Circuit board for bypass diode, bypass diode device, and solar cell module

Abstract

A circuit board for a bypass diode according to the present disclosure has a ceramic substrate and a conductor. The conductor is disposed on the main surface of the ceramic substrate in the form of an abnormally shaped object of varying thickness. The conductor has a first electrode part and a second electrode part. The first electrode part has a bypass diode mounted thereon and is an electrode for electrically connecting the bypass diode. The second electrode part is a region of the conductor excluding the first electrode part. The second electrode part has a portion which is thicker than is the first electrode part.

Description

Circuit Board for Bypass Diode, Bypass Diode Device, and Solar Cell Module

[0001] The present disclosure relates to a circuit board for a bypass diode, a bypass diode device, and a solar cell module.

[0002] In recent years, the spread of solar power generation as a renewable energy has been progressing. Current solar cell modules usually have a junction box on their back surface.

[0003] The junction box has a bypass diode therein. The bypass diode plays a role of bypassing current to protect the solar cell when a problem such as shading occurs in the solar cell module (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2015-185784

[0005] The circuit board for a bypass diode according to one aspect of the present disclosure has a ceramic substrate and a conductor. The conductor is arranged on the main surface of the ceramic substrate in a form of a different-shaped object having different thicknesses. The conductor has a first electrode portion and a second electrode portion. The first electrode portion is an electrode for installing a bypass diode and electrically connecting the bypass diode. The second electrode portion is a region of the conductor excluding the first electrode portion. The second electrode portion has a portion thicker than the first electrode portion.

[0006] Figure 1 is a cross-sectional view of a bypass diode device shown as an example of an embodiment. Figure 2 is an enlarged view of portion S shown in Figure 1. Figure 3 is a cross-sectional view of a solar cell module shown as an example of an embodiment. Figure 4 is a cross-sectional view showing another embodiment of a circuit board for a bypass diode. Figure 5 is a cross-sectional view showing another embodiment of a circuit board for a bypass diode. Figure 6 is a cross-sectional view taken along line A-A shown in Figure 4. Figure 7 is an enlarged view of portion C shown in Figure 6, where the radius of curvature of the corner is small. Figure 8 is an enlarged view of portion C shown in Figure 6, where the radius of curvature of the corner is large. Figure 9 is a cross-sectional view showing another embodiment of a circuit board for a bypass diode. Figure 10 is a schematic diagram of an automobile equipped with a solar cell module. Figure 11 is a cross-sectional view of the circuit board for a bypass diode of sample 1 in the embodiment. Figure 12 is a cross-sectional view of the circuit board for a bypass diode of sample 2 in the comparative example. Figure 13 is a cross-sectional view of the circuit board for a bypass diode of sample 3 in the embodiment. Figure 14 is a schematic diagram showing an example of a method for manufacturing the circuit board for a bypass diode of sample 3 in the embodiment.

[0007] The following describes the circuit board for the bypass diode according to the embodiment, the bypass diode device using the same, and the solar cell module with reference to the drawings.

[0008] However, the embodiments of this disclosure are not limited to the specific embodiments described below. The embodiments of this disclosure include a variety of embodiments, as long as they are consistent with the spirit or scope of the overall concept of the invention as defined by the appended claims.

[0009] Figure 1 is a cross-sectional view of a bypass diode device 1 shown as an example of an embodiment. Figure 2 is an enlarged view of portion S shown in Figure 1. Figure 3 is a cross-sectional view of a solar cell module 2 shown as an example of an embodiment.

[0010] As shown in Figure 1, the bypass diode device 1 shown as an example of an embodiment includes a bypass diode circuit board 11 and a bypass diode 12.

[0011] First, let's explain the circuit board 11 for the bypass diode.

[0012] The bypass diode circuit board 11 comprises a ceramic substrate 111 and a conductor 112. The conductor 112 is arranged on the main surface of the ceramic substrate 111 in the form of an irregularly shaped object. This irregularly shaped object has portions of different thicknesses.

[0013] Here, an irregularly shaped object refers to a conductor 112 having a shape in which parts of different thicknesses are formed, a shape in which steps are formed on the side surface of the conductor 112, or, when the conductor 112 is viewed from above, having at least one of the following shapes selected from the group consisting of a drum or dumbbell shape, a sports track shape, and a rhombus shape, rather than a square or rectangular shape, with a missing part or a part of a different width.

[0014] The conductor 112 has a first electrode portion 112a and a second electrode portion 112b.

