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

Abstract

To provide a rolled copper foil having higher flexibility than conventional ones when made into an FPC.SOLUTION: A rolled copper foil contains 99.9 mass% or more of Cu, and the rest that is composed of inevitable impurities. When heat treatment is carried out at 260°C of an internal temperature of a drier for 30 minutes of heating holding time, an arithmetic mean value of KAM value is 0.41 or less which is obtained by measuring at a total of three points of an arbitrary one point and two points that are away from the one point at equal intervals of 5 mm in a transverse direction.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] A flexible printed wiring board (FPC) is formed by joining a metal, which is a conductive layer, and a flexible insulating substrate typified by a resin film. Generally, a copper foil is used for the conductive layer, and particularly for applications requiring flexibility, a rolled copper foil with excellent flexibility is used.

[0003] A general FPC manufacturing process is as follows. First, a copper foil is joined to a resin film. For joining, there are a method of applying a varnish containing a precursor of a polyimide resin on the copper foil and subjecting it to heat treatment to imidize it (casting method), and a method of laminating an adhesive resin film and a copper foil (laminating method). The copper foil with a resin film joined by these processes is called a copper-clad laminate (CCL). Then, wiring is formed by etching, and the FPC is completed.

[0004] For a rolled copper foil for FPC, flexibility is required as described above. In Patent Document 1, it is proposed to set the final cold working ratio to 90% or more in order to provide a rolled copper foil for FPC that can be easily annealed at the curing temperature of the resin adhesive and has extremely good bending resistance (bending fatigue life) after annealing.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in recent years, with the trend towards thinner, lighter, and more highly functional electronic devices such as smartphones, the required flexibility of rolled copper foil has become increasingly stringent year by year. Along with this, copper foils produced using known techniques are increasingly unable to meet customer needs.

[0007] Therefore, in one embodiment, an object of the present invention is to provide a rolled copper foil having higher flexibility than conventional foils when formed into an FPC.

Means for Solving the Problems

[0008] As a result of various studies, the inventors have found that when a rolled copper foil is heat-treated under predetermined conditions, a rolled copper foil having high flexibility can be obtained by setting the arithmetic mean value of its KAM value to 0.41 or less, as exemplified below. [1] A rolled copper foil containing 99.9 mass% or more of Cu, with the balance consisting of inevitable impurities, wherein when heat-treated at an internal temperature of 260°C in a dryer for a holding time of 30 minutes, the arithmetic mean value of the KAM values measured at any one point and two points spaced at equal intervals of 5 mm each in the direction perpendicular to the rolling direction from that point is 0.41 or less. [2] The rolled copper foil according to [1], further containing 100 to 360 mass ppm of Ag. [3] The rolled copper foil according to [1] or [2], having a thickness of 4 to 35 μm. [4] 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 base material, wherein the step includes performing heat treatment. [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. [6] A method for manufacturing an electronic component, comprising a step of manufacturing an electronic component provided with a flexible printed wiring board manufactured by the method for manufacturing a flexible printed wiring board according to [5].

Advantages of the Invention

[0009] According to an embodiment of the present invention, it is possible to provide a rolled copper foil having higher flexibility than conventional ones when formed into an FPC.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention is not limited to each embodiment, and components can be modified and embodied without departing from the gist thereof. Also, various inventions can be formed by appropriately combining a plurality of components disclosed in each embodiment. In addition, the "KAM value" in this specification is an index indicating the crystal orientation difference between adjacent pixels from the crystal orientation analysis information by EBSD. Also, the "Cube orientation" is the orientation of crystal grains in which the {001} plane is parallel to the rolling plane and the <100> direction is parallel to the rolling direction (RD), and is indicated by the indices of {001}<100>. Also, the "Cube area ratio" indicates the area ratio of crystal grains with the Cube orientation {001}<100>. Also, the "rolling direction" means a direction parallel to the direction in which the object to be rolled passes between a pair of work rolls. Also, the "direction perpendicular to rolling" means a direction perpendicular to the rolling direction on the rolling plane.

