Rolled copper foil, copper-clad laminate, method for producing copper-clad laminate, method for producing flexible printed wiring board, and method for producing electronic component

Abstract

Provided is a rolled copper foil that has higher flexibility than conventional products when made into an FPC. Rolled copper foil containing 99.9 mass% or more of Cu, the balance being unavoidable impurities, and the arithmetic mean value of the Taylor factor being 2.485 or less as measured at a total of three points including a discretionary point and two points each spaced equidistantly 5 mm therefrom in a direction perpendicular to the rolling direction when heat treated for a heating holding time of 30 minutes at a dryer internal temperature of 260°C.

Description

Rolled copper foil, copper-clad laminate, method for manufacturing copper-clad laminate, method for manufacturing flexible printed wiring board, and method for manufacturing electronic components

[0001] The present invention relates to a rolled copper foil, a copper-clad laminate, a method for manufacturing a copper-clad laminate, a method for manufacturing a flexible printed wiring board, and a method for manufacturing 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, flexibility is required for rolled copper foil for FPCs. Patent Document 1 proposes that the final cold working ratio 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] As a result of extensive investigations, the present inventors have found that a rolled copper foil with high flexibility can be obtained by heat-treating the rolled copper foil under specified conditions to have a Taylor factor of 2.485 or less, and have created the invention exemplified below. [1] A rolled copper foil containing 99.9 mass% or more of Cu, with the remainder consisting of unavoidable impurities, wherein, when heat-treated at a dryer temperature of 260°C for a heating holding time of 30 minutes, the arithmetic mean value of the Taylor factors measured at three points (one arbitrary point and two other points equally spaced 5 mm apart in a direction perpendicular to the rolling direction) is 2.485 or less. [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], wherein the arithmetic mean value of the Taylor factor is 2.300 or more. [5] A copper-clad laminate having a rolled copper foil, wherein the arithmetic mean value of the Taylor factor, measured at three points, is 2.485 or less, including one arbitrary point and two points equally spaced 5 mm apart from the arbitrary point in the direction perpendicular to the rolling direction. [6] The copper-clad laminate according to [5], wherein the rolled copper foil has the arithmetic mean value of the Taylor factor of 2.300 or more. [7] 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, wherein the step includes a heat treatment. [8] A method for producing a flexible printed wiring board, comprising a step of forming wiring using a copper-clad laminate produced by the method for producing a copper-clad laminate according to [7] as a material. [9] A method for producing an electronic component, comprising a step of producing an electronic component including a flexible printed wiring board produced by the method for producing a flexible printed wiring board according to [8].

[0009] According to one embodiment of the present invention, it is possible to provide a rolled copper foil that 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 flex test in Example 5 and Comparative Examples 4 to 5. It is a graph in which the arithmetic mean value of the Taylor factor after heat treatment at 260°C for 30 minutes is plotted on the horizontal axis and the number of IPC sliding flexes is plotted on the vertical axis based on Example 5 and Comparative Examples 4 to 5.

[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 "Taylor factor" represents the sum of crystal shear due to slip deformation that must be activated to impart a unit strain amount through rolling. Furthermore, the "rolling direction" refers to the direction parallel to the direction in which the rolled object passes between a pair of work rolls. Furthermore, the "direction perpendicular to the rolling direction" refers to the direction perpendicular to the rolling direction on the rolled surface.

