KR20170113092A - Copper foil, copper-clad laminate, and flexible printed wiring board and electronic device - Google Patents

Abstract

(PROBLEMS) Provided are a copper foil, a copper clad laminate, a flexible printed board, and an electronic apparatus, which are less prone to wrinkle during lamination with the resin layer even if their thickness is thin.
A copper foil having a thickness of 3 to 8 占 퐉 and containing copper of 99.90% or more by mass as a copper foil having a length L of 50 mm along the TD direction according to JIS-B0601 (2013) The average length Wsm of the curved curve elements is 2.5 to 20.0 when the curved line is obtained by cutting off the short wavelength and long wavelength components under the condition of the outline curve filter? C = 2 mm and the outline curve filter? F = Mm.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a copper foil, a copper clad laminate,

The present invention relates to a copper foil preferably used for a copper clad laminate produced by a lamination method and a cast method, a copper clad laminate using the same, and a flexible printed board and an electronic apparatus.

A flexible wiring board (FPC) used in electronic equipment is formed by laminating a copper foil and a resin to produce a copper clad laminate (CCL) and forming a circuit in the copper foil portion of the CCL. CCL can be produced by a lamination method (Patent Document 1) in which a resin film having a thermoplastic resin and a copper foil are thermally fused (Patent Document 1), a casting method in which a resin varnish is coated on a copper foil to cure the resin (Patent Document 2) Patent Document 3).

As the double-belt press method, the double-belt press apparatus 100 shown in Fig. 1 is used. The double belt press apparatus 100 prepares two seamless steel belts 102a and 102b and wraps each of the belts 102a and 102b between the inlet roll 120 and the exit roll 122 respectively.

When the belts 102a and 102b run closely together, the copper foil 2 and the resin film 4 on the side of the inlet roll 120 are pulled in between the belts 102a and 102b, 102b so as to come out from the side of the exit roll 122.

The CCL can be manufactured by thermocompression bonding the copper foil 2 and the resin film 4 by disposing the heating pressurizing device 110 and the cooling pressurizing device 112 between the belts 102a and 102b.

In recent years, fine pitch and thinness have been required in a flexible wiring board. That is, a copper clad laminate (CCL) substrate to be used as a substrate in this application or a copper foil used for a copper clad laminate is required to be thinner than ever.

Japanese Laid-Open Patent Publication No. 2005-305729 Japanese Patent Application Laid-Open No. 2009-286095 Japanese Laid-Open Patent Publication No. 2011-230308

However, when the thickness of the copper foil is reduced, the copper clad laminate easily wrinkles when laminated with the resin, resulting in lowering of productivity and yield.

Particularly, in a casting method in which a resin varnish is coated on a copper foil, if wrinkles are generated in the copper foil, the production becomes difficult. In the lamination method, a heat roll is used to perform heat fusion. However, when a tensile force is applied to the copper foil between the rolls, wrinkles tend to occur parallel to the tensile direction.

Accordingly, an object of the present invention is to provide a copper foil, a copper clad laminate, and a flexible printed circuit board and an electronic apparatus which are less susceptible to wrinkling when they are laminated with a resin layer even though their thickness is small.

The inventors of the present invention have found that the cause of the occurrence of wrinkles when the copper foil having a small thickness is laminated with the resin layer to produce CCL has a correlation with the surface property of the copper foil.

As a surface property of the copper foil, there can be mentioned a height profile (cross-sectional curve) of the surface by an illuminometer. In the copper foil, a cross-sectional curve of a surface having a length of about 0.1 to 5 mm is generally obtained. And so on.

As a result of the studies by the present inventors, it has been found that the surface property (bending curve) obtained from the section curve of the surface of the copper foil with a long distance has a great correlation with the wrinkles generated when adhering to the resin.

That is, the rolled copper foil of the present invention is a copper foil having a thickness of 3 to 8 占 퐉 and containing copper of not less than 99.90% by mass, and has a sectional curve of a surface of 50 mm along the TD direction according to JIS-B0601 (2013) , The average length Wsm of the bending curve elements is 2.5 to 20.0 mm when the bending curve is obtained by cutting off the short wavelength components and the long wavelength components under the condition of the outline curve filter? C = 2 mm and the outline curve filter? F = 25 mm .

