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68 The PCB Design Magazine • November 2017 In my first two columns in this series, I pre- sented a broad introduction to the subject of thermal management of electronic circuits. I hope my "quick start guide" and "problems and solutions" items have sparked readers' interest in this elemental but essential aspect of elec- tronic system design. This month I'm taking a closer look at ther- mal interface materials—how they can be ap- plied to achieve efficient heat transfer, and the significance of bulk thermal conductivity in re- lation to heat transfer and thermal resistance. I'll also be touching on the influence that prod- uct miniaturisation is having on thermal man- agement techniques, and I will return to this recurring question: Why do I have to spread my thermal interface material so thinly? As in previous columns, my approach will be based on the frequently asked questions that our customer support teams field every day on the phone, at exhibitions and when visit- ing customer premises. I've selected five of the most common questions, followed by their re- spective responses, and I hope they offer useful guidance for readers who may be experiencing design problems related to achieving a satisfactory heat transfer performance in their electronic assemblies. First and foremost, read the thermal interface material manufacturer's advice about optimum application methods. They've been around the block a few times and they know what they're talking about! Remember, more is not necessar- ily better; uniform and thin applications of the heat transfer medium always work best. Most products are likely to have an optimum thick- ness of application, as determined by the manu- facturer, and you should try to achieve this for best results. It is important to understand your applica- tion. What are the environmental conditions under which it must operate, and how variable are they? Will the chosen heat transfer com- pound perform consistently as environmen- tal conditions swing from one extreme to the other? Consider the heat sink; is this the actual casing surrounding the assembly or a separate heat sink placed on top of a component? Where cases are concerned, is there a gap between the case and the component? by Jade Bridges ELECTROLUBE SENSIBLE DESIGN What would be your top suggestions for achieving the most efficient heat transfer?

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