Hi Alex- I don't use any given set of rules but more a rule of thumb. The more layers the PWA contains the easier it is to not drop the components off the backside/bottom side. My thermal characterization runs have shown that the board inner layers absorb the reflow heat thus keeping the PWA surface from heating up over the 183C mark - i.e. the more inner layers easier to keep parts in place. The PWA thickness has an effect too but not nearly as influential as the number of inner layers. Have fun. Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: # of Layers? Author: [log in to unmask] at ccmgw1 Date: 12/10/96 5:50 PM Dave/ Rockwell Collins Can you elaborate more on the response you gave concerning "SMT components on both sides of PCB" << some assemblies are hard to do both sides due to design issues (# of layers)>> What is the rules you use as far the # of layer is concerned? Thank you Dave Alex Basauri [log in to unmask] Trimble Navigation LTD The GPS Solution!! 645 N. Mary Avenue B6 Sunnyvale, CA 94086 (408) 481-8751 office (408) 815-0456 Pager (408) 481-6077 Fx *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************