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PCBD-June2017

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70 The PCB Design Magazine • June 2017 RESINS PAST, PRESENT AND FUTURE and encapsulation resins is improved by the in- troduction of fillers, either metallic or ceramic, depending on whether the resin is desired to be electrically conducting or insulating. The clever bit is getting the packing density right to achieve the improvement in thermal conductivity. Unfilled resins have a low thermal con- ductivity, about 0.2W/m.K; we've managed to raise this to 1.54 W/m.K with our epoxy-based ER2220 product. As well as compact, minia- turised electronic assemblies, high thermal con- ductivity potting resins are now increasingly be- ing sought for the protection of LED luminaires, an industry that in a few years has gone from virtually nothing to one that is currently expe- riencing exponential growth. The LED industry has also benefitted from developments in sili- cone and polyurethane resin chemistries, which can provide the necessary optical clarity as well as desirable light diffusing effects. Developments in the automotive indus- try—in particular, the growing availability of electric vehicles—have also seen demand for encapsulating resins with improved tempera- ture stability, greater resistance to thermal shock and generally broader operating tem- perature ranges. Silicone resins, while they tend to be more expensive than their epoxy or polyurethane counterparts, are often the best choice for applications where high continuous operating temperatures (above 180°C) are ex- pected, such as near electric motors and power electronics. The volumes of resin used in an assembly are also more carefully calculated than in the past when the level of protection might have been improved by simply increasing the thickness of the coating or encapsulation. In the case of a modern smartphone, which puts extraordinary computing power in the palm of your hand, that simple expedient is no longer available to the design team, and size and weight consid- erations now dictate the application of much smaller volumes of resin with no compromise in terms of its overall electrical performance. In meeting these requirements, the electri- cal properties of modern resin systems have improved significantly in recent years. New, so- called "ultra-high performance" polyurethane resins, for example, offer excellent electrical properties while also protecting devices from physical shock and vibration. These resins bene- fit from some of the latest developments in filler materials and particle dispersions that improve their dielectric strength, enabling thinner resin applications to deliver the desired electrical per- formance. Environmental considerations and the health of production staff and end-users alike have had a huge impact on the material formu- lation of resins, which are now governed accord- ing to international regulations. These include the European Union' s REACH regulation which has been in force since December 2006 and the RoHS-1 Directive, which was adopted in Febru - ary 2003 by the European Union, now supersed- ed by RoHS-2 in July 2011. Equivalent legisla- tion outside of Europe includes the "Promotion of Clean Production" law in China and "Safer Consumer Product" regulation in California. Clearly, these overarching regulations have had quite an impact on the way we chemists formulate our products and many of the raw materials that we used in the past, such as some specified heavy metals and solvents, are either banned or strictly controlled in terms of their concentrations. Since the introduction of these regulations, and like many of our colleagues in the industry, Electrolube has gone to great lengths to ensure all qualifying products are RoHS-compliant (some being exempt under the rules) and that all comply with current REACH requirements. " The LED industry has also benefitted from developments in silicone and polyurethane resin chemistries, which can provide the necessary optical clarity as well as desirable light diffusing effects. "

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