The growth of Ag3Sn intermetallic compound under a temperature gradient

Three-dimensional integrated circuit (3DIC) technology has become the major trend of electronic packaging in microelectronic industry. To effectively remove heat in stacked ICs, the temperature gradient must be established across the chips. Furthermore, because of the trend of even higher device current density, the joule heating would be more serious and the temperature gradient across the solder joints is expected to be larger. In this study, we investigated thermomigration behavior in SnAg solders under molten-state and solid-state aging, respectively. As compared to isothermal process, the Ag and Ag3Sn IMCs were dissolved near the hot end and asymmetric growth of Ag3Sn on both interfaces was observed. We proposed that asymmetric growth of Ag3Sn behaviors was due to diffusion of Ag toward the cold side under a temperature gradient, and thereby leading abnormal Ag3Sn IMCs growth at cold side. In addition, the corresponding growth mechanism of Ag3Sn IMC caused by thermomigration of Ag was discussed and growth rate of Ag3Sn IMCs at cold side was found to linearly increase with solid-aging time under a temperature gradient. The intrinsic parameter, heat of transport (Q*) of Ag, in molten-state and solid-state solders was calculated as +11.68 kJ/mole and +13.39 kJ/mole, respectively.