2001 Volume 69 Issue 5 Pages 319-323
Electrodeposition of Sn-Cu alloy for use as Pb-free soldering was investigated. Pyrophosphate bath containing potassium iodide was used as a basic Sn-Cu alloy electroplating bath. Polyethylene glycol (mean molecular weight = 600: PEG600) and formaldehyde were used as additives. Electrochemical behavior, composition of electrodeposits, surface morphology and phase structure were studied. Copper content in deposits decreased with increasing current density and Sn-Cu alloys with the composition near the eutectic composition (Sn-1.3 at% Cu) were obtained in the range of current densities from 1 to 2 A dm−2. Dull Sn-Cu alloy was electrodeposited from the basic bath and the bright Sn-Cu alloy was obtained from the bath modified by adding both formaldehyde and PEG600 to the basic bath. It is suggested that the process of the reductive decomposition of formaldehyde on the alloy electrodeposit related to the smoothing of Sn-Cu alloy films. β-Sn phase only or two phases of β-Sn phase and η phase (Cu6Sn5 phase) were observed with the electrodeposited Sn-Cu alloys.