[0011] [1. Rolled Copper Foil] (Composition) In one embodiment, the rolled copper foil according to the present invention contains 99.9 mass% or more of Cu, and the balance consists of inevitable impurities. In another embodiment, the rolled copper foil may be composed of pure Cu. Also, in one embodiment, the rolled copper foil may further contain a total of 100 to 360 mass ppm of Ag as an alloying element from the viewpoint of more surely obtaining higher flexibility than conventional ones when formed into an FPC and controlling the recrystallization temperature appropriately. In particular, it is preferable to contain the above-mentioned additive elements with respect to tough pitch copper (TPC) standardized in JIS-H3100 (C1100) or oxygen-free copper (OFC) of JIS-H3100 (C1020). When the Ag content exceeds 360 mass ppm, recrystallization may be insufficient even when heat treatment by the lamination method is carried out due to the influence of the increase in the recrystallization temperature of the rolled copper foil. If unrecrystallized grains remain in the rolled copper foil, the flexibility of the FPC will be significantly reduced. Also, if the Ag content is 100 mass ppm or more, the amount of rolling strain introduced increases, so the cubic texture after CCL heat treatment tends to grow and the flexibility tends to increase. In addition, the oxygen content in the rolled copper foil is, for example, 500 mass ppm or less as the upper limit. Also, the oxygen content in the rolled copper foil is, for example, 0 mass ppm or more as the lower limit.

[0012] 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 measured using Simultix14 manufactured by Rigaku Corporation. As the analysis surface, one obtained by cutting or mechanical polishing so that the surface maximum height roughness Rz (JIS B0601: 2013) is 6.3 μm or less may be used. When collecting an analysis sample from the molten metal during melting and casting in the manufacturing process of the rolled copper foil, it is cast into a shape of about 30 to 40 mm Φ and a thickness of about 50 to 80 mm, then cut to a thickness of about 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 maximum height roughness Rz (JIS B0601: 2013) becomes 6.3 μm or less. In addition to measurement by X-ray fluorescence analysis, the composition of the rolled copper foil may be measured by ICP emission spectrometry as a wet analysis. Specifically, measurement can be performed using an ICP emission spectrometer (ICP-OES) SPS3100 manufactured by Hitachi High-Technologies Corporation. In the case of ICP emission spectrometry, a sample dissolved in a nitric acid aqueous solution (volume ratio, nitric acid: water = 1: 1) is diluted and used.

[0013] (KAM value when heat-treated at 260 °C for 30 minutes) In one embodiment, the rolled copper foil according to the present invention has an arithmetic mean value of the KAM value of 0.41 or less when measured by the method described below for a rolled copper foil heat-treated at an internal temperature of 260°C in a dryer for a holding time of 30 minutes. According to the research of the present inventors, for the rolled copper foil after the final cold rolling process, if the Cube area ratio is 95.0% or more when measured for the rolled copper foil after heat treatment at an internal temperature of 260°C in a dryer for a holding time of 30 minutes, it is known that it has better bendability than conventional rolled copper foils. However, when the arithmetic mean value of the above KAM value is 0.41 or less, it has been found that the above Cube area ratio becomes 95.0% or more. Regarding the relationship between the arithmetic mean value of the above KAM value and the bendability, the present inventors speculate as follows. First, a small arithmetic mean value of the KAM value means a small crystal orientation difference between adjacent pixels. When the movement of dislocations stops at grain boundaries or the like and dislocations accumulate, a crystal orientation difference occurs. In the vicinity of the grain boundary where dislocations are likely to accumulate, the slip line disappears, so the movement of dislocations is inhibited and dislocation growth proceeds. On the other hand, when the crystal orientation difference is small, the crystal grains deform with the movement of dislocations, so dislocations are less likely to accumulate at specific locations and are less likely to deteriorate even when subjected to repeated bending. Therefore, it is considered that when the arithmetic mean value of the KAM value is as small as 0.41 or less, the bendability increases. The arithmetic mean value of the above KAM value is preferably 0.40 or less as the upper limit side. The arithmetic mean value of the above KAM value is preferably 0.20 or more as the lower limit side. In one embodiment, within this numerical range, recrystallization of Cube-oriented grains is sufficiently performed after heat treatment. For example, if recrystallization is not sufficiently performed in the recrystallization annealing 3 (final annealing) described below, dislocations remain in the material, and when the rolled copper foil that has undergone the final cold rolling is heat-treated thereafter, the KAM value tends to increase.

