Surface Roughness Testers

Surface roughness is measured by scanning a probe or stylus across a sample surface and recording height variations. AFM systems use a cantilever tip that moves across the surface in tapping, contact, or liquid imaging mode, generating a topographic map from which roughness parameters like Ra and Rz are calculated using specialized software.

The 16% rule, defined in ASME Y14.36 and related standards, states that a surface is acceptable if no more than 16% of measured roughness values exceed the specified tolerance. This statistical approach accounts for natural measurement variation while ensuring the majority of the surface meets the required roughness specification.

Standard coordinate measuring machines (CMMs) are primarily designed for dimensional accuracy and typically lack the resolution to capture fine surface roughness. However, some CMMs can be equipped with specialized roughness probes or contact stylus attachments, though dedicated instruments like AFMs or profilometers provide far greater precision for roughness analysis.

AFM-based systems can achieve sub-angstrom lateral resolution and vertical resolution as fine as 0.2 nm, far surpassing optical or stylus-based methods. This makes them suitable for characterizing nanoscale surface features on semiconductors, thin films, polymers, and biological samples where extremely fine detail matters.

Typical AFM systems offer scan ranges from 9 micrometers by 9 micrometers up to 90 micrometers by 90 micrometers, depending on the scanner configuration. Smaller scan ranges provide atomic-scale resolution for detailed feature analysis, while larger ranges allow broader surface area coverage for general roughness assessment.

Yes, many AFM systems support liquid imaging modes, such as MAC Mode, which use magnetic actuation to gently scan soft or biological samples submerged in fluid. This capability is essential for studying live cells, biomolecules, and electrochemical interfaces without disturbing delicate surface structures.