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

Abstract

Provided is a surface-treated copper foil with which it is possible to manufacture a printed wiring board, etc., in which there is exceptional adhesion between a resin base material and the surface-treated copper foil, transmission loss is low, and a gap is less likely to be produced at the interface between the resin base material and the surface-treated copper foil even upon receiving a heat history. This surface-treated copper foil has a roughened surface on which roughened particles are formed. In the surface-treated copper foil, property values measured with respect to the roughened surface satisfy the following: (A) when the surface-treated copper foil is cut to cause a cross-section orthogonal to the roughened surface to appear, and the cross-section is observed using a scanning electron microscope, the presence density X of protrusions of the roughened particles present on the roughened surface is 4 to 10 per 1-μm-long region of the roughened surface in the cross-section; (B) the average value AR of the aspect ratio calculated by dividing the particle height of the roughened particles by the particle diameter thereof is 1.5 to 3.0; and (C) the arithmetic-average height Sa measured in conformance with the optical measurement method stipulated in ISO 25178 is 0.04 μm to 0.10 μm.

Description

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

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

[0002] Development of AI servers with high data processing volumes and core routers with heavy traffic volumes is progressing. To increase communication speed and capacity, high-frequency electrical signals are required to transmit and receive large amounts of information. However, suppressing the attenuation of high-frequency electrical signals during transmission and reception is required. Specifically, it is necessary to reduce transmission loss, which is the degree of attenuation of high-frequency electrical signals when they are transmitted through a circuit board. Furthermore, because copper foil, which serves as a conductor for circuit boards, is affected by the skin effect when transmitting high-frequency electrical signals, efforts have been made to reduce the surface roughness of copper foil. However, reducing the surface roughness of copper foil to reduce transmission loss weakens the anchoring effect on the resin substrate, thereby reducing the adhesion required of copper foil to the resin substrate. Increasing the surface roughness of copper foil to improve adhesion to the resin substrate increases transmission loss. In other words, there is a trade-off between adhesion between the resin substrate and copper foil and transmission loss, and achieving both is not easy. For example, Patent Document 1 discloses a surface-treated copper foil with a roughened layer formed on its surface by roughening treatment. The technique disclosed in Patent Document 1 aims to achieve both good adhesion and low transmission loss by specifying the surface roughness and the average particle size of the particles in the roughened layer.

[0003] Meanwhile, with the trend toward higher density and more functionality in circuit boards, there has been a need to mount components in narrow-pitch through-holes. To achieve this, it is necessary to prevent voids from forming at the interface between the resin substrate and the copper foil during the process of drilling holes in a printed wiring board and then mounting components by solder reflow. If voids form at the interface between the resin substrate and the copper foil, wiring breaks or shorts may occur, potentially hindering normal circuit operation. As described above, printed wiring boards manufactured by bonding a resin substrate to copper foil are required to have both excellent adhesion between the resin substrate and the copper foil and low transmission loss. In addition, printed wiring boards manufactured by bonding a resin substrate to copper foil are also required to prevent voids from forming at the interface between the resin substrate and the copper foil even when subjected to thermal history. The technology disclosed in Patent Document 1 does not take into consideration the ability to prevent voids from forming at the interface between the resin substrate and the copper foil.

[0004] Japanese Patent Application Laid-Open No. 2017-193778

[0005] An object of the present invention is to provide a surface-treated copper foil and a copper-clad laminate that can be used to produce printed wiring boards and the like, which have excellent adhesion between a resin substrate and the surface-treated copper foil, low transmission loss, and are less likely to form voids at the interface between the resin substrate and the surface-treated copper foil even when subjected to thermal history. Another object of the present invention is to provide a printed wiring board, which has excellent adhesion between a resin substrate and the surface-treated copper foil, low transmission loss, and is less likely to form voids at the interface between the resin substrate and the surface-treated copper foil even when subjected to thermal history.

[0006] A surface-treated copper foil according to one embodiment of the present invention is a surface-treated copper foil having, on at least one side thereof, a roughened surface on which roughening particles are formed, wherein the roughening particles have protrusions formed thereon that protrude from the surface of the roughening particles, and wherein physical properties measured on the roughened surface satisfy the following (A), (B), and (C): (A) When the surface-treated copper foil is cut to expose a cross section perpendicular to the roughened surface and the cross section is observed, the density X of the protrusions of the roughening particles present on the roughened surface is 4 to 10 per 1-μm region of the roughened surface in the cross section; (B) The average aspect ratio AR, calculated by dividing the particle height by the particle diameter of the roughening particles, is 1.5 to 3.0; and (C) The arithmetic mean height Sa, measured in accordance with the optical measurement method specified in ISO 25178, is 0.04 μm to 0.10 μm.

[0007] A copper-clad laminate according to another aspect of the present invention comprises the surface-treated copper foil according to the above aspect and a resin substrate bonded to the roughened surface of the surface-treated copper foil. A printed wiring board according to yet another aspect of the present invention comprises the copper-clad laminate according to the above aspect.

