Dummy Faulty Units for Reduced Fail Data Volume From Logic Faults

Fail data collection is carried out for faulty units to allow defect diagnosis to be performed. After passing scan chain tests, fail data collection targets faults in the functional logic. Several approaches addressing the fail data collection process on the tester were developed to ensure that the volume of fail data collected for faulty units with defects in the functional logic is manageable. In addition, the collection of compacted output responses reduces the fail data volume, and the fail data volume can be reduced further by compressing it. This article complements these approaches by considering the storage scheme for fail data, observing that the same fail data may be shared by different faulty units. By storing shared fail data only once, the fail data volume can be reduced. Sharing of fail data occurs when the fail data for a faulty unit u j is contained in the fail data for a faulty unit ui. It also occurs when the intersection of the fail data for ui and u j is nonempty. If there is no faulty unit whose fail data is contained in the intersection, and the sharing is significant, the article defines a dummy faulty unit uk with fail data equal to the intersection. This article develops these observations into a storage scheme for fail data. The experimental results for simulated faulty units based on benchmark circuits demonstrate significant reductions in fail data volume.