An Economics Model of Supportability Through Design for Testability

Design for testability (DFT) is a design activity intended to reduce the cost and effort of testing, diagnosis and consequently support. Built-in self test (BIST) can be thought of as an extension of DFT. While DFT enables external testers to find faults, BIST itself also includes the tester mechanism. In this paper we will include BIST as a form of DFT. A number of DFT techniques have been documented in standards, handbooks, industry guidelines, books and articles. While the need for DFT has been increasingly recognized in the past decades, it has received less than enthusiastic endorsement from designers, or even from their managers. For designers, DFT means yet another constraint and added activity, so their reluctance is not surprising. Managers, concerned with return on investment, however, should be supporting DFT. Yet often, we find that they do not. Probably, the reason is that while the costs of implementing DFT are easy to predict, resulting economic benefits are not easy to predict or calculate. DFT offers many benefits for reducing test costs. Some of these benefits are realized in manufacturing tests. This paper will address the economic aspects of DFT as they affect post-manufacturing supportability.