Earl, there's a big motivation to use solder mask defined pads when you're squeezing lines in between pads because you don't have to account much for soldermask tolerance. With non-soldermask defined pads, you have to consider where your soldermask will wind up (usually a 2 mil tolerance). Soldermask shouldn't be on the pads, and it shouldn't shift so much that you have an exposed line next to a solder ball pad. For this reason, it was the original design recommendation (in 1990) for boards using BGAs. Once the reliability data got out, non-soldermask defined pads became the preferred option. Terri -----Original Message----- From: Earl Moon [mailto:[log in to unmask]] Sent: Thursday, May 23, 2002 1:05 PM To: [log in to unmask]; Houston, Terri Subject: Re: BGA Solderability Totally agree with you on SMDP's. Did much work on this in earlier days and concur about stress. Question I always ask is why, but for this situation though not needed as such, does anyone use solder mask defined pads for anything? Earl --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------