[0015] According to the bypass diode circuit board 11, by providing a thicker portion of the conductor 112 adjacent to a thinner portion of the conductor 112 arranged on the main surface of the ceramic substrate 111, the circuit board equipped with the bypass diode 12 can be made strong even when it is made small and thin.

[0016] Of the conductor 112, the first electrode portion 112a is the portion (mounting portion) on which the bypass diode 12 is mounted. The first electrode portion 112a is an electrode for electrically connecting the bypass diode 12. The first electrode portion 112a is also a component for fixing the bypass diode 12 to the ceramic substrate 111.

[0017] The second electrode portion 112b is the region of the conductor 112 excluding the first electrode portion 112a. A conductive member such as a connecting wire may be connected to the second electrode portion 112b. The first electrode portion 112a and the second electrode portion 112b are electrically connected.

[0018] Since the conductor 112 is a continuous unit on the main surface of the ceramic substrate 111, the first electrode portion 112a and the second electrode portion 112b constituting the conductor 112 have the same polarity. The continuous nature of the conductor 112 means that, as shown in Figure 1, the conductor forms a single, unified unit.

[0019] The first electrode portion 112a and the second electrode portion 112b have the same potential. That is, the first electrode portion 112a and the second electrode portion 112b are the same pole and have the same potential.

[0020] The conductor 112 has portions with different thicknesses between the first electrode portion 112a and the second electrode portion 112b. In this case, the second electrode portion 112b has a portion that is thicker than the first electrode portion 112a.

[0021] Furthermore, if both the first electrode portion 112a and the second electrode portion 112b have flat surfaces, it can also be said that the second electrode portion 112b is thicker than the first electrode portion 112a.

[0022] In Figure 1, the thickness of the first electrode portion 112a is represented as t1, and the thickness of the second electrode portion 112b is represented as t2. In Figure 1, the conductor 112 has the relationship t1 < t2.

[0023] The conductor 112 has a portion of the second electrode portion 112b that is thicker than the first electrode portion 112a, thereby increasing its mechanical strength.

[0024] Furthermore, if the conductor 112 has portions with different thicknesses, it becomes possible to adjust the height between the bypass diode 12 mounted on the first electrode portion 112a and the conductive member connected to the second electrode portion 112b. For example, this is possible when it is desirable to make the height of the bypass diode 12 the same as the height of the conductive member, or to reduce the difference in their heights.

[0025] When the surface of the ceramic substrate 111 is used as the reference plane 111a, the height (thickness t2) of the conductor 112 from the reference plane 111a to the upper surface 112bb of the second electrode portion 112b is preferably the same as the position from the reference plane 111a to the upper surface 12a of the bypass diode 12 when the bypass diode 12 is placed on the first electrode portion 112a. In other words, the height (thickness t2) of the conductor 112 from the reference plane 111a to the upper surface 112bb of the second electrode portion 112b is preferably the same as the height from the reference plane 111a to the upper surface 12a of the bypass diode 12.

[0026] The height from the reference surface 111a to the upper surface 112bb of the second electrode portion 112b is said to be at the same position as the height from the reference surface 111a to the upper surface 12a of the bypass diode 12 when a bypass diode is placed on the first electrode portion 112a, which means that the height from the reference surface 111a to the upper surface 112bb of the second electrode portion 112b is in the range of 2 / 3 or more of the height from the reference surface 111a to the upper surface 12a of the bypass diode 12 to the same height. Furthermore, the height from the reference surface 111a to the upper surface 112bb of the second electrode portion 112b is said to be at the same position as the height from the reference surface 111a to the upper surface 12a of the bypass diode 12 when a bypass diode is placed on the first electrode portion 112a, which includes the case where the height from the reference surface 111a to the upper surface 112bb of the second electrode portion 112b is the same as the height from the reference surface 111a to the upper surface 12a of the bypass diode 12.

[0027] In Figure 1, the conductor 112 and bypass diode 12 of the bypass diode circuit board 11 are depicted facing downwards. Here, the upper surfaces 112bb and 12a are referred to as the upper surfaces because they are located in the thickness direction from the reference surface 111a to the second electrode portion 112b.

[0028] The second electrode portion 112b is a conductor portion for allowing current to flow outside the bypass diode circuit board 11. The second electrode portion 112b is a conductor portion for drawing current from an external circuit (not shown) to the bypass diode 12.

