Hal Smith reflects on some important issues relevant to running a successful cleanroom
There are many twists and turns in the technology of making cleanroom gloves. Latex, one of the two most used polymer bases, in its simplest forms, once formed and cured, will stick to itself unless steps are taken to prevent that. The traditional method was to use a powder, cornstarch and talcum being foremost. Powdered gloves are anathema to cleanrooms. The solution has been to subject the glove to a chlorine source such as bleach or chlorine gas. This deposits a very thin layer of neoprene (chlorinated latex) on the surface and eliminates the sticking problem. One question that is often asked is, "Is there any residual chlorine present or will any chlorine be released during the wearing?" Unless a process is chlorine sensitive, there is no problem. The other common polymer used in cleanroom gloves is polyvinyl chloride (PVC). It has mildly static-dissipative powers. Its main drawback is that it is about 50% plasticizer, usually dioctyl phthalate (DOP), an oil, by volume. For those working with optics, DOP will leave an unacceptable film. PVC and latex are also two of the cheaper polymers to make. Another cheap polymer is polyethylene (PE). It is the least expensive polymer. However, it cannot be easily formed on a mold. Typical PE gloves are welded from flat cutouts. This makes handling small items difficult. PE is also very puncture resistant.
Neoprene and nitrile gloves are chemically modified latexes with better solvent resistance to chlorinated, aliphatic, and aromatic solvents than latex. They are not much more expensive than latex and PVC gloves.
Some other significant polymers are polyurethane - stronger at thinner films but not stretchable, polyvinyl alcohol (PVA) - resistant to strong acids and most solvents, but soluble in water, and Gore-Tex gloves - most expensive, hypoallergenic to those who are allergic to latex proteins and somewhat lessened tactile sensitivity because of their thickness.
These are the factors in choosing cleanroom glove polymers. If there are any safety issues to be resolved, please contact the manufacturer.
Cleanroom janitorial service is challenged today by the need to keep production going 24 hours a day, every day of the year, especially in IC manufacturing. Traditionally, janitorial service was done on down time, usually swing or graveyard shifts when production had ceased or was at a minimum. Mopping, wiping, and other cleaning actions are large muscle activities that create contamination. Traditionally, the cleanroom had a chance to cleanse itself after the janitors left, before the operators came to work.
What new techniques are required to clean effectively without adversely affecting the process yields in the cleanroom? Certainly, slower, more deliberate strokes when wiping a wall section or mopping a floor are required. Much more care must be taken when cleaning - no over saturating the wiper, no flapping the wiper when refolding it to gain a cleaner side, all the things that were tolerated when cleaning a non-operating cleanroom. Technique has become more critical. Slower drying cleaning agents must be used because the use of flammable liquids which evaporate quickly has been curtailed by environmental laws.
Certainly, advantage should be taken of an area where the operators are at lunch or in a meeting. Co-ordination of Operations and janitorial services can utilise these times to refurbish floors without disturbing the operators. The use of in-house vacuums has become widespread. One problem with many cleanrooms is that too much hose is used. The amount of hose needed for anyone area within the cleanroom should be the only length kept in the cleanroom. Often an 80 to 100 ft length is seen sitting in the cleanroom. This amount is a huge particle generator. A shorter length that can be taken room to room and reattached is cleaner.
One of the most often abused disposables in our cleanrooms has been the lowly tacky mat. Whether they are the strip-off type or the washable type, they are often unattended allowing dirt to be tracked into the cleanroom. This is dirt that otherwise would have been adhered to the mat were it capable of retaining it. Further, the selection of strip-off type tacky mats must be made judiciously.
The cleanliness of both kinds of the tacky mats is a discipline problem. Someone must be in charge of either cleaning or replacing the mats to retain cleaning surfaces. The mats also should be positioned so that each person entering the room will take for steps on the mats at a normal walking pace. The adhesion of the sheets on the strip-off type mats is critical. If the adhesion of the top sheet to the foot is greater that its adhesion to the sheet below, the user will feel like he or she were dealing with flypaper instead of a tack mat. Beware, many cheaper grades of tacky mats have this problem.