Rolled copper foil, copper-clad laminate manufacturing method, flexible printed circuit board manufacturing method, and electronic component manufacturing method

Abstract

Provided is a rolled copper foil that, when being formed into an FPC, has higher flexibility than conventional products. This rolled copper foil contains 99.9 mass% or more of Cu, and the remaining portion being unavoidable impurities, and exhibits an orientation distribution density of 21.50 or more for S orientations {123}<634> in the surface.

Description

Methods for manufacturing rolled copper foil, copper-clad laminates, methods for manufacturing flexible printed wiring boards, and methods for manufacturing electronic components

[0001] The present invention relates to a method for manufacturing a rolled copper foil, a copper-clad laminate, a flexible printed wiring board, and an electronic component.

[0002] Flexible printed circuit boards (FPCs) are made by bonding a metal conductive layer to a flexible insulating substrate, typically a resin film. Copper foil is generally used for the conductive layer, and rolled copper foil, which has excellent flexibility, is used for applications requiring particular flexibility.

[0003] The general FPC manufacturing process is as follows: First, copper foil is bonded to a resin film. Bonding can be achieved by applying a varnish containing a polyimide resin precursor to the copper foil and then heat-treating it to imidize it (the casting method), or by laminating an adhesive resin film onto the copper foil (the lamination method). The copper foil with resin film bonded together using these processes is called a copper-clad laminate (CCL). Wiring is then formed by etching, and the FPC is completed.

[0004] As described above, rolled copper foil for FPCs is required to have flexibility. Patent Document 1 proposes that the degree of processing in the final cold rolling be 90% or more in order to provide a rolled copper foil for FPCs that can be easily annealed at the curing temperature of a resin adhesive and has extremely good flex resistance (flex fatigue life) after annealing.

[0005] Japanese Patent Application Publication No. 4-228553

[0006] However, as electronic devices such as smartphones have become lighter, thinner, shorter, and more compact, and their functionality has increased in recent years, the flexibility requirements for rolled copper foil have become increasingly stringent, making it increasingly difficult for copper foils manufactured using known techniques to meet customer needs.

[0007] Therefore, an object of one embodiment of the present invention is to provide a rolled copper foil that has higher flexibility than conventional ones when made into an FPC.

[0008] After extensive investigations, the present inventors discovered that a rolled copper foil with high flexibility can be obtained by increasing the orientation distribution density of the S orientation of the rolled copper foil to a predetermined value or higher, and have created the inventions exemplified below. [1] A rolled copper foil containing 99.9 mass% or more of Cu, the remainder being unavoidable impurities, and having an orientation distribution density of the S orientation {123}<634> on the surface of 21.50 or higher. [2] The rolled copper foil according to [1], further containing 100 to 360 mass ppm of Ag. [3] The rolled copper foil according to [1] or [2], having a thickness of 4 to 35 μm. [4] The rolled copper foil according to any one of [1] to [3], having a thickness of 6 to 35 μm. [5] A method for producing a copper-clad laminate, comprising a step of bonding the rolled copper foil according to any one of [1] to [4] with a substrate. [6] A method for manufacturing a flexible printed wiring board, comprising a step of forming wiring using a copper-clad laminate manufactured by the method for manufacturing a copper-clad laminate described in [5]. [7] A method for manufacturing an electronic component, comprising a step of manufacturing an electronic component equipped with a flexible printed wiring board manufactured by the method for manufacturing a flexible printed wiring board described in [6].

[0009] According to one embodiment of the present invention, a rolled copper foil is provided which has higher flexibility than conventional ones when made into an FPC.

[0010] 1 is a schematic diagram showing a measurement method for an IPC sliding bending test in Examples 6 to 7 and Comparative Example 4. It is a graph plotting the S orientation distribution density on the horizontal axis and the number of IPC sliding bending cycles on the vertical axis based on Examples 6 to 7 and Comparative Example 4.

