JP2019143229A - Copper foil for flexible printed circuit board, and copper clad laminate, flexible printed circuit board and electronic device using the same - Google Patents

Abstract

To provide a copper foil for flexible printed circuit board excellent in etching property, and a copper clad laminate, a flexible printed circuit board, and an electronic device using the same.SOLUTION: There is provided a copper foil for flexible printed circuit board consisting of 99.0 mass% or more of Cu and the balance inevitable impurities, and satisfying one of following (1) to (3) when area percentage of a (101) surface, S, is calculated by applying a rotary treatment by rotation from ND to θ (0 to 90 degrees) with a direction having an angle to MD of φ (0 to 180 degrees) on a surface as a rotation axis on a crystal orientation data of the surface of the copper foil measured by EBSD. (1) Sexpresses a maximum value at θ of 0 degrees or more and less than 30 degrees, and the maximum value is 0.4 or more. (2) Sexpresses a maximum value at θ of 30 degrees to 45 degrees, and the maximum value is 0.2 or more. (3) Sexpresses a maximum value at θ of over 45 degrees and 60 degrees or less, and the maximum value is 0.4 or more.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a copper foil suitable for a wiring member such as a flexible printed circuit board, a copper clad laminate using the copper foil, a flexible wiring board, and an electronic device.

A flexible printed circuit board (flexible wiring board, hereinafter referred to as “FPC”) has flexibility, and is widely used in a bent portion and a movable portion of an electronic circuit. For example, FPCs are used for movable parts of disk-related devices such as HDDs, DVDs, and CD-ROMs, and for folding parts of foldable mobile phones.
The FPC is formed by etching a copper clad laminate (copper-clad laminate, hereinafter referred to as CCL) in which a copper foil and a resin are laminated, and then coating the wiring with a resin layer called a coverlay. The copper foil surface is etched as part of the surface modification step for improving the adhesion between the copper foil and the coverlay before the coverlay is laminated. Further, in order to improve the flexibility by reducing the thickness of the copper foil, thinning etching may be performed.

  By the way, with the miniaturization, thinning, and high performance of electronic devices, miniaturization of FPC circuit width and space width (for example, about 20 to 30 μm) is required. If the circuit of the FPC is miniaturized, there is a problem that the etching factor and circuit linearity are likely to deteriorate when the circuit is formed by etching (Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 2017-141501 JP 2017-179390 A

However, in the conventional technique, the average crystal grain size and the like are optimized as a measure for improving the etching property, but there is room for improvement in the etching property in forming a fine circuit.
The present invention has been made to solve the above-mentioned problems, and aims to provide a copper foil for a flexible printed circuit board excellent in etching property, a copper-clad laminate using the same, a flexible printed circuit board, and an electronic device. To do.

  As a result of various studies, the present inventors have found that the etching rate of crystal grains with 220 orientation (101 plane) is high. Thus, the inventors have succeeded in further improving the etching property by increasing the number of 220-direction crystal grains in a specific direction.

That is, the copper foil for a flexible printed circuit board of the present invention is a copper foil composed of 99.0% by mass or more of Cu and the remaining inevitable impurities, and the crystal surface data of the surface of the copper foil measured by EBSD The area ratio S ₁₀₁ of the (101) plane was obtained by performing a rotation process of rotating θ (0 to 90 degrees) from ND with the direction in which the angle formed with MD is φ (0 to 180 degrees) as the rotation axis. When it is a copper foil for flexible printed circuit boards that satisfies any of the following (1) to (3). (1) theta indicates a maximum value _{S 101} is less than 0 degrees 30 degrees, and the maximum value is 0.4 or more, (2) theta is _{S 101} indicates a maximum value below 45 degrees 30 degrees, And the maximum value is 0.2 or more, (3) S ₁₀₁ shows the maximum value when θ exceeds 45 degrees and 60 degrees or less, and the maximum value is 0.4 or more

