Chip On Board Voids - Application Note 1020
Sample & Method
Many smart cards and hand-held toys use the COB design, where the die is attached and wire bonded directly to the board, then overmolded. This COB was imaged by C-SAM® at an ultrasonic frequency of 15 MHz. Gating of the return echoes was on the die surface level.
In this image, the red area is a void in contact with the interconnect wires along the edge of the die.