Pat,

If the "contaminants" are on the surface, they should be easily rinsed off
with IPA prior to inspection.  We often do this to prevent needless
inspection rejections.  Besides, I don't believe surface contamination is a
legitimate rejection criteria for the coating material - maybe for the
assembly, but not of the coating itself.  If, on the other hand the
contamination is within the coating, check the cleanliness of the bulk
material.  We filter a lot of our coating material first, before mixing.

-----Original Message-----
From: Pat Lujan [mailto:[log in to unmask]]
Sent: Thursday, August 12, 1999 6:06 PM
To: [log in to unmask]
Subject: Re: [TN] Uralane 5750


Hans and Technetters,

Definitely not performing this in a clean room; however we have hepa
filtration.  We have recently aquired a laminar air flow work station where
I have been air curing the boards prior to an oven cure.  I have even gone
through the additional expense of purchasing new ovens with modifications to
filter the incoming air into the oven.

Another form of contamination which I forgot to mention in my previous
e-mail is a snowflake, dandruff looking type of crystallization.  After
talking to vendor (Ciba Specialtly Chemicals) I am suspecting that this is
coming from moisture.  Part A of Uralane  5750 is hygroscopic and this may
be the source.

Thanks for any comments in advance.

Pat

>>> Hinners Hans CIV WRALC/LYPME <[log in to unmask]> 08/12 3:20 PM
>>>
        Hey Pat,

        I don't know Uralane but are you doing this in a Cleanroom
environment?
        If so what Class and flow type?

        Have you tried letting the boards cure in a cleanhood or something?

        Hans

Air Force Material Command - We keep them flying!
~~~~~~~~
Hans M. Hinners                                 WR-ALC/LYPME Bldg. 640
Materials Engineer                                      380 Second Street,
Suite 104
Manufacturing Eng. Sec.                         Robins AFB GA 31098-1638
912-926-1970 (Voice) 468 - 1970 (DSN)   912-926-7974 (Fax)
[log in to unmask]


> I need help with a problem I have been fighting for 6 months.  We
> currently use Uralane 5750 on hi-rel PWA's used in space applications.
> Our method of applying is the brush method per NHB5300.4(3J) April 85.
>
> The quality requirements state that "Coating shall be free from
> contamination or foreign material.  Any contaminant visible under 4- to
> 10- power magnification shall be cause for rejection."
>
> My problem seems to be the properties of Uralane 5750.  It seems to remain
> tacky after it is cured and this appears to attract all airborne
> particles.   Our CSI and GSI inspectors naturally crank up the scopes to
> 10 power.   I used Humiseal 1B31 in the same environment and do not have
> the same problems.
>
> My main customers Boeing and TRW have both issued CAR's against this
> process as it realates to contamination.  I am in need of any input that
> may help me improve my process.  I am a NASA certified Instructor in
> Conformal Coating and Staking and have not been able to solve this
> problem.
>
> Any information that would aid me in continuing my career would be greatly
> appreciated.
>
> Pat Lujan
> Senior Mfg. Eng.
> BFGoodrich Data Systems Div.
> Albuquerque New Mexico   USA
> 505.938.5373
>
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