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Owing to its high thermal conductivity, low dielectric constant, and thermal expansion coefficient matching Si chip, aluminium nitride has attracted much attentions and is considered to be the most promising substrate material for microelecironics applications. However, the AIN powder can not be well densified under the temperature range lower than 2000℃. Besides, at temperature higher than 1000℃, oxygen atoms existing on the surfaces of AIN grain will diffuse into the grain resulting in the decomposition of the aluminium nitride. In order to obtain low temperature sinterable AIN compacts, low softing point glass were added in this study.
Various kinds of borosilicate glass were prepared. After mixing with AIN powders, the mixtures were sintered at 700℃ to 950℃, from 15 to 360 minutes in air.
The composition with 65wt% borosilicate glasses added can achieve achieve a shrinkage higher than 11%, relative density is between 90% and 92%. The dielectric constant is between 4.5 and 5.5, the dielectric factor is lower than 0.5% measured at 1MHz, and the thermal expansion coefficient is between 4.65x10-6/℃ and 4.65 x10-6/℃. From the X-ray diffraction analysis, aluminum nitride still retained the main crystalline. The phase wetting of borosilicate classes to AIN surface was examined by SEM observations.
In the fabrication of multilayer substrates, the ductor-blade technique was employed, substrates process, we mixed compose powder with binder and employed, 30mmx30mm squares of the samples were cut from the green tape, then piled up them to form the 3 layer substrates. After firing, we obtained about 26.7mmx26.7mm and the layer of 1.4mm of the 3-layer ceramic substrates.
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