Clean rooms are used in several industries as a means of controlling airborne particles that may contaminate manufacturing or measurement processes. While several industry standards exist for measuring and controlling particulate count per unit volume, there are very few standards that pertain to temperature or humidity control in clean rooms. This is due in part to the fact that the measurement and control of these parameters are usually determined by the specific industries, applications or processes that use the clean room. This article reviews clean room standards and provides examples of why the control of temperature and humidity together with particulate control may be important considerations for a process. The article will also provide an overview of several Air Innovations’ products, technologies and services that process engineers and clean room designers may implement to control temperature and humidity in their clean room processes.

Clean room standards

Clean rooms are closed environments designed to enable the strict control of environmental contaminants. They are typically classified according to the cleanliness level of the air inside of them. In the U.S. and Canada, ISO 14644-1 classifies clean rooms in accordance with the quantity and size of particles per volume of air, with ISO 1 being the “cleanest” class and ISO 9 being the “dirtiest” class. The alternative U.S. Federal Standard 209 has equivalents for the ISO classes, where Class 1 is equivalent to ISO 3, and Class 100,000 is equivalent to ISO 8. For purposes of comparison, an ISO 1 clean room will allow ten 0.1 micron particles per cubic meter, whereas an ISO 6 cleanroom will allow one million (1 x 106) 0.1 micron particles per cubic meter.

Clean rooms use special equipment, such as HEPA (high efficiency particulate air) filters for environmental control. These are a type of pleated mechanical air filter that removes at least 99.97% of dust, pollen, mold, bacteria and airborne particles. HEPA filters can be used in the primary clean room HVAC system to remove potential contaminants throughout the clean room facility, or they may be installed in separate environmental chambers to remove contaminants around critical tools or equipment.

Clean room temperature and humidity control

While the control of particulates is an important function of most clean rooms, certain industries and applications may require clean rooms that are also capable of temperature and humidity control. These clean rooms may require special considerations with unique requirements. Unlike clean rooms designed only for particulate control, the monitoring and control of temperature and humidity in clean rooms is not highly regulated or standardized. The control of humidity can reduce microbial growth, control static charge build-up and minimize moisture condensation and water absorption among other things. The control of temperature and temperature gradients may be essential to ensure precision parts and assemblies maintain a stable length for measurement or processing purposes. These capabilities may require an in-depth understanding of the equipment and processes that must operate within the clean room environment. A couple of examples of temperature and humidity control in the semiconductor and pharmaceutical industries are provided below.

Semiconductor photolithography

In a typical photolithography process, a silicon wafer is placed on a moving stage positioned underneath an ultraviolet (UV) beam that exposes a mask or pattern onto the wafer. The precise positioning of the stage is critical to achieving the nanometer-sized features found in modern microelectronic chips.

Positioning of the stage is accomplished using interferometers in the wafer (X-Y) plane, which essentially bounce a “measurement” laser beam off mirrors on the stage. When combined with a “reference” laser beam, interference fringe patterns are produced on a photodetector array that is measured and analyzed to precisely determine the X-Y position of the stage.

The biggest source of error in the interferometric measurement system is due to changes in the laser wavelength, which is dependent on the refractive index of the air through which it travels. The refractive index of air can rapidly change due to the presence of particulates, as well as fluctuations in the temperature, pressure and humidity of the air that surrounds the photolithography tool. Such tools must therefore be housed in separate environmental chambers (mini- or micro-environments) that utilize special environmental control units (ECUs) that provide absolute control of particulates, temperature, humidity and pressure (Figure 1).

Figure 1. Custom AdvancAir® ECU for semiconductor processing. Source: Air InnovationsFigure 1. Custom AdvancAir® ECU for semiconductor processing. Source: Air Innovations

Pharmaceutical processing

The processing of pharmaceuticals, such as tablets, powders and other medications, requires a high degree of cleanliness since pharmaceuticals are typically ingested or consumed by humans or animals. The control of particulates has traditionally been a major concern, requiring that pharmaceutical processing and manufacturing be done in clean rooms. These clean rooms not only need to control particulates, but they must also control excess moisture or humidity in the air, which may affect chemical reactions among ingredients or cause improper mixing or coating of powdered drugs or tablets.

