Enhancement of thermal conductivity in ceramics obtained from a combustion synthesized AlN powder by microwave sintering
- PDF / 727,261 Bytes
- 9 Pages / 585 x 783 pts Page_size
- 85 Downloads / 227 Views
A combustion-synthesized AlN powder was investigated for use as a starting material in obtaining a high thermal conductivity AlN by microwave sintering followed by microwave reheating under a reducing atmosphere. Microwave sintering was found to proceed very quickly so that a density of 99.5% of theoretical with a thermal conductivity of 165 W/mK was achieved after sintering at 1900 °C for 5 min. The thermal conductivity could be improved by prolonging the soaking time, which is attributed to decreases in both oxygen content and secondary phases by evaporation and sublimation of the secondary phases. The reducing atmosphere was created by adding carbon particles to the AlN packing powder surrounding the specimen. The thermal conductivity could be significantly improved by microwave reheating of the sintered specimen under the reducing atmosphere. This is considered to be due to enhanced removal of the secondary phases by the reducing atmosphere. Sintering under the reducing atmosphere was found to retard densification because of the earlier removal of the secondary phases, thus resulting in a poor densification and a low thermal conductivity.
I. INTRODUCTION
Aluminum nitride (AlN) has been acknowledged as an important industrial material because of its unique combination of properties such as high thermal conductivity, high electrical resistivity, low thermal expansion coefficient, moderately low dielectric constant, good thermal shock resistance, and good corrosion resistance.1,2 It has been considered for many applications such as a filler for epoxy molding compound (EMC) for microelectronic encapsulation, substrates for semiconductor chips, and an insulating material for radiofrequency and microwave packages.3,4 Recently, it has also been considered3 for application as a loading substrate for high-power lightemitting diode chips because of its high thermal conductivity. In our laboratory, a self-propagating high-temperature synthesis or combustion synthesis5 process has been recently developed6–8 for the synthesis of AlN powder; this process is considered to possess many advantages such as low energy consumption, high production rate, low production cost, and capability of mass production. The a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0094 J. Mater. Res., Vol. 23, No. 3, Mar 2008
http://journals.cambridge.org
Downloaded: 29 Mar 2015
use of the AlN powder as a filler for EMC has been studied,9 and a thermal conductivity of 14 W/mK was obtained for a specimen made up of 80 wt% AlN and 20 wt% cresol novolac epoxy. Sintering of the AlN powder using microwaves has also been investigated,10 and a thermal conductivity of 186 W/mK was obtained for a specimen sintered at 1900 °C for 30 min with the addition of 3 wt% Y2O3 as a sintering aid. Recently, many other researchers11–13 have reported that a high-thermal-conductivity AlN (i.e., higher than 230 W/mK) could be obtained by using specific sintering aids (e.g., Y2O3 and Sm2O3), prolonging soaking time, or
Data Loading...
