Dean rooms

The ability to achieve different dean room grades is determined largely by the number of air changes relative to the size of the room and the number of personnel and equipment in the room, and the efficiency of the air filters. 

N.Y.U. - New York University, New York, N.Y. (dean>room facility has been dismantled). 

The importance of eliminating these contaminants can be understood by comparing the size of human hair (50 im diameter) and a bacterium ( 5 /xm) to a 1-jlm line such as used in a memory chip. To keep particulates from contacting the coating, all machines are maintained in dean rooms where air is filtered to remove contaminants also, people entering the room wear protective dothing that does not shed particulates into the air. The dean rooms are rated by the number of particles present in the air. A dass 100 rating indicates 100 or fewer particles >0.5 fim are present in 1 ft3 (2.83 x 10-2 m3 ) of air a dass 10,000 would have 10,000 or fewer 0.5 im partides. The exact specification depends on need, but class 100 rooms are in routine use. 

A 48 x 48 active-matrix OLED display was completed on flexible PET substrates. The completed display is shown bent, after wire bonding, in Fig. 15.22. Figure 15.23 shows the display brightness under different data voltages, and Fig. 15.24 demonstrates its flexible functionality during operation. Despite the many noticeable defects on the display, which are expected for displays fabricated outside a dean room, the display was characterized by good drive performance and uniformity. 

If you have studied entropy before, you have probably heard the following example "Over time, a dean room will tend to get dirty. This is entropy at work." Entropy is nature s tendency toward disorder. Abetter definition of entropy incorporates the concept of probability. Entropy S is nature s tendency to create the most probable situation that can occur within a system. For instance, imagine four identical jumping beans that bounce randomly back and forth between two containers. If we label each bean A, B, C, and D respectively, we will find that the most likely situation is to have two beans in each container. The least likely situation is to have all four beans in either of the containers. For example, if we choose the left container, there is only one way for all four beans to be in the left container, but there are 6 possible ways that two beans can be in each container. Two beans in each container is six times more likely than four beans in the left container. Since the two-bean container situation is more likely, it has greater entropy. 

Aerosol concentrations are defined in different ways depending on the application. For example, particle riumber concentrations (particles per unit volume of gas) are used to characterize dean rooms and atmospheric cloud condensation nuclei federal air pollution standards both for the atmosphere and for industrial emissions are usually stated in terms of aerosol mass per unit volume of gas. Effects of particles on viscosity depend on the ratio of the volume of particulate matter per unit volume of gas. For aerosols composed of particles all the same size, it is easy to relate the different methods of characterizing the concentration. For aerosols of mixed sizes, concentration measures are easily related only in certain cases as discussed below. 

Willekc, K and Baron, P. A. (Eds,) (1993) Aerosol Measurement, Van Nostrand Reinhold, New York. This isa valuable state-of-the-art compilation of information on aerosol instrumentation written by specialists in the lield. It includes applications in different fields such as air pollution monitoring, industrial hygiene, commercial production of particles, and dean-room monitoring,... 

Sinks and drains should be prohibited in grade A/ areas used for aseptic manufacture. In other areas air breaks should be fitted between the machine or sink and the drains. Floor drains in lower grade dean rooms should be fitted with traps or water seals to prevent back-flow. 

Unloading freeze dryers contaminates the immediate environment. Therefore, for single-ended freeze dryers, the dean rooms should be decontaminated before a further manufacturing batch is introduced into the area, unless this contains the same organisms, a double door freeze dryers should be sterilized after each cyde unless opened in a dean area... 

Laminar Airflow Air flowing in a single pass in a single direction, through a clean room or dean room area with uniform velocity along parallel flow-lines. Laminar air flow systems should provide a homogeneous air speed of O.dOm/s for vertical flow and 0.45m/s for horizontal flow. 

Guidance values for microbiological monitoring of dean rooms in operation... 

For maintenance the columns and/or top plates must be lifted. For this purpose hydraulic/pneumatic lifting pistons integrated in the column or other methods are applied. If several columns are in use a crane suitable for dean rooms can be used. 

Thorough cleaning and the avoidance of any extraneous debris are essential in any membrane fabrication scheme. After EP, a composite membrane can be soaked in hot water or dilute ammonia to help remove any impurities trapped in the porous support that may be detrimental to the palladium film during high temperature operation [72, 73]. However, traces of impurities from the EP bath such as chlorine, sodium, and carbon, inevitably become incorporated into the metal film. Membrane defects can be a consequence of preparation conditions. Fabrication in a dean-room environment has resulted in increased permselectivity [140]. Porous stainless steel (PSS) must be cleaned and pickled before electrodeposition or else activated for electroless plating. 

Basih, V. and Green, S. 1993. The evolution of software processes based upon measurement in the SEL The dean-room example. University of Maryland and NASA/GSFC. 

Fig. I i<-4. Portable dean room, housmg supcisomc noa/Jc aqueous deaning and erdlcatka i equipment (Photo ooutte. y ol United Space Alltaace/WIL iliC,)...

For some manufacturing facilities, an interior room that is conditioned by a unitary air conditioner with 2-in- (5-cm-) thick throwaway filters might be called a dean room that is, it is clean relative to the atmosphere of the surrounding plant. Generally, however, clean rooms are spaces associated with the microchip, laser optics, medical, and other industries where airborne particles as small as 0.5 pm and less are removed. One micrometer equals one-millionth of a meter, or 0.000039 in (0.000001 m). 

Sn, Sb)02/mica Sn(0,F)2/mica Electrically conductive Conductive flooring, antistatic packaging materials, light colored primed plastic surfaces which can be electrostatically painted in further coating process, light colored conducting surfaces in dean room conditions for dust reduction... 

A new passivation process was also developed that eliminates the need for a surface control gate on the detector and greatly reduces latent image effects. Other detector process improvements, sudi as improved statistical process control and moviog the fabrication line to a Class 10 dean room, have improved detector operability. 

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