Cleanroom requirements in the optical industry

The concentration of airborne particles in cleanrooms must be kept as low as possible. Air purity is usually monitored very closely. However, people are the greatest source of risk for particle contamination. Machines and assets in a cleanroom may also contaminate optical assemblies, for example.

Working in a cleanroom – a standard for the optical industry

The cleanroom and cleanliness suitability of all types of equipment will therefore become increasingly important in optics and many other industries in the coming years. The requirements regarding cleaning, assembly, testing, packaging and transport of optical assemblies and components under clean conditions will become standard for many manufacturers in the optical industry.

The main force in this development is microelectronics, as the development of optical measurement technology and peripheral optical devices is growing proportionally with it and is also becoming increasingly important for other fields of application.

In order to guarantee the required purity conditions, special requirements must be fulfilled regarding

• Air purity class (DIN EN ISO 14644-1)
• Maschines, installations and consumables
• Employees' knowledge
• Work clothes

The mentioned requirements entail different fields of activity, both in classical and in micro-optics. It is important to include the entire process chain in the considerations.

Classic Optics

There are few manufacturing processes in which so much process-related particles occur as in the polishing of optics. It is less about the number of particles per se, but much more about the number and size of foreign particles that do not originate from the polishing agent. This is due to the fact that these foreign particles can cause micro-scratches on optical surfaces.

This results in a further difficulty. A high level of purity is achieved by supplying clean air using a filter system and the associated high air exchange rate (bringing clean air to the process and removing contaminated air from the process). However, this leads to fluctuations in the air temperature, which are an obstacle to precision processing of optical surfaces. Processing in the Λ/4 range is therefore almost impossible to realise. The challenge now is to overcome this contradiction with a harmonised technical solution.

Microoptics

In micro-optics, for example in the manufacture and assembly of cameras in mobile devices, the classic particle problems occur on the one side, whereby foreign particles can enter the process and scratch surfaces. On the other side, it should be ensured that no contamination reaches the optical functional surfaces during the assembly process. It is therefore logical that the entire assembly process should be tested for cleanroom suitability. That means, among other things, that the components must be delivered clean or that foreign particles must be removed by appropriate cleaning before the material is processed.

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