[0014] (Method for measuring KAM value) The KAM value is determined by measuring the surface of the sample using EBSD (Electron Backscatter Diffraction). Here, EBSD is a technique for analyzing crystal orientation by utilizing the reflection electron Kikuchi line diffraction (Kikuchi pattern) that occurs when the sample is irradiated with an electron beam in an SEM (Scanning Electron Microscope). First, a part of the rolled copper foil is taken as a sample and put into a dryer (DRH453WA, manufactured by Advantec Toyo Co., Ltd.) maintained at 260°C. After heat-treating the sample in an air atmosphere for 30 minutes, it is taken out of the dryer and allowed to cool in the air atmosphere. Before being put in, in order to prevent oxidation in the air atmosphere and prevent bending and wrinkle generation when taking it out of the dryer, the rolled copper foil is sandwiched between two phosphor bronze (JIS H 3110 (C5210)) plates (thickness: 0.2 mm) to form a laminate, and then the laminate is wrapped and sealed with a rolled foil of tough pitch copper (thickness: 33 μm) that has been sufficiently annealed, and then put into the dryer. After cooling, the heat-treated rolled copper foil is obtained. Next, electrolytic polishing is performed under the following electrolytic solution and test conditions. After removing about 1 μm in thickness from the sample surface, for an arbitrarily set 1 mm × 1 mm observation range where one side of the observation field is parallel to the rolling direction, scanning is performed at a step size of 3 μm to measure the crystal orientation distribution. The measurement is carried out at a total of three points, namely any one point and two points spaced at equal intervals of 5 mm each in the direction perpendicular to rolling from that point. If the arithmetic mean value of the KAM values measured at any one point and two points spaced at equal intervals of 5 mm each in the direction perpendicular to rolling from that point is 0.41 or less, 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 to a certain extent in the manufacturing process, the KAM values measured for the rolled copper foil obtained in the manufacturing process after heat treatment under predetermined conditions are generally controlled within the desired range. Therefore, when the arithmetic mean value of the KAM values at a total of three points, namely any one point and two points spaced at equal intervals of 5 mm each in the direction perpendicular to rolling from that point, is 0.41 or less, although there may be a part where the KAM value exceeds 0.41 in the rolled copper foil, it is assumed that such a part is not so much, and most of them have the desired metallographic structure, and the problems of the present invention can be solved. Furthermore, due to the convenience of manufacturing and handling of the rolled copper foil (for example, cutting out samples for measurement, etc.), there may be some parts where oil pits extremely enter, and abnormal parts such as foreign matter adhesion and rolling streaks may occur. When measuring the KAM value, the measurement locations should be set while avoiding the locations corresponding to the abnormal parts. The abnormal parts can be grasped by observing the sample before electrolytic polishing with an SEM (observation magnification: 100 times), etc. When the measurement location overlaps with the abnormal part, three points should be measured while avoiding the abnormal part. <Composition of electrolytic solution (an example)> · Distilled water 250 ml · Phosphoric acid 125 ml · Urea 2.5 g · Primary ethanol 125 ml · 1-Propanol 25 ml <Electrolytic polishing conditions> Applied voltage: 10 V Electrolytic time: 10 seconds <Measurement conditions of EBSD, etc.> · SEM conditions Apparatus: Scanning electron microscope (JSM-IT500HR or an equivalent apparatus) manufactured by JEOL Ltd. Type of electron gun: Field emission electron gun (Schottky type) Emitter of electron gun: ZrO tungsten cathode Type of objective lens: Out-lens type Presence or absence of 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 - 2 nm Magnification: 90x · EBSD device conditions Detector: Slow-scan CCD camera manufactured by TSL Solutions Co., Ltd. · Data processing conditions Data collection software: OIM Data Collection manufactured by TSL Solutions Co., Ltd. Phase: Copper Number of pixels of CCD camera: 1394 x 1040 pixels Binning: 8 x 8 Exposure time: 8 milliseconds Gain: 0.9 - 0.95 Presence or absence of background processing: Yes Scanning method of measurement points: Hexagonal lattice · Hough transform (1) Hough Type: Classic (2) Hough Resolution: Low (3) Classic Hough · Convolution Mask: 9 x 9 · Min Peak Magnitude: 5 · Min Peak Distance: 23 · Peak Symmetry: 0.75 · Vertical Bias: 0 (4) General Parameter · Binned Pattern Size: 120 ·Theta Step Size (Angular Step Size): 1° ·Rho Fraction: 90% ·Max Peak Count: 8 ·Min Peak Count: 3 For the collection of the above measurement data, OIM Data Collection manufactured by TSL Solutions Co., Ltd. is used, and for data analysis, OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. is used. <OIM Analysis V8 Data Analysis Conditions> ·New Window Select Partition. Formula tab: Select Confidence Index under the Point Properties selection column. Confidence Index Window: Check Absolute under the Method selection column. Confidence Index Window: Select > to the right of the Method selection column and set the value below the display to 0.1. Do not change Minimum, Maximum, and Average under the Method selection column. ·Select New Partition. Select New Chart (Kernel Average Misorientation in the Type selection column). Kernel Average Misorientation (Screen displayed when clicking the Edit >> tab to the right of the Type selection column) Kernel Average Misorientation tab Nearest neighbor: 1st Maximum misorientation: 5 Check Perimer only. Check Set0-point kernels to maximum misorientation. Kernel Average Misorientation (Screen displayed when clicking the Edit >> tab to the right of the Type selection column) Range tab Check the Percentage below the Method selection column. Set the Minimum to the right of the Method selection column to "0" and the Maximum to "100". Set the Minimum, Maximum, and Average below the Method selection column to "0". Kernel Average Misorientation (Screen displayed when clicking the Edit >> tab to the right of the Type selection column) Parameters tab Set the Number of bins to "20". Check the Number Fraction in the Vertical Axis column. Take the value of Number within Average in the measurement result of Kernel Average Misorientation performed under the above - set conditions (average value by the Number method) as the average Kernel Average Misorientation.

