KR20140060580A

KR20140060580A - Copper foil for flexible printed wiring board

Info

Publication number: KR20140060580A
Application number: KR1020147009943A
Authority: KR
Inventors: 슈타로 니시다; 다이스케 사메지마; 가이치로 나카무로
Original assignee: 제이엑스 닛코 닛세키 킨조쿠 가부시키가이샤
Priority date: 2011-09-21
Filing date: 2012-09-18
Publication date: 2014-05-20
Also published as: JP2013069787A; WO2013042663A1; JP5676401B2; TWI528875B; CN103828491B; CN103828491A; KR101522148B1; TW201325333A

Abstract

A copper foil for a flexible printed wiring board having high plate thickness accuracy is provided. The average of the surface roughness in a direction parallel to the rolling Ra _(avg Ra) is 0.01 ~ 0.15 ㎛ and, ΔRa Ra = _max - _min Ra is not more than 0.025 ㎛ copper foil for flexible printed wiring board.

Description

[0001] COPPER FOIL FOR FLEXIBLE PRINTED WIRING BOARD [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper foil for a flexible printed wiring board which is required to have flexibility, and more particularly to a copper foil used for a flexible printed wiring board to which fine wiring processing is applied.

A flexible printed wiring board (FPC) is formed by bonding a metal, which is a conductive layer, and a flexible insulating substrate typified by a resin film. Generally, a copper foil is used for the conductive layer, and a rolled copper foil excellent in flexibility is used particularly for applications requiring bending property.

A general FPC manufacturing process is as follows. First, the copper foil is bonded to the resin film. In the bonding, there is a method of imidizing by applying a heat treatment to a varnish applied on a copper foil, or a method of laminating a resin film and an adhesive by bonding a copper foil. The copper foil on which the resin film joined by these steps is formed is called CCL (copper clad laminate). The copper foil is recrystallized by the heat treatment in this CCL manufacturing process.

After the photoresist is applied to the copper foil surface of the CCL thus produced, baking of the wiring pattern is performed, then UV exposure and development are carried out, and an unnecessary copper foil is removed by etching to produce an FPC. In recent years, along with miniaturization and high functionality of electronic devices, wiring patterns to be formed tend to be miniaturized, and accordingly, copper foils are required to have high etching properties.

Japanese Unexamined Patent Application Publication No. 2006-283146 discloses a technique for improving the orientation property of a copper foil as a method for obtaining a high etching factor. The X-ray diffraction intensity I of the (100) plane of the rolled surface of the rolled copper foil and the X-ray diffraction intensity I ₀ (100) of the (100) plane of the fine copper copper were measured at 200 ° C for 30 minutes and tempered with a recrystallized structure Is 10? I / I ₀ ? 60, preferably 40? I / I ₀ ? 60.

Japanese Laid-Open Patent Publication No. 2011-12297 discloses a technique of covering at least a part of a copper layer surface with a Cu-Zn alloy layer or a Zn layer and a Cr layer on the surface of the copper foil.

Japanese Patent Application Laid-Open No. 2006-283146 Japanese Laid-Open Patent Publication No. 2011-12297

When the wiring pattern becomes finer, the flow of the etching liquid into the etching portion is restricted, so that the rate of the chemical reaction at the interface is predominant in the process of speeding up the etching reaction. Therefore, the etching progresses in the thickness direction of the copper foil, and the etching progresses also in the circuit width direction.

Therefore, if there is a deviation in the thickness of the copper foil, if the etching conditions are determined so that the circuit width becomes constant, the entire copper foil can not be removed in the thick part, and the circuit is short-circuited. On the other hand, if etching is performed under the condition that etching residues of the copper foil do not occur, the circuit width becomes uneven.

That is, the deviation of the thickness of the copper foil greatly affects the processing precision of the circuit. Therefore, a copper foil excellent in plate thickness accuracy is desired.

However, the development direction of the copper foil for a flexible printed wiring board up to now has been overwhelming in controlling the surface property of the copper foil at a micro-viewpoint aiming at improvement in flexibility. For this reason, the problem of improving the accuracy of the thickness of the copper foil at the macroscopic viewpoint and improving the circuit processing precision of the flexible printed wiring board is unresolved.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a copper foil for a flexible printed wiring board suitable for fine pitch processing. It is another object of the present invention to provide a method for producing such a copper foil.

