Metal foil with a coating layer, metal-clad laminate, and method for manufacturing metal foil with a coating layer

Abstract

The objective is to provide a metal foil that exhibits excellent adhesion to other materials and can maintain this adhesion even at high temperatures. [Solution] A coated metal foil, wherein the metal foil is a smooth metal foil and the coating layer has a roughened surface on the side opposite to the metal foil; a metal-clad laminate obtained by laminating the coated metal foil and an insulating substrate with the coating layer of the coated metal foil facing the insulating substrate; and a method for manufacturing a coated metal foil.

Description

[Technical Field]

[0001] The present invention relates to a coated metal foil, a metal-clad laminate, and a method for manufacturing a coated metal foil. [Background technology]

[0002] In recent years, with the increasing performance and functionality of information and communication equipment, and the advancement of networking, there has been a need to transmit and process large amounts of information at higher speeds. As a result, the signals being transmitted tend to be higher in frequency, and printed circuit boards that suppress transmission loss of high-frequency signals are in demand.

[0003] In the manufacture of printed circuit boards, conductive circuits are typically formed using a metal-clad laminate, which is created by laminating metal foil, such as copper foil, with an insulating substrate (resin substrate), and then heating and pressurizing it to bond the layers. To improve the adhesion between the insulating substrate and the metal foil, conventional methods have involved roughening the surface of the metal foil by electroplating or etching, thereby increasing the adhesion between the insulating substrate and the metal foil through physical action (anchor effect). However, as the skin effect becomes more pronounced with higher signal frequencies, the transmission path becomes longer on the roughened surface, resulting in increased transmission loss.

[0004] In addition to roughening the surface of the metal foil, further treatment with a silane coupling agent is performed to enhance the chemical adhesion to the resin substrate. For example, Patent Document 1 describes a surface-treated copper foil for printed wiring boards having a silane coupling agent layer on a surface on which roughened particles are formed, wherein the average height of the roughened particles on the surface of the silane coupling agent layer is 0.05 μm or more and less than 0.5 μm, and the BET surface area ratio of the surface of the silane coupling agent layer is 1.2 or more. It is said that by using the surface-treated copper foil described in Patent Document 1, it is possible to obtain a printed wiring board in which transmission loss is highly suppressed even when transmitting high-frequency signals in the GHz band, adhesion between the copper foil and the resin substrate is high even at high temperatures, durability under harsh conditions is excellent, and short circuits are less likely to occur.

[0005] A known coating technique for substrates is the use of plasma discharge. For example, it has been proposed to coat a substrate by plasma polymerization of a gas containing an organic compound or monomer in order to impart corrosion resistance or oxidation resistance to the substrate, improve adhesion to other materials, or increase surface activity. For example, Patent Document 2 describes a method for forming a coating on a substrate, which includes introducing a spray liquid and / or solid coating-forming material into an atmospheric pressure plasma discharge and / or an ionized gas stream generated therefrom, and exposing the substrate to the spray coating-forming material. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-106068 [Patent Document 2] Special Publication No. 2004-510571 [Overview of the project] [Problems that the invention aims to solve]

[0007] Through repeated investigations, the inventors have found that, in the production of metal-clad laminates, even when the surface roughening of the metal foil and the formation of a silane coupling agent layer are combined as described in Patent Document 1, the adhesion between the metal foil and the insulating substrate tends to decrease when the resulting metal-clad laminate is exposed to a harsh high-temperature environment. Recently, printed circuit boards are sometimes exposed to temperatures of around 100 to 300°C during the manufacturing process and in the operating environment, and there is a need to further improve the heat resistance of the adhesion between the metal foil and the insulating substrate.

[0008] The present invention aims to provide a metal foil and a method for manufacturing the same, which exhibits excellent adhesion to other materials and can maintain this adhesion even at high temperatures. Another object of the present invention is to provide a metal-clad laminate obtained by laminating the above-mentioned metal foil with an insulating substrate.

Means for Solving the Problem

[0009] The above problems of the present invention are solved by the following means. [1] A metal foil with a coating layer, where the metal foil is a smooth metal foil, and the coating layer has a roughened surface on the side opposite to the metal foil, A metal foil with a coating layer. [2] The metal foil with a coating layer according to [1], wherein the coating layer is a plasma polymerization film. [3] The metal foil with a coating layer according to [1] or [2], wherein the nitrogen atom concentration in the coating layer is 2 to 10 at%. [4] The metal foil with a coating layer according to any one of [1] to [3], wherein the silicon atom concentration in the coating layer is 5 to 30 at%. [5] The metal foil with a coating layer according to any one of [1] to [4], wherein the thickness of the coating layer is 1 to 1000 nm. [6] The metal foil with a coating layer according to any one of [1] to [5], wherein the coating layer satisfies [O-Si-O bond strength] / [C-Si-O bond strength]≥0.8 in the Si2p spectrum by X-ray photoelectron spectroscopy. [7] The metal foil with a coating layer according to any one of [1] to [6], wherein the metal foil is a copper foil. [8] A metal-clad laminate obtained by laminating an insulating substrate and the metal foil with a coating layer according to any one of [1] to [7] with the coating layer of the metal foil with a coating layer facing the insulating substrate side. [9] A method for manufacturing a metal foil with a coating layer according to any one of [1] to [7], including forming a coating layer, which is a plasma polymerization film, on the surface of the metal foil by performing plasma polymerization while heating the metal foil at 50 to 300°C.

