Should nanometer circuits be periodically tested in the field?

Escapes from manufacturing test: A large system built out of well-tested components can still have a significant probability of failure due to test escapes. Unfortunately field testing is unlikely to detect such failures because manufacturing tests, carried out on individual parts and on assembled (sub)systems, are far more comprehensive. Indeed, any proposed field test can be applied as part of manufacturing tests, but reapplying all manufacturing tests is generally not possible in the field. Thus it is unrealistic to expect a significant number of manufacturing test escapes to be picked up by subsequent field-testing, unless the defects “grow” in the field and cause additional malfunction. Concurrent test methods, such as self checking, on the other hand, can be effective here since they can detect errors for input conditions not observed during test.