JP2014220323A - Copper foil, method for manufacturing the same, copper clad laminate, and flexible printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil excellent in transparency of resin after removing the copper foil by etching while excellently adhering with the resin, and excellent in an adhesion property with a coverlay.SOLUTION: When arithmetic average roughness Ra prescribed in JIS-B0601 in an MD direction (Machine Direction) of one face is represented by an Ra1, and the Ra in the MD direction of an opposite face is represented by an Ra2, a copper foil satisfies ΔRa=Ra2-Ra1≥0.01.

Description

  The present invention relates to a copper foil and a method for producing the same, and a copper clad laminate and a flexible printed wiring board, and in particular, a copper foil suitable for a field in which transparency of the remaining resin after etching the copper foil is required and the same The present invention relates to a manufacturing method, a copper clad laminate, and a flexible printed wiring board.

In recent years, with the increase in functionality of electronic devices, the frequency of signals has been increased, and accordingly, flexible printed wiring boards (hereinafter referred to as FPC) used as signal wiring have been required to support high frequencies. When the frequency of the signal is increased, the signal current propagates near the surface of the wiring. Therefore, if the surface of the copper foil used as the FPC wiring member is rough, the signal loss increases. Therefore, the smoothness of the surface is required for the high-frequency copper foil.
When FPC is bonded using LCD (liquid crystal display) and anisotropic conductive film (ACF), the marker position is confirmed with a CCD camera over the resin layer (for example, polyimide) serving as the base of FPC. Perform alignment. For this reason, if the transparency of the resin layer is low, alignment becomes difficult.
The resin layer of FPC is obtained by removing the copper layer by etching after bonding the copper foil and the resin layer. Therefore, the resin layer surface is a replica to which the unevenness of the copper foil surface is transferred. That is, if the surface of the copper foil is rough, the surface of the resin layer is also rough, and light is irregularly reflected, so that the transparency is lowered. For this reason, in order to improve the light transmittance of a resin layer, it is necessary to make the adhesive surface with the resin layer of copper foil smooth.
In general, the adhesive surface of the copper foil with the resin layer is subjected to roughening plating in order to increase the adhesive strength. Since the plating particles for the roughening treatment are larger than the surface roughness of the copper foil, the plating conditions have been mainly improved so far as means for smoothing the copper foil surface.

  As such a technique, for example, Patent Document 1 discloses an adhesion layer that is formed of chromium and zinc ions or oxides on the surface of a copper foil and is processed using an aqueous solution containing at least 0.5% of silane. The copper foil is shown.

JP 2012-39126 A

However, the adhesion strength of the demonstration sample disclosed in Patent Document 1 is lower than that of a rough copper foil that is a comparative sample. Thus, if the coarse particles are excessively refined, the adhesion strength with the resin layer decreases. Therefore, there is a limit to smoothing by improving the rough plating. For this reason, it is difficult to achieve both ensuring of the adhesion strength between the resin layer and the copper foil and improving the visibility of the resin layer.
Moreover, the copper foil of patent document 1 will smooth not only the surface (roughening plating side) adhere | attached with resin but the opposite surface which is not adhere | attached with resin. If the surface that is not bonded to the resin (S surface) is smooth, there is a problem that the surface of the copper foil is not easily roughened even by soft etching, and the adhesive strength with the coverlay film is insufficient. In addition, a soft etching process is indispensable, and the number of processes increases and costs increase.

  Therefore, the present invention has a smooth surface even when subjected to the same roughening plating as before, and is excellent in the transparency of the resin after the copper foil is removed by etching while adhering well to the resin. It is an object of the present invention to provide a copper foil excellent in adhesiveness with a coverlay, a method for producing the same, a copper-clad laminate, and a flexible printed wiring board.

  As a result of intensive research, the present inventors smoothed the surface of the copper foil on the surface to be bonded to the resin (roughening plating side), while relatively roughening the opposite surface of the copper foil, By using a rolled copper foil with a controlled difference, the transparency of the resin after removing the copper foil by etching becomes good even after roughing treatment to obtain good adhesion with the resin, and the cover It was found that the adhesiveness with the ray is also excellent.

