TWI903150B - Surface-treated copper foil, copper-clad laminates, and printed circuit boards - Google Patents

Abstract

This invention provides a surface-treated copper foil with excellent circuit machinability and is not prone to transmission loss or foreign matter formation. When the optical roughness of the surface (20a) of the surface-treated layer (20) of the surface-treated copper foil (30) is measured according to the method specified in ISO25178, the arithmetic mean roughness Sa is ≥0.04 μm and ≤0.30 μm. After a resin component (40) is bonded to the surface treatment layer (20) of a surface-treated copper foil (30), the surface-treated copper foil (30) is removed by etching. The remaining surface of the resin component (40) that was bonded to the surface-treated copper foil (30), i.e., the transfer surface (40a), is used to measure the contact angle _θ1 of the distilled water according to the fixation drop method specified in JIS R3257:1999. The non-transfer surface is used to measure the contact angle _θ0 of the distilled water according to the fixation drop method. The difference between the contact angles _θ0 and _θ1 , _θ0 - _θ1, is greater than 5° and less than 35°.

Description

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

The present invention relates to a surface-treated copper foil, and copper-clad laminates and printed circuit boards using the surface-treated copper foil, which is suitable for use in the manufacture of printed circuit boards and the like.

Recent advancements in signal transmission speed have led to an increase in the use of printed circuit boards (PCBs) in electronic devices to transmit high-frequency signals. Therefore, research is underway to develop low-roughness surfaces for surface-treated copper foil used in PCBs to reduce high-frequency signal transmission losses (see, for example, Patent 1). Furthermore, with the increasing density and multifunctionality of PCBs, the miniaturization of circuits is also progressing. Research is being conducted on surface-treated copper foils requiring good circuit machinability for forming fine wiring, aiming to improve circuit machinability (see, for example, Patent 2). Furthermore, the design of the metal used for surface treatment of copper foil (e.g., see Patent 3) and the design of the uneven shape of the surface transferred to the resin (e.g., see Patents 4 and 5) are also being studied. [Prior Art Documents] (Patent Documents)

Patent Document 1: Japanese Patent Publication No. 210521, 2019 Patent Document 2: Japanese Patent Publication No. 20117, 2017 Patent Document 3: Japanese Patent Publication No. 81913, 2019 Patent Document 4: Japanese Patent Publication No. 6945523 Patent Document 5: International Publication No. 2020/105289

[The problem the invention aims to solve]

However, even with reduced surface roughness of the surface-treated copper foil, it is sometimes impossible to obtain the desired fine lines. Previously, the etching factor, derived from the bottom width, top width, and height of the circuit, was widely used as an indicator of circuit machinability. However, it is now known that the angle of the tangent at the bottom edge of the circuit is also important. That is, even if the etching factor was previously considered a good value, migration can sometimes occur if the angle of the tangent at the bottom edge of the circuit is small (i.e., the bottom width of the circuit is greater than the top width, resulting in a cross-section that widens at the bottom). The smaller the angle of the tangent at the bottom edge of the circuit, the more prone it is to migration, which is expected to be caused by poor etching at the interface of the circuit's ends when viewed microscopically.

Furthermore, in the inventors' research, the surface roughness of the surface-treated copper foil was reduced. However, a new problem was discovered: after etching and removing the surface-treated copper foil from the copper-clad laminate, during the step of manufacturing a printed circuit board by laminating a resin substrate, foreign matter easily forms between the resin substrate constituting the copper-clad laminate and the subsequently laminated resin substrate. The purpose of this invention is to provide a surface-treated copper foil, a copper-clad laminate, and a printed circuit board, which exhibit excellent circuit machinability and are less prone to transmission loss and foreign matter formation. [Technical Means for Solving the Problem]

The key features of one aspect of the surface-treated copper foil according to the present invention are: a copper foil substrate; and a surface treatment layer formed on at least one side of the copper foil substrate; wherein the surface treatment layer is composed of one or both of a roughening treatment layer and a rust-proof treatment layer, and when the optical roughness of the surface of the surface treatment layer is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is 0.04 μm or more and 0.30 μm or less; after a resin component is bonded to the surface treatment layer of the surface-treated copper foil, the surface-treated copper foil is removed by etching, and the remaining surface of the resin component that was bonded to the surface-treated copper foil is the transfer surface, according to JIS... R3257:1999 specifies the fixed droplet method for determining the contact angle _θ1 of distilled water. For the surface of a resin component to be bonded to the surface-treated copper foil before bonding, i.e., the non-transfer surface, when the contact angle _θ0 of distilled water is determined by the fixed droplet method, the difference between the contact angle _θ0 and _θ1 , _θ0 - _θ1 , is greater than 5° and less than 35°.

The key feature of another aspect of the copper-clad laminate according to the invention is that it comprises: a surface-treated copper foil according to the first aspect described above; and a resin substrate bonded to the surface-treated layer of the surface-treated copper foil. The key feature of yet another aspect of the printed circuit board according to the invention is that it comprises a surface-treated copper foil according to the second aspect described above. [Effects of the Invention]

According to the present invention, the circuit has excellent processability and is not prone to transmission loss or foreign object occurrence.

This section describes one embodiment of the invention. Furthermore, the embodiment described below is an example illustrating the invention. Also, various modifications or alterations can be made to this embodiment, and forms obtained by such modifications or alterations can also be included within the scope of the invention. To solve the above problems, the inventors focused on the surface wettability of resin-based substrates used in the manufacture of copper-clad laminates and printed circuit boards, and conducted focused research. This will be described in detail below with reference to Figures 1, 2, and 3.

The manufacturing steps of the printed circuit board 60 include: a bonding step, in which a surface-treated copper foil 30 is bonded to a resin substrate 40 to manufacture a copper-clad laminate 50 (see FIG. 3(b)); and an etching step, in which unwanted portions of the surface-treated copper foil 30 of the copper-clad laminate 50 other than those used as circuits 31 are removed by etching with an etching solution (see FIG. 3(c)). In the bonding step, the resin substrate 40 is bonded to the surface-treated layer 20 of the surface-treated copper foil 30 (see FIG. 3(a)).

At this time, the shape of the surface treatment layer 20a of the surface-treated copper foil 30 is transferred onto the surface of the resin substrate 40 remaining after etching, on the surface that was bonded to the surface-treated copper foil 30. That is, the surface of the resin substrate 40 that was bonded to the surface-treated copper foil 30 becomes the transfer surface (replica) 40a of the surface of the surface-treated copper foil 30.

