Cleaning is the daily common process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning occurs in various commercial, industrial, environmental, and domestic contexts, which differ in scale and requirements. Industrial parts cleaning is essential to many processes, as a prelude to surface finishing or to protect sensitive components. For example, electroplating is particularly sensitive to part cleanliness, since molecular layers of oil can prevent adhesion of the coating.
Cleaning occurs in many different contexts, and uses many different methods. Cleaning is broadly achieved through mechanical action or solvent action (washing) and many other methods rely on both processes. Washing usually done with water and often some kind of soap or detergent. Mechanical cleaning includes many kinds: abrasive blasting, acoustic cleaning (ultrasonic cleaning, mega-sonic cleaning for wafer, medical implant and industrial part cleaning), carbon dioxide cleaning, dry cleaning, flame cleaning, green cleaning, plasma cleaning, sputter cleaning, steam cleaning, thermal cleaning, etc.
How clean is clean? This is big question even many standards are available and have been adopted. The question is still remained.
ASTM B322 is a standard guide for cleaning metals prior to electroplating. Cleaning processes include solvent cleaning, hot alkaline detergent cleaning, electrocleaning, and acid etch. How to test the surface cleanliness? The most common, but very rough, industrial test for cleanliness is the waterbreak test, in which the surface is thoroughly rinsed and held vertical. Although a more quantitative measurement for this parameter is contact angle measurement but it is tedious and very subjected to operators, surface roughness, and surface natures. Contact angle is not very practical or time efficient for the industries where need a quick detect on the surface cleanliness. ASTM F22 describes a version of hydrophobic contamination but ignore the external hydrophilic influence. Surfactants such as soap, which can used and seen in many cases, reduce the sensitivity of the test, therefore, there is no effective test method available in current market.