Jerry,
We considered them years ago for our products (used by electric
utilities in outside environment but mounted in NEMA 4/6 enclosures)
and decided against them. Our products have a LONG service life
(20-30 years) we hope and doing a conformal coating pretty much screws
up any chance of repairs without a LOT of effort. Also, we use
sockets for the ICs (for the repair reason) and because we have a
microprocessor and thus a prom. Sockets and conformal coatings, from
what my assy house told me are very much incompatible. Messy stuff -
they didn't like to apply them and the environmental situation is such
that the formulations have had to become so benign that they are less
effective than they used to be. The old hard fugus resistant
varnishes used in WW2 were bullet-proof. If you have a tropical
environment (very high humidity and temp) then you may have no choice.
If you pick one, avoid sockets and mask connectors well. Use a type
that has a UV flurorescent dye that will show you where the pinholes
are for touch up.
May the Schwartz be with you; you will need him if you go conformal
coatings (yuck!)!
Bob
----- Original Message -----
From: Kelly M. Schriver <[log in to unmask]>
To: <[log in to unmask]>
Sent: February 05, 2000 5:54 AM
Subject: Re: [DC] conformal coating
: Hi Jerry -
:
: To start with, get copies of IPC-CC-830 and MIL-I-46058 (obsolete).
Those
: two documents will outline all the tests and test methods you ever
want to
: see, relative to coatings.
:
: All conformal coatings, just like any other materials in the
plastics
: family, provide a vapor permeable barrier. How good or how bad
depends on
: the specific formulation of the coating and the applied thickness.
Each of
: the types of coating brings with it some good charactaristics and
some not
: so good ones.
:
: The acrylics, for instance, are the most easily applied and removed.
Both
: material and process economics are fairly good, but they tend to be
: considerably less durable than some of the other materials.
:
: Urethanes tend to be good all around coatings and they're generally
: mechanically tough and abrasion resistant. (There are a few very
soft
: urethanes for special purposes.) There are now a number of UV
curable
: coatings which qualify as both acrylic and urethane, which are quite
good
: and provide a much shorter cure cycle than the old conventional
urethanes.
:
: The Parylene family of coatings, IMHO, is top of the line
performance wise,
: but its application process and costs are higher than most of the
other
: materials.
:
: Silicones work well for extremely high temperature applications, but
by
: nature tend to be mechanically fragile. The flexibility of
silicones often
: makes them the coating of choice when delicate components are
involved.
:
: Last, but not least, are the epoxies. They are also highly durable
and
: offered in a wide range of formulations.
:
: Need more comment? Drop me a note off line.
:
: Regards - Kelly
:
:
:
:
: -----Original Message-----
: From: Jerome Schwartz x5474 <[log in to unmask]>
: To: [log in to unmask] <[log in to unmask]>
: Date: Friday, February 04, 2000 12:27 PM
: Subject: [DC] conformal coating
:
:
: >All,
: >
: > Can anyone share there experience with conformal coatings ?
: > Mostly in regards to moisture absorption and testing of
such.
: >
: >
: > Regards,
: >
: > Jerry Schwartz, CID
: > IPC Certified Interconnect Designer
: > "May the Schwartz be with you"
: >
: >###################################################
: ># Jerry Schwartz,CID Designer 3 #
: ># Harris Corporation AGCS Voice (321)-727-5474 #
: ># P.O. Box 91000, MS 1/5852 Fax (321)-729-5990 #
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: ># http://harris.com #
: >###################################################
: >"If you trust no man, then no man will ever
: >disappoint you." (Author unknown.)
:
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