Implementing boundary scan test strategies

Board-level boundary scan testing, focusing largely on the boundary scan EXTEST mode for structural testing of interconnects between boundary scan devices on a board and testing of conventional, nonscan components which cannot be accessed using traditional in-circuit or cluster test techniques, is dealt with. Strategies and test-nail placement for implementing various types of boundary scan testing are detailed. The strategies discussed are virtual interconnect, virtual in circuit, standard cluster testing, and virtual cluster testing. It is shown that, where restricted physical access hampers in-circuit or cluster testing, virtual access provided by boundary scan device leads may offer the means of assuring a comprehensive test. When both physical and virtual access is needed, this requirement must be taken into account during board design and factored into board layout to ensure successful implementation of the test