[0010] In the present invention, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

Effects of the Invention

[0011] The metal foil with a coating layer of the present invention has excellent adhesion to other materials and can sufficiently maintain this adhesion even at high temperatures. Further, the metal-clad laminate of the present invention can sufficiently maintain the adhesion between the insulating base material and the metal foil even at high temperatures.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is a SEM image of the cross section of the metal foil with a coating layer of Example 3. [Figure 2] FIG. 2 is a SEM image of the cross section of the metal foil with a coating layer of Comparative Example 1. [Figure 3] FIG. 3 is an AFM image of the surface of the coating layer of the metal foil with a coating layer of Example 9. [Figure 4] FIG. 4 is an explanatory diagram schematically showing a configuration example of a plasma polymerization apparatus for forming a coating layer on the surface of a metal foil.

Modes for Carrying Out the Invention

[0013] Preferred embodiments of the present invention will be described below.

[0014] [Metal Foil with a Coating Layer] The metal foil with a coating layer of the present invention includes a coating layer on the metal foil. The above metal foil is a smooth metal foil. Here, a metal foil is described as a "smooth metal foil" if the surface roughness Rz of at least the surface on the coating layer side of the metal foil satisfies Rz ≤ 1.0 μm. By making the surface roughness Rz ≤ 1.0 μm of the surface on the coating layer side, a smoother surface can be achieved compared to the surface-treated surface of a surface-treated metal foil that has been roughened by electroplating or etching. Note that the metal foil constituting the coated metal foil of the present invention may have a smooth plating layer or the like on the surface on the coating layer side. In this case, the surface of this smooth plating layer or the like satisfies the above-mentioned surface roughness Rz ≤ 1.0 μm. Furthermore, the above-mentioned coating layer has a roughened surface on the side opposite to the above-mentioned metal foil. A "roughened surface" means a surface having particulate irregularities (a surface having roughened particles). In other words, such a "roughened surface" having particulate irregularities is a surface in which the ratio of the coating layer surface distance Lc (Lc / L × 100) (hereinafter also referred to as the "roughness index Rc"), which is the distance of the coating layer surface along the irregularities of the coating layer surface between two points, to the reference distance L, which is the distance between two points on the surface when viewed from above, is 105-200%. Thus, the coated metal foil of the present invention has a coating layer on a smooth metal foil film, and the side of the coating layer opposite to the metal foil has fine irregularities (has the roughened surface described above). In the coated metal foil of the present invention, the coating layer may be provided on one side of the metal foil or on both sides, depending on the purpose. When the coating layer is provided on both sides of the metal foil, both sides of the metal foil satisfy a surface roughness Rz ≤ 1.0 μm.

[0015] <Coat layer> From the viewpoint of adhesion when laminated with other materials and its high-temperature durability, the above coating layer preferably has a roughness index Rc of 110-200%, more preferably 120-200%, even more preferably 130-200%, and still more preferably 140-200%. The above roughness index Rc can be achieved by controlling the type of raw material for the coating layer, the plasma polymerization conditions, and so on. In this invention, the roughness index Rc is determined by cutting a coated metal foil by ion milling to expose the cross-section in the thickness direction, and observing this cross-section with a high-resolution scanning electron microscope (HR-SEM). The observation is performed at a magnification of 20,000x or 200,000x depending on the thickness of the coating layer. Specifically, the magnification is set to 20,000x when the thickness of the coating layer is 300 nm or more, and to 200,000x when the thickness of the coating layer is less than 300 nm. The roughness index Rc is calculated as follows: at a magnification of 20,000x, the surface distance Lca (μm) of the coating layer is measured for a straight length of 5 μm (corresponding to the reference distance L), and the roughness index is calculated as (Lca / 5 μm) × 100. At a magnification of 200,000x, the surface distance Lcb (nm) of the coating layer is measured for a straight length of 500 nm (corresponding to the reference distance L), and the roughness index is calculated as (Lcb / 500 nm) × 100. Ten randomly selected locations (10 cross-sections) are observed, and the average of the 10 calculated values ​​is used as the roughness index Rc.

[0016] The above roughness index Rc will be explained further with reference to Figures 1 and 2. Figure 1 is an SEM image of a cross-section in the thickness direction of the coated metal foil of Example 3, which will be described later. In this SEM image, the boundary line B1, which is above the arrow indicating the reference distance L and is closest to arrow L, is the boundary between the metal foil and the coating layer, and the line indicated as C1 is the surface of the coating layer. Above that, the surface irregularities of the coating layer located behind (towards the back in the depth direction) of the cross-section of the coating layer are visible. It can be seen that fine irregularities are formed on the surface of the coating layer of this coated metal foil. In Figure 1, the surface distance Lc of the coating layer is also shown along with the reference distance L. The surface distance Lc is the distance on C1 between the two dotted lines that intersect C1, and is the distance on C1 between the same two points as L. In the coated metal foil shown in Figure 1, the roughness index Rc is 110%. Figure 2 is an SEM image of a cross-section in the thickness direction of the coated metal foil of Comparative Example 1, which will be described later. In Figure 2, the boundary line B1 between the metal foil and the coated layer and the surface C1 of the coated layer are also shown. In this coated metal foil, the surface of the coated layer, indicated by Lc, is only gently undulating, and no fine irregularities are formed. In the coated metal foil shown in Figure 2, the roughness index Rc is 101%.

[0017] The above coating layer is preferably a plasma polymerized film from the viewpoint of satisfying the above roughness index Rc. In the present invention, the term "plasma polymerized film" means that the state of the film is a structure unique to plasma polymerization, and is a term used to distinguish it structurally from a coating layer formed by methods other than plasma polymerization.

