Parallel-gap resistance welding between gold-plated silver interconnects and silver electrodes in germanium solar cells

Thermal cycling becomes a major factor in the reliability of the interconnect systems of solar cells in Low Earth Orbit Satellite. Low Earth Orbit Satellite (LEO) has the orbit altitude between 200 and 1000 km, thereby leading to its short orbit period and shallow discharge depth. Hence, the power supply experiences a frequent charge-discharge process. In this paper, we study the reliability of the joints between gold-plated silver interconnects and silver electrodes of germanium solar cells of a Low Earth Orbit Satellite, that is, the optimization of the welding process, and the assessment of the reliability. Parallel gap resistance welding was used to fabricate the interconnect-electrode joints. The three main welding parameters were carefully adjusted to investigate their effects on the property of the joints. Particularly, one of the parameters kept the same value to determine the effective welding range of the other parameters in order to minimize the influence of parameter disturbance on the welding quality. Then a pull test with the angle of 45 was carried out to obtain the mechanical property of the joints under the different welding parameters. In addition, the appearance, microstructure, and atom diffusion of the joints were analyzed. We compared the microstructure of the joints obtained with different welding parameters. Particularly, we investigated if it had apparent pores and cracks, and whether each layer in the joints has a full diffusion. Moreover, the EDS analysis of fracture surface demonstrated that broken location is not at the interfaces of the joint, and fracture mode is Ductile. The characteristic of cleavage fracture and dimples is also discovered in the SEM image.