Microstructure and mechanical properties of joints between GaAs solar cell electrode and Ag interconnector under temperature thermal cycle

Spacecraft play an important role in the national economy and other fields. Solar cell array is the most critical power supply component on spacecraft, and its joining quality determines the success and failure of flight missions. The joints operate in high and low temperature alternating environment when the spacecraft is in orbit. Therefore, the thermal reliability of joints is an important factor to a life of spacecraft. In this paper, the joints between GaAs solar cell electrode and Ag interconnector have been joined using a parallel gap resistance welding (PGRW) process. The joints are conducted a thermal cycling test in a temperature range of -160 to 120°C. The heating and cooling rate are 15 °C/min and maintains 10 min at -160°C and 120°C, respectively. The joints are taken out after different thermal cycle number and pull test are performed. To characterize the microstructure evolution and failure mode at the interface before and after thermal cycle, scanning electron microscope (SEM), transmission electron microscopy (TEM) are conducted to investigate the joining interface. According to the obtained results, the PGRW interface between the Ag interconnector and the Au surface of the GaAs solar cell electrode forms a solid-solution layer in low voltage process. The joining mechanism is solid phase diffusion welding. Melting connection occurs in the central region of two electrodes in high voltage process. The performance of joints with a lower welding voltage shows a downward trend after thermal cycles. And failure occurs at interface after 5000 cycles. The performance of joints with a high welding voltage still keeps invariability. This is owing to the boding zone increases and the joining mechanism varies. The fracture surface also varies form characteristics of dimples to characteristics of cleavage fracture with a low voltage process after 5000 cycles.