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. In order to develop new cleaners, phase behavior experiment is a prerequisite in the pertinent surfactant system. 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, the effect of additives on phase behavior and efficiency in systems containing nonionic surfactant was investigated.