihydrate Plating solution pH: 5 Plating solution temperature: 52°C Plating conditions: Current density 1.39 A / dm 2 The electroplating solution used to form the chromate layer consisted of one time step and one time step, with K2Cr2O7 as the Cr salt and AgNO3 as the Ag salt. The pH of the electroplating solution was adjusted using a pH adjuster (sulfuric acid or phosphoric acid). The number of electroplating steps was set to one, the electroplating time to one second, and the electroplating solution temperature to 55°C.

[0037]

[0038] (Comparative Example 1) A rolled copper foil with a thickness of 18 μm (HG foil manufactured by JX Metals Corporation) was prepared. After electrolytic degreasing of both sides of the copper foil, a chromate layer was formed under the following electroplating conditions. Electroplating was performed twice. Plating solution composition: 3 g / L K2Cr2O7 and 1.45 g / L ZnSO4・7H2O Plating solution pH: 3.65 Plating solution temperature: 55°C Plating conditions: Current density 1.39 A / dm 2 , time 1 second

[0039] The surface-treated copper foils obtained in the above examples and comparative examples were evaluated as follows.

[0040] <XPS Analysis of the Chromate Layer Surface> XPS analysis was performed on the surface of the chromate layer under the conditions described above, and the atomic concentration of each element was measured. Based on these measurement results, it was confirmed that the chromate layers of Examples 1 to 11 contain at least one element selected from the group consisting of P, S, and N, as well as Ag and Cr. Furthermore, based on the obtained atomic ratios of each element, the ratio of the sum of the atomic ratios of Ag and Cr to the sum of the atomic ratios of Ag, Cr, P, S, and N was calculated. AgCr, and the ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S and N P The following was calculated. Note that for Comparative Example 1, the type of chromate layer differed from that of Examples 1 to 11 (the plating solution did not contain any of the elements P, S, and N), and therefore the inventor considered it highly probable that it did not contain at least one element selected from the group consisting of P, S, and N, and thus the analysis was omitted.

[0041] <Preparation of Copper-Clad Laminates> Using PTFE (NITOFLON® manufactured by Nitto Denko Corporation) as the resin substrate, surface-treated copper foil obtained in the above examples and comparative examples, PTFE, and surface-treated copper foil (BHY foil) manufactured by JX Metals Corporation were laminated in that order, and a copper-clad laminate was produced by vacuum hot pressing. At this time, the chromate layer side of the surface-treated copper foil obtained in the above examples and comparative examples, and the roughened surface side of the surface-treated copper foil (BHY foil) manufactured by JX Metals Corporation were positioned to face the PTFE. The vacuum hot pressing was performed under the following conditions: temperature 340 degrees Celsius, pressure 10 MPa, pressing time 10 minutes, and cooling time approximately 2 hours.

[0042] <Peel Strength> Surface-treated copper foil obtained in the above examples and comparative examples in copper-clad laminates was chemically etched to form a 3 mm wide circuit in the MD direction (longitudinal direction of the rolled copper foil). The circuit was formed according to the usual method. In addition, the surface-treated copper foil (BHY foil) side manufactured by JX Metals Corporation was bonded to a rigid substrate and cut to a predetermined size to be used as a test piece for measurement. Next, the strength (TD90° peel strength) when peeling the circuit (surface-treated copper foil) of this test piece from the PTFE surface at a 90° angle, that is, vertically upward relative to the surface of the resin substrate, was measured. The pulling speed was set to 50 mm / min. The measurement was performed four times, and the average value was taken as the result of the peel strength.

[0043] The results of each of the above evaluations are shown in Table 2.

[0044]

[0045] As shown in Table 2, the surface-treated copper foils of Examples 1 to 18 were found to have higher peel strength and superior adhesion to the resin layer (circuit) compared to the surface-treated copper foil of Comparative Example 1.

[0046] As can be seen from the above results, according to the embodiments of the present invention, a surface-treated copper foil with excellent adhesion to a resin layer can be provided. Furthermore, according to the embodiments of the present invention, a copper-clad laminate with excellent adhesion to a resin layer can be provided.

