ITS and Transit
Types of Conformal Coatings
Methods of Application
are specially formulated lacquers designed to protect PCBs and related
equipment from the environment. This improves and extends the working
life and ensures security and reliability of performance. These coatings
'conform' to the contours of the board and its components, creating a
thin (25-50 microns) layer which is both lightweight and flexible. This
protects circuitry from hazards such as chemicals (e.g. fuels, coolants
etc.), vibration, moisture, salt spray, humidity and high temperature.
For circuit boards that are not conformally coated these conditions can
cause corrosion, mould growth, and current leakage, resulting in board
Conformal coatings allow higher power and closer track spacing as they
prevent current leakage. This, in turn, enables designers to meet the
demand for miniaturization. Both transparent and pigmented coatings
improve the appearance of PCBs - the latter ensures a high degree of
secrecy by camouflaging the components and layout.
The Electrolube team
consists of some of the world's foremost experts in the formulation and
application of conformal coatings designed to meet international
approvals. The range of products currently available comprises acrylics,
silicones, polyurethanes and solvent free coatings.
offers a full range of ancillary products to complement the use of their
conformal coatings. These include thinners and strippers, peelable coating
masks and thixotropic materials for the effective coating of lead ends. A
specially designed Dip Coating Machine is also available. It provides the
ideal method of applying conformal coatings.
TYPES OF CONFORMAL
Acrylic conformal coatings provide good
flexibility and all round protection. As one part systems, they are easy
to apply and easy to remove. Some acrylics meet military standards, they
dry quickly rather than cure and are solvent removable.
Silicone conformal coatings are available in solvent resistant and solvent
removable forms. They perform at higher temperatures, and provide
excellent chemical and salt spray resistance. The solvent resistant
products are more difficult to remove although they can be soldered
through. They cross-link with time but for maximum performance heat curing
may be required. Silicones have remarkable electrical insulation
properties making them ideal for high power and highly populated boards.
These can be one
or two part systems. The most useful products for coating applications are
single part systems. They offer excellent moisture and chemical resistance
and good electrical characteristics. They are not easily removed once
Coatings that use UV energy to initiate the curing process are
solvent-free. This means that they are non-flammable, do not contain VOC's
and they comply with current and proposed environmental legislation. They
provide high chemical and heat resistance, flexibility and gloss, and give
excellent adhesion and coverage on lead ends. Curing times are a fraction
of other coatings (seconds), greatly reducing production costs by
increasing production speeds.
Water based coatings are non-hazardous, but because of the evaporation
rate of water may require longer drying times and generally require curing
at elevated temperatures (90°C). As water is the only solvent, they are
These specialty acrylics have been introduced to the market because of
their extremely low surface energy. This means that any moisture will be
instantly repelled. They are applied in extremely thin, weak films, making
masking unnecessary as the film is easily removed by mechanical action
e.g. inserting an edge connector.
As the film has low
strength it does not offer the same level of protection as conformal
coatings, but for high volume production where moisture resistance is the
main concern, fluoroacrylics offer enormous benefits.
Initially, conformal coatings were only used in 'high-tech' applications.
As consumers become more concerned with quality and reliability, and
electronic assemblies become more widely used in everyday life, conformal
coatings offer manufacturers the ability to improve the quality of their
products while eliminating costly warranty failures. Typical areas of use
Conformal coatings provide protection for electronic circuitry in a wide
range of domestic appliances and offer resistance against:
Water and detergents
(e.g. washing machines and dishwashers)
humidity (e.g. microwave ovens )
atmospheres (e.g. washer/dryers)
Office and home
hazards (e.g. computers)
environments (e.g. burglar alarms)
The automotive industry specifies conformal coatings to protect circuitry
from attack by agents such as petrol vapor, salt spray and brake fluid.
The use of electronic systems in vehicles continues to grow rapidly,
therefore, the use of conformal coatings becomes essential to ensure long
term reliability. Conformal coatings are used in applications:
hood (e.g. engine management systems), and
compartments (e.g. onboard computers)
The stringent environmental demands of the aerospace industry where
rapid compression and decompression will affect the performance of
circuitry, necessitates the extensive use of conformal coatings. The
coatings are used in both pressurized and depressurized areas:
Both fresh and salt water marine environments will attack electronic circuitry. Conformal coatings are ideal for the protection of equipment used
on the surface, but where equipment is to be installed in a submerged location,
the added protection of a resin will
almost certainly be required. Typical
Radar control systems
Medical / Industrial
There are numerous areas where a conformal coating will be required
for environmental protection:
Tool protection while in storage
to prevent corrosion.
Agriculture machinery to prevent
attack from agrochemicals and farmyard waste.
Pacemakers, where it is vital to
ensure continuous performance.
With such a wide
range of conformal coatings, all with different features and
benefits, it is important that the correct coating and method of
application be chosen. The main questions to be addressed are:
Controlling or predicting the exact operating conditions is difficult to
achieve without expensive, sophisticated test chambers, so the solution is
to protect the circuit completely from the hazards it may face. The
physical demands on equipment range from sudden decompression, as an
aircraft climbs to the constant vibration of an office printer; so
flexibility and the ability to expand and contract are important features
in a conformal coating. Checks should be made to ensure these
characteristics are maintained when sudden pressure and temperature
changes take place, and that the material will retain these properties
throughout the lifetime of the equipment
A conformal coating should exhibit high dielectric strength and breakdown
voltage. The minimum required dielectric strength of the coating can be
determined from the inter-track separations and the potential difference
between adjacent tracks.
The design of the board should include consideration of the placement of
components that must not be coated. These components include connectors,
IC sockets, adjustable potentiometers and test points. If the design
allows, these components should all be placed on one edge of the PCB to
enable the board to be coated with the minimum of masking.
If this is not
possible, Electrolube provide a fast curing peelable coating mask to
protect the relevant components. Component legs should be cropped to the
minimum length to ensure that a coherent film is formed.
Conformal coatings may only fully protect the assembly if the board is
thoroughly cleaned prior to application. This ensures that the coating
will adhere to the surface and that corrosive residues are not trapped on
the PCB. The main application methods include:
is a popular application technique and can give excellent results on
with aerosols is convenient for repair or small production runs, and
spray guns are suitable for larger production. However, both methods can
give "shadowing" (voids under components) and the effectiveness can
depend on operator accuracy.
is excellent for medium volume production. Dipping ensures complete
coverage and there is no overspray or material wastage.
using a programmable XY table is ideal for high volume coating to
Dip Coating Machine
The Electrolube Dipcoater provides a reliable, constant method for the
coating of PCBs and other components. Entirely pneumatic, with no
electrical parts, the machine is safe to use with flammable materials, and
the automatic dip cycle provides a smooth insertion and controlled
withdrawal rate which eliminates air entrapment and ensures an even film.
Rework and Repair
assembly requires repair, consideration must be given to the ease of
removal of the coating. Most coatings may be safely soldered through and
some can be easily removed in a standard solvent. Electrolube can also
supply powerful solvents and strippers to remove the most stubborn, aged
Reliability is the key requirement for today's electronic equipment and
conformal coatings provide a cost effective solution.
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