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-H2 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 Cu6Sn5 adjacent to the solder and Cu3Sn adjacent to the Cu substrate. The intermetallic compounds effectively enhanced the triple line mobility because of reaction product formation at the diffusion frontier.
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