A new reliability test for multilayer ceramic capacitors

Several reliability problems related to insulation resistance (IR) have been reported by multilayer ceramic capacitor ((MLC) users over the years: IR degradation over time at less than rated voltage (low voltage leakage), unsteady dissipation factor with bias applied, partial recovery of IR after repeated application of high voltage, and IR degradation of MLC´s taken from sealed bags in inventory. Current test procedures, as in Mil-C-55681, designed to replicate the particular conditions related to MLC failure cannot effectively separate the root causes of these failures because causal mechanisms are confounded. Although in their entirety they do effectively expose weak lots, their application to commercial lots is cost prohibitive. An alternate test procedure designed to rapidly, effectively, and economically detect the separate root causes of MLC failures is presented. The test procedure focuses on finding the causal defects rather than attempting to reproduce and measure the individual failure mechanisms themselves. An analog megohmmeter and an oven or hot plate are the only equipment necessary for conducting the procedure, making it a good tool for users as well as capacitor suppliers. The premise that electrical stress and thermal stress on MLC´s are linearly independent, and therefore separable, is presented. The separable effects of steady-state voltage and thermal/mechanical stress are applied to the study of MLC failures in this paper. Data are presented comparing the effectiveness of the test procedure to 25°C bias voltage testing, conventional voltage conditioning, and highly accelerated life test (HALT)