NIST HOSTS WORKSHOP ON THERMAL SPRAY PROCESS RELIABILITY.Thermal spray Thermal Spray techniques are coating processes which involve spraying melted (or heated) materials onto a surface. As such thermal spraying is a line-of-sight process. The energy to heat the feedstock (coating precursor) is supplied by electrical (plasma or arc) or chemical means is used to deposit metals and ceramics onto substrates for a wide range of applications. Representatives from industry, universities, and national laboratories took part in a NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. workshop in January 2001, to discuss the role of sensors and diagnostics in improving the reliability of thermal spray processes. In this workshop, NIST scientists presented their work on process sensors, which had been carried out in response to needs identified in earlier workshops and conferences. The NIST work emphasizes issues of process stability, sensor calibration calibration /cal·i·bra·tion/ (kal?i-bra´shun) determination of the accuracy of an instrument, usually by measurement of its variation from a standard, to ascertain necessary correction factors. , and substrate The base layer of a structure such as a chip, multichip module (MCM), printed circuit board or disk platter. Silicon is the most widely used substrate for chips. Fiberglass (FR4) is mostly used for printed circuit boards, and ceramic is used for MCMs. characterization A rather long and fancy word for analyzing a system or process and measuring its "characteristics." For example, a Web characterization would yield the number of current sites on the Web, types of sites, annual growth, etc. . Many process stability problems arise from long- and short-term variations in the temperature and velocity of particles in the thermal spray plume: sensors developed in the NIST work are revealing the magnitude and origin of some of these variations. Calibration of the non-contact sensors used to measure temperatures of particles and substrates requires knowledge of the material emissivity Emissivity The ratio of the radiation intensity of a nonblack body to the radiation intensity of a blackbody. This ratio, which is usually designated by the Greek letter ε, is always less than or just equal to one. , and the NIST work showed how reliable emissivity data can eliminate a significant systematic error that results from the frequently-used gray body assumption. In the area of substrate characterization, non-contact sensors for surface topography topography (təpŏg`rəfē), description or representation of the features and configuration of land surfaces. Topographic maps use symbols and coloring, with particular attention given to the shape and elevations of terrain. and temperature are under development. Speakers from the thermal spray community described some of the factors that make it difficult to obtain reliable and reproducible deposits and some of the sensor needs that would help to overcome these problems. Among the issues cited as important by workshop participants were the need for sensors to be simple, rugged, and reliable for use in industrial environments, the need for more reproducible powder feed stock and thus the need to combine NIST expertise in powder production with thermal spray expertise, the need to sense deposit and substrate characteristics, especially deposit thickness, and the need to correlate improved sensor performance to improved product performance. The workshop results are being used to refine the direction of the MIST projects and to build working collaborations with the thermal spray industry. |
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