In conjunction with a study of the copper electrodeposition process from the acid copper sulfate bath for the fabrication of interconnections of printed circuit boards and semiconductor devices, an investigation was performed of the effect of bath additives on the relationship between the ductility of the copper deposit and its crystallographic structure and electrical resistivity. Room-temperature recrystallization, or so-called self-annealing, is known to occur in copper electrodeposits obtained from baths containing Cl-, polyethylene glycol, and bis(3-sulfopropyl)disulfide as additives. Variation with time of the crystallographic orientation, grain size, and resistivity of the deposit was followed over a period of several weeks after the deposition. During the period of self-annealing, ductility was found to increase by a factor of 1.5. The increase in ductility is shown to be related to a change in microstructure of the copper deposit. (c) 2006 The Electrochemical Society.