Tuesday, June 28, 2011

Some Traditional and Non-Traditional Cleanroom Uses and Related Contamination Control Practices

Products and processes in many high-tech industries may be severely compromised by airborne particles, dust, chemical vapors, electrostatic discharge, and other contaminants. Industries such as semiconductor manufacturing, pharmaceutical processing, and biotechnology research typically use cleanrooms to control these contaminants as well as temperature and humidity.
ISO 14644, the cleanroom standard series issued by the International Organization for Standardization (ISO), defines a cleanroom as “a room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation, and retention of particles inside the room and in which other relevant parameters, e.g. temperature, humidity, and pressure, are controlled as necessary.” This standard provides a method for classifying cleanrooms based on a specified number and size of particles per cubic meter of air. High efficiency particulate air (HEPA) and ultra low particulate air (ULPA) filtration is used to remove airborne contaminants.
Personnel and the activities they perform are a primary source of contamination. The human operator has been characterized as a broad-spectrum particle generator enclosed by inefficient mechanical filters that may also generate and release chemical and biological aerosols to the environment together with potentially destructive electric charges (ESD). To minimize such contamination, cleanroom personnel wear protective apparel such as face masks, gloves, boots, and coveralls, which they put on in a controlled gowning area.
Example Contaminants from Operator
  • Particulate: Skin Flakes, Hair, Eyelashes, Cosmetics, and Tobacco Smoke.
  • Chemical/Organic Matter: Na, Mg, Al, Si, P, S, Cl, K, Ca, Fe - Cosmetics (Bi, Ba, Ti) - Oils - Nasal Effluvia (rich in Na and K) - Oral Effluvia (rich in K and Cl).
  • Biological: Bacteria, Viruses, and Pyrogens.
  • ESD: 20 to 40,000 volts.
Example Contaminants from Street Clothes
  • Particulate: Silica Dust
  • Fibers: Cellulose
  • Chemicals: Varies
  • Biological: Bacteria
Thousands of cleanrooms (controlled environments) around the world host a variety of activities in industries such as the following:
Microelectronics (semiconductor/integrated circuits)
Microcircuits well below the sub-micron level are sensitive to a variety of contaminants, including particles and trace metal impurities (Na, K, Ca, Fe, Ni, Cr, Cu, and Zn). These contaminants cause detrimental device degradation, reliability problems, and manufacturing yield losses. For example a particle as small as 0.5 micrometers can severely impede the coating adhesion on a wafer or chip. To improve yields and lessen production defects, manufacturers put precision instrumentation such as etching and doping devices within a controlled environment such as a cleanroom. In addition to air filtration, the cleanroom must have vibration protection and temperature/humidity control to minimize static electricity.
Food-borne illnesses and microbial contamination, especially pathogenic organisms, are a growing concern worldwide. The major focus of contamination control in the food industry is prevention of cross contamination between ready-to-eat products and raw materials. Food processors are concerned with the spread of bacteria, yeasts, and mold that grow in the moist conditions of processing areas and are carried by air currents throughout the food plant. Meat processing typically takes place in HEPA filtered cleanrooms or “positive pressure” rooms vs. the cold stagnant and contaminated air supplied by refrigeration systems. Cleanrooms allow the use of preservatives to be reduced or eliminated.
Unlike the tightly monitored pharmaceutical industry, in the United States, there is no federal agency responsible for monitoring hospital construction or operation. This function is usually handled at the state level. For example, in California hospital construction comes under the jurisdiction of the Office of Statewide Health Planning and Development (OSHPD). Licensing involves everything from contamination control to emergency procedures, to visitor management.
Tissue Engineering
A branch of biotechnology, this discipline involves growing living tissue, which is very susceptible to contamination. The use of single transit Class M5.5/10,000/ISO-7 cleanrooms with work done in Class M3.5/100/ISO-5 hoods; full multi-level gowning (protocols and apparel) are a must when there is a great concern about non-viable particulate contamination. Viable contamination is certainly also important—genetic engineering (“bacterial farming”).
Per the U.S. Food, Drug, and Cosmetic Act of 1938 as amended (FD&C), cosmetics should not be “adulterated or misbranded” and remain in an uncontaminated condition when used by the consumer (unlike drugs, there is no pre-clearance requirement). Cosmetics are not manufactured in cleanrooms but are tested for microbials in a clean area under aseptic conditions. The industry is self-regulated i.e., testing of raw materials, microbiological controls, air handling, and the many things that go into GMP’s are established voluntarily through industry trade associations.
The application of coatings and paint is subject to two types of contamination: process-related and environmental or human-sourced. Process-related contamination results from the paint, paint distribution system (robotics and spray equipment), airflow, and filtration. The need to control process-related contamination affects facility and booth design, airflow, filtration, humidification, robotics and spray equipment, paint delivery and atomization rates, paint filtration, water systems, and assembly processes. Environmental and human-sourced contaminants, such as personal hygiene products, machine lubricants, packaging materials, and fibers, can account for more than 25% of paint-related defects. Crater-causing contaminants limit paint from adhering to a surface. Particulate contamination under or on a painted surface can produce blemishes ranging from small visual detractors to corrosion-related defects.
The ISO 14644 Series, Cleanrooms and associated controlled environments, is used worldwide to establish the design and operation of cleanrooms. In addition, the Institute of Environmental Sciences and Technology (IEST,has published Standards, Recommended Practices, and Handbooks to assist users in designing, operating, and maintaining cleanrooms and other controlled environments at specification levels.

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