The present invention relates to electrical interconnects for solar cells and other electronic components, particularly to electrical interconnects for thin ( less than 6 mil thick) solar cells whereby breakage due to conventional soldering is eliminated, and more particularly to electrical interconnects and a process for forming same using a silver-silicone paste or a lead-tin solder cream.
Solar cells have a wide variety of applications, and are particularly useful in various space applications. Substantial research and development efforts have been directed toward the use of solar cells for space systems. One such application is the RAPTOR Pathfinder solar electric airplane being developed to enable long endurance high altitude flight for weeks and months, with flight altitudes exceeding 10,000 ft. The Pathfinder uses electric powered flight by covering the upper wing skin with light weight (thin) flexible solar array modules, composed of solar cells up to 25 mil thick.
Experiments have shown that solar cell electrical interconnect soldering can cause solar cell breakages for thin ( less than 6 mil thick) silicon solar cells as well as leave undesired residue on the active surfaces thereof. This is due, in part, to the 200xc2x0 C. temperature required for soldering, and the solder fluxes used to promote good adhesion. Thus, there has been a need for a method of electrically interconnecting thin solar cells which reduces or eliminates the breakage problem due to soldering, as well as eliminating the undesirable residue.
The present invention provides a solution to the above soldering problems which involves forming the electrical interconnects using copper strips and a conductive silver-silicone paste in place of soldering, or using the copper strips and a conductive lead-tin (Pbxe2x80x94Sn) no-clean fluxless surface mount solder cream. Electrical interconnects made by this invention have shown no degradation under high current testing while having a very low contact resistance value, and have eliminated the solder caused breakage problem for thin solar cells.
It is an object of this invention to eliminate solar cell breakage caused by conventional electrical interconnect soldering techniques.
A further object of the invention is to provide electrical interconnects for thin ( less than 6 mil thick) solar cells, using silver-based materials.
Another object of the invention is to provide a process of electrically interconnecting electronic components such as solar cells using either a conductive silver-silicone paste or a conductive Pbxe2x80x94Sn no-clean fluxless solder cream, whereby solar cell breakage and undesired residue on the active surfaces of the solar cell are eliminated.
Other objects and advantages of the present invention will become apparent from the following description. In one example of the invention, the electrical interconnects between solar cells are produced by using electrically conductive members such as copper strips (50 mil wide by 3 mil thick) which are attached to each of the metal electrodes on the solar cell using a conductive silver-silicone paste, which can be applied and cured at room temperature. In a second example, the electrical interconnects are produced using the copper strips which are soldered to each solar cell using a conductive Pbxe2x80x94Sn no-clean surface mount solder cream, which requires no additional flux, applied between the copper strips and the metal electrodes on the solar cells before soldering. Tests have established that with solar cell interconnects made by this invention there was no degradation of the interconnects under high current testing, the contact resistance value was very low, and that breakage of the thin solar cells was eliminated.