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

Abstract

Provided is a rolled copper foil which has higher bendability than conventional copper foil when made into an FPC. This rolled copper foil contains 99.9% by mass or more of Cu, with the remainder comprising unavoidable impurities, and when heat-treated at a dryer internal temperature of 260 DEG C for a heat-holding time of 30 minutes, the copper foil has excellent heat resistance. The arithmetic mean value of the KAM values measured at three points in total, i.e., any one point and two points at equal intervals of 5 mm from the point in the direction perpendicular to the rolling direction is 0.41 or less.

Description

Technical Field

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

[0002] A flexible printed wiring board (FPC) is formed by bonding a metal as a conductive layer to a flexible insulating substrate typified by a resin film. Generally, a copper foil is used as the conductive layer, and particularly, a rolled copper foil having excellent bendability is used in applications requiring bendability.

[0003] A general FPC manufacturing process is as follows. First, a copper foil is bonded to a resin film. The bonding methods include: a method of imidization by applying a varnish containing, for example, a precursor of a polyimide resin to the copper foil and performing heat treatment (casting method); or a method of laminating a resin film having adhesiveness and a copper foil (lamination method). The copper foil with an attached resin film bonded by these processes is called a copper-clad laminate (CCL). Then, wiring is formed by etching to complete the FPC.

[0004] As described above, the rolled copper foil for FPC is required to have bendability. Patent Document 1 proposes that, in order to provide a rolled copper foil for FPC that is easily annealed at the curing temperature of the resin adhesive and has extremely good bend resistance (bending fatigue life) after annealing, the final cold work ratio is set to 90% or more.

[0005] [Background Technical Documents]

[0006] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Laid-Open No. 4-228553 Summary of the Invention

[0008] [Problems to be Solved by the Invention]

[0009] However, in recent years, with the thinning, shortening, and high-performance of electronic devices such as smartphones, the requirements for the bendability of rolled copper foil have become increasingly strict year by year. Along with this, the copper foil made by known techniques gradually fails to meet the customer's needs.

[0010] Therefore, an object of one embodiment of the present invention is to provide a rolled copper foil having higher bendability than before when formed into an FPC.

[0011] [Technical Means for Solving the Problems]

[0012] The inventors conducted various studies and found that, under specified conditions, after heat-treating a rolled copper foil, a rolled copper foil with high bendability can be obtained by making the arithmetic mean of the KAM value 0.41 or less, as exemplified below.

[0013] [1] A rolled copper foil comprising 99.9 mass% or more of Cu, with the balance consisting of inevitable impurities,

[0014] When heat-treated at an internal temperature of 260°C in a dryer for a holding time of 30 minutes, the arithmetic mean of the KAM values measured at any one point and two points spaced 5 mm apart at equal intervals along the direction perpendicular to the rolling direction from that point, i.e., a total of three points, is 0.41 or less.

[0015] [2] The rolled copper foil according to [1], further containing 100 to 360 mass ppm of Ag.

[0016] [3] The rolled copper foil according to [1] or [2], having a thickness of 4 to 35 μm.

[0017] [4] A method for manufacturing a copper-clad laminate, comprising a step of bonding a rolled copper foil according to any one of [1] to [3] to a substrate, and performing a heat treatment in the step.

[0018] [5] A method for manufacturing a flexible printed wiring board, comprising: a step of forming a wiring using a copper-clad laminate manufactured by the method for manufacturing a copper-clad laminate according to [4] as a material.

[0019] [6] A method for manufacturing an electronic component, comprising a step of manufacturing an electronic component having a flexible printed wiring board, the flexible printed wiring board being manufactured by the method for manufacturing a flexible printed wiring board according to [5].

[0020] [Effects of the Invention]

[0021] According to an embodiment of the present invention, a rolled copper foil having bendability higher than that of the prior art during FPC conversion can be provided. Description of the Drawings

[0022] None Detailed Description

[0023] Hereinafter, the present invention is not limited to each embodiment, and components can be changed within the scope not departing from the gist thereof to implement. In addition, by appropriately combining a plurality of components disclosed in each embodiment, various inventions can be formed.

[0024] In addition, the "KAM value" in this specification is an index representing the crystal orientation difference between adjacent pixels based on the crystal orientation analysis information obtained by EBSD. Additionally, the "Cube orientation" is the orientation of grains in which the {001} plane is parallel to the rolling plane and the <100> direction is parallel to the rolling direction (RD), expressed by the indices {001}<100>. Additionally, the "Cube area ratio" represents the area ratio of grains with the Cube orientation of {001}<100>. Additionally, the so-called "rolling direction" means the direction parallel to the "direction in which the rolling target is passed between a pair of working rolls". Additionally, the so-called "direction perpendicular to rolling" means the direction perpendicular to the rolling direction in the rolling plane.

[0025] [1. Rolled copper foil]

[0026] (Composition)

[0027] In one embodiment, the rolled copper foil of the present invention contains 99.9 mass% or more of Cu, and the remainder is composed of inevitable impurities. In another embodiment, the rolled copper foil may also be composed of pure Cu.

[0028] Additionally, in one embodiment, from the viewpoint of more surely obtaining higher bendability than in the past and controlling the recrystallization temperature appropriately during FPC formation, the rolled copper foil may also contain a total of 100 to 360 mass ppm of Ag as an alloy element. In particular, for refined copper (TPC) standardized in JIS-H3100 (C1100) or oxygen-free copper (OFC) in JIS-H3100 (C1020), it is preferable to contain the above-mentioned additive element.

