Patent Publication Number: US-2012024347-A1

Title: Solar package structure and method for fabricating the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solar package structure and a method for fabricating the same, and in particular, to a solar package structure using a wafer level packaging process and a method for fabricating the same. 
     2. Description of the Related Art 
     A solar cell is a device that converts the energy of sunlight directly into electricity by photovoltaic effect. The size and weight of the conventional solar cell is limited to a large module size of 10 cm×10 cm×10-20 cm and a heavy module weight of more than 4 kg, respectively. The lens of conventional solar cell concentrates sunbeams on to only one solar cell chip. Thus, heat from the conventional solar cell dissipates slowly when temperature thereof increases. Accordingly, heat sinks are used to hinder heat dissipation. However, with the added heat sinks, the weight of the module of the conventional solar cell is increased. Meanwhile, the lens of a large-sized conventional solar cell has a long focus length. Thus, a solar cell chip thereof has a small accept angle (half of the angular aperture of an optical system) of less than 0.5 degree. Also, because a highly accurate sun tracker is required in the conventional solar cell to track the sun, fabrication costs are high. 
     Thus, a novel solar package structure and a method for fabricating the same are desired. 
     BRIEF SUMMARY OF INVENTION 
     A solar package structure and a method for fabricating the same are provided. An exemplary embodiment of a solar package structure comprises a carrier wafer. A solar package structure includes a carrier wafer. A conductive pattern layer is disposed on the carrier wafer. A solar cell chip array is disposed on the conductive pattern layer, wherein the solar cell chip array electrically connects to the conductive pattern layer. A first spacer dam is disposed on the carrier wafer, surrounding the solar cell chip array. A first optical element array is disposed over the carrier wafer to concentrate sunbeams onto the solar cell chip array, wherein the first optical element array is spaced apart from the carrier wafer by the first spacer dam. 
     An exemplary embodiment of method for fabricating a solar package structure, comprising providing a carrier wafer. A conductive pattern layer is formed on the carrier wafer. A solar cell chip array having a plurality of solar cell chips is disposed on the conductive pattern layer, wherein each of the solar cell chips electrically connects to the conductive pattern layer. A first spacer dam is disposed on the carrier wafer, surrounding the solar cell chip array. A first optical element array is disposed over the carrier wafer to concentrate sunbeams onto the solar cell chip array, wherein the first optical element array is spaced apart from the carrier wafer by the first spacer dam. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a top view of one exemplary embodiment of a solar package structure of the invention. 
         FIG. 2  is a cross section view taken along line A-A′ of  FIG. 1 . 
         FIGS. 3 to 6  are cross section views showing one exemplary embodiment of a method for fabricating a solar package structure of the invention. 
         FIG. 7  is a cross section view showing another exemplary embodiment of a method for fabricating a solar package structure of the invention. 
         FIG. 8  is a cross section view showing another exemplary embodiment of a solar package structure of the invention. 
         FIG. 9  is a cross section view showing yet another exemplary embodiment of a solar cell chip package 
     
    
    
