JP2008182171A - Solder-plated wire for solar cell and manufacturing method thereof, and solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost solder-plated wire for a solar cell that has a strength lower by 0.2% as compared with a conventional solder-plated wire for a solar cell with tough-pitch copper (TPC) as a conductive material and has 0.2% strength equal to or lower than that of the conventional solder-plated wire for a solar cell with oxygen-free copper (OFC) as a conductor material, to provide a method of manufacturing the solder-plated wire for a solar cell, and to provide the solar cell. <P>SOLUTION: In the solder-plated wire 2 for a solar cell, the surface of a conductor 3 of which a section is formed in a flat-square shape is covered with solder plating 4 partially or wholly for joint to the solar cell 1. In this case, the conductor 3 is made of copper, and a copper material that is an inevitable impurity. The copper contains a sulfur affinity metal of one kind or not less than one kind selected from Nb, Ti, Zr, V, Ta, Fe, Ca, Mg, or Ni and has oxygen content exceeding 10 massppm at the remaining section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solar cell connection lead wire and a manufacturing method thereof, and more particularly to a solar cell solder plating wire suitable for solder connection with a silicon cell of a solar cell, a manufacturing method thereof, and a solar cell.

  A general solar battery cell has a light receiving surface and a flat plate shape, and has a structure in which electrodes are formed on a surface (lower surface) opposite to the light receiving surface (upper surface). A connection lead wire for connecting a plurality of solar cells is made of a rectangular copper foil or the like. As shown in FIG. 2, one end of the connection lead wire 2 is a light receiving surface (upper surface) of the solar cell 1. The other end is connected to the surface (lower surface) facing the light receiving surface of the solar battery cell 1 using solder or the like, and usually a plurality of solar battery cells 1 are connected in series. As shown in FIG. 3, the connecting lead wire 2 is formed with a solder plating 4 on the surface of a flat conductor 3 for connection with a solar battery cell.

  By the way, since the silicon crystal wafer (solar cell) occupies most of the material cost among the members constituting the solar cell, the silicon crystal wafer is being made thinner in order to reduce the manufacturing cost. However, when the silicon crystal wafer is thinned, as shown in FIG. 4B, due to the heating process at the time of soldering the connecting lead wire 2 shown in FIG. The entire solar battery cell 1 to which the connecting lead wire 2 is soldered may be warped and damaged.

  In order to prevent such warpage and damage of the solar battery cell, in recent years, a conductive material having a small difference in thermal expansion coefficient from that of a silicon crystal wafer has been used as a connecting lead wire. As such a material, there are a three-layer clad material provided with a copper layer, a kovar layer, and a copper layer, or a three-layer clad material provided with a copper layer, an invar layer, and a copper layer, and the outer periphery thereof is substantially entirely covered. A solder-plated material is known (for example, Patent Document 1).

  However, when the three-layer clad material described in Patent Document 1 is used as a connecting lead wire, the thermal stress generated in the solar cell can be reduced, but the Kovar layer having a relatively high volume resistivity. In addition, since the invar layer is used as an intermediate layer, there is a problem that the average electric resistance is increased and the power generation efficiency of the solar cell is lowered.

  In view of such circumstances, the surface of a core material made of an annealed material made of pure copper having a volume resistivity of 2.3 μΩ · cm or less, a proof stress of 19.6 to 85 MPa, and an oxygen content of 20 massppm or less. In addition, a solar cell electrode wire having a molten solder plating layer has been studied (for example, Patent Document 2).

  As the types of Cu in the connection lead wires for solar cells, tough pitch copper, oxygen-free Cu, high-purity copper (purity 99.9999% or more), and the like are considered. It has been found that Cu having a high purity is advantageous for minimizing the 2% proof stress, and examples thereof include oxygen-free Cu and high-purity copper (purity of 99.9999% or more) ( Patent Document 3).

JP 2006-73706 A International Publication No. 2005/114751 Pamphlet JP 2006-276709 A

  When manufacturing connection lead wires for solar cells using a continuous casting apparatus using oxygen-free Cu and high-purity copper (purity 99.9999% or more), a step of deoxidizing the copper base material in the manufacturing process, etc. The manufacturing process such as the control becomes complicated, and the manufacturing cost is high, such as requiring large-scale equipment for continuous melting and casting of high-purity copper in non-oxidation protective gas (CO). There is.

  For this reason, a copper material having a relatively soft oxygen characteristic such as tough pitch copper, which has a relatively large oxygen content, is industrially easy to handle and inexpensive, and at least equal to or more than oxygen-free Cu. The development and examination of is urgently needed.

  An object of the present invention is 0.2% lower in proof stress than a conventional solder-plated wire for solar cells using tough pitch copper (TPC) as a conductive material, and for conventional solar cells using oxygen-free copper (OFC) as a conductive material. An object of the present invention is to provide a solar cell solder plated wire having a 0.2% proof stress equal to or lower than that of a solder plated wire and a low cost, a manufacturing method thereof, and a solar cell.

