----- 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? Not all the secrets but main points It is quicker (for the board fab co. anyway) to check board for open circuit tracks as it is easier for the software to find node ends by itself and therfor define prob targets and optimize the route path for the probes. This is most prominent on shops that supply QT prototypes. I stopped using a lot of board shops for this. Miss 1 short, even if you fix it, could mean more than one open tacks later. Most test machines will also check for adjacent shorts (using both board sides & vias) but this takes longer and relies on correct netlist extraction and node definitions and is usually limited to a small area around the nodes being tested. Testing rules are normally defined globbally in order to set pass parameters. Not always a good thing, but it is not so easy for them to define individual rules as they are effectively dealing with their reconstruction of a dumb format (gerber). The test voltage is usually low <5v and the acceptable parameters for, expecially open tracks or shorts is usually left as default, which is sometimes not enough for hiZ shorts on close tolerance boards with badly set rules. A lot of companies also use FP testing to verify a board before using BON testing. Worrying is it not ;-) Like all other areas the engineer in charge of the FP testing & the front end guys are the most important link and as in most companies you get good & bad, and also very varied excuses to why the board comes out bad, even after testing!. John > > 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.com Integrated Controls, Inc. > tel: 415-647-0480 2851 21st Street > fax: 415-647-3003 San 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/[email protected] * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
