A case study of ir-drop in structured at-speed testing

Abstract

At-speed test has become a requirement in IC tech- nologies below 180 nm. Unfortunately, test mode switching activity and IR-drop present special chal- lenges to the successful application of structural at- speed tests. In this paper we characterize these prob- lems on commercial ASICs in order to understand how to implement more effective solutions. consumption. Depending on such parameters as gate count, DFT strategies, package type, and other fac- tors, the impact of this problem can range from non- existent to severe. In this paper, we discuss the prac- tical issues associated with power consumption during at-speed tests. We begin by delineating in more detail the nature of power-related phenomena encountered in structured speed tests. We talk about various de- sign features that can be applied to somewhat miti- gate test mode power dissipation. In Section 2, we give a more precise definition of the IR-drop problem which is the focus of this pa- per. We compare IR-drop in slow speed and at-speed structural tests, and also compare it with functional IR-drop. We narrow the focus further to the topic of toggle activity or "switching density" during struc- tured at-speed tests. In Section 3.4 we describe the notion of "quiet" patterns and how they are gener- ated. We follow up with a report of the results we have obtained in experimentation on industrial ASIC designs. Finally we give our suggestions for future work in this area and conclude the paper.