It is preferable that the maximum height bending Wz of the bending curve is 0.00010 to 0.00200 mm.

The rolled copper foil of the present invention preferably contains 10 to 2000 mass ppm of a total of one or more additional elements selected from the group consisting of Ag, Zn, Sn and P as rolled copper foil.

It is preferable that a plating layer composed of at least one element selected from the group consisting of Cu, Ni, Zn and Co is formed on one surface or both surfaces.

The arithmetic mean roughness Ra calculated from the roughness curve is 0.01 to 0.1 mu m and the maximum height roughness Rz is 0.1 to 0.8 when the roughness curve is cut off at the long wavelength component at? C = 0.25 mm from the section curve, Mu m.

The copper clad laminate of the present invention comprises the copper foil and a resin layer.

The flexible printed board of the present invention is formed by using the copper clad laminate and forming a circuit on the copper foil.

The electronic apparatus of the present invention is formed using the flexible printed circuit board.

According to the present invention, even if the thickness of the copper foil itself is thin, it is possible to obtain a copper foil which is less prone to wrinkles during lamination with the resin layer.

1 is a view showing a configuration of a double-belt press apparatus 100. Fig.
2 is a view showing a method of measuring a section curve along the TD direction of the surface of the copper foil.

Hereinafter, a rolled copper foil according to an embodiment of the present invention will be described. In the present invention, "%" means% by mass unless otherwise specified. The rolled copper foil according to the embodiment of the present invention is useful for a copper clad laminate produced by laminating a resin layer such as a resin film, but it is also applicable to the casting method and the double-belt method described above.

<Composition>

The rolled copper foil contains at least 99.90% by mass of copper. Examples of such compositions include tough pitch copper specified in JIS-H3100 (C1100) or oxygen free copper specified in JIS-H3100 (C1020). It is preferable that the rolled copper foil contains 99.90 to 99.999% of copper and 0 to 500 mass ppm of oxygen at a mass ratio.

In addition, about 10 to 2000 mass ppm of the total of one or more additional elements selected from the group consisting of Ag, Zn, Sn and P may be contained in the tough pitch copper or oxygen free copper. By adding these additional elements, the ratio of the {100} orientation improving the bending property and the bending property is increased.

When the total amount of the above elements is less than 10 mass ppm, the bending property of the copper foil may be lowered. When the total amount of the above elements exceeds 2000 mass ppm, the decrease of the electrical conductivity may become remarkable.

In particular, when these added elements are contained in an amount of 10 to 500 mass ppm, the bending property and the bending property can be further improved. Also, when these added elements are contained in an amount of 500 to 2000 mass ppm, they become hard and wrinkles are less likely to occur in the production of CCL.

<Thickness>

The thickness of the copper foil is 3 to 8 탆. A copper foil having a thickness of less than 3 탆 is difficult to manufacture. The reason why the thickness of the copper foil exceeds 8 占 퐉 is that it is difficult to cause wrinkles to be a problem in the present invention, so that the thickness is not covered.

<Plating layer>

A plating layer composed of at least one element selected from the group consisting of Cu, Ni, Zn and Co may be formed on one side or both sides of the copper foil.

These plating layers improve the adhesion with resins when CCLs are laminated with a resin and are generally used as a roughened plating layer.

&Lt; Surface properties of copper foil &

According to JIS-B0601 (2013), the short wavelength and long wavelength components were cut off on the condition of a contour curve filter? C = 2 mm and a contour curve filter? F = 25 mm from a cross-section curve of a surface having a length of 50 mm along the TD direction, When the curve is obtained, the average length (Wsm) of the curved curve elements is 2.5 to 20.0 mm.

Here, the TD (Transverse Direction) direction is a direction perpendicular to the MD direction (Machine Direction). In the case of a rolled copper foil, the TD direction is the direction perpendicular to the rolling direction.