According to the inventors' research, it was found that as the surface roughness of the surface-treated copper foil 30 decreases, the surface roughness of the transfer surface 40a of the resin substrate 40 also decreases, and the wettability of the transfer surface 40a decreases. It is believed that if the surface wettability of the resin substrate 40 is low, the etching solution becomes less likely to reach the ends (the ends in the line width direction of the circuit 31) of the circuit 31 (the surface-treated copper foil 30 remaining after etching) on the resin substrate 40 during the etching process, thus reducing the circuit machinability. Whether the etching solution reaches the ends of the circuit 31, especially the bottom end 31b of the circuit 31 (the portion of the end of the circuit 31 adjacent to the resin substrate 40 (see Figure 2)), is an important factor for the machinability.

Furthermore, the manufacturing process of the printed circuit board 60 includes a cleaning step, which involves cleaning the resin substrate 40 containing the circuit 31 with a cleaning solution after the etching step. If the surface wettability of the resin substrate 40 is low, the cleaning solution may not be able to cover the entire surface of the resin substrate 40, and thus the foreign matter 100 present on the resin substrate 40 or the circuit 31 may not be able to be adequately cleaned with the cleaning solution (see Figure 3(c)). Then, after the cleaning step, another resin substrate 41 is bonded to the side of the resin substrate 40 with the circuit 31 to manufacture the printed circuit board 60. If the foreign matter 100 is not cleaned sufficiently in the cleaning step, there will be foreign matter 100 residue between the two bonded resin substrates 40 and 41 (see Figure 3(d)).

In other words, the inventors' research found that if the surface wettability of the resin substrate 40 is low, foreign matter 100 is easily generated on the printed circuit board 60. Furthermore, foreign matter 100 includes: deposits that were already attached to the surface-treated copper foil 30 or the resin substrate 40 before bonding, and solidified salts contained in the etching solution.

As described above, the inventors have discovered that the wettability of the transfer surface 40a of the resin substrate 40 after the etching step is a very important factor in the manufacture of the printed circuit board 60. Furthermore, the inventors have discovered that the wettability of the transfer surface 40a of the resin substrate 40 after the etching step can be evaluated by measuring the contact angle of distilled water according to the sessile drop method specified in Japanese Industrial Standard (JIS) R3257:1999.

That is, the surface-treated copper foil 30 according to this embodiment has: a copper foil substrate 10; and a surface treatment layer 20 formed on at least one side of the copper foil substrate 10; wherein the surface treatment layer 20 is composed of one or both of a roughening treatment layer 21 and a rust-proof treatment layer 22 (see FIG. 1). Furthermore, FIG. 1 shows an example of the surface-treated copper foil 30, wherein the surface treatment layer 20 is formed only on one side of the copper foil substrate 10, and the surface treatment layer 20 is composed of both the roughening treatment layer 21 and the rust-proof treatment layer 22. Furthermore, when the optical roughness of the surface 20a of the surface treatment layer 20 of the surface-treated copper foil 30 is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is 0.04 μm or more and 0.30 μm or less.

Furthermore, after the resin substrate 40 (equivalent to the "resin component" that is a constituent element of the present invention) used in manufacturing the copper-clad laminate 50 and the printed circuit board 60 is bonded to the surface treatment layer 20 of the surface-treated copper foil 30, the surface-treated copper foil 30 is removed by etching, and the contact angle _θ1 of the distilled water on the remaining transfer surface 40a of the resin substrate 40 is measured (hereinafter sometimes referred to as "the contact angle _θ1 of the distilled water on the transfer surface after copper foil etching"). The transfer surface 40a of the resin substrate 40 is the surface of the resin substrate 40 that has been bonded to the surface-treated copper foil 30.

Furthermore, the contact angle _θ0 of the distilled water is measured on the non-transfer surface of the resin substrate 40 before it is bonded to the surface-treated copper foil 30 (hereinafter sometimes referred to as "the contact angle _θ0 of the distilled water on the non-transfer surface before bonding with the copper foil"). The non-transfer surface of the resin substrate 40 is the surface of the resin substrate 40 before it is bonded to the surface-treated copper foil 30.

The contact angles _θ0 and _θ1 of distilled water are determined according to the fixed droplet method specified in JIS R3257:1999. In this case, in the surface-treated copper foil 30 according to this embodiment, the difference between contact angles _θ0 and _{θ1 , θ0} - _θ1, is 5° to 35°. That is, the difference between contact angles _θ0 and _θ1 , _θ0 - _θ1 , is a measure of how much the wettability of the resin surface changes due to adhesion to the copper foil.

If copper foil 30 with such surface treatment is used to manufacture copper-clad laminate 50 and printed circuit board 60, the wettability of the transfer surface 40a of the resin substrate 40 used in the manufacture of copper-clad laminate 50 and printed circuit board 60 becomes higher. Therefore, the obtained copper-clad laminate 50 and printed circuit board 60 are not only less prone to transmission loss, but also have excellent circuit processability. Furthermore, foreign matter is less likely to be generated between the resin substrate 40 constituting the copper-clad laminate 50 and another resin substrate 41 subsequently laminated for the manufacture of printed circuit board 60.

That is, by setting the contact angle difference _θ0 - _θ1 within the aforementioned range, the surface wettability of the resin substrate 40 can be maintained well. Therefore, during the etching process, the etching solution easily reaches the bottom end 31b of the circuit 31 on the resin substrate 40, and during the cleaning step after etching, the cleaning solution easily reaches the entire surface of the resin substrate 40. As a result, a copper-clad laminate 50 and a printed circuit board 60 can be manufactured, which possesses both excellent circuit processing performance and foreign matter suppression, and is less prone to transmission loss.

As described above, the surface-treated copper foil 30 according to this embodiment is suitable for manufacturing copper-clad laminates, printed circuit boards, etc. That is, the copper-clad laminate 50 according to this embodiment includes: the surface-treated copper foil 30 according to this embodiment; and a resin substrate 40, which is adhered to the surface-treated layer 20 of the surface-treated copper foil 30. Furthermore, the printed circuit board 60 according to this embodiment includes the copper-clad laminate 50 according to this embodiment.

