Composite metal foil and method for manufacturing the same

Abstract

A composite metal foil in which a second copper layer is laminated on a dissimilar metal layer, capable of forming a circuit by selective etching, having a clear contrast between the dissimilar metal layer and the second copper layer and being easy to identify, and being less likely to cause false detection or detection omission of a circuit pattern in image inspection or misalignment in the case of multilayer formation, and thus providing a composite metal foil suitably used for a printed wiring board. 【Means for solving the problem】 A composite metal foil including at least one layer structure of a first copper layer / a dissimilar metal layer / a second copper layer, wherein the brightness L of the surface of the dissimilar metal layer on which the second copper layer is laminated * A value - the brightness L of the surface of the second copper layer * Cu A composite metal foil having a value of 15 or more.

Description

Technical Field

[0001] The present invention relates to a composite metal foil. Specifically, since it is a composite metal foil in which a second copper layer is laminated on a dissimilar metal layer, a circuit can be formed by selectively etching the second copper layer, and the contrast between the dissimilar metal layer and the second copper layer is clear and easy to distinguish. Therefore, the present invention relates to a composite metal foil that is less likely to cause false detection or detection omission of circuit patterns in image inspection, or misalignment in the case of multilayer formation, and can be suitably used for printed wiring boards.

Background Art

[0002] Printed wiring boards are used in electronic devices and are generally manufactured by subtractive or additive methods using copper foils.

[0003] Depending on the characteristics required for printed wiring boards, the manufacturing methods have also diversified. As described in Patent Documents 1 or 2 to be described later, a manufacturing method using a composite metal foil in which dissimilar metals are compounded and selectively etching each metal (hereinafter referred to as "selective etching"), and a manufacturing method using a selective etching solution capable of selectively etching each metal have also been developed.

[0004] In the manufacturing process of printed wiring boards, it is necessary to accurately identify circuit patterns, such as image inspection (AOI inspection) of circuit patterns and the positions of through holes and vias during multilayer formation.

[0005] However, conventional composite metal foils have a problem that the contrast between dissimilar metals is unclear, making it difficult to accurately identify circuit patterns in image inspection. Therefore, there are problems such as false detection, detection omission, and misalignment of circuit patterns during multilayer formation.

[0006] Therefore, there is a demand for the development of a composite metal foil that can form circuits by selective etching, has a clear contrast between dissimilar metal layers and a second copper layer, can accurately identify circuit patterns by image inspection, is less likely to cause false detection, detection omission, or misalignment during multilayer formation, and can be suitably used for printed wiring boards.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] Patent Document 3 describes a composite copper foil composed of copper / nickel / copper, which is a composite copper foil on which circuits can be formed by selective etching.

[0009] Patent Document 4 describes a method for manufacturing a multilayer wiring board using a dissimilar metal foil having a nickel layer or a nickel alloy layer between a first copper layer and a second copper layer.

[0010] However, the composite copper foil described in Patent Document 3 and the dissimilar metal foil described in Patent Document 4 do not have a clear contrast between the copper layer and the nickel layer. Therefore, there is a risk of false detection, detection omission, or misalignment of circuit patterns during multilayer formation in image inspection.

[0011] The inventors made it a technical problem to solve the above problems, and as a result of repeated trial-and-error prototyping and experiments, on at least one surface of the laminated metal foil in which a first copper layer and a different metal selected from nickel, iron, cobalt, tin, indium, and bismuth are laminated on at least one surface of the first copper layer, and on the different metal layer, a second copper layer is laminated. The composite metal foil has a lightness L defined by JIS-Z8781-4 on the surface of the second copper layer * value as lightness L * Cu value, the lightness L on the surface of the different metal layer on which the second copper layer is laminated * value as lightness L * A value, when the lightness L * A value - lightness L * Cu value is 15 or more, a circuit can be formed by selective etching, and the contrast between the different metal layer and the second copper layer is clear and easy to distinguish. Therefore, false detection and detection omission of the circuit pattern in image inspection, and misalignment during multilayer formation are less likely to occur, and thus a composite metal foil suitable for use in a printed wiring board is obtained, achieving the above technical problem

