Yep, certainly does look like solder balls in flux puddle, could be from
paste spatter or dirty stencil. Some times you can also get this from oven
dripping. But you say board is taped. [What happens if you run an empty
un-pasted board through the oven?] Some paste suppliers can supply a UV
fluorescing version of their product for diagnosing this exact thing. Tiny
spots will show up quite readily under a black light which would other wise
be missed - till reflowed.

Regards 
 
Mike 
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Herring
Sent: Tuesday, July 29, 2014 5:24 PM
To: [log in to unmask]
Subject: Re: [TN] Trying to figure out possible mechanism for contamination

It looks to me like their Screen Printer is doing a poor job of under
stencil wiping, leaving solder paste on the underside of the stencil that
gets transferred to the gold areas on the edge of the pcb.
During reflow, the small balls of paste flow into nice circles.
Not all stencil wiping paper is created equal.

Steven E. Herring
Engineering Manager
Pennatronics
75 Technology Drive
California, Pa 15419-0638
P 724-938-1800 x 214
F 724-938-1809
[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Foster
Sent: Tuesday, July 29, 2014 12:13 PM
To: [log in to unmask]
Subject: [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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