 | Dow Corning ® brand silicone encapsulants are
easily applied by a variety of methods. A general overview of these
processes is given below. For more specifics, please refer to the Gels and
Encapsulants Processing
Tutorial. |
Many of the encapsulants contain fillers for added strength or improved
physical properties, like thermal conductivity. The high density of some
of these fillers means that filler separation can occur. How quickly the
filler settles depends on the viscosity, filler type, and specific
gravity. With some products it can occur in hours, while for others any
settling may take months. If filler settling is detected or suspected, the
products should be remixed either in the original container or in a separate
reservoir before being used. This can be done by hand stirring in pails or
by using mechanical mixing equipment. Drum or can rollers can also be used to
blend the material in their original containers before use. Remixing may
be required periodically or can be done continuously in the dispense reservoirs
to maintain a homogeneous mix. Filler settling does not adversely affect
material performance once re-homogenized.
Most of the encapsulants are supplied as two-parts products that are either
mixed in a 1:1 ratio (Part A & Part B) or a 10:1 ratio (Base & Curing
Agent). They can be applied by hand mixing and manual dispensing, by using
hand-held manual or powered mixing devices, or by using automated meter-mix
equipment. Automated meter-mix is normally used for high volume
processes. In low volume, manual weighing and simple hand mixing may be
used.
For assistance in designing a process tailored to the needs of your
application, visit our Total
Solutions for Electronics Section.
| The two components are added in the proper ratio to a clean
container and then hand stirred gently but thoroughly. |  | Many of the products have color coding for the two parts to
help judge adequate mixing. |  | If air entrapment is a problem, it may be necessary to deair
the material after mixing to ensure that the cured material is bubble
free. |  |
| The mixed material is then poured into the unit to be
encapsulated. The filled unit can also be vacuum de-aired before curing to
remove any last air. |  | Take care during any de-airing process since foaming and
significant expansion of the mixed material can occur . |  | | |
 | Automated meter-mix equipment is typically used for higher
volume production processes. These systems consist of a separate feed reservoir
and pump for each component. The systems are set to achieve the desired ratio
of the two components. The materials are then fed through a dispense head
attached to a static mixer which is used to achieve a uniform mix. The
dispense head is used to control the amount of material that is dispensed into
the part. Static mixer tubes may need to replaced or cleaned when the process
is shut down for long periods to avoid having the encapsulant cure in the mix
tube. If air entrapment in the cured material is a problem, it may be necessary
to deair the material in the feed reservoirs or in extreme cases, deair the
material in the parts. Mixing in the reservoirs may also be needed to keep
the filler distributed uniformly in some products. |
Manual dispense units have separate chambers for each component which
connect to a common static mixer tube. Applying pressure to the plungers on the
chambers pushes the material through the static mixer. This can be done
manually by squeezing a hand trigger or can be gas powered. Static mixers are
typically disposable one-time use units and may need to replaced or cleaned
when not being used for long periods to avoid having the encapsulant cure in
the mix tube. These units can be supplied pre-filled and ready to use or
can be loaded with mixed and de-aired material immediately before use.
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