Effect of Ag nanoparticles on microstructure, damping property and hardness of low melting point eutectic tin-bismuth solder

This paper investigates the effects of nanosized Ag particles on microstructure, physical and mechanical properties of environmental-friendly low melting point eutectic Sn-Bi solder on Au/Ni-plated Cu substrate. During the soldering process a very thin -Ni3Sn4 intermetallic compound (IMC) layer was found to be adhered at their interfaces in both types of solder system. This IMC layer thickness was increased with increasing the reaction time and temperature. However, from microstructural evaluation it was confirmed that the addition of Ag nanoparticles significantly affects the soldering behavior retarding the growth of IMC layer at the solder/substrate surface. The calculated activation energy for the -Ni3Sn4 IMC layer for the reference solder system was about 56.45 kJ/mol, while the activation energy for Ag nanoparticles doped solder system was about 60.73 kJ/mol. Addition of Ag nanoparticles maximize the activation energy which reduce the reaction rate. Furthermore, the adding Ag nanoparticles react with matrix phase and form very fine -Ag3Sn IMC particles that obstacle the formation of coarse matrix grain. This fine matrix grain and fine -Ag3Sn IMC particles act as a second phase strengthening mechanism that positively impact on the storage modulus and hardness values in composite solder systems.