Cleanroom technology has evolved over the years. With more stringent requirements governing manufacturing products, we have progressed to using higher efficiency filters to satisfy production requirements.
Airborne particulates range in sizes from 0.001 microns to several hundred microns. A typical High Efficiency Particulate Air (HEPA) filter is rated to filter out 99.97% of 0.3 microns (or larger) particles. For higher grade filters, there are Ultra-Low Penetration Air (ULPA) filters that have a minimum efficiency 99.999% at 0.1 microns.
The key to creating and maintaining a clean environment is based on the principles of:
Isolating the clean environment to prevent ingress of contaminants from the external environment
Diluting the air within the environment with clean air to keep the particle concentration low
Minimizing the generation and accumulation of contaminants within the clean environment itself
The selection of materials used in a cleanroom varies with the cleanliness class of the environment and the specific requirements of the end-user. The most commonly used standard is ISO 14644: (2015), which has replaced the long-standing US Federal Standards (FS209E). However, many still find it easier to refer to the cleanliness classes with their FS209E designations. This table shows the current ISO classifications and their equivalent FS209E designations:
Airborne Particulate Cleanliness Classes (ISO 14644: 2015)
ISO CLASS NO.
^ Maximum allowable concentrations (particles/m³) for particles equal to and greater than the considered sizes, shown below
* FS209E Designations are near-equivalent and not exact