  The copper foil of the present invention has ΔRa = Ra2-Ra1 ≧ 0.01 when the arithmetic average roughness Ra specified in JIS-B0601 in the MD direction of one surface is Ra1 and Ra in the MD direction of the opposite surface is Ra2. It becomes.

It is preferable that Ra1 is 0.07 μm or less and Ra2 is larger than 0.08 μm.
Ra1 is preferably 0.06 μm or less, and Ra2 is preferably larger than 0.09 μm.
It is preferable that Ra1 is 0.04 μm or less and Ra2 is larger than 0.09 μm.
Ra1 and Ra2 are preferably 0.15 μm or less.

It is preferable to consist of rolled copper foil.
Contains in total 10 to 1500 mass ppm of one or more selected from the group of Ag, Sn, Mg, In, B, Ti, Zr, Zn, Ni, Si, P, Cr and Fe, and the balance Cu and It is preferable to consist of inevitable impurities.

  When a single-sided copper clad laminate having a width of 3 mm or more and 5 mm or less obtained by laminating the copper foil and a polyimide film having a film thickness of 25 μm was subjected to 180 ° adhesion bending with the polyimide film surface inside, the copper It is preferable that the number of bendings until the foil breaks is 3 or more. It is preferable that the number of times of bending until the copper foil breaks is 5 or more.

Two copper foils according to claim 1 having Ra1 of 0.07 μm or less are prepared, and a roughened surface formed by roughening the one surface to form roughened particles is attached to both surfaces of the polyimide resin substrate. After combining, it is preferable that the haze value of the resin substrate from which the copper foil is removed by etching is 72 or less.
When Ra1 is 0.06 μm or less, the haze value of the resin substrate is preferably 67 or less.
When Ra1 is 0.04 μm or less, the haze value of the resin substrate is preferably 55 or less.

Two copper foils having a Ra1 of 0.07 μm or less are prepared, and the roughened surface formed by roughening the one surface to form roughened particles is bonded to both surfaces of the polyimide resin substrate, and then etched. And removing the copper foils on both sides, placing the printed matter printed with line-shaped marks under the exposed resin substrate, and photographing the printed matter with a CCD camera over the resin substrate. In the observation point-brightness graph obtained by measuring the brightness at each observation point along the direction perpendicular to the direction in which the observed line-shaped mark extends, the mark is displayed from the end of the mark. The difference ΔB (ΔB = Bt−Bb) between the top average value Bt and the bottom average value Bb of the lightness curve generated over the portion not drawn is 40 or more, and in the observation point-lightness graph, Of the intersections with t, the intersection closest to the line-shaped mark is t1, and in the depth range from the intersection between the brightness curve and Bt to 0.1ΔB with reference to Bt, the brightness curve and 0.1ΔB It is preferable that Sv defined by the following formula (1) is 3.5 or more when the intersection closest to the line-shaped mark is defined as t2.
Sv = (ΔB × 0.1) / (t1-t2) (1)

Ra1 is preferably 0.06 μm or less, and Sv defined by the formula (1) in the brightness curve is preferably 4.0 or more.
Ra1 is preferably 0.04 μm or less, and Sv defined by the formula (1) in the brightness curve is preferably 5.0 or more.

The manufacturing method of the copper foil of this invention is a manufacturing method of the copper foil in any one of Claims 5-9, Comprising: In the last cold rolling process, the oil film equivalent of said one surface is made into the said opposite surface. Less than oil film equivalent.
The final cold rolling is preferably performed using a rolling roll having an average roughness Ra of 0.1 μm or less when measured in a direction parallel to the rotation axis of the roll.

  The copper clad laminate of the present invention is formed by laminating the copper foil and the resin substrate.

  The flexible printed wiring board of this invention uses the said copper clad laminated board.

  According to the present invention, it is possible to obtain a copper foil that is excellent in the transparency of the resin after etching and removing the copper foil with good adhesion to the resin, and also excellent in adhesion to the coverlay.

