The primary source for the contamination control industry is the Institute of Environmental Sciences and Technology (www.iest.com). The IEST Contamination Control collection of recommended practices is the basis for certification of cleanrooms, selection and maintenance of garments used in cleanrooms, consumable supplies used in cleanrooms, cleaning of the cleanrooms, proper operations in cleanrooms, and the procedures and practices performed by personnel working in the cleanrooms.
There are four key factors that contribute to contamination in the cleanroom.
- The furniture and/or equipment
- The product being produced
- The processes performed in the cleanroom
- The people working inside the cleanroom
The people working inside the cleanroom contribute the most contamination; however, the people working inside the cleanroom exercise the most control over the environment of the cleanroom. Selecting the correct garments and performing the recommended garmenting procedures, selection of the appropriate cleanroom consumable items, proper cleaning of the cleanrooms, and the behavior of the personnel while working in the cleanrooms will increase the level of contamination control in the cleanroom.
The recommended gowning configuration for an ISO Class 8 cleanroom is:
- disposable bouffant
- shoecovers (there also are shoecovers that are static dissipative)
I recommend a reusable cleanroom frock with a durable ESD grid pattern. The frocks can be grounded to the personnel with wrist straps or ESD cuffs. Donning of garments usually occurs in the gown room adjacent to the actual cleanroom. Storage of the cleanroom consumable items and frocks is usually on metal racks allowing for easy access to all required items. At the entrance to the gown room are “sticky” mats that remove the gross soil from the operator’s shoes prior to covering with shoecovers.
The gowning protocol for frocks is similar to the donning and doffing of coveralls:
- All hair is completely covered inside a bouffant including the ears, and if required, a beard cover is used to cover all facial hair.
- The shoes are covered with shoecovers.
- It is imperative that the outside surface of the frock does not touch the walls, floor, or other operators.
- The frock is carefully removed from the cleanroom compatible, static dissipative plastic bag by grasping the inside surface of fabric of the frock just below the collar on the back and allowed to unfold.
- The inside of the frock is folded back at the shoulders to protect the outside surface from contamination during donning.
- The right arm is placed inside the right sleeve to the full length of the sleeve.
- The left arm is placed inside the left sleeve to the full length of the sleeve.
- The frock is pulled onto the shoulders and the zipper is pulled to the full length of the zipper and/or all snaps are snapped.
- Some operations will require gloves to be worn over the hands and wrist areas. The glove should overlap the cuff area of the frock.
When doffing the frock, it is imperative that the outside surface does not touch the walls, floor, or other operators. The frocks worn in ISO Class 7 and 8 cleanrooms are often hung on hangers or hooks during the work week. This area should be clean and preferably under a HEPA filter. The HEPA filtered air will remove some particles and fibers during storage. The IEST recommends that the reusable cleanroom frocks used in ISO Class 8 cleanrooms are changed twice a week.
In all cleanroom classifications, the personnel should follow recommended behavior practices inside the cleanroom. Examples of recommended cleanroom behavior are:
- Only trained, authorized personnel are allowed inside the cleanroom.
- Movement inside the cleanroom should be deliberate and slow. Operators should not lean over the product during production. No running is allowed.
- Operators should not engage in any activity that could contaminate the garments or work surfaces. No horseplay is allowed.
- Cleanroom frocks do not have pockets. Operators may not reach inside or under the frock to obtain objects from street clothes.
- No eating, drinking, chewing gum or tobacco, or application of make-up inside the cleanroom.
- Frocks must be changed immediately if they become contaminated during the production process.
- Silicone is detrimental to automotive, optic, defense, aerospace, microelectronics, and semiconductor cleanroom operations. Therefore, many lotions, sprays, and lubricants that contain silicone are banned from use by personnel working in the cleanroom.
Maintenance of the room temperature (i.e. 60–65ºF) of the cleanroom with an adequate HVAC system is imperative to the comfort of those wearing the cleanroom garments. Additionally, control of the relative humidity (i.e. 45–65% RH) of the cleanroom will enhance the control of static electricity. Cleanrooms must be cleaned correctly to maintain the integrity of the cleanroom. Paper or wood products are never allowed inside the cleanroom. All equipment and supplies must be cleaned prior to entrance into the cleanroom. The work surfaces, equipment, and some products are effectively cleaned by wiping with 70% Isopropyl alcohol. Wipers are available pre-saturated with 70% alcohol for ease of operation. The saturated wiper is folded so as to have eight unique surfaces. One wipe of the surface (back to front) is made with one of the eight unique surfaces. The wiper is turned to another unique surface and an overlapping stroke of the same surface (back to front) is made. This continues until all eight unique surfaces have been used. All work surfaces must be cleaned daily or more often as needed. In vertical flow cleanrooms, the majority of the particles are accumulated on the cleanroom floor. Therefore, the cleanroom floor should be mopped daily with an approved cleanroom mop, two bucket mop system, and cleaner. The mopping action is similar to the wiping action of surfaces, moving from the area furthest from the entrance to the cleanroom and using overlapping strokes.
It is just as critical to control the level of contamination in an ISO Class 8 cleanroom as it is to control the level of contamination in an ISO Class 3 cleanroom. In fact, due to the reduced HEPA filtration of the cleanroom and number of air changes per hour, reduced required garment configurations, and limited cleaning requirements, it is more difficult to control contamination and potential excursions in an ISO Class 8 cleanroom than an ISO Class 3 cleanroom.
The recommended practices that I have referenced in this article are:
- IEST-RP-CC003.3 “Garment Considerations for Cleanrooms and Other Controlled Environments”
- IEST-RP-CC004.3 “Wipers for Cleanrooms and Other Controlled Environments”
- IEST-RP-CC005.3 “Gloves and Finger Cots for Cleanrooms and Other Controlled Environments”
- IEST-RP-CC018.4 “Cleanroom Housekeeping”
- IEST-RP-CC026.2 “Cleanroom Operations”
- IEST-RP-CC027.3 “Personnel, Practices and Procedures in Cleanrooms and Other Controlled Environments.