☙

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
class	0.1 µm	0.2 µm	0.3 µm	0.5 µm	5.0 µm	typical uses
1	35	7.5	3	1	—	integrated circuits
10	350	75	30	10	—	integrated circuits
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
class		0.1 µm		0.2 µm		0.3 µm		0.5 µm		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)
class	0.3 µm	0.5 µm	5 µm	10 µm	25 µm	maximum floor area per sampling position (in square meters)	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

C_n 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
class	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.