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62 SMT007 MAGAZINE I OCTOBER 2018 Selecting a thermal management material that is broadly applicable to a particular elec- tronic assembly and its predicted operating conditions is a good starting point; however, as with many of these things, the devil is very much in the details! There are a host of avail- able materials and methods to choose from—all of which serve a variety of purposes depending on the physical constraints of the application, such as environmental considerations, severity of duty, component layout, geometry of the assembly, etc. Generally, the first questions you should ask your- self are, "What type of thermal manage- ment product should I apply and what should I look out for when applying it?" There are five main groups of thermal management mate- rials that can be broken down further according to varia- tions in their mate- rial chemistries and formulations. These include: curing and non- curing pastes, bonding materials/adhesives, encapsulation resins, thermally conductive gap fillers/pads, and phase change materials. Non-curing pastes, for example, are ideal for applications where rework may be required. They use different base oils to provide a range of desirable properties, such as the wide oper- ating temperature range offered by silicone- based products. Recent advances in non-sili- cone technologies have seen the introduction of products offering higher thermal conduc- tivity with significantly reduced oil bleed and evaporation weight loss. Generally, non- curing products should be applied as thinly as possible with minimal excess. The product must also be well mixed to avoid oil bleed. The golden rule is to not be tempted to apply thicker layers. It doesn't improve the results and may even prove prob- lematic. Remember, the thickness of the thermal interface material becomes the rate-determining step; the thicker it is applied above the minimum amount required, the slower the rate of heat transfer will be. If rework is likely to be unnecessary over the life of the assembly, then you might consider Do's and Don'ts of Thermal Management Materials Sensible Design by Jade Bridges, ELECTROLUBE

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