The copper foil is divided into rolled copper foil and electrolytic copper foil. In the rolled copper foil, the plate thickness precision is often caused by the function (capability) of the rolling mill. However, in the rolling mill in the present situation, the plate thickness precision is limited to ± 1.6% at a target plate thickness of 10 μm. As a fundamental countermeasure, it is desired to modify or develop the rolling mill, but it is difficult to carry out the rolling mill immediately because a large amount of research and development cost is required.

The inventors of the present invention have conducted research to solve the above problems under such circumstances. As a result, the present inventors have found that, in the manufacturing process of the rolled copper foil, most of the rolling is performed for the plate thickness control in the feedforward, It is to be noted that the deviation of the surface roughness before the final pass of the final cold rolling is one of the factors affecting the plate thickness control and the surface roughness is reduced in the previous step of the final pass, And the plate thickness accuracy is improved. Specifically, a work roll having a small surface roughness is used for the rolling before the final pass, and a work roll having a desired surface roughness is used for the final pass, thereby obtaining a copper foil having a final plate thickness accuracy and a desired surface roughness I could see that I could. In the copper foil for a flexible printed wiring board, a certain surface roughness is required from the viewpoint of adhesion with a flexible insulating substrate such as a resin film. By minimizing the surface roughness before the final pass of the final cold rolling, It can have a desired surface roughness.

(Ra _avg ) of the surface roughness Ra in the rolling parallel direction is 0.01 to 0.15 占 퐉, and? Ra = Ra _max - Ra _min is 0.025 占 퐉 or less in the rolling parallel direction. It is a copper foil for a wiring board.

In one embodiment of the copper foil for a flexible printed wiring board according to the present invention, the thickness of the copper foil is 5 to 20 占 퐉.

In another embodiment of the copper foil for a flexible printed wiring board according to the present invention, the difference between the maximum value (t _max ) of the thickness of the copper foil and the average value (t _avg ) of the plate thickness or the difference between the minimum value (t _min ) mean a percentage of the value of any of the larger of the difference between the average value of the plate thickness (t _avg) of (t _avg) is 1.3% or less.

In one embodiment of the copper foil for a flexible printed wiring board according to the present invention, the ratio (RSm / RSm _avg ) of DELTA RSm = RSm _max - RSm _min to the average (RSm _avg ) of the surface roughness RSm in the rolling parallel direction is 0.5 Or less.

In another aspect, the present invention is a flexible printed wiring board using a copper foil according to the present invention as a conductor layer.

In another aspect of the present invention, in the final cold rolling step, the surface roughness Ra of the work roll used for the final pass is 0.03 占 퐉 or more, and the surface roughness Ra of the work roll used for one pass immediately before the final pass is Is less than 0.03 占 퐉.

Since the copper foil according to the present invention is excellent in plate thickness accuracy, it is possible to suppress an error in the amount of etching, so that it is possible to improve the linearity of wiring in a mass-produced flexible printed wiring board. Therefore, the copper foil according to the present invention can be preferably used for fine pitch processing.

The copper foil substrate used in the present invention is a rolled copper foil. &Quot; Copper foil " includes a copper alloy foil. The material of the copper foil is not particularly limited and may be suitably selected in accordance with the application and required characteristics. Ag, Fe, In, Te, or the like is added to copper (oxygen free copper, tough pitch copper, and copper copper) in addition to copper (oxygen free copper, tough pitch copper, Cu-Ni-Si based copper alloy to which Ni, Si or the like is added, Cu-Zr based alloy to which Cr, Zr or the like is added, and copper alloy such as Cu-Cr-Zr based copper alloy. The rolled copper foil is excellent in that it has high strength and can cope with an environment in which vibration is continuously generated, and has high flex resistance.

The thickness of the copper foil is not particularly limited and may be appropriately selected depending on the required characteristics. Generally, it is 1 to 100 占 퐉. However, when the copper foil is used as a conductor layer of a flexible printed wiring board, the copper foil can be made thinner to obtain higher flexibility. From such a point of view, it is typically 2 to 50 μm, more typically about 5 to 20 μm.

