| Summary: | 碩士 === 國立彰化師範大學 === 機電工程學系 === 97 === We present the reliability assessment on high voltage rated, surface mount multilayer ceramic capacitors (HV-MLCCs) using highly step-stress accelerated life testing which allows us rapidly estimate the reliability of devices, rather than the long test duration normally required from constant stress tests. The failure analysis by cross-sectioning was performed to identify the failure site and failure modes of HV-MLCCs, and the failure mechanism in advance.
Devices were thoroughly characterized to evaluate their electrical performance, and a series of exterior inspections were performed prior to step-stress accelerated tests. The time to failure data is of grouping at specific times. The test results show that the cumulative damage model with an exponential life distribution are proper to evaluate the lifetimes of HV-MLCCs, and thus the mean life under the operation voltage (1000 VDC) at accelerated test temperature 125 oC is determined to be 1.8x104 hours. Using the Prokopowicz & Vaskas model, the mean life of the devices at the operation temperature 55 oC and storage temperature 25 oC are obtained to be 9.07x106 hours (1,036 years) and 3.20x108 hours (36,491 years) respectively. As the results, it is a reasonable lifetimes to MLCCs used in many applications.
The failure analysis by cross-sectioning was performed to identify the failure site of HV-MLCCs. The failure mode in failed HV-MLCCs is internal cracks located within ceramic layers due to the larger breakdown electric field imposed by very high voltage. Some advices in materials design, such as higher insulation resistance and higher strength between electrodes and insulation, are proposed in order to improve the issue in terms of increasing the breakdown voltage and enhance the reliability of the device. On the other hand, the breakdown failures are often found in many insulation materials, and they fail in the same time so that it may explain HV-MLCC test data in group.
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