Copper-clad laminate and method for manufacturing the same

Abstract

To provide a copper-clad laminate with excellent fracture resistance and a method for producing the copper-clad laminate.SOLUTION: A copper-clad laminate 1 comprises a base material 10, and a copper plating film 20 formed on a surface of the base material 10. The copper plating film 20 includes: a lower layer 21 formed on the surface of the base material 10; an intermediate layer 22 formed on a surface of the lower layer 21 by electroplating at a low current density; and a surface layer 23 formed on the surface of the intermediate layer 22. Since the intermediate layer 22 formed at a low current density is inserted into the copper plating film 20, the fracture resistance of the copper-clad laminate 1 can be improved.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, laptops, 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 type of copper-clad laminate in which the conductor layer is formed directly on the resin film, known as a two-layer board. [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. The copper plating film comprises a lower layer formed on the surface of the substrate, an intermediate layer formed on the surface of the lower layer by electrolytic plating at a low current density, and a surface layer formed on the surface of the intermediate layer. [Effects of the Invention]

[0008] According to the present invention, since an intermediate layer formed at a low current density is inserted into the copper plating film, the folding endurance of the copper-clad laminate can be improved. [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] 1 is a graph showing the relationship between current density and folding endurance of an intermediate layer. [Figure 4] 1 is a graph showing the relationship between the thickness of the intermediate layer and folding endurance. [Figure 5] 1 is a graph showing the relationship between the position of the intermediate layer 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 three-layer structure consisting of a lower layer 21, an intermediate layer 22, and a surface layer 23. The lower layer 21, intermediate layer 22, and surface layer 23 are laminated in this order on the surface of the substrate 10 (thin copper film layer 14). More specifically, the lower layer 21 is formed directly on the surface of the substrate 10 (thin copper film layer 14). The intermediate layer 22 is formed directly on the surface of the lower layer 21. The surface layer 23 is formed directly on the surface of the intermediate layer 22. The surface layer 23 is located on the outermost side of the copper plating film 20. In other words, the intermediate layer 22 is inserted in the middle of the copper plating film 20 in the thickness direction, and the intermediate layer 22 divides the copper plating film 20 into the lower layer 21 on the substrate 10 side and the surface layer 23 on the surface side.

[0015] The thickness of the copper plating coating 20 is mainly accounted for by the lower layer 21 and the surface layer 23. The intermediate layer 22 is thinner than both the lower layer 21 and the surface layer 23. Specifically, the thickness of each of the lower layer 21 and the surface layer 23 is preferably 20 to 90 times, and more preferably 30 to 60 times, the thickness of the intermediate layer 22.

[0016] Such a three-layer copper plating film 20 can be obtained by providing a period during the electrolytic plating process for forming the copper plating film 20 in which the current density is lower than normal. The layer formed by electrolytic plating at a low current density becomes the intermediate layer 22. The method for forming the copper plating film 20 will be described in detail below.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] A rectifier is connected to each of the multiple anodes 31 arranged inside the plating tank 30. Therefore, a different current density can be set 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. Specifically, from upstream to downstream, a current density increasing zone RZ, a first zone FZ, a second zone SZ, and a third zone TZ are set. Each zone corresponds to an area where one or more consecutive anodes 31 are arranged.

[0026] Since the metal layer 12 formed on the base film 11 is relatively thin, if the current density is increased in the early stage of electroplating, there is a risk that the portion of the metal layer 12 that comes into contact with the power supply part (clamp) will dissolve. On the other hand, to increase productivity, it is preferable to increase the current density as much as possible. Therefore, in the early stage of electroplating, the current density is gradually increased. In the current density increasing zone RZ, electroplating is performed while gradually increasing the current density. Hereinafter, the period in which the current density is gradually increased in the early stage of electroplating, i.e., the period in which the substrate 10 passes through the current density increasing zone RZ, will be referred to as the "current density increasing period." The current density in the current density increasing period is 1 to 5 A / dm 2 It is preferable to gradually increase the temperature within the range of

[0027] After the current density increasing period, when the copper plating film 20 has thickened to a thickness (e.g., 1.0 μm) that does not pose a risk of dissolution, electroplating is performed at a relatively high, constant current density. The zones where such electroplating is performed are the first zone FZ and the third zone TZ. Hereinafter, the current density in the first zone FZ will be referred to as the "first current density D1," and the current density in the third zone TZ will be referred to as the "third current density D3."

[0028] In a second zone SZ between the first zone FZ and the third zone TZ, electrolytic plating is performed at a relatively low current density. Hereinafter, the current density in the second zone SZ is referred to as a "second current density D2."