[0029] When a bypass diode 12 is mounted on the first electrode portion 112a and the second electrode portion 112b is electrically connected to an external circuit, it is preferable that the first electrode portion 112a and the second electrode portion 112b be covered with an organic resin 15, as shown in Figure 1. In this case, it is preferable that the organic resin 15 is also bonded to the ceramic substrate 111.

[0030] When the conductor 112, the bypass diode 12, and the external circuit are coated with organic resin 15, the weather resistance of the conductor 112, the bypass diode 12, and the external circuit itself can be improved. Furthermore, the weather resistance of the bonding material 119 interposed between the bypass diode 12 and the first electrode portion 112a, and the bonding material 121 interposed between the external circuit and the second electrode portion 112b can be improved. Moreover, the bonding strength between the bypass diode 12 and the first electrode portion 112a can be improved. In addition, the bonding strength between the second electrode portion 112b and the external circuit can be improved. In these cases, bonding strength refers to the lifespan of the bond, or in other words, long-term reliability.

[0031] When the organic resin 15 adheres to the ceramic substrate 111, conductor 112, bypass diode 12, and external circuit and covers them, the mechanical strength of the organic resin 15 itself improves as it heat-cures. Therefore, the impact resistance of the bypass diode device 1, including the ceramic substrate 111, conductor 112, bypass diode 12, and external circuit, can also be improved.

[0032] In this case, the organic resin 15 may contain ceramic powder, preferably silica powder or alumina powder. When the organic resin 15 contains ceramic powder, the thermal expansion coefficient of the cured organic resin 15 can be made smaller than that of the organic resin 15 alone. The thermal expansion coefficient of the cured organic resin 15 containing ceramic powder will approach that of the bypass diode 12, conductor 112, and external circuit. As a result, the strain generated between the cured organic resin 15 containing ceramic powder and the ceramic substrate 111, bypass diode 12, conductor 112, and external circuit will be reduced, thereby reducing the stress generated in the bypass diode device 1.

[0033] As shown in Figure 2, the organic resin 15 is preferably bonded to the conductor 112 so as to form a base extending from the side surface of the first electrode portion 112b to the surface of the ceramic substrate 111.

[0034] The material for the conductor 112 should be a metal with high electrical conductivity. Examples of materials for the conductor 112 include one selected from the group consisting of copper, tungsten, molybdenum, aluminum, iron, nickel, cobalt, solder (Sn-Pb), and precious metals.

[0035] The material of the conductor 112 should have high thermal conductivity. In this case, copper and silver are suitable materials for the conductor 112. A material that can be fired together with the ceramic substrate 111 may be selected as the material for the conductor 112. The conductor 112 may also be formed by firing the material onto a pre-sintered ceramic substrate 111. When formed by firing, it is preferable to use a metal-containing composition that can be fixed at a temperature lower than the sintering temperature of the ceramic substrate 111. When forming the metal-containing composition on the ceramic substrate 111 using a coating method or printing method, it is preferable to use a so-called paste-like material which is a mixture of metal powder and an organic vehicle.

[0036] The shape of the ceramic substrate 111 can be selected to any shape according to the design of the bypass diode device 1 and the solar cell module 2 on which the bypass diode device 1 is mounted.

[0037] When the ceramic substrate 111 is viewed from above, its basic shape may be rectangular, circular, elliptical, or a polygonal shape other than rectangular. When the basic shape of the ceramic substrate 111 is rectangular, circular, elliptical, or a polygonal shape other than rectangular, the ceramic substrate 111 may have recesses or protrusions on its corners or on the sides between two corners.

[0038] The material used for the ceramic substrate 111 can be any material that primarily contains at least one selected from the group consisting of alumina, mullite, silicon carbide, silicon nitride, aluminum nitride, silica, forsterite, and glass ceramics. This is because these materials can result in a ceramic substrate that exhibits high properties in terms of insulation, mechanical strength, moisture resistance, weather resistance, and chemical resistance.

[0039] The basic configuration of the bypass diode device 1 of this disclosure is such that a bypass diode 12 is mounted on a conductor 112. The bypass diode 12 is fixed to the bypass diode circuit board 11 via a bonding material 119. The bonding material 119 can be solder or a conductive adhesive, but a conductive adhesive containing metal particles in an organic resin may be selected for its heat resistance.

[0040] In the bypass diode device 1 shown in Figure 1, a first electrode member 13 may be bonded to the surface of the bypass diode 12. The first electrode member 13 is bonded to the surface of the bypass diode 12, for example, via a bonding material 121.

