Low dielectric constant high thermal conductivity porous AlN substrates for microelectronics packaging

A novel approach was undertaken in producing low dielectric constant, high thermal conductivity, AlN substrates for microelectronics packaging. This method essentially utilised polymer microspheres that were used as sacrificial moulds to introduce controlled porosity into green Al₂O₃-rich tapes during pyrolysis. The Al₂O₃-rich porous tapes were then reaction sintered to achieve porous AlN tapes with low dielectric constant and high thermal conductivity. The sintering behaviour of the porous tapes was investigated, and the effects of the microspheres particle size and volume addition were studied. The pyrolysed microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constant of the AlN tapes were reduced to about 6.8 to 7.7 whilst thermal conductivity values were reasonable at about 46 to 60 W/mK. Coefficient of thermal expansion (CTE) values showed a linear trend according to phase composition, with the porous AlN tapes exhibiting CTE values of 4.4 to 4.8 × 10^-6 /°C, showing good CTE compatibility with silicon, at 4.0 × 10^-6 /°C. The added porosity did not significantly affect the CTE values.