Creep deformation behavior in eutectic Sn-Ag solder joints using a novel mapping technique

Abstract

Creep deformation behavior was measured for 60–100 µm thick solder joints. The solder joints investigated consisted of: (a) non-composite solder joints made with eutectic Sn-Ag solder, and (b) composite solder joints with eutectic Sn-Ag solder containing 20 vol. %, 5 µm diameter in-situ Cu6Sn5 intermetallic reinforcements. All creep testing in this study was carried out at room temperature. Qualitative and quantitative assessment of creep deformation was characterized on the solder joints. Creep deformation was analyzed using a novel mapping technique where a geometrical-regular line pattern was etched over the entire solder joint using excimer laser ablation. During creep, the laser-ablation (LA) pattern becomes distorted due to deformation in the solder joint. By imaging the distortion of laser-ablation patterns using the SEM, actual deformation mapping for the entire solder joint is revealed. The technique involves sequential optical/digital imaging of the deformation versus time history during creep. By tracing and recording the deformation of the LA patterns on the solder over intervals of time, local creep data are obtained in many locations in the joint. This analysis enables global and localized creep shear strains and strain rate to be determined.