Hi Drew,

Please correct me if I'm wrong. Are you saying that it could be a layer
of gold in between the layer of intermetallics and E-Ni? I would have a
hard time imagining it as a layer of immersion gold is very thin (o.1 or
less micron) and it gets dissolved in solder, so a layer of Ni-Sn
intermetallics can be formed (some authors say it's in fact Ni/Sn/Au
intermetallics). I've never heard of a layer of NI-Sn intermetallics
sitting on a layer of gold.

Regards,

Vladimir

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Drew meyer
Sent: Monday, February 25, 2008 11:24 AM
To: [log in to unmask]
Subject: Re: [TN] Metallurgists, need assistance, closing this one

Phil,

I'm going to go out on a limb here.  We have witnessed something like
this 
three seperated times now from three different board houses.  

What we experienced follows this process.  The board house decides that 
something associated with the plating on several panels is not right.
They 
removed the gold and start over.  The problem is that they are not
completely 
successful removing the gold.  You form a solder joint to the nickel
layer but 
beneath that layer is a layer of gold.  The nickel bond to the gold is
very weak.

If you have access to a SEM(Scanning Electron Microscope) that has EDS
(Electron Dispersive Spectroscopy) you can neatly locate and plot the
extra 
layer or remnants of gold present.

Not sure it this is true in your case but it can happen and has happened
to 
us.  

It is truly a nightmare as the board house often does not keep detailed
records 
of which panels and which subsquent boards could be affected.  This
leaves 
the entire lot in question unless you can locate all the boards by the
number 
of panels affected.

This what we were forced to do with finished product in one case.

Drew

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