An investigation into a low insulation resistance failure of multilayer ceramic capacitors

An investigation was conducted into failure of a multilayer ceramic capacitor (MLCC) mounted on a printed circuit board assembly. In field use a particular assembled 0.1μF MLCC (0402) was exhibiting low insulation resistance. Failure analysis was conducted to evaluate materials, manufacturing and assembly processes and the testing environment to identify a set of possible failure sites and mechanisms associated with the assembled MLCC that would produce the reduced insulation resistance. A physical analysis plan was developed and executed to investigate identified sites within the failed MLCC assembly. The analysis techniques included X-ray inspection, cross-sectioning with in-situ direct current (DC) resistance monitoring, optical microscopy, environmental scanning electron microscopy (E-SEM) and energy dispersive spectroscopy (EDS). The failure was isolated to a tin-rich material found under the MLCC causing the loss of insulation resistance between the end terminations of the MLCC. Some possible causes for the presence of the metallic material under the capacitor are reviewed and recommended corrective actions are provided.