The transmission of ultrasound requires the continuous medium, and ultrasound signals will exhibit transmission, reflection, and refraction at discontinuous boundaries. When ultrasound passes through the internal structure of the device, due to different acoustic impedances, reflected waves will appear at boundary with defects or poor bonding. The ultrasound probe receives reflected waves and generates different electrical signals, which are analyzed by algorithms to generate easily distinguishable digital images. The scanning acoustic tomography can be used to detect delaminations, cracks, holes and other structural defects at different positions inside the device. Therefor, it is one of the important non-destructive detection in failure analysis.