JP4951856B2 - Manufacturing method of flat conductor - Google Patents

Description

  The present invention relates to a conductor for lead wires for connecting a silicon crystal of a solar cell, and more particularly to a flat conductor having a small thermal stress at the time of solder connection and less deformation such as its own warp and a method for manufacturing the same.

  A semiconductor chip in which a silicon crystal is grown on a substrate is used for a solar cell, and a connection lead wire is joined to a predetermined region of a silicon crystal wafer with solder, and power is supplied through this. Known examples include Patent Document 1 in which a flat copper rectangular conductor such as tough pitch copper or oxygen-free copper is used as the conductor and Sn—Pb eutectic solder is applied as the solder.

  In recent years, switching to a solder that does not contain Pb has been studied in consideration of the environment. Patent Document 2 and the like are known examples.

Japanese Patent Laid-Open No. 11-21660 JP 2002-263880 A JP 2002-164560 A

  The silicon crystal wafer occupies most of the material cost among the members constituting the solar cell. Therefore, the thinning of the silicon crystal wafer has been studied, and the thickness that has been conventionally 350 μm or more is 250 μm or less. However, when the thickness is reduced, the rigidity is lowered, and a problem that the silicon crystal wafer is damaged due to a heating process at the time of joining the connecting lead wires or a temperature change at the time of use tends to occur. In order to cope with this, there is an increasing need for connecting lead wires that have low thermal stress during solder connection.

  As a known example, there is Patent Document 3 in which a strip clad with a material having low thermal expansion such as a copper-invar composite material is used as a lead frame. However, since the lead frame is punched at the time of circuit formation, there is a problem that a large amount of wasted material is generated.

  Further, in the case of a material using a copper-invar-copper clad flat conductor, deformation such as warping may occur due to crystal orientation or crystal grain non-uniformity of the copper material arranged on both sides of the invar. . These are causes of lowering reliability such as lower productivity of solar cell modules and lowering of power generation efficiency when used for a long time.

  Moreover, although the bent part exists in the flat conductor arrange | positioned at a solar cell, the problem that it fractures | ruptures at a bent part and is disconnected depending on the physical property of a flat conductor has also arisen.

  One object of the present invention is to provide a flat conductor that can reduce thermal stress during solder connection while maintaining high conductivity, and that is less prone to deformation of the cell, and a method of manufacturing the same, A second object is to provide a flat conductor used for a connecting lead wire of a solar cell that can be easily flattened by correction. Further, the present invention provides a flat conductor used for a solar cell connection lead wire that has sufficient elongation so that it does not break even when bent, and has no brittle intermetallic compound at the interface between the core and the material on both sides of the core material. Is the third purpose.

In order to achieve the object of the present invention, the invention of claim 1 is characterized in that both sides of a core flat plate made of aluminum or silver have a low volume consisting of gold, silver and copper having a 0.2% proof stress larger than that of the core flat plate. upon manufacturing a rectangular conductor is sandwiched in resistivity conductor, said after preparing clad material wherein both surfaces of the core plate-bonding a low volume resistivity conductors, for 1-2 hours at 200 to 280 ° C. in the cladding heat treatment Is a method for producing a flat conductor.

The invention of claim 2 is a method for producing a rectangular conductor according to claim 1, wherein a thickness of the intermetallic compound at the interface between the core flat and low volume resistivity conductor is 3.0μm or less.

The invention of claim 3 is a method for producing a rectangular conductor according to claim 1 or 2 elongation at break of the flat conductor after heat treatment is 15% or more.

Invention of Claim 4 is a manufacturing method of the flat conductor in any one of Claims 1-3 whose Vickers hardness of the low volume resistivity conductor arrange | positioned on both surfaces of a core flat plate is 1100 or less.

In the invention of claim 5, the low volume resistivity conductor after the heat treatment has an intensity ratio I _R (=) of the intensity I (111) of the X-ray diffraction line (111) and the intensity I (200) of the diffraction line (200). 5. The method for producing a rectangular conductor according to claim 1, wherein I (111) / {I (200) + I (111)}) has a crystal orientation of 0.15 or more.

Invention of Claim 6 is a manufacturing method of the flat conductor in any one of Claims 1-5 whose core flat plate is aluminum and whose low volume resistivity conductor is copper .

