Cleanroom Design
A common approach to controlling contamination in high technology manufacturing cleanrooms is the continuous monitoring of particles. Either dedicated, discrete, “real-time” particle counters or a multi-port pneumatic manifold system to sample multiple locations throughout the cleanroom can be used to accomplish this goal. It only takes a quick monitor of the air in a cleanroom compared to a typical office building to see the difference. Typical office building air contains from 500,000 to 1,000,000 particles (0.5 microns or larger) per cubic foot of air. A Class 100 cleanroom is designed to never allow more than 100 particles (0.5 microns or larger) per cubic foot of air. Class 1000 and Class 10,000 cleanrooms are designed to limit particles to 1000 and 10,000 respectively. A human hair is about 75-100 microns in diameter. A particle 200 times smaller (0.5 micron) than the human hair can cause major disaster in a cleanroom. Contamination can lead to expensive downtime and increased production costs. In fact, the billion dollar NASA Hubble Space Telescope was damaged and did not perform as designed because of a particle smaller than 0.5 microns.
Major Components of Contamination Control
HEPA (High Efficiency Particulate Air Filter) - These filters are extremely important for maintaining contamination control. They filter particles as small as 0.3 microns with a 99.97% minimum particle-collective efficiency.
CLEANROOM ARCHITECTURE - Cleanrooms are designed to achieve and maintain a airflow in which essentially the entire body of air within a confined area moves with uniform velocity along parellel flow lines. This air flow is called laminar flow. The more restriction of air flow the more turbulence. Turbulence can cause particle movement.
FILTRATION - In addition to the HEPA filters commonly used in cleanrooms, there are a number of other filtration mechanisms used to remove particles from gases and liquids. These filters are essential for providing effective contamination control.
CLEANING - Cleaning is an essential element of contamination control. Decisions need to made about the details of cleanroom maintenance and cleaning.
LEANROOM GARMENTS - The requirements for cleanroom garments will vary from location to location.
HUMANS IN CLEANROOMS - There are both physical and psychological concerns when humans are present in cleanrooms.
COMMODITIES - Care is taken when selecting and using commodity items (Wipers, cleanroom paper and pencils and other supplies ) in cleanrooms.
COSMETICS - Many cosmetics contain sodium, magnesium, silicon, calcium, potassium or iron.
MEASUREMENT AND INSTRUMENTATION - Some important measurements related to contamination control are particle count, air flow & velocity, humidity, temperature and surface cleanliness.
ELECTROSTATIC DISCHARGE (ESD) - When two surfaces rub together an electrical charge can be created. Moving air creates a charge. People touching surfaces or walking across the floor can create a triboelectric charge. Special care is taken to use ESD protective materials to prevent damage from ESD. Cleaning managers should work with their personnel to understand where these conditions may be present and how to prevent them.