JP2002167632A - Rolled copper foil for flexible printed circuit board and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide rolled copper foil for FPC having both excellent flexibility and appropriate softening characteristics by appropriately increasing the softening temperature of high flexibility rolled copper foil, and solving troubles to accompany its softening in the process of storage. SOLUTION: The rolled copper foil for a flexible printed circuit board having excellent flexibility and suitable softening characteristics has a composition containing 100 to 500 mass ppm oxygen, and containing one or more kinds selected from Ag, Au, Pd, Pt, Rh, Ir, Ru and Os in the ranges so as to control T defined by the following formula to 100 to 400: T=[Ag]+0.6[Au]+0.6[Pd]+0.4[Pt]+0.4[Rh]+0.3[Ir]+0.3[Ru]+0.3[Os] (wherein, [M] is the mass ppm concentration of the element M), and in which the total content of S, As, Sb, Bi, Se and Te is <=30 mass ppm. The rolled copper foil has a thickness of 5 to 50 μm. The intensity (I) in the 200 plane obtained by X-ray diffraction for the rolled face after annealing at 200 deg.C for 30 min to the intensity (I0) in the 200 plane obtained by X-ray diffraction for the pulverized copper, i.e., I/I0 is >20. The rolled copper foil has a semi-softening temperature of 120 to 150 deg.C, and continuously maintains tensile strength of >=300 N/mm2 at a room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board (Flex) having excellent flexibility and favorable manufacturability.
Flexible printed circuit (hereinafter referred to as FPC).

[0002]

2. Description of the Related Art Printed wiring boards based on organic materials include rigid copper-clad laminates (rigid) made of glass epoxy and paper phenol boards and flexible copper boards made of polyimide and polyester boards. Copper foil is mainly used as a conductive material of a printed wiring board. Copper foils are classified into electrolytic copper foils and rolled copper foils depending on the manufacturing method.

[0003] Among the above printed wiring boards, a flexible printed circuit board (FPC) is formed by laminating a copper foil on a resin substrate and integrating them with an adhesive or heating and pressing. In recent years, a multilayer wiring board called a build-up board is often used as an effective means for high-density mounting. Rolled copper foil is mainly used for the copper foil that is a component of the FPC.

An FPC is widely used in a place where wiring to a movable portion such as a head portion of a printer or a drive portion in a hard disk is required, and a flexion of 1,000,000 times or more is repeated. With the recent miniaturization and higher standards of equipment, the demand for this flexibility has become more sophisticated.

[0005] The material of the copper foil used in the FPC is mainly tough pitch copper (oxygen content: 100 to 500 mass ppm). This tough pitch copper foil is manufactured by hot rolling an ingot and then repeatedly performing cold rolling and annealing to a predetermined thickness. After that, the surface of the copper foil is subjected to rough plating in order to improve the adhesion to the resin substrate. The copper foil after the rough plating is cut and then bonded to a resin substrate. For bonding the copper foil and the resin, for example, an adhesive made of a thermosetting resin such as epoxy is used, and after bonding, it is cured by heating at a temperature of 130 to 170 ° C. for several hours to several tens of hours. Next, various wiring patterns are formed by etching the copper foil.

[0006] The flexibility of the copper foil is remarkably improved by performing recrystallization annealing as compared with the finished roll. Therefore, the copper foil is used as a component of the FPC in an annealed state. This annealing is performed by heat treatment after roughening plating and cutting, or by heating when bonding the copper foil to a resin substrate. As described above, the reason for performing annealing in the middle of the manufacturing process without using the annealed copper foil from the beginning is that, in the soft state after the annealing, the copper foil deforms during cutting or bonding with a resin base, This is because the foil may be wrinkled, and the harder state after rolling is FP
This is because C is advantageous in terms of manufacturability.

[0007] In order to increase the flexibility of FPC, it is effective to increase the flexibility of the rolled copper foil used as the material. The flexibility of the copper foil after annealing increases as the cubic texture develops. In order to develop this cubic texture, it is effective to increase the workability in the final rolling in the copper foil manufacturing process and to reduce the crystal grain size in the annealing just before the final rolling. (Patent No. 3009383
issue).

[0008] However, the copper foil produced by such a process significantly lowers the softening temperature due to an increase in plastic strain accumulated by rolling, and in some cases, the storage period is long even when stored at room temperature. May spread and soften. As described above, when an FPC is manufactured using an already softened copper foil, problems such as deformation of the copper foil occur, and the ease of manufacturing the FPC is significantly reduced. Therefore, when the above manufacturing process is selected to improve the flexibility of the copper foil, it is necessary to simultaneously increase the softening temperature of the copper foil appropriately.

