IMC growth reaction and its effects on solder joint thermal cycling reliability of 3D chip stacking packaging

The study aims at assessing the growth reaction of the Ni3Sn4 intermetallic compound (IMC) during bonding process and its dependences on the thermal-cycling reliability of the Cu/Ni/SnAg micro-joints of an advanced 3D chip stacking package under accelerated thermal cycling (ATC) loading. The growth reaction of the IMC during bonding process is also predicted through experiment and classical diffusion theory, and the relation between the IMC thickness and bonding process temperature and time is derived according to the predicted activation energy of the chemical reaction between Sn and Ni by experiment. Moreover, the micro-joint reliability prediction is made using finite element (FE) analysis incorporated with an empirical Coffin–Manson fatigue life prediction model and also ATC experimental test. To facilitate the FE modeling, the temperature-dependent thermoelastic properties of both single crystal and polycrystalline Ni3Sn4 IMC are characterized through molecular dynamics simulation and the Voigt–Reuss bound and Voigt–Reuss–Hill approximation. Results show that monoclinic single crystal Ni3Sn4 reveals a high elastic anisotropy or direction dependence of elasticity. The diffusion reaction of Sn and Ni exhibits that a longer bonding process time and a higher bonding temperature could not only increase the IMC thickness but also vary its surface morphology. In addition, the thermal–mechanical performance of the micro-joints is strongly affected by the geometry and material of IMC layer, where IMC with a thicker thickness, a less Young’s modulus, a smaller CTE and even a more rounded surface morphology can better the reliability.