[0015] (Cube area ratio) In one embodiment, the rolled copper foil according to the present invention preferably has an arithmetic mean value of the Cube area ratio of 95.0% or more, more preferably 98.0% or more, when measured by the method described below for the rolled copper foil heat - treated at an internal temperature of 260 °C in a dryer for 30 minutes of heating and holding. Thereby, the occurrence of cracks that cause breakage is suppressed, so that it has excellent bendability, and for example, stable bendability can be obtained regardless of the heating conditions during the manufacture of copper - clad laminates. Specific heat - treatment means are the same as those of the heat - treatment means for the KAM value described above, so the description is omitted.

[0016] (Measurement method of Cube area ratio) Next, an example of the method for measuring the Cube area ratio will be described. On the surface of a sample of rolled copper foil heat-treated at an internal temperature of 260 °C for a holding time of 30 minutes in a dryer as described above, the area ratio of the Cube orientation {001}<100> is measured by EBSD. Electropolishing is performed under the following electrolytic solution and test conditions, and after removing about 1 μm in thickness from the sample surface, for an observation range of 1000 μm × 1000 μm arbitrarily set so that one side of the observation field is parallel to the rolling direction, scanning is performed at a step size of 3 μm to measure the crystal orientation distribution. The measurement is carried out at an arbitrary point and two points equally spaced at 5 mm intervals in the direction perpendicular to the rolling direction from that point. If the arithmetic mean value of the Cube area ratio measured at an arbitrary point and two points equally spaced at 5 mm intervals in the direction perpendicular to the rolling direction from that point is 95.0% 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 to a certain extent in the manufacturing process, the Cube area ratio measured after heat-treating the rolled copper foil obtained in the manufacturing process under predetermined conditions is generally controlled within the desired range. Therefore, when the arithmetic mean value of the Cube area ratio of an arbitrary point and two points equally spaced at 5 mm intervals in the direction perpendicular to the rolling direction from that point is 95.0%, although there may be a part where the Cube area ratio is less than 95.0% in the rolled copper foil, it is assumed that such a part is not so much, and most of it has the desired metallographic structure. Furthermore, due to the convenience of manufacturing and handling of the rolled copper foil (for example, cutting out a sample for measurement, etc.), there may be some parts where oil pits are extremely deep, and abnormal parts such as foreign matter adhesion and rolling streaks may occur. When measuring the Cube area ratio, the measurement location should be set avoiding the locations corresponding to the abnormal parts. The abnormal parts can be grasped by observing the sample before electropolishing with SEM (observation magnification: 100 times), etc. When the measurement location overlaps with the abnormal part, a total of 3 points are measured avoiding the abnormal part. <Formulation of electrolytic solution (an example)> · Distilled water 250 ml · Phosphoric acid 125 ml · Urea 2.5 g · Ethanol primary grade 125 ml · 1-Propanol 25 ml <Electropolishing Conditions> Applied Voltage: 10 V Electrolysis Time: 10 seconds <Measurement Conditions of EBSD, etc.> · SEM Conditions Apparatus: Scanning Electron Microscope (JSM-IT500HR or equivalent apparatus) manufactured by JEOL Ltd. Type of Electron Gun: Field Emission Electron Gun (Schottky type) Emitter of Electron Gun: ZrO Tungsten Cathode Type of Objective Lens: Out-lens type Presence or Absence of Focus Correction: Yes (Dynamic Focus: 50) Beam Conditions Accelerating Voltage: 15 kV Working Distance: 15 mm Irradiation Current: 15 nA SEM Probe Diameter: 0.5 - 2 nm Observation Magnification: 90 times · EBSD Apparatus Conditions Detector: Digital CCD Camera manufactured by TSL Solutions Co., Ltd. · Data Processing Conditions Data Collection Software: OIM Data Collection manufactured by TSL Solutions Co., Ltd. Phase: Copper Number of Pixels of CCD Camera: 1394 × 1040 pixels Binning: 8 × 8 Exposure Time: 8 milliseconds Gain: 0.9 - 0.95 Presence or Absence of Background Processing: Yes Scanning Method of Measurement Points: Hexagonal Lattice · Hough Transformation (1) Hough Type: Classic (2) Hough Resolution: Low (3) Classic Hough · Convolution Mask: 9 × 9 ·Min Peak Magnitude: 5 ·Min Peak Distance: 23 ·Peak Symmetry: 0.75 ·Vertical Bias: 0 (4)General Parameter ·Binned Pattern Size: 120 ·Theta Step Size: 1° ·Rho Fraction: 90% ·Max Peak Count: 8 ·Min Peak Count: 3 Then, the analysis of the crystal orientation density function is carried out. The area of the crystal grains with orientations within 15° from the Cube orientation is divided by the measured area to obtain the area ratio. For the collection of the above measurement data, OIM Data Collection manufactured by TSL Solutions Co., Ltd. is used, and for data analysis, OIM Analysis V8 manufactured by TSL Solutions Co., Ltd. is used. Note that the information obtained in the orientation analysis by EBSD includes the orientation information up to a depth of several tens of nanometers where the electron beam penetrates the sample. Since it is sufficiently small compared to the measured area, it is described as the area ratio. <OIM Analysis V8 Data Analysis Conditions> ·New Map Window Map Style Grayscale: <none>Select it. Select Color Coded:Crystal Orientation. Boundaries Second Partition: <none>Select it. · Crystal Orientation window (the screen displayed when clicking Edit of Color Coded in Map Style window) Select Representation: Euler Angles (Bunge). Check box of Enforce Orthotropic Sample Symmetry: Enter a dot. · Add Crystal Orientation Range window (the screen displayed when clicking Add in Crystal Orientation window) Orientation tab Select Phase: Copper. Euler Angles (Bunge): (φ1, Φ, φ2) = (0, 0, 0) Each input value of hkl: 001 Each input value of uvw: 100 Tolerance tab Input value of Minimum: 0 Input value of Maximum: 15 Use the value of Total fraction in the measurement result of Crystal Orientation performed under the above setting conditions as the Cube area ratio.

