Creep behavior in Cu and Ag particle-reinforced composite and eutectic Sn-3.5Ag and Sn-4.0Ag-0.5Cu non-composite solder joints

Creep properties were determined for small, geometrically realistic Pb-free solder joints. Solder joints were prepared with eutectic Sn-3.5Ag and Sn-4.0Ag-0.5Cu solder alloys. Composite solder joints were made using the eutectic Sn-3.5Ag alloy as the matrix with 15 vol % of mechanically added similar to 6 mum size Cu and similar to 4 mum size Ag reinforcing particles. Creep tests were conducted on these joints at 25 degreesC, 65 degreesC and 105 degreesC representing homologous temperatures ranging from 0.61 to 0.78. Qualitative and quantitative evaluations of creep behavior were obtained from the distortion of excimer laser-induced surface ablation markings on the solder joint. Various creep parameters, such as global and localized creep strain, variation of creep strain and strain-rate, activation energy for creep, and the onset of tertiary creep were determined. General findings in this study revealed that the creep resistance in composite solder joints is significantly improved with Cu particle reinforcements. In contrast, the improvement in the creep properties of Ag particle-reinforced composite solder joints was far less even though highly uniform deformation in the joint was observed. The strain noted at the onset of tertiary creep for Cu and Ag reinforced composite solder joints was typically lower compared to non-composite solder joints. The activation energies for creep were similar for all the solder materials investigated in this study. (C) 2001 Kluwer Academic Publishers.