1. Modern Devices: Chapter 5 – Cleanrooms,
Modern Devices: The Simple Physics of Sophisticated Technology
Copyright © John Wiley and Sons, Inc.
Chapter 5 – Cleanrooms,
an enabling technology
Modern Devices:
The Simple Physics of Sophisticated Technology by
Charles L. Joseph and Santiago Bernal

2. Modern Devices: The Simple Physics of Sophisticated Technology
Copyright © John Wiley and Sons, Inc.
Fig. 5.1 A typical floor plan for a cleanroom, showing the multiple decontamination stages used prior to entering the cleanroom.
A floor plan reveals the multistage steps used to minimize contaminants being brought into the cleanroom. The first step is to remove shoe particulates, using treated fiber mats and an electric vacuuming shoe brush. Personnel enter the gowning room where they cover themselves with garments, boots, gloves, and hoods. Then, the individual walks across a sticky mat into an airlock room called the air shower, consisting of a number of jet nozzles. The main room is overpressurized so that any contaminants that have escaped these mitigation techniques will tend to flow away.
There are three principle processes to maintain a pristine environment: 1. prevent external contaminants being introduced via personnel and equipment entering the room, 2. extensive air filtration plus a laminar flow of air, and 3. special cleaning procedures.
Cleanroom
Gowning Area
Air Shower
Small Equipment
Air-Locked
Pass-Through Box
Main
Treated
Fiber Mats
Electric
Shoe Brush
Sticky Mat
Cleanroom Design

3. Protecting Equipment from Inherently Dirty Humans
Modern Devices: The Simple Physics of Sophisticated Technology
Copyright © John Wiley and Sons, Inc.
Fig. 5.2 An individual completely garmented and an air shower that is used prior to entering a cleanroom.
Cleanroom Design
Protecting Equipment from Inherently Dirty Humans
A complete covering is referred to colloquially as a bunny suit. These garments are tightly woven fabrics that retain the numerous particles per minute shed by humans. The fabrics also do not hold static charge that attracts particulates. Note: troublesome areas such as footwear and headwear may have two layers of covering and personnel are required to dress in a particular order. The air shower then becomes very effective at removing dust.

4. Turbulent vs. Laminar Flows
Fig. 5.3 Two approaches to cleanroom design. Left: high turbulent flow that kicks up loose particles and forces these out the exit vents. Right: laminar flow, the more common type of cleanroom, moves and residual loose particles to the floor and traps these there until removed by routine cleaning procedures.
Turbulent vs. Laminar Flows
A pristine environment requires extensive air filtration, using one of two strategies. The vast majority of cleanrooms incorporate laminar airflow, designed to drive any residual particulates towards the floor and hold those there until the surface is cleaned. A key component is the use of high efficiency particulate air (HEPA) filters. Air turbulence tends to knock off particulates on surfaces. A single 0.5 m particle can destroy an integrated circuit. In recent years, a new ultra low particulate air (ULPA) filter has been introduced. ULPA were developed specifically for cleanrooms where the generation of large amounts contaminants were unavoidable. In these few cases, the airflow is deliberately made turbulent, stirring up surface particulates and seeping these out of the room. Laminar flows, however, generally provide superior air quality and ULPA filters have begun to be used in conjunction with HEPA filters to provide the best performance.
Modern Devices: The Simple Physics of Sophisticated Technology
Copyright © John Wiley and Sons, Inc.

5. Maximum Number of Particles / m3
Modern Devices: The Simple Physics of Sophisticated Technology
Copyright © John Wiley and Sons, Inc.
Historically, cleanrooms were classified according to the number of particulates per cubic foot, commonly Class 100, 1,000, and 10,000. This obsolete, but still used, designation has been replaced by an international standard, reflecting the modern requirements. ISO standards place limits on the numerical counts per cubic meter for each range in particle size.
Cleanroom Standards
Table 5.1 ISO Cleanroom Standards
Class
Maximum Number of Particles / m3
FED STD 209E Equivalent
 0.1 m
 0.2 m
 0.3 m
 0.5 m
 1 m
 5 m
ISO 2
100 24 10 4
ISO 3
1,000
237
102 35 8
Class 1
ISO 4
10,000
2,370
1,020
352 83
Class 10
ISO 5
100,000
23,700
10,200
3,520
832 29
Class 100
ISO 6
1,000,000
237,000
102,000
35,200
8,320
293
Class 1,000
ISO 7
352,000
83,200
2,930
Class 10,000