Unraveling the Cannot Duplicate and Retest OK problems by utilizing physics in testing and diagnoses

Automatic Test Equipment (ATE) has been traditionally tasked with supporting field returns. This task includes verification of proper operation and in the alternative to diagnose and provide repair instructions. While ATE has done reasonably well to certify a unit under test as ready for issue (RFI), it has been hampered by diagnostic complications in many instances. Two such complications, Cannot Duplicates (CNDs) and Retest OKs (RTOKs) are particularly troublesome because of the ATEpsilas limited vocabulary of Pass/Fail or Good/Bad determination. When a unit under test (UUT) is returned from the field labeled faulty, yet passes on the ATE, a RTOK, additional testing and diagnosis is required, despite the ldquoPassrdquo result. Similarly, when multiple runs on an ATE provide different results, a CND, the ATE (in conjunction with the test program set -TPS) is not sufficient to unravel the conflict. In such instances, the ATE must be supplemented with various tools that characterize the physics of the circuit in order to assist in diagnoses. This paper will highlight a number of failure modes that can create CND and RTOK, and examine tools that can be used instead of or in conjunction with ATE to help diagnose and repair units that experience such phenomenon.