In order to achieve the above object, the invention of claim 1 is a solar battery solder in which a solder plating is coated on a part or all of the surface of a conductor having a rectangular cross section so as to be joined to a solar battery cell. In plated wire,
Copper containing one or more sulfur-affinity metals selected from Nb, Ti, Zr, V, Ta, Fe, Ca, Mg, or Ni, with the remainder having an oxygen content of more than 10 massppm And it is comprised with the copper material which is an unavoidable impurity, It is the solder plating wire for solar cells characterized by the above-mentioned.

  The invention according to claim 2 is the solder plated wire for a solar cell according to claim 1, wherein the conductor contains 0.0007 to 0.04 mass% of the sulfur affinity metal.

  The invention according to claim 3 is the solder plated wire for a solar cell according to claim 1 or 2, wherein the conductor has a crystal grain size of 270 µm or less.

  A fourth aspect of the present invention is a solar battery characterized in that the solar cell solder-plated wire according to any one of the first to third aspects and a solar battery cell are solder-connected.

The invention of claim 5 is a method of producing a solar cell solder-plated wire from a molten copper using a continuous casting and rolling apparatus,
One or two kinds selected from Nb, Ti, Zr, V, Ta, Fe, Ca, Mg, or Ni in the molten copper stored in the molten metal storage means of the continuous casting and rolling apparatus and having an oxygen content exceeding 10 massppm. After adding the above sulfur-affinity metal, adjusting the ratio of the sulfur-affinity metal contained in the molten copper to 0.0007 to 0.04 mass%, and manufacturing the roughing material using the molten copper A method for producing a solder-plated wire for a solar cell, characterized in that the roughing material is subjected to cold drawing with a reduction in area of 30% or more, and the cold-worked material is subjected to heat treatment at 190 to 750 ° C. is there.

  Invention of Claim 6 is a manufacturing method of the solder plating wire for solar cells of Claim 5 which heat-processes at 400-750 degreeC to the said cold work material.

  The invention according to claim 7 is the method for producing a solder-plated wire for a solar cell according to claim 5 or 6, wherein the heat treatment is performed by a batch-type heating method or a current heating method using a heater.

  According to the solder plated wire for solar cell of the present invention, 0.2% lower proof stress than conventional solder plated wire for solar cell using tough pitch copper (TPC) as a conductor material, and oxygen free copper (OFC) as a conductor material. Thus, 0.2% proof stress equivalent to or lower than that of the conventional solder plated wire for solar cells can be realized, and can be manufactured at low cost.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Solder plating wire for solar cells)
The solar cell solder-plated wire according to a preferred embodiment of the present invention is obtained by applying solder plating 4 to the entire surface of the conductor 3, as shown in FIG. This conductor 3 contains one or more sulfur-affinity metals selected from Nb, Ti, Zr, V, Ta, Fe, Ca, Mg, or Ni, and the remainder has an oxygen content exceeding 10 massppm. It is composed of copper and a copper material that is an inevitable impurity. The conductor 3 contains a sulfur affinity metal in a proportion of 0.0007 to 0.04 mass%. Within this content range, misch metal (MM) may be added in addition to the sulfur-affinity metal.

  The crystal grain size of the conductor 3 is 270 μm or less, and the 0.2% proof stress of the conductor 3 is 23 to 66 MPa. Moreover, the 0.2% yield strength of the entire solar cell solder-plated wire 2 in which the conductor 3 is coated with the solder plating 4 is 43 to 86 MPa.

  The solder plating 4 used for covering the conductor 3 is preferably a lead-free product from an environmental point of view, and is selected from Sn-based solder or Pb, In, Bi, Sb, Ag, Zn, Ni, Cu as the second component. Sn-based alloy solder containing 0.1 mass% or more of at least one element. Each of the Sn-based solder or the Sn-based alloy solder may contain a trace element of 1000 massppm or less as a third component. Further, the coating of the solder plating 4 may be a part of the conductor 3, for example, only the upper and lower surfaces of the conductor.

  The oxygen content of the conductor 3 in the solar cell solder-plated wire 2 according to the present embodiment is not particularly limited, but for example, a range exceeding 10 massppm and within 400 massppm is assumed. In the examples to be described later, since a general-purpose material such as tough pitch copper is used as the raw material of the conductor 3, it exceeds 10 massppm, more precisely, about 150 massppm to 400 massppm, but oxygen-free copper, high-purity copper ( From the viewpoint of obtaining characteristics equivalent to 6N) and the like, the preferable oxygen content of the conductor 3 in the solar cell solder-plated wire 2 according to the present embodiment is 150 massppm or less, and more preferably 10 massppm to 50 massppm.

  By connecting this solar cell solder-plated wire 2 to a predetermined contact region (for example, an Ag plating region) on the silicon cell surface of the silicon crystal wafer 1 (solar cell module) shown in FIG. can get.

(Method for manufacturing solder-plated wire for solar cells)
An example of the manufacturing method of the solar cell solder plated wire 2 according to the present embodiment will be described below.