[0011] The present invention is not limited to the embodiments described below, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the embodiments. In this specification, the S orientation refers to the orientation of crystal grains in which the {123} plane is parallel to the rolled surface and the <634> direction is parallel to the rolling direction (RD), and is expressed by the index {123}<634>. Furthermore, the "rolling direction" refers to the direction parallel to the direction in which the rolled object passes between a pair of work rolls.

[0012] [1. Rolled Copper Foil] (Composition) In one embodiment, the rolled copper foil according to the present invention contains 99.9% by mass or more of Cu, with the remainder consisting of unavoidable impurities. In another embodiment, the rolled copper foil may be composed of pure Cu. In another embodiment, the rolled copper foil may further contain 100 to 360 ppm by mass of Ag as an alloying element, in order to more reliably obtain higher flexibility than conventional copper foils when made into FPCs, while controlling the recrystallization temperature to an appropriate level. In particular, it is preferable to add the above-mentioned additive element to tough pitch copper (TPC) specified in JIS H 3100 (C1100) or oxygen-free copper (OFC) specified in JIS H 3100 (C1020). If the Ag concentration exceeds 360 ppm by mass, the recrystallization temperature of the rolled copper foil increases, which may result in insufficient recrystallization even when heat treatment is performed using a casting or laminating method. If unrecrystallized grains remain in the rolled copper foil, the flexibility of the FPC will be significantly reduced. Furthermore, if the Ag concentration is 100 ppm by mass or more, the amount of rolling strain introduced increases, which makes it easier for a cubic texture to grow after CCL heat treatment and improves flexibility. The upper limit of the oxygen content in the rolled copper foil is, for example, 500 ppm by mass or less. The lower limit of the oxygen content in the rolled copper foil is, for example, 0 ppm by mass or more. From the viewpoint of reducing the amount of cuprous oxide (CuO) in the material, which is thought to adversely affect the flexibility of the FPC, the oxygen content is preferably 50 ppm by mass or less.

[0013] The composition of the rolled copper foil according to the present invention can be measured by X-ray fluorescence analysis as a dry analysis. Specifically, X-ray fluorescence analysis is performed using a Simultix 14 manufactured by Rigaku Corporation. The analysis surface may be cut or mechanically polished so that the surface roughness in maximum height Rz (JIS B0601:2013) is 6.3 μm or less. When an analysis sample is collected from the molten metal during melting and casting in the manufacturing process of the rolled copper foil, the foil is cast into a shape of approximately 30 to 40 mm diameter and a thickness of approximately 50 to 80 mm, and then cut into a thickness of approximately 10 to 20 mm, and the cut surface is used as the analysis surface. The analysis surface is repeatedly cut or mechanically polished until the surface roughness in maximum height Rz (JIS B0601:2013) is 6.3 μm or less. In addition to measurement by X-ray fluorescence analysis, the composition of the rolled copper foil may also be measured by ICP atomic emission spectroscopy as a wet analysis. Specifically, the measurement can be performed using an ICP optical emission spectrometer (ICP-OES) SPS3100 manufactured by Hitachi High-Tech Science Corp. In the case of ICP optical emission spectroscopic analysis, the sample is dissolved in an aqueous nitric acid solution (volume ratio of nitric acid:water = 1:1) and then diluted.

[0014] (Texture) In one embodiment, the rolled copper foil according to the present invention has an orientation distribution density of S orientation {123}<634> (hereinafter also referred to as "S orientation distribution density") on the surface (rolled surface) of 21.50 or more. When S orientation grains are developed in the rolling texture of the rolled copper foil, a recrystallization texture excellent in flexibility is obtained during recrystallization by heat treatment of the rolled copper foil, and stable flexibility can be obtained regardless of the heating conditions during the production of, for example, a copper-clad laminate. From the viewpoint of further improving bendability, the S-orientation distribution density is preferably 22.0 or more as a lower limit, more preferably 22.2 or more, even more preferably 22.3 or more, even more preferably 22.5 or more, even more preferably 22.8 or more, even more preferably 23.0 or more, even more preferably 23.5 or more, even more preferably 23.9 or more, even more preferably 24.0 or more, even more preferably 24.5 or more, even more preferably 24.9 or more, even more preferably 25.0 or more, even more preferably 25.5 or more, and even more preferably 26.0 or more. Taking production costs into consideration, the upper limit of the S-orientation distribution density is typically 30.0 or less, more typically 29.0 or less. Here, texture refers to a statistical bias in crystal orientation formed by processing and heat treatment, and is highly dependent on the processing and heat treatment conditions. Therefore, the present inventors have discovered that controlling the average grain size after final annealing and the degree of reduction in final cold rolling are important for increasing the S-orientation distribution density. The conditions for the average grain size after final annealing and the reduction ratio of the final cold rolling will be described later and will not be described here.

