Assessment of aqueous cleaning of PWAs with wave and reflow soldered components

The authors report results obtained using production machines in a test program that started in the first quarter of 1989. Chemical and physical evaluation of different kinds of commercial water-soluble solder creams and fluxes was first performed. Three products were selected and subjected to test in order to qualify their application in the professional field for wave soldering and reflow processes, and they were compared to the standard CFC (chlorofluorocarbon) cleaning procedure. Ionic contamination and THB (temperature-humidity-bias) tests were performed on ad hoc designed PWAs (printed wiring assemblies). It was found that acceptable cleanliness is obtained with water-soluble products provided that the washing machine has suitable spray pressure, nozzle angles, and drying section. Reliability tests on components are in progress to evaluate the possible detrimental effects of residual contaminants when moisture is present. Preliminary results of this step are given.<>