Spreading kinetics of a Sn-30Bi-0.5Cu alloy on a Cu substrate

Abstract

The reactive wetting kinetics of a Sn-30Bi-0.5Cu Pb-free solder alloy on a Cu substrate was investigated by the sessile drop method from 493 to 623 K. The triple line frontier, characterized by the drop base radius R was recorded dynamically with a high resolution CCD using different spreading processes in an Ar-H 2 flow. We found a good agreement with the De Gennes model for the relationship between ln(dR/dt) and lnR for the spreading processes at 493 and 523 K. However, a significant deviation from the De Gennes model was found for the spreading processes at 548 and 623 K. Our experimental results show a complicated temperature effect on the spreading kinetics. Intermetallics at the Sn-30Bi-0.5Cu/Cu interface were identified as Cu 6Sn 5 adjacent to the solder and Cu 3Sn adjacent to the Cu substrate. The intermetallic compounds effectively enhanced the triple line mobility because of reaction product formation at the diffusion frontier. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.