[0015] (Method for measuring S-orientation distribution density) First, the rolled copper foil is cut into an appropriate size as a measurement sample. The S-orientation distribution density is calculated by measuring the positive pole points on the sample surface using X-ray diffraction. As the X-ray diffraction device, a SmartLab manufactured by Rigaku Corporation or an equivalent device is used, and the measurement is performed using the Schulz reflection method. The measurement conditions are as follows.<Measurement conditions> X-ray tube: Cobalt (3 kW sealed tube) X-ray wavelength: Kα Tube voltage: 40 kV Tube current: 25 mA Entrance Soller slit: 2.5° Divergence slit: 1 / 2° Longitudinal limiting slit: 2 mm Receiving slit: 10 mm Receiving parallel slit: 2.5° Scattering slit: 9.975 mm Attenuator: Automatic α angle step: 5° β angle step: 5° Counting time: 0.5 seconds / step Vacuum degree: 1.00E-5 Pa Distance table settings (1) to (8) (1) Distance between X-ray source and mirror: 90 mm (2) Distance between X-ray source and selection slit: 114 mm (3) Distance between X-ray source and IS (entrance slit): 173.5 mm (4) Distance between X-ray source and sample: 300 mm (5) Distance between sample and RS (receiving slit) 1: 187 mm (6) Distance between sample and RS (receiving slit) 2: 300 mm (7) Distance between RS (receiving slit) 1 and RS (receiving slit) 2: 113 mm (8) Distance between sample and detector: 331 mm Package measurement selection: Schulz reflection method Software Control software: XRD Measurement plug-in Basic data processing: Data Manager plug-in Analysis: Texture plug-in <Pole measurement> Sample information Thickness: 0.012 mm Width: 20 mm Crystal system: Cubic system Linear absorption coefficient: 727.872 (1 / cm) Pole measurement conditions Measurement hkl: 111, 200, 220 Measurement angle 2θ: 50.8°, 59.4°, 89.0° Step: 5° Speed: 600° / min Reflection method: Schultz Background measurement: 1-point measurement Measurement angle 2θ: 47.8°, 56.4°, 86.0° (Measurements were taken at an angle 3° lower than each measurement angle of the test sample, with other conditions being the same as those of the test sample) <Pole figure correction (using SmartLab Studio II Texture)> Check the checkboxes for the following items and enter the various data. - Background correction: Select From external data and enter the background measurement results for each of the above hkl.Absorption: Sample thickness and linear absorption coefficient are taken from the sample information. Defocus correction: Measurement results for previously measured copper fine powder are entered. The copper fine powder used is Kanto Chemical Co., Ltd.'s copper (powder, 2N5), with a purity of over 99.5%, particle size of 75 μm to 150 μm, and grade 1 purity. (Cat. No. 07439-08) Smoothing: Smoothing factor 1.0 Normalization: However, with the Schulz reflection method, measurement becomes difficult when the angle of incidence of the X-rays on the sample surface is shallow. Therefore, the actual measurable angle range on the pole figure is 0°≦α≦75°, 0°≦β≦360°. (Note that α is the axis perpendicular to the rotation axis of the diffraction goniometer specified in the Schulz reflection method, and β is the axis parallel to the rotation axis.)

