Water-Clean Aqueous Fluxes

In-Hne aqueous or semi-aqueous dual-tank cleaning system for the removal of RMA " and water-soluhle OA fluxes... 

A process that has found widespread use in practice is semi-aqueous cleaning with ZESTRON FA. This cleaner was especially developed for removal of no-clean soldering fluxes in ultrasonic batch or spray under immersion cleaning systems. It is used in the cleaning bath, rinsed with demineralized water, and then dried with hot air (see scheme in Figure 14.8.13.). 

Corrosion from Repair. Very often, even water-clean boards are repaired with no-clean formulations to avoid another aqueous cleaning step. Sometimes after a board is totally assembled, components of the board may not be suited for exposure to water. Although no-clean residues after soldering are generally benign, care must be taken to minimize the flux dispensed during board repair. There is a chance that the pooled flux will not be... 

Very often, completed boards that are prepared with a water-clean flux formulation are repaired using no-clean flux. This strategy precludes the need for another wash cycle. In another situation, there may be parts that are on the board or associated with an assembly that are not compatible with a wash cycle (electromagnetic interference [EMI] shields, enclosure pieces, etc.) in such cases, a no-clean repair is necessary. However, once a board is repaired with a no-clean flux, it is important not to subject the board to an aqueous cleaning process for the reasons previously described. Conversely, aqueous cleaning must be used if a water-wash flux chemistry is chosen for repair. 

When wet fluxing is used, the heat exchangers are dried prior to brazing in a separate dry-off oven. Product entering the brazing furnace must be completely dry from water introduced via aqueous cleaning or flux slurry coating. 

Aqueous Cleanable. All parts should preferably be cleanable in water or a safe solvent, unless they come out of the production process clean enough to be double-bagged and shipped directly to the clean-room assembly area. When soldering is involved, for example, the specification should call out for the use of water-soluble or noclean fluxes. Parts and assembly design should allow suppliers to quickly switch to a non-CFC solvent. 

Sodium hydrogen sulfate is used as a cleaning agent, due to its water solubility and the acidity of its aqueous solutions, as a flux, in the textile industry and for the treatment of metal surfaces. 

Aqueous cleaner for removal of rosin, water-soluhle, and all no-clean flux, both eutectic and lead-free applications, from printed-drcuit assemblies... 

A semi-aqueous cleaning process consists of a wash cycle using a mixture of different organic solvents followed by a rinse with deionized water. Organic contaminations, predominantly rosin flux residues, are removed through the lipophilic solvents, whereas the ionics are minimized by the polar rinse media. The different kinds of solvent formulations that are... 

The 1989 adoption of the Montreal Protocol imparted far-reaching changes to electronic manufacturing. In the circuit board assembly arena, it drove the elimination of chloroflnoro-carbons and the reduction of volatile organic compounds for earth s ozone layer preservation. Many fluxes that used volatile organics such as alcohols were reformulated to use water as their solvent. Solvent-clean fluxes, which required non-aqueous cleaning chemicals (alcohols, chlorofluorocarbons [CFCs], hydochlorofluorocarbons [HCFCs], etc.), were practically eliminated from the marketplace. 

Ensure that all parts on the board are compatible with aqueous cleaning. Some surface-mount switches may not be compatible and may need to be removed from the board or masked in some way to prevent water or flux residue leakage. 

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