CleanroomsUSA

Construction of Cleanrooms Part 2

In CleanroomsUSA Construction of Cleanrooms Part 1 blog, each aspects of the construction process was outlined. In this blog, Cleanrooms USA will go more in depth with each section of the process.

Surfaces

Cleanroom surfaces boast a seamless and impermeable design, ensuring resistance against peeling, flaking, corrosion, dust generation, and microbial colonization. They're engineered for easy cleaning and accessibility, crucial in environments like microelectronic and semiconductor Cleanrooms where smoothness is vital to prevent Electrostatic Discharge (ESD) risks. Additionally, these surfaces are crafted to withstand impacts, resisting shattering, denting, and cracking, while also repelling creases.

In Cleanrooms, flooring options typically include epoxy resin or PVC. Epoxy resin floors excel in areas subjected to heavy mechanical loads due to their exceptional durability and strength, making them particularly suitable for spaces with moisture or high humidity. Conversely, PVC floors offer a more cost-effective solution, often installed as tile layouts in low-traffic zones where heavy loads are rare.

Equipment

Cleanroom equipment is crafted from materials that facilitate effortless cleaning, such as stainless steel, polycarbonate, or plastic laminates. This equipment encompasses a diverse array of items, ranging from basic hand tools to essential installations like showers and pass-throughs, all of which are not affixed to the walls or floor.

Among the common Cleanroom equipment are Stainless Steel Shoe Racks, Gowning Benches, Stainless Steel Storage Cabinets, Air Shower Entrances, Glove Dispensers, and various others.

Air Control Systems

Cleanrooms demand a significant volume of air and often require precise regulation of temperature and humidity, with air handling units (AHUs) consuming approximately 60% of a facility's power. As cleanliness increases, so does power consumption. To mitigate costs associated with air control, systems are engineered to recirculate air, maintaining stable temperature and humidity levels.

The air control system stands as the cornerstone of a cleanroom. These environments maintain positive air pressure, causing air to flow outwards into adjacent spaces with lower pressure, exiting through various points such as electrical outlets, light fixtures, window frames, ceiling and floor interfaces, and doors. Typically, leakage rates range from 1% to 2%.

During cleanroom planning, understanding the extent of exfiltration—the air escaping the room—is crucial. In a system comprising supply, return, and exhaust, a 10% disparity between supply and return airflow is necessary for optimal performance.

Common exit paths for air include doors, where exfiltration rates depend on factors like door size, pressure differentials across the floor, and the effectiveness of sealing. For standard doors, exfiltration typically ranges from 190 cfm to 270 cfm.

Balancing airflow is essential to counteract exfiltration, ensuring that the amount of air escaping matches the amount entering. During cleanroom startup, adjustments are made to accommodate exfiltration, considering factors such as turbulence, equipment, and pressure, which influence the air exchange rate—a critical aspect of airflow design.

The diagram below illustrates the interplay between exfiltration and infiltration in a unidirectional airflow system, where "1" represents infiltration and "2" denotes exfiltration. Understanding and optimizing these factors are paramount in developing and constructing effective air control systems.

Number of Personnel

The primary source of contamination in cleanrooms is human presence, as individuals shed approximately one billion skin cells per day, with 10% of these cells carrying microorganisms. Each skin cell measures about 33 µm x 44 µm x 4 µm. Given the potential for contamination, regulating the number of personnel entering cleanrooms is of paramount importance.

Academic research underscores the importance of restricting access to cleanrooms to only trained personnel. Additionally, comprehensive training in cleanroom protocols, including appropriate attire and protective measures, is imperative. Studies indicate a direct correlation between the number of personnel present and the level of contamination, highlighting the critical need for stringent control measures.

Lighting

Cleanroom lighting is meticulously tailored to meet the exacting environmental standards of these specialized facilities. While representing only 1% of the total operational cost, lighting plays a crucial role due to the precision required by instruments within cleanrooms, necessitating high foot-candle intensities (one lumen per square foot). Each cleanroom type is outfitted with lighting fixtures specifically engineered for its unique purposes.

