JP4792713B2 - Lead wire, manufacturing method thereof, and solar cell assembly - Google Patents

Description

  The present invention relates to a lead wire connected to a silicon crystal wafer of a solar cell, a manufacturing method thereof, and a solar cell assembly.

  As a solar cell, a semiconductor chip in which a silicon crystal is grown on a substrate is used. As shown in FIG. 4, a connecting lead wire 42 is joined to a predetermined region (contact region) of a silicon crystal wafer (hereinafter referred to as a silicon cell) 41 obtained by cutting and dividing the semiconductor chip by soldering or the like. Then, power is transmitted (output) through the connecting lead wire 42.

  Usually, as a lead wire for connection, a solder plating film for connection to a silicon cell is formed on the surface of a conductor. For example, as shown in FIG. 5, a connecting lead wire 50 using a pure copper flat conductor 51 such as tough pitch copper or oxygen-free copper as the conductor, and Sn—Pb eutectic solder as the solder plating film 55. (For example, refer to Patent Document 1).

  In recent years, switching to a solder containing no Pb (Pb-free solder) as a constituent material of a solder plating film has been studied in consideration of the environment (for example, see Patent Document 2).

  By the way, since the silicon cell occupies most of the material cost among the members constituting the solar battery, it is considered to reduce the thickness of the silicon cell in order to reduce the manufacturing cost. However, when the silicon cell is thinned, there is a problem that the silicon cell is warped or damaged due to a heating process at the time of soldering the connecting lead wire or a temperature change at the time of using the solar cell. For example, as shown in FIG. 6 (a), the silicon cell 61 and the lead wire 62, which were flat before soldering, are joined by soldering, and heat shrinkage after soldering causes the arrow in FIG. 6 (b). As shown by 65, warping occurs.

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

  In order to cope with this problem, there is an increasing need for a connection lead wire that has a small thermal expansion. For example, as an example of a lead wire with small thermal expansion, as shown in FIG. 7, a lead in which a flat conductor 71, which is a clad material of a copper material 72 a -Invar (registered trademark) material 73 -copper material 72 b, is covered with a solder film 75. There is a line 70.

  By the way, since Invar (registered trademark) has low thermal expansion, the lead wire 70 shown in FIG. 7 is capable of thermal expansion matching with Si constituting the silicon cell. However, since Invar (registered trademark) has a lower conductivity than Cu, the conductivity of the entire lead wire is lowered. As a result, there has been a problem that power generation efficiency as a solar cell is lowered.

  An object of the present invention, which was created in view of the above circumstances, is to provide a lead wire with a small electrical shrinkage after solder bonding and good conductivity, a method for manufacturing the lead wire, and a solar cell assembly.

In order to achieve the above object, the lead wire according to the present invention comprises a solder film on at least a part of the outer periphery of a rectangular body obtained by deforming a composite of a plurality of braided wires made of Cu strands into a rectangular cross section. It is coated.

A lead wire according to the present invention is a lead wire in which at least a part of the outer periphery of a flat conductor is covered with a solder film, and the flat conductor is flattened with a composite of a plurality of braided wires made of Cu strands. It is comprised with the flat body which becomes.

  The 0.5% proof stress of the rectangular body and the rectangular conductor is preferably 70 MPa or less. The solder film is preferably composed of a Sn—Ag—Cu Pb-free solder alloy. The conductivity of the rectangular body and the rectangular conductor is preferably 60% IACS or more.

The lead wire manufacturing method according to the present invention also includes forming a flat body having a flat cross section by rolling a composite body in which a plurality of braided wires made of Cu wire are bundled, and forming the flat body into a flat conductor. And solder plating is performed on at least a part of the outer periphery of the rectangular conductor to form a solder film.

  On the other hand, the solar cell assembly according to the present invention is obtained by soldering the lead wire and the silicon cell according to the present invention described above.

  According to the present invention, it is possible to obtain an excellent effect that a lead wire with less heat shrinkage after soldering can be obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments serving as reference examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a cross-sectional view of a lead wire according to an embodiment as a reference example of the present invention.

