Voids Through Transmission
Chip On Board Voids, Through Transmission - Application Note 1021
Sample & Method
This COB (also shown above) was imaged by THRU-Scan at an ultrasonic frequency of 15 MHz. THRU-Scan uses a second transducer positioned below the sample that collects ultrasound that has penetrated the entire thickness of the sample. In this sample, since the device was mounted on a board, ultrasound traveled through both the device and the board for imaging.
The dark area along the bottom edge of the die is the void.