Impression creep testing and constitutive modeling of Sn-based solder interconnects

The creep behavior of solder joints plays a key role in their reliability in microelectronic applications, necessitating the development of accurate creep testing methodologies and constitutive creep models for the various emerging Pb-free solder alloys. Because of the significant microstructural/compositional differences between bulk solder alloys and tiny microelectronic joints, bulk creep properties are usually not suitable for reliability assessment of flip-chip and ball-grid-array (BGA) solder joints. In this paper, we present results on impression creep of Sn-Ag solder, which allows testing of very small material volumes, and report on the miniaturization of the apparatus to allow direct testing of individual microelectronic solder balls attached to a BGA substrate within relatively short times and with minimal sample preparation. A microstructurally adaptive creep model, which accounts for the effects of microstructural aging on the creep response of solder joints, and is capable of adjusting itself as solder joint microstructures evolve during service, is presented, along with experimental determination of the relevant coarsening kinetics parameters.