November_EDFA_Digital

edfas.org 23 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 22 NO. 4 resistor (denoted by red arrows). This particular failure was interesting because the failure site did not show a characteristic void. In this case, evidence suggested the presence of a fracture originating at the end of the L-trim and propagating to the adjacent edge, thereby severing the resistive element. The presence of a fracture was confirmed by physical cross sectioning. Although the actual fracture path could not be re- solved, the image clearly indicates the failure originated at the end of the L-trim. This indicates that the root cause of the failure was a preexisting manufacturing defect and not the result of application-induced damage. CASE #4: F 0 = 15 MHz In this study, the high-voltage, full-wave-bridge recti- fier failed during 11 kV electrical isolation testing due to a low resistive short between the AC and V- pin. CSAM was able to detect voiding between the AC and V- pin which was later confirmed by physical cross sec- tioning. Further analysis of the void showed a carbonized material on the perimeter of the void confirming that high voltage arcing had been occurring (Fig. 7). CSAMwas then used to screen parts and to quantify themagnitude of the voiding problem in the population. CASE #5: F 0 = 230 MHz In this study, CSAMwasusedtoevaluateacommercially available 14 nm FinFET microprocessor. The part failed electrical testing following radiation susceptibility testing. This testing was conducted to determine how sensitive the various technology nodes were to radiation effects. Themicroprocessor was in a BGA package in a flip chip mounted to anunderlying circuit board allowing the CSAM to image the backside of the IC (Fig. 8). The CSAM image clearly shows featureswhich reside on the front side of the die, demonstrating the ability of CSAM to image through Fig. 6 CSAM images of a thick-film resistor with L-trim void; left image interface is slightly above right image interface. Fig. 7 A short between two pins in a full-wave-bridge rectifier: optical image, left, and CSAM image, right. Fig. 8 CSAM image of a radiation-induced defect in a com- mercial processor.