CN103361509B - Rolled copper foil, copper-clad laminated board, flexible printing wiring board and manufacture method thereof - Google Patents

Abstract

The present invention relates to rolled copper foil, copper-clad laminated board, flexible printing wiring board and manufacture method thereof.Its problem is to provide a kind of for bending rolled copper foil, copper-clad laminated board, the flexible printing wiring board (FPC) with the weather resistance more spent.Its solution is that a kind of interval decreasing the mitigation of the stress in bending bends tolerance Copper Foil.

Description

Rolled copper foil, copper clad laminate, flexible printed wiring board, and manufacturing method thereof

technical field

The present invention relates to a rolled copper foil, a copper clad laminate, a flexible printed wiring board and a manufacturing method thereof.

Background technique

An electronic device is generally composed of a plurality of electronic substrates, and a flexible printed wiring board (hereinafter, sometimes referred to as FPC) that electrically connects these electronic substrates is provided between the electronic substrates. A flexible printed wiring board generally includes an insulating substrate and copper wiring formed on the surface of the substrate. Favorable bendability etc. are required for the flexible printed wiring board which connects electronic board|substrates.

Especially in recent years, due to the popularization of small electronic devices such as cellular phones, digital cameras, and video cameras equipped with movable parts such as folding parts, rotating parts, or slide-out parts, miniaturization, thinning, and high density have continued. Flexibility required for flexible printed wiring boards used in movable parts becomes higher.

As the characteristics required for such flexible printed wiring boards, there are good bendability represented by MIT bendability, and high cycle bendability represented by IPC bendability, and copper foils having such characteristics have been developed in the past. , Copper-resin substrate laminated body (Patent Documents 1~2).

For example, in the sliding bending test (IPC), flexible printed wiring boards that can withstand bending times of more than 100,000 times using a test device, which can withstand a number of bending times that are generally impossible in reality, have been commercialized.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2010-100887;

Patent Document 2: Japanese Unexamined Patent Publication No. 2009-111203.

The problem to be solved by the invention

However, even small electronic devices using flexible printed wiring boards, such as foldable mobile phones, slide covers, etc. In actual products, the failure of the flexible printed wiring board to break does not disappear. As reasons why such failures still occur in actual products even when FPCs that can withstand a large number of bending times are used, contact between parts caused by high density, sandwiching of FPCs by other parts, and problems caused by the tip of sharp parts have been studied. There are countless reasons, such as cracks in the body, heat generation outside the design, and deterioration of the insulating material due to chemical reactions, and countermeasures have been taken.

In view of the fact that failures of flexible printed wiring board breaks do not disappear in actual products, the present inventors considered that the problem can be solved by improving the copper foil of FPC itself without separately seeking the cause of these failures, and conducted research and development. .

Contents of the invention

Therefore, an object of the present invention is to provide a rolled copper foil, a copper-clad laminate, and a flexible printed wiring board (FPC) that have higher durability against bending when used in an actual product in an FPC.

Solution to the problem

Under such circumstances, the present inventors considered that a flexible printed wiring board that can withstand a number of times of bending (for example, 100,000 times) that is generally impossible in reality in the sliding bending test (IPC) can be used in real products (such as folding In fact, fracture failures still occur in mobile phones and slide-type mobile phones), but it is thought that these fractures can be avoided by further improvement of FPC, and intensive research is carried out.

Furthermore, the present inventors conceived that the sliding bending test (IPC), which is now a standard test method, does not reflect the actual product use environment, and instead reduced the number of times of bending (per unit time) in the bending test to conduct various tests. Surprisingly, experimental studies have found a phenomenon that cracks are easily generated by intermittently giving bending.

On this basis, the present inventors discovered that this unexpected phenomenon is caused by the stress relaxation phenomenon of the copper foil, and found that it is precisely because of the pursuit of thinner FPC copper foil that it is generally considered to have a theoretical The possible stress relaxation phenomenon has a great influence on the fracture of actual products, and it was discovered that in the manufacture of copper foil, by minimizing the occurrence of stress relaxation, the bending resistance under the conditions encountered by actual products can be improved. performance is greatly improved, thereby realizing the present invention.

That is, according to the present invention, by manufacturing the copper foil and the FPC in such a manner as to satisfy the conditions for relaxing and reducing the stress of the copper foil of the FPC, the durability against intermittent bending can be improved, and it is possible to reduce the stresses encountered by actual products. The breakage of the FPC. Therefore, FPC and copper foil that reduce stress relaxation and improve intermittent bending resistance are included in the scope of the present invention regardless of the specific means for reducing stress relaxation.

Therefore, the present invention resides in the following (1)~.

(1)

An intermittent bending resistant copper foil with reduced stress relaxation in bending.