[0016] The obtained measurement results are converted into pole figures using Pole Figure Data Processing software manufactured by Rigaku Corporation, and the ODF (Orientation Distribution Function) is calculated using an analysis program for crystal orientation distribution functions for cubes manufactured by Norm Engineering Co., Ltd. (product name: Standard ODF), and the pole density of crystal orientations at all Euler angles is output. <ODF analysis conditions> Pole figure data Face index: (100), (110), (111) Weight: 1 α for each face index max = 75 Δα = 5 Δβ = 5 β angle type: β = 0°, 5°, 10°, ..., 350°, 355° Texture transformation: None Crystal orientation distribution function Expansion order: 22 Threshold of zero density region: 0.3 Display section: Phi2 section Then, from among these, the pole density where the Bunge method Euler angle display (φ1, Φ, φ2) = (60°, 35°, 65°) is read and the S orientation distribution density is calculated.

[0017] (Average grain size after final annealing) In one embodiment, the rolled copper foil according to the present invention preferably has an average grain size of more than 15 μm and less than 35 μm before final cold rolling and after recrystallization annealing 3 (final annealing) in the manufacturing examples described below. By setting the average grain size after final annealing to more than 15 μm and less than 35 μm, it is presumed that crystal rotation is promoted during final cold rolling, thereby increasing the proportion of S-oriented grains, which are the final stable orientation. Furthermore, by increasing the proportion of S-oriented grains, which are the final stable orientation, a recrystallization texture with excellent flexibility develops during recrystallization by heat treatment of the rolled copper foil, improving flexibility.

[0018] (Method for Measuring Average Crystal Grain Size) Next, an example of a method for measuring the average crystal grain size will be described. The average crystal grain size is measured by EBSD on the surface of a sample after final annealing. Here, EBSD (Electron Backscatter Diffraction) is a technique for analyzing crystal orientation, etc., using reflected electron Kikuchi diffraction (Kikuchi pattern) that occurs when a sample is irradiated with an electron beam in a scanning electron microscope (SEM). First, a thickness of about 1 μm is removed from the sample surface by electropolishing, and then a scan is performed with a step size of 3 μm over an arbitrarily set observation range of 1000 μm × 1000 μm. Then, analysis is performed using the area fraction method, and the average crystal grain size is measured when boundaries with a crystal orientation difference of more than 5° are considered to be grain boundaries. The above analysis is carried out using OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. <Electrolyte composition (example)> ・Distilled water 250 ml ・Phosphoric acid 125 ml ・Urea 2.5 g ・Ethanol grade 1 125 ml ・1-propanol 25 ml <Electrolytic polishing conditions> Applied voltage: 10 V Electrolysis time: 10 seconds <EBSD measurement conditions, etc.> ・SEM conditions Equipment: Scanning electron microscope (JSM-IT500HR) manufactured by JEOL Ltd. Electron gun type: Field emission electron gun (Schottky type) Electron gun emitter: ZrO tungsten cathode Objective lens type: Out-lens type Focus correction: Yes (Dynamic focus: 50) Beam conditions Acceleration voltage: 15 kV Working distance: 15 mm Irradiation current: 15 nA SEM probe diameter: 0.5 to 2 nm Observation magnification: 90x ・EBSD equipment conditions Detector: Slow scan CCD camera manufactured by TSL Solutions Co., Ltd. ・Data processing conditions Data collection software: OIM manufactured by TSL Solutions Co., Ltd. Data Collection Phase: Copper Number of pixels of CCD camera: 1394 x 1040 pixels Binning: 8 x 8 Exposure: 8 milliseconds Gain: 0.9 to 0.95 Presence or absence of background processing: Yes Measurement point scanning method: Hexagonal lattice - Hough transformation(1) Hough Type: Classic (2) Hough Resolution: Low (3) Classic Hough Convolution Mask: 9x9 Min Peak Magnitude: 5 Min Peak Distance: 23 Peak Symmetry: 0.75 Vertical Bias: 0 (4) General Parameters Binned Pattern Size: 120 Theta Step Size: 1° Rho Fraction (low fraction): 90% Max Peak Count (maximum number of peaks): 8 Min Peak Count (minimum number of peaks): 3 <Detailed settings of OIM Analysis V8 when calculating the average crystal grain size> Detailed settings of the Partition Properties window Grain Size tab Input value of Grain Tolerance Angle: 5 Minimum Size [points] Input value of Grains: 2 Input value of Anti-grains: 2 Input value of Minimum Confidence Index (minimum value of CI value): 0 Check box of Apply partition before calculation: Enter a check mark. Check the "Include grains at edges of scan in statistics" checkbox: Enter a check mark. Twin Boundaries window (screen displayed when you click "Define" in the "Partition Properties" window) Check the "Enforce matching between twin planes (K1) in grain A and grain B" checkbox: Enter a check mark. Input value for "Allowed tolerance between twin planes (K1s) [degrees]" (allowable deviation angle between twin planes): 1 (There are no specific regulations regarding twins to be excluded. Twins are included in the grain boundaries.)Detailed settings of the New Chart window for calculating the average crystal grain size Type: Grain Size (diameter) The Area value within Average in the results of the grain size measurement performed under the above setting conditions (average value obtained by the Area Fraction method) is taken as the average crystal grain size.

