JP4430733B2 - Method for producing rolled copper foil with excellent flexibility - Google Patents

Description

  The present invention relates to a method for producing a rolled copper foil suitable for flexible wiring members such as a flexible printed circuit board (hereinafter also referred to as FPC).

  FPC is made by laminating a copper foil on a flexible resin base material and integrated by adhesive or heat and pressure, and is widely used as a wiring member for digital cameras, mobile phones, HDDs, printers, liquid crystal panels, etc. Has been. Further, since the FPC can be bent and can be mounted in a narrow space, the FPC is often used for a movable part of a disk-related device such as an HDD, a DVD, and a CD-ROM, and a folding part of a folding mobile phone.

  As a general manufacturing process of FPC, for example, by bonding a surface-treated copper foil to a base material (base film) made of polyimide or polyester with an adhesive, and heating the whole to a temperature of 130 to 180 ° C. After the adhesive is cured, the wiring is patterned, and a coverlay is further applied thereon to protect the wiring. There is also a method of integrating the base film and the copper foil by heating and pressing at 130 to 200 ° C. instead of the adhesive.

  As the copper foil used for the FPC, rolled copper foil of tough pitch copper or oxygen-free copper having higher flexibility than the electrolytic copper foil is used from the above-described use as the wiring member for the bent portion. In order to produce these rolled copper foils, the copper material is hot-rolled, then cold rolling and annealing are repeated until a predetermined thickness is obtained, and finally the final cold rolling is performed to obtain a predetermined plate thickness. In addition, the plate | board thickness of the rolled copper foil for FPC is 50 micrometers or less normally, and it exists in the tendency which becomes still thinner with 10 or less micrometers recently.

  These rolled copper foils of tough pitch copper and oxygen-free copper are used for FPC in an annealed state because they are softened by annealing and have improved flexibility. However, since the flexibility of the FPC is determined by the copper foil that is inferior to the flexibility of the base film and the coverlay, the flexibility of the copper foil is the most important among the FPC constituent materials. For this reason, rolled copper foil made of tough pitch copper or oxygen-free copper for FPC is required to have higher flexibility from the viewpoint of the durability of the equipment.

As such a rolled copper foil having excellent flexibility, for example, in Japanese Patent No. 3009383, it has an elongation of 15% or more in a state where it is tempered to a recrystallized structure by heating at 200 ° C. for 30 minutes, and The strength (I) of the (200) plane determined by X-ray diffraction of the rolled surface is I / I ₀ > 20 with respect to the strength (I ₀ ) of the (200) plane determined by X-ray diffraction of fine powder copper. A rolled copper foil characterized by having a certain cubic texture has been reported.

Japanese Patent No. 3009383

  This invention is made | formed in view of such a conventional situation, and it aims at providing the manufacturing method of the rolled copper foil excellent in the flexibility.

  In order to achieve the above object, the method for producing a rolled copper foil excellent in flexibility provided by the present invention is to hot-roll an ingot of tough pitch copper or oxygen-free copper to a thickness of 18 mm, and further by cold rolling. After thinning to 2.0 mm and intermediate annealing, cold rolling and annealing are repeated to obtain a thickness of 1.4 to 0.14 mm, and a final thickness of 10 to 33 μm is obtained by final rolling. In the sectional structure in the plate thickness direction of the copper foil obtained by final annealing at 130 to 200 ° C. for 30 minutes, the cross-sectional area ratio of the crystal grains penetrating between both surfaces of the copper foil in the plate thickness direction is 41%. Control is as described above.

  ADVANTAGE OF THE INVENTION According to this invention, the rolled copper foil provided with the outstanding flexibility and suitable for flexible wiring members, such as a flexible printed wiring board (FPC), can be provided.

It is a schematic diagram which shows the metal structure of a rolled copper foil cross section. It is the schematic of the bending test apparatus used for the measurement of the bending life of rolled copper foil.

  As a result of earnestly studying the improvement in flexibility in rolled copper foil made of tough pitch copper or oxygen-free copper, the present inventor has obtained a cross-sectional structure of the copper foil in a state where the rolled copper foil is annealed, and both surfaces of the copper foil. It has been found that the flexibility of the copper foil is greatly improved as the ratio (cross-sectional area ratio) of the cross-sectional area of the crystal grains penetrating in the direction of the plate thickness to the total cross-sectional area increases.

  That is, in the rolled copper foil of the present invention, the rolled copper having better flexibility than the conventional one by setting the cross-sectional area ratio of the crystal grains that penetrated between both surfaces in the plate thickness direction to 41% or more. A foil can be obtained. More preferably, by setting the cross-sectional area ratio of the crystal grains penetrating between both surfaces of the copper foil in the plate thickness direction to 61% or more, the crystal grains penetrating the copper foil in the plate thickness direction appear on the copper foil surface. There is a tendency for the ratio to increase rapidly, and thus the flexibility of the copper foil is further improved.