Means for Solving the Problem

[0012] The above technical problem can be solved by the present invention as follows

[0013] The present invention is a composite metal foil in which a first copper layer and a different metal selected from the following Group A are laminated on at least one surface of the laminated metal foil, and on at least one surface of the different metal layer, a second copper layer is laminated. The lightness L defined by JIS-Z8781-4 on the surface of the second copper layer * value as lightness L * Cu value, the lightness L on the surface of the different metal layer on which the second copper layer is laminated * value as lightness L * A value, when the lightness L * A value - lightness L *Cu It is a composite metal foil with a value of 15 or more. Group A: Nickel, iron, cobalt, tin, indium, bismuth

[0014] The present invention is also the above composite metal foil in which the different metal in Group A is nickel.

[0015] The present invention also relates to the above-mentioned lightness L * Cu It is the above composite metal foil with a value of 65 or less.

[0016] The present invention is also the above composite metal foil in which the ten-point average roughness Rzjis of the surface of the different metal layer is 5 μm or less.

[0017] The present invention is also the above composite metal foil in which the purity of nickel in the nickel layer is 99.6% by weight or more and the weight per square meter is 2.7 g / m 2 or more and 27 g / m 2 or less.

[0018] The present invention is also the above composite metal foil in which at least a part of the surface of the first copper layer or the second copper layer on which the different metal layer is not laminated is surface-treated.

[0019] The present invention is also the above composite metal foil for a printed wiring board.

[0020] The present invention is also a method for manufacturing the above composite metal foil, comprising a step of forming the first copper layer, a step of laminating the different metal layer on at least one surface of the first copper layer, and a step of laminating a second copper layer on at least one surface of the laminated different metal layer.

[0021] The present invention is also a method for manufacturing the above composite metal foil, wherein the laminating step is electroplating.

Effects of the Invention

[0022] The composite metal foil in the present invention is a composite metal foil having at least one layer structure of a first copper layer / a different metal layer / a second copper layer, and is a composite metal foil capable of forming a circuit by selectively etching the second copper layer.

[0023] In addition, the lightness L of the different metal layer * A value - the lightness L of the second copper layer * Cu Since the value is 15 or more, the contrast between the different metal layer and the second copper layer is clear and easy to identify. Therefore, false detection, detection omission of the circuit pattern in image inspection, and displacement during multilayer formation are less likely to occur, and it is a composite metal foil that can be suitably used for a printed wiring board.

[0024] In addition, if the lightness L * Cu value is 65 or less, the second copper layer looks sufficiently black, so the contrast with the different metal layer becomes clearer.

[0025] In addition, if the ten-point average roughness Rzjis of the surface of the different metal layer is 5 μm or less, it becomes a composite metal foil capable of forming a circuit with excellent circuit shape accuracy.

[0026] In addition, when nickel is selected as the different metal, the purity of nickel is 99.6% by weight or more, and the weight per square meter is 2.7 g / m 2 or more, and 27 g / m 2 or less, it becomes a composite metal foil excellent in selectivity and removability by selective etching.

[0027] Therefore, with the composite metal foil in the present invention, a circuit can be formed by a general method such as a subtractive method or an additive method, and false detection, detection omission of the circuit pattern in image inspection, and displacement during multilayer formation are less likely to occur.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0029] The composite metal foil in the present invention is a composite metal foil having at least one layer structure of a first copper layer (20) / dissimilar metal layer (30) / second copper layer (40).

[0030] (First copper layer) The first copper layer (20) in the present invention is not particularly limited, and copper foils or copper alloy foils formed by a rolling method or an electrolytic method can be preferably used.

[0031] For the first copper layer, a copper foil or copper alloy foil subjected to a release treatment so that the front and back can be separated in the thickness direction may be used.

[0032] The thickness of the first copper layer is not particularly limited and may be appropriately selected according to the intended use, but is preferably 9 μm to 300 μm, more preferably 12 μm to 105 μm.

