JP6065646B2 - Tape-like conductive material, solar cell interconnector and solar cell module - Google Patents

Description

  The present invention particularly relates to a tape-like conductive material, a solar cell interconnector, and a solar cell module that are used for collecting solar cells.

  Solar cell power generation is a power generation method that converts inexhaustible solar energy directly into electrical energy. For this reason, solar cell power generation has been actively developed in recent years as a technology for greatly reducing energy problems, and the market has greatly expanded.

  Currently, a single-crystal silicon substrate or a polycrystalline silicon substrate is often used as a substrate for solar cells. A solar battery employing a single crystal silicon substrate or the like is formed of a plurality of substrates called solar battery cells having a size of about 5 inches to 6 inches square. A plurality of solar cells forming a solar cell are connected by current collecting wiring to collect electric energy generated in each solar cell. As a connection between the solar battery cell and the current collecting wiring, a melt liquid phase bonding using solder is often employed. This current collecting wiring is called a current collecting interconnector, and is formed by a copper-coated rectangular wire. Generally, a copper flat wire is manufactured by rolling a round wire into a flat wire (metal tape), or rolling a plate to a predetermined thickness and then slitting. The cross-sectional shape of a rectangular copper wire used for a solder-coated rectangular copper wire used for a general current collecting interconnector has a thickness of 0.1 to 0.3 mm and a width of 1 mm to 3 mm. Moreover, the cross-sectional shape of the solder-coated flat copper wire used for the interconnector used in the solar cell module is in the range of about 0.1 to 0.3 mm in thickness and about 3 mm to 10 mm in width. Further, the weight per unit area of the solder is 10 μm to 40 μm on one side in average thickness, but is often 20 μm or more.

  FIG. 1 is a diagram schematically showing a part of a general crystalline solar cell on which a current collecting interconnector is mounted.

  As shown in FIG. 1, the solar cell includes solar cells 1a, 1b, and 1c, and current collector interconnectors 2a, 2b, 2c, and 2d that are metal tapes. The solar cells 1a, 1b, and 1c and the current collecting interconnectors 2a, 2b, 2c, and 2d are respectively mounted by being mechanically and electrically joined with solder or a conductive adhesive. . In this way, the form of joining and mounting with other materials in the longitudinal direction of the side surface of the metal is hereinafter referred to as line mounting.

  The current collecting interconnectors 2a and 2b are line-mounted on the front surface of the solar battery cell 1a and the back surface of the solar battery cell 1b arranged adjacent to the direction of the L direction 3 of the solar battery cell 1a. Here, the front surface refers to a surface facing in the positive direction of the D direction 4, and the back surface refers to a surface facing in the negative direction of the D direction 4. The current collecting interconnectors 2c and 2d are line-mounted on the front surface of the solar cell 1b and the back surface of the solar cell 1c. Thus, the solar cells 1a, 1b, and 1c are electrically connected in series by being connected by the current collecting interconnectors 2a, 2b, 2c, and 2d. The current collecting interconnectors 2a and 2b are arranged at an appropriate interval in the direction of the W direction 5. Similarly, the current collecting interconnectors 2c and 2d are arranged at an appropriate interval in the direction of the W direction 5.

  In such a solar cell, when copper or aluminum, which is a typical material of a conductive material, and silicon, which is a typical material of a semiconductor, are connected, the thermal expansion coefficient of the metal and the semiconductor is limited unless it is joined at room temperature. Thermal stress corresponding to the difference is generated. Even if a metal electrode is interposed between the conductive material and silicon, the metal electrode is generally thinner than silicon and less rigid than silicon. The difference in thermal expansion between the material and silicon is particularly problematic.

In order to join the current collector interconnector to the solar battery cell, it is necessary to perform a process of cooling the current collector interconnector and the solar battery cell to room temperature after raising the temperature of the current collector interconnector and the solar battery cell. In this process, thermal stress is generated due to the difference between the thermal expansion coefficient of silicon, which is the main structure of solar cells, and the thermal expansion coefficient of copper, which is the main structure constituting the current collector interconnector. To do. Typical linear expansion coefficients of metal and silicon near room temperature are 16.6 × 10 ⁻⁶ (K ⁻¹ ) for copper, 19 × 10 ⁻⁶ (K ⁻¹ ) for silver, and 25 × 10 ^{−6 for} aluminum. (K ⁻¹ ) and silicon are 3 × 10 ⁻⁶ (K ⁻¹ ). If copper and silicon are bonded at 200 ° C., a difference in length of about 0.26% occurs, and in fact, thermal stress and warpage occur between copper and silicon. Thus, since the ratio of the thermal expansion coefficient of copper and the thermal expansion coefficient of silicon is as large as about 5 times, the solar cell may be deformed and damaged by the generated thermal stress.

  Since solar cells are energy devices that output generated power as current, the cross-sectional area of the current collector interconnector and the area of the connection surface between the current collector interconnector and solar cells are It is necessary to determine the amount of current flowing through the interconnector.

  On the other hand, in order to cope with the situation where the silicon material is tight and to reduce the cost of the solar cell, the substrate used for the solar cell has been made thinner. For example, a very thin silicon substrate such as a thickness of 180 μm has been used as a solar battery cell. For this reason, the damage of the solar battery cell due to thermal stress is a further serious problem.

  There are roughly two measures for solving this problem. One is a structure-based policy, and many policies have been proposed. (For example, refer to Patent Documents 1 and 2.)

  The invention described in Patent Document 1 is a measure for releasing stress by forming a corrugated portion in the length direction of the current collecting interconnector. Moreover, the invention described in Patent Document 2 is a method in which a non-connecting portion where no electrode is formed is formed at arbitrary intervals in the length direction of the electrode of the solar battery cell, thereby connecting the current collecting interconnector. This is a measure for reducing the thermal stress in the cooling process.

  A technique for relieving thermal stress by changing the connection structure between the solar battery cell and the current collecting interconnector is very effective. However, in the technique described in Patent Document 1, since the required length of the current collecting interconnector is increased, the material cost and electrical resistance of the current collecting interconnector may be increased. Further, in the techniques described in Patent Documents 1 and 2, since the junction area between the solar battery cell and the current collecting interconnector is reduced, the connection resistance is increased and the electrical property of the junction portion (notch portion) is increased. Resistance can increase.

  Therefore, apart from such technology, it is required to improve the mechanical properties of the current collector interconnector by further reducing the Young's modulus and lower yield stress of the material of the current collector interconnector itself. Such an improvement is another measure (see, for example, Non-Patent Document 1).

  In various types of solar cells other than solar cells using a polycrystalline silicon substrate, the same problem arises because the materials of the solar cells and the conductive conductors are different.

  From the thermal expansion coefficients of metal and silicon, softening is particularly important to lower the yield stress, and 0.2% proof stress is often used as an index. That is, it is important to lower the 0.2% yield strength to yield the metal side and reduce thermal stress and warpage. In order to soften the metal, a method of reducing the dislocation density by annealing is employed.

  However, softening by annealing generally used has a limit in reducing 0.2% proof stress, and it is difficult to cope with further thinning of the solar cell substrate. Therefore, various techniques have been proposed (see, for example, Patent Documents 3 to 6).

  In Patent Document 3, by fixing at least one of zirconium and magnesium at 3 to 20 ppm and oxygen at 5 ppm or less by mass parts per million, the sulfur that is an element that inhibits the coarseness of crystal grains is fixed. Thus, a method is adopted in which the deformation resistance of the current collecting interconnector is reduced by setting the average grain size to 300 μm or more.

  In Patent Document 4, if the crystal grains are made too large to 20 μm or more in order to reduce the 0.2% proof stress of the lead wire which is a current collecting interconnector, cracks easily occur due to deformation, There is a problem that fatigue failure easily occurs due to stress concentration. On the other hand, if the thickness is 6 μm or less, the softness of the conductor is lost, and the crystal grain size of the conductor is preferably in the range of 6 to 20 μm.

  In the invention described in Patent Document 5, the 0.2% proof stress of the current collector interconnector is obtained by orienting the crystal orientation (plating line axis orientation) of the conductor center portion in the (211) orientation at a ratio of 30% or more. This is a measure to reduce the warpage of the solar battery cell.

  On the other hand, in Patent Document 3, by aligning the <100> orientation in the longitudinal direction, the Young's modulus and the yield stress in the longitudinal direction of the current collector interconnector are reduced, and the thermal stress when soldering facing each other is reduced. It is possible to reduce the warpage of the semiconductor and reduce the thermal stress on the connection interface, thereby suppressing the destruction of the semiconductor.

  In response to the growing demand for solar cells in recent years, the demand for thinning of crystalline solar cells has increased due to the tightness and low cost of silicon raw materials, and the softening of current collector interconnectors that reduces damage to silicon cells. The demand is growing.

  A collector interconnector for a solar cell is required to have high linearity because it needs to be mounted on a narrow electrode of cells arranged in a straight line. The production of a narrow flat metal wire is generally performed by crushing a round metal wire with a rolling mill to obtain a flat metal wire. Particularly, when a narrow flat metal wire is to be produced, a roll of a rolling mill is used. If the parallelism of the wire is a little bad, there is a problem that the wire is bent in the width direction.

  On the other hand, in recent years, a wire bump has been proposed in which a bump made of metal is soldered on a semiconductor wafer and a metal wire or a metal tape is joined (for example, see Patent Document 7). Even in the case of connecting with solder, thermal stress may be generated, so that the same problem as that of the solar cell current collector interconnect described above may occur.

  Further, there is an application in which a flat metal wire is used as a wire bonding wire called a tab wire that connects a semiconductor chip and an external metal electrode. In the case of a flat metal wire, a technique called wedge bonding is used in which a wide surface of a flat metal wire is bonded to a metal electrode or an external electrode on a semiconductor chip using ultrasonic waves. In this case, in order to increase the bonding force between the metal electrode and the flat metal wire, the flat metal wire must be easily deformed in the width direction and the longitudinal direction of the wire by the ultrasonic wave and the rolling force on the metal electrode. There is a need for metal wires.

  On the other hand, although not aimed at measures for softening in the longitudinal direction, Patent Document 8 devises an inner lead for connecting a solar cell element of a metal foil formed by bundling a plurality of metal materials. The effect of Patent Document 8 is that the surface of the semiconductor substrate of the solar cell element is heated by bundling a plurality of metal materials while heating the inner lead for connecting the solar cell element while ensuring the same cross-sectional area as the conventional copper foil. It is possible to improve the flexibility in the short direction when fixed to the surface electrode provided by soldering. By shifting the metal wires in the short direction, the inner lead for connecting the solar cell element can easily follow the shape of the electrode, and the welding area at the welding point can be increased. It can be effectively suppressed. Further, the metal foil configured by bundling the plurality of metal materials is arranged such that each metal material is arranged in a line in the width direction of the metal foil, thereby further connecting inner leads for connecting solar cell elements. Since the flexibility in the short direction is improved, the welding area between the inner lead for connecting the solar cell element and the electrode can be improved, and the adhesion strength can be improved.

  However, Patent Document 8 does not have a technical idea regarding softening of the current collecting interconnector in the longitudinal direction.

  In recent years, there has been a strong demand for cost reduction for the spread of solar cells. Among them, the cost reduction of interconnectors contributes to the use of sustainable energy sources.