[0008] The surface-treated copper foil and copper-clad laminate of the present invention have excellent adhesion between the resin substrate and the surface-treated copper foil, and can be used to produce printed wiring boards and the like that have low transmission loss and are less likely to produce voids at the interface between the resin substrate and the surface-treated copper foil even when subjected to thermal history. The printed wiring board of the present invention has excellent adhesion between the resin substrate and the surface-treated copper foil, has low transmission loss, and is less likely to produce voids at the interface between the resin substrate and the surface-treated copper foil even when subjected to thermal history.

[0009] 1 is a cross-sectional view illustrating roughening particles formed on a roughened surface of a surface-treated copper foil according to an embodiment of the present invention. 2 is a cross-sectional view illustrating the configuration of a copper-clad laminate according to an embodiment of the present invention.

[0010] An embodiment of the present invention will be described. Note that the embodiment described below is merely an example of the present invention. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0011] As mentioned above, conventionally, printed wiring boards manufactured by laminating a resin substrate to a copper foil have been required to have both excellent adhesion between the resin substrate and the copper foil and low transmission loss. In addition, printed wiring boards manufactured by laminating a resin substrate to a copper foil have also been required to have the ability to prevent voids from forming at the interface between the resin substrate and the copper foil even when subjected to thermal history.

[0012] As a result of extensive research, the present inventors have found that in a surface-treated copper foil obtained by roughening the surface of a raw copper foil to form a roughened surface, all of the above requirements can be met if all of the following are satisfied: (a) Roughening particles are formed on the roughened surface by the roughening treatment, and roughening particles having protrusions on the surface are formed by the roughening treatment; (b) The aspect ratio of the roughening particles is increased; and (c) The surface roughness of the roughened surface is reduced.

[0013] That is, the surface-treated copper foil according to this embodiment has a roughened surface on at least one side on which roughening particles are formed, and the roughening particles have protrusions that protrude from the surface of the roughening particles. The physical properties measured on the roughened surface satisfy the following (A), (B), and (C): (A) When the surface-treated copper foil is cut to expose a cross section perpendicular to the roughened surface and the cross section is observed, the density X of the protrusions of the roughening particles present on the roughened surface is 4 to 10 per 1-μm region of the roughened surface in the cross section; (B) The average aspect ratio AR, calculated by dividing the particle height by the particle diameter of the roughening particles, is 1.5 to 3.0; and (C) The arithmetic mean height Sa, measured in accordance with the optical measurement method specified in ISO 25178, is 0.04 μm to 0.10 μm.

[0014] The surface-treated copper foil according to this embodiment has been subjected to a surface treatment, such as a roughening treatment (e.g., copper plating), on at least one of its front and back surfaces. The roughened surface has roughened particles formed thereon by the roughening treatment. The surface-treated copper foil may have a roughened surface on only one of its front and back surfaces, or on both surfaces. Furthermore, the entire surface of one surface of the surface-treated copper foil may be a roughened surface, or a portion of one surface may be a roughened surface. When producing the surface-treated copper foil, the raw copper foil is subjected to a roughening treatment. Examples of the raw copper foil include electrolytic copper foil and rolled copper foil.

[0015] The surface-treated copper foil of this configuration has excellent adhesion between the resin substrate and the surface-treated copper foil, and can be used to manufacture printed wiring boards and the like that have low transmission loss and are less likely to produce voids at the interface between the resin substrate and the surface-treated copper foil even when subjected to thermal history. Therefore, by using the surface-treated copper foil of this embodiment, it is possible to manufacture printed wiring boards that are compatible with high-density packaging and multi-functionality and that can be processed to mount components in narrow-pitch through-holes. Furthermore, since the transmission loss is low even when high-frequency signals are transmitted to the circuit of the manufactured printed wiring board, the surface-treated copper foil of this embodiment can be suitably used for manufacturing printed wiring boards used in high-frequency bands (printed wiring boards having high-frequency circuits) (i.e., can be used as copper foil for high-frequency circuits).

[0016] The ability to prevent voids from forming at the interface between a resin substrate and a surface-treated copper foil even when subjected to thermal history will be described in detail. A double-sided copper-clad laminate manufactured using a resin substrate and a surface-treated copper foil with a small surface roughness was drilled using a drill, and the double-sided copper-clad laminate was then observed to find that the resin substrate and the surface-treated copper foil had peeled off. Then, when the drilled double-sided copper-clad laminate was subjected to a heat treatment at 260°C, voids were found to have formed at the interface between the resin substrate and the surface-treated copper foil.

[0017] This is thought to be because the heat treatment caused a phase transition of volatile components (e.g., water or low-boiling-point organic substances) contained in the resin substrate, which increased the peeling between the resin substrate and the surface-treated copper foil, resulting in voids. Therefore, in order to prevent voids from forming at the interface between the resin substrate and the surface-treated copper foil even after being subjected to thermal history, it is important that peeling between the resin substrate and the surface-treated copper foil does not easily occur even when drilling is performed using a drill.

