Copper-clad laminate and method for manufacturing the same

Abstract

To provide a copper clad laminate excellent in folding endurance and a method for manufacturing the copper clad laminate.SOLUTION: A copper clad laminate 1 includes a base material 10 and a copper plating film 20 formed on the surface of the base material 10. The copper plating film 10 is obtained by laminating four layers of high current density layers 21 formed by electroplating at a high current density and three layers of low current density layers 22 formed by electroplating at a low current density alternately. The spacing of the low current density layers 22 is 0.3 to 0.6 μm or 0.8 to 1.1 μm. Alternatively, the spacing of the low current density layer 22 is 3.5 to 7.1% or 9.4 to 12.9% of the copper plating thickness.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a copper-clad laminate and a method for manufacturing a copper-clad laminate. More specifically, the present invention relates to a copper-clad laminate used in the manufacture of flexible printed circuit boards (FPCs) and the like, and a method for manufacturing the copper-clad laminate. [Background technology]

[0002] Flexible printed wiring boards, in which wiring patterns are formed on the surface of a resin film, are used in electronic devices such as liquid crystal panels, notebook computers, digital cameras, and mobile phones. Flexible printed wiring boards are manufactured from copper-clad laminates, in which copper foil is laminated on a resin film.

[0003] A metallizing method is known as a method for manufacturing copper-clad laminates (see, for example, Patent Document 1). Manufacturing a copper-clad laminate using the metallizing method is carried out, for example, by the following procedure. First, a base metal layer made of a nickel-chromium alloy is formed on the surface of a resin film. Next, a thin copper layer is formed on the base metal layer. Next, a copper plating film is formed on the thin copper layer. The conductor layer is thickened by copper plating until it has a thickness suitable for forming a wiring pattern. The metallizing method produces a copper-clad laminate of the type known as a two-layer board, in which the conductor layer is formed directly on the resin film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-205799 Summary of the Invention [Problem to be solved by the invention]

[0005] As electronic devices have become smaller and thinner in recent years, flexible printed circuit boards (FPCBs) are increasingly being used in applications that require bending them with small radii of curvature. Repeated bending and straightening of FPCBs with small radii of curvature can cause cracks to form on the surface of the wiring, which can then grow and cause breakage. Therefore, there is a demand for copper-clad laminates with excellent folding resistance.

[0006] In view of the above circumstances, an object of the present invention is to provide a copper-clad laminate having excellent folding endurance and a method for producing the same. [Means for solving the problem]

[0007] The copper-clad laminate of the present invention comprises a substrate and a copper plating film formed on the surface of the substrate, wherein the copper plating film is formed by alternating four high-current-density layers formed by electroplating at a high current density and three low-current-density layers formed by electroplating at a current density lower than the high current density, and the distance between two adjacent low-current-density layers sandwiching one high-current-density layer is 0.3 to 0.6 μm or 0.8 to 1.1 μm. The distance between two adjacent low-current-density layers sandwiching one high-current-density layer may be 3.5 to 7.1% or 9.4 to 12.9% of the thickness of the copper plating film. The method for producing a copper-clad laminate of the present invention includes an electroplating step of forming a copper plating film on the surface of a substrate to obtain a copper-clad laminate, wherein the electroplating step includes alternately performing four high-current-density electroplating processes and three low-current-density electroplating processes, and forming a high-current-density layer having a thickness of 0.3 to 0.6 μm or 0.8 to 1.1 μm by the second and third high-current-density electroplating processes. The second and third high-current-density electroplating processes may also form a high-current-density layer having a thickness of 3.5 to 7.1% or 9.4 to 12.9% of the thickness of the copper plating film. [Effects of the Invention]