[0018] From the viewpoint of adhesion when laminated with other materials and its high-temperature durability, the nitrogen atom concentration (at%) in the above-mentioned coating layer is preferably 2 to 10 at%, more preferably 2 to 8 at%, even more preferably 2 to 5 at%, even more preferably 3 to 5 at%, and even more preferably 3 to 4 at%. From the viewpoint of adhesion when laminated with other materials and its high-temperature durability, the silicon atom concentration (at%) in the above coating layer is preferably 5 to 30 at%, more preferably 7 to 30 at%, even more preferably 10 to 30 at%, and still more preferably 15 to 30 at%. From the viewpoint of adhesion when laminated with other materials and its high-temperature durability, it is more preferable that the nitrogen atom concentration in the coating layer be within the above range, and furthermore, that the silicon atom concentration be within the above range. The above atomic concentrations are those obtained by analyzing the surface of the coating layer using X-ray photoelectron spectroscopy (XPS), with the total concentration of detected atoms set to 100 at%. Each atomic concentration is determined by taking measurements at five random locations on the surface of the coating layer and taking the arithmetic mean of the five measurements. The concentrations of each atom mentioned above can be controlled within the specified range by adjusting the type and amount of raw materials and the manufacturing conditions (especially the plasma polymerization conditions).

[0019] The thickness of the above coating layer is preferably 1 to 1000 nm, more preferably 5 to 1000 nm, even more preferably 10 to 1000 nm, even more preferably 40 to 1000 nm, even more preferably 100 to 1000 nm, even more preferably 150 to 1000 nm, even more preferably 200 to 1000 nm, even more preferably 200 to 990 nm, even more preferably 200 to 960 nm, even more preferably 200 to 940 nm, even more preferably 200 to 920 nm, and even more preferably 250 to 900 nm, from the viewpoint of adhesion when laminated with other materials and its high-temperature durability. The thickness of the above coating layer is preferably thicker than that of a conventional surface treatment layer using a silane coupling agent (approximately 2-3 nm) (i.e., 5-1000 nm). In this invention, the thickness of the coating layer is determined by cutting the coated metal foil by ion milling to expose the cross-section in the thickness direction, and observing this cross-section with a high-resolution scanning electron microscope (HR-SEM). The thickness is measured first at one random location in the SEM image of the cross-section, and then at locations shifted 1 μm and 2 μm perpendicular (lateral) to the thickness from this location, and the arithmetic mean of the thicknesses at a total of 10 locations is taken as the thickness of the coating layer.

[0020] The above coating layer, in terms of adhesion when laminated with other materials and its high-temperature durability, shows in the Si2p spectrum of X-ray photoelectron spectroscopy (XPS) that [O-Si-O bond strength] / [C-Si-O bond strength]≧0.8 It is preferable that the following conditions be met: 40≧[O-Si―O bond strength] / [C-Si―O bond strength]≧1 It is more preferable to satisfy the following conditions: 30≧[O-Si―O bond strength] / [C-Si―O bond strength]≧4 It is even more preferable that the following conditions be met: 28≧[O-Si―O bond strength] / [C-Si―O bond strength]≧6 It is even more preferable that the following conditions be met: 27≧[O-Si―O bond strength] / [C-Si―O bond strength]≧8 It is even more preferable that the following conditions be met: 26≧[O-Si―O bond strength] / [C-Si―O bond strength]≧10 It is even more preferable that the following conditions be met: 25≧[O-Si―O bond strength] / [C-Si―O bond strength]≧12 It is even more preferable that the following conditions be met: 24≧[O-Si―O bond strength] / [C-Si―O bond strength]≧13 It is even more preferable to satisfy the following conditions.

[0021] The XPS analysis described above to determine the [O-Si-O bond strength] / [C-Si-O bond strength] is an XPS analysis of the surface of the coating layer. In the Si2p spectrum of the XPS analysis, the peak areas originating from O-Si-O bonds and C-Si-O bonds detected at 96-110 eV are determined, and the [peak area originating from O-Si-O bonds] / [peak area originating from C-Si-O bonds] is calculated. The obtained calculated value is the [O-Si-O bond strength] / [C-Si-O bond strength]. The XPS analysis of the surface of the coating layer described above involves randomly analyzing five points on the surface of the coating layer using XPS. A Si2p spectrum is obtained from each of the five points, and the [O-Si-O bond strength] / [C-Si-O bond strength] is calculated for each of the five points. The arithmetic mean of the calculated values ​​for each of the five points is defined as the [O-Si-O bond strength] / [C-Si-O bond strength] as defined in this invention. The specific measurement conditions for the XPS analysis are described in the examples below. The above-mentioned [O-Si-O bond strength] / [C-Si-O bond strength] can be controlled to the above range by adjusting the type and amount of raw materials and the manufacturing conditions (especially the plasma polymerization conditions).

