No ‘absolutes’ for cleanliness in ISO 5 design

A cleanroom should be planned as an environmental control system for best results

By Thomas E. Hansz, Facility Planning & Resources, Inc.

Not too long ago, I sat down with a prominent researcher in advanced materials to discuss his upcoming cleanroom requirements. He was currently working in an ISO 6 or Class 1000 laboratory. I asked him to describe the critical nature of the contamination control required for his research. His response was, “I need Class 100.” All right, but what about the type, size, and concentration of “killer particles” that would negatively affect his work? Again, his response was, “I need Class 100.” It took quite a while to convince him that cleanroom design does not begin with designing to the next higher level of cleanliness, but that understanding the contamination characteristics detrimental to the process leads to determining the appropriate level of cleanroom classification. We finally concluded with a sound understanding of his needs.

This example is not uncommon. When one equates cleanroom quality with cleanroom classification levels, it can become a very expensive trap. One of the main objectives of a cleanroom design should be to establish and maintain the appropriate level of contamination control. This will be a recurring theme in both this article and the next part on ISO 7 cleanrooms.

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Like art, the condition of “cleanliness” depends on the point of view of the cleanroom user. So it is important to bear in mind that there are no absolutes for cleanliness. Think of a cleanroom as an environmental control system (part fixed facility and part continuous process) that, once in use, requires regular monitoring and strict adherence to defined operational protocols for the life of the facility.

Therefore, unlike other facility types, there are three critical aspects required in establishing a successfully functioning cleanroom:

  1. Defining the cleanroom program (identifying contaminants; determining size and concentrations; establishing contamination control criteria; identifying process services; and defining facility systems)
  2. Developing design and construction (proceeding from a thoroughly developed definition; coordinating process systems with facility systems; developing operational protocols; and coordinating intent with realization)
  3. Implementing/operating the cleanroom (finalizing operational protocols; developing an appropriate cleaning and maintenance program; and instituting effective management over cleanroom operations)

Who needs an ISO 5 cleanroom?

So, how does all this apply to an ISO 5 cleanroom and who needs one? Generally, the aerospace/defense, microelectronics, and semiconductor industries have been the primary users of ISO 5 cleanrooms. This is by and large due to the scale of their work with silicon-based wafer fabrication. During the 1970s and into the 1980s, protecting silicon-based products during the fabrication process relied primarily on reducing the number of 0.5-


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