Unfiltered: Challenging cleanroom criteria
A good design process challenges pre-existing conceptions of what each user considers a cleanroom requirement
By Norm Toussaint, HDR Architecture
As an end user, you may not always get what you ask for when you engage a team to design a cleanroom for your facility. But this isn’t necessarily a bad thing.
Setting out to achieve a Class 100 (ISO Class 5) or Class 10 (ISO Class 4) cleanroom to meet a particular program statement often results in overdesign. In most cases, overdesign doesn’t just cost more: Following a strict set of protocols dictated by a specified cleanroom classification may actually restrict and discourage researchers’ work.
Learn the facility’s needs
Cleanroom construction for university and government laboratories engaged in interdisciplinary research (e.g., nanotechnology) is on the increase. Designers of these facilities need to understand that cleanroom requirements for research vs. production labs can contrast greatly. Flexible research objectives vs. production yields and focus on one-off product prototypes vs. mass production are examples of these differences. Newer, nontraditional clients may not need to achieve the full ISO standard criteria for their cleanroom to meet their research objectives.
New needs require new solutions. For example, having multiple short- and long-term users of the cleanroom has a direct impact on protocol and training, which can indirectly affect the stability of the cleanroom cleanliness performance. Research processes may not have the same stringent temperature or humidity criteria that semiconductor operations require. Biological and semiconductor processing, which are inherently incompatible, now are often found in the same research cleanroom. And new research facility construction projects may not have the same financial resources as a full production facility.
In good design practice, for cleanrooms as well as other advanced facility types, planners design from the “science out.” This involves detailed discussions of the intended research objectives, methods and operations with users. It is essential for the designer to find out what equipment will be used; what types of research will be conducted; how the facility will be operated; and how materials and products will be moved between processes or labs (see Fig. 1).
Figure 1. Detailed discussions with users result in preliminary conceptual sketches (such as the "cell concept" above). Illustrating these "big picture" concepts helps facilitate the design process.
One approach to planning is the “wall of cards” technique, an interactive process designed to document the planning effort in real time. The process begins with a series of in-depth meetings with the client-meeting with users, scientists, facilities engineers, safety officers, operations staff, and anyone else involved with cleanroom operation or maintenance. The work outcome is literally a wall of cards, each representing an aspect of the evolving design.
Figure 2. Graphic representation of important goals (such as the "module arrangement" above) allows a multidisciplinary group to view the concept and provide real-world feedback.
During this initial phase, the design team defines project goals, needs, identifiable constraints and preliminary concepts. “Goals” are usually big-picture ideas such as the desire to be a world-class research facility. The documented “needs” tend to be very specific: how much area is required for each research component, anticipated equipment, required support functions and similar information. Constraints can include code requirements and specifics of the site such as ambient temperature extremes. Information is made available for everyone involved to view, usually in the form of sketches or written summaries, as soon as it is collected. A highly interactive process and a graphic way of shaping the story of the design, it permits a multidisciplinary group to look at the same thing at the same time and to provide real-world feedback (see Fig. 2).
In cleanroom design projects, contamination-control issues are almost always at the top of the “needs” list. For research facilities, particularly interdisciplinary research facilities, this need is often immediately followed by the need to maintain an open “user” facility, to allow flexible and varied research programs, and to keep construction and operating costs to a minimum. In industrial projects, it is relatively straightforward to set out the design criteria necessary to achieve a given class of cleanroom, since internationally recognized standards for these criteria exist and the design solutions are well established. For cleanrooms where other criteria have equal importance, the design often leads onto uncharted ground. This is when the in-depth planning process is essential.
A building-block approach
When design commenced on the Sandia National Laboratories’ Center for Integrated Nanotechnology (CINT) in Albuquerque, N.M., the planning team used the “wall of cards” process to find out exactly what was needed for each laboratory type, particularly the cleanroom suite. Having state-of-the-art cleanrooms on their site, the laboratory staff understood the operational and cost implications. Rather than focusing on established criteria for contamination control and air management, the design team discussed in detail the types of products the users wished to fabricate, substrate types, material handling methods, and similar issues. The discussions on expected sources of contamination (noise, vibration, EMI, as well as particulates) led the team to identify zones or process “blocks” with similar criteria, grouped to facilitate interaction while at the same time minimizing cross-contamination; these zones evolved into a bay and chase design solution with different air management schemes for different areas inside the cleanroom envelope. The end result is nominally a mix of Class 100 (ISO Class 5) and Class 1000 (ISO Class 6) spaces, some with completely segregated air streams to allow for incompatible process chemistries and some with highly accurate temperature and humidity controls. One bay is set aside as a flexible space to allow for as-yet-unforeseen process demands.
The fact that the final design solution is similar to a “traditional” cleanroom in no way diminishes the value of the discovery process. In many respects, the final design, while not unique, represents the specific needs and constraints voiced by the particular users. For example, one CINT objective is to be a “user facility,” meaning that the cleanroom should be accessible to qualified visiting researchers without the need for overly restrictive protocol or training. Quite uniquely, researchers wanted to be able to work in a “sandbox” environment-side by side on different projects, with a variety of different materials, without contaminating others’ work. The complete air-side separation of process areas was one design solution intended to meet this objective. Another criteria-optimizing the construction budget-was met in part by minimizing the width of processing bays, reducing the area under filter, and using side-wall air returns instead of unidirectional flow through a raised floor.
The approach to developing a cleanroom design solution is no different than the process used to develop the remainder of a complex facility-it needs to respond to specific client needs, and it is the designer’s job to find out exactly what those are. The planning effort employed in the CINT project design illustrates this principle. III
Norm Toussaint is a senior process engineer at HDR Architecture, Inc. He may be reached at email@example.com.