15. A Study of Nanoparticles in SnAg-Based Lead-Free Solders

Tin-lead (Sn-Pb) solder alloy has been widely used as interconnection material in electronic packaging due to its low melting temperatures and good wetting behavior on several substrate platings such as Cu, Ag, Pd, and Au. Recently, due to environmental and health concerns, a variety of new lead-free solders have been developed. Lead-free solders lack the toxicity problems associated with lead-contained solders. However, unlike lead solders, the recently employed lead-free solders do not have a long history and manufacturing process, and also board-level reliability has not been established well. Especially, drop test performance is a serious concern for mobile products like cellular phones, cameras, video, and so on. Sn-Ag-Cu alloys are leading candidates for lead-free solders. In this study, it was found that adding Co, Ni or Pt, located to the left of Cu in the periodic table, to SnAg-based solder alloys, did not increase IMC thickness and grain size significantly after the solder reflow process and thermal aging. hence, these nano particles resulted in good drop test performance compared to Cu, Ag, Au, Zn, Al, In, P, Ge, Sb.