JP6215692B2 - Zygote - Google Patents

Description

  The present invention relates to a joined body in which a base made of a material having different thermal expansion coefficients and a strip-like body are joined.

  There is a need for a technique for joining a base body and a band-shaped body made of materials having different thermal expansion coefficients. A solar cell module can be exemplified as an example in which materials having different thermal expansion coefficients are bonded together.

  A solar cell module is generally a strip of a plurality of solar cell elements having electrodes formed on both main surfaces thereof, such as a pn-junction single crystal silicon substrate, a polycrystalline silicon substrate, or a CIGS (Copper Indium Gallium DiSelenide) substrate. The connection conductors are joined together. Here, the solar cell element is a base having a small coefficient of thermal expansion, the connection conductor is a strip having a high coefficient of thermal expansion, the solder is a joint that connects both, and the solar cell module is It is a joined body in which these are joined together (see, for example, Patent Document 1).

JP 2004-281797 A

  However, in the joined body obtained by using the technique described in Patent Document 1, when temperature change occurs due to heating at the time of joining, daily temperature cycle, or the like, the strip is thermally expanded or contracted, The substrate connected to the substrate cannot absorb the stress caused by the expansion of the belt-like body, and as a result, the substrate may be cracked. In particular, since the amount of thermal expansion and contraction of the band-like body is large at the end of the band-like body in the connection portion between the band-like body and the base body, cracks are likely to occur in the base body connected thereto.

  The present invention has been conceived under the above-described circumstances, and an object of the present invention is to provide a bonded body in which cracks generated in a substrate are suppressed.

A joined body according to one embodiment is a belt-shaped member made of a material having a first main surface and a material having a thermal expansion coefficient larger than that of the substrate, provided at least an end portion is located above the first main surface. A band-shaped body and a band-shaped joint portion made of a material having a smaller coefficient of thermal expansion than the band-shaped body, and connecting the base body and the band-shaped body. Sometimes, a pair of outer lines along the longitudinal direction are substantially parallel to each other, and a joint end that extends from the intermediate part and the distance between the pair of outer lines changes toward the tip. And a first joint surface in which the joint end portion is in contact with the base body, and a second joint surface in which the joint end portion is in contact with the belt-like body, and when the second joint surface is viewed in plan view, located inside the end portion of the strip, with respect to the joint end portion, the A first change portion in which an outline of the joint portion is gradually displaced toward the intermediate portion side from the first joint surface toward the second joint surface when viewed in a cross-section in the normal direction of one main surface; And a second changing portion in which an outline of the joint portion gradually displaces toward the intermediate portion side from the second joint surface toward the first joint surface side, and a rate of change of the first change portion Is smaller than the rate of change of the second change part .

  According to the present invention, it is possible to obtain a bonded body in which the generation of cracks generated in the substrate is suppressed.

It is a top view which shows schematic structure of the conjugate | zygote which concerns on one Embodiment of this invention. (A), (b) is the principal part top view and sectional drawing of the conjugate | zygote which concern on one Embodiment of this invention. (A), (b) is the principal part top view and sectional drawing of the conjugate | zygote which concern on the modification of this invention. (A)-(d) is the principal part top view and sectional drawing of the conjugate | zygote which concern on the modification of this invention. It is a figure which shows the result of having simulated the stress distribution state of the joined body concerning an Example. It is a figure which shows the result of having simulated the stress distribution state of the joined body concerning a comparative example.

  An embodiment of the joined body of the present invention will be described with reference to the drawings.

  FIG. 1 is a plan view of a joined body 10 according to an embodiment of the present invention. In this example, a solar cell module will be described as an example of the bonded body 10. The joined body 10 is a material having a smaller thermal expansion coefficient than that of the belt-like body 2, which joins the base body 1, the belt-like belt-like body 2 made of a material having a larger thermal expansion coefficient than the base body 1, and the base body 1 and the belt-like body 2. And a joint portion 3 made of

The substrate 1 is a solar cell element, and is made of, for example, a single crystal silicon substrate or a polycrystalline silicon substrate having a thickness of about 0.2 mm to 0.4 mm and a size of about 150 mm square. A pn junction is formed on the silicon substrate of the base 1 so that a region containing p-type impurities such as boron (B) and a region containing n-type impurities such as phosphorus (P) are in contact with each other. In addition, when a single crystal silicon substrate is used as the substrate 1, the thermal expansion coefficient can be exemplified by 2.6 μm · m ⁻¹ · K ^−1, for example. Finger electrodes 11 and bus bar electrodes 12 are formed on the surface of the substrate 1.