  In the case of an interconnector of the type in which the most mainstream copper is the core material and the solder is coated and connected by reflow of the coated solder, when comparing the material costs of the main materials copper and tin, The price is about three times the weight of copper. Therefore, it is desirable in terms of cost that the solder weight is as small as possible. However, when joining by solder reflow, it is almost always covered with solder having a weight of 20 μm or more on one surface. Since the standard thickness of the copper core material is 0.2 mm, it is necessary to cover 20% or more of solder by volume. This is because if the basis weight of solder is reduced, sufficient solder is not supplied to the electrodes on the solar battery cells, resulting in poor bonding. As shown in Fig. 1, since the interconnector is alternately connected to the opposite side of the cell's light receiving surface, it is necessary to coat the solder on both sides of the interconnector, and the opposite side of the junction surface that is not used for joining the interconnector This solder is wasted because it does not contribute to bonding. Since the tin component of general lead tin solder is 60 to 70% by weight, and the composition of tin of lead-free solder is 95% by weight or more, reducing the amount of solder in the interconnector is a resource in terms of cost. It is also important to reduce the amount of lead used in an interconnector that uses lead solder. However, due to the above-described problem of jointability, it is difficult to reduce the amount of solder in the current mainstream solder reflow type interconnector.

JP 2006-80217 A JP 2008-21831 A JP 2009-280898 A JP 2010-14050 A JP 2008-168339 A JP 2010-073445 A JP 2006-319002 A JP 2005-191116 A

Hirotoshi Endo, et al., Hitachi Cable: 2007, Vol. 26, No. 1, p15

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to be a tape that is easily deformed with a low yield stress in the longitudinal direction of the wire, and that has low cost and excellent linearity. It is to provide a conductive material, an interconnector for solar cells, and a solar cell module.

The gist of the present invention is as follows.
(1) The tape-shaped conductive material according to the present invention comprises two or more single core wires mainly composed of copper or aluminum, and the two or more single core wires are parallel to the length direction of the single core wires, And it is integrated so as to be electrically connected to each other in the width direction, and the two or more single core wires are directly point-bonded to each other in the width direction at intervals of 5 mm to 60 mm in the longitudinal direction, Or, it is point-bonded to each other in the width direction through a binding material different from the single core wire, and is covered with a material constituting the single core wire or a material having a lower melting point than the binding core material, In a cross section perpendicular to the length direction of the single core wire, the area average diameter corresponding to the circle of crystal grains constituting the single core wire is 5 with respect to the equivalent circle diameter of the cross-sectional area per single core wire. % Or more.
(2) The tape-shaped conductive material of (1) is characterized in that the single core wire is covered with aluminum or silver.
(3) The tape-shaped conductive material according to the present invention comprises two or more single core wires mainly composed of copper or aluminum, and the two or more single core wires are parallel to the length direction of the single core wires, And it is integrated so as to be electrically connected to each other in a row in the width direction, the single core wire is covered with aluminum or silver, and in a cross section perpendicular to the length direction of the single core wire, The area average diameter corresponding to a circle of crystal grains constituting the single core wire is 5% or more with respect to the equivalent circle diameter of the cross-sectional area per single core wire.
(4) In the tape-shaped conductive material of (3), the two or more single core wires are directly point-bonded to each other in the width direction at an interval of 5 mm to 60 mm in the longitudinal direction, or Are point-bonded to each other in the width direction via different bundling bonding materials, and are covered with a material constituting the single core wire or a material having a melting point lower than that of the bundling bonding material.
(5) The tape-like conductive material according to the present invention is composed of two or more single core wires mainly composed of copper or aluminum, and the two or more single core wires are parallel to the length direction of the single core wires, And it is integrated so as to be electrically connected to each other in the width direction, and the two or more single core wires are directly point-bonded to each other in the width direction at intervals of 5 mm to 60 mm in the longitudinal direction, Or, it is point-bonded to each other in the width direction through a binding material different from the single core wire, and is covered with a material constituting the single core wire or a material having a lower melting point than the binding core material, The single core wire is covered with aluminum or silver, and an area average diameter corresponding to a circle of crystal grains constituting the single core wire in a cross section perpendicular to the length direction of the single core wire is the single core wire. Breaks per core wire Characterized in that it is 5% or more with respect to the circle equivalent diameter of the product.
( 6 ) The tape-shaped conductive material according to any one of (1) to (5) is equivalent to a circle of crystal grains constituting the single core wire in a cross section perpendicular to the length direction of the single core wire. The area average diameter is 20% or more with respect to the equivalent circle diameter of the cross-sectional area per single core wire.
( 7 ) The tape-shaped conductive material according to any one of (1) to (6) is equivalent to a circle of crystal grains constituting the single core wire in a cross section perpendicular to the length direction of the single core wire. The area average diameter is 50% or more with respect to the equivalent circle diameter of the cross-sectional area per single core wire.
( 8 ) The tape-shaped conductive material according to any one of (1) to (7) covers the two or more single core wires with a binding material having lower strength or hardness than the single core wires. By doing so, the two or more single core wires are integrated so as to conduct each other.
( 9 ) The tape-shaped conductive material according to any one of (1) to (7) is coated with a binding material on each of the two or more single core wires, and the two or more single core wires are connected to each other. In a cross-section perpendicular to the length direction of the tape-like conductive material, the covering cross-sectional area of the bundling bonding material is the total cross-sectional area of the two or more single core wires. It is characterized by being 10% or less.
( 10 ) The tape-shaped conductive material according to any one of (1) to (7) is integrated so that the two or more single-core wires are in contact with each other in the width direction via a bundling bonding material different from the single-core wires. Or part of the contact surface of the side surface of the single core wire is directly joined to each other.
(11) (1) (2), (4) any one of the tape-shaped conductive material to (10), that the two or more binding bundles bonding material you integrated single core wire, is a solder It is characterized by.
( 12 ) The tape-shaped conductive material according to any one of (1) to (11) is characterized in that a 0.2% proof stress of the tape-shaped conductive material is 20 to 70 MPa.
( 13 ) The solar cell interconnector according to the present invention uses the tape-shaped conductive material of any one of (1) to (12) , and the thickness of the tape-shaped conductive material is 0.1 mm to 0.3 mm, the width of the tape- like conductive material is 1 mm to 10 mm, and the aspect ratio of the width and thickness of the single core wire is 2 or less.
( 14 ) A solar cell module according to the present invention includes a string in which solar cells are connected in series with the tape-shaped conductive material according to any one of (1) to (12) .

  As described above, according to the present invention, it is possible to soften a conductor by facilitating deformation at the time of joining by joining or joining two or more single-core wires with controlled crystal grain sizes. The thermal stress generated between the semiconductor to be formed or the metal electrode provided thereon is relaxed to improve the bondability, and disconnection due to fatigue failure is less likely to occur. As a result, it is possible to provide a tape-like conductive material, a solar cell interconnector, and a solar cell module that are easily deformed with a low yield stress in the longitudinal direction of the wire, are low in cost, and have high linearity and fatigue characteristics. .

  Furthermore, in one embodiment of the present invention, the amount of metal such as solder composed of tin or lead covering the interconnector can be reduced, and resource saving, low cost, and high performance for solar cells can be achieved. An interconnector and a solar cell module can be provided.

It is a figure which shows roughly the solar cell by which the interconnector for current collection which concerns on embodiment of this invention is line-mounted. It is a figure which shows roughly the cross section of the metal electrically-conductive material which concerns on the same embodiment. 1 schematically shows a cross-sectional form of a current collecting interconnector used in a silicon crystal solar cell.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the embodiment of the present invention described below, the conductive material is softened mainly in the length (longitudinal) direction, the thermal stress generated between the semiconductor to be joined or the metal electrode provided thereon, and This form is suitable for improving the bondability by facilitating deformation at the time of joining, and further preventing the disconnection due to fatigue failure.

  The conductive material according to the present invention is a wire, macroscopically a flat wire, and a flat tape-like conductor in a plane perpendicular to the wire length direction. Of the opposing surfaces parallel to the length direction of the tape, the wide surface (that is, the surface generally called the tape surface) is preferably macroscopically parallel, but microscopically uneven. There may be. Other opposing surfaces (that is, generally referred to as side surfaces) do not have to be flat surfaces, and may be curved surfaces. In the present invention, the thickness refers to the macroscopic length between the tape surfaces, that is, the maximum value, and the width refers to the maximum value between the side surfaces. The width direction is also referred to as the short direction.

  A major application of the present invention is a conductive material called a current collector interconnector for collecting and transporting power via a silicon cell constituting a crystalline solar cell and a metal electrode provided on the silicon cell. I will provide a. Therefore, in the following, as a representative example, the form of the present invention will be described by taking as an example the case where the tape-shaped conductive material according to the present invention is used as a current collecting interconnector for a solar cell. It can be used as a conductive material for semiconductor mounting that is soft in the length direction or width direction, or a general conductive material.

  In the case of a current collecting interconnector for a solar cell, solder is generally used to join a metal wire and silicon. The melting point of general solder is between 180 ° C. and 250 ° C., and solder is reflowed at 200 ° C. to 300 ° C. for bonding. In this case, when the difference in thermal expansion between the metal and silicon is taken into consideration, the strain is about 0.3% at the maximum. A temperature of about 180 ° C. is also required in a joining method through a resin called a contact film containing a conductive filler that has recently been used.

  Since silicon is less likely to be plastically deformed than a metal that is a conductive material, the thermal stress at the time of bonding is reduced by facilitating plastic deformation of the metal material that is a conductive material. That is, it is extremely effective to reduce the yield stress in the longitudinal direction of the metal wire, in other words, the proof stress.

  Therefore, in the present invention, 0.2% proof stress, which is a representative index when expressing the yield stress of a metal, is used.

  In general, a small 0.2% proof stress means that the yield stress is small, the stress against strain is small in a strain region of approximately 1% or less, and the elastic modulus and elastic limit are also small. A material with a low yield strength is easily deformed. Therefore, the 0.2% proof stress is not only for conductive materials for silicon crystal solar cells, but also for materials used in applications where thermal stress from the elastic region to the plastic region is a problem during wide bonding and use. It becomes an index representing softness.

<About the configuration of the tape-shaped conductive material>
Since the present invention relates to a conductive material, the main conductor used needs to be a highly conductive material. Examples of the metal and highly conductive material include silver, copper, aluminum, and gold. When considering the raw material price, the conductor to be used is preferably copper or aluminum. Higher purity is generally softer and higher electrical conductivity, so higher purity is desirable. However, higher purity results in higher material costs. In general, purity in the range of 99.9% to 99.999% is common industrially. In the case of copper, it is common to use oxygen-free copper or tough pitch copper.

  Specifically, the tape-like conductive material of the present invention (hereinafter also simply referred to as a conductive material) has a cross-sectional form as shown in FIGS. 2a to 2h, for example. In other words, the tape-shaped conductive material of the present invention has two or more single-core wires (hereinafter also referred to as metal single-core wires) 6 mainly composed of copper or aluminum in the longitudinal direction while maintaining electrical continuity with each other. They are integrated by being joined or bundled in parallel and aligned in one plane. In addition, in the cross section in the direction perpendicular to the length direction of the single core wire, the size of the crystal grains is an area average diameter equivalent to a circle of 5% or more with respect to the equivalent circle diameter of one cross section of the single core wire. It takes the form which has. 2A to 2H are representative examples, and the cross-sectional shape is not limited to the illustrated one as long as it is in a form suitable for the following idea. In the present invention, the cross section or the cross sectional area means a cross section perpendicular to the length direction of the metal wire or its area unless otherwise specified.

  The conductive material of the present invention is a tape-shaped conductor, and is used by being connected to an electrode on a semiconductor at a surface perpendicular to the thickness direction of the tape, that is, the tape surface, and at least a part of the tape surface. The metal is exposed so as to be electrically conductive. In addition, since the present invention aims to soften as much as possible in the length direction while ensuring electrical conductivity, when each single core wire 6 is covered with an insulator, the conductor cross-sectional area becomes small, Does not meet the purpose. Therefore, each single core wire 6 is bundled in a conductive state. Thus, even if a part of the single core wire is disconnected, the current flowing through the disconnected single core wire can be bypassed to another wire. The number of wires to be bound may be two or more.