[0041] (Bypass Diode Device) In addition to the bypass diode 12, the bypass diode device 1 shown in Figure 1 may also have a second electrode member 14 joined to the second electrode portion 112b.

[0042] In the bypass diode device 1, as shown in Figure 1, the bypass diode 12 may be positioned so that it faces the ground surface more than the ceramic substrate 111.

[0043] FIG. 3 shows an example of the solar cell module 2. The solar cell module 2 shown in FIG. 3 includes a solar cell panel 20 and a bypass diode device 1. The solar cell panel 20 has a structure in which a first film 21, a first resin layer 22, a cell group 23, a second resin layer 24, and a second film 25 are laminated in this order.

[0044] The cell group 23 has a plurality of series cell groups 231. Note that FIG. 3 shows only one series cell group 231. The series cell group 231 is formed by electrically connecting a plurality of cells 231a in series. The series cell group 231 may have a portion in the cell group 23 where these are connected in parallel.

[0045] In the solar cell module 2 shown in FIG. 3, the side of the first film 21 is the surface that receives sunlight. The side of the second film 25 is the side facing the ground surface. The side of the second film 25 is also the side close to the ground surface. The first film 21 and the second film 25 are, for example, EVA (ethylene vinyl acetate).

[0046] As shown in FIG. 3, when the bypass diode device 1 is incorporated into the solar cell module 2, the bypass diode device 1 may be arranged such that the bypass diode 12 faces downward. In other words, for the solar cell module 2 installed on the ground, when considering the direction perpendicular to the ground, with the ceramic substrate 111 in the middle, the bypass diode 12 may be located on the side opposite to the position of the sun.

[0047] With the structure in which the bypass diode 12 is located on the side opposite to the position of the sun (the position receiving sunlight), the bypass diode device 1 is arranged such that the ceramic substrate 111 serves as a shielding plate and sunlight does not hit it.

[0048] Since the ceramic substrate 111 blocks sunlight, the temperature rise of the bypass diode 12 can be reduced. Since the time, frequency, and probability of the bypass diode 12 being exposed to sunlight are reduced, deterioration of the bypass diode 12 due to sunlight or the surrounding environment such as dew condensation can be suppressed.

[0049] The solar cell module 2 shown in Figure 3 comprises a solar cell panel 20 and a bypass diode device 1. In this case, the bypass diode device 1 is arranged on a second resin layer 24.

[0050] The bypass diode device 1 is arranged on the same plane as the cell group 23 on the second resin layer 24. The bypass diode device 1 is sandwiched between the first resin layer 22 and the second resin layer 24 on the same plane as the cell group 23.

[0051] The bypass diode device 1 is preferably positioned around the cell group 23 within the solar cell module 2.

[0052] If the bypass diode device 1 is arranged around the cell group 23 within the solar cell module 2, the cell group 23 can be arranged in a concentrated manner within the plane, making it possible to obtain a highly efficient solar cell module 2.

[0053] If the bypass diode device 1 is positioned, for example, inside the cell 231a located at the edge of the cell group 23, a region will be created within the cell group 23 in which no electromotive force is generated.

[0054] If the bypass diode device 1 is positioned, for example, inside the cell 231a located at the edge of the cell group 23, then the length of the conductors used to electrically connect cells within the cell group 23, or series cell groups 231, will increase. This will result in a decrease in electromotive force, a decrease in generated power, and a decrease in power generation efficiency per unit area.

[0055] The thickness of the bypass diode device 1 should be the same as or less than the thickness of cell 231a or cell group 23.

[0056] The area of ​​the bypass diode device 1 when viewed from above should be smaller than the area of ​​a single cell 231a when viewed from above.

[0057] For example, if a conventional junction box is provided on the solar cell module 2, the junction box will protrude significantly from the back surface of the solar cell module 2. However, by using the bypass diode device 1 of this disclosure, the bypass diode device 1 will be contained within the thickness range of the cell group 23, thereby maintaining the flatness of both sides of the solar cell module 2.

[0058] If the solar cell module 2 is a so-called flat plate type structure, it becomes possible to stack multiple solar cell modules 2 together without any gaps in the stacking direction.

[0059] If the solar cell module 2 is a flat plate-type structure, it becomes possible to slightly bend and stack the cell group 23 and the solar cell module 2. This reduces the bulk (volume) when transporting multiple solar cell modules 2, thus increasing transportation efficiency.

