The effect of nickel microalloying on thermal fatigue reliability and microstructure of SAC105 and SAC205 solders

This study explores the effect of a nickel (Ni) microalloy addition on the thermal fatigue performance and microstructure of two low Ag content, Pb-free solder alloys, Sn-1.0Ag-0.5Cu (SAC105) and Sn-2.0Ag-0.5Cu (SAC205). The alloy performance was evaluated using two different area array component test vehicles, an 84-pin chip scale package (CSP) and a 192-pin fine pitch ball grid array (BGA). The baseline alloy microstructures were characterized using polarized light microscopy and scanning electron microscopy with backscattered electron imaging for phase identification. Thermal fatigue performance was assessed with accelerated thermal cycling (ATC) using four temperature cycling profiles with distinct temperature ranges (ΔT) and temperature extremes. Additionally, each temperature profile used a standard 10 minute dwell time or an extended 60 minute dwell time. A microalloy addition of 0.05% Ni was found to alter the base microstructures of the SAC 105 and SAC205 alloys. Generally, the Ni addition improved the thermal fatigue life but the improvement was not consistent in both alloys, both components, and across all thermal cycling profiles. The most consistent response was with the 84CTBGA component, which showed improved reliability with the Ni addition in all of the thermal cycles.