Non-destructive evaluation technique of surface-mounted capacitor based on photothermal frequency modulation technique

A new non-destructive evaluation technique for surface mounted capacitor (SMC) based on photothermal frequency modulation is proposed. The slight change of capacitance by a thermal wave makes an oscillation frequency modulate, enabling detection by frequency demodulation. Defective samples were created artificially in our laboratory from a normal SMC by loading mechanical stress to it. It is confirmed that the capacitance change ratio decreased as the loaded stress increased. The phenomena are discussed qualitatively from the viewpoint of the reflectance of thermal wave caused by an air layer.