For example, during the milling process, excess moisture can cause powder to stick to the delicate grinding blades, making it harder to transmit precise amounts of medicine to the manufacturing phase. During compounding, moisture absorbed by hygroscopic powders can corrupt the proper reactions of different ingredients, potentially lessening their effectiveness or shelf life. When powders are compressed into tablets and coated, moisture can lead to clumping or an uneven finish — potentially destroying entire batches of expensive medication. Pharmaceutical processing and manufacturing must therefore be done in clean rooms that control particulates as well as temperature and humidity (Figure 2).

Figure 2. Pharmaceutical clean room. Source: Air InnovationsFigure 2. Pharmaceutical clean room. Source: Air Innovations

Air Innovations’ products and solutions

Air Innovations, a world leader in the design, fabrication and installation of clean rooms and clean room enclosures for several industries, provides numerous services and products to assist customers that require stringent temperature, humidity and particulate control. Air Innovations’ in-house customer consultants can review and evaluate several customer, process and facility requirements (such as those shown in Table 1) and recommend the implementation of existing products and technologies or the development of new custom-engineered solutions. Once developed, Air Innovations can optimize and qualify the clean room equipment in their psychrometric test facility and evaluate its performance under various temperature, humidity, pressure and air flow conditions. On completion of the design and development of these custom solutions, applications engineers and technicians can assist in system start-up to ensure that all design requirements are satisfied, whether these systems are used on the ground or in transport.

Below is a partial list of clean room and process requirements needed to size and select cleanroom systems:

Table 1. Partial list of clean room and process requirements.Table 1. Partial list of clean room and process requirements.

As a fabricator and integrator of clean room components and systems, Air Innovations can supply turnkey products such as the ones below:

HEPAir® Systems — These are integrated modular and configurable environmental control systems that can be used in clean rooms as well as in industrial and commercial applications such as compounding pharmacies, laboratories, hospitals, facility additions, mini-environments and process isolators.

Figure 3. HEPAir® system. Source: Air InnovationsFigure 3. HEPAir® system. Source: Air Innovations

Post sterile storage cabinets — These are compact systems designed for maximum flexibility, ease of use and transportability. These systems save time and money by preventing unnecessary reprocessing by keeping sterile materials and equipment within the proper environment without the need to retrofit an existing space to meet strict temperature, humidity, pressure and particulate requirements.

Figure 4. SSC4500 sterile storage cabinet. Source: Air InnovationsFigure 4. SSC4500 sterile storage cabinet. Source: Air Innovations

ArrayAir® Systems — These portable environmental control solutions are specially designed to maintain exact clean room humidity, stable temperature and cleanliness in a micro clean room environment up to 30 cubic feet in size. These units feature humidification, de-humidification, heating, thermoelectric cooling and HEPA filtration for biotech, pharmaceutical or research laboratory applications.

Figure 5. ArrayAir® system. Source: Air InnovationsFigure 5. ArrayAir® system. Source: Air Innovations

AdvancAir® Systems — These are custom environmental control units for clean rooms with greater capacity and enhanced performance in a smaller footprint and are built to exact specifications in a variety of system configurations.

Figure 6. AdvancAir® system. Source: Air InnovationsFigure 6. AdvancAir® system. Source: Air Innovations

Air Innovations has the expertise and products that can assist in implementing particulate, temperature and humidity controls within clean room environments.

Air Innovations

Air Innovations was founded in 1986 in Syracuse, New York, and is a world leader in designing and building environmental process control systems for several industries. Their primary business involves the development of customized packaged systems and solutions for temperature, humidity, filtration, pressurization, and with direct-expansion, chilled-water, or thermoelectric capabilities. The company maintains a research and development department dedicated to continuous growth and improvement in the creation, testing and validation of their engineered solutions. Air Innovations’ numerous products currently spans across a variety of industries in over 60 countries. More information about the company and products can be found on the Air Innovations’ website.