Hi, Probably real simple: It was assembled using a Water Soluble flux. You really cannot clean under a QFN so a no-clean would be called for. Bob K. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Tuesday, April 23, 2013 1:12 PM To: [log in to unmask] Subject: [TN] QFN Pad Corrosion? Hi All, I have another question about the QFN16 that I was talking about last week. I was sent a photo of the bottom of one of the devices after it had been removed from a failed board. It is here: http://stevezeva.homestead.com/QFN16_Corrosion.jpg It's pointing out a pad that seemed to have a lot of corrosion on it and I was told that solder would not wet to it. I was asked what might cause this? My first thoughts are that the appearance might have been caused by the rework when it was removed, and that a un-solderable intermetallic has formed on pad but I can't say that for sure. The part is finished with matte tin when it is supplied. When a part is tin finished, they have a barrier nickel plate beneath the tin right? I don't have the part in front of me, I only got sent the photo. I was asked what my thoughts were, so I thought I'd ask my TechNet friends too... :o) Thanks, Steve Gregory ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________