Improving transition delay fault coverage using hybrid scan-based technique

This paper presents a hybrid scan-based transition delay fault test. The proposed technique controls a small subset of scan cells by launch-off-shift method and the rest by launch-off-capture method. An efficient ATPG-based controllability measurement approach is proposed to select the scan cells to be controlled by launch-off-shift or launch-off-capture. In this technique, local scan enable signals are generated on-chip using two local scan enable generator cells. The cells can be inserted anywhere in a scan chain and the area overhead is negligible. The launch and capture information of scan enable signals are transferred into the scan chain during scan-in process. Our technique improves the fault coverage and reduces the pattern count and the scan enable design effort. The proposed hybrid technique is practice-oriented and implemented using current commercial ATPG tools.