  TECHNICAL FIELD The present invention relates to a tape-like conductive material used for a wire connecting solar cells and power semiconductors, and flows a large current of several A. Therefore, the present invention is mainly made of copper or aluminum as much as possible. A larger cross-sectional area of the metal core material is desirable, and the metal core material is preferably a single metal core wire. Metal wires integrated by twisting thin metal wires are preferable because there is a space between the wires, the outer shape becomes the same when the current capacity is the same, and the softening that is the first purpose is not achieved. Absent. In order to facilitate plastic deformation in the length direction, a structure in which a plurality of single metal core wires 6 are aligned in one plane is desirable.

  Since the present invention forms a material having a large cross-sectional aspect ratio by arranging the metal single core wires in the width direction of the tape material, the aspect ratio of the metal single core wire as a component does not have to be large, and from the efficiency of the configuration, The aspect ratio between the maximum diameter and the minimum diameter is preferably 2 or less, for example. The most common single core wire is a round wire, the shape of the cross section is a circle, and the aspect ratio is 1.

  Further, two or more single core wires mainly composed of copper or aluminum need to be integrated because it is necessary to secure a current capacity by making a space in the conductor cross section as dense as possible. Moreover, in the stage before mounting with respect to semiconductors, such as a cell for solar cells, it needs to be integrated also from the handling relationship.

  As a method of integration, as shown in FIGS. 2a to 2c, a method of covering and binding the single core wires with the binding material 7 in a state in which the single core wires are arranged in a line, and the single core wires as shown in FIG. 2e. Examples of the method include welding and joining using different types of binding material 7 as shown in FIG. 2d. Moreover, these two methods can be used together like FIG. 2 f-FIG. 2 h. The conductor as shown in FIG. 2f is obtained by arranging metal single core wires in parallel in a row and welding on the side to form a tape-like conductor, then flattening the tape surface by rolling, and further metallizing with, for example, hot dipping. Can do.

  Note that the bundling bonding material 7 for integrating the single core wires 6 need not be a metal material, and may be a conductive adhesive.

  FIG. 3 is a cross-sectional view of a commonly used solar cell current collecting interconnector, in which a flat single-core copper wire 10 is covered with solder 11. Representative examples of embodiments of the present invention are shown in FIGS. 2a, 2b, and 2f. The coating amount of the solder 11 can be freely selected according to the application. Moreover, the metal single core wire 6 comprised with copper or aluminum does not need to be a round wire, and can take a form like FIG.

<About crystal grains>
The hexagonal lattice 8 shown in FIG. 2 and FIG. 3 schematically shows a crystal grain boundary in the cross-sectional area of the copper or aluminum single core wire 6 of the present invention. The size of one hexagonal lattice 8 shown in FIGS. 2 and 3 corresponds to the size of crystal grains. However, the crystal grains surrounded by the actual crystal grain boundaries are not the same in shape and size. The size of the crystal grains affects the 0.2% yield strength of the solar cell current collector interconnector.

  In particular, the 0.2% proof stress decreases as the size of the crystal grains increases with respect to the cross-sectional area of the single core wire 6, and as shown in FIGS. 2 and 3, the cross-sectional area per single core wire is small. The embodiment of the present invention in which the relative size of the crystal grains with respect to the cross-sectional area is large is effective for realizing a soft conductor. Specific indexes will be described later. In the present invention, the metal single-core wire 6 is bound by binding with a binding material 7 as shown in FIGS. 2a to 2d and 2f or by welding at a contact point as shown in FIG. 2e. A flat metal wire. In the case where the binder material 7 is a metal material such as solder, this region is also a polycrystalline body. However, in the present invention, the surrounding metal including the solder is soft or has a small proportion of the cross-sectional area. Therefore, the influence on the mechanical characteristics is small and therefore omitted.

  In order to achieve the softening of the wire in the longitudinal direction, which is the greatest effect of the present invention, compared to the conductive material composed of one single core wire as shown in FIG. It is not sufficient that they are joined or bound and integrated in parallel in the vertical direction and in one plane. It is a requirement that the metal single core wires are softened, and further, it is necessary that the metal single core wires are not strongly constrained to each other.

  In order to realize the softening of the metal single core wire as described above and the state where the metal single core wires are not strongly restrained from each other, in the present invention, in a cross section in a direction perpendicular to the length direction of the metal single core wire, The size of the crystal grains constituting the metal single core wire has an area average diameter equivalent to a circle of 5% or more with respect to the equivalent circle diameter of the cross-sectional area per metal single core wire.

  As a method of reducing the yield stress of a metal, a method of coarsening crystal grains is known. It is empirically known that the yield stress is inversely proportional to the square root of d, where d is the grain size of the metal crystal grain, and this is called Hall Petch's law. This is explained by the fact that the slip plane responsible for the deformation of the metal crystal becomes discontinuous at the grain boundary and inhibits the movement of dislocations. According to Hall Petch's law, when the crystal grain size in the cross section of the metal wire is sufficiently larger than the cross-sectional area, if the crystal grain size is the same, the yield stress is determined by the crystal grain size itself.

  For example, a material composed of a copper rectangular wire and solder as shown in FIG. 3, which is a form of a general solar cell interconnector, and copper and solder having the same substance and the same total cross-sectional area as FIG. And a conductor having the cross section of FIG. At this time, when the crystal grain size surrounded by the crystal grain boundary 8 is sufficiently fine with respect to the copper single core wire 6, the yield stress in the longitudinal direction of the conductor having the cross section of FIG. The yield stress in the length direction of the conductor having the cross section of FIG. 3 is the same, and the effect of the present invention cannot be obtained. Strictly speaking, if there is a difference in the structure of the solder that is the binding material 7, the difference in the structure of the solder will affect the solder. For example, the influence caused by solder can be ignored.

  However, when the crystal grain size exceeds a certain value relative to the cross-sectional area of the copper single-core wire, the yield stress of the copper single-core wire deviates from Hall Petch's law and further decreases, and the crystal grain size is It has been found that the effect can be obtained when a form having an area average diameter equivalent to a circle of 5% or more with respect to the equivalent circle diameter of the cross-sectional area per core wire is taken. That is, even when the copper crystal grain size is the same when the form having an area average diameter equivalent to a circle of 5% or more with respect to the equivalent circle diameter of the cross-sectional area per single core wire 6 is taken. The yield stress of the conductor having the cross section of FIG. 2a is smaller than the yield stress of the conductor having the cross section of FIG. In particular, when the ratio of the average grain size of the crystal grains to the diameter of one copper single core wire is 20% or more, the 0.2% proof stress is further reduced, and when the ratio is 50% or more, the yield is further reduced.

  The crystal grain size of the actual material is not the same in the material as shown in the schematic diagrams of FIGS. 2 and 3 but has a distribution, and when expressing the size of the crystal grain size, the average grain size Use the diameter.

  When the size of a crystal grain is quantitatively indicated in the present invention, a general standard is used in which the crystal grain is a region surrounded by a crystal grain boundary having an orientation difference of 15 ° or more in rotation angle. The twin boundaries are not included in the grain boundaries. The size of the crystal grain is an average of equivalent circle diameters weighted by area, that is, area average diameter (MA), and is defined by the following equation.

Here, N is the total number of crystal grains in a cross-sectional area having a sufficient area necessary for obtaining the average grain size, A _i is the area of the crystal grain i, and ν _i is a circle of the crystal grain i. Equivalent diameter.

  In the present invention, the crystal grain size of the single metal core wire is desirably larger than the cross sectional area of the single core wire, and ideally it is several tens or less, preferably several or less, relative to the cross section. In this case, some crystal grains are coarsened, and the diameters of the coarse grains and other grains may be greatly different. As a way of expressing the average grain size, the definition by the average of the equivalent circle diameter weighted by the area is defined. Is appropriate. In the present invention, the value measured using a cross section perpendicular to the length direction of the single core wire is used, but when the number of crystal grains in the cross section is 30 or less, measurement is made on a plurality of cross sections. And at least the total number of crystal grains measured was 30 or more, and the area equivalent diameters obtained in the respective cross sections were obtained by simple averaging.

  The aspect ratio of the cross-sectional shape of the metal single core wire of the present invention is preferably as small as 2 (that is, 2 or less) at the maximum, so even if the cross-sectional shape of the metal single core wire is not a circle, The ratio of the desired crystal grain size to the equivalent circle diameter of the cross section is not affected by the cross-sectional shape of the metal single core wire.

  Here, the cross-sectional area of the metal single-core wire can be calculated from the diameter of the metal single-core wire because the cross-sectional shape is a circle when the metal single-core wire is a round wire. On the other hand, when the cross-sectional area of the single metal core wire cannot be easily calculated, a general method for obtaining the cross-sectional area by image processing from the optical microscope image and SEM image of the cross section can be used.

  The most common method for measuring the crystal grain size is the electron backscattered diffraction (EBSD) method, but is not particularly defined. Information obtained by the EBSD method is usually composed of thousands (hundreds of thousands to hundreds of thousands) of pixels (measurement points) having a sufficient number of positions and orientation information, and the rotation angle between pixels is a value greater than the specified angle. In this case, the boundary between the pixels is a grain boundary. Although the angle can be arbitrarily specified, in the present invention, 15 ° or more is defined as a grain boundary. A region closed by the crystal grain boundary is defined as a crystal grain, and the area is obtained from the number of pixels constituting the crystal grain, and the diameter when the area is converted into a circle is defined as the grain size.

  In order to increase the crystal grain size, a method of heating and recrystallizing the material is generally employed. The main driving force of recrystallization is strain energy. The more strain is accumulated, the easier the crystal grains grow. Therefore, the structure of the present invention that binds a single metal core wire when a conductor having the same total cross-sectional area, that is, the same electrical conductivity, is produced from the same base material, for example, the material of FIGS. 3 and 2a. Since the cross-sectional area is smaller, the processing strain is largely accumulated and the crystal grains are likely to be larger. One of the other driving forces for recrystallization is surface energy. In the case where the cores have the same cross-sectional area, the structure of the present invention in which the surface area or the area of the interface is large is extremely advantageous in terms of crystal grain growth.

  Therefore, if a material with the same total cross-sectional area is drawn from a strip with the same cross-sectional area by rolling or rolling, and the thermal history of the same temperature and time is applied in the solder plating process or another heat treatment process, The conductor of the invention has a larger crystal grain size, and the relative size of the crystal grain size with respect to a single metal single-core wire cross-sectional area is overwhelmingly advantageous, and the effect on the softening of the wire is extremely remarkable. become. To obtain a form having an area average diameter equivalent to a circle of 5% or more with respect to the equivalent circle diameter of one cross-sectional area of a single core wire required by the present invention, softening by heat treatment at a lower temperature for a shorter time Therefore, it is advantageous in terms of cost.

  As described above, a rectangular wire is formed by binding or joining a plurality of metal single core wires, and the crystal grains in the metal single core wire to be further configured have an equivalent circle diameter of the cross-sectional area of the single core wire. On the other hand, when it takes a form having an area average diameter equivalent to a circle of 5% or more, it is possible to reduce the yield stress in the longitudinal direction compared to a single metal rectangular wire having the same average crystal grain size. Become. Furthermore, in order to obtain such a structure, the form of the present invention having a small single-core wire cross-sectional area is advantageous in terms of both technology and cost.

  This effect is a rectangular copper having a thickness of 0.1 mm to 0.3 mm and a width in a range of 1 mm to 10 mm, which is a cross-sectional size of a flat wire used for an interconnector used in a solar cell. It is remarkable for substituting wires, and by dividing the width direction into a size equivalent to the size in the thickness direction, it is difficult to obtain a flat copper wire of 50 MPa or less, which is difficult to obtain by a normal industrial process. .2% yield strength is obtained. The yield strength at this time is obtained by dividing the load when 0.2% composition strain is applied in the longitudinal direction of the tape-like conductor hot-plated with 10-40 μm solder by the total cross-sectional area of the single core wire. Value.

