ROLAND, I'M NOT SURE IF THIS WILL BE OF ANY HELP OR NOT, BUT HERE GOES. ABOUT 6 MONTHS AGO WE BEGAN HI-POT TESTING OF SOME NEW PRODUCT, (A MULTILAYER BACKPLANE). WE EXPERIENCE SHORTS ACROSS CONNECTOR PINS IN VARIOUS LOCATIONS ON THE BACKPLANE. WE REDESIGNED THE BOARD WITH LARGER CLEARANCES BETWEEN PRIMARY AND SECONDARY POWERS AND GROUND. IT SHOULD HAVE WORKED, BUT IT DIDN'T. MAJOR FUSTRATION. WE BEGAN LOOKING AT THE SYSTEM. COME TO FIND OUT A CONTRACTED POWER SUPPLY HAD HAD A BRACKET CHANGED, (WHICH DIDN'T EFFECT OUR ENGINEERING SPEC OR SO WE THOUGHT). THIS CHANGED CAUSED A POTENTIAL SHORT IN THE POWER SUPPLY WHICH PASSED DOWN THE WIRING TO THE WEAKEST LINK ON THE MOTHERBOARD. I GUESS WHAT I'M SAYING IS THAT THE PROBLEM MAY NOT BE WITH YOUR BOARD, BUT WITH A POWER SUPPLY OR THE AXIS MOTOR. CONTACT YOUR VENDORS AND SEE IF THEY'VE MADE ANY "IMPROVEMENTS". ROBERT BUTTERWORTH SR PCB DESIGNER ADC VIDEO SYSTEMS [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: FAB:BURNS FROM SHORTS Author: [log in to unmask] at internet-mail Date: 5/12/96 9:58 AM Dear Teknets, We would appreciate your help for solving a though case leading to high costs in the field. To our knowledge this is not very common. A customer have machines that break down due to an electric short on axis motor drivers. The shorts show up at random on the board surface, and are burns. They are not necessarily located on holes. The boards are in machines and a growing percentage is coming back from the field. Some are 3 years old now. Older boards from the same manufacturer don't have this problem. The design being the same. It happens onto two different boards of different building and thicknesses. In both cases, part of the production is made pin-lam in house by the manufacturer, the other is made mass-lam by a Mass-lam manufacturer. REF - 125 4 layers - thickness 2.4 mm - inner + outer copper 1 oz FR4 core is 0.56 mm thick 80 VDC - 10 A 5 VDC - 240 mA +- 12 VDC - 140 mA REF - 126 4 layers - thickness 2.4 mm - inner + outer copper 2 oz FR4 core is 0.41 mm thick 200 VDC - 16.5 A 5 VDC - 10 A 110 VAC - 5 A 124 VDC - 1 A 5 VDC - 1 A 18 VDC - 1 A 24 VDC - 1 A - - ---------- copper outer layer 1 \/\/\] [\/\/\/\/\/\~/\/\/\/\/\/\ FR4 Preg 7628 2 several ~~ ~~ ~~~~ ~ ~~~~~o~~~o~~ x \/\/\] [\/\/\/\/\/\/\/\/\/\/\/\/ FR4 Preg 7628 3 several ] [ --------------------- copper innerlayer 4 =====] [======================== FR4 core 5 ] [ --------------------- copper innerlayer 6 \/\/\] [\/\/\/\/\/\/\/\/\/\/\/\/ FR4 Preg 7628 7 several \/\/\] [\/\/\/\/\/\/\/\/\/\/\/\/ FR4 Preg 7628 8 deveral - - ---------- copper outer layer 9 x = path used by the short on a long distance, 2 + 3 splitted and we can see dark veins (burns)containing copper residues... inside the length of the board. We can see cavities + copper particules. It looks like veines of a tree. o = looks like copper residues trapped between the prepregs. There is no dammage between 4 + 6. An explanation could be that, the prepreg resine is removing oxydated copper fragments and they concentrate in the middle of the two prepregs. Then aging (temperature of the working board) the shorts are possible within those small residues. I don't dare sending you all pictures in .jpg format as an attachment, but if you do like to have a look on the microsections let me know. They are stored in my PC and I will send it to you ASAP. Thank you for your help Roland [log in to unmask] Henri Jaquet SA Geneva Switzerland tel. xx41-22-794-7878 fx. xx41-22-794-3052