[0029] If the Ag content exceeds 360 mass ppm, due to the influence of the increase in the recrystallization temperature of the rolled copper foil, there is a case where recrystallization becomes insufficient even when heat treatment is carried out by the lamination method. Assuming that unrecrystallized grains remain in the rolled copper foil, the bendability of the FPC will be significantly reduced. Additionally, if the Ag content is 100 mass ppm or more, the introduced rolling strain increases, so the cube texture after CCL heat treatment is likely to grow and the bendability is likely to improve.

[0030] In addition, the upper limit of the oxygen content in the rolled copper foil is, for example, 500 mass ppm or less. Additionally, the lower limit of the oxygen content in the rolled copper foil is, for example, 0 mass ppm or more.

[0031] The composition of the rolled copper foil of the present invention can be determined by fluorescence X-ray analysis as a dry analysis. Specifically, the fluorescence X-ray analysis was performed using Simultix14 manufactured by Rigaku Corporation. As the analysis surface, a surface that has been cut or mechanically polished to a maximum surface height roughness Rz (JIS B0601: 2013) of 6.3 μm or less can be used. When taking an analysis sample from the molten liquid in the melting and casting process during the manufacture of the rolled copper foil, it is cast into a shape of 30 - 40 mm Φ and a thickness of about 50 - 80 mm, and then cut into a thickness of about 10 - 20 mm, and the cut surface is used as the analysis surface. The analysis surface is repeatedly cut or mechanically polished until the maximum surface height roughness Rz (JIS B0601: 2013) becomes 6.3 μm or less.

[0032] In addition to being determined by fluorescence X-ray analysis, the composition of the rolled copper foil can also be determined using ICP emission spectrometry as a wet analysis. Specifically, it can be determined using the ICP emission spectrometry device (ICP-OES) SPS3100 manufactured by Hitachi High-Tech Science Corporation. In the case of ICP emission spectrometry, "the one obtained by dissolving the sample in an aqueous nitric acid solution (by volume, nitric acid: water = 1:1)" is diluted and used.

[0033] (KAM value after heat treatment at 260 °C for 30 minutes)

[0034] In one embodiment of the rolled copper foil of the present invention, when heat-treated at a temperature of 260°C in the dryer and a heating holding time of 30 minutes, the arithmetic mean of the KAM value is 0.41 or less when the rolled copper foil obtained is measured by the following method. According to the research of the present inventors, for the rolled copper foil after the final cold rolling process, if the Cube area rate of the heat-treated rolled copper foil is 95.0% or more after heat-treatment at a temperature of 260°C in the dryer and a heating holding time of 30 minutes, it has better bendability than the previous rolled copper foil. It has been found that when the arithmetic mean of the KAM value is less than 0.41, the Cube area rate becomes 95.0% or more. In addition, regarding the relationship between the arithmetic mean of the KAM value and the bendability, the present inventors have made the following inferences. First, the arithmetic mean of the KAM value is small, which means that the crystal orientation difference between adjacent pixels is small. When the dislocation (transposition) movement stops at a grain boundary and the like and dislocations accumulate, a crystal orientation difference will occur. Slip lines disappear near grain boundaries where dislocations are likely to accumulate, so the movement of dislocations is hindered and dislocations multiply. On the other hand, when the crystal orientation difference is small, the grains deform as the dislocations move, so dislocations are not easily accumulated in specific locations, and are not easily degraded even when repeatedly bent. Therefore, if the arithmetic mean of the KAM value is a small value below 0.41, it is considered that the bendability is improved.

[0035] The upper limit of the arithmetic mean of the KAM value is preferably less than 0.40. In addition, the lower limit of the arithmetic mean of the KAM value is preferably greater than 0.20. In one embodiment, by being within this numerical range, the recrystallization of the Cube-oriented grains after heat treatment is fully carried out. For example, if recrystallization is not fully carried out in the following recrystallization annealing 3 (final annealing), dislocations remain in the material, and then the rolled copper foil obtained by the final cold rolling is heat treated to show a trend of increasing KAM value.

[0036] (KAM value measurement method)

[0037] The KAM value is obtained by measuring the surface of the sample by EBSD (Electron Backscatter Diffraction). Here, EBSD is a technology for analyzing crystal orientation using reflected electron Kikuchi line diffraction (Kikuchi pattern, Kikuchi pattern) generated when an electron beam is irradiated on a sample in a SEM (Scanning Electron Microscope).

[0038] First, take a part of the rolled copper foil as a specimen, place the specimen in a dryer (manufactured by ADVANTEC TOYO Co., Ltd.: DRH453WA) maintained at 260°C, perform heat treatment in an atmospheric environment for 30 minutes, then take it out of the dryer and cool it in the atmospheric environment. In addition, in order to prevent the specimen from oxidizing in the atmospheric environment before being placed, and to prevent bending and wrinkling when taken out of the dryer, a laminate is formed by sandwiching the rolled copper foil with two phosphor bronze (JIS H 3110 (C5210)) plates (thickness: 0.2 mm). Furthermore, after covering and sealing the laminate with a fully annealed electrolytically rolled copper foil (thickness: 33 μm), place it in a dryer. Then, the heat-treated rolled copper foil is obtained after cooling.

