Palladium is widely used for metallization of electronic circuits and in electronic packaging. During soldering palladium dissolves in the liquid solder and form various intermetallics both at the solder/substrate interface and in the solder. Diffusion of atomic species lead to the formation of intermetallics in the solid state as well. As the dissolution and interfacial reaction continue, the solder comes in contact with other metallization layer(s) and eventually with copper. This leads to a very complex microstructural evolution process which ultimately affects the interfacial mechanics and transport properties. In order to improve the reliability of electronic packaging, it is necessary to understand and control the dissolution and solid-state reaction mechanisms between the metallization layers and currently used lead-tin solders. As a first step towards modelling and understanding this complex microstructural evolution, here we have undertaken a systematic study of interfacial reaction between lead-tin solders and palladium.

Pure Sn, Sn-38 mass% Pb and Pb-5 mass% Sn were used in this study.