In order to lower the firing temperature of W cofired AlN multilayer substrates, sinterabilities of AlN substrate material and W conductor were investigated at low sintering temperatures around 1650 •C.
In case of AIN substrate material, the effect of AIN powder properties on sinterability and thermal conductivity was evaluated. The powders, with specific surface area between 2.3 and 8.2m2• g−1 and oxygen content between 0.7 and 3.2 wt%, were sintered with CaO and Y2O3 as sintering additives. The finer powder promoted the densification below 1600°C and each powder was fully densified at 1650°C. However thermal conductivity sintered at 1650°C decreased with decreasing particle size due to increasing oxygen content inside AlN grains. The thermal conductivity of optimized AlN substrate sintered at 1650°C had over 100W • m−1 K−1.
W conductor is required dense microstructure for high adhesion strength to AlN substrate. Shrinkage mismatch between AlN and W during sintering caused porous microstructure for coarse W powders or detaching for fine W powders. The optimized W paste was developed for low temperature sintering.