  As described above, the present invention has a configuration in which the low volume resistivity metal material is arranged on both sides of the low-strength material as the core, and the material arranged on both sides of the core has a random orientation that does not have a specific orientation. Therefore, the present invention performs an appropriate heat treatment on the rectangular conductor and suppresses the growth of the compound layer at the interface while removing the processing strain in the rectangular conductor, thereby reducing the yield strength and improving the elongation. It is to have done.

  According to the present invention, it is possible to reduce cell warpage when a rectangular conductor is solder-connected to a cell while maintaining conductivity. In addition, there is little warping of the conductor even after shape correction by applying tension, and both assembly and long-term reliability are good.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a cross-sectional view of a first embodiment of the present invention.

  The flat conductor 5 of the present invention has a structure in which the core flat plate 2 is sandwiched from both sides by the low volume resistivity conductor 1.

  The material of the core flat plate 2 is made of aluminum, which is relatively conductive and has a low proof stress, and the material of the low volume resistivity conductor 1 is made of copper. These are cut into a predetermined width by a mechanical slit device or the like and used as a lead wire conductor.

  FIG. 2 shows a cross-sectional view of a second embodiment of a flat conductor.

  FIG. 2 shows a rectangular conductor 5 in which both sides of a core flat plate 2 are sandwiched between low volume resistivity conductors 1 and the whole is covered with solder 3.

  The solder 3 is Sn—Pb eutectic solder or Pb-free solder.

  In the photovoltaic power generation cell, solder for joining is formed in advance, and the solder is joined to the solder 3 of the flat conductor 5 and the solder of the cell.

  As a first embodiment of the present invention, a (copper / aluminum / copper) clad material (ratio 2: 1: 2) having a flat conductor size of width 2.0 mm and thickness 0.2 mm is manufactured, and silicon having a thickness of 200 μm is manufactured. Solder connected to the cell. The conductivity was a relatively high value of 92% IACS, and the warpage of the cell could be reduced to about 89% compared to a flat copper wire (width 2.0 mm, thickness 0.2 mm).

  In the present invention, a material having a relatively low resistivity and a 0.2% proof stress smaller than that of the low volume resistivity conductor 1 on both sides is selected as the material of the core flat plate 2, and the material sandwiched on both sides is a low volume resistance. The reason for selecting the rate conductor 1 is as follows.

The flat conductor 5 is fixed to the cell by solder connection, but warpage remains in the cell after connection due to the difference in thermal expansion between the two. The stress generated at this time depends on the proof stress (yield stress) of the rectangular conductor as well as the thermal expansion difference, and the lower the proof stress, the smaller the warpage of the cell. Therefore, the warpage is reduced by selecting a material having a 0.2% yield strength smaller than that of the low volume resistivity conductor 1 on both sides of the core flat plate 2. However, conductivity as a conductor is also necessary. Therefore, it is desirable to select a low volume resistivity conductor 1 on both sides having a lower volume resistivity than the material of the core flat plate 2.

  Therefore, usable materials are limited as shown in Table 1, and combinations are as shown in Table 2.

  Here, the 0.2% proof stress is not an inherent value depending on the material, and the numerical values shown in Table 1 are obtained by performing a constant heat treatment exceeding the softening temperature of each metal.

  Specifically, heat treatment is performed at 200 to 280 ° C. for 1 to 2 hours. If a combination of these materials is used, a 0.2% proof stress of 120 MPa or less can be secured as a clad material, and the volume resistivity can be kept relatively low.

  Considering the conductivity and cost of the rectangular conductor 5, the outer material is copper having a low volume resistivity, and the core material is aluminum having a 0.2% proof stress smaller than copper and a relatively small volume resistivity. Is desirable.

  Silver can be used as the core material when emphasizing conductivity. As other combinations, as shown in Table 2, silver / aluminum / silver, gold / aluminum / gold, and the like are also possible.

  In the present invention, the reason why heat treatment is performed at 200 to 280 ° C. for 1 to 2 hours after bonding the materials used on both sides of the core to the core material is as follows.

  A (copper / aluminum / copper) clad material (ratio 2 :: 1: 2) with a flat wire dimension of width 2.0 mm and thickness 0.2 mm is manufactured, with no heat treatment and heat treatment time of 1 hour, heat treatment temperature Table 3 shows the numerical values obtained by evaluating the 0.2% proof stress and elongation when the film was shaken up to 200 to 300 ° C. and the thickness of the intermetallic compound at the interface.

