A wide range of cleaning processes, commonly referred to as “non-chemical” cleaning, do not involve immersion or spray of a liquid. Applications range from paint removal to ultra-critical cleaning of semiconductor wafers. While some “non-chemical” processes involve chemical action, the techniques may be environmentally-preferred ifair toxics and chemical waste streams are eliminated.

DRY MEDIA
Soil removal requires energy to disrupt the adherence of soil to substrate. Most non-chemical processes use energy associated with impact momentum of the cleaning media. Since impact momentum cleaning is essentially line-of-sight,it is typically not applicable to cleaning complex components.

Dry media cleaning is entirely by impact momentum, created by a forced spray or agitation. The media includes hard pellets and powders (e.g., steel shot, sand, and silicon carbide) and softer media, with less potential for surface damage, but also with less energy for soil removal (e.g., baking soda, nut shells, and talc). Microabrasive blasting may be useful for miniature components. Too often, dry media processes are not recognized as cleaning.

NON-DRY MEDIA
Water ice and CO² ice are usually considered dry media. While they clean by momentum impact, both ice and dry ice can liquefy due to the high pressures associated with the momentum of impact, adding a chemical solvent mechanism.Water vapor, as high pressure steam, is a blasting media with gross and fine cleaning applications. The potential for water condensation can be a problem for water sensitive substrates. While liquid and supercriti-cal CO2 can provide a solvency vector, because they are not typical solvents, they are frequentlyclassified as “nonchemical” cleaning agents.

DRY CHEMICAL CLEANING
UV/ozone and plasma cleaning are considered “nonchemical”, even though their cleaning action is inherently chemical. Both use high energies to produce either highly reactive atoms (ozone) or reactive ions (plasma) that convert organic contaminants into simpler, readily-removed compounds. The techniques are not line of sight and are best utilized in critical final cleaning of relatively uncontaminated substrates. However, with the reactive species comes the potentialfor substrate modification.