[0033] If the thickness is less than 9 μm, wrinkles and cracks may occur during the lamination of the dissimilar metal layer. If it exceeds 300 μm, the rigidity of the entire composite metal foil may become too strong and it may be difficult to handle.

[0034] (Dissimilar metal layer) In the composite metal foil of the present invention, a dissimilar metal layer (30) is laminated on the first copper layer (20).

[0035] The surface on which the dissimilar metal layer is laminated may be either both sides or one side of the first copper layer, and may be appropriately selected as needed.

[0036] Surface treatment may be performed on the surface of the first copper layer where the dissimilar metal layer is not laminated.

[0037] The surface treatment is not particularly limited, and examples include roughening treatment, heat resistance and chemical resistance treatment, rust prevention treatment, and chemical conversion treatment.

[0038] The ten-point average roughness Rzjis measured in accordance with JIS-B0601(2013) of the surface of the dissimilar metal layer on which the second copper layer is laminated is preferably 5 μm or less, more preferably 3 μm or less.

[0039] When the ten-point average roughness Rzjis of the surface of the dissimilar metal layer exceeds 5 μm, the unevenness becomes too large, which may cause poor adhesion between the dissimilar metal layer and the second copper layer or deterioration of the circuit shape accuracy.

[0040] The dissimilar metal layer in the present invention is made of a metal selected from nickel, iron, cobalt, tin, indium, and bismuth, which are metals that can be selectively etched with respect to copper.

[0041] The nickel layer and the iron layer will be described as examples of the dissimilar metal layer.

[0042] The purity of nickel in the nickel layer is preferably 99.6% by weight or more.

[0043] If the purity of nickel is low, the selectivity and removability of selective etching may decrease.

[0044] The weight per square meter of the nickel layer in the present invention is 2.7 g / m 2 ~27 g / m 2 is preferable, and more preferably 4.5 g / m 2 ~18 g / m 2 is.

[0045] If it is less than 2.7 g / m 2 there is a risk that the selectivity of selective etching will decrease, and even if it exceeds 27 g / m 2 no further improvement in function can be expected, and the time required for selective etching increases.

[0046] The method for forming the nickel layer is not particularly limited, but it is preferably formed by an electrolytic method.

[0047] This is because, in the case of the electrolysis method, the purity of nickel can be made as high as 99.6% by weight or more.

[0048] When forming the nickel layer in the present invention by the electrolysis method, the plating bath is not particularly limited. However, for a Watts bath (nickel sulfate 240 g / L to 300 g / L, nickel chloride 40 g / L to 70 g / L, boric acid 30 mL / L to 45 mL / L, pH 3.8 to pH 4.2, bath temperature 50 °C to 60 °C, current density 0.5 A / dm 2 ~8 A / dm 2 ) or a sulfamic acid bath (nickel sulfamate 440 g / L to 500 g / L, boric acid 30 mL / L to 50 mL / L, pH 3.8 to pH 4.4, bath temperature 50 °C to 60 °C, current density 2 A / dm 2 ~40 A / dm 2 ), by immersing the first copper layer and performing electrolytic plating, a nickel layer can be formed on the first copper layer.

[0049] To the Watts bath or the sulfamic acid bath, a brightener, sodium naphthalenesulfonate, sodium dodecyl sulfate, saccharin, or additives of known plating baths disclosed in JP-A-55-62188 may be added as necessary.

[0050] The iron layer can be formed as a dissimilar metal layer made of iron on the first copper layer by immersing the first copper layer in a sulfuric acid bath (iron(II) sulfate heptahydrate 200 g / L to 300 g / L, pH 2.8 to pH 3.5, bath temperature 30 °C to 65 °C, current density 4 A / dm 2 ~10 A / dm 2 ) and performing electrolytic plating.

[0051] For other metals, a dissimilar metal layer may be formed by known methods such as electrolytic plating, electroless plating, physical film formation, or chemical film formation.

[0052] (Second copper layer) In the composite metal foil of the present invention, a second copper layer is laminated on the dissimilar metal layer.

[0053] The thickness of the second copper layer is not particularly limited, but is preferably 1 μm to 70 μm.