(2)

A copper foil with intermittent bending resistance according to (1), which satisfies the condition of the following formula I with respect to a deformation of 0.2% at 25° C.:

(T ₀ -T ₅ )/T ₀ ≤ 25 (%) (Formula I)

(where _T0 represents the initial stress, and T5 represents the stress after ₅ hours).

(3)

An intermittent bending resistant copper foil having a grain boundary length of 200 μm or less per observed cross-sectional area of 1000 μm ² when viewed in a rolled parallel section.

(4)

In the intermittent bending resistant copper foil according to (1) or (2), the length of the crystal grain boundary per 1000 μm ² of observed cross-sectional area is 200 μm or less when viewed from a rolling parallel section.

(5)

The intermittent bending resistant copper foil according to any one of (1) to (4), which has a Young's modulus in the range of 60 to 105 GPa.

(6)

The intermittent bending resistance copper foil according to any one of (1) to (5), wherein the copper foil contains copper and unavoidable impurities.

(7)

The intermittent bending resistance copper foil according to any one of (1) to (5), wherein the copper foil contains copper and unavoidable impurities, and further contains Ag, Sn, In, Copper foil made of one or more elements selected from the group consisting of Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and V.

(8)

The intermittent bending resistance copper foil according to any one of (1) to (5), wherein the copper foil is made of oxygen-free copper or tough copper.

(9)

The intermittent bending-resistant copper foil according to any one of (1) to (5), wherein the copper foil contains Ag, Sn , In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B and V constitute the group of one or more elements selected from the copper foil formed.

(10)

The intermittent bending resistant copper foil according to any one of (1) to (9), wherein the copper foil is a rolled copper foil.

(11)

The intermittent bending resistance copper foil according to any one of (1) to (10), wherein the copper foil is a rolled copper foil obtained by rolling with a processing degree of 96% or more.

(12)

The intermittent bending resistance copper foil according to any one of (1) to (11), wherein the copper foil is copper foil for a flexible printed wiring board.

(13)

The intermittent bending resistant copper foil according to any one of (1) to (11), wherein the copper foil is laminated on a flexible printed wiring board.

(14)

The intermittent bending resistant copper foil according to any one of (1) to (11), wherein the copper foil is a copper foil for a copper-clad laminate.

(15)

The intermittent bending resistant copper foil according to any one of (1) to (11), wherein the copper foil is laminated on a copper-clad laminate.

Furthermore, the present invention resides in the following (21)~.

(twenty one)

Copper foil which becomes the intermittent bending resistance copper foil as described in any one of (1)-(14) after heat-processing at 160-400 degreeC for 1 second - 1 hour.

(twenty two)

A copper foil having the intermittent bending resistance described in any one of (1) to (14) after heat treatment at 200°C for 30 minutes or heat treatment at 350°C for 1 second copper foil.

(twenty three)

A flexible printed wiring board in which the intermittent bending-resistant copper foil according to any one of (1) to (10), (11), and (12) is laminated.

(twenty four)

A copper-clad laminate obtained by laminating the intermittent bending-resistant copper foil according to any one of (1) to (10), (13), and (14).

Furthermore, the present invention resides in the following (31)~.

(31)

A method of manufacturing rolled copper foil, comprising:

The process of casting copper ingots;

The process of hot rolling copper ingots;

A process of cold-rolling and annealing hot-rolled copper ingots more than once; and

The final cold rolling process to make the thickness of the finished product is performed.

(32)

According to the production method described in (31), in the process of performing the final cold rolling for making the thickness of the finished product,

The total processing degree (final rolling processing degree) of the final cold rolling used to make the finished product thickness is 96% or more.

(33)

In the production method according to any one of (31) to (32), in the step of performing cold rolling and annealing one or more times on the hot-rolled copper ingot,

The final annealing is performed at a temperature increase rate of 5°C/sec to 40°C/sec.

(34)

In the manufacturing method according to any one of (31) to (33), in the step of performing one or more cold rolling and annealing on the hot-rolled copper ingot,

The cold rolling performed just before the final annealing is performed at a working degree (total working degree) of 60% to 90%.

(35)

In the production method according to any one of (31) to (34), the copper ingot is a copper ingot containing copper and unavoidable impurities.

(36)

According to the production method described in any one of (31) to (35), the copper ingot contains copper and unavoidable impurities, and further contains Ag, Sn, In, Ti, Zn, A copper ingot made of one or more elements selected from the group consisting of Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and V.

(37)

In the production method according to any one of (31) to (34), the copper ingot is a copper ingot made of oxygen-free copper or ductile copper.

(38)

According to the production method described in any one of (31) to (34) and (37), the copper ingot is added with a total of 20 to 500 mass ppm of Ag, A copper ingot made of one or more elements selected from the group consisting of Sn, In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and V.

Furthermore, the present invention resides in the following (41)~.

(41)

A method for manufacturing intermittent bending resistant copper foil, comprising: performing rolling at 160 to 400°C for 1 second to 1 hour on the rolled copper foil manufactured by the manufacturing method of any one of (31) to (36). heat treatment process.

