Scan Chain Masking for Diagnosis of Multiple Chain Failures in a Space Compaction Environment

Diagnosis is extremely important to ramp up the yield during the integrated circuit manufacturing process. It reduces the time to market and product cost. Limited observability due to test response compaction negatively affects the diagnosis procedure. When multiple chains, mapped to a single compactor, fail, diagnosis becomes extremely difficult. The procedure is even more complicated because when a circuit fails the flush test, not all the patterns are applied. Only a few of the patterns are applied and the observed responses are used to diagnose the faulty chains. In this paper, we have proposed an efficient masking strategy that will be very useful for diagnosis of scan chains when multiple scan chains fail. The proposed strategy uses the redundancy in fault detection by the test patterns and masks scan chains in such a way that enough information can be provided with small increase in test pattern count. A new tester architecture that will select and apply only those patterns having enough information for diagnosis has also been proposed. Diagnostic resolution and first hit index achieved by our method are very close to their ideal values, which validate the applicability of our approach.