  The form of the present invention having a small single core wire cross-sectional area is advantageous in obtaining a large crystal grain size both technically and in terms of cost, but in the longitudinal direction, which is the greatest effect of the present invention. In order to obtain a soft conductor, it is necessary that each single core wire is loosely bound or joined and can be deformed independently to some extent. For example, in the case of being firmly joined with the same material, the crystal grains are strongly restrained from each other, and the microscopic deformation behavior of the conductor behaves in the same way as a single rectangular wire. It is.

  Therefore, in this invention, when it is the form of FIG. 2 d-FIG. 2 f where single core wires join by methods, such as welding, adjacent single core wires are partially, preferably with respect to the area of the surrounding surface of a single core wire. The bonding area is preferably as small as 25% or less at the maximum.

  Further, in the length direction, a form in which the single core wires are partially joined to each other is advantageous rather than being continuously joined. Further, partial joining is desirable in terms of supplying solder between the front and back surfaces of the tape surface, which will be described later, in the case of taking the form of FIG. 2f.

  2a to 2d and FIG. 2f, it is desirable that the bundling metal that macroscopically binds the single core wires is softer than the single core wires. A larger difference is advantageous because the soft characteristics of the single core wire reflect the characteristics of the entire conductor.

  The softness of each material can be evaluated by a hardness such as a stress-strain curve or Vickers hardness by a tensile test or the like.

  Even if the bonding and bonding material is stronger and harder than the single metal core wire, if the proportion of the entire conductor is small as shown in FIGS. 2c and 2d, the influence on the yield stress of the entire conductor is small. . Depending on the difference in strength and hardness, when the strength and hardness of the binding material is larger than that of the single metal core wire, the cross sectional area of the binding material relative to the total cross sectional area of the single metal core wire is preferably 10% or less. . At this time, the smaller the value of the ratio of the metal single core wire to the total cross-sectional area, the softer the tape-like conductive material is, but it is desirable, but other functions of the bundling bonding material such as semiconductor bonding, corrosion resistance, optical It is determined in consideration of characteristics.

  Under the condition that the metal single core wire is weakly bundled, the conductor length is the bamboo nodular structure in which the average grain size is 50% or more of the cross-sectional area of one single core wire. The macroscopic deformation of the direction results in deformation of crystal grains facing the slip direction in which copper and aluminum are most likely to slide. At this time, the macroscopic yield strength is very preferable as the material of the present invention because the Schmid factor of the face-centered cubic metal single crystal approaches the yield stress of the largest orientation and can behave very softly.

<Specific materials and physical property values>
Hereinafter, materials and physical properties when used as a general solar cell interconnector will be described in detail.

  Consider a conductor having a cross-sectional shape of a copper rectangular wire of 0.2 × 1.5 mm used as an interconnector for a general solar cell. Consider a conductive material of the present invention having the same cross-sectional area and material as this conductor. In order to obtain the same total cross-sectional area, six materials having a diameter of 252 μm may be bundled. Although the thickness is somewhat thick, it is in the range where there is no problem as an interconnector for solar cells.

  In order to satisfy the provisions of the present invention, the average particle size of the copper core material of this conductor is required to be 12.85 μm or more. When trying to obtain a particle size larger than this size, for example, if oxygen-free copper is used, the cold work rate by drawing is 98% or more in terms of the area reduction rate, and at 200 ° C. for about 1 hour. Recrystallization heat treatment is necessary. These conditions are not general copper wire processing and heat treatment conditions, but are industrially possible.

  Depending on each area reduction during wire drawing, if the copper wire is a tough pitch copper wire, the solder is lead-tin solder, and the basis weight of the lead-tin solder is about 20 μm on one side, a general copper rectangular wire The interconnector has a 0.2% proof stress of about 90 to 120 MPa, while the material of the present invention can be softened to 70 MPa or less. Here, the proof stress value is a value obtained not by the entire cross-sectional area including the solder but by the cross-sectional area of the copper core material portion. When copper is oxygen-free copper or when the core is aluminum, a smaller yield stress can be obtained. However, since aluminum has a larger electrical resistivity value than copper, in order to obtain the same current capacity, it is necessary to increase the cross-sectional area of the core material.

  By conducting a heat treatment at a higher temperature before plating the solder, the conductive material of the present invention can be further softened. When having a typical cross-sectional shape as described above and copper is oxygen-free copper, the crystal grains in the copper single-core wire to be formed are 20% of the equivalent-circle diameter of the cross-sectional area of the single core wire. When taking the form having the area average diameter equivalent to the above circle, the 0.2% proof stress value can be reduced to about 50 MPa, which is close to the lower limit of the 0.2% proof stress of a general solar cell final power interconnector. Furthermore, when the average grain size of the crystal grains is a bamboo-like structure in which the cross-sectional area of one single core wire is 50% or more, the macroscopic deformation in the conductor length direction is the most slip of copper. The crystal grains facing the largest orientation of the Schmid factor that are easily oriented in the slip orientation are deformed, and the 0.2% proof stress value can be reduced to 20 MPa.

  By remarkably purifying the metal single core wire, the 0.2% yield strength can be reduced to less than 20 MPa. However, since the plastic deformation due to the tension during mounting makes handling difficult, the 0.2% yield strength is preferably 20 MPa or more. .

<Concerning Specific Manufacturing Method of Solar Cell Current Collectors>
In the case of a general solar battery current collecting interconnector, solder coated on a rectangular metal wire is melted and joined. When the binding material 7 of FIGS. 2a to 2c is a solder material, it can also serve as a material for bonding with a semiconductor. The solder may be any of Pb—Sn based lead solder alloy, Sn—Ag based, or Su—Ag—Cu based lead free solder alloy, and is not particularly limited in the present invention. Usually, the composition of tin in the lead solder is about 60% by mass, the composition of silver in the lead-free solder material is 1 to 4% by mass, the composition of copper is about 0 to 1% by mass, and the balance is a trace amount. Additive elements and tin. Since the solder material of these compositions is softer than copper, it is a preferable material for the binding material 7 of the present invention.

  Mounting using a solar cell current collector interconnector often takes the form shown in FIG. 1, and is often covered with solder on both sides. In many cases, no solder is supplied from the outside, and the counterpart silver electrode is formed by baking a paste material, so that there are many irregularities. Therefore, thick solder of 10 to 40 μm on one side, generally 20 μm or more on one side is often stacked. Since tin and silver, which occupy a large proportion of solder, are more expensive than copper, particularly when lead-free solder is used, the proportion occupying the price increases. As shown in FIGS. 2a to 2c, the single metal core wire 6 is joined through a single metal core wire made of copper or aluminum by taking a form in which the single metal core wires are bundled in a row in the width direction with solder. Since the solder is supplied to the side opposite to the surface, there is an advantage that the amount of solder per unit area can be reduced as shown in FIGS. 2b and 2c, for example.

  When the binder material 7 is solder and is melted and bonded, the current collector interconnector of the present invention is soft in the conductor length direction and the tape surface is also freely in the width direction. Since it can be deformed, it is particularly convenient for bonding to an electrode with large irregularities.

  One method for binding metal single core wires with a material having a low melting point is a method in which the metal single core wire 6 is continuously submerged in a hot dipping bath and plated. The amount of coating on the metal single-core wire 6 and the interval between the metal single-core wires in the width direction are determined by arranging a drawing die having an appropriately shaped hole at the outlet where the metal single-core wire 6 exits from the surface of the molten plating solution. Adjustment can be made by passing the drawing die or by using a means for blowing an inert gas or the like from a nozzle called a wiping nozzle immediately after plating to blow off the excess molten metal.

  Since the conductive material of the present invention can be manufactured by bundling a tape-shaped conductor with concentric circles or a material having a cross-section with a small aspect ratio, like the conventional process for manufacturing a rectangular metal wire, There is no need for a flat rolling process. Therefore, the production of the conductive material of the present invention does not require a rolling mill, and in particular, produces a tape-like conductor that is not bent in the width direction required for a current collector interconnector for solar cells and has excellent linearity. Is advantageous.

  In recent years, a technique for joining a current collector interconnector and a solar battery cell through a polymer sheet called a contact film in which conductive particles are dispersed has been developed. In this case, the conductor is not necessarily coated with solder metal. There is no need. The conductive material according to the present invention may be an uncoated conductor as shown in FIG. 2e. However, in this case, it is necessary to join the metal single core wires to bind in the width direction. Although the welding / diffusion joint portion 9 as shown in FIG. 2e may be formed continuously in the length direction, the length direction may be partially joined in a spot shape with an appropriate interval. Hereinafter, a state of being partially joined at intervals (ie, discontinuously joined) will be simply referred to as point joining.

  2g and 2h show an example of the interconnector of the present invention bound by point joining, and are schematic views showing a cross section of the point joining part. In addition to the softening of the interconnector, this embodiment has the effect of reducing the solder weight as described in detail below, and is a more preferable embodiment as the interconnector of the present invention.

  FIG. 2g is an example in which the single core wires are spot-bonded to each other in the width direction using a binding material 7 different from the single core wire, and FIG. 2h is an example in which the single core wires are directly bonded to each other.

  Examples of the method for forming the point bonding include diffusion by heating and partial melting. For example, a plurality of single core wires of copper or aluminum are arranged closely in a predetermined plane so as to form a tape in the length direction, and the contact portion is energized from the width direction of the tape material while feeding the wire. Examples thereof include a method of heating and melting and a method of performing spot welding by blowing an arc at an appropriate interval in the length direction. In this case, the binding part of the single core wires in the cross section of the tape material perpendicular to the longitudinal direction (orthogonal to the longitudinal direction) is as shown in FIG. 2e. Also, it may be partially brazed using a binder material made of dissimilar metals having a melting point lower than that of the single core wire, or intermittently in the longitudinal direction of the single core wire using a conductive adhesive. May be bound together. The plating may be performed intermittently in a state where the single core wires are bundled in the longitudinal direction of the single core wires.

  In an interconnector for solar cells that is joined by reflowing solder, the solder for joining is covered around the single core wire. In the solar cell interconnector of the present invention, when the coating material 12 is also used as a solar cell module, it is also a binding material. However, when the interconnector is connected to the solar cell and wired, the coating material 12 melts. At this time, if the binding material 7 has a melting point higher than that of the coating material 12 and does not melt at the wiring temperature, there is no fear that each single-core wire is scattered in the wiring. Also, the single core wire is bundled in advance during the hot dipping process for covering the covering material 12, and handling is easy if it is a solid phase that does not melt during covering. Therefore, it is desirable that the binding material 7 used for point bonding has a melting point higher than that of the coating material 12 or is bonded via the same kind of metal as the single core wire, such as spot welding on the side surface of the single core wire. The junction length of the interconnector on one solar cell is the same as the cell size, and is generally 5 to 6 inches. Therefore, the distance of the point junction in the longitudinal direction of the single core wire is 60 mm or less. It is desirable. This is because if it is 60 mm or less, there will always be two joints per electrode of a 5-inch cell, and this is effective in preventing the single core wire from being scattered during reflow joining.

  The reason why it is desirable to intermittently perform point joining in the longitudinal direction of the single core wire is that the amount of solder weight can be reduced. As described above, in the current method of connecting an interconnector for a solar cell, the solder on the side opposite to the solar cell to be joined has a wide tape-shaped cross-section of the interconnector, and therefore wraps around the joint surface during reflow. Cannot be used. On the other hand, in the interconnector of the present invention, since the coating material 12 melts during reflow, a gap is generated between the single core wires. The solder on the opposite side of the cell is supplied from the gap between the single core wires due to the dropper effect caused by the flow of solder from the interconnector to the cell electrode when the solder spreads on the electrode on the solar cell. This is less than the solder weight per unit interconnector. This effect is significant when the distance of point bonding in the longitudinal direction of the single core wire is 5 mm or more.

