Phase-Field Study of Thermomigration in 3-D IC Micro Interconnects

Abstract

We studied the evolution of the Cu6Sn5 and Cu3Sn intermetallic compounds under large thermal gradients for assisted directional solidification in Cu/Sn/Cu micro solder units for fast bonding in 3-D IC packaging. Thermomigration-enhanced growth and dissolution of the phasesare observed and tracked using a CALPHAD-reinforced multiphase-field model that accounts for the thermodynamics and kinetics of the Cu(Sn) reacting system. The results show that the process of bonding follows a reaction-controlled growth regime ( $n{\sim }1$ ) during thermal gradient bonding, proceeding faster than isothermal conditions. In addition, the asymmetric phase evolution, i.e., simultaneous growth in hot side and dissolution in the cold side of the interconnect, is modeled. The developed model can be used for the proactive control of the complex heat treatment processes for the design of multicomponent low-volume solder interconnects in electronic packaging.