The copper foil according to the present invention is defined by the average (Ra _avg ) of the surface roughness Ra in the rolling parallel direction and? Ra = Ra _max - Ra _min . Ra is a value obtained by folding the roughness curve back from the center line and dividing the area obtained by the roughness curve and the center line by the reference length L, and measured in accordance with JIS B 0601: 2001. In the present invention, the average of the surface roughness Ra (Ra _avg ) is an arbitrary 10 point average, and in the present invention,? Ra means the difference between the maximum value Ra _max and the minimum value Ra _min to be. However, the arbitrary 10 points referred to herein do not mean 10 points in the vicinity of each other, for example, in the case of a coil phase, it is preferable that at least 50 points in the rolling direction, 10 points are selected at an interval of 100 mm or more, more preferably at intervals of 500 mm or more. The Ra at each measurement point is given by an average value measured three times in the vicinity of the measurement point. Each measurement point is set at the center in the width direction. If the measurement interval of 50 mm or more can be ensured even in the state of being laminated with the resin, the surface roughness of the sheet can be measured.

The copper foil according to the present invention is characterized in that it satisfies 0.01 to 0.15 탆 with respect to the average (Ra _avg ) of the surface roughness Ra in the rolling parallel direction. 0.01 ㎛ ≤ reason why the Ra _avg ≤ 0.15 ㎛ a condition, if the Ra _avg is less than 0.01 ㎛, the surface when the smoothing to be greater than the other hand, 0.15 ㎛ is not obtained a sufficient adhesion with the resin layer, even though the rolling before the final pass Even if there is little variation in surface roughness, the deviation becomes large due to the rolling of the final pass. However, from the viewpoint that the surface quality such as surface scratches and the like can be made stable with less appearance defects, _Raavg is preferably 0.03 占 퐉 or more, and more preferably 0.03 占 퐉 _Raavg ? 0.1 占 퐉.

It is further characterized in that? Ra = Ra _max - Ra _min is 0.025 占 퐉 or less. The condition that? Ra = Ra _min - Ra _min is 0.025 占 퐉 or less is that if? Ra of the copper foil after the final rolling as a product is 0.025 占 퐉 or less,? Ra before final pass of final rolling may be 0.025 占 퐉 or less. If ΔRa before the final pass of the final rolling is 0.025 μm or less, the influence on the plate thickness control due to the deviation (variation) of the surface roughness at the final pass of the final rolling is small, . When? Ra exceeds 0.025 占 퐉,? Ra before the final pass of the final rolling is often more than 0.25 占 퐉. In this case, the illuminance at the point where the surface roughness is large and the surface roughness is small is the final pass The influence on the plate thickness control is different, and as a result, the deviation of the thickness of the final rolled plate in the condition becomes large. ? Ra is preferably 0.025 占 퐉 or less, more preferably 0.020 占 퐉 or less, and typically 0.001 to 0.025 占 퐉.

On the other hand, in the rolled copper foil, apart from the surface roughness determined by the roll mark, there exist a large number of depressions unique to the rolled copper foil called oil pits. The oil pit is a depressed portion generated by pressing the rolling oil into the pressurized steel strip, and the density of the oil pit on the surface differs depending on the thickness of the oil film of the rolling oil. If the densities of the oil pits on the surface are different, the thickness of the copper foil obtained by the gravimetric method is also influenced and becomes a factor of the deviation. Therefore, it is preferable that the oil pits are uniformly distributed on the surface of the copper foil.

The amount of oil pits to be generated can be the surface roughness RSm in the rolling parallel direction as an index. When RSm is large, the oil pit on the surface is small and when RSm is small, the amount of oil pit is large. The reason for influencing the specification of the plate thickness precision is that the ratio of? RSm = RSm _max - RSm _min (? RSm / _min ) to the average (RSm _avg ) of the surface roughness RSm in the rolling parallel direction, RSm _avg ) was used as an index. The smaller the? RSm / RSm _avg , the more uniform the oil pits are distributed on the surface of the copper foil. RSm _avg . This is because, in the deviation of the distribution, it can not be said that the deviation is necessarily large even if? RSm is large. That is, even though the same ΔRSm, since the RSm _avg not large as the deviation of the distribution is large the effect is small, and if the RSm _avg is small, the larger the effect size due to a deviation of the distribution.

By increasing the rolling speed, increasing the viscosity of the rolling oil, or decreasing the reduction rate per pass, the amount of oil pits generated increases and RSm tends to be small. On the other hand, if the rolling speed is slow, the viscosity of the rolling oil is low, or the rolling reduction per pass is made large, the amount of oil pits generated is reduced, and RSm tends to increase.

