High-temperature shear strength of lead-free Sn―Sb―Ag/Al2O3 composite solder

Lead-free Sn-1.7Sb-1.5Ag solder alloy and the same material reinforced with 5 vol% of 0.3-micron Al2O3 particles were synthesised using the powder-metallurgy route of blending, compaction, sintering, and extrusion. The mechanical properties of both monolithic and composite solders were studied by shear punch testing at temperatures in the range 25-130 C. Depending on the test temperature, the shear yield stress increased by 4.8-8.8 MPa, and ultimate shear strength increased by 6.2-8.8 MPa in the composite material. The strength improvement was mostly due to the CTE mismatch between the matrix and the particles, and to a lesser extent to the Orowan strengthening mechanism of the submicron-sized Al2O3 particles in the composite solder. The contribution of each of these mechanisms was used in a modified shear lag model to predict the total composite-strengthening achieved.