Multilayer ceramic capacitors (MLCCs) constitute the majority of components used in electronic assemblies and most of their failures are related to cracks. It is often assumed that dissipation factor (DF), insulation resistance (IR), and breakdown voltage (VBR) are characteristics that are sensitive to the presence of mechanical defects, and screening of capacitors by measurements of these characteristics, and by dielectric withstanding voltage (DWV) testing assures high quality products. This work analyzes the effectiveness of these screening techniques for revealing cracks in high-volumetric efficiency, low-voltage ceramic capacitors. Various types of class II dielectric capacitors with rated voltages from 6.3 V to 100 V, and capacitances from 0.1 μF to 100 μF from different manufactures were used in this study. Fractures in the parts were introduced mechanically and by thermal shock stress. It has been shown that cracking results in relatively minor variations of capacitance and DF. Absorption currents prevail over leakage currents during standard IR measurements at room temperatures, and at high temperatures the intrinsic leakage currents exceed substantially leakage currents caused by cracking thus masking the presence of defects. Analysis of distributions of breakdown voltages in normal capacitors and capacitors with cracks showed that the majority of defective capacitors can pass the DWV testing. New, more effective methods of electrical testing and possible improvement of the existing techniques are discussed.
DIAGNOSTIC OF THE INSULATION STATE OF THE ASYNCHRONOUS MOTOR AND THE POWER SUPPLY CABLE UNDER CONDITIONS OF LOCAL COMPENSATION