The copper foil for a flexible printed board of the present invention is preferably made of tough pitch copper standardized to JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1020).
The copper foil for flexible printed circuit boards of the present invention further contains at least one or more selected from the group consisting of P, Ag, Zn and Sn as an additive element in a total amount of 0.2% by mass or less. It is preferable.
In the copper foil for flexible printed circuit boards of the present invention, after annealing at 200 ° C. for 30 minutes (however, the rate of temperature increase is from 100 ° C./min to 300 ° C./min), any of the above (1) to (3) is satisfied. preferable.
The copper foil for a flexible printed circuit board of the present invention is provided by distributing or displaying the value of the angle φ from a printed matter, a seal, or an electronic medium or website bundled with the copper foil for a flexible printed circuit board. It may be.

  The copper clad laminate of the present invention is formed by laminating the flexible printed circuit board copper foil and a resin layer.

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

  The electronic device of the present invention uses the flexible printed circuit board.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil for flexible printed circuit boards excellent in etching property is obtained.

It is a figure which shows the method of measuring the surface of copper foil by EBSD. It is a diagram illustrating a method of determining the S ₁₀₁ for each θ by rotation processing from the measurement results of the EBSD. It is a figure which shows (phi). It is a figure which shows (theta). S ₁₀₁ is a sectional view showing the relationship between the traveling direction of the angle θ and etching indicating the maximum value. It is sectional drawing explaining the cross section of a circuit when angle (theta) progresses in various directions. It is a figure which shows the method of calculating | requiring the etching factor EF from the cross-sectional shape of a circuit.

  Hereinafter, embodiments of the copper foil according to the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.

<Composition>
The copper foil according to the present invention comprises 99.0% by mass or more of Cu and the balance of inevitable impurities. The composition may be made of tough pitch copper (TPC) standardized to JIS-H3100 (C1100) or oxygen-free copper (OFC) of JIS-H3100 (C1020).
Further, when the additive element contains at least one or more selected from the group consisting of P, Ag, Zn, and Sn in a total amount of 0.2% by mass or less, the copper foil for flexible substrate is bent. And flexibility are improved.
The lower limit of the content of the additive element is not particularly limited. However, for example, it is industrially difficult to control the content to less than 0.0005% by mass for each element, so the lower limit of the content of each element is preferably 0.0005% by mass.

The area ratio of the (101) plane In the present invention, the structure of the copper foil with the optimum etching property is defined by EBSD. Specifically, as shown in FIG. 2 to be described later, it is defined by the area ratio of the (101) plane of the target cross section specified by the angles φ and θ.
However, since it is difficult to perform the EBSD measurement by exposing the target cross section specified by the angles φ and θ, the EBSD measurement of the copper foil surface is performed, and the rotation processing described later is performed on the obtained crystal orientation data. And the area ratio S ₁₀₁ of the (101) plane for each θ is obtained by calculation.

Here, as shown in FIG. 1, EBSD (Electron Back Scatter Diffraction) uses reflected electron Kikuchi diffraction (Kikuchi pattern) that occurs when a sample is irradiated with an electron beam in an SEM. This is a technique for analyzing crystal orientation.
This rotation process is performed from ND (thickness direction) to θ (0 As shown in FIGS. 2 to 4, a cross section having a surface normal N as a direction rotated θ from ND (thickness direction) is set as a target cross section. MD is a rolling parallel direction in the rolled copper foil.
Then, the area ratio S ₁₀₁ of the (101) plane in the target cross section where the angle θ is changed between 0 degrees and 90 degrees is obtained.
The rotation process can be calculated (analyzed) with software attached to the EBSD device, and for example, OIM-Analysis of TSL Solutions Inc. can be used.

When area ratio _S101 is calculated _| required as mentioned above, the copper foil for flexible printed circuit boards of this invention satisfy | fills any one of following (1)-(3).
(1) When S is 0 degree or more and less than 30 degrees, S ₁₀₁ shows the maximum value, and the maximum value is 0.4 or more. (2) When θ is 30 degrees or more and 45 degrees or less, S ₁₀₁ shows the maximum value, and The maximum value is 0.2 or more. (3) When S is greater than 45 degrees and 60 degrees or less, S ₁₀₁ shows the maximum value, and the maximum value is 0.4 or more. Note that this is the normal of the (101) plane. A crystal grain having an orientation with an angle of 10 degrees or less is defined as a (101) plane.

