Clock-Skew-Aware Scan Chain Grouping for Mitigating Shift Timing Failures in Low-Power Scan Testing
Yucong Zhang, Xiaoqin Wen, Stefan Holst, Kohei Miyase, Seiji Kajihara, Hans-Joachim Wunderlich, Jun Hao Qian · 2018
High scan shift power often leads to excessive heat as well as shift timing failures. Partial shift (shifting a subset of scan chains at a time) is a widely adopted approach for avoiding excessive heat by reducing global switching activity, we show for the first time that it may actually cause excessive IR-drop on some clock buffers and worsen shift clock skews, thus increasing the risk of shift timing failures. This paper addresses this problem with an innovative method, namely Clock-Skew-Aware Scan Chain Grouping (CSA-SCG). CSA-SCG properly groups scan chains to be shifted simultaneously so as to reduce the imbalance of switching activity around the clock paths for neighboring scan flip-flops in scan chains. Experiments on large ITC'99 benchmark circuits demonstrate the effectiveness of CSA-SCG for reducing scan shift clock skews to lower the risk of shift timing failures in partial shift.