[0039] Next, perform electrolytic polishing using the following electrolyte and test conditions, remove a thickness of about 1 μm from the specimen surface, and then scan a 1 mm × 1 mm observation range arbitrarily set with one side of the observation field parallel to the rolling direction at a step size of 3 μm to measure the crystal orientation distribution.

[0040] The measurement is performed at any one point and two points spaced 5 mm apart at equal intervals along the direction perpendicular to the rolling direction from this point, for a total of three points. In addition, if the arithmetic mean of the KAM values measured at any one point and two points spaced 5 mm apart at equal intervals along the direction perpendicular to the rolling direction from this point is 0.41 or less, there is a tendency that the overall bendability of the rolled copper foil is relatively high. This is because, although there may be slight deviations in a certain degree and manufacturing conditions during the manufacturing process, the KAM value measured after heat-treating the rolled copper foil obtained through this manufacturing process under specified conditions is generally controlled within the desired range. Therefore, when the arithmetic mean of the KAM values at any one point and two points spaced 5 mm apart at equal intervals along the direction perpendicular to the rolling direction from this point is 0.41 or less, there may still be some parts in the rolled copper foil where the KAM value exceeds 0.41, but it is expected that such parts will not be many, and most are the desired metal structures, which can solve the problems of the present invention.

[0041] Furthermore, from the perspective of facilitating the manufacture or handling of the rolled copper foil (for example, cutting of specimens for measurement, etc.), there are cases where there are excessive oil pits in some parts, and abnormal parts such as foreign matter attachment or rolling streaks. When measuring the KAM value, the measurement location should be set to avoid the part corresponding to the abnormal part. For the abnormal part, it can be grasped by observing the specimen before electrolytic polishing using SEM (observation magnification: 100 times). When the measurement location overlaps with the abnormal part, avoid the abnormal part and measure a total of three points.

[0042] <Preparation of electrolyte (an example)>

[0043]

[0044] <Electropolishing Conditions>

[0045] Applied Voltage: 10 V

[0046] Electrolysis Time: 10 seconds

[0047] <EBSD Measurement Conditions, etc.>

[0048] · SEM Conditions

[0049] Device: Scanning Electron Microscope (JSM-IT500HR or equivalent device) manufactured by JEOL Ltd.

[0050] Type of Electron Gun: Field Emission Electron Gun (Schottky type)

[0051] Emitter of Electron Gun: ZrO Tungsten Cathode

[0052] Type of Objective Lens: External Lens Type

[0053] Presence or Absence of Focus Correction: Yes (Dynamic Focus: 50)

[0054] Beam Conditions

[0055] Acceleration Voltage: 15 kV

[0056] Working Distance: 15 mm

[0057] Irradiation Current: 15 nA

[0058] SEM Probe Diameter: 0.5 - 2 nm

[0059] Observation Magnification: 90 times

[0060] · EBSD Device Conditions Detector: Slow Scan CCD Camera manufactured by TSL Solutions Co., Ltd.

[0061] · Data Processing Conditions

[0062] Data Collection Software: OIM Data Collection manufactured by TSL Solutions Co., Ltd. Phase: Copper CCD Camera Pixel Number: 1394 × 1040 pixels

[0063] Binning (Pixel Merging): 8 × 8

[0064] Exposure (Exposure Time): 8 milliseconds

[0065] Gain: 0.9 - 0.95

[0066] Presence or absence of background processing: Yes

[0067] Scanning method of measurement points: Hexagonal grid

[0068] · Hough transform

[0069] (1) Hough Type: Classic

[0070] (2) Hough Resolution: Low

[0071] (3) Classic Hough

[0072] · Convolution Mask: 9×9

[0073] · Min Peak Magnitude: 5

[0074] · Min Peak Distance: 23

[0075] · Peak Symmetry: 0.75

[0076] · Vertical Bias: 0

[0077] (4) General Parameter

[0078] · Binned Pattern Size: 120

[0079] · Theta Step Size: 1°

[0080] · Rho Fraction: 90%

[0081] · Max Peak Count: 8

[0082] · Min Peak Count: 3

[0083] When collecting the above measurement data, OIM DataCollection manufactured by TSL Solutions Co., Ltd. is used, and when performing data analysis, OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. is used.

[0084] <Data analysis conditions of OIM Analysis V8>

[0085] · New window

[0086] Select Partition.

[0087] Formula tab: Select Confidence Index under the Point Properties selection bar.

[0088] Confidence Index window: Check Absolute under the Method selection bar.

[0089] Confidence Index window: Select > on the right side of the Method selection bar and set the displayed value to 0.1.

[0090] Do not change Minimum, Maximum, and Average under the Method selection bar.

[0091] · Select New Partition.

[0092] Select New Chart (Kernel Average Misorientation in the Type selection bar).

[0093] Kernel Average Misorientation (the screen displayed when clicking the Edit>> tab on the right side of the Type selection bar)

[0094] Kernel Average Misorientation tab

[0095] Nearest neighbor: 1st

[0096] Maximum misorientation: 5

[0097] Check Perimer only.

[0098] Check Set0-point kernels to maximum misorientation.