The following provides a more detailed description of the surface-treated copper foil 30, copper-clad laminate 50, and printed circuit board 60 according to this embodiment. (A) Regarding the surface-treated copper foil The copper foil substrate 10, which serves as the raw material for the surface-treated copper foil 30 according to this embodiment, preferably has a ten-point average roughness Rzjis of both surfaces that is 2 μm or less before surface roughening treatment or similar processes. This ten-point average roughness Rzjis can be measured using a contact surface roughness measuring machine according to the method specified in JIS B0601:2001. If the ten-point average roughness Rzjis of the surface is 2 μm or less, the adhesion to the resin substrate 40 is easily improved. Furthermore, the thickness of the copper foil substrate 10 before roughening treatment depends on the target thickness of the copper foil substrate 10 after roughening treatment, and is preferably 5 μm or more and 40 μm or less.

A surface-treated copper foil 30 according to this embodiment is manufactured by applying a surface treatment to at least one side of a copper foil substrate 10, which serves as the raw material, to form a surface-treated layer 20. As the surface treatment, one or both of a roughening treatment and a rust-preventive treatment are performed. That is, the surface-treated layer 20 is composed of one or both of a roughening treatment layer 21 formed by the roughening treatment and a rust-preventive treatment layer 22 formed by the rust-preventive treatment. When the surface-treated layer 20 is composed of both the roughening treatment layer 21 and the rust-preventive treatment layer 22, the roughening treatment layer 21 is formed on the surface of the copper foil substrate 10, and the rust-preventive treatment layer 22 is formed thereon. Furthermore, after the rust-proofing treatment, a chemical adhesive treatment using a silane coupling agent or similar chemical adhesive can be applied to form a silane coupling agent layer or similar chemical adhesive layer on the rust-proofing layer 22. These surface treatments will be described in detail below.

When manufacturing the surface-treated copper foil 30 according to this embodiment, for the purpose of improving the aforementioned wettability, at least one side of the copper foil substrate 10 is subjected to an uneven forming process before or after a general roughening process. Then, a roughening layer 21 is formed by these general roughening processes and uneven forming processes. This uneven forming process is a process in which fine uneven shapes are formed on the surface of the copper foil substrate 10 to a degree that does not affect transmission loss. Examples of this uneven forming process include: capsule coating and etching uneven forming.

First, an example of capsule coating treatment will be explained. Capsule coating treatment is applied before general roughening treatment. By using a mesh-like cathode shield to apply smooth copper plating (capsule coating) to the surface of the copper foil substrate 10, a fine unevenness is formed on the surface of the copper foil substrate 10. By using a mesh-like cathode shield, an unevenness with uniform deviation can be formed on the surface of the copper foil substrate 10.

At this time, by controlling the opening ratio of the mesh-like cathode shield and the coating conditions such as current density and energizing time, it is possible to form a fine uneven shape on the surface of the copper foil substrate 10 to a degree that will not affect transmission loss. As a result, the wettability of the transfer surface 40a of the resin substrate 40 can be well controlled.

As the coating solution, a commonly used copper sulfate coating solution can be used. As the raw material for forming the cathode shielding plate, it is ideally a material with chemical resistance and insulation properties, such as vinyl chloride, polyethylene, polybutylene terephthalate, etc. The open area of the mesh portion is preferably ¹ μm² or more and 100 ^μm² or less, more preferably 10 ^μm² or more and 100 ^μm² or less. Furthermore, the open area ratio of the mesh portion is preferably 5% or more and 15% or less. If the opening area and opening ratio are within the above-mentioned range, a fine uneven shape can be formed on the surface of the copper foil substrate 10 to a degree that will not affect the transmission loss, and the wettability of the transfer surface 40a of the resin substrate 40 becomes good.

Next, an example of etching and protrusion treatment will be explained. Etching and protrusion treatment is applied after general roughening treatment and before rust prevention treatment. After roughening treatment, rust-resistant metals such as nickel (Ni) and cobalt (Co) with chemical resistance are electrodeposited under conditions of high current density and extremely short time. The substrate is then briefly immersed in an etching solution for etching, thereby forming fine unevenness on the surface of the copper foil substrate 10. A typical electrolytic bath containing nickel sulfate or nickel sulfonate can be used for nickel electrodeposition. Furthermore, the current density can be set to, for example, 1.0 A/dm² or ^higher , and the energizing time can be set to, for example, 0.5 seconds or higher and 2.0 seconds or less.

By electrodepositing the rust-resistant metal with high current density and a short time, the rust-resistant metal can be deposited only on the tops of the roughened particles formed by conventional roughening treatment. Therefore, the area on the surface of the copper foil substrate 10 other than the tops of the roughened particles is etched, forming a fine unevenness in that area. Furthermore, by controlling conditions such as the immersion time in the etching solution, a fine unevenness that does not affect transmission loss can be formed on the surface of the copper foil substrate 10. As a result, the wettability of the transfer surface 40a of the resin substrate 40 can be well controlled.

As an etching solution, common copper etching solutions such as a mixture of sulfuric acid and hydrogen peroxide or hydrochloric acid can be used. The immersion time in the etching solution can be set to, for example, more than 2 seconds and less than 10 seconds. If the immersion time in the etching solution is within the above-mentioned range, fine unevenness can be formed on the surface of the copper foil substrate 10 to a degree that will not affect transmission loss. The wettability of the transfer surface 40a of the resin substrate 40 becomes good, and the surface of the copper foil substrate 10 can be uniformly treated in subsequent rust prevention and chemical adhesive treatment steps, thus giving it good adhesion and corrosion resistance.

By means of the uneven forming process described above, a copper foil substrate 10 can be obtained, which has a surface that improves the wettability of the transfer surface 40a of the resin substrate 40 to which it is bonded. As mentioned earlier, the wettability of the transfer surface 40a of the resin substrate 40 can be evaluated by measuring the contact angle of distilled water using the fixation droplet method. The difference between the distilled water contact angle _θ0 of the non-transfer surface before copper foil bonding and the distilled water contact angle _θ1 of the transfer surface 40a after copper foil etching _{, θ0} - _θ1, must be 5° or more and 35° or less.

Preferably, when the optical roughness of the transfer surface 40a is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is ≥0.020 μm and ≤0.070 μm, and the core space volume Vvc is ≥0.030 mL/ ^m² and ≤0.110 mL/ ^m² . If the arithmetic mean roughness Sa and the core space volume Vvc of the transfer surface 40a are within the above-mentioned value range, even if the surface roughness of the surface treatment layer 20 of the surface-treated copper foil 30 is small, the wettability of the transfer surface 40a becomes better, and the processing shape of the circuit can be maintained better. Although the reason is unclear, it is believed that the reason lies in the ability to better control the etching amount at the resin-copper foil interface.

