> Also, in an EMI-sensitive environment, how would you recommend the layer > stack-up? Signal 1, Ground, Supply, Signal 2 OR Ground, S1, S2, Supply? > OR > something else? > In an EMI sensitive environment, the rules of thumb to follow are: * Put only components, pads, and short traces to vias on exterior layers. Fill the rest of the exterior layers free area with ground plane. * Make the board as opaque as possible. Fill all free areas on all signal layers with ground plane. * Treat very high speed (that is, high energy) signals as EMI generators. Shield them as much as possible; both from the exterior world and from other signals. Also avoid any sharp turns with high speed signals, as that vertex will act to radiate energy (EMI). * Provide lots of connections to ground. This will reduce ground impedance. The goal is to trap the electromagnetic energy within the board, letting it be absorbed into the ground planes. Whether you stack signal layers within the board on top of each other is a function of the signal levels you're dealing with, and their susceptibility to crosstalk. Minimizing parallel trace lengths on adjacent layers to less than an inch is a good rule and usually reasonably easily achieved, provided you're routing each layer perpendicular or 45 degrees with respect to adjacent layers (also, of course, providing your design software has some way of checking this criteria for you). Michael Hiteshew Lockheed Martin Launching Systems [log in to unmask] (410) 682-1259 ############################################################## 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 ##############################################################