  The finger electrode 11 and the bus bar electrode 12 are formed by applying and baking a silver paste or the like. A large number of finger electrodes 11 having a width of about 0.1 mm to 0.2 mm are provided in parallel to a predetermined side of the substrate 1. This finger electrode 11 can efficiently collect photogenerated carriers. The bus bar electrode 12 is provided to collect the carriers collected by the finger electrode 11 and is provided perpendicular to the finger electrode 11. Further, in order to collect current efficiently and to ensure connection to the band 2 described later, the width of the bus bar electrode 12 is made wider than the finger electrode 11 and may be about 2 mm, for example.

  Such finger electrodes 11 and bus bar electrodes 12 are formed not only on the first main surface 1a of the base 1 but also on the opposite main surface.

  And the strip | belt-shaped strip | belt-shaped body 2 is arrange | positioned through the junction part 3 mentioned later above the bus-bar electrode 12 of such a base | substrate 1. FIG. The strip-shaped body 2 has a thickness of, for example, about 0.1 mm to 1.0 mm, and its width is such that the bus bar electrode 12 has a width so as not to make a shadow on the first main surface 1a that is the light receiving surface of the substrate 1 that functions as a solar cell element. It is preferable to make it the same level. The length of the belt-like body 2 has a length that extends over almost the entire surface of the bus bar electrode 12 in consideration of the current collection efficiency and electrical resistance from the bus bar electrode 12. However, the belt-like body 2 may have such a length that the other end portion extends to the outside of the base body 1 when at least one end portion 21 is located above the first main surface 1a of the base body 1. Good. As described above, since the belt-like body 2 extends to the outside of the base body 1, it can be connected to another solar cell element disposed adjacent to the base body 1.

Such a band 2 is made of a material having high conductivity such as silver (Ag), copper (Cu), aluminum (Al), iron (Fe), gold (Au), etc. In this example C
u foil is used. The thermal expansion coefficient of Cu can be exemplified by 16.6 μm · m ⁻¹ · K ⁻¹ .

Then, the base body 1 and the belt-like body 2 are joined at the joint portion 3. The joining portion 3 is made of a material having a smaller thermal expansion coefficient than that of the belt-like body 2 and is not limited as long as both can be joined. In this example, since it is necessary to electrically connect the bus bar electrode 12 of the base 1 and the strip 2, a conductive material is used. For example, solder, brazing material, conductive bonding agent, or the like can be used. In this example, solder is used. The thermal expansion coefficient of solder can be exemplified by 3.0 μm · m ⁻¹ · K ⁻¹ . Thus, it is preferable to reduce the difference in thermal expansion coefficient from the substrate 1 because the thermal stress on the substrate 1 can be suppressed.

  The joining portion 3 may be interposed between the base 1 and the strip 2 by applying a solder coat having a desired pattern on the bus bar electrode 12 or on the joining surface side of the strip 2 and heating the solder coat. Good.

  The width of the junction 3 may be narrower than that of the bus bar electrode 12, but the current collection efficiency can be increased by making the width of the junction 3 substantially the same as that of the bus bar electrode 12.

  Here, the shape of the joint portion 3 will be described in detail. In FIG. 2, the typical principal part enlarged view of the junction part of the base | substrate 1, the strip | belt-shaped body 2, and the junction part 3 is shown. FIG. 2A is a plan view of the joint portion, and FIG. 2B is a cross-sectional view taken along the line IIb in FIG.

