Semi-aqueous cleaning

The eomplete proeess in based on a closed-loop principle. Consequently, the cleaning process merely liberates those substances that are to be removed from the pe-boards (i.e., soldering flux residues). Closed-loop operation is not only advisable for eeologieal reasons, but is also a very sound economic proposition as it significantly minimizes process costs. 

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Aqueous and semi-aqueous cleaning systems, used for printed circuit boards and other industrial degreasing operations (Mandich and Krulik, 1992 Davis et al., 1994)... 

Table 4.4 Aqueous and semi-aqueous cleaning solutions... 

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... 

Comparison of the advantages (+) and disadvantages (-) of semi-aqueous cleaning fluids... 

Figure 14.8.13. Diagram of a semi-aqueous cleaning process with ZESTRON FA.

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.). 

Table 4.4. Aqueous and Semi-aqueous Cleaning Solutions... 

Benchmark series Ultrasonic cleaning (20-800 kHz) Alkaline, acid and water dilutable cleaning solutions Terpene, hydrocarbon alcohol-based semi-aqueous cleaning solutions N/A... 

In principle, the media that can be used for semi-aqueous cleaning processes can be classified into two main groups ... 

In other words, a semi-aqueous cleaning S5rstem is not forgiving of change. And almost none of the complexity is associated with removal of soil from parts it is associated with the separation steps. 

For an excellent reference about equipment design, cleaner specification, operations, cleanliness testing, and troubleshooting of semi-aqueous cleaning technology, consult the Post-Solder Semi-Aqueous Cleaning Handbook, IPC-SA-61A, 2005. Contact IPC, 2215 Sanders Road, Northbrook, Illinois, 60062—6135, (847)-509-9700. 

Some semi-aqueous cleaning is done by spray cleaning. In this case, the various solutions which are part of the semi-aqueous technology are successively applied to surfaces (probably large ones) and later collected. Then the solvent and water processing inherent to semi-aqueous technology is practiced in separate facilities. 

Often an emulsion is formed, or made more stable, by addition of a third fluid. Called the emulsifier, in semi-aqueous cleaning it is the surfactant added to make the solvent (SA) and water (RA) form a single fluid temporarily in the immersion chamber. In general, the Bancroft rule applies — the continuous phase (the water) is the one in which the emulsifier (the surfactant) is most soluble. 

Semi-aqueous cleaning technologris an excellent choice where (1) the solvent mixture is matched to soil components, (2) high levels of removal of small amounts of soils are required, (3) soil materials are not changed, and (4) the site is populated by staff educated, trained, and experienced in reprodudbly operating complex chemical processes . 

Semi-aqueous cleaning systems are not forgiving of mediocre skills of process control. 

Figure 3.10 Cutaway View of Multi-stage Semi-aqueous Cleaning Machine...

Said another way, semi-aqueous cleaning apparatus are not the most expensive facilities for cleaning parts, but they are certainly not inexpensive. Automation, necessary to practice the semi-aqueous process, is a nudal component which probably at least doubles the purchase price of new equipment. 

The apparatus of Figure 3.10 is a cutaway view courtesy of Crest Ultrasonic (httpy/www.crest-ultrasonics.com/). Facilities found in both aqueous and semi-aqueous cleaning apparatus include ... 

Solvent Mixtures Used in Semi-Aqueous Cleaning Processes... 

The semi-aqueous cleaning process could be named the nearly aqueous process. Yes, it is a solvent-based process, being based on the solution of soils by solvents. But, the purchased mixture of solvents (and detergents) is always diluted 1/10 or more with water. The fluids being managed within the process are the water/solvent mixture, or a dilute emulsion of the solvent mixture in water, or DI water, or rinse waters, or waste water or a concentrate of soils in the solvent mixture. 

Table 3.1a Types of Semi-Aqueous Cleaning Agents (SAs) ...

Semi-aqueous cleaning processes apply hydrocarbon solvent-surfactant emulsions in concentrated form followed by a water rinse, or emulsions in water are used in processes similar to aqueous cleaning. Semi-aqueous cleaning processes are very effective in removing heavy grease, tar, waxes, and other hydrocarbon-based soils. Cleaning solutions can be made compatible with most metals and polymers and metals are not likely to be etched as the solutions are neutral. 

Aqueous or semi-aqueous cleaning (including immersion with or without agitation, spray, and steam or hot water)... 

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