MEAM molecular dynamics study of lead free solder for electronic packaging applications

The modified embedded atom method (MEAM) was employed in conjunction with molecular dynamics (MD) simulations to investigate whether a physical mixture of nano-Sn and nano-Ag particles at a prescribed ratio would achieve the same intermixing as a nano-Sn/Ag alloy. A Sn sphere and a Ag sphere both with a diameter of 4 nm were prepared by cutting the perfect bulk lattice structure. After energy minimization and structural relaxation, the two spheres were placed next to each other with a gap of 3 Å. The simulation was then performed at 500 K for 3 ns. Simulation results showed that the nano-Ag sphere still maintained its crystalline structure and no significant diffusion between Sn and Ag was observed. Further simulations were performed at 800 K, 850 K, 900 K and 1000 K, respectively, in order to obtain the activation energy of interdiffusion between An and Sn. It was then predicted that 118 ns was required for Sn and Ag to mix with each other at 500 K. The results implied that a physical mixture of nano-Sn and nano-Ag particles may satisfy the requirements of lead free solder for low temperature (∼500 K) reflow applications.