The role of eutectic phase and acicular primary crystallized Zn phase on electrification-fusion induced fracture of Sn-xZn solder alloys

Effect of Sn-xZn solder alloys with varying eutectic phase and acicular primary crystallized Zn phase on the electrification-fusion induced liquidation phenomenon was investigated in this study. The critical fusion current density (CFCD) for liquidation fracture tends to increase with increasing Zn content, the CFCD value required for electrification-fusion induced liquidation are 1457 (×10₄)A·m· ₂ (7Zn), 1504 (×10₄)A·m· ₂ (30Zn) and 2195 (×10₄)A·m· ₂ (70Zn) respectively, which are commonly larger than pure tin (1399 (×10₄) A·m·₂) pertaining to the transformation of current path. Through the in-situ examination of microstructural evolution during electrification-fusion tests, the initial site of electrification-fusion-induced liquidation significantly emerged from Sn/Zn eutectic phase. From the experimental evidences, it should be noted that the pure Sn specimen showing a character that the initiation site for microliquidation were located at the triple junction of electrification induced current path, whereas the Sn-Zn alloy specimens were commonly initiated from the eutectic phase pertaining to the higher conductivity of acicular Zn phase.