I asked the tech service engineer, but he didn't know. Immersion silver is particularly succeptable to creep corrosion. I'll ask him to get more information about the QFN. It also happens under ceramic passives. Thanks Karen Tellefsen - Electrical Testing [log in to unmask] 908-791-3069 George M. Wenger wrote: Karen, What is the surface finish on the QFN and what is the PCB surface finish? Regards, George George M. Wenger Andrew Solutions Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [Office] (732) 309-8964 [Cell] [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen Sent: Friday, June 12, 2009 11:10 AM To: [log in to unmask] Subject: Re: [TN] Strange tin "migration" under OFN soldered with no-clean SAC305 solder paste I though of creep corrosion also, but flux contains no sulfur of halide. That doesn't mean that there is no source of sulfur, but I don't know about it. Karen Tellefsen - Electrical Testing [log in to unmask] 908-791-3069 fabrice pires <[log in to unmask]: It make me think about creep corrosion phenomena. Is there any sulfur in the residues? Just an idea. Karen Tellefsen a écrit : > One of our technical service engineers asked me about a strange migration > phenomenon one of our customers observed under passives and QFN's that have > been soldered with one of our no-clean SAC305 solder pastes. I've attached > an X-ray picture of a QFN exhibiting this strange failure, but I don't know > how it can be posted so you can look at it.. Further analysis after > removing the component showed that the shadows in the X-ray picture is > caused by a black material containing tin. The boards were conditioned 85°C > 85%RH for 500 hr, but no voltage was applied. This phenomenon was not > observed under QFPs (not surprising), and seems to be independent of reflow > profile used. Additionally, the customer has not seen anything like this > with tin lead solder paste, however, the tin-lead solder pastes would have > a different fluxes. The tin "migration" is coming from both adjacent > solder joints, and there is no voltage applied, so it seems to be a > corrosion problem. Certainly QFN and big passives are good at trapping and > retaining water in the flux residue underneath them. > > I've never seen anything like this; has anyone else out in TechNet land > seen this or have any ideas what caused this? > > Thanks > > Karen Tellefsen - Electrical Testing > [log in to unmask] > 908-791-3069 Enthone GmbH Geschäftsführer: Knut Balzer, Luc de Croo, Jürgen Dietrich Amtsgericht Düsseldorf HRB 45276 USt-Id-Nr. DE 811 205 946 This communication is for use by the intended recipient and contains information that may be privileged, confidential or copyrighted under applicable law. If you are not the intended recipient, you are hereby formally notified that any use, copying or distribution of this e-mail, in whole or in part, is strictly prohibited. Please notify the sender by return e-mail and delete this e-mail from your system. Unless explicitly and conspicuously designated as "E-Contract Intended", this e-mail does not constitute a contract offer, a contract amendment, or an acceptance of a contract offer. This e-mail does not constitute a consent to the use of sender's contact information for direct marketing purposes or for transfers of data to third parties. --------------------------------------------------- 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 -----------------------------------------------------