Suppression of microstructural coarsening and creep deformation in a lead-free solder

Abstract

Bi-43% Sn eutectic solder [melting point (m.p.)∼139 °C] undergoes extensive microstructural coarsening and severe creep deformation under stresses at temperatures near 100 °C. It is shown that a relatively uniform dispersion in the solder of essentially insoluble particles such as iron can be accomplished by use of a magnetic field, and that the presence of these dispersoid particles significantly reduces microstructural coarsening and resultant accelerating tertiary creep rates. The useful service ranges of this Bi-Sn lead-free solder can thus be raised to much higher homologous temperatures, allowing its use at or exposure to elevated temperatures (near 100 °C) which are typical for the widely used, lead-containing, eutectic Pb-63-Sn solder alloy (m.p.∼183 °C), but with a greatly reduced creep rate.