Design for Testability in Low Volume Environments
When dealing with electronic board production that must handle a mix of reduced codes and high volumes, the best technology for testing such products is definitely the bed of nails. This is because with this method, the reduced test time speed has a huge advantage, so much that it allows for the amortization of both the test firmware and the fixture.
In cases where production is highly variable, meaning with a high mix of production codes and low volume, the bed of nails technology is not economically viable, because the high costs of acquiring the fixture and test program can never be amortized in reduced production batches. In this situation, the best solution is definitely flying probe technology, which can perform a complete ICT (In Circuit Test) that is just as performant as the classic bed of nails version.
At Prime, we have gathered extensive experience in flying probe testing over the years and we are equipped with a highly programmable and flexible system with which we test most of our productions. With it, we can perform standard ICT testing with guarding techniques, nodal impedance or FNODE measurements, and powered measurements, meaning with the board under test powered up, verifying power consumption and functionality during this phase (check the machine’s capabilities on our website). Alternatively, and in cases where volumes and costs allow, we are able to manage standard bed of nails systems.
Initially, the Flying Probe Test was specifically created to test board prototypes. This is because, assuming you’re in the board design phase and considering that numerous attempts are needed to reach the final product design, it’s unthinkable to purchase a bed of nails fixture for each individual prototype generated. Instead, with a flying probe machine, you only need to modify the test program, which takes extremely reduced time and cost compared to the bed of nails solution. Flying probe technology can also reach smaller test points compared to bed of nails, approximately 0.1mm versus 0.8mm, which actually makes the electronic board design phase and design for testability easier.
Thanks to this technology, designers can make testing much easier and more efficient by inserting test points and taking certain precautions, such as not covering vias with solder. With this method, test coverage levels very close to 100% can be achieved (much more performant design for testability). With these measures, it’s also possible to test latest-generation components that normally cannot be reached by probes, such as BGAs.
In some cases, however, either due to lack of space, impossibility, or simply lack of knowledge, these small modifications to the printed circuit board are not implemented, and other methods must be found to increase test coverage.
Consequently, by combining Flying Probe Test with “careful board design, excellent results can be achieved in terms of coverage, repeatability, and” reliability of the test. On the downside, it’s important to remember that to perform this test optimally, it needs to be considered during the board development phase (design for testability).
The remarkable thing to consider is that generating design for testability for a flying probe test is simpler and faster compared to achieving design for testability for bed of nails testing, which is faster but unsustainable for businesses with low volumes and high mix of codes.