(42)

A method of manufacturing an intermittent bending resistant flexible printed wiring board, comprising:

A step of laminating the rolled copper foil produced by the production method of any one of (31) to (36) with a matrix resin; and

A process of heat-treating the rolled copper foil laminated with the matrix resin at 160-400° C. for 1 second to 1 hour.

(43)

A method for manufacturing a copper-clad laminate, comprising:

A step of laminating the rolled copper foil produced by the production method of any one of (31) to (36) with a matrix resin; and

A process of heat-treating the rolled copper foil laminated with the matrix resin at 160-400° C. for 1 second to 1 hour.

Furthermore, the present invention resides in the following (51)~.

(51)

A rolled copper foil produced by the production method of any one of (31) to (36).

(52)

An intermittent bending resistant copper foil manufactured by the manufacturing method of (41).

(53)

An intermittent bending resistant flexible printed wiring board manufactured by the manufacturing method of (42).

(54)

A copper clad laminate manufactured by the manufacturing method of (43).

The effect of the invention

According to the present invention, copper foil with intermittent bending resistance can be obtained, and rolled copper foil, copper-clad laminate, and flexographic printing with higher durability against bending can be obtained when used in FPC in actual products. Wiring board (FPC). In an electronic device using a flexible printed wiring board (FPC) provided with the intermittent bending-resistant copper foil of the present invention, since the FPC serving as the movable part has bending resistance reflecting the actual usage conditions in the product, Therefore, it is superior in durability and reliability compared with conventional products that only consider the resistance to continuous bending.

Description of drawings

FIG. 1 is an explanatory view showing the state of the curved inner surface and outer surface of copper foil.

FIG. 2 is an explanatory diagram illustrating a shift of a hysteresis loop.

Fig. 3 is an electron micrograph of a rolling parallel section for observing grain boundaries.

Detailed ways

Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

As mentioned above, conventionally, the bendability evaluation of copper foil was performed using continuous bending motion. However, the inventors of the present invention have found that the copper foil may break with a smaller number of times of bending in intermittent bending than in continuous bending. Furthermore, it was found that the change in the fracture life is caused by the stress relaxation phenomenon of the copper foil, and arrived at the present invention.

According to studies by the present inventors, when the copper foil is repeatedly bent, tensile stress and compressive stress act alternately on the surface of the copper foil. In the case of continuous bending, the same tensile/compressive stress acts regardless of how many times the bending is repeated. The bending test performed in this state is a conventional bending test. However, in the case of intermittent bending, stress relaxation occurs between bending and the hysteresis loop (hysteresis loop) shifts to the low-stress side. Therefore, when bending is resumed, the hysteresis loop shifts from the original, resulting in stress The amplitude becomes larger. The present inventors have come to the conclusion that this is the reason why intermittent bending has a shorter lifetime than continuous bending.

An explanatory diagram illustrating this phenomenon is shown in FIG. 1 . Fig. 1 is an illustration showing that the outer surface is in a state of tension and the inner surface is in a state of compression when it is assumed that the inside and outside of the bend of the copper foil are divided into an outer surface (outer surface) and an inner surface (inner surface). picture. As shown in the figure, since the outer surface is in tension, if this state is maintained, stress relaxation in the tension state occurs soon, and as a result, the hysteresis loop shifts toward the compression side with respect to the outer surface. On the other hand, as shown in the figure, since the inner surface is in a compressed state, if this state is maintained, stress relaxation in the compressed state will occur soon, and as a result, the hysteresis loop with respect to the inner surface will shift toward the tension side. status.

FIG. 2 shows an explanatory diagram illustrating such a shift of the hysteresis loop. In FIG. 2 , the horizontal axis represents deformation, and the vertical axis represents stress. In FIG. 2, three hysteresis loops of an upper part, a central part, and a lower part are shown. The hysteresis loop at the center is a hysteresis loop when bending is performed continuously. If no shift due to stress relaxation occurs, the hysteresis loop is originally positioned as the hysteresis loop at the central portion. In the conventional continuous bending test, it can be said that, for example, 100,000 times of bending tests are performed along this hysteresis loop. Therefore, if FBCs are used in actual small electronic devices along such a hysteresis loop, FBCs should all withstand, for example, more than 100,000 bending times, showing the durability expected by various manufacturers.

The upper hysteresis loop in FIG. 2 is a hysteresis loop in which the inner surface side of the copper foil deviates due to stress relaxation and is observed after the copper foil is bent and stress relaxation occurs with the passage of time. The hysteresis loop in the lower part of FIG. 2 is a hysteresis loop in which the outer surface side of the copper foil deviates due to stress relaxation and is observed after the copper foil is bent to cause stress relaxation with the passage of time. In this way, when the copper foil is bent and held to cause stress relaxation over time, the same copper foil has different hysteresis loops on the outer surface side and the inner surface side.

