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74 SMT Magazine • December 2016 by Thomas Wenzel and Enrico Zimmermann GOEPEL ELECTRONIC One of the most serious problems in test- ing is the continuous decline in physical access. Across a range of markets, users unanimously report slumps of up to 20% within the last five years, which inevitably leads to discussions on test methods that can be used in future. JTAG boundary scan has gained a good reputation in this context, but this process alone cannot provide a solution to all problems either, and partners are needed. The main focus of inter- est is the functional test. This report analyses some fundamental aspects of this combination and introduces new technological solution ap- proaches for embedded functional tests, as well as their practical implementation. The Interplay Between Structure and Function No matter which of the common electrical testing strategies are examined, they all fall into two basic categories—structure test and func- tional test. According to table 1, both adhere to completely different principles to trigger and Boundary Scan Meets Functional Test diagnose a fault. While the structure test at- tempts to test the design through access on the element level, the functional test aims to test connected components. However, the success of the structure test is based on securing the required access to the ele- ments, and techniques such as ICT, MDA or FPT are becoming less and less useful in this con- text. The functional test on the other hand typ- ically uses the native connections of a Unit Un- der Test (UUT) as the basis for access, thereby circumventing this problem. As a result, it is no surprise that users are again increasingly focusing on this technology. The so-called cluster test is a subgroup of the functional test. Cluster tests are basically the re- sult of insufficient access, as they include the testing of a partial circuit via the test points that are available at the edge of the partition. The logical consequence of diminishing test access is ever increasing cluster size, as far as the com- plete loss of meaningful clustering. The question if the structure test makes the functional test redundant or vice versa, is also a frequent, hotly debated topic. The main rea- son behind this is the objective to test as little ARTICLE

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