INSTRUMENTATION FEATURE TAKE A MORE SCIENTIFIC APPROACH...
As functional coatings become more advanced, ensuring their effectiveness requires more than traditional process fluid control and monitoring solutions. Jonathan Mitchell, market development manager with HORIBA UK, explains the need for in-line, in-vacuum, real- time control, monitoring and analysis
A
s the phrase suggests, functional coatings do just that; they perform a
function. Popular coating properties include optical (e.g. photoluminescent and antireflective), electrical (e.g. antistatic, conductive and dielectric), thermal (e.g. heat-conductive or heat-resistive), physiochemical (e.g. photocatalytic and hydrophilic) and hygienic (e.g. anti- microbial). Applications for such functional coatings
can be found in virtually all industry sectors and the effectiveness of that ‘functionality’ is at least as important as any aesthetic value. Indeed, in sectors such as aerospace and pharmaceutical, the quality and performance of the coating may be depended on to provide safety and reliability (e.g. the surface coating on jet turbine blades) or to ensure efficacy (e.g. drug administration in the pharmaceutical sector). The reduced effectiveness or failure of a coating could have catastrophic consequences.
However, the application of coatings is
becoming ever-more demanding. Talk to anyone responsible for developing a roll- to-roll machine, for example, and they’ll undoubtedly say that what their customers are requesting is in-line, at speed material characterisation and assurance (with nanometric precision) that the coating is of a uniform thickness. This request is a big enough ask from a
technological perspective, but it is accompanied by the twin commercial drivers of adding value and cutting cost. However, these are not insurmountable problems. It’s all been done before. Increasingly, vacuum coating processes
are employing control and measurement technologies that were developed for use in the semiconductor manufacturing industry. There, all goals are met through the use of process control and monitoring solutions that are highly accurate and produce repeatable results. Technologies employed for process and
Figure 1: Suitable for a variety of industries, Horiba’s MFCs offer high accuracy and a high- speed response
control in functional coating applications include residual gas analysers (RGAs) and mass flow controllers (MFCs). Regarding the former, the current trend is for compact devices that enable operation in low vacuum pressures (e.g. for sputtering applications) without the need for differential pumps, thus simplifying installation and maintenance. As for MFCs, increasingly, users are demanding that devices be calibrated and certified under ISO 17025 (see figure 1). Also used in vacuum coating equipment
are direct injection vaporisers - for water or other liquids that don’t require a carrier gas - vacuum gauges and plasma emission controllers (with fast actuation and reliable feedback responses). Most of the above are off-the-shelf
devices and their integration into closed- loop control systems is relatively easy. Nowadays, equipment manufacturers add value to their equipment by incorporating material analysis and characterisation in response to end-user demands. For the OEMs, this can present challenges. Spectroscopic ellipsometry and x-ray
fluorescence (XRF) can be employed, both in- and ex-situ, as a means of measuring thin-film thickness, uniformity, nucleation, growth parameters and optical properties. Systems are commercially available that can be used for the in-line and non-destructive analysis of single or multilayer coatings and can characterise film thickness of between 0.1nm to 50μm on a range of substrates including polymers, glasses, ceramics and metals. To monitor the chemistries of the
Figure 2: Functional film coating process layout
coating, Raman spectroscopy can be performed in-line too. Fluorometers can also be used. Both are non-contact and non-destructive. Another technique proving increasingly popular is hyperspectral imaging, from shortwave infrared (SWIR) through to UV. It is used for measuring material quality and composition and for detecting surface defects and contamination issues over large surface areas. Understandably, the integration of
scientific analysis techniques normally associated with the laboratory into industrial processes is not without its challenges. Responding to these challenges, HORIBA is currently the only company worldwide that has both traditional process fluid control solutions plus all the scientific analysis technologies required to ensure high process yield, assure quality and future-proof the manufacturing equipment used.
HORIBA UK
www.horiba.com
PROCESS & CONTROL | FEBRUARY 2019 37
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