JP2016191698A - Copper-clad laminate and circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper-clad laminate capable of retaining high visibility even when a light quantity is changed, and a circuit board.SOLUTION: The copper-clad laminate includes a polyimide layer, and a copper foil layer laminated on at least one-side surface of the polyimide layer. A visibility evaluation method includes the steps of: A) preparing a dot pattern two-dimensionally distributed on the copper foil layer; B) imaging the dot pattern via the polyimide layer to generate it as an output image; C) dividing the output image into the number of dots same as that of the dot pattern as an input image, classifying the respective dots into white dots or black dots, digitizing luminance for each dot to acquire a dot number distribution, and calculating an average value and a standard deviation; and D) calculating a signal noise ratio on the basis of a specific expression. When the visibility is evaluated by the visibility evaluation method, with the light quantity in the imaging in the step B set within a range of 1-8 mW/cm, the signal noise ratio is 6 or more.SELECTED DRAWING: None

Description

  The present invention relates to a copper-clad laminate and a circuit board obtained by wiring the same.

  In recent years, with the progress of downsizing, weight reduction, and space saving of electronic devices, flexible printed wiring boards (FPCs) that are thin, light, flexible, and have excellent durability even after repeated bending. The demand for (Flexible Printed Circuits) is increasing. Since FPC can be mounted three-dimensionally and with high density even in a limited space, for example, wiring of movable parts of electronic devices such as HDDs, DVDs, mobile phones, cables, connectors, etc. Applications are expanding to parts.

  Most FPCs are manufactured by forming a circuit on a metal foil of a metal-clad laminate in which a metal foil and a polyimide layer are laminated. In the photolithography process for metal-clad laminates and the FPC mounting process using metal-clad laminates, various processes such as bonding, cutting, exposure, and etching are performed based on the alignment marks provided on the metal-clad laminates. Is done. In order to maintain the processing accuracy in these steps, it is important to accurately recognize the alignment mark through the polyimide layer of the metal-clad laminate.

  However, when the light transmittance of the polyimide layer of the metal-clad laminate is small, when scattering, refraction, etc. are large, or when the thickness of the polyimide layer is uneven and strain is present, the visibility of the polyimide layer is low. Decrease significantly. As a result, the alignment mark cannot be recognized accurately, and processing accuracy may be reduced.

  Under such a background, the present inventors photograph a dot pattern that is two-dimensionally distributed by an imaging device, and calculate a signal-to-noise ratio from the average value and standard deviation of luminance for each type of dot. Proposed a method for evaluating visibility (Japanese Patent Application No. 2014-196039). According to the evaluation method, the visibility of the metal-clad laminate can be grasped as objective numerical data.

  The inventors of the present invention produced a large number of copper-clad laminates having a copper foil layer and a polyimide layer, and evaluated the visibility of the copper-clad laminates based on the visibility evaluation method. As a result, it has been found that in many copper-clad laminates, the visibility tends to fluctuate greatly with changes in the amount of light. Thus, when the change in visibility with respect to conditions such as the amount of light is large, the conditions must be optimized, for example, when the alignment mark is recognized in the circuit board manufacturing process. However, the optimum conditions for obtaining high visibility differ from material to material, and the margin of the optimum conditions tends to be narrow. Therefore, optimization takes time, and work efficiency may be reduced.

  Accordingly, an object of the present invention is to provide a copper-clad laminate and a circuit board that can maintain high visibility even when the amount of light changes.

  In order to solve the above problems, as a result of intensive studies, a copper-clad laminate obtained by combining a specific material of polyimide and a copper foil having a specific surface state is stably high even if the amount of light changes. The present invention has been completed by finding that it shows visibility.

The copper clad laminate of the present invention is a copper clad laminate having a polyimide layer and a copper foil layer laminated on at least one surface of the polyimide layer, and includes the following steps A to D;
A) preparing a dot pattern that is two-dimensionally distributed in the copper foil layer;
B) Step of photographing the dot pattern by the imaging device through the polyimide layer and generating the photographed dot pattern image as an output image;
C) The output image is divided into the same number of dots as the dot pattern that is the input image, and each dot is classified as either a white dot or a black dot, and the classified white dot and black dot for each dot Quantifying the brightness to obtain a frequency distribution, calculating an average value and a standard deviation of the brightness for the white dots and the black dots, and
D) calculating a signal-to-noise ratio based on the following formula (1) from the average value and standard deviation of the luminance;
The signal-to-noise ratio is 6 or more when the visibility is evaluated by setting the amount of light at the time of photographing in the step B within the range of 1 to 8 mW / cm ² by the visibility evaluation method including To do.

