Method for manufacturing copper-clad laminate

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 , copper a method for manufacturing a copper-clad laminate. More specifically, the present invention is used in the manufacture of flexible printed wiring boards (FPCs) and the like copper and relates to a method for manufacturing a copper-clad laminate.

Background Art

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

[0003] A metallizing method is known as a method for manufacturing a copper-clad laminate (for example, Patent Document 1). The manufacture of a copper-clad laminate by the metallizing method is performed, for example, according to 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 copper thin film layer is formed on the base metal layer. Next, a copper plating film is formed on the copper thin film layer. By copper plating, the conductor layer is thickened until it reaches a film thickness suitable for forming a wiring pattern. By the metallizing method, a copper-clad laminate of a type called a so-called two-layer substrate, in which a conductor layer is directly formed on a resin film, is obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, with the miniaturization and thinning of electronic devices, flexible printed wiring boards are increasingly used in ways that involve bending with a small radius of curvature. When a flexible printed wiring board is repeatedly bent and stretched with a small radius of curvature, cracks may occur on the surface of the wiring portion, and the cracks may grow and lead to disconnection. Therefore, a copper-clad laminate with excellent folding resistance is required.

[0006] In view of the above circumstances, an object of the present invention is to provide a method for manufacturing a copper-clad laminate with excellent folding resistance. copper

Means for Solving the Problems

[0007] The copper-clad laminate of the present invention includes a base material and a copper plating film formed on the surface of the base material. The copper plating film includes a lower layer formed on the surface of the base material, 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 resistance of the copper-clad laminate can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

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

[0011] The base material 10 is obtained by forming a metal layer 12 on the surface of an insulating base film 11. As the base film 11, a resin film such as a polyimide film or a liquid crystal polymer (LCP) film can be used. The metal layer 12 is formed by a dry film formation method such as a sputtering method. The metal layer 12 is composed of an underlayer metal layer 13 and a copper thin film layer 14. The underlayer 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 underlayer 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 underlayer 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] Note that the underlayer metal layer 13 may not be provided. The copper thin film layer 14 may be formed on the surface of the base film 11 via the underlayer metal layer 13, or may be formed directly on the surface of the base film 11 without passing through the underlayer metal layer 13.

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

[0014] The copper plating film 20 has a three-layer structure composed of a lower layer 21, an intermediate layer 22, and a surface layer 23. The lower layer 21, the intermediate layer 22, and the surface layer 23 are laminated in this order on the surface of the base material 10 (copper thin film layer 14). More specifically, the lower layer 21 is directly formed on the surface of the base material 10 (copper thin film layer 14). The intermediate layer 22 is directly formed on the surface of the lower layer 21. The surface layer 23 is directly formed 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 in the thickness direction of the copper plating film 20, and the copper plating film 20 is divided into the lower layer 21 on the side of the base material 10 and the surface layer 23 on the surface side from the intermediate layer 22.

[0015] The lower layer 21 and the surface layer 23 mainly bear the thickness of the copper plating film 20. The intermediate layer 22 is thinner than each of the lower layer 21 and the surface layer 23. Specifically, the thicknesses of the lower layer 21 and the surface layer 23 are preferably 10 to 50 times the thickness of the intermediate layer 22, respectively.

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

[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 base material 10 while conveying it by roll-to-roll. The plating apparatus has a supply apparatus that unwinds the base material 10 wound in a roll shape and a winding apparatus that winds up the base material 10 (copper-clad laminate 1) after plating in a roll shape.

[0018] The plating apparatus is provided with a plurality of clamps for transporting the base material 10. The plurality of clamps grip both edges of the base material 10 and transport the base material 10. In the transport path of the base material 10, a pretreatment tank, a plating tank 30, and a post-treatment tank are arranged. While the base material 10 is being transported in the plating tank 30, a copper plating film 20 is formed on its surface by electrolytic plating. Thereby, the long-strip copper-clad laminate 1 is obtained.

[0019] As shown in FIG. 2, the plating tank 30 is a horizontally long single tank along the transport direction of the base material 10. The base material 10 is transported along the center of the plating tank 30. A copper plating solution is stored in the plating tank 30. The entire base material 10 being transported in the plating tank 30 is immersed in the copper plating solution.