[0099] Kernel Average Misorientation (the screen displayed when clicking the Edit>> tab on the right side of the Type selection bar)

[0100] Range tab

[0101] Check Percentage under the Method selection bar.

[0102] Set the Minimum on the right side of the Method selection bar to "0" and the Maximum to "100".

[0103] Set the Minimum, Maximum, and Average under the Method selection bar to "0".

[0104] Kernel Average Misorientation (the screen displayed when clicking the Edit >> tab on the right side of the Type selection bar)

[0105] Parameters tab

[0106] Set the Number of bins to "20".

[0107] Check the Number Fraction in the Vertical Axis column.

[0108] Take the value of Number within Average in the measurement result of Kernel Average Misorientation implemented under the said set conditions (the average value obtained by the Number method) as the average Kernel Average Misorientation.

[0109] (Cube area ratio)

[0110] In one embodiment of the rolled copper foil of the present invention, when heat treatment is performed at an internal temperature of 260 °C and a heating holding time of 30 minutes in a dryer, when the obtained rolled copper foil is measured by the following method, the arithmetic average of the Cube area ratio is preferably 95.0% or more, more preferably 98.0% or more. Thereby, the generation of cracks that cause breakage can be suppressed, and thus the bendability is excellent. For example, regardless of the heating conditions during the manufacture of the copper-clad laminate, stable bendability can be obtained. The specific heat treatment means is the same as the heat treatment means for the KAM value described above, so the description is omitted.

[0111] (Method for measuring the Cube area ratio)

[0112] Next, an example of the method for measuring the Cube area ratio will be described. As described above, on the surface of a sample of the rolled copper foil that has been heat-treated at an internal temperature of 260 °C and a heating holding time of 30 minutes in a dryer, the area ratio of the Cube orientation {001}<100> is measured by EBSD.

[0113] Electrolytic polishing was carried out using the following electrolyte and test conditions to remove a thickness of about 1 μm from the surface of the specimen. Then, a 1000 μm × 1000 μm observation range arbitrarily set with one side of the observation field parallel to the rolling direction was scanned at a step size of 3 μm to measure the crystal orientation distribution.

[0114] The measurement was carried out at an arbitrary point and at two points that were 5 mm apart at equal intervals along the direction perpendicular to the rolling direction from this point. In addition, if the arithmetic mean of the Cube area ratios measured at an arbitrary point and at two points that were 5 mm apart at equal intervals along the direction perpendicular to the rolling direction from this point was 95.0% or more, there was a tendency for the overall bendability of the rolled copper foil to be relatively high. This is because, although there may be some slight deviations in the manufacturing conditions to some extent during the manufacturing process, the Cube area ratio measured after heat-treating the rolled copper foil obtained through this manufacturing process under specified conditions was generally controlled within the desired range. Therefore, when the arithmetic mean of the Cube area ratios at an arbitrary point and at two points that were 5 mm apart at equal intervals along the direction perpendicular to the rolling direction was 95.0%, there might still be a part within the rolled copper foil where the Cube area ratio did not reach 95.0%, but it was expected that such parts would not be many and most would be the desired metal structure.

[0115] Furthermore, from the perspective of facilitating the manufacturing or processing of the rolled copper foil (e.g., cutting of specimens for measurement, etc.), there were parts where there were too many oil pits, as well as abnormal parts such as foreign matter attachment or rolling stripes. When measuring the Cube area ratio, the measurement sites should be set to avoid the parts corresponding to the abnormal parts. For the abnormal parts, the specimens before electrolytic polishing can be observed by SEM (observation magnification: 100 times) to grasp the situation. When the measurement site overlaps with the abnormal part, a total of 3 points are measured while avoiding the abnormal part.

[0116] <Preparation of electrolyte (an example)>

[0117]

[0118] <Electrolytic polishing conditions>

[0119] Applied voltage: 10 V

[0120] Electrolysis time: 10 s

[0121] <EBSD measurement conditions, etc.>

[0122] ·SEM conditions

[0123] Device: Scanning electron microscope (JSM-IT500HR or a device equivalent thereto) manufactured by JEOL Ltd.

[0124] Type of electron gun: Field emission electron gun (Schottky type)

[0125] Emitter of electron gun: ZrO tungsten cathode

[0126] Type of objective lens: External lens type

[0127] Presence or absence of focus correction: Yes (Dynamic focus: 50)

[0128] Beam conditions

[0129] Accelerating voltage: 15 kV

[0130] Working distance: 15 mm

[0131] Irradiation current: 15 nA

[0132] SEM probe diameter: 0.5 - 2 nm

[0133] Observation magnification: 90 times

[0134] ·EBSD device conditions

[0135] Detector: Digital CCD camera manufactured by TSL Solutions Co., Ltd.

[0136] ·Data processing conditions

[0137] Data collection software: OIM Data Collection manufactured by TSL Solutions Co., Ltd.