A lead wire according to an embodiment serving as a reference example of the present invention is one in which at least a part of the outer periphery of a rectangular body obtained by deforming a stranded wire into a rectangular cross section is covered with a solder film 15. More specifically, as shown in FIG. 1, a lead wire 10 according to an embodiment serving as a reference example of the present invention is formed by twisting a plurality of strands 12 (seven cases are shown in FIG. 1). The combined twisted wires are flattened to form a flat body, and the entire outer periphery of the flat body (flat conductor 11) is covered with the solder film 15.

  The stranded wire is composed of a Cu strand, an Al strand, an Ag strand, an Au strand, an Fe—Ni alloy strand, or a combination thereof, and has a large interval between the strands 12 (high porosity). ) Is preferred. The Cu strand, the Al strand, the Ag strand, and the Au strand referred to here are strands made of Cu or Cu alloy, Al or Al alloy, Ag or Ag alloy, Au or Au alloy. As a constituent material of the Fe—Ni alloy strand, Invar (registered trademark) is preferable.

  At this time, when importance is attached to cost performance, it is preferable to use a Cu strand. Further, when importance is attached to low volume resistivity (high conductivity), it is preferable to use an Ag strand. Furthermore, when importance is attached to lightness, it is preferable to use an Al strand. In addition, when importance is attached to low heat shrinkability (less heat shrinkage) after soldering, it is preferable to combine different kinds of strands, particularly Cu strands (or Al strands, Ag strands, Au strands). Any one) and a Fe—Ni alloy wire are preferable. The ratio (Cu / Fe-Ni) of the cross-sectional areas of the Cu strand and the Fe—Ni alloy strand is adjusted to be 3.0 to 5.0, preferably around 4.0. This adjustment is made by adjusting the number of Cu strands and Fe—Ni alloy strands.

The solder film 15 is made of Sn—Pb eutectic solder or Pb free solder, and preferably Sn—Ag—Cu Pb free solder. The Sn—Ag—Cu-based Pb-free solder may further contain In and / or P. The In content is preferably 1 to 10% by weight, and the P content is preferably 0.005 to 0.015% by weight. For example, Sn-Ag-Cu Pb-free solder
Sn-3 (or 4) Ag-0.5Cu-0.01P,
Sn-3 (or 4) Ag-0.5Cu-3In,
Sn-3 (or 4) Ag-0.5Cu-3In-0.01P,
Sn-3 (or 4) Ag-0.5Cu-5In,
Sn-3 (or 4) Ag-0.5Cu-5In-0.01P,
Sn-3 (or 4) Ag-0.5Cu-8In,
Sn-3 (or 4) Ag-0.5Cu-8In-0.01P,
(The unit is weight%). Here, the reason why the content of In is set to 1 to 10% by weight is that when the content exceeds 10% by weight, the viscosity of the molten solder becomes high and the soldering workability decreases. Further, by setting the P content to 0.005 to 0.015% by weight, it is possible to prevent oxidative discoloration of the solder during the soldering operation, so that the reliability of connection (soldering) can be improved.

  The film thickness of the solder film 15 is 1/30 to 1/3, preferably 1/10 to 1/3, particularly preferably 1/5 of the thickness of the flat conductor 11.

  The 0.5% proof stress of the rectangular body, that is, the flat conductor 11, is 70 MPa or less, preferably 60 MPa or less, more preferably 50 MPa or less, and particularly preferably 40 MPa or less. The 0.5% proof stress mentioned here indicates the stress value when 0.5% elongation occurs. The conductivity of the rectangular body, that is, the rectangular conductor 11, is preferably 60% IACS or more.

  The covering of the flat conductor 11 with the solder film 15 may be only a part of the outer periphery of the flat conductor 11 (for example, the upper surface and / or the lower surface of the flat conductor 11). The lead wire 10 is connected to a predetermined contact region (for example, an Ag plating region) on a cell surface in a silicon cell (solar cell module (not shown)) and a predetermined contact region on a frame member (for example, a lead frame). Thus, a solar cell assembly is obtained. Solder films for bonding may also be provided in predetermined contact areas of the cell surface and the lead frame.

Next, the manufacturing method of the lead wire 10 which concerns on embodiment used as the reference example of this invention is demonstrated based on an accompanying drawing.

