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

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 μStr. 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.