I am not aware of any specific studies about solder joint integrity as it relates to the amount of solder mask encroachment onto the SMY pads; however, a number of comparies have done studies about the thickness of solder mask as it relates to good solder joints (DuPont, Morton, Ciba-Geigy, etc). Basically, with solder mask that is higher than the surface mount pads ( for example, 2.0 mil high SMT pads being surrounded byu 3.0 mil high solder mask), you can have a starving effect when stencil screening the solder paste onto the pads (ie, low solder paste deposit or no solder paste at all) on the component side and/or a shadowing effect when wave soldering the SMT components on the solder side. Both of these conditions could lead to poor solder joint integrity. When solder mask does encroach onto the SMT pads, it must obviously be higher than the pads and could cause solder joint problems. My question is: Is the solder mask encroachment caused by the design of the board or by poor registration? I have seen designs where the solder mask does come up onto the land areas of plated through holes (by design) and many designs allow solder mask to completely cover and fill via holes. I'm not sure if I've seen designs where mask is allowed to come up onto SMT pads. Larry Fisher Dexter Electronic Materials [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] * ***************************************************************************