     Table. 1 is a comparison table of one exemplary embodiment of a solar package structure of the invention versus a conventional solar package structure. 
     DETAILED DESCRIPTION OF INVENTION 
     The following description is of a mode for carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. Wherever possible, the same reference numbers are used in the drawings and the descriptions to refer the same or like parts. 
     The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto and is only limited by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual dimensions to practice the invention. 
       FIG. 1  is a top view of one exemplary embodiment of a solar package structure  500   a  of the invention.  FIG. 2  is a cross section view taken along line A-A′ of  FIG. 1 . The solar cell chip package  500   a , such as concentrating photovoltaic (CPV) solar cell chip package  500   a , is fabricated by a wafer level packaging process. As shown in  FIGS. 1 and 2 , the solar cell chip package  500   a  comprises a carrier wafer  200 . A conductive pattern layer  201  is disposed on the carrier wafer  200 . A solar cell array  212  comprising a plurality of solar cell chips  202  is disposed on the conductive pattern layer  201 . A first spacer dam  218  is disposed on the carrier wafer  200 , surrounding the solar cell array  212 . A first optical element array  214   a  is disposed over the carrier wafer  200  for allowing sunbeams  216  to be concentrated to the solar cell chips  202 , wherein the first optical element array  214   a  is spaced apart from the carrier wafer  200  by the first spacer dam  214  connecting therebetween. In one embodiment, the carrier wafer  200  serving as a carrier and/or a heat dissipation element for the solar cell array  212  may comprise dielectric materials such as silicon, ceramic or the like, or metal materials such as Al or the like. In one embodiment, the solar cell chips  202  work with a doped semiconductor to produce two different regions separated by a p-n junction. Each of the solar cell chips  202  may have at least two electrodes thereon, wherein the electrodes comprise an anode electrode and a cathode electrode which are connected to two different regions of the p-n junction. In one embodiment, the conductive pattern layer  201  may have a plurality of isolated conductive patterns to electrically connect to the different electrodes of the solar cell chips  202  to transmit electro signals transformed by the solar cell chips  202  the solar cell chips  202 . The conductive pattern layer  201  may comprise conductive materials such as Al, Cu, Ni, Au, Ag, Sn, Pd, W, Cr or the like. If the carrier wafer  200  is a printed circuit board, the solar cell chips  202  may directly connect to the carrier wafer  200  without the conductive pattern layer  201 . In one embodiment, the first optical element array  214   a  may be a plurality of first optical elements  204   a  arranged as an array. The first optical element array  214   a  may be composed of a first transparent plate  210  and a first lens array having a plurality of first lenses  212  formed thereon. The first transparent plate  210  and the first lenses  212  may be comprised of transparent materials such as glass or acryl. Each of the first lenses  212  is directly over each of the solar cell chips  202 . Alternatively, the first optical element array  214   a  may further comprise reflectors (not shown) to further concentrate the sunbeams  216  onto the solar cell chips  202 . The first spacer dam  218  may serve as a spacer to separate the first optical element array  214   a  and the carrier wafer  200  by a height d 1 , thereby facilitating focus of the sunbeams  216  onto the surfaces of the solar cell chips  202 . In one embodiment, the first spacer dam  218  may comprise inorganic or organic insulating materials such as oxide, nitride, polyimide or the like, or combinations thereof. 
       FIGS. 3 to 6  are cross section views showing one exemplary embodiment of a method for fabricating a solar package structure  500   a  of the invention. As shown in  FIG. 3 , a carrier wafer  200  is provided. Next, a conductive pattern layer  201  having a plurality of isolated conductive patterns is formed on the carrier wafer by a deposition and a patterning processes. 
     Referring to  FIG. 4 , a solar cell chip array  212  having a plurality of solar cell chips  202  is disposed on the conductive pattern layer  201 . For one embodiment as shown in  FIG. 4 , each of the solar cell chips  202  is respectively disposed on one of the conductive patterns, wherein an anode of the solar cell chip  202  electrically connects to the conductive pattern, and a cathode of the solar cell chip  202  electrically connects to the other conductive patterns neighboring the conductive pattern by conductive wires  203 . 
     Next, referring to in  FIG. 5 , a first spacer dam  218  is disposed on the carrier wafer  200 , surrounding each of the solar cell chips  202  by an assembly process, for example, the first spacer dam  218  and the carrier wafer  200  are assembled using a glue. As shown in  FIG. 5 , the first spacer dam  218  may have a height d 1  larger than that of the solar cell chip  202  to assure the following assembling first optical element array  214   a  without contacting to the solar cell chips  202 . 
     Next, referring to  FIG. 6 , the wafer level first optical element array  214   a  is fabricated and assembled to the carrier wafer  200 . As shown in  FIG. 6 , the first lens  212   a  may be formed by a molding process, wherein a focus of the first lens  212   a  defines the height d 1  of the first spacer dam  218 . 
     Next, referring to  FIG. 2 , the fabricated first optical element array  214   a  is assembled to the carrier wafer  200  by disposal thereon, to concentrate sunbeams  216  onto the solar cell chip array  212 . The first optical element array  214   a  is spaced apart from the carrier wafer  200  by the first spacer dam  218  connected therebetween. After the aforementioned fabricating process, one exemplary embodiment of a solar package structure  500   a  is completely formed. 
     As shown in  FIG. 2 , in one embodiment, the first lens  212   a  of the first optical element  204   a  is a biconvex lens having a first convex surface  213   a  facing the direction of sunbeams  216  and a second convex surface  213   b  facing the solar cell chip  202 . In one embodiment as shown in  FIG. 2 , the second convex surface  213   b  is a wave-shaped surface. 
     Table. 1 is a comparison table of one exemplary embodiment of a solar package structure  500   a  of the invention versus a conventional solar package structure. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
               
