Growth kinetic of Ag3Sn intermetallic compound in micro-scale Pb-free solder alloys under a temperature gradient

Abstract

The interfacial reaction of Ag3Sn intermetallic compounds (IMCs) in micro-scale Ag/SnAg/Ag sandwich structure was investigated under a temperature gradient of 168.9 °C/cm at 260 °C. In contrast to a symmetrical growth of Ag3Sn at both interfaces under isothermally annealed at 260 °C, the asymmetric growth of Ag3Sn IMCs at both interfaces was observed under a temperature gradient; the growth rate of Ag3Sn at colder interface was faster than that at hot side because of temperature gradient induced Ag atoms diffusion from the hot end toward the cold end. In addition, the findings indicate two-stage growth behavior of Ag3Sn IMC under a temperature gradient. The growth kinetic analysis suggests that the chemical potential gradient controls the thickness change of Ag3Sn at stage I (0–10 min) whereas force driving thermomigration becomes dominant at stage II (10–30 min). The molar heat of transport (Q*) of Ag in Sn in molten-state was calculated as 14.9 kJ/mol.