JP2012114260A - Solar cell electrode wire rod and base material thereof and base material manufacturing method - Google Patents

Abstract

A flat rectangular base material for an electrode wire for a solar cell before plating, which is formed by a slit material of a pure copper thin plate having good adhesion to solder plating and little increase in 0.2% yield strength after solder plating, A manufacturing method and an electrode wire for solar cells excellent in durability are provided.
It is formed of a pure copper sheet slit material containing 99.90% by mass or more of Cu, and has an arithmetic average roughness Ra of 0.05 to 0.3 μm and a maximum height Rz of 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 all pixels within the measurement area of the surface with a step size of 0.5 μm by the EBSD method. Of the crystal grains in which the average orientation difference between all the pixels in the crystal grain is less than 4 degrees when the boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as the grain boundary. The area ratio 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 °.
[Selection] Figure 1

Description

  The present invention relates to an electrode wire for solar cells, a base material thereof, and a method for producing the base material, and in particular, has good adhesion to solder plating applied to the surface, and 0.2% yield strength after solder plating. The present invention relates to a flat substrate for a solar cell electrode wire formed of a slit material of a pure copper thin plate with a small increase in the temperature and a method for producing the same.

  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, and high purity Cu (99.9999% or more). After hot rolling, cold rolling and annealing of pure copper plate such as tough pitch Cu, oxygen free Cu, phosphorus deoxidized Cu, high purity Cu (99.9999% or more) in a rolling mill 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, there has been a problem that the semiconductor substrate is cracked when the connecting electrode wire is brazed to the semiconductor substrate. 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 are disclosures about the electrode wire base material for solar cells with excellent plastic deformability, it is improved after adhesion and the adhesion between the flat electrode material used as the base material and the solder plating applied to the surface thereof There is no disclosure of measures for preventing the 0.2% proof stress from increasing due to the Cu—Sn alloy layer.
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. No disclosure has been made about measures for improving the adhesion with solder plating applied to the surface and preventing the 0.2% proof stress from increasing due to the Cu—Sn alloy layer formed after solder plating.

  The present invention provides an electrode wire for a solar cell before plating, which is formed of a pure copper thin plate slit material having good adhesion to the solder plating applied to the surface and little increase in 0.2% proof stress after solder plating. An object of the present invention is to provide a flat rectangular substrate, a method for producing the same, and an electrode wire for a solar cell excellent in durability.

As a result of intensive investigations in view of the above circumstances, the inventors of the present invention have been subjected to hot rolling, intermediate cold rolling, annealing, and final cold rolling on a pure copper plate containing 99.90% by mass or more of Cu, and a pure copper sheet material A thin plate material is slit with a cutting machine, and further subjected to final annealing to produce a flat base material, and a solar cell electrode wire having a part or all of its surface plated with solder. When manufacturing, a rectangular base material before plating is formed of a pure copper thin plate slit material containing 99.90% by mass or more of Cu, and the step size is measured by an EBSD method using a scanning electron microscope with a backscattered electron diffraction image system. Crystal grains when measuring the orientation of all pixels within the measurement area of the surface of a flat substrate at 0.5 μm and considering a boundary where the orientation difference between adjacent pixels is 5 ° or more as a grain boundary The average azimuth difference between all pixels is 4 ° When the area ratio of the crystal grains that are full 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 °, the surface is hard after solder plating. And a brittle Cu—Sn alloy layer, mainly a Cu ₆ Sn ₅ layer, was hardly formed, and it was found that 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% yield strength 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. When the ratio Rq / Rz of Rz is 0.06 to 1.1, the adhesion with solder plating applied to 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 formed of a slit material of a pure copper thin plate 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 with an average misorientation of less than 4 ° is It 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 °.

  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

  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 in that it is carried out in an atmosphere of 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 existing in the measurement area within a predetermined range, and final annealing at 700 to 900 ° C. Is held in the atmosphere for 5 to 60 seconds, the average orientation difference between all the pixels in the crystal grain is 4 ° when a boundary where the orientation difference between adjacent pixels is 5 ° or more is regarded as a grain boundary. 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 in the slit processed material.

Furthermore, the electrode wire for solar cells 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 cells manufactured by the manufacturing 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.
Moreover, it is preferable that the solder plating is 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 yield strength of the electrode wire for solar cells. A large-diameter winding drum is provided on the downstream side, and the rectangular substrate immediately after the final annealing is passed through a solder plating bath adjusted to a temperature higher by about 50 to 100 ° C. 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 base material for an electrode wire for a solar cell before plating, which is formed of a slit material of a pure copper thin plate having good adhesion to solder plating and little increase in 0.2% proof stress after solder plating In addition, a solar cell electrode wire excellent in durability 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.

