Been there done that...................8-( Unfortunately sometimes where you need a memory array with matched signal lengths there is not an alternative .... One thing to watch though is that with BGA both sides the thermal stresses will be worse since you are pushing heat into both sides of the board at the same time on the same real estate. John Burke (408) 515 4992 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Monday, May 05, 2008 12:09 PM To: [log in to unmask] Subject: Re: [TN] BGAs on opposing sides We used to have an assembly with mirrored BGAs. Whenever we needed one reworked I called the design engineer responsible for this fiasco and told him to get his sorry butt down to the Airvac rework machine. It wasn't long before it was completely redesigned. Here is what you can do. Use Loctite 3609 to cornerbond the BGA on the opposite side. Cure at 150 for about 10 minutes, no more. Mask off the adjacent components around the BGA you wish to rework with a high-temp, ESD-safe, non-polyimid tape such as Tapes II T-32 (this is actually a 3M product). http://www.tapes2.com/electronics.htm Flux the BGA you are about to rework, and flux the mirror-image BGA on the opposite side of the assembly as well. That way if it goes into reflow it will have the advantage of a flux application. Allow to cool after removing the BGA. Perform the site prep, replace with the new BGA and reflow that in place. X-ray at an angle so you can verify both BGAs are good. If X-ray looks good, then remove the masking tape, run the board through the wash process, and finally chip off the cornerbonds using a small exacto knife. Do not cut into the PWB. If the customer allows it, you can leave the cornerbonds on. Qualify this process on your product before you jump in and rework a number of BGAs this way. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard Olsen Sent: Monday, May 05, 2008 1:29 PM To: [log in to unmask] Subject: [TN] BGAs on opposing sides Hello, I have a board before me with multiple BGA's on both sides. In some places they oppose each other. Does anyone have any manufacturing ideas for soldering the BGA's? One I have heard is to mask the first side BGA's and heat through the mask, BGA, board and finally the pads of the second BGA, finally removing the mask when done. Thanks, Rich Richard Olsen Quality Manager/ Sales & Customer Service RNB Enterprises 17816 North 25th Avenue Phoenix Arizona 85023-2108 Tel - 602-889-3463 Cel - 602-740-2244 Fax - 602-863-2274 Toll Free (800)-270-7585 www.rnbent.com --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------