OK� Nap time�s over!
Technically speaking, water soluble flux is just that, soluble in water. Technically speaking, one does not need a saponifier or any other chemical agent to remove water soluble (OA) flux residues.
However, one must consider the following factor: Water must get to the flux. If the flux is under a very low stand-off component, water may not be able to contact the flux. The cleaning agent (water) must have vigorous contact with the flux in order to remove it.
In tightly spaced applications such as BGA�s, Flip-Chip, etc, a chemical additive is helpful to lower the wash solution�s surface tension, allowing adequate contact with the flux residues.
Most wash systems place all of their effort on the wash cycle. After all, you are cleaning the boards primarily to remove flux residues. As a chemical additive is normally required for low stand-off components, regardless of flux type, one should give greater consideration to the rinse cycle.
With the right chemical, the correctly sized wash pump, strategically placed nozzles producing the right spray pattern, one will solubilize the flux. But what about the wash chemical? The rinse process removes the wash chemical and displaces it with high quality DI water. The only thing worse than leaving flux on a board is leaving cleaning chemicals on a board. It is imperative that the wash chemical be thoroughly removed. Failure to remove the wash chemical will normally result in board failures.
If you choose to include a wash chemical in your cleaning process, be sure that your cleaning system has a robust rinse ability. In reality, the rinse section of your cleaning system should actually be more powerful than your wash system. Rinsing is the most critical of the Wash, Rinse, Dry processes.
As for acceptable chemicals are concerned, our friend Dave�s list is spot-on. For water soluble applications, the chemical requirement is not as precise as in no-clean and RMA applications. Almost any chemical additive will do the trick. You will be able to cut the recommended chemical percentage in half compared to other applications. Another advantage of using a chemical additive is the neutralizing effect a high pH chemical has on an acid-based OA flux. The chemical will also remove other �environmental� contaminants such as human hand oils, and other contaminants picked up through your assembly process.
I hope this helps!
Mike Konrad Aqueous Technologies (909) 944-7771 ext 29 www.aqueoustech.com konrad@aqueoustech.com
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