Effects of Co nanoparticle addition to Sn–3.8Ag–0.7Cu solder on interfacial structure after reflow and ageing

Effects of Co nanoparticle additions to Sn–3.8Ag–0.7Cu on the structure of solder/copper interface have been studied after reflow and high temperature ageing (150 °C, up to 1008 h). Results show that the Co nanoparticles substantially suppress the growth of Cu3Sn but enhance Cu6Sn5 growth. Cobalt nanoparticles reduce interdiffusion coefficient in Cu3Sn. It is suggested that the Co nanoparticles undergo surface dissolution during reflow and exert their influence, at least partially, through alloying effect.