[0017] (Manufacturing example of rolled copper foil) As an example of the method for manufacturing a rolled copper foil, first, raw materials such as copper are melted in a melting furnace to obtain a molten metal of a desired composition. Then, an ingot is manufactured by pouring this molten metal into a mold (casting). To prevent oxidation loss of copper, it is preferable to perform melting and casting in a vacuum or an inert gas atmosphere. Thereafter, homogenization annealing, hot rolling, cold rolling 1, recrystallization annealing 1, surface machining, cold rolling 2, recrystallization annealing 2, pickling and polishing, cold rolling 3, recrystallization annealing 3 (final annealing), and final cold rolling are performed in this order to finish a rolled copper foil having a desired thickness and desired properties. That is, in one embodiment, the rolled copper foil can basically be the one immediately after the final cold rolling. As a result of intensive studies by the present inventors, in order to make the arithmetic mean value of the KAM value of the rolled copper foil within a predetermined range when heat-treated at an internal temperature of the dryer of 260°C and a heating retention time of 30 minutes, when manufacturing in the process described below, 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.

[0018] (Final annealing) The conditions for final annealing are appropriately set so that the arithmetic mean value of the KAM value of the rolled copper foil when heat-treated at an internal temperature of the dryer of 260°C and a heating retention time of 30 minutes is controlled within a predetermined range. Specifically, the conditions for final annealing may be appropriately set so that the arithmetic mean value of the KAM value of the strip-shaped metal material after final annealing is 0.27 to 0.40. In one embodiment, due to this numerical range, the driving force for recrystallization becomes high, and the KAM value when heat-treated at an internal temperature of the dryer of 260°C and a heating retention time of 30 minutes can be appropriately controlled. For example, if recrystallization is not sufficiently carried out during final annealing, dislocations or non-recrystallized regions may remain in the material, and the KAM value may increase when the rolled copper foil that has undergone final cold rolling is heat-treated thereafter. Although the conditions may vary depending on the composition of the copper material, those skilled in the art can experimentally obtain the annealing conditions without excessive trial and error based on the final annealing conditions such as annealing temperature and retention time.

[0019] Since dislocations preferentially accumulate at grain boundaries, a high KAM value of the strip-shaped metal material after final annealing means that there are many grain boundaries. That is, by making the KAM value after final annealing within the above range, it becomes easier to control the KAM value of the rolled copper foil when heat-treated after final cold rolling. On the other hand, when the arithmetic mean value of the KAM value after final annealing exceeds 0.40, the annihilation of dislocations exceeds the growth of dislocations during the process of final cold rolling, and as a result, the driving force for recrystallization may decrease and there is a possibility that recrystallization is not sufficiently completed after final annealing.

