Some more clues that we are missing are:
What is the population....is this on two boards out of 100, 75 out of 80, etc.
Is the EMS using Type 4 solderpaste?
Is there a record of what serial numbers were misprints and cleaned.....etc.
The fact that they were using Kapton tape to mask the gold rails off seems suspicious all by itself.
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, July 30, 2014 6:56 AM
To: [log in to unmask]
Subject: Re: [TN] Spots on Gold
I think there are actually two defect conditions, one where some of the tiny solder fines are reflowing, absorbing the gold, and leaving exposed nickel. Another for simply having the solder fines wet on the gold finish. If you look closely at the second picture, you can see many solder fines from a paste smear in the gold areas.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Theodore J Tontis
Sent: Wednesday, July 30, 2014 8:37 AM
To: [log in to unmask]
Subject: Re: [TN] Spots on Gold
If this is solder, it could be linked to misprint that was not completely wiped cleaned and then reprinted.
May years ago I did an experiment on cleaning misprints and the effectiveness of getting all the paste residue off the boards.
The reason why we performed this experiment was that we noticed solder bridging on fine pitch assemblies that were to random to be a miss-print or dirty stencil. During further investigation we found solder in vias and on the corner of some pads.
What we found was the process we were using to clean PCB's after miss-prints was in-effective when using no-clean solder paste and the only true way to insure the board was free of solder paste was to put it in the ultrasonic cleaner if it was a unpopulated board or, the batch wash if it was populated on one side.
Ted T.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, July 30, 2014 8:08 AM
To: [log in to unmask]
Subject: Re: [TN] Spots on Gold
Yup. Solder fines, all right.
Take a magnified X-ray, and all of those little fines will show up clearly.
Fire the contract assembler.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, July 30, 2014 7:02 AM
To: [log in to unmask]
Subject: [TN] Spots on Gold
Morning John,
I have your second photo posted, it's here:
http://stevezeva.homestead.com/ring.jpg
This looks interesting!
Steve
On Tue, Jul 29, 2014 at 5:56 PM, <[log in to unmask]> wrote:
> Hi steve
>
> I managed to get to a good microscope this afternoon. Everyone of
> these spots looks like someone circled it* w*ith a magic marker.
>
> Would you mind posting one more pic for me.
>
> Thanks
>
> John Foster
>
>
>
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