[0018] The surface-treated copper foil having the above configurations (A) and (B) has a high anchoring effect on the resin substrate, and therefore has excellent adhesion to the surface-treated copper foil. Therefore, peeling between the resin substrate and the surface-treated copper foil is unlikely to occur, and voids are unlikely to form at the interface between the resin substrate and the surface-treated copper foil even when subjected to thermal history. For example, during the process of drilling holes in a printed wiring board and then mounting components by solder reflow, the printed wiring board is subjected to thermal history, but even in this case, voids are unlikely to form at the interface between the resin substrate and the surface-treated copper foil.

[0019] The surface-treated copper foil, copper-clad laminate, and printed wiring board according to the present embodiment will now be described in more detail. [Roughening Treatment] The method of roughening treatment for forming roughening particles on the surface of the raw copper foil to form a roughened surface is not particularly limited, but copper plating is one example.

[0020] By controlling the solution composition of the copper plating solution, plating conditions such as current density and current flow time, and the linear speed of the raw copper foil moving through the plating solution (treatment speed of the raw copper foil), it is possible to form roughening particles with protrusions protruding from the surface of the raw copper foil, and to adjust the aspect ratio of the roughening particles and the density X of the protrusions to desired values. By controlling the treatment speed of the raw copper foil, it is possible to adjust the amount of charge of copper (Cu) treated on the raw copper foil and the immersion time of the raw copper foil in the copper plating solution.

[0021] The current density is preferably high, for example, 20 A / m ２ 40A / m or more ２ The energization time is preferably short, and more preferably, for example, 1.0 second or more and 3.0 seconds or less.

[0022] The copper plating solution may contain components other than copper. For example, additives may be added to the copper plating solution. Examples of components that may be contained in the copper plating solution include molybdenum (Mo), arsenic (As), antimony (Sb), bismuth (Bi), selenium (Se), tellurium (Te), tungsten (W), and cobalt (Co).

[0023] The mesh cathode shielding plate used for copper plating is preferably made of a material having chemical resistance and insulating properties, such as a resin such as polyvinyl chloride. The opening area of ​​the mesh portion of the cathode shielding plate is, for example, 1 μm ２ 100 μm or more ２ The opening area and opening rate of the mesh portion may be 5% or more and 15% or less. If the opening area and opening rate are within the above numerical ranges, roughening particles of suitable dimensions are likely to be formed.

[0024] [Roughened Surface, Roughening Particles, and Protrusions] The roughened surface, roughening particles, and protrusions will be described with reference to Fig. 1. The surface-treated copper foil 10 shown in Fig. 1 has a roughened surface 10a on only one of its front and back surfaces, on which a plurality of roughening particles 1 are formed by roughening treatment. That is, the roughened surface 10a is formed by forming a plurality of roughening particles 1 on the surface of the raw copper foil by roughening treatment.

[0025] The roughening particles 1 may be formed so as to protrude in a direction perpendicular to the roughened surface 10a (surface of the raw copper foil), or may be formed so as to protrude in a direction inclined relative to the roughened surface 10a. That is, the angle formed between the protruding direction of the roughening particles 1 and the roughened surface 10a may be 90°, or may be greater than 0° and less than 90°. Figure 1 shows the case where the roughening particles 1 are formed so as to protrude in a direction perpendicular to the roughened surface 10a.

[0026] The roughening particles 1 are preferably made of copper or a copper alloy. The shape of the roughening particles 1 is not particularly limited, but examples thereof include a convex shape with a pointed tip, and specific examples thereof include a cone, a triangular pyramid, a square pyramid, an ellipsoid, and a hemisphere. Alternatively, the portion other than the tip is cylindrical or prismatic, and the tip is conical, triangular pyramid, square pyramid, ellipsoid, or hemisphere.

[0027] The roughening particle 1 has protrusions 2 formed thereon, protruding from the surface of the roughening particle 1. The number of protrusions 2 formed on one roughening particle 1 is not particularly limited, and may be one or more. The protrusions 2 may be formed so as to protrude in a direction perpendicular to the surface of the roughening particle 1, or may be formed so as to protrude in a direction oblique to the surface of the roughening particle 1. That is, the angle formed between the protrusion direction of the protrusions 2 and the surface of the roughening particle 1 may be 90°, or may be greater than 0° and less than 90°. FIG. 1 illustrates the case where the protrusions are formed so as to protrude in a direction oblique to the surface of the roughening particle 1.

[0028] The protrusions 2 are preferably formed of copper or a copper alloy, similar to the roughening particles 1. The shape of the protrusions 2 is not particularly limited, but an example is a convex shape with a pointed tip, similar to the roughening particles 1. Specific examples are the same as those for the roughening particles 1, and therefore will not be described here.

[0029] The density X of the protrusions 2 on the roughened surface 10a is as defined in (A) above. Here, a method for calculating the density X of the protrusions 2 will be described in detail with reference to an example. First, the surface-treated copper foil 10 is cut to reveal a cross section perpendicular to the roughened surface 10a, and the cross section is observed. The method for observing the cross section is not particularly limited, but examples include a method using a scanning electron microscope (SEM). FIG. 1 corresponds to a cross-sectional view of the surface-treated copper foil 10 obtained by observation using a scanning electron microscope.

