From simple slab to an intricate piece of an airflow scheme, the raised cleanroom floor is now more than a support system
By Brian Mazur
Manufacturing flooring never commanded much respect since the dawning of the Industrial Revolution. Even in plants that took great pride in keeping their factory floors gleaming, floors could never compete with the status accorded the more exotic components of high-tech manufacturing.
But that all changed with the advent of the cleanroom. If there's ever been a floor deserving of admiration, it's the modern cleanroom floor.
Eminence didn't come to cleanroom floors easily, however. Today's floors have come a long way since the pioneering days of cleanrooms in the early 1980s. In those early days, even the concept of a raised cleanroom floor was controversial, when detractors argued that raised floors would only raise costs and conceal critical fluid spills.
The slow rise in value
Traditionalists insisted upon good, reliable slab-on-grade cleanroom floors. They believed that a floor was simply a floor and deserved no role in controlling air management—that was the responsibility of ceilings aided by low-wall returns.
That thinking wouldn't change until a few pioneers dared to experiment with raised floors in cleanroom bays—but not in the chases. The value of the raised floor was originally thought to be limited in its practicality as a storage area, handy for keeping process piping and other utility supports out of the way of the production area. However, the cleanroom floor still wasn't looked upon as a vital contributor to the formula for cleanroom air management.
An elevated floor lets the owner accommodate subfloor piping and cabling for utility support without impeding the optimal airflows designed to pass through the floor.
The quest for vertical cleanroom airflows helped elevate the value of the cleanroom floor. The combination of ceiling-driven airflows and low-wall returns was no longer able to achieve laminarity throughout the more expansive cleanrooms being designed. Inevitably, the cleanroom floor had to be designed into the airflow scheme.
Once floors were considered capable of helping manage a cleanroom's airflow characteristics, the struggle to harness the floor's full potential as an airflow control tool began. Crude attempts to adjust airflows using grated floor tiles included jury-rigged foils that were sometimes affixed to individual tiles with nothing more than adhesive tape.
Floor tiles were then designed with built-in adjustable dampers as a more advanced strategy to balance airflows. The concept made sense, but the application of the dampered tiles was often lacking in logic. It was common to design cleanroom floors with a blend of solid and dampered tiles, sprinkled in an arbitrary mix based on the intuitive judgement of owners and installers. Another hitch was that floor tiles were manufactured in asymmetrical patterns. If tiles weren't installed carefully, the appearance of the entire cleanroom could be thrown off.
Balancing the airflows of a cleanroom could take months following completion of construction. Laborious, repetitive testing and tweaking of airflow velocity and laminarity was carried out. Strands of dental floss hanging from a cleanroom's ceiling were often the high-tech tool of the day, used to detect patterns of vertical and horizontal flows throughout a cleanroom. If airflow velocity, cleanliness and other conditions didn't meet specs, this tedious tuning process would be repeated until the cleanroom's performance finally fell within a tolerable range.
Meanwhile, owners lost valuable time to market as they waited impatiently until their new cleanroom was capable of delivering adequate product yields. Cleanroom ramp-up times were, and continue to be, critical in the electronics market, where the producer who's the first to market with a new manufacturing process can capture the high competitive ground.
A better-defined role
Cleanroom floors have earned their enhanced respectability through this trying evolutionary process. Today, few would question the role of the floor as a pivotal piece in the cleanroom performance puzzle. Cleanroom owners understand that the design of the floor is as critical to a modern cleanroom as the design of the facility's filtration and air handling systems—and that floors can potentially make or break a cleanroom's viability.
Reliability and strength of cleanroom floor systems have never been more crucial. Floor heights have increased due to the increasing demands on subfloor space, and this has intensified the focus on adding structural strength to floors, especially in critical seismic areas.
Today's heavier tools require that floors support rolling loads of 2,000 pounds or more generated by the latest 300-mm tools. Off-the-shelf cleanroom understructures are no longer always enough to meet the increasing demands for height and weight being placed on today's floors. Increasingly, owners are custom-engineering cleanroom floors to accommodate subfloor piping and cabling for utility support without impeding the optimal airflows designed to pass through the floor.
