Microstructure of solar cell interconnections by resistance welding

摘要

All the time, longer life is a goal for Low Earth Orbit Satellite (LEO). LEO has short orbit period (about 97min), so it will experience thermal shock for approximately 5500 times per year. Long and frequent thermal recycling becomes a big challenge to the reliability of these systems, particularly to the reliability of solar cell interconnections. Hence, effective assessment of the welding quality of the interconnections is an essential prerequisite. In this paper, we study the microstructure of interconnect systems (including the joints between gold-plated silver interconnects and silver-plated germanium electrodes, the joints between silver-plated copper cables and silver-plated copper cables, and the joints between silver-plated copper cables and gold-plated silver/silver-plated molybdenum interconnects) in LEO Satellite's solar cells. All the joints were fabricated by resistance welding under different welding parameters. Through analyzing SEM images of these joints, we found eutectic structures. With the help of phase diagram, we illustrated reasons of the formation of these structures. And the results suggested that metallurgical bonding had appeared in the interconnect systems. Moreover, the EDS analysis of the interface demonstrated the diffusion of atoms at the interface, which also proved the formation of metallurgical bonding. In addition, a pull test was carried out to obtain the mechanical property of the joints, which assessed the strength of interconnect systems more accurately.