Jim
Having kicked this around here, the general consensus is that you do NOT
ship the product.
Without knowing the exact coating material, nor your end product, we could
not say how the "overcooked / oxidised" coating will behave. We would figure
that its moisture and chemical resistance might be improved but, its
potentially less flexible nature might over-stress components.
As to removing it, I think that a chemical stripper would probably be safer
but it will have to be done very carefully by hand, a little at a time. I
could not comment upon its effect on components and understand why your
customer would be unhappy with this. This is a space product, and the cost
of launch, much less manufacture, would probably demand that you re-make the
product - it might give all the data acquisition to the Aliens on planet
Tharg.
Sorry, but I don't think we can give you an acceptable alternative. Best of
luck.
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 Marsico, James
> Sent: 30 January 2002 18:39
> To: [log in to unmask]
> Subject: Re: [TN] Conformal Coating
>
>
> 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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