JP2013095933A - Rolled copper foil, copper-clad laminate, flexible printed wiring board and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolled copper foil in which when the foil is used as a wiring for printed wiring board even for long time using, any crack in the wiring is not developed; and a copper-clad laminate, flexible printed wiring board and electronic equipment, using the foil.SOLUTION: When a portion having ≥2° of an azimuthal difference between the crystal orientation obtained by irradiating a measuring point of metallurgical structure of the crystal with an electron beam and the crystal orientation obtained by irradiating a plurality of adjacent measuring points positioned the electron beam by 0.5 μm separating distance around the measuring point, is determined as Σvalue in the crystal grain boundary as the crystal grain boundary; the rolled copper foil is the one that the total of the length of the crystal grain boundaries ≥Σ19 as measured after annealing at 400°C for one hour is 8 cm/mmor less.

Description

  The present invention relates to a rolled copper foil, a copper clad laminate, a flexible printed wiring board, and an electronic device.

Since electronic devices are subjected to repeated thermal shocks depending on the product environment, reliability that can withstand this is required. As a test assuming such a thermal shock, test methods such as JISITED-4701 / 001, ED-47011 / 100, and JIS-C60068-2-14 have been proposed. Durability against temperature cycling is required.
Moreover, the electronic device is normally comprised with the some electronic board, and the flexible printed wiring board which electrically connects these electronic boards is provided between the electronic boards. A flexible printed wiring board usually includes an insulating substrate and copper wiring formed on the surface of the substrate. A flexible printed wiring board that connects electronic boards is required to have good flexibility and the like because tensile stress and compressive stress are applied due to differences in thermal expansion and contraction between the two substrates. The characteristics required for such a flexible printed circuit board include good bendability represented by MIT bendability and high cycle bendability represented by IPC bendability. Copper foils and copper-resin substrate laminates have been developed (Patent Documents 1 and 2).

  In order to establish electrical connection with the electronic components to be mounted on the printed wiring board in which many copper wirings are formed on the surface of the insulating substrate, or to interconnect the printed wiring board, the terminal portion In general, a plating layer made of Sn or the like is formed.

  A printed wiring board is generally manufactured through a process of forming a circuit pattern on a copper foil surface by etching after bonding an insulating substrate to a copper foil to form a copper-clad laminate. Then, a fusing treatment (heat treatment) for diffusing copper into the plating layer is performed.

  However, when the copper foil on which the Sn plating layer is formed is subjected to a fusing treatment, voids and cracks that may be caused by the Kirkendall effect occur at the interface between the copper foil and the Sn plating layer, the copper foil becomes brittle and the circuit is disconnected. May arise.

  As a technique for solving such a problem, for example, Patent Document 3 discloses a flexible insulating substrate, a circuit pattern formed on one surface of the insulating substrate, and a region adjacent to the connection terminal portion of the circuit pattern. A first solder resist excellent in Sn plating solution resistance, and a second solder resist excellent in flexibility provided on the circuit pattern except at least the connection terminal portion of the circuit pattern; A flexible printed wiring board including Sn alloy plating provided on connection terminal portions of a circuit pattern is disclosed. And if it is made to perform Sn plating after forming the 1st and 2nd solder resist by such composition, copper of a circuit pattern will diffuse into Sn plating by heat processing at the time of applying a solder resist. It is described that it is possible to provide a flexible printed wiring board with improved reliability without disconnection by preventing the formation of a brittle Sn-copper alloy.

JP 2010-100877 A JP 2009-111203 A JP 2006-253247 A

  The flexible printed wiring board is provided between two substrates in an electronic device as described above, and electrically connects the two. If these two boards have the same coefficient of linear thermal expansion, there will be no problem, but if the boards have a difference in coefficient of linear thermal expansion, power on / off of electronic equipment and temperature change at the place of use Stress concentration occurs in the flexible printed wiring board due to the above. On the other hand, the flexible printed wiring board is designed in consideration of good bendability represented by MIT bendability and high cycle bendability represented by IPC bendability. Such stress concentrations are not planned and are not designed to withstand.