The calculation of the area ratio S _{101 and} the determinations (1) to (3) are performed as follows.
First, when φ is made constant between 0 and 180 degrees, θ is changed to 0 to 90 degrees, and S ₁₀₁ at each θ is calculated. This calculation is performed by changing φ.
Table 2 shows S ₁₀₁ when φ and θ are changed in Example 21, which will be described later. When φ = 22.5 degrees, S ₁₀₁ showed the maximum value at θ = 45 degrees, and the maximum value was 0.4. The symbol “-” in Table 2 indicates that S ₁₀₁ is less than 0.4.
Therefore, (1) to (3) are regulations at any angle between 0 and 180 degrees.
In addition, since enormous time is required to calculate by dividing φ and θ into fine pieces, it is preferable to set the angle interval to φ every 22.5 degrees and θ every 15 degrees, for example.

Next, the relationship between the etching factor EF and θ will be described with reference to FIGS. As shown in Examples and Comparative Examples (Table 1) described later, the etching factors EF were inferior in all Comparative Examples in which θ exceeded 60 degrees. Therefore, the range where θ is 0 to 60 degrees is examined.
First, as shown in FIG. 5, the etching proceeds in the direction of the angle θ at which S ₁₀₁ has a maximum value. In the etching for forming the circuit, the stage until the etching reaches the bottom in the thickness direction, and then in the lateral direction. It is divided into two stages where the circuit width becomes narrower as etching progresses.

As shown in FIG. 6, when the etching proceeds in the direction of the angle θ = 45 degrees, the etching progresses in the oblique direction (45 degrees direction) when the etching reaches the bottom. After the bottom portion becomes thinner and the etching reaches the bottom, the bottom etching progresses preferentially. This results in a sharp (close to rectangular) circuit cross-section that leaves the top width of the circuit. Therefore, the etching factor EF is good.
Further, when the etching proceeds in the direction of the angle θ = 0 degree, the etching is likely to advance preferentially in the depth direction. Therefore, when the etching reaches the bottom, the etching in the width direction has not yet progressed. For this reason, the thickness of the bottom part of the circuit is thicker than when θ = 45 degrees, but the width of the circuit top remains when the etching reaches the bottom. For this reason, although it is slightly inferior to the case of θ = 45 degrees (sharp circuit section having a large top width), the etching factor EF is good.
On the other hand, when the etching proceeds in the direction of the angle θ = 90 degrees, the etching is difficult to proceed in the thickness direction. On the other hand, the etching is excessively spread in the plate surface direction. Not sharp, etching factor EF is inferior.

From the above, at the 45 degree boundary, (1) θ is 0 degree or more and less than 30 degree, (2) θ is 30 degree or more and 45 degree or less, and (3) θ is over 45 degree and less than 60 degree. An angle range was set.
And as shown in the Example and comparative example (Table 1) mentioned later, EBSD measurement and the etching factor EF are measured for various copper foil samples, and the quality of the etching factor EF and S ₁₀₁ show the maximum value. θ is classified into three angle ranges (1) to (3), and a threshold value of the maximum value is obtained from the maximum value of S ₁₀₁ when the etching factor EF is good for each angle range. It was.
As described above, since EF is the best at θ = 45 °, the maximum value of S ₁₀₁ is smaller in the range (2) including θ = 45 ° than in other ranges as will be described later. However, good EF can be obtained.

実際のＥＦの測定方法は種々存在するが、本発明では、上述の図５、図６の説明のように、深さ方向と幅方向に十分にエッチングが進行したときの回路の断面形状がθに関係するので、ボトム幅が一定となったときにエッチングを停止し、式（１）からＥＦを求める。 Here, the etching factor EF is defined by the following formula (1) from the bottom width, top width, and height of the cross section of the circuit shown in FIG.

