Noise Problems in Testing VLSI Hardware

Noise resulting from the switching of high-current, off-product drivers in VLSI circuits cause substantial problems during manufacturing test and may lead to zero yield. These problems, seldom addressed during product design, can be mitigated or eliminated either during the design phase or at mauufacturing test. In this article, we present some of our experiences with noise during manufacturing test, and discuss several solutions to the problem. These remedies include such manufacturing test options as relaxing the test specification, or "guardbanding" which requires both substantial study of the impact on quality and continual tracking of the problem level; modifying the test program to eliminate the need for a guardband; or having the logic designer create a new set of functional test patterns specifically designed to avoid simultaneously switching drivers. We also examine alternative design methods for use during both product and tester design.