WO2012057002A1 - Electrode wire for solar cell, substrate thereof, and substrate manufacturing method - Google Patents

Abstract

Provided is a pre-coating straight-angle substrate of an electrode wire for a solar cell having superior resistance to cracking and being formed of slit materials of pure copper plate which has desirable adhesion with a coating applied on the obverse face thereof. The substrate is formed of slit materials of pure copper thin plate containing 99.90mass% or more copper, with an obverse face arithmetical mean deviation (Ra) of 0.05-0.3μm, an obverse face maximum height (Rz) of 0.05-2.5μm, a ratio (Rq/Rz) of a root mean square (Rq) to the maximum height (Rz) of the obverse face of 0.06-1.1, and a ratio (Lσ/L) of a total special grain boundary length (Lσ) of a special grain boundary to a total length of a crystalline grain boundary (L), as measured with EBSD by a scanning electron microscope with backscatter electron diffraction pattern system attached within a depth of 10μm from the obverse surface, of 40-90%.

Description

ELECTRODE WIRE FOR SOLAR CELL, ITS SUBSTRATE, AND METHOD FOR PRODUCING SUBSTRATE

TECHNICAL FIELD The present invention relates to an electrode wire for solar cells, a substrate thereof, and a method for producing the substrate, and more particularly, for a solar cell formed of a pure copper thin plate slit material having good adhesion to plating applied to the surface. The present invention relates to a flat substrate for an electrode wire and a method for producing the same.
This application claims priority based on Japanese Patent Application No. 2010-241952 filed on October 28, 2010 and Japanese Patent Application No. 2010-262228 filed on November 25, 2010, the contents of which are incorporated herein by reference. To do.

Solar cells are usually soldered to a semiconductor substrate formed of a silicon semiconductor having a PN junction and a solder band formed so as to cross a plurality of surface electrodes provided linearly on the surface of the semiconductor substrate. A connecting electrode wire is provided, and a plurality of solar cells are connected in series to obtain a desired electromotive force. In series connection, one surface (lower surface) of the connecting electrode wire is soldered to the surface electrode of one solar cell, and the other surface (upper surface) is soldered to the back electrode of a relatively large area of the adjacent solar cell. Made by doing.

The manufacturing method of the flat electrode material used as the base material for the electrode wire for connection is to roll a copper wire having a round cross section such as tough pitch Cu, oxygen-free Cu, phosphorus deoxidized Cu, high purity Cu (99.9999% or more). After rolling, flat rolling such as tough pitch Cu, oxygen-free Cu, phosphorus deoxidized Cu, high purity Cu (99.9999% or more) in a rolling mill, hot rolling, cold rolling, annealing There is a slit processing method of cutting with a slitter, and the electrode wire for connection is manufactured by performing solder plating on the surface of the formed flat electrode material.

However, in recent years, with the thinning of the semiconductor substrate, when the connecting electrode wire is brazed to the semiconductor substrate, there is a problem that the semiconductor substrate is cracked. This is because the thermal expansion coefficient of copper, which is a flat base material for connecting electrode wires, is larger than that of a semiconductor substrate, and the shrinkage of the electrode wires generates bending stress in the semiconductor substrate during cooling shrinkage after brazing. is there.

In order to solve these problems, Patent Document 1 discloses rolling of pure copper in which the base material before plating of the electrode wire for solar cells in which the surface of the base material is subjected to molten solder plating contains 99.90 mass% or more of Cu. When the peak intensities by X-ray diffraction of the crystal orientation <100>, <114>, <112> in the rolling direction are expressed as P <100>, P <114>, P <112>, respectively. The peak intensity ratio PR (%) = (P <114> + P <112>) · 100 / (P <100> + P <114> + <112>) is 50 to 90%, which is superior to the conventional one. A method of manufacturing an electrode wire for solar cells and a base material having plastic deformability is disclosed.

In Patent Document 2, in a solder plating wire for a solar cell in which a part or all of the surface of a conductor formed in a rectangular shape is coated with solder plating, a 0.2% proof stress value in a conductor tensile test is 90 MPa or less. In addition, there is disclosed a solar cell solder-plated wire that has a conductor crystal grain size of 20 μm or more and 300 μm or less and is less likely to warp or break the solar cell when the connecting lead wire is joined even when the solar cell is thinned. .

JP 2009-16593 A JP 2008-140787 A

In Patent Document 1, a pure copper plate containing 99.90 mass% or more of Cu is finally rolled at various rolling reductions, slit in a linear shape along the rolling direction, and then softened and annealed to produce a base material. Although there is a disclosure of an electrode wire base material for solar cells with excellent plastic deformability, there is no solution for improving the adhesion between the flat electrode material that is the base material and the solder plating applied to the surface. Not disclosed.
Patent Document 2 discloses a solar cell solder-plated wire that is less likely to warp or break the solar cell when the connecting lead wire is joined even when the solar cell is thinned. There is no disclosure regarding the adhesion to the solder plating applied to the surface.

The present invention provides a flat substrate for a solar cell electrode wire before plating formed with a slit material of a pure copper thin plate having good adhesion to the plating applied to the surface, a manufacturing method thereof, and durability. An object is to provide an excellent electrode wire for solar cells.

As a result of intensive studies in view of the above circumstances, the present inventors have performed a pure copper sheet containing 99.90% by mass or more of Cu by hot rolling, intermediate cold rolling, annealing, and final cold rolling to obtain a pure copper sheet material. Produce, slit the thin plate with a cutting machine, further subject to final annealing to produce a flat substrate, and manufacture a solar cell electrode wire with a part or all of its surface plated with solder When measuring, the measurement is such that the azimuth difference between adjacent measurement points is 15 ° or more measured by the EBSD method with a scanning electron microscope with a backscattered electron diffraction image system within a depth of 10 μm from the surface of the flat substrate. The ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundary to the total grain boundary length L of the crystal grain boundary (Lσ / L) when the point boundary is regarded as the crystal grain boundary is 40 to 90%. The solar cell electrode wire is incorporated into solar cell panels, etc. It is possible to prevent cracking of the rectangular-shaped substrate during processing, crack resistance and found that long-term reliability is improved increased.

