JP2007107036A - Rolled copper alloy foil to be bent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolled copper alloy foil to be bent which little increases electric resistance even after having been bent and has superior electrification reliability. <P>SOLUTION: The rolled copper alloy foil firstly has a composition comprising one or more elements selected from Fe, Ni, Ag and Al in such an amount as to be dissolved in Cu and the balance Cu with unavoidable impurities; secondly has a ratio I/I<SB>0</SB>(200) of an X-ray diffracted intensity I of the surface (200) determined on a rolled surface to an X-ray diffracted intensity I<SB>0</SB>of the surface (200) on a copper alloy in a value of 60 or more, in a state of having been tempered into a recrystallized structure by being annealed at 200°C for 30 minutes; thirdly has a crystal structure in the state of having been tempered into a recrystallized structure by being annealed at 200°C for 30 minutes, in which crystal grains having an orientational face mainly on which the crystal grains can slide when the foil has been flection-deformed (having the orientational face of 40 degrees to 50 degrees with respect to a deformed direction, mainly on which crystal grains can slide) occupy 80% or more by an area ratio when observed from the rolled surface; and fourthly has the surface roughness Ra of 0.2 μm or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolled copper alloy foil for bending. In particular, the present invention relates to a rolled copper alloy foil for bending suitable as a flexible wiring member used for a flexible printed wiring board (FPC).

  Printed wiring boards (PWB) are frequently used in electronic circuits of electronic devices. The printed wiring board is a rigid printed wiring board using a hard insulating substrate such as a paper base phenolic resin or a glass cloth base epoxy resin, and a flexible printed wiring using a flexible resin substrate such as a polyimide film or a polyester film. Broadly divided into plates (FPC). Among these, the FPC is made by bonding a copper foil to a resin substrate using an adhesive made of a thermosetting resin such as an epoxy, and integrating by heating and pressing to form a copper-clad laminate, and then etching the copper foil to variously In general, the circuit pattern is formed.

  The biggest feature of FPC is flexibility. Using this feature, FPC can be folded into a small space inside small electronic devices such as cameras, sewing machines, calculators, personal computers, word processors, etc., and mounted in high density (static flexibility), or the printer head or hard disk drive It is used for wiring to movable parts such as (dynamic flexibility).

  Bending of one million times or more can be repeated in the movable part of the electronic device. At this time, if the copper foil forming the circuit pattern reaches a condition equal to or higher than the fatigue limit, the fatigue deteriorates and the flexibility is lowered. Finally, a crack may be generated in the circuit, resulting in disconnection. Even if the circuit does not break, the electrical resistance of the circuit increases with the occurrence of cracks, and the performance as a circuit decreases.

  Therefore, especially when considering application to a movable part of an electronic device, high flexibility is required for the copper foil for FPC. For this reason, rolled copper foils that are more flexible than electrolytic copper foils are used for FPCs used in such applications, but with the recent downsizing and higher standards of equipment, demands for flexibility are required. Is more sophisticated.

As a method for improving the flexibility of the copper foil, for example, a method of bringing the copper foil into an annealed state is generally performed. This utilizes the fact that the flexibility of the copper foil is remarkably improved over the rolling up due to the recrystallization annealing. This annealing is usually carried out after roughing plating and cutting, or is performed in combination with heating at the time of bonding to the resin substrate, typically at 130 to 250 ° C. for 15 minutes to 24 hours. In particular, it is performed by heating at 200 ° C. for 30 minutes, whereby the copper foil is tempered to a recrystallized structure.
The reason for annealing in the middle of the manufacturing process without using the annealed copper foil from the beginning is that the copper foil is deformed or wrinkled in the soft state after annealing when it is cut or bonded to the resin substrate This is because a hard state after rolling is more advantageous from the viewpoint of manufacturability of the FPC.

Further, it is known that when copper rolled at a high workability is recrystallized and annealed, a cubic orientation develops as the recrystallized texture, which improves the flexibility. In the invention described in Japanese Patent No. 3009383, the average degree of recrystallization obtained by annealing is performed at a final cold rolling work degree of 90% or more on tough pitch copper or oxygen-free copper. By carrying out under the condition that the diameter becomes 5 to 20 μm, the cube orientation of the copper foil is developed and the flexibility is improved. According to the present invention, the strength (I) of the (200) plane obtained by X-ray diffraction of the rolled surface in a state where the recrystallized structure is tempered by heating at 200 ° C. for 30 minutes has an X-ray of fine powder copper. It has a cubic texture with I / I ₀ > 20 with respect to the strength (I ₀ ) of the (200) plane determined by diffraction, and the number of bendings (fatigue life) until fracture increases.

