Jack,

We have done exactly that due to the shrinkage of the hard overcoat during curing.

Phil Nutting

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Wednesday, June 29, 2011 12:16 PM
To: [log in to unmask]
Subject: Re: [TN] Potting over Conformal Coat?

profound thoughts, sensei...
(thanks)

Another colleague here speculated that the type of potting compound being
used was so "hard" that the conformal coat provided a buffer zone for
thermal cycling.
That was a new concept to me, this is an older product.

onward thru the fog,
Jack


.
On Wed, Jun 29, 2011 at 10:59 AM, <[log in to unmask]> wrote:

>
> Jack you ask a very broad question.  I shall use my stock answer of "It
> Depends".
>
> Conformal coating can be applied prior to conformal coating, but you have
> to ask why. Usually your potting material provides your environmental
> protection.  Conformal coating is then non-value added.  If it is there to
> protect your assembly from the potting material, you probably have the wrong
> potting material chosen.
>
> Are there constituents in potting compounds that can affect components?
>  Sure.  There are lots of compounds out there.  Choose wisely.
>
> Are there residues that can inhibit potting cure?  Absolutely.  Clean
> carefully.  Test thoroughly.  Choose wisely.
>
> I feel like the Knight in Indiana Jones and the Last Crusade....
>
> Doug Pauls
>
>
>  *Jack Olson <[log in to unmask]>*
> Sent by: TechNet <[log in to unmask]>
>
> 06/29/2011 10:39 AM
>  Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Jack Olson <[log in to unmask]>
>
>   To
> <[log in to unmask]>
> cc
>   Subject
> [TN] Potting over Conformal Coat?
>
>
>
>
> Are any of you familiar with conformal coating assemblies before applying
> potting compound?
>
> Are there potting compounds that contain harsh chemicals that could affect
> components?
> or
> Are there residues on boards that can affect the curing properties of
> potting compounds?
>
> I can only find one vague sentence about this in the Working Draft of
> IPC-HDBK-850
> (3.12.9.1 Compatibility)
>
> thanks,
> Jack
>
>
>
>


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