Re: [PEDA] OT - bd testing
Dennis Just small follow up Flying probe test Test voltage 250 V Leak threshold 59 MOHS Continuity test 200 MA Resistance threshold 10 OHMS Jig Test Test voltage 40 V Test current 100 MA Low threshold 5 OHM High threshold 250 * 10 KOHM Best Regards John A. Ross RSD Communications Ltd 8 BorrowMeadow Road, Springkerse Industrial Estate Stirling, Scotland FK7 7UW Tel (Office) +44 [0]1786 450572 Ext 225 Tel ( Lab ) +44 [0]1786 450572 Ext 248 Fax +44 [0]1786 474653 GSM +44 [0]7831 373727 Email[EMAIL PROTECTED] WWW http://www.rsd.tv == - Original Message - From: Dennis Saputelli [EMAIL PROTECTED] To: Protel EDA Forum [EMAIL PROTECTED] Sent: Thursday, September 26, 2002 12:58 AM Subject: Re: [PEDA] OT - bd testing 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 whereas the good old bed of nails would (or could?) find both anybody know the down and dirty secrets of all this? Dennis Saputelli Dennis Saputelli wrote: it has happened to me twice 2 different shops they charged for test setup, testing, but there were short all over some of them and they were only double sided Dennis Saputelli Jon Elson wrote: Bagotronix Tech Support wrote: With a board that complex, your board vendor had better actually be doing electrical test, instead of just charging for it and not doing it... What? This is endemic in the industry? I've had to can several vendors for pulling this stunt. But, when they get caught by me, with my (in comparison) quite modest boards, there's no doubt what is going on, because the boards come back with 50% failure rate. IE. 50% of the boards have at least one internal short or open. I usually get the test report from Advanced Circuits, so I know what their yield is on multilayer boards. And, it is somewhere between 50 and 75% on most runs. The 2-sided usually come back at 90% or better passing. So, it is real hard for me to believe that many fabricators pull these stunts of pretending to do electrical test as a routine matter. I think they'd get caught WAY too often. Jon -- ___ www.integratedcontrolsinc.comIntegrated Controls, Inc. tel: 415-647-04802851 21st Street fax: 415-647-3003San Francisco, CA 94110 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Re: [PEDA] OT - bd testing
We need to come up with some kind of online blacklist (or whitelist) of PCB fabs. I certainly would not want to be a victim of inadequate (or fraudulent) board testing. How could we do this? Some sort of blog with anecdotal entries? Best regards, Ivan Baggett Bagotronix Inc. website: www.bagotronix.com - Original Message - From: Dennis Saputelli [EMAIL PROTECTED] To: Protel EDA Forum [EMAIL PROTECTED] Sent: Friday, September 27, 2002 12:31 AM Subject: Re: [PEDA] OT - bd testing thanks for all of your comments on bare board testing i learned a lot and also see better the dark underbelly of this beast Dennis Saputelli * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Re: [PEDA] OT - bd testing
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 It should ALWAYS find 100% of opens, as it should either test all possible combinations of points on a net, or walk down the net, checking from one end down to the farthest end. Checking all possible shorts, especially when opens may be present on the board, is not possible, due to combinatorial explosion. So, they have to use some sort of algorithm to figure out which nets are most likely to be shorted to another. nets which pass close to other nets, or have pads adjacent to another net, are the most likely. It is SUPPOSED to be correct practice to run the board again after fixing opens, so that the short detection can have a better chance of finding a short. whereas the good old bed of nails would (or could?) find both I think a flying probe may do better on large boards. The number of pins needed for a good-sized modern SMT board can run to the many thousands. The cost of the dedicated test fixtures, and the cost of wiring them up is a killer for low-volume boards. I suspect many outfits cheat on the test fixtures, and only place pins on the ends of nets. If you have a long, meandering net on an SMT board, it may not go through the pads much, so many small gaps in the traces could be missed. If you examine a tested board closely, you can actually see the marks made by the probes (either kind) and see how many points are being tested, and whether they are only testing from via to via, or pad to pad, etc. When volume gets above several tens of units, then the bed of nails is needed, as test time on the flying probe machine will become excessive. anybody know the down and dirty secrets of all this? This is one of those dark areas, where the fabricators don't care to have the buyers know exactly what they are doing. One reason is that many fabricators who CLAIM to have in house test, DON'T! There are test outfits that will test boards on a few hours notice, and the fabricators ship stuff all around to whoever has available time on their machines. I also would not be surprised, since I caught a manufacturer on this, once, that instead of generating a net list from the gerber and drill info, or from info supplied by the designer, they test the boards AGAINST EACH OTHER. IF they all have the same connectivity, they ALL PASS! I had a 6-layer board with some very convoluted split power planes in them. The fabricator increased the clearance around the non-connecting through holes on the inner planes without my approval, although I had already provided the clearance called out on their design rules. This split one of the planes into several sections. All the boards passed, because they all were split like that. They couldn't explain how this could happen, but I had a pretty good idea. This would be fine if they were supplied a golden board from a previous run, but testing a run against all members of that run allows all sorts of gremlins to get in, like corrupted Gerber files, Gerber files that trigger different interpretations of the way to draw something, missing layers, etc. Jon * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Re: [PEDA] OT - bd testing
thanks for all of your comments on bare board testing i learned a lot and also see better the dark underbelly of this beast Dennis Saputelli Jon Elson wrote: 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 It should ALWAYS find 100% of opens, as it should either test all possible combinations of points on a net, or walk down the net, checking from one end down to the farthest end. Checking all possible shorts, especially when opens may be present on the board, is not possible, due to combinatorial explosion. So, they have to use some sort of algorithm to figure out which nets are most likely to be shorted to another. nets which pass close to other nets, or have pads adjacent to another net, are the most likely. It is SUPPOSED to be correct practice to run the board again after fixing opens, so that the short detection can have a better chance of finding a short. -- ___ www.integratedcontrolsinc.comIntegrated Controls, Inc. tel: 415-647-04802851 21st Street fax: 415-647-3003San Francisco, CA 94110 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Re: [PEDA] OT - bd testing
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 whereas the good old bed of nails would (or could?) find both anybody know the down and dirty secrets of all this? Dennis Saputelli Dennis Saputelli wrote: it has happened to me twice 2 different shops they charged for test setup, testing, but there were short all over some of them and they were only double sided Dennis Saputelli Jon Elson wrote: Bagotronix Tech Support wrote: With a board that complex, your board vendor had better actually be doing electrical test, instead of just charging for it and not doing it... What? This is endemic in the industry? I've had to can several vendors for pulling this stunt. But, when they get caught by me, with my (in comparison) quite modest boards, there's no doubt what is going on, because the boards come back with 50% failure rate. IE. 50% of the boards have at least one internal short or open. I usually get the test report from Advanced Circuits, so I know what their yield is on multilayer boards. And, it is somewhere between 50 and 75% on most runs. The 2-sided usually come back at 90% or better passing. So, it is real hard for me to believe that many fabricators pull these stunts of pretending to do electrical test as a routine matter. I think they'd get caught WAY too often. Jon -- ___ www.integratedcontrolsinc.comIntegrated Controls, Inc. tel: 415-647-04802851 21st Street fax: 415-647-3003San Francisco, CA 94110 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 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/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Re: [PEDA] OT - bd testing
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/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
