Improved organic potting and conformal coating materials protect fragile electronic components and circuitry from mechanical shock and vibration, moisture, and corrosion. These materials meet specifications covering resistance to cycling, radiation, flammability, and sterilizing agents for certain space applications

Webster, J. A.

English

NASA Technical Reports Server

October 1969	 Brief 69-10559 
NASA TECH BRIEF 
r-	 •1	 - 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information-, Springfield, Virginia 22151. 
Development of Improved Potting and Conformal Coating Compounds 
4-
.
A program was conducted to develop improved 
organic potting and conformal coating (encapsulating) 
materials for protection of fragile electronic compo-
nents and circuitry from mechanical shock and vibra-
tion, moisture, and corrosion. The materials were re-
quired to meet stringent specifications covering 
mechanical and electrical properties and resistance to 
thermal shock and cycling, radiation, flammability, 
and sterilizing agents (dry heat and ethylene oxide) 
for certain space applications. The results of the 
development program are summarized below. 
Potting Compounds 
Epoxy resins have a combination of desirable 
characteristics, such as ready cure and good chemical 
and thermal stability, that make them particularly 
suitable for potting resins. Considerable improvement 
in thermal cycling performance was realized with the 
development of an experimental epoxy resin based on 
I propyldimeth-
ylsilyl] benzene. This material closely approached 
specification requirements with respect to thermal 
cycling performance. Dielectric constants were well 
below 3.0, while dissipation factors approached the 
objective of 0.005. 
Within experimental limits the performance of a 
potting resin prepared from bisphenol A diglycidyl 
ether (a commercial product) and xylylenediamine 
compared favorably under thermal cycling conditions 
with the experimental epoxy resin but was slightly 
inferior in dielectric constant and fluidity of the resin 
mix. 
Correlation of thermal cycling evaluations of these 
and other experimental epoxy resins with expansion 
coefficient data did not indicate a simple, direct 
relationship. It was concluded that factors such as
modulus and transition temperature of the resin also 
affect the performance under thermal cycling condi-
tions. 
Polyisocyanurate compositions were considered to 
be potentially useful as potting materials because of 
their good thermal stability, low temperature curabil-
ity, and excellent dielectric constants and dissipation 
factors. Cordwood modules potted with polyisocyanu-
rate compositions were tested and found to be inferior 
to epoxy resin-potted modules. The shrinkage-on-cure 
of two unfilled isocyanurate compositions was deter-
mined and found to be 5 and 17 percent depending on 
molecular weight of the monomer. 
Conformal Coatings 
Various elastomeric materials were prepared and 
evaluated for application as conformal coatings. The 
major effort was on materials prepared from a com-
mercial hydroxy-terminated hydrocarbon prepolymer. 
By reaction of this prepolymer with excess hexameth-
ylene diisocyanate or tolylene diisocyanate, versatile 
reactive intermediates were prepared for further 
polymerization to urea-, urethane-, oxazolidone- and 
isocyanurate-linked polymers. 
Urethane and urea-urethane-linked conformal coat-
ings showed a combination of properties superior to 
that of conventional materials and closely approxi-
mates specification objectives. These elastomeric 
coating materials had high tensile strength and elonga-
tion, good low-temperature flexibility, and dielectric 
constants well below 3.0. They showed good compati-
bility with ethylene oxide and no damage to printed 
circuit boards under thermal cycling conditions. The 
isocyanurate-linked polymers cured less readily and 
had low tensile strengths and elongations. In addition, 
the curing reaction was adversely sensitive to moisture. 
(continued overleal( 
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41 
Their dielectric constants and dissipation factors were 
excellent, however. 
The oxazolidone-linked hydrocarbon material result-
ing from the combination of the more reactive oxirane 
and isocyanate intermediates approached the tensile-
strength and elongation requirements and showed a 
satisfactory dielectric constant. The utility of the 
oxazolidone-linking reaction depends on the degree 
of improvement in properties that can be attained with 
a better catalyst or more reactive intermediates. 
Two types of epoxy systems were investigated for 
the preparation of elastomeric materials. The reaction 
of epoxy intermediates with amine-terminated hydro-
carbon prepolymer produced elastomeric materials 
having good dielectric constants but low tensile 
strengths and elongations. Considerable improvement 
in this system is believed possible. 
Elastomeric epoxy coatings were also prepared by 
reactions of monomeric secondary diamines with di-i-
epoxyoxy intermediates. High tensile strengths and 
elongation were offset by poor dielectric properties 
and poor compatibility with ethylene oxide. 
Note: 
No further documentation is available. Inquiries 
may be directed to: 
Technology Utilization Officer 
National Aeronautics and Space Administration 
Washington, D.C. 20546 
Reference: B69-10559 
Patent Status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code GP, 
Washington, D.C. 20546.
Source: J. A. Webster of

Monsanto Research Corp.

under contract to

Marshall Space Flight Center

(MFS-20219 through MFS-20223)
. 
. 
.-
Brief 69-10559	 Category 03


Development of improved potting and conformal coating compounds

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