Moisture induced degradation of multilayer ceramic capacitors

Abstract

When both precious metal electrode and base metal electrode (BME) capacitors were subjected to autoclave (121 °C/100% RH) testing for 500 h, it was found that the precious metal capacitors aged according to a well known aging mechanism (average capacitance degraded less than 3% from their starting values), but the BME capacitors degraded to below the −30% specification limit. One hypothesis for this new failure mechanism was that there could be oxidation or corrosion of the nickel plates. Another hypothesis was that the loss of capacitance was due to chemical changes in the barium titanate. This paper presents the evaluation of the two hypotheses and the physics of the degradation mechanism. It is concluded that there are chemical changes in the barium titanate resulting from the interaction of residual point defects from BME manufacturing and humidity in the field. The continuous reduction in capacitor size makes the newer base metal electrode capacitors more vulnerable to moisture degradation than the older generation precious metal capacitors. In addition, standard humidity life testing, such as JESD-22 THB and HAST, will likely not uncover this problem. Therefore, poor reliability due to degradation of base metal electrode multilayer ceramic capacitors may catch manufacturers and consumers by surprise.