  As shown in FIG. 2, the joint portion 3 includes an intermediate portion 31 and a joint end portion 32 in plan view. The intermediate portion 31 refers to a region in which outlines in the width direction are substantially parallel. In other words, the outline in the width direction refers to an outline along the longitudinal direction. The joining end portion 32 is a region that is ½ or less of the length in the longitudinal direction, and refers to a region that reaches the distal end by changing the width from the portion having the width of the intermediate portion 31.

In this example, the outline of the joining end portion 32 is located inside the width of the outline of the intermediate portion 31. In other words, the width in the intermediate portion 31 is the maximum, and the joining end portion 32 is continuously reduced from the intermediate portion 31. A region where such a bonding end portion 32 is in contact with the substrate 1 is a first bonding surface 33, and a region where the bonding end portion 32 is in contact with the belt-like body 2 is a second bonding surface 34. FIG. 2 (a)
The outline of the second joint surface 34 is indicated by a broken line.

  The outline shape formed by the outline line of the first joint surface 33 is not particularly limited, but in this example, all the curves or corners are obtuse. In other words, it is configured not to include an acute angle portion of 90 ° or less. In this example, an arc is drawn. When attention is paid to the joint portion between the arc portion and the contour line in the width direction of the intermediate portion 31, the vicinity of the arc junction portion formed by the straight contour line of the intermediate portion 31 and the contour line of the first joint surface 33. The angle made with the tangent line is obtuse.

  The second bonding surface 34 is located on the inner side of the end portion 21 of the strip 2 in plan view. In other words, the second bonding surface 34 does not exist immediately below the end portion 21 of the strip 2. In addition, although the shape of the outline of the 2nd junction surface 34 is not specifically limited, In this example, it is set as the curve on a circular arc similarly to the outline shape formed of the outline of the 1st junction surface 33. And a part is located in the outer side of the strip | belt-shaped body 2 by planar view.

As described above, by making the shape of the outline of the first joint surface 33 not include an acute angle, it is possible to disperse the stress caused by the thermal contraction / thermal expansion from the belt-like body 2. Further, since the second joining surface 34 is located inside the joining end portion 32 of the strip 2, the joining portion 3 is formed at the corner of the end 21 where the thermal contraction / thermal expansion of the strip 2 is greatest. Will not touch. From this, it is possible to reduce the stress itself due to the thermal contraction and thermal expansion transmitted from the belt-like body 2 to the base body 1 through the joint portion 3. Furthermore, in this example, since the shape of the outline of the second joint surface 34 is also curved so as not to have an acute angle, the stress from the belt-like body 2 can be reduced.

  Further, as shown in FIG. 2B, the cross-sectional shape of the joint end portion 32 of the joint portion 3 is a shape that is recessed inward from both sides of the base body 1 side and the belt-like body 2 side. In other words, from the first joint surface 33 toward the second joint surface 34 side (the band-like body 2 side, upward), the first change portion 35 that is displaced so as to be recessed toward the intermediate portion 31 side, and the second joint surface 34 And a second changing portion 36 that is displaced so as to be recessed toward the intermediate portion 31 side toward the first bonding surface 33 side (base 1 side, downward). With such a configuration, the stress from the belt-like body 2 side is received while being dispersed, and the stress is transmitted while being dispersed toward the base body 1 side.

  Particularly in this example, the rate of change (absolute value of inclination) of the first change unit 35 is smaller than the rate of change (absolute value of inclination) of the second change unit 36. As a result, the stress from the belt-like body 2 is more gently transmitted to the base body 1.

  Moreover, since the thermal expansion coefficient of the material constituting the joint portion 3 is intermediate between the base 1 and the belt-like body 2, the stress caused by the thermal history can be relaxed at the joint portion 3. Furthermore, in this example, since the thermal expansion coefficient of the material constituting the joint portion 3 is closer to the base body 1 in the thermal expansion between the base body 1 and the belt-like body 2, Generation of stress due to a difference in thermal expansion coefficient can be suppressed.

  As described above, the joint 3 absorbs the stress caused by the thermal history from the band 2 by the shape and material of the joint 3. Thereby, generation | occurrence | production of the crack which generate | occur | produces in the base | substrate 1 can be suppressed.

