Rolled copper foil, copper-clad laminated plate, production method for copper-clad laminated plate, production method for flexible printed circuit, and production method for electronic component

Abstract

Provided is a rolled copper foil which has bending properties superior to those of conventional rolled copper foils when made into an FPC. The rolled copper foil contains at least 99.9 mass% Cu, with the balance being unavoidable impurities, and has a cube orientation area ratio of at least 94.0% as measured after being subjected to a heat treatment at a temperature of 260 °C for 30 minutes in a dryer.

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, 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] 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 Cube area ratio of 94.0% or more, and have created the following inventions: [1] A rolled copper foil containing 99.9% by mass or more of Cu, the remainder consisting of unavoidable impurities, and having a Cube area ratio of 94.0% or more measured when heat-treated at a dryer temperature of 260°C and a heating holding time of 30 minutes. [2] A rolled copper foil containing 99.9% by mass or more of Cu, the remainder consisting of unavoidable impurities, and having an arithmetic mean value of the Cube area ratios of 94.0% or more measured at any two points when heat-treated at a dryer temperature of 260°C and a heating holding time of 30 minutes. [3] A rolled copper foil containing 99.9% by mass or more of Cu, the remainder consisting of unavoidable impurities, and having a median Cube area ratio of 94.0% or more when measured at three points: one arbitrary point and two other points equally spaced 5 mm apart in the direction perpendicular to the rolling direction from the arbitrary point when heat-treated at a dryer temperature of 260°C for a heating holding time of 30 minutes. [4] A rolled copper foil containing 99.9% by mass or more of Cu, the remainder consisting of unavoidable impurities, and having a median Cube area ratio of 94.0% or more when measured at three points: one arbitrary point and two or more points equally spaced 5 mm apart in the direction perpendicular to the rolling direction from the arbitrary point when heat-treated at a dryer temperature of 260°C for a heating holding time of 30 minutes, excluding the maximum and minimum values. [5] The rolled copper foil according to any one of [1] to [4], further containing 100 to 360 ppm of Ag. [6] The rolled copper foil according to any one of [1] to [5], having a thickness of 4 to 35 μm. [7] The rolled copper foil according to any one of [1] to [6], having a thickness of 6 to 35 μm. [8] A copper-clad laminate having a rolled copper foil having a Cube area ratio of 94.0% or more. [9] A method for producing a copper-clad laminate, comprising a step of bonding the rolled copper foil according to any one of [1] to [7] and a substrate, wherein the step comprises a heat treatment.

[10] 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 [9] as a material.

[11] 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

[10] .

[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 bending test in Example 6 and Comparative Examples 4 to 5. It is a graph in which the Cube area ratio after heat treatment at 260°C for 30 minutes is plotted on the horizontal axis and the number of IPC sliding bending cycles is plotted on the vertical axis based on Example 6 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. Various inventions can be realized by appropriately combining the components disclosed in each embodiment. In this specification, the term "Cube orientation" refers to the orientation of crystal grains in which the {001} plane is parallel to the rolled surface and the <100> direction is parallel to the rolling direction (RD), and is expressed by the index {001}<100>. The term "Cube area ratio" refers to the area ratio of the Cube orientation {001}<100>. The term "rolling direction" refers to the direction parallel to the direction in which the rolled object passes between a pair of work rolls. The term "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, 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 B 0601:2013) 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 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 B 0601:2013) 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] (Cube Area Ratio) In one embodiment, the rolled copper foil according to the present invention has a Cube area ratio of 94.0% or more 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 and creases during removal from the dryer. This laminate was then wrapped and sealed in a 33 μm thick rolled foil of thoroughly annealed tough-pitch copper before being loaded into the dryer. Rolled copper foil with a relatively high rate of Cube orientation development under specified heat treatment conditions and a Cube area ratio of at least a specified level is less susceptible to dislocation accumulation at grain boundaries during bending. This suppresses cracking, which can lead to fracture, resulting in excellent flexibility. For example, stable flexibility can be achieved regardless of the heating conditions during the manufacture of copper-clad laminates. The lower limit of the Cube area ratio is preferably 95.0% or more, more preferably 95.5% or more, even more preferably 96.0% or more, even more preferably 96.5% or more, even more preferably 96.6% or more, even more preferably 97.0% or more, even more preferably 97.5% or more, even more preferably 97.8% or more, even more preferably 98.0% or more, even more preferably 98.5% or more, even more preferably 99.0% or more, even more preferably 99.5% or more, even more preferably 99.6% or more, and even more preferably 99.7% or more. On the other hand, the upper limit of the Cube area ratio is 100.0% or less. The inventors have discovered that in order to increase the Cube area ratio after heat treatment, it is important to control the average grain size after final annealing and the working ratio of final cold rolling. The conditions for the average grain size after final annealing and the working ratio of final cold rolling will be described later and will not be repeated here.