[0138] Phase: Copper

[0139] Number of pixels of CCD camera: 1394 × 1040 pixels

[0140] Binning (pixel merging): 8 × 8

[0141] Exposure (exposure time): 8 milliseconds

[0142] Gain: 0.9 - 0.95

[0143] Presence or absence of background processing: Yes

[0144] Scanning method of measurement points: Hexagonal grid

[0145] ·Hough transform

[0146] (1) Hough Type: Classic

[0147] (2) Hough Resolution: Low

[0148] (3) Classic Hough

[0149] ·Convolution Mask: 9×9

[0150] ·Min Peak Magnitude: 5

[0151] ·Min Peak Distance: 23

[0152] ·Peak Symmetry: 0.75

[0153] ·Vertical Bias: 0

[0154] (4)General Parameter

[0155] ·Binned Pattern Size: 120

[0156] ·Theta Step Size: 1°

[0157] ·Rho Fraction: 90%

[0158] ·Max Peak Count: 8

[0159] ·Min Peak Count: 3

[0160] Then, perform the analysis of the crystal orientation density function. Divide the area of the grains with orientations within 15° of the Cube orientation by the measured area as the area ratio. When collecting the above measurement data, use OIM Data Collection manufactured by TSL Solutions Co., Ltd., and when performing data analysis, use OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. In addition, the information obtained in the orientation analysis using EBSD contains the orientation information up to a depth of dozens of nanometers where the electron beam penetrates the specimen. However, since it is sufficiently small relative to the measured area, it is recorded as the area ratio.

[0161] <Data analysis conditions of OIM Analysis V8>

[0162] ·New Map window

[0163] Map Style

[0164] Grayscale: Select <None>.

[0165] Color Coded: Select Crystal Orientation.

[0166] Boundaries

[0167] Second Partition: Select <None>.

[0168] · Crystal Orientation window (the screen displayed when Edit of Color Coded in the Map Style window is clicked)

[0169] Representation: Select Euler Angles (Bunge).

[0170] Checkbox for Enforce Orthotropic Sample Symmetry: Enter a check mark.

[0171] · Add Crystal Orientation Range window (the screen displayed when Add in the Crystal Orientation window is clicked)

[0172] Orientation tab

[0173] Phase: Select Copper.

[0174] Euler Angles (Bunge):

[0175] Input value for each of hkl: 001

[0176] Input value for each of uvw: 100

[0177] Tolerance tab

[0178] Input value for Minimum: 0

[0179] Input value for Maximum: 15

[0180] Use the value of Total fraction in the measurement result of Crystal Orientation to be implemented under the said set conditions as the Cube area ratio.

[0181] (Manufacturing example of rolled copper foil)

[0182] As an example of a method for manufacturing rolled copper foil, first, raw materials such as copper are melted in a melting furnace to obtain a molten liquid with the desired composition. Then, the molten liquid is poured into a mold (casting) to form an ingot. To prevent oxidation loss of copper, melting and casting are preferably carried out in a vacuum or an inert gas environment. Then, homogenization annealing, hot rolling, cold rolling 1, recrystallization annealing 1, surface shaving, cold rolling 2, recrystallization annealing 2, pickling and grinding, cold rolling 3, recrystallization annealing 3 (final annealing), and final cold rolling are successively performed to complete the rolled copper foil with the desired thickness and desired properties. That is, in one embodiment, the rolled copper foil basically refers to the rolled copper foil immediately after the final cold rolling.

[0183] In addition, the present inventors have intensively studied and found that in order to make the arithmetic mean value of the KAM value of the rolled copper foil within a specified range when heat treatment is carried out at an internal temperature of 260 °C and a heating holding time of 30 minutes in a dryer, it is important to adjust the arithmetic mean value of the KAM value of the strip-shaped metal material after final annealing to 0.27 to 0.40 when manufacturing in the following process.

[0184] (Final annealing)

[0185] Appropriately set the conditions for final annealing to control the arithmetic mean value of the KAM value of the rolled copper foil within a specified range when heat treatment is carried out at an internal temperature of 260 °C and a heating holding time of 30 minutes in a dryer. Specifically, it is only necessary to appropriately set the conditions for final annealing so that the arithmetic mean value of the KAM value of the strip-shaped metal material after final annealing becomes 0.27 to 0.40. In one embodiment, by being within this numerical range, the driving force for recrystallization is increased, and the KAM value when heat treatment is carried out at an internal temperature of 260 °C and a heating holding time of 30 minutes in a dryer can be appropriately controlled. For example, if recrystallization is not sufficiently carried out in the final annealing, dislocations or unrecrystallized regions will remain in the material, and then the KAM value may increase after heat treatment of the rolled copper foil after final cold rolling. These conditions may also vary depending on the composition of the copper material, but those skilled in the art can experimentally obtain the annealing conditions based on the final annealing conditions such as annealing temperature or holding time without excessive trial and error.

[0186] Since dislocations preferentially accumulate at grain boundaries, a higher KAM value of the strip-shaped metal material after final annealing means more grain boundaries. That is, by making the KAM value after final annealing within the above range, it is easy to control the KAM value of the rolled copper foil after heat treatment after final cold rolling. On the other hand, if the arithmetic mean value of the KAM value after final annealing exceeds 0.40, there is a concern that the annihilation of dislocations during final cold rolling exceeds the dislocation multiplication, resulting in a decrease in the driving force for recrystallization, and thus recrystallization is not fully completed after final annealing.

[0187] Regarding the method for measuring the KAM value after final annealing, since the strip metal material should be generally controlled within a specified range as a whole, the KAM value can be measured by observing and measuring any two points avoiding abnormal parts. Regarding the measurement conditions, since they are the same as those for measuring the KAM value of the rolled copper foil after the aforementioned heat treatment, the description is omitted.

