Interfacial reaction of Ni3Sn4 intermetallic compound in Ni/SnAg solder/Ni system under thermomigration

• Interfacial reaction in Ni/SnAg solder/Ni system under thermal gradient.
• Growth rate of Ni3Sn4 at cold end is faster than that at hot end.
• Critical length-temperature gradient product at hot end is 489.2 μm°C/cm at 260 °C.
• Velocity of Ni3Sn4 moving interface is 0.134 μm/h during dynamic equilibrium.
• Molar heat of transport (Q*) of Ni in molten SnAg was +0.76 kJ/mol.

The growth of Ni3Sn4 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 Ni3Sn4 on both interfaces under isothermally annealed at 260 °C, the interfacial Ni3Sn4 IMC exhibited asymmetric growth under a temperature gradient; the growth of Ni3Sn4 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 Ni3Sn4 IMC under a temperature gradient. A growth model was established and growth kinetic analysis suggested that the chemical potential gradient controlled the growth of Ni3Sn4 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 Ni3Sn4 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.

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