Sensible Design: Thermal Management—The Heat is On


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For some months now, my colleague Alistair Little has been taking a close look at resins and their role in circuit protection across an array of applications. He now hands the reins over to me, and in this, the first of what I hope will be a series of informative columns, I am going to focus on the all-important subject of thermal management. First, though, let me introduce myself.

I've worked for Electrolube for 14 years now, starting as a development chemist, then as the research & development manager working with the product development team. In 2011, I moved into a more commercial role, working alongside the sales team to help with technical enquiries and product application queries. Last year, I was appointed manager of Electrolube's Ashby-based technical support team, working alongside sales, marketing and the R&D teams to provide more in-depth product support for both existing and new customers.

Thermal management—the science and the products—is my specialty, so let's start this series of columns (as Alistair did for his series on resins) with a five-point guide based on some typical questions that our technical support team fields every day on the phone, at exhibitions and when visiting customers.

Why use thermal management materials?

During use, some electronic components can generate significant amounts of heat. Failure to effectively dissipate this heat away from the component and the equipment in which it is installed can compromise reliability and reduce operational life. Thermal management materials are designed to prolong equipment life and reduce incidences of failure. They also maintain equipment performance parameters and reduce energy consumption by reducing operating temperatures, and minimising the risk of damage to surrounding components. Indirectly, they maintain brand reputation, as the reliability of the equipment will be very dependent 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 thermal gap pad, or some other thermally conductive 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 material 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 carrier 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 adhesives are used to bond the heat sink to the component while also offering an effective heat transfer medium.

Innovative new phase change materials offer several advantages over thermal pastes. Their low phase change temperature allows low thermal resistance over a wide temperature range, ensuring minimal bond line thickness with improved 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 resistance when compared with thermal pastes due to the thickness of the gap pad versus the very low thickness achievable with a thermal paste. 

To read this entire column, which appeared in the August 2017 issue of The PCB Design Magazine, click here.

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