[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, causing the crystal grains to grow larger after the CCL heat treatment. This controls the Taylor factor within a predetermined range, making it easier to improve 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 analytical 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] (Taylor Factor) In one embodiment, the rolled copper foil according to the present invention has an arithmetic mean Taylor factor of 2.485 or less when the rolled copper foil is heat-treated at a dryer temperature of 260°C for a heating holding time of 30 minutes and measured by the method described below. Specifically, a portion of the rolled copper foil is taken as a sample, placed in a dryer (DRH453WA, manufactured by Advantec Toyo Kaisha, Ltd.) held at 260°C, heat-treated in the air for 30 minutes, and then removed from the dryer and allowed to cool in the air. Before loading, the sample was sandwiched between two 0.2 mm thick sheets of phosphor bronze (JIS H 3110 (C5210)) to prevent oxidation in the atmosphere and to prevent folding and wrinkling during removal from the dryer. This laminate was then wrapped and sealed in a 33 μm thick rolled copper foil made of fully annealed tough-pitch copper, and then loaded into the dryer. Rolled copper foils with a surface Taylor factor within a specified range under specified heat treatment conditions can achieve uniform slip deformation during bending without the assistance of shear bands, thereby minimizing the accumulation of dislocation strain associated with deformation. This suppresses the occurrence of cracks that can cause fracture, resulting in excellent flexibility. For example, stable flexibility can be achieved regardless of the heating conditions during the production of copper-clad laminates. The upper limit of the arithmetic mean Taylor factor is 2.485 or less. On the other hand, the arithmetic mean value of the Taylor factor is preferably 2.300 or more as the lower limit. If the arithmetic mean value of the Taylor factor is too small, distortion may easily occur in the copper foil when bent as an FPC, which may adversely affect flexibility. Therefore, the present inventors have discovered that in order to control the arithmetic mean value of the Taylor factor after heat treatment within a predetermined range, it is important to control the average crystal grain size after final annealing and the working ratio of the final cold rolling. The conditions for the average crystal grain size after final annealing and the working ratio of the final cold rolling will be described later and will not be repeated here.

[0015] (Method for Measuring Taylor Factor) Next, an example of a method for measuring the Taylor factor will be described. As described above, the Taylor factor is measured by EBSD on the surface of a rolled copper foil sample that has been heat-treated at 260°C for 30 minutes. Here, EBSD (Electron Backscatter Diffraction) is a technique for analyzing crystal orientation using reflected electron Kikuchi pattern diffraction (Kikuchi pattern) that occurs when a sample is irradiated with an electron beam in a scanning electron microscope (SEM). Electrolytic polishing is performed using the following electrolyte and test conditions to remove a thickness of approximately 1 μm from the sample surface. After that, a 1000 μm × 1000 μm observation area arbitrarily set so that one side of the observation field is parallel to the rolling direction is scanned with a step size of 3 μm to measure the crystal orientation distribution. The measurements are performed at three points: an arbitrary point and two points equally spaced 5 mm apart in the direction perpendicular to the rolling direction. If the arithmetic mean value of the Taylor factors measured at three points (an arbitrary point and two points equally spaced 5 mm apart in the direction perpendicular to the rolling direction) is 2.485 or less, the rolled copper foil tends to have high flexibility as a whole. This is because, although there may be some variation in the manufacturing conditions in the manufacturing process, the Taylor factors measured after the rolled copper foil obtained in the manufacturing process is heat-treated under predetermined conditions are generally controlled within the desired range. Therefore, if the arithmetic mean value of the Taylor factors measured at three points (an arbitrary point and two points equally spaced 5 mm apart in the direction perpendicular to the rolling direction) is 2.485 or less, although there may be some portions in the rolled copper foil where the arithmetic mean value of the Taylor factors exceeds 2.485, it is expected that such portions will not be very numerous, and the majority of the rolled copper foil will have the desired metal structure, thereby solving the problem of the present invention.Furthermore, due to the manufacturing and handling of rolled copper foil (for example, cutting out measurement samples), some abnormalities such as excessive oil pits, foreign matter adhesion, and rolling marks may occur. When measuring the Taylor factor, the measurement point should be set to avoid areas corresponding to abnormalities. Abnormal areas can be identified by observing the sample before electropolishing with an SEM (observation magnification: 100x). If the measurement point above and an abnormal area overlap, a total of three points should be measured, avoiding the abnormal area. <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 manufactured by JEOL Ltd. (JSM-IT500HR or equivalent) 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: 9 x 9 Min Peak Magnitude (minimum peak intensity): 5 Min Peak Distance (minimum peak distance): 23 Peak Symmetry (peak symmetry): 0.75Vertical Bias: 0 (4) General Parameters Binned Pattern Size: 120 Theta Step Size: 1° Rho Fraction: 90% Max Peak Count: 8 Min Peak Count: 3 The above measurement data is collected using OIM Data Collection manufactured by TSL Solutions Co., Ltd., and data analysis is performed using OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. <Data analysis conditions for OIM Analysis V8> - New Map window Map Style Grayscale: Select <None>. Color Coded: Select <None>. Second Partition: Select <None>. - Taylor Factor window (screen displayed when you click Edit under Color Coded in the Map Style window) - Edit window (screen displayed when you click Add next to the Type selection field) Taylor Factor tab Phase: Select Copper. Slip System window (screen displayed when you click Add under the Phase selection column) Input values ​​for hkl: 111 Input values ​​for uvw: 1-10 CRSS value: 0.2 Deformation Gradient window X-axis values: 1, 0, 0 Y-axis values: 0, -0.5, 0 Z-axis values: 0, 0, -0.5 Range tab Method: Check the Percentage radio button. Minimum input value: 0 Maximum input value: 100 Parameters tab Number of bins value: 20 Vertical Axis: Check the Number Fraction radio button. The area average value of the Taylor Factor measurement results carried out under the above set conditions is defined as the Taylor Factor.

