Quality testing requires quality thinking

The stuck-at fault (SAF) model originated from malfunctions in the first types of digital circuits. Many defects in these primitive diode, tube, and bipolar transistor circuits produced symptoms of a node stuck at logic zero or one. Diagnosis of failures was therefore usually based on the assumption of a logically stuck node. As a result, the primary concern for testing at that time was to evaluate the ability of the circuit to perform the intended Boolean function. This history and the compatibility of the SAF model to computer modeling led over the years to the focus on SAF coverage for test pattern generation and grading. It gradually became etched in stone that SAF coverage is an effective and accepted measure of test quality, without supporting defect level data from manufacturers of newer technologies