Fault Diagnosis under Transparent-Scan

Transparent-scan provides opportunities for test compaction that do not exist with the conventional test application scheme for scan circuits. However, test compaction can reduce the ability of a transparent-scan sequence to diagnose faults. We describe a static test compaction procedure that reduces the length of a transparent-scan sequence while maintaining its stuck-at fault coverage and the number of stuck-at fault pairs it distinguishes. We use the static test compaction process as part of a process that constructs the transparent-scan sequence gradually, using test compaction to prevent the length of the sequence from becoming unnecessarily long.