［式中、ＳＮＲは信号ノイズ比を示し、μ_０は黒ドットの輝度の平均値を意味し、μ_１は白ドットの輝度の平均値を意味し、σ_Ｌは黒ドットの輝度の標準偏差と白ドットの輝度の標準偏差のいずれか大きい方を意味する。］

[In the formula, SNR represents the signal-to-noise ratio, μ ₀ represents the average value of the luminance of the black dots, μ ₁ represents the average value of the luminance of the white dots, and σ _L represents the standard deviation of the luminance of the black dots. Or the standard deviation of brightness of white dots, whichever is greater. ]

  In the copper clad laminate of the present invention, the surface roughness (Rz) of the copper foil layer on the side in contact with the polyimide layer may be 0.8 μm or less.

When the surface of the copper foil layer on the side in contact with the polyimide layer is measured through the polyimide layer, the copper-clad laminate of the present invention has a color difference Δa ^* and L ^* a ^* b ^* color system. Both Δb ^* may be within ± 20, and the brightness difference ΔL ^* may be −75 or less.

  In the copper clad laminate of the present invention, the polyimide layer may have a total light transmittance of 70% or more and a haze of 30% to 80%.

  The circuit board of the present invention is obtained by processing the copper foil layer of any one of the above copper-clad laminates.

  The copper-clad laminate of the present invention has excellent visibility, and even when the amount of light is changed, the visibility variation is small. Therefore, by using the copper-clad laminate of the present invention, it is possible to improve the alignment accuracy in the wiring formation process and the mounting process of the circuit board, and to provide a highly reliable electronic device.

It is explanatory drawing which expands and shows the preferable example of the dot pattern using a 2/4 modulation code. It is drawing which simplifies and shows the principle of the visibility evaluation method. It is drawing which expands and shows a part of dot pattern image which is an output image. It is drawing which shows the example of the histogram produced based on the brightness | luminance of each dot.

  Hereinafter, the present invention will be described in detail.

[Copper-clad laminate]
The copper-clad laminate of this embodiment includes a polyimide layer and a copper foil layer laminated on at least one surface of the polyimide layer. The copper-clad laminate is formed into a long sheet having a width of about several hundred mm so that it can be easily processed into an FPC, for example, and may be usually wound into a roll.

The copper clad laminate of the present embodiment has a signal-to-noise ratio (SNR) of 6 when the visibility is evaluated by setting the light amount in the range of 1 to 8 mW / cm ² in the following visibility evaluation method. That's it.

<Visibility evaluation>
The visibility evaluation is performed by the following steps A to D;
A) preparing a two-dimensionally distributed dot pattern on the copper foil layer of the copper clad laminate,
B) Photographing the dot pattern with an imaging device through the polyimide layer of the copper clad laminate, and generating a photographed dot pattern image as an output image;
C) The output image is divided into the same number of dots as the dot pattern that is the input image, and each dot is classified as either a white dot or a black dot, and the classified white dot and black dot for each dot Quantifying the brightness to obtain a frequency distribution, calculating an average value and a standard deviation of the brightness for the white dots and the black dots, and
D) calculating a signal-to-noise ratio based on the following formula (1) from the average value and standard deviation of the luminance;
Can be included.

［式中、ＳＮＲは信号ノイズ比を示し、μ_０は黒ドットの輝度の平均値を意味し、μ_１は白ドットの輝度の平均値を意味し、σ_Ｌは黒ドットの輝度の標準偏差と白ドットの輝度の標準偏差のいずれか大きい方を意味する。］

[In the formula, SNR represents the signal-to-noise ratio, μ ₀ represents the average value of the luminance of the black dots, μ ₁ represents the average value of the luminance of the white dots, and σ _L represents the standard deviation of the luminance of the black dots. Or the standard deviation of brightness of white dots, whichever is greater. ]

  The step (A) will be described in detail. A two-dimensionally distributed dot pattern as shown in FIG. 1 is formed on the copper foil on one side of the copper clad laminate used for evaluation. The dot pattern can be formed, for example, by etching the copper foil layer using a mask or the like. At that time, for the double-sided copper-clad laminate, the copper foil on which the dot pattern is not formed is all etched to expose the polyimide layer.

