Microstructures at degraded local areas have been analyzed, using ‘prebreakdown’ multilayer ceramic capacitors (MLCCs), degraded by a highly accelerated life test (HALT). We have investigated influencing factors of the local microstructures on the lifetime of MLCCs. We have fabricated two lots of the MLCCs, sintered under different temperatures. The degraded local areas have shown some large grains exist, while other normal areas have not. Analyses at the degraded local area revealed a clear correlation between the lifetime and the minimum number of grains per unit dielectric layer. Dependences of the lifetime on the number of grains were different between the two lots. Further analyses showed a difference of Dy distribution in the large grains between the two lots. We have quantitatively shown dependences of the lifetime on the local microstructural nonuniformities.

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