Furthermore, and more preferably, when the optical roughness of the transfer surface 40a is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is ≥0.020 μm and ≤0.051 μm, and the volume Vvc of the core space is ≥0.030 mL/ ^m² and ≤0.071 mL/ ^m² . If the arithmetic mean roughness Sa of the transfer surface 40a and the volume Vvc of the core space are within the above-mentioned value range, the occurrence of foreign matter can be further suppressed. Although the reason is unclear, it is believed that the reason lies in the gap that can limit the entry of foreign matter.

As described above, by applying an uneven forming process and a general roughening process to at least one side of the copper foil substrate 10 for the purpose of improving wettability, a surface-treated copper foil 30 according to this embodiment can be obtained. The surface roughness of the surface treatment layer 20 of the obtained surface-treated copper foil 30 must be as described below. That is, when the optical roughness of the surface 20a of the surface treatment layer 20 is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa must be 0.04 μm or more and 0.30 μm or less. In order to further reduce transmission loss, the arithmetic mean roughness Sa of the surface 20a of the surface treatment layer 20 is preferably 0.04 μm or more and 0.20 μm or less, and more preferably 0.04 μm or more and 0.150 μm or less.

Next, a method for manufacturing the surface-treated copper foil 30 according to this embodiment will be described. The surface-treated copper foil 30 according to this embodiment can be manufactured by performing the steps (1) to (5) as described below in the order described. When manufacturing the surface-treated copper foil 30, an unevenness forming process is performed to improve wettability. As an unevenness forming process, the following two specific examples will be given for explanation: an example using capsule coating process and an example using etching unevenness forming process.

[Example of Capsule Coating Treatment] (1) Manufacturing of Copper Foil Substrate In manufacturing the surface-treated copper foil 30 according to this embodiment, it is preferable to use electrolytic copper foil or rolled copper foil with a smooth and glossy surface free of roughness or unevenness as the copper foil substrate 10. From a production and cost perspective, electrolytic copper foil is preferred, and more particularly, double-sided smooth electrolytic copper foil, commonly referred to as "double-sided gloss foil," is even more preferable.

In conventional electrolytic copper foil, the smooth and glossy surface is the polished surface (S-side). In double-sided polished foil, the smooth and glossy surface is both a polished surface and a matte surface (M-side), but the smoother and glossier surface is the matte surface. In this embodiment, it is preferable that, when using any electrolytic copper foil, the smoother and glossier surface is subjected to the following roughening treatment.

(2) Capsule Coating Treatment A capsule coating treatment is performed to improve wettability, forming a fine unevenness on at least one surface of the copper foil substrate 10. As described above, the capsule coating treatment allows for partial copper plating (capsule coating) of the surface of the copper foil substrate 10 using a mesh-like cathode shield. Specific examples of the composition of the plating solution and the plating conditions are illustrated below. By appropriately setting the current density, a smooth copper plating (capsule coating) is applied only to the openings of the mesh portion. As a result, a fine unevenness can be formed without altering the overall surface roughness of the copper foil.

<Composition of the Coating Solution> Copper sulfate pentahydrate concentration: 50-65 g/L (in copper atoms) Sulfuric acid concentration: 80-170 g/L <Coating Conditions> Processing speed: 5-18 m/min Current density: 1-5 A/ ^dm²

(3) Formation of the Roughening Layer Preferably, a two-stage plating process, as shown below, is performed as the roughening treatment. Alternatively, the second-stage fixed plating process may be omitted if necessary. The first-stage roughening plating process involves forming roughening particles on the surface of the copper foil substrate 10 after capsule plating. For example, the first-stage roughening plating process can be performed using a copper sulfate bath. Specific examples of the composition of the plating solution and the plating conditions are shown below.

In order to prevent the shedding of roughened particles, i.e. "powder shedding", additives containing molybdenum (Mo), arsenic (As), antimony (Sb), bismuth (Bi), selenium (Se), tellurium (Te), tungsten (W) can be added to the copper sulfate bath. Additives containing molybdenum are particularly preferred.

<Composition of the Coating Solution> Concentration of copper sulfate pentahydrate: 5-15 g/L (in copper atoms) Concentration of sulfuric acid: 120-250 g/L Concentration of ammonium molybdate: 500-1000 mg/L (in molybdenum atoms)

<Conditions for Coating Treatment> Treatment speed: 8-22 m/min; Current density: 15-55 A/dm² ^; Treatment time: 0.5-5.0 seconds; Bath temperature: 8-20℃

The second-stage fixation coating process involves applying a smooth coating to the copper foil substrate 10 after the roughening coating process of the first stage. This forms a roughening layer 21 on the surface of the copper foil substrate 10. For example, the second-stage fixation coating process can be performed using a copper sulfate bath. Specific examples of the composition of the coating solution and the coating conditions are given below.

Typically, this fixation coating process is performed to prevent the roughening particles from falling off, that is, to fix the roughening particles. For example, in the manufacture of copper-clad laminates, when a flexible substrate using a harder resin such as polyimide resin is combined with a surface-treated copper foil 30 according to this embodiment, the roughening particles can be prevented from falling off by applying a fixation coating process to the roughened surface.

<Composition of the Coating Solution> Concentration of copper sulfate pentahydrate: 50-65 g/L (in copper atoms) Concentration of sulfuric acid: 90-160 g/L <Coating Conditions> Processing speed: 5-20 m/min Current density: 1-7 A/ ^dm²

(4) Formation of the anti-rust treatment layer A silane coupling agent layer can be further formed directly on or through an intermediate layer on the roughening treatment layer 21. Examples of intermediate layers include: a nickel-containing base layer, a zinc (Zn) heat-resistant treatment layer, and a chromium (Cr) anti-rust treatment layer 22. Furthermore, because the intermediate layer and the silane coupling agent layer are very thin, they do not affect the particle shape of the roughened particles in the roughened surface of the surface-treated copper foil 30. The particle shape of the roughened particles in the roughened surface of the surface-treated copper foil 30 is essentially determined by the particle shape of the roughened particles on the surface of the roughening treatment layer 21 corresponding to the roughened surface.

For example, in cases where copper (Cu) in the copper foil substrate 10 or roughening layer 21 diffuses to the resin substrate 40 and causes copper damage, resulting in decreased adhesion, the base layer is preferably formed between the roughening layer 21 and the silane coupling agent layer. The base layer is preferably formed of at least one material selected from nickel, nickel-phosphorus (P), nickel-zinc, and nickel-molybdenum.

