| Due to the adoption of "green" manufacturing practices in Europe, as well as the need for solders with better creep resistance at higher temperatures, there has been new interest in developing lead-free solders. Understanding and quantification of the effects of creep deformation is essential for lifetime prediction of electronic systems. Miniature single shear-lap creep specimens, similar in size to actual solder joints used in electronic packaging, have been developed to examine the effect of in-situ composite microstructures on the creep resistance and damage accumulation in lead-free solder joints. Average and localized strain measurements have been made optically, by monitoring the displacement of a scratch across the thickness of the solder joint. By analysis of the local strains, criteria for damage initiation are expressed in terms of the onset of tertiary creep, which starts sooner in some regions of the microstructure than others, leading to heterogeneous strain in the joint. The in-situ composite solders result in a more homogeneous strain evolution, which causes an improved creep resistance at lower temperatures, and much greater uniform strain at higher strain-rates before a critical damage level is reached. |