[0020] Regarding the method for measuring the KAM value after final annealing, since it should be generally controlled within a predetermined range as a whole for the strip metal material, 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 heat treatment described above, the description is omitted.

[0021] (Thickness of strip copper material) 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. Regarding the thickness of the strip copper material, for example, an X-ray generator is arranged on the surface side of the strip copper material, and an X-ray detector is arranged on the other surface side. The attenuation amount by the rolled copper foil is obtained from the measured transmitted X-ray amount and converted into the thickness of the strip copper material for measurement. Also, for example, measurement by the gravimetric method is possible. The gravimetric method means measuring the weight of a 20 mm square strip copper material, and calculating the thickness of the strip copper material from (weight of strip copper material (g) / density of strip copper material (g / cm 3 )) × area of strip copper material (cm 2 ). (Note that the density is, for example, 8.94 g / cm 3 for oxygen-free copper of JIS-H3100 (C1020), and the density is treated as unchanged for the strip copper material and the rolled copper foil in the present invention.) Further, for example, using a digital length measuring instrument (for example, Digimicro MH-15M manufactured by Nikon Corporation), measurement is performed at any two or more points, and the thickness of the strip copper material is calculated from the arithmetic mean value of each thickness.

[0022] (Final cold rolling) 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 can be obtained. The thickness of the rolled copper foil at this time is about 4 to 35 μm. Regarding the degree of working, the degree of working (%) = { (thickness before final cold rolling (mm) - thickness after final cold rolling (mm)) / thickness before final cold rolling (mm)} × 100 is defined.

[0023] (Thickness) In one embodiment, the thickness of the rolled copper foil is, for example, 4 to 35 μm. The thickness of the rolled copper foil is, for example, 35 μm or less on the upper limit side, also for example 18 μm or less, and on the lower limit side, for example, 4 μm or more, also for example 6 μm or more, and also for example 9 μm or more. Regarding the measurement of the thickness of the rolled copper foil, the method for measuring the thickness of the strip-shaped copper material described above can be adopted. When using the gravimetric method for measuring the thickness of the rolled copper foil, the size of the sample shall be 12.7 mm (in the rolling right-angle direction) × 70 mm (in the rolling parallel direction).

[0024] [2. Method for manufacturing copper-clad laminate] In one embodiment of the method for manufacturing a copper-clad laminate according to the present invention, it includes a step of bonding the above-described rolled copper foil and a base material. Examples of the base material include resin films. Several methods can be adopted to bond the resin film and the rolled copper foil. First, as a method for manufacturing a copper-clad laminate, there is a method generally called the lamination method. According to the lamination method, a copper-clad laminate (CCL) composed of a rolled copper foil and a resin film can be obtained by pressing a resin film (base film) such as polyimide onto the rolled copper foil using a heat treatment device such as a laminator. As an example of a manufacturing method using the lamination method, for example, for a 25-μm-thick polyimide resin film such as Pixio (trademark) film manufactured by Kaneka Corporation, the roughened surface of a 12-μm rolled copper foil is aligned, passed between heat rolls heated to about 300°C to 370°C, and pressed by the lamination method to manufacture a copper-clad laminate. The time for passing between the heat rolls (pressing time) is about 1 second. Next, apart from 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 a method of applying a varnish containing polyamic acid, which is a precursor of polyimide resin, onto at least one surface of a rolled copper foil, and subjecting it to heat treatment for curing to form a polyimide film on at least one surface of the rolled copper foil. Also, for example, when laminating rolled copper foils on both sides of a polyimide resin film, after forming a single-sided copper-clad laminate, there are methods of pressure-bonding the rolled copper foil by hot pressing, or sandwiching a polyimide resin film between two copper foil layers and pressure-bonding it by hot pressing. The heat treatment by the casting method is generally carried out under the conditions of 125 to 360 °C for 30 to 400 minutes. In addition, in the lamination method and the casting method, an example using a polyimide resin film has been described, but it is not limited to the resin film. As the resin film, in addition to the polyimide resin film, for example, polyester, polyethylene terephthalate, polyethylene naphthalate, etc. may also be used. Typically, in the lamination method, the heat treatment speed is overwhelmingly faster than that of the casting method, and the flexibility when made into an FPC is likely to decrease compared to the casting method.

[0025] Also, before laminating the rolled copper foil and the resin film, the rolled copper foil can be subjected to a roughening treatment. Thereby, the adhesive strength between the resin film and the rolled copper foil can be improved. For example, the roughening treatment can be carried out 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

[0026] According to the manufacturing method, by the above heat treatment, a copper-clad laminate having a copper foil (rolled copper foil) with an arithmetic mean value of the KAM value of 0.41 or less and a base material (resin film) can be manufactured. The method for measuring the KAM value is the same as the method described above.

