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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