  In addition, due to the effect that the solder turns from the opposite side of the joint surface to the joint surface through the gap on the side surface of the single core wire, irregularities reflecting the shape of the single core wire are generated on the light receiving surface, which is incident when the solar cell module is assembled. The light entering the interconnector is diffusely reflected by the uneven shape, and the diffused and reflected light is re-reflected at the glass or resin interface to increase the probability of entering the cell light-receiving surface, thereby increasing the efficiency.

  In the case of joining the metal single core wires having a square cross section, the form of joining all over the side surfaces cannot be achieved because the object of the invention of softening cannot be achieved. It is necessary to join at a part of the adjacent side surfaces of the single core wire, for example, by partially joining in the length direction.

  Moreover, when it is the copper wire which the conductor of this invention does not coat | cover, it is desirable to apply | coat rust preventive materials, such as a benzotrianol, to the surface.

  In the case of a current collector interconnector or a semiconductor connection tab wire that is joined to a solar battery cell using a contact film, the binding material 7 need not be a material such as solder having a low melting point. In such a case, the bundling bonding material 7 may be coated with a noble metal such as gold or silver which can easily come into electrical contact with the contact film, or may be coated with a metal such as nickel, tin or noble metal having corrosion resistance. .

  In particular, in a current collector interconnector that uses a contact film to join solar cells, the light reflected by the current collector interconnect is re-reflected on the glass surface by applying a glossy coating of silver or aluminum. The effect of entering the light is obtained, and the effect of improving the conversion efficiency of the solar cell is provided. In particular, the configuration as shown in FIG. 2c has the effect of irregularly reflecting sunlight due to the unevenness of the surface, and the irregularly reflected light is re-reflected at the interface of the glass layer on the surface and enters the power generation cell to generate power. Can be improved.

  In addition, such a configuration is excellent as a tab line for bonding because it is easy to deform because the bonding pressure increases when the same bonding force and ultrasonic waves are applied due to the unevenness, and the ultrasonic waves also concentrate.

  As a metal coating method, in addition to wet plating and hot dipping, there is a process of drawing a clad material as a base material by shrink fitting or the like.

  Such a multilayer material may be bundled by the above-described heat bonding to form the conductor of the present invention, or the metal single-core wires 6 may be bundled with metal coating by wet plating instead of hot dipping. Moreover, you may use these together.

  For example, a material obtained by binding a copper single core wire with soft aluminum is inexpensive, has high electrical conductivity, and has excellent surface reflectivity, and is excellent as a tab wire for bonding. In the case of aluminum, it is common to perform hot dipping. Since aluminum has a high reaction temperature, a hard intermetallic compound layer that is a reaction phase may be formed at the interface with copper. In order to suppress the growth of the intermetallic compound layer, a thin metal such as nickel may be coated on copper beforehand by chemical plating or the like. Thus, any material may be used as long as it does not significantly affect the overall mechanical properties. Thus, when the conductive material of the present invention is composed of three or more kinds of materials, the proportion of the cross-sectional area of the material harder than the metal single core wire in the entire cross-section of the conductive material is 10% or less. It is desirable to be.

  Further, the bundling bonding material 7 does not need to be a metal material, and may be conductive, and may be a conductive resin. Since the conductive resin is generally softer than copper or aluminum, which is a metal single core wire, it is suitable as a binding material in the present invention.

<Summary>
As described above, the tape-like conductive material according to the present invention is a semiconductor connection conductor that is easily deformed with a low yield stress in the longitudinal direction of the wire, is low in cost, and has excellent linearity. The tape-shaped conductive material according to the present invention softens the conductor to ease the thermal stress generated between the semiconductor to be joined or the metal electrode provided thereon, and to facilitate deformation during joining. In addition, bondability is improved and disconnection due to fatigue failure is less likely to occur. In particular, familiarity with the opposing electrode is good and the amount of solder used is small. Moreover, the tape-shaped conductive material according to the present invention can be used as a tape-shaped metal conductive material used for a current collector interconnector or a semiconductor connection tab wire that increases the power generation efficiency of a solar cell.

  Furthermore, as an effect of the present invention, in particular, the solar cell current collector interconnector is exposed to repeated thermal stress caused by being installed in an external environment in addition to the thermal stress during bonding. As shown in Fig. 2, by forming a multi-core metal single core wire by joining, a crack is formed in one single core wire, and even if the cracked single core wire is broken due to fatigue, the progress of the crack is prevented there Therefore, it is possible to prevent the tape material from being disconnected, and to form a solar cell current collector interconnector with high long-term reliability that is resistant to fatigue failure.

  Hereinafter, the tape-shaped conductive material according to the embodiment of the present invention will be specifically described with reference to examples. In addition, the Example shown below is only an example of the tape-shaped conductive material which concerns on embodiment of this invention, Comprising: The tape-shaped conductive material which concerns on embodiment of this invention is not necessarily limited to the following example.

Example 1
Two types of tape-shaped conductors (Sample 1 and Sample 2) were manufactured from a pure aluminum annealed round bar material with a purity of 99.99%, and the mechanical properties were compared. Sample 1 is a tape-like conductive material belonging to the form of the present invention in which aluminum single core wires are bundled by silver plating, and sample 2 is a silver-plated conductor of aluminum flat wire produced for comparison.

The tape-shaped conductive material of Sample 1 was manufactured as follows.
That is, the surface of an annealed round bar having a diameter of 25 mm was reduced to a diameter of 2 mm with a swage, and then drawn to a diameter of 200 μm by drawing using a wire drawing die. Thereafter, heat treatment was performed in vacuum at 500 ° C. for 1 hour, and the surface of the obtained wire was subjected to zinc substitution plating of about 0.1 μm. Next, three surface-treated wires are arranged in parallel, and the wires are brought into contact with each other by passing through a guide roller having a width of 0.6 mm. Turned into. The cross section of aluminum of this tape material was 0.0942 mm ² . Sample 1 is in the form of the present invention. Moreover, the cross-sectional area of silver with respect to the total cross-sectional area of the aluminum core was 4.04%.

The tape-shaped conductive material of Sample 2 was manufactured as follows.
In other words, after Φ54mm annealed round bar was swaged down to Φ2mm, drawn to Φ0.4mm by drawing using a wire drawing die, rolled to a thickness of 0.24mm by rolling, The cross-sectional form was 0.6 mm and the thickness was 0.18 mm. Then, heat treatment is performed in vacuum at 500 ° C. for 1 hour, and zinc substitution plating of about 0.1 μm is performed while feeding the surface of the obtained wire, and silver plating with a thickness of 2 μm is formed thereon by electroplating. gave. Both ends of this tape-shaped conductor were rounded, and the cross section of aluminum was 0.0942 mm ² , which was the same as Sample 1. Moreover, the cold working rate from the annealing round bar was slightly larger in the sample 2. Sample 2 is a comparative material.

  The cross sections of these materials were polished, and the average value of equivalent circle diameters weighted by area, that is, the area average diameter was evaluated by the EBSD method. A crystal grain was defined as a region surrounded by a crystal grain boundary having an orientation difference of 15 ° or more at a rotation angle excluding twin boundaries. As a result, the area average diameters of Sample 1 and Sample 2 were almost the same, and were about 102 μm. This is 29.4% of the equivalent circle diameter calculated from the cross-sectional area of the entire aluminum single core wire. In the case of Sample 1, since the aluminum core material is composed of three single core wires, the size of the area average diameter of crystal grains with respect to 200 μm, which is the diameter of one single core wire, is 51.0%.

  Next, the tensile test was done about these materials and 0.2% yield strength was evaluated. The tensile test is performed according to JIS Z2201, and the distance between the gauge points is 100 mm and the tensile speed is 10 mm / min. It carried out on condition of this. The 0.2% proof stress was calculated by dividing by the cross-sectional area of the aluminum core using the offset method.

  Comparing the load-elongation diagrams of Sample 1 and Sample 2, the stress at the same elongation value was always lower than that of Sample 1. The elongation at break was almost the same in both cases and was about 30%. On the other hand, the 0.2% proof stress was 20.1 MPa for sample 1 whereas it was 50.4 MPa for sample 2.

  The reason why the sample 1 is softer than the sample 2 because the size of the crystal grains is the same level is that the cross-sectional area per one aluminum single core wire of the sample 1 is 1/3 of that of the sample 2, 3 It can be said that each single core wire is weakly coupled to each other, so that each of them can be freely deformed to some extent. That is, the effect is that the crystal grains of sample 1 are relatively large and softened.

(Example 2)
Manufactures current collector interconnectors for solar cells in which solder is plated on tough pitch copper wire (C1100) with a purity of 99.9%, compares 0.2% proof stress, and joins actual silicon crystal solar cells Then, the amount of warpage was compared.

  Sample 3 is a tape-like conductive material belonging to the embodiment of the present invention in which copper single-core wires are bundled with solder, and sample 4 is a copper-plated solder-plated conductor manufactured for comparison.

The tape-shaped conductive material of Sample 3 was manufactured as follows.
That is, after the surface of a continuous cast material having a diameter of 8 mm was reduced to a diameter of 2 mm with a swage, it was drawn to a diameter of 250 μm by drawing using a wire drawing die. Then, 5 m of the obtained single core wires were simultaneously applied to a tube furnace having a furnace length of 1 m and heated to 600 ° C. in an N ₂ -5% by volume H ₂ stream at 2 m / min. Immediately after passing through the wire, it was leached into a Sn-1.0 mass% Ag-0.5 mass% Cu plating bath heated and melted at 230 ° C. without being exposed to the atmosphere, and placed on the plating bath liquid surface. It was manufactured by passing through an alumina drawing die of × 0.27 mm. Thus, the sample 3 is a tape-like conductive material in which five tough pitch copper single core wires having a diameter of 250 μm are joined and integrated in parallel in the length direction and in one plane via solder. The total cross-sectional area of copper is 0.245 mm ^2. The weight of solder was 0.39 g per meter. The sample 3 is macroscopically in the form shown in FIG. 2a and is a form of the present invention.

The solder plating conductor of Sample 4 was manufactured as follows.
In other words, after Φ8mm continuous cast material was reduced to Φ2mm with a swage, it was drawn to Φ1.2mm by drawing using a wire drawing die, then rolled to flatten to a thickness of 0.2, The shape was molded to 0.2 × 1.30 mm to obtain a tape material. Subsequently, 2m / min The tape material in a tubular furnace heated oven length 1m to 600 ° C. in _N 2 -5 vol% _{H 2} gas stream. Immediately after passing through the wire, it was leached and passed through a Sn-1% by mass Ag-0.5% by mass Cu plating bath heated and melted to 230 ° C. without being exposed to the atmosphere. The total cross-sectional area of copper was 0.246 mm ² which was almost the same as Sample 3, and the solder weight was adjusted to be the same as 0.39 g. The average value of the solder basis weight of Sample 4 was 20 μm on one side, and the macroscopic form was thickest at the center as shown in FIG. 3 and about 40 μm on one side. Sample 4 is a comparative material.

  The cross sections of these materials were polished, and the average value of equivalent circle diameters weighted by area using the EBSD method, that is, the area average diameter was evaluated. A crystal grain was defined as a region surrounded by a crystal grain boundary having an orientation difference of 15 ° or more at a rotation angle excluding twin boundaries. As a result, the area average diameters of Sample 3 and Sample 4 were 12.6 μm and 9.1 μm, respectively. Despite starting from the same base material, the grain size is different because the processing rate of sample 3 is larger and the driving force of grain growth during recrystallization is larger, and the surface (actually the interface with the solder) ) Energy contribution. That is, when obtaining conductors having the same total cross-sectional area, it was confirmed that the present invention facilitates obtaining large crystal grains.

  As a result of measuring the Vickers hardness of the cross section according to JIS Z2244, the hardness of the copper part of sample 3 was 52, the solder part was 15, the hardness of the copper part of sample 3 was 58, and the solder part was 15.

