Effects of plating parameters on alloy composition and microstructure of Sn–Bi electrodeposits from methane sulphonate bath

Abstract

Alloy deposits of Sn–Bi were electroplated on Cu in an organic sulphonate bath using direct or pulsed currents, and the effects of the plating parameters on the composition and microstructure of the electrodeposits were investigated. Addition of grain refiner to the bath increased the cathodic polarization and reduced the difference in the deposition potential between Sn and Bi. Thus, Sn–Bi alloy could be electrodeposited such that it exhibited fine and rounded grains in the bath with the additive. Sn content in deposits increased with an increase of Sn content in the bath. The preferred deposition trend of Sn was stronger than that of Bi at a certain current density because the deposition potential of Sn was nobler than that of Bi in a bath with the additive. Sn content in deposits decreased with increasing current density, and the grains of the deposits became finer due to the increased cathodic overpotential. When Sn–Bi alloy was electrodeposited through a pulse current exhibiting a peak current density of 4 A dm −2, Sn content in the deposits increased with increasing the pulse frequency and decreasing the duty cycle. In addition, the grains of the Sn–Bi deposits became finer with decreasing pulse frequency and increasing duty cycle.