In addition, the arithmetic average roughness Ra of the surface of the flat substrate is 0.05 to 0.3 μm, the maximum height Rz is 0.5 to 2.5 μm, and the root mean square roughness Rq and the maximum height are When the ratio Rq / Rz of Rz is 0.06 to 1.1, adhesion to solder plating applied to a part or all of the surface of the flat substrate is improved, and the electrode wire for solar cells is severe. It has also been found that the durability is improved without peeling of the solder plating even under use conditions.

That is, the flat substrate before plating of the electrode wire for solar cell of the present invention is a flat substrate before plating of the electrode wire for solar cell in which a part or all of the surface is solder-plated, Cu Is made of a pure copper thin plate slit material containing 99.90% by mass or more, the arithmetic average roughness Ra of the surface is 0.05 to 0.3 μm, and the maximum height Rz is 0.5 to 2.5 μm. The ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1, and EBSD by a scanning electron microscope with a backscattered electron diffraction imaging system within a depth of 10 μm from the surface. Special grain boundary with respect to the total grain boundary length L of the grain boundary when the difference in orientation between adjacent measurement points measured by the method is considered to be a crystal grain boundary. The ratio of grain boundary length Lσ (Lσ / L) is 40 to 90%. The features.

In this case, all of the special grain boundaries with respect to the total grain boundary length L of the grain boundaries measured by the EBSD method with a scanning electron microscope with a backscattered electron diffraction image system within a depth of 10 μm from the surface of the flat substrate. When the ratio (Lσ / L) of the special grain boundary length Lσ is less than 40%, the crack resistance is lowered, and when it exceeds 90%, the effect is saturated and the production cost is excessively increased.
A special grain boundary is a crystal having a crystal value of 3 ≦ Σ ≦ 29 with a Σ value defined crystallographically based on CSL theory (Kronberg et.al.:Trans. Met. Soc. AIME, 185, 501 (1949)). A crystal that is a grain boundary (corresponding grain boundary) and has an inherent corresponding site lattice orientation defect Dq at the grain boundary satisfying Dq ≦ 15 ° / Σ ^1/2 (DGBrandon: Acta. Metallurgica. Vol. 14, p1479, 1966) It is a grain boundary.
The ratio (Lσ / L) of the special grain boundary length Lσ with respect to the total grain boundary length L of this grain boundary is such that the orientation difference between adjacent measurement points is 15 ° or more by orientation analysis by backscattered electron diffraction. Measure the total grain boundary length L of the crystal grain boundary, and determine the position of the crystal grain boundary where the interface between adjacent crystal grains constitutes the special grain boundary. It is calculated from the total special grain boundary length Lσ and the total grain boundary length L of the measured grain boundary.

Also, the arithmetic average roughness Ra of the surface of the rectangular substrate is less than 0.05 μm, the maximum height Rz is less than 0.5 μm, or the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / If Rz) is less than 0.06, the adhesion with the solder plating applied to a part or all of the surface is deteriorated. Arithmetic average roughness Ra of the surface of the rectangular substrate exceeds 0.3 μm, or maximum height Rz exceeds 2.5 μm, or ratio of root mean square roughness Rq to maximum height Rz (Rq / If Rz) exceeds 1.1, adhesion to solder plating applied to a part or all of the surface, particularly heat-resistant peelability, is deteriorated, which is inconvenient.

Further, the present inventors perform hot rolling, intermediate cold rolling, annealing, and final cold rolling on a pure copper plate containing 99.90% by mass or more of Cu to produce a pure copper thin plate material, and cut the thin plate material. When making an electrode wire for a solar cell in which a part or all of its surface is subjected to solder plating, it is processed into a rectangular shape before plating. The substrate is formed of a pure copper sheet slit material containing 99.90% by mass or more of Cu, and is a rectangular substrate with a step size of 0.5 μm by an EBSD method using a scanning electron microscope with a backscattered electron diffraction image system. The average orientation difference between all pixels in a crystal grain when measuring the orientation of all pixels within the measurement area of the surface of the surface and considering the boundary where the orientation difference between adjacent pixels is 5 ° or more as the grain boundary Ratio of crystal grain area whose angle is less than 4 ° 80% to 95% of the measurement area, and if the area average GAM of the crystal grains existing in the measurement area is less than 4 °, a hard and brittle Cu—Sn alloy layer on the surface after solder plating, It was found that the Cu ₆ Sn ₅ layer was difficult to be formed and the 0.2% yield strength increase after solder plating was small.
The Cu-Sn alloy layer is important for improving the solder plating adhesion, but it is hard and brittle. If the amount of the Cu-Sn alloy layer is large, the 0.2% proof stress of the electrode wire for solar cells after solder plating increases. However, during the cooling shrinkage after brazing, the shrinkage of the electrode wire material causes a bending stress in the semiconductor substrate and causes a crack.

In addition, the arithmetic average roughness Ra of the surface of the flat substrate is 0.05 to 0.3 μm, the maximum height Rz is 0.5 to 2.5 μm, and the root mean square roughness Rq and the maximum height are When the ratio Rq / Rz of Rz is 0.06 to 1.1, adhesion to solder plating applied to a part or all of the surface of the flat substrate is improved, and the electrode wire for solar cells is severe. It has also been found that the durability is improved without peeling of the solder plating even under use conditions.

That is, the flat substrate before plating of the electrode wire for solar cell of the present invention is a flat substrate before plating of the electrode wire for solar cell in which a part or all of the surface is solder-plated, Cu Is made of a pure copper thin plate slit material containing 99.90% by mass or more, the arithmetic average roughness Ra of the surface is 0.05 to 0.3 μm, and the maximum height Rz is 0.5 to 2.5 μm. The ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1, and the step size is 0 by the EBSD method using a scanning electron microscope with a backscattered electron diffraction image system. When measuring the orientation of all the pixels within the measurement area of the surface at 5 μm and considering the boundary where the orientation difference between adjacent pixels is 5 ° or more as the grain boundary, between all the pixels in the crystal grain The area ratio of crystal grains having an average misorientation of less than 4 ° is It is 80 to 95% of the measurement area, and the area average GAM of crystal grains existing in the measurement area is less than 4 °.