The step (B) will be described in detail. FIG. 2 shows a simplified principle of the visibility evaluation method. The dot pattern DP is photographed by the imaging device through the sample produced in the step (A), and the photographed dot pattern image DPI is generated as an output image. In this visibility evaluation method, the dot pattern DP is photographed with a polyimide layer interposed between the dot pattern DP as an input image and the imaging device. For example, LED ring illumination is used as the light source, and the amount of light is set within a range of 1 to 8 mW / cm ² .

Step (C) will be described in detail. The dot pattern image DPI that is the output image is divided into the same number of dots as the original dot pattern DP that is the input image, and each dot is classified as either a white dot or a black dot, and the classified white dots and black dots For each dot, the luminance was digitized to obtain a frequency distribution, and the average value and standard deviation of the luminance were calculated for white dots and black dots. FIG. 3 shows an enlarged portion of a dot pattern image DPI that is an output image. The output image is divided into the same number of dots (m × n dots) as the input image. All the dots are classified into two types, black dots or white dots, based on the dots of the input image. Then, for the classified white dots and black dots, the luminance is digitized for each dot to obtain a frequency distribution. FIG. 4 shows an example of a histogram created based on the brightness of each dot. In this example, a black dot is “0”, a white dot is “1”, and a luminance signal level (horizontal axis in the figure) is divided into 256 scales to create a histogram. Based on such a histogram, the average luminance values μ ₀ and μ ₁ and the standard deviations σ ₀ and σ ₁ are calculated for each of the black dot distribution and the white dot distribution. Furthermore, the larger one of the standard deviation of the luminance of the black dots and the standard deviation of the luminance of the white dots is defined as σ _L.

In step (D), the average values μ ₀ and μ ₁ and standard deviation σ _L of the luminance obtained in step (C) can be inserted into the above equation (1) to obtain the SNR. The SNR obtained in this way represents the visibility when objectively observing the two-dimensional dot pattern formed on the copper foil layer through the polyimide layer as objective numerical data.

<Copper surface over polyimide layer>
In order to obtain a high SNR regardless of the amount of light, the copper clad laminate of the present embodiment is obtained when the surface of the copper foil layer in contact with the polyimide layer is measured over the polyimide layer (via the polyimide layer). In the L ^* a ^* b ^* color system, the color differences Δa ^* and Δb ^* are both in the range of ± 20, and the lightness difference ΔL ^* is preferably −75 or less. If the color difference and the lightness difference are outside the above ranges, the color of the copper foil surface on the side in contact with the polyimide layer is thin, and the alignment mark recognition is reduced.

Next, in the above-described visibility evaluation method, when the light intensity is set within the range of 1 to 8 mW / cm ² and the visibility is evaluated, the copper-clad laminate for setting the signal-to-noise ratio (SNR) to 6 or more The configuration of the plate will be described in detail.

<Polyimide layer>
As the polyimide layer, a commercially available polyimide film can be used as it is. However, in order to easily control the thickness of the insulating layer and the physical properties, a polyamic acid solution is directly applied on the copper foil, and then heat treatment is performed. A so-called cast (coating) method for drying and curing is preferred. Moreover, although a polyimide layer may be formed only from a single layer, when the adhesiveness etc. of a polyimide layer and a copper foil layer are considered, what consists of multiple layers is preferable. In the case where a plurality of polyimide layers are used, other polyamic acid solutions can be sequentially formed on a polyamic acid solution composed of different components. When a polyimide layer consists of multiple layers, you may use the polyimide precursor resin of the same structure twice or more.

  The thickness of the polyimide layer of the copper clad laminate in the present invention is preferably in the range of 8 to 52 μm, for example, and more preferably in the range of 8 to 27 μm. If the thickness of the polyimide layer is less than 8 μm, the impedance matching property when joining with other components is lowered. When the thickness of the polyimide layer exceeds 52 μm, it becomes difficult to mount the polyimide layer by folding it in the casing of the electronic device.

  In this invention, it is preferable that the total light transmittance of the polyimide layer obtained when etching the copper foil laminated | stacked on the single side | surface or both surfaces of the copper clad laminated board is 70% or more, for example. Moreover, it is preferable that the haze of this polyimide layer exists in the range of 30 to 80%, for example. When the total light transmittance is less than 70% or the haze is out of the above range, the transparency of the polyimide layer is not sufficiently ensured, and the surface of the copper foil layer on the side in contact with the polyimide layer is covered with the polyimide layer. When observed through the copper foil, the color of the copper foil becomes unclear.

