Electrodeposition of Sn-Cu alloy from pyrophosphate bath

Electrodeposition of Sn-Cu alloy for use as Pb-free soldering was investiga ted. 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 behav ior, 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 compositio n (Sn-1.3 % 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 th e bright Sn-Cu alloy was obtained from the bath modified by adding both for maldehyde and PEG600 to the basic bath. It is suggested that the process of the reductive decomposition of formaldehyde on the alloy electrodeposit re lated to the smoothing of Sn-Cu alloy films. beta -Sn phase only or two pha ses of beta -Sn phase and eta phase (Cu6Sn5 phase) were observed with the e lectrodeposited Sn-Cu alloys.