cleanrooms

There have been a variety of national standards for cleanrooms. The most widely referenced is that of the United States, which first appeared in 1963. The first 5 versions (A through D) are roughly as follows. As you can see, the classes are named after the number of particles 0.5 micrometers or more in diameter found in a cubic foot of air.

class maximum number of particles
per cubic foot of air
of diameter greater than or equal to
each indicated size
typical
uses
0.1 µm 0.2 µm 0.3 µm 0.5 µm 5.0 µm
1 35 7.5 3 1 integrated circuits
10 350 75 30 10
100 7502 300 100 miniature ball bearings;
photo labs; medical implants
1000 1000 7  
10000 10000 70 color TV tubes;
hospital operating room
100000 100000 700 ball bearings

Revision E (1992) introduced metric units and new classes based on them.

Federal Standard 209E Airborne Particulate Cleanliness Classes
class maximum number of particles per volume unit
equal to or greater than the specified size
0.1 µmm 0.2 µm 0.3 µm 0.5 µmm 5 µm
SI English m3 ft3 m3 ft3 m3 ft3 m3 ft3 m3 ft3
M 1   350 9.91 75.7 2.14 30.9 0.875 10.0 0.283
M 1.5 1 1240 35.0 265 7.50 106 3.00 35.3 1.00
M 2   3500 99.1 757 21.4 309 8.75 100 2.83
M 2.5 10 12400 350 2650 75.0 1060 30.0 353 10.0
M 3   35000 991 7570 214 3090 87.5 1000 28.3
M 3.5 100 26500 750 10600 300 3530 100
M 4       75700 2140 30900 875 10000 283
M 4.5 1000 35300 1000 247 7.00
M 5 100000 2830 618 17.5
M 5.5 10000 353000 10000 2470 70.0
M 6 1000000 28300 6180 175
M 6.5 100000 3350000 100000 24700 700
M 7 10000000 283000 61800 1750

The British Standard

class maximum number of particles
in each cubic meter
equal to or greater than the specified size
maximum
floor area
per sampling position
(in square meters)
minimum pressure
difference
(in pascals)
0.3 µm 0.5 µm 5 µm 10 µm 25 µm Note 1 Note 2
C 100 35       10 15 10
D 1000 350       10 15 10
E 10,000 3500       10 15 10
F   3500       25 15 10
G 100,000 35,000 200 0   25 15 10
H   35,000 200 0   25 15 10
J   350,000 2000 450 0 25 15 10
K   3,500,000 20,000 4500 500 50 15 10
L     200,000 45,000 5,000 50 10 10
M         50,000 50

10

 

1. The pressure difference required between a classified area and an adjoining unclassified area.

2. The pressure difference required between a classified area and any adjacent area with a lower (i.e., dirtier) classification.

The International Standard

In June 1999 the ISO published a standard.3 The classes are based on the formula

An equation. C sub n equals 10 to the Nth power times the fraction 0.1 over D, the fraction raised to the power 2.08, where

Cn is the maximum permitted number of particles per cubic meter equal to or greater than the specified particle size.  It is rounded to a whole number.

N is the ISO class number, which must be a multiple of 0.1, and be 9 or less.

D is the particle size in micrometers.

Whole number ISO airborne particulate cleanliness classes
class maximum number of particles in each cubic meter
equal to or greater than the specified size
0.1 µm 0.2 µm 0.3 µm 0.5 µm 1 µm 5 µm
ISO 1 10 2        
ISO 2 100 24 10

4

   
ISO 3 1000 237 102 35 8  
ISO 4 10,000 2370 1020 352 83  
ISO 5 100,000 23,700 10,200 3520 832 29
ISO 6 1,000,000 237,000 102,000 35,200 8320 293
ISO 7       352,000 83,200 2930
ISO 8       3,520,000 832,000 29,300
ISO 9       35,200,000 8,320,000 293,000

 

Federal Standard 209
Clean Room and Work Station Requirements, Controlled Environments.

Version history: A (1963), B (1973), C (1987), D (1988) and E (1992).

British Standard 5295:1989

3.
ISO 14644-1. Classification of Air Cleanliness.

Australian Standard AS 1386 (1989)

France. AFNOR X44101 (1972)

Germany: VD I.2083 (1990)

resources

(Intel, who manufacture microprocessors, provide an informative and amusing account of suiting up to work in their cleanrooms at www.intel.com/education/cleanroom/index2.htm) Unfortunately, this link is now dead, and we haven't been able to find its content anywhere on Intel's current site.

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