Complex electronic devices can generate large amounts of heat. To reduce
operating temperatures, heat sinks are often used with the device. Thermal
compounds or greases can be used between the device and the heat sink for
better coupling and efficiency in carrying away the heat. These non-curing
materials are particularly useful for applications where the heat sink may need
to be removed and reattached later, or when no-cure processes must be used in
the electronics assembly. Mechanical fasteners are generally needed to hold the
assembly in place during use. Newly developed thermally conductive
grease offers excellent thermal resistance with the capability of very thin
bond lines (<25 microns). It provides a wide processing window,
independent of applied pressure.
Another method of coupling heat-generating devices with heat sinks is by the
use of adhesives. As supplied, they range from flowable liquids to non-flowing
pastes. When cured, they convert to a strong, but stress-relieving elastomer
that holds the heat sink in place without the use of mechanical fasteners.
Adhesives are also used to adhere and couple entire circuit boards to metal
base plates or outer cases.
Dow Corning offers a variety of noncorrosive, thermally conductive silicone
adhesives that are ideally suited for use in bonding hybrid circuit substrates,
power semiconductor components and devices to heat sinks as well as for use in
other bonding applications where flexibility and thermal conductivity are major
concerns. The flowable versions are also ideal for use as thermally conductive
encapsulating materials for transformers, power supplies, coils and other
electronic devices that require improved thermal dissipation.
Encapsulants and Gels
Additionally, entire circuit assemblies can be embedded in encapsulants or
gels with enhanced thermal conductivity for better heat removal. Encapsulants
cure to a firm elastomer. Gels are much softer and provide additional relief
from environmental and mechanical stresses. These flowable materials can also
be used as liquid gap fillers or as an alternative to pre-cured pads to couple
circuits and heat sinks, facilitating high volume processes in automated