I just tried to clean some PCB's and I guess I need to find a solution to assist in getting the flux off. Just water and a half teaspoon of Dawn may have worked for the greasy and dirty 100 year old sewing machine parts but it didn't get the boards quite clean enough. Back in the day, like everybody else, we used things that were not only toxic for the body, they were toxic for the environment. The Navy had us use a substance in our ultrasonic machines which worked SO WELL, we should have known it was not good for body or earth... This is what we used.....
Trichlorotrifluoroethane is a clear, colorless liquid with an ether-like odor. It was banned from use as a chlorofluorocarbon for its ozone-layer destroying properties. Trichlorotrifluoroethane was primarily used as a dry cleaning solvent. It was also used as a refrigerant.
Obviously I don't wan't to use anything like that but it took the old flux right off. I see some ho-made solutions but I don't like some of the ingredients so I will keep looking. Some of the "stuff" they are using are expensive so time for some research.