Furthermore, after that, when the copper foil is bent to the opposite side, that is, the previous outer side becomes the inner side this time, and the former inner side becomes the outer side this time, the hysteresis from the upper part of FIG. The loop goes to the lower hysteresis loop, and at the same time, from the lower hysteresis loop to the upper hysteresis loop, a large amplitude exceeding each hysteresis loop is applied to both surfaces of the copper foil. Then, if the copper foil is bent to the opposite side again and held, a large amplitude exceeding each hysteresis loop is applied to both sides of the copper foil again. Stress relaxation occurs, and the amplitude of stress and deformation increases. Arrows in FIG. 2 indicate the occurrence of such a shift (amplitude) of the hysteresis loop. When intermittent bending is continued in this way, compared with the case of continuous bending that only circulates the hysteresis loop in the center, severe deformation is applied to the copper foil. The copper foil is broken when the number of times of bending is endured.

Then, in order to avoid such damage, this inventor thought the idea of improving the stress relaxation characteristic of copper foil. Therefore, the present invention resides in improving intermittent bendability of copper foil by reducing stress relaxation or preventing occurrence of stress relaxation, and further resides in copper foil (including copper foil in FPC) with improved intermittent bendability. In this specification, although the concrete embodiment for improving the intermittent bendability of copper foil was given and this invention was demonstrated, this invention is not limited to the concrete embodiment mentioned above.

Furthermore, in order to avoid such breakage, the present inventors thought that by reducing the Young's modulus of copper foil, the stress change with respect to deformation|transformation amount can be made small. This makes it possible to suppress increases in stress and deformation amplitude even when stress relaxation occurs. Therefore, the present invention also resides in improving the intermittent bendability of the copper foil by reducing the Young's modulus of the copper foil, and further resides in the copper foil (including the copper foil in FPC) in which the intermittent bendability is improved. In this regard, in this specification, specific embodiments for improving the intermittent bendability of copper foil are given and the present invention is described, but the present invention is not limited to the specific embodiments mentioned in this way.

[stress relief]

Stress relaxation is a phenomenon in which the stress applied to a metal decreases over time under the conditions of a fixed temperature and a fixed deformation.

Stress relaxation is a phenomenon produced by movement of dislocations in a material microscopically. Such movement of dislocations tends to occur at grain boundaries. Therefore, in the present invention, the length of the crystal grain boundary of copper foil is reduced as a means for stress relaxation and reduction, thereby improving tolerance to intermittent bending.

[Grain boundary length]

The length of the grain boundary (grain boundary length) can be obtained, for example, by forming a rolled parallel cross-section on a copper foil annealed at 200° C. for 30 minutes using CP (Cross section polisher). EBSD (Electron Back Scattering Diffraction, backscattered electron diffraction, JXA8500F manufactured by JEOL Ltd.), with a step size of 0.5 μm, an acceleration voltage of 15 kV, a WD of 23 mm, and a current of 5×10 ^-8 A to measure the crystal orientation in the observation range of 1000 μm ² , The case where the crystal orientation difference from the adjacent measurement point was 15 degrees or more was regarded as a grain boundary, and the length of the grain boundary included in the observation range was measured.

In a preferred embodiment, the length of the grain boundary per observed cross ^- sectional area of 1000 μm seen from the rolling parallel section can be set to, for example, 200 μm or less, preferably 100 μm or less, more preferably 90 μm or less, more preferably set to It is 70 μm or less, more preferably 50 μm or less. From the viewpoint of reducing stress relaxation, the smaller the length of the grain boundary, the better. On the other hand, in a preferred embodiment, the length of the crystal grain boundary can be set to, for example, 0.1 μm or more, for example, 1.0 μm or more, for example, 5.0 μm or more. From the viewpoint of the strength of the copper foil, it is preferable that the length of the grain boundary is a value equal to or greater than this value.

In order to show the length of the grain boundary, FIG. 3 shows an example of an electron micrograph of the observed rolling parallel section. In FIG. 3 , three cross-sectional photographs of upper, middle and lower are shown as horizontally long photographs. In the cross-sectional photograph in the upper part of FIG. 3 , crystal grain boundaries are hardly visible. This sample sheet in which crystal grain boundaries were hardly seen showed good intermittent bending resistance (good). In addition, since the copper foil is extremely thin, in order to obtain an electron micrograph, the support body was brought into contact with the copper foil for observation. The uppermost black part of the upper cross-sectional photo is the gap between the support body and the copper foil. The lower white part is a support. In the lower cross-sectional photograph of FIG. 3 , many grain boundaries are observed. This sample piece in which many grain boundaries were observed was a sample poor in intermittent bending resistance (poor). In the cross-sectional photograph in the middle of FIG. 3 , moderate grain boundaries are observed. The sample sheet was superior in intermittent bending resistance to the sample of the above-mentioned lower cross-sectional photograph, but inferior to the sample of the above-mentioned upper cross-sectional photograph.