In this case, the arithmetic average roughness Ra of the surface of the rectangular substrate is less than 0.05 μm, or the maximum height Rz is less than 0.5 μm, or the ratio of the root mean square roughness Rq to the maximum height Rz (Rq If / Rz) is less than 0.06, the adhesion with the solder plating applied to a part or all of the surface is deteriorated. Arithmetic average roughness Ra of the surface of the rectangular substrate exceeds 0.3 μm, or maximum height Rz exceeds 2.5 μm, or ratio of root mean square roughness Rq to maximum height Rz (Rq / If Rz) exceeds 1.1, adhesion to solder plating applied to a part or all of the surface, particularly heat-resistant peelability, is deteriorated, which is inconvenient.

Further, the azimuth of all the pixels within the measurement area of the surface is measured with a step size of 0.5 μm by an EBSD method using a scanning electron microscope with a backscattered electron diffraction image system, and the azimuth difference between adjacent pixels is 5 When the boundary that is greater than or equal to ° is regarded as a crystal grain boundary, the area ratio of crystal grains having an average orientation difference between all the pixels in the crystal grains of less than 4 ° is less than 80% of the measured area, and is 0.2. If there is no effect on% proof stress and the measured area exceeds 95% or the area average GAM of the crystal grains existing in the measured area is 4 ° or more, the adhesion with the solder plating deteriorates.
Here, the area average GAM of the crystal grains existing within the measurement area meant in the present invention is calculated by the following method.
GAM is the average value of misorientation between adjacent measurement points (pixels) in the same crystal grain. When the difference in orientation at the boundary i between adjacent measurement points is expressed by equation (1), the boundary between pixels in the crystal grain is When m exist, the GAM value of this crystal grain is expressed by the equation (2).

When the value of the GAM in individual grains (GAM) _k, the area of each crystal grain and S _k, if there are M grain within the measurement range, area average GAM is expressed by equation (3) The

Furthermore, the manufacturing method of the rectangular base material before plating of the electrode wire material for solar cells of the present invention includes hot rolling, intermediate cold rolling, annealing, and final cold rolling to a pure copper plate containing 99.90% by mass or more of Cu. Are made in this order to form a pure copper thin plate, and the thin plate is slit by a cutting machine to form a flat rectangular substrate, and the flat rectangular substrate is finally annealed to plate the flat electrode substrate for solar cell electrode wire. The intermediate cold rolling is performed at a rolling reduction of 50 to 70%, the final cold rolling is performed at a rolling reduction of 50 to 70%, and the final annealing is performed at 200 to 400 ° C. For 150 to 240 minutes.

In this case, by carrying out the rolling reduction of the intermediate cold rolling at 50 to 70%, a substrate for growing the ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundaries is created, and the final annealing is performed. By carrying out the treatment at 200 to 400 ° C. for 150 to 240 minutes, the ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundaries is grown in the range of 40 to 90%. In this case, in the continuous annealing, it is difficult to carry out the final annealing at the above-mentioned time and temperature because of the line speed, and it is preferable to carry out the final annealing by batch processing.
If the rolling reduction of intermediate cold rolling is less than 50% or more than 70%, the effect is insufficient, and if the final annealing temperature is less than 200 ° C. or the time is less than 150 minutes, the total special grain boundary length of the special grain boundary The ratio of Lσ (Lσ / L) is less than 40%, and the ratio of all special grain boundary lengths Lσ of special grain boundaries (Lσ / L) even when the temperature exceeds 400 ° C or the time exceeds 240 minutes. Is less than 40%, which may adversely affect the crack resistance of the flat substrate.

Further, by carrying out the rolling reduction of the final cold rolling at 50 to 70%, the arithmetic average roughness Ra of the surface of the flat substrate is 0.05 to 0.3 μm, and the maximum height Rz is 0. The ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1.
When the rolling reduction of the final cold rolling is less than 50%, the surface roughness of the optimally selected rolling work roll is not reflected in the surface roughness of the pure copper sheet as the rolled material, and the surface of the flat base material is arithmetic If the average roughness Ra, maximum height Rz, root mean square roughness Rq and maximum height Rz ratio (Rq / Rz) cannot fall within the predetermined range, and the rolling reduction exceeds 70% In addition to saturation of the effect, there is a possibility of adversely affecting the yield strength of the flat substrate. Further, by setting the reduction ratio of the final cold rolling to 50 to 70%, there is a secondary effect that subsequent slit processing becomes easy and burrs are hardly generated on the slit processed material.

Moreover, the manufacturing method of the flat base material before plating of the electrode wire for solar cells of this invention is hot rolling, intermediate | middle cold rolling, annealing, and final cold rolling to the pure copper plate which contains 99.90 mass% or more of Cu. Are made in this order to form a pure copper thin plate, and the thin plate is slit by a cutting machine to form a flat rectangular substrate, and the flat rectangular substrate is finally annealed to plate the flat electrode substrate for solar cell electrode wire. The rolling reduction of the intermediate cold rolling is performed at 50 to 70%, the rolling reduction of the final cold rolling is performed at 50 to 70%, and the final annealing is performed at 700 to 900 ° C. It is characterized by being held for 5 to 60 seconds.

In this case, by carrying out the rolling reduction of the intermediate cold rolling at 50 to 70%, the boundary within the crystal grains when the boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as the crystal grain boundary. Create a substrate that keeps the area ratio of crystal grains whose average orientation difference between all pixels is less than 4 ° and the area average GAM of crystal grains in the measurement area within the specified range, and final annealing at 700-900 ° C When the boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as a crystal grain boundary, the average orientation difference between all the pixels in the crystal grain is 4 °. The area ratio of the crystal grains that are less than the average area and the area average GAM of the crystal grains existing in the measurement area are within a predetermined range.
If the rolling reduction of the intermediate cold rolling is less than 50% or more than 70%, the substrate effect is insufficient, and if the final annealing temperature is less than 700 ° C. or the time is less than 5 seconds, the orientation difference between adjacent pixels When the boundary where the angle is 5 ° or more is regarded as the crystal grain boundary, the area ratio of the crystal grains in which the average orientation difference between all the pixels in the crystal grains is less than 4 ° is less than 80% of the measured area. When the annealing temperature exceeds 900 ° C. or the time exceeds 60 seconds, the area ratio of the crystal grains in which the average orientation difference between all the pixels in the crystal grains is less than 4 ° exceeds 95% of the measurement area. Alternatively, the area average GAM of the crystal grains existing in the measurement area is 4 ° or more.