  The flat body constituting the flat conductor 11 is manufactured using the roll mill 20 shown in FIG. 2 or a normal rolling mill. Specifically, the stranded wire is flattened by passing the stranded wire between the rolling rolls 21a and 21b of the roll mill 20, and a flat body is obtained. At this time, the strand 22a of the stranded wire located at the center in the width direction (left and right in FIG. 2) has a high compression rate, and the strand 22b of the stranded wire located at both sides in the width direction has a low compression rate. Become. Moreover, when a twisted wire is comprised with the composite wire of a dissimilar strand, it is preferable to arrange | position a strand (for example, an Invar (trademark) strand) with few heat shrinks on the outer side of a twisted wire. This is because the outer peripheral portion of the rectangular conductor 11 is most thermally affected (high temperature) during solder joining.

The flat body is used as a flat conductor 11, and solder film 15 is formed by performing solder plating on at least a part of the outer periphery of the flat conductor 11, and the lead according to the embodiment serving as a reference example of the present invention shown in FIG. Line 10 is obtained. At this time, the method for forming the solder film 15 is not particularly limited, and all conventional plating methods for conductors can be applied.

  The obtained lead wire 10 is joined to a predetermined contact region of the silicon cell to form a solar cell assembly.

Next, the operation of the lead wire 10 according to the embodiment serving as a reference example of the present invention will be described.

When soldering the lead wire and the silicon cell, the rectangular conductor of the lead wire is thermally expanded by heat application. For example, the coefficient of thermal expansion of the Cu conductor is about 0.3%. The lead wire is soldered to the silicon cell in a state where the flat conductor is thermally expanded. Thereafter, the solder is cooled and solidified by stopping the application of heat, but the flat conductor is thermally shrunk during this cooling, so that the silicon cell is warped. Here, flat as close to zero 0.5% yield strength when causing elongation of about 0.5% by applying a tension to the conductor, the effect of thermal shrinkage has on the silicon cell is small Kunar.

  When a solid conductor and a stranded wire conductor having the same cross-sectional area are manufactured using the same material, the thermal expansion amount at a certain temperature is the same. However, when a lead wire using a solid conductor as a flat conductor (see FIG. 5) and a lead wire using a twisted conductor as a flat conductor (see FIG. 1) are soldered to a silicon cell, respectively, after heat application The residual stress in each lead wire is different. This residual stress value is a factor that determines the amount of warpage of the silicon cell.

Here, in the lead wire 10 according to the embodiment which is a reference example of the present invention , the flat conductor 11 is formed of a stranded wire flat body, and the 0.5% proof stress of the flat conductor 11 is adjusted to 70 MPa or less. The 0.5% proof stress value can be freely adjusted by adjusting the distance between the strands 12 of the stranded wire constituting the flat conductor 11, and the 0.5% proof stress value decreases as the strand distance increases. Since the stranded wire has a space between the strands, even a flat body obtained by flattening the stranded wire has a slight space between the strands. For this reason, even if an external force (tension) acts on the flat conductor 11, the external force is relaxed and buffered by moving each strand using the space between the strands.

Therefore, when the lead wire 10 and the silicon cell according to the embodiment which is a reference example of the present invention are solder-bonded, the flat conductor 11 is thermally expanded when heat is applied, but the flat conductor 11 is moved by moving each strand. (5% proof stress value of the rectangular conductor 11 is reduced). As a result, since the stress remaining in the flat conductor 11 is also reduced, the influence of the heat shrinkage of the flat conductor 11 on the silicon cell is reduced during heat shrinkage after heat application.

  On the other hand, in a lead wire using a solid conductor as a flat conductor, even if an external force (tension) is applied to the solid conductor, the external force is not relaxed or buffered. Therefore, when this lead wire and the silicon cell are soldered together, the rectangular conductor is thermally expanded when heat is applied, and remains in the rectangular conductor as stress as it is. As a result, during the heat shrinkage after heat application, the silicon cell is greatly warped by the heat shrinkage of the flat conductor.

As described above, by using the lead wire 10 according to the embodiment serving as a reference example of the present invention as the connecting lead wire of the solar battery, warpage hardly occurs in the silicon cell after soldering. The warpage amount of the silicon cell is preferably less than 2.5 mm, more preferably 2.0 mm or less, and particularly preferably 1.5 mm or less. In addition, since the lead wire 10 according to the embodiment serving as a reference example of the present invention hardly causes cell warping after soldering with a silicon cell, the productivity of the solar cell assembly can be improved.

