Online-offline laser ultrasonic quality inspection tool for multilayer ceramic capacitors-Part I

The advent of surface-mounted devices has allowed continued size decreases in electronic packages. However, the decrease in device size has led to other manufacturing problems. Therefore, as devices decrease in size, inspection technology must be developed to maintain consistent levels of quality without increasing manufacturing process time. The focus of most inspection technologies, such as X-ray inspection, in-circuit testing, and acoustic microscopy, is on finding defects with solder joint interconnects, but some devices, such as multilayer ceramic capacitors (MLCC), have failures not relating to the solder connection. Defects in MLCCs, known as flex cracks, are commonly caused by manufacturing processes, and no current means of detection exists, unless the cracks cause a device to fail a functional test. A laser ultrasonic and interferometric system, providing a noncontact, nondestructive, and online approach for microelectronic package quality inspection is designed and presented. A pulsed infrared laser excites a specimen into vibration through laser-generated ultrasound, and the vibration displacement is measured using an interferometer. Differentiation between acceptable and unacceptable devices is achieved using signal-processing techniques that compare waveforms between two devices, where one of the waveforms is a reference waveform from a good MLCC. Results are presented for a case study involving MLCCs that have intentionally induced flex cracks, causing the devices to fail a capacitance leakage test. The system has the capability of detecting open connections and flex cracks in the MLCC packages.