JP2009016593A - Electrode wire for solar cell, its base material, and manufacturing method of base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode wire for a solar cell having excellent plastic deformability relative to a conventional one; its base material; and a manufacturing method of a base material. <P>SOLUTION: This base material of this electrode wire 1 for a solar cell before plating with molten solder plating applied to a surface of the base material 2 is formed of a rolled material of pure copper containing 99.90 mass% of Cu. When peak intensities by X-ray diffraction of crystal orientations <100>, <114> and <112> in the rolling direction are represented by P<100>, P<114> and P<112>, respectively, a peak intensity ratio PR (%) of the crystal orientations of <114> and <112> represented by expression: PR (%) =( P<114>+P<112>)*100/(P<100>+P<114>+P<112>) is set to 50-90%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode wire used as a connecting lead wire of a solar cell and a base material thereof.

  A solar cell is a connection that is soldered to a semiconductor substrate formed of a silicon semiconductor having a PN junction and a solder band provided so as to cross a plurality of surface electrodes provided linearly on the surface of the semiconductor substrate. For use with lead wires. Usually, 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 lead 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.

  Conventionally, the electrode wire used as the material of the connecting lead wire is based on a crushed copper wire that is rolled and flattened by rolling a copper wire having a round cross section formed of tough pitch copper, and the surface thereof is a molten solder. What was laminated | stacked and formed the plating layer was used. However, in recent years, with the thinning of the substrate, there has been a problem that the substrate is cracked when the electrode wire is brazed to the substrate. This is because the thermal expansion coefficient of copper forming the base material of the electrode wire is larger than that of the semiconductor substrate, and the shrinkage of the electrode wire is constrained by the substrate during cooling shrinkage after brazing, and as a reaction, stress is applied to the substrate. This is because it is generated.

In order to solve such a problem, as described in International Publication WO 2005/114751 (Patent Document 1), the present inventors have used pure copper whose proof stress is reduced to 19.6 to 85 MPa. A solar cell electrode wire was proposed in which the formed substrate was subjected to molten solder plating. According to such an electrode wire, since the base material of the electrode wire is plastically deformed by itself during cooling shrinkage after brazing and the restraint by the substrate is reduced, the stress generated on the substrate is also reduced, and the substrate is prevented from being damaged. Can do.
International Publication WO 2005/114751

  Conventionally, a semiconductor substrate having a thickness of about 200 to 250 μm has been used as a thin semiconductor substrate. However, in recent years, there has been a tendency to reduce the thickness of the substrate for cost reduction. In particular, this trend has become more prominent with the recent increase in raw materials.

  For this reason, even the electrode wire proposed in the above-mentioned Patent Document 1 cannot be said to have sufficient breakage resistance to the semiconductor substrate, and a further plastic deformability is required. This invention is made | formed in view of this problem, and it aims at providing the manufacturing method of the electrode wire for solar cells provided with the plastic deformation ability superior to the conventional electrode wire, the base material, and a base material.

  The present inventor rolled a pure copper sheet at various rolling reductions, cut it linearly along the rolling direction, and then softened and annealed to produce a base material. Depending on the rolling conditions, the base material yield strength was significantly reduced. I found out that Then, when the crystal orientation with respect to the rolling direction of the base material was examined by X-ray diffraction, <100>, <114>, <112> were dominant, and in the base material having a low yield strength, <114>, <112 > Was found to be more dominant. The present invention has been made based on such findings.

The base material which concerns on 1st form of this invention is a base material before the plating of the electrode wire material for solar cells by which the surface of the base material was hot-melt-plated, Comprising: The said base material is 99.90 mass% of Cu. The peak intensities by X-ray diffraction of the crystal orientations <100>, <114>, <112> in the rolling direction are P <100>, P <114>, P <112> respectively. When expressed, the peak intensity ratio PR (%) of crystal orientations <114> and <112> shown in the following formula is 50 to 90%.
PR (%) = (P <114> + P <112>) / 100 / (P <100> + P <114> + P <112>)

  According to the base material of the present invention, the peak strength ratio PR (%) of <114> and <112> crystal orientation with respect to the rolling direction is 50 to 90%, so that the proof stress in the rolling direction is reduced to about 15 MPa or less. be able to. For this reason, it becomes easy to be plastically deformed in the rolling direction, and by using an electrode wire material that has been subjected to molten solder plating on the base material, even if the semiconductor substrate is shrunk in the shrinkage after cooling, the base material However, since it is easily plastically deformed, it has excellent breakage resistance against a semiconductor substrate.

