Hi Phil! Sorry to hear such bad news. I recommend you double check to make sure that you are indeed hitting the required minimum cure times/temperatures necessary to complete a full cure reaction. Some of the underfill formulation providers do have databases which include which solderpastes their underfill materials have compatibility issues. The cleaning chemistry suppliers and the fabricators of cleaning equipment do a great job of pulling together cleaning processes that do amazing jobs of removing residues given the size and complexity of our modern electronic products. But - if you have a BGA that is sufficiently large and has significant I/O, you are going to have some flux residue remaining under the component. Your underfill material must be able to accommodate that residue. Many folks don't realize that they should conduct solder paste - underfill compatibility studies. Good Luck. Happy Holidays! Dave Hillman Rockwell Collins [log in to unmask] Phillip Bavaro <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 12/22/2008 05:02 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Phillip Bavaro <[log in to unmask]> To [log in to unmask] cc Subject [TN] Underfill, inhibition due to leftover activators in the flux residue I have made quite a few test samples and discovered that a certain underfill material will exhibit inhibited cure when it comes in contact with solderpaste flux residues at the center of a very dense BGA component. The rest of the underfill beneath the BGA will harden like normal. We don't clean nor plan on starting to clean our assemblies. DVT testing does not show any defects due to underfill adhesion. Background: We used a four up ABAB panel which goes through SMT twice. BGAs only passing through the oven once consistently show the problem. Two passes through the reflow oven (ABAB flip) and the problem goes away. This means that half of our test samples still have soft material in the pocket at the center where the power ground pins are located. We measure peak temperature in this area and have found that raising the peak temperature helps quite a bit but does not eliminate the inhibition entirely. The manufacturers of the paste and the underfill acknowledge the issue but do not have a solution. Has anyone else run into similar compatibility issues with a paste and underfill? In the event that we cannot work out the root cause, and decide to make a change, I am trying to come up with a list of all the manufacturers of underfill. So far I have found 8 major underfill manufacturers but would appreciate knowing about more if there are any. 3M Ablestik Epotek Henkel Hysol SP&S Sunstar Zymet Thanks in advance, Phil --------------------------------------------------- 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 -----------------------------------------------------