[0020] The copper plating solution contains a water-soluble copper salt. Any water-soluble copper salt generally used in the copper plating solution can be used without particular limitation. The copper plating solution may contain sulfuric acid. By adjusting the addition amount of sulfuric acid, the pH and sulfate ion concentration of the copper plating solution can be adjusted. The copper plating solution may generally contain additives added to the plating solution. As the additive, one type selected from brightener components, leveler components, polymer components, chlorine components, etc. may be used alone, or two or more types may be used in combination.

[0021] The content of each component of the copper plating solution can be arbitrarily selected. However, the copper plating solution preferably contains 15 to 70 g / L of copper and 20 to 250 g / L of sulfuric acid. By doing so, the copper plating film 20 can be formed at a sufficient speed. The copper plating solution preferably contains 1 to 50 mg / L of a brightener component. By doing so, the deposited crystals can be refined and the surface of the copper plating film 20 can be smoothed. The copper plating solution preferably contains 1 to 300 mg / L of a leveler component. By doing so, protrusions can be suppressed and a flat copper plating film 20 can be formed. The copper plating solution preferably contains 10 to 1,500 mg / L of a polymer component. By doing so, the current concentration at the end of the base material 10 can be alleviated and a uniform copper plating film 20 can be formed. The copper plating solution preferably contains 20 to 80 mg / L of a chlorine component. By doing so, abnormal deposition can be suppressed.

[0022] The temperature of the copper plating solution is preferably 20 to 35°C. Also, it is 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 ejected from the nozzle onto the base material 10.

[0023] Inside the plating tank 30, a plurality of anodes 31 are arranged along the conveyance direction of the base material 10. Also, the clamp that holds the base material 10 also functions as a cathode. By passing an electric current between the anode 31 and the clamp (cathode), a copper plating film 20 can be formed on the surface of the base material 10.

[0024] In the plating tank 30 shown in FIG. 2, anodes 31 are arranged on both the front and back sides of the base material 10. Therefore, if the base material 10 with the metal layers 12 formed on both sides of the base film 11 is used, copper plating films 20 can be formed on both sides of the base material 10.

[0025] Each of the plurality of anodes 31 arranged inside the plating tank 30 is connected to a rectifier. Therefore, it can be set so that different current densities are obtained for each anode 31. In the present embodiment, the inside of the plating tank 30 is divided into a plurality of regions along the conveyance direction of the base material 10. Specifically, a current density increasing region RZ, a first region FZ, a second region SZ, and a third region TZ are set from upstream to downstream. Each region corresponds to a region where one or a plurality of continuous 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 at the initial stage of electrolytic plating, the portion of the metal layer 12 that comes into contact with the power supply part (clamp) may dissolve. On the other hand, to increase productivity, it is preferable to increase the current density as much as possible. Therefore, at the initial stage of electrolytic plating, the current density is gradually increased. In the current density increasing region RZ, electrolytic plating is performed while gradually increasing the current density. Hereinafter, the period during which the current density at the initial stage of electrolytic plating is gradually increased, that is, the period during which the base material 10 passes through the current density increasing region RZ, is referred to as the "current density increasing period". The current density during the current density increasing period is preferably gradually increased within the range of 1 to 5 A / dm 2 ².

[0027] After the copper plating film 20 has become thick enough (for example, 1.0 μm) so that there is no risk of dissolution after passing through the current density increasing period, electrolytic plating is performed at a relatively high constant current density. The regions where such electrolytic plating is performed are the first region FZ and the third region TZ. Hereinafter, the current density in the first region FZ is referred to as the "first current density D1", and the current density in the third region TZ is referred to as the "third current density D3".

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

[0029] The base material 10 passes through the current density increasing region RZ, the first region FZ, the second region SZ, and the third region TZ in this order. Thereby, a copper plating film 20 is formed on the surface of the base material 10. More specifically, the lower layer 21 is formed by electrolytic plating in the current density increasing region RZ and the first region FZ (lower layer forming step). Next, the intermediate layer 22 is formed by electrolytic plating in the second region SZ (intermediate layer forming step). Finally, the surface layer 23 is formed by electrolytic plating in the third region TZ (surface layer forming step).

