In a message dated 9/10/99 8:10:11 PM Central Daylight Time, [log in to unmask] writes: > Steve: > > Since you're referring to internal shorts, I'm assuming that the short is > occurring > between two features on the same layer. I recommend that you perform an > examination of > the board artwork. FR-4 has the ability to withstand (I think) about 500 > volts per mil > (0.001 inch) perpendicular to laminations, i.e. between layers. It has > significantly > lower withstanding capability parallel to laminations (on the same layer) of > 45 volts > per mil. > > I have seen perfectly good video power supply boards fail after relatively > short field > service because of carbon filament growth creating an internal short. The > short grew > from the barrel of a plated hole to a ground plane. We modified the artwork > by > increasing the ground plane clearance around the barrel of that hole and the > field > failures ceased. Note that the 45 volt per mil figure is a laminate > specification and > an appropriate safety factor should be added to allow for manufacturing > tolerances, > etc. > > Hope you found this useful, > > Don Vischulis > Hi Don, First, I wanna say; I really think this list is great! I only say that because I see when I send a message (as the rest of you do), I get one back that tells me how many list members my message has been distributed to seems to be decreasing, I hope it's not because of me...but if it is, screw em'!...hehehe...(I don't really mean that)...those of you that unsubscribe, may miss something that will cure your headaches! I may come off as irrelevant sometimes, and sometimes pretty crass, but I'm just like many of you, in a position where we're supposed to solve all the problems that might occur during manufacturing. Nevermind that we don't have any input on the design of a product, the layout, or the components used, we just have to deal with why we can't ship...or why we get boards sent back...I feel sometimes like the boy that has his finger in the leak in the dike...you understand? I don't want to drive people away from the TechNet because of my style, I hope I'm not doing that...I just try to be as down to earth as I can...no fluff here. Apart from my boring dissertation, I'm attempting to get possesion of the gerbers for this board so that I can see what has been designed. I don't think that I'll find any problems with the design because this particular problem hasn't been experienced in the past few years that this assembly has been built here...and the gerbers haven't changed as far as I know... Learning more about things, this fab is pure polyimide, very brittle, and difficult to drill large diameter holes without problems. I've looked at the unplated holes that were drilled, and I see a very rough, crazed, and chipped surface on the insides of the holes...not very smooth. This was something that the fab vendor suggested I should do...take a look at the unplated holes to see how they looked. I recieved a phone call from them after I first posted about this problem. Just goes to show ya' how many people look at this list. I didn't mention any names, companies, or anything like that at all, but it was within a couple of hours after I posted my message that I recieved the phone call, from the fab vendor...pretty nifty, huh? That don't mean that I always post to the TechNet with a problem before I talk to a vendor, it's just that sometimes you get in a organization that it's really tough to find out who a vendor is (believe it or not!)...I know some fab vendor logos are etched into fabs, but hey! I don't have a photographic memory!...and some vendors don't put their logos at all on their fabs. Anyhoo, it's looking like there indeed maybe a problem with the bare fab...a learning experience for more than just a few people. These particular assemblies were built before I even started here anyway...so I can't be blamed...woo-woo! (GRIN) -Steve Gregory- ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################