RSm is the mean value of the peak-to-period spacing obtained from the intersection where the roughness curve intersects the mean line, measured according to JIS B 0601: 2001. In the present invention, the average (RSm _avg ) of the surface roughness RSm is an average of 10 arbitrary points, and? RSm is the difference between the maximum value RSm _max and the minimum value RSm _min among the measured 10 points Ra. However, the arbitrary 10 points herein do not mean 10 points in the vicinity of each other, for example, in the case of a coil phase, the intervals of at least 50 mm in the rolling direction, preferably 100 10 points are selected at an interval of at least mm, more preferably at intervals of 500 mm or more. The RSm at each measurement point is given by an average value measured three times in the vicinity of the measurement point. Further, each measurement point is set as RSm at the center in the width direction. If the measurement interval of 50 mm or more can be ensured even in the state of being laminated with the resin, the surface roughness of the sheet can be measured.

In a preferred embodiment of the copper foil according to the present invention,? RSm / RSm _avg is 0.5 or less, typically 0.3 to 0.5.

In a preferred embodiment of the copper foil according to the present invention, the difference between the maximum value t _max of the thickness of the copper foil and the average value t _avg of the plate thickness or the difference between the minimum value t _min and the average value of the plate thickness t _avg ) To the average value (t _avg ) of the plate thickness can be set to 1.3% or less. This ratio may be preferably 1.2% or less, more preferably 1.1% or less, and typically 0.05 to 1.2%.

Next, a method of manufacturing a copper foil according to the present invention will be described. The surface roughness Ra can be controlled by adjusting the surface roughness of the work roll. For example, Ra of the rolled copper foil obtained by using a work roll having a large Ra is also increased. On the other hand, The Ra of the rolled copper foil is also reduced. On the other hand, in general, the value of the deviation itself becomes larger as the average value becomes larger. Similarly, with respect to the value of the deviation of the surface roughness Ra, the larger the average value of the surface roughness Ra is, the larger the value of the deviation is, so that the average value of the surface roughness Ra can be reduced in order to reduce the value of the deviation of the surface roughness Ra.

However, in each product, there is a demand for surface roughness required from the viewpoint of adhesion with a flexible insulating substrate, and therefore, it is necessary to finally set the value to a desired value. In cold rolling, it is preferable that the surface roughness is rough to some extent from the viewpoint of the rolling efficiency that the rolling speed can be set high.

Thus, for example, a work roll having a small surface roughness is used only for one pass just before the final pass of the final cold rolling to form a copper foil having a small surface roughness, that is, a smooth surface, To obtain the desired surface roughness Ra.

This makes it possible to obtain a copper foil having a desired surface roughness while having a high thickness accuracy and having good adhesion with an active material. That is, the surface roughness Ra may be a coarse roll up to two passes before the final pass, and only one pass immediately before the final pass, and a roll having a roughness smaller than the entire pass and the final pass are used.

A work roll having a small surface roughness may be used for not only one pass immediately before the final pass but also for the previous passes. However, a roll having a small surface roughness can not increase the rolling speed. Therefore, usually only the work roll used for the pass just before the final pass reduces the surface roughness. However, in the case of ignoring the productivity aspect, it is more effective to reduce the variation in the surface roughness by using a roll having a smaller surface roughness even for a path before one pass just before the final pass. For example, it is effective to use a roll having a small surface roughness only in the two passes immediately before the final pass.

The work roll having a surface roughness Ra exceeding 0.01 mu m is used so that the average (Ra _avg ) of Ra in the rolling parallel direction of the copper foil is 0.01 to 0.15 mu m in the final pass, In order to reduce the value of the deviation, the surface roughness Ra of the work roll used for one pass just before the final pass must be smaller than the work roll used for the final pass. Therefore, the surface roughness Ra of the work roll used in one pass just before the final pass is preferably 0.01 탆 or less.

However, if a surface roughness Ra of 0.01 mu m or less is used to stably produce a roll having no apparent problems such as surface scratches, a high technique is required and the cost is relatively high.

Therefore, it is preferable that the work roll used in the final pass has a surface roughness Ra of 0.03 mu m or more, and therefore, the surface roughness Ra of the work roll used for one pass just before the final pass is preferably less than 0.03 mu m.

