Reliability of micro-resistance welded dissimilar connection between Ag-plated Kovar foil and GaAs space solar cell: Processing, microstructure and bonding strength

Abstract

Solar panels in low earth orbit (LEO) can suffer from damage caused by atomic oxygen (AO) exposure and thermal shock, which may shorten the service life of their interconnectors and joints. Ag-plated Kovar foil has emerged as a promising material for interconnecting solar cell arrays. This study uses parallel gap resistance welding (PGRW) to conduct ultrafast Ag-plated Kovar foil and solar cell bonding in just 190 ms. The bonding strength depends on the current densities, with a diffused interface observed at a density of 475 A/mm2. The EBSD results show that grains of Ag layer and Au layer grow at the central bonding interface, whereas grains of Ag layer and Au layer form a weakened bonded line at the edge bonding interface. The thermal reliability of joints with Ag-plated Kovar foil is better than traditional Ag foil, with no decline in tensile-shear force observed even after multiple thermal cycles. Although the Ag layer of Kovar foil oxidizes as AgO and Ag2O in an AO environment, the joining interface remains unaffected. This investigation into PGRW joints of Ag-plated Kovar foil is critical for enhancing the high reliability of solar arrays in harsh temperatures and AO space environments.