The heat-resistant coating is preferably formed when it is necessary to improve the heat resistance of the surface-treated copper foil 30. For example, the heat-resistant coating is preferably formed of zinc or a zinc-containing alloy. Examples of zinc-containing alloys include: zinc-tin (Sn) alloy, zinc-nickel alloy, zinc-cobalt alloy, zinc-copper alloy, zinc-molybdenum alloy, zinc-chromium alloy, and zinc-vanadium (V) alloy.

The rust-resistant treatment layer 22 is preferably formed when further enhanced corrosion resistance is required. Examples of rust-resistant treatment layers 22 include, for example, a chromium layer formed by chromium plating and a chromate layer formed by chromate treatment. When forming all three layers—the base layer, the heat-resistant treatment layer, and the rust-resistant treatment layer 22—it is preferable to form them on the roughening treatment layer 21 in this order. Alternatively, depending on the application or intended use, only one or two of the base layer, the heat-resistant treatment layer, and the rust-resistant treatment layer 22 may be formed.

(5) Formation of the silane coupling agent layer As a method for forming the silane coupling agent layer, examples include the following: applying a silane coupling agent solution directly or through an intermediate layer to the roughened surface 21 of the surface-treated copper foil 30, followed by air drying (natural drying) or heat drying. The silane coupling agent layer will form as soon as the water in the applied coupling agent solution evaporates. Heating at a temperature of 50–180°C is preferred as it promotes the reaction between the silane coupling agent and the copper foil.

The silane coupling agent layer preferably contains one or more of the following: epoxy silane coupling agent, amino silane coupling agent, vinyl silane coupling agent, methacrylic acid silane coupling agent, acrylic acid silane coupling agent, azole silane coupling agent, styryl silane coupling agent, urea silane coupling agent, methyl methacrylate silane coupling agent, thioether silane coupling agent, and isocyanate silane coupling agent.

[Example of using etching and protrusion processing] (1) Manufacturing of the copper foil substrate Same as the example using capsule coating. (2) Formation of the roughening layer Same as the example using capsule coating.

(3) Etching and protrusion treatment: Etching and protrusion treatment is performed to improve wettability, forming fine uneven shapes on the surface of the copper foil substrate 10. The content of etching and protrusion treatment is as described above, and the treatment conditions are further explained in detail. An electrolytic bath containing nickel sulfate with a nickel concentration of 30 to 150 g/L is used. Electrodeposition is performed by setting the current density to 1.0 to 4.0 A/ ^dm² and the current application time to 0.5 to 2.0 seconds. Then, the substrate is briefly immersed in the etching solution for etching, thereby forming fine uneven shapes on the surface of the copper foil substrate 10 that do not affect transmission loss.

This etching process creates unevenness on the surface of the roughened particles formed by the roughening treatment. Other etching methods include immersion treatment in solutions containing inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid. By immersing the copper foil substrate 10 in an aqueous solution of an inorganic acid of a specified concentration for several seconds to tens of seconds, fine unevenness is formed on the surface of the roughened particles. For example, if hydrochloric acid is used, fine unevenness is formed on the surface of the roughened particles by immersing in hydrochloric acid with a concentration of 5-20% by volume for more than 2 seconds.

Furthermore, as other etching methods, in addition to immersion treatment in solutions containing the aforementioned inorganic acids, the following can also be used: immersion treatment in solutions containing organic acids such as acetic acid and formic acid; immersion treatment in solutions containing ferric chloride and copper chloride; and electrolytic etching by anodic oxidation. Two or more of these methods can be combined to perform the etching.

(4) Formation of the anti-rust coating Same as in the example using capsule coating. (5) Formation of the silane coupling agent layer Same as in the example using capsule coating.

(B) Regarding the wettability of the transfer surface Next, the method for evaluating the wettability of the transfer surface 40a will be explained. The wettability of the transfer surface 40a of the resin substrate 40, which is bonded to the surface-treated copper foil 30 during the manufacture of the copper-clad laminate 50 and the printed circuit board 60, can be evaluated by measuring the contact angle of distilled water using the fixation droplet method as specified in JIS R3257:1999.

For the surface of the resin substrate 40 before it is bonded to the surface-treated copper foil 30, the contact angle _θ0 of the distilled water is measured according to the above-described fixation droplet method. The surface for which the contact angle _θ0 of the distilled water on the non-transfer surface before bonding to the copper foil is measured is the non-transfer surface whose shape has not been transferred with the surface-treated copper foil 30.

Furthermore, after the resin substrate 40 is bonded to the surface treatment layer 20 of the surface-treated copper foil 30, the surface-treated copper foil 30 is removed by etching. The contact angle _θ1 of distilled water on the remaining surface of the resin substrate 40, which was previously bonded to the surface-treated copper foil 30, is measured using the aforementioned fixed droplet method. The surface on which the distilled water contact angle _θ1 of the transferred surface after copper foil etching was measured is the transfer surface 40a, which has the shape of the bonded surface-treated copper foil 30. Then, the wettability of the transfer surface 40a of the resin substrate 40 is evaluated by the difference between the contact angle _θ0 and the contact angle _{θ1 , θ0} - _θ1 . If the difference between the contact angle _θ0 and the contact angle _{θ1 , θ0} - _θ1, is greater than 5° and less than 35°, then the wettability of the transfer surface 40a is good.

As described above, the resin components used to measure the contact angles _θ0 and _θ1 can be the same type as the resin substrate 40 used in manufacturing the copper-clad laminate 50 and the printed circuit board 60, or different types can be used to measure the contact angles _θ0 and _θ1 . That is, the resin substrate 40 used in manufacturing the copper-clad laminate 50 and the printed circuit board 60 can use components with different types, shapes, and sizes of resin as resin components.

The resin used to form the resin component for measuring the contact angles _θ0 and _θ1 can be a heat-curing resin or a thermoplastic resin. In the case of a heat-curing resin, the contact angles _θ0 and _θ1 are measured after the resin component has hardened. That is, in the case of a contact angle _θ1 , the uncured resin component is bonded to the surface treatment layer 20 of the surface-treated copper foil 30, and after the resin component has hardened, the surface-treated copper foil 30 is removed by etching. Then, the contact angle _θ1 of the distilled water is measured on the transfer surface of the resin component according to the above-described fixed droplet method.