New generation cleanroom floor tiles feature micro-scale smoothness to achieve levels of resistance to particles never before imaginable. Technology has also helped dissipate much of the traditional concern about electrostatic buildup in cleanrooms. These tiles contain conductive carbon elements that are randomly, but evenly, distributed throughout the body of the tile.
The tiles are then configured in sandwiched layers of conductive vinyl and adhesive. Once installed, the floor tiles coalesce their tile-to-tile conductivity to comprise a symbiotic system that collects and channels static charges to ground.
Improvements via airflow modeling
In addition to physical improvements in the floor materials, there have also been huge advances in the speed, quality and cost-effectiveness of cleanroom installation approaches. No longer do owners have to endure the ordeal of a cleanroom balancing act that can rob months from their time-to-market targets. No longer do technicians need to tinker with dampered tiles as their primary tools for balancing a room's fickle airflow.
A blend of floor tile styles may be used to achieve a specific airflow scheme.
Thanks to advanced design methods, dampered cleanroom floor tiles are often not necessary. Desired airflow schemes can be achieved with a careful blending of several interchangeable styles of tile that are all less expensive than dampered flooring.
Subflooring support structures such as this adjustable cleanroom floor pedestal may by tailored for the needs of each phase of the project.
An example of how this approach works is a recently completed ISO Class 4 cleanroom for a West Coast microelectronics manufacturer, a project delivered on a design/build basis. The design firm began the project with a computerized airflow model of the cleanroom based on the ideal airflow scheme needed for the type of process and tools intended for the space.
A view of a completed cleanroom corridor with grated tiles dominating the center and a combination of perforated and solid tiles on the periphery.
Airflow modeling has proven to be highly effective and efficient in defining precise layouts for cleanroom floors. It took approximately 10 days to complete the entire model for the 50,000-square-foot cleanroom. Airflow modeling advocates claim that the relatively modest cost of airflow modeling can more than pay for itself, often within a matter of weeks, by reducing construction time and getting cleanrooms ramped up to begin producing revenue more quickly.
The deliverable of the airflow modeling effort is a “map” of the cleanroom floor that removes all of the guesswork for cleanroom owners and installation contractors. In this case, the model was programmed to define the desired airflow scheme using a mix of three tile varieties: grated, perforated and solid. By revealing the exact pattern of tiles needed to achieve the desired airflow, the model's map made the cleanroom floor seem like a jigsaw puzzle that arrives already assembled.
In addition to speed, airflow modeling brought economic value to this project's floor installation. The model had revealed not only where each type of tile belonged on the floor, but also accurately tallied how many tiles of each kind would be needed to complete the job.
This valuable data allowed the owner to escape a cost penalty common to cleanroom jobs—having to stock unneeded floor tiles. Under conventional cleanroom construction approaches, it's customary to estimate the number of floor tiles needed for a job based on traditional estimating methods, and then place a material order exceeding the estimate by an error factor to avoid running short of a particular tile type. Modeling the floor ahead of time saved the owner money by eliminating the need for an “insurance policy” of over-ordering floor tiles.
The constructor worked closely with the flooring manufacturer to arrange special provisions for shipment of flooring materials. Instead of receiving all materials in a single shipment, the manufacturer agreed to break the order into an orderly sequence of four separate shipments that were carefully paced over the course of the six-week project. Each shipment contained an exact “just in time” quantity and blend of tiles and subflooring support structures tailored for the needs of each phase of the project.
Additional adjustments to the balance of cleanroom airflows are often needed once tools are introduced or added to the room. But, once again, the modern cleanroom floor plays an important role in this final tuning process. Adjustments can be made more easily by using the airflow model as a guide, and making some minor moves of interchangeable floor tiles to achieve the final desired flows in the furnished cleanroom.
Cleanroom floors may have only moved up in height a matter of inches since their days of slab on grade. But in terms of earning stature as a vital cleanroom component, floors have come many miles indeed.
Brian Mazur is a specialist in HVAC design and the design/build delivery of cleanroom systems. Mazur works for IDC (Portland, Ore.) and has been involved in a number of cleanroom projects requiring innovative fast-track design and construction approaches. He can be reached at [email protected].