A Consideration of Interaction between Burning Out of Polyvinyl Butylar Binder and Sintering of Alumina Ceramics in a Reducing Atmosphere

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  • アルミナ質セラミックスの還元ふん囲気焼成におけるポリビニルブチラール系バインダの除去とセラミック焼結の相互関係　Ｉ
  • アルミナシツ セラミックス ノ カンゲン フンイキ ショウセイ ニ オケル ポ

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Electronic ceramics, which require the cofiring for metalization and sintering, are fired in a reducing atmosphere to prevent the oxidation of metals. The burning out of an organic binder used for forming the ceramic materials in the reducing atmosphere is recognized as one of the most difficult processes in this industry. Considering this, the firing phenomena of the 92% alumina ceramics (Al2O3-MgO-SiO2) and the polyvinyl butylar binder system in the reducing atmosphere, which are generally used in a semiconductor package, are discussed. These include the mechanisms of the burning out of the binder, sintering of the ceramics and the interaction of both.<br>In the theoretical equilibrium of carbon in a H2+N2+H2O gas atmosphere, the decomposition of remaining carbon produced from the binder begins at 680°C. This is a much lower temperature than the sintering temperature for the ceramics. However, the actual burning out temperature was found to be from 1000°C to 1200°C in the same atmosphere.<br>At the heating rate of 500°C/h in the same atmosphere, the remaining carbon from the binder became enclosed in the ceramics during sintering. As a result, the ceramic bulk density was found to be lower than that of pre-burned out samples.<br>The reason for this phenomenon was interpreted as follows: Under such quick heating conditions, for instance, 500°C/h, the ceramic sintering rate was shown to be more rapid than the burning out rate of the remaining carbon from the binder. The remaining carbon was trapped in the ceramics, and it was partially burned by oxygen in the ceramics. To produce ceramics with the same density as the pre-burned out samples, the preferable heating rate for burning out of the binder in the atmosphere was lower than 200°C/h in the temperature range of 680°C to 1450°C.<br>The phenomena of interaction between burning out of the polyvinyl butylar binder and sintering of the alumina ceramics in a H2+N2+H2O gas atmosphere could be defined by an analysis of the problems encountered during the study.

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