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68 DESIGN007 MAGAZINE I MAY 2019 inadequately thermally managed components will almost certainly overheat, which will neg- atively impact the surrounding components and lead to reduced life expectancy for those components or even their complete failure in service. Poor reliability arising from thermally in- duced circuit failures might prove detrimental to brand reputation, but what if the applica- tion served a critical role? Applications might include the following: • A safety-critical device upon which the safety of personnel working in a hazardous environment might depend • A device that simply would not function without proper thermal management procedures in place • A device with a defined working temperature range when in use • A piece of equipment designed to work in harsh or extreme conditions, which must work reliably regardless of those conditions Silicone or Non-silicone? Traditionally, silicones have always provided the higher temperature option, offering great- er stability at temperatures in excess of 150°C compared with other chemistries. However, recent advances have seen the gap between the thermal performance of silicone and some non-silicone materials narrow slightly with new non-silicone market entrants now offering excellent stability at temperatures up to 180°C. As well as providing excellent high-tempera- ture performance, silicones offer very good en- vironmental stability, particularly where elec- tronic devices are operated in areas of high hu- midity. Their very low viscosity ensures fast flow and thorough coverage during applica- tion, and also makes them an excellent choice for application via screen/stencil printing. Whilst possessing some clear thermal ad- vantages over non-silicone technologies, sili- cones do have some negative issues, includ- ing a phenomenon called migration. Migration occurs when volatile low molecular weight si- loxanes are released from the silicone, caus- ing problems in the surrounding environment. Where electronics are concerned, migration re- sults in the formation of silicon carbide on PCB surfaces, leading to failures. In the wider production environment, depos- its of low molecular weight siloxanes on sur- faces in other parts of the factory can also lead to problems with the adhesion of surface fin- ishes, particularly paint, the quality of which may be compromised. Such siloxanes can also find their way around factories through ven- tilation and extraction systems, causing even wider spread problems, and in some incidenc- es, a total ban on silicone containing materials may be in place at certain production plants. Thus, there is an increasing demand for non- silicone products. One contributing factor is the global shortage of silicone, which is forc- ing suppliers to pass on price increases to cus- tomers. Indeed, some manufacturers of sili- cone-based thermal management products are warning about hefty price increases of up to 25%. It is also perhaps the escalating growth of the global LED market that is fuelling the move towards non-silicone solutions as the long- term reliability of silicones in LED applications is now in question [1] . Non-silicone thermal management solutions now deliver a high-per- formance alternative to silicone materials and provide manufacturers, such as those involved in the LED lighting industry, with an immedi- ate drop-in solution. The New Kids on the Block Thermal pastes are at the forefront of ther- mal management applications and are expect- ed to remain so for some years to come. They are easy to apply and rework whilst providing a cost-effective alternative to thermally con- ductive bonding products, such as RTVs and two component epoxies, for example. Thermal pastes have offered some of the lowest thermal resistance values available in the market for thermal interface applications, but in recent years, a new rival to this mate- rial technology has appeared on the scene— phase-change materials. Like pastes, phase- change materials can also be applied very thin-

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