[0188] (Thickness of strip copper material)

[0189] In one embodiment, the thickness of the strip copper material used as the material to be rolled in the final cold rolling process is, for example, 0.45 mm to 1.5 mm.

[0190] In addition, regarding the thickness of the strip copper material, for example, it is measured as follows: an X-ray generator is arranged on one surface side of the strip copper material, and an X-ray detector is arranged on the other surface side. The attenuation amount caused by the rolled copper foil is obtained based on the measured transmitted X-ray amount, and it is converted into the thickness of the strip copper material. Additionally, for example, the gravimetric method can also be used. The gravimetric method means measuring the weight of a 20 mm square strip copper material and using (weight of strip copper material (g) / density of strip copper material (g / cm 3 )) × area of strip copper material (cm 2 ) to calculate the thickness of the strip copper material (in addition, as an example of density, for oxygen-free copper in JIS-H3100 (C1020), it is 8.94 g / cm 3 , and the density of the strip copper material or rolled copper foil in the present invention is also treated in the same way as this example). Further, for example, a digital length gauge (as an example, Digimicro MH-15M manufactured by Nikon Corporation) is used to measure at any two or more points, and then the thickness of the strip copper material is calculated based on the arithmetic mean of each thickness.

[0191] (Final cold rolling)

[0192] By performing final cold rolling under the condition that the degree of working is more than 98% and less than 99%, a rolled copper foil is obtained. At this time, the thickness of the rolled copper foil is about 4 to 35 μm. In addition, regarding the degree of working, it is defined as degree of working (%) = { (thickness before final cold rolling (mm) - thickness after final cold rolling (mm)) / thickness before final cold rolling (mm)} × 100.

[0193] (Thickness)

[0194] 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. Additionally, the lower limit is, for example, 4 μm or more, or for example, 6 μm or more, or for example, 9 μm or more.

[0195] In addition, for the measurement of the thickness of the rolled copper foil, the measurement method of the thickness of the aforementioned strip-shaped copper material can be adopted. When measuring the thickness of the rolled copper foil using the gravimetric method, the specimen size is set to 12.7 mm (in the direction perpendicular to rolling) × 70 mm (in the direction parallel to rolling).

[0196] [2. Method for manufacturing copper-clad laminate]

[0197] In one embodiment of the method for manufacturing the copper-clad laminate of the present invention, it includes a step of bonding the aforementioned rolled copper foil to a substrate. As this substrate, for example, a resin film can be cited. Several methods can be adopted to bond the resin film to the rolled copper foil.

[0198] First, as a method for manufacturing a copper-clad laminate, there is generally a method called the lamination method. According to the lamination method, by using a heat processor such as a laminator to press a resin film (base film) such as polyimide onto the rolled copper foil, a copper-clad laminate (CCL) including the rolled copper foil and the resin film can be obtained. As an example of the manufacturing method using the lamination method, a copper-clad laminate can be manufactured in the following manner: overlap the roughened surface of a rolled copper foil of, for example, 12 μm and a polyimide resin film with a thickness of, for example, 25 μm such as the Pixeo (trademark) film manufactured by Kaneka Corporation, and pass it between heating rollers heated to about 300°C to 370°C, and perform lamination by the lamination method. The time passing between these heating rollers (lamination time) is about 1 second.

[0199] Next, in addition to the lamination method, as a method for manufacturing a copper-clad laminate, there is generally a method called the casting method. For example, there is the following method: coat a varnish containing a precursor of polyimide, i.e., polyamic acid, on at least one surface of the rolled copper foil, and perform heat treatment to harden it, thereby forming a polyimide film on at least one surface of the rolled copper foil. Also, for example, there is the following method: when laminating the rolled copper foil on both sides of a polyimide resin film, after forming a single-sided copper-clad laminate, press the rolled copper foil using a hot press; or sandwich the polyimide resin film between two copper foil layers and perform pressing using a hot press. The heat treatment of the casting method is usually carried out under the conditions of 125 to 360°C and 30 to 400 minutes.

[0200] In addition, although an example of using a polyimide resin film in the lamination method and the casting method is described, it is not limited to this resin film. As the resin film, in addition to the polyimide resin film, it can also be, for example, polyester, polyethylene terephthalate, polyethylene naphthalate, etc.

[0201] Furthermore, the heat treatment speed of the lamination method is typically significantly faster than that of the casting method, and the bendability of the FPC produced by the lamination method is likely to be reduced compared to the casting method.

[0202] In addition, the rolled copper foil may be subjected to a roughening treatment before laminating the rolled copper foil and the resin film. This can improve the bonding strength between the resin film and the rolled copper foil. For example, the roughening treatment may be performed under the following conditions.

[0203] <Roughening treatment conditions>

[0204] Liquid composition: Cu 10~20g / L, Co 1~10g / L, Ni 1~15g / L

[0205] pH: 1-4

[0206] Temperature: 30~50℃

[0207] Current density (Dk): 20~50A / dm 2

[0208] Time: 1 to 5 seconds

[0209] According to this manufacturing method, a copper-clad laminate having a copper foil (rolled copper foil) and a substrate (resin film) having an arithmetic mean KAM value of 0.41 or less can be manufactured by the heat treatment. The method for measuring the KAM value is the same as the above method.