It is a schematic diagram which defines Bt and Bb. It is a schematic diagram which defines t1, t2, and Sv. It is a schematic diagram showing the structure of an imaging device and the measuring method of the inclination of a lightness curve in the case of evaluation of the lightness curve inclination.

Hereinafter, the copper foil which concerns on embodiment of this invention is demonstrated. In the present invention, “%” means “% by mass” unless otherwise specified.
<Form and composition of copper foil>
The copper foil of this invention is suitable for the use used by laminating | stacking with a resin substrate, producing a copper clad laminated board, and removing copper foil partially by an etching. Usually, the surface of the copper foil that adheres to the resin substrate, that is, the roughened surface, has a fist-like shape on the surface of the copper foil after degreasing for the purpose of improving the peel strength of the copper foil after lamination. A roughening process for electrodeposition is performed. This roughening treatment can be performed by copper-cobalt-nickel alloy plating, copper-nickel-phosphorus alloy plating, or the like.
Although copper foil thickness is not specifically limited, Preferably it is 5-50 micrometers, More preferably, it is 5-35 micrometers. The conductivity of the copper foil is preferably 50% IACS or more, more preferably 60% IACS or more, and still more preferably 80% IACS or more.

The copper foil contains 99.9% or more of copper by mass ratio, and electrolytic copper foil and rolled copper foil can be used.
Examples of the rolled copper foil include oxygen-free copper standardized by JIS-H3510 (C1011) or JIS-H3100 (C1020) or tough pitch copper standardized by JIS-H3100 (C1100).
The rolled copper foil contains one or more selected from the group consisting of Ag, Sn, Mg, In, B, Ti, Zr, Zn, Ni, Si, P, Cr, and Fe in a total of 1500 ppm by mass or less. May be. If the total amount of the above elements exceeds 1500 ppm by mass, the conductivity may decrease. The lower limit of the total amount of the above elements is, for example, 10 mass ppm or more.

The copper foil of the present invention conforms to JIS-B0601 in the MD direction (Machine Direction) on one side (corresponding to the surface laminated with the resin substrate); the rolling parallel direction in the rolled copper foil, and the flow direction in the electrolytic copper foil). When the arithmetic average roughness Ra is Ra1 and Ra in the MD direction of the opposite surface (corresponding to a surface on which the resin substrate is not laminated) is Ra2, ΔRa = Ra2−Ra1 ≧ 0.01 is satisfied.
When ΔRa = Ra2−Ra1 ≧ 0.01 is satisfied, the smoothness of one surface becomes good, and the copper foil is removed by etching even if roughening treatment is performed to obtain good adhesion to the resin. The transparency of the resin becomes good. Further, since the opposite surface is relatively rough, the surface of the copper foil after the soft etching becomes moderately rough, and the adhesion to the coverlay film is improved. In some cases, the soft etching process can be omitted.

Ra1 is 0.07 μm or less, Ra2 is preferably larger than 0.08 μm, Ra1 is 0.06 μm or less, Ra2 is more preferably larger than 0.09 μm, Ra1 is 0.04 μm or less, and Ra2 is 0. Most preferably, it is larger than 0.09 μm.
When Ra1 exceeds 0.07 μm, it becomes difficult to obtain good transparency of the resin after removing the copper foil by etching when roughening treatment is performed to obtain good adhesion to the resin. There is. On the other hand, when Ra2 is 0.08 μm or less, the adhesiveness with the coverlay described above is lowered, and the adhesive strength with the coverlay film becomes insufficient.
Although there is no lower limit for Ra1, it can be 0.02 μm in consideration of manufacturability and the like.
Ra1 and Ra2 are preferably 0.15 μm or less. When Ra1 or Ra2 exceeds 0.15 μm, when the copper foil is bent, the stress concentration on the surface recesses is increased, which tends to be a starting point of breakage, and a fine circuit is formed when the copper foil is etched. May be difficult.

