Mimicking of Functional State Space with Structural Tests for the Diagnosis of Board-Level Functional Failures

A common scenario in industry today is “No Trouble Found” (NTF) due to functional failures. A component on a board fails during board-level functional test, but it passes the Automatic Test Equipment (ATE) test when it is returned to the supplier for warranty replacement or service repair. To find the root cause of NTF, we define an innovative deterministic test, namely functional scan test. We also propose two approaches for using functional scan test to adequately mimic functional state space. The first approach allows us to select a given number of initial states in linear time and functional scan tests resulting from these selected states are used to mimic the functional state space effectively. The second approach adopts a state-injection technique. Experiments on an industry design show that by using either multiple initial states or state injection, functional scan test with appropriate functional constraints can mimic the functional state space well, measured by appropriate coverage metrics. Therefore, it is feasible to use functional scan test to detect board-level functional failures in a controlled deterministic environment and diagnose the root cause to faulty wires/gates inside a component. It is also shown that the proposed method outperforms a random method in selecting the given number of effective initial states.