military/aerospace
Effective Thermal Management Is Key to
Military/Aerospace Microelectronics
Electronics used in military and aerospace applications are becoming
increasingly smaller, more powerful, and more complex. This makes
them much hotter. As cockpit microelectronics take on more
functionality, beyond communications and sensing, thermal management
can no longer be an afterthought. Design engineers understand that
electronics in most military/aerospace applications tend to generate
excessive heat, and that thermal management issues need to be
addressed at the very beginning of the design process. Fabrico works
with its customers in these applications to ensure that these issues are
addressed early in the design to avoid costly changes in manufacturing.
As military and aerospace electronics become smaller and more
powerful, they also become hotter.
In military/aerospace applications, everything is driven by size, weight,
and power (SWaP) considerations. As more powerful electronics and
microelectronics systems are squeezed into a cockpit, thermal
management needs to be addressed from system to board to device.
New thermal interface materials can manage thermal issues locally,
at the device. Liquid cooling, spray cooling, forced air cooling,
even fuel cooling, are being used to remove excess heat through the
package and off the platform, out of the vehicle and into the ambient.
The Earlier Thermal Management
Enters Your Design, the Better
Leaving thermal management as an afterthought is no longer possible
with advanced avionics. Thermal management has to be addressed early
in design at the box, board, and device level. New materials are being
investigated and developed with low coefficients of thermal expansion
(CTEs), low density, and high thermal conductivity. They help manage,
block, and dissipate heat in mil/aero electronics applications as thermal
interface materials (TIMs). They range from improved thermal grease
to the latest polymer matrix composites, metal matrix composites,
carbon composites, insulating papers, and solder formulations.
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TIMs are essentially the material between the device/heat source
and the heat sink. They fill the voids between two imperfect
mating surfaces, and replace air, a poor thermal conductor,
with a much better thermal conductor.
To effectively manage heat, design engineers working in mil/aero
applications must use TIMs with very high thermal conductivity,
Cleavage Load
low CTE (to minimize thermal stress that can affect reliability
and performance), and low density. Using material with high
CTEs can result in significant design compromises and reduced
cooling efficiency. A mismatch in CTEs between the PCB
substrate and the TIM can cause thermal stress, warping,
and failure. High density TIMs can create thermal impedance
instead of thermal conductance.
TIMs need to match the CTE of the material to which they are
attached: printed circuit board (PCB), ceramic substrate, and
semiconductor. Advanced materials suitable for use as TIMs
are chiefly from the following categories:
• Polymer matrix composites (PMCs) – different types of carbon
fibers combined with a variety of thermosetting and thermoplastic resins, including epoxy, cyanate ester, liquid crystal,
nylon, polycarbonate, ABS, PBT, and polyphenylene sulfide;
• Metal matrix composites (MMCs) – silicon carbide particle
reinforced aluminum, beryilia particle-reinforced beryilium,
carbon fiber-reinforced aluminum, copper-tungsten, copper
molybdenum, aluminum silicon, and Invar silver;
• Carbon/carbon composites (CCCs) – carbon nanofibers,
vapor grown carbon fibers, nano-graphene platelets,
pyrolitic graphite, and other carbon/carbon mixes.
Recent research has uncovered several promising applications
using nanotechnology such as carbon nanotubes and graphene
nanocomposites. In addition, work with high thermal conductivity
graphite foams used as heat sinks also offers promise for
aircraft applications.
All these new materials promise the following advantages in
managing heat at the device level, and perhaps eliminating the
need for heat pipes and other thermal dissipation components:
• High thermal conductivity
• Low density
• Low/customized CTEs
• Affordability
• High strength and stiffness
Cooling Device
Thermal Interface
Material (TIM)
Heat-Sensitive
Component
Thermal Interface Material
New thermal interface materials (TIMs) manage, block, and dissipate heat in
microelectronics for mil/aero.
These characteristics can lead to improved thermal
performance, weight savings, size reduction, simplification of
design, and manufacturing savings, all significant advantages
for advanced military/aerospace applications.
Selecting the Appropriate TIM
Thermal interface materials come in a wide variety with
different thermal impedance and thermal conductivities,
different gap filling capabilities, compressibility, temperature
ranges, and ease of application. Some common TIMs are:
Phase Change Materials
Phase change materials (PCMs) are solids at room temperature
but change to liquid once the excess heat of a device pushes
the material past its melting point. Typically composed of a
coating of phase change compound on an aluminum or
polyimide substrate, new PCMs can be coated directly onto
a release liner without using a substrate. This improves
performance by creating a better flow when the PCM is in
the liquid stage, and better gap and void filling. The interface
is thinner without the substrate, resulting in more efficient
heat transfer.
Thermal Grease
The traditional interface material in electronics is thermal
grease. Available in silicone or non-silicone varieties, thermal
grease provides low thermal resistance and excellent gap filling,
a thin bond line, easy application which may include automated
dispensing, and low cost. Conversely, it is messy, and can
“pump-out” or run during application and use, leaving new voids.
