Traditional test equipment using probing techniques to access pins and signals on Printed Circuit Board Assemblies (PCBA’s) faces increasing challenges. First the increasing use of Surface Mount Devices (SMD), and in particular Ball Grid Array (BGA) packages, makes external probing of device pins and nets more and more complicated. Secondly the ongoing integration of functionality in a single chip, resulting in System-on-Chip (SoC) devices, results in an increase of the complexity of such devices making external control increasingly challenging. As a result the possible test coverage and the diagnostic resolution of traditional test methods decreases for boards using these technologies. When an increasing part of a PCBA can be reached via JTAG testing, both the test coverage and the diagnostic resolution via JTAG increase.

If no JTAG devices are used on a board, then of course only traditional test methods can be used to test and program a board. However, if JTAG devices are used on a PCBA then their capabilities can be used for test and programming. Depending on the design of the board and the percentage of JTAG access it is possible that only JTAG-based test and programing tools are sufficient to test and program the entire board. If only a part of the board is accessible though JTAG a combination of traditional test methods and JTAG testing provides a high test coverage.

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