Particle Analysis for Cleanroom Cleanliness Monitoring

Airborne particles usually originate from human activities, equipment operation, and materials handling in cleanrooms. The size and type of airborne particles are of important consideration. Sub-micron particles, or ultrafine particles, can remain suspended in the air for extended periods, while larger particles settle quickly and pose a higher risk of surface contamination. In particular, particles larger than 5 μm are crucial in assessing contamination risk and surface cleanliness. Effective control measures are necessary to prevent these particles from depositing on vulnerable parts.

ISO 14644 is an international standard that provides guidelines for cleanroom classification, design, operation, and monitoring. According to ISO 14644-1:2015, cleanrooms are classified based on the maximum allowable particle concentration per cubic meter of air, with Class 1 being the strictest and Class 9 the least strict. While monitoring airborne particles is critical, surface cleanliness, as addressed in ISO 14644-9:2012, and particle deposition rates, covered in ISO 14644-3:2019, are also essential. The recent ISO 14644-17:2021 offers practical guidance on particle deposition rate applications in cleanrooms.

Microscopes, such as optical microscopes and scanning electron microscopes (SEM), can be used to count and visualize deposited particles. SEM can provide additional information on particle composition through energy-dispersive X-ray spectroscopy (EDS). SEM- EDS offers several advantages:

High detail and resolution—SEM provides a high level of detail and resolution, allowing for the visualization and characterization of particles at the microscopic level, which are crucial for understanding contamination sources.

Elemental composition identification—The EDS detector allows for determination of the elemental composition of particles. This information can be used to pinpoint the possible sources of contamination and to implement targeted control measures.

Automated quantitative analysis—Integrated software enables accurate counting and sizing of particles. Automated software can be employed to process the SEM-EDS data, providing essential statistical data on particle concentration.

Cleanrooms are pivotal in industries requiring stringent environmental control to ensure product quality and reliability. Monitoring and controlling airborne particle contamination are essential for maintaining surface cleanliness. Other methods for measuring surface cleanliness may struggle with accuracy, secondary contamination, or damage to fragile parts. In contrast, SEM-EDS combined with gravitational samplers provides a high-resolution, detailed approach to particle analysis, making it an effective tool for cleanroom management and quality control. Adhering to ISO protocols and standards helps assess contamination levels and implement effective control measures.

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