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JULY 2021 I SMT007 MAGAZINE 39 and make it hard to remove during cleaning. Indeed, if proper care is taken in selecting the cleaning processes and equipment, and if the soldering and cleaning processes are properly controlled, cleaning surface mount assemblies should not be an issue even when aggressive fluxes are used. It does need to be emphasized, however, that good process control is essential when using aggressive water-soluble fluxes. e selection of a cleaning process depends upon the type of flux being used. See Table 2 for a quick summary of cleaning processes for different types of fluxes. Rosin and resin fluxes can be cleaned by various types of solvents such as organic sol- vents or aqueous and semi-aqueous solvents. When cleaned by aqueous solvents, additives are needed. If no-clean fluxes are to be cleaned (sometimes they are), they can also be cleaned with these solvents, although at times, spe- cial formulations may be required. Water sol- uble fluxes can be cleaned with water with and without additives. e cleaning process selected may use sol- vents or deionized (DI) water or a combina- tion of these two processes. In the past, the commonly used solvents were CFCs (chloro- fluorocarbons) such as Freon but they were banned decades ago due to environmental con- cerns. e industry has had no choice but to Table 1: Flux classification based on material composition and halide content. (Source: Ray Prasad, Surface Mount Technology, Principles and Practice, second edition, Table 13.1)