The effect of triethanolamine (TEA) and heliotropin (FIT) oil the cathodic polarization of weakly acidic baths and the properties of Sn-Ag-Cu alloy electrodeposits were investigated. Lead-free Sn-Ag-Cu solder alloy were electrodeposited in weakly acidic baths (pH 5.5) containing Sn(CH3SO3)2, AgI, Cu(CH3SO3)2, K4P2O7, KI, hydroquinone, TEA, HT and methylsullonic acid (MSA). The cathodic polarization of baths and the properties of electrodeposits were evaluated by Liner sweep voltammetry (LSV), scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectrometer(FT IR) and X-ray photoelectron spectroscopy (XPS). The results indicate that FIT is a main brightening agent that increases the cathodic polarization of baths and refines the grains of electrodeposits; TEA is a complexing agent lor copper ions and a brightening promoter that decreases the cathodic polarization of' baths and densities the electrodeposits. The bright, compact, and smooth Sn-Ag-CU alloy electrodeposits contain 88-95 wt% tin, 5- 10 wt% silver and 0.5-2 wt% copper. Organic compounds used in the baths neither adsorb oil the electrodeposits St-Irlaces not- are included in the clectrodeposits. It can be therelore concluded that the use of both TEA and FIT is better than that ot'thein either in the process of electroplating bright Sn-Ag-Cu alloy. (c) 2007 Elsevier Ltd. All rights reserved.