The problem that rolled copper foil softens during storage at room temperature is also pointed out in Japanese Patent Application Laid-Open No. Hei 10-230303, and as a means for avoiding this problem, it is necessary to manufacture copper foil with a low rolling degree of 50 to 90%. Has been advocated. However, when a copper foil is manufactured at such a low rolling degree, the flexibility of the copper foil is remarkably reduced. Therefore, this method cannot be used for manufacturing a copper foil having excellent flexibility. Therefore, the present invention aims to increase the softening temperature to an appropriate range by adding a small amount of an alloy element to a conventional tough pitch copper foil. In addition,
Various copper alloy foils with various elements added for FPC have been proposed in the past. For example, one of the purposes of adding alloy elements is to suppress the development of cubic texture ((100) orientation). In addition, the softening temperature of this alloy foil is abnormally high (Japanese Patent No. 2505480), and a large amount of alloying elements are added to copper for the purpose of improving the flexibility (Japanese Patent Laid-Open No. 59-785).
92), etc., did not serve as a reference for solving this problem.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the flexibility and moderate softening by appropriately raising the softening temperature of a high-flexibility rolled copper foil to eliminate troubles associated with softening during storage. An object of the present invention is to provide a rolled copper foil for FPC having characteristics.

[0011]

That is, the present invention has solved the above-mentioned problems.

(1) It contains 100 to 500 mass ppm of oxygen, and at least one of Ag, Au, Pd, Pt, Rh, Ir, Ru, and Os has a T defined by the following equation of 100 to 400. T = [Ag] +0.6 [Au] +0.6 [Pd] +0.4 [Pt] +0.4 [Rh] +0.3
[Ir] +0.3 [Ru] +0.3 [Os] (where [M] is the mass ppm concentration of element M) The total amount of S, As, Sb, Bi, Se and Te is 30 mass ppm or less , The thickness of 5 to 50 μm, and the strength (I) of 200 planes determined by X-ray diffraction of the rolled surface after annealing at 200 ° C for 30 minutes is the strength of 200 planes determined by X-ray diffraction of fine powder copper I / I ₀ for (I ₀ )
> 20, has a semi-softening temperature of 120 to 150 ° C, maintains a tensile strength of 300 N / mm ² or more at room temperature continuously, and has excellent flexibility and moderate softening characteristics. Rolled copper foil for flexible printed circuit boards.

(2) After hot rolling the ingot, cold rolling and annealing are repeated, and finally, in the process of finishing the foil by cold rolling, the annealing immediately before the last cold rolling can be obtained by this annealing. The process is performed under the condition that the average grain size of recrystallized grains is 20μm or less, the workability of the last cold rolling is set to a value exceeding 90%, and excellent flexibility and moderate softening characteristics are obtained. The present invention relates to the method (1) for producing a rolled copper foil for a flexible printed circuit board.

If a copper foil is manufactured by a process of high workability or fine crystal grains to develop a cubic texture, the flexibility is improved, but the softening temperature is too low. However, when the softening temperature is increased by controlling the trace components of the raw material, it becomes possible to obtain a copper foil having an appropriate softening temperature.

The appropriate softening temperature is as follows: (1) Although the tensile strength of the copper foil after rolling is 400 to 500 N / mm ^2, it is left at room temperature (20 to 35 ° C.) for one year. also keep the 300 N / mm ² or more tensile strength, (2) heat treatment at the time of bonding the heat-treated or resin substrate after roughened plating to cut, the copper foil is softened, two conditions The half-softening temperature during annealing for 30 minutes (the annealing temperature at which the tensile strength reaches an intermediate value between before annealing and when completely softened)
This corresponds to a range of 120 to 150 ° C.

In order to keep the softening temperature of the tough pitch copper foil manufactured by the process of obtaining excellent flexibility within the target range, the present inventors have proposed to use noble metal elements (Ag , Au) or platinum group elements (P
d, Pt, Rh, Ir, Ru, Os) were found to be appropriate. This is for the following reason.

Since tough pitch copper contains 100 to 500 mass ppm of oxygen, active elements are oxidized when added to the molten metal, and it is difficult to control the concentration. In addition, since the additive element increases the softening temperature of Cu by forming a solid solution in Cu, if the additive element forms an oxide or a compound with other impurities in the copper foil, a sufficient softening suppression effect is obtained. Can not be obtained. Noble metal elements such as Ag and Au and platinum group elements such as Pd, Pt, Rh, Ir, Ru, and Os are inactive, so that the concentration can be easily controlled at the time of addition. Does not form a compound with the impurities of

As described above, according to the present invention, Ag, Au, Pd, Pt, Rh, Ir, Ru or Os is added to conventional tough pitch copper,
The main aim is to control the softening temperature after processing into foil to an appropriate range. In this case, controlling the impurities contained in the tough pitch copper to a specified level or less can more accurately control the softening temperature. it can.