[0030] The cross section of the surface-treated copper foil 10 is observed, and the number of protrusions 2 is counted. In this case, a region of the roughened surface 10a in the cross section where the number of protrusions 2 is to be counted is determined, and the number of protrusions 2 of the roughening particles 1 present in that region is counted. Any protrusions protruding from the outline of the roughening particles 1 in the cross section are counted as protrusions 2, regardless of the protrusion direction. However, roughening particles present further back than the observed cross section may appear in the SEM image, and such protrusions of the roughening particles are not counted.

[0031] After measuring the number of protrusions 2, the number is divided by the length (unit: μm) of the region to calculate the density X of protrusions 2 of the roughening particles 1 present on the roughened surface 10a. The length of the region is the length of the roughened surface 10a in cross section. In the example of FIG. 1, the upper long side of the rectangular surface-treated copper foil 10 corresponds to the roughened surface 10a, and the length of this long side corresponds to the length of the region where the number of protrusions 2 is to be counted. Therefore, the density X of protrusions 2 is the number of protrusions 2 per 1 μm long region of the roughened surface 10a in cross section.

[0032] The density X of the protrusions 2 must be 4 or more and 10 or less per 1 μm long region of the roughened surface 10a in the cross section, but the lower limit is preferably 6 or more, and the upper limit is preferably 10 or less.

[0033] The average aspect ratio AR calculated by dividing the particle height of the roughening particles 1 by their particle diameter is as defined in (B) above. Here, a method for calculating the average aspect ratio AR of the roughening particles 1 will be described in detail with reference to an example. First, the particle height h and particle diameter r of the roughening particles 1 are measured. The method for measuring the particle height h and particle diameter r of the roughening particles 1 is not particularly limited, but can be measured by observing the cross section of the surface-treated copper foil 10, as in the case of (A) above. The method for observing the cross section is not particularly limited, but examples include a method using a scanning electron microscope. A method for measuring the particle height h and particle diameter r of the roughening particles 1 will be described with reference to FIG. 1 .

[0034] The particle height h of the roughening particle 1 is defined as follows: The roughening particle 1 is formed so as to protrude from the roughened surface 10a, and when a virtual line is drawn that is parallel to the protruding direction of the roughening particle 1 and passes through the tip of the roughening particle 1 (this line is referred to as a first virtual line), the first virtual line intersects with the roughened surface 10a. The distance between this intersection and the tip of the roughening particle 1 is referred to as the particle height h of the roughening particle 1.

[0035] The particle diameter r of the roughening particle 1 is defined as follows: When a line perpendicular to the first virtual line is drawn (this line is referred to as the second virtual line), the second virtual line intersects with the outline of the roughening particle 1 and the protrusions 2 at multiple points. The longest distance between these intersections is referred to as the particle diameter r of the roughening particle 1. As shown in FIG. 1 , the roughening particle 1 has protrusions 2 formed thereon, and therefore the diameter of the portion of the roughening particle 1 where the protrusions 2 are formed is the particle diameter r of the roughening particle 1.

[0036] Then, the particle height h and particle diameter r of a specific roughening particle 1 are measured, and the particle height h is divided by the particle diameter r to calculate the aspect ratio of that roughening particle 1. The aspect ratios of multiple roughening particles 1 are calculated, and the average value is taken as the average aspect ratio AR. The average aspect ratio AR of the roughening particles 1 must be 1.5 or more and 3.0 or less, with the lower limit being preferably 2.0 or more and the upper limit being preferably 2.5 or less.

[0037] Furthermore, the arithmetic mean height Sa of the roughened surface 10a measured in accordance with the optical measurement method specified in ISO 25178 must be 0.04 μm or more and 0.10 μm or less, with the upper limit preferably being 0.08 μm or less.

[0038] Furthermore, in the surface-treated copper foil according to this embodiment, it is preferable that the roughened surface 10a has a 60-degree specular gloss Gs(60°) of 27 or more and 45 or less, and a 75-degree specular gloss Gs(75°) of 65 or more and 80 or less. By using a surface-treated copper foil having such a configuration, it is possible to manufacture printed wiring boards and the like with smaller transmission loss.

[0039] The 60-degree specular gloss Gs(60°) of the roughened surface 10a is preferably 27 or more and 45 or less, and more preferably the lower limit is 30 or more. The 75-degree specular gloss Gs(75°) of the roughened surface 10a is preferably 65 or more and 80 or less, and more preferably the lower limit is 70 or more.

[0040] The measurement direction is not particularly limited when measuring the 60° specular gloss Gs (60°) and 75° specular gloss Gs (75°) of the roughened surface 10a. That is, when raw copper foil is continuously produced, the physical properties of the obtained raw copper foil may differ depending on the direction. For example, the physical properties of the obtained raw copper foil may differ between the machine direction (MD) of the copper foil when producing the raw copper foil and the transverse direction (TD) perpendicular to the machine direction. However, when measuring the 60° specular gloss Gs (60°) and 75° specular gloss Gs (75°) of the roughened surface 10a, there is no problem even if the measurement direction is not taken into consideration.

