FAILURE ANALYSIS OF THE TRIPLE JUNCTION SOLAR CELLS USINGGAPWELDING PROCESS

摘要

Gap welding is currently used for developing advanced triple junction solar cells (ATJ) joining processes. The main advantage of using gap welding process is that the joints between interconnect and solar cell can stand much higher temperature in comparison to solder joints. Gap welding processes have been found more maneuverable and deliverd more consistent results in the robot automatic processing. A gap welding process was successfully used on silicon solar cell joining in NGST solar array manufacturing line previously. To achieve weld joining, optimum gap welding schedules should be developed. A good gap welding process profile mainly consists of a combination of force, power and duration, as well as electrode tip and gap sizes. During the course of process development cracked cells were discovered on advanced triple junction solar cells. Investigations and tests were conducted on the cracked cells. The initial results show that cell cracking occurred at various welding conditions, which indicated the failure of the cells was not directly related to the selected welding conditions. SEM analysis on more than twenty pairs of tungsten electrodes discovered a high percentage of voids and micro-cracks. The voids and micro-cracks on the electrodes lead to a conclusion that these defects were processing defects, which generated in tungsten material processing and propagated during welding processing. The defects caused local non-uniform power and stress distribution and cell cracking. This work introduces the failure analysis on the triple junction solar cell in developing gap welding schedules for spacecraft applications.