Reply to: RE>[TN] Use of Solder Mask Defined pads for BGA ? Hi Johannes, There is some debate about Solder Mask Defined (SMD) pads for BGAs. Some papers indicate that Non Solder Mask Defined (NSMD) pads increase the fatigue life of the solder joint (SMD pads cause stress concentration point in solder joint). However, it is interesting to note that many of the BGA component suppliers actually use SMD pads on the BGA substrate. So, although you can choose SMD vs NSMD for your board, the supplier dictates the substrate design (typically SMD). To address your overprinting question (printing paste on solder mask), we have been using overprinting for Ceramic BGAs successfully for the past couple of years without problems. The paste will pull back to the solder joint. You may want to verify on your particular assembly (X-sections, etc.). Hope this helps. Charles Elliott Newbridge Networks -------------------------------------- The pads of PBGA`s that we use are defined by solder mask on our multilayer FR4 pcb`s The diameter of stensil aperture is bigger than the pad diameter , so we are actually printing ( no-clean ) paste on the soldermask. Is this OK, or should it be avoided ? I presume that the adhesion between stensil aperture-paste is bigger than the other one between soldermask and paste, resulting to increased risk to solder balls, which could be fatal under PBGA ( pitch .05" ) Stencil width is 0.15 mm ( 6 Mils ), laser cut Stensil diameter .56 mm ( 0.22" ) Pad diameter 0.72 mm ( 0.28" ) max Solder Mask diameter 0.52 mm ( 0.20" ) Any opinions? Brs, Johannes ################################################################ TechNet E-Mail Forum 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://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################