  The pure copper forming the substrate preferably regulates impurities O and P to O: 0 to 500 ppm and P: 0 to 150 ppm. Impurities contained in pure copper include As, Sb, Bi, Pb, S, Fe, etc. in addition to O and P. However, since O and P are very small, their plastic deformability decreases, so these are within the above range. By restricting, it is possible to easily reduce the strength of the base material in combination with the control of the crystal orientation.

  It is preferable that the base material is formed with a molten solder accommodating recess along the length direction. By providing the molten solder accommodating recess, when the molten solder supplied to the recess is solidified, the central portion of the molten solder is difficult to swell and tends to be flat. For this reason, the electrode wire material obtained by subjecting the base material to molten solder plating is improved in solderability by soldering the flattened molten solder layer to the semiconductor substrate.

  Moreover, the electrode wire for solar cells of the present invention comprises the above base material and a molten solder plating layer formed on the surface of the base material. The yield strength of the base material is greatly reduced, and therefore the yield strength of the electrode wire after hot-dip solder plating is also lowered. Therefore, according to the solar cell electrode wire according to the present invention, the breakage resistance to the semiconductor substrate is improved. Can be improved.

  Moreover, the manufacturing method of the base material of the electrode wire material for solar cells of this invention performs intermediate rolling and intermediate annealing with respect to the pure copper plate which contains 99.90 mass% or more of Cu, and is a final reduction rate of 55-90% after that. Rolling is performed to obtain a plate-shaped intermediate material, and the plate-shaped intermediate material is cut into a line along the rolling direction to obtain a line-shaped intermediate material, and the linear intermediate material is subjected to final annealing. In the pure copper plate, O and P, which are impurities, are preferably O: 0 to 500 ppm and P: 0 to 150 ppm. Conventionally, in order to anneal and soften a rolled copper material, it has been considered effective to perform rolling and annealing at a reduction rate of about 95% in the final rolling.

  By setting the rolling reduction of the final rolling as low as 55 to 90%, the peak intensity ratio PR (%) of the crystal orientation of <114> and <112> with respect to the rolling direction of the linear base material after annealing is 50 to 90. %. Moreover, since the final annealing is performed on the linear intermediate material after the cutting process, it can be recrystallized by heating in a short time, and the base material having the specific crystal orientation can be easily and efficiently manufactured. .

  According to the base material of the present invention, it is formed of a rolled material of pure copper containing 99.90 mass% or more of Cu, and a peak intensity ratio PR (%) of <114> and <112> crystal orientation with respect to the rolling direction is 50 to 90. %, The electrical conductivity is excellent, and the proof stress in the rolling direction can be reduced to about 15 MPa or less, and an excellent plastic deformability is provided. For this reason, the electrode wire material obtained by subjecting the base material to molten solder plating has excellent breakage resistance with respect to the semiconductor substrate, and is suitable as a wiring material for a solar cell of a semiconductor substrate that is thinner than the conventional one.

  Hereinafter, an electrode wire and a substrate thereof according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross section of an electrode wire 1 according to the first embodiment. A linear base material 2 having a rectangular cross section formed of pure copper containing 99.90 mass% or more of Cu, and the base material 2 Are provided on the outer peripheral surface of the molten solder plating layers 3A and 3B. In addition, although the molten solder plating layer is laminated | stacked only on the surface and the back surface of the base material 2 in the example of a figure, in fact, it forms inevitable also on the side surface of the base material 2. In FIG. 1 and FIG. 2 described later, the description of the molten solder plating layer on the side surface of the substrate is omitted.

  The pure copper has a Cu content of 99.90 mass% or more. Preferably it is 99.95 mass% or more, more preferably 99.99 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 300 ppm, more preferably 0 to 100 ppm, and the amount of P is desirably 0 to 150 ppm, preferably 0 to 50 ppm. Tappitch copper, oxygen-free copper (OFHC), and phosphorus deoxidized copper are suitable materials because they satisfy the above components.

