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February 1998

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Subject:
From:
Aric Parr <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 17 Feb 1998 07:06:37 EST
Content-Type:
text/plain
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text/plain (95 lines)
I did a major evaluation of coatings over no clean a few years ago at a
previous employer. PQFP adhesion (actually non-wetting) on one specific
part number (or supplier, I can't remember) killed some coatings, while
other coatings had no problems. Excess no clean flux residues also could
cause problems for many coatings (i.e fluxer at maximum, SIR at minimum
acceptable may cause problems, but SIR at maximum, fluxer at minimum will
coat fine.

Sounds like you need to do more research. Call the PQFP manufacturer and
see why the coating dewets. They should know the material, filler and mold
release used, if any.  Then talk to the coating manufacturer and see what
they recommend. If you need to clean, find another coating or PQFP
supplier. That particular employer made several suppliers improve product
cleanliness to fix coating and SIR problems. You may want to do the same.
-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/TechNet(a)IPC.ORG, on 2/16/98 6:37 PM:
Dear T-Net:

We have a few customers who require conformally coated versions of our
standard products (network interface cards). This is sporadic, only a few
times a year, and normally in quantities of a few dozen.

We have previously used a local contractor who applies a type AR (acrylic)
coating to the boards in these small lots, masking by hand.

As of last fall, we have changed from water soluble paste/flux and aqueous
cleaning to "no-clean" products (this is just to make things complex).

Our customers have complained a couple of times about the poor adhesion of
the coating on the larger PQFP packages. My guess is that these packages
have mold release agents, or some other contaminant not cleaned in our (old
and new) process here.

So, the immediate concern is to find:

1) A vendor who can clean the assemblies (as my be required) and apply a
type AR coating.

2) Assurance that the cleaning will not be necessary, in the event we must
stay with the same vendor here (who has no cleaning facilities).


Of course, I prefer free consulting and advice, and hopefully a fast,
thorough, scientifically validated solution to my problem. I can live
without any smart remarks or comments about the information which should
have been included to permit an answer. The obvious question: "Why would
anybody in their right mind want conformal coating?" should not be asked.

I hearby apologize for any such potentially offensive postings of my own to
all readers at this time, and promise never to do it again if you help me
out this once.


;-)


cheers,


Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

p.s. if you are going to be at NEPCON, suppose we find a watering hole we
could all agree to meet at on say, Monday afternoon...send email and I will
reply to any interested in such arrangements

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