In the past, Sn-Pb eutectic solder having a low melting point has been frequently used as the solder constituting the solder film 15 when importance is attached to reducing the amount of thermal expansion at the time of solder joining between the lead wire and the silicon cell. It was. This was a factor that hindered Pb-free. However, since the lead wire 10 according to the embodiment serving as a reference example of the present invention has less thermal shrinkage after solder bonding, it is possible to use Pb-free solder having a higher melting point than Sn—Pb eutectic solder. Become.

  In general, Pb-free solder has a higher melting temperature than Sn—Pb eutectic solder, so there is a concern about damage to the connection member (cell surface and lead frame contact area) due to solder bonding. However, among Pb-free solders, Sn-3Ag-0.5Cu solder and Sn-4Ag-0.5Cu solder (both units are weight%) have a feature that the melting temperature is low. Moreover, by further including In and / or P in these solders, the melting temperature of the solder can be further lowered. By using Sn—Ag—Cu-based Pb-free solder having these compositions, it is possible to further reduce the risk of deformation or breakage of the silicon cell during solder joining.

When the lead wire 10 according to the embodiment which is a reference example of the present invention is used for solder bonding with a silicon cell, the amount of warpage of the cell is the same as when the lead wires 50 and 70 shown in FIGS. 5 and 7 are used. When it may be the same, the electrical conductivity of the lead wire 10 can be improved. Further, when the lead wire 10 according to the embodiment serving as a reference example of the present invention is used for solder bonding with a silicon cell, the case where the lead wires 50 and 70 shown in FIGS. Can be the same, the cell warpage of the lead wire 10 can be further reduced.

The lead wire 10 according to the embodiment serving as a reference example of the present invention can be used as a lead wire of a solar cell assembly, and also used as a lead wire for all components in which warpage after soldering is a problem. It is possible.

It will now be described with reference to the implementation of the present invention in the accompanying drawings.

A cross-sectional view of the lead according to good proper one embodiment of the present invention shown in FIG. In addition, about the solder film which is the same member as FIG. 1, the same code | symbol is attached | subjected also in FIG. 3, and description is abbreviate | omitted about this member.

  In the lead wire according to the present embodiment, at least a part of the outer periphery of a rectangular body obtained by deforming a composite body in which a plurality of braided wires are bundled into a rectangular cross section is covered with a solder film 15. More specifically, as shown in FIG. 3, a composite 33 is formed by bundling a plurality of braided wires 32 (in FIG. 3, the case of four bundles is shown). A bundle of a plurality of the composite bodies 33 (in the case of 18 in FIG. 3) is a flat body, and the entire outer periphery of the flat body (flat conductor 31) is covered with the solder film 15. The lead wire 30 according to the embodiment is used. The composite 33 may be one in which a plurality of braided wires 32 are twisted together.

Braided wire 32 is comprised of C u wire. The smaller the diameter of the braided wire 32, the higher the solid ratio of the flat conductor 31.

  Next, a method for manufacturing the lead wire 30 according to the present embodiment will be described with reference to the accompanying drawings.

  The flat body constituting the rectangular conductor 31 is manufactured by arranging a plurality of composite bodies 33 shown in FIG. 3 in parallel (9 cases shown in FIG. 3) to form a composite group. A flat body is formed by overlapping a plurality of layers (in the case of two layers in FIG. 3). Here, a stranded wire obtained by twisting a plurality of composite bodies 33 may be rolled and flattened using the roll rolling machine 20 shown in FIG.

  This flat body is used as a flat conductor 31, and solder plating is performed on at least a part of the outer periphery of the flat conductor 31 to form the solder film 15, and the lead wire 30 according to the present embodiment shown in FIG. 3 is obtained.

  Also in the lead wire 30 according to the present embodiment, the same effect as the lead wire 10 according to the previous embodiment is expected. Moreover, the braided wire 32 which comprises the flat conductor 31 of the lead wire 30 which concerns on this Embodiment has a large ratio of the space which occupies for the whole wire compared with the twisted wire 12 shown in FIG. For this reason, the lead wire 30 has a higher stress relaxation effect than the lead wire 10, and as a result, the amount of warpage of the silicon cell becomes smaller.