[0041] [Copper-clad laminate] The copper-clad laminate 30 according to this embodiment includes the surface-treated copper foil 10 according to this embodiment and a resin substrate 20 bonded to the roughened surface 10 a of the surface-treated copper foil 10 (see FIG. 2).

[0042] The copper-clad laminate 30 according to this embodiment includes the surface-treated copper foil 10 according to this embodiment. Therefore, by using the copper-clad laminate 30 according to this embodiment, it is possible to manufacture a printed wiring board or the like that has excellent adhesion between the resin substrate 20 and the surface-treated copper foil 10, has small transmission loss, and is less likely to produce voids at the interface between the resin substrate 20 and the surface-treated copper foil 10 even when subjected to thermal history.

[0043] The type of resin forming the resin substrate 20 is not particularly limited, but examples thereof include thermoplastic resins such as liquid crystal polymer, polyether ether ketone, polyphenylene sulfide, polyphenylene ether, polyphenylene oxide, polyetherimide, polyethersulfone, polyethylene naphthalate, polyethylene terephthalate, and thermoplastic polyimide, as well as thermosetting resins such as polyimide, heat-resistant epoxy resin, cyanate-based resin (e.g., bismaleimide triazine), and thermosetting modified polyphenylene ether.

[0044] Among these resins, preferred are liquid crystal polymers such as thermotropic liquid crystal polymers, rheotropic liquid crystal polymers, etc. Examples of thermotropic liquid crystal polymers include liquid crystal polyesters, and examples of liquid crystal polyesters include aromatic polyesters obtained by reacting an aromatic hydroxycarboxylic acid as an essential monomer with an aromatic dicarboxylic acid or an aromatic diol.

[0045] Specific examples of aromatic polyesters include polyesters synthesized from parahydroxybenzoic acid (PHB), phthalic acid, and 4,4'-biphenol, polyesters synthesized from PHB and 2,6-hydroxynaphthoic acid, and polyesters synthesized from PHB, terephthalic acid, and ethylene glycol.

[0046] [Printed Wiring Board] The printed wiring board according to this embodiment includes the copper-clad laminate 30 according to this embodiment. Since the printed wiring board according to this embodiment includes the surface-treated copper foil 10 according to this embodiment, the adhesion between the resinous substrate 20 and the surface-treated copper foil 10 is excellent, the transmission loss is small, and voids are unlikely to form at the interface between the resinous substrate 20 and the surface-treated copper foil 10 even when subjected to thermal history.

[0047] The printed wiring board according to this embodiment can be manufactured by bonding a resin substrate 20 and a surface-treated copper foil 10 together to form a copper-clad laminate 30, and then removing unnecessary portions of the surface-treated copper foil 10 of the copper-clad laminate 30 other than the portions that will become the circuit by etching using an etching solution.

[0048] [Examples] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples. Electrodeposited copper foil was used as the raw copper foil, and only one of the front and back surfaces of the raw copper foil was subjected to a roughening treatment to form roughening particles with protrusions protruding from the surface, thereby producing a surface-treated copper foil having the entire surface of one of the front and back surfaces roughened. The roughening treatment was copper plating.

[0049] [1] Preparation of Copper Foil Substrate Electrodeposited copper foil was prepared as the raw copper foil for the surface-treated copper foil. This electrolytic copper foil served as the copper foil substrate for the roughening treatment. The electrolytic copper foil was produced by electrolysis under the following electrolysis conditions using the following cathode and anode and a copper sulfate electrolyte solution of the following composition. The obtained electrolytic copper foil was a roll-shaped double-sided glossy foil with a thickness of 18 to 35 μm.

[0050] <Cathode and anode> Cathode: Titanium rotating drum with surface roughness adjusted by buffing with #1000 to #2000 Anode: Dimensionally stable anode DSA (registered trademark)

[0051] <Electrolyte composition> Copper concentration: 80 g / L H ２ SO ４ Concentration: 70g / L Chlorine concentration: 25mg / L

[0052] <Additives and concentrations in the electrolyte> Sodium 3-mercapto-1-propanesulfonate: 2 mg / L Hydroxyethyl cellulose: 10 mg / L Low molecular weight glue (molecular weight 3000): 50 mg / L <Electrolysis conditions> Bath temperature: 55°C Current density: 45 A / dm ２

[0053] A copper foil substrate was subjected to a roughening treatment to produce a surface-treated copper foil. Specifically, the following steps [2], [3], and [4] were carried out to obtain the surface-treated copper foil. The solution composition of the copper plating solution and plating conditions such as current density and current application time were variously changed to obtain surface-treated copper foils of Examples 1 to 15 and Comparative Examples 1 to 6 having various physical properties of the roughened surface. The production conditions for the surface-treated copper foils of Examples 1 to 15 and Comparative Examples 1 to 6 are as shown in Table 1.