[0019] (Thickness) In one embodiment, the thickness of the rolled copper foil is, for example, 4 to 35 μm, or for example, 6 to 35 μm. The upper limit of the thickness of the rolled copper foil is, for example, 35 μm or less, or for example, 18 μm or less. The lower limit is, for example, 4 μm or more, or for example, 6 μm or more, or for example, 9 μm or more, or for example, 12 μm or more. The thickness of the rolled copper foil is measured, for example, by placing an X-ray generator on the surface side of the rolled copper foil and an X-ray detector on the other surface side, determining the amount of attenuation by the rolled copper foil from the measured amount of transmitted X-rays, and converting this to the thickness of the rolled copper foil. Alternatively, for example, the weight of a 20 cm square rolled copper foil is measured, and the ratio of weight (g) / (density of rolled copper foil (g / cm)) is calculated. 3 ) × area of ​​rolled copper foil (cm 2 )) to calculate the thickness of the rolled copper foil (for example, the density of the rolled copper foil is 8.94 g / cm for oxygen-free copper according to JIS-H3100 (C1020) 3 Furthermore, for example, measurements are taken at any two or more points using a digital length measuring machine (for example, Nikon Digimicro MH-15M), and the thickness of the rolled copper foil is calculated from the arithmetic mean value of the thicknesses.

[0020] (Example of Manufacturing Rolled Copper Foil) In one example of a method for manufacturing rolled copper foil, raw materials such as copper are first melted in a melting furnace to obtain a molten metal of the desired composition. This molten metal is then poured (cast) into a mold to produce an ingot. To prevent oxidation wear of copper, the melting and casting are preferably carried out in a vacuum or in an inert gas atmosphere. The foil is then subjected to homogenization annealing, hot rolling, cold rolling 1, recrystallization annealing 1, facing, cold rolling 2, recrystallization annealing 2, pickling and polishing, cold rolling 3, recrystallization annealing 3 (final annealing), and final cold rolling in this order to produce a rolled copper foil having the desired thickness and properties. In other words, in the present invention, the rolled copper foil is essentially the foil immediately after final cold rolling. According to the experience of the present inventors, it is presumed that the S-orientation distribution density of the rolled copper foil after the final cold rolling is greatly affected by the average crystal grain size after the final annealing and the working ratio of the final cold rolling when the rolled copper foil is manufactured by the process described below.

[0021] (Final annealing) The conditions for final annealing are appropriately set so that the S-orientation distribution density of the rolled copper foil after final cold rolling is easily developed. Specifically, the conditions for final annealing may be appropriately set so that the average crystal grain size after final annealing is more than 15 μm and less than 35 μm. Although these conditions may vary depending on the composition of the copper material, a person skilled in the art can experimentally determine the annealing conditions without excessive trial and error based on the annealing conditions disclosed in the present examples and comparative examples.

[0022] (Final Cold Rolling) A rolled copper foil is obtained by performing final cold rolling under conditions of a working ratio of more than 98% and less than 99%. The thickness of the rolled copper foil at this time is, for example, 4 to 35 μm, or, for example, about 6 to 35 μm. The working ratio is defined as working ratio (%) = {(thickness before final cold rolling (mm) - thickness after final cold rolling (mm)) / thickness before final cold rolling (mm)} × 100.