[0008] According to the present invention, three low current density layers are inserted into the copper plating film, thereby improving the folding resistance of the copper clad laminate. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a copper clad laminate according to one embodiment of the present invention. [Figure 2] FIG. [Figure 3] 10 is a graph showing the relationship between the current density of a low current density layer and folding endurance. [Figure 4] 1 is a graph showing the relationship between the thickness of a low current density layer and folding endurance. [Figure 5] 1 is a graph showing the relationship between the position of a low current density layer and folding endurance. [Figure 6] 1 is a graph showing the relationship between the number of low current density layers and folding endurance. [Figure 7] 10 is a graph showing the arrangement of a low current density layer. [Figure 8] 10 is a graph showing the relationship between the interval between low current density layers and folding endurance. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, a copper-clad laminate 1 according to one embodiment of the present invention comprises a substrate 10 and a copper plating film 20 formed on the surface of the substrate 10. As shown in Fig. 1, the copper plating film 20 may be formed on only one side of the substrate 10, or the copper plating film 20 may be formed on both sides of the substrate 10.

[0011] The substrate 10 is formed by depositing a metal layer 12 on the surface of an insulating base film 11. A resin film such as a polyimide film or a liquid crystal polymer (LCP) film can be used as the base film 11. The metal layer 12 is deposited by a dry deposition method such as sputtering. The metal layer 12 is composed of a base metal layer 13 and a copper thin film layer 14. The base metal layer 13 and the copper thin film layer 14 are laminated in this order on the surface of the base film 11. Generally, the base metal layer 13 is made of nickel, chromium, or a nickel-chromium alloy. Although not particularly limited, the thickness of the base film 11 is generally 10 to 100 μm, the thickness of the base metal layer 13 is generally 5 to 50 nm, and the thickness of the copper thin film layer 14 is generally 50 to 400 nm.

[0012] The underlying metal layer 13 may be omitted. The copper thin film layer 14 may be formed on the surface of the base film 11 via the underlying metal layer 13, or may be formed directly on the surface of the base film 11 without the underlying metal layer 13.

[0013] The copper plating film 20 is formed on the surface of the thin copper layer 14. Although not particularly limited, the thickness of the copper plating film 20 is generally 8 to 12 μm in the case of a copper-clad laminate 1 processed by a subtractive method. The metal layer 12 and the copper plating film 20 are collectively referred to as the "conductor layer."

[0014] The copper plating film 20 has a seven-layer structure in which four high-current density layers 21 and three low-current density layers 22 are alternately stacked. The layer deposited directly on the surface of the substrate 10 (thin copper layer 14) is a high-current density layer 21. The outermost layer of the copper plating film 20 is also a high-current density layer 21. Each low-current density layer 22 is sandwiched between two high-current density layers 21 on the top and bottom. In other words, three low-current density layers 22 are inserted in the middle of the copper plating film 20 in the thickness direction.

[0015] The copper plating film 20 having such a structure can be obtained by providing three periods during the electrolytic plating process in which the current density is lower than normal during the electrolytic plating process for forming the copper plating film 20 on the surface of the substrate 10. The method for forming the copper plating film 20 will be specifically described below.

[0016] The copper plating film 20 can be formed, for example, by a roll-to-roll plating apparatus. This type of plating apparatus is an apparatus that performs electrolytic plating on the long strip-shaped substrate 10 while transporting the substrate 10 by roll-to-roll. The plating apparatus has a supply device that pays out the substrate 10 wound in a roll, and a winding device that winds up the substrate 10 (copper-clad laminate 1) after plating into a roll.

[0017] The plating apparatus is provided with a plurality of clamps for transporting the substrate 10. The clamps grip both edges of the substrate 10 while transporting the substrate 10. A pre-treatment tank, a plating tank 30, and a post-treatment tank are arranged along the transport path of the substrate 10. As the substrate 10 is transported through the plating tank 30, a copper plating film 20 is formed on its surface by electroplating. This results in a long strip of copper-clad laminate 1.

[0018] As shown in Figure 2, the plating tank 30 is a single tank that is long horizontally along the transport direction of the substrate 10. The substrate 10 is transported along the center of the plating tank 30. A copper plating solution is stored in the plating tank 30. The substrate 10 transported within the plating tank 30 is entirely immersed in the copper plating solution.

