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104 The PCB Magazine • December 2015 With Thanksgiving in the U.S. a recent memory and many of us not on speaking terms with our bathroom scale, we now look forward to Christmas and the continuance and closure of the Holiday Season. With that comes the clo- sure of 2015 and the new challenges of 2016. With my last column of the year I thought I would publish some of the highlight questions I received over the past year: Q: My print says "Test to IPC-6012 Class 3/A." What is the difference between Class 3 and Class 3/A? A: IPC Class 3 is standard commercial/military/ medical/communication product where high re- liability is demanded. Continuity thresholds are 10 ohms or less and isolation thresholds are 10M ohms or greater. A mandatory test voltage is not specified other than IPC-9252A requirements of either the test voltage specified on the print or procurement document, the rated voltage of the PCB as a minimum if stated on the print or 40 volts minimum if no other direction is given. IPC Class 3/A is the IPC-6012 Exception for Aerospace and Military Avionics. When this re- quirement is specified the test voltage shall be 250 V minimum, the isolation resistance shall be 100 M ohms minimum and the continuity resistance shall be 10 ohms or less. Q: What is adjacency testing? A: Flying probe machines use what is called "adjacency testing" when performing isolation (shorts) testing. Unlike a fixture tester that tests all nets to one another during the test, the fly- ing probes test only nets that are adjacent (next to each other). In most applications, the flying probe performs line-of-sight or horizontal adja- by Todd Kolmodin GardIen SerVIceS testiNg todd 2015: It's a Wrap! ColuMn