  The copper foil of the present invention was subjected to 180 ° adhesion bending with a polyimide film surface on the inside of a sample of a single-sided copper clad laminate having a width of 3 mm to 5 mm obtained by laminating a copper foil and a polyimide film having a film thickness of 25 μm. Sometimes, the number of times of bending until the copper foil breaks is preferably 3 times or more, and more preferably 5 times or more. If the flexibility is good so as to satisfy such conditions, the copper foil of the present invention can be suitably used as an FPC for an LCD module.

The copper foil of the present invention can be bonded to a resin substrate from the roughened surface side to constitute a copper clad laminate. The resin substrate is not particularly limited as long as it has characteristics applicable to a printed wiring board and the like. For example, a polyester film such as polyethylene terephthalate (PET), a polyimide film, a liquid crystal polymer (LCP) film, etc. are used. I can do it.
The method of laminating is by laminating and bonding (thermocompression bonding) to a rolled copper foil under a high temperature and high pressure without using an adhesive on a base material such as a polyimide film, or a polyimide precursor. A laminate can be produced by applying, drying, curing, and the like.

(Sv value)
The value of “Sv” is obtained as follows. First, after copper foil is bonded to both sides of the polyimide resin substrate, the copper foil on both sides is removed by etching, and the printed material printed with line-shaped marks is laid under the exposed resin substrate, and the printed material is passed over the resin substrate. Take a picture with a CCD camera. For an image obtained by photographing, the brightness at each observation point is measured along a direction perpendicular to the direction in which the observed line-shaped mark extends, and an observation point-lightness graph is created. In this graph, the difference between the top average value Bt and the bottom average value Bb of the brightness curve generated from the end of the mark to the portion where the mark is not drawn is the gradation difference of brightness, and this is expressed as ΔB (= Bt−Bb). ), The gradation of brightness is set so that ΔB is 40 or more. Further, of the intersections of the lightness curve and Bt, the intersection closest to the line-shaped mark is t1, and the lightness curve and 0. 0 in the depth range from the intersection of the lightness curve and Bt to 0.1 ΔB with reference to Bt. The value of Sv is defined by the following equation (1), where t2 is the intersection closest to the line mark among the intersections with 1ΔB.
(Equation 2)
Sv = (ΔB × 0.1) / (t1-t2) (1)
In the observation position-lightness graph, the horizontal axis represents position information (pixel × 0.1), and the vertical axis represents the value of brightness (gradation).

Here, “top average value Bt of the lightness curve”, “bottom average value Bb of the lightness curve”, and “t1”, “t2”, and “Sv” described later will be described with reference to the drawings.
FIGS. 1A and 1B are schematic views for defining Bt and Bb when the mark width is about 0.3 mm. When the mark width is about 0.3 mm, a V-shaped brightness curve may be obtained as shown in FIG. 1A, or a brightness curve having a bottom as shown in FIG. 1B. . In any case, the “top average value Bt of the lightness curve” indicates the average value of lightness when measured at 5 locations (a total of 10 locations on both sides) at 30 μm intervals from the positions 50 μm away from the end positions on both sides of the mark . On the other hand, the “bottom average value Bb of the lightness curve” indicates the minimum value of lightness at the tip of the V-shaped valley when the lightness curve is V-shaped as shown in FIG. When it has the bottom of (b), the value of the center part of about 0.3 mm is shown.

  FIG. 2 is a schematic diagram that defines t1, t2, and Sv. “T1 (pixel × 0.1)” is a value indicating an intersection point closest to the line-shaped mark among intersection points of the lightness curve and Bt and a position of the intersection point (value on the horizontal axis of the observation point-lightness graph) ). “T2 (pixel × 0.1)” is the line-shaped mark among the intersections of the lightness curve and 0.1ΔB in the depth range from the intersection of the lightness curve and Bt to 0.1ΔB with reference to Bt. And the value (the value on the horizontal axis of the observation point-brightness graph) indicating the position of the intersection closest to. At this time, regarding the slope of the brightness curve indicated by the line connecting t1 and t2, Sv (gradation / pixel × 0.1) calculated by 0.1 ΔB in the y-axis direction and (t1−t2) in the x-axis direction. ). One pixel on the horizontal axis corresponds to a length of 10 μm. Further, Sv is measured on both sides of the mark, and a small value is adopted. Further, when the shape of the lightness curve is unstable and there are a plurality of the “intersections between the lightness curve and Bt”, the intersection closest to the mark is adopted.

