Scanning acoustic microscopy (SAM) is a non-invasive, non-destructive technique that can be used to image the internal features of a specimen. It is currently less used than X-ray due its less familiar underlying technology, and a more complex process requiring greater skill and training to operate and interpret. Nonetheless, SAM provides some advantages over other available NDT technologies which make it a superior tool for certain materials and processes. SAM is highly sensitive to the presence of delaminations, which are difficult to detect using X-ray radiography. SAM can detect delaminations at sub-micron thicknesses. It is one of the only techniques capable of efficiently evaluating popcorning in PBGA’s. SAM can also evaluate low and high-density plastic materials. SAM is particularly useful for inspection of small, complex devices. It can detect sub-micron air gaps, as thin as 0.13µm and has a defect resolution of 5µm, allowing for inspection of interconnects. SAM can also be used to measure the thickness of an internal layer of material.  Overall, SAM is an efficient tool for evaluating such things as printed circuit boards, underfills, BGAs, wire bonds, discrete components, and wafers.

SAM systems use sound energy to image a sample through the use of transducers. Samples are submerged in a liquid medium such as distilled water or alcohol to ensure that the ultrasound waves are delivered to and from the samples. The ultrasonic transducers send pulses into the liquid and through the samples. The transducer also receives reflected pulses (echoes) from discontinuities and disturbances from the sample. The transducer transforms the reflected sound pulses into electromagnetic pulses which are displayed as pixels with defined gray values thereby creating an image.

A complementary imaging technology developed by Sonix called Tomographic Acoustic Micro Imaging (TAMI) allows users to slice a sample into as many as 100 images using a single scan. The image data set allows the user to investigate different interfaces and/or determine the proper gate position for specific interfaces. An update to this technology, called Flexible TAMI, allows independent spacing and length for each gate, so that fewer gates are required and each gate contains more meaningful data.

A more complete discussion of ultrasonic technology and its applications is contained in the downloadable files of our product and applications libraries.