ATE test time reduction using asynchronous clock period

A conventional wafer sort test on an automatic test equipment (ATE) uses a fixed synchronous clock period. Typical test cycles may produce high signal activity and to keep the power dissipation under control, a relatively slow test clock is used. This results in long test times, especially for large scan based circuits. Observing that each test clock cycle may consume different amount of power, we propose an asynchronous clock test methodology to reduce the test time. Smallest customized clock periods for test cycles or sets of cycles are computed based on power and critical path constraints. A theoretical analysis shows that the total energy consumed by the entire test is invariant and the test time depends on the rate it is dissipated during test. An asynchronous clock test dissipates this energy at the maximum allowable rate, while the conventional synchronous clock test dissipates it at a lower average rate. The asynchronous clock test method is first implemented in simulation using several ISCAS´89 benchmark circuits. These results show test time reductions up to 47%. To establish the test programming feasibility of the new methodology the Advantest T2000GS ATE at Auburn University Test Lab was used. Test time reduction of 38% is demonstrated for scan test of a circuit. The paper ends with an investigation showing that for a circuit under test, given its power budget and a test there exists a supply voltage that minimizes the test time. An analysis determines whether the shortest test must use a synchronous or an asynchronous clock.