[0027] [3. Manufacturing method of flexible printed wiring board] In one embodiment, the manufacturing method of the flexible printed wiring board according to the present invention includes a step of forming a wiring using a copper-clad laminate manufactured by the manufacturing method of the copper-clad laminate described above as a material. At this time, it is possible to form a wiring according to a known procedure using the copper-clad laminate as a material to manufacture a flexible printed wiring board (FPC). For example, an etching resist is applied only to the necessary portions as conductor patterns on the rolled copper foil surface of the copper-clad laminate, and an etching solution is sprayed onto the rolled copper foil surface to remove the unnecessary rolled copper foil to form a conductor pattern, and then the etching resist is peeled off and removed to expose the conductor pattern. After forming the conductor pattern, it is common to attach a protective coverlay film.

[0028] [Applications] Such FPCs are applicable to FPCs used in movable parts within hard disks, hinge parts and slide sliding parts of mobile phones, inside mobile phones, head parts of printers, optical pickup parts, movable parts of notebook PCs, etc. in electronic components such as electronic and electrical equipment. In addition, in the manufacturing method of electronic components, a step of manufacturing an electronic component including the flexible printed wiring board manufactured by the manufacturing method of the flexible printed wiring board described above may be included.

Examples

[0029] The present invention will be specifically described based on examples and comparative examples. The following descriptions of the examples and comparative examples are specific examples only 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. Note that "CI>0.1" in Table 1 means that the analysis is performed excluding the measurement points where the CI value analyzed by the data analysis OIM Analysis V8 is 0.1 or less. Also, "CI" is an abbreviation for Confidence Index.

[0030] [Examples 1 to 3, Comparative Examples 1 to 2] [Manufacture of rolled copper foil] First, in Examples 1 to 3 and Comparative Example 1, ingots having an alloy composition containing Ag described in Table 1 were melt-cast using a copper material containing 99.9 mass% or more of Cu. The Ag content of the ingot was measured by the ICP emission spectrometry described above. This ingot was processed in the following process sequence to produce a rolled copper foil. Regarding the degree of working in Table 1, it is the sheet thickness reduction rate in the final cold rolling, and the degree of working (%) = { (thickness before the final cold rolling (mm) - thickness after the final cold rolling (final product) (mm)) / thickness before the final cold rolling (mm)} × 100 was calculated. <Processes (1) to (11)> Process (1) Homogenization annealing: The above ingot was heated and held at 920°C for 2.5 hours. Process (2) Hot rolling: The ingot heated at 920°C was rolled to a thickness of 16 mm at room temperature. Then, it was rapidly cooled to room temperature by water cooling to obtain a strip-shaped metal material. Process (3) Cold rolling 1: Rolled to a thickness of 10.5 mm. Process (4) Recrystallization annealing 1: The above strip-shaped metal material was heated and held at 400°C for 7.5 hours. Process (5) Surface machining: The oxide scale on the surface was removed by surface machining. Process (6) Cold rolling 2: Rolled to a thickness of 1.5 mm. Process (7) Recrystallization annealing 2: Held in a furnace heated to 750°C for 30 to 120 seconds. Process (8) Pickling and polishing: After immersion in a mixed acid of sulfuric acid and hydrogen peroxide water, buff polishing was performed to remove the oxide film on the material surface. Process (9) Cold rolling 3: Rolled to a thickness of 0.8 mm to 1.0 mm. Process (10) Recrystallization Annealing 3 (Final Annealing): The annealing temperature and holding time were appropriately adjusted so that the KAM value of the surface of the strip-shaped metal material after recrystallization annealing 3 described in Table 1 was obtained, and the strip-shaped metal materials after cold rolling 3 were each heated and held. In addition, in order to prevent oxidation of the strip-shaped metal material, a sealed body in which the strip-shaped metal material was wrapped and sealed with a rolled copper foil (thickness: 33 μm) of fully annealed tough pitch copper (JIS H 3100 (C1100)) was put into a dryer. After heating and holding, the sealed body was taken out of the dryer and allowed to cool in the air atmosphere. After cooling, the strip-shaped metal material was taken out of the sealed body. Also, regarding the KAM value after the final annealing, any two points were measured by the method described above. Process (11) Final Cold Rolling: The rolled copper foil was finished to a thickness of 0.012 mm (12 μm). In the final cold rolling, the strip-shaped metal material was passed between a pair of work rolls with both ends on both sides in the rolling direction of the strip-shaped metal material not fixed (in a free end state), and rolled without applying a tension in the direction parallel to the rolling direction. In Comparative Example 2, after rolling to 1.0 mm in Process (9), annealing and rolling were further performed again, and after making the thickness 0.5 mm, Process (10) was carried out.