[0060] The area of ​​the first electrode portion 112a in a plan view should be larger than the area of ​​the bonding surface of the bypass diode 12. This reduces the heat generated within the bypass diode circuit board 11 due to conductivity. It also reduces the resistance of the current flowing into or out of the bypass diode 12 within the bypass diode circuit board 11. Furthermore, it suppresses the heat generated in the bypass diode 12 due to the connection between the bypass diode circuit board 11 and the conductor 112.

[0061] Figure 4 is a cross-sectional view showing another embodiment of the bypass diode circuit board 11. In Figure 4, for convenience, a configuration is shown in which the bypass diode 12 is arranged in the same way as in Figure 1, in order to show the positional relationship with the bypass diode 12.

[0062] As shown in Figure 4, the ceramic substrate 111 may have an internal space 115. In this case, the area of ​​the space 115 in a plan view should be at least equal to or greater than the area of ​​the conductor 112 in a plan view. In this case, the thermal conductivity of the ceramic substrate 111 can be reduced. In particular, when the side opposite to the side on which the conductor 112 is provided is the light-receiving side of the solar cell module 2, the diffusion of heat from the light-receiving side to the side on which the conductor 112 is provided within the ceramic substrate 111 can be suppressed. Furthermore, since the temperature rise of the bypass diode 12 can be suppressed, the operation stability and lifespan of the bypass diode 12 can be improved.

[0063] The space 115 does not have to be a single unit. Furthermore, the space 115 may be divided by a partition member. Here, the partition member is preferably integrally formed from the same material as the ceramic substrate 111. This is because, even if the width or thickness of the partition member is small, it can have high mechanical strength due to its integral connection to the ceramic substrate 111.

[0064] Figure 5 is a cross-sectional view showing another embodiment of the bypass diode circuit board 11. In Figure 4, for convenience, a configuration is shown in which the bypass diode 12 is arranged in the same way as in Figure 1, in order to show the positional relationship with the bypass diode 12.

[0065] As shown in Figure 5, in the disclosed bypass diode circuit board 11, the ceramic substrate 111 comprises two ceramic layers 111A and 111B sandwiching a space 115 in the thickness direction. Of the two ceramic layers 111A and 111B, the ceramic layer on the side to which the conductor 112 is attached is designated as the first ceramic layer 111A. Of the two ceramic layers 111A and 111B, the ceramic layer located on the opposite side of the space 115 from the first ceramic layer 111A is designated as the second ceramic layer 111B. In this case, the shape of the second ceramic layer 111B is preferably a curved shape that is convex in the thickness direction toward the conductor 112 side.

[0066] In a structure where the ceramic substrate 111 has a space 115, the volume of the space 115 reduces the effective volume of the ceramic substrate 111. Therefore, there is a concern that the mechanical strength of the ceramic substrate 111 will decrease.

[0067] As described above, if the second ceramic layer 111B, which does not have a conductor 112, of the two ceramic layers 111A and 111B sandwiching the space 115 in the thickness direction, is curved in a convex shape in the thickness direction toward the conductor 112, then when the conductor 112 shrinks due to heat, the second ceramic layer 111B will resist the direction of shrinkage of the conductor 112. This makes it possible to make the ceramic substrate 111 less prone to bending even if its actual volume is reduced.

[0068] Figure 6 is a cross-sectional view taken along line A-A as shown in Figure 4. Figure 7 is an enlarged view of section C shown in Figure 6, where the radius of curvature of the corner is small. Figure 8 is an enlarged view of section C shown in Figure 6, where the radius of curvature of the corner is large. Note that Figure 6 corresponds to a plan view of the ceramic substrate 111 obtained when the bypass diode circuit board shown in Figure 4 is cut horizontally along line A-A. In this case, it is a plan view that allows a plan view of the space 115 formed inside the ceramic substrate 111.

[0069] As shown in Figure 6, in the bypass diode circuit board 11, when the ceramic substrate 111 is viewed through from above, it is preferable that the corner 115c of the space 115 forms an arc shape.

[0070] As shown in comparison to Figures 7 and 8, when the ceramic substrate 111 is viewed from above, if the corner 115c of the space 115 is arc-shaped, then in the case of Figure 8, even when the ceramic substrate 111 (bypass diode circuit board 11) deforms, the stress is more easily distributed over an area corresponding to the radius of curvature of the corner 115c, compared to the case of Figure 7 where the corner 115c of the space 115 is right-angled or close to right-angled, thus improving the resistance to mechanical strength.