[0022] The surface of the coating layer opposite to the metal foil (roughened surface) has granular protrusions (roughened particles), and when the surface of the coating layer is viewed in plan view, there are 40 to 80 granular protrusions / μm with a diameter of 50 to 200 nm. 2 It is preferable to include it at a density of [value]. The diameter of the granular protrusions is more preferably 50 to 150 nm, even more preferably 50 to 100 nm, and even more preferably 50 to 80 nm. The density of the above-mentioned granular protrusions is 50-80 particles / μm 2 More preferably, 60-80 particles / μm 2 More preferably, 70-80 particles / μm 2 That is even more preferable. The diameter and density of the granular protrusions described above are determined by atomic force microscopy (AFM measurement) of the surface of the coating layer. Here, "diameter" refers to the equivalent circular diameter of the granular protrusions observed when the roughened surface is viewed in plan view. (40,000 μm of the surface of the coating layer) 2 Measurements were taken at 10 locations within the specified range, and the average values ​​were taken as the diameter and density, respectively. In a plan view, the entire contour of the granular protrusions was 40,000 μm. 2 If a granular protrusion lies within the line that defines its range, it shall be subject to measurement of diameter and density (i.e., granular protrusions whose contour is partly outside the above range shall not be subject to measurement). Even if granular protrusions overlap in a plan view, if the non-overlapping portion is sufficiently large and the shape of the portion not visible due to the overlap can be predicted from the shape of the non-overlapping portion, the diameter shall be determined for that predicted shape. If granular protrusions are connected in a plan view and the boundary between particles cannot be determined, the entire area shall be considered as a single granular protrusion, its diameter shall be measured, and the number of granular protrusions shall be counted. Figure 3 shows a photograph of the surface of the coated metal foil of Example 9, described later, after AFM measurement. It can be seen that granular protrusions are formed on the surface of the coated layer. The diameter and density of the granular protrusions (roughened particles) described above can be controlled within the above range by adjusting the type and amount of raw materials and the manufacturing conditions (especially the plasma polymerization conditions). The diameter of the roughened particles tends to decrease as the temperature of the metal foil during plasma polymerization increases.

[0023] <Metal foil> The above metal foil has a surface roughness Rz of the coated layer side satisfying Rz ≤ 1.0 μm. More preferably, the coated layer side surface of the metal foil satisfies 0.1 μm ≤ Rz ≤ 1.0 μm, even more preferably 0.3 μm ≤ Rz ≤ 1.0 μm, even more preferably 0.5 μm ≤ Rz ≤ 1.0 μm, and even more preferably 0.6 μm ≤ Rz ≤ 0.9 μm. The surface roughness Rz mentioned above is the maximum height roughness Rz specified in JIS B0601:2013, and can be calculated using the measuring device's program. The specific measurement conditions for surface roughness Rz are described in the examples below.

[0024] The type of metal foil used in the coated metal foil of the present invention is not particularly limited and can be appropriately selected according to the purpose. This metal foil may be an alloy composed of two or more metals. For example, when the coated metal foil of the present invention is used in a metal-clad laminate of a printed circuit board, the metal foil can be copper foil or aluminum foil. The metal foil (preferably copper foil) may have at least one smooth plating layer on its surface, such as a nickel (Ni) underlayer, a zinc (Zn) heat-resistant treatment layer, and a chromium (Cr) rust-preventive treatment layer (hereinafter also referred to as the "Ni plating layer," "Zn plating layer," and "Cr plating layer," respectively). These plating layers may be combined. In the present invention, the metal foil is preferably copper foil (Ni-plated-Zn-plated-Cr plated copper foil) having an underlayer, a heat-resistant treatment layer, and a rust-preventive treatment layer. The coated metal foil of the present invention can also be used for other applications besides use in metal-clad laminates, and examples of metal foils in such cases include aluminum foil, Ni-plated copper foil, Sn-plated copper foil, etc. The thickness of the coated metal foil is not particularly limited and can be set appropriately depending on the purpose. For example, a thickness of 0.03 to 3 mm including the coating layer is preferred, and 0.03 to 0.5 mm is more preferred. The thickness of the coated metal foil can be determined in the same manner as the measurement of the coating layer thickness described above.

[0025] [Method for manufacturing coated metal foil] The method for manufacturing a coated metal foil according to the present invention is not particularly limited as long as the coated layer and the metal foil can form the surface state specified in the present invention. A preferred embodiment of the method for manufacturing a coated metal foil of the present invention is a method of forming a coating layer on the surface of a metal foil by plasma polymerization. A more preferred embodiment of the method for manufacturing a coated metal foil of the present invention includes forming a coating layer, which is a plasma polymerized film, on the surface of a metal foil by performing plasma polymerization while heating the metal foil to 50 to 300°C. Plasma polymerization forms a coating layer on the surface of metal foil by generating plasma using high-frequency waves. This plasma fragments and simultaneously activates the raw materials (monomers), and the activated fragmented materials react to polymerize, forming a plasma polymer film on the surface of the metal foil. In plasma polymerization, the raw materials are fragmented and activated, and then polymerization reactions occur randomly, resulting in the formation of various chemical structures such as linear, branched, cyclic, and crosslinked structures. Plasma polymerization technology itself is well known.

[0026] Plasma polymerization is carried out while heating the metal foil to 50-300°C. From the viewpoint of controlling the roughness index Rc of the coating layer to 105-200%, the metal foil temperature during plasma polymerization is more preferably 80-300°C, even more preferably 100-300°C, even more preferably 150-300°C, and even more preferably 200-300°C. If the metal foil temperature during plasma polymerization is too low compared to the above range, the surface of the coating layer opposite the metal foil tends to become smooth, and the above roughness index Rc tends not to be satisfied. Furthermore, if the metal foil temperature during plasma polymerization exceeds 400°C, the metal foil surface may oxidize due to heating or deteriorate due to metal diffusion, and even if a roughness index Rc of 105-200% is achieved on the surface of the coating layer, the adhesion between the coating layer and the metal foil may be poor. The mechanism by which the roughness index Rc of the coating layer can be controlled by performing plasma polymerization while keeping the metal foil temperature within the above range is unknown, but it is thought that this is because, during plasma polymerization, the raw material is supplied onto the metal foil in the form of a mist, and a coating layer having granular protrusions derived from the shape of the mist is obtained on the metal foil.

