Formation of microstructure in Ag-In-Sn solder alloys

A metallographic study is reported of the phases and reactions that occur in Ag-In-Sn (Pb-free) solder alloys containing approximately 3 wt-%Ag and up to 10 wt-%In. Specimens were prepared by very slow unidirectional solidification and as small castings. Three different intermetallic compound phases and two different matrix phases were observed, depending on the In content of the alloy. The probable reactions that produce these phases are discussed and compared with data from the published ternary liquidus projection. This study was carried out in the Department of Materials Science and E-ngineering, University of Toronto, as part of the CMAP program.