In order to reduce the deviation of the surface roughness RSm, it becomes important to make the distribution of the oil pits uniform. To make the distribution of oil pits uniform, it is important to keep the viscosity of the rolling oil constant during rolling among several factors. The viscosity of the rolling oil is basically determined depending on the kind of the rolling oil, but the viscosity of the rolling oil gradually decreases due to the processing heat during rolling. As the degree of compression of the rolling oil into the surface of the copper foil changes with the change of the viscosity of the rolling oil, the variation of the oil pit distribution results.

For example, when the rolling oil is kept at about 25 占 폚 in the temperature adjustment before rolling, the rolling oil is sprayed on the work roll during rolling, heat is transferred from the work roll raised by the processing heat, and the rolling oil is raised to about 40 占 폚. If this state can be maintained, the deviation of the distribution of the oil pits is small, and there is no problem in the shape of the copper foil. However, when the temperature of the rolling oil is insufficient and the rolling oil temperature is more than 40 占 폚, the surface properties of the copper foil become not only uniform but also affects the plate shape. Therefore, in order to adjust the temperature of the rolling oil during rolling to about 40 캜, it is necessary to comprehensively adjust the rolling oil temperature, the rolling speed, the degree of processing, and the like before the rolling.

A flexible printed wiring board can be manufactured by a conventional means using a conductor layer made of a rolled copper foil according to the present invention. Hereinafter, a production method will be exemplified.

First, a copper foil and a flexible insulating substrate are bonded to each other to produce a copper clad laminate. The flexible insulating substrate on which the copper foil is laminated is not particularly limited as long as it has characteristics applicable to a flexible printed wiring board. For example, a resin film such as a polyester film or a polyimide film can be used.

The polyimide film or the polyester film and the copper foil can be bonded using an epoxy or acrylic adhesive (three-layer structure). As a method of not using an adhesive (two-layer structure), a casting method in which a polyimide varnish (polyamide varnish) which is a precursor of polyimide is applied to a copper foil and imidization is performed by heating, A lamination method in which a thermoplastic polyimide is applied, a copper foil is laminated thereon, and the mixture is heated and pressed. In the casting method, it is effective to apply an anchor coat material such as thermoplastic polyimide in advance before applying the polyimide varnish.

The process for producing a printed wiring board from a copper clad laminate may be carried out by a method well known to those skilled in the art. For example, an etching resist may be applied only to a necessary portion of a copper foil surface of a copper clad laminate as a conductor pattern, The unnecessary copper foil is removed to form a conductor pattern, and then the etching resist is peeled off and removed to expose the conductor pattern.

Example

Hereinafter, embodiments of the present invention will be described, which are provided for easier understanding of the present invention, and are not intended to limit the present invention.

&Lt; Example 1 (Influence of deviation of surface roughness Ra) >

[Production of rolled copper foil]

The ingot with tough pitch copper was hot-rolled, annealing and cold rolling were repeated, and finally cold-rolled to obtain rolled copper foils (No. 1 to 6) having a thickness of 10 m or more in the rolling direction. The thickness of the copper foil is as follows. 1 to 4 were set to 12 탆, 18 탆, 36 탆 and 6 탆, respectively. 5 to 6 were set to 10 탆. Table 1 shows the surface roughness of the work roll used only in one pass just before the final pass in the final cold rolling and the work roll surface roughness used in the final pass. The viscosity of the used rolling oil was 7.0 cSt (40 캜), and the temperature of the rolling oil in the final cold rolling was controlled to about 40 캜. The surface roughness of the work roll was measured by a contact type surface roughness meter according to JIS B 0601: 2001.

The obtained rolled copper foil was placed on a glass plate and fixed, and Ra _avg , ΔRa, RSm _avg (Example 2 only) and ΔRSm (Example 2 only) were calculated based on the measurement method described above using a confocal microscope HD100D manufactured by Laser Tec Corporation Respectively. The results are shown in Table 1. The distance between each measuring point was set to 50 mm in the rolling direction.

[Evaluation of plate thickness accuracy]

The thickness of the rolled copper foil was measured in accordance with the gravimetric method (IPC-TM-650). An arbitrary length in the rolling direction of 10 m was selected from the obtained copper foil, and 10 points of the plate thickness were measured at 1 m intervals therebetween. The plate thickness T of each measurement point was taken as an average value measured three times. T _avg is the average value of T at 10 points, T _max is the maximum value of T at 10 points, and T _min is the minimum value of T at 10 points. In Table 1, the larger one of (T _avg - T _min ) / T _avg and (T _max - T _avg ) / T _avg is described as "plate thickness deviation (%)".