In the image taken by the CCD camera, the brightness is high at the portion where the mark is not attached, but the brightness decreases as soon as the end of the mark is reached. If the visibility of the polyimide resin substrate is good, such a lowered state of brightness is clearly observed. On the other hand, if the visibility of the polyimide resin substrate is poor, the brightness does not suddenly drop from “high” to “low” in the vicinity of the edge of the mark, but the decline is moderate and the brightness decline is not good. It becomes clear.
For this reason, with respect to the polyimide resin substrate from which the copper foil has been bonded and removed, the printed matter with the mark placed underneath, the observation point-brightness graph obtained from the image of the mark portion taken with the CCD camera over the polyimide resin substrate It is preferable to control the slope of the lightness curve near the mark end drawn in FIG. More specifically, the difference between the top average value Bt and the bottom average value Bb of the lightness curve is ΔB (ΔB = Bt−Bb), and the line of the intersections of the lightness curve and Bt in the observation point-lightness graph. In the depth range from the intersection of the lightness curve and Bt to 0.1 ΔB with reference to Bt, the value indicating the position of the intersection closest to the shape mark (the value on the horizontal axis of the observation point-lightness graph) is t1. When the value indicating the position of the intersection closest to the line-shaped mark among the intersections of the lightness curve and 0.1ΔB (the observation point—the value on the horizontal axis of the lightness graph) is t2, the above equation (1) It is preferable that Sv defined by is 3.5 or more.
According to such a configuration, the discrimination power of the mark over the polyimide by the CCD camera is improved without being affected by the type and thickness of the resin substrate. For this reason, it is possible to produce a polyimide resin substrate having excellent visibility, and the positioning accuracy by marking when performing a predetermined process on the polyimide resin substrate in an electronic substrate manufacturing process, etc., thereby improving the yield, etc. An effect is obtained. Sv is preferably 3.5 or more, more preferably 4.0 or more, and still more preferably 5.0 or more. The upper limit of Sv is not particularly limited, but is, for example, 70 or less, 30 or less, 15 or less, and 10 or less. According to such a configuration, the boundary between the mark and the non-mark portion becomes clearer, the positioning accuracy is improved, the error due to the mark image recognition is reduced, and the alignment can be performed more accurately.

<Manufacturing method of copper foil>
When the copper foil of the present invention is an electrolytic copper foil, it can be produced by a conventional method.
When the copper foil of the present invention is a rolled copper foil, after hot rolling and chamfering an ingot having a desired composition, cold rolling and annealing are repeated several times (usually about twice), and then the final recrystallization annealing is performed. It can be manufactured by final cold rolling. In order to remove the surface oxide film after annealing, pickling or polishing of the surface may be performed. In the final cold rolling, the material is finished to a predetermined thickness by repeatedly passing (passing) the material through a rolling mill.

In the final cold rolling, it is possible to control ΔRa = Ra2−Ra1 ≧ 0.01 by making the oil film equivalent on one surface of the copper foil smaller than the oil film equivalent on the opposite surface. By controlling the oil film equivalent, deformation of the material surface is constrained by the roll, and an increase in surface roughness accompanying a change in thickness due to rolling can be suppressed. Here, the oil film equivalent is defined by the following equation.
Oil film equivalent = {(rolling oil viscosity [cSt]) × (feeding plate speed [mpm] + roll peripheral speed [mpm])} / {(roll biting angle [rad]) × (yield stress of material [kRa / mm ² ])}
As a method for changing the oil film equivalent on both sides of the copper foil, a known method such as changing the viscosity of the rolling oil on both sides may be used, but it is convenient and preferable to change the temperature of the rolling oil on both sides.
What is necessary is just to adjust the oil film equivalent in both surfaces of copper foil, for example in the range of 10000-30000. The ratio of oil film equivalents on both sides of the copper foil can be (oil film equivalent on one side) / (oil film equivalent on the opposite side) = 0.5 to 0.9.
Moreover, since the unevenness | corrugation of the rolling roll surface used for rolling is easy to transcribe | transfer to a material surface when the value of an oil film equivalent is small, it is preferable that the rolling roll surface is also smooth. For this reason, it is preferable that Ra when it measures in the direction parallel to the rotating shaft of a rolling roll is 0.1 micrometer or less.

