Hi Tom! Have you done destructive analysis? You simply take a diamond burr, a Dremel tool or equivalent, and a few drops of water and carefully grind through the failed device to get down to the interface without affecting the failed solder joint. Studying that joint usually shows what the problem is pretty quickly. Also, is there any pattern to the failures with respect to the BGA geometry or the geometry of the pads it is being soldered too? Wayne Thayer -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Gervascio, Thomas Sent: Monday, November 12, 2007 3:34 PM To: [log in to unmask] Subject: [TN] BGA failures after OMPAC underfill We have a problem - we are using Loctite 3568 to underfill a 19mm plastic BGA- 256 pin 1 mm pitch eutectic solder BGA. We test the board before underfill and after (after underfill and conformal coat). We are seeing about 10 percent of the BGAs failing after the second functional test- the same part passes the first test but will fail the second. The boards fail for open solder joints- when heated with a heat gun they work- intermittent open that seems to work when the part is heated (expands) I have reviewed the process but can find no smoking guns that might point to the root cause of the problem. THe BGAs are all baked out prior to reflow, THe reflow profile peak temp is adequate- a little on the cool side for me- but the time above reflow doesn't seem excessive. THe boards are not subjected to any other mechancial fastening operations that might subject the BGA joints to strain. The board is not routed out after assembly. U10 is the BGA in question. THe peak temp is 212 C and is above reflow for 71 seconds. Note the part is MSL Class 3 but the parts are baked out and then stored in sealed Moisture Barrier Bags purged with nitrogen. Anyone else run into something like this before? I have run into situations where conformal coat under BGAs would expand and stress and crack the solder joints but I would think that an underfill would be designed to avoid this situation. Thanks Tom --------------------------------------------------- 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 -----------------------------------------------------