Although there are various actual EF measurement methods, in the present invention, as described with reference to FIGS. 5 and 6, the cross-sectional shape of the circuit when the etching proceeds sufficiently in the depth direction and the width direction is θ. Therefore, when the bottom width becomes constant, the etching is stopped, and EF is obtained from Equation (1).

<Heat treatment at 200 ° C for 30 minutes>
Copper foil according to the present invention is used for a flexible printed circuit board, in which, CCL formed by laminating the copper foil and the resin in order to perform the heat treatment for curing the resin at 200 to 400 ° C., S ₁₀₁ is the maximum value The indicated θ and the maximum value change.
Therefore, the maximum values of θ and S ₁₀₁ change before and after lamination with the resin. Then, the copper foil for flexible printed circuit boards concerning Claim 1 of this application has prescribed | regulated the copper foil of the state which received the hardening heat processing of resin after it became a copper clad laminated body laminated | stacked with resin. In other words, the copper foil is in a state in which a new heat treatment is not performed because it has already been subjected to a heat treatment.
On the other hand, the copper foil for a flexible printed circuit board according to claim 4 of the present application is in the state when the heat treatment is performed on the copper foil before being laminated with the resin (for example, the copper foil coil before the heat treatment is delivered to the CCL manufacturing factory. The heated state when being stacked on the CCL). This heat treatment at 200 ° C. for 30 minutes simulates the temperature condition for curing and heat-treating the resin during CCL lamination. In order to prevent oxidation of the copper foil surface due to the heat treatment, the atmosphere of the heat treatment is preferably a reducing or non-oxidizing atmosphere, for example, a vacuum atmosphere, argon, nitrogen, hydrogen, carbon monoxide, or the like. An atmosphere made of a mixed gas may be used. The heating rate may be between 100 and 300 ° C./min.

The copper foil of this invention can be manufactured as follows, for example. First, after melting and casting a copper ingot, it is hot-rolled, cold-rolled and annealed, preferably recrystallized and annealed at the initial stage of cold-rolling, and finally recrystallized and final cold-rolled. By doing so, a foil can be produced.
By adjusting the temperature increase rate in the final recrystallization annealing, the crystal orientation generated during recrystallization can be adjusted, and the maximum values of θ and S ₁₀₁ can be controlled. The rate of temperature increase in the final recrystallization annealing is preferably 2 ° C./min or less. In the case of (2) in which θ is 30 degrees or more and 45 degrees or less, the rate of temperature rise is preferably 10 ° C./min or less.
Similarly, by adjusting the strain rate of the final pass of final cold rolling, the crystal orientation generated during recrystallization can be adjusted, and the maximum values of θ and S ₁₀₁ can be controlled. The strain rate is preferably 100 to 5000 (/ second), more preferably 200 to 500 (/ second).

<Copper-clad laminate and flexible printed circuit board>
Also, (1) a resin precursor (for example, a polyimide precursor called varnish) is cast on the copper foil of the present invention and polymerized by applying heat, and (2) a thermoplastic adhesive of the same type as the base film is used. By laminating the base film on the copper foil of the present invention, a copper clad laminate (CCL) composed of two layers of the copper foil and the resin base material is obtained. Further, by laminating a base film obtained by applying an adhesive to the copper foil of the present invention, a copper clad laminate (CCL) comprising three layers of a copper foil, a resin base material, and an adhesive layer therebetween is obtained. During the production of these CCLs, the copper foil is heat-treated and recrystallized.
A circuit is formed on these using a photolithographic technique, a circuit is plated as needed, and a cover-lay film is laminated, and a flexible printed circuit board (flexible wiring board) is obtained.

Therefore, the copper clad laminate of the present invention is formed by laminating a copper foil and a resin layer. Moreover, the flexible printed circuit board of this invention forms a circuit in the copper foil of a copper clad laminated body.
Examples of the resin layer include, but are not limited to, PET (polyethylene terephthalate), PI (polyimide), LCP (liquid crystal polymer), and PEN (polyethylene naphthalate). Moreover, you may use these resin films as a resin layer.
As a method of laminating the resin layer and the copper foil, a material for forming the resin layer may be applied to the surface of the copper foil and heated to form a film. Further, a resin film may be used as the resin layer, and the following adhesive may be used between the resin film and the copper foil, or the resin film may be thermocompression bonded to the copper foil without using the adhesive. However, it is preferable to use an adhesive from the viewpoint of not applying excessive heat to the resin film.

