M. Azarian, M. Keimasi, and M. Pecht
University of Maryland
College Park, MD 20742
Multilayer ceramic capacitors (MLCCs) are known to be susceptible to cracking due to mechanical flexure and thermal stresses. In addition to cracks other defects, such as voids and delamination, can be introduced during the manufacturing process. Frequently the nature and severity of these defects allow the capacitor to function close to or within specification while raising the risk of future reliability problems in the application environment. In the case of cracks which extend to the outside surface of the capacitor the potential exists for eventual electrical shorting between opposing electrodes. This is especially likely in environments conducive to capillary condensation or electrochemical migration. For capacitors used in power supply circuits or near combustible materials this represents a risk of fire and catastrophic failure.
For the purpose of failure analysis, destructive analysis consisting of cross-sectioning followed by microscopic examination remains unequalled for positive identification of defects. Nonetheless, non-destructive testing (NDT) for screening of defective MLCCs has been an important objective for users of these components in military and other high reliability applications, as well as for general quality control in mass production. A variety of non-destructive test methods have been reported, including X-ray radiography, scanning acoustic microscopy (SAM), scanning laser acoustic microscopy (SLAM), methanol testing, and impedance spectroscopy. Due to their small inter-layer spacings and large number of interfaces, MLCCs remain a challenge for those seeking an NDT approach to defect detection. In this paper a number of non-destructive techniques for defect detection in MLCCs are reviewed and their relative merits are discussed.
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