Further, by carrying out the rolling reduction of the final cold rolling at 50 to 70%, the arithmetic average roughness Ra of the surface of the flat substrate is 0.05 to 0.3 μm, and the maximum height Rz is 0. The ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1.
When the rolling reduction of the final cold rolling is less than 50%, the surface roughness of the optimally selected rolling work roll is not reflected in the surface roughness of the pure copper sheet as the rolled material, and the surface of the flat base material is arithmetic If the average roughness Ra, maximum height Rz, root mean square roughness Rq and maximum height Rz ratio (Rq / Rz) cannot fall within the predetermined range, and the rolling reduction exceeds 70% In addition to saturation of the effect, there is a possibility of adversely affecting the yield strength of the flat substrate. Further, by setting the reduction ratio of the final cold rolling to 50 to 70%, there is a secondary effect that subsequent slit processing becomes easy and burrs are hardly generated on the slit processed material.

Furthermore, the electrode wire for solar cell of the present invention has a solder plating of 40 to 150 μm on part or all of the surface of the flat substrate before plating of the electrode wire for solar cell produced by the production method of the present invention. It was manufactured by applying to thickness.
In this case, when the plating thickness is less than 40 μm, the plating adhesion is insufficient, and when the plating thickness exceeds 150 μm, the proof stress of the solar cell electrode wire is increased, which adversely affects the warpage of the silicon cell.

Also, the solder plating is preferably performed continuously immediately after the final annealing of the flat base material from the viewpoint of reducing the manufacturing cost and the fluctuation in the proof stress of the electrode wire for solar cells. A large-diameter winding drum is provided on the downstream side, and the rectangular base material immediately after the final annealing is passed through a solder plating bath adjusted to a temperature about 50 to 100 ° C. higher than the melting point of the solder alloy. From the viewpoint of production cost, it is preferable to wind the film while pulling it with a proper tension, thereby immersing the flat substrate in a solder plating bath and pulling it up. In this case, tension is applied to the flat base material, and the proof stress of the solar cell electrode wire after solder plating is increased, so care must be taken in adjusting the tension.

According to the present invention, a flat substrate of a solar cell electrode wire formed by a slit material of a pure copper thin plate having good adhesion to the plating applied to the surface, a manufacturing method thereof, and durability An excellent electrode wire for solar cell is provided.

It is a cross-sectional view of the flat base material before plating of the solar cell electrode wire of the present invention. It is the schematic of the solar cell provided with the connection lead which cut | disconnected the electrode wire for solar cells of this invention by predetermined length.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an electrode wire for a solar cell, a base material thereof, and a manufacturing method thereof will be described with reference to the drawings.
<Alloy composition and surface properties, solder plating layer>
FIG. 1 shows a cross section of a solar cell electrode wire according to the present invention. A solar cell electrode wire 1 has a rectangular base 2 having a square cross section formed of pure copper containing 99.90% by mass or more of Cu. And a solder plating layer 3 applied to a part or all of the surface of the flat substrate 2 to a thickness of 40 to 150 μm.

The rectangular substrate 2 has a Cu content of 99.90% by mass or more, preferably 99.99% by mass or more. Impurities include As, Sb, Bi, Pb, S, Fe, O, P, etc. In particular, O and P are small amounts and the plastic deformability is lowered, so the amount of O is preferably 0 to 500 ppm. Is 0 to 100 ppm, and the amount of P is desirably regulated to 0 to 150 ppm, preferably 0 to 50 ppm. Tappitch copper, oxygen-free copper, and phosphorus deoxidized copper are suitable materials because they satisfy the above components.

The flat substrate 2 is obtained by subjecting a pure copper plate containing 99.90% by mass or more of Cu to hot rolling, intermediate cold rolling, annealing, and final cold rolling in this order to form a pure copper thin plate. It is manufactured by slitting with a cutting machine to form a flat base material, and the flat base material is finally annealed. The arithmetic average roughness Ra of the surface is 0.05 to 0.3 μm, and the maximum height Rz is 0.5 to 2.5 μm, and the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1.

The arithmetic average roughness Ra of the surface of the flat substrate 2 is less than 0.05 μm, the maximum height Rz is less than 0.5 μm, or the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz ) Is less than 0.06, the adhesiveness with solder plating or molten solder plating applied to a part or all of the surface is deteriorated. The arithmetic average roughness Ra of the surface of the flat substrate 2 exceeds 0.3 μm, or the maximum height Rz exceeds 2.5 μm, or the ratio of the root mean square roughness Rq to the maximum height Rz (Rq If / Rz) exceeds 1.1, adhesion to solder plating applied to a part or all of the surface, particularly heat-resistant peelability, deteriorates.

The thickness of the solder plating layer 3 is 40 to 150 μm. If the plating thickness is less than 40 μm, the adhesion of the plating is insufficient, and if the plating thickness exceeds 150 μm, the yield strength of the solar cell electrode wire is increased. It has an adverse effect on warpage.
Solder plating includes Sn-based solder or Sn-based alloy solder containing 0.1% by mass or more of at least one element selected from Pb, In, Bi, Sb, Ag, Zn, Ni, and Cu as a second component. To do.

The solder plating is particularly preferably a molten solder plating from the viewpoint of manufacturing cost and equipment, and a Sn—Pb alloy having a melting point of about 130 to 300 ° C., a Sn— (0.5 to 5 mass%) Ag alloy, Sn- (0.5-5% by mass) Ag- (0.3-1.0% by mass) Cu alloy, Sn- (0.3-1.0% by mass) Cu alloy, Sn- (1.0- 5.0 mass%) Ag- (5-8 mass%) In alloy, Sn- (1.0-5.0 mass%) Ag- (40-50 mass%) Bi alloy, Sn- (40-50 mass%) %) Bi alloy, Sn- (1.0-5.0 mass%) Ag- (40-50 mass%) Bi- (5-8 mass%) In alloy, etc. are used. Since Pb is harmful to the human body and may contaminate the natural environment, Pb-free Sn—Ag alloy, Sn—Ag—Cu alloy, Sn—Cu alloy, Sn—Ag—In alloy are used from the viewpoint of pollution prevention. A solder material such as a Sn—Ag—Bi alloy is particularly preferable.
In each solder material, in order to prevent oxidation of the molten solder itself, one or two of P of about 50 to 200 ppm, Ga of several to several tens of ppm, Gd of several to several tens of ppm, and Ge of several to several tens of ppm are used. More seeds can be added.