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

[0031] In addition, when there is no risk of dissolution of the metal layer 12, the current density rising region RZ may not be provided in the plating bath 30. In this case, inside the plating bath 30, a first region FZ, a second region SZ, and a third region TZ are set from upstream to downstream. The lower layer 21 is formed by electrolytic plating at the first current density D1 without going through the current density rising period.

[0032] The copper plating film 20 can also be formed by a single-sheet plating apparatus. The sheet-shaped substrate 10 is immersed in the copper plating solution in the plating bath for electrolytic plating to form a copper plating film 20 on the surface of the substrate 10. At this time, the current density is changed with the passage of time. Specifically, the lower layer 21 is formed by electrolytic plating at the first current density D1 with or without going through the current density rising period (lower layer forming step). Next, the intermediate layer 22 is formed by electrolytic plating at the second current density D2 (intermediate layer forming step). Finally, the surface layer 23 is formed by electrolytic plating at the third current density D3 (surface layer forming step).

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

[0034] Although the reason for the improvement in the folding resistance is not clear in some respects, it is generally considered 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, when the bending and stretching are repeated, cracks occur on the surface of the copper plating film 20 starting from grain boundaries and the like. 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 in a state of being divided above and below the copper plating film 20. Therefore, the tensile stress applied to the outermost surface of the copper plating film 20 when the copper-clad laminate 1 is bent is relaxed, and cracks are less likely to occur. Thus, it is considered that the folding resistance is improved.

[0035] The folding resistance of the copper-clad laminate 1 is affected by the current density (second current density D2) when forming the intermediate layer 22 and the thickness of the intermediate layer 22. From the viewpoint of improving the folding resistance, the second current density D2 is 0.25 to 0.5 A / dm 2 and it is preferable that the thickness of the intermediate layer 22 is 0.1 to 0.15 μm. Or, the second current density D2 is 0.5 to 0.75 A / dm 2 and it is preferable that the thickness of the intermediate layer 22 is 0.1 to 0.25 μm. Or, the second current density D2 is 0.75 to 1.0 A / dm 2 and it is preferable that the thickness of the intermediate layer 22 is 0.1 to 0.3 μm.

[0036] Here, the thickness of the layer is obtained from the current density and the plating time in electroplating. Specifically, as shown in Equation (1), the thickness d [μm] is obtained by multiplying the current density J [A / dm 2 , the plating time T [minutes], and a predetermined coefficient k. Note that the coefficient k is a value that depends on conditions such as the plating solution and is determined by tests.

Equation

[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 are 4 to 10 A / dm 2is preferred. 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 in the thickness direction of the copper plating film 20 of the intermediate layer 22. From the viewpoint of improving the folding resistance, it is preferable that the intermediate layer 22 is located within the range of 35 to 65% in the thickness direction of the copper plating film 20. Here, 0% means the surface of the base material 10, and 100% means the surface of the copper plating film 20.

Examples

[0039] (Common conditions) As a base film, a polyimide film with a thickness of 35 μm (Upilex-35SGAV1 manufactured by Ube Industries, Ltd.) was prepared. The base film was set in a magnetron sputtering apparatus. A nickel-chromium alloy target and a copper target were installed in the magnetron sputtering apparatus. The composition of the nickel-chromium alloy target is 20% by mass of Cr and 80% by mass of Ni. Under a vacuum atmosphere, a base metal layer made of nickel-chromium alloy with a thickness of 25 nm was formed on one side of the base film, and a copper thin film layer with a thickness of 150 nm was formed thereon.

