System Perspective on Diagnostic Testing

Testing is performed for a variety of reasons-performance verification, experimentation, manufacturing assurance, diagnosis, process improvement, etc. Tlhe growing complexity of full-scale systems has outstripped our ability to provide detailed simulations for micro level diagnosis. When we have completed the experimentation and the verification through brass-board, we begin full scale engineering development. During this process we often redesign or include design features that allow us to have a high confidence that the part was manufactured correctly. For example, boundary scan may allow us ta examine and verify every gate in a chip, or a test block on a board will allow us direct access to a number of devices on the board. System level diagnosis, however, is not addressed. In fact we go to great lengths to avoid it by incoming screening, chip test, board test, etc. Even 0.1% rejection at system delivery (because it fails some performance test) is unacceptable. Finding fault and f ~ n g tlhe system is expensive and time consuming, and it is better to avoid the problem all together. But-this is precisely the problem we give to the customer. We provide a full-up system, that after a certain number of operating hours fails and the customer has to repair it.