As described above, the polyimide layer is preferably a plurality of layers. As a specific example, the polyimide layer includes a low thermal expansion polyimide layer having a thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K and a thermal expansion coefficient of 30. It is preferable to make it the laminated structure containing the high thermal expansion polyimide layer of * 10 < ^-6 > / K or more. More preferably, the polyimide layer is a laminated structure having a high thermal expansion polyimide layer on at least one of the low thermal expansion polyimide layers, preferably on both sides thereof, and the high thermal expansion polyimide layer is a copper that directly becomes a circuit wiring layer. It is preferable to be in contact with the foil layer. Here, the “low thermal expansion polyimide layer” means a thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K, preferably in the range of 1 × 10 ^{−6 to} 25 × 10 ⁻⁶ / K, particularly preferably 3 ×. A polyimide layer in the range of 10 ^{−6 to} 20 × 10 ⁻⁶ / K. The “high thermal expansion polyimide layer” refers to a polyimide layer having a thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more, preferably in the range of 30 × 10 ⁻⁶ to 80 × 10 ⁻⁶ / K, particularly Preferably, it means a polyimide layer in the range of 30 × 10 ⁻⁶ to 70 × 10 ⁻⁶ / K. Such a polyimide layer can be made into a polyimide layer having a desired thermal expansion coefficient by appropriately changing the combination of raw materials used, thickness, and drying / curing conditions.

  The polyamic acid solution that gives the polyimide layer can be produced by polymerizing a known diamine and acid anhydride in the presence of a solvent, and the viscosity of the polymerized resin is 500 cps or more and 35,000 cps or less. It is preferable to be within the range.

  Examples of the diamine used as a raw material for polyimide include 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, and 4,4′-methylenedi-o-. Toluidine, 4,4′-methylenedi-2,6-xylidine, 4,4′-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4 ′ -Diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2, 2-bis [4- (4-aminophenoxy) phenyl] propane, 4,4′-dia Nodiphenyl sulfide, 3,3′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether -Tell, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, benzidine, 3,3'-diamino Biphenyl, 3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxybenzidine, 4,4′-diamino-p-terphenyl, 3,3′-diamino-p-terphenyl, bis (P-aminocyclohexyl) methane, bis (p-β-amino-t-butylphenyl) ether, bis (p-β-methyl) δ-aminopentyl) benzene, p-bis (2-methyl-4-aminopentyl) benzene, p-bis (1,1-dimethyl-5-aminopentyl) benzene, 1,5-diaminonaphthalene, 2,6- Diaminonaphthalene, 2,4-bis (β-amino-t-butyl) toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylene diene Amine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazol, piperazine, 2,2'-dimethyl-4,4 '-Diaminobiphenyl, 3,7-diaminodibenzofuran, 1,5-diaminofluorene, dibenzo-p-dioxin-2,7-diamine, 4,4'-diaminobenzene Such as Jill, and the like.

  Examples of the acid anhydride used as a raw material for polyimide include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,2 ′, 3,3 ′. -Benzophenone tetracarboxylic dianhydride, 2,3,3,4'-benzophenone tetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4 , 5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 4,8-dimethyl- 1,2,3,5,6,7-hexahydronaphthalene-1,4,5,6-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexa Hydronaphthalene-2,3,6 -Tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid bis Anhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7- Tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ″, 4,4 ″ -p-terphenyltetracarboxylic dianhydride, 2,2 ″, 3,3 ″ -p-terphenyl Tetracarboxylic dianhydride, 2,3,3 ″, 4 ″ -p-ter Phenyltetracarboxylic dianhydride, 2,2′-bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) -propane dianhydride, Bis (2,3-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2 , 3-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1- Bis (3,4-dicarboxyphenyl) ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene -4, 5, 1 , 11-tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene-1,2, 6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2, 3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-3,4,5-tetracarboxylic dianhydride, 4,4'- Examples thereof include oxydiphthalic dianhydride and -2,3,6,7-naphthalene tetracarboxylic dianhydride.

  Each of the diamine and acid anhydride may be used alone or in combination of two or more. Moreover, the solvent used for superposition | polymerization includes dimethylacetamide, N-methylpyrrolidinone, 2-butanone, diglyme, xylene and the like, and can be used alone or in combination of two or more.

