Testing surface cleanliness is an essential task in many industries. In addition to visual methods, wetting analysis plays a particularly important role. Systems such as the PCA 200 from DataPhysics Instruments provide users with a tool that enables precise testing of surface cleanliness in quality control.
Cleanliness of surfaces
The cleanliness of surfaces is a decisive quality feature in many industrial applications. Whether in medical technology, automotive engineering or semiconductor production - wherever components are processed or coated, the cleanliness of the surface plays a key role. Residues of dust, oil, grease or cleaning agents can impair the functionality and service life of a product, and can lead to safety and quality issues.
There is no general answer to the question of when a surface is truly clean. Cleanliness always depends on the intended use case. Industrial practice demonstrates a wide range of requirements: In semiconductor production, for instance, even the smallest residue on wafers can prevent coating or cause defects. In medical technology, implants and surgical instruments must be completely clean to prevent infections or immune reactions.
In the automotive industry, car body parts that are to be painted must be free of oil residues and dust particles, as these can impair the adhesion of paints and promote corrosion. In the food industry, production facilities and packaging machines must be free of dirt, grease or microbial residues to ensure food safety.
Cleanliness standards also play a key role in the optical industry. Lenses, mirrors or glass surfaces must be completely free of fingerprints or dust particles, since even the smallest impurities can severely impair the refraction of light. Therefore, the decisive factor is not only the absence of visible soiling, but also compliance with clearly defined technical requirements.
How can the cleanliness of surfaces be analyzed?
Various methods of analysis are available to reliably assess surface cleanliness. The first step is a visual inspection. This can be supported by magnifying glasses, microscopes or camera systems. However, this approach is only sufficient for coarser soiling. Further measuring methods are required for a more precise analysis.
One proven option is to test the wettability of a surface. This involves applying test inks, which are liquids with a defined surface tension. However, this method is very subjective and only allows rough conclusions to be drawn about the wettability of the surface. A contact angle measurement or the determination of the surface energy is more accurate. It is carried out by applying drops of liquid to the surface and determining the angle between the liquid and the substrate. Clean surfaces have characteristic contact angles, whereas impurities alter this value.
In addition to even finer analyses, optical methods such as microscopy or laser scattering methods are used to detect particles and surface structures. Chemical analyses, such as FTIR or X-ray photoelectron spectroscopy (XPS), are used to identify the type and quantity of chemical residues. Finally, gravimetric methods determine the weight of residues obtained by washing or wiping them off the surface.