  When a film is used as the resin layer, this film may be laminated on the copper foil via an adhesive layer. In this case, it is preferable to use an adhesive having the same component as the film. For example, when a polyimide film is used as the resin layer, it is preferable to use a polyimide-based adhesive for the adhesive layer. In addition, the polyimide adhesive here refers to the adhesive agent containing an imide bond, and polyether imide etc. are also included.

In addition, this invention is not limited to the said embodiment. Moreover, as long as there exists an effect of this invention, the copper alloy in the said embodiment may contain another component. Moreover, an electrolytic copper foil may be used.
For example, the surface of the copper foil may be subjected to a surface treatment by roughening treatment, rust prevention treatment, heat resistance treatment, or a combination thereof.

In the present invention, S ₁₀₁ at a predetermined θ is defined by the aforementioned angle φ, and the etching property is excellent in the vicinity of the angle φ. Here, a rolled copper foil manufacturer measures each φ for each copper foil coil, etc., while a copper foil user (for example, a circuit manufacturer) has an angle at which the etching performance is best for the circuit itself. It is customary to search for φ.
Therefore, it is not necessary to present the angle φ at the time of shipment of the rolled copper foil, but the value of the angle φ can be bundled with a printed matter or a seal in a package of a copper foil product (for example, a coil product) for a flexible printed circuit board. The value of the angle φ is provided or displayed from the server when the value of the angle φ is provided on a bundled or separate electronic medium (CD-ROM, etc.) or the coil number of the product is entered on the website. This is preferable because it is convenient for the user.

EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these. Each element shown in Table 1 was added to electrolytic copper to obtain the composition shown in Table 1, and cast in an Ar atmosphere to obtain an ingot. The oxygen content in the ingot was less than 15 ppm. The ingot was homogenized and annealed at 900 ° C., and then hot-rolled. Then, cold rolling and recrystallization annealing were repeated, and final recrystallization annealing and final cold rolling were further performed to obtain a rolled copper foil.
The obtained rolled copper foil was subjected to heat treatment at 200 ° C. for 30 minutes in an argon atmosphere to obtain a copper foil sample. The copper foil after the heat treatment imitates a state where the heat treatment is performed during the lamination of the CCL.

<A. Evaluation of copper foil sample>
1. Area ratio of (101) surface For each copper foil sample after the above heat treatment, after electrolytic polishing of the copper foil surface, as shown in FIG. 1, EBSD analysis (backscattered electron diffraction device, JEOL Ltd. JXA8500F, acceleration Voltage 20 kV, current 2e-8A, observation range 1000 μm × 1000 μm, step width 0.5 μm). Based on the EBSD analysis result of the copper foil surface, the area ratio S ₁₀₁ of the (101) plane was obtained with the measurement plane defined by the angle θ as a reference as described above.
θ = 0 ° to 90 ° (15 ° increments).

2. Etching factor EF
The copper foil and the resin were bonded together, and then a dry film resist was laminated on the copper foil surface to form a strip-like (L / S = 30/20) circuit pattern on the resist. Note that the angle φ formed by the longitudinal direction in which the strip of the circuit pattern extends and the MD is changed for each example, and S ₁₀₁ when any one of the above (1) to (3) is satisfied shows the maximum value The angle φ was matched. For example, as shown in Table 2, in the case of Example 21, the circuit pattern was formed with φ = 22.5 degrees.
For each comparative example, the same calculation as in Table 2 was performed, and the circuit pattern was formed by adopting the angle φ when S ₁₀₁ showed the maximum value.
Thereafter, spray etching of a cupric chloride etchant was performed to obtain a circuit in which the bottom width in FIG. 7 was constant. The bottom width was controlled by adjusting the etching time. And the cross-sectional shape of the circuit obtained by etching was measured by FIG. 7 and Formula (1), and the etching factor EF was calculated. The following indices were evaluated according to the EF value. If evaluation is (double-circle) and (circle), etching property is favorable.
◎: EF is 5.0 or more ○: EF is 3.0 or more and less than 5.0 ×: EF is less than 3.0

  The obtained results are shown in Tables 1 and 2.