(C) Regarding Copper-Clad Laminates The copper-clad laminate 50 according to this embodiment is not particularly limited in its composition, and it includes a surface-treated copper foil 30 and a resin substrate 40. Furthermore, the resin substrate 40 is bonded to the surface-treated layer 20 of the surface-treated copper foil 30. This copper-clad laminate 50 can be used, for example, in the manufacture of a printed circuit board 60. Furthermore, examples of resins used to form the resin substrate 40 include: epoxy resins, polyphenylene ether, phenolic resins, bis(phenoxyphenoxy)benzene, polyimide, liquid crystal polymers, and fluoropolymers (e.g., polytetrafluoroethylene).

(D) Regarding the Printed Circuit Board The configuration of the printed circuit board 60 according to this embodiment is not particularly limited, and it includes the copper-clad laminate 50 according to this embodiment. For example, as long as the surface-treated copper foil 30 of the copper-clad laminate 50 is etched to form the circuit 31, and another resin substrate 41 is bonded over the circuit 31, the printed circuit board 60 can be obtained (see FIG. 3(d)). The resin substrate 41 bonded over the circuit 31 can be the same type as the resin substrate 40 of the copper-clad laminate 50, or it can be a different type.

[Examples] The following examples and comparative examples further illustrate the present invention. First, the surface-treated copper foil of Comparative Example 7 is manufactured according to the manufacturing method described in Patent Document 1. Similarly, the surface-treated copper foil of Comparative Example 8 is manufactured according to the manufacturing method described in Patent Document 2, the surface-treated copper foil of Comparative Example 9 is manufactured according to the manufacturing method described in Patent Document 3, the surface-treated copper foil of Comparative Example 10 is manufactured according to the manufacturing method described in Patent Document 4, and the surface-treated copper foil of Comparative Example 11 is manufactured according to the manufacturing method described in Patent Document 5.

Subsequently, the surface-treated copper foils of Examples 1-23 and Comparative Examples 1-6, 12-14 were manufactured according to the following description: (i) Copper Foil Substrate A roll of electrolytic copper foil (double-sided glossy foil) with a thickness of 18 μm was prepared as the raw material, i.e., the copper foil substrate, for manufacturing the surface-treated copper foils of Examples 1-23 and Comparative Examples 1-6, 12-14. The cathode used in the manufacture of the electrolytic copper foil was a titanium rotating cylinder with its surface roughness adjusted by polishing with #1000 to #2000 steel. The anode was a dimensionally stable anode, DSA (registered trademark). The composition of the electrolyte and the electrolysis conditions are shown below.

<Electrolyte Composition> Copper: 75g/L Sulfuric Acid: 65g/L Chlorine: 20mg/L Sodium 3-Pyro-1-propanesulfonate: 2mg/L Hydroxyethyl Cellulose: 10mg/L Low Molecular Weight Gel (Molecular Weight 3000): 50mg/L <Electrolysis Conditions> Bath Temperature: 50℃ Current Density: 45A/ ^dm²

Next, the copper foil substrate produced in the above manner is subjected to the aforementioned general roughening treatment and the raised surface treatment for improving wettability. Regarding Examples 1-8, 17-23 and Comparative Examples 2, 3, and 6, after applying the raised surface treatment for improving wettability (i.e., capsule plating) to the copper foil substrate, a general roughening treatment is applied. Regarding Examples 9-16 and Comparative Examples 4 and 5, after applying the general roughening treatment to the copper foil substrate, an raised surface treatment for improving wettability (i.e., etching raised surface treatment) is applied. The general roughening treatment, capsule plating treatment, and etching raised surface treatment will be explained below.

(ii) General Roughening Treatment The rough surface of the copper foil substrate is roughened using a roll-to-roll method. This roughening treatment is a two-stage electroplating process. The composition of the plating solution and plating conditions for the first-stage electroplating process are shown below. The composition of the plating solution and plating conditions for the second-stage electroplating process (fixed plating) are also shown below. By varying the current density and energizing time of the first-stage electroplating process, as shown in Tables 1 and 2, roughening particles of different heights and shapes are formed on the surface of the copper foil.

<Composition of the plating solution for the first stage of electroplating> Concentration of copper sulfate pentahydrate: 10 g/L (copper atoms only) Concentration of sulfuric acid: 150 g/L Concentration of ammonium molybdate: 600 mg/L (molybdenum atoms only) <Conditions for the first stage of electroplating> Processing speed: 15 m/min Current density: 15–55 A/dm² ^Bath temperature: 15℃ Current application time: 4–6 seconds

<Composition of the plating solution for the second-stage electroplating treatment> Concentration of copper sulfate pentahydrate: 55 g/L (in copper atoms) Concentration of sulfuric acid: 120 g/L <Conditions for the second-stage electroplating treatment> Processing speed: 15 m/min Current density: ² A/dm² Irradiation time: 3 seconds

(iii) Capsule Coating Treatment: A capsule coating treatment, which forms an uneven surface, is applied to the copper foil substrate in a roll-to-roll manner. A mesh-shaped cathode shield with an opening area of 50 ^μm² and an opening ratio of 5–15% is placed near the copper foil substrate in an electrolytic bath, and electroplating is performed using a coating solution with the following composition under the following coating conditions. Copper foil substrates with different surface unevenness are produced by varying the opening ratio of the cathode shield, the electroplating current density, and the energizing time, as shown in Tables 1 and 2.

<Composition of the Coating Solution> Concentration of copper sulfate pentahydrate: 60 g/L (in copper atoms) Concentration of sulfuric acid: 150 g/L <Concentration of Coating Treatment> Processing speed: 18 m/min

(iv) Etching and Roughening Treatment An etching and roughening treatment is applied to the roughened surfaces of a copper foil substrate to create an uneven surface. This treatment involves electrodepositing nickel and then immersing the substrate in an etching solution for etching. The composition of the electrolyte used for electrodeposition, the electrodeposition conditions, and the etching conditions are shown below. Copper foil substrates with different surface roughness are fabricated by varying the electrodeposition current density and current-carrying time, as shown in Tables 1 and 2.

<Electrolyte Composition> Nickel concentration: 60 g/L; Boric acid ( _H₃BO₃ ) concentration: 15 g/L _; Bath temperature: 20℃; pH: 3.5

<Electrodeposition Conditions> Current density: 1–2.5 A/dm² ^; Current application time: 1–3 seconds. <Etching Conditions> Etching solution: 10% hydrochloric acid concentration; Bath temperature: 30°C; Processing time: 0.5–2 seconds.

