Hello Brad, Thanks for responding! Our board design is two layer (1/2 oz. copper sandwiching .030" FR4). I only took one semester of deformable solids, but I agree that a standard layer of LPI should not be able to bow a .030" stack to any significant extent... The concern was raised by our vendor (three letters - starts with a D) Your input has emboldened me; we're going to stick with a full mask on the BGA side. I'll keep you posted :o) Thanks again! Tom Ochenas Maxtek Components Corporation -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Thursday, May 30, 2002 5:58 PM To: [log in to unmask] Subject: Re: [TN] soldermask ring v. full coat for BGA design Hello Tom, My that is an unusual request/requirement. .004 is the min I like, it can go down to .003. Below that... I wouldn't trust it. Actually the "ring" configuration you speak of is unique enough that I believe it will be problematic. I would not do it. As to the statement of board warping due to soldermask on one side; I disagree. Soldermask, especially LPI is pretty friendy stuff relative to warp. Unless there is some unusual condition of board thickness or finish, one side solder mask will not warp a board. Brad Saunders Coretec Boston Office 781 858 0783