[Stress relaxation rate]

The stress relaxation ratio is obtained by cutting, for example, copper foil annealed at 200°C for 30 minutes into strips with a width of 12.7 mm using a precision cutter, and using a tensile testing machine (Shimadzu Corporation AGS-X), fixed at a distance of 50mm between the chucks, stretched to 50.1mm between the chucks and measured the change of stress at 25°C, the stress T _t obtained after t hours and the initial (0 hours After dividing the difference of stress T ₀ by the initial stress T ₀ {(T ₀ -T _t )/T ₀ } as the stress relaxation rate (%) after t hours.

In a preferred embodiment, the stress relaxation ratio (%) of the intermittent bending resistant copper foil of the present invention can satisfy the following formula I with respect to a deformation of 0.2% at 25°C when t=5 hours conditions of:

(T ₀ -T ₅ )/T ₀ ≤ 25 (%) (Formula I)

(where _T0 represents the initial stress and T5 represents the stress after ₅ h),

And then preferably can satisfy the condition of following formula II:

(T ₀ -T ₅ )/T ₀ ≤ 20 (%) (Formula II)

conditions of. More preferably, the value of (T ₀ −T ₅ )/T ₀ can be set to 19% or less.

[Young's modulus]

The Young's modulus can be measured, for example, using a resonant measuring device (TE-RT manufactured by Nippon Technoplas Co., Ltd.). In a preferred embodiment of the present invention, the Young's modulus of the intermittent bending resistance copper foil can be set to, for example, 60 to 105 GPa, preferably 70 to 105 GPa, more preferably 70 to 100 GPa, more preferably 70 ~90GPa, more preferably in the range of 75~85GPa.

[components]

The components of the copper foil of the present invention can be used as long as they reduce stress relaxation. For example, pure copper containing copper and unavoidable impurities can be used. In a preferred embodiment, as a component of the copper foil, tough copper conforming to the standard of alloy number C1100 of JIS-H3100 or oxygen-free copper conforming to the standard of alloy number C1020 of JIS-H3100 can be used as a component. When such a component close to pure copper is used, the conductivity of the copper foil will not decrease, which is suitable for FPC and COF. Usually, the oxygen concentration contained in the rolled copper foil is 0.01 to 0.05% by mass in the case of tough copper, and 0.001% by mass or less in the case of oxygen-free copper. In addition, as the oxygen-free copper, oxygen-free copper conforming to the standard of alloy number C1011 of JIS-H3510 can be used.

In a preferable embodiment, as a component of the copper foil, one or more selected from the group of Ag and Sn may be contained in a total of 500 mass ppm or less of the above-mentioned component close to pure copper. Among them, the content of Sn is preferably 300 ppm or less. When the total amount of Ag or Sn added to the rolled copper foil exceeds 500 mass ppm, the electrical conductivity decreases and the recrystallization temperature rises, and the growth of recrystallized grains is suppressed during final annealing, and the grain boundary length may become longer. Although the lower limit of the total addition amount of Ag and Sn is not particularly specified, it is usually 20 mass ppm or more in total.

In a preferred embodiment, in the above-mentioned copper having a composition close to pure copper, for example, in the above-mentioned tough copper or the above-mentioned oxygen-free copper, Ag, Sn, In, Ti, Zn are contained in a total of 20 to 500 mass ppm One or more elements selected from the group of , Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and V may be used.

In addition, it is also possible to add Ag, Sn, In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb to the above-mentioned copper having a composition close to pure copper at a total of 500 mass ppm or more. One or more elements selected from the group of , B, and V can also improve stress relaxation characteristics by, for example, applying heat treatment at a high temperature of 600° C. or higher for 30 minutes or more to grow recrystallized grains. However, this step is disadvantageous in that the recrystallized soft copper foil and resin must be laminated in order to manufacture a copper-clad laminate.

[production of copper foil]

The production of the copper foil (intermittent bending resistance copper foil) of the present invention is not particularly limited as long as it is a method capable of producing a copper foil with reduced stress relaxation as described above. In a preferred embodiment, the process of casting a copper ingot using copper (copper alloy) having the above-mentioned composition, the process of hot rolling the copper ingot, and performing the hot-rolled copper ingot The production method of cold rolling and annealing one or more times, and the final cold rolling process for making the thickness of the finished product is to produce rolled copper foil, and the rolled copper foil is 1 Second to 1 hour heat treatment process, so that intermittent bending resistance copper foil can be produced. In addition, the above-mentioned heat treatment at 160 to 400° C. for 1 second to 1 hour may also be used as heat treatment in the manufacturing process of a copper-clad laminate for bonding copper foil and a resin layer.