[0023] [2. Manufacturing Method of Copper-Clad Laminate] In one embodiment, the manufacturing method of a copper-clad laminate according to the present invention includes a step of bonding the rolled copper foil described above to a substrate. Examples of the substrate include a resin film. Several techniques can be used to bond the resin film to the rolled copper foil. For example, a method can be used in which the rolled copper foil and a polyimide resin film are bonded together using an adhesive made of a thermosetting resin such as epoxy, followed by heat treatment. Alternatively, a method can be used in which a varnish containing a polyamic acid, a precursor of polyimide resin, is applied to at least one surface of the rolled copper foil and heat-cured to form a polyimide coating on at least one surface of the rolled copper foil. Furthermore, when laminating rolled copper foil on both sides, methods include forming a single-sided copper-clad laminate and then compressing the rolled copper foil layer by hot pressing, or sandwiching a polyimide resin film between two rolled copper foil layers and compressing them by hot pressing. These heat treatments are generally performed at 125 to 360°C for 30 to 400 minutes. Furthermore, there is also a method of laminating the rolled copper foil and the resin film using an adhesive without a heat treatment process. Materials for the resin film include, but are not limited to, polyester, polyimide, polyethylene terephthalate, polyethylene naphthalate, etc.

[0024] Furthermore, before laminating the rolled copper foil and the resin film, the rolled copper foil can be subjected to a roughening treatment. This can improve the adhesive strength between the resin film and the rolled copper foil. For example, the roughening treatment can be performed under the following conditions. <Roughening Treatment Conditions> Liquid composition: Cu 10-20 g / L, Co 1-10 g / L, Ni 1-15 g / L pH: 1-4 Temperature: 30-50°C Current density (Dk): 20-50 A / dm 2 Time: 1-5 seconds

[0025] [3. Manufacturing Method of Flexible Printed Wiring Board] One embodiment of the manufacturing method of a flexible printed wiring board according to the present invention includes a step of forming wiring using a copper-clad laminate manufactured by the aforementioned copper-clad laminate manufacturing method as a material. At this time, wiring can be formed using the copper-clad laminate as a material according to known procedures to manufacture a flexible printed wiring board (FPC). For example, an etching resist is applied to only the necessary portions of the conductor pattern on the rolled copper foil surface of the copper-clad laminate, and an etching solution is sprayed onto the rolled copper foil surface to remove unnecessary rolled copper foil, forming the conductor pattern. The etching resist is then peeled off and removed to expose the conductor pattern. After forming the conductor pattern, a protective coverlay film is typically applied.

[0026] (Applications) Such FPCs correspond to FPCs used in moving parts in hard disks in electronic components of electronic and electrical devices, hinge parts and sliding parts of mobile phones, the inside of mobile phones, head parts of printers, optical pickup parts, moving parts of notebook PCs, etc. The manufacturing method for electronic components may include a step of manufacturing electronic components including a flexible printed wiring board manufactured by the manufacturing method for a flexible printed wiring board described above.

[0027] The present invention will be specifically described based on examples and comparative examples. The following examples and comparative examples are merely specific examples for facilitating understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these specific examples. In Tables 1 and 2, "OFC" stands for oxygen-free copper as specified in JIS H 3100 (C1020), and "TPC" stands for tough pitch copper as specified in JIS H 3100 (C1100).

