The effect of Aluminium addition on the microstructure of lead-free solder alloys: A short review

The ban on using lead in electronic packaging has been taken effect since the year 2006. The alternative to replacing lead (Pb) based solder has been given highly concerns by the electronic industry. Both Sn- Ag-Cu and Sn-Cu solder alloys were considered to be the most acceptable candidates to replace SnPb solder alloy. From the findings, it showed that β-Sn appears as island-liked shape and eutectic phases appear as a darker shade. The grain size is refined significantly after incorporated with a suitable amount of Al. When exorbitant amount of Al addition will cause Al-rich particles, which has high potential to acts as the heterogeneous nucleation site and result in a lower degree of undercooling. The most desired amount of Al addition is between 0.025 - 0.05 wt%. The primary intermetallic compounds found in Sn-based solder alloy are Cu₆Sn₅ and Ag3Sn. New intermetallic compouds were found after addition of Al, which are Cu-Al and Ag-Al intermetallic. The formation of new intermetallic compounds causes the formation of Cu₆Sn₅ and Ag3Sn to be suppressed. (paper)