  Next, the tensile test was done about these materials and 0.2% yield strength was evaluated. The tensile test is performed according to JIS Z2201, and the distance between the gauge points is 100 mm and the tensile speed is 10 mm / min. It carried out on condition of this. The 0.2% yield strength was calculated by dividing by the total cross-sectional area of copper using the offset method.

  When the load-elongation diagrams of Sample 3 and Sample 4 were compared, the stress at the same elongation value was always lower than that of Sample 3. On the other hand, the 0.2% proof stress was 70.0 MPa for sample 3, whereas it was 98.1 MPa for sample 4.

  The reason why the sample 3 is softer than the sample 4 is that the crystal particle diameter of the copper core material consisting of five single core wires of the sample 3 is large and the cross section per one copper single core wire of the sample 3 is compared with the sample 4. This is because each of the five single-core wires is weakly coupled with a soft solder material, and as a result, each can be freely deformed to some extent. In other words, in the sample 3, the ratio of the equivalent area diameter per single core wire is 5.04%, and in the sample 4, the ratio of the equivalent area diameter to the equivalent circle diameter calculated from the cross-sectional area of the entire copper single core wire is 1. This is because the sample 3 behaves as a wire having a large crystal grain larger than the actual crystal grain size difference with respect to the sample 4.

  Sample 3 and sample 4 were bonded to an actual solar cell wafer, and the degree of warpage of the wafer was examined. The used solar cell wafer is polycrystalline silicon having a size of 150 × 155 mm and a thickness of 200 μm. The silver electrode width for wiring the current collector interconnector is 3 mm, and three electrodes on one side are formed in parallel. ing. Three power collecting interconnectors of Sample 3 and Sample 4 were separately joined to three electrodes on the light receiving surface side, for a total of six.

  Place the cell on a hot plate heated to 175 ° C, apply flux to the electrode on the cell, place the current collector interconnector on the silver electrode over the entire length between the cell edges, hold it with a pin, and use hot air. By heating, the solder was melted and joined.

  All the current collector interconnectors could be uniformly joined in the length direction of the silver electrode. When viewed from directly above the joint, the amount of solder protruding in the width direction of the current collecting interconnector was greater in the sample 4, whereas the current collecting interconnector in the sample 3 formed a uniform fillet. There was very little protrusion. The current collecting interconnector of Sample 3 is sufficiently supplied from the opposite side of the electrode through the single core wire, but the unnecessary solder can be adequately returned to the opposite side of the electrode through the single core wire due to the dropper effect. In addition, as a result of supplying the necessary amount of solder, it is considered that there was little protrusion in the width direction of the current collecting interconnector.

  After cooling the wafer, it was found that the cell was warped in the length direction of the current collecting interconnector with the surface where the current collecting interconnector was joined inside. This is because the thermal contraction rate of copper was larger than that of silicon. When one end of the cell was used as a fulcrum and the amount of warpage was measured at the end opposite to the fulcrum, the curvature of the cell joined with the current collector interconnector of Sample 3 of the present invention was 2.1 mm. The amount of warpage of the cell joined with the current collecting interconnector of Sample 4 as a comparative material was 5.3 mm. This is because the sample connector 3 has a low proof stress, a large amount of plastic deformation, and a small thermal stress.

  Next, an interconnector for current collection is also arranged on the cell separation surface. On the hot plate heated to 200 ° C., the interconnector for current collection is disposed on the silver electrode over the entire length between the cell edges. Suppressed by hot air heating, melted solder and joined 3 cells for sample 3 and sample 4, forming a circuit from the front and back of the cell, and using solar simulator to improve power generation efficiency under the same conditions It was measured. As a result, the average power generation efficiency of the cell to which the current collector interconnector of sample 3 of the present invention was joined was 15.1%, whereas the current collector interconnector of sample 4 as a comparative material was joined. The power generation efficiency of the obtained cell was 14.5%. This is because, since the proof stress of the current collecting interconnector is small in sample 3, the amount of plastic deformation is large and the thermal stress is small, so that there is no fine crack and a more sound joint is formed.

(Example 3)
In this example, a solar cell current collector interconnector in which solder is plated on an oxygen-free copper wire (C1020) having a purity of 99.99% is manufactured, and 0.2% proof stress is compared, and an actual silicon crystal The solar cell was joined and the amount of warpage was compared.

  Samples 5 to 9 are tape-like conductive materials obtained by binding copper single core wires with solder. Samples 6 to 9 are examples of the present invention, but sample 5 is a comparative example that did not satisfy the structural requirements of the present invention. Samples 10 to 11 are copper-plated rectangular solder-plated conductors and are comparative examples.

The tape-shaped conductive material of Sample 5 was manufactured as follows.
That is, the surface of an annealed round bar having a diameter of 25 mm was reduced to a diameter of 2 mm with a swage, and then drawn to a diameter of 250 μm by drawing using a wire drawing die. Thereafter, six single-core wires obtained were simultaneously applied to a tube furnace having a furnace length of 1 m and heated to 600 ° C. in a N ₂ -5 vol% H ₂ air flow at 30 m / min. Immediately after wire annealing and continuous annealing, 1.6 × 0.30 mm alumina leached into a Pb-60 mass% Sn plating bath heated and melted to 205 ° C. without being exposed to the atmosphere and disposed on the plating bath liquid surface A drawing die was passed. That is, the sample 3 is a tape-like conductive material in which six oxygen-free copper single core wires having a diameter of 250 μm are joined and aligned in parallel in the length direction and in one plane via solder. The total cross-sectional area of copper was 0.294 mm ² . The basis weight of the solder was adjusted by blowing argon gas from both sides of the tape surface with a wiping nozzle immediately after passing through the drawing die and controlling the flow rate so as to be 0.5 g per meter. Sample 5 was close to the form of the present invention, but became a comparative material from the average crystal grain size.

In addition, the tape-shaped conductive materials of Samples 6 to 9 were wound around a stainless bobbin with a material drawn to Φ250 μm in the same manner as Sample 5, and each was 200 ° C. in a vacuum using a batch furnace (Sample 6), A single core wire annealed at 300 ° C. (Sample 7), 400 ° C. (Sample 8), and 500 ° C. (Sample 9) for 1 hour was subjected to continuous annealing and solder plating in a tubular furnace under the same conditions as Sample 5. . The total cross-sectional area of copper was 0.294 mm ² . The basis weight of solder was the same as that of Sample 5. Samples 5 to 9 are forms of the present invention. In this example, since the batch annealing time is sufficiently longer than the subsequent continuous annealing, the influence of the annealing is larger in the batch annealing.

The solder plating conductors of Sample 10 and Sample 11 were manufactured as follows.
That is, after Φ25mm annealed round bar material was swaged down to Φ2mm, drawn using a wire drawing die to Φ1.2mm, then rolled and flattened to a thickness of 0.2, The shape was molded to 0.2 × 1.52 mm to obtain a tape material. Then, this tape material was wound around a stainless bobbin, and using a batch furnace, sample 10 was annealed in vacuum at 300 ° C. for 1 hour, sample 11 was annealed in vacuum at 500 ° C. for 1 hour, and each was used as a wire rod. . Subsequently, each of the obtained wires was put into a tube furnace having a furnace length of 1 m heated to 600 ° C. in a N ₂ -5 vol% H ₂ air stream at 20 m / min. Immediately after passing through the wire, it was produced by leaching and passing through a Pb-60 mass% Sn plating tank heated and melted at 205 ° C. without being exposed to the atmosphere. The amount of solder per unit area was adjusted by blowing argon gas from both sides of the tape surface with a wiping nozzle immediately after passing through the drawing die and controlling the flow rate, and matched to samples 5 to 8. Therefore, the total cross-sectional area of copper is 0.294 mm ² as in Samples 5 to 9, and the solder weight is the same as 0.5 g. The average value of the solder weight per sample of Sample 10 and Sample 11 was 20 μm on one side, the center part was the thickest, and was about 40 μm on one side. Samples 10 and 11 are comparative materials.

  The cross sections of these materials were polished, and the average value of equivalent circle diameters weighted by area using the EBSD method, that is, the area average diameter was evaluated. A crystal grain was defined as a region surrounded by a crystal grain boundary having an orientation difference of 15 ° or more at a rotation angle excluding twin boundaries. Moreover, the Vickers hardness of the part of copper and solder was measured according to JIS Z2244 using the cross section.

  Next, a tensile test was performed on Samples 5 to 11, and 0.2% yield strength was evaluated. The tensile test is performed according to JIS Z2201, and the distance between the gauge points is 100 mm and the tensile speed is 5 mm / min. It carried out on condition of this. The 0.2% yield strength was calculated by using the offset method and dividing the load value when the plastic strain was 0.2 by the total cross-sectional area of copper. In all the samples, in the region where the elongation value was 10% or less, the stress value at the same strain was smaller as the sample having a smaller 0.2% proof stress value.

  Next, the solder plating wires of Sample 5 to Sample 11 were bonded to an actual solar cell wafer, and the degree of warpage of the wafer was examined. The used solar cell wafer is polycrystalline silicon having a size of 150 × 155 mm and a thickness of 200 μm. The silver electrode width for wiring the current collector interconnector is 3 mm, and three electrodes on one side are formed in parallel. ing. A total of 45 current-collecting interconnectors, 3 for each type, were joined to the three electrodes on the light-receiving surface side.

  Place the cell on a hot plate heated to 175 ° C, apply flux to the electrode on the cell, place the current collector interconnector on the silver electrode over the entire length of the cell edge, hold it with a pin, and heat it with hot air Then, the solder was melted and joined.

  After cooling the wafer, it was found that the cell was warped in the length direction of the current collecting interconnector with the surface where the interconnector was joined inside. This is because the thermal contraction rate of copper was larger than that of silicon. Using one end of the cell as a fulcrum, the amount of warpage was measured at the end opposite to the fulcrum.

  The above test results are summarized in Table 1.

  The average particle size (area average particle size) of the crystal grains expressed by the equivalent area diameter of copper in the sample obtained as a result of EBSD measurement of the sample cross section is a sample in which six single-core wires not subjected to batch annealing are bundled Sample 10 composed of one flat copper wire annealed at 5 and 300 ° C. was approximately the same, about 9 μm. Also, the 0.2% proof stress value was almost the same. The relative size of the area average diameter of the copper crystal grains with respect to the equivalent circle diameter of one copper single core wire was found to vary greatly, but both were less than 5%, and the cross-sectional area of one copper single core wire was one. The 0.2% yield strength value depended on the absolute value of the average grain size.

  Samples 7 and 10 have the same heat history after processing. Despite starting from the same base material, the grain size after recrystallization is different because the processing rate of sample 6 is larger and the driving force of grain growth during recrystallization is greater, and the surface (actually This is the contribution of energy to the interface with the solder. That is, when obtaining conductors having the same total cross-sectional area, it was confirmed that the present invention facilitates obtaining large crystal grains.

  A sample in which six single core wires are bundled is subjected to batch annealing, so that the equivalent area diameter of the copper crystal grains exceeds 5% with respect to the equivalent circle diameter of one copper single core wire, and the 0.2% proof stress value is greatly reduced. And a value lower than 50 MPa was obtained.

  On the other hand, Sample 11 composed of a single flat copper wire was subjected to batch annealing at 500 ° C. and grown to an average crystal grain size of 28.3 μm, but the 0.2% proof stress value was not less than 50 MPa. On the other hand, the 0.2% yield strength of Sample 7 having approximately the same area average diameter was 46.1 MPa. This is an effect of increasing the crystal grain size by exceeding 5% with respect to one copper single core wire diameter in the sample 7.

