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July 2003

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Subject:
From:
Jack Evans <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 30 Jul 2003 13:06:54 -0500
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Hi Frank,

Funny, these pictures look just like some of my own.  If you have
established that all of your processes are in order, then check the board
itself. Check to see if the board will take solder in these locations with
an iron. If no, as it was in my case, then check other boards in this lot
to see if you have an issue in the same ref designated areas. If you do,
then your board manufacture may have had a process issue with the plating
or cleanliness. You will need to investigate a cross section of the suspect
solder joint and see what is going on. In my case, it turned out to be a
poor tin/nickel plating process which resulted in a phenomena called "Black
Pad". http://www.omg-
galvano.com/pdfs/VeroeffentlichungenEnglisch/GT_2281_2286.pdf. This, in a
nutshell, is hyper oxidation which can be caused by several factors. Ours
has turned out to be poor plating (nickel layer was too thin) by the board
manufacture. I don't claim to know anything about this phenomena however,
as I understand it, the causes can be:

1. poor plating processes (nickel layer too thin)!
2. oxidation through the gold layer (thin porus gold can allow oxidation)
3. Excessive heat cycles (clean and bake, smt cycles prior to wave???)
4. Pre cleaning chemistry accelerating oxidation
5. Copper contamination or phosphorous content.

Keep in mind, if all of your other boards are going through your process
without this problem, the issue is likely with your board supplier.
Good luck

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