Defect coverage of boundary-scan tests: what does it mean when a boundary-scan test passes?

A new coverage definition and metric, called the 'PCOLA/SOQ" model, introduced in K. Hird et al. (2002), has great utility in allowing the test coverage of defects on boards to be measured and compared rationally. This paper discusses the general topic of measuring test coverage of boundary-scan tests within this framework. A conclusion is that boundary-scan tests offer a large amount of test coverage when boundary-scan is implemented on a board, even if that implementation is partial. However, coverage is not perfect for certain defects in the PCOLA/SOQ model, as shown by example.