After soldering, the electronic assemblies must be cleaned to remove excess solder flux. The subjects of flux and cleaning are closely intertwined. The selection of solvent and cleaning equipment depends of the flux used and the cleanliness requirements.
The cleaning process has received considerable attention because of efforts to eliminate chlorofluorocarbons (CFCs) and other ozone depleting chemicals. CFCs were banned at the end of 1995.
Electronic PCB assemblies are presently soldered using various fluxes and solder paste whose residues may require cleaning after the soldering process. The use of rosin-based fluxes has mandated a cleaning stem for any manufacturer who performs bed-of-nails testing, because the rosin acts as an insulator and, additionally, it can transfer sticky residue to the problems, making them ineffective for electrical testing.
Military specifications have always required cleaning of Mil-approved RMA or RA fluxes and pastes; with ionic contamination testing to assure that the remaining residues do not deteriote the assembly. Others require cleaning of rosin flux for cosmetic reasons. Cleaning is also required prior to conformal coating. So those who must use rosin pastes or flux use alternate solvents (non-ozone depleting solvents), semi-aqueous solutions, and saponifying detergents.
In most commercial applications, water soluble solder pastes and fluxes are used. They are generally cleaned with de-ionized water. Any many electronic companies have chosen to use low residue, no-clean pastes and fluxes that require no cleaning at all.
No matter which alternative is chosen, there is a cost associated with new equipment and material purchases for the chosen alternative. Numerous cleaning technologies are available. One must choose the cleaning process based on the product being built and the cost, performance, and environmental impact of the options. The use of alternative cleaning methods must be coupled with an understanding of the flux type being used.