Spreading process and interfacial characteristic of Sn–17Bi–0.5Cu/Ni at temperatures ranging from 523 K to 673 K

Spreading behaviors in the reactive Sn–Bi–Cu/Ni system were investigated by the sessile drop method at temperatures ranging from 523 K to 673 K. Contact angles and the triple line frontier, characterized by the drop base radius R, were recorded dynamically with a high resolution CCD in an Ar–H2 flow. Equilibrium contact angles between Sn–17Bi–0.5Cu solder and Ni substrate decrease monotonously with the temperature increasing, which are 43.51°, 25.80°, 24.51° and 20.00° at 523 K, 573 K, 623 K and 673 K, respectively. Triple line mobility is obtained when calculating the derivative of R. The maximal triple line velocity approximately increases with the temperature by comparison of the four different spreading processes. Double layer intermetallics formed at the Sn–17Bi–0.5Cu/Ni interface are identified by EPMA and EDS analysis, which are (Cu,Ni)6Sn5 adjacent to the solder and Ni3Sn4 adjacent to the Ni substrate, respectively. The intermetallic compounds could effectively enhance the triple line mobility because of reaction product formation at the diffusion frontier.

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► Equilibrium contact angle varies as exponential decaying equation with the temperature.
► The maximal triple line velocity approximately increases with the temperature.
► Intermetallics at the Sn–17Bi–0.5Cu/Ni interface are identified as (Cu,Ni)6Sn5 and Ni3Sn4.
► Linear spreading is found in the D(t) curves for the Sn–17Bi–0.5Cu/Ni spreading system.
► Intermetallics enhance the triple line mobility due to their formation at the diffusion frontier.