Despite its relatively small cost, lighting design in cleanrooms demands meticulous attention, with the air control system taking precedence. Energy-efficient options such as LER lamps are commonly utilized for their longevity and ease of maintenance. Alternative lighting types include incandescent, high intensity, LED, and UV lighting, providing additional bacterial and contaminant control for specific cleanroom applications.

Lighting fixtures typically feature steel housings with sealed openings and gaskets to prevent contamination. In most cases, ballasts and lamp holders are designed for easy removal to minimize disruptions to cleanroom conditions.

Recent advancements include the integration of automated lighting systems equipped with passive infrared motion detectors, ensuring energy efficiency while maintaining consistent illumination as needed.

During the design phase, engineers determine the required lux level—unit of illuminance—based on the nature of the tasks to be performed. Factors such as the IP rating for enclosures and lighting color are also carefully considered, tailored to the specific requirements of the work conducted within the cleanroom. The IP rating reflects the effectiveness of the lights in sealing out contaminants from the surrounding environment.

Doors

Cleanroom doors play a critical role in preserving the integrity of the controlled environment by effectively sealing the room from external contaminants. Like every component within a cleanroom, doors must adhere to stringent standards and be meticulously designed. Here are some key considerations when assessing a cleanroom door:

First and foremost, in line with the requirements for all cleanroom surfaces, doors must exhibit a smooth and impermeable surface.

Completely flat
Easy to integrate into any Cleanroom
Resistant to bending and shock with a thickness of 60 mm or 2.36 in.
Air tightness
Resistant to strong chemicals in cleaning products
Safety glazed glass
Resistant to ESDs
Swing into the room
High quality hardware
Able to be locked
Closed cell non-organic core
Seamlessly molded
Fire resistant

Viewing Panels

Viewing panels serve the purpose of enhancing operator efficiency and facilitating visual contact within cleanroom environments. Positioned strategically for convenient access, they streamline supervision, inspection, and eliminate the need for supervisors to undergo entry protocols.

These panels are meticulously designed to be flush with both sides of the wall, shatterproof, and equipped with a drying agent within the void between glass panels to prevent moisture accumulation. Additionally, they are fire-resistant and, in ultraviolet-lit rooms, feature a coating that filters ultraviolet wavelengths.

Low Humidity

The optimal relative humidity (RH) range for a cleanroom typically falls between 30 to 60%, carefully balanced to mitigate the risks associated with excessively moist or dry conditions. Maintaining this balance is crucial for safeguarding against potential electrostatic discharge (ESD) that could compromise product integrity. Additionally, humidity control is essential for inhibiting bacterial growth within the cleanroom environment.

Two primary methods are employed for humidity control: air conditioning and desiccants—substances designed to induce dryness. Air conditioning functions by lowering the surface temperature in a cleanroom, while the desiccant process absorbs moisture in the air. Desiccants significantly reduce dew points to five times lower than an HVAC system.

Different Levels of Cleanrooms

The level of a cleanroom is determined by its air. All cleanrooms are built the same with airtight walls, doors, windows, and very clean air. To move from one classification to another, there has to be an increase in airflow since air removes the contaminants. The cleaner the room, the higher rate of air exchange.

Lower levels of cleanrooms such as ISO level 9 to ISO level 6, cleanliness is based on the amount of air exchanged each hour, while rooms at ISO levels 1 through 5, airflow is measure per second. Equipment and furniture can block airflow and raise a cleanroom‘s level of classification.

There are three different states in the determination of the level of a cleanroom: as built, at rest, and operational. As built refers to the cleanroom‘s performance without people, equipment, or furniture, its built state. At rest is when everything has been added before performing processes.

The change in level takes a significant up or down move when it is in full operation. It is at this state that its classification level will be determined.

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