Then, as shown in Fig. 2, the cross-sectional curve S showing the height profile is measured along the length L of 50 mm along the TD direction of the surface of the copper foil 2. When the above-described plating layer is formed on one side of the copper foil, the section curve S of the surface of the copper foil which is not plated is measured. When the above-described plating layer is formed on both surfaces of the copper foil, the arithmetic mean roughness (Ra) is first measured on the surfaces of both plating layers by a method to be described later, and the cross-sectional curve S .

The section curve is a &quot; primary profile &quot; described in JIS-B0601-2013 &quot; 3.1.5 &quot;.

Next, the &quot; bending curve &quot; is obtained as follows. First, from the cross-sectional curve, a curve of a contour curve c: 2 mm (where? C is a filter that defines the boundary between the roughness component and the bending component described in JIS-B0601-2013 "3.1.1.2" The components are removed by a low-pass filter. From this curve, the contour curve filter? F: 25 mm (where? F is the filter defining the boundary between the bending component and the longer wavelength component described in JIS-B0601-2013 &quot; 3.1.1.3 &quot; The roughness component is removed by a high-pass filter, and a bending curve is obtained.

The average length (Wsm) of the bending curve elements is &quot; mean width of the profile elements &quot; described in JIS-B0601-2013 &quot; 4.3.1 &quot;.

The maximum height bend Wz of the bending curve element is the &quot; maximum height of profile &quot; described in JIS-B0601-2013 4.1.3.

The roughness curve is a "roughness profile" described in "3.1.6" of JIS-B0601-2013.

The arithmetic average roughness (Ra) is an arithmetical mean deviation of the assessed profile as described in JIS-B0601-2013 (3.1.6).

The maximum height of roughness (Rz) is the "maximum height of profile" described in "4.1.3" in JIS-B0601-2013.

The shape of the copper foil which causes the wrinkles can be detected by obtaining the cross-sectional curve S from the surface of the length L of 50 mm along the CD direction.

The contour curve filter? C = 2 mm is because the surface irregularities having a wavelength of less than 2 mm have no correlation with the wrinkles. The reason for setting the contour curve filter? F = 25 mm is because the surface irregularities having a wavelength exceeding 25 mm can be regarded as measurement irregularities not caused by the surface shape of the copper foil. The surface irregularities having a wavelength exceeding 25 mm had no correlation with the wrinkles.

By controlling the average length Wsm of the bending curve elements to 2.5 to 20.0 mm, wrinkles are less likely to occur in the copper foil when adhered to the resin, and productivity and yield are improved.

This is because when the CCL is produced using a thin copper foil, the copper foil is sandwiched by a pair of heat rolls in the lamination method and the copper foil 2 is sandwiched between the belts 102a and 102b (see Fig. 1) And is thermally pressed. At this time, if the copper foil has appropriate bending, a gap is formed between the heat roll and each of the belts 102a, 102b and the copper foil, and this gap is a length through which the air passes. Therefore, when a force generating wrinkles is applied to the copper foil at the time of thermocompression bonding, it is considered that the copper foil moves from this gap to disperse the force and is difficult to wrinkle.

As described above, it is considered that the copper foil having the appropriate length of curvature suppresses wrinkles, but even if the period of bending is small, the effect of suppressing wrinkles does not occur.

In short, a slight bending with Wsm of less than 2.5 mm is less effective in suppressing wrinkles, and wrinkles tend to occur even if Wsm exceeds 20.0 mm.

It is preferable that the maximum height bending Wz of the bending curve is 0.00010 to 0.00200 mm.

When Wz is a suitable height in the above range, a clearance is formed between the heat roll or the belts 102a and 102b and the copper foil for the same reason as described above, and when a force that causes wrinkles is applied to the copper foil at the time of thermocompression, It is considered that the copper foil moves from this gap to disperse the force and is hard to wrinkle.

As described above, it is considered that the copper foil having a bend of a suitable height suppresses wrinkles, but even if the height of bending is small, the effect of suppressing wrinkles does not occur.

In short, small bending with Wz of less than 0.00010 mm is less effective in suppressing wrinkles, and wrinkles tend to occur even when Wz exceeds 0.00200 mm.

The arithmetic mean roughness Ra calculated from the roughness curve is 0.01 to 0.1 占 퐉 and the maximum height roughness Rz is calculated from the roughness curve when the roughness curve is obtained by cutting off the long wavelength component at? C = 0.25 mm from the section curve S And is preferably 0.1 to 0.8 mu m.

