Abstract
Cu–(Sn37Pb) and Cu–(Sn3.5Ag0.5Cu) solder joints were prepared at the same reflow temperature of 230 °C. The microstructural observation of the solder assemblies in scanning and transmission electron microscopes confirmed the presence of η-Cu 6Sn 5 in case of the former, and Cu 3Sn + η-Cu 6Sn 5 for the latter in the reaction zone. The findings are correlated with the electrical and mechanical properties of the joints. Lead free solder-Cu joint exhibited lower reaction zone thickness and improved electrical conductivity (0.28 × 10 6Ω − 1 cm − 1 ) and shear strength ∼ 68MPa compared to conventional lead–tin solder-Cu joint. The latter showed electrical conductivity and shear strength of 0.22 × 10 6Ω − 1 cm − 1 and ∼ 55 MPa, respectively. The difference in reaction zone thickness is explained on the basis of melt superheat, with Sn being the primary diffusing species in the intermetallic layer.
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