Mapping Stress with Ultrasound Comparison between stress, time of flight and thickness imaging.
Bright colors show the concentration of stress at the edges of delamination.
Presence of delamination is confirmed by phase inversion imaging. The graphical representation of the amplitude in the top image was taken at the edges of the die. The highest concentration of the shear stresses is located at the corners of the die. The same location of the highest concentration of stress is seen also at the lower corners of the die. It is well known that the areas of the highest concentration of shear stresses initiate cracks in plastic encapsulation.