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November 2007

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Subject:
From:
Kathy Kuhlow <[log in to unmask]>
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Date:
Wed, 14 Nov 2007 13:47:02 -0600
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I had lived through a green growth similar to this but it was a long time
ago (late 1980's early 1990's).  It was on gold tabs and gold plated simm
sockets. It was caused partially to poor water quality (live bacteria in the
water wash although we were originally told it was a DI wash) along with
un-activated flux during the manufacturing process.  The manufacturing was
in a warmer environment, which allowed the bacteria once deposited on the
PCB during wash, to grow and feed on the flux residues. When we went to a
lab with the boards, they found the bacteria and flux along with a silicon
oil.  The oil was thought to have come from some maintenance done on the
Pick and place machine but this was never confirmed as a factor or not. We
just threw everything away and went to a more reputable source that actually
had a DI wash and did not leave flux on the PCBs. 

I also saw another issue like this with some parts from Asia but it was
found to be caused by poor air quality that caused the growth to appear
blamed on pollution that became entrapped in the case, parts were replaced
with same parts different plant with no issues (old style sealed case
crystal). 

Good luck. 

Kat

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, November 14, 2007 1:33 PM
To: [log in to unmask]
Subject: Re: [TN] Green Growth between PCB traces

Hi Everybody!

I have Tom's pictures posted. They're at:

http://stevezeva.homestead.com/files/GreenStuff2.JPG

http://stevezeva.homestead.com/files/GreenStuff3.JPG

http://stevezeva.homestead.com/files/GreenStuff4.JPG

http://stevezeva.homestead.com/files/GreenStuff5.JPG

http://stevezeva.homestead.com/files/GreenStuff6.JPG

Those boards look like they've either been slimed or in Linda Blair's
bedroom while her head was spinning around! YUCK!

Seriously, looks like some sort of dendritic growth to me. I've seen
dendrites before, but not green ones...

Steve Gregory 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tom Burek
Sent: Wednesday, November 14, 2007 11:44 AM
To: [log in to unmask]
Subject: [TN] Green Growth between PCB traces

Hello everyone,
Has anyone ever seen or experienced the phenomenon of this green growth
between the traces and even on some of the pads.
It almost appears as if it is leaching out from under the etchback of the
traces into the space between the traces. 
Oddly enough it is only on one side of the board, the bottom side, opposite
the component side.
It will not wash off with DI or Alcohol and a Q-tip, however it will scrub
off with a stiff bristle brush or very gently with an exacto knife.
The soldermask is very thin in spots, (white solder mask).

The PCB is ENIG with white soldermask.  FR4 material (IPC-1401/21).
The boards had just gone through HALT testing, (Thermal Shock: 2 hrs. @ 85°C
then 2 min. 5 sec. swing to  -40°C for 2 hrs. This was repeated until it
failed after 136 hrs.) We think this green stuff might have caused the
failure. 
 With the temperature swings, often there is condensation created so,
possibly created by humidity? 
Is there something in the PCB fabrication process that could have lay
dormant until it experienced thermal shock?

I know an analysis of the green stuff is necessary, but I was wondering if
anyone has ever seen of experienced this type of growth before.

Thank you in advance.

I have attached some pictures, but I know somehow they are suppose to get to
Steve to post. 



Tom Burek, CID+

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