A comparison of acoustic and infrared inspection techniques for die attach

Two die attach inspection techniques, acoustic C-scan and infrared imaging, were compared to determine the size of silver-filled epoxy flaws that could be detected. Using a 25-MHz signal, the acoustic technique was able to find voids as small as 1 mm in diameter. It was not possible to see 0.5-mm-diameter voids clearly. Infrared images detected voids of a 2-mm diameter and larger. Small voids could not be seen distinctly. However, overall chip temperature increases due to small voids could be detected, indicating possible die attach flaws. Severe delaminations, created by removing epoxy, could be seen easily by both techniques. Poor adhesion could be detected acoustically by skilled operators, but would not be obvious to the untrained eye. Poor adhesion was not obvious using infrared imaging; however, overall chip temperature did increase