Steve, I have read this before but what concerns me is when do you know how much stretch is to much stretch. Not knowing anything about the BGA discussed in your example, .46 mm to .68 mm seems like a lot of stretch. I would think that stretching the solder joint may lessens its ability to survive a drop test. joe -----Original Message----- From: Steve Gregory [mailto:[log in to unmask]] Sent: Tuesday, July 01, 2003 12:40 PM To: [log in to unmask] Subject: Re: [TN] double sided reflows and BGAs Hi Joe! I have to agree with Bev about taller joints being a good thing. In fact, one of the seminars I attended at APEX this past year (Solder Joint Reliability of BGA Assemblies given by Jean-Paul Clech) stated precisely that. SRS (Solder Reliability Solution) Models predicted that you would see over 1000 thermal cycles more before failure with a double sided reflow BGA than with a single reflow. Tests actually proved that. Tests were done on a 540 I/O cavity-down Enhanced BGA under thermal cycling conditions that were cycles from 0° C. - 100° C., with dwell times of 5 mins. at 72-cycles per day. Single reflow stand-off height was .46mm, double reflow stand-off was stretched to a height of .68mm. Single reflow BGA's made it to 8328 cycles, while double-reflow BGA's made it to 9271 cycles. -Steve Gregory- Hello Tech Netters, New board designs are incorporating BGAs on both sides of the board. During the 2nd side reflow, it appears that some of the larger BGAs installed on the 1st side reflowed which are now upside down are dropping slightly I suspect due to gravity. Dropping in the wrong direction, away from the pwb. Who can shed some info on how to either stop the BGAs from dropping, or apply some type of adhesive to the corners after 1st side reflow to secure the BGA in place? I am worried that securing the corners with an adhesive my later cause a reliability problem since you are now securing the corners to the pwb. thanks joe --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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/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 1.8e 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------