The purpose of wiping a surface with a cleanroom wipe is to remove contaminants including dust, dirt, oil, greases, soot, and flux. But, after wiping, how clean is the surface? How can an operator or quality inspector be sure?
Visually inspecting the wipe is the quickest and easiest way to check cleanliness. If the wipe looks dirty and the substrate looks clean, the wiping process was successful. That works well if the wipe and the contaminants are contrasting colors. Since most wipes are white, black or dark color soils are easily seen. However, many contaminants are not dark colored. Instead they are white or light colored. Since they are the same color as the wipe, visually inspecting the used wipe is not completely useful. This is especially true if the contaminant is particulate; especially small particulates.