[0019] The copper plating solution contains a water-soluble copper salt. Any water-soluble copper salt commonly used in copper plating solutions can be used without any particular limitation. The copper plating solution may contain sulfuric acid. The pH and sulfate ion concentration of the copper plating solution can be adjusted by adjusting the amount of sulfuric acid added. The copper plating solution may contain additives that are commonly added to plating solutions. As the additive, one selected from a brightener component, a leveler component, a polymer component, a chlorine component, etc. may be used alone, or two or more may be used in combination.

[0020] The content of each component in the copper plating solution can be selected arbitrarily. However, the copper plating solution preferably contains 15 to 70 g / L of copper and 20 to 250 g / L of sulfuric acid. This allows the copper plating film 20 to be formed at a sufficient rate. The copper plating solution preferably contains 1 to 50 mg / L of a brightener component. This allows the precipitated crystals to be finer and the surface of the copper plating film 20 to be smooth. The copper plating solution preferably contains 1 to 300 mg / L of a leveler component. This allows protrusions to be suppressed and a flat copper plating film 20 to be formed. The copper plating solution preferably contains 10 to 1,500 mg / L of a polymer component. This allows current concentration at the edge of the substrate 10 to be reduced and a uniform copper plating film 20 to be formed. The copper plating solution preferably contains 20 to 80 mg / L of a chlorine component. This allows abnormal deposition to be suppressed.

[0021] The temperature of the copper plating solution is preferably 20 to 35° C. It is also preferable to stir the copper plating solution in the plating tank 30. For example, the copper plating solution can be stirred by spraying the copper plating solution from a nozzle onto the substrate 10.

[0022] A plurality of anodes 31 are arranged inside the plating tank 30 along the transport direction of the substrate 10. The clamps that hold the substrate 10 also function as cathodes. By passing a current between the anodes 31 and the clamps (cathodes), a copper plating film 20 can be formed on the surface of the substrate 10.

[0023] 2, anodes 31 are placed on both the front and back sides of the substrate 10. Therefore, if a substrate 10 having a metal layer 12 formed on both sides of a base film 11 is used, copper plating films 20 can be formed on both sides of the substrate 10.

[0024] A rectifier is connected to each of the multiple anodes 31 arranged inside the plating tank 30. Therefore, it is possible to set a different current density for each anode 31. In this embodiment, the interior of the plating tank 30 is divided into multiple zones along the transport direction of the substrate 10. Each zone corresponds to an area where one or more continuous anodes 31 are arranged.

[0025] Each zone is a high current density zone HZ or a low current density zone LZ. In the high current density zone HZ, the current density is set to a relatively high "high current density," and electrolytic plating is performed on the substrate 10 at a high current density. In the low current density zone LZ, the current density is set to a "low current density," which is lower than the high current density, and electrolytic plating is performed on the substrate 10 at a low current density.

[0026] The high current density zones HZ and the low current density zones LZ are alternately arranged along the transport direction of the substrate 10. The number of high current density zones HZ is four. The number of low current density zones LZ is three. With respect to the transport direction of the substrate 10 as the reference, the most upstream zone and the most downstream zone are both high current density zones HZ.

[0027] Because the metal layer 12 formed on the base film 11 is relatively thin, increasing the current density in the early stages of electroplating may result in dissolution of the portion of the metal layer 12 that is in contact with the power supply (clamp). On the other hand, to increase productivity, it is preferable to increase the current density as much as possible. Therefore, in the early stages of electroplating, the current density is gradually increased. In the most upstream high-current-density zone HZ, electroplating may be performed while gradually increasing the current density. If there is no risk of dissolution of the metal layer 12, the current density may be constant even in the most upstream high-current-density zone HZ.

[0028] The substrate 10 is electroplated while passing alternately through a high current density zone HZ and a low current density zone LZ. That is, in the plating tank 30, the substrate 10 is subjected to four cycles of high current density electroplating and three cycles of low current density electroplating. This results in the formation of a copper plating film 20.

