In situ observation of electrode melting in multilayer ceramic capacitors

Abstract

In the usage of multilayer ceramic capacitors, we are concerned with the intrinsic dielectric properties of the ceramic and its long-term stability/reliability under external stresses in service conditions. Of equal importance to long-term reliability is the short-term survivability under current (power)-surge conditions. It differs from the ability to withstand voltage surge, which is determined by the dielectric strength of the ceramic. In this paper, we present some observations on sectioned and polished multilayer ceramic capacitors, which were subjected to “controlled” current-surge test conditions. Capacitors from several vendors were examined. The samples were examinedin situ under an optical microscope while current pulses of varying magnitude were applied at a constant voltage. Subsequently some samples were further examined by scanning electron microscopy. The failure mechanism appeared to be the heat-induced local melting of internal electrodes, which might then lead to a blow-out or charring of the capacitor. In less severe cases, we observed local melting and crack formation in the surrounding ceramic as well. The primary change in capacitor properties was in the degradation of the insulation resistance. In severe cases, this also led to an increase in the dissipation factor.