Gap Fillers
Gap fillers can be pads or liquids. They easily conform to
dimensional discrepancies, and their pliancy reduces
component stress. Pad versions can blanket multiple components
of different sizes and act as a common heat spreader.
Thermally Conductive Adhesives
Adhesives provide unique options for thermal management.
They are often the best choice where components are not
connected by mechanical attachment, or where the micromovement of substrates requires adhesion for a component to
maintain contact with the substrate. These are often used with
semiconductor packages as an interface between a chip and a
heat spreader. Thermally conductive adhesives can be used as:
• Interface pads – conformable adhesive pads that are easy to
handle and provide high conductivity;
• Liquids – usually epoxies, ultra-thin bond line and easy
integration into manufacturing dispensing equipment;
• Pressure-sensitive Adhesive (PSA) Tapes – high mechanical
strength plus good surface wetting and excellent
shock absorption.
Thermal Gels
Gels are paste-like materials that perform like grease but with
reduced pump-out. They exhibit good gap filling characteristics
and compressibility.
Selecting the right type of TIM for your application requires
assessing the advantages and disadvantages of each type and
matching the characteristics to your specific requirements.
Working with Fabrico on Thermal
Management Solutions
It has never been more important for a design engineer working
in military/aerospace applications to work with a materials
partner, like Fabrico, who has expertise in thermal management
and adhesives.
From identification and selection of the appropriate materials
and adhesives, to slitting, layering, laminating, precision
die-cutting, and packaging of the finished product, an
experienced converter can provide the design, prototyping,
testing, and manufacturing knowledge required for success.
TIMs can include phase change materials, thermal grease, gap fillers, conductive
adhesives, and thermal gels.
When designing in mil/aero applications, finding the right
adhesives and materials is often a process of elimination.
The more knowledge of how much heat the component
generates, its place within the overall product, and other
thermal management details, the shorter the process of
selecting and matching appropriate adhesives and materials.
Fabrico provides:
• Precision die-cutting, multi-layer laminating, and slitting
to tight tolerances
• Access to a range of thermal management solutions
• Testing capabilities
Fabrico selects from servo driven rotary die-cutting, CNC
die-cutting, laser cutting, and water jet cutting to meet the complex specifications of thermal management for electronic components. For example, a servo driven rotary die-cutter can
maintain tight tolerances ranging from 0.015” to +/-0.005”
at speeds up to 500 fpm and is ideal for the complex,
multi-layer die-cutting and lamination that a thermal
interface pad or tape may require.
For complex foam tape converting, water jet technology
provides clean edges with no distortion. Laser cutting,
kiss-cutting, slitting, and laminating can also be used in
converting applications.
If a grease or liquid TIM is selected, Fabrico provides a plan
for easy integration into the manufacturer’s process with
dispensing recommendations and solutions.
About Fabrico
Fabrico’s materials converting capabilities include: custom design
solutions for applications that require slitting, laminating, and
die-cutting. Laser cutting, kiss-cutting, and water jet cutting are
available depending on the application and materials
being used.
Fabrico’s test lab conducts materials, adhesive, and electrical testing to
meet application specifications.
With a fully equipped test laboratory, Fabrico ensures that
customer materials meet designed-in specifications before they
move to the factory floor. Fabrico’s test lab offers:
• Accurate and precise part dimension measurement
and verification;
• Adhesive/release liner to determine converting properties and
high speed application characteristics;
• Material strength measured to ensure that material meets
application requirements;
• Static shear testing to measure the cohesive strength
of the adhesive to withstand a fixed load over time;
• Material weight measurement to determine adhesive
coating weight;
• Microscopic imaging to determine differences between
adhesive and material over time;
• Dielectric testing to determine a material’s electrical
insulation properties;
• Thermal testing for materials and adhesives;
• Resistance and voltage testing to provide a complete profile
of the electrical properties of a material or adhesive.
Fabrico Headquarters
4175 Royal Drive, Suite 800, Kennesaw, GA 30144
Phone: 678-202-2700 | Fax: 678-202-2702
Toll Free: 800-351-8273 | E-mail: info@fabrico.com
With more than 30 years of materials experience, Fabrico
engineers also understand the impact of a material selection on
the overall manufacturing process, and design material systems
that optimize production efficiency and improve overall
cost-effectiveness.
Material Partners
Fabrico has strategic relationships with world-class materials
suppliers, such as 3M, Loctite, Adhesives Research, DuPont,
ITW Formex, and others, to assist its customers in selecting
the best material for the intended use and to expedite materials
sourcing. Whether adhesive films or liquid, all critical material
properties are considered in any Fabrico project, including
chemical, thermal, and moisture resistance.
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Fabrico is a trademark of EIS, Inc.; 3M is a trademark of the 3M Company.
Loctite is a Registered Trademark of Henkel AG & Co. KGaA.