  With respect to one copper single-core wire diameter, the sample 8 with a crystal grain size exceeding 20% had a 0.2% yield strength of less than 40 MPa, and the sample 9 with more than 50% obtained a value of 34.9 MPa. . This is because the crystal grain size is further increased with respect to a single copper single-core wire diameter, and these are bound by softer lead tin solder, so that the constraint on the deformation of each single wire is small. It is an effect.

  That is, when a conductor composed of one flat copper core wire and a conductor composed of six copper single core wires bound with soft solder are compared, the latter conductor can obtain large crystal grains by recrystallization. In addition, since the cross section of one copper single core wire is 1/6 of the cross section of the flat copper core wire, the crystal grains relative to the cross section of one copper single core wire can be relatively coarsened. As a result of being weakly bonded with a soft solder material, each can be freely deformed to some extent, and a soft conductor in the longitudinal direction can be obtained.

  All of the current collecting interconnectors of Sample 5 to Sample 11 could be uniformly joined in the silver electrode length direction. The amount of solder protruding in the width direction of the current collecting interconnector when viewed from directly above the joint was larger in the samples 10 and 11, whereas the current collecting interconnectors in the samples 5 to 9 were used. A uniform fillet was formed, and the protrusion was very small. The current collecting interconnector of Sample 5 to Sample 9 is sufficiently supplied from the opposite side of the electrode through the single core wire, but the unnecessary solder returns to the opposite side of the electrode through the single wire due to the dropper effect. As a result, it is considered that as a result of supplying sufficient and necessary solder, there was little protrusion in the width direction of the current collecting interconnector.

  The cell after cooling the wafer was warped in the length direction of the current collecting interconnector with the surface where the current collecting interconnector was joined inside, but the amount of warping varied between samples. The cells joined using the current collector interconnectors of Sample 6 to Sample 9 according to the present invention have a warpage amount as compared to the cells joined using the current collector interconnectors. Although it is small, this is because the 0.2% proof stress of Sample 6 to Sample 9 is small.

  When the ratio of the average grain diameter of the crystal grains expressed by the equivalent area diameter of copper in the sample to the diameter of one copper single core wire is 5% or more, the proof stress is reduced by 0.2%, and the crystal of the copper single core wire is further reduced. When the grain size is 50 μm or more and the ratio of the average grain size of the crystal grains to the diameter of one copper single core wire is 20% or more, the proof stress is further reduced by 0.2%. The current collector interconnector has a large amount of plastic deformation at the time of joining and a small thermal stress. As a result, the warpage of the cell is small. As a result, if the cell damage is small and the cell warpage is small, the correction amount of the cell during the subsequent laminating process is also small, so that the module yield reduction due to the destruction of the cell during correction is small.

Example 4
Metal tape conductors in which nickel, aluminum, or solder was plated on an oxygen-free copper wire (C1020) having a purity of 99.99% were manufactured, and 0.2% proof stress was compared and reflectance was measured. Sample 12 is a nickel-plated material and is a comparative example. Sample 13 is a material manufactured by annealing sample 12 and is an example of the present invention. Samples 14 and 15 are samples produced by subjecting sample 13 to hot-dip plating of solder and aluminum, respectively, and are examples of the present invention.

The tape-shaped conductive material of Sample 12 was manufactured as follows.
That is, after the surface of a continuous cast material having a diameter of 8 mm was reduced to a diameter of 2 mm with a swage, the wire was drawn to a diameter of 200 μm by drawing using a wire drawing die. Next, three surface-treated single core wires are arranged in parallel, and the thickness is 1 μm by electroplating in a nickel sulfate bath while the single core wires are brought into contact with each other by passing through a guide roller having a width of 0.6 mm. It was integrated by covering the nickel. The tape-shaped conductive material had a copper cross section of 0.0942 mm ² . Moreover, the cross-sectional area of nickel with respect to the total cross-sectional area of the copper core material was 2.01%.

  Sample 13 was manufactured by heat-treating the tape-shaped conductive material manufactured in the same manner as Sample 12 in argon at 350 ° C. for 30 minutes.

The tape-shaped conductive material of Sample 14 was manufactured as follows.
That is, the same continuous casting material as the sample 12 was used, and the single core wire drawn and surface-treated by the same method was utilized. After arranging these three single core wires in parallel, a tube furnace having a furnace length of 1 m heated to 600 ° C. in an N ₂ -5% by volume H ₂ stream was supplied with 20 m / min. Immediately after passing through the wire, a 0.8 × 0.25 mm drawing die made of alumina leached into an Sn-40 mass% Pb plating bath heated to 200 ° C. without being exposed to the atmosphere and placed on the plating bath liquid surface. The sample 14 was manufactured by performing solder plating. Sample 14 was made of a solder-plated material by controlling the solder plating thickness to an average of 10 μm by blowing argon gas from the direction opposite to the direction of wiring using a wiping nozzle immediately after passing through the drawing die. is there.

The tape-shaped conductive material of Sample 15 was manufactured as follows.
In other words, a continuous image cast material similar to that of Sample 12 was used, and a single-core wire drawn and surface-treated by the same method was used. After arranging these three single core wires in parallel, a tube furnace having a furnace length of 1 m heated to 700 ° C. in a N ₂ -5 vol% H ₂ air stream was supplied with 2 m / min. Immediately after passing through the wire, it was leached into an Al plating bath heated and melted to 700 ° C. without being exposed to the atmosphere, and passed through a 0.8 × 0.25 mm alumina drawing die placed on the surface of the plating bath. Aluminum plating was performed to manufacture Sample 15. Sample 15 was made of an aluminum-plated material by controlling the aluminum plating thickness to an average of 10 μm by blowing argon gas from the direction opposite to the direction of wiring using a wiping nozzle immediately after passing through the drawing die. is there.

  Since all of Samples 12 to 15 were thin plating with respect to the wire diameter of the copper single core wire, they had irregularities according to the wire diameter.

  The cross sections of these materials were polished, and the average value of equivalent circle diameters weighted by area using the EBSD method, that is, the area average diameter was evaluated. A crystal grain was defined as a region surrounded by a crystal grain boundary having an orientation difference of 15 ° or more at a rotation angle excluding twin boundaries. Moreover, the Vickers hardness measurement of the copper and solder or aluminum plating part was performed according to JIS Z2244 using the obtained cross section. The hardness of nickel could not be measured because the nickel plating thickness was small. However, since the cross-sectional area of nickel plating relative to the cross-sectional area of the copper core material is small, the influence on mechanical properties such as proof stress is small.

  Next, the tensile test was done about Sample 12-Sample 15, and 0.2% yield strength was evaluated. The tensile test is performed according to JIS Z2201, and the distance between the gauge points is 100 mm and the tensile speed is 5 mm / min. It carried out on condition of this. The 0.2% yield strength was calculated by dividing the load value when the plastic strain was 0.2 by the total cross-sectional area of copper by the offset method. In all the samples, in the region where the elongation value was 10% or less, the stress value at the same strain was smaller as the sample having a smaller 0.2% proof stress value.

  Next, the reflectance of the tape surfaces of the tape wires of Sample 12 to Sample 15 was measured. The reflectance was measured by using so-called diffuse reflection, which is a sum of reflections in various directions, using an aluminum vapor deposition mirror as a reference sample. For the measurement wavelength range, an average value in a wavelength region of 240 nm to 800 nm that is often used for power generation in a solar cell was calculated.

  The above test results are summarized in Table 2.

  The average grain size (area average grain size) of the crystal grains expressed by the equivalent area diameter of copper in the sample obtained as a result of the EBSD measurement of the sample cross section is the smallest in the sample 12 of the sample 12 that has not been batch-annealed. It was 8 μm. The relative size of the area average diameter of the copper crystal grains with respect to the equivalent circle diameter of one copper single core wire of this sample was 5% or less, and the 0.2% proof stress showed a large value.

  On the other hand, the average particle diameter of the copper core material of the sample (sample 13) batch-annealed at 350 ° C. was 40.1 μm. The relative size of the area average diameter of the copper crystal grains relative to the equivalent circle diameter of one copper single core wire of this sample is 20%, the plating thickness may be small, and the 0.2% proof stress is small. A value was obtained.

  The average grain size (area average grain size) of the crystal grains represented by the area equivalent diameter of copper in Sample 14 and Sample 15 was smaller than the average grain size of Sample 13 because of the amount that was not batch-annealed. Crystal grains grew due to the thermal history of plating. As a result, the relative size of the area average diameter of the copper crystal grains with respect to the equivalent circle diameter of one copper single core wire in Sample 14 and Sample 15 exceeds 5% which is the standard of the present invention, and the low proof stress value is low. Obtained. Although the specimen 14 was plated with aluminum harder than solder, the proof stress value was smaller than that of the specimen 13 because the crystal grains grew due to the high thermal history of the molten aluminum plating.

  The reflectivity was highest in the sample 15 subjected to aluminum plating. Reflected light is scattered by the unevenness caused by bundling the round wires. When this sample is used as an interconnector for a solar cell, sunlight rays blocked by the interconnector are irregularly reflected at a high reflectance by the interconnector. Therefore, it can be expected that the reflected light is reflected again at the interface between the transparent mold material made of EVA or the like and the surface glass, and is incident on the light receiving surface of the solar battery cell again, which contributes to improving the efficiency of the solar module.

(Example 5)
In the present embodiment, a solar cell current collector interconnector obtained by plating solder of different basis weights on oxygen free copper wire (C1020) having a purity of 99.99% is manufactured and bonded to an actual silicon crystal solar cell. The junction margin was compared.

  Samples 16 to 21 are tape-like conductive materials of the present invention in which copper round wires are bound. Sample 22 is a copper-plated rectangular solder-plated conductor and is a comparative example.

The tape-shaped conductive materials of Sample 16 to Sample 21 were manufactured as follows.
That is, the surface of an annealed round bar having a diameter of 25 mm was reduced to a diameter of 2 mm with a swage, and then drawn to a diameter of 250 μm by drawing using a wire drawing die. After that, the copper single core wire drawn out from the eight samples wound on the bobbin was passed through two guides with holes having a width of 2.7 mm and a height of 200 μm arranged in parallel in eight rows, An electrode facing the other side surface from one side surface in the width direction of the copper single core wire bundle is provided, and the copper single core wire is intermittently energized while sending the copper single core wire, and the eight copper single core wires are joined in parallel. . The length of the junction between the copper single core wires was about 1 mm in the length direction. Samples 16 to 21 are samples in which the intervals between the junctions are different by changing the energization interval. Sample 16 has a junction interval of 4 mm, Sample 17 has a junction interval of 5 mm, Sample 18 has a junction interval of 30 mm, Sample 19 has a joining interval of 60 mm, Sample 20 has a joining interval of 63 mm, and Sample 21 has a joining interval of 70 mm. Then, it rolled, constraining the width direction, and wound up on one roll of stainless bobbins.

The tape-shaped copper wire thus produced was annealed at 500 ° C. for 1 hour in a vacuum together with the bobbin. Thereafter, a tube furnace having a length of 1 m heated to 600 ° C. in a N ₂ -5% by volume H ₂ stream was supplied with 30 m / min. Immediately after the continuous wire annealing and continuous annealing, the steel plate was leached into a 98.5% Sn-1.0Ag-0.5Cu plating bath heated and melted at 240 ° C. without being exposed to the atmosphere, and was subjected to solder plating. That is, the samples 16 to 21 are tapes in which the wide surfaces are flattened as shown in FIG. 2f, and the eight oxygen-free copper wires are joined and aligned in parallel in the length direction and in one plane via solder. It is a conductive material. The total cross-sectional area of copper was 0.31 mm ² . The basis weight of the solder was adjusted by blowing argon gas from both sides of the tape surface with a wiping nozzle immediately after passing through the drawing die and controlling the flow rate so as to be 2.96 g per meter. Since the wires are already bundled, it was not necessary to use a guide or a drawing die for aligning the single core wires.

