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Design007-Aug2019

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68 DESIGN007 MAGAZINE I AUGUST 2019 terial; for example, if operating temperatures are likely to range between -50°C and 200°C, a silicone-based thermal paste would be the go- to option. It is important to consider the type of product used; for instance, a thermal paste compared to a thermal phase change material are entirely different entities. If we take one of our phase change materials—such as the sil- icone-free TPM350—it is similar to a thermal paste in the sense that it is a non-curing, non- bonding product, but it eliminates the mess and inconsistencies associated with pump-out. Phase change materials offer efficient ther- mal transfer along with an enhanced perfor- mance with thermal shock cycles and greater thermal protection where temperature spikes can occur due to their ability to store and re- lease thermal energy (latent heat) during the phase change process. Once heated above their softening temperature, the phase change mate- rials alter to a liquid-/gel-like state that per- form equally as well as—and sometimes even better than—a thermal grease. Thermal pastes are often designed to be ap- plied in as thin a layer as possible. They im- prove the contact between the device and its heat sink by eliminating air gaps and ensuring that the full surface contact area is available for heat transfer. There is, however, a critical thickness that determines maximum thermal transfer with minimal thermal resistance, and while this will depend on the roughness of the substrates and required spacing, it is generally between 30 and 100 microns. It's always advis- able to refer to the manufacturer's instructions to apply the correct amount of thermal man- agement product and test thoroughly under re- alistic accelerated conditions using the actual unit where possible. Do I Really Need to Use a Thermal Management Product? The short answer is yes! During use, some electronic components can generate significant amounts of heat. Failure to effectively dissipate this heat away from the component and the device can lead to reliability concerns and re- duced operational lifetimes. It is in such cas- es that thermal management measures need to be taken for heat transfer efficiency to prolong the working life and ensure all components op- erate within their ideal temperature range for maximum performance. Thermal Management Products Come in Many Shapes and Sizes Thermal bonding materials can be used as interface materials either for thermal conduc- tivity alone or to secure the heat sink or elec- tronic component in place. In addition, such curing materials can be used for filling gaps and providing some structural support. By way of example, Electrolube's Thermal Bond- ing System (TBS) is a two-part epoxy bonding system, which utilises metal oxides to provide high thermal conductivity whilst being electri- cally insulating. The bonding system is useful in the manufacturing of heat sink assemblies where piggyback arrangements are applied and where the manufacturing design of heat sinks does not allow for welding or brazing techniques to be employed due to complexity or geometry of the fins. Coming back to the main topic, the fact that these types of products are curing systems means that in general, they do not experience the same issues of pump-out as a non-curing product. With bonding products, it is impor- tant to test the strength of the bond during the operational use of the device to ensure the bond strength and physical properties of the product—such as coefficient of thermal expan- sion—allow the product to perform consistent- ly over the lifetime of the device. Thermally conductive potting compounds are resins designed to encapsulate compo- nents or pot the entire PCB unit, dissipating heat away from the electronic components and in the process and offering additional protec- tion from environmental elements such as wa- ter or chemicals. For certain types of heat-gen- erating circuitry, such as power supplies and LEDs, it may be beneficial to encapsulate the device in a heat-sink enclosure using a ther- mally conductive potting compound. The pot- ting compounds provide excellent resistance to extreme temperatures, chemicals, shock, and vibration. There are a number of thermally

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