Design & Construction
by Richard V. Pavlotsky Ph.D., P.E.
It's imperative that we emphasize the need for all parties involved in a cleanroom design/build project to thoroughly comprehend the affect that each design feature will have on the overall cost
This article is the second in a series of Design & Construction columns.
According to a recent report issued by Gartner Dataquest, the cleanroom industry experienced its worst decline in history during 2001. In this report, Klaus Rinnen, chief analyst and director of Gartner Dataquest's semiconductor manufacturing group stated, “As demand weakened and capacity utilization decreased, financial considerations became foremost in everyone's mind. Thus capital expenditures took a back seat to everyday production needs.”
The good news is that cleanroom design and construction is at least a $40 billion industry even at its lowest. Case in point, worldwide semiconductor capital spending totaled some $44.4 billion in 2001. Cleanrooms are in demand and will continue to be, in one shape or another. This year shows promise, especially within the relatively new and exciting fields of genetic engineering and cell harvesting as well as the manufacturer of ultra-fine chemicals and thin films.
Finding the optimal and most economical solution for cleanroom air changes is a fundamental goal and will help eliminate “design overkill.” Use this chart as a starting point and assess your cleanroom air change needs.
While recent economic downturns and market spirals cannot stop the growth in high-tech industries and the corresponding upturn in demand for cleanrooms, there is a critical need for us all to pay close attention to the economics of cleanroom design/build. Further, a solid understanding of the user's manufacturing process requirements is essential to economically efficient design and construction.
The challenge today is to satisfy the demands of “ever-purer” cleanrooms, while controlling the escalating costs of construction and facility operation. The recommendation to meet this challenge is a key-value “holistic” approach to the evaluation of different design criteria and concept economics.
Allow me to elaborate upon and, more importantly, validate this approach.
Our operating premise should be as follows: The most valuable time for quality design is in the planning of the project. As consistency is critical to success, it shall remain the basis of our approach. Extremely sophisticated systems are built to ensure the purity of manufacturing processes in cleanrooms. Any combination of design criteria variables will produce a cleanroom of a specific quality. These same variables are what determine the construction cost of a cleanroom. This cost can vary from $180 per square foot to $1,800 per square foota vast range.
Design overkill is a waste of money
The Eskimo have hundreds of words for snow, while our industry has only one word for cleanroom. Far too often clients pay for design overkill; unnecessarily spending money for a cleanroom that exceeds their process needs.
Why is this?
The design and construction of cleanroom facilities are typically performed under very tight time constraints that limit opportunities for options, changes and other in-progress improvements. Thus, “cookie-cutter repeats” are encouraged in an attempt to avoid potential risks of new design approaches. These standardized cleanroom recipes may make the designer's task easier, but will not necessarily improve the economics of the project or lower the cost of construction.
The requirements of each and every cleanroom are different in subtle ways, which makes it inefficient, if not impossible, to address all cases with the same design/build template.
Therefore, if the client does not have confidence in a particular design template, the engineer is often asked to design a cleanroom with more stringent specifications than are required in hopes that if something goes wrong, they will at least get what they need.
But, it is inevitable when a detailed assessment of real needs has not been developed and agreed upon by all parties involved. And so, the cost of the cleanroom grows in reverse proportion to the mutual trust between the design and construction professionals, cleanroom developers and client.
Take charge of the project
The optimum arrangement of the tools and utilities connections to the production equipment, location of service aisles, chases, corridors, mechanical equipment rooms and utilities rooms plays a major part in cleanroom economy decisions. At the onset of the project, as part of the Key Planning Session (see CleanRooms, January, 2002, pg.12) these factors should be considered and simultaneously evaluated by the team of architects, engineers and contractors with the client as an equal partner. This will ensure a thorough and shared understanding of the user's manufacturing process goals and requirements, which is the key to an economically successful design/build project.
Put simply, the selection of the right design features for the type of cleanroom a client requires has a monumental impact on the final cost of the venture. There is no “paint by numbers” solution. Client, engineer, architect and contractor must understand the cost impact of the selected combination of factors/variables that are not necessarily regulated ISO Standars and need be determined by evaluating the specifics of each process and manufacturing requirements (see List 1). The team must then work together to finalize the goals, needs and expectations before any design activity begins.
Simple economy dictates that we shall improve both the quality of our relations and the quality of our designs just to survive; we shall eliminate waste and design overkill to be competitive in the world today and in the future.
Richard V. Pavlotsky is director of advanced technology for San Jose, CA-based ENCOMPASS Facility Services. He can be contacted at [email protected].
List 1. Factors/variables that influence cleanroom construction cost
- Air changes per hour from 20 to 640 air changes per hour.
- Unidirectional or turbulent airflow, vertical or horizontal, air jets. Minienvironments.
- Air Filtration from 99.99% HEPA filter efficiency at particles 0.5 micron in size to 99.999995% ULPA Filter efficiency at particles 0.12 micron in size, where a micron is one millionth of one meter.
- Air handlers. Make-up AHUs, recirculating AHUs, fan-filters.
- Air pressure differential from 0.3 to 0.005 in.w.g. Active or passive differential pressure control.
- Temperature control: from ±2.0 deg. F. to ±0.15 deg. F. Rate of deviation from the set point.
- Humidity control from ±10 %RH to ±1.0 %RH (Dew point variation from ± 5.0 deg. F. to ± 0.2 deg. F.). Rate of deviation from the set point.
- Exhaust systems: acid exhaust, ammonia exhaust, solvents and VOC exhaust, toxic exhaust, heat exhaust, general exhaust. Sizing, materials of construction and abatement equipment.
- Vibration limits between 600 and 150 micro-inches per second or less, peak to peak, 0-15 Hz. Noise control criteria from 65 NC to 40 NC.
- Magnetic and electromagnetic flux criteria. Process specific requirements.
- Electrostatic charge of air and surfaces: from 1.0 mJ per sq. meter to less than 0.1 mJ per sq. meter.
- Energy consumption: a Class 10 cleanroom may consume between 4,000,000 BTU/sq. ft/year and 500,000 BTU/year/year. (Operating 24hr./day, 365 days.)
- Form, function and site-specific requirements.
- Particulate. From particles per cubic foot, 0.5µ in size < 1; 0.12µ in size < 35 to particles per cubic foot, 0.5µ in size < 10,000; 0.12µ in size <345,000.
- Process piping and utilities. Sizing, materials of construction and equipment.