The base material 2 represents peak intensities by X-ray diffraction of crystal orientations <100>, <114>, and <112> with respect to the rolling direction as P <100>, P <114>, and P <112>, respectively. The peak intensity ratio PR (%) of crystal orientations <114> and <112> shown in the following formula is set to 50 to 90%.
PR (%) = (P <114> + P <112>) / 100 / (P <100> + P <114> + P <112>)

  Conventionally, the rolled material after squeezing the final rolling and annealing is easy to align the crystal orientation in the rolling direction to <100>. However, according to the investigation of the present inventors, <114> and < It has been found that a crystal orientation of 112> as a main component is effective in improving the plastic deformability. As will be apparent from the examples described later, when the PR is less than 50% and more than 90%, the proof stress once lowered increases. For this reason, in the present invention, the PR is set to 50 to 90%, preferably 65 to 85%.

  As a solder material for forming the molten solder plating layers 3A and 3B, Sn—Pb alloy having a melting point of about 130 to 300 ° C., Sn— (0.5 to 5 mass%) Ag alloy, Sn— (0.5 to 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 or the like is 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 preferable. Further, in each of the solder materials, in order to prevent the molten solder from being oxidized, one of the 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. Seeds or two or more can be added.

  FIG. 2 shows an electrode wire 1A according to the second embodiment. Since the cross-sectional shape thereof is different from that of the first embodiment, the explanation will be focused on the same. Omitted. The cross-sectional shape of the substrate 2A of the electrode wire 1A is such that the central portion of one surface (the lower surface in the illustrated example) is flat along the length direction, whereas the substrate of the first embodiment is rectangular. It has a dish-shaped cross section that is recessed in a shape, and the recessed side is a recessed portion 6 for accommodating molten solder. The material of the substrate 2A and the crystal orientation in the rolling direction are the same as in the first embodiment.

  The depth of the molten solder accommodating recess 6 may be about 20 to 40 μm at the deepest portion, and the opening width is preferably about 90% or more of the lateral width of the substrate 2A. The upper limit of the opening width is not particularly limited, and it may be opened over the entire bottom surface. In addition, the cross-sectional shape of the recessed part for accommodating a molten solder is not limited to the above-mentioned dish shape, and may be an arcuate cross section in which the whole is recessed in an arc shape.

  In the base material 2A having the molten solder accommodating recess 6, when the solder 2 is plated on the base 2 A, a molten solder plating layer 3 B whose surface is substantially flat due to the action of surface tension is formed in the recess 6. The Since the surface of the molten solder plating layer 3B is substantially flat, good solderability can be obtained.

  Next, the manufacturing method of the base material and electrode wire according to the first and second embodiments will be described. First, a plate material (rolled plate or rolled annealed plate) made of pure copper of a predetermined purity is prepared, and this is subjected to intermediate rolling and intermediate annealing (softening annealing) as many times as necessary, and then the final rolling. To obtain a plate-like intermediate material having a target plate thickness. The target plate thickness is the thickness of the substrate, and is usually about 80 to 300 μm.

  The plate-like intermediate material is usually slit along the rolling direction so as to have a width of about 0.8 to 15 mm to be a long linear intermediate material. The linear intermediate material is subjected to final annealing (softening annealing) to obtain a linear base material. By adjusting the interval and rotation speed of the slitting blades at the time of slitting, the dish-shaped recess for accommodating molten solder can be easily formed in the linear intermediate material.

  The rolling reduction in the intermediate rolling may be about 20 to 80% and is not particularly limited, but the rolling reduction in the final rolling is 55 to 90%, preferably 65 to 85%. If it is less than 55% and more than 90%, it becomes difficult to obtain a crystal structure in which the crystal orientations <114> and <112> are dominant with respect to the rolling direction, and the plastic deformability is lowered. The softening annealing temperature in the intermediate annealing and final annealing is about 850 to 1000 ° C., and the holding time is about 30 to 60 seconds at 850 to 950 ° C. and about 10 to 60 seconds at 950 to 1000 ° C.