[0015] (Method for measuring Cube area ratio) Next, an example of a method for measuring the Cube area ratio will be described. As described above, the area ratio of the Cube orientation {001}<100> is measured by EBSD on the surface of a sample of rolled copper foil 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 diffraction (Kikuchi pattern) that occurs when a sample is irradiated with an electron beam in a SEM (Scanning Electron Microscope). Electrolytic polishing was performed using the following electrolyte and test conditions, and a thickness of approximately 1 μm was removed from the sample surface. After that, a 1000 μm × 1000 μm observation area was arbitrarily set so that one side of the observation field was parallel to the rolling direction, and the observation area was scanned at a step size of 3 μm to measure the crystal orientation distribution. Measurements were performed at two or more locations, avoiding abnormal areas. Note that if the arithmetic mean value of the Cube area ratios at any two locations is 94.0% or more, the rolled copper foil as a whole tends to have high flexibility. This is because, although there may be some variation in the manufacturing conditions within the rolled copper foil during the manufacturing process, the Cube area ratio measured after heat treatment under specified conditions of the rolled copper foil obtained during the manufacturing process is generally controlled within the desired range. Therefore, when the arithmetic mean value of the Cube area ratios at any two locations is 94.0% or more, there may be some portions in the rolled foil where the Cube area ratio is less than 94.0%, but it is expected that such portions will not be very numerous, and most of the rolled foil will have the desired metal structure, thereby solving the problem of the present invention. Furthermore, due to the convenience of manufacturing and handling of the rolled copper foil (e.g., cutting out a sample for measurement), some abnormalities such as excessive oil pits, foreign matter adhesion, or rolling streaks may occur. When measuring the Cube area ratio, the measurement location should be set to avoid locations corresponding to abnormal areas. Abnormal areas can be identified by observing the sample before electropolishing with an SEM (observation magnification: 100x). As described above, the rolled copper foil as a whole should be controlled generally within a predetermined range, so the Cube area ratio can be measured by observing and measuring any two points avoiding abnormal areas, and it is preferable to observe and measure points at least 5 mm apart.The Cube area ratio may be determined from the arithmetic mean value of n-2 points obtained by measuring an arbitrary point and two or more points equally spaced 5 mm apart from the arbitrary point in the direction perpendicular to the rolling direction, excluding the maximum and minimum values ​​(the median value is used when the measurement points are three points, i.e., an arbitrary point and two points equally spaced 5 mm apart from the arbitrary point in the direction perpendicular to the rolling direction). If the measurement point overlaps with an abnormal portion, a total of three points are measured, avoiding the abnormal portion. Here, "n" refers to the total number of measurement points. The total number of measurement points may be 3 or more and 10 or less, or may be 3 or more and 5 or less. The total number of measurement points may be any of 3, 4, 5, 6, 7, 8, 9, and 10. <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): 5Min Peak Distance (minimum distance between peaks): 23 Peak Symmetry (peak symmetry): 0.75 Vertical Bias (vertical bias): 0 (4) General Parameters Binned Pattern Size (compressed pattern size): 120 Theta Step Size (angle step size): 1° Rho Fraction (rho fraction): 90% Max Peak Count (maximum number of peaks): 8 Min Peak Count (minimum number of peaks): 3 Then, the crystal orientation density function is analyzed, and the area of ​​crystal grains having an orientation within 15° of the Cube orientation is divided by the measured area to obtain the area ratio. The above measurement data was collected using OIM Data Collection manufactured by TSL Solutions Co., Ltd., and the data was analyzed using OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. Note that the information obtained in the orientation analysis using EBSD includes orientation information up to a depth of several tens of nanometers, the depth at which the electron beam penetrates into the sample, but since this is sufficiently small compared to the area being measured, it is reported as an area ratio. <Data analysis conditions for OIM Analysis V8> New Map window Map Style Grayscale: Select <None>. Color Coded: Select Crystal Orientation. Boundaries Second Partition: Select <None>.・Crystal Orientation window (screen displayed when you click Edit under Color Coded in the Map Style window) Representation: Select Euler Angles (Bunge). Enforce Orthotropic Sample Symmetry checkbox: Check the box. ・Add Crystal Orientation Range window (screen displayed when you click Add in the Crystal Orientation window) Orientation tab Phase: Select Copper.Euler Angles (Bunge): (φ1, Φ, φ2) = (0, 0, 0) Input values ​​for hkl: 001 Input values ​​for uvw: 100 Tolerance tab Minimum input value: 0 Maximum input value: 15 The total fraction value in the results of the Crystal Orientation measurement performed under the above setting conditions is defined as the Cube area ratio.

