Thinking outside the box - from the air cleanliness to product contamination

The performance of cleanrooms is still mainly defined by classification of the air cleanliness in regards of particles according ISO 14644-1. Nowadays, more and more cleanrooms are classified additionally regarding airborne chemicals according ISO 14644-8. But regarding clean manufacturing environments, the focus is actually shifting from "what do we need as airborne cleanliness level" to "what for a surface cleanliness level do we accept on our product surfaces?" Up until today, cleanroom classes are defined during the planning phase regarding the air cleanliness based on best practice and NOT based on maximum allowable contamination rates of particles and chemicals on surfaces. In order to evaluate the risk to the final product or the process, the surface contamination is the main metric. If a particle will not settle on a wafer, there is no contamination on it! If a solvent as an outgassing chemical compound from plastic materials will not condense on an optical system, no one cares about fogging on the lenses! Therefore, the maximum allowable cleanliness limit of the final product surface has to be defined. Surface cleanliness levels are standardized in ISO 14644-9 (particles) and ISO 14644-10 (chemicals). But what do we finally need to predict a surface contamination depending on the exposure duration of a product surface? A contamination rate as main metric to calculate a product cleanliness during exposure! The cleanroom itself only enables the user to significantly reduce the contamination rate, not more, not less! Several other factors have a direct impact on the cleanliness level of the final product: Dressing and behaviour of personnel, used gloves, cleaning agents, consumables, packaging material, equipment and so on. Different partly standardized methods for the quantification of contamination rates are available using witness surfaces followed by microscopic inspection or chemical analysis (Microscopy, SEM-EDX, GC/MS, IC, FTIR, HPLC, ICP-MS). Different examples from space industries, optics, semiconductor, pharmaceutical and life science applications will demonstrate the feasibility of the different methods. As outlook, a proposal for a future standard dealing with particulate and chemical contamination rates will be addressed.