In the present embodiment, in order to form a polyimide layer having a high SNR regardless of the amount of light and having a low thermal expansion coefficient of less than 30 × 10 ⁻⁶ / K, for example, a raw material acid Pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as the anhydride component, 2,2′-dimethyl-4,4′-diaminobiphenyl as the diamine component, 2-Methoxy-4,4′-diaminobenzanilide is preferably used, and particularly preferably, pyromellitic dianhydride and 2,2′-dimethyl-4,4′-diaminobiphenyl are used as main components of the raw materials. What is said to be good.

Further, in order to form a polyimide layer having a high thermal expansion coefficient of 30 × 10 ⁻⁶ / K or more, which can obtain a high SNR regardless of the amount of light, for example, as a raw acid anhydride component Pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4 4'-diphenylsulfonetetracarboxylic dianhydride is used as a diamine component, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, 4,4'-diaminodiphenyl ether, 1, It is preferable to use 3′-bis (4-aminophenoxy) benzene, particularly preferably pyromellitic dianhydride and 2,2′-bis [4- (4-aminophenoxy) phenyl] propane as raw materials. It is intended that a component. In addition, the preferable glass transition temperature of the high thermal expansibility polyimide layer obtained in this way exists in the range of 300-400 degreeC.

<Copper foil layer>
In this Embodiment, as copper foil which comprises a copper foil layer, both an electrolytic copper foil and a rolled copper foil can be used. In this case, the copper foil preferably has a surface roughness represented by Rz of 0.8 μm or less. When Rz exceeds 0.8, sufficient total light transmittance and haze cannot be secured due to the unevenness of the polyimide transferred when the copper foil layer of the copper clad laminate is etched.

  The thickness of the copper foil layer is preferably in the range of 8 to 20 μm, for example. If the thickness of the copper foil layer is less than 8 μm, the rigidity of the copper foil itself is reduced in the process of forming a polyimide layer on the copper foil, for example, during the production of the copper clad laminate. Problems such as wrinkles may occur. On the other hand, when the thickness of the copper foil layer exceeds 20 μm, bending resistance applied to the copper wiring when the flexible circuit board is bent increases, and the bending resistance decreases.

[Circuit board]
The circuit board according to the present embodiment is obtained by circuit processing of a copper foil layer of a copper clad laminate, and alignment marks are formed at both ends thereof. The circuit board may be subjected to circuit processing on both sides, but the alignment mark recognizing part is assumed that the copper foil on one side is etched and removed. The circuit board may be a flexible circuit board (FPC).

  Hereinafter, based on an Example, this invention is demonstrated in detail. In addition, each characteristic evaluation in the following Example was performed with the following method.

<Measurement of surface roughness (Rz)>
The surface roughness on the contact surface side with the polyimide layer of the copper foil was measured using a contact-type surface roughness measuring machine (SURFACE CORDER ET3000 manufactured by Kosaka Laboratory Ltd.).

<Evaluation of visibility>
According to the evaluation method of the visibility, in step B, using LED lighting (Nisshin electronic WDR-90), respectively the amount ^{1mW / cm 2, 3mW / cm} 2, 5mW / cm 2, or, to 8 mW / cm ² Set and implemented. Further, the image was captured at an ISO sensitivity of 400 and a shutter speed of 1/125 seconds to obtain a black and white image.

<Measurement of color difference Δa ^* , Δb ^* , brightness difference ΔL ^* >
Using a color difference meter (Color Densitor nR-1 manufactured by Nippon Denshoku Industries Co., Ltd.), the color difference Δa ^* , Δb ^* , brightness difference ΔL ^* on the back surface of the copper foil layer over the polyimide layer is determined in accordance with JIS Z 8730. It was measured.

<Total light transmittance and haze measurement>
Using a turbidimeter (Nippon Denshoku Industries Co., Ltd. turbidimeter), the total light transmittance is in accordance with JIS K 7361-1, and the haze is in accordance with JIS K 7136. The total light transmittance and haze of the polyimide layer obtained by etching were measured.

