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June 2006

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Subject:
From:
"Dehoyos, Ramon" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dehoyos, Ramon
Date:
Thu, 22 Jun 2006 11:46:55 -0400
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        You are having a case of dewetting. It happens with some kapton
dots. I have tried to cover them with UR coating and the coating pulls
away from the dot leaving the dot untouched no matter how many times I
brush the dots. There is also a ring around the dots where there is no
coating.  It could be static build up or a chemical that rejects the
coating. Suggestion: after the board is totally cleaned, rinse it one
more time with DI. Submerge it in alcohol and brush the concerned areas.
Rinse it again with DI water, bake and then try to coat it. Second
suggestion: Place board in front of an Ion Generator for a few minutes.
        Ramon
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bloomquist, Ken
Sent: Thursday, June 22, 2006 9:19 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat Voids

Hi Graham,

I have not noticed any dewetting anywhere else on these boards. There is
always a possibility that something could be coming out of the holes but
I'd think that it would get cooked away during wave solder or washed off
during cleaning.

Hi Amol,

We are doing some tests right now to see if there might be something in
the cleaning process. The flux is water soluble and the board gets run
through an inline washer two to three times during the process. The
board goes through one final saponified wash in a batch washer before
coating. We have not seen any residues on these solder joints after all
this cleaning.

What brought this to our attention was a test failure during a dust
test. It's a very difficult test with materials that are conductive.

We can apply a drop of water on the via's and create a failure of the
board so we know there's not much coating over the solder.

Is there any possibility that the really smooth slick domed surface is
allowing the coating to be pulled off of it?

Thanks,

KennyB

-----Original Message-----
From: Graham Naisbitt [mailto:[log in to unmask]]
Sent: Thursday, June 22, 2006 4:15 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coat Voids

Hi Kenny

Clutching at straws here - any chance you have "drilling" residues
before the via is plated?

Can it be something from the via plating operation that has changed?

Have you noticed de-wetting anywhere other than the via's?

Regards
Graham Naisbitt
[log in to unmask]
Phone: +44 (0)12 5252 1500
Mobile: +44 (0) 79 6858 2121
______________________________________________________

Hi,
How are the boards cleaned before coating? For a test sample of boards,
take a Q-tip with a solvent like Xylene and manually scrub the problem
areas and then try the coating process. That way you can change the
cleaning procedure if necessary for those particular boards.

Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]

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