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54 SMT Magazine • June 2014 TRenDS In THeRMAL MAnAgeMenT MATeRIALS FOR eLeCTROnIC CIRCuITS continues feaTure The copper and silver thick-film conductors offer up to 300 µm fired conductor thickness, with excellent thermal, electrical, wire bond- ing, and soldering properties. They are com- patible with standard 96-percent alumina and aluminum nitride sub- strates. By using the ad- ditive screen-printing deposition process, a single substrate can con- tain both thin-printed, dense circuitry for signal processing and thick- printed areas for pow- er-device monitoring. The materials also allow through-hole connec- tions for thermal and electrical connections on both sides of a sub- strate. The improved bond- ing mechanisms of these thick-film pastes to the substrate, as opposed to thin film or direct bond copper, offer the advan- tage of increased ther- mal cycling and thermal shock performance. Managing LeDs As government man- dates dictate the ne- cessity for reducing lighting energy use, LED light bulbs are quickly becoming a viable, cost- efficient alternative to standard incandescent bulbs. Energy-efficient LED lighting products offer low-energy consumption and long service life in a compact size. LED light bulbs are find- ing acceptance not only in home use, but for high-power, high-brightness applications such as traffic lights, streetlamps and automotive headlights. Thermal management is also a crucial com- ponent of LED lighting design. LEDs convert only 20–30% of their electric power into vis- ible light. The excess energy is dissipated into the substrate as heat, allowing the bulb to run cooler for brighter light output and longer life expectancy. Although many LED configura- tions are built onto metal-core circuit boards (MCPBSs), better thermal management sub- strates are available. Aluminum is a substrate that offers good thermal con- ductivity and is be- coming more popu- lar for LED design. However, aluminum requires an insula- tion layer on the sub- strate to isolate the circuit from ground. New products such as Celcion ® , a thick-film materials system pro- duced by Heraeus, are designed to insulate aluminum substrates. As the trend to smaller and smaller electronic devices intensifies, thermal management of cir- cuitry will become all the more essen- tial. Smaller devices, with more circuits packed into tinier ar- eas, translate to more heat generated and more heat that must be dissipated as the circuits get closer to each other. The challenge for the thermal manage- ment industry will be to continue developing materials and systems that allow electronic products to operate reliably in extreme high- temperature applications. SMT Mark Challingsworth is the technology director for heraeus' Circuits and Components busi- ness unit within the electronic Materials Division. Tips for Designing Thermal/Power Circuits designing thermal/power circuits can be challenging, especially when dealing with thermal management issues. following these design tips can make the design process a bit easier: Q Closely matching the thermal expansion coefficients of the various materials used in a circuit is critical for long-term reliability Q Minimizing or eliminating thermal interfaces is key to minimizing thermal resistance Q using the highest thermal conductivity materials possible also helps to minimize thermal resistance Q It is essential to use materials that can withstand high temperatures without degradation Q Thick-film materials can provide the solutions for these critical design issues

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