Corrosion and hardness properties of SAC305/Cu solder joint by microwave hybrid heating

Purpose – This study aims to investigate the effect of microwave hybrid heating (MHH) reflow on the corrosion immersion and mechanical reliability of SAC305/Cu solder. SAC305/Cu solder joints were reflowed by MHH using controlled processing durations. Design/methodology/approach – Corrosion behavior was evaluated through 3.5 Wt.% NaCl immersion for up to 28 days. Structural phase evolution, interfacial morphology and elemental distribution were analyzed. Metallic ion dissolution was quantified to evaluate corrosion-induced ion release behavior, and Vickers hardness measurements were conducted to assess mechanical integrity. Findings – Uniform scalloped Cu6Sn5 intermetallic layers with stable ß-Sn matrix were formed by MHH reflow method. Immersion exposure induced progressive pitting corrosion dominated by Cl⁻-assisted ß-Sn dissolution. Oxide phases (SnO, SnO2) and complex Sn3O(OH)2Cl2 formed, contributing to partial passivation. Immersion corrosion was more severe at solder edges, whereas pitting dominated at peak regions. High initial dissolution of the Cu element was observed, followed by stabilization attributed to the formation of a protective oxide layer. A noticeable reduction in hardness (9.43%) was observed after 28 days, reflecting corrosion-induced degradation of the ß-Sn matrix. Originality/value – This work provides a comprehensive correlation between MHH-induced microstructure, electrochemical degradation mechanisms and mechanical reliability of SAC305/Cu solder joints in saline environments.