Hima started using boundary-scan in 1997, when it became impossible to give a new complex digital board the test coverage they were used to with conventional tools. The implementation of boundary-scan - and the selection of which boundary-scan components to be used - must be considered right from the development and prototype phases, says mr. Thielemann, Test Engineer in Test Preparation.
"Many components now incorporate boundary-scan technology, which is even giving test access to non-boundary-scan components. Manual calculation of the scan-chain shift lengths and TAP controller states is no longer necessary with the advanced hardware and software products provided by JTAG Technologies."
"The cost of adding boundary-scan to trivial logic sections is balanced by using programmable logic. Naturally, it takes time to learn how to use boundary-scan tools and build experience in handling application problems. But although the flexibility of the tools may make testing and programming complicated to learn, it is quite easy when mastered. Hima have learned design techniques for keeping the number of cluster tests (which test the interconnectivity of non-B/S components) low, and using the interconnect test (which tests the connections of boundary-scan components) to cover as many failures as possible.
With testability built in at the design phase, blanks in the test coverage for prototypes are avoided. This is essential, particularly for high-safety control systems where 100% test coverage is a customer requirement. With our current production levels, our job would just be impossible without boundary-scan.
Hima's test strategy is to run an in-circuit test, static functional test, boundary-scan, and final system test, allowing them to optimize the results from each method individually. "In-circuit test program generation is performed automatically and gives us very good fault localization. You do need to contact all the nets and the information is very detailed, down to every component and pin. Next, static functional test picks out many operating faults, but it cannot perform ‘real' dynamic tests. Although it can test op-amps and other components, this requires manual programming. Boundary-scan gives us a practically automatic test for digital components - again giving us an exact pin-level failure description. Lastly, the system test thoroughly checks the board through a range of environmental conditions".
Hima's focus is on fault prevention, and boundary-scan has helped to improve the production process itself. Boundary-scan gives a very good fault diagnosis, and consequently information for improving the process. With ever more complex designs demanding BGAs (ball grid arrays) to save board space, boundary-scan is the only method to give 100% coverage, and also indicate fault locations.
Stefan Thielemann, Test Engineer in Test Preparation, Hima Bruhl