In the step of cold-rolling and annealing the hot-rolled copper ingot one or more times, the cold-rolling and annealing can be repeated as appropriate to obtain a desired thickness. In a preferred embodiment, it is preferable that in the last annealing of the annealing, that is, in the annealing performed just before the final cold rolling process for making the finished product thickness, the temperature increase rate is set to be 5° C./second or more and 40° C. °C/sec or less. When the temperature increase rate is 5°C/sec or less, the crystal grains are coarsened, and the recrystallized structure becomes non-uniform. On the other hand, in the case of 40° C./sec or more, since fine recrystallized grains grow separately, the recrystallized structure becomes inhomogeneous.

In a preferred embodiment, in the rolling performed just before the last annealing, the workability (total workability) can be set to, for example, 90% or less, preferably 89% or less, more preferably 88% Below, for example, it can be set to 60% or more, preferably 65% or more, and more preferably 67% or more. By adopting such a range, a uniform recrystallized structure can be realized after the annealing step, and an appropriate rolled structure can be produced in the final rolling step. When the total working ratio of the rolling step performed just before the final annealing exceeds 90%, the texture is excessively developed, and the crystal grains after the annealing step tend to be coarsened.

In a preferred embodiment, in the process of performing the final cold rolling for making the thickness of the finished product, the total processing degree of the final cold rolling (final rolling processing degree) can be set to 96% or more, preferably set to 97% or more, more preferably 97.5% or more.

Furthermore, those skilled in the art understand that in each rolling process of the present invention, one rolling process can also be implemented by passing the material through the rolling rolls multiple times (multiple passes). Therefore, in the specification of this application, the working degree of a certain rolling process means that in the case where the rolling process is carried out through such multiple passes, the comprehensive working degree achieved by multiple passes does not mean In order to clarify the processing degree of any one pass (processing degree of one pass) included in this rolling process, the processing degree of a certain rolling process may be described as the total processing degree.

In a preferred embodiment, in the process of heat-treating the rolled copper foil at 160-400° C. for 1 second to 1 hour, for example, heat treatment can be performed at 200-400° C. for 1 second to 30 minutes. The heat treatment can be performed at 200° C. for 30 minutes, for example, at 350° C. for 1 second. In addition, the heating time may be shorter than 1 second, for example, 0.1 second to 1 second. By this heat treatment, the rolled copper foil subjected to the above-mentioned final cold rolling becomes the intermittent bending resistance copper foil of the present invention in which stress relaxation is reduced. This heat treatment may be performed as an independent process for rolling copper foil, but for example, when laminating resins for manufacturing copper-clad laminates and thermocompression-bonding film-like resins, the heat treatment conditions should be set Heat treatment may be performed, or, for example, when laminating a resin for manufacturing a copper-clad laminate, coating a resin material, and thermally curing it to form a film layer, heat treatment may be performed so as to meet the conditions of the heat treatment.

[Flexible printed wiring board]

The copper foil (intermittent bending resistance copper foil) of the present invention has excellent intermittent bending resistance as described above, and can be suitably used as a conductive wiring portion of a flexible printed wiring board. Therefore, this invention also resides in the flexible printed wiring board provided with the said copper foil laminated|stacked.

A flexible printed wiring board is usually formed by laminating conductive wiring on insulating resin, and is flexible and bendable. The wiring is laminated on the resin layer of the insulating base material via an adhesive layer as needed. The copper foil of the present invention shows excellent intermittent bending resistance in any laminated form. Therefore, as long as the flexible printed wiring board of the present invention is a flexible printed wiring board that is laminated with the copper foil of the present invention, various types can be used. various specific methods. In a preferred embodiment, for example, a flexible printed wiring board in which the copper foil of the present invention is bonded to a film-shaped resin layer may be a flexible printed circuit board in which the copper foil of the present invention is coated with a resin material to form a film. Wiring boards are also available. For the resin layer, resins that can be used for flexible printed wiring boards can be used without particular limitation. In a preferred embodiment, for example, polyimide resin can be used.

The flexible printed wiring board of this invention can be manufactured as follows, for example. A polyimide precursor mainly made of polyamic acid is coated on one side of a rolled copper foil, dried and cured, and processed into a copper-clad laminate with a polyimide resin layer and a copper foil layer, which is processed by photolithography A predetermined circuit is formed, and a polyimide film is bonded to the surface of the copper foil layer on the wiring side to obtain a flexible printed wiring board. In the above-mentioned copper-clad laminate, it is only necessary that the layer of copper foil is an intermittent bending-resistant copper foil. Therefore, as the above-mentioned rolled copper foil, heat treatment for forming a polyimide resin layer is used, such as What is necessary is just to receive heat processing at 200 degreeC for 30 minutes, and to become the intermittent bending resistance copper foil of this invention. In addition, for example, a polyimide film is bonded to one side of a rolled copper foil, and a polyimide resin layer and a copper foil layer are processed into a copper-clad laminate, and the subsequent photolithography and subsequent processes are performed to make flexographic printing. Wiring boards are also available. In this case, in the above-mentioned copper-clad laminate, as long as the layer of copper foil is an intermittent bending-resistant copper foil, it is used as the above-mentioned rolled copper foil, and it is used for bonding polyimide films. What is necessary is just to heat-process at 200 degreeC for 30 minutes, for example, and to become the copper foil of intermittent bending resistance copper foil of this invention.