  The inventor has found that a problem with copper foil is caused by the stress concentration described above. That is, when the stress concentration described above is applied, a crack is first generated in the Sn copper alloy layer, which is a relatively brittle part of the circuit surface (FIG. 4a). Once a crack is generated, the stress is concentrated at that location, and when a grain boundary exists in the copper foil portion near the crack, the crack develops inside the copper foil along this grain boundary (FIG. 4b). In a copper foil having a large number of grain boundaries on the surface, cracks in the Sn copper alloy layer that occur first tend to develop into cracks in the copper foil along the grain boundaries. At this time, the more easily the copper foil grain boundaries are dissociated, the easier it is for cracks to propagate into the copper foil. In other words, long-term use of electronic equipment causes repeated stress concentration, and eventually the circuit breaks along the copper grain boundary of the wiring part, which is one of the causes of failure of electronic equipment. .

  Therefore, the present invention provides a rolled copper foil that does not crack in wiring even when used for a long time when used as a wiring of a printed wiring board, and a copper-clad laminate, a flexible printed wiring board, and an electronic device using the same. It is an object to provide a device.

  As a result of diligent study, the present inventor, as a copper foil of the wiring of a printed wiring board, when a portion where the angle difference of crystal orientation in the crystal is 2 ° or more is a crystal grain boundary, the total of the grain boundaries of Σ19 or more It has been found that by using a rolled copper foil whose length is controlled to a predetermined value or less, the occurrence of cracks in the wiring of the printed wiring board can be satisfactorily suppressed even when used for a long time.

  Grain boundaries measured by EBSP are classified and calculated from the properties of the grain boundaries into an index called Σ (sigma) value. The Σ value is expressed as the ratio of the unit cell volume of the original crystal lattice to the unit cell volume of the corresponding lattice formed as an overlap at the grain boundary. That is, the smaller the Σ value, the larger the corresponding number of lattices per unit volume of the grain boundary. Conversely, the larger the Σ value, the smaller the corresponding number of lattices per unit cell volume of the grain boundary. The larger the Σ value, the smaller the number of lattices that overlap the unit grain interface. Therefore, it is considered that the grain boundary delamination tends to occur, and the cracks tend to easily develop.

The present invention completed on the basis of the above knowledge is, in one aspect, positioned at a distance of 0.5 μm around the crystal orientation obtained by irradiating the measurement point of the crystallographic metal structure with an electron beam and the measurement point. When the Σ value of the crystal grain boundary is determined with a part having an azimuth angle difference of 2 ° or more from the crystal orientation obtained by irradiating a plurality of adjacent measurement points with an electron beam as the crystal grain boundary, at 400 ° C. for 1 hour Is a rolled copper foil in which the total length of the grain boundaries of Σ19 or more measured after annealing is 8 cm / mm ² or less.

In one embodiment of the rolled copper foil according to the present invention, the total length of the grain boundaries of Σ19 or more measured after annealing at 400 ° C. for 1 hour is 6 cm / mm ² or less.

  In yet another embodiment of the rolled copper foil according to the present invention, the wiring of the flexible printed wiring board that electrically connects the first substrate and the second substrate having a linear thermal expansion coefficient difference of 1.2 times or more. When used as a crack, the wiring does not crack even if the temperature change of −65 ° C. to + 150 ° C. is repeated 300 times on the flexible printed wiring board.

  In still another embodiment of the rolled copper foil according to the present invention, 10 to 1300 mass ppm in total of one or more selected from the group consisting of Ag, Sn, In, Zr and Zn is included.

  In still another embodiment of the rolled copper foil according to the present invention, the thickness is 5 to 70 μm.

  In another aspect, the present invention is a copper clad laminate comprising the copper foil according to the present invention.

