2-006 Traceability for areal surface texture measurement Richard K. Leach*, Claudiu Giusca*, Kazuya Naoi** *National Physical Laboratory Hampton Road, Teddington, Middlesex TW11 0LW, UK **National Measurement Institute of Japan, Umezono 1-1-1, Tsukuba, Ibaraki, 305-8563, Japan Tel.: + 44 [208] 943 6303 Fax: +44 [208] 614 0420 E-mail: richard.leach@npl.co.uk Abstract The deterministic structuring of a surface is having a profound effect on many industrial products by allowing the manufacturer to significantly alter the way in which a surface functions. This has led to a clear need in industry and academia for traceable areal surface texture measurements. To address this need traceable transfer artefacts and primary instrumentation are required. The National Physical Laboratory (NPL) is working on two projects – one to develop areal transfer artefacts and one to develop a traceable areal surface texture measuring instrument. The authors describe the development of the artefacts and instrument, and present some of the challenges that are still required to be able to offer an areal traceability measurement service to industry. The instrument has a working volume of 8 mm x 8 mm x 0.1 mm and uses a co-planar air-bearing slideway to move the sample. It also uses a novel vertical displacement measuring probe, incorporating an air-bearing and an electromagnetic force control mechanism. The motions of the slideway and the probe are measured by laser interferometers thus ensuring traceability of the measurements to the definition of the metre. The artefacts were manufactured using a range of machining technologies and in a range of geometries suitable for stylus and optical based instruments. Keywords: Areal surface texture measurement, areal transfer artefacts, traceability 1. Introduction Surface texture plays a vital role in the functionality of modern engineered products. Traditionally, surface texture data has been used to monitor changes in a manufacturing process. For this form of monitoring, only a two-dimensional, profile measurement is required. Many industrial companies have a need to engineer or structure a surface in three dimensions to impart functionality into the surface and the resulting device. Examples include micro-lens arrays for modern displays, MEMS for sensing applications, and glasses that are patterned so as to make them hydrophobic and hence essentially self-cleaning. Three- dimensional or “areal” surface texture measurements have a number of advantages over profile measurements including:  The areal approach comes closer to fully describing a “real” surface and the derived parameters usually possess greater functional significance.  The areal technique allows parameters to be derived relating to area, for example, texture “strength” and direction, material and void volumes.  Since the areal technique takes data from an area rather than a profile, the parameters often have greater statistical significance and better repeatability between different parts of the same surface.  Areal measurements are visually more informative as a characterisation tool.