[0028] [Examples 1 to 5, Comparative Examples 1 to 3] [Production of Rolled Copper Foil] First, ingots having the alloy compositions shown in Table 1, in which predetermined metals were added to oxygen-free copper, were melted and cast in Examples 1 to 5 and Comparative Examples 1 to 3. The Ag content of the ingots was measured by the above-mentioned ICP atomic emission spectroscopy. These ingots were processed in the following order to produce rolled copper foils. The reduction ratio in Table 1 refers to the thickness reduction rate in the final cold rolling, and was calculated as follows: reduction ratio (%) = {(thickness before final cold rolling (mm) - thickness after final cold rolling (final product) (mm)) / thickness before final cold rolling (mm)} × 100. <Steps (1) to (11)> (Step 1) Homogenization annealing: The ingots were heated and held at 920°C for 2.5 hours. (Step 2) Hot rolling: The ingots heated at 920°C were rolled to a thickness of 16 mm at room temperature. The strip was then rapidly cooled to room temperature by water cooling to obtain a strip-shaped metal material. (Step 3) Cold rolling 1: Rolled to a thickness of 10.5 mm. (Step 4) Recrystallization annealing 1: The strip-shaped metal material was heated and held at 400°C for 7.5 hours. (Step 5) Surface grinding: Oxide scale on the surface was removed by facing. (Step 6) Cold rolling 2: Rolled to a thickness of 1.5 mm. (Step 7) Recrystallization annealing 2: Heated in a furnace heated to 750°C for 30 to 120 seconds. (Step 8) Pickling and polishing: Immersed in a mixed acid of sulfuric acid and hydrogen peroxide, followed by buffing, the oxide film on the surface of the material was removed. (Step 9) Cold rolling 3: Rolled to a thickness of 0.8 mm. (Step 10) Recrystallization annealing 3 (final annealing): The annealing temperature and holding time were adjusted to obtain the desired crystal grain size, and the strip-shaped metal material after cold rolling 3 was heated and held. The annealing conditions for each sample are shown in Table 1. To prevent oxidation, the strip metal material was wrapped in a rolled copper foil (thickness: 33 μm) made of thoroughly annealed tough pitch copper (JIS H 3100 (C1100)), sealed, and the resulting sealed body was placed in a dryer. After heating and holding, the sealed body was removed from the dryer and allowed to cool in the air. After cooling, the strip metal material was removed from the sealed body. The average crystal grain size after final annealing was measured using the method described above. (Step 11) Final cold rolling: The rolled copper foil was finished to a thickness of 0.012 mm (12 μm) to obtain a rolled copper foil.In the final cold rolling, the strip metal material was passed between a pair of work rolls without fixing both ends in the rolling direction (free ends), so that the strip metal material was rolled without applying tension in a direction parallel to the rolling direction. Note that in Examples 1 to 5 and Comparative Examples 1 to 3, recrystallization annealing 3 was performed at the annealing temperature and holding time shown in Table 1.

[0029] [Characteristics Evaluation] Next, in Examples 1 to 5 and Comparative Examples 1 to 3, a portion of the rolled copper foil obtained by the above-mentioned production was taken as a measurement sample, and the S orientation distribution density on the surface of the rolled copper foil was measured by the above-mentioned method using SmartLab manufactured by Rigaku Corporation. The results are shown in Table 1.

[0030]

[0031] (Discussion 1 based on Examples) As a result of comparing Examples 1 to 5 with Comparative Examples 1 to 3, it was confirmed that the S-orientation distribution density can be controlled by setting the working ratio of the final cold rolling to more than 98 and less than 99% and then appropriately setting the average grain size after final annealing. Furthermore, as a result of comparing Example 3 with Example 4, it was confirmed that the S-orientation distribution density tends to increase as the average grain size after final annealing decreases.

