A couple of things come to mind. First, check to make sure no solder bridges have formed. You didn't mention if this happened to all assembled boards or just some. Second, make sure the screw heads don't make contact with any copper under them. The solder mask will not prevent electrical contact through the screw head if there is a trace running tangent or under the screw head. Put some kapton tape or non-cunductive material under the screw head. Lastly, make sure the copper at the mounting holes is not up to the edge of the hole. If the copper comes to the hole edge, the screw may make contact with it and short to ground, or any other trace that may also come to the hole edge. Hopefully, it is something minor which will surface quickly. If the short is in every assembly I would expect it to be a layout problem. If it is in some, or most assemblies, it could be soldering, assembly, or even still a layout problem. Larry Campbell BFGoodrich, Avionics Systems >>> Bock Ming Gai Joanne <[log in to unmask]> 09/01/98 03:17am >>> Hi all, Currently I'm facing a problem at work. I have a few 6 layers of PCBs that are perfectly alright, meaning that they passed the ET. However, when our engineers did some testing after board assembly, problem surface. When they tighten the board with mounting screws, they found that one of the supply trace was shorted to the Gnd. This was not shown during the ET because PCB suppliers only did the test on the bare boards. So now I am looking into what could possibly cause them to short together. I appreciate anyone who can help to provide me with a solution. Thanks & Best Regards! Joanne Bock ################################################################ DesignerCouncil E-Mail Forum 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 DesignerCouncil <your full name> To unsubscribe: SIGNOFF DesignerCouncil ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ DesignerCouncil E-Mail Forum 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 DesignerCouncil <your full name> To unsubscribe: SIGNOFF DesignerCouncil ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################