Hi John,
These are definitely solder splashes coming most likely from printing. If the assembler is covering the gold areas, you'll need to find out if they apply the Kapton prior to printing. Judging by the 0603 (or 0402?) caps and the miniBGA in the neighborhood, something tells me they would not want the Kapton there during printing, as it pushes the stencil up, increasing the paste volume with all the goodies that this can generate (shorts, tombstones, etc.).
To make it more complicated, those tiny solder balls might even come from the table where taping is done. If the PCB is laid face down for some reason, it would gather no matter what. I know this situation, I've faced it many, many times and it's very hard to completely get rid of those splashes.
One question: why would you want spotless gold on that large of a trace? If it's for grounding, as long as the splashes don't bulge up and hinder contact, there's plenty of Au surface to make a very good ground. Otherwise said, if you don't know for sure that small splashes like this affect form, fit or function, it would be a lot easier to live with them than trying to eliminate them. Of course, I'm talking about a reasonable amount of splashes, comparable to what shows in your photo.
I guess at L3 you are doing intensive qualification of hardware and it would be easier to prove these splashes are benign than create massive rework.
Regards,
Ioan Tempea, P. Eng.
Manufacturing Engineer
Satellite Systems
MDA
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-----Message d'origine-----
De : TechNet [mailto:[log in to unmask]] De la part de John Foster
Envoyé : Tuesday, July 29, 2014 12:13 PM
À : [log in to unmask]
Objet : [TN] Trying to figure out possible mechanism for contamination
We have been seeing a problem recently on several different CCA'S that we are having assembled.
The boards are ENIG with plug and plate. The assembly shop is assuring us that these gold areas are being Protected during the entire assembly process with kapton tape.
I was thinking it was flux splatter since the areas are always almost perfectly circular.
The locations are very random and range from nothing to what is in the picture.
Is there any other mechanism that might be causing this? On our next run I am going to go to the shop To witness the taping. But I was curious if maybe it's some other cause.
Mr. Gregory was kind enough to post a picture.
http://stevezeva.homestead.com/spots.jpg
Any thoughts would be appreciated
Thank You
John Foster
L3 Communicatons
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