Surface Measurement & Manufacturing
By Christopher Brown, Ph.D.
In the world of industrial manufacturing, surface measurement plays a pivotal role in product development, process enhancement, and quality assurance. Industrial surface measurement began in the 1930s as part of the automobile industry, with most measurement instruments relying on contact sensors. In the 1960s, as the complex structures associated with microelectronics emerged, the need arose to reduce the measuring force on contact sensors’ magnetic tape. Noncontact measuring
technologies were developed as additional industries began using surface measurement as part of their production and quality assurance processes.
From Contact Styluses to Optical Sensors
To provide effective measurement of the smaller, softer objects associated with microelectronics, optical sensors were developed that could provide measurements that would be extremely difficult or impossible with contact styluses. Initially used only in microelectronics, optical sensors began finding a role in mechanical applications as well. For example, high-pressure injectors—critical for high-performance diesel engines—demand an exceptional sealing surface, with a manufacturing process requiring optical measurement. Following the space shuttle Challenger disaster, optical sensors were used to analyze the roughness of O-ring grooves, believed to be a contributing factor to the explosion of the shuttle.
Understanding “Noise”: Interpreting Large Amounts of Optical Data
One outstanding feature of optical instruments is their ability to deliver large amounts of measurement data. Initially, users of optical sensors were unsure of how to extract all of the useable data from the measurement and their resulting images. For example, in the early days of optical sensors, some of the fine-scale detail that was now available looked like “noise” to viewers. As data interpretation methods improved, optical sensor users began to understand that much of this “noise” was actually extremely meaningful measurement data. Today, researchers and national and international standard organizations are still advancing the ways we can interpret this data to ensure that optical measurement is being used closer to its potential.
Seeing All Sides: Areal Measurement & Surface Metrology
Optical areal measurement allows the user to generate images in 3D. It is currently used to measure surfaces in critical sealing applications, microelectronics, MEMS systems, nanotechnoogy, medical devices, abrasives, advanced manufacturing, and anthropology,. Areal measurements can add a tremendous amount of value to surface metrology by discriminating between surfaces and finding valuable correlations between measurements and both processing and performance. Seeing more surfaces enables a wide range of new opportunities, from shrinking the size of cell phone cameras to making jet engines more fuel-efficient. Areal measurement is also critical in making high-precision molds and developing machining tools such as diamond turning machines.
Establishing Worldwide Measurement Standards
In the United States, ASME B46, which I currently chair, publishes a book of standards for the measurement and characterization of surfaces. Historically, the majority of our committee members have been from the automotive industry; today, however, we are attracting participants from a wide range of industries as well as natural sciences like physical anthropology.
The first standards for surface metrology were developed in the United States in 1940. Since that time, our U.S. standards have been widely used throughout the world (the United States pioneered many areal standards). ISO committee TC213, on which I serve, currently provides a large number of surface standards that are available individually.
Laser Scanning Confocal Microscopes and Future Challenges
Noncontact optical measuring systems offer a number of advantages in terms of object size, resolution, acquisition speed, and other factors. Their overall capabilities are remarkable, and they are able to achieve the highest resolutions theoretically possible (researchers are able to observe and measure topographic details on 500 nanometer grooves).
In my research work, the laser scanning confocal microscope is one of the most useful optical measuring systems. This is because of its well-balanced, high resolution in both horizontal and vertical directions. Growth in this field over the past 30 years has been phenomenal—for example, we have seen measurements go from profiles of a few thousand heights to areal measurements of over 16 million heights (available selection of pixel size is 1024 or 4096) with laser scanning microscopes, and even larger when using stitching.
