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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.

Basics of clean room technology

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

Test procedure for checking cleanroom suitability

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

Suitable products for use in the cleanroom

The components certified for use in cleanrooms include various products from the broad portfolio of vacuum technology. This means that a wide range of different process requirements can be met. It is clear from the test results that most of the products can be used in very clean working environments (up to Class 1 according to DIN EN ISO 14644-1) without any additional measures.

When selecting a piece of equipment, it is essential to look closely at its actual location in the cleanroom and thus interpret the requirements correctly. For example, in a clean area with laminar air flow, not all locations need to meet the targeted ISO class. Due to the straight vertical flow, particle emission sources spatially below or at some distance from the workpiece usually have little influence on it.

Certification Fraunhofer TESTED DEVICE® / Cleanroom Suitable Materials (CSM®)

The Clean and Micro Production department of the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) in Stuttgart independently tests equipment and materials for their cleanliness and cleanroom suitability. These tests are carried out in a clean room that is 10 times cleaner than Class 1 according to DIN EN ISO 14644-1. As a result, the equipment and / or materials are certified with a TESTED DEVICE® or CSM® test mark. In this work, the institute draws on over 30 years of experience and know-how in the field of cleanliness and cleanroom suitability.

Cleanroom Certification – Fraunhofer IPA

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