Characterisation of Areal Surface Texture by Richard Leach

Author:Richard Leach
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

8.1 Surface Metrology and the Characterisation of Individual Areal Features

Surface metrology is conventionally concerned with the characterisation of surface finish. Once form has been removed from an areal topography dataset, the remaining information is surface texture, which is described over the entire scale-limited surface (see Chap. 2). For this reason, the recent ISO 25178 part 2 (2012) standard stresses the concept of field parameters, i.e. parameters that define surface texture over the entire scale-limited surface (Chap. 2, Blateyron 2006; Jiang et al. 2007). ISO 25178 part 2 also refers to feature parameters, which are computed by aggregating attributes (area, perimeter, depth, etc.) originally extracted from individual topographic features (Maxwellian hills and dales) (Chap. 3, Scott 2004). However, feature parameters are still representative of topographic properties which pertain to the entire surface.

In spite of the conventional approach, there is a strong and growing interest in the characterisation of individual areal surface features considered as standalone entities, i.e. without the need to revert the results back into an indication of the overall surface state. For the purposes of this chapter, an individual areal feature can be simply considered as a portion/region of the scale-limited surface, whose topography is of interest in some application.

The example MEMS illustrated in Fig. 8.1a is a typical micro-fabricated product that can undergo dimensional/geometric verification through the measurement of its surfaces. A surface metrology instrument can be used to acquire its areal surface topography. However, a simple characterisation of overall surface texture would not solve the verification problem. The groove shown in Fig. 8.1b is a scratch mark generated by a scratch test. As with the MEMS example, a surface metrology instrument can be used to acquire the topography where the groove is located, but field parameters may not provide meaningful insight on groove geometry.

Fig. 8.1Example typical areal features which need to be characterised individually; a geometric elements of a MEMS (courtesy of D. Gohil, National Physical Laboratory), b groove from scratch testing (courtesy of G. Campatelli, University of Firenze)

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