Hereinafter, with reference to drawings, one embodiment of the electrode wire for solar cells of the present invention, its substrate, and a manufacturing method is described.
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 flat substrate 2 has a Cu content of 99.90% by mass or more, preferably 99.99% by mass or more. Further, as impurities, As, Sb, Bi, Pb, S, Fe, O, P, etc. are included. Particularly, since O and P are small amounts and the plastic deformability is reduced, the amount of O is preferably 0 to 500 ppm, preferably Is 0 to 100 ppm, and the P content is 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 substrate, and the flat substrate 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, the ratio of the root mean square roughness Rq to the maximum height Rz (Rq / Rz) is 0.06 to 1.1, and the backscattered electron diffraction image system is attached. The orientation of all pixels within the measurement area of the surface of the flat substrate 2 is measured with a step size of 0.5 μm by an EBSD method using a scanning electron microscope, and the orientation difference between adjacent pixels is 5 ° or more. Between all pixels in a crystal grain when the boundary is regarded as a grain boundary Area ratio of crystal grains average misorientation is less than 4 ° is a 80% to 95% of the measured area, the crystal grains of the area average GAM that 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

  Further, 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 When / Rz) is less than 0.06, the adhesion with solder plating or hot-dip 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 plating adhesion is insufficient, and if the plating thickness exceeds 150 μm, the yield strength of the solar cell electrode wire increases, 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.

In addition, 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 mass%) Ag- (0.3-1.0 mass%) Cu alloy, Sn- (0.3-1.0 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 Sn—Ag—Bi alloy is particularly preferable.
Moreover, 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.

  Such a 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 rolling reduction of the intermediate cold rolling is performed at 50 to 70%, and the final cold rolling is performed. It is important that the rolling reduction 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 existing in the measurement area within a predetermined range, and the final annealing is 700 to 900 ° C. By maintaining the atmosphere in 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 this case, 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 measurement 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.

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 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 large-diameter winding drum is provided on the downstream side of the solder plating bath, rather than the method of performing solder plating on this short substrate, and the rectangular substrate 2 immediately after final annealing is soldered. It is passed through a solder plating bath adjusted to a temperature about 50-100 ° C. higher than the melting point of the alloy, wound while pulling with an appropriate tension, whereby the flat substrate 2 is continuously immersed in the solder plating bath, It is preferable from a viewpoint of manufacturing cost to be performed by the method of pulling up. 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.

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, a plurality of back electrodes having a large surface of about 40 to 80 mm ² are provided. On the semiconductor substrate 12 before the connection 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 thin plates were subjected to final annealing under the conditions shown in Table 1 to obtain flat rectangular base materials before plating in Examples 1 to 6 and Comparative Examples 1 to 6.

  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 2 and 3.

  The surface roughness Ra, Rz, and Rq were measured using a scanning confocal laser microscope LEXT OLS-3000 manufactured by Olympus Corporation on the surface of a sample cut out from each rectangular 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 pretreatment, a 2 mm × 2 mm sample collected from a flat substrate was immersed in 10% sulfuric acid for 10 minutes, then rinsed with water and air blown. ) 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 with air blow, and 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 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 soldering each flat rectangular substrate immediately after the final annealing of Examples 1 to 6 and Comparative Examples 1 to 6 with a tension of about 10 MPa on the downstream side of the molten solder plating bath, molten solder 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 partially 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 bend (R = 0.6, where R is the bend radius (mm)), and the surface of the bent portion is subjected to a plating peeling test using a cellophane adhesive tape specified in JISZ1522. 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 “×”.
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 1, Table 2, and Table 3, the flat substrate 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, such as performing appropriate intermediate annealing between intermediate cold rolling and final cold rolling. Various modifications can be made without departing from the spirit of the invention.

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 (3)

  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 at 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% to 95%, and the presence of the crystals 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 °.   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 producing a flat base material before plating of a solar cell electrode wire by subjecting the flat base material to final annealing, a reduction rate of the intermediate cold rolling is performed at 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.   A solar battery manufactured by applying solder plating to a thickness of 40 to 150 μm on part or all of the surface of a flat substrate before plating of an electrode wire for a solar battery manufactured by the manufacturing method according to claim 2. Battery electrode wire.

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