The intermittent bending resistance copper foil of the present invention and the flexible printed wiring board using the same can be used in mobile phones, notebook computers, wiring members of lens barrels of cameras, movable parts of electronic equipment such as HDDs, automatic processing machines, and robots. It is suitably used for industrial machinery such as arms.

[Example]

Hereinafter, examples and comparative examples of the present invention will be shown together, but these examples are provided for better understanding of the present invention and its advantages, and do not limit the present invention.

[production of copper foil]

Dissolve oxygen-free copper (JIS alloy number C1020) (OFC: Oxygen-Free Copper) or tough copper (JIS alloy number C1100) (TPC: Tough-Pitch Copper), add the elements shown in Table 1 as needed, and cast to make the thickness 200mm ingot with a width of 600mm. After the ingot was hot rolled to a thickness of 10mm, cold rolling and annealing were repeated, and the final cold rolling processing degree (final rolling processing degree) used to make the finished product thickness was as described in Table 1, respectively. Making copper foil. The final rolling degree and the foil thickness at this time are as described in Table 1, respectively.

In addition, the total working ratio in the rolling step performed just before the final cold rolling and the temperature increase rate in the annealing step just before the final cold rolling are as shown in Table 1. In addition, "circle" of a temperature increase rate means that a temperature increase rate is 5 degrees C/sec or more and 40 degrees C/sec or less. In addition, "x" in Comparative Example 7 means that the annealing was performed at a temperature increase rate exceeding 40°C/sec.

[evaluate]

After the obtained rolled copper foil is annealed at 200°C for 30 minutes, or an FPC for evaluation is produced, and used for Young's modulus, grain boundary length, stress relaxation rate, and bendability (continuous bending, intermittent bending) described later evaluation of. The results obtained are summarized in Tables 1 and 2. However, in Example 2 and Comparative Example 2, the polyimide and the cover layer (cover layer) were not laminated, but they were annealed by passing through a lamination processing machine with the roller temperature adjusted to 350°C, and the production and fabrication will be described later. The same heat treatment as the heat treatment of the case of FPC was used for the evaluation. The heat treatment time at this time was set to 1 second.

[Young's modulus]

The Young's modulus was measured using a resonant measuring device (TE-RT manufactured by Nippon Technoplas Co., Ltd.).

[Grain boundary length]

The copper foil annealed under the above conditions (200°C or 350°C) is formed by using CP (Cross section polisher, section polishing) to form a rolled parallel section, using EBSD (Electron Back Scattering Diffraction, backscattered electron diffraction, JEOL Ltd. JXA8500F), the crystal orientation in the observation range of 1000 μm ² was measured with a step size of 0.5 μm, an accelerating voltage of 15 kV, a WD of 23 mm, and a current of 5×10 ^-8 A. The case where the crystal orientation difference from the adjacent measurement point was 15 degrees or more was regarded as a grain boundary, and the length of the grain boundary included in the observation range was measured.

[Stress relaxation rate]

The obtained rolled copper foil was cut into strips with a width of 12.7 mm using a precision cutter, annealed under the above conditions (200°C or 350°C), and a tensile tester (AGS-X manufactured by Shimadzu Corporation) was used. Fix with a distance of 50mm between the chucks. After that, the distance between the chucks was stretched to 50.1 mm (corresponding to 0.2% deformation), and the change in load was measured at 25°C. As the stress relaxation rate (%), a value obtained by dividing the difference between the stress T _t obtained after t hours and the initial (after 0 hours) stress T ₀ by the initial stress T ₀ {(T ₀ -T _t ) /T ₀ }. Table 2 shows the stress relaxation rate (%) in the case of t=5 hours.

[flexibility evaluation]

Copper foil obtained by rolling and a polyimide film (NIKAFLEX manufactured by Nikkan Industry Co., Ltd.: polyimide thickness 12.5 μm, adhesive thickness 15 μm) were thermocompressed (200°C, 30 minutes) to obtain Copper Clad Laminates. The obtained copper-clad laminate was etched to form an FPC with a circuit width of 100 μm, and then the cover layer (NIKAFLEX manufactured by Nikkan Industry Co., Ltd.: polyimide thickness 12.5 μm, adhesive thickness 15 μm) was thermocompressed (200°C , 30 points) to the circuit side, and made an FPC for evaluation. However, for Example 2 and Comparative Example 2, the copper foil obtained by rolling and the above-mentioned polyimide film were made into a copper-clad laminate using a laminating machine adjusted to a roll temperature of 350° C. After the FPC was produced by the method described above, the above-mentioned cover layer was bonded to the circuit surface using a lamination machine adjusted to a roll temperature of 350° C., and an FPC for evaluation was produced. Note that the total heating time at this time is 1 second.