  First, in the molten metal storage means of the continuous casting and rolling apparatus, tough pitch copper having an oxygen content exceeding 10 massppm is dissolved, and a sulfur-affinity metal is added to the molten copper at a ratio of 0.0007 to 0.05 mass%. Not all sulfur-affinity metals remain in the molten copper, and the final ratio of sulfur-affinity metals contained in the molten copper is 0.0007 to 0.04 mass%. A copper roughening material is continuously produced using this molten copper. Further, this roughing material is subjected to cold drawing with a reduction in area of 30% or more to produce a conductor 3 having a flat cross section. Thereafter, the flat rectangular conductor 3 is subjected to heat treatment. By this processing and heat treatment, the average grain size of the copper crystals constituting the conductor 3 is adjusted to 270 μm or less, and the 0.2% proof stress of the conductor 3 is adjusted to 23 to 66 MPa. As heat processing, it heats for 30 to 90 minutes in the temperature range of 190-750 degreeC, for example, Preferably it is 30-90 minutes in the temperature range of 400-750 degreeC.

  After the heat treatment, the surface of the conductor 3 is covered with the solder plating 4 to obtain the solar cell solder plating wire 2 according to the present embodiment. The plating type and the plating thickness of the solder plating 4 are adjusted so that the 0.2% proof stress of the solder plating wire 2 for solar cells is 43 to 86 MPa.

  Here, the area reduction rate at the time of cold area reduction is specified to be 30% or more, preferably 30 to 99.9%. If the area reduction ratio is less than 30%, it is sufficient for roughing lines at the time of processing. This is because distortion cannot be generated, and dislocations inside the roughing lines cannot be sufficiently increased and grown. As a result, S, Pb, etc., dissolved in the copper material cannot be sufficiently precipitated, and as a result, the softening temperature of the copper material cannot be sufficiently lowered.

In addition, the area reduction rate is the following formula (1)
Area reduction ratio = [1− (wire cross-sectional area after surface reduction processing / wire cross-sectional area before surface reduction processing)] × 100 (1)
Ask for.

  As a heat treatment method for reducing the 0.2% proof stress of the conductor 3, a batch-type heating method using a heater or an electric heating method (for example, an electric annealing) can be applied. When stable heat treatment is required, a method of winding the conductor 3 in a coil shape and then placing it in a furnace and heating in a batch method is preferable, and an electric heating method is desirable when heat-treating continuously over a long length. Further, from the viewpoint of preventing oxidation, heat treatment may be performed using a furnace in a hydrogen reducing atmosphere.

  As the continuous casting and rolling method, for example, SCR, Hesley type, Upcast method and the like can be applied.

  Next, the effect | action of the solder plating wire 2 for solar cells which concerns on this Embodiment is demonstrated.

(Sulfur affinity metal content)
In the present embodiment, the sulfur-affinity metal content in the conductor 3 is defined as 0.0007 to 0.04 mass%, preferably 0.001 to 0.04 mass%. This is because, if it is less than 0007% by mass, the sulfur-soluble metal and S dissolved in the copper base material do not sufficiently react. On the other hand, if the content exceeds 0.04% by mass, the amount of sulfur-affinity metal dissolved in the conductor 3 is excessively increased, preventing copper crystal growth and reducing the crystal grain size of the conductor 3. It is because it is too much (for example, less than 19 micrometers).

  In normal tough pitch copper, about 10 mass ppm of S was dissolved, and this S was a factor inhibiting the softness of the tough pitch copper material. Therefore, in the solar cell solder-plated wire 2 of the present embodiment, as a constituent material of the conductor 3, a copper base material (tough pitch copper material) having an oxygen content exceeding 10 massppm, Nb, Ti, Zr, V, Ta, The thing which contained 1 type, or 2 or more types of sulfur affinity metals selected from Fe, Ca, Mg, or Ni in the ratio of 0.0007-0.04 mass% is employ | adopted.

(Relationship between sulfur-affinity metal addition and softening properties)
This sulfur-affinity metal (for example, Ti) reacts with S dissolved in a copper melt having an oxygen content exceeding 10 massppm, so that S precipitates as a sulfide (for example, TiS), and the copper melt The amount of S solid solution of is reduced. For this reason, even if a tough pitch copper having a relatively high S content is used as a starting material, S can be deposited from a copper matrix, and in terms of softening characteristics, it is almost the same as that of high-purity copper (for example, OFC). Equivalent characteristics can be obtained.

  In addition, when the above-described rough drawn wire is produced using a molten copper containing a sulfur-affinity metal, sulfide that is a compound of S is deposited around the copper matrix (crystal grains). Since these sulfides are fine compounds and are deposited at intervals, there is no possibility of hindering copper crystal growth. Therefore, the crystal grain of the rough drawing line can be grown greatly, and the rough drawing line having a low yield stress, that is, the conductor 3 can be obtained.

(Crystal grain size of conductor)
It is known that the 0.2% proof stress has a large correlation with the crystal grain size of the conductor 3, while the smaller the grain boundary, that is, the larger the crystal grain size, the smaller the deformation resistance. On the other hand, if the crystal grain size becomes too large, the elongation of the material is lowered and the material becomes brittle. Therefore, the crystal grain size needs to be within a certain range. The crystal grain size referred to here is an average of the crystal grain size of the conductor 3.

