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84 PCB007 MAGAZINE I OCTOBER 2022 Historically electrical test has processed product with passive inductor features with- out really knowing what they were, other than causing continuity threshold violations. is is usually due to the long traces that exhibit higher resistance than the 10- or 20-ohms threshold. Typically, these have been delaying traces or heater traces. Usually, a waiver of allowance is made for these high resistive traces and busi- ness carries on as usual. However, there can be a lot more going on than just a long or coiled trace. Figure 1 shows a typical heater scenario. As you can see in the illustration, each is a single net with a long trace. e characteris- tic of this design is spe- cific, and the entire trace is necessary. e prob- lem is whether any of the long trace shorts to itself. In a standard continu- ity test, this defect will go undetected as a short to itself and will not pres- ent a change in resistance significant enough to fault. However, the circuit itself now fails against its intended design. ere are two possible solutions to capturing this defect. e 4-wire Kelvin Test may capture the small Induction Junction, What's Your Function? change in resistance, but with this much cop- per the accuracy of the test may be compro- mised to the point that the change would have to be too significant to trigger a fault. e other option is testing the inductance of the network. ere is technology available to perform this test on a flying probe. Pre-programmed val- ues can be provided to the machine and when the test encounters this device it will check the value and compare to expected. is test records all values and can provide a report for post-test analysis. Now, in my above example we discussed a very basic scenario of a heater or timing trace. Testing Todd by Todd Kolmodin, GARDIEN SERVICES USA Figure 1: Heater trace.

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