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

•Applying DC has a noticeable effect on the wetting of oxidized Cu by molten Sn.•Current polarity does not have a strong effect on wettability but on microstructure.•The IMC layer greatly thickens with increasing current intensity.•An unusual morphology was formed at the interface under a larger current intensity. The effect of applying a direct electric current on the wetting behavior of molten Sn on Cu substrates at a nominal temperature of 510K 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 2.5A to 7.5A. 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.