[0047] Accordingly, embodiments of the present invention can be as follows: [1] A copper foil and a chromate layer provided on at least one surface of the copper foil, wherein the chromate layer contains at least one selected from the group consisting of P, S, and N, Ag, and Cr, and when the surface of the chromate layer is measured by XPS, the ratio of the sum of the atomic ratios of Ag and Cr to the sum of the atomic ratios of Ag, Cr, P, S, and N AgCr However, the ratio is 0.400 to 0.999, surface-treated copper foil. [2] The ratio AgCr The surface-treated copper foil according to [1], wherein the ratio is 0.516 to 0.949. [3] The ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S and N when the surface of the chromate layer is measured by XPS. P However, it is less than 0.20, and the ratio AgCr However, the surface-treated copper foil described in [1] is 0.700 to 0.980. [4] The ratio AgCr However, the surface-treated copper foil described in [3] is 0.750 to 0.949. [5] The ratio AgCr The surface-treated copper foil described in [4], wherein the ratio is 0.801 to 0.949. [6] The ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S and N when the surface of the chromate layer is measured by XPS. P However, it is 0.20 or more, and the ratio AgCr However, the surface-treated copper foil described in [1] is 0.450 to 0.800. [7] The ratio AgCr However, the surface-treated copper foil described in [6] is 0.516 to 0.749. [8] The ratio AgCr[7] Surface-treated copper foil, wherein the ratio is 0.601 to 0.749. [9] Surface-treated copper foil according to any one of [1] to [8], further comprising a base layer provided between the copper foil and the chromate layer, wherein the base layer contains Ni and W.

[10] Surface-treated copper foil according to any one of [1] to [8], wherein the chromate layer is provided directly on the surface of the copper foil.

[11] Copper-clad laminate comprising a surface-treated copper foil according to any one of [1] to

[10] and a resin layer provided on the surface of the chromate layer of the surface-treated copper foil.

[0048] (Potential Contribution to SDGs) According to the above embodiment, it is possible to provide surface-treated copper foil and copper-clad laminates with excellent adhesion to resin layers, which may improve product yield in the manufacture of electronic devices and the like. Improved product yield leads to a stable supply of products and a reduction in the loss of metal raw materials, which are limited resources. Therefore, the above embodiment may contribute to Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," and Goal 12, "Ensure sustainable consumption and production patterns," of the United Nations-led Sustainable Development Goals (SDGs).

Claims

1. A copper foil and a chromate layer provided on at least one surface of the copper foil, wherein the chromate layer contains at least one element selected from the group consisting of P, S, and N, Ag, and Cr, and when the surface of the chromate layer is measured by XPS, the ratio of the sum of the atomic ratios of Ag and Cr to the sum of the atomic ratios of Ag, Cr, P, S, and N AgCr However, the surface-treated copper foil has a coefficient of 0.400 to 0.

999.

2. The ratio AgCr The surface-treated copper foil according to claim 1, wherein the coefficient is 0.516 to 0.

949.

3. When the surface of the chromate layer is measured by XPS, the ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S, and N. P However, it is less than 0.20, and the ratio AgCr The surface-treated copper foil according to claim 1, wherein the coefficient is 0.700 to 0.

980.

4. The above ratio AgCr The surface-treated copper foil according to claim 3, wherein the coefficient is 0.750 to 0.

949.

5. The ratio AgCr The surface-treated copper foil according to claim 4, wherein the coefficient is 0.801 to 0.

949.

6. When the surface of the chromate layer is measured by XPS, the ratio of the atomic ratio of P to the sum of the atomic ratios of Ag, Cr, P, S, and N. P However, it is 0.20 or more, and the ratio AgCr The surface-treated copper foil according to claim 1, wherein the coefficient is 0.450 to 0.

800.

7. The aforementioned ratio AgCr is 0.516 to 0.749, the surface-treated copper foil according to claim 6.

8. The above ratio AgCr The surface-treated copper foil according to claim 7, wherein the coefficient is 0.601 to 0.

749.

9. The surface-treated copper foil according to claim 1, further comprising a base layer provided between the copper foil and the chromate layer, wherein the base layer contains Ni and W.

10. The surface-treated copper foil according to claim 1, wherein the chromate layer is provided directly on the surface of the copper foil.

11. A copper-clad laminate comprising a surface-treated copper foil according to any one of claims 1 to 10, and a resin layer provided on the surface of the chromate layer of the surface-treated copper foil.

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