[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, a cube texture will develop significantly during heat treatment of the rolled copper foil, improving its 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 rolling, and shear bands will easily develop in the rolled structure. Shear bands are likely to become nucleation sites for non-Cube orientation during heat treatment of the rolled copper foil, and a cube texture will not easily develop.

[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, 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. 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 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 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 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.

[0019] (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 cube area ratio of the rolled copper foil when heat treated at 260°C for 30 minutes is greatly affected by the average crystal 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 Cube area ratio is high when heat treated at 260°C for 30 minutes. Specifically, the conditions for final annealing are 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 layer by hot pressing, or sandwiching a polyimide resin film between two rolled 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 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.

[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, the Cube orientation is developed by the heat treatment, and thus it is possible to manufacture a copper-clad laminate having a copper foil (rolled copper foil) and a substrate (resin film) with a Cube area ratio of 94.0% or more. The method for measuring the Cube area ratio is the same as the method 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 above-described 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, 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 and removed to expose the conductor pattern. After forming the conductor pattern, it is common to apply a protective coverlay film.

[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) 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 5 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 Cube Area Ratio> 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. 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 sample surface of the heat-treated rolled copper foil was used as the measurement object, and the area ratio of the Cube orientation {001}<100> of the heat-treated rolled copper foil was measured by the above-mentioned method using a scanning electron microscope (JSM-IT500HR) manufactured by JEOL Ltd. In Tables 1 and 2, the arithmetic average of the area ratios of the Cube orientation {001}<100> measured at two points while avoiding abnormal areas is shown as the Cube area ratio. Note that an attempt was made to measure the Cube area ratio in the same manner for the rolled copper foil after final cold rolling but before the heat treatment at 260°C for 30 minutes, but because the size of the subgrains and dislocation cell structure in the rolled structure was less than the step size (3 μm) of the EBSD measurement conditions, it was not possible to measure it under the same conditions as the measurement conditions for the heat-treated rolled copper foil sample.

[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 by setting the working ratio of the final cold rolling to more than 98% and less than 99% and appropriately setting the average crystal grain size after final annealing, it was possible to increase the cube area ratio of the rolled copper foil when heat treated at 260°C for 30 minutes. Furthermore, as a result of comparing Example 3 with Example 4, it was confirmed that the smaller the average crystal grain size after final annealing, the higher the cube area ratio of the rolled copper foil when heat treated at 260°C for 30 minutes.

