Dispersion strengthening for dimensional stability in low-melting-point solders

An improved solder structure with an ultrafine grain size of ∼200–500 nm and significantly enhanced mechanical properties has been created by incorporating nanosized, nonreacting, noncoarsening oxide dispersoids into solder alloys. These solders display up to three orders of magnitude reduction in the steady-state creep rate, 4–5 times higher tensile strength at low strain rates, and improved ductility under highstrain-rate deformation. With a dispersion of TiO2 particles, the Pb-Sn eutectic solder with a low-melting point of 183°C can be made more creep resistant than the Au-20Sn eutectic solder with a much higher melting point of 278°C. This technique can be extended to other solder systems, such as the emerging lead-free solder alloys, and used to achieve enhanced dimensional stability.