  In addition, as a method for developing the cube orientation, Japanese Patent Application Laid-Open No. 2003-193411 discloses control of the total amount of impurities in Cu (40 ppm or less for tough pitch copper and 20 ppm or less for oxygen-free copper), and Ag into Cu. It is described that it is effective to add in the range of 100 ppm to 700 ppm.

Japanese Patent No. 3009383 Japanese Patent Laid-Open No. 2003-19311

Fatigue life is one of the important characteristics of copper foil bendability, but copper foil fatigues as the number of bends increases, and there is a problem that electrical resistance continues to increase from an early stage with the occurrence of fine cracks. . Therefore, suppressing the increase in electrical resistance due to bending is also considered an important characteristic for maintaining the circuit performance.
Accordingly, one of the objects of the present invention is to provide a rolled copper alloy foil for bending that has little increase in electrical resistance due to bending and is excellent in current-carrying reliability. Another object of the present invention is to provide a copper clad laminate using the bending rolled copper alloy foil. Still another object of the present invention is to provide an FPC using the bending rolled copper alloy foil.

The increase in electrical resistance due to the bending of the FPC occurs when the effective cross-sectional area of the conductor portion is reduced due to cracks caused by metal fatigue. Although it is impossible to prevent the occurrence of cracks due to metal fatigue in a system that undergoes repeated plastic deformation, an increase in electrical resistance can be suppressed by suppressing the progress of cracks. The development of cracks due to metal fatigue is generally considered to go through the following process.
1st stage: stage where cracks along the slip surface develop due to shear component of stress 2nd stage: stage where crack progresses perpendicular to the stress direction due to cleavage component of stress In the 1st stage, cracks shear along the slip surface Therefore, there is almost no increase in electrical resistance. On the other hand, in the second stage, since the crack spreads in the cleavage direction, the electrical resistance increases.

  In view of this, the present inventor has conducted intensive research to improve the energization reliability of the rolled copper alloy foil for bending, with the primary purpose of facilitating shear deformation along the sliding surface in the first stage and suppressing the increase in electrical resistance. As a result, it has been found that a rolled copper foil having one or more of the following characteristics, and preferably having all of them, has particularly excellent energization reliability. In the present specification, excellent energization reliability means that, for example, an FPC having a circuit width of 1 mm having a wiring pattern as shown in FIG. It is 5% or less after 100,000 times of bending and 10% or less after 150,000 times of bending.

The characteristics to be possessed by the copper alloy foil according to the present invention are as follows. First, one or more elements selected from Fe, Ni, Ag and Al are contained at a concentration in a range where they are dissolved in Cu, with the balance being Cu and inevitable. And having a composition consisting of mechanical impurities. Secondly, in a state of annealing at 200 ° C. for 30 minutes and tempering to a recrystallized structure, the (200) plane X-ray diffraction intensity I obtained on the rolled surface and the (200) plane X in the copper powder are obtained. The ratio I / I ₀ (200) to the line diffraction intensity I ₀ is 60 or more. Third, in a state where annealing is performed at 200 ° C. for 30 minutes and the recrystallized structure is tempered, the orientation in which the main slip surface can be active with respect to bending deformation (the main slip surface is 40 ° to the deformation direction). The ratio of the crystal grains oriented in the direction of 50 ° is usually 80% or more in terms of the area ratio as observed from the rolling surface. Fourth, the surface roughness Ra is 0.2 μm or less.

  By using the copper alloy foil according to the present invention, a copper-clad laminate is manufactured according to a conventional method, and further FPC is manufactured, whereby an FPC with high conduction reliability is obtained. For example, by introducing an annealing process in which the copper foil is tempered into a recrystallized structure during the FPC manufacturing process, it is possible to manufacture an FPC with high conduction reliability.

  According to the present invention, it is possible to provide a rolled copper alloy foil for bending excellent in energization reliability, and an FPC employing the copper alloy foil according to the present invention can have high energization reliability.

The rolled copper alloy foil for bending according to the present invention has a concentration in a range in which one or more elements selected from Fe, Ni, Ag and Al, particularly Ag is dissolved in Cu (for example, 0.005 to 0.500 in total amount). It is preferable that the composition has a composition composed of Cu and inevitable impurities. Fe, Ni, Ag, and Al have a function of increasing the stacking fault energy by dissolving in copper, which contributes to facilitating shear deformation along the slip surface.
Further, as will be described later, it is desirable that the workability during finish rolling be as high as possible. However, if finish rolling is performed at a high workability (for example, 99% or more), cracks are likely to occur. However, the addition of the above-described additive element suppresses the generation of cracks and makes it easy to adopt such a high degree of processing.
Furthermore, Ag has the effect of promoting the development of the cubic orientation and increasing the flexibility when annealing and refining to a recrystallized structure.

