Pb-free Sn-Ag alloy solder bumps for flip-chip bonding were formed by electroplating with the aid of a photolithography. Pyrophosphate-iodide baths were used for the plating bath. Smooth, fine-grained Sn-Ag alloy films were obtained using a bath containing both polyethylene glycol ͑mean molecular weight 600, PEG600͒ and formaldehyde ͑HCHO͒ additives. Sn-Ag alloy films with near eutectic compositions ͑Sn-3.8 atom % Ag͒ were obtained under both galvanostatic and potentiostatic conditions. All of the Sn-Ag alloy films deposited consisted of ␤-Sn phase and (Ag 3 Sn) phase. Straight-walled bumps and mushroom bumps were formed under both galvanostatic and potentiostatic conditions from the pyrophosphate-iodide bath containing both PEG600 and HCHO. Mushroom bumps with smooth surfaces and homogeneous composition were obtained under potentiostatic conditions.