(Modification 1)
Next, a modified example of the joined body 10 will be described. FIG. 3 is a schematic enlarged view of the main part of the joining portion of the base 1A, the strip 2A, and the joining portion 3A. FIG. 3A is a plan view of the joining portion, and FIG. 3B is a cross-sectional view taken along the line IIIb in FIG.

  A bonded body 1A shown in FIG. 3 is different in that a bonded portion 3A is provided instead of the bonded portion 3 of the bonded body 1 shown in FIG. Hereinafter, only different points will be described, and redundant description will be omitted. The outline of the first joint surface 33A is indicated by a dotted line, and the outline of the second joint surface 34A is indicated by a broken line.

  In the joining portion 3A, the first joining surface 33A is located on the inner side of the end portion 21A of the belt-like body 2A in plan view. With such a configuration, the distance between the strip 2 and the bus bar electrode 12 does not increase at the bus bar electrode 12, the joint 3A, and the end of the strip 2A. Thereby, current collection efficiency can be improved.

(Modification 2)
Furthermore, it is good also as a structure shown to Fig.4 (a)-(d). As shown in FIG. 4A, the cross-sectional shape of the joint end portion 32B of the joint portion 3B does not need to be recessed inward from both sides of the base body 1B side and the belt-like body 2B side, but the belt-like body 2B side. From the side toward the base body 1B, it may be gradually protruded (inflated) to the opposite side (outside) of the intermediate portion 31B. Although FIG. 4A shows an example in which the outline of the cross section draws a curve, it may be linear. Further, it may be vertical from the belt-like body 2B side to the base body 1B side.

  Moreover, as shown in FIG.4 (b), the shape of the outline of the 2nd joining surface 34C in the joining end part 32C of the joining part 3C is good also as a linear form instead of a curve. Since the joining portion 3C is not in contact with the corner portion of the end portion 21C and the shape of the first joining surface 33C is curved, even in such a configuration, stress transmission to the base 1C is suppressed. be able to.

  Further, as shown in FIG. 4C, the width of the outline of the first joint surface 33D at the joint end portion 32D of the joint portion 3D does not necessarily maximize the width of the intermediate portion 31 as shown in FIG. There is no need, and the shape may be such that it once swells from the width of the intermediate portion 31D and gradually decreases toward the tip. In other words, an arc portion having a radius of curvature larger than the width of the intermediate portion 31D may be connected.

  Furthermore, as shown in FIG. 4D, the planar shape of the joint end portion 32D of the joint portion 3E may be formed such that all corner portions thereof are obtuse.

(Modification 3)
In the above-described example, the example in which the material having the thermal expansion coefficient between the base body 1 and the belt-like body 2 is used as the bonding portion 3 has been described. However, the bonding section 3 may have a smaller thermal expansion coefficient than the base body 1. . In that case, cracks in the base 1 are suppressed, and cracks are generated in the joint 3. For this reason, even if it is a case where a big thermal stress is added by any chance, it can suppress that the base | substrate 1 (solar cell element) is damaged.

  In addition, although the solar cell element module has been described as an example of the joined body 10 in the above-described embodiment, it is a belt-like structure having a corner portion having a large thermal expansion coefficient on a base having a plane having a small thermal expansion coefficient. If it connects a certain strip | belt-shaped body, it will not be limited to this.

  In both the above-described embodiment and its modified example, the formation of cracks in the base body 1 can be suppressed only by forming a solder pattern to be the joint portion 3, so that the productivity is improved. Specifically, the solder pattern to be the joint portion 3 may be devised, solder coat is applied to the base 1 side and the band-like body 2 side, and a solder resist is disposed in a portion corresponding to the non-formation portion of the joint portion 3 If it does so, when both are made to contact and it heats, the junction part 3 which has a desired shape can be comprised automatically.

