HIGH THERMAL CONDUCTIVITY AlN MATERIALS

High thermal conductivity materials are of interest in a variety of electronic applications including packaging for high power electronics and high power microwave communication devices. AlN has replaced BeO as the high thermal conductivity ceramic of choice due to the adverse health effects associated with BeO. The development of high thermal conductivity AlN materials is reviewed in terms of properties, conventional, microwave processing and spark plasma sintering. High thermal conductivity AlN much now easier to produce than it was the past. Liquid phase sintering additives, especially yttria as used to enhance densification process and scavenge oxygen. Recent studies indicate that it is possible to get high thermal conductivity and full density with fine experimental and commercial powders as well as larger commercial powders. Thermal conductivity is a strong function of microstructure with grain-grain connectivity as critical a feature as oxygen content. While process times have decreased over the past 10-15 years, the highest conductivities are still observed in materials that have experienced 1900 degrees C for at least 2-4 hours. 'Activated' approaches that include plasmas (spark source sintering and microwave sintering) and reducing atmospheres (C description) seem to be beneficial to the development of thermal conductivity.