Real-time surface particulate cleanliness characterization

It is well established that particulate contamination plays a role in degrading system performance, thus surface cleanliness measurements are critical from the perspective of contamination risk assessment and requirement verification. The dimension of particulate contaminants of interest in the aerospace industry ranges from five to above 1000 microns per IEST-STD-CC-1246 or MIL-STD-1246, thus the characterization of surface cleanliness requires measurements of particles using optical microscopes. Direct measurements from surfaces of interest are highly desirable, however it may not be feasible when particulate contaminants are not easily differentiated from surfaces due to a complicated background. For surfaces not feasible for direct measurements, indirect measurements via sampling have been implemented. The tapelift method per ASTM E1216-21 has been used in the aerospace industry, however tape surfaces have been found challenging for particle counting using automated imaging analysis. This study examines a commercially available surface particle counter that enables real-time characterization for surfaces cleanliness using alternative sampling substrates. The particle counts per size bins and the percent area coverage (PAC) measurements per IEST-STD-CC-1246E are compared between the real-time surface particle counter, PartSens+ 4.0, and a high-quality optical microscope. The validation results show that PartSens+ 4.0 provides reasonable estimates of PAC values and particle size distribution in a matter of seconds when recommended settings are implemented.