| Alloy deposits of Sn-Bi, were electroplated on a Cu plate from an organic sulfonate bath using direct or pulsed currents, and the effects of the plating parameters on the composition and the microstructure of the electrodeposits were investigated. In addition, the effects of alloy composition of the electrodeposits on the formation kinetics of intermetallic compounds were examined. Addition of grain refiner to the bath increased the cathodic polarization, and reduced the difference of the deposit potential between Sn and Bi. Thus, Sn-Bi alloy can be electrodeposited with fine and rounded grains in bath with the additive. The Sn content in the deposits was increased with an increase of Sn content in the bath. The preferred deposition trend of Sn was stronger than that of Bi, because the deposit potential of Sn was more positive than that of Bi in the bath with the additive. The Sn content in the deposits was decreased with an increase of current density, and the grains of deposit became finer because of the increased cathodic overpotential. When Sn-Bi alloy was electrodeposited using pulse current at 4 A/d㎡ peak current density, the Sn content in the deposit was increased with increasing the pulse frequency and decreasing the duty cycle. The morphology of Sn-Bi deposits became finer with decreasing pulse frequency and increasing duty cycle. When the depostis of Sn-Bi alloy were aged at 80℃, the growth of Cu-Sn intermetallic compound layer [ε(Cu_3Sn) +η`(Cu_6Sn_5)] showed a parabolic time dependence, and the growth rate of that depended significantly on the composition of Sn-Bi electrodeposits. The apparent activation energy for the growth of intermetallic compound in 42Sn-58Bi electrodeposit was 52.48 kJ/㏖, that in 70Sn-30Bi elecrodeposit was 43.32 kJ/㏖, and that in 90Sn-10Bi was 41.35 kJ/mol. |
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