Surface cleanliness monitoring
- Particle deposition causes an increase in particle concentration on all surfaces in a cleanroom.
- Activity in combination with unclean surfaces increases the particle deposition rate.
- Unclean surfaces contaminate product in contact.
- The impact of human contamination can be demonstrated with UV light inspection.
- The surface cleanliness with respect to fluorescence particles can be measured with the MOSC, an UV Surface Cleanliness Monitor.
No direct correlation between the cleanroom class and surface cleanliness
In a cleanroom, the air cleanliness is classified for particles from 0,1 to 5 µm. These particles stay airborne and can be removed with the cleanroom installation. Particles larger than 5 µm tend to deposit depending on their size, mass, shape and momentum. Particles get momentum by air currents and turbulence from people and moving objects. Above the 25 µm field data proves that there is no direct correlation between cleanroom class and surface cleanliness which changes by particle deposition.
Particles > 25 µm will not be removed by the ventilation system
Particle deposition monitoring data in ISO 5 to 8 cleanrooms show a dramatic change in the deposition rate of particles > 25 µm. Tests prove these particles are not removed by the ventilation system. They can only be removed by cleaning.
APMON field results: 24/7, valuable data
In many applications cleanroom users and managers are surprised by the measured particle deposition rate levels. These are in most cases much higher than expected. Often particles ≥ 100 µm determine the particle deposition rate level.
The real-time data show the moments of deposition, often when people and/or goods are entering the cleanroom. But also, when work is prepared or when people come together in the cleanroom.
The particle size distribution helps to decide where improvements should be made: cleaning (cleanroom, work benches, tools and equipment), people (number, garments, changing, working methods) and cleanroom installation.
Monitoring the quality of cleaning
By cleaning a surface the concentration of all particles is reduced. In a cleanroom the majority of the particles arises from human contamination and is therefore fluorescent.
The way to select and validate a cleaning process is described in ISO 14644-13:2017.
By measuring the surface cleanliness before and after cleaning the cleaning efficiency of the cleaning activity can be determined.
By comparing the end result with the required cleanliness the effectiveness of the cleaning activity can be determined.
The Monitor for Surface Cleanliness, the MOSC, provides data on surface cleanliness in terms of particle concentration, differential and cumulative particle size distribution, VDI 2083-9.1 and ISO 14644-9 levels or classes and particle area coverage in ppm (µm²/mm²).