<Alloy structure>
The alloy structure of the flat substrate 2 has the following embodiment.
In the rectangular substrate of the first embodiment, the total grain boundary length of the grain boundaries measured by the EBSD method with a scanning electron microscope with a backscattered electron diffraction image system within a depth of 10 μm from the surface of the rectangular substrate. The ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundary to the thickness L is 40 to 90%.

All special grains of the special grain boundary with respect to the total grain boundary length L of the grain boundary measured by the EBSD method with a scanning electron microscope with a backscattered electron diffraction image system within a depth of 10 μm from the surface of the flat substrate 2 If the ratio of the field length Lσ (Lσ / L) is less than 40%, the crack resistance is lowered, and if it exceeds 90%, the effect is saturated and the production cost is too high.

Further, in the flat substrate of the second embodiment, within the measurement area of the surface of the flat substrate 2 with a step size of 0.5 μm by the EBSD method using a scanning electron microscope with a backscattered electron diffraction image system. A crystal whose average orientation difference between all pixels in a crystal grain is less than 4 ° when the orientation of all pixels is measured and a boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as a grain boundary. The area ratio of the grains is 80 to 95% of the measurement area, and the area average GAM of the crystal grains existing in the measurement area is less than 4 °.

Here, by the EBSD method using a scanning electron microscope with a backscattered electron diffraction image system, the orientations of all the pixels within the measurement area of the surface of the flat substrate 2 are measured with a step size of 0.5 μm and adjacent to each other. When a boundary having an orientation difference between pixels of 5 ° or more is regarded as a grain boundary, an area ratio of crystal grains having an average orientation difference between all pixels in the crystal grain of less than 4 ° is 80% of the measurement area. If it is less than%, there is no effect on 0.2% proof stress, and if it exceeds 95% of the measurement area, or if the area average GAM of the crystal grains present in the measurement area is 4 ° or more, the adhesion with the solder plating is Deteriorate.
The area average GAM of crystal grains existing within the measurement area as used in the present invention is calculated by the following method.
GAM is the average value of misorientation between adjacent measurement points (pixels) in the same crystal grain. When the difference in orientation at the boundary i between adjacent measurement points is expressed by equation (1), the boundary between pixels in the crystal grain is When m exist, the GAM value of this crystal grain is expressed by the equation (2).

When the value of the GAM in individual grains (GAM) _k, the area of each crystal grain and S _k, if there are M grain within the measurement range, area average GAM is expressed by equation (3) The

<Manufacturing method>
The flat substrate 2 of the first embodiment is a pure copper sheet that is obtained by subjecting a pure copper sheet containing 99.90% by mass or more of Cu to hot rolling, intermediate cold rolling, annealing, and final cold rolling in this order. It is manufactured by slitting a thin plate with a cutting machine to make a flat base material, and final annealing the flat base material. The rolling reduction of the intermediate cold rolling is performed at 50 to 70%, and the final cold It is important that the rolling reduction of the hot rolling is performed at 50 to 70% and the final annealing is performed at 200 to 400 ° C. for 150 to 240 minutes.

In this case, by carrying out the rolling reduction of the intermediate cold rolling at 50 to 70%, a substrate for growing the ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundaries is created, and the final annealing is performed. By carrying out the treatment at 200 to 400 ° C. for 150 to 240 minutes, the ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundaries grows in the range of 40 to 90%. In this case, in the continuous annealing, it is difficult to perform the final annealing at the above-described time and temperature because of the line speed, and it is preferable to perform the final annealing by batch processing.
If the rolling reduction of intermediate cold rolling is less than 50% or more than 70%, the effect is insufficient, and if the final annealing temperature is less than 200 ° C. or the time is less than 150 minutes, the total special grain boundary length of the special grain boundary The ratio of Lσ (Lσ / L) is less than 40%, and the ratio of the total special grain boundary length Lσ of the special grain boundary (Lσ / L) even if the temperature exceeds 400 ° C. or the time exceeds 240 minutes. Is less than 40%, which may adversely affect the crack resistance of the flat substrate.

On the other hand, the flat substrate 2 of the second embodiment is a pure copper sheet obtained by subjecting a pure copper plate containing 99.90% by mass or more of Cu to hot rolling, intermediate cold rolling, annealing, and final cold rolling in this order. The thin plate is slit by a cutting machine to form a flat substrate, and the flat substrate is finally annealed. The rolling reduction of the intermediate cold rolling is performed at 50 to 70%, It is important that the rolling reduction of the final cold rolling is performed at 50 to 70% and the final annealing is performed at 700 to 900 ° C. for 5 to 60 seconds.

In this case, by carrying out the rolling reduction of the intermediate cold rolling at 50 to 70%, the boundary in which the orientation difference between adjacent pixels is 5 ° or more is regarded as the crystal grain boundary. Create a substrate that keeps the area ratio of crystal grains whose average orientation difference between all pixels is less than 4 ° and the area average GAM of crystal grains in the measurement area within a predetermined range, and the final annealing is 700-900 ° C By maintaining the atmosphere for 5 to 60 seconds, the average orientation difference between all the pixels in the crystal grain is 4 when the boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as the grain boundary. The area ratio of crystal grains that are less than 0 ° and the area average GAM of crystal grains existing in the measurement area are within a predetermined range. When the rolling reduction ratio of intermediate cold rolling is less than 50% or more than 70%, the above-mentioned base ratio for keeping the area ratio of the crystal grains whose average orientation difference is less than 4 ° and the area average GAM within a predetermined range If the atmosphere temperature of the final annealing is less than 700 ° C or the time is less than 5 seconds, the boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as a grain boundary. In the case where the average orientation difference between all the pixels in the crystal grains is less than 4 °, the area ratio of the crystal grains is less than 80% of the measured area, and the atmosphere temperature of the final annealing exceeds 900 ° C., or the time Exceeds 60 seconds, the area ratio of the crystal grains in which the average orientation difference between all the pixels in the crystal grains is less than 4 ° exceeds 95% of the measurement area, or the crystal grains existing within the measurement area The area average GAM is 4 ° or more.

