NDE-Based Failure Analysis of an LTCC-Eddy Current Sensor Exposed to High Temperature Using 3-D X-Ray μ-CT

Sensors based on low-temperature co-fired ceramic (LTCC) technology have shown great potential for in situ structural health monitoring (SHM) of engineering components exposed to high temperatures (HTs). LTCC is a unique of its kind materials technology offering significant advantages for the development of microsystems with integrated sensors. Nevertheless, there are still metrological issues like thermal and mechanical stresses associated with the fabrication process, and subsequently, the sensor fails while in use. This communication deals with the nondestructive evaluation (NDE)-based failure analysis of an LTCC-based eddy current (EC) sensor exposed to HT. It aims at monitoring the in situ performance and efficacy of the sensor exposed to HT for prolonged duration. The sensor was instrumented and placed inside the furnace ( $\sim $ 650 °C), and in situ EC response was monitored using an automated EC measurement setup. We found that the sensor failed to operate by losing its electrical attributes after $\sim $ 350 h of continuous operation. Subsequently, a detailed investigation on NDE-based failure analysis of the sensor was carried out using an ultrahigh resolution 3-D X-ray $\mu $ -computer tomography ( $\mu $ -CT) imaging system. The most common flaws include alignment errors, conductor swelling, conductor creeps, layer shrinkage, interconnect via voids, coil expansion, and microcracks on conductor tracks and pads. A comparison study is drawn to create a database that will lead to optimizing the fabrication process flow and setting operational limits of the LTCC sensor.