An Expression For The Property Degradation Of The Ceramic Encapsulation Capacitor Under Thermal Cycling And Co-60γ Radiation

Effects of thermal cycling and irradiations on the property degradation of the ceramic encapsulation capacitor were investigated by space environment simulators for thermal cycling and Co-60γirradiation. The structure and invalidation pattern of the ceramic encapsulation capacitor were analyzed by means of scanning electron microscopy. The composition of metal electrode and ceramic medium layer was studied by the energy spectrometer. The planar finite element mode for the cross section of the ceramic encapsulation capacitor was set up. The thermal stress distribution for the structure layers was analyzed.The experimental results show that the change ratio of capacity presents a peak value with increasing temperature in heating stage of thermal cycling. There is a relationship of Lorentz between the change rate of the capacity and temperature. The tangent angle of wastage decreases in heating stage of thermal cycling. The capacity decreases with increasing the cycles, and there is a relationship of parabola between the change rate of capacity and cycles. The tangent angle of wastage increases with increasing the cycles. There is a relationship of liner between the tangent angle of wastage and cycles.During thermal cycling, the metal electrodes are oxidated that results in the decreasing in the value of capacity. The thermal mismatch stresses between the metal electrode and ceramic medium generate damage to the structure of capacitor. When the damage was accumulated to a certainty extent, the structural fracture of the layers will occur and result in the invalidation of capacitor.The maximal equivalent stress existed in the segment near the interface between metal electrode and ceramic medium at up and down limit temperature during thermal cycling, which was corresponding with the invalidation pattern of capacitorThe capacity of ceramic encapsulation capacitor decreases and the tangent angle of wastage increases after Co-60γradiation in three dosages of 5×105rad,5×106rad and 1×107rad.