The rolling reduction of the final cold rolling is common to both the embodiments, and the arithmetic average roughness Ra of the surface of the flat substrate is 0 by performing the rolling reduction of the final cold rolling at 50 to 70%. .05 to 0.3 μm, the maximum height Rz is 0.5 to 2.5 μm, and the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1. It becomes.
When the rolling reduction of the final cold rolling is less than 50%, the surface roughness of the optimally selected rolling work roll is not reflected in the surface roughness of the pure copper sheet as the rolled material, and the surface of the flat base material is arithmetic If the average roughness Ra, maximum height Rz, root mean square roughness Rq and maximum height Rz ratio (Rq / Rz) cannot fall within the predetermined range, and the rolling reduction exceeds 70% In addition to saturation of the effect, there is a possibility of adversely affecting the yield strength of the flat substrate. Further, by setting the reduction ratio of the final cold rolling to 50 to 70%, there is a secondary effect that subsequent slit processing becomes easy and burrs are hardly generated in the slit processed material.

In order to form the solder plating layer 3 having a thickness of 40 to 150 μm on a part or all of the surface of the flat substrate 2 manufactured in this way, the flat substrate 2 is formed to a predetermined length. After cutting, a winding drum having a large diameter is provided on the downstream side of the solder plating bath, rather than the method of performing solder plating on this short base material, and the flat base material 2 is 50 to 100 ° C. above the melting point of the solder alloy. It is manufactured by passing it through a solder plating bath adjusted to a relatively high temperature, winding it with an appropriate tension while pulling it, and continuously immersing and pulling up the flat substrate 2 in the solder plating bath. It is preferable from the viewpoint of cost. In this case, tension is applied to the flat rectangular base material 2, and the proof stress of the solar cell electrode wire 1 after solder plating is increased, so care must be taken in adjusting the tension.
In addition, in the flat base material of 2nd Embodiment, continuous annealing is possible and it is good to plate continuously the flat base material just after the final annealing by continuous annealing was passed through a solder plating bath.

<Schematic configuration of solar cell>
FIG. 2 is a schematic view of a solar cell provided with a connection lead 14 obtained by cutting the solar cell electrode wire 1 of the present invention into a predetermined length. The solar cell 11 is formed of a silicon semiconductor having a PN junction. And a connecting lead wire 14 soldered to a plurality of surface electrodes 13 linearly provided on the surface of the semiconductor substrate 12. On the back surface of the semiconductor substrate 12, 40 to 80 mm ²
A plurality of back electrodes having a large surface to the extent are provided. On the semiconductor substrate 12 before the connecting lead wires 14 are soldered, solder bands arranged perpendicular to the surface electrodes 13 are formed so as to be electrically connected to the plurality of linear surface electrodes 13. . The connecting lead wire 14 is placed on the semiconductor substrate 12 so that the plating layer 3 of the solar cell electrode wire 1 is in contact with the solder band, and is soldered to the surface of the semiconductor substrate 12.

An oxygen-free copper plate (Cu: 99.96%, O: 5 ppm, P: 0 ppm) and tough pitch copper (Cu: 99.92%, O: 300 ppm, P: 0 ppm) manufactured by Mitsubishi Materials Corporation with a thickness of 3.0 mm The plate is subjected to hot rolling, intermediate cold rolling (the rolling reduction is shown in Table 1) and annealing in this order to produce an oxygen-free copper sheet and a tough pitch copper sheet, and then the final cold rolling (rolling ratio) Are shown in Table 1) to obtain an oxygen-free copper thin plate and a tough pitch copper thin plate having a thickness of 0.15 mm. Next, the oxygen-free copper thin plate and the tough pitch copper thin plate were slit with a cutting machine to obtain a flat rectangular plate having a width of 2 mm. Furthermore, these flat rectangular sheets were subjected to final annealing by batch treatment under the conditions shown in Table 1, and the flat rectangular substrates before plating of Examples 1 to 6 and Comparative Examples 1 to 6 were obtained.

The surface roughness Ra, Rz, Rq / Rz, the ratio of the total special grain boundary length Lσ of the special grain boundary to the total grain boundary length L of the grain boundary (Lσ / L), the proof stress It was measured. The measurement results are shown in Tables 2 and 3.
The surface roughness Ra, Rz, and Rq were measured using a scanning confocal laser microscope LEXT OLS-3000 manufactured by Olympus Co., Ltd. on the surface of the sample cut out from each of the rectangular strips. Irradiation was performed, the distance was measured from the reflected light, and the distance was continuously measured while the laser light was scanned linearly along the surface of the sample.

The ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundary to the total grain boundary length L of the crystal grain boundary was determined by the following method.
First, the sample cut out from each rectangular substrate was mechanically polished using water-resistant abrasive paper and diamond abrasive grains, and then final polished using a colloidal silica solution.
Next, using an EBSD measuring apparatus (HITACHI: S4300-SE, EDAX / TSL, OIM Data Collection) and analysis software (EDAX / TSL: OIM Data Analysis ver. 5.2), a sample Irradiation of individual measurement points (pixels) within the measurement range of the surface with an electron beam, and an azimuth difference between adjacent measurement points measured at a step size of 0.5 μm by azimuth analysis by backscattered electron diffraction is 15 °. The special grain boundary length ratio was analyzed by specifying a special grain boundary with the above measurement points as crystal grain boundaries and calculating the length.
Measure the total grain boundary length L of the grain boundary in the measurement range, determine the position of the crystal grain boundary where the interface of adjacent crystal grains constitutes the special grain boundary, and the total special grain boundary length of the special grain boundary A grain boundary length ratio Lσ / L between Lσ and the total grain boundary length L of the crystal grain boundary measured above was determined to obtain a special grain boundary length ratio.
The yield strength was determined by a tensile test in which a tensile test piece having a length of 150 mm was collected from each flat base material and pulled in the length direction (rolling direction) by a method specified in JISZ2241.

Next, each flat rectangular substrate before plating in Examples 1 to 6 and Comparative Examples 1 to 6 was passed through a molten solder plating bath while being pulled with a tension of about 10 MPa on the downstream side of the molten solder plating bath. Molten solder plating was applied to produce a solar cell electrode wire. The molten solder plating bath had a solder composition of Sn-3.0% Ag-0.5Cu (melting point: 218 ° C.) and a bath temperature of 300 ° C.

