March, 2014 Continued from previous page
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Boundary Scan Integration on Flying Probe Testers Software integration typically requires spe-
perform tests for shorts on IC pins, flying probes must be placed on the pins first. Once shorts tests for a current group of pins have been performed, the probes must be moved to other pins to test for shorts.
Boundary-scan testing does not rely on any
physical movements, so shorts tests can be per- formed much faster than shorts tests performed using the flying probe approach. Generally speaking, boundary-scan testers
are equipped to detect lifted pins on ICs if a bound- ary-scan cell can sense a logic level coming from an external source. This external source in this case may be another boundary scan cell from another IC interconnected through a PCB trace. Other pos- sibilities include pull up, pull down circuit configu- rations, and also other non-boundary-scan devices that are capable of supplying a logic level to the boundary-scan cell. There are some general guide-
lines that a design engineer should use to increase testability on a PCB but, generally speaking, a lack of
Boundary-scan testers are equipped to detect lifted pins on ICs if a boundary-scan cell can sense a logic level coming from an external source.
Design for Test (DFT) on a circuit board is not a problem for a flying probe test. In contrast, boundary-scan testers depend heavily on DFT imple- mented on the circuit board and ICs to be tested. A design engineer needs to implement boundary-scan condi- tions on a circuit board by providing TAP connections and proper connec- tions for ICs, whereas a product engi- neer may need to ensure that the boundary-scan-compatible version of an IC is available and the connector for the TAP can be mounted. For measurements performed
with a flying probe tester, a benefit can be to speed up a test. When test speed is important, a flying probe test program may be optimized to take advantage of the shorts and open pins tests that are already performed by a boundary-scan tester.
Added Access For measurements performed
with a boundary-scan tester, a benefit may be in terms of added access and therefore increased nets and pins cov- erage. Flying probes in this case can be programmed to function as virtual boundary-scan cells to provide input signals to boundary-scan cells and to measure the output signals from the boundary-scan cells. In a typical test setup, bound-
ary-scan hardware will control all of the digital vectors involved in the boundary-scan test. The digital boundary-scan vectors include both the TAP port and the digital signals through flying probes. The TAP port signals are generated directly by the boundary-scan controller, whereas the digital signals on flying probes are generated and sensed by the fly- ing probe tester. Flying probe hardware must be
in control of the probe movements. This is done for safety reasons and also to avoid any probe collisions. If the boundary-scan controller must either drive or sense a signal on a net on a circuit board under test, the boundary-scan software will specify which net it needs and the flying probe will move and position an appropriate probe in that location.
See at APEX, Booth 324 cially written dynamic-link-library (DLL) files for
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the boundary-scan controller to communicate with the flying probe tester. The DLL files facilitate sev- eral aspects of integration including proper test flow, sharing of information to optimize the tests, test result reporting, and combined test coverage reporting.
Case Studies Several case studies have been performed on
Increase of coverage possible with flying probe and boundary-scan integration.
the integration of the two test approaches. These studies reveal that one technology may benefit more from the integration than the other, and also that the combined test time is not always faster than when performing the two tests separately. Either way, the studies reveal, the combined final test coverage is greater compared to each of the technologies used separately. In the first case study, the circuit board under
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