[0029] The copper plating film 20 formed by this method has a structure in which layers formed by electrolytic plating at different current densities are stacked, as shown in Figure 1. Specifically, the copper plating film 20 has a structure in which high-current-density layers 22 and low-current-density layers 21 are alternately stacked in the thickness direction. Here, the high-current-density layers 22 are layers formed by electrolytic plating at a high current density, and the low-current-density layers 21 are layers formed by electrolytic plating at a low current density.

[0030] The copper plating film 20 can also be formed using a single-wafer plating apparatus. Electroplating is performed by immersing the substrate 10 in a copper plating solution in a plating tank, forming the copper plating film 20 on the surface of the substrate 10. During this process, the current density is changed over time. Specifically, electroplating at a high current density is performed four times, and electroplating at a low current density is performed three times, alternating.

[0031] The copper-clad laminate 1 of this embodiment has excellent folding resistance because three low-current-density layers 22 are inserted into the copper plating film 20. Here, folding resistance means strength against repeated bending and stretching, and is evaluated by the MIT test.

[0032] Although the reason for the improved folding resistance is not entirely clear, it is thought to be roughly as follows. When the copper-clad laminate 1 is bent with a small radius of curvature, a strong tensile stress is applied to the outermost surface of the copper plating film 20. Therefore, repeated bending and straightening causes cracks to form on the surface of the copper plating film 20, triggered by grain boundaries, etc. When a low-current-density layer 22 is inserted into the copper plating film 20, recrystallization proceeds separately for each high-current-density layer 21, suppressing the growth of crystal grains. Therefore, when the copper-clad laminate 1 is bent, the tensile stress applied to the outermost surface of the copper plating film 20 is alleviated, making cracks less likely to occur. This is thought to improve folding resistance.

[0033] The folding endurance of the copper-clad laminate 1 is affected by the spacing between the low-current density layers 22. Here, the spacing between the low-current density layers 22 refers to the distance between two adjacent low-current density layers 22 that sandwich one high-current density layer 21 between them. Therefore, the spacing between the two low-current density layers 22 is the same as the thickness of the high-current density layer 21 sandwiched between them. From the perspective of improving folding endurance, the spacing between the low-current density layers 22 is preferably 0.3 to 0.6 μm or 0.8 to 1.1 μm. Alternatively, in terms of the ratio to the thickness of the copper plating film 20, the spacing between the low-current density layers 22 is preferably 3.5 to 7.1% or 9.4 to 12.9% of the thickness of the copper plating film 20. Counting from the surface of the substrate 10, the distance between the first low current density layer 22 and the second low current density layer 22 and the distance between the second low current density layer 22 and the third low current density layer 22 may be the same or different.

[0034] Here, the thickness of the layer can be calculated from the current density and plating time in electroplating. Specifically, as shown in equation (1), the current density J [A / dm 2 ], plating time T [min], and a predetermined coefficient k to obtain the thickness d [μm]. Note that the coefficient k is a value that depends on conditions such as the plating solution, and is determined by testing.

number

[0035] Therefore, to set the interval between the low-current-density layers 22 to 0.3 to 0.6 μm or 0.8 to 1.1 μm, the current density and plating time may be adjusted in the second and third high-current-density electroplating steps so as to form high-current-density layers 21 having a thickness of 0.3 to 0.6 μm or 0.8 to 1.1 μm. Alternatively, the current density and plating time may be adjusted in the second and third high-current-density electroplating steps so as to form high-current-density layers 21 having a thickness of 3.5 to 7.1% or 9.4 to 12.9% of the thickness of the copper plating film 20.

[0036] From the viewpoint of improving folding endurance, a low current density of 0.13 to 0.38 A / dm2 is preferable, and 0.16 to 0.22 A / dm 2 It is more preferable that the three low-current-density layers 22 have the same or different current densities. Therefore, the current densities in the three low-current-density zones LZ may be the same or different.

