Steve, if it is plating defect, you might not see on incoming board-  
you need heat to drive the bubble pop open - get the trapped  
subsurface material out - usually, a thin plate due to either  
insufficient oxide removing, or a surface non wetting localized  
defect due to chemical difference on the surface, such as air  
bubbles, or large organic molecules, as plating additives... unless  
you know the plating chemistry (down to the additive and pH  
adjustment frequency, monitoring feedback loop, it hard to do FA -  
something simple as one of the panel just not processed normally,  
such as lifted in the air during coffee break... etc.etc.).
Best of luck John.  I am sure L3 got SEM/EDX somewhere or have access  
to one without doubt. ;-)
           jk
On Jul 29, 2014, at 7:13 PM, Steven Creswick wrote:

> John,
>
> I go with random gold flash plating defects and as Joyce indicated,  
> a quick check under the SEM would tell you whether there was Sn or  
> Ni visible in the center of the defect.  That at least gives you a  
> direction to travel towards.
>
> If plating defect, will be there on the incoming boards...
>
>
> Steve Creswick
> Sr Associate - Balanced Enterprise Solutions
> http://www.linkedin.com/in/stevencreswick
>                          616 834 1883
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of John Foster
> Sent: Tuesday, July 29, 2014 6:59 PM
> To: [log in to unmask]
> Subject: Re: [TN] Trying to figure out possible mechanism for  
> contamination
>
> Thanks for all of the responses. There are through hole plugged  
> vias on a very Definite grid which are very visible. They are on a  
> 2mm grid. But other than that There are no structures in this area.  
> The spots are very random and very hit and miss some boards Clean  
> as a whistle other boards like this.
> I certainly have a lot of ideas to check out now.
> I was also wondering about These black dots in the center of each  
> of the spots. It just seems strange.
> I was thinking that was the nickel plating underneath the ENIG.
> This is really not my expertise so I really do appreciate all of  
> the input
>
> John
>
>
>
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