[0071] The radius of curvature at the location of circle D shown in Figure 8 should be 10 μm or more. 50 μm or more, 100 μm or more, and even 500 μm or more would be even better.

[0072] Figure 9 is a cross-sectional view showing another embodiment of the bypass diode circuit board 11. In the disclosed bypass diode circuit board 11, the conductor 112 may be a laminate 112A in which a plurality of metal layers 113 of different compositions are fixed to each other.

[0073] If the conductor 112 is a laminate in which multiple metal layers 113 of different compositions are fixed together, it becomes possible to introduce a change in at least one of the coefficient of thermal expansion and Young's modulus between these multiple metal layers 113 in the direction of the thickness (height) of the conductor 112. This makes it possible to create a state in which the thermal stress generated due to temperature changes between the bypass diode 12 or external wiring mounted on the surface of the conductor 112 gradually changes in the direction of the thickness (height) of the conductor.

[0074] In other words, when strain is generated between the ceramic substrate 111 and the conductor 112 constituting the bypass diode circuit board 11 due to the operation of the bypass diode 12 or a change in the external ambient temperature, a stress relaxation mechanism is activated in the conductor 112 even when internal stress is generated as a result, thereby reducing the probability of the bypass diode circuit board 11 failing.

[0075] For example, a copper plating film may be formed on the surface of the second electrode portion 112b in the shape of a metal post. In this case, the conductor may have interfaces where metal layers are bonded or joined together.

[0076] The ceramic substrate 111 is preferably black in color. If the ceramic substrate 111 is black, it will be the same color as the solar cell, so the design will not be compromised.

[0077] As shown in Figure 1, the bypass diode device 1 is equipped with a bypass diode 12 on one of the bypass diode circuit boards 11 described above. Because the bypass diode device 1 uses a thin bypass diode circuit board 11, a thinner and smaller bypass diode device 1 can be obtained compared to the conventional junction box type.

[0078] As shown in Figure 3, the solar cell module 2 includes a solar cell panel 20 and a bypass diode device 1.

[0079] Because the bypass diode device 1 uses a thin bypass diode circuit board 11, it is possible to create a thin solar cell module 2 that does not protrude from the solar cell panel 20, unlike conventional junction box type modules.

[0080] As described above, the solar cell panel 20, the first film 21, the first resin layer 22 (transparent resin layer), the cell group 23 (solar cell), the second resin layer 24 (white resin layer), and the second film 25 are stacked in this order. The bypass diode device 1 is housed within the thickness range of the solar cell panel 20. As a result, the solar cell module 2 takes the form of a plate-like body with equal thickness.

[0081] The solar cell module 2 of this disclosure can reduce transportation costs or improve ease of installation in applications such as automobiles. Figure 10 is a schematic diagram of an automobile 50 equipped with the solar cell module 2. The solar cell module 2 of this disclosure allows for a flatter roof structure for the automobile 50.

[0082] A circuit board for bypass diodes was fabricated and evaluated using the following method.

[0083] (Sample description) The cross-sectional structure of each prepared sample is shown in Figures 11 to 13.

[0084] Sample 1, as shown in Figure 11, is a portion of the circuit board for a bypass diode in a bypass diode device having the conductor shape shown in Figure 1. The conductor of Sample 1 has an irregular shape. Sample 1 has a tall metal post in the second electrode portion. The metal post in Sample 1 was formed by layering conductor patterns. In this way, a circuit board for a bypass diode with an irregularly shaped conductor was formed. The portion of the conductor excluding the metal post was formed by a single application of conductor paste.

[0085] Sample 2, as shown in Figure 12, is a circuit board for a bypass diode having a thin film shape in the second electrode portion without a metal post. The conductor of Sample 2 was formed by a single coat of conductor pattern on both the first and second electrode portions.

[0086] Sample 3 is a bypass diode circuit board with a structure in which a space is formed in the ceramic substrate of the bypass diode circuit board shown in Figure 11, as shown in Figure 13.

[0087] For samples 1 and 2, deflection tests were performed to evaluate their resistance to deformation. Thermal conductivity was evaluated between sample 1 and sample 3.

[0088] (Method of sample preparation) First, silicon nitride powder was used as the ceramic material for preparing the ceramic substrate, and a green sheet containing these ceramic powders was prepared.

