How is scanning acoustic microscopy used for failure analysis?
Scanning acoustic microscopy (SAM) is a tool used to identify the non-uniformity of interface layers (cracks, delamination and voids) within a package. SAM is a nondestructive test, in which an ultrasonic transducer transmits and receives ultrasound through a sample under water. The most common modes of SAM are the through transmission mode (also known as TSAM, Thru-scan, T-scan, TT-image) and the pulse-echo or reflectance mode (also called CSAM, C-scan, PE-image). TSAM is used to determine whether or not a defect is present. Then CSAM is used to verify the location of defect in the package. Since ultrasound propagates freely through solids and liquids, but not as well through air (such as delamination, voids, or cracks), defects appear a different color on the SAM image.