The bending test was carried out at room temperature with the sliding speed set at 120 times per minute. In order to make the deformation applied to the copper foil uniform during bending, the bending radius is set to 1.5 mm when the copper foil thickness is 18 μm, 1.0 mm when the copper foil is 12 μm, and 0.75 mm when the copper foil is 9 μm. The number of times until breaking was evaluated. The sample is energized, and the fracture is detected by breaking the conduction. In continuous bending, if the number of breaking times is less than 100,000, then it is x, if it is 100,000 to less than 300,000, it is ○, and if it is 300,000 or more, it is ◎. In addition, in intermittent bending, 1,000 bendings were performed continuously at intervals of 5 hours. If the number of breaks is less than 50,000 times, then it is ×, if it is more than 50,000 times and less than 100,000 times, it is ○, and if it is more than 100,000 times, it is ○. ◎.

[Table 1]

[Table 2]

Industrial Utilization Possibility

According to the present invention, intermittent bending resistance copper foil can be obtained, and rolled copper foil, copper clad laminate, and flexible printed wiring having higher durability against bending when used in FPC in actual products can be obtained board (FPC). In an electronic device using a flexible printed wiring board (FPC) provided with the intermittent bending-resistant copper foil of the present invention, since the FPC serving as the movable part has bending resistance reflecting the actual usage conditions in the product, Therefore, it is superior in durability and reliability compared with conventional products that only consider the resistance to continuous bending. The present invention is an industrially useful invention.

Claims (12)

1. An intermittent bending resistant copper foil, Stress relaxation in bending is such that the condition of the following formula I is satisfied with respect to a deformation of 0.2% at 25°C: (T ₀ -T ₅ )/T ₀ ≤ 25 (%) (Formula I) where _T0 represents the initial stress, T5 represents the stress after ₅ hours, Among them, copper foil is: Contains copper and unavoidable impurities from the group consisting of Ag, Sn, In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and V at a total of 20 to 500 mass ppm Copper foil formed from one or more selected elements; or In addition to oxygen-free copper or ductile copper, Ag, Sn, In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and Copper foil made of one or more elements selected from the group consisting of V. 2. The intermittent bending resistant copper foil according to claim 1, wherein the length of the crystal grain boundary per 1000 μm ² of observed cross-sectional area is 200 μm or less when viewed in a rolled parallel section. 3 . The intermittent bending resistant copper foil according to claim 1 , which has a Young's modulus in the range of 60 to 105 GPa. 4. The intermittent bending resistant copper foil according to claim 1, wherein the copper foil is a rolled copper foil. 5 . The intermittent bending resistant copper foil according to claim 1 , wherein the copper foil is a rolled copper foil with a processing degree of 96% or more. 5 . 6. The intermittent bending resistant copper foil according to claim 1, which is laminated in a flexible printed wiring board. 7 . A copper foil which becomes the intermittent bending resistant copper foil according to claim 1 , after heat-processing at 160 to 400° C. for 1 second to 1 hour. 8 . 8. A copper foil having the intermittent bending resistance according to any one of claims 1 to 6 after heat treatment at 200°C for 30 minutes, or heat treatment at 350°C for 1 second copper foil. 9. A flexible printed wiring board in which the intermittent bending-resistant copper foil according to any one of claims 1 to 6 is laminated. 10. A method of manufacturing the intermittent bending resistant copper foil according to claim 1, comprising: The process of casting copper ingots; The process of hot rolling copper ingots; A process of cold-rolling and annealing hot-rolled copper ingots more than once; and The final cold-rolling process for making the finished product thickness is performed so that the total working ratio, that is, the final rolling working ratio, is 96% or more, wherein the hot-rolled copper ingot is cold-rolled once or more and annealing process, The final annealing is carried out at a temperature increase rate of 5°C/sec to 40°C/sec, Among them, copper ingots are: Contains copper and unavoidable impurities, and also contains Ag, Sn, In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and V in a total of 20 to 500 mass ppm Ingots of copper formed from one or more elements selected from ; or In addition to oxygen-free copper or ductile copper, Ag, Sn, In, Ti, Zn, Zr, Fe, P, Ni, Si, Te, Cr, Nb, B, and A copper ingot made of one or more elements selected from the group consisting of V. 11. The manufacturing method according to claim 10, in the step of cold-rolling and annealing the hot-rolled copper ingot more than once, The cold rolling performed just before the final annealing is performed at a working degree of 60% to 90%, that is, a total working degree. 12. A method of manufacturing intermittent bending resistant copper foil, comprising: heat-treating the rolled copper foil manufactured by the manufacturing method according to claim 10 or 11 at 160 to 400° C. for 1 second to 1 hour process.