(v) Rust Prevention Treatment Subsequently, a rust prevention treatment is applied to the surface of the copper foil substrate that has undergone roughening and unevenness forming as described above, to form a rust prevention layer. The rust prevention treatment involves sequentially applying nickel plating, zinc plating, and chromium plating. The conditions for nickel plating, zinc plating, and chromium plating are shown.

<Composition of Nickel Plating Solution> Nickel concentration: 45 g/L; Boric acid concentration: 20 g/L; Bath temperature: 20℃; pH: 3.5 <Nickel Plating Conditions> Current density: 0.4 A/ ^dm²; Processing time: 8 seconds

<Composition of Zinc Plating Bath> Zinc concentration: 2.5 g/L Sodium hydroxide (NaOH) concentration: 25 g/L Bath temperature: 20℃ <Zinc Plating Conditions> Current density: 0.7 A/ ^dm² Processing time: 4 seconds

<Composition of Chromium Plating Solution> Chromium Concentration: 8 g/L Bath Temperature: 30℃ pH: 2.4 <Chromium Plating Conditions> Current Density: 5 A/ ^dm² Processing Time: 4 seconds

(vi) Silane Coupling Agent Treatment Finally, a silane coupling agent treatment is applied to form a silane coupling agent layer on the chromium plating layer at the outermost surface of the rust-proof layer. The silane coupling agent layer is formed by applying a 0.2% by mass aqueous solution of 3-aminopropyltrimethoxysilane and drying it at 100°C.

[Table 1]

[Table 2]

Various evaluations were performed on the surface-treated copper foils of Examples 1-23 and Comparative Examples 1-14 obtained in the manner described above. The evaluation items and methods are explained below. The evaluation results are shown in Tables 1 and 2. <Contact Angle of Distilled Water> A copper-clad laminate was manufactured by bonding a resin component to the surface-treated layer (i.e., the silane coupling agent layer) of the surface-treated copper foil. The following material was used as the resin component. That is, in Examples 1-20 and Comparative Examples 1-11, the resin components were made by overlapping and bonding two low-dielectric polyphenylene ether resin substrate films (MEGTRON7N (trade name), ultra-low transmission loss/high heat resistance multilayer substrate material manufactured by Panasonic Corporation, 60 μm thick).

Furthermore, in Embodiment 21 and Comparative Example 12, ThunderClad3+ (trade name) manufactured by Tai-Yao Technology Co., Ltd. was used; in Embodiment 22 and Comparative Example 13, ESPANEX (registered trademark) manufactured by NIPPON STEEL Chemical & Material Co., Ltd. was used; and in Embodiment 23 and Comparative Example 14, Vecstar (registered trademark) liquid crystal polymer film manufactured by Kuraray Co., Ltd. was used. Furthermore, the bonding of the surface-treated copper foil to the resin-made components was performed in accordance with the process guidelines for each resin.

The copper-clad laminate was etched using a mixture of copper chloride and hydrochloric acid as the etching solution to remove all the surface-treated copper foil. After thoroughly washing the remaining resin components with water, the contact angle θ1 of the distilled water on the surface of the resin components where the surface-treated copper foil was bonded (transfer surface) was measured according to the fixation droplet method specified in JIS R3257: ₁₉₉₉ .

On the other hand, another resin component of the same type as the resin component bonded to the surface treatment layer of the surface-treated copper foil is prepared. For this other resin component, without adhering to the surface-treated copper foil, the same operation as described above when manufacturing the copper-clad laminate is performed, and the contact angle _θ0 of the distilled water on its surface (non-transfer surface) is measured using the aforementioned fixed droplet method. However, the difference between the contact angle _θ0 and the contact angle _θ1 , _θ0 - _θ1 , is calculated.

<Arithmetic mean roughness Sa of surface-treated copper foil and arithmetic mean roughness Sa of resin components, and volume Vvc of the core space> Using laser confocal microscopes VK-X1050 and VK-X1000 manufactured by Keynes Corporation, the arithmetic mean roughness Sa of the surface treatment layer (i.e., silane coupling agent layer) of surface-treated copper foil and the arithmetic mean roughness Sa of the transfer surface of resin components after etching the copper foil at a distilled water contact angle _θ1 were measured in accordance with ISO25178.

Furthermore, the laser confocal microscope has an objective magnification of 100x, a scanning mode of laser confocal, a measurement size of 2048 × 1536, a measurement quality of high precision, and a pitch of 0.08 μm. Also, the arithmetic mean roughness Sa and the core space volume Vvc are calculated according to the filter processing and calculation conditions shown below.

Image Processing: Smoothing, 3×3, Median S-Filter: None F-Operation: Plane Tilt Correction L-Filter: 0.025μm Calculated Object Area: 100μm×100μm Load Area Ratio of Load Curve: 10% and 90%

<Circuit Processability> On a surface-treated copper foil of the same type used to measure the distilled water contact angle _θ1 of the transfer surface after copper foil etching, a resist pattern with a line spacing and pitch (L&S) of 50/50 μm was formed by subtraction. Then, the surface-treated copper foil was etched to form a circuit with the circuit pattern. A dry etching film was used as the resist, and a mixture containing copper chloride and hydrochloric acid was used as the etching solution.

Then, the etching factor (Ef) of the obtained circuit is measured. The etching factor is a value expressed by the formula Ef = 2H/(B-T) when the copper foil thickness is set to H, the bottom width of the formed circuit is set to B, and the top width of the formed circuit is set to T. The copper-clad laminate with the circuit is cut to expose a cross-section orthogonal to the surface of the resin component. The cross-section of the circuit is observed using a scanning electron microscope. Then, angles X and Y on the cross-section shown in Figure 2 are measured. Angle X is the angle between the straight line connecting the top end 31a and the bottom end 31b of circuit 31 and the surface of the resin component. Angle Y is the angle between the tangent of the bottom end 31b of circuit 31 and the surface of the resin component.

The tangent at the bottom end 31b of circuit 31 is defined in more detail. A straight line parallel to the surface of the resin component is drawn at a height of 1.5 μm from the bottom side surface of the resin component. The straight line connecting the intersection point 31c of this line and the side surface of circuit 31 with the bottom end 31b is defined as the "tangent at the bottom end 31b of circuit 31". The angle between this tangent and the surface of the resin component is defined as angle Y.

