How Clean Is ‘Clean’?
This is a simple question but the answer can be more complex. Establishing what is an acceptable standard of cleanliness needs to take into account factors such as the application and the required functionality of the part.
In a maintenance cleaning environment, or where it is necessary to clean a part between manufacturing stages, ‘clean’ may simply mean removal of the specific contaminant to such an extent as to facilitate further working of the part. By contrast, a surgical implant, or a printed circuit board that forms part of a missile guidance system must be cleaned to a much higher standard.
Thus, determining what is ‘clean’ will involve some form of assessment and comparison with an established pass/fail criterion. Assessment methods can be of two, basic types:
1. Qualitative methods e.g. visual inspection, which may include wiping to look for a visible residue.
2. Quantitative methods e.g. measuring contamination using established surface analysis techniques.