  Next, the finally annealed linear base material is subjected to molten solder plating. In the molten solder plating, a winding drum having a large diameter is provided on the downstream side of the molten solder plating bath, the linear substrate is passed through the plating bath, and the wire is wound while being pulled with a tension of about 10 MPa. This is done by continuously immersing the substrate in a molten solder plating bath and pulling it up. The plating temperature is adjusted to a temperature about 50 to 100 ° C. higher than the melting point of the solder alloy. By molten solder plating, a molten solder plating layer is formed on the surface of the linear base material to obtain a linear electrode wire. In the case of a linear base material in which a molten solder accommodating recess is formed, a flat molten solder plating layer is formed on the recess side only by passing through a molten solder plating bath.

  During the molten solder plating, the linear base material is pulled, and strain is introduced into the linear base material. For this reason, the proof stress of a base material rises about 2 times compared with plating. However, since the proof stress of the base material before plating is as low as about 15 MPa or less, even after plating, it is kept at a sufficiently low value as compared with the conventional case. In addition, after cut | disconnecting a linear base material to predetermined length, it is good also as an electrode wire material by performing molten solder plating to this short base material. In this case, since the tension is not applied to the substrate during plating, the proof strength of the electrode wire is further reduced.

  As described above, a base material on which a molten solder plating layer is laminated, that is, an electrode wire is manufactured, and a member cut to a required length is used as a connecting lead wire of a solar cell.

A solar cell using the electrode wire according to the embodiment as a connecting lead wire will be described with reference to the drawings. FIG. 3 shows a solar cell including the connection lead wire 13 obtained by cutting the electrode wire 1 or 1A according to the embodiment into a predetermined length. This solar cell includes a semiconductor substrate 11 formed of a silicon semiconductor having a PN junction, and the connecting lead wires 13 soldered to a plurality of surface electrodes 12 linearly provided on the surface of the semiconductor substrate 11. I have. On the back surface of the semiconductor substrate 11, a plurality of back electrodes having a large surface of about 40 to 80 mm ² are provided.

The semiconductor substrate 11 before the connection lead wire 13 is soldered is formed with a solder band arranged perpendicular to the surface electrodes 12 so as to be electrically connected to the plurality of linear surface electrodes 12. Yes. The connecting lead wire 13 is placed on the semiconductor substrate 11 so that the molten solder plating layer 3A or 3B of the electrode wire 1 or the molten solder plating layer 3B of the electrode wire 1A on the recessed portion for accommodating the molten solder contacts the solder band. Then, the connecting lead wire 13 is soldered to the surface of the semiconductor substrate 11 by melting the solder band of the semiconductor substrate 11 and the molten solder plating layer of the connecting lead wire 13 together. Since the back electrode has a relatively large exposed area (about 40 to 80 mm ² ), soldering to the back electrode of the adjacent solar cell is easier than soldering to the front electrode.

  According to this solar cell, when soldering the connecting lead made of the electrode wire to the semiconductor substrate, the semiconductor substrate easily deforms plastically even if the electrode wire is restrained by the semiconductor substrate due to cooling shrinkage after heating. It is possible to relieve and reduce the stress generated in. For this reason, it is difficult for cracks to enter the semiconductor substrate, and the base material of the electrode wire is high-purity pure copper, so that it has excellent electrical conductivity and good power generation efficiency.

  Hereinafter, although an example is given and an electrode wire material and the substrate of the present invention are explained concretely, the present invention is not limitedly interpreted by this example.

  Rolled annealed sheet of pure copper A (oxygen-free copper, Cu: 99.96%, O: 5 ppm, P: 0 ppm) or pure copper B (tough pitch copper, Cu: 99.92%, O: 300 ppm, P: 0 ppm) Thickness 3.0 mm) is prepared, and intermediate rolling in the cold and intermediate annealing (1000 ° C. × 30 sec) are each performed once to obtain an intermediate material having a thickness of 0.2 to 2.0 mm, as shown in Table 1. The final rolling was performed cold at a reduction rate to produce a plate-like intermediate material having a plate thickness of 0.1 mm. This was slit to a width of 3 mm, and the obtained plurality of linear intermediate materials were passed through a tunnel furnace under the conditions shown in the same table, and finally annealed to obtain a plurality of linear substrates. Some of the plurality of linear substrates were subjected to molten solder plating by passing 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. The plating bath had a solder composition of Sn-3.0 mass% Ag-0.5 mass% Cu (melting point: 218 ° C) and a bath temperature of 300 ° C. In addition, the other part of the plurality of linear substrates was heated by passing through a salt bath under the same bath temperature and wiring conditions as those of the molten solder plating.

