Cleanroom in the industry

The roots of cleanroom technology lie in nuclear technology. The semiconductor industry also recognized early on the need for production in a very clean environment. But above all, increasing miniaturization (layer thicknesses, structure widths, functional dimensions) and the constantly growing demands for precision, are reasons for other industries to control the cleanliness of the working environment. Only production in a clean working environment makes it possible to carry out and control cleanliness-critical processes. This is why cleanroom technology is being used in more and more industrial sectors, for example in the electronics and automotive industries.

In cleanroom technology, particular attention must be paid to the use of suitable operating equipment. All components of the equipment used in the cleanroom have a direct influence on the product to be produced. Thus, the cleanroom suitability of the equipment used is a decisive property for ensuring the required quality.

In a cleanroom, various measures (ventilation technology, employee clothing, selection of materials and equipment, etc.) are used to control airborne particles so that a defined limit is not exceeded. This serves to fulfill various protection goals. Depending on the area of application, this involves the protection of products or processes (product protection) or the protection of people or the environment (personnel protection).

The established standard for defining a cleanroom is the size and quantity of particles occurring according to DIN EN ISO 14644-1. The basis for this was the US Federal Standard 209E, which was used internationally in industry for a long time but has officially no longer been valid since November 2001. The following tables show the maximum number of particles permitted in the individual cleanroom classes according to DIN EN ISO 16441-1 (first table in the unit particles/cft, the second table in the unit particles/m³).

Comparison of Class Thresholds Between DIN EN ISO 14644-1 and US Federal Standard 209E:

ISO-class	Maximum allowable concentrations (particulates/cft) equal to or greater than the considered quantities shown below (rounded values)						US Federal Standard 209E
	≥ 0.1 µm	≥ 0.2 µmv	≥ 0.3 µm	≥ 0.5 µm	≥ 1.0 µm	≥ 5.0 µm
1	0.3	*	*	*	*	*	-
2	3	1	*	*	*	*	-
3	28	7	3	1	*	*	1
4	283	67	29	10	2	*	10
5	2,832	671	289	100	24	1	100
6	28,321	6,712	2,889	997	236	8	1,000
7	*	*	*	9,967	2,356	83	10,000
8	*	*	*	99,674	23,559	830	100,000
9	*	*	*	996,744	235,594	8,298	-

*Values are not representative for classification

Comparison of Class Thresholds Between DIN EN ISO 14644-1 and US Federal Standard 209E:

ISO-class	Maximum permissible concentrations (particles/m³) equal to or greater than the quantities considered, which are shown below						US Federal Standard 209E
	≥ 0.1 µm	≥ 0.2 µmv	≥ 0.3 µm	≥ 0.5 µm	≥ 1.0 µm	≥ 5.0 µm
1	10	*	*	*	*	*	-
2	100	24	10	*	*	*	-
3	1,000	237	102	35	*	*	1
4	10,000	2,370	1,020	352	83	*	10
5	100,000	23,700	10,200	3,520	832	*	100
6	1,000,000	237,000	102,000	35,200	8,320	293	1,000
7	*	*	*	352,000	83,200	2,930	10,000
8	*	*	*	3,520,000	832,000	29,300	100,000
9	*	*	*	35,200,000	8,320,000	293,000	-

*Values are not representative for classification

All products are tested for cleanroom suitability in accordance with the requirements of DIN EN ISO 14644-14 (formerly VDI 2083 Sheet 9.1). Such a measurement must take place in a cleanroom (according to ISO 14644-1) that is at least one class better than the target suitability for which the product is to be certified. Exception is an intended suitability for class 1.

In order not to introduce any interfering particles when the test object is introduced into the clean test environment, it is previously subjected to wipe cleaning with an ultrapure water-isopropanol mixture and blown on with ultra-pure compressed air. In addition, the product runs in the clean room 24 hours before the certification measurement. This ensures that previous impurities are removed, the tribologically stressed elements (frictional stress) have run in and the following measurement is not influenced by this.

Now the test object is analyzed with the aid of an optical particle counter (OPS) to identify possible particle sources. A particle probe is attached to these locations during the measurement process. In most cases, these particle sources occur at locations subject to tribological stress during operation. During the subsequent qualification measurement, which lasts 100 minutes, the particle emission is determined for each measuring point. A statistical evaluation, as described in the ISO 14644-1 standard, is used to define the minimum air purity class in which the test object can be used.

Scale comparison of potentially occurring airborne particles:

	Ions	Molecules	Macromolecules	Microparticles	Macroparticles
Visible with	Scanning electron microscope (SEM)		Microscope		Naked eye
Examples	Atomic radius Metal ions	Sugar Herbicides	Soot Viruses Tobacco smokeh	Bacteria Red blood cells	Pollen Sand Human hair Mist
Size [µm (LOG)]	0.001	0.01	0.1-1.0	10	100-1,000