The rate of deposition of airborne particles determines the risk of product contamination and demonstrates the operational quality of a cleanroom. The particle deposition rate at a particular location and time depends on the deposition velocity and the concentration of articles. The concentration of particles larger than 10 μm cannot be measured easily; therefore the deposition rate of falling particles should be measured.
Specific particle deposition meters, that measure the particle size distribution and rate of particle deposition, have been available since the end of 2013. In the past, particle deposition measurements were complicated and expensive and were therefore only carried out in specific cleanroom applications or to investigate contamination problems. Nowadays it is easy to carry out particle deposition measurement in various cleanrooms where operator activities are important. The new instruments also make real time particle deposition measurements
possible. Practical experiences with these instruments in various applications are described in this article.
Keywords: cleanroom, cleanroom monitoring, particle deposition, surface cleanliness, operational quality.
The most important reason for using cleanrooms is to prevent particle contamination of vulnerable product
surfaces. Contamination occurs through particle deposition and by contact transfer with less clean surfaces such as gloves, equipment, tooling, packaging and workbenches.
In relation to the control of particles, the ISO 14644 series of standards (Cleanrooms and associated controlled environments) provides cleanliness
classifications of air (Part 1) and surface (Part 9). There are various additional Parts like measurement methods (Part 3) [1, 2].
Particle deposition determines the rate at which the surface cleanliness at a location will change. Up until 2013 particle deposition measurements were laborious or expensive and did not provide information that could help to reduce the risk of particle deposition.
Particle fall out measurement based on the increase of mass or surface coverage by particles have been available for a long time and accepted in the space industry. Particle deposition
in cleanrooms, based on particle size distributions, has been investigated by various research programs [3, 4, 5].
The first easy to use particle deposition meters made use of silicon or glass witness plates [6, 7, 8]. In 2013 the digital holographic measurement  of particle deposition was implemented in a commercial available cleanroom monitoring instrument.
- author: Koos Agricola