[0027] The plasma polymerization is preferably atmospheric pressure plasma polymerization. By adopting atmospheric pressure plasma polymerization, it becomes easier to incorporate nitrogen into the plasma polymerization film obtained as compared with low pressure plasma polymerization using a vacuum chamber. As a result, it becomes easier to control the nitrogen atom concentration to 2 to 10 at%. Also, by controlling the selection of the raw material for plasma polymerization, the applied energy to the raw material (usually the plasma irradiation time (which is the time for fragmenting (activating) the raw material by contact with the plasma and is also referred to as the decomposition reaction time)), and the contact time of the fragmented (activated) raw material with the metal foil surface (the time for the polymerization reaction to occur on the substrate surface or in its vicinity (polymerization reaction time)), it is possible to control the roughness index Rc defined in the present invention to a range of 105 to 200% or an even more limited range.

[0028] The higher the applied energy, the higher the plasma concentration. On the other hand, if the applied energy is too small, plasma polymerization may not be possible or it may take an extremely long time for plasma polymerization, which is not practical. The above-mentioned applied energy is preferably 0.24 to 36 mJ / mm from the viewpoints of adhesion when laminated with other materials and its high-temperature durability. 3 Preferably 0.5 to 36 mJ / mm. 3 More preferably 1 to 36 mJ / mm. 3 Even more preferably 2 to 36 mJ / mm. 3 Even more preferably 5 to 36 mJ / mm. 3 Even more preferably 10 to 36 mJ / mm. 3 Even more preferably 20 to 36 mJ / mm. 3 Even more preferably. Also, the greater the applied energy, the thicker the resulting coat layer tends to be. The above-mentioned applied energy is calculated by the following formula. Applied energy (mJ / mm 3 ) = Output (W) × Plasma irradiation time (s) ÷ Volume of the processing space (mm 3 ) × 1000 Here, "processing space" refers to the space between planar electrodes in the apparatus described later. In this processing space, power is applied to the fragmented raw material.

[0029] The polymerization reaction time (s) is preferably 0.5 to 200 seconds, more preferably 1 to 200 seconds, even more preferably 10 to 200 seconds, even more preferably 50 to 200 seconds, even more preferably 100 to 200 seconds, and even more preferably 150 to 200 seconds, from the viewpoint of adhesion when laminated with other materials and its high-temperature durability.

[0030] The raw materials used in plasma polymerization are not particularly limited as long as a coating layer as defined in the present invention can be obtained. Preferred examples of raw materials include organic solvents (lower alcohols such as ethanol, methanol, and 2-propanol), metal alkoxide compounds, etc., which can be used alone or in combination of two or more. Examples of metal alkoxide compounds include silicon alkoxide compounds (silane coupling agents, e.g., 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-(trimethoxysilyl)propyl methacrylate), titanium alkoxide compounds (titanate coupling agents), aluminum alkoxide compounds (aluminate coupling agents), zirconium alkoxide compounds (zirconate coupling agents), etc. Metal alkoxide compounds selected from silicon alkoxide compounds, titanium alkoxide compounds, and aluminum alkoxide compounds are preferred, and silicon alkoxide compounds are more preferred. Metal alkoxide compounds may contain sulfur atoms, phosphorus atoms, etc. The molecular weight of the raw materials is preferably 100 to 300. In particular, it is preferable to use a combination of an organic solvent and a silicon alkoxide compound as raw materials. In this case, it is preferable to use, for example, an alcohol (for example, a lower alcohol having 1 to 3 carbon atoms) as the organic solvent. The raw materials can also be compounds containing a siloxane structure (e.g., hexamethyldisiloxane), compounds having an isocyanuric structure (e.g., isocyanuric acid ester compounds, silane-modified isocyanuric acid ester compounds), compounds having a glycidyl group (epoxy group) (e.g., allyl glycidyl ether, glycidyl methacrylate), cresol compounds (e.g., 2,6-di-tert-butyl-p-cresol), etc.

[0031] In plasma polymerization, it is preferable to use an inert gas such as argon, nitrogen, or helium as the carrier gas. The raw materials are supplied by volatilizing and mixing with the carrier gas, or by dispersing them in the carrier gas by bubbling or the like. The temperature of the raw materials or carrier gas is appropriately controlled according to the film deposition rate, etc. For example, when a silane coupling agent is used as a raw material, the temperature can be controlled to about 10 to 90°C.

[0032] Figure 4 is a schematic diagram showing an example of the configuration of a plasma polymerization reactor applicable to the formation of a coating layer in the present invention. By passing an alternating current between the planar electrodes 4, the carrier gas CG between the planar electrodes 4 is converted into plasma, and the raw materials supplied from the raw material supply device 3 to the planar electrodes 4 are fragmented (activated) by the action of this plasma. By exposing the surface of the metal foil to this fragmented activated raw material 5, a plasma polymer is deposited on the surface of the metal foil, forming a coating layer (plasma polymerized film). In Figure 4, the matching box 2 plays the role of adjusting the impedance so that the reflected wave is minimized with respect to the applied high-frequency output.

[0033] The frequency of the alternating current flowing between the planar electrodes 4 is not particularly limited as long as the desired plasma gas is generated. For example, it can be 1 kHz to 27.12 MHz. Similarly, the output power of the alternating current is not particularly limited as long as the desired plasma gas is generated. For example, it can be around 10 to 500 W, and preferably around 50 to 200 W. Copper, aluminum, or the like can be used for the planar electrode 4. Alternatively, a dielectric material such as glass may be attached to the electrode surfaces facing each other.