The linear base material after the final annealing is cut perpendicularly to the rolling direction, and an observation piece is collected. By using an X-ray diffraction method (Schulz reflection method), a surface perpendicular to the rolling direction is used as a reflecting surface, and the rolling direction Of the crystal orientations <100>, <114>, and <112>, and the intensity ratio (%) of each orientation when the sum of the three intensities is 100, and <114> and <112> The azimuth peak intensity ratio PR (%) was determined. These are also shown in Table 1. The X-ray diffraction apparatus used was RINT-2200 (manufactured by RIGAKU), and the measurement conditions were as follows.
Measurement conditions: Scanning axis 2θ / θ, angle measurement range 10 ° to 90 °, divergence slit 0.15 mm, scattering slit 4 mm, light receiving slit 5 mm

  Further, a tensile test piece having a length of 150 mm was collected from the linear base material and subjected to a tensile test by pulling in the length direction (rolling direction) by a method defined in JISZ2241, and the proof stress before plating was measured. The measurement results are also shown in Table 1.

  Furthermore, the salt adhering to the surface was removed from the linear base material passed through the salt bath by washing with water, and the proof stress in the rolling direction was measured in the same manner as the linear base material. Since this proof stress was equivalent to the proof strength of the base material which carried out the hot-dip solder plating, it was considered as the proof strength of the base material after plating. The measurement results are also shown in Table 1.

  From Table 1, since the proof stress before plating of the base material according to the invention example is 15 MPa or less, the proof stress after plating is about 30 MPa or less, which is a low proof stress. Sample No. 12, which is a conventional base material, Compared to 32, it was confirmed that the yield strength was greatly reduced.

It is a cross-sectional view of the electrode wire according to the first embodiment of the present invention. It is a cross-sectional view of the electrode wire material concerning 2nd Embodiment of this invention. It is a schematic perspective view of the solar cell using the electrode wire of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A Electrode wire material 2,2A Base material 3A, 3B Molten solder plating layer 6 Concave part for molten solder accommodation

Claims (6)

It is a base material before plating of an electrode wire for a solar cell in which molten solder plating is applied to the surface of the base material,
The base is formed of a rolled material of pure copper containing 99.90 mass% or more of Cu, and the peak intensities by X-ray diffraction of crystal orientations <100>, <114>, and <112> in the rolling direction are P <100>, respectively. When represented by P <114> and P <112>, the peak intensity ratio PR (%) of the crystal orientation of <114> and <112> shown in the following formula is 50 to 90%. Wood.
PR (%) = (P <114> + P <112>) / 100 / (P <100> + P <114> + P <112>)   The said pure copper is a base material of the electrode wire material for solar cells of Claim 1 by which O and P which are impurities were O: 0-500 ppm and P: 0-150 ppm.   The said base material is a base material of the electrode wire material for solar cells of Claim 1 or 2 in which the recessed part for molten solder accommodation was formed along the length direction.   A solar cell electrode wire having a surface of the base material subjected to molten solder plating, wherein the base material according to any one of claims 1 to 3 is used as the base material. .   Intermediate rolling and intermediate annealing are performed on a pure copper plate containing 99.90 mass% or more of Cu, and then final rolling with a rolling reduction of 55 to 90% is performed to obtain a plate-like intermediate material. A method for producing a substrate for an electrode wire for a solar cell, wherein a linear intermediate material is obtained by cutting into a linear shape along a rolling direction, and the linear intermediate material is subjected to final annealing.   The said pure copper is a manufacturing method of the base material of the electrode wire material for solar cells of Claim 5 by which O and P which are impurities were O: 0-500 ppm and P: 0-150 ppm.

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