[0032] [Examples 6 to 7 and Comparative Example 4] [Evaluation of Rolled Copper Foils] <IPC Sliding Bending Test> In Examples 6 to 7 and Comparative Example 4, rolled copper foils having the S-orientation distribution densities on the surfaces (rolled surfaces) shown in Table 2 were prepared to confirm the relationship between the S-orientation distribution density and the flexibility. A portion of each rolled copper foil was taken as a measurement sample. One surface of each measurement sample was subjected to a roughening plating treatment in accordance with the roughening plating treatment conditions described above. Then, a polyimide resin film, Pixio (trademark) FRS grade (thickness: 25 μm) manufactured by Kaneka Corporation, was laminated on the roughening-plated surface of the rolled copper foil, and the laminate was heat-pressed at 360°C for 30 minutes to produce a single-sided copper-clad laminate consisting of two layers of rolled copper foil and polyimide resin film. Subsequently, using known photolithography techniques, wiring was formed on the rolled copper foil so that the circuit width (Line) and the spacing (Space) between adjacent circuits were Line / Space = 300 μm / 300 μm, thereby producing an FPC. Next, the resulting FPC was cut into test pieces measuring 12.7 mm wide and 130 mm long, with the length of the test piece parallel to the rolling direction. The IPC sliding flex count was measured for this test piece using an IPC (Imprinted Circuit Council) flex tester 100 shown in Figure 1. This IPC flex tester 100 has a structure in which a vibration transmission member 20 is connected to an oscillation driver 10, and the test piece 30 is fixed to the device at four points: the screw 40 indicated by the arrow and the tip of the vibration transmission member 20. When the vibration transmission member 20 is driven up and down, the middle portion of the test piece 30 is bent into a hairpin shape with a predetermined curvature radius r. The IPC sliding flex test was performed under the following conditions: radius of curvature r: 2.5 mm (outer radius), vibration stroke: 20 mm, and vibration speed: 1,500 flexes / min. The number of flexes until breakage was counted under the above conditions, and the IPC sliding flex test was performed four times for each condition. The average number of flexes until breakage is shown in Table 2 as the IPC sliding flex count. Breakage here refers to a 20% increase in electrical resistance compared to the electrical resistance of the FPC before the IPC sliding flex test. Electrical resistance was measured using a four-terminal method.

[0033]

[0034] (Considerations Based on Examples 2) Based on a comparison of the results obtained in Examples 6 and 7 with the results obtained in Comparative Example 4, it was confirmed that by using a rolled copper foil having an orientation distribution density of 24.9 or more in the S orientation {123}<634>, when an FPC was made from the rolled copper foil obtained in Examples 6 and 7, it had better flexibility than conventional FPCs.

[0035] The results of plotting the S orientation distribution density of each sample on the horizontal axis and the number of IPC sliding flexes on the vertical axis are shown in Figure 2. The results of calculating an approximate line using the linear approximation function of Microsoft (registered trademark) Excel for approximating curves are also shown in Figure 2. The approximate formula of the line and the squared value of R are also shown. The closer the squared value of R is to 1, the more appropriately the approximate line represents the trend of the experimental data, and it can be seen that there is a directly proportional correlation between the S orientation distribution density and the number of IPC sliding flexes.

[0036] When the IPC sliding bending number is set to 230,000 or more for the FPC compatible line, the IPC sliding bending number increases by approximately 20% or more compared to the conventional product, Comparative Example 4. The S-orientation distribution density at which the IPC sliding bending number is 230,000 is calculated to be 21.499 based on the approximation line in Figure 2. Taking this into consideration, it is presumed that by using a rolled copper foil with an S-orientation distribution density of 21.50 or more, it is possible to provide a rolled copper foil with higher flexibility than conventional ones when made into an FPC.

[0037] 10 Oscillation driver 20 Vibration transmission member 30 Test piece 40 Screw 100 IPC bending test device r Radius of curvature

Claims

1. Contains 99.9% by mass or more of Cu, with the remainder consisting of unavoidable impurities; A rolled copper foil having an orientation distribution density of S orientation {123}<634> on the surface of 21.50 or more.

2. The rolled copper foil according to claim 1, further comprising 100 to 360 ppm by mass of Ag.

3. The rolled copper foil according to claim 1 or 2, having a thickness of 4 to 35 μm.

4. The rolled copper foil according to claim 1 or 2, having a thickness of 6 to 35 μm.

5. A method for producing a copper-clad laminate, comprising a step of bonding the rolled copper foil according to claim 1 or 2 to a substrate.

6. A method for producing a flexible printed wiring board, comprising the step of forming wiring using a copper clad laminate produced by the method for producing a copper clad laminate according to claim 5 as a material.

7. A method for manufacturing an electronic component, comprising the step of manufacturing an electronic component including a flexible printed wiring board manufactured by the method for manufacturing a flexible printed wiring board according to claim 6.