Adhesives for Thermal Management

We receive a lot of calls for adhesives with high thermal conductivity to achieve maximum heat transfer across an interface. Invariably the next question is whether electrical conductivity is required. The answer makes a big difference on thermal performance since filler material is the driver. For electrically insulating applications, the filler is a ceramic and the most common is alumina (aluminum oxide). The tradeoff with any filler is achieving a fill rate that yields good thermal conductivity without compromising mechanical or process performance. Very high fill rates produce such highly viscous materials that they can’t be effectively dispensed. A typical unfilled adhesive has a thermal conductivity around 0.2 W/mK. Ceramic fillers enable conductivities around 1 W/mK. If electrical conductivity is needed or allowed, then metal fillers further enhance effectiveness. Silver is the classic and conductivities from 2 to 20 (or more) W/mK are possible. The wide variety of particle shapes (spheres to flat flakes) and sizes allow for maximizing particle contact, and hence the conductivity. Ultimately, adhesive formulators strive to balance high fill ratios for increased conductivity with conflicting performance (adhesion, modulus) and handling (viscosity) needs. While alumina and silver are the most common fillers, many others are available, such as aluminum, graphite, copper, aluminum nitride, boron nitride, etc.

Adhesives compete with grease, pads, phase change materials, etc. as “thermal interface materials” in electronic assembly. While each product has its key benefit, only adhesives add mechanical support as part of the total package. This can be a significant advantage for size and weight reduction, eliminating clamps or screws. Thermally conductive adhesives bring thermal, electrical, and mechanical performance together in a single multifunctional answer.
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