Clean Room Applications

Some ceramic membranes are used for filtering particulate matters for reasons of process requirements or protection of equipment Clean room applications constitute some major commercial usage of these membranes. 

Currently commercial installations of inorganic membranes in gas- and vapor-phase applications besides the isotope separation are mostly in the area of particulate filtration, although there have been very limited cases of separation of gaseous mixtures reported. Removal of fine particles from gas streams can be achieved by means of porous inorganic membranes. The major challenge, however, lies in the strict requirements in some of the commercial applications. This is the case in microelectronic packaging and some food and pharmaceutical processes where clean air is needed. 

Until recently, air filtration for clean rooms uses dead-end fabric filters. They are not efficient in the particle diameter range of 0.1 to 0.5 pm and also suffer in many cases from two of the most important problems in clean room gases applications particle shedding and gas reactivity (or called hydrocarbon outgassing). Some ceramic membranes such as alumina membranes have made a visible entry into the clean room market as in-line gas filters. 

To ensure the cleanliness of the ceramic membrane gas filters, the housing typically made of stainless steel should have electropolished internal wetted surfaces and welded parts free of flux materials. In addition, considerations need to be given to the materials of construction for housing (e.g., stainless steel) and seals. 

These ceramic membranes are relatively easy to operate for filtering particulates. The pressure drop across the thickness of a membrane element and the gas flow rate follows a linear or nearly linear relationship. It has been found, however, that not all inorganic membranes are suitable for clean room air filtration. Glass membranes, for example, suffer from the problem of particle shedding under mechanical shock conditions [Jensen and Goldsmith, 1987]. Sometimes high moisture content in the filtered air can be a problem. Some chemical treatments to ceramic membranes prior to their utilization as 

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Organic contamination The contamination of products by organic matter, particularly in clean room applications. 

HEPA (or absolute) filters provide the greatest degree of air cleaning. These filters, which are akin to paper or felt, will capture particles down to 0.01 pm with efficiencies of up to 99.995 per cent. They are generally used for clean room applications and are expensive. 

When bringing the utilities to the point of use, care should be taken to ensure that the clean room is not compromised. A clean construction protocol should be implemented and wall, ceiling, and floor penetrations, if needed, should be flashed and sealed in such a manner as to prevent contaminants from entering the clean room. Such entry points should also be smoothly sealed to ensure that there are no crevices to harbor organisms. Drains should be avoided in the clean room wherever possible. When this is not possible, the drains should be covered when not in use with a means specifically designed for biopharmaceutical clean-room application. Such means are tight, smooth, cleanable, and corrosion resistant. 

Other than isotopes separation for uranium enrichment described in Chapter 2, inorganic membranes are commercially used for particulate filtration of air or other gases in clean room applications, airborne contaminant analysis and high-purity hydrogen production. In addition, some inorganic membranes are us in pH and ion selective electrodes. 

Ljungqvist, B. Reinmiiller, B. Hazard analyses of airborne contamination in clean rooms application of a method for limitation of risks. PDA J. Pharm. Sci. Technol. 1995, 49, 239-243. 

Wipes are used to clean surfaces and can be used in either dry or wet/impregnated form. Disposable nonwoven wipes are increasingly used for diverse personal, household, industrial and medical applications. Global market size of wipes is more than 4 billion USD and is growing rapidly. There are some of foe application areas where foe contaminated environment is undesirable. For example, medical applications, clean room applications, skin care wipes. In such applications we require high level of cleanliness and thus release of particles from foe wipe used for cleaning the surface is totally undesirable and we need to assess lint release characteristics of foe wipes before their use in these applications. The major properties desired in a medical wipe material... 

N on woven wipes includes products for babies and adults, the food service and electronics industries, medical and clean room applications, dusters, shoe cleaning cloths and hand towels. Nonwoven fabrics are used to filter air, water, petroleum, food, and beverages. Nonwovens loaded with abrasives, cleansers, or finishes are used in a wide range of products for cleaning and scouring. Also, many protective garments are made from nonwoven fabrics. 

The shaking and continuous filters are regenerative, but there is a third group usually associated with ventilation work rather than dust and fume. These are throwaway filters, which, as the name implies, means that when they become too caked with dust to operate correctly the filters are removed and replaced with new ones. They will only handle low incoming dust burdens, but their efficiencies are the highest of any filter. Typical applications are fresh air input plants, clean-room filtration and nuclear processes. 

Electric storage hot water heaters and instantaneous water heaters are used for simple domestic applications and are not considered in this text. For many smaller HW and lower pressure steam generation applications (including bakery ovens and proofers, jacketed kettles, fish pots and other cooking equipment, wineries, breweries, textiles, laundries, phosphatizing processes, humidification, steam baths, clean rooms, and pharmaceuticals), electric boilers offer significant advantages over fossil-fuel boilers and are often the product of choice. 

IMS can be used for chemical analysis of vapours from electronics packaging [287]. IMS-QMS has been used to analyse headspace vapours in sealed electronic packages [275,288] and to follow outgassing of polymers [287]. Various types of photoresist solvents, phtha-late plasticisers and other polymer additives, such as BHT, were detected. Other applications of IMS in semiconductor technology involve failure analysis control of the efficiency of cleaning and etching steps characterisation of process media and surveillance of the atmosphere of clean rooms. 

All ductwork should be sealed in accordance with SMACNA Class A rating, which requires all seams, joints, fasteners, penetrations, and connections to be sealed. Sealant should be FDA acceptable for the application, and nonhydrocarbon based. Leakage rates as low as 1% total airflow are not uncommon. All ducts passing through a clean room wall or floor should be provided with stainless steel sheet metal collars and sealed at the opening. Details of sealing methods should be provided on the design documents. 

Air flow velocity (nonunidirectional) test In a nonunidirectional clean room or clean zone, air flow velocity measurements should be made for each terminal HEPA Alter (or supply air diffuser, if applicable) there is no entrance plane as such. 

The clean room or clean zone is deemed to have met the specified air cleanliness classification if the averages of the particle concentrations measured at each of the locations and, when applicable, the 95% upper confidence limit, do not exceed the concentration limits required [13,15,19],... 

The American CPAC initiative NeSSI [23] developed a micro reactor sampling and calibration system intended for analytical applications in the oil industry. Industrial partners such as Swagelok and Parker/Hannifin developed the system originally designed for the gas supply in clean room facilities. This approach is well advanced with respect to valves, gauges, analytical sensors and pipe fittings. 

It should also be noted that this reactor has to occupy space in the clean room, and is not operated under computer control. For application to modern fab lines, these are two disadvantages of this system. 

In demanding applications, for example barriers for OLED displays, control of polymer smoothness and cleanliness by the routes mentioned above may not be sufficient. In such circumstances it is necessary to lay down a further coating under clean-room conditions which acts both as a planarizing coating and as a hard coat to prevent scratching on subsequent processing. This has been discussed elsewhere [6, 12, 13]. 

For the pharmaceutical and food industries, surface finish is very important to enable effective cleaning and sterilization or sanitization. Equipment should be specified with a polished internal finish, possibly with electropolishing for critical applications, and designed with a minimum of crevices or dead spaces where dirt can collect. Welds must be finished to the same standard as the plates and ground flush with the internal surface and must be pinhole and crevice free. External surface finish may also be important for visual reasons and to enable cleaning down for surface decontamination in clean room locations. 

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