edfas.org 19 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 4 voltage in FIB-SEM and were only visible when using a lower acceleration voltage. This is because at higher accelerating voltages, electrons penetrate deeper into the sample increasing the interaction volume, thus making the image appear more transparent and obscuring other areas. In contrast, lower accelerating voltages have a smaller interaction volume, which enhances surface visibility and improves spatial resolution, allowing for better distinction between closely spaced points on a sample. See Fig. 9. CONCLUSION The unit failed due to open vias of metal lines connecting the VDD and a resistor R1 in the start-up circuitry within the bias circuitry block of the transformer driver die of the unit, as evidenced by the nanogaps on the via sidewalls during FIB cross-section. Exposure of the unit to cold temperatures before power up causes the vias to contract and the nanogap to widen, increasing contact resistance. This reduces the start-up current, preventing the bias circuitry from being established. As a result, other circuit blocks remain unpowered, leading to no oscillation in the transformer dri- vers. However, when the unit is exposed to cold temperatures after being powered up at ambient temperature, the effect of the nanogap anomaly is negligible. This is because the bias circuitry has already been established prior to the anomaly occurring, allowing the unit to continue functioning normally. The nanogap anomaly is attributed to a carbon-rich residue layer between the sides of the vias and their barriers. Subsequent investigation revealed specific process‑related contributors, and the appropriate corrective measures have since been implemented. Fig. 8 Images showing the TEM results.
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