<Copper foil and polyimide film>
The copper foil and polyimide film used in the examples and comparative examples are as follows.
Copper foil A: thickness: 12 μm, surface roughness: Rz 0.8 μm, Ra 0.1 μm, Rq 0.2 μm
Copper foil B: Thickness: 12 μm, surface roughness: Rz 1.2 μm, Ra 0.2 μm, Rq 0.3 μm
Copper foil C: thickness: 12 μm, surface roughness: Rz 0.4 μm, Ra 0.1 μm, Rq 0.1 μm
Copper foil D: Thickness: 12 μm, surface roughness: Rz 2.2 μm, Ra 0.3 μm, Rq 0.4 μm
Copper foil E: thickness; 12 μm, surface roughness; Rz 0.5 μm, Ra 0.1 μm, Rq 0.1 μm
Copper foil F: thickness: 12 μm, surface roughness: Rz 0.4 μm, Ra 0.1 μm, Rq 0.1 μm
Polyimide film B: thickness; 25 μm

<Synthesis of polyamic acid solution>
(Synthesis Example 1)
A reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen is charged with N, N-dimethylacetamide, and 2,2-bis [4- (4-aminophenoxy) phenyl] propane (BAPP) is added to the reaction vessel. ) Was added and dissolved in the container with stirring. Next, pyromellitic dianhydride (PMDA) was added so that the total amount of monomers introduced was 12 wt%. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid a. The thermal expansion coefficient (CTE) of the polyimide film having a thickness of 25 μm formed from the polyamic acid a was 55 × 10 ⁻⁶ / K.

<Synthesis Example 2>
A reaction vessel equipped with a thermocouple and a stirrer and capable of introducing nitrogen is charged with N, N-dimethylacetamide, and this reaction vessel is further filled with 2,2′-dimethyl-4,4′-diaminobiphenyl (m-TB). Was dissolved while stirring in a container. Next, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were added in a total monomer amount of 15 wt%, and the molar ratio of each acid anhydride. (BPDA: PMDA) was added at 20:80. Thereafter, stirring was continued for 3 hours to carry out a polymerization reaction to obtain a resin solution of polyamic acid b. The thermal expansion coefficient (CTE) of the 25 μm thick polyimide film formed from the polyamic acid b was 22 × 10 ⁻⁶ / K.

Example 1
Resin of polyamic acid a prepared in Synthesis Example 1 on a commercially available copper foil A having a characteristic shown in Table 1 and having a thickness of 12 μm and a long length (coating surface roughness Rz = 0.8 μm) The solution was uniformly applied so that the thickness after curing was 2.5 μm, and then dried by heating at 130 ° C. to remove the solvent. Next, the resin solution of the polyamic acid b prepared in Synthesis Example 2 was uniformly applied to the coated surface side so that the thickness after curing was 20.0 μm, and the solvent was removed by heating and drying at 120 ° C. Furthermore, the same polyamic acid a resin solution as that applied in the first layer is applied on the coated surface side uniformly so that the thickness after curing is 2.5 μm, and the solvent is removed by heating at 130 ° C. did. This long laminate was heat-treated in a continuous curing furnace set so that the temperature gradually increased from 300 ° C. to 300 ° C. over a period of about 6 minutes, and a polyimide having a thickness of 25 μm A single-sided copper clad laminate having layer A was obtained. A double-sided copper-clad laminate was obtained by thermocompression bonding of this single-sided copper-clad laminate and a commercially available copper foil A having a thickness of 12 μm and a separate length at 300 to 400 ° C. A sample for measurement was obtained after forming a dot pattern by etching the double-sided copper-clad laminate. Table 1 shows the evaluation results of SNR of the obtained circuit board.

  Table 1 shows the total light transmittance and haze value of the polyimide layer A constituting the obtained copper-clad laminate, the color difference on the back surface of the copper foil through the polyimide, and the visibility evaluation results. The polyimide layer A was evaluated by removing the copper foil from the manufactured flexible copper-clad laminate.

(Comparative Example 1)
After the polyimide layer A was formed on the copper foil B in the same manner as in Example 1, the double-sided copper-clad laminate was obtained by pasting the copper foil B on the polyimide layer A side. A sample for evaluation was obtained after forming a dot pattern by etching the double-sided copper-clad laminate. Table 1 shows the respective physical property values and visibility evaluation results of the obtained double-sided copper-clad laminate.

(Comparative Example 2)
After the polyimide layer A was formed on the copper foil C in the same manner as in Example 1, the double-sided copper-clad laminate was obtained by pasting the copper foil C on the polyimide layer side. A sample for evaluation was obtained after forming a dot pattern by etching the double-sided copper-clad laminate. Table 1 shows the respective physical property values and visibility evaluation results of the obtained double-sided copper-clad laminate.

