Static verification of test vectors for IR drop failure

ATPG tools generate test vectors assuming zero delay model for logic gates. In reality, however, gates have finite rise and fall delays that are dependent on process, voltage, and temperature variations across different dies on a wafer and within a die. A test engineer must verify the vectors for timing correctness before they are handed off to the product engineer. Currently, validation of tests is done using dynamic simulation of the circuit using the test vectors. A test vector is invalidated if it cannot reliably distinguish between a good and a faulty circuit under the signal placement and observation error window of the tester equipment. Since structural tests can result in much more switching activity in the circuit than what is estimated during normal functioning, the IR drop in the power & ground lines can be significant, adversely impacting path delays. As a result, the validation performed by simulation can be error prone. Oversizing the power rails to address this problem impacts the yield. We therefore propose the verification of test vectors for IR drop failure and present a flow for identifying failing vectors. Attempting to address this verification in dynamic simulation will force the use of circuit simulation or mixed-level simulation techniques, which are expensive in terms of run time. We discuss a static approach to validate the test vectors for failure in the presence of IR drop problems.