September 24, 2021
Understanding environmental factors is an important element when designing and building a cleanroom. Not having proper airflow, temperature control, or understanding the various airborne contaminants can put your product, process, and personnel at risk. As product complexity continues to grow and particles become more problematic, there are several variables you should consider when you design and plan your next cleanroom.
1. Temperature: Typically, indoor temperature can range from 65˚F to 75˚F based on personnel comfort, process-related considerations, and construction materials. For personnel, to maintain comfort, the temperature range typically fluctuates +2˚F. If the worker feels too hot or too cold, this can affect their ability to work efficiently. For process-related temperature control, certain chemicals are affected if temperatures are too high or low as well as achieving specific reactions. Another consideration to take into account would be heat-generating equipment which can cause fluctuations in temperature. When looking at cleanroom construction materials, you need to select materials that can withstand any temperature cycles as well as provide a non-shedding, low-off-gassing surface.
2. Humidity: Typical cleanroom control range for humidity is 30% to 50% relative humidity for year-round operations. If the humidity is high in the cleanroom, bacterial growth can flourish, metal products or equipment can corrode, photolithographic degradation can occur, and condensation and water absorption can occur. If humidity is too low, static build-up and discharge can become an issue. Just like temperature, specifications for humidity control should be handled on a project-to-project basis.
3. Cost: Meeting the environmental requirements of a cleanroom requires large amounts of HVAC equipment which comes with a cost. Typically, the more stringent the environmental requirements, the more advanced and larger HVAC systems are implemented. Other factors that go into cost are cleanliness classifications, temperature, humidity specifications, exhaust requirements, and even operation requirements.
4. Filtration Systems: The quality of filters is determined by the room cleanliness and filter integrity testing requirements. It is recommended to use higher filtration at the final stage downstream of the coils and the fan which can range from MERV 16 filters to HEPA filters at 99.97% at the MPPS to control the particulates at the source. Critical nonunidirectional-flow cleanrooms and all unidirectional flow cleanrooms typically have the HEPA/ULPA filters mounted in the cleanroom ceiling.
5. Pressurization: Pressure control is limited to directional airflow into or out of the cleanroom. Positive pressure prevents contaminated air from entering the cleanroom while negative airflow is the opposite. Airlocks are commonly used in cleanrooms to help maintain pressure in the environment.
6. Makeup Air: Makeup air-handling units require a series of filters to remove particulates from the ambient air. These filters protect the coils and extend the life of the cleanroom’s final HEPA/ULPA filters. Coarse prefilters or roughing filters of 25% to 30% dust spot efficiency or MERV 7 are followed by bag or box extended-surface filters with a rating of 85% dust spot efficiency, MERV 13 or greater. Carbon or other adsorbents may be a consideration in facilities where airborne molecular contamination is a concern to the process or product.
7. Exhaust: The exhaust of large quantities of air from the cleanroom requires a large volume of makeup air to be introduced into the space to replace the exhaust air. This replacement air should be conditioned before entering the cleanroom. The greater the amount of outdoor air introduced, the higher the cost of conditioning. Exhaust air should be kept to a minimum, consistent with code, personnel, and process requirements.
8. Airborne Molecular Contamination: Contaminants may be smaller than or have different characteristics from those specified in the standards used for classifying cleanrooms. Possible contamination by particulate contaminants that are smaller than 0.1 µm or have characteristics other than physical size that may make them detrimental to the cleanroom. Some examples of contamination can be from solvent evaporation, plasticizers from off-gassing of polymers, acidic and basic compounds that react to form salts, dopants, and metallic or other elemental compounds.
You shouldn’t approach your cleanroom design lightly. Other variables that can affect your cleanroom are size, the number of people working in your space, outside temperature, equipment layout, lighting systems, and much more. Cleanrooms are complex environments, and that is why we utilize our Cleanroom IP platform. We create an ideal environment for your process and your technology hitting your time to market requirements. See for yourself and let us know how we can help with your next cleanroom project!
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