Hi all!
The topic thread seems to be leaning toward why do we use conformal coating
materials and what is their purpose. I would echo that eliminating or
preventing moisture absorption of the component is not one of the reasons.
However, there are many other valid reasons to coat and they do require
adhesion to be effective in their purpose.
To name a few off of the top of my head and there are others that I'm sure
experienced techneters can contribute.
Reduce surface contamination of circuits from atmosphere, ventilation,
airborne and other mobile debris types of contaminates.
Reduce contamination from physical handling and its access to the conductor
and component surfaces.
Localize contaminates that exist (things like solder balls/leads) to prevent
their relocation during stress environments.
Mechanically support components and other elements during vibration and
mechanical shock.
Thermal management.
Encapsulate surface contaminates.
Delay penetration of condensation, water and other fluids.
Limited dielectric isolation.
Reduce the impact from and formation of whiskers.
Reduce formation of surface dendrites.
Reduce fungus growth potential.
Reduce surface damage from handling and mechanical abrasion.
Mel Parrish
Director of Training
Soldering Technology International
102 Tribble Drive
Madison, AL 35758
256 705 5530
256 705 5538 Fax
[log in to unmask]
www.solderingtech.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Randy Bock Sr.
Sent: Thursday, August 15, 2002 12:29 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating on top of plastic IC's
and have a better client/customer relationship..
----- Original Message -----
From: Dave Chapman <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 15, 2002 11:49 AM
Subject: Re: [TN] Conformal coating on top of plastic IC's
> Our experience is that if that is what the Customer wants, the Customer
> gets. Whether it is needed or not. As long as the joints are covered that
> will be sufficient (technically). IPC loosely states that everything
> specified to be covered needs coverage. Our method of operation here says
> coat everything thus creating no questions from the customer even if you
are
> correct about moisture not being a factor after assembly. Our approach is,
> if customer is trainable then work with them to educate them. Educate
rather
> than argue. You will both appreciate the experience.
> Dave Chapman
> CSI
>
> -----Original Message-----
> From: Graham Naisbitt [mailto:[log in to unmask]]
> Sent: Thursday, August 15, 2002 8:43 AM
> To: [log in to unmask]
> Subject: Re: [TN] Conformal coating on top of plastic IC's
>
>
> > Dear Technetters,
> >
> > We've just finished our first few boards with Humiseal 1B31 conformal
> > coating, applied with a selective spraycoating machine, and we asked the
> > customer to inspect the products.
> > He commented that some areas on top of the IC's were not covered
> > completely, which is required (so he says) because these are plastic
> > components which may absorb moisture if left uncovered.
> >
> > I'm not gonne argue about this with the customer, but still I'm
> > interested to hear from you wether the fact that the IC's are plastic is
> > indeed a reason to require them to be completely covered with coating.
> > As far as my knowledge goes the problem with plastic IC's and moisture
> > is limited to the soldering process only, but I may be wrong.....
> > Anyone can comment ?
> >
> > Daan Terstegge
> > Unclassified mail
> > Personal Website: http://www.smtinfo.net
>
> Daan,
>
> I suspect that the reason for the lack of coverage to the IC covers is due
> to dewetting. The dewetting will probably be caused by the presence of
some
> mould release residues. Is this a problem?
>
> Not really, although it would be a good idea to try and obtain IC's that
do
> not exhibit this problem, as it may be that if you clean the assembly, and
> the mould release is silicone, then you might be spreading the silicone
over
> the surface of the assembly.
>
> Is this a problem? Yes. Inspect under UV and check for dewetting in other
> areas.
>
> As to the issue of component reliability due to moisture ingress, this is
> highly unlikely with the IC. However the customer is right to require it
for
> the reason I just outlined. It should not happen...
>
> Hope this helps
>
> Regards, Graham Naisbitt
> --
> [log in to unmask]
>
> Concoat - Engineering Reliability in Electronics
> Concoat Systems - Measuring Electronics Reliability
> Synergie - Electro-chemically compatible process chemistries
>
> Concoat Limited
> Alasan House, Albany Park
> Camberley, GU16 7PH - UK
>
> Phone: +44 (0)1276 691100
> Fax: +44 (0)1276 691227
> Mobile: +44 (0)79 6858 2121
> Web: www.concoat.co.uk & www.concoatsystems.com
>
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