  The reason why the flexibility of the copper foil is improved as the number of crystal grains penetrating the plate thickness increases is as follows. That is, dislocations are usually generated from within the crystal grains due to deformation due to bending, and the dislocations accumulate at the grain boundary part, and breakage occurs at the grain boundary part. On the other hand, in the part where the crystal grain penetrates the plate thickness of the copper foil, the deformation due to bending becomes the deformation of the single crystal itself, and the dislocation generated in the crystal grain escapes to the surface. It is considered that breakage is less likely to occur with respect to the deformation of.

  As shown in FIG. 1, the cross-sectional area ratio of the crystal grains penetrating through the copper foil in the thickness direction is determined by observing the cross-sectional metal structure of the copper foil 1 between the surface 1a and the surface 1b of the copper foil 1. The sectional area A of the penetrating crystal grain 2 penetrating in the direction of the thickness d is obtained, and the ratio of the sectional area A to the sectional area B of the entire copper foil 1 including the non-penetrating crystal grain 3 not penetrating, that is, the sectional area A / Calculated as the cross-sectional area B. Specifically, the cross-sectional area is measured by embedding a copper foil in a resin, mechanically polishing the cross-section of the copper foil to give a mirror surface, etching with ammonia-hydrogen peroxide, and then measuring the structure photograph with an optical microscope.

  The thickness of the rolled copper foil used for the flexible printed wiring board (FPC) is generally 50 μm or less, and recently it is becoming thinner. Therefore, when measuring the cross-sectional area of the crystal grains of the copper foil, it is preferable that the copper foil is folded and laminated into several layers and embedded in the resin. In addition, the sampling of the copper foil used for microscopic observation of the cross-sectional area is preferably at least 100 times longer than the thickness of the copper foil in order to reduce the influence of local coarse crystal grains and fine crystal grains. .

  In the manufacturing method of the rolled copper foil of the present invention, in order to obtain the above-described rolled copper foil having excellent flexibility, an ingot of tough pitch copper or oxygen-free copper is hot rolled to a thickness of 18 mm, and further cold rolled. After thinning to a thickness of 2.0 mm by intermediate annealing, cold rolling and annealing are subsequently repeated to a thickness of 1.4 to 0.14 mm, and a final thickness of 10 to 33 μm is obtained by final rolling. To do. This rolled copper foil is used in an annealed state, and the tempering (final tempering) for that purpose is 130-200 ° C. for 30 minutes.

  The final annealing is performed at a temperature of 130 to 200 ° C. that is exposed during heat treatment performed after surface treatment such as plating in the roughening process of the rolled copper foil or when integrated with the base film in the FPC manufacturing process. The heat treatment is performed. Therefore, according to the present invention, for the rolled copper foil in the state used for FPC production, that is, the annealed state after the final rolling, the flexibility of the rolled copper foil is inspected only by examining the cross-sectional area ratio of the crystal grains. Is possible.

  The copper foil obtained by the manufacturing method of the present invention can control the cross-sectional area ratio of crystal grains penetrating between both surfaces of the copper foil in the plate thickness direction under the following conditions. That is, (1) If the average grain size before the final rolling is the same, the larger the rolling reduction of the final rolling, the larger the cross-sectional area ratio of the through crystal grains. Further, (2) if the rolling reduction of the final rolling is the same, the cross-sectional area ratio of the through crystal grains can be increased as the average crystal grain size before the final rolling is smaller.

  The rolled copper foil thus obtained has a cross-sectional structure in the plate thickness direction of the copper foil, by controlling the cross-sectional area ratio of crystal grains penetrating between both surfaces of the copper foil in the plate thickness direction to 41% or more. Further, the number of bendings can be improved to 3.2 million times or more, and a rolled copper foil having better flexibility than the conventional one can be obtained.

  High-purity electrolytic copper was melted to produce an ingot of tough pitch copper (oxygen content 250 ppm) having a thickness of 200 mm and a width of 650 mm. This ingot is thinned by hot rolling to a plate thickness of 18 mm, the scale on the surface is removed by chamfering, then thinned to a plate thickness of 2.0 mm by cold rolling, intermediate annealing and cleaning are performed, and an edge is obtained. The part was trimmed to a width of 600 mm. Thereafter, cold rolling and annealing / washing were repeated to obtain a predetermined plate thickness, and then the copper foil having the predetermined plate thickness was subjected to final cold rolling to produce a 0.016 mm (16 μm) rolled copper foil.

