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September 2002

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 24 Sep 2002 14:22:45 -0700
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Rick:
We ran a fairly in depth study with Kester, looking at the compatibility of
their no-clean fluxes and our non-cleaned PCA's with conformal coating(CC).
The test used Kester's 256 no-clean solderpaste and the 245 no-clean core
solder. We looked at them individually and also combined on the same board.
This was done for both acrylic and urethane CC. We did not test Humiseal's
1B31 LOC acrylic.

The test consisted of SIR and adhesion.

SIR was done on B25 coupons, 65C/85%RH, 168 hours, readings were taken at
1,4,7 days under test conditions and recovery after removal from the
chamber. We did not see any significant difference between controls,
fluxed/coated and fluxed uncoated boards. They were all within one order of
magnitude under test conditions.
Visual inspection after SIR testing showed some signs of
blistering/vesication on the boards with 256/245 with urethane coating but
not on the acrylic. However there was no drop off in SIR on the urethane
boards.

The adhesion testing was done per ASTM Method D 3359-92a. They were all
acceptable however the combined 256 and 245 residues showed the lowest level
of adhesion. The 245 alone was better. The acrylic had better adhesion than
the urethane.

Conclusion:
If you are applying the acrylic CC over just the 245 no-clean you "maybe"
OK. When you start mixing different flux residues with other conformal
coating chemistries you can create a chemical stew that's not compatible.
Obviously you also need to consider incoming board cleanliness,
contamination added by your handling and processing, adhesive properties of
the soldermask, electrical requirements of the board, service life and
conditions of the product, etc etc. So you will need to do some testing
yourself to qualify the materials and performance.



Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076


-----Original Message-----
From: Rick Thompson [mailto:[log in to unmask]]
Sent: Tuesday, September 24, 2002 10:50 AM
To: [log in to unmask]
Subject: [TN] Humiseal 1B31 LOC Compatible with No-Clean?


Hi,

I'm wondering if anyone has experience using Humiseal 1B31 LOC Acrylic
Coating over low residue no-clean flux?  Specifically, over Kester 245
no-clean used in cored wire?  I'm looking for any data that would support
use of this coating over the flux residue, adhesion, long-term reliability,
etc.  If anyone has information they'd care to share it would be greatly
appreciated.

Thanks in advance,

Rick Thompson

Sr. SMT Process Engineer
SMTEK International, Inc.
+1 (805) 532-2800
[log in to unmask]

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