Casting of Lead-free Solder Bulk Specimens With Various Solidification Rates

The casting of lead-free solder bulk samples has been investigated by varying the conditions of solidification. Two sets of samples were generated, one water-quenched and the other air-cooled. From these cast samples, tensile testing specimens were produced for the investigation of their mechanical properties. Cooling rate effects were specifically analyzed using small solder droplets. Excellent correlations between secondary dendrite arm spacings, microhardness measurements and tensile properties with the cooling rates were found. The results indicated that samples produced in accordance with the recommendations of the National Center for Manufacturing Sciences exhibited coarser microstructures (indicative of slower cooling) than the microstructures of actual solder joints (indicative of faster cooling). Based on this study, the predicted performance (lifetime and reliability) of actual soldering joints will not compare well with that of actual solder joints.