[0210] [3. Method for manufacturing flexible printed wiring board]

[0211] In one embodiment, the method for manufacturing a flexible printed wiring board of the present invention includes a process for forming wiring using a copper-clad laminate manufactured by the method for manufacturing the copper-clad laminate as a material. At this time, the copper-clad laminate can be used as a material to form wiring in a known order to manufacture a flexible printed wiring board (FPC). For example, the following method can be cited: on the rolled copper foil surface of the copper-clad laminate, an etching resist is applied only to the portion required as a conductor pattern, and an etching solution is sprayed onto the rolled copper foil surface to remove excess rolled copper foil to form a conductor pattern, followed by peeling and removing the etching resist, and then exposing the conductor pattern. After the conductor pattern is formed, a protective cover film is usually attached.

[0212] (use)

[0213] This FPC is used for electronic components such as electronic and electrical equipment, such as the movable part inside a hard disk, the hinge part (hinge part) or sliding part of a mobile phone, the inside of a mobile phone, the print head of a printer, an optical reading head, the movable part of a notebook computer, etc. In addition, in the manufacturing method of electronic components, as long as it includes the process of manufacturing an electronic component having a flexible printed wiring board, the flexible printed wiring board is manufactured by the manufacturing method of the flexible printed wiring board.

[0214] [Examples]

[0215] The present invention will be specifically described based on examples and comparative examples. The following descriptions of examples and comparative examples are only specific examples for facilitating the understanding of the technical content of the present invention, and the technical scope of the present invention is not limited by these specific examples.

[0216] In addition, "CI > 0.1" in Table 1 means that when performing analysis, measurement points with a CI value of 0.1 or less analyzed by OIM Analysis V8 through data analysis are excluded. In addition, "CI" is an abbreviation for Confidence Index.

[0217] [Examples 1 - 3, Comparative Examples 1 - 2]

[0218] [Manufacture of Rolled Copper Foil]

[0219] First, in Examples 1 - 3 and Comparative Example 1, an ingot having the following alloy composition is melted and cast, that is, Ag described in Table 1 is contained in a copper material containing 99.9 mass% or more of Cu. In addition, the Ag content of the ingot is measured by the ICP emission spectrometry method. The ingot is processed in the following process sequence to make a rolled copper foil. In addition, the degree of working in Table 1 refers to the sheet thickness reduction rate during the final cold rolling, and is calculated using the degree of working (%) = { (thickness (mm) before the final cold rolling - thickness (mm) after the final cold rolling (final product)) / thickness (mm) before the final cold rolling} × 100.

[0220] <Processes (1) - (11)>

[0221] Process (1) Homogenization annealing: The ingot is heated and held at 920 °C for 2.5 hours.

[0222] Process (2) Hot rolling: The ingot heated at 920 °C is rolled at room temperature to a thickness of 16 mm. Then, it is rapidly cooled to room temperature by water cooling to obtain a strip-shaped metal material.

[0223] Process (3) Cold rolling 1: Rolled to a thickness of 10.5 mm.

[0224] Process (4) Recrystallization annealing 1: The strip-shaped metal material is heated and held at 400 °C for 7.5 hours.

[0225] Process (5) Surface cutting: Remove the scale on the surface by surface cutting.

[0226] Process (6) Cold rolling 2: Roll to a thickness of 1.5 mm.

[0227] Process (7) Recrystallization annealing 2: Hold for 30 to 120 seconds in a furnace heated to 750 °C.

[0228] Process (8) Pickling and polishing: Immerse in a mixed acid of sulfuric acid and hydrogen peroxide water, and then perform polishing, thereby removing the oxide film on the surface of the material.

[0229] Process (9) Cold rolling 3: Roll to a thickness of 0.8 mm to 1.0 mm.

[0230] Process (10) Recrystallization annealing 3 (final annealing): Appropriately adjust the annealing temperature and holding time so that the KAM value on the surface of the strip-shaped metal material after recrystallization annealing 3 as described in Table 1 is obtained, and heat and hold the strip-shaped metal material after cold rolling 3 respectively. In addition, for the strip-shaped metal material, in order to prevent oxidation, a sealed body formed by covering and sealing the strip-shaped metal material with a rolled copper foil (thickness: 33 μm) of fully annealed electrolytic copper (JIS H 3100 (C1100)) is placed in a dryer. After heat and hold, take out the sealed body from the dryer and cool it in the atmospheric environment. After cooling, take out the strip-shaped metal material from the sealed body. In addition, regarding the KAM value after the final annealing, measure any two points by the aforementioned method.

[0231] Process (11) Final cold rolling: Finish machining to a thickness of 0.012 mm (12 μm) to obtain a rolled copper foil. In the final cold rolling, the two end sides in the rolling direction of the strip-shaped metal material are not fixed (in a free end state), and the strip-shaped metal material is passed between a pair of working rolls, thereby performing rolling in a state where no tension acts in the direction parallel to the rolling direction.

[0232] In addition, in Comparative Example 2, after rolling to 1.0 mm in Process (9), annealing and rolling are performed again, and after making a thickness of 0.5 mm, Process (10) is carried out.

