Approved as an
IEEE standard since February of 1990, under the title of "A standard
boundary scan architecture and test access port", the BST technology
met an increasing acceptance in a broad spectrum of sectors related to
digital electronics design and manufacturing. A wide variety of BST
components is now available, together with tools that cover a wide range
of activities, from the design of the BST infrastructure to the automatic
test vector generation for boards with BST components.
Two main reasons led during the 80s to the development of the BST
technology:
- The increasing complexity
of integrated circuits (ICs) made it exceedingly difficult to develop
test programs for the functional test of complex printed circuit
boards (PCBs), requiring extensive access to internal control and
observation points (functional test equipment relies heavily on access
through edge connectors and therefore became increasingly inefficient
in these cases)
- The shrinking effect of
using small outline surface mount devices and advanced mounting
technologies almost disabled physical access to internal PCB nodes
(in-circuit test equipment relies on the use of bed-of-nail fixtures
to provide direct contact to internal PCB nodes, but is limited in
terms of mechanical precision and reliability)
In-circuit and
functional automatic test equipment (ATE) were traditionally used in
combination to overcome each other’s limitations, but the packaging and
mounting technologies that emerged in the late 80s made it clear that the
design and manufacturing of advanced digital electronics modules was about
to face a major bottleneck. Unless an alternative test technology was
developed to overcome the challenge of testing new circuits and electronic
assemblies, the complexity of the problems at hand was guaranteed to leave
all traditional ad hoc and in-house structured test methodologies
way behind.
An international group of companies was set up in 1985 to develop a
proposal for a new standard (design for) test technology able to
gather a wide support in the design, test and manufacturing worlds. This
group was known as JETAG (Joint European Test Action Group) but rapidly
incorporated US companies and dropped the E, leading to an IEEE working
group that managed to have an approved standard in five years time. Due to
the very nature of the problem that led to its development, the BST
technology, such as defined in the IEEE 1149.1 std, addresses a very
specific domain: the structural test of digital printed circuit
boards (note the keywords structural, digital and PCB).
These three attributes were sufficiently narrow to enable a quick
development of solutions taking place immediately in the early 90s, but at
the same time they somehow limited the application domain of a technology
which may still live to see a much broader scope. |