[0016] (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. Generally, the smaller the grain size, the more likely it is that dislocation strain, which serves as the driving force for primary recrystallization, will accumulate during final cold rolling. Therefore, by setting the average grain size before final cold rolling and after final annealing to more than 15 μm and less than 35 μm, the arithmetic mean value of the Taylor factor during heat treatment of the rolled copper foil will be within a predetermined range, thereby improving flexibility. On the other hand, if the average grain size after final annealing is 35 μm or more, dislocation strain will not easily accumulate during final cold rolling, and shear bands will easily develop in the rolled structure. The presence of shear bands tends to cause the Taylor factor to become excessively large during heat treatment of the rolled copper foil.

[0017] (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 sample surface after final annealing. Electrolytic polishing is performed under the conditions described above to remove a thickness of about 1 μm from the sample surface, and then scanning is performed with a step size of 3 μm over an observation range of 1000 μm × 1000 μm set arbitrarily. Analysis is then performed using the Area Fraction method to measure the average crystal grain size when boundaries with a crystal orientation difference of more than 5° are considered to be grain boundaries. For the above analysis, OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. is used. EBSD measurement conditions and the like not shown below are as described above. <Detailed settings of OIM Analysis V8 when calculating the average 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 the Apply partition before calculation checkbox: 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 box for Enforce matching between twin planes (K1) in grain A and grain B: Enter a check mark. Input value for Allowed tolerance between twin planes (K1s) [degrees] (allowable deviation angle between twin planes): 1 (There are no particular restrictions on 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.

[0018] (Thickness) In one embodiment, the thickness of the rolled copper foil is, for example, 4 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, and the lower limit is, for example, 4 μm or more, or, for example, 6 μm or more, or, for example, 9 μm or more. The thickness of the rolled copper foil is measured, for example, by arranging an X-ray generator on the surface side of the rolled copper foil and an X-ray detector on the other main surface side, determining the amount of attenuation by the rolled copper foil from the measured amount of transmitted X-rays, and converting this into 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 H 3100 (C1020) 3 Furthermore, for example, measurements are taken at any two or more points using a digital length measuring device (for example, Nikon Digimicro MH-15M), and the thickness of the rolled copper foil is calculated from the arithmetic mean value of the thicknesses.

[0019] (Manufacturing Example of 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 into a mold (casting) 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 estimated that the arithmetic mean value of the Taylor factor of a rolled copper foil when heat-treated at 260°C for 30 minutes is greatly affected by the average grain size after final annealing and the degree of processing in the final cold rolling when produced by the process described below.

[0020] (Final annealing) The conditions for final annealing are appropriately set so that the arithmetic mean value of the Taylor factor when heat-treated at 260°C for 30 minutes is controlled within a predetermined range. 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 the 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.

[0021] (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 about 4 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.

[0022] [2. Manufacturing Method of Copper-Clad Laminate] One embodiment of the manufacturing method of a copper-clad laminate according to the present invention includes a step of bonding the rolled copper foil 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 a 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 by hot pressing, or sandwiching a polyimide resin film between two copper foil layers and then 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 in which the rolled copper foil and the resin film are laminated 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.

