Patent Grant
4992138
"METHOD OF MAKING DOPED SILICON SPHERES", by G. B. Hotckiss et al., filed July 31, 1989, Ser. No. 387,677. "METHOD OF AFFIXING SILICON SPHERES TO A FOIL MATRIX", by G. B. Hotchkiss, filed July 31, 1989, Ser. No. 388,105, "METHOD OF ISOLATING SHORTED SILICON SPHERES", by S. G. Parker et at., filed July 31, 1989, Ser. No. 387,144, "SOLAR CELL WITH FOIL CONTACT POINT AND METHOD FOR ITS MANUFACTURE", by G. B. Hotchkiss, filed July 31, 1989, Ser. No. 388,280, and "METHOD FOR APPLYING AN ORGANIC INSULATOR TO A SOLAR ARRAY", by M. D. Hammerbacher, filed July 31, 1989, Ser. No. 387,929, This invention relates generally to solar arrays and more particularly to a method of making a foil matrix for use in a solar array. A number of systems for converting sunlight to electricity are known. One such system that has proven useful in efficiently producing electricity from the sun's radiation is described in U.S. Pat. No. 4,691,076. In that system, an array is formed of semi-conductor spheres. Each sphere has a P-type interior and an N-type skin. A plurality of the spheres are housed in a pair of aluminum foil members which form the contacts to the P-type and N-type regions. The foils are electrically insulated from one another and are flexible Multiple arrays can be interconnected to form a module of solar cell elements for converting sunlight into electricity. In order to produce sufficient quantities of the arrays, it is necessary to have a process for their manufacture that is uncomplicated, low cost and efficient. An uncomplicated system would be one using currently available technology constructed in such a way that the applicable process steps can be conducted in a highly repeatable manner. Moreover, the less complicated the process steps, generally the more cost effective will the entire process be carried out. Finally, the more repeatable the process, the more efficiently the operation and the higher production of solar arrays. A key process step in the making of silicon solar cells is the preparation of an apertured foil matrix. Several techniques for embossing thin (2 to 3 mils) aluminum foil are known. One technique is called impact embossing and is described in U.S. Pat. No. 4,691,076 assigned to the assignee of the present application. Another approach is to etch the foil using known photolithography techniques. A third method is to use a two-high rolling mill with a pattern of embossing posts etched or cut directly onto one of the solid, hardened steel cylinders with the foil fed between two rollers. These techniques all have various difficulties and drawbacks making them undesirable. For instance, impact embossing has the disadvantage of creating non-uniform pressures across the foil resulting in non-uniform thickness. Also, impact embossing leaves foil flaps along the edges of the solar sphere receiving apertures. These flaps inhibit good bonding between sphere and foil. A major problem with the photolithographic method is that it is too costly and too lengthy in time. Finally, the technique employing cylindrical rollers has serious problems with achieving uniform post positions Another disadvantage with a roller or cylindrical embosser is that the foil is unacceptably thinned as it is pulled through the rollers In accordance with the present invention, there is provided a method of producing a solar array having the noted advantages in that products are efficiently produced using an uncomplicated and low cost process. In one embodiment of the invention, a method for constructing an apertured foil matrix, suitable for receiving silicon spheres, comprises four steps. In step one, a foil is located between an upper plate and an embossing tool. In step two, the upper plate, foil and embossing tool are fed through a roller mill. In step three, regions of lesser thickness are pressed into the foil. In the final step, the regions of lesser thickness pressed into the foil are etched to remove the regions and provide apertures for receiving silicon spheres. A technical advantage of the invention is that the foil flaps along the apertures are alleviated. Another technical advantage is that a more constant foil thickness is achieved Still another technical advantage is that fairly even post penetration is obtained with the etched foils showing a fairly equal thickness across its width. Still another technical advantage is that a planar embossing tool minimizes machining problems resulting in accurately shaped posts having proper depth. In a second embodiment, an apparatus for producing an aperture pattern in a foil matrix comprises a number of elements There is an embossing means for producing regions of lesser thickness in the foil. There is also a flexible cover plate. A pair of rollers has a nip therebetween such that the height of the nip is less than the thickness of the embossing means, foil and flexible cover plate. A feeding means is provided for directing the flexible cover plate, foil and embossing means to the nip of the rollers.
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