  In still another aspect, the present invention is a flexible printed wiring board made of the copper clad laminate according to the present invention.

  In another embodiment of the flexible printed wiring board according to the present invention, a Sn layer and / or a Sn copper alloy layer is applied to at least a part of the terminal portion or the wiring portion.

  In still another aspect, the present invention is an electronic device including the flexible printed wiring board according to the present invention, and a first substrate and a second substrate electrically connected by the flexible printed wiring board.

  According to the present invention, when used as a wiring of a printed wiring board, a rolled copper foil that does not generate cracks even after long-term use, and a copper-clad laminate, a flexible printed wiring board, and an electronic device using the rolled copper foil Equipment can be provided.

It is a schematic diagram showing the measurement aspect of the crystal orientation of rolled copper foil. It is an example of the connection form of the 1st board | substrate and the 2nd board | substrate, and the flexible printed wiring board formed between them. It is explanatory drawing of the repeated test of the temperature change performed with respect to a flexible printed wiring board. (A) It is sectional drawing of the conventional copper foil which the crack produced in the Sn copper alloy layer under stress concentration. (B) It is sectional drawing of the conventional copper foil in which the crack has propagated inside copper foil along a grain boundary.

(Configuration of rolled copper foil)
As a material of the rolled copper foil for a flexible printed wiring board, tough pitch copper (JIS-H3100 C1100) or oxygen-free copper (JIS-H3100 C1020, JIS-H3510 C1011) can be used.
Furthermore, copper alloy foils based on tough pitch copper and oxygen-free copper can also be used. Specifically, the copper alloy foil based on tough pitch copper and oxygen-free copper contains 10 to 1300 mass ppm in total of one or more selected from the group consisting of Ag, Sn, In, Zr and Zn. .
In this specification, “copper foil” includes copper alloy foil, and copper foil formed of “tough pitch copper” and “oxygen-free copper” includes copper alloy foil based on tough pitch copper and oxygen-free copper. Is also included.

  As thickness of the rolled copper foil which can be used for this invention, 5-70 micrometers is preferable and 5-40 micrometers is more preferable. When the thickness of the copper foil is less than 5 μm, the handling of the copper foil may be deteriorated, and when it is more than 40 μm, the flexibility may be deteriorated. As for the thickness of rolled copper foil, 5-12 micrometers is still more preferable.

The rolled copper foil of the present invention has a crystal orientation obtained by irradiating a measurement point of a metal structure of a crystal with an electron beam and a plurality of adjacent measurement points located 0.5 μm apart around the measurement point. Σ19 or more measured after annealing at 400 ° C. for 1 hour when the Σ value of the crystal grain boundary was determined with a region having an azimuth angle difference of 2 ° or more as a crystal grain boundary obtained by irradiation with a line The total length of the crystal grain boundaries is controlled to 8 cm / mm ² or less.

  Here, the determination method of the crystal grain boundary and the calculation method of the length of the crystal grain boundary will be specifically described. In FIG. 1, the schematic diagram showing the measurement aspect of the crystal orientation of the rolled copper foil of this invention is shown. First, the measurement point in the metal structure of the rolled copper foil crystal is determined. In FIG. 1 (hereinafter referred to as measurement point 1). Further, a regular hexagon whose center is the measurement point 1 and whose distance between the measurement point 1 and each side is 0.25 μm is determined. Adjacent measurement points (measurement points 2 to 7) are located at a distance of 0.5 μm around the measurement point 1 (referred to as measurement step 0.5 μm). And the crystal orientation obtained by irradiating an electron beam about the measurement points 1-7 is measured, and the azimuth angle difference between the measurement point 1 and the adjacent measurement points (measurement points 2 to 7) is obtained. When the orientation angle difference thus obtained is 2 ° or more, the adjacent measurement point is determined as a crystal grain boundary.

