When two worlds collide
09 December 2009
Testing electronic boards requires more sophisticated tools that must be fast and easy to use, and meet the requirements of high quality and cost-effectiveness for the manufacturing and repair environment. Luca Carli, Product Manager at Seica SpA (Italy) looks into the subject.
To ensure the highest fault coverage possible and the highest capability of specific fault identification, a good electric test program dedicated to an electronic board is usually executed to combine several measurement techniques, assuming that there are different categories of possible faults while there is not a single test method capable to detect and identify them all.
The automatic test equipment best suited to the philosophy of combining different test techniques in a single program is the flying probe ATE, which Seica proposed as a test platform and not as a system capable of a single specific test. The nature of an ATE flying prober, which does not require a dedicated test fixture for a specific kind of board, enables the set-up of different test methods such as in-circuit, vectorless, functional test, and AOI, and the possibility to create programs automatically through the CAD files. An essential requirement for the use of a flying probe system is the possibility to contact the board under test by physically placing a probe on every net in order to execute measurements.
When this is not possible, perhaps due to the inaccessibility of the components or test points, the flying probe system presents an insuperable limit, which decreases its diagnostic capability on those inaccessible nets.
This limit may be broken with the integration in the ATE flying probes of a test technique such as boundary scan, which, by virtually accessing to the nets of these components equipped with this technology through a four or five-wire bus, essentially solves the problem of the physical access with a flying probe.
Integration between boundary scan and ATE flying probes
When a new test technique is integrated on a flying probe system, it is essential to maintain some basic characteristics typical of the flying probe ATE.
This provides a number of advantages to the user without increasing the costs for development, such as:
• Fast generation of the test program
• Easy to use
• Increased fault coverage and high ratio capabilities/price
• Fast time of execution
• A single test report for the different techniques employed
For a long time, the boundary scan test technique, (conceived in the same period of the first rudimentary flying probes test systems), remained light-years ahead. Back then, the flying probe systems didn’t power the UUT (Unit Under Test) and were limited to the MDA test (Manufacturing Defects Analysis) of the passive components of a board, while the boundary scan could not spread due to the cost of the technology needed to equip the components with the JTAG port. Over a number of years, the flying probe systems had a considerable evolution, while the complexity of electronic boards increased (as did the employment of IC equipped with JTAG port), until both the flying probe and boundary scan testers found their right place in the market of electronic test, although remaining quite separated.
In addition, there have recently been several attempts to combine these two capabilities; to equip a flying probe system with boundary scan test capabilities. However, the results achieved often did not meet the expectations of the end users, since the integration of two rather complex worlds provided the following disappointing results:
• Two different software environments with a partial and slow mutual integration
• Necessity of two different environments to create test programs
• Redundancy of tests instead of measurement optimisation
• Two test reports for the same board
• High costs
• Two active suppliers to support single test equipment
FlyScan: true and deep integration
Aiming to further enrich its range of solutions for the test and repair of electronic boards, Seica, in partnership with Temento Systems, has developed the FlyScan module as a new approach to the integration of the boundary scan technique and flying probe test systems. The true innovation of FlyScan, available on the complete line of Pilot/Aerial flying probe testers, is full integration at the core system level, ensuring the following capabilities:
• Automatic generation of the test program in a single software environment (Seica VIVA)
• Automatic generation of the boundary scan program for the nets which are not JTAG, using the extended test function and the flying probes to transform them into JTAG testable nets
• Automatic elimination of test redundancies
• Automatic fault diagnostics, with real-time generation of additional tests executed by the flying probes for the specific identification of the faulty component
• A single test report in the VIVA environment
• Management of the errors detected by the boundary scan test in the Seica Repair Station environment
• Cost restraint
Even though its development and integration is the result of a significant investment in R&D, the basic idea of the FlyScan module is very simple; it exploits the specific benefits of flying probe and boundary scan testers, creating a single test program which utilises the full capabilities of both, not as two entities working independently, but in a fully integrated system.
The possible advantages of an integration between flying probe and boundary scan testers are numerous.
In phase of program creation, the CAD data import is performed only once and this benefits the automatic generation of the MDA/ICT/AOI/functional measurements of the flying prober and the automatic generation of the boundary scan tests (programming time saving). In addition, the opens/shorts test on the JTAG type nets may be executed by the boundary scan much faster than a flying probe tester. Furthermore, the nets which may not be accessed by a flying probe tester and related to components equipped with JTAG port (for example, a net which connects only two pins of BGA components and where no test point is scheduled) can be tested by boundary scan; increasing fault coverage.
The nets not related to JTAG components may become JTAG type nets if contacted by the flying probe tester, so it is possible to include them in the automatic generation of the boundary scan program without requiring manual cluster test. And in case of error detected by the boundary scan test, the diagnostic tests are generated real-time and require the use of the flying probe to detect the specific faulty component on the net, in a more specific way than if compared to the standard boundary scan, which can not distinguish two nets related to a buffer or to a serial resistance.
The examples discussed above are amongst the most significant, but there are others that make the deep integration between flying probe and boundary scan testers considerably more attractive for those who need a complete tool to detect and diagnose the faults present on an electronic board; whether it comes from the production line or from a lot of repair from the field. It is important to remember that FlyScan should not be confused with the usual basic integration performed in the past, such as the capsuling of a POD equipped with some TAP port boundary scan into the flying probe system, as the latter uses its own power supply to power up the UUT.
FlyScan provides a low-level dialogue between the two operating systems (flying probe and boundary scan) with a steady interaction at the programming level and test execution; together with a constant data exchange, aimed to test time and fault coverage optimization. This is the real introduction of the flying probe system in the chain which links the different JTAG components on the UUT. The flying probes work like the pins of a new JTAG component, placed (as indicated by the test program generated automatically) on nets that are not of the JTAG type, and transform them into JTAG testable nets.
When compared to the classic approach where a board is subjected to a standard flying probe test and then to a boundary scan test on a separate test station, the core interaction between the worlds of flying probe and boundary scan enabled by the Seica FlyScan module provides a decidedly improved test result, easily measurable in terms of speed, throughput, and fault coverage.
FlyScan is now available on all of Seica’s Pilot/Aerial flying probe systems, from the entry-level Aerial M2 up to the top of the range Pilot V8.
Luca Carli is Product Manager, Seica SpA (Italy)
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