[0054] The lightness L of the surface of the second copper layer * Cu The value is preferably 65 or less. This is because the contrast between the dissimilar metal layer and the second copper layer becomes clear and it becomes easier to identify.

[0055] Surface treatment may be performed on the surface of the second copper layer on the side opposite to the dissimilar metal layer.

[0056] The surface treatment is not particularly limited, and examples include roughening treatment, heat resistance and chemical resistance treatment, rust prevention treatment, and chemical conversion treatment.

[0057] The method for forming the second copper layer is not particularly limited, but a copper sulfate - sulfuric acid bath (copper sulfate pentahydrate 100 g / L to 300 g / L, sulfuric acid 50 g / L to 200 g / L, bath temperature 20°C to 50°C, current density 2 A / dm 2 ~60 A / dm 2 ) can be immersed for electrolytic plating to form the second copper layer on the dissimilar metal layer.

[0058] When forming the second copper layer by electroplating, additives may be added to the plating bath.

[0059] An example of the additive is gelatin.

[0060] Regarding the second copper layer, for the lightness L of the surface not in contact with the dissimilar metal layer * Cu To make the value 65 or less, a blackening treatment for forming acicular crystals of copper oxide on the surface of the second copper layer or a known technique such as that disclosed in JP-A-2011-179078 may be applied.

[0061] In the composite metal foil of the present invention, the lightness L defined by JIS-Z8781-4 of the surface of the second copper layer * value as the lightness L * Cu , and the lightness of the surface of the dissimilar metal layer on which the second copper layer is laminated as the lightness L *A The brightness L when taking a value * A Value - brightness L * Cu The value is preferably 15 or more, more preferably 20 or more.

[0062] Brightness L * If the difference in values is less than 15, the contrast between the dissimilar metal layer and the second copper layer becomes unclear, making it difficult to accurately identify the circuit pattern by image inspection or causing pattern misalignment during multilayer formation.

Examples

[0063] Examples and comparative examples of the present invention are shown below, but the present invention is not limited thereto.

[0064] (Examples 1 to 6) As the first copper layer, an electrolytic copper foil with a thickness of 70 μm was used.

[0065] The first copper layer was immersed in a Watts bath (bath composition: nickel sulfate 250 g / L, nickel chloride 50 g / L, boric acid 30 mL / L, pH 4.0, bath temperature 50 °C), and treated at a current density of 5 A / dm 2 for 120 seconds to form a nickel layer.

[0066] The surface on which the nickel layer was formed was immersed in a copper sulfate - sulfuric acid bath (bath composition: copper sulfate pentahydrate 250 g / L, sulfuric acid 100 g / L, bath temperature 40 °C), and treated at a current density of 5 A / dm 2 for 18 minutes to form a second copper layer on the nickel layer.

[0067] The surface on which the second copper layer was formed was treated under the conditions described in Table 1 to perform surface treatment to lower the brightness of the second copper layer.

[0068] (Example 7) The same procedure as in Example 1 was performed except that 30 ppm of chloride ions and 1.5 ppm of gelatin were added to the copper sulfate - sulfuric acid bath for forming the second copper layer.

[0069] (Example 8) The same procedure as in Example 1 was carried out, except that 30 ppm of chloride ions, 100 ppm of polyethylene glycol, and 5 ppm of disodium bis-3-sulfopropyl disulfide were added to the copper sulfate-sulfuric acid bath for forming the second copper layer.

[0070] (Example 9) The dissimilar metal layer was produced in the same procedure as in Example 1, except that iron plating was performed using a sulfuric acid bath (250 g / L of iron(II) sulfate heptahydrate, pH 3.2, bath temperature 45 °C, current density 7 A / dm 2 , treatment time 120 seconds).

[0071] (Comparative Example 1) It was produced in the same procedure as in Example 1, except that the surface treatment was not performed on the second copper layer.

[0072] (Comparative Example 2) It was produced in the same procedure as in Comparative Example 1, except that the treated surface was made the deposited surface.

