Aerospace & Defense Technology - February 2021 - 13

Thermal Management

gle-component compounds - and feature
a cross-linked gel structure that provides
long-term thermal stability and reliability. Key features and benefits include:
* One-component dispensable
° Eliminates multiple part sizes/
numbers
° Aids in automation
* Fully cured
° Requires no refrigeration
° No mixing or additional curing
° No settling in storage
* Highly conformable at low pressure
° Applies minimal stress, making it effective for delicate components
* High surface tack

This schematic represents two surfaces in contact and heat flow across the interface without (left) and
with thermal interface material applied.

Pads vs. Gels - Understanding Key
Differences
Both pads and dispensable materials
have proven to be effective means of
thermal management in many industries and applications. While pads have
a longer proven track record, recent advances in gels have closed the performance gap and gels have, in some cases,
surpassed the performance of pads. Following are ways newly engineered gels
compare to gap pads in matters of critical importance to design engineers:
* Performance Characteristics
Conformability - Both gels and pads
are conformable to a degree, but the
maximum configurability of a gap pad
is less than that of a dispensable due to
its solid structure.
Flow rate - The goal when developing gels is to achieve the highest and
most repeatable flow rate. Customers
want to be able to set their dispensing
equipment for the same flow rate batchto-batch to maintain a consistent volume of material and avoid waste. Newer
dispensable technologies achieve a
higher, more repeatable flow rate that
improves throughput and reduces
waste.
Thermal conductivity - Identifying
the amount of heat [Watts] in need of
dissipation will determine the thermal
conductivity performance needed in
that application's gap filler. This is usually calculated and measured in Watts
per meter Kelvin, or W/m-K. The higher
the value, the more heat the material
can theoretically dissipate. Both pads
and gels are capable of dissipating a

Thermally conductive gap filler pads are cut-toshape and applied manually to offer thermal properties and high conformability at low clamping forces.

Pads are cut from sheets of various options of material
carriers with peel liners to expose the tack surface.

large amount of heat, generally from 1
W/m-K to 10 W/m-K, depending on the
specific product used.
Long-term reliability - While this
issue might be the great unknown in
real-world applications because of the
newness of advanced gels, rigorous accelerated aging, thermal shock, and vibration tests have shown that gels are
capable of achieving long-term reliability.
* Manufacturing/Assembly/Cost Dynamics
Automation - The opportunity for
automation is a significant advantage
for gels because dispensing systems are
quite versatile. While pad placement
can be automated to an extent, the
equipment and fixturing required to do
so is typically quite specialized and may
not be readily adapted from one job to
another. Even with dispensing equipment programming time built into the

setup cost, the process can be cost-efficient compared to the time required to
design and produce pad-application
tooling and the additional effort to then
qualify the application process.
Throughput - Speed in part production is application-dependent, but to illustrate the potential advantage of gels
we will cite a specific customer example. This particular customer was considering a switch from pads to gels and
ran a test of both materials to gauge the
difference in throughput. Their study
revealed that it required an operator 18
seconds to apply one pad, including
handling the pad, placing it properly
and then moving on to the next component. Using a dispensable and an automated process, those same steps required only four seconds.
The argument favoring gels grows
even more convincing if there are multiple dispense locations on a single part.

Aerospace & Defense Technology, February 2021

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Aerospace & Defense Technology - February 2021

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