Testing vias may be acceptable, but not preferred. If you do test by via, it�s a last resort type of thing. Vias are always a pain in the real world. Generally, they are soldered by wave, so they aren�t always doomed correctly, plus residue build-up occurs on the pins as well. Not the end of the world but then mix in a couple of new board vendors who can�t seem to get the via openings right now and then and it becomes more of a struggle. Now toss in the fact that on any new board spin, most ICT guys prefer all vias open for ICT development. Now you have to go back and cover the unused vias after development or you get a rash of solder shorts. Then, you always get that one or two vias that are 0.010� away from a pad that has to remain open for test, yet not solder short to the pad. Sure, vias are acceptable as a last gasp alternative to not testing at all, but never preferred.
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