Formation of Intermetallics in Sn-0.9Cu and Sn-0.7Cu-0.08Ni Solders

A study of the crystallography and composition of the constituent intermetallics in a binary eutectic Sn-0.9Cu and a ternary Sn-0.7Cu-0.08Ni solder alloy was carried out by systematic transmission electron microscopy. The results are analyzed and discussed in relation to the phase diagrams available in the literature. The intermetallic phases formed at different stages during solidification are present in different sizes and morphologies and also appear to exhibit different crystallographic properties and composition. The fine eutectic intermetallic in the Ni-containing alloy could not be matched with any of the known intermetallics in the ternary Sn-Cu-Ni system