Hi Technet, well for once I can post some information instead of asking!!! Awhile back I posted some questions regarding the failure of a glass zener diode, wanting to know what the failure was. Well after some research and money, I came up with the root cause, thought I would share my findings. Some pictures of the diodes can be viewed at http://www.driveway.com/web/catalogView.jsp?dwSession=vapp03-36a84655aeb859b c (thanks Steve) The module is used in an harsh environment, exposed to various thermal cycles, and moisture. A polyurethane compound encapsulates the components and a nylon-glass case houses the package. The zener is used in the circuit for clamping transient voltage levels, the failure mode of the zener is a short. Modules were being returned exhibiting high current draw, following some circuit troubleshooting I determined that the zener diode was the fault, after removing the potting compound the observed diode conditions were noted, (see photos) Removal of the nylon case revealed evidence of moisture ingress, white residue, the diode being located on the edge of the board was visible through the compound. The presence of moisture and voltage, as well as contamination (board level, salt water from road) caused cathodic reduction. which in turn created a leakage path through the diode. This leads me to one question, what is the minimum distance components and signal tracks should be placed from the edge of the board,? (through hole components) Hope the information is interesting Jason Larson ############################################################## 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 Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################