[0032] [Example 6, Comparative Examples 4 to 5] In Example 6 and Comparative Examples 4 to 5, in order to confirm the relationship between the Cube area ratio and flexibility, rolled copper foils having the Cube area ratios shown in Table 2 when heat-treated at 260°C for 30 minutes were prepared. As in the evaluation of the Cube area ratio described above, the Cube area ratio is shown as the arithmetic mean value of the area ratios of the Cube orientation {001}<100> measured at two points while avoiding abnormal areas. In addition, an attempt was made to measure the Cube area ratio 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 the Cube area ratio under the same conditions as those of the rolled copper foil sample after heat treatment.

[0033] <IPC Sliding Bending Test> In Example 6 and Comparative Examples 4 and 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 onto the roughened-plated 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 circuit width (Line) of the rolled copper foil 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 6 with the results obtained in Comparative Examples 4 and 5, it was confirmed that by using rolled copper foil with a high Cube area ratio, which was measured after heat treatment at a dryer temperature of 260°C and a heating holding time of 30 minutes, superior flexibility was achieved when made into an FPC compared to conventional FPCs.

[0036] The results of plotting the Cube area ratio of each sample in Table 2 after heat treatment at 260°C for 30 minutes 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® Excel for approximating curves are also shown in Figure 2. The approximate equation 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 Cube area ratio after heat treatment at 260°C for 30 minutes and the number of IPC sliding flexes.

[0037] 2 , the Cube area ratio after heat treatment at 260°C for 30 minutes, which increases the IPC sliding flex count by 15% or more compared to Comparative Example 4 (the conventional product), i.e., the IPC sliding flex count is 220,000 or more, is calculated to be 93.5%, and it is inferred that by using a rolled copper foil having a Cube area ratio of 94.0% or more after heat treatment at 260°C for 30 minutes, it is possible to provide a rolled copper foil with higher flexibility than conventional FPCs. Furthermore, the Cube area ratio after heat treatment at 260°C for 30 minutes, which increases the IPC sliding flex count by 20% or more compared to Comparative Example 4 (the conventional product), i.e., the IPC sliding flex count is 230,000 or more, is calculated to be 94.9%, and it is inferred that by using a rolled copper foil having a Cube area ratio of 95.0% or more after heat treatment at 260°C for 30 minutes, it is possible to provide a rolled copper foil with higher flexibility than conventional FPCs.

[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 a cube area ratio of 94.0% or more when measured after heat treatment at a dryer temperature of 260°C and a heating holding time of 30 minutes.

2. Contains 99.9% by mass or more of Cu, with the remainder consisting of unavoidable impurities; A rolled copper foil having an arithmetic average value of the Cube area ratio of 94.0% or more, measured at any two points when heat-treated at a dryer temperature of 260°C and a heating holding time of 30 minutes.

3. Contains 99.9% by mass or more of Cu, with the remainder consisting of unavoidable impurities; A rolled copper foil having a median Cube area ratio of 94.0% or more, 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.

4. Contains 99.9% by mass or more of Cu, with the remainder consisting of unavoidable impurities; A rolled copper foil in which, when heat-treated at a dryer temperature of 260°C for a heating holding time of 30 minutes, measurements are taken at one arbitrary point and at least two points equally spaced 5 mm apart from that point in the direction perpendicular to the rolling direction, and the arithmetic mean value of the cube area ratio, excluding the maximum and minimum values, is 94.0% or more.

5. The rolled copper foil according to any one of claims 1 to 4, further containing 100 to 360 ppm by mass of Ag.

6. The rolled copper foil according to any one of claims 1 to 4, having a thickness of 4 to 35 µm.

7. The rolled copper foil according to any one of claims 1 to 4, having a thickness of 6 to 35 µm.

8. A copper clad laminate having rolled copper foil with a Cube area ratio of 94.0% or more.

9. A method for producing a copper-clad laminate, comprising: a step of bonding the rolled copper foil according to any one of claims 1 to 4 to a substrate, wherein the step includes a heat treatment.

10. 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 9 as a material.

11. 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 10.