[0037] The high current density should be higher than the low current density. However, the high current density should be 4 to 10 A / dm 2 It is preferable that the four high current density layers 21 have the same or different current densities. Therefore, the current densities in the four high current density zones HZ may be the same or different. Furthermore, in the most upstream high current density zone HZ, electroplating may be performed while gradually increasing the current density. In this case, the current density during the period in which the current density is gradually increased in the initial stage of electroplating (current density increasing period) is 1 to 6 A / dm 2 It is preferable to gradually increase the temperature within the range of

[0038] From the viewpoint of improving folding endurance, the thickness of the low current density layer 22 is preferably 0.05 to 0.15 μm, and more preferably 0.08 to 0.12 μm.

[0039] Furthermore, from the viewpoint of improving folding resistance, it is preferable that all three low-current-density layers 22 are located within a range of 35 to 65% of the thickness of the copper plating film 20. Here, 0% means the surface of the substrate 10, and 100% means the surface of the copper plating film 20. [Example]

[0040] (Common conditions) A 35 μm-thick polyimide film (Upilex-35SGAV1 manufactured by Ube Industries, Ltd.) was prepared as the base film. The base film was set in a magnetron sputtering device. A nickel-chromium alloy target and a copper target were installed inside the magnetron sputtering device. The nickel-chromium alloy target had a composition of 20 mass % Cr and 80 mass % Ni. In a vacuum atmosphere, a 25 nm-thick base metal layer made of nickel-chromium alloy was formed on one side of the base film, and a 150 nm-thick copper thin film layer was formed on top of that.

[0041] Next, a copper plating solution was prepared. The copper plating solution contained 120 g / L of copper sulfate, 70 g / L of sulfuric acid, 16 mg / L of brightener, 20 mg / L of leveler, 1,100 mg / L of polymer, and 50 mg / L of chlorine. Bis(3-sulfopropyl) disulfide (a reagent manufactured by RASCHIG GmbH) was used as the brightener. Diallyldimethylammonium chloride-sulfur dioxide copolymer (PAS-A-5 manufactured by Nittobo Medical Co., Ltd.) was used as the leveler. Polyethylene glycol-polypropylene glycol copolymer (UNILUBE 50MB-11 manufactured by NOF Corporation) was used as the polymer. Hydrochloric acid (35% hydrochloric acid manufactured by Wako Pure Chemical Industries, Ltd.) was used as the chlorine.

[0042] A substrate was supplied to a plating tank containing the copper plating solution. An 8.5 μm thick copper plating film was formed on one side of the substrate by electroplating. The temperature of the copper plating solution was set to 31°C. During electroplating, the copper plating solution was agitated by spraying the copper plating solution from a nozzle substantially perpendicularly to the surface of the substrate.

[0043] (reference sample) The current density and plating time for electroplating were set as shown in Table 1, and four samples were prepared. 2 , 3.02A / dm 2 Then, the current density was increased to 5.03 A / dm 2A copper plating film was formed to a thickness of 8.5 μm using the same method. The copper plating film did not have a low current density layer. The resulting copper-clad laminate was used as a reference sample.

[0044] [Table 1]

[0045] The folding endurance of the reference sample was evaluated using the MIT test. The MIT test was performed in accordance with JIS C6471 (1995). The tester used was a Toyo Seiki Seisakusho MIT Folding Fatigue Tester, Model D. A 1 mm wide wiring pattern was formed on the sample. The sample was repeatedly bent 135° in the opposite direction under the following conditions: a radius of curvature of 0.36 mm, a load of 500 gf, and a repetition rate of 175 cpm (175 bends per minute). The number of times the wiring was broken (number of breaks) was measured. MIT evaluation was performed on four samples 1, 10, 20, and 30 days after electroplating.

