Particle fallout in cleanrooms is a primary concern for industries manufacturing critical products with surfaces highly susceptible to particulate contamination.1, 2, 3 Particulate contaminants can be hazardous to lasers, optics and to spacecraft in a number of ways including failure of precision mechanisms, light absorption and scattering, points of high local electric field and associated electrostatic discharge, and noise on electrical contacts.
The objective of the ECSS-Q-70-50-C standard, as an example, was to ensure that the particle monitoring of spacecraft systems and cleanrooms utilised in the production of such systems, was carried out in an appropriate manner.4 The device used for the fall out particles is a photometer which measures the optical effect of particle contamination and is not a precise particle classification.
The ISO 14644-3: 2005 standard (in the annex dealing with particle deposition testing) describes the procedures and methods to be used to measure and count particles that have been or may be deposited from the air onto the work surfaces or products inside cleanrooms.5 Deposited particles are collected on suitable witness plates, similar to the surfaces considered to be at-risk, and the size and number of these particles are analysed using an optical microscope, an electron microscope or other surface analysis equipment.
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