The reasons for limiting the rolled copper foil according to the present invention will be described below. In the present invention, the rolled copper foil is continuously
The goal was to maintain a tensile strength of 300 N / mm ² or more. More desirably, it can maintain a tensile strength of 300 N / mm ² or more even when stored at 30 ° C. for one year.

Here, 30 ° C. corresponds to a temperature exceeding the annual average temperature in Japan, and the storage period until the copper foil is processed into FPC is often stored continuously, and is longer. Is also one year. If the tensile strength is 300 N / mm ² or more, no trouble such as wrinkling occurs during processing of the copper foil. Therefore, even if left at 30 ° C for 1 year, 300N
There is no practical problem if a tensile strength of / mm ² or more can be maintained. Such softening characteristics correspond to a temperature of 120 ° C. or more when converted to a half-softening temperature after annealing for 30 minutes.

On the other hand, the half-softening temperature after annealing for 30 minutes
If the temperature exceeds 150 ° C, the copper foil may not be softened by heat treatment after roughening plating and cutting or heat treatment for bonding to a resin substrate. Therefore, the half-softening temperature after annealing for 30 minutes was specified to be 120 to 150 ° C.

In order to increase the flexibility of the FPC, it is necessary to increase the flexibility of the copper foil. The copper foil is incorporated into the FPC in a recrystallized state. However, if a cubic texture, which is a recrystallization texture of pure Cu, is developed, the flexibility of the copper foil is improved. The degree of development of the cubic texture when satisfactory bending properties can be obtained is as follows: the strength of 200 faces determined by X-ray diffraction is higher than the strength (I ₀ ) of 200 faces determined by X-ray diffraction of fine powdered copper. It is defined by the relation of I ₀ > 20, and more preferably by the relation of I / I ₀ > 40. Here, annealing at 200 ° C. for 30 minutes is performed to recrystallize the copper foil when measuring the X-ray intensity.

Ag, Au, Pd, Pt, Rh, Ir, Ru and Os are:
It is added for the purpose of increasing the semi-softening temperature, but since each element has a different contribution to the increase in the softening temperature, it is necessary to weight the elements. Therefore, the softening temperature rise index (T) was defined by the following equation. T = [Ag] + 0.6 [Au] + 0.6 [Pd] + 0.4 [Pt] + 0.4 [Rh] + 0.3
[Ir] +0.3 [Ru] +0.3 [Os] (where [M] is the mass ppm concentration of the element M) Here, [M] is the mass ppm concentration of the element M. This T is 1
If the above elements are added so as to be in the range of 00 to 400,
The semi-softening temperature of the copper foil manufactured by the process that can obtain high bending can be kept in the range of 120 to 150 ° C. On the other hand, T is 1
If it becomes smaller than 00, the half-softening temperature becomes lower than 120 ° C and T
Exceeds 400, the semi-softening temperature becomes higher than 150 ° C.

S, As, Sb, Bi, Se and Te are impurities contained in ordinary tough pitch copper and have a relatively large effect on the half-softening temperature. Therefore, Ag, Au, Pd, Pt,
When controlling the half-softening temperature by adding Rh, Ir, Ru, and Os, controlling the half-softening temperature is easier if the concentration of these impurities is suppressed to a low level. Since these elements are mainly mixed from the copper used as a raw material of the tough pitch copper foil, it is necessary to control the amount of impurities in the copper used in order to adjust the concentration.

S, As, Sb, Bi, Se and Te are desirably at least 30 mass ppm in total of at least one of the respective components. If the total exceeds 30 mass ppm, the above-mentioned softening temperature rise index T However, even if they are the same, the semi-softening temperature varies greatly, or the semi-softening temperature exceeds 150 ° C depending on the value of T.

It is known that oxygen-free copper of normal purity has a significantly higher softening temperature than tough pitch copper due to the low oxygen concentration. In addition, oxygen excessively contained in tough pitch copper forms inclusions of Cu ₂ O. Oxygen concentration of 10
The reason for specifying 0 to 500 mass ppm is that the oxygen concentration is 100 mas
Ag, Au, Pd, Pt, Rh, Ir, Ru or O at less than s ppm
When s is added, the half-softening temperature exceeds 150 ° C and the oxygen
If the content exceeds 00 mass ppm, Cu ₂ O inclusions increase and the flexibility deteriorates.

