On Wed, 25 Sep 2002 16:58:42 -0700, Dennis Saputelli wrote: >so how does a 'flying probe' test really work? >i understand the general idea of a couple of probes walking around the >comparing connectivity to a 'netlist' made from the gerbers
>but it seems to me and i think i read somewhere that this is better at >finding opens than shorts I know the guy who runs a flying probe tester at my board shop. Depends, checking continuity between all 'terminal' nodes of a net is pretty easy. Testing for shorts between a net and every other net on the PCB would take forever. The test preparation software runs an adjacency algorithm trying to identify which other nets a particular net might be shorted to. This software hasn't been perfect and they had at least one instance of shipping boards with an undetected short. For boards with planes the tester they have can do a high frequency impedance analysis against the planes. It continuity checks one PCB to ensure it is 'gold' and measures 'something' at high frequency (I guess a MHz or so) with a single probe on each net. Subsequent boards are mostly tested using the impedance test, a single probe on each net being way faster. They find this testing method pretty reliable. If you are worried about your boards not been tested, if they are surface mount you can look for tiny holes left in the pads from the probes. I don't know if "bed of nails" testers leave the same indication. They recently got an optical inspection system which is very impressive. It tests almost as fast as you can load boards. It does actually inspect against gerber data with a rather complicated rule system for what is acceptable. It presents anything dubious to the operator on a video display. It was impressive to see the tiny nicks in tracks or bits of copper or dirt it picked up. It's like a manual inspection with a microscope but 1000 times faster and doesn't miss anything. They got it especially for inspecting the inner layers of multilayers (to avoid the waste of putting a faulty layer though subsequent processing) but it is so fast and effective they now seem to put all but the most basic jobs through it. Cheers, Terry. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/[email protected] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