[0040] Next, the copper plating solution was adjusted. The copper plating solution contains 120 g / L of copper sulfate, 70 g / L of sulfuric acid, 16 mg / L of brightener component, 20 mg / L of leveler component, 1,100 mg / L of polymer component, and 50 mg / L of chlorine component. As the brightener component, bis(3-sulfopropyl) disulfide (a reagent manufactured by RASCHIG GmbH) was used. As the leveler component, a diallyldimethylammonium chloride-sulfur dioxide copolymer (PAS-A-5 manufactured by Nitto Boehringer Medical Co., Ltd.) was used. As the polymer component, a polyethylene glycol-polypropylene glycol copolymer (Unirupe 50MB-11 manufactured by NOF Corporation) was used. As the chlorine component, hydrochloric acid (35% hydrochloric acid manufactured by Wako Pure Chemical Industries, Ltd.) was used.

[0041] A substrate was supplied to a plating bath in which the copper plating solution was stored. A copper plating film with a thickness of 8.5 μm was formed on one side of the substrate by electrolytic plating. Here, the temperature of the copper plating solution was set at 31°C. Also, during the electrolytic plating, the copper plating solution ejected from the nozzle was sprayed substantially perpendicularly to the surface of the substrate to stir the copper plating solution.

[0042] (Reference sample) The current density and plating time in the electrolytic plating 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, at the initial stage of electrolytic plating, the current density was 1.38 A / dm 2 , 3.02 A / dm 2 and gradually increased step by step, and then the current density was set at 5.03 A / dm 2 to form a copper plating film until the thickness reached 8.5 μm. Therefore, the copper plating film does not have an intermediate layer. The obtained copper-clad laminate was used as a reference sample.

[0043]

Table 1

[0044] The flex resistance of the reference sample was evaluated by the MIT test. The MIT test was conducted according to JIS C6471 (1995). As a test machine, a type D MIT flex fatigue tester manufactured by Toyo Seiki Seisakusho was used. A wiring pattern with a width of 1 mm was formed on the sample. The sample was bent at a curvature radius of 0.36 mm by 135°, and then the operation of bending it by 135° in the opposite direction was repeated, and the number of times (number of breakage-resistant times) when the conduction of the wiring was interrupted was measured. Hereinafter, taking the number of breakage-resistant times of the reference sample as 100%, the number of breakage-resistant times of other samples was evaluated.

[0045] (Evaluation of current density and thickness) Next, the relationship between the current density and thickness of the intermediate layer of the copper plating film and the flex resistance was evaluated. The current density and plating time in the electrolytic plating were set as shown in Table 2. That is, at the initial stage of electrolytic plating, the current density was 1.38 A / dm 2 , 3.02 A / dm 2and increased step by step, and then the current density (first current density) was set to 5.03 A / dm 2 to form a lower layer with a thickness of 4.17 μm. Next, an intermediate layer was formed with a current density (second current density) of 0.25 A / dm 2 Then, a surface layer was formed with a current density (third current density) of 5.03 A / dm 2 Here, the plating time of the intermediate layer was changed to form three types of copper plating films with intermediate layer thicknesses of 0.10, 0.15, and 0.20 μm. The obtained copper-clad laminates are designated as Samples 1 to 3.

[0046]

Table 2

[0047] The current density and plating time in electrolytic plating were set as shown in Table 3. That is, the current density (second current density) when forming the intermediate layer was 0.50 A / dm 2 and the plating time of the intermediate layer was changed to form five types of copper plating films with intermediate layer thicknesses of 0.10, 0.15, 0.20, 0.25, and 0.30 μm. The obtained copper-clad laminates are designated as Samples 5 to 8.

[0048]

Table 3

[0049] The current density and plating time in electrolytic plating were set as shown in Table 4. That is, the current density (second current density) when forming the intermediate layer was 0.75 A / dm 2 and the plating time of the intermediate layer was changed to form five types of copper plating films with intermediate layer thicknesses of 0.10, 0.15, 0.20, 0.25, and 0.30 μm. The obtained copper-clad laminates are designated as Samples 9 to 13.

[0050]

Table 4

[0051] The current density and plating time in electrolytic plating were set as shown in Table 5. That is, the current density (second current density) when forming the intermediate layer was 1.00 A / dm 2 And the plating time of the intermediate layer was varied to form five types of copper plating films with intermediate layer thicknesses of 0.10, 0.15, 0.20, 0.25, and 0.30 μm. The obtained copper-clad laminates are designated as Samples 14 to 18.

