Guided shifting of test pattern to minimize test time in serial scan

Scan test time has always been one of the priority issues for test researchers because it directly impact cost of the design. In this work we have addressed the issue through scan chain and test pattern reordering. The idea of limited scan shift is explored. We have proposed a graph theoretical framework for reordering of scan chain and test pattern. Graph theoretic problem is formulated for each, scan chain and test pattern, reordering. For each of the formulated problems corresponding approximation algorithms are proposed. The experimental results show that the proposed methodology reduces the scan shift time compared to the ordering provided by atpg tool.