Regarding the thickness of the copper foil, the thinner the copper foil is, the less the distortion generated on the outer periphery of the bent portion is, so that the flexibility is improved.
If the thickness of the copper foil exceeds 50 μm, the desired flexibility cannot be obtained even if a cubic texture is developed. On the other hand, if the thickness of the copper foil is less than 5 μm, the strength of the foil becomes too low, and the handling of the foil becomes difficult due to breakage or the like. Therefore, the thickness of the copper foil was set to 5 to 50 μm.

Next, the copper foil according to the present invention has an average particle size.
After performing recrystallization annealing under the condition of 20μm or less, 90%
The foil can be finished by performing cold rolling with a working ratio exceeding 200%. If the average grain size in annealing before rolling exceeds 20 μm or the working ratio is 90% or less, I / I ₀ <20.0
As a result, good flexibility cannot be obtained. The annealing before the final cold rolling can be performed by hot rolling, but also in this case, it is desirable to adjust the crystal grain size after hot rolling to 20 μm or less.

[0029]

The embodiments of the present invention will be described below with reference to examples. A copper ingot having a thickness of 200 mm and a width of 600 mm with the components shown in Table 1 was manufactured and rolled to 10 mm by hot rolling.

[0030]

[Table 1]

Next, annealing and cold rolling are repeated to obtain a thickness.
A rolled plate of t ₀ mm was obtained. The sheet was annealed and recrystallized to remove oxide scale, and then cold-rolled to a predetermined thickness t mm. Here, the degree of work R in the last cold rolling
Is given by R = (t ₀ −t) / t ₀ × 100 (%). In the annealing before final cold rolling, the grain size after annealing was measured by a cutting method in a cross section perpendicular to the rolling direction.

The following characteristics were evaluated for the copper foil samples manufactured under the various intermediate annealing conditions and the final rolling degree as described above. (1) Cube texture After the sample was heated at 200 ° C. for 30 minutes, the integrated value (I) of the (200) plane strength obtained by X-ray diffraction of the rolled plane was obtained. This value was divided by the previously measured integral value (I ₀ ) of the (200) plane strength of fine powder copper, and the value of I / I ₀ was calculated. The integrated value of the peak intensity was measured using a Co tube and 2θ = 57 to 63 °.
(Θ is the diffraction angle).

(2) Flexibility After the sample was heated at 200 ° C. for 30 minutes to recrystallize, the bending fatigue life was measured by the apparatus shown in FIG. This device has a structure in which a vibration transmitting member 3 is coupled to an oscillation driver 4. The copper foil 1 to be tested has a total of four points of a screw 2 indicated by an arrow and a tip of the vibration transmitting member 3. Fixed to the device. When the vibration transmitting member 3 is driven up and down, the middle portion of the copper foil 1 is bent into a hairpin shape with a predetermined radius of curvature r. In this test, the number of times until breakage when bending was repeated under the following conditions was determined.

Specimen width: 12.7 mm, specimen length: 200 m
m, Specimen sampling direction: Sampling was performed so that the length direction of the specimen was parallel to the rolling direction, radius of curvature r: 2.5 mm, vibration stroke: 25 mm, vibration speed: 1500 times / min. It was judged that it had excellent flexibility when it was 30,000 times or more. In addition, this test is an accelerated test and is performed under severer conditions than those actually used by FPC.

(3) Semi-softening temperature Tensile strength after annealing at various temperatures for 30 minutes was measured. Then, the annealing temperature at which the tensile strength after annealing reached an intermediate value between the tensile strength after rolling and the tensile strength after completely softening by annealing at 300 ° C. for 30 minutes was determined. If the semi-softening temperature was in the range of 120 to 150 ° C, it was determined that the material had appropriate softening characteristics.

(4) Softening behavior at room temperature The rolled material is stored in a thermostat adjusted to 30 ° C.
Tensile strength was measured every month from the start of storage, and the period until the tensile strength reached a value of 300 N / mm ² or less was determined. This evaluation continued for up to 12 months.

The components of the copper foil evaluated in Table 1, the production method and
And characteristics. Nos. 1 to 18 are examples related to the present invention.
Nos. 1 to 9 of Comparative Examples deviate from the present invention in the components or the production method.
This is an example. The rolled copper foil according to the present invention
200 faces I / I with cubic texture developed ₀Exceeds 20.0,
As a result, it shows an excellent flex life of more than 30,000 times.
You. The softening temperature is within the target range of 120 to 150 ° C.
Tensile strength of 300 N / m even after storage at room temperature (30 ℃) for 1 year
m^TwoThe above values are maintained.