  Further, for these adjacent measurement points (measurement points 2 to 7), similarly to the measurement point 1, a regular hexagon having a distance of 0.25 μm from each side is determined. When the regular hexagons are sequentially determined in this way, the metal structure of the copper foil is filled with a plurality of regular hexagons in contact with each other as shown in FIG. And for each measurement point, the azimuth angle difference between the measurement point and the adjacent measurement point is determined in the same manner as described above, and when the azimuth angle difference is 2 ° or more, the adjacent measurement point is defined as a grain boundary. judge.

The Σ value of the crystal grain boundary is determined from the orientation and angle difference between adjacent crystal grains of the crystal grain boundary thus determined. From the determined Σ values, the lengths of grain boundaries of Σ19 or more are summed. By dividing this value by the measurement area, the length (cm / mm ² ) of the crystal grain boundary of Σ19 or more is calculated.

In a rolled copper foil after annealing at 400 ° C. for 1 hour, when a Σ value is determined by determining a portion having a crystal orientation difference of 2 ° or more as a crystal grain boundary, the length of the crystal grain boundary of Σ19 or more The inventor has found that the smaller the total thickness, the better the fatigue resistance. In this respect, the rolled copper foil of the present invention has good fatigue resistance because the total length of grain boundaries of Σ19 or more is controlled to 8 cm / mm ² or less. The total length of the grain boundaries of Σ19 or more is preferably controlled to 8 cm / mm ² or less, more preferably 6 cm / mm ² or less, and 3 cm / mm ² or less. More preferably, it is most preferably controlled to 1 cm / mm ² or less. Further, the lower limit of the total length of the crystal grain boundaries of Σ19 or more is not particularly required, but is 0.001 cm / mm ² or more considering the manufacturability of the copper foil.

(Configuration of flexible printed wiring board)
A flexible printed wiring board according to the present invention includes an insulating substrate and a wiring pattern formed on the surface of the insulating substrate. The insulating substrate is not particularly limited as long as it has good bendability and bendability applicable to flexible printed wiring boards. For example, polyimide film, liquid crystal polymer film, polyethylene naphthalate, polyethylene terephthalate, etc. Can be used. The thickness of the insulating substrate is preferably 12 to 50 μm. When the thickness is less than 12 μm, the handling becomes worse, and when it exceeds 50 μm, the flexibility is lowered. The wiring pattern is formed using the above-mentioned rolled copper foil for flexible printed wiring boards. The shape of the wiring pattern is not particularly limited, and any shape may be used. Further, an Sn layer and / or an Sn copper alloy layer may be formed on a part of the terminal portion or the wiring portion of the flexible printed wiring board.

(Characteristics of flexible printed wiring board)
Since the flexible printed wiring board which concerns on this invention is formed using the above rolled copper foil, it has the following characteristics. That is, with respect to the first printed circuit board and the second printed circuit board to which the flexible printed wiring board is electrically connected, when both boards have a difference in linear thermal expansion coefficient of 1.2 times or more, the flexible printed wiring board Even if the temperature change from −65 ° C. to + 150 ° C. is repeated 300 times, the wiring does not crack. The greater the difference in coefficient of linear thermal expansion between the first substrate and the second substrate to which the flexible printed wiring board is electrically connected, the greater the concentration of stress applied to the flexible printed wiring board. Normally, if the difference in linear thermal expansion coefficient between the first substrate and the second substrate is 1.5 times or more, it cannot withstand the stress concentration caused by the difference in expansion between the two substrates due to temperature change, and the flexible printed wiring board There is a high possibility of cracks in the wiring. On the other hand, in the present invention, the occurrence of cracks in the wiring is well suppressed even in such a state.
Here, FIG. 2 shows, as an example, a connection form between the first substrate (FR4) and the second substrate (glass substrate) and a flexible printed wiring board formed therebetween. The linear thermal expansion coefficient is an expansion coefficient in a direction parallel to the direction in which the substrate end extends as shown in FIG. 2, and a value at room temperature is used. Moreover, the above-mentioned “repeating the temperature change of −65 ° C. to + 150 ° C. 300 times with respect to the flexible printed wiring board” means that, as shown in FIG. It means holding at 150 ° C. and −65 ° C. for 30 minutes and repeating this for 300 cycles as one cycle. In addition, the transfer between a high temperature tank and a low temperature tank is performed within 1 minute. Other conditions are performed according to JIS-C60068-2-14.