[0089] Next, a conductive pattern was formed over a predetermined area on one of these green sheets, which would become a ceramic substrate after firing. The green sheet on which the conductive pattern was formed is referred to as the first green sheet. A green sheet on which a conductive pattern was formed is sometimes called a pattern sheet. A conductive paste containing tungsten powder was used to form the conductive pattern.

[0090] All of these samples were made using a green sheet measuring 200 mm x 200 mm x 0.21 mm (thickness). This size of green sheet allowed for the creation of 25 samples at a time. After firing, the sample dimensions, when viewed from above, were 10 mm x 10 mm (the area of ​​the bypass diode circuit board). The ceramic substrate thickness was 0.16 mm. These dimensions are the design dimensions; the fired samples include dimensional deviations.

[0091] The method for preparing sample 3 is shown in Figure 14. Here, in order to make the thickness of the ceramic substrate the same as that of sample 1, a separate green sheet was prepared, with a thickness of 1 / 3 that of the green sheet used to prepare sample 1.

[0092] As shown in Figure 14, a base laminate was created by stacking a plain green sheet (fifth green sheet), a perforated green sheet (fourth green sheet), and a patterned sheet (third green sheet) in that order from the bottom.

[0093] In the case of the ceramic substrate of sample 3, the ceramic layers are defined as the components arranged to sandwich the space between them. The ceramic substrate of sample 3 can be described as having two ceramic layers arranged with the space between them.

[0094] In this case, the ceramic layer on the conductor side where the bypass diode is placed is designated as the first ceramic layer, and the ceramic layer on the opposite side of the first ceramic layer, separated by a space, is designated as the second ceramic layer. Although not shown in Figure 14, a metal post is also formed in the conductor pattern of sample 3 in the portion that will become the second electrode.

[0095] Next, the base laminate, which would become samples 1 to 3, was cut at predetermined locations to form individual laminate segments. Then, the resulting laminate segments were fired.

[0096] The firing conditions were set to a reducing atmosphere containing nitrogen gas, with a maximum temperature of 1950°C for 2 hours. In this way, sintered bodies that would serve as circuit boards for bypass diodes were obtained for samples 1 to 3.

[0097] (Plating) Next, these sintered bodies were plated with nickel (Ni) and copper.

[0098] (Ag paste bonding) After this, bypass diode elements were bonded to the first electrode portion of the prepared samples 1 to 3 using Ag paste.

[0099] (Bypass Diode) The bypass diode used was of a type in which the element shape is a rectangular parallelepiped and terminal electrodes are formed to cover almost the entire surface of both main surfaces. In this case, in samples 1 and 3, the top surface of the bypass diode element and the top surface of the second electrode were at approximately the same height. In sample 2, the thickness of the second electrode was the same as the thickness of the first electrode and remained thin. In sample 3, the ceramic layer that forms the space, the so-called back side ceramic layer (second ceramic layer) which does not have a conductor, had a shape in which the area near the center of the space was recessed compared to the periphery within the range of the space. All four corners of the space in sample 3 were arc-shaped.

[0100] (Evaluation) For both deflection and thermal conductivity, the number of samples used for evaluation was set to n=5, and the average value was calculated from these samples.

[0101] The evaluation began by measuring the deflection of samples 1 and 2 using an autograph, based on the relationship between time and deformation when pressure was applied from the back side of the ceramic substrate. The results showed that the deflection of sample 2 was greater than that of sample 1. When the deflection of sample 2 was normalized to 1, the value for sample 1 was 0.4.

[0102] Next, the difference in thermal conductivity between sample 1 and sample 3 was evaluated.

[0103] A Peltier element was bonded to the back surface of a ceramic substrate, and a thermocouple was bonded to the surface of one of the bypass diode elements. The temperature change over time was then investigated. When the rate of temperature change (gradient) of sample 1 was set to 1, the rate of temperature change (gradient) of sample 3 was 0.6.