  When the crystal grain size of the conductor 3 is more than 270 μm, the conductor 3 becomes brittle and the crack resistance is lowered. For this reason, if the crystal grain size of the conductor 3 exceeds 270 μm, cracks may occur in the solar cell solder-plated wire 2, for example, the solder-coated conductor rectangular wire, during long-term reliability, during the molding process incorporated into a solar cell panel or the like. This may cause problems such as insufficiency. If the crystal grain size of the conductor 3 is too small, for example, less than 19 μm, there is no problem with crack resistance, but the flexibility of the conductor 3 is lost, so that the silicon cell (solar cell 1) warps. growing. Therefore, the crystal grain size of the conductor 3 is preferably in the range of 270 μm or less.

  As described above, according to the solar cell solder-plated wire 2 according to the present embodiment, the proof stress is 0.2% lower than that of the conventional solar cell solder-plated wire using tough pitch copper (TPC) as a conductive material, 0.2% proof stress equivalent to or lower than that of conventional solder plated wires for solar cells using oxygen copper (OFC) as the conductor material can be realized, so it can be used in wiring processes that require heating and temperature changes when using solar cells. It is possible to minimize the influence of distortion due to the difference in thermal expansion / contraction rate.

  Moreover, according to the manufacturing method of the solar cell solder-plated wire 2 according to the present embodiment, tough pitch copper having an oxygen content of 10 mass ppm or more without using high-purity copper (6N) or the like as the raw material of the conductor 3. Therefore, the manufacturing process of the conductor 3 can be simplified as compared with the case where high purity copper (6N) or the like is used, and the cost can be reduced.

  Furthermore, as for the solder composition of the solder plating wire 4 of the solar cell solder plating wire, it has been required to use Cu as the conductor so that it can be connected at low temperature in consideration of thermal expansion matching with the silicon cell. However, in the solar cell solder-plated wire 2 according to the present embodiment, the use of the conductor 3 made of the above-described copper material reduces the warpage of the silicon cell, so that the connection temperature is high. It is possible to use a solder having an Ag-Cu composition.

  Furthermore, the solder used for covering the conductor is not limited to a Sn—Ag—Cu-based solder, and at least one selected from Pb, In, Bi, Sb, Ag, Zn, Ni, and Cu as the second component. Any Sn-based alloy solder containing 0.1 wt% or more of the above element may be used, and a solder containing a trace element of 1000 ppm or less as the third component may be used.

  Moreover, the wiring conductor for connecting solar cells and the solder plating wire according to the present invention may include a deformed portion that is easily deformed at a plurality of locations connected to the cell, and etching, pressing, and bending as processing methods. Any one or a plurality of them may be used in combination. Further, the processing may be applied to any of a material wire, a rolled wire obtained by rolling the material wire, and a foil-like wire obtained by slitting a plate material.

