The removal of organic flux residues in the fabrication of circuit boards has been carried out by mainly CFC-113 or other solvents. However, restriction on the use of ozone-depleting CFCs forced a development of environmentally favorable cleaners such as terpene hydrocarbon based cleaners. Previous studies have shown that the removal of representative flux residues using aqueous nonionic surfactant solutions is closely related to the formation of a microemulsion. In this study, flux removal by a microemulsion in systems containing nonionic surfactant was investigated.