<Manufacture of rolled copper foil>
An ingot was cast using tough pitch copper or oxygen-free copper added with an element having the composition shown in Table 1 as a raw material, and hot rolled at 800 ° C. or higher to chamfer the oxide scale on the surface. Thereafter, cold rolling and annealing at 300 to 800 ° C. were repeated to obtain a rolled plate coil having a thickness of 1.0 to 2.0 mm. After the final cold rolling, the copper strip was passed through a continuous annealing furnace at 300 to 800 ° C. to perform final recrystallization annealing.
Next, it was finished to the thickness shown in Table 1 by final cold rolling. In the final cold rolling process, rolling was performed with different oil viscosities on both sides by changing the temperature of the rolling oil between the copper foil on one side and the opposite side and the rolling roll. If the oil viscosity is different, the oil film equivalent on one side and the oil film equivalent on the opposite side are changed, and foils having different surface states after rolling can be obtained.
Moreover, the average roughness Ra when the rolling roll used at this time measured in the direction parallel to the rotating shaft of a roll was 0.08 micrometer.
“TPC + Ag 200 ppm” in the column of composition in Table 1 means that 200 mass ppm of Ag was added to tough pitch copper (TPC) of JIS-H3100 (C1100). “OFC + 1200 ppm Sn” means that 1200 mass ppm of Sn was added to oxygen-free copper (OFC) of JIS-H3100. The same applies to other addition amounts.

One surface of the obtained sample (surface where the glossiness is RA1) was roughened under the following conditions. The conditions for the roughening treatment were generally used for FPC applications as those that would give practically sufficient peel strength.
・ Plating bath composition: Cu15Ra / L, Co8.5Ra / L, Ni8.6Ra / L
-Treatment solution pH: 2.5
・ Processing temperature: 38 ℃
・ Current density: 20 A / dm ²
・ Plating time: 2.0 seconds

Various evaluation was performed as follows about each sample of the Example and comparative example which were produced as mentioned above.
Glossiness;
Using a gloss meter Handy Gloss Meter PRA-1 manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS Z8741, the glossiness of the copper foil before the roughening treatment was determined at an incident angle of 60 degrees in the rolling direction.

Bendability;
When a sample of a single-sided copper clad laminate with a width of 3 mm was prepared by laminating a roughened surface side of a copper foil and a polyimide film with a film thickness of 25 μm, and when 180 ° contact bending was performed with the polyimide film surface on the inside, The number of bendings until the foil broke was measured. If the number of times of bending is 3 or more, the bendability is good.
Peel strength (adhesive strength);
With respect to the single-sided copper-clad laminate, the peel strength was measured in a normal state (left at room temperature for 24 hours) with a tensile tester in accordance with IPC-TM-650. If the above normal peel strength is 0.7 N / mm or more, it can be used for a copper-clad laminate (judgment “◯”), and those with less than 0.7 N / mm cannot be used (judgment “x”) did.

Peel strength (adhesive strength) between the opposite surface of copper foil (surface with arithmetic average roughness Ra2) and coverlay;
The above single-sided copper-clad laminate is overlaid with a cover lay (polyimide film (trade name: CISA) manufactured by Nikkan Kogyo Co., Ltd., thickness 25 μm), and heated and pressure bonded for 1 hour under conditions of 160 ° C. and 3 MPa pressure by hot pressing. A press sample was made. The obtained press samples were evaluated for peel strength (adhesive strength) according to JPCA-BM-02. If the peel strength is 0.6 N / mm or more, it shall be one with excellent adhesion that can be used for copper clad laminates (judgment “◯”), and one with less than 0.6 N / mm cannot be used due to poor adhesion (Judgment “x”).