             
            
               
                   
                   
                 Focus 
                   
                   
                 Chip 
               
               
                 1. Module Characters 
                 Cell Area 
                 length 
                 Weight 
                 Chip Size 
                 Number 
               
               
                   
               
               
                 Conventional solar cell 
                 12 cm × 12 cm 
                  &gt;10 cm 
                 &gt;2000 g 
                 5.5 mm × 5.5 mm 
                  ×1 ea 
               
               
                 Solar package structure 
                 12 cm × 12 cm 
                 &lt;1.0 cm 
                  &lt;100 g 
                 400 μm × 400 μm 
                 ×200 ea 
               
               
                 500a 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Power 
                 Acceptance 
                 Tracker 
                 Temp. 
                   
               
               
                 2. Performance 
                 Generate 
                 Angle 
                 Used 
                 Generation 
                 Heat Sink 
               
               
                   
               
               
                 Conventional solar cell 
                 ~3 W 
                 0.5-1.5 
                 complicated 
                 &gt;50° C. 
                 Need 
               
               
                   
                   
                 degree 
               
               
                 Solar package structure 
                 ~3 W 
                 &gt;2 degree 
                 simple 
                 &lt;10° C. 
                 No 
               
               
                 500a 
               
               
                   
               
            
           
         
       
     