On the other hand, since the softening temperature rise index (T) of Comparative Example No. 3 is smaller than 100, the semi-softening temperature is lower than 120 ° C., and the storage strength at 30 ° C. becomes less than 300 N within one year. / mm ² or less. No. 4 of the comparative example has T exceeding 400,
No. 6 of the comparative example is the impurities S, As, Sb, Bi, Se and T
Since the total amount of e exceeds 30 mass ppm, N
In o.1, since the oxygen concentration is lower than 100 mass ppm, the half-softening temperature exceeds 150 ° C, and there is a high risk of not recrystallizing during the FPC manufacturing stage.

In Comparative Example No. 2, since the oxygen concentration exceeded 500 mass ppm, Cu ₂ O inclusions increased and the number of flexions was 30,000 times despite the development of cubic texture. It shows a low value of less than. No. 5 of the comparative example is an impurity
The total amount of S, As, Sb, Bi, Se, and Te exceeded 30 mass ppm. Especially, the S content was so high that cracking occurred during hot rolling of the ingot, and it could not be processed into foil. It is known that when S is increased, segregation occurs at the grain boundaries, which promotes hot cracking. Similarly, when other additive elements exceeded the specified concentrations, the production yield also decreased. No. 8 of the comparative example had a crystal grain size of 20μ before rolling.
No. 9 of the comparative example has a rolling reduction of 90%
Because of the following, the I / I ₀ of the 200 surface is less than 20.0, the number of bending is less than 30,000, and the plastic deformation accumulated by rolling is small, so that the semi-softening temperature exceeds 150 ° C. No. 7 of Comparative Example
Since the thickness exceeds 50 μm, the number of flexures is less than 30,000 times despite the development of cubic texture.

FIG. 2 shows that S, As, S
With respect to Nos. 1 to 7 of the examples of the present invention and Nos. 3 and 4 of the comparative examples manufactured by the same process with the total amount of b, Bi, Se and Te being 30 mass ppm or less, the softening temperature rise index T and the half The relationship with the softening temperature is shown. As the softening temperature rise index T increases, the semi-softening temperature increases, and the target is 120 to 150 ° C in the range of T = 100 to 400.
It can be seen that the semi-softening temperature was obtained.

[0041]

The rolled copper foil for flexible printed circuits of the present invention has excellent flexibility. In addition, it has an appropriate softening temperature and does not cause troubles such as softening during storage or softening during annealing, and therefore has favorable manufacturability as a flexible printed circuit board. Of course, this copper foil is also suitable for uses other than flexible printed circuits, such as electrodes for lithium ion batteries.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a bending test apparatus used for measuring a bending fatigue life.

FIG. 2 is a graph showing a relationship between a semi-softening rise index T and a half-softening temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copper foil 2 Screw 3 Vibration transmission member 4 Oscillation driver

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Claims (2)

[Claims] Claims: 1. An oxygen containing 100 to 500 mass ppm of oxygen,
Contains at least one of Au, Pd, Pt, Rh, Ir, Ru, and Os in a range where T defined by the following equation is 100 to 400, and T = [Ag] + 0.6 [Au] + 0. 6 [Pd] + 0.4 [Pt] + 0.4 [Rh] + 0.3
[Ir] +0.3 [Ru] +0.3 [Os] (where [M] is the mass ppm concentration of element M) The total amount of S, As, Sb, Bi, Se and Te is 30 mass ppm or less The strength (I) of the rolled surface after annealing at 200 ° C for 30 minutes with a thickness of 5 to 50 μm was determined by the X-ray diffraction of the 200 powder. I / I ₀ for (I ₀ )
> 20, has a semi-softening temperature of 120 to 150 ° C, maintains a tensile strength of 300 N / mm ² or more at room temperature continuously, and has excellent flexibility and moderate softening characteristics. Rolled copper foil for flexible printed circuit boards. 2. A process of hot rolling an ingot, repeating cold rolling and annealing, and finally, in a process of finishing the foil by cold rolling, the annealing immediately before the last cold rolling is performed again by the annealing obtained by this annealing. The process is performed under the condition that the average grain size of the crystal grains is 20μm or less, the workability of the last cold rolling is set to a value exceeding 90%, and excellent flexibility and moderate softening characteristics are obtained. Item 10. A method for producing a rolled copper foil for a flexible printed circuit board according to item 1.