An overview of scanning acoustic microscope, a reliable method for non-destructive failure analysis of microelectronic components

In a highly competitive and demanding microelectronics market, reliable non-destructive methods for quality control and failure analysis of electronic components are highly demanded. Any robust non-destructive method should be capable of dealing with the complexity of miniaturized assemblies such as chip-scale packages and 3D IC stacks. Scanning acoustic microscopy (SAM) is indeed one the best non-destructive tools for failure analysis purposes. It is also a useful technique for imaging the morphology, location and size distribution of defects in different microelectronics components. SAM can detect delaminations at sub-micron thicknesses. It is also one of the only available techniques capable of efficiently evaluating popcorning in PBGA's and is a also useful device to detect sub-micron air gaps. SAM can also be used to measure the thickness of an internal layer of material. Overall, SAM is an efficient tool for evaluating such a wide range of different defects in printed circuit boards, underfills, BGAs, wire bonds, discrete components, and wafers. In SAM a focused sound is directed from a transducer at a small point on a target object, as is schematically shown here. Sound, hitting a defect, inhomogeneity or a boundary inside material, is partly scatted and will be detected. The transducer transforms the reflected sound pulses into electromagnetic pulses which are displayed as pixels with defined gray values thereby creating an image. This article aims at giving an overview of scanning acoustic microscope (SAM) and explaining its operating principles and its limitations. A few examples are also given for further clarification.