Characterization of Nanoparticles of Lead Free Solder Alloys

Nanoparticles of Sn-4.0Ag-0.5Cu and Sn-0.4Co-0.7Cu (wt% composition) lead free solder alloys were manufactured and characterized for potential applications in microelectronics packaging. Scanning electron microscopy (SEM) analysis was carried out in order to study the morphology and size distribution of the nanoparticles. It was observed that nanoparticles of lead free alloys were almost spherical in shape. The observed size distribution of both lead free solder alloy nanoparticles is between 20 ~ 80 nm. High resolution transmission electron microscopy (HRTEM) was used to analyse the detailed nanostructure and oxide layer present on the nanoparticles surface. The observed oxide layer thickness is about 25Aring (2.5 nm). The depression in melting point due to nanosize effect was calculated theoretically as a function of particle size for the above mentioned lead free solder alloys and the theoretical results were compared with differential scanning calorimeter (DSC). Onset calculation was used to determine the depression in melting point due to nanosize effect in respect to bulk material. The melting point difference obtained by DSC for Sn-4.0Ag-0.5Cu and Sn-0.4Co-0.7Cu lead free solders are between 1.1 to 7.8degC and 0.24 to 2.4degC respectively depending on the definition of the melting point determination by DSC