[previous] [next] [contents]    Boundary-scan test - Introduction

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 otherís 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.