(Example 1, Sample 1)
Using an SCR-type continuous casting and rolling apparatus connected to a shaft furnace, a rough drawn wire having a diameter of φ8 mm mainly composed of tough pitch copper (oxygen content: 300 mass ppm) was produced. The constituent material of the rough drawing wire is obtained by adding 0.006 mass% of Nb as a sulfur affinity metal to a tough pitch copper melt. The rough drawn wire was drawn to φ2.6 mm and then heat-treated at 600 ° C. for 1 hr, and cold-reduced at a workability of 91% to produce a copper wire having a diameter of φ0.8 mm. This was rolled to produce a flat copper wire (thickness 0.16 mm, width 2.0 mm), subjected to a softening annealing treatment at 500 ° C. × 1 hr, and then cut to 150 mm to obtain a core material (conductor).
This core material is immersed in a molten solder plating bath (Sn-3 mass% Ag-0.5 mass% Cu-based lead-free solder) and quickly pulled up, and a molten solder plating layer (thickness 0.03 mm) is formed on the surface of the core material. Was formed, and a solder-coated copper rectangular wire (solder-plated wire for solar cell) was produced.
(Example 2, sample 2)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.012 mass% of Nb is added to the tough pitch copper molten metal.
(Example 3, Sample 3)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.04 mass% of Nb is added to the tough pitch copper molten metal.
(Example 4, sample 4)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.003 mass% of Ti is added to the tough pitch copper molten metal.
(Example 5, sample 5)
The constituent material of the rough drawn wire is the same as that of Example 1 except that 0.003 mass% of Fe is added to the tough pitch copper molten metal.
(Example 6, sample 6)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.003 mass% of Mg is added to the tough pitch copper molten metal.
(Example 7, Sample 7)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.003 mass% of Zr is added to the tough pitch copper molten metal.
(Example 8, sample 8)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.04 mass% of Ta is added to the tough pitch copper molten metal.
(Example 9, sample 9)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.006 mass% of Ta is added to the tough pitch copper molten metal.
(Example 10, sample 10)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.005 mass% of Ni is added to the tough pitch copper molten metal.
(Example 11, sample 11)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.01 mass% of Ni is added to the tough pitch copper molten metal.
(Example 12, sample 12)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.01 mass% of Ni and 0.001 mass% of Ti are added to the tough pitch copper molten metal.
(Example 13, sample 13)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.01 mass% of Ni and 0.001 mass% of Mn are added to the tough pitch copper molten metal.
(Example 14, sample 14)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.01 mass% of Ni and 0.0005 mass% of Ca are added to the tough pitch copper molten metal.
(Example 15, sample 15)
The constituent material of the rough drawing wire is the same as in Example 1 except that 0.01 mass% of Ni and 0.001 mass% of V are added to the tough pitch copper molten metal.
(Example 16, sample 16)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.012 mass% of Nb and 0.003 mass% of Ti are added to the tough pitch copper molten metal.
(Example 17, sample 17)
The constituent material of the rough drawing wire is the same as in Example 1 except that 0.012 mass% of Nb and 0.006 mass% of Zr are added to the tough pitch copper melt.
(Example 18, sample 18)
The constituent material of the rough drawing wire was the same as that of Example 1 except that 0.012 mass% of Nb and 0.01 mass% of Hf were added to the tough pitch copper melt.
(Example 19, sample 19)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.012 mass% of Nb and 0.03 mass% of V are added to the tough pitch copper molten metal.
(Example 20, sample 20)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.012 mass% of Nb and 0.02 mass% of Ta are added to the tough pitch copper molten metal.
(Example 21, Sample 21)
The constituent material of the rough drawing wire was the same as that of Example 1 except that 0.012 mass% of Nb and 0.003 mass% of Fe were added to the tough pitch copper molten metal.
(Example 22, sample 22)
The constituent material of the rough drawing wire was the same as that of Example 1 except that 0.012 mass% of Nb and 0.002 mass% of B were added to the tough pitch copper molten metal.
(Example 23, sample 23)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.012 mass% of Nb and 0.002 mass% of Ca are added to the tough pitch copper molten metal.
(Example 24, sample 24)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.012 mass% of Nb and 0.002 mass% of Mg are added to the tough pitch copper molten metal.
(Example 25, sample 25)
The constituent material of the rough drawing wire was the same as that of Example 1 except that 0.012 mass% of Nb and 0.002 mass% of MM (Misch metal) were added to the tough pitch copper molten metal.
(Conventional example 1, sample 26)
The constituent material of the rough drawn wire is the same as that of Example 1 except that no sulfur-affinity metal is added to the tough pitch copper melt.
(Conventional example 2, sample 27)
The constituent material of the rough drawing wire is the same as that of Example 1 except that a melt of oxygen-free copper (OFC) is used and a sulfur-affinity metal is not added.
(Comparative Example 1, Sample 28)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.0003 mass% of Ti is added to the tough pitch copper molten metal.
(Comparative Example 2, Sample 29)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.06 mass% of Ti is added to the tough pitch copper molten metal.
(Comparative Example 3, Sample 30)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.06 mass% of Nb is added to the tough pitch copper molten metal.
(Comparative Example 4, Sample 31)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.0005 mass% of Nb is added to the tough pitch copper molten metal.
(Comparative Example 5, Sample 32)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.0005 mass% of Ni is added to the tough pitch copper molten metal.
(Comparative Example 6, Sample 33)
The constituent material of the rough drawing wire is the same as that of Example 1 except that 0.05 mass% of Ni is added to the tough pitch copper molten metal.

(Evaluation methods)
Each solder-coated Cu rectangular wire was solder-connected to a silicon cell having a length of 150 mm × width of 150 mm and a thickness of 200 μm, and the crack resistance and warpage of the silicon cell were examined.

  Example 1 to Example 25, Conventional Examples 1 and 2 and Comparative Examples 1 to 6 of each solder-coated Cu rectangular wire 0.2% proof stress (MPa), crystal grain size, warp of silicon substrate The measured results are shown in Table 1.

  In Table 1, “x” of the evaluation mark in the column of warpage occurrence of the silicon substrate indicates a case where warpage exceeding 2.1 mm occurs, and “◯” indicates a case where warpage is 2.1 mm or less.

  The 0.2% yield strength σ of the solder-coated Cu rectangular wire is obtained by dividing the load (external force) F in a tensile test that gives a strain of 0.2% to the conductor by the cross-sectional area A of the conductor excluding the solder. Yes. This can be expressed by the following formula.

σ = F / A
Further, the crystal grain size referred to here is, for example, 10 grains selected from the larger crystal grains in the cross section of the solder-coated Cu rectangular wire, and the grain diameters of those crystal grains are averaged.

  According to Table 1, the solder plating wires for solar cells of Examples 1 to 24 (Samples 1 to 24) all have a 0.2% proof stress of the Cu core material before plating of 49 MPa or less, and the solder after plating. The 0.2% yield strength of the coated Cu rectangular wire was 69 MPa or less, and the crystal grain size was 19 μm or more. These are all characteristics of tough pitch copper (sample 26, 0.2% proof stress of Cu core material before plating: 70 MPa, 0.2% proof stress of solder-coated Cu rectangular wire after plating: 90 MPa, crystal grain size: 18 μm) ) And oxygen-free copper characteristics (sample 27, 0.2% proof stress of Cu core material before plating: 50 MPa, 0.2% proof stress of solder-coated Cu rectangular wire after plating: 70 MPa, crystal grain size: 25 μm) The amount of warpage of the silicon substrate when solder-connected to a 200 μm thin silicon substrate was within an allowable range (2.1 mm or less).