Visibility (haze value);
The evaluation of the transparency of the resin after removing the copper foil by etching was performed using the haze value. Here, the haze value (%) is a value calculated by (diffuse transmittance) / (total light transmittance) × 100.
The said roughening process was performed to one side (surface where glossiness becomes G1) of each sample rolled copper foil.
Next, using the two copper foils after the roughening treatment, the roughened surface side of each copper foil is bonded to both sides of a polyimide film with a thermosetting adhesive for lamination (thickness 50 μm, Upilex made by Ube Industries). The copper foil was removed by etching (ferric chloride aqueous solution) to prepare a sample film. A haze value of a sample film was measured using a haze meter HM-150 manufactured by Murakami Color Research Laboratory based on JIS K7136 (2000). A haze value of 70 or less was marked with ○, and a haze value greater than 70 was marked with ×.

Visibility (Sv value);
Using two copper foils after the above roughening treatment, the roughened surface side of each copper foil was bonded to both sides of a polyimide film (Kaneka thickness 50 μm), and the copper foil was dissolved and removed with a ferric chloride aqueous solution. A sample film was prepared. Next, a printed material on which a line-shaped black mark is printed is laid under the sample film, the printed material is photographed with a CCD camera through the sample film, and the observed line-shaped mark extends in the image obtained by photographing. The brightness at each observation point was measured along the direction perpendicular to the direction. In the observation point-lightness graph thus measured, the slope (angle) of the lightness curve generated from the end of the mark to the portion where no mark was drawn was measured. FIG. 3 is a schematic diagram showing the configuration of the measuring apparatus used at this time and the method of measuring the slope of the brightness curve. Further, ΔB, t1, t2, and Sv were measured by the following photographing apparatus as shown in FIG. One pixel on the horizontal axis corresponds to a length of 10 μm.
The photographing device includes a CCD camera, a stage (white) on which a polyimide resin substrate is placed with a marked paper underneath, an illumination power source that irradiates light onto the polyimide film photographing unit, and a paper with a mark to be photographed. Is provided with a transfer machine for transferring the polyimide film for evaluation placed on the stage. The main specifications of the set of imaging devices used for the measurement are shown below.
・ Photographing device: Sheet inspection device Mujken manufactured by Nireco Corporation
CCD camera: 8192 pixels (160 MHz), 1024 gradation digital (10 bits)
・ Power supply for lighting: High frequency lighting power supply ・ Lighting: Fluorescent lamp (30W)
For the lightness shown in FIG. 3, 0 means “black”, lightness 255 means “white”, and the gray level from “black” to “white” (black and white shading, gray scale) Is divided into 256 gradations for display. Those having an Sv value of 3.5 or more were marked with ◯, and those with an Sv value less than 3.5 were marked with ×.

  The obtained results are shown in Table 1.

  As is apparent from Table 1, in each example satisfying ΔRa = Ra2−Ra1 ≧ 0.01, the adhesion of the copper foil to the resin, the visibility of the resin, the bendability, and the adhesiveness to the coverlay are It was good. In each example, Ra1 was 0.07 μm or less, and Ra2 was larger than 0.08 μm.

On the other hand, in the case of Comparative Examples 1 and 2 where ΔRa = Ra2−Ra1 <0.01, the visibility of the resin was poor. Moreover, in the case of the comparative example 1, since Ra2 was 0.08 micrometer or less and the opposite surface became too smooth, the adhesiveness with a coverlay was also inferior.
In the case of Comparative Example 3 where ΔRa = Ra2−Ra1 <0.01 and Ra2 is 0.08 μm or less, the visibility of the resin was good, but the adhesiveness with the coverlay was inferior.

