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Silicone conformal coatings from Dow Corning are easily applied by a variety
of methods. A general overview of these processes is given below. For more
specifics, see some of the application bulletins on conformal coatings.
All of the coatings can be applied by the traditional methods of dipping,
spraying or simple flow coating. For high volume, spraying or dipping is best.
In low volume, simple flow coating can be used. Because of differences in
curing mechanisms, special considerations must be made for removal of any
solvents present or for curing higher thickness or curing under large area
components.
Environmental compliance is globally creating some strong trends. There is a
desire to avoid solvents that are frequently seen in non-silicone materials.
This trend has generated a growing interest in the Elastomeric Heat Cure and
Elastomeric Room Temperature Cure products. Similarly there has been a
growing usage of no-clean fluxes, making the compatibility with the conformal
coating and the underlying no-clean residues an issue to be considered. Contact us for assistance in testing compatibility, or for samples of
solventless conformal coatings.
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Dip Coating
Dip coating offers complete encapsulation and represents the lowest process
cost for high-volume applications. Boards are dipped into the liquid conformal
coating, withdrawn, and excess material allowed to drip off before curing.
With this method, masking is difficult. Board and tank temperature, withdrawal
rate from the tank, cure temperature and amount of drip time affect applied
thickness.
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Spray Coating
Spray coating is usually used for medium-volume production; at medium- or
high-volume production rates, application costs are low to moderate. Masking
is easier but spray application makes it difficult to coat under components,
and requires slightly more maintenance. The type of feed system, line speed,
temperature of the material and atomization pressure used will affect the
applied thickness.
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Select Coating
Select coating can be used for moderate- to high-volume applications and often
eliminates the need for masking because the material is dispensed only on
selected areas of the circuit. It uses more expensive equipment for high
volume processes and requires more maintenance than either dip or spray
coating. Coating thickness is affected by material viscosity, temperature,
pressures used and dispense head configuration.
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Flow Coating or Brush Coating
Flow or brush coating is used for low-volume production or for making repairs.
Equipment costs are very low. The coating is simply poured or brushed onto the
boards and then cured.
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All of Dow Corning's silicone conformal coatings contain additives that allow
easy UV inspection to ensure complete coverage on the circuit board.
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