  In the above-described example, the case where the thermal expansion coefficient of the joint portion 3 is smaller than that of the belt-like body 2 has been described as an example. However, the outer shape of the first joint surface 33 does not include an acute angle and the second joint surface 34 When the outer shape is located inside the end portion 21 of the strip 2 in plan view, a material having a larger thermal expansion coefficient than that of the strip 2 may be used. In this case, since stress concentration at the end portion 21 of the belt-like body 2 is suppressed and stress generated by the belt-like body 2 and the joint portion 3 is gently transmitted to the base body 1, cracks in the base body 1 are generated. Can be suppressed.

The conjugate of examples and comparative examples, the stress applied to the substrate 1 and push from Mi configuration. Specifically, the joined body shown in FIG. 4A was used as a model as an example. Further, as a comparative example, a model is used in which the joint is in contact with the corner of the end of the strip and the shape of the joint with the base (corresponding to the first joint surface) is linear. . In other words, a model having the same shape as that of the belt-like body and using a joint portion in which ends are combined was used as a comparative example. The specific conditions were as follows.

Substrate: Silicon (thermal expansion coefficient: 8.3 μm · m ⁻¹ · K ⁻¹ )
Band: Copper (thermal expansion coefficient: 16.8 μm · m ⁻¹ · K ⁻¹ ),
Width: 3mm, thickness: 0.15mm
Joint: Solder (Coefficient of thermal expansion: 15 μm · m ⁻¹ · K ⁻¹ )
Conditions for thermal stress: Addition of temperature load of −100 ° C. Simulation results under such conditions are shown in FIGS. 5 and 6, respectively. FIG. 5 which is an example is compared with FIG. 6 which is a comparative example, and stress is not concentrated on one point at the corner portion of the end portion 21 of the strip 2 and the joint end portion 32 of the joint portion 3. It was confirmed that the stress was distributed and transmitted. As a result of the simulation, the region other than the portion adjacent to the joint end portion 32 and the end portion 21 was outside the range of the displayed range. That is, the stress was extremely small, and it was not confirmed that the stress was concentrated. Furthermore, when the maximum stress of both models is compared, it is 25.4 MPa in the example, and in the comparative example is 26.1 MPa, it is confirmed that the stress from the strip 2 can be suppressed. did it.

DESCRIPTION OF SYMBOLS 10 Bonded body 1 Base | substrate 1a 1st main surface 11 Finger electrode 12 Bus-bar electrode 2 Band-shaped body 21 End part 3 Joining part 31 Intermediate part 32 Joining end part 33 1st joined surface 34 2nd joined surface 35 1st change part 36 2nd Change section

Claims (5)

A base body having a first main surface, a belt-like belt body made of a material having a thermal expansion coefficient larger than that of the base body, provided at least at an end portion above the first main surface; Is made of a material having a small thermal expansion coefficient, and is a joined body including a strip-shaped joint portion that connects the base body and the strip-shaped body,
The joint portion, when viewed in plan, has an intermediate portion in which a pair of outline lines along the longitudinal direction are substantially parallel to each other, and a distance between the pair of outline lines extending from the intermediate portion toward the tip. A joining end portion in which the joining end portion is in contact with the base, and a second joining surface in which the joining end portion is in contact with the belt-like body,
It said second joint surface, when viewed in a plan view, is located inside the end portion of the strip,
When the cross-section is viewed in the normal direction of the first main surface with respect to the joint end portion, the outline of the joint portion gradually extends from the first joint surface toward the second joint surface. A first changing portion that is displaced toward the portion side, and a second changing portion in which an outline of the joint portion is gradually displaced toward the intermediate portion side from the second joint surface toward the first joint surface side. And the joined body whose change rate of the said 1st change part is smaller than the change rate of the said 2nd change part . Before SL contour of the first joint surface is curved or corner portions are all obtuse, conjugate of claim 1.   3. The joined body according to claim 1, wherein the outer shape of the second joint surface is a curved shape or all corners are obtuse. 4. The joined body according to claim 3 , wherein the first joined surface is located inside the end portion of the belt-like body when viewed in a plan view. The base is a solar cell element on which an electrode is formed, and the strip is a conductor that is joined to the electrode and functions as an extraction electrode for taking out a current from the solar cell element, the junction parts are made of solder, the conjugate according to any one of claims 1 to 4.