In order to facilitate shear deformation along the slip surface, it is desirable to control the crystal orientation. It is advantageous to control the crystal orientation by increasing the workability of the finish cold rolling as much as possible, generally 90% or more, preferably 98%, more preferably 99% or more (for example, 99.5%, 99.9%), the development of the cubic orientation is promoted when the recrystallized structure is tempered later, and the flexibility is improved. Here, the rolling degree (R)% is defined by R = (t ₀ −t) / t ₀ × 100 (t ₀ : thickness before rolling, t: thickness after rolling).
In the present invention, the degree of alignment of the crystal orientation is 200 ° C., annealed at 30 ° C., and tempered to a recrystallized structure. The ratio I / I ₀ (200) of the (200) plane to the X-ray diffraction intensity I ₀ is preferably 60 or more, more preferably 70 or more, for example, 70 to 80. The intensity I ₀ of the (200) plane obtained by X-ray diffraction with copper powder was selected as a reference value for the state in which the crystals were disorderly oriented (the state where the (200) plane was not developed).

Further, the rolled copper alloy foil for bending according to the present invention is oriented in an orientation in which the main sliding surface can be active against bending deformation in a state where the recrystallization structure is tempered by annealing at 200 ° C. for 30 minutes. It is preferable to have a crystal structure in which the proportion of crystal grains is 80% or more, particularly 90% or more in terms of area ratio as observed from the rolling surface. This is because shear deformation along the slip surface becomes easy.
Such a crystal structure can be obtained by adjusting additive elements and intermediate annealing and cold rolling conditions.

Further, when the arithmetic average roughness (surface roughness Ra) on the surface of the copper foil is reduced, the generation of cracks from the surface recesses is suppressed, and the deformation of the copper foil is easily performed by shear deformation along the sliding surface. Therefore, it is preferable to control the surface roughness Ra to 0.2 μm or less, particularly 0.1 μm or less. In the present invention, the surface roughness Ra indicates a value when measured using a stylus type surface roughness meter (SE-3400 manufactured by Kosaka Seisakusho Co., Ltd.) under conditions based on JIS B-0601-2001.
The control of the surface roughness Ra can be performed by a known method, and those skilled in the art will understand the degree of processing for each pass during rolling, the rolling speed, the viscosity of the rolling oil, the diameter of the rolling roll, the roughness of the rolling roll surface, And it can adjust by changing a rolling reduction etc. suitably.

The rolled copper alloy foil for bending according to the present invention can be tempered to a recrystallized structure by typically annealing at 200 ° C. for about 30 minutes. When the copper foil is annealed and recrystallized, cubic orientation grains are formed at the initial stage of recrystallization. Thereafter, even if annealing is continued, the degree of development of the cube texture hardly changes. In addition, since the degree of cube orientation development does not depend greatly on the annealing temperature, when combined with the process of refining copper foil to a recrystallized structure in the bonding process with the resin substrate, it is compared with the temperature conditions required on the resin side. Easy to adapt.
Therefore, when the bending rolled copper alloy foil according to the present invention is used as an FPC wiring member, cutting and bonding with a resin substrate are performed in a rolled state from the viewpoint of FPC manufacturability, and then the resin substrate and It is convenient to anneal at the time of heating in the bonding process and to temper the recrystallized structure (however, this means that the copper foil is tempered to the recrystallized structure before or after the bonding process with the resin substrate. It is not something that is excluded.)
For example, in a three-layer flexible substrate, a copper foil and a resin film such as polyimide are bonded together using an adhesive made of a thermosetting resin such as epoxy. In order to cure the adhesive, heat treatment is performed at a temperature of 130 to 170 ° C. for several hours to several tens of hours. By this heat treatment, the copper foil can be tempered to a recrystallized structure. In the casting method, which is one of the methods for producing a two-layer flexible substrate, a varnish containing polyamic acid, which is a precursor of a polyimide resin, is applied on a copper foil and cured by heating to form a polyimide film on the copper foil. . In this heat curing treatment, heating is performed at a temperature of about 300 ° C. for several tens of minutes to several hours, and the copper foil can be tempered to a recrystallized structure by this heat treatment.

