| Owing to the intensified movement against lead (Pb) and lead compounds in electronic assemblies the world over, Sn-Ag, Sn-Cu and their ternary alloy system i.e. Sn-Ag-Cu are widely proposed as replacements to the hereto ubiquitously used Sn-Pb solder system. However, as of this date, a comprehensive understanding of the various mechanical performance parameters is still lacking especially at the size scale of actual solder interconnects. In the current investigation, reflowed Sn-3.5Ag and Sn-3.0Ag-0.5Cu monolithic and their Cu and Ag reinforced composite lead free solders were evaluated to determine the creep mechanism using indentation creep testing. Furthermore, the effect of material (alloy composition, reinforcement type and reinforcement percentage) and process (reflow time and cooling mode) variables and interactions among them on the creep behavior of the above lead free systems was evaluated using a Design of Experiments (DoE) approach. In addition to the above variables, the effect of surface finish/metallization was also studied on the shear behavior of lead free Ball Grid Arrays (BGA's). It was found that while reinforcements were beneficial in increasing creep resistance, they were detrimental to the shear strength. And Ni-Au surface finish resulted in significantly higher shear strength as compared to the copper finish. |
