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December 2006

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Subject:
From:
"Douglas O. Pauls" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 6 Dec 2006 06:59:32 -0600
Content-Type:
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What you are hearing is that no organic conformal coating makes an
electronic assembly absolutely bulletproof against the environment.  All of
them pass water vapor, and sometimes other gasses, to varying extents.  It
impedes the flow of moisture but does not completely eliminate moisture.
Important distinction.

Doug Pauls




             Bill Kasprzak
             <[log in to unmask]
             OM>                                                        To
             Sent by: TechNet          [log in to unmask]
             <[log in to unmask]>                                          cc

                                                                   Subject
             12/06/2006 06:56          Re: [TN] conformal coatings as
             AM                        water proofing


             Please respond to
              TechNet E-Mail
                   Forum
             <[log in to unmask]>
             ; Please respond
                    to
               Bill Kasprzak
             <[log in to unmask]
                    OM>






Good morning,

I am surprised that there are such opposing views on whether conformal
coating is effective as a moisture barrier.

My impression has always been that the primary purpose for coating boards
was to act as a moisture and corrosion barrier. It has dielectric strength
as a secondary property.

So, I am I hearing from Brian that conformal coating is useless as a
moisture barrier on PC Boards?

Bill Kasprzak
Moog Inc
Process Engineer, Electronic Assembly




Brian Ellis <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/06/2006 01:31 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Brian Ellis <[log in to unmask]>


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Subject
Re: [TN] conformal coatings as water proofing






I disagree with your disagreement. CC CANNOT protect against atmospheric
moisture as they are all as porous as a sieve. The best they can do is
to delay the onset of undesirable effects. CCs SHOULD cover everything
except contacts on 2- or 3-D assemblies and, as such, protect against
the effects of condensation. They do not allow the passage of water in
liquid phase, only in vapour phase.

Brian

Edward Mines wrote:
> Doug Pauls wrote than conformal coatings protect against condensation. I
disagree.
>
>   Conformal coatings protect against atmospheric moisture. It is giant
leap of faith that many engineers make that they protect against
condensation. When I left the industry 2 years ago there was no reference
to condensation in IPC-CC-830 or MIL-I-46058 or UL746.
>
>   Conformal coatings do not always completely cover all conducting items
on 3 dimensional boards.
>
>   Doug's employer is not the only one that uses a thicker layer of
conformal coating or similar material to protect against moisture.
IPC-CC-830 (and predecessor MIL-I-46058) specify a maximum coating
thickness for conformal coating. I am sure there are reasons for this. By
putting on more coating (a thicker layer) the assembler is out of
compliance with IPC & MIL
>   conformal coating specs.
>
>   If industry wants to use a material to protect PC boards from liquid
water that material should be called a different name (I called the one we
sold at HumiSeal a selective encapsulant). Tests should be developed to
insure that that material does the job for which it was intended; a QPL
should be established.
>
>   IPC, MIL & UL tests for conformal coating all include  accelerated
aging and thermal cycling tests for conformal coatings within a specified
thickness range. Would qualified coatings pass those tests in thicknesses
outside those ranges? Can the user be certain that conformal coatings cure
properly in thicknesses outside those ranges? Might overly thick coatings
crack if subjected to those tests? Or in the field? If a board fails
because the conformal coating was used incorrectly is the board
manufacturer negligent? I am aware of one instance where this last issue
was seriously addressed in the automotive industry.
>
>   Are the tests in MIL-I-46058 (and grandfathered into IPC-CC-830)
realistic? Are they overkill?
>   Is there a reason for the thickness limitation?
>
>   At HumiSeal I heard of several instances each year where customers
tried to put more conformal coating on a board than specified by
MIL-I-46058 and recommended by HumiSeal (it seems like more would be
better). I know for a fact that some conformal coatings do not cure
properly above a certain thickness.
>
>
>   Edward Mines
>
>
>
>
>
>
>
> ---------------------------------
>
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