Design for testing: Difference between revisions

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== History ==

DFT techniques have been used at least since the early days of electric/electronic data processing equipment. Early examples from the 1940s/50s are the switches and instruments that allowed an engineer to “scan” (i.e., selectively) probe) the voltage/current at some internal nodes in an analog computer [analog scan]. DFT often is associated with design modifications that provide improved access to internal circuit elements such that the local internal state can be controlled ([[controllability]]) and/or observed ([[observability]]) more easily. The design modifications can be strictly physical in nature (e.g., adding a physical probe point to a net) and/or add active circuit elements to facilitate controllability/observability (e.g., inserting a [[multiplexer]] into a net). While controllability and observability improvements for internal circuit elements definitely are important for test, they are not the only type of DFT. Other guidelines, for example, deal with the [[Electromechanics|electromechanical]] characteristics of the interface between the product under test and the test equipment. Examples are guidelines for the size, shape, and spacing of probe points, or the suggestion to add a [[Tri-state buffer|high-impedance state]] to drivers attached to probed nets such that the risk of damage from back-driving is mitigated.

Over the years the industry has developed and used a large variety of more or less detailed and more or less formal guidelines for desired and/or mandatory DFT circuit modifications. The common understanding of DFT in the context of [[Electronic design automation|Electronic Design Automation]] (EDA) for modern microelectronics is shaped to a large extent by the capabilities of commercial DFT software tools as well as by the expertise and experience of a professional community of DFT engineers researching, developing, and using such tools. Much of the related body of DFT knowledge focuses on digital circuits while DFT for analog/mixed-signal circuits takes somewhat of a backseat.

Over the years the industry has developed and used a large variety of more or less detailed and more or less formal guidelines for desired and/or mandatory DFT circuit modifications. The common understanding of DFT in the context of [[Electronic design automation|Electronic Design Automation]] (EDA) for modern microelectronics is shaped to a large extent by the capabilities of commercial DFT software tools as well as by the expertise and experience of a professional community of DFT engineers researching, developing, and using such tools. Much of the related body of DFT knowledge focuses on digital circuits while DFT for analog/mixed-signal circuits takes somewhat of a backseat.

== Objectives of DFT for Microelectronics Products ==

DFT affects and depends on the methods used for test development, test application, and diagnostics.