During board level testing this part was determined to be dysfunctional. The Board was not seeing telemetry from the Power Board as expected. The problem was troubleshot back to the ADC128S device. Troubleshooting steps revealed that the VDD voltage to three chips, including the ADC128S, was at a reduced level. Also, several analog inputs into U33 A2D were over the maximum input currents. The A/D converter was not being powered correctly. This was an indicator that something was loading it down as well as several analog inputs are stressed due to overcurrent.
A few of the key troubleshooting findings were that the analog supply input VA (pin 2) measured 5V as expected, analog inputs IN0 → IN4 (pins 4 → 8) were drawing excessive current, analog input IN5 (pin 9) was loaded down, digital voltage input VD measured 1.32V when 5V was expected. The digital output was also not as expected.
The device was removed from the board and submitted for failure analysis. The FA revealed a fused aluminum wire bond. The open bond wire was at pin 2 (VA). Inspection of the die revealed three aluminum melt balls that were squeezed out from under the die glassivation at areas along the positive analog supply die metal routing VA around the die. Two of these areas also show visible damage near the protruding melt balls that are displaced aluminum. This is the result of thermal overstress causing the underlying metal to melt and expand, forcing itself out cracks in the glassivation layer.
Can someone tell me what type of current or level of current could cause such a failure?
