Lock-in Thermography Failure Detection on Multilayer Ceramic Capacitors After Flex Cracking and Temperature–Humidity–Bias Stress

Abstract

A nondestructive method using lock-in thermography (LIT) to detect failures in multilayer ceramic capacitors (MLCCs) is presented. The thermal response of new 25-V MLCCs is compared to the thermal response of the same capacitors after the insertion of flex cracks as well as after 24 and 96 h of total exposure time to a temperature of 75 °C, 75% relative humidity, and 25-V bias. The thermal response was measured before the introduction of any flex cracks, as well as directly after flex cracks were inserted by bending the printed circuit board to $6000~\mu $ Str. No significant change was detected in the thermal profile upon the introduction of flex cracks of which the presence was verified by X-ray imaging. After the MLCCs were subjected to a total of 96 h of temperature–humidity–bias stress, a significant increase in leakage current could be detected as a hotspot in one of the initially 24 samples by LIT. The influence of the different parameters, such as lock-in frequency, bias voltage, and measurement time, on the detectability of the hotspot is presented. Finally, the hotspot location is correlated with the cross-sectional analysis of the capacitor, where melting and solidifying into nickel spheres are found.