Abstract:This study investigates the impact of low density current stressing on the shear performance of thermally aged Sn58Bi solder joints and elucidates the underlying mechanisms. Cu/Sn58Bi/Cu joints were subjected to isothermal aging at 120 °C for different durations (0 h, 240 h, 480 h, 720 h, 960 h, 1200 h, 1440 h, 1680 h) and tested under current densities of 0, 1×103, 2×103, and 3×103 A/cm2. The results indicate a non-monotonic "rise-fall" trend in the shear strength of aged joints with increasing current density. Notably, a maximum strength increase of 12.85 % was observed in joint aged for 480 h under a current density of 2×103 A/cm2, comparing with the unaged and current-free ones. This strengthening behavior at 480 h is primarily attributed to two mechanisms: (1) the applied current promotes the multiplication of geometrically necessary dislocations (GNDs), elevating strength via dislocation strengthening; and (2) higher current density facilitates an increase in the subgrain fraction of the Bi phase, which effectively impedes dislocation motion. Conversely, at higher current densities, shear strength decreases due to Joule heating, which induces thermal mismatch and compromises the interfacial bonding between the interfacial intermetallic compounds (IMC) layer and the solder matrix. These findings provide theoretical insights for the reliability assessment of low-temperature solder joints in electronic packaging.