Screening for Faults in High Density SRAMs

Because of the high defect rate of outside purchased, Mil-Std- 883, Class B screened 16K SRAMs destined for an AT&T system, AT&T-Bell Laboratories began an electrical and failure analysis of returned parts. There were many board failures that translated to a defect rate of .5% with an apparent increasing failure rate with time. It was important to the analysis to determine the failure mechanisms and their synergism and to develop, if possible, a screen at the board level.