Asynchronous multiple scan chains

The long test application times needed for scan designs increase the costs of testing. In this paper we introduce the concept of asynchronous multiple scan chains in which groups of scan chains operate independently. This is achieved by using more than one made signal to control the scan flip-flops. Asynchronous multiple chains can provide large reductions in the test application time. We present an efficient test application scheme to exploit the asynchronous operation of the chains. Based on this scheme, we outline techniques to configure the chains so as to minimize the test time. Implementation results show significant savings in test application time and highlight interesting design tradeoffs between the control complexity, I/O pin count and test time.