  As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various other things are assumed.

Next, although this invention is demonstrated based on a reference example, this invention is not limited to this reference example.

( Reference Example 1)
Seven tough pitch copper (TPC) wires having an outer diameter of 0.26 mm were twisted to produce a stranded wire (cross-sectional area of about 0.37 mm ² ). The strand spacing of the stranded wires was 0.003 mm, and the 0.5% proof stress was 50 MPa.

  This stranded wire was rolled using the roll mill shown in FIG. 2 to produce a flat rectangular body (flat conductor). A Sn-3Ag-0.5Cu Pb-free solder plating film with a thickness of 0.02 mm was formed around the flat conductor to produce a lead having the structure shown in FIG.

( Reference Example 2)
A lead wire was produced in the same manner as in Reference Example 1 except that the strand spacing of the stranded wires was 0.010 mm and the 0.5% proof stress was 0 MPa.

(Conventional example 1)
Invar (registered trademark) made of Cu with a width of 2.0 mm and a thickness of 0.037 mm, made of Cu, with a width of 2.0 mm and a thickness of 0.074 mm sandwiched between the plates, a width of 2.0 mm and a thickness of 0.185 mm A clad material (flat rectangular conductor) was produced (cross-sectional area was 0.37 mm ² ).

  A Sn-3Ag-0.5Cu Pb-free solder plating film with a thickness of 0.02 mm was formed around the flat conductor to produce a lead having the structure shown in FIG.

Each lead wire of Reference Examples 1 and 2 and Conventional Example 1 and a 200 μm thick silicon cell were connected by soldering, and the warpage amount (cell warpage: mm) of the silicon cell after connection was evaluated. Table 1 shows the structures and evaluation results of the lead wires of Reference Examples 1 and 2 and Conventional Example 1.

As shown in Table 1, when the lead wire of Conventional Example 1 was used, the cell warpage was as large as 2.5 mm.

On the other hand, when each lead wire of Reference Examples 1 and 2 was used, the cell warpage was 1.6 mm and 0.3 mm, and both satisfied the specified value (less than 2.5 mm). From this, it was confirmed that by setting the 0.5% proof stress to 50 MPa or less, the cell warpage can be reduced to 1.6 mm or less, which is suitable as a lead wire for a solar cell.

It is a cross-sectional view of a lead wire according to an embodiment as a reference example of the present invention. It is a schematic diagram for demonstrating the manufacturing method of a flat conductor. It is a cross-sectional view of the lead according to good proper one embodiment of the present invention. It is a figure which shows the connection state of a silicon cell and a lead wire. It is a cross-sectional view of a conventional lead wire. It is a schematic diagram which shows the state before and behind the solder joint of a silicon cell and a lead wire. It is a cross-sectional view of a lead wire using a low thermal expansion type flat conductor.

10 Lead wire 11 Flat conductor 12 Wire 15 Solder film

Claims (7)

  A lead wire characterized by covering at least a part of the outer periphery of a rectangular body obtained by deforming a composite body in which a plurality of braided wires made of Cu strands are bundled into a rectangular cross section with a solder film.   In a lead wire in which at least a part of the outer periphery of a flat conductor is covered with a solder film, the flat conductor is composed of a flat body obtained by flattening a composite of a plurality of braided wires made of Cu strands. Characteristic lead wire.   The lead wire according to claim 1 or 2, wherein 0.5% proof stress of the rectangular body and the rectangular conductor is 70 MPa or less.   The lead wire according to any one of claims 1 to 3, wherein the solder film is made of a Sn-Ag-Cu-based Pb-free solder alloy.   The lead wire according to any one of claims 1 to 4, wherein conductivity of the rectangular body and the rectangular conductor is 60% IACS or more.   A composite body in which a plurality of braided wires made of Cu strands are bundled is rolled to form a flat body having a flat cross section, and the flat body is a flat conductor, and at least part of the outer periphery of each flat conductor A method for producing a lead wire, comprising performing solder plating to form a solder film. Solar cell assembly, characterized in that the soldered a lead wire and a silicon cell according to claims 1 to 5 or.

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