The thermomechanical fatigue properties of Sn-Pb eutectic based solders in a single lap shear configuration were investigated. The development of fatigue cracks through heterogeneously coarsened, Sn enriched, bands near the solder-intermetallic interface were observed in eutectic and solid solution strengthened alloys. Other authors had not previously reported the Sn enrichment of coarsened bands in eutectic solders. However, analysis of micrographs found in published literature found evidence of the development of Sn enriched regions in Sn-Pb eutectic solders with initially globular microstructures. Solder microstructures, which were initially lamellar eutectic, displayed no evidence of Sn enrichment in the coarsened bands. Dispersion strengthening was effective in inhibiting heterogeneous coarsening, and resulted in solders with the greatest themomechanical fatigue lifetimes.