Why There is No Such Thing as an ISO Class 5 Wipe

By David P. Nobile

The issue of classifying or certifying wipes for use in particular cleanroom environments arises with increasing frequency. While the desire to be able to point to documentation that specifies that a particular wipe be used in a particular clean environment is understandable, it is not currently possible.

The classification of cleanroom cleanliness, begun at the dawn of the existence of cleanrooms in the early 1970’s with Fed-Std-209, is concerned with the cleanliness of the air inside the cleanroom. In this original format, the classification number (e.g. Class 100, Class 1,000 etc.) refers to the number of particles, larger than 0.5 micrometers, per cubic foot of air in the room.

As controlled environments became cleaner over the years, and as the use of cleanrooms extended to other countries worldwide, the scope of specifications for cleanrooms became international, and the nomenclature adapted accordingly. So today we have remnants of several older nomenclatures still sometimes used, and the current ISO standard nomenclature. As a result, Class 100, Class M3.5, and ISO Class 5 all refer to the same level of environment cleanliness.

How then does this relate to suitability or certification of a wipe (or glove, or gown, or face mask, or any other consumable material) for a particular cleanroom environment? The short and factual answer is; it doesn’t.

As technologies evolved in the 1980’s and ‘90’s, cleanrooms became much cleaner in response to the needs of the processes within them (think disc drive and semiconductor). Wipe technology and cleanliness followed to meet the needs. So in the mid 1980’s, when a Class 100 cleanroom was the height of cleanliness, the wipe of choice was a laundered, knife-cut knit polyester wipe - not because such a wipe was determined to be suitable for that environment, but because that was the cleanest wipe available at the time, for use in the cleanest environment at the time. As cleanroom environments evolved to greater levels of cleanliness, wipe technology again followed, with the introduction of sealed edge wipes, material treatments, and no-contact processing.

While tests exist for determining the inherent cleanliness of a specific wipe, and this can be useful in selecting the wipe best suited to the needs of the application and environment, there is no valid, accurate, and accepted test to determine or certify any wipe relative to the cleanliness level (remember - particles per volume of air) of the cleanroom itself.

Thus the determination of what wipe can be used in a particular cleanroom has always been, and remains, dependent on what processes are conducted within the cleanroom environment, what wipe is most appropriate to the application (poses the least contamination risk to the process, absorbs liquids the best, is most durable, etc.), and how the wipe is used, while still fulfilling the needs of the wiping or cleaning activity required.

This is why it is not possible to definitively categorize or certify wipes for a specific class of cleanroom environment.

By. David P. Nobile