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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