Effect of energy input on mechanical and thermal fatigue property of parallel gap resistance welded joint between Si planar diode and Ag interconnector

Abstract

Due to the capability of protecting solar cell from local shadow induced thermal damage, bypass diode is a necessary component in solar cell array of spacecraft. During the service of solar array in space orbit, extreme temperature cycling would degrade the performance of connection between diode and interconnector. Therefore, establishment of the relationship between joining parameters and connection thermal fatigue property is significant for extending the solar array service life. In the present research, connections between Si planar diode and pure Ag interconnector are performed using parallel gap resistance welding (PGRW) with various energy input. By conducting certain temperature cycling (−160 ~ 130 °C) to the samples, the specific thermal fatigue resistances are investigated. The results indicate that welding voltage and electrode force have great influence on the strength of joints. The energy input increases with the increase of welding voltage and electrode force. It is found that along with the increase of temperature cycles, Ag interconnector performs a greater waving deformation owing to the different coefficients of thermal expansion (CTE) between Ag and Si wafer. Such deformation further results in alternative compressive and tensile stress concentrations in the interface, especially at the joint edge, where subsequently becomes the failure location. In general, this investigation clarifies the failure procedure and mechanism of PGRW made spot joint.