Defect coverage of non-intrusive board tests (NBT): What does it mean when a non-intrusive board test passes?

Non-intrusive board test (NBT) is an emerging test methodology that integrates several complementary test technologies to restore test coverage lost due to diminishing physical (probe) access to printed circuit boards. While NBT boundary-scan test provides a core capability for structural test (e.g., shorts & opens), NBT processor-controlled test adds an element of functional test (e.g., at-speed operation) and NBT built-in self test delivers performance test (e.g., on-margin operation). A framework to consider the overall test coverage in these multiple dimensions is required to assess the full impact of the test strategy.