Influence of Grain Refinement via ECAP to the Corrosion Behaviour of SAC 305 Solder

Equal Channel Angular Pressing or ECAP has been generating interest due to the ability to form bulk ultra-fine grains (UFG) or nanostructured materials. This formation of ultra-fine grains leads to a favorable combination of strength and ductility. Solder materials, which function as the mechanical bridge joining chip to substrate, or package to mother board, could very well benefit from this combination. High strength would offer better joint, and enhanced ductility would enable solder to have better fracture toughness and drop-impact resistance as solder joint regularly being subjected to vibration and impact. This paper reports about corrosion behaviour of ECAPed SAC 305 alloy formed via route Bc up to four passes. The focus is on the effect of grain refinement on corrosion behaviour of bulk solder in 3.5 wt.% NaCl solution. The resulting microstructure was observed by Scanning Electron Microscope (SEM). The grains formed after different passes of ECAP were observed, along with the distribution of intermetallic compound or IMC within the bulk solder. Finer grains were formed with increasing number of ECAP passes leading to reduction of corrosion rate and increased strength of SAC305. The high fraction of grain boundaries in the microstructure with increased of ECAP passes reduced the corrosion rates by accelerating the passivation process.