The plating adhesion, plating heat release resistance, and crack resistance of each sample after the molten solder plating were measured. Table 3 shows the measurement results.
The plating adhesion was measured by a plating adhesion test defined in JIS H8504. The dimensions of the test piece were 2 mm in width, 5 mm in length, and 0.15 mm in thickness. The surface of the test piece after the thermal shock was applied was observed with a 4 × magnifier, and the presence or absence and degree of peeling of the film were examined. . The case where no delamination due to thermal shock was observed over the entire surface of the test piece was rated as “◯”, and the case where a layer delamination was observed in part was marked as “X”.

Plating heat-resistant peelability is determined by holding each test piece (width 2 mm, length 5 mm, thickness 0.15 mm) in a constant temperature bath (atmosphere) at 105 ° C. for 500 hours, and then the bending axis is parallel to the rolling direction. 90 ° W bending (R = 0.6, where R is the bending radius (mm)).
A plating peeling test was carried out using a cellophane adhesive tape defined in Z1522, and the case where peeling of the plating layer was not observed by visual observation was evaluated as “◯”, and the case where it was recognized as “X”.
For crack resistance, the crack resistance at the time of assembling and processing a solar cell panel or the like, which was solder-connected to a silicon cell having a length of 150 mm × width 150 mm and a thickness of 200 μm, was examined. A sample in which no crack was observed was rated as ◯, and a sample in which a crack was recognized was marked as ×.

From the results of Table 1, Table 2, and Table 3, the flat substrate of the solar cell electrode wire before plating of the present invention has excellent crack resistance and adheres to the solder plating applied to the surface thereof. It can be seen that the properties are good.

In addition, as described above, an oxygen-free copper plate (Cu: 99.96%, O: 5 ppm, P: 0 ppm) and tough pitch copper (Cu: 99.92%, O made by Mitsubishi Materials Corporation) having a thickness of 3.0 mm. : 300 ppm, P: 0 ppm), hot rolling, intermediate cold rolling (the rolling reduction is shown in Table 4) and annealing in this order to produce an oxygen-free copper sheet and a tough pitch copper sheet, Final cold rolling (the rolling reduction is shown in Table 4) was performed to obtain an oxygen-free copper sheet and a tough pitch copper sheet having a thickness of 0.15 mm. Next, the oxygen-free copper thin plate and the tough pitch copper thin plate were slit with a cutting machine to obtain a flat rectangular plate having a width of 2 mm. Further, these flat rectangular sheets were subjected to final annealing under the conditions shown in Table 4, and the flat rectangular substrates before plating of Examples 11 to 16 and Comparative Examples 11 to 16 were obtained.

The surface roughness Ra, Rz, Rq / Rz of these rectangular substrates, the area ratio of crystal grains in which the average orientation difference between all the pixels in the crystal grains is less than 4 °, and the crystal grains present in the measurement area Area average GAM, 0.2% yield strength was measured. The measurement results are shown in Tables 5 and 6.

The surface roughness Ra, Rz, Rq was measured using a scanning confocal laser microscope LEXT OLS-3000 manufactured by Olympus Corporation on the surface of the sample cut out from each flat substrate, and the laser light was irradiated under the condition of 100 times the objective lens. Irradiation was performed, the distance was measured from the reflected light, and the distance was continuously measured while the laser light was scanned linearly along the surface of the sample.

The area ratio of the crystal grains in which the average orientation difference between all the pixels in the crystal grains is less than 4 ° was determined as follows.
As a pre-treatment, a 2 mm × 2 mm sample collected from a flat substrate was immersed in 10% sulfuric acid for 10 minutes, then washed with water and sprinkled by air blow, and then the sprinkled sample was flat milled by Hitachi High-Technologies Corporation (ion milling) ) The apparatus was subjected to surface treatment at an acceleration voltage of 5 kV, an incident angle of 5 °, and an irradiation time of 1 hour.
Next, the sample surface was observed with a scanning electron microscope S-3400N manufactured by Hitachi High-Technologies Corporation equipped with an EBSD system manufactured by TSL. The observation conditions were an acceleration voltage of 25 kV and a measurement area of 150 μm × 150 μm (including 1000 or more crystal grains).
From the observation results, the area ratio with respect to the total measurement area of the crystal grains in which the average orientation difference between all the pixels in the crystal grains is less than 4 ° was obtained under the following conditions.
At a step size of 0.5 μm, the orientation of all pixels within the measurement area range was measured, and a boundary where the orientation difference between adjacent pixels was 5 ° or more was regarded as a crystal grain boundary. Next, for each crystal grain surrounded by the crystal grain boundary, the average value of the orientation difference between all the pixels in the crystal grain is calculated, and the area of the crystal grain whose average value is less than 4 ° is calculated. Dividing by the total measurement area, the ratio of the area of the crystal grains having an average orientation difference of less than 4 ° in the crystal grains in the total crystal grains was determined. In addition, what connected 2 pixels or more was made into the crystal grain.
The measurement location was changed by this method and measurement was performed 5 times, and the average value of the respective area ratios was defined as the area ratio.

The area average GAM of the crystal grains existing within the measurement area was determined as follows.
As a pre-treatment, a 2 mm × 2 mm sample collected from a flat substrate was immersed in 10% sulfuric acid for 10 minutes, then washed with water and sprinkled by air blow, and then the sprinkled sample was flat milled by Hitachi High-Technologies Corporation (ion milling) ) The apparatus was subjected to surface treatment at an acceleration voltage of 5 kV, an incident angle of 5 °, and an irradiation time of 1 hour.
Next, the surface of the sample was observed with a scanning electron microscope S-3400N manufactured by Hitachi High-Technologies Corporation equipped with an EBSD system manufactured by TSL. The observation conditions were an acceleration voltage of 25 kV and a measurement area of 150 μm × 150 μm (including 1000 or more crystal grains).
From the observation results, the average value of the orientation difference between adjacent pixels in the same crystal grain was determined as follows.
At a step size of 0.5 μm, the orientation of all pixels within the measurement area range was measured, and a boundary where the orientation difference between adjacent pixels was 5 ° or more was regarded as a crystal grain boundary. Next, for each crystal grain surrounded by the crystal grain boundary, the area average GAM of the crystal grain was calculated by the above equation (3). In addition, what connected 2 pixels or more was made into the crystal grain.
The 0.2% proof stress was obtained by a tensile test in which a tensile test piece having a length of 150 mm was sampled from each rectangular base material and pulled in the length direction (rolling direction) by the method specified in JIS Z2241.

