Scanning Acoustic Microscopy (SAM) or Scanning Acoustic Tomography (SAT)

SAM / SAT is a non-invasive & non-destructive failure analysis technique that inspects for voids, cracks, delaminations in a sample.  SAM sends a focused sound wave through the package and interprets the change of the sound wave with the package.  SAM is a superior tool to detect delaminations of sub-micron (down to 100nm) thicknesses.  SAM can also measure thickness of an internal layer of s specimen.  Scanning acoustic microscopy has many modes.  The following are the most common modes used in failure analysis of an IC.
A-Scan Mode (Amplitude Scan) – is a real time oscilloscope waveform of the sound waves collected at a single X-Y section or point.
C-Scan Mode (Confocal Scan)– is an image of acoustic reflection collected at the focused plane (X-Y plane) of interest at a particular depth (Z).  The image plane is parallel to the surface of device.
Through-Scan Mode – two separate transducers are used to send and receive acoustic waves.  These transducers are positioned on opposite sides of the specimen.