[0052]

Table 5

[0053] The folding resistance of Samples 1 to 18 was evaluated by the MIT test. The results are shown in Figure 3. From the graph in Figure 3, it can be seen that in order to obtain a copper-clad laminate with better folding resistance than the reference sample, the current density (second current density) when forming the intermediate layer should be 0.25 to 0.5 A / dm 2 And the thickness of the intermediate layer should be 0.1 to 0.15 μm, or the second current density should be 0.5 to 0.75 A / dm 2 And the thickness of the intermediate layer should be 0.1 to 0.25 μm, or the second current density should be 0.75 to 1.0 A / dm 2 And the thickness of the intermediate layer should be 0.1 to 0.3 μm.

[0054] Also, from the perspective of improving the folding resistance, the second current density is preferably 0.5 to 1 A / dm 2 More preferably 0.75 to 1 A / dm 2 Even more preferably 0.75 A / dm 2 When the second current density is 0.25 to 0.5 or 1 A / dm 2 The thinner the intermediate layer, the better the folding resistance. When the second current density is 0.75 A / dm 2 The thickness of the intermediate layer is preferably 0.1 to 0.25 μm, more preferably 0.1 to 0.2 μm, and even more preferably 0.15 to 0.2 μm.

[0055] (Evaluation of the position in the thickness direction) Next, the relationship between the position of the intermediate layer in the thickness direction of the copper plating film and the folding resistance was evaluated. The current density and plating time in electrolytic plating were set as shown in Table 6. That is, at the initial stage of electrolytic plating, the current density was gradually increased in steps of 1.38 A / dm 2 and 3.02 A / dm 2 , and then the lower layer was formed with the current density (the first current density) being 5.03 A / dm 2 . Next, an intermediate layer with a thickness of 0.2 μm was formed with the current density (the second current density) being 0.75 A / dm 2 . Finally, the surface layer was formed with the current density (the third current density) being 5.03 A / dm 2 . Here, the electrolytic plating time with the first and third current densities was changed, and five types of copper plating films with different positions of the intermediate layer in the thickness direction of the copper plating film were formed. The obtained copper-clad laminates are designated as Samples 19 to 23.

[0056]

Table 6

[0057] The folding resistance of Samples 19 to 23 was evaluated by the MIT test. The results are shown in Fig. 4. From the graph in Fig. 4, it can be seen that in order to obtain a copper-clad laminate with better folding resistance than the reference sample, it is preferable to position the intermediate layer within the range of 35 to 65% of the thickness of the copper plating film, more preferably within the range of 40 to 60%, and even more preferably within the range of 45 to 55%.

Explanation of Symbols

[0058] 1 Copper-clad laminate 10 Base material 11 Base film 12 Metal layer 13 Underlying metal layer 14 Copper thin film layer 20 Copper plating film 21 Lower layer 22 Intermediate layer 23 Surface layer

Claims

1. A method for obtaining a copper-clad laminate by forming a copper plating film composed of a lower layer, an intermediate layer, and a surface layer on the surface of a base material, comprising: A lower layer forming step of forming the lower layer on the surface of the base material by electrolytic plating at a first current density with or without passing through 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 the surface of the intermediate layer by electrolytic plating at a third current density, The second current density is 0.25 to 0.5 A / dm 2 and the thickness of the intermediate layer is 0.1 to 0.15 μm, or The second current density is 0.5 to 0.75 A / dm 2 and the thickness of the intermediate layer is 0.1 to 0.25 μm, or The second current density is 0.75 to 1.0 A / dm 2 and the thickness of the intermediate layer is 0.1 to 0.3 μm, wherein the first current density and the third current density are higher than the second current density, and the intermediate layer is located within a range of 35% to 65% of the thickness of the copper plating film. A method for manufacturing a copper-clad laminate, characterized by the above.

2. The first current density and the third current density are 4 to 10 A / dm 2 are The method for manufacturing a copper-clad laminate according to Claim 1, characterized by the above.

3. The thicknesses of the lower layer and the surface layer are each 10 to 50 times the thickness of the intermediate layer. The method for manufacturing a copper-clad laminate according to Claim 1 or 2, characterized by the above.

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