[0073] (Surface roughness) The ten-point average roughness Rzjis of the surface of the dissimilar metal layer before forming the second copper layer was measured with a surface roughness measuring instrument SE-600 (manufactured by Kosaka Laboratory Ltd.) in accordance with JIS-B0601 (2013).

[0074] (Brightness L * value) For the dissimilar metal layer and the second copper layer before forming the second copper layer, the brightness L * A value and the brightness L * Cu value were measured with a spectrocolorimeter CM-600d (manufactured by Konica Minolta Inc.). After that, the value of the brightness L * A value - the brightness L * Cu value was calculated.

[0075] (Possibility of binarization) A part of the second copper layer was removed with a copper selective etching solution to expose the dissimilar metal layer, and binarization was performed on the image of the boundary between the exposed dissimilar metal layer and the second copper layer using the Threshold function of the image processing software ImageJ. Those that could be binarized were evaluated as 〇, and those that could not be binarized were evaluated as ×.

[0076] The conditions for the surface treatment that reduces the brightness of the surface of the second copper layer are shown in Table 1. Also, each evaluation of the examples and comparative examples is shown in Table 2.

[0077]

Table 1

[0078]

Table 2

[0079] From the examples and comparative examples, it was proved that in the case of the composite metal foil of the present invention, the contrast between the dissimilar metal layer and the second copper layer becomes clear and can be binarized, so that the identification of the circuit pattern becomes easy.

[0080] In Comparative Examples 1 and 2, binarization was impossible because the contrast was not clear.

[0081] Also, even if the interface between the dissimilar metal layer and the second copper layer was extremely roughened, the contrast did not become clear.

Industrial Applicability

[0082] Since the composite metal foil in the present invention has a second copper layer laminated on the dissimilar metal layer, a circuit can be formed by selective etching. Also, the difference in the lightness L * value between the dissimilar metal layer and the second copper layer is 15 or more, and the contrast between the dissimilar metal layer and the second copper layer is clear and easy to distinguish. Therefore, false detection and detection omission of the circuit pattern in image inspection, and positional deviation when multi-layered are less likely to occur, so it is a composite metal foil that can be suitably used for printed wiring boards. Therefore, the present invention is an invention with high industrial applicability.

Explanation of Signs

[0083] 10 Composite metal foil 20 First copper layer 30 Dissimilar metal layer 40 Second copper layer

Claims

1. A composite metal foil in which a second copper layer is laminated on at least one surface of a laminated metal foil obtained by laminating a first copper layer and a dissimilar metal selected from the following Group A on at least one surface of the first copper layer, and the lightness L defined by JIS-Z8781-4 on the surface of the second copper layer ＊ value is lightness L ＊ Ｃｕ value, the lightness L on the surface of the dissimilar metal layer on which the second copper layer is laminated ＊ value is lightness L ＊ Ａ value, when the lightness L ＊ Ａ value - lightness L ＊ Ｃｕ value is 15 or more. Group A: nickel, iron, cobalt, tin, indium, bismuth

2. The composite metal foil according to Claim 1, wherein the dissimilar metal in Group A is nickel.

3. the brightness L ＊ Ｃｕ The composite metal foil according to claim 1 or 2, wherein the value is 65 or less.

4. The composite metal foil according to Claim 1 or 2, wherein the ten-point average roughness Rzjis of the surface of the dissimilar metal layer is 5 μm or less.

5. The purity of nickel in the nickel layer is 99.6% by weight or more, and the weight per square meter is 2.7 g / m ２ or more and 27 g / m ２ or less. The composite metal foil according to claim 2.

6. The composite metal foil according to Claim 1 or 2, wherein at least a part of the surface of the first copper layer or the second copper layer on which the dissimilar metal layer is not laminated is surface-treated.

7. The composite metal foil according to Claim 1 or 2, which is for a printed wiring board.

8. A step of forming the first copper layer, A step of laminating the dissimilar metal layer on at least one surface of the first copper layer, and A method for manufacturing a composite metal foil according to Claim 1 or 2, comprising a step of laminating a second copper layer on at least one surface of the laminated dissimilar metal layer.

9. The method for manufacturing a composite metal foil according to Claim 8, wherein the laminating step is electroplating.

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