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

Non-intrusive board test (NBT) [1] 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.