[0023] 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

[0024] According to this manufacturing method, it is possible to manufacture a copper-clad laminate having a copper foil (rolled copper foil) and a substrate (resin film) by the heat treatment, in which the arithmetic mean value of the Taylor factor measured at three points, that is, one arbitrary point and two points equally spaced 5 mm apart from the arbitrary point in the direction perpendicular to the rolling direction, is 2.485 or less. The method for measuring the Taylor factor is the same as that described above.

[0025] [3. Manufacturing Method of Flexible Printed Wiring Board] In one embodiment, 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. At this time, wiring can be formed using the copper-clad laminate 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, an etching solution is sprayed onto the rolled copper foil surface to remove unnecessary rolled copper foil, forming the conductor pattern, and then the etching resist is 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 4, 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 4 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) Facing: 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) of thoroughly annealed tough pitch copper (JIS H 3100 (C1100)), sealed, and then 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 4 and Comparative Examples 1 to 3, recrystallization annealing 3 was performed at the annealing temperature and holding time shown in Table 1.

[0029] [Characteristic Evaluation] <Evaluation of Taylor Factor> Next, in Examples 1 to 4 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. Using the method described above, the measurement sample was sandwiched between two phosphor bronze (JIS H 3110 (C5210) standard) plates (thickness: 0.2 mm) to form a laminate. The laminate was further wrapped and sealed in a rolled copper foil (thickness: 33 μm) made of fully annealed tough pitch copper (JIS H 3100 (C1100)). The sealed body was placed in a dryer and heat-treated at an internal temperature of 260°C for 30 minutes. After heat treatment, the sample was removed from the dryer and allowed to cool in the air. After cooling, the rolled copper foil serving as the measurement sample was removed from the sealed body. The surface of the heat-treated rolled copper foil sample was used as the measurement target, and the Taylor factor of the heat-treated rolled copper foil was measured by the method described above using a scanning electron microscope (JSM-IT500HR) manufactured by JEOL Ltd. Tables 1 and 2 show the Taylor factor values ​​and arithmetic mean values ​​of three points (an arbitrary point N1, a point N2 5 mm away from N1 in the direction perpendicular to the rolling direction, and a point N3 5 mm away from N1 in the direction perpendicular to the rolling direction and in the opposite direction from N1 to N2) measured at 5 mm intervals while avoiding abnormal areas. N1 to N3 are rounded to the fourth decimal place, and the arithmetic mean value is calculated from each value to the third decimal place after rounding, and is also rounded to the fourth decimal place. An attempt was made to measure the Taylor factor of the rolled copper foil after the final cold rolling but before the heat treatment at 260°C for 30 minutes. However, since the sizes of the subgrains and dislocation cell structures in the rolled structure were less than the step size (3 µm) of the EBSD measurement conditions, it was not possible to measure the Taylor factor under the same conditions as those of the rolled copper foil sample after the heat treatment.

[0030]

[0031] (Considerations 1 based on Examples) As a result of comparing Examples 1 to 4 with Comparative Examples 1 to 3, it was confirmed that the arithmetic mean value of the Taylor factor of the rolled copper foil when heat-treated at 260°C for 30 minutes 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 crystal grain size after final annealing.

[0032] [Example 5, Comparative Examples 4-5] In Example 5 and Comparative Examples 4-5, in order to confirm the relationship between the arithmetic mean value of the Taylor factor and flexibility, rolled copper foils having the Taylor factors listed in Table 2 when heat-treated at 260°C for 30 minutes were prepared. As with the evaluation of the Taylor factor described above, the Taylor factor values ​​and arithmetic mean values ​​are shown for three points measured at 5 mm intervals in the direction perpendicular to the rolling direction, avoiding abnormal areas. The notation of each value and arithmetic mean value is as described above. Furthermore, an attempt was made to measure the Taylor factor of the rolled copper foil after final cold rolling but before heat treatment at 260°C for 30 minutes. However, as in Example 1, it was not possible to measure it under the same conditions as those for the rolled copper foil sample after heat treatment.

