Higher mag would be great to discern anomaly.  You have to see it to call it, baseball

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, April 23, 2013 12:12 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


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