Contamination can crop up in your cleanroom from often overlooked places, it is a difficult job to predict all of these before they have detrimental affects. Lance Ochs and Jennifer Nunes from US-based UltraTape explain
The objective of an environmentally controlled cleanroom is to provide a contamination-free space in which to manufacture and/or test products that cannot tolerate even the smallest particles.
Cleanroom classification ratings range from 1 to 100,000 according to the number and size of particles permitted per volume of air. However, cleanrooms specialising in semiconductor, microelectronics and medical device/pharmaceutical manufacturing are among the most stringent. Such facilities require implementation of specific processes to reduce all sources of contamination. This also means using products within the cleanroom that are designed to meet specific cleanliness standards.
Contamination can occur unexpectedly without any obvious indication of its origin. It can come from the materials and equipment used for manufacturing, the people in the cleanroom and even consumables like tapes or other paper-based products that shed particulates.
Outlined below are five hidden causes of contamination that can compromise a facility's cleanroom standards as well as approaches to minimise these sources' impact.
Perhaps the most well known source, most airborne particles from people migrate out of their cleanroom garments. Using improper cleanroom garments, not following proper gowning protocol, gowning insufficiently for a particular facility class or going too long between changing suits, smocks, other garments or floor mats can all increase particle levels in a cleanroom.
Particles can escape from even the smallest defects in cleanroom garments, such as tears, loose fabric, etc. Consistent use of cleanroom-optimised cuff sealing tape is one simple way to minimise opportunities for contamination.
Often overlooked in terms of contamination potential, traditional labels and tapes are an unexpected source of cleanroom contamination, especially if they are made from paper, have paper cores and/or have adhesives that outgas or leave behind sticky residue. Let's examine these issues one at a time.
Cores: Most tape products are manufactured on cardboard cores, which tend to particulate. To prevent particulation from the core, use tape rolls that have plastic cores with smooth finishes. This is important because plastic burrs and sharp edges could cut through cleanroom gloves or bags, exposing the cleanroom to additional sources of contamination.
Backings and Liners: For other tapes and labels, paper backings or face stocks also cause particulation in the cleanroom. Further, release liners and paper tend to leave behind particulates that could contaminate a cleanroom. Using synthetic materials for these uses eliminates particle generation.
Packaging: Beyond the use of paper materials in tapes and labels, contamination can even be present in the packaging itself (printed bags, electrostatic-discharge bags, and single bagged items). For maximum protection, items should be double-bagged and properly de-bagged inside the facility so that contamination from outside packaging is not brought into the cleanroom.
Adhesives: Another source of contamination related to tapes and labels comes from adhesives that can leave sticky residue that can outgas, leaving an invisible layer of contamination in the cleanroom. Chemical contamination is a major concern in both semiconductor and medical/pharmaceutical manufacturing; therefore, eliminating any sources of outgassing or adhesive residue is vital. Organic contaminants adhering to silicon wafer surfaces, as well as the lenses used in lithographic processes, have become a serious problem for chip, medical device and pharmaceutical manufacturers.
All of the above-cited label- and tape-generated sources of contamination can easily be eliminated by using residue-free and cleanroom-certified tapes, release liners and packages from a certified cleanroom consumable supplier.
Traditional labels and tapes are an unexpected source of cleanroom contamination, especially if they are made from paper
A necessary evil in terms of contamination sources, all equipment to be used in a cleanroom must be inspected and cleaned prior to installation and before each use. While this requirement seems obvious, its importance can't be overemphasised, as examining process tools thoroughly can reveal hidden sources of potential contamination that could otherwise be overlooked.
Monitoring should take place before, during and after use since tools typically generate gases, volatiles and solid airborne particulates in all stages of operation. Consistently evaluating a facility's equipment and having a plan in place to minimise the impact of these known sources of contamination will have major positive impact on the cleanliness of your environment.
Before any raw material or manufacturing product is brought into a cleanroom, it must itself be cleaned thoroughly. Contaminants can lurk on packaging or arise if materials and consumables (e.g., face masks, gloves, mats, etc.) are not handled properly. The extent of cleaning required varies depending upon the class of cleanroom, the destination of the raw material and the possibility of any cross contamination to other processes.
Cleanliness standards for cleanroom maintenance are much higher than for other environments, meaning that household and even industrial cleaning products are not sufficient. In addition to requiring dedicated cleanroom supplies, the cleaning solutions themselves are also purpose-specific (e.g., products that can only be used to clean the floor and not counters). Examples of proper cleaning products include nonparticulating wipes and mops, as well as solutions that minimise off-gassing. Additionally, vacuums must have a classification rating equal to or better than the cleanroom in which they are to be used.
Contamination can derive from a range of hidden sources, from the people occupying and working in a cleanroom, to the process equipment and materials used, even down to consumables such as tapes and labels. By taking proper steps to minimise the impact of these seemingly benign but potentially harmful sources, you can ensure the level of foreign object debris in your cleanroom meets or exceeds the specific rating.
Simple but crucial actions, such as securing particulate-free materials and consistently implementing proper protocols, will help maximise manufacturing yields and shorten your time to market.