The formation and growth of intermetallic compounds at the interface between four solder alloys, Sn-3.5Ag, Sn-0.7Cu, Sn-3.2Ag0.8Cu and Sn-9Zn, and Cu-plated substrates have been studied. Thermal aging tests for 20, 100, 200, 500 hours at 70, 100 and 150 ºC were carried out. As expected, results indicate that the formation of the intermetallic layer is a diffusion-controlled process. Nevertheless, migration and dissolution of Cu into the solder was observed, especially at lower temperatures. The thickness of the layer of intermetallic compound increased with increasing aging temperature and time. The Sn-3.5Ag alloy showed the smallest intermetallic growth and the Sn-9Zn alloy the highest, compared to the other alloys. The results also show definite morphological differences between the Cu/Cu3Sn, the Cu3Sn/Cu6Sn5 and the Cu6Sn5/solder-matrix interfaces.
Tin-based solder alloys; Intermetallic compounds; Isothermal aging; Morphology; Interface; IMC layer growth front