  Moreover, about the solder plating wire for solar cells (sample 25) of Example 25, the 0.2% yield strength of the Cu core material before plating is 50 MPa, and the 0.2% yield strength of the solder-coated Cu rectangular wire after plating is 70 MPa. In addition, the crystal grain size is 25 μm, which is superior to the above-described characteristics of tough pitch copper (sample 26), and is equivalent to the characteristics of oxygen-free copper (sample 27) described above. It was within an acceptable range.

  On the other hand, in the solder plating wires for solar cells (samples 28 to 33) of the comparative example, the 0.2% proof stress of the Cu core material before plating is larger than 70 MPa. Since the 2% proof stress is greater than 90 MPa and the crystal grain size is less than 19 μm, it is inferior to the characteristics of tough pitch copper (sample 26) and oxygen-free copper (sample 27), and the amount of warpage of the silicon substrate Exceeded the allowable range (2.1 mm).

  Next, in sample 1 (product of the present invention), sample 26 (TPC), and sample 27 (OFC), softening characteristics when heat treatment was attempted under a plurality of heat treatment conditions on the rough drawn wire drawn to φ2.6 mm. The results are shown in FIG. FIG. 1 shows an evaluation of 0.2% proof stress for each of the roughing lines held at a predetermined temperature for 1 hour and then taken out and water-cooled.

  As shown in FIG. 1, each sample has a high 0.2% proof stress of about 400 MPa before heat treatment (when the temperature is 20 ° C. in FIG. 1). % Proof stress decreased, and it decreased to a level of 100 MPa or less near 300 ° C., and only sample 1 of the present invention was below 50 MPa near 400 ° C. When each material (sample 1, sample 26, sample 27) was compared, sample 1 (product of the present invention) showed the smallest value, followed by sample 26 (TPC) and sample 27 (OFC).

  Next, the crystal grain size, 0.2% proof stress (MPa), when the heat treatment conditions (temperature, time) of the solder plated wire for solar cells (sample 1) of Example 1 which is the present invention product are changed, The crack resistance and warpage of the silicon substrate were examined. The results are shown in Table 2.

  The term “crack-resistant” as used herein means a break that occurs in a solder plating wire for solar cells after being connected to a silicon substrate. In Table 2, “◯” and “x” of the evaluation mark in the column of crack resistance mean that no crack occurred in the solder plating wire for solar cell and that a crack occurred. In Table 2, the evaluation marks ◯ and X in the warp column of the silicon cell are based on the same criteria as in Table 1.

  As shown in Table 2, when the heat treatment condition is 800 ° C. for 60 minutes, the crystal grain size becomes 300 μm, the deformation progresses easily, and the crack resistance deteriorates. It was confirmed that the material was brittle.

  On the other hand, when the heat treatment conditions are 190 ° C. for 60 minutes and 180 ° C. for 60 minutes, the crystal grain size is 18, 16 μm, the 0.2% proof stress of the Cu core material before plating is 70, 78 MPa, and the solder coating after plating The 0.2% yield strength of the Cu rectangular wire is 90, 98 MPa, which is the same as or inferior to that of the sample 26 shown in Table 1, and the warpage amount of the silicon substrate exceeded the allowable range (2.1 mm). .

  From the above results, when the heat treatment conditions are 750 ° C. (× 30 to 90 minutes) to 200 ° C. (× 30 to 90 minutes), characteristics superior to those of the sample 26 can be obtained, and the solder plating for solar cells The warp amount of the silicon substrate was within an allowable range (2.1 mm or less) without causing cracks in the wires. Better heat treatment conditions are when the heat treatment conditions are 750 ° C. (× 30 to 90 minutes) to 400 ° C. (× 30 to 90 minutes). At this time, characteristics superior to those of the sample 27 shown in Table 1 are obtained. Or the characteristic substantially equivalent to the sample 27 was acquired, the crack was not produced in the solder plating wire for solar cells, and the curvature amount of the silicon substrate became in the tolerance | permissible_range.