[0054] [2] Roughening Treatment One side (M side) of the copper foil substrate prepared in [1] above was subjected to a roll-to-roll plating treatment as a roughening treatment to form a roughened surface. This plating treatment was a two-stage electroplating treatment. The first stage of plating treatment was a roughening plating treatment, and the second stage was a H ２ SO ４ A roughening plating solution with a concentration of 150 g / L was used, and the copper concentration of the roughening plating solution was as shown in Table 1. The plating conditions in the roughening plating treatment, i.e., the treatment speed, whether or not multiple anodes with a length ratio in the copper foil transport direction of 1:2:3 were used (whether or not lattice-shaped anodes were used), the bath temperature, the average current density, the treatment time, and the charge density, were as shown in Table 1.

[0055] The second plating step was a fixed plating step, with a copper concentration of 60 g / L and H ２ SO ４ A fixed plating solution with a concentration of 120 g / L was used, and the bath temperature was set to 60° C. The plating conditions for the fixed plating treatment, i.e., the current density, treatment time, treatment speed, and charge density, were as shown in Table 1.

[0056]

[0057] [3] Formation of Metal Treatment Layer Subsequently, metal plating of nickel, zinc (Zn), and chromium (Cr) was carried out in this order on the roughened surface of the surface-treated copper foil produced in [2] above under the following conditions to form a metal treatment layer (intermediate layer).

[0058] <Ni plating> Ni concentration of plating solution: 40 g / L ３ BO ３ Concentration: 5 g / L Bath temperature: 20°C Plating solution pH: 3.6 Current density: 0.2 A / dm ２ Processing time: 10 seconds

[0059] <Zn plating> Zn concentration in plating solution: 2.5 g / L NaOH concentration in plating solution: 40 g / L Bath temperature: 20°C Current density: 5 A / dm ２ Processing time: 5 seconds

[0060] <Cr plating> Cr concentration of plating solution: 5 g / L Bath temperature: 20°C pH of plating solution: 2.2 Current density: 5 A / dm ２ Processing time: 5 seconds

[0061] [4] Formation of Silane Coupling Agent Layer Finally, a silane coupling agent layer was formed on the metallization layer (particularly the outermost Cr plating layer) formed in [3] above. The silane coupling agent layer was formed by applying a 0.2 mass% aqueous solution of 3-glycidoxypropyltrimethoxysilane onto the metallization layer and drying it at 100°C.

[0062] The roughened surfaces of the surface-treated copper foils obtained in Examples 1 to 15 and Comparative Examples 1 to 6 were measured for the density X of protrusions of the roughening particles present on the roughened surface, the particle height of the roughening particles, the particle diameter of the roughening particles, the average aspect ratio AR of the roughening particles, the arithmetic mean height Sa, the 60-degree specular gloss Gs(60°), and the 75-degree specular gloss Gs(75°). The measurement methods are shown below, and the measurement results are shown in Table 2.

[0063] <Density X of Roughening Particle Protrusions on Roughened Surface> The surface-treated copper foil was cut to expose a cross section perpendicular to the roughened surface, and the cross section was observed using a scanning electron microscope at an acceleration voltage of 3.0 kV and a magnification of 50,000 times.

[0064] The SEM image of the cross section of the surface-treated copper foil was observed, and the number of protrusions was counted. A region of the roughened surface in the cross section where the number of protrusions was to be counted was determined, and the number of all protrusions of the roughening particles present in that region was counted. In this example and this comparative example, a range of 2.5 μm in length on the roughened surface in the cross section was used as the region to be measured. Note that all protrusions in the cross section that protruded beyond the outline of the roughening particle (the outline of the main body of the roughening particle excluding the protrusions) were counted as protrusions, regardless of the protruding direction.

[0065] After measuring the number of protrusions, the number was divided by the length of the region (i.e., 2.5 μm) to calculate the density X of protrusions of the roughening particles present on the roughened surface. The density X is the number of protrusions per region of 1 μm in length on the roughened surface in the cross section. The density X was calculated for any five fields of view in the SEM image, and the average value was used as the density X for each example and comparative example.

[0066] <Average value AR of particle height, particle diameter, and aspect ratio of roughening particles> The surface-treated copper foil was cut to expose a cross section perpendicular to the roughened surface, and the cross section was observed using a scanning electron microscope at an accelerating voltage of 3.0 kV and a magnification of 50,000 times.

[0067] The SEM image of the cross section of the surface-treated copper foil was observed, and the particle height and particle diameter of each roughening particle were measured. The particle height was divided by the particle diameter to calculate the aspect ratio of each roughening particle. A region of the roughened surface in the cross section where the particle height and particle diameter of the roughening particles were measured was determined, and the particle height and particle diameter of all roughening particles present in that region were measured to calculate the aspect ratio. In this example and this comparative example, a 2.5 μm long range of the roughened surface in the cross section was used as the region where the particle height and particle diameter of the roughening particles were measured. The calculated aspect ratios were then averaged to obtain the average value AR. The average value AR of the aspect ratios was calculated for any five fields of view in the SEM image, and this average value was used as the average value AR of the aspect ratios of each example and comparative example.