Claims (19)

  A copper foil in which ΔRa = Ra2−Ra1 ≧ 0.01, where Ra1 is the arithmetic average roughness Ra specified in JIS-B0601 in the MD direction of one surface and Ra2 is the Ra in the MD direction of the opposite surface.   The copper foil according to claim 1, wherein Ra1 is 0.07 µm or less and Ra2 is larger than 0.08 µm.   The copper foil according to claim 1, wherein Ra1 is 0.06 μm or less and Ra2 is larger than 0.09 μm.   The copper foil according to claim 1, wherein Ra1 is 0.04 μm or less and Ra2 is larger than 0.09 μm.   Ra1 and Ra2 are 0.15 micrometer or less, The copper foil in any one of Claims 1-4.   The copper foil according to claim 1, comprising a rolled copper foil.   Contains in total 10 to 1500 mass ppm of one or more selected from the group of Ag, Sn, Mg, In, B, Ti, Zr, Zn, Ni, Si, P, Cr and Fe, and the balance Cu and The copper foil according to claim 6, comprising inevitable impurities.   When a single-sided copper clad laminate having a width of 3 mm or more and 5 mm or less obtained by laminating the copper foil and a polyimide film having a film thickness of 25 μm was subjected to 180 ° adhesion bending with the polyimide film surface inside, the copper The copper foil according to any one of claims 1 to 7, wherein the number of bending times until the foil breaks is 3 or more.   The copper foil according to claim 8, wherein the number of times of bending until the copper foil breaks is 5 or more.   Two copper foils having a Ra1 of 0.07 μm or less are prepared, and the roughened surface formed by roughening the one surface to form roughened particles is bonded to both surfaces of the polyimide resin substrate, and then etched. The copper foil according to claim 1, wherein the resin substrate from which the copper foil has been removed has a haze value of 72 or less.   The copper foil according to claim 10, wherein when Ra1 is 0.06 µm or less, the haze value of the resin substrate is 67 or less.   The copper foil according to claim 10, wherein when Ra1 is 0.04 µm or less, the haze value of the resin substrate is 55 or less. Two copper foils having a Ra1 of 0.07 μm or less are prepared, and the roughened surface formed by roughening the one surface to form roughened particles is bonded to both surfaces of the polyimide resin substrate, and then etched. To remove the copper foil on both sides,
When the printed matter on which the line-shaped mark is printed is laid under the exposed resin substrate, and the printed matter is photographed with a CCD camera through the resin substrate,
For the image obtained by the photographing, the observation point-lightness graph was obtained by measuring the brightness for each observation point along the direction perpendicular to the direction in which the observed line-shaped mark extends,
The difference ΔB (ΔB = Bt−Bb) between the top average value Bt and the bottom average value Bb of the brightness curve generated from the end of the mark to the portion where the mark is not drawn is 40 or more, and the observation point-lightness graph In the depth range from the intersection of the lightness curve and Bt to 0.1 ΔB with reference to Bt, the intersection point closest to the line-shaped mark is the intersection point of the lightness curve and Bt. The copper foil according to claim 1, wherein Sv defined by the following equation (1) is 3.5 or more when an intersection closest to the line-shaped mark among intersections with 0.1ΔB is t2. .
Sv = (ΔB × 0.1) / (t1-t2) (1)   The copper foil according to claim 13, wherein Ra1 is 0.06 μm or less, and Sv defined by the formula (1) in the brightness curve is 4.0 or more.   The copper foil according to claim 13, wherein Ra1 is set to 0.04 μm or less, and Sv defined by the formula (1) in the brightness curve is 5.0 or more.   It is a manufacturing method of the copper foil in any one of Claims 5-9, Comprising: In the last cold rolling process, the manufacturing method of the copper foil which makes the oil film equivalent of said one surface less than the oil film equivalent of the said opposite surface .   The manufacturing method of the copper foil of Claim 16 which performs the said last cold rolling using the rolling roll whose Ra when measured to the direction parallel to the rotating shaft of a roll is 0.1 micrometer or less.   The copper clad laminated board comprised by laminating | stacking the copper foil and resin substrate in any one of Claims 1-15.   The flexible printed wiring board using the copper clad laminated board of Claim 18.