(Production method of flexible printed wiring board)
The flexible printed wiring board can be manufactured using the rolled copper foil. Below, the manufacture example of a flexible printed wiring board is shown.
First, a copper clad laminate is manufactured by laminating a rolled copper foil and an insulating substrate such as a polyimide film or a liquid crystal polymer film having good flexibility and foldability.

  In the case of a polyimide film, the bonding is performed by applying a thermoplastic polyimide adhesive to a thermosetting polyimide film, drying it, laminating it with a copper foil, and thermocompression bonding. As a pressure bonding method, there are a method of hot pressing under normal pressure or vacuum and a method of laminating by a hot roll. In the case of a polyimide film, there is a method for producing a copper-clad laminate by applying a polyimide precursor to a copper foil, drying and curing.

  As a process for producing a flexible printed wiring board (FPC) from a copper clad laminate, a method known to those skilled in the art may be used. For example, an etching resist is formed only on a necessary portion as a wiring pattern on the copper foil surface of the copper clad laminate, and an unnecessary liquid foil is removed by spraying an etching solution onto the copper foil surface to form a circuit pattern. Next, a flexible printed wiring board is produced by peeling and removing the etching resist to expose the wiring pattern. Next, for the purpose of connection to the wiring terminal portion and rust prevention, a tin plating and whisker prevention fusing treatment is performed, and then a solder resist film is formed at a necessary location for the purpose of protecting the conductor pattern. The thickness of tin plating is generally 0.1 to 2.0 μm. The total thickness of the Sn layer and / or Sn copper alloy layer generated by the fusing treatment is generally 0.1 to 3.0 μm.

  Various electronic devices can be manufactured by providing this flexible printed wiring board between two electronic substrates and electrically connecting them. The electronic device is not particularly limited, and examples thereof include a liquid crystal display, a car navigation system, a mobile phone, a game machine, a CD player, a digital camera, a TV, a DVD player, an electronic notebook, an electronic dictionary, a calculator, a video camera, a printer, and the like. It is done.

  EXAMPLES Examples of the present invention will be described below, but these are provided for better understanding of the present invention and are not intended to limit the present invention.

(Example 1: Examples 1 to 21)
Table 1 in tough pitch copper [TPC] (Examples 1, 8-14, 19) (JIS-H3100 C1100), oxygen-free copper (Examples 2-7, 15-18, 20, 21) (JIS-H3100 C1020) After the ingot produced by adding the element described in the above is processed into a plate having a thickness of 7 mm by hot rolling and the oxide is removed by surface grinding, the thickness is increased by repeating cold rolling, annealing, and pickling. 0.1 mm. Thereafter, cold rolling to the thickness shown in Table 1 was performed by performing cold rolling under the conditions shown in Table 1 so that the average degree of processing in each pass was 10% or less. Moreover, when the workability of 1 pass exceeded 10% by cold rolling of 0.1 mm or less, it annealed to 80-120 degreeC after the pass, and moved to the next pass.
In addition, the average degree of processing of each pass was a value obtained by dividing the total degree of processing of each pass by the number of passes as in the following equation.
Average machining degree of each pass (%) = (First pass machining degree (%) + Second pass machining degree (%) + ... + Final pass machining degree (%)) / (Number of passes)
Subsequently, annealing was performed at 400 ° C. for 1 hour.
Subsequently, a surface treatment was applied to the copper foil surface by sputtering. As the surface treatment, Cr and Ni were attached to the surface to be bonded to the base film of the flexible printed wiring board by sputtering. Further, Pd and Ni were deposited on the surface side opposite to the above surface by sputtering.
Subsequently, in Examples 1 to 17 and 19 to 21, a 38.5 μm-thick resin layer formed by applying 1 μm of a thermoplastic PI adhesive to Kapton EN (registered trademark) and drying it was laminated on a copper foil to form a vacuum. A copper clad laminate was produced by hot pressing. In Example 18, polyimide varnish (U varnish S manufactured by Ube Industries Co., Ltd.) was applied to a copper foil, dried and cured to form a 37.5 μm resin layer to prepare a copper clad laminate.
Subsequently, a circuit was formed with L (line) / S (space) = 20 μm / 30 μm on the copper foil of the produced laminate, and after electroless Sn plating, a fusing treatment was performed at 170 ° C. for 2 hours. did. This was used as an FPC specimen. The area ratio with respect to the copper foil surface of the wiring of the test material was 30% because a portion where no circuit was formed was included.