[0068] The particle height and particle diameter of the roughening particles are measured as follows. In an SEM image of the cross section of the surface-treated copper foil, the roughening particles are formed so as to protrude from the roughened surface. When a virtual line is drawn parallel to the protruding direction of the roughening particles and passing through the tips of the roughening particles (this line is referred to as a first virtual line), the first virtual line intersects with the roughened surface. The distance between this intersection and the tip of the roughening particle is measured, and this is taken as the particle height of the roughening particle.

[0069] Furthermore, when a line perpendicular to the first imaginary line is drawn in an SEM image of the cross section of the surface-treated copper foil (this line is referred to as the second imaginary line), the second imaginary line intersects with the outlines of the roughening particles and protrusions at multiple points. The longest distance between these intersections is measured and taken as the particle diameter of the roughening particles.

[0070] <Arithmetic mean height Sa of roughened surface> Using a confocal laser microscope VK-X3100 manufactured by Keyence Corporation, the arithmetic mean height Sa of the roughened surface of the surface-treated copper foil was measured in accordance with the optical measurement method specified in ISO 25178.

[0071] The objective lens magnification of the confocal laser microscope was 100x, the scan mode was laser confocal, the measurement size was 2048 x 1536, the measurement quality was High Precision, and the pitch was 0.08 μm. The calculation of the arithmetic mean height Sa was performed using the following filter processing and calculation conditions: Image processing: averaging, 3 x 3, median S filter: none F-operation: plane tilt correction L filter: 0.025 μm Calculation target area: 100 μm x 100 μm

[0072] <Specular Gloss of Roughened Surface> Using a glossmeter VG7000 manufactured by Nippon Denshoku Industries Co., Ltd., the 60-degree specular gloss Gs(60°) of the roughened surface of the surface-treated copper foil and the 75-degree specular gloss Gs(75°) of the roughened surface were measured in accordance with the method specified in JIS Z 8741:1997.

[0073] The specular gloss was measured five times at each receiving angle in the machine direction (MD) of the electrodeposited copper foil, which is the raw copper foil of the surface-treated copper foil, and in the transverse direction (TD) perpendicular to the machine direction (MD) of the electrodeposited copper foil. The five measured values ​​in both the machine direction and the transverse direction were then averaged to determine the specular gloss at each receiving angle.

[0074] <Adhesion> A normal peel test was performed based on the method specified in JIS C6481:1996. A resin substrate was bonded to the roughened surface of the surface-treated copper foil to prepare a copper-clad laminate. The resin substrate was a laminate of two low-dielectric polyphenylene ether resin films (MEGTRON7, a multilayer substrate material manufactured by Panasonic Corporation, with a thickness of 60 μm).

[0075] Masking tape was applied to this copper-clad laminate, copper chloride etching was performed, and then the masking tape was removed to prepare a printed wiring board with a circuit wiring width of 10 mm. Next, in a room temperature environment, the circuit wiring portion (copper foil portion) of the printed wiring board was pulled at a speed of 50 mm / min in a 90-degree direction using a Tensilon tester manufactured by Toyo Seiki Seisakusho Co., Ltd. to peel it off from the resin substrate, and the normal peel strength was measured and used as the adhesion strength. In Table 2, adhesion strengths of 0.55 N / mm or more are indicated by "◎", adhesion strengths of 0.44 N / mm or more but less than 0.55 N / mm are indicated by "◯", adhesion strengths of 0.44 N / mm or more but less than 0.55 N / mm are indicated by "◯", and adhesion strengths of less than 0.44 N / mm are indicated by "×".

[0076] <Heat Resistance Test> Using surface-treated copper foil and a low-dielectric polyphenylene ether resin film (MEGTRON7, a multilayer substrate material manufactured by Panasonic Corporation, thickness 60 μm) as a resin substrate, a double-sided copper-clad laminate consisting of two layers of surface-treated copper foil and seven layers of resin layers (resin substrate) was produced.

[0077] This double-sided copper-clad laminate was drilled using a drill to form multiple through holes. The through-hole pitches were 0.25, 0.3, 0.35, 0.4, 0.5, and 0.7 mm. 500 through holes were formed for each through-hole pitch condition. The drill used for drilling was replaced with a new one every time 1,000 through holes were formed.

[0078] Smears (resin dissolved in the through-holes during drilling) on ​​a double-sided copper-clad laminate with through-holes were removed using a potassium permanganate solution, and then further removed using plasma.The smear-removed double-sided copper-clad laminate was then subjected to electroless copper plating to produce a drilled substrate.