[0034] [Metal-clad laminate] The coated metal foil of the present invention can be suitably used as metal foil in metal-clad laminates used in printed circuit boards. A metal-clad laminate can be obtained by laminating the coated metal foil of the present invention with an insulating substrate (resin substrate) and bonding them by heating and pressurizing using a conventional method. When laminating the coated metal foil of the present invention with an insulating substrate, it is preferable to have the coated metal foil with the coated layer side facing the insulating substrate side. If the coated metal foil of the present invention has a coated layer on both sides, either side may face the insulating substrate side. The coated metal foil of the present invention that can be applied to metal-clad laminates can be coated copper foil, coated aluminum foil, coated Ni-plated copper foil, coated Sn-plated copper foil, etc., with coated copper foil being preferred. [Examples]

[0035] [Analysis method]

[0036] <Roughness Index Rc> Using an ion milling system (product name: IM4000) manufactured by Hitachi, Ltd., the cross-section in the thickness direction of a coated metal foil (cross-section of the coating layer and cross-section of the metal foil) was exposed by ion milling. SEM images of these cross-sections were obtained using a Hitachi HR-SEM (product name: SU8020) at an acceleration voltage of 3kV and a magnification of 20,000x or 200,000x. The magnification of 20,000x or 200,000x was determined according to the thickness of the coating layer being measured. Specifically, a magnification of 20,000x was used when the coating layer thickness was 300nm or more, and a magnification of 200,000x was used when the thickness was less than 300nm. The roughness index Rc of the coating layer was calculated from these SEM images. For a magnification of 20,000x, the surface roughness index Rc was calculated by measuring the surface distance Lca of the coating layer for a straight length of 5 μm (corresponding to the reference distance L), and then (Lca / 5 μm) × 100. For a magnification of 200,000x, the surface roughness index Rc was calculated by measuring the surface distance Lcb of the coating layer for a straight length of 500 nm (corresponding to the reference distance L), and then (Lcb / 500 nm) × 100. Ten randomly selected locations (10 cross-sections) were observed, and the average of the 10 calculated values ​​was used as the roughness index Rc.

[0037] <Surface roughness Rz> The surface roughness Rz of the coated layer side of the metal foil was determined according to JIS B0601:2013. More specifically, the Rz of the metal foil surface was measured using a Keyence laser microscope (VK-X200). A coated metal foil was used as the sample, and the surface roughness Rz of the areas where the coating layer was not formed on the surface was measured.

[0038] <Nitrogen atom concentration (N concentration) and silicon atom concentration (Si concentration)> The surface of the coating layer was analyzed using XPS, and the concentration of each atom was measured at five arbitrary locations on the surface of the coating layer. The arithmetic mean of these five measurements was used to determine the final concentration.

[0039] <Coat layer thickness> Using an IM4000 manufactured by Hitachi, Ltd., the cross-section in the thickness direction of the coated metal foil was exposed by ion milling. An SEM image of this cross-section was obtained using an HR-SEM (product name: SU8020) manufactured by Hitachi, Ltd. at an acceleration voltage of 3kV. As described above, the thickness of the coated layer was measured at 10 locations on this SEM image, and the arithmetic mean of the 10 measured values ​​was taken as the thickness of the coated layer (nm).

[0040] <[O-Si-O bond strength] / [C-Si-O bond strength]> Surface analysis of the coating layer surface of coated metal foil was performed using XPS with a PHI Quantes system from ULVAC-PHI. The excitation X-ray was a monochromatic Al-Kα line (1486.6 eV), with an escape angle of 45° and an analysis area of ​​100 μmφ. For the Si2p spectrum in the 96-110 eV range, the spectral components were separated by peak fitting, and the peak areas derived from the O-Si-O bond (A1) and the peak areas derived from the C-Si-O bond (A2) were measured. A1 / A2 was defined as [O-Si-O bond strength] / [C-Si-O bond strength]. As stated above, the [O-Si-O bond strength] / [C-Si-O bond strength] defined in this invention is the arithmetic mean of the calculated values ​​of [O-Si-O bond strength] / [C-Si-O bond strength] at five measurement points on the surface.

[0041] <Diameter and density of granular protrusions> AFM measurements were performed on the roughened surface of the coating layer of each coated metal foil. In a plan view of the surface of each coating layer, the surface of the coating layer is 40,000 μm 2 Measurements were taken at 10 locations within the specified range. The average values ​​of the granular protrusion diameter and density measured at the 10 locations were used as the diameter and density, respectively. The diameter is the equivalent diameter of a circle. In a plan view, the entire contour of the granular protrusion was 40,000 μm. 2 If a granular protrusion lies within the defined range, its diameter and density were measured (i.e., granular protrusions whose contour is partially outside the range were not measured). Even if granular protrusions overlap in a plan view, if the non-overlapping portion is sufficiently large and the shape (contour) of the portion not visible due to overlap can be predicted from the shape of the non-overlapping portion, the diameter was determined for that predicted shape. If granular protrusions are connected and the boundaries between particles cannot be determined, the entire area is considered a single granular protrusion, its diameter is measured, and the number of granular protrusions is counted.