When Ra or Rz is less than the above range, the surface of the copper foil is excessively smooth and the adhesion with the resin layer may be lowered. When Ra or Rz exceeds the above range, Ra or Rz exceeds 10% with respect to the thickness (3 to 8 占 퐉) of the copper foil, so that the precision of the thickness of the copper foil is lowered and is not suitable for CCL or FPC applications .

Since Ra and Rz are also calculated from the sectional curve S, Ra and Rz are values along the TD direction.

The rolled copper foil of the present invention can be usually produced by repeating several times (usually about twice) of cold rolling and annealing after hot rolling and after machining, then performing final recrystallization annealing, and finally cold rolling to a desired thickness have. Further, after the copper foil is degreased, copper plating may be applied to the one surface (laminate surface with the resin layer) to further improve the adhesion with the resin layer, and further, rust-proofing treatment may be performed and used for the copper clad laminate.

Further, the higher the degree of processing in the final cold rolling step, the finer the deformation-removing annealing is, and the individual recrystallized grains are liable to become larger. From this viewpoint, the degree of processing in the final cold rolling step is usually 95% or more and 99.9% or less, preferably 96% or more and 99% or less.

Alternatively, it may be an electrolytic copper foil.

The copper clad laminate of the present invention is formed by laminating copper foils having the above characteristics on both sides or one side of a resin layer. The resin layer is not particularly limited as long as it has properties applicable to a printed wiring board and the like. For example, a polyester film, a polyimide film, a liquid crystal polymer (LCP) film, a Teflon (registered trademark) film, a polyethylene terephthalate A film, a polyethylene naphthalate film, or the like can be used.

The resin layer itself may be multilayered. For the rigid PWB, paper base phenol resin, paper base epoxy resin, synthetic fiber base epoxy resin, glass / paper composite epoxy resin, glass / glass nonwoven composite base epoxy resin and glass cloth base epoxy resin can be used have.

A method of laminating a copper foil and a resin includes a method of preparing a prepreg in which a substrate such as a glass foil is impregnated with a resin and the resin is hardened to a semi-hardened state in the case of a rigid PWB and the copper foil is superimposed on the prepreg to be heated and pressed . In the case of an FPC, a copper clad laminate can be manufactured by adhering a copper foil to a resin layer such as a polyimide film through an adhesive, or by laminating copper foil under high temperature and high pressure without using an adhesive.

For example, as described in Japanese Laid-Open Patent Publication No. 2011-148192, as a condition for the lamination treatment, a polyimide film coated with a thermoplastic polyimide having adhesive strength in advance is superimposed on a copper foil, A method called a lamination method or a method called a casting method in which a liquid resin is applied to a copper foil and dried on a copper foil. The flexible copper clad laminate obtained by these methods is called a two-layer flexible copper clad laminate. Alternatively, a three-layer flexible copper clad laminate in which a copper foil and a polyimide film are adhered with an adhesive such as an epoxy-based adhesive may be used.

The thickness of the resin (layer) is not particularly limited, but generally about 9 to 50 占 퐉 is used. In addition, a thick resin having a thickness of 50 占 퐉 or more may be used. The upper limit of the thickness of the resin is not particularly limited, but is, for example, 150 占 퐉.

The copper clad laminate of the present invention can be used for various flexible printed boards (printed wiring board (PWB)). The printed wiring board is not particularly limited, but is applicable to single-sided PWB, double-sided PWB, and multi-layer PWB (three or more layers) from the viewpoint of the number of layers of the conductor pattern, for example. The present invention is applicable to Rigid PWB, Flexible PWB (FPC) and Rigid Flex PWB from the viewpoint of kinds of insulating substrate materials.

(Example 1)

<Production of rolled copper foil>

An ingot having a thickness of 100 mm was cast using tough pitch copper or oxygen-free copper added with an element of the composition shown in Table 1 as a raw material, and hot rolling was performed at 800 캜 or higher to a thickness of 10 탆, . Thereafter, cold rolling and annealing were repeated to obtain a rolled sheet coil having a thickness of 0.5 mm.

