Trends in nondestructive imaging of IC packages

Abstract

Since the industry-wide conversion to surface mount packages in the mid-1980’s, nondestructive imaging of moisture induced delaminations and cracks in plastic packaged ICs by scanning acoustic microscopy has been a critically important capability. Subsurface imaging and phase analysis of echoes has allowed scanning acoustic microscopy to become the primary nondestructive technique for component level inspection of packaged ICs and is sensitive to defects that are undetectable by real time x-ray inspection. It has become the preferred method for evaluating moisture sensitivity, and for many package processes, provides more reliable detection of wire bond degradation than physical cross sectioning or conventional electrical testing. However, the introduction of new technologies such as ball grid array (BGA) and flip chip packages demands improvements in acoustic inspection techniques. Echoes from the laminated substrates in BGA packages produce interference problems. Phase inversion detection is an important advantage of pulse-echo imaging of molded surface mount packages. However, phase inversion is not always helpful for delamination detection in these new packages, due to the properties of the materials involved. The requirement to nondestructively inspect flip chip interconnect bumps has arisen. Alternative approaches such as through-transmission screening of BGAs and high frequency (>200 MHz) pulse-echo inspection of flip chip bumps are addressing these new issues. As the acoustic frequency approaches the limits dictated by attenuation, new methods of frequency-domain signal analysis will become important for routine inspection and may give acoustic microscopy a predictive capability.