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Subject:
From:
Douglas Pauls <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 20 Oct 2010 16:40:17 -0500
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Thank you all for your responses.  As indicated earlier, how I wish I 
would have had this kind of resource back in the 80s.  Here are my 
thoughts on the matter.

At Rockwell, home of truth justice and the American way, we do a great 
deal of coating by hand.  A classic case of LEAN principles applied wrong, 
though I am told it made sense at the time.  I am working on bringing back 
spray coating, but it is tough to change an entrenced culture.

We have often required coating the board edges on our drawings, generally 
because "we have always done it that way".  We may have done it for some 
of the reasons you all have given, but the technical rationale is probably 
buried somewhere in our archives.  However, this edge coat requirement is 
selective in application.  When the edges of the board have metal clad 
areas on top and bottom, such as with card guides, the edges are not 
coated, because it is very difficult to coat just the edge and not get any 
on the top or bottom card guide.  Similarly, if we have a large high 
density connector on the board edge, that is flush mounted to the board, 
we do not coat the edge under that connector as it is next to impossible 
to do without flooding the connector surfaces.  It is not unusual to have 
three out of four sides of an assembly uncoated (two card guides, one 
connector, one coated edge).  So our apparent philosophy is to coat board 
edges unless it is too hard.

One of the things that having a LEAN philosophy as a driver does for you 
is that you are constantly evaluating processes asking "is this really 
necessary?", or "is this value added?".  For us, coating the edges of the 
board takes additional time and effort.  It can also lead to rework or 
touch up activities as well.  I cannot say we have ever had field failures 
or problems from board edges that are uncoated.  Since we deal with some 
pretty harsh environments, if this had truly been a failure mechanism, 
such as for moisture ingress, we would have seen it by now.

One of the key points for me, is that we are dealing with board edges that 
are routed, which has a tendency to seal the board edge, as opposed to 
punching or V-scoring, which can leave exposed fibers and has a greater 
risk of moisture intrusion.  If I had punched or scored/snapped edges, I 
would consider edge coating to be necessary.  But since I have routed 
edges, I ask myself the question of whether edge coating is value added.

Would you agree with my reasoning?

Inge, when you say board that are sensitive to water ingress, what do you 
mean?  Is there a particular laminate material, such as Teflon or the high 
speed laminates, that is a consideration?  Second, how do you determine 
how harsh an environment  has to be in order to coat the edges?

As for Parylene, remember, a nightmare is also a dream.............

Now, to be perfectly honest, I can't really pass all this questioning off 
as high minded LEAN driven noble pondering.  It's actually because I 
messed up last week.  I used this reasoning on one, ONE mind you, program 
to relax the edge coat requirement for  a tough application.  Now I have a 
hundred requests, many along the lines of "Why do I have to coat my board 
edges if Donna does not have to coat hers, huh, huh?".  There are some 
days here I REALLY don't want to be the coating expert.........

Doug Pauls



Inge <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
10/20/2010 03:46 PM
Please respond to
Inge <[log in to unmask]>


To
[log in to unmask]
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Subject
Re: [TN] Conformal Coating Board Edges






Well, it depends..

example 1: boards sensitive to water ingress via edges: we used 
multilayers 
of cc along edges
example 2: boards with rough edges damaged the rack slides: we used cc 
along 
edges
example 3: boards with smooth edges, no harsh environment: we did not use 
cc 
along edges
there are more examples of course

Conformal coating the edges was tricky, because of the sharp edges. The 
viscosity was therefore very important. Someone mentioned Parylene, that 
one 
has no such problem. Parylene is a dream stuff.

Lately, we have skipped edge coating, except when the customer wants it.


I had a look into MoonMan's POD, which covers most about PCB 
manufacturing. 
Strange enough, nothing about edge coating.

Inge

----- Original Message ----- 
From: "Douglas Pauls" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, October 20, 2010 8:20 PM
Subject: [TN] Conformal Coating Board Edges


> Good afternoon all,
>
> I am glad we all appreciate Inge and the time he puts into making this a
> fun and interesting forum.  To sum up: Ditto.
>
> I have a question related to conformal coating, a sort of survey.  For
> those of you that conformally coat your assemblies, do you coat the 
edges
> of the boards?  Why or why not?
>
> There is an internal debate here and I wanted some other viewpoints 
before
> offering my own.
>
> Doug Pauls
> Rockwell Collins
>
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