Abstract
The growth of Ni 3 Sn 4 intermetallic compound (IMC) between liquid-solid interface in micro-scale Ni/SnAg/Ni system was investigated under a temperature gradient of 160 °C/cm at 260 °C on a hot plate. In contrast to a symmetrical growth of Ni 3 Sn 4 on both interfaces under isothermally annealed at 260 °C, the interfacial Ni 3 Sn 4 IMC exhibited asymmetric growth under a temperature gradient; the growth of Ni 3 Sn 4 at cold interface was faster than that at hot side because of temperature gradient induced mass migration of Ni atoms from the hot end toward the cold end. It was found that two-stage growth behavior of Ni 3 Sn 4 IMC under a temperature gradient. A growth model was established and growth kinetic analysis suggested that the chemical potential gradient controlled the growth of Ni 3 Sn 4 at stage I (0-120 min) whereas the dynamic equilibrium between chemical potential gradient and temperature gradient forces was attained at the hot end at stage II (120-210 min). When dynamic equilibrium was achieved at 260 °C, the critical length-temperature gradient product at the hot end was experimentally estimated to be 489.18 μm × °C/cm and the moving velocity of Ni 3 Sn 4 interface due to Ni consumption was calculated to be 0.134 μm/h. The molar heat of transport (Q∗) of Ni atoms in molten SnAg solder was calculated to be +0.76 kJ/mol.