Previous work on determining the minimal air gap detectable in scanning acoustic microscope (SAM) focused on the gap thickness detectable in an idealized Newton ring sample using a 75 MHz transducer. However, air gaps thinner than 0.130 microns have been detected by SAM. These findings have prompted a return to the question of what is the minimal air gap detectability of SAM. To answer this question, further, Newton Ring experiments using transducers across the SAM frequency range have been performed. This article discusses the processes involved in these experiments and provides the results of SAM from actual packages. The procedure involved in cross-sectioning and scanning electron microscopy (SEM) imaging for correlating samples is also provided. Based on the SAM-cross-sectioning-SEM analysis, a detection of 0.056 - 0.183 micron air gaps was concluded for the delamination areas detected by SAM using a 35 MHz 12 mm transducer.

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