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Fundamental of Cleanroom

What is cleanroom?


According to International Organization for Standarization (ISO) standard 14644-1, cleanroom is defined as:

 

"A room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation and retention of particles inside the room in which other relevant parameters, e.g. temperature, humidity, and pressure, are controlled as necessary." 

 

Source of contamination


The source of the contamination is categorized as external sources and internal sources.

 

1. External Sources


For any given space, there exists the external influence of gross atmospheric contamination. External contamination is brought in primarily through the air conditioning system through makeup air. Also, external contamination can filtrate through building doors, window, cracks, and wall penetrations for pipes, cables and ducts. The external contamination is controlled primarily by

 

-          High efficiency filtration

-          Space pressurization and

-          Sealing of space penetrations

 

2. Internal Sources


The potentially largest source is from people in the clean room, plus shedding of surfaces, process equipment and the process itself. People in the workspace generate particles in the form of skin flakes, lint, cosmetics, and respiratory emissions. Industry generates particles from combustion processes, chemical vapors, soldering fumes, and cleaning agents. Other sources of internal contamination are generated through the activity in combustion, chemical and manufacturing processes.

 

The size of these particles ranges from 0.001 to several hundred microns. Particle larger than 5 microns tends to settle quickly unless air blown. The greatest concern is that the actual particle deposits on the product.

 

The need for cleanroom


Cleanrooms are needed because people, production machinery and the building structure generate contamination. They produce millions of particles, and conventional building materials can easily break up. A cleanroom controls this dispersion and allows manufacturing to be carried out in a clean environment.

 

The uses of cleanrooms are diverse; shown in the table below is a selection of products that are now being made in cleanrooms.

 

Industry

Product

Electronics

Computers, TV-tubes, flat screens

Semiconductor

Production of integrated circuits

Micromechanics

Gyroscopes, compact disc players, bearings

Optics

Lenses, photographic film, laser equipment

Biotechnology

Antibiotic production, genetic engineering

Pharmacy

Sterile pharmaceuticals, sterile disposables

Medical Devices

Heart Valves, cardiac by-pass systems

Food and Drink

Brewery production, unsterilized food and drink

Aerospace

Manufacturing and assembling of aerospace electronics

 

However, in general daily life, cleanrooms are typically used in manufacturing, packaging, and research facilities associated with semiconductor, pharmaceutical, food and drink and aerospace.

 

Types of Cleanrooms


Cleanrooms, in general, have two major types that are differentiated by their method of ventilation.

 

1. Unidirectional flow cleanroom


This type of cleanrooms was originally known as "laminar flow" cleanroom. It uses very much more air than the other type and gives superior cleanliness inside the room.

 

2. Non-directional flow cleanroom


This can be also known as "Turbulently ventilated" cleanroom. Airflow characteristic inside the room is much more turbulent and moves in random motion more than the unidirectional flow cleanroom.

 

Application Guidelines


The industry differentiates between the cleanliness of rooms by referring to class numbers. Federal Standard 209E, Airborne Particulate Cleanliness Classes in Clean Rooms and Clean Zones, September 11, 1992, categorize cleanrooms in six general classes, depending of the particle count (particles per cubic foot) and size in micron (mm). The table below describes classification of cleanrooms based on particle counted.

 

Cleanroom Class

Class Limits not to exceed particles per cu.ft for particle size between

 

0.1 mm

0.2 mm

0.3 mm

0.5 mm

5.0 mm

1

35.0

7.50

3.0

1.0

--

10

350

75.0

30.0

10.0

--

100

--

750

300

100

--

1000

--

--

--

1000

7.0

10000

--

--

--

10000

70.0

100000

--

--

--

100000

700

 

Interpreting the table above, a class 100000 cleanroom limits the concentration of airborne particles equal to or grater than 0.5mm to 100000 particles in cubic foot of air.

 

Currently, Federal Standard 209E cleanroom ratings are replaced by ISO 14644 which is based on metric measurements where as FED STD 209E is based on imperial measurements. The classes, according to ISO 14644-1 are in terms of class level 3, 4, 5 of airborne particulate cleanliness. A class 5 means that less than 3520 particles (0,5mm in size) are presented per cubic meter, which equals 100 particles per cubic foot. The higher the class number, the more are the particles present.

 

FED STD 209E

ISO 14644-1

1

3

10

4

100

5

1000

6

10000

7

100000

8

 

Important Regulatory and Guideline Information


  1. The Institute of Environmental Sciences (IES): Consideration for Clean room Design, IES-RP-CC012.1
  2. Testing Clean Rooms (IES-RP-CC-006-84-T), outlines performance tests procedures
  3. IES-RP-CC-006: Testing Clean rooms
  4. IES-RP-CC007: Testing ULPA Filters
  5. Fed Std. 209E: Prepared by the Institute for Environmental Sciences, under the authority of the General Services Administration of the Federal Government offers specific guidelines terms of non-viable particulate levels
  6. Chapter 32 of ASHRAE Guide and data book on Systems and Application, 1997 provides information of Clean Spaces
  7. NEBB, Procedural Standards for Certified Testing of Clean rooms

 

Reference:

 

  1. Cleanroom Technology, W. Whyte
  2. A Basic Design Guide for Clean Room Application, PHD course M143