The coating supplier's technical staff stated that the discoloration was
probably due to oxidation of the double bond of the molecules. He also
stated, as you, that the material may have become somewhat harder due to
further cross linking.
I don't think that moisture permeability is an issue, but what is a concern
is if the modulus increased which might affect chip component reliability,
if coating was actually under some ceramic or glass components. In your
opinion, would additional cross linking, oxidation, reversion or being at
150C for 2 hours cause the modulus to increase?
As far as stripping the coating, we crossed this path once before and our
customer will not allow us to use any chemical stripping solution to remove
polyurethane coating. They don't know how it will affect components,
boards, etc.
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
-----Original Message-----
From: Graham Naisbitt [SMTP:[log in to unmask]]
Sent: Wednesday, January 30, 2002 11:37 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coating
Jim
I know this is a late posting, because I have only just come back
on-line
however, what you have encountered is reversion.
The UR materials tend to discolour when exposed to high
temperatures, but
this does not generally affect their subsequent performance - if
anything it
might improve it because you have ensured a full x-link of the
polymer -
fully reacted.
The discoloration may however, be an unacceptable visual condition
to your
customer, depending upon their inspection criteria.
Whatever, it will be possible to remove and re-coat if you desire.
You mention that this is a space application, therefore this
material will
probably have excellent outgassing characteristics and I can only
think of 1
or 2 UR space (NASA / ESA) approved coatings. I am surprised that
you have
this reversion, what did their technical staff advise? I would like
to know
for my own record.
Regards Graham Naisbitt
[log in to unmask] <mailto:[log in to unmask]>
Concoat Limited
Alasan House, Albany Park
Camberley GU16 7PH - UK
www.concoat.co.uk <http://www.concoat.co.uk>
Phone: +44 1276 691100
Fax: +44 1276 691227
Mobile: +44 79 6858 2121
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of David Douthit
> Sent: 29 January 2002 00:49
> To: [log in to unmask]
> Subject: Re: [TN] Conformal Coating
>
>
> Jim,
>
> You have chemically altered the polymer. It will no longer
> perform it's designed function.
>
> David A. Douthit
> Manager
> LoCan LLC
>
> "Marsico, James" wrote:
>
> > Help! Emergency!
> >
> > We have a completed assembly (top assembly with many boards,
> hybrids, etc.)
> > ready for shipment to our customer (space product). The last
> operation was
> > to ink mark a S/N. The ink is cured at 150 F for 2 hours. The
> assembly was
> > put in an oven at 150 C for two hours. After hours of
> reviewing all of the
> > materials and bill of material, component by component
(component data,
> > supplier phone calls, etc.), the only item that is not rated
> for 150 C is
> > the polyurethane conformal coating, which turned yellow/brown
> in color. Can
> > anyone explain what actually happened to the coating and if it
> can be used
> > as is?
> >
> > Thanks,
> >
> > Jim Marsico
> > Senior Engineer
> > Production Engineering
> > EDO Electronics Systems Group
> > [log in to unmask] <mailto:[log in to unmask]>
> > 631-595-5879
> >
> >
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