Joyce,

True, but I've also seen it occur on wire bond pads where the Au flash
didn't plate in small spots.  No solder involved on the board.

I think the plater called it 'skip plate'.  I don't recall if we ever found
out what the contaminant was.  The problem 'just went away ...'   I
love/hate it when they do that!

Steve

-----Original Message-----
From: Yuan-chia Joyce Koo [mailto:[log in to unmask]] 
Sent: Tuesday, July 29, 2014 9:21 PM
To: TechNet E-Mail Forum; Steven Creswick
Subject: Re: [TN] Trying to figure out possible mechanism for contamination

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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