[0233] [Characteristic evaluation]

[0234] <KAM value>

[0235] In Examples 1 to 3 and Comparative Examples 1 to 2, using a scanning electron microscope (JSM-IT500HR) manufactured by JEOL Ltd., according to the aforementioned method, for the strip-shaped metal material after Process (10) and the rolled copper foil after heat treatment at 260 °C for 30 minutes in Process (11), the arithmetic mean value of each KAM value was measured.

[0236] In addition, for the strip-shaped metal material, two points are measured while avoiding the abnormal part. Further, for the rolled copper foil after the heat treatment at 260°C for 30 minutes, three points are measured while avoiding the abnormal part, namely any one point and two points spaced 5 mm apart at equal intervals in the direction perpendicular to the rolling direction from this point, for a total of three points. For each point, the value that can be obtained as the original data on the software is read up to the limit, and for the arithmetic mean, the fourth decimal place is rounded off and displayed to the third decimal place.

[0237] <Evaluation of Cube area ratio>

[0238] Next, in Examples 1 to 3 and Comparative Examples 1 to 2, a part of the rolled copper foil obtained by the above manufacturing is taken as a measurement sample respectively. By the above method, a laminate is formed by sandwiching the measurement sample with two plates (thickness: 0.2 mm) of phosphor bronze (JIS H 3110 (C5210) standard). A sealed body obtained by further coating and sealing the laminate with a rolled copper foil (thickness: 33 μm) of electrolytic tough pitch copper (JIS H 3100 (C1100)) after full annealing is placed in a dryer, and heat treatment is performed at an internal temperature of 260°C for a holding time of 30 minutes in the dryer. After the heat treatment, it is taken out from the dryer and cooled in the atmospheric environment. After cooling, the rolled copper foil used as the measurement sample is taken out from the sealed body. The surface of the sample of the rolled copper foil after the heat treatment is taken as the measurement object, and the area ratio of the Cube orientation {001}<100> of the rolled copper foil after the heat treatment is measured by the above method using a scanning electron microscope (JSM-IT500HR) manufactured by JEOL Ltd. In addition, in Table 1, the arithmetic mean of the area ratios of the Cube orientation {001}<100> of any one point avoiding the abnormal part and two points spaced 5 mm apart at equal intervals in the direction perpendicular to the rolling direction from this point, for a total of three points, is shown as the Cube area ratio. For each point, the calculation is carried out to the second decimal place, and for the arithmetic mean, the third decimal place is rounded off and displayed to the second decimal place. In addition, for the rolled copper foil before the final cold rolling and before the heat treatment at 260°C for 30 minutes, an attempt was made to measure the Cube area ratio in the same manner, but since the size of the sub-grains or dislocation cell structures in the rolling texture did not reach the step size (3 μm) of the EBSD measurement conditions, it was impossible to measure under the same conditions as those for the sample of the rolled copper foil after the heat treatment.

[0239] [Table 1]

[0240]

[0241] (Research on Examples)

[0242] Comparing Examples 1 to 3 with Comparative Examples 1 to 2, it was confirmed that by appropriately adjusting the KAM value of the recrystallization annealing 3 (final annealing) within the range of 0.27 to 0.40, the arithmetic mean value of the KAM value of the rolled copper foil during heat treatment at 260°C for 30 minutes could be controlled to 0.41 or less. In addition, it was also confirmed that the Cube area ratio after this heat treatment could be increased to 95.0% or more. Further, in Examples 1 and 3 where the arithmetic mean value of the KAM value of the rolled copper foil during heat treatment at 260°C for 30 minutes was 0.40 or less, the Cube area ratio after this heat treatment could be further increased to 98.0% or more.

[0243] Incidentally, regarding the advantage of bendability, the IPC sliding bend test can confirm the number of IPC sliding bends. Here, when using "the rolled copper foil with a higher Cube area ratio measured after heat treatment at an internal temperature of 260°C in a dryer for 30 minutes of heating and holding", it is empirically known that there is a positive proportional relationship between the Cube area ratio after heat treatment at 260°C for 30 minutes and the number of IPC sliding bends. Therefore, it can be said that the rolled copper foil with a higher Cube area ratio after the heat treatment has more excellent bendability than before when made into an FPC.

[0244] Therefore, as in Examples 1 to 3, it can be speculated that by using "the rolled copper foil with a Cube area ratio of 95.0% or more after heat treatment at 260°C for 30 minutes", a rolled copper foil with bendability superior to that of the past when made into an FPC can be provided.

Claims

1. A rolled copper foil comprising 99.9 mass % or more of Cu, the remainder of which is composed of unavoidable impurities, When heat treatment was carried out at an internal temperature of 260°C in the dryer and a heating holding time of 30 minutes, the arithmetic mean of the KAM values ​​measured at three points, namely, any one point and two points equally spaced 5 mm from the point in the direction perpendicular to the rolling direction, was less than 0.

41. 2 . The rolled copper foil according to claim 1 , further comprising 100 to 360 mass ppm of Ag.

3. The rolled copper foil according to claim 1 or 2, which has a thickness of 4 to 35 μm. 4 . A method for producing a copper-clad laminate, comprising a step of bonding the rolled copper foil according to claim 1 to a substrate, wherein a heat treatment is performed in the step.

5. A method for manufacturing a flexible printed wiring board, comprising: A step of forming wiring using the copper-clad laminate produced by the method for producing a copper-clad laminate according to claim 4 as a material. 6 . A method for producing an electronic component, comprising the 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 claim 5 .

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