[0033] <IPC Sliding Bending Test> In Example 5 and Comparative Examples 4 to 5, a portion of the rolled copper foil was collected as a measurement sample before heat treatment at 260°C for 30 minutes, i.e., after final cold rolling. One surface of the measurement sample was subjected to a roughening treatment in accordance with the roughening treatment conditions described above. A polyimide resin film, Pixio™ FRS grade (thickness 25 μm) manufactured by Kaneka Corporation, was then laminated on the roughening-treated surface of the rolled copper foil. The film was then 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. Then, using known photolithography techniques, wiring was formed so that the copper foil 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 a test specimen measuring 12.7 mm wide and 130 mm long, with the length of the specimen parallel to the rolling direction. The IPC sliding flex test was performed on this test specimen using an IPC (Industrial Printed Circuit Council) flex tester 100 shown in Figure 1. The IPC flex tester 100 is configured with an oscillation driver 10 connected to a vibration transmission member 20. The test specimen 30 is fixed to the test specimen at four points: the screw 40 indicated by the arrows 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 specimen 30 is bent into a hairpin shape with a predetermined radius of curvature r. The IPC sliding flex test was performed under conditions of a radius of curvature r of 2.5 mm (outer radius), a vibration stroke of 20 mm, and a vibration speed of 1,500 flexes / min. In the IPC sliding flex test, the number of times until breakage occurred when bending was repeated under the above conditions was counted, and the IPC sliding flex test was performed four times for each condition. The average number of times until breakage was obtained is shown in Table 2 as the IPC sliding flex count. Note that breakage here means that the electrical resistance of the FPC increased by 20% compared to the electrical resistance before the IPC sliding flex test. The electrical resistance was measured using a four-terminal method.

[0034]

[0035] (Considerations from Examples 2) Based on a comparison of the results obtained in Example 5 with the results obtained in Comparative Examples 4 and 5, it was confirmed that by using a rolled copper foil in which the arithmetic mean value of the Taylor factor, measured after heat treatment at an internal temperature of a dryer of 260°C and a heating holding time of 30 minutes, is controlled within a predetermined range, the FPC has better flexibility than conventional ones.

[0036] The results of plotting the arithmetic mean Taylor factor values ​​after heat treatment at 260°C for 30 minutes for each sample in Table 2 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 straight line using the linear approximation function of Microsoft® Excel for approximating curves are also shown in Figure 2. The approximate equation of the straight line and the R-squared value are also shown. The closer the R-squared value is to 1, the more appropriately the approximate straight line represents the trend of the experimental data, and it can be seen that there is a negative proportional correlation between the arithmetic mean Taylor factor values ​​after heat treatment at 260°C for 30 minutes and the number of IPC sliding flexes.

[0037] 2, the arithmetic mean value of the Taylor factor after heat treatment at 260°C for 30 minutes, which increases the number of IPC sliding flexes by 20% or more compared to Comparative Example 4 (the conventional product), i.e., which increases the number of IPC sliding flexes by 230,000 or more, is calculated to be 2.4855. Therefore, it is presumed that by using a rolled copper foil whose arithmetic mean value of the Taylor factor after heat treatment at 260°C for 30 minutes is 2.485 or less, it is possible to provide a rolled copper foil having higher flexibility than conventional ones when made into an FPC.

[0038] 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 arithmetic mean value of Taylor factors of 2.485 or less, measured at three points: one arbitrary point and two points equally spaced 5 mm apart from the arbitrary point in the direction perpendicular to the rolling direction, when heat-treated at a dryer temperature of 260°C for a heating holding time of 30 minutes.

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, wherein the arithmetic mean value of the Taylor factor is 2.300 or more.

5. A copper-clad laminate having rolled copper foil with an arithmetic mean value of Taylor factors of 2.485 or less, measured at three points: one arbitrary point and two points equally spaced 5 mm apart in the direction perpendicular to the rolling direction.

6. The copper clad laminate according to claim 5, having a rolled copper foil having an arithmetic mean value of the Taylor factor of 2.300 or more.

7. 3. A method for producing a copper-clad laminate, comprising the step of bonding the rolled copper foil according to claim 1 or 2 to a substrate, wherein the step comprises performing a heat treatment.

8. 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 7 as a material.

9. 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 8.