What role does rinsing play in the cleaning process?
This addresses the seventh variable "RINSE" in Alconox's acronym BATHCARD, factors that contribute to successful cleaning. Click here to learn more.
With aqueous cleaning, the last thing to come into contact with the cleaned surface is the rinse water. A thorough rinse will remove soils which have been cleaned from the surface as well as detergent residue. Rinsing is where much of the actual removal of residues from the vicinity of the surface occurs.
After the residue/detergent mixture is rinsed away, any contaminants, present in the rinse water, may be deposited on the surface when rinse water is evaporated. For many applications, it is possible to rinse with tap water and then do a final purified water rinse to remove tap water residues. For higher level medical device, semiconductor, and electronics cleaning, all rinses should be done using purified water. Rinsing is primarily a mass displacement mechanism and should involve exchanges of water. This is why a running water rinse is typically the most effective rinse. With soak or ultrasonically agitated rinsing, it is desirable to have two counter-flow cascade rinse tanks dripping "over the tank" to reduce dragout. In all cases, running water or an otherwise agitated rinse is better than a static soak-tank rinse. Higher levels of cleaning may require the exclusive use of deionized or distilled water and in some cases more than three times the volume of rinse water.
In most clean-room, electronic-component and circuit board cleaning, deionized water is preferred over either tap or distilled water. There is less potential for metallic cation deposition on sensitive electronic components, leaving conductive residues. On metal parts, the use of deionized rinse water reduces the likelihood of depositing calcium, magnesium, or other water spotting salts. For medical device rinsing, distilled or reverse-osmosis grade water is typically used because it contains fewer organic contaminants.