Effect of thermomigration on evolution of interfacial intermetallic compounds in Cu/Ni/Sn-3.5Ag microsolder joints for 3D interconnection

Abstract

In recent years, the increasing emphasis on higher package density, richer functionality and smaller size in commercial electronics has spurred the advancement of three-dimensional integrated circuits (3DICs). However, the high power density and severe heat generation in 3DIC packages often require liquid cooling to dissipate heat, which induces higher temperature gradients than in 2DIC packages. To study the growth of Ni3Sn4 intermetallic compound (IMC) at the interface of 100 µm diameter microsolder joints, we used a heat sink and heat source device to create a temperature gradient of 16667 °C/cm and an average temperature of 150°C in the solder joint. Due to the temperature gradient, Ni atoms migrated from the hot side to the cold side and the Ni3Sn4 IMC at the interface grew asymmetrically, with the Ni3Sn4 layer growing faster at the cold side than at the hot side. After applying a temperature gradient to the solder joint for 100 hours, significant depletion of the Ni layer was noticed at the hot end in a serrated shape. The kinetic equations of IMC growth are used to obtain the diffusion fluxes of Ni atoms in microsolder joints under temperature gradient and isothermal aging conditions, respectively. The consumption rate of the Ni barrier layer is explored to provide guidance for the thermal reliability of microsolder joints in 3D packages.