Next, while each of the rectangular base materials immediately after the final annealing in Examples 1 to 6 and Comparative Examples 1 to 6 was applied with a tension of about 10 MPa on the downstream side of the molten solder plating bath, the molten solder was pulled. It passed through the plating bath and was subjected to molten solder plating to produce a solar cell electrode wire. The molten solder plating bath had a solder composition of Sn-3.0% Ag-0.5% Cu (melting point: 218 ° C.) and a bath temperature of 300 ° C.

The plating adhesion, plating heat release resistance, and 0.2% proof stress of each sample after the molten solder plating were measured. Table 3 shows the measurement results.
The plating adhesion was measured by a plating adhesion test defined in JIS H8504. The dimensions of the test piece were 2 mm in width, 5 mm in length, and 0.15 mm in thickness. The surface of the test piece after the thermal shock was applied was observed with a 4 × magnifier, and the presence or absence and degree of peeling of the film were examined. . The case where no delamination due to thermal shock was observed over the entire surface of the test piece was rated as “◯”, and the case where a layer delamination was observed in part was marked as “X”.
Plating heat-resistant peelability is determined by holding each test piece (width 2 mm, length 5 mm, thickness 0.15 mm) in a constant temperature bath (atmosphere) at 105 ° C. for 500 hours, and then the bending axis is parallel to the rolling direction. 90 ° W bending (R = 0.6, where R is the bending radius (mm)).
A plating peeling test was carried out using a cellophane adhesive tape defined in Z1522, and the case where peeling of the plating layer was not observed by visual observation was evaluated as “◯”, and the case where it was recognized as “X”.
The 0.2% proof stress was obtained by a tensile test in which a tensile test piece having a length of 150 mm was taken from each electrode wire and pulled in the length direction (rolling direction) by the method specified in JIS Z2241.

From the results of Table 4, Table 5, and Table 6, the flat base material of the solar cell electrode wire before plating formed with the slit material of the pure copper thin plate of the present invention has good adhesion to the solder plating, It can be seen that the 0.2% yield strength increase is small even after solder plating. Moreover, it turns out that the electrode wire for solar cells manufactured by the manufacturing method of this invention is excellent in durability.

As mentioned above, although the manufacturing method of embodiment of this invention was demonstrated, this invention is not limited to this description, A various change can be added in the range which does not deviate from the meaning of this invention.

The present invention provides a flat base material for a solar cell electrode wire before plating formed of a pure copper thin plate slit material having good adhesion to the plating applied to the surface, and has excellent durability. It can be used for battery electrode wires.

DESCRIPTION OF SYMBOLS 1 Solar cell electrode wire 2 Flat base material 3 Solder plating layer 11 Solar cell 12 Semiconductor substrate 13 Linear surface electrode 14 Lead for connection

Claims (5)

1. It is a flat rectangular base material before plating of an electrode wire for a solar cell in which a part or all of the surface is solder-plated, and is formed of a pure copper thin plate slit material containing 99.90% by mass or more of Cu, and the surface arithmetic The average roughness Ra is 0.05 to 0.3 μm, the maximum height Rz is 0.5 to 2.5 μm, and the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0. .06 to 1.1, and the azimuth difference between adjacent measurement points measured by the EBSD method using a scanning electron microscope with a backscattered electron diffraction image system within a depth of 10 μm from the surface is 15 ° or more. The ratio (Lσ / L) of the total special grain boundary length Lσ of the special grain boundary to the total grain boundary length L of the crystal grain boundary (Lσ / L) when the interval between the measurement points is regarded as the crystal grain boundary is 40 to 90% A flat substrate before plating of a solar cell electrode wire.
2. It is a flat rectangular base material before plating of an electrode wire for a solar cell in which a part or all of the surface is solder-plated, and is formed of a pure copper thin plate slit material containing 99.90% by mass or more of Cu, and the surface arithmetic The average roughness Ra is 0.05 to 0.3 μm, the maximum height Rz is 0.5 to 2.5 μm, and the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0. .06 to 1.1, the orientation of all pixels within the measurement area of the surface is measured with an EBSD method using a scanning electron microscope with a backscattered electron diffraction image system, with a step size of 0.5 μm, and adjacent to each other. When the boundary where the orientation difference between the pixels is 5 ° or more is regarded as a crystal grain boundary, the area ratio of the crystal grains where the average orientation difference between all the pixels in the crystal grain is less than 4 ° is the measurement area. 80-95%, existing within the measurement area A flat substrate before plating of an electrode wire for a solar cell, wherein the area average GAM of crystal grains is less than 4 °.
3. A pure copper sheet containing 99.90% by mass or more of Cu is subjected to hot rolling, intermediate cold rolling, annealing, and final cold rolling in this order to form a pure copper sheet, and the sheet is slitted with a cutting machine to have a rectangular shape. In the method of manufacturing a flat base material before plating of a solar cell electrode wire by subjecting the flat base material to final annealing, the intermediate cold rolling is performed at a reduction rate of 50 to 70%. The rectangular shape before plating of the electrode wire for a solar cell, wherein the rolling reduction of the final cold rolling is performed at 50 to 70%, and the final annealing is performed at 200 to 400 ° C. for 150 to 240 minutes. A method for producing a substrate.
4. A pure copper sheet containing 99.90% by mass or more of Cu is subjected to hot rolling, intermediate cold rolling, annealing, and final cold rolling in this order to form a pure copper sheet, and the sheet is slitted with a cutting machine to have a rectangular shape. In the method of manufacturing a flat base material before plating of a solar cell electrode wire by subjecting the flat base material to final annealing, the intermediate cold rolling is performed at a reduction rate of 50 to 70%. The plating of a solar cell electrode wire, wherein the rolling reduction of the final cold rolling is performed at 50 to 70%, and the final annealing is performed in an atmosphere of 700 to 900 ° C. for 5 to 60 seconds. The manufacturing method of the previous flat base material.
5. It is manufactured by applying solder plating to a thickness of 40 to 150 μm on a part or all of the surface of the flat substrate before plating of the electrode wire for solar cell manufactured by the manufacturing method according to claim 3 or 4. Solar cell electrode wire.

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