2.5D/3D device package level defect localization with the use of multiple curve tracings and repeated thermal emission analyses

Defect localization becomes ever more challenging for low leakage failures especially with the dies stacking. More fault localization tools and innovative analytical techniques and procedures will be required during failure analysis. In this case, a very low leakage failure was reported in Xilinx 28nm technology node 2.5D SSIT package device. Low leakage was confirmed however both OBIRCH and thermal emission analyses could not detect any hotspot from the front side of the package. TDR analysis also showed no obvious anomaly as compared to a reference unit. Unit was flipped to the solder-ball side and repeated thermal emission successfully detected one big diffused emission hotspot in the package substrate region. Upon removing every substrate metal layer, curve trace verification was repeated to ensure confirm the leakage failure; while thermal emission analysis was repetitively performed and the emission hotspot tends to become more solid. Further package delayering revealed the dendrite defect located exactly at the thermal emission hotspot location along the long substrate metal trace, shorted to the neighboring ground plane and caused the reported failure.