High dielectric AlN/Al₂O₃ composite powder using a plasma spray approach for microelectronics application

Increasing demand for higher performance dielectric material for multi-layer ceramics packaging has led to the use of the AlN system due to its very high thermal conductivity and coefficient of expansion compatibility with silicon. This paper reports on a novel process method used to produce an AlN/Al₂O₃ composite powder system which can be subsequently tape cast as a dielectric substrate. The mixture of both Al₂O₃ and AlN was first mechanically alloyed and then spray-dried to obtain a suitable agglomerated powder that was subsequently plasma-sprayed, resulting in a fine micrometer level integrated composite powder. The two main criteria used to ascertain the optimal process parameters during plasma spraying were a high gamma/alpha Al₂O₃ phase ratio, which ensured that all the Al₂O₃ phase had melted during plasma spraying, and a minimal reduction in the AlN/Al₂O₃ ratio to ensure minimal change in the AlN during processing. For the plasma-sprayed composite powders, fully sintered ceramic tapes were produced attaining >99.0% of the theoretical density after sintering at 1650 °C for 6 h, which yielded a thermal conductivity value of 32.0 W m^-1 K^-1.