[0029] The substrate 10 passes through the current density increase zone RZ, first zone FZ, second zone SZ, and third zone TZ in this order. As a result, a copper plating film 20 is formed on the surface of the substrate 10. More specifically, a lower layer 21 is formed by electroplating in the current density increase zone RZ and first zone FZ (lower layer formation process). Next, an intermediate layer 22 is formed by electroplating in the second zone SZ (intermediate layer formation process). Finally, a surface layer 23 is formed by electroplating in the third zone TZ (surface layer formation process).

[0030] In other words, the layer formed by electroplating at first current density D1 after the current density increasing period is lower layer 21. The layer formed by electroplating at second current density D2 is middle layer 22. The layer formed by electroplating at third current density D3 is surface layer 23. In this way, a copper plating film 20 having a three-layer structure can be formed.

[0031] If there is no risk of dissolution of the metal layer 12, the current density increase zone RZ need not be provided in the plating tank 30. In this case, a first zone FZ, a second zone SZ, and a third zone TZ are defined from upstream to downstream inside the plating tank 30. The lower layer 21 is formed by electroplating at the first current density D1 without going through the current density increase period.

[0032] The copper plating film 20 can also be formed using a single-wafer plating apparatus. The substrate 10 is immersed in a copper plating solution in a plating tank for electroplating, 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 is performed at a first current density D1 with or without a current density increase period to form the lower layer 21 (lower layer formation process). Next, electroplating is performed at a second current density D2 to form the intermediate layer 22 (intermediate layer formation process). Finally, electroplating is performed at a third current density D3 to form the surface layer 23 (surface layer formation process).

[0033] The copper-clad laminate 1 of this embodiment has excellent folding resistance because the intermediate layer 22 formed at a low current density is inserted into the copper plating film 20. Here, folding resistance means strength against repeated bending and stretching, and is evaluated by the MIT test.

[0034] 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 the intermediate layer 22 is inserted into the copper plating film 20, recrystallization proceeds separately in the lower layer 21 and the surface layer 23, and the crystal grains are separated at the top and bottom of the copper plating film 20. 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.

[0035] The folding endurance of the copper clad laminate 1 is affected by the current density (second current density D2) when depositing the intermediate layer 22 and the thickness of the intermediate layer 22. From the viewpoint of improving the folding endurance, it is preferable that the second current density D2 is 0.13 to 0.38 A / dm 2 and the thickness of the intermediate layer 22 is preferably 0.05 to 0.15 μm.

[0036] 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

[0037] The first current density D1 and the third current density D3 may be higher than the second current density D2. However, the first current density D1 and the third current density D3 should be 4 to 10 A / dm 2 The first current density D1 and the third current density D3 may be the same or different.

[0038] The folding resistance of the copper-clad laminate 1 is also affected by the position of the intermediate layer 22 in the thickness direction of the copper plating film 20. From the viewpoint of improving folding resistance, it is preferable that the intermediate layer 22 is located within a range of 40 to 60% of the thickness direction 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]

[0039] (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.

[0040] 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.

[0041] 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.

[0042] (reference sample) The current density and plating time for electroplating were set as shown in Table 1. The layer numbers in Table 1 are numbered in order from the layer in contact with the surface of the substrate. That is, in the initial stage of electroplating, 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 copper plating film was formed to a thickness of 8.5 μm using a copper plating method. Therefore, the copper plating film did not have an intermediate layer. The resulting copper-clad laminate was used as a reference sample.

[0043] [Table 1]

[0044] 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 conditions of a 0.36 mm radius of curvature, a 500 gf load, and a repetition rate of 175 cpm (175 bends per minute). The number of times the wiring was broken (number of breaks) was measured. The MIT test was performed twice, one day and 10 days after the completion of electroplating, and the number of breaks was obtained at each timing. Hereinafter, the number of breaks for the reference sample is set to 100%, and the number of breaks for the other samples is evaluated.

[0045] (Current density, thickness evaluation) Next, the relationship between the current density and thickness of the intermediate layer of the copper plating film and the folding endurance was evaluated. The current density and plating time for electroplating were set as shown in Table 2. That is, in the initial stage of electroplating, the current density was set to 1.38 A / dm 2 , 3.02A / dm 2 Then, the current density (first current density) was increased to 5.03 A / dm 2 A lower layer having a thickness of 4.17 μm was formed at a current density of 1.00 μm. Next, a middle layer having a thickness of 0.10 μm was formed at a current density of 1.00 μm. Finally, the current density (third current density) was increased to 5.03 A / dm. 2 The surface layer was formed to a thickness of 4.23 μm with the second current density set to 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 intermediate layer was 0.10 μm. The obtained copper-clad laminates were designated as Samples 1 to 5.

