Reducing scan shifts using folding scan trees

In this paper, a new method for reducing scan shifts is presented. Scan design is one of the most popular design for test technologies for sequential circuits. However, it requires much test application time and test data when applied to circuits with many flip-flops. The new scan method utilizes two configurations of scan chains, a folding scan tree and a fully compatible scan tree. A test pattern including many don't care values is used to configure a fully compatible scan tree in order to reduce the scan shift without degrading fault coverage. And then a folding scan tree is configured to reduce the length of the scan chain and thus reduce the scan shift. Experimental results for benchmark circuits shows this scan method can reduce many scan shifts.