Thereafter, in the cold rolling after the thickness became 20 占 퐉, the roll of the ceramic sintered body was rolled by a rolling roll different in Wsm of the surface in the axial direction between 2.5 and 20 mm. The Ra of the surface in the direction of the rolling roll was set to 0.04 to 0.1 mu m.

In Comparative Examples 1 and 3, a cold rolled steel sheet having a thickness of 20 占 퐉 was subjected to ultimate steel roll rolling to a final thickness. The Ra of the ultra-hard roll of Comparative Example 3 in the above-mentioned direction was 0.03 mu m.

Comparative Example 2 was a roll of a ceramic sintered body in cold rolling after the thickness became 20 占 퐉, and a rolling roll having a surface Wsm in the above direction exceeding 20 mm was used. The Ra of the rolled roll in the above-mentioned direction was 0.04 to 0.1 탆.

&Quot; OFC-100 ppmAg &quot; in the column of composition in Table 1 means that 100 mass ppm of Ag was added to oxygen-free copper OFC of JIS-H3100 (C1020). "TPC-200 ppmAg" means that 200 mass ppm of Ag was added to tough pitch copper (TPC) of JIS-H3100 (C1100). The same is true for other addition amounts.

&Lt; Surface properties of copper foil &

The surface of the obtained copper foil (without plating) was subjected to measurement of a cross-sectional curve S using a three-dimensional shape measuring instrument (manufactured by KEYENCE Corporation, product name: One shot 3D shape measuring instrument VR-3200) as shown in Fig. Then, Wsm and Wz were acquired with the software attached to the measuring instrument.

The section curves S, curves, and roughness curves were obtained as described above in accordance with JIS-B0601 (2013). Wsm and Wz were also calculated in accordance with JIS-B0601 (2013) as described above.

Ra and Rz were measured using a contact type surface roughness meter (trade name: SE-3400, manufactured by Kosaka Laboratory). Ra and Rz are calculated as described above in accordance with JIS-B0601 (2013).

&Lt; Thickness of copper foil &

And measured according to IPC-TM-650 by gravimetric method.

<Whether or not wrinkles occur during lamination>

The hot roll laminate group shown in Fig. 3 was used to laminate the copper foil 2 on both sides of the polyimide film 4 between the pair of heated rolls 10 and 10, A copper clad laminate was prepared. The heating temperature of the roll 10 was set to 350 캜 and the pressing pressure of the roll 10 and the feeding speed and the tension value of the copper foil 2 and the polyimide film 4 were made equal.

The presence or absence of wrinkles on the front and back copper foils (2) in the two-layer double-side copper-clad laminate after thermocompression was visually confirmed and evaluated according to the following criteria. When the evaluation is &amp; cir &amp; &amp; cir &amp;, it is possible to effectively suppress the occurrence of wrinkles at the time of laminating.

A: No wrinkles were found on any copper foil (2) on the front and back sides

○: Depending on the manner in which the light is irradiated, a light wrinkle which can be visually confirmed on any of the front and back surfaces

X: Wrinkles that can be visually confirmed by at least any of the front and back surfaces regardless of the manner in which light is irradiated

<Flexibility>

First, the following plating treatment of harmonization (International Patent Publication No. 2013108414) was carried out on one side of the copper foil.

Harmonious plating: 3-element copper-cobalt-nickel alloy plating

Plating bath composition: 10 to 20 g / l of Cu, 1 to 10 g / l of Co, 1 to 10 g / l of Ni

Plating bath pH: 1-4

Plating temperature: 40 ~ 50 ℃

Plating current density: 20 to 30 A / dm 2

Electrolytic plating time: 1 to 5 seconds

Next, on both sides of a commercially available polyimide film having a thickness of 12.5 탆 (UFIREX VT, manufactured by Ube Industries, Ltd.), the roughened surface of the copper foil was laminated on each other, followed by thermocompression bonding to produce double-side CCL. With respect to this CCL, the copper foil on one side was removed by etching, and a circuit pattern having a circuit width of 0.3 mm and a space width of 0.3 mm was formed on the copper foil on the opposite side by etching. Thereafter, this circuit was covered with a coverlay film having a thickness of 25 mu m and processed by FPC.

