Molecular dynamics simulation of lead free solder for low temperature reflow 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 /spl Aring/. The simulation was then performed at 500 K for 3000 ps. Simulation results showed that nano Ag sphere still maintained its crystalline structure and no significant diffusion between Sn and Ag was observed. Based on the time frame involved in simulation (3 ns), the results implied that a physical mixture of nano Sn and nano Ag particles may not suffice the requirements of lead free solder for low temperature reflow applications.