Future challenges that need to be addressed with laser scanning microscopes are largely computational these would include measuring specific geometries, cleanup, sample size, and flexibility. The rapid ongoing growth of this technology assures me that these challenges and others will be addressed as laser scanning microscopes continue to evolve.
 | Dr. Christopher Brown is a professor of mechanical engineering and the director of the Surface Metrology Lab at Worcester Polytechnic Institute. He previously worked in the Materials Department at the Swiss Federal Institute of Technology studying machined surfaces and worked on product and process development at Atlas Copco's European research center. |
Publications by Prof. Christopher Brown with Olympus LEXT Laser Scanning Confocal Microscope
- Matthew A. Gleason, Stephen Kordel, Adam Lemoine, Christopher A. Brown, Profile Curvatures by Heron’s Formula as a Function of Scale and Position on an Edge Rounded by Mass Finishing, 14th International Conference on Metrology and Properties of Engineering Surfaces (Met & Props 2013),Taipei, Taiwan, June 17-21, 2013.
- G. LeGoic, C.A. Brown, H. Favreliere, S. Samper, F. Formosa1 (2013) Outlier filtering: a new method for improving the quality of surface measurements, Meas. Sci. Technol. 24 doi:10.1088/0957-0233/24/1/015001
- S.A. Hacking, P. Boyraz, B.M. Powers, E. Sen-Gupta, W. Kucharski, C.A. Brown, E.P. Cook (2012) Surface roughness enhances the osseointegration of titanium headposts in non-human primates, Journal of Neuroscience Methods, vol. 211 issue 2, 237-244. DOI: 10.1016/j.jneumeth.2012.09.002. ISSN: 0165-0270.
- Powers, B.M., Cohen, D.K., O’Hearn, J., Brown, C.A. (2010) Scale-based comparison of interferometric, confocal and stylus measurements and their ability to discriminate, Proceedings Precision Interferometric Metrology, 2010 ASPE Summer Topical Meeting, ASPE, Raleigh, 86-90.
- C.A.Brown, B.Powers, Design of Surface Metrology Systems, North American Manufacturing Research Conference, NAMRC 3, Queen’s University, Kingston, Ontario, May 25-28, 2010.
- C.A.Brown, On the Importance of Scale-based Characterization for Discrimination and Correlation, International Conference on Surface Metrology, C.A.Brown, M. Massey and O.Paracha, eds., WPI, Worcester, MA 26-28 October 2009, p IX 12-14 (extend abstract).
- D.R.S.Brown, C.A.Brown Investigation of the Surface Topography Differences in Native and Exotic Invertebrates in the St. Lawrence River, International Conference on Surface Metrology, C.A.Brown, M. Massey and O.Paracha, eds., WPI, Worcester, MA 26-28 October 2009, p V30-33 (extend abstract).
- D.R.S.Brown, C.A.Brown, On the Assessment of the Quality and Utility of Texture Measurements of Unusual Surfaces, Proceedings of the 12th International Conference on Metrology and Properties of Engineering Surfaces, Ed Pawlus et al., Rzeszów University of Technology, July 8-10, 2009, Rzeszów, Poland, 231-236.
- Christopher A. Brown, Brendan M. Powers and Gergory Hesler, The Non-uniqueness of Surface Area with Respect to Scale in Roughness Characterization, Microscopical Society of Canada, University of Manitoba, Winnipeg, Manitoba, 17-19 June 2009 (extended abstract).
- Christopher A. Brown, Douglas R. S. Brown*, Joseph A. Feula, Gregory Hesler, Brendan M. Powers Discrimination of Surfaces using Surface Texture Measurements and Area-scale Analysis, Microscopical Society of Canada, Winnipeg, 17-19 June 2009 (extended abstract).
- Powers, B.M., Cohen, D.K., O’Hearn, J., Brown, C.A. (2010) Scale-based comparison of interferometric, confocal and stylus measurements and their ability to discriminate, Proceedings Precision Interferometric Metrology, 2010 ASPE Summer Topical Meeting, ASPE, Raleigh, 86-90.
- T. S. Vincent, I. Bar-On, C.A. Brown ,“Examination of Surface Roughness Effect on Insertion loss at Microwave Frequencies using Conventional Surface Roughness Parameters within LTCC Structures” ICIMT IMAPS/ACerS April 2007 proceedings pp 138-144