[0079] Next, a heat resistance test was performed in which the temperature of the drilled substrate was raised to 260 ° C. using an infrared reflow soldering device, and then allowed to cool to room temperature. This operation was repeated 10 times. The drilled substrate after the heat resistance test was then cut to reveal a cross section perpendicular to the surface of the drilled substrate, and the cross section was observed using a scanning electron microscope. In an SEM image of the cross section magnified 10,000 times, it was confirmed whether or not voids were formed at the interface between the resin substrate and the surface-treated copper foil. In Table 2, if no voids were present at the interface between the resin substrate and the surface-treated copper foil, it is indicated as "◯", and if voids were present, it is indicated as "×".

[0080] <Transmission loss> A printed wiring board was fabricated using a surface-treated copper foil and a low-dielectric polyphenylene ether resin film (MEGTRON7, a multilayer board material manufactured by Panasonic Corporation, thickness 60 μm) on which a strip line was formed, and the transmission characteristics were evaluated. The circuit width of the strip line formed on the printed wiring board was 140 μm and the circuit length was 1000 mm.

[0081] A high-frequency signal was transmitted to the circuit formed on the copper foil of this printed wiring board using a network analyzer N5291A manufactured by Keysight Technologies, and the transmission loss was measured. The characteristic impedance was set to 50Ω. The smaller the absolute value of the measured transmission loss, the smaller the transmission loss, which means that the high-frequency signal can be transmitted well.

[0082] In Table 2, the absolute value of the transmission loss at 20 GHz is indicated as "A" if it is 25 dB / 1000 mm or more and less than 28 dB / 1000 mm, "B" if it is 28 dB / 1000 mm or more and less than 30 dB / 1000 mm, and "C" if it is 30 dB / 1000 mm or more.

[0083]

[0084] As can be seen from Table 2, the surface-treated copper foils of Examples 1 to 11 all satisfied the requirements of the present invention in terms of the density X of the protrusions, the average aspect ratio AR of the roughening particles, the arithmetic mean height Sa, the 60-degree specular gloss Gs (60°), and the 75-degree specular gloss Gs (75°) of the roughened surface, and therefore had good adhesion to the resin substrate and heat resistance, and had small transmission loss.

[0085] The surface-treated copper foils of Examples 12 to 15 had protrusion density X, average aspect ratio AR of roughening particles, and arithmetic mean height Sa that satisfied the requirements of the present invention, and therefore had good adhesion to the resin substrate and heat resistance, and low transmission loss. However, the 60-degree specular gloss Gs (60°) and the 75-degree specular gloss Gs (75°) of the roughened surface were outside the preferred ranges, and therefore the transmission loss was slightly higher than in Examples 1 to 11.

[0086] The surface-treated copper foil of Comparative Example 1 had a large transmission loss because the density X of the protrusions of the roughening particles present on the roughened surface did not satisfy the requirements of the present invention.The surface-treated copper foil of Comparative Example 2 had a low heat resistance because the density X of the protrusions of the roughening particles present on the roughened surface did not satisfy the requirements of the present invention, and voids were generated at the interface between the resin substrate and the surface-treated copper foil due to exposure to heat.

[0087] The surface-treated copper foil of Comparative Example 3 had poor heat resistance because the average aspect ratio AR of the roughening particles did not satisfy the requirements of the present invention. The surface-treated copper foil of Comparative Example 4 had poor heat resistance because the average aspect ratio AR of the roughening particles did not satisfy the requirements of the present invention. The surface-treated copper foil of Comparative Example 5 had high transmission loss because the arithmetic mean height Sa did not satisfy the requirements of the present invention. The surface-treated copper foil of Comparative Example 6 had poor adhesion to the resin substrate and poor heat resistance because the arithmetic mean height Sa did not satisfy the requirements of the present invention.

[0088] REFERENCE SIGNS LIST 1: Roughening particle 2: Protrusion 10: Surface-treated copper foil 10a: Roughened surface 20: Resin substrate 30: Copper-clad laminate h: Particle height r: Particle diameter

Claims

1. A surface-treated copper foil having a roughened surface on at least one side on which roughening particles are formed, wherein the roughening particles have protrusions that protrude from the surface of the roughening particles, and physical property values ​​measured on the roughened surface satisfy the following (A), (B), and (C): (A) When the surface-treated copper foil is cut to expose a cross section perpendicular to the roughened surface and the cross section is observed, the density X of the protrusions of the roughening particles present on the roughened surface is 4 to 10 per 1 μm long region of the roughened surface on the cross section; (B) The average aspect ratio AR calculated by dividing the particle height by the particle diameter of the roughening particles is 1.5 to 3.0; and (C) The arithmetic mean height Sa measured in accordance with the optical measurement method specified in ISO 25178 is 0.04 μm to 0.10 μm.

2. A surface-treated copper foil according to claim 1, wherein the 60-degree specular gloss Gs(60°) of the roughened surface is 27 or more and 45 or less, and the 75-degree specular gloss Gs(75°) is 65 or more and 80 or less.

3. A copper clad laminate comprising the surface-treated copper foil according to claim 1 or 2 and a resin substrate bonded to the roughened surface of the surface-treated copper foil.

4. A printed wiring board comprising the copper clad laminate of claim 3.

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