  As is clear from Tables 1 and 2, the etching properties were good in each Example satisfying any one of (1) to (3). Specifically, Examples 1, 2, 9, 10, 11, 17, and 18 satisfy (1), and Examples 3, 4, 6, 7, and 8 satisfy (2). , 12, 13, 15, 16, 19, 20, 21 and those satisfying (3) are Examples 5, 14, and 22.

Of the examples satisfying (1), Example 9 had the best etching property and the maximum value of S ₁₀₁ was 0.7 or more. Therefore, it is preferable that the maximum value of S ₁₀₁ is 0.7 or more in the θ range of (1).
Similarly, among the examples satisfying (2), the maximum value of _{S 101} good most etching resistance Examples 3,4,8,12,13,15,16,19,20,21 0. 4 (Example 21) or more. Therefore, it is preferable that the maximum value of S ₁₀₁ is 0.4 or more in the θ range of (2).

On the other hand, in the case of Comparative Examples 1 to 5 in which the temperature increase rate in the final recrystallization annealing exceeded 2 ° C./min, the etching property was inferior. Specifically, Comparative Examples 1 and 2 did not satisfy (1), Comparative Examples 3 and 4 did not satisfy (2), and Comparative Example 5 did not satisfy (3).
In the case of Comparative Examples 6 and 7 in which the strain rate of the final pass of the final cold rolling was less than 100 (/ sec) 2 ° C./min, θ exceeded 60 degrees and the etching property was inferior.

Claims (8)

99.0% by mass or more of Cu, the remaining copper foil consisting of inevitable impurities,
With respect to the crystal orientation data of the surface of the copper foil measured by EBSD, rotation from ND to θ (0 to 90 degrees) with the direction where the angle formed with MD on the surface is φ (0 to 180 degrees) as the rotation axis The copper foil for flexible printed boards which satisfy | fills any of following (1)-(3), when the rotation process to give is performed and area ratio S101 of (101) plane is calculated _| required.
(1) When S is 0 degree or more and less than 30 degrees, S ₁₀₁ shows the maximum value, and the maximum value is 0.4 or more. (2) When θ is 30 degrees or more and 45 degrees or less, S ₁₀₁ shows the maximum value, and The maximum value is 0.2 or more. (3) When S is greater than 45 degrees and 60 degrees or less, S ₁₀₁ shows the maximum value, and the maximum value is 0.4 or more.   The copper foil for flexible printed circuit boards of Claim 1 which consists of a tough pitch copper specified to JIS-H3100 (C1100) or an oxygen free copper of JIS-H3100 (C1020).   The flexible printed circuit board according to claim 1 or 2, further comprising at least one or more selected from the group consisting of P, Ag, Zn and Sn as additive elements in a total amount of 0.2% by mass or less. Copper foil.   The method according to any one of claims 1 to 3, which satisfies any one of (1) to (3) after annealing at 200 ° C for 30 minutes (however, a temperature increase rate of 100 ° C / min to 300 ° C / min). Copper foil for flexible printed circuit boards.   The value of the said angle (phi) is provided by delivering or displaying from the printed matter enclosed with the said copper foil for flexible printed circuit boards, a seal | sticker, or an electronic medium or a website. The copper foil for flexible printed circuit boards of description.   The copper clad laminated body formed by laminating | stacking the copper foil for flexible printed circuit boards as described in any one of Claims 1-5, and a resin layer.   The flexible printed board formed by forming a circuit in the said copper foil in the copper clad laminated body of Claim 6.   An electronic apparatus using the flexible printed circuit board according to claim 7.

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