When the thickness of the copper foil is reduced, the bendability is improved because the strain generated on the outer periphery of the bent portion during bending is reduced. Since the rolled copper alloy foil for bending according to the present invention is suitable as a flexible wiring member, and particularly intended for application to FPC, the thickness of the copper foil is preferably 50 μm or less, and 20 μm or less. More preferably, it is 10-20 micrometers, for example. Further, the thickness can be reduced to 10 μm or less by performing thinning etching after bonding with the resin substrate. When the rolled copper alloy foil for bending according to the present invention is annealed at 200 ° C. for 30 minutes and tempered to a recrystallized structure, for example, FPC with a circuit width of 1 mm is subjected to a repeated stress with a surface strain of 0.3% or more. In the receiving system, the electric resistance increase rate is 5% or less after 100,000 bending, 10% or less after 150,000 bending, preferably 1% or less after 100,000 bending, and 150,000 bending 4% or less. Here, the surface strain is given by the following equation.
(Surface strain) = (Deformation amount of copper foil surface by bending) / (Bending length)
The deformation amount of the copper foil surface indicates (AB-A′B ′) in FIG. 5, and the bent portion length indicates AB.
Illustratively, when a bending test is performed on a copper foil having a bending speed of 1000 times / minute, a sliding width of 20 mm, a bending radius of 2.5 mm, and a thickness of 18 μm, the increase rate of electrical resistance is 5 when the number of bendings is 100,000. %, And it is 10% or less after 150,000 flexions. Preferably, it is 1% or less at 100,000 times of bending and 4% or less at 150,000 times of bending.

  For this reason, the FPC manufactured using the rolled copper alloy foil for bending according to the present invention has high energization reliability, wiring to a movable part such as a head part of a printer or a drive part in a hard disk, and also a mobile phone or a notebook. It can be suitably used for wiring to a portion that is repeatedly bent, such as wiring of a folded portion of a personal computer, or wiring that repeatedly receives stress due to contraction due to thermal cycling.

  The following examples are provided to better understand the present invention and its advantages, but are not intended to limit the present invention.

Example 200 ppm of Ag was added to tough pitch copper to melt an ingot having a thickness of 170 mm. This ingot is hot-rolled to a thickness of 8 mm, and then cold-rolling and annealing are repeated. Finally, finish cold-rolling is performed at a workability of 99% to obtain a rolled copper foil having a thickness of 18 μm. It was. In finish cold rolling, the surface roughness was controlled by adjusting the thickness of the rolling oil film. The crystal structure was controlled by adjusting the additive elements, intermediate annealing conditions, and the finishing degree of finish rolling.
Comparative Example 1
An ingot of tough pitch copper having a thickness of 170 mm was melted. This ingot is hot-rolled to a thickness of 8 mm, and then cold-rolling and annealing are repeated. Finally, finish cold-rolling is performed at a workability of 80% to obtain a rolled copper foil having a thickness of 18 μm. It was. In finish cold rolling, the surface roughness was controlled by adjusting the thickness of the rolling oil film. The crystal structure was controlled by adjusting the intermediate annealing conditions and the finishing degree of finish rolling.
Comparative Example 2
An ingot having a thickness of 170 mm was melted by adding 1200 ppm of Sn to tough pitch copper. This ingot is hot rolled to a thickness of 8 mm, and then cold rolling and annealing are repeated. Finally, finish cold rolling is performed at a workability of 80% or more, and a finished copper foil having a thickness of 18 μm is obtained. Obtained. In finish cold rolling, the surface roughness was controlled by adjusting the thickness of the rolling oil film. The crystal structure was controlled by adjusting the intermediate annealing conditions and the finishing degree of finish rolling.
Comparative Example 3
An electrolytic copper foil (thickness: 18 μm) made on the assumption that it is used for bending applications was used.

  These copper foils were processed into a two-layer copper clad laminate (CCL) coated with 25 μm polyimide. During the heat curing of the polyimide, heat treatment was performed at 350 ° C. for 15 minutes. The obtained two-layer CCL was subjected to wiring pattern processing to produce an FPC sample, and the following evaluation was performed. In addition, it is thought that copper foil was tempered by the said heat processing to the recrystallized structure similar to annealing by 200 degreeC and 30 minutes.

The integral value (I) of the diffraction intensity of the (200) plane on the X-ray diffraction rolled surface was determined. This value was divided by the integrated diffraction intensity value (I ₀ ) of the (200) plane of copper powder (sample with random orientation) manufactured by Kanto Chemical Co., which had been measured in advance, to calculate I / I ₀ . For measurement of the integrated value of peak intensity, a Co tube was used for both the copper foil and the copper powder. The results are shown in Table 1.

