But some conformal coatings do not adhere to certain materials,
therefore a blanket declaration becomes problematic. To fully comply can
be very costly, with no value added.
R. Dean Stadem
Consulting Engineer
Analog Technologies Corp./Lumagine, Inc.
11441 Rupp Drive
Burnsville, MN 55431
(952)894-9228
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Thursday, June 25, 2009 2:00 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating coverage
I agree with Richard who agrees with Dewey......
As others have indicated, it is very much an "it depends" type of
proposition, including factors like design life, consequences of
failure,
hostility of the end use environment, the materials involved, etc. A
generic document like A-610 or J-STD-001 can't address all the multitude
of factors, so the engineering drawing has to predominate.
That issue has come up here internally before. An example: If, in the
process of machine spray coating, we leave a very narrow strip of the
top
of a ceramic DIP package uncoated. Is this a defect? Yes, per the
drawing and our requirements. Will there be any degradation in
reliability as a result of not coating that narrow strip. Probably not.
Ceramic, or even the epoxy of plastic encapsulated microcircuits are
better insulators than conformal coating. But, if you allow that narrow
strip, you then have to determine how much you can leave uncoated
without
impacting reliability. What are the tolerances? How do you measure it?
Does it depend on the application? Our engineering department does not
want to spend the money for what would certainly be a massive study to
determine this. Hence, 100% coverage is specified on our drawings.
Doug Pauls
Rockwell Collins
"Stadem, Richard D." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/25/2009 01:01 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Stadem, Richard D." <[log in to unmask]>
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cc
Subject
Re: [TN] Conformal coating coverage
Thanks, I like that language, Dewey.
In any case, to help Ioan in his initial question; there can be no
concrete, comprehensive standard that works for everything when it comes
to conformal coating. The requirements need to be tailored AABUS. They
seldom work perfectly as defined on the print during the first build,
thus
the "out card" where any deviations are documented, adjudicated, and
approved by the customer before shipping the assemblies.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(EHCOE)
Sent: Thursday, June 25, 2009 12:33 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating coverage
I changed Richard's note to be in line with the new approach. After it I
added a note I add to all drawings that may have need of the wiggle room
or a get-out-of-jail-free card.
The conformal coating requirements shall be defined and documented on
the
PBA (printed board assembly) drawing.
Deviations to these requirements shall be AABUS.
Conformal coating may or may not be present in non-critical laminate
areas
of the PB (printed board) or on the top and side of non-critical,
non-conductive surfaces of large scale packages, unless otherwise
specified. This exception is for the coating coverage requirement and
shall not be used to accept uncoated areas due to bubbles, voids and
other
workmanship issues.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, June 25, 2009 9:28 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating coverage
That may not be covered under any standard, because the requirements for
CC coverage vary by component, assembly, program, customer, and usage
requirements.
Usually, coating over the component body has no value added, as most
component bodies are impervious to moisture. The primary purpose of the
CC
is to prevent moisture buildup on the metal terminations and solder
connections on the CCA.
The coating requirements need to be defined and agreed upon between the
user and the supplier (AABUS) and documented on the CCA drawing. They
are
unique and specific to the product.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Thursday, June 25, 2009 10:51 AM
To: [log in to unmask]
Subject: [TN] Conformal coating coverage
Dear Technos,
Since the PCB edges have been already discussed, I would like to get
your
input on tall components coverage. Do tall parts, like radial TH parts,
inductors, electrolytic caps, etc. need to have the vertical sides
coated?
What about the coils with apparent windings?
IPC-610 is not detailed at all at this level and I have quickly browsed
IPC-HDBK-830 without being able to find anything. What would be the IPC
or
MIL standard covering this particular issue?
Thank you,
Ioan Tempea, ing.
Ingénieur Principal Fabrication / Sr. Manufacturing Engineer
30 ans déjà! - Already 30 years!
950 rue Bergar, Laval, Québec, H7L 5A1
t : 450-967-7100 ext : 244
Mtl : 514-990-5762
f : 450-967-7444
[log in to unmask] <mailto:[log in to unmask]>
www.digico.cc <http://www.digico.cc/>
P N'imprimer que si nécessaire - Print only if you must
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