For a single circuit, observe any five cross-sections and measure angles X and Y respectively. Then, calculate the average of the five measured values for both angle X and angle Y. The results are shown in Tables 1 and 2. In Tables 1 and 2, circuits with Ef greater than 2.5 and angle Y larger than angle X are denoted as "A", circuits with Ef greater than 2.0 but less than 2.5 and angle Y larger than angle X are denoted as "B", and all others are denoted as "C". Furthermore, Figure 2(a) shows an example of circuit 31 where angle Y is smaller than angle X, and Figure 2(b) shows an example of circuit 31 where angle Y is larger than angle X.

<Transmission Loss> A printed circuit board with strip lines was fabricated using the same copper-clad laminate used to measure the distilled water contact angle _θ1 of the transfer surface after copper foil etching, and the transmission characteristics were evaluated. The circuit width of the strip lines formed on this printed circuit board was set to 140 μm, and the circuit length was set to 76 mm.

A Keysight Technologies N5291A network analyzer was used to measure the transmission loss of high-frequency signals transmitted on this printed circuit board. The characteristic impedance was set to 50Ω. The measured transmission loss value means that the smaller the absolute value, the less the transmission loss (i.e., the better the transmission of high-frequency signals). The results are shown in Tables 1 and 2. In Tables 1 and 2, an absolute value of transmission loss at 40GHz less than 3.0dB/76mm is represented as "A", a value greater than or equal to 3.0dB/76mm but less than 3.6dB/76mm is represented as "B", and a value greater than or equal to 3.6dB/76mm is represented as "C".

<Foreign Object Occurrence> A mixture of copper chloride and hydrochloric acid was used as the etching solution to etch a copper-clad laminate identical to those used to measure the distilled water contact angle _θ1 of the transfer surface after copper foil etching, removing all surface-treated copper foil. After thoroughly washing the remaining resin components, the surface of the resin components with the surface-treated copper foil (transfer surface) was sequentially overlapped with a resin component and surface-treated copper foil of the same type used to make the aforementioned copper-clad laminate, and then etched again in the same order to remove all surface-treated copper foil. In this way, a resin sample consisting of two resin components bonded together was obtained.

Next, the obtained resin sample was cut into squares with each side measuring 5 cm. The cut resin sample was then observed under a microscope at 35x magnification to determine the number of black spots with a diameter greater than 1 mm. These black spots were caused by foreign matter generated between the two bonded resin components. Microscopic observation was performed by observing the transfer surface of the resin component that initially formed the copper-clad laminate from the side of the later-bonded resin component. The results are shown in Tables 1 and 2. In Tables 1 and 2, when the number of black spots in each cut resin sample is 2 or less, it is represented as "A"; when it is 3 or more but less than 5, it is represented as "B"; and when it is more than 5, it is represented as "C".

As shown in Tables 1 and 2, although the arithmetic mean roughness Sa of the surface treatment layer of the surface-treated copper foil in Examples 1 to 23 is controlled between 0.04 μm and 0.30 μm, the difference _θ0 - _θ1 between the contact angle _θ0 and the contact angle _θ1, which is used to represent the wettability of the transfer surface of the resin substrate, is well controlled. Therefore, the circuit processing performance is excellent, and transmission loss and foreign matter are not easily generated.

Furthermore, in Examples 1-4, 10-14, 17, 18, and 21-23, the surface-treated copper foils exhibit superior circuit processability and are less prone to foreign matter formation due to well-controlled arithmetic mean roughness Sa of the resin-based transfer surface and Vvc of the core space. In contrast, the surface-treated copper foils in Comparative Examples 1-14 suffer from lower wettability of the resin-based transfer surface, resulting in insufficient circuit processability, transmission loss, and foreign matter formation.

10: Copper foil substrate 20: Surface treatment layer 20a: Surface of the surface treatment layer 21: Roughening treatment layer 22: Rust-proof treatment layer 30: Surface-treated copper foil 31: Circuit 31a: Top end 31b: Bottom end 40: Resin substrate (resin component) 40a: Transfer surface 41: Resin substrate 50: Copper-clad laminate 60: Printed circuit board 100: Foreign object

Figure 1 is a cross-sectional view illustrating the structure of a surface-treated copper foil according to an embodiment of the present invention. Figure 2 is a diagram illustrating the wettability of the transfer surface of a resin-based substrate. Figure 3 is a diagram illustrating a method for manufacturing a copper-clad laminate and a printed circuit board according to an embodiment of the present invention.

Domestic Storage Information (Please record in order of storage institution, date, and number) None International Storage Information (Please record in order of storage country, institution, date, and number) None

20a: Surface of the surface treatment layer 30: Surface-treated copper foil 31: Circuit 40: Resin substrate (resin component) 40a: Transfer surface 41: Resin substrate 50: Copper-clad laminate 60: Printed circuit board 100: Foreign matter

Claims (5)

A surface-treated copper foil comprises: a copper foil substrate; and a surface-treated layer formed on at least one side of the copper foil substrate; wherein the surface-treated layer is composed of one or both of a roughening layer and a rust-resistant layer, and when the optical roughness of the surface of the surface-treated layer is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is 0.04 μm or more and 0.30 μm or less. After a resin component is bonded to the surface-treated copper foil, the surface-treated copper foil is removed by etching, and the remaining surface of the resin component that was bonded to the surface-treated copper foil is the transfer surface, according to JIS... R3257:1999 specifies the fixed droplet method for determining the contact angle _θ1 of distilled water. For the surface of the resin component to be bonded to the aforementioned surface-treated copper foil before bonding with the aforementioned surface-treated copper foil (i.e., the non-transfer surface), when the contact angle _θ0 of distilled water is determined according to the aforementioned fixed droplet method, the difference between the aforementioned contact angle _θ0 and the aforementioned contact angle _{θ1 , θ0} - _θ1, is 5° or more and 35° or less. The surface-treated copper foil as described in claim 1, wherein, when the optical roughness of the aforementioned transfer surface is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is 0.020 μm or more and 0.070 μm or less, and the volume Vvc of the core space is 0.030 mL/ ^m² or more and 0.110 mL/ ^m² or less. The surface-treated copper foil as described in claim 1, wherein, when the optical roughness of the aforementioned transfer surface is measured according to the method specified in ISO 25178, the arithmetic mean roughness Sa is 0.020 μm or more and 0.051 μm or less, and the volume Vvc of the core space is 0.030 mL/ ^m² or more and 0.071 mL/ ^m² or less. A copper-clad laminate comprising: a surface-treated copper foil as described in any one of claims 1 to 3; and a resin substrate bonded to the aforementioned surface-treated layer of the aforementioned surface-treated copper foil. A printed circuit board having the copper-clad laminate described in claim 4.