We examined sintering additives for alumina. When using CuO-TiO2-Nb2O5 additive, dense
sintered alumina was obtained by firing at 1000°C or below, even though additive content was at
most 10 mass%. It is considered that the formation of mixed oxide consists of CuO, TiO2 and
Nb2O5 has an important role for low temperature sintering of alumina. Thermal conductivity of the
above sample was 15 W/mK, which was the highest value yet reported within LTCC (Low
Temperature Co-fired Ceramics) materials.
We studied the dielectric properties of Al 2 O 3 -MgO-ReO x (Re: rare earth) systems in the microwave region and found that the magnetoplumbite phases in the MgO-poor regions of MgReAl 11 O 19 (Re: La ∼ Tb) compositions had positive TCF (temperature coefficient of resonance frequency) values in spite of having low dielectric constants of under 20. By mixing a lead-free glass with the above system, a novel LTCC (which we term an AMSG) was obtained that was characterized by a low dielectric constant (<10), a near zero TCF, and high bending strength. When firing these AMSG green sheets inserted between HTCC alumina or magnesia green sheets that cannot be sintered at the AMSG sintering temperature, the AMSG sheets were seen to shrink not in the x-y directions but in the z direction due to the constraining effects of the HTCC layers. The obtained non-shrinkage substrate had precise dimensions and a high degree of flatness. The AMSG and the non-shrinking techniques have potential for application to integrated RF modules in mobile communications equipment.
For the purpose of enabling the low-temperature sintering of alumina, the addition of Ag 2 O to CuO-TiO 2 -Nb 2 O 5 type sintering additive was examined. The use of CuO-TiO 2 -Nb 2 O 5 -Ag 2 O type sintering additive by 5 wt% enabled the low-temperature sintering of alumina at 860 • C. It is presumed that the formation of Cu 4 TiNb 4 O x solid solution has an important role for low temperature sintering of alumina. The obtained sintered material showed high thermal conductivity of 18 W/mK, higher than that of conventional LTCC materials, and that the material could be co-fired with silver electrodes.
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