Welcome to the Designers Council Steve. I have visited your website many times. My approach to vias under BGAs has always been to fill the vias with solder mask. We never had any failures due to solder ball shorting under the part, although there have been some occasions where loose balls of solder were left under the part and had to be cleaned out. I'm not familiar with this method of encroaching the solder mask to the edge of the hole and then leaving the hole open... does that not make an opportunity for loose solder balls to get trapped under the part at the via hole edge or in the barrel? Although it may prevent trapped moisture from exploding under the part when out gassing I still really see no advantage to that method as yet... It just seems like any flux or other liquid materials used in processing would get trapped in the vias and present a cleaning challenge. Maybe someone could explain why they would do that so I can understand what the goal is there. Glad to see your comments on the DC list server. Best regards, Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 http://pcbwizards.com -----Original Message----- From: Steve Gregory [mailto:[log in to unmask]] Sent: Wednesday, September 29, 2004 5:14 PM To: [log in to unmask] Subject: [DC] Via protection beneath a fine pitch BGA... Hi All! This is my first post to the Designers Council. I have a question about solder masking via's in a BGA pattern, and want to see if I'm thinking correctly. I'd like your opinions about this. I think it's a bad idea to leave the via's free from solder mask on the topside of the board beneath the BGA, and then tent (or plug) the via's from the bottomside. To me, you're just asking for trouble down the road because you're creating a little "cup" if you will, that willl trap flux residue and all kinds of stuff in the via's that won't be able to be cleaned out well. This is a 676 ball 1.0mm pitch BGA pattern. This assembly will be put together using double-sided reflow, there will be no wave soldering. All through-hole is going to be hand-soldered. My opinion is that either you leave the via's free from solder mask on both sides, or cover them on the topside only, or ideally, plug them completely. Am I wrong about this? Thanks! -Steve Gregory- ---------------------------------------------------------------------------- ----- DesignerCouncil 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 DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- DesignerCouncil 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 DesignerCouncil. To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ---------------------------------------------------------------------------------