[0031] [Characteristic Evaluation] <KAM Value> 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 method described above, for the strip-shaped metal material after Process (10) and the rolled copper foil heat-treated at 260 °C for 30 minutes after Process (11), the arithmetic mean value of each KAM value was measured. Regarding the above strip-shaped metal material, two points were measured avoiding abnormal parts. Also, regarding the rolled copper foil when heat-treated at 260 °C for 30 minutes, three points including any one point avoiding abnormal parts and two points equally spaced 5 mm each in the direction perpendicular to the rolling from that point were measured. For each point, the numerical value up to the limit obtained as raw data on the software was read, and for the arithmetic mean value, the fourth decimal place was rounded off to show up to the third decimal place.

[0032] <Evaluation of Cube Area Ratio> Next, in Examples 1 to 3 and Comparative Examples 1 and 2, a part of the rolled copper foil obtained by the above manufacturing was collected as a measurement sample for each. By 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, and the laminate was further wrapped and sealed with a rolled copper foil (thickness: 33 μm) of fully annealed tough pitch copper (JIS H 3100 (C1100)), and the sealed body was put into a dryer. The dryer was heated and held at an internal temperature of 260°C for 30 minutes for heat treatment. After the heat treatment, it was taken out from the dryer and allowed to cool in the air atmosphere. After cooling, the rolled copper foil, which was the measurement sample, was taken out from the sealed body. The sample surface of the rolled copper foil after the heat treatment was used as the measurement target, and the area ratio of the Cube orientation {001}<100> of the rolled copper foil after the heat treatment was measured by the method described above using a scanning electron microscope (JSM-IT500HR) manufactured by JEOL Ltd. In Table 1, the arithmetic mean value of the area ratios of the Cube orientation {001}<100> at an arbitrary one point avoiding the abnormal part and two points equally spaced 5 mm each in the direction perpendicular to rolling from that point is shown as the Cube area ratio. For each point, up to the second decimal place was calculated, and for the arithmetic mean value, up to the second decimal place was shown by rounding the third decimal place. Regarding the rolled copper foil after 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. However, since the sizes of the sub-grain and dislocation cell structures in the rolling texture were less than the step size (3 μm) of the EBSD measurement conditions, it was not possible to measure under the same conditions as the measurement conditions of the sample of the rolled copper foil after the heat treatment.

[0033]

Table 1

[0034] (Consideration according to the example) As a result of comparing Examples 1 to 3 with Comparative Examples 1 to 2, it was confirmed that the arithmetic mean value of the KAM value of the rolled copper foil when heat-treated at 260°C for 30 minutes can be controlled to 0.41 or less by appropriately adjusting the KAM value of the recrystallization annealing 3 (final annealing) within the range of 0.27 to 0.40. It was also confirmed that the cube area ratio after the heat treatment can be increased to 95.0% or more. It was also confirmed that in Examples 1 and 3, in which the arithmetic mean value of the KAM value of the rolled copper foil when heat-treated at 260°C for 30 minutes is 0.40 or less, the cube area ratio after the heat treatment can be increased to 98.0% or more.

[0035] By the way, the IPC sliding bending test can confirm the number of IPC sliding bending to confirm the superiority of bending. Here, when using rolled copper foil with a high cube area ratio measured after heat treatment at a temperature of 260°C in the dryer and a heating holding time of 30 minutes, it has been empirically found that there is a direct proportional correlation between the cube area ratio after heat treatment at 260°C for 30 minutes and the number of IPC sliding bending. Therefore, it can be said that rolled copper foil with a high cube area ratio after the above heat treatment has better bending properties than conventional ones when made into FPCs. Therefore, it is presumed 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 as in Examples 1 to 3, it is possible to provide a rolled copper foil having higher flexibility than conventional ones when made into an FPC.< / none> < / none>

Claims

1. containing 99.9 mass% or more of Cu, with the balance consisting of inevitable impurities, a rolled copper foil having an arithmetic mean value of the KAM value of 0.41 or less, measured at any one point and two points spaced at equal intervals of 5 mm each in the direction perpendicular to rolling from that point, when heat-treated at an internal temperature of 260 °C in a dryer for a holding time of 30 minutes.

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

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

4. A method for manufacturing a copper-clad laminate, comprising a step of bonding the rolled copper foil according to Claim 1 or 2 to a base material, and performing a heat treatment in said step.

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

6. A method for manufacturing an electronic component, comprising a step of manufacturing an electronic component provided with the flexible printed wiring board manufactured by the method for manufacturing a flexible printed wiring board according to Claim 5.

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