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24 SMT Magazine • June 2015 ed into the ICT, which can save fighting code that needs to be debugged and potential fixture problems all at the same time. Flying Probe + Boundary-Scan Flying probe machines work around the constraints of physical access needed for ICT test fixtures. With the help of automated pro- gramming and debugging, which helps to mi- nimise development time, a new application can be turned round in an afternoon instead of weeks needed to deliver an ICT fixture. However, components with inaccessible pins can still compromise test coverage. By in- tegrating boundary-scan capability in the flying probe tester, it becomes possible to apply pow- ered-test vectors directly to pins of a bound- ary-scan device. Testing can also be extended to non boundary-scan capable devices on the board. Monitoring the response then allows the status of the device and its connections to be assessed. Moreover, the benefits associated with library re-use are as applicable to flying probe as they are to ICT, and help flying probe to retain its quick-turn advantage. Boundary-scan also allows processes not normally possible using conventional flying probe methods—such as oscillator testing, pro- grammable part verification and complex logic disabling—without adding excessive complex- ity and so defeating the purpose of a flying probe tester. With boundary-scan added to the mix, test- ing is no longer limited to four, six, or eight probes. Tests can drive and receive as many sig- nals as the board design allows, which opens up test coverage and diagnostic usability previ- ously impossible to attain. Increased test coverage means better defect detection at test and fewer defects and product returns after the customer hits the "on" switch for the first time. Depending on the type of board, this com- bination of flying probe and boundary-scan test may exceed the test coverage achievable using ICT with a bed-of-nails fixture! Engineers can add the benefits of boundary- scan to flying probe without also adding the difficulty of a fixture-based test program. Di- agnostics are improved, and operators do not need to be taught how to interpret ambiguous test failures since boundary-scan is a digital test technology and points directly to the problem. It is even possible to run the same bound- ary-scan test on the flying probe and on an ICT platform like the 3070. A project can start with flying probe boundary-scan and then transition smoothly to ICT when higher volume testing is required, since the boundary-scan tests are re- usable. Conclusion Specialist boundary-scan is an ideal com- panion to ICT and flying probe testing. Users can benefit from better fault coverage, better test re-use, faster test development and fuller diagnostics. Popular ICT platforms have the necessary expansion capability built in, and specialty boundary-scan can be integrated suc- cessfully with flying probe equipment. SMT robert Thompson is a field application engineer for XJTAG. Figure 4: Typical flying probe tester. Feature TeST MATCH—PARTneRInG SPeCIALIST BOunDARy-SCAn WITH ICT continues

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