     Table. 1 is a comparison table of one exemplary embodiment of a solar package structure  500   a  of the invention versus  45   a  conventional solar package structure. From Table 1, it is shown that the solar package structure  500   a  has the following advantages. First, the size of the solar package structure  500   a  fabricated by using a wafer level packaging process, may be a small size of about 400 μm×400 μm. When considering the standard module area of 12 cm×12 cm, for only one chip of the conventional solar cell, the solar package structure  500   a  may allow about 200 chips versus 1 chip for the conventional solar cell. Also, the module weight of the solar package structure  500   a  is less than 100 g, which is much lighter than the conventional solar cell. Thus, because of the smaller size of the solar package structure  500   a , focus length thereof may be reduced to less than 1 cm. Accordingly, an accepted angle of the solar package structure  500   a  may be larger than 2 degrees. Therefore, a sun tracker used in the solar package structure  500   a  having a larger accepted angle may be simpler or with a lower accuracy for tracking sun than the conventional solar cell. Additionally, due to the increased chip number of the solar package structure  500   a , the sunbeams may be concentrated on various positions of the carrier wafer  200  where the solar cell chips are disposed, so that heat from the sunbeams may dissipate more easily. As shown in Table 1, the solar package structure  500   a  may have a low temperature of less than 10° C. due to sunbeams, without the use of additional heat sink devices. Therefore, the solar package structure  500   a  may have improved efficiency and reliability. Accordingly, fabrication of the solar package structure  500   a  may be reduced. 
     Alternatively, the solar package structure may comprise two or more than two concentrating optical element arrays, which are laminated vertically, for further light concentration requirements.  FIG. 7  is a cross section view showing another exemplary embodiment of a method for fabricating a solar cell chip package structure  500   b  of the invention. Elements of the embodiments hereinafter, that are the same or similar as those previously described with reference to  FIGS. 2 to 6 , are not repeated for brevity. After disposing the first optical element array  214   a  over the carrier wafer  200 , a second spacer dam  234  is then disposed on the first optical element array  214   a . As shown in  FIG. 7 , the second spacer dam  234  may be disposed directly over the first spacer dam  218 , and the materials of the second spacer dam  234  may be the same as that of the first spacer dam  218 . The second spacer dam  234  may have a height d 2  larger than that of first lenses  212   b  to assure following assembling second optical element array  214   b  without contacting to the first lenses  212   b . Next, another wafer level second optical element array  214   b  is fabricated and provided for assembly to the carrier wafer  200 , and disposed over the first optical element array  214   a . Similar to the first optical element array  214   a , the second optical element array  214   b  may comprise a second transparent plate  230  with a second lens array comprising a plurality of second lenses  232  formed thereon, wherein each of the second lenses  232  is directly over one the first lenses  212   b . The first and second optical element arrays  214   a  and  214   b  are spaced apart from each other by the second spacer dam  234  connecting therebetween, and a focus of the second lenses  232  defines the height d 2  of the second spacer dam  234 . After the aforementioned fabricating process, another exemplary embodiment of a solar package structure  500   b  is completely formed. 
     As shown in  FIG. 7 , the first lens  212   b  of the first optical element array  214   a  is a plano-convex lens having a convex surface  213   c  facing the direction of sunbeams  216  and a plane surface  213   d  facing the solar cell chip  202 . In one embodiment as shown in  FIG. 7 , the convex surface  213   c  is a wave-shaped surface. The second optical element array  214   b  is a plano-convex lens having a convex surface  233   a  facing the direction of sunbeams  216  and a plane surface  233   b  facing the solar cell chip  202 . The solar package structure  500   b  may have advantages, such as improved light concentration, in addition to the previously mentioned advantages of the solar package structure  500   a.    
     Alternatively, several embodiments may be employed to further concentrate sunbeams onto the solar cell chips as shown in  FIGS. 8 to 9 .  FIG. 8  is a cross section view showing another exemplary embodiment of a solar cell chip package  500   c . The solar cell chip package  500   c  with the first optical element array  214   a  may have a plurality of transparent molds  236  disposed directly under first lenses  212   c , respectively encapsulating the solar cell chips  202 , the conductive pattern layer  201  and the conductive wires  203 . Each of the transparent molds  236  has a convex surface  237  facing the first optical element  204   a , and a focus of the transparent molds  236  is designed on the surface of the solar cell chip  202  for further concentration of sunbeams. In one embodiment, the transparent molds  236  may be formed by a molding process before forming the first dam  210 . In one embodiment, the transparent molds  236  may comprise transparent insulating materials such as polyimide or epoxy. The first lenses  212   c  of the first optical element array  214   a  is a plano-convex lens having a convex surface  213   e  facing the direction of sunbeams  216  and a plane surface  213   f  facing the solar cell chip  202 . 
       FIG. 9  is a cross section view showing yet another exemplary embodiment of a solar cell chip package  500   d . The solar cell chip package  500   d , with vertically laminated first and second optical element arrays  214   a  and  214   b , may also have a plurality transparent molds  236  disposed directly under a first lenses  212   b , respectively encapsulating the solar cell chip  202 , the conductive pattern layer  201  and the conductive wires  203 . Each of the transparent molds  236  has a convex surface  237  facing the first optical element  204   a , and a focus of the transparent molds  236  is designed on the surface of the solar cell chip  202  for further light concentration. In one embodiment, the transparent molds  236  may be formed by a molding process before forming the first dam  210 . In one embodiment, the transparent molds  236  may comprise transparent insulating materials such as polyimide or epoxy. The characteristics of the first lenses  212   b  of the first optical element array  214   a  and the second lenses  232  of the second optical element array  214   b  are similar to those of the solar cell chip package  500   b.    
     Compared with the conventional solar cell, the solar package structure fabricated using a wafer level packaging process is smaller. When considering the standard module area, for only one chip of the conventional solar cell, the solar package structure of the invention may allow a greater number of chips to be disposed thereon. Also, the module weight of the solar package structure of the invention is much lighter than the conventional solar cell. Thus, because of the smaller size of the solar package structure of the invention, focus length thereof may be reduced. Accordingly, an accepted angle of the solar package structure  500   a  may be larger than 2 degrees. Therefore, a sun tracker used in the solar package structure of the invention may have a large accepted angle, and a simpler assembly process. Additionally, because the number of chips of the solar package structure  500  is increased, sunbeams may be concentrated on various positions of the carrier wafer where the solar cell chips are disposed, so that heat from the sunbeams may dissipate more easily. The solar package structure of the invention may have a low enough operation temperature, such that additional heat sink devices are not required. Therefore, the solar package structure of the invention may be more efficient and reliable than the conventional solar cell. Therefore, the solar package structure of the invention has reduced fabrication costs, and can be applied to small-size concentrating photovoltaic (CPV) systems. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.