[0042] [Example 1] A mixture of 3-aminopropyltrimethoxysilane and ethanol was used as the raw material for plasma polymerization. Argon gas was used as the carrier gas. Copper foil (manufactured by Furukawa Electric Co., Ltd., smooth copper foil, surface roughness Rz: 0.8 μm on the coated layer side) (400 mm long side × 300 mm short side × 35 μm thick) was used as the metal foil. A base layer, a heat-resistant treatment layer, and a rust-preventive treatment layer were laminated on the surface of the copper foil in this order. The base layer was formed by nickel plating under the following conditions, the heat-resistant treatment layer was formed by zinc plating under the following conditions, and the rust-preventive treatment layer was formed by chromium plating under the following conditions. These plated layers were smooth, and no change was observed in the surface roughness of the coated layer side even after forming these plated layers. <Conditions for nickel plating> Nickel concentration in the plating bath: 45 g / L Concentration of boric acid (H3BO3) in the plating bath: 4g / L Plating bath temperature: 20℃ pH of the plating bath: 3.5 Current density: 0.2A / dm 2 Processing time: 8 seconds <Conditions for zinc plating> Zinc concentration in the plating bath: 2.5 g / L Sodium hydroxide concentration in the plating bath: 35 g / L Plating bath temperature: 20℃ Current density: 0.5A / dm 2 Processing time: 4 seconds <Conditions for chrome plating> Chromium concentration in the plating bath: 6g / L Plating bath temperature: 30℃ pH of the plating bath: 2.3 Current density: 5A / dm 2 Processing time: 3 seconds During plasma polymerization, the temperatures of the raw materials and carrier gas were controlled to 25°C. The temperature of the copper foil was controlled to 50°C. Using an apparatus with the same configuration as shown in Figure 4, an AC current with a frequency of 13.56 MHz and an output of 125 W was passed between the planar electrodes. The applied energy was 0.25 mJ / mm². 3The polymerization reaction time was set to 0.5 seconds. The processing space was 250,000 mm². 2 In this way, plasma polymerization was performed on the copper foil while heating it to 50°C, forming a coating layer, which is a plasma polymerized film, on the surface (one side) of the plated layer of the copper foil. Thus, the coated metal foil of Example 1 was obtained.

[0043] [Example 2] In Example 1, the applied energy for plasma polymerization was set to 1 mJ / mm². 3 Except for the fact that the polymerization reaction time was set to 1 second, the coated metal foil of Example 2 shown in the table below was obtained in the same manner as in Example 1.

[0044] [Example 3] In Example 2, the polymerization reaction time in plasma polymerization was set to 5 seconds, but otherwise, the coated metal foil of Example 3 shown in the table below was obtained in the same manner as in Example 2.

[0045] [Example 4] In Example 1, the applied energy for plasma polymerization was 2 mJ / mm². 3 Except for the following differences, the polymerization reaction time was set to 10 seconds and the metal foil temperature to 100°C, the coated metal foil of Example 4 shown in the table below was obtained in the same manner as in Example 1.

[0046] [Example 5] In Example 4, the polymerization reaction time in plasma polymerization was set to 50 seconds, but otherwise the same procedure was followed to obtain the coated metal foil of Example 5 shown in the table below.

[0047] [Example 6] In Example 5, a coated metal foil of Example 6, shown in the table below, was obtained in the same manner as in Example 5, except that an aluminum foil (400 mm long side × 300 mm short side × 35 μm thick) (manufactured by Furukawa Electric Co., Ltd.) with a surface roughness Rz of 0.7 μm on the coated layer side was used instead of copper foil.

[0048] [Example 7] In Example 5, the applied energy in plasma polymerization was set to 5 mJ / mm². 3 Except for the following, and the polymerization reaction time being set to 100 seconds, the coated metal foil of Example 7 shown in the table below was obtained in the same manner as in Example 5.

[0049] [Example 8] In Example 7, a coated metal foil of Example 8, shown in the table below, was obtained in the same manner as in Example 7, except that an aluminum foil (400 mm long side × 300 mm short side × 35 μm thick) with a surface roughness Rz of 0.9 μm on the coated layer side was used instead of copper foil.

[0050] [Example 9] In Example 7, the applied energy for plasma polymerization was 20 mJ / mm². 3 Except for the above and the metal foil temperature being set to 200°C, the coated metal foil of Example 9 shown in the table below was obtained in the same manner as in Example 7.

[0051] [Example 10] In Example 1, the applied energy for plasma polymerization was 35 mJ / mm². 3 Except for the following differences, the polymerization reaction time was set to 200 seconds and the metal foil temperature to 300°C, the coated metal foil of Example 10 shown in the table below was obtained in the same manner as in Example 1.

[0052] [Example 11] In Example 7, a mixture of 3-(2-aminoethylamino)propyltrimethoxysilane and methanol was used as the raw material, and a copper foil (400 mm long side × 300 mm short side × 35 μm thick) (manufactured by Furukawa Electric Co., Ltd.) with a surface roughness Rz of 0.7 μm on the coated surface side was used as the copper foil. Except for these differences, the coated metal foil of Example 11 shown in the table below was obtained in the same manner as in Example 7.

[0053] [Example 12] In Example 12, a coated metal foil was obtained in the same manner as in Example 11, except that a mixture of a silane-modified isocyanuric acid ester compound and an isocyanuric acid ester compound was used as a raw material.

[0054] [Comparative Example 1] In Example 5, the metal foil with a coated layer, Comparative Example 1, shown in the table below, was obtained in the same manner as in Example 5, except that the metal foil temperature during plasma polymerization was set to 20°C.

[0055] [Comparative Example 2] In Example 5, the coated metal foil of Comparative Example 2, shown in the table below, was obtained in the same manner as in Example 5, except that ethanol was used as a raw material and the metal foil temperature in plasma polymerization was set to 50°C.