[0104] Furthermore, this technology can take the following configurations: (1) A circuit board for a bypass diode, comprising a ceramic substrate and a conductor, wherein the conductor is arranged on the main surface of the ceramic substrate in the form of irregularly shaped objects of different thicknesses, the conductor has a first electrode portion and a second electrode portion, the first electrode portion has a bypass diode installed on it and electrically connects the bypass diode, the second electrode portion is the region of the conductor excluding the first electrode portion, and the second electrode portion has a portion that is thicker than the first electrode portion. (2) The circuit board for a bypass diode according to (1), wherein, when the surface of the ceramic substrate is used as a reference plane, the height from the reference plane to the upper surface of the second electrode portion is at the position from the reference plane to the upper surface of the bypass diode when the bypass diode is placed on the first electrode portion. (3) The circuit board for a bypass diode according to (1) or (2), wherein the ceramic substrate has a space portion inside. (4) The circuit board for a bypass diode according to (3), wherein the ceramic substrate comprises two ceramic layers sandwiching the space in the thickness direction, and when the ceramic layer on the side having the conductor is designated as the first ceramic layer and the ceramic layer located on the opposite side of the space from the first ceramic layer is designated as the second ceramic layer, the shape of the second ceramic layer is a curved shape that is convex in the thickness direction toward the conductor side. (5) The circuit board for a bypass diode according to (4), wherein when the ceramic substrate is viewed through a plane, the corners of the space form an arc shape. (6) The circuit board for a bypass diode according to any one of (1) to (5), wherein the conductor is a laminate in which a plurality of metal layers of different compositions are fixed together. (7) The circuit board for a bypass diode according to any one of (1) to (6), wherein the ceramic substrate is black in color. (8) The circuit board for a bypass diode according to any one of (1) to (7), wherein the ceramic substrate mainly comprises at least one selected from the group consisting of alumina, mullite, silicon carbide, silicon nitride, aluminum nitride, silica, forsterite, and glass ceramics.(9) A bypass diode device having the bypass diode on a circuit board for a bypass diode as described in any one of (1) to (8) above. (10) A solar cell module having the bypass diode device described in (9) above and a solar cell panel. (11) The solar cell module described in (10) above, wherein the solar cell panel is laminated in the order of a first film, a transparent resin layer, a solar cell, a white resin layer, and a second film, and the bypass diode device is housed within the thickness range of the solar cell panel.

[0105] 1 Bypass diode device 2 Solar cell module 11 Circuit board for bypass diode 12 Bypass diode 13 First electrode member 14 Second electrode member 15 Organic resin 111 Ceramic substrate 111a Reference surface 112 Conductor 112a First electrode portion 112b Second electrode portion 113 Metal layer 115 Space

Claims

1. A circuit board for a bypass diode, comprising a ceramic substrate and a conductor, wherein the conductor is arranged on the main surface of the ceramic substrate in the form of irregularly shaped objects of different thicknesses, the conductor has a first electrode portion and a second electrode portion, the first electrode portion has a bypass diode installed on it and electrically connects the bypass diode, the second electrode portion is the region of the conductor excluding the first electrode portion, and the second electrode portion has a portion that is thicker than the first electrode portion.

2. The circuit board for a bypass diode according to claim 1, wherein, when the surface of the ceramic substrate is used as the reference plane, the height from the reference plane to the upper surface of the second electrode portion is at the same position as when the bypass diode is placed on the first electrode portion, from the reference plane to the upper surface of the bypass diode.

3. The circuit board for a bypass diode according to claim 1, wherein the ceramic substrate has a space inside.

4. The circuit board for a bypass diode according to claim 3, wherein the ceramic substrate comprises two ceramic layers sandwiching the space in the thickness direction, and of the two ceramic layers, the ceramic layer on the side having the conductor is designated as the first ceramic layer, and the ceramic layer located on the opposite side of the space from the first ceramic layer is designated as the second ceramic layer, and the shape of the second ceramic layer is a curved shape that is convex in the thickness direction toward the conductor side.

5. The circuit board for a bypass diode according to claim 4, wherein when the ceramic substrate is viewed through a plane, the corners of the space are arc-shaped.

6. The circuit board for a bypass diode according to claim 1, wherein the conductor is a laminate in which a plurality of metal layers of different compositions are fixed together.

7. The circuit board for a bypass diode according to claim 1, wherein the ceramic substrate has a black color.

8. The circuit board for a bypass diode according to claim 1, wherein the ceramic substrate mainly comprises at least one selected from the group consisting of alumina, mullite, silicon carbide, silicon nitride, aluminum nitride, silica, forsterite, and glass ceramics.

9. A bypass diode device having a bypass diode on a circuit board for a bypass diode according to any one of claims 1 to 8.

10. A solar cell module comprising the bypass diode device described in claim 9 and a solar cell panel.

11. The solar cell module according to claim 10, wherein the solar cell panel is arranged in the order of a first film, a transparent resin layer, a solar cell, a white resin layer, and a second film, and the bypass diode device is housed within the thickness range of the solar cell panel.

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