[0046] (Evaluation of current density and thickness of low current density layer) Next, the relationship between the current density and thickness of the low current density layer of the copper plating film and folding endurance was evaluated. The current density and plating time for electrolytic plating were set as shown in Table 2. That is, in the initial stage of electrolytic plating, the current density was set to 1.38 A / dm 2 , 3.02A / dm 2 Then, the current density was increased to 5.03 A / dm 2 A first layer (high current density layer) with a thickness of 4.17 μm was formed at a high current density. Next, a second layer (low current density layer) with a thickness of 0.10 μm was formed at a low current density. Finally, the current density was increased to 5.03 A / dm 2 The third layer (high current density layer) was deposited with a thickness of 4.23 μm. The low current densities were 0.13, 0.19, 0.25, 0.31, and 0.38 A / dm 2 The plating time was adjusted so that the thickness of the low current density layer was 0.10 μm. The obtained copper-clad laminates were designated as Samples 1 to 5.

[0047] [Table 2]

[0048] The current density and plating time for electroplating were set as shown in Table 3. That is, the low current density was 0.19 A / dm 2 In addition, the plating time of the low current density layer was changed to form five types of copper plating films with low current density layer thicknesses of 0.05, 0.07, 0.10, 0.13, and 0.15 μm. The obtained copper-clad laminates are designated as Samples 6 to 10.

[0049] [Table 3]

[0050] The folding endurance of samples 1 to 10 was evaluated by the MIT test. The results are shown in Figures 3 and 4. The MIT evaluation was carried out 1 day and 10 days after electrolytic plating. In Figures 3 and 4, the number of times samples 1 to 10 withstood breaking after 1 day is expressed as a ratio, with the number of times the reference sample withstood breaking after 1 day set to 100%. Furthermore, the number of times samples 1 to 10 withstood breaking after 10 days is expressed as a ratio, with the number of times the reference sample withstood breaking after 10 days set to 100%.

[0051] As can be seen from Figures 3 and 4, the tendency of folding resistance differs between one day and ten days after electrolytic plating. This is thought to be influenced by the degree of recrystallization of the copper plating film. In reality, folding resistance becomes an issue when electronic devices are in use, that is, when recrystallization of the copper plating film has been completed. Therefore, folding resistance after 10 days, when recrystallization has been completed, is more in line with reality. Therefore, the following analysis focuses on folding resistance after 10 days.

[0052] From the graph in Figure 3, the low current density is 0.13 to 0.38 A / dm 2 In particular, the bending resistance is superior to that of the reference sample in the low current density range of 0.16 to 0.22 A / dm 2If this is the case, the number of times that the wire can withstand breakage is 115% or more of that of the reference sample. In other words, the low current density is 0.13 to 0.38 A / dm 2 is preferable, and 0.16 to 0.22 A / dm 2 It is presumed that this tendency will not change even when the copper plating film has multiple low current density layers.

[0053] From the graph in Figure 4, it can be seen that when the low-current density layer is in the range of 0.05 to 0.15 μm in thickness, the folding endurance is superior to that of the reference sample. In particular, when the low-current density layer is in the range of 0.08 to 0.12 μm in thickness, the number of times that the wire breaks withstands is 115% or more of that of the reference sample. In other words, it can be said that the thickness of the low-current density layer is preferably 0.05 to 0.15 μm, and more preferably 0.08 to 0.12 μm. It is expected that this tendency will not change even when the copper plating film has multiple low-current density layers.

[0054] (Evaluation of the location of the low current density layer) Next, the relationship between the position of the low current density layer in the thickness direction of the copper plating film and folding endurance was evaluated. The current density and plating time for electrolytic plating were set as shown in Table 4. That is, in the initial stage of electrolytic plating, the current density was set to 1.38 A / dm 2 , 3.02A / dm 2 Then, the current density was increased to 5.03 A / dm 2 The first layer (high current density layer) was deposited at a current density of 0.19 A / dm 2 The second layer (low current density layer) was deposited with a thickness of 0.10 μm at a current density of 5.03 A / dm 2 The third layer (high current density layer) was formed using a high current density (high current density). Five types of copper plating films were formed by varying the position of the low current density layer in the thickness direction of the copper plating film by changing the time of electrolytic plating using a high current density. The obtained copper-clad laminates are designated as Samples 11 to 15.