  The obtained rolled copper foil with a plate thickness of 16 μm was subjected to heat treatment at 180 ° C. for 30 minutes, imitating heat treatment in the manufacturing process of the flexible printed wiring board (FPC). For the rolled copper foil in the annealed state, the cross-sectional area ratio and the bending life of the through crystal grains penetrating in the plate thickness direction were measured. Further, in the same manner as above, however, a rolled copper foil having a thickness of 33 μm and 10 μm was manufactured by changing the thickness and the average crystal grain size before the final rolling, and subjected to the same heat treatment. Thereafter, the cross-sectional area ratio and the bending life of the through crystal grains were measured. The obtained results are shown in Table 1 below.

  In addition, the cross-sectional area ratio of the through crystal grain in the rolled copper foil in the annealed state after the heat treatment was obtained as follows. That is, sampling is performed so that the length is 200 times the plate thickness, the copper foil is laminated and embedded in a resin, and then the copper foil is mechanically polished to a mirror finish. Etching was performed with water, and the metal structure of the copper foil cross section was observed with an optical microscope. Specifically, a microphotograph of 400 times is taken, and from the structure photograph, the penetrating crystal grains penetrating the copper foil in the plate thickness direction are colored, and the area of the colored portion relative to the total cross-sectional area is measured using image software. The ratio was measured.

  Further, the bending life of the rolled copper foil was measured by a bending test apparatus shown in FIG. That is, the test copper foil piece 5 is fixed to the fixed plate 6 and the movable plate 7 of this apparatus, and the movable plate 7 is periodically vibrated so that the intermediate portion of the test copper foil piece 5 has a predetermined radius of curvature. It bends into a hairpin shape and breaks when it reaches a certain number of bends. The number of bendings until this breakage was defined as the bending life. The test copper foil pieces 5 were collected so that the length direction thereof was parallel to the rolling direction. The measurement conditions were as follows: the width of the test copper foil piece 12.7 mm, the length of the test copper foil piece 5 200 mm, the radius of curvature 2.5 mm, the vibration stroke 25 mm, and the vibration speed 500 times / minute.

  According to Table 1 above, in the case of a rolled copper foil having a final plate thickness of 16 μm, each sample having a cross-sectional area ratio of the through crystal grains of 41% or more in the cross-sectional structure of the annealed copper foil is a bending of the copper foil. It can be seen that the flexibility is significantly improved as compared with each sample having a lifetime exceeding 320,000 times and a cross-sectional area ratio of less than 41%. Moreover, if the cross-sectional area ratio of the through crystal grains of the copper foil is 61% or more, the bending life exceeds 420,000 times, which is more preferable. Sample 7 is a rolled copper foil manufactured under conventional general conditions, and its bending life is less than 300,000 times.

  Further, in the case where the final plate thickness is 33 μm and 10 μm, the flexibility is improved when the plate thickness is reduced, and the flexibility is lowered when the plate thickness is increased. Therefore, the final plate thickness is simply compared with the sample having the final plate thickness of 16 μm. It is not possible. However, when Samples 10 and 12 are compared with Samples 11 and 13, when the cross-sectional area ratio of the penetrating crystal grains is set to 41% or more, the number of bends until fracture increases, and the cross-sectional area ratio is less than 41%. It is clear that the flexibility is greatly improved as compared with that.

DESCRIPTION OF SYMBOLS 1 Copper foil 1a, 1b Surface 2 Through crystal grain 3 Non-penetrating crystal grain 5 Copper foil piece for a test 6 Fixed plate 7 Movable plate

Claims (4)

  An ingot of tough pitch copper or oxygen-free copper is hot-rolled to a thickness of 18 mm, further thinned to a thickness of 2.0 mm by cold rolling and subjected to intermediate smelting, and then cold rolling and annealing are repeated. A thickness of 1.4 to 0.14 mm, a final thickness of 10 to 33 μm by final rolling, and then a final annealing at 130 to 200 ° C. for 30 minutes to obtain a cross-sectional structure in the thickness direction of the obtained copper foil. A method for producing a rolled copper foil having excellent flexibility, characterized in that the cross-sectional area ratio of crystal grains penetrating between both surfaces of the copper foil in the thickness direction is controlled to 41% or more.   The method for producing a rolled copper foil having excellent flexibility according to claim 1, wherein an average crystal grain size of the copper foil before final rolling is controlled to 7 to 20 μm.   The method for producing a rolled copper foil having excellent flexibility according to claim 1 or 2, wherein an area ratio of a cross section of crystal grains penetrating between both surfaces in a plate thickness direction is controlled to 61% or more. .   The cross-sectional area ratio of crystal grains penetrating between both surfaces in the plate thickness direction is obtained for a length of at least 100 times the plate thickness. A method for producing a rolled copper foil having excellent flexibility as described in 1.

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