IMO, provided that the solder mask is intact, I have nothing against from the electrical point of view for assemblies not requiring the highest reliability under arduous conditions. On the other hand, from the physical point of view, if the bottom side of a component is plane and the solder mask is thick, it is clear that both component lands cannot be pulled down in intimate contact with the copper, with just the intermetallic layer in between. This I don't like. I feel that a very thin solder mask is required under these conditions. FWIW Brian Park Matthew wrote: > > We want to place traces under 1206, 805 and low-profile SOT23 components. > We are currently doing that for some designs and desginers are pushing for > it even further. I am against placing traces under these components because > of greater potential for causing tomstoning, shorting possibilities, and not > being a robust design. What are your thoughts for this? Is there any data > or studies done to show it is ok or not ok to run traces under chip > components. > > We ran a typical SMT process with LPI solder mask, water-soluble and > no-clean (very soon) and reflowed using convection ovens. > > thanks > Matthew S. Park > Sr. Process Engineer > Phoenix International Inc. Fargo, ND. > Tel: 701-282-9364, ext 434 > Fax: 701-282-9365 > > ############################################################## > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d > ############################################################## > 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 > ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d ############################################################## 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 ##############################################################