Surface roughness (Ra)
According to JIS B0601-2001, the surface roughness (Ra) was calculated | required using the stylus type surface roughness meter (SE-3400 by Kosaka Manufacturing Co., Ltd.). The reference length was set to 0.8 mm and measured in the rolling parallel direction. Ra was measured three times at different locations, and the average value was obtained. The results are shown in Table 1.

Bending test Next, each of the obtained two-layer CCL width is etched into the shape shown in FIG. 2 1 mm, circuit and four form of length 100 mm (polyimide thickness 25 [mu] m, copper foil thickness 18 [mu] m), 3 Using the apparatus, the rate of increase in electrical resistance due to bending was measured. This apparatus has a structure in which a vibration transmission member 3 is coupled to an oscillation driver 4, and the test piece 1 is attached to the apparatus at a total of four points including a screw 2 portion indicated by an arrow and a tip portion of the vibration transmission member 3. Fixed. When the vibration transmitting member 3 is driven up and down, the intermediate portion of the test piece 1 is bent into a hairpin shape with a predetermined bending radius r. The test conditions are as follows. The electric resistance was measured between both ends of a circuit formed in a W shape. The results are shown in FIG.
Specimen width: 1mm
Test piece length: 100 mm
Specimen sampling direction: Collected so that the length direction of the specimen is parallel to the rolling direction Bending radius r: 2.5 mm
Bending direction: Resin surface is outside Sliding width: 20 mm
Bending speed: 1000 times / min Surface strain: 0.4%

The ratio of the crystal grains oriented in the orientation in which the main slip surface can be active with respect to the bending deformation of the crystal structure was evaluated by observing the surface of the copper foil after bending 10,000 times with an optical microscope. Crystals with active slip planes appear dark in optical observations because of the development of slip bands on the surface. Therefore, the area ratio occupied by the crystal grains with slip bands developed on the surface of the copper foil due to the activity of the slip surface was determined based on the difference in brightness. The results are shown in FIG.

It is a figure showing the relationship between the frequency | count of bending of copper foil, and the increase rate of an electrical resistance. It is a figure which shows the wiring pattern of the sample used for evaluation this time. It is the schematic of a bending test apparatus. It is the photograph by the optical microscope of the crystal structure of the copper foil observed on the rolling surface. It is a schematic diagram of the cross section of a CCL bending part.

Explanation of symbols

1: Test piece 2: Screw 3: Vibration transmission member 4: Oscillation drive

Claims (10)

  When the FPC with a circuit width of 1 mm is annealed at 200 ° C. for 30 minutes to obtain a recrystallized structure, the electrical resistance increase rate is 100,000 times in a system that undergoes repeated stress with a surface strain of 0.3% or more. A rolled copper alloy foil for bending with a rolling finish, characterized by being 5% or less after bending and 10% or less after bending 150,000 times. When annealed at 200 ° C. for 30 minutes and tempered to a recrystallized structure, the (200) plane X-ray diffraction intensity I obtained on the rolled surface and the (200) plane X-ray diffraction intensity I obtained on the copper powder _The rolled copper alloy foil for bending according to claim 1, wherein the ratio I / I ₀ (200) to ₀ is 60 or more.   When annealed at 200 ° C. for 30 minutes and tempered to a recrystallized structure, the proportion of crystal grains oriented in the orientation in which the main slip surface can be active with respect to bending deformation is the area by observation from the rolling surface. The rolled copper alloy foil for bending according to claim 1 or 2, having a crystal structure that is 80% or more in terms of rate.   One or more elements selected from Fe, Ni, Ag and Al are contained at a concentration in a range where they are solid-solved in copper, and the balance has a composition consisting of Cu and inevitable impurities. Rolled copper alloy foil for bending as described in 1.   The rolled copper alloy foil for bending according to any one of claims 1 to 4, wherein the finished cold rolling has a workability of 90% or more.   The rolled copper alloy foil for bending after rolling according to any one of claims 1 to 5, wherein the surface roughness Ra is 0.2 µm or less.   The copper alloy foil which annealed the bending finished alloy foil as described in any one of Claims 1-6, and refined it to the recrystallized structure.   A copper-clad laminate using the copper alloy foil according to claim 7.   An FPC using the copper alloy foil according to claim 7.   The FPC according to claim 9, wherein the FPC is used in a wiring portion where the electronic device is repeatedly bent.