Test coverage: what does it mean when a board test passes?

Characterizing board test coverage as a percentage of devices or nodes having tests does not accurately portray coverage, especially in a limited access testing environment that today includes a variety of diverse testing approaches from visual and penetrative inspection to classical in-circuit test. A better depiction of test coverage is achieved by developing a list of potential defects referred to as the defect universe, where the capabilities of the chosen test strategy are not considered in development of this defect list. Coverage is measured by grading the capabilities of each test process against the defect universe. The defect universe is defined to be meaningful to the bulk of the electronics industry and to provide a consistent framework for coverage metrics and comparisons.