JP4430509B2 - Rolled copper foil - Google Patents

Description

  The present invention relates to a rolled copper foil suitable for a flexible wiring member 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 bending resistance than the electrolytic copper foil is used from the above-described use as a wiring member for a 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 bending resistance. However, since the bending resistance of FPC is determined by a copper foil that is inferior in bending resistance compared to a base film or coverlay, the bending resistance of 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 bending resistance from the viewpoint of the durability of the equipment.

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

To achieve the above object, the rolled copper foil provided by the present invention, the final thickness is 10～16Myuemu, in the cross-sectional structure of a copper foil of annealed state after the final rolling, between both surfaces of the copper foil A cross-sectional area ratio of crystal grains penetrating in the plate thickness direction is 70% or more, and a test copper foil piece made of the copper foil and having a width of 12.7 mm and a length of 200 mm is fixed to a fixed plate and a movable plate, and is movable. The plate is periodically vibrated to bend the test copper foil piece with a radius of curvature of 2.5 mm, and the bending life obtained as the number of bending times until breakage is 684,000 times or more .

In the rolled copper foil of the present invention, it is preferable that the cross-sectional area ratio is determined for a length at least 100 times the thickness of the copper foil . Moreover, it is preferable that it is 130-200 degreeC as heat processing temperature at the time of the said annealing.

  According to the present invention, it is possible to provide a rolled copper foil having excellent bending resistance and suitable for a flexible wiring member such as a flexible printed wiring board (FPC).

  As a result of earnestly examining the improvement in bending resistance of 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. It has been found that the bending resistance of the copper foil is greatly improved as the ratio of the cross-sectional area of the crystal grains penetrating between the surfaces in the plate thickness direction to the total cross-sectional area (cross-sectional area ratio) increases. .

  That is, in the rolled copper foil of the present invention, by making the cross-sectional area ratio of the crystal grains of the crystal grains penetrating between both surfaces in the plate thickness direction to be 40% or more, the rolled copper having better flexibility than conventional ones. A foil can be obtained. More preferably, the crystal grains penetrating the copper foil in the plate thickness direction appear on the copper foil surface 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 60% or more. There is a tendency for the ratio to increase rapidly, which further improves the flexibility of the copper foil.

  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 in 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 production of the rolled copper foil of the present invention, after hot rolling a tough pitch copper or oxygen-free copper material, cold rolling and annealing are repeated until a predetermined thickness is obtained, and finally the final cold rolling is performed to obtain a predetermined thickness. Finish to plate thickness, preferably 50 μm or less. Thereafter, the rolled copper foil is used in an annealed state. For the annealing, the heat treatment is performed after the surface treatment such as plating in the roughening process of the rolled copper foil, or the base film in the FPC manufacturing process. It is performed by a heat treatment at a temperature of 130 to 200 ° C. exposed during the integration. Therefore, according to the present invention, the bending resistance of the rolled copper foil is inspected only by examining the cross-sectional area ratio of the crystal grains of the rolled copper foil in the state used for FPC manufacture, that is, in the state annealed after the final rolling. It is possible.

  In the rolled copper foil in the state annealed after the final rolling, the cross-sectional area ratio of the crystal grains penetrating the plate thickness can be controlled by 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.

  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 according to the example of the present invention in which the cross-sectional area ratio of the through crystal grains is 40% or more in the cross-sectional structure of the annealed copper foil It can be seen that the bending life of the copper foil exceeds 300,000 times, and the bending resistance is greatly improved as compared with each sample of the comparative example. Moreover, if the cross-sectional area ratio of the penetrating crystal grains of the copper foil is 60% or more, a result that the bending life exceeds 400,000 times can be obtained, which is further preferable. Sample 7 is a rolled copper foil manufactured under conventional general conditions, but 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 bending resistance is improved as the plate thickness is reduced, and the bending resistance is lowered as the plate thickness is increased. It cannot be compared. However, when the samples 10 and 12 according to the embodiment of the present invention are compared with the samples 11 and 13 of the comparative example, the number of bends until breakage is increased by setting the cross-sectional area ratio of the through crystal grains to 40% or more. It is clear that the bending resistance is greatly improved as compared with the case where the area ratio is less than 40%.

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.

Explanation of symbols

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 (3)

Final thickness is 10～16Myuemu, in the cross-sectional structure of a copper foil in a state of being annealed after the final rolling, in cross-section area ratio of crystal grains through between both surfaces of the copper foil in the thickness direction is 70% or more Then, a test copper foil piece made of the copper foil and having a width of 12.7 mm and a length of 200 mm is fixed to the fixed plate and the movable plate, and the movable plate is periodically vibrated to change the radius of curvature of the test copper foil piece. A rolled copper foil having excellent bending resistance, characterized by having a bending life of 684,000 times or more obtained by bending at 2.5 mm and obtaining the number of bendings until breakage . The rolled copper foil according to claim 1, wherein the cross-sectional area ratio is obtained for a length at least 100 times the plate thickness of the copper foil.   The rolled copper foil according to claim 1 or 2, wherein a heat treatment temperature during the annealing is 130 to 200 ° C.

Images