Boron-nitride filled epoxy adhesives

Thermally conductive adhesives may be filled with metal, ceramic, or inorganic particles. Silver-filled epoxies have high thermal conductivities, but may not be used where there is a risk of electrical shorting. In such cases, epoxies or other polymers filled with electrically resistive, but thermally conductive materials such as aluminum nitride, boron nitride, alumina, or beryllia must be used. Some applications for thermally conductive adhesives include attachment of power devices, heat sinks, large components such as capacitors and transformers, large ceramic substrates, and edge connectors. 

Thermal-transfer adhesives that are electrically insulating also exhibit wide ranges of thermal conductivities, depending on the filler type and amount. The thermal conductivities of epoxies filled with boron nitride or diamond are approximately 4 W/m K and 12 W/m K, respectively, while those of the more common aluminum-oxide-filled adhesives range from 1 to 2 W/m K. 

K would cause a AT of almost 100 °C. For at least two decades, alumina and crystaUine silica have been used to boost the thermal conductivity of epoxy resins. When highly conductive fillers such as boron nitride, aluminum niliide, and diamond powders become commercially available, these materials have been incorporated in adhesive compositions. The expected target was the attainment of kg values of at least 10 W m K if not better. Such high values have been claimed for diamond-filled adhesives but they remain currently questionable with regard to the experimental results. summarized in the graph of Fig. 12.18. 

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