(Example 2: Comparative Examples 1 to 4)
In Comparative Examples 1 and 2, an ingot of tough pitch copper [TPC] is used, and the average workability is not reduced to 10% or less by cold rolling with a thickness of 0.1 mm or less, or by cold rolling with a thickness of 0.1 mm or less. Even if the processing degree of 1 pass exceeded 10%, it was not annealed thereafter. Table 1 shows the conditions of cold rolling with a thickness of 0.1 mm or less in Comparative Examples 1 and 2 and the presence or absence of annealing after the workability of one pass exceeds 10% in the cold rolling with a thickness of 0.1 mm or less. Shown in Further, the same processing as in Example 1 was performed until the thickness was 0.1 mm. The copper clad laminate and its circuit according to Comparative Examples 1 and 2 were produced in the same manner as in Example 1.
In Comparative Example 3, a NiCr layer as a seed layer was formed on Kapton 150EN (resin thickness: 37.5 μm) by sputtering using a metallization method, and then copper plating was performed so that the copper thickness became 8 μm. A circuit of L / S = 20 μm / 30 μm was formed on the copper foil of the produced laminate, and after electroless Sn plating, heat treatment was performed at 170 ° C. for 2 hours. This was used as an FPC specimen.
In Comparative Example 4, polyimide varnish (U varnish S manufactured by Ube Industries Co., Ltd.) was applied to a commercially available special electrolytic copper foil, dried, and cured (400 ° C. for 1 hour) to form a 37.5 μm resin layer. A stretched laminate was produced. A circuit of L / S = 20 μm / 30 μm was formed on the copper foil of the produced laminate, and after electroless Sn plating, fusing treatment was performed at 170 ° C. for 2 hours. This was used as an FPC specimen.

For the FPC specimens of Examples 1 to 21 and Comparative Examples 1 to 4 thus produced, a commercially available anisotropic conductive film as shown in FIG. 2 was prepared by using a 3 ppm linear thermal expansion glass substrate and a 13 ppm FR4 substrate. Thermocompression bonding was performed via (ACF), and the temperature change from −65 ° C. to + 150 ° C. was repeated up to 1000 times.
Here, the circuit disconnection was determined as follows. That is, the resistance value of the wiring circuit of the flexible printed wiring board was continuously measured using a digital multimeter. It was determined that the circuit was disconnected when the measured resistance value was 150% or more of the initial value (resistance value before applying the repeated strain). Table 1 shows the number of cycles (fracture cycle) for applying repeated strain when it is determined that the circuit is disconnected.

