Hi again All -
The issue of sockets and/or connectors and conformal coatings has several
solutions -
First -- if you're using a urethane or similar, that has a tendency to wick
in areas which provide an opportunity for capillary action, then you must
first use some form of sealant to close off that area. The basic conformal
coating, thickened with silicone dioxide (spelled Cab-O-Sil from the Cabbot
Corp. or similar) may work quite well. Otherwise, one of the sealant grade
silicones (for electrical applications - avoid the acetic acid curables) may
also do the job. (The coating, unless a compatible silicone, will normally
not bond to this material.)
Second - a good masking job on the connector or socket face is necessary to
prevent coating the contact areas.
If you are using an acrylic, or similar, that tends to dry almost instantly
and does not wick, then the sealant may be unnecessary. Vapor deposited
coatings, such as the Parylene family bring on another situation - masking
requires a very professional masking job to prevent coating entry into the
contact area of connectors/sockets and in some cases switch bodies.
Lastly - dip coating application, as opposed to brush or spray, can impose a
whole new set of rules. All of these items have to be weighed out in the
course of design materials selection to avoid blowing the cost envelope.
Hint -- a really good solder mask (one of the LPI epoxy resins) can do a
great job of providing improved surface dielectic properties on the board
and under component bodies. Coupled with a moderately good conformal
coating job, it provides a lot of protection.
Regards -- Kelly
PS/ There are a whole bunch of different ways to mask items for volume
production, provided the manufacturing engineer has some flexibility in the
material and application requirements.
-----Original Message-----
From: Bob Landman <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Saturday, February 05, 2000 8:48 AM
Subject: Re: [DC] conformal coating
>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 #
>: ># Melbourne, FL 32902-9100 Pager (321)-690-9797 #
>: ># mailto:[log in to unmask] #
>: ># http://harris.com #
>: >###################################################
>: >"If you trust no man, then no man will ever
>: >disappoint you." (Author unknown.)
>:
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