Minienvironments and barrier isolation technology: Another glimpse into the future?

08/01/2001

by Ken Goldstein, Ph.D.

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At the end of my last column (CleanRooms, May, 2001), I concluded by suggesting something that is not politically correct in today's contamination control environment. At some point in the foreseeable future, the column read, we might once again ask the question about the acceptability of cosmetics in cleanrooms—but this time the answer will be in the affirmative.

Allow me to explain.

Cleanrooms are highly artificial environments with strict rules for gowning, production and operator behaviors. People who work in these facilities often complain that their work is challenging, confining, hot, difficult and claustrophobic.

Unfortunately, the stringent controls on people's gowning and behavior are necessary to protect the product and process. But just because contamination control technology forces people to behave in ergonomically strange ways does not imply that this unnatural state of affairs will continue into the future.

In the mid-1980s, a "new" technology appeared that may eventually offer us a graceful way out of forcing people to work in difficult conditions. Called "minienvironments" by the microelectronics people and "barrier/isolation technology" by the pharmaceutically oriented, the new technique started with the premise that the product and process occupied only a very small portion of the cleanroom. Why can't we just design some form of physical barrier to enclose and protect the critical space immediately surrounding the product or process?

As long as this critical area is controlled, we can let the rest of the room drift to some cleanliness level much less stringent than required in the sensitive area. It has taken a while to implement this technology but there have been significant developments in the past few years and we are surely heading in this direction. In the not too distant future, this technology coupled with advances in automation may effectively remove the human operator from the immediate environment surrounding the product.

Let's point out some of the obvious and not so obvious advantages of this approach. Let's also look for the potential landmines buried somewhere along this road to our glorious future.

A lower cleanliness level means fewer HEPA/ULPA filters. And because these filters are expensive, surely this is a good thing for those who must pay for these facilities. Similarly, some facilities designers, constructors and operators may also have trouble in learning to do business in this new environment with a changed contamination control paradigm. As with all new successful technologies, the benefits outweigh the costs but both tend to be unevenly distributed.

With fewer ceiling filters we will need fewer or smaller fans to push less air through the reduced number of filters. Fewer fans create less fan heat inside the cleanroom envelope, which in turn leads to several financial, mechanical and structural benefits. Less fan heat to remove from the cleanroom implies a lower chilled water requirement for our facility. Less chilled water means fewer or smaller chilled water coils, fewer or smaller chilled water pumps and fewer or smaller pipes used to move chilled water to and from our reduced number of air handling units—which, in turn, leads to fewer or smaller chillers.

Because we are pushing less air through our cleanroom with fewer air handling units and fewer coils, our structure required to support these air handling units and related mechanical components can be smaller and lighter. In other words, less steel and concrete. And simpler, fewer and lighter forms for pouring the concrete. This translates into easier design and faster construction because we are building "less" building structure to hold up less facility support hardware. In other words, we not only save on hardware costs but can improve our construction schedule as well.

Shortly after this minienvironment/barrier isolation technology evolved, people estimated that savings on the order of 15 percent to 30 percent of the facility's budget might be achieved. If all this sounds too good to be true, congratulations on your perceptiveness.

The zeroth law—that's the one that comes just before the first law—of economics tells us that "goods are scarce" and warns us that there is no such thing as a free lunch. Alas, the extraordinary claims concerning the ability of this new technology to reduce cleanroom costs were overblown. Specifically, the early financial projections lacked a sound basis because they failed to consider the entire project.

It turns out that some significant "big ticket" items were ignored:

• the costs of the minienvironments themselves;
• the cost of wafer boxes, cassettes, pods, etc. used to house the product and protect it during transport through the now "dirtier" cleanroom;
• the costs of hardware associated with the critical input and output functions at the interface between the tightly controlled interior of the minienvironment and the less controlled cleanroom ambient;
• the costs of the automation required to move materials, sequence the opening and closing of doors into the minienvironments and track the movement of materials through the production process in our cleanroom.

The combined costs of these items exceeded the facility's savings described earlier. In other words, the total project cost of the new cleanrooms using minienvironments and lower airborne cleanliness often turned out to be more expensive than standard cleanrooms that did not use minienvironments but did specify a higher level of airborne cleanliness.

This did not seem a promising beginning and tended to argue against their use. But then a funny thing happened. People stepped back and looked at the big picture. And it turned out that other benefits of minienvironment technology—not yet described—tended to outweigh these increased costs.

In a future column, I will consider these significant benefits and discuss why they may outweigh the increased costs. We will also consider the difficulties that must be addressed by anyone considering the new approach.

Dr. Ken Goldstein is a principal with Cleanroom Consultants Inc. (Scottsdale, AZ) and is a recognized expert in planning and designing of cleanrooms and ultrahigh purity systems. He has been associated with the cleanrooms industry for 20 years, and is a senior member of the IEST. He is active in WG-012 (Cleanroom Design) and WG-028 (Minienvironments).