In Examples 1 to 21 and Comparative Examples 1 and 2, the copper foil surface of the sample after heating at 400 ° C. for 1 hour after the final cold rolling was OIM manufactured by TSL using an electron microscope JEOL JXA-8500F. EBSP analysis was performed to determine the Σ value of the grain boundary, and the total length (cm) of crystal grain boundaries of Σ19 or more per copper foil unit area (mm ² ) was measured. Since the Σ value was measured using OIM Analysis 5.31 software, the grain boundary length of each Σ value from Σ1 to the upper limit Σ49 was obtained. For this reason, the “total length of grain boundaries of Σ19 or more” indicates the total length of each grain boundary per copper foil unit area (mm ² ) from Σ19 to Σ49. In addition, the length of the grain boundary where Σ value is not assigned on the software was excluded. In Comparative Example 3, the sample after copper plating was measured in the same manner. The comparative example 4 measured the sample after heating the commercially available special electrolytic copper foil at 400 degreeC for 1 hour similarly.
In addition, “heating at 400 ° C. for 1 hour” in the sample preparation of the above examples and comparative examples simulates the curing process of the polyimide varnish when the laminated plate is manufactured.
The measurement results are shown in Table 1.

(Evaluation)
In each of Examples 1 to 21, the total length of the grain boundaries of Σ19 or more is controlled to 8 cm / mm ² or less, and the first substrate (glass) having a difference of 1.5 times or more in linear thermal expansion coefficient Board) and a second printed circuit board (FR4 board) are used as wiring for a flexible printed wiring board to electrically connect the wiring to the flexible printed wiring board even if the temperature change of −65 ° C. to + 150 ° C. is repeated 300 times. There was no disconnection.
In Comparative Example 1, even if the degree of processing in one pass exceeds 10% by cold rolling with a thickness of 0.1 mm or less, annealing is not performed thereafter, and the total length of the grain boundaries of Σ19 or more is 8 cm / It exceeds the mm ^2, and the wire is broken when given the repeated strain 210 times.
In Comparative Example 2, the average workability was not reduced to 10% or less by cold rolling with a thickness of 0.1 mm or less, the total length of the grain boundaries of Σ19 or more exceeded 8 cm / mm ² , and repeated strain When 200 times was given, the wiring was disconnected.
In Comparative Examples 3 and 4, when a rolled copper foil was not used, the total length of the grain boundaries of Σ19 or more exceeded 8 cm / mm ² , and repeated strain was applied 150 times and 240 times, respectively. The wiring was disconnected.

Claims (9)

The crystal orientation obtained by irradiating an electron beam to a measurement point of the metallographic structure of the crystal, and obtained by irradiating an electron beam to a plurality of adjacent measurement points located 0.5 μm apart around the measurement point When the Σ value of the crystal grain boundary is determined by setting a part having an orientation angle difference with the crystal orientation of 2 ° or more as the crystal grain boundary, the length of the crystal grain boundary of Σ19 or more measured after annealing at 400 ° C. for 1 hour. A rolled copper foil having a total of 8 cm / mm ² or less. The rolled copper foil according to claim 1, wherein the total length of the grain boundaries of Σ19 or more measured after annealing at 400 ° C for 1 hour is 6 cm / mm ² or less.   When used as a wiring of a flexible printed wiring board that electrically connects a first board and a second board having a linear expansion coefficient difference of 1.2 times or more, −65 ° C. to 150 ° C. is applied to the flexible printed wiring board. The rolled copper foil according to claim 1 or 2, wherein no crack is generated in the wiring even when the temperature change is repeated 300 times.   The rolled copper foil in any one of Claims 1-3 which contain 10-1300 mass ppm in total of 1 type, or 2 or more types selected from the group which consists of Ag, Sn, In, Zr, and Zn.   The rolled copper foil according to any one of claims 1 to 4, having a thickness of 5 to 70 µm.   The copper clad laminated board provided with the copper foil in any one of Claims 1-5.   A flexible printed wiring board made of the copper-clad laminate according to claim 6.   The flexible printed wiring board of Claim 7 by which Sn layer and / or Sn copper alloy layer were given to at least one part of the terminal part or the wiring part.   An electronic apparatus comprising: the flexible printed wiring board according to claim 8; and a first substrate and a second substrate electrically connected by the flexible printed wiring board.