The solder plating conductor of Sample 22 was manufactured as follows.
That is, after Φ25mm annealed round bar material was swaged down to Φ2mm, drawn using a wire drawing die to Φ1.2mm, then rolled and flattened to a thickness of 0.2, The shape was molded to 0.16 × 2.0 mm to obtain a tape material. Then, this tape material was wound around a stainless steel bobbin, and annealed in a vacuum at 500 ° C. for 1 hour using a batch furnace to obtain a wire material. Subsequently, each of the obtained wires was put into a tube furnace having a furnace length of 1 m heated to 600 ° C. in a N ₂ -5 vol% H ₂ air stream at 20 m / min. Immediately after passing through the wire, it was produced by leaching and passing through a 98.5% Sn-3.0Ag-0.5Cu plating bath heated and melted at 240 ° C. without being exposed to the atmosphere.

The basis weight of the solder was adjusted by spraying argon gas from both sides of the tape surface with a wiping nozzle and controlling the flow rate thereof, and adjusted to the samples 16 to 21. Therefore, the total cross-sectional area of copper is 0.31 mm ² as in Samples 16 to 21, and the solder weight is the same as 0.296 g. The average value of the solder basis weight of the sample 22 is 20 μm on one side.

  The cross sections of these materials were polished, and the average value of equivalent circle diameters weighted by area using the EBSD method, that is, the area average diameter was evaluated. A crystal grain was defined as a region surrounded by a crystal grain boundary having an orientation difference of 15 ° or more at a rotation angle excluding twin boundaries. Moreover, the Vickers hardness of the part of copper and solder was measured according to JIS Z2244 using the cross section.

  Next, the tensile test was done about the sample 16-22, and 0.2% yield strength was evaluated. The tensile test is performed according to JIS Z2201, and the distance between the gauge points is 100 mm and the tensile speed is 5 mm / min. It carried out on condition of this. The 0.2% yield strength was calculated by using the offset method and dividing the load value when the plastic strain was 0.2 by the total cross-sectional area of copper. In all the samples, in the region where the elongation value was 10% or less, the stress value at the same strain was smaller as the sample having a smaller 0.2% proof stress value.

  Next, the solder plating wires of Sample 16 to Sample 22 were bonded to an actual solar cell wafer, and the bonding state was examined. The solar cell wafer used is a single crystal silicon having a size of 125 × 125 mm and a thickness of 160 μm, the silver electrode width for wiring the current collector interconnector is 3 mm, and two electrodes on one side are formed in parallel. ing. As the cell, an automatic wiring device manufactured by NPC Co., Ltd. was used, and a string in which three cells were connected in series was produced. The joining conditions were a welding table temperature of 180 ° C., a hot air set temperature: 350 ° C., and a pin press time of 3 seconds.

  After observing the appearance of the prepared strings, the interconnector connecting the three cells was cut between the cells to form a single cell, covered with EVA from above, and further tempered glass was placed and reduced to 160 ° C under reduced pressure. Heated to produce a pseudo module. About this module, the IV characteristic was measured under the solar cell simulator, and the efficiency as a solar cell was measured.

  The results obtained are summarized in Table 3.

  In samples 16 to 21, the relative size of the area average diameter of the copper crystal grains with respect to the equivalent circle diameter of one copper single core wire exceeded 50%, and a very low proof stress value was obtained. On the other hand, since the sample 22 had a low cold working rate and a large cross-sectional area per single copper core wire, the proof stress value was larger than those of the samples 16 to 21. When the difference between Sample 16 to Sample 21 was compared in detail, the proof stress value of the interconnector of Sample 16 was slightly inferior. This is presumably because the interval between the point bondings was too small, and when the tensile stress was applied to the single core wires, the constraints between the single core wires were large.

  The overall warping of the strings reflected their strength. Although it was difficult to measure quantitatively, the strings produced using the interconnectors of Samples 16 to 21 did not float when placed on a flat surface, whereas the interconnectors of Sample 22 were used. The strings produced in this way were slightly lifted when placed on a flat surface. This is because the stress of the interconnector when the same thermal strain was applied was large in the sample 22 having a high proof stress.

  When the appearance of the strings was examined, all of the current collecting interconnectors of Samples 16 to 21 could be uniformly joined in the length direction of the silver electrode. When evaluating the protrusion of the solder in the width direction of the current collecting interconnector when viewed from directly above the joint, the strings using the interconnectors of Sample 16 to Sample 21 formed a uniform fillet, and the protrusion was extremely There were few. When the state of the light receiving surface of the interconnector of Samples 16 to 21 in which the strings were formed was observed, the unevenness reflecting the shape of the single core wire was larger than before joining. That is, the current collecting interconnectors of Samples 16 to 21 are sufficiently supplied from the opposite surface of the electrode through the single core wires, but unnecessary solder passes between the single core wires to the opposite side of the electrode due to the dropper effect. As a result of returning the solder to the necessary and sufficient amount, it is considered that there was little protrusion in the width direction of the current collecting interconnector.

  When observing the strings in which the interconnectors of Sample 20 and Sample 21 were joined, there were two joint points per electrode in most cells, but there were cells that were not bound only at one central portion. It was observed. Commonly used solar cells include a 5-inch cell and a 6-inch cell, but the cell used in this example is a small cell of a 5-inch cell. It is better that one electrode in one cell has two or more binding points, and the joining interval is preferably 60 mm or less.

  When the efficiency as a solar cell was compared, it was found that the efficiency of the cell produced using the interconnector of sample 16 to sample 21 was higher than that of the cell produced using the interconnector of sample 22. This is because the strength was small and the stress applied to the cells was small, and the bonding was sound, and the unevenness of the interconnector on the light-receiving surface caused irregular reflection of the light hitting the interconnector, and the light from the EVA resin or glass interface. This is considered to be due to the effect of re-reflecting and returning to the cell.

(Example 6)
Next, the amount of argon gas sprayed from both sides of the tape surface was changed by a wiping nozzle, and an interconnector having a basis weight of solder of 0.26 g and 0.24 g, which was reduced from the case of Example 5, was produced. Compared. Other than that, the manufacturing method of Sample 16 to Sample 21 in Example 5 was the same process. The conditions for producing the strings are the same as those in Example 5.

  In the spot-connected interconnector, when the spot joint interval was 4 mm and the weight per unit area was 0.24 g, a part that was not partly joined was seen, but the three-strings formed without stopping the device done. On the other hand, in the interconnector composed of one copper flat wire similar to the sample 22 having a weight per unit area of 0.24 g, it is impossible to perform sound joining due to insufficient supply of solder, the interconnector peels off, and the device automatically continues. I couldn't drive. On the other hand, in the interconnector that was spot-joined, even if the basis weight was reduced, the interconnector did not peel off because solder was supplied from the opposite side of the joining surface.

  As described above, by taking the form of the present invention, it is possible to soften the conductor while securing the conductor cross-sectional area, that is, the current capacity, and to reduce the amount of solder per unit area. It is possible to provide an excellent material as a mounting material for semiconductors such as an interconnector for a semiconductor.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Current collection interconnector 3 L direction 4 D direction 5 W direction 6 Single core wire 7 Bundling bonding material 8 Grain boundary 9 Welding / diffusion bonding part 10 Flat single core copper wire 11 Solder material for joining 12 Coating material

Claims (14)

Consists of two or more single core wires mainly composed of copper or aluminum,
The two or more single core wires are integrated so as to be parallel to the length direction of the single core wires and to be electrically connected to each other in a row in the width direction,
The two or more single core wires are directly point-bonded to each other in the width direction at intervals of 5 mm or more and 60 mm or less in the longitudinal direction, or points to each other in the width direction via a bundling bonding material different from the single core wire. And is covered with a material having a melting point lower than that of the material constituting the single core wire or the binding material,
In a cross section perpendicular to the length direction of the single core wire, the area average diameter corresponding to the circle of crystal grains constituting the single core wire is 5 with respect to the equivalent circle diameter of the cross-sectional area per single core wire. % Of a tape-like conductive material, characterized in that it is at least%. The single core wire is covered with aluminum or silver
The tape-like conductive material according to claim 1, wherein Consists of two or more single core wires mainly composed of copper or aluminum,
  The two or more single core wires are integrated so as to be parallel to the length direction of the single core wires and to be electrically connected to each other in a row in the width direction,
  The single core wire is covered with aluminum or silver,
  In a cross section perpendicular to the length direction of the single core wire, the area average diameter corresponding to the circle of crystal grains constituting the single core wire is 5 with respect to the equivalent circle diameter of the cross-sectional area per single core wire. % Or more
A tape-like conductive material characterized by the above. The two or more single core wires are directly point-bonded to each other in the width direction at intervals of 5 mm or more and 60 mm or less in the longitudinal direction, or points to each other in the width direction via a bundling bonding material different from the single core wire. Bonded and covered with a material having a melting point lower than that of the material constituting the single core wire or the bundling bonding material
The tape-like conductive material according to claim 3, wherein Consists of two or more single core wires mainly composed of copper or aluminum,
  The two or more single core wires are integrated so as to be parallel to the length direction of the single core wires and to be electrically connected to each other in a row in the width direction,
  The two or more single core wires are directly point-bonded to each other in the width direction at intervals of 5 mm or more and 60 mm or less in the longitudinal direction, or points to each other in the width direction via a bundling bonding material different from the single core wire. And is covered with a material having a melting point lower than that of the material constituting the single core wire or the binding material,
  The single core wire is covered with aluminum or silver,
  In a cross section perpendicular to the length direction of the single core wire, the area average diameter corresponding to the circle of crystal grains constituting the single core wire is 5 with respect to the equivalent circle diameter of the cross-sectional area per single core wire. % Or more
A tape-like conductive material characterized by the above. In the cross section perpendicular to the length direction of the single core wire, the area average diameter corresponding to the circle of the crystal grains constituting the single core wire is 20 with respect to the equivalent circle diameter of the cross-sectional area per single core wire. The tape-shaped conductive material according to claim 1 , wherein the tape-shaped conductive material is at least%. In the cross section perpendicular to the length direction of the single core wire, the area average diameter corresponding to the circle of crystal grains constituting the single core wire is 50 with respect to the equivalent circle diameter of the cross-sectional area per single core wire. The tape-shaped conductive material according to claim 1 , wherein the tape-shaped conductive material is at least%. Each of the two or more single-core wires is integrated so that the two or more single-core wires are electrically connected to each other by coating a binding material having lower strength or hardness than the single-core wires. The tape-shaped conductive material according to any one of claims 1 to 7 , wherein Each of the two or more single core wires is coated with a binding bonding material, and the two or more single core wires are integrated so as to conduct each other.
In the cross section perpendicular to the length direction of the tape-like conductive material, the covering cross-sectional area of the binding material is 10% or less of the total cross-sectional area of the two or more single core wires. The tape-shaped conductive material according to any one of claims 1 to 7 . The two or more single core wires are integrated so as to be in contact with each other in the width direction through a binding material different from the single core wire, or directly joined to each other at a part of the contact surface on the side surface of the single core wire. characterized in that it is a tape-like conductive material according to any one of claims 1-7. It said sintered bundle joining material you integrated two or more single core wire, characterized in that a solder, according to claim 1, the tape-shaped conductive material according to any one of 4-10. The tape-shaped conductive material according to any one of claims 1 to 11 , wherein the tape-shaped conductive material has a 0.2% yield strength of 20 to 70 MPa. It uses the tape-like conductive material according to any one of claims 1 to 12 ,
The tape-shaped conductive material has a thickness of 0.1 mm to 0.3 mm,
The tape- shaped conductive material has a width of 1 mm to 10 mm,
The interconnector for solar cells, wherein the aspect ratio of the width and thickness of the single core wire is 2 or less. Characterized in that it comprises a string of serially connected solar cell in a tape-like conductive material according to any one of claims 1 to 12 solar cell module.

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