(3.10) INTERMETALLICS FORMATION AND GROWTH AT THE INTERFACE OF TIN-BASED SOLDER ALLOYS AND COPPER SUBTRATES

摘要

Increasing concerns regarding environmental contamination is driving the soldering research community to develop lead-free solder alloys. Previous studies have shown that Sn-based alloys such as Sn-3.5Ag, Sn-0.7Cu, Sn-9Zn, and Sn-3.2Ag-0.8Cu have promising mechanical properties, and can be considered as serious candidates to replace the Sn-Pb alloy. However, for joint life and reliability predictions, information about the interaction between these alloys and the most used substrates is needed. In that sense, the formation and growth of intermetallic compounds at the interface between the Cu-plated substrates and Sn-3.5Ag, Sn-0.7Cu, Sn-3.2Ag-0.8Cu, and Sn-9Zn have been studied. Coupons of joints prepared with each solder alloy on a Cu-plated circuit board were subjected to thermal aging test for 20, 100, 200, 500 hours at 70, 100 and 150 degrees Celsius. Each sample was analyzed using metallographic techniques, light microscopy, SEM and EDS. The results indicate that the formation of intermetallic layers is a diffusion-controlled process. The thickness of the intermetallic compounds increased with increasing aging temperature and time. The Sn-3.5Ag alloy showed the smallest intermetallic growth and the Sn-9Zn alloy the highest. The results also suggest that at shorter aging times the chemical reaction between the substrate and the solder alloys result in the formation of small number of nucleation sites of intermetallic compounds.