[0056] [Comparative Example 3] In Example 2, the applied energy for plasma polymerization was 0.05 mJ / mm². 3 Except for the above, a coated metal foil of Comparative Example 3, shown in the table below, was obtained in the same manner as in Example 2.

[0057] [Comparative Example 4] An aqueous solution of 3-aminopropyltrimethoxysilane with a concentration of 0.2% by mass was prepared. A copper foil (400 mm long side × 300 mm short side × 35 μm thick) with a surface roughness Rz of 0.7 μm on the coated layer side (manufactured by Furukawa Electric Co., Ltd.) was used as the metal foil. On the surface of the copper foil, a base layer, a heat-resistant treatment layer, and a rust-preventive treatment layer were laminated in this order, as in Example 1. The aqueous solution was applied to the surface of the plated layer of the copper foil and dried at 100°C to form a coating layer (silane coupling agent layer) on the surface of the plated layer of the copper foil. In this way, a metal foil with a coated layer of Comparative Example 4 was obtained.

[0058] [Example Test] <Peel Strength Test> The adhesion of coated metal foil to a resin substrate was evaluated using peel strength as an indicator. A normal peel test was performed according to the method specified in JIS C 6481:1996. A resin substrate was bonded to the surface of the coated layer of the coated metal foil of Examples 1 to 12 and Comparative Examples 1 to 4 (pressed for 2 hours under surface pressure of 2.9 MPa and 210°C) to obtain a laminate, and this laminate was used as a metal-clad laminate. As the resin substrate, two sheets of TU-933P+ (thickness 50 μm), a resin substrate for printed circuit boards manufactured by TUC Corporation, were laminated together. Masking tape was applied to the metal foil surface of this metal-clad laminate, and copper chloride etching was performed (etching with a sodium hydroxide aqueous solution was performed in Examples 6 and 8, which used aluminum foil). After that, the masking tape was removed to create a printed circuit board with circuit wiring 10 mm wide. From this circuit board, test piece a, which will be used for the peel strength test, and test piece b, which will be used for the heat resistance test described later, were cut out. Next, at room temperature (25°C), the circuit wiring portion (copper foil portion) of test piece a was peeled from the resin substrate by pulling it at a speed of 50 mm / min in a 90-degree direction using a Tensilon tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The peel strength a (normal peel strength, kN / m) during this peeling was measured. This peel strength a is shown in the "Peel Strength" column of the table below.

[0059] <Heat resistance (peel strength retention rate) test> The adhesion of coated metal foil to a resin substrate at high temperatures was evaluated using the peel strength retention rate as an indicator. Using the above test specimen b, a peel strength test after heat treatment was performed in accordance with JIS C 6481:1996. Details are described below. Test specimen b was heated on a 290°C heating plate for 5 minutes, and then allowed to cool naturally to room temperature. Subsequently, the peel strength b (kN / m) was measured using a Tensilon tester manufactured by Toyo Seiki Seisakusho Co., Ltd., when a 10 mm wide circuit wiring portion of test specimen b was peeled from the resin substrate at a speed of 50 mm / min in a 90-degree direction. The peel strength retention rate (%) was calculated as 100 × [peel strength b / peel strength a] and is shown in the table below.

[0060] [Table 1]

[0061] As shown in the table above, the coated metal foils of Comparative Examples 1-3, where the roughness index Rc on the side opposite the coated metal foil was 101%, and the coated metal foil of Comparative Example 4, where the roughness index Rc was 102%, had a peel strength retention rate of 40% or less, and were unable to maintain adhesion when exposed to harsh high-temperature environments. In contrast, the coated metal foils of Examples 1 to 12, which satisfy the provisions of the present invention, were found to have excellent adhesion strength with other components and to be able to maintain sufficient adhesion even in harsh high-temperature environments. Furthermore, by increasing the silicon atom concentration in the coating layer to 10 at% or more, or by increasing the [O-Si-O bond strength] / [C-Si-O bond strength] to 10 or more, it was shown that the peel strength could be increased to 0.6 kN / m or more, while maintaining a peel strength retention rate of 50% or more even under harsh high-temperature treatment. [Explanation of Symbols]

[0062] 1 power supply 2 Matching Boxes 3 Raw material supply device 4 Planar electrode 5. Plasma (activating raw material, fragmenting raw material) CG carrier gas

Claims

1. Metal foil with a coating layer, The metal foil used is a smooth metal foil. The coating layer has a roughened surface on the side opposite to the metal foil. Metal foil with a coating layer.

2. The coated metal foil according to claim 1, wherein the coating layer is a plasma polymerized film.

3. The coated metal foil according to claim 2, wherein the nitrogen atom concentration in the coating layer is 2 to 10 at%.

4. The coated metal foil according to claim 3, wherein the silicon atom concentration in the coating layer is 5 to 30 at%.

5. The coated metal foil according to claim 4, wherein the thickness of the coating layer is 1 to 1000 nm.

6. The coated metal foil according to claim 5, wherein the coating layer satisfies [O-Si-O bond strength] / [C-Si-O bond strength] ≥ 0.8 in the Si2p spectrum obtained by X-ray photoelectron spectroscopy.

7. The coated metal foil according to claim 6, wherein the metal foil is copper foil.

8. A metal-clad laminate comprising an insulating substrate and a coated metal foil according to any one of claims 1 to 7, wherein the coated metal foil has the coated layer facing the insulating substrate.

9. A method for manufacturing a coated metal foil according to any one of claims 1 to 7, comprising forming a coating layer, which is a plasma polymerized film, on the surface of the metal foil by performing plasma polymerization while heating the metal foil to 50 to 300°C.

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