[0055] [Table 4]

[0056] The folding endurance of samples 11 to 15 was evaluated using the MIT test. The results are shown in Figure 5. The horizontal axis in Figure 5 represents the position in the thickness direction of the copper plating film, with 0% representing the surface of the substrate and 100% representing the surface of the copper plating film. The number of times that the wire breakage was tolerated shown in Figure 5 is the value 10 days after electrolytic plating and is expressed as a ratio, with the number of times that the reference sample withstood the breakage after 10 days being 100%. The approximate curve is the result of fitting the measured values ​​with a quadratic function.

[0057] The graph in Figure 5 shows that to obtain a copper-clad laminate with superior folding endurance to the reference sample, it is preferable to position the low-current-density layer within a range of 35 to 65% of the thickness of the copper plating film. When the copper plating film has multiple low-current-density layers, it is considered sufficient for at least one low-current-density layer to be positioned within a range of 35 to 65% of the thickness of the copper plating film. However, it is presumed that it is preferable for all low-current-density layers to be positioned within a range of 35 to 65% of the thickness of the copper plating film.

[0058] (Evaluation of the number of low current density layers) Next, the relationship between the number of low-current-density layers in the copper plating film and folding endurance was evaluated. The current density and plating time for electrolytic plating were set as shown in Table 5, and four samples with one low-current-density layer were prepared. Here, the low current density was 0.19 A / dm 2 The thickness of the low current density layer was set to 0.10 μm. The obtained copper-clad laminate was designated Sample 16.

[0059] [Table 5]

[0060] The current density and plating time for electroplating were set as shown in Table 6, and four samples with three low-current-density layers were prepared. 2 The thickness of each low current density layer was set to 0.10 μm. The obtained copper-clad laminate was designated Sample 17.

[0061] [Table 6]

[0062] The folding endurance of samples 16 and 17 was evaluated by the MIT test. The MIT evaluation was carried out 1 day, 10 days, 20 days, and 30 days after electrolytic plating. The results are shown in Figure 6. In Figure 6, "no low-current-density layer" refers to the reference sample, "one low-current-density layer" refers to sample 16, and "three low-current-density layers" refers to sample 17. The number of times that samples withstood breakage is expressed as a percentage, with the number of times that the reference sample withstood breakage after one day being set to 100%.

[0063] The graph in Figure 6 shows that, as a general trend, samples with one low-current density layer have better folding resistance than reference samples that do not include a low-current-density layer, and samples with three low-current-density layers have even better folding resistance. Focusing particularly on folding resistance 30 days after electroplating, samples with three low-current-density layers have 123% of the number of breakages that can be tolerated compared to the reference sample. Therefore, it can be said that three low-current-density layers are preferable.

[0064] The surface resistivity of the copper plating film of the reference sample and samples 16 and 17 was measured. A Mitsubishi Chemical Analytical Loresta AX MCP-T370 was used for the measurements. Measurements were conducted 1, 10, 20, and 30 days after electrolytic plating. The results are shown in Figure 6. It is known that surface resistivity decreases as recrystallization of the copper plating film progresses. The graph in Figure 6 shows that when there are three low-current-density layers, the surface resistivity remains high even 30 days after electrolytic plating, indicating that the progression of recrystallization has been suppressed. This suggests that the progression of recrystallization of the copper plating film is interrupted by the low-current-density layers, improving folding endurance.

[0065] (Evaluation of low current density layer spacing) Next, the relationship between the spacing of the low-current-density layers of the copper plating film and folding endurance was evaluated. The current density and plating time for electrolytic plating were set as shown in Table 7. That is, the number of low-current-density layers was set to 3, and the low current density was set to 0.19 A / dm 2The thickness of the low current density layer was set to 0.10 μm. The spacing between the low current density layers (the thickness of the third and fifth layers) was varied in six patterns: 0.24, 0.48, 0.73, 0.97, 1.21, and 1.45 μm. The obtained copper-clad laminates are designated Samples 18 to 23.

