 | Dow Corning® Thermal Interface Materials are
supplied as dispensable liquids and pastes or as fabricated films and pads that
are easily applied by a variety of methods. Liquids or pastes are typically
applied using automated needle dispense systems or by stencil/screen
printing.
Liquid products supplied in one part form are generally ready for dispensing as
is. Two part formulations, however, require mixing. Automated
meter/mix equipment is available for this purpose.
Hand mixing with manual dispensing or using hand-held mixing/dispense devices
may also be used in low volume processes. In automated equipment, the two
components are drawn from their individual containers or from storage
reservoirs to a metering device which measures out the appropriate quantities
of each part, dictated by shot size and mix ratio of the product (either 1:1 or
10:1 mix ratios). The two parts are then combined and moved through a
static mixer. When properly sized for the viscosity and flow rate of the
material being applied, the two parts are blended uniformly and without the
incorporation of air. After mixing, the two part products can now be handled
similarly to one parts and can be dispensed by one of the two methods described
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Also, during normal storage, filler separation may occur in some of the
materials. The filler particles, used in some formulations, are dense
enough that gravity can cause them to settle over time, leaving a clear polymer
layer on top. The longer the material is stored, the more likely some
filler separation will occur. In some cases, it may be necessary to re-mix the
material before being used in your application and it may be helpful to have a
gentle agitation system in the feed reservoirs to keep the fillers
uniform. Care should be taken to avoid introducing air into the product
when re-mixing the filler.
For assistance in designing a process tailored to the needs of your
application, contact Dow Corning’s technical experts in the Application Center.
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Needle Dispense
Liquid thermally conductive materials are typically moved through the
dispensing equipment from their original container or material reservoir using
pumps or other mechanical force. Sometimes, gas pressure on the backside
of a plunger or pressure plate is used to control the amount of material being
applied. If gas pressure is used, a barrier is needed to separate to the
gas from the material to reduce bubbles in the cured adhesive. A precision
metering pump is typically used when small amounts of material are being
applied to control the amount of material dispensed, while a valve may be used
when dispensing larger quantities of material. For high production rate
processes, the pattern of application can be robotically controlled. The
dispense head moves to allow the material to be applied in the desired
configuration. Alternatively, multiple needles or slits in the dispense
head can apply the desired pattern.
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Stencil/Screen printing
Dow Corning Thermal Interface Materials that are liquids can also be stencil
or screen printed onto substrates, which can be done reliably and quickly.
Using stencils or screens allows the material to be placed onto the device only
in the areas needed and in the amount required for the application.
Stencils are typically made of stainless steel with openings cut where the
material is to be applied. The material is applied to the top of the stencil
and a squeegee is drawn across pushing the material through the stencil
openings and onto the substrate. A fixture is typically used to hold the
substrate and maintain uniform positioning.
Several factors affect the quality of the print including snap-off distance,
stencil thickness, squeegee speed and down force, etc. It is important to keep
the stencil clean of debris and cured adhesive to ensure print
quality. Wear on the squeegee blade can also cause problems, as it will
create uneven pressure on the adhesive as it is applied.
Screen printing is very similar except that material is printed through a
patterned mesh (screen) rather than openings cut into a stencil.
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