(Example 26, sample 34)
Using an SCR-type continuous casting and rolling apparatus connected to a shaft furnace, a rough drawn wire having a diameter of φ8 mm mainly composed of copper containing an oxygen concentration of 30 mass ppm was manufactured. The constituent material of the rough drawing wire is obtained by adding 0.006 mass% (mass%) of Nb as a sulfur-affinity metal to the molten copper. The rough drawn wire was drawn to φ2.6 mm and then heat-treated at 600 ° C. for 1 hr, and cold-reduced at a workability of 91% to produce a copper wire having a diameter of φ0.8 mm. This was rolled to produce a flat copper wire (thickness 0.16 mm, width 2.0 mm), subjected to a softening annealing treatment at 500 ° C. × 1 hr, and then cut to 150 mm to obtain a core material (conductor).
This core material is immersed in a molten solder plating bath (Sn-3 mass% Ag-0.5 mass% Cu-based lead-free solder) and quickly pulled up, and a molten solder plating layer (thickness 0.03 mm) is formed on the surface of the core material. Was formed, and a solder-coated copper rectangular wire (solder-plated wire for solar cell) was produced.
(Example 27, Sample 35)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.012% by mass of Nb is added to the molten copper.
(Example 28, Sample 36)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.04% by mass of Nb is added to the molten copper.
(Example 29, Sample 37)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.003% by mass of Ti is added to the molten copper.
(Example 30, sample 38)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.003% by mass of Fe is added to the molten copper.
(Example 31, sample 39)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.003% by mass of Mg is added to the molten copper.
(Example 32, sample 40)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.003% by mass of Zr is added to the molten copper.
(Example 33, Sample 41)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.04% by mass of Ta is added to the molten copper.
(Example 34, sample 42)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.006% by mass of Ta is added to the molten copper.
(Example 35, Sample 43)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.005 mass% of Ni is added to the molten copper.
(Example 36, Sample 44)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.01% by mass of Ni is added to the molten copper.
(Example 37, sample 45)
The roughening wire was the same as in Example 26 except that 0.01 mass% Ni and 0.001 mass% Ti were added to the molten copper.
(Example 38, Sample 46)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.01 mass% of Ni and 0.001 mass% of Mn are added to the molten copper.
(Example 39, sample 47)
The roughening wire was the same as in Example 26 except that 0.01 mass% Ni and 0.0005 mass% Ca were added to the molten copper.
(Example 40, sample 48)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.01% by mass of Ni and 0.001% by mass of V are added to the molten copper.
(Example 41, sample 49)
The constituent material of the rough wire was the same as that of Example 26 except that 0.012 mass% of Nb and 0.003 mass% of Ti were added to the molten copper.
(Example 42, sample 50)
The constituent material of the rough wire was the same as that of Example 26 except that 0.012 mass% of Nb and 0.006 mass% of Zr were added to the molten copper.
(Example 43, Sample 51)
The constituent material of the rough drawing wire was the same as that of Example 26 except that 0.012 mass% of Nb and 0.01 mass% of Hf were added to the molten copper.
(Example 44, Sample 52)
The constituent material of the rough drawing wire was the same as that of Example 26 except that 0.012 mass% of Nb and 0.03% by mass of V were added to the molten copper.
(Example 45, Sample 53)
The constituent material of the rough drawing wire was the same as that of Example 26 except that 0.012 mass% of Nb and 0.02 mass% of Ta were added to the molten copper.
(Example 46, Sample 54)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.012 mass% of Nb and 0.003 mass% of Fe are added to the molten copper.
(Example 47, sample 55)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.012 mass% of Nb and 0.002 mass% of B are added to the molten copper.
(Example 48, Sample 56)
The constituent material of the rough drawing wire was the same as that of Example 26 except that 0.012 mass% of Nb and 0.002 mass% of Ca were added to the molten copper.
(Example 49, Sample 57)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.012 mass% of Nb and 0.002 mass% of Mg are added to the molten copper.
(Example 50, Sample 58)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.012 mass% of Nb and 0.002 mass% of MM (Misch metal) are added to the molten copper.
(Comparative Example 7, Sample 59)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.0003 mass% of Ti is added to the molten copper.
(Comparative Example 8, Sample 60)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.06% by mass of Ti is added to the molten copper.
(Comparative Example 9, Sample 61)
The constituent material of the rough drawn wire is the same as that of Example 26 except that 0.06% by mass of Nb is added to the molten copper.
(Comparative Example 10, Sample 62)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.0005 mass% of Nb is added to the molten copper.
(Comparative Example 11, Sample 63)
The constituent material of the rough drawing wire is the same as that of Example 26 except that 0.0005 mass% of Ni is added to the molten copper.
(Comparative Example 12, Sample 64)
The roughening wire was the same as in Example 26 except that 0.05% by mass of Ni was added to the molten copper.
(Evaluation methods)
The evaluation method was evaluated according to the same criteria as in Examples 1 to 25, Conventional Examples 1 and 2, and Comparative Examples 1 to 6. The results are shown in Table 3.

  According to Table 3, the solder plating wires for solar cells of Examples 26 to 50 (Sample 34 to Sample 58) all have a 0.2% proof stress of the Cu core material before plating of 48 MPa or less, and the solder after plating. The 0.2% yield strength of the coated Cu rectangular wire was 68 MPa or less, and the crystal grain size was 25 μm or more. These are all characteristics of tough pitch copper (sample 26, 0.2% proof stress of Cu core material before plating: 70 MPa, 0.2% proof stress of solder-coated Cu rectangular wire after plating: 90 MPa, crystal grain size: 18 μm) ) And oxygen-free copper characteristics (sample 27, 0.2% proof stress of Cu core material before plating: 50 MPa, 0.2% proof stress of solder-coated Cu rectangular wire after plating: 70 MPa, crystal grain size: 25 μm) The amount of warpage of the silicon substrate when solder-connected to a 200 μm thin silicon substrate was within an allowable range (2.1 mm or less).