(Comparative Example 3)
Using a copper foil A with a thickness of 12 μm, forming a dot pattern by etching a double-sided copper-clad laminate produced by laminating copper foil A and a commercially available polyimide film B with a thickness of 25 μm with a laminating roll Thereafter, an evaluation sample was obtained. Table 1 shows the respective physical property values and visibility evaluation results of the obtained double-sided copper-clad laminate.

(Comparative Example 4)
In the same manner as in Comparative Example 3, after forming a dot pattern by etching a double-sided copper-clad laminate produced by laminating a commercially available copper foil D and a commercially available polyimide film B with a laminate roll, an evaluation sample was prepared. Obtained. Table 1 shows the respective physical property values and visibility evaluation results of the obtained double-sided copper-clad laminate.

(Comparative Example 5)
In the same manner as in Comparative Example 3, after forming a dot pattern by etching a double-sided copper-clad laminate produced by laminating a commercially available copper foil E and a commercially available polyimide film B with a laminate roll, an evaluation sample was prepared. Obtained. Table 1 shows the respective physical property values and visibility evaluation results of the obtained double-sided copper-clad laminate.

(Comparative Example 6)
In the same manner as in Comparative Example 3, after forming a dot pattern by etching a double-sided copper clad laminate produced by laminating a commercially available copper foil F and a commercially available polyimide film B with a laminate roll, an evaluation sample was prepared. Obtained. Table 1 shows the respective physical property values and visibility evaluation results of the obtained double-sided copper-clad laminate.

  The results of Example 1 and Comparative Examples 1 to 6 are summarized in Table 1. “Polyimide A” in Table 1 means the polyimide layer A formed by the casting method, “Polyimide B” means the polyimide layer formed from the polyimide film B, and “Color difference” means copper over the polyimide layer. It means the color difference on the back side of the foil layer.

From Table 1, all of the circuit boards of Example 1 have the above-described configuration, so that the SNR is 6 or more in any case of the light amount 1, 3, 5, 8 mW / cm ² , and is visually recognized. The result was satisfactory. On the other hand, in Comparative Examples 1 to 6, although the SNR is 6 or more at any of the light amounts 1, 3, 5, and 8 mW / cm ² , it does not exceed 6 for all the light amounts, and is inferior to Example 1. Met.

  As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible.

Claims (5)

A copper clad laminate having a polyimide layer and a copper foil layer laminated on at least one side of the polyimide layer,
Next step A to step D;
A) preparing a dot pattern that is two-dimensionally distributed in the copper foil layer;
B) Step of photographing the dot pattern by the imaging device through the polyimide layer and generating the photographed dot pattern image as an output image;
C) The output image is divided into the same number of dots as the dot pattern that is the input image, and each dot is classified as either a white dot or a black dot, and the classified white dot and black dot for each dot Quantifying the brightness to obtain a frequency distribution, calculating an average value and a standard deviation of the brightness for the white dots and the black dots, and
D) From the average value and standard deviation of the luminance, the following formula (1);

[In the formula, SNR represents the signal-to-noise ratio, μ ₀ represents the average value of the luminance of the black dots, μ ₁ represents the average value of the luminance of the white dots, and σ _L represents the standard deviation of the luminance of the black dots. Or the standard deviation of brightness of white dots, whichever is greater. ]
Calculating a signal-to-noise ratio based on
The signal-to-noise ratio is 6 or more when the visibility is evaluated by setting the amount of light at the time of photographing in the step B within the range of 1 to 8 mW / cm ² by the visibility evaluation method including Copper-clad laminate.   The copper clad laminate according to claim 1, wherein the copper foil layer on the side in contact with the polyimide layer has a surface roughness (Rz) of 0.8 μm or less. When the surface of the copper foil layer in contact with the polyimide layer is measured through the polyimide layer, the color difference Δa ^* and Δb ^* are both within ± 20 in the L ^* a ^* b ^* color system. The copper clad laminate according to claim 1, wherein the brightness difference ΔL ^* is −75 or less.   4. The copper-clad laminate according to claim 1, wherein the polyimide layer has a total light transmittance of 70% or more and a haze of 30% or more and 80% or less.   The circuit board formed by carrying out circuit processing of the said copper foil layer of the copper clad laminated board of any one of Claim 1 to 4.

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