[0066] [Table 7]

[0067] Figure 7 shows the arrangement of the low current density layer for samples 18 to 23. The vertical axis in Figure 7 represents the position in the thickness direction of the copper plating film, with 0 μm and 0% representing the surface of the substrate and 8.5 μm and 100% representing the surface of the copper plating film. The folding endurance of samples 18 to 23 was evaluated using the MIT test. The results are shown in Figure 8. In Figure 8, the number of times samples 18 to 23 withstood breakage after one day is expressed as a ratio, with the number of times the reference sample withstood breakage after one day being 100%. The number of times samples 18 to 23 withstood breakage after 10 days is expressed as a ratio, with the number of times the reference sample withstood breakage after 10 days being 100%.

[0068] As mentioned above, the folding endurance after 10 days, when recrystallization is complete, is more accurate, so we will focus on the folding endurance after 10 days for analysis. The graph in Figure 8 shows that folding endurance varies depending on the spacing of the low-current-density layers. In particular, Sample 19, with a low-current-density layer spacing of 0.48 μm, and Sample 21, with a low-current-density layer spacing of 0.97 μm, exhibit excellent folding endurance. This suggests that a spacing of 0.3 to 0.6 μm or 0.8 to 1.1 μm is preferable. Considering the ratio to the thickness of the copper-plated coating, a spacing of 3.5 to 7.1% or 9.4 to 12.9% is preferable. This approach ensures a wire breakage resistance of 120% or more of that of the reference sample. [Explanation of symbols]

[0069] 1 Copper-clad laminate 10 Base material 11 Base film 12 metal layer 13 Undercoat metal layer 14 Copper thin film layer 20 Copper plating film 21 High current density layer 22 Low current density layer

Claims

1. A substrate; a copper plating film formed on the surface of the substrate, the copper plating film is formed by alternately laminating four high-current-density layers formed by electrolytic plating at a high current density and three low-current-density layers formed by electrolytic plating at a current density lower than the high current density, The distance between two adjacent low current density layers with one high current density layer sandwiched therebetween is 0.8 to 1.1 μm. A copper clad laminate characterized by:

2. A substrate; a copper plating film formed on the surface of the substrate, the copper plating film is formed by alternately laminating four high-current-density layers formed by electrolytic plating at a high current density and three low-current-density layers formed by electrolytic plating at a current density lower than the high current density, The distance between two adjacent low current density layers sandwiching one high current density layer is 3.5 to 7.1% or 9.4 to 12.9% of the thickness of the copper plating film. A copper clad laminate characterized by:

3. The low current density is 0.13 to 0.38 A / dm 2 is 3. The copper clad laminate according to claim 1 or 2.

4. Each of the low current density layers has a thickness of 0.05 to 0.15 μm. The copper clad laminate according to any one of claims 1 to 3.

5. The low current density layers are each located within a range of 35 to 65% of the thickness of the copper plating film. The copper clad laminate according to any one of claims 1 to 4.

6. an electrolytic plating step of forming a copper plating film on the surface of the substrate to obtain a copper-clad laminate; the electrolytic plating step includes alternately performing four high current density electrolytic plating processes and three low current density electrolytic plating processes to form the copper plating film; A high current density layer having a thickness of 0.8 to 1.1 μm is formed by the second and third electrolytic plating at the high current density. A method for producing a copper clad laminate.

7. an electrolytic plating step of forming a copper plating film on the surface of the substrate to obtain a copper-clad laminate; the electrolytic plating step includes alternately performing four high current density electrolytic plating processes and three low current density electrolytic plating processes to form the copper plating film; By the second and third electrolytic plating at the high current density, a high current density layer having a thickness of 3.5 to 7.1% or 9.4 to 12.9% of the thickness of the copper plating film is formed. A method for producing a copper clad laminate.

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