  Further, comparing Example 1 and Example 26, in Example 1, 0.2% proof stress of the Cu core material before plating: 41 MPa, and 0.2% proof stress of the solder-coated Cu rectangular wire after plating: 61 MPa. In Example 26, while the crystal grain size is 30 μm, the 0.2% proof stress of the Cu core material before plating: 39 MPa, the 0.2% proof stress of the solder-coated Cu rectangular wire after plating: 59 MPa, crystals It can be seen that the particle size is 30 μm, and the copper material of Example 26 is a copper material having a lower 0.2% proof stress.

  This is the same when Example 2 to Example 25 and Example 27 to Example 50 are compared. When the oxygen content in the copper base material is lowered (for example, the oxygen content is 10 to 50 massppm). It can be seen that a copper material having a lower 0.2% proof stress and a large crystal grain size can be obtained.

  Next, the crystal grain size, 0.2% proof stress (MPa) when the heat treatment conditions (temperature, time) of the solar cell solder-plated wire (sample 34) of Example 26 which is the present invention product are changed, The crack resistance and warpage of the silicon substrate were examined. The results are shown in Table 4. The evaluations in the “crack resistance” and “warp of the silicon substrate” columns were based on the same criteria as in Examples 1 to 25.

  As shown in Table 4, when the heat treatment condition is 800 ° C. for 60 minutes, the crystal grain size becomes 307 μm, the deformation progresses easily, and the crack resistance deteriorates. It was confirmed that the material was brittle.

  On the other hand, when the heat treatment condition is 180 ° C. for 60 minutes, the crystal grain size is 18 μm, the 0.2% proof stress of the Cu core material before plating is 75 MPa, and the 0.2% proof stress of the solder-coated Cu rectangular wire after plating is The result was 95 MPa, which was equivalent to or inferior to sample 27 shown in Table 1, and the warpage amount of the silicon substrate exceeded the allowable range (2.1 mm).

  From the above results, when the heat treatment conditions are 190 ° C. to 750 ° C., it is possible to obtain characteristics superior to those of the sample 26, without causing cracks in the solar cell solder plated wires, and the amount of warpage of the silicon substrate Was within an allowable range (2.1 mm or less). Better heat treatment conditions are when the heat treatment conditions are 750 ° C. (× 30 to 90 minutes) to 400 ° C. (× 30 to 90 minutes). At this time, characteristics superior to those of the sample 27 shown in Table 1 are obtained. The crack amount of the silicon substrate was not allowed to crack, and the warpage amount of the silicon substrate was within the allowable range.

It is a figure which shows the relationship between the heat processing temperature of a copper conductor, and 0.2% yield strength. It is a figure which shows the connection state of the solder plating rectangular wire to a photovoltaic cell. It is a cross-sectional view of a general solder plating wire for solar cells. It is a figure which shows the connection state of the Si cell and the solder plating wire for solar cells, Fig.4 (a) has shown the state before solder connection, FIG.4 (b) has shown the state which the curvature generate | occur | produced after solder connection.

Explanation of symbols

1 Solar cell (Si cell)
2 Solder-plated wire for solar cells (Solder-plated flat wire)
3 Conductor 4 Solder plating

Claims (7)

In a solder plating wire for a solar battery in which a part or all of the surface of a conductor formed in a rectangular cross section is coated with a solder plating to be joined to a solar battery cell,
Copper containing one or more sulfur-affinity metals selected from Nb, Ti, Zr, V, Ta, Fe, Ca, Mg, or Ni, with the remainder having an oxygen content of more than 10 massppm And a solder-plated wire for a solar cell, characterized by comprising a copper material which is an inevitable impurity.   The solder plating wire for solar cells according to claim 1, wherein the conductor contains 0.0007 to 0.04 mass% of the sulfur affinity metal.   The solder-plated wire for a solar cell according to claim 1 or 2, wherein the conductor has a crystal grain size of 270 µm or less.   A solar battery comprising the solar battery solder-plated wire according to claim 1 and a solar battery cell connected by soldering. A method for producing a solar cell solder-plated wire from molten copper using a continuous casting and rolling device,
One or two kinds selected from Nb, Ti, Zr, V, Ta, Fe, Ca, Mg, or Ni in the molten copper stored in the molten metal storage means of the continuous casting and rolling apparatus and having an oxygen content exceeding 10 massppm. After adding the above sulfur-affinity metal, adjusting the ratio of the sulfur-affinity metal contained in the molten copper to 0.0007 to 0.04 mass%, and manufacturing the roughing material using the molten copper A method for producing a solder-plated wire for a solar cell, comprising subjecting the roughened material to cold drawing with a reduction in area of 30% or more, and subjecting the cold-worked material to heat treatment at 190 to 750 ° C.   The manufacturing method of the solder plating wire for solar cells of Claim 5 which heat-processes at 400-750 degreeC to the said cold work material.   The manufacturing method of the solder plating wire for solar cells of Claim 5 or 6 which performs the said heat processing by the batch type heating system or electric current heating system with a heater.

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