Porous reaction-sintered AlN tapes for high-performance microelectronics application

A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method involved polymer microspherical powders used as a sacrificial mold to introduce controlled porosity into the green tapes during pyrolysis. The Al2O3-rich porous green tapes were then reaction sintered at 1680 degreesC for 12 h to create porous AlN tapes. This work builds upon a previously developed novel reaction sintering process that densified and converted Al2O3-rich tapes (Al2O3-20 wt% AlN-5 wt% Y2O3) to AlN tapes at a relatively low sintering temperature of 1680 degreesC. The sintering behavior of the porous tapes was investigated, and the effects of the microsphere particle size and volume addition were studied. The microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constants of the AlN tapes were reduced to about 6.8 to 7.7 while 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 x 10(-6) to 4.8 x 10(-6)/degreesC, showing good CTE compatibility with silicon at 4.0 x 10(-6)/degreesC. The added porosity did not significantly affect the CTE values.