March 17, 2017
Conformal Coating in Low Humidity Environments
Whereas conformal coating is excellent for high humidity protection - is there any performance impact when subjected to very low humidity environments?
Dr. Pauls, could you expand on your answer slightly? We very much respect your knowledge on the subject of conformal
coatings, and we are wondering which coating would provide the best protection
from Diet Mountain Dew?
Richard D. Stadem
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.
I will give you my
favorite engineering answer - It Depends.|
What do you mean by
"low humidity"? And what conformal coating are we talking
about? Different chemistries respond to the environment differently.
In general, in low
humidity environments, there is no humidity challenge to the coating. Any
humidity that may have passed through the coating during humid exposures would
diffuse out during very dry periods. The only impact I can see if if you
are talking about dessicated storage, like in pure nitrogen or 0-1% RH
environments. Conformal coatings are all organic materials and can dry
out with time, though I have not ever seen this. Potentially, coating
could crack under such situations as the plasticizers leave the material
(assuming they are there in the first place). You would be best to
contact the vendor of the coating you are interested and pose the question. Coating vendors test their products in a lot of weird environments.
Principal Materials and Process Engineer
Doug Pauls has a bachelors in Chemistry & Physics, Carthage College, BSEE, Univ of Wisc Madison. He has 9 years working experience for US Navy - Materials Lab, Naval Avionics Center Indianapolis. 8 years Technical Director, Contamination Studies Laboratories. 11 years Rockwell Collins Advanced Operations Engineering.
if it is fully cured.
SME - PWB Technologies
Mahendra Gandhi has been working in interconnect industry since 1972.
provide a breathable membrane protecting from humidity and contamination. They
will all vary slightly in resistivity depending on the exposure time to varying
humidity levels. The optimum properties
of a conformal coating are measured when it is fully cured and dry therefore
there is no performance impact when they are subjected to very low humidity
environments. This is possibly the
environment when they are protecting from contamination such as dust!|
Some polyurethane and
silicone coatings rely on moisture in the air to fully cross link the polymer
Curing times could be affected if applied in a
very dry environment.
Chris Palin is currently managing European sales and support for HumiSeal Conformal Coatings. His expertise is in test & reliability, solder technology, power die attach and conformal coating.
As far as I can tell, there is no downside to using
conformal coating in a low humidity environment. I believe the coating would
also act as a barrier to prevent particulate matter from attaching itself to
the laminate material and it will also act as a mechanical barrier to protect
the surfaces of the board and the components.
Vice President, Technical Director
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
environments have no impact on the performance of a cured conformal coating.
However, in some cases the relative humidity level may impact the cure
process itself whereby impacting the post cure performance. To understand
this it is important to understand how conformal coatings work.|
To begin it is
important to note with every polymeric material water absorption will
inevitably occur. The design of conformal coatings is unique in that the
material is able to maintain adhesion to the respective surfaces coated while
it absorbs moisture and ultimately reaches equilibrium. With this in
mind, the performance of a conformal coating is only as good as the strength to
the surface after cure. Some conformal coatings utilize UV light to
polymerize the reaction. Depending on the configuration of the parts, the
material may not see sufficient direct exposure from the source to fully drive
the reaction. These are called shadow areas, requiring a secondary cure
mechanism to complete the reaction. Many conformal coatings use heat or
oddly enough moisture to drive the secondary cure. Wants sufficient
moisture is absorbed by the unreacted parts of the polymer and the material
fully sets. At this point moisture penetration is defined by the
saturation characteristics of the material and the strength of the conformal coating
to the surface. If the relative humidity is low in the surrounding
environment during cure is low than there is a chance the material may not
reach its optimal adhesion whereby affecting performance.
With a fully cured
conformal coating the relative performance in a moisture rich (i.e. wet) versus
moisture starved (i.e. dry) environment is negligible. The operational
life time achieved in a moisture rich environment, such as south east Asia,
would be matched or exceeded in a dryer environment, such as the western United
States. The main item to consider is how well was the material cured...
Global Marketing Director
Mr. Dixon has been in the electronics field for over twenty years and is the Global Marketing Director with the electronics group of Henkel. Prior to joining Henkel, he worked for Raytheon, Camalot Systems, and Universal Instruments.