  Thus, the rectangular conductor can be softened by heat treatment at 200 ° C. or higher, and the 0.2% proof stress is 120 MPa or less and the elongation is 15% or more. Further, as the heat treatment temperature increases, an intermetallic compound grows at the interface and the elongation decreases. This is presumably because intermetallic compounds are highly brittle and the overall elongation decreases as the proportion increases.

  Further, if the thickness of the interface metal compound layer is thicker than 3.0 μm, the interface metal compound layer portion breaks because it cannot follow the bending when the flat conductor is connected to the solar cell, and the entire flat conductor is broken. Conductivity falls. In order to make the thickness of the interfacial metal compound layer 3.0 μm or less, as shown in Table 3, the heat treatment temperature needs to be 280 ° C. or less.

  In the present invention, the reason why the Vickers hardness of the low volume resistivity material is defined as 100 or less is as follows.

  These are for imparting flexibility to the conductor to improve the handleability. When the hardness is not less than a specified value, the conductor rigidity becomes too high, which is not preferable.

In addition, the crystal orientation of the low volume resistivity material of the composite material is expressed by an intensity ratio I _R (= I) of the intensity I (111) of the X-ray diffraction line (111) and the intensity I (200) of the diffraction line (200). The reason for defining (111) / {I (200) + I (111)}) to have a crystal orientation of 0.15 or more is as follows.

  The in-plane orientation (normal direction orientation of the clad material surface) of the crystal grains of the low volume resistivity material is predominantly the (111) plane and the (200) plane.

  In the manufacturing process of the clad material, when the recrystallization orientation (texture) of the low volume resistivity material obtained through cold working becomes dominant (200) plane, the recrystallized grains become coarse, and the clad material When a tensile stress is applied so as to easily solder the lead wire made of the above to the cell surface and straighten, the warp tends to occur.

  Table 4 shows an example of X-ray measurement.

In the production line for soldering, the ratio (I _R ) (= I (111) / {I (200) + I (111)}) of the diffraction intensity of (111) and the diffraction intensity of (200) is Thus, if it is 0.15 or less, warpage occurs, and soldering with the cell cannot be performed satisfactorily.

On the other hand, when the heat treatment is performed as in the present invention product, the diffraction intensity ratio (I _R ) becomes larger than 0.15, the crystal orientation becomes a random and isotropic material, and no warpage occurs. It can be.

  This heat treatment (200 to 280 ° C.) may be performed immediately after the cold working at the time of processing the clad material or after the clad material is cut into a flat conductor.

1 is a cross-sectional view showing a first embodiment of the present invention. In this invention, it is a cross-sectional view which shows 2nd Embodiment with which the whole surface was covered with the solder.

Explanation of symbols

1 Low Volume Resistance Conductor 2 Core Flat Plate 3 Solder 5 Flat Rectangular Conductor

Claims (6)

When manufacturing a rectangular conductor by sandwiching both sides of a core flat plate made of aluminum or silver with a low volume resistivity conductor made of a material having a 0.2% proof stress greater than that of the core flat plate of gold, silver and copper , A method for producing a rectangular conductor, comprising: producing a clad material by bonding the low volume resistivity conductor to both surfaces of the core flat plate, and then subjecting the clad material to heat treatment at 200 to 280 ° C. for 1 to 2 hours. 2. The method for producing a rectangular conductor according to claim 1, wherein the thickness of the intermetallic compound at the interface between the core flat plate and the low volume resistivity conductor is 3.0 μm or less. Method for manufacturing a rectangular conductor according to claim 1 or 2 elongation at break of the flat conductor after heat treatment is 15% or more. The method for producing a rectangular conductor according to any one of claims 1 to 3, wherein the low volume resistivity conductor disposed on both surfaces of the core flat plate has a Vickers hardness of 100 or less. The low volume resistivity conductor after the heat treatment has an intensity ratio I _R (= I (111) / {I) of the intensity I (111) of the X-ray diffraction line (111) and the intensity I (200) of the diffraction line (200). (200) + I
(111)}) has a crystal orientation of 0.15 or more. The method for producing a rectangular conductor according to any one of claims 1 to 4. The method for producing a rectangular conductor according to any one of claims 1 to 5 , wherein the core flat plate is aluminum and the low volume resistivity conductor is copper .

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