The influence of nucleation potential, nucleation time, growth potential and substrate roughness on the surface roughness of thin copper foils deposited electrolytically on titanium substrates from a 83 g dm(-3) Cu2+ and 140 g dm(-3) H2SO4 solution at a temperature of 65 degreesC, using 2k(4) factorial design, was studied. A mathematical model to determine the average surface roughness, a quality parameter of thin copper foils, was established. Statistical adjustment of the model enables its use in accurate prediction (error lower than 5%) of the average surface roughness of thin copper foils. The initial steps of copper nucleation and growth are particularly important for the quality of thin (18 mum) copper foils, because during its manufacture, a rapid and homogeneous covering of the entire surface of the electrode becomes fundamental in order to obtain foils with a low surface roughness and a low degree of pinholes per unit area. Mechanisms for copper nucleation on titanium, based on the Thirsk and Harrison model for different experimental conditions, were determined with the aid of potentiostatic current transients. It was shown that the roughness of the thin copper foils is a function of not only the growth process, but also the nucleation process and that the lowest surface roughness is related to a pre-nucleation step at -0.590 V for 10 ms on a titanium substrate polished with 600-grit paper.