New whitepaper explores NBT test coverage

Adam Ley
Chief technologist—boundary scan

A new whitepaper by Adam Ley, chief technologist—boundary scan, and entitled “Defect Coverage for Non-intrusive Board Tests” makes the point that non-intrusive board test (NBT) is an emerging test methodology that integrates several complementary embedded instrumentation test technologies to restore the test coverage that older intrusive test technologies have lost in recent years. The access needed by the older intrusive test technologies to physically probe circuit boards has been diminishing significantly for quite some time now.

Intrusive test technologies such as in-circuit test (ICT), flying probe test, manufacturing defect analyzers (MDA) and others are hardware intense. They rely on physical probes, expensive bed-of-nail fixtures and other hardware features. In contrast, NBT and other applications of embedded instrumentation are a software-driven methodology. As such, it allows the integration of complementary test technologies like boundary scan, processor-controlled test and built-in self test (BIST) to deliver the test coverage that is disappearing from the older intrusive test technologies.

The whitepaper reviews some of the frameworks that have been suggested recently for measuring test coverage. PCOLA/SOQ was one such proposal and it was added to by iNEMI in the PCOLA/SOQ/FAM framework. Since NBT can include elements of structural test, such as boundary-scan test, at-speed functional test (processor-controlled test) and self test (BIST) to discover faults involving insufficient operational margins, the test coverage provided by NBT meets many if not most of the criteria of the coverage frameworks most prevalent today.

Figure 1 – NBT covers the defect universe

The whitepaper also makes the point that providing extensive test coverage is not enough. NBT must do so cost-effectively. The cost-of-coverage is a critical advantage of NBT. Since it is software-driven, NBT avoids the expensive and complex hardware systems that dominate the intrusive test technologies. An ICT system on a manufacturing line, for example, can have a life-cycle cost of more than $1 million. In contrast, an NBT test station typically consists only of a personal computer (PC) with a low-cost adapter linked to the circuit board under test by a simple connector. As a result, NBT is emerging as a cost-effective alternative or a complementary test method to existing intrusive test technologies.

Click here to download Adam’s full whitepaper.