Effects of direct current on the wetting behavior and interfacial morphology between molten Sn and Cu substrate

The effect of applying a direct electric current on the wetting behavior of molten Sn on Cu substrates at a nominal temperature of 510 K was investigated using a sessile drop method. The final stable contact angles were 37 ± 5° without employing a direct current (DC) while they decreased from 29 ± 3° to 16 ± 2° when the current increased from 2.5 A to 7.5 A. The current polarity does not have a noticeable effect on the wetting behavior but on interfacial morphology. Cross-sectional microstructure observations revealed that applying a current promoted the dissolution of the Cu substrate in molten Sn and the effect was enhanced with increasing current intensity. An unusual morphology with Cu3Sn being the principal phase and Cu6Sn5 being the secondary phase was observed under a relatively large current intensity, particularly for the case of electrons flowing from the Cu substrate to the molten Sn side. Joule heat-induced Marangoni convection in the liquid droplet and electromigration are likely to play significant roles in determining the wettability and interfacial microstructure under the application of a direct electric current.