No. 1 to No. 4 is an example of the invention, and the variation of the plate thickness can be suppressed to 1.3% or less.

No. 5, the surface roughness of one pass just before the final pass was large, so that? Ra could not be sufficiently controlled. No. 6, instead of increasing the surface roughness of the 1-pass work roll just before the final pass, the surface roughness of the work roll of the last pass was made small, but the value of? Ra could still not be sufficiently controlled.

[Evaluation of Linearity of Circuit]

Each rolled copper foil obtained by the above production method was annealed at 350 占 폚 for 15 minutes and then laminated with a dry film resist (SUNFORT, thickness 20 占 퐉, Asahi Kasei Co., Ltd.), and a circuit having a circuit width of 50 占 퐉 and a circuit interval of 50 占 퐉 A book pattern circuit pattern was exposed and developed. The etching factor ((copper foil thickness) x 2 / (bottom width of each circuit - top width of each circuit)) of 3.5 to 4.5 is obtained by using an aqueous ferric chloride solution of 45 캜 and 45 캜 as an etching solution The copper foil was etched under the conditions. The circuit after the etching was observed with a microscope from above, and the outline of the periphery of the circuit was visually evaluated.

⊚: When observed under a microscope, the outline of the peripheral portion of the circuit is close to a straight line.

A: When observed under a microscope, a curvature is observed at half or less of the observation length of the outline of the peripheral portion of the circuit.

B: When observed under a microscope, the curvature is observed at a portion exceeding half of the observation length of the contour of the peripheral portion of the circuit, but there is also a point at which the curvature is not seen.

X: When observed under a microscope, the entire outline of the peripheral portion of the circuit is wavy with curvature.

&Lt; Example 2 (Influence of oil pit distribution) >

[Production of rolled copper foil]

The ingot with tough pitch copper was subjected to hot rolling, annealing and cold rolling were repeated, and finally cold rolling was performed to obtain rolled copper foil (No. 7 to 12) having a thickness of 10 m and a rolling direction length of 10 m or more. In the final cold rolling, the surface roughness Ra of the work roll used before the final pass was 0.010 mu m, and the work roll surface roughness Ra used in the final pass was 0.050 mu m. The viscosity of the used rolling oil was 7.0 cSt (40 캜), and in the present example, the temperature of the rolling oil during the final cold rolling was adjusted to be around 40 캜. Various properties were evaluated in the same manner as in Example 1. The test results are shown in Table 2.

Inventive No. 7 to 9, since the temperature control of the rolling oil of the final rolling mill is controlled at 40 占 폚, the distribution of the oil pits is uniform, the deviation is small, and the deviation of the plate thickness is as small as less than 1.2%.

Inventive No. 10 to 12 are graphs showing the results of evaluation of tensile strengths of rolling oils in the final cold rolling mill. 7 to 9 under the same conditions. Here, since the temperature of the rolling oil in the final cold rolling mill was not sufficiently controlled, the temperature rose to more than 40 ° C and to about 45 ° C. As a result, the distribution of the oil pits could not be made uniform, and the case where the deviation of the plate thickness exceeded 1.2% was shown.

Claims

The average of the surface roughness in a direction parallel to the rolling Ra _(avg Ra) is 0.01 ~ 0.15 ㎛ and, ΔRa Ra = _max - _min Ra is not more than 0.025 ㎛ copper foil for flexible printed wiring board.

The method according to claim 1,
Wherein the thickness of the copper foil is 5 to 20 占 퐉.

3. The method according to claim 1 or 2,
The difference between the maximum value t _max of the thickness of the copper foil and the average value t _avg of the plate thickness or the difference between the minimum value t _min and the average value t _avg of the plate thickness, (T _avg ) of the copper foil is 1.3% or less.

4. The method according to any one of claims 1 to 3,
Wherein a ratio (DELTA RSm / RSm _avg ) of DELTA RSm = RSm _max - RSmin _min to an average (RSm _avg ) of the surface roughness RSm in the rolling parallel direction is 0.5 or less.

A flexible printed wiring board using the copper foil according to any one of claims 1 to 4 as a conductor layer.

Wherein the surface roughness Ra of the work roll used in the final pass is 0.03 占 퐉 or more and the surface roughness Ra of the work roll used in one pass immediately before the final pass is less than 0.03 占 퐉 in the final cold rolling step, A method for manufacturing a copper foil for use.