It's probably not the vias under the BGA causing the board to sink. You are seeing the response of the board to isolated expansion caused by heating a small portion of the board. Try preheating a larger portion of the bottom side of the board. It is very common to have vias under the BGA, they provide escapes for the I/O in the array. > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of Rick Howieson > Sent: Wednesday, January 16, 2002 12:41 PM > To: [log in to unmask] > Subject: [TN] BGA/Vias > > > We have a board with a BGA that has quite a few vias on the board located > under the BGA. My question is...Should there be a limit of vias > on the board > located under the BGA? When we need to rework the BGA that area > of the board > seems to "sink" causing more problems, not to mention the integrity of the > vias. > Thanks, > Rick Howieson > Delta Group Electronics, Inc. > > ------------------------------------------------------------------ > --------------- > 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 previous postings at: www.ipc.org > On-Line Resources & > Databases > E-mail 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 > ------------------------------------------------------------------ > --------------- > --------------------------------------------------------------------------------- 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 previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------