The FPC was subjected to a slide bending test to evaluate its bending property. Specifically, a sliding tester (type TK-107 manufactured by Applied Technology Co., Ltd.) was used, and the slide radius r (mm) was r = 4 mm for Example 9, and for the other Examples and Comparative Examples r = 0.72 mm. In all cases, the FPC was bent at a slide speed of 120 times / minute.

And evaluated according to the following criteria. When the evaluation is &quot; &amp; cir &amp; &amp; cir &amp;

◎: When the electric resistance of the circuit of the copper foil is increased by 5% as compared with that before the test, the number of times of bending is more than 100,000 times

○: When the electric resistance of the circuit of the copper foil is increased by 10% compared with that before the test, the number of bending times is more than 100,000 times

X: The number of bends when the electrical resistance of the circuit of the copper foil was increased by 10% as compared with before the test was less than 100,000 times

&Lt; Adhesion &gt;

Two-sided CCLs were prepared in the same manner as in the evaluation of the bending properties. For this CCL, the copper foil on one side was removed by etching, and the following circuit pattern was formed on the copper foil on the opposite side. Thereafter, it was measured according to "Peeling strength of copper foil" specified in JIS-C6471 (1995), and the adhesion was evaluated. In addition, the dimensions of the double-sided CCL and the circuit pattern formed on the copper foil are in accordance with the subdivision 4 of JIS-C6471 (1995).

And evaluated according to the following criteria. When the evaluation is ○, the flexibility is excellent.

?: 0.7 kN / m or more

X: less than 0.7 kN / m

The obtained results are shown in Table 1.

As is apparent from Table 1, in each of the examples having Wsm of 2.5 to 20.0 mm, it was possible to suppress occurrence of wrinkles of the copper foil in the lamination treatment at the time of CCL production even if the thickness was thin. In addition, the flexural and adhesion properties of CCL were excellent.

In particular, in Examples 1 to 16, in which Wz was 0.00010 to 0.00200 mm, generation of wrinkles of the copper foil in the lamination treatment was more effectively suppressed as compared with the other Examples.

On the other hand, in Comparative Examples 1 and 3 in which Wsm was less than 2.5 mm and Comparative Example 2 in which Wsm exceeded 20.0 mm, wrinkles were remarkably generated in the copper foil in the lamination treatment at the time of CCL production.

In the case of Comparative Example 2, Ra and Rz were less than the specified range, and the surface of the copper foil was too flat and the adhesion was also deteriorated.

2: Surface of copper foil
L: length of 50 mm along the TD direction
S: section curve

Claims (8)

A copper foil having a thickness of 3 to 8 占 퐉 and containing 99.90% or more of copper by mass,
According to JIS-B0601 (2013), the short-wavelength and long-wavelength components were cut off from the sectional curves of the surface having a length of 50 mm along the TD direction under the condition of the outline curve filter? C = 2 mm and the outline curve filter? F = 25 mm, Characterized in that, when a curve is obtained, the average length (Wsm) of the bending curve elements is 2.5 to 20.0 mm. The method according to claim 1,
Wherein the maximum curvature (Wz) of the curved line is 0.00010 to 0.00200 mm. The method according to claim 1,
Wherein the rolled copper foil contains 10 to 2000 mass ppm of a total of one or more additional elements selected from the group consisting of Ag, Zn, Sn and P. The method according to claim 1,
Wherein a plating layer composed of at least one element selected from the group consisting of Cu, Ni, Zn and Co is formed on one surface or both surfaces thereof. The method according to claim 1,
The arithmetic mean roughness Ra calculated from the roughness curve is 0.01 to 0.1 mu m and the maximum height roughness Rz is 0.1 to 0.8 when the roughness curve is cut off at the long wavelength component at? C = 0.25 mm from the section curve, Mu m. A copper clad laminate comprising the copper foil according to any one of claims 1 to 5 and a resin layer laminated. A flexible printed circuit board comprising the copper clad laminate according to claim 6 and a circuit formed on the copper foil. An electronic device using the flexible printed circuit board according to claim 7.

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