[0046] [Table 2]

[0047] The current density and plating time for electroplating were set as shown in Table 3. That is, the current density (second current density) for forming the intermediate layer was set to 0.19 A / dm 2 The plating time for the intermediate layer was also changed to form five different copper plating films with intermediate layer thicknesses of 0.05, 0.07, 0.10, 0.13, and 0.15 μm. The resulting copper-clad laminates were designated Samples 6 to 10.

[0048] [Table 3]

[0049] 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 test was conducted twice, one day and ten days after the completion of electrolytic plating, and the number of times the samples withstood breakage was obtained at each timing. In Figures 3 and 4, the number of times the samples withstood breakage after one day for samples 1 to 10 is expressed as a ratio, with the number of times the reference sample withstood breakage after one day being 100%. Furthermore, the number of times the samples withstood breakage after 10 days for samples 1 to 10 is expressed as a ratio, with the number of times the reference sample withstood breakage after 10 days being 100%.

[0050] As can be seen from Figures 3 and 4, the tendency of folding resistance differs between one day and 10 days after the completion of 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, the 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.

[0051] From the graph in Figure 3, the current density (second current density) when forming the intermediate layer is 0.13 to 0.38 A / dm 2 In particular, when the second current density is in the range of 0.16 to 0.22 A / dm 2 In other words, the second current density is 0.13 to 0.38 A / dm 2 is preferable, and 0.16 to 0.22 A / dm 2 is more preferable.

[0052] From the graph in Figure 4, it can be seen that when the intermediate layer thickness is in the range of 0.05 to 0.15 μm, the folding endurance is superior to that of the reference sample. In particular, when the intermediate layer thickness is 0.08 to 0.12 μm, 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 intermediate layer thickness is preferably 0.05 to 0.15 μm, and more preferably 0.08 to 0.12 μm.

[0053] (Evaluation of position in thickness direction) Next, the relationship between the position of the intermediate layer in the thickness direction of the copper plating film and folding endurance was evaluated. The current density and plating time for electroplating were set as shown in Table 4. That is, in the initial stage of electroplating, the current density was set to 1.38 A / dm 2 , 3.02A / dm 2 Then, the current density (first current density) was increased to 5.03 A / dm 2 Next, the current density (second current density) was set to 0.19 A / dm 2 Finally, the current density (third current density) was set to 5.03 A / dm 2 The surface layer was formed as follows. The electrolytic plating time at the first and third current densities was varied to form five types of copper plating films with different intermediate layer positions in the thickness direction of the copper plating film. The resulting copper-clad laminates were designated Samples 11 to 15.

[0054] [Table 4]

[0055] The folding resistance of Samples 11 to 15 was evaluated by the MIT test. The results are shown in Figure 5. The number of times that wire breakage was observed in Figure 5 was measured 10 days after electrolytic plating. The graph in Figure 5 shows that in order to obtain a copper-clad laminate with superior folding resistance to the reference sample, it is preferable to position the intermediate layer within a range of 40 to 60% of the thickness of the copper plating film, and more preferably within a range of 45 to 55%. [Explanation of symbols]

[0056] 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 Lower layer 22 Middle Class 23 Surface layer

Claims

1. A substrate; a copper plating film formed on the surface of the substrate, The copper plating film is a lower layer formed on the surface of the substrate by electrolytic plating at a first current density with or without a current density ramp-up period; an intermediate layer formed on the surface of the lower layer by electrolytic plating at a second current density; a surface layer formed on the surface of the intermediate layer by electrolytic plating at a third current density; The second current density is 0.13 to 0.38 A / dm 2 and the thickness of the intermediate layer is 0.05 to 0.15 μm; the first current density and the third current density are higher than the second current density; The thickness of the lower layer and the surface layer is 20 to 90 times the thickness of the intermediate layer. A copper clad laminate characterized by:

2. The first current density and the third current density are 4 to 10 A / dm 2 is 2. The copper clad laminate according to claim 1.

3. A method for obtaining a copper-clad laminate by forming a copper plating film consisting of a lower layer, an intermediate layer, and a surface layer on the surface of a substrate, comprising: an underlayer deposition step of depositing the underlayer on the surface of the base material by electrolytic plating at a first current density with or without a current density increasing period; an intermediate layer forming step of forming the intermediate layer on the surface of the lower layer by electrolytic plating at a second current density; a surface layer forming step of forming the surface layer on a surface of the intermediate layer by electrolytic plating at a third current density, The second current density is 0.13 to 0.38 A / dm 2 and the thickness of the intermediate layer is 0.05 to 0.15 μm; the first current density and the third current density are higher than the second current density; The thickness of the lower layer and the surface layer is 20 to 90 times the thickness of the intermediate layer. A method for producing a copper clad laminate.

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