To add to the discussion I'd like to reference a quote from Dewey on the
TechNet about AR coatings back in March 2004;
"Why wear a latex suit, when a dust bag will do just fine"...
That about says it all, don't ya' think? B^D)
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(EHCOE)
Sent: Friday, February 16, 2007 8:19 AM
To: [log in to unmask]
Subject: Re: [TN] Using Type AR Conformal Coating
It is relatively easy to adequately conformal coat assemblies with type
AR for Military applications. I've even heard Doug can do it. Having
said that I want you to know that I consider type AR a glorified dust
bag, but if that's all you need and not a Gucci as Phil wants with his
Bunny suit, then fine.
I have always believed that one should not rely on any additional
electrical benefits derived from the application of a conformal coat to
achieve the functional intent of the design. It should only be used to
negate the need to derate operational parameters when used in harsh
environments.
Assessing your needs and understanding your liabilities will make the
material choice a lot easier. Process techniques and application
guidelines are available for all the materials.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of - Bogert
Sent: Thursday, February 15, 2007 5:24 PM
To: [log in to unmask]
Subject: [TN] Using Type AR Conformal Coating
February 15, 2007
Folks, we have some military OEM'S that are switching from Type UR
conformal coating to Type AR. The main reason for the switch is because
it is hard to remove Type UR coating in event of a rework, and certain
chemicals sold by the coating manufacturers for UR coating removal are
highly conductive and have caused problems since the cleaning process
did not adequately remove them. The other reason is we wanted a coating
that could be easily removed in event product failed in the field so we
could do ATE to quickly find the source of the problem. Our product is
used in a military application but it is contained in a cabinet that is
dust tight. We have some assemblies that are not coated at all with no
known problems.
Do any of you folks use Type AR for military product, and if so, what
are your experiences using the coating? I have heard about problems
using alcohol for coating removal since it goes where you do not want it
to go. I have also heard that if a spray process is used, it takes 4 or
more passes on each side of the board to achieve the minimum J-STD-001
thickness. At least one source indicated using AR may cause some solder
joint reliability issues.
Any info you have would be a help. Thanks.
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