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54 The PCB Design Magazine • August 2017 Indirectly, they maintain brand reputation, as the reliability of the equipment will be very de- pendent upon the effectiveness of the thermal management technique used. What choices are available with thermal management materials? These can take the form of a thermal paste, an adhesive, a room-temperature vulcanized (RTV) silicone, phase change material, a ther- mal gap pad, or some other thermally conduc- tive medium, the choice of which will depend upon the application. Commonly used thermal interface materials, including pastes, RTVs and adhesives, are introduced via a thin layer of ma- terial between the component and its heatsink to minimise its thermal resistance. Pastes are non-curing, allowing rework, and consist of thermally conductive fillers in a car- rier fluid, the former being a blend of one or more mineral fillers depending on the desired thermal properties, and the latter a silicone or non-silicone based medium. RTVs and ad- hesives are used to bond the heat sink to the component while also offering an effective heat transfer medium. Innovative new phase change materials of- fer several advantages over thermal pastes. Their low phase change temperature allows low ther- mal resistance over a wide temperature range, ensuring minimal bond line thickness with im- proved stability and pump out resistance when compared with a thermal paste. Other methods include thermal gap filler pads, which can be silicone or non-silicone based sheet materials that can be cut to size and applied by hand. They are highly thermally conductive, but have a higher thermal resis- tance when compared with thermal pastes due to the thickness of the gap pad versus the very low thickness achievable with a thermal paste For certain types and designs of heat gen- erating circuitry, it may be more beneficial to encapsulate the device in a heatsink enclosure using a thermally conductive encapsulation compound. This provides both heat dissipation and environmental protection all in one. Electrolube's thermal management products are all non-electrically conductive, ensuring that there are no issues with electro-migration due to the transfer of electrically conductive particles. Why is resistance to thermal cycling important with thermal management? Thermal cycling (alternate heating and cool- ing) happens with the majority of applications that require a thermal management material. Non-curing products offer the lowest thermal resistance as they allow for a very low bond line thickness. However, they do suffer from pump- out, which occurs when differences in the coef- ficient of thermal expansion cause a non-curing product to move at the interface. This can lead to uneven coverage and therefore an increase in thermal resistance. Hotspots may form and at worst, the thermal interface material may be 'pumped out' of the interface. A thin, even cov- erage is needed throughout the life of the prod- uct, so the more stable the thermal interface material is to thermal cycling, the more consis- tent will be its heat transfer properties. Are all thermal management materials suitable for manual or automated application? Except for thermal gap pads, which can be difficult to place automatically, most thermal management materials can be both manually and automatically applied (though manual is more likely in the case of prototyping/small production runs). Whether manual or automat- ic, the aim is to achieve a thin, uniform layer. Screen printing and application with a syringe can be achieved manually or automatically, but " RTVs and adhesives are used to bond the heat sink to the component while also offering an effective heat transfer medium. " THERMAL MANAGEMENT: THE HEAT IS ON